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) :
67 action_trace(new action_list_t()),
69 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
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 thread_map.put(id_to_int(model_thread->get_id()), 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 thread_map.get(i);
96 for (unsigned int i = 0; i < promises.size(); i++)
103 int ModelExecution::get_execution_number() const
105 return model->get_execution_number();
108 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
110 action_list_t *tmp = hash->get(ptr);
112 tmp = new action_list_t();
118 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
120 SnapVector<action_list_t> *tmp = hash->get(ptr);
122 tmp = new SnapVector<action_list_t>();
128 action_list_t * ModelExecution::get_actions_on_obj(void * obj, thread_id_t tid) const
130 SnapVector<action_list_t> *wrv = obj_thrd_map.get(obj);
133 unsigned int thread=id_to_int(tid);
134 if (thread < wrv->size())
135 return &(*wrv)[thread];
140 /** @return a thread ID for a new Thread */
141 thread_id_t ModelExecution::get_next_id()
143 return priv->next_thread_id++;
146 /** @return the number of user threads created during this execution */
147 unsigned int ModelExecution::get_num_threads() const
149 return priv->next_thread_id;
152 /** @return a sequence number for a new ModelAction */
153 modelclock_t ModelExecution::get_next_seq_num()
155 return ++priv->used_sequence_numbers;
159 * @brief Should the current action wake up a given thread?
161 * @param curr The current action
162 * @param thread The thread that we might wake up
163 * @return True, if we should wake up the sleeping thread; false otherwise
165 bool ModelExecution::should_wake_up(const ModelAction *curr, const Thread *thread) const
167 const ModelAction *asleep = thread->get_pending();
168 /* Don't allow partial RMW to wake anyone up */
171 /* Synchronizing actions may have been backtracked */
172 if (asleep->could_synchronize_with(curr))
174 /* All acquire/release fences and fence-acquire/store-release */
175 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
177 /* Fence-release + store can awake load-acquire on the same location */
178 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
179 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
180 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
186 void ModelExecution::wake_up_sleeping_actions(ModelAction *curr)
188 for (unsigned int i = 0; i < get_num_threads(); i++) {
189 Thread *thr = get_thread(int_to_id(i));
190 if (scheduler->is_sleep_set(thr)) {
191 if (should_wake_up(curr, thr))
192 /* Remove this thread from sleep set */
193 scheduler->remove_sleep(thr);
198 /** @brief Alert the model-checker that an incorrectly-ordered
199 * synchronization was made */
200 void ModelExecution::set_bad_synchronization()
202 priv->bad_synchronization = true;
205 bool ModelExecution::assert_bug(const char *msg)
207 priv->bugs.push_back(new bug_message(msg));
209 if (isfeasibleprefix()) {
216 /** @return True, if any bugs have been reported for this execution */
217 bool ModelExecution::have_bug_reports() const
219 return priv->bugs.size() != 0;
222 SnapVector<bug_message *> * ModelExecution::get_bugs() const
228 * Check whether the current trace has triggered an assertion which should halt
231 * @return True, if the execution should be aborted; false otherwise
233 bool ModelExecution::has_asserted() const
235 return priv->asserted;
239 * Trigger a trace assertion which should cause this execution to be halted.
240 * This can be due to a detected bug or due to an infeasibility that should
243 void ModelExecution::set_assert()
245 priv->asserted = true;
249 * Check if we are in a deadlock. Should only be called at the end of an
250 * execution, although it should not give false positives in the middle of an
251 * execution (there should be some ENABLED thread).
253 * @return True if program is in a deadlock; false otherwise
255 bool ModelExecution::is_deadlocked() const
257 bool blocking_threads = false;
258 for (unsigned int i = 0; i < get_num_threads(); i++) {
259 thread_id_t tid = int_to_id(i);
262 Thread *t = get_thread(tid);
263 if (!t->is_model_thread() && t->get_pending())
264 blocking_threads = true;
266 return blocking_threads;
270 * Check if this is a complete execution. That is, have all thread completed
271 * execution (rather than exiting because sleep sets have forced a redundant
274 * @return True if the execution is complete.
276 bool ModelExecution::is_complete_execution() const
278 for (unsigned int i = 0; i < get_num_threads(); i++)
279 if (is_enabled(int_to_id(i)))
285 * @brief Find the last fence-related backtracking conflict for a ModelAction
287 * This function performs the search for the most recent conflicting action
288 * against which we should perform backtracking, as affected by fence
289 * operations. This includes pairs of potentially-synchronizing actions which
290 * occur due to fence-acquire or fence-release, and hence should be explored in
291 * the opposite execution order.
293 * @param act The current action
294 * @return The most recent action which conflicts with act due to fences
296 ModelAction * ModelExecution::get_last_fence_conflict(ModelAction *act) const
298 /* Only perform release/acquire fence backtracking for stores */
299 if (!act->is_write())
302 /* Find a fence-release (or, act is a release) */
303 ModelAction *last_release;
304 if (act->is_release())
307 last_release = get_last_fence_release(act->get_tid());
311 /* Skip past the release */
312 action_list_t *list = action_trace;
313 action_list_t::reverse_iterator rit;
314 for (rit = list->rbegin(); rit != list->rend(); rit++)
315 if (*rit == last_release)
317 ASSERT(rit != list->rend());
322 * load --sb-> fence-acquire */
323 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
324 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
325 bool found_acquire_fences = false;
326 for ( ; rit != list->rend(); rit++) {
327 ModelAction *prev = *rit;
328 if (act->same_thread(prev))
331 int tid = id_to_int(prev->get_tid());
333 if (prev->is_read() && act->same_var(prev)) {
334 if (prev->is_acquire()) {
335 /* Found most recent load-acquire, don't need
336 * to search for more fences */
337 if (!found_acquire_fences)
340 prior_loads[tid] = prev;
343 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
344 found_acquire_fences = true;
345 acquire_fences[tid] = prev;
349 ModelAction *latest_backtrack = NULL;
350 for (unsigned int i = 0; i < acquire_fences.size(); i++)
351 if (acquire_fences[i] && prior_loads[i])
352 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
353 latest_backtrack = acquire_fences[i];
354 return latest_backtrack;
358 * @brief Find the last backtracking conflict for a ModelAction
360 * This function performs the search for the most recent conflicting action
361 * against which we should perform backtracking. This primary includes pairs of
362 * synchronizing actions which should be explored in the opposite execution
365 * @param act The current action
366 * @return The most recent action which conflicts with act
368 ModelAction * ModelExecution::get_last_conflict(ModelAction *act) const
370 switch (act->get_type()) {
371 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
375 ModelAction *ret = NULL;
377 /* linear search: from most recent to oldest */
378 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
379 action_list_t::reverse_iterator rit;
380 for (rit = list->rbegin(); rit != list->rend(); rit++) {
381 ModelAction *prev = *rit;
382 if (prev->could_synchronize_with(act)) {
388 ModelAction *ret2 = get_last_fence_conflict(act);
398 case ATOMIC_TRYLOCK: {
399 /* linear search: from most recent to oldest */
400 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
401 action_list_t::reverse_iterator rit;
402 for (rit = list->rbegin(); rit != list->rend(); rit++) {
403 ModelAction *prev = *rit;
404 if (act->is_conflicting_lock(prev))
409 case ATOMIC_UNLOCK: {
410 /* linear search: from most recent to oldest */
411 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
412 action_list_t::reverse_iterator rit;
413 for (rit = list->rbegin(); rit != list->rend(); rit++) {
414 ModelAction *prev = *rit;
415 if (!act->same_thread(prev) && prev->is_failed_trylock())
421 /* linear search: from most recent to oldest */
422 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
423 action_list_t::reverse_iterator rit;
424 for (rit = list->rbegin(); rit != list->rend(); rit++) {
425 ModelAction *prev = *rit;
426 if (!act->same_thread(prev) && prev->is_failed_trylock())
428 if (!act->same_thread(prev) && prev->is_notify())
434 case ATOMIC_NOTIFY_ALL:
435 case ATOMIC_NOTIFY_ONE: {
436 /* linear search: from most recent to oldest */
437 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
438 action_list_t::reverse_iterator rit;
439 for (rit = list->rbegin(); rit != list->rend(); rit++) {
440 ModelAction *prev = *rit;
441 if (!act->same_thread(prev) && prev->is_wait())
452 /** This method finds backtracking points where we should try to
453 * reorder the parameter ModelAction against.
455 * @param the ModelAction to find backtracking points for.
457 void ModelExecution::set_backtracking(ModelAction *act)
459 Thread *t = get_thread(act);
460 ModelAction *prev = get_last_conflict(act);
464 Node *node = prev->get_node()->get_parent();
466 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
467 int low_tid, high_tid;
468 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
469 low_tid = id_to_int(act->get_tid());
470 high_tid = low_tid + 1;
473 high_tid = get_num_threads();
476 for (int i = low_tid; i < high_tid; i++) {
477 thread_id_t tid = int_to_id(i);
479 /* Make sure this thread can be enabled here. */
480 if (i >= node->get_num_threads())
483 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
484 /* Don't backtrack into a point where the thread is disabled or sleeping. */
485 if (node->enabled_status(tid) != THREAD_ENABLED)
488 /* Check if this has been explored already */
489 if (node->has_been_explored(tid))
492 /* See if fairness allows */
493 if (params->fairwindow != 0 && !node->has_priority(tid)) {
495 for (int t = 0; t < node->get_num_threads(); t++) {
496 thread_id_t tother = int_to_id(t);
497 if (node->is_enabled(tother) && node->has_priority(tother)) {
506 /* See if CHESS-like yield fairness allows */
507 if (params->yieldon) {
509 for (int t = 0; t < node->get_num_threads(); t++) {
510 thread_id_t tother = int_to_id(t);
511 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
520 /* Cache the latest backtracking point */
521 set_latest_backtrack(prev);
523 /* If this is a new backtracking point, mark the tree */
524 if (!node->set_backtrack(tid))
526 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
527 id_to_int(prev->get_tid()),
528 id_to_int(t->get_id()));
537 * @brief Cache the a backtracking point as the "most recent", if eligible
539 * Note that this does not prepare the NodeStack for this backtracking
540 * operation, it only caches the action on a per-execution basis
542 * @param act The operation at which we should explore a different next action
543 * (i.e., backtracking point)
544 * @return True, if this action is now the most recent backtracking point;
547 bool ModelExecution::set_latest_backtrack(ModelAction *act)
549 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
550 priv->next_backtrack = act;
557 * Returns last backtracking point. The model checker will explore a different
558 * path for this point in the next execution.
559 * @return The ModelAction at which the next execution should diverge.
561 ModelAction * ModelExecution::get_next_backtrack()
563 ModelAction *next = priv->next_backtrack;
564 priv->next_backtrack = NULL;
569 * Processes a read model action.
570 * @param curr is the read model action to process.
571 * @return True if processing this read updates the mo_graph.
573 bool ModelExecution::process_read(ModelAction *curr)
575 Node *node = curr->get_node();
577 bool updated = false;
578 switch (node->get_read_from_status()) {
579 case READ_FROM_PAST: {
580 const ModelAction *rf = node->get_read_from_past();
583 mo_graph->startChanges();
585 ASSERT(!is_infeasible());
586 if (!check_recency(curr, rf)) {
587 if (node->increment_read_from()) {
588 mo_graph->rollbackChanges();
591 priv->too_many_reads = true;
595 updated = r_modification_order(curr, rf);
597 mo_graph->commitChanges();
598 mo_check_promises(curr, true);
601 case READ_FROM_PROMISE: {
602 Promise *promise = curr->get_node()->get_read_from_promise();
603 if (promise->add_reader(curr))
604 priv->failed_promise = true;
605 curr->set_read_from_promise(promise);
606 mo_graph->startChanges();
607 if (!check_recency(curr, promise))
608 priv->too_many_reads = true;
609 updated = r_modification_order(curr, promise);
610 mo_graph->commitChanges();
613 case READ_FROM_FUTURE: {
614 /* Read from future value */
615 struct future_value fv = node->get_future_value();
616 Promise *promise = new Promise(this, curr, fv);
617 curr->set_read_from_promise(promise);
618 promises.push_back(promise);
619 mo_graph->startChanges();
620 updated = r_modification_order(curr, promise);
621 mo_graph->commitChanges();
627 get_thread(curr)->set_return_value(curr->get_return_value());
633 * Processes a lock, trylock, or unlock model action. @param curr is
634 * the read model action to process.
636 * The try lock operation checks whether the lock is taken. If not,
637 * it falls to the normal lock operation case. If so, it returns
640 * The lock operation has already been checked that it is enabled, so
641 * it just grabs the lock and synchronizes with the previous unlock.
643 * The unlock operation has to re-enable all of the threads that are
644 * waiting on the lock.
646 * @return True if synchronization was updated; false otherwise
648 bool ModelExecution::process_mutex(ModelAction *curr)
650 std::mutex *mutex = curr->get_mutex();
651 struct std::mutex_state *state = NULL;
654 state = mutex->get_state();
656 switch (curr->get_type()) {
657 case ATOMIC_TRYLOCK: {
658 bool success = !state->locked;
659 curr->set_try_lock(success);
661 get_thread(curr)->set_return_value(0);
664 get_thread(curr)->set_return_value(1);
666 //otherwise fall into the lock case
668 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
669 assert_bug("Lock access before initialization");
670 state->locked = get_thread(curr);
671 ModelAction *unlock = get_last_unlock(curr);
672 //synchronize with the previous unlock statement
673 if (unlock != NULL) {
674 synchronize(unlock, curr);
680 case ATOMIC_UNLOCK: {
681 /* wake up the other threads */
682 for (unsigned int i = 0; i < get_num_threads(); i++) {
683 Thread *t = get_thread(int_to_id(i));
684 Thread *curr_thrd = get_thread(curr);
685 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
689 /* unlock the lock - after checking who was waiting on it */
690 state->locked = NULL;
692 if (!curr->is_wait())
693 break; /* The rest is only for ATOMIC_WAIT */
695 /* Should we go to sleep? (simulate spurious failures) */
696 if (curr->get_node()->get_misc() == 0) {
697 get_safe_ptr_action(&condvar_waiters_map, curr->get_location())->push_back(curr);
699 scheduler->sleep(get_thread(curr));
703 case ATOMIC_NOTIFY_ALL: {
704 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
705 //activate all the waiting threads
706 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
707 scheduler->wake(get_thread(*rit));
712 case ATOMIC_NOTIFY_ONE: {
713 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
714 int wakeupthread = curr->get_node()->get_misc();
715 action_list_t::iterator it = waiters->begin();
716 advance(it, wakeupthread);
717 scheduler->wake(get_thread(*it));
729 * @brief Check if the current pending promises allow a future value to be sent
731 * If one of the following is true:
732 * (a) there are no pending promises
733 * (b) the reader and writer do not cross any promises
734 * Then, it is safe to pass a future value back now.
736 * Otherwise, we must save the pending future value until (a) or (b) is true
738 * @param writer The operation which sends the future value. Must be a write.
739 * @param reader The operation which will observe the value. Must be a read.
740 * @return True if the future value can be sent now; false if it must wait.
742 bool ModelExecution::promises_may_allow(const ModelAction *writer,
743 const ModelAction *reader) const
745 if (promises.empty())
747 for (int i = promises.size() - 1; i >= 0; i--) {
748 ModelAction *pr = promises[i]->get_reader(0);
749 //reader is after promise...doesn't cross any promise
752 //writer is after promise, reader before...bad...
760 * @brief Add a future value to a reader
762 * This function performs a few additional checks to ensure that the future
763 * value can be feasibly observed by the reader
765 * @param writer The operation whose value is sent. Must be a write.
766 * @param reader The read operation which may read the future value. Must be a read.
768 void ModelExecution::add_future_value(const ModelAction *writer, ModelAction *reader)
770 /* Do more ambitious checks now that mo is more complete */
771 if (!mo_may_allow(writer, reader))
774 Node *node = reader->get_node();
776 /* Find an ancestor thread which exists at the time of the reader */
777 Thread *write_thread = get_thread(writer);
778 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
779 write_thread = write_thread->get_parent();
781 struct future_value fv = {
782 writer->get_write_value(),
783 writer->get_seq_number() + params->maxfuturedelay,
784 write_thread->get_id(),
786 if (node->add_future_value(fv))
787 set_latest_backtrack(reader);
791 * Process a write ModelAction
792 * @param curr The ModelAction to process
793 * @return True if the mo_graph was updated or promises were resolved
795 bool ModelExecution::process_write(ModelAction *curr)
797 /* Readers to which we may send our future value */
798 ModelVector<ModelAction *> send_fv;
800 const ModelAction *earliest_promise_reader;
801 bool updated_promises = false;
803 bool updated_mod_order = w_modification_order(curr, &send_fv);
804 Promise *promise = pop_promise_to_resolve(curr);
807 earliest_promise_reader = promise->get_reader(0);
808 updated_promises = resolve_promise(curr, promise);
810 earliest_promise_reader = NULL;
812 for (unsigned int i = 0; i < send_fv.size(); i++) {
813 ModelAction *read = send_fv[i];
815 /* Don't send future values to reads after the Promise we resolve */
816 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
817 /* Check if future value can be sent immediately */
818 if (promises_may_allow(curr, read)) {
819 add_future_value(curr, read);
821 futurevalues.push_back(PendingFutureValue(curr, read));
826 /* Check the pending future values */
827 for (int i = (int)futurevalues.size() - 1; i >= 0; i--) {
828 struct PendingFutureValue pfv = futurevalues[i];
829 if (promises_may_allow(pfv.writer, pfv.reader)) {
830 add_future_value(pfv.writer, pfv.reader);
831 futurevalues.erase(futurevalues.begin() + i);
835 mo_graph->commitChanges();
836 mo_check_promises(curr, false);
838 get_thread(curr)->set_return_value(VALUE_NONE);
839 return updated_mod_order || updated_promises;
843 * Process a fence ModelAction
844 * @param curr The ModelAction to process
845 * @return True if synchronization was updated
847 bool ModelExecution::process_fence(ModelAction *curr)
850 * fence-relaxed: no-op
851 * fence-release: only log the occurence (not in this function), for
852 * use in later synchronization
853 * fence-acquire (this function): search for hypothetical release
855 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
857 bool updated = false;
858 if (curr->is_acquire()) {
859 action_list_t *list = action_trace;
860 action_list_t::reverse_iterator rit;
861 /* Find X : is_read(X) && X --sb-> curr */
862 for (rit = list->rbegin(); rit != list->rend(); rit++) {
863 ModelAction *act = *rit;
866 if (act->get_tid() != curr->get_tid())
868 /* Stop at the beginning of the thread */
869 if (act->is_thread_start())
871 /* Stop once we reach a prior fence-acquire */
872 if (act->is_fence() && act->is_acquire())
876 /* read-acquire will find its own release sequences */
877 if (act->is_acquire())
880 /* Establish hypothetical release sequences */
881 rel_heads_list_t release_heads;
882 get_release_seq_heads(curr, act, &release_heads);
883 for (unsigned int i = 0; i < release_heads.size(); i++)
884 synchronize(release_heads[i], curr);
885 if (release_heads.size() != 0)
893 * @brief Process the current action for thread-related activity
895 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
896 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
897 * synchronization, etc. This function is a no-op for non-THREAD actions
898 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
900 * @param curr The current action
901 * @return True if synchronization was updated or a thread completed
903 bool ModelExecution::process_thread_action(ModelAction *curr)
905 bool updated = false;
907 switch (curr->get_type()) {
908 case THREAD_CREATE: {
909 thrd_t *thrd = (thrd_t *)curr->get_location();
910 struct thread_params *params = (struct thread_params *)curr->get_value();
911 Thread *th = new Thread(get_next_id(), thrd, params->func, params->arg, get_thread(curr));
913 th->set_creation(curr);
914 /* Promises can be satisfied by children */
915 for (unsigned int i = 0; i < promises.size(); i++) {
916 Promise *promise = promises[i];
917 if (promise->thread_is_available(curr->get_tid()))
918 promise->add_thread(th->get_id());
923 Thread *blocking = curr->get_thread_operand();
924 ModelAction *act = get_last_action(blocking->get_id());
925 synchronize(act, curr);
926 updated = true; /* trigger rel-seq checks */
929 case THREAD_FINISH: {
930 Thread *th = get_thread(curr);
931 /* Wake up any joining threads */
932 for (unsigned int i = 0; i < get_num_threads(); i++) {
933 Thread *waiting = get_thread(int_to_id(i));
934 if (waiting->waiting_on() == th &&
935 waiting->get_pending()->is_thread_join())
936 scheduler->wake(waiting);
939 /* Completed thread can't satisfy promises */
940 for (unsigned int i = 0; i < promises.size(); i++) {
941 Promise *promise = promises[i];
942 if (promise->thread_is_available(th->get_id()))
943 if (promise->eliminate_thread(th->get_id()))
944 priv->failed_promise = true;
946 updated = true; /* trigger rel-seq checks */
950 check_promises(curr->get_tid(), NULL, curr->get_cv());
961 * @brief Process the current action for release sequence fixup activity
963 * Performs model-checker release sequence fixups for the current action,
964 * forcing a single pending release sequence to break (with a given, potential
965 * "loose" write) or to complete (i.e., synchronize). If a pending release
966 * sequence forms a complete release sequence, then we must perform the fixup
967 * synchronization, mo_graph additions, etc.
969 * @param curr The current action; must be a release sequence fixup action
970 * @param work_queue The work queue to which to add work items as they are
973 void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
975 const ModelAction *write = curr->get_node()->get_relseq_break();
976 struct release_seq *sequence = pending_rel_seqs.back();
977 pending_rel_seqs.pop_back();
979 ModelAction *acquire = sequence->acquire;
980 const ModelAction *rf = sequence->rf;
981 const ModelAction *release = sequence->release;
985 ASSERT(release->same_thread(rf));
989 * @todo Forcing a synchronization requires that we set
990 * modification order constraints. For instance, we can't allow
991 * a fixup sequence in which two separate read-acquire
992 * operations read from the same sequence, where the first one
993 * synchronizes and the other doesn't. Essentially, we can't
994 * allow any writes to insert themselves between 'release' and
998 /* Must synchronize */
999 if (!synchronize(release, acquire))
1001 /* Re-check all pending release sequences */
1002 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1003 /* Re-check act for mo_graph edges */
1004 work_queue->push_back(MOEdgeWorkEntry(acquire));
1006 /* propagate synchronization to later actions */
1007 action_list_t::reverse_iterator rit = action_trace->rbegin();
1008 for (; (*rit) != acquire; rit++) {
1009 ModelAction *propagate = *rit;
1010 if (acquire->happens_before(propagate)) {
1011 synchronize(acquire, propagate);
1012 /* Re-check 'propagate' for mo_graph edges */
1013 work_queue->push_back(MOEdgeWorkEntry(propagate));
1017 /* Break release sequence with new edges:
1018 * release --mo--> write --mo--> rf */
1019 mo_graph->addEdge(release, write);
1020 mo_graph->addEdge(write, rf);
1023 /* See if we have realized a data race */
1028 * Initialize the current action by performing one or more of the following
1029 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1030 * in the NodeStack, manipulating backtracking sets, allocating and
1031 * initializing clock vectors, and computing the promises to fulfill.
1033 * @param curr The current action, as passed from the user context; may be
1034 * freed/invalidated after the execution of this function, with a different
1035 * action "returned" its place (pass-by-reference)
1036 * @return True if curr is a newly-explored action; false otherwise
1038 bool ModelExecution::initialize_curr_action(ModelAction **curr)
1040 ModelAction *newcurr;
1042 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1043 newcurr = process_rmw(*curr);
1046 if (newcurr->is_rmw())
1047 compute_promises(newcurr);
1053 (*curr)->set_seq_number(get_next_seq_num());
1055 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1057 /* First restore type and order in case of RMW operation */
1058 if ((*curr)->is_rmwr())
1059 newcurr->copy_typeandorder(*curr);
1061 ASSERT((*curr)->get_location() == newcurr->get_location());
1062 newcurr->copy_from_new(*curr);
1064 /* Discard duplicate ModelAction; use action from NodeStack */
1067 /* Always compute new clock vector */
1068 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1071 return false; /* Action was explored previously */
1075 /* Always compute new clock vector */
1076 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1078 /* Assign most recent release fence */
1079 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1082 * Perform one-time actions when pushing new ModelAction onto
1085 if (newcurr->is_write())
1086 compute_promises(newcurr);
1087 else if (newcurr->is_relseq_fixup())
1088 compute_relseq_breakwrites(newcurr);
1089 else if (newcurr->is_wait())
1090 newcurr->get_node()->set_misc_max(2);
1091 else if (newcurr->is_notify_one()) {
1092 newcurr->get_node()->set_misc_max(get_safe_ptr_action(&condvar_waiters_map, newcurr->get_location())->size());
1094 return true; /* This was a new ModelAction */
1099 * @brief Establish reads-from relation between two actions
1101 * Perform basic operations involved with establishing a concrete rf relation,
1102 * including setting the ModelAction data and checking for release sequences.
1104 * @param act The action that is reading (must be a read)
1105 * @param rf The action from which we are reading (must be a write)
1107 * @return True if this read established synchronization
1109 bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
1112 ASSERT(rf->is_write());
1114 act->set_read_from(rf);
1115 if (act->is_acquire()) {
1116 rel_heads_list_t release_heads;
1117 get_release_seq_heads(act, act, &release_heads);
1118 int num_heads = release_heads.size();
1119 for (unsigned int i = 0; i < release_heads.size(); i++)
1120 if (!synchronize(release_heads[i], act))
1122 return num_heads > 0;
1128 * @brief Synchronizes two actions
1130 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1131 * This function performs the synchronization as well as providing other hooks
1132 * for other checks along with synchronization.
1134 * @param first The left-hand side of the synchronizes-with relation
1135 * @param second The right-hand side of the synchronizes-with relation
1136 * @return True if the synchronization was successful (i.e., was consistent
1137 * with the execution order); false otherwise
1139 bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
1141 if (*second < *first) {
1142 set_bad_synchronization();
1145 check_promises(first->get_tid(), second->get_cv(), first->get_cv());
1146 return second->synchronize_with(first);
1150 * Check promises and eliminate potentially-satisfying threads when a thread is
1151 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1152 * no longer satisfy a promise generated from that thread.
1154 * @param blocker The thread on which a thread is waiting
1155 * @param waiting The waiting thread
1157 void ModelExecution::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1159 for (unsigned int i = 0; i < promises.size(); i++) {
1160 Promise *promise = promises[i];
1161 if (!promise->thread_is_available(waiting->get_id()))
1163 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1164 ModelAction *reader = promise->get_reader(j);
1165 if (reader->get_tid() != blocker->get_id())
1167 if (promise->eliminate_thread(waiting->get_id())) {
1168 /* Promise has failed */
1169 priv->failed_promise = true;
1171 /* Only eliminate the 'waiting' thread once */
1179 * @brief Check whether a model action is enabled.
1181 * Checks whether a lock or join operation would be successful (i.e., is the
1182 * lock already locked, or is the joined thread already complete). If not, put
1183 * the action in a waiter list.
1185 * @param curr is the ModelAction to check whether it is enabled.
1186 * @return a bool that indicates whether the action is enabled.
1188 bool ModelExecution::check_action_enabled(ModelAction *curr) {
1189 if (curr->is_lock()) {
1190 std::mutex *lock = curr->get_mutex();
1191 struct std::mutex_state *state = lock->get_state();
1194 } else if (curr->is_thread_join()) {
1195 Thread *blocking = curr->get_thread_operand();
1196 if (!blocking->is_complete()) {
1197 thread_blocking_check_promises(blocking, get_thread(curr));
1206 * This is the heart of the model checker routine. It performs model-checking
1207 * actions corresponding to a given "current action." Among other processes, it
1208 * calculates reads-from relationships, updates synchronization clock vectors,
1209 * forms a memory_order constraints graph, and handles replay/backtrack
1210 * execution when running permutations of previously-observed executions.
1212 * @param curr The current action to process
1213 * @return The ModelAction that is actually executed; may be different than
1214 * curr; may be NULL, if the current action is not enabled to run
1216 ModelAction * ModelExecution::check_current_action(ModelAction *curr)
1219 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1220 bool newly_explored = initialize_curr_action(&curr);
1224 wake_up_sleeping_actions(curr);
1226 /* Compute fairness information for CHESS yield algorithm */
1227 if (params->yieldon) {
1228 curr->get_node()->update_yield(scheduler);
1231 /* Add the action to lists before any other model-checking tasks */
1232 if (!second_part_of_rmw)
1233 add_action_to_lists(curr);
1235 /* Build may_read_from set for newly-created actions */
1236 if (newly_explored && curr->is_read())
1237 build_may_read_from(curr);
1239 /* Initialize work_queue with the "current action" work */
1240 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1241 while (!work_queue.empty() && !has_asserted()) {
1242 WorkQueueEntry work = work_queue.front();
1243 work_queue.pop_front();
1245 switch (work.type) {
1246 case WORK_CHECK_CURR_ACTION: {
1247 ModelAction *act = work.action;
1248 bool update = false; /* update this location's release seq's */
1249 bool update_all = false; /* update all release seq's */
1251 if (process_thread_action(curr))
1254 if (act->is_read() && !second_part_of_rmw && process_read(act))
1257 if (act->is_write() && process_write(act))
1260 if (act->is_fence() && process_fence(act))
1263 if (act->is_mutex_op() && process_mutex(act))
1266 if (act->is_relseq_fixup())
1267 process_relseq_fixup(curr, &work_queue);
1270 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1272 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1275 case WORK_CHECK_RELEASE_SEQ:
1276 resolve_release_sequences(work.location, &work_queue);
1278 case WORK_CHECK_MO_EDGES: {
1279 /** @todo Complete verification of work_queue */
1280 ModelAction *act = work.action;
1281 bool updated = false;
1283 if (act->is_read()) {
1284 const ModelAction *rf = act->get_reads_from();
1285 const Promise *promise = act->get_reads_from_promise();
1287 if (r_modification_order(act, rf))
1289 } else if (promise) {
1290 if (r_modification_order(act, promise))
1294 if (act->is_write()) {
1295 if (w_modification_order(act, NULL))
1298 mo_graph->commitChanges();
1301 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1310 check_curr_backtracking(curr);
1311 set_backtracking(curr);
1315 void ModelExecution::check_curr_backtracking(ModelAction *curr)
1317 Node *currnode = curr->get_node();
1318 Node *parnode = currnode->get_parent();
1320 if ((parnode && !parnode->backtrack_empty()) ||
1321 !currnode->misc_empty() ||
1322 !currnode->read_from_empty() ||
1323 !currnode->promise_empty() ||
1324 !currnode->relseq_break_empty()) {
1325 set_latest_backtrack(curr);
1329 bool ModelExecution::promises_expired() const
1331 for (unsigned int i = 0; i < promises.size(); i++) {
1332 Promise *promise = promises[i];
1333 if (promise->get_expiration() < priv->used_sequence_numbers)
1340 * This is the strongest feasibility check available.
1341 * @return whether the current trace (partial or complete) must be a prefix of
1344 bool ModelExecution::isfeasibleprefix() const
1346 return pending_rel_seqs.size() == 0 && is_feasible_prefix_ignore_relseq();
1350 * Print disagnostic information about an infeasible execution
1351 * @param prefix A string to prefix the output with; if NULL, then a default
1352 * message prefix will be provided
1354 void ModelExecution::print_infeasibility(const char *prefix) const
1358 if (mo_graph->checkForCycles())
1359 ptr += sprintf(ptr, "[mo cycle]");
1360 if (priv->failed_promise)
1361 ptr += sprintf(ptr, "[failed promise]");
1362 if (priv->too_many_reads)
1363 ptr += sprintf(ptr, "[too many reads]");
1364 if (priv->no_valid_reads)
1365 ptr += sprintf(ptr, "[no valid reads-from]");
1366 if (priv->bad_synchronization)
1367 ptr += sprintf(ptr, "[bad sw ordering]");
1368 if (promises_expired())
1369 ptr += sprintf(ptr, "[promise expired]");
1370 if (promises.size() != 0)
1371 ptr += sprintf(ptr, "[unresolved promise]");
1373 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1377 * Returns whether the current completed trace is feasible, except for pending
1378 * release sequences.
1380 bool ModelExecution::is_feasible_prefix_ignore_relseq() const
1382 return !is_infeasible() && promises.size() == 0;
1386 * Check if the current partial trace is infeasible. Does not check any
1387 * end-of-execution flags, which might rule out the execution. Thus, this is
1388 * useful only for ruling an execution as infeasible.
1389 * @return whether the current partial trace is infeasible.
1391 bool ModelExecution::is_infeasible() const
1393 return mo_graph->checkForCycles() ||
1394 priv->no_valid_reads ||
1395 priv->failed_promise ||
1396 priv->too_many_reads ||
1397 priv->bad_synchronization ||
1401 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1402 ModelAction * ModelExecution::process_rmw(ModelAction *act) {
1403 ModelAction *lastread = get_last_action(act->get_tid());
1404 lastread->process_rmw(act);
1405 if (act->is_rmw()) {
1406 if (lastread->get_reads_from())
1407 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1409 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1410 mo_graph->commitChanges();
1416 * A helper function for ModelExecution::check_recency, to check if the current
1417 * thread is able to read from a different write/promise for 'params.maxreads'
1418 * number of steps and if that write/promise should become visible (i.e., is
1419 * ordered later in the modification order). This helps model memory liveness.
1421 * @param curr The current action. Must be a read.
1422 * @param rf The write/promise from which we plan to read
1423 * @param other_rf The write/promise from which we may read
1424 * @return True if we were able to read from other_rf for params.maxreads steps
1426 template <typename T, typename U>
1427 bool ModelExecution::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1429 /* Need a different write/promise */
1430 if (other_rf->equals(rf))
1433 /* Only look for "newer" writes/promises */
1434 if (!mo_graph->checkReachable(rf, other_rf))
1437 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1438 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1439 action_list_t::reverse_iterator rit = list->rbegin();
1440 ASSERT((*rit) == curr);
1441 /* Skip past curr */
1444 /* Does this write/promise work for everyone? */
1445 for (int i = 0; i < params->maxreads; i++, rit++) {
1446 ModelAction *act = *rit;
1447 if (!act->may_read_from(other_rf))
1454 * Checks whether a thread has read from the same write or Promise for too many
1455 * times without seeing the effects of a later write/Promise.
1458 * 1) there must a different write/promise that we could read from,
1459 * 2) we must have read from the same write/promise in excess of maxreads times,
1460 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1461 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1463 * If so, we decide that the execution is no longer feasible.
1465 * @param curr The current action. Must be a read.
1466 * @param rf The ModelAction/Promise from which we might read.
1467 * @return True if the read should succeed; false otherwise
1469 template <typename T>
1470 bool ModelExecution::check_recency(ModelAction *curr, const T *rf) const
1472 if (!params->maxreads)
1475 //NOTE: Next check is just optimization, not really necessary....
1476 if (curr->get_node()->get_read_from_past_size() +
1477 curr->get_node()->get_read_from_promise_size() <= 1)
1480 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1481 int tid = id_to_int(curr->get_tid());
1482 ASSERT(tid < (int)thrd_lists->size());
1483 action_list_t *list = &(*thrd_lists)[tid];
1484 action_list_t::reverse_iterator rit = list->rbegin();
1485 ASSERT((*rit) == curr);
1486 /* Skip past curr */
1489 action_list_t::reverse_iterator ritcopy = rit;
1490 /* See if we have enough reads from the same value */
1491 for (int count = 0; count < params->maxreads; ritcopy++, count++) {
1492 if (ritcopy == list->rend())
1494 ModelAction *act = *ritcopy;
1495 if (!act->is_read())
1497 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1499 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1501 if (act->get_node()->get_read_from_past_size() +
1502 act->get_node()->get_read_from_promise_size() <= 1)
1505 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1506 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1507 if (should_read_instead(curr, rf, write))
1508 return false; /* liveness failure */
1510 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1511 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1512 if (should_read_instead(curr, rf, promise))
1513 return false; /* liveness failure */
1519 * @brief Updates the mo_graph with the constraints imposed from the current
1522 * Basic idea is the following: Go through each other thread and find
1523 * the last action that happened before our read. Two cases:
1525 * -# The action is a write: that write must either occur before
1526 * the write we read from or be the write we read from.
1527 * -# The action is a read: the write that that action read from
1528 * must occur before the write we read from or be the same write.
1530 * @param curr The current action. Must be a read.
1531 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1532 * @return True if modification order edges were added; false otherwise
1534 template <typename rf_type>
1535 bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
1537 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1540 ASSERT(curr->is_read());
1542 /* Last SC fence in the current thread */
1543 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1544 ModelAction *last_sc_write = NULL;
1545 if (curr->is_seqcst())
1546 last_sc_write = get_last_seq_cst_write(curr);
1548 /* Iterate over all threads */
1549 for (i = 0; i < thrd_lists->size(); i++) {
1550 /* Last SC fence in thread i */
1551 ModelAction *last_sc_fence_thread_local = NULL;
1552 if (int_to_id((int)i) != curr->get_tid())
1553 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1555 /* Last SC fence in thread i, before last SC fence in current thread */
1556 ModelAction *last_sc_fence_thread_before = NULL;
1557 if (last_sc_fence_local)
1558 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1560 /* Iterate over actions in thread, starting from most recent */
1561 action_list_t *list = &(*thrd_lists)[i];
1562 action_list_t::reverse_iterator rit;
1563 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1564 ModelAction *act = *rit;
1569 /* Don't want to add reflexive edges on 'rf' */
1570 if (act->equals(rf)) {
1571 if (act->happens_before(curr))
1577 if (act->is_write()) {
1578 /* C++, Section 29.3 statement 5 */
1579 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1580 *act < *last_sc_fence_thread_local) {
1581 added = mo_graph->addEdge(act, rf) || added;
1584 /* C++, Section 29.3 statement 4 */
1585 else if (act->is_seqcst() && last_sc_fence_local &&
1586 *act < *last_sc_fence_local) {
1587 added = mo_graph->addEdge(act, rf) || added;
1590 /* C++, Section 29.3 statement 6 */
1591 else if (last_sc_fence_thread_before &&
1592 *act < *last_sc_fence_thread_before) {
1593 added = mo_graph->addEdge(act, rf) || added;
1598 /* C++, Section 29.3 statement 3 (second subpoint) */
1599 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1600 added = mo_graph->addEdge(act, rf) || added;
1605 * Include at most one act per-thread that "happens
1608 if (act->happens_before(curr)) {
1609 if (act->is_write()) {
1610 added = mo_graph->addEdge(act, rf) || added;
1612 const ModelAction *prevrf = act->get_reads_from();
1613 const Promise *prevrf_promise = act->get_reads_from_promise();
1615 if (!prevrf->equals(rf))
1616 added = mo_graph->addEdge(prevrf, rf) || added;
1617 } else if (!prevrf_promise->equals(rf)) {
1618 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1627 * All compatible, thread-exclusive promises must be ordered after any
1628 * concrete loads from the same thread
1630 for (unsigned int i = 0; i < promises.size(); i++)
1631 if (promises[i]->is_compatible_exclusive(curr))
1632 added = mo_graph->addEdge(rf, promises[i]) || added;
1638 * Updates the mo_graph with the constraints imposed from the current write.
1640 * Basic idea is the following: Go through each other thread and find
1641 * the lastest action that happened before our write. Two cases:
1643 * (1) The action is a write => that write must occur before
1646 * (2) The action is a read => the write that that action read from
1647 * must occur before the current write.
1649 * This method also handles two other issues:
1651 * (I) Sequential Consistency: Making sure that if the current write is
1652 * seq_cst, that it occurs after the previous seq_cst write.
1654 * (II) Sending the write back to non-synchronizing reads.
1656 * @param curr The current action. Must be a write.
1657 * @param send_fv A vector for stashing reads to which we may pass our future
1658 * value. If NULL, then don't record any future values.
1659 * @return True if modification order edges were added; false otherwise
1661 bool ModelExecution::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1663 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1666 ASSERT(curr->is_write());
1668 if (curr->is_seqcst()) {
1669 /* We have to at least see the last sequentially consistent write,
1670 so we are initialized. */
1671 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1672 if (last_seq_cst != NULL) {
1673 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1677 /* Last SC fence in the current thread */
1678 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1680 /* Iterate over all threads */
1681 for (i = 0; i < thrd_lists->size(); i++) {
1682 /* Last SC fence in thread i, before last SC fence in current thread */
1683 ModelAction *last_sc_fence_thread_before = NULL;
1684 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1685 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1687 /* Iterate over actions in thread, starting from most recent */
1688 action_list_t *list = &(*thrd_lists)[i];
1689 action_list_t::reverse_iterator rit;
1690 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1691 ModelAction *act = *rit;
1694 * 1) If RMW and it actually read from something, then we
1695 * already have all relevant edges, so just skip to next
1698 * 2) If RMW and it didn't read from anything, we should
1699 * whatever edge we can get to speed up convergence.
1701 * 3) If normal write, we need to look at earlier actions, so
1702 * continue processing list.
1704 if (curr->is_rmw()) {
1705 if (curr->get_reads_from() != NULL)
1713 /* C++, Section 29.3 statement 7 */
1714 if (last_sc_fence_thread_before && act->is_write() &&
1715 *act < *last_sc_fence_thread_before) {
1716 added = mo_graph->addEdge(act, curr) || added;
1721 * Include at most one act per-thread that "happens
1724 if (act->happens_before(curr)) {
1726 * Note: if act is RMW, just add edge:
1728 * The following edge should be handled elsewhere:
1729 * readfrom(act) --mo--> act
1731 if (act->is_write())
1732 added = mo_graph->addEdge(act, curr) || added;
1733 else if (act->is_read()) {
1734 //if previous read accessed a null, just keep going
1735 if (act->get_reads_from() == NULL)
1737 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1740 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1741 !act->same_thread(curr)) {
1742 /* We have an action that:
1743 (1) did not happen before us
1744 (2) is a read and we are a write
1745 (3) cannot synchronize with us
1746 (4) is in a different thread
1748 that read could potentially read from our write. Note that
1749 these checks are overly conservative at this point, we'll
1750 do more checks before actually removing the
1754 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1755 if (!is_infeasible())
1756 send_fv->push_back(act);
1757 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1758 add_future_value(curr, act);
1765 * All compatible, thread-exclusive promises must be ordered after any
1766 * concrete stores to the same thread, or else they can be merged with
1769 for (unsigned int i = 0; i < promises.size(); i++)
1770 if (promises[i]->is_compatible_exclusive(curr))
1771 added = mo_graph->addEdge(curr, promises[i]) || added;
1776 /** Arbitrary reads from the future are not allowed. Section 29.3
1777 * part 9 places some constraints. This method checks one result of constraint
1778 * constraint. Others require compiler support. */
1779 bool ModelExecution::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
1781 if (!writer->is_rmw())
1784 if (!reader->is_rmw())
1787 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1788 if (search == reader)
1790 if (search->get_tid() == reader->get_tid() &&
1791 search->happens_before(reader))
1799 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1800 * some constraints. This method checks one the following constraint (others
1801 * require compiler support):
1803 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1805 bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1807 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(reader->get_location());
1809 /* Iterate over all threads */
1810 for (i = 0; i < thrd_lists->size(); i++) {
1811 const ModelAction *write_after_read = NULL;
1813 /* Iterate over actions in thread, starting from most recent */
1814 action_list_t *list = &(*thrd_lists)[i];
1815 action_list_t::reverse_iterator rit;
1816 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1817 ModelAction *act = *rit;
1819 /* Don't disallow due to act == reader */
1820 if (!reader->happens_before(act) || reader == act)
1822 else if (act->is_write())
1823 write_after_read = act;
1824 else if (act->is_read() && act->get_reads_from() != NULL)
1825 write_after_read = act->get_reads_from();
1828 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
1835 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1836 * The ModelAction under consideration is expected to be taking part in
1837 * release/acquire synchronization as an object of the "reads from" relation.
1838 * Note that this can only provide release sequence support for RMW chains
1839 * which do not read from the future, as those actions cannot be traced until
1840 * their "promise" is fulfilled. Similarly, we may not even establish the
1841 * presence of a release sequence with certainty, as some modification order
1842 * constraints may be decided further in the future. Thus, this function
1843 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1844 * and a boolean representing certainty.
1846 * @param rf The action that might be part of a release sequence. Must be a
1848 * @param release_heads A pass-by-reference style return parameter. After
1849 * execution of this function, release_heads will contain the heads of all the
1850 * relevant release sequences, if any exists with certainty
1851 * @param pending A pass-by-reference style return parameter which is only used
1852 * when returning false (i.e., uncertain). Returns most information regarding
1853 * an uncertain release sequence, including any write operations that might
1854 * break the sequence.
1855 * @return true, if the ModelExecution is certain that release_heads is complete;
1858 bool ModelExecution::release_seq_heads(const ModelAction *rf,
1859 rel_heads_list_t *release_heads,
1860 struct release_seq *pending) const
1862 /* Only check for release sequences if there are no cycles */
1863 if (mo_graph->checkForCycles())
1866 for ( ; rf != NULL; rf = rf->get_reads_from()) {
1867 ASSERT(rf->is_write());
1869 if (rf->is_release())
1870 release_heads->push_back(rf);
1871 else if (rf->get_last_fence_release())
1872 release_heads->push_back(rf->get_last_fence_release());
1874 break; /* End of RMW chain */
1876 /** @todo Need to be smarter here... In the linux lock
1877 * example, this will run to the beginning of the program for
1879 /** @todo The way to be smarter here is to keep going until 1
1880 * thread has a release preceded by an acquire and you've seen
1883 /* acq_rel RMW is a sufficient stopping condition */
1884 if (rf->is_acquire() && rf->is_release())
1885 return true; /* complete */
1888 /* read from future: need to settle this later */
1890 return false; /* incomplete */
1893 if (rf->is_release())
1894 return true; /* complete */
1896 /* else relaxed write
1897 * - check for fence-release in the same thread (29.8, stmt. 3)
1898 * - check modification order for contiguous subsequence
1899 * -> rf must be same thread as release */
1901 const ModelAction *fence_release = rf->get_last_fence_release();
1902 /* Synchronize with a fence-release unconditionally; we don't need to
1903 * find any more "contiguous subsequence..." for it */
1905 release_heads->push_back(fence_release);
1907 int tid = id_to_int(rf->get_tid());
1908 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(rf->get_location());
1909 action_list_t *list = &(*thrd_lists)[tid];
1910 action_list_t::const_reverse_iterator rit;
1912 /* Find rf in the thread list */
1913 rit = std::find(list->rbegin(), list->rend(), rf);
1914 ASSERT(rit != list->rend());
1916 /* Find the last {write,fence}-release */
1917 for (; rit != list->rend(); rit++) {
1918 if (fence_release && *(*rit) < *fence_release)
1920 if ((*rit)->is_release())
1923 if (rit == list->rend()) {
1924 /* No write-release in this thread */
1925 return true; /* complete */
1926 } else if (fence_release && *(*rit) < *fence_release) {
1927 /* The fence-release is more recent (and so, "stronger") than
1928 * the most recent write-release */
1929 return true; /* complete */
1930 } /* else, need to establish contiguous release sequence */
1931 ModelAction *release = *rit;
1933 ASSERT(rf->same_thread(release));
1935 pending->writes.clear();
1937 bool certain = true;
1938 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1939 if (id_to_int(rf->get_tid()) == (int)i)
1941 list = &(*thrd_lists)[i];
1943 /* Can we ensure no future writes from this thread may break
1944 * the release seq? */
1945 bool future_ordered = false;
1947 ModelAction *last = get_last_action(int_to_id(i));
1948 Thread *th = get_thread(int_to_id(i));
1949 if ((last && rf->happens_before(last)) ||
1952 future_ordered = true;
1954 ASSERT(!th->is_model_thread() || future_ordered);
1956 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1957 const ModelAction *act = *rit;
1958 /* Reach synchronization -> this thread is complete */
1959 if (act->happens_before(release))
1961 if (rf->happens_before(act)) {
1962 future_ordered = true;
1966 /* Only non-RMW writes can break release sequences */
1967 if (!act->is_write() || act->is_rmw())
1970 /* Check modification order */
1971 if (mo_graph->checkReachable(rf, act)) {
1972 /* rf --mo--> act */
1973 future_ordered = true;
1976 if (mo_graph->checkReachable(act, release))
1977 /* act --mo--> release */
1979 if (mo_graph->checkReachable(release, act) &&
1980 mo_graph->checkReachable(act, rf)) {
1981 /* release --mo-> act --mo--> rf */
1982 return true; /* complete */
1984 /* act may break release sequence */
1985 pending->writes.push_back(act);
1988 if (!future_ordered)
1989 certain = false; /* This thread is uncertain */
1993 release_heads->push_back(release);
1994 pending->writes.clear();
1996 pending->release = release;
2003 * An interface for getting the release sequence head(s) with which a
2004 * given ModelAction must synchronize. This function only returns a non-empty
2005 * result when it can locate a release sequence head with certainty. Otherwise,
2006 * it may mark the internal state of the ModelExecution so that it will handle
2007 * the release sequence at a later time, causing @a acquire to update its
2008 * synchronization at some later point in execution.
2010 * @param acquire The 'acquire' action that may synchronize with a release
2012 * @param read The read action that may read from a release sequence; this may
2013 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2014 * when 'acquire' is a fence-acquire)
2015 * @param release_heads A pass-by-reference return parameter. Will be filled
2016 * with the head(s) of the release sequence(s), if they exists with certainty.
2017 * @see ModelExecution::release_seq_heads
2019 void ModelExecution::get_release_seq_heads(ModelAction *acquire,
2020 ModelAction *read, rel_heads_list_t *release_heads)
2022 const ModelAction *rf = read->get_reads_from();
2023 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2024 sequence->acquire = acquire;
2025 sequence->read = read;
2027 if (!release_seq_heads(rf, release_heads, sequence)) {
2028 /* add act to 'lazy checking' list */
2029 pending_rel_seqs.push_back(sequence);
2031 snapshot_free(sequence);
2036 * Attempt to resolve all stashed operations that might synchronize with a
2037 * release sequence for a given location. This implements the "lazy" portion of
2038 * determining whether or not a release sequence was contiguous, since not all
2039 * modification order information is present at the time an action occurs.
2041 * @param location The location/object that should be checked for release
2042 * sequence resolutions. A NULL value means to check all locations.
2043 * @param work_queue The work queue to which to add work items as they are
2045 * @return True if any updates occurred (new synchronization, new mo_graph
2048 bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
2050 bool updated = false;
2051 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs.begin();
2052 while (it != pending_rel_seqs.end()) {
2053 struct release_seq *pending = *it;
2054 ModelAction *acquire = pending->acquire;
2055 const ModelAction *read = pending->read;
2057 /* Only resolve sequences on the given location, if provided */
2058 if (location && read->get_location() != location) {
2063 const ModelAction *rf = read->get_reads_from();
2064 rel_heads_list_t release_heads;
2066 complete = release_seq_heads(rf, &release_heads, pending);
2067 for (unsigned int i = 0; i < release_heads.size(); i++)
2068 if (!acquire->has_synchronized_with(release_heads[i]))
2069 if (synchronize(release_heads[i], acquire))
2073 /* Re-check all pending release sequences */
2074 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2075 /* Re-check read-acquire for mo_graph edges */
2076 if (acquire->is_read())
2077 work_queue->push_back(MOEdgeWorkEntry(acquire));
2079 /* propagate synchronization to later actions */
2080 action_list_t::reverse_iterator rit = action_trace->rbegin();
2081 for (; (*rit) != acquire; rit++) {
2082 ModelAction *propagate = *rit;
2083 if (acquire->happens_before(propagate)) {
2084 synchronize(acquire, propagate);
2085 /* Re-check 'propagate' for mo_graph edges */
2086 work_queue->push_back(MOEdgeWorkEntry(propagate));
2091 it = pending_rel_seqs.erase(it);
2092 snapshot_free(pending);
2098 // If we resolved promises or data races, see if we have realized a data race.
2105 * Performs various bookkeeping operations for the current ModelAction. For
2106 * instance, adds action to the per-object, per-thread action vector and to the
2107 * action trace list of all thread actions.
2109 * @param act is the ModelAction to add.
2111 void ModelExecution::add_action_to_lists(ModelAction *act)
2113 int tid = id_to_int(act->get_tid());
2114 ModelAction *uninit = NULL;
2116 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2117 if (list->empty() && act->is_atomic_var()) {
2118 uninit = get_uninitialized_action(act);
2119 uninit_id = id_to_int(uninit->get_tid());
2120 list->push_front(uninit);
2122 list->push_back(act);
2124 action_trace->push_back(act);
2126 action_trace->push_front(uninit);
2128 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
2129 if (tid >= (int)vec->size())
2130 vec->resize(priv->next_thread_id);
2131 (*vec)[tid].push_back(act);
2133 (*vec)[uninit_id].push_front(uninit);
2135 if ((int)thrd_last_action.size() <= tid)
2136 thrd_last_action.resize(get_num_threads());
2137 thrd_last_action[tid] = act;
2139 thrd_last_action[uninit_id] = uninit;
2141 if (act->is_fence() && act->is_release()) {
2142 if ((int)thrd_last_fence_release.size() <= tid)
2143 thrd_last_fence_release.resize(get_num_threads());
2144 thrd_last_fence_release[tid] = act;
2147 if (act->is_wait()) {
2148 void *mutex_loc = (void *) act->get_value();
2149 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2151 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, mutex_loc);
2152 if (tid >= (int)vec->size())
2153 vec->resize(priv->next_thread_id);
2154 (*vec)[tid].push_back(act);
2159 * @brief Get the last action performed by a particular Thread
2160 * @param tid The thread ID of the Thread in question
2161 * @return The last action in the thread
2163 ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
2165 int threadid = id_to_int(tid);
2166 if (threadid < (int)thrd_last_action.size())
2167 return thrd_last_action[id_to_int(tid)];
2173 * @brief Get the last fence release performed by a particular Thread
2174 * @param tid The thread ID of the Thread in question
2175 * @return The last fence release in the thread, if one exists; NULL otherwise
2177 ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
2179 int threadid = id_to_int(tid);
2180 if (threadid < (int)thrd_last_fence_release.size())
2181 return thrd_last_fence_release[id_to_int(tid)];
2187 * Gets the last memory_order_seq_cst write (in the total global sequence)
2188 * performed on a particular object (i.e., memory location), not including the
2190 * @param curr The current ModelAction; also denotes the object location to
2192 * @return The last seq_cst write
2194 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
2196 void *location = curr->get_location();
2197 action_list_t *list = get_safe_ptr_action(obj_map, location);
2198 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2199 action_list_t::reverse_iterator rit;
2200 for (rit = list->rbegin(); (*rit) != curr; rit++)
2202 rit++; /* Skip past curr */
2203 for ( ; rit != list->rend(); rit++)
2204 if ((*rit)->is_write() && (*rit)->is_seqcst())
2210 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2211 * performed in a particular thread, prior to a particular fence.
2212 * @param tid The ID of the thread to check
2213 * @param before_fence The fence from which to begin the search; if NULL, then
2214 * search for the most recent fence in the thread.
2215 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2217 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2219 /* All fences should have NULL location */
2220 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2221 action_list_t::reverse_iterator rit = list->rbegin();
2224 for (; rit != list->rend(); rit++)
2225 if (*rit == before_fence)
2228 ASSERT(*rit == before_fence);
2232 for (; rit != list->rend(); rit++)
2233 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2239 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2240 * location). This function identifies the mutex according to the current
2241 * action, which is presumed to perform on the same mutex.
2242 * @param curr The current ModelAction; also denotes the object location to
2244 * @return The last unlock operation
2246 ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
2248 void *location = curr->get_location();
2249 action_list_t *list = get_safe_ptr_action(obj_map, location);
2250 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2251 action_list_t::reverse_iterator rit;
2252 for (rit = list->rbegin(); rit != list->rend(); rit++)
2253 if ((*rit)->is_unlock() || (*rit)->is_wait())
2258 ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
2260 ModelAction *parent = get_last_action(tid);
2262 parent = get_thread(tid)->get_creation();
2267 * Returns the clock vector for a given thread.
2268 * @param tid The thread whose clock vector we want
2269 * @return Desired clock vector
2271 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
2273 return get_parent_action(tid)->get_cv();
2277 * @brief Find the promise (if any) to resolve for the current action and
2278 * remove it from the pending promise vector
2279 * @param curr The current ModelAction. Should be a write.
2280 * @return The Promise to resolve, if any; otherwise NULL
2282 Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
2284 for (unsigned int i = 0; i < promises.size(); i++)
2285 if (curr->get_node()->get_promise(i)) {
2286 Promise *ret = promises[i];
2287 promises.erase(promises.begin() + i);
2294 * Resolve a Promise with a current write.
2295 * @param write The ModelAction that is fulfilling Promises
2296 * @param promise The Promise to resolve
2297 * @return True if the Promise was successfully resolved; false otherwise
2299 bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise)
2301 ModelVector<ModelAction *> actions_to_check;
2303 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2304 ModelAction *read = promise->get_reader(i);
2305 read_from(read, write);
2306 actions_to_check.push_back(read);
2308 /* Make sure the promise's value matches the write's value */
2309 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2310 if (!mo_graph->resolvePromise(promise, write))
2311 priv->failed_promise = true;
2314 * @todo It is possible to end up in an inconsistent state, where a
2315 * "resolved" promise may still be referenced if
2316 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2318 * Note that the inconsistency only matters when dumping mo_graph to
2324 //Check whether reading these writes has made threads unable to
2326 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2327 ModelAction *read = actions_to_check[i];
2328 mo_check_promises(read, true);
2335 * Compute the set of promises that could potentially be satisfied by this
2336 * action. Note that the set computation actually appears in the Node, not in
2338 * @param curr The ModelAction that may satisfy promises
2340 void ModelExecution::compute_promises(ModelAction *curr)
2342 for (unsigned int i = 0; i < promises.size(); i++) {
2343 Promise *promise = promises[i];
2344 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2347 bool satisfy = true;
2348 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2349 const ModelAction *act = promise->get_reader(j);
2350 if (act->happens_before(curr) ||
2351 act->could_synchronize_with(curr)) {
2357 curr->get_node()->set_promise(i);
2361 /** Checks promises in response to change in ClockVector Threads. */
2362 void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2364 for (unsigned int i = 0; i < promises.size(); i++) {
2365 Promise *promise = promises[i];
2366 if (!promise->thread_is_available(tid))
2368 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2369 const ModelAction *act = promise->get_reader(j);
2370 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2371 merge_cv->synchronized_since(act)) {
2372 if (promise->eliminate_thread(tid)) {
2373 /* Promise has failed */
2374 priv->failed_promise = true;
2382 void ModelExecution::check_promises_thread_disabled()
2384 for (unsigned int i = 0; i < promises.size(); i++) {
2385 Promise *promise = promises[i];
2386 if (promise->has_failed()) {
2387 priv->failed_promise = true;
2394 * @brief Checks promises in response to addition to modification order for
2397 * We test whether threads are still available for satisfying promises after an
2398 * addition to our modification order constraints. Those that are unavailable
2399 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2400 * that promise has failed.
2402 * @param act The ModelAction which updated the modification order
2403 * @param is_read_check Should be true if act is a read and we must check for
2404 * updates to the store from which it read (there is a distinction here for
2405 * RMW's, which are both a load and a store)
2407 void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
2409 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2411 for (unsigned int i = 0; i < promises.size(); i++) {
2412 Promise *promise = promises[i];
2414 // Is this promise on the same location?
2415 if (!promise->same_location(write))
2418 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2419 const ModelAction *pread = promise->get_reader(j);
2420 if (!pread->happens_before(act))
2422 if (mo_graph->checkPromise(write, promise)) {
2423 priv->failed_promise = true;
2429 // Don't do any lookups twice for the same thread
2430 if (!promise->thread_is_available(act->get_tid()))
2433 if (mo_graph->checkReachable(promise, write)) {
2434 if (mo_graph->checkPromise(write, promise)) {
2435 priv->failed_promise = true;
2443 * Compute the set of writes that may break the current pending release
2444 * sequence. This information is extracted from previou release sequence
2447 * @param curr The current ModelAction. Must be a release sequence fixup
2450 void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
2452 if (pending_rel_seqs.empty())
2455 struct release_seq *pending = pending_rel_seqs.back();
2456 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2457 const ModelAction *write = pending->writes[i];
2458 curr->get_node()->add_relseq_break(write);
2461 /* NULL means don't break the sequence; just synchronize */
2462 curr->get_node()->add_relseq_break(NULL);
2466 * Build up an initial set of all past writes that this 'read' action may read
2467 * from, as well as any previously-observed future values that must still be valid.
2469 * @param curr is the current ModelAction that we are exploring; it must be a
2472 void ModelExecution::build_may_read_from(ModelAction *curr)
2474 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
2476 ASSERT(curr->is_read());
2478 ModelAction *last_sc_write = NULL;
2480 if (curr->is_seqcst())
2481 last_sc_write = get_last_seq_cst_write(curr);
2483 /* Iterate over all threads */
2484 for (i = 0; i < thrd_lists->size(); i++) {
2485 /* Iterate over actions in thread, starting from most recent */
2486 action_list_t *list = &(*thrd_lists)[i];
2487 action_list_t::reverse_iterator rit;
2488 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2489 ModelAction *act = *rit;
2491 /* Only consider 'write' actions */
2492 if (!act->is_write() || act == curr)
2495 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2496 bool allow_read = true;
2498 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2500 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2504 /* Only add feasible reads */
2505 mo_graph->startChanges();
2506 r_modification_order(curr, act);
2507 if (!is_infeasible())
2508 curr->get_node()->add_read_from_past(act);
2509 mo_graph->rollbackChanges();
2512 /* Include at most one act per-thread that "happens before" curr */
2513 if (act->happens_before(curr))
2518 /* Inherit existing, promised future values */
2519 for (i = 0; i < promises.size(); i++) {
2520 const Promise *promise = promises[i];
2521 const ModelAction *promise_read = promise->get_reader(0);
2522 if (promise_read->same_var(curr)) {
2523 /* Only add feasible future-values */
2524 mo_graph->startChanges();
2525 r_modification_order(curr, promise);
2526 if (!is_infeasible())
2527 curr->get_node()->add_read_from_promise(promise_read);
2528 mo_graph->rollbackChanges();
2532 /* We may find no valid may-read-from only if the execution is doomed */
2533 if (!curr->get_node()->read_from_size()) {
2534 priv->no_valid_reads = true;
2538 if (DBG_ENABLED()) {
2539 model_print("Reached read action:\n");
2541 model_print("Printing read_from_past\n");
2542 curr->get_node()->print_read_from_past();
2543 model_print("End printing read_from_past\n");
2547 bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2549 for ( ; write != NULL; write = write->get_reads_from()) {
2550 /* UNINIT actions don't have a Node, and they never sleep */
2551 if (write->is_uninitialized())
2553 Node *prevnode = write->get_node()->get_parent();
2555 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2556 if (write->is_release() && thread_sleep)
2558 if (!write->is_rmw())
2565 * @brief Get an action representing an uninitialized atomic
2567 * This function may create a new one or try to retrieve one from the NodeStack
2569 * @param curr The current action, which prompts the creation of an UNINIT action
2570 * @return A pointer to the UNINIT ModelAction
2572 ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
2574 Node *node = curr->get_node();
2575 ModelAction *act = node->get_uninit_action();
2577 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
2578 node->set_uninit_action(act);
2580 act->create_cv(NULL);
2584 static void print_list(action_list_t *list)
2586 action_list_t::iterator it;
2588 model_print("---------------------------------------------------------------------\n");
2590 unsigned int hash = 0;
2592 for (it = list->begin(); it != list->end(); it++) {
2593 const ModelAction *act = *it;
2594 if (act->get_seq_number() > 0)
2596 hash = hash^(hash<<3)^((*it)->hash());
2598 model_print("HASH %u\n", hash);
2599 model_print("---------------------------------------------------------------------\n");
2602 #if SUPPORT_MOD_ORDER_DUMP
2603 void ModelExecution::dumpGraph(char *filename) const
2606 sprintf(buffer, "%s.dot", filename);
2607 FILE *file = fopen(buffer, "w");
2608 fprintf(file, "digraph %s {\n", filename);
2609 mo_graph->dumpNodes(file);
2610 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2612 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2613 ModelAction *act = *it;
2614 if (act->is_read()) {
2615 mo_graph->dot_print_node(file, act);
2616 if (act->get_reads_from())
2617 mo_graph->dot_print_edge(file,
2618 act->get_reads_from(),
2620 "label=\"rf\", color=red, weight=2");
2622 mo_graph->dot_print_edge(file,
2623 act->get_reads_from_promise(),
2625 "label=\"rf\", color=red");
2627 if (thread_array[act->get_tid()]) {
2628 mo_graph->dot_print_edge(file,
2629 thread_array[id_to_int(act->get_tid())],
2631 "label=\"sb\", color=blue, weight=400");
2634 thread_array[act->get_tid()] = act;
2636 fprintf(file, "}\n");
2637 model_free(thread_array);
2642 /** @brief Prints an execution trace summary. */
2643 void ModelExecution::print_summary() const
2645 #if SUPPORT_MOD_ORDER_DUMP
2646 char buffername[100];
2647 sprintf(buffername, "exec%04u", get_execution_number());
2648 mo_graph->dumpGraphToFile(buffername);
2649 sprintf(buffername, "graph%04u", get_execution_number());
2650 dumpGraph(buffername);
2653 model_print("Execution %d:", get_execution_number());
2654 if (isfeasibleprefix()) {
2655 if (scheduler->all_threads_sleeping())
2656 model_print(" SLEEP-SET REDUNDANT");
2659 print_infeasibility(" INFEASIBLE");
2660 print_list(action_trace);
2662 if (!promises.empty()) {
2663 model_print("Pending promises:\n");
2664 for (unsigned int i = 0; i < promises.size(); i++) {
2665 model_print(" [P%u] ", i);
2666 promises[i]->print();
2673 * Add a Thread to the system for the first time. Should only be called once
2675 * @param t The Thread to add
2677 void ModelExecution::add_thread(Thread *t)
2679 thread_map.put(id_to_int(t->get_id()), t);
2680 if (!t->is_model_thread())
2681 scheduler->add_thread(t);
2685 * @brief Get a Thread reference by its ID
2686 * @param tid The Thread's ID
2687 * @return A Thread reference
2689 Thread * ModelExecution::get_thread(thread_id_t tid) const
2691 return thread_map.get(id_to_int(tid));
2695 * @brief Get a reference to the Thread in which a ModelAction was executed
2696 * @param act The ModelAction
2697 * @return A Thread reference
2699 Thread * ModelExecution::get_thread(const ModelAction *act) const
2701 return get_thread(act->get_tid());
2705 * @brief Get a Promise's "promise number"
2707 * A "promise number" is an index number that is unique to a promise, valid
2708 * only for a specific snapshot of an execution trace. Promises may come and go
2709 * as they are generated an resolved, so an index only retains meaning for the
2712 * @param promise The Promise to check
2713 * @return The promise index, if the promise still is valid; otherwise -1
2715 int ModelExecution::get_promise_number(const Promise *promise) const
2717 for (unsigned int i = 0; i < promises.size(); i++)
2718 if (promises[i] == promise)
2725 * @brief Check if a Thread is currently enabled
2726 * @param t The Thread to check
2727 * @return True if the Thread is currently enabled
2729 bool ModelExecution::is_enabled(Thread *t) const
2731 return scheduler->is_enabled(t);
2735 * @brief Check if a Thread is currently enabled
2736 * @param tid The ID of the Thread to check
2737 * @return True if the Thread is currently enabled
2739 bool ModelExecution::is_enabled(thread_id_t tid) const
2741 return scheduler->is_enabled(tid);
2745 * @brief Select the next thread to execute based on the curren action
2747 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
2748 * actions should be followed by the execution of their child thread. In either
2749 * case, the current action should determine the next thread schedule.
2751 * @param curr The current action
2752 * @return The next thread to run, if the current action will determine this
2753 * selection; otherwise NULL
2755 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
2757 /* Do not split atomic RMW */
2758 if (curr->is_rmwr())
2759 return get_thread(curr);
2760 /* Follow CREATE with the created thread */
2761 if (curr->get_type() == THREAD_CREATE)
2762 return curr->get_thread_operand();
2766 /** @return True if the execution has taken too many steps */
2767 bool ModelExecution::too_many_steps() const
2769 return params->bound != 0 && priv->used_sequence_numbers > params->bound;
2773 * Takes the next step in the execution, if possible.
2774 * @param curr The current step to take
2775 * @return Returns the next Thread to run, if any; NULL if this execution
2778 Thread * ModelExecution::take_step(ModelAction *curr)
2780 Thread *curr_thrd = get_thread(curr);
2781 ASSERT(curr_thrd->get_state() == THREAD_READY);
2783 ASSERT(check_action_enabled(curr)); /* May have side effects? */
2784 curr = check_current_action(curr);
2787 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2788 scheduler->remove_thread(curr_thrd);
2790 return action_select_next_thread(curr);
2794 * Launch end-of-execution release sequence fixups only when
2795 * the execution is otherwise feasible AND there are:
2797 * (1) pending release sequences
2798 * (2) pending assertions that could be invalidated by a change
2799 * in clock vectors (i.e., data races)
2800 * (3) no pending promises
2802 void ModelExecution::fixup_release_sequences()
2804 while (!pending_rel_seqs.empty() &&
2805 is_feasible_prefix_ignore_relseq() &&
2806 !unrealizedraces.empty()) {
2807 model_print("*** WARNING: release sequence fixup action "
2808 "(%zu pending release seuqence(s)) ***\n",
2809 pending_rel_seqs.size());
2810 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2811 std::memory_order_seq_cst, NULL, VALUE_NONE,