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 const 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);
85 node_stack->register_engine(this);
88 /** @brief Destructor */
89 ModelExecution::~ModelExecution()
91 for (unsigned int i = 0; i < get_num_threads(); i++)
92 delete get_thread(int_to_id(i));
94 for (unsigned int i = 0; i < promises.size(); i++)
101 int ModelExecution::get_execution_number() const
103 return model->get_execution_number();
106 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
108 action_list_t *tmp = hash->get(ptr);
110 tmp = new action_list_t();
116 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
118 SnapVector<action_list_t> *tmp = hash->get(ptr);
120 tmp = new SnapVector<action_list_t>();
126 action_list_t * ModelExecution::get_actions_on_obj(void * obj, thread_id_t tid) const
128 SnapVector<action_list_t> *wrv = obj_thrd_map.get(obj);
131 unsigned int thread=id_to_int(tid);
132 if (thread < wrv->size())
133 return &(*wrv)[thread];
138 /** @return a thread ID for a new Thread */
139 thread_id_t ModelExecution::get_next_id()
141 return priv->next_thread_id++;
144 /** @return the number of user threads created during this execution */
145 unsigned int ModelExecution::get_num_threads() const
147 return priv->next_thread_id;
150 /** @return a sequence number for a new ModelAction */
151 modelclock_t ModelExecution::get_next_seq_num()
153 return ++priv->used_sequence_numbers;
157 * @brief Should the current action wake up a given thread?
159 * @param curr The current action
160 * @param thread The thread that we might wake up
161 * @return True, if we should wake up the sleeping thread; false otherwise
163 bool ModelExecution::should_wake_up(const ModelAction *curr, const Thread *thread) const
165 const ModelAction *asleep = thread->get_pending();
166 /* Don't allow partial RMW to wake anyone up */
169 /* Synchronizing actions may have been backtracked */
170 if (asleep->could_synchronize_with(curr))
172 /* All acquire/release fences and fence-acquire/store-release */
173 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
175 /* Fence-release + store can awake load-acquire on the same location */
176 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
177 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
178 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
184 void ModelExecution::wake_up_sleeping_actions(ModelAction *curr)
186 for (unsigned int i = 0; i < get_num_threads(); i++) {
187 Thread *thr = get_thread(int_to_id(i));
188 if (scheduler->is_sleep_set(thr)) {
189 if (should_wake_up(curr, thr))
190 /* Remove this thread from sleep set */
191 scheduler->remove_sleep(thr);
196 /** @brief Alert the model-checker that an incorrectly-ordered
197 * synchronization was made */
198 void ModelExecution::set_bad_synchronization()
200 priv->bad_synchronization = true;
203 bool ModelExecution::assert_bug(const char *msg)
205 priv->bugs.push_back(new bug_message(msg));
207 if (isfeasibleprefix()) {
214 /** @return True, if any bugs have been reported for this execution */
215 bool ModelExecution::have_bug_reports() const
217 return priv->bugs.size() != 0;
220 SnapVector<bug_message *> * ModelExecution::get_bugs() const
226 * Check whether the current trace has triggered an assertion which should halt
229 * @return True, if the execution should be aborted; false otherwise
231 bool ModelExecution::has_asserted() const
233 return priv->asserted;
237 * Trigger a trace assertion which should cause this execution to be halted.
238 * This can be due to a detected bug or due to an infeasibility that should
241 void ModelExecution::set_assert()
243 priv->asserted = true;
247 * Check if we are in a deadlock. Should only be called at the end of an
248 * execution, although it should not give false positives in the middle of an
249 * execution (there should be some ENABLED thread).
251 * @return True if program is in a deadlock; false otherwise
253 bool ModelExecution::is_deadlocked() const
255 bool blocking_threads = false;
256 for (unsigned int i = 0; i < get_num_threads(); i++) {
257 thread_id_t tid = int_to_id(i);
260 Thread *t = get_thread(tid);
261 if (!t->is_model_thread() && t->get_pending())
262 blocking_threads = true;
264 return blocking_threads;
267 bool ModelExecution::is_yieldblocked() const
269 for (unsigned int i = 0; i < get_num_threads(); i++) {
270 thread_id_t tid = int_to_id(i);
271 Thread *t = get_thread(tid);
272 if (t->get_pending() && t->get_pending()->is_yield())
279 * Check if this is a complete execution. That is, have all thread completed
280 * execution (rather than exiting because sleep sets have forced a redundant
283 * @return True if the execution is complete.
285 bool ModelExecution::is_complete_execution() const
287 if (params->yieldblock && is_yieldblocked())
289 for (unsigned int i = 0; i < get_num_threads(); i++)
290 if (is_enabled(int_to_id(i)))
296 * @brief Find the last fence-related backtracking conflict for a ModelAction
298 * This function performs the search for the most recent conflicting action
299 * against which we should perform backtracking, as affected by fence
300 * operations. This includes pairs of potentially-synchronizing actions which
301 * occur due to fence-acquire or fence-release, and hence should be explored in
302 * the opposite execution order.
304 * @param act The current action
305 * @return The most recent action which conflicts with act due to fences
307 ModelAction * ModelExecution::get_last_fence_conflict(ModelAction *act) const
309 /* Only perform release/acquire fence backtracking for stores */
310 if (!act->is_write())
313 /* Find a fence-release (or, act is a release) */
314 ModelAction *last_release;
315 if (act->is_release())
318 last_release = get_last_fence_release(act->get_tid());
322 /* Skip past the release */
323 const action_list_t *list = &action_trace;
324 action_list_t::const_reverse_iterator rit;
325 for (rit = list->rbegin(); rit != list->rend(); rit++)
326 if (*rit == last_release)
328 ASSERT(rit != list->rend());
333 * load --sb-> fence-acquire */
334 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
335 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
336 bool found_acquire_fences = false;
337 for ( ; rit != list->rend(); rit++) {
338 ModelAction *prev = *rit;
339 if (act->same_thread(prev))
342 int tid = id_to_int(prev->get_tid());
344 if (prev->is_read() && act->same_var(prev)) {
345 if (prev->is_acquire()) {
346 /* Found most recent load-acquire, don't need
347 * to search for more fences */
348 if (!found_acquire_fences)
351 prior_loads[tid] = prev;
354 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
355 found_acquire_fences = true;
356 acquire_fences[tid] = prev;
360 ModelAction *latest_backtrack = NULL;
361 for (unsigned int i = 0; i < acquire_fences.size(); i++)
362 if (acquire_fences[i] && prior_loads[i])
363 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
364 latest_backtrack = acquire_fences[i];
365 return latest_backtrack;
369 * @brief Find the last backtracking conflict for a ModelAction
371 * This function performs the search for the most recent conflicting action
372 * against which we should perform backtracking. This primary includes pairs of
373 * synchronizing actions which should be explored in the opposite execution
376 * @param act The current action
377 * @return The most recent action which conflicts with act
379 ModelAction * ModelExecution::get_last_conflict(ModelAction *act) const
381 switch (act->get_type()) {
383 /* Only seq-cst fences can (directly) cause backtracking */
384 if (!act->is_seqcst())
389 ModelAction *ret = NULL;
391 /* linear search: from most recent to oldest */
392 action_list_t *list = obj_map.get(act->get_location());
393 action_list_t::reverse_iterator rit;
394 for (rit = list->rbegin(); rit != list->rend(); rit++) {
395 ModelAction *prev = *rit;
398 if (prev->could_synchronize_with(act)) {
404 ModelAction *ret2 = get_last_fence_conflict(act);
414 case ATOMIC_TRYLOCK: {
415 /* linear search: from most recent to oldest */
416 action_list_t *list = obj_map.get(act->get_location());
417 action_list_t::reverse_iterator rit;
418 for (rit = list->rbegin(); rit != list->rend(); rit++) {
419 ModelAction *prev = *rit;
420 if (act->is_conflicting_lock(prev))
425 case ATOMIC_UNLOCK: {
426 /* linear search: from most recent to oldest */
427 action_list_t *list = obj_map.get(act->get_location());
428 action_list_t::reverse_iterator rit;
429 for (rit = list->rbegin(); rit != list->rend(); rit++) {
430 ModelAction *prev = *rit;
431 if (!act->same_thread(prev) && prev->is_failed_trylock())
437 /* linear search: from most recent to oldest */
438 action_list_t *list = obj_map.get(act->get_location());
439 action_list_t::reverse_iterator rit;
440 for (rit = list->rbegin(); rit != list->rend(); rit++) {
441 ModelAction *prev = *rit;
442 if (!act->same_thread(prev) && prev->is_failed_trylock())
444 if (!act->same_thread(prev) && prev->is_notify())
450 case ATOMIC_NOTIFY_ALL:
451 case ATOMIC_NOTIFY_ONE: {
452 /* linear search: from most recent to oldest */
453 action_list_t *list = obj_map.get(act->get_location());
454 action_list_t::reverse_iterator rit;
455 for (rit = list->rbegin(); rit != list->rend(); rit++) {
456 ModelAction *prev = *rit;
457 if (!act->same_thread(prev) && prev->is_wait())
468 /** This method finds backtracking points where we should try to
469 * reorder the parameter ModelAction against.
471 * @param the ModelAction to find backtracking points for.
473 void ModelExecution::set_backtracking(ModelAction *act)
475 Thread *t = get_thread(act);
476 ModelAction *prev = get_last_conflict(act);
480 Node *node = prev->get_node()->get_parent();
482 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
483 int low_tid, high_tid;
484 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
485 low_tid = id_to_int(act->get_tid());
486 high_tid = low_tid + 1;
489 high_tid = get_num_threads();
492 for (int i = low_tid; i < high_tid; i++) {
493 thread_id_t tid = int_to_id(i);
495 /* Make sure this thread can be enabled here. */
496 if (i >= node->get_num_threads())
499 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
500 /* Don't backtrack into a point where the thread is disabled or sleeping. */
501 if (node->enabled_status(tid) != THREAD_ENABLED)
504 /* Check if this has been explored already */
505 if (node->has_been_explored(tid))
508 /* See if fairness allows */
509 if (params->fairwindow != 0 && !node->has_priority(tid)) {
511 for (int t = 0; t < node->get_num_threads(); t++) {
512 thread_id_t tother = int_to_id(t);
513 if (node->is_enabled(tother) && node->has_priority(tother)) {
522 /* See if CHESS-like yield fairness allows */
523 if (params->yieldon) {
525 for (int t = 0; t < node->get_num_threads(); t++) {
526 thread_id_t tother = int_to_id(t);
527 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
536 /* Cache the latest backtracking point */
537 set_latest_backtrack(prev);
539 /* If this is a new backtracking point, mark the tree */
540 if (!node->set_backtrack(tid))
542 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
543 id_to_int(prev->get_tid()),
544 id_to_int(t->get_id()));
553 * @brief Cache the a backtracking point as the "most recent", if eligible
555 * Note that this does not prepare the NodeStack for this backtracking
556 * operation, it only caches the action on a per-execution basis
558 * @param act The operation at which we should explore a different next action
559 * (i.e., backtracking point)
560 * @return True, if this action is now the most recent backtracking point;
563 bool ModelExecution::set_latest_backtrack(ModelAction *act)
565 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
566 priv->next_backtrack = act;
573 * Returns last backtracking point. The model checker will explore a different
574 * path for this point in the next execution.
575 * @return The ModelAction at which the next execution should diverge.
577 ModelAction * ModelExecution::get_next_backtrack()
579 ModelAction *next = priv->next_backtrack;
580 priv->next_backtrack = NULL;
585 * Processes a read model action.
586 * @param curr is the read model action to process.
587 * @return True if processing this read updates the mo_graph.
589 bool ModelExecution::process_read(ModelAction *curr)
591 Node *node = curr->get_node();
593 bool updated = false;
594 switch (node->get_read_from_status()) {
595 case READ_FROM_PAST: {
596 const ModelAction *rf = node->get_read_from_past();
599 mo_graph->startChanges();
601 ASSERT(!is_infeasible());
602 if (!check_recency(curr, rf)) {
603 if (node->increment_read_from()) {
604 mo_graph->rollbackChanges();
607 priv->too_many_reads = true;
611 updated = r_modification_order(curr, rf);
613 mo_graph->commitChanges();
614 mo_check_promises(curr, true);
617 case READ_FROM_PROMISE: {
618 Promise *promise = curr->get_node()->get_read_from_promise();
619 if (promise->add_reader(curr))
620 priv->failed_promise = true;
621 curr->set_read_from_promise(promise);
622 mo_graph->startChanges();
623 if (!check_recency(curr, promise))
624 priv->too_many_reads = true;
625 updated = r_modification_order(curr, promise);
626 mo_graph->commitChanges();
629 case READ_FROM_FUTURE: {
630 /* Read from future value */
631 struct future_value fv = node->get_future_value();
632 Promise *promise = new Promise(this, curr, fv);
633 curr->set_read_from_promise(promise);
634 promises.push_back(promise);
635 mo_graph->startChanges();
636 updated = r_modification_order(curr, promise);
637 mo_graph->commitChanges();
643 get_thread(curr)->set_return_value(curr->get_return_value());
649 * Processes a lock, trylock, or unlock model action. @param curr is
650 * the read model action to process.
652 * The try lock operation checks whether the lock is taken. If not,
653 * it falls to the normal lock operation case. If so, it returns
656 * The lock operation has already been checked that it is enabled, so
657 * it just grabs the lock and synchronizes with the previous unlock.
659 * The unlock operation has to re-enable all of the threads that are
660 * waiting on the lock.
662 * @return True if synchronization was updated; false otherwise
664 bool ModelExecution::process_mutex(ModelAction *curr)
666 std::mutex *mutex = curr->get_mutex();
667 struct std::mutex_state *state = NULL;
670 state = mutex->get_state();
672 switch (curr->get_type()) {
673 case ATOMIC_TRYLOCK: {
674 bool success = !state->locked;
675 curr->set_try_lock(success);
677 get_thread(curr)->set_return_value(0);
680 get_thread(curr)->set_return_value(1);
682 //otherwise fall into the lock case
684 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
685 assert_bug("Lock access before initialization");
686 state->locked = get_thread(curr);
687 ModelAction *unlock = get_last_unlock(curr);
688 //synchronize with the previous unlock statement
689 if (unlock != NULL) {
690 synchronize(unlock, curr);
696 case ATOMIC_UNLOCK: {
697 /* wake up the other threads */
698 for (unsigned int i = 0; i < get_num_threads(); i++) {
699 Thread *t = get_thread(int_to_id(i));
700 Thread *curr_thrd = get_thread(curr);
701 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
705 /* unlock the lock - after checking who was waiting on it */
706 state->locked = NULL;
708 if (!curr->is_wait())
709 break; /* The rest is only for ATOMIC_WAIT */
711 /* Should we go to sleep? (simulate spurious failures) */
712 if (curr->get_node()->get_misc() == 0) {
713 get_safe_ptr_action(&condvar_waiters_map, curr->get_location())->push_back(curr);
715 scheduler->sleep(get_thread(curr));
719 case ATOMIC_NOTIFY_ALL: {
720 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
721 //activate all the waiting threads
722 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
723 scheduler->wake(get_thread(*rit));
728 case ATOMIC_NOTIFY_ONE: {
729 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
730 int wakeupthread = curr->get_node()->get_misc();
731 action_list_t::iterator it = waiters->begin();
732 advance(it, wakeupthread);
733 scheduler->wake(get_thread(*it));
745 * @brief Check if the current pending promises allow a future value to be sent
747 * If one of the following is true:
748 * (a) there are no pending promises
749 * (b) the reader and writer do not cross any promises
750 * Then, it is safe to pass a future value back now.
752 * Otherwise, we must save the pending future value until (a) or (b) is true
754 * @param writer The operation which sends the future value. Must be a write.
755 * @param reader The operation which will observe the value. Must be a read.
756 * @return True if the future value can be sent now; false if it must wait.
758 bool ModelExecution::promises_may_allow(const ModelAction *writer,
759 const ModelAction *reader) const
761 if (promises.empty())
763 for (int i = promises.size() - 1; i >= 0; i--) {
764 ModelAction *pr = promises[i]->get_reader(0);
765 //reader is after promise...doesn't cross any promise
768 //writer is after promise, reader before...bad...
776 * @brief Add a future value to a reader
778 * This function performs a few additional checks to ensure that the future
779 * value can be feasibly observed by the reader
781 * @param writer The operation whose value is sent. Must be a write.
782 * @param reader The read operation which may read the future value. Must be a read.
784 void ModelExecution::add_future_value(const ModelAction *writer, ModelAction *reader)
786 /* Do more ambitious checks now that mo is more complete */
787 if (!mo_may_allow(writer, reader))
790 Node *node = reader->get_node();
792 /* Find an ancestor thread which exists at the time of the reader */
793 Thread *write_thread = get_thread(writer);
794 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
795 write_thread = write_thread->get_parent();
797 struct future_value fv = {
798 writer->get_write_value(),
799 writer->get_seq_number() + params->maxfuturedelay,
800 write_thread->get_id(),
802 if (node->add_future_value(fv))
803 set_latest_backtrack(reader);
807 * Process a write ModelAction
808 * @param curr The ModelAction to process
809 * @return True if the mo_graph was updated or promises were resolved
811 bool ModelExecution::process_write(ModelAction *curr)
813 /* Readers to which we may send our future value */
814 ModelVector<ModelAction *> send_fv;
816 const ModelAction *earliest_promise_reader;
817 bool updated_promises = false;
819 bool updated_mod_order = w_modification_order(curr, &send_fv);
820 Promise *promise = pop_promise_to_resolve(curr);
823 earliest_promise_reader = promise->get_reader(0);
824 updated_promises = resolve_promise(curr, promise);
826 earliest_promise_reader = NULL;
828 for (unsigned int i = 0; i < send_fv.size(); i++) {
829 ModelAction *read = send_fv[i];
831 /* Don't send future values to reads after the Promise we resolve */
832 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
833 /* Check if future value can be sent immediately */
834 if (promises_may_allow(curr, read)) {
835 add_future_value(curr, read);
837 futurevalues.push_back(PendingFutureValue(curr, read));
842 /* Check the pending future values */
843 for (int i = (int)futurevalues.size() - 1; i >= 0; i--) {
844 struct PendingFutureValue pfv = futurevalues[i];
845 if (promises_may_allow(pfv.writer, pfv.reader)) {
846 add_future_value(pfv.writer, pfv.reader);
847 futurevalues.erase(futurevalues.begin() + i);
851 mo_graph->commitChanges();
852 mo_check_promises(curr, false);
854 get_thread(curr)->set_return_value(VALUE_NONE);
855 return updated_mod_order || updated_promises;
859 * Process a fence ModelAction
860 * @param curr The ModelAction to process
861 * @return True if synchronization was updated
863 bool ModelExecution::process_fence(ModelAction *curr)
866 * fence-relaxed: no-op
867 * fence-release: only log the occurence (not in this function), for
868 * use in later synchronization
869 * fence-acquire (this function): search for hypothetical release
871 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
873 bool updated = false;
874 if (curr->is_acquire()) {
875 action_list_t *list = &action_trace;
876 action_list_t::reverse_iterator rit;
877 /* Find X : is_read(X) && X --sb-> curr */
878 for (rit = list->rbegin(); rit != list->rend(); rit++) {
879 ModelAction *act = *rit;
882 if (act->get_tid() != curr->get_tid())
884 /* Stop at the beginning of the thread */
885 if (act->is_thread_start())
887 /* Stop once we reach a prior fence-acquire */
888 if (act->is_fence() && act->is_acquire())
892 /* read-acquire will find its own release sequences */
893 if (act->is_acquire())
896 /* Establish hypothetical release sequences */
897 rel_heads_list_t release_heads;
898 get_release_seq_heads(curr, act, &release_heads);
899 for (unsigned int i = 0; i < release_heads.size(); i++)
900 synchronize(release_heads[i], curr);
901 if (release_heads.size() != 0)
909 * @brief Process the current action for thread-related activity
911 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
912 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
913 * synchronization, etc. This function is a no-op for non-THREAD actions
914 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
916 * @param curr The current action
917 * @return True if synchronization was updated or a thread completed
919 bool ModelExecution::process_thread_action(ModelAction *curr)
921 bool updated = false;
923 switch (curr->get_type()) {
924 case THREAD_CREATE: {
925 thrd_t *thrd = (thrd_t *)curr->get_location();
926 struct thread_params *params = (struct thread_params *)curr->get_value();
927 Thread *th = new Thread(get_next_id(), thrd, params->func, params->arg, get_thread(curr));
929 th->set_creation(curr);
930 /* Promises can be satisfied by children */
931 for (unsigned int i = 0; i < promises.size(); i++) {
932 Promise *promise = promises[i];
933 if (promise->thread_is_available(curr->get_tid()))
934 promise->add_thread(th->get_id());
939 Thread *blocking = curr->get_thread_operand();
940 ModelAction *act = get_last_action(blocking->get_id());
941 synchronize(act, curr);
942 updated = true; /* trigger rel-seq checks */
945 case THREAD_FINISH: {
946 Thread *th = get_thread(curr);
947 /* Wake up any joining threads */
948 for (unsigned int i = 0; i < get_num_threads(); i++) {
949 Thread *waiting = get_thread(int_to_id(i));
950 if (waiting->waiting_on() == th &&
951 waiting->get_pending()->is_thread_join())
952 scheduler->wake(waiting);
955 /* Completed thread can't satisfy promises */
956 for (unsigned int i = 0; i < promises.size(); i++) {
957 Promise *promise = promises[i];
958 if (promise->thread_is_available(th->get_id()))
959 if (promise->eliminate_thread(th->get_id()))
960 priv->failed_promise = true;
962 updated = true; /* trigger rel-seq checks */
966 check_promises(curr->get_tid(), NULL, curr->get_cv());
977 * @brief Process the current action for release sequence fixup activity
979 * Performs model-checker release sequence fixups for the current action,
980 * forcing a single pending release sequence to break (with a given, potential
981 * "loose" write) or to complete (i.e., synchronize). If a pending release
982 * sequence forms a complete release sequence, then we must perform the fixup
983 * synchronization, mo_graph additions, etc.
985 * @param curr The current action; must be a release sequence fixup action
986 * @param work_queue The work queue to which to add work items as they are
989 void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
991 const ModelAction *write = curr->get_node()->get_relseq_break();
992 struct release_seq *sequence = pending_rel_seqs.back();
993 pending_rel_seqs.pop_back();
995 ModelAction *acquire = sequence->acquire;
996 const ModelAction *rf = sequence->rf;
997 const ModelAction *release = sequence->release;
1001 ASSERT(release->same_thread(rf));
1003 if (write == NULL) {
1005 * @todo Forcing a synchronization requires that we set
1006 * modification order constraints. For instance, we can't allow
1007 * a fixup sequence in which two separate read-acquire
1008 * operations read from the same sequence, where the first one
1009 * synchronizes and the other doesn't. Essentially, we can't
1010 * allow any writes to insert themselves between 'release' and
1014 /* Must synchronize */
1015 if (!synchronize(release, acquire))
1017 /* Re-check all pending release sequences */
1018 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1019 /* Re-check act for mo_graph edges */
1020 work_queue->push_back(MOEdgeWorkEntry(acquire));
1022 /* propagate synchronization to later actions */
1023 action_list_t::reverse_iterator rit = action_trace.rbegin();
1024 for (; (*rit) != acquire; rit++) {
1025 ModelAction *propagate = *rit;
1026 if (acquire->happens_before(propagate)) {
1027 synchronize(acquire, propagate);
1028 /* Re-check 'propagate' for mo_graph edges */
1029 work_queue->push_back(MOEdgeWorkEntry(propagate));
1033 /* Break release sequence with new edges:
1034 * release --mo--> write --mo--> rf */
1035 mo_graph->addEdge(release, write);
1036 mo_graph->addEdge(write, rf);
1039 /* See if we have realized a data race */
1044 * Initialize the current action by performing one or more of the following
1045 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1046 * in the NodeStack, manipulating backtracking sets, allocating and
1047 * initializing clock vectors, and computing the promises to fulfill.
1049 * @param curr The current action, as passed from the user context; may be
1050 * freed/invalidated after the execution of this function, with a different
1051 * action "returned" its place (pass-by-reference)
1052 * @return True if curr is a newly-explored action; false otherwise
1054 bool ModelExecution::initialize_curr_action(ModelAction **curr)
1056 ModelAction *newcurr;
1058 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1059 newcurr = process_rmw(*curr);
1062 if (newcurr->is_rmw())
1063 compute_promises(newcurr);
1069 (*curr)->set_seq_number(get_next_seq_num());
1071 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1073 /* First restore type and order in case of RMW operation */
1074 if ((*curr)->is_rmwr())
1075 newcurr->copy_typeandorder(*curr);
1077 ASSERT((*curr)->get_location() == newcurr->get_location());
1078 newcurr->copy_from_new(*curr);
1080 /* Discard duplicate ModelAction; use action from NodeStack */
1083 /* Always compute new clock vector */
1084 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1087 return false; /* Action was explored previously */
1091 /* Always compute new clock vector */
1092 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1094 /* Assign most recent release fence */
1095 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1098 * Perform one-time actions when pushing new ModelAction onto
1101 if (newcurr->is_write())
1102 compute_promises(newcurr);
1103 else if (newcurr->is_relseq_fixup())
1104 compute_relseq_breakwrites(newcurr);
1105 else if (newcurr->is_wait())
1106 newcurr->get_node()->set_misc_max(2);
1107 else if (newcurr->is_notify_one()) {
1108 newcurr->get_node()->set_misc_max(get_safe_ptr_action(&condvar_waiters_map, newcurr->get_location())->size());
1110 return true; /* This was a new ModelAction */
1115 * @brief Establish reads-from relation between two actions
1117 * Perform basic operations involved with establishing a concrete rf relation,
1118 * including setting the ModelAction data and checking for release sequences.
1120 * @param act The action that is reading (must be a read)
1121 * @param rf The action from which we are reading (must be a write)
1123 * @return True if this read established synchronization
1125 bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
1128 ASSERT(rf->is_write());
1130 act->set_read_from(rf);
1131 if (act->is_acquire()) {
1132 rel_heads_list_t release_heads;
1133 get_release_seq_heads(act, act, &release_heads);
1134 int num_heads = release_heads.size();
1135 for (unsigned int i = 0; i < release_heads.size(); i++)
1136 if (!synchronize(release_heads[i], act))
1138 return num_heads > 0;
1144 * @brief Synchronizes two actions
1146 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1147 * This function performs the synchronization as well as providing other hooks
1148 * for other checks along with synchronization.
1150 * @param first The left-hand side of the synchronizes-with relation
1151 * @param second The right-hand side of the synchronizes-with relation
1152 * @return True if the synchronization was successful (i.e., was consistent
1153 * with the execution order); false otherwise
1155 bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
1157 if (*second < *first) {
1158 set_bad_synchronization();
1161 check_promises(first->get_tid(), second->get_cv(), first->get_cv());
1162 return second->synchronize_with(first);
1166 * Check promises and eliminate potentially-satisfying threads when a thread is
1167 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1168 * no longer satisfy a promise generated from that thread.
1170 * @param blocker The thread on which a thread is waiting
1171 * @param waiting The waiting thread
1173 void ModelExecution::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1175 for (unsigned int i = 0; i < promises.size(); i++) {
1176 Promise *promise = promises[i];
1177 if (!promise->thread_is_available(waiting->get_id()))
1179 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1180 ModelAction *reader = promise->get_reader(j);
1181 if (reader->get_tid() != blocker->get_id())
1183 if (promise->eliminate_thread(waiting->get_id())) {
1184 /* Promise has failed */
1185 priv->failed_promise = true;
1187 /* Only eliminate the 'waiting' thread once */
1195 * @brief Check whether a model action is enabled.
1197 * Checks whether a lock or join operation would be successful (i.e., is the
1198 * lock already locked, or is the joined thread already complete). If not, put
1199 * the action in a waiter list.
1201 * @param curr is the ModelAction to check whether it is enabled.
1202 * @return a bool that indicates whether the action is enabled.
1204 bool ModelExecution::check_action_enabled(ModelAction *curr) {
1205 if (curr->is_lock()) {
1206 std::mutex *lock = curr->get_mutex();
1207 struct std::mutex_state *state = lock->get_state();
1210 } else if (curr->is_thread_join()) {
1211 Thread *blocking = curr->get_thread_operand();
1212 if (!blocking->is_complete()) {
1213 thread_blocking_check_promises(blocking, get_thread(curr));
1216 } else if (params->yieldblock && curr->is_yield()) {
1224 * This is the heart of the model checker routine. It performs model-checking
1225 * actions corresponding to a given "current action." Among other processes, it
1226 * calculates reads-from relationships, updates synchronization clock vectors,
1227 * forms a memory_order constraints graph, and handles replay/backtrack
1228 * execution when running permutations of previously-observed executions.
1230 * @param curr The current action to process
1231 * @return The ModelAction that is actually executed; may be different than
1234 ModelAction * ModelExecution::check_current_action(ModelAction *curr)
1237 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1238 bool newly_explored = initialize_curr_action(&curr);
1242 wake_up_sleeping_actions(curr);
1244 /* Compute fairness information for CHESS yield algorithm */
1245 if (params->yieldon) {
1246 curr->get_node()->update_yield(scheduler);
1249 /* Add the action to lists before any other model-checking tasks */
1250 if (!second_part_of_rmw)
1251 add_action_to_lists(curr);
1253 /* Build may_read_from set for newly-created actions */
1254 if (newly_explored && curr->is_read())
1255 build_may_read_from(curr);
1257 /* Initialize work_queue with the "current action" work */
1258 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1259 while (!work_queue.empty() && !has_asserted()) {
1260 WorkQueueEntry work = work_queue.front();
1261 work_queue.pop_front();
1263 switch (work.type) {
1264 case WORK_CHECK_CURR_ACTION: {
1265 ModelAction *act = work.action;
1266 bool update = false; /* update this location's release seq's */
1267 bool update_all = false; /* update all release seq's */
1269 if (process_thread_action(curr))
1272 if (act->is_read() && !second_part_of_rmw && process_read(act))
1275 if (act->is_write() && process_write(act))
1278 if (act->is_fence() && process_fence(act))
1281 if (act->is_mutex_op() && process_mutex(act))
1284 if (act->is_relseq_fixup())
1285 process_relseq_fixup(curr, &work_queue);
1288 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1290 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1293 case WORK_CHECK_RELEASE_SEQ:
1294 resolve_release_sequences(work.location, &work_queue);
1296 case WORK_CHECK_MO_EDGES: {
1297 /** @todo Complete verification of work_queue */
1298 ModelAction *act = work.action;
1299 bool updated = false;
1301 if (act->is_read()) {
1302 const ModelAction *rf = act->get_reads_from();
1303 const Promise *promise = act->get_reads_from_promise();
1305 if (r_modification_order(act, rf))
1307 } else if (promise) {
1308 if (r_modification_order(act, promise))
1312 if (act->is_write()) {
1313 if (w_modification_order(act, NULL))
1316 mo_graph->commitChanges();
1319 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1328 check_curr_backtracking(curr);
1329 set_backtracking(curr);
1333 void ModelExecution::check_curr_backtracking(ModelAction *curr)
1335 Node *currnode = curr->get_node();
1336 Node *parnode = currnode->get_parent();
1338 if ((parnode && !parnode->backtrack_empty()) ||
1339 !currnode->misc_empty() ||
1340 !currnode->read_from_empty() ||
1341 !currnode->promise_empty() ||
1342 !currnode->relseq_break_empty()) {
1343 set_latest_backtrack(curr);
1347 bool ModelExecution::promises_expired() const
1349 for (unsigned int i = 0; i < promises.size(); i++) {
1350 Promise *promise = promises[i];
1351 if (promise->get_expiration() < priv->used_sequence_numbers)
1358 * This is the strongest feasibility check available.
1359 * @return whether the current trace (partial or complete) must be a prefix of
1362 bool ModelExecution::isfeasibleprefix() const
1364 return pending_rel_seqs.size() == 0 && is_feasible_prefix_ignore_relseq();
1368 * Print disagnostic information about an infeasible execution
1369 * @param prefix A string to prefix the output with; if NULL, then a default
1370 * message prefix will be provided
1372 void ModelExecution::print_infeasibility(const char *prefix) const
1376 if (mo_graph->checkForCycles())
1377 ptr += sprintf(ptr, "[mo cycle]");
1378 if (priv->failed_promise)
1379 ptr += sprintf(ptr, "[failed promise]");
1380 if (priv->too_many_reads)
1381 ptr += sprintf(ptr, "[too many reads]");
1382 if (priv->no_valid_reads)
1383 ptr += sprintf(ptr, "[no valid reads-from]");
1384 if (priv->bad_synchronization)
1385 ptr += sprintf(ptr, "[bad sw ordering]");
1386 if (promises_expired())
1387 ptr += sprintf(ptr, "[promise expired]");
1388 if (promises.size() != 0)
1389 ptr += sprintf(ptr, "[unresolved promise]");
1391 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1395 * Returns whether the current completed trace is feasible, except for pending
1396 * release sequences.
1398 bool ModelExecution::is_feasible_prefix_ignore_relseq() const
1400 return !is_infeasible() && promises.size() == 0;
1404 * Check if the current partial trace is infeasible. Does not check any
1405 * end-of-execution flags, which might rule out the execution. Thus, this is
1406 * useful only for ruling an execution as infeasible.
1407 * @return whether the current partial trace is infeasible.
1409 bool ModelExecution::is_infeasible() const
1411 return mo_graph->checkForCycles() ||
1412 priv->no_valid_reads ||
1413 priv->failed_promise ||
1414 priv->too_many_reads ||
1415 priv->bad_synchronization ||
1419 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1420 ModelAction * ModelExecution::process_rmw(ModelAction *act) {
1421 ModelAction *lastread = get_last_action(act->get_tid());
1422 lastread->process_rmw(act);
1423 if (act->is_rmw()) {
1424 if (lastread->get_reads_from())
1425 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1427 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1428 mo_graph->commitChanges();
1434 * A helper function for ModelExecution::check_recency, to check if the current
1435 * thread is able to read from a different write/promise for 'params.maxreads'
1436 * number of steps and if that write/promise should become visible (i.e., is
1437 * ordered later in the modification order). This helps model memory liveness.
1439 * @param curr The current action. Must be a read.
1440 * @param rf The write/promise from which we plan to read
1441 * @param other_rf The write/promise from which we may read
1442 * @return True if we were able to read from other_rf for params.maxreads steps
1444 template <typename T, typename U>
1445 bool ModelExecution::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1447 /* Need a different write/promise */
1448 if (other_rf->equals(rf))
1451 /* Only look for "newer" writes/promises */
1452 if (!mo_graph->checkReachable(rf, other_rf))
1455 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1456 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1457 action_list_t::reverse_iterator rit = list->rbegin();
1458 ASSERT((*rit) == curr);
1459 /* Skip past curr */
1462 /* Does this write/promise work for everyone? */
1463 for (int i = 0; i < params->maxreads; i++, rit++) {
1464 ModelAction *act = *rit;
1465 if (!act->may_read_from(other_rf))
1472 * Checks whether a thread has read from the same write or Promise for too many
1473 * times without seeing the effects of a later write/Promise.
1476 * 1) there must a different write/promise that we could read from,
1477 * 2) we must have read from the same write/promise in excess of maxreads times,
1478 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1479 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1481 * If so, we decide that the execution is no longer feasible.
1483 * @param curr The current action. Must be a read.
1484 * @param rf The ModelAction/Promise from which we might read.
1485 * @return True if the read should succeed; false otherwise
1487 template <typename T>
1488 bool ModelExecution::check_recency(ModelAction *curr, const T *rf) const
1490 if (!params->maxreads)
1493 //NOTE: Next check is just optimization, not really necessary....
1494 if (curr->get_node()->get_read_from_past_size() +
1495 curr->get_node()->get_read_from_promise_size() <= 1)
1498 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1499 int tid = id_to_int(curr->get_tid());
1500 ASSERT(tid < (int)thrd_lists->size());
1501 action_list_t *list = &(*thrd_lists)[tid];
1502 action_list_t::reverse_iterator rit = list->rbegin();
1503 ASSERT((*rit) == curr);
1504 /* Skip past curr */
1507 action_list_t::reverse_iterator ritcopy = rit;
1508 /* See if we have enough reads from the same value */
1509 for (int count = 0; count < params->maxreads; ritcopy++, count++) {
1510 if (ritcopy == list->rend())
1512 ModelAction *act = *ritcopy;
1513 if (!act->is_read())
1515 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1517 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1519 if (act->get_node()->get_read_from_past_size() +
1520 act->get_node()->get_read_from_promise_size() <= 1)
1523 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1524 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1525 if (should_read_instead(curr, rf, write))
1526 return false; /* liveness failure */
1528 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1529 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1530 if (should_read_instead(curr, rf, promise))
1531 return false; /* liveness failure */
1537 * @brief Updates the mo_graph with the constraints imposed from the current
1540 * Basic idea is the following: Go through each other thread and find
1541 * the last action that happened before our read. Two cases:
1543 * -# The action is a write: that write must either occur before
1544 * the write we read from or be the write we read from.
1545 * -# The action is a read: the write that that action read from
1546 * must occur before the write we read from or be the same write.
1548 * @param curr The current action. Must be a read.
1549 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1550 * @return True if modification order edges were added; false otherwise
1552 template <typename rf_type>
1553 bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
1555 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1558 ASSERT(curr->is_read());
1560 /* Last SC fence in the current thread */
1561 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1562 ModelAction *last_sc_write = NULL;
1563 if (curr->is_seqcst())
1564 last_sc_write = get_last_seq_cst_write(curr);
1566 /* Iterate over all threads */
1567 for (i = 0; i < thrd_lists->size(); i++) {
1568 /* Last SC fence in thread i */
1569 ModelAction *last_sc_fence_thread_local = NULL;
1570 if (int_to_id((int)i) != curr->get_tid())
1571 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1573 /* Last SC fence in thread i, before last SC fence in current thread */
1574 ModelAction *last_sc_fence_thread_before = NULL;
1575 if (last_sc_fence_local)
1576 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1578 /* Iterate over actions in thread, starting from most recent */
1579 action_list_t *list = &(*thrd_lists)[i];
1580 action_list_t::reverse_iterator rit;
1581 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1582 ModelAction *act = *rit;
1587 /* Don't want to add reflexive edges on 'rf' */
1588 if (act->equals(rf)) {
1589 if (act->happens_before(curr))
1595 if (act->is_write()) {
1596 /* C++, Section 29.3 statement 5 */
1597 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1598 *act < *last_sc_fence_thread_local) {
1599 added = mo_graph->addEdge(act, rf) || added;
1602 /* C++, Section 29.3 statement 4 */
1603 else if (act->is_seqcst() && last_sc_fence_local &&
1604 *act < *last_sc_fence_local) {
1605 added = mo_graph->addEdge(act, rf) || added;
1608 /* C++, Section 29.3 statement 6 */
1609 else if (last_sc_fence_thread_before &&
1610 *act < *last_sc_fence_thread_before) {
1611 added = mo_graph->addEdge(act, rf) || added;
1616 /* C++, Section 29.3 statement 3 (second subpoint) */
1617 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1618 added = mo_graph->addEdge(act, rf) || added;
1623 * Include at most one act per-thread that "happens
1626 if (act->happens_before(curr)) {
1627 if (act->is_write()) {
1628 added = mo_graph->addEdge(act, rf) || added;
1630 const ModelAction *prevrf = act->get_reads_from();
1631 const Promise *prevrf_promise = act->get_reads_from_promise();
1633 if (!prevrf->equals(rf))
1634 added = mo_graph->addEdge(prevrf, rf) || added;
1635 } else if (!prevrf_promise->equals(rf)) {
1636 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1645 * All compatible, thread-exclusive promises must be ordered after any
1646 * concrete loads from the same thread
1648 for (unsigned int i = 0; i < promises.size(); i++)
1649 if (promises[i]->is_compatible_exclusive(curr))
1650 added = mo_graph->addEdge(rf, promises[i]) || added;
1656 * Updates the mo_graph with the constraints imposed from the current write.
1658 * Basic idea is the following: Go through each other thread and find
1659 * the lastest action that happened before our write. Two cases:
1661 * (1) The action is a write => that write must occur before
1664 * (2) The action is a read => the write that that action read from
1665 * must occur before the current write.
1667 * This method also handles two other issues:
1669 * (I) Sequential Consistency: Making sure that if the current write is
1670 * seq_cst, that it occurs after the previous seq_cst write.
1672 * (II) Sending the write back to non-synchronizing reads.
1674 * @param curr The current action. Must be a write.
1675 * @param send_fv A vector for stashing reads to which we may pass our future
1676 * value. If NULL, then don't record any future values.
1677 * @return True if modification order edges were added; false otherwise
1679 bool ModelExecution::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1681 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1684 ASSERT(curr->is_write());
1686 if (curr->is_seqcst()) {
1687 /* We have to at least see the last sequentially consistent write,
1688 so we are initialized. */
1689 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1690 if (last_seq_cst != NULL) {
1691 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1695 /* Last SC fence in the current thread */
1696 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1698 /* Iterate over all threads */
1699 for (i = 0; i < thrd_lists->size(); i++) {
1700 /* Last SC fence in thread i, before last SC fence in current thread */
1701 ModelAction *last_sc_fence_thread_before = NULL;
1702 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1703 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1705 /* Iterate over actions in thread, starting from most recent */
1706 action_list_t *list = &(*thrd_lists)[i];
1707 action_list_t::reverse_iterator rit;
1708 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1709 ModelAction *act = *rit;
1712 * 1) If RMW and it actually read from something, then we
1713 * already have all relevant edges, so just skip to next
1716 * 2) If RMW and it didn't read from anything, we should
1717 * whatever edge we can get to speed up convergence.
1719 * 3) If normal write, we need to look at earlier actions, so
1720 * continue processing list.
1722 if (curr->is_rmw()) {
1723 if (curr->get_reads_from() != NULL)
1731 /* C++, Section 29.3 statement 7 */
1732 if (last_sc_fence_thread_before && act->is_write() &&
1733 *act < *last_sc_fence_thread_before) {
1734 added = mo_graph->addEdge(act, curr) || added;
1739 * Include at most one act per-thread that "happens
1742 if (act->happens_before(curr)) {
1744 * Note: if act is RMW, just add edge:
1746 * The following edge should be handled elsewhere:
1747 * readfrom(act) --mo--> act
1749 if (act->is_write())
1750 added = mo_graph->addEdge(act, curr) || added;
1751 else if (act->is_read()) {
1752 //if previous read accessed a null, just keep going
1753 if (act->get_reads_from() == NULL)
1755 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1758 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1759 !act->same_thread(curr)) {
1760 /* We have an action that:
1761 (1) did not happen before us
1762 (2) is a read and we are a write
1763 (3) cannot synchronize with us
1764 (4) is in a different thread
1766 that read could potentially read from our write. Note that
1767 these checks are overly conservative at this point, we'll
1768 do more checks before actually removing the
1772 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1773 if (!is_infeasible())
1774 send_fv->push_back(act);
1775 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1776 add_future_value(curr, act);
1783 * All compatible, thread-exclusive promises must be ordered after any
1784 * concrete stores to the same thread, or else they can be merged with
1787 for (unsigned int i = 0; i < promises.size(); i++)
1788 if (promises[i]->is_compatible_exclusive(curr))
1789 added = mo_graph->addEdge(curr, promises[i]) || added;
1794 /** Arbitrary reads from the future are not allowed. Section 29.3
1795 * part 9 places some constraints. This method checks one result of constraint
1796 * constraint. Others require compiler support. */
1797 bool ModelExecution::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
1799 if (!writer->is_rmw())
1802 if (!reader->is_rmw())
1805 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1806 if (search == reader)
1808 if (search->get_tid() == reader->get_tid() &&
1809 search->happens_before(reader))
1817 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1818 * some constraints. This method checks one the following constraint (others
1819 * require compiler support):
1821 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1823 bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1825 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(reader->get_location());
1827 /* Iterate over all threads */
1828 for (i = 0; i < thrd_lists->size(); i++) {
1829 const ModelAction *write_after_read = NULL;
1831 /* Iterate over actions in thread, starting from most recent */
1832 action_list_t *list = &(*thrd_lists)[i];
1833 action_list_t::reverse_iterator rit;
1834 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1835 ModelAction *act = *rit;
1837 /* Don't disallow due to act == reader */
1838 if (!reader->happens_before(act) || reader == act)
1840 else if (act->is_write())
1841 write_after_read = act;
1842 else if (act->is_read() && act->get_reads_from() != NULL)
1843 write_after_read = act->get_reads_from();
1846 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
1853 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1854 * The ModelAction under consideration is expected to be taking part in
1855 * release/acquire synchronization as an object of the "reads from" relation.
1856 * Note that this can only provide release sequence support for RMW chains
1857 * which do not read from the future, as those actions cannot be traced until
1858 * their "promise" is fulfilled. Similarly, we may not even establish the
1859 * presence of a release sequence with certainty, as some modification order
1860 * constraints may be decided further in the future. Thus, this function
1861 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1862 * and a boolean representing certainty.
1864 * @param rf The action that might be part of a release sequence. Must be a
1866 * @param release_heads A pass-by-reference style return parameter. After
1867 * execution of this function, release_heads will contain the heads of all the
1868 * relevant release sequences, if any exists with certainty
1869 * @param pending A pass-by-reference style return parameter which is only used
1870 * when returning false (i.e., uncertain). Returns most information regarding
1871 * an uncertain release sequence, including any write operations that might
1872 * break the sequence.
1873 * @return true, if the ModelExecution is certain that release_heads is complete;
1876 bool ModelExecution::release_seq_heads(const ModelAction *rf,
1877 rel_heads_list_t *release_heads,
1878 struct release_seq *pending) const
1880 /* Only check for release sequences if there are no cycles */
1881 if (mo_graph->checkForCycles())
1884 for ( ; rf != NULL; rf = rf->get_reads_from()) {
1885 ASSERT(rf->is_write());
1887 if (rf->is_release())
1888 release_heads->push_back(rf);
1889 else if (rf->get_last_fence_release())
1890 release_heads->push_back(rf->get_last_fence_release());
1892 break; /* End of RMW chain */
1894 /** @todo Need to be smarter here... In the linux lock
1895 * example, this will run to the beginning of the program for
1897 /** @todo The way to be smarter here is to keep going until 1
1898 * thread has a release preceded by an acquire and you've seen
1901 /* acq_rel RMW is a sufficient stopping condition */
1902 if (rf->is_acquire() && rf->is_release())
1903 return true; /* complete */
1906 /* read from future: need to settle this later */
1908 return false; /* incomplete */
1911 if (rf->is_release())
1912 return true; /* complete */
1914 /* else relaxed write
1915 * - check for fence-release in the same thread (29.8, stmt. 3)
1916 * - check modification order for contiguous subsequence
1917 * -> rf must be same thread as release */
1919 const ModelAction *fence_release = rf->get_last_fence_release();
1920 /* Synchronize with a fence-release unconditionally; we don't need to
1921 * find any more "contiguous subsequence..." for it */
1923 release_heads->push_back(fence_release);
1925 int tid = id_to_int(rf->get_tid());
1926 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(rf->get_location());
1927 action_list_t *list = &(*thrd_lists)[tid];
1928 action_list_t::const_reverse_iterator rit;
1930 /* Find rf in the thread list */
1931 rit = std::find(list->rbegin(), list->rend(), rf);
1932 ASSERT(rit != list->rend());
1934 /* Find the last {write,fence}-release */
1935 for (; rit != list->rend(); rit++) {
1936 if (fence_release && *(*rit) < *fence_release)
1938 if ((*rit)->is_release())
1941 if (rit == list->rend()) {
1942 /* No write-release in this thread */
1943 return true; /* complete */
1944 } else if (fence_release && *(*rit) < *fence_release) {
1945 /* The fence-release is more recent (and so, "stronger") than
1946 * the most recent write-release */
1947 return true; /* complete */
1948 } /* else, need to establish contiguous release sequence */
1949 ModelAction *release = *rit;
1951 ASSERT(rf->same_thread(release));
1953 pending->writes.clear();
1955 bool certain = true;
1956 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1957 if (id_to_int(rf->get_tid()) == (int)i)
1959 list = &(*thrd_lists)[i];
1961 /* Can we ensure no future writes from this thread may break
1962 * the release seq? */
1963 bool future_ordered = false;
1965 ModelAction *last = get_last_action(int_to_id(i));
1966 Thread *th = get_thread(int_to_id(i));
1967 if ((last && rf->happens_before(last)) ||
1970 future_ordered = true;
1972 ASSERT(!th->is_model_thread() || future_ordered);
1974 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1975 const ModelAction *act = *rit;
1976 /* Reach synchronization -> this thread is complete */
1977 if (act->happens_before(release))
1979 if (rf->happens_before(act)) {
1980 future_ordered = true;
1984 /* Only non-RMW writes can break release sequences */
1985 if (!act->is_write() || act->is_rmw())
1988 /* Check modification order */
1989 if (mo_graph->checkReachable(rf, act)) {
1990 /* rf --mo--> act */
1991 future_ordered = true;
1994 if (mo_graph->checkReachable(act, release))
1995 /* act --mo--> release */
1997 if (mo_graph->checkReachable(release, act) &&
1998 mo_graph->checkReachable(act, rf)) {
1999 /* release --mo-> act --mo--> rf */
2000 return true; /* complete */
2002 /* act may break release sequence */
2003 pending->writes.push_back(act);
2006 if (!future_ordered)
2007 certain = false; /* This thread is uncertain */
2011 release_heads->push_back(release);
2012 pending->writes.clear();
2014 pending->release = release;
2021 * An interface for getting the release sequence head(s) with which a
2022 * given ModelAction must synchronize. This function only returns a non-empty
2023 * result when it can locate a release sequence head with certainty. Otherwise,
2024 * it may mark the internal state of the ModelExecution so that it will handle
2025 * the release sequence at a later time, causing @a acquire to update its
2026 * synchronization at some later point in execution.
2028 * @param acquire The 'acquire' action that may synchronize with a release
2030 * @param read The read action that may read from a release sequence; this may
2031 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2032 * when 'acquire' is a fence-acquire)
2033 * @param release_heads A pass-by-reference return parameter. Will be filled
2034 * with the head(s) of the release sequence(s), if they exists with certainty.
2035 * @see ModelExecution::release_seq_heads
2037 void ModelExecution::get_release_seq_heads(ModelAction *acquire,
2038 ModelAction *read, rel_heads_list_t *release_heads)
2040 const ModelAction *rf = read->get_reads_from();
2041 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2042 sequence->acquire = acquire;
2043 sequence->read = read;
2045 if (!release_seq_heads(rf, release_heads, sequence)) {
2046 /* add act to 'lazy checking' list */
2047 pending_rel_seqs.push_back(sequence);
2049 snapshot_free(sequence);
2054 * Attempt to resolve all stashed operations that might synchronize with a
2055 * release sequence for a given location. This implements the "lazy" portion of
2056 * determining whether or not a release sequence was contiguous, since not all
2057 * modification order information is present at the time an action occurs.
2059 * @param location The location/object that should be checked for release
2060 * sequence resolutions. A NULL value means to check all locations.
2061 * @param work_queue The work queue to which to add work items as they are
2063 * @return True if any updates occurred (new synchronization, new mo_graph
2066 bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
2068 bool updated = false;
2069 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs.begin();
2070 while (it != pending_rel_seqs.end()) {
2071 struct release_seq *pending = *it;
2072 ModelAction *acquire = pending->acquire;
2073 const ModelAction *read = pending->read;
2075 /* Only resolve sequences on the given location, if provided */
2076 if (location && read->get_location() != location) {
2081 const ModelAction *rf = read->get_reads_from();
2082 rel_heads_list_t release_heads;
2084 complete = release_seq_heads(rf, &release_heads, pending);
2085 for (unsigned int i = 0; i < release_heads.size(); i++)
2086 if (!acquire->has_synchronized_with(release_heads[i]))
2087 if (synchronize(release_heads[i], acquire))
2091 /* Re-check all pending release sequences */
2092 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2093 /* Re-check read-acquire for mo_graph edges */
2094 if (acquire->is_read())
2095 work_queue->push_back(MOEdgeWorkEntry(acquire));
2097 /* propagate synchronization to later actions */
2098 action_list_t::reverse_iterator rit = action_trace.rbegin();
2099 for (; (*rit) != acquire; rit++) {
2100 ModelAction *propagate = *rit;
2101 if (acquire->happens_before(propagate)) {
2102 synchronize(acquire, propagate);
2103 /* Re-check 'propagate' for mo_graph edges */
2104 work_queue->push_back(MOEdgeWorkEntry(propagate));
2109 it = pending_rel_seqs.erase(it);
2110 snapshot_free(pending);
2116 // If we resolved promises or data races, see if we have realized a data race.
2123 * Performs various bookkeeping operations for the current ModelAction. For
2124 * instance, adds action to the per-object, per-thread action vector and to the
2125 * action trace list of all thread actions.
2127 * @param act is the ModelAction to add.
2129 void ModelExecution::add_action_to_lists(ModelAction *act)
2131 int tid = id_to_int(act->get_tid());
2132 ModelAction *uninit = NULL;
2134 action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
2135 if (list->empty() && act->is_atomic_var()) {
2136 uninit = get_uninitialized_action(act);
2137 uninit_id = id_to_int(uninit->get_tid());
2138 list->push_front(uninit);
2140 list->push_back(act);
2142 action_trace.push_back(act);
2144 action_trace.push_front(uninit);
2146 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
2147 if (tid >= (int)vec->size())
2148 vec->resize(priv->next_thread_id);
2149 (*vec)[tid].push_back(act);
2151 (*vec)[uninit_id].push_front(uninit);
2153 if ((int)thrd_last_action.size() <= tid)
2154 thrd_last_action.resize(get_num_threads());
2155 thrd_last_action[tid] = act;
2157 thrd_last_action[uninit_id] = uninit;
2159 if (act->is_fence() && act->is_release()) {
2160 if ((int)thrd_last_fence_release.size() <= tid)
2161 thrd_last_fence_release.resize(get_num_threads());
2162 thrd_last_fence_release[tid] = act;
2165 if (act->is_wait()) {
2166 void *mutex_loc = (void *) act->get_value();
2167 get_safe_ptr_action(&obj_map, mutex_loc)->push_back(act);
2169 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, mutex_loc);
2170 if (tid >= (int)vec->size())
2171 vec->resize(priv->next_thread_id);
2172 (*vec)[tid].push_back(act);
2177 * @brief Get the last action performed by a particular Thread
2178 * @param tid The thread ID of the Thread in question
2179 * @return The last action in the thread
2181 ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
2183 int threadid = id_to_int(tid);
2184 if (threadid < (int)thrd_last_action.size())
2185 return thrd_last_action[id_to_int(tid)];
2191 * @brief Get the last fence release performed by a particular Thread
2192 * @param tid The thread ID of the Thread in question
2193 * @return The last fence release in the thread, if one exists; NULL otherwise
2195 ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
2197 int threadid = id_to_int(tid);
2198 if (threadid < (int)thrd_last_fence_release.size())
2199 return thrd_last_fence_release[id_to_int(tid)];
2205 * Gets the last memory_order_seq_cst write (in the total global sequence)
2206 * performed on a particular object (i.e., memory location), not including the
2208 * @param curr The current ModelAction; also denotes the object location to
2210 * @return The last seq_cst write
2212 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
2214 void *location = curr->get_location();
2215 action_list_t *list = obj_map.get(location);
2216 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2217 action_list_t::reverse_iterator rit;
2218 for (rit = list->rbegin(); (*rit) != curr; rit++)
2220 rit++; /* Skip past curr */
2221 for ( ; rit != list->rend(); rit++)
2222 if ((*rit)->is_write() && (*rit)->is_seqcst())
2228 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2229 * performed in a particular thread, prior to a particular fence.
2230 * @param tid The ID of the thread to check
2231 * @param before_fence The fence from which to begin the search; if NULL, then
2232 * search for the most recent fence in the thread.
2233 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2235 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2237 /* All fences should have location FENCE_LOCATION */
2238 action_list_t *list = obj_map.get(FENCE_LOCATION);
2243 action_list_t::reverse_iterator rit = list->rbegin();
2246 for (; rit != list->rend(); rit++)
2247 if (*rit == before_fence)
2250 ASSERT(*rit == before_fence);
2254 for (; rit != list->rend(); rit++)
2255 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2261 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2262 * location). This function identifies the mutex according to the current
2263 * action, which is presumed to perform on the same mutex.
2264 * @param curr The current ModelAction; also denotes the object location to
2266 * @return The last unlock operation
2268 ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
2270 void *location = curr->get_location();
2271 action_list_t *list = obj_map.get(location);
2272 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2273 action_list_t::reverse_iterator rit;
2274 for (rit = list->rbegin(); rit != list->rend(); rit++)
2275 if ((*rit)->is_unlock() || (*rit)->is_wait())
2280 ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
2282 ModelAction *parent = get_last_action(tid);
2284 parent = get_thread(tid)->get_creation();
2289 * Returns the clock vector for a given thread.
2290 * @param tid The thread whose clock vector we want
2291 * @return Desired clock vector
2293 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
2295 return get_parent_action(tid)->get_cv();
2299 * @brief Find the promise (if any) to resolve for the current action and
2300 * remove it from the pending promise vector
2301 * @param curr The current ModelAction. Should be a write.
2302 * @return The Promise to resolve, if any; otherwise NULL
2304 Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
2306 for (unsigned int i = 0; i < promises.size(); i++)
2307 if (curr->get_node()->get_promise(i)) {
2308 Promise *ret = promises[i];
2309 promises.erase(promises.begin() + i);
2316 * Resolve a Promise with a current write.
2317 * @param write The ModelAction that is fulfilling Promises
2318 * @param promise The Promise to resolve
2319 * @return True if the Promise was successfully resolved; false otherwise
2321 bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise)
2323 ModelVector<ModelAction *> actions_to_check;
2325 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2326 ModelAction *read = promise->get_reader(i);
2327 read_from(read, write);
2328 actions_to_check.push_back(read);
2330 /* Make sure the promise's value matches the write's value */
2331 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2332 if (!mo_graph->resolvePromise(promise, write))
2333 priv->failed_promise = true;
2336 * @todo It is possible to end up in an inconsistent state, where a
2337 * "resolved" promise may still be referenced if
2338 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2340 * Note that the inconsistency only matters when dumping mo_graph to
2346 //Check whether reading these writes has made threads unable to
2348 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2349 ModelAction *read = actions_to_check[i];
2350 mo_check_promises(read, true);
2357 * Compute the set of promises that could potentially be satisfied by this
2358 * action. Note that the set computation actually appears in the Node, not in
2360 * @param curr The ModelAction that may satisfy promises
2362 void ModelExecution::compute_promises(ModelAction *curr)
2364 for (unsigned int i = 0; i < promises.size(); i++) {
2365 Promise *promise = promises[i];
2366 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2369 bool satisfy = true;
2370 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2371 const ModelAction *act = promise->get_reader(j);
2372 if (act->happens_before(curr) ||
2373 act->could_synchronize_with(curr)) {
2379 curr->get_node()->set_promise(i);
2383 /** Checks promises in response to change in ClockVector Threads. */
2384 void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2386 for (unsigned int i = 0; i < promises.size(); i++) {
2387 Promise *promise = promises[i];
2388 if (!promise->thread_is_available(tid))
2390 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2391 const ModelAction *act = promise->get_reader(j);
2392 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2393 merge_cv->synchronized_since(act)) {
2394 if (promise->eliminate_thread(tid)) {
2395 /* Promise has failed */
2396 priv->failed_promise = true;
2404 void ModelExecution::check_promises_thread_disabled()
2406 for (unsigned int i = 0; i < promises.size(); i++) {
2407 Promise *promise = promises[i];
2408 if (promise->has_failed()) {
2409 priv->failed_promise = true;
2416 * @brief Checks promises in response to addition to modification order for
2419 * We test whether threads are still available for satisfying promises after an
2420 * addition to our modification order constraints. Those that are unavailable
2421 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2422 * that promise has failed.
2424 * @param act The ModelAction which updated the modification order
2425 * @param is_read_check Should be true if act is a read and we must check for
2426 * updates to the store from which it read (there is a distinction here for
2427 * RMW's, which are both a load and a store)
2429 void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
2431 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2433 for (unsigned int i = 0; i < promises.size(); i++) {
2434 Promise *promise = promises[i];
2436 // Is this promise on the same location?
2437 if (!promise->same_location(write))
2440 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2441 const ModelAction *pread = promise->get_reader(j);
2442 if (!pread->happens_before(act))
2444 if (mo_graph->checkPromise(write, promise)) {
2445 priv->failed_promise = true;
2451 // Don't do any lookups twice for the same thread
2452 if (!promise->thread_is_available(act->get_tid()))
2455 if (mo_graph->checkReachable(promise, write)) {
2456 if (mo_graph->checkPromise(write, promise)) {
2457 priv->failed_promise = true;
2465 * Compute the set of writes that may break the current pending release
2466 * sequence. This information is extracted from previou release sequence
2469 * @param curr The current ModelAction. Must be a release sequence fixup
2472 void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
2474 if (pending_rel_seqs.empty())
2477 struct release_seq *pending = pending_rel_seqs.back();
2478 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2479 const ModelAction *write = pending->writes[i];
2480 curr->get_node()->add_relseq_break(write);
2483 /* NULL means don't break the sequence; just synchronize */
2484 curr->get_node()->add_relseq_break(NULL);
2488 * Build up an initial set of all past writes that this 'read' action may read
2489 * from, as well as any previously-observed future values that must still be valid.
2491 * @param curr is the current ModelAction that we are exploring; it must be a
2494 void ModelExecution::build_may_read_from(ModelAction *curr)
2496 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
2498 ASSERT(curr->is_read());
2500 ModelAction *last_sc_write = NULL;
2502 if (curr->is_seqcst())
2503 last_sc_write = get_last_seq_cst_write(curr);
2505 /* Iterate over all threads */
2506 for (i = 0; i < thrd_lists->size(); i++) {
2507 /* Iterate over actions in thread, starting from most recent */
2508 action_list_t *list = &(*thrd_lists)[i];
2509 action_list_t::reverse_iterator rit;
2510 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2511 ModelAction *act = *rit;
2513 /* Only consider 'write' actions */
2514 if (!act->is_write() || act == curr)
2517 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2518 bool allow_read = true;
2520 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2522 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2526 /* Only add feasible reads */
2527 mo_graph->startChanges();
2528 r_modification_order(curr, act);
2529 if (!is_infeasible())
2530 curr->get_node()->add_read_from_past(act);
2531 mo_graph->rollbackChanges();
2534 /* Include at most one act per-thread that "happens before" curr */
2535 if (act->happens_before(curr))
2540 /* Inherit existing, promised future values */
2541 for (i = 0; i < promises.size(); i++) {
2542 const Promise *promise = promises[i];
2543 const ModelAction *promise_read = promise->get_reader(0);
2544 if (promise_read->same_var(curr)) {
2545 /* Only add feasible future-values */
2546 mo_graph->startChanges();
2547 r_modification_order(curr, promise);
2548 if (!is_infeasible())
2549 curr->get_node()->add_read_from_promise(promise_read);
2550 mo_graph->rollbackChanges();
2554 /* We may find no valid may-read-from only if the execution is doomed */
2555 if (!curr->get_node()->read_from_size()) {
2556 priv->no_valid_reads = true;
2560 if (DBG_ENABLED()) {
2561 model_print("Reached read action:\n");
2563 model_print("Printing read_from_past\n");
2564 curr->get_node()->print_read_from_past();
2565 model_print("End printing read_from_past\n");
2569 bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2571 for ( ; write != NULL; write = write->get_reads_from()) {
2572 /* UNINIT actions don't have a Node, and they never sleep */
2573 if (write->is_uninitialized())
2575 Node *prevnode = write->get_node()->get_parent();
2577 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2578 if (write->is_release() && thread_sleep)
2580 if (!write->is_rmw())
2587 * @brief Get an action representing an uninitialized atomic
2589 * This function may create a new one or try to retrieve one from the NodeStack
2591 * @param curr The current action, which prompts the creation of an UNINIT action
2592 * @return A pointer to the UNINIT ModelAction
2594 ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
2596 Node *node = curr->get_node();
2597 ModelAction *act = node->get_uninit_action();
2599 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
2600 node->set_uninit_action(act);
2602 act->create_cv(NULL);
2606 static void print_list(const action_list_t *list)
2608 action_list_t::const_iterator it;
2610 model_print("---------------------------------------------------------------------\n");
2612 unsigned int hash = 0;
2614 for (it = list->begin(); it != list->end(); it++) {
2615 const ModelAction *act = *it;
2616 if (act->get_seq_number() > 0)
2618 hash = hash^(hash<<3)^((*it)->hash());
2620 model_print("HASH %u\n", hash);
2621 model_print("---------------------------------------------------------------------\n");
2624 #if SUPPORT_MOD_ORDER_DUMP
2625 void ModelExecution::dumpGraph(char *filename) const
2628 sprintf(buffer, "%s.dot", filename);
2629 FILE *file = fopen(buffer, "w");
2630 fprintf(file, "digraph %s {\n", filename);
2631 mo_graph->dumpNodes(file);
2632 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2634 for (action_list_t::iterator it = action_trace.begin(); it != action_trace.end(); it++) {
2635 ModelAction *act = *it;
2636 if (act->is_read()) {
2637 mo_graph->dot_print_node(file, act);
2638 if (act->get_reads_from())
2639 mo_graph->dot_print_edge(file,
2640 act->get_reads_from(),
2642 "label=\"rf\", color=red, weight=2");
2644 mo_graph->dot_print_edge(file,
2645 act->get_reads_from_promise(),
2647 "label=\"rf\", color=red");
2649 if (thread_array[act->get_tid()]) {
2650 mo_graph->dot_print_edge(file,
2651 thread_array[id_to_int(act->get_tid())],
2653 "label=\"sb\", color=blue, weight=400");
2656 thread_array[act->get_tid()] = act;
2658 fprintf(file, "}\n");
2659 model_free(thread_array);
2664 /** @brief Prints an execution trace summary. */
2665 void ModelExecution::print_summary() const
2667 #if SUPPORT_MOD_ORDER_DUMP
2668 char buffername[100];
2669 sprintf(buffername, "exec%04u", get_execution_number());
2670 mo_graph->dumpGraphToFile(buffername);
2671 sprintf(buffername, "graph%04u", get_execution_number());
2672 dumpGraph(buffername);
2675 model_print("Execution %d:", get_execution_number());
2676 if (isfeasibleprefix()) {
2677 if (params->yieldblock && is_yieldblocked())
2678 model_print(" YIELD BLOCKED");
2679 if (scheduler->all_threads_sleeping())
2680 model_print(" SLEEP-SET REDUNDANT");
2683 print_infeasibility(" INFEASIBLE");
2684 print_list(&action_trace);
2686 if (!promises.empty()) {
2687 model_print("Pending promises:\n");
2688 for (unsigned int i = 0; i < promises.size(); i++) {
2689 model_print(" [P%u] ", i);
2690 promises[i]->print();
2697 * Add a Thread to the system for the first time. Should only be called once
2699 * @param t The Thread to add
2701 void ModelExecution::add_thread(Thread *t)
2703 unsigned int i = id_to_int(t->get_id());
2704 if (i >= thread_map.size())
2705 thread_map.resize(i + 1);
2707 if (!t->is_model_thread())
2708 scheduler->add_thread(t);
2712 * @brief Get a Thread reference by its ID
2713 * @param tid The Thread's ID
2714 * @return A Thread reference
2716 Thread * ModelExecution::get_thread(thread_id_t tid) const
2718 unsigned int i = id_to_int(tid);
2719 if (i < thread_map.size())
2720 return thread_map[i];
2725 * @brief Get a reference to the Thread in which a ModelAction was executed
2726 * @param act The ModelAction
2727 * @return A Thread reference
2729 Thread * ModelExecution::get_thread(const ModelAction *act) const
2731 return get_thread(act->get_tid());
2735 * @brief Get a Promise's "promise number"
2737 * A "promise number" is an index number that is unique to a promise, valid
2738 * only for a specific snapshot of an execution trace. Promises may come and go
2739 * as they are generated an resolved, so an index only retains meaning for the
2742 * @param promise The Promise to check
2743 * @return The promise index, if the promise still is valid; otherwise -1
2745 int ModelExecution::get_promise_number(const Promise *promise) const
2747 for (unsigned int i = 0; i < promises.size(); i++)
2748 if (promises[i] == promise)
2755 * @brief Check if a Thread is currently enabled
2756 * @param t The Thread to check
2757 * @return True if the Thread is currently enabled
2759 bool ModelExecution::is_enabled(Thread *t) const
2761 return scheduler->is_enabled(t);
2765 * @brief Check if a Thread is currently enabled
2766 * @param tid The ID of the Thread to check
2767 * @return True if the Thread is currently enabled
2769 bool ModelExecution::is_enabled(thread_id_t tid) const
2771 return scheduler->is_enabled(tid);
2775 * @brief Select the next thread to execute based on the curren action
2777 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
2778 * actions should be followed by the execution of their child thread. In either
2779 * case, the current action should determine the next thread schedule.
2781 * @param curr The current action
2782 * @return The next thread to run, if the current action will determine this
2783 * selection; otherwise NULL
2785 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
2787 /* Do not split atomic RMW */
2788 if (curr->is_rmwr())
2789 return get_thread(curr);
2790 /* Follow CREATE with the created thread */
2791 if (curr->get_type() == THREAD_CREATE)
2792 return curr->get_thread_operand();
2796 /** @return True if the execution has taken too many steps */
2797 bool ModelExecution::too_many_steps() const
2799 return params->bound != 0 && priv->used_sequence_numbers > params->bound;
2803 * Takes the next step in the execution, if possible.
2804 * @param curr The current step to take
2805 * @return Returns the next Thread to run, if any; NULL if this execution
2808 Thread * ModelExecution::take_step(ModelAction *curr)
2810 Thread *curr_thrd = get_thread(curr);
2811 ASSERT(curr_thrd->get_state() == THREAD_READY);
2813 ASSERT(check_action_enabled(curr)); /* May have side effects? */
2814 curr = check_current_action(curr);
2817 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2818 scheduler->remove_thread(curr_thrd);
2820 return action_select_next_thread(curr);
2824 * Launch end-of-execution release sequence fixups only when
2825 * the execution is otherwise feasible AND there are:
2827 * (1) pending release sequences
2828 * (2) pending assertions that could be invalidated by a change
2829 * in clock vectors (i.e., data races)
2830 * (3) no pending promises
2832 void ModelExecution::fixup_release_sequences()
2834 while (!pending_rel_seqs.empty() &&
2835 is_feasible_prefix_ignore_relseq() &&
2836 haveUnrealizedRaces()) {
2837 model_print("*** WARNING: release sequence fixup action "
2838 "(%zu pending release seuqence(s)) ***\n",
2839 pending_rel_seqs.size());
2840 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2841 std::memory_order_seq_cst, NULL, VALUE_NONE,