10 #include "nodestack.h"
13 #include "clockvector.h"
14 #include "cyclegraph.h"
17 #include "threads-model.h"
18 #include "bugmessage.h"
20 #define INITIAL_THREAD_ID 0
23 * Structure for holding small ModelChecker members that should be snapshotted
25 struct model_snapshot_members {
26 model_snapshot_members() :
27 /* First thread created will have id INITIAL_THREAD_ID */
28 next_thread_id(INITIAL_THREAD_ID),
29 used_sequence_numbers(0),
32 failed_promise(false),
33 too_many_reads(false),
34 no_valid_reads(false),
35 bad_synchronization(false),
39 ~model_snapshot_members() {
40 for (unsigned int i = 0; i < bugs.size(); i++)
45 unsigned int next_thread_id;
46 modelclock_t used_sequence_numbers;
47 ModelAction *next_backtrack;
48 SnapVector<bug_message *> bugs;
52 /** @brief Incorrectly-ordered synchronization was made */
53 bool bad_synchronization;
59 /** @brief Constructor */
60 ModelExecution::ModelExecution(ModelChecker *m,
61 struct model_params *params,
63 NodeStack *node_stack) :
67 action_trace(new action_list_t()),
68 thread_map(new HashTable<int, Thread *, int>()),
69 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
70 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
71 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
72 promises(new SnapVector<Promise *>()),
73 futurevalues(new SnapVector<struct PendingFutureValue>()),
74 pending_rel_seqs(new SnapVector<struct release_seq *>()),
75 thrd_last_action(new SnapVector<ModelAction *>(1)),
76 thrd_last_fence_release(new SnapVector<ModelAction *>()),
77 node_stack(node_stack),
78 priv(new struct model_snapshot_members()),
79 mo_graph(new CycleGraph())
81 /* Initialize a model-checker thread, for special ModelActions */
82 model_thread = new Thread(get_next_id());
83 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
84 scheduler->register_engine(this);
87 /** @brief Destructor */
88 ModelExecution::~ModelExecution()
90 for (unsigned int i = 0; i < get_num_threads(); i++)
91 delete thread_map->get(i);
96 delete condvar_waiters_map;
99 for (unsigned int i = 0; i < promises->size(); i++)
100 delete (*promises)[i];
103 delete pending_rel_seqs;
105 delete thrd_last_action;
106 delete thrd_last_fence_release;
111 int ModelExecution::get_execution_number() const
113 return model->get_execution_number();
116 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
118 action_list_t *tmp = hash->get(ptr);
120 tmp = new action_list_t();
126 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
128 SnapVector<action_list_t> *tmp = hash->get(ptr);
130 tmp = new SnapVector<action_list_t>();
136 action_list_t * ModelExecution::get_actions_on_obj(void * obj, thread_id_t tid) const
138 SnapVector<action_list_t> *wrv=obj_thrd_map->get(obj);
141 unsigned int thread=id_to_int(tid);
142 if (thread < wrv->size())
143 return &(*wrv)[thread];
148 /** @return a thread ID for a new Thread */
149 thread_id_t ModelExecution::get_next_id()
151 return priv->next_thread_id++;
154 /** @return the number of user threads created during this execution */
155 unsigned int ModelExecution::get_num_threads() const
157 return priv->next_thread_id;
160 /** @return a sequence number for a new ModelAction */
161 modelclock_t ModelExecution::get_next_seq_num()
163 return ++priv->used_sequence_numbers;
167 * @brief Should the current action wake up a given thread?
169 * @param curr The current action
170 * @param thread The thread that we might wake up
171 * @return True, if we should wake up the sleeping thread; false otherwise
173 bool ModelExecution::should_wake_up(const ModelAction *curr, const Thread *thread) const
175 const ModelAction *asleep = thread->get_pending();
176 /* Don't allow partial RMW to wake anyone up */
179 /* Synchronizing actions may have been backtracked */
180 if (asleep->could_synchronize_with(curr))
182 /* All acquire/release fences and fence-acquire/store-release */
183 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
185 /* Fence-release + store can awake load-acquire on the same location */
186 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
187 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
188 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
194 void ModelExecution::wake_up_sleeping_actions(ModelAction *curr)
196 for (unsigned int i = 0; i < get_num_threads(); i++) {
197 Thread *thr = get_thread(int_to_id(i));
198 if (scheduler->is_sleep_set(thr)) {
199 if (should_wake_up(curr, thr))
200 /* Remove this thread from sleep set */
201 scheduler->remove_sleep(thr);
206 /** @brief Alert the model-checker that an incorrectly-ordered
207 * synchronization was made */
208 void ModelExecution::set_bad_synchronization()
210 priv->bad_synchronization = true;
213 bool ModelExecution::assert_bug(const char *msg)
215 priv->bugs.push_back(new bug_message(msg));
217 if (isfeasibleprefix()) {
224 /** @return True, if any bugs have been reported for this execution */
225 bool ModelExecution::have_bug_reports() const
227 return priv->bugs.size() != 0;
230 SnapVector<bug_message *> * ModelExecution::get_bugs() const
236 * Check whether the current trace has triggered an assertion which should halt
239 * @return True, if the execution should be aborted; false otherwise
241 bool ModelExecution::has_asserted() const
243 return priv->asserted;
247 * Trigger a trace assertion which should cause this execution to be halted.
248 * This can be due to a detected bug or due to an infeasibility that should
251 void ModelExecution::set_assert()
253 priv->asserted = true;
257 * Check if we are in a deadlock. Should only be called at the end of an
258 * execution, although it should not give false positives in the middle of an
259 * execution (there should be some ENABLED thread).
261 * @return True if program is in a deadlock; false otherwise
263 bool ModelExecution::is_deadlocked() const
265 bool blocking_threads = false;
266 for (unsigned int i = 0; i < get_num_threads(); i++) {
267 thread_id_t tid = int_to_id(i);
270 Thread *t = get_thread(tid);
271 if (!t->is_model_thread() && t->get_pending())
272 blocking_threads = true;
274 return blocking_threads;
278 * Check if this is a complete execution. That is, have all thread completed
279 * execution (rather than exiting because sleep sets have forced a redundant
282 * @return True if the execution is complete.
284 bool ModelExecution::is_complete_execution() const
286 for (unsigned int i = 0; i < get_num_threads(); i++)
287 if (is_enabled(int_to_id(i)))
293 * @brief Find the last fence-related backtracking conflict for a ModelAction
295 * This function performs the search for the most recent conflicting action
296 * against which we should perform backtracking, as affected by fence
297 * operations. This includes pairs of potentially-synchronizing actions which
298 * occur due to fence-acquire or fence-release, and hence should be explored in
299 * the opposite execution order.
301 * @param act The current action
302 * @return The most recent action which conflicts with act due to fences
304 ModelAction * ModelExecution::get_last_fence_conflict(ModelAction *act) const
306 /* Only perform release/acquire fence backtracking for stores */
307 if (!act->is_write())
310 /* Find a fence-release (or, act is a release) */
311 ModelAction *last_release;
312 if (act->is_release())
315 last_release = get_last_fence_release(act->get_tid());
319 /* Skip past the release */
320 action_list_t *list = action_trace;
321 action_list_t::reverse_iterator rit;
322 for (rit = list->rbegin(); rit != list->rend(); rit++)
323 if (*rit == last_release)
325 ASSERT(rit != list->rend());
330 * load --sb-> fence-acquire */
331 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
332 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
333 bool found_acquire_fences = false;
334 for ( ; rit != list->rend(); rit++) {
335 ModelAction *prev = *rit;
336 if (act->same_thread(prev))
339 int tid = id_to_int(prev->get_tid());
341 if (prev->is_read() && act->same_var(prev)) {
342 if (prev->is_acquire()) {
343 /* Found most recent load-acquire, don't need
344 * to search for more fences */
345 if (!found_acquire_fences)
348 prior_loads[tid] = prev;
351 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
352 found_acquire_fences = true;
353 acquire_fences[tid] = prev;
357 ModelAction *latest_backtrack = NULL;
358 for (unsigned int i = 0; i < acquire_fences.size(); i++)
359 if (acquire_fences[i] && prior_loads[i])
360 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
361 latest_backtrack = acquire_fences[i];
362 return latest_backtrack;
366 * @brief Find the last backtracking conflict for a ModelAction
368 * This function performs the search for the most recent conflicting action
369 * against which we should perform backtracking. This primary includes pairs of
370 * synchronizing actions which should be explored in the opposite execution
373 * @param act The current action
374 * @return The most recent action which conflicts with act
376 ModelAction * ModelExecution::get_last_conflict(ModelAction *act) const
378 switch (act->get_type()) {
379 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
383 ModelAction *ret = NULL;
385 /* linear search: from most recent to oldest */
386 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
387 action_list_t::reverse_iterator rit;
388 for (rit = list->rbegin(); rit != list->rend(); rit++) {
389 ModelAction *prev = *rit;
390 if (prev->could_synchronize_with(act)) {
396 ModelAction *ret2 = get_last_fence_conflict(act);
406 case ATOMIC_TRYLOCK: {
407 /* linear search: from most recent to oldest */
408 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
409 action_list_t::reverse_iterator rit;
410 for (rit = list->rbegin(); rit != list->rend(); rit++) {
411 ModelAction *prev = *rit;
412 if (act->is_conflicting_lock(prev))
417 case ATOMIC_UNLOCK: {
418 /* linear search: from most recent to oldest */
419 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
420 action_list_t::reverse_iterator rit;
421 for (rit = list->rbegin(); rit != list->rend(); rit++) {
422 ModelAction *prev = *rit;
423 if (!act->same_thread(prev) && prev->is_failed_trylock())
429 /* linear search: from most recent to oldest */
430 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
431 action_list_t::reverse_iterator rit;
432 for (rit = list->rbegin(); rit != list->rend(); rit++) {
433 ModelAction *prev = *rit;
434 if (!act->same_thread(prev) && prev->is_failed_trylock())
436 if (!act->same_thread(prev) && prev->is_notify())
442 case ATOMIC_NOTIFY_ALL:
443 case ATOMIC_NOTIFY_ONE: {
444 /* linear search: from most recent to oldest */
445 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
446 action_list_t::reverse_iterator rit;
447 for (rit = list->rbegin(); rit != list->rend(); rit++) {
448 ModelAction *prev = *rit;
449 if (!act->same_thread(prev) && prev->is_wait())
460 /** This method finds backtracking points where we should try to
461 * reorder the parameter ModelAction against.
463 * @param the ModelAction to find backtracking points for.
465 void ModelExecution::set_backtracking(ModelAction *act)
467 Thread *t = get_thread(act);
468 ModelAction *prev = get_last_conflict(act);
472 Node *node = prev->get_node()->get_parent();
474 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
475 int low_tid, high_tid;
476 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
477 low_tid = id_to_int(act->get_tid());
478 high_tid = low_tid + 1;
481 high_tid = get_num_threads();
484 for (int i = low_tid; i < high_tid; i++) {
485 thread_id_t tid = int_to_id(i);
487 /* Make sure this thread can be enabled here. */
488 if (i >= node->get_num_threads())
491 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
492 /* Don't backtrack into a point where the thread is disabled or sleeping. */
493 if (node->enabled_status(tid) != THREAD_ENABLED)
496 /* Check if this has been explored already */
497 if (node->has_been_explored(tid))
500 /* See if fairness allows */
501 if (params->fairwindow != 0 && !node->has_priority(tid)) {
503 for (int t = 0; t < node->get_num_threads(); t++) {
504 thread_id_t tother = int_to_id(t);
505 if (node->is_enabled(tother) && node->has_priority(tother)) {
514 /* See if CHESS-like yield fairness allows */
515 if (params->yieldon) {
517 for (int t = 0; t < node->get_num_threads(); t++) {
518 thread_id_t tother = int_to_id(t);
519 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
528 /* Cache the latest backtracking point */
529 set_latest_backtrack(prev);
531 /* If this is a new backtracking point, mark the tree */
532 if (!node->set_backtrack(tid))
534 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
535 id_to_int(prev->get_tid()),
536 id_to_int(t->get_id()));
545 * @brief Cache the a backtracking point as the "most recent", if eligible
547 * Note that this does not prepare the NodeStack for this backtracking
548 * operation, it only caches the action on a per-execution basis
550 * @param act The operation at which we should explore a different next action
551 * (i.e., backtracking point)
552 * @return True, if this action is now the most recent backtracking point;
555 bool ModelExecution::set_latest_backtrack(ModelAction *act)
557 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
558 priv->next_backtrack = act;
565 * Returns last backtracking point. The model checker will explore a different
566 * path for this point in the next execution.
567 * @return The ModelAction at which the next execution should diverge.
569 ModelAction * ModelExecution::get_next_backtrack()
571 ModelAction *next = priv->next_backtrack;
572 priv->next_backtrack = NULL;
577 * Processes a read model action.
578 * @param curr is the read model action to process.
579 * @return True if processing this read updates the mo_graph.
581 bool ModelExecution::process_read(ModelAction *curr)
583 Node *node = curr->get_node();
585 bool updated = false;
586 switch (node->get_read_from_status()) {
587 case READ_FROM_PAST: {
588 const ModelAction *rf = node->get_read_from_past();
591 mo_graph->startChanges();
593 ASSERT(!is_infeasible());
594 if (!check_recency(curr, rf)) {
595 if (node->increment_read_from()) {
596 mo_graph->rollbackChanges();
599 priv->too_many_reads = true;
603 updated = r_modification_order(curr, rf);
605 mo_graph->commitChanges();
606 mo_check_promises(curr, true);
609 case READ_FROM_PROMISE: {
610 Promise *promise = curr->get_node()->get_read_from_promise();
611 if (promise->add_reader(curr))
612 priv->failed_promise = true;
613 curr->set_read_from_promise(promise);
614 mo_graph->startChanges();
615 if (!check_recency(curr, promise))
616 priv->too_many_reads = true;
617 updated = r_modification_order(curr, promise);
618 mo_graph->commitChanges();
621 case READ_FROM_FUTURE: {
622 /* Read from future value */
623 struct future_value fv = node->get_future_value();
624 Promise *promise = new Promise(this, curr, fv);
625 curr->set_read_from_promise(promise);
626 promises->push_back(promise);
627 mo_graph->startChanges();
628 updated = r_modification_order(curr, promise);
629 mo_graph->commitChanges();
635 get_thread(curr)->set_return_value(curr->get_return_value());
641 * Processes a lock, trylock, or unlock model action. @param curr is
642 * the read model action to process.
644 * The try lock operation checks whether the lock is taken. If not,
645 * it falls to the normal lock operation case. If so, it returns
648 * The lock operation has already been checked that it is enabled, so
649 * it just grabs the lock and synchronizes with the previous unlock.
651 * The unlock operation has to re-enable all of the threads that are
652 * waiting on the lock.
654 * @return True if synchronization was updated; false otherwise
656 bool ModelExecution::process_mutex(ModelAction *curr)
658 std::mutex *mutex = curr->get_mutex();
659 struct std::mutex_state *state = NULL;
662 state = mutex->get_state();
664 switch (curr->get_type()) {
665 case ATOMIC_TRYLOCK: {
666 bool success = !state->locked;
667 curr->set_try_lock(success);
669 get_thread(curr)->set_return_value(0);
672 get_thread(curr)->set_return_value(1);
674 //otherwise fall into the lock case
676 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
677 assert_bug("Lock access before initialization");
678 state->locked = get_thread(curr);
679 ModelAction *unlock = get_last_unlock(curr);
680 //synchronize with the previous unlock statement
681 if (unlock != NULL) {
682 synchronize(unlock, curr);
688 case ATOMIC_UNLOCK: {
689 /* wake up the other threads */
690 for (unsigned int i = 0; i < get_num_threads(); i++) {
691 Thread *t = get_thread(int_to_id(i));
692 Thread *curr_thrd = get_thread(curr);
693 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
697 /* unlock the lock - after checking who was waiting on it */
698 state->locked = NULL;
700 if (!curr->is_wait())
701 break; /* The rest is only for ATOMIC_WAIT */
703 /* Should we go to sleep? (simulate spurious failures) */
704 if (curr->get_node()->get_misc() == 0) {
705 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
707 scheduler->sleep(get_thread(curr));
711 case ATOMIC_NOTIFY_ALL: {
712 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
713 //activate all the waiting threads
714 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
715 scheduler->wake(get_thread(*rit));
720 case ATOMIC_NOTIFY_ONE: {
721 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
722 int wakeupthread = curr->get_node()->get_misc();
723 action_list_t::iterator it = waiters->begin();
724 advance(it, wakeupthread);
725 scheduler->wake(get_thread(*it));
737 * @brief Check if the current pending promises allow a future value to be sent
739 * If one of the following is true:
740 * (a) there are no pending promises
741 * (b) the reader and writer do not cross any promises
742 * Then, it is safe to pass a future value back now.
744 * Otherwise, we must save the pending future value until (a) or (b) is true
746 * @param writer The operation which sends the future value. Must be a write.
747 * @param reader The operation which will observe the value. Must be a read.
748 * @return True if the future value can be sent now; false if it must wait.
750 bool ModelExecution::promises_may_allow(const ModelAction *writer,
751 const ModelAction *reader) const
753 if (promises->empty())
755 for(int i=promises->size()-1;i>=0;i--) {
756 ModelAction *pr=(*promises)[i]->get_reader(0);
757 //reader is after promise...doesn't cross any promise
760 //writer is after promise, reader before...bad...
768 * @brief Add a future value to a reader
770 * This function performs a few additional checks to ensure that the future
771 * value can be feasibly observed by the reader
773 * @param writer The operation whose value is sent. Must be a write.
774 * @param reader The read operation which may read the future value. Must be a read.
776 void ModelExecution::add_future_value(const ModelAction *writer, ModelAction *reader)
778 /* Do more ambitious checks now that mo is more complete */
779 if (!mo_may_allow(writer, reader))
782 Node *node = reader->get_node();
784 /* Find an ancestor thread which exists at the time of the reader */
785 Thread *write_thread = get_thread(writer);
786 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
787 write_thread = write_thread->get_parent();
789 struct future_value fv = {
790 writer->get_write_value(),
791 writer->get_seq_number() + params->maxfuturedelay,
792 write_thread->get_id(),
794 if (node->add_future_value(fv))
795 set_latest_backtrack(reader);
799 * Process a write ModelAction
800 * @param curr The ModelAction to process
801 * @return True if the mo_graph was updated or promises were resolved
803 bool ModelExecution::process_write(ModelAction *curr)
805 /* Readers to which we may send our future value */
806 ModelVector<ModelAction *> send_fv;
808 const ModelAction *earliest_promise_reader;
809 bool updated_promises = false;
811 bool updated_mod_order = w_modification_order(curr, &send_fv);
812 Promise *promise = pop_promise_to_resolve(curr);
815 earliest_promise_reader = promise->get_reader(0);
816 updated_promises = resolve_promise(curr, promise);
818 earliest_promise_reader = NULL;
820 for (unsigned int i = 0; i < send_fv.size(); i++) {
821 ModelAction *read = send_fv[i];
823 /* Don't send future values to reads after the Promise we resolve */
824 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
825 /* Check if future value can be sent immediately */
826 if (promises_may_allow(curr, read)) {
827 add_future_value(curr, read);
829 futurevalues->push_back(PendingFutureValue(curr, read));
834 /* Check the pending future values */
835 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
836 struct PendingFutureValue pfv = (*futurevalues)[i];
837 if (promises_may_allow(pfv.writer, pfv.reader)) {
838 add_future_value(pfv.writer, pfv.reader);
839 futurevalues->erase(futurevalues->begin() + i);
843 mo_graph->commitChanges();
844 mo_check_promises(curr, false);
846 get_thread(curr)->set_return_value(VALUE_NONE);
847 return updated_mod_order || updated_promises;
851 * Process a fence ModelAction
852 * @param curr The ModelAction to process
853 * @return True if synchronization was updated
855 bool ModelExecution::process_fence(ModelAction *curr)
858 * fence-relaxed: no-op
859 * fence-release: only log the occurence (not in this function), for
860 * use in later synchronization
861 * fence-acquire (this function): search for hypothetical release
863 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
865 bool updated = false;
866 if (curr->is_acquire()) {
867 action_list_t *list = action_trace;
868 action_list_t::reverse_iterator rit;
869 /* Find X : is_read(X) && X --sb-> curr */
870 for (rit = list->rbegin(); rit != list->rend(); rit++) {
871 ModelAction *act = *rit;
874 if (act->get_tid() != curr->get_tid())
876 /* Stop at the beginning of the thread */
877 if (act->is_thread_start())
879 /* Stop once we reach a prior fence-acquire */
880 if (act->is_fence() && act->is_acquire())
884 /* read-acquire will find its own release sequences */
885 if (act->is_acquire())
888 /* Establish hypothetical release sequences */
889 rel_heads_list_t release_heads;
890 get_release_seq_heads(curr, act, &release_heads);
891 for (unsigned int i = 0; i < release_heads.size(); i++)
892 synchronize(release_heads[i], curr);
893 if (release_heads.size() != 0)
901 * @brief Process the current action for thread-related activity
903 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
904 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
905 * synchronization, etc. This function is a no-op for non-THREAD actions
906 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
908 * @param curr The current action
909 * @return True if synchronization was updated or a thread completed
911 bool ModelExecution::process_thread_action(ModelAction *curr)
913 bool updated = false;
915 switch (curr->get_type()) {
916 case THREAD_CREATE: {
917 thrd_t *thrd = (thrd_t *)curr->get_location();
918 struct thread_params *params = (struct thread_params *)curr->get_value();
919 Thread *th = new Thread(get_next_id(), thrd, params->func, params->arg, get_thread(curr));
921 th->set_creation(curr);
922 /* Promises can be satisfied by children */
923 for (unsigned int i = 0; i < promises->size(); i++) {
924 Promise *promise = (*promises)[i];
925 if (promise->thread_is_available(curr->get_tid()))
926 promise->add_thread(th->get_id());
931 Thread *blocking = curr->get_thread_operand();
932 ModelAction *act = get_last_action(blocking->get_id());
933 synchronize(act, curr);
934 updated = true; /* trigger rel-seq checks */
937 case THREAD_FINISH: {
938 Thread *th = get_thread(curr);
939 /* Wake up any joining threads */
940 for (unsigned int i = 0; i < get_num_threads(); i++) {
941 Thread *waiting = get_thread(int_to_id(i));
942 if (waiting->waiting_on() == th &&
943 waiting->get_pending()->is_thread_join())
944 scheduler->wake(waiting);
947 /* Completed thread can't satisfy promises */
948 for (unsigned int i = 0; i < promises->size(); i++) {
949 Promise *promise = (*promises)[i];
950 if (promise->thread_is_available(th->get_id()))
951 if (promise->eliminate_thread(th->get_id()))
952 priv->failed_promise = true;
954 updated = true; /* trigger rel-seq checks */
958 check_promises(curr->get_tid(), NULL, curr->get_cv());
969 * @brief Process the current action for release sequence fixup activity
971 * Performs model-checker release sequence fixups for the current action,
972 * forcing a single pending release sequence to break (with a given, potential
973 * "loose" write) or to complete (i.e., synchronize). If a pending release
974 * sequence forms a complete release sequence, then we must perform the fixup
975 * synchronization, mo_graph additions, etc.
977 * @param curr The current action; must be a release sequence fixup action
978 * @param work_queue The work queue to which to add work items as they are
981 void ModelExecution::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
983 const ModelAction *write = curr->get_node()->get_relseq_break();
984 struct release_seq *sequence = pending_rel_seqs->back();
985 pending_rel_seqs->pop_back();
987 ModelAction *acquire = sequence->acquire;
988 const ModelAction *rf = sequence->rf;
989 const ModelAction *release = sequence->release;
993 ASSERT(release->same_thread(rf));
997 * @todo Forcing a synchronization requires that we set
998 * modification order constraints. For instance, we can't allow
999 * a fixup sequence in which two separate read-acquire
1000 * operations read from the same sequence, where the first one
1001 * synchronizes and the other doesn't. Essentially, we can't
1002 * allow any writes to insert themselves between 'release' and
1006 /* Must synchronize */
1007 if (!synchronize(release, acquire))
1009 /* Re-check all pending release sequences */
1010 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1011 /* Re-check act for mo_graph edges */
1012 work_queue->push_back(MOEdgeWorkEntry(acquire));
1014 /* propagate synchronization to later actions */
1015 action_list_t::reverse_iterator rit = action_trace->rbegin();
1016 for (; (*rit) != acquire; rit++) {
1017 ModelAction *propagate = *rit;
1018 if (acquire->happens_before(propagate)) {
1019 synchronize(acquire, propagate);
1020 /* Re-check 'propagate' for mo_graph edges */
1021 work_queue->push_back(MOEdgeWorkEntry(propagate));
1025 /* Break release sequence with new edges:
1026 * release --mo--> write --mo--> rf */
1027 mo_graph->addEdge(release, write);
1028 mo_graph->addEdge(write, rf);
1031 /* See if we have realized a data race */
1036 * Initialize the current action by performing one or more of the following
1037 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1038 * in the NodeStack, manipulating backtracking sets, allocating and
1039 * initializing clock vectors, and computing the promises to fulfill.
1041 * @param curr The current action, as passed from the user context; may be
1042 * freed/invalidated after the execution of this function, with a different
1043 * action "returned" its place (pass-by-reference)
1044 * @return True if curr is a newly-explored action; false otherwise
1046 bool ModelExecution::initialize_curr_action(ModelAction **curr)
1048 ModelAction *newcurr;
1050 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1051 newcurr = process_rmw(*curr);
1054 if (newcurr->is_rmw())
1055 compute_promises(newcurr);
1061 (*curr)->set_seq_number(get_next_seq_num());
1063 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1065 /* First restore type and order in case of RMW operation */
1066 if ((*curr)->is_rmwr())
1067 newcurr->copy_typeandorder(*curr);
1069 ASSERT((*curr)->get_location() == newcurr->get_location());
1070 newcurr->copy_from_new(*curr);
1072 /* Discard duplicate ModelAction; use action from NodeStack */
1075 /* Always compute new clock vector */
1076 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1079 return false; /* Action was explored previously */
1083 /* Always compute new clock vector */
1084 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1086 /* Assign most recent release fence */
1087 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1090 * Perform one-time actions when pushing new ModelAction onto
1093 if (newcurr->is_write())
1094 compute_promises(newcurr);
1095 else if (newcurr->is_relseq_fixup())
1096 compute_relseq_breakwrites(newcurr);
1097 else if (newcurr->is_wait())
1098 newcurr->get_node()->set_misc_max(2);
1099 else if (newcurr->is_notify_one()) {
1100 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1102 return true; /* This was a new ModelAction */
1107 * @brief Establish reads-from relation between two actions
1109 * Perform basic operations involved with establishing a concrete rf relation,
1110 * including setting the ModelAction data and checking for release sequences.
1112 * @param act The action that is reading (must be a read)
1113 * @param rf The action from which we are reading (must be a write)
1115 * @return True if this read established synchronization
1117 bool ModelExecution::read_from(ModelAction *act, const ModelAction *rf)
1120 ASSERT(rf->is_write());
1122 act->set_read_from(rf);
1123 if (act->is_acquire()) {
1124 rel_heads_list_t release_heads;
1125 get_release_seq_heads(act, act, &release_heads);
1126 int num_heads = release_heads.size();
1127 for (unsigned int i = 0; i < release_heads.size(); i++)
1128 if (!synchronize(release_heads[i], act))
1130 return num_heads > 0;
1136 * @brief Synchronizes two actions
1138 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1139 * This function performs the synchronization as well as providing other hooks
1140 * for other checks along with synchronization.
1142 * @param first The left-hand side of the synchronizes-with relation
1143 * @param second The right-hand side of the synchronizes-with relation
1144 * @return True if the synchronization was successful (i.e., was consistent
1145 * with the execution order); false otherwise
1147 bool ModelExecution::synchronize(const ModelAction *first, ModelAction *second)
1149 if (*second < *first) {
1150 set_bad_synchronization();
1153 check_promises(first->get_tid(), second->get_cv(), first->get_cv());
1154 return second->synchronize_with(first);
1158 * Check promises and eliminate potentially-satisfying threads when a thread is
1159 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1160 * no longer satisfy a promise generated from that thread.
1162 * @param blocker The thread on which a thread is waiting
1163 * @param waiting The waiting thread
1165 void ModelExecution::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1167 for (unsigned int i = 0; i < promises->size(); i++) {
1168 Promise *promise = (*promises)[i];
1169 if (!promise->thread_is_available(waiting->get_id()))
1171 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1172 ModelAction *reader = promise->get_reader(j);
1173 if (reader->get_tid() != blocker->get_id())
1175 if (promise->eliminate_thread(waiting->get_id())) {
1176 /* Promise has failed */
1177 priv->failed_promise = true;
1179 /* Only eliminate the 'waiting' thread once */
1187 * @brief Check whether a model action is enabled.
1189 * Checks whether a lock or join operation would be successful (i.e., is the
1190 * lock already locked, or is the joined thread already complete). If not, put
1191 * the action in a waiter list.
1193 * @param curr is the ModelAction to check whether it is enabled.
1194 * @return a bool that indicates whether the action is enabled.
1196 bool ModelExecution::check_action_enabled(ModelAction *curr) {
1197 if (curr->is_lock()) {
1198 std::mutex *lock = curr->get_mutex();
1199 struct std::mutex_state *state = lock->get_state();
1202 } else if (curr->is_thread_join()) {
1203 Thread *blocking = curr->get_thread_operand();
1204 if (!blocking->is_complete()) {
1205 thread_blocking_check_promises(blocking, get_thread(curr));
1214 * This is the heart of the model checker routine. It performs model-checking
1215 * actions corresponding to a given "current action." Among other processes, it
1216 * calculates reads-from relationships, updates synchronization clock vectors,
1217 * forms a memory_order constraints graph, and handles replay/backtrack
1218 * execution when running permutations of previously-observed executions.
1220 * @param curr The current action to process
1221 * @return The ModelAction that is actually executed; may be different than
1222 * curr; may be NULL, if the current action is not enabled to run
1224 ModelAction * ModelExecution::check_current_action(ModelAction *curr)
1227 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1228 bool newly_explored = initialize_curr_action(&curr);
1232 wake_up_sleeping_actions(curr);
1234 /* Compute fairness information for CHESS yield algorithm */
1235 if (params->yieldon) {
1236 curr->get_node()->update_yield(scheduler);
1239 /* Add the action to lists before any other model-checking tasks */
1240 if (!second_part_of_rmw)
1241 add_action_to_lists(curr);
1243 /* Build may_read_from set for newly-created actions */
1244 if (newly_explored && curr->is_read())
1245 build_may_read_from(curr);
1247 /* Initialize work_queue with the "current action" work */
1248 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1249 while (!work_queue.empty() && !has_asserted()) {
1250 WorkQueueEntry work = work_queue.front();
1251 work_queue.pop_front();
1253 switch (work.type) {
1254 case WORK_CHECK_CURR_ACTION: {
1255 ModelAction *act = work.action;
1256 bool update = false; /* update this location's release seq's */
1257 bool update_all = false; /* update all release seq's */
1259 if (process_thread_action(curr))
1262 if (act->is_read() && !second_part_of_rmw && process_read(act))
1265 if (act->is_write() && process_write(act))
1268 if (act->is_fence() && process_fence(act))
1271 if (act->is_mutex_op() && process_mutex(act))
1274 if (act->is_relseq_fixup())
1275 process_relseq_fixup(curr, &work_queue);
1278 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1280 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1283 case WORK_CHECK_RELEASE_SEQ:
1284 resolve_release_sequences(work.location, &work_queue);
1286 case WORK_CHECK_MO_EDGES: {
1287 /** @todo Complete verification of work_queue */
1288 ModelAction *act = work.action;
1289 bool updated = false;
1291 if (act->is_read()) {
1292 const ModelAction *rf = act->get_reads_from();
1293 const Promise *promise = act->get_reads_from_promise();
1295 if (r_modification_order(act, rf))
1297 } else if (promise) {
1298 if (r_modification_order(act, promise))
1302 if (act->is_write()) {
1303 if (w_modification_order(act, NULL))
1306 mo_graph->commitChanges();
1309 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1318 check_curr_backtracking(curr);
1319 set_backtracking(curr);
1323 void ModelExecution::check_curr_backtracking(ModelAction *curr)
1325 Node *currnode = curr->get_node();
1326 Node *parnode = currnode->get_parent();
1328 if ((parnode && !parnode->backtrack_empty()) ||
1329 !currnode->misc_empty() ||
1330 !currnode->read_from_empty() ||
1331 !currnode->promise_empty() ||
1332 !currnode->relseq_break_empty()) {
1333 set_latest_backtrack(curr);
1337 bool ModelExecution::promises_expired() const
1339 for (unsigned int i = 0; i < promises->size(); i++) {
1340 Promise *promise = (*promises)[i];
1341 if (promise->get_expiration() < priv->used_sequence_numbers)
1348 * This is the strongest feasibility check available.
1349 * @return whether the current trace (partial or complete) must be a prefix of
1352 bool ModelExecution::isfeasibleprefix() const
1354 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1358 * Print disagnostic information about an infeasible execution
1359 * @param prefix A string to prefix the output with; if NULL, then a default
1360 * message prefix will be provided
1362 void ModelExecution::print_infeasibility(const char *prefix) const
1366 if (mo_graph->checkForCycles())
1367 ptr += sprintf(ptr, "[mo cycle]");
1368 if (priv->failed_promise)
1369 ptr += sprintf(ptr, "[failed promise]");
1370 if (priv->too_many_reads)
1371 ptr += sprintf(ptr, "[too many reads]");
1372 if (priv->no_valid_reads)
1373 ptr += sprintf(ptr, "[no valid reads-from]");
1374 if (priv->bad_synchronization)
1375 ptr += sprintf(ptr, "[bad sw ordering]");
1376 if (promises_expired())
1377 ptr += sprintf(ptr, "[promise expired]");
1378 if (promises->size() != 0)
1379 ptr += sprintf(ptr, "[unresolved promise]");
1381 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1385 * Returns whether the current completed trace is feasible, except for pending
1386 * release sequences.
1388 bool ModelExecution::is_feasible_prefix_ignore_relseq() const
1390 return !is_infeasible() && promises->size() == 0;
1394 * Check if the current partial trace is infeasible. Does not check any
1395 * end-of-execution flags, which might rule out the execution. Thus, this is
1396 * useful only for ruling an execution as infeasible.
1397 * @return whether the current partial trace is infeasible.
1399 bool ModelExecution::is_infeasible() const
1401 return mo_graph->checkForCycles() ||
1402 priv->no_valid_reads ||
1403 priv->failed_promise ||
1404 priv->too_many_reads ||
1405 priv->bad_synchronization ||
1409 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1410 ModelAction * ModelExecution::process_rmw(ModelAction *act) {
1411 ModelAction *lastread = get_last_action(act->get_tid());
1412 lastread->process_rmw(act);
1413 if (act->is_rmw()) {
1414 if (lastread->get_reads_from())
1415 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1417 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1418 mo_graph->commitChanges();
1424 * A helper function for ModelExecution::check_recency, to check if the current
1425 * thread is able to read from a different write/promise for 'params.maxreads'
1426 * number of steps and if that write/promise should become visible (i.e., is
1427 * ordered later in the modification order). This helps model memory liveness.
1429 * @param curr The current action. Must be a read.
1430 * @param rf The write/promise from which we plan to read
1431 * @param other_rf The write/promise from which we may read
1432 * @return True if we were able to read from other_rf for params.maxreads steps
1434 template <typename T, typename U>
1435 bool ModelExecution::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1437 /* Need a different write/promise */
1438 if (other_rf->equals(rf))
1441 /* Only look for "newer" writes/promises */
1442 if (!mo_graph->checkReachable(rf, other_rf))
1445 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1446 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1447 action_list_t::reverse_iterator rit = list->rbegin();
1448 ASSERT((*rit) == curr);
1449 /* Skip past curr */
1452 /* Does this write/promise work for everyone? */
1453 for (int i = 0; i < params->maxreads; i++, rit++) {
1454 ModelAction *act = *rit;
1455 if (!act->may_read_from(other_rf))
1462 * Checks whether a thread has read from the same write or Promise for too many
1463 * times without seeing the effects of a later write/Promise.
1466 * 1) there must a different write/promise that we could read from,
1467 * 2) we must have read from the same write/promise in excess of maxreads times,
1468 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1469 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1471 * If so, we decide that the execution is no longer feasible.
1473 * @param curr The current action. Must be a read.
1474 * @param rf The ModelAction/Promise from which we might read.
1475 * @return True if the read should succeed; false otherwise
1477 template <typename T>
1478 bool ModelExecution::check_recency(ModelAction *curr, const T *rf) const
1480 if (!params->maxreads)
1483 //NOTE: Next check is just optimization, not really necessary....
1484 if (curr->get_node()->get_read_from_past_size() +
1485 curr->get_node()->get_read_from_promise_size() <= 1)
1488 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1489 int tid = id_to_int(curr->get_tid());
1490 ASSERT(tid < (int)thrd_lists->size());
1491 action_list_t *list = &(*thrd_lists)[tid];
1492 action_list_t::reverse_iterator rit = list->rbegin();
1493 ASSERT((*rit) == curr);
1494 /* Skip past curr */
1497 action_list_t::reverse_iterator ritcopy = rit;
1498 /* See if we have enough reads from the same value */
1499 for (int count = 0; count < params->maxreads; ritcopy++, count++) {
1500 if (ritcopy == list->rend())
1502 ModelAction *act = *ritcopy;
1503 if (!act->is_read())
1505 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1507 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1509 if (act->get_node()->get_read_from_past_size() +
1510 act->get_node()->get_read_from_promise_size() <= 1)
1513 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1514 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1515 if (should_read_instead(curr, rf, write))
1516 return false; /* liveness failure */
1518 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1519 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1520 if (should_read_instead(curr, rf, promise))
1521 return false; /* liveness failure */
1527 * @brief Updates the mo_graph with the constraints imposed from the current
1530 * Basic idea is the following: Go through each other thread and find
1531 * the last action that happened before our read. Two cases:
1533 * -# The action is a write: that write must either occur before
1534 * the write we read from or be the write we read from.
1535 * -# The action is a read: the write that that action read from
1536 * must occur before the write we read from or be the same write.
1538 * @param curr The current action. Must be a read.
1539 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1540 * @return True if modification order edges were added; false otherwise
1542 template <typename rf_type>
1543 bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
1545 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1548 ASSERT(curr->is_read());
1550 /* Last SC fence in the current thread */
1551 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1552 ModelAction *last_sc_write = NULL;
1553 if (curr->is_seqcst())
1554 last_sc_write = get_last_seq_cst_write(curr);
1556 /* Iterate over all threads */
1557 for (i = 0; i < thrd_lists->size(); i++) {
1558 /* Last SC fence in thread i */
1559 ModelAction *last_sc_fence_thread_local = NULL;
1560 if (int_to_id((int)i) != curr->get_tid())
1561 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1563 /* Last SC fence in thread i, before last SC fence in current thread */
1564 ModelAction *last_sc_fence_thread_before = NULL;
1565 if (last_sc_fence_local)
1566 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1568 /* Iterate over actions in thread, starting from most recent */
1569 action_list_t *list = &(*thrd_lists)[i];
1570 action_list_t::reverse_iterator rit;
1571 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1572 ModelAction *act = *rit;
1577 /* Don't want to add reflexive edges on 'rf' */
1578 if (act->equals(rf)) {
1579 if (act->happens_before(curr))
1585 if (act->is_write()) {
1586 /* C++, Section 29.3 statement 5 */
1587 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1588 *act < *last_sc_fence_thread_local) {
1589 added = mo_graph->addEdge(act, rf) || added;
1592 /* C++, Section 29.3 statement 4 */
1593 else if (act->is_seqcst() && last_sc_fence_local &&
1594 *act < *last_sc_fence_local) {
1595 added = mo_graph->addEdge(act, rf) || added;
1598 /* C++, Section 29.3 statement 6 */
1599 else if (last_sc_fence_thread_before &&
1600 *act < *last_sc_fence_thread_before) {
1601 added = mo_graph->addEdge(act, rf) || added;
1606 /* C++, Section 29.3 statement 3 (second subpoint) */
1607 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1608 added = mo_graph->addEdge(act, rf) || added;
1613 * Include at most one act per-thread that "happens
1616 if (act->happens_before(curr)) {
1617 if (act->is_write()) {
1618 added = mo_graph->addEdge(act, rf) || added;
1620 const ModelAction *prevrf = act->get_reads_from();
1621 const Promise *prevrf_promise = act->get_reads_from_promise();
1623 if (!prevrf->equals(rf))
1624 added = mo_graph->addEdge(prevrf, rf) || added;
1625 } else if (!prevrf_promise->equals(rf)) {
1626 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1635 * All compatible, thread-exclusive promises must be ordered after any
1636 * concrete loads from the same thread
1638 for (unsigned int i = 0; i < promises->size(); i++)
1639 if ((*promises)[i]->is_compatible_exclusive(curr))
1640 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1646 * Updates the mo_graph with the constraints imposed from the current write.
1648 * Basic idea is the following: Go through each other thread and find
1649 * the lastest action that happened before our write. Two cases:
1651 * (1) The action is a write => that write must occur before
1654 * (2) The action is a read => the write that that action read from
1655 * must occur before the current write.
1657 * This method also handles two other issues:
1659 * (I) Sequential Consistency: Making sure that if the current write is
1660 * seq_cst, that it occurs after the previous seq_cst write.
1662 * (II) Sending the write back to non-synchronizing reads.
1664 * @param curr The current action. Must be a write.
1665 * @param send_fv A vector for stashing reads to which we may pass our future
1666 * value. If NULL, then don't record any future values.
1667 * @return True if modification order edges were added; false otherwise
1669 bool ModelExecution::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1671 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1674 ASSERT(curr->is_write());
1676 if (curr->is_seqcst()) {
1677 /* We have to at least see the last sequentially consistent write,
1678 so we are initialized. */
1679 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1680 if (last_seq_cst != NULL) {
1681 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1685 /* Last SC fence in the current thread */
1686 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1688 /* Iterate over all threads */
1689 for (i = 0; i < thrd_lists->size(); i++) {
1690 /* Last SC fence in thread i, before last SC fence in current thread */
1691 ModelAction *last_sc_fence_thread_before = NULL;
1692 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1693 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1695 /* Iterate over actions in thread, starting from most recent */
1696 action_list_t *list = &(*thrd_lists)[i];
1697 action_list_t::reverse_iterator rit;
1698 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1699 ModelAction *act = *rit;
1702 * 1) If RMW and it actually read from something, then we
1703 * already have all relevant edges, so just skip to next
1706 * 2) If RMW and it didn't read from anything, we should
1707 * whatever edge we can get to speed up convergence.
1709 * 3) If normal write, we need to look at earlier actions, so
1710 * continue processing list.
1712 if (curr->is_rmw()) {
1713 if (curr->get_reads_from() != NULL)
1721 /* C++, Section 29.3 statement 7 */
1722 if (last_sc_fence_thread_before && act->is_write() &&
1723 *act < *last_sc_fence_thread_before) {
1724 added = mo_graph->addEdge(act, curr) || added;
1729 * Include at most one act per-thread that "happens
1732 if (act->happens_before(curr)) {
1734 * Note: if act is RMW, just add edge:
1736 * The following edge should be handled elsewhere:
1737 * readfrom(act) --mo--> act
1739 if (act->is_write())
1740 added = mo_graph->addEdge(act, curr) || added;
1741 else if (act->is_read()) {
1742 //if previous read accessed a null, just keep going
1743 if (act->get_reads_from() == NULL)
1745 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1748 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1749 !act->same_thread(curr)) {
1750 /* We have an action that:
1751 (1) did not happen before us
1752 (2) is a read and we are a write
1753 (3) cannot synchronize with us
1754 (4) is in a different thread
1756 that read could potentially read from our write. Note that
1757 these checks are overly conservative at this point, we'll
1758 do more checks before actually removing the
1762 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1763 if (!is_infeasible())
1764 send_fv->push_back(act);
1765 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1766 add_future_value(curr, act);
1773 * All compatible, thread-exclusive promises must be ordered after any
1774 * concrete stores to the same thread, or else they can be merged with
1777 for (unsigned int i = 0; i < promises->size(); i++)
1778 if ((*promises)[i]->is_compatible_exclusive(curr))
1779 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1784 /** Arbitrary reads from the future are not allowed. Section 29.3
1785 * part 9 places some constraints. This method checks one result of constraint
1786 * constraint. Others require compiler support. */
1787 bool ModelExecution::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
1789 if (!writer->is_rmw())
1792 if (!reader->is_rmw())
1795 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1796 if (search == reader)
1798 if (search->get_tid() == reader->get_tid() &&
1799 search->happens_before(reader))
1807 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1808 * some constraints. This method checks one the following constraint (others
1809 * require compiler support):
1811 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1813 bool ModelExecution::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1815 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1817 /* Iterate over all threads */
1818 for (i = 0; i < thrd_lists->size(); i++) {
1819 const ModelAction *write_after_read = NULL;
1821 /* Iterate over actions in thread, starting from most recent */
1822 action_list_t *list = &(*thrd_lists)[i];
1823 action_list_t::reverse_iterator rit;
1824 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1825 ModelAction *act = *rit;
1827 /* Don't disallow due to act == reader */
1828 if (!reader->happens_before(act) || reader == act)
1830 else if (act->is_write())
1831 write_after_read = act;
1832 else if (act->is_read() && act->get_reads_from() != NULL)
1833 write_after_read = act->get_reads_from();
1836 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
1843 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1844 * The ModelAction under consideration is expected to be taking part in
1845 * release/acquire synchronization as an object of the "reads from" relation.
1846 * Note that this can only provide release sequence support for RMW chains
1847 * which do not read from the future, as those actions cannot be traced until
1848 * their "promise" is fulfilled. Similarly, we may not even establish the
1849 * presence of a release sequence with certainty, as some modification order
1850 * constraints may be decided further in the future. Thus, this function
1851 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1852 * and a boolean representing certainty.
1854 * @param rf The action that might be part of a release sequence. Must be a
1856 * @param release_heads A pass-by-reference style return parameter. After
1857 * execution of this function, release_heads will contain the heads of all the
1858 * relevant release sequences, if any exists with certainty
1859 * @param pending A pass-by-reference style return parameter which is only used
1860 * when returning false (i.e., uncertain). Returns most information regarding
1861 * an uncertain release sequence, including any write operations that might
1862 * break the sequence.
1863 * @return true, if the ModelExecution is certain that release_heads is complete;
1866 bool ModelExecution::release_seq_heads(const ModelAction *rf,
1867 rel_heads_list_t *release_heads,
1868 struct release_seq *pending) const
1870 /* Only check for release sequences if there are no cycles */
1871 if (mo_graph->checkForCycles())
1874 for ( ; rf != NULL; rf = rf->get_reads_from()) {
1875 ASSERT(rf->is_write());
1877 if (rf->is_release())
1878 release_heads->push_back(rf);
1879 else if (rf->get_last_fence_release())
1880 release_heads->push_back(rf->get_last_fence_release());
1882 break; /* End of RMW chain */
1884 /** @todo Need to be smarter here... In the linux lock
1885 * example, this will run to the beginning of the program for
1887 /** @todo The way to be smarter here is to keep going until 1
1888 * thread has a release preceded by an acquire and you've seen
1891 /* acq_rel RMW is a sufficient stopping condition */
1892 if (rf->is_acquire() && rf->is_release())
1893 return true; /* complete */
1896 /* read from future: need to settle this later */
1898 return false; /* incomplete */
1901 if (rf->is_release())
1902 return true; /* complete */
1904 /* else relaxed write
1905 * - check for fence-release in the same thread (29.8, stmt. 3)
1906 * - check modification order for contiguous subsequence
1907 * -> rf must be same thread as release */
1909 const ModelAction *fence_release = rf->get_last_fence_release();
1910 /* Synchronize with a fence-release unconditionally; we don't need to
1911 * find any more "contiguous subsequence..." for it */
1913 release_heads->push_back(fence_release);
1915 int tid = id_to_int(rf->get_tid());
1916 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
1917 action_list_t *list = &(*thrd_lists)[tid];
1918 action_list_t::const_reverse_iterator rit;
1920 /* Find rf in the thread list */
1921 rit = std::find(list->rbegin(), list->rend(), rf);
1922 ASSERT(rit != list->rend());
1924 /* Find the last {write,fence}-release */
1925 for (; rit != list->rend(); rit++) {
1926 if (fence_release && *(*rit) < *fence_release)
1928 if ((*rit)->is_release())
1931 if (rit == list->rend()) {
1932 /* No write-release in this thread */
1933 return true; /* complete */
1934 } else if (fence_release && *(*rit) < *fence_release) {
1935 /* The fence-release is more recent (and so, "stronger") than
1936 * the most recent write-release */
1937 return true; /* complete */
1938 } /* else, need to establish contiguous release sequence */
1939 ModelAction *release = *rit;
1941 ASSERT(rf->same_thread(release));
1943 pending->writes.clear();
1945 bool certain = true;
1946 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1947 if (id_to_int(rf->get_tid()) == (int)i)
1949 list = &(*thrd_lists)[i];
1951 /* Can we ensure no future writes from this thread may break
1952 * the release seq? */
1953 bool future_ordered = false;
1955 ModelAction *last = get_last_action(int_to_id(i));
1956 Thread *th = get_thread(int_to_id(i));
1957 if ((last && rf->happens_before(last)) ||
1960 future_ordered = true;
1962 ASSERT(!th->is_model_thread() || future_ordered);
1964 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1965 const ModelAction *act = *rit;
1966 /* Reach synchronization -> this thread is complete */
1967 if (act->happens_before(release))
1969 if (rf->happens_before(act)) {
1970 future_ordered = true;
1974 /* Only non-RMW writes can break release sequences */
1975 if (!act->is_write() || act->is_rmw())
1978 /* Check modification order */
1979 if (mo_graph->checkReachable(rf, act)) {
1980 /* rf --mo--> act */
1981 future_ordered = true;
1984 if (mo_graph->checkReachable(act, release))
1985 /* act --mo--> release */
1987 if (mo_graph->checkReachable(release, act) &&
1988 mo_graph->checkReachable(act, rf)) {
1989 /* release --mo-> act --mo--> rf */
1990 return true; /* complete */
1992 /* act may break release sequence */
1993 pending->writes.push_back(act);
1996 if (!future_ordered)
1997 certain = false; /* This thread is uncertain */
2001 release_heads->push_back(release);
2002 pending->writes.clear();
2004 pending->release = release;
2011 * An interface for getting the release sequence head(s) with which a
2012 * given ModelAction must synchronize. This function only returns a non-empty
2013 * result when it can locate a release sequence head with certainty. Otherwise,
2014 * it may mark the internal state of the ModelExecution so that it will handle
2015 * the release sequence at a later time, causing @a acquire to update its
2016 * synchronization at some later point in execution.
2018 * @param acquire The 'acquire' action that may synchronize with a release
2020 * @param read The read action that may read from a release sequence; this may
2021 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2022 * when 'acquire' is a fence-acquire)
2023 * @param release_heads A pass-by-reference return parameter. Will be filled
2024 * with the head(s) of the release sequence(s), if they exists with certainty.
2025 * @see ModelExecution::release_seq_heads
2027 void ModelExecution::get_release_seq_heads(ModelAction *acquire,
2028 ModelAction *read, rel_heads_list_t *release_heads)
2030 const ModelAction *rf = read->get_reads_from();
2031 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2032 sequence->acquire = acquire;
2033 sequence->read = read;
2035 if (!release_seq_heads(rf, release_heads, sequence)) {
2036 /* add act to 'lazy checking' list */
2037 pending_rel_seqs->push_back(sequence);
2039 snapshot_free(sequence);
2044 * Attempt to resolve all stashed operations that might synchronize with a
2045 * release sequence for a given location. This implements the "lazy" portion of
2046 * determining whether or not a release sequence was contiguous, since not all
2047 * modification order information is present at the time an action occurs.
2049 * @param location The location/object that should be checked for release
2050 * sequence resolutions. A NULL value means to check all locations.
2051 * @param work_queue The work queue to which to add work items as they are
2053 * @return True if any updates occurred (new synchronization, new mo_graph
2056 bool ModelExecution::resolve_release_sequences(void *location, work_queue_t *work_queue)
2058 bool updated = false;
2059 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2060 while (it != pending_rel_seqs->end()) {
2061 struct release_seq *pending = *it;
2062 ModelAction *acquire = pending->acquire;
2063 const ModelAction *read = pending->read;
2065 /* Only resolve sequences on the given location, if provided */
2066 if (location && read->get_location() != location) {
2071 const ModelAction *rf = read->get_reads_from();
2072 rel_heads_list_t release_heads;
2074 complete = release_seq_heads(rf, &release_heads, pending);
2075 for (unsigned int i = 0; i < release_heads.size(); i++)
2076 if (!acquire->has_synchronized_with(release_heads[i]))
2077 if (synchronize(release_heads[i], acquire))
2081 /* Re-check all pending release sequences */
2082 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2083 /* Re-check read-acquire for mo_graph edges */
2084 if (acquire->is_read())
2085 work_queue->push_back(MOEdgeWorkEntry(acquire));
2087 /* propagate synchronization to later actions */
2088 action_list_t::reverse_iterator rit = action_trace->rbegin();
2089 for (; (*rit) != acquire; rit++) {
2090 ModelAction *propagate = *rit;
2091 if (acquire->happens_before(propagate)) {
2092 synchronize(acquire, propagate);
2093 /* Re-check 'propagate' for mo_graph edges */
2094 work_queue->push_back(MOEdgeWorkEntry(propagate));
2099 it = pending_rel_seqs->erase(it);
2100 snapshot_free(pending);
2106 // If we resolved promises or data races, see if we have realized a data race.
2113 * Performs various bookkeeping operations for the current ModelAction. For
2114 * instance, adds action to the per-object, per-thread action vector and to the
2115 * action trace list of all thread actions.
2117 * @param act is the ModelAction to add.
2119 void ModelExecution::add_action_to_lists(ModelAction *act)
2121 int tid = id_to_int(act->get_tid());
2122 ModelAction *uninit = NULL;
2124 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2125 if (list->empty() && act->is_atomic_var()) {
2126 uninit = get_uninitialized_action(act);
2127 uninit_id = id_to_int(uninit->get_tid());
2128 list->push_front(uninit);
2130 list->push_back(act);
2132 action_trace->push_back(act);
2134 action_trace->push_front(uninit);
2136 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2137 if (tid >= (int)vec->size())
2138 vec->resize(priv->next_thread_id);
2139 (*vec)[tid].push_back(act);
2141 (*vec)[uninit_id].push_front(uninit);
2143 if ((int)thrd_last_action->size() <= tid)
2144 thrd_last_action->resize(get_num_threads());
2145 (*thrd_last_action)[tid] = act;
2147 (*thrd_last_action)[uninit_id] = uninit;
2149 if (act->is_fence() && act->is_release()) {
2150 if ((int)thrd_last_fence_release->size() <= tid)
2151 thrd_last_fence_release->resize(get_num_threads());
2152 (*thrd_last_fence_release)[tid] = act;
2155 if (act->is_wait()) {
2156 void *mutex_loc = (void *) act->get_value();
2157 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2159 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2160 if (tid >= (int)vec->size())
2161 vec->resize(priv->next_thread_id);
2162 (*vec)[tid].push_back(act);
2167 * @brief Get the last action performed by a particular Thread
2168 * @param tid The thread ID of the Thread in question
2169 * @return The last action in the thread
2171 ModelAction * ModelExecution::get_last_action(thread_id_t tid) const
2173 int threadid = id_to_int(tid);
2174 if (threadid < (int)thrd_last_action->size())
2175 return (*thrd_last_action)[id_to_int(tid)];
2181 * @brief Get the last fence release performed by a particular Thread
2182 * @param tid The thread ID of the Thread in question
2183 * @return The last fence release in the thread, if one exists; NULL otherwise
2185 ModelAction * ModelExecution::get_last_fence_release(thread_id_t tid) const
2187 int threadid = id_to_int(tid);
2188 if (threadid < (int)thrd_last_fence_release->size())
2189 return (*thrd_last_fence_release)[id_to_int(tid)];
2195 * Gets the last memory_order_seq_cst write (in the total global sequence)
2196 * performed on a particular object (i.e., memory location), not including the
2198 * @param curr The current ModelAction; also denotes the object location to
2200 * @return The last seq_cst write
2202 ModelAction * ModelExecution::get_last_seq_cst_write(ModelAction *curr) const
2204 void *location = curr->get_location();
2205 action_list_t *list = get_safe_ptr_action(obj_map, location);
2206 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2207 action_list_t::reverse_iterator rit;
2208 for (rit = list->rbegin(); (*rit) != curr; rit++)
2210 rit++; /* Skip past curr */
2211 for ( ; rit != list->rend(); rit++)
2212 if ((*rit)->is_write() && (*rit)->is_seqcst())
2218 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2219 * performed in a particular thread, prior to a particular fence.
2220 * @param tid The ID of the thread to check
2221 * @param before_fence The fence from which to begin the search; if NULL, then
2222 * search for the most recent fence in the thread.
2223 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2225 ModelAction * ModelExecution::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2227 /* All fences should have NULL location */
2228 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2229 action_list_t::reverse_iterator rit = list->rbegin();
2232 for (; rit != list->rend(); rit++)
2233 if (*rit == before_fence)
2236 ASSERT(*rit == before_fence);
2240 for (; rit != list->rend(); rit++)
2241 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2247 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2248 * location). This function identifies the mutex according to the current
2249 * action, which is presumed to perform on the same mutex.
2250 * @param curr The current ModelAction; also denotes the object location to
2252 * @return The last unlock operation
2254 ModelAction * ModelExecution::get_last_unlock(ModelAction *curr) const
2256 void *location = curr->get_location();
2257 action_list_t *list = get_safe_ptr_action(obj_map, location);
2258 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2259 action_list_t::reverse_iterator rit;
2260 for (rit = list->rbegin(); rit != list->rend(); rit++)
2261 if ((*rit)->is_unlock() || (*rit)->is_wait())
2266 ModelAction * ModelExecution::get_parent_action(thread_id_t tid) const
2268 ModelAction *parent = get_last_action(tid);
2270 parent = get_thread(tid)->get_creation();
2275 * Returns the clock vector for a given thread.
2276 * @param tid The thread whose clock vector we want
2277 * @return Desired clock vector
2279 ClockVector * ModelExecution::get_cv(thread_id_t tid) const
2281 return get_parent_action(tid)->get_cv();
2285 * @brief Find the promise (if any) to resolve for the current action and
2286 * remove it from the pending promise vector
2287 * @param curr The current ModelAction. Should be a write.
2288 * @return The Promise to resolve, if any; otherwise NULL
2290 Promise * ModelExecution::pop_promise_to_resolve(const ModelAction *curr)
2292 for (unsigned int i = 0; i < promises->size(); i++)
2293 if (curr->get_node()->get_promise(i)) {
2294 Promise *ret = (*promises)[i];
2295 promises->erase(promises->begin() + i);
2302 * Resolve a Promise with a current write.
2303 * @param write The ModelAction that is fulfilling Promises
2304 * @param promise The Promise to resolve
2305 * @return True if the Promise was successfully resolved; false otherwise
2307 bool ModelExecution::resolve_promise(ModelAction *write, Promise *promise)
2309 ModelVector<ModelAction *> actions_to_check;
2311 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2312 ModelAction *read = promise->get_reader(i);
2313 read_from(read, write);
2314 actions_to_check.push_back(read);
2316 /* Make sure the promise's value matches the write's value */
2317 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2318 if (!mo_graph->resolvePromise(promise, write))
2319 priv->failed_promise = true;
2322 * @todo It is possible to end up in an inconsistent state, where a
2323 * "resolved" promise may still be referenced if
2324 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2326 * Note that the inconsistency only matters when dumping mo_graph to
2332 //Check whether reading these writes has made threads unable to
2334 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2335 ModelAction *read = actions_to_check[i];
2336 mo_check_promises(read, true);
2343 * Compute the set of promises that could potentially be satisfied by this
2344 * action. Note that the set computation actually appears in the Node, not in
2346 * @param curr The ModelAction that may satisfy promises
2348 void ModelExecution::compute_promises(ModelAction *curr)
2350 for (unsigned int i = 0; i < promises->size(); i++) {
2351 Promise *promise = (*promises)[i];
2352 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2355 bool satisfy = true;
2356 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2357 const ModelAction *act = promise->get_reader(j);
2358 if (act->happens_before(curr) ||
2359 act->could_synchronize_with(curr)) {
2365 curr->get_node()->set_promise(i);
2369 /** Checks promises in response to change in ClockVector Threads. */
2370 void ModelExecution::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2372 for (unsigned int i = 0; i < promises->size(); i++) {
2373 Promise *promise = (*promises)[i];
2374 if (!promise->thread_is_available(tid))
2376 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2377 const ModelAction *act = promise->get_reader(j);
2378 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2379 merge_cv->synchronized_since(act)) {
2380 if (promise->eliminate_thread(tid)) {
2381 /* Promise has failed */
2382 priv->failed_promise = true;
2390 void ModelExecution::check_promises_thread_disabled()
2392 for (unsigned int i = 0; i < promises->size(); i++) {
2393 Promise *promise = (*promises)[i];
2394 if (promise->has_failed()) {
2395 priv->failed_promise = true;
2402 * @brief Checks promises in response to addition to modification order for
2405 * We test whether threads are still available for satisfying promises after an
2406 * addition to our modification order constraints. Those that are unavailable
2407 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2408 * that promise has failed.
2410 * @param act The ModelAction which updated the modification order
2411 * @param is_read_check Should be true if act is a read and we must check for
2412 * updates to the store from which it read (there is a distinction here for
2413 * RMW's, which are both a load and a store)
2415 void ModelExecution::mo_check_promises(const ModelAction *act, bool is_read_check)
2417 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2419 for (unsigned int i = 0; i < promises->size(); i++) {
2420 Promise *promise = (*promises)[i];
2422 // Is this promise on the same location?
2423 if (!promise->same_location(write))
2426 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2427 const ModelAction *pread = promise->get_reader(j);
2428 if (!pread->happens_before(act))
2430 if (mo_graph->checkPromise(write, promise)) {
2431 priv->failed_promise = true;
2437 // Don't do any lookups twice for the same thread
2438 if (!promise->thread_is_available(act->get_tid()))
2441 if (mo_graph->checkReachable(promise, write)) {
2442 if (mo_graph->checkPromise(write, promise)) {
2443 priv->failed_promise = true;
2451 * Compute the set of writes that may break the current pending release
2452 * sequence. This information is extracted from previou release sequence
2455 * @param curr The current ModelAction. Must be a release sequence fixup
2458 void ModelExecution::compute_relseq_breakwrites(ModelAction *curr)
2460 if (pending_rel_seqs->empty())
2463 struct release_seq *pending = pending_rel_seqs->back();
2464 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2465 const ModelAction *write = pending->writes[i];
2466 curr->get_node()->add_relseq_break(write);
2469 /* NULL means don't break the sequence; just synchronize */
2470 curr->get_node()->add_relseq_break(NULL);
2474 * Build up an initial set of all past writes that this 'read' action may read
2475 * from, as well as any previously-observed future values that must still be valid.
2477 * @param curr is the current ModelAction that we are exploring; it must be a
2480 void ModelExecution::build_may_read_from(ModelAction *curr)
2482 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2484 ASSERT(curr->is_read());
2486 ModelAction *last_sc_write = NULL;
2488 if (curr->is_seqcst())
2489 last_sc_write = get_last_seq_cst_write(curr);
2491 /* Iterate over all threads */
2492 for (i = 0; i < thrd_lists->size(); i++) {
2493 /* Iterate over actions in thread, starting from most recent */
2494 action_list_t *list = &(*thrd_lists)[i];
2495 action_list_t::reverse_iterator rit;
2496 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2497 ModelAction *act = *rit;
2499 /* Only consider 'write' actions */
2500 if (!act->is_write() || act == curr)
2503 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2504 bool allow_read = true;
2506 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2508 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2512 /* Only add feasible reads */
2513 mo_graph->startChanges();
2514 r_modification_order(curr, act);
2515 if (!is_infeasible())
2516 curr->get_node()->add_read_from_past(act);
2517 mo_graph->rollbackChanges();
2520 /* Include at most one act per-thread that "happens before" curr */
2521 if (act->happens_before(curr))
2526 /* Inherit existing, promised future values */
2527 for (i = 0; i < promises->size(); i++) {
2528 const Promise *promise = (*promises)[i];
2529 const ModelAction *promise_read = promise->get_reader(0);
2530 if (promise_read->same_var(curr)) {
2531 /* Only add feasible future-values */
2532 mo_graph->startChanges();
2533 r_modification_order(curr, promise);
2534 if (!is_infeasible())
2535 curr->get_node()->add_read_from_promise(promise_read);
2536 mo_graph->rollbackChanges();
2540 /* We may find no valid may-read-from only if the execution is doomed */
2541 if (!curr->get_node()->read_from_size()) {
2542 priv->no_valid_reads = true;
2546 if (DBG_ENABLED()) {
2547 model_print("Reached read action:\n");
2549 model_print("Printing read_from_past\n");
2550 curr->get_node()->print_read_from_past();
2551 model_print("End printing read_from_past\n");
2555 bool ModelExecution::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2557 for ( ; write != NULL; write = write->get_reads_from()) {
2558 /* UNINIT actions don't have a Node, and they never sleep */
2559 if (write->is_uninitialized())
2561 Node *prevnode = write->get_node()->get_parent();
2563 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2564 if (write->is_release() && thread_sleep)
2566 if (!write->is_rmw())
2573 * @brief Get an action representing an uninitialized atomic
2575 * This function may create a new one or try to retrieve one from the NodeStack
2577 * @param curr The current action, which prompts the creation of an UNINIT action
2578 * @return A pointer to the UNINIT ModelAction
2580 ModelAction * ModelExecution::get_uninitialized_action(const ModelAction *curr) const
2582 Node *node = curr->get_node();
2583 ModelAction *act = node->get_uninit_action();
2585 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), params->uninitvalue, model_thread);
2586 node->set_uninit_action(act);
2588 act->create_cv(NULL);
2592 static void print_list(action_list_t *list)
2594 action_list_t::iterator it;
2596 model_print("---------------------------------------------------------------------\n");
2598 unsigned int hash = 0;
2600 for (it = list->begin(); it != list->end(); it++) {
2601 const ModelAction *act = *it;
2602 if (act->get_seq_number() > 0)
2604 hash = hash^(hash<<3)^((*it)->hash());
2606 model_print("HASH %u\n", hash);
2607 model_print("---------------------------------------------------------------------\n");
2610 #if SUPPORT_MOD_ORDER_DUMP
2611 void ModelExecution::dumpGraph(char *filename) const
2614 sprintf(buffer, "%s.dot", filename);
2615 FILE *file = fopen(buffer, "w");
2616 fprintf(file, "digraph %s {\n", filename);
2617 mo_graph->dumpNodes(file);
2618 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2620 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2621 ModelAction *act = *it;
2622 if (act->is_read()) {
2623 mo_graph->dot_print_node(file, act);
2624 if (act->get_reads_from())
2625 mo_graph->dot_print_edge(file,
2626 act->get_reads_from(),
2628 "label=\"rf\", color=red, weight=2");
2630 mo_graph->dot_print_edge(file,
2631 act->get_reads_from_promise(),
2633 "label=\"rf\", color=red");
2635 if (thread_array[act->get_tid()]) {
2636 mo_graph->dot_print_edge(file,
2637 thread_array[id_to_int(act->get_tid())],
2639 "label=\"sb\", color=blue, weight=400");
2642 thread_array[act->get_tid()] = act;
2644 fprintf(file, "}\n");
2645 model_free(thread_array);
2650 /** @brief Prints an execution trace summary. */
2651 void ModelExecution::print_summary() const
2653 #if SUPPORT_MOD_ORDER_DUMP
2654 char buffername[100];
2655 sprintf(buffername, "exec%04u", get_execution_number());
2656 mo_graph->dumpGraphToFile(buffername);
2657 sprintf(buffername, "graph%04u", get_execution_number());
2658 dumpGraph(buffername);
2661 model_print("Execution %d:", get_execution_number());
2662 if (isfeasibleprefix()) {
2663 if (scheduler->all_threads_sleeping())
2664 model_print(" SLEEP-SET REDUNDANT");
2667 print_infeasibility(" INFEASIBLE");
2668 print_list(action_trace);
2670 if (!promises->empty()) {
2671 model_print("Pending promises:\n");
2672 for (unsigned int i = 0; i < promises->size(); i++) {
2673 model_print(" [P%u] ", i);
2674 (*promises)[i]->print();
2681 * Add a Thread to the system for the first time. Should only be called once
2683 * @param t The Thread to add
2685 void ModelExecution::add_thread(Thread *t)
2687 thread_map->put(id_to_int(t->get_id()), t);
2688 if (!t->is_model_thread())
2689 scheduler->add_thread(t);
2693 * @brief Get a Thread reference by its ID
2694 * @param tid The Thread's ID
2695 * @return A Thread reference
2697 Thread * ModelExecution::get_thread(thread_id_t tid) const
2699 return thread_map->get(id_to_int(tid));
2703 * @brief Get a reference to the Thread in which a ModelAction was executed
2704 * @param act The ModelAction
2705 * @return A Thread reference
2707 Thread * ModelExecution::get_thread(const ModelAction *act) const
2709 return get_thread(act->get_tid());
2713 * @brief Get a Promise's "promise number"
2715 * A "promise number" is an index number that is unique to a promise, valid
2716 * only for a specific snapshot of an execution trace. Promises may come and go
2717 * as they are generated an resolved, so an index only retains meaning for the
2720 * @param promise The Promise to check
2721 * @return The promise index, if the promise still is valid; otherwise -1
2723 int ModelExecution::get_promise_number(const Promise *promise) const
2725 for (unsigned int i = 0; i < promises->size(); i++)
2726 if ((*promises)[i] == promise)
2733 * @brief Check if a Thread is currently enabled
2734 * @param t The Thread to check
2735 * @return True if the Thread is currently enabled
2737 bool ModelExecution::is_enabled(Thread *t) const
2739 return scheduler->is_enabled(t);
2743 * @brief Check if a Thread is currently enabled
2744 * @param tid The ID of the Thread to check
2745 * @return True if the Thread is currently enabled
2747 bool ModelExecution::is_enabled(thread_id_t tid) const
2749 return scheduler->is_enabled(tid);
2753 * @brief Select the next thread to execute based on the curren action
2755 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
2756 * actions should be followed by the execution of their child thread. In either
2757 * case, the current action should determine the next thread schedule.
2759 * @param curr The current action
2760 * @return The next thread to run, if the current action will determine this
2761 * selection; otherwise NULL
2763 Thread * ModelExecution::action_select_next_thread(const ModelAction *curr) const
2765 /* Do not split atomic RMW */
2766 if (curr->is_rmwr())
2767 return get_thread(curr);
2768 /* Follow CREATE with the created thread */
2769 if (curr->get_type() == THREAD_CREATE)
2770 return curr->get_thread_operand();
2774 /** @return True if the execution has taken too many steps */
2775 bool ModelExecution::too_many_steps() const
2777 return params->bound != 0 && priv->used_sequence_numbers > params->bound;
2781 * Takes the next step in the execution, if possible.
2782 * @param curr The current step to take
2783 * @return Returns the next Thread to run, if any; NULL if this execution
2786 Thread * ModelExecution::take_step(ModelAction *curr)
2788 Thread *curr_thrd = get_thread(curr);
2789 ASSERT(curr_thrd->get_state() == THREAD_READY);
2791 ASSERT(check_action_enabled(curr)); /* May have side effects? */
2792 curr = check_current_action(curr);
2795 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2796 scheduler->remove_thread(curr_thrd);
2798 return action_select_next_thread(curr);
2802 * Launch end-of-execution release sequence fixups only when
2803 * the execution is otherwise feasible AND there are:
2805 * (1) pending release sequences
2806 * (2) pending assertions that could be invalidated by a change
2807 * in clock vectors (i.e., data races)
2808 * (3) no pending promises
2810 void ModelExecution::fixup_release_sequences()
2812 while (!pending_rel_seqs->empty() &&
2813 is_feasible_prefix_ignore_relseq() &&
2814 !unrealizedraces.empty()) {
2815 model_print("*** WARNING: release sequence fixup action "
2816 "(%zu pending release seuqence(s)) ***\n",
2817 pending_rel_seqs->size());
2818 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2819 std::memory_order_seq_cst, NULL, VALUE_NONE,