11 #include "snapshot-interface.h"
13 #include "clockvector.h"
14 #include "cyclegraph.h"
17 #include "threads-model.h"
20 #define INITIAL_THREAD_ID 0
25 bug_message(const char *str) {
26 const char *fmt = " [BUG] %s\n";
27 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
28 sprintf(msg, fmt, str);
30 ~bug_message() { if (msg) snapshot_free(msg); }
33 void print() { model_print("%s", msg); }
39 * Structure for holding small ModelChecker members that should be snapshotted
41 struct model_snapshot_members {
42 model_snapshot_members() :
43 /* First thread created will have id INITIAL_THREAD_ID */
44 next_thread_id(INITIAL_THREAD_ID),
45 used_sequence_numbers(0),
49 failed_promise(false),
50 too_many_reads(false),
51 no_valid_reads(false),
52 bad_synchronization(false),
56 ~model_snapshot_members() {
57 for (unsigned int i = 0; i < bugs.size(); i++)
62 unsigned int next_thread_id;
63 modelclock_t used_sequence_numbers;
64 ModelAction *next_backtrack;
65 SnapVector<bug_message *> bugs;
66 struct execution_stats stats;
70 /** @brief Incorrectly-ordered synchronization was made */
71 bool bad_synchronization;
77 /** @brief Constructor */
78 ModelChecker::ModelChecker(struct model_params params) :
79 /* Initialize default scheduler */
81 scheduler(new Scheduler()),
83 earliest_diverge(NULL),
84 action_trace(new action_list_t()),
85 thread_map(new HashTable<int, Thread *, int>()),
86 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
87 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new SnapVector<Promise *>()),
90 futurevalues(new SnapVector<struct PendingFutureValue>()),
91 pending_rel_seqs(new SnapVector<struct release_seq *>()),
92 thrd_last_action(new SnapVector<ModelAction *>(1)),
93 thrd_last_fence_release(new SnapVector<ModelAction *>()),
94 node_stack(new NodeStack()),
95 priv(new struct model_snapshot_members()),
96 mo_graph(new CycleGraph())
98 /* Initialize a model-checker thread, for special ModelActions */
99 model_thread = new Thread(get_next_id());
100 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
103 /** @brief Destructor */
104 ModelChecker::~ModelChecker()
106 for (unsigned int i = 0; i < get_num_threads(); i++)
107 delete thread_map->get(i);
112 delete condvar_waiters_map;
115 for (unsigned int i = 0; i < promises->size(); i++)
116 delete (*promises)[i];
119 delete pending_rel_seqs;
121 delete thrd_last_action;
122 delete thrd_last_fence_release;
129 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
131 action_list_t *tmp = hash->get(ptr);
133 tmp = new action_list_t();
139 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
141 SnapVector<action_list_t> *tmp = hash->get(ptr);
143 tmp = new SnapVector<action_list_t>();
150 * Restores user program to initial state and resets all model-checker data
153 void ModelChecker::reset_to_initial_state()
155 DEBUG("+++ Resetting to initial state +++\n");
156 node_stack->reset_execution();
159 * FIXME: if we utilize partial rollback, we will need to free only
160 * those pending actions which were NOT pending before the rollback
163 for (unsigned int i = 0; i < get_num_threads(); i++)
164 delete get_thread(int_to_id(i))->get_pending();
166 snapshot_backtrack_before(0);
169 /** @return a thread ID for a new Thread */
170 thread_id_t ModelChecker::get_next_id()
172 return priv->next_thread_id++;
175 /** @return the number of user threads created during this execution */
176 unsigned int ModelChecker::get_num_threads() const
178 return priv->next_thread_id;
182 * Must be called from user-thread context (e.g., through the global
183 * thread_current() interface)
185 * @return The currently executing Thread.
187 Thread * ModelChecker::get_current_thread() const
189 return scheduler->get_current_thread();
192 /** @return a sequence number for a new ModelAction */
193 modelclock_t ModelChecker::get_next_seq_num()
195 return ++priv->used_sequence_numbers;
198 Node * ModelChecker::get_curr_node() const
200 return node_stack->get_head();
204 * @brief Select the next thread to execute based on the curren action
206 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
207 * actions should be followed by the execution of their child thread. In either
208 * case, the current action should determine the next thread schedule.
210 * @param curr The current action
211 * @return The next thread to run, if the current action will determine this
212 * selection; otherwise NULL
214 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
216 /* Do not split atomic RMW */
218 return get_thread(curr);
219 /* Follow CREATE with the created thread */
220 if (curr->get_type() == THREAD_CREATE)
221 return curr->get_thread_operand();
226 * @brief Choose the next thread to execute.
228 * This function chooses the next thread that should execute. It can enforce
229 * execution replay/backtracking or, if the model-checker has no preference
230 * regarding the next thread (i.e., when exploring a new execution ordering),
231 * we defer to the scheduler.
233 * @return The next chosen thread to run, if any exist. Or else if the current
234 * execution should terminate, return NULL.
236 Thread * ModelChecker::get_next_thread()
241 * Have we completed exploring the preselected path? Then let the
245 return scheduler->select_next_thread();
247 /* Else, we are trying to replay an execution */
248 ModelAction *next = node_stack->get_next()->get_action();
250 if (next == diverge) {
251 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
252 earliest_diverge = diverge;
254 Node *nextnode = next->get_node();
255 Node *prevnode = nextnode->get_parent();
256 scheduler->update_sleep_set(prevnode);
258 /* Reached divergence point */
259 if (nextnode->increment_behaviors()) {
260 /* Execute the same thread with a new behavior */
261 tid = next->get_tid();
262 node_stack->pop_restofstack(2);
265 /* Make a different thread execute for next step */
266 scheduler->add_sleep(get_thread(next->get_tid()));
267 tid = prevnode->get_next_backtrack();
268 /* Make sure the backtracked thread isn't sleeping. */
269 node_stack->pop_restofstack(1);
270 if (diverge == earliest_diverge) {
271 earliest_diverge = prevnode->get_action();
274 /* Start the round robin scheduler from this thread id */
275 scheduler->set_scheduler_thread(tid);
276 /* The correct sleep set is in the parent node. */
279 DEBUG("*** Divergence point ***\n");
283 tid = next->get_tid();
285 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
286 ASSERT(tid != THREAD_ID_T_NONE);
287 return get_thread(id_to_int(tid));
291 * We need to know what the next actions of all threads in the sleep
292 * set will be. This method computes them and stores the actions at
293 * the corresponding thread object's pending action.
296 void ModelChecker::execute_sleep_set()
298 for (unsigned int i = 0; i < get_num_threads(); i++) {
299 thread_id_t tid = int_to_id(i);
300 Thread *thr = get_thread(tid);
301 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
302 thr->get_pending()->set_sleep_flag();
308 * @brief Should the current action wake up a given thread?
310 * @param curr The current action
311 * @param thread The thread that we might wake up
312 * @return True, if we should wake up the sleeping thread; false otherwise
314 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
316 const ModelAction *asleep = thread->get_pending();
317 /* Don't allow partial RMW to wake anyone up */
320 /* Synchronizing actions may have been backtracked */
321 if (asleep->could_synchronize_with(curr))
323 /* All acquire/release fences and fence-acquire/store-release */
324 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
326 /* Fence-release + store can awake load-acquire on the same location */
327 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
328 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
329 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
335 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
337 for (unsigned int i = 0; i < get_num_threads(); i++) {
338 Thread *thr = get_thread(int_to_id(i));
339 if (scheduler->is_sleep_set(thr)) {
340 if (should_wake_up(curr, thr))
341 /* Remove this thread from sleep set */
342 scheduler->remove_sleep(thr);
347 /** @brief Alert the model-checker that an incorrectly-ordered
348 * synchronization was made */
349 void ModelChecker::set_bad_synchronization()
351 priv->bad_synchronization = true;
355 * Check whether the current trace has triggered an assertion which should halt
358 * @return True, if the execution should be aborted; false otherwise
360 bool ModelChecker::has_asserted() const
362 return priv->asserted;
366 * Trigger a trace assertion which should cause this execution to be halted.
367 * This can be due to a detected bug or due to an infeasibility that should
370 void ModelChecker::set_assert()
372 priv->asserted = true;
376 * Check if we are in a deadlock. Should only be called at the end of an
377 * execution, although it should not give false positives in the middle of an
378 * execution (there should be some ENABLED thread).
380 * @return True if program is in a deadlock; false otherwise
382 bool ModelChecker::is_deadlocked() const
384 bool blocking_threads = false;
385 for (unsigned int i = 0; i < get_num_threads(); i++) {
386 thread_id_t tid = int_to_id(i);
389 Thread *t = get_thread(tid);
390 if (!t->is_model_thread() && t->get_pending())
391 blocking_threads = true;
393 return blocking_threads;
397 * Check if this is a complete execution. That is, have all thread completed
398 * execution (rather than exiting because sleep sets have forced a redundant
401 * @return True if the execution is complete.
403 bool ModelChecker::is_complete_execution() const
405 for (unsigned int i = 0; i < get_num_threads(); i++)
406 if (is_enabled(int_to_id(i)))
412 * @brief Assert a bug in the executing program.
414 * Use this function to assert any sort of bug in the user program. If the
415 * current trace is feasible (actually, a prefix of some feasible execution),
416 * then this execution will be aborted, printing the appropriate message. If
417 * the current trace is not yet feasible, the error message will be stashed and
418 * printed if the execution ever becomes feasible.
420 * @param msg Descriptive message for the bug (do not include newline char)
421 * @return True if bug is immediately-feasible
423 bool ModelChecker::assert_bug(const char *msg, ...)
429 vsnprintf(str, sizeof(str), msg, ap);
432 priv->bugs.push_back(new bug_message(str));
434 if (isfeasibleprefix()) {
442 * @brief Assert a bug in the executing program, asserted by a user thread
443 * @see ModelChecker::assert_bug
444 * @param msg Descriptive message for the bug (do not include newline char)
446 void ModelChecker::assert_user_bug(const char *msg)
448 /* If feasible bug, bail out now */
450 switch_to_master(NULL);
453 /** @return True, if any bugs have been reported for this execution */
454 bool ModelChecker::have_bug_reports() const
456 return priv->bugs.size() != 0;
459 /** @brief Print bug report listing for this execution (if any bugs exist) */
460 void ModelChecker::print_bugs() const
462 if (have_bug_reports()) {
463 model_print("Bug report: %zu bug%s detected\n",
465 priv->bugs.size() > 1 ? "s" : "");
466 for (unsigned int i = 0; i < priv->bugs.size(); i++)
467 priv->bugs[i]->print();
472 * @brief Record end-of-execution stats
474 * Must be run when exiting an execution. Records various stats.
475 * @see struct execution_stats
477 void ModelChecker::record_stats()
480 if (!isfeasibleprefix())
481 stats.num_infeasible++;
482 else if (have_bug_reports())
483 stats.num_buggy_executions++;
484 else if (is_complete_execution())
485 stats.num_complete++;
487 stats.num_redundant++;
490 * @todo We can violate this ASSERT() when fairness/sleep sets
491 * conflict to cause an execution to terminate, e.g. with:
492 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
494 //ASSERT(scheduler->all_threads_sleeping());
498 /** @brief Print execution stats */
499 void ModelChecker::print_stats() const
501 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
502 model_print("Number of redundant executions: %d\n", stats.num_redundant);
503 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
504 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
505 model_print("Total executions: %d\n", stats.num_total);
506 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
510 * @brief End-of-exeuction print
511 * @param printbugs Should any existing bugs be printed?
513 void ModelChecker::print_execution(bool printbugs) const
515 print_program_output();
517 if (params.verbose) {
518 model_print("Earliest divergence point since last feasible execution:\n");
519 if (earliest_diverge)
520 earliest_diverge->print();
522 model_print("(Not set)\n");
528 /* Don't print invalid bugs */
537 * Queries the model-checker for more executions to explore and, if one
538 * exists, resets the model-checker state to execute a new execution.
540 * @return If there are more executions to explore, return true. Otherwise,
543 bool ModelChecker::next_execution()
546 /* Is this execution a feasible execution that's worth bug-checking? */
547 bool complete = isfeasibleprefix() && (is_complete_execution() ||
550 /* End-of-execution bug checks */
553 assert_bug("Deadlock detected");
561 if (params.verbose || (complete && have_bug_reports()))
562 print_execution(complete);
564 clear_program_output();
567 earliest_diverge = NULL;
569 if ((diverge = get_next_backtrack()) == NULL)
573 model_print("Next execution will diverge at:\n");
577 reset_to_initial_state();
582 * @brief Find the last fence-related backtracking conflict for a ModelAction
584 * This function performs the search for the most recent conflicting action
585 * against which we should perform backtracking, as affected by fence
586 * operations. This includes pairs of potentially-synchronizing actions which
587 * occur due to fence-acquire or fence-release, and hence should be explored in
588 * the opposite execution order.
590 * @param act The current action
591 * @return The most recent action which conflicts with act due to fences
593 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
595 /* Only perform release/acquire fence backtracking for stores */
596 if (!act->is_write())
599 /* Find a fence-release (or, act is a release) */
600 ModelAction *last_release;
601 if (act->is_release())
604 last_release = get_last_fence_release(act->get_tid());
608 /* Skip past the release */
609 action_list_t *list = action_trace;
610 action_list_t::reverse_iterator rit;
611 for (rit = list->rbegin(); rit != list->rend(); rit++)
612 if (*rit == last_release)
614 ASSERT(rit != list->rend());
619 * load --sb-> fence-acquire */
620 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
621 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
622 bool found_acquire_fences = false;
623 for ( ; rit != list->rend(); rit++) {
624 ModelAction *prev = *rit;
625 if (act->same_thread(prev))
628 int tid = id_to_int(prev->get_tid());
630 if (prev->is_read() && act->same_var(prev)) {
631 if (prev->is_acquire()) {
632 /* Found most recent load-acquire, don't need
633 * to search for more fences */
634 if (!found_acquire_fences)
637 prior_loads[tid] = prev;
640 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
641 found_acquire_fences = true;
642 acquire_fences[tid] = prev;
646 ModelAction *latest_backtrack = NULL;
647 for (unsigned int i = 0; i < acquire_fences.size(); i++)
648 if (acquire_fences[i] && prior_loads[i])
649 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
650 latest_backtrack = acquire_fences[i];
651 return latest_backtrack;
655 * @brief Find the last backtracking conflict for a ModelAction
657 * This function performs the search for the most recent conflicting action
658 * against which we should perform backtracking. This primary includes pairs of
659 * synchronizing actions which should be explored in the opposite execution
662 * @param act The current action
663 * @return The most recent action which conflicts with act
665 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
667 switch (act->get_type()) {
668 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
672 ModelAction *ret = NULL;
674 /* linear search: from most recent to oldest */
675 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
676 action_list_t::reverse_iterator rit;
677 for (rit = list->rbegin(); rit != list->rend(); rit++) {
678 ModelAction *prev = *rit;
679 if (prev->could_synchronize_with(act)) {
685 ModelAction *ret2 = get_last_fence_conflict(act);
695 case ATOMIC_TRYLOCK: {
696 /* linear search: from most recent to oldest */
697 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
698 action_list_t::reverse_iterator rit;
699 for (rit = list->rbegin(); rit != list->rend(); rit++) {
700 ModelAction *prev = *rit;
701 if (act->is_conflicting_lock(prev))
706 case ATOMIC_UNLOCK: {
707 /* linear search: from most recent to oldest */
708 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
709 action_list_t::reverse_iterator rit;
710 for (rit = list->rbegin(); rit != list->rend(); rit++) {
711 ModelAction *prev = *rit;
712 if (!act->same_thread(prev) && prev->is_failed_trylock())
718 /* linear search: from most recent to oldest */
719 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
720 action_list_t::reverse_iterator rit;
721 for (rit = list->rbegin(); rit != list->rend(); rit++) {
722 ModelAction *prev = *rit;
723 if (!act->same_thread(prev) && prev->is_failed_trylock())
725 if (!act->same_thread(prev) && prev->is_notify())
731 case ATOMIC_NOTIFY_ALL:
732 case ATOMIC_NOTIFY_ONE: {
733 /* linear search: from most recent to oldest */
734 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
735 action_list_t::reverse_iterator rit;
736 for (rit = list->rbegin(); rit != list->rend(); rit++) {
737 ModelAction *prev = *rit;
738 if (!act->same_thread(prev) && prev->is_wait())
749 /** This method finds backtracking points where we should try to
750 * reorder the parameter ModelAction against.
752 * @param the ModelAction to find backtracking points for.
754 void ModelChecker::set_backtracking(ModelAction *act)
756 Thread *t = get_thread(act);
757 ModelAction *prev = get_last_conflict(act);
761 Node *node = prev->get_node()->get_parent();
763 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
764 int low_tid, high_tid;
765 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
766 low_tid = id_to_int(act->get_tid());
767 high_tid = low_tid + 1;
770 high_tid = get_num_threads();
773 for (int i = low_tid; i < high_tid; i++) {
774 thread_id_t tid = int_to_id(i);
776 /* Make sure this thread can be enabled here. */
777 if (i >= node->get_num_threads())
780 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
781 /* Don't backtrack into a point where the thread is disabled or sleeping. */
782 if (node->enabled_status(tid) != THREAD_ENABLED)
785 /* Check if this has been explored already */
786 if (node->has_been_explored(tid))
789 /* See if fairness allows */
790 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
792 for (int t = 0; t < node->get_num_threads(); t++) {
793 thread_id_t tother = int_to_id(t);
794 if (node->is_enabled(tother) && node->has_priority(tother)) {
803 /* See if CHESS-like yield fairness allows */
804 if (model->params.yieldon) {
806 for (int t = 0; t < node->get_num_threads(); t++) {
807 thread_id_t tother = int_to_id(t);
808 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
817 /* Cache the latest backtracking point */
818 set_latest_backtrack(prev);
820 /* If this is a new backtracking point, mark the tree */
821 if (!node->set_backtrack(tid))
823 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
824 id_to_int(prev->get_tid()),
825 id_to_int(t->get_id()));
834 * @brief Cache the a backtracking point as the "most recent", if eligible
836 * Note that this does not prepare the NodeStack for this backtracking
837 * operation, it only caches the action on a per-execution basis
839 * @param act The operation at which we should explore a different next action
840 * (i.e., backtracking point)
841 * @return True, if this action is now the most recent backtracking point;
844 bool ModelChecker::set_latest_backtrack(ModelAction *act)
846 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
847 priv->next_backtrack = act;
854 * Returns last backtracking point. The model checker will explore a different
855 * path for this point in the next execution.
856 * @return The ModelAction at which the next execution should diverge.
858 ModelAction * ModelChecker::get_next_backtrack()
860 ModelAction *next = priv->next_backtrack;
861 priv->next_backtrack = NULL;
866 * Processes a read model action.
867 * @param curr is the read model action to process.
868 * @return True if processing this read updates the mo_graph.
870 bool ModelChecker::process_read(ModelAction *curr)
872 Node *node = curr->get_node();
874 bool updated = false;
875 switch (node->get_read_from_status()) {
876 case READ_FROM_PAST: {
877 const ModelAction *rf = node->get_read_from_past();
880 mo_graph->startChanges();
882 ASSERT(!is_infeasible());
883 if (!check_recency(curr, rf)) {
884 if (node->increment_read_from()) {
885 mo_graph->rollbackChanges();
888 priv->too_many_reads = true;
892 updated = r_modification_order(curr, rf);
894 mo_graph->commitChanges();
895 mo_check_promises(curr, true);
898 case READ_FROM_PROMISE: {
899 Promise *promise = curr->get_node()->get_read_from_promise();
900 if (promise->add_reader(curr))
901 priv->failed_promise = true;
902 curr->set_read_from_promise(promise);
903 mo_graph->startChanges();
904 if (!check_recency(curr, promise))
905 priv->too_many_reads = true;
906 updated = r_modification_order(curr, promise);
907 mo_graph->commitChanges();
910 case READ_FROM_FUTURE: {
911 /* Read from future value */
912 struct future_value fv = node->get_future_value();
913 Promise *promise = new Promise(curr, fv);
914 curr->set_read_from_promise(promise);
915 promises->push_back(promise);
916 mo_graph->startChanges();
917 updated = r_modification_order(curr, promise);
918 mo_graph->commitChanges();
924 get_thread(curr)->set_return_value(curr->get_return_value());
930 * Processes a lock, trylock, or unlock model action. @param curr is
931 * the read model action to process.
933 * The try lock operation checks whether the lock is taken. If not,
934 * it falls to the normal lock operation case. If so, it returns
937 * The lock operation has already been checked that it is enabled, so
938 * it just grabs the lock and synchronizes with the previous unlock.
940 * The unlock operation has to re-enable all of the threads that are
941 * waiting on the lock.
943 * @return True if synchronization was updated; false otherwise
945 bool ModelChecker::process_mutex(ModelAction *curr)
947 std::mutex *mutex = curr->get_mutex();
948 struct std::mutex_state *state = NULL;
951 state = mutex->get_state();
953 switch (curr->get_type()) {
954 case ATOMIC_TRYLOCK: {
955 bool success = !state->locked;
956 curr->set_try_lock(success);
958 get_thread(curr)->set_return_value(0);
961 get_thread(curr)->set_return_value(1);
963 //otherwise fall into the lock case
965 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
966 assert_bug("Lock access before initialization");
967 state->locked = get_thread(curr);
968 ModelAction *unlock = get_last_unlock(curr);
969 //synchronize with the previous unlock statement
970 if (unlock != NULL) {
971 curr->synchronize_with(unlock);
977 case ATOMIC_UNLOCK: {
978 /* wake up the other threads */
979 for (unsigned int i = 0; i < get_num_threads(); i++) {
980 Thread *t = get_thread(int_to_id(i));
981 Thread *curr_thrd = get_thread(curr);
982 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
986 /* unlock the lock - after checking who was waiting on it */
987 state->locked = NULL;
989 if (!curr->is_wait())
990 break; /* The rest is only for ATOMIC_WAIT */
992 /* Should we go to sleep? (simulate spurious failures) */
993 if (curr->get_node()->get_misc() == 0) {
994 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
996 scheduler->sleep(get_thread(curr));
1000 case ATOMIC_NOTIFY_ALL: {
1001 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1002 //activate all the waiting threads
1003 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1004 scheduler->wake(get_thread(*rit));
1009 case ATOMIC_NOTIFY_ONE: {
1010 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1011 int wakeupthread = curr->get_node()->get_misc();
1012 action_list_t::iterator it = waiters->begin();
1013 advance(it, wakeupthread);
1014 scheduler->wake(get_thread(*it));
1026 * @brief Check if the current pending promises allow a future value to be sent
1028 * If one of the following is true:
1029 * (a) there are no pending promises
1030 * (b) the reader and writer do not cross any promises
1031 * Then, it is safe to pass a future value back now.
1033 * Otherwise, we must save the pending future value until (a) or (b) is true
1035 * @param writer The operation which sends the future value. Must be a write.
1036 * @param reader The operation which will observe the value. Must be a read.
1037 * @return True if the future value can be sent now; false if it must wait.
1039 bool ModelChecker::promises_may_allow(const ModelAction *writer,
1040 const ModelAction *reader) const
1042 if (promises->empty())
1044 for(int i=promises->size()-1;i>=0;i--) {
1045 ModelAction *pr=(*promises)[i]->get_reader(0);
1046 //reader is after promise...doesn't cross any promise
1049 //writer is after promise, reader before...bad...
1057 * @brief Add a future value to a reader
1059 * This function performs a few additional checks to ensure that the future
1060 * value can be feasibly observed by the reader
1062 * @param writer The operation whose value is sent. Must be a write.
1063 * @param reader The read operation which may read the future value. Must be a read.
1065 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1067 /* Do more ambitious checks now that mo is more complete */
1068 if (!mo_may_allow(writer, reader))
1071 Node *node = reader->get_node();
1073 /* Find an ancestor thread which exists at the time of the reader */
1074 Thread *write_thread = get_thread(writer);
1075 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1076 write_thread = write_thread->get_parent();
1078 struct future_value fv = {
1079 writer->get_write_value(),
1080 writer->get_seq_number() + params.maxfuturedelay,
1081 write_thread->get_id(),
1083 if (node->add_future_value(fv))
1084 set_latest_backtrack(reader);
1088 * Process a write ModelAction
1089 * @param curr The ModelAction to process
1090 * @return True if the mo_graph was updated or promises were resolved
1092 bool ModelChecker::process_write(ModelAction *curr)
1094 /* Readers to which we may send our future value */
1095 ModelVector<ModelAction *> send_fv;
1097 const ModelAction *earliest_promise_reader;
1098 bool updated_promises = false;
1100 bool updated_mod_order = w_modification_order(curr, &send_fv);
1101 Promise *promise = pop_promise_to_resolve(curr);
1104 earliest_promise_reader = promise->get_reader(0);
1105 updated_promises = resolve_promise(curr, promise);
1107 earliest_promise_reader = NULL;
1109 for (unsigned int i = 0; i < send_fv.size(); i++) {
1110 ModelAction *read = send_fv[i];
1112 /* Don't send future values to reads after the Promise we resolve */
1113 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
1114 /* Check if future value can be sent immediately */
1115 if (promises_may_allow(curr, read)) {
1116 add_future_value(curr, read);
1118 futurevalues->push_back(PendingFutureValue(curr, read));
1123 /* Check the pending future values */
1124 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
1125 struct PendingFutureValue pfv = (*futurevalues)[i];
1126 if (promises_may_allow(pfv.writer, pfv.reader)) {
1127 add_future_value(pfv.writer, pfv.reader);
1128 futurevalues->erase(futurevalues->begin() + i);
1132 mo_graph->commitChanges();
1133 mo_check_promises(curr, false);
1135 get_thread(curr)->set_return_value(VALUE_NONE);
1136 return updated_mod_order || updated_promises;
1140 * Process a fence ModelAction
1141 * @param curr The ModelAction to process
1142 * @return True if synchronization was updated
1144 bool ModelChecker::process_fence(ModelAction *curr)
1147 * fence-relaxed: no-op
1148 * fence-release: only log the occurence (not in this function), for
1149 * use in later synchronization
1150 * fence-acquire (this function): search for hypothetical release
1152 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1154 bool updated = false;
1155 if (curr->is_acquire()) {
1156 action_list_t *list = action_trace;
1157 action_list_t::reverse_iterator rit;
1158 /* Find X : is_read(X) && X --sb-> curr */
1159 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1160 ModelAction *act = *rit;
1163 if (act->get_tid() != curr->get_tid())
1165 /* Stop at the beginning of the thread */
1166 if (act->is_thread_start())
1168 /* Stop once we reach a prior fence-acquire */
1169 if (act->is_fence() && act->is_acquire())
1171 if (!act->is_read())
1173 /* read-acquire will find its own release sequences */
1174 if (act->is_acquire())
1177 /* Establish hypothetical release sequences */
1178 rel_heads_list_t release_heads;
1179 get_release_seq_heads(curr, act, &release_heads);
1180 for (unsigned int i = 0; i < release_heads.size(); i++)
1181 if (!curr->synchronize_with(release_heads[i]))
1182 set_bad_synchronization();
1183 if (release_heads.size() != 0)
1191 * @brief Process the current action for thread-related activity
1193 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1194 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1195 * synchronization, etc. This function is a no-op for non-THREAD actions
1196 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1198 * @param curr The current action
1199 * @return True if synchronization was updated or a thread completed
1201 bool ModelChecker::process_thread_action(ModelAction *curr)
1203 bool updated = false;
1205 switch (curr->get_type()) {
1206 case THREAD_CREATE: {
1207 thrd_t *thrd = (thrd_t *)curr->get_location();
1208 struct thread_params *params = (struct thread_params *)curr->get_value();
1209 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1211 th->set_creation(curr);
1212 /* Promises can be satisfied by children */
1213 for (unsigned int i = 0; i < promises->size(); i++) {
1214 Promise *promise = (*promises)[i];
1215 if (promise->thread_is_available(curr->get_tid()))
1216 promise->add_thread(th->get_id());
1221 Thread *blocking = curr->get_thread_operand();
1222 ModelAction *act = get_last_action(blocking->get_id());
1223 curr->synchronize_with(act);
1224 updated = true; /* trigger rel-seq checks */
1227 case THREAD_FINISH: {
1228 Thread *th = get_thread(curr);
1229 /* Wake up any joining threads */
1230 for (unsigned int i = 0; i < get_num_threads(); i++) {
1231 Thread *waiting = get_thread(int_to_id(i));
1232 if (waiting->waiting_on() == th &&
1233 waiting->get_pending()->is_thread_join())
1234 scheduler->wake(waiting);
1237 /* Completed thread can't satisfy promises */
1238 for (unsigned int i = 0; i < promises->size(); i++) {
1239 Promise *promise = (*promises)[i];
1240 if (promise->thread_is_available(th->get_id()))
1241 if (promise->eliminate_thread(th->get_id()))
1242 priv->failed_promise = true;
1244 updated = true; /* trigger rel-seq checks */
1247 case THREAD_START: {
1248 check_promises(curr->get_tid(), NULL, curr->get_cv());
1259 * @brief Process the current action for release sequence fixup activity
1261 * Performs model-checker release sequence fixups for the current action,
1262 * forcing a single pending release sequence to break (with a given, potential
1263 * "loose" write) or to complete (i.e., synchronize). If a pending release
1264 * sequence forms a complete release sequence, then we must perform the fixup
1265 * synchronization, mo_graph additions, etc.
1267 * @param curr The current action; must be a release sequence fixup action
1268 * @param work_queue The work queue to which to add work items as they are
1271 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1273 const ModelAction *write = curr->get_node()->get_relseq_break();
1274 struct release_seq *sequence = pending_rel_seqs->back();
1275 pending_rel_seqs->pop_back();
1277 ModelAction *acquire = sequence->acquire;
1278 const ModelAction *rf = sequence->rf;
1279 const ModelAction *release = sequence->release;
1283 ASSERT(release->same_thread(rf));
1285 if (write == NULL) {
1287 * @todo Forcing a synchronization requires that we set
1288 * modification order constraints. For instance, we can't allow
1289 * a fixup sequence in which two separate read-acquire
1290 * operations read from the same sequence, where the first one
1291 * synchronizes and the other doesn't. Essentially, we can't
1292 * allow any writes to insert themselves between 'release' and
1296 /* Must synchronize */
1297 if (!acquire->synchronize_with(release)) {
1298 set_bad_synchronization();
1301 /* Re-check all pending release sequences */
1302 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1303 /* Re-check act for mo_graph edges */
1304 work_queue->push_back(MOEdgeWorkEntry(acquire));
1306 /* propagate synchronization to later actions */
1307 action_list_t::reverse_iterator rit = action_trace->rbegin();
1308 for (; (*rit) != acquire; rit++) {
1309 ModelAction *propagate = *rit;
1310 if (acquire->happens_before(propagate)) {
1311 propagate->synchronize_with(acquire);
1312 /* Re-check 'propagate' for mo_graph edges */
1313 work_queue->push_back(MOEdgeWorkEntry(propagate));
1317 /* Break release sequence with new edges:
1318 * release --mo--> write --mo--> rf */
1319 mo_graph->addEdge(release, write);
1320 mo_graph->addEdge(write, rf);
1323 /* See if we have realized a data race */
1328 * Initialize the current action by performing one or more of the following
1329 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1330 * in the NodeStack, manipulating backtracking sets, allocating and
1331 * initializing clock vectors, and computing the promises to fulfill.
1333 * @param curr The current action, as passed from the user context; may be
1334 * freed/invalidated after the execution of this function, with a different
1335 * action "returned" its place (pass-by-reference)
1336 * @return True if curr is a newly-explored action; false otherwise
1338 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1340 ModelAction *newcurr;
1342 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1343 newcurr = process_rmw(*curr);
1346 if (newcurr->is_rmw())
1347 compute_promises(newcurr);
1353 (*curr)->set_seq_number(get_next_seq_num());
1355 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1357 /* First restore type and order in case of RMW operation */
1358 if ((*curr)->is_rmwr())
1359 newcurr->copy_typeandorder(*curr);
1361 ASSERT((*curr)->get_location() == newcurr->get_location());
1362 newcurr->copy_from_new(*curr);
1364 /* Discard duplicate ModelAction; use action from NodeStack */
1367 /* Always compute new clock vector */
1368 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1371 return false; /* Action was explored previously */
1375 /* Always compute new clock vector */
1376 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1378 /* Assign most recent release fence */
1379 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1382 * Perform one-time actions when pushing new ModelAction onto
1385 if (newcurr->is_write())
1386 compute_promises(newcurr);
1387 else if (newcurr->is_relseq_fixup())
1388 compute_relseq_breakwrites(newcurr);
1389 else if (newcurr->is_wait())
1390 newcurr->get_node()->set_misc_max(2);
1391 else if (newcurr->is_notify_one()) {
1392 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1394 return true; /* This was a new ModelAction */
1399 * @brief Establish reads-from relation between two actions
1401 * Perform basic operations involved with establishing a concrete rf relation,
1402 * including setting the ModelAction data and checking for release sequences.
1404 * @param act The action that is reading (must be a read)
1405 * @param rf The action from which we are reading (must be a write)
1407 * @return True if this read established synchronization
1409 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1412 ASSERT(rf->is_write());
1414 act->set_read_from(rf);
1415 if (act->is_acquire()) {
1416 rel_heads_list_t release_heads;
1417 get_release_seq_heads(act, act, &release_heads);
1418 int num_heads = release_heads.size();
1419 for (unsigned int i = 0; i < release_heads.size(); i++)
1420 if (!act->synchronize_with(release_heads[i])) {
1421 set_bad_synchronization();
1424 return num_heads > 0;
1430 * Check promises and eliminate potentially-satisfying threads when a thread is
1431 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1432 * no longer satisfy a promise generated from that thread.
1434 * @param blocker The thread on which a thread is waiting
1435 * @param waiting The waiting thread
1437 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1439 for (unsigned int i = 0; i < promises->size(); i++) {
1440 Promise *promise = (*promises)[i];
1441 if (!promise->thread_is_available(waiting->get_id()))
1443 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1444 ModelAction *reader = promise->get_reader(j);
1445 if (reader->get_tid() != blocker->get_id())
1447 if (promise->eliminate_thread(waiting->get_id())) {
1448 /* Promise has failed */
1449 priv->failed_promise = true;
1451 /* Only eliminate the 'waiting' thread once */
1459 * @brief Check whether a model action is enabled.
1461 * Checks whether a lock or join operation would be successful (i.e., is the
1462 * lock already locked, or is the joined thread already complete). If not, put
1463 * the action in a waiter list.
1465 * @param curr is the ModelAction to check whether it is enabled.
1466 * @return a bool that indicates whether the action is enabled.
1468 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1469 if (curr->is_lock()) {
1470 std::mutex *lock = curr->get_mutex();
1471 struct std::mutex_state *state = lock->get_state();
1474 } else if (curr->is_thread_join()) {
1475 Thread *blocking = curr->get_thread_operand();
1476 if (!blocking->is_complete()) {
1477 thread_blocking_check_promises(blocking, get_thread(curr));
1486 * This is the heart of the model checker routine. It performs model-checking
1487 * actions corresponding to a given "current action." Among other processes, it
1488 * calculates reads-from relationships, updates synchronization clock vectors,
1489 * forms a memory_order constraints graph, and handles replay/backtrack
1490 * execution when running permutations of previously-observed executions.
1492 * @param curr The current action to process
1493 * @return The ModelAction that is actually executed; may be different than
1494 * curr; may be NULL, if the current action is not enabled to run
1496 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1499 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1500 bool newly_explored = initialize_curr_action(&curr);
1504 wake_up_sleeping_actions(curr);
1506 /* Compute fairness information for CHESS yield algorithm */
1507 if (model->params.yieldon) {
1508 curr->get_node()->update_yield(scheduler);
1511 /* Add the action to lists before any other model-checking tasks */
1512 if (!second_part_of_rmw)
1513 add_action_to_lists(curr);
1515 /* Build may_read_from set for newly-created actions */
1516 if (newly_explored && curr->is_read())
1517 build_may_read_from(curr);
1519 /* Initialize work_queue with the "current action" work */
1520 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1521 while (!work_queue.empty() && !has_asserted()) {
1522 WorkQueueEntry work = work_queue.front();
1523 work_queue.pop_front();
1525 switch (work.type) {
1526 case WORK_CHECK_CURR_ACTION: {
1527 ModelAction *act = work.action;
1528 bool update = false; /* update this location's release seq's */
1529 bool update_all = false; /* update all release seq's */
1531 if (process_thread_action(curr))
1534 if (act->is_read() && !second_part_of_rmw && process_read(act))
1537 if (act->is_write() && process_write(act))
1540 if (act->is_fence() && process_fence(act))
1543 if (act->is_mutex_op() && process_mutex(act))
1546 if (act->is_relseq_fixup())
1547 process_relseq_fixup(curr, &work_queue);
1550 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1552 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1555 case WORK_CHECK_RELEASE_SEQ:
1556 resolve_release_sequences(work.location, &work_queue);
1558 case WORK_CHECK_MO_EDGES: {
1559 /** @todo Complete verification of work_queue */
1560 ModelAction *act = work.action;
1561 bool updated = false;
1563 if (act->is_read()) {
1564 const ModelAction *rf = act->get_reads_from();
1565 const Promise *promise = act->get_reads_from_promise();
1567 if (r_modification_order(act, rf))
1569 } else if (promise) {
1570 if (r_modification_order(act, promise))
1574 if (act->is_write()) {
1575 if (w_modification_order(act, NULL))
1578 mo_graph->commitChanges();
1581 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1590 check_curr_backtracking(curr);
1591 set_backtracking(curr);
1595 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1597 Node *currnode = curr->get_node();
1598 Node *parnode = currnode->get_parent();
1600 if ((parnode && !parnode->backtrack_empty()) ||
1601 !currnode->misc_empty() ||
1602 !currnode->read_from_empty() ||
1603 !currnode->promise_empty() ||
1604 !currnode->relseq_break_empty()) {
1605 set_latest_backtrack(curr);
1609 bool ModelChecker::promises_expired() const
1611 for (unsigned int i = 0; i < promises->size(); i++) {
1612 Promise *promise = (*promises)[i];
1613 if (promise->get_expiration() < priv->used_sequence_numbers)
1620 * This is the strongest feasibility check available.
1621 * @return whether the current trace (partial or complete) must be a prefix of
1624 bool ModelChecker::isfeasibleprefix() const
1626 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1630 * Print disagnostic information about an infeasible execution
1631 * @param prefix A string to prefix the output with; if NULL, then a default
1632 * message prefix will be provided
1634 void ModelChecker::print_infeasibility(const char *prefix) const
1638 if (mo_graph->checkForCycles())
1639 ptr += sprintf(ptr, "[mo cycle]");
1640 if (priv->failed_promise)
1641 ptr += sprintf(ptr, "[failed promise]");
1642 if (priv->too_many_reads)
1643 ptr += sprintf(ptr, "[too many reads]");
1644 if (priv->no_valid_reads)
1645 ptr += sprintf(ptr, "[no valid reads-from]");
1646 if (priv->bad_synchronization)
1647 ptr += sprintf(ptr, "[bad sw ordering]");
1648 if (promises_expired())
1649 ptr += sprintf(ptr, "[promise expired]");
1650 if (promises->size() != 0)
1651 ptr += sprintf(ptr, "[unresolved promise]");
1653 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1657 * Returns whether the current completed trace is feasible, except for pending
1658 * release sequences.
1660 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1662 return !is_infeasible() && promises->size() == 0;
1666 * Check if the current partial trace is infeasible. Does not check any
1667 * end-of-execution flags, which might rule out the execution. Thus, this is
1668 * useful only for ruling an execution as infeasible.
1669 * @return whether the current partial trace is infeasible.
1671 bool ModelChecker::is_infeasible() const
1673 return mo_graph->checkForCycles() ||
1674 priv->no_valid_reads ||
1675 priv->failed_promise ||
1676 priv->too_many_reads ||
1677 priv->bad_synchronization ||
1681 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1682 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1683 ModelAction *lastread = get_last_action(act->get_tid());
1684 lastread->process_rmw(act);
1685 if (act->is_rmw()) {
1686 if (lastread->get_reads_from())
1687 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1689 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1690 mo_graph->commitChanges();
1696 * A helper function for ModelChecker::check_recency, to check if the current
1697 * thread is able to read from a different write/promise for 'params.maxreads'
1698 * number of steps and if that write/promise should become visible (i.e., is
1699 * ordered later in the modification order). This helps model memory liveness.
1701 * @param curr The current action. Must be a read.
1702 * @param rf The write/promise from which we plan to read
1703 * @param other_rf The write/promise from which we may read
1704 * @return True if we were able to read from other_rf for params.maxreads steps
1706 template <typename T, typename U>
1707 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1709 /* Need a different write/promise */
1710 if (other_rf->equals(rf))
1713 /* Only look for "newer" writes/promises */
1714 if (!mo_graph->checkReachable(rf, other_rf))
1717 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1718 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1719 action_list_t::reverse_iterator rit = list->rbegin();
1720 ASSERT((*rit) == curr);
1721 /* Skip past curr */
1724 /* Does this write/promise work for everyone? */
1725 for (int i = 0; i < params.maxreads; i++, rit++) {
1726 ModelAction *act = *rit;
1727 if (!act->may_read_from(other_rf))
1734 * Checks whether a thread has read from the same write or Promise for too many
1735 * times without seeing the effects of a later write/Promise.
1738 * 1) there must a different write/promise that we could read from,
1739 * 2) we must have read from the same write/promise in excess of maxreads times,
1740 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1741 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1743 * If so, we decide that the execution is no longer feasible.
1745 * @param curr The current action. Must be a read.
1746 * @param rf The ModelAction/Promise from which we might read.
1747 * @return True if the read should succeed; false otherwise
1749 template <typename T>
1750 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1752 if (!params.maxreads)
1755 //NOTE: Next check is just optimization, not really necessary....
1756 if (curr->get_node()->get_read_from_past_size() +
1757 curr->get_node()->get_read_from_promise_size() <= 1)
1760 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1761 int tid = id_to_int(curr->get_tid());
1762 ASSERT(tid < (int)thrd_lists->size());
1763 action_list_t *list = &(*thrd_lists)[tid];
1764 action_list_t::reverse_iterator rit = list->rbegin();
1765 ASSERT((*rit) == curr);
1766 /* Skip past curr */
1769 action_list_t::reverse_iterator ritcopy = rit;
1770 /* See if we have enough reads from the same value */
1771 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1772 if (ritcopy == list->rend())
1774 ModelAction *act = *ritcopy;
1775 if (!act->is_read())
1777 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1779 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1781 if (act->get_node()->get_read_from_past_size() +
1782 act->get_node()->get_read_from_promise_size() <= 1)
1785 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1786 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1787 if (should_read_instead(curr, rf, write))
1788 return false; /* liveness failure */
1790 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1791 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1792 if (should_read_instead(curr, rf, promise))
1793 return false; /* liveness failure */
1799 * Updates the mo_graph with the constraints imposed from the current
1802 * Basic idea is the following: Go through each other thread and find
1803 * the last action that happened before our read. Two cases:
1805 * (1) The action is a write => that write must either occur before
1806 * the write we read from or be the write we read from.
1808 * (2) The action is a read => the write that that action read from
1809 * must occur before the write we read from or be the same write.
1811 * @param curr The current action. Must be a read.
1812 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1813 * @return True if modification order edges were added; false otherwise
1815 template <typename rf_type>
1816 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1818 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1821 ASSERT(curr->is_read());
1823 /* Last SC fence in the current thread */
1824 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1825 ModelAction *last_sc_write = NULL;
1826 if (curr->is_seqcst())
1827 last_sc_write = get_last_seq_cst_write(curr);
1829 /* Iterate over all threads */
1830 for (i = 0; i < thrd_lists->size(); i++) {
1831 /* Last SC fence in thread i */
1832 ModelAction *last_sc_fence_thread_local = NULL;
1833 if (int_to_id((int)i) != curr->get_tid())
1834 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1836 /* Last SC fence in thread i, before last SC fence in current thread */
1837 ModelAction *last_sc_fence_thread_before = NULL;
1838 if (last_sc_fence_local)
1839 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1841 /* Iterate over actions in thread, starting from most recent */
1842 action_list_t *list = &(*thrd_lists)[i];
1843 action_list_t::reverse_iterator rit;
1844 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1845 ModelAction *act = *rit;
1850 /* Don't want to add reflexive edges on 'rf' */
1851 if (act->equals(rf)) {
1852 if (act->happens_before(curr))
1858 if (act->is_write()) {
1859 /* C++, Section 29.3 statement 5 */
1860 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1861 *act < *last_sc_fence_thread_local) {
1862 added = mo_graph->addEdge(act, rf) || added;
1865 /* C++, Section 29.3 statement 4 */
1866 else if (act->is_seqcst() && last_sc_fence_local &&
1867 *act < *last_sc_fence_local) {
1868 added = mo_graph->addEdge(act, rf) || added;
1871 /* C++, Section 29.3 statement 6 */
1872 else if (last_sc_fence_thread_before &&
1873 *act < *last_sc_fence_thread_before) {
1874 added = mo_graph->addEdge(act, rf) || added;
1879 /* C++, Section 29.3 statement 3 (second subpoint) */
1880 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1881 added = mo_graph->addEdge(act, rf) || added;
1886 * Include at most one act per-thread that "happens
1889 if (act->happens_before(curr)) {
1890 if (act->is_write()) {
1891 added = mo_graph->addEdge(act, rf) || added;
1893 const ModelAction *prevrf = act->get_reads_from();
1894 const Promise *prevrf_promise = act->get_reads_from_promise();
1896 if (!prevrf->equals(rf))
1897 added = mo_graph->addEdge(prevrf, rf) || added;
1898 } else if (!prevrf_promise->equals(rf)) {
1899 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1908 * All compatible, thread-exclusive promises must be ordered after any
1909 * concrete loads from the same thread
1911 for (unsigned int i = 0; i < promises->size(); i++)
1912 if ((*promises)[i]->is_compatible_exclusive(curr))
1913 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1919 * Updates the mo_graph with the constraints imposed from the current write.
1921 * Basic idea is the following: Go through each other thread and find
1922 * the lastest action that happened before our write. Two cases:
1924 * (1) The action is a write => that write must occur before
1927 * (2) The action is a read => the write that that action read from
1928 * must occur before the current write.
1930 * This method also handles two other issues:
1932 * (I) Sequential Consistency: Making sure that if the current write is
1933 * seq_cst, that it occurs after the previous seq_cst write.
1935 * (II) Sending the write back to non-synchronizing reads.
1937 * @param curr The current action. Must be a write.
1938 * @param send_fv A vector for stashing reads to which we may pass our future
1939 * value. If NULL, then don't record any future values.
1940 * @return True if modification order edges were added; false otherwise
1942 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1944 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1947 ASSERT(curr->is_write());
1949 if (curr->is_seqcst()) {
1950 /* We have to at least see the last sequentially consistent write,
1951 so we are initialized. */
1952 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1953 if (last_seq_cst != NULL) {
1954 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1958 /* Last SC fence in the current thread */
1959 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1961 /* Iterate over all threads */
1962 for (i = 0; i < thrd_lists->size(); i++) {
1963 /* Last SC fence in thread i, before last SC fence in current thread */
1964 ModelAction *last_sc_fence_thread_before = NULL;
1965 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1966 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1968 /* Iterate over actions in thread, starting from most recent */
1969 action_list_t *list = &(*thrd_lists)[i];
1970 action_list_t::reverse_iterator rit;
1971 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1972 ModelAction *act = *rit;
1975 * 1) If RMW and it actually read from something, then we
1976 * already have all relevant edges, so just skip to next
1979 * 2) If RMW and it didn't read from anything, we should
1980 * whatever edge we can get to speed up convergence.
1982 * 3) If normal write, we need to look at earlier actions, so
1983 * continue processing list.
1985 if (curr->is_rmw()) {
1986 if (curr->get_reads_from() != NULL)
1994 /* C++, Section 29.3 statement 7 */
1995 if (last_sc_fence_thread_before && act->is_write() &&
1996 *act < *last_sc_fence_thread_before) {
1997 added = mo_graph->addEdge(act, curr) || added;
2002 * Include at most one act per-thread that "happens
2005 if (act->happens_before(curr)) {
2007 * Note: if act is RMW, just add edge:
2009 * The following edge should be handled elsewhere:
2010 * readfrom(act) --mo--> act
2012 if (act->is_write())
2013 added = mo_graph->addEdge(act, curr) || added;
2014 else if (act->is_read()) {
2015 //if previous read accessed a null, just keep going
2016 if (act->get_reads_from() == NULL)
2018 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2021 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2022 !act->same_thread(curr)) {
2023 /* We have an action that:
2024 (1) did not happen before us
2025 (2) is a read and we are a write
2026 (3) cannot synchronize with us
2027 (4) is in a different thread
2029 that read could potentially read from our write. Note that
2030 these checks are overly conservative at this point, we'll
2031 do more checks before actually removing the
2035 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2036 if (!is_infeasible())
2037 send_fv->push_back(act);
2038 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2039 add_future_value(curr, act);
2046 * All compatible, thread-exclusive promises must be ordered after any
2047 * concrete stores to the same thread, or else they can be merged with
2050 for (unsigned int i = 0; i < promises->size(); i++)
2051 if ((*promises)[i]->is_compatible_exclusive(curr))
2052 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2057 /** Arbitrary reads from the future are not allowed. Section 29.3
2058 * part 9 places some constraints. This method checks one result of constraint
2059 * constraint. Others require compiler support. */
2060 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2062 if (!writer->is_rmw())
2065 if (!reader->is_rmw())
2068 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2069 if (search == reader)
2071 if (search->get_tid() == reader->get_tid() &&
2072 search->happens_before(reader))
2080 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2081 * some constraints. This method checks one the following constraint (others
2082 * require compiler support):
2084 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2086 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2088 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2090 /* Iterate over all threads */
2091 for (i = 0; i < thrd_lists->size(); i++) {
2092 const ModelAction *write_after_read = NULL;
2094 /* Iterate over actions in thread, starting from most recent */
2095 action_list_t *list = &(*thrd_lists)[i];
2096 action_list_t::reverse_iterator rit;
2097 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2098 ModelAction *act = *rit;
2100 /* Don't disallow due to act == reader */
2101 if (!reader->happens_before(act) || reader == act)
2103 else if (act->is_write())
2104 write_after_read = act;
2105 else if (act->is_read() && act->get_reads_from() != NULL)
2106 write_after_read = act->get_reads_from();
2109 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2116 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2117 * The ModelAction under consideration is expected to be taking part in
2118 * release/acquire synchronization as an object of the "reads from" relation.
2119 * Note that this can only provide release sequence support for RMW chains
2120 * which do not read from the future, as those actions cannot be traced until
2121 * their "promise" is fulfilled. Similarly, we may not even establish the
2122 * presence of a release sequence with certainty, as some modification order
2123 * constraints may be decided further in the future. Thus, this function
2124 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2125 * and a boolean representing certainty.
2127 * @param rf The action that might be part of a release sequence. Must be a
2129 * @param release_heads A pass-by-reference style return parameter. After
2130 * execution of this function, release_heads will contain the heads of all the
2131 * relevant release sequences, if any exists with certainty
2132 * @param pending A pass-by-reference style return parameter which is only used
2133 * when returning false (i.e., uncertain). Returns most information regarding
2134 * an uncertain release sequence, including any write operations that might
2135 * break the sequence.
2136 * @return true, if the ModelChecker is certain that release_heads is complete;
2139 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2140 rel_heads_list_t *release_heads,
2141 struct release_seq *pending) const
2143 /* Only check for release sequences if there are no cycles */
2144 if (mo_graph->checkForCycles())
2147 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2148 ASSERT(rf->is_write());
2150 if (rf->is_release())
2151 release_heads->push_back(rf);
2152 else if (rf->get_last_fence_release())
2153 release_heads->push_back(rf->get_last_fence_release());
2155 break; /* End of RMW chain */
2157 /** @todo Need to be smarter here... In the linux lock
2158 * example, this will run to the beginning of the program for
2160 /** @todo The way to be smarter here is to keep going until 1
2161 * thread has a release preceded by an acquire and you've seen
2164 /* acq_rel RMW is a sufficient stopping condition */
2165 if (rf->is_acquire() && rf->is_release())
2166 return true; /* complete */
2169 /* read from future: need to settle this later */
2171 return false; /* incomplete */
2174 if (rf->is_release())
2175 return true; /* complete */
2177 /* else relaxed write
2178 * - check for fence-release in the same thread (29.8, stmt. 3)
2179 * - check modification order for contiguous subsequence
2180 * -> rf must be same thread as release */
2182 const ModelAction *fence_release = rf->get_last_fence_release();
2183 /* Synchronize with a fence-release unconditionally; we don't need to
2184 * find any more "contiguous subsequence..." for it */
2186 release_heads->push_back(fence_release);
2188 int tid = id_to_int(rf->get_tid());
2189 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2190 action_list_t *list = &(*thrd_lists)[tid];
2191 action_list_t::const_reverse_iterator rit;
2193 /* Find rf in the thread list */
2194 rit = std::find(list->rbegin(), list->rend(), rf);
2195 ASSERT(rit != list->rend());
2197 /* Find the last {write,fence}-release */
2198 for (; rit != list->rend(); rit++) {
2199 if (fence_release && *(*rit) < *fence_release)
2201 if ((*rit)->is_release())
2204 if (rit == list->rend()) {
2205 /* No write-release in this thread */
2206 return true; /* complete */
2207 } else if (fence_release && *(*rit) < *fence_release) {
2208 /* The fence-release is more recent (and so, "stronger") than
2209 * the most recent write-release */
2210 return true; /* complete */
2211 } /* else, need to establish contiguous release sequence */
2212 ModelAction *release = *rit;
2214 ASSERT(rf->same_thread(release));
2216 pending->writes.clear();
2218 bool certain = true;
2219 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2220 if (id_to_int(rf->get_tid()) == (int)i)
2222 list = &(*thrd_lists)[i];
2224 /* Can we ensure no future writes from this thread may break
2225 * the release seq? */
2226 bool future_ordered = false;
2228 ModelAction *last = get_last_action(int_to_id(i));
2229 Thread *th = get_thread(int_to_id(i));
2230 if ((last && rf->happens_before(last)) ||
2233 future_ordered = true;
2235 ASSERT(!th->is_model_thread() || future_ordered);
2237 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2238 const ModelAction *act = *rit;
2239 /* Reach synchronization -> this thread is complete */
2240 if (act->happens_before(release))
2242 if (rf->happens_before(act)) {
2243 future_ordered = true;
2247 /* Only non-RMW writes can break release sequences */
2248 if (!act->is_write() || act->is_rmw())
2251 /* Check modification order */
2252 if (mo_graph->checkReachable(rf, act)) {
2253 /* rf --mo--> act */
2254 future_ordered = true;
2257 if (mo_graph->checkReachable(act, release))
2258 /* act --mo--> release */
2260 if (mo_graph->checkReachable(release, act) &&
2261 mo_graph->checkReachable(act, rf)) {
2262 /* release --mo-> act --mo--> rf */
2263 return true; /* complete */
2265 /* act may break release sequence */
2266 pending->writes.push_back(act);
2269 if (!future_ordered)
2270 certain = false; /* This thread is uncertain */
2274 release_heads->push_back(release);
2275 pending->writes.clear();
2277 pending->release = release;
2284 * An interface for getting the release sequence head(s) with which a
2285 * given ModelAction must synchronize. This function only returns a non-empty
2286 * result when it can locate a release sequence head with certainty. Otherwise,
2287 * it may mark the internal state of the ModelChecker so that it will handle
2288 * the release sequence at a later time, causing @a acquire to update its
2289 * synchronization at some later point in execution.
2291 * @param acquire The 'acquire' action that may synchronize with a release
2293 * @param read The read action that may read from a release sequence; this may
2294 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2295 * when 'acquire' is a fence-acquire)
2296 * @param release_heads A pass-by-reference return parameter. Will be filled
2297 * with the head(s) of the release sequence(s), if they exists with certainty.
2298 * @see ModelChecker::release_seq_heads
2300 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2301 ModelAction *read, rel_heads_list_t *release_heads)
2303 const ModelAction *rf = read->get_reads_from();
2304 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2305 sequence->acquire = acquire;
2306 sequence->read = read;
2308 if (!release_seq_heads(rf, release_heads, sequence)) {
2309 /* add act to 'lazy checking' list */
2310 pending_rel_seqs->push_back(sequence);
2312 snapshot_free(sequence);
2317 * Attempt to resolve all stashed operations that might synchronize with a
2318 * release sequence for a given location. This implements the "lazy" portion of
2319 * determining whether or not a release sequence was contiguous, since not all
2320 * modification order information is present at the time an action occurs.
2322 * @param location The location/object that should be checked for release
2323 * sequence resolutions. A NULL value means to check all locations.
2324 * @param work_queue The work queue to which to add work items as they are
2326 * @return True if any updates occurred (new synchronization, new mo_graph
2329 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2331 bool updated = false;
2332 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2333 while (it != pending_rel_seqs->end()) {
2334 struct release_seq *pending = *it;
2335 ModelAction *acquire = pending->acquire;
2336 const ModelAction *read = pending->read;
2338 /* Only resolve sequences on the given location, if provided */
2339 if (location && read->get_location() != location) {
2344 const ModelAction *rf = read->get_reads_from();
2345 rel_heads_list_t release_heads;
2347 complete = release_seq_heads(rf, &release_heads, pending);
2348 for (unsigned int i = 0; i < release_heads.size(); i++) {
2349 if (!acquire->has_synchronized_with(release_heads[i])) {
2350 if (acquire->synchronize_with(release_heads[i]))
2353 set_bad_synchronization();
2358 /* Re-check all pending release sequences */
2359 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2360 /* Re-check read-acquire for mo_graph edges */
2361 if (acquire->is_read())
2362 work_queue->push_back(MOEdgeWorkEntry(acquire));
2364 /* propagate synchronization to later actions */
2365 action_list_t::reverse_iterator rit = action_trace->rbegin();
2366 for (; (*rit) != acquire; rit++) {
2367 ModelAction *propagate = *rit;
2368 if (acquire->happens_before(propagate)) {
2369 propagate->synchronize_with(acquire);
2370 /* Re-check 'propagate' for mo_graph edges */
2371 work_queue->push_back(MOEdgeWorkEntry(propagate));
2376 it = pending_rel_seqs->erase(it);
2377 snapshot_free(pending);
2383 // If we resolved promises or data races, see if we have realized a data race.
2390 * Performs various bookkeeping operations for the current ModelAction. For
2391 * instance, adds action to the per-object, per-thread action vector and to the
2392 * action trace list of all thread actions.
2394 * @param act is the ModelAction to add.
2396 void ModelChecker::add_action_to_lists(ModelAction *act)
2398 int tid = id_to_int(act->get_tid());
2399 ModelAction *uninit = NULL;
2401 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2402 if (list->empty() && act->is_atomic_var()) {
2403 uninit = get_uninitialized_action(act);
2404 uninit_id = id_to_int(uninit->get_tid());
2405 list->push_front(uninit);
2407 list->push_back(act);
2409 action_trace->push_back(act);
2411 action_trace->push_front(uninit);
2413 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2414 if (tid >= (int)vec->size())
2415 vec->resize(priv->next_thread_id);
2416 (*vec)[tid].push_back(act);
2418 (*vec)[uninit_id].push_front(uninit);
2420 if ((int)thrd_last_action->size() <= tid)
2421 thrd_last_action->resize(get_num_threads());
2422 (*thrd_last_action)[tid] = act;
2424 (*thrd_last_action)[uninit_id] = uninit;
2426 if (act->is_fence() && act->is_release()) {
2427 if ((int)thrd_last_fence_release->size() <= tid)
2428 thrd_last_fence_release->resize(get_num_threads());
2429 (*thrd_last_fence_release)[tid] = act;
2432 if (act->is_wait()) {
2433 void *mutex_loc = (void *) act->get_value();
2434 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2436 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2437 if (tid >= (int)vec->size())
2438 vec->resize(priv->next_thread_id);
2439 (*vec)[tid].push_back(act);
2444 * @brief Get the last action performed by a particular Thread
2445 * @param tid The thread ID of the Thread in question
2446 * @return The last action in the thread
2448 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2450 int threadid = id_to_int(tid);
2451 if (threadid < (int)thrd_last_action->size())
2452 return (*thrd_last_action)[id_to_int(tid)];
2458 * @brief Get the last fence release performed by a particular Thread
2459 * @param tid The thread ID of the Thread in question
2460 * @return The last fence release in the thread, if one exists; NULL otherwise
2462 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2464 int threadid = id_to_int(tid);
2465 if (threadid < (int)thrd_last_fence_release->size())
2466 return (*thrd_last_fence_release)[id_to_int(tid)];
2472 * Gets the last memory_order_seq_cst write (in the total global sequence)
2473 * performed on a particular object (i.e., memory location), not including the
2475 * @param curr The current ModelAction; also denotes the object location to
2477 * @return The last seq_cst write
2479 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2481 void *location = curr->get_location();
2482 action_list_t *list = get_safe_ptr_action(obj_map, location);
2483 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2484 action_list_t::reverse_iterator rit;
2485 for (rit = list->rbegin(); (*rit) != curr; rit++)
2487 rit++; /* Skip past curr */
2488 for ( ; rit != list->rend(); rit++)
2489 if ((*rit)->is_write() && (*rit)->is_seqcst())
2495 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2496 * performed in a particular thread, prior to a particular fence.
2497 * @param tid The ID of the thread to check
2498 * @param before_fence The fence from which to begin the search; if NULL, then
2499 * search for the most recent fence in the thread.
2500 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2502 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2504 /* All fences should have NULL location */
2505 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2506 action_list_t::reverse_iterator rit = list->rbegin();
2509 for (; rit != list->rend(); rit++)
2510 if (*rit == before_fence)
2513 ASSERT(*rit == before_fence);
2517 for (; rit != list->rend(); rit++)
2518 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2524 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2525 * location). This function identifies the mutex according to the current
2526 * action, which is presumed to perform on the same mutex.
2527 * @param curr The current ModelAction; also denotes the object location to
2529 * @return The last unlock operation
2531 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2533 void *location = curr->get_location();
2534 action_list_t *list = get_safe_ptr_action(obj_map, location);
2535 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2536 action_list_t::reverse_iterator rit;
2537 for (rit = list->rbegin(); rit != list->rend(); rit++)
2538 if ((*rit)->is_unlock() || (*rit)->is_wait())
2543 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2545 ModelAction *parent = get_last_action(tid);
2547 parent = get_thread(tid)->get_creation();
2552 * Returns the clock vector for a given thread.
2553 * @param tid The thread whose clock vector we want
2554 * @return Desired clock vector
2556 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2558 return get_parent_action(tid)->get_cv();
2562 * @brief Find the promise (if any) to resolve for the current action and
2563 * remove it from the pending promise vector
2564 * @param curr The current ModelAction. Should be a write.
2565 * @return The Promise to resolve, if any; otherwise NULL
2567 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2569 for (unsigned int i = 0; i < promises->size(); i++)
2570 if (curr->get_node()->get_promise(i)) {
2571 Promise *ret = (*promises)[i];
2572 promises->erase(promises->begin() + i);
2579 * Resolve a Promise with a current write.
2580 * @param write The ModelAction that is fulfilling Promises
2581 * @param promise The Promise to resolve
2582 * @return True if the Promise was successfully resolved; false otherwise
2584 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2586 ModelVector<ModelAction *> actions_to_check;
2588 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2589 ModelAction *read = promise->get_reader(i);
2590 read_from(read, write);
2591 actions_to_check.push_back(read);
2593 /* Make sure the promise's value matches the write's value */
2594 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2595 if (!mo_graph->resolvePromise(promise, write))
2596 priv->failed_promise = true;
2599 * @todo It is possible to end up in an inconsistent state, where a
2600 * "resolved" promise may still be referenced if
2601 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2603 * Note that the inconsistency only matters when dumping mo_graph to
2609 //Check whether reading these writes has made threads unable to
2611 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2612 ModelAction *read = actions_to_check[i];
2613 mo_check_promises(read, true);
2620 * Compute the set of promises that could potentially be satisfied by this
2621 * action. Note that the set computation actually appears in the Node, not in
2623 * @param curr The ModelAction that may satisfy promises
2625 void ModelChecker::compute_promises(ModelAction *curr)
2627 for (unsigned int i = 0; i < promises->size(); i++) {
2628 Promise *promise = (*promises)[i];
2629 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2632 bool satisfy = true;
2633 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2634 const ModelAction *act = promise->get_reader(j);
2635 if (act->happens_before(curr) ||
2636 act->could_synchronize_with(curr)) {
2642 curr->get_node()->set_promise(i);
2646 /** Checks promises in response to change in ClockVector Threads. */
2647 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2649 for (unsigned int i = 0; i < promises->size(); i++) {
2650 Promise *promise = (*promises)[i];
2651 if (!promise->thread_is_available(tid))
2653 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2654 const ModelAction *act = promise->get_reader(j);
2655 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2656 merge_cv->synchronized_since(act)) {
2657 if (promise->eliminate_thread(tid)) {
2658 /* Promise has failed */
2659 priv->failed_promise = true;
2667 void ModelChecker::check_promises_thread_disabled()
2669 for (unsigned int i = 0; i < promises->size(); i++) {
2670 Promise *promise = (*promises)[i];
2671 if (promise->has_failed()) {
2672 priv->failed_promise = true;
2679 * @brief Checks promises in response to addition to modification order for
2682 * We test whether threads are still available for satisfying promises after an
2683 * addition to our modification order constraints. Those that are unavailable
2684 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2685 * that promise has failed.
2687 * @param act The ModelAction which updated the modification order
2688 * @param is_read_check Should be true if act is a read and we must check for
2689 * updates to the store from which it read (there is a distinction here for
2690 * RMW's, which are both a load and a store)
2692 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2694 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2696 for (unsigned int i = 0; i < promises->size(); i++) {
2697 Promise *promise = (*promises)[i];
2699 // Is this promise on the same location?
2700 if (!promise->same_location(write))
2703 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2704 const ModelAction *pread = promise->get_reader(j);
2705 if (!pread->happens_before(act))
2707 if (mo_graph->checkPromise(write, promise)) {
2708 priv->failed_promise = true;
2714 // Don't do any lookups twice for the same thread
2715 if (!promise->thread_is_available(act->get_tid()))
2718 if (mo_graph->checkReachable(promise, write)) {
2719 if (mo_graph->checkPromise(write, promise)) {
2720 priv->failed_promise = true;
2728 * Compute the set of writes that may break the current pending release
2729 * sequence. This information is extracted from previou release sequence
2732 * @param curr The current ModelAction. Must be a release sequence fixup
2735 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2737 if (pending_rel_seqs->empty())
2740 struct release_seq *pending = pending_rel_seqs->back();
2741 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2742 const ModelAction *write = pending->writes[i];
2743 curr->get_node()->add_relseq_break(write);
2746 /* NULL means don't break the sequence; just synchronize */
2747 curr->get_node()->add_relseq_break(NULL);
2751 * Build up an initial set of all past writes that this 'read' action may read
2752 * from, as well as any previously-observed future values that must still be valid.
2754 * @param curr is the current ModelAction that we are exploring; it must be a
2757 void ModelChecker::build_may_read_from(ModelAction *curr)
2759 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2761 ASSERT(curr->is_read());
2763 ModelAction *last_sc_write = NULL;
2765 if (curr->is_seqcst())
2766 last_sc_write = get_last_seq_cst_write(curr);
2768 /* Iterate over all threads */
2769 for (i = 0; i < thrd_lists->size(); i++) {
2770 /* Iterate over actions in thread, starting from most recent */
2771 action_list_t *list = &(*thrd_lists)[i];
2772 action_list_t::reverse_iterator rit;
2773 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2774 ModelAction *act = *rit;
2776 /* Only consider 'write' actions */
2777 if (!act->is_write() || act == curr)
2780 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2781 bool allow_read = true;
2783 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2785 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2789 /* Only add feasible reads */
2790 mo_graph->startChanges();
2791 r_modification_order(curr, act);
2792 if (!is_infeasible())
2793 curr->get_node()->add_read_from_past(act);
2794 mo_graph->rollbackChanges();
2797 /* Include at most one act per-thread that "happens before" curr */
2798 if (act->happens_before(curr))
2803 /* Inherit existing, promised future values */
2804 for (i = 0; i < promises->size(); i++) {
2805 const Promise *promise = (*promises)[i];
2806 const ModelAction *promise_read = promise->get_reader(0);
2807 if (promise_read->same_var(curr)) {
2808 /* Only add feasible future-values */
2809 mo_graph->startChanges();
2810 r_modification_order(curr, promise);
2811 if (!is_infeasible())
2812 curr->get_node()->add_read_from_promise(promise_read);
2813 mo_graph->rollbackChanges();
2817 /* We may find no valid may-read-from only if the execution is doomed */
2818 if (!curr->get_node()->read_from_size()) {
2819 priv->no_valid_reads = true;
2823 if (DBG_ENABLED()) {
2824 model_print("Reached read action:\n");
2826 model_print("Printing read_from_past\n");
2827 curr->get_node()->print_read_from_past();
2828 model_print("End printing read_from_past\n");
2832 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2834 for ( ; write != NULL; write = write->get_reads_from()) {
2835 /* UNINIT actions don't have a Node, and they never sleep */
2836 if (write->is_uninitialized())
2838 Node *prevnode = write->get_node()->get_parent();
2840 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2841 if (write->is_release() && thread_sleep)
2843 if (!write->is_rmw())
2850 * @brief Get an action representing an uninitialized atomic
2852 * This function may create a new one or try to retrieve one from the NodeStack
2854 * @param curr The current action, which prompts the creation of an UNINIT action
2855 * @return A pointer to the UNINIT ModelAction
2857 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2859 Node *node = curr->get_node();
2860 ModelAction *act = node->get_uninit_action();
2862 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2863 node->set_uninit_action(act);
2865 act->create_cv(NULL);
2869 static void print_list(action_list_t *list)
2871 action_list_t::iterator it;
2873 model_print("---------------------------------------------------------------------\n");
2875 unsigned int hash = 0;
2877 for (it = list->begin(); it != list->end(); it++) {
2878 const ModelAction *act = *it;
2879 if (act->get_seq_number() > 0)
2881 hash = hash^(hash<<3)^((*it)->hash());
2883 model_print("HASH %u\n", hash);
2884 model_print("---------------------------------------------------------------------\n");
2887 #if SUPPORT_MOD_ORDER_DUMP
2888 void ModelChecker::dumpGraph(char *filename) const
2891 sprintf(buffer, "%s.dot", filename);
2892 FILE *file = fopen(buffer, "w");
2893 fprintf(file, "digraph %s {\n", filename);
2894 mo_graph->dumpNodes(file);
2895 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2897 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2898 ModelAction *act = *it;
2899 if (act->is_read()) {
2900 mo_graph->dot_print_node(file, act);
2901 if (act->get_reads_from())
2902 mo_graph->dot_print_edge(file,
2903 act->get_reads_from(),
2905 "label=\"rf\", color=red, weight=2");
2907 mo_graph->dot_print_edge(file,
2908 act->get_reads_from_promise(),
2910 "label=\"rf\", color=red");
2912 if (thread_array[act->get_tid()]) {
2913 mo_graph->dot_print_edge(file,
2914 thread_array[id_to_int(act->get_tid())],
2916 "label=\"sb\", color=blue, weight=400");
2919 thread_array[act->get_tid()] = act;
2921 fprintf(file, "}\n");
2922 model_free(thread_array);
2927 /** @brief Prints an execution trace summary. */
2928 void ModelChecker::print_summary() const
2930 #if SUPPORT_MOD_ORDER_DUMP
2931 char buffername[100];
2932 sprintf(buffername, "exec%04u", stats.num_total);
2933 mo_graph->dumpGraphToFile(buffername);
2934 sprintf(buffername, "graph%04u", stats.num_total);
2935 dumpGraph(buffername);
2938 model_print("Execution %d:", stats.num_total);
2939 if (isfeasibleprefix()) {
2940 if (scheduler->all_threads_sleeping())
2941 model_print(" SLEEP-SET REDUNDANT");
2944 print_infeasibility(" INFEASIBLE");
2945 print_list(action_trace);
2947 if (!promises->empty()) {
2948 model_print("Pending promises:\n");
2949 for (unsigned int i = 0; i < promises->size(); i++) {
2950 model_print(" [P%u] ", i);
2951 (*promises)[i]->print();
2958 * Add a Thread to the system for the first time. Should only be called once
2960 * @param t The Thread to add
2962 void ModelChecker::add_thread(Thread *t)
2964 thread_map->put(id_to_int(t->get_id()), t);
2965 scheduler->add_thread(t);
2969 * @brief Get a Thread reference by its ID
2970 * @param tid The Thread's ID
2971 * @return A Thread reference
2973 Thread * ModelChecker::get_thread(thread_id_t tid) const
2975 return thread_map->get(id_to_int(tid));
2979 * @brief Get a reference to the Thread in which a ModelAction was executed
2980 * @param act The ModelAction
2981 * @return A Thread reference
2983 Thread * ModelChecker::get_thread(const ModelAction *act) const
2985 return get_thread(act->get_tid());
2989 * @brief Get a Promise's "promise number"
2991 * A "promise number" is an index number that is unique to a promise, valid
2992 * only for a specific snapshot of an execution trace. Promises may come and go
2993 * as they are generated an resolved, so an index only retains meaning for the
2996 * @param promise The Promise to check
2997 * @return The promise index, if the promise still is valid; otherwise -1
2999 int ModelChecker::get_promise_number(const Promise *promise) const
3001 for (unsigned int i = 0; i < promises->size(); i++)
3002 if ((*promises)[i] == promise)
3009 * @brief Check if a Thread is currently enabled
3010 * @param t The Thread to check
3011 * @return True if the Thread is currently enabled
3013 bool ModelChecker::is_enabled(Thread *t) const
3015 return scheduler->is_enabled(t);
3019 * @brief Check if a Thread is currently enabled
3020 * @param tid The ID of the Thread to check
3021 * @return True if the Thread is currently enabled
3023 bool ModelChecker::is_enabled(thread_id_t tid) const
3025 return scheduler->is_enabled(tid);
3029 * Switch from a model-checker context to a user-thread context. This is the
3030 * complement of ModelChecker::switch_to_master and must be called from the
3031 * model-checker context
3033 * @param thread The user-thread to switch to
3035 void ModelChecker::switch_from_master(Thread *thread)
3037 scheduler->set_current_thread(thread);
3038 Thread::swap(&system_context, thread);
3042 * Switch from a user-context to the "master thread" context (a.k.a. system
3043 * context). This switch is made with the intention of exploring a particular
3044 * model-checking action (described by a ModelAction object). Must be called
3045 * from a user-thread context.
3047 * @param act The current action that will be explored. May be NULL only if
3048 * trace is exiting via an assertion (see ModelChecker::set_assert and
3049 * ModelChecker::has_asserted).
3050 * @return Return the value returned by the current action
3052 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3055 Thread *old = thread_current();
3056 scheduler->set_current_thread(NULL);
3057 ASSERT(!old->get_pending());
3058 old->set_pending(act);
3059 if (Thread::swap(old, &system_context) < 0) {
3060 perror("swap threads");
3063 return old->get_return_value();
3067 * Takes the next step in the execution, if possible.
3068 * @param curr The current step to take
3069 * @return Returns the next Thread to run, if any; NULL if this execution
3072 Thread * ModelChecker::take_step(ModelAction *curr)
3074 Thread *curr_thrd = get_thread(curr);
3075 ASSERT(curr_thrd->get_state() == THREAD_READY);
3077 ASSERT(check_action_enabled(curr)); /* May have side effects? */
3078 curr = check_current_action(curr);
3081 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3082 scheduler->remove_thread(curr_thrd);
3084 return action_select_next_thread(curr);
3087 /** Wrapper to run the user's main function, with appropriate arguments */
3088 void user_main_wrapper(void *)
3090 user_main(model->params.argc, model->params.argv);
3093 bool ModelChecker::should_terminate_execution()
3095 /* Infeasible -> don't take any more steps */
3096 if (is_infeasible())
3098 else if (isfeasibleprefix() && have_bug_reports()) {
3103 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3108 /** @brief Run ModelChecker for the user program */
3109 void ModelChecker::run()
3113 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3118 * Stash next pending action(s) for thread(s). There
3119 * should only need to stash one thread's action--the
3120 * thread which just took a step--plus the first step
3121 * for any newly-created thread
3123 for (unsigned int i = 0; i < get_num_threads(); i++) {
3124 thread_id_t tid = int_to_id(i);
3125 Thread *thr = get_thread(tid);
3126 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3127 switch_from_master(thr);
3128 if (thr->is_waiting_on(thr))
3129 assert_bug("Deadlock detected (thread %u)", i);
3133 /* Don't schedule threads which should be disabled */
3134 for (unsigned int i = 0; i < get_num_threads(); i++) {
3135 Thread *th = get_thread(int_to_id(i));
3136 ModelAction *act = th->get_pending();
3137 if (act && is_enabled(th) && !check_action_enabled(act)) {
3138 scheduler->sleep(th);
3142 /* Catch assertions from prior take_step or from
3143 * between-ModelAction bugs (e.g., data races) */
3148 t = get_next_thread();
3149 if (!t || t->is_model_thread())
3152 /* Consume the next action for a Thread */
3153 ModelAction *curr = t->get_pending();
3154 t->set_pending(NULL);
3155 t = take_step(curr);
3156 } while (!should_terminate_execution());
3159 * Launch end-of-execution release sequence fixups only when
3160 * the execution is otherwise feasible AND there are:
3162 * (1) pending release sequences
3163 * (2) pending assertions that could be invalidated by a change
3164 * in clock vectors (i.e., data races)
3165 * (3) no pending promises
3167 while (!pending_rel_seqs->empty() &&
3168 is_feasible_prefix_ignore_relseq() &&
3169 !unrealizedraces.empty()) {
3170 model_print("*** WARNING: release sequence fixup action "
3171 "(%zu pending release seuqence(s)) ***\n",
3172 pending_rel_seqs->size());
3173 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3174 std::memory_order_seq_cst, NULL, VALUE_NONE,
3178 } while (next_execution());
3180 model_print("******* Model-checking complete: *******\n");