model: refactor build_reads_from_past
[c11tester.git] / model.cc
index de3b3259d79c1b47c78c75ed7fd41e3352fa764a..d6ebfe5abc9f4e60920f9b08bed0112746c3afce 100644 (file)
--- a/model.cc
+++ b/model.cc
 #include "promise.h"
 #include "datarace.h"
 #include "threads-model.h"
+#include "output.h"
 
 #define INITIAL_THREAD_ID      0
 
 ModelChecker *model;
 
+struct bug_message {
+       bug_message(const char *str) {
+               const char *fmt = "  [BUG] %s\n";
+               msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
+               sprintf(msg, fmt, str);
+       }
+       ~bug_message() { if (msg) snapshot_free(msg); }
+
+       char *msg;
+       void print() { model_print("%s", msg); }
+
+       SNAPSHOTALLOC
+};
+
 /**
  * Structure for holding small ModelChecker members that should be snapshotted
  */
 struct model_snapshot_members {
+       model_snapshot_members() :
+               current_action(NULL),
+               /* First thread created will have id INITIAL_THREAD_ID */
+               next_thread_id(INITIAL_THREAD_ID),
+               used_sequence_numbers(0),
+               nextThread(NULL),
+               next_backtrack(NULL),
+               bugs(),
+               stats(),
+               failed_promise(false),
+               too_many_reads(false),
+               bad_synchronization(false),
+               asserted(false)
+       { }
+
+       ~model_snapshot_members() {
+               for (unsigned int i = 0; i < bugs.size(); i++)
+                       delete bugs[i];
+               bugs.clear();
+       }
+
        ModelAction *current_action;
        unsigned int next_thread_id;
        modelclock_t used_sequence_numbers;
        Thread *nextThread;
        ModelAction *next_backtrack;
+       std::vector< bug_message *, SnapshotAlloc<bug_message *> > bugs;
+       struct execution_stats stats;
+       bool failed_promise;
+       bool too_many_reads;
+       /** @brief Incorrectly-ordered synchronization was made */
+       bool bad_synchronization;
+       bool asserted;
+
+       SNAPSHOTALLOC
 };
 
 /** @brief Constructor */
@@ -34,8 +79,6 @@ ModelChecker::ModelChecker(struct model_params params) :
        /* Initialize default scheduler */
        params(params),
        scheduler(new Scheduler()),
-       num_executions(0),
-       num_feasible_executions(0),
        diverge(NULL),
        earliest_diverge(NULL),
        action_trace(new action_list_t()),
@@ -49,17 +92,9 @@ ModelChecker::ModelChecker(struct model_params params) :
        pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
        thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
        node_stack(new NodeStack()),
-       mo_graph(new CycleGraph()),
-       failed_promise(false),
-       too_many_reads(false),
-       asserted(false),
-       bad_synchronization(false)
+       priv(new struct model_snapshot_members()),
+       mo_graph(new CycleGraph())
 {
-       /* Allocate this "size" on the snapshotting heap */
-       priv = (struct model_snapshot_members *)snapshot_calloc(1, sizeof(*priv));
-       /* First thread created will have id INITIAL_THREAD_ID */
-       priv->next_thread_id = INITIAL_THREAD_ID;
-
        /* 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);
@@ -88,8 +123,7 @@ ModelChecker::~ModelChecker()
        delete node_stack;
        delete scheduler;
        delete mo_graph;
-
-       snapshot_free(priv);
+       delete priv;
 }
 
 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr) {
@@ -118,10 +152,10 @@ void ModelChecker::reset_to_initial_state()
 {
        DEBUG("+++ Resetting to initial state +++\n");
        node_stack->reset_execution();
-       failed_promise = false;
-       too_many_reads = false;
-       bad_synchronization = false;
-       reset_asserted();
+
+       /* Print all model-checker output before rollback */
+       fflush(model_out);
+
        snapshotObject->backTrackBeforeStep(0);
 }
 
@@ -138,7 +172,7 @@ unsigned int ModelChecker::get_num_threads() const
 }
 
 /** @return The currently executing Thread. */
-Thread * ModelChecker::get_current_thread()
+Thread * ModelChecker::get_current_thread() const
 {
        return scheduler->get_current_thread();
 }
@@ -149,7 +183,8 @@ modelclock_t ModelChecker::get_next_seq_num()
        return ++priv->used_sequence_numbers;
 }
 
-Node * ModelChecker::get_curr_node() {
+Node * ModelChecker::get_curr_node() const
+{
        return node_stack->get_head();
 }
 
@@ -275,6 +310,23 @@ void ModelChecker::wake_up_sleeping_actions(ModelAction * curr) {
        }
 }
 
+/** @brief Alert the model-checker that an incorrectly-ordered
+ * synchronization was made */
+void ModelChecker::set_bad_synchronization()
+{
+       priv->bad_synchronization = true;
+}
+
+bool ModelChecker::has_asserted() const
+{
+       return priv->asserted;
+}
+
+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
@@ -312,45 +364,153 @@ bool ModelChecker::is_complete_execution() const
 }
 
 /**
- * Queries the model-checker for more executions to explore and, if one
- * exists, resets the model-checker state to execute a new execution.
+ * @brief Assert a bug in the executing program.
  *
- * @return If there are more executions to explore, return true. Otherwise,
- * return false.
+ * Use this function to assert any sort of bug in the user program. If the
+ * current trace is feasible (actually, a prefix of some feasible execution),
+ * then this execution will be aborted, printing the appropriate message. If
+ * the current trace is not yet feasible, the error message will be stashed and
+ * printed if the execution ever becomes feasible.
+ *
+ * @param msg Descriptive message for the bug (do not include newline char)
+ * @return True if bug is immediately-feasible
  */
-bool ModelChecker::next_execution()
+bool ModelChecker::assert_bug(const char *msg)
 {
-       DBG();
+       priv->bugs.push_back(new bug_message(msg));
 
-       num_executions++;
+       if (isfeasibleprefix()) {
+               set_assert();
+               return true;
+       }
+       return false;
+}
 
-       if (is_deadlocked())
-               printf("ERROR: DEADLOCK\n");
-       if (isfinalfeasible()) {
-               printf("Earliest divergence point since last feasible execution:\n");
+/**
+ * @brief Assert a bug in the executing program, asserted by a user thread
+ * @see ModelChecker::assert_bug
+ * @param msg Descriptive message for the bug (do not include newline char)
+ */
+void ModelChecker::assert_user_bug(const char *msg)
+{
+       /* If feasible bug, bail out now */
+       if (assert_bug(msg))
+               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
+{
+       if (have_bug_reports()) {
+               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();
+       }
+}
+
+/**
+ * @brief Record end-of-execution stats
+ *
+ * Must be run when exiting an execution. Records various stats.
+ * @see struct execution_stats
+ */
+void ModelChecker::record_stats()
+{
+       stats.num_total++;
+       if (!isfeasibleprefix())
+               stats.num_infeasible++;
+       else if (have_bug_reports())
+               stats.num_buggy_executions++;
+       else if (is_complete_execution())
+               stats.num_complete++;
+       else
+               stats.num_redundant++;
+}
+
+/** @brief Print execution stats */
+void ModelChecker::print_stats() const
+{
+       model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
+       model_print("Number of redundant executions: %d\n", stats.num_redundant);
+       model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
+       model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
+       model_print("Total executions: %d\n", stats.num_total);
+       model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
+}
+
+/**
+ * @brief End-of-exeuction print
+ * @param printbugs Should any existing bugs be printed?
+ */
+void ModelChecker::print_execution(bool printbugs) const
+{
+       print_program_output();
+
+       if (DBG_ENABLED() || params.verbose) {
+               model_print("Earliest divergence point since last feasible execution:\n");
                if (earliest_diverge)
                        earliest_diverge->print();
                else
-                       printf("(Not set)\n");
+                       model_print("(Not set)\n");
 
-               earliest_diverge = NULL;
-               num_feasible_executions++;
+               model_print("\n");
+               print_stats();
        }
 
-       DEBUG("Number of acquires waiting on pending release sequences: %zu\n",
-                       pending_rel_seqs->size());
+       /* Don't print invalid bugs */
+       if (printbugs)
+               print_bugs();
+
+       model_print("\n");
+       print_summary();
+}
+
+/**
+ * Queries the model-checker for more executions to explore and, if one
+ * exists, resets the model-checker state to execute a new execution.
+ *
+ * @return If there are more executions to explore, return true. Otherwise,
+ * return false.
+ */
+bool ModelChecker::next_execution()
+{
+       DBG();
+       /* Is this execution a feasible execution that's worth bug-checking? */
+       bool complete = isfeasibleprefix() && (is_complete_execution() ||
+                       have_bug_reports());
 
+       /* End-of-execution bug checks */
+       if (complete) {
+               if (is_deadlocked())
+                       assert_bug("Deadlock detected");
 
-       if (isfinalfeasible() || DBG_ENABLED()) {
                checkDataRaces();
-               print_summary();
        }
 
+       record_stats();
+
+       /* Output */
+       if (DBG_ENABLED() || params.verbose || have_bug_reports())
+               print_execution(complete);
+       else
+               clear_program_output();
+
+       if (complete)
+               earliest_diverge = NULL;
+
        if ((diverge = get_next_backtrack()) == NULL)
                return false;
 
        if (DBG_ENABLED()) {
-               printf("Next execution will diverge at:\n");
+               model_print("Next execution will diverge at:\n");
                diverge->print();
        }
 
@@ -364,6 +524,9 @@ ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
        case ATOMIC_READ:
        case ATOMIC_WRITE:
        case ATOMIC_RMW: {
+               /* Optimization: relaxed operations don't need backtracking */
+               if (act->is_relaxed())
+                       return 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;
@@ -533,9 +696,9 @@ bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
                        }
 
 
-                       if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
+                       if (!second_part_of_rmw&&is_infeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
                                mo_graph->rollbackChanges();
-                               too_many_reads = false;
+                               priv->too_many_reads = false;
                                continue;
                        }
 
@@ -597,10 +760,8 @@ bool ModelChecker::process_mutex(ModelAction *curr) {
        }
                //otherwise fall into the lock case
        case ATOMIC_LOCK: {
-               if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
-                       printf("Lock access before initialization\n");
-                       set_assert();
-               }
+               if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
+                       assert_bug("Lock access before initialization");
                state->islocked = true;
                ModelAction *unlock = get_last_unlock(curr);
                //synchronize with the previous unlock statement
@@ -809,8 +970,7 @@ void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_qu
        }
 
        /* See if we have realized a data race */
-       if (checkDataRaces())
-               set_assert();
+       checkDataRaces();
 }
 
 /**
@@ -841,7 +1001,7 @@ bool ModelChecker::initialize_curr_action(ModelAction **curr)
 
        (*curr)->set_seq_number(get_next_seq_num());
 
-       newcurr = node_stack->explore_action(*curr, scheduler->get_enabled());
+       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())
@@ -959,7 +1119,7 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
 
        /* Initialize work_queue with the "current action" work */
        work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
-       while (!work_queue.empty()) {
+       while (!work_queue.empty() && !has_asserted()) {
                WorkQueueEntry work = work_queue.front();
                work_queue.pop_front();
 
@@ -1051,48 +1211,67 @@ bool ModelChecker::promises_expired() const
        return false;
 }
 
-/** @return whether the current partial trace must be a prefix of a
- * feasible trace. */
+/**
+ * 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 promises->size() == 0 && pending_rel_seqs->size() == 0 && isfeasible();
+       return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
 }
 
-/** @return whether the current partial trace is feasible. */
-bool ModelChecker::isfeasible() const
+/**
+ * Returns whether the current completed trace is feasible, except for pending
+ * release sequences.
+ */
+bool ModelChecker::is_feasible_prefix_ignore_relseq() const
+{
+       if (DBG_ENABLED() && promises->size() != 0)
+               DEBUG("Infeasible: unrevolved promises\n");
+
+       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
 {
        if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
                DEBUG("Infeasible: RMW violation\n");
 
-       return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
+       return mo_graph->checkForRMWViolation() || is_infeasible_ignoreRMW();
 }
 
-/** @return whether the current partial trace is feasible other than
- * multiple RMW reading from the same store. */
-bool ModelChecker::isfeasibleotherthanRMW() const
+/**
+ * Check If the current partial trace is infeasible, while ignoring
+ * infeasibility related to 2 RMW's reading from the same store. It does not
+ * check end-of-execution feasibility.
+ * @see ModelChecker::is_infeasible
+ * @return whether the current partial trace is infeasible, ignoring multiple
+ * RMWs reading from the same store.
+ * */
+bool ModelChecker::is_infeasible_ignoreRMW() const
 {
        if (DBG_ENABLED()) {
                if (mo_graph->checkForCycles())
                        DEBUG("Infeasible: modification order cycles\n");
-               if (failed_promise)
+               if (priv->failed_promise)
                        DEBUG("Infeasible: failed promise\n");
-               if (too_many_reads)
+               if (priv->too_many_reads)
                        DEBUG("Infeasible: too many reads\n");
-               if (bad_synchronization)
+               if (priv->bad_synchronization)
                        DEBUG("Infeasible: bad synchronization ordering\n");
                if (promises_expired())
                        DEBUG("Infeasible: promises expired\n");
        }
-       return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
-}
-
-/** Returns whether the current completed trace is feasible. */
-bool ModelChecker::isfinalfeasible() const
-{
-       if (DBG_ENABLED() && promises->size() != 0)
-               DEBUG("Infeasible: unrevolved promises\n");
-
-       return isfeasible() && promises->size() == 0;
+       return mo_graph->checkForCycles() || 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. */
@@ -1124,7 +1303,7 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
                        return;
                //Must make sure that execution is currently feasible...  We could
                //accidentally clear by rolling back
-               if (!isfeasible())
+               if (is_infeasible())
                        return;
                std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
                int tid = id_to_int(curr->get_tid());
@@ -1167,7 +1346,7 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
                        /* Test to see whether this is a feasible write to read from*/
                        mo_graph->startChanges();
                        r_modification_order(curr, write);
-                       bool feasiblereadfrom = isfeasible();
+                       bool feasiblereadfrom = !is_infeasible();
                        mo_graph->rollbackChanges();
 
                        if (!feasiblereadfrom)
@@ -1192,7 +1371,7 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
                                }
                        }
                        if (feasiblewrite) {
-                               too_many_reads = true;
+                               priv->too_many_reads = true;
                                return;
                        }
                }
@@ -1356,7 +1535,7 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
        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(curr);
+               ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
                if (last_seq_cst != NULL) {
                        mo_graph->addEdge(last_seq_cst, curr);
                        added = true;
@@ -1427,8 +1606,8 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
 
                                 */
                                if (thin_air_constraint_may_allow(curr, act)) {
-                                       if (isfeasible() ||
-                                                       (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
+                                       if (!is_infeasible() ||
+                                                       (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && !is_infeasible_ignoreRMW())) {
                                                struct PendingFutureValue pfv = {curr,act};
                                                futurevalues->push_back(pfv);
                                        }
@@ -1741,9 +1920,7 @@ bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_
        }
 
        // If we resolved promises or data races, see if we have realized a data race.
-       if (checkDataRaces()) {
-               set_assert();
-       }
+       checkDataRaces();
 
        return updated;
 }
@@ -1808,7 +1985,7 @@ ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
  * check
  * @return The last seq_cst write
  */
-ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
+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);
@@ -1820,6 +1997,35 @@ ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
        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
@@ -1840,7 +2046,7 @@ ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
        return NULL;
 }
 
-ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
+ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
 {
        ModelAction *parent = get_last_action(tid);
        if (!parent)
@@ -1853,7 +2059,7 @@ ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
  * @param tid The thread whose clock vector we want
  * @return Desired clock vector
  */
-ClockVector * ModelChecker::get_cv(thread_id_t tid)
+ClockVector * ModelChecker::get_cv(thread_id_t tid) const
 {
        return get_parent_action(tid)->get_cv();
 }
@@ -1936,7 +2142,7 @@ void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVec
                                merge_cv->synchronized_since(act)) {
                        if (promise->increment_threads(tid)) {
                                //Promise has failed
-                               failed_promise = true;
+                               priv->failed_promise = true;
                                return;
                        }
                }
@@ -1947,7 +2153,7 @@ void ModelChecker::check_promises_thread_disabled() {
        for (unsigned int i = 0; i < promises->size(); i++) {
                Promise *promise = (*promises)[i];
                if (promise->check_promise()) {
-                       failed_promise = true;
+                       priv->failed_promise = true;
                        return;
                }
        }
@@ -1998,12 +2204,12 @@ void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write)
                                promise->set_write(write);
                                //The pwrite cannot happen before the promise
                                if (write->happens_before(act) && (write != act)) {
-                                       failed_promise = true;
+                                       priv->failed_promise = true;
                                        return;
                                }
                        }
                        if (mo_graph->checkPromise(write, promise)) {
-                               failed_promise = true;
+                               priv->failed_promise = true;
                                return;
                        }
                }
@@ -2014,7 +2220,7 @@ void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write)
 
                if (promise->get_write()&&mo_graph->checkReachable(promise->get_write(), write)) {
                        if (promise->increment_threads(tid)) {
-                               failed_promise = true;
+                               priv->failed_promise = true;
                                return;
                        }
                }
@@ -2057,16 +2263,16 @@ void ModelChecker::build_reads_from_past(ModelAction *curr)
        unsigned int i;
        ASSERT(curr->is_read());
 
-       ModelAction *last_seq_cst = NULL;
+       ModelAction *last_sc_write = NULL;
 
        /* Track whether this object has been initialized */
        bool initialized = false;
 
        if (curr->is_seqcst()) {
-               last_seq_cst = get_last_seq_cst(curr);
+               last_sc_write = get_last_seq_cst_write(curr);
                /* We have to at least see the last sequentially consistent write,
                         so we are initialized. */
-               if (last_seq_cst != NULL)
+               if (last_sc_write != NULL)
                        initialized = true;
        }
 
@@ -2083,15 +2289,20 @@ void ModelChecker::build_reads_from_past(ModelAction *curr)
                                continue;
 
                        /* Don't consider more than one seq_cst write if we are a seq_cst read. */
-                       if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
-                               if (!curr->get_sleep_flag() || curr->is_seqcst() || sleep_can_read_from(curr, act)) {
-                                       DEBUG("Adding action to may_read_from:\n");
-                                       if (DBG_ENABLED()) {
-                                               act->print();
-                                               curr->print();
-                                       }
-                                       curr->get_node()->add_read_from(act);
+                       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) {
+                               DEBUG("Adding action to may_read_from:\n");
+                               if (DBG_ENABLED()) {
+                                       act->print();
+                                       curr->print();
                                }
+                               curr->get_node()->add_read_from(act);
                        }
 
                        /* Include at most one act per-thread that "happens before" curr */
@@ -2102,18 +2313,15 @@ void ModelChecker::build_reads_from_past(ModelAction *curr)
                }
        }
 
-       if (!initialized) {
-               /** @todo Need a more informative way of reporting errors. */
-               printf("ERROR: may read from uninitialized atomic\n");
-               set_assert();
-       }
+       if (!initialized)
+               assert_bug("May read from uninitialized atomic");
 
        if (DBG_ENABLED() || !initialized) {
-               printf("Reached read action:\n");
+               model_print("Reached read action:\n");
                curr->print();
-               printf("Printing may_read_from\n");
+               model_print("Printing may_read_from\n");
                curr->get_node()->print_may_read_from();
-               printf("End printing may_read_from\n");
+               model_print("End printing may_read_from\n");
        }
 }
 
@@ -2133,20 +2341,22 @@ bool ModelChecker::sleep_can_read_from(ModelAction * curr, const ModelAction *wr
        }
 }
 
-static void print_list(action_list_t *list)
+static void print_list(action_list_t *list, int exec_num = -1)
 {
        action_list_t::iterator it;
 
-       printf("---------------------------------------------------------------------\n");
-       printf("Trace:\n");
+       model_print("---------------------------------------------------------------------\n");
+       if (exec_num >= 0)
+               model_print("Execution %d:\n", exec_num);
+
        unsigned int hash=0;
 
        for (it = list->begin(); it != list->end(); it++) {
                (*it)->print();
                hash=hash^(hash<<3)^((*it)->hash());
        }
-       printf("HASH %u\n", hash);
-       printf("---------------------------------------------------------------------\n");
+       model_print("HASH %u\n", hash);
+       model_print("---------------------------------------------------------------------\n");
 }
 
 #if SUPPORT_MOD_ORDER_DUMP
@@ -2177,26 +2387,22 @@ void ModelChecker::dumpGraph(char *filename) {
 }
 #endif
 
-void ModelChecker::print_summary()
+/** @brief Prints an execution trace summary. */
+void ModelChecker::print_summary() const
 {
-       printf("\n");
-       printf("Number of executions: %d\n", num_executions);
-       printf("Number of feasible executions: %d\n", num_feasible_executions);
-       printf("Total nodes created: %d\n", node_stack->get_total_nodes());
-
 #if SUPPORT_MOD_ORDER_DUMP
        scheduler->print();
        char buffername[100];
-       sprintf(buffername, "exec%04u", num_executions);
+       sprintf(buffername, "exec%04u", stats.num_total);
        mo_graph->dumpGraphToFile(buffername);
-       sprintf(buffername, "graph%04u", num_executions);
+       sprintf(buffername, "graph%04u", stats.num_total);
        dumpGraph(buffername);
 #endif
 
-       if (!isfinalfeasible())
-               printf("INFEASIBLE EXECUTION!\n");
-       print_list(action_trace);
-       printf("\n");
+       if (!isfeasibleprefix())
+               model_print("INFEASIBLE EXECUTION!\n");
+       print_list(action_trace, stats.num_total);
+       model_print("\n");
 }
 
 /**
@@ -2304,8 +2510,12 @@ bool ModelChecker::take_step() {
        Thread *next = scheduler->next_thread(priv->nextThread);
 
        /* Infeasible -> don't take any more steps */
-       if (!isfeasible())
+       if (is_infeasible())
+               return false;
+       else if (isfeasibleprefix() && have_bug_reports()) {
+               set_assert();
                return false;
+       }
 
        if (params.bound != 0) {
                if (priv->used_sequence_numbers > params.bound) {
@@ -2326,8 +2536,8 @@ bool ModelChecker::take_step() {
         * (4) no pending promises
         */
        if (!pending_rel_seqs->empty() && (!next || next->is_model_thread()) &&
-                       isfinalfeasible() && !unrealizedraces.empty()) {
-               printf("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
+                       is_feasible_prefix_ignore_relseq() && !unrealizedraces.empty()) {
+               model_print("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
                                pending_rel_seqs->size());
                ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
                                std::memory_order_seq_cst, NULL, VALUE_NONE,
@@ -2354,9 +2564,24 @@ bool ModelChecker::take_step() {
        return (Thread::swap(&system_context, next) == 0);
 }
 
-/** Runs the current execution until threre are no more steps to take. */
-void ModelChecker::finish_execution() {
-       DBG();
+/** 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 Run ModelChecker for the user program */
+void ModelChecker::run()
+{
+       do {
+               thrd_t user_thread;
+
+               /* Start user program */
+               add_thread(new Thread(&user_thread, &user_main_wrapper, NULL));
+
+               /* Wait for all threads to complete */
+               while (take_step());
+       } while (next_execution());
 
-       while (take_step());
+       print_stats();
 }