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 * @param work The work queue, for adding fixup work
821 * @return True if the mo_graph was updated or promises were resolved
823 bool ModelExecution::process_write(ModelAction *curr, work_queue_t *work)
825 /* Readers to which we may send our future value */
826 ModelVector<ModelAction *> send_fv;
828 const ModelAction *earliest_promise_reader;
829 bool updated_promises = false;
831 bool updated_mod_order = w_modification_order(curr, &send_fv);
832 Promise *promise = pop_promise_to_resolve(curr);
835 earliest_promise_reader = promise->get_reader(0);
836 updated_promises = resolve_promise(curr, promise, work);
838 earliest_promise_reader = NULL;
840 for (unsigned int i = 0; i < send_fv.size(); i++) {
841 ModelAction *read = send_fv[i];
843 /* Don't send future values to reads after the Promise we resolve */
844 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
845 /* Check if future value can be sent immediately */
846 if (promises_may_allow(curr, read)) {
847 add_future_value(curr, read);
849 futurevalues.push_back(PendingFutureValue(curr, read));
854 /* Check the pending future values */
855 for (int i = (int)futurevalues.size() - 1; i >= 0; i--) {
856 struct PendingFutureValue pfv = futurevalues[i];
857 if (promises_may_allow(pfv.writer, pfv.reader)) {
858 add_future_value(pfv.writer, pfv.reader);
859 futurevalues.erase(futurevalues.begin() + i);
863 mo_graph->commitChanges();
864 mo_check_promises(curr, false);
866 get_thread(curr)->set_return_value(VALUE_NONE);
867 return updated_mod_order || updated_promises;
871 * Process a fence ModelAction
872 * @param curr The ModelAction to process
873 * @return True if synchronization was updated
875 bool ModelExecution::process_fence(ModelAction *curr)
878 * fence-relaxed: no-op
879 * fence-release: only log the occurence (not in this function), for
880 * use in later synchronization
881 * fence-acquire (this function): search for hypothetical release
883 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
885 bool updated = false;
886 if (curr->is_acquire()) {
887 action_list_t *list = &action_trace;
888 action_list_t::reverse_iterator rit;
889 /* Find X : is_read(X) && X --sb-> curr */
890 for (rit = list->rbegin(); rit != list->rend(); rit++) {
891 ModelAction *act = *rit;
894 if (act->get_tid() != curr->get_tid())
896 /* Stop at the beginning of the thread */
897 if (act->is_thread_start())
899 /* Stop once we reach a prior fence-acquire */
900 if (act->is_fence() && act->is_acquire())
904 /* read-acquire will find its own release sequences */
905 if (act->is_acquire())
908 /* Establish hypothetical release sequences */
909 rel_heads_list_t release_heads;
910 get_release_seq_heads(curr, act, &release_heads);
911 for (unsigned int i = 0; i < release_heads.size(); i++)
912 synchronize(release_heads[i], curr);
913 if (release_heads.size() != 0)
921 * @brief Process the current action for thread-related activity
923 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
924 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
925 * synchronization, etc. This function is a no-op for non-THREAD actions
926 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
928 * @param curr The current action
929 * @return True if synchronization was updated or a thread completed
931 bool ModelExecution::process_thread_action(ModelAction *curr)
933 bool updated = false;
935 switch (curr->get_type()) {
936 case THREAD_CREATE: {
937 thrd_t *thrd = (thrd_t *)curr->get_location();
938 struct thread_params *params = (struct thread_params *)curr->get_value();
939 Thread *th = new Thread(get_next_id(), thrd, params->func, params->arg, get_thread(curr));
941 th->set_creation(curr);
942 /* Promises can be satisfied by children */
943 for (unsigned int i = 0; i < promises.size(); i++) {
944 Promise *promise = promises[i];
945 if (promise->thread_is_available(curr->get_tid()))
946 promise->add_thread(th->get_id());
951 Thread *blocking = curr->get_thread_operand();
952 ModelAction *act = get_last_action(blocking->get_id());
953 synchronize(act, curr);
954 updated = true; /* trigger rel-seq checks */
957 case THREAD_FINISH: {
958 Thread *th = get_thread(curr);
959 /* Wake up any joining threads */
960 for (unsigned int i = 0; i < get_num_threads(); i++) {
961 Thread *waiting = get_thread(int_to_id(i));
962 if (waiting->waiting_on() == th &&
963 waiting->get_pending()->is_thread_join())
964 scheduler->wake(waiting);
967 /* Completed thread can't satisfy promises */
968 for (unsigned int i = 0; i < promises.size(); i++) {
969 Promise *promise = promises[i];
970 if (promise->thread_is_available(th->get_id()))
971 if (promise->eliminate_thread(th->get_id()))
972 priv->failed_promise = true;
974 updated = true; /* trigger rel-seq checks */
978 check_promises(curr->get_tid(), NULL, curr->get_cv());
989 * @brief Process the current action for release sequence fixup activity
991 * Performs model-checker release sequence fixups for the current action,
992 * forcing a single pending release sequence to break (with a given, potential
993 * "loose" write) or to complete (i.e., synchronize). If a pending release
994 * sequence forms a complete release sequence, then we must perform the fixup
995 * synchronization, mo_graph additions, etc.
997 * @param curr The current action; must be a release sequence fixup action
998 * @param work_queue The work queue to which to add work items as they are
1001 void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1003 const ModelAction *write = curr->get_node()->get_relseq_break();
1004 struct release_seq *sequence = pending_rel_seqs.back();
1005 pending_rel_seqs.pop_back();
1007 ModelAction *acquire = sequence->acquire;
1008 const ModelAction *rf = sequence->rf;
1009 const ModelAction *release = sequence->release;
1013 ASSERT(release->same_thread(rf));
1015 if (write == NULL) {
1017 * @todo Forcing a synchronization requires that we set
1018 * modification order constraints. For instance, we can't allow
1019 * a fixup sequence in which two separate read-acquire
1020 * operations read from the same sequence, where the first one
1021 * synchronizes and the other doesn't. Essentially, we can't
1022 * allow any writes to insert themselves between 'release' and
1026 /* Must synchronize */
1027 if (!synchronize(release, acquire))
1030 /* Propagate the changed clock vector */
1031 propagate_clockvector(acquire, work_queue);
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 an operation would be successful (i.e., is a lock already
1198 * locked, or is the joined thread already complete).
1200 * For yield-blocking, yields are never enabled.
1202 * @param curr is the ModelAction to check whether it is enabled.
1203 * @return a bool that indicates whether the action is enabled.
1205 bool ModelExecution::check_action_enabled(ModelAction *curr) {
1206 if (curr->is_lock()) {
1207 std::mutex *lock = curr->get_mutex();
1208 struct std::mutex_state *state = lock->get_state();
1211 } else if (curr->is_thread_join()) {
1212 Thread *blocking = curr->get_thread_operand();
1213 if (!blocking->is_complete()) {
1214 thread_blocking_check_promises(blocking, get_thread(curr));
1217 } else if (params->yieldblock && curr->is_yield()) {
1225 * This is the heart of the model checker routine. It performs model-checking
1226 * actions corresponding to a given "current action." Among other processes, it
1227 * calculates reads-from relationships, updates synchronization clock vectors,
1228 * forms a memory_order constraints graph, and handles replay/backtrack
1229 * execution when running permutations of previously-observed executions.
1231 * @param curr The current action to process
1232 * @return The ModelAction that is actually executed; may be different than
1235 ModelAction * ModelExecution::check_current_action(ModelAction *curr)
1238 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1239 bool newly_explored = initialize_curr_action(&curr);
1243 wake_up_sleeping_actions(curr);
1245 /* Compute fairness information for CHESS yield algorithm */
1246 if (params->yieldon) {
1247 curr->get_node()->update_yield(scheduler);
1250 /* Add the action to lists before any other model-checking tasks */
1251 if (!second_part_of_rmw)
1252 add_action_to_lists(curr);
1254 /* Build may_read_from set for newly-created actions */
1255 if (newly_explored && curr->is_read())
1256 build_may_read_from(curr);
1258 /* Initialize work_queue with the "current action" work */
1259 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1260 while (!work_queue.empty() && !has_asserted()) {
1261 WorkQueueEntry work = work_queue.front();
1262 work_queue.pop_front();
1264 switch (work.type) {
1265 case WORK_CHECK_CURR_ACTION: {
1266 ModelAction *act = work.action;
1267 bool update = false; /* update this location's release seq's */
1268 bool update_all = false; /* update all release seq's */
1270 if (process_thread_action(curr))
1273 if (act->is_read() && !second_part_of_rmw && process_read(act))
1276 if (act->is_write() && process_write(act, &work_queue))
1279 if (act->is_fence() && process_fence(act))
1282 if (act->is_mutex_op() && process_mutex(act))
1285 if (act->is_relseq_fixup())
1286 process_relseq_fixup(curr, &work_queue);
1289 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1291 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1294 case WORK_CHECK_RELEASE_SEQ:
1295 resolve_release_sequences(work.location, &work_queue);
1297 case WORK_CHECK_MO_EDGES: {
1298 /** @todo Complete verification of work_queue */
1299 ModelAction *act = work.action;
1300 bool updated = false;
1302 if (act->is_read()) {
1303 const ModelAction *rf = act->get_reads_from();
1304 const Promise *promise = act->get_reads_from_promise();
1306 if (r_modification_order(act, rf))
1308 } else if (promise) {
1309 if (r_modification_order(act, promise))
1313 if (act->is_write()) {
1314 if (w_modification_order(act, NULL))
1317 mo_graph->commitChanges();
1320 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1329 check_curr_backtracking(curr);
1330 set_backtracking(curr);
1334 void ModelExecution::check_curr_backtracking(ModelAction *curr)
1336 Node *currnode = curr->get_node();
1337 Node *parnode = currnode->get_parent();
1339 if ((parnode && !parnode->backtrack_empty()) ||
1340 !currnode->misc_empty() ||
1341 !currnode->read_from_empty() ||
1342 !currnode->promise_empty() ||
1343 !currnode->relseq_break_empty()) {
1344 set_latest_backtrack(curr);
1348 bool ModelExecution::promises_expired() const
1350 for (unsigned int i = 0; i < promises.size(); i++) {
1351 Promise *promise = promises[i];
1352 if (promise->get_expiration() < priv->used_sequence_numbers)
1359 * This is the strongest feasibility check available.
1360 * @return whether the current trace (partial or complete) must be a prefix of
1363 bool ModelExecution::isfeasibleprefix() const
1365 return pending_rel_seqs.size() == 0 && is_feasible_prefix_ignore_relseq();
1369 * Print disagnostic information about an infeasible execution
1370 * @param prefix A string to prefix the output with; if NULL, then a default
1371 * message prefix will be provided
1373 void ModelExecution::print_infeasibility(const char *prefix) const
1377 if (mo_graph->checkForCycles())
1378 ptr += sprintf(ptr, "[mo cycle]");
1379 if (priv->failed_promise)
1380 ptr += sprintf(ptr, "[failed promise]");
1381 if (priv->too_many_reads)
1382 ptr += sprintf(ptr, "[too many reads]");
1383 if (priv->no_valid_reads)
1384 ptr += sprintf(ptr, "[no valid reads-from]");
1385 if (priv->bad_synchronization)
1386 ptr += sprintf(ptr, "[bad sw ordering]");
1387 if (promises_expired())
1388 ptr += sprintf(ptr, "[promise expired]");
1389 if (promises.size() != 0)
1390 ptr += sprintf(ptr, "[unresolved promise]");
1392 model_print("%s: %s", prefix ? prefix : "Infeasible", buf);
1396 * Returns whether the current completed trace is feasible, except for pending
1397 * release sequences.
1399 bool ModelExecution::is_feasible_prefix_ignore_relseq() const
1401 return !is_infeasible() && promises.size() == 0;
1405 * Check if the current partial trace is infeasible. Does not check any
1406 * end-of-execution flags, which might rule out the execution. Thus, this is
1407 * useful only for ruling an execution as infeasible.
1408 * @return whether the current partial trace is infeasible.
1410 bool ModelExecution::is_infeasible() const
1412 return mo_graph->checkForCycles() ||
1413 priv->no_valid_reads ||
1414 priv->failed_promise ||
1415 priv->too_many_reads ||
1416 priv->bad_synchronization ||
1420 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1421 ModelAction * ModelExecution::process_rmw(ModelAction *act) {
1422 ModelAction *lastread = get_last_action(act->get_tid());
1423 lastread->process_rmw(act);
1424 if (act->is_rmw()) {
1425 if (lastread->get_reads_from())
1426 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1428 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1429 mo_graph->commitChanges();
1435 * A helper function for ModelExecution::check_recency, to check if the current
1436 * thread is able to read from a different write/promise for 'params.maxreads'
1437 * number of steps and if that write/promise should become visible (i.e., is
1438 * ordered later in the modification order). This helps model memory liveness.
1440 * @param curr The current action. Must be a read.
1441 * @param rf The write/promise from which we plan to read
1442 * @param other_rf The write/promise from which we may read
1443 * @return True if we were able to read from other_rf for params.maxreads steps
1445 template <typename T, typename U>
1446 bool ModelExecution::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1448 /* Need a different write/promise */
1449 if (other_rf->equals(rf))
1452 /* Only look for "newer" writes/promises */
1453 if (!mo_graph->checkReachable(rf, other_rf))
1456 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1457 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1458 action_list_t::reverse_iterator rit = list->rbegin();
1459 ASSERT((*rit) == curr);
1460 /* Skip past curr */
1463 /* Does this write/promise work for everyone? */
1464 for (int i = 0; i < params->maxreads; i++, rit++) {
1465 ModelAction *act = *rit;
1466 if (!act->may_read_from(other_rf))
1473 * Checks whether a thread has read from the same write or Promise for too many
1474 * times without seeing the effects of a later write/Promise.
1477 * 1) there must a different write/promise that we could read from,
1478 * 2) we must have read from the same write/promise in excess of maxreads times,
1479 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1480 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1482 * If so, we decide that the execution is no longer feasible.
1484 * @param curr The current action. Must be a read.
1485 * @param rf The ModelAction/Promise from which we might read.
1486 * @return True if the read should succeed; false otherwise
1488 template <typename T>
1489 bool ModelExecution::check_recency(ModelAction *curr, const T *rf) const
1491 if (!params->maxreads)
1494 //NOTE: Next check is just optimization, not really necessary....
1495 if (curr->get_node()->get_read_from_past_size() +
1496 curr->get_node()->get_read_from_promise_size() <= 1)
1499 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1500 int tid = id_to_int(curr->get_tid());
1501 ASSERT(tid < (int)thrd_lists->size());
1502 action_list_t *list = &(*thrd_lists)[tid];
1503 action_list_t::reverse_iterator rit = list->rbegin();
1504 ASSERT((*rit) == curr);
1505 /* Skip past curr */
1508 action_list_t::reverse_iterator ritcopy = rit;
1509 /* See if we have enough reads from the same value */
1510 for (int count = 0; count < params->maxreads; ritcopy++, count++) {
1511 if (ritcopy == list->rend())
1513 ModelAction *act = *ritcopy;
1514 if (!act->is_read())
1516 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1518 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1520 if (act->get_node()->get_read_from_past_size() +
1521 act->get_node()->get_read_from_promise_size() <= 1)
1524 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1525 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1526 if (should_read_instead(curr, rf, write))
1527 return false; /* liveness failure */
1529 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1530 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1531 if (should_read_instead(curr, rf, promise))
1532 return false; /* liveness failure */
1538 * @brief Updates the mo_graph with the constraints imposed from the current
1541 * Basic idea is the following: Go through each other thread and find
1542 * the last action that happened before our read. Two cases:
1544 * -# The action is a write: that write must either occur before
1545 * the write we read from or be the write we read from.
1546 * -# The action is a read: the write that that action read from
1547 * must occur before the write we read from or be the same write.
1549 * @param curr The current action. Must be a read.
1550 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1551 * @return True if modification order edges were added; false otherwise
1553 template <typename rf_type>
1554 bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
1556 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1559 ASSERT(curr->is_read());
1561 /* Last SC fence in the current thread */
1562 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1563 ModelAction *last_sc_write = NULL;
1564 if (curr->is_seqcst())
1565 last_sc_write = get_last_seq_cst_write(curr);
1567 /* Iterate over all threads */
1568 for (i = 0; i < thrd_lists->size(); i++) {
1569 /* Last SC fence in thread i */
1570 ModelAction *last_sc_fence_thread_local = NULL;
1571 if (int_to_id((int)i) != curr->get_tid())
1572 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1574 /* Last SC fence in thread i, before last SC fence in current thread */
1575 ModelAction *last_sc_fence_thread_before = NULL;
1576 if (last_sc_fence_local)
1577 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1579 /* Iterate over actions in thread, starting from most recent */
1580 action_list_t *list = &(*thrd_lists)[i];
1581 action_list_t::reverse_iterator rit;
1582 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1583 ModelAction *act = *rit;
1588 /* Don't want to add reflexive edges on 'rf' */
1589 if (act->equals(rf)) {
1590 if (act->happens_before(curr))
1596 if (act->is_write()) {
1597 /* C++, Section 29.3 statement 5 */
1598 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1599 *act < *last_sc_fence_thread_local) {
1600 added = mo_graph->addEdge(act, rf) || added;
1603 /* C++, Section 29.3 statement 4 */
1604 else if (act->is_seqcst() && last_sc_fence_local &&
1605 *act < *last_sc_fence_local) {
1606 added = mo_graph->addEdge(act, rf) || added;
1609 /* C++, Section 29.3 statement 6 */
1610 else if (last_sc_fence_thread_before &&
1611 *act < *last_sc_fence_thread_before) {
1612 added = mo_graph->addEdge(act, rf) || added;
1617 /* C++, Section 29.3 statement 3 (second subpoint) */
1618 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1619 added = mo_graph->addEdge(act, rf) || added;
1624 * Include at most one act per-thread that "happens
1627 if (act->happens_before(curr)) {
1628 if (act->is_write()) {
1629 added = mo_graph->addEdge(act, rf) || added;
1631 const ModelAction *prevrf = act->get_reads_from();
1632 const Promise *prevrf_promise = act->get_reads_from_promise();
1634 if (!prevrf->equals(rf))
1635 added = mo_graph->addEdge(prevrf, rf) || added;
1636 } else if (!prevrf_promise->equals(rf)) {
1637 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1646 * All compatible, thread-exclusive promises must be ordered after any
1647 * concrete loads from the same thread
1649 for (unsigned int i = 0; i < promises.size(); i++)
1650 if (promises[i]->is_compatible_exclusive(curr))
1651 added = mo_graph->addEdge(rf, promises[i]) || added;
1657 * Updates the mo_graph with the constraints imposed from the current write.
1659 * Basic idea is the following: Go through each other thread and find
1660 * the lastest action that happened before our write. Two cases:
1662 * (1) The action is a write => that write must occur before
1665 * (2) The action is a read => the write that that action read from
1666 * must occur before the current write.
1668 * This method also handles two other issues:
1670 * (I) Sequential Consistency: Making sure that if the current write is
1671 * seq_cst, that it occurs after the previous seq_cst write.
1673 * (II) Sending the write back to non-synchronizing reads.
1675 * @param curr The current action. Must be a write.
1676 * @param send_fv A vector for stashing reads to which we may pass our future
1677 * value. If NULL, then don't record any future values.
1678 * @return True if modification order edges were added; false otherwise
1680 bool ModelExecution::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1682 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
1685 ASSERT(curr->is_write());
1687 if (curr->is_seqcst()) {
1688 /* We have to at least see the last sequentially consistent write,
1689 so we are initialized. */
1690 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1691 if (last_seq_cst != NULL) {
1692 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1696 /* Last SC fence in the current thread */
1697 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1699 /* Iterate over all threads */
1700 for (i = 0; i < thrd_lists->size(); i++) {
1701 /* Last SC fence in thread i, before last SC fence in current thread */
1702 ModelAction *last_sc_fence_thread_before = NULL;
1703 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1704 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1706 /* Iterate over actions in thread, starting from most recent */
1707 action_list_t *list = &(*thrd_lists)[i];
1708 action_list_t::reverse_iterator rit;
1709 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1710 ModelAction *act = *rit;
1713 * 1) If RMW and it actually read from something, then we
1714 * already have all relevant edges, so just skip to next
1717 * 2) If RMW and it didn't read from anything, we should
1718 * whatever edge we can get to speed up convergence.
1720 * 3) If normal write, we need to look at earlier actions, so
1721 * continue processing list.
1723 if (curr->is_rmw()) {
1724 if (curr->get_reads_from() != NULL)
1732 /* C++, Section 29.3 statement 7 */
1733 if (last_sc_fence_thread_before && act->is_write() &&
1734 *act < *last_sc_fence_thread_before) {
1735 added = mo_graph->addEdge(act, curr) || added;
1740 * Include at most one act per-thread that "happens
1743 if (act->happens_before(curr)) {
1745 * Note: if act is RMW, just add edge:
1747 * The following edge should be handled elsewhere:
1748 * readfrom(act) --mo--> act
1750 if (act->is_write())
1751 added = mo_graph->addEdge(act, curr) || added;
1752 else if (act->is_read()) {
1753 //if previous read accessed a null, just keep going
1754 if (act->get_reads_from() == NULL)
1756 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1759 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1760 !act->same_thread(curr)) {
1761 /* We have an action that:
1762 (1) did not happen before us
1763 (2) is a read and we are a write
1764 (3) cannot synchronize with us
1765 (4) is in a different thread
1767 that read could potentially read from our write. Note that
1768 these checks are overly conservative at this point, we'll
1769 do more checks before actually removing the
1773 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1774 if (!is_infeasible())
1775 send_fv->push_back(act);
1776 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1777 add_future_value(curr, act);
1784 * All compatible, thread-exclusive promises must be ordered after any
1785 * concrete stores to the same thread, or else they can be merged with
1788 for (unsigned int i = 0; i < promises.size(); i++)
1789 if (promises[i]->is_compatible_exclusive(curr))
1790 added = mo_graph->addEdge(curr, promises[i]) || added;
1795 /** Arbitrary reads from the future are not allowed. Section 29.3
1796 * part 9 places some constraints. This method checks one result of constraint
1797 * constraint. Others require compiler support. */
1798 bool ModelExecution::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
1800 if (!writer->is_rmw())
1803 if (!reader->is_rmw())
1806 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1807 if (search == reader)
1809 if (search->get_tid() == reader->get_tid() &&
1810 search->happens_before(reader))
1818 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1819 * some constraints. This method checks one the following constraint (others
1820 * require compiler support):
1822 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1824 bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1826 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(reader->get_location());
1828 /* Iterate over all threads */
1829 for (i = 0; i < thrd_lists->size(); i++) {
1830 const ModelAction *write_after_read = NULL;
1832 /* Iterate over actions in thread, starting from most recent */
1833 action_list_t *list = &(*thrd_lists)[i];
1834 action_list_t::reverse_iterator rit;
1835 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1836 ModelAction *act = *rit;
1838 /* Don't disallow due to act == reader */
1839 if (!reader->happens_before(act) || reader == act)
1841 else if (act->is_write())
1842 write_after_read = act;
1843 else if (act->is_read() && act->get_reads_from() != NULL)
1844 write_after_read = act->get_reads_from();
1847 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
1854 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1855 * The ModelAction under consideration is expected to be taking part in
1856 * release/acquire synchronization as an object of the "reads from" relation.
1857 * Note that this can only provide release sequence support for RMW chains
1858 * which do not read from the future, as those actions cannot be traced until
1859 * their "promise" is fulfilled. Similarly, we may not even establish the
1860 * presence of a release sequence with certainty, as some modification order
1861 * constraints may be decided further in the future. Thus, this function
1862 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1863 * and a boolean representing certainty.
1865 * @param rf The action that might be part of a release sequence. Must be a
1867 * @param release_heads A pass-by-reference style return parameter. After
1868 * execution of this function, release_heads will contain the heads of all the
1869 * relevant release sequences, if any exists with certainty
1870 * @param pending A pass-by-reference style return parameter which is only used
1871 * when returning false (i.e., uncertain). Returns most information regarding
1872 * an uncertain release sequence, including any write operations that might
1873 * break the sequence.
1874 * @return true, if the ModelExecution is certain that release_heads is complete;
1877 bool ModelExecution::release_seq_heads(const ModelAction *rf,
1878 rel_heads_list_t *release_heads,
1879 struct release_seq *pending) const
1881 /* Only check for release sequences if there are no cycles */
1882 if (mo_graph->checkForCycles())
1885 for ( ; rf != NULL; rf = rf->get_reads_from()) {
1886 ASSERT(rf->is_write());
1888 if (rf->is_release())
1889 release_heads->push_back(rf);
1890 else if (rf->get_last_fence_release())
1891 release_heads->push_back(rf->get_last_fence_release());
1893 break; /* End of RMW chain */
1895 /** @todo Need to be smarter here... In the linux lock
1896 * example, this will run to the beginning of the program for
1898 /** @todo The way to be smarter here is to keep going until 1
1899 * thread has a release preceded by an acquire and you've seen
1902 /* acq_rel RMW is a sufficient stopping condition */
1903 if (rf->is_acquire() && rf->is_release())
1904 return true; /* complete */
1907 /* read from future: need to settle this later */
1909 return false; /* incomplete */
1912 if (rf->is_release())
1913 return true; /* complete */
1915 /* else relaxed write
1916 * - check for fence-release in the same thread (29.8, stmt. 3)
1917 * - check modification order for contiguous subsequence
1918 * -> rf must be same thread as release */
1920 const ModelAction *fence_release = rf->get_last_fence_release();
1921 /* Synchronize with a fence-release unconditionally; we don't need to
1922 * find any more "contiguous subsequence..." for it */
1924 release_heads->push_back(fence_release);
1926 int tid = id_to_int(rf->get_tid());
1927 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(rf->get_location());
1928 action_list_t *list = &(*thrd_lists)[tid];
1929 action_list_t::const_reverse_iterator rit;
1931 /* Find rf in the thread list */
1932 rit = std::find(list->rbegin(), list->rend(), rf);
1933 ASSERT(rit != list->rend());
1935 /* Find the last {write,fence}-release */
1936 for (; rit != list->rend(); rit++) {
1937 if (fence_release && *(*rit) < *fence_release)
1939 if ((*rit)->is_release())
1942 if (rit == list->rend()) {
1943 /* No write-release in this thread */
1944 return true; /* complete */
1945 } else if (fence_release && *(*rit) < *fence_release) {
1946 /* The fence-release is more recent (and so, "stronger") than
1947 * the most recent write-release */
1948 return true; /* complete */
1949 } /* else, need to establish contiguous release sequence */
1950 ModelAction *release = *rit;
1952 ASSERT(rf->same_thread(release));
1954 pending->writes.clear();
1956 bool certain = true;
1957 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1958 if (id_to_int(rf->get_tid()) == (int)i)
1960 list = &(*thrd_lists)[i];
1962 /* Can we ensure no future writes from this thread may break
1963 * the release seq? */
1964 bool future_ordered = false;
1966 ModelAction *last = get_last_action(int_to_id(i));
1967 Thread *th = get_thread(int_to_id(i));
1968 if ((last && rf->happens_before(last)) ||
1971 future_ordered = true;
1973 ASSERT(!th->is_model_thread() || future_ordered);
1975 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1976 const ModelAction *act = *rit;
1977 /* Reach synchronization -> this thread is complete */
1978 if (act->happens_before(release))
1980 if (rf->happens_before(act)) {
1981 future_ordered = true;
1985 /* Only non-RMW writes can break release sequences */
1986 if (!act->is_write() || act->is_rmw())
1989 /* Check modification order */
1990 if (mo_graph->checkReachable(rf, act)) {
1991 /* rf --mo--> act */
1992 future_ordered = true;
1995 if (mo_graph->checkReachable(act, release))
1996 /* act --mo--> release */
1998 if (mo_graph->checkReachable(release, act) &&
1999 mo_graph->checkReachable(act, rf)) {
2000 /* release --mo-> act --mo--> rf */
2001 return true; /* complete */
2003 /* act may break release sequence */
2004 pending->writes.push_back(act);
2007 if (!future_ordered)
2008 certain = false; /* This thread is uncertain */
2012 release_heads->push_back(release);
2013 pending->writes.clear();
2015 pending->release = release;
2022 * An interface for getting the release sequence head(s) with which a
2023 * given ModelAction must synchronize. This function only returns a non-empty
2024 * result when it can locate a release sequence head with certainty. Otherwise,
2025 * it may mark the internal state of the ModelExecution so that it will handle
2026 * the release sequence at a later time, causing @a acquire to update its
2027 * synchronization at some later point in execution.
2029 * @param acquire The 'acquire' action that may synchronize with a release
2031 * @param read The read action that may read from a release sequence; this may
2032 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2033 * when 'acquire' is a fence-acquire)
2034 * @param release_heads A pass-by-reference return parameter. Will be filled
2035 * with the head(s) of the release sequence(s), if they exists with certainty.
2036 * @see ModelExecution::release_seq_heads
2038 void ModelExecution::get_release_seq_heads(ModelAction *acquire,
2039 ModelAction *read, rel_heads_list_t *release_heads)
2041 const ModelAction *rf = read->get_reads_from();
2042 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2043 sequence->acquire = acquire;
2044 sequence->read = read;
2046 if (!release_seq_heads(rf, release_heads, sequence)) {
2047 /* add act to 'lazy checking' list */
2048 pending_rel_seqs.push_back(sequence);
2050 snapshot_free(sequence);
2055 * @brief Propagate a modified clock vector to actions later in the execution
2058 * After an acquire operation lazily completes a release-sequence
2059 * synchronization, we must update all clock vectors for operations later than
2060 * the acquire in the execution order.
2062 * @param acquire The ModelAction whose clock vector must be propagated
2063 * @param work The work queue to which we can add work items, if this
2064 * propagation triggers more updates (e.g., to the modification order)
2066 void ModelExecution::propagate_clockvector(ModelAction *acquire, work_queue_t *work)
2068 /* Re-check all pending release sequences */
2069 work->push_back(CheckRelSeqWorkEntry(NULL));
2070 /* Re-check read-acquire for mo_graph edges */
2071 work->push_back(MOEdgeWorkEntry(acquire));
2073 /* propagate synchronization to later actions */
2074 action_list_t::reverse_iterator rit = action_trace.rbegin();
2075 for (; (*rit) != acquire; rit++) {
2076 ModelAction *propagate = *rit;
2077 if (acquire->happens_before(propagate)) {
2078 synchronize(acquire, propagate);
2079 /* Re-check 'propagate' for mo_graph edges */
2080 work->push_back(MOEdgeWorkEntry(propagate));
2086 * Attempt to resolve all stashed operations that might synchronize with a
2087 * release sequence for a given location. This implements the "lazy" portion of
2088 * determining whether or not a release sequence was contiguous, since not all
2089 * modification order information is present at the time an action occurs.
2091 * @param location The location/object that should be checked for release
2092 * sequence resolutions. A NULL value means to check all locations.
2093 * @param work_queue The work queue to which to add work items as they are
2095 * @return True if any updates occurred (new synchronization, new mo_graph
2098 bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
2100 bool updated = false;
2101 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs.begin();
2102 while (it != pending_rel_seqs.end()) {
2103 struct release_seq *pending = *it;
2104 ModelAction *acquire = pending->acquire;
2105 const ModelAction *read = pending->read;
2107 /* Only resolve sequences on the given location, if provided */
2108 if (location && read->get_location() != location) {
2113 const ModelAction *rf = read->get_reads_from();
2114 rel_heads_list_t release_heads;
2116 complete = release_seq_heads(rf, &release_heads, pending);
2117 for (unsigned int i = 0; i < release_heads.size(); i++)
2118 if (!acquire->has_synchronized_with(release_heads[i]))
2119 if (synchronize(release_heads[i], acquire))
2123 /* Propagate the changed clock vector */
2124 propagate_clockvector(acquire, work_queue);
2127 it = pending_rel_seqs.erase(it);
2128 snapshot_free(pending);
2134 // If we resolved promises or data races, see if we have realized a data race.
2141 * Performs various bookkeeping operations for the current ModelAction. For
2142 * instance, adds action to the per-object, per-thread action vector and to the
2143 * action trace list of all thread actions.
2145 * @param act is the ModelAction to add.
2147 void ModelExecution::add_action_to_lists(ModelAction *act)
2149 int tid = id_to_int(act->get_tid());
2150 ModelAction *uninit = NULL;
2152 action_list_t *list = get_safe_ptr_action(&obj_map, act->get_location());
2153 if (list->empty() && act->is_atomic_var()) {
2154 uninit = get_uninitialized_action(act);
2155 uninit_id = id_to_int(uninit->get_tid());
2156 list->push_front(uninit);
2158 list->push_back(act);
2160 action_trace.push_back(act);
2162 action_trace.push_front(uninit);
2164 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, act->get_location());
2165 if (tid >= (int)vec->size())
2166 vec->resize(priv->next_thread_id);
2167 (*vec)[tid].push_back(act);
2169 (*vec)[uninit_id].push_front(uninit);
2171 if ((int)thrd_last_action.size() <= tid)
2172 thrd_last_action.resize(get_num_threads());
2173 thrd_last_action[tid] = act;
2175 thrd_last_action[uninit_id] = uninit;
2177 if (act->is_fence() && act->is_release()) {
2178 if ((int)thrd_last_fence_release.size() <= tid)
2179 thrd_last_fence_release.resize(get_num_threads());
2180 thrd_last_fence_release[tid] = act;
2183 if (act->is_wait()) {
2184 void *mutex_loc = (void *) act->get_value();
2185 get_safe_ptr_action(&obj_map, mutex_loc)->push_back(act);
2187 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(&obj_thrd_map, mutex_loc);
2188 if (tid >= (int)vec->size())
2189 vec->resize(priv->next_thread_id);
2190 (*vec)[tid].push_back(act);
2195 * @brief Get the last action performed by a particular Thread
2196 * @param tid The thread ID of the Thread in question
2197 * @return The last action in the thread
2199 ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
2201 int threadid = id_to_int(tid);
2202 if (threadid < (int)thrd_last_action.size())
2203 return thrd_last_action[id_to_int(tid)];
2209 * @brief Get the last fence release performed by a particular Thread
2210 * @param tid The thread ID of the Thread in question
2211 * @return The last fence release in the thread, if one exists; NULL otherwise
2213 ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
2215 int threadid = id_to_int(tid);
2216 if (threadid < (int)thrd_last_fence_release.size())
2217 return thrd_last_fence_release[id_to_int(tid)];
2223 * Gets the last memory_order_seq_cst write (in the total global sequence)
2224 * performed on a particular object (i.e., memory location), not including the
2226 * @param curr The current ModelAction; also denotes the object location to
2228 * @return The last seq_cst write
2230 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
2232 void *location = curr->get_location();
2233 action_list_t *list = obj_map.get(location);
2234 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2235 action_list_t::reverse_iterator rit;
2236 for (rit = list->rbegin(); (*rit) != curr; rit++)
2238 rit++; /* Skip past curr */
2239 for ( ; rit != list->rend(); rit++)
2240 if ((*rit)->is_write() && (*rit)->is_seqcst())
2246 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2247 * performed in a particular thread, prior to a particular fence.
2248 * @param tid The ID of the thread to check
2249 * @param before_fence The fence from which to begin the search; if NULL, then
2250 * search for the most recent fence in the thread.
2251 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2253 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2255 /* All fences should have location FENCE_LOCATION */
2256 action_list_t *list = obj_map.get(FENCE_LOCATION);
2261 action_list_t::reverse_iterator rit = list->rbegin();
2264 for (; rit != list->rend(); rit++)
2265 if (*rit == before_fence)
2268 ASSERT(*rit == before_fence);
2272 for (; rit != list->rend(); rit++)
2273 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2279 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2280 * location). This function identifies the mutex according to the current
2281 * action, which is presumed to perform on the same mutex.
2282 * @param curr The current ModelAction; also denotes the object location to
2284 * @return The last unlock operation
2286 ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
2288 void *location = curr->get_location();
2289 action_list_t *list = obj_map.get(location);
2290 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2291 action_list_t::reverse_iterator rit;
2292 for (rit = list->rbegin(); rit != list->rend(); rit++)
2293 if ((*rit)->is_unlock() || (*rit)->is_wait())
2298 ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
2300 ModelAction *parent = get_last_action(tid);
2302 parent = get_thread(tid)->get_creation();
2307 * Returns the clock vector for a given thread.
2308 * @param tid The thread whose clock vector we want
2309 * @return Desired clock vector
2311 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
2313 return get_parent_action(tid)->get_cv();
2317 * @brief Find the promise (if any) to resolve for the current action and
2318 * remove it from the pending promise vector
2319 * @param curr The current ModelAction. Should be a write.
2320 * @return The Promise to resolve, if any; otherwise NULL
2322 Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
2324 for (unsigned int i = 0; i < promises.size(); i++)
2325 if (curr->get_node()->get_promise(i)) {
2326 Promise *ret = promises[i];
2327 promises.erase(promises.begin() + i);
2334 * Resolve a Promise with a current write.
2335 * @param write The ModelAction that is fulfilling Promises
2336 * @param promise The Promise to resolve
2337 * @param work The work queue, for adding new fixup work
2338 * @return True if the Promise was successfully resolved; false otherwise
2340 bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise,
2343 ModelVector<ModelAction *> actions_to_check;
2345 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2346 ModelAction *read = promise->get_reader(i);
2347 if (read_from(read, write)) {
2348 /* Propagate the changed clock vector */
2349 propagate_clockvector(read, work);
2351 actions_to_check.push_back(read);
2353 /* Make sure the promise's value matches the write's value */
2354 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2355 if (!mo_graph->resolvePromise(promise, write))
2356 priv->failed_promise = true;
2359 * @todo It is possible to end up in an inconsistent state, where a
2360 * "resolved" promise may still be referenced if
2361 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2363 * Note that the inconsistency only matters when dumping mo_graph to
2369 //Check whether reading these writes has made threads unable to
2371 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2372 ModelAction *read = actions_to_check[i];
2373 mo_check_promises(read, true);
2380 * Compute the set of promises that could potentially be satisfied by this
2381 * action. Note that the set computation actually appears in the Node, not in
2383 * @param curr The ModelAction that may satisfy promises
2385 void ModelExecution::compute_promises(ModelAction *curr)
2387 for (unsigned int i = 0; i < promises.size(); i++) {
2388 Promise *promise = promises[i];
2389 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2392 bool satisfy = true;
2393 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2394 const ModelAction *act = promise->get_reader(j);
2395 if (act->happens_before(curr) ||
2396 act->could_synchronize_with(curr)) {
2402 curr->get_node()->set_promise(i);
2406 /** Checks promises in response to change in ClockVector Threads. */
2407 void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2409 for (unsigned int i = 0; i < promises.size(); i++) {
2410 Promise *promise = promises[i];
2411 if (!promise->thread_is_available(tid))
2413 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2414 const ModelAction *act = promise->get_reader(j);
2415 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2416 merge_cv->synchronized_since(act)) {
2417 if (promise->eliminate_thread(tid)) {
2418 /* Promise has failed */
2419 priv->failed_promise = true;
2427 void ModelExecution::check_promises_thread_disabled()
2429 for (unsigned int i = 0; i < promises.size(); i++) {
2430 Promise *promise = promises[i];
2431 if (promise->has_failed()) {
2432 priv->failed_promise = true;
2439 * @brief Checks promises in response to addition to modification order for
2442 * We test whether threads are still available for satisfying promises after an
2443 * addition to our modification order constraints. Those that are unavailable
2444 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2445 * that promise has failed.
2447 * @param act The ModelAction which updated the modification order
2448 * @param is_read_check Should be true if act is a read and we must check for
2449 * updates to the store from which it read (there is a distinction here for
2450 * RMW's, which are both a load and a store)
2452 void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
2454 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2456 for (unsigned int i = 0; i < promises.size(); i++) {
2457 Promise *promise = promises[i];
2459 // Is this promise on the same location?
2460 if (!promise->same_location(write))
2463 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2464 const ModelAction *pread = promise->get_reader(j);
2465 if (!pread->happens_before(act))
2467 if (mo_graph->checkPromise(write, promise)) {
2468 priv->failed_promise = true;
2474 // Don't do any lookups twice for the same thread
2475 if (!promise->thread_is_available(act->get_tid()))
2478 if (mo_graph->checkReachable(promise, write)) {
2479 if (mo_graph->checkPromise(write, promise)) {
2480 priv->failed_promise = true;
2488 * Compute the set of writes that may break the current pending release
2489 * sequence. This information is extracted from previou release sequence
2492 * @param curr The current ModelAction. Must be a release sequence fixup
2495 void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
2497 if (pending_rel_seqs.empty())
2500 struct release_seq *pending = pending_rel_seqs.back();
2501 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2502 const ModelAction *write = pending->writes[i];
2503 curr->get_node()->add_relseq_break(write);
2506 /* NULL means don't break the sequence; just synchronize */
2507 curr->get_node()->add_relseq_break(NULL);
2511 * Build up an initial set of all past writes that this 'read' action may read
2512 * from, as well as any previously-observed future values that must still be valid.
2514 * @param curr is the current ModelAction that we are exploring; it must be a
2517 void ModelExecution::build_may_read_from(ModelAction *curr)
2519 SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
2521 ASSERT(curr->is_read());
2523 ModelAction *last_sc_write = NULL;
2525 if (curr->is_seqcst())
2526 last_sc_write = get_last_seq_cst_write(curr);
2528 /* Iterate over all threads */
2529 for (i = 0; i < thrd_lists->size(); i++) {
2530 /* Iterate over actions in thread, starting from most recent */
2531 action_list_t *list = &(*thrd_lists)[i];
2532 action_list_t::reverse_iterator rit;
2533 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2534 ModelAction *act = *rit;
2536 /* Only consider 'write' actions */
2537 if (!act->is_write() || act == curr)
2540 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2541 bool allow_read = true;
2543 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2545 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2549 /* Only add feasible reads */
2550 mo_graph->startChanges();
2551 r_modification_order(curr, act);
2552 if (!is_infeasible())
2553 curr->get_node()->add_read_from_past(act);
2554 mo_graph->rollbackChanges();
2557 /* Include at most one act per-thread that "happens before" curr */
2558 if (act->happens_before(curr))
2563 /* Inherit existing, promised future values */
2564 for (i = 0; i < promises.size(); i++) {
2565 const Promise *promise = promises[i];
2566 const ModelAction *promise_read = promise->get_reader(0);
2567 if (promise_read->same_var(curr)) {
2568 /* Only add feasible future-values */
2569 mo_graph->startChanges();
2570 r_modification_order(curr, promise);
2571 if (!is_infeasible())
2572 curr->get_node()->add_read_from_promise(promise_read);
2573 mo_graph->rollbackChanges();
2577 /* We may find no valid may-read-from only if the execution is doomed */
2578 if (!curr->get_node()->read_from_size()) {
2579 priv->no_valid_reads = true;
2583 if (DBG_ENABLED()) {
2584 model_print("Reached read action:\n");
2586 model_print("Printing read_from_past\n");
2587 curr->get_node()->print_read_from_past();
2588 model_print("End printing read_from_past\n");
2592 bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2594 for ( ; write != NULL; write = write->get_reads_from()) {
2595 /* UNINIT actions don't have a Node, and they never sleep */
2596 if (write->is_uninitialized())
2598 Node *prevnode = write->get_node()->get_parent();
2600 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2601 if (write->is_release() && thread_sleep)
2603 if (!write->is_rmw())
2610 * @brief Get an action representing an uninitialized atomic
2612 * This function may create a new one or try to retrieve one from the NodeStack
2614 * @param curr The current action, which prompts the creation of an UNINIT action
2615 * @return A pointer to the UNINIT ModelAction
2617 ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
2619 Node *node = curr->get_node();
2620 ModelAction *act = node->get_uninit_action();
2622 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
2623 node->set_uninit_action(act);
2625 act->create_cv(NULL);
2629 static void print_list(const action_list_t *list)
2631 action_list_t::const_iterator it;
2633 model_print("------------------------------------------------------------------------------------\n");
2634 model_print("# t Action type MO Location Value Rf CV\n");
2635 model_print("------------------------------------------------------------------------------------\n");
2637 unsigned int hash = 0;
2639 for (it = list->begin(); it != list->end(); it++) {
2640 const ModelAction *act = *it;
2641 if (act->get_seq_number() > 0)
2643 hash = hash^(hash<<3)^((*it)->hash());
2645 model_print("HASH %u\n", hash);
2646 model_print("------------------------------------------------------------------------------------\n");
2649 #if SUPPORT_MOD_ORDER_DUMP
2650 void ModelExecution::dumpGraph(char *filename) const
2653 sprintf(buffer, "%s.dot", filename);
2654 FILE *file = fopen(buffer, "w");
2655 fprintf(file, "digraph %s {\n", filename);
2656 mo_graph->dumpNodes(file);
2657 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2659 for (action_list_t::const_iterator it = action_trace.begin(); it != action_trace.end(); it++) {
2660 ModelAction *act = *it;
2661 if (act->is_read()) {
2662 mo_graph->dot_print_node(file, act);
2663 if (act->get_reads_from())
2664 mo_graph->dot_print_edge(file,
2665 act->get_reads_from(),
2667 "label=\"rf\", color=red, weight=2");
2669 mo_graph->dot_print_edge(file,
2670 act->get_reads_from_promise(),
2672 "label=\"rf\", color=red");
2674 if (thread_array[act->get_tid()]) {
2675 mo_graph->dot_print_edge(file,
2676 thread_array[id_to_int(act->get_tid())],
2678 "label=\"sb\", color=blue, weight=400");
2681 thread_array[act->get_tid()] = act;
2683 fprintf(file, "}\n");
2684 model_free(thread_array);
2689 /** @brief Prints an execution trace summary. */
2690 void ModelExecution::print_summary() const
2692 #if SUPPORT_MOD_ORDER_DUMP
2693 char buffername[100];
2694 sprintf(buffername, "exec%04u", get_execution_number());
2695 mo_graph->dumpGraphToFile(buffername);
2696 sprintf(buffername, "graph%04u", get_execution_number());
2697 dumpGraph(buffername);
2700 model_print("Execution trace %d:", get_execution_number());
2701 if (isfeasibleprefix()) {
2702 if (is_yieldblocked())
2703 model_print(" YIELD BLOCKED");
2704 if (scheduler->all_threads_sleeping())
2705 model_print(" SLEEP-SET REDUNDANT");
2706 if (have_bug_reports())
2707 model_print(" DETECTED BUG(S)");
2709 print_infeasibility(" INFEASIBLE");
2712 print_list(&action_trace);
2715 if (!promises.empty()) {
2716 model_print("Pending promises:\n");
2717 for (unsigned int i = 0; i < promises.size(); i++) {
2718 model_print(" [P%u] ", i);
2719 promises[i]->print();
2726 * Add a Thread to the system for the first time. Should only be called once
2728 * @param t The Thread to add
2730 void ModelExecution::add_thread(Thread *t)
2732 unsigned int i = id_to_int(t->get_id());
2733 if (i >= thread_map.size())
2734 thread_map.resize(i + 1);
2736 if (!t->is_model_thread())
2737 scheduler->add_thread(t);
2741 * @brief Get a Thread reference by its ID
2742 * @param tid The Thread's ID
2743 * @return A Thread reference
2745 Thread * ModelExecution::get_thread(thread_id_t tid) const
2747 unsigned int i = id_to_int(tid);
2748 if (i < thread_map.size())
2749 return thread_map[i];
2754 * @brief Get a reference to the Thread in which a ModelAction was executed
2755 * @param act The ModelAction
2756 * @return A Thread reference
2758 Thread * ModelExecution::get_thread(const ModelAction *act) const
2760 return get_thread(act->get_tid());
2764 * @brief Get a Promise's "promise number"
2766 * A "promise number" is an index number that is unique to a promise, valid
2767 * only for a specific snapshot of an execution trace. Promises may come and go
2768 * as they are generated an resolved, so an index only retains meaning for the
2771 * @param promise The Promise to check
2772 * @return The promise index, if the promise still is valid; otherwise -1
2774 int ModelExecution::get_promise_number(const Promise *promise) const
2776 for (unsigned int i = 0; i < promises.size(); i++)
2777 if (promises[i] == promise)
2784 * @brief Check if a Thread is currently enabled
2785 * @param t The Thread to check
2786 * @return True if the Thread is currently enabled
2788 bool ModelExecution::is_enabled(Thread *t) const
2790 return scheduler->is_enabled(t);
2794 * @brief Check if a Thread is currently enabled
2795 * @param tid The ID of the Thread to check
2796 * @return True if the Thread is currently enabled
2798 bool ModelExecution::is_enabled(thread_id_t tid) const
2800 return scheduler->is_enabled(tid);
2804 * @brief Select the next thread to execute based on the curren action
2806 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
2807 * actions should be followed by the execution of their child thread. In either
2808 * case, the current action should determine the next thread schedule.
2810 * @param curr The current action
2811 * @return The next thread to run, if the current action will determine this
2812 * selection; otherwise NULL
2814 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
2816 /* Do not split atomic RMW */
2817 if (curr->is_rmwr())
2818 return get_thread(curr);
2819 /* Follow CREATE with the created thread */
2820 if (curr->get_type() == THREAD_CREATE)
2821 return curr->get_thread_operand();
2825 /** @return True if the execution has taken too many steps */
2826 bool ModelExecution::too_many_steps() const
2828 return params->bound != 0 && priv->used_sequence_numbers > params->bound;
2832 * Takes the next step in the execution, if possible.
2833 * @param curr The current step to take
2834 * @return Returns the next Thread to run, if any; NULL if this execution
2837 Thread * ModelExecution::take_step(ModelAction *curr)
2839 Thread *curr_thrd = get_thread(curr);
2840 ASSERT(curr_thrd->get_state() == THREAD_READY);
2842 ASSERT(check_action_enabled(curr)); /* May have side effects? */
2843 curr = check_current_action(curr);
2846 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2847 scheduler->remove_thread(curr_thrd);
2849 return action_select_next_thread(curr);
2853 * Launch end-of-execution release sequence fixups only when
2854 * the execution is otherwise feasible AND there are:
2856 * (1) pending release sequences
2857 * (2) pending assertions that could be invalidated by a change
2858 * in clock vectors (i.e., data races)
2859 * (3) no pending promises
2861 void ModelExecution::fixup_release_sequences()
2863 while (!pending_rel_seqs.empty() &&
2864 is_feasible_prefix_ignore_relseq() &&
2865 haveUnrealizedRaces()) {
2866 model_print("*** WARNING: release sequence fixup action "
2867 "(%zu pending release seuqence(s)) ***\n",
2868 pending_rel_seqs.size());
2869 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2870 std::memory_order_seq_cst, NULL, VALUE_NONE,