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 = curr->get_mutex();
931 struct std::mutex_state *state = NULL;
934 state = mutex->get_state();
936 switch (curr->get_type()) {
937 case ATOMIC_TRYLOCK: {
938 bool success = !state->locked;
939 curr->set_try_lock(success);
941 get_thread(curr)->set_return_value(0);
944 get_thread(curr)->set_return_value(1);
946 //otherwise fall into the lock case
948 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
949 assert_bug("Lock access before initialization");
950 state->locked = get_thread(curr);
951 ModelAction *unlock = get_last_unlock(curr);
952 //synchronize with the previous unlock statement
953 if (unlock != NULL) {
954 curr->synchronize_with(unlock);
959 case ATOMIC_UNLOCK: {
961 state->locked = NULL;
962 //wake up the other threads
963 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
964 //activate all the waiting threads
965 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
966 scheduler->wake(get_thread(*rit));
973 state->locked = NULL;
974 //wake up the other threads
975 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
976 //activate all the waiting threads
977 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
978 scheduler->wake(get_thread(*rit));
981 //check whether we should go to sleep or not...simulate spurious failures
982 if (curr->get_node()->get_misc() == 0) {
983 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
985 scheduler->sleep(get_thread(curr));
989 case ATOMIC_NOTIFY_ALL: {
990 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
991 //activate all the waiting threads
992 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
993 scheduler->wake(get_thread(*rit));
998 case ATOMIC_NOTIFY_ONE: {
999 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1000 int wakeupthread = curr->get_node()->get_misc();
1001 action_list_t::iterator it = waiters->begin();
1002 advance(it, wakeupthread);
1003 scheduler->wake(get_thread(*it));
1014 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1016 /* Do more ambitious checks now that mo is more complete */
1017 if (mo_may_allow(writer, reader)) {
1018 Node *node = reader->get_node();
1020 /* Find an ancestor thread which exists at the time of the reader */
1021 Thread *write_thread = get_thread(writer);
1022 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1023 write_thread = write_thread->get_parent();
1025 struct future_value fv = {
1026 writer->get_write_value(),
1027 writer->get_seq_number() + params.maxfuturedelay,
1028 write_thread->get_id(),
1030 if (node->add_future_value(fv))
1031 set_latest_backtrack(reader);
1036 * Process a write ModelAction
1037 * @param curr The ModelAction to process
1038 * @return True if the mo_graph was updated or promises were resolved
1040 bool ModelChecker::process_write(ModelAction *curr)
1042 /* Readers to which we may send our future value */
1043 std::vector< ModelAction *, ModelAlloc<ModelAction *> > send_fv;
1045 bool updated_mod_order = w_modification_order(curr, &send_fv);
1046 int promise_idx = get_promise_to_resolve(curr);
1047 const ModelAction *earliest_promise_reader;
1048 bool updated_promises = false;
1050 if (promise_idx >= 0) {
1051 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1052 updated_promises = resolve_promise(curr, promise_idx);
1054 earliest_promise_reader = NULL;
1056 /* Don't send future values to reads after the Promise we resolve */
1057 for (unsigned int i = 0; i < send_fv.size(); i++) {
1058 ModelAction *read = send_fv[i];
1059 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1060 futurevalues->push_back(PendingFutureValue(curr, read));
1063 if (promises->size() == 0) {
1064 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1065 struct PendingFutureValue pfv = (*futurevalues)[i];
1066 add_future_value(pfv.writer, pfv.act);
1068 futurevalues->clear();
1071 mo_graph->commitChanges();
1072 mo_check_promises(curr, false);
1074 get_thread(curr)->set_return_value(VALUE_NONE);
1075 return updated_mod_order || updated_promises;
1079 * Process a fence ModelAction
1080 * @param curr The ModelAction to process
1081 * @return True if synchronization was updated
1083 bool ModelChecker::process_fence(ModelAction *curr)
1086 * fence-relaxed: no-op
1087 * fence-release: only log the occurence (not in this function), for
1088 * use in later synchronization
1089 * fence-acquire (this function): search for hypothetical release
1092 bool updated = false;
1093 if (curr->is_acquire()) {
1094 action_list_t *list = action_trace;
1095 action_list_t::reverse_iterator rit;
1096 /* Find X : is_read(X) && X --sb-> curr */
1097 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1098 ModelAction *act = *rit;
1101 if (act->get_tid() != curr->get_tid())
1103 /* Stop at the beginning of the thread */
1104 if (act->is_thread_start())
1106 /* Stop once we reach a prior fence-acquire */
1107 if (act->is_fence() && act->is_acquire())
1109 if (!act->is_read())
1111 /* read-acquire will find its own release sequences */
1112 if (act->is_acquire())
1115 /* Establish hypothetical release sequences */
1116 rel_heads_list_t release_heads;
1117 get_release_seq_heads(curr, act, &release_heads);
1118 for (unsigned int i = 0; i < release_heads.size(); i++)
1119 if (!curr->synchronize_with(release_heads[i]))
1120 set_bad_synchronization();
1121 if (release_heads.size() != 0)
1129 * @brief Process the current action for thread-related activity
1131 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1132 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1133 * synchronization, etc. This function is a no-op for non-THREAD actions
1134 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1136 * @param curr The current action
1137 * @return True if synchronization was updated or a thread completed
1139 bool ModelChecker::process_thread_action(ModelAction *curr)
1141 bool updated = false;
1143 switch (curr->get_type()) {
1144 case THREAD_CREATE: {
1145 thrd_t *thrd = (thrd_t *)curr->get_location();
1146 struct thread_params *params = (struct thread_params *)curr->get_value();
1147 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1149 th->set_creation(curr);
1150 /* Promises can be satisfied by children */
1151 for (unsigned int i = 0; i < promises->size(); i++) {
1152 Promise *promise = (*promises)[i];
1153 if (promise->thread_is_available(curr->get_tid()))
1154 promise->add_thread(th->get_id());
1159 Thread *blocking = curr->get_thread_operand();
1160 ModelAction *act = get_last_action(blocking->get_id());
1161 curr->synchronize_with(act);
1162 updated = true; /* trigger rel-seq checks */
1165 case THREAD_FINISH: {
1166 Thread *th = get_thread(curr);
1167 while (!th->wait_list_empty()) {
1168 ModelAction *act = th->pop_wait_list();
1169 scheduler->wake(get_thread(act));
1172 /* Completed thread can't satisfy promises */
1173 for (unsigned int i = 0; i < promises->size(); i++) {
1174 Promise *promise = (*promises)[i];
1175 if (promise->thread_is_available(th->get_id()))
1176 if (promise->eliminate_thread(th->get_id()))
1177 priv->failed_promise = true;
1179 updated = true; /* trigger rel-seq checks */
1182 case THREAD_START: {
1183 check_promises(curr->get_tid(), NULL, curr->get_cv());
1194 * @brief Process the current action for release sequence fixup activity
1196 * Performs model-checker release sequence fixups for the current action,
1197 * forcing a single pending release sequence to break (with a given, potential
1198 * "loose" write) or to complete (i.e., synchronize). If a pending release
1199 * sequence forms a complete release sequence, then we must perform the fixup
1200 * synchronization, mo_graph additions, etc.
1202 * @param curr The current action; must be a release sequence fixup action
1203 * @param work_queue The work queue to which to add work items as they are
1206 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1208 const ModelAction *write = curr->get_node()->get_relseq_break();
1209 struct release_seq *sequence = pending_rel_seqs->back();
1210 pending_rel_seqs->pop_back();
1212 ModelAction *acquire = sequence->acquire;
1213 const ModelAction *rf = sequence->rf;
1214 const ModelAction *release = sequence->release;
1218 ASSERT(release->same_thread(rf));
1220 if (write == NULL) {
1222 * @todo Forcing a synchronization requires that we set
1223 * modification order constraints. For instance, we can't allow
1224 * a fixup sequence in which two separate read-acquire
1225 * operations read from the same sequence, where the first one
1226 * synchronizes and the other doesn't. Essentially, we can't
1227 * allow any writes to insert themselves between 'release' and
1231 /* Must synchronize */
1232 if (!acquire->synchronize_with(release)) {
1233 set_bad_synchronization();
1236 /* Re-check all pending release sequences */
1237 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1238 /* Re-check act for mo_graph edges */
1239 work_queue->push_back(MOEdgeWorkEntry(acquire));
1241 /* propagate synchronization to later actions */
1242 action_list_t::reverse_iterator rit = action_trace->rbegin();
1243 for (; (*rit) != acquire; rit++) {
1244 ModelAction *propagate = *rit;
1245 if (acquire->happens_before(propagate)) {
1246 propagate->synchronize_with(acquire);
1247 /* Re-check 'propagate' for mo_graph edges */
1248 work_queue->push_back(MOEdgeWorkEntry(propagate));
1252 /* Break release sequence with new edges:
1253 * release --mo--> write --mo--> rf */
1254 mo_graph->addEdge(release, write);
1255 mo_graph->addEdge(write, rf);
1258 /* See if we have realized a data race */
1263 * Initialize the current action by performing one or more of the following
1264 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1265 * in the NodeStack, manipulating backtracking sets, allocating and
1266 * initializing clock vectors, and computing the promises to fulfill.
1268 * @param curr The current action, as passed from the user context; may be
1269 * freed/invalidated after the execution of this function, with a different
1270 * action "returned" its place (pass-by-reference)
1271 * @return True if curr is a newly-explored action; false otherwise
1273 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1275 ModelAction *newcurr;
1277 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1278 newcurr = process_rmw(*curr);
1281 if (newcurr->is_rmw())
1282 compute_promises(newcurr);
1288 (*curr)->set_seq_number(get_next_seq_num());
1290 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1292 /* First restore type and order in case of RMW operation */
1293 if ((*curr)->is_rmwr())
1294 newcurr->copy_typeandorder(*curr);
1296 ASSERT((*curr)->get_location() == newcurr->get_location());
1297 newcurr->copy_from_new(*curr);
1299 /* Discard duplicate ModelAction; use action from NodeStack */
1302 /* Always compute new clock vector */
1303 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1306 return false; /* Action was explored previously */
1310 /* Always compute new clock vector */
1311 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1313 /* Assign most recent release fence */
1314 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1317 * Perform one-time actions when pushing new ModelAction onto
1320 if (newcurr->is_write())
1321 compute_promises(newcurr);
1322 else if (newcurr->is_relseq_fixup())
1323 compute_relseq_breakwrites(newcurr);
1324 else if (newcurr->is_wait())
1325 newcurr->get_node()->set_misc_max(2);
1326 else if (newcurr->is_notify_one()) {
1327 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1329 return true; /* This was a new ModelAction */
1334 * @brief Establish reads-from relation between two actions
1336 * Perform basic operations involved with establishing a concrete rf relation,
1337 * including setting the ModelAction data and checking for release sequences.
1339 * @param act The action that is reading (must be a read)
1340 * @param rf The action from which we are reading (must be a write)
1342 * @return True if this read established synchronization
1344 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1347 act->set_read_from(rf);
1348 if (act->is_acquire()) {
1349 rel_heads_list_t release_heads;
1350 get_release_seq_heads(act, act, &release_heads);
1351 int num_heads = release_heads.size();
1352 for (unsigned int i = 0; i < release_heads.size(); i++)
1353 if (!act->synchronize_with(release_heads[i])) {
1354 set_bad_synchronization();
1357 return num_heads > 0;
1363 * Check promises and eliminate potentially-satisfying threads when a thread is
1364 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1365 * no longer satisfy a promise generated from that thread.
1367 * @param blocker The thread on which a thread is waiting
1368 * @param waiting The waiting thread
1370 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1372 for (unsigned int i = 0; i < promises->size(); i++) {
1373 Promise *promise = (*promises)[i];
1374 if (!promise->thread_is_available(waiting->get_id()))
1376 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1377 ModelAction *reader = promise->get_reader(j);
1378 if (reader->get_tid() != blocker->get_id())
1380 if (promise->eliminate_thread(waiting->get_id())) {
1381 /* Promise has failed */
1382 priv->failed_promise = true;
1384 /* Only eliminate the 'waiting' thread once */
1392 * @brief Check whether a model action is enabled.
1394 * Checks whether a lock or join operation would be successful (i.e., is the
1395 * lock already locked, or is the joined thread already complete). If not, put
1396 * the action in a waiter list.
1398 * @param curr is the ModelAction to check whether it is enabled.
1399 * @return a bool that indicates whether the action is enabled.
1401 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1402 if (curr->is_lock()) {
1403 std::mutex *lock = (std::mutex *)curr->get_location();
1404 struct std::mutex_state *state = lock->get_state();
1405 if (state->locked) {
1406 //Stick the action in the appropriate waiting queue
1407 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1410 } else if (curr->get_type() == THREAD_JOIN) {
1411 Thread *blocking = (Thread *)curr->get_location();
1412 if (!blocking->is_complete()) {
1413 blocking->push_wait_list(curr);
1414 thread_blocking_check_promises(blocking, get_thread(curr));
1423 * This is the heart of the model checker routine. It performs model-checking
1424 * actions corresponding to a given "current action." Among other processes, it
1425 * calculates reads-from relationships, updates synchronization clock vectors,
1426 * forms a memory_order constraints graph, and handles replay/backtrack
1427 * execution when running permutations of previously-observed executions.
1429 * @param curr The current action to process
1430 * @return The ModelAction that is actually executed; may be different than
1431 * curr; may be NULL, if the current action is not enabled to run
1433 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1436 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1438 if (!check_action_enabled(curr)) {
1439 /* Make the execution look like we chose to run this action
1440 * much later, when a lock/join can succeed */
1441 get_thread(curr)->set_pending(curr);
1442 scheduler->sleep(get_thread(curr));
1446 bool newly_explored = initialize_curr_action(&curr);
1452 wake_up_sleeping_actions(curr);
1454 /* Add the action to lists before any other model-checking tasks */
1455 if (!second_part_of_rmw)
1456 add_action_to_lists(curr);
1458 /* Build may_read_from set for newly-created actions */
1459 if (newly_explored && curr->is_read())
1460 build_may_read_from(curr);
1462 /* Initialize work_queue with the "current action" work */
1463 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1464 while (!work_queue.empty() && !has_asserted()) {
1465 WorkQueueEntry work = work_queue.front();
1466 work_queue.pop_front();
1468 switch (work.type) {
1469 case WORK_CHECK_CURR_ACTION: {
1470 ModelAction *act = work.action;
1471 bool update = false; /* update this location's release seq's */
1472 bool update_all = false; /* update all release seq's */
1474 if (process_thread_action(curr))
1477 if (act->is_read() && !second_part_of_rmw && process_read(act))
1480 if (act->is_write() && process_write(act))
1483 if (act->is_fence() && process_fence(act))
1486 if (act->is_mutex_op() && process_mutex(act))
1489 if (act->is_relseq_fixup())
1490 process_relseq_fixup(curr, &work_queue);
1493 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1495 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1498 case WORK_CHECK_RELEASE_SEQ:
1499 resolve_release_sequences(work.location, &work_queue);
1501 case WORK_CHECK_MO_EDGES: {
1502 /** @todo Complete verification of work_queue */
1503 ModelAction *act = work.action;
1504 bool updated = false;
1506 if (act->is_read()) {
1507 const ModelAction *rf = act->get_reads_from();
1508 const Promise *promise = act->get_reads_from_promise();
1510 if (r_modification_order(act, rf))
1512 } else if (promise) {
1513 if (r_modification_order(act, promise))
1517 if (act->is_write()) {
1518 if (w_modification_order(act, NULL))
1521 mo_graph->commitChanges();
1524 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1533 check_curr_backtracking(curr);
1534 set_backtracking(curr);
1538 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1540 Node *currnode = curr->get_node();
1541 Node *parnode = currnode->get_parent();
1543 if ((parnode && !parnode->backtrack_empty()) ||
1544 !currnode->misc_empty() ||
1545 !currnode->read_from_empty() ||
1546 !currnode->promise_empty() ||
1547 !currnode->relseq_break_empty()) {
1548 set_latest_backtrack(curr);
1552 bool ModelChecker::promises_expired() const
1554 for (unsigned int i = 0; i < promises->size(); i++) {
1555 Promise *promise = (*promises)[i];
1556 if (promise->get_expiration() < priv->used_sequence_numbers)
1563 * This is the strongest feasibility check available.
1564 * @return whether the current trace (partial or complete) must be a prefix of
1567 bool ModelChecker::isfeasibleprefix() const
1569 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1573 * Print disagnostic information about an infeasible execution
1574 * @param prefix A string to prefix the output with; if NULL, then a default
1575 * message prefix will be provided
1577 void ModelChecker::print_infeasibility(const char *prefix) const
1581 if (mo_graph->checkForCycles())
1582 ptr += sprintf(ptr, "[mo cycle]");
1583 if (priv->failed_promise)
1584 ptr += sprintf(ptr, "[failed promise]");
1585 if (priv->too_many_reads)
1586 ptr += sprintf(ptr, "[too many reads]");
1587 if (priv->no_valid_reads)
1588 ptr += sprintf(ptr, "[no valid reads-from]");
1589 if (priv->bad_synchronization)
1590 ptr += sprintf(ptr, "[bad sw ordering]");
1591 if (promises_expired())
1592 ptr += sprintf(ptr, "[promise expired]");
1593 if (promises->size() != 0)
1594 ptr += sprintf(ptr, "[unresolved promise]");
1596 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1600 * Returns whether the current completed trace is feasible, except for pending
1601 * release sequences.
1603 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1605 return !is_infeasible() && promises->size() == 0;
1609 * Check if the current partial trace is infeasible. Does not check any
1610 * end-of-execution flags, which might rule out the execution. Thus, this is
1611 * useful only for ruling an execution as infeasible.
1612 * @return whether the current partial trace is infeasible.
1614 bool ModelChecker::is_infeasible() const
1616 return mo_graph->checkForCycles() ||
1617 priv->no_valid_reads ||
1618 priv->failed_promise ||
1619 priv->too_many_reads ||
1620 priv->bad_synchronization ||
1624 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1625 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1626 ModelAction *lastread = get_last_action(act->get_tid());
1627 lastread->process_rmw(act);
1628 if (act->is_rmw()) {
1629 if (lastread->get_reads_from())
1630 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1632 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1633 mo_graph->commitChanges();
1639 * A helper function for ModelChecker::check_recency, to check if the current
1640 * thread is able to read from a different write/promise for 'params.maxreads'
1641 * number of steps and if that write/promise should become visible (i.e., is
1642 * ordered later in the modification order). This helps model memory liveness.
1644 * @param curr The current action. Must be a read.
1645 * @param rf The write/promise from which we plan to read
1646 * @param other_rf The write/promise from which we may read
1647 * @return True if we were able to read from other_rf for params.maxreads steps
1649 template <typename T, typename U>
1650 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1652 /* Need a different write/promise */
1653 if (other_rf->equals(rf))
1656 /* Only look for "newer" writes/promises */
1657 if (!mo_graph->checkReachable(rf, other_rf))
1660 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1661 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1662 action_list_t::reverse_iterator rit = list->rbegin();
1663 ASSERT((*rit) == curr);
1664 /* Skip past curr */
1667 /* Does this write/promise work for everyone? */
1668 for (int i = 0; i < params.maxreads; i++, rit++) {
1669 ModelAction *act = *rit;
1670 if (!act->may_read_from(other_rf))
1677 * Checks whether a thread has read from the same write or Promise for too many
1678 * times without seeing the effects of a later write/Promise.
1681 * 1) there must a different write/promise that we could read from,
1682 * 2) we must have read from the same write/promise in excess of maxreads times,
1683 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1684 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1686 * If so, we decide that the execution is no longer feasible.
1688 * @param curr The current action. Must be a read.
1689 * @param rf The ModelAction/Promise from which we might read.
1690 * @return True if the read should succeed; false otherwise
1692 template <typename T>
1693 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1695 if (!params.maxreads)
1698 //NOTE: Next check is just optimization, not really necessary....
1699 if (curr->get_node()->get_read_from_past_size() +
1700 curr->get_node()->get_read_from_promise_size() <= 1)
1703 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1704 int tid = id_to_int(curr->get_tid());
1705 ASSERT(tid < (int)thrd_lists->size());
1706 action_list_t *list = &(*thrd_lists)[tid];
1707 action_list_t::reverse_iterator rit = list->rbegin();
1708 ASSERT((*rit) == curr);
1709 /* Skip past curr */
1712 action_list_t::reverse_iterator ritcopy = rit;
1713 /* See if we have enough reads from the same value */
1714 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1715 if (ritcopy == list->rend())
1717 ModelAction *act = *ritcopy;
1718 if (!act->is_read())
1720 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1722 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1724 if (act->get_node()->get_read_from_past_size() +
1725 act->get_node()->get_read_from_promise_size() <= 1)
1728 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1729 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1730 if (should_read_instead(curr, rf, write))
1731 return false; /* liveness failure */
1733 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1734 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1735 if (should_read_instead(curr, rf, promise))
1736 return false; /* liveness failure */
1742 * Updates the mo_graph with the constraints imposed from the current
1745 * Basic idea is the following: Go through each other thread and find
1746 * the last action that happened before our read. Two cases:
1748 * (1) The action is a write => that write must either occur before
1749 * the write we read from or be the write we read from.
1751 * (2) The action is a read => the write that that action read from
1752 * must occur before the write we read from or be the same write.
1754 * @param curr The current action. Must be a read.
1755 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1756 * @return True if modification order edges were added; false otherwise
1758 template <typename rf_type>
1759 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1761 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1764 ASSERT(curr->is_read());
1766 /* Last SC fence in the current thread */
1767 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1769 /* Iterate over all threads */
1770 for (i = 0; i < thrd_lists->size(); i++) {
1771 /* Last SC fence in thread i */
1772 ModelAction *last_sc_fence_thread_local = NULL;
1773 if (int_to_id((int)i) != curr->get_tid())
1774 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1776 /* Last SC fence in thread i, before last SC fence in current thread */
1777 ModelAction *last_sc_fence_thread_before = NULL;
1778 if (last_sc_fence_local)
1779 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1781 /* Iterate over actions in thread, starting from most recent */
1782 action_list_t *list = &(*thrd_lists)[i];
1783 action_list_t::reverse_iterator rit;
1784 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1785 ModelAction *act = *rit;
1787 if (act->is_write() && !act->equals(rf) && act != curr) {
1788 /* C++, Section 29.3 statement 5 */
1789 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1790 *act < *last_sc_fence_thread_local) {
1791 added = mo_graph->addEdge(act, rf) || added;
1794 /* C++, Section 29.3 statement 4 */
1795 else if (act->is_seqcst() && last_sc_fence_local &&
1796 *act < *last_sc_fence_local) {
1797 added = mo_graph->addEdge(act, rf) || added;
1800 /* C++, Section 29.3 statement 6 */
1801 else if (last_sc_fence_thread_before &&
1802 *act < *last_sc_fence_thread_before) {
1803 added = mo_graph->addEdge(act, rf) || added;
1809 * Include at most one act per-thread that "happens
1810 * before" curr. Don't consider reflexively.
1812 if (act->happens_before(curr) && act != curr) {
1813 if (act->is_write()) {
1814 if (!act->equals(rf)) {
1815 added = mo_graph->addEdge(act, rf) || added;
1818 const ModelAction *prevrf = act->get_reads_from();
1819 const Promise *prevrf_promise = act->get_reads_from_promise();
1821 if (!prevrf->equals(rf))
1822 added = mo_graph->addEdge(prevrf, rf) || added;
1823 } else if (!prevrf_promise->equals(rf)) {
1824 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1833 * All compatible, thread-exclusive promises must be ordered after any
1834 * concrete loads from the same thread
1836 for (unsigned int i = 0; i < promises->size(); i++)
1837 if ((*promises)[i]->is_compatible_exclusive(curr))
1838 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1844 * Updates the mo_graph with the constraints imposed from the current write.
1846 * Basic idea is the following: Go through each other thread and find
1847 * the lastest action that happened before our write. Two cases:
1849 * (1) The action is a write => that write must occur before
1852 * (2) The action is a read => the write that that action read from
1853 * must occur before the current write.
1855 * This method also handles two other issues:
1857 * (I) Sequential Consistency: Making sure that if the current write is
1858 * seq_cst, that it occurs after the previous seq_cst write.
1860 * (II) Sending the write back to non-synchronizing reads.
1862 * @param curr The current action. Must be a write.
1863 * @param send_fv A vector for stashing reads to which we may pass our future
1864 * value. If NULL, then don't record any future values.
1865 * @return True if modification order edges were added; false otherwise
1867 bool ModelChecker::w_modification_order(ModelAction *curr, std::vector< ModelAction *, ModelAlloc<ModelAction *> > *send_fv)
1869 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1872 ASSERT(curr->is_write());
1874 if (curr->is_seqcst()) {
1875 /* We have to at least see the last sequentially consistent write,
1876 so we are initialized. */
1877 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1878 if (last_seq_cst != NULL) {
1879 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1883 /* Last SC fence in the current thread */
1884 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1886 /* Iterate over all threads */
1887 for (i = 0; i < thrd_lists->size(); i++) {
1888 /* Last SC fence in thread i, before last SC fence in current thread */
1889 ModelAction *last_sc_fence_thread_before = NULL;
1890 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1891 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1893 /* Iterate over actions in thread, starting from most recent */
1894 action_list_t *list = &(*thrd_lists)[i];
1895 action_list_t::reverse_iterator rit;
1896 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1897 ModelAction *act = *rit;
1900 * 1) If RMW and it actually read from something, then we
1901 * already have all relevant edges, so just skip to next
1904 * 2) If RMW and it didn't read from anything, we should
1905 * whatever edge we can get to speed up convergence.
1907 * 3) If normal write, we need to look at earlier actions, so
1908 * continue processing list.
1910 if (curr->is_rmw()) {
1911 if (curr->get_reads_from() != NULL)
1919 /* C++, Section 29.3 statement 7 */
1920 if (last_sc_fence_thread_before && act->is_write() &&
1921 *act < *last_sc_fence_thread_before) {
1922 added = mo_graph->addEdge(act, curr) || added;
1927 * Include at most one act per-thread that "happens
1930 if (act->happens_before(curr)) {
1932 * Note: if act is RMW, just add edge:
1934 * The following edge should be handled elsewhere:
1935 * readfrom(act) --mo--> act
1937 if (act->is_write())
1938 added = mo_graph->addEdge(act, curr) || added;
1939 else if (act->is_read()) {
1940 //if previous read accessed a null, just keep going
1941 if (act->get_reads_from() == NULL)
1943 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1946 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1947 !act->same_thread(curr)) {
1948 /* We have an action that:
1949 (1) did not happen before us
1950 (2) is a read and we are a write
1951 (3) cannot synchronize with us
1952 (4) is in a different thread
1954 that read could potentially read from our write. Note that
1955 these checks are overly conservative at this point, we'll
1956 do more checks before actually removing the
1960 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1961 if (!is_infeasible())
1962 send_fv->push_back(act);
1963 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1964 add_future_value(curr, act);
1971 * All compatible, thread-exclusive promises must be ordered after any
1972 * concrete stores to the same thread, or else they can be merged with
1975 for (unsigned int i = 0; i < promises->size(); i++)
1976 if ((*promises)[i]->is_compatible_exclusive(curr))
1977 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1982 /** Arbitrary reads from the future are not allowed. Section 29.3
1983 * part 9 places some constraints. This method checks one result of constraint
1984 * constraint. Others require compiler support. */
1985 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1987 if (!writer->is_rmw())
1990 if (!reader->is_rmw())
1993 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1994 if (search == reader)
1996 if (search->get_tid() == reader->get_tid() &&
1997 search->happens_before(reader))
2005 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2006 * some constraints. This method checks one the following constraint (others
2007 * require compiler support):
2009 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2011 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2013 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2015 /* Iterate over all threads */
2016 for (i = 0; i < thrd_lists->size(); i++) {
2017 const ModelAction *write_after_read = NULL;
2019 /* Iterate over actions in thread, starting from most recent */
2020 action_list_t *list = &(*thrd_lists)[i];
2021 action_list_t::reverse_iterator rit;
2022 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2023 ModelAction *act = *rit;
2025 /* Don't disallow due to act == reader */
2026 if (!reader->happens_before(act) || reader == act)
2028 else if (act->is_write())
2029 write_after_read = act;
2030 else if (act->is_read() && act->get_reads_from() != NULL)
2031 write_after_read = act->get_reads_from();
2034 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2041 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2042 * The ModelAction under consideration is expected to be taking part in
2043 * release/acquire synchronization as an object of the "reads from" relation.
2044 * Note that this can only provide release sequence support for RMW chains
2045 * which do not read from the future, as those actions cannot be traced until
2046 * their "promise" is fulfilled. Similarly, we may not even establish the
2047 * presence of a release sequence with certainty, as some modification order
2048 * constraints may be decided further in the future. Thus, this function
2049 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2050 * and a boolean representing certainty.
2052 * @param rf The action that might be part of a release sequence. Must be a
2054 * @param release_heads A pass-by-reference style return parameter. After
2055 * execution of this function, release_heads will contain the heads of all the
2056 * relevant release sequences, if any exists with certainty
2057 * @param pending A pass-by-reference style return parameter which is only used
2058 * when returning false (i.e., uncertain). Returns most information regarding
2059 * an uncertain release sequence, including any write operations that might
2060 * break the sequence.
2061 * @return true, if the ModelChecker is certain that release_heads is complete;
2064 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2065 rel_heads_list_t *release_heads,
2066 struct release_seq *pending) const
2068 /* Only check for release sequences if there are no cycles */
2069 if (mo_graph->checkForCycles())
2072 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2073 ASSERT(rf->is_write());
2075 if (rf->is_release())
2076 release_heads->push_back(rf);
2077 else if (rf->get_last_fence_release())
2078 release_heads->push_back(rf->get_last_fence_release());
2080 break; /* End of RMW chain */
2082 /** @todo Need to be smarter here... In the linux lock
2083 * example, this will run to the beginning of the program for
2085 /** @todo The way to be smarter here is to keep going until 1
2086 * thread has a release preceded by an acquire and you've seen
2089 /* acq_rel RMW is a sufficient stopping condition */
2090 if (rf->is_acquire() && rf->is_release())
2091 return true; /* complete */
2094 /* read from future: need to settle this later */
2096 return false; /* incomplete */
2099 if (rf->is_release())
2100 return true; /* complete */
2102 /* else relaxed write
2103 * - check for fence-release in the same thread (29.8, stmt. 3)
2104 * - check modification order for contiguous subsequence
2105 * -> rf must be same thread as release */
2107 const ModelAction *fence_release = rf->get_last_fence_release();
2108 /* Synchronize with a fence-release unconditionally; we don't need to
2109 * find any more "contiguous subsequence..." for it */
2111 release_heads->push_back(fence_release);
2113 int tid = id_to_int(rf->get_tid());
2114 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2115 action_list_t *list = &(*thrd_lists)[tid];
2116 action_list_t::const_reverse_iterator rit;
2118 /* Find rf in the thread list */
2119 rit = std::find(list->rbegin(), list->rend(), rf);
2120 ASSERT(rit != list->rend());
2122 /* Find the last {write,fence}-release */
2123 for (; rit != list->rend(); rit++) {
2124 if (fence_release && *(*rit) < *fence_release)
2126 if ((*rit)->is_release())
2129 if (rit == list->rend()) {
2130 /* No write-release in this thread */
2131 return true; /* complete */
2132 } else if (fence_release && *(*rit) < *fence_release) {
2133 /* The fence-release is more recent (and so, "stronger") than
2134 * the most recent write-release */
2135 return true; /* complete */
2136 } /* else, need to establish contiguous release sequence */
2137 ModelAction *release = *rit;
2139 ASSERT(rf->same_thread(release));
2141 pending->writes.clear();
2143 bool certain = true;
2144 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2145 if (id_to_int(rf->get_tid()) == (int)i)
2147 list = &(*thrd_lists)[i];
2149 /* Can we ensure no future writes from this thread may break
2150 * the release seq? */
2151 bool future_ordered = false;
2153 ModelAction *last = get_last_action(int_to_id(i));
2154 Thread *th = get_thread(int_to_id(i));
2155 if ((last && rf->happens_before(last)) ||
2158 future_ordered = true;
2160 ASSERT(!th->is_model_thread() || future_ordered);
2162 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2163 const ModelAction *act = *rit;
2164 /* Reach synchronization -> this thread is complete */
2165 if (act->happens_before(release))
2167 if (rf->happens_before(act)) {
2168 future_ordered = true;
2172 /* Only non-RMW writes can break release sequences */
2173 if (!act->is_write() || act->is_rmw())
2176 /* Check modification order */
2177 if (mo_graph->checkReachable(rf, act)) {
2178 /* rf --mo--> act */
2179 future_ordered = true;
2182 if (mo_graph->checkReachable(act, release))
2183 /* act --mo--> release */
2185 if (mo_graph->checkReachable(release, act) &&
2186 mo_graph->checkReachable(act, rf)) {
2187 /* release --mo-> act --mo--> rf */
2188 return true; /* complete */
2190 /* act may break release sequence */
2191 pending->writes.push_back(act);
2194 if (!future_ordered)
2195 certain = false; /* This thread is uncertain */
2199 release_heads->push_back(release);
2200 pending->writes.clear();
2202 pending->release = release;
2209 * An interface for getting the release sequence head(s) with which a
2210 * given ModelAction must synchronize. This function only returns a non-empty
2211 * result when it can locate a release sequence head with certainty. Otherwise,
2212 * it may mark the internal state of the ModelChecker so that it will handle
2213 * the release sequence at a later time, causing @a acquire to update its
2214 * synchronization at some later point in execution.
2216 * @param acquire The 'acquire' action that may synchronize with a release
2218 * @param read The read action that may read from a release sequence; this may
2219 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2220 * when 'acquire' is a fence-acquire)
2221 * @param release_heads A pass-by-reference return parameter. Will be filled
2222 * with the head(s) of the release sequence(s), if they exists with certainty.
2223 * @see ModelChecker::release_seq_heads
2225 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2226 ModelAction *read, rel_heads_list_t *release_heads)
2228 const ModelAction *rf = read->get_reads_from();
2229 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2230 sequence->acquire = acquire;
2231 sequence->read = read;
2233 if (!release_seq_heads(rf, release_heads, sequence)) {
2234 /* add act to 'lazy checking' list */
2235 pending_rel_seqs->push_back(sequence);
2237 snapshot_free(sequence);
2242 * Attempt to resolve all stashed operations that might synchronize with a
2243 * release sequence for a given location. This implements the "lazy" portion of
2244 * determining whether or not a release sequence was contiguous, since not all
2245 * modification order information is present at the time an action occurs.
2247 * @param location The location/object that should be checked for release
2248 * sequence resolutions. A NULL value means to check all locations.
2249 * @param work_queue The work queue to which to add work items as they are
2251 * @return True if any updates occurred (new synchronization, new mo_graph
2254 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2256 bool updated = false;
2257 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2258 while (it != pending_rel_seqs->end()) {
2259 struct release_seq *pending = *it;
2260 ModelAction *acquire = pending->acquire;
2261 const ModelAction *read = pending->read;
2263 /* Only resolve sequences on the given location, if provided */
2264 if (location && read->get_location() != location) {
2269 const ModelAction *rf = read->get_reads_from();
2270 rel_heads_list_t release_heads;
2272 complete = release_seq_heads(rf, &release_heads, pending);
2273 for (unsigned int i = 0; i < release_heads.size(); i++) {
2274 if (!acquire->has_synchronized_with(release_heads[i])) {
2275 if (acquire->synchronize_with(release_heads[i]))
2278 set_bad_synchronization();
2283 /* Re-check all pending release sequences */
2284 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2285 /* Re-check read-acquire for mo_graph edges */
2286 if (acquire->is_read())
2287 work_queue->push_back(MOEdgeWorkEntry(acquire));
2289 /* propagate synchronization to later actions */
2290 action_list_t::reverse_iterator rit = action_trace->rbegin();
2291 for (; (*rit) != acquire; rit++) {
2292 ModelAction *propagate = *rit;
2293 if (acquire->happens_before(propagate)) {
2294 propagate->synchronize_with(acquire);
2295 /* Re-check 'propagate' for mo_graph edges */
2296 work_queue->push_back(MOEdgeWorkEntry(propagate));
2301 it = pending_rel_seqs->erase(it);
2302 snapshot_free(pending);
2308 // If we resolved promises or data races, see if we have realized a data race.
2315 * Performs various bookkeeping operations for the current ModelAction. For
2316 * instance, adds action to the per-object, per-thread action vector and to the
2317 * action trace list of all thread actions.
2319 * @param act is the ModelAction to add.
2321 void ModelChecker::add_action_to_lists(ModelAction *act)
2323 int tid = id_to_int(act->get_tid());
2324 ModelAction *uninit = NULL;
2326 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2327 if (list->empty() && act->is_atomic_var()) {
2328 uninit = new_uninitialized_action(act->get_location());
2329 uninit_id = id_to_int(uninit->get_tid());
2330 list->push_back(uninit);
2332 list->push_back(act);
2334 action_trace->push_back(act);
2336 action_trace->push_front(uninit);
2338 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2339 if (tid >= (int)vec->size())
2340 vec->resize(priv->next_thread_id);
2341 (*vec)[tid].push_back(act);
2343 (*vec)[uninit_id].push_front(uninit);
2345 if ((int)thrd_last_action->size() <= tid)
2346 thrd_last_action->resize(get_num_threads());
2347 (*thrd_last_action)[tid] = act;
2349 (*thrd_last_action)[uninit_id] = uninit;
2351 if (act->is_fence() && act->is_release()) {
2352 if ((int)thrd_last_fence_release->size() <= tid)
2353 thrd_last_fence_release->resize(get_num_threads());
2354 (*thrd_last_fence_release)[tid] = act;
2357 if (act->is_wait()) {
2358 void *mutex_loc = (void *) act->get_value();
2359 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2361 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2362 if (tid >= (int)vec->size())
2363 vec->resize(priv->next_thread_id);
2364 (*vec)[tid].push_back(act);
2369 * @brief Get the last action performed by a particular Thread
2370 * @param tid The thread ID of the Thread in question
2371 * @return The last action in the thread
2373 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2375 int threadid = id_to_int(tid);
2376 if (threadid < (int)thrd_last_action->size())
2377 return (*thrd_last_action)[id_to_int(tid)];
2383 * @brief Get the last fence release performed by a particular Thread
2384 * @param tid The thread ID of the Thread in question
2385 * @return The last fence release in the thread, if one exists; NULL otherwise
2387 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2389 int threadid = id_to_int(tid);
2390 if (threadid < (int)thrd_last_fence_release->size())
2391 return (*thrd_last_fence_release)[id_to_int(tid)];
2397 * Gets the last memory_order_seq_cst write (in the total global sequence)
2398 * performed on a particular object (i.e., memory location), not including the
2400 * @param curr The current ModelAction; also denotes the object location to
2402 * @return The last seq_cst write
2404 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2406 void *location = curr->get_location();
2407 action_list_t *list = get_safe_ptr_action(obj_map, location);
2408 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2409 action_list_t::reverse_iterator rit;
2410 for (rit = list->rbegin(); rit != list->rend(); rit++)
2411 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2417 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2418 * performed in a particular thread, prior to a particular fence.
2419 * @param tid The ID of the thread to check
2420 * @param before_fence The fence from which to begin the search; if NULL, then
2421 * search for the most recent fence in the thread.
2422 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2424 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2426 /* All fences should have NULL location */
2427 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2428 action_list_t::reverse_iterator rit = list->rbegin();
2431 for (; rit != list->rend(); rit++)
2432 if (*rit == before_fence)
2435 ASSERT(*rit == before_fence);
2439 for (; rit != list->rend(); rit++)
2440 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2446 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2447 * location). This function identifies the mutex according to the current
2448 * action, which is presumed to perform on the same mutex.
2449 * @param curr The current ModelAction; also denotes the object location to
2451 * @return The last unlock operation
2453 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2455 void *location = curr->get_location();
2456 action_list_t *list = get_safe_ptr_action(obj_map, location);
2457 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2458 action_list_t::reverse_iterator rit;
2459 for (rit = list->rbegin(); rit != list->rend(); rit++)
2460 if ((*rit)->is_unlock() || (*rit)->is_wait())
2465 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2467 ModelAction *parent = get_last_action(tid);
2469 parent = get_thread(tid)->get_creation();
2474 * Returns the clock vector for a given thread.
2475 * @param tid The thread whose clock vector we want
2476 * @return Desired clock vector
2478 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2480 return get_parent_action(tid)->get_cv();
2484 * @brief Find the promise, if any to resolve for the current action
2485 * @param curr The current ModelAction. Should be a write.
2486 * @return The (non-negative) index for the Promise to resolve, if any;
2489 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2491 for (unsigned int i = 0; i < promises->size(); i++)
2492 if (curr->get_node()->get_promise(i))
2498 * Resolve a Promise with a current write.
2499 * @param write The ModelAction that is fulfilling Promises
2500 * @param promise_idx The index corresponding to the promise
2501 * @return True if the Promise was successfully resolved; false otherwise
2503 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2505 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2506 Promise *promise = (*promises)[promise_idx];
2508 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2509 ModelAction *read = promise->get_reader(i);
2510 read_from(read, write);
2511 actions_to_check.push_back(read);
2513 /* Make sure the promise's value matches the write's value */
2514 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2515 if (!mo_graph->resolvePromise(promise, write))
2516 priv->failed_promise = true;
2518 promises->erase(promises->begin() + promise_idx);
2520 * @todo It is possible to end up in an inconsistent state, where a
2521 * "resolved" promise may still be referenced if
2522 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2524 * Note that the inconsistency only matters when dumping mo_graph to
2530 //Check whether reading these writes has made threads unable to
2532 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2533 ModelAction *read = actions_to_check[i];
2534 mo_check_promises(read, true);
2541 * Compute the set of promises that could potentially be satisfied by this
2542 * action. Note that the set computation actually appears in the Node, not in
2544 * @param curr The ModelAction that may satisfy promises
2546 void ModelChecker::compute_promises(ModelAction *curr)
2548 for (unsigned int i = 0; i < promises->size(); i++) {
2549 Promise *promise = (*promises)[i];
2550 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2553 bool satisfy = true;
2554 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2555 const ModelAction *act = promise->get_reader(j);
2556 if (act->happens_before(curr) ||
2557 act->could_synchronize_with(curr)) {
2563 curr->get_node()->set_promise(i);
2567 /** Checks promises in response to change in ClockVector Threads. */
2568 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2570 for (unsigned int i = 0; i < promises->size(); i++) {
2571 Promise *promise = (*promises)[i];
2572 if (!promise->thread_is_available(tid))
2574 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2575 const ModelAction *act = promise->get_reader(j);
2576 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2577 merge_cv->synchronized_since(act)) {
2578 if (promise->eliminate_thread(tid)) {
2579 /* Promise has failed */
2580 priv->failed_promise = true;
2588 void ModelChecker::check_promises_thread_disabled()
2590 for (unsigned int i = 0; i < promises->size(); i++) {
2591 Promise *promise = (*promises)[i];
2592 if (promise->has_failed()) {
2593 priv->failed_promise = true;
2600 * @brief Checks promises in response to addition to modification order for
2603 * We test whether threads are still available for satisfying promises after an
2604 * addition to our modification order constraints. Those that are unavailable
2605 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2606 * that promise has failed.
2608 * @param act The ModelAction which updated the modification order
2609 * @param is_read_check Should be true if act is a read and we must check for
2610 * updates to the store from which it read (there is a distinction here for
2611 * RMW's, which are both a load and a store)
2613 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2615 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2617 for (unsigned int i = 0; i < promises->size(); i++) {
2618 Promise *promise = (*promises)[i];
2620 // Is this promise on the same location?
2621 if (!promise->same_location(write))
2624 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2625 const ModelAction *pread = promise->get_reader(j);
2626 if (!pread->happens_before(act))
2628 if (mo_graph->checkPromise(write, promise)) {
2629 priv->failed_promise = true;
2635 // Don't do any lookups twice for the same thread
2636 if (!promise->thread_is_available(act->get_tid()))
2639 if (mo_graph->checkReachable(promise, write)) {
2640 if (mo_graph->checkPromise(write, promise)) {
2641 priv->failed_promise = true;
2649 * Compute the set of writes that may break the current pending release
2650 * sequence. This information is extracted from previou release sequence
2653 * @param curr The current ModelAction. Must be a release sequence fixup
2656 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2658 if (pending_rel_seqs->empty())
2661 struct release_seq *pending = pending_rel_seqs->back();
2662 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2663 const ModelAction *write = pending->writes[i];
2664 curr->get_node()->add_relseq_break(write);
2667 /* NULL means don't break the sequence; just synchronize */
2668 curr->get_node()->add_relseq_break(NULL);
2672 * Build up an initial set of all past writes that this 'read' action may read
2673 * from, as well as any previously-observed future values that must still be valid.
2675 * @param curr is the current ModelAction that we are exploring; it must be a
2678 void ModelChecker::build_may_read_from(ModelAction *curr)
2680 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2682 ASSERT(curr->is_read());
2684 ModelAction *last_sc_write = NULL;
2686 if (curr->is_seqcst())
2687 last_sc_write = get_last_seq_cst_write(curr);
2689 /* Iterate over all threads */
2690 for (i = 0; i < thrd_lists->size(); i++) {
2691 /* Iterate over actions in thread, starting from most recent */
2692 action_list_t *list = &(*thrd_lists)[i];
2693 action_list_t::reverse_iterator rit;
2694 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2695 ModelAction *act = *rit;
2697 /* Only consider 'write' actions */
2698 if (!act->is_write() || act == curr)
2701 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2702 bool allow_read = true;
2704 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2706 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2710 /* Only add feasible reads */
2711 mo_graph->startChanges();
2712 r_modification_order(curr, act);
2713 if (!is_infeasible())
2714 curr->get_node()->add_read_from_past(act);
2715 mo_graph->rollbackChanges();
2718 /* Include at most one act per-thread that "happens before" curr */
2719 if (act->happens_before(curr))
2724 /* Inherit existing, promised future values */
2725 for (i = 0; i < promises->size(); i++) {
2726 const Promise *promise = (*promises)[i];
2727 const ModelAction *promise_read = promise->get_reader(0);
2728 if (promise_read->same_var(curr)) {
2729 /* Only add feasible future-values */
2730 mo_graph->startChanges();
2731 r_modification_order(curr, promise);
2732 if (!is_infeasible())
2733 curr->get_node()->add_read_from_promise(promise_read);
2734 mo_graph->rollbackChanges();
2738 /* We may find no valid may-read-from only if the execution is doomed */
2739 if (!curr->get_node()->read_from_size()) {
2740 priv->no_valid_reads = true;
2744 if (DBG_ENABLED()) {
2745 model_print("Reached read action:\n");
2747 model_print("Printing read_from_past\n");
2748 curr->get_node()->print_read_from_past();
2749 model_print("End printing read_from_past\n");
2753 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2755 for ( ; write != NULL; write = write->get_reads_from()) {
2756 /* UNINIT actions don't have a Node, and they never sleep */
2757 if (write->is_uninitialized())
2759 Node *prevnode = write->get_node()->get_parent();
2761 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2762 if (write->is_release() && thread_sleep)
2764 if (!write->is_rmw())
2771 * @brief Create a new action representing an uninitialized atomic
2772 * @param location The memory location of the atomic object
2773 * @return A pointer to a new ModelAction
2775 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2777 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2778 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2779 act->create_cv(NULL);
2783 static void print_list(action_list_t *list)
2785 action_list_t::iterator it;
2787 model_print("---------------------------------------------------------------------\n");
2789 unsigned int hash = 0;
2791 for (it = list->begin(); it != list->end(); it++) {
2793 hash = hash^(hash<<3)^((*it)->hash());
2795 model_print("HASH %u\n", hash);
2796 model_print("---------------------------------------------------------------------\n");
2799 #if SUPPORT_MOD_ORDER_DUMP
2800 void ModelChecker::dumpGraph(char *filename) const
2803 sprintf(buffer, "%s.dot", filename);
2804 FILE *file = fopen(buffer, "w");
2805 fprintf(file, "digraph %s {\n", filename);
2806 mo_graph->dumpNodes(file);
2807 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2809 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2810 ModelAction *act = *it;
2811 if (act->is_read()) {
2812 mo_graph->dot_print_node(file, act);
2813 if (act->get_reads_from())
2814 mo_graph->dot_print_edge(file,
2815 act->get_reads_from(),
2817 "label=\"rf\", color=red, weight=2");
2819 mo_graph->dot_print_edge(file,
2820 act->get_reads_from_promise(),
2822 "label=\"rf\", color=red");
2824 if (thread_array[act->get_tid()]) {
2825 mo_graph->dot_print_edge(file,
2826 thread_array[id_to_int(act->get_tid())],
2828 "label=\"sb\", color=blue, weight=400");
2831 thread_array[act->get_tid()] = act;
2833 fprintf(file, "}\n");
2834 model_free(thread_array);
2839 /** @brief Prints an execution trace summary. */
2840 void ModelChecker::print_summary() const
2842 #if SUPPORT_MOD_ORDER_DUMP
2843 char buffername[100];
2844 sprintf(buffername, "exec%04u", stats.num_total);
2845 mo_graph->dumpGraphToFile(buffername);
2846 sprintf(buffername, "graph%04u", stats.num_total);
2847 dumpGraph(buffername);
2850 model_print("Execution %d:", stats.num_total);
2851 if (isfeasibleprefix()) {
2852 if (scheduler->all_threads_sleeping())
2853 model_print(" SLEEP-SET REDUNDANT");
2856 print_infeasibility(" INFEASIBLE");
2857 print_list(action_trace);
2862 * Add a Thread to the system for the first time. Should only be called once
2864 * @param t The Thread to add
2866 void ModelChecker::add_thread(Thread *t)
2868 thread_map->put(id_to_int(t->get_id()), t);
2869 scheduler->add_thread(t);
2873 * Removes a thread from the scheduler.
2874 * @param the thread to remove.
2876 void ModelChecker::remove_thread(Thread *t)
2878 scheduler->remove_thread(t);
2882 * @brief Get a Thread reference by its ID
2883 * @param tid The Thread's ID
2884 * @return A Thread reference
2886 Thread * ModelChecker::get_thread(thread_id_t tid) const
2888 return thread_map->get(id_to_int(tid));
2892 * @brief Get a reference to the Thread in which a ModelAction was executed
2893 * @param act The ModelAction
2894 * @return A Thread reference
2896 Thread * ModelChecker::get_thread(const ModelAction *act) const
2898 return get_thread(act->get_tid());
2902 * @brief Get a Promise's "promise number"
2904 * A "promise number" is an index number that is unique to a promise, valid
2905 * only for a specific snapshot of an execution trace. Promises may come and go
2906 * as they are generated an resolved, so an index only retains meaning for the
2909 * @param promise The Promise to check
2910 * @return The promise index, if the promise still is valid; otherwise -1
2912 int ModelChecker::get_promise_number(const Promise *promise) const
2914 for (unsigned int i = 0; i < promises->size(); i++)
2915 if ((*promises)[i] == promise)
2922 * @brief Check if a Thread is currently enabled
2923 * @param t The Thread to check
2924 * @return True if the Thread is currently enabled
2926 bool ModelChecker::is_enabled(Thread *t) const
2928 return scheduler->is_enabled(t);
2932 * @brief Check if a Thread is currently enabled
2933 * @param tid The ID of the Thread to check
2934 * @return True if the Thread is currently enabled
2936 bool ModelChecker::is_enabled(thread_id_t tid) const
2938 return scheduler->is_enabled(tid);
2942 * Switch from a model-checker context to a user-thread context. This is the
2943 * complement of ModelChecker::switch_to_master and must be called from the
2944 * model-checker context
2946 * @param thread The user-thread to switch to
2948 void ModelChecker::switch_from_master(Thread *thread)
2950 scheduler->set_current_thread(thread);
2951 Thread::swap(&system_context, thread);
2955 * Switch from a user-context to the "master thread" context (a.k.a. system
2956 * context). This switch is made with the intention of exploring a particular
2957 * model-checking action (described by a ModelAction object). Must be called
2958 * from a user-thread context.
2960 * @param act The current action that will be explored. May be NULL only if
2961 * trace is exiting via an assertion (see ModelChecker::set_assert and
2962 * ModelChecker::has_asserted).
2963 * @return Return the value returned by the current action
2965 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2968 Thread *old = thread_current();
2969 ASSERT(!old->get_pending());
2970 old->set_pending(act);
2971 if (Thread::swap(old, &system_context) < 0) {
2972 perror("swap threads");
2975 return old->get_return_value();
2979 * Takes the next step in the execution, if possible.
2980 * @param curr The current step to take
2981 * @return Returns the next Thread to run, if any; NULL if this execution
2984 Thread * ModelChecker::take_step(ModelAction *curr)
2986 Thread *curr_thrd = get_thread(curr);
2987 ASSERT(curr_thrd->get_state() == THREAD_READY);
2989 curr = check_current_action(curr);
2991 /* Infeasible -> don't take any more steps */
2992 if (is_infeasible())
2994 else if (isfeasibleprefix() && have_bug_reports()) {
2999 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3002 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3003 scheduler->remove_thread(curr_thrd);
3005 Thread *next_thrd = get_next_thread(curr);
3007 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3008 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3013 /** Wrapper to run the user's main function, with appropriate arguments */
3014 void user_main_wrapper(void *)
3016 user_main(model->params.argc, model->params.argv);
3019 /** @brief Run ModelChecker for the user program */
3020 void ModelChecker::run()
3024 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3029 * Stash next pending action(s) for thread(s). There
3030 * should only need to stash one thread's action--the
3031 * thread which just took a step--plus the first step
3032 * for any newly-created thread
3034 for (unsigned int i = 0; i < get_num_threads(); i++) {
3035 thread_id_t tid = int_to_id(i);
3036 Thread *thr = get_thread(tid);
3037 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3038 switch_from_master(thr);
3042 /* Catch assertions from prior take_step or from
3043 * between-ModelAction bugs (e.g., data races) */
3047 /* Consume the next action for a Thread */
3048 ModelAction *curr = t->get_pending();
3049 t->set_pending(NULL);
3050 t = take_step(curr);
3051 } while (t && !t->is_model_thread());
3054 * Launch end-of-execution release sequence fixups only when
3055 * the execution is otherwise feasible AND there are:
3057 * (1) pending release sequences
3058 * (2) pending assertions that could be invalidated by a change
3059 * in clock vectors (i.e., data races)
3060 * (3) no pending promises
3062 while (!pending_rel_seqs->empty() &&
3063 is_feasible_prefix_ignore_relseq() &&
3064 !unrealizedraces.empty()) {
3065 model_print("*** WARNING: release sequence fixup action "
3066 "(%zu pending release seuqence(s)) ***\n",
3067 pending_rel_seqs->size());
3068 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3069 std::memory_order_seq_cst, NULL, VALUE_NONE,
3073 } while (next_execution());
3075 model_print("******* Model-checking complete: *******\n");