8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
15 #include "threads-model.h"
17 #define INITIAL_THREAD_ID 0
21 /** @brief Constructor */
22 ModelChecker::ModelChecker(struct model_params params) :
23 /* Initialize default scheduler */
25 scheduler(new Scheduler()),
27 num_feasible_executions(0),
29 earliest_diverge(NULL),
30 action_trace(new action_list_t()),
31 thread_map(new HashTable<int, Thread *, int>()),
32 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
33 lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
34 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
35 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
36 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
37 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
38 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
39 node_stack(new NodeStack()),
40 mo_graph(new CycleGraph()),
41 failed_promise(false),
42 too_many_reads(false),
44 bad_synchronization(false)
46 /* Allocate this "size" on the snapshotting heap */
47 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
48 /* First thread created will have id INITIAL_THREAD_ID */
49 priv->next_thread_id = INITIAL_THREAD_ID;
51 /* Initialize a model-checker thread, for special ModelActions */
52 model_thread = new Thread(get_next_id());
53 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
56 /** @brief Destructor */
57 ModelChecker::~ModelChecker()
59 for (unsigned int i = 0; i < get_num_threads(); i++)
60 delete thread_map->get(i);
65 delete lock_waiters_map;
68 for (unsigned int i = 0; i < promises->size(); i++)
69 delete (*promises)[i];
72 delete pending_rel_seqs;
74 delete thrd_last_action;
81 * Restores user program to initial state and resets all model-checker data
84 void ModelChecker::reset_to_initial_state()
86 DEBUG("+++ Resetting to initial state +++\n");
87 node_stack->reset_execution();
88 failed_promise = false;
89 too_many_reads = false;
90 bad_synchronization = false;
92 snapshotObject->backTrackBeforeStep(0);
95 /** @return a thread ID for a new Thread */
96 thread_id_t ModelChecker::get_next_id()
98 return priv->next_thread_id++;
101 /** @return the number of user threads created during this execution */
102 unsigned int ModelChecker::get_num_threads()
104 return priv->next_thread_id;
107 /** @return The currently executing Thread. */
108 Thread * ModelChecker::get_current_thread()
110 return scheduler->get_current_thread();
113 /** @return a sequence number for a new ModelAction */
114 modelclock_t ModelChecker::get_next_seq_num()
116 return ++priv->used_sequence_numbers;
120 * @brief Choose the next thread to execute.
122 * This function chooses the next thread that should execute. It can force the
123 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
124 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
125 * The model-checker may have no preference regarding the next thread (i.e.,
126 * when exploring a new execution ordering), in which case this will return
128 * @param curr The current ModelAction. This action might guide the choice of
130 * @return The next thread to run. If the model-checker has no preference, NULL.
132 Thread * ModelChecker::get_next_thread(ModelAction *curr)
137 /* Do not split atomic actions. */
139 return thread_current();
140 /* The THREAD_CREATE action points to the created Thread */
141 else if (curr->get_type() == THREAD_CREATE)
142 return (Thread *)curr->get_location();
145 /* Have we completed exploring the preselected path? */
149 /* Else, we are trying to replay an execution */
150 ModelAction *next = node_stack->get_next()->get_action();
152 if (next == diverge) {
153 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
154 earliest_diverge=diverge;
156 Node *nextnode = next->get_node();
157 Node *prevnode = nextnode->get_parent();
158 scheduler->update_sleep_set(prevnode);
160 /* Reached divergence point */
161 if (nextnode->increment_promise()) {
162 /* The next node will try to satisfy a different set of promises. */
163 tid = next->get_tid();
164 node_stack->pop_restofstack(2);
165 } else if (nextnode->increment_read_from()) {
166 /* The next node will read from a different value. */
167 tid = next->get_tid();
168 node_stack->pop_restofstack(2);
169 } else if (nextnode->increment_future_value()) {
170 /* The next node will try to read from a different future value. */
171 tid = next->get_tid();
172 node_stack->pop_restofstack(2);
173 } else if (nextnode->increment_relseq_break()) {
174 /* The next node will try to resolve a release sequence differently */
175 tid = next->get_tid();
176 node_stack->pop_restofstack(2);
178 /* Make a different thread execute for next step */
179 scheduler->add_sleep(thread_map->get(id_to_int(next->get_tid())));
180 tid = prevnode->get_next_backtrack();
181 /* Make sure the backtracked thread isn't sleeping. */
182 node_stack->pop_restofstack(1);
183 if (diverge==earliest_diverge) {
184 earliest_diverge=prevnode->get_action();
187 /* The correct sleep set is in the parent node. */
190 DEBUG("*** Divergence point ***\n");
194 tid = next->get_tid();
196 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
197 ASSERT(tid != THREAD_ID_T_NONE);
198 return thread_map->get(id_to_int(tid));
202 * We need to know what the next actions of all threads in the sleep
203 * set will be. This method computes them and stores the actions at
204 * the corresponding thread object's pending action.
207 void ModelChecker::execute_sleep_set() {
208 for(unsigned int i=0;i<get_num_threads();i++) {
209 thread_id_t tid=int_to_id(i);
210 Thread *thr=get_thread(tid);
211 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
212 thr->set_state(THREAD_RUNNING);
213 scheduler->next_thread(thr);
214 Thread::swap(&system_context, thr);
215 priv->current_action->set_sleep_flag();
216 thr->set_pending(priv->current_action);
219 priv->current_action = NULL;
222 void ModelChecker::wake_up_sleeping_actions(ModelAction * curr) {
223 for(unsigned int i=0;i<get_num_threads();i++) {
224 thread_id_t tid=int_to_id(i);
225 Thread *thr=get_thread(tid);
226 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
227 ModelAction *pending_act=thr->get_pending();
228 if (pending_act->could_synchronize_with(curr)) {
229 //Remove this thread from sleep set
230 scheduler->remove_sleep(thr);
237 * Queries the model-checker for more executions to explore and, if one
238 * exists, resets the model-checker state to execute a new execution.
240 * @return If there are more executions to explore, return true. Otherwise,
243 bool ModelChecker::next_execution()
249 if (isfinalfeasible()) {
250 printf("Earliest divergence point since last feasible execution:\n");
251 if (earliest_diverge)
252 earliest_diverge->print();
254 printf("(Not set)\n");
256 earliest_diverge = NULL;
257 num_feasible_executions++;
260 DEBUG("Number of acquires waiting on pending release sequences: %zu\n",
261 pending_rel_seqs->size());
264 if (isfinalfeasible() || (params.bound != 0 && priv->used_sequence_numbers > params.bound ) || DBG_ENABLED() )
267 if ((diverge = get_next_backtrack()) == NULL)
271 printf("Next execution will diverge at:\n");
275 reset_to_initial_state();
279 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
281 switch (act->get_type()) {
285 /* linear search: from most recent to oldest */
286 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
287 action_list_t::reverse_iterator rit;
288 for (rit = list->rbegin(); rit != list->rend(); rit++) {
289 ModelAction *prev = *rit;
290 if (prev->could_synchronize_with(act))
296 case ATOMIC_TRYLOCK: {
297 /* linear search: from most recent to oldest */
298 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
299 action_list_t::reverse_iterator rit;
300 for (rit = list->rbegin(); rit != list->rend(); rit++) {
301 ModelAction *prev = *rit;
302 if (act->is_conflicting_lock(prev))
307 case ATOMIC_UNLOCK: {
308 /* linear search: from most recent to oldest */
309 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
310 action_list_t::reverse_iterator rit;
311 for (rit = list->rbegin(); rit != list->rend(); rit++) {
312 ModelAction *prev = *rit;
313 if (!act->same_thread(prev)&&prev->is_failed_trylock())
324 /** This method finds backtracking points where we should try to
325 * reorder the parameter ModelAction against.
327 * @param the ModelAction to find backtracking points for.
329 void ModelChecker::set_backtracking(ModelAction *act)
331 Thread *t = get_thread(act);
332 ModelAction * prev = get_last_conflict(act);
336 Node * node = prev->get_node()->get_parent();
338 int low_tid, high_tid;
339 if (node->is_enabled(t)) {
340 low_tid = id_to_int(act->get_tid());
341 high_tid = low_tid+1;
344 high_tid = get_num_threads();
347 for(int i = low_tid; i < high_tid; i++) {
348 thread_id_t tid = int_to_id(i);
350 /* Don't backtrack into a point where the thread is disabled or sleeping. */
351 if (node->get_enabled_array()[i]!=THREAD_ENABLED)
354 /* Check if this has been explored already */
355 if (node->has_been_explored(tid))
358 /* See if fairness allows */
359 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
361 for(int t=0;t<node->get_num_threads();t++) {
362 thread_id_t tother=int_to_id(t);
363 if (node->is_enabled(tother) && node->has_priority(tother)) {
371 /* Cache the latest backtracking point */
372 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
373 priv->next_backtrack = prev;
375 /* If this is a new backtracking point, mark the tree */
376 if (!node->set_backtrack(tid))
378 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
379 id_to_int(prev->get_tid()),
380 id_to_int(t->get_id()));
389 * Returns last backtracking point. The model checker will explore a different
390 * path for this point in the next execution.
391 * @return The ModelAction at which the next execution should diverge.
393 ModelAction * ModelChecker::get_next_backtrack()
395 ModelAction *next = priv->next_backtrack;
396 priv->next_backtrack = NULL;
401 * Processes a read or rmw model action.
402 * @param curr is the read model action to process.
403 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
404 * @return True if processing this read updates the mo_graph.
406 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
409 bool updated = false;
411 const ModelAction *reads_from = curr->get_node()->get_read_from();
412 if (reads_from != NULL) {
413 mo_graph->startChanges();
415 value = reads_from->get_value();
416 bool r_status = false;
418 if (!second_part_of_rmw) {
419 check_recency(curr, reads_from);
420 r_status = r_modification_order(curr, reads_from);
424 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
425 mo_graph->rollbackChanges();
426 too_many_reads = false;
430 curr->read_from(reads_from);
431 mo_graph->commitChanges();
432 mo_check_promises(curr->get_tid(), reads_from);
435 } else if (!second_part_of_rmw) {
436 /* Read from future value */
437 value = curr->get_node()->get_future_value();
438 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
439 curr->read_from(NULL);
440 Promise *valuepromise = new Promise(curr, value, expiration);
441 promises->push_back(valuepromise);
443 get_thread(curr)->set_return_value(value);
449 * Processes a lock, trylock, or unlock model action. @param curr is
450 * the read model action to process.
452 * The try lock operation checks whether the lock is taken. If not,
453 * it falls to the normal lock operation case. If so, it returns
456 * The lock operation has already been checked that it is enabled, so
457 * it just grabs the lock and synchronizes with the previous unlock.
459 * The unlock operation has to re-enable all of the threads that are
460 * waiting on the lock.
462 * @return True if synchronization was updated; false otherwise
464 bool ModelChecker::process_mutex(ModelAction *curr) {
465 std::mutex *mutex = (std::mutex *)curr->get_location();
466 struct std::mutex_state *state = mutex->get_state();
467 switch (curr->get_type()) {
468 case ATOMIC_TRYLOCK: {
469 bool success = !state->islocked;
470 curr->set_try_lock(success);
472 get_thread(curr)->set_return_value(0);
475 get_thread(curr)->set_return_value(1);
477 //otherwise fall into the lock case
479 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
480 printf("Lock access before initialization\n");
483 state->islocked = true;
484 ModelAction *unlock = get_last_unlock(curr);
485 //synchronize with the previous unlock statement
486 if (unlock != NULL) {
487 curr->synchronize_with(unlock);
492 case ATOMIC_UNLOCK: {
494 state->islocked = false;
495 //wake up the other threads
496 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
497 //activate all the waiting threads
498 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
499 scheduler->wake(get_thread(*rit));
511 * Process a write ModelAction
512 * @param curr The ModelAction to process
513 * @return True if the mo_graph was updated or promises were resolved
515 bool ModelChecker::process_write(ModelAction *curr)
517 bool updated_mod_order = w_modification_order(curr);
518 bool updated_promises = resolve_promises(curr);
520 if (promises->size() == 0) {
521 for (unsigned int i = 0; i < futurevalues->size(); i++) {
522 struct PendingFutureValue pfv = (*futurevalues)[i];
523 //Do more ambitious checks now that mo is more complete
524 if (mo_may_allow(pfv.writer, pfv.act)&&
525 pfv.act->get_node()->add_future_value(pfv.writer->get_value(), pfv.writer->get_seq_number()+params.maxfuturedelay) &&
526 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
527 priv->next_backtrack = pfv.act;
529 futurevalues->resize(0);
532 mo_graph->commitChanges();
533 mo_check_promises(curr->get_tid(), curr);
535 get_thread(curr)->set_return_value(VALUE_NONE);
536 return updated_mod_order || updated_promises;
540 * @brief Process the current action for thread-related activity
542 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
543 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
544 * synchronization, etc. This function is a no-op for non-THREAD actions
545 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
547 * @param curr The current action
548 * @return True if synchronization was updated or a thread completed
550 bool ModelChecker::process_thread_action(ModelAction *curr)
552 bool updated = false;
554 switch (curr->get_type()) {
555 case THREAD_CREATE: {
556 Thread *th = (Thread *)curr->get_location();
557 th->set_creation(curr);
561 Thread *blocking = (Thread *)curr->get_location();
562 ModelAction *act = get_last_action(blocking->get_id());
563 curr->synchronize_with(act);
564 updated = true; /* trigger rel-seq checks */
567 case THREAD_FINISH: {
568 Thread *th = get_thread(curr);
569 while (!th->wait_list_empty()) {
570 ModelAction *act = th->pop_wait_list();
571 scheduler->wake(get_thread(act));
574 updated = true; /* trigger rel-seq checks */
578 check_promises(curr->get_tid(), NULL, curr->get_cv());
589 * @brief Process the current action for release sequence fixup activity
591 * Performs model-checker release sequence fixups for the current action,
592 * forcing a single pending release sequence to break (with a given, potential
593 * "loose" write) or to complete (i.e., synchronize). If a pending release
594 * sequence forms a complete release sequence, then we must perform the fixup
595 * synchronization, mo_graph additions, etc.
597 * @param curr The current action; must be a release sequence fixup action
598 * @param work_queue The work queue to which to add work items as they are
601 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
603 const ModelAction *write = curr->get_node()->get_relseq_break();
604 struct release_seq *sequence = pending_rel_seqs->back();
605 pending_rel_seqs->pop_back();
607 ModelAction *acquire = sequence->acquire;
608 const ModelAction *rf = sequence->rf;
609 const ModelAction *release = sequence->release;
613 ASSERT(release->same_thread(rf));
617 * @todo Forcing a synchronization requires that we set
618 * modification order constraints. For instance, we can't allow
619 * a fixup sequence in which two separate read-acquire
620 * operations read from the same sequence, where the first one
621 * synchronizes and the other doesn't. Essentially, we can't
622 * allow any writes to insert themselves between 'release' and
626 /* Must synchronize */
627 if (!acquire->synchronize_with(release)) {
628 set_bad_synchronization();
631 /* Re-check all pending release sequences */
632 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
633 /* Re-check act for mo_graph edges */
634 work_queue->push_back(MOEdgeWorkEntry(acquire));
636 /* propagate synchronization to later actions */
637 action_list_t::reverse_iterator rit = action_trace->rbegin();
638 for (; (*rit) != acquire; rit++) {
639 ModelAction *propagate = *rit;
640 if (acquire->happens_before(propagate)) {
641 propagate->synchronize_with(acquire);
642 /* Re-check 'propagate' for mo_graph edges */
643 work_queue->push_back(MOEdgeWorkEntry(propagate));
647 /* Break release sequence with new edges:
648 * release --mo--> write --mo--> rf */
649 mo_graph->addEdge(release, write);
650 mo_graph->addEdge(write, rf);
653 /* See if we have realized a data race */
654 if (checkDataRaces())
659 * Initialize the current action by performing one or more of the following
660 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
661 * in the NodeStack, manipulating backtracking sets, allocating and
662 * initializing clock vectors, and computing the promises to fulfill.
664 * @param curr The current action, as passed from the user context; may be
665 * freed/invalidated after the execution of this function
666 * @return The current action, as processed by the ModelChecker. Is only the
667 * same as the parameter @a curr if this is a newly-explored action.
669 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
671 ModelAction *newcurr;
673 if (curr->is_rmwc() || curr->is_rmw()) {
674 newcurr = process_rmw(curr);
677 if (newcurr->is_rmw())
678 compute_promises(newcurr);
682 curr->set_seq_number(get_next_seq_num());
684 newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
686 /* First restore type and order in case of RMW operation */
688 newcurr->copy_typeandorder(curr);
690 ASSERT(curr->get_location() == newcurr->get_location());
691 newcurr->copy_from_new(curr);
693 /* Discard duplicate ModelAction; use action from NodeStack */
696 /* Always compute new clock vector */
697 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
701 /* Always compute new clock vector */
702 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
704 * Perform one-time actions when pushing new ModelAction onto
707 if (newcurr->is_write())
708 compute_promises(newcurr);
709 else if (newcurr->is_relseq_fixup())
710 compute_relseq_breakwrites(newcurr);
716 * @brief Check whether a model action is enabled.
718 * Checks whether a lock or join operation would be successful (i.e., is the
719 * lock already locked, or is the joined thread already complete). If not, put
720 * the action in a waiter list.
722 * @param curr is the ModelAction to check whether it is enabled.
723 * @return a bool that indicates whether the action is enabled.
725 bool ModelChecker::check_action_enabled(ModelAction *curr) {
726 if (curr->is_lock()) {
727 std::mutex * lock = (std::mutex *)curr->get_location();
728 struct std::mutex_state * state = lock->get_state();
729 if (state->islocked) {
730 //Stick the action in the appropriate waiting queue
731 lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
734 } else if (curr->get_type() == THREAD_JOIN) {
735 Thread *blocking = (Thread *)curr->get_location();
736 if (!blocking->is_complete()) {
737 blocking->push_wait_list(curr);
746 * This is the heart of the model checker routine. It performs model-checking
747 * actions corresponding to a given "current action." Among other processes, it
748 * calculates reads-from relationships, updates synchronization clock vectors,
749 * forms a memory_order constraints graph, and handles replay/backtrack
750 * execution when running permutations of previously-observed executions.
752 * @param curr The current action to process
753 * @return The next Thread that must be executed. May be NULL if ModelChecker
754 * makes no choice (e.g., according to replay execution, combining RMW actions,
757 Thread * ModelChecker::check_current_action(ModelAction *curr)
760 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
762 if (!check_action_enabled(curr)) {
763 /* Make the execution look like we chose to run this action
764 * much later, when a lock/join can succeed */
765 get_current_thread()->set_pending(curr);
766 scheduler->sleep(get_current_thread());
767 return get_next_thread(NULL);
770 wake_up_sleeping_actions(curr);
772 ModelAction *newcurr = initialize_curr_action(curr);
775 /* Add the action to lists before any other model-checking tasks */
776 if (!second_part_of_rmw)
777 add_action_to_lists(newcurr);
779 /* Build may_read_from set for newly-created actions */
780 if (curr == newcurr && curr->is_read())
781 build_reads_from_past(curr);
784 /* Initialize work_queue with the "current action" work */
785 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
786 while (!work_queue.empty()) {
787 WorkQueueEntry work = work_queue.front();
788 work_queue.pop_front();
791 case WORK_CHECK_CURR_ACTION: {
792 ModelAction *act = work.action;
793 bool update = false; /* update this location's release seq's */
794 bool update_all = false; /* update all release seq's */
796 if (process_thread_action(curr))
799 if (act->is_read() && process_read(act, second_part_of_rmw))
802 if (act->is_write() && process_write(act))
805 if (act->is_mutex_op() && process_mutex(act))
808 if (act->is_relseq_fixup())
809 process_relseq_fixup(curr, &work_queue);
812 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
814 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
817 case WORK_CHECK_RELEASE_SEQ:
818 resolve_release_sequences(work.location, &work_queue);
820 case WORK_CHECK_MO_EDGES: {
821 /** @todo Complete verification of work_queue */
822 ModelAction *act = work.action;
823 bool updated = false;
825 if (act->is_read()) {
826 const ModelAction *rf = act->get_reads_from();
827 if (rf != NULL && r_modification_order(act, rf))
830 if (act->is_write()) {
831 if (w_modification_order(act))
834 mo_graph->commitChanges();
837 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
846 check_curr_backtracking(curr);
847 set_backtracking(curr);
848 return get_next_thread(curr);
851 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
852 Node *currnode = curr->get_node();
853 Node *parnode = currnode->get_parent();
855 if ((!parnode->backtrack_empty() ||
856 !currnode->read_from_empty() ||
857 !currnode->future_value_empty() ||
858 !currnode->promise_empty() ||
859 !currnode->relseq_break_empty())
860 && (!priv->next_backtrack ||
861 *curr > *priv->next_backtrack)) {
862 priv->next_backtrack = curr;
866 bool ModelChecker::promises_expired() {
867 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
868 Promise *promise = (*promises)[promise_index];
869 if (promise->get_expiration()<priv->used_sequence_numbers) {
876 /** @return whether the current partial trace must be a prefix of a
878 bool ModelChecker::isfeasibleprefix() {
879 return promises->size() == 0 && pending_rel_seqs->size() == 0;
882 /** @return whether the current partial trace is feasible. */
883 bool ModelChecker::isfeasible() {
884 if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
885 DEBUG("Infeasible: RMW violation\n");
887 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
890 /** @return whether the current partial trace is feasible other than
891 * multiple RMW reading from the same store. */
892 bool ModelChecker::isfeasibleotherthanRMW() {
894 if (mo_graph->checkForCycles())
895 DEBUG("Infeasible: modification order cycles\n");
897 DEBUG("Infeasible: failed promise\n");
899 DEBUG("Infeasible: too many reads\n");
900 if (bad_synchronization)
901 DEBUG("Infeasible: bad synchronization ordering\n");
902 if (promises_expired())
903 DEBUG("Infeasible: promises expired\n");
905 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
908 /** Returns whether the current completed trace is feasible. */
909 bool ModelChecker::isfinalfeasible() {
910 if (DBG_ENABLED() && promises->size() != 0)
911 DEBUG("Infeasible: unrevolved promises\n");
913 return isfeasible() && promises->size() == 0;
916 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
917 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
918 ModelAction *lastread = get_last_action(act->get_tid());
919 lastread->process_rmw(act);
920 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
921 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
922 mo_graph->commitChanges();
928 * Checks whether a thread has read from the same write for too many times
929 * without seeing the effects of a later write.
932 * 1) there must a different write that we could read from that would satisfy the modification order,
933 * 2) we must have read from the same value in excess of maxreads times, and
934 * 3) that other write must have been in the reads_from set for maxreads times.
936 * If so, we decide that the execution is no longer feasible.
938 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
939 if (params.maxreads != 0) {
941 if (curr->get_node()->get_read_from_size() <= 1)
943 //Must make sure that execution is currently feasible... We could
944 //accidentally clear by rolling back
947 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
948 int tid = id_to_int(curr->get_tid());
951 if ((int)thrd_lists->size() <= tid)
953 action_list_t *list = &(*thrd_lists)[tid];
955 action_list_t::reverse_iterator rit = list->rbegin();
957 for (; (*rit) != curr; rit++)
959 /* go past curr now */
962 action_list_t::reverse_iterator ritcopy = rit;
963 //See if we have enough reads from the same value
965 for (; count < params.maxreads; rit++,count++) {
966 if (rit==list->rend())
968 ModelAction *act = *rit;
972 if (act->get_reads_from() != rf)
974 if (act->get_node()->get_read_from_size() <= 1)
977 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
979 const ModelAction * write = curr->get_node()->get_read_from_at(i);
981 //Need a different write
985 /* Test to see whether this is a feasible write to read from*/
986 mo_graph->startChanges();
987 r_modification_order(curr, write);
988 bool feasiblereadfrom = isfeasible();
989 mo_graph->rollbackChanges();
991 if (!feasiblereadfrom)
995 bool feasiblewrite = true;
996 //new we need to see if this write works for everyone
998 for (int loop = count; loop>0; loop--,rit++) {
999 ModelAction *act=*rit;
1000 bool foundvalue = false;
1001 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
1002 if (act->get_node()->get_read_from_at(i)==write) {
1008 feasiblewrite = false;
1012 if (feasiblewrite) {
1013 too_many_reads = true;
1021 * Updates the mo_graph with the constraints imposed from the current
1024 * Basic idea is the following: Go through each other thread and find
1025 * the lastest action that happened before our read. Two cases:
1027 * (1) The action is a write => that write must either occur before
1028 * the write we read from or be the write we read from.
1030 * (2) The action is a read => the write that that action read from
1031 * must occur before the write we read from or be the same write.
1033 * @param curr The current action. Must be a read.
1034 * @param rf The action that curr reads from. Must be a write.
1035 * @return True if modification order edges were added; false otherwise
1037 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
1039 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1042 ASSERT(curr->is_read());
1044 /* Iterate over all threads */
1045 for (i = 0; i < thrd_lists->size(); i++) {
1046 /* Iterate over actions in thread, starting from most recent */
1047 action_list_t *list = &(*thrd_lists)[i];
1048 action_list_t::reverse_iterator rit;
1049 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1050 ModelAction *act = *rit;
1053 * Include at most one act per-thread that "happens
1054 * before" curr. Don't consider reflexively.
1056 if (act->happens_before(curr) && act != curr) {
1057 if (act->is_write()) {
1059 mo_graph->addEdge(act, rf);
1063 const ModelAction *prevreadfrom = act->get_reads_from();
1064 //if the previous read is unresolved, keep going...
1065 if (prevreadfrom == NULL)
1068 if (rf != prevreadfrom) {
1069 mo_graph->addEdge(prevreadfrom, rf);
1081 /** This method fixes up the modification order when we resolve a
1082 * promises. The basic problem is that actions that occur after the
1083 * read curr could not property add items to the modification order
1086 * So for each thread, we find the earliest item that happens after
1087 * the read curr. This is the item we have to fix up with additional
1088 * constraints. If that action is write, we add a MO edge between
1089 * the Action rf and that action. If the action is a read, we add a
1090 * MO edge between the Action rf, and whatever the read accessed.
1092 * @param curr is the read ModelAction that we are fixing up MO edges for.
1093 * @param rf is the write ModelAction that curr reads from.
1096 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
1098 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1100 ASSERT(curr->is_read());
1102 /* Iterate over all threads */
1103 for (i = 0; i < thrd_lists->size(); i++) {
1104 /* Iterate over actions in thread, starting from most recent */
1105 action_list_t *list = &(*thrd_lists)[i];
1106 action_list_t::reverse_iterator rit;
1107 ModelAction *lastact = NULL;
1109 /* Find last action that happens after curr that is either not curr or a rmw */
1110 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1111 ModelAction *act = *rit;
1112 if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
1118 /* Include at most one act per-thread that "happens before" curr */
1119 if (lastact != NULL) {
1120 if (lastact==curr) {
1121 //Case 1: The resolved read is a RMW, and we need to make sure
1122 //that the write portion of the RMW mod order after rf
1124 mo_graph->addEdge(rf, lastact);
1125 } else if (lastact->is_read()) {
1126 //Case 2: The resolved read is a normal read and the next
1127 //operation is a read, and we need to make sure the value read
1128 //is mod ordered after rf
1130 const ModelAction *postreadfrom = lastact->get_reads_from();
1131 if (postreadfrom != NULL&&rf != postreadfrom)
1132 mo_graph->addEdge(rf, postreadfrom);
1134 //Case 3: The resolved read is a normal read and the next
1135 //operation is a write, and we need to make sure that the
1136 //write is mod ordered after rf
1138 mo_graph->addEdge(rf, lastact);
1146 * Updates the mo_graph with the constraints imposed from the current write.
1148 * Basic idea is the following: Go through each other thread and find
1149 * the lastest action that happened before our write. Two cases:
1151 * (1) The action is a write => that write must occur before
1154 * (2) The action is a read => the write that that action read from
1155 * must occur before the current write.
1157 * This method also handles two other issues:
1159 * (I) Sequential Consistency: Making sure that if the current write is
1160 * seq_cst, that it occurs after the previous seq_cst write.
1162 * (II) Sending the write back to non-synchronizing reads.
1164 * @param curr The current action. Must be a write.
1165 * @return True if modification order edges were added; false otherwise
1167 bool ModelChecker::w_modification_order(ModelAction *curr)
1169 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1172 ASSERT(curr->is_write());
1174 if (curr->is_seqcst()) {
1175 /* We have to at least see the last sequentially consistent write,
1176 so we are initialized. */
1177 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1178 if (last_seq_cst != NULL) {
1179 mo_graph->addEdge(last_seq_cst, curr);
1184 /* Iterate over all threads */
1185 for (i = 0; i < thrd_lists->size(); i++) {
1186 /* Iterate over actions in thread, starting from most recent */
1187 action_list_t *list = &(*thrd_lists)[i];
1188 action_list_t::reverse_iterator rit;
1189 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1190 ModelAction *act = *rit;
1193 * 1) If RMW and it actually read from something, then we
1194 * already have all relevant edges, so just skip to next
1197 * 2) If RMW and it didn't read from anything, we should
1198 * whatever edge we can get to speed up convergence.
1200 * 3) If normal write, we need to look at earlier actions, so
1201 * continue processing list.
1203 if (curr->is_rmw()) {
1204 if (curr->get_reads_from()!=NULL)
1213 * Include at most one act per-thread that "happens
1216 if (act->happens_before(curr)) {
1218 * Note: if act is RMW, just add edge:
1220 * The following edge should be handled elsewhere:
1221 * readfrom(act) --mo--> act
1223 if (act->is_write())
1224 mo_graph->addEdge(act, curr);
1225 else if (act->is_read()) {
1226 //if previous read accessed a null, just keep going
1227 if (act->get_reads_from() == NULL)
1229 mo_graph->addEdge(act->get_reads_from(), curr);
1233 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1234 !act->same_thread(curr)) {
1235 /* We have an action that:
1236 (1) did not happen before us
1237 (2) is a read and we are a write
1238 (3) cannot synchronize with us
1239 (4) is in a different thread
1241 that read could potentially read from our write. Note that
1242 these checks are overly conservative at this point, we'll
1243 do more checks before actually removing the
1247 if (thin_air_constraint_may_allow(curr, act)) {
1249 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1250 struct PendingFutureValue pfv = {curr,act};
1251 futurevalues->push_back(pfv);
1261 /** Arbitrary reads from the future are not allowed. Section 29.3
1262 * part 9 places some constraints. This method checks one result of constraint
1263 * constraint. Others require compiler support. */
1264 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1265 if (!writer->is_rmw())
1268 if (!reader->is_rmw())
1271 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1272 if (search == reader)
1274 if (search->get_tid() == reader->get_tid() &&
1275 search->happens_before(reader))
1282 /** Arbitrary reads from the future are not allowed. Section 29.3
1283 * part 9 places some constraints. This method checks one result of constraint
1284 * constraint. Others require compiler support. */
1285 bool ModelChecker::mo_may_allow(const ModelAction * writer, const ModelAction *reader) {
1286 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(reader->get_location());
1288 //Get write that follows reader action
1289 action_list_t *list = &(*thrd_lists)[id_to_int(reader->get_tid())];
1290 action_list_t::reverse_iterator rit;
1291 ModelAction *first_write_after_read=NULL;
1293 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1294 ModelAction *act = *rit;
1297 if (act->is_write())
1298 first_write_after_read=act;
1301 if (first_write_after_read==NULL)
1304 return !mo_graph->checkReachable(first_write_after_read, writer);
1310 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1311 * The ModelAction under consideration is expected to be taking part in
1312 * release/acquire synchronization as an object of the "reads from" relation.
1313 * Note that this can only provide release sequence support for RMW chains
1314 * which do not read from the future, as those actions cannot be traced until
1315 * their "promise" is fulfilled. Similarly, we may not even establish the
1316 * presence of a release sequence with certainty, as some modification order
1317 * constraints may be decided further in the future. Thus, this function
1318 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1319 * and a boolean representing certainty.
1321 * @param rf The action that might be part of a release sequence. Must be a
1323 * @param release_heads A pass-by-reference style return parameter. After
1324 * execution of this function, release_heads will contain the heads of all the
1325 * relevant release sequences, if any exists with certainty
1326 * @param pending A pass-by-reference style return parameter which is only used
1327 * when returning false (i.e., uncertain). Returns most information regarding
1328 * an uncertain release sequence, including any write operations that might
1329 * break the sequence.
1330 * @return true, if the ModelChecker is certain that release_heads is complete;
1333 bool ModelChecker::release_seq_heads(const ModelAction *rf,
1334 rel_heads_list_t *release_heads,
1335 struct release_seq *pending) const
1337 /* Only check for release sequences if there are no cycles */
1338 if (mo_graph->checkForCycles())
1342 ASSERT(rf->is_write());
1344 if (rf->is_release())
1345 release_heads->push_back(rf);
1347 break; /* End of RMW chain */
1349 /** @todo Need to be smarter here... In the linux lock
1350 * example, this will run to the beginning of the program for
1352 /** @todo The way to be smarter here is to keep going until 1
1353 * thread has a release preceded by an acquire and you've seen
1356 /* acq_rel RMW is a sufficient stopping condition */
1357 if (rf->is_acquire() && rf->is_release())
1358 return true; /* complete */
1360 rf = rf->get_reads_from();
1363 /* read from future: need to settle this later */
1365 return false; /* incomplete */
1368 if (rf->is_release())
1369 return true; /* complete */
1371 /* else relaxed write; check modification order for contiguous subsequence
1372 * -> rf must be same thread as release */
1373 int tid = id_to_int(rf->get_tid());
1374 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1375 action_list_t *list = &(*thrd_lists)[tid];
1376 action_list_t::const_reverse_iterator rit;
1378 /* Find rf in the thread list */
1379 rit = std::find(list->rbegin(), list->rend(), rf);
1380 ASSERT(rit != list->rend());
1382 /* Find the last write/release */
1383 for (; rit != list->rend(); rit++)
1384 if ((*rit)->is_release())
1386 if (rit == list->rend()) {
1387 /* No write-release in this thread */
1388 return true; /* complete */
1390 ModelAction *release = *rit;
1392 ASSERT(rf->same_thread(release));
1394 pending->writes.clear();
1396 bool certain = true;
1397 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1398 if (id_to_int(rf->get_tid()) == (int)i)
1400 list = &(*thrd_lists)[i];
1402 /* Can we ensure no future writes from this thread may break
1403 * the release seq? */
1404 bool future_ordered = false;
1406 ModelAction *last = get_last_action(int_to_id(i));
1407 Thread *th = get_thread(int_to_id(i));
1408 if ((last && rf->happens_before(last)) ||
1409 !scheduler->is_enabled(th) ||
1411 future_ordered = true;
1413 ASSERT(!th->is_model_thread() || future_ordered);
1415 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1416 const ModelAction *act = *rit;
1417 /* Reach synchronization -> this thread is complete */
1418 if (act->happens_before(release))
1420 if (rf->happens_before(act)) {
1421 future_ordered = true;
1425 /* Only writes can break release sequences */
1426 if (!act->is_write())
1429 /* Check modification order */
1430 if (mo_graph->checkReachable(rf, act)) {
1431 /* rf --mo--> act */
1432 future_ordered = true;
1435 if (mo_graph->checkReachable(act, release))
1436 /* act --mo--> release */
1438 if (mo_graph->checkReachable(release, act) &&
1439 mo_graph->checkReachable(act, rf)) {
1440 /* release --mo-> act --mo--> rf */
1441 return true; /* complete */
1443 /* act may break release sequence */
1444 pending->writes.push_back(act);
1447 if (!future_ordered)
1448 certain = false; /* This thread is uncertain */
1452 release_heads->push_back(release);
1453 pending->writes.clear();
1455 pending->release = release;
1462 * A public interface for getting the release sequence head(s) with which a
1463 * given ModelAction must synchronize. This function only returns a non-empty
1464 * result when it can locate a release sequence head with certainty. Otherwise,
1465 * it may mark the internal state of the ModelChecker so that it will handle
1466 * the release sequence at a later time, causing @a act to update its
1467 * synchronization at some later point in execution.
1468 * @param act The 'acquire' action that may read from a release sequence
1469 * @param release_heads A pass-by-reference return parameter. Will be filled
1470 * with the head(s) of the release sequence(s), if they exists with certainty.
1471 * @see ModelChecker::release_seq_heads
1473 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1475 const ModelAction *rf = act->get_reads_from();
1476 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
1477 sequence->acquire = act;
1479 if (!release_seq_heads(rf, release_heads, sequence)) {
1480 /* add act to 'lazy checking' list */
1481 pending_rel_seqs->push_back(sequence);
1483 snapshot_free(sequence);
1488 * Attempt to resolve all stashed operations that might synchronize with a
1489 * release sequence for a given location. This implements the "lazy" portion of
1490 * determining whether or not a release sequence was contiguous, since not all
1491 * modification order information is present at the time an action occurs.
1493 * @param location The location/object that should be checked for release
1494 * sequence resolutions. A NULL value means to check all locations.
1495 * @param work_queue The work queue to which to add work items as they are
1497 * @return True if any updates occurred (new synchronization, new mo_graph
1500 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1502 bool updated = false;
1503 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
1504 while (it != pending_rel_seqs->end()) {
1505 struct release_seq *pending = *it;
1506 ModelAction *act = pending->acquire;
1508 /* Only resolve sequences on the given location, if provided */
1509 if (location && act->get_location() != location) {
1514 const ModelAction *rf = act->get_reads_from();
1515 rel_heads_list_t release_heads;
1517 complete = release_seq_heads(rf, &release_heads, pending);
1518 for (unsigned int i = 0; i < release_heads.size(); i++) {
1519 if (!act->has_synchronized_with(release_heads[i])) {
1520 if (act->synchronize_with(release_heads[i]))
1523 set_bad_synchronization();
1528 /* Re-check all pending release sequences */
1529 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1530 /* Re-check act for mo_graph edges */
1531 work_queue->push_back(MOEdgeWorkEntry(act));
1533 /* propagate synchronization to later actions */
1534 action_list_t::reverse_iterator rit = action_trace->rbegin();
1535 for (; (*rit) != act; rit++) {
1536 ModelAction *propagate = *rit;
1537 if (act->happens_before(propagate)) {
1538 propagate->synchronize_with(act);
1539 /* Re-check 'propagate' for mo_graph edges */
1540 work_queue->push_back(MOEdgeWorkEntry(propagate));
1545 it = pending_rel_seqs->erase(it);
1546 snapshot_free(pending);
1552 // If we resolved promises or data races, see if we have realized a data race.
1553 if (checkDataRaces()) {
1561 * Performs various bookkeeping operations for the current ModelAction. For
1562 * instance, adds action to the per-object, per-thread action vector and to the
1563 * action trace list of all thread actions.
1565 * @param act is the ModelAction to add.
1567 void ModelChecker::add_action_to_lists(ModelAction *act)
1569 int tid = id_to_int(act->get_tid());
1570 action_trace->push_back(act);
1572 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1574 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1575 if (tid >= (int)vec->size())
1576 vec->resize(priv->next_thread_id);
1577 (*vec)[tid].push_back(act);
1579 if ((int)thrd_last_action->size() <= tid)
1580 thrd_last_action->resize(get_num_threads());
1581 (*thrd_last_action)[tid] = act;
1585 * @brief Get the last action performed by a particular Thread
1586 * @param tid The thread ID of the Thread in question
1587 * @return The last action in the thread
1589 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1591 int threadid = id_to_int(tid);
1592 if (threadid < (int)thrd_last_action->size())
1593 return (*thrd_last_action)[id_to_int(tid)];
1599 * Gets the last memory_order_seq_cst write (in the total global sequence)
1600 * performed on a particular object (i.e., memory location), not including the
1602 * @param curr The current ModelAction; also denotes the object location to
1604 * @return The last seq_cst write
1606 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1608 void *location = curr->get_location();
1609 action_list_t *list = obj_map->get_safe_ptr(location);
1610 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1611 action_list_t::reverse_iterator rit;
1612 for (rit = list->rbegin(); rit != list->rend(); rit++)
1613 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1619 * Gets the last unlock operation performed on a particular mutex (i.e., memory
1620 * location). This function identifies the mutex according to the current
1621 * action, which is presumed to perform on the same mutex.
1622 * @param curr The current ModelAction; also denotes the object location to
1624 * @return The last unlock operation
1626 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1628 void *location = curr->get_location();
1629 action_list_t *list = obj_map->get_safe_ptr(location);
1630 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1631 action_list_t::reverse_iterator rit;
1632 for (rit = list->rbegin(); rit != list->rend(); rit++)
1633 if ((*rit)->is_unlock())
1638 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1640 ModelAction *parent = get_last_action(tid);
1642 parent = get_thread(tid)->get_creation();
1647 * Returns the clock vector for a given thread.
1648 * @param tid The thread whose clock vector we want
1649 * @return Desired clock vector
1651 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1653 return get_parent_action(tid)->get_cv();
1657 * Resolve a set of Promises with a current write. The set is provided in the
1658 * Node corresponding to @a write.
1659 * @param write The ModelAction that is fulfilling Promises
1660 * @return True if promises were resolved; false otherwise
1662 bool ModelChecker::resolve_promises(ModelAction *write)
1664 bool resolved = false;
1665 std::vector< thread_id_t, ModelAlloc<thread_id_t> > threads_to_check;
1667 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1668 Promise *promise = (*promises)[promise_index];
1669 if (write->get_node()->get_promise(i)) {
1670 ModelAction *read = promise->get_action();
1671 if (read->is_rmw()) {
1672 mo_graph->addRMWEdge(write, read);
1674 read->read_from(write);
1675 //First fix up the modification order for actions that happened
1677 r_modification_order(read, write);
1678 //Next fix up the modification order for actions that happened
1680 post_r_modification_order(read, write);
1681 //Make sure the promise's value matches the write's value
1682 ASSERT(promise->get_value() == write->get_value());
1685 promises->erase(promises->begin() + promise_index);
1686 threads_to_check.push_back(read->get_tid());
1693 //Check whether reading these writes has made threads unable to
1696 for(unsigned int i=0;i<threads_to_check.size();i++)
1697 mo_check_promises(threads_to_check[i], write);
1703 * Compute the set of promises that could potentially be satisfied by this
1704 * action. Note that the set computation actually appears in the Node, not in
1706 * @param curr The ModelAction that may satisfy promises
1708 void ModelChecker::compute_promises(ModelAction *curr)
1710 for (unsigned int i = 0; i < promises->size(); i++) {
1711 Promise *promise = (*promises)[i];
1712 const ModelAction *act = promise->get_action();
1713 if (!act->happens_before(curr) &&
1715 !act->could_synchronize_with(curr) &&
1716 !act->same_thread(curr) &&
1717 promise->get_value() == curr->get_value()) {
1718 curr->get_node()->set_promise(i);
1723 /** Checks promises in response to change in ClockVector Threads. */
1724 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
1726 for (unsigned int i = 0; i < promises->size(); i++) {
1727 Promise *promise = (*promises)[i];
1728 const ModelAction *act = promise->get_action();
1729 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1730 merge_cv->synchronized_since(act)) {
1731 if (promise->increment_threads(tid)) {
1732 //Promise has failed
1733 failed_promise = true;
1740 /** Checks promises in response to addition to modification order for threads.
1742 * pthread is the thread that performed the read that created the promise
1744 * pread is the read that created the promise
1746 * pwrite is either the first write to same location as pread by
1747 * pthread that is sequenced after pread or the value read by the
1748 * first read to the same lcoation as pread by pthread that is
1749 * sequenced after pread..
1751 * 1. If tid=pthread, then we check what other threads are reachable
1752 * through the mode order starting with pwrite. Those threads cannot
1753 * perform a write that will resolve the promise due to modification
1754 * order constraints.
1756 * 2. If the tid is not pthread, we check whether pwrite can reach the
1757 * action write through the modification order. If so, that thread
1758 * cannot perform a future write that will resolve the promise due to
1759 * modificatin order constraints.
1761 * @parem tid The thread that either read from the model action
1762 * write, or actually did the model action write.
1764 * @parem write The ModelAction representing the relevant write.
1767 void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write) {
1768 void * location = write->get_location();
1769 for (unsigned int i = 0; i < promises->size(); i++) {
1770 Promise *promise = (*promises)[i];
1771 const ModelAction *act = promise->get_action();
1773 //Is this promise on the same location?
1774 if ( act->get_location() != location )
1777 //same thread as the promise
1778 if ( act->get_tid()==tid ) {
1780 //do we have a pwrite for the promise, if not, set it
1781 if (promise->get_write() == NULL ) {
1782 promise->set_write(write);
1783 //The pwrite cannot happen before the promise
1784 if (write->happens_before(act) && (write != act)) {
1785 failed_promise = true;
1789 if (mo_graph->checkPromise(write, promise)) {
1790 failed_promise = true;
1795 //Don't do any lookups twice for the same thread
1796 if (promise->has_sync_thread(tid))
1799 if (mo_graph->checkReachable(promise->get_write(), write)) {
1800 if (promise->increment_threads(tid)) {
1801 failed_promise = true;
1809 * Compute the set of writes that may break the current pending release
1810 * sequence. This information is extracted from previou release sequence
1813 * @param curr The current ModelAction. Must be a release sequence fixup
1816 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
1818 if (pending_rel_seqs->empty())
1821 struct release_seq *pending = pending_rel_seqs->back();
1822 for (unsigned int i = 0; i < pending->writes.size(); i++) {
1823 const ModelAction *write = pending->writes[i];
1824 curr->get_node()->add_relseq_break(write);
1827 /* NULL means don't break the sequence; just synchronize */
1828 curr->get_node()->add_relseq_break(NULL);
1832 * Build up an initial set of all past writes that this 'read' action may read
1833 * from. This set is determined by the clock vector's "happens before"
1835 * @param curr is the current ModelAction that we are exploring; it must be a
1838 void ModelChecker::build_reads_from_past(ModelAction *curr)
1840 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1842 ASSERT(curr->is_read());
1844 ModelAction *last_seq_cst = NULL;
1846 /* Track whether this object has been initialized */
1847 bool initialized = false;
1849 if (curr->is_seqcst()) {
1850 last_seq_cst = get_last_seq_cst(curr);
1851 /* We have to at least see the last sequentially consistent write,
1852 so we are initialized. */
1853 if (last_seq_cst != NULL)
1857 /* Iterate over all threads */
1858 for (i = 0; i < thrd_lists->size(); i++) {
1859 /* Iterate over actions in thread, starting from most recent */
1860 action_list_t *list = &(*thrd_lists)[i];
1861 action_list_t::reverse_iterator rit;
1862 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1863 ModelAction *act = *rit;
1865 /* Only consider 'write' actions */
1866 if (!act->is_write() || act == curr)
1869 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1870 if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1871 DEBUG("Adding action to may_read_from:\n");
1872 if (DBG_ENABLED()) {
1877 if (curr->get_sleep_flag() && ! curr->is_seqcst()) {
1878 if (sleep_can_read_from(curr, act))
1879 curr->get_node()->add_read_from(act);
1881 curr->get_node()->add_read_from(act);
1884 /* Include at most one act per-thread that "happens before" curr */
1885 if (act->happens_before(curr)) {
1893 /** @todo Need a more informative way of reporting errors. */
1894 printf("ERROR: may read from uninitialized atomic\n");
1897 if (DBG_ENABLED() || !initialized) {
1898 printf("Reached read action:\n");
1900 printf("Printing may_read_from\n");
1901 curr->get_node()->print_may_read_from();
1902 printf("End printing may_read_from\n");
1905 ASSERT(initialized);
1908 bool ModelChecker::sleep_can_read_from(ModelAction * curr, const ModelAction *write) {
1910 Node *prevnode=write->get_node()->get_parent();
1911 bool thread_sleep=prevnode->get_enabled_array()[id_to_int(curr->get_tid())]==THREAD_SLEEP_SET;
1912 if (write->is_release()&&thread_sleep)
1914 if (!write->is_rmw()) {
1917 if (write->get_reads_from()==NULL)
1919 write=write->get_reads_from();
1923 static void print_list(action_list_t *list)
1925 action_list_t::iterator it;
1927 printf("---------------------------------------------------------------------\n");
1929 unsigned int hash=0;
1931 for (it = list->begin(); it != list->end(); it++) {
1933 hash=hash^(hash<<3)^((*it)->hash());
1935 printf("HASH %u\n", hash);
1936 printf("---------------------------------------------------------------------\n");
1939 #if SUPPORT_MOD_ORDER_DUMP
1940 void ModelChecker::dumpGraph(char *filename) {
1942 sprintf(buffer, "%s.dot",filename);
1943 FILE *file=fopen(buffer, "w");
1944 fprintf(file, "digraph %s {\n",filename);
1945 mo_graph->dumpNodes(file);
1946 ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
1948 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
1949 ModelAction *action=*it;
1950 if (action->is_read()) {
1951 fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
1952 if (action->get_reads_from()!=NULL)
1953 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
1955 if (thread_array[action->get_tid()] != NULL) {
1956 fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
1959 thread_array[action->get_tid()]=action;
1961 fprintf(file,"}\n");
1962 model_free(thread_array);
1967 void ModelChecker::print_summary()
1970 printf("Number of executions: %d\n", num_executions);
1971 printf("Number of feasible executions: %d\n", num_feasible_executions);
1972 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1974 #if SUPPORT_MOD_ORDER_DUMP
1976 char buffername[100];
1977 sprintf(buffername, "exec%04u", num_executions);
1978 mo_graph->dumpGraphToFile(buffername);
1979 sprintf(buffername, "graph%04u", num_executions);
1980 dumpGraph(buffername);
1983 if (!isfinalfeasible())
1984 printf("INFEASIBLE EXECUTION!\n");
1985 print_list(action_trace);
1990 * Add a Thread to the system for the first time. Should only be called once
1992 * @param t The Thread to add
1994 void ModelChecker::add_thread(Thread *t)
1996 thread_map->put(id_to_int(t->get_id()), t);
1997 scheduler->add_thread(t);
2001 * Removes a thread from the scheduler.
2002 * @param the thread to remove.
2004 void ModelChecker::remove_thread(Thread *t)
2006 scheduler->remove_thread(t);
2010 * @brief Get a Thread reference by its ID
2011 * @param tid The Thread's ID
2012 * @return A Thread reference
2014 Thread * ModelChecker::get_thread(thread_id_t tid) const
2016 return thread_map->get(id_to_int(tid));
2020 * @brief Get a reference to the Thread in which a ModelAction was executed
2021 * @param act The ModelAction
2022 * @return A Thread reference
2024 Thread * ModelChecker::get_thread(ModelAction *act) const
2026 return get_thread(act->get_tid());
2030 * Switch from a user-context to the "master thread" context (a.k.a. system
2031 * context). This switch is made with the intention of exploring a particular
2032 * model-checking action (described by a ModelAction object). Must be called
2033 * from a user-thread context.
2035 * @param act The current action that will be explored. May be NULL only if
2036 * trace is exiting via an assertion (see ModelChecker::set_assert and
2037 * ModelChecker::has_asserted).
2038 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
2040 int ModelChecker::switch_to_master(ModelAction *act)
2043 Thread *old = thread_current();
2044 set_current_action(act);
2045 old->set_state(THREAD_READY);
2046 return Thread::swap(old, &system_context);
2050 * Takes the next step in the execution, if possible.
2051 * @return Returns true (success) if a step was taken and false otherwise.
2053 bool ModelChecker::take_step() {
2057 Thread *curr = priv->current_action ? get_thread(priv->current_action) : NULL;
2059 if (curr->get_state() == THREAD_READY) {
2060 ASSERT(priv->current_action);
2062 priv->nextThread = check_current_action(priv->current_action);
2063 priv->current_action = NULL;
2065 if (curr->is_blocked() || curr->is_complete())
2066 scheduler->remove_thread(curr);
2071 Thread *next = scheduler->next_thread(priv->nextThread);
2073 /* Infeasible -> don't take any more steps */
2077 if (params.bound != 0) {
2078 if (priv->used_sequence_numbers > params.bound) {
2083 DEBUG("(%d, %d)\n", curr ? id_to_int(curr->get_id()) : -1,
2084 next ? id_to_int(next->get_id()) : -1);
2087 * Launch end-of-execution release sequence fixups only when there are:
2089 * (1) no more user threads to run (or when execution replay chooses
2090 * the 'model_thread')
2091 * (2) pending release sequences
2092 * (3) pending assertions (i.e., data races)
2093 * (4) no pending promises
2095 if (!pending_rel_seqs->empty() && (!next || next->is_model_thread()) &&
2096 isfinalfeasible() && !unrealizedraces.empty()) {
2097 printf("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
2098 pending_rel_seqs->size());
2099 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2100 std::memory_order_seq_cst, NULL, VALUE_NONE,
2102 set_current_action(fixup);
2106 /* next == NULL -> don't take any more steps */
2110 next->set_state(THREAD_RUNNING);
2112 if (next->get_pending() != NULL) {
2113 /* restart a pending action */
2114 set_current_action(next->get_pending());
2115 next->set_pending(NULL);
2116 next->set_state(THREAD_READY);
2120 /* Return false only if swap fails with an error */
2121 return (Thread::swap(&system_context, next) == 0);
2124 /** Runs the current execution until threre are no more steps to take. */
2125 void ModelChecker::finish_execution() {
2128 while (take_step());