10 #include "nodestack.h"
13 #include "clockvector.h"
14 #include "cyclegraph.h"
17 #include "threads-model.h"
18 #include "bugmessage.h"
20 #define INITIAL_THREAD_ID 0
23 * Structure for holding small ModelChecker members that should be snapshotted
25 struct model_snapshot_members {
26 model_snapshot_members() :
27 /* First thread created will have id INITIAL_THREAD_ID */
28 next_thread_id(INITIAL_THREAD_ID),
29 used_sequence_numbers(0),
32 failed_promise(false),
33 too_many_reads(false),
34 no_valid_reads(false),
35 bad_synchronization(false),
39 ~model_snapshot_members() {
40 for (unsigned int i = 0; i < bugs.size(); i++)
45 unsigned int next_thread_id;
46 modelclock_t used_sequence_numbers;
47 ModelAction *next_backtrack;
48 SnapVector<bug_message *> bugs;
52 /** @brief Incorrectly-ordered synchronization was made */
53 bool bad_synchronization;
59 /** @brief Constructor */
60 ModelExecution::ModelExecution(ModelChecker *m,
61 struct model_params *params,
63 NodeStack *node_stack) :
68 thread_map(2), /* We'll always need at least 2 threads */
70 condvar_waiters_map(),
76 thrd_last_fence_release(),
77 node_stack(node_stack),
78 priv(new struct model_snapshot_members()),
79 mo_graph(new CycleGraph())
81 /* Initialize a model-checker thread, for special ModelActions */
82 model_thread = new Thread(get_next_id());
83 add_thread(model_thread);
84 scheduler->register_engine(this);
87 /** @brief Destructor */
88 ModelExecution::~ModelExecution()
90 for (unsigned int i = 0; i < get_num_threads(); i++)
91 delete get_thread(int_to_id(i));
93 for (unsigned int i = 0; i < promises.size(); i++)
100 int ModelExecution::get_execution_number() const
102 return model->get_execution_number();
105 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
107 action_list_t *tmp = hash->get(ptr);
109 tmp = new action_list_t();
115 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
117 SnapVector<action_list_t> *tmp = hash->get(ptr);
119 tmp = new SnapVector<action_list_t>();
125 action_list_t * ModelExecution::get_actions_on_obj(void * obj, thread_id_t tid) const
127 SnapVector<action_list_t> *wrv = obj_thrd_map.get(obj);
130 unsigned int thread=id_to_int(tid);
131 if (thread < wrv->size())
132 return &(*wrv)[thread];
137 /** @return a thread ID for a new Thread */
138 thread_id_t ModelExecution::get_next_id()
140 return priv->next_thread_id++;
143 /** @return the number of user threads created during this execution */
144 unsigned int ModelExecution::get_num_threads() const
146 return priv->next_thread_id;
149 /** @return a sequence number for a new ModelAction */
150 modelclock_t ModelExecution::get_next_seq_num()
152 return ++priv->used_sequence_numbers;
156 * @brief Should the current action wake up a given thread?
158 * @param curr The current action
159 * @param thread The thread that we might wake up
160 * @return True, if we should wake up the sleeping thread; false otherwise
162 bool ModelExecution::should_wake_up(const ModelAction *curr, const Thread *thread) const
164 const ModelAction *asleep = thread->get_pending();
165 /* Don't allow partial RMW to wake anyone up */
168 /* Synchronizing actions may have been backtracked */
169 if (asleep->could_synchronize_with(curr))
171 /* All acquire/release fences and fence-acquire/store-release */
172 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
174 /* Fence-release + store can awake load-acquire on the same location */
175 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
176 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
177 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
183 void ModelExecution::wake_up_sleeping_actions(ModelAction *curr)
185 for (unsigned int i = 0; i < get_num_threads(); i++) {
186 Thread *thr = get_thread(int_to_id(i));
187 if (scheduler->is_sleep_set(thr)) {
188 if (should_wake_up(curr, thr))
189 /* Remove this thread from sleep set */
190 scheduler->remove_sleep(thr);
195 /** @brief Alert the model-checker that an incorrectly-ordered
196 * synchronization was made */
197 void ModelExecution::set_bad_synchronization()
199 priv->bad_synchronization = true;
202 bool ModelExecution::assert_bug(const char *msg)
204 priv->bugs.push_back(new bug_message(msg));
206 if (isfeasibleprefix()) {
213 /** @return True, if any bugs have been reported for this execution */
214 bool ModelExecution::have_bug_reports() const
216 return priv->bugs.size() != 0;
219 SnapVector<bug_message *> * ModelExecution::get_bugs() const
225 * Check whether the current trace has triggered an assertion which should halt
228 * @return True, if the execution should be aborted; false otherwise
230 bool ModelExecution::has_asserted() const
232 return priv->asserted;
236 * Trigger a trace assertion which should cause this execution to be halted.
237 * This can be due to a detected bug or due to an infeasibility that should
240 void ModelExecution::set_assert()
242 priv->asserted = true;
246 * Check if we are in a deadlock. Should only be called at the end of an
247 * execution, although it should not give false positives in the middle of an
248 * execution (there should be some ENABLED thread).
250 * @return True if program is in a deadlock; false otherwise
252 bool ModelExecution::is_deadlocked() const
254 bool blocking_threads = false;
255 for (unsigned int i = 0; i < get_num_threads(); i++) {
256 thread_id_t tid = int_to_id(i);
259 Thread *t = get_thread(tid);
260 if (!t->is_model_thread() && t->get_pending())
261 blocking_threads = true;
263 return blocking_threads;
267 * Check if this is a complete execution. That is, have all thread completed
268 * execution (rather than exiting because sleep sets have forced a redundant
271 * @return True if the execution is complete.
273 bool ModelExecution::is_complete_execution() const
275 for (unsigned int i = 0; i < get_num_threads(); i++)
276 if (is_enabled(int_to_id(i)))
282 * @brief Find the last fence-related backtracking conflict for a ModelAction
284 * This function performs the search for the most recent conflicting action
285 * against which we should perform backtracking, as affected by fence
286 * operations. This includes pairs of potentially-synchronizing actions which
287 * occur due to fence-acquire or fence-release, and hence should be explored in
288 * the opposite execution order.
290 * @param act The current action
291 * @return The most recent action which conflicts with act due to fences
293 ModelAction * ModelExecution::get_last_fence_conflict(ModelAction *act) const
295 /* Only perform release/acquire fence backtracking for stores */
296 if (!act->is_write())
299 /* Find a fence-release (or, act is a release) */
300 ModelAction *last_release;
301 if (act->is_release())
304 last_release = get_last_fence_release(act->get_tid());
308 /* Skip past the release */
309 const action_list_t *list = &action_trace;
310 action_list_t::const_reverse_iterator rit;
311 for (rit = list->rbegin(); rit != list->rend(); rit++)
312 if (*rit == last_release)
314 ASSERT(rit != list->rend());
319 * load --sb-> fence-acquire */
320 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
321 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
322 bool found_acquire_fences = false;
323 for ( ; rit != list->rend(); rit++) {
324 ModelAction *prev = *rit;
325 if (act->same_thread(prev))
328 int tid = id_to_int(prev->get_tid());
330 if (prev->is_read() && act->same_var(prev)) {
331 if (prev->is_acquire()) {
332 /* Found most recent load-acquire, don't need
333 * to search for more fences */
334 if (!found_acquire_fences)
337 prior_loads[tid] = prev;
340 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
341 found_acquire_fences = true;
342 acquire_fences[tid] = prev;
346 ModelAction *latest_backtrack = NULL;
347 for (unsigned int i = 0; i < acquire_fences.size(); i++)
348 if (acquire_fences[i] && prior_loads[i])
349 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
350 latest_backtrack = acquire_fences[i];
351 return latest_backtrack;
355 * @brief Find the last backtracking conflict for a ModelAction
357 * This function performs the search for the most recent conflicting action
358 * against which we should perform backtracking. This primary includes pairs of
359 * synchronizing actions which should be explored in the opposite execution
362 * @param act The current action
363 * @return The most recent action which conflicts with act
365 ModelAction * ModelExecution::get_last_conflict(ModelAction *act) const
367 switch (act->get_type()) {
368 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
372 ModelAction *ret = NULL;
374 /* linear search: from most recent to oldest */
375 action_list_t *list = obj_map.get(act->get_location());
376 action_list_t::reverse_iterator rit;
377 for (rit = list->rbegin(); rit != list->rend(); rit++) {
378 ModelAction *prev = *rit;
379 if (prev->could_synchronize_with(act)) {
385 ModelAction *ret2 = get_last_fence_conflict(act);
395 case ATOMIC_TRYLOCK: {
396 /* linear search: from most recent to oldest */
397 action_list_t *list = obj_map.get(act->get_location());
398 action_list_t::reverse_iterator rit;
399 for (rit = list->rbegin(); rit != list->rend(); rit++) {
400 ModelAction *prev = *rit;
401 if (act->is_conflicting_lock(prev))
406 case ATOMIC_UNLOCK: {
407 /* linear search: from most recent to oldest */
408 action_list_t *list = obj_map.get(act->get_location());
409 action_list_t::reverse_iterator rit;
410 for (rit = list->rbegin(); rit != list->rend(); rit++) {
411 ModelAction *prev = *rit;
412 if (!act->same_thread(prev) && prev->is_failed_trylock())
418 /* linear search: from most recent to oldest */
419 action_list_t *list = obj_map.get(act->get_location());
420 action_list_t::reverse_iterator rit;
421 for (rit = list->rbegin(); rit != list->rend(); rit++) {
422 ModelAction *prev = *rit;
423 if (!act->same_thread(prev) && prev->is_failed_trylock())
425 if (!act->same_thread(prev) && prev->is_notify())
431 case ATOMIC_NOTIFY_ALL:
432 case ATOMIC_NOTIFY_ONE: {
433 /* linear search: from most recent to oldest */
434 action_list_t *list = obj_map.get(act->get_location());
435 action_list_t::reverse_iterator rit;
436 for (rit = list->rbegin(); rit != list->rend(); rit++) {
437 ModelAction *prev = *rit;
438 if (!act->same_thread(prev) && prev->is_wait())
449 /** This method finds backtracking points where we should try to
450 * reorder the parameter ModelAction against.
452 * @param the ModelAction to find backtracking points for.
454 void ModelExecution::set_backtracking(ModelAction *act)
456 Thread *t = get_thread(act);
457 ModelAction *prev = get_last_conflict(act);
461 Node *node = prev->get_node()->get_parent();
463 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
464 int low_tid, high_tid;
465 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
466 low_tid = id_to_int(act->get_tid());
467 high_tid = low_tid + 1;
470 high_tid = get_num_threads();
473 for (int i = low_tid; i < high_tid; i++) {
474 thread_id_t tid = int_to_id(i);
476 /* Make sure this thread can be enabled here. */
477 if (i >= node->get_num_threads())
480 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
481 /* Don't backtrack into a point where the thread is disabled or sleeping. */
482 if (node->enabled_status(tid) != THREAD_ENABLED)
485 /* Check if this has been explored already */
486 if (node->has_been_explored(tid))
489 /* See if fairness allows */
490 if (params->fairwindow != 0 && !node->has_priority(tid)) {
492 for (int t = 0; t < node->get_num_threads(); t++) {
493 thread_id_t tother = int_to_id(t);
494 if (node->is_enabled(tother) && node->has_priority(tother)) {
503 /* See if CHESS-like yield fairness allows */
504 if (params->yieldon) {
506 for (int t = 0; t < node->get_num_threads(); t++) {
507 thread_id_t tother = int_to_id(t);
508 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
517 /* Cache the latest backtracking point */
518 set_latest_backtrack(prev);
520 /* If this is a new backtracking point, mark the tree */
521 if (!node->set_backtrack(tid))
523 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
524 id_to_int(prev->get_tid()),
525 id_to_int(t->get_id()));
534 * @brief Cache the a backtracking point as the "most recent", if eligible
536 * Note that this does not prepare the NodeStack for this backtracking
537 * operation, it only caches the action on a per-execution basis
539 * @param act The operation at which we should explore a different next action
540 * (i.e., backtracking point)
541 * @return True, if this action is now the most recent backtracking point;
544 bool ModelExecution::set_latest_backtrack(ModelAction *act)
546 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
547 priv->next_backtrack = act;
554 * Returns last backtracking point. The model checker will explore a different
555 * path for this point in the next execution.
556 * @return The ModelAction at which the next execution should diverge.
558 ModelAction * ModelExecution::get_next_backtrack()
560 ModelAction *next = priv->next_backtrack;
561 priv->next_backtrack = NULL;
566 * Processes a read model action.
567 * @param curr is the read model action to process.
568 * @return True if processing this read updates the mo_graph.
570 bool ModelExecution::process_read(ModelAction *curr)
572 Node *node = curr->get_node();
574 bool updated = false;
575 switch (node->get_read_from_status()) {
576 case READ_FROM_PAST: {
577 const ModelAction *rf = node->get_read_from_past();
580 mo_graph->startChanges();
582 ASSERT(!is_infeasible());
583 if (!check_recency(curr, rf)) {
584 if (node->increment_read_from()) {
585 mo_graph->rollbackChanges();
588 priv->too_many_reads = true;
592 updated = r_modification_order(curr, rf);
594 mo_graph->commitChanges();
595 mo_check_promises(curr, true);
598 case READ_FROM_PROMISE: {
599 Promise *promise = curr->get_node()->get_read_from_promise();
600 if (promise->add_reader(curr))
601 priv->failed_promise = true;
602 curr->set_read_from_promise(promise);
603 mo_graph->startChanges();
604 if (!check_recency(curr, promise))
605 priv->too_many_reads = true;
606 updated = r_modification_order(curr, promise);
607 mo_graph->commitChanges();
610 case READ_FROM_FUTURE: {
611 /* Read from future value */
612 struct future_value fv = node->get_future_value();
613 Promise *promise = new Promise(this, curr, fv);
614 curr->set_read_from_promise(promise);
615 promises.push_back(promise);
616 mo_graph->startChanges();
617 updated = r_modification_order(curr, promise);
618 mo_graph->commitChanges();
624 get_thread(curr)->set_return_value(curr->get_return_value());
630 * Processes a lock, trylock, or unlock model action. @param curr is
631 * the read model action to process.
633 * The try lock operation checks whether the lock is taken. If not,
634 * it falls to the normal lock operation case. If so, it returns
637 * The lock operation has already been checked that it is enabled, so
638 * it just grabs the lock and synchronizes with the previous unlock.
640 * The unlock operation has to re-enable all of the threads that are
641 * waiting on the lock.
643 * @return True if synchronization was updated; false otherwise
645 bool ModelExecution::process_mutex(ModelAction *curr)
647 std::mutex *mutex = curr->get_mutex();
648 struct std::mutex_state *state = NULL;
651 state = mutex->get_state();
653 switch (curr->get_type()) {
654 case ATOMIC_TRYLOCK: {
655 bool success = !state->locked;
656 curr->set_try_lock(success);
658 get_thread(curr)->set_return_value(0);
661 get_thread(curr)->set_return_value(1);
663 //otherwise fall into the lock case
665 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
666 assert_bug("Lock access before initialization");
667 state->locked = get_thread(curr);
668 ModelAction *unlock = get_last_unlock(curr);
669 //synchronize with the previous unlock statement
670 if (unlock != NULL) {
671 synchronize(unlock, curr);
677 case ATOMIC_UNLOCK: {
678 /* wake up the other threads */
679 for (unsigned int i = 0; i < get_num_threads(); i++) {
680 Thread *t = get_thread(int_to_id(i));
681 Thread *curr_thrd = get_thread(curr);
682 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
686 /* unlock the lock - after checking who was waiting on it */
687 state->locked = NULL;
689 if (!curr->is_wait())
690 break; /* The rest is only for ATOMIC_WAIT */
692 /* Should we go to sleep? (simulate spurious failures) */
693 if (curr->get_node()->get_misc() == 0) {
694 get_safe_ptr_action(&condvar_waiters_map, curr->get_location())->push_back(curr);
696 scheduler->sleep(get_thread(curr));
700 case ATOMIC_NOTIFY_ALL: {
701 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
702 //activate all the waiting threads
703 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
704 scheduler->wake(get_thread(*rit));
709 case ATOMIC_NOTIFY_ONE: {
710 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
711 int wakeupthread = curr->get_node()->get_misc();
712 action_list_t::iterator it = waiters->begin();
713 advance(it, wakeupthread);
714 scheduler->wake(get_thread(*it));
726 * @brief Check if the current pending promises allow a future value to be sent
728 * If one of the following is true:
729 * (a) there are no pending promises
730 * (b) the reader and writer do not cross any promises
731 * Then, it is safe to pass a future value back now.
733 * Otherwise, we must save the pending future value until (a) or (b) is true
735 * @param writer The operation which sends the future value. Must be a write.
736 * @param reader The operation which will observe the value. Must be a read.
737 * @return True if the future value can be sent now; false if it must wait.
739 bool ModelExecution::promises_may_allow(const ModelAction *writer,
740 const ModelAction *reader) const
742 if (promises.empty())
744 for (int i = promises.size() - 1; i >= 0; i--) {
745 ModelAction *pr = promises[i]->get_reader(0);
746 //reader is after promise...doesn't cross any promise
749 //writer is after promise, reader before...bad...
757 * @brief Add a future value to a reader
759 * This function performs a few additional checks to ensure that the future
760 * value can be feasibly observed by the reader
762 * @param writer The operation whose value is sent. Must be a write.
763 * @param reader The read operation which may read the future value. Must be a read.
765 void ModelExecution::add_future_value(const ModelAction *writer, ModelAction *reader)
767 /* Do more ambitious checks now that mo is more complete */
768 if (!mo_may_allow(writer, reader))
771 Node *node = reader->get_node();
773 /* Find an ancestor thread which exists at the time of the reader */
774 Thread *write_thread = get_thread(writer);
775 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
776 write_thread = write_thread->get_parent();
778 struct future_value fv = {
779 writer->get_write_value(),
780 writer->get_seq_number() + params->maxfuturedelay,
781 write_thread->get_id(),
783 if (node->add_future_value(fv))
784 set_latest_backtrack(reader);
788 * Process a write ModelAction
789 * @param curr The ModelAction to process
790 * @return True if the mo_graph was updated or promises were resolved
792 bool ModelExecution::process_write(ModelAction *curr)
794 /* Readers to which we may send our future value */
795 ModelVector<ModelAction *> send_fv;
797 const ModelAction *earliest_promise_reader;
798 bool updated_promises = false;
800 bool updated_mod_order = w_modification_order(curr, &send_fv);
801 Promise *promise = pop_promise_to_resolve(curr);
804 earliest_promise_reader = promise->get_reader(0);
805 updated_promises = resolve_promise(curr, promise);
807 earliest_promise_reader = NULL;
809 for (unsigned int i = 0; i < send_fv.size(); i++) {
810 ModelAction *read = send_fv[i];
812 /* Don't send future values to reads after the Promise we resolve */
813 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
814 /* Check if future value can be sent immediately */
815 if (promises_may_allow(curr, read)) {
816 add_future_value(curr, read);
818 futurevalues.push_back(PendingFutureValue(curr, read));
823 /* Check the pending future values */
824 for (int i = (int)futurevalues.size() - 1; i >= 0; i--) {
825 struct PendingFutureValue pfv = futurevalues[i];
826 if (promises_may_allow(pfv.writer, pfv.reader)) {
827 add_future_value(pfv.writer, pfv.reader);
828 futurevalues.erase(futurevalues.begin() + i);
832 mo_graph->commitChanges();
833 mo_check_promises(curr, false);
835 get_thread(curr)->set_return_value(VALUE_NONE);
836 return updated_mod_order || updated_promises;
840 * Process a fence ModelAction
841 * @param curr The ModelAction to process
842 * @return True if synchronization was updated
844 bool ModelExecution::process_fence(ModelAction *curr)
847 * fence-relaxed: no-op
848 * fence-release: only log the occurence (not in this function), for
849 * use in later synchronization
850 * fence-acquire (this function): search for hypothetical release
852 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
854 bool updated = false;
855 if (curr->is_acquire()) {
856 action_list_t *list = &action_trace;
857 action_list_t::reverse_iterator rit;
858 /* Find X : is_read(X) && X --sb-> curr */
859 for (rit = list->rbegin(); rit != list->rend(); rit++) {
860 ModelAction *act = *rit;
863 if (act->get_tid() != curr->get_tid())
865 /* Stop at the beginning of the thread */
866 if (act->is_thread_start())
868 /* Stop once we reach a prior fence-acquire */
869 if (act->is_fence() && act->is_acquire())
873 /* read-acquire will find its own release sequences */
874 if (act->is_acquire())
877 /* Establish hypothetical release sequences */
878 rel_heads_list_t release_heads;
879 get_release_seq_heads(curr, act, &release_heads);
880 for (unsigned int i = 0; i < release_heads.size(); i++)
881 synchronize(release_heads[i], curr);
882 if (release_heads.size() != 0)
890 * @brief Process the current action for thread-related activity
892 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
893 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
894 * synchronization, etc. This function is a no-op for non-THREAD actions
895 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
897 * @param curr The current action
898 * @return True if synchronization was updated or a thread completed
900 bool ModelExecution::process_thread_action(ModelAction *curr)
902 bool updated = false;
904 switch (curr->get_type()) {
905 case THREAD_CREATE: {
906 thrd_t *thrd = (thrd_t *)curr->get_location();
907 struct thread_params *params = (struct thread_params *)curr->get_value();
908 Thread *th = new Thread(get_next_id(), thrd, params->func, params->arg, get_thread(curr));
910 th->set_creation(curr);
911 /* Promises can be satisfied by children */
912 for (unsigned int i = 0; i < promises.size(); i++) {
913 Promise *promise = promises[i];
914 if (promise->thread_is_available(curr->get_tid()))
915 promise->add_thread(th->get_id());
920 Thread *blocking = curr->get_thread_operand();
921 ModelAction *act = get_last_action(blocking->get_id());
922 synchronize(act, curr);
923 updated = true; /* trigger rel-seq checks */
926 case THREAD_FINISH: {
927 Thread *th = get_thread(curr);
928 /* Wake up any joining threads */
929 for (unsigned int i = 0; i < get_num_threads(); i++) {
930 Thread *waiting = get_thread(int_to_id(i));
931 if (waiting->waiting_on() == th &&
932 waiting->get_pending()->is_thread_join())
933 scheduler->wake(waiting);
936 /* Completed thread can't satisfy promises */
937 for (unsigned int i = 0; i < promises.size(); i++) {
938 Promise *promise = promises[i];
939 if (promise->thread_is_available(th->get_id()))
940 if (promise->eliminate_thread(th->get_id()))
941 priv->failed_promise = true;
943 updated = true; /* trigger rel-seq checks */
947 check_promises(curr->get_tid(), NULL, curr->get_cv());
958 * @brief Process the current action for release sequence fixup activity
960 * Performs model-checker release sequence fixups for the current action,
961 * forcing a single pending release sequence to break (with a given, potential
962 * "loose" write) or to complete (i.e., synchronize). If a pending release
963 * sequence forms a complete release sequence, then we must perform the fixup
964 * synchronization, mo_graph additions, etc.
966 * @param curr The current action; must be a release sequence fixup action
967 * @param work_queue The work queue to which to add work items as they are
970 void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
972 const ModelAction *write = curr->get_node()->get_relseq_break();
973 struct release_seq *sequence = pending_rel_seqs.back();
974 pending_rel_seqs.pop_back();
976 ModelAction *acquire = sequence->acquire;
977 const ModelAction *rf = sequence->rf;
978 const ModelAction *release = sequence->release;
982 ASSERT(release->same_thread(rf));
986 * @todo Forcing a synchronization requires that we set
987 * modification order constraints. For instance, we can't allow
988 * a fixup sequence in which two separate read-acquire
989 * operations read from the same sequence, where the first one
990 * synchronizes and the other doesn't. Essentially, we can't
991 * allow any writes to insert themselves between 'release' and
995 /* Must synchronize */
996 if (!synchronize(release, acquire))
998 /* Re-check all pending release sequences */
999 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1000 /* Re-check act for mo_graph edges */
1001 work_queue->push_back(MOEdgeWorkEntry(acquire));
1003 /* propagate synchronization to later actions */
1004 action_list_t::reverse_iterator rit = action_trace.rbegin();
1005 for (; (*rit) != acquire; rit++) {
1006 ModelAction *propagate = *rit;
1007 if (acquire->happens_before(propagate)) {
1008 synchronize(acquire, propagate);
1009 /* Re-check 'propagate' for mo_graph edges */
1010 work_queue->push_back(MOEdgeWorkEntry(propagate));
1014 /* Break release sequence with new edges:
1015 * release --mo--> write --mo--> rf */
1016 mo_graph->addEdge(release, write);
1017 mo_graph->addEdge(write, rf);
1020 /* See if we have realized a data race */
1025 * Initialize the current action by performing one or more of the following
1026 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1027 * in the NodeStack, manipulating backtracking sets, allocating and
1028 * initializing clock vectors, and computing the promises to fulfill.
1030 * @param curr The current action, as passed from the user context; may be
1031 * freed/invalidated after the execution of this function, with a different
1032 * action "returned" its place (pass-by-reference)
1033 * @return True if curr is a newly-explored action; false otherwise
1035 bool ModelExecution::initialize_curr_action(ModelAction **curr)
1037 ModelAction *newcurr;
1039 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1040 newcurr = process_rmw(*curr);
1043 if (newcurr->is_rmw())
1044 compute_promises(newcurr);
1050 (*curr)->set_seq_number(get_next_seq_num());
1052 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1054 /* First restore type and order in case of RMW operation */
1055 if ((*curr)->is_rmwr())
1056 newcurr->copy_typeandorder(*curr);
1058 ASSERT((*curr)->get_location() == newcurr->get_location());
1059 newcurr->copy_from_new(*curr);
1061 /* Discard duplicate ModelAction; use action from NodeStack */
1064 /* Always compute new clock vector */
1065 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1068 return false; /* Action was explored previously */
1072 /* Always compute new clock vector */
1073 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1075 /* Assign most recent release fence */
1076 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1079 * Perform one-time actions when pushing new ModelAction onto
1082 if (newcurr->is_write())
1083 compute_promises(newcurr);
1084 else if (newcurr->is_relseq_fixup())
1085 compute_relseq_breakwrites(newcurr);
1086 else if (newcurr->is_wait())
1087 newcurr->get_node()->set_misc_max(2);
1088 else if (newcurr->is_notify_one()) {
1089 newcurr->get_node()->set_misc_max(get_safe_ptr_action(&condvar_waiters_map, newcurr->get_location())->size());
1091 return true; /* This was a new ModelAction */
1096 * @brief Establish reads-from relation between two actions
1098 * Perform basic operations involved with establishing a concrete rf relation,
1099 * including setting the ModelAction data and checking for release sequences.
1101 * @param act The action that is reading (must be a read)
1102 * @param rf The action from which we are reading (must be a write)
1104 * @return True if this read established synchronization
1106 bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
1109 ASSERT(rf->is_write());
1111 act->set_read_from(rf);
1112 if (act->is_acquire()) {
1113 rel_heads_list_t release_heads;
1114 get_release_seq_heads(act, act, &release_heads);
1115 int num_heads = release_heads.size();
1116 for (unsigned int i = 0; i < release_heads.size(); i++)
1117 if (!synchronize(release_heads[i], act))
1119 return num_heads > 0;
1125 * @brief Synchronizes two actions
1127 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1128 * This function performs the synchronization as well as providing other hooks
1129 * for other checks along with synchronization.
1131 * @param first The left-hand side of the synchronizes-with relation
1132 * @param second The right-hand side of the synchronizes-with relation
1133 * @return True if the synchronization was successful (i.e., was consistent
1134 * with the execution order); false otherwise
1136 bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
1138 if (*second < *first) {
1139 set_bad_synchronization();
1142 check_promises(first->get_tid(), second->get_cv(), first->get_cv());
1143 return second->synchronize_with(first);
1147 * Check promises and eliminate potentially-satisfying threads when a thread is
1148 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1149 * no longer satisfy a promise generated from that thread.
1151 * @param blocker The thread on which a thread is waiting
1152 * @param waiting The waiting thread
1154 void ModelExecution::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1156 for (unsigned int i = 0; i < promises.size(); i++) {
1157 Promise *promise = promises[i];
1158 if (!promise->thread_is_available(waiting->get_id()))
1160 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1161 ModelAction *reader = promise->get_reader(j);
1162 if (reader->get_tid() != blocker->get_id())
1164 if (promise->eliminate_thread(waiting->get_id())) {
1165 /* Promise has failed */
1166 priv->failed_promise = true;
1168 /* Only eliminate the 'waiting' thread once */
1176 * @brief Check whether a model action is enabled.
1178 * Checks whether a lock or join operation would be successful (i.e., is the
1179 * lock already locked, or is the joined thread already complete). If not, put
1180 * the action in a waiter list.
1182 * @param curr is the ModelAction to check whether it is enabled.
1183 * @return a bool that indicates whether the action is enabled.
1185 bool ModelExecution::check_action_enabled(ModelAction *curr) {
1186 if (curr->is_lock()) {
1187 std::mutex *lock = curr->get_mutex();
1188 struct std::mutex_state *state = lock->get_state();
1191 } else if (curr->is_thread_join()) {
1192 Thread *blocking = curr->get_thread_operand();
1193 if (!blocking->is_complete()) {
1194 thread_blocking_check_promises(blocking, get_thread(curr));
1203 * This is the heart of the model checker routine. It performs model-checking
1204 * actions corresponding to a given "current action." Among other processes, it
1205 * calculates reads-from relationships, updates synchronization clock vectors,
1206 * forms a memory_order constraints graph, and handles replay/backtrack
1207 * execution when running permutations of previously-observed executions.
1209 * @param curr The current action to process
1210 * @return The ModelAction that is actually executed; may be different than
1211 * curr; may be NULL, if the current action is not enabled to run
1213 ModelAction * ModelExecution::check_current_action(ModelAction *curr)
1216 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1217 bool newly_explored = initialize_curr_action(&curr);
1221 wake_up_sleeping_actions(curr);
1223 /* Compute fairness information for CHESS yield algorithm */
1224 if (params->yieldon) {
1225 curr->get_node()->update_yield(scheduler);
1228 /* Add the action to lists before any other model-checking tasks */
1229 if (!second_part_of_rmw)
1230 add_action_to_lists(curr);
1232 /* Build may_read_from set for newly-created actions */
1233 if (newly_explored && curr->is_read())
1234 build_may_read_from(curr);
1236 /* Initialize work_queue with the "current action" work */
1237 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1238 while (!work_queue.empty() && !has_asserted()) {
1239 WorkQueueEntry work = work_queue.front();
1240 work_queue.pop_front();
1242 switch (work.type) {
1243 case WORK_CHECK_CURR_ACTION: {
1244 ModelAction *act = work.action;
1245 bool update = false; /* update this location's release seq's */
1246 bool update_all = false; /* update all release seq's */
1248 if (process_thread_action(curr))
1251 if (act->is_read() && !second_part_of_rmw && process_read(act))
1254 if (act->is_write() && process_write(act))
1257 if (act->is_fence() && process_fence(act))
1260 if (act->is_mutex_op() && process_mutex(act))
1263 if (act->is_relseq_fixup())
1264 process_relseq_fixup(curr, &work_queue);
1267 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1269 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1272 case WORK_CHECK_RELEASE_SEQ:
1273 resolve_release_sequences(work.location, &work_queue);
1275 case WORK_CHECK_MO_EDGES: {
1276 /** @todo Complete verification of work_queue */
1277 ModelAction *act = work.action;
1278 bool updated = false;
1280 if (act->is_read()) {
1281 const ModelAction *rf = act->get_reads_from();
1282 const Promise *promise = act->get_reads_from_promise();
1284 if (r_modification_order(act, rf))
1286 } else if (promise) {
1287 if (r_modification_order(act, promise))
1291 if (act->is_write()) {
1292 if (w_modification_order(act, NULL))
1295 mo_graph->commitChanges();
1298 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1307 check_curr_backtracking(curr);
1308 set_backtracking(curr);
1312 void ModelExecution::check_curr_backtracking(ModelAction *curr)
1314 Node *currnode = curr->get_node();
1315 Node *parnode = currnode->get_parent();
1317 if ((parnode && !parnode->backtrack_empty()) ||
1318 !currnode->misc_empty() ||
1319 !currnode->read_from_empty() ||
1320 !currnode->promise_empty() ||
1321 !currnode->relseq_break_empty()) {
1322 set_latest_backtrack(curr);
1326 bool ModelExecution::promises_expired() const
1328 for (unsigned int i = 0; i < promises.size(); i++) {
1329 Promise *promise = promises[i];
1330 if (promise->get_expiration() < priv->used_sequence_numbers)
1337 * This is the strongest feasibility check available.
1338 * @return whether the current trace (partial or complete) must be a prefix of
1341 bool ModelExecution::isfeasibleprefix() const
1343 return pending_rel_seqs.size() == 0 && is_feasible_prefix_ignore_relseq();
1347 * Print disagnostic information about an infeasible execution
1348 * @param prefix A string to prefix the output with; if NULL, then a default
1349 * message prefix will be provided
1351 void ModelExecution::print_infeasibility(const char *prefix) const
1355 if (mo_graph->checkForCycles())
1356 ptr += sprintf(ptr, "[mo cycle]");
1357 if (priv->failed_promise)
1358 ptr += sprintf(ptr, "[failed promise]");
1359 if (priv->too_many_reads)
1360 ptr += sprintf(ptr, "[too many reads]");
1361 if (priv->no_valid_reads)
1362 ptr += sprintf(ptr, "[no valid reads-from]");
1363 if (priv->bad_synchronization)
1364 ptr += sprintf(ptr, "[bad sw ordering]");
1365 if (promises_expired())
1366 ptr += sprintf(ptr, "[promise expired]");
1367 if (promises.size() != 0)
1368 ptr += sprintf(ptr, "[unresolved promise]");
1370 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1374 * Returns whether the current completed trace is feasible, except for pending
1375 * release sequences.
1377 bool ModelExecution::is_feasible_prefix_ignore_relseq() const
1379 return !is_infeasible() && promises.size() == 0;
1383 * Check if the current partial trace is infeasible. Does not check any
1384 * end-of-execution flags, which might rule out the execution. Thus, this is
1385 * useful only for ruling an execution as infeasible.
1386 * @return whether the current partial trace is infeasible.
1388 bool ModelExecution::is_infeasible() const
1390 return mo_graph->checkForCycles() ||
1391 priv->no_valid_reads ||
1392 priv->failed_promise ||
1393 priv->too_many_reads ||
1394 priv->bad_synchronization ||
1398 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1399 ModelAction * ModelExecution::process_rmw(ModelAction *act) {
1400 ModelAction *lastread = get_last_action(act->get_tid());
1401 lastread->process_rmw(act);
1402 if (act->is_rmw()) {
1403 if (lastread->get_reads_from())
1404 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1406 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1407 mo_graph->commitChanges();
1413 * A helper function for ModelExecution::check_recency, to check if the current
1414 * thread is able to read from a different write/promise for 'params.maxreads'
1415 * number of steps and if that write/promise should become visible (i.e., is
1416 * ordered later in the modification order). This helps model memory liveness.
1418 * @param curr The current action. Must be a read.
1419 * @param rf The write/promise from which we plan to read
1420 * @param other_rf The write/promise from which we may read
1421 * @return True if we were able to read from other_rf for params.maxreads steps
1423 template <typename T, typename U>
1424 bool ModelExecution::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1426 /* Need a different write/promise */
1427 if (other_rf->equals(rf))
1430 /* Only look for "newer" writes/promises */
1431 if (!mo_graph->checkReachable(rf, other_rf))
1434 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1435 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1436 action_list_t::reverse_iterator rit = list->rbegin();
1437 ASSERT((*rit) == curr);
1438 /* Skip past curr */
1441 /* Does this write/promise work for everyone? */
1442 for (int i = 0; i < params->maxreads; i++, rit++) {
1443 ModelAction *act = *rit;
1444 if (!act->may_read_from(other_rf))
1451 * Checks whether a thread has read from the same write or Promise for too many
1452 * times without seeing the effects of a later write/Promise.
1455 * 1) there must a different write/promise that we could read from,
1456 * 2) we must have read from the same write/promise in excess of maxreads times,
1457 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1458 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1460 * If so, we decide that the execution is no longer feasible.
1462 * @param curr The current action. Must be a read.
1463 * @param rf The ModelAction/Promise from which we might read.
1464 * @return True if the read should succeed; false otherwise
1466 template <typename T>
1467 bool ModelExecution::check_recency(ModelAction *curr, const T *rf) const
1469 if (!params->maxreads)
1472 //NOTE: Next check is just optimization, not really necessary....
1473 if (curr->get_node()->get_read_from_past_size() +
1474 curr->get_node()->get_read_from_promise_size() <= 1)
1477 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1478 int tid = id_to_int(curr->get_tid());
1479 ASSERT(tid < (int)thrd_lists->size());
1480 action_list_t *list = &(*thrd_lists)[tid];
1481 action_list_t::reverse_iterator rit = list->rbegin();
1482 ASSERT((*rit) == curr);
1483 /* Skip past curr */
1486 action_list_t::reverse_iterator ritcopy = rit;
1487 /* See if we have enough reads from the same value */
1488 for (int count = 0; count < params->maxreads; ritcopy++, count++) {
1489 if (ritcopy == list->rend())
1491 ModelAction *act = *ritcopy;
1492 if (!act->is_read())
1494 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1496 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1498 if (act->get_node()->get_read_from_past_size() +
1499 act->get_node()->get_read_from_promise_size() <= 1)
1502 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1503 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1504 if (should_read_instead(curr, rf, write))
1505 return false; /* liveness failure */
1507 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1508 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1509 if (should_read_instead(curr, rf, promise))
1510 return false; /* liveness failure */
1516 * @brief Updates the mo_graph with the constraints imposed from the current
1519 * Basic idea is the following: Go through each other thread and find
1520 * the last action that happened before our read. Two cases:
1522 * -# The action is a write: that write must either occur before
1523 * the write we read from or be the write we read from.
1524 * -# The action is a read: the write that that action read from
1525 * must occur before the write we read from or be the same write.
1527 * @param curr The current action. Must be a read.
1528 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1529 * @return True if modification order edges were added; false otherwise
1531 template <typename rf_type>
1532 bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
1534 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1537 ASSERT(curr->is_read());
1539 /* Last SC fence in the current thread */
1540 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1541 ModelAction *last_sc_write = NULL;
1542 if (curr->is_seqcst())
1543 last_sc_write = get_last_seq_cst_write(curr);
1545 /* Iterate over all threads */
1546 for (i = 0; i < thrd_lists->size(); i++) {
1547 /* Last SC fence in thread i */
1548 ModelAction *last_sc_fence_thread_local = NULL;
1549 if (int_to_id((int)i) != curr->get_tid())
1550 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1552 /* Last SC fence in thread i, before last SC fence in current thread */
1553 ModelAction *last_sc_fence_thread_before = NULL;
1554 if (last_sc_fence_local)
1555 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1557 /* Iterate over actions in thread, starting from most recent */
1558 action_list_t *list = &(*thrd_lists)[i];
1559 action_list_t::reverse_iterator rit;
1560 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1561 ModelAction *act = *rit;
1566 /* Don't want to add reflexive edges on 'rf' */
1567 if (act->equals(rf)) {
1568 if (act->happens_before(curr))
1574 if (act->is_write()) {
1575 /* C++, Section 29.3 statement 5 */
1576 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1577 *act < *last_sc_fence_thread_local) {
1578 added = mo_graph->addEdge(act, rf) || added;
1581 /* C++, Section 29.3 statement 4 */
1582 else if (act->is_seqcst() && last_sc_fence_local &&
1583 *act < *last_sc_fence_local) {
1584 added = mo_graph->addEdge(act, rf) || added;
1587 /* C++, Section 29.3 statement 6 */
1588 else if (last_sc_fence_thread_before &&
1589 *act < *last_sc_fence_thread_before) {
1590 added = mo_graph->addEdge(act, rf) || added;
1595 /* C++, Section 29.3 statement 3 (second subpoint) */
1596 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1597 added = mo_graph->addEdge(act, rf) || added;
1602 * Include at most one act per-thread that "happens
1605 if (act->happens_before(curr)) {
1606 if (act->is_write()) {
1607 added = mo_graph->addEdge(act, rf) || added;
1609 const ModelAction *prevrf = act->get_reads_from();
1610 const Promise *prevrf_promise = act->get_reads_from_promise();
1612 if (!prevrf->equals(rf))
1613 added = mo_graph->addEdge(prevrf, rf) || added;
1614 } else if (!prevrf_promise->equals(rf)) {
1615 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1624 * All compatible, thread-exclusive promises must be ordered after any
1625 * concrete loads from the same thread
1627 for (unsigned int i = 0; i < promises.size(); i++)
1628 if (promises[i]->is_compatible_exclusive(curr))
1629 added = mo_graph->addEdge(rf, promises[i]) || added;
1635 * Updates the mo_graph with the constraints imposed from the current write.
1637 * Basic idea is the following: Go through each other thread and find
1638 * the lastest action that happened before our write. Two cases:
1640 * (1) The action is a write => that write must occur before
1643 * (2) The action is a read => the write that that action read from
1644 * must occur before the current write.
1646 * This method also handles two other issues:
1648 * (I) Sequential Consistency: Making sure that if the current write is
1649 * seq_cst, that it occurs after the previous seq_cst write.
1651 * (II) Sending the write back to non-synchronizing reads.
1653 * @param curr The current action. Must be a write.
1654 * @param send_fv A vector for stashing reads to which we may pass our future
1655 * value. If NULL, then don't record any future values.
1656 * @return True if modification order edges were added; false otherwise
1658 bool ModelExecution::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1660 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1663 ASSERT(curr->is_write());
1665 if (curr->is_seqcst()) {
1666 /* We have to at least see the last sequentially consistent write,
1667 so we are initialized. */
1668 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1669 if (last_seq_cst != NULL) {
1670 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1674 /* Last SC fence in the current thread */
1675 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1677 /* Iterate over all threads */
1678 for (i = 0; i < thrd_lists->size(); i++) {
1679 /* Last SC fence in thread i, before last SC fence in current thread */
1680 ModelAction *last_sc_fence_thread_before = NULL;
1681 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1682 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1684 /* Iterate over actions in thread, starting from most recent */
1685 action_list_t *list = &(*thrd_lists)[i];
1686 action_list_t::reverse_iterator rit;
1687 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1688 ModelAction *act = *rit;
1691 * 1) If RMW and it actually read from something, then we
1692 * already have all relevant edges, so just skip to next
1695 * 2) If RMW and it didn't read from anything, we should
1696 * whatever edge we can get to speed up convergence.
1698 * 3) If normal write, we need to look at earlier actions, so
1699 * continue processing list.
1701 if (curr->is_rmw()) {
1702 if (curr->get_reads_from() != NULL)
1710 /* C++, Section 29.3 statement 7 */
1711 if (last_sc_fence_thread_before && act->is_write() &&
1712 *act < *last_sc_fence_thread_before) {
1713 added = mo_graph->addEdge(act, curr) || added;
1718 * Include at most one act per-thread that "happens
1721 if (act->happens_before(curr)) {
1723 * Note: if act is RMW, just add edge:
1725 * The following edge should be handled elsewhere:
1726 * readfrom(act) --mo--> act
1728 if (act->is_write())
1729 added = mo_graph->addEdge(act, curr) || added;
1730 else if (act->is_read()) {
1731 //if previous read accessed a null, just keep going
1732 if (act->get_reads_from() == NULL)
1734 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1737 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1738 !act->same_thread(curr)) {
1739 /* We have an action that:
1740 (1) did not happen before us
1741 (2) is a read and we are a write
1742 (3) cannot synchronize with us
1743 (4) is in a different thread
1745 that read could potentially read from our write. Note that
1746 these checks are overly conservative at this point, we'll
1747 do more checks before actually removing the
1751 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1752 if (!is_infeasible())
1753 send_fv->push_back(act);
1754 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1755 add_future_value(curr, act);
1762 * All compatible, thread-exclusive promises must be ordered after any
1763 * concrete stores to the same thread, or else they can be merged with
1766 for (unsigned int i = 0; i < promises.size(); i++)
1767 if (promises[i]->is_compatible_exclusive(curr))
1768 added = mo_graph->addEdge(curr, promises[i]) || added;
1773 /** Arbitrary reads from the future are not allowed. Section 29.3
1774 * part 9 places some constraints. This method checks one result of constraint
1775 * constraint. Others require compiler support. */
1776 bool ModelExecution::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
1778 if (!writer->is_rmw())
1781 if (!reader->is_rmw())
1784 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1785 if (search == reader)
1787 if (search->get_tid() == reader->get_tid() &&
1788 search->happens_before(reader))
1796 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1797 * some constraints. This method checks one the following constraint (others
1798 * require compiler support):
1800 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1802 bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1804 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(reader->get_location());
1806 /* Iterate over all threads */
1807 for (i = 0; i < thrd_lists->size(); i++) {
1808 const ModelAction *write_after_read = NULL;
1810 /* Iterate over actions in thread, starting from most recent */
1811 action_list_t *list = &(*thrd_lists)[i];
1812 action_list_t::reverse_iterator rit;
1813 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1814 ModelAction *act = *rit;
1816 /* Don't disallow due to act == reader */
1817 if (!reader->happens_before(act) || reader == act)
1819 else if (act->is_write())
1820 write_after_read = act;
1821 else if (act->is_read() && act->get_reads_from() != NULL)
1822 write_after_read = act->get_reads_from();
1825 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
1832 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1833 * The ModelAction under consideration is expected to be taking part in
1834 * release/acquire synchronization as an object of the "reads from" relation.
1835 * Note that this can only provide release sequence support for RMW chains
1836 * which do not read from the future, as those actions cannot be traced until
1837 * their "promise" is fulfilled. Similarly, we may not even establish the
1838 * presence of a release sequence with certainty, as some modification order
1839 * constraints may be decided further in the future. Thus, this function
1840 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1841 * and a boolean representing certainty.
1843 * @param rf The action that might be part of a release sequence. Must be a
1845 * @param release_heads A pass-by-reference style return parameter. After
1846 * execution of this function, release_heads will contain the heads of all the
1847 * relevant release sequences, if any exists with certainty
1848 * @param pending A pass-by-reference style return parameter which is only used
1849 * when returning false (i.e., uncertain). Returns most information regarding
1850 * an uncertain release sequence, including any write operations that might
1851 * break the sequence.
1852 * @return true, if the ModelExecution is certain that release_heads is complete;
1855 bool ModelExecution::release_seq_heads(const ModelAction *rf,
1856 rel_heads_list_t *release_heads,
1857 struct release_seq *pending) const
1859 /* Only check for release sequences if there are no cycles */
1860 if (mo_graph->checkForCycles())
1863 for ( ; rf != NULL; rf = rf->get_reads_from()) {
1864 ASSERT(rf->is_write());
1866 if (rf->is_release())
1867 release_heads->push_back(rf);
1868 else if (rf->get_last_fence_release())
1869 release_heads->push_back(rf->get_last_fence_release());
1871 break; /* End of RMW chain */
1873 /** @todo Need to be smarter here... In the linux lock
1874 * example, this will run to the beginning of the program for
1876 /** @todo The way to be smarter here is to keep going until 1
1877 * thread has a release preceded by an acquire and you've seen
1880 /* acq_rel RMW is a sufficient stopping condition */
1881 if (rf->is_acquire() && rf->is_release())
1882 return true; /* complete */
1885 /* read from future: need to settle this later */
1887 return false; /* incomplete */
1890 if (rf->is_release())
1891 return true; /* complete */
1893 /* else relaxed write
1894 * - check for fence-release in the same thread (29.8, stmt. 3)
1895 * - check modification order for contiguous subsequence
1896 * -> rf must be same thread as release */
1898 const ModelAction *fence_release = rf->get_last_fence_release();
1899 /* Synchronize with a fence-release unconditionally; we don't need to
1900 * find any more "contiguous subsequence..." for it */
1902 release_heads->push_back(fence_release);
1904 int tid = id_to_int(rf->get_tid());
1905 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(rf->get_location());
1906 action_list_t *list = &(*thrd_lists)[tid];
1907 action_list_t::const_reverse_iterator rit;
1909 /* Find rf in the thread list */
1910 rit = std::find(list->rbegin(), list->rend(), rf);
1911 ASSERT(rit != list->rend());
1913 /* Find the last {write,fence}-release */
1914 for (; rit != list->rend(); rit++) {
1915 if (fence_release && *(*rit) < *fence_release)
1917 if ((*rit)->is_release())
1920 if (rit == list->rend()) {
1921 /* No write-release in this thread */
1922 return true; /* complete */
1923 } else if (fence_release && *(*rit) < *fence_release) {
1924 /* The fence-release is more recent (and so, "stronger") than
1925 * the most recent write-release */
1926 return true; /* complete */
1927 } /* else, need to establish contiguous release sequence */
1928 ModelAction *release = *rit;
1930 ASSERT(rf->same_thread(release));
1932 pending->writes.clear();
1934 bool certain = true;
1935 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1936 if (id_to_int(rf->get_tid()) == (int)i)
1938 list = &(*thrd_lists)[i];
1940 /* Can we ensure no future writes from this thread may break
1941 * the release seq? */
1942 bool future_ordered = false;
1944 ModelAction *last = get_last_action(int_to_id(i));
1945 Thread *th = get_thread(int_to_id(i));
1946 if ((last && rf->happens_before(last)) ||
1949 future_ordered = true;
1951 ASSERT(!th->is_model_thread() || future_ordered);
1953 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1954 const ModelAction *act = *rit;
1955 /* Reach synchronization -> this thread is complete */
1956 if (act->happens_before(release))
1958 if (rf->happens_before(act)) {
1959 future_ordered = true;
1963 /* Only non-RMW writes can break release sequences */
1964 if (!act->is_write() || act->is_rmw())
1967 /* Check modification order */
1968 if (mo_graph->checkReachable(rf, act)) {
1969 /* rf --mo--> act */
1970 future_ordered = true;
1973 if (mo_graph->checkReachable(act, release))
1974 /* act --mo--> release */
1976 if (mo_graph->checkReachable(release, act) &&
1977 mo_graph->checkReachable(act, rf)) {
1978 /* release --mo-> act --mo--> rf */
1979 return true; /* complete */
1981 /* act may break release sequence */
1982 pending->writes.push_back(act);
1985 if (!future_ordered)
1986 certain = false; /* This thread is uncertain */
1990 release_heads->push_back(release);
1991 pending->writes.clear();
1993 pending->release = release;
2000 * An interface for getting the release sequence head(s) with which a
2001 * given ModelAction must synchronize. This function only returns a non-empty
2002 * result when it can locate a release sequence head with certainty. Otherwise,
2003 * it may mark the internal state of the ModelExecution so that it will handle
2004 * the release sequence at a later time, causing @a acquire to update its
2005 * synchronization at some later point in execution.
2007 * @param acquire The 'acquire' action that may synchronize with a release
2009 * @param read The read action that may read from a release sequence; this may
2010 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2011 * when 'acquire' is a fence-acquire)
2012 * @param release_heads A pass-by-reference return parameter. Will be filled
2013 * with the head(s) of the release sequence(s), if they exists with certainty.
2014 * @see ModelExecution::release_seq_heads
2016 void ModelExecution::get_release_seq_heads(ModelAction *acquire,
2017 ModelAction *read, rel_heads_list_t *release_heads)
2019 const ModelAction *rf = read->get_reads_from();
2020 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2021 sequence->acquire = acquire;
2022 sequence->read = read;
2024 if (!release_seq_heads(rf, release_heads, sequence)) {
2025 /* add act to 'lazy checking' list */
2026 pending_rel_seqs.push_back(sequence);
2028 snapshot_free(sequence);
2033 * Attempt to resolve all stashed operations that might synchronize with a
2034 * release sequence for a given location. This implements the "lazy" portion of
2035 * determining whether or not a release sequence was contiguous, since not all
2036 * modification order information is present at the time an action occurs.
2038 * @param location The location/object that should be checked for release
2039 * sequence resolutions. A NULL value means to check all locations.
2040 * @param work_queue The work queue to which to add work items as they are
2042 * @return True if any updates occurred (new synchronization, new mo_graph
2045 bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
2047 bool updated = false;
2048 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs.begin();
2049 while (it != pending_rel_seqs.end()) {
2050 struct release_seq *pending = *it;
2051 ModelAction *acquire = pending->acquire;
2052 const ModelAction *read = pending->read;
2054 /* Only resolve sequences on the given location, if provided */
2055 if (location && read->get_location() != location) {
2060 const ModelAction *rf = read->get_reads_from();
2061 rel_heads_list_t release_heads;
2063 complete = release_seq_heads(rf, &release_heads, pending);
2064 for (unsigned int i = 0; i < release_heads.size(); i++)
2065 if (!acquire->has_synchronized_with(release_heads[i]))
2066 if (synchronize(release_heads[i], acquire))
2070 /* Re-check all pending release sequences */
2071 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2072 /* Re-check read-acquire for mo_graph edges */
2073 if (acquire->is_read())
2074 work_queue->push_back(MOEdgeWorkEntry(acquire));
2076 /* propagate synchronization to later actions */
2077 action_list_t::reverse_iterator rit = action_trace.rbegin();
2078 for (; (*rit) != acquire; rit++) {
2079 ModelAction *propagate = *rit;
2080 if (acquire->happens_before(propagate)) {
2081 synchronize(acquire, propagate);
2082 /* Re-check 'propagate' for mo_graph edges */
2083 work_queue->push_back(MOEdgeWorkEntry(propagate));
2088 it = pending_rel_seqs.erase(it);
2089 snapshot_free(pending);
2095 // If we resolved promises or data races, see if we have realized a data race.
2102 * Performs various bookkeeping operations for the current ModelAction. For
2103 * instance, adds action to the per-object, per-thread action vector and to the
2104 * action trace list of all thread actions.
2106 * @param act is the ModelAction to add.
2108 void ModelExecution::add_action_to_lists(ModelAction *act)
2110 int tid = id_to_int(act->get_tid());
2111 ModelAction *uninit = NULL;
2113 action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
2114 if (list->empty() && act->is_atomic_var()) {
2115 uninit = get_uninitialized_action(act);
2116 uninit_id = id_to_int(uninit->get_tid());
2117 list->push_front(uninit);
2119 list->push_back(act);
2121 action_trace.push_back(act);
2123 action_trace.push_front(uninit);
2125 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
2126 if (tid >= (int)vec->size())
2127 vec->resize(priv->next_thread_id);
2128 (*vec)[tid].push_back(act);
2130 (*vec)[uninit_id].push_front(uninit);
2132 if ((int)thrd_last_action.size() <= tid)
2133 thrd_last_action.resize(get_num_threads());
2134 thrd_last_action[tid] = act;
2136 thrd_last_action[uninit_id] = uninit;
2138 if (act->is_fence() && act->is_release()) {
2139 if ((int)thrd_last_fence_release.size() <= tid)
2140 thrd_last_fence_release.resize(get_num_threads());
2141 thrd_last_fence_release[tid] = act;
2144 if (act->is_wait()) {
2145 void *mutex_loc = (void *) act->get_value();
2146 get_safe_ptr_action(&obj_map, mutex_loc)->push_back(act);
2148 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, mutex_loc);
2149 if (tid >= (int)vec->size())
2150 vec->resize(priv->next_thread_id);
2151 (*vec)[tid].push_back(act);
2156 * @brief Get the last action performed by a particular Thread
2157 * @param tid The thread ID of the Thread in question
2158 * @return The last action in the thread
2160 ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
2162 int threadid = id_to_int(tid);
2163 if (threadid < (int)thrd_last_action.size())
2164 return thrd_last_action[id_to_int(tid)];
2170 * @brief Get the last fence release performed by a particular Thread
2171 * @param tid The thread ID of the Thread in question
2172 * @return The last fence release in the thread, if one exists; NULL otherwise
2174 ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
2176 int threadid = id_to_int(tid);
2177 if (threadid < (int)thrd_last_fence_release.size())
2178 return thrd_last_fence_release[id_to_int(tid)];
2184 * Gets the last memory_order_seq_cst write (in the total global sequence)
2185 * performed on a particular object (i.e., memory location), not including the
2187 * @param curr The current ModelAction; also denotes the object location to
2189 * @return The last seq_cst write
2191 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
2193 void *location = curr->get_location();
2194 action_list_t *list = obj_map.get(location);
2195 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2196 action_list_t::reverse_iterator rit;
2197 for (rit = list->rbegin(); (*rit) != curr; rit++)
2199 rit++; /* Skip past curr */
2200 for ( ; rit != list->rend(); rit++)
2201 if ((*rit)->is_write() && (*rit)->is_seqcst())
2207 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2208 * performed in a particular thread, prior to a particular fence.
2209 * @param tid The ID of the thread to check
2210 * @param before_fence The fence from which to begin the search; if NULL, then
2211 * search for the most recent fence in the thread.
2212 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2214 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2216 /* All fences should have location FENCE_LOCATION */
2217 action_list_t *list = obj_map.get(FENCE_LOCATION);
2222 action_list_t::reverse_iterator rit = list->rbegin();
2225 for (; rit != list->rend(); rit++)
2226 if (*rit == before_fence)
2229 ASSERT(*rit == before_fence);
2233 for (; rit != list->rend(); rit++)
2234 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2240 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2241 * location). This function identifies the mutex according to the current
2242 * action, which is presumed to perform on the same mutex.
2243 * @param curr The current ModelAction; also denotes the object location to
2245 * @return The last unlock operation
2247 ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
2249 void *location = curr->get_location();
2250 action_list_t *list = obj_map.get(location);
2251 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2252 action_list_t::reverse_iterator rit;
2253 for (rit = list->rbegin(); rit != list->rend(); rit++)
2254 if ((*rit)->is_unlock() || (*rit)->is_wait())
2259 ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
2261 ModelAction *parent = get_last_action(tid);
2263 parent = get_thread(tid)->get_creation();
2268 * Returns the clock vector for a given thread.
2269 * @param tid The thread whose clock vector we want
2270 * @return Desired clock vector
2272 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
2274 return get_parent_action(tid)->get_cv();
2278 * @brief Find the promise (if any) to resolve for the current action and
2279 * remove it from the pending promise vector
2280 * @param curr The current ModelAction. Should be a write.
2281 * @return The Promise to resolve, if any; otherwise NULL
2283 Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
2285 for (unsigned int i = 0; i < promises.size(); i++)
2286 if (curr->get_node()->get_promise(i)) {
2287 Promise *ret = promises[i];
2288 promises.erase(promises.begin() + i);
2295 * Resolve a Promise with a current write.
2296 * @param write The ModelAction that is fulfilling Promises
2297 * @param promise The Promise to resolve
2298 * @return True if the Promise was successfully resolved; false otherwise
2300 bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise)
2302 ModelVector<ModelAction *> actions_to_check;
2304 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2305 ModelAction *read = promise->get_reader(i);
2306 read_from(read, write);
2307 actions_to_check.push_back(read);
2309 /* Make sure the promise's value matches the write's value */
2310 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2311 if (!mo_graph->resolvePromise(promise, write))
2312 priv->failed_promise = true;
2315 * @todo It is possible to end up in an inconsistent state, where a
2316 * "resolved" promise may still be referenced if
2317 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2319 * Note that the inconsistency only matters when dumping mo_graph to
2325 //Check whether reading these writes has made threads unable to
2327 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2328 ModelAction *read = actions_to_check[i];
2329 mo_check_promises(read, true);
2336 * Compute the set of promises that could potentially be satisfied by this
2337 * action. Note that the set computation actually appears in the Node, not in
2339 * @param curr The ModelAction that may satisfy promises
2341 void ModelExecution::compute_promises(ModelAction *curr)
2343 for (unsigned int i = 0; i < promises.size(); i++) {
2344 Promise *promise = promises[i];
2345 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2348 bool satisfy = true;
2349 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2350 const ModelAction *act = promise->get_reader(j);
2351 if (act->happens_before(curr) ||
2352 act->could_synchronize_with(curr)) {
2358 curr->get_node()->set_promise(i);
2362 /** Checks promises in response to change in ClockVector Threads. */
2363 void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2365 for (unsigned int i = 0; i < promises.size(); i++) {
2366 Promise *promise = promises[i];
2367 if (!promise->thread_is_available(tid))
2369 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2370 const ModelAction *act = promise->get_reader(j);
2371 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2372 merge_cv->synchronized_since(act)) {
2373 if (promise->eliminate_thread(tid)) {
2374 /* Promise has failed */
2375 priv->failed_promise = true;
2383 void ModelExecution::check_promises_thread_disabled()
2385 for (unsigned int i = 0; i < promises.size(); i++) {
2386 Promise *promise = promises[i];
2387 if (promise->has_failed()) {
2388 priv->failed_promise = true;
2395 * @brief Checks promises in response to addition to modification order for
2398 * We test whether threads are still available for satisfying promises after an
2399 * addition to our modification order constraints. Those that are unavailable
2400 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2401 * that promise has failed.
2403 * @param act The ModelAction which updated the modification order
2404 * @param is_read_check Should be true if act is a read and we must check for
2405 * updates to the store from which it read (there is a distinction here for
2406 * RMW's, which are both a load and a store)
2408 void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
2410 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2412 for (unsigned int i = 0; i < promises.size(); i++) {
2413 Promise *promise = promises[i];
2415 // Is this promise on the same location?
2416 if (!promise->same_location(write))
2419 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2420 const ModelAction *pread = promise->get_reader(j);
2421 if (!pread->happens_before(act))
2423 if (mo_graph->checkPromise(write, promise)) {
2424 priv->failed_promise = true;
2430 // Don't do any lookups twice for the same thread
2431 if (!promise->thread_is_available(act->get_tid()))
2434 if (mo_graph->checkReachable(promise, write)) {
2435 if (mo_graph->checkPromise(write, promise)) {
2436 priv->failed_promise = true;
2444 * Compute the set of writes that may break the current pending release
2445 * sequence. This information is extracted from previou release sequence
2448 * @param curr The current ModelAction. Must be a release sequence fixup
2451 void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
2453 if (pending_rel_seqs.empty())
2456 struct release_seq *pending = pending_rel_seqs.back();
2457 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2458 const ModelAction *write = pending->writes[i];
2459 curr->get_node()->add_relseq_break(write);
2462 /* NULL means don't break the sequence; just synchronize */
2463 curr->get_node()->add_relseq_break(NULL);
2467 * Build up an initial set of all past writes that this 'read' action may read
2468 * from, as well as any previously-observed future values that must still be valid.
2470 * @param curr is the current ModelAction that we are exploring; it must be a
2473 void ModelExecution::build_may_read_from(ModelAction *curr)
2475 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
2477 ASSERT(curr->is_read());
2479 ModelAction *last_sc_write = NULL;
2481 if (curr->is_seqcst())
2482 last_sc_write = get_last_seq_cst_write(curr);
2484 /* Iterate over all threads */
2485 for (i = 0; i < thrd_lists->size(); i++) {
2486 /* Iterate over actions in thread, starting from most recent */
2487 action_list_t *list = &(*thrd_lists)[i];
2488 action_list_t::reverse_iterator rit;
2489 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2490 ModelAction *act = *rit;
2492 /* Only consider 'write' actions */
2493 if (!act->is_write() || act == curr)
2496 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2497 bool allow_read = true;
2499 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2501 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2505 /* Only add feasible reads */
2506 mo_graph->startChanges();
2507 r_modification_order(curr, act);
2508 if (!is_infeasible())
2509 curr->get_node()->add_read_from_past(act);
2510 mo_graph->rollbackChanges();
2513 /* Include at most one act per-thread that "happens before" curr */
2514 if (act->happens_before(curr))
2519 /* Inherit existing, promised future values */
2520 for (i = 0; i < promises.size(); i++) {
2521 const Promise *promise = promises[i];
2522 const ModelAction *promise_read = promise->get_reader(0);
2523 if (promise_read->same_var(curr)) {
2524 /* Only add feasible future-values */
2525 mo_graph->startChanges();
2526 r_modification_order(curr, promise);
2527 if (!is_infeasible())
2528 curr->get_node()->add_read_from_promise(promise_read);
2529 mo_graph->rollbackChanges();
2533 /* We may find no valid may-read-from only if the execution is doomed */
2534 if (!curr->get_node()->read_from_size()) {
2535 priv->no_valid_reads = true;
2539 if (DBG_ENABLED()) {
2540 model_print("Reached read action:\n");
2542 model_print("Printing read_from_past\n");
2543 curr->get_node()->print_read_from_past();
2544 model_print("End printing read_from_past\n");
2548 bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2550 for ( ; write != NULL; write = write->get_reads_from()) {
2551 /* UNINIT actions don't have a Node, and they never sleep */
2552 if (write->is_uninitialized())
2554 Node *prevnode = write->get_node()->get_parent();
2556 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2557 if (write->is_release() && thread_sleep)
2559 if (!write->is_rmw())
2566 * @brief Get an action representing an uninitialized atomic
2568 * This function may create a new one or try to retrieve one from the NodeStack
2570 * @param curr The current action, which prompts the creation of an UNINIT action
2571 * @return A pointer to the UNINIT ModelAction
2573 ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
2575 Node *node = curr->get_node();
2576 ModelAction *act = node->get_uninit_action();
2578 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
2579 node->set_uninit_action(act);
2581 act->create_cv(NULL);
2585 static void print_list(const action_list_t *list)
2587 action_list_t::const_iterator it;
2589 model_print("---------------------------------------------------------------------\n");
2591 unsigned int hash = 0;
2593 for (it = list->begin(); it != list->end(); it++) {
2594 const ModelAction *act = *it;
2595 if (act->get_seq_number() > 0)
2597 hash = hash^(hash<<3)^((*it)->hash());
2599 model_print("HASH %u\n", hash);
2600 model_print("---------------------------------------------------------------------\n");
2603 #if SUPPORT_MOD_ORDER_DUMP
2604 void ModelExecution::dumpGraph(char *filename) const
2607 sprintf(buffer, "%s.dot", filename);
2608 FILE *file = fopen(buffer, "w");
2609 fprintf(file, "digraph %s {\n", filename);
2610 mo_graph->dumpNodes(file);
2611 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2613 for (action_list_t::iterator it = action_trace.begin(); it != action_trace.end(); it++) {
2614 ModelAction *act = *it;
2615 if (act->is_read()) {
2616 mo_graph->dot_print_node(file, act);
2617 if (act->get_reads_from())
2618 mo_graph->dot_print_edge(file,
2619 act->get_reads_from(),
2621 "label=\"rf\", color=red, weight=2");
2623 mo_graph->dot_print_edge(file,
2624 act->get_reads_from_promise(),
2626 "label=\"rf\", color=red");
2628 if (thread_array[act->get_tid()]) {
2629 mo_graph->dot_print_edge(file,
2630 thread_array[id_to_int(act->get_tid())],
2632 "label=\"sb\", color=blue, weight=400");
2635 thread_array[act->get_tid()] = act;
2637 fprintf(file, "}\n");
2638 model_free(thread_array);
2643 /** @brief Prints an execution trace summary. */
2644 void ModelExecution::print_summary() const
2646 #if SUPPORT_MOD_ORDER_DUMP
2647 char buffername[100];
2648 sprintf(buffername, "exec%04u", get_execution_number());
2649 mo_graph->dumpGraphToFile(buffername);
2650 sprintf(buffername, "graph%04u", get_execution_number());
2651 dumpGraph(buffername);
2654 model_print("Execution %d:", get_execution_number());
2655 if (isfeasibleprefix()) {
2656 if (scheduler->all_threads_sleeping())
2657 model_print(" SLEEP-SET REDUNDANT");
2660 print_infeasibility(" INFEASIBLE");
2661 print_list(&action_trace);
2663 if (!promises.empty()) {
2664 model_print("Pending promises:\n");
2665 for (unsigned int i = 0; i < promises.size(); i++) {
2666 model_print(" [P%u] ", i);
2667 promises[i]->print();
2674 * Add a Thread to the system for the first time. Should only be called once
2676 * @param t The Thread to add
2678 void ModelExecution::add_thread(Thread *t)
2680 unsigned int i = id_to_int(t->get_id());
2681 if (i >= thread_map.size())
2682 thread_map.resize(i + 1);
2684 if (!t->is_model_thread())
2685 scheduler->add_thread(t);
2689 * @brief Get a Thread reference by its ID
2690 * @param tid The Thread's ID
2691 * @return A Thread reference
2693 Thread * ModelExecution::get_thread(thread_id_t tid) const
2695 unsigned int i = id_to_int(tid);
2696 if (i < thread_map.size())
2697 return thread_map[i];
2702 * @brief Get a reference to the Thread in which a ModelAction was executed
2703 * @param act The ModelAction
2704 * @return A Thread reference
2706 Thread * ModelExecution::get_thread(const ModelAction *act) const
2708 return get_thread(act->get_tid());
2712 * @brief Get a Promise's "promise number"
2714 * A "promise number" is an index number that is unique to a promise, valid
2715 * only for a specific snapshot of an execution trace. Promises may come and go
2716 * as they are generated an resolved, so an index only retains meaning for the
2719 * @param promise The Promise to check
2720 * @return The promise index, if the promise still is valid; otherwise -1
2722 int ModelExecution::get_promise_number(const Promise *promise) const
2724 for (unsigned int i = 0; i < promises.size(); i++)
2725 if (promises[i] == promise)
2732 * @brief Check if a Thread is currently enabled
2733 * @param t The Thread to check
2734 * @return True if the Thread is currently enabled
2736 bool ModelExecution::is_enabled(Thread *t) const
2738 return scheduler->is_enabled(t);
2742 * @brief Check if a Thread is currently enabled
2743 * @param tid The ID of the Thread to check
2744 * @return True if the Thread is currently enabled
2746 bool ModelExecution::is_enabled(thread_id_t tid) const
2748 return scheduler->is_enabled(tid);
2752 * @brief Select the next thread to execute based on the curren action
2754 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
2755 * actions should be followed by the execution of their child thread. In either
2756 * case, the current action should determine the next thread schedule.
2758 * @param curr The current action
2759 * @return The next thread to run, if the current action will determine this
2760 * selection; otherwise NULL
2762 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
2764 /* Do not split atomic RMW */
2765 if (curr->is_rmwr())
2766 return get_thread(curr);
2767 /* Follow CREATE with the created thread */
2768 if (curr->get_type() == THREAD_CREATE)
2769 return curr->get_thread_operand();
2773 /** @return True if the execution has taken too many steps */
2774 bool ModelExecution::too_many_steps() const
2776 return params->bound != 0 && priv->used_sequence_numbers > params->bound;
2780 * Takes the next step in the execution, if possible.
2781 * @param curr The current step to take
2782 * @return Returns the next Thread to run, if any; NULL if this execution
2785 Thread * ModelExecution::take_step(ModelAction *curr)
2787 Thread *curr_thrd = get_thread(curr);
2788 ASSERT(curr_thrd->get_state() == THREAD_READY);
2790 ASSERT(check_action_enabled(curr)); /* May have side effects? */
2791 curr = check_current_action(curr);
2794 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2795 scheduler->remove_thread(curr_thrd);
2797 return action_select_next_thread(curr);
2801 * Launch end-of-execution release sequence fixups only when
2802 * the execution is otherwise feasible AND there are:
2804 * (1) pending release sequences
2805 * (2) pending assertions that could be invalidated by a change
2806 * in clock vectors (i.e., data races)
2807 * (3) no pending promises
2809 void ModelExecution::fixup_release_sequences()
2811 while (!pending_rel_seqs.empty() &&
2812 is_feasible_prefix_ignore_relseq() &&
2813 !unrealizedraces.empty()) {
2814 model_print("*** WARNING: release sequence fixup action "
2815 "(%zu pending release seuqence(s)) ***\n",
2816 pending_rel_seqs.size());
2817 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2818 std::memory_order_seq_cst, NULL, VALUE_NONE,