9 #include "snapshot-interface.h"
11 #include "clockvector.h"
12 #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 condvar_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
35 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
36 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
37 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
38 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
39 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
40 node_stack(new NodeStack()),
41 mo_graph(new CycleGraph()),
42 failed_promise(false),
43 too_many_reads(false),
45 bad_synchronization(false)
47 /* Allocate this "size" on the snapshotting heap */
48 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
49 /* First thread created will have id INITIAL_THREAD_ID */
50 priv->next_thread_id = INITIAL_THREAD_ID;
52 /* Initialize a model-checker thread, for special ModelActions */
53 model_thread = new Thread(get_next_id());
54 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
57 /** @brief Destructor */
58 ModelChecker::~ModelChecker()
60 for (unsigned int i = 0; i < get_num_threads(); i++)
61 delete thread_map->get(i);
66 delete lock_waiters_map;
67 delete condvar_waiters_map;
70 for (unsigned int i = 0; i < promises->size(); i++)
71 delete (*promises)[i];
74 delete pending_rel_seqs;
76 delete thrd_last_action;
83 * Restores user program to initial state and resets all model-checker data
86 void ModelChecker::reset_to_initial_state()
88 DEBUG("+++ Resetting to initial state +++\n");
89 node_stack->reset_execution();
90 failed_promise = false;
91 too_many_reads = false;
92 bad_synchronization = false;
94 snapshotObject->backTrackBeforeStep(0);
97 /** @return a thread ID for a new Thread */
98 thread_id_t ModelChecker::get_next_id()
100 return priv->next_thread_id++;
103 /** @return the number of user threads created during this execution */
104 unsigned int ModelChecker::get_num_threads()
106 return priv->next_thread_id;
109 /** @return The currently executing Thread. */
110 Thread * ModelChecker::get_current_thread()
112 return scheduler->get_current_thread();
115 /** @return a sequence number for a new ModelAction */
116 modelclock_t ModelChecker::get_next_seq_num()
118 return ++priv->used_sequence_numbers;
121 Node * ModelChecker::get_curr_node() {
122 return node_stack->get_head();
126 * @brief Choose the next thread to execute.
128 * This function chooses the next thread that should execute. It can force the
129 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
130 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
131 * The model-checker may have no preference regarding the next thread (i.e.,
132 * when exploring a new execution ordering), in which case this will return
134 * @param curr The current ModelAction. This action might guide the choice of
136 * @return The next thread to run. If the model-checker has no preference, NULL.
138 Thread * ModelChecker::get_next_thread(ModelAction *curr)
143 /* Do not split atomic actions. */
145 return thread_current();
146 /* The THREAD_CREATE action points to the created Thread */
147 else if (curr->get_type() == THREAD_CREATE)
148 return (Thread *)curr->get_location();
151 /* Have we completed exploring the preselected path? */
155 /* Else, we are trying to replay an execution */
156 ModelAction *next = node_stack->get_next()->get_action();
158 if (next == diverge) {
159 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
160 earliest_diverge=diverge;
162 Node *nextnode = next->get_node();
163 Node *prevnode = nextnode->get_parent();
164 scheduler->update_sleep_set(prevnode);
166 /* Reached divergence point */
167 if (nextnode->increment_misc()) {
168 /* The next node will try to satisfy a different misc_index values. */
169 tid = next->get_tid();
170 node_stack->pop_restofstack(2);
171 } else if (nextnode->increment_promise()) {
172 /* The next node will try to satisfy a different set of promises. */
173 tid = next->get_tid();
174 node_stack->pop_restofstack(2);
175 } else if (nextnode->increment_read_from()) {
176 /* The next node will read from a different value. */
177 tid = next->get_tid();
178 node_stack->pop_restofstack(2);
179 } else if (nextnode->increment_future_value()) {
180 /* The next node will try to read from a different future value. */
181 tid = next->get_tid();
182 node_stack->pop_restofstack(2);
183 } else if (nextnode->increment_relseq_break()) {
184 /* The next node will try to resolve a release sequence differently */
185 tid = next->get_tid();
186 node_stack->pop_restofstack(2);
188 /* Make a different thread execute for next step */
189 scheduler->add_sleep(thread_map->get(id_to_int(next->get_tid())));
190 tid = prevnode->get_next_backtrack();
191 /* Make sure the backtracked thread isn't sleeping. */
192 node_stack->pop_restofstack(1);
193 if (diverge==earliest_diverge) {
194 earliest_diverge=prevnode->get_action();
197 /* The correct sleep set is in the parent node. */
200 DEBUG("*** Divergence point ***\n");
204 tid = next->get_tid();
206 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
207 ASSERT(tid != THREAD_ID_T_NONE);
208 return thread_map->get(id_to_int(tid));
212 * We need to know what the next actions of all threads in the sleep
213 * set will be. This method computes them and stores the actions at
214 * the corresponding thread object's pending action.
217 void ModelChecker::execute_sleep_set() {
218 for(unsigned int i=0;i<get_num_threads();i++) {
219 thread_id_t tid=int_to_id(i);
220 Thread *thr=get_thread(tid);
221 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
222 thr->set_state(THREAD_RUNNING);
223 scheduler->next_thread(thr);
224 Thread::swap(&system_context, thr);
225 priv->current_action->set_sleep_flag();
226 thr->set_pending(priv->current_action);
229 priv->current_action = NULL;
232 void ModelChecker::wake_up_sleeping_actions(ModelAction * curr) {
233 for(unsigned int i=0;i<get_num_threads();i++) {
234 thread_id_t tid=int_to_id(i);
235 Thread *thr=get_thread(tid);
236 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
237 ModelAction *pending_act=thr->get_pending();
238 if (pending_act->could_synchronize_with(curr)) {
239 //Remove this thread from sleep set
240 scheduler->remove_sleep(thr);
247 * Queries the model-checker for more executions to explore and, if one
248 * exists, resets the model-checker state to execute a new execution.
250 * @return If there are more executions to explore, return true. Otherwise,
253 bool ModelChecker::next_execution()
259 if (isfinalfeasible()) {
260 printf("Earliest divergence point since last feasible execution:\n");
261 if (earliest_diverge)
262 earliest_diverge->print();
264 printf("(Not set)\n");
266 earliest_diverge = NULL;
267 num_feasible_executions++;
270 DEBUG("Number of acquires waiting on pending release sequences: %zu\n",
271 pending_rel_seqs->size());
274 if (isfinalfeasible() || (params.bound != 0 && priv->used_sequence_numbers > params.bound ) || DBG_ENABLED() )
277 if ((diverge = get_next_backtrack()) == NULL)
281 printf("Next execution will diverge at:\n");
285 reset_to_initial_state();
289 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
291 switch (act->get_type()) {
295 /* linear search: from most recent to oldest */
296 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
297 action_list_t::reverse_iterator rit;
298 for (rit = list->rbegin(); rit != list->rend(); rit++) {
299 ModelAction *prev = *rit;
300 if (prev->could_synchronize_with(act))
306 case ATOMIC_TRYLOCK: {
307 /* linear search: from most recent to oldest */
308 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
309 action_list_t::reverse_iterator rit;
310 for (rit = list->rbegin(); rit != list->rend(); rit++) {
311 ModelAction *prev = *rit;
312 if (act->is_conflicting_lock(prev))
317 case ATOMIC_UNLOCK: {
318 /* linear search: from most recent to oldest */
319 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
320 action_list_t::reverse_iterator rit;
321 for (rit = list->rbegin(); rit != list->rend(); rit++) {
322 ModelAction *prev = *rit;
323 if (!act->same_thread(prev)&&prev->is_failed_trylock())
329 /* linear search: from most recent to oldest */
330 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
331 action_list_t::reverse_iterator rit;
332 for (rit = list->rbegin(); rit != list->rend(); rit++) {
333 ModelAction *prev = *rit;
334 if (!act->same_thread(prev)&&prev->is_failed_trylock())
336 if (!act->same_thread(prev)&&prev->is_notify())
342 case ATOMIC_NOTIFY_ALL:
343 case ATOMIC_NOTIFY_ONE: {
344 /* linear search: from most recent to oldest */
345 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
346 action_list_t::reverse_iterator rit;
347 for (rit = list->rbegin(); rit != list->rend(); rit++) {
348 ModelAction *prev = *rit;
349 if (!act->same_thread(prev)&&prev->is_wait())
360 /** This method finds backtracking points where we should try to
361 * reorder the parameter ModelAction against.
363 * @param the ModelAction to find backtracking points for.
365 void ModelChecker::set_backtracking(ModelAction *act)
367 Thread *t = get_thread(act);
368 ModelAction * prev = get_last_conflict(act);
372 Node * node = prev->get_node()->get_parent();
374 int low_tid, high_tid;
375 if (node->is_enabled(t)) {
376 low_tid = id_to_int(act->get_tid());
377 high_tid = low_tid+1;
380 high_tid = get_num_threads();
383 for(int i = low_tid; i < high_tid; i++) {
384 thread_id_t tid = int_to_id(i);
386 /* Don't backtrack into a point where the thread is disabled or sleeping. */
387 if (node->get_enabled_array()[i]!=THREAD_ENABLED)
390 /* Check if this has been explored already */
391 if (node->has_been_explored(tid))
394 /* See if fairness allows */
395 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
397 for(int t=0;t<node->get_num_threads();t++) {
398 thread_id_t tother=int_to_id(t);
399 if (node->is_enabled(tother) && node->has_priority(tother)) {
407 /* Cache the latest backtracking point */
408 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
409 priv->next_backtrack = prev;
411 /* If this is a new backtracking point, mark the tree */
412 if (!node->set_backtrack(tid))
414 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
415 id_to_int(prev->get_tid()),
416 id_to_int(t->get_id()));
425 * Returns last backtracking point. The model checker will explore a different
426 * path for this point in the next execution.
427 * @return The ModelAction at which the next execution should diverge.
429 ModelAction * ModelChecker::get_next_backtrack()
431 ModelAction *next = priv->next_backtrack;
432 priv->next_backtrack = NULL;
437 * Processes a read or rmw model action.
438 * @param curr is the read model action to process.
439 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
440 * @return True if processing this read updates the mo_graph.
442 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
445 bool updated = false;
447 const ModelAction *reads_from = curr->get_node()->get_read_from();
448 if (reads_from != NULL) {
449 mo_graph->startChanges();
451 value = reads_from->get_value();
452 bool r_status = false;
454 if (!second_part_of_rmw) {
455 check_recency(curr, reads_from);
456 r_status = r_modification_order(curr, reads_from);
460 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
461 mo_graph->rollbackChanges();
462 too_many_reads = false;
466 curr->read_from(reads_from);
467 mo_graph->commitChanges();
468 mo_check_promises(curr->get_tid(), reads_from);
471 } else if (!second_part_of_rmw) {
472 /* Read from future value */
473 value = curr->get_node()->get_future_value();
474 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
475 curr->read_from(NULL);
476 Promise *valuepromise = new Promise(curr, value, expiration);
477 promises->push_back(valuepromise);
479 get_thread(curr)->set_return_value(value);
485 * Processes a lock, trylock, or unlock model action. @param curr is
486 * the read model action to process.
488 * The try lock operation checks whether the lock is taken. If not,
489 * it falls to the normal lock operation case. If so, it returns
492 * The lock operation has already been checked that it is enabled, so
493 * it just grabs the lock and synchronizes with the previous unlock.
495 * The unlock operation has to re-enable all of the threads that are
496 * waiting on the lock.
498 * @return True if synchronization was updated; false otherwise
500 bool ModelChecker::process_mutex(ModelAction *curr) {
501 std::mutex *mutex = (std::mutex *)curr->get_location();
502 struct std::mutex_state *state = mutex->get_state();
503 switch (curr->get_type()) {
504 case ATOMIC_TRYLOCK: {
505 bool success = !state->islocked;
506 curr->set_try_lock(success);
508 get_thread(curr)->set_return_value(0);
511 get_thread(curr)->set_return_value(1);
513 //otherwise fall into the lock case
515 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
516 printf("Lock access before initialization\n");
519 state->islocked = true;
520 ModelAction *unlock = get_last_unlock(curr);
521 //synchronize with the previous unlock statement
522 if (unlock != NULL) {
523 curr->synchronize_with(unlock);
528 case ATOMIC_UNLOCK: {
530 state->islocked = false;
531 //wake up the other threads
532 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
533 //activate all the waiting threads
534 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
535 scheduler->wake(get_thread(*rit));
542 state->islocked = false;
543 //wake up the other threads
544 action_list_t *waiters = lock_waiters_map->get_safe_ptr((void *) curr->get_value());
545 //activate all the waiting threads
546 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
547 scheduler->wake(get_thread(*rit));
550 //check whether we should go to sleep or not...simulate spurious failures
551 if (curr->get_node()->get_misc()==0) {
552 condvar_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
554 scheduler->sleep(get_current_thread());
558 case ATOMIC_NOTIFY_ALL: {
559 action_list_t *waiters = condvar_waiters_map->get_safe_ptr(curr->get_location());
560 //activate all the waiting threads
561 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
562 scheduler->wake(get_thread(*rit));
567 case ATOMIC_NOTIFY_ONE: {
568 action_list_t *waiters = condvar_waiters_map->get_safe_ptr(curr->get_location());
569 int wakeupthread=curr->get_node()->get_misc();
570 action_list_t::iterator it = waiters->begin();
571 advance(it, wakeupthread);
572 scheduler->wake(get_thread(*it));
584 * Process a write ModelAction
585 * @param curr The ModelAction to process
586 * @return True if the mo_graph was updated or promises were resolved
588 bool ModelChecker::process_write(ModelAction *curr)
590 bool updated_mod_order = w_modification_order(curr);
591 bool updated_promises = resolve_promises(curr);
593 if (promises->size() == 0) {
594 for (unsigned int i = 0; i < futurevalues->size(); i++) {
595 struct PendingFutureValue pfv = (*futurevalues)[i];
596 //Do more ambitious checks now that mo is more complete
597 if (mo_may_allow(pfv.writer, pfv.act)&&
598 pfv.act->get_node()->add_future_value(pfv.writer->get_value(), pfv.writer->get_seq_number()+params.maxfuturedelay) &&
599 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
600 priv->next_backtrack = pfv.act;
602 futurevalues->resize(0);
605 mo_graph->commitChanges();
606 mo_check_promises(curr->get_tid(), curr);
608 get_thread(curr)->set_return_value(VALUE_NONE);
609 return updated_mod_order || updated_promises;
613 * @brief Process the current action for thread-related activity
615 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
616 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
617 * synchronization, etc. This function is a no-op for non-THREAD actions
618 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
620 * @param curr The current action
621 * @return True if synchronization was updated or a thread completed
623 bool ModelChecker::process_thread_action(ModelAction *curr)
625 bool updated = false;
627 switch (curr->get_type()) {
628 case THREAD_CREATE: {
629 Thread *th = (Thread *)curr->get_location();
630 th->set_creation(curr);
634 Thread *blocking = (Thread *)curr->get_location();
635 ModelAction *act = get_last_action(blocking->get_id());
636 curr->synchronize_with(act);
637 updated = true; /* trigger rel-seq checks */
640 case THREAD_FINISH: {
641 Thread *th = get_thread(curr);
642 while (!th->wait_list_empty()) {
643 ModelAction *act = th->pop_wait_list();
644 scheduler->wake(get_thread(act));
647 updated = true; /* trigger rel-seq checks */
651 check_promises(curr->get_tid(), NULL, curr->get_cv());
662 * @brief Process the current action for release sequence fixup activity
664 * Performs model-checker release sequence fixups for the current action,
665 * forcing a single pending release sequence to break (with a given, potential
666 * "loose" write) or to complete (i.e., synchronize). If a pending release
667 * sequence forms a complete release sequence, then we must perform the fixup
668 * synchronization, mo_graph additions, etc.
670 * @param curr The current action; must be a release sequence fixup action
671 * @param work_queue The work queue to which to add work items as they are
674 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
676 const ModelAction *write = curr->get_node()->get_relseq_break();
677 struct release_seq *sequence = pending_rel_seqs->back();
678 pending_rel_seqs->pop_back();
680 ModelAction *acquire = sequence->acquire;
681 const ModelAction *rf = sequence->rf;
682 const ModelAction *release = sequence->release;
686 ASSERT(release->same_thread(rf));
690 * @todo Forcing a synchronization requires that we set
691 * modification order constraints. For instance, we can't allow
692 * a fixup sequence in which two separate read-acquire
693 * operations read from the same sequence, where the first one
694 * synchronizes and the other doesn't. Essentially, we can't
695 * allow any writes to insert themselves between 'release' and
699 /* Must synchronize */
700 if (!acquire->synchronize_with(release)) {
701 set_bad_synchronization();
704 /* Re-check all pending release sequences */
705 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
706 /* Re-check act for mo_graph edges */
707 work_queue->push_back(MOEdgeWorkEntry(acquire));
709 /* propagate synchronization to later actions */
710 action_list_t::reverse_iterator rit = action_trace->rbegin();
711 for (; (*rit) != acquire; rit++) {
712 ModelAction *propagate = *rit;
713 if (acquire->happens_before(propagate)) {
714 propagate->synchronize_with(acquire);
715 /* Re-check 'propagate' for mo_graph edges */
716 work_queue->push_back(MOEdgeWorkEntry(propagate));
720 /* Break release sequence with new edges:
721 * release --mo--> write --mo--> rf */
722 mo_graph->addEdge(release, write);
723 mo_graph->addEdge(write, rf);
726 /* See if we have realized a data race */
727 if (checkDataRaces())
732 * Initialize the current action by performing one or more of the following
733 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
734 * in the NodeStack, manipulating backtracking sets, allocating and
735 * initializing clock vectors, and computing the promises to fulfill.
737 * @param curr The current action, as passed from the user context; may be
738 * freed/invalidated after the execution of this function
739 * @return The current action, as processed by the ModelChecker. Is only the
740 * same as the parameter @a curr if this is a newly-explored action.
742 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
744 ModelAction *newcurr;
746 if (curr->is_rmwc() || curr->is_rmw()) {
747 newcurr = process_rmw(curr);
750 if (newcurr->is_rmw())
751 compute_promises(newcurr);
755 curr->set_seq_number(get_next_seq_num());
757 newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
759 /* First restore type and order in case of RMW operation */
761 newcurr->copy_typeandorder(curr);
763 ASSERT(curr->get_location() == newcurr->get_location());
764 newcurr->copy_from_new(curr);
766 /* Discard duplicate ModelAction; use action from NodeStack */
769 /* Always compute new clock vector */
770 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
774 /* Always compute new clock vector */
775 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
777 * Perform one-time actions when pushing new ModelAction onto
780 if (newcurr->is_write())
781 compute_promises(newcurr);
782 else if (newcurr->is_relseq_fixup())
783 compute_relseq_breakwrites(newcurr);
784 else if (newcurr->is_wait())
785 newcurr->get_node()->set_misc_max(2);
786 else if (newcurr->is_notify_one()) {
787 newcurr->get_node()->set_misc_max(condvar_waiters_map->get_safe_ptr(newcurr->get_location())->size());
794 * @brief Check whether a model action is enabled.
796 * Checks whether a lock or join operation would be successful (i.e., is the
797 * lock already locked, or is the joined thread already complete). If not, put
798 * the action in a waiter list.
800 * @param curr is the ModelAction to check whether it is enabled.
801 * @return a bool that indicates whether the action is enabled.
803 bool ModelChecker::check_action_enabled(ModelAction *curr) {
804 if (curr->is_lock()) {
805 std::mutex * lock = (std::mutex *)curr->get_location();
806 struct std::mutex_state * state = lock->get_state();
807 if (state->islocked) {
808 //Stick the action in the appropriate waiting queue
809 lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
812 } else if (curr->get_type() == THREAD_JOIN) {
813 Thread *blocking = (Thread *)curr->get_location();
814 if (!blocking->is_complete()) {
815 blocking->push_wait_list(curr);
824 * This is the heart of the model checker routine. It performs model-checking
825 * actions corresponding to a given "current action." Among other processes, it
826 * calculates reads-from relationships, updates synchronization clock vectors,
827 * forms a memory_order constraints graph, and handles replay/backtrack
828 * execution when running permutations of previously-observed executions.
830 * @param curr The current action to process
831 * @return The next Thread that must be executed. May be NULL if ModelChecker
832 * makes no choice (e.g., according to replay execution, combining RMW actions,
835 Thread * ModelChecker::check_current_action(ModelAction *curr)
838 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
840 if (!check_action_enabled(curr)) {
841 /* Make the execution look like we chose to run this action
842 * much later, when a lock/join can succeed */
843 get_current_thread()->set_pending(curr);
844 scheduler->sleep(get_current_thread());
845 return get_next_thread(NULL);
848 ModelAction *newcurr = initialize_curr_action(curr);
850 wake_up_sleeping_actions(curr);
852 /* Add the action to lists before any other model-checking tasks */
853 if (!second_part_of_rmw)
854 add_action_to_lists(newcurr);
856 /* Build may_read_from set for newly-created actions */
857 if (curr == newcurr && curr->is_read())
858 build_reads_from_past(curr);
861 /* Initialize work_queue with the "current action" work */
862 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
863 while (!work_queue.empty()) {
864 WorkQueueEntry work = work_queue.front();
865 work_queue.pop_front();
868 case WORK_CHECK_CURR_ACTION: {
869 ModelAction *act = work.action;
870 bool update = false; /* update this location's release seq's */
871 bool update_all = false; /* update all release seq's */
873 if (process_thread_action(curr))
876 if (act->is_read() && process_read(act, second_part_of_rmw))
879 if (act->is_write() && process_write(act))
882 if (act->is_mutex_op() && process_mutex(act))
885 if (act->is_relseq_fixup())
886 process_relseq_fixup(curr, &work_queue);
889 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
891 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
894 case WORK_CHECK_RELEASE_SEQ:
895 resolve_release_sequences(work.location, &work_queue);
897 case WORK_CHECK_MO_EDGES: {
898 /** @todo Complete verification of work_queue */
899 ModelAction *act = work.action;
900 bool updated = false;
902 if (act->is_read()) {
903 const ModelAction *rf = act->get_reads_from();
904 if (rf != NULL && r_modification_order(act, rf))
907 if (act->is_write()) {
908 if (w_modification_order(act))
911 mo_graph->commitChanges();
914 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
923 check_curr_backtracking(curr);
924 set_backtracking(curr);
925 return get_next_thread(curr);
928 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
929 Node *currnode = curr->get_node();
930 Node *parnode = currnode->get_parent();
932 if ((!parnode->backtrack_empty() ||
933 !currnode->misc_empty() ||
934 !currnode->read_from_empty() ||
935 !currnode->future_value_empty() ||
936 !currnode->promise_empty() ||
937 !currnode->relseq_break_empty())
938 && (!priv->next_backtrack ||
939 *curr > *priv->next_backtrack)) {
940 priv->next_backtrack = curr;
944 bool ModelChecker::promises_expired() {
945 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
946 Promise *promise = (*promises)[promise_index];
947 if (promise->get_expiration()<priv->used_sequence_numbers) {
954 /** @return whether the current partial trace must be a prefix of a
956 bool ModelChecker::isfeasibleprefix() {
957 return promises->size() == 0 && pending_rel_seqs->size() == 0;
960 /** @return whether the current partial trace is feasible. */
961 bool ModelChecker::isfeasible() {
962 if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
963 DEBUG("Infeasible: RMW violation\n");
965 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
968 /** @return whether the current partial trace is feasible other than
969 * multiple RMW reading from the same store. */
970 bool ModelChecker::isfeasibleotherthanRMW() {
972 if (mo_graph->checkForCycles())
973 DEBUG("Infeasible: modification order cycles\n");
975 DEBUG("Infeasible: failed promise\n");
977 DEBUG("Infeasible: too many reads\n");
978 if (bad_synchronization)
979 DEBUG("Infeasible: bad synchronization ordering\n");
980 if (promises_expired())
981 DEBUG("Infeasible: promises expired\n");
983 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
986 /** Returns whether the current completed trace is feasible. */
987 bool ModelChecker::isfinalfeasible() {
988 if (DBG_ENABLED() && promises->size() != 0)
989 DEBUG("Infeasible: unrevolved promises\n");
991 return isfeasible() && promises->size() == 0;
994 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
995 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
996 ModelAction *lastread = get_last_action(act->get_tid());
997 lastread->process_rmw(act);
998 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
999 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1000 mo_graph->commitChanges();
1006 * Checks whether a thread has read from the same write for too many times
1007 * without seeing the effects of a later write.
1010 * 1) there must a different write that we could read from that would satisfy the modification order,
1011 * 2) we must have read from the same value in excess of maxreads times, and
1012 * 3) that other write must have been in the reads_from set for maxreads times.
1014 * If so, we decide that the execution is no longer feasible.
1016 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
1017 if (params.maxreads != 0) {
1019 if (curr->get_node()->get_read_from_size() <= 1)
1021 //Must make sure that execution is currently feasible... We could
1022 //accidentally clear by rolling back
1025 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1026 int tid = id_to_int(curr->get_tid());
1029 if ((int)thrd_lists->size() <= tid)
1031 action_list_t *list = &(*thrd_lists)[tid];
1033 action_list_t::reverse_iterator rit = list->rbegin();
1034 /* Skip past curr */
1035 for (; (*rit) != curr; rit++)
1037 /* go past curr now */
1040 action_list_t::reverse_iterator ritcopy = rit;
1041 //See if we have enough reads from the same value
1043 for (; count < params.maxreads; rit++,count++) {
1044 if (rit==list->rend())
1046 ModelAction *act = *rit;
1047 if (!act->is_read())
1050 if (act->get_reads_from() != rf)
1052 if (act->get_node()->get_read_from_size() <= 1)
1055 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
1057 const ModelAction * write = curr->get_node()->get_read_from_at(i);
1059 //Need a different write
1063 /* Test to see whether this is a feasible write to read from*/
1064 mo_graph->startChanges();
1065 r_modification_order(curr, write);
1066 bool feasiblereadfrom = isfeasible();
1067 mo_graph->rollbackChanges();
1069 if (!feasiblereadfrom)
1073 bool feasiblewrite = true;
1074 //new we need to see if this write works for everyone
1076 for (int loop = count; loop>0; loop--,rit++) {
1077 ModelAction *act=*rit;
1078 bool foundvalue = false;
1079 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
1080 if (act->get_node()->get_read_from_at(i)==write) {
1086 feasiblewrite = false;
1090 if (feasiblewrite) {
1091 too_many_reads = true;
1099 * Updates the mo_graph with the constraints imposed from the current
1102 * Basic idea is the following: Go through each other thread and find
1103 * the lastest action that happened before our read. Two cases:
1105 * (1) The action is a write => that write must either occur before
1106 * the write we read from or be the write we read from.
1108 * (2) The action is a read => the write that that action read from
1109 * must occur before the write we read from or be the same write.
1111 * @param curr The current action. Must be a read.
1112 * @param rf The action that curr reads from. Must be a write.
1113 * @return True if modification order edges were added; false otherwise
1115 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
1117 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1120 ASSERT(curr->is_read());
1122 /* Iterate over all threads */
1123 for (i = 0; i < thrd_lists->size(); i++) {
1124 /* Iterate over actions in thread, starting from most recent */
1125 action_list_t *list = &(*thrd_lists)[i];
1126 action_list_t::reverse_iterator rit;
1127 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1128 ModelAction *act = *rit;
1131 * Include at most one act per-thread that "happens
1132 * before" curr. Don't consider reflexively.
1134 if (act->happens_before(curr) && act != curr) {
1135 if (act->is_write()) {
1137 mo_graph->addEdge(act, rf);
1141 const ModelAction *prevreadfrom = act->get_reads_from();
1142 //if the previous read is unresolved, keep going...
1143 if (prevreadfrom == NULL)
1146 if (rf != prevreadfrom) {
1147 mo_graph->addEdge(prevreadfrom, rf);
1159 /** This method fixes up the modification order when we resolve a
1160 * promises. The basic problem is that actions that occur after the
1161 * read curr could not property add items to the modification order
1164 * So for each thread, we find the earliest item that happens after
1165 * the read curr. This is the item we have to fix up with additional
1166 * constraints. If that action is write, we add a MO edge between
1167 * the Action rf and that action. If the action is a read, we add a
1168 * MO edge between the Action rf, and whatever the read accessed.
1170 * @param curr is the read ModelAction that we are fixing up MO edges for.
1171 * @param rf is the write ModelAction that curr reads from.
1174 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
1176 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1178 ASSERT(curr->is_read());
1180 /* Iterate over all threads */
1181 for (i = 0; i < thrd_lists->size(); i++) {
1182 /* Iterate over actions in thread, starting from most recent */
1183 action_list_t *list = &(*thrd_lists)[i];
1184 action_list_t::reverse_iterator rit;
1185 ModelAction *lastact = NULL;
1187 /* Find last action that happens after curr that is either not curr or a rmw */
1188 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1189 ModelAction *act = *rit;
1190 if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
1196 /* Include at most one act per-thread that "happens before" curr */
1197 if (lastact != NULL) {
1198 if (lastact==curr) {
1199 //Case 1: The resolved read is a RMW, and we need to make sure
1200 //that the write portion of the RMW mod order after rf
1202 mo_graph->addEdge(rf, lastact);
1203 } else if (lastact->is_read()) {
1204 //Case 2: The resolved read is a normal read and the next
1205 //operation is a read, and we need to make sure the value read
1206 //is mod ordered after rf
1208 const ModelAction *postreadfrom = lastact->get_reads_from();
1209 if (postreadfrom != NULL&&rf != postreadfrom)
1210 mo_graph->addEdge(rf, postreadfrom);
1212 //Case 3: The resolved read is a normal read and the next
1213 //operation is a write, and we need to make sure that the
1214 //write is mod ordered after rf
1216 mo_graph->addEdge(rf, lastact);
1224 * Updates the mo_graph with the constraints imposed from the current write.
1226 * Basic idea is the following: Go through each other thread and find
1227 * the lastest action that happened before our write. Two cases:
1229 * (1) The action is a write => that write must occur before
1232 * (2) The action is a read => the write that that action read from
1233 * must occur before the current write.
1235 * This method also handles two other issues:
1237 * (I) Sequential Consistency: Making sure that if the current write is
1238 * seq_cst, that it occurs after the previous seq_cst write.
1240 * (II) Sending the write back to non-synchronizing reads.
1242 * @param curr The current action. Must be a write.
1243 * @return True if modification order edges were added; false otherwise
1245 bool ModelChecker::w_modification_order(ModelAction *curr)
1247 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1250 ASSERT(curr->is_write());
1252 if (curr->is_seqcst()) {
1253 /* We have to at least see the last sequentially consistent write,
1254 so we are initialized. */
1255 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1256 if (last_seq_cst != NULL) {
1257 mo_graph->addEdge(last_seq_cst, curr);
1262 /* Iterate over all threads */
1263 for (i = 0; i < thrd_lists->size(); i++) {
1264 /* Iterate over actions in thread, starting from most recent */
1265 action_list_t *list = &(*thrd_lists)[i];
1266 action_list_t::reverse_iterator rit;
1267 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1268 ModelAction *act = *rit;
1271 * 1) If RMW and it actually read from something, then we
1272 * already have all relevant edges, so just skip to next
1275 * 2) If RMW and it didn't read from anything, we should
1276 * whatever edge we can get to speed up convergence.
1278 * 3) If normal write, we need to look at earlier actions, so
1279 * continue processing list.
1281 if (curr->is_rmw()) {
1282 if (curr->get_reads_from()!=NULL)
1291 * Include at most one act per-thread that "happens
1294 if (act->happens_before(curr)) {
1296 * Note: if act is RMW, just add edge:
1298 * The following edge should be handled elsewhere:
1299 * readfrom(act) --mo--> act
1301 if (act->is_write())
1302 mo_graph->addEdge(act, curr);
1303 else if (act->is_read()) {
1304 //if previous read accessed a null, just keep going
1305 if (act->get_reads_from() == NULL)
1307 mo_graph->addEdge(act->get_reads_from(), curr);
1311 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1312 !act->same_thread(curr)) {
1313 /* We have an action that:
1314 (1) did not happen before us
1315 (2) is a read and we are a write
1316 (3) cannot synchronize with us
1317 (4) is in a different thread
1319 that read could potentially read from our write. Note that
1320 these checks are overly conservative at this point, we'll
1321 do more checks before actually removing the
1325 if (thin_air_constraint_may_allow(curr, act)) {
1327 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1328 struct PendingFutureValue pfv = {curr,act};
1329 futurevalues->push_back(pfv);
1339 /** Arbitrary reads from the future are not allowed. Section 29.3
1340 * part 9 places some constraints. This method checks one result of constraint
1341 * constraint. Others require compiler support. */
1342 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1343 if (!writer->is_rmw())
1346 if (!reader->is_rmw())
1349 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1350 if (search == reader)
1352 if (search->get_tid() == reader->get_tid() &&
1353 search->happens_before(reader))
1360 /** Arbitrary reads from the future are not allowed. Section 29.3
1361 * part 9 places some constraints. This method checks one result of constraint
1362 * constraint. Others require compiler support. */
1363 bool ModelChecker::mo_may_allow(const ModelAction * writer, const ModelAction *reader) {
1364 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(reader->get_location());
1366 //Get write that follows reader action
1367 action_list_t *list = &(*thrd_lists)[id_to_int(reader->get_tid())];
1368 action_list_t::reverse_iterator rit;
1369 ModelAction *first_write_after_read=NULL;
1371 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1372 ModelAction *act = *rit;
1375 if (act->is_write())
1376 first_write_after_read=act;
1379 if (first_write_after_read==NULL)
1382 return !mo_graph->checkReachable(first_write_after_read, writer);
1388 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1389 * The ModelAction under consideration is expected to be taking part in
1390 * release/acquire synchronization as an object of the "reads from" relation.
1391 * Note that this can only provide release sequence support for RMW chains
1392 * which do not read from the future, as those actions cannot be traced until
1393 * their "promise" is fulfilled. Similarly, we may not even establish the
1394 * presence of a release sequence with certainty, as some modification order
1395 * constraints may be decided further in the future. Thus, this function
1396 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1397 * and a boolean representing certainty.
1399 * @param rf The action that might be part of a release sequence. Must be a
1401 * @param release_heads A pass-by-reference style return parameter. After
1402 * execution of this function, release_heads will contain the heads of all the
1403 * relevant release sequences, if any exists with certainty
1404 * @param pending A pass-by-reference style return parameter which is only used
1405 * when returning false (i.e., uncertain). Returns most information regarding
1406 * an uncertain release sequence, including any write operations that might
1407 * break the sequence.
1408 * @return true, if the ModelChecker is certain that release_heads is complete;
1411 bool ModelChecker::release_seq_heads(const ModelAction *rf,
1412 rel_heads_list_t *release_heads,
1413 struct release_seq *pending) const
1415 /* Only check for release sequences if there are no cycles */
1416 if (mo_graph->checkForCycles())
1420 ASSERT(rf->is_write());
1422 if (rf->is_release())
1423 release_heads->push_back(rf);
1425 break; /* End of RMW chain */
1427 /** @todo Need to be smarter here... In the linux lock
1428 * example, this will run to the beginning of the program for
1430 /** @todo The way to be smarter here is to keep going until 1
1431 * thread has a release preceded by an acquire and you've seen
1434 /* acq_rel RMW is a sufficient stopping condition */
1435 if (rf->is_acquire() && rf->is_release())
1436 return true; /* complete */
1438 rf = rf->get_reads_from();
1441 /* read from future: need to settle this later */
1443 return false; /* incomplete */
1446 if (rf->is_release())
1447 return true; /* complete */
1449 /* else relaxed write; check modification order for contiguous subsequence
1450 * -> rf must be same thread as release */
1451 int tid = id_to_int(rf->get_tid());
1452 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1453 action_list_t *list = &(*thrd_lists)[tid];
1454 action_list_t::const_reverse_iterator rit;
1456 /* Find rf in the thread list */
1457 rit = std::find(list->rbegin(), list->rend(), rf);
1458 ASSERT(rit != list->rend());
1460 /* Find the last write/release */
1461 for (; rit != list->rend(); rit++)
1462 if ((*rit)->is_release())
1464 if (rit == list->rend()) {
1465 /* No write-release in this thread */
1466 return true; /* complete */
1468 ModelAction *release = *rit;
1470 ASSERT(rf->same_thread(release));
1472 pending->writes.clear();
1474 bool certain = true;
1475 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1476 if (id_to_int(rf->get_tid()) == (int)i)
1478 list = &(*thrd_lists)[i];
1480 /* Can we ensure no future writes from this thread may break
1481 * the release seq? */
1482 bool future_ordered = false;
1484 ModelAction *last = get_last_action(int_to_id(i));
1485 Thread *th = get_thread(int_to_id(i));
1486 if ((last && rf->happens_before(last)) ||
1487 !scheduler->is_enabled(th) ||
1489 future_ordered = true;
1491 ASSERT(!th->is_model_thread() || future_ordered);
1493 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1494 const ModelAction *act = *rit;
1495 /* Reach synchronization -> this thread is complete */
1496 if (act->happens_before(release))
1498 if (rf->happens_before(act)) {
1499 future_ordered = true;
1503 /* Only writes can break release sequences */
1504 if (!act->is_write())
1507 /* Check modification order */
1508 if (mo_graph->checkReachable(rf, act)) {
1509 /* rf --mo--> act */
1510 future_ordered = true;
1513 if (mo_graph->checkReachable(act, release))
1514 /* act --mo--> release */
1516 if (mo_graph->checkReachable(release, act) &&
1517 mo_graph->checkReachable(act, rf)) {
1518 /* release --mo-> act --mo--> rf */
1519 return true; /* complete */
1521 /* act may break release sequence */
1522 pending->writes.push_back(act);
1525 if (!future_ordered)
1526 certain = false; /* This thread is uncertain */
1530 release_heads->push_back(release);
1531 pending->writes.clear();
1533 pending->release = release;
1540 * A public interface for getting the release sequence head(s) with which a
1541 * given ModelAction must synchronize. This function only returns a non-empty
1542 * result when it can locate a release sequence head with certainty. Otherwise,
1543 * it may mark the internal state of the ModelChecker so that it will handle
1544 * the release sequence at a later time, causing @a act to update its
1545 * synchronization at some later point in execution.
1546 * @param act The 'acquire' action that may read from a release sequence
1547 * @param release_heads A pass-by-reference return parameter. Will be filled
1548 * with the head(s) of the release sequence(s), if they exists with certainty.
1549 * @see ModelChecker::release_seq_heads
1551 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1553 const ModelAction *rf = act->get_reads_from();
1554 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
1555 sequence->acquire = act;
1557 if (!release_seq_heads(rf, release_heads, sequence)) {
1558 /* add act to 'lazy checking' list */
1559 pending_rel_seqs->push_back(sequence);
1561 snapshot_free(sequence);
1566 * Attempt to resolve all stashed operations that might synchronize with a
1567 * release sequence for a given location. This implements the "lazy" portion of
1568 * determining whether or not a release sequence was contiguous, since not all
1569 * modification order information is present at the time an action occurs.
1571 * @param location The location/object that should be checked for release
1572 * sequence resolutions. A NULL value means to check all locations.
1573 * @param work_queue The work queue to which to add work items as they are
1575 * @return True if any updates occurred (new synchronization, new mo_graph
1578 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1580 bool updated = false;
1581 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
1582 while (it != pending_rel_seqs->end()) {
1583 struct release_seq *pending = *it;
1584 ModelAction *act = pending->acquire;
1586 /* Only resolve sequences on the given location, if provided */
1587 if (location && act->get_location() != location) {
1592 const ModelAction *rf = act->get_reads_from();
1593 rel_heads_list_t release_heads;
1595 complete = release_seq_heads(rf, &release_heads, pending);
1596 for (unsigned int i = 0; i < release_heads.size(); i++) {
1597 if (!act->has_synchronized_with(release_heads[i])) {
1598 if (act->synchronize_with(release_heads[i]))
1601 set_bad_synchronization();
1606 /* Re-check all pending release sequences */
1607 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1608 /* Re-check act for mo_graph edges */
1609 work_queue->push_back(MOEdgeWorkEntry(act));
1611 /* propagate synchronization to later actions */
1612 action_list_t::reverse_iterator rit = action_trace->rbegin();
1613 for (; (*rit) != act; rit++) {
1614 ModelAction *propagate = *rit;
1615 if (act->happens_before(propagate)) {
1616 propagate->synchronize_with(act);
1617 /* Re-check 'propagate' for mo_graph edges */
1618 work_queue->push_back(MOEdgeWorkEntry(propagate));
1623 it = pending_rel_seqs->erase(it);
1624 snapshot_free(pending);
1630 // If we resolved promises or data races, see if we have realized a data race.
1631 if (checkDataRaces()) {
1639 * Performs various bookkeeping operations for the current ModelAction. For
1640 * instance, adds action to the per-object, per-thread action vector and to the
1641 * action trace list of all thread actions.
1643 * @param act is the ModelAction to add.
1645 void ModelChecker::add_action_to_lists(ModelAction *act)
1647 int tid = id_to_int(act->get_tid());
1648 action_trace->push_back(act);
1650 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1652 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1653 if (tid >= (int)vec->size())
1654 vec->resize(priv->next_thread_id);
1655 (*vec)[tid].push_back(act);
1657 if ((int)thrd_last_action->size() <= tid)
1658 thrd_last_action->resize(get_num_threads());
1659 (*thrd_last_action)[tid] = act;
1663 * @brief Get the last action performed by a particular Thread
1664 * @param tid The thread ID of the Thread in question
1665 * @return The last action in the thread
1667 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1669 int threadid = id_to_int(tid);
1670 if (threadid < (int)thrd_last_action->size())
1671 return (*thrd_last_action)[id_to_int(tid)];
1677 * Gets the last memory_order_seq_cst write (in the total global sequence)
1678 * performed on a particular object (i.e., memory location), not including the
1680 * @param curr The current ModelAction; also denotes the object location to
1682 * @return The last seq_cst write
1684 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1686 void *location = curr->get_location();
1687 action_list_t *list = obj_map->get_safe_ptr(location);
1688 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1689 action_list_t::reverse_iterator rit;
1690 for (rit = list->rbegin(); rit != list->rend(); rit++)
1691 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1697 * Gets the last unlock operation performed on a particular mutex (i.e., memory
1698 * location). This function identifies the mutex according to the current
1699 * action, which is presumed to perform on the same mutex.
1700 * @param curr The current ModelAction; also denotes the object location to
1702 * @return The last unlock operation
1704 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1706 void *location = curr->get_location();
1707 action_list_t *list = obj_map->get_safe_ptr(location);
1708 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1709 action_list_t::reverse_iterator rit;
1710 for (rit = list->rbegin(); rit != list->rend(); rit++)
1711 if ((*rit)->is_unlock())
1716 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1718 ModelAction *parent = get_last_action(tid);
1720 parent = get_thread(tid)->get_creation();
1725 * Returns the clock vector for a given thread.
1726 * @param tid The thread whose clock vector we want
1727 * @return Desired clock vector
1729 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1731 return get_parent_action(tid)->get_cv();
1735 * Resolve a set of Promises with a current write. The set is provided in the
1736 * Node corresponding to @a write.
1737 * @param write The ModelAction that is fulfilling Promises
1738 * @return True if promises were resolved; false otherwise
1740 bool ModelChecker::resolve_promises(ModelAction *write)
1742 bool resolved = false;
1743 std::vector< thread_id_t, ModelAlloc<thread_id_t> > threads_to_check;
1745 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1746 Promise *promise = (*promises)[promise_index];
1747 if (write->get_node()->get_promise(i)) {
1748 ModelAction *read = promise->get_action();
1749 if (read->is_rmw()) {
1750 mo_graph->addRMWEdge(write, read);
1752 read->read_from(write);
1753 //First fix up the modification order for actions that happened
1755 r_modification_order(read, write);
1756 //Next fix up the modification order for actions that happened
1758 post_r_modification_order(read, write);
1759 //Make sure the promise's value matches the write's value
1760 ASSERT(promise->get_value() == write->get_value());
1763 promises->erase(promises->begin() + promise_index);
1764 threads_to_check.push_back(read->get_tid());
1771 //Check whether reading these writes has made threads unable to
1774 for(unsigned int i=0;i<threads_to_check.size();i++)
1775 mo_check_promises(threads_to_check[i], write);
1781 * Compute the set of promises that could potentially be satisfied by this
1782 * action. Note that the set computation actually appears in the Node, not in
1784 * @param curr The ModelAction that may satisfy promises
1786 void ModelChecker::compute_promises(ModelAction *curr)
1788 for (unsigned int i = 0; i < promises->size(); i++) {
1789 Promise *promise = (*promises)[i];
1790 const ModelAction *act = promise->get_action();
1791 if (!act->happens_before(curr) &&
1793 !act->could_synchronize_with(curr) &&
1794 !act->same_thread(curr) &&
1795 promise->get_value() == curr->get_value()) {
1796 curr->get_node()->set_promise(i);
1801 /** Checks promises in response to change in ClockVector Threads. */
1802 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
1804 for (unsigned int i = 0; i < promises->size(); i++) {
1805 Promise *promise = (*promises)[i];
1806 const ModelAction *act = promise->get_action();
1807 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1808 merge_cv->synchronized_since(act)) {
1809 if (promise->increment_threads(tid)) {
1810 //Promise has failed
1811 failed_promise = true;
1818 /** Checks promises in response to addition to modification order for threads.
1820 * pthread is the thread that performed the read that created the promise
1822 * pread is the read that created the promise
1824 * pwrite is either the first write to same location as pread by
1825 * pthread that is sequenced after pread or the value read by the
1826 * first read to the same lcoation as pread by pthread that is
1827 * sequenced after pread..
1829 * 1. If tid=pthread, then we check what other threads are reachable
1830 * through the mode order starting with pwrite. Those threads cannot
1831 * perform a write that will resolve the promise due to modification
1832 * order constraints.
1834 * 2. If the tid is not pthread, we check whether pwrite can reach the
1835 * action write through the modification order. If so, that thread
1836 * cannot perform a future write that will resolve the promise due to
1837 * modificatin order constraints.
1839 * @parem tid The thread that either read from the model action
1840 * write, or actually did the model action write.
1842 * @parem write The ModelAction representing the relevant write.
1845 void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write) {
1846 void * location = write->get_location();
1847 for (unsigned int i = 0; i < promises->size(); i++) {
1848 Promise *promise = (*promises)[i];
1849 const ModelAction *act = promise->get_action();
1851 //Is this promise on the same location?
1852 if ( act->get_location() != location )
1855 //same thread as the promise
1856 if ( act->get_tid()==tid ) {
1858 //do we have a pwrite for the promise, if not, set it
1859 if (promise->get_write() == NULL ) {
1860 promise->set_write(write);
1861 //The pwrite cannot happen before the promise
1862 if (write->happens_before(act) && (write != act)) {
1863 failed_promise = true;
1867 if (mo_graph->checkPromise(write, promise)) {
1868 failed_promise = true;
1873 //Don't do any lookups twice for the same thread
1874 if (promise->has_sync_thread(tid))
1877 if (mo_graph->checkReachable(promise->get_write(), write)) {
1878 if (promise->increment_threads(tid)) {
1879 failed_promise = true;
1887 * Compute the set of writes that may break the current pending release
1888 * sequence. This information is extracted from previou release sequence
1891 * @param curr The current ModelAction. Must be a release sequence fixup
1894 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
1896 if (pending_rel_seqs->empty())
1899 struct release_seq *pending = pending_rel_seqs->back();
1900 for (unsigned int i = 0; i < pending->writes.size(); i++) {
1901 const ModelAction *write = pending->writes[i];
1902 curr->get_node()->add_relseq_break(write);
1905 /* NULL means don't break the sequence; just synchronize */
1906 curr->get_node()->add_relseq_break(NULL);
1910 * Build up an initial set of all past writes that this 'read' action may read
1911 * from. This set is determined by the clock vector's "happens before"
1913 * @param curr is the current ModelAction that we are exploring; it must be a
1916 void ModelChecker::build_reads_from_past(ModelAction *curr)
1918 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1920 ASSERT(curr->is_read());
1922 ModelAction *last_seq_cst = NULL;
1924 /* Track whether this object has been initialized */
1925 bool initialized = false;
1927 if (curr->is_seqcst()) {
1928 last_seq_cst = get_last_seq_cst(curr);
1929 /* We have to at least see the last sequentially consistent write,
1930 so we are initialized. */
1931 if (last_seq_cst != NULL)
1935 /* Iterate over all threads */
1936 for (i = 0; i < thrd_lists->size(); i++) {
1937 /* Iterate over actions in thread, starting from most recent */
1938 action_list_t *list = &(*thrd_lists)[i];
1939 action_list_t::reverse_iterator rit;
1940 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1941 ModelAction *act = *rit;
1943 /* Only consider 'write' actions */
1944 if (!act->is_write() || act == curr)
1947 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1948 if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1949 DEBUG("Adding action to may_read_from:\n");
1950 if (DBG_ENABLED()) {
1955 if (curr->get_sleep_flag() && ! curr->is_seqcst()) {
1956 if (sleep_can_read_from(curr, act))
1957 curr->get_node()->add_read_from(act);
1959 curr->get_node()->add_read_from(act);
1962 /* Include at most one act per-thread that "happens before" curr */
1963 if (act->happens_before(curr)) {
1971 /** @todo Need a more informative way of reporting errors. */
1972 printf("ERROR: may read from uninitialized atomic\n");
1975 if (DBG_ENABLED() || !initialized) {
1976 printf("Reached read action:\n");
1978 printf("Printing may_read_from\n");
1979 curr->get_node()->print_may_read_from();
1980 printf("End printing may_read_from\n");
1983 ASSERT(initialized);
1986 bool ModelChecker::sleep_can_read_from(ModelAction * curr, const ModelAction *write) {
1988 Node *prevnode=write->get_node()->get_parent();
1989 bool thread_sleep=prevnode->get_enabled_array()[id_to_int(curr->get_tid())]==THREAD_SLEEP_SET;
1990 if (write->is_release()&&thread_sleep)
1992 if (!write->is_rmw()) {
1995 if (write->get_reads_from()==NULL)
1997 write=write->get_reads_from();
2001 static void print_list(action_list_t *list)
2003 action_list_t::iterator it;
2005 printf("---------------------------------------------------------------------\n");
2007 unsigned int hash=0;
2009 for (it = list->begin(); it != list->end(); it++) {
2011 hash=hash^(hash<<3)^((*it)->hash());
2013 printf("HASH %u\n", hash);
2014 printf("---------------------------------------------------------------------\n");
2017 #if SUPPORT_MOD_ORDER_DUMP
2018 void ModelChecker::dumpGraph(char *filename) {
2020 sprintf(buffer, "%s.dot",filename);
2021 FILE *file=fopen(buffer, "w");
2022 fprintf(file, "digraph %s {\n",filename);
2023 mo_graph->dumpNodes(file);
2024 ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
2026 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2027 ModelAction *action=*it;
2028 if (action->is_read()) {
2029 fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
2030 if (action->get_reads_from()!=NULL)
2031 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
2033 if (thread_array[action->get_tid()] != NULL) {
2034 fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
2037 thread_array[action->get_tid()]=action;
2039 fprintf(file,"}\n");
2040 model_free(thread_array);
2045 void ModelChecker::print_summary()
2048 printf("Number of executions: %d\n", num_executions);
2049 printf("Number of feasible executions: %d\n", num_feasible_executions);
2050 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
2052 #if SUPPORT_MOD_ORDER_DUMP
2054 char buffername[100];
2055 sprintf(buffername, "exec%04u", num_executions);
2056 mo_graph->dumpGraphToFile(buffername);
2057 sprintf(buffername, "graph%04u", num_executions);
2058 dumpGraph(buffername);
2061 if (!isfinalfeasible())
2062 printf("INFEASIBLE EXECUTION!\n");
2063 print_list(action_trace);
2068 * Add a Thread to the system for the first time. Should only be called once
2070 * @param t The Thread to add
2072 void ModelChecker::add_thread(Thread *t)
2074 thread_map->put(id_to_int(t->get_id()), t);
2075 scheduler->add_thread(t);
2079 * Removes a thread from the scheduler.
2080 * @param the thread to remove.
2082 void ModelChecker::remove_thread(Thread *t)
2084 scheduler->remove_thread(t);
2088 * @brief Get a Thread reference by its ID
2089 * @param tid The Thread's ID
2090 * @return A Thread reference
2092 Thread * ModelChecker::get_thread(thread_id_t tid) const
2094 return thread_map->get(id_to_int(tid));
2098 * @brief Get a reference to the Thread in which a ModelAction was executed
2099 * @param act The ModelAction
2100 * @return A Thread reference
2102 Thread * ModelChecker::get_thread(ModelAction *act) const
2104 return get_thread(act->get_tid());
2108 * Switch from a user-context to the "master thread" context (a.k.a. system
2109 * context). This switch is made with the intention of exploring a particular
2110 * model-checking action (described by a ModelAction object). Must be called
2111 * from a user-thread context.
2113 * @param act The current action that will be explored. May be NULL only if
2114 * trace is exiting via an assertion (see ModelChecker::set_assert and
2115 * ModelChecker::has_asserted).
2116 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
2118 int ModelChecker::switch_to_master(ModelAction *act)
2121 Thread *old = thread_current();
2122 set_current_action(act);
2123 old->set_state(THREAD_READY);
2124 return Thread::swap(old, &system_context);
2128 * Takes the next step in the execution, if possible.
2129 * @return Returns true (success) if a step was taken and false otherwise.
2131 bool ModelChecker::take_step() {
2135 Thread *curr = priv->current_action ? get_thread(priv->current_action) : NULL;
2137 if (curr->get_state() == THREAD_READY) {
2138 ASSERT(priv->current_action);
2140 priv->nextThread = check_current_action(priv->current_action);
2141 priv->current_action = NULL;
2143 if (curr->is_blocked() || curr->is_complete())
2144 scheduler->remove_thread(curr);
2149 Thread *next = scheduler->next_thread(priv->nextThread);
2151 /* Infeasible -> don't take any more steps */
2155 if (params.bound != 0) {
2156 if (priv->used_sequence_numbers > params.bound) {
2161 DEBUG("(%d, %d)\n", curr ? id_to_int(curr->get_id()) : -1,
2162 next ? id_to_int(next->get_id()) : -1);
2165 * Launch end-of-execution release sequence fixups only when there are:
2167 * (1) no more user threads to run (or when execution replay chooses
2168 * the 'model_thread')
2169 * (2) pending release sequences
2170 * (3) pending assertions (i.e., data races)
2171 * (4) no pending promises
2173 if (!pending_rel_seqs->empty() && (!next || next->is_model_thread()) &&
2174 isfinalfeasible() && !unrealizedraces.empty()) {
2175 printf("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
2176 pending_rel_seqs->size());
2177 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2178 std::memory_order_seq_cst, NULL, VALUE_NONE,
2180 set_current_action(fixup);
2184 /* next == NULL -> don't take any more steps */
2188 next->set_state(THREAD_RUNNING);
2190 if (next->get_pending() != NULL) {
2191 /* restart a pending action */
2192 set_current_action(next->get_pending());
2193 next->set_pending(NULL);
2194 next->set_state(THREAD_READY);
2198 /* Return false only if swap fails with an error */
2199 return (Thread::swap(&system_context, next) == 0);
2202 /** Runs the current execution until threre are no more steps to take. */
2203 void ModelChecker::finish_execution() {
2206 while (take_step());