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 Select the next thread to execute based on the curren action
210 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
211 * actions should be followed by the execution of their child thread. In either
212 * case, the current action should determine the next thread schedule.
214 * @param curr The current action
215 * @return The next thread to run, if the current action will determine this
216 * selection; otherwise NULL
218 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
220 /* Do not split atomic RMW */
222 return get_thread(curr);
223 /* Follow CREATE with the created thread */
224 if (curr->get_type() == THREAD_CREATE)
225 return curr->get_thread_operand();
230 * @brief Choose the next thread to execute.
232 * This function chooses the next thread that should execute. It can enforce
233 * execution replay/backtracking or, if the model-checker has no preference
234 * regarding the next thread (i.e., when exploring a new execution ordering),
235 * we defer to the scheduler.
237 * @return The next chosen thread to run, if any exist. Or else if the current
238 * execution should terminate, return NULL.
240 Thread * ModelChecker::get_next_thread()
245 * Have we completed exploring the preselected path? Then let the
249 return scheduler->select_next_thread();
251 /* Else, we are trying to replay an execution */
252 ModelAction *next = node_stack->get_next()->get_action();
254 if (next == diverge) {
255 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
256 earliest_diverge = diverge;
258 Node *nextnode = next->get_node();
259 Node *prevnode = nextnode->get_parent();
260 scheduler->update_sleep_set(prevnode);
262 /* Reached divergence point */
263 if (nextnode->increment_misc()) {
264 /* The next node will try to satisfy a different misc_index values. */
265 tid = next->get_tid();
266 node_stack->pop_restofstack(2);
267 } else if (nextnode->increment_promise()) {
268 /* The next node will try to satisfy a different set of promises. */
269 tid = next->get_tid();
270 node_stack->pop_restofstack(2);
271 } else if (nextnode->increment_read_from()) {
272 /* The next node will read from a different value. */
273 tid = next->get_tid();
274 node_stack->pop_restofstack(2);
275 } else if (nextnode->increment_relseq_break()) {
276 /* The next node will try to resolve a release sequence differently */
277 tid = next->get_tid();
278 node_stack->pop_restofstack(2);
281 /* Make a different thread execute for next step */
282 scheduler->add_sleep(get_thread(next->get_tid()));
283 tid = prevnode->get_next_backtrack();
284 /* Make sure the backtracked thread isn't sleeping. */
285 node_stack->pop_restofstack(1);
286 if (diverge == earliest_diverge) {
287 earliest_diverge = prevnode->get_action();
290 /* Start the round robin scheduler from this thread id */
291 scheduler->set_scheduler_thread(tid);
292 /* The correct sleep set is in the parent node. */
295 DEBUG("*** Divergence point ***\n");
299 tid = next->get_tid();
301 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
302 ASSERT(tid != THREAD_ID_T_NONE);
303 return thread_map->get(id_to_int(tid));
307 * We need to know what the next actions of all threads in the sleep
308 * set will be. This method computes them and stores the actions at
309 * the corresponding thread object's pending action.
312 void ModelChecker::execute_sleep_set()
314 for (unsigned int i = 0; i < get_num_threads(); i++) {
315 thread_id_t tid = int_to_id(i);
316 Thread *thr = get_thread(tid);
317 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
318 thr->get_pending()->set_sleep_flag();
324 * @brief Should the current action wake up a given thread?
326 * @param curr The current action
327 * @param thread The thread that we might wake up
328 * @return True, if we should wake up the sleeping thread; false otherwise
330 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
332 const ModelAction *asleep = thread->get_pending();
333 /* Don't allow partial RMW to wake anyone up */
336 /* Synchronizing actions may have been backtracked */
337 if (asleep->could_synchronize_with(curr))
339 /* All acquire/release fences and fence-acquire/store-release */
340 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
342 /* Fence-release + store can awake load-acquire on the same location */
343 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
344 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
345 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
351 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
353 for (unsigned int i = 0; i < get_num_threads(); i++) {
354 Thread *thr = get_thread(int_to_id(i));
355 if (scheduler->is_sleep_set(thr)) {
356 if (should_wake_up(curr, thr))
357 /* Remove this thread from sleep set */
358 scheduler->remove_sleep(thr);
363 /** @brief Alert the model-checker that an incorrectly-ordered
364 * synchronization was made */
365 void ModelChecker::set_bad_synchronization()
367 priv->bad_synchronization = true;
371 * Check whether the current trace has triggered an assertion which should halt
374 * @return True, if the execution should be aborted; false otherwise
376 bool ModelChecker::has_asserted() const
378 return priv->asserted;
382 * Trigger a trace assertion which should cause this execution to be halted.
383 * This can be due to a detected bug or due to an infeasibility that should
386 void ModelChecker::set_assert()
388 priv->asserted = true;
392 * Check if we are in a deadlock. Should only be called at the end of an
393 * execution, although it should not give false positives in the middle of an
394 * execution (there should be some ENABLED thread).
396 * @return True if program is in a deadlock; false otherwise
398 bool ModelChecker::is_deadlocked() const
400 bool blocking_threads = false;
401 for (unsigned int i = 0; i < get_num_threads(); i++) {
402 thread_id_t tid = int_to_id(i);
405 Thread *t = get_thread(tid);
406 if (!t->is_model_thread() && t->get_pending())
407 blocking_threads = true;
409 return blocking_threads;
413 * Check if a Thread has entered a circular wait deadlock situation. This will
414 * not check other threads for potential deadlock situations, and may miss
415 * deadlocks involving WAIT.
417 * @param t The thread which may have entered a deadlock
418 * @return True if this Thread entered a deadlock; false otherwise
420 bool ModelChecker::is_circular_wait(const Thread *t) const
422 for (Thread *waiting = t->waiting_on() ; waiting != NULL; waiting = waiting->waiting_on())
429 * Check if this is a complete execution. That is, have all thread completed
430 * execution (rather than exiting because sleep sets have forced a redundant
433 * @return True if the execution is complete.
435 bool ModelChecker::is_complete_execution() const
437 for (unsigned int i = 0; i < get_num_threads(); i++)
438 if (is_enabled(int_to_id(i)))
444 * @brief Assert a bug in the executing program.
446 * Use this function to assert any sort of bug in the user program. If the
447 * current trace is feasible (actually, a prefix of some feasible execution),
448 * then this execution will be aborted, printing the appropriate message. If
449 * the current trace is not yet feasible, the error message will be stashed and
450 * printed if the execution ever becomes feasible.
452 * @param msg Descriptive message for the bug (do not include newline char)
453 * @return True if bug is immediately-feasible
455 bool ModelChecker::assert_bug(const char *msg)
457 priv->bugs.push_back(new bug_message(msg));
459 if (isfeasibleprefix()) {
467 * @brief Assert a bug in the executing program, asserted by a user thread
468 * @see ModelChecker::assert_bug
469 * @param msg Descriptive message for the bug (do not include newline char)
471 void ModelChecker::assert_user_bug(const char *msg)
473 /* If feasible bug, bail out now */
475 switch_to_master(NULL);
478 /** @return True, if any bugs have been reported for this execution */
479 bool ModelChecker::have_bug_reports() const
481 return priv->bugs.size() != 0;
484 /** @brief Print bug report listing for this execution (if any bugs exist) */
485 void ModelChecker::print_bugs() const
487 if (have_bug_reports()) {
488 model_print("Bug report: %zu bug%s detected\n",
490 priv->bugs.size() > 1 ? "s" : "");
491 for (unsigned int i = 0; i < priv->bugs.size(); i++)
492 priv->bugs[i]->print();
497 * @brief Record end-of-execution stats
499 * Must be run when exiting an execution. Records various stats.
500 * @see struct execution_stats
502 void ModelChecker::record_stats()
505 if (!isfeasibleprefix())
506 stats.num_infeasible++;
507 else if (have_bug_reports())
508 stats.num_buggy_executions++;
509 else if (is_complete_execution())
510 stats.num_complete++;
512 stats.num_redundant++;
515 * @todo We can violate this ASSERT() when fairness/sleep sets
516 * conflict to cause an execution to terminate, e.g. with:
517 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
519 //ASSERT(scheduler->all_threads_sleeping());
523 /** @brief Print execution stats */
524 void ModelChecker::print_stats() const
526 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
527 model_print("Number of redundant executions: %d\n", stats.num_redundant);
528 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
529 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
530 model_print("Total executions: %d\n", stats.num_total);
531 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
535 * @brief End-of-exeuction print
536 * @param printbugs Should any existing bugs be printed?
538 void ModelChecker::print_execution(bool printbugs) const
540 print_program_output();
542 if (params.verbose) {
543 model_print("Earliest divergence point since last feasible execution:\n");
544 if (earliest_diverge)
545 earliest_diverge->print();
547 model_print("(Not set)\n");
553 /* Don't print invalid bugs */
562 * Queries the model-checker for more executions to explore and, if one
563 * exists, resets the model-checker state to execute a new execution.
565 * @return If there are more executions to explore, return true. Otherwise,
568 bool ModelChecker::next_execution()
571 /* Is this execution a feasible execution that's worth bug-checking? */
572 bool complete = isfeasibleprefix() && (is_complete_execution() ||
575 /* End-of-execution bug checks */
578 assert_bug("Deadlock detected");
586 if (params.verbose || (complete && have_bug_reports()))
587 print_execution(complete);
589 clear_program_output();
592 earliest_diverge = NULL;
594 if ((diverge = get_next_backtrack()) == NULL)
598 model_print("Next execution will diverge at:\n");
602 reset_to_initial_state();
607 * @brief Find the last fence-related backtracking conflict for a ModelAction
609 * This function performs the search for the most recent conflicting action
610 * against which we should perform backtracking, as affected by fence
611 * operations. This includes pairs of potentially-synchronizing actions which
612 * occur due to fence-acquire or fence-release, and hence should be explored in
613 * the opposite execution order.
615 * @param act The current action
616 * @return The most recent action which conflicts with act due to fences
618 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
620 /* Only perform release/acquire fence backtracking for stores */
621 if (!act->is_write())
624 /* Find a fence-release (or, act is a release) */
625 ModelAction *last_release;
626 if (act->is_release())
629 last_release = get_last_fence_release(act->get_tid());
633 /* Skip past the release */
634 action_list_t *list = action_trace;
635 action_list_t::reverse_iterator rit;
636 for (rit = list->rbegin(); rit != list->rend(); rit++)
637 if (*rit == last_release)
639 ASSERT(rit != list->rend());
644 * load --sb-> fence-acquire */
645 std::vector< ModelAction *, ModelAlloc<ModelAction *> > acquire_fences(get_num_threads(), NULL);
646 std::vector< ModelAction *, ModelAlloc<ModelAction *> > prior_loads(get_num_threads(), NULL);
647 bool found_acquire_fences = false;
648 for ( ; rit != list->rend(); rit++) {
649 ModelAction *prev = *rit;
650 if (act->same_thread(prev))
653 int tid = id_to_int(prev->get_tid());
655 if (prev->is_read() && act->same_var(prev)) {
656 if (prev->is_acquire()) {
657 /* Found most recent load-acquire, don't need
658 * to search for more fences */
659 if (!found_acquire_fences)
662 prior_loads[tid] = prev;
665 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
666 found_acquire_fences = true;
667 acquire_fences[tid] = prev;
671 ModelAction *latest_backtrack = NULL;
672 for (unsigned int i = 0; i < acquire_fences.size(); i++)
673 if (acquire_fences[i] && prior_loads[i])
674 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
675 latest_backtrack = acquire_fences[i];
676 return latest_backtrack;
680 * @brief Find the last backtracking conflict for a ModelAction
682 * This function performs the search for the most recent conflicting action
683 * against which we should perform backtracking. This primary includes pairs of
684 * synchronizing actions which should be explored in the opposite execution
687 * @param act The current action
688 * @return The most recent action which conflicts with act
690 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
692 switch (act->get_type()) {
693 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
697 ModelAction *ret = NULL;
699 /* linear search: from most recent to oldest */
700 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
701 action_list_t::reverse_iterator rit;
702 for (rit = list->rbegin(); rit != list->rend(); rit++) {
703 ModelAction *prev = *rit;
704 if (prev->could_synchronize_with(act)) {
710 ModelAction *ret2 = get_last_fence_conflict(act);
720 case ATOMIC_TRYLOCK: {
721 /* linear search: from most recent to oldest */
722 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
723 action_list_t::reverse_iterator rit;
724 for (rit = list->rbegin(); rit != list->rend(); rit++) {
725 ModelAction *prev = *rit;
726 if (act->is_conflicting_lock(prev))
731 case ATOMIC_UNLOCK: {
732 /* linear search: from most recent to oldest */
733 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
734 action_list_t::reverse_iterator rit;
735 for (rit = list->rbegin(); rit != list->rend(); rit++) {
736 ModelAction *prev = *rit;
737 if (!act->same_thread(prev) && prev->is_failed_trylock())
743 /* linear search: from most recent to oldest */
744 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
745 action_list_t::reverse_iterator rit;
746 for (rit = list->rbegin(); rit != list->rend(); rit++) {
747 ModelAction *prev = *rit;
748 if (!act->same_thread(prev) && prev->is_failed_trylock())
750 if (!act->same_thread(prev) && prev->is_notify())
756 case ATOMIC_NOTIFY_ALL:
757 case ATOMIC_NOTIFY_ONE: {
758 /* linear search: from most recent to oldest */
759 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
760 action_list_t::reverse_iterator rit;
761 for (rit = list->rbegin(); rit != list->rend(); rit++) {
762 ModelAction *prev = *rit;
763 if (!act->same_thread(prev) && prev->is_wait())
774 /** This method finds backtracking points where we should try to
775 * reorder the parameter ModelAction against.
777 * @param the ModelAction to find backtracking points for.
779 void ModelChecker::set_backtracking(ModelAction *act)
781 Thread *t = get_thread(act);
782 ModelAction *prev = get_last_conflict(act);
786 Node *node = prev->get_node()->get_parent();
788 int low_tid, high_tid;
789 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
790 low_tid = id_to_int(act->get_tid());
791 high_tid = low_tid + 1;
794 high_tid = get_num_threads();
797 for (int i = low_tid; i < high_tid; i++) {
798 thread_id_t tid = int_to_id(i);
800 /* Make sure this thread can be enabled here. */
801 if (i >= node->get_num_threads())
804 /* Don't backtrack into a point where the thread is disabled or sleeping. */
805 if (node->enabled_status(tid) != THREAD_ENABLED)
808 /* Check if this has been explored already */
809 if (node->has_been_explored(tid))
812 /* See if fairness allows */
813 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
815 for (int t = 0; t < node->get_num_threads(); t++) {
816 thread_id_t tother = int_to_id(t);
817 if (node->is_enabled(tother) && node->has_priority(tother)) {
825 /* Cache the latest backtracking point */
826 set_latest_backtrack(prev);
828 /* If this is a new backtracking point, mark the tree */
829 if (!node->set_backtrack(tid))
831 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
832 id_to_int(prev->get_tid()),
833 id_to_int(t->get_id()));
842 * @brief Cache the a backtracking point as the "most recent", if eligible
844 * Note that this does not prepare the NodeStack for this backtracking
845 * operation, it only caches the action on a per-execution basis
847 * @param act The operation at which we should explore a different next action
848 * (i.e., backtracking point)
849 * @return True, if this action is now the most recent backtracking point;
852 bool ModelChecker::set_latest_backtrack(ModelAction *act)
854 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
855 priv->next_backtrack = act;
862 * Returns last backtracking point. The model checker will explore a different
863 * path for this point in the next execution.
864 * @return The ModelAction at which the next execution should diverge.
866 ModelAction * ModelChecker::get_next_backtrack()
868 ModelAction *next = priv->next_backtrack;
869 priv->next_backtrack = NULL;
874 * Processes a read model action.
875 * @param curr is the read model action to process.
876 * @return True if processing this read updates the mo_graph.
878 bool ModelChecker::process_read(ModelAction *curr)
880 Node *node = curr->get_node();
882 bool updated = false;
883 switch (node->get_read_from_status()) {
884 case READ_FROM_PAST: {
885 const ModelAction *rf = node->get_read_from_past();
888 mo_graph->startChanges();
890 ASSERT(!is_infeasible());
891 if (!check_recency(curr, rf)) {
892 if (node->increment_read_from()) {
893 mo_graph->rollbackChanges();
896 priv->too_many_reads = true;
900 updated = r_modification_order(curr, rf);
902 mo_graph->commitChanges();
903 mo_check_promises(curr, true);
906 case READ_FROM_PROMISE: {
907 Promise *promise = curr->get_node()->get_read_from_promise();
908 if (promise->add_reader(curr))
909 priv->failed_promise = true;
910 curr->set_read_from_promise(promise);
911 mo_graph->startChanges();
912 if (!check_recency(curr, promise))
913 priv->too_many_reads = true;
914 updated = r_modification_order(curr, promise);
915 mo_graph->commitChanges();
918 case READ_FROM_FUTURE: {
919 /* Read from future value */
920 struct future_value fv = node->get_future_value();
921 Promise *promise = new Promise(curr, fv);
922 curr->set_read_from_promise(promise);
923 promises->push_back(promise);
924 mo_graph->startChanges();
925 updated = r_modification_order(curr, promise);
926 mo_graph->commitChanges();
932 get_thread(curr)->set_return_value(curr->get_return_value());
938 * Processes a lock, trylock, or unlock model action. @param curr is
939 * the read model action to process.
941 * The try lock operation checks whether the lock is taken. If not,
942 * it falls to the normal lock operation case. If so, it returns
945 * The lock operation has already been checked that it is enabled, so
946 * it just grabs the lock and synchronizes with the previous unlock.
948 * The unlock operation has to re-enable all of the threads that are
949 * waiting on the lock.
951 * @return True if synchronization was updated; false otherwise
953 bool ModelChecker::process_mutex(ModelAction *curr)
955 std::mutex *mutex = curr->get_mutex();
956 struct std::mutex_state *state = NULL;
959 state = mutex->get_state();
961 switch (curr->get_type()) {
962 case ATOMIC_TRYLOCK: {
963 bool success = !state->locked;
964 curr->set_try_lock(success);
966 get_thread(curr)->set_return_value(0);
969 get_thread(curr)->set_return_value(1);
971 //otherwise fall into the lock case
973 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
974 assert_bug("Lock access before initialization");
975 state->locked = get_thread(curr);
976 ModelAction *unlock = get_last_unlock(curr);
977 //synchronize with the previous unlock statement
978 if (unlock != NULL) {
979 curr->synchronize_with(unlock);
984 case ATOMIC_UNLOCK: {
986 state->locked = NULL;
987 //wake up the other threads
988 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
989 //activate all the waiting threads
990 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
991 scheduler->wake(get_thread(*rit));
998 state->locked = NULL;
999 //wake up the other threads
1000 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
1001 //activate all the waiting threads
1002 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1003 scheduler->wake(get_thread(*rit));
1006 //check whether we should go to sleep or not...simulate spurious failures
1007 if (curr->get_node()->get_misc() == 0) {
1008 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1010 scheduler->sleep(get_thread(curr));
1014 case ATOMIC_NOTIFY_ALL: {
1015 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1016 //activate all the waiting threads
1017 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1018 scheduler->wake(get_thread(*rit));
1023 case ATOMIC_NOTIFY_ONE: {
1024 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1025 int wakeupthread = curr->get_node()->get_misc();
1026 action_list_t::iterator it = waiters->begin();
1027 advance(it, wakeupthread);
1028 scheduler->wake(get_thread(*it));
1039 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1041 /* Do more ambitious checks now that mo is more complete */
1042 if (mo_may_allow(writer, reader)) {
1043 Node *node = reader->get_node();
1045 /* Find an ancestor thread which exists at the time of the reader */
1046 Thread *write_thread = get_thread(writer);
1047 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1048 write_thread = write_thread->get_parent();
1050 struct future_value fv = {
1051 writer->get_write_value(),
1052 writer->get_seq_number() + params.maxfuturedelay,
1053 write_thread->get_id(),
1055 if (node->add_future_value(fv))
1056 set_latest_backtrack(reader);
1061 * Process a write ModelAction
1062 * @param curr The ModelAction to process
1063 * @return True if the mo_graph was updated or promises were resolved
1065 bool ModelChecker::process_write(ModelAction *curr)
1067 /* Readers to which we may send our future value */
1068 std::vector< ModelAction *, ModelAlloc<ModelAction *> > send_fv;
1070 bool updated_mod_order = w_modification_order(curr, &send_fv);
1071 int promise_idx = get_promise_to_resolve(curr);
1072 const ModelAction *earliest_promise_reader;
1073 bool updated_promises = false;
1075 if (promise_idx >= 0) {
1076 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1077 updated_promises = resolve_promise(curr, promise_idx);
1079 earliest_promise_reader = NULL;
1081 /* Don't send future values to reads after the Promise we resolve */
1082 for (unsigned int i = 0; i < send_fv.size(); i++) {
1083 ModelAction *read = send_fv[i];
1084 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1085 futurevalues->push_back(PendingFutureValue(curr, read));
1088 if (promises->size() == 0) {
1089 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1090 struct PendingFutureValue pfv = (*futurevalues)[i];
1091 add_future_value(pfv.writer, pfv.act);
1093 futurevalues->clear();
1096 mo_graph->commitChanges();
1097 mo_check_promises(curr, false);
1099 get_thread(curr)->set_return_value(VALUE_NONE);
1100 return updated_mod_order || updated_promises;
1104 * Process a fence ModelAction
1105 * @param curr The ModelAction to process
1106 * @return True if synchronization was updated
1108 bool ModelChecker::process_fence(ModelAction *curr)
1111 * fence-relaxed: no-op
1112 * fence-release: only log the occurence (not in this function), for
1113 * use in later synchronization
1114 * fence-acquire (this function): search for hypothetical release
1117 bool updated = false;
1118 if (curr->is_acquire()) {
1119 action_list_t *list = action_trace;
1120 action_list_t::reverse_iterator rit;
1121 /* Find X : is_read(X) && X --sb-> curr */
1122 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1123 ModelAction *act = *rit;
1126 if (act->get_tid() != curr->get_tid())
1128 /* Stop at the beginning of the thread */
1129 if (act->is_thread_start())
1131 /* Stop once we reach a prior fence-acquire */
1132 if (act->is_fence() && act->is_acquire())
1134 if (!act->is_read())
1136 /* read-acquire will find its own release sequences */
1137 if (act->is_acquire())
1140 /* Establish hypothetical release sequences */
1141 rel_heads_list_t release_heads;
1142 get_release_seq_heads(curr, act, &release_heads);
1143 for (unsigned int i = 0; i < release_heads.size(); i++)
1144 if (!curr->synchronize_with(release_heads[i]))
1145 set_bad_synchronization();
1146 if (release_heads.size() != 0)
1154 * @brief Process the current action for thread-related activity
1156 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1157 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1158 * synchronization, etc. This function is a no-op for non-THREAD actions
1159 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1161 * @param curr The current action
1162 * @return True if synchronization was updated or a thread completed
1164 bool ModelChecker::process_thread_action(ModelAction *curr)
1166 bool updated = false;
1168 switch (curr->get_type()) {
1169 case THREAD_CREATE: {
1170 thrd_t *thrd = (thrd_t *)curr->get_location();
1171 struct thread_params *params = (struct thread_params *)curr->get_value();
1172 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1174 th->set_creation(curr);
1175 /* Promises can be satisfied by children */
1176 for (unsigned int i = 0; i < promises->size(); i++) {
1177 Promise *promise = (*promises)[i];
1178 if (promise->thread_is_available(curr->get_tid()))
1179 promise->add_thread(th->get_id());
1184 Thread *blocking = curr->get_thread_operand();
1185 ModelAction *act = get_last_action(blocking->get_id());
1186 curr->synchronize_with(act);
1187 updated = true; /* trigger rel-seq checks */
1190 case THREAD_FINISH: {
1191 Thread *th = get_thread(curr);
1192 while (!th->wait_list_empty()) {
1193 ModelAction *act = th->pop_wait_list();
1194 scheduler->wake(get_thread(act));
1197 /* Completed thread can't satisfy promises */
1198 for (unsigned int i = 0; i < promises->size(); i++) {
1199 Promise *promise = (*promises)[i];
1200 if (promise->thread_is_available(th->get_id()))
1201 if (promise->eliminate_thread(th->get_id()))
1202 priv->failed_promise = true;
1204 updated = true; /* trigger rel-seq checks */
1207 case THREAD_START: {
1208 check_promises(curr->get_tid(), NULL, curr->get_cv());
1219 * @brief Process the current action for release sequence fixup activity
1221 * Performs model-checker release sequence fixups for the current action,
1222 * forcing a single pending release sequence to break (with a given, potential
1223 * "loose" write) or to complete (i.e., synchronize). If a pending release
1224 * sequence forms a complete release sequence, then we must perform the fixup
1225 * synchronization, mo_graph additions, etc.
1227 * @param curr The current action; must be a release sequence fixup action
1228 * @param work_queue The work queue to which to add work items as they are
1231 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1233 const ModelAction *write = curr->get_node()->get_relseq_break();
1234 struct release_seq *sequence = pending_rel_seqs->back();
1235 pending_rel_seqs->pop_back();
1237 ModelAction *acquire = sequence->acquire;
1238 const ModelAction *rf = sequence->rf;
1239 const ModelAction *release = sequence->release;
1243 ASSERT(release->same_thread(rf));
1245 if (write == NULL) {
1247 * @todo Forcing a synchronization requires that we set
1248 * modification order constraints. For instance, we can't allow
1249 * a fixup sequence in which two separate read-acquire
1250 * operations read from the same sequence, where the first one
1251 * synchronizes and the other doesn't. Essentially, we can't
1252 * allow any writes to insert themselves between 'release' and
1256 /* Must synchronize */
1257 if (!acquire->synchronize_with(release)) {
1258 set_bad_synchronization();
1261 /* Re-check all pending release sequences */
1262 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1263 /* Re-check act for mo_graph edges */
1264 work_queue->push_back(MOEdgeWorkEntry(acquire));
1266 /* propagate synchronization to later actions */
1267 action_list_t::reverse_iterator rit = action_trace->rbegin();
1268 for (; (*rit) != acquire; rit++) {
1269 ModelAction *propagate = *rit;
1270 if (acquire->happens_before(propagate)) {
1271 propagate->synchronize_with(acquire);
1272 /* Re-check 'propagate' for mo_graph edges */
1273 work_queue->push_back(MOEdgeWorkEntry(propagate));
1277 /* Break release sequence with new edges:
1278 * release --mo--> write --mo--> rf */
1279 mo_graph->addEdge(release, write);
1280 mo_graph->addEdge(write, rf);
1283 /* See if we have realized a data race */
1288 * Initialize the current action by performing one or more of the following
1289 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1290 * in the NodeStack, manipulating backtracking sets, allocating and
1291 * initializing clock vectors, and computing the promises to fulfill.
1293 * @param curr The current action, as passed from the user context; may be
1294 * freed/invalidated after the execution of this function, with a different
1295 * action "returned" its place (pass-by-reference)
1296 * @return True if curr is a newly-explored action; false otherwise
1298 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1300 ModelAction *newcurr;
1302 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1303 newcurr = process_rmw(*curr);
1306 if (newcurr->is_rmw())
1307 compute_promises(newcurr);
1313 (*curr)->set_seq_number(get_next_seq_num());
1315 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1317 /* First restore type and order in case of RMW operation */
1318 if ((*curr)->is_rmwr())
1319 newcurr->copy_typeandorder(*curr);
1321 ASSERT((*curr)->get_location() == newcurr->get_location());
1322 newcurr->copy_from_new(*curr);
1324 /* Discard duplicate ModelAction; use action from NodeStack */
1327 /* Always compute new clock vector */
1328 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1331 return false; /* Action was explored previously */
1335 /* Always compute new clock vector */
1336 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1338 /* Assign most recent release fence */
1339 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1342 * Perform one-time actions when pushing new ModelAction onto
1345 if (newcurr->is_write())
1346 compute_promises(newcurr);
1347 else if (newcurr->is_relseq_fixup())
1348 compute_relseq_breakwrites(newcurr);
1349 else if (newcurr->is_wait())
1350 newcurr->get_node()->set_misc_max(2);
1351 else if (newcurr->is_notify_one()) {
1352 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1354 return true; /* This was a new ModelAction */
1359 * @brief Establish reads-from relation between two actions
1361 * Perform basic operations involved with establishing a concrete rf relation,
1362 * including setting the ModelAction data and checking for release sequences.
1364 * @param act The action that is reading (must be a read)
1365 * @param rf The action from which we are reading (must be a write)
1367 * @return True if this read established synchronization
1369 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1372 act->set_read_from(rf);
1373 if (act->is_acquire()) {
1374 rel_heads_list_t release_heads;
1375 get_release_seq_heads(act, act, &release_heads);
1376 int num_heads = release_heads.size();
1377 for (unsigned int i = 0; i < release_heads.size(); i++)
1378 if (!act->synchronize_with(release_heads[i])) {
1379 set_bad_synchronization();
1382 return num_heads > 0;
1388 * Check promises and eliminate potentially-satisfying threads when a thread is
1389 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1390 * no longer satisfy a promise generated from that thread.
1392 * @param blocker The thread on which a thread is waiting
1393 * @param waiting The waiting thread
1395 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1397 for (unsigned int i = 0; i < promises->size(); i++) {
1398 Promise *promise = (*promises)[i];
1399 if (!promise->thread_is_available(waiting->get_id()))
1401 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1402 ModelAction *reader = promise->get_reader(j);
1403 if (reader->get_tid() != blocker->get_id())
1405 if (promise->eliminate_thread(waiting->get_id())) {
1406 /* Promise has failed */
1407 priv->failed_promise = true;
1409 /* Only eliminate the 'waiting' thread once */
1417 * @brief Check whether a model action is enabled.
1419 * Checks whether a lock or join operation would be successful (i.e., is the
1420 * lock already locked, or is the joined thread already complete). If not, put
1421 * the action in a waiter list.
1423 * @param curr is the ModelAction to check whether it is enabled.
1424 * @return a bool that indicates whether the action is enabled.
1426 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1427 if (curr->is_lock()) {
1428 std::mutex *lock = (std::mutex *)curr->get_location();
1429 struct std::mutex_state *state = lock->get_state();
1430 if (state->locked) {
1431 //Stick the action in the appropriate waiting queue
1432 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1435 } else if (curr->get_type() == THREAD_JOIN) {
1436 Thread *blocking = (Thread *)curr->get_location();
1437 if (!blocking->is_complete()) {
1438 blocking->push_wait_list(curr);
1439 thread_blocking_check_promises(blocking, get_thread(curr));
1448 * This is the heart of the model checker routine. It performs model-checking
1449 * actions corresponding to a given "current action." Among other processes, it
1450 * calculates reads-from relationships, updates synchronization clock vectors,
1451 * forms a memory_order constraints graph, and handles replay/backtrack
1452 * execution when running permutations of previously-observed executions.
1454 * @param curr The current action to process
1455 * @return The ModelAction that is actually executed; may be different than
1456 * curr; may be NULL, if the current action is not enabled to run
1458 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1461 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1463 if (!check_action_enabled(curr)) {
1464 /* Make the execution look like we chose to run this action
1465 * much later, when a lock/join can succeed */
1466 get_thread(curr)->set_pending(curr);
1467 scheduler->sleep(get_thread(curr));
1471 bool newly_explored = initialize_curr_action(&curr);
1477 wake_up_sleeping_actions(curr);
1479 /* Add the action to lists before any other model-checking tasks */
1480 if (!second_part_of_rmw)
1481 add_action_to_lists(curr);
1483 /* Build may_read_from set for newly-created actions */
1484 if (newly_explored && curr->is_read())
1485 build_may_read_from(curr);
1487 /* Initialize work_queue with the "current action" work */
1488 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1489 while (!work_queue.empty() && !has_asserted()) {
1490 WorkQueueEntry work = work_queue.front();
1491 work_queue.pop_front();
1493 switch (work.type) {
1494 case WORK_CHECK_CURR_ACTION: {
1495 ModelAction *act = work.action;
1496 bool update = false; /* update this location's release seq's */
1497 bool update_all = false; /* update all release seq's */
1499 if (process_thread_action(curr))
1502 if (act->is_read() && !second_part_of_rmw && process_read(act))
1505 if (act->is_write() && process_write(act))
1508 if (act->is_fence() && process_fence(act))
1511 if (act->is_mutex_op() && process_mutex(act))
1514 if (act->is_relseq_fixup())
1515 process_relseq_fixup(curr, &work_queue);
1518 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1520 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1523 case WORK_CHECK_RELEASE_SEQ:
1524 resolve_release_sequences(work.location, &work_queue);
1526 case WORK_CHECK_MO_EDGES: {
1527 /** @todo Complete verification of work_queue */
1528 ModelAction *act = work.action;
1529 bool updated = false;
1531 if (act->is_read()) {
1532 const ModelAction *rf = act->get_reads_from();
1533 const Promise *promise = act->get_reads_from_promise();
1535 if (r_modification_order(act, rf))
1537 } else if (promise) {
1538 if (r_modification_order(act, promise))
1542 if (act->is_write()) {
1543 if (w_modification_order(act, NULL))
1546 mo_graph->commitChanges();
1549 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1558 check_curr_backtracking(curr);
1559 set_backtracking(curr);
1563 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1565 Node *currnode = curr->get_node();
1566 Node *parnode = currnode->get_parent();
1568 if ((parnode && !parnode->backtrack_empty()) ||
1569 !currnode->misc_empty() ||
1570 !currnode->read_from_empty() ||
1571 !currnode->promise_empty() ||
1572 !currnode->relseq_break_empty()) {
1573 set_latest_backtrack(curr);
1577 bool ModelChecker::promises_expired() const
1579 for (unsigned int i = 0; i < promises->size(); i++) {
1580 Promise *promise = (*promises)[i];
1581 if (promise->get_expiration() < priv->used_sequence_numbers)
1588 * This is the strongest feasibility check available.
1589 * @return whether the current trace (partial or complete) must be a prefix of
1592 bool ModelChecker::isfeasibleprefix() const
1594 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1598 * Print disagnostic information about an infeasible execution
1599 * @param prefix A string to prefix the output with; if NULL, then a default
1600 * message prefix will be provided
1602 void ModelChecker::print_infeasibility(const char *prefix) const
1606 if (mo_graph->checkForCycles())
1607 ptr += sprintf(ptr, "[mo cycle]");
1608 if (priv->failed_promise)
1609 ptr += sprintf(ptr, "[failed promise]");
1610 if (priv->too_many_reads)
1611 ptr += sprintf(ptr, "[too many reads]");
1612 if (priv->no_valid_reads)
1613 ptr += sprintf(ptr, "[no valid reads-from]");
1614 if (priv->bad_synchronization)
1615 ptr += sprintf(ptr, "[bad sw ordering]");
1616 if (promises_expired())
1617 ptr += sprintf(ptr, "[promise expired]");
1618 if (promises->size() != 0)
1619 ptr += sprintf(ptr, "[unresolved promise]");
1621 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1625 * Returns whether the current completed trace is feasible, except for pending
1626 * release sequences.
1628 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1630 return !is_infeasible() && promises->size() == 0;
1634 * Check if the current partial trace is infeasible. Does not check any
1635 * end-of-execution flags, which might rule out the execution. Thus, this is
1636 * useful only for ruling an execution as infeasible.
1637 * @return whether the current partial trace is infeasible.
1639 bool ModelChecker::is_infeasible() const
1641 return mo_graph->checkForCycles() ||
1642 priv->no_valid_reads ||
1643 priv->failed_promise ||
1644 priv->too_many_reads ||
1645 priv->bad_synchronization ||
1649 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1650 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1651 ModelAction *lastread = get_last_action(act->get_tid());
1652 lastread->process_rmw(act);
1653 if (act->is_rmw()) {
1654 if (lastread->get_reads_from())
1655 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1657 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1658 mo_graph->commitChanges();
1664 * A helper function for ModelChecker::check_recency, to check if the current
1665 * thread is able to read from a different write/promise for 'params.maxreads'
1666 * number of steps and if that write/promise should become visible (i.e., is
1667 * ordered later in the modification order). This helps model memory liveness.
1669 * @param curr The current action. Must be a read.
1670 * @param rf The write/promise from which we plan to read
1671 * @param other_rf The write/promise from which we may read
1672 * @return True if we were able to read from other_rf for params.maxreads steps
1674 template <typename T, typename U>
1675 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1677 /* Need a different write/promise */
1678 if (other_rf->equals(rf))
1681 /* Only look for "newer" writes/promises */
1682 if (!mo_graph->checkReachable(rf, other_rf))
1685 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1686 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1687 action_list_t::reverse_iterator rit = list->rbegin();
1688 ASSERT((*rit) == curr);
1689 /* Skip past curr */
1692 /* Does this write/promise work for everyone? */
1693 for (int i = 0; i < params.maxreads; i++, rit++) {
1694 ModelAction *act = *rit;
1695 if (!act->may_read_from(other_rf))
1702 * Checks whether a thread has read from the same write or Promise for too many
1703 * times without seeing the effects of a later write/Promise.
1706 * 1) there must a different write/promise that we could read from,
1707 * 2) we must have read from the same write/promise in excess of maxreads times,
1708 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1709 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1711 * If so, we decide that the execution is no longer feasible.
1713 * @param curr The current action. Must be a read.
1714 * @param rf The ModelAction/Promise from which we might read.
1715 * @return True if the read should succeed; false otherwise
1717 template <typename T>
1718 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1720 if (!params.maxreads)
1723 //NOTE: Next check is just optimization, not really necessary....
1724 if (curr->get_node()->get_read_from_past_size() +
1725 curr->get_node()->get_read_from_promise_size() <= 1)
1728 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1729 int tid = id_to_int(curr->get_tid());
1730 ASSERT(tid < (int)thrd_lists->size());
1731 action_list_t *list = &(*thrd_lists)[tid];
1732 action_list_t::reverse_iterator rit = list->rbegin();
1733 ASSERT((*rit) == curr);
1734 /* Skip past curr */
1737 action_list_t::reverse_iterator ritcopy = rit;
1738 /* See if we have enough reads from the same value */
1739 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1740 if (ritcopy == list->rend())
1742 ModelAction *act = *ritcopy;
1743 if (!act->is_read())
1745 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1747 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1749 if (act->get_node()->get_read_from_past_size() +
1750 act->get_node()->get_read_from_promise_size() <= 1)
1753 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1754 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1755 if (should_read_instead(curr, rf, write))
1756 return false; /* liveness failure */
1758 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1759 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1760 if (should_read_instead(curr, rf, promise))
1761 return false; /* liveness failure */
1767 * Updates the mo_graph with the constraints imposed from the current
1770 * Basic idea is the following: Go through each other thread and find
1771 * the last action that happened before our read. Two cases:
1773 * (1) The action is a write => that write must either occur before
1774 * the write we read from or be the write we read from.
1776 * (2) The action is a read => the write that that action read from
1777 * must occur before the write we read from or be the same write.
1779 * @param curr The current action. Must be a read.
1780 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1781 * @return True if modification order edges were added; false otherwise
1783 template <typename rf_type>
1784 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1786 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1789 ASSERT(curr->is_read());
1791 /* Last SC fence in the current thread */
1792 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1794 /* Iterate over all threads */
1795 for (i = 0; i < thrd_lists->size(); i++) {
1796 /* Last SC fence in thread i */
1797 ModelAction *last_sc_fence_thread_local = NULL;
1798 if (int_to_id((int)i) != curr->get_tid())
1799 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1801 /* Last SC fence in thread i, before last SC fence in current thread */
1802 ModelAction *last_sc_fence_thread_before = NULL;
1803 if (last_sc_fence_local)
1804 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1806 /* Iterate over actions in thread, starting from most recent */
1807 action_list_t *list = &(*thrd_lists)[i];
1808 action_list_t::reverse_iterator rit;
1809 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1810 ModelAction *act = *rit;
1812 if (act->is_write() && !act->equals(rf) && act != curr) {
1813 /* C++, Section 29.3 statement 5 */
1814 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1815 *act < *last_sc_fence_thread_local) {
1816 added = mo_graph->addEdge(act, rf) || added;
1819 /* C++, Section 29.3 statement 4 */
1820 else if (act->is_seqcst() && last_sc_fence_local &&
1821 *act < *last_sc_fence_local) {
1822 added = mo_graph->addEdge(act, rf) || added;
1825 /* C++, Section 29.3 statement 6 */
1826 else if (last_sc_fence_thread_before &&
1827 *act < *last_sc_fence_thread_before) {
1828 added = mo_graph->addEdge(act, rf) || added;
1834 * Include at most one act per-thread that "happens
1835 * before" curr. Don't consider reflexively.
1837 if (act->happens_before(curr) && act != curr) {
1838 if (act->is_write()) {
1839 if (!act->equals(rf)) {
1840 added = mo_graph->addEdge(act, rf) || added;
1843 const ModelAction *prevrf = act->get_reads_from();
1844 const Promise *prevrf_promise = act->get_reads_from_promise();
1846 if (!prevrf->equals(rf))
1847 added = mo_graph->addEdge(prevrf, rf) || added;
1848 } else if (!prevrf_promise->equals(rf)) {
1849 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1858 * All compatible, thread-exclusive promises must be ordered after any
1859 * concrete loads from the same thread
1861 for (unsigned int i = 0; i < promises->size(); i++)
1862 if ((*promises)[i]->is_compatible_exclusive(curr))
1863 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1869 * Updates the mo_graph with the constraints imposed from the current write.
1871 * Basic idea is the following: Go through each other thread and find
1872 * the lastest action that happened before our write. Two cases:
1874 * (1) The action is a write => that write must occur before
1877 * (2) The action is a read => the write that that action read from
1878 * must occur before the current write.
1880 * This method also handles two other issues:
1882 * (I) Sequential Consistency: Making sure that if the current write is
1883 * seq_cst, that it occurs after the previous seq_cst write.
1885 * (II) Sending the write back to non-synchronizing reads.
1887 * @param curr The current action. Must be a write.
1888 * @param send_fv A vector for stashing reads to which we may pass our future
1889 * value. If NULL, then don't record any future values.
1890 * @return True if modification order edges were added; false otherwise
1892 bool ModelChecker::w_modification_order(ModelAction *curr, std::vector< ModelAction *, ModelAlloc<ModelAction *> > *send_fv)
1894 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1897 ASSERT(curr->is_write());
1899 if (curr->is_seqcst()) {
1900 /* We have to at least see the last sequentially consistent write,
1901 so we are initialized. */
1902 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1903 if (last_seq_cst != NULL) {
1904 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1908 /* Last SC fence in the current thread */
1909 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1911 /* Iterate over all threads */
1912 for (i = 0; i < thrd_lists->size(); i++) {
1913 /* Last SC fence in thread i, before last SC fence in current thread */
1914 ModelAction *last_sc_fence_thread_before = NULL;
1915 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1916 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1918 /* Iterate over actions in thread, starting from most recent */
1919 action_list_t *list = &(*thrd_lists)[i];
1920 action_list_t::reverse_iterator rit;
1921 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1922 ModelAction *act = *rit;
1925 * 1) If RMW and it actually read from something, then we
1926 * already have all relevant edges, so just skip to next
1929 * 2) If RMW and it didn't read from anything, we should
1930 * whatever edge we can get to speed up convergence.
1932 * 3) If normal write, we need to look at earlier actions, so
1933 * continue processing list.
1935 if (curr->is_rmw()) {
1936 if (curr->get_reads_from() != NULL)
1944 /* C++, Section 29.3 statement 7 */
1945 if (last_sc_fence_thread_before && act->is_write() &&
1946 *act < *last_sc_fence_thread_before) {
1947 added = mo_graph->addEdge(act, curr) || added;
1952 * Include at most one act per-thread that "happens
1955 if (act->happens_before(curr)) {
1957 * Note: if act is RMW, just add edge:
1959 * The following edge should be handled elsewhere:
1960 * readfrom(act) --mo--> act
1962 if (act->is_write())
1963 added = mo_graph->addEdge(act, curr) || added;
1964 else if (act->is_read()) {
1965 //if previous read accessed a null, just keep going
1966 if (act->get_reads_from() == NULL)
1968 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1971 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1972 !act->same_thread(curr)) {
1973 /* We have an action that:
1974 (1) did not happen before us
1975 (2) is a read and we are a write
1976 (3) cannot synchronize with us
1977 (4) is in a different thread
1979 that read could potentially read from our write. Note that
1980 these checks are overly conservative at this point, we'll
1981 do more checks before actually removing the
1985 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
1986 if (!is_infeasible())
1987 send_fv->push_back(act);
1988 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1989 add_future_value(curr, act);
1996 * All compatible, thread-exclusive promises must be ordered after any
1997 * concrete stores to the same thread, or else they can be merged with
2000 for (unsigned int i = 0; i < promises->size(); i++)
2001 if ((*promises)[i]->is_compatible_exclusive(curr))
2002 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2007 /** Arbitrary reads from the future are not allowed. Section 29.3
2008 * part 9 places some constraints. This method checks one result of constraint
2009 * constraint. Others require compiler support. */
2010 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
2012 if (!writer->is_rmw())
2015 if (!reader->is_rmw())
2018 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2019 if (search == reader)
2021 if (search->get_tid() == reader->get_tid() &&
2022 search->happens_before(reader))
2030 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2031 * some constraints. This method checks one the following constraint (others
2032 * require compiler support):
2034 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2036 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2038 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2040 /* Iterate over all threads */
2041 for (i = 0; i < thrd_lists->size(); i++) {
2042 const ModelAction *write_after_read = NULL;
2044 /* Iterate over actions in thread, starting from most recent */
2045 action_list_t *list = &(*thrd_lists)[i];
2046 action_list_t::reverse_iterator rit;
2047 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2048 ModelAction *act = *rit;
2050 /* Don't disallow due to act == reader */
2051 if (!reader->happens_before(act) || reader == act)
2053 else if (act->is_write())
2054 write_after_read = act;
2055 else if (act->is_read() && act->get_reads_from() != NULL)
2056 write_after_read = act->get_reads_from();
2059 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2066 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2067 * The ModelAction under consideration is expected to be taking part in
2068 * release/acquire synchronization as an object of the "reads from" relation.
2069 * Note that this can only provide release sequence support for RMW chains
2070 * which do not read from the future, as those actions cannot be traced until
2071 * their "promise" is fulfilled. Similarly, we may not even establish the
2072 * presence of a release sequence with certainty, as some modification order
2073 * constraints may be decided further in the future. Thus, this function
2074 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2075 * and a boolean representing certainty.
2077 * @param rf The action that might be part of a release sequence. Must be a
2079 * @param release_heads A pass-by-reference style return parameter. After
2080 * execution of this function, release_heads will contain the heads of all the
2081 * relevant release sequences, if any exists with certainty
2082 * @param pending A pass-by-reference style return parameter which is only used
2083 * when returning false (i.e., uncertain). Returns most information regarding
2084 * an uncertain release sequence, including any write operations that might
2085 * break the sequence.
2086 * @return true, if the ModelChecker is certain that release_heads is complete;
2089 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2090 rel_heads_list_t *release_heads,
2091 struct release_seq *pending) const
2093 /* Only check for release sequences if there are no cycles */
2094 if (mo_graph->checkForCycles())
2097 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2098 ASSERT(rf->is_write());
2100 if (rf->is_release())
2101 release_heads->push_back(rf);
2102 else if (rf->get_last_fence_release())
2103 release_heads->push_back(rf->get_last_fence_release());
2105 break; /* End of RMW chain */
2107 /** @todo Need to be smarter here... In the linux lock
2108 * example, this will run to the beginning of the program for
2110 /** @todo The way to be smarter here is to keep going until 1
2111 * thread has a release preceded by an acquire and you've seen
2114 /* acq_rel RMW is a sufficient stopping condition */
2115 if (rf->is_acquire() && rf->is_release())
2116 return true; /* complete */
2119 /* read from future: need to settle this later */
2121 return false; /* incomplete */
2124 if (rf->is_release())
2125 return true; /* complete */
2127 /* else relaxed write
2128 * - check for fence-release in the same thread (29.8, stmt. 3)
2129 * - check modification order for contiguous subsequence
2130 * -> rf must be same thread as release */
2132 const ModelAction *fence_release = rf->get_last_fence_release();
2133 /* Synchronize with a fence-release unconditionally; we don't need to
2134 * find any more "contiguous subsequence..." for it */
2136 release_heads->push_back(fence_release);
2138 int tid = id_to_int(rf->get_tid());
2139 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2140 action_list_t *list = &(*thrd_lists)[tid];
2141 action_list_t::const_reverse_iterator rit;
2143 /* Find rf in the thread list */
2144 rit = std::find(list->rbegin(), list->rend(), rf);
2145 ASSERT(rit != list->rend());
2147 /* Find the last {write,fence}-release */
2148 for (; rit != list->rend(); rit++) {
2149 if (fence_release && *(*rit) < *fence_release)
2151 if ((*rit)->is_release())
2154 if (rit == list->rend()) {
2155 /* No write-release in this thread */
2156 return true; /* complete */
2157 } else if (fence_release && *(*rit) < *fence_release) {
2158 /* The fence-release is more recent (and so, "stronger") than
2159 * the most recent write-release */
2160 return true; /* complete */
2161 } /* else, need to establish contiguous release sequence */
2162 ModelAction *release = *rit;
2164 ASSERT(rf->same_thread(release));
2166 pending->writes.clear();
2168 bool certain = true;
2169 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2170 if (id_to_int(rf->get_tid()) == (int)i)
2172 list = &(*thrd_lists)[i];
2174 /* Can we ensure no future writes from this thread may break
2175 * the release seq? */
2176 bool future_ordered = false;
2178 ModelAction *last = get_last_action(int_to_id(i));
2179 Thread *th = get_thread(int_to_id(i));
2180 if ((last && rf->happens_before(last)) ||
2183 future_ordered = true;
2185 ASSERT(!th->is_model_thread() || future_ordered);
2187 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2188 const ModelAction *act = *rit;
2189 /* Reach synchronization -> this thread is complete */
2190 if (act->happens_before(release))
2192 if (rf->happens_before(act)) {
2193 future_ordered = true;
2197 /* Only non-RMW writes can break release sequences */
2198 if (!act->is_write() || act->is_rmw())
2201 /* Check modification order */
2202 if (mo_graph->checkReachable(rf, act)) {
2203 /* rf --mo--> act */
2204 future_ordered = true;
2207 if (mo_graph->checkReachable(act, release))
2208 /* act --mo--> release */
2210 if (mo_graph->checkReachable(release, act) &&
2211 mo_graph->checkReachable(act, rf)) {
2212 /* release --mo-> act --mo--> rf */
2213 return true; /* complete */
2215 /* act may break release sequence */
2216 pending->writes.push_back(act);
2219 if (!future_ordered)
2220 certain = false; /* This thread is uncertain */
2224 release_heads->push_back(release);
2225 pending->writes.clear();
2227 pending->release = release;
2234 * An interface for getting the release sequence head(s) with which a
2235 * given ModelAction must synchronize. This function only returns a non-empty
2236 * result when it can locate a release sequence head with certainty. Otherwise,
2237 * it may mark the internal state of the ModelChecker so that it will handle
2238 * the release sequence at a later time, causing @a acquire to update its
2239 * synchronization at some later point in execution.
2241 * @param acquire The 'acquire' action that may synchronize with a release
2243 * @param read The read action that may read from a release sequence; this may
2244 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2245 * when 'acquire' is a fence-acquire)
2246 * @param release_heads A pass-by-reference return parameter. Will be filled
2247 * with the head(s) of the release sequence(s), if they exists with certainty.
2248 * @see ModelChecker::release_seq_heads
2250 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2251 ModelAction *read, rel_heads_list_t *release_heads)
2253 const ModelAction *rf = read->get_reads_from();
2254 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2255 sequence->acquire = acquire;
2256 sequence->read = read;
2258 if (!release_seq_heads(rf, release_heads, sequence)) {
2259 /* add act to 'lazy checking' list */
2260 pending_rel_seqs->push_back(sequence);
2262 snapshot_free(sequence);
2267 * Attempt to resolve all stashed operations that might synchronize with a
2268 * release sequence for a given location. This implements the "lazy" portion of
2269 * determining whether or not a release sequence was contiguous, since not all
2270 * modification order information is present at the time an action occurs.
2272 * @param location The location/object that should be checked for release
2273 * sequence resolutions. A NULL value means to check all locations.
2274 * @param work_queue The work queue to which to add work items as they are
2276 * @return True if any updates occurred (new synchronization, new mo_graph
2279 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2281 bool updated = false;
2282 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2283 while (it != pending_rel_seqs->end()) {
2284 struct release_seq *pending = *it;
2285 ModelAction *acquire = pending->acquire;
2286 const ModelAction *read = pending->read;
2288 /* Only resolve sequences on the given location, if provided */
2289 if (location && read->get_location() != location) {
2294 const ModelAction *rf = read->get_reads_from();
2295 rel_heads_list_t release_heads;
2297 complete = release_seq_heads(rf, &release_heads, pending);
2298 for (unsigned int i = 0; i < release_heads.size(); i++) {
2299 if (!acquire->has_synchronized_with(release_heads[i])) {
2300 if (acquire->synchronize_with(release_heads[i]))
2303 set_bad_synchronization();
2308 /* Re-check all pending release sequences */
2309 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2310 /* Re-check read-acquire for mo_graph edges */
2311 if (acquire->is_read())
2312 work_queue->push_back(MOEdgeWorkEntry(acquire));
2314 /* propagate synchronization to later actions */
2315 action_list_t::reverse_iterator rit = action_trace->rbegin();
2316 for (; (*rit) != acquire; rit++) {
2317 ModelAction *propagate = *rit;
2318 if (acquire->happens_before(propagate)) {
2319 propagate->synchronize_with(acquire);
2320 /* Re-check 'propagate' for mo_graph edges */
2321 work_queue->push_back(MOEdgeWorkEntry(propagate));
2326 it = pending_rel_seqs->erase(it);
2327 snapshot_free(pending);
2333 // If we resolved promises or data races, see if we have realized a data race.
2340 * Performs various bookkeeping operations for the current ModelAction. For
2341 * instance, adds action to the per-object, per-thread action vector and to the
2342 * action trace list of all thread actions.
2344 * @param act is the ModelAction to add.
2346 void ModelChecker::add_action_to_lists(ModelAction *act)
2348 int tid = id_to_int(act->get_tid());
2349 ModelAction *uninit = NULL;
2351 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2352 if (list->empty() && act->is_atomic_var()) {
2353 uninit = new_uninitialized_action(act->get_location());
2354 uninit_id = id_to_int(uninit->get_tid());
2355 list->push_back(uninit);
2357 list->push_back(act);
2359 action_trace->push_back(act);
2361 action_trace->push_front(uninit);
2363 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2364 if (tid >= (int)vec->size())
2365 vec->resize(priv->next_thread_id);
2366 (*vec)[tid].push_back(act);
2368 (*vec)[uninit_id].push_front(uninit);
2370 if ((int)thrd_last_action->size() <= tid)
2371 thrd_last_action->resize(get_num_threads());
2372 (*thrd_last_action)[tid] = act;
2374 (*thrd_last_action)[uninit_id] = uninit;
2376 if (act->is_fence() && act->is_release()) {
2377 if ((int)thrd_last_fence_release->size() <= tid)
2378 thrd_last_fence_release->resize(get_num_threads());
2379 (*thrd_last_fence_release)[tid] = act;
2382 if (act->is_wait()) {
2383 void *mutex_loc = (void *) act->get_value();
2384 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2386 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2387 if (tid >= (int)vec->size())
2388 vec->resize(priv->next_thread_id);
2389 (*vec)[tid].push_back(act);
2394 * @brief Get the last action performed by a particular Thread
2395 * @param tid The thread ID of the Thread in question
2396 * @return The last action in the thread
2398 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2400 int threadid = id_to_int(tid);
2401 if (threadid < (int)thrd_last_action->size())
2402 return (*thrd_last_action)[id_to_int(tid)];
2408 * @brief Get the last fence release performed by a particular Thread
2409 * @param tid The thread ID of the Thread in question
2410 * @return The last fence release in the thread, if one exists; NULL otherwise
2412 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2414 int threadid = id_to_int(tid);
2415 if (threadid < (int)thrd_last_fence_release->size())
2416 return (*thrd_last_fence_release)[id_to_int(tid)];
2422 * Gets the last memory_order_seq_cst write (in the total global sequence)
2423 * performed on a particular object (i.e., memory location), not including the
2425 * @param curr The current ModelAction; also denotes the object location to
2427 * @return The last seq_cst write
2429 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2431 void *location = curr->get_location();
2432 action_list_t *list = get_safe_ptr_action(obj_map, location);
2433 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2434 action_list_t::reverse_iterator rit;
2435 for (rit = list->rbegin(); rit != list->rend(); rit++)
2436 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2442 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2443 * performed in a particular thread, prior to a particular fence.
2444 * @param tid The ID of the thread to check
2445 * @param before_fence The fence from which to begin the search; if NULL, then
2446 * search for the most recent fence in the thread.
2447 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2449 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2451 /* All fences should have NULL location */
2452 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2453 action_list_t::reverse_iterator rit = list->rbegin();
2456 for (; rit != list->rend(); rit++)
2457 if (*rit == before_fence)
2460 ASSERT(*rit == before_fence);
2464 for (; rit != list->rend(); rit++)
2465 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2471 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2472 * location). This function identifies the mutex according to the current
2473 * action, which is presumed to perform on the same mutex.
2474 * @param curr The current ModelAction; also denotes the object location to
2476 * @return The last unlock operation
2478 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2480 void *location = curr->get_location();
2481 action_list_t *list = get_safe_ptr_action(obj_map, location);
2482 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2483 action_list_t::reverse_iterator rit;
2484 for (rit = list->rbegin(); rit != list->rend(); rit++)
2485 if ((*rit)->is_unlock() || (*rit)->is_wait())
2490 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2492 ModelAction *parent = get_last_action(tid);
2494 parent = get_thread(tid)->get_creation();
2499 * Returns the clock vector for a given thread.
2500 * @param tid The thread whose clock vector we want
2501 * @return Desired clock vector
2503 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2505 return get_parent_action(tid)->get_cv();
2509 * @brief Find the promise, if any to resolve for the current action
2510 * @param curr The current ModelAction. Should be a write.
2511 * @return The (non-negative) index for the Promise to resolve, if any;
2514 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2516 for (unsigned int i = 0; i < promises->size(); i++)
2517 if (curr->get_node()->get_promise(i))
2523 * Resolve a Promise with a current write.
2524 * @param write The ModelAction that is fulfilling Promises
2525 * @param promise_idx The index corresponding to the promise
2526 * @return True if the Promise was successfully resolved; false otherwise
2528 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2530 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2531 Promise *promise = (*promises)[promise_idx];
2533 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2534 ModelAction *read = promise->get_reader(i);
2535 read_from(read, write);
2536 actions_to_check.push_back(read);
2538 /* Make sure the promise's value matches the write's value */
2539 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2540 if (!mo_graph->resolvePromise(promise, write))
2541 priv->failed_promise = true;
2543 promises->erase(promises->begin() + promise_idx);
2545 * @todo It is possible to end up in an inconsistent state, where a
2546 * "resolved" promise may still be referenced if
2547 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2549 * Note that the inconsistency only matters when dumping mo_graph to
2555 //Check whether reading these writes has made threads unable to
2557 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2558 ModelAction *read = actions_to_check[i];
2559 mo_check_promises(read, true);
2566 * Compute the set of promises that could potentially be satisfied by this
2567 * action. Note that the set computation actually appears in the Node, not in
2569 * @param curr The ModelAction that may satisfy promises
2571 void ModelChecker::compute_promises(ModelAction *curr)
2573 for (unsigned int i = 0; i < promises->size(); i++) {
2574 Promise *promise = (*promises)[i];
2575 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2578 bool satisfy = true;
2579 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2580 const ModelAction *act = promise->get_reader(j);
2581 if (act->happens_before(curr) ||
2582 act->could_synchronize_with(curr)) {
2588 curr->get_node()->set_promise(i);
2592 /** Checks promises in response to change in ClockVector Threads. */
2593 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2595 for (unsigned int i = 0; i < promises->size(); i++) {
2596 Promise *promise = (*promises)[i];
2597 if (!promise->thread_is_available(tid))
2599 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2600 const ModelAction *act = promise->get_reader(j);
2601 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2602 merge_cv->synchronized_since(act)) {
2603 if (promise->eliminate_thread(tid)) {
2604 /* Promise has failed */
2605 priv->failed_promise = true;
2613 void ModelChecker::check_promises_thread_disabled()
2615 for (unsigned int i = 0; i < promises->size(); i++) {
2616 Promise *promise = (*promises)[i];
2617 if (promise->has_failed()) {
2618 priv->failed_promise = true;
2625 * @brief Checks promises in response to addition to modification order for
2628 * We test whether threads are still available for satisfying promises after an
2629 * addition to our modification order constraints. Those that are unavailable
2630 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2631 * that promise has failed.
2633 * @param act The ModelAction which updated the modification order
2634 * @param is_read_check Should be true if act is a read and we must check for
2635 * updates to the store from which it read (there is a distinction here for
2636 * RMW's, which are both a load and a store)
2638 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2640 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2642 for (unsigned int i = 0; i < promises->size(); i++) {
2643 Promise *promise = (*promises)[i];
2645 // Is this promise on the same location?
2646 if (!promise->same_location(write))
2649 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2650 const ModelAction *pread = promise->get_reader(j);
2651 if (!pread->happens_before(act))
2653 if (mo_graph->checkPromise(write, promise)) {
2654 priv->failed_promise = true;
2660 // Don't do any lookups twice for the same thread
2661 if (!promise->thread_is_available(act->get_tid()))
2664 if (mo_graph->checkReachable(promise, write)) {
2665 if (mo_graph->checkPromise(write, promise)) {
2666 priv->failed_promise = true;
2674 * Compute the set of writes that may break the current pending release
2675 * sequence. This information is extracted from previou release sequence
2678 * @param curr The current ModelAction. Must be a release sequence fixup
2681 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2683 if (pending_rel_seqs->empty())
2686 struct release_seq *pending = pending_rel_seqs->back();
2687 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2688 const ModelAction *write = pending->writes[i];
2689 curr->get_node()->add_relseq_break(write);
2692 /* NULL means don't break the sequence; just synchronize */
2693 curr->get_node()->add_relseq_break(NULL);
2697 * Build up an initial set of all past writes that this 'read' action may read
2698 * from, as well as any previously-observed future values that must still be valid.
2700 * @param curr is the current ModelAction that we are exploring; it must be a
2703 void ModelChecker::build_may_read_from(ModelAction *curr)
2705 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2707 ASSERT(curr->is_read());
2709 ModelAction *last_sc_write = NULL;
2711 if (curr->is_seqcst())
2712 last_sc_write = get_last_seq_cst_write(curr);
2714 /* Iterate over all threads */
2715 for (i = 0; i < thrd_lists->size(); i++) {
2716 /* Iterate over actions in thread, starting from most recent */
2717 action_list_t *list = &(*thrd_lists)[i];
2718 action_list_t::reverse_iterator rit;
2719 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2720 ModelAction *act = *rit;
2722 /* Only consider 'write' actions */
2723 if (!act->is_write() || act == curr)
2726 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2727 bool allow_read = true;
2729 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2731 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2735 /* Only add feasible reads */
2736 mo_graph->startChanges();
2737 r_modification_order(curr, act);
2738 if (!is_infeasible())
2739 curr->get_node()->add_read_from_past(act);
2740 mo_graph->rollbackChanges();
2743 /* Include at most one act per-thread that "happens before" curr */
2744 if (act->happens_before(curr))
2749 /* Inherit existing, promised future values */
2750 for (i = 0; i < promises->size(); i++) {
2751 const Promise *promise = (*promises)[i];
2752 const ModelAction *promise_read = promise->get_reader(0);
2753 if (promise_read->same_var(curr)) {
2754 /* Only add feasible future-values */
2755 mo_graph->startChanges();
2756 r_modification_order(curr, promise);
2757 if (!is_infeasible())
2758 curr->get_node()->add_read_from_promise(promise_read);
2759 mo_graph->rollbackChanges();
2763 /* We may find no valid may-read-from only if the execution is doomed */
2764 if (!curr->get_node()->read_from_size()) {
2765 priv->no_valid_reads = true;
2769 if (DBG_ENABLED()) {
2770 model_print("Reached read action:\n");
2772 model_print("Printing read_from_past\n");
2773 curr->get_node()->print_read_from_past();
2774 model_print("End printing read_from_past\n");
2778 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2780 for ( ; write != NULL; write = write->get_reads_from()) {
2781 /* UNINIT actions don't have a Node, and they never sleep */
2782 if (write->is_uninitialized())
2784 Node *prevnode = write->get_node()->get_parent();
2786 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2787 if (write->is_release() && thread_sleep)
2789 if (!write->is_rmw())
2796 * @brief Create a new action representing an uninitialized atomic
2797 * @param location The memory location of the atomic object
2798 * @return A pointer to a new ModelAction
2800 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2802 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2803 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2804 act->create_cv(NULL);
2808 static void print_list(action_list_t *list)
2810 action_list_t::iterator it;
2812 model_print("---------------------------------------------------------------------\n");
2814 unsigned int hash = 0;
2816 for (it = list->begin(); it != list->end(); it++) {
2818 hash = hash^(hash<<3)^((*it)->hash());
2820 model_print("HASH %u\n", hash);
2821 model_print("---------------------------------------------------------------------\n");
2824 #if SUPPORT_MOD_ORDER_DUMP
2825 void ModelChecker::dumpGraph(char *filename) const
2828 sprintf(buffer, "%s.dot", filename);
2829 FILE *file = fopen(buffer, "w");
2830 fprintf(file, "digraph %s {\n", filename);
2831 mo_graph->dumpNodes(file);
2832 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2834 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2835 ModelAction *act = *it;
2836 if (act->is_read()) {
2837 mo_graph->dot_print_node(file, act);
2838 if (act->get_reads_from())
2839 mo_graph->dot_print_edge(file,
2840 act->get_reads_from(),
2842 "label=\"rf\", color=red, weight=2");
2844 mo_graph->dot_print_edge(file,
2845 act->get_reads_from_promise(),
2847 "label=\"rf\", color=red");
2849 if (thread_array[act->get_tid()]) {
2850 mo_graph->dot_print_edge(file,
2851 thread_array[id_to_int(act->get_tid())],
2853 "label=\"sb\", color=blue, weight=400");
2856 thread_array[act->get_tid()] = act;
2858 fprintf(file, "}\n");
2859 model_free(thread_array);
2864 /** @brief Prints an execution trace summary. */
2865 void ModelChecker::print_summary() const
2867 #if SUPPORT_MOD_ORDER_DUMP
2868 char buffername[100];
2869 sprintf(buffername, "exec%04u", stats.num_total);
2870 mo_graph->dumpGraphToFile(buffername);
2871 sprintf(buffername, "graph%04u", stats.num_total);
2872 dumpGraph(buffername);
2875 model_print("Execution %d:", stats.num_total);
2876 if (isfeasibleprefix()) {
2877 if (scheduler->all_threads_sleeping())
2878 model_print(" SLEEP-SET REDUNDANT");
2881 print_infeasibility(" INFEASIBLE");
2882 print_list(action_trace);
2884 if (!promises->empty()) {
2885 model_print("Pending promises:\n");
2886 for (unsigned int i = 0; i < promises->size(); i++) {
2887 model_print(" [P%u] ", i);
2888 (*promises)[i]->print();
2895 * Add a Thread to the system for the first time. Should only be called once
2897 * @param t The Thread to add
2899 void ModelChecker::add_thread(Thread *t)
2901 thread_map->put(id_to_int(t->get_id()), t);
2902 scheduler->add_thread(t);
2906 * Removes a thread from the scheduler.
2907 * @param the thread to remove.
2909 void ModelChecker::remove_thread(Thread *t)
2911 scheduler->remove_thread(t);
2915 * @brief Get a Thread reference by its ID
2916 * @param tid The Thread's ID
2917 * @return A Thread reference
2919 Thread * ModelChecker::get_thread(thread_id_t tid) const
2921 return thread_map->get(id_to_int(tid));
2925 * @brief Get a reference to the Thread in which a ModelAction was executed
2926 * @param act The ModelAction
2927 * @return A Thread reference
2929 Thread * ModelChecker::get_thread(const ModelAction *act) const
2931 return get_thread(act->get_tid());
2935 * @brief Get a Promise's "promise number"
2937 * A "promise number" is an index number that is unique to a promise, valid
2938 * only for a specific snapshot of an execution trace. Promises may come and go
2939 * as they are generated an resolved, so an index only retains meaning for the
2942 * @param promise The Promise to check
2943 * @return The promise index, if the promise still is valid; otherwise -1
2945 int ModelChecker::get_promise_number(const Promise *promise) const
2947 for (unsigned int i = 0; i < promises->size(); i++)
2948 if ((*promises)[i] == promise)
2955 * @brief Check if a Thread is currently enabled
2956 * @param t The Thread to check
2957 * @return True if the Thread is currently enabled
2959 bool ModelChecker::is_enabled(Thread *t) const
2961 return scheduler->is_enabled(t);
2965 * @brief Check if a Thread is currently enabled
2966 * @param tid The ID of the Thread to check
2967 * @return True if the Thread is currently enabled
2969 bool ModelChecker::is_enabled(thread_id_t tid) const
2971 return scheduler->is_enabled(tid);
2975 * Switch from a model-checker context to a user-thread context. This is the
2976 * complement of ModelChecker::switch_to_master and must be called from the
2977 * model-checker context
2979 * @param thread The user-thread to switch to
2981 void ModelChecker::switch_from_master(Thread *thread)
2983 scheduler->set_current_thread(thread);
2984 Thread::swap(&system_context, thread);
2988 * Switch from a user-context to the "master thread" context (a.k.a. system
2989 * context). This switch is made with the intention of exploring a particular
2990 * model-checking action (described by a ModelAction object). Must be called
2991 * from a user-thread context.
2993 * @param act The current action that will be explored. May be NULL only if
2994 * trace is exiting via an assertion (see ModelChecker::set_assert and
2995 * ModelChecker::has_asserted).
2996 * @return Return the value returned by the current action
2998 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3001 Thread *old = thread_current();
3002 ASSERT(!old->get_pending());
3003 old->set_pending(act);
3004 if (Thread::swap(old, &system_context) < 0) {
3005 perror("swap threads");
3008 return old->get_return_value();
3012 * Takes the next step in the execution, if possible.
3013 * @param curr The current step to take
3014 * @return Returns the next Thread to run, if any; NULL if this execution
3017 Thread * ModelChecker::take_step(ModelAction *curr)
3019 Thread *curr_thrd = get_thread(curr);
3020 ASSERT(curr_thrd->get_state() == THREAD_READY);
3022 curr = check_current_action(curr);
3024 /* Infeasible -> don't take any more steps */
3025 if (is_infeasible())
3027 else if (isfeasibleprefix() && have_bug_reports()) {
3032 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3035 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3036 scheduler->remove_thread(curr_thrd);
3038 Thread *next_thrd = NULL;
3040 next_thrd = action_select_next_thread(curr);
3042 next_thrd = get_next_thread();
3044 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3045 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3050 /** Wrapper to run the user's main function, with appropriate arguments */
3051 void user_main_wrapper(void *)
3053 user_main(model->params.argc, model->params.argv);
3056 /** @brief Run ModelChecker for the user program */
3057 void ModelChecker::run()
3061 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3066 * Stash next pending action(s) for thread(s). There
3067 * should only need to stash one thread's action--the
3068 * thread which just took a step--plus the first step
3069 * for any newly-created thread
3071 for (unsigned int i = 0; i < get_num_threads(); i++) {
3072 thread_id_t tid = int_to_id(i);
3073 Thread *thr = get_thread(tid);
3074 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3075 switch_from_master(thr);
3076 if (is_circular_wait(thr))
3077 assert_bug("Deadlock detected");
3081 /* Catch assertions from prior take_step or from
3082 * between-ModelAction bugs (e.g., data races) */
3086 /* Consume the next action for a Thread */
3087 ModelAction *curr = t->get_pending();
3088 t->set_pending(NULL);
3089 t = take_step(curr);
3090 } while (t && !t->is_model_thread());
3093 * Launch end-of-execution release sequence fixups only when
3094 * the execution is otherwise feasible AND there are:
3096 * (1) pending release sequences
3097 * (2) pending assertions that could be invalidated by a change
3098 * in clock vectors (i.e., data races)
3099 * (3) no pending promises
3101 while (!pending_rel_seqs->empty() &&
3102 is_feasible_prefix_ignore_relseq() &&
3103 !unrealizedraces.empty()) {
3104 model_print("*** WARNING: release sequence fixup action "
3105 "(%zu pending release seuqence(s)) ***\n",
3106 pending_rel_seqs->size());
3107 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3108 std::memory_order_seq_cst, NULL, VALUE_NONE,
3112 } while (next_execution());
3114 model_print("******* Model-checking complete: *******\n");