More code towards freeing old actions
[c11tester.git] / execution.cc
index 524c6fa2f2dded24e3421f533c88bb55a621fb6e..5aaabbcf00060a1ffe55cb77ad11f049037d7648 100644 (file)
@@ -28,7 +28,6 @@ struct model_snapshot_members {
                next_thread_id(INITIAL_THREAD_ID),
                used_sequence_numbers(0),
                bugs(),
-               bad_synchronization(false),
                asserted(false)
        { }
 
@@ -42,7 +41,6 @@ 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
@@ -53,10 +51,10 @@ 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(1),
+       action_trace(),
        obj_map(),
        condvar_waiters_map(),
        obj_thrd_map(),
@@ -66,15 +64,16 @@ ModelExecution::ModelExecution(ModelChecker *m, Scheduler *scheduler) :
        priv(new struct model_snapshot_members ()),
        mo_graph(new CycleGraph()),
        fuzzer(new NewFuzzer()),
-       thrd_func_list(),
-       thrd_func_act_lists(),
        isfinished(false)
 {
        /* Initialize a model-checker thread, for special ModelActions */
        model_thread = new Thread(get_next_id());
        add_thread(model_thread);
-       scheduler->register_engine(this);
        fuzzer->register_engine(m->get_history(), this);
+       scheduler->register_engine(this);
+#ifdef TLS
+       pthread_key_create(&pthreadkey, tlsdestructor);
+#endif
 }
 
 /** @brief Destructor */
@@ -92,7 +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) {
@@ -102,7 +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<const 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) {
@@ -130,6 +129,12 @@ modelclock_t ModelExecution::get_next_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?
  *
@@ -155,6 +160,7 @@ 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;
@@ -168,29 +174,20 @@ 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 */
@@ -282,17 +279,29 @@ ModelAction * ModelExecution::convertNonAtomicStore(void * location) {
  * @param rf_set is the set of model actions we can possibly read from
  * @return True if processing this read updates the mo_graph.
  */
-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 *>();
+       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);
+
                ModelAction *rf = (*rf_set)[index];
 
                ASSERT(rf);
@@ -307,9 +316,13 @@ void ModelExecution::process_read(ModelAction *curr, SnapVector<ModelAction *> *
                        if (canprune && curr->get_type() == ATOMIC_READ) {
                                int tid = id_to_int(curr->get_tid());
                                (*obj_thrd_map.get(curr->get_location()))[tid].pop_back();
+                               curr->setThrdMapRef(NULL);
                        }
-                       return;
+                       return true;
                }
+
+               ASSERT(false);
+               /* TODO: Following code not needed anymore */
                priorset->clear();
                (*rf_set)[index] = rf_set->back();
                rf_set->pop_back();
@@ -364,7 +377,27 @@ bool ModelExecution::process_mutex(ModelAction *curr)
                }
                break;
        }
-       case ATOMIC_WAIT:
+       case ATOMIC_WAIT: {
+               /* wake up the other threads */
+               for (unsigned int i = 0;i < get_num_threads();i++) {
+                       Thread *t = get_thread(int_to_id(i));
+                       Thread *curr_thrd = get_thread(curr);
+                       if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
+                               scheduler->wake(t);
+               }
+
+               /* unlock the lock - after checking who was waiting on it */
+               state->locked = NULL;
+
+               if (fuzzer->shouldWait(curr)) {
+                       /* 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...
 
@@ -378,10 +411,6 @@ 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: {
@@ -540,6 +569,12 @@ void ModelExecution::process_thread_action(ModelAction *curr)
        case THREAD_START: {
                break;
        }
+       case THREAD_SLEEP: {
+               Thread *th = get_thread(curr);
+               th->set_pending(curr);
+               scheduler->add_sleep(th);
+               break;
+       }
        default:
                break;
        }
@@ -619,7 +654,7 @@ void ModelExecution::read_from(ModelAction *act, 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);
@@ -676,26 +711,25 @@ 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 && curr->get_type() != NOOP)
-               add_action_to_lists(curr);
-
-       if (curr->is_write())
-               add_write_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);
-
        if (curr->is_read() && !second_part_of_rmw) {
                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);
+
+       if (curr->is_write())
+               add_write_to_lists(curr);
+
+       process_thread_action(curr);
 
        if (curr->is_write())
                process_write(curr);
@@ -709,42 +743,6 @@ 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());
@@ -769,10 +767,14 @@ 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 * canprune)
+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;
@@ -825,7 +827,8 @@ 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 */
@@ -833,7 +836,8 @@ 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 */
@@ -841,7 +845,8 @@ 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;
                                }
                        }
@@ -860,17 +865,20 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *
                                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
-                                                       *canprune = true;
+                                                       if (!check_only)
+                                                               *canprune = true;
                                                }
                                        }
                                }
@@ -1093,48 +1101,29 @@ ClockVector * ModelExecution::get_hb_from_write(ModelAction *rf) const {
 void ModelExecution::add_action_to_lists(ModelAction *act)
 {
        int tid = id_to_int(act->get_tid());
-       ModelAction *uninit = NULL;
-       int uninit_id = -1;
-       action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
-       if (list->empty() && act->is_atomic_var()) {
-               uninit = get_uninitialized_action(act);
-               uninit_id = id_to_int(uninit->get_tid());
-               list->push_front(uninit);
-               SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_wr_thrd_map, act->get_location());
-               if (uninit_id >= (int)vec->size()) {
-                       int oldsize = (int) vec->size();
-                       vec->resize(uninit_id + 1);
-                       for(int i=oldsize;i<uninit_id+1;i++) {
-                               new(&(*vec)[i]) action_list_t();
-                       }
-               }
-               (*vec)[uninit_id].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);
 
        // Update action trace, a total order of all actions
-       action_trace.push_back(act);
-       if (uninit)
-               action_trace.push_front(uninit);
+       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()) {
-               uint oldsize =vec->size();
+       if ((int)vec->size() <= tid) {
+               uint oldsize = vec->size();
                vec->resize(priv->next_thread_id);
-               for(uint i=oldsize;i<priv->next_thread_id;i++)
+               for(uint i = oldsize;i < priv->next_thread_id;i++)
                        new (&(*vec)[i]) action_list_t();
        }
-       (*vec)[tid].push_back(act);
-       if (uninit)
-               (*vec)[uninit_id].push_front(uninit);
+       act->setThrdMapRef((*vec)[tid].add_back(act));
 
-       // Update thrd_last_action, the last action taken by each thrad
+       // 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()) {
@@ -1145,50 +1134,51 @@ 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);
-                       for(uint i=oldsize;i<priv->next_thread_id;i++)
+                       for(uint i = oldsize;i < priv->next_thread_id;i++)
                                new (&(*vec)[i]) action_list_t();
                }
-               (*vec)[tid].push_back(act);
+               act->setThrdMapRef((*vec)[tid].add_back(act));
        }
 }
 
-void insertIntoActionList(action_list_t *list, ModelAction *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))
-               list->push_back(act);
+               return list->add_back(act);
        else {
                for(;rit != NULL;rit=rit->getPrev()) {
                        if (rit->getVal()->get_seq_number() == next_seq) {
-                               list->insertAfter(rit, act);
-                               break;
+                               return list->insertAfter(rit, act);
                        }
                }
+               return NULL;
        }
 }
 
-void insertIntoActionListAndSetCV(action_list_t *list, ModelAction *act) {
+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());
-               list->push_back(act);
+               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());
-                               list->insertAfter(rit, act);
-                               break;
+                               return list->insertAfter(rit, act);
                        }
                }
+               return NULL;
        }
 }
 
@@ -1203,10 +1193,7 @@ void insertIntoActionListAndSetCV(action_list_t *list, ModelAction *act) {
 void ModelExecution::add_normal_write_to_lists(ModelAction *act)
 {
        int tid = id_to_int(act->get_tid());
-       insertIntoActionListAndSetCV(&action_trace, act);
-
-       action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
-       insertIntoActionList(list, act);
+       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());
@@ -1216,7 +1203,7 @@ void ModelExecution::add_normal_write_to_lists(ModelAction *act)
                for(uint i=oldsize;i<priv->next_thread_id;i++)
                        new (&(*vec)[i]) action_list_t();
        }
-       insertIntoActionList(&(*vec)[tid],act);
+       act->setThrdMapRef(insertIntoActionList(&(*vec)[tid],act));
 
        // Update thrd_last_action, the last action taken by each thrad
        if (thrd_last_action[tid]->get_seq_number() == act->get_seq_number())
@@ -1233,7 +1220,7 @@ void ModelExecution::add_write_to_lists(ModelAction *write) {
                for(uint i=oldsize;i<priv->next_thread_id;i++)
                        new (&(*vec)[i]) action_list_t();
        }
-       (*vec)[tid].push_back(write);
+       write->setActionRef((*vec)[tid].add_back(write));
 }
 
 /**
@@ -1326,6 +1313,9 @@ 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)}) */
        sllnode<ModelAction*>* rit;
        for (rit = list->end();rit != NULL;rit=rit->getPrev())
@@ -1439,25 +1429,6 @@ 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.
- *
- * @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(ModelAction *curr) const
-{
-       ModelAction *act = curr->get_uninit_action();
-       if (!act) {
-               act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
-               curr->set_uninit_action(act);
-       }
-       act->create_cv(NULL);
-       return act;
-}
-
 static void print_list(action_list_t *list)
 {
        sllnode<ModelAction*> *it;
@@ -1524,13 +1495,11 @@ void ModelExecution::print_summary()
 #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);
@@ -1626,7 +1595,7 @@ 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);
        /* Follow CREATE with the created thread */
        /* which is not needed, because model.cc takes care of this */
@@ -1638,6 +1607,15 @@ 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
@@ -1662,6 +1640,150 @@ Thread * ModelExecution::take_step(ModelAction *curr)
        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_write()) {
+               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;
+       for(unsigned int i = 0;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;
+}
+
+void ModelExecution::collectActions() {
+       //Compute minimal clock vector for all live threads
+       ClockVector *cvmin = computeMinimalCV();
+       SnapVector<CycleNode *> * queue = new SnapVector<CycleNode *>();
+       //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
+       for (sllnode<ModelAction*>* it = action_trace.begin();it != NULL;it=it->getNext()) {
+               ModelAction *act = it->getVal();
+               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) {
+                       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
+                       queue->push_back(mo_graph->getNode_noCreate(write));
+                       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 (sllnode<ModelAction*>* it = action_trace.end();it != NULL;it=it->getPrev()) {
+               ModelAction *act = it->getVal();
+               if (act->is_free()) {
+                       removeAction(act);
+                       delete act;
+               } else if (act->is_read()) {
+                       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);
+                               }
+                       }
+               } 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
+               }
+       }
+
+       delete cvmin;
+       delete queue;
+}
+
+
+
 Fuzzer * ModelExecution::getFuzzer() {
        return fuzzer;
 }