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 if (node->increment_read_from()) {
869 mo_graph->rollbackChanges();
872 priv->too_many_reads = true;
876 updated = r_modification_order(curr, rf);
877 value = rf->get_value();
879 mo_graph->commitChanges();
880 mo_check_promises(curr, true);
883 case READ_FROM_PROMISE: {
884 Promise *promise = curr->get_node()->get_read_from_promise();
885 if (promise->add_reader(curr))
886 priv->failed_promise = true;
887 value = promise->get_value();
888 curr->set_read_from_promise(promise);
889 mo_graph->startChanges();
890 if (!check_recency(curr, promise))
891 priv->too_many_reads = true;
892 updated = r_modification_order(curr, promise);
893 mo_graph->commitChanges();
896 case READ_FROM_FUTURE: {
897 /* Read from future value */
898 struct future_value fv = node->get_future_value();
899 Promise *promise = new Promise(curr, fv);
901 curr->set_read_from_promise(promise);
902 promises->push_back(promise);
903 mo_graph->startChanges();
904 updated = r_modification_order(curr, promise);
905 mo_graph->commitChanges();
911 get_thread(curr)->set_return_value(value);
917 * Processes a lock, trylock, or unlock model action. @param curr is
918 * the read model action to process.
920 * The try lock operation checks whether the lock is taken. If not,
921 * it falls to the normal lock operation case. If so, it returns
924 * The lock operation has already been checked that it is enabled, so
925 * it just grabs the lock and synchronizes with the previous unlock.
927 * The unlock operation has to re-enable all of the threads that are
928 * waiting on the lock.
930 * @return True if synchronization was updated; false otherwise
932 bool ModelChecker::process_mutex(ModelAction *curr)
934 std::mutex *mutex = NULL;
935 struct std::mutex_state *state = NULL;
937 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
938 mutex = (std::mutex *)curr->get_location();
939 state = mutex->get_state();
940 } else if (curr->is_wait()) {
941 mutex = (std::mutex *)curr->get_value();
942 state = mutex->get_state();
945 switch (curr->get_type()) {
946 case ATOMIC_TRYLOCK: {
947 bool success = !state->islocked;
948 curr->set_try_lock(success);
950 get_thread(curr)->set_return_value(0);
953 get_thread(curr)->set_return_value(1);
955 //otherwise fall into the lock case
957 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
958 assert_bug("Lock access before initialization");
959 state->islocked = true;
960 ModelAction *unlock = get_last_unlock(curr);
961 //synchronize with the previous unlock statement
962 if (unlock != NULL) {
963 curr->synchronize_with(unlock);
968 case ATOMIC_UNLOCK: {
970 state->islocked = false;
971 //wake up the other threads
972 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
973 //activate all the waiting threads
974 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
975 scheduler->wake(get_thread(*rit));
982 state->islocked = false;
983 //wake up the other threads
984 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
985 //activate all the waiting threads
986 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
987 scheduler->wake(get_thread(*rit));
990 //check whether we should go to sleep or not...simulate spurious failures
991 if (curr->get_node()->get_misc() == 0) {
992 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
994 scheduler->sleep(get_thread(curr));
998 case ATOMIC_NOTIFY_ALL: {
999 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1000 //activate all the waiting threads
1001 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1002 scheduler->wake(get_thread(*rit));
1007 case ATOMIC_NOTIFY_ONE: {
1008 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1009 int wakeupthread = curr->get_node()->get_misc();
1010 action_list_t::iterator it = waiters->begin();
1011 advance(it, wakeupthread);
1012 scheduler->wake(get_thread(*it));
1023 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1025 /* Do more ambitious checks now that mo is more complete */
1026 if (mo_may_allow(writer, reader)) {
1027 Node *node = reader->get_node();
1029 /* Find an ancestor thread which exists at the time of the reader */
1030 Thread *write_thread = get_thread(writer);
1031 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1032 write_thread = write_thread->get_parent();
1034 struct future_value fv = {
1035 writer->get_write_value(),
1036 writer->get_seq_number() + params.maxfuturedelay,
1037 write_thread->get_id(),
1039 if (node->add_future_value(fv))
1040 set_latest_backtrack(reader);
1045 * Process a write ModelAction
1046 * @param curr The ModelAction to process
1047 * @return True if the mo_graph was updated or promises were resolved
1049 bool ModelChecker::process_write(ModelAction *curr)
1051 /* Readers to which we may send our future value */
1052 std::vector< ModelAction *, ModelAlloc<ModelAction *> > send_fv;
1054 bool updated_mod_order = w_modification_order(curr, &send_fv);
1055 int promise_idx = get_promise_to_resolve(curr);
1056 const ModelAction *earliest_promise_reader;
1057 bool updated_promises = false;
1059 if (promise_idx >= 0) {
1060 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1061 updated_promises = resolve_promise(curr, promise_idx);
1063 earliest_promise_reader = NULL;
1065 /* Don't send future values to reads after the Promise we resolve */
1066 for (unsigned int i = 0; i < send_fv.size(); i++) {
1067 ModelAction *read = send_fv[i];
1068 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1069 futurevalues->push_back(PendingFutureValue(curr, read));
1072 if (promises->size() == 0) {
1073 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1074 struct PendingFutureValue pfv = (*futurevalues)[i];
1075 add_future_value(pfv.writer, pfv.act);
1077 futurevalues->clear();
1080 mo_graph->commitChanges();
1081 mo_check_promises(curr, false);
1083 get_thread(curr)->set_return_value(VALUE_NONE);
1084 return updated_mod_order || updated_promises;
1088 * Process a fence ModelAction
1089 * @param curr The ModelAction to process
1090 * @return True if synchronization was updated
1092 bool ModelChecker::process_fence(ModelAction *curr)
1095 * fence-relaxed: no-op
1096 * fence-release: only log the occurence (not in this function), for
1097 * use in later synchronization
1098 * fence-acquire (this function): search for hypothetical release
1101 bool updated = false;
1102 if (curr->is_acquire()) {
1103 action_list_t *list = action_trace;
1104 action_list_t::reverse_iterator rit;
1105 /* Find X : is_read(X) && X --sb-> curr */
1106 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1107 ModelAction *act = *rit;
1110 if (act->get_tid() != curr->get_tid())
1112 /* Stop at the beginning of the thread */
1113 if (act->is_thread_start())
1115 /* Stop once we reach a prior fence-acquire */
1116 if (act->is_fence() && act->is_acquire())
1118 if (!act->is_read())
1120 /* read-acquire will find its own release sequences */
1121 if (act->is_acquire())
1124 /* Establish hypothetical release sequences */
1125 rel_heads_list_t release_heads;
1126 get_release_seq_heads(curr, act, &release_heads);
1127 for (unsigned int i = 0; i < release_heads.size(); i++)
1128 if (!curr->synchronize_with(release_heads[i]))
1129 set_bad_synchronization();
1130 if (release_heads.size() != 0)
1138 * @brief Process the current action for thread-related activity
1140 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1141 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1142 * synchronization, etc. This function is a no-op for non-THREAD actions
1143 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1145 * @param curr The current action
1146 * @return True if synchronization was updated or a thread completed
1148 bool ModelChecker::process_thread_action(ModelAction *curr)
1150 bool updated = false;
1152 switch (curr->get_type()) {
1153 case THREAD_CREATE: {
1154 thrd_t *thrd = (thrd_t *)curr->get_location();
1155 struct thread_params *params = (struct thread_params *)curr->get_value();
1156 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1158 th->set_creation(curr);
1159 /* Promises can be satisfied by children */
1160 for (unsigned int i = 0; i < promises->size(); i++) {
1161 Promise *promise = (*promises)[i];
1162 if (promise->thread_is_available(curr->get_tid()))
1163 promise->add_thread(th->get_id());
1168 Thread *blocking = curr->get_thread_operand();
1169 ModelAction *act = get_last_action(blocking->get_id());
1170 curr->synchronize_with(act);
1171 updated = true; /* trigger rel-seq checks */
1174 case THREAD_FINISH: {
1175 Thread *th = get_thread(curr);
1176 while (!th->wait_list_empty()) {
1177 ModelAction *act = th->pop_wait_list();
1178 scheduler->wake(get_thread(act));
1181 /* Completed thread can't satisfy promises */
1182 for (unsigned int i = 0; i < promises->size(); i++) {
1183 Promise *promise = (*promises)[i];
1184 if (promise->thread_is_available(th->get_id()))
1185 if (promise->eliminate_thread(th->get_id()))
1186 priv->failed_promise = true;
1188 updated = true; /* trigger rel-seq checks */
1191 case THREAD_START: {
1192 check_promises(curr->get_tid(), NULL, curr->get_cv());
1203 * @brief Process the current action for release sequence fixup activity
1205 * Performs model-checker release sequence fixups for the current action,
1206 * forcing a single pending release sequence to break (with a given, potential
1207 * "loose" write) or to complete (i.e., synchronize). If a pending release
1208 * sequence forms a complete release sequence, then we must perform the fixup
1209 * synchronization, mo_graph additions, etc.
1211 * @param curr The current action; must be a release sequence fixup action
1212 * @param work_queue The work queue to which to add work items as they are
1215 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1217 const ModelAction *write = curr->get_node()->get_relseq_break();
1218 struct release_seq *sequence = pending_rel_seqs->back();
1219 pending_rel_seqs->pop_back();
1221 ModelAction *acquire = sequence->acquire;
1222 const ModelAction *rf = sequence->rf;
1223 const ModelAction *release = sequence->release;
1227 ASSERT(release->same_thread(rf));
1229 if (write == NULL) {
1231 * @todo Forcing a synchronization requires that we set
1232 * modification order constraints. For instance, we can't allow
1233 * a fixup sequence in which two separate read-acquire
1234 * operations read from the same sequence, where the first one
1235 * synchronizes and the other doesn't. Essentially, we can't
1236 * allow any writes to insert themselves between 'release' and
1240 /* Must synchronize */
1241 if (!acquire->synchronize_with(release)) {
1242 set_bad_synchronization();
1245 /* Re-check all pending release sequences */
1246 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1247 /* Re-check act for mo_graph edges */
1248 work_queue->push_back(MOEdgeWorkEntry(acquire));
1250 /* propagate synchronization to later actions */
1251 action_list_t::reverse_iterator rit = action_trace->rbegin();
1252 for (; (*rit) != acquire; rit++) {
1253 ModelAction *propagate = *rit;
1254 if (acquire->happens_before(propagate)) {
1255 propagate->synchronize_with(acquire);
1256 /* Re-check 'propagate' for mo_graph edges */
1257 work_queue->push_back(MOEdgeWorkEntry(propagate));
1261 /* Break release sequence with new edges:
1262 * release --mo--> write --mo--> rf */
1263 mo_graph->addEdge(release, write);
1264 mo_graph->addEdge(write, rf);
1267 /* See if we have realized a data race */
1272 * Initialize the current action by performing one or more of the following
1273 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1274 * in the NodeStack, manipulating backtracking sets, allocating and
1275 * initializing clock vectors, and computing the promises to fulfill.
1277 * @param curr The current action, as passed from the user context; may be
1278 * freed/invalidated after the execution of this function, with a different
1279 * action "returned" its place (pass-by-reference)
1280 * @return True if curr is a newly-explored action; false otherwise
1282 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1284 ModelAction *newcurr;
1286 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1287 newcurr = process_rmw(*curr);
1290 if (newcurr->is_rmw())
1291 compute_promises(newcurr);
1297 (*curr)->set_seq_number(get_next_seq_num());
1299 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1301 /* First restore type and order in case of RMW operation */
1302 if ((*curr)->is_rmwr())
1303 newcurr->copy_typeandorder(*curr);
1305 ASSERT((*curr)->get_location() == newcurr->get_location());
1306 newcurr->copy_from_new(*curr);
1308 /* Discard duplicate ModelAction; use action from NodeStack */
1311 /* Always compute new clock vector */
1312 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1315 return false; /* Action was explored previously */
1319 /* Always compute new clock vector */
1320 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1322 /* Assign most recent release fence */
1323 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1326 * Perform one-time actions when pushing new ModelAction onto
1329 if (newcurr->is_write())
1330 compute_promises(newcurr);
1331 else if (newcurr->is_relseq_fixup())
1332 compute_relseq_breakwrites(newcurr);
1333 else if (newcurr->is_wait())
1334 newcurr->get_node()->set_misc_max(2);
1335 else if (newcurr->is_notify_one()) {
1336 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1338 return true; /* This was a new ModelAction */
1343 * @brief Establish reads-from relation between two actions
1345 * Perform basic operations involved with establishing a concrete rf relation,
1346 * including setting the ModelAction data and checking for release sequences.
1348 * @param act The action that is reading (must be a read)
1349 * @param rf The action from which we are reading (must be a write)
1351 * @return True if this read established synchronization
1353 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1356 act->set_read_from(rf);
1357 if (act->is_acquire()) {
1358 rel_heads_list_t release_heads;
1359 get_release_seq_heads(act, act, &release_heads);
1360 int num_heads = release_heads.size();
1361 for (unsigned int i = 0; i < release_heads.size(); i++)
1362 if (!act->synchronize_with(release_heads[i])) {
1363 set_bad_synchronization();
1366 return num_heads > 0;
1372 * Check promises and eliminate potentially-satisfying threads when a thread is
1373 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1374 * no longer satisfy a promise generated from that thread.
1376 * @param blocker The thread on which a thread is waiting
1377 * @param waiting The waiting thread
1379 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1381 for (unsigned int i = 0; i < promises->size(); i++) {
1382 Promise *promise = (*promises)[i];
1383 if (!promise->thread_is_available(waiting->get_id()))
1385 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1386 ModelAction *reader = promise->get_reader(j);
1387 if (reader->get_tid() != blocker->get_id())
1389 if (promise->eliminate_thread(waiting->get_id())) {
1390 /* Promise has failed */
1391 priv->failed_promise = true;
1393 /* Only eliminate the 'waiting' thread once */
1401 * @brief Check whether a model action is enabled.
1403 * Checks whether a lock or join operation would be successful (i.e., is the
1404 * lock already locked, or is the joined thread already complete). If not, put
1405 * the action in a waiter list.
1407 * @param curr is the ModelAction to check whether it is enabled.
1408 * @return a bool that indicates whether the action is enabled.
1410 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1411 if (curr->is_lock()) {
1412 std::mutex *lock = (std::mutex *)curr->get_location();
1413 struct std::mutex_state *state = lock->get_state();
1414 if (state->islocked) {
1415 //Stick the action in the appropriate waiting queue
1416 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1419 } else if (curr->get_type() == THREAD_JOIN) {
1420 Thread *blocking = (Thread *)curr->get_location();
1421 if (!blocking->is_complete()) {
1422 blocking->push_wait_list(curr);
1423 thread_blocking_check_promises(blocking, get_thread(curr));
1432 * This is the heart of the model checker routine. It performs model-checking
1433 * actions corresponding to a given "current action." Among other processes, it
1434 * calculates reads-from relationships, updates synchronization clock vectors,
1435 * forms a memory_order constraints graph, and handles replay/backtrack
1436 * execution when running permutations of previously-observed executions.
1438 * @param curr The current action to process
1439 * @return The ModelAction that is actually executed; may be different than
1440 * curr; may be NULL, if the current action is not enabled to run
1442 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1445 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1447 if (!check_action_enabled(curr)) {
1448 /* Make the execution look like we chose to run this action
1449 * much later, when a lock/join can succeed */
1450 get_thread(curr)->set_pending(curr);
1451 scheduler->sleep(get_thread(curr));
1455 bool newly_explored = initialize_curr_action(&curr);
1461 wake_up_sleeping_actions(curr);
1463 /* Add the action to lists before any other model-checking tasks */
1464 if (!second_part_of_rmw)
1465 add_action_to_lists(curr);
1467 /* Build may_read_from set for newly-created actions */
1468 if (newly_explored && curr->is_read())
1469 build_may_read_from(curr);
1471 /* Initialize work_queue with the "current action" work */
1472 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1473 while (!work_queue.empty() && !has_asserted()) {
1474 WorkQueueEntry work = work_queue.front();
1475 work_queue.pop_front();
1477 switch (work.type) {
1478 case WORK_CHECK_CURR_ACTION: {
1479 ModelAction *act = work.action;
1480 bool update = false; /* update this location's release seq's */
1481 bool update_all = false; /* update all release seq's */
1483 if (process_thread_action(curr))
1486 if (act->is_read() && !second_part_of_rmw && process_read(act))
1489 if (act->is_write() && process_write(act))
1492 if (act->is_fence() && process_fence(act))
1495 if (act->is_mutex_op() && process_mutex(act))
1498 if (act->is_relseq_fixup())
1499 process_relseq_fixup(curr, &work_queue);
1502 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1504 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1507 case WORK_CHECK_RELEASE_SEQ:
1508 resolve_release_sequences(work.location, &work_queue);
1510 case WORK_CHECK_MO_EDGES: {
1511 /** @todo Complete verification of work_queue */
1512 ModelAction *act = work.action;
1513 bool updated = false;
1515 if (act->is_read()) {
1516 const ModelAction *rf = act->get_reads_from();
1517 const Promise *promise = act->get_reads_from_promise();
1519 if (r_modification_order(act, rf))
1521 } else if (promise) {
1522 if (r_modification_order(act, promise))
1526 if (act->is_write()) {
1527 if (w_modification_order(act, NULL))
1530 mo_graph->commitChanges();
1533 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1542 check_curr_backtracking(curr);
1543 set_backtracking(curr);
1547 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1549 Node *currnode = curr->get_node();
1550 Node *parnode = currnode->get_parent();
1552 if ((parnode && !parnode->backtrack_empty()) ||
1553 !currnode->misc_empty() ||
1554 !currnode->read_from_empty() ||
1555 !currnode->promise_empty() ||
1556 !currnode->relseq_break_empty()) {
1557 set_latest_backtrack(curr);
1561 bool ModelChecker::promises_expired() const
1563 for (unsigned int i = 0; i < promises->size(); i++) {
1564 Promise *promise = (*promises)[i];
1565 if (promise->get_expiration() < priv->used_sequence_numbers)
1572 * This is the strongest feasibility check available.
1573 * @return whether the current trace (partial or complete) must be a prefix of
1576 bool ModelChecker::isfeasibleprefix() const
1578 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1582 * Print disagnostic information about an infeasible execution
1583 * @param prefix A string to prefix the output with; if NULL, then a default
1584 * message prefix will be provided
1586 void ModelChecker::print_infeasibility(const char *prefix) const
1590 if (mo_graph->checkForCycles())
1591 ptr += sprintf(ptr, "[mo cycle]");
1592 if (priv->failed_promise)
1593 ptr += sprintf(ptr, "[failed promise]");
1594 if (priv->too_many_reads)
1595 ptr += sprintf(ptr, "[too many reads]");
1596 if (priv->no_valid_reads)
1597 ptr += sprintf(ptr, "[no valid reads-from]");
1598 if (priv->bad_synchronization)
1599 ptr += sprintf(ptr, "[bad sw ordering]");
1600 if (promises_expired())
1601 ptr += sprintf(ptr, "[promise expired]");
1602 if (promises->size() != 0)
1603 ptr += sprintf(ptr, "[unresolved promise]");
1605 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1609 * Returns whether the current completed trace is feasible, except for pending
1610 * release sequences.
1612 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1614 return !is_infeasible() && promises->size() == 0;
1618 * Check if the current partial trace is infeasible. Does not check any
1619 * end-of-execution flags, which might rule out the execution. Thus, this is
1620 * useful only for ruling an execution as infeasible.
1621 * @return whether the current partial trace is infeasible.
1623 bool ModelChecker::is_infeasible() const
1625 return mo_graph->checkForCycles() ||
1626 priv->no_valid_reads ||
1627 priv->failed_promise ||
1628 priv->too_many_reads ||
1629 priv->bad_synchronization ||
1633 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1634 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1635 ModelAction *lastread = get_last_action(act->get_tid());
1636 lastread->process_rmw(act);
1637 if (act->is_rmw()) {
1638 if (lastread->get_reads_from())
1639 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1641 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1642 mo_graph->commitChanges();
1648 * A helper function for ModelChecker::check_recency, to check if the current
1649 * thread is able to read from a different write/promise for 'params.maxreads'
1650 * number of steps and if that write/promise should become visible (i.e., is
1651 * ordered later in the modification order). This helps model memory liveness.
1653 * @param curr The current action. Must be a read.
1654 * @param rf The write/promise from which we plan to read
1655 * @param other_rf The write/promise from which we may read
1656 * @return True if we were able to read from other_rf for params.maxreads steps
1658 template <typename T, typename U>
1659 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1661 /* Need a different write/promise */
1662 if (other_rf->equals(rf))
1665 /* Only look for "newer" writes/promises */
1666 if (!mo_graph->checkReachable(rf, other_rf))
1669 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1670 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1671 action_list_t::reverse_iterator rit = list->rbegin();
1672 ASSERT((*rit) == curr);
1673 /* Skip past curr */
1676 /* Does this write/promise work for everyone? */
1677 for (int i = 0; i < params.maxreads; i++, rit++) {
1678 ModelAction *act = *rit;
1679 if (!act->may_read_from(other_rf))
1686 * Checks whether a thread has read from the same write or Promise for too many
1687 * times without seeing the effects of a later write/Promise.
1690 * 1) there must a different write/promise that we could read from,
1691 * 2) we must have read from the same write/promise in excess of maxreads times,
1692 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1693 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1695 * If so, we decide that the execution is no longer feasible.
1697 * @param curr The current action. Must be a read.
1698 * @param rf The ModelAction/Promise from which we might read.
1699 * @return True if the read should succeed; false otherwise
1701 template <typename T>
1702 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1704 if (!params.maxreads)
1707 //NOTE: Next check is just optimization, not really necessary....
1708 if (curr->get_node()->get_read_from_past_size() +
1709 curr->get_node()->get_read_from_promise_size() <= 1)
1712 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1713 int tid = id_to_int(curr->get_tid());
1714 ASSERT(tid < (int)thrd_lists->size());
1715 action_list_t *list = &(*thrd_lists)[tid];
1716 action_list_t::reverse_iterator rit = list->rbegin();
1717 ASSERT((*rit) == curr);
1718 /* Skip past curr */
1721 action_list_t::reverse_iterator ritcopy = rit;
1722 /* See if we have enough reads from the same value */
1723 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1724 if (ritcopy == list->rend())
1726 ModelAction *act = *ritcopy;
1727 if (!act->is_read())
1729 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1731 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1733 if (act->get_node()->get_read_from_past_size() +
1734 act->get_node()->get_read_from_promise_size() <= 1)
1737 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1738 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1739 if (should_read_instead(curr, rf, write))
1740 return false; /* liveness failure */
1742 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1743 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1744 if (should_read_instead(curr, rf, promise))
1745 return false; /* liveness failure */
1751 * Updates the mo_graph with the constraints imposed from the current
1754 * Basic idea is the following: Go through each other thread and find
1755 * the last action that happened before our read. Two cases:
1757 * (1) The action is a write => that write must either occur before
1758 * the write we read from or be the write we read from.
1760 * (2) The action is a read => the write that that action read from
1761 * must occur before the write we read from or be the same write.
1763 * @param curr The current action. Must be a read.
1764 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1765 * @return True if modification order edges were added; false otherwise
1767 template <typename rf_type>
1768 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1770 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1773 ASSERT(curr->is_read());
1775 /* Last SC fence in the current thread */
1776 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1778 /* Iterate over all threads */
1779 for (i = 0; i < thrd_lists->size(); i++) {
1780 /* Last SC fence in thread i */
1781 ModelAction *last_sc_fence_thread_local = NULL;
1782 if (int_to_id((int)i) != curr->get_tid())
1783 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1785 /* Last SC fence in thread i, before last SC fence in current thread */
1786 ModelAction *last_sc_fence_thread_before = NULL;
1787 if (last_sc_fence_local)
1788 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1790 /* Iterate over actions in thread, starting from most recent */
1791 action_list_t *list = &(*thrd_lists)[i];
1792 action_list_t::reverse_iterator rit;
1793 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1794 ModelAction *act = *rit;
1796 if (act->is_write() && !act->equals(rf) && act != curr) {
1797 /* C++, Section 29.3 statement 5 */
1798 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1799 *act < *last_sc_fence_thread_local) {
1800 added = mo_graph->addEdge(act, rf) || added;
1803 /* C++, Section 29.3 statement 4 */
1804 else if (act->is_seqcst() && last_sc_fence_local &&
1805 *act < *last_sc_fence_local) {
1806 added = mo_graph->addEdge(act, rf) || added;
1809 /* C++, Section 29.3 statement 6 */
1810 else if (last_sc_fence_thread_before &&
1811 *act < *last_sc_fence_thread_before) {
1812 added = mo_graph->addEdge(act, rf) || added;
1818 * Include at most one act per-thread that "happens
1819 * before" curr. Don't consider reflexively.
1821 if (act->happens_before(curr) && act != curr) {
1822 if (act->is_write()) {
1823 if (!act->equals(rf)) {
1824 added = mo_graph->addEdge(act, rf) || added;
1827 const ModelAction *prevrf = act->get_reads_from();
1828 const Promise *prevrf_promise = act->get_reads_from_promise();
1830 if (!prevrf->equals(rf))
1831 added = mo_graph->addEdge(prevrf, rf) || added;
1832 } else if (!prevrf_promise->equals(rf)) {
1833 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1842 * All compatible, thread-exclusive promises must be ordered after any
1843 * concrete loads from the same thread
1845 for (unsigned int i = 0; i < promises->size(); i++)
1846 if ((*promises)[i]->is_compatible_exclusive(curr))
1847 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1853 * Updates the mo_graph with the constraints imposed from the current write.
1855 * Basic idea is the following: Go through each other thread and find
1856 * the lastest action that happened before our write. Two cases:
1858 * (1) The action is a write => that write must occur before
1861 * (2) The action is a read => the write that that action read from
1862 * must occur before the current write.
1864 * This method also handles two other issues:
1866 * (I) Sequential Consistency: Making sure that if the current write is
1867 * seq_cst, that it occurs after the previous seq_cst write.
1869 * (II) Sending the write back to non-synchronizing reads.
1871 * @param curr The current action. Must be a write.
1872 * @param send_fv A vector for stashing reads to which we may pass our future
1873 * value. If NULL, then don't record any future values.
1874 * @return True if modification order edges were added; false otherwise
1876 bool ModelChecker::w_modification_order(ModelAction *curr, std::vector< ModelAction *, ModelAlloc<ModelAction *> > *send_fv)
1878 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1881 ASSERT(curr->is_write());
1883 if (curr->is_seqcst()) {
1884 /* We have to at least see the last sequentially consistent write,
1885 so we are initialized. */
1886 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1887 if (last_seq_cst != NULL) {
1888 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1892 /* Last SC fence in the current thread */
1893 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1895 /* Iterate over all threads */
1896 for (i = 0; i < thrd_lists->size(); i++) {
1897 /* Last SC fence in thread i, before last SC fence in current thread */
1898 ModelAction *last_sc_fence_thread_before = NULL;
1899 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1900 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1902 /* Iterate over actions in thread, starting from most recent */
1903 action_list_t *list = &(*thrd_lists)[i];
1904 action_list_t::reverse_iterator rit;
1905 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1906 ModelAction *act = *rit;
1909 * 1) If RMW and it actually read from something, then we
1910 * already have all relevant edges, so just skip to next
1913 * 2) If RMW and it didn't read from anything, we should
1914 * whatever edge we can get to speed up convergence.
1916 * 3) If normal write, we need to look at earlier actions, so
1917 * continue processing list.
1919 if (curr->is_rmw()) {
1920 if (curr->get_reads_from() != NULL)
1928 /* C++, Section 29.3 statement 7 */
1929 if (last_sc_fence_thread_before && act->is_write() &&
1930 *act < *last_sc_fence_thread_before) {
1931 added = mo_graph->addEdge(act, curr) || added;
1936 * Include at most one act per-thread that "happens
1939 if (act->happens_before(curr)) {
1941 * Note: if act is RMW, just add edge:
1943 * The following edge should be handled elsewhere:
1944 * readfrom(act) --mo--> act
1946 if (act->is_write())
1947 added = mo_graph->addEdge(act, curr) || added;
1948 else if (act->is_read()) {
1949 //if previous read accessed a null, just keep going
1950 if (act->get_reads_from() == NULL)
1952 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1955 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1956 !act->same_thread(curr)) {
1957 /* We have an action that:
1958 (1) did not happen before us
1959 (2) is a read and we are a write
1960 (3) cannot synchronize with us
1961 (4) is in a different thread
1963 that read could potentially read from our write. Note that
1964 these checks are overly conservative at this point, we'll
1965 do more checks before actually removing the
1969 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1970 if (!is_infeasible())
1971 send_fv->push_back(act);
1972 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1973 add_future_value(curr, act);
1980 * All compatible, thread-exclusive promises must be ordered after any
1981 * concrete stores to the same thread, or else they can be merged with
1984 for (unsigned int i = 0; i < promises->size(); i++)
1985 if ((*promises)[i]->is_compatible_exclusive(curr))
1986 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1991 /** Arbitrary reads from the future are not allowed. Section 29.3
1992 * part 9 places some constraints. This method checks one result of constraint
1993 * constraint. Others require compiler support. */
1994 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1996 if (!writer->is_rmw())
1999 if (!reader->is_rmw())
2002 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2003 if (search == reader)
2005 if (search->get_tid() == reader->get_tid() &&
2006 search->happens_before(reader))
2014 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2015 * some constraints. This method checks one the following constraint (others
2016 * require compiler support):
2018 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2020 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2022 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2024 /* Iterate over all threads */
2025 for (i = 0; i < thrd_lists->size(); i++) {
2026 const ModelAction *write_after_read = NULL;
2028 /* Iterate over actions in thread, starting from most recent */
2029 action_list_t *list = &(*thrd_lists)[i];
2030 action_list_t::reverse_iterator rit;
2031 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2032 ModelAction *act = *rit;
2034 /* Don't disallow due to act == reader */
2035 if (!reader->happens_before(act) || reader == act)
2037 else if (act->is_write())
2038 write_after_read = act;
2039 else if (act->is_read() && act->get_reads_from() != NULL)
2040 write_after_read = act->get_reads_from();
2043 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2050 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2051 * The ModelAction under consideration is expected to be taking part in
2052 * release/acquire synchronization as an object of the "reads from" relation.
2053 * Note that this can only provide release sequence support for RMW chains
2054 * which do not read from the future, as those actions cannot be traced until
2055 * their "promise" is fulfilled. Similarly, we may not even establish the
2056 * presence of a release sequence with certainty, as some modification order
2057 * constraints may be decided further in the future. Thus, this function
2058 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2059 * and a boolean representing certainty.
2061 * @param rf The action that might be part of a release sequence. Must be a
2063 * @param release_heads A pass-by-reference style return parameter. After
2064 * execution of this function, release_heads will contain the heads of all the
2065 * relevant release sequences, if any exists with certainty
2066 * @param pending A pass-by-reference style return parameter which is only used
2067 * when returning false (i.e., uncertain). Returns most information regarding
2068 * an uncertain release sequence, including any write operations that might
2069 * break the sequence.
2070 * @return true, if the ModelChecker is certain that release_heads is complete;
2073 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2074 rel_heads_list_t *release_heads,
2075 struct release_seq *pending) const
2077 /* Only check for release sequences if there are no cycles */
2078 if (mo_graph->checkForCycles())
2081 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2082 ASSERT(rf->is_write());
2084 if (rf->is_release())
2085 release_heads->push_back(rf);
2086 else if (rf->get_last_fence_release())
2087 release_heads->push_back(rf->get_last_fence_release());
2089 break; /* End of RMW chain */
2091 /** @todo Need to be smarter here... In the linux lock
2092 * example, this will run to the beginning of the program for
2094 /** @todo The way to be smarter here is to keep going until 1
2095 * thread has a release preceded by an acquire and you've seen
2098 /* acq_rel RMW is a sufficient stopping condition */
2099 if (rf->is_acquire() && rf->is_release())
2100 return true; /* complete */
2103 /* read from future: need to settle this later */
2105 return false; /* incomplete */
2108 if (rf->is_release())
2109 return true; /* complete */
2111 /* else relaxed write
2112 * - check for fence-release in the same thread (29.8, stmt. 3)
2113 * - check modification order for contiguous subsequence
2114 * -> rf must be same thread as release */
2116 const ModelAction *fence_release = rf->get_last_fence_release();
2117 /* Synchronize with a fence-release unconditionally; we don't need to
2118 * find any more "contiguous subsequence..." for it */
2120 release_heads->push_back(fence_release);
2122 int tid = id_to_int(rf->get_tid());
2123 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2124 action_list_t *list = &(*thrd_lists)[tid];
2125 action_list_t::const_reverse_iterator rit;
2127 /* Find rf in the thread list */
2128 rit = std::find(list->rbegin(), list->rend(), rf);
2129 ASSERT(rit != list->rend());
2131 /* Find the last {write,fence}-release */
2132 for (; rit != list->rend(); rit++) {
2133 if (fence_release && *(*rit) < *fence_release)
2135 if ((*rit)->is_release())
2138 if (rit == list->rend()) {
2139 /* No write-release in this thread */
2140 return true; /* complete */
2141 } else if (fence_release && *(*rit) < *fence_release) {
2142 /* The fence-release is more recent (and so, "stronger") than
2143 * the most recent write-release */
2144 return true; /* complete */
2145 } /* else, need to establish contiguous release sequence */
2146 ModelAction *release = *rit;
2148 ASSERT(rf->same_thread(release));
2150 pending->writes.clear();
2152 bool certain = true;
2153 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2154 if (id_to_int(rf->get_tid()) == (int)i)
2156 list = &(*thrd_lists)[i];
2158 /* Can we ensure no future writes from this thread may break
2159 * the release seq? */
2160 bool future_ordered = false;
2162 ModelAction *last = get_last_action(int_to_id(i));
2163 Thread *th = get_thread(int_to_id(i));
2164 if ((last && rf->happens_before(last)) ||
2167 future_ordered = true;
2169 ASSERT(!th->is_model_thread() || future_ordered);
2171 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2172 const ModelAction *act = *rit;
2173 /* Reach synchronization -> this thread is complete */
2174 if (act->happens_before(release))
2176 if (rf->happens_before(act)) {
2177 future_ordered = true;
2181 /* Only non-RMW writes can break release sequences */
2182 if (!act->is_write() || act->is_rmw())
2185 /* Check modification order */
2186 if (mo_graph->checkReachable(rf, act)) {
2187 /* rf --mo--> act */
2188 future_ordered = true;
2191 if (mo_graph->checkReachable(act, release))
2192 /* act --mo--> release */
2194 if (mo_graph->checkReachable(release, act) &&
2195 mo_graph->checkReachable(act, rf)) {
2196 /* release --mo-> act --mo--> rf */
2197 return true; /* complete */
2199 /* act may break release sequence */
2200 pending->writes.push_back(act);
2203 if (!future_ordered)
2204 certain = false; /* This thread is uncertain */
2208 release_heads->push_back(release);
2209 pending->writes.clear();
2211 pending->release = release;
2218 * An interface for getting the release sequence head(s) with which a
2219 * given ModelAction must synchronize. This function only returns a non-empty
2220 * result when it can locate a release sequence head with certainty. Otherwise,
2221 * it may mark the internal state of the ModelChecker so that it will handle
2222 * the release sequence at a later time, causing @a acquire to update its
2223 * synchronization at some later point in execution.
2225 * @param acquire The 'acquire' action that may synchronize with a release
2227 * @param read The read action that may read from a release sequence; this may
2228 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2229 * when 'acquire' is a fence-acquire)
2230 * @param release_heads A pass-by-reference return parameter. Will be filled
2231 * with the head(s) of the release sequence(s), if they exists with certainty.
2232 * @see ModelChecker::release_seq_heads
2234 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2235 ModelAction *read, rel_heads_list_t *release_heads)
2237 const ModelAction *rf = read->get_reads_from();
2238 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2239 sequence->acquire = acquire;
2240 sequence->read = read;
2242 if (!release_seq_heads(rf, release_heads, sequence)) {
2243 /* add act to 'lazy checking' list */
2244 pending_rel_seqs->push_back(sequence);
2246 snapshot_free(sequence);
2251 * Attempt to resolve all stashed operations that might synchronize with a
2252 * release sequence for a given location. This implements the "lazy" portion of
2253 * determining whether or not a release sequence was contiguous, since not all
2254 * modification order information is present at the time an action occurs.
2256 * @param location The location/object that should be checked for release
2257 * sequence resolutions. A NULL value means to check all locations.
2258 * @param work_queue The work queue to which to add work items as they are
2260 * @return True if any updates occurred (new synchronization, new mo_graph
2263 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2265 bool updated = false;
2266 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2267 while (it != pending_rel_seqs->end()) {
2268 struct release_seq *pending = *it;
2269 ModelAction *acquire = pending->acquire;
2270 const ModelAction *read = pending->read;
2272 /* Only resolve sequences on the given location, if provided */
2273 if (location && read->get_location() != location) {
2278 const ModelAction *rf = read->get_reads_from();
2279 rel_heads_list_t release_heads;
2281 complete = release_seq_heads(rf, &release_heads, pending);
2282 for (unsigned int i = 0; i < release_heads.size(); i++) {
2283 if (!acquire->has_synchronized_with(release_heads[i])) {
2284 if (acquire->synchronize_with(release_heads[i]))
2287 set_bad_synchronization();
2292 /* Re-check all pending release sequences */
2293 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2294 /* Re-check read-acquire for mo_graph edges */
2295 if (acquire->is_read())
2296 work_queue->push_back(MOEdgeWorkEntry(acquire));
2298 /* propagate synchronization to later actions */
2299 action_list_t::reverse_iterator rit = action_trace->rbegin();
2300 for (; (*rit) != acquire; rit++) {
2301 ModelAction *propagate = *rit;
2302 if (acquire->happens_before(propagate)) {
2303 propagate->synchronize_with(acquire);
2304 /* Re-check 'propagate' for mo_graph edges */
2305 work_queue->push_back(MOEdgeWorkEntry(propagate));
2310 it = pending_rel_seqs->erase(it);
2311 snapshot_free(pending);
2317 // If we resolved promises or data races, see if we have realized a data race.
2324 * Performs various bookkeeping operations for the current ModelAction. For
2325 * instance, adds action to the per-object, per-thread action vector and to the
2326 * action trace list of all thread actions.
2328 * @param act is the ModelAction to add.
2330 void ModelChecker::add_action_to_lists(ModelAction *act)
2332 int tid = id_to_int(act->get_tid());
2333 ModelAction *uninit = NULL;
2335 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2336 if (list->empty() && act->is_atomic_var()) {
2337 uninit = new_uninitialized_action(act->get_location());
2338 uninit_id = id_to_int(uninit->get_tid());
2339 list->push_back(uninit);
2341 list->push_back(act);
2343 action_trace->push_back(act);
2345 action_trace->push_front(uninit);
2347 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2348 if (tid >= (int)vec->size())
2349 vec->resize(priv->next_thread_id);
2350 (*vec)[tid].push_back(act);
2352 (*vec)[uninit_id].push_front(uninit);
2354 if ((int)thrd_last_action->size() <= tid)
2355 thrd_last_action->resize(get_num_threads());
2356 (*thrd_last_action)[tid] = act;
2358 (*thrd_last_action)[uninit_id] = uninit;
2360 if (act->is_fence() && act->is_release()) {
2361 if ((int)thrd_last_fence_release->size() <= tid)
2362 thrd_last_fence_release->resize(get_num_threads());
2363 (*thrd_last_fence_release)[tid] = act;
2366 if (act->is_wait()) {
2367 void *mutex_loc = (void *) act->get_value();
2368 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2370 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2371 if (tid >= (int)vec->size())
2372 vec->resize(priv->next_thread_id);
2373 (*vec)[tid].push_back(act);
2378 * @brief Get the last action performed by a particular Thread
2379 * @param tid The thread ID of the Thread in question
2380 * @return The last action in the thread
2382 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2384 int threadid = id_to_int(tid);
2385 if (threadid < (int)thrd_last_action->size())
2386 return (*thrd_last_action)[id_to_int(tid)];
2392 * @brief Get the last fence release performed by a particular Thread
2393 * @param tid The thread ID of the Thread in question
2394 * @return The last fence release in the thread, if one exists; NULL otherwise
2396 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2398 int threadid = id_to_int(tid);
2399 if (threadid < (int)thrd_last_fence_release->size())
2400 return (*thrd_last_fence_release)[id_to_int(tid)];
2406 * Gets the last memory_order_seq_cst write (in the total global sequence)
2407 * performed on a particular object (i.e., memory location), not including the
2409 * @param curr The current ModelAction; also denotes the object location to
2411 * @return The last seq_cst write
2413 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2415 void *location = curr->get_location();
2416 action_list_t *list = get_safe_ptr_action(obj_map, location);
2417 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2418 action_list_t::reverse_iterator rit;
2419 for (rit = list->rbegin(); rit != list->rend(); rit++)
2420 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2426 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2427 * performed in a particular thread, prior to a particular fence.
2428 * @param tid The ID of the thread to check
2429 * @param before_fence The fence from which to begin the search; if NULL, then
2430 * search for the most recent fence in the thread.
2431 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2433 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2435 /* All fences should have NULL location */
2436 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2437 action_list_t::reverse_iterator rit = list->rbegin();
2440 for (; rit != list->rend(); rit++)
2441 if (*rit == before_fence)
2444 ASSERT(*rit == before_fence);
2448 for (; rit != list->rend(); rit++)
2449 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2455 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2456 * location). This function identifies the mutex according to the current
2457 * action, which is presumed to perform on the same mutex.
2458 * @param curr The current ModelAction; also denotes the object location to
2460 * @return The last unlock operation
2462 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2464 void *location = curr->get_location();
2465 action_list_t *list = get_safe_ptr_action(obj_map, location);
2466 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2467 action_list_t::reverse_iterator rit;
2468 for (rit = list->rbegin(); rit != list->rend(); rit++)
2469 if ((*rit)->is_unlock() || (*rit)->is_wait())
2474 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2476 ModelAction *parent = get_last_action(tid);
2478 parent = get_thread(tid)->get_creation();
2483 * Returns the clock vector for a given thread.
2484 * @param tid The thread whose clock vector we want
2485 * @return Desired clock vector
2487 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2489 return get_parent_action(tid)->get_cv();
2493 * @brief Find the promise, if any to resolve for the current action
2494 * @param curr The current ModelAction. Should be a write.
2495 * @return The (non-negative) index for the Promise to resolve, if any;
2498 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2500 for (unsigned int i = 0; i < promises->size(); i++)
2501 if (curr->get_node()->get_promise(i))
2507 * Resolve a Promise with a current write.
2508 * @param write The ModelAction that is fulfilling Promises
2509 * @param promise_idx The index corresponding to the promise
2510 * @return True if the Promise was successfully resolved; false otherwise
2512 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2514 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2515 Promise *promise = (*promises)[promise_idx];
2517 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2518 ModelAction *read = promise->get_reader(i);
2519 read_from(read, write);
2520 actions_to_check.push_back(read);
2522 /* Make sure the promise's value matches the write's value */
2523 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2524 if (!mo_graph->resolvePromise(promise, write))
2525 priv->failed_promise = true;
2527 promises->erase(promises->begin() + promise_idx);
2529 * @todo It is possible to end up in an inconsistent state, where a
2530 * "resolved" promise may still be referenced if
2531 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2533 * Note that the inconsistency only matters when dumping mo_graph to
2539 //Check whether reading these writes has made threads unable to
2541 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2542 ModelAction *read = actions_to_check[i];
2543 mo_check_promises(read, true);
2550 * Compute the set of promises that could potentially be satisfied by this
2551 * action. Note that the set computation actually appears in the Node, not in
2553 * @param curr The ModelAction that may satisfy promises
2555 void ModelChecker::compute_promises(ModelAction *curr)
2557 for (unsigned int i = 0; i < promises->size(); i++) {
2558 Promise *promise = (*promises)[i];
2559 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2562 bool satisfy = true;
2563 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2564 const ModelAction *act = promise->get_reader(j);
2565 if (act->happens_before(curr) ||
2566 act->could_synchronize_with(curr)) {
2572 curr->get_node()->set_promise(i);
2576 /** Checks promises in response to change in ClockVector Threads. */
2577 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2579 for (unsigned int i = 0; i < promises->size(); i++) {
2580 Promise *promise = (*promises)[i];
2581 if (!promise->thread_is_available(tid))
2583 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2584 const ModelAction *act = promise->get_reader(j);
2585 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2586 merge_cv->synchronized_since(act)) {
2587 if (promise->eliminate_thread(tid)) {
2588 /* Promise has failed */
2589 priv->failed_promise = true;
2597 void ModelChecker::check_promises_thread_disabled()
2599 for (unsigned int i = 0; i < promises->size(); i++) {
2600 Promise *promise = (*promises)[i];
2601 if (promise->has_failed()) {
2602 priv->failed_promise = true;
2609 * @brief Checks promises in response to addition to modification order for
2612 * We test whether threads are still available for satisfying promises after an
2613 * addition to our modification order constraints. Those that are unavailable
2614 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2615 * that promise has failed.
2617 * @param act The ModelAction which updated the modification order
2618 * @param is_read_check Should be true if act is a read and we must check for
2619 * updates to the store from which it read (there is a distinction here for
2620 * RMW's, which are both a load and a store)
2622 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2624 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2626 for (unsigned int i = 0; i < promises->size(); i++) {
2627 Promise *promise = (*promises)[i];
2629 // Is this promise on the same location?
2630 if (!promise->same_location(write))
2633 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2634 const ModelAction *pread = promise->get_reader(j);
2635 if (!pread->happens_before(act))
2637 if (mo_graph->checkPromise(write, promise)) {
2638 priv->failed_promise = true;
2644 // Don't do any lookups twice for the same thread
2645 if (!promise->thread_is_available(act->get_tid()))
2648 if (mo_graph->checkReachable(promise, write)) {
2649 if (mo_graph->checkPromise(write, promise)) {
2650 priv->failed_promise = true;
2658 * Compute the set of writes that may break the current pending release
2659 * sequence. This information is extracted from previou release sequence
2662 * @param curr The current ModelAction. Must be a release sequence fixup
2665 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2667 if (pending_rel_seqs->empty())
2670 struct release_seq *pending = pending_rel_seqs->back();
2671 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2672 const ModelAction *write = pending->writes[i];
2673 curr->get_node()->add_relseq_break(write);
2676 /* NULL means don't break the sequence; just synchronize */
2677 curr->get_node()->add_relseq_break(NULL);
2681 * Build up an initial set of all past writes that this 'read' action may read
2682 * from, as well as any previously-observed future values that must still be valid.
2684 * @param curr is the current ModelAction that we are exploring; it must be a
2687 void ModelChecker::build_may_read_from(ModelAction *curr)
2689 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2691 ASSERT(curr->is_read());
2693 ModelAction *last_sc_write = NULL;
2695 if (curr->is_seqcst())
2696 last_sc_write = get_last_seq_cst_write(curr);
2698 /* Iterate over all threads */
2699 for (i = 0; i < thrd_lists->size(); i++) {
2700 /* Iterate over actions in thread, starting from most recent */
2701 action_list_t *list = &(*thrd_lists)[i];
2702 action_list_t::reverse_iterator rit;
2703 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2704 ModelAction *act = *rit;
2706 /* Only consider 'write' actions */
2707 if (!act->is_write() || act == curr)
2710 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2711 bool allow_read = true;
2713 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2715 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2719 /* Only add feasible reads */
2720 mo_graph->startChanges();
2721 r_modification_order(curr, act);
2722 if (!is_infeasible())
2723 curr->get_node()->add_read_from_past(act);
2724 mo_graph->rollbackChanges();
2727 /* Include at most one act per-thread that "happens before" curr */
2728 if (act->happens_before(curr))
2733 /* Inherit existing, promised future values */
2734 for (i = 0; i < promises->size(); i++) {
2735 const Promise *promise = (*promises)[i];
2736 const ModelAction *promise_read = promise->get_reader(0);
2737 if (promise_read->same_var(curr)) {
2738 /* Only add feasible future-values */
2739 mo_graph->startChanges();
2740 r_modification_order(curr, promise);
2741 if (!is_infeasible())
2742 curr->get_node()->add_read_from_promise(promise_read);
2743 mo_graph->rollbackChanges();
2747 /* We may find no valid may-read-from only if the execution is doomed */
2748 if (!curr->get_node()->read_from_size()) {
2749 priv->no_valid_reads = true;
2753 if (DBG_ENABLED()) {
2754 model_print("Reached read action:\n");
2756 model_print("Printing read_from_past\n");
2757 curr->get_node()->print_read_from_past();
2758 model_print("End printing read_from_past\n");
2762 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2764 for ( ; write != NULL; write = write->get_reads_from()) {
2765 /* UNINIT actions don't have a Node, and they never sleep */
2766 if (write->is_uninitialized())
2768 Node *prevnode = write->get_node()->get_parent();
2770 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2771 if (write->is_release() && thread_sleep)
2773 if (!write->is_rmw())
2780 * @brief Create a new action representing an uninitialized atomic
2781 * @param location The memory location of the atomic object
2782 * @return A pointer to a new ModelAction
2784 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2786 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2787 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2788 act->create_cv(NULL);
2792 static void print_list(action_list_t *list)
2794 action_list_t::iterator it;
2796 model_print("---------------------------------------------------------------------\n");
2798 unsigned int hash = 0;
2800 for (it = list->begin(); it != list->end(); it++) {
2802 hash = hash^(hash<<3)^((*it)->hash());
2804 model_print("HASH %u\n", hash);
2805 model_print("---------------------------------------------------------------------\n");
2808 #if SUPPORT_MOD_ORDER_DUMP
2809 void ModelChecker::dumpGraph(char *filename) const
2812 sprintf(buffer, "%s.dot", filename);
2813 FILE *file = fopen(buffer, "w");
2814 fprintf(file, "digraph %s {\n", filename);
2815 mo_graph->dumpNodes(file);
2816 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2818 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2819 ModelAction *act = *it;
2820 if (act->is_read()) {
2821 mo_graph->dot_print_node(file, act);
2822 if (act->get_reads_from())
2823 mo_graph->dot_print_edge(file,
2824 act->get_reads_from(),
2826 "label=\"rf\", color=red, weight=2");
2828 mo_graph->dot_print_edge(file,
2829 act->get_reads_from_promise(),
2831 "label=\"rf\", color=red");
2833 if (thread_array[act->get_tid()]) {
2834 mo_graph->dot_print_edge(file,
2835 thread_array[id_to_int(act->get_tid())],
2837 "label=\"sb\", color=blue, weight=400");
2840 thread_array[act->get_tid()] = act;
2842 fprintf(file, "}\n");
2843 model_free(thread_array);
2848 /** @brief Prints an execution trace summary. */
2849 void ModelChecker::print_summary() const
2851 #if SUPPORT_MOD_ORDER_DUMP
2852 char buffername[100];
2853 sprintf(buffername, "exec%04u", stats.num_total);
2854 mo_graph->dumpGraphToFile(buffername);
2855 sprintf(buffername, "graph%04u", stats.num_total);
2856 dumpGraph(buffername);
2859 model_print("Execution %d:", stats.num_total);
2860 if (isfeasibleprefix()) {
2861 if (scheduler->all_threads_sleeping())
2862 model_print(" SLEEP-SET REDUNDANT");
2865 print_infeasibility(" INFEASIBLE");
2866 print_list(action_trace);
2871 * Add a Thread to the system for the first time. Should only be called once
2873 * @param t The Thread to add
2875 void ModelChecker::add_thread(Thread *t)
2877 thread_map->put(id_to_int(t->get_id()), t);
2878 scheduler->add_thread(t);
2882 * Removes a thread from the scheduler.
2883 * @param the thread to remove.
2885 void ModelChecker::remove_thread(Thread *t)
2887 scheduler->remove_thread(t);
2891 * @brief Get a Thread reference by its ID
2892 * @param tid The Thread's ID
2893 * @return A Thread reference
2895 Thread * ModelChecker::get_thread(thread_id_t tid) const
2897 return thread_map->get(id_to_int(tid));
2901 * @brief Get a reference to the Thread in which a ModelAction was executed
2902 * @param act The ModelAction
2903 * @return A Thread reference
2905 Thread * ModelChecker::get_thread(const ModelAction *act) const
2907 return get_thread(act->get_tid());
2911 * @brief Get a Promise's "promise number"
2913 * A "promise number" is an index number that is unique to a promise, valid
2914 * only for a specific snapshot of an execution trace. Promises may come and go
2915 * as they are generated an resolved, so an index only retains meaning for the
2918 * @param promise The Promise to check
2919 * @return The promise index, if the promise still is valid; otherwise -1
2921 int ModelChecker::get_promise_number(const Promise *promise) const
2923 for (unsigned int i = 0; i < promises->size(); i++)
2924 if ((*promises)[i] == promise)
2931 * @brief Check if a Thread is currently enabled
2932 * @param t The Thread to check
2933 * @return True if the Thread is currently enabled
2935 bool ModelChecker::is_enabled(Thread *t) const
2937 return scheduler->is_enabled(t);
2941 * @brief Check if a Thread is currently enabled
2942 * @param tid The ID of the Thread to check
2943 * @return True if the Thread is currently enabled
2945 bool ModelChecker::is_enabled(thread_id_t tid) const
2947 return scheduler->is_enabled(tid);
2951 * Switch from a model-checker context to a user-thread context. This is the
2952 * complement of ModelChecker::switch_to_master and must be called from the
2953 * model-checker context
2955 * @param thread The user-thread to switch to
2957 void ModelChecker::switch_from_master(Thread *thread)
2959 scheduler->set_current_thread(thread);
2960 Thread::swap(&system_context, thread);
2964 * Switch from a user-context to the "master thread" context (a.k.a. system
2965 * context). This switch is made with the intention of exploring a particular
2966 * model-checking action (described by a ModelAction object). Must be called
2967 * from a user-thread context.
2969 * @param act The current action that will be explored. May be NULL only if
2970 * trace is exiting via an assertion (see ModelChecker::set_assert and
2971 * ModelChecker::has_asserted).
2972 * @return Return the value returned by the current action
2974 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2977 Thread *old = thread_current();
2978 ASSERT(!old->get_pending());
2979 old->set_pending(act);
2980 if (Thread::swap(old, &system_context) < 0) {
2981 perror("swap threads");
2984 return old->get_return_value();
2988 * Takes the next step in the execution, if possible.
2989 * @param curr The current step to take
2990 * @return Returns the next Thread to run, if any; NULL if this execution
2993 Thread * ModelChecker::take_step(ModelAction *curr)
2995 Thread *curr_thrd = get_thread(curr);
2996 ASSERT(curr_thrd->get_state() == THREAD_READY);
2998 curr = check_current_action(curr);
3000 /* Infeasible -> don't take any more steps */
3001 if (is_infeasible())
3003 else if (isfeasibleprefix() && have_bug_reports()) {
3008 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3011 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3012 scheduler->remove_thread(curr_thrd);
3014 Thread *next_thrd = get_next_thread(curr);
3016 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3017 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3022 /** Wrapper to run the user's main function, with appropriate arguments */
3023 void user_main_wrapper(void *)
3025 user_main(model->params.argc, model->params.argv);
3028 /** @brief Run ModelChecker for the user program */
3029 void ModelChecker::run()
3033 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3038 * Stash next pending action(s) for thread(s). There
3039 * should only need to stash one thread's action--the
3040 * thread which just took a step--plus the first step
3041 * for any newly-created thread
3043 for (unsigned int i = 0; i < get_num_threads(); i++) {
3044 thread_id_t tid = int_to_id(i);
3045 Thread *thr = get_thread(tid);
3046 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3047 switch_from_master(thr);
3051 /* Catch assertions from prior take_step or from
3052 * between-ModelAction bugs (e.g., data races) */
3056 /* Consume the next action for a Thread */
3057 ModelAction *curr = t->get_pending();
3058 t->set_pending(NULL);
3059 t = take_step(curr);
3060 } while (t && !t->is_model_thread());
3063 * Launch end-of-execution release sequence fixups only when
3064 * the execution is otherwise feasible AND there are:
3066 * (1) pending release sequences
3067 * (2) pending assertions that could be invalidated by a change
3068 * in clock vectors (i.e., data races)
3069 * (3) no pending promises
3071 while (!pending_rel_seqs->empty() &&
3072 is_feasible_prefix_ignore_relseq() &&
3073 !unrealizedraces.empty()) {
3074 model_print("*** WARNING: release sequence fixup action "
3075 "(%zu pending release seuqence(s)) ***\n",
3076 pending_rel_seqs->size());
3077 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3078 std::memory_order_seq_cst, NULL, VALUE_NONE,
3082 } while (next_execution());
3084 model_print("******* Model-checking complete: *******\n");