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();
857 bool updated = false;
858 switch (node->get_read_from_status()) {
859 case READ_FROM_PAST: {
860 const ModelAction *rf = node->get_read_from_past();
863 mo_graph->startChanges();
865 ASSERT(!is_infeasible());
866 if (!check_recency(curr, rf)) {
867 if (node->increment_read_from()) {
868 mo_graph->rollbackChanges();
871 priv->too_many_reads = true;
875 updated = r_modification_order(curr, rf);
877 mo_graph->commitChanges();
878 mo_check_promises(curr, true);
881 case READ_FROM_PROMISE: {
882 Promise *promise = curr->get_node()->get_read_from_promise();
883 if (promise->add_reader(curr))
884 priv->failed_promise = true;
885 curr->set_read_from_promise(promise);
886 mo_graph->startChanges();
887 if (!check_recency(curr, promise))
888 priv->too_many_reads = true;
889 updated = r_modification_order(curr, promise);
890 mo_graph->commitChanges();
893 case READ_FROM_FUTURE: {
894 /* Read from future value */
895 struct future_value fv = node->get_future_value();
896 Promise *promise = new Promise(curr, fv);
897 curr->set_read_from_promise(promise);
898 promises->push_back(promise);
899 mo_graph->startChanges();
900 updated = r_modification_order(curr, promise);
901 mo_graph->commitChanges();
907 get_thread(curr)->set_return_value(curr->get_return_value());
913 * Processes a lock, trylock, or unlock model action. @param curr is
914 * the read model action to process.
916 * The try lock operation checks whether the lock is taken. If not,
917 * it falls to the normal lock operation case. If so, it returns
920 * The lock operation has already been checked that it is enabled, so
921 * it just grabs the lock and synchronizes with the previous unlock.
923 * The unlock operation has to re-enable all of the threads that are
924 * waiting on the lock.
926 * @return True if synchronization was updated; false otherwise
928 bool ModelChecker::process_mutex(ModelAction *curr)
930 std::mutex *mutex = NULL;
931 struct std::mutex_state *state = NULL;
933 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
934 mutex = (std::mutex *)curr->get_location();
935 state = mutex->get_state();
936 } else if (curr->is_wait()) {
937 mutex = (std::mutex *)curr->get_value();
938 state = mutex->get_state();
941 switch (curr->get_type()) {
942 case ATOMIC_TRYLOCK: {
943 bool success = !state->islocked;
944 curr->set_try_lock(success);
946 get_thread(curr)->set_return_value(0);
949 get_thread(curr)->set_return_value(1);
951 //otherwise fall into the lock case
953 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
954 assert_bug("Lock access before initialization");
955 state->islocked = true;
956 ModelAction *unlock = get_last_unlock(curr);
957 //synchronize with the previous unlock statement
958 if (unlock != NULL) {
959 curr->synchronize_with(unlock);
964 case ATOMIC_UNLOCK: {
966 state->islocked = false;
967 //wake up the other threads
968 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
969 //activate all the waiting threads
970 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
971 scheduler->wake(get_thread(*rit));
978 state->islocked = false;
979 //wake up the other threads
980 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
981 //activate all the waiting threads
982 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
983 scheduler->wake(get_thread(*rit));
986 //check whether we should go to sleep or not...simulate spurious failures
987 if (curr->get_node()->get_misc() == 0) {
988 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
990 scheduler->sleep(get_thread(curr));
994 case ATOMIC_NOTIFY_ALL: {
995 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
996 //activate all the waiting threads
997 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
998 scheduler->wake(get_thread(*rit));
1003 case ATOMIC_NOTIFY_ONE: {
1004 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1005 int wakeupthread = curr->get_node()->get_misc();
1006 action_list_t::iterator it = waiters->begin();
1007 advance(it, wakeupthread);
1008 scheduler->wake(get_thread(*it));
1019 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1021 /* Do more ambitious checks now that mo is more complete */
1022 if (mo_may_allow(writer, reader)) {
1023 Node *node = reader->get_node();
1025 /* Find an ancestor thread which exists at the time of the reader */
1026 Thread *write_thread = get_thread(writer);
1027 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1028 write_thread = write_thread->get_parent();
1030 struct future_value fv = {
1031 writer->get_write_value(),
1032 writer->get_seq_number() + params.maxfuturedelay,
1033 write_thread->get_id(),
1035 if (node->add_future_value(fv))
1036 set_latest_backtrack(reader);
1041 * Process a write ModelAction
1042 * @param curr The ModelAction to process
1043 * @return True if the mo_graph was updated or promises were resolved
1045 bool ModelChecker::process_write(ModelAction *curr)
1047 /* Readers to which we may send our future value */
1048 std::vector< ModelAction *, ModelAlloc<ModelAction *> > send_fv;
1050 bool updated_mod_order = w_modification_order(curr, &send_fv);
1051 int promise_idx = get_promise_to_resolve(curr);
1052 const ModelAction *earliest_promise_reader;
1053 bool updated_promises = false;
1055 if (promise_idx >= 0) {
1056 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1057 updated_promises = resolve_promise(curr, promise_idx);
1059 earliest_promise_reader = NULL;
1061 /* Don't send future values to reads after the Promise we resolve */
1062 for (unsigned int i = 0; i < send_fv.size(); i++) {
1063 ModelAction *read = send_fv[i];
1064 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1065 futurevalues->push_back(PendingFutureValue(curr, read));
1068 if (promises->size() == 0) {
1069 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1070 struct PendingFutureValue pfv = (*futurevalues)[i];
1071 add_future_value(pfv.writer, pfv.act);
1073 futurevalues->clear();
1076 mo_graph->commitChanges();
1077 mo_check_promises(curr, false);
1079 get_thread(curr)->set_return_value(VALUE_NONE);
1080 return updated_mod_order || updated_promises;
1084 * Process a fence ModelAction
1085 * @param curr The ModelAction to process
1086 * @return True if synchronization was updated
1088 bool ModelChecker::process_fence(ModelAction *curr)
1091 * fence-relaxed: no-op
1092 * fence-release: only log the occurence (not in this function), for
1093 * use in later synchronization
1094 * fence-acquire (this function): search for hypothetical release
1097 bool updated = false;
1098 if (curr->is_acquire()) {
1099 action_list_t *list = action_trace;
1100 action_list_t::reverse_iterator rit;
1101 /* Find X : is_read(X) && X --sb-> curr */
1102 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1103 ModelAction *act = *rit;
1106 if (act->get_tid() != curr->get_tid())
1108 /* Stop at the beginning of the thread */
1109 if (act->is_thread_start())
1111 /* Stop once we reach a prior fence-acquire */
1112 if (act->is_fence() && act->is_acquire())
1114 if (!act->is_read())
1116 /* read-acquire will find its own release sequences */
1117 if (act->is_acquire())
1120 /* Establish hypothetical release sequences */
1121 rel_heads_list_t release_heads;
1122 get_release_seq_heads(curr, act, &release_heads);
1123 for (unsigned int i = 0; i < release_heads.size(); i++)
1124 if (!curr->synchronize_with(release_heads[i]))
1125 set_bad_synchronization();
1126 if (release_heads.size() != 0)
1134 * @brief Process the current action for thread-related activity
1136 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1137 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1138 * synchronization, etc. This function is a no-op for non-THREAD actions
1139 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1141 * @param curr The current action
1142 * @return True if synchronization was updated or a thread completed
1144 bool ModelChecker::process_thread_action(ModelAction *curr)
1146 bool updated = false;
1148 switch (curr->get_type()) {
1149 case THREAD_CREATE: {
1150 thrd_t *thrd = (thrd_t *)curr->get_location();
1151 struct thread_params *params = (struct thread_params *)curr->get_value();
1152 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1154 th->set_creation(curr);
1155 /* Promises can be satisfied by children */
1156 for (unsigned int i = 0; i < promises->size(); i++) {
1157 Promise *promise = (*promises)[i];
1158 if (promise->thread_is_available(curr->get_tid()))
1159 promise->add_thread(th->get_id());
1164 Thread *blocking = curr->get_thread_operand();
1165 ModelAction *act = get_last_action(blocking->get_id());
1166 curr->synchronize_with(act);
1167 updated = true; /* trigger rel-seq checks */
1170 case THREAD_FINISH: {
1171 Thread *th = get_thread(curr);
1172 while (!th->wait_list_empty()) {
1173 ModelAction *act = th->pop_wait_list();
1174 scheduler->wake(get_thread(act));
1177 /* Completed thread can't satisfy promises */
1178 for (unsigned int i = 0; i < promises->size(); i++) {
1179 Promise *promise = (*promises)[i];
1180 if (promise->thread_is_available(th->get_id()))
1181 if (promise->eliminate_thread(th->get_id()))
1182 priv->failed_promise = true;
1184 updated = true; /* trigger rel-seq checks */
1187 case THREAD_START: {
1188 check_promises(curr->get_tid(), NULL, curr->get_cv());
1199 * @brief Process the current action for release sequence fixup activity
1201 * Performs model-checker release sequence fixups for the current action,
1202 * forcing a single pending release sequence to break (with a given, potential
1203 * "loose" write) or to complete (i.e., synchronize). If a pending release
1204 * sequence forms a complete release sequence, then we must perform the fixup
1205 * synchronization, mo_graph additions, etc.
1207 * @param curr The current action; must be a release sequence fixup action
1208 * @param work_queue The work queue to which to add work items as they are
1211 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1213 const ModelAction *write = curr->get_node()->get_relseq_break();
1214 struct release_seq *sequence = pending_rel_seqs->back();
1215 pending_rel_seqs->pop_back();
1217 ModelAction *acquire = sequence->acquire;
1218 const ModelAction *rf = sequence->rf;
1219 const ModelAction *release = sequence->release;
1223 ASSERT(release->same_thread(rf));
1225 if (write == NULL) {
1227 * @todo Forcing a synchronization requires that we set
1228 * modification order constraints. For instance, we can't allow
1229 * a fixup sequence in which two separate read-acquire
1230 * operations read from the same sequence, where the first one
1231 * synchronizes and the other doesn't. Essentially, we can't
1232 * allow any writes to insert themselves between 'release' and
1236 /* Must synchronize */
1237 if (!acquire->synchronize_with(release)) {
1238 set_bad_synchronization();
1241 /* Re-check all pending release sequences */
1242 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1243 /* Re-check act for mo_graph edges */
1244 work_queue->push_back(MOEdgeWorkEntry(acquire));
1246 /* propagate synchronization to later actions */
1247 action_list_t::reverse_iterator rit = action_trace->rbegin();
1248 for (; (*rit) != acquire; rit++) {
1249 ModelAction *propagate = *rit;
1250 if (acquire->happens_before(propagate)) {
1251 propagate->synchronize_with(acquire);
1252 /* Re-check 'propagate' for mo_graph edges */
1253 work_queue->push_back(MOEdgeWorkEntry(propagate));
1257 /* Break release sequence with new edges:
1258 * release --mo--> write --mo--> rf */
1259 mo_graph->addEdge(release, write);
1260 mo_graph->addEdge(write, rf);
1263 /* See if we have realized a data race */
1268 * Initialize the current action by performing one or more of the following
1269 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1270 * in the NodeStack, manipulating backtracking sets, allocating and
1271 * initializing clock vectors, and computing the promises to fulfill.
1273 * @param curr The current action, as passed from the user context; may be
1274 * freed/invalidated after the execution of this function, with a different
1275 * action "returned" its place (pass-by-reference)
1276 * @return True if curr is a newly-explored action; false otherwise
1278 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1280 ModelAction *newcurr;
1282 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1283 newcurr = process_rmw(*curr);
1286 if (newcurr->is_rmw())
1287 compute_promises(newcurr);
1293 (*curr)->set_seq_number(get_next_seq_num());
1295 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1297 /* First restore type and order in case of RMW operation */
1298 if ((*curr)->is_rmwr())
1299 newcurr->copy_typeandorder(*curr);
1301 ASSERT((*curr)->get_location() == newcurr->get_location());
1302 newcurr->copy_from_new(*curr);
1304 /* Discard duplicate ModelAction; use action from NodeStack */
1307 /* Always compute new clock vector */
1308 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1311 return false; /* Action was explored previously */
1315 /* Always compute new clock vector */
1316 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1318 /* Assign most recent release fence */
1319 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1322 * Perform one-time actions when pushing new ModelAction onto
1325 if (newcurr->is_write())
1326 compute_promises(newcurr);
1327 else if (newcurr->is_relseq_fixup())
1328 compute_relseq_breakwrites(newcurr);
1329 else if (newcurr->is_wait())
1330 newcurr->get_node()->set_misc_max(2);
1331 else if (newcurr->is_notify_one()) {
1332 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1334 return true; /* This was a new ModelAction */
1339 * @brief Establish reads-from relation between two actions
1341 * Perform basic operations involved with establishing a concrete rf relation,
1342 * including setting the ModelAction data and checking for release sequences.
1344 * @param act The action that is reading (must be a read)
1345 * @param rf The action from which we are reading (must be a write)
1347 * @return True if this read established synchronization
1349 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1352 act->set_read_from(rf);
1353 if (act->is_acquire()) {
1354 rel_heads_list_t release_heads;
1355 get_release_seq_heads(act, act, &release_heads);
1356 int num_heads = release_heads.size();
1357 for (unsigned int i = 0; i < release_heads.size(); i++)
1358 if (!act->synchronize_with(release_heads[i])) {
1359 set_bad_synchronization();
1362 return num_heads > 0;
1368 * Check promises and eliminate potentially-satisfying threads when a thread is
1369 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1370 * no longer satisfy a promise generated from that thread.
1372 * @param blocker The thread on which a thread is waiting
1373 * @param waiting The waiting thread
1375 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1377 for (unsigned int i = 0; i < promises->size(); i++) {
1378 Promise *promise = (*promises)[i];
1379 if (!promise->thread_is_available(waiting->get_id()))
1381 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1382 ModelAction *reader = promise->get_reader(j);
1383 if (reader->get_tid() != blocker->get_id())
1385 if (promise->eliminate_thread(waiting->get_id())) {
1386 /* Promise has failed */
1387 priv->failed_promise = true;
1389 /* Only eliminate the 'waiting' thread once */
1397 * @brief Check whether a model action is enabled.
1399 * Checks whether a lock or join operation would be successful (i.e., is the
1400 * lock already locked, or is the joined thread already complete). If not, put
1401 * the action in a waiter list.
1403 * @param curr is the ModelAction to check whether it is enabled.
1404 * @return a bool that indicates whether the action is enabled.
1406 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1407 if (curr->is_lock()) {
1408 std::mutex *lock = (std::mutex *)curr->get_location();
1409 struct std::mutex_state *state = lock->get_state();
1410 if (state->islocked) {
1411 //Stick the action in the appropriate waiting queue
1412 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1415 } else if (curr->get_type() == THREAD_JOIN) {
1416 Thread *blocking = (Thread *)curr->get_location();
1417 if (!blocking->is_complete()) {
1418 blocking->push_wait_list(curr);
1419 thread_blocking_check_promises(blocking, get_thread(curr));
1428 * This is the heart of the model checker routine. It performs model-checking
1429 * actions corresponding to a given "current action." Among other processes, it
1430 * calculates reads-from relationships, updates synchronization clock vectors,
1431 * forms a memory_order constraints graph, and handles replay/backtrack
1432 * execution when running permutations of previously-observed executions.
1434 * @param curr The current action to process
1435 * @return The ModelAction that is actually executed; may be different than
1436 * curr; may be NULL, if the current action is not enabled to run
1438 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1441 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1443 if (!check_action_enabled(curr)) {
1444 /* Make the execution look like we chose to run this action
1445 * much later, when a lock/join can succeed */
1446 get_thread(curr)->set_pending(curr);
1447 scheduler->sleep(get_thread(curr));
1451 bool newly_explored = initialize_curr_action(&curr);
1457 wake_up_sleeping_actions(curr);
1459 /* Add the action to lists before any other model-checking tasks */
1460 if (!second_part_of_rmw)
1461 add_action_to_lists(curr);
1463 /* Build may_read_from set for newly-created actions */
1464 if (newly_explored && curr->is_read())
1465 build_may_read_from(curr);
1467 /* Initialize work_queue with the "current action" work */
1468 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1469 while (!work_queue.empty() && !has_asserted()) {
1470 WorkQueueEntry work = work_queue.front();
1471 work_queue.pop_front();
1473 switch (work.type) {
1474 case WORK_CHECK_CURR_ACTION: {
1475 ModelAction *act = work.action;
1476 bool update = false; /* update this location's release seq's */
1477 bool update_all = false; /* update all release seq's */
1479 if (process_thread_action(curr))
1482 if (act->is_read() && !second_part_of_rmw && process_read(act))
1485 if (act->is_write() && process_write(act))
1488 if (act->is_fence() && process_fence(act))
1491 if (act->is_mutex_op() && process_mutex(act))
1494 if (act->is_relseq_fixup())
1495 process_relseq_fixup(curr, &work_queue);
1498 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1500 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1503 case WORK_CHECK_RELEASE_SEQ:
1504 resolve_release_sequences(work.location, &work_queue);
1506 case WORK_CHECK_MO_EDGES: {
1507 /** @todo Complete verification of work_queue */
1508 ModelAction *act = work.action;
1509 bool updated = false;
1511 if (act->is_read()) {
1512 const ModelAction *rf = act->get_reads_from();
1513 const Promise *promise = act->get_reads_from_promise();
1515 if (r_modification_order(act, rf))
1517 } else if (promise) {
1518 if (r_modification_order(act, promise))
1522 if (act->is_write()) {
1523 if (w_modification_order(act, NULL))
1526 mo_graph->commitChanges();
1529 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1538 check_curr_backtracking(curr);
1539 set_backtracking(curr);
1543 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1545 Node *currnode = curr->get_node();
1546 Node *parnode = currnode->get_parent();
1548 if ((parnode && !parnode->backtrack_empty()) ||
1549 !currnode->misc_empty() ||
1550 !currnode->read_from_empty() ||
1551 !currnode->promise_empty() ||
1552 !currnode->relseq_break_empty()) {
1553 set_latest_backtrack(curr);
1557 bool ModelChecker::promises_expired() const
1559 for (unsigned int i = 0; i < promises->size(); i++) {
1560 Promise *promise = (*promises)[i];
1561 if (promise->get_expiration() < priv->used_sequence_numbers)
1568 * This is the strongest feasibility check available.
1569 * @return whether the current trace (partial or complete) must be a prefix of
1572 bool ModelChecker::isfeasibleprefix() const
1574 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1578 * Print disagnostic information about an infeasible execution
1579 * @param prefix A string to prefix the output with; if NULL, then a default
1580 * message prefix will be provided
1582 void ModelChecker::print_infeasibility(const char *prefix) const
1586 if (mo_graph->checkForCycles())
1587 ptr += sprintf(ptr, "[mo cycle]");
1588 if (priv->failed_promise)
1589 ptr += sprintf(ptr, "[failed promise]");
1590 if (priv->too_many_reads)
1591 ptr += sprintf(ptr, "[too many reads]");
1592 if (priv->no_valid_reads)
1593 ptr += sprintf(ptr, "[no valid reads-from]");
1594 if (priv->bad_synchronization)
1595 ptr += sprintf(ptr, "[bad sw ordering]");
1596 if (promises_expired())
1597 ptr += sprintf(ptr, "[promise expired]");
1598 if (promises->size() != 0)
1599 ptr += sprintf(ptr, "[unresolved promise]");
1601 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1605 * Returns whether the current completed trace is feasible, except for pending
1606 * release sequences.
1608 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1610 return !is_infeasible() && promises->size() == 0;
1614 * Check if the current partial trace is infeasible. Does not check any
1615 * end-of-execution flags, which might rule out the execution. Thus, this is
1616 * useful only for ruling an execution as infeasible.
1617 * @return whether the current partial trace is infeasible.
1619 bool ModelChecker::is_infeasible() const
1621 return mo_graph->checkForCycles() ||
1622 priv->no_valid_reads ||
1623 priv->failed_promise ||
1624 priv->too_many_reads ||
1625 priv->bad_synchronization ||
1629 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1630 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1631 ModelAction *lastread = get_last_action(act->get_tid());
1632 lastread->process_rmw(act);
1633 if (act->is_rmw()) {
1634 if (lastread->get_reads_from())
1635 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1637 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1638 mo_graph->commitChanges();
1644 * A helper function for ModelChecker::check_recency, to check if the current
1645 * thread is able to read from a different write/promise for 'params.maxreads'
1646 * number of steps and if that write/promise should become visible (i.e., is
1647 * ordered later in the modification order). This helps model memory liveness.
1649 * @param curr The current action. Must be a read.
1650 * @param rf The write/promise from which we plan to read
1651 * @param other_rf The write/promise from which we may read
1652 * @return True if we were able to read from other_rf for params.maxreads steps
1654 template <typename T, typename U>
1655 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1657 /* Need a different write/promise */
1658 if (other_rf->equals(rf))
1661 /* Only look for "newer" writes/promises */
1662 if (!mo_graph->checkReachable(rf, other_rf))
1665 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1666 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1667 action_list_t::reverse_iterator rit = list->rbegin();
1668 ASSERT((*rit) == curr);
1669 /* Skip past curr */
1672 /* Does this write/promise work for everyone? */
1673 for (int i = 0; i < params.maxreads; i++, rit++) {
1674 ModelAction *act = *rit;
1675 if (!act->may_read_from(other_rf))
1682 * Checks whether a thread has read from the same write or Promise for too many
1683 * times without seeing the effects of a later write/Promise.
1686 * 1) there must a different write/promise that we could read from,
1687 * 2) we must have read from the same write/promise in excess of maxreads times,
1688 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1689 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1691 * If so, we decide that the execution is no longer feasible.
1693 * @param curr The current action. Must be a read.
1694 * @param rf The ModelAction/Promise from which we might read.
1695 * @return True if the read should succeed; false otherwise
1697 template <typename T>
1698 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1700 if (!params.maxreads)
1703 //NOTE: Next check is just optimization, not really necessary....
1704 if (curr->get_node()->get_read_from_past_size() +
1705 curr->get_node()->get_read_from_promise_size() <= 1)
1708 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1709 int tid = id_to_int(curr->get_tid());
1710 ASSERT(tid < (int)thrd_lists->size());
1711 action_list_t *list = &(*thrd_lists)[tid];
1712 action_list_t::reverse_iterator rit = list->rbegin();
1713 ASSERT((*rit) == curr);
1714 /* Skip past curr */
1717 action_list_t::reverse_iterator ritcopy = rit;
1718 /* See if we have enough reads from the same value */
1719 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1720 if (ritcopy == list->rend())
1722 ModelAction *act = *ritcopy;
1723 if (!act->is_read())
1725 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1727 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1729 if (act->get_node()->get_read_from_past_size() +
1730 act->get_node()->get_read_from_promise_size() <= 1)
1733 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1734 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1735 if (should_read_instead(curr, rf, write))
1736 return false; /* liveness failure */
1738 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1739 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1740 if (should_read_instead(curr, rf, promise))
1741 return false; /* liveness failure */
1747 * Updates the mo_graph with the constraints imposed from the current
1750 * Basic idea is the following: Go through each other thread and find
1751 * the last action that happened before our read. Two cases:
1753 * (1) The action is a write => that write must either occur before
1754 * the write we read from or be the write we read from.
1756 * (2) The action is a read => the write that that action read from
1757 * must occur before the write we read from or be the same write.
1759 * @param curr The current action. Must be a read.
1760 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1761 * @return True if modification order edges were added; false otherwise
1763 template <typename rf_type>
1764 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1766 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1769 ASSERT(curr->is_read());
1771 /* Last SC fence in the current thread */
1772 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1774 /* Iterate over all threads */
1775 for (i = 0; i < thrd_lists->size(); i++) {
1776 /* Last SC fence in thread i */
1777 ModelAction *last_sc_fence_thread_local = NULL;
1778 if (int_to_id((int)i) != curr->get_tid())
1779 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1781 /* Last SC fence in thread i, before last SC fence in current thread */
1782 ModelAction *last_sc_fence_thread_before = NULL;
1783 if (last_sc_fence_local)
1784 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1786 /* Iterate over actions in thread, starting from most recent */
1787 action_list_t *list = &(*thrd_lists)[i];
1788 action_list_t::reverse_iterator rit;
1789 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1790 ModelAction *act = *rit;
1792 if (act->is_write() && !act->equals(rf) && act != curr) {
1793 /* C++, Section 29.3 statement 5 */
1794 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1795 *act < *last_sc_fence_thread_local) {
1796 added = mo_graph->addEdge(act, rf) || added;
1799 /* C++, Section 29.3 statement 4 */
1800 else if (act->is_seqcst() && last_sc_fence_local &&
1801 *act < *last_sc_fence_local) {
1802 added = mo_graph->addEdge(act, rf) || added;
1805 /* C++, Section 29.3 statement 6 */
1806 else if (last_sc_fence_thread_before &&
1807 *act < *last_sc_fence_thread_before) {
1808 added = mo_graph->addEdge(act, rf) || added;
1814 * Include at most one act per-thread that "happens
1815 * before" curr. Don't consider reflexively.
1817 if (act->happens_before(curr) && act != curr) {
1818 if (act->is_write()) {
1819 if (!act->equals(rf)) {
1820 added = mo_graph->addEdge(act, rf) || added;
1823 const ModelAction *prevrf = act->get_reads_from();
1824 const Promise *prevrf_promise = act->get_reads_from_promise();
1826 if (!prevrf->equals(rf))
1827 added = mo_graph->addEdge(prevrf, rf) || added;
1828 } else if (!prevrf_promise->equals(rf)) {
1829 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1838 * All compatible, thread-exclusive promises must be ordered after any
1839 * concrete loads from the same thread
1841 for (unsigned int i = 0; i < promises->size(); i++)
1842 if ((*promises)[i]->is_compatible_exclusive(curr))
1843 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1849 * Updates the mo_graph with the constraints imposed from the current write.
1851 * Basic idea is the following: Go through each other thread and find
1852 * the lastest action that happened before our write. Two cases:
1854 * (1) The action is a write => that write must occur before
1857 * (2) The action is a read => the write that that action read from
1858 * must occur before the current write.
1860 * This method also handles two other issues:
1862 * (I) Sequential Consistency: Making sure that if the current write is
1863 * seq_cst, that it occurs after the previous seq_cst write.
1865 * (II) Sending the write back to non-synchronizing reads.
1867 * @param curr The current action. Must be a write.
1868 * @param send_fv A vector for stashing reads to which we may pass our future
1869 * value. If NULL, then don't record any future values.
1870 * @return True if modification order edges were added; false otherwise
1872 bool ModelChecker::w_modification_order(ModelAction *curr, std::vector< ModelAction *, ModelAlloc<ModelAction *> > *send_fv)
1874 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1877 ASSERT(curr->is_write());
1879 if (curr->is_seqcst()) {
1880 /* We have to at least see the last sequentially consistent write,
1881 so we are initialized. */
1882 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1883 if (last_seq_cst != NULL) {
1884 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1888 /* Last SC fence in the current thread */
1889 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1891 /* Iterate over all threads */
1892 for (i = 0; i < thrd_lists->size(); i++) {
1893 /* Last SC fence in thread i, before last SC fence in current thread */
1894 ModelAction *last_sc_fence_thread_before = NULL;
1895 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1896 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1898 /* Iterate over actions in thread, starting from most recent */
1899 action_list_t *list = &(*thrd_lists)[i];
1900 action_list_t::reverse_iterator rit;
1901 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1902 ModelAction *act = *rit;
1905 * 1) If RMW and it actually read from something, then we
1906 * already have all relevant edges, so just skip to next
1909 * 2) If RMW and it didn't read from anything, we should
1910 * whatever edge we can get to speed up convergence.
1912 * 3) If normal write, we need to look at earlier actions, so
1913 * continue processing list.
1915 if (curr->is_rmw()) {
1916 if (curr->get_reads_from() != NULL)
1924 /* C++, Section 29.3 statement 7 */
1925 if (last_sc_fence_thread_before && act->is_write() &&
1926 *act < *last_sc_fence_thread_before) {
1927 added = mo_graph->addEdge(act, curr) || added;
1932 * Include at most one act per-thread that "happens
1935 if (act->happens_before(curr)) {
1937 * Note: if act is RMW, just add edge:
1939 * The following edge should be handled elsewhere:
1940 * readfrom(act) --mo--> act
1942 if (act->is_write())
1943 added = mo_graph->addEdge(act, curr) || added;
1944 else if (act->is_read()) {
1945 //if previous read accessed a null, just keep going
1946 if (act->get_reads_from() == NULL)
1948 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1951 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1952 !act->same_thread(curr)) {
1953 /* We have an action that:
1954 (1) did not happen before us
1955 (2) is a read and we are a write
1956 (3) cannot synchronize with us
1957 (4) is in a different thread
1959 that read could potentially read from our write. Note that
1960 these checks are overly conservative at this point, we'll
1961 do more checks before actually removing the
1965 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1966 if (!is_infeasible())
1967 send_fv->push_back(act);
1968 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1969 add_future_value(curr, act);
1976 * All compatible, thread-exclusive promises must be ordered after any
1977 * concrete stores to the same thread, or else they can be merged with
1980 for (unsigned int i = 0; i < promises->size(); i++)
1981 if ((*promises)[i]->is_compatible_exclusive(curr))
1982 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1987 /** Arbitrary reads from the future are not allowed. Section 29.3
1988 * part 9 places some constraints. This method checks one result of constraint
1989 * constraint. Others require compiler support. */
1990 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1992 if (!writer->is_rmw())
1995 if (!reader->is_rmw())
1998 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1999 if (search == reader)
2001 if (search->get_tid() == reader->get_tid() &&
2002 search->happens_before(reader))
2010 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2011 * some constraints. This method checks one the following constraint (others
2012 * require compiler support):
2014 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2016 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2018 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2020 /* Iterate over all threads */
2021 for (i = 0; i < thrd_lists->size(); i++) {
2022 const ModelAction *write_after_read = NULL;
2024 /* Iterate over actions in thread, starting from most recent */
2025 action_list_t *list = &(*thrd_lists)[i];
2026 action_list_t::reverse_iterator rit;
2027 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2028 ModelAction *act = *rit;
2030 /* Don't disallow due to act == reader */
2031 if (!reader->happens_before(act) || reader == act)
2033 else if (act->is_write())
2034 write_after_read = act;
2035 else if (act->is_read() && act->get_reads_from() != NULL)
2036 write_after_read = act->get_reads_from();
2039 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2046 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2047 * The ModelAction under consideration is expected to be taking part in
2048 * release/acquire synchronization as an object of the "reads from" relation.
2049 * Note that this can only provide release sequence support for RMW chains
2050 * which do not read from the future, as those actions cannot be traced until
2051 * their "promise" is fulfilled. Similarly, we may not even establish the
2052 * presence of a release sequence with certainty, as some modification order
2053 * constraints may be decided further in the future. Thus, this function
2054 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2055 * and a boolean representing certainty.
2057 * @param rf The action that might be part of a release sequence. Must be a
2059 * @param release_heads A pass-by-reference style return parameter. After
2060 * execution of this function, release_heads will contain the heads of all the
2061 * relevant release sequences, if any exists with certainty
2062 * @param pending A pass-by-reference style return parameter which is only used
2063 * when returning false (i.e., uncertain). Returns most information regarding
2064 * an uncertain release sequence, including any write operations that might
2065 * break the sequence.
2066 * @return true, if the ModelChecker is certain that release_heads is complete;
2069 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2070 rel_heads_list_t *release_heads,
2071 struct release_seq *pending) const
2073 /* Only check for release sequences if there are no cycles */
2074 if (mo_graph->checkForCycles())
2077 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2078 ASSERT(rf->is_write());
2080 if (rf->is_release())
2081 release_heads->push_back(rf);
2082 else if (rf->get_last_fence_release())
2083 release_heads->push_back(rf->get_last_fence_release());
2085 break; /* End of RMW chain */
2087 /** @todo Need to be smarter here... In the linux lock
2088 * example, this will run to the beginning of the program for
2090 /** @todo The way to be smarter here is to keep going until 1
2091 * thread has a release preceded by an acquire and you've seen
2094 /* acq_rel RMW is a sufficient stopping condition */
2095 if (rf->is_acquire() && rf->is_release())
2096 return true; /* complete */
2099 /* read from future: need to settle this later */
2101 return false; /* incomplete */
2104 if (rf->is_release())
2105 return true; /* complete */
2107 /* else relaxed write
2108 * - check for fence-release in the same thread (29.8, stmt. 3)
2109 * - check modification order for contiguous subsequence
2110 * -> rf must be same thread as release */
2112 const ModelAction *fence_release = rf->get_last_fence_release();
2113 /* Synchronize with a fence-release unconditionally; we don't need to
2114 * find any more "contiguous subsequence..." for it */
2116 release_heads->push_back(fence_release);
2118 int tid = id_to_int(rf->get_tid());
2119 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2120 action_list_t *list = &(*thrd_lists)[tid];
2121 action_list_t::const_reverse_iterator rit;
2123 /* Find rf in the thread list */
2124 rit = std::find(list->rbegin(), list->rend(), rf);
2125 ASSERT(rit != list->rend());
2127 /* Find the last {write,fence}-release */
2128 for (; rit != list->rend(); rit++) {
2129 if (fence_release && *(*rit) < *fence_release)
2131 if ((*rit)->is_release())
2134 if (rit == list->rend()) {
2135 /* No write-release in this thread */
2136 return true; /* complete */
2137 } else if (fence_release && *(*rit) < *fence_release) {
2138 /* The fence-release is more recent (and so, "stronger") than
2139 * the most recent write-release */
2140 return true; /* complete */
2141 } /* else, need to establish contiguous release sequence */
2142 ModelAction *release = *rit;
2144 ASSERT(rf->same_thread(release));
2146 pending->writes.clear();
2148 bool certain = true;
2149 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2150 if (id_to_int(rf->get_tid()) == (int)i)
2152 list = &(*thrd_lists)[i];
2154 /* Can we ensure no future writes from this thread may break
2155 * the release seq? */
2156 bool future_ordered = false;
2158 ModelAction *last = get_last_action(int_to_id(i));
2159 Thread *th = get_thread(int_to_id(i));
2160 if ((last && rf->happens_before(last)) ||
2163 future_ordered = true;
2165 ASSERT(!th->is_model_thread() || future_ordered);
2167 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2168 const ModelAction *act = *rit;
2169 /* Reach synchronization -> this thread is complete */
2170 if (act->happens_before(release))
2172 if (rf->happens_before(act)) {
2173 future_ordered = true;
2177 /* Only non-RMW writes can break release sequences */
2178 if (!act->is_write() || act->is_rmw())
2181 /* Check modification order */
2182 if (mo_graph->checkReachable(rf, act)) {
2183 /* rf --mo--> act */
2184 future_ordered = true;
2187 if (mo_graph->checkReachable(act, release))
2188 /* act --mo--> release */
2190 if (mo_graph->checkReachable(release, act) &&
2191 mo_graph->checkReachable(act, rf)) {
2192 /* release --mo-> act --mo--> rf */
2193 return true; /* complete */
2195 /* act may break release sequence */
2196 pending->writes.push_back(act);
2199 if (!future_ordered)
2200 certain = false; /* This thread is uncertain */
2204 release_heads->push_back(release);
2205 pending->writes.clear();
2207 pending->release = release;
2214 * An interface for getting the release sequence head(s) with which a
2215 * given ModelAction must synchronize. This function only returns a non-empty
2216 * result when it can locate a release sequence head with certainty. Otherwise,
2217 * it may mark the internal state of the ModelChecker so that it will handle
2218 * the release sequence at a later time, causing @a acquire to update its
2219 * synchronization at some later point in execution.
2221 * @param acquire The 'acquire' action that may synchronize with a release
2223 * @param read The read action that may read from a release sequence; this may
2224 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2225 * when 'acquire' is a fence-acquire)
2226 * @param release_heads A pass-by-reference return parameter. Will be filled
2227 * with the head(s) of the release sequence(s), if they exists with certainty.
2228 * @see ModelChecker::release_seq_heads
2230 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2231 ModelAction *read, rel_heads_list_t *release_heads)
2233 const ModelAction *rf = read->get_reads_from();
2234 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2235 sequence->acquire = acquire;
2236 sequence->read = read;
2238 if (!release_seq_heads(rf, release_heads, sequence)) {
2239 /* add act to 'lazy checking' list */
2240 pending_rel_seqs->push_back(sequence);
2242 snapshot_free(sequence);
2247 * Attempt to resolve all stashed operations that might synchronize with a
2248 * release sequence for a given location. This implements the "lazy" portion of
2249 * determining whether or not a release sequence was contiguous, since not all
2250 * modification order information is present at the time an action occurs.
2252 * @param location The location/object that should be checked for release
2253 * sequence resolutions. A NULL value means to check all locations.
2254 * @param work_queue The work queue to which to add work items as they are
2256 * @return True if any updates occurred (new synchronization, new mo_graph
2259 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2261 bool updated = false;
2262 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2263 while (it != pending_rel_seqs->end()) {
2264 struct release_seq *pending = *it;
2265 ModelAction *acquire = pending->acquire;
2266 const ModelAction *read = pending->read;
2268 /* Only resolve sequences on the given location, if provided */
2269 if (location && read->get_location() != location) {
2274 const ModelAction *rf = read->get_reads_from();
2275 rel_heads_list_t release_heads;
2277 complete = release_seq_heads(rf, &release_heads, pending);
2278 for (unsigned int i = 0; i < release_heads.size(); i++) {
2279 if (!acquire->has_synchronized_with(release_heads[i])) {
2280 if (acquire->synchronize_with(release_heads[i]))
2283 set_bad_synchronization();
2288 /* Re-check all pending release sequences */
2289 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2290 /* Re-check read-acquire for mo_graph edges */
2291 if (acquire->is_read())
2292 work_queue->push_back(MOEdgeWorkEntry(acquire));
2294 /* propagate synchronization to later actions */
2295 action_list_t::reverse_iterator rit = action_trace->rbegin();
2296 for (; (*rit) != acquire; rit++) {
2297 ModelAction *propagate = *rit;
2298 if (acquire->happens_before(propagate)) {
2299 propagate->synchronize_with(acquire);
2300 /* Re-check 'propagate' for mo_graph edges */
2301 work_queue->push_back(MOEdgeWorkEntry(propagate));
2306 it = pending_rel_seqs->erase(it);
2307 snapshot_free(pending);
2313 // If we resolved promises or data races, see if we have realized a data race.
2320 * Performs various bookkeeping operations for the current ModelAction. For
2321 * instance, adds action to the per-object, per-thread action vector and to the
2322 * action trace list of all thread actions.
2324 * @param act is the ModelAction to add.
2326 void ModelChecker::add_action_to_lists(ModelAction *act)
2328 int tid = id_to_int(act->get_tid());
2329 ModelAction *uninit = NULL;
2331 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2332 if (list->empty() && act->is_atomic_var()) {
2333 uninit = new_uninitialized_action(act->get_location());
2334 uninit_id = id_to_int(uninit->get_tid());
2335 list->push_back(uninit);
2337 list->push_back(act);
2339 action_trace->push_back(act);
2341 action_trace->push_front(uninit);
2343 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2344 if (tid >= (int)vec->size())
2345 vec->resize(priv->next_thread_id);
2346 (*vec)[tid].push_back(act);
2348 (*vec)[uninit_id].push_front(uninit);
2350 if ((int)thrd_last_action->size() <= tid)
2351 thrd_last_action->resize(get_num_threads());
2352 (*thrd_last_action)[tid] = act;
2354 (*thrd_last_action)[uninit_id] = uninit;
2356 if (act->is_fence() && act->is_release()) {
2357 if ((int)thrd_last_fence_release->size() <= tid)
2358 thrd_last_fence_release->resize(get_num_threads());
2359 (*thrd_last_fence_release)[tid] = act;
2362 if (act->is_wait()) {
2363 void *mutex_loc = (void *) act->get_value();
2364 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2366 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2367 if (tid >= (int)vec->size())
2368 vec->resize(priv->next_thread_id);
2369 (*vec)[tid].push_back(act);
2374 * @brief Get the last action performed by a particular Thread
2375 * @param tid The thread ID of the Thread in question
2376 * @return The last action in the thread
2378 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2380 int threadid = id_to_int(tid);
2381 if (threadid < (int)thrd_last_action->size())
2382 return (*thrd_last_action)[id_to_int(tid)];
2388 * @brief Get the last fence release performed by a particular Thread
2389 * @param tid The thread ID of the Thread in question
2390 * @return The last fence release in the thread, if one exists; NULL otherwise
2392 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2394 int threadid = id_to_int(tid);
2395 if (threadid < (int)thrd_last_fence_release->size())
2396 return (*thrd_last_fence_release)[id_to_int(tid)];
2402 * Gets the last memory_order_seq_cst write (in the total global sequence)
2403 * performed on a particular object (i.e., memory location), not including the
2405 * @param curr The current ModelAction; also denotes the object location to
2407 * @return The last seq_cst write
2409 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2411 void *location = curr->get_location();
2412 action_list_t *list = get_safe_ptr_action(obj_map, location);
2413 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2414 action_list_t::reverse_iterator rit;
2415 for (rit = list->rbegin(); rit != list->rend(); rit++)
2416 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2422 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2423 * performed in a particular thread, prior to a particular fence.
2424 * @param tid The ID of the thread to check
2425 * @param before_fence The fence from which to begin the search; if NULL, then
2426 * search for the most recent fence in the thread.
2427 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2429 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2431 /* All fences should have NULL location */
2432 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2433 action_list_t::reverse_iterator rit = list->rbegin();
2436 for (; rit != list->rend(); rit++)
2437 if (*rit == before_fence)
2440 ASSERT(*rit == before_fence);
2444 for (; rit != list->rend(); rit++)
2445 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2451 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2452 * location). This function identifies the mutex according to the current
2453 * action, which is presumed to perform on the same mutex.
2454 * @param curr The current ModelAction; also denotes the object location to
2456 * @return The last unlock operation
2458 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2460 void *location = curr->get_location();
2461 action_list_t *list = get_safe_ptr_action(obj_map, location);
2462 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2463 action_list_t::reverse_iterator rit;
2464 for (rit = list->rbegin(); rit != list->rend(); rit++)
2465 if ((*rit)->is_unlock() || (*rit)->is_wait())
2470 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2472 ModelAction *parent = get_last_action(tid);
2474 parent = get_thread(tid)->get_creation();
2479 * Returns the clock vector for a given thread.
2480 * @param tid The thread whose clock vector we want
2481 * @return Desired clock vector
2483 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2485 return get_parent_action(tid)->get_cv();
2489 * @brief Find the promise, if any to resolve for the current action
2490 * @param curr The current ModelAction. Should be a write.
2491 * @return The (non-negative) index for the Promise to resolve, if any;
2494 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2496 for (unsigned int i = 0; i < promises->size(); i++)
2497 if (curr->get_node()->get_promise(i))
2503 * Resolve a Promise with a current write.
2504 * @param write The ModelAction that is fulfilling Promises
2505 * @param promise_idx The index corresponding to the promise
2506 * @return True if the Promise was successfully resolved; false otherwise
2508 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2510 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2511 Promise *promise = (*promises)[promise_idx];
2513 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2514 ModelAction *read = promise->get_reader(i);
2515 read_from(read, write);
2516 actions_to_check.push_back(read);
2518 /* Make sure the promise's value matches the write's value */
2519 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2520 if (!mo_graph->resolvePromise(promise, write))
2521 priv->failed_promise = true;
2523 promises->erase(promises->begin() + promise_idx);
2525 * @todo It is possible to end up in an inconsistent state, where a
2526 * "resolved" promise may still be referenced if
2527 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2529 * Note that the inconsistency only matters when dumping mo_graph to
2535 //Check whether reading these writes has made threads unable to
2537 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2538 ModelAction *read = actions_to_check[i];
2539 mo_check_promises(read, true);
2546 * Compute the set of promises that could potentially be satisfied by this
2547 * action. Note that the set computation actually appears in the Node, not in
2549 * @param curr The ModelAction that may satisfy promises
2551 void ModelChecker::compute_promises(ModelAction *curr)
2553 for (unsigned int i = 0; i < promises->size(); i++) {
2554 Promise *promise = (*promises)[i];
2555 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2558 bool satisfy = true;
2559 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2560 const ModelAction *act = promise->get_reader(j);
2561 if (act->happens_before(curr) ||
2562 act->could_synchronize_with(curr)) {
2568 curr->get_node()->set_promise(i);
2572 /** Checks promises in response to change in ClockVector Threads. */
2573 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2575 for (unsigned int i = 0; i < promises->size(); i++) {
2576 Promise *promise = (*promises)[i];
2577 if (!promise->thread_is_available(tid))
2579 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2580 const ModelAction *act = promise->get_reader(j);
2581 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2582 merge_cv->synchronized_since(act)) {
2583 if (promise->eliminate_thread(tid)) {
2584 /* Promise has failed */
2585 priv->failed_promise = true;
2593 void ModelChecker::check_promises_thread_disabled()
2595 for (unsigned int i = 0; i < promises->size(); i++) {
2596 Promise *promise = (*promises)[i];
2597 if (promise->has_failed()) {
2598 priv->failed_promise = true;
2605 * @brief Checks promises in response to addition to modification order for
2608 * We test whether threads are still available for satisfying promises after an
2609 * addition to our modification order constraints. Those that are unavailable
2610 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2611 * that promise has failed.
2613 * @param act The ModelAction which updated the modification order
2614 * @param is_read_check Should be true if act is a read and we must check for
2615 * updates to the store from which it read (there is a distinction here for
2616 * RMW's, which are both a load and a store)
2618 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2620 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2622 for (unsigned int i = 0; i < promises->size(); i++) {
2623 Promise *promise = (*promises)[i];
2625 // Is this promise on the same location?
2626 if (!promise->same_location(write))
2629 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2630 const ModelAction *pread = promise->get_reader(j);
2631 if (!pread->happens_before(act))
2633 if (mo_graph->checkPromise(write, promise)) {
2634 priv->failed_promise = true;
2640 // Don't do any lookups twice for the same thread
2641 if (!promise->thread_is_available(act->get_tid()))
2644 if (mo_graph->checkReachable(promise, write)) {
2645 if (mo_graph->checkPromise(write, promise)) {
2646 priv->failed_promise = true;
2654 * Compute the set of writes that may break the current pending release
2655 * sequence. This information is extracted from previou release sequence
2658 * @param curr The current ModelAction. Must be a release sequence fixup
2661 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2663 if (pending_rel_seqs->empty())
2666 struct release_seq *pending = pending_rel_seqs->back();
2667 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2668 const ModelAction *write = pending->writes[i];
2669 curr->get_node()->add_relseq_break(write);
2672 /* NULL means don't break the sequence; just synchronize */
2673 curr->get_node()->add_relseq_break(NULL);
2677 * Build up an initial set of all past writes that this 'read' action may read
2678 * from, as well as any previously-observed future values that must still be valid.
2680 * @param curr is the current ModelAction that we are exploring; it must be a
2683 void ModelChecker::build_may_read_from(ModelAction *curr)
2685 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2687 ASSERT(curr->is_read());
2689 ModelAction *last_sc_write = NULL;
2691 if (curr->is_seqcst())
2692 last_sc_write = get_last_seq_cst_write(curr);
2694 /* Iterate over all threads */
2695 for (i = 0; i < thrd_lists->size(); i++) {
2696 /* Iterate over actions in thread, starting from most recent */
2697 action_list_t *list = &(*thrd_lists)[i];
2698 action_list_t::reverse_iterator rit;
2699 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2700 ModelAction *act = *rit;
2702 /* Only consider 'write' actions */
2703 if (!act->is_write() || act == curr)
2706 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2707 bool allow_read = true;
2709 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2711 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2715 /* Only add feasible reads */
2716 mo_graph->startChanges();
2717 r_modification_order(curr, act);
2718 if (!is_infeasible())
2719 curr->get_node()->add_read_from_past(act);
2720 mo_graph->rollbackChanges();
2723 /* Include at most one act per-thread that "happens before" curr */
2724 if (act->happens_before(curr))
2729 /* Inherit existing, promised future values */
2730 for (i = 0; i < promises->size(); i++) {
2731 const Promise *promise = (*promises)[i];
2732 const ModelAction *promise_read = promise->get_reader(0);
2733 if (promise_read->same_var(curr)) {
2734 /* Only add feasible future-values */
2735 mo_graph->startChanges();
2736 r_modification_order(curr, promise);
2737 if (!is_infeasible())
2738 curr->get_node()->add_read_from_promise(promise_read);
2739 mo_graph->rollbackChanges();
2743 /* We may find no valid may-read-from only if the execution is doomed */
2744 if (!curr->get_node()->read_from_size()) {
2745 priv->no_valid_reads = true;
2749 if (DBG_ENABLED()) {
2750 model_print("Reached read action:\n");
2752 model_print("Printing read_from_past\n");
2753 curr->get_node()->print_read_from_past();
2754 model_print("End printing read_from_past\n");
2758 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2760 for ( ; write != NULL; write = write->get_reads_from()) {
2761 /* UNINIT actions don't have a Node, and they never sleep */
2762 if (write->is_uninitialized())
2764 Node *prevnode = write->get_node()->get_parent();
2766 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2767 if (write->is_release() && thread_sleep)
2769 if (!write->is_rmw())
2776 * @brief Create a new action representing an uninitialized atomic
2777 * @param location The memory location of the atomic object
2778 * @return A pointer to a new ModelAction
2780 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2782 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2783 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2784 act->create_cv(NULL);
2788 static void print_list(action_list_t *list)
2790 action_list_t::iterator it;
2792 model_print("---------------------------------------------------------------------\n");
2794 unsigned int hash = 0;
2796 for (it = list->begin(); it != list->end(); it++) {
2798 hash = hash^(hash<<3)^((*it)->hash());
2800 model_print("HASH %u\n", hash);
2801 model_print("---------------------------------------------------------------------\n");
2804 #if SUPPORT_MOD_ORDER_DUMP
2805 void ModelChecker::dumpGraph(char *filename) const
2808 sprintf(buffer, "%s.dot", filename);
2809 FILE *file = fopen(buffer, "w");
2810 fprintf(file, "digraph %s {\n", filename);
2811 mo_graph->dumpNodes(file);
2812 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2814 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2815 ModelAction *act = *it;
2816 if (act->is_read()) {
2817 mo_graph->dot_print_node(file, act);
2818 if (act->get_reads_from())
2819 mo_graph->dot_print_edge(file,
2820 act->get_reads_from(),
2822 "label=\"rf\", color=red, weight=2");
2824 mo_graph->dot_print_edge(file,
2825 act->get_reads_from_promise(),
2827 "label=\"rf\", color=red");
2829 if (thread_array[act->get_tid()]) {
2830 mo_graph->dot_print_edge(file,
2831 thread_array[id_to_int(act->get_tid())],
2833 "label=\"sb\", color=blue, weight=400");
2836 thread_array[act->get_tid()] = act;
2838 fprintf(file, "}\n");
2839 model_free(thread_array);
2844 /** @brief Prints an execution trace summary. */
2845 void ModelChecker::print_summary() const
2847 #if SUPPORT_MOD_ORDER_DUMP
2848 char buffername[100];
2849 sprintf(buffername, "exec%04u", stats.num_total);
2850 mo_graph->dumpGraphToFile(buffername);
2851 sprintf(buffername, "graph%04u", stats.num_total);
2852 dumpGraph(buffername);
2855 model_print("Execution %d:", stats.num_total);
2856 if (isfeasibleprefix()) {
2857 if (scheduler->all_threads_sleeping())
2858 model_print(" SLEEP-SET REDUNDANT");
2861 print_infeasibility(" INFEASIBLE");
2862 print_list(action_trace);
2867 * Add a Thread to the system for the first time. Should only be called once
2869 * @param t The Thread to add
2871 void ModelChecker::add_thread(Thread *t)
2873 thread_map->put(id_to_int(t->get_id()), t);
2874 scheduler->add_thread(t);
2878 * Removes a thread from the scheduler.
2879 * @param the thread to remove.
2881 void ModelChecker::remove_thread(Thread *t)
2883 scheduler->remove_thread(t);
2887 * @brief Get a Thread reference by its ID
2888 * @param tid The Thread's ID
2889 * @return A Thread reference
2891 Thread * ModelChecker::get_thread(thread_id_t tid) const
2893 return thread_map->get(id_to_int(tid));
2897 * @brief Get a reference to the Thread in which a ModelAction was executed
2898 * @param act The ModelAction
2899 * @return A Thread reference
2901 Thread * ModelChecker::get_thread(const ModelAction *act) const
2903 return get_thread(act->get_tid());
2907 * @brief Get a Promise's "promise number"
2909 * A "promise number" is an index number that is unique to a promise, valid
2910 * only for a specific snapshot of an execution trace. Promises may come and go
2911 * as they are generated an resolved, so an index only retains meaning for the
2914 * @param promise The Promise to check
2915 * @return The promise index, if the promise still is valid; otherwise -1
2917 int ModelChecker::get_promise_number(const Promise *promise) const
2919 for (unsigned int i = 0; i < promises->size(); i++)
2920 if ((*promises)[i] == promise)
2927 * @brief Check if a Thread is currently enabled
2928 * @param t The Thread to check
2929 * @return True if the Thread is currently enabled
2931 bool ModelChecker::is_enabled(Thread *t) const
2933 return scheduler->is_enabled(t);
2937 * @brief Check if a Thread is currently enabled
2938 * @param tid The ID of the Thread to check
2939 * @return True if the Thread is currently enabled
2941 bool ModelChecker::is_enabled(thread_id_t tid) const
2943 return scheduler->is_enabled(tid);
2947 * Switch from a model-checker context to a user-thread context. This is the
2948 * complement of ModelChecker::switch_to_master and must be called from the
2949 * model-checker context
2951 * @param thread The user-thread to switch to
2953 void ModelChecker::switch_from_master(Thread *thread)
2955 scheduler->set_current_thread(thread);
2956 Thread::swap(&system_context, thread);
2960 * Switch from a user-context to the "master thread" context (a.k.a. system
2961 * context). This switch is made with the intention of exploring a particular
2962 * model-checking action (described by a ModelAction object). Must be called
2963 * from a user-thread context.
2965 * @param act The current action that will be explored. May be NULL only if
2966 * trace is exiting via an assertion (see ModelChecker::set_assert and
2967 * ModelChecker::has_asserted).
2968 * @return Return the value returned by the current action
2970 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2973 Thread *old = thread_current();
2974 ASSERT(!old->get_pending());
2975 old->set_pending(act);
2976 if (Thread::swap(old, &system_context) < 0) {
2977 perror("swap threads");
2980 return old->get_return_value();
2984 * Takes the next step in the execution, if possible.
2985 * @param curr The current step to take
2986 * @return Returns the next Thread to run, if any; NULL if this execution
2989 Thread * ModelChecker::take_step(ModelAction *curr)
2991 Thread *curr_thrd = get_thread(curr);
2992 ASSERT(curr_thrd->get_state() == THREAD_READY);
2994 curr = check_current_action(curr);
2996 /* Infeasible -> don't take any more steps */
2997 if (is_infeasible())
2999 else if (isfeasibleprefix() && have_bug_reports()) {
3004 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3007 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3008 scheduler->remove_thread(curr_thrd);
3010 Thread *next_thrd = get_next_thread(curr);
3012 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3013 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3018 /** Wrapper to run the user's main function, with appropriate arguments */
3019 void user_main_wrapper(void *)
3021 user_main(model->params.argc, model->params.argv);
3024 /** @brief Run ModelChecker for the user program */
3025 void ModelChecker::run()
3029 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3034 * Stash next pending action(s) for thread(s). There
3035 * should only need to stash one thread's action--the
3036 * thread which just took a step--plus the first step
3037 * for any newly-created thread
3039 for (unsigned int i = 0; i < get_num_threads(); i++) {
3040 thread_id_t tid = int_to_id(i);
3041 Thread *thr = get_thread(tid);
3042 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3043 switch_from_master(thr);
3047 /* Catch assertions from prior take_step or from
3048 * between-ModelAction bugs (e.g., data races) */
3052 /* Consume the next action for a Thread */
3053 ModelAction *curr = t->get_pending();
3054 t->set_pending(NULL);
3055 t = take_step(curr);
3056 } while (t && !t->is_model_thread());
3059 * Launch end-of-execution release sequence fixups only when
3060 * the execution is otherwise feasible AND there are:
3062 * (1) pending release sequences
3063 * (2) pending assertions that could be invalidated by a change
3064 * in clock vectors (i.e., data races)
3065 * (3) no pending promises
3067 while (!pending_rel_seqs->empty() &&
3068 is_feasible_prefix_ignore_relseq() &&
3069 !unrealizedraces.empty()) {
3070 model_print("*** WARNING: release sequence fixup action "
3071 "(%zu pending release seuqence(s)) ***\n",
3072 pending_rel_seqs->size());
3073 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3074 std::memory_order_seq_cst, NULL, VALUE_NONE,
3078 } while (next_execution());
3080 model_print("******* Model-checking complete: *******\n");