fix bug
[model-checker.git] / model.cc
index 2be1c82e9861760b321df7a8a54fcfad4ac82dd9..fb492a5363d1cfea467d3a8ef1438c812fd11e83 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -21,6 +21,7 @@ ModelChecker::ModelChecker(struct model_params params) :
        /* Initialize default scheduler */
        scheduler(new Scheduler()),
        num_executions(0),
+       num_feasible_executions(0),
        params(params),
        diverge(NULL),
        action_trace(new action_list_t()),
@@ -28,6 +29,7 @@ ModelChecker::ModelChecker(struct model_params params) :
        obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
        obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
        promises(new std::vector<Promise *>()),
+       futurevalues(new std::vector<struct PendingFutureValue>()),
        lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
        thrd_last_action(new std::vector<ModelAction *>(1)),
        node_stack(new NodeStack()),
@@ -100,16 +102,29 @@ modelclock_t ModelChecker::get_next_seq_num()
 }
 
 /**
- * Choose the next thread in the replay sequence.
+ * @brief Choose the next thread to execute.
  *
- * If the replay sequence has reached the 'diverge' point, returns a thread
- * from the backtracking set. Otherwise, simply returns the next thread in the
- * sequence that is being replayed.
+ * This function chooses the next thread that should execute. It can force the
+ * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
+ * followed by a THREAD_START, or it can enforce execution replay/backtracking.
+ * The model-checker may have no preference regarding the next thread (i.e.,
+ * when exploring a new execution ordering), in which case this will return
+ * NULL.
+ * @param curr The current ModelAction. This action might guide the choice of
+ * next thread.
+ * @return The next thread to run. If the model-checker has no preference, NULL.
  */
-Thread * ModelChecker::get_next_replay_thread()
+Thread * ModelChecker::get_next_thread(ModelAction *curr)
 {
        thread_id_t tid;
 
+       /* Do not split atomic actions. */
+       if (curr->is_rmwr())
+               return thread_current();
+       /* The THREAD_CREATE action points to the created Thread */
+       else if (curr->get_type() == THREAD_CREATE)
+               return (Thread *)curr->get_location();
+
        /* Have we completed exploring the preselected path? */
        if (diverge == NULL)
                return NULL;
@@ -160,6 +175,8 @@ bool ModelChecker::next_execution()
        DBG();
 
        num_executions++;
+       if (isfinalfeasible())
+               num_feasible_executions++;
 
        if (isfinalfeasible() || DBG_ENABLED())
                print_summary();
@@ -180,21 +197,33 @@ ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 {
        action_type type = act->get_type();
 
-       switch (type) {
-               case ATOMIC_READ:
-               case ATOMIC_WRITE:
-               case ATOMIC_RMW:
-                       break;
-               default:
-                       return NULL;
-       }
-       /* linear search: from most recent to oldest */
-       action_list_t *list = obj_map->get_safe_ptr(act->get_location());
-       action_list_t::reverse_iterator rit;
-       for (rit = list->rbegin(); rit != list->rend(); rit++) {
-               ModelAction *prev = *rit;
-               if (act->is_synchronizing(prev))
-                       return prev;
+       if (type==ATOMIC_READ||type==ATOMIC_WRITE||type==ATOMIC_RMW) {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = obj_map->get_safe_ptr(act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (act->is_synchronizing(prev))
+                               return prev;
+               }
+       } else if (type==ATOMIC_LOCK||type==ATOMIC_TRYLOCK) {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = obj_map->get_safe_ptr(act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (prev->is_success_lock())
+                               return prev;
+               }
+       } else if (type==ATOMIC_UNLOCK) {
+               /* linear search: from most recent to oldest */
+               action_list_t *list = obj_map->get_safe_ptr(act->get_location());
+               action_list_t::reverse_iterator rit;
+               for (rit = list->rbegin(); rit != list->rend(); rit++) {
+                       ModelAction *prev = *rit;
+                       if (prev->is_failed_trylock())
+                               return prev;
+               }
        }
        return NULL;
 }
@@ -203,7 +232,7 @@ void ModelChecker::set_backtracking(ModelAction *act)
 {
        ModelAction *prev;
        Node *node;
-       Thread *t = get_thread(act->get_tid());
+       Thread *t = get_thread(act);
 
        prev = get_last_conflict(act);
        if (prev == NULL)
@@ -245,6 +274,77 @@ ModelAction * ModelChecker::get_next_backtrack()
        return next;
 }
 
+/**
+ * Processes a read or rmw model action.
+ * @param curr is the read model action to process.
+ * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
+ * @return True if processing this read updates the mo_graph.
+ */
+bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
+{
+       uint64_t value;
+       bool updated = false;
+       while (true) {
+               const ModelAction *reads_from = curr->get_node()->get_read_from();
+               if (reads_from != NULL) {
+                       mo_graph->startChanges();
+
+                       value = reads_from->get_value();
+                       bool r_status = false;
+
+                       if (!second_part_of_rmw) {
+                               check_recency(curr,false);
+                               r_status = r_modification_order(curr, reads_from);
+                       }
+
+
+                       if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
+                               mo_graph->rollbackChanges();
+                               too_many_reads = false;
+                               continue;
+                       }
+
+                       curr->read_from(reads_from);
+                       mo_graph->commitChanges();
+                       updated |= r_status;
+               } else if (!second_part_of_rmw) {
+                       /* Read from future value */
+                       value = curr->get_node()->get_future_value();
+                       modelclock_t expiration = curr->get_node()->get_future_value_expiration();
+                       curr->read_from(NULL);
+                       Promise *valuepromise = new Promise(curr, value, expiration);
+                       promises->push_back(valuepromise);
+               }
+               get_thread(curr)->set_return_value(value);
+               return updated;
+       }
+}
+
+/**
+ * Process a write ModelAction
+ * @param curr The ModelAction to process
+ * @return True if the mo_graph was updated or promises were resolved
+ */
+bool ModelChecker::process_write(ModelAction *curr)
+{
+       bool updated_mod_order = w_modification_order(curr);
+       bool updated_promises = resolve_promises(curr);
+
+       if (promises->size() == 0) {
+               for (unsigned int i = 0; i<futurevalues->size(); i++) {
+                       struct PendingFutureValue pfv = (*futurevalues)[i];
+                       if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
+                                       (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
+                               priv->next_backtrack = pfv.act;
+               }
+               futurevalues->resize(0);
+       }
+
+       mo_graph->commitChanges();
+       get_thread(curr)->set_return_value(VALUE_NONE);
+       return updated_mod_order || updated_promises;
+}
+
 /**
  * This is the heart of the model checker routine. It performs model-checking
  * actions corresponding to a given "current action." Among other processes, it
@@ -268,17 +368,20 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
                second_part_of_rmw = true;
                delete curr;
                curr = tmp;
+               compute_promises(curr);
        } else {
-               ModelAction *tmp = node_stack->explore_action(curr);
+               ModelAction *tmp = node_stack->explore_action(curr, scheduler->get_enabled());
                if (tmp) {
                        /* Discard duplicate ModelAction; use action from NodeStack */
                        /* First restore type and order in case of RMW operation */
                        if (curr->is_rmwr())
                                tmp->copy_typeandorder(curr);
-
+                       
                        /* If we have diverged, we need to reset the clock vector. */
                        if (diverge == NULL)
                                tmp->create_cv(get_parent_action(tmp->get_tid()));
+                       
+                       ASSERT(curr->get_location()==tmp->get_location());
 
                        delete curr;
                        curr = tmp;
@@ -296,97 +399,105 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
                }
        }
 
-       /* Assign 'creation' parent */
-       if (curr->get_type() == THREAD_CREATE) {
+       /* Thread specific actions */
+       switch (curr->get_type()) {
+       case THREAD_CREATE: {
                Thread *th = (Thread *)curr->get_location();
                th->set_creation(curr);
-       } else if (curr->get_type() == THREAD_JOIN) {
-               Thread *wait, *join;
-               wait = get_thread(curr->get_tid());
-               join = (Thread *)curr->get_location();
-               if (!join->is_complete())
-                       scheduler->wait(wait, join);
-       } else if (curr->get_type() == THREAD_FINISH) {
-               Thread *th = get_thread(curr->get_tid());
+               break;
+       }
+       case THREAD_JOIN: {
+               Thread *waiting, *blocking;
+               waiting = get_thread(curr);
+               blocking = (Thread *)curr->get_location();
+               if (!blocking->is_complete()) {
+                       blocking->push_wait_list(curr);
+                       scheduler->sleep(waiting);
+               }
+               break;
+       }
+       case THREAD_FINISH: {
+               Thread *th = get_thread(curr);
                while (!th->wait_list_empty()) {
-                       Thread *wake = th->pop_wait_list();
+                       ModelAction *act = th->pop_wait_list();
+                       Thread *wake = get_thread(act);
                        scheduler->wake(wake);
                }
                th->complete();
+               break;
        }
-
-       /* Deal with new thread */
-       if (curr->get_type() == THREAD_START)
+       case THREAD_START: {
                check_promises(NULL, curr->get_cv());
+               break;
+       }
+       default:
+               break;
+       }
 
-       /* Assign reads_from values */
-       Thread *th = get_thread(curr->get_tid());
-       uint64_t value = VALUE_NONE;
-       bool updated = false;
-       if (curr->is_read()) {
-               while(true) {
-                       const ModelAction *reads_from = curr->get_node()->get_read_from();
-                       if (reads_from != NULL) {
-                               value = reads_from->get_value();
-                               /* Assign reads_from, perform release/acquire synchronization */
-                               curr->read_from(reads_from);
-                               if (!second_part_of_rmw)
-                                       check_recency(curr,false);
-
-                               bool r_status=r_modification_order(curr,reads_from);
-
-                               if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
-                                       mo_graph->rollbackChanges();
-                                       too_many_reads=false;
-                                       continue;
-                               }
+       work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 
-                               mo_graph->commitChanges();
-                               updated |= r_status;
-                       } else {
-                               /* Read from future value */
-                               value = curr->get_node()->get_future_value();
-                               curr->read_from(NULL);
-                               Promise *valuepromise = new Promise(curr, value);
-                               promises->push_back(valuepromise);
-                       }
+       while (!work_queue.empty()) {
+               WorkQueueEntry work = work_queue.front();
+               work_queue.pop_front();
+
+               switch (work.type) {
+               case WORK_CHECK_CURR_ACTION: {
+                       ModelAction *act = work.action;
+                       bool updated = false;
+                       if (act->is_read() && process_read(act, second_part_of_rmw))
+                               updated = true;
+
+                       if (act->is_write() && process_write(act))
+                               updated = true;
+
+                       if (updated)
+                               work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
+                       break;
+               }
+               case WORK_CHECK_RELEASE_SEQ:
+                       resolve_release_sequences(work.location, &work_queue);
+                       break;
+               case WORK_CHECK_MO_EDGES:
+                       /** @todo Perform follow-up mo_graph checks */
+               default:
+                       ASSERT(false);
                        break;
                }
-       } else if (curr->is_write()) {
-               if (w_modification_order(curr))
-                       updated = true;
-               if (resolve_promises(curr))
-                       updated = true;
-               mo_graph->commitChanges();
        }
 
-       if (updated)
-               resolve_release_sequences(curr->get_location());
-
-       th->set_return_value(value);
-
        /* Add action to list.  */
        if (!second_part_of_rmw)
                add_action_to_lists(curr);
 
+       check_curr_backtracking(curr);
+
+       set_backtracking(curr);
+
+       return get_next_thread(curr);
+}
+
+void ModelChecker::check_curr_backtracking(ModelAction * curr) {
        Node *currnode = curr->get_node();
        Node *parnode = currnode->get_parent();
 
-       if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
-                 !currnode->future_value_empty() || !currnode->promise_empty())
-               if (!priv->next_backtrack || *curr > *priv->next_backtrack)
-                       priv->next_backtrack = curr;
-
-       set_backtracking(curr);
+       if ((!parnode->backtrack_empty() ||
+                        !currnode->read_from_empty() ||
+                        !currnode->future_value_empty() ||
+                        !currnode->promise_empty())
+                       && (!priv->next_backtrack ||
+                                       *curr > *priv->next_backtrack)) {
+               priv->next_backtrack = curr;
+       }
+}
 
-       /* Do not split atomic actions. */
-       if (curr->is_rmwr())
-               return thread_current();
-       /* The THREAD_CREATE action points to the created Thread */
-       else if (curr->get_type() == THREAD_CREATE)
-               return (Thread *)curr->get_location();
-       else
-               return get_next_replay_thread();
+bool ModelChecker::promises_expired() {
+       for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
+               Promise *promise = (*promises)[promise_index];
+               if (promise->get_expiration()<priv->used_sequence_numbers) {
+                       return true;
+               }
+       }
+       return false;
 }
 
 /** @returns whether the current partial trace must be a prefix of a
@@ -397,7 +508,13 @@ bool ModelChecker::isfeasibleprefix() {
 
 /** @returns whether the current partial trace is feasible. */
 bool ModelChecker::isfeasible() {
-       return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
+       return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
+}
+
+/** @returns whether the current partial trace is feasible other than
+ * multiple RMW reading from the same store. */
+bool ModelChecker::isfeasibleotherthanRMW() {
+       return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 }
 
 /** Returns whether the current completed trace is feasible. */
@@ -410,8 +527,10 @@ ModelAction * ModelChecker::process_rmw(ModelAction *act) {
        int tid = id_to_int(act->get_tid());
        ModelAction *lastread = get_last_action(tid);
        lastread->process_rmw(act);
-       if (act->is_rmw())
+       if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
                mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
+               mo_graph->commitChanges();
+       }
        return lastread;
 }
 
@@ -447,16 +566,16 @@ void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 
                action_list_t::reverse_iterator rit = list->rbegin();
                /* Skip past curr */
-               if (!already_added) {
+               if (already_added) {
                        for (; (*rit) != curr; rit++)
                                ;
                        /* go past curr now */
                        rit++;
                }
 
-               action_list_t::reverse_iterator ritcopy=rit;
+               action_list_t::reverse_iterator ritcopy = rit;
                //See if we have enough reads from the same value
-               int count=0;
+               int count = 0;
                for (; count < params.maxreads; rit++,count++) {
                        if (rit==list->rend())
                                return;
@@ -469,36 +588,37 @@ void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
                                return;
                }
 
-               for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
+               for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
                        //Get write
-                       const ModelAction * write=curr->get_node()->get_read_from_at(i);
+                       const ModelAction * write = curr->get_node()->get_read_from_at(i);
                        //Need a different write
                        if (write==curr->get_reads_from())
                                continue;
 
                        /* 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 = isfeasible();
                        mo_graph->rollbackChanges();
 
                        if (!feasiblereadfrom)
                                continue;
-                       rit=ritcopy;
+                       rit = ritcopy;
 
-                       bool feasiblewrite=true;
+                       bool feasiblewrite = true;
                        //new we need to see if this write works for everyone
 
-                       for (int loop=count;loop>0;loop--,rit++) {
+                       for (int loop = count; loop>0; loop--,rit++) {
                                ModelAction *act=*rit;
-                               bool foundvalue=false;
-                               for(int j=0;j<act->get_node()->get_read_from_size();j++) {
+                               bool foundvalue = false;
+                               for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
                                        if (act->get_node()->get_read_from_at(i)==write) {
-                                               foundvalue=true;
+                                               foundvalue = true;
                                                break;
                                        }
                                }
                                if (!foundvalue) {
-                                       feasiblewrite=false;
+                                       feasiblewrite = false;
                                        break;
                                }
                        }
@@ -511,7 +631,18 @@ void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 }
 
 /**
- * Updates the mo_graph with the constraints imposed from the current read.
+ * Updates the mo_graph with the constraints imposed from the current
+ * read.  
+ *
+ * Basic idea is the following: Go through each other thread and find
+ * the lastest action that happened before our read.  Two cases:
+ *
+ * (1) The action is a write => that write must either occur before
+ * the write we read from or be the write we read from.
+ *
+ * (2) The action is a read => the write that that action read from
+ * must occur before the write we read from or be the same write.
+ *
  * @param curr The current action. Must be a read.
  * @param rf The action that curr reads from. Must be a write.
  * @return True if modification order edges were added; false otherwise
@@ -533,16 +664,19 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf
 
                        /* Include at most one act per-thread that "happens before" curr */
                        if (act->happens_before(curr)) {
-                               if (act->is_read()) {
+                               if (act->is_write()) {
+                                       if (rf != act && act != curr) {
+                                               mo_graph->addEdge(act, rf);
+                                               added = true;
+                                       }
+                               } else {
                                        const ModelAction *prevreadfrom = act->get_reads_from();
                                        if (prevreadfrom != NULL && rf != prevreadfrom) {
                                                mo_graph->addEdge(prevreadfrom, rf);
                                                added = true;
                                        }
-                               } else if (rf != act) {
-                                       mo_graph->addEdge(act, rf);
-                                       added = true;
                                }
+
                                break;
                        }
                }
@@ -551,7 +685,22 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf
        return added;
 }
 
-/** Updates the mo_graph with the constraints imposed from the current read. */
+/** This method fixes up the modification order when we resolve a
+ *  promises.  The basic problem is that actions that occur after the
+ *  read curr could not property add items to the modification order
+ *  for our read.
+ *  
+ *  So for each thread, we find the earliest item that happens after
+ *  the read curr.  This is the item we have to fix up with additional
+ *  constraints.  If that action is write, we add a MO edge between
+ *  the Action rf and that action.  If the action is a read, we add a
+ *  MO edge between the Action rf, and whatever the read accessed.
+ *
+ * @param curr is the read ModelAction that we are fixing up MO edges for.
+ * @param rf is the write ModelAction that curr reads from.
+ *
+ */
+
 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 {
        std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
@@ -590,6 +739,23 @@ void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelActio
 
 /**
  * Updates the mo_graph with the constraints imposed from the current write.
+ *
+ * Basic idea is the following: Go through each other thread and find
+ * the lastest action that happened before our write.  Two cases:
+ *
+ * (1) The action is a write => that write must occur before
+ * the current write
+ *
+ * (2) The action is a read => the write that that action read from
+ * must occur before the current write.
+ *
+ * This method also handles two other issues:
+ *
+ * (I) Sequential Consistency: Making sure that if the current write is
+ * seq_cst, that it occurs after the previous seq_cst write.
+ *
+ * (II) Sending the write back to non-synchronizing reads.
+ *
  * @param curr The current action. Must be a write.
  * @return True if modification order edges were added; false otherwise
  */
@@ -620,10 +786,18 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
 
                        /* Include at most one act per-thread that "happens before" curr */
                        if (act->happens_before(curr)) {
-                               if (act->is_read())
+                               /*
+                                * Note: if act is RMW, just add edge:
+                                *   act --mo--> curr
+                                * The following edge should be handled elsewhere:
+                                *   readfrom(act) --mo--> act
+                                */
+                               if (act->is_write()) {
+                                       //RMW shouldn't have an edge to themselves
+                                       if (act!=curr)
+                                               mo_graph->addEdge(act, curr);
+                               } else if (act->is_read() && act->get_reads_from() != NULL)
                                        mo_graph->addEdge(act->get_reads_from(), curr);
-                               else
-                                       mo_graph->addEdge(act, curr);
                                added = true;
                                break;
                        } else if (act->is_read() && !act->is_synchronizing(curr) &&
@@ -636,9 +810,13 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
                                   =>
                                   that read could potentially read from our write.
                                 */
-                               if (act->get_node()->add_future_value(curr->get_value()) &&
-                                               (!priv->next_backtrack || *act > *priv->next_backtrack))
-                                       priv->next_backtrack = act;
+                               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())) {
+                                               struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
+                                               futurevalues->push_back(pfv);
+                                       }
+                               }
                        }
                }
        }
@@ -646,6 +824,28 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
        return added;
 }
 
+/** Arbitrary reads from the future are not allowed.  Section 29.3
+ * part 9 places some constraints.  This method checks one result of constraint
+ * constraint.  Others require compiler support. */
+
+bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
+       if (!writer->is_rmw())
+               return true;
+
+       if (!reader->is_rmw())
+               return true;
+
+       for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
+               if (search==reader)
+                       return false;
+               if (search->get_tid() == reader->get_tid() &&
+                               search->happens_before(reader))
+                       break;
+       }
+
+       return true;
+}
+
 /**
  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
  * The ModelAction under consideration is expected to be taking part in
@@ -668,13 +868,15 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
  * false otherwise
  */
 bool ModelChecker::release_seq_head(const ModelAction *rf,
-                std::vector<const ModelAction *> *release_heads) const
+                std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 {
-       ASSERT(rf->is_write());
        if (!rf) {
                /* read from future: need to settle this later */
                return false; /* incomplete */
        }
+
+       ASSERT(rf->is_write());
+
        if (rf->is_release())
                release_heads->push_back(rf);
        if (rf->is_rmw()) {
@@ -772,7 +974,7 @@ bool ModelChecker::release_seq_head(const ModelAction *rf,
  * @see ModelChecker::release_seq_head
  */
 void ModelChecker::get_release_seq_heads(ModelAction *act,
-                std::vector<const ModelAction *> *release_heads)
+                std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 {
        const ModelAction *rf = act->get_reads_from();
        bool complete;
@@ -794,9 +996,12 @@ void ModelChecker::get_release_seq_heads(ModelAction *act,
  *
  * @param location The location/object that should be checked for release
  * sequence resolutions
- * @return True if any updates occurred (new synchronization, new mo_graph edges)
+ * @param work_queue The work queue to which to add work items as they are
+ * generated
+ * @return True if any updates occurred (new synchronization, new mo_graph
+ * edges)
  */
-bool ModelChecker::resolve_release_sequences(void *location)
+bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
 {
        std::list<ModelAction *> *list;
        list = lazy_sync_with_release->getptr(location);
@@ -808,7 +1013,7 @@ bool ModelChecker::resolve_release_sequences(void *location)
        while (it != list->end()) {
                ModelAction *act = *it;
                const ModelAction *rf = act->get_reads_from();
-               std::vector<const ModelAction *> release_heads;
+               std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
                bool complete;
                complete = release_seq_head(rf, &release_heads);
                for (unsigned int i = 0; i < release_heads.size(); i++) {
@@ -819,14 +1024,18 @@ bool ModelChecker::resolve_release_sequences(void *location)
                }
 
                if (updated) {
+                       /* Re-check act for mo_graph edges */
+                       work_queue->push_back(MOEdgeWorkEntry(act));
+
                        /* propagate synchronization to later actions */
                        action_list_t::reverse_iterator it = action_trace->rbegin();
                        while ((*it) != act) {
                                ModelAction *propagate = *it;
-                               if (act->happens_before(propagate))
-                                       /** @todo new mo_graph edges along with
-                                        * this synchronization? */
+                               if (act->happens_before(propagate)) {
                                        propagate->synchronize_with(act);
+                                       /* Re-check 'propagate' for mo_graph edges */
+                                       work_queue->push_back(MOEdgeWorkEntry(propagate));
+                               }
                        }
                }
                if (complete) {
@@ -870,10 +1079,11 @@ void ModelChecker::add_action_to_lists(ModelAction *act)
 
 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 {
-       int nthreads = get_num_threads();
-       if ((int)thrd_last_action->size() < nthreads)
-               thrd_last_action->resize(nthreads);
-       return (*thrd_last_action)[id_to_int(tid)];
+       int threadid=id_to_int(tid);
+       if (threadid<(int)thrd_last_action->size())
+               return (*thrd_last_action)[id_to_int(tid)];
+       else
+               return NULL;
 }
 
 /**
@@ -920,19 +1130,26 @@ ClockVector * ModelChecker::get_cv(thread_id_t tid)
 bool ModelChecker::resolve_promises(ModelAction *write)
 {
        bool resolved = false;
+
        for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
                Promise *promise = (*promises)[promise_index];
                if (write->get_node()->get_promise(i)) {
                        ModelAction *read = promise->get_action();
                        read->read_from(write);
+                       if (read->is_rmw()) {
+                               mo_graph->addRMWEdge(write, read);
+                       }
+                       //First fix up the modification order for actions that happened
+                       //before the read
                        r_modification_order(read, write);
+                       //Next fix up the modification order for actions that happened
+                       //after the read.
                        post_r_modification_order(read, write);
                        promises->erase(promises->begin() + promise_index);
                        resolved = true;
                } else
                        promise_index++;
        }
-
        return resolved;
 }
 
@@ -1015,7 +1232,7 @@ 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 (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
+                       if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
                                DEBUG("Adding action to may_read_from:\n");
                                if (DBG_ENABLED()) {
                                        act->print();
@@ -1065,9 +1282,15 @@ void ModelChecker::print_summary()
 {
        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%u",num_executions);
+       mo_graph->dumpGraphToFile(buffername);
+#endif
 
        if (!isfinalfeasible())
                printf("INFEASIBLE EXECUTION!\n");
@@ -1113,24 +1336,23 @@ int ModelChecker::switch_to_master(ModelAction *act)
  * @return Returns true (success) if a step was taken and false otherwise.
  */
 bool ModelChecker::take_step() {
-       Thread *curr, *next;
-
        if (has_asserted())
                return false;
 
-       curr = thread_current();
+       Thread * curr = thread_current();
        if (curr) {
                if (curr->get_state() == THREAD_READY) {
                        ASSERT(priv->current_action);
+
                        priv->nextThread = check_current_action(priv->current_action);
                        priv->current_action = NULL;
-                       if (!curr->is_blocked() && !curr->is_complete())
-                               scheduler->add_thread(curr);
+                       if (curr->is_blocked() || curr->is_complete())
+                               scheduler->remove_thread(curr);
                } else {
                        ASSERT(false);
                }
        }
-       next = scheduler->next_thread(priv->nextThread);
+       Thread * next = scheduler->next_thread(priv->nextThread);
 
        /* Infeasible -> don't take any more steps */
        if (!isfeasible())