10 #include "snapshot-interface.h"
12 #include "clockvector.h"
13 #include "cyclegraph.h"
16 #include "threads-model.h"
19 #define INITIAL_THREAD_ID 0
24 bug_message(const char *str) {
25 const char *fmt = " [BUG] %s\n";
26 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
27 sprintf(msg, fmt, str);
29 ~bug_message() { if (msg) snapshot_free(msg); }
32 void print() { model_print("%s", msg); }
38 * Structure for holding small ModelChecker members that should be snapshotted
40 struct model_snapshot_members {
41 model_snapshot_members() :
42 /* First thread created will have id INITIAL_THREAD_ID */
43 next_thread_id(INITIAL_THREAD_ID),
44 used_sequence_numbers(0),
48 failed_promise(false),
49 too_many_reads(false),
50 no_valid_reads(false),
51 bad_synchronization(false),
55 ~model_snapshot_members() {
56 for (unsigned int i = 0; i < bugs.size(); i++)
61 unsigned int next_thread_id;
62 modelclock_t used_sequence_numbers;
63 ModelAction *next_backtrack;
64 std::vector< bug_message *, SnapshotAlloc<bug_message *> > bugs;
65 struct execution_stats stats;
69 /** @brief Incorrectly-ordered synchronization was made */
70 bool bad_synchronization;
76 /** @brief Constructor */
77 ModelChecker::ModelChecker(struct model_params params) :
78 /* Initialize default scheduler */
80 scheduler(new Scheduler()),
82 earliest_diverge(NULL),
83 action_trace(new action_list_t()),
84 thread_map(new HashTable<int, Thread *, int>()),
85 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
86 lock_waiters_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 *, std::vector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
90 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
91 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
92 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
93 thrd_last_fence_release(new std::vector< ModelAction *, SnapshotAlloc<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 lock_waiters_map;
113 delete condvar_waiters_map;
116 for (unsigned int i = 0; i < promises->size(); i++)
117 delete (*promises)[i];
120 delete pending_rel_seqs;
122 delete thrd_last_action;
123 delete thrd_last_fence_release;
130 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
132 action_list_t *tmp = hash->get(ptr);
134 tmp = new action_list_t();
140 static std::vector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
142 std::vector<action_list_t> *tmp = hash->get(ptr);
144 tmp = new std::vector<action_list_t>();
151 * Restores user program to initial state and resets all model-checker data
154 void ModelChecker::reset_to_initial_state()
156 DEBUG("+++ Resetting to initial state +++\n");
157 node_stack->reset_execution();
159 /* Print all model-checker output before rollback */
163 * FIXME: if we utilize partial rollback, we will need to free only
164 * those pending actions which were NOT pending before the rollback
167 for (unsigned int i = 0; i < get_num_threads(); i++)
168 delete get_thread(int_to_id(i))->get_pending();
170 snapshot_backtrack_before(0);
173 /** @return a thread ID for a new Thread */
174 thread_id_t ModelChecker::get_next_id()
176 return priv->next_thread_id++;
179 /** @return the number of user threads created during this execution */
180 unsigned int ModelChecker::get_num_threads() const
182 return priv->next_thread_id;
186 * Must be called from user-thread context (e.g., through the global
187 * thread_current() interface)
189 * @return The currently executing Thread.
191 Thread * ModelChecker::get_current_thread() const
193 return scheduler->get_current_thread();
196 /** @return a sequence number for a new ModelAction */
197 modelclock_t ModelChecker::get_next_seq_num()
199 return ++priv->used_sequence_numbers;
202 Node * ModelChecker::get_curr_node() const
204 return node_stack->get_head();
208 * @brief Choose the next thread to execute.
210 * This function chooses the next thread that should execute. It can force the
211 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
212 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
213 * The model-checker may have no preference regarding the next thread (i.e.,
214 * when exploring a new execution ordering), in which case we defer to the
217 * @param curr Optional: The current ModelAction. Only used if non-NULL and it
218 * might guide the choice of next thread (i.e., THREAD_CREATE should be
219 * followed by THREAD_START, or ATOMIC_RMWR followed by ATOMIC_{RMW,RMWC})
220 * @return The next chosen thread to run, if any exist. Or else if no threads
221 * remain to be executed, return NULL.
223 Thread * ModelChecker::get_next_thread(ModelAction *curr)
228 /* Do not split atomic actions. */
230 return get_thread(curr);
231 else if (curr->get_type() == THREAD_CREATE)
232 return curr->get_thread_operand();
236 * Have we completed exploring the preselected path? Then let the
240 return scheduler->select_next_thread();
242 /* Else, we are trying to replay an execution */
243 ModelAction *next = node_stack->get_next()->get_action();
245 if (next == diverge) {
246 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
247 earliest_diverge = diverge;
249 Node *nextnode = next->get_node();
250 Node *prevnode = nextnode->get_parent();
251 scheduler->update_sleep_set(prevnode);
253 /* Reached divergence point */
254 if (nextnode->increment_misc()) {
255 /* The next node will try to satisfy a different misc_index values. */
256 tid = next->get_tid();
257 node_stack->pop_restofstack(2);
258 } else if (nextnode->increment_promise()) {
259 /* The next node will try to satisfy a different set of promises. */
260 tid = next->get_tid();
261 node_stack->pop_restofstack(2);
262 } else if (nextnode->increment_read_from()) {
263 /* The next node will read from a different value. */
264 tid = next->get_tid();
265 node_stack->pop_restofstack(2);
266 } else if (nextnode->increment_relseq_break()) {
267 /* The next node will try to resolve a release sequence differently */
268 tid = next->get_tid();
269 node_stack->pop_restofstack(2);
272 /* Make a different thread execute for next step */
273 scheduler->add_sleep(get_thread(next->get_tid()));
274 tid = prevnode->get_next_backtrack();
275 /* Make sure the backtracked thread isn't sleeping. */
276 node_stack->pop_restofstack(1);
277 if (diverge == earliest_diverge) {
278 earliest_diverge = prevnode->get_action();
281 /* Start the round robin scheduler from this thread id */
282 scheduler->set_scheduler_thread(tid);
283 /* The correct sleep set is in the parent node. */
286 DEBUG("*** Divergence point ***\n");
290 tid = next->get_tid();
292 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
293 ASSERT(tid != THREAD_ID_T_NONE);
294 return thread_map->get(id_to_int(tid));
298 * We need to know what the next actions of all threads in the sleep
299 * set will be. This method computes them and stores the actions at
300 * the corresponding thread object's pending action.
303 void ModelChecker::execute_sleep_set()
305 for (unsigned int i = 0; i < get_num_threads(); i++) {
306 thread_id_t tid = int_to_id(i);
307 Thread *thr = get_thread(tid);
308 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
309 thr->get_pending()->set_sleep_flag();
315 * @brief Should the current action wake up a given thread?
317 * @param curr The current action
318 * @param thread The thread that we might wake up
319 * @return True, if we should wake up the sleeping thread; false otherwise
321 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
323 const ModelAction *asleep = thread->get_pending();
324 /* Don't allow partial RMW to wake anyone up */
327 /* Synchronizing actions may have been backtracked */
328 if (asleep->could_synchronize_with(curr))
330 /* All acquire/release fences and fence-acquire/store-release */
331 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
333 /* Fence-release + store can awake load-acquire on the same location */
334 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
335 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
336 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
342 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
344 for (unsigned int i = 0; i < get_num_threads(); i++) {
345 Thread *thr = get_thread(int_to_id(i));
346 if (scheduler->is_sleep_set(thr)) {
347 if (should_wake_up(curr, thr))
348 /* Remove this thread from sleep set */
349 scheduler->remove_sleep(thr);
354 /** @brief Alert the model-checker that an incorrectly-ordered
355 * synchronization was made */
356 void ModelChecker::set_bad_synchronization()
358 priv->bad_synchronization = true;
362 * Check whether the current trace has triggered an assertion which should halt
365 * @return True, if the execution should be aborted; false otherwise
367 bool ModelChecker::has_asserted() const
369 return priv->asserted;
373 * Trigger a trace assertion which should cause this execution to be halted.
374 * This can be due to a detected bug or due to an infeasibility that should
377 void ModelChecker::set_assert()
379 priv->asserted = true;
383 * Check if we are in a deadlock. Should only be called at the end of an
384 * execution, although it should not give false positives in the middle of an
385 * execution (there should be some ENABLED thread).
387 * @return True if program is in a deadlock; false otherwise
389 bool ModelChecker::is_deadlocked() const
391 bool blocking_threads = false;
392 for (unsigned int i = 0; i < get_num_threads(); i++) {
393 thread_id_t tid = int_to_id(i);
396 Thread *t = get_thread(tid);
397 if (!t->is_model_thread() && t->get_pending())
398 blocking_threads = true;
400 return blocking_threads;
404 * Check if this is a complete execution. That is, have all thread completed
405 * execution (rather than exiting because sleep sets have forced a redundant
408 * @return True if the execution is complete.
410 bool ModelChecker::is_complete_execution() const
412 for (unsigned int i = 0; i < get_num_threads(); i++)
413 if (is_enabled(int_to_id(i)))
419 * @brief Assert a bug in the executing program.
421 * Use this function to assert any sort of bug in the user program. If the
422 * current trace is feasible (actually, a prefix of some feasible execution),
423 * then this execution will be aborted, printing the appropriate message. If
424 * the current trace is not yet feasible, the error message will be stashed and
425 * printed if the execution ever becomes feasible.
427 * @param msg Descriptive message for the bug (do not include newline char)
428 * @return True if bug is immediately-feasible
430 bool ModelChecker::assert_bug(const char *msg)
432 priv->bugs.push_back(new bug_message(msg));
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 (DBG_ENABLED() || 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 (DBG_ENABLED() || 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 std::vector< ModelAction *, ModelAlloc<ModelAction *> > acquire_fences(get_num_threads(), NULL);
621 std::vector< ModelAction *, ModelAlloc<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 int low_tid, high_tid;
764 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
765 low_tid = id_to_int(act->get_tid());
766 high_tid = low_tid + 1;
769 high_tid = get_num_threads();
772 for (int i = low_tid; i < high_tid; i++) {
773 thread_id_t tid = int_to_id(i);
775 /* Make sure this thread can be enabled here. */
776 if (i >= node->get_num_threads())
779 /* Don't backtrack into a point where the thread is disabled or sleeping. */
780 if (node->enabled_status(tid) != THREAD_ENABLED)
783 /* Check if this has been explored already */
784 if (node->has_been_explored(tid))
787 /* See if fairness allows */
788 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
790 for (int t = 0; t < node->get_num_threads(); t++) {
791 thread_id_t tother = int_to_id(t);
792 if (node->is_enabled(tother) && node->has_priority(tother)) {
800 /* Cache the latest backtracking point */
801 set_latest_backtrack(prev);
803 /* If this is a new backtracking point, mark the tree */
804 if (!node->set_backtrack(tid))
806 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
807 id_to_int(prev->get_tid()),
808 id_to_int(t->get_id()));
817 * @brief Cache the a backtracking point as the "most recent", if eligible
819 * Note that this does not prepare the NodeStack for this backtracking
820 * operation, it only caches the action on a per-execution basis
822 * @param act The operation at which we should explore a different next action
823 * (i.e., backtracking point)
824 * @return True, if this action is now the most recent backtracking point;
827 bool ModelChecker::set_latest_backtrack(ModelAction *act)
829 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
830 priv->next_backtrack = act;
837 * Returns last backtracking point. The model checker will explore a different
838 * path for this point in the next execution.
839 * @return The ModelAction at which the next execution should diverge.
841 ModelAction * ModelChecker::get_next_backtrack()
843 ModelAction *next = priv->next_backtrack;
844 priv->next_backtrack = NULL;
849 * Processes a read model action.
850 * @param curr is the read model action to process.
851 * @return True if processing this read updates the mo_graph.
853 bool ModelChecker::process_read(ModelAction *curr)
855 Node *node = curr->get_node();
856 uint64_t value = VALUE_NONE;
858 bool updated = false;
859 switch (node->get_read_from_status()) {
860 case READ_FROM_PAST: {
861 const ModelAction *rf = node->get_read_from_past();
864 mo_graph->startChanges();
866 ASSERT(!is_infeasible());
867 if (!check_recency(curr, rf))
868 priv->too_many_reads = true;
869 updated = r_modification_order(curr, rf);
871 if (is_infeasible() && node->increment_read_from()) {
872 mo_graph->rollbackChanges();
873 priv->too_many_reads = false;
877 value = rf->get_value();
879 mo_graph->commitChanges();
880 mo_check_promises(curr, true);
884 case READ_FROM_PROMISE: {
885 Promise *promise = curr->get_node()->get_read_from_promise();
886 promise->add_reader(curr);
887 value = promise->get_value();
888 curr->set_read_from_promise(promise);
889 mo_graph->startChanges();
890 updated = r_modification_order(curr, promise);
891 mo_graph->commitChanges();
894 case READ_FROM_FUTURE: {
895 /* Read from future value */
896 struct future_value fv = node->get_future_value();
897 Promise *promise = new Promise(curr, fv);
899 curr->set_read_from_promise(promise);
900 promises->push_back(promise);
901 mo_graph->startChanges();
902 updated = r_modification_order(curr, promise);
903 mo_graph->commitChanges();
909 get_thread(curr)->set_return_value(value);
915 * Processes a lock, trylock, or unlock model action. @param curr is
916 * the read model action to process.
918 * The try lock operation checks whether the lock is taken. If not,
919 * it falls to the normal lock operation case. If so, it returns
922 * The lock operation has already been checked that it is enabled, so
923 * it just grabs the lock and synchronizes with the previous unlock.
925 * The unlock operation has to re-enable all of the threads that are
926 * waiting on the lock.
928 * @return True if synchronization was updated; false otherwise
930 bool ModelChecker::process_mutex(ModelAction *curr)
932 std::mutex *mutex = NULL;
933 struct std::mutex_state *state = NULL;
935 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
936 mutex = (std::mutex *)curr->get_location();
937 state = mutex->get_state();
938 } else if (curr->is_wait()) {
939 mutex = (std::mutex *)curr->get_value();
940 state = mutex->get_state();
943 switch (curr->get_type()) {
944 case ATOMIC_TRYLOCK: {
945 bool success = !state->islocked;
946 curr->set_try_lock(success);
948 get_thread(curr)->set_return_value(0);
951 get_thread(curr)->set_return_value(1);
953 //otherwise fall into the lock case
955 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
956 assert_bug("Lock access before initialization");
957 state->islocked = true;
958 ModelAction *unlock = get_last_unlock(curr);
959 //synchronize with the previous unlock statement
960 if (unlock != NULL) {
961 curr->synchronize_with(unlock);
966 case ATOMIC_UNLOCK: {
968 state->islocked = false;
969 //wake up the other threads
970 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
971 //activate all the waiting threads
972 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
973 scheduler->wake(get_thread(*rit));
980 state->islocked = false;
981 //wake up the other threads
982 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
983 //activate all the waiting threads
984 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
985 scheduler->wake(get_thread(*rit));
988 //check whether we should go to sleep or not...simulate spurious failures
989 if (curr->get_node()->get_misc() == 0) {
990 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
992 scheduler->sleep(get_thread(curr));
996 case ATOMIC_NOTIFY_ALL: {
997 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
998 //activate all the waiting threads
999 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1000 scheduler->wake(get_thread(*rit));
1005 case ATOMIC_NOTIFY_ONE: {
1006 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1007 int wakeupthread = curr->get_node()->get_misc();
1008 action_list_t::iterator it = waiters->begin();
1009 advance(it, wakeupthread);
1010 scheduler->wake(get_thread(*it));
1021 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1023 /* Do more ambitious checks now that mo is more complete */
1024 if (mo_may_allow(writer, reader)) {
1025 Node *node = reader->get_node();
1027 /* Find an ancestor thread which exists at the time of the reader */
1028 Thread *write_thread = get_thread(writer);
1029 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1030 write_thread = write_thread->get_parent();
1032 struct future_value fv = {
1033 writer->get_write_value(),
1034 writer->get_seq_number() + params.maxfuturedelay,
1035 write_thread->get_id(),
1037 if (node->add_future_value(fv))
1038 set_latest_backtrack(reader);
1043 * Process a write ModelAction
1044 * @param curr The ModelAction to process
1045 * @return True if the mo_graph was updated or promises were resolved
1047 bool ModelChecker::process_write(ModelAction *curr)
1049 /* Readers to which we may send our future value */
1050 std::vector< ModelAction *, ModelAlloc<ModelAction *> > send_fv;
1052 bool updated_mod_order = w_modification_order(curr, &send_fv);
1053 int promise_idx = get_promise_to_resolve(curr);
1054 const ModelAction *earliest_promise_reader;
1055 bool updated_promises = false;
1057 if (promise_idx >= 0) {
1058 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1059 updated_promises = resolve_promise(curr, promise_idx);
1061 earliest_promise_reader = NULL;
1063 /* Don't send future values to reads after the Promise we resolve */
1064 for (unsigned int i = 0; i < send_fv.size(); i++) {
1065 ModelAction *read = send_fv[i];
1066 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1067 futurevalues->push_back(PendingFutureValue(curr, read));
1070 if (promises->size() == 0) {
1071 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1072 struct PendingFutureValue pfv = (*futurevalues)[i];
1073 add_future_value(pfv.writer, pfv.act);
1075 futurevalues->clear();
1078 mo_graph->commitChanges();
1079 mo_check_promises(curr, false);
1081 get_thread(curr)->set_return_value(VALUE_NONE);
1082 return updated_mod_order || updated_promises;
1086 * Process a fence ModelAction
1087 * @param curr The ModelAction to process
1088 * @return True if synchronization was updated
1090 bool ModelChecker::process_fence(ModelAction *curr)
1093 * fence-relaxed: no-op
1094 * fence-release: only log the occurence (not in this function), for
1095 * use in later synchronization
1096 * fence-acquire (this function): search for hypothetical release
1099 bool updated = false;
1100 if (curr->is_acquire()) {
1101 action_list_t *list = action_trace;
1102 action_list_t::reverse_iterator rit;
1103 /* Find X : is_read(X) && X --sb-> curr */
1104 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1105 ModelAction *act = *rit;
1108 if (act->get_tid() != curr->get_tid())
1110 /* Stop at the beginning of the thread */
1111 if (act->is_thread_start())
1113 /* Stop once we reach a prior fence-acquire */
1114 if (act->is_fence() && act->is_acquire())
1116 if (!act->is_read())
1118 /* read-acquire will find its own release sequences */
1119 if (act->is_acquire())
1122 /* Establish hypothetical release sequences */
1123 rel_heads_list_t release_heads;
1124 get_release_seq_heads(curr, act, &release_heads);
1125 for (unsigned int i = 0; i < release_heads.size(); i++)
1126 if (!curr->synchronize_with(release_heads[i]))
1127 set_bad_synchronization();
1128 if (release_heads.size() != 0)
1136 * @brief Process the current action for thread-related activity
1138 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1139 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1140 * synchronization, etc. This function is a no-op for non-THREAD actions
1141 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1143 * @param curr The current action
1144 * @return True if synchronization was updated or a thread completed
1146 bool ModelChecker::process_thread_action(ModelAction *curr)
1148 bool updated = false;
1150 switch (curr->get_type()) {
1151 case THREAD_CREATE: {
1152 thrd_t *thrd = (thrd_t *)curr->get_location();
1153 struct thread_params *params = (struct thread_params *)curr->get_value();
1154 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1156 th->set_creation(curr);
1157 /* Promises can be satisfied by children */
1158 for (unsigned int i = 0; i < promises->size(); i++) {
1159 Promise *promise = (*promises)[i];
1160 if (promise->thread_is_available(curr->get_tid()))
1161 promise->add_thread(th->get_id());
1166 Thread *blocking = curr->get_thread_operand();
1167 ModelAction *act = get_last_action(blocking->get_id());
1168 curr->synchronize_with(act);
1169 updated = true; /* trigger rel-seq checks */
1172 case THREAD_FINISH: {
1173 Thread *th = get_thread(curr);
1174 while (!th->wait_list_empty()) {
1175 ModelAction *act = th->pop_wait_list();
1176 scheduler->wake(get_thread(act));
1179 /* Completed thread can't satisfy promises */
1180 for (unsigned int i = 0; i < promises->size(); i++) {
1181 Promise *promise = (*promises)[i];
1182 if (promise->thread_is_available(th->get_id()))
1183 if (promise->eliminate_thread(th->get_id()))
1184 priv->failed_promise = true;
1186 updated = true; /* trigger rel-seq checks */
1189 case THREAD_START: {
1190 check_promises(curr->get_tid(), NULL, curr->get_cv());
1201 * @brief Process the current action for release sequence fixup activity
1203 * Performs model-checker release sequence fixups for the current action,
1204 * forcing a single pending release sequence to break (with a given, potential
1205 * "loose" write) or to complete (i.e., synchronize). If a pending release
1206 * sequence forms a complete release sequence, then we must perform the fixup
1207 * synchronization, mo_graph additions, etc.
1209 * @param curr The current action; must be a release sequence fixup action
1210 * @param work_queue The work queue to which to add work items as they are
1213 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1215 const ModelAction *write = curr->get_node()->get_relseq_break();
1216 struct release_seq *sequence = pending_rel_seqs->back();
1217 pending_rel_seqs->pop_back();
1219 ModelAction *acquire = sequence->acquire;
1220 const ModelAction *rf = sequence->rf;
1221 const ModelAction *release = sequence->release;
1225 ASSERT(release->same_thread(rf));
1227 if (write == NULL) {
1229 * @todo Forcing a synchronization requires that we set
1230 * modification order constraints. For instance, we can't allow
1231 * a fixup sequence in which two separate read-acquire
1232 * operations read from the same sequence, where the first one
1233 * synchronizes and the other doesn't. Essentially, we can't
1234 * allow any writes to insert themselves between 'release' and
1238 /* Must synchronize */
1239 if (!acquire->synchronize_with(release)) {
1240 set_bad_synchronization();
1243 /* Re-check all pending release sequences */
1244 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1245 /* Re-check act for mo_graph edges */
1246 work_queue->push_back(MOEdgeWorkEntry(acquire));
1248 /* propagate synchronization to later actions */
1249 action_list_t::reverse_iterator rit = action_trace->rbegin();
1250 for (; (*rit) != acquire; rit++) {
1251 ModelAction *propagate = *rit;
1252 if (acquire->happens_before(propagate)) {
1253 propagate->synchronize_with(acquire);
1254 /* Re-check 'propagate' for mo_graph edges */
1255 work_queue->push_back(MOEdgeWorkEntry(propagate));
1259 /* Break release sequence with new edges:
1260 * release --mo--> write --mo--> rf */
1261 mo_graph->addEdge(release, write);
1262 mo_graph->addEdge(write, rf);
1265 /* See if we have realized a data race */
1270 * Initialize the current action by performing one or more of the following
1271 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1272 * in the NodeStack, manipulating backtracking sets, allocating and
1273 * initializing clock vectors, and computing the promises to fulfill.
1275 * @param curr The current action, as passed from the user context; may be
1276 * freed/invalidated after the execution of this function, with a different
1277 * action "returned" its place (pass-by-reference)
1278 * @return True if curr is a newly-explored action; false otherwise
1280 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1282 ModelAction *newcurr;
1284 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1285 newcurr = process_rmw(*curr);
1288 if (newcurr->is_rmw())
1289 compute_promises(newcurr);
1295 (*curr)->set_seq_number(get_next_seq_num());
1297 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1299 /* First restore type and order in case of RMW operation */
1300 if ((*curr)->is_rmwr())
1301 newcurr->copy_typeandorder(*curr);
1303 ASSERT((*curr)->get_location() == newcurr->get_location());
1304 newcurr->copy_from_new(*curr);
1306 /* Discard duplicate ModelAction; use action from NodeStack */
1309 /* Always compute new clock vector */
1310 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1313 return false; /* Action was explored previously */
1317 /* Always compute new clock vector */
1318 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1320 /* Assign most recent release fence */
1321 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1324 * Perform one-time actions when pushing new ModelAction onto
1327 if (newcurr->is_write())
1328 compute_promises(newcurr);
1329 else if (newcurr->is_relseq_fixup())
1330 compute_relseq_breakwrites(newcurr);
1331 else if (newcurr->is_wait())
1332 newcurr->get_node()->set_misc_max(2);
1333 else if (newcurr->is_notify_one()) {
1334 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1336 return true; /* This was a new ModelAction */
1341 * @brief Establish reads-from relation between two actions
1343 * Perform basic operations involved with establishing a concrete rf relation,
1344 * including setting the ModelAction data and checking for release sequences.
1346 * @param act The action that is reading (must be a read)
1347 * @param rf The action from which we are reading (must be a write)
1349 * @return True if this read established synchronization
1351 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1354 act->set_read_from(rf);
1355 if (act->is_acquire()) {
1356 rel_heads_list_t release_heads;
1357 get_release_seq_heads(act, act, &release_heads);
1358 int num_heads = release_heads.size();
1359 for (unsigned int i = 0; i < release_heads.size(); i++)
1360 if (!act->synchronize_with(release_heads[i])) {
1361 set_bad_synchronization();
1364 return num_heads > 0;
1370 * Check promises and eliminate potentially-satisfying threads when a thread is
1371 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1372 * no longer satisfy a promise generated from that thread.
1374 * @param blocker The thread on which a thread is waiting
1375 * @param waiting The waiting thread
1377 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1379 for (unsigned int i = 0; i < promises->size(); i++) {
1380 Promise *promise = (*promises)[i];
1381 if (!promise->thread_is_available(waiting->get_id()))
1383 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1384 ModelAction *reader = promise->get_reader(j);
1385 if (reader->get_tid() != blocker->get_id())
1387 if (promise->eliminate_thread(waiting->get_id())) {
1388 /* Promise has failed */
1389 priv->failed_promise = true;
1391 /* Only eliminate the 'waiting' thread once */
1399 * @brief Check whether a model action is enabled.
1401 * Checks whether a lock or join operation would be successful (i.e., is the
1402 * lock already locked, or is the joined thread already complete). If not, put
1403 * the action in a waiter list.
1405 * @param curr is the ModelAction to check whether it is enabled.
1406 * @return a bool that indicates whether the action is enabled.
1408 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1409 if (curr->is_lock()) {
1410 std::mutex *lock = (std::mutex *)curr->get_location();
1411 struct std::mutex_state *state = lock->get_state();
1412 if (state->islocked) {
1413 //Stick the action in the appropriate waiting queue
1414 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1417 } else if (curr->get_type() == THREAD_JOIN) {
1418 Thread *blocking = (Thread *)curr->get_location();
1419 if (!blocking->is_complete()) {
1420 blocking->push_wait_list(curr);
1421 thread_blocking_check_promises(blocking, get_thread(curr));
1430 * This is the heart of the model checker routine. It performs model-checking
1431 * actions corresponding to a given "current action." Among other processes, it
1432 * calculates reads-from relationships, updates synchronization clock vectors,
1433 * forms a memory_order constraints graph, and handles replay/backtrack
1434 * execution when running permutations of previously-observed executions.
1436 * @param curr The current action to process
1437 * @return The ModelAction that is actually executed; may be different than
1438 * curr; may be NULL, if the current action is not enabled to run
1440 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1443 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1445 if (!check_action_enabled(curr)) {
1446 /* Make the execution look like we chose to run this action
1447 * much later, when a lock/join can succeed */
1448 get_thread(curr)->set_pending(curr);
1449 scheduler->sleep(get_thread(curr));
1453 bool newly_explored = initialize_curr_action(&curr);
1459 wake_up_sleeping_actions(curr);
1461 /* Add the action to lists before any other model-checking tasks */
1462 if (!second_part_of_rmw)
1463 add_action_to_lists(curr);
1465 /* Build may_read_from set for newly-created actions */
1466 if (newly_explored && curr->is_read())
1467 build_may_read_from(curr);
1469 /* Initialize work_queue with the "current action" work */
1470 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1471 while (!work_queue.empty() && !has_asserted()) {
1472 WorkQueueEntry work = work_queue.front();
1473 work_queue.pop_front();
1475 switch (work.type) {
1476 case WORK_CHECK_CURR_ACTION: {
1477 ModelAction *act = work.action;
1478 bool update = false; /* update this location's release seq's */
1479 bool update_all = false; /* update all release seq's */
1481 if (process_thread_action(curr))
1484 if (act->is_read() && !second_part_of_rmw && process_read(act))
1487 if (act->is_write() && process_write(act))
1490 if (act->is_fence() && process_fence(act))
1493 if (act->is_mutex_op() && process_mutex(act))
1496 if (act->is_relseq_fixup())
1497 process_relseq_fixup(curr, &work_queue);
1500 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1502 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1505 case WORK_CHECK_RELEASE_SEQ:
1506 resolve_release_sequences(work.location, &work_queue);
1508 case WORK_CHECK_MO_EDGES: {
1509 /** @todo Complete verification of work_queue */
1510 ModelAction *act = work.action;
1511 bool updated = false;
1513 if (act->is_read()) {
1514 const ModelAction *rf = act->get_reads_from();
1515 const Promise *promise = act->get_reads_from_promise();
1517 if (r_modification_order(act, rf))
1519 } else if (promise) {
1520 if (r_modification_order(act, promise))
1524 if (act->is_write()) {
1525 if (w_modification_order(act, NULL))
1528 mo_graph->commitChanges();
1531 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1540 check_curr_backtracking(curr);
1541 set_backtracking(curr);
1545 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1547 Node *currnode = curr->get_node();
1548 Node *parnode = currnode->get_parent();
1550 if ((parnode && !parnode->backtrack_empty()) ||
1551 !currnode->misc_empty() ||
1552 !currnode->read_from_empty() ||
1553 !currnode->promise_empty() ||
1554 !currnode->relseq_break_empty()) {
1555 set_latest_backtrack(curr);
1559 bool ModelChecker::promises_expired() const
1561 for (unsigned int i = 0; i < promises->size(); i++) {
1562 Promise *promise = (*promises)[i];
1563 if (promise->get_expiration() < priv->used_sequence_numbers)
1570 * This is the strongest feasibility check available.
1571 * @return whether the current trace (partial or complete) must be a prefix of
1574 bool ModelChecker::isfeasibleprefix() const
1576 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1580 * Print disagnostic information about an infeasible execution
1581 * @param prefix A string to prefix the output with; if NULL, then a default
1582 * message prefix will be provided
1584 void ModelChecker::print_infeasibility(const char *prefix) const
1588 if (mo_graph->checkForCycles())
1589 ptr += sprintf(ptr, "[mo cycle]");
1590 if (priv->failed_promise)
1591 ptr += sprintf(ptr, "[failed promise]");
1592 if (priv->too_many_reads)
1593 ptr += sprintf(ptr, "[too many reads]");
1594 if (priv->no_valid_reads)
1595 ptr += sprintf(ptr, "[no valid reads-from]");
1596 if (priv->bad_synchronization)
1597 ptr += sprintf(ptr, "[bad sw ordering]");
1598 if (promises_expired())
1599 ptr += sprintf(ptr, "[promise expired]");
1600 if (promises->size() != 0)
1601 ptr += sprintf(ptr, "[unresolved promise]");
1603 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1607 * Returns whether the current completed trace is feasible, except for pending
1608 * release sequences.
1610 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1612 return !is_infeasible() && promises->size() == 0;
1616 * Check if the current partial trace is infeasible. Does not check any
1617 * end-of-execution flags, which might rule out the execution. Thus, this is
1618 * useful only for ruling an execution as infeasible.
1619 * @return whether the current partial trace is infeasible.
1621 bool ModelChecker::is_infeasible() const
1623 return mo_graph->checkForCycles() ||
1624 priv->no_valid_reads ||
1625 priv->failed_promise ||
1626 priv->too_many_reads ||
1627 priv->bad_synchronization ||
1631 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1632 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1633 ModelAction *lastread = get_last_action(act->get_tid());
1634 lastread->process_rmw(act);
1635 if (act->is_rmw()) {
1636 if (lastread->get_reads_from())
1637 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1639 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1640 mo_graph->commitChanges();
1645 template <typename T>
1646 bool ModelChecker::should_read_instead(const ModelAction *curr, const ModelAction *rf, const T *other_rf) const
1648 /* Need a different write/promise */
1649 if (other_rf->equals(rf))
1652 /* Only look for "newer" writes/promises */
1653 if (!mo_graph->checkReachable(rf, other_rf))
1656 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1657 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1658 action_list_t::reverse_iterator rit = list->rbegin();
1659 ASSERT((*rit) == curr);
1660 /* Skip past curr */
1663 /* Does this write/promise work for everyone? */
1664 for (int i = 0; i < params.maxreads; i++, rit++) {
1665 ModelAction *act = *rit;
1666 if (!act->may_read_from(other_rf))
1673 * Checks whether a thread has read from the same write for too many times
1674 * without seeing the effects of a later write.
1677 * 1) there must a different write that we could read from that would satisfy the modification order,
1678 * 2) we must have read from the same value in excess of maxreads times, and
1679 * 3) that other write must have been in the reads_from set for maxreads times.
1681 * If so, we decide that the execution is no longer feasible.
1683 * @param curr The current action. Must be a read.
1684 * @param rf The store from which we might read.
1685 * @return True if the read should succeed; false otherwise
1687 bool ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) const
1689 if (!params.maxreads)
1692 //NOTE: Next check is just optimization, not really necessary....
1693 if (curr->get_node()->get_read_from_past_size() +
1694 curr->get_node()->get_read_from_promise_size() <= 1)
1697 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1698 int tid = id_to_int(curr->get_tid());
1699 ASSERT(tid < (int)thrd_lists->size());
1700 action_list_t *list = &(*thrd_lists)[tid];
1701 action_list_t::reverse_iterator rit = list->rbegin();
1702 ASSERT((*rit) == curr);
1703 /* Skip past curr */
1706 action_list_t::reverse_iterator ritcopy = rit;
1707 /* See if we have enough reads from the same value */
1708 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1709 if (ritcopy == list->rend())
1711 ModelAction *act = *ritcopy;
1712 if (!act->is_read())
1714 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1716 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1718 if (act->get_node()->get_read_from_past_size() +
1719 act->get_node()->get_read_from_promise_size() <= 1)
1722 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1723 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1724 if (should_read_instead(curr, rf, write))
1725 return false; /* liveness failure */
1727 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1728 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1729 if (should_read_instead(curr, rf, promise))
1730 return false; /* liveness failure */
1736 * Updates the mo_graph with the constraints imposed from the current
1739 * Basic idea is the following: Go through each other thread and find
1740 * the last action that happened before our read. Two cases:
1742 * (1) The action is a write => that write must either occur before
1743 * the write we read from or be the write we read from.
1745 * (2) The action is a read => the write that that action read from
1746 * must occur before the write we read from or be the same write.
1748 * @param curr The current action. Must be a read.
1749 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1750 * @return True if modification order edges were added; false otherwise
1752 template <typename rf_type>
1753 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1755 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1758 ASSERT(curr->is_read());
1760 /* Last SC fence in the current thread */
1761 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1763 /* Iterate over all threads */
1764 for (i = 0; i < thrd_lists->size(); i++) {
1765 /* Last SC fence in thread i */
1766 ModelAction *last_sc_fence_thread_local = NULL;
1767 if (int_to_id((int)i) != curr->get_tid())
1768 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1770 /* Last SC fence in thread i, before last SC fence in current thread */
1771 ModelAction *last_sc_fence_thread_before = NULL;
1772 if (last_sc_fence_local)
1773 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1775 /* Iterate over actions in thread, starting from most recent */
1776 action_list_t *list = &(*thrd_lists)[i];
1777 action_list_t::reverse_iterator rit;
1778 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1779 ModelAction *act = *rit;
1781 if (act->is_write() && !act->equals(rf) && act != curr) {
1782 /* C++, Section 29.3 statement 5 */
1783 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1784 *act < *last_sc_fence_thread_local) {
1785 added = mo_graph->addEdge(act, rf) || added;
1788 /* C++, Section 29.3 statement 4 */
1789 else if (act->is_seqcst() && last_sc_fence_local &&
1790 *act < *last_sc_fence_local) {
1791 added = mo_graph->addEdge(act, rf) || added;
1794 /* C++, Section 29.3 statement 6 */
1795 else if (last_sc_fence_thread_before &&
1796 *act < *last_sc_fence_thread_before) {
1797 added = mo_graph->addEdge(act, rf) || added;
1803 * Include at most one act per-thread that "happens
1804 * before" curr. Don't consider reflexively.
1806 if (act->happens_before(curr) && act != curr) {
1807 if (act->is_write()) {
1808 if (!act->equals(rf)) {
1809 added = mo_graph->addEdge(act, rf) || added;
1812 const ModelAction *prevrf = act->get_reads_from();
1813 const Promise *prevrf_promise = act->get_reads_from_promise();
1815 if (!prevrf->equals(rf))
1816 added = mo_graph->addEdge(prevrf, rf) || added;
1817 } else if (!prevrf_promise->equals(rf)) {
1818 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1827 * All compatible, thread-exclusive promises must be ordered after any
1828 * concrete loads from the same thread
1830 for (unsigned int i = 0; i < promises->size(); i++)
1831 if ((*promises)[i]->is_compatible_exclusive(curr))
1832 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1838 * Updates the mo_graph with the constraints imposed from the current write.
1840 * Basic idea is the following: Go through each other thread and find
1841 * the lastest action that happened before our write. Two cases:
1843 * (1) The action is a write => that write must occur before
1846 * (2) The action is a read => the write that that action read from
1847 * must occur before the current write.
1849 * This method also handles two other issues:
1851 * (I) Sequential Consistency: Making sure that if the current write is
1852 * seq_cst, that it occurs after the previous seq_cst write.
1854 * (II) Sending the write back to non-synchronizing reads.
1856 * @param curr The current action. Must be a write.
1857 * @param send_fv A vector for stashing reads to which we may pass our future
1858 * value. If NULL, then don't record any future values.
1859 * @return True if modification order edges were added; false otherwise
1861 bool ModelChecker::w_modification_order(ModelAction *curr, std::vector< ModelAction *, ModelAlloc<ModelAction *> > *send_fv)
1863 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1866 ASSERT(curr->is_write());
1868 if (curr->is_seqcst()) {
1869 /* We have to at least see the last sequentially consistent write,
1870 so we are initialized. */
1871 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1872 if (last_seq_cst != NULL) {
1873 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1877 /* Last SC fence in the current thread */
1878 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1880 /* Iterate over all threads */
1881 for (i = 0; i < thrd_lists->size(); i++) {
1882 /* Last SC fence in thread i, before last SC fence in current thread */
1883 ModelAction *last_sc_fence_thread_before = NULL;
1884 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1885 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1887 /* Iterate over actions in thread, starting from most recent */
1888 action_list_t *list = &(*thrd_lists)[i];
1889 action_list_t::reverse_iterator rit;
1890 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1891 ModelAction *act = *rit;
1894 * 1) If RMW and it actually read from something, then we
1895 * already have all relevant edges, so just skip to next
1898 * 2) If RMW and it didn't read from anything, we should
1899 * whatever edge we can get to speed up convergence.
1901 * 3) If normal write, we need to look at earlier actions, so
1902 * continue processing list.
1904 if (curr->is_rmw()) {
1905 if (curr->get_reads_from() != NULL)
1913 /* C++, Section 29.3 statement 7 */
1914 if (last_sc_fence_thread_before && act->is_write() &&
1915 *act < *last_sc_fence_thread_before) {
1916 added = mo_graph->addEdge(act, curr) || added;
1921 * Include at most one act per-thread that "happens
1924 if (act->happens_before(curr)) {
1926 * Note: if act is RMW, just add edge:
1928 * The following edge should be handled elsewhere:
1929 * readfrom(act) --mo--> act
1931 if (act->is_write())
1932 added = mo_graph->addEdge(act, curr) || added;
1933 else if (act->is_read()) {
1934 //if previous read accessed a null, just keep going
1935 if (act->get_reads_from() == NULL)
1937 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1940 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1941 !act->same_thread(curr)) {
1942 /* We have an action that:
1943 (1) did not happen before us
1944 (2) is a read and we are a write
1945 (3) cannot synchronize with us
1946 (4) is in a different thread
1948 that read could potentially read from our write. Note that
1949 these checks are overly conservative at this point, we'll
1950 do more checks before actually removing the
1954 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1955 if (!is_infeasible())
1956 send_fv->push_back(act);
1957 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1958 add_future_value(curr, act);
1965 * All compatible, thread-exclusive promises must be ordered after any
1966 * concrete stores to the same thread, or else they can be merged with
1969 for (unsigned int i = 0; i < promises->size(); i++)
1970 if ((*promises)[i]->is_compatible_exclusive(curr))
1971 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1976 /** Arbitrary reads from the future are not allowed. Section 29.3
1977 * part 9 places some constraints. This method checks one result of constraint
1978 * constraint. Others require compiler support. */
1979 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1981 if (!writer->is_rmw())
1984 if (!reader->is_rmw())
1987 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1988 if (search == reader)
1990 if (search->get_tid() == reader->get_tid() &&
1991 search->happens_before(reader))
1999 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2000 * some constraints. This method checks one the following constraint (others
2001 * require compiler support):
2003 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2005 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2007 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2009 /* Iterate over all threads */
2010 for (i = 0; i < thrd_lists->size(); i++) {
2011 const ModelAction *write_after_read = NULL;
2013 /* Iterate over actions in thread, starting from most recent */
2014 action_list_t *list = &(*thrd_lists)[i];
2015 action_list_t::reverse_iterator rit;
2016 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2017 ModelAction *act = *rit;
2019 /* Don't disallow due to act == reader */
2020 if (!reader->happens_before(act) || reader == act)
2022 else if (act->is_write())
2023 write_after_read = act;
2024 else if (act->is_read() && act->get_reads_from() != NULL)
2025 write_after_read = act->get_reads_from();
2028 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2035 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2036 * The ModelAction under consideration is expected to be taking part in
2037 * release/acquire synchronization as an object of the "reads from" relation.
2038 * Note that this can only provide release sequence support for RMW chains
2039 * which do not read from the future, as those actions cannot be traced until
2040 * their "promise" is fulfilled. Similarly, we may not even establish the
2041 * presence of a release sequence with certainty, as some modification order
2042 * constraints may be decided further in the future. Thus, this function
2043 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2044 * and a boolean representing certainty.
2046 * @param rf The action that might be part of a release sequence. Must be a
2048 * @param release_heads A pass-by-reference style return parameter. After
2049 * execution of this function, release_heads will contain the heads of all the
2050 * relevant release sequences, if any exists with certainty
2051 * @param pending A pass-by-reference style return parameter which is only used
2052 * when returning false (i.e., uncertain). Returns most information regarding
2053 * an uncertain release sequence, including any write operations that might
2054 * break the sequence.
2055 * @return true, if the ModelChecker is certain that release_heads is complete;
2058 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2059 rel_heads_list_t *release_heads,
2060 struct release_seq *pending) const
2062 /* Only check for release sequences if there are no cycles */
2063 if (mo_graph->checkForCycles())
2066 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2067 ASSERT(rf->is_write());
2069 if (rf->is_release())
2070 release_heads->push_back(rf);
2071 else if (rf->get_last_fence_release())
2072 release_heads->push_back(rf->get_last_fence_release());
2074 break; /* End of RMW chain */
2076 /** @todo Need to be smarter here... In the linux lock
2077 * example, this will run to the beginning of the program for
2079 /** @todo The way to be smarter here is to keep going until 1
2080 * thread has a release preceded by an acquire and you've seen
2083 /* acq_rel RMW is a sufficient stopping condition */
2084 if (rf->is_acquire() && rf->is_release())
2085 return true; /* complete */
2088 /* read from future: need to settle this later */
2090 return false; /* incomplete */
2093 if (rf->is_release())
2094 return true; /* complete */
2096 /* else relaxed write
2097 * - check for fence-release in the same thread (29.8, stmt. 3)
2098 * - check modification order for contiguous subsequence
2099 * -> rf must be same thread as release */
2101 const ModelAction *fence_release = rf->get_last_fence_release();
2102 /* Synchronize with a fence-release unconditionally; we don't need to
2103 * find any more "contiguous subsequence..." for it */
2105 release_heads->push_back(fence_release);
2107 int tid = id_to_int(rf->get_tid());
2108 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2109 action_list_t *list = &(*thrd_lists)[tid];
2110 action_list_t::const_reverse_iterator rit;
2112 /* Find rf in the thread list */
2113 rit = std::find(list->rbegin(), list->rend(), rf);
2114 ASSERT(rit != list->rend());
2116 /* Find the last {write,fence}-release */
2117 for (; rit != list->rend(); rit++) {
2118 if (fence_release && *(*rit) < *fence_release)
2120 if ((*rit)->is_release())
2123 if (rit == list->rend()) {
2124 /* No write-release in this thread */
2125 return true; /* complete */
2126 } else if (fence_release && *(*rit) < *fence_release) {
2127 /* The fence-release is more recent (and so, "stronger") than
2128 * the most recent write-release */
2129 return true; /* complete */
2130 } /* else, need to establish contiguous release sequence */
2131 ModelAction *release = *rit;
2133 ASSERT(rf->same_thread(release));
2135 pending->writes.clear();
2137 bool certain = true;
2138 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2139 if (id_to_int(rf->get_tid()) == (int)i)
2141 list = &(*thrd_lists)[i];
2143 /* Can we ensure no future writes from this thread may break
2144 * the release seq? */
2145 bool future_ordered = false;
2147 ModelAction *last = get_last_action(int_to_id(i));
2148 Thread *th = get_thread(int_to_id(i));
2149 if ((last && rf->happens_before(last)) ||
2152 future_ordered = true;
2154 ASSERT(!th->is_model_thread() || future_ordered);
2156 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2157 const ModelAction *act = *rit;
2158 /* Reach synchronization -> this thread is complete */
2159 if (act->happens_before(release))
2161 if (rf->happens_before(act)) {
2162 future_ordered = true;
2166 /* Only non-RMW writes can break release sequences */
2167 if (!act->is_write() || act->is_rmw())
2170 /* Check modification order */
2171 if (mo_graph->checkReachable(rf, act)) {
2172 /* rf --mo--> act */
2173 future_ordered = true;
2176 if (mo_graph->checkReachable(act, release))
2177 /* act --mo--> release */
2179 if (mo_graph->checkReachable(release, act) &&
2180 mo_graph->checkReachable(act, rf)) {
2181 /* release --mo-> act --mo--> rf */
2182 return true; /* complete */
2184 /* act may break release sequence */
2185 pending->writes.push_back(act);
2188 if (!future_ordered)
2189 certain = false; /* This thread is uncertain */
2193 release_heads->push_back(release);
2194 pending->writes.clear();
2196 pending->release = release;
2203 * An interface for getting the release sequence head(s) with which a
2204 * given ModelAction must synchronize. This function only returns a non-empty
2205 * result when it can locate a release sequence head with certainty. Otherwise,
2206 * it may mark the internal state of the ModelChecker so that it will handle
2207 * the release sequence at a later time, causing @a acquire to update its
2208 * synchronization at some later point in execution.
2210 * @param acquire The 'acquire' action that may synchronize with a release
2212 * @param read The read action that may read from a release sequence; this may
2213 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2214 * when 'acquire' is a fence-acquire)
2215 * @param release_heads A pass-by-reference return parameter. Will be filled
2216 * with the head(s) of the release sequence(s), if they exists with certainty.
2217 * @see ModelChecker::release_seq_heads
2219 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2220 ModelAction *read, rel_heads_list_t *release_heads)
2222 const ModelAction *rf = read->get_reads_from();
2223 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2224 sequence->acquire = acquire;
2225 sequence->read = read;
2227 if (!release_seq_heads(rf, release_heads, sequence)) {
2228 /* add act to 'lazy checking' list */
2229 pending_rel_seqs->push_back(sequence);
2231 snapshot_free(sequence);
2236 * Attempt to resolve all stashed operations that might synchronize with a
2237 * release sequence for a given location. This implements the "lazy" portion of
2238 * determining whether or not a release sequence was contiguous, since not all
2239 * modification order information is present at the time an action occurs.
2241 * @param location The location/object that should be checked for release
2242 * sequence resolutions. A NULL value means to check all locations.
2243 * @param work_queue The work queue to which to add work items as they are
2245 * @return True if any updates occurred (new synchronization, new mo_graph
2248 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2250 bool updated = false;
2251 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2252 while (it != pending_rel_seqs->end()) {
2253 struct release_seq *pending = *it;
2254 ModelAction *acquire = pending->acquire;
2255 const ModelAction *read = pending->read;
2257 /* Only resolve sequences on the given location, if provided */
2258 if (location && read->get_location() != location) {
2263 const ModelAction *rf = read->get_reads_from();
2264 rel_heads_list_t release_heads;
2266 complete = release_seq_heads(rf, &release_heads, pending);
2267 for (unsigned int i = 0; i < release_heads.size(); i++) {
2268 if (!acquire->has_synchronized_with(release_heads[i])) {
2269 if (acquire->synchronize_with(release_heads[i]))
2272 set_bad_synchronization();
2277 /* Re-check all pending release sequences */
2278 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2279 /* Re-check read-acquire for mo_graph edges */
2280 if (acquire->is_read())
2281 work_queue->push_back(MOEdgeWorkEntry(acquire));
2283 /* propagate synchronization to later actions */
2284 action_list_t::reverse_iterator rit = action_trace->rbegin();
2285 for (; (*rit) != acquire; rit++) {
2286 ModelAction *propagate = *rit;
2287 if (acquire->happens_before(propagate)) {
2288 propagate->synchronize_with(acquire);
2289 /* Re-check 'propagate' for mo_graph edges */
2290 work_queue->push_back(MOEdgeWorkEntry(propagate));
2295 it = pending_rel_seqs->erase(it);
2296 snapshot_free(pending);
2302 // If we resolved promises or data races, see if we have realized a data race.
2309 * Performs various bookkeeping operations for the current ModelAction. For
2310 * instance, adds action to the per-object, per-thread action vector and to the
2311 * action trace list of all thread actions.
2313 * @param act is the ModelAction to add.
2315 void ModelChecker::add_action_to_lists(ModelAction *act)
2317 int tid = id_to_int(act->get_tid());
2318 ModelAction *uninit = NULL;
2320 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2321 if (list->empty() && act->is_atomic_var()) {
2322 uninit = new_uninitialized_action(act->get_location());
2323 uninit_id = id_to_int(uninit->get_tid());
2324 list->push_back(uninit);
2326 list->push_back(act);
2328 action_trace->push_back(act);
2330 action_trace->push_front(uninit);
2332 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2333 if (tid >= (int)vec->size())
2334 vec->resize(priv->next_thread_id);
2335 (*vec)[tid].push_back(act);
2337 (*vec)[uninit_id].push_front(uninit);
2339 if ((int)thrd_last_action->size() <= tid)
2340 thrd_last_action->resize(get_num_threads());
2341 (*thrd_last_action)[tid] = act;
2343 (*thrd_last_action)[uninit_id] = uninit;
2345 if (act->is_fence() && act->is_release()) {
2346 if ((int)thrd_last_fence_release->size() <= tid)
2347 thrd_last_fence_release->resize(get_num_threads());
2348 (*thrd_last_fence_release)[tid] = act;
2351 if (act->is_wait()) {
2352 void *mutex_loc = (void *) act->get_value();
2353 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2355 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2356 if (tid >= (int)vec->size())
2357 vec->resize(priv->next_thread_id);
2358 (*vec)[tid].push_back(act);
2363 * @brief Get the last action performed by a particular Thread
2364 * @param tid The thread ID of the Thread in question
2365 * @return The last action in the thread
2367 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2369 int threadid = id_to_int(tid);
2370 if (threadid < (int)thrd_last_action->size())
2371 return (*thrd_last_action)[id_to_int(tid)];
2377 * @brief Get the last fence release performed by a particular Thread
2378 * @param tid The thread ID of the Thread in question
2379 * @return The last fence release in the thread, if one exists; NULL otherwise
2381 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2383 int threadid = id_to_int(tid);
2384 if (threadid < (int)thrd_last_fence_release->size())
2385 return (*thrd_last_fence_release)[id_to_int(tid)];
2391 * Gets the last memory_order_seq_cst write (in the total global sequence)
2392 * performed on a particular object (i.e., memory location), not including the
2394 * @param curr The current ModelAction; also denotes the object location to
2396 * @return The last seq_cst write
2398 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2400 void *location = curr->get_location();
2401 action_list_t *list = get_safe_ptr_action(obj_map, location);
2402 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2403 action_list_t::reverse_iterator rit;
2404 for (rit = list->rbegin(); rit != list->rend(); rit++)
2405 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2411 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2412 * performed in a particular thread, prior to a particular fence.
2413 * @param tid The ID of the thread to check
2414 * @param before_fence The fence from which to begin the search; if NULL, then
2415 * search for the most recent fence in the thread.
2416 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2418 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2420 /* All fences should have NULL location */
2421 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2422 action_list_t::reverse_iterator rit = list->rbegin();
2425 for (; rit != list->rend(); rit++)
2426 if (*rit == before_fence)
2429 ASSERT(*rit == before_fence);
2433 for (; rit != list->rend(); rit++)
2434 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2440 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2441 * location). This function identifies the mutex according to the current
2442 * action, which is presumed to perform on the same mutex.
2443 * @param curr The current ModelAction; also denotes the object location to
2445 * @return The last unlock operation
2447 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2449 void *location = curr->get_location();
2450 action_list_t *list = get_safe_ptr_action(obj_map, location);
2451 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2452 action_list_t::reverse_iterator rit;
2453 for (rit = list->rbegin(); rit != list->rend(); rit++)
2454 if ((*rit)->is_unlock() || (*rit)->is_wait())
2459 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2461 ModelAction *parent = get_last_action(tid);
2463 parent = get_thread(tid)->get_creation();
2468 * Returns the clock vector for a given thread.
2469 * @param tid The thread whose clock vector we want
2470 * @return Desired clock vector
2472 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2474 return get_parent_action(tid)->get_cv();
2478 * @brief Find the promise, if any to resolve for the current action
2479 * @param curr The current ModelAction. Should be a write.
2480 * @return The (non-negative) index for the Promise to resolve, if any;
2483 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2485 for (unsigned int i = 0; i < promises->size(); i++)
2486 if (curr->get_node()->get_promise(i))
2492 * Resolve a Promise with a current write.
2493 * @param write The ModelAction that is fulfilling Promises
2494 * @param promise_idx The index corresponding to the promise
2495 * @return True if the Promise was successfully resolved; false otherwise
2497 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2499 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2500 promise_list_t mustResolve;
2501 Promise *promise = (*promises)[promise_idx];
2503 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2504 ModelAction *read = promise->get_reader(i);
2505 read_from(read, write);
2506 actions_to_check.push_back(read);
2508 /* Make sure the promise's value matches the write's value */
2509 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2510 mo_graph->resolvePromise(promise, write, &mustResolve);
2512 promises->erase(promises->begin() + promise_idx);
2514 /** @todo simplify the 'mustResolve' stuff */
2515 ASSERT(mustResolve.size() <= 1);
2517 if (!mustResolve.empty() && mustResolve[0] != promise)
2518 priv->failed_promise = true;
2521 //Check whether reading these writes has made threads unable to
2524 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2525 ModelAction *read = actions_to_check[i];
2526 mo_check_promises(read, true);
2533 * Compute the set of promises that could potentially be satisfied by this
2534 * action. Note that the set computation actually appears in the Node, not in
2536 * @param curr The ModelAction that may satisfy promises
2538 void ModelChecker::compute_promises(ModelAction *curr)
2540 for (unsigned int i = 0; i < promises->size(); i++) {
2541 Promise *promise = (*promises)[i];
2542 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2545 bool satisfy = true;
2546 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2547 const ModelAction *act = promise->get_reader(j);
2548 if (act->happens_before(curr) ||
2549 act->could_synchronize_with(curr)) {
2555 curr->get_node()->set_promise(i);
2559 /** Checks promises in response to change in ClockVector Threads. */
2560 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2562 for (unsigned int i = 0; i < promises->size(); i++) {
2563 Promise *promise = (*promises)[i];
2564 if (!promise->thread_is_available(tid))
2566 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2567 const ModelAction *act = promise->get_reader(j);
2568 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2569 merge_cv->synchronized_since(act)) {
2570 if (promise->eliminate_thread(tid)) {
2571 /* Promise has failed */
2572 priv->failed_promise = true;
2580 void ModelChecker::check_promises_thread_disabled()
2582 for (unsigned int i = 0; i < promises->size(); i++) {
2583 Promise *promise = (*promises)[i];
2584 if (promise->has_failed()) {
2585 priv->failed_promise = true;
2592 * @brief Checks promises in response to addition to modification order for
2595 * We test whether threads are still available for satisfying promises after an
2596 * addition to our modification order constraints. Those that are unavailable
2597 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2598 * that promise has failed.
2600 * @param act The ModelAction which updated the modification order
2601 * @param is_read_check Should be true if act is a read and we must check for
2602 * updates to the store from which it read (there is a distinction here for
2603 * RMW's, which are both a load and a store)
2605 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2607 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2609 for (unsigned int i = 0; i < promises->size(); i++) {
2610 Promise *promise = (*promises)[i];
2612 // Is this promise on the same location?
2613 if (!promise->same_location(write))
2616 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2617 const ModelAction *pread = promise->get_reader(j);
2618 if (!pread->happens_before(act))
2620 if (mo_graph->checkPromise(write, promise)) {
2621 priv->failed_promise = true;
2627 // Don't do any lookups twice for the same thread
2628 if (!promise->thread_is_available(act->get_tid()))
2631 if (mo_graph->checkReachable(promise, write)) {
2632 if (mo_graph->checkPromise(write, promise)) {
2633 priv->failed_promise = true;
2641 * Compute the set of writes that may break the current pending release
2642 * sequence. This information is extracted from previou release sequence
2645 * @param curr The current ModelAction. Must be a release sequence fixup
2648 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2650 if (pending_rel_seqs->empty())
2653 struct release_seq *pending = pending_rel_seqs->back();
2654 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2655 const ModelAction *write = pending->writes[i];
2656 curr->get_node()->add_relseq_break(write);
2659 /* NULL means don't break the sequence; just synchronize */
2660 curr->get_node()->add_relseq_break(NULL);
2664 * Build up an initial set of all past writes that this 'read' action may read
2665 * from, as well as any previously-observed future values that must still be valid.
2667 * @param curr is the current ModelAction that we are exploring; it must be a
2670 void ModelChecker::build_may_read_from(ModelAction *curr)
2672 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2674 ASSERT(curr->is_read());
2676 ModelAction *last_sc_write = NULL;
2678 if (curr->is_seqcst())
2679 last_sc_write = get_last_seq_cst_write(curr);
2681 /* Iterate over all threads */
2682 for (i = 0; i < thrd_lists->size(); i++) {
2683 /* Iterate over actions in thread, starting from most recent */
2684 action_list_t *list = &(*thrd_lists)[i];
2685 action_list_t::reverse_iterator rit;
2686 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2687 ModelAction *act = *rit;
2689 /* Only consider 'write' actions */
2690 if (!act->is_write() || act == curr)
2693 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2694 bool allow_read = true;
2696 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2698 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2702 /* Only add feasible reads */
2703 mo_graph->startChanges();
2704 r_modification_order(curr, act);
2705 if (!is_infeasible())
2706 curr->get_node()->add_read_from_past(act);
2707 mo_graph->rollbackChanges();
2710 /* Include at most one act per-thread that "happens before" curr */
2711 if (act->happens_before(curr))
2716 /* Inherit existing, promised future values */
2717 for (i = 0; i < promises->size(); i++) {
2718 const Promise *promise = (*promises)[i];
2719 const ModelAction *promise_read = promise->get_reader(0);
2720 if (promise_read->same_var(curr)) {
2721 /* Only add feasible future-values */
2722 mo_graph->startChanges();
2723 r_modification_order(curr, promise);
2724 if (!is_infeasible())
2725 curr->get_node()->add_read_from_promise(promise_read);
2726 mo_graph->rollbackChanges();
2730 /* We may find no valid may-read-from only if the execution is doomed */
2731 if (!curr->get_node()->read_from_size()) {
2732 priv->no_valid_reads = true;
2736 if (DBG_ENABLED()) {
2737 model_print("Reached read action:\n");
2739 model_print("Printing read_from_past\n");
2740 curr->get_node()->print_read_from_past();
2741 model_print("End printing read_from_past\n");
2745 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2747 for ( ; write != NULL; write = write->get_reads_from()) {
2748 /* UNINIT actions don't have a Node, and they never sleep */
2749 if (write->is_uninitialized())
2751 Node *prevnode = write->get_node()->get_parent();
2753 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2754 if (write->is_release() && thread_sleep)
2756 if (!write->is_rmw())
2763 * @brief Create a new action representing an uninitialized atomic
2764 * @param location The memory location of the atomic object
2765 * @return A pointer to a new ModelAction
2767 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2769 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2770 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2771 act->create_cv(NULL);
2775 static void print_list(action_list_t *list)
2777 action_list_t::iterator it;
2779 model_print("---------------------------------------------------------------------\n");
2781 unsigned int hash = 0;
2783 for (it = list->begin(); it != list->end(); it++) {
2785 hash = hash^(hash<<3)^((*it)->hash());
2787 model_print("HASH %u\n", hash);
2788 model_print("---------------------------------------------------------------------\n");
2791 #if SUPPORT_MOD_ORDER_DUMP
2792 void ModelChecker::dumpGraph(char *filename) const
2795 sprintf(buffer, "%s.dot", filename);
2796 FILE *file = fopen(buffer, "w");
2797 fprintf(file, "digraph %s {\n", filename);
2798 mo_graph->dumpNodes(file);
2799 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2801 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2802 ModelAction *act = *it;
2803 if (act->is_read()) {
2804 mo_graph->dot_print_node(file, act);
2805 if (act->get_reads_from())
2806 mo_graph->dot_print_edge(file,
2807 act->get_reads_from(),
2809 "label=\"rf\", color=red, weight=2");
2811 mo_graph->dot_print_edge(file,
2812 act->get_reads_from_promise(),
2814 "label=\"rf\", color=red");
2816 if (thread_array[act->get_tid()]) {
2817 mo_graph->dot_print_edge(file,
2818 thread_array[id_to_int(act->get_tid())],
2820 "label=\"sb\", color=blue, weight=400");
2823 thread_array[act->get_tid()] = act;
2825 fprintf(file, "}\n");
2826 model_free(thread_array);
2831 /** @brief Prints an execution trace summary. */
2832 void ModelChecker::print_summary() const
2834 #if SUPPORT_MOD_ORDER_DUMP
2835 char buffername[100];
2836 sprintf(buffername, "exec%04u", stats.num_total);
2837 mo_graph->dumpGraphToFile(buffername);
2838 sprintf(buffername, "graph%04u", stats.num_total);
2839 dumpGraph(buffername);
2842 model_print("Execution %d:", stats.num_total);
2843 if (isfeasibleprefix()) {
2844 if (scheduler->all_threads_sleeping())
2845 model_print(" SLEEP-SET REDUNDANT");
2848 print_infeasibility(" INFEASIBLE");
2849 print_list(action_trace);
2854 * Add a Thread to the system for the first time. Should only be called once
2856 * @param t The Thread to add
2858 void ModelChecker::add_thread(Thread *t)
2860 thread_map->put(id_to_int(t->get_id()), t);
2861 scheduler->add_thread(t);
2865 * Removes a thread from the scheduler.
2866 * @param the thread to remove.
2868 void ModelChecker::remove_thread(Thread *t)
2870 scheduler->remove_thread(t);
2874 * @brief Get a Thread reference by its ID
2875 * @param tid The Thread's ID
2876 * @return A Thread reference
2878 Thread * ModelChecker::get_thread(thread_id_t tid) const
2880 return thread_map->get(id_to_int(tid));
2884 * @brief Get a reference to the Thread in which a ModelAction was executed
2885 * @param act The ModelAction
2886 * @return A Thread reference
2888 Thread * ModelChecker::get_thread(const ModelAction *act) const
2890 return get_thread(act->get_tid());
2894 * @brief Get a Promise's "promise number"
2896 * A "promise number" is an index number that is unique to a promise, valid
2897 * only for a specific snapshot of an execution trace. Promises may come and go
2898 * as they are generated an resolved, so an index only retains meaning for the
2901 * @param promise The Promise to check
2902 * @return The promise index, if the promise still is valid; otherwise -1
2904 int ModelChecker::get_promise_number(const Promise *promise) const
2906 for (unsigned int i = 0; i < promises->size(); i++)
2907 if ((*promises)[i] == promise)
2914 * @brief Check if a Thread is currently enabled
2915 * @param t The Thread to check
2916 * @return True if the Thread is currently enabled
2918 bool ModelChecker::is_enabled(Thread *t) const
2920 return scheduler->is_enabled(t);
2924 * @brief Check if a Thread is currently enabled
2925 * @param tid The ID of the Thread to check
2926 * @return True if the Thread is currently enabled
2928 bool ModelChecker::is_enabled(thread_id_t tid) const
2930 return scheduler->is_enabled(tid);
2934 * Switch from a model-checker context to a user-thread context. This is the
2935 * complement of ModelChecker::switch_to_master and must be called from the
2936 * model-checker context
2938 * @param thread The user-thread to switch to
2940 void ModelChecker::switch_from_master(Thread *thread)
2942 scheduler->set_current_thread(thread);
2943 Thread::swap(&system_context, thread);
2947 * Switch from a user-context to the "master thread" context (a.k.a. system
2948 * context). This switch is made with the intention of exploring a particular
2949 * model-checking action (described by a ModelAction object). Must be called
2950 * from a user-thread context.
2952 * @param act The current action that will be explored. May be NULL only if
2953 * trace is exiting via an assertion (see ModelChecker::set_assert and
2954 * ModelChecker::has_asserted).
2955 * @return Return the value returned by the current action
2957 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2960 Thread *old = thread_current();
2961 ASSERT(!old->get_pending());
2962 old->set_pending(act);
2963 if (Thread::swap(old, &system_context) < 0) {
2964 perror("swap threads");
2967 return old->get_return_value();
2971 * Takes the next step in the execution, if possible.
2972 * @param curr The current step to take
2973 * @return Returns the next Thread to run, if any; NULL if this execution
2976 Thread * ModelChecker::take_step(ModelAction *curr)
2978 Thread *curr_thrd = get_thread(curr);
2979 ASSERT(curr_thrd->get_state() == THREAD_READY);
2981 curr = check_current_action(curr);
2983 /* Infeasible -> don't take any more steps */
2984 if (is_infeasible())
2986 else if (isfeasibleprefix() && have_bug_reports()) {
2991 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
2994 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2995 scheduler->remove_thread(curr_thrd);
2997 Thread *next_thrd = get_next_thread(curr);
2999 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3000 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3005 /** Wrapper to run the user's main function, with appropriate arguments */
3006 void user_main_wrapper(void *)
3008 user_main(model->params.argc, model->params.argv);
3011 /** @brief Run ModelChecker for the user program */
3012 void ModelChecker::run()
3016 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3021 * Stash next pending action(s) for thread(s). There
3022 * should only need to stash one thread's action--the
3023 * thread which just took a step--plus the first step
3024 * for any newly-created thread
3026 for (unsigned int i = 0; i < get_num_threads(); i++) {
3027 thread_id_t tid = int_to_id(i);
3028 Thread *thr = get_thread(tid);
3029 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3030 switch_from_master(thr);
3034 /* Catch assertions from prior take_step or from
3035 * between-ModelAction bugs (e.g., data races) */
3039 /* Consume the next action for a Thread */
3040 ModelAction *curr = t->get_pending();
3041 t->set_pending(NULL);
3042 t = take_step(curr);
3043 } while (t && !t->is_model_thread());
3046 * Launch end-of-execution release sequence fixups only when
3047 * the execution is otherwise feasible AND there are:
3049 * (1) pending release sequences
3050 * (2) pending assertions that could be invalidated by a change
3051 * in clock vectors (i.e., data races)
3052 * (3) no pending promises
3054 while (!pending_rel_seqs->empty() &&
3055 is_feasible_prefix_ignore_relseq() &&
3056 !unrealizedraces.empty()) {
3057 model_print("*** WARNING: release sequence fixup action "
3058 "(%zu pending release seuqence(s)) ***\n",
3059 pending_rel_seqs->size());
3060 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3061 std::memory_order_seq_cst, NULL, VALUE_NONE,
3065 } while (next_execution());
3067 model_print("******* Model-checking complete: *******\n");