10 #include "snapshot-interface.h"
12 #include "clockvector.h"
13 #include "cyclegraph.h"
16 #include "threads-model.h"
19 #define INITIAL_THREAD_ID 0
24 bug_message(const char *str) {
25 const char *fmt = " [BUG] %s\n";
26 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
27 sprintf(msg, fmt, str);
29 ~bug_message() { if (msg) snapshot_free(msg); }
32 void print() { model_print("%s", msg); }
38 * Structure for holding small ModelChecker members that should be snapshotted
40 struct model_snapshot_members {
41 model_snapshot_members() :
42 /* First thread created will have id INITIAL_THREAD_ID */
43 next_thread_id(INITIAL_THREAD_ID),
44 used_sequence_numbers(0),
48 failed_promise(false),
49 too_many_reads(false),
50 no_valid_reads(false),
51 bad_synchronization(false),
55 ~model_snapshot_members() {
56 for (unsigned int i = 0; i < bugs.size(); i++)
61 unsigned int next_thread_id;
62 modelclock_t used_sequence_numbers;
63 ModelAction *next_backtrack;
64 SnapVector<bug_message *> bugs;
65 struct execution_stats stats;
69 /** @brief Incorrectly-ordered synchronization was made */
70 bool bad_synchronization;
76 /** @brief Constructor */
77 ModelChecker::ModelChecker(struct model_params params) :
78 /* Initialize default scheduler */
80 scheduler(new Scheduler()),
82 earliest_diverge(NULL),
83 action_trace(new action_list_t()),
84 thread_map(new HashTable<int, Thread *, int>()),
85 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
86 lock_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
87 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new SnapVector<Promise *>()),
90 futurevalues(new SnapVector<struct PendingFutureValue>()),
91 pending_rel_seqs(new SnapVector<struct release_seq *>()),
92 thrd_last_action(new SnapVector<ModelAction *>(1)),
93 thrd_last_fence_release(new SnapVector<ModelAction *>()),
94 node_stack(new NodeStack()),
95 priv(new struct model_snapshot_members()),
96 mo_graph(new CycleGraph())
98 /* Initialize a model-checker thread, for special ModelActions */
99 model_thread = new Thread(get_next_id());
100 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
103 /** @brief Destructor */
104 ModelChecker::~ModelChecker()
106 for (unsigned int i = 0; i < get_num_threads(); i++)
107 delete thread_map->get(i);
112 delete lock_waiters_map;
113 delete condvar_waiters_map;
116 for (unsigned int i = 0; i < promises->size(); i++)
117 delete (*promises)[i];
120 delete pending_rel_seqs;
122 delete thrd_last_action;
123 delete thrd_last_fence_release;
130 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
132 action_list_t *tmp = hash->get(ptr);
134 tmp = new action_list_t();
140 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
142 SnapVector<action_list_t> *tmp = hash->get(ptr);
144 tmp = new SnapVector<action_list_t>();
151 * Restores user program to initial state and resets all model-checker data
154 void ModelChecker::reset_to_initial_state()
156 DEBUG("+++ Resetting to initial state +++\n");
157 node_stack->reset_execution();
159 /* Print all model-checker output before rollback */
163 * FIXME: if we utilize partial rollback, we will need to free only
164 * those pending actions which were NOT pending before the rollback
167 for (unsigned int i = 0; i < get_num_threads(); i++)
168 delete get_thread(int_to_id(i))->get_pending();
170 snapshot_backtrack_before(0);
173 /** @return a thread ID for a new Thread */
174 thread_id_t ModelChecker::get_next_id()
176 return priv->next_thread_id++;
179 /** @return the number of user threads created during this execution */
180 unsigned int ModelChecker::get_num_threads() const
182 return priv->next_thread_id;
186 * Must be called from user-thread context (e.g., through the global
187 * thread_current() interface)
189 * @return The currently executing Thread.
191 Thread * ModelChecker::get_current_thread() const
193 return scheduler->get_current_thread();
196 /** @return a sequence number for a new ModelAction */
197 modelclock_t ModelChecker::get_next_seq_num()
199 return ++priv->used_sequence_numbers;
202 Node * ModelChecker::get_curr_node() const
204 return node_stack->get_head();
208 * @brief Select the next thread to execute based on the curren action
210 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
211 * actions should be followed by the execution of their child thread. In either
212 * case, the current action should determine the next thread schedule.
214 * @param curr The current action
215 * @return The next thread to run, if the current action will determine this
216 * selection; otherwise NULL
218 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
220 /* Do not split atomic RMW */
222 return get_thread(curr);
223 /* Follow CREATE with the created thread */
224 if (curr->get_type() == THREAD_CREATE)
225 return curr->get_thread_operand();
230 * @brief Choose the next thread to execute.
232 * This function chooses the next thread that should execute. It can enforce
233 * execution replay/backtracking or, if the model-checker has no preference
234 * regarding the next thread (i.e., when exploring a new execution ordering),
235 * we defer to the scheduler.
237 * @return The next chosen thread to run, if any exist. Or else if the current
238 * execution should terminate, return NULL.
240 Thread * ModelChecker::get_next_thread()
245 * Have we completed exploring the preselected path? Then let the
249 return scheduler->select_next_thread();
251 /* Else, we are trying to replay an execution */
252 ModelAction *next = node_stack->get_next()->get_action();
254 if (next == diverge) {
255 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
256 earliest_diverge = diverge;
258 Node *nextnode = next->get_node();
259 Node *prevnode = nextnode->get_parent();
260 scheduler->update_sleep_set(prevnode);
262 /* Reached divergence point */
263 if (nextnode->increment_misc()) {
264 /* The next node will try to satisfy a different misc_index values. */
265 tid = next->get_tid();
266 node_stack->pop_restofstack(2);
267 } else if (nextnode->increment_promise()) {
268 /* The next node will try to satisfy a different set of promises. */
269 tid = next->get_tid();
270 node_stack->pop_restofstack(2);
271 } else if (nextnode->increment_read_from()) {
272 /* The next node will read from a different value. */
273 tid = next->get_tid();
274 node_stack->pop_restofstack(2);
275 } else if (nextnode->increment_relseq_break()) {
276 /* The next node will try to resolve a release sequence differently */
277 tid = next->get_tid();
278 node_stack->pop_restofstack(2);
281 /* Make a different thread execute for next step */
282 scheduler->add_sleep(get_thread(next->get_tid()));
283 tid = prevnode->get_next_backtrack();
284 /* Make sure the backtracked thread isn't sleeping. */
285 node_stack->pop_restofstack(1);
286 if (diverge == earliest_diverge) {
287 earliest_diverge = prevnode->get_action();
290 /* Start the round robin scheduler from this thread id */
291 scheduler->set_scheduler_thread(tid);
292 /* The correct sleep set is in the parent node. */
295 DEBUG("*** Divergence point ***\n");
299 tid = next->get_tid();
301 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
302 ASSERT(tid != THREAD_ID_T_NONE);
303 return thread_map->get(id_to_int(tid));
307 * We need to know what the next actions of all threads in the sleep
308 * set will be. This method computes them and stores the actions at
309 * the corresponding thread object's pending action.
312 void ModelChecker::execute_sleep_set()
314 for (unsigned int i = 0; i < get_num_threads(); i++) {
315 thread_id_t tid = int_to_id(i);
316 Thread *thr = get_thread(tid);
317 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
318 thr->get_pending()->set_sleep_flag();
324 * @brief Should the current action wake up a given thread?
326 * @param curr The current action
327 * @param thread The thread that we might wake up
328 * @return True, if we should wake up the sleeping thread; false otherwise
330 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
332 const ModelAction *asleep = thread->get_pending();
333 /* Don't allow partial RMW to wake anyone up */
336 /* Synchronizing actions may have been backtracked */
337 if (asleep->could_synchronize_with(curr))
339 /* All acquire/release fences and fence-acquire/store-release */
340 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
342 /* Fence-release + store can awake load-acquire on the same location */
343 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
344 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
345 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
351 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
353 for (unsigned int i = 0; i < get_num_threads(); i++) {
354 Thread *thr = get_thread(int_to_id(i));
355 if (scheduler->is_sleep_set(thr)) {
356 if (should_wake_up(curr, thr))
357 /* Remove this thread from sleep set */
358 scheduler->remove_sleep(thr);
363 /** @brief Alert the model-checker that an incorrectly-ordered
364 * synchronization was made */
365 void ModelChecker::set_bad_synchronization()
367 priv->bad_synchronization = true;
371 * Check whether the current trace has triggered an assertion which should halt
374 * @return True, if the execution should be aborted; false otherwise
376 bool ModelChecker::has_asserted() const
378 return priv->asserted;
382 * Trigger a trace assertion which should cause this execution to be halted.
383 * This can be due to a detected bug or due to an infeasibility that should
386 void ModelChecker::set_assert()
388 priv->asserted = true;
392 * Check if we are in a deadlock. Should only be called at the end of an
393 * execution, although it should not give false positives in the middle of an
394 * execution (there should be some ENABLED thread).
396 * @return True if program is in a deadlock; false otherwise
398 bool ModelChecker::is_deadlocked() const
400 bool blocking_threads = false;
401 for (unsigned int i = 0; i < get_num_threads(); i++) {
402 thread_id_t tid = int_to_id(i);
405 Thread *t = get_thread(tid);
406 if (!t->is_model_thread() && t->get_pending())
407 blocking_threads = true;
409 return blocking_threads;
413 * Check if a Thread has entered a circular wait deadlock situation. This will
414 * not check other threads for potential deadlock situations, and may miss
415 * deadlocks involving WAIT.
417 * @param t The thread which may have entered a deadlock
418 * @return True if this Thread entered a deadlock; false otherwise
420 bool ModelChecker::is_circular_wait(const Thread *t) const
422 for (Thread *waiting = t->waiting_on() ; waiting != NULL; waiting = waiting->waiting_on())
429 * Check if this is a complete execution. That is, have all thread completed
430 * execution (rather than exiting because sleep sets have forced a redundant
433 * @return True if the execution is complete.
435 bool ModelChecker::is_complete_execution() const
437 for (unsigned int i = 0; i < get_num_threads(); i++)
438 if (is_enabled(int_to_id(i)))
444 * @brief Assert a bug in the executing program.
446 * Use this function to assert any sort of bug in the user program. If the
447 * current trace is feasible (actually, a prefix of some feasible execution),
448 * then this execution will be aborted, printing the appropriate message. If
449 * the current trace is not yet feasible, the error message will be stashed and
450 * printed if the execution ever becomes feasible.
452 * @param msg Descriptive message for the bug (do not include newline char)
453 * @return True if bug is immediately-feasible
455 bool ModelChecker::assert_bug(const char *msg)
457 priv->bugs.push_back(new bug_message(msg));
459 if (isfeasibleprefix()) {
467 * @brief Assert a bug in the executing program, asserted by a user thread
468 * @see ModelChecker::assert_bug
469 * @param msg Descriptive message for the bug (do not include newline char)
471 void ModelChecker::assert_user_bug(const char *msg)
473 /* If feasible bug, bail out now */
475 switch_to_master(NULL);
478 /** @return True, if any bugs have been reported for this execution */
479 bool ModelChecker::have_bug_reports() const
481 return priv->bugs.size() != 0;
484 /** @brief Print bug report listing for this execution (if any bugs exist) */
485 void ModelChecker::print_bugs() const
487 if (have_bug_reports()) {
488 model_print("Bug report: %zu bug%s detected\n",
490 priv->bugs.size() > 1 ? "s" : "");
491 for (unsigned int i = 0; i < priv->bugs.size(); i++)
492 priv->bugs[i]->print();
497 * @brief Record end-of-execution stats
499 * Must be run when exiting an execution. Records various stats.
500 * @see struct execution_stats
502 void ModelChecker::record_stats()
505 if (!isfeasibleprefix())
506 stats.num_infeasible++;
507 else if (have_bug_reports())
508 stats.num_buggy_executions++;
509 else if (is_complete_execution())
510 stats.num_complete++;
512 stats.num_redundant++;
515 * @todo We can violate this ASSERT() when fairness/sleep sets
516 * conflict to cause an execution to terminate, e.g. with:
517 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
519 //ASSERT(scheduler->all_threads_sleeping());
523 /** @brief Print execution stats */
524 void ModelChecker::print_stats() const
526 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
527 model_print("Number of redundant executions: %d\n", stats.num_redundant);
528 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
529 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
530 model_print("Total executions: %d\n", stats.num_total);
531 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
535 * @brief End-of-exeuction print
536 * @param printbugs Should any existing bugs be printed?
538 void ModelChecker::print_execution(bool printbugs) const
540 print_program_output();
542 if (params.verbose) {
543 model_print("Earliest divergence point since last feasible execution:\n");
544 if (earliest_diverge)
545 earliest_diverge->print();
547 model_print("(Not set)\n");
553 /* Don't print invalid bugs */
562 * Queries the model-checker for more executions to explore and, if one
563 * exists, resets the model-checker state to execute a new execution.
565 * @return If there are more executions to explore, return true. Otherwise,
568 bool ModelChecker::next_execution()
571 /* Is this execution a feasible execution that's worth bug-checking? */
572 bool complete = isfeasibleprefix() && (is_complete_execution() ||
575 /* End-of-execution bug checks */
578 assert_bug("Deadlock detected");
586 if (params.verbose || (complete && have_bug_reports()))
587 print_execution(complete);
589 clear_program_output();
592 earliest_diverge = NULL;
594 if ((diverge = get_next_backtrack()) == NULL)
598 model_print("Next execution will diverge at:\n");
602 reset_to_initial_state();
607 * @brief Find the last fence-related backtracking conflict for a ModelAction
609 * This function performs the search for the most recent conflicting action
610 * against which we should perform backtracking, as affected by fence
611 * operations. This includes pairs of potentially-synchronizing actions which
612 * occur due to fence-acquire or fence-release, and hence should be explored in
613 * the opposite execution order.
615 * @param act The current action
616 * @return The most recent action which conflicts with act due to fences
618 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
620 /* Only perform release/acquire fence backtracking for stores */
621 if (!act->is_write())
624 /* Find a fence-release (or, act is a release) */
625 ModelAction *last_release;
626 if (act->is_release())
629 last_release = get_last_fence_release(act->get_tid());
633 /* Skip past the release */
634 action_list_t *list = action_trace;
635 action_list_t::reverse_iterator rit;
636 for (rit = list->rbegin(); rit != list->rend(); rit++)
637 if (*rit == last_release)
639 ASSERT(rit != list->rend());
644 * load --sb-> fence-acquire */
645 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
646 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
647 bool found_acquire_fences = false;
648 for ( ; rit != list->rend(); rit++) {
649 ModelAction *prev = *rit;
650 if (act->same_thread(prev))
653 int tid = id_to_int(prev->get_tid());
655 if (prev->is_read() && act->same_var(prev)) {
656 if (prev->is_acquire()) {
657 /* Found most recent load-acquire, don't need
658 * to search for more fences */
659 if (!found_acquire_fences)
662 prior_loads[tid] = prev;
665 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
666 found_acquire_fences = true;
667 acquire_fences[tid] = prev;
671 ModelAction *latest_backtrack = NULL;
672 for (unsigned int i = 0; i < acquire_fences.size(); i++)
673 if (acquire_fences[i] && prior_loads[i])
674 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
675 latest_backtrack = acquire_fences[i];
676 return latest_backtrack;
680 * @brief Find the last backtracking conflict for a ModelAction
682 * This function performs the search for the most recent conflicting action
683 * against which we should perform backtracking. This primary includes pairs of
684 * synchronizing actions which should be explored in the opposite execution
687 * @param act The current action
688 * @return The most recent action which conflicts with act
690 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
692 switch (act->get_type()) {
693 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
697 ModelAction *ret = NULL;
699 /* linear search: from most recent to oldest */
700 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
701 action_list_t::reverse_iterator rit;
702 for (rit = list->rbegin(); rit != list->rend(); rit++) {
703 ModelAction *prev = *rit;
704 if (prev->could_synchronize_with(act)) {
710 ModelAction *ret2 = get_last_fence_conflict(act);
720 case ATOMIC_TRYLOCK: {
721 /* linear search: from most recent to oldest */
722 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
723 action_list_t::reverse_iterator rit;
724 for (rit = list->rbegin(); rit != list->rend(); rit++) {
725 ModelAction *prev = *rit;
726 if (act->is_conflicting_lock(prev))
731 case ATOMIC_UNLOCK: {
732 /* linear search: from most recent to oldest */
733 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
734 action_list_t::reverse_iterator rit;
735 for (rit = list->rbegin(); rit != list->rend(); rit++) {
736 ModelAction *prev = *rit;
737 if (!act->same_thread(prev) && prev->is_failed_trylock())
743 /* linear search: from most recent to oldest */
744 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
745 action_list_t::reverse_iterator rit;
746 for (rit = list->rbegin(); rit != list->rend(); rit++) {
747 ModelAction *prev = *rit;
748 if (!act->same_thread(prev) && prev->is_failed_trylock())
750 if (!act->same_thread(prev) && prev->is_notify())
756 case ATOMIC_NOTIFY_ALL:
757 case ATOMIC_NOTIFY_ONE: {
758 /* linear search: from most recent to oldest */
759 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
760 action_list_t::reverse_iterator rit;
761 for (rit = list->rbegin(); rit != list->rend(); rit++) {
762 ModelAction *prev = *rit;
763 if (!act->same_thread(prev) && prev->is_wait())
774 /** This method finds backtracking points where we should try to
775 * reorder the parameter ModelAction against.
777 * @param the ModelAction to find backtracking points for.
779 void ModelChecker::set_backtracking(ModelAction *act)
781 Thread *t = get_thread(act);
782 ModelAction *prev = get_last_conflict(act);
786 Node *node = prev->get_node()->get_parent();
788 int low_tid, high_tid;
789 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
790 low_tid = id_to_int(act->get_tid());
791 high_tid = low_tid + 1;
794 high_tid = get_num_threads();
797 for (int i = low_tid; i < high_tid; i++) {
798 thread_id_t tid = int_to_id(i);
800 /* Make sure this thread can be enabled here. */
801 if (i >= node->get_num_threads())
804 /* Don't backtrack into a point where the thread is disabled or sleeping. */
805 if (node->enabled_status(tid) != THREAD_ENABLED)
808 /* Check if this has been explored already */
809 if (node->has_been_explored(tid))
812 /* See if fairness allows */
813 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
815 for (int t = 0; t < node->get_num_threads(); t++) {
816 thread_id_t tother = int_to_id(t);
817 if (node->is_enabled(tother) && node->has_priority(tother)) {
826 /* See if CHESS-like yield fairness allows */
827 if (model->params.yieldon) {
829 for (int t = 0; t < node->get_num_threads(); t++) {
830 thread_id_t tother = int_to_id(t);
831 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
840 /* Cache the latest backtracking point */
841 set_latest_backtrack(prev);
843 /* If this is a new backtracking point, mark the tree */
844 if (!node->set_backtrack(tid))
846 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
847 id_to_int(prev->get_tid()),
848 id_to_int(t->get_id()));
857 * @brief Cache the a backtracking point as the "most recent", if eligible
859 * Note that this does not prepare the NodeStack for this backtracking
860 * operation, it only caches the action on a per-execution basis
862 * @param act The operation at which we should explore a different next action
863 * (i.e., backtracking point)
864 * @return True, if this action is now the most recent backtracking point;
867 bool ModelChecker::set_latest_backtrack(ModelAction *act)
869 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
870 priv->next_backtrack = act;
877 * Returns last backtracking point. The model checker will explore a different
878 * path for this point in the next execution.
879 * @return The ModelAction at which the next execution should diverge.
881 ModelAction * ModelChecker::get_next_backtrack()
883 ModelAction *next = priv->next_backtrack;
884 priv->next_backtrack = NULL;
889 * Processes a read model action.
890 * @param curr is the read model action to process.
891 * @return True if processing this read updates the mo_graph.
893 bool ModelChecker::process_read(ModelAction *curr)
895 Node *node = curr->get_node();
897 bool updated = false;
898 switch (node->get_read_from_status()) {
899 case READ_FROM_PAST: {
900 const ModelAction *rf = node->get_read_from_past();
903 mo_graph->startChanges();
905 ASSERT(!is_infeasible());
906 if (!check_recency(curr, rf)) {
907 if (node->increment_read_from()) {
908 mo_graph->rollbackChanges();
911 priv->too_many_reads = true;
915 updated = r_modification_order(curr, rf);
917 mo_graph->commitChanges();
918 mo_check_promises(curr, true);
921 case READ_FROM_PROMISE: {
922 Promise *promise = curr->get_node()->get_read_from_promise();
923 if (promise->add_reader(curr))
924 priv->failed_promise = true;
925 curr->set_read_from_promise(promise);
926 mo_graph->startChanges();
927 if (!check_recency(curr, promise))
928 priv->too_many_reads = true;
929 updated = r_modification_order(curr, promise);
930 mo_graph->commitChanges();
933 case READ_FROM_FUTURE: {
934 /* Read from future value */
935 struct future_value fv = node->get_future_value();
936 Promise *promise = new Promise(curr, fv);
937 curr->set_read_from_promise(promise);
938 promises->push_back(promise);
939 mo_graph->startChanges();
940 updated = r_modification_order(curr, promise);
941 mo_graph->commitChanges();
947 get_thread(curr)->set_return_value(curr->get_return_value());
953 * Processes a lock, trylock, or unlock model action. @param curr is
954 * the read model action to process.
956 * The try lock operation checks whether the lock is taken. If not,
957 * it falls to the normal lock operation case. If so, it returns
960 * The lock operation has already been checked that it is enabled, so
961 * it just grabs the lock and synchronizes with the previous unlock.
963 * The unlock operation has to re-enable all of the threads that are
964 * waiting on the lock.
966 * @return True if synchronization was updated; false otherwise
968 bool ModelChecker::process_mutex(ModelAction *curr)
970 std::mutex *mutex = curr->get_mutex();
971 struct std::mutex_state *state = NULL;
974 state = mutex->get_state();
976 switch (curr->get_type()) {
977 case ATOMIC_TRYLOCK: {
978 bool success = !state->locked;
979 curr->set_try_lock(success);
981 get_thread(curr)->set_return_value(0);
984 get_thread(curr)->set_return_value(1);
986 //otherwise fall into the lock case
988 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
989 assert_bug("Lock access before initialization");
990 state->locked = get_thread(curr);
991 ModelAction *unlock = get_last_unlock(curr);
992 //synchronize with the previous unlock statement
993 if (unlock != NULL) {
994 curr->synchronize_with(unlock);
999 case ATOMIC_UNLOCK: {
1001 state->locked = NULL;
1002 //wake up the other threads
1003 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
1004 //activate all the waiting threads
1005 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1006 scheduler->wake(get_thread(*rit));
1013 state->locked = NULL;
1014 //wake up the other threads
1015 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
1016 //activate all the waiting threads
1017 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1018 scheduler->wake(get_thread(*rit));
1021 //check whether we should go to sleep or not...simulate spurious failures
1022 if (curr->get_node()->get_misc() == 0) {
1023 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1025 scheduler->sleep(get_thread(curr));
1029 case ATOMIC_NOTIFY_ALL: {
1030 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1031 //activate all the waiting threads
1032 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1033 scheduler->wake(get_thread(*rit));
1038 case ATOMIC_NOTIFY_ONE: {
1039 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1040 int wakeupthread = curr->get_node()->get_misc();
1041 action_list_t::iterator it = waiters->begin();
1042 advance(it, wakeupthread);
1043 scheduler->wake(get_thread(*it));
1055 * @brief Add a future value to a reader
1057 * This function performs a few additional checks to ensure that the future
1058 * value can be feasibly observed by the reader
1060 * @param writer The operation whose value is sent. Must be a write.
1061 * @param reader The read operation which may read the future value. Must be a read.
1063 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1065 /* Do more ambitious checks now that mo is more complete */
1066 if (!mo_may_allow(writer, reader))
1069 Node *node = reader->get_node();
1071 /* Find an ancestor thread which exists at the time of the reader */
1072 Thread *write_thread = get_thread(writer);
1073 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1074 write_thread = write_thread->get_parent();
1076 struct future_value fv = {
1077 writer->get_write_value(),
1078 writer->get_seq_number() + params.maxfuturedelay,
1079 write_thread->get_id(),
1081 if (node->add_future_value(fv))
1082 set_latest_backtrack(reader);
1086 * Process a write ModelAction
1087 * @param curr The ModelAction to process
1088 * @return True if the mo_graph was updated or promises were resolved
1090 bool ModelChecker::process_write(ModelAction *curr)
1092 /* Readers to which we may send our future value */
1093 ModelVector<ModelAction *> send_fv;
1095 const ModelAction *earliest_promise_reader;
1096 bool updated_promises = false;
1098 bool updated_mod_order = w_modification_order(curr, &send_fv);
1099 Promise *promise = pop_promise_to_resolve(curr);
1102 earliest_promise_reader = promise->get_reader(0);
1103 updated_promises = resolve_promise(curr, promise);
1105 earliest_promise_reader = NULL;
1107 /* Don't send future values to reads after the Promise we resolve */
1108 for (unsigned int i = 0; i < send_fv.size(); i++) {
1109 ModelAction *read = send_fv[i];
1110 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1111 futurevalues->push_back(PendingFutureValue(curr, read));
1114 if (promises->empty()) {
1115 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1116 struct PendingFutureValue pfv = (*futurevalues)[i];
1117 add_future_value(pfv.writer, pfv.reader);
1119 futurevalues->clear();
1122 mo_graph->commitChanges();
1123 mo_check_promises(curr, false);
1125 get_thread(curr)->set_return_value(VALUE_NONE);
1126 return updated_mod_order || updated_promises;
1130 * Process a fence ModelAction
1131 * @param curr The ModelAction to process
1132 * @return True if synchronization was updated
1134 bool ModelChecker::process_fence(ModelAction *curr)
1137 * fence-relaxed: no-op
1138 * fence-release: only log the occurence (not in this function), for
1139 * use in later synchronization
1140 * fence-acquire (this function): search for hypothetical release
1142 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1144 bool updated = false;
1145 if (curr->is_acquire()) {
1146 action_list_t *list = action_trace;
1147 action_list_t::reverse_iterator rit;
1148 /* Find X : is_read(X) && X --sb-> curr */
1149 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1150 ModelAction *act = *rit;
1153 if (act->get_tid() != curr->get_tid())
1155 /* Stop at the beginning of the thread */
1156 if (act->is_thread_start())
1158 /* Stop once we reach a prior fence-acquire */
1159 if (act->is_fence() && act->is_acquire())
1161 if (!act->is_read())
1163 /* read-acquire will find its own release sequences */
1164 if (act->is_acquire())
1167 /* Establish hypothetical release sequences */
1168 rel_heads_list_t release_heads;
1169 get_release_seq_heads(curr, act, &release_heads);
1170 for (unsigned int i = 0; i < release_heads.size(); i++)
1171 if (!curr->synchronize_with(release_heads[i]))
1172 set_bad_synchronization();
1173 if (release_heads.size() != 0)
1181 * @brief Process the current action for thread-related activity
1183 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1184 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1185 * synchronization, etc. This function is a no-op for non-THREAD actions
1186 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1188 * @param curr The current action
1189 * @return True if synchronization was updated or a thread completed
1191 bool ModelChecker::process_thread_action(ModelAction *curr)
1193 bool updated = false;
1195 switch (curr->get_type()) {
1196 case THREAD_CREATE: {
1197 thrd_t *thrd = (thrd_t *)curr->get_location();
1198 struct thread_params *params = (struct thread_params *)curr->get_value();
1199 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1201 th->set_creation(curr);
1202 /* Promises can be satisfied by children */
1203 for (unsigned int i = 0; i < promises->size(); i++) {
1204 Promise *promise = (*promises)[i];
1205 if (promise->thread_is_available(curr->get_tid()))
1206 promise->add_thread(th->get_id());
1211 Thread *blocking = curr->get_thread_operand();
1212 ModelAction *act = get_last_action(blocking->get_id());
1213 curr->synchronize_with(act);
1214 updated = true; /* trigger rel-seq checks */
1217 case THREAD_FINISH: {
1218 Thread *th = get_thread(curr);
1219 while (!th->wait_list_empty()) {
1220 ModelAction *act = th->pop_wait_list();
1221 scheduler->wake(get_thread(act));
1224 /* Completed thread can't satisfy promises */
1225 for (unsigned int i = 0; i < promises->size(); i++) {
1226 Promise *promise = (*promises)[i];
1227 if (promise->thread_is_available(th->get_id()))
1228 if (promise->eliminate_thread(th->get_id()))
1229 priv->failed_promise = true;
1231 updated = true; /* trigger rel-seq checks */
1234 case THREAD_START: {
1235 check_promises(curr->get_tid(), NULL, curr->get_cv());
1246 * @brief Process the current action for release sequence fixup activity
1248 * Performs model-checker release sequence fixups for the current action,
1249 * forcing a single pending release sequence to break (with a given, potential
1250 * "loose" write) or to complete (i.e., synchronize). If a pending release
1251 * sequence forms a complete release sequence, then we must perform the fixup
1252 * synchronization, mo_graph additions, etc.
1254 * @param curr The current action; must be a release sequence fixup action
1255 * @param work_queue The work queue to which to add work items as they are
1258 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1260 const ModelAction *write = curr->get_node()->get_relseq_break();
1261 struct release_seq *sequence = pending_rel_seqs->back();
1262 pending_rel_seqs->pop_back();
1264 ModelAction *acquire = sequence->acquire;
1265 const ModelAction *rf = sequence->rf;
1266 const ModelAction *release = sequence->release;
1270 ASSERT(release->same_thread(rf));
1272 if (write == NULL) {
1274 * @todo Forcing a synchronization requires that we set
1275 * modification order constraints. For instance, we can't allow
1276 * a fixup sequence in which two separate read-acquire
1277 * operations read from the same sequence, where the first one
1278 * synchronizes and the other doesn't. Essentially, we can't
1279 * allow any writes to insert themselves between 'release' and
1283 /* Must synchronize */
1284 if (!acquire->synchronize_with(release)) {
1285 set_bad_synchronization();
1288 /* Re-check all pending release sequences */
1289 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1290 /* Re-check act for mo_graph edges */
1291 work_queue->push_back(MOEdgeWorkEntry(acquire));
1293 /* propagate synchronization to later actions */
1294 action_list_t::reverse_iterator rit = action_trace->rbegin();
1295 for (; (*rit) != acquire; rit++) {
1296 ModelAction *propagate = *rit;
1297 if (acquire->happens_before(propagate)) {
1298 propagate->synchronize_with(acquire);
1299 /* Re-check 'propagate' for mo_graph edges */
1300 work_queue->push_back(MOEdgeWorkEntry(propagate));
1304 /* Break release sequence with new edges:
1305 * release --mo--> write --mo--> rf */
1306 mo_graph->addEdge(release, write);
1307 mo_graph->addEdge(write, rf);
1310 /* See if we have realized a data race */
1315 * Initialize the current action by performing one or more of the following
1316 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1317 * in the NodeStack, manipulating backtracking sets, allocating and
1318 * initializing clock vectors, and computing the promises to fulfill.
1320 * @param curr The current action, as passed from the user context; may be
1321 * freed/invalidated after the execution of this function, with a different
1322 * action "returned" its place (pass-by-reference)
1323 * @return True if curr is a newly-explored action; false otherwise
1325 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1327 ModelAction *newcurr;
1329 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1330 newcurr = process_rmw(*curr);
1333 if (newcurr->is_rmw())
1334 compute_promises(newcurr);
1340 (*curr)->set_seq_number(get_next_seq_num());
1342 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1344 /* First restore type and order in case of RMW operation */
1345 if ((*curr)->is_rmwr())
1346 newcurr->copy_typeandorder(*curr);
1348 ASSERT((*curr)->get_location() == newcurr->get_location());
1349 newcurr->copy_from_new(*curr);
1351 /* Discard duplicate ModelAction; use action from NodeStack */
1354 /* Always compute new clock vector */
1355 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1358 return false; /* Action was explored previously */
1362 /* Always compute new clock vector */
1363 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1365 /* Assign most recent release fence */
1366 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1369 * Perform one-time actions when pushing new ModelAction onto
1372 if (newcurr->is_write())
1373 compute_promises(newcurr);
1374 else if (newcurr->is_relseq_fixup())
1375 compute_relseq_breakwrites(newcurr);
1376 else if (newcurr->is_wait())
1377 newcurr->get_node()->set_misc_max(2);
1378 else if (newcurr->is_notify_one()) {
1379 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1381 return true; /* This was a new ModelAction */
1386 * @brief Establish reads-from relation between two actions
1388 * Perform basic operations involved with establishing a concrete rf relation,
1389 * including setting the ModelAction data and checking for release sequences.
1391 * @param act The action that is reading (must be a read)
1392 * @param rf The action from which we are reading (must be a write)
1394 * @return True if this read established synchronization
1396 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1399 ASSERT(rf->is_write());
1401 act->set_read_from(rf);
1402 if (act->is_acquire()) {
1403 rel_heads_list_t release_heads;
1404 get_release_seq_heads(act, act, &release_heads);
1405 int num_heads = release_heads.size();
1406 for (unsigned int i = 0; i < release_heads.size(); i++)
1407 if (!act->synchronize_with(release_heads[i])) {
1408 set_bad_synchronization();
1411 return num_heads > 0;
1417 * Check promises and eliminate potentially-satisfying threads when a thread is
1418 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1419 * no longer satisfy a promise generated from that thread.
1421 * @param blocker The thread on which a thread is waiting
1422 * @param waiting The waiting thread
1424 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1426 for (unsigned int i = 0; i < promises->size(); i++) {
1427 Promise *promise = (*promises)[i];
1428 if (!promise->thread_is_available(waiting->get_id()))
1430 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1431 ModelAction *reader = promise->get_reader(j);
1432 if (reader->get_tid() != blocker->get_id())
1434 if (promise->eliminate_thread(waiting->get_id())) {
1435 /* Promise has failed */
1436 priv->failed_promise = true;
1438 /* Only eliminate the 'waiting' thread once */
1446 * @brief Check whether a model action is enabled.
1448 * Checks whether a lock or join operation would be successful (i.e., is the
1449 * lock already locked, or is the joined thread already complete). If not, put
1450 * the action in a waiter list.
1452 * @param curr is the ModelAction to check whether it is enabled.
1453 * @return a bool that indicates whether the action is enabled.
1455 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1456 if (curr->is_lock()) {
1457 std::mutex *lock = (std::mutex *)curr->get_location();
1458 struct std::mutex_state *state = lock->get_state();
1459 if (state->locked) {
1460 //Stick the action in the appropriate waiting queue
1461 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1464 } else if (curr->get_type() == THREAD_JOIN) {
1465 Thread *blocking = (Thread *)curr->get_location();
1466 if (!blocking->is_complete()) {
1467 blocking->push_wait_list(curr);
1468 thread_blocking_check_promises(blocking, get_thread(curr));
1477 * This is the heart of the model checker routine. It performs model-checking
1478 * actions corresponding to a given "current action." Among other processes, it
1479 * calculates reads-from relationships, updates synchronization clock vectors,
1480 * forms a memory_order constraints graph, and handles replay/backtrack
1481 * execution when running permutations of previously-observed executions.
1483 * @param curr The current action to process
1484 * @return The ModelAction that is actually executed; may be different than
1485 * curr; may be NULL, if the current action is not enabled to run
1487 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1490 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1492 if (!check_action_enabled(curr)) {
1493 /* Make the execution look like we chose to run this action
1494 * much later, when a lock/join can succeed */
1495 get_thread(curr)->set_pending(curr);
1496 scheduler->sleep(get_thread(curr));
1500 bool newly_explored = initialize_curr_action(&curr);
1506 wake_up_sleeping_actions(curr);
1508 /* Compute fairness information for CHESS yield algorithm */
1509 if (model->params.yieldon) {
1510 curr->get_node()->update_yield(scheduler);
1513 /* Add the action to lists before any other model-checking tasks */
1514 if (!second_part_of_rmw)
1515 add_action_to_lists(curr);
1517 /* Build may_read_from set for newly-created actions */
1518 if (newly_explored && curr->is_read())
1519 build_may_read_from(curr);
1521 /* Initialize work_queue with the "current action" work */
1522 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1523 while (!work_queue.empty() && !has_asserted()) {
1524 WorkQueueEntry work = work_queue.front();
1525 work_queue.pop_front();
1527 switch (work.type) {
1528 case WORK_CHECK_CURR_ACTION: {
1529 ModelAction *act = work.action;
1530 bool update = false; /* update this location's release seq's */
1531 bool update_all = false; /* update all release seq's */
1533 if (process_thread_action(curr))
1536 if (act->is_read() && !second_part_of_rmw && process_read(act))
1539 if (act->is_write() && process_write(act))
1542 if (act->is_fence() && process_fence(act))
1545 if (act->is_mutex_op() && process_mutex(act))
1548 if (act->is_relseq_fixup())
1549 process_relseq_fixup(curr, &work_queue);
1552 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1554 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1557 case WORK_CHECK_RELEASE_SEQ:
1558 resolve_release_sequences(work.location, &work_queue);
1560 case WORK_CHECK_MO_EDGES: {
1561 /** @todo Complete verification of work_queue */
1562 ModelAction *act = work.action;
1563 bool updated = false;
1565 if (act->is_read()) {
1566 const ModelAction *rf = act->get_reads_from();
1567 const Promise *promise = act->get_reads_from_promise();
1569 if (r_modification_order(act, rf))
1571 } else if (promise) {
1572 if (r_modification_order(act, promise))
1576 if (act->is_write()) {
1577 if (w_modification_order(act, NULL))
1580 mo_graph->commitChanges();
1583 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1592 check_curr_backtracking(curr);
1593 set_backtracking(curr);
1597 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1599 Node *currnode = curr->get_node();
1600 Node *parnode = currnode->get_parent();
1602 if ((parnode && !parnode->backtrack_empty()) ||
1603 !currnode->misc_empty() ||
1604 !currnode->read_from_empty() ||
1605 !currnode->promise_empty() ||
1606 !currnode->relseq_break_empty()) {
1607 set_latest_backtrack(curr);
1611 bool ModelChecker::promises_expired() const
1613 for (unsigned int i = 0; i < promises->size(); i++) {
1614 Promise *promise = (*promises)[i];
1615 if (promise->get_expiration() < priv->used_sequence_numbers)
1622 * This is the strongest feasibility check available.
1623 * @return whether the current trace (partial or complete) must be a prefix of
1626 bool ModelChecker::isfeasibleprefix() const
1628 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1632 * Print disagnostic information about an infeasible execution
1633 * @param prefix A string to prefix the output with; if NULL, then a default
1634 * message prefix will be provided
1636 void ModelChecker::print_infeasibility(const char *prefix) const
1640 if (mo_graph->checkForCycles())
1641 ptr += sprintf(ptr, "[mo cycle]");
1642 if (priv->failed_promise)
1643 ptr += sprintf(ptr, "[failed promise]");
1644 if (priv->too_many_reads)
1645 ptr += sprintf(ptr, "[too many reads]");
1646 if (priv->no_valid_reads)
1647 ptr += sprintf(ptr, "[no valid reads-from]");
1648 if (priv->bad_synchronization)
1649 ptr += sprintf(ptr, "[bad sw ordering]");
1650 if (promises_expired())
1651 ptr += sprintf(ptr, "[promise expired]");
1652 if (promises->size() != 0)
1653 ptr += sprintf(ptr, "[unresolved promise]");
1655 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1659 * Returns whether the current completed trace is feasible, except for pending
1660 * release sequences.
1662 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1664 return !is_infeasible() && promises->size() == 0;
1668 * Check if the current partial trace is infeasible. Does not check any
1669 * end-of-execution flags, which might rule out the execution. Thus, this is
1670 * useful only for ruling an execution as infeasible.
1671 * @return whether the current partial trace is infeasible.
1673 bool ModelChecker::is_infeasible() const
1675 return mo_graph->checkForCycles() ||
1676 priv->no_valid_reads ||
1677 priv->failed_promise ||
1678 priv->too_many_reads ||
1679 priv->bad_synchronization ||
1683 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1684 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1685 ModelAction *lastread = get_last_action(act->get_tid());
1686 lastread->process_rmw(act);
1687 if (act->is_rmw()) {
1688 if (lastread->get_reads_from())
1689 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1691 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1692 mo_graph->commitChanges();
1698 * A helper function for ModelChecker::check_recency, to check if the current
1699 * thread is able to read from a different write/promise for 'params.maxreads'
1700 * number of steps and if that write/promise should become visible (i.e., is
1701 * ordered later in the modification order). This helps model memory liveness.
1703 * @param curr The current action. Must be a read.
1704 * @param rf The write/promise from which we plan to read
1705 * @param other_rf The write/promise from which we may read
1706 * @return True if we were able to read from other_rf for params.maxreads steps
1708 template <typename T, typename U>
1709 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1711 /* Need a different write/promise */
1712 if (other_rf->equals(rf))
1715 /* Only look for "newer" writes/promises */
1716 if (!mo_graph->checkReachable(rf, other_rf))
1719 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1720 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1721 action_list_t::reverse_iterator rit = list->rbegin();
1722 ASSERT((*rit) == curr);
1723 /* Skip past curr */
1726 /* Does this write/promise work for everyone? */
1727 for (int i = 0; i < params.maxreads; i++, rit++) {
1728 ModelAction *act = *rit;
1729 if (!act->may_read_from(other_rf))
1736 * Checks whether a thread has read from the same write or Promise for too many
1737 * times without seeing the effects of a later write/Promise.
1740 * 1) there must a different write/promise that we could read from,
1741 * 2) we must have read from the same write/promise in excess of maxreads times,
1742 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1743 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1745 * If so, we decide that the execution is no longer feasible.
1747 * @param curr The current action. Must be a read.
1748 * @param rf The ModelAction/Promise from which we might read.
1749 * @return True if the read should succeed; false otherwise
1751 template <typename T>
1752 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1754 if (!params.maxreads)
1757 //NOTE: Next check is just optimization, not really necessary....
1758 if (curr->get_node()->get_read_from_past_size() +
1759 curr->get_node()->get_read_from_promise_size() <= 1)
1762 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1763 int tid = id_to_int(curr->get_tid());
1764 ASSERT(tid < (int)thrd_lists->size());
1765 action_list_t *list = &(*thrd_lists)[tid];
1766 action_list_t::reverse_iterator rit = list->rbegin();
1767 ASSERT((*rit) == curr);
1768 /* Skip past curr */
1771 action_list_t::reverse_iterator ritcopy = rit;
1772 /* See if we have enough reads from the same value */
1773 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1774 if (ritcopy == list->rend())
1776 ModelAction *act = *ritcopy;
1777 if (!act->is_read())
1779 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1781 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1783 if (act->get_node()->get_read_from_past_size() +
1784 act->get_node()->get_read_from_promise_size() <= 1)
1787 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1788 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1789 if (should_read_instead(curr, rf, write))
1790 return false; /* liveness failure */
1792 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1793 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1794 if (should_read_instead(curr, rf, promise))
1795 return false; /* liveness failure */
1801 * Updates the mo_graph with the constraints imposed from the current
1804 * Basic idea is the following: Go through each other thread and find
1805 * the last action that happened before our read. Two cases:
1807 * (1) The action is a write => that write must either occur before
1808 * the write we read from or be the write we read from.
1810 * (2) The action is a read => the write that that action read from
1811 * must occur before the write we read from or be the same write.
1813 * @param curr The current action. Must be a read.
1814 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1815 * @return True if modification order edges were added; false otherwise
1817 template <typename rf_type>
1818 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1820 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1823 ASSERT(curr->is_read());
1825 /* Last SC fence in the current thread */
1826 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1827 ModelAction *last_sc_write = NULL;
1828 if (curr->is_seqcst())
1829 last_sc_write = get_last_seq_cst_write(curr);
1831 /* Iterate over all threads */
1832 for (i = 0; i < thrd_lists->size(); i++) {
1833 /* Last SC fence in thread i */
1834 ModelAction *last_sc_fence_thread_local = NULL;
1835 if (int_to_id((int)i) != curr->get_tid())
1836 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1838 /* Last SC fence in thread i, before last SC fence in current thread */
1839 ModelAction *last_sc_fence_thread_before = NULL;
1840 if (last_sc_fence_local)
1841 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1843 /* Iterate over actions in thread, starting from most recent */
1844 action_list_t *list = &(*thrd_lists)[i];
1845 action_list_t::reverse_iterator rit;
1846 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1847 ModelAction *act = *rit;
1852 /* Don't want to add reflexive edges on 'rf' */
1853 if (act->equals(rf)) {
1854 if (act->happens_before(curr))
1860 if (act->is_write()) {
1861 /* C++, Section 29.3 statement 5 */
1862 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1863 *act < *last_sc_fence_thread_local) {
1864 added = mo_graph->addEdge(act, rf) || added;
1867 /* C++, Section 29.3 statement 4 */
1868 else if (act->is_seqcst() && last_sc_fence_local &&
1869 *act < *last_sc_fence_local) {
1870 added = mo_graph->addEdge(act, rf) || added;
1873 /* C++, Section 29.3 statement 6 */
1874 else if (last_sc_fence_thread_before &&
1875 *act < *last_sc_fence_thread_before) {
1876 added = mo_graph->addEdge(act, rf) || added;
1881 /* C++, Section 29.3 statement 3 (second subpoint) */
1882 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1883 added = mo_graph->addEdge(act, rf) || added;
1888 * Include at most one act per-thread that "happens
1891 if (act->happens_before(curr)) {
1892 if (act->is_write()) {
1893 added = mo_graph->addEdge(act, rf) || added;
1895 const ModelAction *prevrf = act->get_reads_from();
1896 const Promise *prevrf_promise = act->get_reads_from_promise();
1898 if (!prevrf->equals(rf))
1899 added = mo_graph->addEdge(prevrf, rf) || added;
1900 } else if (!prevrf_promise->equals(rf)) {
1901 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1910 * All compatible, thread-exclusive promises must be ordered after any
1911 * concrete loads from the same thread
1913 for (unsigned int i = 0; i < promises->size(); i++)
1914 if ((*promises)[i]->is_compatible_exclusive(curr))
1915 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1921 * Updates the mo_graph with the constraints imposed from the current write.
1923 * Basic idea is the following: Go through each other thread and find
1924 * the lastest action that happened before our write. Two cases:
1926 * (1) The action is a write => that write must occur before
1929 * (2) The action is a read => the write that that action read from
1930 * must occur before the current write.
1932 * This method also handles two other issues:
1934 * (I) Sequential Consistency: Making sure that if the current write is
1935 * seq_cst, that it occurs after the previous seq_cst write.
1937 * (II) Sending the write back to non-synchronizing reads.
1939 * @param curr The current action. Must be a write.
1940 * @param send_fv A vector for stashing reads to which we may pass our future
1941 * value. If NULL, then don't record any future values.
1942 * @return True if modification order edges were added; false otherwise
1944 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1946 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1949 ASSERT(curr->is_write());
1951 if (curr->is_seqcst()) {
1952 /* We have to at least see the last sequentially consistent write,
1953 so we are initialized. */
1954 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1955 if (last_seq_cst != NULL) {
1956 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1960 /* Last SC fence in the current thread */
1961 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1963 /* Iterate over all threads */
1964 for (i = 0; i < thrd_lists->size(); i++) {
1965 /* Last SC fence in thread i, before last SC fence in current thread */
1966 ModelAction *last_sc_fence_thread_before = NULL;
1967 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1968 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1970 /* Iterate over actions in thread, starting from most recent */
1971 action_list_t *list = &(*thrd_lists)[i];
1972 action_list_t::reverse_iterator rit;
1973 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1974 ModelAction *act = *rit;
1977 * 1) If RMW and it actually read from something, then we
1978 * already have all relevant edges, so just skip to next
1981 * 2) If RMW and it didn't read from anything, we should
1982 * whatever edge we can get to speed up convergence.
1984 * 3) If normal write, we need to look at earlier actions, so
1985 * continue processing list.
1987 if (curr->is_rmw()) {
1988 if (curr->get_reads_from() != NULL)
1996 /* C++, Section 29.3 statement 7 */
1997 if (last_sc_fence_thread_before && act->is_write() &&
1998 *act < *last_sc_fence_thread_before) {
1999 added = mo_graph->addEdge(act, curr) || added;
2004 * Include at most one act per-thread that "happens
2007 if (act->happens_before(curr)) {
2009 * Note: if act is RMW, just add edge:
2011 * The following edge should be handled elsewhere:
2012 * readfrom(act) --mo--> act
2014 if (act->is_write())
2015 added = mo_graph->addEdge(act, curr) || added;
2016 else if (act->is_read()) {
2017 //if previous read accessed a null, just keep going
2018 if (act->get_reads_from() == NULL)
2020 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2023 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2024 !act->same_thread(curr)) {
2025 /* We have an action that:
2026 (1) did not happen before us
2027 (2) is a read and we are a write
2028 (3) cannot synchronize with us
2029 (4) is in a different thread
2031 that read could potentially read from our write. Note that
2032 these checks are overly conservative at this point, we'll
2033 do more checks before actually removing the
2037 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2038 if (!is_infeasible())
2039 send_fv->push_back(act);
2040 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2041 add_future_value(curr, act);
2048 * All compatible, thread-exclusive promises must be ordered after any
2049 * concrete stores to the same thread, or else they can be merged with
2052 for (unsigned int i = 0; i < promises->size(); i++)
2053 if ((*promises)[i]->is_compatible_exclusive(curr))
2054 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2059 /** Arbitrary reads from the future are not allowed. Section 29.3
2060 * part 9 places some constraints. This method checks one result of constraint
2061 * constraint. Others require compiler support. */
2062 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2064 if (!writer->is_rmw())
2067 if (!reader->is_rmw())
2070 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2071 if (search == reader)
2073 if (search->get_tid() == reader->get_tid() &&
2074 search->happens_before(reader))
2082 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2083 * some constraints. This method checks one the following constraint (others
2084 * require compiler support):
2086 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2088 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2090 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2092 /* Iterate over all threads */
2093 for (i = 0; i < thrd_lists->size(); i++) {
2094 const ModelAction *write_after_read = NULL;
2096 /* Iterate over actions in thread, starting from most recent */
2097 action_list_t *list = &(*thrd_lists)[i];
2098 action_list_t::reverse_iterator rit;
2099 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2100 ModelAction *act = *rit;
2102 /* Don't disallow due to act == reader */
2103 if (!reader->happens_before(act) || reader == act)
2105 else if (act->is_write())
2106 write_after_read = act;
2107 else if (act->is_read() && act->get_reads_from() != NULL)
2108 write_after_read = act->get_reads_from();
2111 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2118 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2119 * The ModelAction under consideration is expected to be taking part in
2120 * release/acquire synchronization as an object of the "reads from" relation.
2121 * Note that this can only provide release sequence support for RMW chains
2122 * which do not read from the future, as those actions cannot be traced until
2123 * their "promise" is fulfilled. Similarly, we may not even establish the
2124 * presence of a release sequence with certainty, as some modification order
2125 * constraints may be decided further in the future. Thus, this function
2126 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2127 * and a boolean representing certainty.
2129 * @param rf The action that might be part of a release sequence. Must be a
2131 * @param release_heads A pass-by-reference style return parameter. After
2132 * execution of this function, release_heads will contain the heads of all the
2133 * relevant release sequences, if any exists with certainty
2134 * @param pending A pass-by-reference style return parameter which is only used
2135 * when returning false (i.e., uncertain). Returns most information regarding
2136 * an uncertain release sequence, including any write operations that might
2137 * break the sequence.
2138 * @return true, if the ModelChecker is certain that release_heads is complete;
2141 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2142 rel_heads_list_t *release_heads,
2143 struct release_seq *pending) const
2145 /* Only check for release sequences if there are no cycles */
2146 if (mo_graph->checkForCycles())
2149 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2150 ASSERT(rf->is_write());
2152 if (rf->is_release())
2153 release_heads->push_back(rf);
2154 else if (rf->get_last_fence_release())
2155 release_heads->push_back(rf->get_last_fence_release());
2157 break; /* End of RMW chain */
2159 /** @todo Need to be smarter here... In the linux lock
2160 * example, this will run to the beginning of the program for
2162 /** @todo The way to be smarter here is to keep going until 1
2163 * thread has a release preceded by an acquire and you've seen
2166 /* acq_rel RMW is a sufficient stopping condition */
2167 if (rf->is_acquire() && rf->is_release())
2168 return true; /* complete */
2171 /* read from future: need to settle this later */
2173 return false; /* incomplete */
2176 if (rf->is_release())
2177 return true; /* complete */
2179 /* else relaxed write
2180 * - check for fence-release in the same thread (29.8, stmt. 3)
2181 * - check modification order for contiguous subsequence
2182 * -> rf must be same thread as release */
2184 const ModelAction *fence_release = rf->get_last_fence_release();
2185 /* Synchronize with a fence-release unconditionally; we don't need to
2186 * find any more "contiguous subsequence..." for it */
2188 release_heads->push_back(fence_release);
2190 int tid = id_to_int(rf->get_tid());
2191 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2192 action_list_t *list = &(*thrd_lists)[tid];
2193 action_list_t::const_reverse_iterator rit;
2195 /* Find rf in the thread list */
2196 rit = std::find(list->rbegin(), list->rend(), rf);
2197 ASSERT(rit != list->rend());
2199 /* Find the last {write,fence}-release */
2200 for (; rit != list->rend(); rit++) {
2201 if (fence_release && *(*rit) < *fence_release)
2203 if ((*rit)->is_release())
2206 if (rit == list->rend()) {
2207 /* No write-release in this thread */
2208 return true; /* complete */
2209 } else if (fence_release && *(*rit) < *fence_release) {
2210 /* The fence-release is more recent (and so, "stronger") than
2211 * the most recent write-release */
2212 return true; /* complete */
2213 } /* else, need to establish contiguous release sequence */
2214 ModelAction *release = *rit;
2216 ASSERT(rf->same_thread(release));
2218 pending->writes.clear();
2220 bool certain = true;
2221 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2222 if (id_to_int(rf->get_tid()) == (int)i)
2224 list = &(*thrd_lists)[i];
2226 /* Can we ensure no future writes from this thread may break
2227 * the release seq? */
2228 bool future_ordered = false;
2230 ModelAction *last = get_last_action(int_to_id(i));
2231 Thread *th = get_thread(int_to_id(i));
2232 if ((last && rf->happens_before(last)) ||
2235 future_ordered = true;
2237 ASSERT(!th->is_model_thread() || future_ordered);
2239 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2240 const ModelAction *act = *rit;
2241 /* Reach synchronization -> this thread is complete */
2242 if (act->happens_before(release))
2244 if (rf->happens_before(act)) {
2245 future_ordered = true;
2249 /* Only non-RMW writes can break release sequences */
2250 if (!act->is_write() || act->is_rmw())
2253 /* Check modification order */
2254 if (mo_graph->checkReachable(rf, act)) {
2255 /* rf --mo--> act */
2256 future_ordered = true;
2259 if (mo_graph->checkReachable(act, release))
2260 /* act --mo--> release */
2262 if (mo_graph->checkReachable(release, act) &&
2263 mo_graph->checkReachable(act, rf)) {
2264 /* release --mo-> act --mo--> rf */
2265 return true; /* complete */
2267 /* act may break release sequence */
2268 pending->writes.push_back(act);
2271 if (!future_ordered)
2272 certain = false; /* This thread is uncertain */
2276 release_heads->push_back(release);
2277 pending->writes.clear();
2279 pending->release = release;
2286 * An interface for getting the release sequence head(s) with which a
2287 * given ModelAction must synchronize. This function only returns a non-empty
2288 * result when it can locate a release sequence head with certainty. Otherwise,
2289 * it may mark the internal state of the ModelChecker so that it will handle
2290 * the release sequence at a later time, causing @a acquire to update its
2291 * synchronization at some later point in execution.
2293 * @param acquire The 'acquire' action that may synchronize with a release
2295 * @param read The read action that may read from a release sequence; this may
2296 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2297 * when 'acquire' is a fence-acquire)
2298 * @param release_heads A pass-by-reference return parameter. Will be filled
2299 * with the head(s) of the release sequence(s), if they exists with certainty.
2300 * @see ModelChecker::release_seq_heads
2302 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2303 ModelAction *read, rel_heads_list_t *release_heads)
2305 const ModelAction *rf = read->get_reads_from();
2306 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2307 sequence->acquire = acquire;
2308 sequence->read = read;
2310 if (!release_seq_heads(rf, release_heads, sequence)) {
2311 /* add act to 'lazy checking' list */
2312 pending_rel_seqs->push_back(sequence);
2314 snapshot_free(sequence);
2319 * Attempt to resolve all stashed operations that might synchronize with a
2320 * release sequence for a given location. This implements the "lazy" portion of
2321 * determining whether or not a release sequence was contiguous, since not all
2322 * modification order information is present at the time an action occurs.
2324 * @param location The location/object that should be checked for release
2325 * sequence resolutions. A NULL value means to check all locations.
2326 * @param work_queue The work queue to which to add work items as they are
2328 * @return True if any updates occurred (new synchronization, new mo_graph
2331 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2333 bool updated = false;
2334 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2335 while (it != pending_rel_seqs->end()) {
2336 struct release_seq *pending = *it;
2337 ModelAction *acquire = pending->acquire;
2338 const ModelAction *read = pending->read;
2340 /* Only resolve sequences on the given location, if provided */
2341 if (location && read->get_location() != location) {
2346 const ModelAction *rf = read->get_reads_from();
2347 rel_heads_list_t release_heads;
2349 complete = release_seq_heads(rf, &release_heads, pending);
2350 for (unsigned int i = 0; i < release_heads.size(); i++) {
2351 if (!acquire->has_synchronized_with(release_heads[i])) {
2352 if (acquire->synchronize_with(release_heads[i]))
2355 set_bad_synchronization();
2360 /* Re-check all pending release sequences */
2361 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2362 /* Re-check read-acquire for mo_graph edges */
2363 if (acquire->is_read())
2364 work_queue->push_back(MOEdgeWorkEntry(acquire));
2366 /* propagate synchronization to later actions */
2367 action_list_t::reverse_iterator rit = action_trace->rbegin();
2368 for (; (*rit) != acquire; rit++) {
2369 ModelAction *propagate = *rit;
2370 if (acquire->happens_before(propagate)) {
2371 propagate->synchronize_with(acquire);
2372 /* Re-check 'propagate' for mo_graph edges */
2373 work_queue->push_back(MOEdgeWorkEntry(propagate));
2378 it = pending_rel_seqs->erase(it);
2379 snapshot_free(pending);
2385 // If we resolved promises or data races, see if we have realized a data race.
2392 * Performs various bookkeeping operations for the current ModelAction. For
2393 * instance, adds action to the per-object, per-thread action vector and to the
2394 * action trace list of all thread actions.
2396 * @param act is the ModelAction to add.
2398 void ModelChecker::add_action_to_lists(ModelAction *act)
2400 int tid = id_to_int(act->get_tid());
2401 ModelAction *uninit = NULL;
2403 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2404 if (list->empty() && act->is_atomic_var()) {
2405 uninit = get_uninitialized_action(act);
2406 uninit_id = id_to_int(uninit->get_tid());
2407 list->push_front(uninit);
2409 list->push_back(act);
2411 action_trace->push_back(act);
2413 action_trace->push_front(uninit);
2415 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2416 if (tid >= (int)vec->size())
2417 vec->resize(priv->next_thread_id);
2418 (*vec)[tid].push_back(act);
2420 (*vec)[uninit_id].push_front(uninit);
2422 if ((int)thrd_last_action->size() <= tid)
2423 thrd_last_action->resize(get_num_threads());
2424 (*thrd_last_action)[tid] = act;
2426 (*thrd_last_action)[uninit_id] = uninit;
2428 if (act->is_fence() && act->is_release()) {
2429 if ((int)thrd_last_fence_release->size() <= tid)
2430 thrd_last_fence_release->resize(get_num_threads());
2431 (*thrd_last_fence_release)[tid] = act;
2434 if (act->is_wait()) {
2435 void *mutex_loc = (void *) act->get_value();
2436 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2438 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2439 if (tid >= (int)vec->size())
2440 vec->resize(priv->next_thread_id);
2441 (*vec)[tid].push_back(act);
2446 * @brief Get the last action performed by a particular Thread
2447 * @param tid The thread ID of the Thread in question
2448 * @return The last action in the thread
2450 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2452 int threadid = id_to_int(tid);
2453 if (threadid < (int)thrd_last_action->size())
2454 return (*thrd_last_action)[id_to_int(tid)];
2460 * @brief Get the last fence release performed by a particular Thread
2461 * @param tid The thread ID of the Thread in question
2462 * @return The last fence release in the thread, if one exists; NULL otherwise
2464 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2466 int threadid = id_to_int(tid);
2467 if (threadid < (int)thrd_last_fence_release->size())
2468 return (*thrd_last_fence_release)[id_to_int(tid)];
2474 * Gets the last memory_order_seq_cst write (in the total global sequence)
2475 * performed on a particular object (i.e., memory location), not including the
2477 * @param curr The current ModelAction; also denotes the object location to
2479 * @return The last seq_cst write
2481 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2483 void *location = curr->get_location();
2484 action_list_t *list = get_safe_ptr_action(obj_map, location);
2485 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2486 action_list_t::reverse_iterator rit;
2487 for (rit = list->rbegin(); (*rit) != curr; rit++)
2489 rit++; /* Skip past curr */
2490 for ( ; rit != list->rend(); rit++)
2491 if ((*rit)->is_write() && (*rit)->is_seqcst())
2497 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2498 * performed in a particular thread, prior to a particular fence.
2499 * @param tid The ID of the thread to check
2500 * @param before_fence The fence from which to begin the search; if NULL, then
2501 * search for the most recent fence in the thread.
2502 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2504 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2506 /* All fences should have NULL location */
2507 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2508 action_list_t::reverse_iterator rit = list->rbegin();
2511 for (; rit != list->rend(); rit++)
2512 if (*rit == before_fence)
2515 ASSERT(*rit == before_fence);
2519 for (; rit != list->rend(); rit++)
2520 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2526 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2527 * location). This function identifies the mutex according to the current
2528 * action, which is presumed to perform on the same mutex.
2529 * @param curr The current ModelAction; also denotes the object location to
2531 * @return The last unlock operation
2533 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2535 void *location = curr->get_location();
2536 action_list_t *list = get_safe_ptr_action(obj_map, location);
2537 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2538 action_list_t::reverse_iterator rit;
2539 for (rit = list->rbegin(); rit != list->rend(); rit++)
2540 if ((*rit)->is_unlock() || (*rit)->is_wait())
2545 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2547 ModelAction *parent = get_last_action(tid);
2549 parent = get_thread(tid)->get_creation();
2554 * Returns the clock vector for a given thread.
2555 * @param tid The thread whose clock vector we want
2556 * @return Desired clock vector
2558 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2560 return get_parent_action(tid)->get_cv();
2564 * @brief Find the promise (if any) to resolve for the current action and
2565 * remove it from the pending promise vector
2566 * @param curr The current ModelAction. Should be a write.
2567 * @return The Promise to resolve, if any; otherwise NULL
2569 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2571 for (unsigned int i = 0; i < promises->size(); i++)
2572 if (curr->get_node()->get_promise(i)) {
2573 Promise *ret = (*promises)[i];
2574 promises->erase(promises->begin() + i);
2581 * Resolve a Promise with a current write.
2582 * @param write The ModelAction that is fulfilling Promises
2583 * @param promise The Promise to resolve
2584 * @return True if the Promise was successfully resolved; false otherwise
2586 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2588 ModelVector<ModelAction *> actions_to_check;
2590 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2591 ModelAction *read = promise->get_reader(i);
2592 read_from(read, write);
2593 actions_to_check.push_back(read);
2595 /* Make sure the promise's value matches the write's value */
2596 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2597 if (!mo_graph->resolvePromise(promise, write))
2598 priv->failed_promise = true;
2601 * @todo It is possible to end up in an inconsistent state, where a
2602 * "resolved" promise may still be referenced if
2603 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2605 * Note that the inconsistency only matters when dumping mo_graph to
2611 //Check whether reading these writes has made threads unable to
2613 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2614 ModelAction *read = actions_to_check[i];
2615 mo_check_promises(read, true);
2622 * Compute the set of promises that could potentially be satisfied by this
2623 * action. Note that the set computation actually appears in the Node, not in
2625 * @param curr The ModelAction that may satisfy promises
2627 void ModelChecker::compute_promises(ModelAction *curr)
2629 for (unsigned int i = 0; i < promises->size(); i++) {
2630 Promise *promise = (*promises)[i];
2631 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2634 bool satisfy = true;
2635 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2636 const ModelAction *act = promise->get_reader(j);
2637 if (act->happens_before(curr) ||
2638 act->could_synchronize_with(curr)) {
2644 curr->get_node()->set_promise(i);
2648 /** Checks promises in response to change in ClockVector Threads. */
2649 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2651 for (unsigned int i = 0; i < promises->size(); i++) {
2652 Promise *promise = (*promises)[i];
2653 if (!promise->thread_is_available(tid))
2655 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2656 const ModelAction *act = promise->get_reader(j);
2657 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2658 merge_cv->synchronized_since(act)) {
2659 if (promise->eliminate_thread(tid)) {
2660 /* Promise has failed */
2661 priv->failed_promise = true;
2669 void ModelChecker::check_promises_thread_disabled()
2671 for (unsigned int i = 0; i < promises->size(); i++) {
2672 Promise *promise = (*promises)[i];
2673 if (promise->has_failed()) {
2674 priv->failed_promise = true;
2681 * @brief Checks promises in response to addition to modification order for
2684 * We test whether threads are still available for satisfying promises after an
2685 * addition to our modification order constraints. Those that are unavailable
2686 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2687 * that promise has failed.
2689 * @param act The ModelAction which updated the modification order
2690 * @param is_read_check Should be true if act is a read and we must check for
2691 * updates to the store from which it read (there is a distinction here for
2692 * RMW's, which are both a load and a store)
2694 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2696 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2698 for (unsigned int i = 0; i < promises->size(); i++) {
2699 Promise *promise = (*promises)[i];
2701 // Is this promise on the same location?
2702 if (!promise->same_location(write))
2705 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2706 const ModelAction *pread = promise->get_reader(j);
2707 if (!pread->happens_before(act))
2709 if (mo_graph->checkPromise(write, promise)) {
2710 priv->failed_promise = true;
2716 // Don't do any lookups twice for the same thread
2717 if (!promise->thread_is_available(act->get_tid()))
2720 if (mo_graph->checkReachable(promise, write)) {
2721 if (mo_graph->checkPromise(write, promise)) {
2722 priv->failed_promise = true;
2730 * Compute the set of writes that may break the current pending release
2731 * sequence. This information is extracted from previou release sequence
2734 * @param curr The current ModelAction. Must be a release sequence fixup
2737 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2739 if (pending_rel_seqs->empty())
2742 struct release_seq *pending = pending_rel_seqs->back();
2743 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2744 const ModelAction *write = pending->writes[i];
2745 curr->get_node()->add_relseq_break(write);
2748 /* NULL means don't break the sequence; just synchronize */
2749 curr->get_node()->add_relseq_break(NULL);
2753 * Build up an initial set of all past writes that this 'read' action may read
2754 * from, as well as any previously-observed future values that must still be valid.
2756 * @param curr is the current ModelAction that we are exploring; it must be a
2759 void ModelChecker::build_may_read_from(ModelAction *curr)
2761 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2763 ASSERT(curr->is_read());
2765 ModelAction *last_sc_write = NULL;
2767 if (curr->is_seqcst())
2768 last_sc_write = get_last_seq_cst_write(curr);
2770 /* Iterate over all threads */
2771 for (i = 0; i < thrd_lists->size(); i++) {
2772 /* Iterate over actions in thread, starting from most recent */
2773 action_list_t *list = &(*thrd_lists)[i];
2774 action_list_t::reverse_iterator rit;
2775 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2776 ModelAction *act = *rit;
2778 /* Only consider 'write' actions */
2779 if (!act->is_write() || act == curr)
2782 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2783 bool allow_read = true;
2785 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2787 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2791 /* Only add feasible reads */
2792 mo_graph->startChanges();
2793 r_modification_order(curr, act);
2794 if (!is_infeasible())
2795 curr->get_node()->add_read_from_past(act);
2796 mo_graph->rollbackChanges();
2799 /* Include at most one act per-thread that "happens before" curr */
2800 if (act->happens_before(curr))
2805 /* Inherit existing, promised future values */
2806 for (i = 0; i < promises->size(); i++) {
2807 const Promise *promise = (*promises)[i];
2808 const ModelAction *promise_read = promise->get_reader(0);
2809 if (promise_read->same_var(curr)) {
2810 /* Only add feasible future-values */
2811 mo_graph->startChanges();
2812 r_modification_order(curr, promise);
2813 if (!is_infeasible())
2814 curr->get_node()->add_read_from_promise(promise_read);
2815 mo_graph->rollbackChanges();
2819 /* We may find no valid may-read-from only if the execution is doomed */
2820 if (!curr->get_node()->read_from_size()) {
2821 priv->no_valid_reads = true;
2825 if (DBG_ENABLED()) {
2826 model_print("Reached read action:\n");
2828 model_print("Printing read_from_past\n");
2829 curr->get_node()->print_read_from_past();
2830 model_print("End printing read_from_past\n");
2834 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2836 for ( ; write != NULL; write = write->get_reads_from()) {
2837 /* UNINIT actions don't have a Node, and they never sleep */
2838 if (write->is_uninitialized())
2840 Node *prevnode = write->get_node()->get_parent();
2842 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2843 if (write->is_release() && thread_sleep)
2845 if (!write->is_rmw())
2852 * @brief Get an action representing an uninitialized atomic
2854 * This function may create a new one or try to retrieve one from the NodeStack
2856 * @param curr The current action, which prompts the creation of an UNINIT action
2857 * @return A pointer to the UNINIT ModelAction
2859 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2861 Node *node = curr->get_node();
2862 ModelAction *act = node->get_uninit_action();
2864 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2865 node->set_uninit_action(act);
2867 act->create_cv(NULL);
2871 static void print_list(action_list_t *list)
2873 action_list_t::iterator it;
2875 model_print("---------------------------------------------------------------------\n");
2877 unsigned int hash = 0;
2879 for (it = list->begin(); it != list->end(); it++) {
2880 const ModelAction *act = *it;
2881 if (act->get_seq_number() > 0)
2883 hash = hash^(hash<<3)^((*it)->hash());
2885 model_print("HASH %u\n", hash);
2886 model_print("---------------------------------------------------------------------\n");
2889 #if SUPPORT_MOD_ORDER_DUMP
2890 void ModelChecker::dumpGraph(char *filename) const
2893 sprintf(buffer, "%s.dot", filename);
2894 FILE *file = fopen(buffer, "w");
2895 fprintf(file, "digraph %s {\n", filename);
2896 mo_graph->dumpNodes(file);
2897 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2899 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2900 ModelAction *act = *it;
2901 if (act->is_read()) {
2902 mo_graph->dot_print_node(file, act);
2903 if (act->get_reads_from())
2904 mo_graph->dot_print_edge(file,
2905 act->get_reads_from(),
2907 "label=\"rf\", color=red, weight=2");
2909 mo_graph->dot_print_edge(file,
2910 act->get_reads_from_promise(),
2912 "label=\"rf\", color=red");
2914 if (thread_array[act->get_tid()]) {
2915 mo_graph->dot_print_edge(file,
2916 thread_array[id_to_int(act->get_tid())],
2918 "label=\"sb\", color=blue, weight=400");
2921 thread_array[act->get_tid()] = act;
2923 fprintf(file, "}\n");
2924 model_free(thread_array);
2929 /** @brief Prints an execution trace summary. */
2930 void ModelChecker::print_summary() const
2932 #if SUPPORT_MOD_ORDER_DUMP
2933 char buffername[100];
2934 sprintf(buffername, "exec%04u", stats.num_total);
2935 mo_graph->dumpGraphToFile(buffername);
2936 sprintf(buffername, "graph%04u", stats.num_total);
2937 dumpGraph(buffername);
2940 model_print("Execution %d:", stats.num_total);
2941 if (isfeasibleprefix()) {
2942 if (scheduler->all_threads_sleeping())
2943 model_print(" SLEEP-SET REDUNDANT");
2946 print_infeasibility(" INFEASIBLE");
2947 print_list(action_trace);
2949 if (!promises->empty()) {
2950 model_print("Pending promises:\n");
2951 for (unsigned int i = 0; i < promises->size(); i++) {
2952 model_print(" [P%u] ", i);
2953 (*promises)[i]->print();
2960 * Add a Thread to the system for the first time. Should only be called once
2962 * @param t The Thread to add
2964 void ModelChecker::add_thread(Thread *t)
2966 thread_map->put(id_to_int(t->get_id()), t);
2967 scheduler->add_thread(t);
2971 * @brief Get a Thread reference by its ID
2972 * @param tid The Thread's ID
2973 * @return A Thread reference
2975 Thread * ModelChecker::get_thread(thread_id_t tid) const
2977 return thread_map->get(id_to_int(tid));
2981 * @brief Get a reference to the Thread in which a ModelAction was executed
2982 * @param act The ModelAction
2983 * @return A Thread reference
2985 Thread * ModelChecker::get_thread(const ModelAction *act) const
2987 return get_thread(act->get_tid());
2991 * @brief Get a Promise's "promise number"
2993 * A "promise number" is an index number that is unique to a promise, valid
2994 * only for a specific snapshot of an execution trace. Promises may come and go
2995 * as they are generated an resolved, so an index only retains meaning for the
2998 * @param promise The Promise to check
2999 * @return The promise index, if the promise still is valid; otherwise -1
3001 int ModelChecker::get_promise_number(const Promise *promise) const
3003 for (unsigned int i = 0; i < promises->size(); i++)
3004 if ((*promises)[i] == promise)
3011 * @brief Check if a Thread is currently enabled
3012 * @param t The Thread to check
3013 * @return True if the Thread is currently enabled
3015 bool ModelChecker::is_enabled(Thread *t) const
3017 return scheduler->is_enabled(t);
3021 * @brief Check if a Thread is currently enabled
3022 * @param tid The ID of the Thread to check
3023 * @return True if the Thread is currently enabled
3025 bool ModelChecker::is_enabled(thread_id_t tid) const
3027 return scheduler->is_enabled(tid);
3031 * Switch from a model-checker context to a user-thread context. This is the
3032 * complement of ModelChecker::switch_to_master and must be called from the
3033 * model-checker context
3035 * @param thread The user-thread to switch to
3037 void ModelChecker::switch_from_master(Thread *thread)
3039 scheduler->set_current_thread(thread);
3040 Thread::swap(&system_context, thread);
3044 * Switch from a user-context to the "master thread" context (a.k.a. system
3045 * context). This switch is made with the intention of exploring a particular
3046 * model-checking action (described by a ModelAction object). Must be called
3047 * from a user-thread context.
3049 * @param act The current action that will be explored. May be NULL only if
3050 * trace is exiting via an assertion (see ModelChecker::set_assert and
3051 * ModelChecker::has_asserted).
3052 * @return Return the value returned by the current action
3054 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3057 Thread *old = thread_current();
3058 scheduler->set_current_thread(NULL);
3059 ASSERT(!old->get_pending());
3060 old->set_pending(act);
3061 if (Thread::swap(old, &system_context) < 0) {
3062 perror("swap threads");
3065 return old->get_return_value();
3069 * Takes the next step in the execution, if possible.
3070 * @param curr The current step to take
3071 * @return Returns the next Thread to run, if any; NULL if this execution
3074 Thread * ModelChecker::take_step(ModelAction *curr)
3076 Thread *curr_thrd = get_thread(curr);
3077 ASSERT(curr_thrd->get_state() == THREAD_READY);
3079 curr = check_current_action(curr);
3081 /* Infeasible -> don't take any more steps */
3082 if (is_infeasible())
3084 else if (isfeasibleprefix() && have_bug_reports()) {
3089 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3092 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3093 scheduler->remove_thread(curr_thrd);
3095 Thread *next_thrd = NULL;
3097 next_thrd = action_select_next_thread(curr);
3099 next_thrd = get_next_thread();
3101 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3102 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3107 /** Wrapper to run the user's main function, with appropriate arguments */
3108 void user_main_wrapper(void *)
3110 user_main(model->params.argc, model->params.argv);
3113 /** @brief Run ModelChecker for the user program */
3114 void ModelChecker::run()
3118 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3123 * Stash next pending action(s) for thread(s). There
3124 * should only need to stash one thread's action--the
3125 * thread which just took a step--plus the first step
3126 * for any newly-created thread
3128 for (unsigned int i = 0; i < get_num_threads(); i++) {
3129 thread_id_t tid = int_to_id(i);
3130 Thread *thr = get_thread(tid);
3131 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3132 switch_from_master(thr);
3133 if (is_circular_wait(thr))
3134 assert_bug("Deadlock detected");
3138 /* Catch assertions from prior take_step or from
3139 * between-ModelAction bugs (e.g., data races) */
3143 /* Consume the next action for a Thread */
3144 ModelAction *curr = t->get_pending();
3145 t->set_pending(NULL);
3146 t = take_step(curr);
3147 } while (t && !t->is_model_thread());
3150 * Launch end-of-execution release sequence fixups only when
3151 * the execution is otherwise feasible AND there are:
3153 * (1) pending release sequences
3154 * (2) pending assertions that could be invalidated by a change
3155 * in clock vectors (i.e., data races)
3156 * (3) no pending promises
3158 while (!pending_rel_seqs->empty() &&
3159 is_feasible_prefix_ignore_relseq() &&
3160 !unrealizedraces.empty()) {
3161 model_print("*** WARNING: release sequence fixup action "
3162 "(%zu pending release seuqence(s)) ***\n",
3163 pending_rel_seqs->size());
3164 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3165 std::memory_order_seq_cst, NULL, VALUE_NONE,
3169 } while (next_execution());
3171 model_print("******* Model-checking complete: *******\n");