model: always re-calculate clock vectors
[c11tester.git] / model.cc
index fba2fe5c3ede9f821e1d54743d3f8ea894ebd017..c4bc693ef5560f646684b3a2cb002e685f4be848 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -20,10 +20,10 @@ ModelChecker *model;
 /** @brief Constructor */
 ModelChecker::ModelChecker(struct model_params params) :
        /* Initialize default scheduler */
+       params(params),
        scheduler(new Scheduler()),
        num_executions(0),
        num_feasible_executions(0),
-       params(params),
        diverge(NULL),
        action_trace(new action_list_t()),
        thread_map(new HashTable<int, Thread *, int>()),
@@ -32,20 +32,19 @@ ModelChecker::ModelChecker(struct model_params params) :
        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 *, action_list_t, uintptr_t, 4>()),
+       pending_acq_rel_seq(new std::vector<ModelAction *>()),
        thrd_last_action(new std::vector<ModelAction *>(1)),
        node_stack(new NodeStack()),
        mo_graph(new CycleGraph()),
        failed_promise(false),
        too_many_reads(false),
-       asserted(false)
+       asserted(false),
+       bad_synchronization(false)
 {
        /* Allocate this "size" on the snapshotting heap */
        priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
        /* First thread created will have id INITIAL_THREAD_ID */
        priv->next_thread_id = INITIAL_THREAD_ID;
-
-       lazy_sync_size = &priv->lazy_sync_size;
 }
 
 /** @brief Destructor */
@@ -64,7 +63,7 @@ ModelChecker::~ModelChecker()
                delete (*promises)[i];
        delete promises;
 
-       delete lazy_sync_with_release;
+       delete pending_acq_rel_seq;
 
        delete thrd_last_action;
        delete node_stack;
@@ -82,23 +81,24 @@ void ModelChecker::reset_to_initial_state()
        node_stack->reset_execution();
        failed_promise = false;
        too_many_reads = false;
+       bad_synchronization = false;
        reset_asserted();
        snapshotObject->backTrackBeforeStep(0);
 }
 
-/** @returns a thread ID for a new Thread */
+/** @return a thread ID for a new Thread */
 thread_id_t ModelChecker::get_next_id()
 {
        return priv->next_thread_id++;
 }
 
-/** @returns the number of user threads created during this execution */
+/** @return the number of user threads created during this execution */
 int ModelChecker::get_num_threads()
 {
        return priv->next_thread_id;
 }
 
-/** @returns a sequence number for a new ModelAction */
+/** @return a sequence number for a new ModelAction */
 modelclock_t ModelChecker::get_next_seq_num()
 {
        return ++priv->used_sequence_numbers;
@@ -243,6 +243,11 @@ ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
        return NULL;
 }
 
+/** This method find backtracking points where we should try to
+ * reorder the parameter ModelAction against.
+ *
+ * @param the ModelAction to find backtracking points for.
+ */
 void ModelChecker::set_backtracking(ModelAction *act)
 {
        Thread *t = get_thread(act);
@@ -254,26 +259,40 @@ void ModelChecker::set_backtracking(ModelAction *act)
 
        int low_tid, high_tid;
        if (node->is_enabled(t)) {
-               low_tid=id_to_int(act->get_tid());
-               high_tid=low_tid+1;
+               low_tid = id_to_int(act->get_tid());
+               high_tid = low_tid+1;
        } else {
-               low_tid=0;
-               high_tid=get_num_threads();
+               low_tid = 0;
+               high_tid = get_num_threads();
        }
-       
-       for(int i=low_tid;i<high_tid;i++) {
-               thread_id_t tid=int_to_id(i);
+
+       for(int i = low_tid; i < high_tid; i++) {
+               thread_id_t tid = int_to_id(i);
                if (!node->is_enabled(tid))
                        continue;
 
                /* Check if this has been explored already */
                if (node->has_been_explored(tid))
                        continue;
-               
+
+               /* See if fairness allows */
+               if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
+                       bool unfair=false;
+                       for(int t=0;t<node->get_num_threads();t++) {
+                               thread_id_t tother=int_to_id(t);
+                               if (node->is_enabled(tother) && node->has_priority(tother)) {
+                                       unfair=true;
+                                       break;
+                               }
+                       }
+                       if (unfair)
+                               continue;
+               }
+
                /* Cache the latest backtracking point */
                if (!priv->next_backtrack || *prev > *priv->next_backtrack)
                        priv->next_backtrack = prev;
-               
+
                /* If this is a new backtracking point, mark the tree */
                if (!node->set_backtrack(tid))
                        continue;
@@ -317,7 +336,7 @@ bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
                        bool r_status = false;
 
                        if (!second_part_of_rmw) {
-                               check_recency(curr);
+                               check_recency(curr, reads_from);
                                r_status = r_modification_order(curr, reads_from);
                        }
 
@@ -344,12 +363,28 @@ bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
        }
 }
 
-void ModelChecker::process_mutex(ModelAction *curr) {
-       std::mutex * mutex=(std::mutex *) curr->get_location();
-       struct std::mutex_state * state=mutex->get_state();
-       switch(curr->get_type()) {
+/**
+ * Processes a lock, trylock, or unlock model action.  @param curr is
+ * the read model action to process.
+ *
+ * The try lock operation checks whether the lock is taken.  If not,
+ * it falls to the normal lock operation case.  If so, it returns
+ * fail.
+ *
+ * The lock operation has already been checked that it is enabled, so
+ * it just grabs the lock and synchronizes with the previous unlock.
+ *
+ * The unlock operation has to re-enable all of the threads that are
+ * waiting on the lock.
+ *
+ * @return True if synchronization was updated; false otherwise
+ */
+bool ModelChecker::process_mutex(ModelAction *curr) {
+       std::mutex *mutex = (std::mutex *)curr->get_location();
+       struct std::mutex_state *state = mutex->get_state();
+       switch (curr->get_type()) {
        case ATOMIC_TRYLOCK: {
-               bool success=!state->islocked;
+               bool success = !state->islocked;
                curr->set_try_lock(success);
                if (!success) {
                        get_thread(curr)->set_return_value(0);
@@ -359,25 +394,27 @@ void 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) {
+               if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
                        printf("Lock access before initialization\n");
                        set_assert();
                }
-               state->islocked=true;
-               ModelAction *unlock=get_last_unlock(curr);
+               state->islocked = true;
+               ModelAction *unlock = get_last_unlock(curr);
                //synchronize with the previous unlock statement
-               if ( unlock != NULL )
+               if (unlock != NULL) {
                        curr->synchronize_with(unlock);
+                       return true;
+               }
                break;
        }
        case ATOMIC_UNLOCK: {
                //unlock the lock
-               state->islocked=false;
+               state->islocked = false;
                //wake up the other threads
-               action_list_t * waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
+               action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
                //activate all the waiting threads
-               for(action_list_t::iterator rit = waiters->begin(); rit!=waiters->end(); rit++) {
-                       add_thread(get_thread((*rit)->get_tid()));
+               for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
+                       scheduler->add_thread(get_thread((*rit)->get_tid()));
                }
                waiters->clear();
                break;
@@ -385,9 +422,9 @@ void ModelChecker::process_mutex(ModelAction *curr) {
        default:
                ASSERT(0);
        }
+       return false;
 }
 
-
 /**
  * Process a write ModelAction
  * @param curr The ModelAction to process
@@ -399,7 +436,7 @@ bool ModelChecker::process_write(ModelAction *curr)
        bool updated_promises = resolve_promises(curr);
 
        if (promises->size() == 0) {
-               for (unsigned int i = 0; i<futurevalues->size(); i++) {
+               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))
@@ -413,6 +450,63 @@ bool ModelChecker::process_write(ModelAction *curr)
        return updated_mod_order || updated_promises;
 }
 
+/**
+ * @brief Process the current action for thread-related activity
+ *
+ * Performs current-action processing for a THREAD_* ModelAction. Proccesses
+ * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
+ * synchronization, etc.  This function is a no-op for non-THREAD actions
+ * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
+ *
+ * @param curr The current action
+ * @return True if synchronization was updated
+ */
+bool ModelChecker::process_thread_action(ModelAction *curr)
+{
+       bool synchronized = false;
+
+       switch (curr->get_type()) {
+       case THREAD_CREATE: {
+               Thread *th = (Thread *)curr->get_location();
+               th->set_creation(curr);
+               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);
+               } else {
+                       do_complete_join(curr);
+                       synchronized = true;
+               }
+               break;
+       }
+       case THREAD_FINISH: {
+               Thread *th = get_thread(curr);
+               while (!th->wait_list_empty()) {
+                       ModelAction *act = th->pop_wait_list();
+                       Thread *wake = get_thread(act);
+                       scheduler->wake(wake);
+                       do_complete_join(act);
+                       synchronized = true;
+               }
+               th->complete();
+               break;
+       }
+       case THREAD_START: {
+               check_promises(NULL, curr->get_cv());
+               break;
+       }
+       default:
+               break;
+       }
+
+       return synchronized;
+}
+
 /**
  * Initialize the current action by performing one or more of the following
  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
@@ -431,7 +525,9 @@ ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
        if (curr->is_rmwc() || curr->is_rmw()) {
                newcurr = process_rmw(curr);
                delete curr;
-               compute_promises(newcurr);
+
+               if (newcurr->is_rmw())
+                       compute_promises(newcurr);
                return newcurr;
        }
 
@@ -441,15 +537,13 @@ ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
                if (curr->is_rmwr())
                        newcurr->copy_typeandorder(curr);
 
-               ASSERT(curr->get_location()==newcurr->get_location());
+               ASSERT(curr->get_location() == newcurr->get_location());
                newcurr->copy_from_new(curr);
 
                /* Discard duplicate ModelAction; use action from NodeStack */
                delete curr;
 
-               /* If we have diverged, we need to reset the clock vector. */
-               if (diverge == NULL)
-                       newcurr->create_cv(get_parent_action(newcurr->get_tid()));
+               newcurr->create_cv(get_parent_action(newcurr->get_tid()));
        } else {
                newcurr = curr;
                /*
@@ -463,9 +557,16 @@ ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
        return newcurr;
 }
 
+/**
+ * This method checks whether a model action is enabled at the given point.
+ * At this point, it checks whether a lock operation would be successful at this point.
+ * If not, it puts the thread in a waiter list.
+ * @param curr is the ModelAction to check whether it is enabled.
+ * @return a bool that indicates whether the action is enabled.
+ */
 bool ModelChecker::check_action_enabled(ModelAction *curr) {
        if (curr->is_lock()) {
-               std::mutex * lock=(std::mutex *) curr->get_location();
+               std::mutex * lock = (std::mutex *)curr->get_location();
                struct std::mutex_state * state = lock->get_state();
                if (state->islocked) {
                        //Stick the action in the appropriate waiting queue
@@ -496,8 +597,8 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
        bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 
        if (!check_action_enabled(curr)) {
-               //we'll make the execution look like we chose to run this action
-               //much later...when a lock is actually available to relese
+               /* Make the execution look like we chose to run this action
+                * much later, when a lock is actually available to release */
                get_current_thread()->set_pending(curr);
                remove_thread(get_current_thread());
                return get_next_thread(NULL);
@@ -514,44 +615,7 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
                build_reads_from_past(curr);
        curr = newcurr;
 
-       /* Thread specific actions */
-       switch (curr->get_type()) {
-       case THREAD_CREATE: {
-               Thread *th = (Thread *)curr->get_location();
-               th->set_creation(curr);
-               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);
-               } else {
-                       do_complete_join(curr);
-               }
-               break;
-       }
-       case THREAD_FINISH: {
-               Thread *th = get_thread(curr);
-               while (!th->wait_list_empty()) {
-                       ModelAction *act = th->pop_wait_list();
-                       Thread *wake = get_thread(act);
-                       scheduler->wake(wake);
-                       do_complete_join(act);
-               }
-               th->complete();
-               break;
-       }
-       case THREAD_START: {
-               check_promises(NULL, curr->get_cv());
-               break;
-       }
-       default:
-               break;
-       }
-
+       /* Initialize work_queue with the "current action" work */
        work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 
        while (!work_queue.empty()) {
@@ -561,17 +625,24 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
                switch (work.type) {
                case WORK_CHECK_CURR_ACTION: {
                        ModelAction *act = work.action;
-                       bool updated = false;
+                       bool update = false; /* update this location's release seq's */
+                       bool update_all = false; /* update all release seq's */
+
+                       if (process_thread_action(curr))
+                               update_all = true;
+
                        if (act->is_read() && process_read(act, second_part_of_rmw))
-                               updated = true;
+                               update = true;
 
                        if (act->is_write() && process_write(act))
-                               updated = true;
+                               update = true;
 
-                       if (act->is_mutex_op()
-                               process_mutex(act);
+                       if (act->is_mutex_op() && process_mutex(act))
+                               update_all = true;
 
-                       if (updated)
+                       if (update_all)
+                               work_queue.push_back(CheckRelSeqWorkEntry(NULL));
+                       else if (update)
                                work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
                        break;
                }
@@ -591,6 +662,7 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
                                if (w_modification_order(act))
                                        updated = true;
                        }
+                       mo_graph->commitChanges();
 
                        if (updated)
                                work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
@@ -646,18 +718,21 @@ bool ModelChecker::promises_expired() {
        return false;
 }
 
-/** @returns whether the current partial trace must be a prefix of a
+/** @return whether the current partial trace must be a prefix of a
  * feasible trace. */
 bool ModelChecker::isfeasibleprefix() {
-       return promises->size() == 0 && *lazy_sync_size == 0;
+       return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
 }
 
-/** @returns whether the current partial trace is feasible. */
+/** @return whether the current partial trace is feasible. */
 bool ModelChecker::isfeasible() {
+       if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
+               DEBUG("Infeasible: RMW violation\n");
+
        return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 }
 
-/** @returns whether the current partial trace is feasible other than
+/** @return whether the current partial trace is feasible other than
  * multiple RMW reading from the same store. */
 bool ModelChecker::isfeasibleotherthanRMW() {
        if (DBG_ENABLED()) {
@@ -667,10 +742,12 @@ bool ModelChecker::isfeasibleotherthanRMW() {
                        DEBUG("Infeasible: failed promise\n");
                if (too_many_reads)
                        DEBUG("Infeasible: too many reads\n");
+               if (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 && !promises_expired();
+       return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
 }
 
 /** Returns whether the current completed trace is feasible. */
@@ -704,23 +781,21 @@ ModelAction * ModelChecker::process_rmw(ModelAction *act) {
  *
  * If so, we decide that the execution is no longer feasible.
  */
-void ModelChecker::check_recency(ModelAction *curr) {
+void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
        if (params.maxreads != 0) {
+
                if (curr->get_node()->get_read_from_size() <= 1)
                        return;
-
                //Must make sure that execution is currently feasible...  We could
                //accidentally clear by rolling back
                if (!isfeasible())
                        return;
-
                std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
                int tid = id_to_int(curr->get_tid());
 
                /* Skip checks */
                if ((int)thrd_lists->size() <= tid)
                        return;
-
                action_list_t *list = &(*thrd_lists)[tid];
 
                action_list_t::reverse_iterator rit = list->rbegin();
@@ -739,17 +814,18 @@ void ModelChecker::check_recency(ModelAction *curr) {
                        ModelAction *act = *rit;
                        if (!act->is_read())
                                return;
-                       if (act->get_reads_from() != curr->get_reads_from())
+                       
+                       if (act->get_reads_from() != rf)
                                return;
                        if (act->get_node()->get_read_from_size() <= 1)
                                return;
                }
-
                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);
+
                        //Need a different write
-                       if (write==curr->get_reads_from())
+                       if (write==rf)
                                continue;
 
                        /* Test to see whether this is a feasible write to read from*/
@@ -789,7 +865,7 @@ void ModelChecker::check_recency(ModelAction *curr) {
 
 /**
  * Updates the mo_graph with the constraints imposed from the current
- * read.  
+ * read.
  *
  * Basic idea is the following: Go through each other thread and find
  * the lastest action that happened before our read.  Two cases:
@@ -848,7 +924,7 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf
  *  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
@@ -859,7 +935,6 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf
  * @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());
@@ -873,10 +948,10 @@ void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelActio
                action_list_t::reverse_iterator rit;
                ModelAction *lastact = NULL;
 
-               /* Find last action that happens after curr */
+               /* Find last action that happens after curr that is either not curr or a rmw */
                for (rit = list->rbegin(); rit != list->rend(); rit++) {
                        ModelAction *act = *rit;
-                       if (curr->happens_before(act)) {
+                       if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
                                lastact = act;
                        } else
                                break;
@@ -884,12 +959,25 @@ void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelActio
 
                        /* Include at most one act per-thread that "happens before" curr */
                if (lastact != NULL) {
-                       if (lastact->is_read()) {
+                       if (lastact==curr) {
+                               //Case 1: The resolved read is a RMW, and we need to make sure
+                               //that the write portion of the RMW mod order after rf
+
+                               mo_graph->addEdge(rf, lastact);
+                       } else if (lastact->is_read()) {
+                               //Case 2: The resolved read is a normal read and the next
+                               //operation is a read, and we need to make sure the value read
+                               //is mod ordered after rf
+
                                const ModelAction *postreadfrom = lastact->get_reads_from();
                                if (postreadfrom != NULL&&rf != postreadfrom)
                                        mo_graph->addEdge(rf, postreadfrom);
-                       } else if (rf != lastact) {
-                               mo_graph->addEdge(rf, lastact);
+                       } else {
+                               //Case 3: The resolved read is a normal read and the next
+                               //operation is a write, and we need to make sure that the
+                               //write is mod ordered after rf
+                               if (lastact!=rf)
+                                       mo_graph->addEdge(rf, lastact);
                        }
                        break;
                }
@@ -984,7 +1072,7 @@ 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())) {
+                                                       (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);
                                        }
@@ -999,7 +1087,6 @@ bool ModelChecker::w_modification_order(ModelAction *curr)
 /** 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;
@@ -1008,7 +1095,7 @@ bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, con
                return true;
 
        for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
-               if (search==reader)
+               if (search == reader)
                        return false;
                if (search->get_tid() == reader->get_tid() &&
                                search->happens_before(reader))
@@ -1041,24 +1128,36 @@ bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, con
  */
 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
 {
-       if (!rf) {
-               /* read from future: need to settle this later */
-               return false; /* incomplete */
-       }
+       /* Only check for release sequences if there are no cycles */
+       if (mo_graph->checkForCycles())
+               return false;
 
-       ASSERT(rf->is_write());
+       while (rf) {
+               ASSERT(rf->is_write());
+
+               if (rf->is_release())
+                       release_heads->push_back(rf);
+               if (!rf->is_rmw())
+                       break; /* End of RMW chain */
 
-       if (rf->is_release())
-               release_heads->push_back(rf);
-       if (rf->is_rmw()) {
-               /* We need a RMW action that is both an acquire and release to stop */
                /** @todo Need to be smarter here...  In the linux lock
                 * example, this will run to the beginning of the program for
                 * every acquire. */
+               /** @todo The way to be smarter here is to keep going until 1
+                * thread has a release preceded by an acquire and you've seen
+                *       both. */
+
+               /* acq_rel RMW is a sufficient stopping condition */
                if (rf->is_acquire() && rf->is_release())
                        return true; /* complete */
-               return release_seq_head(rf->get_reads_from(), release_heads);
+
+               rf = rf->get_reads_from();
+       };
+       if (!rf) {
+               /* read from future: need to settle this later */
+               return false; /* incomplete */
        }
+
        if (rf->is_release())
                return true; /* complete */
 
@@ -1095,10 +1194,13 @@ bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *rel
                 * the release seq? */
                bool future_ordered = false;
 
+               ModelAction *last = get_last_action(int_to_id(i));
+               if (last && (rf->happens_before(last) ||
+                               last->get_type() == THREAD_FINISH))
+                       future_ordered = true;
+
                for (rit = list->rbegin(); rit != list->rend(); rit++) {
                        const ModelAction *act = *rit;
-                       if (!act->is_write())
-                               continue;
                        /* Reach synchronization -> this thread is complete */
                        if (act->happens_before(release))
                                break;
@@ -1107,6 +1209,10 @@ bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *rel
                                continue;
                        }
 
+                       /* Only writes can break release sequences */
+                       if (!act->is_write())
+                               continue;
+
                        /* Check modification order */
                        if (mo_graph->checkReachable(rf, act)) {
                                /* rf --mo--> act */
@@ -1151,10 +1257,7 @@ void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *rel
        complete = release_seq_head(rf, release_heads);
        if (!complete) {
                /* add act to 'lazy checking' list */
-               action_list_t *list;
-               list = lazy_sync_with_release->get_safe_ptr(act->get_location());
-               list->push_back(act);
-               (*lazy_sync_size)++;
+               pending_acq_rel_seq->push_back(act);
        }
 }
 
@@ -1165,7 +1268,7 @@ void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *rel
  * modification order information is present at the time an action occurs.
  *
  * @param location The location/object that should be checked for release
- * sequence resolutions
+ * sequence resolutions. A NULL value means to check all locations.
  * @param work_queue The work queue to which to add work items as they are
  * generated
  * @return True if any updates occurred (new synchronization, new mo_graph
@@ -1173,23 +1276,27 @@ void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *rel
  */
 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
 {
-       action_list_t *list;
-       list = lazy_sync_with_release->getptr(location);
-       if (!list)
-               return false;
-
        bool updated = false;
-       action_list_t::iterator it = list->begin();
-       while (it != list->end()) {
+       std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
+       while (it != pending_acq_rel_seq->end()) {
                ModelAction *act = *it;
+
+               /* Only resolve sequences on the given location, if provided */
+               if (location && act->get_location() != location) {
+                       it++;
+                       continue;
+               }
+
                const ModelAction *rf = act->get_reads_from();
                rel_heads_list_t release_heads;
                bool complete;
                complete = release_seq_head(rf, &release_heads);
                for (unsigned int i = 0; i < release_heads.size(); i++) {
                        if (!act->has_synchronized_with(release_heads[i])) {
-                               updated = true;
-                               act->synchronize_with(release_heads[i]);
+                               if (act->synchronize_with(release_heads[i]))
+                                       updated = true;
+                               else
+                                       set_bad_synchronization();
                        }
                }
 
@@ -1198,9 +1305,9 @@ bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_
                        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;
+                       action_list_t::reverse_iterator rit = action_trace->rbegin();
+                       for (; (*rit) != act; rit++) {
+                               ModelAction *propagate = *rit;
                                if (act->happens_before(propagate)) {
                                        propagate->synchronize_with(act);
                                        /* Re-check 'propagate' for mo_graph edges */
@@ -1208,10 +1315,9 @@ bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_
                                }
                        }
                }
-               if (complete) {
-                       it = list->erase(it);
-                       (*lazy_sync_size)--;
-               } else
+               if (complete)
+                       it = pending_acq_rel_seq->erase(it);
+               else
                        it++;
        }
 
@@ -1247,10 +1353,15 @@ void ModelChecker::add_action_to_lists(ModelAction *act)
        (*thrd_last_action)[tid] = act;
 }
 
-ModelAction * ModelChecker::get_last_action(thread_id_t tid)
+/**
+ * @brief Get the last action performed by a particular Thread
+ * @param tid The thread ID of the Thread in question
+ * @return The last action in the thread
+ */
+ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
 {
-       int threadid=id_to_int(tid);
-       if (threadid<(int)thrd_last_action->size())
+       int threadid = id_to_int(tid);
+       if (threadid < (int)thrd_last_action->size())
                return (*thrd_last_action)[id_to_int(tid)];
        else
                return NULL;
@@ -1264,7 +1375,7 @@ ModelAction * ModelChecker::get_last_action(thread_id_t tid)
  * check
  * @return The last seq_cst write
  */
-ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
+ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
 {
        void *location = curr->get_location();
        action_list_t *list = obj_map->get_safe_ptr(location);
@@ -1276,11 +1387,19 @@ ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
        return NULL;
 }
 
-ModelAction * ModelChecker::get_last_unlock(ModelAction *curr)
+/**
+ * Gets the last unlock operation performed on a particular mutex (i.e., memory
+ * location). This function identifies the mutex according to the current
+ * action, which is presumed to perform on the same mutex.
+ * @param curr The current ModelAction; also denotes the object location to
+ * check
+ * @return The last unlock operation
+ */
+ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
 {
        void *location = curr->get_location();
        action_list_t *list = obj_map->get_safe_ptr(location);
-       /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
+       /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
        action_list_t::reverse_iterator rit;
        for (rit = list->rbegin(); rit != list->rend(); rit++)
                if ((*rit)->is_unlock())
@@ -1320,16 +1439,19 @@ bool ModelChecker::resolve_promises(ModelAction *write)
                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);
                        }
+                       read->read_from(write);
                        //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);
+                       //Make sure the promise's value matches the write's value
+                       ASSERT(promise->get_value() == write->get_value());
+
                        promises->erase(promises->begin() + promise_index);
                        resolved = true;
                } else
@@ -1417,7 +1539,7 @@ 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 (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || 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();
@@ -1473,7 +1595,7 @@ void ModelChecker::print_summary()
 #if SUPPORT_MOD_ORDER_DUMP
        scheduler->print();
        char buffername[100];
-       sprintf(buffername, "exec%u",num_executions);
+       sprintf(buffername, "exec%04u", num_executions);
        mo_graph->dumpGraphToFile(buffername);
 #endif
 
@@ -1494,6 +1616,10 @@ void ModelChecker::add_thread(Thread *t)
        scheduler->add_thread(t);
 }
 
+/**
+ * Removes a thread from the scheduler. 
+ * @param the thread to remove.
+ */
 void ModelChecker::remove_thread(Thread *t)
 {
        scheduler->remove_thread(t);
@@ -1531,6 +1657,7 @@ bool ModelChecker::take_step() {
 
                        priv->nextThread = check_current_action(priv->current_action);
                        priv->current_action = NULL;
+
                        if (curr->is_blocked() || curr->is_complete())
                                scheduler->remove_thread(curr);
                } else {