BROKEN: restructure much of ModelChecker as ModelExecution class
authorBrian Norris <banorris@uci.edu>
Tue, 16 Apr 2013 01:25:53 +0000 (18:25 -0700)
committerBrian Norris <banorris@uci.edu>
Tue, 16 Apr 2013 01:53:50 +0000 (18:53 -0700)
This will *not* compile fully. It is an interim step in which I move
much of the ModelChecker code into a separate class which does not need
to be globally-accessible. The next few commits should fix the compile
problems as I rewrite/remove some interfaces.

Makefile
execution.cc [new file with mode: 0644]
execution.h [new file with mode: 0644]
model.cc
model.h

index 7539aca..26aadc9 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ OBJECTS = libthreads.o schedule.o model.o threads.o librace.o action.o \
          nodestack.o clockvector.o main.o snapshot-interface.o cyclegraph.o \
          datarace.o impatomic.o cmodelint.o \
          snapshot.o malloc.o mymemory.o common.o mutex.o promise.o conditionvariable.o \
          nodestack.o clockvector.o main.o snapshot-interface.o cyclegraph.o \
          datarace.o impatomic.o cmodelint.o \
          snapshot.o malloc.o mymemory.o common.o mutex.o promise.o conditionvariable.o \
-         context.o scanalysis.o
+         context.o scanalysis.o execution.o
 
 CPPFLAGS += -Iinclude -I.
 LDFLAGS = -ldl -lrt -rdynamic
 
 CPPFLAGS += -Iinclude -I.
 LDFLAGS = -ldl -lrt -rdynamic
diff --git a/execution.cc b/execution.cc
new file mode 100644 (file)
index 0000000..0006c66
--- /dev/null
@@ -0,0 +1,2817 @@
+#include <stdio.h>
+#include <algorithm>
+#include <mutex>
+#include <new>
+#include <stdarg.h>
+
+#include "execution.h"
+#include "model.h"
+#include "action.h"
+#include "nodestack.h"
+#include "schedule.h"
+#include "snapshot-interface.h"
+#include "common.h"
+#include "clockvector.h"
+#include "cyclegraph.h"
+#include "promise.h"
+#include "datarace.h"
+#include "threads-model.h"
+#include "output.h"
+#include "bugmessage.h"
+
+#define INITIAL_THREAD_ID      0
+
+/**
+ * Structure for holding small ModelChecker members that should be snapshotted
+ */
+struct model_snapshot_members {
+       model_snapshot_members() :
+               /* First thread created will have id INITIAL_THREAD_ID */
+               next_thread_id(INITIAL_THREAD_ID),
+               used_sequence_numbers(0),
+               next_backtrack(NULL),
+               bugs(),
+               stats(),
+               failed_promise(false),
+               too_many_reads(false),
+               no_valid_reads(false),
+               bad_synchronization(false),
+               asserted(false)
+       { }
+
+       ~model_snapshot_members() {
+               for (unsigned int i = 0; i < bugs.size(); i++)
+                       delete bugs[i];
+               bugs.clear();
+       }
+
+       unsigned int next_thread_id;
+       modelclock_t used_sequence_numbers;
+       ModelAction *next_backtrack;
+       SnapVector<bug_message *> bugs;
+       struct execution_stats stats;
+       bool failed_promise;
+       bool too_many_reads;
+       bool no_valid_reads;
+       /** @brief Incorrectly-ordered synchronization was made */
+       bool bad_synchronization;
+       bool asserted;
+
+       SNAPSHOTALLOC
+};
+
+/** @brief Constructor */
+ModelExecution::ModelExecution(struct model_params *params, Scheduler *scheduler, NodeStack *node_stack) :
+       params(params),
+       scheduler(scheduler),
+       action_trace(new action_list_t()),
+       thread_map(new HashTable<int, Thread *, int>()),
+       obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
+       condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
+       obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
+       promises(new SnapVector<Promise *>()),
+       futurevalues(new SnapVector<struct PendingFutureValue>()),
+       pending_rel_seqs(new SnapVector<struct release_seq *>()),
+       thrd_last_action(new SnapVector<ModelAction *>(1)),
+       thrd_last_fence_release(new SnapVector<ModelAction *>()),
+       node_stack(node_stack),
+       priv(new struct model_snapshot_members()),
+       mo_graph(new CycleGraph()),
+       execution_number(1)
+{
+       /* Initialize a model-checker thread, for special ModelActions */
+       model_thread = new Thread(get_next_id());
+       thread_map->put(id_to_int(model_thread->get_id()), model_thread);
+}
+
+/** @brief Destructor */
+ModelExecution::~ModelExecution()
+{
+       for (unsigned int i = 0; i < get_num_threads(); i++)
+               delete thread_map->get(i);
+       delete thread_map;
+
+       delete obj_thrd_map;
+       delete obj_map;
+       delete condvar_waiters_map;
+       delete action_trace;
+
+       for (unsigned int i = 0; i < promises->size(); i++)
+               delete (*promises)[i];
+       delete promises;
+
+       delete pending_rel_seqs;
+
+       delete thrd_last_action;
+       delete thrd_last_fence_release;
+       delete mo_graph;
+       delete priv;
+}
+
+static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
+{
+       action_list_t *tmp = hash->get(ptr);
+       if (tmp == NULL) {
+               tmp = new action_list_t();
+               hash->put(ptr, tmp);
+       }
+       return tmp;
+}
+
+static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
+{
+       SnapVector<action_list_t> *tmp = hash->get(ptr);
+       if (tmp == NULL) {
+               tmp = new SnapVector<action_list_t>();
+               hash->put(ptr, tmp);
+       }
+       return tmp;
+}
+
+action_list_t * ModelExecution::get_actions_on_obj(void * obj, thread_id_t tid) {
+       SnapVector<action_list_t> *wrv=obj_thrd_map->get(obj);
+       if (wrv==NULL)
+               return NULL;
+       unsigned int thread=id_to_int(tid);
+       if (thread < wrv->size())
+               return &(*wrv)[thread];
+       else
+               return NULL;
+}
+
+/** @return a thread ID for a new Thread */
+thread_id_t ModelExecution::get_next_id()
+{
+       return priv->next_thread_id++;
+}
+
+/** @return the number of user threads created during this execution */
+unsigned int ModelExecution::get_num_threads() const
+{
+       return priv->next_thread_id;
+}
+
+/** @return a sequence number for a new ModelAction */
+modelclock_t ModelExecution::get_next_seq_num()
+{
+       return ++priv->used_sequence_numbers;
+}
+
+/**
+ * @brief Should the current action wake up a given thread?
+ *
+ * @param curr The current action
+ * @param thread The thread that we might wake up
+ * @return True, if we should wake up the sleeping thread; false otherwise
+ */
+bool ModelExecution::should_wake_up(const ModelAction *curr, const Thread *thread) const
+{
+       const ModelAction *asleep = thread->get_pending();
+       /* Don't allow partial RMW to wake anyone up */
+       if (curr->is_rmwr())
+               return false;
+       /* Synchronizing actions may have been backtracked */
+       if (asleep->could_synchronize_with(curr))
+               return true;
+       /* All acquire/release fences and fence-acquire/store-release */
+       if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
+               return true;
+       /* Fence-release + store can awake load-acquire on the same location */
+       if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
+               ModelAction *fence_release = get_last_fence_release(curr->get_tid());
+               if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
+                       return true;
+       }
+       return false;
+}
+
+void ModelExecution::wake_up_sleeping_actions(ModelAction *curr)
+{
+       for (unsigned int i = 0; i < get_num_threads(); i++) {
+               Thread *thr = get_thread(int_to_id(i));
+               if (scheduler->is_sleep_set(thr)) {
+                       if (should_wake_up(curr, thr))
+                               /* Remove this thread from sleep set */
+                               scheduler->remove_sleep(thr);
+               }
+       }
+}
+
+/** @brief Alert the model-checker that an incorrectly-ordered
+ * synchronization was made */
+void ModelExecution::set_bad_synchronization()
+{
+       priv->bad_synchronization = true;
+}
+
+bool ModelExecution::assert_bug(const char *msg)
+{
+       priv->bugs.push_back(new bug_message(msg));
+
+       if (isfeasibleprefix()) {
+               set_assert();
+               return true;
+       }
+       return false;
+}
+
+/** @return True, if any bugs have been reported for this execution */
+bool ModelExecution::have_bug_reports() const
+{
+       return priv->bugs.size() != 0;
+}
+
+SnapVector<bug_message *> * ModelExecution::get_bugs() const
+{
+       return &priv->bugs;
+}
+
+/**
+ * Check whether the current trace has triggered an assertion which should halt
+ * its execution.
+ *
+ * @return True, if the execution should be aborted; false otherwise
+ */
+bool ModelExecution::has_asserted() const
+{
+       return priv->asserted;
+}
+
+/**
+ * Trigger a trace assertion which should cause this execution to be halted.
+ * This can be due to a detected bug or due to an infeasibility that should
+ * halt ASAP.
+ */
+void ModelExecution::set_assert()
+{
+       priv->asserted = true;
+}
+
+/**
+ * Check if we are in a deadlock. Should only be called at the end of an
+ * execution, although it should not give false positives in the middle of an
+ * execution (there should be some ENABLED thread).
+ *
+ * @return True if program is in a deadlock; false otherwise
+ */
+bool ModelExecution::is_deadlocked() const
+{
+       bool blocking_threads = false;
+       for (unsigned int i = 0; i < get_num_threads(); i++) {
+               thread_id_t tid = int_to_id(i);
+               if (is_enabled(tid))
+                       return false;
+               Thread *t = get_thread(tid);
+               if (!t->is_model_thread() && t->get_pending())
+                       blocking_threads = true;
+       }
+       return blocking_threads;
+}
+
+/**
+ * Check if this is a complete execution. That is, have all thread completed
+ * execution (rather than exiting because sleep sets have forced a redundant
+ * execution).
+ *
+ * @return True if the execution is complete.
+ */
+bool ModelExecution::is_complete_execution() const
+{
+       for (unsigned int i = 0; i < get_num_threads(); i++)
+               if (is_enabled(int_to_id(i)))
+                       return false;
+       return true;
+}
+
+/**
+ * @brief Find the last fence-related backtracking conflict for a ModelAction
+ *
+ * This function performs the search for the most recent conflicting action
+ * against which we should perform backtracking, as affected by fence
+ * operations. This includes pairs of potentially-synchronizing actions which
+ * occur due to fence-acquire or fence-release, and hence should be explored in
+ * the opposite execution order.
+ *
+ * @param act The current action
+ * @return The most recent action which conflicts with act due to fences
+ */
+ModelAction * ModelExecution::get_last_fence_conflict(ModelAction *act) const
+{
+       /* Only perform release/acquire fence backtracking for stores */
+       if (!act->is_write())
+               return NULL;
+
+       /* Find a fence-release (or, act is a release) */
+       ModelAction *last_release;
+       if (act->is_release())
+               last_release = act;
+       else
+               last_release = get_last_fence_release(act->get_tid());
+       if (!last_release)
+               return NULL;
+
+       /* Skip past the release */
+       action_list_t *list = action_trace;
+       action_list_t::reverse_iterator rit;
+       for (rit = list->rbegin(); rit != list->rend(); rit++)
+               if (*rit == last_release)
+                       break;
+       ASSERT(rit != list->rend());
+
+       /* Find a prior:
+        *   load-acquire
+        * or
+        *   load --sb-> fence-acquire */
+       ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
+       ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
+       bool found_acquire_fences = false;
+       for ( ; rit != list->rend(); rit++) {
+               ModelAction *prev = *rit;
+               if (act->same_thread(prev))
+                       continue;
+
+               int tid = id_to_int(prev->get_tid());
+
+               if (prev->is_read() && act->same_var(prev)) {
+                       if (prev->is_acquire()) {
+                               /* Found most recent load-acquire, don't need
+                                * to search for more fences */
+                               if (!found_acquire_fences)
+                                       return NULL;
+                       } else {
+                               prior_loads[tid] = prev;
+                       }
+               }
+               if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
+                       found_acquire_fences = true;
+                       acquire_fences[tid] = prev;
+               }
+       }
+
+       ModelAction *latest_backtrack = NULL;
+       for (unsigned int i = 0; i < acquire_fences.size(); i++)
+               if (acquire_fences[i] && prior_loads[i])
+                       if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
+                               latest_backtrack = acquire_fences[i];
+       return latest_backtrack;
+}
+
+/**
+ * @brief Find the last backtracking conflict for a ModelAction
+ *
+ * This function performs the search for the most recent conflicting action
+ * against which we should perform backtracking. This primary includes pairs of
+ * synchronizing actions which should be explored in the opposite execution
+ * order.
+ *
+ * @param act The current action
+ * @return The most recent action which conflicts with act
+ */
+ModelAction * ModelExecution::get_last_conflict(ModelAction *act) const
+{
+       switch (act->get_type()) {
+       /* case ATOMIC_FENCE: fences don't directly cause backtracking */
+       case ATOMIC_READ:
+       case ATOMIC_WRITE:
+       case ATOMIC_RMW: {
+               ModelAction *ret = NULL;
+
+               /* linear search: from most recent to oldest */
+               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (prev->could_synchronize_with(act)) {
+                               ret = prev;
+                               break;
+                       }
+               }
+
+               ModelAction *ret2 = get_last_fence_conflict(act);
+               if (!ret2)
+                       return ret;
+               if (!ret)
+                       return ret2;
+               if (*ret < *ret2)
+                       return ret2;
+               return ret;
+       }
+       case ATOMIC_LOCK:
+       case ATOMIC_TRYLOCK: {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (act->is_conflicting_lock(prev))
+                               return prev;
+               }
+               break;
+       }
+       case ATOMIC_UNLOCK: {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (!act->same_thread(prev) && prev->is_failed_trylock())
+                               return prev;
+               }
+               break;
+       }
+       case ATOMIC_WAIT: {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (!act->same_thread(prev) && prev->is_failed_trylock())
+                               return prev;
+                       if (!act->same_thread(prev) && prev->is_notify())
+                               return prev;
+               }
+               break;
+       }
+
+       case ATOMIC_NOTIFY_ALL:
+       case ATOMIC_NOTIFY_ONE: {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (!act->same_thread(prev) && prev->is_wait())
+                               return prev;
+               }
+               break;
+       }
+       default:
+               break;
+       }
+       return NULL;
+}
+
+/** This method finds backtracking points where we should try to
+ * reorder the parameter ModelAction against.
+ *
+ * @param the ModelAction to find backtracking points for.
+ */
+void ModelExecution::set_backtracking(ModelAction *act)
+{
+       Thread *t = get_thread(act);
+       ModelAction *prev = get_last_conflict(act);
+       if (prev == NULL)
+               return;
+
+       Node *node = prev->get_node()->get_parent();
+
+       /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
+       int low_tid, high_tid;
+       if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
+               low_tid = id_to_int(act->get_tid());
+               high_tid = low_tid + 1;
+       } else {
+               low_tid = 0;
+               high_tid = get_num_threads();
+       }
+
+       for (int i = low_tid; i < high_tid; i++) {
+               thread_id_t tid = int_to_id(i);
+
+               /* Make sure this thread can be enabled here. */
+               if (i >= node->get_num_threads())
+                       break;
+
+               /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
+               /* Don't backtrack into a point where the thread is disabled or sleeping. */
+               if (node->enabled_status(tid) != THREAD_ENABLED)
+                       continue;
+
+               /* Check if this has been explored already */
+               if (node->has_been_explored(tid))
+                       continue;
+
+               /* See if fairness allows */
+               if (params->fairwindow != 0 && !node->has_priority(tid)) {
+                       bool unfair = false;
+                       for (int t = 0; t < node->get_num_threads(); t++) {
+                               thread_id_t tother = int_to_id(t);
+                               if (node->is_enabled(tother) && node->has_priority(tother)) {
+                                       unfair = true;
+                                       break;
+                               }
+                       }
+                       if (unfair)
+                               continue;
+               }
+
+               /* See if CHESS-like yield fairness allows */
+               if (params->yieldon) {
+                       bool unfair = false;
+                       for (int t = 0; t < node->get_num_threads(); t++) {
+                               thread_id_t tother = int_to_id(t);
+                               if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
+                                       unfair = true;
+                                       break;
+                               }
+                       }
+                       if (unfair)
+                               continue;
+               }
+
+               /* Cache the latest backtracking point */
+               set_latest_backtrack(prev);
+
+               /* If this is a new backtracking point, mark the tree */
+               if (!node->set_backtrack(tid))
+                       continue;
+               DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
+                                       id_to_int(prev->get_tid()),
+                                       id_to_int(t->get_id()));
+               if (DBG_ENABLED()) {
+                       prev->print();
+                       act->print();
+               }
+       }
+}
+
+/**
+ * @brief Cache the a backtracking point as the "most recent", if eligible
+ *
+ * Note that this does not prepare the NodeStack for this backtracking
+ * operation, it only caches the action on a per-execution basis
+ *
+ * @param act The operation at which we should explore a different next action
+ * (i.e., backtracking point)
+ * @return True, if this action is now the most recent backtracking point;
+ * false otherwise
+ */
+bool ModelExecution::set_latest_backtrack(ModelAction *act)
+{
+       if (!priv->next_backtrack || *act > *priv->next_backtrack) {
+               priv->next_backtrack = act;
+               return true;
+       }
+       return false;
+}
+
+/**
+ * Returns last backtracking point. The model checker will explore a different
+ * path for this point in the next execution.
+ * @return The ModelAction at which the next execution should diverge.
+ */
+ModelAction * ModelExecution::get_next_backtrack()
+{
+       ModelAction *next = priv->next_backtrack;
+       priv->next_backtrack = NULL;
+       return next;
+}
+
+/**
+ * Processes a read model action.
+ * @param curr is the read model action to process.
+ * @return True if processing this read updates the mo_graph.
+ */
+bool ModelExecution::process_read(ModelAction *curr)
+{
+       Node *node = curr->get_node();
+       while (true) {
+               bool updated = false;
+               switch (node->get_read_from_status()) {
+               case READ_FROM_PAST: {
+                       const ModelAction *rf = node->get_read_from_past();
+                       ASSERT(rf);
+
+                       mo_graph->startChanges();
+
+                       ASSERT(!is_infeasible());
+                       if (!check_recency(curr, rf)) {
+                               if (node->increment_read_from()) {
+                                       mo_graph->rollbackChanges();
+                                       continue;
+                               } else {
+                                       priv->too_many_reads = true;
+                               }
+                       }
+
+                       updated = r_modification_order(curr, rf);
+                       read_from(curr, rf);
+                       mo_graph->commitChanges();
+                       mo_check_promises(curr, true);
+                       break;
+               }
+               case READ_FROM_PROMISE: {
+                       Promise *promise = curr->get_node()->get_read_from_promise();
+                       if (promise->add_reader(curr))
+                               priv->failed_promise = true;
+                       curr->set_read_from_promise(promise);
+                       mo_graph->startChanges();
+                       if (!check_recency(curr, promise))
+                               priv->too_many_reads = true;
+                       updated = r_modification_order(curr, promise);
+                       mo_graph->commitChanges();
+                       break;
+               }
+               case READ_FROM_FUTURE: {
+                       /* Read from future value */
+                       struct future_value fv = node->get_future_value();
+                       Promise *promise = new Promise(curr, fv);
+                       curr->set_read_from_promise(promise);
+                       promises->push_back(promise);
+                       mo_graph->startChanges();
+                       updated = r_modification_order(curr, promise);
+                       mo_graph->commitChanges();
+                       break;
+               }
+               default:
+                       ASSERT(false);
+               }
+               get_thread(curr)->set_return_value(curr->get_return_value());
+               return updated;
+       }
+}
+
+/**
+ * Processes a lock, trylock, or unlock model action.  @param curr is
+ * the read model action to process.
+ *
+ * The try lock operation checks whether the lock is taken.  If not,
+ * it falls to the normal lock operation case.  If so, it returns
+ * fail.
+ *
+ * The lock operation has already been checked that it is enabled, so
+ * it just grabs the lock and synchronizes with the previous unlock.
+ *
+ * The unlock operation has to re-enable all of the threads that are
+ * waiting on the lock.
+ *
+ * @return True if synchronization was updated; false otherwise
+ */
+bool ModelExecution::process_mutex(ModelAction *curr)
+{
+       std::mutex *mutex = curr->get_mutex();
+       struct std::mutex_state *state = NULL;
+
+       if (mutex)
+               state = mutex->get_state();
+
+       switch (curr->get_type()) {
+       case ATOMIC_TRYLOCK: {
+               bool success = !state->locked;
+               curr->set_try_lock(success);
+               if (!success) {
+                       get_thread(curr)->set_return_value(0);
+                       break;
+               }
+               get_thread(curr)->set_return_value(1);
+       }
+               //otherwise fall into the lock case
+       case ATOMIC_LOCK: {
+               if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
+                       assert_bug("Lock access before initialization");
+               state->locked = get_thread(curr);
+               ModelAction *unlock = get_last_unlock(curr);
+               //synchronize with the previous unlock statement
+               if (unlock != NULL) {
+                       synchronize(unlock, curr);
+                       return true;
+               }
+               break;
+       }
+       case ATOMIC_WAIT:
+       case ATOMIC_UNLOCK: {
+               /* wake up the other threads */
+               for (unsigned int i = 0; i < get_num_threads(); i++) {
+                       Thread *t = get_thread(int_to_id(i));
+                       Thread *curr_thrd = get_thread(curr);
+                       if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
+                               scheduler->wake(t);
+               }
+
+               /* unlock the lock - after checking who was waiting on it */
+               state->locked = NULL;
+
+               if (!curr->is_wait())
+                       break; /* The rest is only for ATOMIC_WAIT */
+
+               /* Should we go to sleep? (simulate spurious failures) */
+               if (curr->get_node()->get_misc() == 0) {
+                       get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
+                       /* disable us */
+                       scheduler->sleep(get_thread(curr));
+               }
+               break;
+       }
+       case ATOMIC_NOTIFY_ALL: {
+               action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
+               //activate all the waiting threads
+               for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
+                       scheduler->wake(get_thread(*rit));
+               }
+               waiters->clear();
+               break;
+       }
+       case ATOMIC_NOTIFY_ONE: {
+               action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
+               int wakeupthread = curr->get_node()->get_misc();
+               action_list_t::iterator it = waiters->begin();
+               advance(it, wakeupthread);
+               scheduler->wake(get_thread(*it));
+               waiters->erase(it);
+               break;
+       }
+
+       default:
+               ASSERT(0);
+       }
+       return false;
+}
+
+/**
+ * @brief Check if the current pending promises allow a future value to be sent
+ *
+ * If one of the following is true:
+ *  (a) there are no pending promises
+ *  (b) the reader and writer do not cross any promises
+ * Then, it is safe to pass a future value back now.
+ *
+ * Otherwise, we must save the pending future value until (a) or (b) is true
+ *
+ * @param writer The operation which sends the future value. Must be a write.
+ * @param reader The operation which will observe the value. Must be a read.
+ * @return True if the future value can be sent now; false if it must wait.
+ */
+bool ModelExecution::promises_may_allow(const ModelAction *writer,
+               const ModelAction *reader) const
+{
+       if (promises->empty())
+               return true;
+       for(int i=promises->size()-1;i>=0;i--) {
+               ModelAction *pr=(*promises)[i]->get_reader(0);
+               //reader is after promise...doesn't cross any promise
+               if (*reader > *pr)
+                       return true;
+               //writer is after promise, reader before...bad...
+               if (*writer > *pr)
+                       return false;
+       }
+       return true;
+}
+
+/**
+ * @brief Add a future value to a reader
+ *
+ * This function performs a few additional checks to ensure that the future
+ * value can be feasibly observed by the reader
+ *
+ * @param writer The operation whose value is sent. Must be a write.
+ * @param reader The read operation which may read the future value. Must be a read.
+ */
+void ModelExecution::add_future_value(const ModelAction *writer, ModelAction *reader)
+{
+       /* Do more ambitious checks now that mo is more complete */
+       if (!mo_may_allow(writer, reader))
+               return;
+
+       Node *node = reader->get_node();
+
+       /* Find an ancestor thread which exists at the time of the reader */
+       Thread *write_thread = get_thread(writer);
+       while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
+               write_thread = write_thread->get_parent();
+
+       struct future_value fv = {
+               writer->get_write_value(),
+               writer->get_seq_number() + params->maxfuturedelay,
+               write_thread->get_id(),
+       };
+       if (node->add_future_value(fv))
+               set_latest_backtrack(reader);
+}
+
+/**
+ * Process a write ModelAction
+ * @param curr The ModelAction to process
+ * @return True if the mo_graph was updated or promises were resolved
+ */
+bool ModelExecution::process_write(ModelAction *curr)
+{
+       /* Readers to which we may send our future value */
+       ModelVector<ModelAction *> send_fv;
+
+       const ModelAction *earliest_promise_reader;
+       bool updated_promises = false;
+
+       bool updated_mod_order = w_modification_order(curr, &send_fv);
+       Promise *promise = pop_promise_to_resolve(curr);
+
+       if (promise) {
+               earliest_promise_reader = promise->get_reader(0);
+               updated_promises = resolve_promise(curr, promise);
+       } else
+               earliest_promise_reader = NULL;
+
+       for (unsigned int i = 0; i < send_fv.size(); i++) {
+               ModelAction *read = send_fv[i];
+
+               /* Don't send future values to reads after the Promise we resolve */
+               if (!earliest_promise_reader || *read < *earliest_promise_reader) {
+                       /* Check if future value can be sent immediately */
+                       if (promises_may_allow(curr, read)) {
+                               add_future_value(curr, read);
+                       } else {
+                               futurevalues->push_back(PendingFutureValue(curr, read));
+                       }
+               }
+       }
+
+       /* Check the pending future values */
+       for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
+               struct PendingFutureValue pfv = (*futurevalues)[i];
+               if (promises_may_allow(pfv.writer, pfv.reader)) {
+                       add_future_value(pfv.writer, pfv.reader);
+                       futurevalues->erase(futurevalues->begin() + i);
+               }
+       }
+
+       mo_graph->commitChanges();
+       mo_check_promises(curr, false);
+
+       get_thread(curr)->set_return_value(VALUE_NONE);
+       return updated_mod_order || updated_promises;
+}
+
+/**
+ * Process a fence ModelAction
+ * @param curr The ModelAction to process
+ * @return True if synchronization was updated
+ */
+bool ModelExecution::process_fence(ModelAction *curr)
+{
+       /*
+        * fence-relaxed: no-op
+        * fence-release: only log the occurence (not in this function), for
+        *   use in later synchronization
+        * fence-acquire (this function): search for hypothetical release
+        *   sequences
+        * fence-seq-cst: MO constraints formed in {r,w}_modification_order
+        */
+       bool updated = false;
+       if (curr->is_acquire()) {
+               action_list_t *list = action_trace;
+               action_list_t::reverse_iterator rit;
+               /* Find X : is_read(X) && X --sb-> curr */
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *act = *rit;
+                       if (act == curr)
+                               continue;
+                       if (act->get_tid() != curr->get_tid())
+                               continue;
+                       /* Stop at the beginning of the thread */
+                       if (act->is_thread_start())
+                               break;
+                       /* Stop once we reach a prior fence-acquire */
+                       if (act->is_fence() && act->is_acquire())
+                               break;
+                       if (!act->is_read())
+                               continue;
+                       /* read-acquire will find its own release sequences */
+                       if (act->is_acquire())
+                               continue;
+
+                       /* Establish hypothetical release sequences */
+                       rel_heads_list_t release_heads;
+                       get_release_seq_heads(curr, act, &release_heads);
+                       for (unsigned int i = 0; i < release_heads.size(); i++)
+                               synchronize(release_heads[i], curr);
+                       if (release_heads.size() != 0)
+                               updated = true;
+               }
+       }
+       return updated;
+}
+
+/**
+ * @brief Process the current action for thread-related activity
+ *
+ * Performs current-action processing for a THREAD_* ModelAction. Proccesses
+ * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
+ * synchronization, etc.  This function is a no-op for non-THREAD actions
+ * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
+ *
+ * @param curr The current action
+ * @return True if synchronization was updated or a thread completed
+ */
+bool ModelExecution::process_thread_action(ModelAction *curr)
+{
+       bool updated = false;
+
+       switch (curr->get_type()) {
+       case THREAD_CREATE: {
+               thrd_t *thrd = (thrd_t *)curr->get_location();
+               struct thread_params *params = (struct thread_params *)curr->get_value();
+               Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
+               add_thread(th);
+               th->set_creation(curr);
+               /* Promises can be satisfied by children */
+               for (unsigned int i = 0; i < promises->size(); i++) {
+                       Promise *promise = (*promises)[i];
+                       if (promise->thread_is_available(curr->get_tid()))
+                               promise->add_thread(th->get_id());
+               }
+               break;
+       }
+       case THREAD_JOIN: {
+               Thread *blocking = curr->get_thread_operand();
+               ModelAction *act = get_last_action(blocking->get_id());
+               synchronize(act, curr);
+               updated = true; /* trigger rel-seq checks */
+               break;
+       }
+       case THREAD_FINISH: {
+               Thread *th = get_thread(curr);
+               /* Wake up any joining threads */
+               for (unsigned int i = 0; i < get_num_threads(); i++) {
+                       Thread *waiting = get_thread(int_to_id(i));
+                       if (waiting->waiting_on() == th &&
+                                       waiting->get_pending()->is_thread_join())
+                               scheduler->wake(waiting);
+               }
+               th->complete();
+               /* Completed thread can't satisfy promises */
+               for (unsigned int i = 0; i < promises->size(); i++) {
+                       Promise *promise = (*promises)[i];
+                       if (promise->thread_is_available(th->get_id()))
+                               if (promise->eliminate_thread(th->get_id()))
+                                       priv->failed_promise = true;
+               }
+               updated = true; /* trigger rel-seq checks */
+               break;
+       }
+       case THREAD_START: {
+               check_promises(curr->get_tid(), NULL, curr->get_cv());
+               break;
+       }
+       default:
+               break;
+       }
+
+       return updated;
+}
+
+/**
+ * @brief Process the current action for release sequence fixup activity
+ *
+ * Performs model-checker release sequence fixups for the current action,
+ * forcing a single pending release sequence to break (with a given, potential
+ * "loose" write) or to complete (i.e., synchronize). If a pending release
+ * sequence forms a complete release sequence, then we must perform the fixup
+ * synchronization, mo_graph additions, etc.
+ *
+ * @param curr The current action; must be a release sequence fixup action
+ * @param work_queue The work queue to which to add work items as they are
+ * generated
+ */
+void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
+{
+       const ModelAction *write = curr->get_node()->get_relseq_break();
+       struct release_seq *sequence = pending_rel_seqs->back();
+       pending_rel_seqs->pop_back();
+       ASSERT(sequence);
+       ModelAction *acquire = sequence->acquire;
+       const ModelAction *rf = sequence->rf;
+       const ModelAction *release = sequence->release;
+       ASSERT(acquire);
+       ASSERT(release);
+       ASSERT(rf);
+       ASSERT(release->same_thread(rf));
+
+       if (write == NULL) {
+               /**
+                * @todo Forcing a synchronization requires that we set
+                * modification order constraints. For instance, we can't allow
+                * a fixup sequence in which two separate read-acquire
+                * operations read from the same sequence, where the first one
+                * synchronizes and the other doesn't. Essentially, we can't
+                * allow any writes to insert themselves between 'release' and
+                * 'rf'
+                */
+
+               /* Must synchronize */
+               if (!synchronize(release, acquire))
+                       return;
+               /* Re-check all pending release sequences */
+               work_queue->push_back(CheckRelSeqWorkEntry(NULL));
+               /* Re-check act for mo_graph edges */
+               work_queue->push_back(MOEdgeWorkEntry(acquire));
+
+               /* propagate synchronization to later actions */
+               action_list_t::reverse_iterator rit = action_trace->rbegin();
+               for (; (*rit) != acquire; rit++) {
+                       ModelAction *propagate = *rit;
+                       if (acquire->happens_before(propagate)) {
+                               synchronize(acquire, propagate);
+                               /* Re-check 'propagate' for mo_graph edges */
+                               work_queue->push_back(MOEdgeWorkEntry(propagate));
+                       }
+               }
+       } else {
+               /* Break release sequence with new edges:
+                *   release --mo--> write --mo--> rf */
+               mo_graph->addEdge(release, write);
+               mo_graph->addEdge(write, rf);
+       }
+
+       /* See if we have realized a data race */
+       checkDataRaces();
+}
+
+/**
+ * Initialize the current action by performing one or more of the following
+ * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
+ * in the NodeStack, manipulating backtracking sets, allocating and
+ * initializing clock vectors, and computing the promises to fulfill.
+ *
+ * @param curr The current action, as passed from the user context; may be
+ * freed/invalidated after the execution of this function, with a different
+ * action "returned" its place (pass-by-reference)
+ * @return True if curr is a newly-explored action; false otherwise
+ */
+bool ModelExecution::initialize_curr_action(ModelAction **curr)
+{
+       ModelAction *newcurr;
+
+       if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
+               newcurr = process_rmw(*curr);
+               delete *curr;
+
+               if (newcurr->is_rmw())
+                       compute_promises(newcurr);
+
+               *curr = newcurr;
+               return false;
+       }
+
+       (*curr)->set_seq_number(get_next_seq_num());
+
+       newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
+       if (newcurr) {
+               /* First restore type and order in case of RMW operation */
+               if ((*curr)->is_rmwr())
+                       newcurr->copy_typeandorder(*curr);
+
+               ASSERT((*curr)->get_location() == newcurr->get_location());
+               newcurr->copy_from_new(*curr);
+
+               /* Discard duplicate ModelAction; use action from NodeStack */
+               delete *curr;
+
+               /* Always compute new clock vector */
+               newcurr->create_cv(get_parent_action(newcurr->get_tid()));
+
+               *curr = newcurr;
+               return false; /* Action was explored previously */
+       } else {
+               newcurr = *curr;
+
+               /* Always compute new clock vector */
+               newcurr->create_cv(get_parent_action(newcurr->get_tid()));
+
+               /* Assign most recent release fence */
+               newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
+
+               /*
+                * Perform one-time actions when pushing new ModelAction onto
+                * NodeStack
+                */
+               if (newcurr->is_write())
+                       compute_promises(newcurr);
+               else if (newcurr->is_relseq_fixup())
+                       compute_relseq_breakwrites(newcurr);
+               else if (newcurr->is_wait())
+                       newcurr->get_node()->set_misc_max(2);
+               else if (newcurr->is_notify_one()) {
+                       newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
+               }
+               return true; /* This was a new ModelAction */
+       }
+}
+
+/**
+ * @brief Establish reads-from relation between two actions
+ *
+ * Perform basic operations involved with establishing a concrete rf relation,
+ * including setting the ModelAction data and checking for release sequences.
+ *
+ * @param act The action that is reading (must be a read)
+ * @param rf The action from which we are reading (must be a write)
+ *
+ * @return True if this read established synchronization
+ */
+bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
+{
+       ASSERT(rf);
+       ASSERT(rf->is_write());
+
+       act->set_read_from(rf);
+       if (act->is_acquire()) {
+               rel_heads_list_t release_heads;
+               get_release_seq_heads(act, act, &release_heads);
+               int num_heads = release_heads.size();
+               for (unsigned int i = 0; i < release_heads.size(); i++)
+                       if (!synchronize(release_heads[i], act))
+                               num_heads--;
+               return num_heads > 0;
+       }
+       return false;
+}
+
+/**
+ * @brief Synchronizes two actions
+ *
+ * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
+ * This function performs the synchronization as well as providing other hooks
+ * for other checks along with synchronization.
+ *
+ * @param first The left-hand side of the synchronizes-with relation
+ * @param second The right-hand side of the synchronizes-with relation
+ * @return True if the synchronization was successful (i.e., was consistent
+ * with the execution order); false otherwise
+ */
+bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
+{
+       if (*second < *first) {
+               set_bad_synchronization();
+               return false;
+       }
+       check_promises(first->get_tid(), second->get_cv(), first->get_cv());
+       return second->synchronize_with(first);
+}
+
+/**
+ * Check promises and eliminate potentially-satisfying threads when a thread is
+ * blocked (e.g., join, lock). A thread which is waiting on another thread can
+ * no longer satisfy a promise generated from that thread.
+ *
+ * @param blocker The thread on which a thread is waiting
+ * @param waiting The waiting thread
+ */
+void ModelExecution::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
+{
+       for (unsigned int i = 0; i < promises->size(); i++) {
+               Promise *promise = (*promises)[i];
+               if (!promise->thread_is_available(waiting->get_id()))
+                       continue;
+               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
+                       ModelAction *reader = promise->get_reader(j);
+                       if (reader->get_tid() != blocker->get_id())
+                               continue;
+                       if (promise->eliminate_thread(waiting->get_id())) {
+                               /* Promise has failed */
+                               priv->failed_promise = true;
+                       } else {
+                               /* Only eliminate the 'waiting' thread once */
+                               return;
+                       }
+               }
+       }
+}
+
+/**
+ * @brief Check whether a model action is enabled.
+ *
+ * Checks whether a lock or join operation would be successful (i.e., is the
+ * lock already locked, or is the joined thread already complete). If not, put
+ * the action in a waiter list.
+ *
+ * @param curr is the ModelAction to check whether it is enabled.
+ * @return a bool that indicates whether the action is enabled.
+ */
+bool ModelExecution::check_action_enabled(ModelAction *curr) {
+       if (curr->is_lock()) {
+               std::mutex *lock = curr->get_mutex();
+               struct std::mutex_state *state = lock->get_state();
+               if (state->locked)
+                       return false;
+       } else if (curr->is_thread_join()) {
+               Thread *blocking = curr->get_thread_operand();
+               if (!blocking->is_complete()) {
+                       thread_blocking_check_promises(blocking, get_thread(curr));
+                       return false;
+               }
+       }
+
+       return true;
+}
+
+/**
+ * This is the heart of the model checker routine. It performs model-checking
+ * actions corresponding to a given "current action." Among other processes, it
+ * calculates reads-from relationships, updates synchronization clock vectors,
+ * forms a memory_order constraints graph, and handles replay/backtrack
+ * execution when running permutations of previously-observed executions.
+ *
+ * @param curr The current action to process
+ * @return The ModelAction that is actually executed; may be different than
+ * curr; may be NULL, if the current action is not enabled to run
+ */
+ModelAction * ModelExecution::check_current_action(ModelAction *curr)
+{
+       ASSERT(curr);
+       bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
+       bool newly_explored = initialize_curr_action(&curr);
+
+       DBG();
+
+       wake_up_sleeping_actions(curr);
+
+       /* Compute fairness information for CHESS yield algorithm */
+       if (params->yieldon) {
+               curr->get_node()->update_yield(scheduler);
+       }
+
+       /* Add the action to lists before any other model-checking tasks */
+       if (!second_part_of_rmw)
+               add_action_to_lists(curr);
+
+       /* Build may_read_from set for newly-created actions */
+       if (newly_explored && curr->is_read())
+               build_may_read_from(curr);
+
+       /* Initialize work_queue with the "current action" work */
+       work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
+       while (!work_queue.empty() && !has_asserted()) {
+               WorkQueueEntry work = work_queue.front();
+               work_queue.pop_front();
+
+               switch (work.type) {
+               case WORK_CHECK_CURR_ACTION: {
+                       ModelAction *act = work.action;
+                       bool update = false; /* update this location's release seq's */
+                       bool update_all = false; /* update all release seq's */
+
+                       if (process_thread_action(curr))
+                               update_all = true;
+
+                       if (act->is_read() && !second_part_of_rmw && process_read(act))
+                               update = true;
+
+                       if (act->is_write() && process_write(act))
+                               update = true;
+
+                       if (act->is_fence() && process_fence(act))
+                               update_all = true;
+
+                       if (act->is_mutex_op() && process_mutex(act))
+                               update_all = true;
+
+                       if (act->is_relseq_fixup())
+                               process_relseq_fixup(curr, &work_queue);
+
+                       if (update_all)
+                               work_queue.push_back(CheckRelSeqWorkEntry(NULL));
+                       else if (update)
+                               work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
+                       break;
+               }
+               case WORK_CHECK_RELEASE_SEQ:
+                       resolve_release_sequences(work.location, &work_queue);
+                       break;
+               case WORK_CHECK_MO_EDGES: {
+                       /** @todo Complete verification of work_queue */
+                       ModelAction *act = work.action;
+                       bool updated = false;
+
+                       if (act->is_read()) {
+                               const ModelAction *rf = act->get_reads_from();
+                               const Promise *promise = act->get_reads_from_promise();
+                               if (rf) {
+                                       if (r_modification_order(act, rf))
+                                               updated = true;
+                               } else if (promise) {
+                                       if (r_modification_order(act, promise))
+                                               updated = true;
+                               }
+                       }
+                       if (act->is_write()) {
+                               if (w_modification_order(act, NULL))
+                                       updated = true;
+                       }
+                       mo_graph->commitChanges();
+
+                       if (updated)
+                               work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
+                       break;
+               }
+               default:
+                       ASSERT(false);
+                       break;
+               }
+       }
+
+       check_curr_backtracking(curr);
+       set_backtracking(curr);
+       return curr;
+}
+
+void ModelExecution::check_curr_backtracking(ModelAction *curr)
+{
+       Node *currnode = curr->get_node();
+       Node *parnode = currnode->get_parent();
+
+       if ((parnode && !parnode->backtrack_empty()) ||
+                        !currnode->misc_empty() ||
+                        !currnode->read_from_empty() ||
+                        !currnode->promise_empty() ||
+                        !currnode->relseq_break_empty()) {
+               set_latest_backtrack(curr);
+       }
+}
+
+bool ModelExecution::promises_expired() const
+{
+       for (unsigned int i = 0; i < promises->size(); i++) {
+               Promise *promise = (*promises)[i];
+               if (promise->get_expiration() < priv->used_sequence_numbers)
+                       return true;
+       }
+       return false;
+}
+
+/**
+ * This is the strongest feasibility check available.
+ * @return whether the current trace (partial or complete) must be a prefix of
+ * a feasible trace.
+ */
+bool ModelExecution::isfeasibleprefix() const
+{
+       return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
+}
+
+/**
+ * Print disagnostic information about an infeasible execution
+ * @param prefix A string to prefix the output with; if NULL, then a default
+ * message prefix will be provided
+ */
+void ModelExecution::print_infeasibility(const char *prefix) const
+{
+       char buf[100];
+       char *ptr = buf;
+       if (mo_graph->checkForCycles())
+               ptr += sprintf(ptr, "[mo cycle]");
+       if (priv->failed_promise)
+               ptr += sprintf(ptr, "[failed promise]");
+       if (priv->too_many_reads)
+               ptr += sprintf(ptr, "[too many reads]");
+       if (priv->no_valid_reads)
+               ptr += sprintf(ptr, "[no valid reads-from]");
+       if (priv->bad_synchronization)
+               ptr += sprintf(ptr, "[bad sw ordering]");
+       if (promises_expired())
+               ptr += sprintf(ptr, "[promise expired]");
+       if (promises->size() != 0)
+               ptr += sprintf(ptr, "[unresolved promise]");
+       if (ptr != buf)
+               model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
+}
+
+/**
+ * Returns whether the current completed trace is feasible, except for pending
+ * release sequences.
+ */
+bool ModelExecution::is_feasible_prefix_ignore_relseq() const
+{
+       return !is_infeasible() && promises->size() == 0;
+}
+
+/**
+ * Check if the current partial trace is infeasible. Does not check any
+ * end-of-execution flags, which might rule out the execution. Thus, this is
+ * useful only for ruling an execution as infeasible.
+ * @return whether the current partial trace is infeasible.
+ */
+bool ModelExecution::is_infeasible() const
+{
+       return mo_graph->checkForCycles() ||
+               priv->no_valid_reads ||
+               priv->failed_promise ||
+               priv->too_many_reads ||
+               priv->bad_synchronization ||
+               promises_expired();
+}
+
+/** Close out a RMWR by converting previous RMWR into a RMW or READ. */
+ModelAction * ModelExecution::process_rmw(ModelAction *act) {
+       ModelAction *lastread = get_last_action(act->get_tid());
+       lastread->process_rmw(act);
+       if (act->is_rmw()) {
+               if (lastread->get_reads_from())
+                       mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
+               else
+                       mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
+               mo_graph->commitChanges();
+       }
+       return lastread;
+}
+
+/**
+ * A helper function for ModelExecution::check_recency, to check if the current
+ * thread is able to read from a different write/promise for 'params.maxreads'
+ * number of steps and if that write/promise should become visible (i.e., is
+ * ordered later in the modification order). This helps model memory liveness.
+ *
+ * @param curr The current action. Must be a read.
+ * @param rf The write/promise from which we plan to read
+ * @param other_rf The write/promise from which we may read
+ * @return True if we were able to read from other_rf for params.maxreads steps
+ */
+template <typename T, typename U>
+bool ModelExecution::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
+{
+       /* Need a different write/promise */
+       if (other_rf->equals(rf))
+               return false;
+
+       /* Only look for "newer" writes/promises */
+       if (!mo_graph->checkReachable(rf, other_rf))
+               return false;
+
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
+       action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
+       action_list_t::reverse_iterator rit = list->rbegin();
+       ASSERT((*rit) == curr);
+       /* Skip past curr */
+       rit++;
+
+       /* Does this write/promise work for everyone? */
+       for (int i = 0; i < params->maxreads; i++, rit++) {
+               ModelAction *act = *rit;
+               if (!act->may_read_from(other_rf))
+                       return false;
+       }
+       return true;
+}
+
+/**
+ * Checks whether a thread has read from the same write or Promise for too many
+ * times without seeing the effects of a later write/Promise.
+ *
+ * Basic idea:
+ * 1) there must a different write/promise that we could read from,
+ * 2) we must have read from the same write/promise in excess of maxreads times,
+ * 3) that other write/promise must have been in the reads_from set for maxreads times, and
+ * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
+ *
+ * If so, we decide that the execution is no longer feasible.
+ *
+ * @param curr The current action. Must be a read.
+ * @param rf The ModelAction/Promise from which we might read.
+ * @return True if the read should succeed; false otherwise
+ */
+template <typename T>
+bool ModelExecution::check_recency(ModelAction *curr, const T *rf) const
+{
+       if (!params->maxreads)
+               return true;
+
+       //NOTE: Next check is just optimization, not really necessary....
+       if (curr->get_node()->get_read_from_past_size() +
+                       curr->get_node()->get_read_from_promise_size() <= 1)
+               return true;
+
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
+       int tid = id_to_int(curr->get_tid());
+       ASSERT(tid < (int)thrd_lists->size());
+       action_list_t *list = &(*thrd_lists)[tid];
+       action_list_t::reverse_iterator rit = list->rbegin();
+       ASSERT((*rit) == curr);
+       /* Skip past curr */
+       rit++;
+
+       action_list_t::reverse_iterator ritcopy = rit;
+       /* See if we have enough reads from the same value */
+       for (int count = 0; count < params->maxreads; ritcopy++, count++) {
+               if (ritcopy == list->rend())
+                       return true;
+               ModelAction *act = *ritcopy;
+               if (!act->is_read())
+                       return true;
+               if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
+                       return true;
+               if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
+                       return true;
+               if (act->get_node()->get_read_from_past_size() +
+                               act->get_node()->get_read_from_promise_size() <= 1)
+                       return true;
+       }
+       for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
+               const ModelAction *write = curr->get_node()->get_read_from_past(i);
+               if (should_read_instead(curr, rf, write))
+                       return false; /* liveness failure */
+       }
+       for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
+               const Promise *promise = curr->get_node()->get_read_from_promise(i);
+               if (should_read_instead(curr, rf, promise))
+                       return false; /* liveness failure */
+       }
+       return true;
+}
+
+/**
+ * @brief Updates the mo_graph with the constraints imposed from the current
+ * read.
+ *
+ * Basic idea is the following: Go through each other thread and find
+ * the last action that happened before our read.  Two cases:
+ *
+ * -# The action is a write: that write must either occur before
+ * the write we read from or be the write we read from.
+ * -# The action is a read: the write that that action read from
+ * must occur before the write we read from or be the same write.
+ *
+ * @param curr The current action. Must be a read.
+ * @param rf The ModelAction or Promise that curr reads from. Must be a write.
+ * @return True if modification order edges were added; false otherwise
+ */
+template <typename rf_type>
+bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
+{
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
+       unsigned int i;
+       bool added = false;
+       ASSERT(curr->is_read());
+
+       /* Last SC fence in the current thread */
+       ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
+       ModelAction *last_sc_write = NULL;
+       if (curr->is_seqcst())
+               last_sc_write = get_last_seq_cst_write(curr);
+
+       /* Iterate over all threads */
+       for (i = 0; i < thrd_lists->size(); i++) {
+               /* Last SC fence in thread i */
+               ModelAction *last_sc_fence_thread_local = NULL;
+               if (int_to_id((int)i) != curr->get_tid())
+                       last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
+
+               /* Last SC fence in thread i, before last SC fence in current thread */
+               ModelAction *last_sc_fence_thread_before = NULL;
+               if (last_sc_fence_local)
+                       last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
+
+               /* Iterate over actions in thread, starting from most recent */
+               action_list_t *list = &(*thrd_lists)[i];
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *act = *rit;
+
+                       /* Skip curr */
+                       if (act == curr)
+                               continue;
+                       /* Don't want to add reflexive edges on 'rf' */
+                       if (act->equals(rf)) {
+                               if (act->happens_before(curr))
+                                       break;
+                               else
+                                       continue;
+                       }
+
+                       if (act->is_write()) {
+                               /* C++, Section 29.3 statement 5 */
+                               if (curr->is_seqcst() && last_sc_fence_thread_local &&
+                                               *act < *last_sc_fence_thread_local) {
+                                       added = mo_graph->addEdge(act, rf) || added;
+                                       break;
+                               }
+                               /* C++, Section 29.3 statement 4 */
+                               else if (act->is_seqcst() && last_sc_fence_local &&
+                                               *act < *last_sc_fence_local) {
+                                       added = mo_graph->addEdge(act, rf) || added;
+                                       break;
+                               }
+                               /* C++, Section 29.3 statement 6 */
+                               else if (last_sc_fence_thread_before &&
+                                               *act < *last_sc_fence_thread_before) {
+                                       added = mo_graph->addEdge(act, rf) || added;
+                                       break;
+                               }
+                       }
+
+                       /* C++, Section 29.3 statement 3 (second subpoint) */
+                       if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
+                               added = mo_graph->addEdge(act, rf) || added;
+                               break;
+                       }
+
+                       /*
+                        * Include at most one act per-thread that "happens
+                        * before" curr
+                        */
+                       if (act->happens_before(curr)) {
+                               if (act->is_write()) {
+                                       added = mo_graph->addEdge(act, rf) || added;
+                               } else {
+                                       const ModelAction *prevrf = act->get_reads_from();
+                                       const Promise *prevrf_promise = act->get_reads_from_promise();
+                                       if (prevrf) {
+                                               if (!prevrf->equals(rf))
+                                                       added = mo_graph->addEdge(prevrf, rf) || added;
+                                       } else if (!prevrf_promise->equals(rf)) {
+                                               added = mo_graph->addEdge(prevrf_promise, rf) || added;
+                                       }
+                               }
+                               break;
+                       }
+               }
+       }
+
+       /*
+        * All compatible, thread-exclusive promises must be ordered after any
+        * concrete loads from the same thread
+        */
+       for (unsigned int i = 0; i < promises->size(); i++)
+               if ((*promises)[i]->is_compatible_exclusive(curr))
+                       added = mo_graph->addEdge(rf, (*promises)[i]) || added;
+
+       return added;
+}
+
+/**
+ * Updates the mo_graph with the constraints imposed from the current write.
+ *
+ * Basic idea is the following: Go through each other thread and find
+ * the lastest action that happened before our write.  Two cases:
+ *
+ * (1) The action is a write => that write must occur before
+ * the current write
+ *
+ * (2) The action is a read => the write that that action read from
+ * must occur before the current write.
+ *
+ * This method also handles two other issues:
+ *
+ * (I) Sequential Consistency: Making sure that if the current write is
+ * seq_cst, that it occurs after the previous seq_cst write.
+ *
+ * (II) Sending the write back to non-synchronizing reads.
+ *
+ * @param curr The current action. Must be a write.
+ * @param send_fv A vector for stashing reads to which we may pass our future
+ * value. If NULL, then don't record any future values.
+ * @return True if modification order edges were added; false otherwise
+ */
+bool ModelExecution::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
+{
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
+       unsigned int i;
+       bool added = false;
+       ASSERT(curr->is_write());
+
+       if (curr->is_seqcst()) {
+               /* We have to at least see the last sequentially consistent write,
+                        so we are initialized. */
+               ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
+               if (last_seq_cst != NULL) {
+                       added = mo_graph->addEdge(last_seq_cst, curr) || added;
+               }
+       }
+
+       /* Last SC fence in the current thread */
+       ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
+
+       /* Iterate over all threads */
+       for (i = 0; i < thrd_lists->size(); i++) {
+               /* Last SC fence in thread i, before last SC fence in current thread */
+               ModelAction *last_sc_fence_thread_before = NULL;
+               if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
+                       last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
+
+               /* Iterate over actions in thread, starting from most recent */
+               action_list_t *list = &(*thrd_lists)[i];
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *act = *rit;
+                       if (act == curr) {
+                               /*
+                                * 1) If RMW and it actually read from something, then we
+                                * already have all relevant edges, so just skip to next
+                                * thread.
+                                *
+                                * 2) If RMW and it didn't read from anything, we should
+                                * whatever edge we can get to speed up convergence.
+                                *
+                                * 3) If normal write, we need to look at earlier actions, so
+                                * continue processing list.
+                                */
+                               if (curr->is_rmw()) {
+                                       if (curr->get_reads_from() != NULL)
+                                               break;
+                                       else
+                                               continue;
+                               } else
+                                       continue;
+                       }
+
+                       /* C++, Section 29.3 statement 7 */
+                       if (last_sc_fence_thread_before && act->is_write() &&
+                                       *act < *last_sc_fence_thread_before) {
+                               added = mo_graph->addEdge(act, curr) || added;
+                               break;
+                       }
+
+                       /*
+                        * Include at most one act per-thread that "happens
+                        * before" curr
+                        */
+                       if (act->happens_before(curr)) {
+                               /*
+                                * Note: if act is RMW, just add edge:
+                                *   act --mo--> curr
+                                * The following edge should be handled elsewhere:
+                                *   readfrom(act) --mo--> act
+                                */
+                               if (act->is_write())
+                                       added = mo_graph->addEdge(act, curr) || added;
+                               else if (act->is_read()) {
+                                       //if previous read accessed a null, just keep going
+                                       if (act->get_reads_from() == NULL)
+                                               continue;
+                                       added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
+                               }
+                               break;
+                       } else if (act->is_read() && !act->could_synchronize_with(curr) &&
+                                                    !act->same_thread(curr)) {
+                               /* We have an action that:
+                                  (1) did not happen before us
+                                  (2) is a read and we are a write
+                                  (3) cannot synchronize with us
+                                  (4) is in a different thread
+                                  =>
+                                  that read could potentially read from our write.  Note that
+                                  these checks are overly conservative at this point, we'll
+                                  do more checks before actually removing the
+                                  pendingfuturevalue.
+
+                                */
+                               if (send_fv && thin_air_constraint_may_allow(curr, act)) {
+                                       if (!is_infeasible())
+                                               send_fv->push_back(act);
+                                       else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
+                                               add_future_value(curr, act);
+                               }
+                       }
+               }
+       }
+
+       /*
+        * All compatible, thread-exclusive promises must be ordered after any
+        * concrete stores to the same thread, or else they can be merged with
+        * this store later
+        */
+       for (unsigned int i = 0; i < promises->size(); i++)
+               if ((*promises)[i]->is_compatible_exclusive(curr))
+                       added = mo_graph->addEdge(curr, (*promises)[i]) || added;
+
+       return added;
+}
+
+/** Arbitrary reads from the future are not allowed.  Section 29.3
+ * part 9 places some constraints.  This method checks one result of constraint
+ * constraint.  Others require compiler support. */
+bool ModelExecution::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
+{
+       if (!writer->is_rmw())
+               return true;
+
+       if (!reader->is_rmw())
+               return true;
+
+       for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
+               if (search == reader)
+                       return false;
+               if (search->get_tid() == reader->get_tid() &&
+                               search->happens_before(reader))
+                       break;
+       }
+
+       return true;
+}
+
+/**
+ * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
+ * some constraints. This method checks one the following constraint (others
+ * require compiler support):
+ *
+ *   If X --hb-> Y --mo-> Z, then X should not read from Z.
+ */
+bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
+{
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
+       unsigned int i;
+       /* Iterate over all threads */
+       for (i = 0; i < thrd_lists->size(); i++) {
+               const ModelAction *write_after_read = NULL;
+
+               /* Iterate over actions in thread, starting from most recent */
+               action_list_t *list = &(*thrd_lists)[i];
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *act = *rit;
+
+                       /* Don't disallow due to act == reader */
+                       if (!reader->happens_before(act) || reader == act)
+                               break;
+                       else if (act->is_write())
+                               write_after_read = act;
+                       else if (act->is_read() && act->get_reads_from() != NULL)
+                               write_after_read = act->get_reads_from();
+               }
+
+               if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
+                       return false;
+       }
+       return true;
+}
+
+/**
+ * Finds the head(s) of the release sequence(s) containing a given ModelAction.
+ * The ModelAction under consideration is expected to be taking part in
+ * release/acquire synchronization as an object of the "reads from" relation.
+ * Note that this can only provide release sequence support for RMW chains
+ * which do not read from the future, as those actions cannot be traced until
+ * their "promise" is fulfilled. Similarly, we may not even establish the
+ * presence of a release sequence with certainty, as some modification order
+ * constraints may be decided further in the future. Thus, this function
+ * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
+ * and a boolean representing certainty.
+ *
+ * @param rf The action that might be part of a release sequence. Must be a
+ * write.
+ * @param release_heads A pass-by-reference style return parameter. After
+ * execution of this function, release_heads will contain the heads of all the
+ * relevant release sequences, if any exists with certainty
+ * @param pending A pass-by-reference style return parameter which is only used
+ * when returning false (i.e., uncertain). Returns most information regarding
+ * an uncertain release sequence, including any write operations that might
+ * break the sequence.
+ * @return true, if the ModelExecution is certain that release_heads is complete;
+ * false otherwise
+ */
+bool ModelExecution::release_seq_heads(const ModelAction *rf,
+               rel_heads_list_t *release_heads,
+               struct release_seq *pending) const
+{
+       /* Only check for release sequences if there are no cycles */
+       if (mo_graph->checkForCycles())
+               return false;
+
+       for ( ; rf != NULL; rf = rf->get_reads_from()) {
+               ASSERT(rf->is_write());
+
+               if (rf->is_release())
+                       release_heads->push_back(rf);
+               else if (rf->get_last_fence_release())
+                       release_heads->push_back(rf->get_last_fence_release());
+               if (!rf->is_rmw())
+                       break; /* End of RMW chain */
+
+               /** @todo Need to be smarter here...  In the linux lock
+                * example, this will run to the beginning of the program for
+                * every acquire. */
+               /** @todo The way to be smarter here is to keep going until 1
+                * thread has a release preceded by an acquire and you've seen
+                *       both. */
+
+               /* acq_rel RMW is a sufficient stopping condition */
+               if (rf->is_acquire() && rf->is_release())
+                       return true; /* complete */
+       };
+       if (!rf) {
+               /* read from future: need to settle this later */
+               pending->rf = NULL;
+               return false; /* incomplete */
+       }
+
+       if (rf->is_release())
+               return true; /* complete */
+
+       /* else relaxed write
+        * - check for fence-release in the same thread (29.8, stmt. 3)
+        * - check modification order for contiguous subsequence
+        *   -> rf must be same thread as release */
+
+       const ModelAction *fence_release = rf->get_last_fence_release();
+       /* Synchronize with a fence-release unconditionally; we don't need to
+        * find any more "contiguous subsequence..." for it */
+       if (fence_release)
+               release_heads->push_back(fence_release);
+
+       int tid = id_to_int(rf->get_tid());
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
+       action_list_t *list = &(*thrd_lists)[tid];
+       action_list_t::const_reverse_iterator rit;
+
+       /* Find rf in the thread list */
+       rit = std::find(list->rbegin(), list->rend(), rf);
+       ASSERT(rit != list->rend());
+
+       /* Find the last {write,fence}-release */
+       for (; rit != list->rend(); rit++) {
+               if (fence_release && *(*rit) < *fence_release)
+                       break;
+               if ((*rit)->is_release())
+                       break;
+       }
+       if (rit == list->rend()) {
+               /* No write-release in this thread */
+               return true; /* complete */
+       } else if (fence_release && *(*rit) < *fence_release) {
+               /* The fence-release is more recent (and so, "stronger") than
+                * the most recent write-release */
+               return true; /* complete */
+       } /* else, need to establish contiguous release sequence */
+       ModelAction *release = *rit;
+
+       ASSERT(rf->same_thread(release));
+
+       pending->writes.clear();
+
+       bool certain = true;
+       for (unsigned int i = 0; i < thrd_lists->size(); i++) {
+               if (id_to_int(rf->get_tid()) == (int)i)
+                       continue;
+               list = &(*thrd_lists)[i];
+
+               /* Can we ensure no future writes from this thread may break
+                * the release seq? */
+               bool future_ordered = false;
+
+               ModelAction *last = get_last_action(int_to_id(i));
+               Thread *th = get_thread(int_to_id(i));
+               if ((last && rf->happens_before(last)) ||
+                               !is_enabled(th) ||
+                               th->is_complete())
+                       future_ordered = true;
+
+               ASSERT(!th->is_model_thread() || future_ordered);
+
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       const ModelAction *act = *rit;
+                       /* Reach synchronization -> this thread is complete */
+                       if (act->happens_before(release))
+                               break;
+                       if (rf->happens_before(act)) {
+                               future_ordered = true;
+                               continue;
+                       }
+
+                       /* Only non-RMW writes can break release sequences */
+                       if (!act->is_write() || act->is_rmw())
+                               continue;
+
+                       /* Check modification order */
+                       if (mo_graph->checkReachable(rf, act)) {
+                               /* rf --mo--> act */
+                               future_ordered = true;
+                               continue;
+                       }
+                       if (mo_graph->checkReachable(act, release))
+                               /* act --mo--> release */
+                               break;
+                       if (mo_graph->checkReachable(release, act) &&
+                                     mo_graph->checkReachable(act, rf)) {
+                               /* release --mo-> act --mo--> rf */
+                               return true; /* complete */
+                       }
+                       /* act may break release sequence */
+                       pending->writes.push_back(act);
+                       certain = false;
+               }
+               if (!future_ordered)
+                       certain = false; /* This thread is uncertain */
+       }
+
+       if (certain) {
+               release_heads->push_back(release);
+               pending->writes.clear();
+       } else {
+               pending->release = release;
+               pending->rf = rf;
+       }
+       return certain;
+}
+
+/**
+ * An interface for getting the release sequence head(s) with which a
+ * given ModelAction must synchronize. This function only returns a non-empty
+ * result when it can locate a release sequence head with certainty. Otherwise,
+ * it may mark the internal state of the ModelExecution so that it will handle
+ * the release sequence at a later time, causing @a acquire to update its
+ * synchronization at some later point in execution.
+ *
+ * @param acquire The 'acquire' action that may synchronize with a release
+ * sequence
+ * @param read The read action that may read from a release sequence; this may
+ * be the same as acquire, or else an earlier action in the same thread (i.e.,
+ * when 'acquire' is a fence-acquire)
+ * @param release_heads A pass-by-reference return parameter. Will be filled
+ * with the head(s) of the release sequence(s), if they exists with certainty.
+ * @see ModelExecution::release_seq_heads
+ */
+void ModelExecution::get_release_seq_heads(ModelAction *acquire,
+               ModelAction *read, rel_heads_list_t *release_heads)
+{
+       const ModelAction *rf = read->get_reads_from();
+       struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
+       sequence->acquire = acquire;
+       sequence->read = read;
+
+       if (!release_seq_heads(rf, release_heads, sequence)) {
+               /* add act to 'lazy checking' list */
+               pending_rel_seqs->push_back(sequence);
+       } else {
+               snapshot_free(sequence);
+       }
+}
+
+/**
+ * Attempt to resolve all stashed operations that might synchronize with a
+ * release sequence for a given location. This implements the "lazy" portion of
+ * determining whether or not a release sequence was contiguous, since not all
+ * modification order information is present at the time an action occurs.
+ *
+ * @param location The location/object that should be checked for release
+ * sequence resolutions. A NULL value means to check all locations.
+ * @param work_queue The work queue to which to add work items as they are
+ * generated
+ * @return True if any updates occurred (new synchronization, new mo_graph
+ * edges)
+ */
+bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
+{
+       bool updated = false;
+       SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
+       while (it != pending_rel_seqs->end()) {
+               struct release_seq *pending = *it;
+               ModelAction *acquire = pending->acquire;
+               const ModelAction *read = pending->read;
+
+               /* Only resolve sequences on the given location, if provided */
+               if (location && read->get_location() != location) {
+                       it++;
+                       continue;
+               }
+
+               const ModelAction *rf = read->get_reads_from();
+               rel_heads_list_t release_heads;
+               bool complete;
+               complete = release_seq_heads(rf, &release_heads, pending);
+               for (unsigned int i = 0; i < release_heads.size(); i++)
+                       if (!acquire->has_synchronized_with(release_heads[i]))
+                               if (synchronize(release_heads[i], acquire))
+                                       updated = true;
+
+               if (updated) {
+                       /* Re-check all pending release sequences */
+                       work_queue->push_back(CheckRelSeqWorkEntry(NULL));
+                       /* Re-check read-acquire for mo_graph edges */
+                       if (acquire->is_read())
+                               work_queue->push_back(MOEdgeWorkEntry(acquire));
+
+                       /* propagate synchronization to later actions */
+                       action_list_t::reverse_iterator rit = action_trace->rbegin();
+                       for (; (*rit) != acquire; rit++) {
+                               ModelAction *propagate = *rit;
+                               if (acquire->happens_before(propagate)) {
+                                       synchronize(acquire, propagate);
+                                       /* Re-check 'propagate' for mo_graph edges */
+                                       work_queue->push_back(MOEdgeWorkEntry(propagate));
+                               }
+                       }
+               }
+               if (complete) {
+                       it = pending_rel_seqs->erase(it);
+                       snapshot_free(pending);
+               } else {
+                       it++;
+               }
+       }
+
+       // If we resolved promises or data races, see if we have realized a data race.
+       checkDataRaces();
+
+       return updated;
+}
+
+/**
+ * Performs various bookkeeping operations for the current ModelAction. For
+ * instance, adds action to the per-object, per-thread action vector and to the
+ * action trace list of all thread actions.
+ *
+ * @param act is the ModelAction to add.
+ */
+void ModelExecution::add_action_to_lists(ModelAction *act)
+{
+       int tid = id_to_int(act->get_tid());
+       ModelAction *uninit = NULL;
+       int uninit_id = -1;
+       action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
+       if (list->empty() && act->is_atomic_var()) {
+               uninit = get_uninitialized_action(act);
+               uninit_id = id_to_int(uninit->get_tid());
+               list->push_front(uninit);
+       }
+       list->push_back(act);
+
+       action_trace->push_back(act);
+       if (uninit)
+               action_trace->push_front(uninit);
+
+       SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
+       if (tid >= (int)vec->size())
+               vec->resize(priv->next_thread_id);
+       (*vec)[tid].push_back(act);
+       if (uninit)
+               (*vec)[uninit_id].push_front(uninit);
+
+       if ((int)thrd_last_action->size() <= tid)
+               thrd_last_action->resize(get_num_threads());
+       (*thrd_last_action)[tid] = act;
+       if (uninit)
+               (*thrd_last_action)[uninit_id] = uninit;
+
+       if (act->is_fence() && act->is_release()) {
+               if ((int)thrd_last_fence_release->size() <= tid)
+                       thrd_last_fence_release->resize(get_num_threads());
+               (*thrd_last_fence_release)[tid] = act;
+       }
+
+       if (act->is_wait()) {
+               void *mutex_loc = (void *) act->get_value();
+               get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
+
+               SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
+               if (tid >= (int)vec->size())
+                       vec->resize(priv->next_thread_id);
+               (*vec)[tid].push_back(act);
+       }
+}
+
+/**
+ * @brief Get the last action performed by a particular Thread
+ * @param tid The thread ID of the Thread in question
+ * @return The last action in the thread
+ */
+ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
+{
+       int threadid = id_to_int(tid);
+       if (threadid < (int)thrd_last_action->size())
+               return (*thrd_last_action)[id_to_int(tid)];
+       else
+               return NULL;
+}
+
+/**
+ * @brief Get the last fence release performed by a particular Thread
+ * @param tid The thread ID of the Thread in question
+ * @return The last fence release in the thread, if one exists; NULL otherwise
+ */
+ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
+{
+       int threadid = id_to_int(tid);
+       if (threadid < (int)thrd_last_fence_release->size())
+               return (*thrd_last_fence_release)[id_to_int(tid)];
+       else
+               return NULL;
+}
+
+/**
+ * Gets the last memory_order_seq_cst write (in the total global sequence)
+ * performed on a particular object (i.e., memory location), not including the
+ * current action.
+ * @param curr The current ModelAction; also denotes the object location to
+ * check
+ * @return The last seq_cst write
+ */
+ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
+{
+       void *location = curr->get_location();
+       action_list_t *list = get_safe_ptr_action(obj_map, location);
+       /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
+       action_list_t::reverse_iterator rit;
+       for (rit = list->rbegin(); (*rit) != curr; rit++)
+               ;
+       rit++; /* Skip past curr */
+       for ( ; rit != list->rend(); rit++)
+               if ((*rit)->is_write() && (*rit)->is_seqcst())
+                       return *rit;
+       return NULL;
+}
+
+/**
+ * Gets the last memory_order_seq_cst fence (in the total global sequence)
+ * performed in a particular thread, prior to a particular fence.
+ * @param tid The ID of the thread to check
+ * @param before_fence The fence from which to begin the search; if NULL, then
+ * search for the most recent fence in the thread.
+ * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
+ */
+ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
+{
+       /* All fences should have NULL location */
+       action_list_t *list = get_safe_ptr_action(obj_map, NULL);
+       action_list_t::reverse_iterator rit = list->rbegin();
+
+       if (before_fence) {
+               for (; rit != list->rend(); rit++)
+                       if (*rit == before_fence)
+                               break;
+
+               ASSERT(*rit == before_fence);
+               rit++;
+       }
+
+       for (; rit != list->rend(); rit++)
+               if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
+                       return *rit;
+       return NULL;
+}
+
+/**
+ * Gets the last unlock operation performed on a particular mutex (i.e., memory
+ * location). This function identifies the mutex according to the current
+ * action, which is presumed to perform on the same mutex.
+ * @param curr The current ModelAction; also denotes the object location to
+ * check
+ * @return The last unlock operation
+ */
+ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
+{
+       void *location = curr->get_location();
+       action_list_t *list = get_safe_ptr_action(obj_map, location);
+       /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
+       action_list_t::reverse_iterator rit;
+       for (rit = list->rbegin(); rit != list->rend(); rit++)
+               if ((*rit)->is_unlock() || (*rit)->is_wait())
+                       return *rit;
+       return NULL;
+}
+
+ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
+{
+       ModelAction *parent = get_last_action(tid);
+       if (!parent)
+               parent = get_thread(tid)->get_creation();
+       return parent;
+}
+
+/**
+ * Returns the clock vector for a given thread.
+ * @param tid The thread whose clock vector we want
+ * @return Desired clock vector
+ */
+ClockVector * ModelExecution::get_cv(thread_id_t tid) const
+{
+       return get_parent_action(tid)->get_cv();
+}
+
+/**
+ * @brief Find the promise (if any) to resolve for the current action and
+ * remove it from the pending promise vector
+ * @param curr The current ModelAction. Should be a write.
+ * @return The Promise to resolve, if any; otherwise NULL
+ */
+Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
+{
+       for (unsigned int i = 0; i < promises->size(); i++)
+               if (curr->get_node()->get_promise(i)) {
+                       Promise *ret = (*promises)[i];
+                       promises->erase(promises->begin() + i);
+                       return ret;
+               }
+       return NULL;
+}
+
+/**
+ * Resolve a Promise with a current write.
+ * @param write The ModelAction that is fulfilling Promises
+ * @param promise The Promise to resolve
+ * @return True if the Promise was successfully resolved; false otherwise
+ */
+bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise)
+{
+       ModelVector<ModelAction *> actions_to_check;
+
+       for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
+               ModelAction *read = promise->get_reader(i);
+               read_from(read, write);
+               actions_to_check.push_back(read);
+       }
+       /* Make sure the promise's value matches the write's value */
+       ASSERT(promise->is_compatible(write) && promise->same_value(write));
+       if (!mo_graph->resolvePromise(promise, write))
+               priv->failed_promise = true;
+
+       /**
+        * @todo  It is possible to end up in an inconsistent state, where a
+        * "resolved" promise may still be referenced if
+        * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
+        *
+        * Note that the inconsistency only matters when dumping mo_graph to
+        * file.
+        *
+        * delete promise;
+        */
+
+       //Check whether reading these writes has made threads unable to
+       //resolve promises
+       for (unsigned int i = 0; i < actions_to_check.size(); i++) {
+               ModelAction *read = actions_to_check[i];
+               mo_check_promises(read, true);
+       }
+
+       return true;
+}
+
+/**
+ * Compute the set of promises that could potentially be satisfied by this
+ * action. Note that the set computation actually appears in the Node, not in
+ * ModelExecution.
+ * @param curr The ModelAction that may satisfy promises
+ */
+void ModelExecution::compute_promises(ModelAction *curr)
+{
+       for (unsigned int i = 0; i < promises->size(); i++) {
+               Promise *promise = (*promises)[i];
+               if (!promise->is_compatible(curr) || !promise->same_value(curr))
+                       continue;
+
+               bool satisfy = true;
+               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
+                       const ModelAction *act = promise->get_reader(j);
+                       if (act->happens_before(curr) ||
+                                       act->could_synchronize_with(curr)) {
+                               satisfy = false;
+                               break;
+                       }
+               }
+               if (satisfy)
+                       curr->get_node()->set_promise(i);
+       }
+}
+
+/** Checks promises in response to change in ClockVector Threads. */
+void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
+{
+       for (unsigned int i = 0; i < promises->size(); i++) {
+               Promise *promise = (*promises)[i];
+               if (!promise->thread_is_available(tid))
+                       continue;
+               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
+                       const ModelAction *act = promise->get_reader(j);
+                       if ((!old_cv || !old_cv->synchronized_since(act)) &&
+                                       merge_cv->synchronized_since(act)) {
+                               if (promise->eliminate_thread(tid)) {
+                                       /* Promise has failed */
+                                       priv->failed_promise = true;
+                                       return;
+                               }
+                       }
+               }
+       }
+}
+
+void ModelExecution::check_promises_thread_disabled()
+{
+       for (unsigned int i = 0; i < promises->size(); i++) {
+               Promise *promise = (*promises)[i];
+               if (promise->has_failed()) {
+                       priv->failed_promise = true;
+                       return;
+               }
+       }
+}
+
+/**
+ * @brief Checks promises in response to addition to modification order for
+ * threads.
+ *
+ * We test whether threads are still available for satisfying promises after an
+ * addition to our modification order constraints. Those that are unavailable
+ * are "eliminated". Once all threads are eliminated from satisfying a promise,
+ * that promise has failed.
+ *
+ * @param act The ModelAction which updated the modification order
+ * @param is_read_check Should be true if act is a read and we must check for
+ * updates to the store from which it read (there is a distinction here for
+ * RMW's, which are both a load and a store)
+ */
+void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
+{
+       const ModelAction *write = is_read_check ? act->get_reads_from() : act;
+
+       for (unsigned int i = 0; i < promises->size(); i++) {
+               Promise *promise = (*promises)[i];
+
+               // Is this promise on the same location?
+               if (!promise->same_location(write))
+                       continue;
+
+               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
+                       const ModelAction *pread = promise->get_reader(j);
+                       if (!pread->happens_before(act))
+                              continue;
+                       if (mo_graph->checkPromise(write, promise)) {
+                               priv->failed_promise = true;
+                               return;
+                       }
+                       break;
+               }
+
+               // Don't do any lookups twice for the same thread
+               if (!promise->thread_is_available(act->get_tid()))
+                       continue;
+
+               if (mo_graph->checkReachable(promise, write)) {
+                       if (mo_graph->checkPromise(write, promise)) {
+                               priv->failed_promise = true;
+                               return;
+                       }
+               }
+       }
+}
+
+/**
+ * Compute the set of writes that may break the current pending release
+ * sequence. This information is extracted from previou release sequence
+ * calculations.
+ *
+ * @param curr The current ModelAction. Must be a release sequence fixup
+ * action.
+ */
+void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
+{
+       if (pending_rel_seqs->empty())
+               return;
+
+       struct release_seq *pending = pending_rel_seqs->back();
+       for (unsigned int i = 0; i < pending->writes.size(); i++) {
+               const ModelAction *write = pending->writes[i];
+               curr->get_node()->add_relseq_break(write);
+       }
+
+       /* NULL means don't break the sequence; just synchronize */
+       curr->get_node()->add_relseq_break(NULL);
+}
+
+/**
+ * Build up an initial set of all past writes that this 'read' action may read
+ * from, as well as any previously-observed future values that must still be valid.
+ *
+ * @param curr is the current ModelAction that we are exploring; it must be a
+ * 'read' operation.
+ */
+void ModelExecution::build_may_read_from(ModelAction *curr)
+{
+       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
+       unsigned int i;
+       ASSERT(curr->is_read());
+
+       ModelAction *last_sc_write = NULL;
+
+       if (curr->is_seqcst())
+               last_sc_write = get_last_seq_cst_write(curr);
+
+       /* Iterate over all threads */
+       for (i = 0; i < thrd_lists->size(); i++) {
+               /* Iterate over actions in thread, starting from most recent */
+               action_list_t *list = &(*thrd_lists)[i];
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *act = *rit;
+
+                       /* Only consider 'write' actions */
+                       if (!act->is_write() || act == curr)
+                               continue;
+
+                       /* Don't consider more than one seq_cst write if we are a seq_cst read. */
+                       bool allow_read = true;
+
+                       if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
+                               allow_read = false;
+                       else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
+                               allow_read = false;
+
+                       if (allow_read) {
+                               /* Only add feasible reads */
+                               mo_graph->startChanges();
+                               r_modification_order(curr, act);
+                               if (!is_infeasible())
+                                       curr->get_node()->add_read_from_past(act);
+                               mo_graph->rollbackChanges();
+                       }
+
+                       /* Include at most one act per-thread that "happens before" curr */
+                       if (act->happens_before(curr))
+                               break;
+               }
+       }
+
+       /* Inherit existing, promised future values */
+       for (i = 0; i < promises->size(); i++) {
+               const Promise *promise = (*promises)[i];
+               const ModelAction *promise_read = promise->get_reader(0);
+               if (promise_read->same_var(curr)) {
+                       /* Only add feasible future-values */
+                       mo_graph->startChanges();
+                       r_modification_order(curr, promise);
+                       if (!is_infeasible())
+                               curr->get_node()->add_read_from_promise(promise_read);
+                       mo_graph->rollbackChanges();
+               }
+       }
+
+       /* We may find no valid may-read-from only if the execution is doomed */
+       if (!curr->get_node()->read_from_size()) {
+               priv->no_valid_reads = true;
+               set_assert();
+       }
+
+       if (DBG_ENABLED()) {
+               model_print("Reached read action:\n");
+               curr->print();
+               model_print("Printing read_from_past\n");
+               curr->get_node()->print_read_from_past();
+               model_print("End printing read_from_past\n");
+       }
+}
+
+bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
+{
+       for ( ; write != NULL; write = write->get_reads_from()) {
+               /* UNINIT actions don't have a Node, and they never sleep */
+               if (write->is_uninitialized())
+                       return true;
+               Node *prevnode = write->get_node()->get_parent();
+
+               bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
+               if (write->is_release() && thread_sleep)
+                       return true;
+               if (!write->is_rmw())
+                       return false;
+       }
+       return true;
+}
+
+/**
+ * @brief Get an action representing an uninitialized atomic
+ *
+ * This function may create a new one or try to retrieve one from the NodeStack
+ *
+ * @param curr The current action, which prompts the creation of an UNINIT action
+ * @return A pointer to the UNINIT ModelAction
+ */
+ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
+{
+       Node *node = curr->get_node();
+       ModelAction *act = node->get_uninit_action();
+       if (!act) {
+               act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
+               node->set_uninit_action(act);
+       }
+       act->create_cv(NULL);
+       return act;
+}
+
+static void print_list(action_list_t *list)
+{
+       action_list_t::iterator it;
+
+       model_print("---------------------------------------------------------------------\n");
+
+       unsigned int hash = 0;
+
+       for (it = list->begin(); it != list->end(); it++) {
+               const ModelAction *act = *it;
+               if (act->get_seq_number() > 0)
+                       act->print();
+               hash = hash^(hash<<3)^((*it)->hash());
+       }
+       model_print("HASH %u\n", hash);
+       model_print("---------------------------------------------------------------------\n");
+}
+
+#if SUPPORT_MOD_ORDER_DUMP
+void ModelExecution::dumpGraph(char *filename) const
+{
+       char buffer[200];
+       sprintf(buffer, "%s.dot", filename);
+       FILE *file = fopen(buffer, "w");
+       fprintf(file, "digraph %s {\n", filename);
+       mo_graph->dumpNodes(file);
+       ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
+
+       for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
+               ModelAction *act = *it;
+               if (act->is_read()) {
+                       mo_graph->dot_print_node(file, act);
+                       if (act->get_reads_from())
+                               mo_graph->dot_print_edge(file,
+                                               act->get_reads_from(),
+                                               act,
+                                               "label=\"rf\", color=red, weight=2");
+                       else
+                               mo_graph->dot_print_edge(file,
+                                               act->get_reads_from_promise(),
+                                               act,
+                                               "label=\"rf\", color=red");
+               }
+               if (thread_array[act->get_tid()]) {
+                       mo_graph->dot_print_edge(file,
+                                       thread_array[id_to_int(act->get_tid())],
+                                       act,
+                                       "label=\"sb\", color=blue, weight=400");
+               }
+
+               thread_array[act->get_tid()] = act;
+       }
+       fprintf(file, "}\n");
+       model_free(thread_array);
+       fclose(file);
+}
+#endif
+
+/** @brief Prints an execution trace summary. */
+void ModelExecution::print_summary() const
+{
+#if SUPPORT_MOD_ORDER_DUMP
+       char buffername[100];
+       sprintf(buffername, "exec%04u", execution_number);
+       mo_graph->dumpGraphToFile(buffername);
+       sprintf(buffername, "graph%04u", execution_number);
+       dumpGraph(buffername);
+#endif
+
+       model_print("Execution %d:", execution_number);
+       if (isfeasibleprefix()) {
+               if (scheduler->all_threads_sleeping())
+                       model_print(" SLEEP-SET REDUNDANT");
+               model_print("\n");
+       } else
+               print_infeasibility(" INFEASIBLE");
+       print_list(action_trace);
+       model_print("\n");
+       if (!promises->empty()) {
+               model_print("Pending promises:\n");
+               for (unsigned int i = 0; i < promises->size(); i++) {
+                       model_print(" [P%u] ", i);
+                       (*promises)[i]->print();
+               }
+               model_print("\n");
+       }
+}
+
+/**
+ * Add a Thread to the system for the first time. Should only be called once
+ * per thread.
+ * @param t The Thread to add
+ */
+void ModelExecution::add_thread(Thread *t)
+{
+       thread_map->put(id_to_int(t->get_id()), t);
+       if (!t->is_model_thread())
+               scheduler->add_thread(t);
+}
+
+/**
+ * @brief Get a Thread reference by its ID
+ * @param tid The Thread's ID
+ * @return A Thread reference
+ */
+Thread * ModelExecution::get_thread(thread_id_t tid) const
+{
+       return thread_map->get(id_to_int(tid));
+}
+
+/**
+ * @brief Get a reference to the Thread in which a ModelAction was executed
+ * @param act The ModelAction
+ * @return A Thread reference
+ */
+Thread * ModelExecution::get_thread(const ModelAction *act) const
+{
+       return get_thread(act->get_tid());
+}
+
+/**
+ * @brief Get a Promise's "promise number"
+ *
+ * A "promise number" is an index number that is unique to a promise, valid
+ * only for a specific snapshot of an execution trace. Promises may come and go
+ * as they are generated an resolved, so an index only retains meaning for the
+ * current snapshot.
+ *
+ * @param promise The Promise to check
+ * @return The promise index, if the promise still is valid; otherwise -1
+ */
+int ModelExecution::get_promise_number(const Promise *promise) const
+{
+       for (unsigned int i = 0; i < promises->size(); i++)
+               if ((*promises)[i] == promise)
+                       return i;
+       /* Not found */
+       return -1;
+}
+
+/**
+ * @brief Check if a Thread is currently enabled
+ * @param t The Thread to check
+ * @return True if the Thread is currently enabled
+ */
+bool ModelExecution::is_enabled(Thread *t) const
+{
+       return scheduler->is_enabled(t);
+}
+
+/**
+ * @brief Check if a Thread is currently enabled
+ * @param tid The ID of the Thread to check
+ * @return True if the Thread is currently enabled
+ */
+bool ModelExecution::is_enabled(thread_id_t tid) const
+{
+       return scheduler->is_enabled(tid);
+}
+
+/**
+ * @brief Select the next thread to execute based on the curren action
+ *
+ * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
+ * actions should be followed by the execution of their child thread. In either
+ * case, the current action should determine the next thread schedule.
+ *
+ * @param curr The current action
+ * @return The next thread to run, if the current action will determine this
+ * selection; otherwise NULL
+ */
+Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
+{
+       /* Do not split atomic RMW */
+       if (curr->is_rmwr())
+               return get_thread(curr);
+       /* Follow CREATE with the created thread */
+       if (curr->get_type() == THREAD_CREATE)
+               return curr->get_thread_operand();
+       return NULL;
+}
+
+/** @return True if the execution has taken too many steps */
+bool ModelExecution::too_many_steps() const
+{
+       return params->bound != 0 && priv->used_sequence_numbers > params->bound;
+}
+
+/**
+ * Takes the next step in the execution, if possible.
+ * @param curr The current step to take
+ * @return Returns the next Thread to run, if any; NULL if this execution
+ * should terminate
+ */
+Thread * ModelExecution::take_step(ModelAction *curr)
+{
+       Thread *curr_thrd = get_thread(curr);
+       ASSERT(curr_thrd->get_state() == THREAD_READY);
+
+       ASSERT(check_action_enabled(curr)); /* May have side effects? */
+       curr = check_current_action(curr);
+       ASSERT(curr);
+
+       if (curr_thrd->is_blocked() || curr_thrd->is_complete())
+               scheduler->remove_thread(curr_thrd);
+
+       return action_select_next_thread(curr);
+}
+
+/**
+ * Launch end-of-execution release sequence fixups only when
+ * the execution is otherwise feasible AND there are:
+ *
+ * (1) pending release sequences
+ * (2) pending assertions that could be invalidated by a change
+ * in clock vectors (i.e., data races)
+ * (3) no pending promises
+ */
+void ModelExecution::fixup_release_sequences()
+{
+       while (!pending_rel_seqs->empty() &&
+                       is_feasible_prefix_ignore_relseq() &&
+                       !unrealizedraces.empty()) {
+               model_print("*** WARNING: release sequence fixup action "
+                               "(%zu pending release seuqence(s)) ***\n",
+                               pending_rel_seqs->size());
+               ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
+                               std::memory_order_seq_cst, NULL, VALUE_NONE,
+                               model_thread);
+               take_step(fixup);
+       };
+}
diff --git a/execution.h b/execution.h
new file mode 100644 (file)
index 0000000..9ae0b4f
--- /dev/null
@@ -0,0 +1,240 @@
+/** @file execution.h
+ *  @brief Model-checker core
+ */
+
+#ifndef __EXECUTION_H__
+#define __EXECUTION_H__
+
+#include <cstddef>
+#include <inttypes.h>
+
+#include "mymemory.h"
+#include "hashtable.h"
+#include "workqueue.h"
+#include "config.h"
+#include "modeltypes.h"
+#include "stl-model.h"
+#include "context.h"
+#include "params.h"
+
+/* Forward declaration */
+class Node;
+class NodeStack;
+class CycleGraph;
+class Promise;
+class Scheduler;
+class Thread;
+class ClockVector;
+struct model_snapshot_members;
+class ModelChecker;
+struct bug_message;
+
+/** @brief Shorthand for a list of release sequence heads */
+typedef ModelVector<const ModelAction *> rel_heads_list_t;
+typedef SnapList<ModelAction *> action_list_t;
+
+struct PendingFutureValue {
+       PendingFutureValue(ModelAction *writer, ModelAction *reader) :
+               writer(writer), reader(reader)
+       { }
+       const ModelAction *writer;
+       ModelAction *reader;
+};
+
+/** @brief Records information regarding a single pending release sequence */
+struct release_seq {
+       /** @brief The acquire operation */
+       ModelAction *acquire;
+       /** @brief The read operation that may read from a release sequence;
+        *  may be the same as acquire, or else an earlier action in the same
+        *  thread (i.e., when 'acquire' is a fence-acquire) */
+       const ModelAction *read;
+       /** @brief The head of the RMW chain from which 'read' reads; may be
+        *  equal to 'release' */
+       const ModelAction *rf;
+       /** @brief The head of the potential longest release sequence chain */
+       const ModelAction *release;
+       /** @brief The write(s) that may break the release sequence */
+       SnapVector<const ModelAction *> writes;
+};
+
+/** @brief The central structure for model-checking */
+class ModelExecution {
+public:
+       ModelExecution(struct model_params *params, Scheduler *scheduler, NodeStack *node_stack);
+       ~ModelExecution();
+
+       Thread * take_step(ModelAction *curr);
+       void fixup_release_sequences();
+
+       void print_summary() const;
+#if SUPPORT_MOD_ORDER_DUMP
+       void dumpGraph(char *filename) const;
+#endif
+
+       void add_thread(Thread *t);
+       Thread * get_thread(thread_id_t tid) const;
+       Thread * get_thread(const ModelAction *act) const;
+       int get_promise_number(const Promise *promise) const;
+
+       bool is_enabled(Thread *t) const;
+       bool is_enabled(thread_id_t tid) const;
+
+       thread_id_t get_next_id();
+       unsigned int get_num_threads() const;
+
+       ClockVector * get_cv(thread_id_t tid) const;
+       ModelAction * get_parent_action(thread_id_t tid) const;
+       void check_promises_thread_disabled();
+       bool isfeasibleprefix() const;
+
+       action_list_t * get_actions_on_obj(void * obj, thread_id_t tid);
+       ModelAction * get_last_action(thread_id_t tid) const;
+
+       bool check_action_enabled(ModelAction *curr);
+
+       bool assert_bug(const char *msg);
+       bool have_bug_reports() const;
+       SnapVector<bug_message *> * get_bugs() const;
+
+       bool has_asserted() const;
+       void set_assert();
+       bool is_complete_execution() const;
+
+       void print_infeasibility(const char *prefix) const;
+       bool is_feasible_prefix_ignore_relseq() const;
+       bool is_infeasible() const;
+       bool is_deadlocked() const;
+       bool too_many_steps() const;
+
+       ModelAction * get_next_backtrack();
+
+       action_list_t * get_action_trace() const { return action_trace; }
+
+       void increment_execution_number() { execution_number++; }
+
+       MEMALLOC
+private:
+       const model_params * const params;
+
+       /** The scheduler to use: tracks the running/ready Threads */
+       Scheduler * const scheduler;
+
+       bool sleep_can_read_from(ModelAction *curr, const ModelAction *write);
+       bool thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const;
+       bool mo_may_allow(const ModelAction *writer, const ModelAction *reader);
+       bool promises_may_allow(const ModelAction *writer, const ModelAction *reader) const;
+       void set_bad_synchronization();
+       bool promises_expired() const;
+       bool should_wake_up(const ModelAction *curr, const Thread *thread) const;
+       void wake_up_sleeping_actions(ModelAction *curr);
+       modelclock_t get_next_seq_num();
+
+       bool next_execution();
+       ModelAction * check_current_action(ModelAction *curr);
+       bool initialize_curr_action(ModelAction **curr);
+       bool process_read(ModelAction *curr);
+       bool process_write(ModelAction *curr);
+       bool process_fence(ModelAction *curr);
+       bool process_mutex(ModelAction *curr);
+       bool process_thread_action(ModelAction *curr);
+       void process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue);
+       bool read_from(ModelAction *act, const ModelAction *rf);
+       bool synchronize(const ModelAction *first, ModelAction *second);
+
+       template <typename T>
+       bool check_recency(ModelAction *curr, const T *rf) const;
+
+       template <typename T, typename U>
+       bool should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const;
+
+       ModelAction * get_last_fence_conflict(ModelAction *act) const;
+       ModelAction * get_last_conflict(ModelAction *act) const;
+       void set_backtracking(ModelAction *act);
+       bool set_latest_backtrack(ModelAction *act);
+       Promise * pop_promise_to_resolve(const ModelAction *curr);
+       bool resolve_promise(ModelAction *curr, Promise *promise);
+       void compute_promises(ModelAction *curr);
+       void compute_relseq_breakwrites(ModelAction *curr);
+
+       void check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv);
+       void mo_check_promises(const ModelAction *act, bool is_read_check);
+       void thread_blocking_check_promises(Thread *blocker, Thread *waiting);
+
+       void check_curr_backtracking(ModelAction *curr);
+       void add_action_to_lists(ModelAction *act);
+       ModelAction * get_last_fence_release(thread_id_t tid) const;
+       ModelAction * get_last_seq_cst_write(ModelAction *curr) const;
+       ModelAction * get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const;
+       ModelAction * get_last_unlock(ModelAction *curr) const;
+       void build_may_read_from(ModelAction *curr);
+       ModelAction * process_rmw(ModelAction *curr);
+
+       template <typename rf_type>
+       bool r_modification_order(ModelAction *curr, const rf_type *rf);
+
+       bool w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv);
+       void get_release_seq_heads(ModelAction *acquire, ModelAction *read, rel_heads_list_t *release_heads);
+       bool release_seq_heads(const ModelAction *rf, rel_heads_list_t *release_heads, struct release_seq *pending) const;
+       bool resolve_release_sequences(void *location, work_queue_t *work_queue);
+       void add_future_value(const ModelAction *writer, ModelAction *reader);
+
+       ModelAction * get_uninitialized_action(const ModelAction *curr) const;
+
+       action_list_t * const action_trace;
+       HashTable<int, Thread *, int> * const thread_map;
+
+       /** Per-object list of actions. Maps an object (i.e., memory location)
+        * to a trace of all actions performed on the object. */
+       HashTable<const void *, action_list_t *, uintptr_t, 4> * const obj_map;
+
+       /** Per-object list of actions. Maps an object (i.e., memory location)
+        * to a trace of all actions performed on the object. */
+       HashTable<const void *, action_list_t *, uintptr_t, 4> * const condvar_waiters_map;
+
+       HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 > * const obj_thrd_map;
+       SnapVector<Promise *> * const promises;
+       SnapVector<struct PendingFutureValue> * const futurevalues;
+
+       /**
+        * List of pending release sequences. Release sequences might be
+        * determined lazily as promises are fulfilled and modification orders
+        * are established. Each entry in the list may only be partially
+        * filled, depending on its pending status.
+        */
+       SnapVector<struct release_seq *> * const pending_rel_seqs;
+
+       SnapVector<ModelAction *> * const thrd_last_action;
+       SnapVector<ModelAction *> * const thrd_last_fence_release;
+       NodeStack * const node_stack;
+
+       /** A special model-checker Thread; used for associating with
+        *  model-checker-related ModelAcitons */
+       Thread *model_thread;
+
+       /** Private data members that should be snapshotted. They are grouped
+        * together for efficiency and maintainability. */
+       struct model_snapshot_members * const priv;
+
+       /**
+        * @brief The modification order graph
+        *
+        * A directed acyclic graph recording observations of the modification
+        * order on all the atomic objects in the system. This graph should
+        * never contain any cycles, as that represents a violation of the
+        * memory model (total ordering). This graph really consists of many
+        * disjoint (unconnected) subgraphs, each graph corresponding to a
+        * separate ordering on a distinct object.
+        *
+        * The edges in this graph represent the "ordered before" relation,
+        * such that <tt>a --> b</tt> means <tt>a</tt> was ordered before
+        * <tt>b</tt>.
+        */
+       CycleGraph * const mo_graph;
+
+       int execution_number;
+
+       Thread * action_select_next_thread(const ModelAction *curr) const;
+};
+
+#endif /* __EXECUTION_H__ */
index c0f81ea..5594973 100644 (file)
--- a/model.cc
+++ b/model.cc
 #include "schedule.h"
 #include "snapshot-interface.h"
 #include "common.h"
 #include "schedule.h"
 #include "snapshot-interface.h"
 #include "common.h"
-#include "clockvector.h"
-#include "cyclegraph.h"
-#include "promise.h"
 #include "datarace.h"
 #include "threads-model.h"
 #include "output.h"
 #include "traceanalysis.h"
 #include "datarace.h"
 #include "threads-model.h"
 #include "output.h"
 #include "traceanalysis.h"
+#include "execution.h"
 #include "bugmessage.h"
 
 #define INITIAL_THREAD_ID      0
 
 ModelChecker *model;
 
 #include "bugmessage.h"
 
 #define INITIAL_THREAD_ID      0
 
 ModelChecker *model;
 
-/**
- * Structure for holding small ModelChecker members that should be snapshotted
- */
-struct model_snapshot_members {
-       model_snapshot_members() :
-               /* First thread created will have id INITIAL_THREAD_ID */
-               next_thread_id(INITIAL_THREAD_ID),
-               used_sequence_numbers(0),
-               next_backtrack(NULL),
-               bugs(),
-               stats(),
-               failed_promise(false),
-               too_many_reads(false),
-               no_valid_reads(false),
-               bad_synchronization(false),
-               asserted(false)
-       { }
-
-       ~model_snapshot_members() {
-               for (unsigned int i = 0; i < bugs.size(); i++)
-                       delete bugs[i];
-               bugs.clear();
-       }
-
-       unsigned int next_thread_id;
-       modelclock_t used_sequence_numbers;
-       ModelAction *next_backtrack;
-       SnapVector<bug_message *> bugs;
-       struct execution_stats stats;
-       bool failed_promise;
-       bool too_many_reads;
-       bool no_valid_reads;
-       /** @brief Incorrectly-ordered synchronization was made */
-       bool bad_synchronization;
-       bool asserted;
-
-       SNAPSHOTALLOC
-};
-
 /** @brief Constructor */
 ModelChecker::ModelChecker(struct model_params params) :
        /* Initialize default scheduler */
        params(params),
        scheduler(new Scheduler()),
 /** @brief Constructor */
 ModelChecker::ModelChecker(struct model_params params) :
        /* Initialize default scheduler */
        params(params),
        scheduler(new Scheduler()),
+       node_stack(new NodeStack()),
+       execution(new ModelExecution(&params, scheduler, node_stack)),
        diverge(NULL),
        earliest_diverge(NULL),
        diverge(NULL),
        earliest_diverge(NULL),
-       action_trace(new action_list_t()),
-       thread_map(new HashTable<int, Thread *, int>()),
-       obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
-       condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
-       obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
-       promises(new SnapVector<Promise *>()),
-       futurevalues(new SnapVector<struct PendingFutureValue>()),
-       pending_rel_seqs(new SnapVector<struct release_seq *>()),
-       thrd_last_action(new SnapVector<ModelAction *>(1)),
-       thrd_last_fence_release(new SnapVector<ModelAction *>()),
-       node_stack(new NodeStack()),
-       trace_analyses(new ModelVector<TraceAnalysis *>()),
-       priv(new struct model_snapshot_members()),
-       mo_graph(new CycleGraph())
+       trace_analyses(new ModelVector<TraceAnalysis *>())
 {
 {
-       /* Initialize a model-checker thread, for special ModelActions */
-       model_thread = new Thread(get_next_id());
-       thread_map->put(id_to_int(model_thread->get_id()), model_thread);
 }
 
 /** @brief Destructor */
 ModelChecker::~ModelChecker()
 {
 }
 
 /** @brief Destructor */
 ModelChecker::~ModelChecker()
 {
-       for (unsigned int i = 0; i < get_num_threads(); i++)
-               delete thread_map->get(i);
-       delete thread_map;
-
-       delete obj_thrd_map;
-       delete obj_map;
-       delete condvar_waiters_map;
-       delete action_trace;
-
-       for (unsigned int i = 0; i < promises->size(); i++)
-               delete (*promises)[i];
-       delete promises;
-
-       delete pending_rel_seqs;
-
-       delete thrd_last_action;
-       delete thrd_last_fence_release;
        delete node_stack;
        for (unsigned int i = 0; i < trace_analyses->size(); i++)
                delete (*trace_analyses)[i];
        delete trace_analyses;
        delete scheduler;
        delete node_stack;
        for (unsigned int i = 0; i < trace_analyses->size(); i++)
                delete (*trace_analyses)[i];
        delete trace_analyses;
        delete scheduler;
-       delete mo_graph;
-       delete priv;
-}
-
-static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
-{
-       action_list_t *tmp = hash->get(ptr);
-       if (tmp == NULL) {
-               tmp = new action_list_t();
-               hash->put(ptr, tmp);
-       }
-       return tmp;
-}
-
-static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
-{
-       SnapVector<action_list_t> *tmp = hash->get(ptr);
-       if (tmp == NULL) {
-               tmp = new SnapVector<action_list_t>();
-               hash->put(ptr, tmp);
-       }
-       return tmp;
-}
-
-action_list_t * ModelChecker::get_actions_on_obj(void * obj, thread_id_t tid) {
-       SnapVector<action_list_t> *wrv=obj_thrd_map->get(obj);
-       if (wrv==NULL)
-               return NULL;
-       unsigned int thread=id_to_int(tid);
-       if (thread < wrv->size())
-               return &(*wrv)[thread];
-       else
-               return NULL;
 }
 
 }
 
-
 /**
  * Restores user program to initial state and resets all model-checker data
  * structures.
 /**
  * Restores user program to initial state and resets all model-checker data
  * structures.
@@ -170,16 +64,10 @@ void ModelChecker::reset_to_initial_state()
        snapshot_backtrack_before(0);
 }
 
        snapshot_backtrack_before(0);
 }
 
-/** @return a thread ID for a new Thread */
-thread_id_t ModelChecker::get_next_id()
-{
-       return priv->next_thread_id++;
-}
-
 /** @return the number of user threads created during this execution */
 unsigned int ModelChecker::get_num_threads() const
 {
 /** @return the number of user threads created during this execution */
 unsigned int ModelChecker::get_num_threads() const
 {
-       return priv->next_thread_id;
+       return execution->get_num_threads();
 }
 
 /**
 }
 
 /**
@@ -193,34 +81,6 @@ Thread * ModelChecker::get_current_thread() const
        return scheduler->get_current_thread();
 }
 
        return scheduler->get_current_thread();
 }
 
-/** @return a sequence number for a new ModelAction */
-modelclock_t ModelChecker::get_next_seq_num()
-{
-       return ++priv->used_sequence_numbers;
-}
-
-/**
- * @brief Select the next thread to execute based on the curren action
- *
- * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
- * actions should be followed by the execution of their child thread. In either
- * case, the current action should determine the next thread schedule.
- *
- * @param curr The current action
- * @return The next thread to run, if the current action will determine this
- * selection; otherwise NULL
- */
-Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
-{
-       /* Do not split atomic RMW */
-       if (curr->is_rmwr())
-               return get_thread(curr);
-       /* Follow CREATE with the created thread */
-       if (curr->get_type() == THREAD_CREATE)
-               return curr->get_thread_operand();
-       return NULL;
-}
-
 /**
  * @brief Choose the next thread to execute.
  *
 /**
  * @brief Choose the next thread to execute.
  *
@@ -243,6 +103,7 @@ Thread * ModelChecker::get_next_thread()
        if (diverge == NULL)
                return scheduler->select_next_thread(node_stack->get_head());
 
        if (diverge == NULL)
                return scheduler->select_next_thread(node_stack->get_head());
 
+
        /* Else, we are trying to replay an execution */
        ModelAction *next = node_stack->get_next()->get_action();
 
        /* Else, we are trying to replay an execution */
        ModelAction *next = node_stack->get_next()->get_action();
 
@@ -291,7 +152,6 @@ Thread * ModelChecker::get_next_thread()
  * set will be.  This method computes them and stores the actions at
  * the corresponding thread object's pending action.
  */
  * set will be.  This method computes them and stores the actions at
  * the corresponding thread object's pending action.
  */
-
 void ModelChecker::execute_sleep_set()
 {
        for (unsigned int i = 0; i < get_num_threads(); i++) {
 void ModelChecker::execute_sleep_set()
 {
        for (unsigned int i = 0; i < get_num_threads(); i++) {
@@ -303,110 +163,6 @@ void ModelChecker::execute_sleep_set()
        }
 }
 
        }
 }
 
-/**
- * @brief Should the current action wake up a given thread?
- *
- * @param curr The current action
- * @param thread The thread that we might wake up
- * @return True, if we should wake up the sleeping thread; false otherwise
- */
-bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
-{
-       const ModelAction *asleep = thread->get_pending();
-       /* Don't allow partial RMW to wake anyone up */
-       if (curr->is_rmwr())
-               return false;
-       /* Synchronizing actions may have been backtracked */
-       if (asleep->could_synchronize_with(curr))
-               return true;
-       /* All acquire/release fences and fence-acquire/store-release */
-       if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
-               return true;
-       /* Fence-release + store can awake load-acquire on the same location */
-       if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
-               ModelAction *fence_release = get_last_fence_release(curr->get_tid());
-               if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
-                       return true;
-       }
-       return false;
-}
-
-void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
-{
-       for (unsigned int i = 0; i < get_num_threads(); i++) {
-               Thread *thr = get_thread(int_to_id(i));
-               if (scheduler->is_sleep_set(thr)) {
-                       if (should_wake_up(curr, thr))
-                               /* Remove this thread from sleep set */
-                               scheduler->remove_sleep(thr);
-               }
-       }
-}
-
-/** @brief Alert the model-checker that an incorrectly-ordered
- * synchronization was made */
-void ModelChecker::set_bad_synchronization()
-{
-       priv->bad_synchronization = true;
-}
-
-/**
- * Check whether the current trace has triggered an assertion which should halt
- * its execution.
- *
- * @return True, if the execution should be aborted; false otherwise
- */
-bool ModelChecker::has_asserted() const
-{
-       return priv->asserted;
-}
-
-/**
- * Trigger a trace assertion which should cause this execution to be halted.
- * This can be due to a detected bug or due to an infeasibility that should
- * halt ASAP.
- */
-void ModelChecker::set_assert()
-{
-       priv->asserted = true;
-}
-
-/**
- * Check if we are in a deadlock. Should only be called at the end of an
- * execution, although it should not give false positives in the middle of an
- * execution (there should be some ENABLED thread).
- *
- * @return True if program is in a deadlock; false otherwise
- */
-bool ModelChecker::is_deadlocked() const
-{
-       bool blocking_threads = false;
-       for (unsigned int i = 0; i < get_num_threads(); i++) {
-               thread_id_t tid = int_to_id(i);
-               if (is_enabled(tid))
-                       return false;
-               Thread *t = get_thread(tid);
-               if (!t->is_model_thread() && t->get_pending())
-                       blocking_threads = true;
-       }
-       return blocking_threads;
-}
-
-/**
- * Check if this is a complete execution. That is, have all thread completed
- * execution (rather than exiting because sleep sets have forced a redundant
- * execution).
- *
- * @return True if the execution is complete.
- */
-bool ModelChecker::is_complete_execution() const
-{
-       for (unsigned int i = 0; i < get_num_threads(); i++)
-               if (is_enabled(int_to_id(i)))
-                       return false;
-       return true;
-}
-
 /**
  * @brief Assert a bug in the executing program.
  *
 /**
  * @brief Assert a bug in the executing program.
  *
@@ -428,13 +184,7 @@ bool ModelChecker::assert_bug(const char *msg, ...)
        vsnprintf(str, sizeof(str), msg, ap);
        va_end(ap);
 
        vsnprintf(str, sizeof(str), msg, ap);
        va_end(ap);
 
-       priv->bugs.push_back(new bug_message(str));
-
-       if (isfeasibleprefix()) {
-               set_assert();
-               return true;
-       }
-       return false;
+       return execution->assert_bug(str);
 }
 
 /**
 }
 
 /**
@@ -449,21 +199,17 @@ void ModelChecker::assert_user_bug(const char *msg)
                switch_to_master(NULL);
 }
 
                switch_to_master(NULL);
 }
 
-/** @return True, if any bugs have been reported for this execution */
-bool ModelChecker::have_bug_reports() const
-{
-       return priv->bugs.size() != 0;
-}
-
 /** @brief Print bug report listing for this execution (if any bugs exist) */
 void ModelChecker::print_bugs() const
 {
 /** @brief Print bug report listing for this execution (if any bugs exist) */
 void ModelChecker::print_bugs() const
 {
-       if (have_bug_reports()) {
+       if (execution->have_bug_reports()) {
+               SnapVector<bug_message *> *bugs = execution->get_bugs();
+
                model_print("Bug report: %zu bug%s detected\n",
                model_print("Bug report: %zu bug%s detected\n",
-                               priv->bugs.size(),
-                               priv->bugs.size() > 1 ? "s" : "");
-               for (unsigned int i = 0; i < priv->bugs.size(); i++)
-                       priv->bugs[i]->print();
+                               bugs->size(),
+                               bugs->size() > 1 ? "s" : "");
+               for (unsigned int i = 0; i < bugs->size(); i++)
+                       (*bugs)[i]->print();
        }
 }
 
        }
 }
 
@@ -476,11 +222,11 @@ void ModelChecker::print_bugs() const
 void ModelChecker::record_stats()
 {
        stats.num_total++;
 void ModelChecker::record_stats()
 {
        stats.num_total++;
-       if (!isfeasibleprefix())
+       if (!execution->isfeasibleprefix())
                stats.num_infeasible++;
                stats.num_infeasible++;
-       else if (have_bug_reports())
+       else if (execution->have_bug_reports())
                stats.num_buggy_executions++;
                stats.num_buggy_executions++;
-       else if (is_complete_execution())
+       else if (execution->is_complete_execution())
                stats.num_complete++;
        else {
                stats.num_redundant++;
                stats.num_complete++;
        else {
                stats.num_redundant++;
@@ -529,7 +275,7 @@ void ModelChecker::print_execution(bool printbugs) const
                print_bugs();
 
        model_print("\n");
                print_bugs();
 
        model_print("\n");
-       print_summary();
+       execution->print_summary();
 }
 
 /**
 }
 
 /**
@@ -543,12 +289,13 @@ bool ModelChecker::next_execution()
 {
        DBG();
        /* Is this execution a feasible execution that's worth bug-checking? */
 {
        DBG();
        /* Is this execution a feasible execution that's worth bug-checking? */
-       bool complete = isfeasibleprefix() && (is_complete_execution() ||
-                       have_bug_reports());
+       bool complete = execution->isfeasibleprefix() &&
+               (execution->is_complete_execution() ||
+                execution->have_bug_reports());
 
        /* End-of-execution bug checks */
        if (complete) {
 
        /* End-of-execution bug checks */
        if (complete) {
-               if (is_deadlocked())
+               if (execution->is_deadlocked())
                        assert_bug("Deadlock detected");
 
                checkDataRaces();
                        assert_bug("Deadlock detected");
 
                checkDataRaces();
@@ -558,7 +305,7 @@ bool ModelChecker::next_execution()
        record_stats();
 
        /* Output */
        record_stats();
 
        /* Output */
-       if (params.verbose || (complete && have_bug_reports()))
+       if (params.verbose || (complete && execution->have_bug_reports()))
                print_execution(complete);
        else
                clear_program_output();
                print_execution(complete);
        else
                clear_program_output();
@@ -566,7 +313,7 @@ bool ModelChecker::next_execution()
        if (complete)
                earliest_diverge = NULL;
 
        if (complete)
                earliest_diverge = NULL;
 
-       if ((diverge = get_next_backtrack()) == NULL)
+       if ((diverge = execution->get_next_backtrack()) == NULL)
                return false;
 
        if (DBG_ENABLED()) {
                return false;
 
        if (DBG_ENABLED()) {
@@ -574,6 +321,7 @@ bool ModelChecker::next_execution()
                diverge->print();
        }
 
                diverge->print();
        }
 
+       execution->increment_execution_number();
        reset_to_initial_state();
        return true;
 }
        reset_to_initial_state();
        return true;
 }
@@ -581,2561 +329,115 @@ bool ModelChecker::next_execution()
 /** @brief Run trace analyses on complete trace */
 void ModelChecker::run_trace_analyses() {
        for (unsigned int i = 0; i < trace_analyses->size(); i++)
 /** @brief Run trace analyses on complete trace */
 void ModelChecker::run_trace_analyses() {
        for (unsigned int i = 0; i < trace_analyses->size(); i++)
-               (*trace_analyses)[i]->analyze(action_trace);
+               (*trace_analyses)[i]->analyze(execution->get_action_trace());
 }
 
 /**
 }
 
 /**
- * @brief Find the last fence-related backtracking conflict for a ModelAction
- *
- * This function performs the search for the most recent conflicting action
- * against which we should perform backtracking, as affected by fence
- * operations. This includes pairs of potentially-synchronizing actions which
- * occur due to fence-acquire or fence-release, and hence should be explored in
- * the opposite execution order.
- *
- * @param act The current action
- * @return The most recent action which conflicts with act due to fences
+ * @brief Get a Thread reference by its ID
+ * @param tid The Thread's ID
+ * @return A Thread reference
  */
  */
-ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
+Thread * ModelChecker::get_thread(thread_id_t tid) const
 {
 {
-       /* Only perform release/acquire fence backtracking for stores */
-       if (!act->is_write())
-               return NULL;
-
-       /* Find a fence-release (or, act is a release) */
-       ModelAction *last_release;
-       if (act->is_release())
-               last_release = act;
-       else
-               last_release = get_last_fence_release(act->get_tid());
-       if (!last_release)
-               return NULL;
-
-       /* Skip past the release */
-       action_list_t *list = action_trace;
-       action_list_t::reverse_iterator rit;
-       for (rit = list->rbegin(); rit != list->rend(); rit++)
-               if (*rit == last_release)
-                       break;
-       ASSERT(rit != list->rend());
-
-       /* Find a prior:
-        *   load-acquire
-        * or
-        *   load --sb-> fence-acquire */
-       ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
-       ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
-       bool found_acquire_fences = false;
-       for ( ; rit != list->rend(); rit++) {
-               ModelAction *prev = *rit;
-               if (act->same_thread(prev))
-                       continue;
-
-               int tid = id_to_int(prev->get_tid());
-
-               if (prev->is_read() && act->same_var(prev)) {
-                       if (prev->is_acquire()) {
-                               /* Found most recent load-acquire, don't need
-                                * to search for more fences */
-                               if (!found_acquire_fences)
-                                       return NULL;
-                       } else {
-                               prior_loads[tid] = prev;
-                       }
-               }
-               if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
-                       found_acquire_fences = true;
-                       acquire_fences[tid] = prev;
-               }
-       }
-
-       ModelAction *latest_backtrack = NULL;
-       for (unsigned int i = 0; i < acquire_fences.size(); i++)
-               if (acquire_fences[i] && prior_loads[i])
-                       if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
-                               latest_backtrack = acquire_fences[i];
-       return latest_backtrack;
+       return execution->get_thread(tid);
 }
 
 /**
 }
 
 /**
- * @brief Find the last backtracking conflict for a ModelAction
- *
- * This function performs the search for the most recent conflicting action
- * against which we should perform backtracking. This primary includes pairs of
- * synchronizing actions which should be explored in the opposite execution
- * order.
- *
- * @param act The current action
- * @return The most recent action which conflicts with act
- */
-ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
-{
-       switch (act->get_type()) {
-       /* case ATOMIC_FENCE: fences don't directly cause backtracking */
-       case ATOMIC_READ:
-       case ATOMIC_WRITE:
-       case ATOMIC_RMW: {
-               ModelAction *ret = NULL;
-
-               /* linear search: from most recent to oldest */
-               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *prev = *rit;
-                       if (prev->could_synchronize_with(act)) {
-                               ret = prev;
-                               break;
-                       }
-               }
-
-               ModelAction *ret2 = get_last_fence_conflict(act);
-               if (!ret2)
-                       return ret;
-               if (!ret)
-                       return ret2;
-               if (*ret < *ret2)
-                       return ret2;
-               return ret;
-       }
-       case ATOMIC_LOCK:
-       case ATOMIC_TRYLOCK: {
-               /* linear search: from most recent to oldest */
-               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *prev = *rit;
-                       if (act->is_conflicting_lock(prev))
-                               return prev;
-               }
-               break;
-       }
-       case ATOMIC_UNLOCK: {
-               /* linear search: from most recent to oldest */
-               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *prev = *rit;
-                       if (!act->same_thread(prev) && prev->is_failed_trylock())
-                               return prev;
-               }
-               break;
-       }
-       case ATOMIC_WAIT: {
-               /* linear search: from most recent to oldest */
-               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *prev = *rit;
-                       if (!act->same_thread(prev) && prev->is_failed_trylock())
-                               return prev;
-                       if (!act->same_thread(prev) && prev->is_notify())
-                               return prev;
-               }
-               break;
-       }
-
-       case ATOMIC_NOTIFY_ALL:
-       case ATOMIC_NOTIFY_ONE: {
-               /* linear search: from most recent to oldest */
-               action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *prev = *rit;
-                       if (!act->same_thread(prev) && prev->is_wait())
-                               return prev;
-               }
-               break;
-       }
-       default:
-               break;
-       }
-       return NULL;
-}
-
-/** This method finds backtracking points where we should try to
- * reorder the parameter ModelAction against.
- *
- * @param the ModelAction to find backtracking points for.
+ * @brief Get a reference to the Thread in which a ModelAction was executed
+ * @param act The ModelAction
+ * @return A Thread reference
  */
  */
-void ModelChecker::set_backtracking(ModelAction *act)
+Thread * ModelChecker::get_thread(const ModelAction *act) const
 {
 {
-       Thread *t = get_thread(act);
-       ModelAction *prev = get_last_conflict(act);
-       if (prev == NULL)
-               return;
-
-       Node *node = prev->get_node()->get_parent();
-
-       /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
-       int low_tid, high_tid;
-       if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
-               low_tid = id_to_int(act->get_tid());
-               high_tid = low_tid + 1;
-       } else {
-               low_tid = 0;
-               high_tid = get_num_threads();
-       }
-
-       for (int i = low_tid; i < high_tid; i++) {
-               thread_id_t tid = int_to_id(i);
-
-               /* Make sure this thread can be enabled here. */
-               if (i >= node->get_num_threads())
-                       break;
-
-               /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
-               /* Don't backtrack into a point where the thread is disabled or sleeping. */
-               if (node->enabled_status(tid) != THREAD_ENABLED)
-                       continue;
-
-               /* Check if this has been explored already */
-               if (node->has_been_explored(tid))
-                       continue;
-
-               /* See if fairness allows */
-               if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
-                       bool unfair = false;
-                       for (int t = 0; t < node->get_num_threads(); t++) {
-                               thread_id_t tother = int_to_id(t);
-                               if (node->is_enabled(tother) && node->has_priority(tother)) {
-                                       unfair = true;
-                                       break;
-                               }
-                       }
-                       if (unfair)
-                               continue;
-               }
-
-               /* See if CHESS-like yield fairness allows */
-               if (model->params.yieldon) {
-                       bool unfair = false;
-                       for (int t = 0; t < node->get_num_threads(); t++) {
-                               thread_id_t tother = int_to_id(t);
-                               if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
-                                       unfair = true;
-                                       break;
-                               }
-                       }
-                       if (unfair)
-                               continue;
-               }
-               
-               /* Cache the latest backtracking point */
-               set_latest_backtrack(prev);
-
-               /* If this is a new backtracking point, mark the tree */
-               if (!node->set_backtrack(tid))
-                       continue;
-               DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
-                                       id_to_int(prev->get_tid()),
-                                       id_to_int(t->get_id()));
-               if (DBG_ENABLED()) {
-                       prev->print();
-                       act->print();
-               }
-       }
+       return execution->get_thread(act);
 }
 
 /**
 }
 
 /**
- * @brief Cache the a backtracking point as the "most recent", if eligible
- *
- * Note that this does not prepare the NodeStack for this backtracking
- * operation, it only caches the action on a per-execution basis
- *
- * @param act The operation at which we should explore a different next action
- * (i.e., backtracking point)
- * @return True, if this action is now the most recent backtracking point;
- * false otherwise
+ * @brief Check if a Thread is currently enabled
+ * @param t The Thread to check
+ * @return True if the Thread is currently enabled
  */
  */
-bool ModelChecker::set_latest_backtrack(ModelAction *act)
+bool ModelChecker::is_enabled(Thread *t) const
 {
 {
-       if (!priv->next_backtrack || *act > *priv->next_backtrack) {
-               priv->next_backtrack = act;
-               return true;
-       }
-       return false;
+       return scheduler->is_enabled(t);
 }
 
 /**
 }
 
 /**
- * Returns last backtracking point. The model checker will explore a different
- * path for this point in the next execution.
- * @return The ModelAction at which the next execution should diverge.
+ * @brief Check if a Thread is currently enabled
+ * @param tid The ID of the Thread to check
+ * @return True if the Thread is currently enabled
  */
  */
-ModelAction * ModelChecker::get_next_backtrack()
+bool ModelChecker::is_enabled(thread_id_t tid) const
 {
 {
-       ModelAction *next = priv->next_backtrack;
-       priv->next_backtrack = NULL;
-       return next;
+       return scheduler->is_enabled(tid);
 }
 
 /**
 }
 
 /**
- * Processes a read model action.
- * @param curr is the read model action to process.
- * @return True if processing this read updates the mo_graph.
+ * Switch from a model-checker context to a user-thread context. This is the
+ * complement of ModelChecker::switch_to_master and must be called from the
+ * model-checker context
+ *
+ * @param thread The user-thread to switch to
  */
  */
-bool ModelChecker::process_read(ModelAction *curr)
+void ModelChecker::switch_from_master(Thread *thread)
 {
 {
-       Node *node = curr->get_node();
-       while (true) {
-               bool updated = false;
-               switch (node->get_read_from_status()) {
-               case READ_FROM_PAST: {
-                       const ModelAction *rf = node->get_read_from_past();
-                       ASSERT(rf);
-
-                       mo_graph->startChanges();
-
-                       ASSERT(!is_infeasible());
-                       if (!check_recency(curr, rf)) {
-                               if (node->increment_read_from()) {
-                                       mo_graph->rollbackChanges();
-                                       continue;
-                               } else {
-                                       priv->too_many_reads = true;
-                               }
-                       }
-
-                       updated = r_modification_order(curr, rf);
-                       read_from(curr, rf);
-                       mo_graph->commitChanges();
-                       mo_check_promises(curr, true);
-                       break;
-               }
-               case READ_FROM_PROMISE: {
-                       Promise *promise = curr->get_node()->get_read_from_promise();
-                       if (promise->add_reader(curr))
-                               priv->failed_promise = true;
-                       curr->set_read_from_promise(promise);
-                       mo_graph->startChanges();
-                       if (!check_recency(curr, promise))
-                               priv->too_many_reads = true;
-                       updated = r_modification_order(curr, promise);
-                       mo_graph->commitChanges();
-                       break;
-               }
-               case READ_FROM_FUTURE: {
-                       /* Read from future value */
-                       struct future_value fv = node->get_future_value();
-                       Promise *promise = new Promise(curr, fv);
-                       curr->set_read_from_promise(promise);
-                       promises->push_back(promise);
-                       mo_graph->startChanges();
-                       updated = r_modification_order(curr, promise);
-                       mo_graph->commitChanges();
-                       break;
-               }
-               default:
-                       ASSERT(false);
-               }
-               get_thread(curr)->set_return_value(curr->get_return_value());
-               return updated;
-       }
+       scheduler->set_current_thread(thread);
+       Thread::swap(&system_context, thread);
 }
 
 /**
 }
 
 /**
- * Processes a lock, trylock, or unlock model action.  @param curr is
- * the read model action to process.
- *
- * The try lock operation checks whether the lock is taken.  If not,
- * it falls to the normal lock operation case.  If so, it returns
- * fail.
- *
- * The lock operation has already been checked that it is enabled, so
- * it just grabs the lock and synchronizes with the previous unlock.
- *
- * The unlock operation has to re-enable all of the threads that are
- * waiting on the lock.
+ * Switch from a user-context to the "master thread" context (a.k.a. system
+ * context). This switch is made with the intention of exploring a particular
+ * model-checking action (described by a ModelAction object). Must be called
+ * from a user-thread context.
  *
  *
- * @return True if synchronization was updated; false otherwise
+ * @param act The current action that will be explored. May be NULL only if
+ * trace is exiting via an assertion (see ModelExecution::set_assert and
+ * ModelExecution::has_asserted).
+ * @return Return the value returned by the current action
  */
  */
-bool ModelChecker::process_mutex(ModelAction *curr)
+uint64_t ModelChecker::switch_to_master(ModelAction *act)
 {
 {
-       std::mutex *mutex = curr->get_mutex();
-       struct std::mutex_state *state = NULL;
-
-       if (mutex)
-               state = mutex->get_state();
-
-       switch (curr->get_type()) {
-       case ATOMIC_TRYLOCK: {
-               bool success = !state->locked;
-               curr->set_try_lock(success);
-               if (!success) {
-                       get_thread(curr)->set_return_value(0);
-                       break;
-               }
-               get_thread(curr)->set_return_value(1);
-       }
-               //otherwise fall into the lock case
-       case ATOMIC_LOCK: {
-               if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
-                       assert_bug("Lock access before initialization");
-               state->locked = get_thread(curr);
-               ModelAction *unlock = get_last_unlock(curr);
-               //synchronize with the previous unlock statement
-               if (unlock != NULL) {
-                       synchronize(unlock, curr);
-                       return true;
-               }
-               break;
-       }
-       case ATOMIC_WAIT:
-       case ATOMIC_UNLOCK: {
-               /* wake up the other threads */
-               for (unsigned int i = 0; i < get_num_threads(); i++) {
-                       Thread *t = get_thread(int_to_id(i));
-                       Thread *curr_thrd = get_thread(curr);
-                       if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
-                               scheduler->wake(t);
-               }
-
-               /* unlock the lock - after checking who was waiting on it */
-               state->locked = NULL;
-
-               if (!curr->is_wait())
-                       break; /* The rest is only for ATOMIC_WAIT */
-
-               /* Should we go to sleep? (simulate spurious failures) */
-               if (curr->get_node()->get_misc() == 0) {
-                       get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
-                       /* disable us */
-                       scheduler->sleep(get_thread(curr));
-               }
-               break;
-       }
-       case ATOMIC_NOTIFY_ALL: {
-               action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
-               //activate all the waiting threads
-               for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
-                       scheduler->wake(get_thread(*rit));
-               }
-               waiters->clear();
-               break;
-       }
-       case ATOMIC_NOTIFY_ONE: {
-               action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
-               int wakeupthread = curr->get_node()->get_misc();
-               action_list_t::iterator it = waiters->begin();
-               advance(it, wakeupthread);
-               scheduler->wake(get_thread(*it));
-               waiters->erase(it);
-               break;
+       DBG();
+       Thread *old = thread_current();
+       scheduler->set_current_thread(NULL);
+       ASSERT(!old->get_pending());
+       old->set_pending(act);
+       if (Thread::swap(old, &system_context) < 0) {
+               perror("swap threads");
+               exit(EXIT_FAILURE);
        }
        }
+       return old->get_return_value();
+}
 
 
-       default:
-               ASSERT(0);
-       }
-       return false;
+/** Wrapper to run the user's main function, with appropriate arguments */
+void user_main_wrapper(void *)
+{
+       user_main(model->params.argc, model->params.argv);
 }
 
 }
 
-/**
- * @brief Check if the current pending promises allow a future value to be sent
- *
- * If one of the following is true:
- *  (a) there are no pending promises
- *  (b) the reader and writer do not cross any promises
- * Then, it is safe to pass a future value back now.
- *
- * Otherwise, we must save the pending future value until (a) or (b) is true
- *
- * @param writer The operation which sends the future value. Must be a write.
- * @param reader The operation which will observe the value. Must be a read.
- * @return True if the future value can be sent now; false if it must wait.
- */
-bool ModelChecker::promises_may_allow(const ModelAction *writer,
-               const ModelAction *reader) const
+bool ModelChecker::should_terminate_execution()
 {
 {
-       if (promises->empty())
+       /* Infeasible -> don't take any more steps */
+       if (execution->is_infeasible())
+               return true;
+       else if (execution->isfeasibleprefix() && execution->have_bug_reports()) {
+               execution->set_assert();
                return true;
                return true;
-       for(int i=promises->size()-1;i>=0;i--) {
-               ModelAction *pr=(*promises)[i]->get_reader(0);
-               //reader is after promise...doesn't cross any promise
-               if (*reader > *pr)
-                       return true;
-               //writer is after promise, reader before...bad...
-               if (*writer > *pr)
-                       return false;
        }
        }
-       return true;
+
+       if (execution->too_many_steps())
+               return true;
+       return false;
 }
 
 }
 
-/**
- * @brief Add a future value to a reader
- *
- * This function performs a few additional checks to ensure that the future
- * value can be feasibly observed by the reader
- *
- * @param writer The operation whose value is sent. Must be a write.
- * @param reader The read operation which may read the future value. Must be a read.
- */
-void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
+/** @brief Run ModelChecker for the user program */
+void ModelChecker::run()
 {
 {
-       /* Do more ambitious checks now that mo is more complete */
-       if (!mo_may_allow(writer, reader))
-               return;
-
-       Node *node = reader->get_node();
-
-       /* Find an ancestor thread which exists at the time of the reader */
-       Thread *write_thread = get_thread(writer);
-       while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
-               write_thread = write_thread->get_parent();
-
-       struct future_value fv = {
-               writer->get_write_value(),
-               writer->get_seq_number() + params.maxfuturedelay,
-               write_thread->get_id(),
-       };
-       if (node->add_future_value(fv))
-               set_latest_backtrack(reader);
-}
-
-/**
- * Process a write ModelAction
- * @param curr The ModelAction to process
- * @return True if the mo_graph was updated or promises were resolved
- */
-bool ModelChecker::process_write(ModelAction *curr)
-{
-       /* Readers to which we may send our future value */
-       ModelVector<ModelAction *> send_fv;
-
-       const ModelAction *earliest_promise_reader;
-       bool updated_promises = false;
-
-       bool updated_mod_order = w_modification_order(curr, &send_fv);
-       Promise *promise = pop_promise_to_resolve(curr);
-
-       if (promise) {
-               earliest_promise_reader = promise->get_reader(0);
-               updated_promises = resolve_promise(curr, promise);
-       } else
-               earliest_promise_reader = NULL;
-
-       for (unsigned int i = 0; i < send_fv.size(); i++) {
-               ModelAction *read = send_fv[i];
-
-               /* Don't send future values to reads after the Promise we resolve */
-               if (!earliest_promise_reader || *read < *earliest_promise_reader) {
-                       /* Check if future value can be sent immediately */
-                       if (promises_may_allow(curr, read)) {
-                               add_future_value(curr, read);
-                       } else {
-                               futurevalues->push_back(PendingFutureValue(curr, read));
-                       }
-               }
-       }
-
-       /* Check the pending future values */
-       for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
-               struct PendingFutureValue pfv = (*futurevalues)[i];
-               if (promises_may_allow(pfv.writer, pfv.reader)) {
-                       add_future_value(pfv.writer, pfv.reader);
-                       futurevalues->erase(futurevalues->begin() + i);
-               }
-       }
-
-       mo_graph->commitChanges();
-       mo_check_promises(curr, false);
-
-       get_thread(curr)->set_return_value(VALUE_NONE);
-       return updated_mod_order || updated_promises;
-}
-
-/**
- * Process a fence ModelAction
- * @param curr The ModelAction to process
- * @return True if synchronization was updated
- */
-bool ModelChecker::process_fence(ModelAction *curr)
-{
-       /*
-        * fence-relaxed: no-op
-        * fence-release: only log the occurence (not in this function), for
-        *   use in later synchronization
-        * fence-acquire (this function): search for hypothetical release
-        *   sequences
-        * fence-seq-cst: MO constraints formed in {r,w}_modification_order
-        */
-       bool updated = false;
-       if (curr->is_acquire()) {
-               action_list_t *list = action_trace;
-               action_list_t::reverse_iterator rit;
-               /* Find X : is_read(X) && X --sb-> curr */
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *act = *rit;
-                       if (act == curr)
-                               continue;
-                       if (act->get_tid() != curr->get_tid())
-                               continue;
-                       /* Stop at the beginning of the thread */
-                       if (act->is_thread_start())
-                               break;
-                       /* Stop once we reach a prior fence-acquire */
-                       if (act->is_fence() && act->is_acquire())
-                               break;
-                       if (!act->is_read())
-                               continue;
-                       /* read-acquire will find its own release sequences */
-                       if (act->is_acquire())
-                               continue;
-
-                       /* Establish hypothetical release sequences */
-                       rel_heads_list_t release_heads;
-                       get_release_seq_heads(curr, act, &release_heads);
-                       for (unsigned int i = 0; i < release_heads.size(); i++)
-                               synchronize(release_heads[i], curr);
-                       if (release_heads.size() != 0)
-                               updated = true;
-               }
-       }
-       return updated;
-}
-
-/**
- * @brief Process the current action for thread-related activity
- *
- * Performs current-action processing for a THREAD_* ModelAction. Proccesses
- * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
- * synchronization, etc.  This function is a no-op for non-THREAD actions
- * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
- *
- * @param curr The current action
- * @return True if synchronization was updated or a thread completed
- */
-bool ModelChecker::process_thread_action(ModelAction *curr)
-{
-       bool updated = false;
-
-       switch (curr->get_type()) {
-       case THREAD_CREATE: {
-               thrd_t *thrd = (thrd_t *)curr->get_location();
-               struct thread_params *params = (struct thread_params *)curr->get_value();
-               Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
-               add_thread(th);
-               th->set_creation(curr);
-               /* Promises can be satisfied by children */
-               for (unsigned int i = 0; i < promises->size(); i++) {
-                       Promise *promise = (*promises)[i];
-                       if (promise->thread_is_available(curr->get_tid()))
-                               promise->add_thread(th->get_id());
-               }
-               break;
-       }
-       case THREAD_JOIN: {
-               Thread *blocking = curr->get_thread_operand();
-               ModelAction *act = get_last_action(blocking->get_id());
-               synchronize(act, curr);
-               updated = true; /* trigger rel-seq checks */
-               break;
-       }
-       case THREAD_FINISH: {
-               Thread *th = get_thread(curr);
-               /* Wake up any joining threads */
-               for (unsigned int i = 0; i < get_num_threads(); i++) {
-                       Thread *waiting = get_thread(int_to_id(i));
-                       if (waiting->waiting_on() == th &&
-                                       waiting->get_pending()->is_thread_join())
-                               scheduler->wake(waiting);
-               }
-               th->complete();
-               /* Completed thread can't satisfy promises */
-               for (unsigned int i = 0; i < promises->size(); i++) {
-                       Promise *promise = (*promises)[i];
-                       if (promise->thread_is_available(th->get_id()))
-                               if (promise->eliminate_thread(th->get_id()))
-                                       priv->failed_promise = true;
-               }
-               updated = true; /* trigger rel-seq checks */
-               break;
-       }
-       case THREAD_START: {
-               check_promises(curr->get_tid(), NULL, curr->get_cv());
-               break;
-       }
-       default:
-               break;
-       }
-
-       return updated;
-}
-
-/**
- * @brief Process the current action for release sequence fixup activity
- *
- * Performs model-checker release sequence fixups for the current action,
- * forcing a single pending release sequence to break (with a given, potential
- * "loose" write) or to complete (i.e., synchronize). If a pending release
- * sequence forms a complete release sequence, then we must perform the fixup
- * synchronization, mo_graph additions, etc.
- *
- * @param curr The current action; must be a release sequence fixup action
- * @param work_queue The work queue to which to add work items as they are
- * generated
- */
-void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
-{
-       const ModelAction *write = curr->get_node()->get_relseq_break();
-       struct release_seq *sequence = pending_rel_seqs->back();
-       pending_rel_seqs->pop_back();
-       ASSERT(sequence);
-       ModelAction *acquire = sequence->acquire;
-       const ModelAction *rf = sequence->rf;
-       const ModelAction *release = sequence->release;
-       ASSERT(acquire);
-       ASSERT(release);
-       ASSERT(rf);
-       ASSERT(release->same_thread(rf));
-
-       if (write == NULL) {
-               /**
-                * @todo Forcing a synchronization requires that we set
-                * modification order constraints. For instance, we can't allow
-                * a fixup sequence in which two separate read-acquire
-                * operations read from the same sequence, where the first one
-                * synchronizes and the other doesn't. Essentially, we can't
-                * allow any writes to insert themselves between 'release' and
-                * 'rf'
-                */
-
-               /* Must synchronize */
-               if (!synchronize(release, acquire))
-                       return;
-               /* Re-check all pending release sequences */
-               work_queue->push_back(CheckRelSeqWorkEntry(NULL));
-               /* Re-check act for mo_graph edges */
-               work_queue->push_back(MOEdgeWorkEntry(acquire));
-
-               /* propagate synchronization to later actions */
-               action_list_t::reverse_iterator rit = action_trace->rbegin();
-               for (; (*rit) != acquire; rit++) {
-                       ModelAction *propagate = *rit;
-                       if (acquire->happens_before(propagate)) {
-                               synchronize(acquire, propagate);
-                               /* Re-check 'propagate' for mo_graph edges */
-                               work_queue->push_back(MOEdgeWorkEntry(propagate));
-                       }
-               }
-       } else {
-               /* Break release sequence with new edges:
-                *   release --mo--> write --mo--> rf */
-               mo_graph->addEdge(release, write);
-               mo_graph->addEdge(write, rf);
-       }
-
-       /* See if we have realized a data race */
-       checkDataRaces();
-}
-
-/**
- * Initialize the current action by performing one or more of the following
- * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
- * in the NodeStack, manipulating backtracking sets, allocating and
- * initializing clock vectors, and computing the promises to fulfill.
- *
- * @param curr The current action, as passed from the user context; may be
- * freed/invalidated after the execution of this function, with a different
- * action "returned" its place (pass-by-reference)
- * @return True if curr is a newly-explored action; false otherwise
- */
-bool ModelChecker::initialize_curr_action(ModelAction **curr)
-{
-       ModelAction *newcurr;
-
-       if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
-               newcurr = process_rmw(*curr);
-               delete *curr;
-
-               if (newcurr->is_rmw())
-                       compute_promises(newcurr);
-
-               *curr = newcurr;
-               return false;
-       }
-
-       (*curr)->set_seq_number(get_next_seq_num());
-
-       newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
-       if (newcurr) {
-               /* First restore type and order in case of RMW operation */
-               if ((*curr)->is_rmwr())
-                       newcurr->copy_typeandorder(*curr);
-
-               ASSERT((*curr)->get_location() == newcurr->get_location());
-               newcurr->copy_from_new(*curr);
-
-               /* Discard duplicate ModelAction; use action from NodeStack */
-               delete *curr;
-
-               /* Always compute new clock vector */
-               newcurr->create_cv(get_parent_action(newcurr->get_tid()));
-
-               *curr = newcurr;
-               return false; /* Action was explored previously */
-       } else {
-               newcurr = *curr;
-
-               /* Always compute new clock vector */
-               newcurr->create_cv(get_parent_action(newcurr->get_tid()));
-
-               /* Assign most recent release fence */
-               newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
-
-               /*
-                * Perform one-time actions when pushing new ModelAction onto
-                * NodeStack
-                */
-               if (newcurr->is_write())
-                       compute_promises(newcurr);
-               else if (newcurr->is_relseq_fixup())
-                       compute_relseq_breakwrites(newcurr);
-               else if (newcurr->is_wait())
-                       newcurr->get_node()->set_misc_max(2);
-               else if (newcurr->is_notify_one()) {
-                       newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
-               }
-               return true; /* This was a new ModelAction */
-       }
-}
-
-/**
- * @brief Establish reads-from relation between two actions
- *
- * Perform basic operations involved with establishing a concrete rf relation,
- * including setting the ModelAction data and checking for release sequences.
- *
- * @param act The action that is reading (must be a read)
- * @param rf The action from which we are reading (must be a write)
- *
- * @return True if this read established synchronization
- */
-bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
-{
-       ASSERT(rf);
-       ASSERT(rf->is_write());
-
-       act->set_read_from(rf);
-       if (act->is_acquire()) {
-               rel_heads_list_t release_heads;
-               get_release_seq_heads(act, act, &release_heads);
-               int num_heads = release_heads.size();
-               for (unsigned int i = 0; i < release_heads.size(); i++)
-                       if (!synchronize(release_heads[i], act))
-                               num_heads--;
-               return num_heads > 0;
-       }
-       return false;
-}
-
-/**
- * @brief Synchronizes two actions
- *
- * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
- * This function performs the synchronization as well as providing other hooks
- * for other checks along with synchronization.
- *
- * @param first The left-hand side of the synchronizes-with relation
- * @param second The right-hand side of the synchronizes-with relation
- * @return True if the synchronization was successful (i.e., was consistent
- * with the execution order); false otherwise
- */
-bool ModelChecker::synchronize(const ModelAction *first, ModelAction *second)
-{
-       if (*second < *first) {
-               set_bad_synchronization();
-               return false;
-       }
-       check_promises(first->get_tid(), second->get_cv(), first->get_cv());
-       return second->synchronize_with(first);
-}
-
-/**
- * Check promises and eliminate potentially-satisfying threads when a thread is
- * blocked (e.g., join, lock). A thread which is waiting on another thread can
- * no longer satisfy a promise generated from that thread.
- *
- * @param blocker The thread on which a thread is waiting
- * @param waiting The waiting thread
- */
-void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
-{
-       for (unsigned int i = 0; i < promises->size(); i++) {
-               Promise *promise = (*promises)[i];
-               if (!promise->thread_is_available(waiting->get_id()))
-                       continue;
-               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
-                       ModelAction *reader = promise->get_reader(j);
-                       if (reader->get_tid() != blocker->get_id())
-                               continue;
-                       if (promise->eliminate_thread(waiting->get_id())) {
-                               /* Promise has failed */
-                               priv->failed_promise = true;
-                       } else {
-                               /* Only eliminate the 'waiting' thread once */
-                               return;
-                       }
-               }
-       }
-}
-
-/**
- * @brief Check whether a model action is enabled.
- *
- * Checks whether a lock or join operation would be successful (i.e., is the
- * lock already locked, or is the joined thread already complete). If not, put
- * the action in a waiter list.
- *
- * @param curr is the ModelAction to check whether it is enabled.
- * @return a bool that indicates whether the action is enabled.
- */
-bool ModelChecker::check_action_enabled(ModelAction *curr) {
-       if (curr->is_lock()) {
-               std::mutex *lock = curr->get_mutex();
-               struct std::mutex_state *state = lock->get_state();
-               if (state->locked)
-                       return false;
-       } else if (curr->is_thread_join()) {
-               Thread *blocking = curr->get_thread_operand();
-               if (!blocking->is_complete()) {
-                       thread_blocking_check_promises(blocking, get_thread(curr));
-                       return false;
-               }
-       }
-
-       return true;
-}
-
-/**
- * This is the heart of the model checker routine. It performs model-checking
- * actions corresponding to a given "current action." Among other processes, it
- * calculates reads-from relationships, updates synchronization clock vectors,
- * forms a memory_order constraints graph, and handles replay/backtrack
- * execution when running permutations of previously-observed executions.
- *
- * @param curr The current action to process
- * @return The ModelAction that is actually executed; may be different than
- * curr; may be NULL, if the current action is not enabled to run
- */
-ModelAction * ModelChecker::check_current_action(ModelAction *curr)
-{
-       ASSERT(curr);
-       bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
-       bool newly_explored = initialize_curr_action(&curr);
-
-       DBG();
-
-       wake_up_sleeping_actions(curr);
-
-       /* Compute fairness information for CHESS yield algorithm */
-       if (model->params.yieldon) {
-               curr->get_node()->update_yield(scheduler);
-       }
-
-       /* Add the action to lists before any other model-checking tasks */
-       if (!second_part_of_rmw)
-               add_action_to_lists(curr);
-
-       /* Build may_read_from set for newly-created actions */
-       if (newly_explored && curr->is_read())
-               build_may_read_from(curr);
-
-       /* Initialize work_queue with the "current action" work */
-       work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
-       while (!work_queue.empty() && !has_asserted()) {
-               WorkQueueEntry work = work_queue.front();
-               work_queue.pop_front();
-
-               switch (work.type) {
-               case WORK_CHECK_CURR_ACTION: {
-                       ModelAction *act = work.action;
-                       bool update = false; /* update this location's release seq's */
-                       bool update_all = false; /* update all release seq's */
-
-                       if (process_thread_action(curr))
-                               update_all = true;
-
-                       if (act->is_read() && !second_part_of_rmw && process_read(act))
-                               update = true;
-
-                       if (act->is_write() && process_write(act))
-                               update = true;
-
-                       if (act->is_fence() && process_fence(act))
-                               update_all = true;
-
-                       if (act->is_mutex_op() && process_mutex(act))
-                               update_all = true;
-
-                       if (act->is_relseq_fixup())
-                               process_relseq_fixup(curr, &work_queue);
-
-                       if (update_all)
-                               work_queue.push_back(CheckRelSeqWorkEntry(NULL));
-                       else if (update)
-                               work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
-                       break;
-               }
-               case WORK_CHECK_RELEASE_SEQ:
-                       resolve_release_sequences(work.location, &work_queue);
-                       break;
-               case WORK_CHECK_MO_EDGES: {
-                       /** @todo Complete verification of work_queue */
-                       ModelAction *act = work.action;
-                       bool updated = false;
-
-                       if (act->is_read()) {
-                               const ModelAction *rf = act->get_reads_from();
-                               const Promise *promise = act->get_reads_from_promise();
-                               if (rf) {
-                                       if (r_modification_order(act, rf))
-                                               updated = true;
-                               } else if (promise) {
-                                       if (r_modification_order(act, promise))
-                                               updated = true;
-                               }
-                       }
-                       if (act->is_write()) {
-                               if (w_modification_order(act, NULL))
-                                       updated = true;
-                       }
-                       mo_graph->commitChanges();
-
-                       if (updated)
-                               work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
-                       break;
-               }
-               default:
-                       ASSERT(false);
-                       break;
-               }
-       }
-
-       check_curr_backtracking(curr);
-       set_backtracking(curr);
-       return curr;
-}
-
-void ModelChecker::check_curr_backtracking(ModelAction *curr)
-{
-       Node *currnode = curr->get_node();
-       Node *parnode = currnode->get_parent();
-
-       if ((parnode && !parnode->backtrack_empty()) ||
-                        !currnode->misc_empty() ||
-                        !currnode->read_from_empty() ||
-                        !currnode->promise_empty() ||
-                        !currnode->relseq_break_empty()) {
-               set_latest_backtrack(curr);
-       }
-}
-
-bool ModelChecker::promises_expired() const
-{
-       for (unsigned int i = 0; i < promises->size(); i++) {
-               Promise *promise = (*promises)[i];
-               if (promise->get_expiration() < priv->used_sequence_numbers)
-                       return true;
-       }
-       return false;
-}
-
-/**
- * This is the strongest feasibility check available.
- * @return whether the current trace (partial or complete) must be a prefix of
- * a feasible trace.
- */
-bool ModelChecker::isfeasibleprefix() const
-{
-       return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
-}
-
-/**
- * Print disagnostic information about an infeasible execution
- * @param prefix A string to prefix the output with; if NULL, then a default
- * message prefix will be provided
- */
-void ModelChecker::print_infeasibility(const char *prefix) const
-{
-       char buf[100];
-       char *ptr = buf;
-       if (mo_graph->checkForCycles())
-               ptr += sprintf(ptr, "[mo cycle]");
-       if (priv->failed_promise)
-               ptr += sprintf(ptr, "[failed promise]");
-       if (priv->too_many_reads)
-               ptr += sprintf(ptr, "[too many reads]");
-       if (priv->no_valid_reads)
-               ptr += sprintf(ptr, "[no valid reads-from]");
-       if (priv->bad_synchronization)
-               ptr += sprintf(ptr, "[bad sw ordering]");
-       if (promises_expired())
-               ptr += sprintf(ptr, "[promise expired]");
-       if (promises->size() != 0)
-               ptr += sprintf(ptr, "[unresolved promise]");
-       if (ptr != buf)
-               model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
-}
-
-/**
- * Returns whether the current completed trace is feasible, except for pending
- * release sequences.
- */
-bool ModelChecker::is_feasible_prefix_ignore_relseq() const
-{
-       return !is_infeasible() && promises->size() == 0;
-}
-
-/**
- * Check if the current partial trace is infeasible. Does not check any
- * end-of-execution flags, which might rule out the execution. Thus, this is
- * useful only for ruling an execution as infeasible.
- * @return whether the current partial trace is infeasible.
- */
-bool ModelChecker::is_infeasible() const
-{
-       return mo_graph->checkForCycles() ||
-               priv->no_valid_reads ||
-               priv->failed_promise ||
-               priv->too_many_reads ||
-               priv->bad_synchronization ||
-               promises_expired();
-}
-
-/** Close out a RMWR by converting previous RMWR into a RMW or READ. */
-ModelAction * ModelChecker::process_rmw(ModelAction *act) {
-       ModelAction *lastread = get_last_action(act->get_tid());
-       lastread->process_rmw(act);
-       if (act->is_rmw()) {
-               if (lastread->get_reads_from())
-                       mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
-               else
-                       mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
-               mo_graph->commitChanges();
-       }
-       return lastread;
-}
-
-/**
- * A helper function for ModelChecker::check_recency, to check if the current
- * thread is able to read from a different write/promise for 'params.maxreads'
- * number of steps and if that write/promise should become visible (i.e., is
- * ordered later in the modification order). This helps model memory liveness.
- *
- * @param curr The current action. Must be a read.
- * @param rf The write/promise from which we plan to read
- * @param other_rf The write/promise from which we may read
- * @return True if we were able to read from other_rf for params.maxreads steps
- */
-template <typename T, typename U>
-bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
-{
-       /* Need a different write/promise */
-       if (other_rf->equals(rf))
-               return false;
-
-       /* Only look for "newer" writes/promises */
-       if (!mo_graph->checkReachable(rf, other_rf))
-               return false;
-
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
-       action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
-       action_list_t::reverse_iterator rit = list->rbegin();
-       ASSERT((*rit) == curr);
-       /* Skip past curr */
-       rit++;
-
-       /* Does this write/promise work for everyone? */
-       for (int i = 0; i < params.maxreads; i++, rit++) {
-               ModelAction *act = *rit;
-               if (!act->may_read_from(other_rf))
-                       return false;
-       }
-       return true;
-}
-
-/**
- * Checks whether a thread has read from the same write or Promise for too many
- * times without seeing the effects of a later write/Promise.
- *
- * Basic idea:
- * 1) there must a different write/promise that we could read from,
- * 2) we must have read from the same write/promise in excess of maxreads times,
- * 3) that other write/promise must have been in the reads_from set for maxreads times, and
- * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
- *
- * If so, we decide that the execution is no longer feasible.
- *
- * @param curr The current action. Must be a read.
- * @param rf The ModelAction/Promise from which we might read.
- * @return True if the read should succeed; false otherwise
- */
-template <typename T>
-bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
-{
-       if (!params.maxreads)
-               return true;
-
-       //NOTE: Next check is just optimization, not really necessary....
-       if (curr->get_node()->get_read_from_past_size() +
-                       curr->get_node()->get_read_from_promise_size() <= 1)
-               return true;
-
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
-       int tid = id_to_int(curr->get_tid());
-       ASSERT(tid < (int)thrd_lists->size());
-       action_list_t *list = &(*thrd_lists)[tid];
-       action_list_t::reverse_iterator rit = list->rbegin();
-       ASSERT((*rit) == curr);
-       /* Skip past curr */
-       rit++;
-
-       action_list_t::reverse_iterator ritcopy = rit;
-       /* See if we have enough reads from the same value */
-       for (int count = 0; count < params.maxreads; ritcopy++, count++) {
-               if (ritcopy == list->rend())
-                       return true;
-               ModelAction *act = *ritcopy;
-               if (!act->is_read())
-                       return true;
-               if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
-                       return true;
-               if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
-                       return true;
-               if (act->get_node()->get_read_from_past_size() +
-                               act->get_node()->get_read_from_promise_size() <= 1)
-                       return true;
-       }
-       for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
-               const ModelAction *write = curr->get_node()->get_read_from_past(i);
-               if (should_read_instead(curr, rf, write))
-                       return false; /* liveness failure */
-       }
-       for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
-               const Promise *promise = curr->get_node()->get_read_from_promise(i);
-               if (should_read_instead(curr, rf, promise))
-                       return false; /* liveness failure */
-       }
-       return true;
-}
-
-/**
- * @brief Updates the mo_graph with the constraints imposed from the current
- * read.
- *
- * Basic idea is the following: Go through each other thread and find
- * the last action that happened before our read.  Two cases:
- *
- * -# The action is a write: that write must either occur before
- * the write we read from or be the write we read from.
- * -# The action is a read: the write that that action read from
- * must occur before the write we read from or be the same write.
- *
- * @param curr The current action. Must be a read.
- * @param rf The ModelAction or Promise that curr reads from. Must be a write.
- * @return True if modification order edges were added; false otherwise
- */
-template <typename rf_type>
-bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
-{
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
-       unsigned int i;
-       bool added = false;
-       ASSERT(curr->is_read());
-
-       /* Last SC fence in the current thread */
-       ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
-       ModelAction *last_sc_write = NULL;
-       if (curr->is_seqcst())
-               last_sc_write = get_last_seq_cst_write(curr);
-
-       /* Iterate over all threads */
-       for (i = 0; i < thrd_lists->size(); i++) {
-               /* Last SC fence in thread i */
-               ModelAction *last_sc_fence_thread_local = NULL;
-               if (int_to_id((int)i) != curr->get_tid())
-                       last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
-
-               /* Last SC fence in thread i, before last SC fence in current thread */
-               ModelAction *last_sc_fence_thread_before = NULL;
-               if (last_sc_fence_local)
-                       last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
-
-               /* Iterate over actions in thread, starting from most recent */
-               action_list_t *list = &(*thrd_lists)[i];
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *act = *rit;
-
-                       /* Skip curr */
-                       if (act == curr)
-                               continue;
-                       /* Don't want to add reflexive edges on 'rf' */
-                       if (act->equals(rf)) {
-                               if (act->happens_before(curr))
-                                       break;
-                               else
-                                       continue;
-                       }
-
-                       if (act->is_write()) {
-                               /* C++, Section 29.3 statement 5 */
-                               if (curr->is_seqcst() && last_sc_fence_thread_local &&
-                                               *act < *last_sc_fence_thread_local) {
-                                       added = mo_graph->addEdge(act, rf) || added;
-                                       break;
-                               }
-                               /* C++, Section 29.3 statement 4 */
-                               else if (act->is_seqcst() && last_sc_fence_local &&
-                                               *act < *last_sc_fence_local) {
-                                       added = mo_graph->addEdge(act, rf) || added;
-                                       break;
-                               }
-                               /* C++, Section 29.3 statement 6 */
-                               else if (last_sc_fence_thread_before &&
-                                               *act < *last_sc_fence_thread_before) {
-                                       added = mo_graph->addEdge(act, rf) || added;
-                                       break;
-                               }
-                       }
-
-                       /* C++, Section 29.3 statement 3 (second subpoint) */
-                       if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
-                               added = mo_graph->addEdge(act, rf) || added;
-                               break;
-                       }
-
-                       /*
-                        * Include at most one act per-thread that "happens
-                        * before" curr
-                        */
-                       if (act->happens_before(curr)) {
-                               if (act->is_write()) {
-                                       added = mo_graph->addEdge(act, rf) || added;
-                               } else {
-                                       const ModelAction *prevrf = act->get_reads_from();
-                                       const Promise *prevrf_promise = act->get_reads_from_promise();
-                                       if (prevrf) {
-                                               if (!prevrf->equals(rf))
-                                                       added = mo_graph->addEdge(prevrf, rf) || added;
-                                       } else if (!prevrf_promise->equals(rf)) {
-                                               added = mo_graph->addEdge(prevrf_promise, rf) || added;
-                                       }
-                               }
-                               break;
-                       }
-               }
-       }
-
-       /*
-        * All compatible, thread-exclusive promises must be ordered after any
-        * concrete loads from the same thread
-        */
-       for (unsigned int i = 0; i < promises->size(); i++)
-               if ((*promises)[i]->is_compatible_exclusive(curr))
-                       added = mo_graph->addEdge(rf, (*promises)[i]) || added;
-
-       return added;
-}
-
-/**
- * Updates the mo_graph with the constraints imposed from the current write.
- *
- * Basic idea is the following: Go through each other thread and find
- * the lastest action that happened before our write.  Two cases:
- *
- * (1) The action is a write => that write must occur before
- * the current write
- *
- * (2) The action is a read => the write that that action read from
- * must occur before the current write.
- *
- * This method also handles two other issues:
- *
- * (I) Sequential Consistency: Making sure that if the current write is
- * seq_cst, that it occurs after the previous seq_cst write.
- *
- * (II) Sending the write back to non-synchronizing reads.
- *
- * @param curr The current action. Must be a write.
- * @param send_fv A vector for stashing reads to which we may pass our future
- * value. If NULL, then don't record any future values.
- * @return True if modification order edges were added; false otherwise
- */
-bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
-{
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
-       unsigned int i;
-       bool added = false;
-       ASSERT(curr->is_write());
-
-       if (curr->is_seqcst()) {
-               /* We have to at least see the last sequentially consistent write,
-                        so we are initialized. */
-               ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
-               if (last_seq_cst != NULL) {
-                       added = mo_graph->addEdge(last_seq_cst, curr) || added;
-               }
-       }
-
-       /* Last SC fence in the current thread */
-       ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
-
-       /* Iterate over all threads */
-       for (i = 0; i < thrd_lists->size(); i++) {
-               /* Last SC fence in thread i, before last SC fence in current thread */
-               ModelAction *last_sc_fence_thread_before = NULL;
-               if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
-                       last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
-
-               /* Iterate over actions in thread, starting from most recent */
-               action_list_t *list = &(*thrd_lists)[i];
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *act = *rit;
-                       if (act == curr) {
-                               /*
-                                * 1) If RMW and it actually read from something, then we
-                                * already have all relevant edges, so just skip to next
-                                * thread.
-                                *
-                                * 2) If RMW and it didn't read from anything, we should
-                                * whatever edge we can get to speed up convergence.
-                                *
-                                * 3) If normal write, we need to look at earlier actions, so
-                                * continue processing list.
-                                */
-                               if (curr->is_rmw()) {
-                                       if (curr->get_reads_from() != NULL)
-                                               break;
-                                       else
-                                               continue;
-                               } else
-                                       continue;
-                       }
-
-                       /* C++, Section 29.3 statement 7 */
-                       if (last_sc_fence_thread_before && act->is_write() &&
-                                       *act < *last_sc_fence_thread_before) {
-                               added = mo_graph->addEdge(act, curr) || added;
-                               break;
-                       }
-
-                       /*
-                        * Include at most one act per-thread that "happens
-                        * before" curr
-                        */
-                       if (act->happens_before(curr)) {
-                               /*
-                                * Note: if act is RMW, just add edge:
-                                *   act --mo--> curr
-                                * The following edge should be handled elsewhere:
-                                *   readfrom(act) --mo--> act
-                                */
-                               if (act->is_write())
-                                       added = mo_graph->addEdge(act, curr) || added;
-                               else if (act->is_read()) {
-                                       //if previous read accessed a null, just keep going
-                                       if (act->get_reads_from() == NULL)
-                                               continue;
-                                       added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
-                               }
-                               break;
-                       } else if (act->is_read() && !act->could_synchronize_with(curr) &&
-                                                    !act->same_thread(curr)) {
-                               /* We have an action that:
-                                  (1) did not happen before us
-                                  (2) is a read and we are a write
-                                  (3) cannot synchronize with us
-                                  (4) is in a different thread
-                                  =>
-                                  that read could potentially read from our write.  Note that
-                                  these checks are overly conservative at this point, we'll
-                                  do more checks before actually removing the
-                                  pendingfuturevalue.
-
-                                */
-                               if (send_fv && thin_air_constraint_may_allow(curr, act)) {
-                                       if (!is_infeasible())
-                                               send_fv->push_back(act);
-                                       else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
-                                               add_future_value(curr, act);
-                               }
-                       }
-               }
-       }
-
-       /*
-        * All compatible, thread-exclusive promises must be ordered after any
-        * concrete stores to the same thread, or else they can be merged with
-        * this store later
-        */
-       for (unsigned int i = 0; i < promises->size(); i++)
-               if ((*promises)[i]->is_compatible_exclusive(curr))
-                       added = mo_graph->addEdge(curr, (*promises)[i]) || added;
-
-       return added;
-}
-
-/** Arbitrary reads from the future are not allowed.  Section 29.3
- * part 9 places some constraints.  This method checks one result of constraint
- * constraint.  Others require compiler support. */
-bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
-{
-       if (!writer->is_rmw())
-               return true;
-
-       if (!reader->is_rmw())
-               return true;
-
-       for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
-               if (search == reader)
-                       return false;
-               if (search->get_tid() == reader->get_tid() &&
-                               search->happens_before(reader))
-                       break;
-       }
-
-       return true;
-}
-
-/**
- * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
- * some constraints. This method checks one the following constraint (others
- * require compiler support):
- *
- *   If X --hb-> Y --mo-> Z, then X should not read from Z.
- */
-bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
-{
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
-       unsigned int i;
-       /* Iterate over all threads */
-       for (i = 0; i < thrd_lists->size(); i++) {
-               const ModelAction *write_after_read = NULL;
-
-               /* Iterate over actions in thread, starting from most recent */
-               action_list_t *list = &(*thrd_lists)[i];
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *act = *rit;
-
-                       /* Don't disallow due to act == reader */
-                       if (!reader->happens_before(act) || reader == act)
-                               break;
-                       else if (act->is_write())
-                               write_after_read = act;
-                       else if (act->is_read() && act->get_reads_from() != NULL)
-                               write_after_read = act->get_reads_from();
-               }
-
-               if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
-                       return false;
-       }
-       return true;
-}
-
-/**
- * Finds the head(s) of the release sequence(s) containing a given ModelAction.
- * The ModelAction under consideration is expected to be taking part in
- * release/acquire synchronization as an object of the "reads from" relation.
- * Note that this can only provide release sequence support for RMW chains
- * which do not read from the future, as those actions cannot be traced until
- * their "promise" is fulfilled. Similarly, we may not even establish the
- * presence of a release sequence with certainty, as some modification order
- * constraints may be decided further in the future. Thus, this function
- * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
- * and a boolean representing certainty.
- *
- * @param rf The action that might be part of a release sequence. Must be a
- * write.
- * @param release_heads A pass-by-reference style return parameter. After
- * execution of this function, release_heads will contain the heads of all the
- * relevant release sequences, if any exists with certainty
- * @param pending A pass-by-reference style return parameter which is only used
- * when returning false (i.e., uncertain). Returns most information regarding
- * an uncertain release sequence, including any write operations that might
- * break the sequence.
- * @return true, if the ModelChecker is certain that release_heads is complete;
- * false otherwise
- */
-bool ModelChecker::release_seq_heads(const ModelAction *rf,
-               rel_heads_list_t *release_heads,
-               struct release_seq *pending) const
-{
-       /* Only check for release sequences if there are no cycles */
-       if (mo_graph->checkForCycles())
-               return false;
-
-       for ( ; rf != NULL; rf = rf->get_reads_from()) {
-               ASSERT(rf->is_write());
-
-               if (rf->is_release())
-                       release_heads->push_back(rf);
-               else if (rf->get_last_fence_release())
-                       release_heads->push_back(rf->get_last_fence_release());
-               if (!rf->is_rmw())
-                       break; /* End of RMW chain */
-
-               /** @todo Need to be smarter here...  In the linux lock
-                * example, this will run to the beginning of the program for
-                * every acquire. */
-               /** @todo The way to be smarter here is to keep going until 1
-                * thread has a release preceded by an acquire and you've seen
-                *       both. */
-
-               /* acq_rel RMW is a sufficient stopping condition */
-               if (rf->is_acquire() && rf->is_release())
-                       return true; /* complete */
-       };
-       if (!rf) {
-               /* read from future: need to settle this later */
-               pending->rf = NULL;
-               return false; /* incomplete */
-       }
-
-       if (rf->is_release())
-               return true; /* complete */
-
-       /* else relaxed write
-        * - check for fence-release in the same thread (29.8, stmt. 3)
-        * - check modification order for contiguous subsequence
-        *   -> rf must be same thread as release */
-
-       const ModelAction *fence_release = rf->get_last_fence_release();
-       /* Synchronize with a fence-release unconditionally; we don't need to
-        * find any more "contiguous subsequence..." for it */
-       if (fence_release)
-               release_heads->push_back(fence_release);
-
-       int tid = id_to_int(rf->get_tid());
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
-       action_list_t *list = &(*thrd_lists)[tid];
-       action_list_t::const_reverse_iterator rit;
-
-       /* Find rf in the thread list */
-       rit = std::find(list->rbegin(), list->rend(), rf);
-       ASSERT(rit != list->rend());
-
-       /* Find the last {write,fence}-release */
-       for (; rit != list->rend(); rit++) {
-               if (fence_release && *(*rit) < *fence_release)
-                       break;
-               if ((*rit)->is_release())
-                       break;
-       }
-       if (rit == list->rend()) {
-               /* No write-release in this thread */
-               return true; /* complete */
-       } else if (fence_release && *(*rit) < *fence_release) {
-               /* The fence-release is more recent (and so, "stronger") than
-                * the most recent write-release */
-               return true; /* complete */
-       } /* else, need to establish contiguous release sequence */
-       ModelAction *release = *rit;
-
-       ASSERT(rf->same_thread(release));
-
-       pending->writes.clear();
-
-       bool certain = true;
-       for (unsigned int i = 0; i < thrd_lists->size(); i++) {
-               if (id_to_int(rf->get_tid()) == (int)i)
-                       continue;
-               list = &(*thrd_lists)[i];
-
-               /* Can we ensure no future writes from this thread may break
-                * the release seq? */
-               bool future_ordered = false;
-
-               ModelAction *last = get_last_action(int_to_id(i));
-               Thread *th = get_thread(int_to_id(i));
-               if ((last && rf->happens_before(last)) ||
-                               !is_enabled(th) ||
-                               th->is_complete())
-                       future_ordered = true;
-
-               ASSERT(!th->is_model_thread() || future_ordered);
-
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       const ModelAction *act = *rit;
-                       /* Reach synchronization -> this thread is complete */
-                       if (act->happens_before(release))
-                               break;
-                       if (rf->happens_before(act)) {
-                               future_ordered = true;
-                               continue;
-                       }
-
-                       /* Only non-RMW writes can break release sequences */
-                       if (!act->is_write() || act->is_rmw())
-                               continue;
-
-                       /* Check modification order */
-                       if (mo_graph->checkReachable(rf, act)) {
-                               /* rf --mo--> act */
-                               future_ordered = true;
-                               continue;
-                       }
-                       if (mo_graph->checkReachable(act, release))
-                               /* act --mo--> release */
-                               break;
-                       if (mo_graph->checkReachable(release, act) &&
-                                     mo_graph->checkReachable(act, rf)) {
-                               /* release --mo-> act --mo--> rf */
-                               return true; /* complete */
-                       }
-                       /* act may break release sequence */
-                       pending->writes.push_back(act);
-                       certain = false;
-               }
-               if (!future_ordered)
-                       certain = false; /* This thread is uncertain */
-       }
-
-       if (certain) {
-               release_heads->push_back(release);
-               pending->writes.clear();
-       } else {
-               pending->release = release;
-               pending->rf = rf;
-       }
-       return certain;
-}
-
-/**
- * An interface for getting the release sequence head(s) with which a
- * given ModelAction must synchronize. This function only returns a non-empty
- * result when it can locate a release sequence head with certainty. Otherwise,
- * it may mark the internal state of the ModelChecker so that it will handle
- * the release sequence at a later time, causing @a acquire to update its
- * synchronization at some later point in execution.
- *
- * @param acquire The 'acquire' action that may synchronize with a release
- * sequence
- * @param read The read action that may read from a release sequence; this may
- * be the same as acquire, or else an earlier action in the same thread (i.e.,
- * when 'acquire' is a fence-acquire)
- * @param release_heads A pass-by-reference return parameter. Will be filled
- * with the head(s) of the release sequence(s), if they exists with certainty.
- * @see ModelChecker::release_seq_heads
- */
-void ModelChecker::get_release_seq_heads(ModelAction *acquire,
-               ModelAction *read, rel_heads_list_t *release_heads)
-{
-       const ModelAction *rf = read->get_reads_from();
-       struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
-       sequence->acquire = acquire;
-       sequence->read = read;
-
-       if (!release_seq_heads(rf, release_heads, sequence)) {
-               /* add act to 'lazy checking' list */
-               pending_rel_seqs->push_back(sequence);
-       } else {
-               snapshot_free(sequence);
-       }
-}
-
-/**
- * Attempt to resolve all stashed operations that might synchronize with a
- * release sequence for a given location. This implements the "lazy" portion of
- * determining whether or not a release sequence was contiguous, since not all
- * modification order information is present at the time an action occurs.
- *
- * @param location The location/object that should be checked for release
- * sequence resolutions. A NULL value means to check all locations.
- * @param work_queue The work queue to which to add work items as they are
- * generated
- * @return True if any updates occurred (new synchronization, new mo_graph
- * edges)
- */
-bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
-{
-       bool updated = false;
-       SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
-       while (it != pending_rel_seqs->end()) {
-               struct release_seq *pending = *it;
-               ModelAction *acquire = pending->acquire;
-               const ModelAction *read = pending->read;
-
-               /* Only resolve sequences on the given location, if provided */
-               if (location && read->get_location() != location) {
-                       it++;
-                       continue;
-               }
-
-               const ModelAction *rf = read->get_reads_from();
-               rel_heads_list_t release_heads;
-               bool complete;
-               complete = release_seq_heads(rf, &release_heads, pending);
-               for (unsigned int i = 0; i < release_heads.size(); i++)
-                       if (!acquire->has_synchronized_with(release_heads[i]))
-                               if (synchronize(release_heads[i], acquire))
-                                       updated = true;
-
-               if (updated) {
-                       /* Re-check all pending release sequences */
-                       work_queue->push_back(CheckRelSeqWorkEntry(NULL));
-                       /* Re-check read-acquire for mo_graph edges */
-                       if (acquire->is_read())
-                               work_queue->push_back(MOEdgeWorkEntry(acquire));
-
-                       /* propagate synchronization to later actions */
-                       action_list_t::reverse_iterator rit = action_trace->rbegin();
-                       for (; (*rit) != acquire; rit++) {
-                               ModelAction *propagate = *rit;
-                               if (acquire->happens_before(propagate)) {
-                                       synchronize(acquire, propagate);
-                                       /* Re-check 'propagate' for mo_graph edges */
-                                       work_queue->push_back(MOEdgeWorkEntry(propagate));
-                               }
-                       }
-               }
-               if (complete) {
-                       it = pending_rel_seqs->erase(it);
-                       snapshot_free(pending);
-               } else {
-                       it++;
-               }
-       }
-
-       // If we resolved promises or data races, see if we have realized a data race.
-       checkDataRaces();
-
-       return updated;
-}
-
-/**
- * Performs various bookkeeping operations for the current ModelAction. For
- * instance, adds action to the per-object, per-thread action vector and to the
- * action trace list of all thread actions.
- *
- * @param act is the ModelAction to add.
- */
-void ModelChecker::add_action_to_lists(ModelAction *act)
-{
-       int tid = id_to_int(act->get_tid());
-       ModelAction *uninit = NULL;
-       int uninit_id = -1;
-       action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
-       if (list->empty() && act->is_atomic_var()) {
-               uninit = get_uninitialized_action(act);
-               uninit_id = id_to_int(uninit->get_tid());
-               list->push_front(uninit);
-       }
-       list->push_back(act);
-
-       action_trace->push_back(act);
-       if (uninit)
-               action_trace->push_front(uninit);
-
-       SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
-       if (tid >= (int)vec->size())
-               vec->resize(priv->next_thread_id);
-       (*vec)[tid].push_back(act);
-       if (uninit)
-               (*vec)[uninit_id].push_front(uninit);
-
-       if ((int)thrd_last_action->size() <= tid)
-               thrd_last_action->resize(get_num_threads());
-       (*thrd_last_action)[tid] = act;
-       if (uninit)
-               (*thrd_last_action)[uninit_id] = uninit;
-
-       if (act->is_fence() && act->is_release()) {
-               if ((int)thrd_last_fence_release->size() <= tid)
-                       thrd_last_fence_release->resize(get_num_threads());
-               (*thrd_last_fence_release)[tid] = act;
-       }
-
-       if (act->is_wait()) {
-               void *mutex_loc = (void *) act->get_value();
-               get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
-
-               SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
-               if (tid >= (int)vec->size())
-                       vec->resize(priv->next_thread_id);
-               (*vec)[tid].push_back(act);
-       }
-}
-
-/**
- * @brief Get the last action performed by a particular Thread
- * @param tid The thread ID of the Thread in question
- * @return The last action in the thread
- */
-ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
-{
-       int threadid = id_to_int(tid);
-       if (threadid < (int)thrd_last_action->size())
-               return (*thrd_last_action)[id_to_int(tid)];
-       else
-               return NULL;
-}
-
-/**
- * @brief Get the last fence release performed by a particular Thread
- * @param tid The thread ID of the Thread in question
- * @return The last fence release in the thread, if one exists; NULL otherwise
- */
-ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
-{
-       int threadid = id_to_int(tid);
-       if (threadid < (int)thrd_last_fence_release->size())
-               return (*thrd_last_fence_release)[id_to_int(tid)];
-       else
-               return NULL;
-}
-
-/**
- * Gets the last memory_order_seq_cst write (in the total global sequence)
- * performed on a particular object (i.e., memory location), not including the
- * current action.
- * @param curr The current ModelAction; also denotes the object location to
- * check
- * @return The last seq_cst write
- */
-ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
-{
-       void *location = curr->get_location();
-       action_list_t *list = get_safe_ptr_action(obj_map, location);
-       /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
-       action_list_t::reverse_iterator rit;
-       for (rit = list->rbegin(); (*rit) != curr; rit++)
-               ;
-       rit++; /* Skip past curr */
-       for ( ; rit != list->rend(); rit++)
-               if ((*rit)->is_write() && (*rit)->is_seqcst())
-                       return *rit;
-       return NULL;
-}
-
-/**
- * Gets the last memory_order_seq_cst fence (in the total global sequence)
- * performed in a particular thread, prior to a particular fence.
- * @param tid The ID of the thread to check
- * @param before_fence The fence from which to begin the search; if NULL, then
- * search for the most recent fence in the thread.
- * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
- */
-ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
-{
-       /* All fences should have NULL location */
-       action_list_t *list = get_safe_ptr_action(obj_map, NULL);
-       action_list_t::reverse_iterator rit = list->rbegin();
-
-       if (before_fence) {
-               for (; rit != list->rend(); rit++)
-                       if (*rit == before_fence)
-                               break;
-
-               ASSERT(*rit == before_fence);
-               rit++;
-       }
-
-       for (; rit != list->rend(); rit++)
-               if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
-                       return *rit;
-       return NULL;
-}
-
-/**
- * Gets the last unlock operation performed on a particular mutex (i.e., memory
- * location). This function identifies the mutex according to the current
- * action, which is presumed to perform on the same mutex.
- * @param curr The current ModelAction; also denotes the object location to
- * check
- * @return The last unlock operation
- */
-ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
-{
-       void *location = curr->get_location();
-       action_list_t *list = get_safe_ptr_action(obj_map, location);
-       /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
-       action_list_t::reverse_iterator rit;
-       for (rit = list->rbegin(); rit != list->rend(); rit++)
-               if ((*rit)->is_unlock() || (*rit)->is_wait())
-                       return *rit;
-       return NULL;
-}
-
-ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
-{
-       ModelAction *parent = get_last_action(tid);
-       if (!parent)
-               parent = get_thread(tid)->get_creation();
-       return parent;
-}
-
-/**
- * Returns the clock vector for a given thread.
- * @param tid The thread whose clock vector we want
- * @return Desired clock vector
- */
-ClockVector * ModelChecker::get_cv(thread_id_t tid) const
-{
-       return get_parent_action(tid)->get_cv();
-}
-
-/**
- * @brief Find the promise (if any) to resolve for the current action and
- * remove it from the pending promise vector
- * @param curr The current ModelAction. Should be a write.
- * @return The Promise to resolve, if any; otherwise NULL
- */
-Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
-{
-       for (unsigned int i = 0; i < promises->size(); i++)
-               if (curr->get_node()->get_promise(i)) {
-                       Promise *ret = (*promises)[i];
-                       promises->erase(promises->begin() + i);
-                       return ret;
-               }
-       return NULL;
-}
-
-/**
- * Resolve a Promise with a current write.
- * @param write The ModelAction that is fulfilling Promises
- * @param promise The Promise to resolve
- * @return True if the Promise was successfully resolved; false otherwise
- */
-bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
-{
-       ModelVector<ModelAction *> actions_to_check;
-
-       for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
-               ModelAction *read = promise->get_reader(i);
-               read_from(read, write);
-               actions_to_check.push_back(read);
-       }
-       /* Make sure the promise's value matches the write's value */
-       ASSERT(promise->is_compatible(write) && promise->same_value(write));
-       if (!mo_graph->resolvePromise(promise, write))
-               priv->failed_promise = true;
-
-       /**
-        * @todo  It is possible to end up in an inconsistent state, where a
-        * "resolved" promise may still be referenced if
-        * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
-        *
-        * Note that the inconsistency only matters when dumping mo_graph to
-        * file.
-        *
-        * delete promise;
-        */
-
-       //Check whether reading these writes has made threads unable to
-       //resolve promises
-       for (unsigned int i = 0; i < actions_to_check.size(); i++) {
-               ModelAction *read = actions_to_check[i];
-               mo_check_promises(read, true);
-       }
-
-       return true;
-}
-
-/**
- * Compute the set of promises that could potentially be satisfied by this
- * action. Note that the set computation actually appears in the Node, not in
- * ModelChecker.
- * @param curr The ModelAction that may satisfy promises
- */
-void ModelChecker::compute_promises(ModelAction *curr)
-{
-       for (unsigned int i = 0; i < promises->size(); i++) {
-               Promise *promise = (*promises)[i];
-               if (!promise->is_compatible(curr) || !promise->same_value(curr))
-                       continue;
-
-               bool satisfy = true;
-               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
-                       const ModelAction *act = promise->get_reader(j);
-                       if (act->happens_before(curr) ||
-                                       act->could_synchronize_with(curr)) {
-                               satisfy = false;
-                               break;
-                       }
-               }
-               if (satisfy)
-                       curr->get_node()->set_promise(i);
-       }
-}
-
-/** Checks promises in response to change in ClockVector Threads. */
-void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
-{
-       for (unsigned int i = 0; i < promises->size(); i++) {
-               Promise *promise = (*promises)[i];
-               if (!promise->thread_is_available(tid))
-                       continue;
-               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
-                       const ModelAction *act = promise->get_reader(j);
-                       if ((!old_cv || !old_cv->synchronized_since(act)) &&
-                                       merge_cv->synchronized_since(act)) {
-                               if (promise->eliminate_thread(tid)) {
-                                       /* Promise has failed */
-                                       priv->failed_promise = true;
-                                       return;
-                               }
-                       }
-               }
-       }
-}
-
-void ModelChecker::check_promises_thread_disabled()
-{
-       for (unsigned int i = 0; i < promises->size(); i++) {
-               Promise *promise = (*promises)[i];
-               if (promise->has_failed()) {
-                       priv->failed_promise = true;
-                       return;
-               }
-       }
-}
-
-/**
- * @brief Checks promises in response to addition to modification order for
- * threads.
- *
- * We test whether threads are still available for satisfying promises after an
- * addition to our modification order constraints. Those that are unavailable
- * are "eliminated". Once all threads are eliminated from satisfying a promise,
- * that promise has failed.
- *
- * @param act The ModelAction which updated the modification order
- * @param is_read_check Should be true if act is a read and we must check for
- * updates to the store from which it read (there is a distinction here for
- * RMW's, which are both a load and a store)
- */
-void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
-{
-       const ModelAction *write = is_read_check ? act->get_reads_from() : act;
-
-       for (unsigned int i = 0; i < promises->size(); i++) {
-               Promise *promise = (*promises)[i];
-
-               // Is this promise on the same location?
-               if (!promise->same_location(write))
-                       continue;
-
-               for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
-                       const ModelAction *pread = promise->get_reader(j);
-                       if (!pread->happens_before(act))
-                              continue;
-                       if (mo_graph->checkPromise(write, promise)) {
-                               priv->failed_promise = true;
-                               return;
-                       }
-                       break;
-               }
-
-               // Don't do any lookups twice for the same thread
-               if (!promise->thread_is_available(act->get_tid()))
-                       continue;
-
-               if (mo_graph->checkReachable(promise, write)) {
-                       if (mo_graph->checkPromise(write, promise)) {
-                               priv->failed_promise = true;
-                               return;
-                       }
-               }
-       }
-}
-
-/**
- * Compute the set of writes that may break the current pending release
- * sequence. This information is extracted from previou release sequence
- * calculations.
- *
- * @param curr The current ModelAction. Must be a release sequence fixup
- * action.
- */
-void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
-{
-       if (pending_rel_seqs->empty())
-               return;
-
-       struct release_seq *pending = pending_rel_seqs->back();
-       for (unsigned int i = 0; i < pending->writes.size(); i++) {
-               const ModelAction *write = pending->writes[i];
-               curr->get_node()->add_relseq_break(write);
-       }
-
-       /* NULL means don't break the sequence; just synchronize */
-       curr->get_node()->add_relseq_break(NULL);
-}
-
-/**
- * Build up an initial set of all past writes that this 'read' action may read
- * from, as well as any previously-observed future values that must still be valid.
- *
- * @param curr is the current ModelAction that we are exploring; it must be a
- * 'read' operation.
- */
-void ModelChecker::build_may_read_from(ModelAction *curr)
-{
-       SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
-       unsigned int i;
-       ASSERT(curr->is_read());
-
-       ModelAction *last_sc_write = NULL;
-
-       if (curr->is_seqcst())
-               last_sc_write = get_last_seq_cst_write(curr);
-
-       /* Iterate over all threads */
-       for (i = 0; i < thrd_lists->size(); i++) {
-               /* Iterate over actions in thread, starting from most recent */
-               action_list_t *list = &(*thrd_lists)[i];
-               action_list_t::reverse_iterator rit;
-               for (rit = list->rbegin(); rit != list->rend(); rit++) {
-                       ModelAction *act = *rit;
-
-                       /* Only consider 'write' actions */
-                       if (!act->is_write() || act == curr)
-                               continue;
-
-                       /* Don't consider more than one seq_cst write if we are a seq_cst read. */
-                       bool allow_read = true;
-
-                       if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
-                               allow_read = false;
-                       else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
-                               allow_read = false;
-
-                       if (allow_read) {
-                               /* Only add feasible reads */
-                               mo_graph->startChanges();
-                               r_modification_order(curr, act);
-                               if (!is_infeasible())
-                                       curr->get_node()->add_read_from_past(act);
-                               mo_graph->rollbackChanges();
-                       }
-
-                       /* Include at most one act per-thread that "happens before" curr */
-                       if (act->happens_before(curr))
-                               break;
-               }
-       }
-
-       /* Inherit existing, promised future values */
-       for (i = 0; i < promises->size(); i++) {
-               const Promise *promise = (*promises)[i];
-               const ModelAction *promise_read = promise->get_reader(0);
-               if (promise_read->same_var(curr)) {
-                       /* Only add feasible future-values */
-                       mo_graph->startChanges();
-                       r_modification_order(curr, promise);
-                       if (!is_infeasible())
-                               curr->get_node()->add_read_from_promise(promise_read);
-                       mo_graph->rollbackChanges();
-               }
-       }
-
-       /* We may find no valid may-read-from only if the execution is doomed */
-       if (!curr->get_node()->read_from_size()) {
-               priv->no_valid_reads = true;
-               set_assert();
-       }
-
-       if (DBG_ENABLED()) {
-               model_print("Reached read action:\n");
-               curr->print();
-               model_print("Printing read_from_past\n");
-               curr->get_node()->print_read_from_past();
-               model_print("End printing read_from_past\n");
-       }
-}
-
-bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
-{
-       for ( ; write != NULL; write = write->get_reads_from()) {
-               /* UNINIT actions don't have a Node, and they never sleep */
-               if (write->is_uninitialized())
-                       return true;
-               Node *prevnode = write->get_node()->get_parent();
-
-               bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
-               if (write->is_release() && thread_sleep)
-                       return true;
-               if (!write->is_rmw())
-                       return false;
-       }
-       return true;
-}
-
-/**
- * @brief Get an action representing an uninitialized atomic
- *
- * This function may create a new one or try to retrieve one from the NodeStack
- *
- * @param curr The current action, which prompts the creation of an UNINIT action
- * @return A pointer to the UNINIT ModelAction
- */
-ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
-{
-       Node *node = curr->get_node();
-       ModelAction *act = node->get_uninit_action();
-       if (!act) {
-               act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
-               node->set_uninit_action(act);
-       }
-       act->create_cv(NULL);
-       return act;
-}
-
-static void print_list(action_list_t *list)
-{
-       action_list_t::iterator it;
-
-       model_print("---------------------------------------------------------------------\n");
-
-       unsigned int hash = 0;
-
-       for (it = list->begin(); it != list->end(); it++) {
-               const ModelAction *act = *it;
-               if (act->get_seq_number() > 0)
-                       act->print();
-               hash = hash^(hash<<3)^((*it)->hash());
-       }
-       model_print("HASH %u\n", hash);
-       model_print("---------------------------------------------------------------------\n");
-}
-
-#if SUPPORT_MOD_ORDER_DUMP
-void ModelChecker::dumpGraph(char *filename) const
-{
-       char buffer[200];
-       sprintf(buffer, "%s.dot", filename);
-       FILE *file = fopen(buffer, "w");
-       fprintf(file, "digraph %s {\n", filename);
-       mo_graph->dumpNodes(file);
-       ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
-
-       for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
-               ModelAction *act = *it;
-               if (act->is_read()) {
-                       mo_graph->dot_print_node(file, act);
-                       if (act->get_reads_from())
-                               mo_graph->dot_print_edge(file,
-                                               act->get_reads_from(),
-                                               act,
-                                               "label=\"rf\", color=red, weight=2");
-                       else
-                               mo_graph->dot_print_edge(file,
-                                               act->get_reads_from_promise(),
-                                               act,
-                                               "label=\"rf\", color=red");
-               }
-               if (thread_array[act->get_tid()]) {
-                       mo_graph->dot_print_edge(file,
-                                       thread_array[id_to_int(act->get_tid())],
-                                       act,
-                                       "label=\"sb\", color=blue, weight=400");
-               }
-
-               thread_array[act->get_tid()] = act;
-       }
-       fprintf(file, "}\n");
-       model_free(thread_array);
-       fclose(file);
-}
-#endif
-
-/** @brief Prints an execution trace summary. */
-void ModelChecker::print_summary() const
-{
-#if SUPPORT_MOD_ORDER_DUMP
-       char buffername[100];
-       sprintf(buffername, "exec%04u", stats.num_total);
-       mo_graph->dumpGraphToFile(buffername);
-       sprintf(buffername, "graph%04u", stats.num_total);
-       dumpGraph(buffername);
-#endif
-
-       model_print("Execution %d:", stats.num_total);
-       if (isfeasibleprefix()) {
-               if (scheduler->all_threads_sleeping())
-                       model_print(" SLEEP-SET REDUNDANT");
-               model_print("\n");
-       } else
-               print_infeasibility(" INFEASIBLE");
-       print_list(action_trace);
-       model_print("\n");
-       if (!promises->empty()) {
-               model_print("Pending promises:\n");
-               for (unsigned int i = 0; i < promises->size(); i++) {
-                       model_print(" [P%u] ", i);
-                       (*promises)[i]->print();
-               }
-               model_print("\n");
-       }
-}
-
-/**
- * Add a Thread to the system for the first time. Should only be called once
- * per thread.
- * @param t The Thread to add
- */
-void ModelChecker::add_thread(Thread *t)
-{
-       thread_map->put(id_to_int(t->get_id()), t);
-       scheduler->add_thread(t);
-}
-
-/**
- * @brief Get a Thread reference by its ID
- * @param tid The Thread's ID
- * @return A Thread reference
- */
-Thread * ModelChecker::get_thread(thread_id_t tid) const
-{
-       return thread_map->get(id_to_int(tid));
-}
-
-/**
- * @brief Get a reference to the Thread in which a ModelAction was executed
- * @param act The ModelAction
- * @return A Thread reference
- */
-Thread * ModelChecker::get_thread(const ModelAction *act) const
-{
-       return get_thread(act->get_tid());
-}
-
-/**
- * @brief Get a Promise's "promise number"
- *
- * A "promise number" is an index number that is unique to a promise, valid
- * only for a specific snapshot of an execution trace. Promises may come and go
- * as they are generated an resolved, so an index only retains meaning for the
- * current snapshot.
- *
- * @param promise The Promise to check
- * @return The promise index, if the promise still is valid; otherwise -1
- */
-int ModelChecker::get_promise_number(const Promise *promise) const
-{
-       for (unsigned int i = 0; i < promises->size(); i++)
-               if ((*promises)[i] == promise)
-                       return i;
-       /* Not found */
-       return -1;
-}
-
-/**
- * @brief Check if a Thread is currently enabled
- * @param t The Thread to check
- * @return True if the Thread is currently enabled
- */
-bool ModelChecker::is_enabled(Thread *t) const
-{
-       return scheduler->is_enabled(t);
-}
-
-/**
- * @brief Check if a Thread is currently enabled
- * @param tid The ID of the Thread to check
- * @return True if the Thread is currently enabled
- */
-bool ModelChecker::is_enabled(thread_id_t tid) const
-{
-       return scheduler->is_enabled(tid);
-}
-
-/**
- * Switch from a model-checker context to a user-thread context. This is the
- * complement of ModelChecker::switch_to_master and must be called from the
- * model-checker context
- *
- * @param thread The user-thread to switch to
- */
-void ModelChecker::switch_from_master(Thread *thread)
-{
-       scheduler->set_current_thread(thread);
-       Thread::swap(&system_context, thread);
-}
-
-/**
- * Switch from a user-context to the "master thread" context (a.k.a. system
- * context). This switch is made with the intention of exploring a particular
- * model-checking action (described by a ModelAction object). Must be called
- * from a user-thread context.
- *
- * @param act The current action that will be explored. May be NULL only if
- * trace is exiting via an assertion (see ModelChecker::set_assert and
- * ModelChecker::has_asserted).
- * @return Return the value returned by the current action
- */
-uint64_t ModelChecker::switch_to_master(ModelAction *act)
-{
-       DBG();
-       Thread *old = thread_current();
-       scheduler->set_current_thread(NULL);
-       ASSERT(!old->get_pending());
-       old->set_pending(act);
-       if (Thread::swap(old, &system_context) < 0) {
-               perror("swap threads");
-               exit(EXIT_FAILURE);
-       }
-       return old->get_return_value();
-}
-
-/**
- * Takes the next step in the execution, if possible.
- * @param curr The current step to take
- * @return Returns the next Thread to run, if any; NULL if this execution
- * should terminate
- */
-Thread * ModelChecker::take_step(ModelAction *curr)
-{
-       Thread *curr_thrd = get_thread(curr);
-       ASSERT(curr_thrd->get_state() == THREAD_READY);
-
-       ASSERT(check_action_enabled(curr)); /* May have side effects? */
-       curr = check_current_action(curr);
-       ASSERT(curr);
-
-       if (curr_thrd->is_blocked() || curr_thrd->is_complete())
-               scheduler->remove_thread(curr_thrd);
-
-       return action_select_next_thread(curr);
-}
-
-/** Wrapper to run the user's main function, with appropriate arguments */
-void user_main_wrapper(void *)
-{
-       user_main(model->params.argc, model->params.argv);
-}
-
-/** @return True if the execution has taken too many steps */
-bool ModelChecker::too_many_steps() const
-{
-       return params.bound != 0 && priv->used_sequence_numbers > params.bound;
-}
-
-bool ModelChecker::should_terminate_execution()
-{
-       /* Infeasible -> don't take any more steps */
-       if (is_infeasible())
-               return true;
-       else if (isfeasibleprefix() && have_bug_reports()) {
-               set_assert();
-               return true;
-       }
-
-       if (too_many_steps())
-               return true;
-       return false;
-}
-
-/** @brief Run ModelChecker for the user program */
-void ModelChecker::run()
-{
-       do {
-               thrd_t user_thread;
-               Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
-               add_thread(t);
+       do {
+               thrd_t user_thread;
+               Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
+               execution->add_thread(t);
 
                do {
                        /*
 
                do {
                        /*
@@ -3144,7 +446,7 @@ void ModelChecker::run()
                         * thread which just took a step--plus the first step
                         * for any newly-created thread
                         */
                         * thread which just took a step--plus the first step
                         * for any newly-created thread
                         */
-                       for (unsigned int i = 0; i < get_num_threads(); i++) {
+                       for (unsigned int i = 0; i < execution->get_num_threads(); i++) {
                                thread_id_t tid = int_to_id(i);
                                Thread *thr = get_thread(tid);
                                if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
                                thread_id_t tid = int_to_id(i);
                                Thread *thr = get_thread(tid);
                                if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
@@ -3158,14 +460,14 @@ void ModelChecker::run()
                        for (unsigned int i = 0; i < get_num_threads(); i++) {
                                Thread *th = get_thread(int_to_id(i));
                                ModelAction *act = th->get_pending();
                        for (unsigned int i = 0; i < get_num_threads(); i++) {
                                Thread *th = get_thread(int_to_id(i));
                                ModelAction *act = th->get_pending();
-                               if (act && is_enabled(th) && !check_action_enabled(act)) {
+                               if (act && is_enabled(th) && !execution->check_action_enabled(act)) {
                                        scheduler->sleep(th);
                                }
                        }
 
                        /* Catch assertions from prior take_step or from
                         * between-ModelAction bugs (e.g., data races) */
                                        scheduler->sleep(th);
                                }
                        }
 
                        /* Catch assertions from prior take_step or from
                         * between-ModelAction bugs (e.g., data races) */
-                       if (has_asserted())
+                       if (execution->has_asserted())
                                break;
 
                        if (!t)
                                break;
 
                        if (!t)
@@ -3176,31 +478,13 @@ void ModelChecker::run()
                        /* Consume the next action for a Thread */
                        ModelAction *curr = t->get_pending();
                        t->set_pending(NULL);
                        /* Consume the next action for a Thread */
                        ModelAction *curr = t->get_pending();
                        t->set_pending(NULL);
-                       t = take_step(curr);
+                       t = execution->take_step(curr);
                } while (!should_terminate_execution());
 
                } while (!should_terminate_execution());
 
-               /*
-                * Launch end-of-execution release sequence fixups only when
-                * the execution is otherwise feasible AND there are:
-                *
-                * (1) pending release sequences
-                * (2) pending assertions that could be invalidated by a change
-                * in clock vectors (i.e., data races)
-                * (3) no pending promises
-                */
-               while (!pending_rel_seqs->empty() &&
-                               is_feasible_prefix_ignore_relseq() &&
-                               !unrealizedraces.empty()) {
-                       model_print("*** WARNING: release sequence fixup action "
-                                       "(%zu pending release seuqence(s)) ***\n",
-                                       pending_rel_seqs->size());
-                       ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
-                                       std::memory_order_seq_cst, NULL, VALUE_NONE,
-                                       model_thread);
-                       take_step(fixup);
-               };
        } while (next_execution());
 
        } while (next_execution());
 
+       execution->fixup_release_sequences();
+
        model_print("******* Model-checking complete: *******\n");
        print_stats();
 }
        model_print("******* Model-checking complete: *******\n");
        print_stats();
 }
diff --git a/model.h b/model.h
index 3d13855..89ae2b8 100644 (file)
--- a/model.h
+++ b/model.h
@@ -10,7 +10,6 @@
 
 #include "mymemory.h"
 #include "hashtable.h"
 
 #include "mymemory.h"
 #include "hashtable.h"
-#include "workqueue.h"
 #include "config.h"
 #include "modeltypes.h"
 #include "stl-model.h"
 #include "config.h"
 #include "modeltypes.h"
 #include "stl-model.h"
@@ -26,10 +25,9 @@ class Scheduler;
 class Thread;
 class ClockVector;
 class TraceAnalysis;
 class Thread;
 class ClockVector;
 class TraceAnalysis;
-struct model_snapshot_members;
+class ModelExecution;
+class ModelAction;
 
 
-/** @brief Shorthand for a list of release sequence heads */
-typedef ModelVector<const ModelAction *> rel_heads_list_t;
 typedef SnapList<ModelAction *> action_list_t;
 
 /** @brief Model checker execution stats */
 typedef SnapList<ModelAction *> action_list_t;
 
 /** @brief Model checker execution stats */
@@ -41,31 +39,6 @@ struct execution_stats {
        int num_redundant; /**< @brief Number of redundant, aborted executions */
 };
 
        int num_redundant; /**< @brief Number of redundant, aborted executions */
 };
 
-struct PendingFutureValue {
-       PendingFutureValue(ModelAction *writer, ModelAction *reader) :
-               writer(writer), reader(reader)
-       { }
-       const ModelAction *writer;
-       ModelAction *reader;
-};
-
-/** @brief Records information regarding a single pending release sequence */
-struct release_seq {
-       /** @brief The acquire operation */
-       ModelAction *acquire;
-       /** @brief The read operation that may read from a release sequence;
-        *  may be the same as acquire, or else an earlier action in the same
-        *  thread (i.e., when 'acquire' is a fence-acquire) */
-       const ModelAction *read;
-       /** @brief The head of the RMW chain from which 'read' reads; may be
-        *  equal to 'release' */
-       const ModelAction *rf;
-       /** @brief The head of the potential longest release sequence chain */
-       const ModelAction *release;
-       /** @brief The write(s) that may break the release sequence */
-       SnapVector<const ModelAction *> writes;
-};
-
 /** @brief The central structure for model-checking */
 class ModelChecker {
 public:
 /** @brief The central structure for model-checking */
 class ModelChecker {
 public:
@@ -77,11 +50,6 @@ public:
        /** @returns the context for the main model-checking system thread */
        ucontext_t * get_system_context() { return &system_context; }
 
        /** @returns the context for the main model-checking system thread */
        ucontext_t * get_system_context() { return &system_context; }
 
-       void print_summary() const;
-#if SUPPORT_MOD_ORDER_DUMP
-       void dumpGraph(char *filename) const;
-#endif
-
        Thread * get_thread(thread_id_t tid) const;
        Thread * get_thread(const ModelAction *act) const;
        int get_promise_number(const Promise *promise) const;
        Thread * get_thread(thread_id_t tid) const;
        Thread * get_thread(const ModelAction *act) const;
        int get_promise_number(const Promise *promise) const;
@@ -115,149 +83,29 @@ public:
 private:
        /** The scheduler to use: tracks the running/ready Threads */
        Scheduler * const scheduler;
 private:
        /** The scheduler to use: tracks the running/ready Threads */
        Scheduler * const scheduler;
+       NodeStack * const node_stack;
+       ModelExecution *execution;
 
 
-       void add_thread(Thread *t);
-
-       bool sleep_can_read_from(ModelAction *curr, const ModelAction *write);
-       bool thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const;
-       bool mo_may_allow(const ModelAction *writer, const ModelAction *reader);
-       bool promises_may_allow(const ModelAction *writer, const ModelAction *reader) const;
-       bool has_asserted() const;
-       void set_assert();
-       void set_bad_synchronization();
-       bool promises_expired() const;
        void execute_sleep_set();
        void execute_sleep_set();
-       bool should_wake_up(const ModelAction *curr, const Thread *thread) const;
-       void wake_up_sleeping_actions(ModelAction *curr);
-       modelclock_t get_next_seq_num();
 
        bool next_execution();
 
        bool next_execution();
-       ModelAction * check_current_action(ModelAction *curr);
-       bool initialize_curr_action(ModelAction **curr);
-       bool process_read(ModelAction *curr);
-       bool process_write(ModelAction *curr);
-       bool process_fence(ModelAction *curr);
-       bool process_mutex(ModelAction *curr);
-       bool process_thread_action(ModelAction *curr);
-       void process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue);
-       bool read_from(ModelAction *act, const ModelAction *rf);
-       bool synchronize(const ModelAction *first, ModelAction *second);
-       bool check_action_enabled(ModelAction *curr);
-
-       Thread * take_step(ModelAction *curr);
        bool should_terminate_execution();
 
        bool should_terminate_execution();
 
-       template <typename T>
-       bool check_recency(ModelAction *curr, const T *rf) const;
-
-       template <typename T, typename U>
-       bool should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const;
-
-       ModelAction * get_last_fence_conflict(ModelAction *act) const;
-       ModelAction * get_last_conflict(ModelAction *act) const;
-       void set_backtracking(ModelAction *act);
-       Thread * action_select_next_thread(const ModelAction *curr) const;
        Thread * get_next_thread();
        Thread * get_next_thread();
-       bool set_latest_backtrack(ModelAction *act);
-       ModelAction * get_next_backtrack();
        void reset_to_initial_state();
        void reset_to_initial_state();
-       Promise * pop_promise_to_resolve(const ModelAction *curr);
-       bool resolve_promise(ModelAction *curr, Promise *promise);
-       void compute_promises(ModelAction *curr);
-       void compute_relseq_breakwrites(ModelAction *curr);
-
-       void check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv);
-       void mo_check_promises(const ModelAction *act, bool is_read_check);
-       void thread_blocking_check_promises(Thread *blocker, Thread *waiting);
-
-       void check_curr_backtracking(ModelAction *curr);
-       void add_action_to_lists(ModelAction *act);
-       ModelAction * get_last_fence_release(thread_id_t tid) const;
-       ModelAction * get_last_seq_cst_write(ModelAction *curr) const;
-       ModelAction * get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const;
-       ModelAction * get_last_unlock(ModelAction *curr) const;
-       void build_may_read_from(ModelAction *curr);
-       ModelAction * process_rmw(ModelAction *curr);
 
 
-       template <typename rf_type>
-       bool r_modification_order(ModelAction *curr, const rf_type *rf);
-
-       bool w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv);
-       void get_release_seq_heads(ModelAction *acquire, ModelAction *read, rel_heads_list_t *release_heads);
-       bool release_seq_heads(const ModelAction *rf, rel_heads_list_t *release_heads, struct release_seq *pending) const;
-       bool resolve_release_sequences(void *location, work_queue_t *work_queue);
-       void add_future_value(const ModelAction *writer, ModelAction *reader);
-
-       ModelAction * get_uninitialized_action(const ModelAction *curr) const;
 
        ModelAction *diverge;
        ModelAction *earliest_diverge;
 
        ucontext_t system_context;
 
        ModelAction *diverge;
        ModelAction *earliest_diverge;
 
        ucontext_t system_context;
-       action_list_t * const action_trace;
-       HashTable<int, Thread *, int> * const thread_map;
-
-       /** Per-object list of actions. Maps an object (i.e., memory location)
-        * to a trace of all actions performed on the object. */
-       HashTable<const void *, action_list_t *, uintptr_t, 4> * const obj_map;
-
-       /** Per-object list of actions. Maps an object (i.e., memory location)
-        * to a trace of all actions performed on the object. */
-       HashTable<const void *, action_list_t *, uintptr_t, 4> * const condvar_waiters_map;
-
-       HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 > * const obj_thrd_map;
-       SnapVector<Promise *> * const promises;
-       SnapVector<struct PendingFutureValue> * const futurevalues;
-
-       /**
-        * List of pending release sequences. Release sequences might be
-        * determined lazily as promises are fulfilled and modification orders
-        * are established. Each entry in the list may only be partially
-        * filled, depending on its pending status.
-        */
-       SnapVector<struct release_seq *> * const pending_rel_seqs;
 
 
-       SnapVector<ModelAction *> * const thrd_last_action;
-       SnapVector<ModelAction *> * const thrd_last_fence_release;
-       NodeStack * const node_stack;
        ModelVector<TraceAnalysis *> * trace_analyses;
 
        ModelVector<TraceAnalysis *> * trace_analyses;
 
-
-       /** Private data members that should be snapshotted. They are grouped
-        * together for efficiency and maintainability. */
-       struct model_snapshot_members * const priv;
-
-       /** A special model-checker Thread; used for associating with
-        *  model-checker-related ModelAcitons */
-       Thread *model_thread;
-
-       /**
-        * @brief The modification order graph
-        *
-        * A directed acyclic graph recording observations of the modification
-        * order on all the atomic objects in the system. This graph should
-        * never contain any cycles, as that represents a violation of the
-        * memory model (total ordering). This graph really consists of many
-        * disjoint (unconnected) subgraphs, each graph corresponding to a
-        * separate ordering on a distinct object.
-        *
-        * The edges in this graph represent the "ordered before" relation,
-        * such that <tt>a --> b</tt> means <tt>a</tt> was ordered before
-        * <tt>b</tt>.
-        */
-       CycleGraph * const mo_graph;
-
        /** @brief The cumulative execution stats */
        struct execution_stats stats;
        void record_stats();
        void run_trace_analyses();
        /** @brief The cumulative execution stats */
        struct execution_stats stats;
        void record_stats();
        void run_trace_analyses();
-       void print_infeasibility(const char *prefix) const;
-       bool is_feasible_prefix_ignore_relseq() const;
-       bool is_infeasible() const;
-       bool is_deadlocked() const;
-       bool too_many_steps() const;
-       bool is_complete_execution() const;
-       bool have_bug_reports() const;
        void print_bugs() const;
        void print_execution(bool printbugs) const;
        void print_stats() const;
        void print_bugs() const;
        void print_execution(bool printbugs) const;
        void print_stats() const;