Bug fix
[c11tester.git] / execution.cc
index 213b26067bfda027be973d0166a1a7e1db634f51..504f7f52a6ee2c40c551f23d49c63d90bb6b485f 100644 (file)
@@ -6,7 +6,6 @@
 #include "model.h"
 #include "execution.h"
 #include "action.h"
-#include "nodestack.h"
 #include "schedule.h"
 #include "common.h"
 #include "clockvector.h"
@@ -14,7 +13,9 @@
 #include "datarace.h"
 #include "threads-model.h"
 #include "bugmessage.h"
+#include "history.h"
 #include "fuzzer.h"
+#include "newfuzzer.h"
 
 #define INITIAL_THREAD_ID       0
 
@@ -27,7 +28,6 @@ struct model_snapshot_members {
                next_thread_id(INITIAL_THREAD_ID),
                used_sequence_numbers(0),
                bugs(),
-               bad_synchronization(false),
                asserted(false)
        { }
 
@@ -41,37 +41,39 @@ struct model_snapshot_members {
        modelclock_t used_sequence_numbers;
        SnapVector<bug_message *> bugs;
        /** @brief Incorrectly-ordered synchronization was made */
-       bool bad_synchronization;
        bool asserted;
 
        SNAPSHOTALLOC
 };
 
 /** @brief Constructor */
-ModelExecution::ModelExecution(ModelChecker *m, Scheduler *scheduler, NodeStack *node_stack) :
+ModelExecution::ModelExecution(ModelChecker *m, Scheduler *scheduler) :
        model(m),
        params(NULL),
        scheduler(scheduler),
-       action_trace(),
        thread_map(2),  /* We'll always need at least 2 threads */
        pthread_map(0),
-       pthread_counter(0),
+       pthread_counter(1),
+       action_trace(),
        obj_map(),
        condvar_waiters_map(),
        obj_thrd_map(),
        mutex_map(),
        thrd_last_action(1),
        thrd_last_fence_release(),
-       node_stack(node_stack),
        priv(new struct model_snapshot_members ()),
-                        mo_graph(new CycleGraph()),
-       fuzzer(new Fuzzer())
+       mo_graph(new CycleGraph()),
+       fuzzer(new Fuzzer()),
+       isfinished(false)
 {
        /* Initialize a model-checker thread, for special ModelActions */
        model_thread = new Thread(get_next_id());
        add_thread(model_thread);
+       fuzzer->register_engine(this);
        scheduler->register_engine(this);
-       node_stack->register_engine(this);
+#ifdef TLS
+       pthread_key_create(&pthreadkey, tlsdestructor);
+#endif
 }
 
 /** @brief Destructor */
@@ -89,7 +91,7 @@ int ModelExecution::get_execution_number() const
        return model->get_execution_number();
 }
 
-static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
+static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 2> * hash, void * ptr)
 {
        action_list_t *tmp = hash->get(ptr);
        if (tmp == NULL) {
@@ -99,7 +101,7 @@ static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t
        return tmp;
 }
 
-static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
+static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<const void *, SnapVector<action_list_t> *, uintptr_t, 2> * hash, void * ptr)
 {
        SnapVector<action_list_t> *tmp = hash->get(ptr);
        if (tmp == NULL) {
@@ -109,18 +111,6 @@ static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, Sn
        return tmp;
 }
 
-action_list_t * ModelExecution::get_actions_on_obj(void * obj, thread_id_t tid) const
-{
-       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()
 {
@@ -139,6 +129,18 @@ modelclock_t ModelExecution::get_next_seq_num()
        return ++priv->used_sequence_numbers;
 }
 
+/** @return a sequence number for a new ModelAction */
+modelclock_t ModelExecution::get_curr_seq_num()
+{
+       return priv->used_sequence_numbers;
+}
+
+/** Restore the last used sequence number when actions of a thread are postponed by Fuzzer */
+void ModelExecution::restore_last_seq_num()
+{
+       priv->used_sequence_numbers--;
+}
+
 /**
  * @brief Should the current action wake up a given thread?
  *
@@ -164,6 +166,12 @@ bool ModelExecution::should_wake_up(const ModelAction *curr, const Thread *threa
                if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
                        return true;
        }
+       /* The sleep is literally sleeping */
+       if (asleep->is_sleep()) {
+               if (fuzzer->shouldWake(asleep))
+                       return true;
+       }
+
        return false;
 }
 
@@ -172,29 +180,20 @@ 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))
+                       if (should_wake_up(curr, thr)) {
                                /* Remove this thread from sleep set */
                                scheduler->remove_sleep(thr);
+                               if (thr->get_pending()->is_sleep())
+                                       thr->set_wakeup_state(true);
+                       }
                }
        }
 }
 
-/** @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)
+void ModelExecution::assert_bug(const char *msg)
 {
        priv->bugs.push_back(new bug_message(msg));
-
-       if (isfeasibleprefix()) {
-               set_assert();
-               return true;
-       }
-       return false;
+       set_assert();
 }
 
 /** @return True, if any bugs have been reported for this execution */
@@ -265,32 +264,63 @@ bool ModelExecution::is_complete_execution() const
        return true;
 }
 
+ModelAction * ModelExecution::convertNonAtomicStore(void * location) {
+       uint64_t value = *((const uint64_t *) location);
+       modelclock_t storeclock;
+       thread_id_t storethread;
+       getStoreThreadAndClock(location, &storethread, &storeclock);
+       setAtomicStoreFlag(location);
+       ModelAction * act = new ModelAction(NONATOMIC_WRITE, memory_order_relaxed, location, value, get_thread(storethread));
+       act->set_seq_number(storeclock);
+       add_normal_write_to_lists(act);
+       add_write_to_lists(act);
+       w_modification_order(act);
+       model->get_history()->process_action(act, act->get_tid());
+       return act;
+}
 
 /**
  * Processes a read model action.
  * @param curr is the read model action to process.
  * @param rf_set is the set of model actions we can possibly read from
- * @return True if processing this read updates the mo_graph.
+ * @return True if the read can be pruned from the thread map list.
  */
-void ModelExecution::process_read(ModelAction *curr, SnapVector<ModelAction *> * rf_set)
+bool ModelExecution::process_read(ModelAction *curr, SnapVector<ModelAction *> * rf_set)
 {
-       SnapVector<const ModelAction *> * priorset = new SnapVector<const ModelAction *>();
-       while(true) {
+       SnapVector<ModelAction *> * priorset = new SnapVector<ModelAction *>();
+       bool hasnonatomicstore = hasNonAtomicStore(curr->get_location());
+       if (hasnonatomicstore) {
+               ModelAction * nonatomicstore = convertNonAtomicStore(curr->get_location());
+               rf_set->push_back(nonatomicstore);
+       }
+
+       // Remove writes that violate read modification order
+       /*
+          uint i = 0;
+          while (i < rf_set->size()) {
+               ModelAction * rf = (*rf_set)[i];
+               if (!r_modification_order(curr, rf, NULL, NULL, true)) {
+                       (*rf_set)[i] = rf_set->back();
+                       rf_set->pop_back();
+               } else
+                       i++;
+          }*/
 
+       while(true) {
                int index = fuzzer->selectWrite(curr, rf_set);
-               const ModelAction *rf = (*rf_set)[index];
 
+               ModelAction *rf = (*rf_set)[index];
 
                ASSERT(rf);
-
-               if (r_modification_order(curr, rf, priorset)) {
+               bool canprune = false;
+               if (r_modification_order(curr, rf, priorset, &canprune)) {
                        for(unsigned int i=0;i<priorset->size();i++) {
                                mo_graph->addEdge((*priorset)[i], rf);
                        }
                        read_from(curr, rf);
                        get_thread(curr)->set_return_value(curr->get_return_value());
                        delete priorset;
-                       return;
+                       return canprune && (curr->get_type() == ATOMIC_READ);
                }
                priorset->clear();
                (*rf_set)[index] = rf_set->back();
@@ -334,8 +364,9 @@ bool ModelExecution::process_mutex(ModelAction *curr)
        }
        //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");
+               //TODO: FIND SOME BETTER WAY TO CHECK LOCK INITIALIZED OR NOT
+               //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
@@ -345,8 +376,38 @@ bool ModelExecution::process_mutex(ModelAction *curr)
                }
                break;
        }
-       case ATOMIC_WAIT:
+       case ATOMIC_WAIT: {
+               //TODO: DOESN'T REALLY IMPLEMENT SPURIOUS WAKEUPS CORRECTLY
+               if (fuzzer->shouldWait(curr)) {
+                       /* 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;
+
+                       /* disable this thread */
+                       get_safe_ptr_action(&condvar_waiters_map, curr->get_location())->push_back(curr);
+                       scheduler->sleep(get_thread(curr));
+               }
+
+               break;
+       }
+       case ATOMIC_TIMEDWAIT:
        case ATOMIC_UNLOCK: {
+               //TODO: FIX WAIT SITUATION...WAITS CAN SPURIOUSLY
+               //FAIL...TIMED WAITS SHOULD PROBABLY JUST BE THE SAME
+               //AS NORMAL WAITS...THINK ABOUT PROBABILITIES
+               //THOUGH....AS IN TIMED WAIT MUST FAIL TO GUARANTEE
+               //PROGRESS...NORMAL WAIT MAY FAIL...SO NEED NORMAL
+               //WAIT TO WORK CORRECTLY IN THE CASE IT SPURIOUSLY
+               //FAILS AND IN THE CASE IT DOESN'T...  TIMED WAITS
+               //MUST EVENMTUALLY RELEASE...
+
                /* wake up the other threads */
                for (unsigned int i = 0;i < get_num_threads();i++) {
                        Thread *t = get_thread(int_to_id(i));
@@ -357,25 +418,23 @@ bool ModelExecution::process_mutex(ModelAction *curr)
 
                /* 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 */
-
                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));
+               for (sllnode<ModelAction *> * rit = waiters->begin();rit != NULL;rit=rit->getNext()) {
+                       scheduler->wake(get_thread(rit->getVal()));
                }
                waiters->clear();
                break;
        }
        case ATOMIC_NOTIFY_ONE: {
                action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
-               Thread * thread = fuzzer->selectNotify(waiters);
-               scheduler->wake(thread);
+               if (waiters->size() != 0) {
+                       Thread * thread = fuzzer->selectNotify(waiters);
+                       scheduler->wake(thread);
+               }
                break;
        }
 
@@ -392,10 +451,7 @@ bool ModelExecution::process_mutex(ModelAction *curr)
  */
 void ModelExecution::process_write(ModelAction *curr)
 {
-
        w_modification_order(curr);
-
-
        get_thread(curr)->set_return_value(VALUE_NONE);
 }
 
@@ -417,10 +473,10 @@ bool ModelExecution::process_fence(ModelAction *curr)
        bool updated = false;
        if (curr->is_acquire()) {
                action_list_t *list = &action_trace;
-               action_list_t::reverse_iterator rit;
+               sllnode<ModelAction *> * rit;
                /* Find X : is_read(X) && X --sb-> curr */
-               for (rit = list->rbegin();rit != list->rend();rit++) {
-                       ModelAction *act = *rit;
+               for (rit = list->end();rit != NULL;rit=rit->getPrev()) {
+                       ModelAction *act = rit->getVal();
                        if (act == curr)
                                continue;
                        if (act->get_tid() != curr->get_tid())
@@ -438,11 +494,8 @@ bool ModelExecution::process_fence(ModelAction *curr)
                                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)
+                       ClockVector *cv = get_hb_from_write(act->get_reads_from());
+                       if (cv != NULL && curr->get_cv()->merge(cv))
                                updated = true;
                }
        }
@@ -460,10 +513,8 @@ bool ModelExecution::process_fence(ModelAction *curr)
  * @param curr The current action
  * @return True if synchronization was updated or a thread completed
  */
-bool ModelExecution::process_thread_action(ModelAction *curr)
+void ModelExecution::process_thread_action(ModelAction *curr)
 {
-       bool updated = false;
-
        switch (curr->get_type()) {
        case THREAD_CREATE: {
                thrd_t *thrd = (thrd_t *)curr->get_location();
@@ -493,19 +544,25 @@ bool ModelExecution::process_thread_action(ModelAction *curr)
                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 PTHREAD_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;  // WL: to be add (modified)
        }
 
+       case THREADONLY_FINISH:
        case THREAD_FINISH: {
                Thread *th = get_thread(curr);
+               if (curr->get_type() == THREAD_FINISH &&
+                               th == model->getInitThread()) {
+                       th->complete();
+                       setFinished();
+                       break;
+               }
+
                /* Wake up any joining threads */
                for (unsigned int i = 0;i < get_num_threads();i++) {
                        Thread *waiting = get_thread(int_to_id(i));
@@ -514,23 +571,26 @@ bool ModelExecution::process_thread_action(ModelAction *curr)
                                scheduler->wake(waiting);
                }
                th->complete();
-               updated = true; /* trigger rel-seq checks */
                break;
        }
        case THREAD_START: {
                break;
        }
+       case THREAD_SLEEP: {
+               Thread *th = get_thread(curr);
+               th->set_pending(curr);
+               scheduler->add_sleep(th);
+               break;
+       }
        default:
                break;
        }
-
-       return updated;
 }
 
 /**
  * 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
+ * actions, as appropriate: merging RMWR and RMWC/RMW actions,
+ * 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
@@ -540,38 +600,16 @@ bool ModelExecution::process_thread_action(ModelAction *curr)
  */
 bool ModelExecution::initialize_curr_action(ModelAction **curr)
 {
-       ModelAction *newcurr;
-
        if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
-               newcurr = process_rmw(*curr);
+               ModelAction *newcurr = process_rmw(*curr);
                delete *curr;
 
                *curr = newcurr;
                return false;
-       }
-
-       (*curr)->set_seq_number(get_next_seq_num());
-
-       newcurr = node_stack->explore_action(*curr);
-       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;
+               ModelAction *newcurr = *curr;
 
+               newcurr->set_seq_number(get_next_seq_num());
                /* Always compute new clock vector */
                newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 
@@ -594,22 +632,18 @@ bool ModelExecution::initialize_curr_action(ModelAction **curr)
  * @return True if this read established synchronization
  */
 
-bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
+void ModelExecution::read_from(ModelAction *act, 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;
+               ClockVector *cv = get_hb_from_write(rf);
+               if (cv == NULL)
+                       return;
+               act->get_cv()->merge(cv);
        }
-       return false;
 }
 
 /**
@@ -627,7 +661,7 @@ bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
 bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
 {
        if (*second < *first) {
-               set_bad_synchronization();
+               ASSERT(0);      //This should not happend
                return false;
        }
        return second->synchronize_with(first);
@@ -655,6 +689,9 @@ bool ModelExecution::check_action_enabled(ModelAction *curr) {
                if (!blocking->is_complete()) {
                        return false;
                }
+       } else if (curr->is_sleep()) {
+               if (!fuzzer->shouldSleep(curr))
+                       return false;
        }
 
        return true;
@@ -681,23 +718,27 @@ ModelAction * ModelExecution::check_current_action(ModelAction *curr)
 
        wake_up_sleeping_actions(curr);
 
-       /* Add the action to lists before any other model-checking tasks */
-       if (!second_part_of_rmw)
-               add_action_to_lists(curr);
-
        SnapVector<ModelAction *> * rf_set = NULL;
        /* Build may_read_from set for newly-created actions */
        if (newly_explored && curr->is_read())
                rf_set = build_may_read_from(curr);
 
-       process_thread_action(curr);
+       bool canprune = false;
 
        if (curr->is_read() && !second_part_of_rmw) {
-               process_read(curr, rf_set);
+               canprune = process_read(curr, rf_set);
                delete rf_set;
-       } else {
+       } else
                ASSERT(rf_set == NULL);
-       }
+
+       /* Add the action to lists */
+       if (!second_part_of_rmw)
+               add_action_to_lists(curr, canprune);
+
+       if (curr->is_write())
+               add_write_to_lists(curr);
+
+       process_thread_action(curr);
 
        if (curr->is_write())
                process_write(curr);
@@ -711,42 +752,6 @@ ModelAction * ModelExecution::check_current_action(ModelAction *curr)
        return curr;
 }
 
-/**
- * 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 !is_infeasible();
-}
-
-/**
- * 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 (priv->bad_synchronization)
-               ptr += sprintf(ptr, "[bad sw ordering]");
-       if (ptr != buf)
-               model_print("%s: %s", prefix ? prefix : "Infeasible", buf);
-}
-
-/**
- * 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 priv->bad_synchronization;
-}
-
 /** 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());
@@ -771,38 +776,56 @@ ModelAction * ModelExecution::process_rmw(ModelAction *act) {
  *
  * @param curr The current action. Must be a read.
  * @param rf The ModelAction or Promise that curr reads from. Must be a write.
+ * @param check_only If true, then only check whether the current action satisfies
+ *        read modification order or not, without modifiying priorset and canprune.
+ *        False by default.
  * @return True if modification order edges were added; false otherwise
  */
 
-bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *rf, SnapVector<const ModelAction *> * priorset)
+bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *rf,
+                                                                                                                                                                       SnapVector<ModelAction *> * priorset, bool * canprune, bool check_only)
 {
        SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
-       unsigned int i;
        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);
 
+       int tid = curr->get_tid();
+
+       /* Need to ensure thrd_lists is big enough because we have not added the curr actions yet.  */
+       if ((int)thrd_lists->size() <= tid) {
+               uint oldsize = thrd_lists->size();
+               thrd_lists->resize(priv->next_thread_id);
+               for(uint i = oldsize;i < priv->next_thread_id;i++)
+                       new (&(*thrd_lists)[i]) action_list_t();
+       }
+
+       ModelAction *prev_same_thread = NULL;
        /* Iterate over all threads */
-       for (i = 0;i < thrd_lists->size();i++) {
-               /* Last SC fence in thread i */
+       for (unsigned int i = 0;i < thrd_lists->size();i++, tid = (((unsigned int)(tid+1)) == thrd_lists->size()) ? 0 : tid + 1) {
+               /* Last SC fence in thread tid */
                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);
+               if (i != 0)
+                       last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(tid), NULL);
 
-               /* Last SC fence in thread i, before last SC fence in current thread */
+               /* Last SC fence in thread tid, 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);
+                       last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(tid), last_sc_fence_local);
+
+               //Only need to iterate if either hb has changed for thread in question or SC fence after last operation...
+               if (prev_same_thread != NULL &&
+                               (prev_same_thread->get_cv()->getClock(tid) == curr->get_cv()->getClock(tid)) &&
+                               (last_sc_fence_thread_local == NULL || *last_sc_fence_thread_local < *prev_same_thread)) {
+                       continue;
+               }
 
                /* 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;
+               action_list_t *list = &(*thrd_lists)[tid];
+               sllnode<ModelAction *> * rit;
+               for (rit = list->end();rit != NULL;rit=rit->getPrev()) {
+                       ModelAction *act = rit->getVal();
 
                        /* Skip curr */
                        if (act == curr)
@@ -821,7 +844,8 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *
                                                *act < *last_sc_fence_thread_local) {
                                        if (mo_graph->checkReachable(rf, act))
                                                return false;
-                                       priorset->push_back(act);
+                                       if (!check_only)
+                                               priorset->push_back(act);
                                        break;
                                }
                                /* C++, Section 29.3 statement 4 */
@@ -829,7 +853,8 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *
                                                                 *act < *last_sc_fence_local) {
                                        if (mo_graph->checkReachable(rf, act))
                                                return false;
-                                       priorset->push_back(act);
+                                       if (!check_only)
+                                               priorset->push_back(act);
                                        break;
                                }
                                /* C++, Section 29.3 statement 6 */
@@ -837,7 +862,8 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *
                                                                 *act < *last_sc_fence_thread_before) {
                                        if (mo_graph->checkReachable(rf, act))
                                                return false;
-                                       priorset->push_back(act);
+                                       if (!check_only)
+                                               priorset->push_back(act);
                                        break;
                                }
                        }
@@ -847,16 +873,30 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *
                         * before" curr
                         */
                        if (act->happens_before(curr)) {
+                               if (i==0) {
+                                       if (last_sc_fence_local == NULL ||
+                                                       (*last_sc_fence_local < *act)) {
+                                               prev_same_thread = act;
+                                       }
+                               }
                                if (act->is_write()) {
                                        if (mo_graph->checkReachable(rf, act))
                                                return false;
-                                       priorset->push_back(act);
+                                       if (!check_only)
+                                               priorset->push_back(act);
                                } else {
-                                       const ModelAction *prevrf = act->get_reads_from();
+                                       ModelAction *prevrf = act->get_reads_from();
                                        if (!prevrf->equals(rf)) {
                                                if (mo_graph->checkReachable(rf, prevrf))
                                                        return false;
-                                               priorset->push_back(prevrf);
+                                               if (!check_only)
+                                                       priorset->push_back(prevrf);
+                                       } else {
+                                               if (act->get_tid() == curr->get_tid()) {
+                                                       //Can prune curr from obj list
+                                                       if (!check_only)
+                                                               *canprune = true;
+                                               }
                                        }
                                }
                                break;
@@ -896,13 +936,17 @@ void ModelExecution::w_modification_order(ModelAction *curr)
        unsigned int i;
        ASSERT(curr->is_write());
 
+       SnapList<ModelAction *> edgeset;
+
        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) {
-                       mo_graph->addEdge(last_seq_cst, curr);
+                       edgeset.push_back(last_seq_cst);
                }
+               //update map for next query
+               obj_last_sc_map.put(curr->get_location(), curr);
        }
 
        /* Last SC fence in the current thread */
@@ -917,10 +961,9 @@ void ModelExecution::w_modification_order(ModelAction *curr)
 
                /* Iterate over actions in thread, starting from most recent */
                action_list_t *list = &(*thrd_lists)[i];
-               action_list_t::reverse_iterator rit;
-               bool force_edge = false;
-               for (rit = list->rbegin();rit != list->rend();rit++) {
-                       ModelAction *act = *rit;
+               sllnode<ModelAction*>* rit;
+               for (rit = list->end();rit != NULL;rit=rit->getPrev()) {
+                       ModelAction *act = rit->getVal();
                        if (act == curr) {
                                /*
                                 * 1) If RMW and it actually read from something, then we
@@ -933,7 +976,6 @@ void ModelExecution::w_modification_order(ModelAction *curr)
                                 * 3) If normal write, we need to look at earlier actions, so
                                 * continue processing list.
                                 */
-                               force_edge = true;
                                if (curr->is_rmw()) {
                                        if (curr->get_reads_from() != NULL)
                                                break;
@@ -946,7 +988,7 @@ void ModelExecution::w_modification_order(ModelAction *curr)
                        /* C++, Section 29.3 statement 7 */
                        if (last_sc_fence_thread_before && act->is_write() &&
                                        *act < *last_sc_fence_thread_before) {
-                               mo_graph->addEdge(act, curr, force_edge);
+                               edgeset.push_back(act);
                                break;
                        }
 
@@ -962,30 +1004,17 @@ void ModelExecution::w_modification_order(ModelAction *curr)
                                 *   readfrom(act) --mo--> act
                                 */
                                if (act->is_write())
-                                       mo_graph->addEdge(act, curr, force_edge);
+                                       edgeset.push_back(act);
                                else if (act->is_read()) {
                                        //if previous read accessed a null, just keep going
-                                       mo_graph->addEdge(act->get_reads_from(), curr, force_edge);
+                                       edgeset.push_back(act->get_reads_from());
                                }
                                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.
-
-                                */
-
                        }
                }
        }
+       mo_graph->addEdges(&edgeset, curr);
+
 }
 
 /**
@@ -1006,9 +1035,9 @@ bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *
 
                /* 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;
+               sllnode<ModelAction *>* rit;
+               for (rit = list->end();rit != NULL;rit=rit->getPrev()) {
+                       ModelAction *act = rit->getVal();
 
                        /* Don't disallow due to act == reader */
                        if (!reader->happens_before(act) || reader == act)
@@ -1026,91 +1055,57 @@ bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *
 }
 
 /**
- * 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.
+ * Computes the clock vector that happens before propagates from this write.
  *
  * @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
- * @return true, if the ModelExecution is certain that release_heads is complete;
- * false otherwise
+ * @return ClockVector of happens before relation.
  */
-bool ModelExecution::release_seq_heads(const ModelAction *rf, rel_heads_list_t *release_heads) const
-{
 
+ClockVector * ModelExecution::get_hb_from_write(ModelAction *rf) const {
+       SnapVector<ModelAction *> * processset = NULL;
        for ( ;rf != NULL;rf = rf->get_reads_from()) {
                ASSERT(rf->is_write());
+               if (!rf->is_rmw() || (rf->is_acquire() && rf->is_release()) || rf->get_rfcv() != NULL)
+                       break;
+               if (processset == NULL)
+                       processset = new SnapVector<ModelAction *>();
+               processset->push_back(rf);
+       }
 
-               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 */
-       };
-       ASSERT(rf);     // Needs to be real write
-
-       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);
-
-       return true;    /* complete */
-}
-
-/**
- * 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();
+       int i = (processset == NULL) ? 0 : processset->size();
 
-       release_seq_heads(rf, release_heads);
+       ClockVector * vec = NULL;
+       while(true) {
+               if (rf->get_rfcv() != NULL) {
+                       vec = rf->get_rfcv();
+               } else if (rf->is_acquire() && rf->is_release()) {
+                       vec = rf->get_cv();
+               } else if (rf->is_release() && !rf->is_rmw()) {
+                       vec = rf->get_cv();
+               } else if (rf->is_release()) {
+                       //have rmw that is release and doesn't have a rfcv
+                       (vec = new ClockVector(vec, NULL))->merge(rf->get_cv());
+                       rf->set_rfcv(vec);
+               } else {
+                       //operation that isn't release
+                       if (rf->get_last_fence_release()) {
+                               if (vec == NULL)
+                                       vec = rf->get_last_fence_release()->get_cv();
+                               else
+                                       (vec=new ClockVector(vec, NULL))->merge(rf->get_last_fence_release()->get_cv());
+                       }
+                       rf->set_rfcv(vec);
+               }
+               i--;
+               if (i >= 0) {
+                       rf = (*processset)[i];
+               } else
+                       break;
+       }
+       if (processset != NULL)
+               delete processset;
+       return vec;
 }
 
 /**
@@ -1120,36 +1115,35 @@ void ModelExecution::get_release_seq_heads(ModelAction *acquire,
  *
  * @param act is the ModelAction to add.
  */
-void ModelExecution::add_action_to_lists(ModelAction *act)
+void ModelExecution::add_action_to_lists(ModelAction *act, bool canprune)
 {
        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);
+       if ((act->is_fence() && act->is_seqcst()) || act->is_unlock()) {
+               action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
+               act->setActionRef(list->add_back(act));
        }
-       list->push_back(act);
 
-       action_trace.push_back(act);
-       if (uninit)
-               action_trace.push_front(uninit);
+       // Update action trace, a total order of all actions
+       act->setTraceRef(action_trace.add_back(act));
+
 
+       // Update obj_thrd_map, a per location, per thread, order of actions
        SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
-       if (tid >= (int)vec->size())
+       if ((int)vec->size() <= tid) {
+               uint oldsize = vec->size();
                vec->resize(priv->next_thread_id);
-       (*vec)[tid].push_back(act);
-       if (uninit)
-               (*vec)[uninit_id].push_front(uninit);
+               for(uint i = oldsize;i < priv->next_thread_id;i++)
+                       new (&(*vec)[i]) action_list_t();
+       }
+       if (!canprune)
+               act->setThrdMapRef((*vec)[tid].add_back(act));
 
+       // Update thrd_last_action, the last action taken by each thread
        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;
 
+       // Update thrd_last_fence_release, the last release fence taken by each thread
        if (act->is_fence() && act->is_release()) {
                if ((int)thrd_last_fence_release.size() <= tid)
                        thrd_last_fence_release.resize(get_num_threads());
@@ -1158,13 +1152,94 @@ void ModelExecution::add_action_to_lists(ModelAction *act)
 
        if (act->is_wait()) {
                void *mutex_loc = (void *) act->get_value();
-               get_safe_ptr_action(&obj_map, mutex_loc)->push_back(act);
+               act->setActionRef(get_safe_ptr_action(&obj_map, mutex_loc)->add_back(act));
 
                SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, mutex_loc);
-               if (tid >= (int)vec->size())
+               if ((int)vec->size() <= tid) {
+                       uint oldsize = vec->size();
                        vec->resize(priv->next_thread_id);
-               (*vec)[tid].push_back(act);
+                       for(uint i = oldsize;i < priv->next_thread_id;i++)
+                               new (&(*vec)[i]) action_list_t();
+               }
+               act->setThrdMapRef((*vec)[tid].add_back(act));
+       }
+}
+
+sllnode<ModelAction *>* insertIntoActionList(action_list_t *list, ModelAction *act) {
+       sllnode<ModelAction*> * rit = list->end();
+       modelclock_t next_seq = act->get_seq_number();
+       if (rit == NULL || (rit->getVal()->get_seq_number() == next_seq))
+               return list->add_back(act);
+       else {
+               for(;rit != NULL;rit=rit->getPrev()) {
+                       if (rit->getVal()->get_seq_number() == next_seq) {
+                               return list->insertAfter(rit, act);
+                       }
+               }
+               return NULL;
+       }
+}
+
+sllnode<ModelAction *>* insertIntoActionListAndSetCV(action_list_t *list, ModelAction *act) {
+       sllnode<ModelAction*> * rit = list->end();
+       modelclock_t next_seq = act->get_seq_number();
+       if (rit == NULL) {
+               act->create_cv(NULL);
+               return NULL;
+       } else if (rit->getVal()->get_seq_number() == next_seq) {
+               act->create_cv(rit->getVal());
+               return list->add_back(act);
+       } else {
+               for(;rit != NULL;rit=rit->getPrev()) {
+                       if (rit->getVal()->get_seq_number() == next_seq) {
+                               act->create_cv(rit->getVal());
+                               return list->insertAfter(rit, act);
+                       }
+               }
+               return NULL;
+       }
+}
+
+/**
+ * Performs various bookkeeping operations for a normal write.  The
+ * complication is that we are typically inserting a normal write
+ * lazily, so we need to insert it into the middle of lists.
+ *
+ * @param act is the ModelAction to add.
+ */
+
+void ModelExecution::add_normal_write_to_lists(ModelAction *act)
+{
+       int tid = id_to_int(act->get_tid());
+       act->setTraceRef(insertIntoActionListAndSetCV(&action_trace, act));
+
+       // Update obj_thrd_map, a per location, per thread, order of actions
+       SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
+       if (tid >= (int)vec->size()) {
+               uint oldsize =vec->size();
+               vec->resize(priv->next_thread_id);
+               for(uint i=oldsize;i<priv->next_thread_id;i++)
+                       new (&(*vec)[i]) action_list_t();
        }
+       act->setThrdMapRef(insertIntoActionList(&(*vec)[tid],act));
+
+       ModelAction * lastact = thrd_last_action[tid];
+       // Update thrd_last_action, the last action taken by each thrad
+       if (lastact == NULL || lastact->get_seq_number() == act->get_seq_number())
+               thrd_last_action[tid] = act;
+}
+
+
+void ModelExecution::add_write_to_lists(ModelAction *write) {
+       SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_wr_thrd_map, write->get_location());
+       int tid = id_to_int(write->get_tid());
+       if (tid >= (int)vec->size()) {
+               uint oldsize =vec->size();
+               vec->resize(priv->next_thread_id);
+               for(uint i=oldsize;i<priv->next_thread_id;i++)
+                       new (&(*vec)[i]) action_list_t();
+       }
+       write->setActionRef((*vec)[tid].add_back(write));
 }
 
 /**
@@ -1206,16 +1281,7 @@ ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
 {
        void *location = curr->get_location();
-       action_list_t *list = obj_map.get(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;
+       return obj_last_sc_map.get(location);
 }
 
 /**
@@ -1234,20 +1300,22 @@ ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const Mode
        if (!list)
                return NULL;
 
-       action_list_t::reverse_iterator rit = list->rbegin();
+       sllnode<ModelAction*>* rit = list->end();
 
        if (before_fence) {
-               for (;rit != list->rend();rit++)
-                       if (*rit == before_fence)
+               for (;rit != NULL;rit=rit->getPrev())
+                       if (rit->getVal() == before_fence)
                                break;
 
-               ASSERT(*rit == before_fence);
-               rit++;
+               ASSERT(rit->getVal() == before_fence);
+               rit=rit->getPrev();
        }
 
-       for (;rit != list->rend();rit++)
-               if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
-                       return *rit;
+       for (;rit != NULL;rit=rit->getPrev()) {
+               ModelAction *act = rit->getVal();
+               if (act->is_fence() && (tid == act->get_tid()) && act->is_seqcst())
+                       return act;
+       }
        return NULL;
 }
 
@@ -1264,11 +1332,14 @@ ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
        void *location = curr->get_location();
 
        action_list_t *list = obj_map.get(location);
+       if (list == NULL)
+               return NULL;
+
        /* 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;
+       sllnode<ModelAction*>* rit;
+       for (rit = list->end();rit != NULL;rit=rit->getPrev())
+               if (rit->getVal()->is_unlock() || rit->getVal()->is_wait())
+                       return rit->getVal();
        return NULL;
 }
 
@@ -1287,7 +1358,8 @@ ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
  */
 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
 {
-       return get_parent_action(tid)->get_cv();
+       ModelAction *firstaction=get_parent_action(tid);
+       return firstaction != NULL ? firstaction->get_cv() : NULL;
 }
 
 bool valequals(uint64_t val1, uint64_t val2, int size) {
@@ -1315,7 +1387,7 @@ bool valequals(uint64_t val1, uint64_t val2, int size) {
  */
 SnapVector<ModelAction *> *  ModelExecution::build_may_read_from(ModelAction *curr)
 {
-       SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
+       SnapVector<action_list_t> *thrd_lists = obj_wr_thrd_map.get(curr->get_location());
        unsigned int i;
        ASSERT(curr->is_read());
 
@@ -1327,47 +1399,47 @@ SnapVector<ModelAction *> *  ModelExecution::build_may_read_from(ModelAction *cu
        SnapVector<ModelAction *> * rf_set = new SnapVector<ModelAction *>();
 
        /* 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;
+       if (thrd_lists != NULL)
+               for (i = 0;i < thrd_lists->size();i++) {
+                       /* Iterate over actions in thread, starting from most recent */
+                       action_list_t *list = &(*thrd_lists)[i];
+                       sllnode<ModelAction *> * rit;
+                       for (rit = list->end();rit != NULL;rit=rit->getPrev()) {
+                               ModelAction *act = rit->getVal();
+
+                               if (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;
-
-                       /* Need to check whether we will have two RMW reading from the same value */
-                       if (curr->is_rmwr()) {
-                               /* It is okay if we have a failing CAS */
-                               if (!curr->is_rmwrcas() ||
-                                               valequals(curr->get_value(), act->get_value(), curr->getSize())) {
-                                       //Need to make sure we aren't the second RMW
-                                       CycleNode * node = mo_graph->getNode_noCreate(act);
-                                       if (node != NULL && node->getRMW() != NULL) {
-                                               //we are the second RMW
-                                               allow_read = false;
+                               /* 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;
+
+                               /* Need to check whether we will have two RMW reading from the same value */
+                               if (curr->is_rmwr()) {
+                                       /* It is okay if we have a failing CAS */
+                                       if (!curr->is_rmwrcas() ||
+                                                       valequals(curr->get_value(), act->get_value(), curr->getSize())) {
+                                               //Need to make sure we aren't the second RMW
+                                               CycleNode * node = mo_graph->getNode_noCreate(act);
+                                               if (node != NULL && node->getRMW() != NULL) {
+                                                       //we are the second RMW
+                                                       allow_read = false;
+                                               }
                                        }
                                }
-                       }
 
-                       if (allow_read) {
-                               /* Only add feasible reads */
-                               rf_set->push_back(act);
-                       }
+                               if (allow_read) {
+                                       /* Only add feasible reads */
+                                       rf_set->push_back(act);
+                               }
 
-                       /* Include at most one act per-thread that "happens before" curr */
-                       if (act->happens_before(curr))
-                               break;
+                               /* Include at most one act per-thread that "happens before" curr */
+                               if (act->happens_before(curr))
+                                       break;
+                       }
                }
-       }
 
        if (DBG_ENABLED()) {
                model_print("Reached read action:\n");
@@ -1377,29 +1449,9 @@ SnapVector<ModelAction *> *  ModelExecution::build_may_read_from(ModelAction *cu
        return rf_set;
 }
 
-/**
- * @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
+static void print_list(action_list_t *list)
 {
-       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(const action_list_t *list)
-{
-       action_list_t::const_iterator it;
+       sllnode<ModelAction*> *it;
 
        model_print("------------------------------------------------------------------------------------\n");
        model_print("#    t    Action type     MO       Location         Value               Rf  CV\n");
@@ -1407,18 +1459,18 @@ static void print_list(const action_list_t *list)
 
        unsigned int hash = 0;
 
-       for (it = list->begin();it != list->end();it++) {
-               const ModelAction *act = *it;
+       for (it = list->begin();it != NULL;it=it->getNext()) {
+               const ModelAction *act = it->getVal();
                if (act->get_seq_number() > 0)
                        act->print();
-               hash = hash^(hash<<3)^((*it)->hash());
+               hash = hash^(hash<<3)^(it->getVal()->hash());
        }
        model_print("HASH %u\n", hash);
        model_print("------------------------------------------------------------------------------------\n");
 }
 
 #if SUPPORT_MOD_ORDER_DUMP
-void ModelExecution::dumpGraph(char *filename) const
+void ModelExecution::dumpGraph(char *filename)
 {
        char buffer[200];
        sprintf(buffer, "%s.dot", filename);
@@ -1427,8 +1479,8 @@ void ModelExecution::dumpGraph(char *filename) const
        mo_graph->dumpNodes(file);
        ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
 
-       for (action_list_t::const_iterator it = action_trace.begin();it != action_trace.end();it++) {
-               ModelAction *act = *it;
+       for (sllnode<ModelAction*>* it = action_trace.begin();it != NULL;it=it->getNext()) {
+               ModelAction *act = it->getVal();
                if (act->is_read()) {
                        mo_graph->dot_print_node(file, act);
                        mo_graph->dot_print_edge(file,
@@ -1452,7 +1504,7 @@ void ModelExecution::dumpGraph(char *filename) const
 #endif
 
 /** @brief Prints an execution trace summary. */
-void ModelExecution::print_summary() const
+void ModelExecution::print_summary()
 {
 #if SUPPORT_MOD_ORDER_DUMP
        char buffername[100];
@@ -1463,13 +1515,11 @@ void ModelExecution::print_summary() const
 #endif
 
        model_print("Execution trace %d:", get_execution_number());
-       if (isfeasibleprefix()) {
-               if (scheduler->all_threads_sleeping())
-                       model_print(" SLEEP-SET REDUNDANT");
-               if (have_bug_reports())
-                       model_print(" DETECTED BUG(S)");
-       } else
-               print_infeasibility(" INFEASIBLE");
+       if (scheduler->all_threads_sleeping())
+               model_print(" SLEEP-SET REDUNDANT");
+       if (have_bug_reports())
+               model_print(" DETECTED BUG(S)");
+
        model_print("\n");
 
        print_list(&action_trace);
@@ -1565,20 +1615,8 @@ bool ModelExecution::is_enabled(thread_id_t tid) const
 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
 {
        /* Do not split atomic RMW */
-       if (curr->is_rmwr())
+       if (curr->is_rmwr() && !paused_by_fuzzer(curr))
                return get_thread(curr);
-       if (curr->is_write()) {
-               std::memory_order order = curr->get_mo();
-               switch(order) {
-               case std::memory_order_relaxed:
-                       return get_thread(curr);
-               case std::memory_order_release:
-                       return get_thread(curr);
-               default:
-                       return NULL;
-               }
-       }
-
        /* Follow CREATE with the created thread */
        /* which is not needed, because model.cc takes care of this */
        if (curr->get_type() == THREAD_CREATE)
@@ -1589,6 +1627,15 @@ Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) cons
        return NULL;
 }
 
+/** @param act A read atomic action */
+bool ModelExecution::paused_by_fuzzer(const ModelAction * act) const
+{
+       ASSERT(act->is_read());
+
+       // Actions paused by fuzzer have their sequence number reset to 0
+       return act->get_seq_number() == 0;
+}
+
 /**
  * Takes the next step in the execution, if possible.
  * @param curr The current step to take
@@ -1604,12 +1651,210 @@ Thread * ModelExecution::take_step(ModelAction *curr)
        curr = check_current_action(curr);
        ASSERT(curr);
 
+       /* Process this action in ModelHistory for records */
+       model->get_history()->process_action( curr, curr->get_tid() );
+
        if (curr_thrd->is_blocked() || curr_thrd->is_complete())
                scheduler->remove_thread(curr_thrd);
 
        return action_select_next_thread(curr);
 }
 
+void ModelExecution::removeAction(ModelAction *act) {
+       {
+               sllnode<ModelAction *> * listref = act->getTraceRef();
+               if (listref != NULL) {
+                       action_trace.erase(listref);
+               }
+       }
+       {
+               sllnode<ModelAction *> * listref = act->getThrdMapRef();
+               if (listref != NULL) {
+                       SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
+                       (*vec)[act->get_tid()].erase(listref);
+               }
+       }
+       if ((act->is_fence() && act->is_seqcst()) || act->is_unlock()) {
+               sllnode<ModelAction *> * listref = act->getActionRef();
+               if (listref != NULL) {
+                       action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
+                       list->erase(listref);
+               }
+       } else if (act->is_wait()) {
+               sllnode<ModelAction *> * listref = act->getActionRef();
+               if (listref != NULL) {
+                       void *mutex_loc = (void *) act->get_value();
+                       get_safe_ptr_action(&obj_map, mutex_loc)->erase(listref);
+               }
+       } else if (act->is_free()) {
+               sllnode<ModelAction *> * listref = act->getActionRef();
+               if (listref != NULL) {
+                       SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_wr_thrd_map, act->get_location());
+                       (*vec)[act->get_tid()].erase(listref);
+               }
+               //Remove from Cyclegraph
+               mo_graph->freeAction(act);
+       }
+}
+
+ClockVector * ModelExecution::computeMinimalCV() {
+       ClockVector *cvmin = NULL;
+       //Thread 0 isn't a real thread, so skip it..
+       for(unsigned int i = 1;i < thread_map.size();i++) {
+               Thread * t = thread_map[i];
+               if (t->get_state() == THREAD_COMPLETED)
+                       continue;
+               thread_id_t tid = int_to_id(i);
+               ClockVector * cv = get_cv(tid);
+               if (cvmin == NULL)
+                       cvmin = new ClockVector(cv, NULL);
+               else
+                       cvmin->minmerge(cv);
+       }
+       return cvmin;
+}
+
+//Options...
+//How often to check for memory
+//How much of the trace to always keep
+//Whether to sacrifice completeness...i.e., remove visible writes
+
+void ModelExecution::collectActions() {
+       //Compute minimal clock vector for all live threads
+       ClockVector *cvmin = computeMinimalCV();
+       cvmin->print();
+       SnapVector<CycleNode *> * queue = new SnapVector<CycleNode *>();
+       modelclock_t maxtofree = priv->used_sequence_numbers - params->traceminsize;
+
+       //Next walk action trace...  When we hit an action, see if it is
+       //invisible (e.g., earlier than the first before the minimum
+       //clock for the thread...  if so erase it and all previous
+       //actions in cyclegraph
+       sllnode<ModelAction*> * it;
+       for (it = action_trace.begin();it != NULL;it=it->getNext()) {
+               ModelAction *act = it->getVal();
+               modelclock_t actseq = act->get_seq_number();
+
+               //See if we are done
+               if (actseq > maxtofree)
+                       break;
+
+               thread_id_t act_tid = act->get_tid();
+               modelclock_t tid_clock = cvmin->getClock(act_tid);
+               if (actseq <= tid_clock || params->removevisible) {
+                       ModelAction * write;
+                       if (act->is_write()) {
+                               write = act;
+                       } else if (act->is_read()) {
+                               write = act->get_reads_from();
+                       } else
+                               continue;
+
+                       //Mark everything earlier in MO graph to be freed
+                       CycleNode * cn = mo_graph->getNode_noCreate(write);
+                       if (cn != NULL) {
+                               queue->push_back(cn);
+                               while(!queue->empty()) {
+                                       CycleNode * node = queue->back();
+                                       queue->pop_back();
+                                       for(unsigned int i=0;i<node->getNumInEdges();i++) {
+                                               CycleNode * prevnode = node->getInEdge(i);
+                                               ModelAction * prevact = prevnode->getAction();
+                                               if (prevact->get_type() != READY_FREE) {
+                                                       prevact->set_free();
+                                                       queue->push_back(prevnode);
+                                               }
+                                       }
+                               }
+                       }
+               }
+       }
+       for (;it != NULL;) {
+               ModelAction *act = it->getVal();
+               //Do iteration early since we may delete node...
+               it=it->getPrev();
+               bool islastact = false;
+               ModelAction *lastact = get_last_action(act->get_tid());
+               if (act == lastact) {
+                       Thread * th = get_thread(act);
+                       islastact = !th->is_complete();
+               }
+
+               if (act->is_read()) {
+                       if (islastact) {
+                               act->set_read_from(NULL);
+                       }
+                       if (act->get_reads_from()->is_free()) {
+                               removeAction(act);
+                               delete act;
+                       } else {
+                               const ModelAction *rel_fence =act->get_last_fence_release();
+                               if (rel_fence != NULL) {
+                                       modelclock_t relfenceseq = rel_fence->get_seq_number();
+                                       thread_id_t relfence_tid = rel_fence->get_tid();
+                                       modelclock_t tid_clock = cvmin->getClock(relfence_tid);
+                                       //Remove references to irrelevant release fences
+                                       if (relfenceseq <= tid_clock)
+                                               act->set_last_fence_release(NULL);
+                               }
+                       }
+               }
+
+               if (islastact) {
+                       continue;
+               } else if (act->is_free()) {
+                       removeAction(act);
+                       delete act;
+               } else if (act->is_write()) {
+                       //Do nothing with write that hasn't been marked to be freed
+               } else if (act->is_fence()) {
+                       //Note that acquire fences can always be safely
+                       //removed, but could incur extra overheads in
+                       //traversals.  Removing them before the cvmin seems
+                       //like a good compromise.
+
+                       //Release fences before the cvmin don't do anything
+                       //because everyone has already synchronized.
+
+                       //Sequentially fences before cvmin are redundant
+                       //because happens-before will enforce same
+                       //orderings.
+
+                       modelclock_t actseq = act->get_seq_number();
+                       thread_id_t act_tid = act->get_tid();
+                       modelclock_t tid_clock = cvmin->getClock(act_tid);
+                       if (actseq <= tid_clock) {
+                               removeAction(act);
+                               delete act;
+                       }
+               } else {
+                       //need to deal with lock, annotation, wait, notify, thread create, start, join, yield, finish
+                       //lock, notify thread create, thread finish, yield, finish are dead as soon as they are in the trace
+                       //need to keep most recent unlock/wait for each lock
+                       if(act->is_unlock() || act->is_wait()) {
+                               ModelAction * lastlock = get_last_unlock(act);
+                               if (lastlock != act) {
+                                       removeAction(act);
+                                       delete act;
+                               }
+                       } else if (act->is_create()) {
+                               if (act->get_thread_operand()->is_complete()) {
+                                       removeAction(act);
+                                       delete act;
+                               }
+                       } else {
+                               removeAction(act);
+                               delete act;
+                       }
+               }
+       }
+
+       delete cvmin;
+       delete queue;
+}
+
+
+
 Fuzzer * ModelExecution::getFuzzer() {
        return fuzzer;
 }