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));
1054 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1056 /* Do more ambitious checks now that mo is more complete */
1057 if (mo_may_allow(writer, reader)) {
1058 Node *node = reader->get_node();
1060 /* Find an ancestor thread which exists at the time of the reader */
1061 Thread *write_thread = get_thread(writer);
1062 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1063 write_thread = write_thread->get_parent();
1065 struct future_value fv = {
1066 writer->get_write_value(),
1067 writer->get_seq_number() + params.maxfuturedelay,
1068 write_thread->get_id(),
1070 if (node->add_future_value(fv))
1071 set_latest_backtrack(reader);
1076 * Process a write ModelAction
1077 * @param curr The ModelAction to process
1078 * @return True if the mo_graph was updated or promises were resolved
1080 bool ModelChecker::process_write(ModelAction *curr)
1082 /* Readers to which we may send our future value */
1083 ModelVector<ModelAction *> send_fv;
1085 bool updated_mod_order = w_modification_order(curr, &send_fv);
1086 int promise_idx = get_promise_to_resolve(curr);
1087 const ModelAction *earliest_promise_reader;
1088 bool updated_promises = false;
1090 if (promise_idx >= 0) {
1091 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1092 updated_promises = resolve_promise(curr, promise_idx);
1094 earliest_promise_reader = NULL;
1096 /* Don't send future values to reads after the Promise we resolve */
1097 for (unsigned int i = 0; i < send_fv.size(); i++) {
1098 ModelAction *read = send_fv[i];
1099 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1100 futurevalues->push_back(PendingFutureValue(curr, read));
1103 if (promises->size() == 0) {
1104 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1105 struct PendingFutureValue pfv = (*futurevalues)[i];
1106 add_future_value(pfv.writer, pfv.act);
1108 futurevalues->clear();
1111 mo_graph->commitChanges();
1112 mo_check_promises(curr, false);
1114 get_thread(curr)->set_return_value(VALUE_NONE);
1115 return updated_mod_order || updated_promises;
1119 * Process a fence ModelAction
1120 * @param curr The ModelAction to process
1121 * @return True if synchronization was updated
1123 bool ModelChecker::process_fence(ModelAction *curr)
1126 * fence-relaxed: no-op
1127 * fence-release: only log the occurence (not in this function), for
1128 * use in later synchronization
1129 * fence-acquire (this function): search for hypothetical release
1131 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1133 bool updated = false;
1134 if (curr->is_acquire()) {
1135 action_list_t *list = action_trace;
1136 action_list_t::reverse_iterator rit;
1137 /* Find X : is_read(X) && X --sb-> curr */
1138 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1139 ModelAction *act = *rit;
1142 if (act->get_tid() != curr->get_tid())
1144 /* Stop at the beginning of the thread */
1145 if (act->is_thread_start())
1147 /* Stop once we reach a prior fence-acquire */
1148 if (act->is_fence() && act->is_acquire())
1150 if (!act->is_read())
1152 /* read-acquire will find its own release sequences */
1153 if (act->is_acquire())
1156 /* Establish hypothetical release sequences */
1157 rel_heads_list_t release_heads;
1158 get_release_seq_heads(curr, act, &release_heads);
1159 for (unsigned int i = 0; i < release_heads.size(); i++)
1160 if (!curr->synchronize_with(release_heads[i]))
1161 set_bad_synchronization();
1162 if (release_heads.size() != 0)
1170 * @brief Process the current action for thread-related activity
1172 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1173 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1174 * synchronization, etc. This function is a no-op for non-THREAD actions
1175 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1177 * @param curr The current action
1178 * @return True if synchronization was updated or a thread completed
1180 bool ModelChecker::process_thread_action(ModelAction *curr)
1182 bool updated = false;
1184 switch (curr->get_type()) {
1185 case THREAD_CREATE: {
1186 thrd_t *thrd = (thrd_t *)curr->get_location();
1187 struct thread_params *params = (struct thread_params *)curr->get_value();
1188 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1190 th->set_creation(curr);
1191 /* Promises can be satisfied by children */
1192 for (unsigned int i = 0; i < promises->size(); i++) {
1193 Promise *promise = (*promises)[i];
1194 if (promise->thread_is_available(curr->get_tid()))
1195 promise->add_thread(th->get_id());
1200 Thread *blocking = curr->get_thread_operand();
1201 ModelAction *act = get_last_action(blocking->get_id());
1202 curr->synchronize_with(act);
1203 updated = true; /* trigger rel-seq checks */
1206 case THREAD_FINISH: {
1207 Thread *th = get_thread(curr);
1208 while (!th->wait_list_empty()) {
1209 ModelAction *act = th->pop_wait_list();
1210 scheduler->wake(get_thread(act));
1213 /* Completed thread can't satisfy promises */
1214 for (unsigned int i = 0; i < promises->size(); i++) {
1215 Promise *promise = (*promises)[i];
1216 if (promise->thread_is_available(th->get_id()))
1217 if (promise->eliminate_thread(th->get_id()))
1218 priv->failed_promise = true;
1220 updated = true; /* trigger rel-seq checks */
1223 case THREAD_START: {
1224 check_promises(curr->get_tid(), NULL, curr->get_cv());
1235 * @brief Process the current action for release sequence fixup activity
1237 * Performs model-checker release sequence fixups for the current action,
1238 * forcing a single pending release sequence to break (with a given, potential
1239 * "loose" write) or to complete (i.e., synchronize). If a pending release
1240 * sequence forms a complete release sequence, then we must perform the fixup
1241 * synchronization, mo_graph additions, etc.
1243 * @param curr The current action; must be a release sequence fixup action
1244 * @param work_queue The work queue to which to add work items as they are
1247 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1249 const ModelAction *write = curr->get_node()->get_relseq_break();
1250 struct release_seq *sequence = pending_rel_seqs->back();
1251 pending_rel_seqs->pop_back();
1253 ModelAction *acquire = sequence->acquire;
1254 const ModelAction *rf = sequence->rf;
1255 const ModelAction *release = sequence->release;
1259 ASSERT(release->same_thread(rf));
1261 if (write == NULL) {
1263 * @todo Forcing a synchronization requires that we set
1264 * modification order constraints. For instance, we can't allow
1265 * a fixup sequence in which two separate read-acquire
1266 * operations read from the same sequence, where the first one
1267 * synchronizes and the other doesn't. Essentially, we can't
1268 * allow any writes to insert themselves between 'release' and
1272 /* Must synchronize */
1273 if (!acquire->synchronize_with(release)) {
1274 set_bad_synchronization();
1277 /* Re-check all pending release sequences */
1278 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1279 /* Re-check act for mo_graph edges */
1280 work_queue->push_back(MOEdgeWorkEntry(acquire));
1282 /* propagate synchronization to later actions */
1283 action_list_t::reverse_iterator rit = action_trace->rbegin();
1284 for (; (*rit) != acquire; rit++) {
1285 ModelAction *propagate = *rit;
1286 if (acquire->happens_before(propagate)) {
1287 propagate->synchronize_with(acquire);
1288 /* Re-check 'propagate' for mo_graph edges */
1289 work_queue->push_back(MOEdgeWorkEntry(propagate));
1293 /* Break release sequence with new edges:
1294 * release --mo--> write --mo--> rf */
1295 mo_graph->addEdge(release, write);
1296 mo_graph->addEdge(write, rf);
1299 /* See if we have realized a data race */
1304 * Initialize the current action by performing one or more of the following
1305 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1306 * in the NodeStack, manipulating backtracking sets, allocating and
1307 * initializing clock vectors, and computing the promises to fulfill.
1309 * @param curr The current action, as passed from the user context; may be
1310 * freed/invalidated after the execution of this function, with a different
1311 * action "returned" its place (pass-by-reference)
1312 * @return True if curr is a newly-explored action; false otherwise
1314 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1316 ModelAction *newcurr;
1318 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1319 newcurr = process_rmw(*curr);
1322 if (newcurr->is_rmw())
1323 compute_promises(newcurr);
1329 (*curr)->set_seq_number(get_next_seq_num());
1331 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1333 /* First restore type and order in case of RMW operation */
1334 if ((*curr)->is_rmwr())
1335 newcurr->copy_typeandorder(*curr);
1337 ASSERT((*curr)->get_location() == newcurr->get_location());
1338 newcurr->copy_from_new(*curr);
1340 /* Discard duplicate ModelAction; use action from NodeStack */
1343 /* Always compute new clock vector */
1344 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1347 return false; /* Action was explored previously */
1351 /* Always compute new clock vector */
1352 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1354 /* Assign most recent release fence */
1355 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1358 * Perform one-time actions when pushing new ModelAction onto
1361 if (newcurr->is_write())
1362 compute_promises(newcurr);
1363 else if (newcurr->is_relseq_fixup())
1364 compute_relseq_breakwrites(newcurr);
1365 else if (newcurr->is_wait())
1366 newcurr->get_node()->set_misc_max(2);
1367 else if (newcurr->is_notify_one()) {
1368 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1370 return true; /* This was a new ModelAction */
1375 * @brief Establish reads-from relation between two actions
1377 * Perform basic operations involved with establishing a concrete rf relation,
1378 * including setting the ModelAction data and checking for release sequences.
1380 * @param act The action that is reading (must be a read)
1381 * @param rf The action from which we are reading (must be a write)
1383 * @return True if this read established synchronization
1385 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1388 ASSERT(rf->is_write());
1390 act->set_read_from(rf);
1391 if (act->is_acquire()) {
1392 rel_heads_list_t release_heads;
1393 get_release_seq_heads(act, act, &release_heads);
1394 int num_heads = release_heads.size();
1395 for (unsigned int i = 0; i < release_heads.size(); i++)
1396 if (!act->synchronize_with(release_heads[i])) {
1397 set_bad_synchronization();
1400 return num_heads > 0;
1406 * Check promises and eliminate potentially-satisfying threads when a thread is
1407 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1408 * no longer satisfy a promise generated from that thread.
1410 * @param blocker The thread on which a thread is waiting
1411 * @param waiting The waiting thread
1413 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1415 for (unsigned int i = 0; i < promises->size(); i++) {
1416 Promise *promise = (*promises)[i];
1417 if (!promise->thread_is_available(waiting->get_id()))
1419 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1420 ModelAction *reader = promise->get_reader(j);
1421 if (reader->get_tid() != blocker->get_id())
1423 if (promise->eliminate_thread(waiting->get_id())) {
1424 /* Promise has failed */
1425 priv->failed_promise = true;
1427 /* Only eliminate the 'waiting' thread once */
1435 * @brief Check whether a model action is enabled.
1437 * Checks whether a lock or join operation would be successful (i.e., is the
1438 * lock already locked, or is the joined thread already complete). If not, put
1439 * the action in a waiter list.
1441 * @param curr is the ModelAction to check whether it is enabled.
1442 * @return a bool that indicates whether the action is enabled.
1444 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1445 if (curr->is_lock()) {
1446 std::mutex *lock = (std::mutex *)curr->get_location();
1447 struct std::mutex_state *state = lock->get_state();
1448 if (state->locked) {
1449 //Stick the action in the appropriate waiting queue
1450 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1453 } else if (curr->get_type() == THREAD_JOIN) {
1454 Thread *blocking = (Thread *)curr->get_location();
1455 if (!blocking->is_complete()) {
1456 blocking->push_wait_list(curr);
1457 thread_blocking_check_promises(blocking, get_thread(curr));
1466 * This is the heart of the model checker routine. It performs model-checking
1467 * actions corresponding to a given "current action." Among other processes, it
1468 * calculates reads-from relationships, updates synchronization clock vectors,
1469 * forms a memory_order constraints graph, and handles replay/backtrack
1470 * execution when running permutations of previously-observed executions.
1472 * @param curr The current action to process
1473 * @return The ModelAction that is actually executed; may be different than
1474 * curr; may be NULL, if the current action is not enabled to run
1476 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1479 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1481 if (!check_action_enabled(curr)) {
1482 /* Make the execution look like we chose to run this action
1483 * much later, when a lock/join can succeed */
1484 get_thread(curr)->set_pending(curr);
1485 scheduler->sleep(get_thread(curr));
1489 bool newly_explored = initialize_curr_action(&curr);
1495 wake_up_sleeping_actions(curr);
1497 /* Compute fairness information for CHESS yield algorithm */
1498 if (model->params.yieldon) {
1499 curr->get_node()->update_yield(scheduler);
1502 /* Add the action to lists before any other model-checking tasks */
1503 if (!second_part_of_rmw)
1504 add_action_to_lists(curr);
1506 /* Build may_read_from set for newly-created actions */
1507 if (newly_explored && curr->is_read())
1508 build_may_read_from(curr);
1510 /* Initialize work_queue with the "current action" work */
1511 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1512 while (!work_queue.empty() && !has_asserted()) {
1513 WorkQueueEntry work = work_queue.front();
1514 work_queue.pop_front();
1516 switch (work.type) {
1517 case WORK_CHECK_CURR_ACTION: {
1518 ModelAction *act = work.action;
1519 bool update = false; /* update this location's release seq's */
1520 bool update_all = false; /* update all release seq's */
1522 if (process_thread_action(curr))
1525 if (act->is_read() && !second_part_of_rmw && process_read(act))
1528 if (act->is_write() && process_write(act))
1531 if (act->is_fence() && process_fence(act))
1534 if (act->is_mutex_op() && process_mutex(act))
1537 if (act->is_relseq_fixup())
1538 process_relseq_fixup(curr, &work_queue);
1541 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1543 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1546 case WORK_CHECK_RELEASE_SEQ:
1547 resolve_release_sequences(work.location, &work_queue);
1549 case WORK_CHECK_MO_EDGES: {
1550 /** @todo Complete verification of work_queue */
1551 ModelAction *act = work.action;
1552 bool updated = false;
1554 if (act->is_read()) {
1555 const ModelAction *rf = act->get_reads_from();
1556 const Promise *promise = act->get_reads_from_promise();
1558 if (r_modification_order(act, rf))
1560 } else if (promise) {
1561 if (r_modification_order(act, promise))
1565 if (act->is_write()) {
1566 if (w_modification_order(act, NULL))
1569 mo_graph->commitChanges();
1572 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1581 check_curr_backtracking(curr);
1582 set_backtracking(curr);
1586 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1588 Node *currnode = curr->get_node();
1589 Node *parnode = currnode->get_parent();
1591 if ((parnode && !parnode->backtrack_empty()) ||
1592 !currnode->misc_empty() ||
1593 !currnode->read_from_empty() ||
1594 !currnode->promise_empty() ||
1595 !currnode->relseq_break_empty()) {
1596 set_latest_backtrack(curr);
1600 bool ModelChecker::promises_expired() const
1602 for (unsigned int i = 0; i < promises->size(); i++) {
1603 Promise *promise = (*promises)[i];
1604 if (promise->get_expiration() < priv->used_sequence_numbers)
1611 * This is the strongest feasibility check available.
1612 * @return whether the current trace (partial or complete) must be a prefix of
1615 bool ModelChecker::isfeasibleprefix() const
1617 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1621 * Print disagnostic information about an infeasible execution
1622 * @param prefix A string to prefix the output with; if NULL, then a default
1623 * message prefix will be provided
1625 void ModelChecker::print_infeasibility(const char *prefix) const
1629 if (mo_graph->checkForCycles())
1630 ptr += sprintf(ptr, "[mo cycle]");
1631 if (priv->failed_promise)
1632 ptr += sprintf(ptr, "[failed promise]");
1633 if (priv->too_many_reads)
1634 ptr += sprintf(ptr, "[too many reads]");
1635 if (priv->no_valid_reads)
1636 ptr += sprintf(ptr, "[no valid reads-from]");
1637 if (priv->bad_synchronization)
1638 ptr += sprintf(ptr, "[bad sw ordering]");
1639 if (promises_expired())
1640 ptr += sprintf(ptr, "[promise expired]");
1641 if (promises->size() != 0)
1642 ptr += sprintf(ptr, "[unresolved promise]");
1644 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1648 * Returns whether the current completed trace is feasible, except for pending
1649 * release sequences.
1651 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1653 return !is_infeasible() && promises->size() == 0;
1657 * Check if the current partial trace is infeasible. Does not check any
1658 * end-of-execution flags, which might rule out the execution. Thus, this is
1659 * useful only for ruling an execution as infeasible.
1660 * @return whether the current partial trace is infeasible.
1662 bool ModelChecker::is_infeasible() const
1664 return mo_graph->checkForCycles() ||
1665 priv->no_valid_reads ||
1666 priv->failed_promise ||
1667 priv->too_many_reads ||
1668 priv->bad_synchronization ||
1672 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1673 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1674 ModelAction *lastread = get_last_action(act->get_tid());
1675 lastread->process_rmw(act);
1676 if (act->is_rmw()) {
1677 if (lastread->get_reads_from())
1678 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1680 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1681 mo_graph->commitChanges();
1687 * A helper function for ModelChecker::check_recency, to check if the current
1688 * thread is able to read from a different write/promise for 'params.maxreads'
1689 * number of steps and if that write/promise should become visible (i.e., is
1690 * ordered later in the modification order). This helps model memory liveness.
1692 * @param curr The current action. Must be a read.
1693 * @param rf The write/promise from which we plan to read
1694 * @param other_rf The write/promise from which we may read
1695 * @return True if we were able to read from other_rf for params.maxreads steps
1697 template <typename T, typename U>
1698 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1700 /* Need a different write/promise */
1701 if (other_rf->equals(rf))
1704 /* Only look for "newer" writes/promises */
1705 if (!mo_graph->checkReachable(rf, other_rf))
1708 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1709 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1710 action_list_t::reverse_iterator rit = list->rbegin();
1711 ASSERT((*rit) == curr);
1712 /* Skip past curr */
1715 /* Does this write/promise work for everyone? */
1716 for (int i = 0; i < params.maxreads; i++, rit++) {
1717 ModelAction *act = *rit;
1718 if (!act->may_read_from(other_rf))
1725 * Checks whether a thread has read from the same write or Promise for too many
1726 * times without seeing the effects of a later write/Promise.
1729 * 1) there must a different write/promise that we could read from,
1730 * 2) we must have read from the same write/promise in excess of maxreads times,
1731 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1732 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1734 * If so, we decide that the execution is no longer feasible.
1736 * @param curr The current action. Must be a read.
1737 * @param rf The ModelAction/Promise from which we might read.
1738 * @return True if the read should succeed; false otherwise
1740 template <typename T>
1741 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1743 if (!params.maxreads)
1746 //NOTE: Next check is just optimization, not really necessary....
1747 if (curr->get_node()->get_read_from_past_size() +
1748 curr->get_node()->get_read_from_promise_size() <= 1)
1751 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1752 int tid = id_to_int(curr->get_tid());
1753 ASSERT(tid < (int)thrd_lists->size());
1754 action_list_t *list = &(*thrd_lists)[tid];
1755 action_list_t::reverse_iterator rit = list->rbegin();
1756 ASSERT((*rit) == curr);
1757 /* Skip past curr */
1760 action_list_t::reverse_iterator ritcopy = rit;
1761 /* See if we have enough reads from the same value */
1762 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1763 if (ritcopy == list->rend())
1765 ModelAction *act = *ritcopy;
1766 if (!act->is_read())
1768 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1770 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1772 if (act->get_node()->get_read_from_past_size() +
1773 act->get_node()->get_read_from_promise_size() <= 1)
1776 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1777 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1778 if (should_read_instead(curr, rf, write))
1779 return false; /* liveness failure */
1781 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1782 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1783 if (should_read_instead(curr, rf, promise))
1784 return false; /* liveness failure */
1790 * Updates the mo_graph with the constraints imposed from the current
1793 * Basic idea is the following: Go through each other thread and find
1794 * the last action that happened before our read. Two cases:
1796 * (1) The action is a write => that write must either occur before
1797 * the write we read from or be the write we read from.
1799 * (2) The action is a read => the write that that action read from
1800 * must occur before the write we read from or be the same write.
1802 * @param curr The current action. Must be a read.
1803 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1804 * @return True if modification order edges were added; false otherwise
1806 template <typename rf_type>
1807 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1809 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1812 ASSERT(curr->is_read());
1814 /* Last SC fence in the current thread */
1815 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1816 ModelAction *last_sc_write = NULL;
1817 if (curr->is_seqcst())
1818 last_sc_write = get_last_seq_cst_write(curr);
1820 /* Iterate over all threads */
1821 for (i = 0; i < thrd_lists->size(); i++) {
1822 /* Last SC fence in thread i */
1823 ModelAction *last_sc_fence_thread_local = NULL;
1824 if (int_to_id((int)i) != curr->get_tid())
1825 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1827 /* Last SC fence in thread i, before last SC fence in current thread */
1828 ModelAction *last_sc_fence_thread_before = NULL;
1829 if (last_sc_fence_local)
1830 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1832 /* Iterate over actions in thread, starting from most recent */
1833 action_list_t *list = &(*thrd_lists)[i];
1834 action_list_t::reverse_iterator rit;
1835 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1836 ModelAction *act = *rit;
1841 /* Don't want to add reflexive edges on 'rf' */
1842 if (act->equals(rf)) {
1843 if (act->happens_before(curr))
1849 if (act->is_write()) {
1850 /* C++, Section 29.3 statement 5 */
1851 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1852 *act < *last_sc_fence_thread_local) {
1853 added = mo_graph->addEdge(act, rf) || added;
1856 /* C++, Section 29.3 statement 4 */
1857 else if (act->is_seqcst() && last_sc_fence_local &&
1858 *act < *last_sc_fence_local) {
1859 added = mo_graph->addEdge(act, rf) || added;
1862 /* C++, Section 29.3 statement 6 */
1863 else if (last_sc_fence_thread_before &&
1864 *act < *last_sc_fence_thread_before) {
1865 added = mo_graph->addEdge(act, rf) || added;
1870 /* C++, Section 29.3 statement 3 (second subpoint) */
1871 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1872 added = mo_graph->addEdge(act, rf) || added;
1877 * Include at most one act per-thread that "happens
1880 if (act->happens_before(curr)) {
1881 if (act->is_write()) {
1882 added = mo_graph->addEdge(act, rf) || added;
1884 const ModelAction *prevrf = act->get_reads_from();
1885 const Promise *prevrf_promise = act->get_reads_from_promise();
1887 if (!prevrf->equals(rf))
1888 added = mo_graph->addEdge(prevrf, rf) || added;
1889 } else if (!prevrf_promise->equals(rf)) {
1890 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1899 * All compatible, thread-exclusive promises must be ordered after any
1900 * concrete loads from the same thread
1902 for (unsigned int i = 0; i < promises->size(); i++)
1903 if ((*promises)[i]->is_compatible_exclusive(curr))
1904 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1910 * Updates the mo_graph with the constraints imposed from the current write.
1912 * Basic idea is the following: Go through each other thread and find
1913 * the lastest action that happened before our write. Two cases:
1915 * (1) The action is a write => that write must occur before
1918 * (2) The action is a read => the write that that action read from
1919 * must occur before the current write.
1921 * This method also handles two other issues:
1923 * (I) Sequential Consistency: Making sure that if the current write is
1924 * seq_cst, that it occurs after the previous seq_cst write.
1926 * (II) Sending the write back to non-synchronizing reads.
1928 * @param curr The current action. Must be a write.
1929 * @param send_fv A vector for stashing reads to which we may pass our future
1930 * value. If NULL, then don't record any future values.
1931 * @return True if modification order edges were added; false otherwise
1933 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1935 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1938 ASSERT(curr->is_write());
1940 if (curr->is_seqcst()) {
1941 /* We have to at least see the last sequentially consistent write,
1942 so we are initialized. */
1943 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1944 if (last_seq_cst != NULL) {
1945 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1949 /* Last SC fence in the current thread */
1950 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1952 /* Iterate over all threads */
1953 for (i = 0; i < thrd_lists->size(); i++) {
1954 /* Last SC fence in thread i, before last SC fence in current thread */
1955 ModelAction *last_sc_fence_thread_before = NULL;
1956 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1957 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1959 /* Iterate over actions in thread, starting from most recent */
1960 action_list_t *list = &(*thrd_lists)[i];
1961 action_list_t::reverse_iterator rit;
1962 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1963 ModelAction *act = *rit;
1966 * 1) If RMW and it actually read from something, then we
1967 * already have all relevant edges, so just skip to next
1970 * 2) If RMW and it didn't read from anything, we should
1971 * whatever edge we can get to speed up convergence.
1973 * 3) If normal write, we need to look at earlier actions, so
1974 * continue processing list.
1976 if (curr->is_rmw()) {
1977 if (curr->get_reads_from() != NULL)
1985 /* C++, Section 29.3 statement 7 */
1986 if (last_sc_fence_thread_before && act->is_write() &&
1987 *act < *last_sc_fence_thread_before) {
1988 added = mo_graph->addEdge(act, curr) || added;
1993 * Include at most one act per-thread that "happens
1996 if (act->happens_before(curr)) {
1998 * Note: if act is RMW, just add edge:
2000 * The following edge should be handled elsewhere:
2001 * readfrom(act) --mo--> act
2003 if (act->is_write())
2004 added = mo_graph->addEdge(act, curr) || added;
2005 else if (act->is_read()) {
2006 //if previous read accessed a null, just keep going
2007 if (act->get_reads_from() == NULL)
2009 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2012 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2013 !act->same_thread(curr)) {
2014 /* We have an action that:
2015 (1) did not happen before us
2016 (2) is a read and we are a write
2017 (3) cannot synchronize with us
2018 (4) is in a different thread
2020 that read could potentially read from our write. Note that
2021 these checks are overly conservative at this point, we'll
2022 do more checks before actually removing the
2026 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2027 if (!is_infeasible())
2028 send_fv->push_back(act);
2029 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2030 add_future_value(curr, act);
2037 * All compatible, thread-exclusive promises must be ordered after any
2038 * concrete stores to the same thread, or else they can be merged with
2041 for (unsigned int i = 0; i < promises->size(); i++)
2042 if ((*promises)[i]->is_compatible_exclusive(curr))
2043 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2048 /** Arbitrary reads from the future are not allowed. Section 29.3
2049 * part 9 places some constraints. This method checks one result of constraint
2050 * constraint. Others require compiler support. */
2051 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
2053 if (!writer->is_rmw())
2056 if (!reader->is_rmw())
2059 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2060 if (search == reader)
2062 if (search->get_tid() == reader->get_tid() &&
2063 search->happens_before(reader))
2071 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2072 * some constraints. This method checks one the following constraint (others
2073 * require compiler support):
2075 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2077 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2079 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2081 /* Iterate over all threads */
2082 for (i = 0; i < thrd_lists->size(); i++) {
2083 const ModelAction *write_after_read = NULL;
2085 /* Iterate over actions in thread, starting from most recent */
2086 action_list_t *list = &(*thrd_lists)[i];
2087 action_list_t::reverse_iterator rit;
2088 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2089 ModelAction *act = *rit;
2091 /* Don't disallow due to act == reader */
2092 if (!reader->happens_before(act) || reader == act)
2094 else if (act->is_write())
2095 write_after_read = act;
2096 else if (act->is_read() && act->get_reads_from() != NULL)
2097 write_after_read = act->get_reads_from();
2100 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2107 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2108 * The ModelAction under consideration is expected to be taking part in
2109 * release/acquire synchronization as an object of the "reads from" relation.
2110 * Note that this can only provide release sequence support for RMW chains
2111 * which do not read from the future, as those actions cannot be traced until
2112 * their "promise" is fulfilled. Similarly, we may not even establish the
2113 * presence of a release sequence with certainty, as some modification order
2114 * constraints may be decided further in the future. Thus, this function
2115 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2116 * and a boolean representing certainty.
2118 * @param rf The action that might be part of a release sequence. Must be a
2120 * @param release_heads A pass-by-reference style return parameter. After
2121 * execution of this function, release_heads will contain the heads of all the
2122 * relevant release sequences, if any exists with certainty
2123 * @param pending A pass-by-reference style return parameter which is only used
2124 * when returning false (i.e., uncertain). Returns most information regarding
2125 * an uncertain release sequence, including any write operations that might
2126 * break the sequence.
2127 * @return true, if the ModelChecker is certain that release_heads is complete;
2130 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2131 rel_heads_list_t *release_heads,
2132 struct release_seq *pending) const
2134 /* Only check for release sequences if there are no cycles */
2135 if (mo_graph->checkForCycles())
2138 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2139 ASSERT(rf->is_write());
2141 if (rf->is_release())
2142 release_heads->push_back(rf);
2143 else if (rf->get_last_fence_release())
2144 release_heads->push_back(rf->get_last_fence_release());
2146 break; /* End of RMW chain */
2148 /** @todo Need to be smarter here... In the linux lock
2149 * example, this will run to the beginning of the program for
2151 /** @todo The way to be smarter here is to keep going until 1
2152 * thread has a release preceded by an acquire and you've seen
2155 /* acq_rel RMW is a sufficient stopping condition */
2156 if (rf->is_acquire() && rf->is_release())
2157 return true; /* complete */
2160 /* read from future: need to settle this later */
2162 return false; /* incomplete */
2165 if (rf->is_release())
2166 return true; /* complete */
2168 /* else relaxed write
2169 * - check for fence-release in the same thread (29.8, stmt. 3)
2170 * - check modification order for contiguous subsequence
2171 * -> rf must be same thread as release */
2173 const ModelAction *fence_release = rf->get_last_fence_release();
2174 /* Synchronize with a fence-release unconditionally; we don't need to
2175 * find any more "contiguous subsequence..." for it */
2177 release_heads->push_back(fence_release);
2179 int tid = id_to_int(rf->get_tid());
2180 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2181 action_list_t *list = &(*thrd_lists)[tid];
2182 action_list_t::const_reverse_iterator rit;
2184 /* Find rf in the thread list */
2185 rit = std::find(list->rbegin(), list->rend(), rf);
2186 ASSERT(rit != list->rend());
2188 /* Find the last {write,fence}-release */
2189 for (; rit != list->rend(); rit++) {
2190 if (fence_release && *(*rit) < *fence_release)
2192 if ((*rit)->is_release())
2195 if (rit == list->rend()) {
2196 /* No write-release in this thread */
2197 return true; /* complete */
2198 } else if (fence_release && *(*rit) < *fence_release) {
2199 /* The fence-release is more recent (and so, "stronger") than
2200 * the most recent write-release */
2201 return true; /* complete */
2202 } /* else, need to establish contiguous release sequence */
2203 ModelAction *release = *rit;
2205 ASSERT(rf->same_thread(release));
2207 pending->writes.clear();
2209 bool certain = true;
2210 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2211 if (id_to_int(rf->get_tid()) == (int)i)
2213 list = &(*thrd_lists)[i];
2215 /* Can we ensure no future writes from this thread may break
2216 * the release seq? */
2217 bool future_ordered = false;
2219 ModelAction *last = get_last_action(int_to_id(i));
2220 Thread *th = get_thread(int_to_id(i));
2221 if ((last && rf->happens_before(last)) ||
2224 future_ordered = true;
2226 ASSERT(!th->is_model_thread() || future_ordered);
2228 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2229 const ModelAction *act = *rit;
2230 /* Reach synchronization -> this thread is complete */
2231 if (act->happens_before(release))
2233 if (rf->happens_before(act)) {
2234 future_ordered = true;
2238 /* Only non-RMW writes can break release sequences */
2239 if (!act->is_write() || act->is_rmw())
2242 /* Check modification order */
2243 if (mo_graph->checkReachable(rf, act)) {
2244 /* rf --mo--> act */
2245 future_ordered = true;
2248 if (mo_graph->checkReachable(act, release))
2249 /* act --mo--> release */
2251 if (mo_graph->checkReachable(release, act) &&
2252 mo_graph->checkReachable(act, rf)) {
2253 /* release --mo-> act --mo--> rf */
2254 return true; /* complete */
2256 /* act may break release sequence */
2257 pending->writes.push_back(act);
2260 if (!future_ordered)
2261 certain = false; /* This thread is uncertain */
2265 release_heads->push_back(release);
2266 pending->writes.clear();
2268 pending->release = release;
2275 * An interface for getting the release sequence head(s) with which a
2276 * given ModelAction must synchronize. This function only returns a non-empty
2277 * result when it can locate a release sequence head with certainty. Otherwise,
2278 * it may mark the internal state of the ModelChecker so that it will handle
2279 * the release sequence at a later time, causing @a acquire to update its
2280 * synchronization at some later point in execution.
2282 * @param acquire The 'acquire' action that may synchronize with a release
2284 * @param read The read action that may read from a release sequence; this may
2285 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2286 * when 'acquire' is a fence-acquire)
2287 * @param release_heads A pass-by-reference return parameter. Will be filled
2288 * with the head(s) of the release sequence(s), if they exists with certainty.
2289 * @see ModelChecker::release_seq_heads
2291 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2292 ModelAction *read, rel_heads_list_t *release_heads)
2294 const ModelAction *rf = read->get_reads_from();
2295 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2296 sequence->acquire = acquire;
2297 sequence->read = read;
2299 if (!release_seq_heads(rf, release_heads, sequence)) {
2300 /* add act to 'lazy checking' list */
2301 pending_rel_seqs->push_back(sequence);
2303 snapshot_free(sequence);
2308 * Attempt to resolve all stashed operations that might synchronize with a
2309 * release sequence for a given location. This implements the "lazy" portion of
2310 * determining whether or not a release sequence was contiguous, since not all
2311 * modification order information is present at the time an action occurs.
2313 * @param location The location/object that should be checked for release
2314 * sequence resolutions. A NULL value means to check all locations.
2315 * @param work_queue The work queue to which to add work items as they are
2317 * @return True if any updates occurred (new synchronization, new mo_graph
2320 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2322 bool updated = false;
2323 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2324 while (it != pending_rel_seqs->end()) {
2325 struct release_seq *pending = *it;
2326 ModelAction *acquire = pending->acquire;
2327 const ModelAction *read = pending->read;
2329 /* Only resolve sequences on the given location, if provided */
2330 if (location && read->get_location() != location) {
2335 const ModelAction *rf = read->get_reads_from();
2336 rel_heads_list_t release_heads;
2338 complete = release_seq_heads(rf, &release_heads, pending);
2339 for (unsigned int i = 0; i < release_heads.size(); i++) {
2340 if (!acquire->has_synchronized_with(release_heads[i])) {
2341 if (acquire->synchronize_with(release_heads[i]))
2344 set_bad_synchronization();
2349 /* Re-check all pending release sequences */
2350 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2351 /* Re-check read-acquire for mo_graph edges */
2352 if (acquire->is_read())
2353 work_queue->push_back(MOEdgeWorkEntry(acquire));
2355 /* propagate synchronization to later actions */
2356 action_list_t::reverse_iterator rit = action_trace->rbegin();
2357 for (; (*rit) != acquire; rit++) {
2358 ModelAction *propagate = *rit;
2359 if (acquire->happens_before(propagate)) {
2360 propagate->synchronize_with(acquire);
2361 /* Re-check 'propagate' for mo_graph edges */
2362 work_queue->push_back(MOEdgeWorkEntry(propagate));
2367 it = pending_rel_seqs->erase(it);
2368 snapshot_free(pending);
2374 // If we resolved promises or data races, see if we have realized a data race.
2381 * Performs various bookkeeping operations for the current ModelAction. For
2382 * instance, adds action to the per-object, per-thread action vector and to the
2383 * action trace list of all thread actions.
2385 * @param act is the ModelAction to add.
2387 void ModelChecker::add_action_to_lists(ModelAction *act)
2389 int tid = id_to_int(act->get_tid());
2390 ModelAction *uninit = NULL;
2392 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2393 if (list->empty() && act->is_atomic_var()) {
2394 uninit = get_uninitialized_action(act);
2395 uninit_id = id_to_int(uninit->get_tid());
2396 list->push_front(uninit);
2398 list->push_back(act);
2400 action_trace->push_back(act);
2402 action_trace->push_front(uninit);
2404 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2405 if (tid >= (int)vec->size())
2406 vec->resize(priv->next_thread_id);
2407 (*vec)[tid].push_back(act);
2409 (*vec)[uninit_id].push_front(uninit);
2411 if ((int)thrd_last_action->size() <= tid)
2412 thrd_last_action->resize(get_num_threads());
2413 (*thrd_last_action)[tid] = act;
2415 (*thrd_last_action)[uninit_id] = uninit;
2417 if (act->is_fence() && act->is_release()) {
2418 if ((int)thrd_last_fence_release->size() <= tid)
2419 thrd_last_fence_release->resize(get_num_threads());
2420 (*thrd_last_fence_release)[tid] = act;
2423 if (act->is_wait()) {
2424 void *mutex_loc = (void *) act->get_value();
2425 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2427 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2428 if (tid >= (int)vec->size())
2429 vec->resize(priv->next_thread_id);
2430 (*vec)[tid].push_back(act);
2435 * @brief Get the last action performed by a particular Thread
2436 * @param tid The thread ID of the Thread in question
2437 * @return The last action in the thread
2439 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2441 int threadid = id_to_int(tid);
2442 if (threadid < (int)thrd_last_action->size())
2443 return (*thrd_last_action)[id_to_int(tid)];
2449 * @brief Get the last fence release performed by a particular Thread
2450 * @param tid The thread ID of the Thread in question
2451 * @return The last fence release in the thread, if one exists; NULL otherwise
2453 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2455 int threadid = id_to_int(tid);
2456 if (threadid < (int)thrd_last_fence_release->size())
2457 return (*thrd_last_fence_release)[id_to_int(tid)];
2463 * Gets the last memory_order_seq_cst write (in the total global sequence)
2464 * performed on a particular object (i.e., memory location), not including the
2466 * @param curr The current ModelAction; also denotes the object location to
2468 * @return The last seq_cst write
2470 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2472 void *location = curr->get_location();
2473 action_list_t *list = get_safe_ptr_action(obj_map, location);
2474 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2475 action_list_t::reverse_iterator rit;
2476 for (rit = list->rbegin(); (*rit) != curr; rit++)
2478 rit++; /* Skip past curr */
2479 for ( ; rit != list->rend(); rit++)
2480 if ((*rit)->is_write() && (*rit)->is_seqcst())
2486 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2487 * performed in a particular thread, prior to a particular fence.
2488 * @param tid The ID of the thread to check
2489 * @param before_fence The fence from which to begin the search; if NULL, then
2490 * search for the most recent fence in the thread.
2491 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2493 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2495 /* All fences should have NULL location */
2496 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2497 action_list_t::reverse_iterator rit = list->rbegin();
2500 for (; rit != list->rend(); rit++)
2501 if (*rit == before_fence)
2504 ASSERT(*rit == before_fence);
2508 for (; rit != list->rend(); rit++)
2509 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2515 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2516 * location). This function identifies the mutex according to the current
2517 * action, which is presumed to perform on the same mutex.
2518 * @param curr The current ModelAction; also denotes the object location to
2520 * @return The last unlock operation
2522 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2524 void *location = curr->get_location();
2525 action_list_t *list = get_safe_ptr_action(obj_map, location);
2526 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2527 action_list_t::reverse_iterator rit;
2528 for (rit = list->rbegin(); rit != list->rend(); rit++)
2529 if ((*rit)->is_unlock() || (*rit)->is_wait())
2534 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2536 ModelAction *parent = get_last_action(tid);
2538 parent = get_thread(tid)->get_creation();
2543 * Returns the clock vector for a given thread.
2544 * @param tid The thread whose clock vector we want
2545 * @return Desired clock vector
2547 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2549 return get_parent_action(tid)->get_cv();
2553 * @brief Find the promise, if any to resolve for the current action
2554 * @param curr The current ModelAction. Should be a write.
2555 * @return The (non-negative) index for the Promise to resolve, if any;
2558 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2560 for (unsigned int i = 0; i < promises->size(); i++)
2561 if (curr->get_node()->get_promise(i))
2567 * Resolve a Promise with a current write.
2568 * @param write The ModelAction that is fulfilling Promises
2569 * @param promise_idx The index corresponding to the promise
2570 * @return True if the Promise was successfully resolved; false otherwise
2572 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2574 ModelVector<ModelAction *> actions_to_check;
2575 Promise *promise = (*promises)[promise_idx];
2577 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2578 ModelAction *read = promise->get_reader(i);
2579 read_from(read, write);
2580 actions_to_check.push_back(read);
2582 /* Make sure the promise's value matches the write's value */
2583 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2584 if (!mo_graph->resolvePromise(promise, write))
2585 priv->failed_promise = true;
2587 promises->erase(promises->begin() + promise_idx);
2589 * @todo It is possible to end up in an inconsistent state, where a
2590 * "resolved" promise may still be referenced if
2591 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2593 * Note that the inconsistency only matters when dumping mo_graph to
2599 //Check whether reading these writes has made threads unable to
2601 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2602 ModelAction *read = actions_to_check[i];
2603 mo_check_promises(read, true);
2610 * Compute the set of promises that could potentially be satisfied by this
2611 * action. Note that the set computation actually appears in the Node, not in
2613 * @param curr The ModelAction that may satisfy promises
2615 void ModelChecker::compute_promises(ModelAction *curr)
2617 for (unsigned int i = 0; i < promises->size(); i++) {
2618 Promise *promise = (*promises)[i];
2619 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2622 bool satisfy = true;
2623 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2624 const ModelAction *act = promise->get_reader(j);
2625 if (act->happens_before(curr) ||
2626 act->could_synchronize_with(curr)) {
2632 curr->get_node()->set_promise(i);
2636 /** Checks promises in response to change in ClockVector Threads. */
2637 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2639 for (unsigned int i = 0; i < promises->size(); i++) {
2640 Promise *promise = (*promises)[i];
2641 if (!promise->thread_is_available(tid))
2643 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2644 const ModelAction *act = promise->get_reader(j);
2645 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2646 merge_cv->synchronized_since(act)) {
2647 if (promise->eliminate_thread(tid)) {
2648 /* Promise has failed */
2649 priv->failed_promise = true;
2657 void ModelChecker::check_promises_thread_disabled()
2659 for (unsigned int i = 0; i < promises->size(); i++) {
2660 Promise *promise = (*promises)[i];
2661 if (promise->has_failed()) {
2662 priv->failed_promise = true;
2669 * @brief Checks promises in response to addition to modification order for
2672 * We test whether threads are still available for satisfying promises after an
2673 * addition to our modification order constraints. Those that are unavailable
2674 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2675 * that promise has failed.
2677 * @param act The ModelAction which updated the modification order
2678 * @param is_read_check Should be true if act is a read and we must check for
2679 * updates to the store from which it read (there is a distinction here for
2680 * RMW's, which are both a load and a store)
2682 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2684 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2686 for (unsigned int i = 0; i < promises->size(); i++) {
2687 Promise *promise = (*promises)[i];
2689 // Is this promise on the same location?
2690 if (!promise->same_location(write))
2693 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2694 const ModelAction *pread = promise->get_reader(j);
2695 if (!pread->happens_before(act))
2697 if (mo_graph->checkPromise(write, promise)) {
2698 priv->failed_promise = true;
2704 // Don't do any lookups twice for the same thread
2705 if (!promise->thread_is_available(act->get_tid()))
2708 if (mo_graph->checkReachable(promise, write)) {
2709 if (mo_graph->checkPromise(write, promise)) {
2710 priv->failed_promise = true;
2718 * Compute the set of writes that may break the current pending release
2719 * sequence. This information is extracted from previou release sequence
2722 * @param curr The current ModelAction. Must be a release sequence fixup
2725 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2727 if (pending_rel_seqs->empty())
2730 struct release_seq *pending = pending_rel_seqs->back();
2731 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2732 const ModelAction *write = pending->writes[i];
2733 curr->get_node()->add_relseq_break(write);
2736 /* NULL means don't break the sequence; just synchronize */
2737 curr->get_node()->add_relseq_break(NULL);
2741 * Build up an initial set of all past writes that this 'read' action may read
2742 * from, as well as any previously-observed future values that must still be valid.
2744 * @param curr is the current ModelAction that we are exploring; it must be a
2747 void ModelChecker::build_may_read_from(ModelAction *curr)
2749 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2751 ASSERT(curr->is_read());
2753 ModelAction *last_sc_write = NULL;
2755 if (curr->is_seqcst())
2756 last_sc_write = get_last_seq_cst_write(curr);
2758 /* Iterate over all threads */
2759 for (i = 0; i < thrd_lists->size(); i++) {
2760 /* Iterate over actions in thread, starting from most recent */
2761 action_list_t *list = &(*thrd_lists)[i];
2762 action_list_t::reverse_iterator rit;
2763 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2764 ModelAction *act = *rit;
2766 /* Only consider 'write' actions */
2767 if (!act->is_write() || act == curr)
2770 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2771 bool allow_read = true;
2773 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2775 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2779 /* Only add feasible reads */
2780 mo_graph->startChanges();
2781 r_modification_order(curr, act);
2782 if (!is_infeasible())
2783 curr->get_node()->add_read_from_past(act);
2784 mo_graph->rollbackChanges();
2787 /* Include at most one act per-thread that "happens before" curr */
2788 if (act->happens_before(curr))
2793 /* Inherit existing, promised future values */
2794 for (i = 0; i < promises->size(); i++) {
2795 const Promise *promise = (*promises)[i];
2796 const ModelAction *promise_read = promise->get_reader(0);
2797 if (promise_read->same_var(curr)) {
2798 /* Only add feasible future-values */
2799 mo_graph->startChanges();
2800 r_modification_order(curr, promise);
2801 if (!is_infeasible())
2802 curr->get_node()->add_read_from_promise(promise_read);
2803 mo_graph->rollbackChanges();
2807 /* We may find no valid may-read-from only if the execution is doomed */
2808 if (!curr->get_node()->read_from_size()) {
2809 priv->no_valid_reads = true;
2813 if (DBG_ENABLED()) {
2814 model_print("Reached read action:\n");
2816 model_print("Printing read_from_past\n");
2817 curr->get_node()->print_read_from_past();
2818 model_print("End printing read_from_past\n");
2822 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2824 for ( ; write != NULL; write = write->get_reads_from()) {
2825 /* UNINIT actions don't have a Node, and they never sleep */
2826 if (write->is_uninitialized())
2828 Node *prevnode = write->get_node()->get_parent();
2830 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2831 if (write->is_release() && thread_sleep)
2833 if (!write->is_rmw())
2840 * @brief Get an action representing an uninitialized atomic
2842 * This function may create a new one or try to retrieve one from the NodeStack
2844 * @param curr The current action, which prompts the creation of an UNINIT action
2845 * @return A pointer to the UNINIT ModelAction
2847 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2849 Node *node = curr->get_node();
2850 ModelAction *act = node->get_uninit_action();
2852 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2853 node->set_uninit_action(act);
2855 act->create_cv(NULL);
2859 static void print_list(action_list_t *list)
2861 action_list_t::iterator it;
2863 model_print("---------------------------------------------------------------------\n");
2865 unsigned int hash = 0;
2867 for (it = list->begin(); it != list->end(); it++) {
2868 const ModelAction *act = *it;
2869 if (act->get_seq_number() > 0)
2871 hash = hash^(hash<<3)^((*it)->hash());
2873 model_print("HASH %u\n", hash);
2874 model_print("---------------------------------------------------------------------\n");
2877 #if SUPPORT_MOD_ORDER_DUMP
2878 void ModelChecker::dumpGraph(char *filename) const
2881 sprintf(buffer, "%s.dot", filename);
2882 FILE *file = fopen(buffer, "w");
2883 fprintf(file, "digraph %s {\n", filename);
2884 mo_graph->dumpNodes(file);
2885 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2887 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2888 ModelAction *act = *it;
2889 if (act->is_read()) {
2890 mo_graph->dot_print_node(file, act);
2891 if (act->get_reads_from())
2892 mo_graph->dot_print_edge(file,
2893 act->get_reads_from(),
2895 "label=\"rf\", color=red, weight=2");
2897 mo_graph->dot_print_edge(file,
2898 act->get_reads_from_promise(),
2900 "label=\"rf\", color=red");
2902 if (thread_array[act->get_tid()]) {
2903 mo_graph->dot_print_edge(file,
2904 thread_array[id_to_int(act->get_tid())],
2906 "label=\"sb\", color=blue, weight=400");
2909 thread_array[act->get_tid()] = act;
2911 fprintf(file, "}\n");
2912 model_free(thread_array);
2917 /** @brief Prints an execution trace summary. */
2918 void ModelChecker::print_summary() const
2920 #if SUPPORT_MOD_ORDER_DUMP
2921 char buffername[100];
2922 sprintf(buffername, "exec%04u", stats.num_total);
2923 mo_graph->dumpGraphToFile(buffername);
2924 sprintf(buffername, "graph%04u", stats.num_total);
2925 dumpGraph(buffername);
2928 model_print("Execution %d:", stats.num_total);
2929 if (isfeasibleprefix()) {
2930 if (scheduler->all_threads_sleeping())
2931 model_print(" SLEEP-SET REDUNDANT");
2934 print_infeasibility(" INFEASIBLE");
2935 print_list(action_trace);
2937 if (!promises->empty()) {
2938 model_print("Pending promises:\n");
2939 for (unsigned int i = 0; i < promises->size(); i++) {
2940 model_print(" [P%u] ", i);
2941 (*promises)[i]->print();
2948 * Add a Thread to the system for the first time. Should only be called once
2950 * @param t The Thread to add
2952 void ModelChecker::add_thread(Thread *t)
2954 thread_map->put(id_to_int(t->get_id()), t);
2955 scheduler->add_thread(t);
2959 * @brief Get a Thread reference by its ID
2960 * @param tid The Thread's ID
2961 * @return A Thread reference
2963 Thread * ModelChecker::get_thread(thread_id_t tid) const
2965 return thread_map->get(id_to_int(tid));
2969 * @brief Get a reference to the Thread in which a ModelAction was executed
2970 * @param act The ModelAction
2971 * @return A Thread reference
2973 Thread * ModelChecker::get_thread(const ModelAction *act) const
2975 return get_thread(act->get_tid());
2979 * @brief Get a Promise's "promise number"
2981 * A "promise number" is an index number that is unique to a promise, valid
2982 * only for a specific snapshot of an execution trace. Promises may come and go
2983 * as they are generated an resolved, so an index only retains meaning for the
2986 * @param promise The Promise to check
2987 * @return The promise index, if the promise still is valid; otherwise -1
2989 int ModelChecker::get_promise_number(const Promise *promise) const
2991 for (unsigned int i = 0; i < promises->size(); i++)
2992 if ((*promises)[i] == promise)
2999 * @brief Check if a Thread is currently enabled
3000 * @param t The Thread to check
3001 * @return True if the Thread is currently enabled
3003 bool ModelChecker::is_enabled(Thread *t) const
3005 return scheduler->is_enabled(t);
3009 * @brief Check if a Thread is currently enabled
3010 * @param tid The ID of the Thread to check
3011 * @return True if the Thread is currently enabled
3013 bool ModelChecker::is_enabled(thread_id_t tid) const
3015 return scheduler->is_enabled(tid);
3019 * Switch from a model-checker context to a user-thread context. This is the
3020 * complement of ModelChecker::switch_to_master and must be called from the
3021 * model-checker context
3023 * @param thread The user-thread to switch to
3025 void ModelChecker::switch_from_master(Thread *thread)
3027 scheduler->set_current_thread(thread);
3028 Thread::swap(&system_context, thread);
3032 * Switch from a user-context to the "master thread" context (a.k.a. system
3033 * context). This switch is made with the intention of exploring a particular
3034 * model-checking action (described by a ModelAction object). Must be called
3035 * from a user-thread context.
3037 * @param act The current action that will be explored. May be NULL only if
3038 * trace is exiting via an assertion (see ModelChecker::set_assert and
3039 * ModelChecker::has_asserted).
3040 * @return Return the value returned by the current action
3042 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3045 Thread *old = thread_current();
3046 scheduler->set_current_thread(NULL);
3047 ASSERT(!old->get_pending());
3048 old->set_pending(act);
3049 if (Thread::swap(old, &system_context) < 0) {
3050 perror("swap threads");
3053 return old->get_return_value();
3057 * Takes the next step in the execution, if possible.
3058 * @param curr The current step to take
3059 * @return Returns the next Thread to run, if any; NULL if this execution
3062 Thread * ModelChecker::take_step(ModelAction *curr)
3064 Thread *curr_thrd = get_thread(curr);
3065 ASSERT(curr_thrd->get_state() == THREAD_READY);
3067 curr = check_current_action(curr);
3069 /* Infeasible -> don't take any more steps */
3070 if (is_infeasible())
3072 else if (isfeasibleprefix() && have_bug_reports()) {
3077 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3080 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3081 scheduler->remove_thread(curr_thrd);
3083 Thread *next_thrd = NULL;
3085 next_thrd = action_select_next_thread(curr);
3087 next_thrd = get_next_thread();
3089 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3090 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3095 /** Wrapper to run the user's main function, with appropriate arguments */
3096 void user_main_wrapper(void *)
3098 user_main(model->params.argc, model->params.argv);
3101 /** @brief Run ModelChecker for the user program */
3102 void ModelChecker::run()
3106 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3111 * Stash next pending action(s) for thread(s). There
3112 * should only need to stash one thread's action--the
3113 * thread which just took a step--plus the first step
3114 * for any newly-created thread
3116 for (unsigned int i = 0; i < get_num_threads(); i++) {
3117 thread_id_t tid = int_to_id(i);
3118 Thread *thr = get_thread(tid);
3119 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3120 switch_from_master(thr);
3121 if (is_circular_wait(thr))
3122 assert_bug("Deadlock detected");
3126 /* Catch assertions from prior take_step or from
3127 * between-ModelAction bugs (e.g., data races) */
3131 /* Consume the next action for a Thread */
3132 ModelAction *curr = t->get_pending();
3133 t->set_pending(NULL);
3134 t = take_step(curr);
3135 } while (t && !t->is_model_thread());
3138 * Launch end-of-execution release sequence fixups only when
3139 * the execution is otherwise feasible AND there are:
3141 * (1) pending release sequences
3142 * (2) pending assertions that could be invalidated by a change
3143 * in clock vectors (i.e., data races)
3144 * (3) no pending promises
3146 while (!pending_rel_seqs->empty() &&
3147 is_feasible_prefix_ignore_relseq() &&
3148 !unrealizedraces.empty()) {
3149 model_print("*** WARNING: release sequence fixup action "
3150 "(%zu pending release seuqence(s)) ***\n",
3151 pending_rel_seqs->size());
3152 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3153 std::memory_order_seq_cst, NULL, VALUE_NONE,
3157 } while (next_execution());
3159 model_print("******* Model-checking complete: *******\n");