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;
268 * @brief Check if we are yield-blocked
270 * A program can be "yield-blocked" if all threads are ready to execute a
273 * @return True if the program is yield-blocked; false otherwise
275 bool ModelExecution::is_yieldblocked() const
277 if (!params->yieldblock)
280 for (unsigned int i = 0; i < get_num_threads(); i++) {
281 thread_id_t tid = int_to_id(i);
282 Thread *t = get_thread(tid);
283 if (t->get_pending() && t->get_pending()->is_yield())
290 * Check if this is a complete execution. That is, have all thread completed
291 * execution (rather than exiting because sleep sets have forced a redundant
294 * @return True if the execution is complete.
296 bool ModelExecution::is_complete_execution() const
298 if (is_yieldblocked())
300 for (unsigned int i = 0; i < get_num_threads(); i++)
301 if (is_enabled(int_to_id(i)))
307 * @brief Find the last fence-related backtracking conflict for a ModelAction
309 * This function performs the search for the most recent conflicting action
310 * against which we should perform backtracking, as affected by fence
311 * operations. This includes pairs of potentially-synchronizing actions which
312 * occur due to fence-acquire or fence-release, and hence should be explored in
313 * the opposite execution order.
315 * @param act The current action
316 * @return The most recent action which conflicts with act due to fences
318 ModelAction * ModelExecution::get_last_fence_conflict(ModelAction *act) const
320 /* Only perform release/acquire fence backtracking for stores */
321 if (!act->is_write())
324 /* Find a fence-release (or, act is a release) */
325 ModelAction *last_release;
326 if (act->is_release())
329 last_release = get_last_fence_release(act->get_tid());
333 /* Skip past the release */
334 const action_list_t *list = &action_trace;
335 action_list_t::const_reverse_iterator rit;
336 for (rit = list->rbegin(); rit != list->rend(); rit++)
337 if (*rit == last_release)
339 ASSERT(rit != list->rend());
344 * load --sb-> fence-acquire */
345 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
346 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
347 bool found_acquire_fences = false;
348 for ( ; rit != list->rend(); rit++) {
349 ModelAction *prev = *rit;
350 if (act->same_thread(prev))
353 int tid = id_to_int(prev->get_tid());
355 if (prev->is_read() && act->same_var(prev)) {
356 if (prev->is_acquire()) {
357 /* Found most recent load-acquire, don't need
358 * to search for more fences */
359 if (!found_acquire_fences)
362 prior_loads[tid] = prev;
365 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
366 found_acquire_fences = true;
367 acquire_fences[tid] = prev;
371 ModelAction *latest_backtrack = NULL;
372 for (unsigned int i = 0; i < acquire_fences.size(); i++)
373 if (acquire_fences[i] && prior_loads[i])
374 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
375 latest_backtrack = acquire_fences[i];
376 return latest_backtrack;
380 * @brief Find the last backtracking conflict for a ModelAction
382 * This function performs the search for the most recent conflicting action
383 * against which we should perform backtracking. This primary includes pairs of
384 * synchronizing actions which should be explored in the opposite execution
387 * @param act The current action
388 * @return The most recent action which conflicts with act
390 ModelAction * ModelExecution::get_last_conflict(ModelAction *act) const
392 switch (act->get_type()) {
394 /* Only seq-cst fences can (directly) cause backtracking */
395 if (!act->is_seqcst())
400 ModelAction *ret = NULL;
402 /* linear search: from most recent to oldest */
403 action_list_t *list = obj_map.get(act->get_location());
404 action_list_t::reverse_iterator rit;
405 for (rit = list->rbegin(); rit != list->rend(); rit++) {
406 ModelAction *prev = *rit;
409 if (prev->could_synchronize_with(act)) {
415 ModelAction *ret2 = get_last_fence_conflict(act);
425 case ATOMIC_TRYLOCK: {
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->is_conflicting_lock(prev))
436 case ATOMIC_UNLOCK: {
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())
448 /* linear search: from most recent to oldest */
449 action_list_t *list = obj_map.get(act->get_location());
450 action_list_t::reverse_iterator rit;
451 for (rit = list->rbegin(); rit != list->rend(); rit++) {
452 ModelAction *prev = *rit;
453 if (!act->same_thread(prev) && prev->is_failed_trylock())
455 if (!act->same_thread(prev) && prev->is_notify())
461 case ATOMIC_NOTIFY_ALL:
462 case ATOMIC_NOTIFY_ONE: {
463 /* linear search: from most recent to oldest */
464 action_list_t *list = obj_map.get(act->get_location());
465 action_list_t::reverse_iterator rit;
466 for (rit = list->rbegin(); rit != list->rend(); rit++) {
467 ModelAction *prev = *rit;
468 if (!act->same_thread(prev) && prev->is_wait())
479 /** This method finds backtracking points where we should try to
480 * reorder the parameter ModelAction against.
482 * @param the ModelAction to find backtracking points for.
484 void ModelExecution::set_backtracking(ModelAction *act)
486 Thread *t = get_thread(act);
487 ModelAction *prev = get_last_conflict(act);
491 Node *node = prev->get_node()->get_parent();
493 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
494 int low_tid, high_tid;
495 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
496 low_tid = id_to_int(act->get_tid());
497 high_tid = low_tid + 1;
500 high_tid = get_num_threads();
503 for (int i = low_tid; i < high_tid; i++) {
504 thread_id_t tid = int_to_id(i);
506 /* Make sure this thread can be enabled here. */
507 if (i >= node->get_num_threads())
510 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
511 /* Don't backtrack into a point where the thread is disabled or sleeping. */
512 if (node->enabled_status(tid) != THREAD_ENABLED)
515 /* Check if this has been explored already */
516 if (node->has_been_explored(tid))
519 /* See if fairness allows */
520 if (params->fairwindow != 0 && !node->has_priority(tid)) {
522 for (int t = 0; t < node->get_num_threads(); t++) {
523 thread_id_t tother = int_to_id(t);
524 if (node->is_enabled(tother) && node->has_priority(tother)) {
533 /* See if CHESS-like yield fairness allows */
534 if (params->yieldon) {
536 for (int t = 0; t < node->get_num_threads(); t++) {
537 thread_id_t tother = int_to_id(t);
538 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
547 /* Cache the latest backtracking point */
548 set_latest_backtrack(prev);
550 /* If this is a new backtracking point, mark the tree */
551 if (!node->set_backtrack(tid))
553 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
554 id_to_int(prev->get_tid()),
555 id_to_int(t->get_id()));
564 * @brief Cache the a backtracking point as the "most recent", if eligible
566 * Note that this does not prepare the NodeStack for this backtracking
567 * operation, it only caches the action on a per-execution basis
569 * @param act The operation at which we should explore a different next action
570 * (i.e., backtracking point)
571 * @return True, if this action is now the most recent backtracking point;
574 bool ModelExecution::set_latest_backtrack(ModelAction *act)
576 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
577 priv->next_backtrack = act;
584 * Returns last backtracking point. The model checker will explore a different
585 * path for this point in the next execution.
586 * @return The ModelAction at which the next execution should diverge.
588 ModelAction * ModelExecution::get_next_backtrack()
590 ModelAction *next = priv->next_backtrack;
591 priv->next_backtrack = NULL;
596 * Processes a read model action.
597 * @param curr is the read model action to process.
598 * @return True if processing this read updates the mo_graph.
600 bool ModelExecution::process_read(ModelAction *curr)
602 Node *node = curr->get_node();
604 bool updated = false;
605 switch (node->get_read_from_status()) {
606 case READ_FROM_PAST: {
607 const ModelAction *rf = node->get_read_from_past();
610 mo_graph->startChanges();
612 ASSERT(!is_infeasible());
613 if (!check_recency(curr, rf)) {
614 if (node->increment_read_from()) {
615 mo_graph->rollbackChanges();
618 priv->too_many_reads = true;
622 updated = r_modification_order(curr, rf);
624 mo_graph->commitChanges();
625 mo_check_promises(curr, true);
628 case READ_FROM_PROMISE: {
629 Promise *promise = curr->get_node()->get_read_from_promise();
630 if (promise->add_reader(curr))
631 priv->failed_promise = true;
632 curr->set_read_from_promise(promise);
633 mo_graph->startChanges();
634 if (!check_recency(curr, promise))
635 priv->too_many_reads = true;
636 updated = r_modification_order(curr, promise);
637 mo_graph->commitChanges();
640 case READ_FROM_FUTURE: {
641 /* Read from future value */
642 struct future_value fv = node->get_future_value();
643 Promise *promise = new Promise(this, curr, fv);
644 curr->set_read_from_promise(promise);
645 promises.push_back(promise);
646 mo_graph->startChanges();
647 updated = r_modification_order(curr, promise);
648 mo_graph->commitChanges();
654 get_thread(curr)->set_return_value(curr->get_return_value());
660 * Processes a lock, trylock, or unlock model action. @param curr is
661 * the read model action to process.
663 * The try lock operation checks whether the lock is taken. If not,
664 * it falls to the normal lock operation case. If so, it returns
667 * The lock operation has already been checked that it is enabled, so
668 * it just grabs the lock and synchronizes with the previous unlock.
670 * The unlock operation has to re-enable all of the threads that are
671 * waiting on the lock.
673 * @return True if synchronization was updated; false otherwise
675 bool ModelExecution::process_mutex(ModelAction *curr)
677 std::mutex *mutex = curr->get_mutex();
678 struct std::mutex_state *state = NULL;
681 state = mutex->get_state();
683 switch (curr->get_type()) {
684 case ATOMIC_TRYLOCK: {
685 bool success = !state->locked;
686 curr->set_try_lock(success);
688 get_thread(curr)->set_return_value(0);
691 get_thread(curr)->set_return_value(1);
693 //otherwise fall into the lock case
695 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
696 assert_bug("Lock access before initialization");
697 state->locked = get_thread(curr);
698 ModelAction *unlock = get_last_unlock(curr);
699 //synchronize with the previous unlock statement
700 if (unlock != NULL) {
701 synchronize(unlock, curr);
707 case ATOMIC_UNLOCK: {
708 /* wake up the other threads */
709 for (unsigned int i = 0; i < get_num_threads(); i++) {
710 Thread *t = get_thread(int_to_id(i));
711 Thread *curr_thrd = get_thread(curr);
712 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
716 /* unlock the lock - after checking who was waiting on it */
717 state->locked = NULL;
719 if (!curr->is_wait())
720 break; /* The rest is only for ATOMIC_WAIT */
722 /* Should we go to sleep? (simulate spurious failures) */
723 if (curr->get_node()->get_misc() == 0) {
724 get_safe_ptr_action(&condvar_waiters_map, curr->get_location())->push_back(curr);
726 scheduler->sleep(get_thread(curr));
730 case ATOMIC_NOTIFY_ALL: {
731 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
732 //activate all the waiting threads
733 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
734 scheduler->wake(get_thread(*rit));
739 case ATOMIC_NOTIFY_ONE: {
740 action_list_t *waiters = get_safe_ptr_action(&condvar_waiters_map, curr->get_location());
741 int wakeupthread = curr->get_node()->get_misc();
742 action_list_t::iterator it = waiters->begin();
743 advance(it, wakeupthread);
744 scheduler->wake(get_thread(*it));
756 * @brief Check if the current pending promises allow a future value to be sent
758 * If one of the following is true:
759 * (a) there are no pending promises
760 * (b) the reader and writer do not cross any promises
761 * Then, it is safe to pass a future value back now.
763 * Otherwise, we must save the pending future value until (a) or (b) is true
765 * @param writer The operation which sends the future value. Must be a write.
766 * @param reader The operation which will observe the value. Must be a read.
767 * @return True if the future value can be sent now; false if it must wait.
769 bool ModelExecution::promises_may_allow(const ModelAction *writer,
770 const ModelAction *reader) const
772 if (promises.empty())
774 for (int i = promises.size() - 1; i >= 0; i--) {
775 ModelAction *pr = promises[i]->get_reader(0);
776 //reader is after promise...doesn't cross any promise
779 //writer is after promise, reader before...bad...
787 * @brief Add a future value to a reader
789 * This function performs a few additional checks to ensure that the future
790 * value can be feasibly observed by the reader
792 * @param writer The operation whose value is sent. Must be a write.
793 * @param reader The read operation which may read the future value. Must be a read.
795 void ModelExecution::add_future_value(const ModelAction *writer, ModelAction *reader)
797 /* Do more ambitious checks now that mo is more complete */
798 if (!mo_may_allow(writer, reader))
801 Node *node = reader->get_node();
803 /* Find an ancestor thread which exists at the time of the reader */
804 Thread *write_thread = get_thread(writer);
805 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
806 write_thread = write_thread->get_parent();
808 struct future_value fv = {
809 writer->get_write_value(),
810 writer->get_seq_number() + params->maxfuturedelay,
811 write_thread->get_id(),
813 if (node->add_future_value(fv))
814 set_latest_backtrack(reader);
818 * Process a write ModelAction
819 * @param curr The ModelAction to process
820 * @return True if the mo_graph was updated or promises were resolved
822 bool ModelExecution::process_write(ModelAction *curr)
824 /* Readers to which we may send our future value */
825 ModelVector<ModelAction *> send_fv;
827 const ModelAction *earliest_promise_reader;
828 bool updated_promises = false;
830 bool updated_mod_order = w_modification_order(curr, &send_fv);
831 Promise *promise = pop_promise_to_resolve(curr);
834 earliest_promise_reader = promise->get_reader(0);
835 updated_promises = resolve_promise(curr, promise);
837 earliest_promise_reader = NULL;
839 for (unsigned int i = 0; i < send_fv.size(); i++) {
840 ModelAction *read = send_fv[i];
842 /* Don't send future values to reads after the Promise we resolve */
843 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
844 /* Check if future value can be sent immediately */
845 if (promises_may_allow(curr, read)) {
846 add_future_value(curr, read);
848 futurevalues.push_back(PendingFutureValue(curr, read));
853 /* Check the pending future values */
854 for (int i = (int)futurevalues.size() - 1; i >= 0; i--) {
855 struct PendingFutureValue pfv = futurevalues[i];
856 if (promises_may_allow(pfv.writer, pfv.reader)) {
857 add_future_value(pfv.writer, pfv.reader);
858 futurevalues.erase(futurevalues.begin() + i);
862 mo_graph->commitChanges();
863 mo_check_promises(curr, false);
865 get_thread(curr)->set_return_value(VALUE_NONE);
866 return updated_mod_order || updated_promises;
870 * Process a fence ModelAction
871 * @param curr The ModelAction to process
872 * @return True if synchronization was updated
874 bool ModelExecution::process_fence(ModelAction *curr)
877 * fence-relaxed: no-op
878 * fence-release: only log the occurence (not in this function), for
879 * use in later synchronization
880 * fence-acquire (this function): search for hypothetical release
882 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
884 bool updated = false;
885 if (curr->is_acquire()) {
886 action_list_t *list = &action_trace;
887 action_list_t::reverse_iterator rit;
888 /* Find X : is_read(X) && X --sb-> curr */
889 for (rit = list->rbegin(); rit != list->rend(); rit++) {
890 ModelAction *act = *rit;
893 if (act->get_tid() != curr->get_tid())
895 /* Stop at the beginning of the thread */
896 if (act->is_thread_start())
898 /* Stop once we reach a prior fence-acquire */
899 if (act->is_fence() && act->is_acquire())
903 /* read-acquire will find its own release sequences */
904 if (act->is_acquire())
907 /* Establish hypothetical release sequences */
908 rel_heads_list_t release_heads;
909 get_release_seq_heads(curr, act, &release_heads);
910 for (unsigned int i = 0; i < release_heads.size(); i++)
911 synchronize(release_heads[i], curr);
912 if (release_heads.size() != 0)
920 * @brief Process the current action for thread-related activity
922 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
923 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
924 * synchronization, etc. This function is a no-op for non-THREAD actions
925 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
927 * @param curr The current action
928 * @return True if synchronization was updated or a thread completed
930 bool ModelExecution::process_thread_action(ModelAction *curr)
932 bool updated = false;
934 switch (curr->get_type()) {
935 case THREAD_CREATE: {
936 thrd_t *thrd = (thrd_t *)curr->get_location();
937 struct thread_params *params = (struct thread_params *)curr->get_value();
938 Thread *th = new Thread(get_next_id(), thrd, params->func, params->arg, get_thread(curr));
940 th->set_creation(curr);
941 /* Promises can be satisfied by children */
942 for (unsigned int i = 0; i < promises.size(); i++) {
943 Promise *promise = promises[i];
944 if (promise->thread_is_available(curr->get_tid()))
945 promise->add_thread(th->get_id());
950 Thread *blocking = curr->get_thread_operand();
951 ModelAction *act = get_last_action(blocking->get_id());
952 synchronize(act, curr);
953 updated = true; /* trigger rel-seq checks */
956 case THREAD_FINISH: {
957 Thread *th = get_thread(curr);
958 /* Wake up any joining threads */
959 for (unsigned int i = 0; i < get_num_threads(); i++) {
960 Thread *waiting = get_thread(int_to_id(i));
961 if (waiting->waiting_on() == th &&
962 waiting->get_pending()->is_thread_join())
963 scheduler->wake(waiting);
966 /* Completed thread can't satisfy promises */
967 for (unsigned int i = 0; i < promises.size(); i++) {
968 Promise *promise = promises[i];
969 if (promise->thread_is_available(th->get_id()))
970 if (promise->eliminate_thread(th->get_id()))
971 priv->failed_promise = true;
973 updated = true; /* trigger rel-seq checks */
977 check_promises(curr->get_tid(), NULL, curr->get_cv());
988 * @brief Process the current action for release sequence fixup activity
990 * Performs model-checker release sequence fixups for the current action,
991 * forcing a single pending release sequence to break (with a given, potential
992 * "loose" write) or to complete (i.e., synchronize). If a pending release
993 * sequence forms a complete release sequence, then we must perform the fixup
994 * synchronization, mo_graph additions, etc.
996 * @param curr The current action; must be a release sequence fixup action
997 * @param work_queue The work queue to which to add work items as they are
1000 void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1002 const ModelAction *write = curr->get_node()->get_relseq_break();
1003 struct release_seq *sequence = pending_rel_seqs.back();
1004 pending_rel_seqs.pop_back();
1006 ModelAction *acquire = sequence->acquire;
1007 const ModelAction *rf = sequence->rf;
1008 const ModelAction *release = sequence->release;
1012 ASSERT(release->same_thread(rf));
1014 if (write == NULL) {
1016 * @todo Forcing a synchronization requires that we set
1017 * modification order constraints. For instance, we can't allow
1018 * a fixup sequence in which two separate read-acquire
1019 * operations read from the same sequence, where the first one
1020 * synchronizes and the other doesn't. Essentially, we can't
1021 * allow any writes to insert themselves between 'release' and
1025 /* Must synchronize */
1026 if (!synchronize(release, acquire))
1029 /* Propagate the changed clock vector */
1030 propagate_clockvector(acquire, work_queue);
1032 /* Break release sequence with new edges:
1033 * release --mo--> write --mo--> rf */
1034 mo_graph->addEdge(release, write);
1035 mo_graph->addEdge(write, rf);
1038 /* See if we have realized a data race */
1043 * Initialize the current action by performing one or more of the following
1044 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1045 * in the NodeStack, manipulating backtracking sets, allocating and
1046 * initializing clock vectors, and computing the promises to fulfill.
1048 * @param curr The current action, as passed from the user context; may be
1049 * freed/invalidated after the execution of this function, with a different
1050 * action "returned" its place (pass-by-reference)
1051 * @return True if curr is a newly-explored action; false otherwise
1053 bool ModelExecution::initialize_curr_action(ModelAction **curr)
1055 ModelAction *newcurr;
1057 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1058 newcurr = process_rmw(*curr);
1061 if (newcurr->is_rmw())
1062 compute_promises(newcurr);
1068 (*curr)->set_seq_number(get_next_seq_num());
1070 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1072 /* First restore type and order in case of RMW operation */
1073 if ((*curr)->is_rmwr())
1074 newcurr->copy_typeandorder(*curr);
1076 ASSERT((*curr)->get_location() == newcurr->get_location());
1077 newcurr->copy_from_new(*curr);
1079 /* Discard duplicate ModelAction; use action from NodeStack */
1082 /* Always compute new clock vector */
1083 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1086 return false; /* Action was explored previously */
1090 /* Always compute new clock vector */
1091 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1093 /* Assign most recent release fence */
1094 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1097 * Perform one-time actions when pushing new ModelAction onto
1100 if (newcurr->is_write())
1101 compute_promises(newcurr);
1102 else if (newcurr->is_relseq_fixup())
1103 compute_relseq_breakwrites(newcurr);
1104 else if (newcurr->is_wait())
1105 newcurr->get_node()->set_misc_max(2);
1106 else if (newcurr->is_notify_one()) {
1107 newcurr->get_node()->set_misc_max(get_safe_ptr_action(&condvar_waiters_map, newcurr->get_location())->size());
1109 return true; /* This was a new ModelAction */
1114 * @brief Establish reads-from relation between two actions
1116 * Perform basic operations involved with establishing a concrete rf relation,
1117 * including setting the ModelAction data and checking for release sequences.
1119 * @param act The action that is reading (must be a read)
1120 * @param rf The action from which we are reading (must be a write)
1122 * @return True if this read established synchronization
1124 bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
1127 ASSERT(rf->is_write());
1129 act->set_read_from(rf);
1130 if (act->is_acquire()) {
1131 rel_heads_list_t release_heads;
1132 get_release_seq_heads(act, act, &release_heads);
1133 int num_heads = release_heads.size();
1134 for (unsigned int i = 0; i < release_heads.size(); i++)
1135 if (!synchronize(release_heads[i], act))
1137 return num_heads > 0;
1143 * @brief Synchronizes two actions
1145 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1146 * This function performs the synchronization as well as providing other hooks
1147 * for other checks along with synchronization.
1149 * @param first The left-hand side of the synchronizes-with relation
1150 * @param second The right-hand side of the synchronizes-with relation
1151 * @return True if the synchronization was successful (i.e., was consistent
1152 * with the execution order); false otherwise
1154 bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
1156 if (*second < *first) {
1157 set_bad_synchronization();
1160 check_promises(first->get_tid(), second->get_cv(), first->get_cv());
1161 return second->synchronize_with(first);
1165 * Check promises and eliminate potentially-satisfying threads when a thread is
1166 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1167 * no longer satisfy a promise generated from that thread.
1169 * @param blocker The thread on which a thread is waiting
1170 * @param waiting The waiting thread
1172 void ModelExecution::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1174 for (unsigned int i = 0; i < promises.size(); i++) {
1175 Promise *promise = promises[i];
1176 if (!promise->thread_is_available(waiting->get_id()))
1178 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1179 ModelAction *reader = promise->get_reader(j);
1180 if (reader->get_tid() != blocker->get_id())
1182 if (promise->eliminate_thread(waiting->get_id())) {
1183 /* Promise has failed */
1184 priv->failed_promise = true;
1186 /* Only eliminate the 'waiting' thread once */
1194 * @brief Check whether a model action is enabled.
1196 * Checks whether an operation would be successful (i.e., is a lock already
1197 * locked, or is the joined thread already complete).
1199 * For yield-blocking, yields are never enabled.
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 * @brief Propagate a modified clock vector to actions later in the execution
2057 * After an acquire operation lazily completes a release-sequence
2058 * synchronization, we must update all clock vectors for operations later than
2059 * the acquire in the execution order.
2061 * @param acquire The ModelAction whose clock vector must be propagated
2062 * @param work The work queue to which we can add work items, if this
2063 * propagation triggers more updates (e.g., to the modification order)
2065 void ModelExecution::propagate_clockvector(ModelAction *acquire, work_queue_t *work)
2067 /* Re-check all pending release sequences */
2068 work->push_back(CheckRelSeqWorkEntry(NULL));
2069 /* Re-check read-acquire for mo_graph edges */
2070 work->push_back(MOEdgeWorkEntry(acquire));
2072 /* propagate synchronization to later actions */
2073 action_list_t::reverse_iterator rit = action_trace.rbegin();
2074 for (; (*rit) != acquire; rit++) {
2075 ModelAction *propagate = *rit;
2076 if (acquire->happens_before(propagate)) {
2077 synchronize(acquire, propagate);
2078 /* Re-check 'propagate' for mo_graph edges */
2079 work->push_back(MOEdgeWorkEntry(propagate));
2085 * Attempt to resolve all stashed operations that might synchronize with a
2086 * release sequence for a given location. This implements the "lazy" portion of
2087 * determining whether or not a release sequence was contiguous, since not all
2088 * modification order information is present at the time an action occurs.
2090 * @param location The location/object that should be checked for release
2091 * sequence resolutions. A NULL value means to check all locations.
2092 * @param work_queue The work queue to which to add work items as they are
2094 * @return True if any updates occurred (new synchronization, new mo_graph
2097 bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
2099 bool updated = false;
2100 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs.begin();
2101 while (it != pending_rel_seqs.end()) {
2102 struct release_seq *pending = *it;
2103 ModelAction *acquire = pending->acquire;
2104 const ModelAction *read = pending->read;
2106 /* Only resolve sequences on the given location, if provided */
2107 if (location && read->get_location() != location) {
2112 const ModelAction *rf = read->get_reads_from();
2113 rel_heads_list_t release_heads;
2115 complete = release_seq_heads(rf, &release_heads, pending);
2116 for (unsigned int i = 0; i < release_heads.size(); i++)
2117 if (!acquire->has_synchronized_with(release_heads[i]))
2118 if (synchronize(release_heads[i], acquire))
2122 /* Propagate the changed clock vector */
2123 propagate_clockvector(acquire, work_queue);
2126 it = pending_rel_seqs.erase(it);
2127 snapshot_free(pending);
2133 // If we resolved promises or data races, see if we have realized a data race.
2140 * Performs various bookkeeping operations for the current ModelAction. For
2141 * instance, adds action to the per-object, per-thread action vector and to the
2142 * action trace list of all thread actions.
2144 * @param act is the ModelAction to add.
2146 void ModelExecution::add_action_to_lists(ModelAction *act)
2148 int tid = id_to_int(act->get_tid());
2149 ModelAction *uninit = NULL;
2151 action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
2152 if (list->empty() && act->is_atomic_var()) {
2153 uninit = get_uninitialized_action(act);
2154 uninit_id = id_to_int(uninit->get_tid());
2155 list->push_front(uninit);
2157 list->push_back(act);
2159 action_trace.push_back(act);
2161 action_trace.push_front(uninit);
2163 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
2164 if (tid >= (int)vec->size())
2165 vec->resize(priv->next_thread_id);
2166 (*vec)[tid].push_back(act);
2168 (*vec)[uninit_id].push_front(uninit);
2170 if ((int)thrd_last_action.size() <= tid)
2171 thrd_last_action.resize(get_num_threads());
2172 thrd_last_action[tid] = act;
2174 thrd_last_action[uninit_id] = uninit;
2176 if (act->is_fence() && act->is_release()) {
2177 if ((int)thrd_last_fence_release.size() <= tid)
2178 thrd_last_fence_release.resize(get_num_threads());
2179 thrd_last_fence_release[tid] = act;
2182 if (act->is_wait()) {
2183 void *mutex_loc = (void *) act->get_value();
2184 get_safe_ptr_action(&obj_map, mutex_loc)->push_back(act);
2186 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, mutex_loc);
2187 if (tid >= (int)vec->size())
2188 vec->resize(priv->next_thread_id);
2189 (*vec)[tid].push_back(act);
2194 * @brief Get the last action performed by a particular Thread
2195 * @param tid The thread ID of the Thread in question
2196 * @return The last action in the thread
2198 ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
2200 int threadid = id_to_int(tid);
2201 if (threadid < (int)thrd_last_action.size())
2202 return thrd_last_action[id_to_int(tid)];
2208 * @brief Get the last fence release performed by a particular Thread
2209 * @param tid The thread ID of the Thread in question
2210 * @return The last fence release in the thread, if one exists; NULL otherwise
2212 ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
2214 int threadid = id_to_int(tid);
2215 if (threadid < (int)thrd_last_fence_release.size())
2216 return thrd_last_fence_release[id_to_int(tid)];
2222 * Gets the last memory_order_seq_cst write (in the total global sequence)
2223 * performed on a particular object (i.e., memory location), not including the
2225 * @param curr The current ModelAction; also denotes the object location to
2227 * @return The last seq_cst write
2229 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
2231 void *location = curr->get_location();
2232 action_list_t *list = obj_map.get(location);
2233 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2234 action_list_t::reverse_iterator rit;
2235 for (rit = list->rbegin(); (*rit) != curr; rit++)
2237 rit++; /* Skip past curr */
2238 for ( ; rit != list->rend(); rit++)
2239 if ((*rit)->is_write() && (*rit)->is_seqcst())
2245 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2246 * performed in a particular thread, prior to a particular fence.
2247 * @param tid The ID of the thread to check
2248 * @param before_fence The fence from which to begin the search; if NULL, then
2249 * search for the most recent fence in the thread.
2250 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2252 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2254 /* All fences should have location FENCE_LOCATION */
2255 action_list_t *list = obj_map.get(FENCE_LOCATION);
2260 action_list_t::reverse_iterator rit = list->rbegin();
2263 for (; rit != list->rend(); rit++)
2264 if (*rit == before_fence)
2267 ASSERT(*rit == before_fence);
2271 for (; rit != list->rend(); rit++)
2272 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2278 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2279 * location). This function identifies the mutex according to the current
2280 * action, which is presumed to perform on the same mutex.
2281 * @param curr The current ModelAction; also denotes the object location to
2283 * @return The last unlock operation
2285 ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
2287 void *location = curr->get_location();
2288 action_list_t *list = obj_map.get(location);
2289 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2290 action_list_t::reverse_iterator rit;
2291 for (rit = list->rbegin(); rit != list->rend(); rit++)
2292 if ((*rit)->is_unlock() || (*rit)->is_wait())
2297 ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
2299 ModelAction *parent = get_last_action(tid);
2301 parent = get_thread(tid)->get_creation();
2306 * Returns the clock vector for a given thread.
2307 * @param tid The thread whose clock vector we want
2308 * @return Desired clock vector
2310 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
2312 return get_parent_action(tid)->get_cv();
2316 * @brief Find the promise (if any) to resolve for the current action and
2317 * remove it from the pending promise vector
2318 * @param curr The current ModelAction. Should be a write.
2319 * @return The Promise to resolve, if any; otherwise NULL
2321 Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
2323 for (unsigned int i = 0; i < promises.size(); i++)
2324 if (curr->get_node()->get_promise(i)) {
2325 Promise *ret = promises[i];
2326 promises.erase(promises.begin() + i);
2333 * Resolve a Promise with a current write.
2334 * @param write The ModelAction that is fulfilling Promises
2335 * @param promise The Promise to resolve
2336 * @return True if the Promise was successfully resolved; false otherwise
2338 bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise)
2340 ModelVector<ModelAction *> actions_to_check;
2342 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2343 ModelAction *read = promise->get_reader(i);
2344 read_from(read, write);
2345 actions_to_check.push_back(read);
2347 /* Make sure the promise's value matches the write's value */
2348 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2349 if (!mo_graph->resolvePromise(promise, write))
2350 priv->failed_promise = true;
2353 * @todo It is possible to end up in an inconsistent state, where a
2354 * "resolved" promise may still be referenced if
2355 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2357 * Note that the inconsistency only matters when dumping mo_graph to
2363 //Check whether reading these writes has made threads unable to
2365 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2366 ModelAction *read = actions_to_check[i];
2367 mo_check_promises(read, true);
2374 * Compute the set of promises that could potentially be satisfied by this
2375 * action. Note that the set computation actually appears in the Node, not in
2377 * @param curr The ModelAction that may satisfy promises
2379 void ModelExecution::compute_promises(ModelAction *curr)
2381 for (unsigned int i = 0; i < promises.size(); i++) {
2382 Promise *promise = promises[i];
2383 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2386 bool satisfy = true;
2387 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2388 const ModelAction *act = promise->get_reader(j);
2389 if (act->happens_before(curr) ||
2390 act->could_synchronize_with(curr)) {
2396 curr->get_node()->set_promise(i);
2400 /** Checks promises in response to change in ClockVector Threads. */
2401 void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2403 for (unsigned int i = 0; i < promises.size(); i++) {
2404 Promise *promise = promises[i];
2405 if (!promise->thread_is_available(tid))
2407 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2408 const ModelAction *act = promise->get_reader(j);
2409 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2410 merge_cv->synchronized_since(act)) {
2411 if (promise->eliminate_thread(tid)) {
2412 /* Promise has failed */
2413 priv->failed_promise = true;
2421 void ModelExecution::check_promises_thread_disabled()
2423 for (unsigned int i = 0; i < promises.size(); i++) {
2424 Promise *promise = promises[i];
2425 if (promise->has_failed()) {
2426 priv->failed_promise = true;
2433 * @brief Checks promises in response to addition to modification order for
2436 * We test whether threads are still available for satisfying promises after an
2437 * addition to our modification order constraints. Those that are unavailable
2438 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2439 * that promise has failed.
2441 * @param act The ModelAction which updated the modification order
2442 * @param is_read_check Should be true if act is a read and we must check for
2443 * updates to the store from which it read (there is a distinction here for
2444 * RMW's, which are both a load and a store)
2446 void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
2448 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2450 for (unsigned int i = 0; i < promises.size(); i++) {
2451 Promise *promise = promises[i];
2453 // Is this promise on the same location?
2454 if (!promise->same_location(write))
2457 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2458 const ModelAction *pread = promise->get_reader(j);
2459 if (!pread->happens_before(act))
2461 if (mo_graph->checkPromise(write, promise)) {
2462 priv->failed_promise = true;
2468 // Don't do any lookups twice for the same thread
2469 if (!promise->thread_is_available(act->get_tid()))
2472 if (mo_graph->checkReachable(promise, write)) {
2473 if (mo_graph->checkPromise(write, promise)) {
2474 priv->failed_promise = true;
2482 * Compute the set of writes that may break the current pending release
2483 * sequence. This information is extracted from previou release sequence
2486 * @param curr The current ModelAction. Must be a release sequence fixup
2489 void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
2491 if (pending_rel_seqs.empty())
2494 struct release_seq *pending = pending_rel_seqs.back();
2495 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2496 const ModelAction *write = pending->writes[i];
2497 curr->get_node()->add_relseq_break(write);
2500 /* NULL means don't break the sequence; just synchronize */
2501 curr->get_node()->add_relseq_break(NULL);
2505 * Build up an initial set of all past writes that this 'read' action may read
2506 * from, as well as any previously-observed future values that must still be valid.
2508 * @param curr is the current ModelAction that we are exploring; it must be a
2511 void ModelExecution::build_may_read_from(ModelAction *curr)
2513 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
2515 ASSERT(curr->is_read());
2517 ModelAction *last_sc_write = NULL;
2519 if (curr->is_seqcst())
2520 last_sc_write = get_last_seq_cst_write(curr);
2522 /* Iterate over all threads */
2523 for (i = 0; i < thrd_lists->size(); i++) {
2524 /* Iterate over actions in thread, starting from most recent */
2525 action_list_t *list = &(*thrd_lists)[i];
2526 action_list_t::reverse_iterator rit;
2527 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2528 ModelAction *act = *rit;
2530 /* Only consider 'write' actions */
2531 if (!act->is_write() || act == curr)
2534 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2535 bool allow_read = true;
2537 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2539 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2543 /* Only add feasible reads */
2544 mo_graph->startChanges();
2545 r_modification_order(curr, act);
2546 if (!is_infeasible())
2547 curr->get_node()->add_read_from_past(act);
2548 mo_graph->rollbackChanges();
2551 /* Include at most one act per-thread that "happens before" curr */
2552 if (act->happens_before(curr))
2557 /* Inherit existing, promised future values */
2558 for (i = 0; i < promises.size(); i++) {
2559 const Promise *promise = promises[i];
2560 const ModelAction *promise_read = promise->get_reader(0);
2561 if (promise_read->same_var(curr)) {
2562 /* Only add feasible future-values */
2563 mo_graph->startChanges();
2564 r_modification_order(curr, promise);
2565 if (!is_infeasible())
2566 curr->get_node()->add_read_from_promise(promise_read);
2567 mo_graph->rollbackChanges();
2571 /* We may find no valid may-read-from only if the execution is doomed */
2572 if (!curr->get_node()->read_from_size()) {
2573 priv->no_valid_reads = true;
2577 if (DBG_ENABLED()) {
2578 model_print("Reached read action:\n");
2580 model_print("Printing read_from_past\n");
2581 curr->get_node()->print_read_from_past();
2582 model_print("End printing read_from_past\n");
2586 bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2588 for ( ; write != NULL; write = write->get_reads_from()) {
2589 /* UNINIT actions don't have a Node, and they never sleep */
2590 if (write->is_uninitialized())
2592 Node *prevnode = write->get_node()->get_parent();
2594 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2595 if (write->is_release() && thread_sleep)
2597 if (!write->is_rmw())
2604 * @brief Get an action representing an uninitialized atomic
2606 * This function may create a new one or try to retrieve one from the NodeStack
2608 * @param curr The current action, which prompts the creation of an UNINIT action
2609 * @return A pointer to the UNINIT ModelAction
2611 ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
2613 Node *node = curr->get_node();
2614 ModelAction *act = node->get_uninit_action();
2616 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
2617 node->set_uninit_action(act);
2619 act->create_cv(NULL);
2623 static void print_list(const action_list_t *list)
2625 action_list_t::const_iterator it;
2627 model_print("---------------------------------------------------------------------\n");
2629 unsigned int hash = 0;
2631 for (it = list->begin(); it != list->end(); it++) {
2632 const ModelAction *act = *it;
2633 if (act->get_seq_number() > 0)
2635 hash = hash^(hash<<3)^((*it)->hash());
2637 model_print("HASH %u\n", hash);
2638 model_print("---------------------------------------------------------------------\n");
2641 #if SUPPORT_MOD_ORDER_DUMP
2642 void ModelExecution::dumpGraph(char *filename) const
2645 sprintf(buffer, "%s.dot", filename);
2646 FILE *file = fopen(buffer, "w");
2647 fprintf(file, "digraph %s {\n", filename);
2648 mo_graph->dumpNodes(file);
2649 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2651 for (action_list_t::const_iterator it = action_trace.begin(); it != action_trace.end(); it++) {
2652 ModelAction *act = *it;
2653 if (act->is_read()) {
2654 mo_graph->dot_print_node(file, act);
2655 if (act->get_reads_from())
2656 mo_graph->dot_print_edge(file,
2657 act->get_reads_from(),
2659 "label=\"rf\", color=red, weight=2");
2661 mo_graph->dot_print_edge(file,
2662 act->get_reads_from_promise(),
2664 "label=\"rf\", color=red");
2666 if (thread_array[act->get_tid()]) {
2667 mo_graph->dot_print_edge(file,
2668 thread_array[id_to_int(act->get_tid())],
2670 "label=\"sb\", color=blue, weight=400");
2673 thread_array[act->get_tid()] = act;
2675 fprintf(file, "}\n");
2676 model_free(thread_array);
2681 /** @brief Prints an execution trace summary. */
2682 void ModelExecution::print_summary() const
2684 #if SUPPORT_MOD_ORDER_DUMP
2685 char buffername[100];
2686 sprintf(buffername, "exec%04u", get_execution_number());
2687 mo_graph->dumpGraphToFile(buffername);
2688 sprintf(buffername, "graph%04u", get_execution_number());
2689 dumpGraph(buffername);
2692 model_print("Execution %d:", get_execution_number());
2693 if (isfeasibleprefix()) {
2694 if (is_yieldblocked())
2695 model_print(" YIELD BLOCKED");
2696 if (scheduler->all_threads_sleeping())
2697 model_print(" SLEEP-SET REDUNDANT");
2700 print_infeasibility(" INFEASIBLE");
2701 print_list(&action_trace);
2703 if (!promises.empty()) {
2704 model_print("Pending promises:\n");
2705 for (unsigned int i = 0; i < promises.size(); i++) {
2706 model_print(" [P%u] ", i);
2707 promises[i]->print();
2714 * Add a Thread to the system for the first time. Should only be called once
2716 * @param t The Thread to add
2718 void ModelExecution::add_thread(Thread *t)
2720 unsigned int i = id_to_int(t->get_id());
2721 if (i >= thread_map.size())
2722 thread_map.resize(i + 1);
2724 if (!t->is_model_thread())
2725 scheduler->add_thread(t);
2729 * @brief Get a Thread reference by its ID
2730 * @param tid The Thread's ID
2731 * @return A Thread reference
2733 Thread * ModelExecution::get_thread(thread_id_t tid) const
2735 unsigned int i = id_to_int(tid);
2736 if (i < thread_map.size())
2737 return thread_map[i];
2742 * @brief Get a reference to the Thread in which a ModelAction was executed
2743 * @param act The ModelAction
2744 * @return A Thread reference
2746 Thread * ModelExecution::get_thread(const ModelAction *act) const
2748 return get_thread(act->get_tid());
2752 * @brief Get a Promise's "promise number"
2754 * A "promise number" is an index number that is unique to a promise, valid
2755 * only for a specific snapshot of an execution trace. Promises may come and go
2756 * as they are generated an resolved, so an index only retains meaning for the
2759 * @param promise The Promise to check
2760 * @return The promise index, if the promise still is valid; otherwise -1
2762 int ModelExecution::get_promise_number(const Promise *promise) const
2764 for (unsigned int i = 0; i < promises.size(); i++)
2765 if (promises[i] == promise)
2772 * @brief Check if a Thread is currently enabled
2773 * @param t The Thread to check
2774 * @return True if the Thread is currently enabled
2776 bool ModelExecution::is_enabled(Thread *t) const
2778 return scheduler->is_enabled(t);
2782 * @brief Check if a Thread is currently enabled
2783 * @param tid The ID of the Thread to check
2784 * @return True if the Thread is currently enabled
2786 bool ModelExecution::is_enabled(thread_id_t tid) const
2788 return scheduler->is_enabled(tid);
2792 * @brief Select the next thread to execute based on the curren action
2794 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
2795 * actions should be followed by the execution of their child thread. In either
2796 * case, the current action should determine the next thread schedule.
2798 * @param curr The current action
2799 * @return The next thread to run, if the current action will determine this
2800 * selection; otherwise NULL
2802 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
2804 /* Do not split atomic RMW */
2805 if (curr->is_rmwr())
2806 return get_thread(curr);
2807 /* Follow CREATE with the created thread */
2808 if (curr->get_type() == THREAD_CREATE)
2809 return curr->get_thread_operand();
2813 /** @return True if the execution has taken too many steps */
2814 bool ModelExecution::too_many_steps() const
2816 return params->bound != 0 && priv->used_sequence_numbers > params->bound;
2820 * Takes the next step in the execution, if possible.
2821 * @param curr The current step to take
2822 * @return Returns the next Thread to run, if any; NULL if this execution
2825 Thread * ModelExecution::take_step(ModelAction *curr)
2827 Thread *curr_thrd = get_thread(curr);
2828 ASSERT(curr_thrd->get_state() == THREAD_READY);
2830 ASSERT(check_action_enabled(curr)); /* May have side effects? */
2831 curr = check_current_action(curr);
2834 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2835 scheduler->remove_thread(curr_thrd);
2837 return action_select_next_thread(curr);
2841 * Launch end-of-execution release sequence fixups only when
2842 * the execution is otherwise feasible AND there are:
2844 * (1) pending release sequences
2845 * (2) pending assertions that could be invalidated by a change
2846 * in clock vectors (i.e., data races)
2847 * (3) no pending promises
2849 void ModelExecution::fixup_release_sequences()
2851 while (!pending_rel_seqs.empty() &&
2852 is_feasible_prefix_ignore_relseq() &&
2853 haveUnrealizedRaces()) {
2854 model_print("*** WARNING: release sequence fixup action "
2855 "(%zu pending release seuqence(s)) ***\n",
2856 pending_rel_seqs.size());
2857 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2858 std::memory_order_seq_cst, NULL, VALUE_NONE,