11 #include "snapshot-interface.h"
13 #include "clockvector.h"
14 #include "cyclegraph.h"
17 #include "threads-model.h"
19 #include "traceanalysis.h"
20 #include "bugmessage.h"
22 #define INITIAL_THREAD_ID 0
27 * Structure for holding small ModelChecker members that should be snapshotted
29 struct model_snapshot_members {
30 model_snapshot_members() :
31 /* First thread created will have id INITIAL_THREAD_ID */
32 next_thread_id(INITIAL_THREAD_ID),
33 used_sequence_numbers(0),
37 failed_promise(false),
38 too_many_reads(false),
39 no_valid_reads(false),
40 bad_synchronization(false),
44 ~model_snapshot_members() {
45 for (unsigned int i = 0; i < bugs.size(); i++)
50 unsigned int next_thread_id;
51 modelclock_t used_sequence_numbers;
52 ModelAction *next_backtrack;
53 SnapVector<bug_message *> bugs;
54 struct execution_stats stats;
58 /** @brief Incorrectly-ordered synchronization was made */
59 bool bad_synchronization;
65 /** @brief Constructor */
66 ModelChecker::ModelChecker(struct model_params params) :
67 /* Initialize default scheduler */
69 scheduler(new Scheduler()),
71 earliest_diverge(NULL),
72 action_trace(new action_list_t()),
73 thread_map(new HashTable<int, Thread *, int>()),
74 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
75 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
76 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
77 promises(new SnapVector<Promise *>()),
78 futurevalues(new SnapVector<struct PendingFutureValue>()),
79 pending_rel_seqs(new SnapVector<struct release_seq *>()),
80 thrd_last_action(new SnapVector<ModelAction *>(1)),
81 thrd_last_fence_release(new SnapVector<ModelAction *>()),
82 node_stack(new NodeStack()),
83 trace_analyses(new ModelVector<TraceAnalysis *>()),
84 priv(new struct model_snapshot_members()),
85 mo_graph(new CycleGraph())
87 /* Initialize a model-checker thread, for special ModelActions */
88 model_thread = new Thread(get_next_id());
89 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
92 /** @brief Destructor */
93 ModelChecker::~ModelChecker()
95 for (unsigned int i = 0; i < get_num_threads(); i++)
96 delete thread_map->get(i);
101 delete condvar_waiters_map;
104 for (unsigned int i = 0; i < promises->size(); i++)
105 delete (*promises)[i];
108 delete pending_rel_seqs;
110 delete thrd_last_action;
111 delete thrd_last_fence_release;
113 for (unsigned int i = 0; i < trace_analyses->size(); i++)
114 delete (*trace_analyses)[i];
115 delete trace_analyses;
121 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
123 action_list_t *tmp = hash->get(ptr);
125 tmp = new action_list_t();
131 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
133 SnapVector<action_list_t> *tmp = hash->get(ptr);
135 tmp = new SnapVector<action_list_t>();
141 action_list_t * ModelChecker::get_actions_on_obj(void * obj, thread_id_t tid) {
142 SnapVector<action_list_t> *wrv=obj_thrd_map->get(obj);
145 unsigned int thread=id_to_int(tid);
146 if (thread < wrv->size())
147 return &(*wrv)[thread];
154 * Restores user program to initial state and resets all model-checker data
157 void ModelChecker::reset_to_initial_state()
159 DEBUG("+++ Resetting to initial state +++\n");
160 node_stack->reset_execution();
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;
203 * @brief Select the next thread to execute based on the curren action
205 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
206 * actions should be followed by the execution of their child thread. In either
207 * case, the current action should determine the next thread schedule.
209 * @param curr The current action
210 * @return The next thread to run, if the current action will determine this
211 * selection; otherwise NULL
213 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
215 /* Do not split atomic RMW */
217 return get_thread(curr);
218 /* Follow CREATE with the created thread */
219 if (curr->get_type() == THREAD_CREATE)
220 return curr->get_thread_operand();
225 * @brief Choose the next thread to execute.
227 * This function chooses the next thread that should execute. It can enforce
228 * execution replay/backtracking or, if the model-checker has no preference
229 * regarding the next thread (i.e., when exploring a new execution ordering),
230 * we defer to the scheduler.
232 * @return The next chosen thread to run, if any exist. Or else if the current
233 * execution should terminate, return NULL.
235 Thread * ModelChecker::get_next_thread()
240 * Have we completed exploring the preselected path? Then let the
244 return scheduler->select_next_thread(node_stack->get_head());
246 /* Else, we are trying to replay an execution */
247 ModelAction *next = node_stack->get_next()->get_action();
249 if (next == diverge) {
250 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
251 earliest_diverge = diverge;
253 Node *nextnode = next->get_node();
254 Node *prevnode = nextnode->get_parent();
255 scheduler->update_sleep_set(prevnode);
257 /* Reached divergence point */
258 if (nextnode->increment_behaviors()) {
259 /* Execute the same thread with a new behavior */
260 tid = next->get_tid();
261 node_stack->pop_restofstack(2);
264 /* Make a different thread execute for next step */
265 scheduler->add_sleep(get_thread(next->get_tid()));
266 tid = prevnode->get_next_backtrack();
267 /* Make sure the backtracked thread isn't sleeping. */
268 node_stack->pop_restofstack(1);
269 if (diverge == earliest_diverge) {
270 earliest_diverge = prevnode->get_action();
273 /* Start the round robin scheduler from this thread id */
274 scheduler->set_scheduler_thread(tid);
275 /* The correct sleep set is in the parent node. */
278 DEBUG("*** Divergence point ***\n");
282 tid = next->get_tid();
284 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
285 ASSERT(tid != THREAD_ID_T_NONE);
286 return get_thread(id_to_int(tid));
290 * We need to know what the next actions of all threads in the sleep
291 * set will be. This method computes them and stores the actions at
292 * the corresponding thread object's pending action.
295 void ModelChecker::execute_sleep_set()
297 for (unsigned int i = 0; i < get_num_threads(); i++) {
298 thread_id_t tid = int_to_id(i);
299 Thread *thr = get_thread(tid);
300 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
301 thr->get_pending()->set_sleep_flag();
307 * @brief Should the current action wake up a given thread?
309 * @param curr The current action
310 * @param thread The thread that we might wake up
311 * @return True, if we should wake up the sleeping thread; false otherwise
313 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
315 const ModelAction *asleep = thread->get_pending();
316 /* Don't allow partial RMW to wake anyone up */
319 /* Synchronizing actions may have been backtracked */
320 if (asleep->could_synchronize_with(curr))
322 /* All acquire/release fences and fence-acquire/store-release */
323 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
325 /* Fence-release + store can awake load-acquire on the same location */
326 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
327 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
328 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
334 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
336 for (unsigned int i = 0; i < get_num_threads(); i++) {
337 Thread *thr = get_thread(int_to_id(i));
338 if (scheduler->is_sleep_set(thr)) {
339 if (should_wake_up(curr, thr))
340 /* Remove this thread from sleep set */
341 scheduler->remove_sleep(thr);
346 /** @brief Alert the model-checker that an incorrectly-ordered
347 * synchronization was made */
348 void ModelChecker::set_bad_synchronization()
350 priv->bad_synchronization = true;
354 * Check whether the current trace has triggered an assertion which should halt
357 * @return True, if the execution should be aborted; false otherwise
359 bool ModelChecker::has_asserted() const
361 return priv->asserted;
365 * Trigger a trace assertion which should cause this execution to be halted.
366 * This can be due to a detected bug or due to an infeasibility that should
369 void ModelChecker::set_assert()
371 priv->asserted = true;
375 * Check if we are in a deadlock. Should only be called at the end of an
376 * execution, although it should not give false positives in the middle of an
377 * execution (there should be some ENABLED thread).
379 * @return True if program is in a deadlock; false otherwise
381 bool ModelChecker::is_deadlocked() const
383 bool blocking_threads = false;
384 for (unsigned int i = 0; i < get_num_threads(); i++) {
385 thread_id_t tid = int_to_id(i);
388 Thread *t = get_thread(tid);
389 if (!t->is_model_thread() && t->get_pending())
390 blocking_threads = true;
392 return blocking_threads;
396 * Check if this is a complete execution. That is, have all thread completed
397 * execution (rather than exiting because sleep sets have forced a redundant
400 * @return True if the execution is complete.
402 bool ModelChecker::is_complete_execution() const
404 for (unsigned int i = 0; i < get_num_threads(); i++)
405 if (is_enabled(int_to_id(i)))
411 * @brief Assert a bug in the executing program.
413 * Use this function to assert any sort of bug in the user program. If the
414 * current trace is feasible (actually, a prefix of some feasible execution),
415 * then this execution will be aborted, printing the appropriate message. If
416 * the current trace is not yet feasible, the error message will be stashed and
417 * printed if the execution ever becomes feasible.
419 * @param msg Descriptive message for the bug (do not include newline char)
420 * @return True if bug is immediately-feasible
422 bool ModelChecker::assert_bug(const char *msg, ...)
428 vsnprintf(str, sizeof(str), msg, ap);
431 priv->bugs.push_back(new bug_message(str));
433 if (isfeasibleprefix()) {
441 * @brief Assert a bug in the executing program, asserted by a user thread
442 * @see ModelChecker::assert_bug
443 * @param msg Descriptive message for the bug (do not include newline char)
445 void ModelChecker::assert_user_bug(const char *msg)
447 /* If feasible bug, bail out now */
449 switch_to_master(NULL);
452 /** @return True, if any bugs have been reported for this execution */
453 bool ModelChecker::have_bug_reports() const
455 return priv->bugs.size() != 0;
458 /** @brief Print bug report listing for this execution (if any bugs exist) */
459 void ModelChecker::print_bugs() const
461 if (have_bug_reports()) {
462 model_print("Bug report: %zu bug%s detected\n",
464 priv->bugs.size() > 1 ? "s" : "");
465 for (unsigned int i = 0; i < priv->bugs.size(); i++)
466 priv->bugs[i]->print();
471 * @brief Record end-of-execution stats
473 * Must be run when exiting an execution. Records various stats.
474 * @see struct execution_stats
476 void ModelChecker::record_stats()
479 if (!isfeasibleprefix())
480 stats.num_infeasible++;
481 else if (have_bug_reports())
482 stats.num_buggy_executions++;
483 else if (is_complete_execution())
484 stats.num_complete++;
486 stats.num_redundant++;
489 * @todo We can violate this ASSERT() when fairness/sleep sets
490 * conflict to cause an execution to terminate, e.g. with:
491 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
493 //ASSERT(scheduler->all_threads_sleeping());
497 /** @brief Print execution stats */
498 void ModelChecker::print_stats() const
500 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
501 model_print("Number of redundant executions: %d\n", stats.num_redundant);
502 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
503 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
504 model_print("Total executions: %d\n", stats.num_total);
505 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
509 * @brief End-of-exeuction print
510 * @param printbugs Should any existing bugs be printed?
512 void ModelChecker::print_execution(bool printbugs) const
514 print_program_output();
516 if (params.verbose) {
517 model_print("Earliest divergence point since last feasible execution:\n");
518 if (earliest_diverge)
519 earliest_diverge->print();
521 model_print("(Not set)\n");
527 /* Don't print invalid bugs */
536 * Queries the model-checker for more executions to explore and, if one
537 * exists, resets the model-checker state to execute a new execution.
539 * @return If there are more executions to explore, return true. Otherwise,
542 bool ModelChecker::next_execution()
545 /* Is this execution a feasible execution that's worth bug-checking? */
546 bool complete = isfeasibleprefix() && (is_complete_execution() ||
549 /* End-of-execution bug checks */
552 assert_bug("Deadlock detected");
555 run_trace_analyses();
561 if (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();
581 /** @brief Run trace analyses on complete trace */
582 void ModelChecker::run_trace_analyses() {
583 for (unsigned int i = 0; i < trace_analyses->size(); i++)
584 (*trace_analyses)[i]->analyze(action_trace);
588 * @brief Find the last fence-related backtracking conflict for a ModelAction
590 * This function performs the search for the most recent conflicting action
591 * against which we should perform backtracking, as affected by fence
592 * operations. This includes pairs of potentially-synchronizing actions which
593 * occur due to fence-acquire or fence-release, and hence should be explored in
594 * the opposite execution order.
596 * @param act The current action
597 * @return The most recent action which conflicts with act due to fences
599 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
601 /* Only perform release/acquire fence backtracking for stores */
602 if (!act->is_write())
605 /* Find a fence-release (or, act is a release) */
606 ModelAction *last_release;
607 if (act->is_release())
610 last_release = get_last_fence_release(act->get_tid());
614 /* Skip past the release */
615 action_list_t *list = action_trace;
616 action_list_t::reverse_iterator rit;
617 for (rit = list->rbegin(); rit != list->rend(); rit++)
618 if (*rit == last_release)
620 ASSERT(rit != list->rend());
625 * load --sb-> fence-acquire */
626 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
627 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
628 bool found_acquire_fences = false;
629 for ( ; rit != list->rend(); rit++) {
630 ModelAction *prev = *rit;
631 if (act->same_thread(prev))
634 int tid = id_to_int(prev->get_tid());
636 if (prev->is_read() && act->same_var(prev)) {
637 if (prev->is_acquire()) {
638 /* Found most recent load-acquire, don't need
639 * to search for more fences */
640 if (!found_acquire_fences)
643 prior_loads[tid] = prev;
646 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
647 found_acquire_fences = true;
648 acquire_fences[tid] = prev;
652 ModelAction *latest_backtrack = NULL;
653 for (unsigned int i = 0; i < acquire_fences.size(); i++)
654 if (acquire_fences[i] && prior_loads[i])
655 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
656 latest_backtrack = acquire_fences[i];
657 return latest_backtrack;
661 * @brief Find the last backtracking conflict for a ModelAction
663 * This function performs the search for the most recent conflicting action
664 * against which we should perform backtracking. This primary includes pairs of
665 * synchronizing actions which should be explored in the opposite execution
668 * @param act The current action
669 * @return The most recent action which conflicts with act
671 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
673 switch (act->get_type()) {
674 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
678 ModelAction *ret = NULL;
680 /* linear search: from most recent to oldest */
681 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
682 action_list_t::reverse_iterator rit;
683 for (rit = list->rbegin(); rit != list->rend(); rit++) {
684 ModelAction *prev = *rit;
685 if (prev->could_synchronize_with(act)) {
691 ModelAction *ret2 = get_last_fence_conflict(act);
701 case ATOMIC_TRYLOCK: {
702 /* linear search: from most recent to oldest */
703 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
704 action_list_t::reverse_iterator rit;
705 for (rit = list->rbegin(); rit != list->rend(); rit++) {
706 ModelAction *prev = *rit;
707 if (act->is_conflicting_lock(prev))
712 case ATOMIC_UNLOCK: {
713 /* linear search: from most recent to oldest */
714 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
715 action_list_t::reverse_iterator rit;
716 for (rit = list->rbegin(); rit != list->rend(); rit++) {
717 ModelAction *prev = *rit;
718 if (!act->same_thread(prev) && prev->is_failed_trylock())
724 /* linear search: from most recent to oldest */
725 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
726 action_list_t::reverse_iterator rit;
727 for (rit = list->rbegin(); rit != list->rend(); rit++) {
728 ModelAction *prev = *rit;
729 if (!act->same_thread(prev) && prev->is_failed_trylock())
731 if (!act->same_thread(prev) && prev->is_notify())
737 case ATOMIC_NOTIFY_ALL:
738 case ATOMIC_NOTIFY_ONE: {
739 /* linear search: from most recent to oldest */
740 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
741 action_list_t::reverse_iterator rit;
742 for (rit = list->rbegin(); rit != list->rend(); rit++) {
743 ModelAction *prev = *rit;
744 if (!act->same_thread(prev) && prev->is_wait())
755 /** This method finds backtracking points where we should try to
756 * reorder the parameter ModelAction against.
758 * @param the ModelAction to find backtracking points for.
760 void ModelChecker::set_backtracking(ModelAction *act)
762 Thread *t = get_thread(act);
763 ModelAction *prev = get_last_conflict(act);
767 Node *node = prev->get_node()->get_parent();
769 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
770 int low_tid, high_tid;
771 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
772 low_tid = id_to_int(act->get_tid());
773 high_tid = low_tid + 1;
776 high_tid = get_num_threads();
779 for (int i = low_tid; i < high_tid; i++) {
780 thread_id_t tid = int_to_id(i);
782 /* Make sure this thread can be enabled here. */
783 if (i >= node->get_num_threads())
786 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
787 /* Don't backtrack into a point where the thread is disabled or sleeping. */
788 if (node->enabled_status(tid) != THREAD_ENABLED)
791 /* Check if this has been explored already */
792 if (node->has_been_explored(tid))
795 /* See if fairness allows */
796 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
798 for (int t = 0; t < node->get_num_threads(); t++) {
799 thread_id_t tother = int_to_id(t);
800 if (node->is_enabled(tother) && node->has_priority(tother)) {
809 /* See if CHESS-like yield fairness allows */
810 if (model->params.yieldon) {
812 for (int t = 0; t < node->get_num_threads(); t++) {
813 thread_id_t tother = int_to_id(t);
814 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
823 /* Cache the latest backtracking point */
824 set_latest_backtrack(prev);
826 /* If this is a new backtracking point, mark the tree */
827 if (!node->set_backtrack(tid))
829 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
830 id_to_int(prev->get_tid()),
831 id_to_int(t->get_id()));
840 * @brief Cache the a backtracking point as the "most recent", if eligible
842 * Note that this does not prepare the NodeStack for this backtracking
843 * operation, it only caches the action on a per-execution basis
845 * @param act The operation at which we should explore a different next action
846 * (i.e., backtracking point)
847 * @return True, if this action is now the most recent backtracking point;
850 bool ModelChecker::set_latest_backtrack(ModelAction *act)
852 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
853 priv->next_backtrack = act;
860 * Returns last backtracking point. The model checker will explore a different
861 * path for this point in the next execution.
862 * @return The ModelAction at which the next execution should diverge.
864 ModelAction * ModelChecker::get_next_backtrack()
866 ModelAction *next = priv->next_backtrack;
867 priv->next_backtrack = NULL;
872 * Processes a read model action.
873 * @param curr is the read model action to process.
874 * @return True if processing this read updates the mo_graph.
876 bool ModelChecker::process_read(ModelAction *curr)
878 Node *node = curr->get_node();
880 bool updated = false;
881 switch (node->get_read_from_status()) {
882 case READ_FROM_PAST: {
883 const ModelAction *rf = node->get_read_from_past();
886 mo_graph->startChanges();
888 ASSERT(!is_infeasible());
889 if (!check_recency(curr, rf)) {
890 if (node->increment_read_from()) {
891 mo_graph->rollbackChanges();
894 priv->too_many_reads = true;
898 updated = r_modification_order(curr, rf);
900 mo_graph->commitChanges();
901 mo_check_promises(curr, true);
904 case READ_FROM_PROMISE: {
905 Promise *promise = curr->get_node()->get_read_from_promise();
906 if (promise->add_reader(curr))
907 priv->failed_promise = true;
908 curr->set_read_from_promise(promise);
909 mo_graph->startChanges();
910 if (!check_recency(curr, promise))
911 priv->too_many_reads = true;
912 updated = r_modification_order(curr, promise);
913 mo_graph->commitChanges();
916 case READ_FROM_FUTURE: {
917 /* Read from future value */
918 struct future_value fv = node->get_future_value();
919 Promise *promise = new Promise(curr, fv);
920 curr->set_read_from_promise(promise);
921 promises->push_back(promise);
922 mo_graph->startChanges();
923 updated = r_modification_order(curr, promise);
924 mo_graph->commitChanges();
930 get_thread(curr)->set_return_value(curr->get_return_value());
936 * Processes a lock, trylock, or unlock model action. @param curr is
937 * the read model action to process.
939 * The try lock operation checks whether the lock is taken. If not,
940 * it falls to the normal lock operation case. If so, it returns
943 * The lock operation has already been checked that it is enabled, so
944 * it just grabs the lock and synchronizes with the previous unlock.
946 * The unlock operation has to re-enable all of the threads that are
947 * waiting on the lock.
949 * @return True if synchronization was updated; false otherwise
951 bool ModelChecker::process_mutex(ModelAction *curr)
953 std::mutex *mutex = curr->get_mutex();
954 struct std::mutex_state *state = NULL;
957 state = mutex->get_state();
959 switch (curr->get_type()) {
960 case ATOMIC_TRYLOCK: {
961 bool success = !state->locked;
962 curr->set_try_lock(success);
964 get_thread(curr)->set_return_value(0);
967 get_thread(curr)->set_return_value(1);
969 //otherwise fall into the lock case
971 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
972 assert_bug("Lock access before initialization");
973 state->locked = get_thread(curr);
974 ModelAction *unlock = get_last_unlock(curr);
975 //synchronize with the previous unlock statement
976 if (unlock != NULL) {
977 synchronize(unlock, curr);
983 case ATOMIC_UNLOCK: {
984 /* wake up the other threads */
985 for (unsigned int i = 0; i < get_num_threads(); i++) {
986 Thread *t = get_thread(int_to_id(i));
987 Thread *curr_thrd = get_thread(curr);
988 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
992 /* unlock the lock - after checking who was waiting on it */
993 state->locked = NULL;
995 if (!curr->is_wait())
996 break; /* The rest is only for ATOMIC_WAIT */
998 /* Should we go to sleep? (simulate spurious failures) */
999 if (curr->get_node()->get_misc() == 0) {
1000 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1002 scheduler->sleep(get_thread(curr));
1006 case ATOMIC_NOTIFY_ALL: {
1007 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1008 //activate all the waiting threads
1009 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1010 scheduler->wake(get_thread(*rit));
1015 case ATOMIC_NOTIFY_ONE: {
1016 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1017 int wakeupthread = curr->get_node()->get_misc();
1018 action_list_t::iterator it = waiters->begin();
1019 advance(it, wakeupthread);
1020 scheduler->wake(get_thread(*it));
1032 * @brief Check if the current pending promises allow a future value to be sent
1034 * If one of the following is true:
1035 * (a) there are no pending promises
1036 * (b) the reader and writer do not cross any promises
1037 * Then, it is safe to pass a future value back now.
1039 * Otherwise, we must save the pending future value until (a) or (b) is true
1041 * @param writer The operation which sends the future value. Must be a write.
1042 * @param reader The operation which will observe the value. Must be a read.
1043 * @return True if the future value can be sent now; false if it must wait.
1045 bool ModelChecker::promises_may_allow(const ModelAction *writer,
1046 const ModelAction *reader) const
1048 if (promises->empty())
1050 for(int i=promises->size()-1;i>=0;i--) {
1051 ModelAction *pr=(*promises)[i]->get_reader(0);
1052 //reader is after promise...doesn't cross any promise
1055 //writer is after promise, reader before...bad...
1063 * @brief Add a future value to a reader
1065 * This function performs a few additional checks to ensure that the future
1066 * value can be feasibly observed by the reader
1068 * @param writer The operation whose value is sent. Must be a write.
1069 * @param reader The read operation which may read the future value. Must be a read.
1071 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1073 /* Do more ambitious checks now that mo is more complete */
1074 if (!mo_may_allow(writer, reader))
1077 Node *node = reader->get_node();
1079 /* Find an ancestor thread which exists at the time of the reader */
1080 Thread *write_thread = get_thread(writer);
1081 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1082 write_thread = write_thread->get_parent();
1084 struct future_value fv = {
1085 writer->get_write_value(),
1086 writer->get_seq_number() + params.maxfuturedelay,
1087 write_thread->get_id(),
1089 if (node->add_future_value(fv))
1090 set_latest_backtrack(reader);
1094 * Process a write ModelAction
1095 * @param curr The ModelAction to process
1096 * @return True if the mo_graph was updated or promises were resolved
1098 bool ModelChecker::process_write(ModelAction *curr)
1100 /* Readers to which we may send our future value */
1101 ModelVector<ModelAction *> send_fv;
1103 const ModelAction *earliest_promise_reader;
1104 bool updated_promises = false;
1106 bool updated_mod_order = w_modification_order(curr, &send_fv);
1107 Promise *promise = pop_promise_to_resolve(curr);
1110 earliest_promise_reader = promise->get_reader(0);
1111 updated_promises = resolve_promise(curr, promise);
1113 earliest_promise_reader = NULL;
1115 for (unsigned int i = 0; i < send_fv.size(); i++) {
1116 ModelAction *read = send_fv[i];
1118 /* Don't send future values to reads after the Promise we resolve */
1119 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
1120 /* Check if future value can be sent immediately */
1121 if (promises_may_allow(curr, read)) {
1122 add_future_value(curr, read);
1124 futurevalues->push_back(PendingFutureValue(curr, read));
1129 /* Check the pending future values */
1130 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
1131 struct PendingFutureValue pfv = (*futurevalues)[i];
1132 if (promises_may_allow(pfv.writer, pfv.reader)) {
1133 add_future_value(pfv.writer, pfv.reader);
1134 futurevalues->erase(futurevalues->begin() + i);
1138 mo_graph->commitChanges();
1139 mo_check_promises(curr, false);
1141 get_thread(curr)->set_return_value(VALUE_NONE);
1142 return updated_mod_order || updated_promises;
1146 * Process a fence ModelAction
1147 * @param curr The ModelAction to process
1148 * @return True if synchronization was updated
1150 bool ModelChecker::process_fence(ModelAction *curr)
1153 * fence-relaxed: no-op
1154 * fence-release: only log the occurence (not in this function), for
1155 * use in later synchronization
1156 * fence-acquire (this function): search for hypothetical release
1158 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1160 bool updated = false;
1161 if (curr->is_acquire()) {
1162 action_list_t *list = action_trace;
1163 action_list_t::reverse_iterator rit;
1164 /* Find X : is_read(X) && X --sb-> curr */
1165 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1166 ModelAction *act = *rit;
1169 if (act->get_tid() != curr->get_tid())
1171 /* Stop at the beginning of the thread */
1172 if (act->is_thread_start())
1174 /* Stop once we reach a prior fence-acquire */
1175 if (act->is_fence() && act->is_acquire())
1177 if (!act->is_read())
1179 /* read-acquire will find its own release sequences */
1180 if (act->is_acquire())
1183 /* Establish hypothetical release sequences */
1184 rel_heads_list_t release_heads;
1185 get_release_seq_heads(curr, act, &release_heads);
1186 for (unsigned int i = 0; i < release_heads.size(); i++)
1187 synchronize(release_heads[i], curr);
1188 if (release_heads.size() != 0)
1196 * @brief Process the current action for thread-related activity
1198 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1199 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1200 * synchronization, etc. This function is a no-op for non-THREAD actions
1201 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1203 * @param curr The current action
1204 * @return True if synchronization was updated or a thread completed
1206 bool ModelChecker::process_thread_action(ModelAction *curr)
1208 bool updated = false;
1210 switch (curr->get_type()) {
1211 case THREAD_CREATE: {
1212 thrd_t *thrd = (thrd_t *)curr->get_location();
1213 struct thread_params *params = (struct thread_params *)curr->get_value();
1214 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1216 th->set_creation(curr);
1217 /* Promises can be satisfied by children */
1218 for (unsigned int i = 0; i < promises->size(); i++) {
1219 Promise *promise = (*promises)[i];
1220 if (promise->thread_is_available(curr->get_tid()))
1221 promise->add_thread(th->get_id());
1226 Thread *blocking = curr->get_thread_operand();
1227 ModelAction *act = get_last_action(blocking->get_id());
1228 synchronize(act, curr);
1229 updated = true; /* trigger rel-seq checks */
1232 case THREAD_FINISH: {
1233 Thread *th = get_thread(curr);
1234 /* Wake up any joining threads */
1235 for (unsigned int i = 0; i < get_num_threads(); i++) {
1236 Thread *waiting = get_thread(int_to_id(i));
1237 if (waiting->waiting_on() == th &&
1238 waiting->get_pending()->is_thread_join())
1239 scheduler->wake(waiting);
1242 /* Completed thread can't satisfy promises */
1243 for (unsigned int i = 0; i < promises->size(); i++) {
1244 Promise *promise = (*promises)[i];
1245 if (promise->thread_is_available(th->get_id()))
1246 if (promise->eliminate_thread(th->get_id()))
1247 priv->failed_promise = true;
1249 updated = true; /* trigger rel-seq checks */
1252 case THREAD_START: {
1253 check_promises(curr->get_tid(), NULL, curr->get_cv());
1264 * @brief Process the current action for release sequence fixup activity
1266 * Performs model-checker release sequence fixups for the current action,
1267 * forcing a single pending release sequence to break (with a given, potential
1268 * "loose" write) or to complete (i.e., synchronize). If a pending release
1269 * sequence forms a complete release sequence, then we must perform the fixup
1270 * synchronization, mo_graph additions, etc.
1272 * @param curr The current action; must be a release sequence fixup action
1273 * @param work_queue The work queue to which to add work items as they are
1276 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1278 const ModelAction *write = curr->get_node()->get_relseq_break();
1279 struct release_seq *sequence = pending_rel_seqs->back();
1280 pending_rel_seqs->pop_back();
1282 ModelAction *acquire = sequence->acquire;
1283 const ModelAction *rf = sequence->rf;
1284 const ModelAction *release = sequence->release;
1288 ASSERT(release->same_thread(rf));
1290 if (write == NULL) {
1292 * @todo Forcing a synchronization requires that we set
1293 * modification order constraints. For instance, we can't allow
1294 * a fixup sequence in which two separate read-acquire
1295 * operations read from the same sequence, where the first one
1296 * synchronizes and the other doesn't. Essentially, we can't
1297 * allow any writes to insert themselves between 'release' and
1301 /* Must synchronize */
1302 if (!synchronize(release, acquire))
1304 /* Re-check all pending release sequences */
1305 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1306 /* Re-check act for mo_graph edges */
1307 work_queue->push_back(MOEdgeWorkEntry(acquire));
1309 /* propagate synchronization to later actions */
1310 action_list_t::reverse_iterator rit = action_trace->rbegin();
1311 for (; (*rit) != acquire; rit++) {
1312 ModelAction *propagate = *rit;
1313 if (acquire->happens_before(propagate)) {
1314 synchronize(acquire, propagate);
1315 /* Re-check 'propagate' for mo_graph edges */
1316 work_queue->push_back(MOEdgeWorkEntry(propagate));
1320 /* Break release sequence with new edges:
1321 * release --mo--> write --mo--> rf */
1322 mo_graph->addEdge(release, write);
1323 mo_graph->addEdge(write, rf);
1326 /* See if we have realized a data race */
1331 * Initialize the current action by performing one or more of the following
1332 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1333 * in the NodeStack, manipulating backtracking sets, allocating and
1334 * initializing clock vectors, and computing the promises to fulfill.
1336 * @param curr The current action, as passed from the user context; may be
1337 * freed/invalidated after the execution of this function, with a different
1338 * action "returned" its place (pass-by-reference)
1339 * @return True if curr is a newly-explored action; false otherwise
1341 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1343 ModelAction *newcurr;
1345 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1346 newcurr = process_rmw(*curr);
1349 if (newcurr->is_rmw())
1350 compute_promises(newcurr);
1356 (*curr)->set_seq_number(get_next_seq_num());
1358 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1360 /* First restore type and order in case of RMW operation */
1361 if ((*curr)->is_rmwr())
1362 newcurr->copy_typeandorder(*curr);
1364 ASSERT((*curr)->get_location() == newcurr->get_location());
1365 newcurr->copy_from_new(*curr);
1367 /* Discard duplicate ModelAction; use action from NodeStack */
1370 /* Always compute new clock vector */
1371 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1374 return false; /* Action was explored previously */
1378 /* Always compute new clock vector */
1379 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1381 /* Assign most recent release fence */
1382 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1385 * Perform one-time actions when pushing new ModelAction onto
1388 if (newcurr->is_write())
1389 compute_promises(newcurr);
1390 else if (newcurr->is_relseq_fixup())
1391 compute_relseq_breakwrites(newcurr);
1392 else if (newcurr->is_wait())
1393 newcurr->get_node()->set_misc_max(2);
1394 else if (newcurr->is_notify_one()) {
1395 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1397 return true; /* This was a new ModelAction */
1402 * @brief Establish reads-from relation between two actions
1404 * Perform basic operations involved with establishing a concrete rf relation,
1405 * including setting the ModelAction data and checking for release sequences.
1407 * @param act The action that is reading (must be a read)
1408 * @param rf The action from which we are reading (must be a write)
1410 * @return True if this read established synchronization
1412 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1415 ASSERT(rf->is_write());
1417 act->set_read_from(rf);
1418 if (act->is_acquire()) {
1419 rel_heads_list_t release_heads;
1420 get_release_seq_heads(act, act, &release_heads);
1421 int num_heads = release_heads.size();
1422 for (unsigned int i = 0; i < release_heads.size(); i++)
1423 if (!synchronize(release_heads[i], act))
1425 return num_heads > 0;
1431 * @brief Synchronizes two actions
1433 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1434 * This function performs the synchronization as well as providing other hooks
1435 * for other checks along with synchronization.
1437 * @param first The left-hand side of the synchronizes-with relation
1438 * @param second The right-hand side of the synchronizes-with relation
1439 * @return True if the synchronization was successful (i.e., was consistent
1440 * with the execution order); false otherwise
1442 bool ModelChecker::synchronize(const ModelAction *first, ModelAction *second)
1444 if (*second < *first) {
1445 set_bad_synchronization();
1448 check_promises(first->get_tid(), second->get_cv(), first->get_cv());
1449 return second->synchronize_with(first);
1453 * Check promises and eliminate potentially-satisfying threads when a thread is
1454 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1455 * no longer satisfy a promise generated from that thread.
1457 * @param blocker The thread on which a thread is waiting
1458 * @param waiting The waiting thread
1460 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1462 for (unsigned int i = 0; i < promises->size(); i++) {
1463 Promise *promise = (*promises)[i];
1464 if (!promise->thread_is_available(waiting->get_id()))
1466 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1467 ModelAction *reader = promise->get_reader(j);
1468 if (reader->get_tid() != blocker->get_id())
1470 if (promise->eliminate_thread(waiting->get_id())) {
1471 /* Promise has failed */
1472 priv->failed_promise = true;
1474 /* Only eliminate the 'waiting' thread once */
1482 * @brief Check whether a model action is enabled.
1484 * Checks whether a lock or join operation would be successful (i.e., is the
1485 * lock already locked, or is the joined thread already complete). If not, put
1486 * the action in a waiter list.
1488 * @param curr is the ModelAction to check whether it is enabled.
1489 * @return a bool that indicates whether the action is enabled.
1491 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1492 if (curr->is_lock()) {
1493 std::mutex *lock = curr->get_mutex();
1494 struct std::mutex_state *state = lock->get_state();
1497 } else if (curr->is_thread_join()) {
1498 Thread *blocking = curr->get_thread_operand();
1499 if (!blocking->is_complete()) {
1500 thread_blocking_check_promises(blocking, get_thread(curr));
1509 * This is the heart of the model checker routine. It performs model-checking
1510 * actions corresponding to a given "current action." Among other processes, it
1511 * calculates reads-from relationships, updates synchronization clock vectors,
1512 * forms a memory_order constraints graph, and handles replay/backtrack
1513 * execution when running permutations of previously-observed executions.
1515 * @param curr The current action to process
1516 * @return The ModelAction that is actually executed; may be different than
1517 * curr; may be NULL, if the current action is not enabled to run
1519 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1522 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1523 bool newly_explored = initialize_curr_action(&curr);
1527 wake_up_sleeping_actions(curr);
1529 /* Compute fairness information for CHESS yield algorithm */
1530 if (model->params.yieldon) {
1531 curr->get_node()->update_yield(scheduler);
1534 /* Add the action to lists before any other model-checking tasks */
1535 if (!second_part_of_rmw)
1536 add_action_to_lists(curr);
1538 /* Build may_read_from set for newly-created actions */
1539 if (newly_explored && curr->is_read())
1540 build_may_read_from(curr);
1542 /* Initialize work_queue with the "current action" work */
1543 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1544 while (!work_queue.empty() && !has_asserted()) {
1545 WorkQueueEntry work = work_queue.front();
1546 work_queue.pop_front();
1548 switch (work.type) {
1549 case WORK_CHECK_CURR_ACTION: {
1550 ModelAction *act = work.action;
1551 bool update = false; /* update this location's release seq's */
1552 bool update_all = false; /* update all release seq's */
1554 if (process_thread_action(curr))
1557 if (act->is_read() && !second_part_of_rmw && process_read(act))
1560 if (act->is_write() && process_write(act))
1563 if (act->is_fence() && process_fence(act))
1566 if (act->is_mutex_op() && process_mutex(act))
1569 if (act->is_relseq_fixup())
1570 process_relseq_fixup(curr, &work_queue);
1573 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1575 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1578 case WORK_CHECK_RELEASE_SEQ:
1579 resolve_release_sequences(work.location, &work_queue);
1581 case WORK_CHECK_MO_EDGES: {
1582 /** @todo Complete verification of work_queue */
1583 ModelAction *act = work.action;
1584 bool updated = false;
1586 if (act->is_read()) {
1587 const ModelAction *rf = act->get_reads_from();
1588 const Promise *promise = act->get_reads_from_promise();
1590 if (r_modification_order(act, rf))
1592 } else if (promise) {
1593 if (r_modification_order(act, promise))
1597 if (act->is_write()) {
1598 if (w_modification_order(act, NULL))
1601 mo_graph->commitChanges();
1604 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1613 check_curr_backtracking(curr);
1614 set_backtracking(curr);
1618 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1620 Node *currnode = curr->get_node();
1621 Node *parnode = currnode->get_parent();
1623 if ((parnode && !parnode->backtrack_empty()) ||
1624 !currnode->misc_empty() ||
1625 !currnode->read_from_empty() ||
1626 !currnode->promise_empty() ||
1627 !currnode->relseq_break_empty()) {
1628 set_latest_backtrack(curr);
1632 bool ModelChecker::promises_expired() const
1634 for (unsigned int i = 0; i < promises->size(); i++) {
1635 Promise *promise = (*promises)[i];
1636 if (promise->get_expiration() < priv->used_sequence_numbers)
1643 * This is the strongest feasibility check available.
1644 * @return whether the current trace (partial or complete) must be a prefix of
1647 bool ModelChecker::isfeasibleprefix() const
1649 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1653 * Print disagnostic information about an infeasible execution
1654 * @param prefix A string to prefix the output with; if NULL, then a default
1655 * message prefix will be provided
1657 void ModelChecker::print_infeasibility(const char *prefix) const
1661 if (mo_graph->checkForCycles())
1662 ptr += sprintf(ptr, "[mo cycle]");
1663 if (priv->failed_promise)
1664 ptr += sprintf(ptr, "[failed promise]");
1665 if (priv->too_many_reads)
1666 ptr += sprintf(ptr, "[too many reads]");
1667 if (priv->no_valid_reads)
1668 ptr += sprintf(ptr, "[no valid reads-from]");
1669 if (priv->bad_synchronization)
1670 ptr += sprintf(ptr, "[bad sw ordering]");
1671 if (promises_expired())
1672 ptr += sprintf(ptr, "[promise expired]");
1673 if (promises->size() != 0)
1674 ptr += sprintf(ptr, "[unresolved promise]");
1676 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1680 * Returns whether the current completed trace is feasible, except for pending
1681 * release sequences.
1683 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1685 return !is_infeasible() && promises->size() == 0;
1689 * Check if the current partial trace is infeasible. Does not check any
1690 * end-of-execution flags, which might rule out the execution. Thus, this is
1691 * useful only for ruling an execution as infeasible.
1692 * @return whether the current partial trace is infeasible.
1694 bool ModelChecker::is_infeasible() const
1696 return mo_graph->checkForCycles() ||
1697 priv->no_valid_reads ||
1698 priv->failed_promise ||
1699 priv->too_many_reads ||
1700 priv->bad_synchronization ||
1704 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1705 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1706 ModelAction *lastread = get_last_action(act->get_tid());
1707 lastread->process_rmw(act);
1708 if (act->is_rmw()) {
1709 if (lastread->get_reads_from())
1710 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1712 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1713 mo_graph->commitChanges();
1719 * A helper function for ModelChecker::check_recency, to check if the current
1720 * thread is able to read from a different write/promise for 'params.maxreads'
1721 * number of steps and if that write/promise should become visible (i.e., is
1722 * ordered later in the modification order). This helps model memory liveness.
1724 * @param curr The current action. Must be a read.
1725 * @param rf The write/promise from which we plan to read
1726 * @param other_rf The write/promise from which we may read
1727 * @return True if we were able to read from other_rf for params.maxreads steps
1729 template <typename T, typename U>
1730 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1732 /* Need a different write/promise */
1733 if (other_rf->equals(rf))
1736 /* Only look for "newer" writes/promises */
1737 if (!mo_graph->checkReachable(rf, other_rf))
1740 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1741 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1742 action_list_t::reverse_iterator rit = list->rbegin();
1743 ASSERT((*rit) == curr);
1744 /* Skip past curr */
1747 /* Does this write/promise work for everyone? */
1748 for (int i = 0; i < params.maxreads; i++, rit++) {
1749 ModelAction *act = *rit;
1750 if (!act->may_read_from(other_rf))
1757 * Checks whether a thread has read from the same write or Promise for too many
1758 * times without seeing the effects of a later write/Promise.
1761 * 1) there must a different write/promise that we could read from,
1762 * 2) we must have read from the same write/promise in excess of maxreads times,
1763 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1764 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1766 * If so, we decide that the execution is no longer feasible.
1768 * @param curr The current action. Must be a read.
1769 * @param rf The ModelAction/Promise from which we might read.
1770 * @return True if the read should succeed; false otherwise
1772 template <typename T>
1773 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1775 if (!params.maxreads)
1778 //NOTE: Next check is just optimization, not really necessary....
1779 if (curr->get_node()->get_read_from_past_size() +
1780 curr->get_node()->get_read_from_promise_size() <= 1)
1783 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1784 int tid = id_to_int(curr->get_tid());
1785 ASSERT(tid < (int)thrd_lists->size());
1786 action_list_t *list = &(*thrd_lists)[tid];
1787 action_list_t::reverse_iterator rit = list->rbegin();
1788 ASSERT((*rit) == curr);
1789 /* Skip past curr */
1792 action_list_t::reverse_iterator ritcopy = rit;
1793 /* See if we have enough reads from the same value */
1794 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1795 if (ritcopy == list->rend())
1797 ModelAction *act = *ritcopy;
1798 if (!act->is_read())
1800 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1802 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1804 if (act->get_node()->get_read_from_past_size() +
1805 act->get_node()->get_read_from_promise_size() <= 1)
1808 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1809 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1810 if (should_read_instead(curr, rf, write))
1811 return false; /* liveness failure */
1813 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1814 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1815 if (should_read_instead(curr, rf, promise))
1816 return false; /* liveness failure */
1822 * @brief Updates the mo_graph with the constraints imposed from the current
1825 * Basic idea is the following: Go through each other thread and find
1826 * the last action that happened before our read. Two cases:
1828 * -# The action is a write: that write must either occur before
1829 * the write we read from or be the write we read from.
1830 * -# The action is a read: the write that that action read from
1831 * must occur before the write we read from or be the same write.
1833 * @param curr The current action. Must be a read.
1834 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1835 * @return True if modification order edges were added; false otherwise
1837 template <typename rf_type>
1838 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1840 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1843 ASSERT(curr->is_read());
1845 /* Last SC fence in the current thread */
1846 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1847 ModelAction *last_sc_write = NULL;
1848 if (curr->is_seqcst())
1849 last_sc_write = get_last_seq_cst_write(curr);
1851 /* Iterate over all threads */
1852 for (i = 0; i < thrd_lists->size(); i++) {
1853 /* Last SC fence in thread i */
1854 ModelAction *last_sc_fence_thread_local = NULL;
1855 if (int_to_id((int)i) != curr->get_tid())
1856 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1858 /* Last SC fence in thread i, before last SC fence in current thread */
1859 ModelAction *last_sc_fence_thread_before = NULL;
1860 if (last_sc_fence_local)
1861 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1863 /* Iterate over actions in thread, starting from most recent */
1864 action_list_t *list = &(*thrd_lists)[i];
1865 action_list_t::reverse_iterator rit;
1866 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1867 ModelAction *act = *rit;
1872 /* Don't want to add reflexive edges on 'rf' */
1873 if (act->equals(rf)) {
1874 if (act->happens_before(curr))
1880 if (act->is_write()) {
1881 /* C++, Section 29.3 statement 5 */
1882 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1883 *act < *last_sc_fence_thread_local) {
1884 added = mo_graph->addEdge(act, rf) || added;
1887 /* C++, Section 29.3 statement 4 */
1888 else if (act->is_seqcst() && last_sc_fence_local &&
1889 *act < *last_sc_fence_local) {
1890 added = mo_graph->addEdge(act, rf) || added;
1893 /* C++, Section 29.3 statement 6 */
1894 else if (last_sc_fence_thread_before &&
1895 *act < *last_sc_fence_thread_before) {
1896 added = mo_graph->addEdge(act, rf) || added;
1901 /* C++, Section 29.3 statement 3 (second subpoint) */
1902 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1903 added = mo_graph->addEdge(act, rf) || added;
1908 * Include at most one act per-thread that "happens
1911 if (act->happens_before(curr)) {
1912 if (act->is_write()) {
1913 added = mo_graph->addEdge(act, rf) || added;
1915 const ModelAction *prevrf = act->get_reads_from();
1916 const Promise *prevrf_promise = act->get_reads_from_promise();
1918 if (!prevrf->equals(rf))
1919 added = mo_graph->addEdge(prevrf, rf) || added;
1920 } else if (!prevrf_promise->equals(rf)) {
1921 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1930 * All compatible, thread-exclusive promises must be ordered after any
1931 * concrete loads from the same thread
1933 for (unsigned int i = 0; i < promises->size(); i++)
1934 if ((*promises)[i]->is_compatible_exclusive(curr))
1935 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1941 * Updates the mo_graph with the constraints imposed from the current write.
1943 * Basic idea is the following: Go through each other thread and find
1944 * the lastest action that happened before our write. Two cases:
1946 * (1) The action is a write => that write must occur before
1949 * (2) The action is a read => the write that that action read from
1950 * must occur before the current write.
1952 * This method also handles two other issues:
1954 * (I) Sequential Consistency: Making sure that if the current write is
1955 * seq_cst, that it occurs after the previous seq_cst write.
1957 * (II) Sending the write back to non-synchronizing reads.
1959 * @param curr The current action. Must be a write.
1960 * @param send_fv A vector for stashing reads to which we may pass our future
1961 * value. If NULL, then don't record any future values.
1962 * @return True if modification order edges were added; false otherwise
1964 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1966 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1969 ASSERT(curr->is_write());
1971 if (curr->is_seqcst()) {
1972 /* We have to at least see the last sequentially consistent write,
1973 so we are initialized. */
1974 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1975 if (last_seq_cst != NULL) {
1976 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1980 /* Last SC fence in the current thread */
1981 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1983 /* Iterate over all threads */
1984 for (i = 0; i < thrd_lists->size(); i++) {
1985 /* Last SC fence in thread i, before last SC fence in current thread */
1986 ModelAction *last_sc_fence_thread_before = NULL;
1987 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1988 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1990 /* Iterate over actions in thread, starting from most recent */
1991 action_list_t *list = &(*thrd_lists)[i];
1992 action_list_t::reverse_iterator rit;
1993 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1994 ModelAction *act = *rit;
1997 * 1) If RMW and it actually read from something, then we
1998 * already have all relevant edges, so just skip to next
2001 * 2) If RMW and it didn't read from anything, we should
2002 * whatever edge we can get to speed up convergence.
2004 * 3) If normal write, we need to look at earlier actions, so
2005 * continue processing list.
2007 if (curr->is_rmw()) {
2008 if (curr->get_reads_from() != NULL)
2016 /* C++, Section 29.3 statement 7 */
2017 if (last_sc_fence_thread_before && act->is_write() &&
2018 *act < *last_sc_fence_thread_before) {
2019 added = mo_graph->addEdge(act, curr) || added;
2024 * Include at most one act per-thread that "happens
2027 if (act->happens_before(curr)) {
2029 * Note: if act is RMW, just add edge:
2031 * The following edge should be handled elsewhere:
2032 * readfrom(act) --mo--> act
2034 if (act->is_write())
2035 added = mo_graph->addEdge(act, curr) || added;
2036 else if (act->is_read()) {
2037 //if previous read accessed a null, just keep going
2038 if (act->get_reads_from() == NULL)
2040 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2043 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2044 !act->same_thread(curr)) {
2045 /* We have an action that:
2046 (1) did not happen before us
2047 (2) is a read and we are a write
2048 (3) cannot synchronize with us
2049 (4) is in a different thread
2051 that read could potentially read from our write. Note that
2052 these checks are overly conservative at this point, we'll
2053 do more checks before actually removing the
2057 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2058 if (!is_infeasible())
2059 send_fv->push_back(act);
2060 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2061 add_future_value(curr, act);
2068 * All compatible, thread-exclusive promises must be ordered after any
2069 * concrete stores to the same thread, or else they can be merged with
2072 for (unsigned int i = 0; i < promises->size(); i++)
2073 if ((*promises)[i]->is_compatible_exclusive(curr))
2074 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2079 /** Arbitrary reads from the future are not allowed. Section 29.3
2080 * part 9 places some constraints. This method checks one result of constraint
2081 * constraint. Others require compiler support. */
2082 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2084 if (!writer->is_rmw())
2087 if (!reader->is_rmw())
2090 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2091 if (search == reader)
2093 if (search->get_tid() == reader->get_tid() &&
2094 search->happens_before(reader))
2102 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2103 * some constraints. This method checks one the following constraint (others
2104 * require compiler support):
2106 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2108 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2110 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2112 /* Iterate over all threads */
2113 for (i = 0; i < thrd_lists->size(); i++) {
2114 const ModelAction *write_after_read = NULL;
2116 /* Iterate over actions in thread, starting from most recent */
2117 action_list_t *list = &(*thrd_lists)[i];
2118 action_list_t::reverse_iterator rit;
2119 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2120 ModelAction *act = *rit;
2122 /* Don't disallow due to act == reader */
2123 if (!reader->happens_before(act) || reader == act)
2125 else if (act->is_write())
2126 write_after_read = act;
2127 else if (act->is_read() && act->get_reads_from() != NULL)
2128 write_after_read = act->get_reads_from();
2131 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2138 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2139 * The ModelAction under consideration is expected to be taking part in
2140 * release/acquire synchronization as an object of the "reads from" relation.
2141 * Note that this can only provide release sequence support for RMW chains
2142 * which do not read from the future, as those actions cannot be traced until
2143 * their "promise" is fulfilled. Similarly, we may not even establish the
2144 * presence of a release sequence with certainty, as some modification order
2145 * constraints may be decided further in the future. Thus, this function
2146 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2147 * and a boolean representing certainty.
2149 * @param rf The action that might be part of a release sequence. Must be a
2151 * @param release_heads A pass-by-reference style return parameter. After
2152 * execution of this function, release_heads will contain the heads of all the
2153 * relevant release sequences, if any exists with certainty
2154 * @param pending A pass-by-reference style return parameter which is only used
2155 * when returning false (i.e., uncertain). Returns most information regarding
2156 * an uncertain release sequence, including any write operations that might
2157 * break the sequence.
2158 * @return true, if the ModelChecker is certain that release_heads is complete;
2161 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2162 rel_heads_list_t *release_heads,
2163 struct release_seq *pending) const
2165 /* Only check for release sequences if there are no cycles */
2166 if (mo_graph->checkForCycles())
2169 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2170 ASSERT(rf->is_write());
2172 if (rf->is_release())
2173 release_heads->push_back(rf);
2174 else if (rf->get_last_fence_release())
2175 release_heads->push_back(rf->get_last_fence_release());
2177 break; /* End of RMW chain */
2179 /** @todo Need to be smarter here... In the linux lock
2180 * example, this will run to the beginning of the program for
2182 /** @todo The way to be smarter here is to keep going until 1
2183 * thread has a release preceded by an acquire and you've seen
2186 /* acq_rel RMW is a sufficient stopping condition */
2187 if (rf->is_acquire() && rf->is_release())
2188 return true; /* complete */
2191 /* read from future: need to settle this later */
2193 return false; /* incomplete */
2196 if (rf->is_release())
2197 return true; /* complete */
2199 /* else relaxed write
2200 * - check for fence-release in the same thread (29.8, stmt. 3)
2201 * - check modification order for contiguous subsequence
2202 * -> rf must be same thread as release */
2204 const ModelAction *fence_release = rf->get_last_fence_release();
2205 /* Synchronize with a fence-release unconditionally; we don't need to
2206 * find any more "contiguous subsequence..." for it */
2208 release_heads->push_back(fence_release);
2210 int tid = id_to_int(rf->get_tid());
2211 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2212 action_list_t *list = &(*thrd_lists)[tid];
2213 action_list_t::const_reverse_iterator rit;
2215 /* Find rf in the thread list */
2216 rit = std::find(list->rbegin(), list->rend(), rf);
2217 ASSERT(rit != list->rend());
2219 /* Find the last {write,fence}-release */
2220 for (; rit != list->rend(); rit++) {
2221 if (fence_release && *(*rit) < *fence_release)
2223 if ((*rit)->is_release())
2226 if (rit == list->rend()) {
2227 /* No write-release in this thread */
2228 return true; /* complete */
2229 } else if (fence_release && *(*rit) < *fence_release) {
2230 /* The fence-release is more recent (and so, "stronger") than
2231 * the most recent write-release */
2232 return true; /* complete */
2233 } /* else, need to establish contiguous release sequence */
2234 ModelAction *release = *rit;
2236 ASSERT(rf->same_thread(release));
2238 pending->writes.clear();
2240 bool certain = true;
2241 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2242 if (id_to_int(rf->get_tid()) == (int)i)
2244 list = &(*thrd_lists)[i];
2246 /* Can we ensure no future writes from this thread may break
2247 * the release seq? */
2248 bool future_ordered = false;
2250 ModelAction *last = get_last_action(int_to_id(i));
2251 Thread *th = get_thread(int_to_id(i));
2252 if ((last && rf->happens_before(last)) ||
2255 future_ordered = true;
2257 ASSERT(!th->is_model_thread() || future_ordered);
2259 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2260 const ModelAction *act = *rit;
2261 /* Reach synchronization -> this thread is complete */
2262 if (act->happens_before(release))
2264 if (rf->happens_before(act)) {
2265 future_ordered = true;
2269 /* Only non-RMW writes can break release sequences */
2270 if (!act->is_write() || act->is_rmw())
2273 /* Check modification order */
2274 if (mo_graph->checkReachable(rf, act)) {
2275 /* rf --mo--> act */
2276 future_ordered = true;
2279 if (mo_graph->checkReachable(act, release))
2280 /* act --mo--> release */
2282 if (mo_graph->checkReachable(release, act) &&
2283 mo_graph->checkReachable(act, rf)) {
2284 /* release --mo-> act --mo--> rf */
2285 return true; /* complete */
2287 /* act may break release sequence */
2288 pending->writes.push_back(act);
2291 if (!future_ordered)
2292 certain = false; /* This thread is uncertain */
2296 release_heads->push_back(release);
2297 pending->writes.clear();
2299 pending->release = release;
2306 * An interface for getting the release sequence head(s) with which a
2307 * given ModelAction must synchronize. This function only returns a non-empty
2308 * result when it can locate a release sequence head with certainty. Otherwise,
2309 * it may mark the internal state of the ModelChecker so that it will handle
2310 * the release sequence at a later time, causing @a acquire to update its
2311 * synchronization at some later point in execution.
2313 * @param acquire The 'acquire' action that may synchronize with a release
2315 * @param read The read action that may read from a release sequence; this may
2316 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2317 * when 'acquire' is a fence-acquire)
2318 * @param release_heads A pass-by-reference return parameter. Will be filled
2319 * with the head(s) of the release sequence(s), if they exists with certainty.
2320 * @see ModelChecker::release_seq_heads
2322 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2323 ModelAction *read, rel_heads_list_t *release_heads)
2325 const ModelAction *rf = read->get_reads_from();
2326 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2327 sequence->acquire = acquire;
2328 sequence->read = read;
2330 if (!release_seq_heads(rf, release_heads, sequence)) {
2331 /* add act to 'lazy checking' list */
2332 pending_rel_seqs->push_back(sequence);
2334 snapshot_free(sequence);
2339 * Attempt to resolve all stashed operations that might synchronize with a
2340 * release sequence for a given location. This implements the "lazy" portion of
2341 * determining whether or not a release sequence was contiguous, since not all
2342 * modification order information is present at the time an action occurs.
2344 * @param location The location/object that should be checked for release
2345 * sequence resolutions. A NULL value means to check all locations.
2346 * @param work_queue The work queue to which to add work items as they are
2348 * @return True if any updates occurred (new synchronization, new mo_graph
2351 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2353 bool updated = false;
2354 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2355 while (it != pending_rel_seqs->end()) {
2356 struct release_seq *pending = *it;
2357 ModelAction *acquire = pending->acquire;
2358 const ModelAction *read = pending->read;
2360 /* Only resolve sequences on the given location, if provided */
2361 if (location && read->get_location() != location) {
2366 const ModelAction *rf = read->get_reads_from();
2367 rel_heads_list_t release_heads;
2369 complete = release_seq_heads(rf, &release_heads, pending);
2370 for (unsigned int i = 0; i < release_heads.size(); i++)
2371 if (!acquire->has_synchronized_with(release_heads[i]))
2372 if (synchronize(release_heads[i], acquire))
2376 /* Re-check all pending release sequences */
2377 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2378 /* Re-check read-acquire for mo_graph edges */
2379 if (acquire->is_read())
2380 work_queue->push_back(MOEdgeWorkEntry(acquire));
2382 /* propagate synchronization to later actions */
2383 action_list_t::reverse_iterator rit = action_trace->rbegin();
2384 for (; (*rit) != acquire; rit++) {
2385 ModelAction *propagate = *rit;
2386 if (acquire->happens_before(propagate)) {
2387 synchronize(acquire, propagate);
2388 /* Re-check 'propagate' for mo_graph edges */
2389 work_queue->push_back(MOEdgeWorkEntry(propagate));
2394 it = pending_rel_seqs->erase(it);
2395 snapshot_free(pending);
2401 // If we resolved promises or data races, see if we have realized a data race.
2408 * Performs various bookkeeping operations for the current ModelAction. For
2409 * instance, adds action to the per-object, per-thread action vector and to the
2410 * action trace list of all thread actions.
2412 * @param act is the ModelAction to add.
2414 void ModelChecker::add_action_to_lists(ModelAction *act)
2416 int tid = id_to_int(act->get_tid());
2417 ModelAction *uninit = NULL;
2419 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2420 if (list->empty() && act->is_atomic_var()) {
2421 uninit = get_uninitialized_action(act);
2422 uninit_id = id_to_int(uninit->get_tid());
2423 list->push_front(uninit);
2425 list->push_back(act);
2427 action_trace->push_back(act);
2429 action_trace->push_front(uninit);
2431 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2432 if (tid >= (int)vec->size())
2433 vec->resize(priv->next_thread_id);
2434 (*vec)[tid].push_back(act);
2436 (*vec)[uninit_id].push_front(uninit);
2438 if ((int)thrd_last_action->size() <= tid)
2439 thrd_last_action->resize(get_num_threads());
2440 (*thrd_last_action)[tid] = act;
2442 (*thrd_last_action)[uninit_id] = uninit;
2444 if (act->is_fence() && act->is_release()) {
2445 if ((int)thrd_last_fence_release->size() <= tid)
2446 thrd_last_fence_release->resize(get_num_threads());
2447 (*thrd_last_fence_release)[tid] = act;
2450 if (act->is_wait()) {
2451 void *mutex_loc = (void *) act->get_value();
2452 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2454 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2455 if (tid >= (int)vec->size())
2456 vec->resize(priv->next_thread_id);
2457 (*vec)[tid].push_back(act);
2462 * @brief Get the last action performed by a particular Thread
2463 * @param tid The thread ID of the Thread in question
2464 * @return The last action in the thread
2466 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2468 int threadid = id_to_int(tid);
2469 if (threadid < (int)thrd_last_action->size())
2470 return (*thrd_last_action)[id_to_int(tid)];
2476 * @brief Get the last fence release performed by a particular Thread
2477 * @param tid The thread ID of the Thread in question
2478 * @return The last fence release in the thread, if one exists; NULL otherwise
2480 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2482 int threadid = id_to_int(tid);
2483 if (threadid < (int)thrd_last_fence_release->size())
2484 return (*thrd_last_fence_release)[id_to_int(tid)];
2490 * Gets the last memory_order_seq_cst write (in the total global sequence)
2491 * performed on a particular object (i.e., memory location), not including the
2493 * @param curr The current ModelAction; also denotes the object location to
2495 * @return The last seq_cst write
2497 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2499 void *location = curr->get_location();
2500 action_list_t *list = get_safe_ptr_action(obj_map, location);
2501 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2502 action_list_t::reverse_iterator rit;
2503 for (rit = list->rbegin(); (*rit) != curr; rit++)
2505 rit++; /* Skip past curr */
2506 for ( ; rit != list->rend(); rit++)
2507 if ((*rit)->is_write() && (*rit)->is_seqcst())
2513 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2514 * performed in a particular thread, prior to a particular fence.
2515 * @param tid The ID of the thread to check
2516 * @param before_fence The fence from which to begin the search; if NULL, then
2517 * search for the most recent fence in the thread.
2518 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2520 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2522 /* All fences should have NULL location */
2523 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2524 action_list_t::reverse_iterator rit = list->rbegin();
2527 for (; rit != list->rend(); rit++)
2528 if (*rit == before_fence)
2531 ASSERT(*rit == before_fence);
2535 for (; rit != list->rend(); rit++)
2536 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2542 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2543 * location). This function identifies the mutex according to the current
2544 * action, which is presumed to perform on the same mutex.
2545 * @param curr The current ModelAction; also denotes the object location to
2547 * @return The last unlock operation
2549 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2551 void *location = curr->get_location();
2552 action_list_t *list = get_safe_ptr_action(obj_map, location);
2553 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2554 action_list_t::reverse_iterator rit;
2555 for (rit = list->rbegin(); rit != list->rend(); rit++)
2556 if ((*rit)->is_unlock() || (*rit)->is_wait())
2561 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2563 ModelAction *parent = get_last_action(tid);
2565 parent = get_thread(tid)->get_creation();
2570 * Returns the clock vector for a given thread.
2571 * @param tid The thread whose clock vector we want
2572 * @return Desired clock vector
2574 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2576 return get_parent_action(tid)->get_cv();
2580 * @brief Find the promise (if any) to resolve for the current action and
2581 * remove it from the pending promise vector
2582 * @param curr The current ModelAction. Should be a write.
2583 * @return The Promise to resolve, if any; otherwise NULL
2585 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2587 for (unsigned int i = 0; i < promises->size(); i++)
2588 if (curr->get_node()->get_promise(i)) {
2589 Promise *ret = (*promises)[i];
2590 promises->erase(promises->begin() + i);
2597 * Resolve a Promise with a current write.
2598 * @param write The ModelAction that is fulfilling Promises
2599 * @param promise The Promise to resolve
2600 * @return True if the Promise was successfully resolved; false otherwise
2602 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2604 ModelVector<ModelAction *> actions_to_check;
2606 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2607 ModelAction *read = promise->get_reader(i);
2608 read_from(read, write);
2609 actions_to_check.push_back(read);
2611 /* Make sure the promise's value matches the write's value */
2612 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2613 if (!mo_graph->resolvePromise(promise, write))
2614 priv->failed_promise = true;
2617 * @todo It is possible to end up in an inconsistent state, where a
2618 * "resolved" promise may still be referenced if
2619 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2621 * Note that the inconsistency only matters when dumping mo_graph to
2627 //Check whether reading these writes has made threads unable to
2629 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2630 ModelAction *read = actions_to_check[i];
2631 mo_check_promises(read, true);
2638 * Compute the set of promises that could potentially be satisfied by this
2639 * action. Note that the set computation actually appears in the Node, not in
2641 * @param curr The ModelAction that may satisfy promises
2643 void ModelChecker::compute_promises(ModelAction *curr)
2645 for (unsigned int i = 0; i < promises->size(); i++) {
2646 Promise *promise = (*promises)[i];
2647 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2650 bool satisfy = true;
2651 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2652 const ModelAction *act = promise->get_reader(j);
2653 if (act->happens_before(curr) ||
2654 act->could_synchronize_with(curr)) {
2660 curr->get_node()->set_promise(i);
2664 /** Checks promises in response to change in ClockVector Threads. */
2665 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2667 for (unsigned int i = 0; i < promises->size(); i++) {
2668 Promise *promise = (*promises)[i];
2669 if (!promise->thread_is_available(tid))
2671 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2672 const ModelAction *act = promise->get_reader(j);
2673 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2674 merge_cv->synchronized_since(act)) {
2675 if (promise->eliminate_thread(tid)) {
2676 /* Promise has failed */
2677 priv->failed_promise = true;
2685 void ModelChecker::check_promises_thread_disabled()
2687 for (unsigned int i = 0; i < promises->size(); i++) {
2688 Promise *promise = (*promises)[i];
2689 if (promise->has_failed()) {
2690 priv->failed_promise = true;
2697 * @brief Checks promises in response to addition to modification order for
2700 * We test whether threads are still available for satisfying promises after an
2701 * addition to our modification order constraints. Those that are unavailable
2702 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2703 * that promise has failed.
2705 * @param act The ModelAction which updated the modification order
2706 * @param is_read_check Should be true if act is a read and we must check for
2707 * updates to the store from which it read (there is a distinction here for
2708 * RMW's, which are both a load and a store)
2710 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2712 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2714 for (unsigned int i = 0; i < promises->size(); i++) {
2715 Promise *promise = (*promises)[i];
2717 // Is this promise on the same location?
2718 if (!promise->same_location(write))
2721 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2722 const ModelAction *pread = promise->get_reader(j);
2723 if (!pread->happens_before(act))
2725 if (mo_graph->checkPromise(write, promise)) {
2726 priv->failed_promise = true;
2732 // Don't do any lookups twice for the same thread
2733 if (!promise->thread_is_available(act->get_tid()))
2736 if (mo_graph->checkReachable(promise, write)) {
2737 if (mo_graph->checkPromise(write, promise)) {
2738 priv->failed_promise = true;
2746 * Compute the set of writes that may break the current pending release
2747 * sequence. This information is extracted from previou release sequence
2750 * @param curr The current ModelAction. Must be a release sequence fixup
2753 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2755 if (pending_rel_seqs->empty())
2758 struct release_seq *pending = pending_rel_seqs->back();
2759 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2760 const ModelAction *write = pending->writes[i];
2761 curr->get_node()->add_relseq_break(write);
2764 /* NULL means don't break the sequence; just synchronize */
2765 curr->get_node()->add_relseq_break(NULL);
2769 * Build up an initial set of all past writes that this 'read' action may read
2770 * from, as well as any previously-observed future values that must still be valid.
2772 * @param curr is the current ModelAction that we are exploring; it must be a
2775 void ModelChecker::build_may_read_from(ModelAction *curr)
2777 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2779 ASSERT(curr->is_read());
2781 ModelAction *last_sc_write = NULL;
2783 if (curr->is_seqcst())
2784 last_sc_write = get_last_seq_cst_write(curr);
2786 /* Iterate over all threads */
2787 for (i = 0; i < thrd_lists->size(); i++) {
2788 /* Iterate over actions in thread, starting from most recent */
2789 action_list_t *list = &(*thrd_lists)[i];
2790 action_list_t::reverse_iterator rit;
2791 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2792 ModelAction *act = *rit;
2794 /* Only consider 'write' actions */
2795 if (!act->is_write() || act == curr)
2798 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2799 bool allow_read = true;
2801 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2803 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2807 /* Only add feasible reads */
2808 mo_graph->startChanges();
2809 r_modification_order(curr, act);
2810 if (!is_infeasible())
2811 curr->get_node()->add_read_from_past(act);
2812 mo_graph->rollbackChanges();
2815 /* Include at most one act per-thread that "happens before" curr */
2816 if (act->happens_before(curr))
2821 /* Inherit existing, promised future values */
2822 for (i = 0; i < promises->size(); i++) {
2823 const Promise *promise = (*promises)[i];
2824 const ModelAction *promise_read = promise->get_reader(0);
2825 if (promise_read->same_var(curr)) {
2826 /* Only add feasible future-values */
2827 mo_graph->startChanges();
2828 r_modification_order(curr, promise);
2829 if (!is_infeasible())
2830 curr->get_node()->add_read_from_promise(promise_read);
2831 mo_graph->rollbackChanges();
2835 /* We may find no valid may-read-from only if the execution is doomed */
2836 if (!curr->get_node()->read_from_size()) {
2837 priv->no_valid_reads = true;
2841 if (DBG_ENABLED()) {
2842 model_print("Reached read action:\n");
2844 model_print("Printing read_from_past\n");
2845 curr->get_node()->print_read_from_past();
2846 model_print("End printing read_from_past\n");
2850 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2852 for ( ; write != NULL; write = write->get_reads_from()) {
2853 /* UNINIT actions don't have a Node, and they never sleep */
2854 if (write->is_uninitialized())
2856 Node *prevnode = write->get_node()->get_parent();
2858 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2859 if (write->is_release() && thread_sleep)
2861 if (!write->is_rmw())
2868 * @brief Get an action representing an uninitialized atomic
2870 * This function may create a new one or try to retrieve one from the NodeStack
2872 * @param curr The current action, which prompts the creation of an UNINIT action
2873 * @return A pointer to the UNINIT ModelAction
2875 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2877 Node *node = curr->get_node();
2878 ModelAction *act = node->get_uninit_action();
2880 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2881 node->set_uninit_action(act);
2883 act->create_cv(NULL);
2887 static void print_list(action_list_t *list)
2889 action_list_t::iterator it;
2891 model_print("---------------------------------------------------------------------\n");
2893 unsigned int hash = 0;
2895 for (it = list->begin(); it != list->end(); it++) {
2896 const ModelAction *act = *it;
2897 if (act->get_seq_number() > 0)
2899 hash = hash^(hash<<3)^((*it)->hash());
2901 model_print("HASH %u\n", hash);
2902 model_print("---------------------------------------------------------------------\n");
2905 #if SUPPORT_MOD_ORDER_DUMP
2906 void ModelChecker::dumpGraph(char *filename) const
2909 sprintf(buffer, "%s.dot", filename);
2910 FILE *file = fopen(buffer, "w");
2911 fprintf(file, "digraph %s {\n", filename);
2912 mo_graph->dumpNodes(file);
2913 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2915 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2916 ModelAction *act = *it;
2917 if (act->is_read()) {
2918 mo_graph->dot_print_node(file, act);
2919 if (act->get_reads_from())
2920 mo_graph->dot_print_edge(file,
2921 act->get_reads_from(),
2923 "label=\"rf\", color=red, weight=2");
2925 mo_graph->dot_print_edge(file,
2926 act->get_reads_from_promise(),
2928 "label=\"rf\", color=red");
2930 if (thread_array[act->get_tid()]) {
2931 mo_graph->dot_print_edge(file,
2932 thread_array[id_to_int(act->get_tid())],
2934 "label=\"sb\", color=blue, weight=400");
2937 thread_array[act->get_tid()] = act;
2939 fprintf(file, "}\n");
2940 model_free(thread_array);
2945 /** @brief Prints an execution trace summary. */
2946 void ModelChecker::print_summary() const
2948 #if SUPPORT_MOD_ORDER_DUMP
2949 char buffername[100];
2950 sprintf(buffername, "exec%04u", stats.num_total);
2951 mo_graph->dumpGraphToFile(buffername);
2952 sprintf(buffername, "graph%04u", stats.num_total);
2953 dumpGraph(buffername);
2956 model_print("Execution %d:", stats.num_total);
2957 if (isfeasibleprefix()) {
2958 if (scheduler->all_threads_sleeping())
2959 model_print(" SLEEP-SET REDUNDANT");
2962 print_infeasibility(" INFEASIBLE");
2963 print_list(action_trace);
2965 if (!promises->empty()) {
2966 model_print("Pending promises:\n");
2967 for (unsigned int i = 0; i < promises->size(); i++) {
2968 model_print(" [P%u] ", i);
2969 (*promises)[i]->print();
2976 * Add a Thread to the system for the first time. Should only be called once
2978 * @param t The Thread to add
2980 void ModelChecker::add_thread(Thread *t)
2982 thread_map->put(id_to_int(t->get_id()), t);
2983 scheduler->add_thread(t);
2987 * @brief Get a Thread reference by its ID
2988 * @param tid The Thread's ID
2989 * @return A Thread reference
2991 Thread * ModelChecker::get_thread(thread_id_t tid) const
2993 return thread_map->get(id_to_int(tid));
2997 * @brief Get a reference to the Thread in which a ModelAction was executed
2998 * @param act The ModelAction
2999 * @return A Thread reference
3001 Thread * ModelChecker::get_thread(const ModelAction *act) const
3003 return get_thread(act->get_tid());
3007 * @brief Get a Promise's "promise number"
3009 * A "promise number" is an index number that is unique to a promise, valid
3010 * only for a specific snapshot of an execution trace. Promises may come and go
3011 * as they are generated an resolved, so an index only retains meaning for the
3014 * @param promise The Promise to check
3015 * @return The promise index, if the promise still is valid; otherwise -1
3017 int ModelChecker::get_promise_number(const Promise *promise) const
3019 for (unsigned int i = 0; i < promises->size(); i++)
3020 if ((*promises)[i] == promise)
3027 * @brief Check if a Thread is currently enabled
3028 * @param t The Thread to check
3029 * @return True if the Thread is currently enabled
3031 bool ModelChecker::is_enabled(Thread *t) const
3033 return scheduler->is_enabled(t);
3037 * @brief Check if a Thread is currently enabled
3038 * @param tid The ID of the Thread to check
3039 * @return True if the Thread is currently enabled
3041 bool ModelChecker::is_enabled(thread_id_t tid) const
3043 return scheduler->is_enabled(tid);
3047 * Switch from a model-checker context to a user-thread context. This is the
3048 * complement of ModelChecker::switch_to_master and must be called from the
3049 * model-checker context
3051 * @param thread The user-thread to switch to
3053 void ModelChecker::switch_from_master(Thread *thread)
3055 scheduler->set_current_thread(thread);
3056 Thread::swap(&system_context, thread);
3060 * Switch from a user-context to the "master thread" context (a.k.a. system
3061 * context). This switch is made with the intention of exploring a particular
3062 * model-checking action (described by a ModelAction object). Must be called
3063 * from a user-thread context.
3065 * @param act The current action that will be explored. May be NULL only if
3066 * trace is exiting via an assertion (see ModelChecker::set_assert and
3067 * ModelChecker::has_asserted).
3068 * @return Return the value returned by the current action
3070 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3073 Thread *old = thread_current();
3074 scheduler->set_current_thread(NULL);
3075 ASSERT(!old->get_pending());
3076 old->set_pending(act);
3077 if (Thread::swap(old, &system_context) < 0) {
3078 perror("swap threads");
3081 return old->get_return_value();
3085 * Takes the next step in the execution, if possible.
3086 * @param curr The current step to take
3087 * @return Returns the next Thread to run, if any; NULL if this execution
3090 Thread * ModelChecker::take_step(ModelAction *curr)
3092 Thread *curr_thrd = get_thread(curr);
3093 ASSERT(curr_thrd->get_state() == THREAD_READY);
3095 ASSERT(check_action_enabled(curr)); /* May have side effects? */
3096 curr = check_current_action(curr);
3099 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3100 scheduler->remove_thread(curr_thrd);
3102 return action_select_next_thread(curr);
3105 /** Wrapper to run the user's main function, with appropriate arguments */
3106 void user_main_wrapper(void *)
3108 user_main(model->params.argc, model->params.argv);
3111 /** @return True if the execution has taken too many steps */
3112 bool ModelChecker::too_many_steps() const
3114 return params.bound != 0 && priv->used_sequence_numbers > params.bound;
3117 bool ModelChecker::should_terminate_execution()
3119 /* Infeasible -> don't take any more steps */
3120 if (is_infeasible())
3122 else if (isfeasibleprefix() && have_bug_reports()) {
3127 if (too_many_steps())
3132 /** @brief Run ModelChecker for the user program */
3133 void ModelChecker::run()
3137 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3142 * Stash next pending action(s) for thread(s). There
3143 * should only need to stash one thread's action--the
3144 * thread which just took a step--plus the first step
3145 * for any newly-created thread
3147 for (unsigned int i = 0; i < get_num_threads(); i++) {
3148 thread_id_t tid = int_to_id(i);
3149 Thread *thr = get_thread(tid);
3150 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3151 switch_from_master(thr);
3152 if (thr->is_waiting_on(thr))
3153 assert_bug("Deadlock detected (thread %u)", i);
3157 /* Don't schedule threads which should be disabled */
3158 for (unsigned int i = 0; i < get_num_threads(); i++) {
3159 Thread *th = get_thread(int_to_id(i));
3160 ModelAction *act = th->get_pending();
3161 if (act && is_enabled(th) && !check_action_enabled(act)) {
3162 scheduler->sleep(th);
3166 /* Catch assertions from prior take_step or from
3167 * between-ModelAction bugs (e.g., data races) */
3172 t = get_next_thread();
3173 if (!t || t->is_model_thread())
3176 /* Consume the next action for a Thread */
3177 ModelAction *curr = t->get_pending();
3178 t->set_pending(NULL);
3179 t = take_step(curr);
3180 } while (!should_terminate_execution());
3183 * Launch end-of-execution release sequence fixups only when
3184 * the execution is otherwise feasible AND there are:
3186 * (1) pending release sequences
3187 * (2) pending assertions that could be invalidated by a change
3188 * in clock vectors (i.e., data races)
3189 * (3) no pending promises
3191 while (!pending_rel_seqs->empty() &&
3192 is_feasible_prefix_ignore_relseq() &&
3193 !unrealizedraces.empty()) {
3194 model_print("*** WARNING: release sequence fixup action "
3195 "(%zu pending release seuqence(s)) ***\n",
3196 pending_rel_seqs->size());
3197 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3198 std::memory_order_seq_cst, NULL, VALUE_NONE,
3202 } while (next_execution());
3204 model_print("******* Model-checking complete: *******\n");