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
1132 bool updated = false;
1133 if (curr->is_acquire()) {
1134 action_list_t *list = action_trace;
1135 action_list_t::reverse_iterator rit;
1136 /* Find X : is_read(X) && X --sb-> curr */
1137 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1138 ModelAction *act = *rit;
1141 if (act->get_tid() != curr->get_tid())
1143 /* Stop at the beginning of the thread */
1144 if (act->is_thread_start())
1146 /* Stop once we reach a prior fence-acquire */
1147 if (act->is_fence() && act->is_acquire())
1149 if (!act->is_read())
1151 /* read-acquire will find its own release sequences */
1152 if (act->is_acquire())
1155 /* Establish hypothetical release sequences */
1156 rel_heads_list_t release_heads;
1157 get_release_seq_heads(curr, act, &release_heads);
1158 for (unsigned int i = 0; i < release_heads.size(); i++)
1159 if (!curr->synchronize_with(release_heads[i]))
1160 set_bad_synchronization();
1161 if (release_heads.size() != 0)
1169 * @brief Process the current action for thread-related activity
1171 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1172 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1173 * synchronization, etc. This function is a no-op for non-THREAD actions
1174 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1176 * @param curr The current action
1177 * @return True if synchronization was updated or a thread completed
1179 bool ModelChecker::process_thread_action(ModelAction *curr)
1181 bool updated = false;
1183 switch (curr->get_type()) {
1184 case THREAD_CREATE: {
1185 thrd_t *thrd = (thrd_t *)curr->get_location();
1186 struct thread_params *params = (struct thread_params *)curr->get_value();
1187 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1189 th->set_creation(curr);
1190 /* Promises can be satisfied by children */
1191 for (unsigned int i = 0; i < promises->size(); i++) {
1192 Promise *promise = (*promises)[i];
1193 if (promise->thread_is_available(curr->get_tid()))
1194 promise->add_thread(th->get_id());
1199 Thread *blocking = curr->get_thread_operand();
1200 ModelAction *act = get_last_action(blocking->get_id());
1201 curr->synchronize_with(act);
1202 updated = true; /* trigger rel-seq checks */
1205 case THREAD_FINISH: {
1206 Thread *th = get_thread(curr);
1207 while (!th->wait_list_empty()) {
1208 ModelAction *act = th->pop_wait_list();
1209 scheduler->wake(get_thread(act));
1212 /* Completed thread can't satisfy promises */
1213 for (unsigned int i = 0; i < promises->size(); i++) {
1214 Promise *promise = (*promises)[i];
1215 if (promise->thread_is_available(th->get_id()))
1216 if (promise->eliminate_thread(th->get_id()))
1217 priv->failed_promise = true;
1219 updated = true; /* trigger rel-seq checks */
1222 case THREAD_START: {
1223 check_promises(curr->get_tid(), NULL, curr->get_cv());
1234 * @brief Process the current action for release sequence fixup activity
1236 * Performs model-checker release sequence fixups for the current action,
1237 * forcing a single pending release sequence to break (with a given, potential
1238 * "loose" write) or to complete (i.e., synchronize). If a pending release
1239 * sequence forms a complete release sequence, then we must perform the fixup
1240 * synchronization, mo_graph additions, etc.
1242 * @param curr The current action; must be a release sequence fixup action
1243 * @param work_queue The work queue to which to add work items as they are
1246 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1248 const ModelAction *write = curr->get_node()->get_relseq_break();
1249 struct release_seq *sequence = pending_rel_seqs->back();
1250 pending_rel_seqs->pop_back();
1252 ModelAction *acquire = sequence->acquire;
1253 const ModelAction *rf = sequence->rf;
1254 const ModelAction *release = sequence->release;
1258 ASSERT(release->same_thread(rf));
1260 if (write == NULL) {
1262 * @todo Forcing a synchronization requires that we set
1263 * modification order constraints. For instance, we can't allow
1264 * a fixup sequence in which two separate read-acquire
1265 * operations read from the same sequence, where the first one
1266 * synchronizes and the other doesn't. Essentially, we can't
1267 * allow any writes to insert themselves between 'release' and
1271 /* Must synchronize */
1272 if (!acquire->synchronize_with(release)) {
1273 set_bad_synchronization();
1276 /* Re-check all pending release sequences */
1277 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1278 /* Re-check act for mo_graph edges */
1279 work_queue->push_back(MOEdgeWorkEntry(acquire));
1281 /* propagate synchronization to later actions */
1282 action_list_t::reverse_iterator rit = action_trace->rbegin();
1283 for (; (*rit) != acquire; rit++) {
1284 ModelAction *propagate = *rit;
1285 if (acquire->happens_before(propagate)) {
1286 propagate->synchronize_with(acquire);
1287 /* Re-check 'propagate' for mo_graph edges */
1288 work_queue->push_back(MOEdgeWorkEntry(propagate));
1292 /* Break release sequence with new edges:
1293 * release --mo--> write --mo--> rf */
1294 mo_graph->addEdge(release, write);
1295 mo_graph->addEdge(write, rf);
1298 /* See if we have realized a data race */
1303 * Initialize the current action by performing one or more of the following
1304 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1305 * in the NodeStack, manipulating backtracking sets, allocating and
1306 * initializing clock vectors, and computing the promises to fulfill.
1308 * @param curr The current action, as passed from the user context; may be
1309 * freed/invalidated after the execution of this function, with a different
1310 * action "returned" its place (pass-by-reference)
1311 * @return True if curr is a newly-explored action; false otherwise
1313 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1315 ModelAction *newcurr;
1317 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1318 newcurr = process_rmw(*curr);
1321 if (newcurr->is_rmw())
1322 compute_promises(newcurr);
1328 (*curr)->set_seq_number(get_next_seq_num());
1330 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1332 /* First restore type and order in case of RMW operation */
1333 if ((*curr)->is_rmwr())
1334 newcurr->copy_typeandorder(*curr);
1336 ASSERT((*curr)->get_location() == newcurr->get_location());
1337 newcurr->copy_from_new(*curr);
1339 /* Discard duplicate ModelAction; use action from NodeStack */
1342 /* Always compute new clock vector */
1343 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1346 return false; /* Action was explored previously */
1350 /* Always compute new clock vector */
1351 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1353 /* Assign most recent release fence */
1354 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1357 * Perform one-time actions when pushing new ModelAction onto
1360 if (newcurr->is_write())
1361 compute_promises(newcurr);
1362 else if (newcurr->is_relseq_fixup())
1363 compute_relseq_breakwrites(newcurr);
1364 else if (newcurr->is_wait())
1365 newcurr->get_node()->set_misc_max(2);
1366 else if (newcurr->is_notify_one()) {
1367 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1369 return true; /* This was a new ModelAction */
1374 * @brief Establish reads-from relation between two actions
1376 * Perform basic operations involved with establishing a concrete rf relation,
1377 * including setting the ModelAction data and checking for release sequences.
1379 * @param act The action that is reading (must be a read)
1380 * @param rf The action from which we are reading (must be a write)
1382 * @return True if this read established synchronization
1384 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1387 ASSERT(rf->is_write());
1389 act->set_read_from(rf);
1390 if (act->is_acquire()) {
1391 rel_heads_list_t release_heads;
1392 get_release_seq_heads(act, act, &release_heads);
1393 int num_heads = release_heads.size();
1394 for (unsigned int i = 0; i < release_heads.size(); i++)
1395 if (!act->synchronize_with(release_heads[i])) {
1396 set_bad_synchronization();
1399 return num_heads > 0;
1405 * Check promises and eliminate potentially-satisfying threads when a thread is
1406 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1407 * no longer satisfy a promise generated from that thread.
1409 * @param blocker The thread on which a thread is waiting
1410 * @param waiting The waiting thread
1412 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1414 for (unsigned int i = 0; i < promises->size(); i++) {
1415 Promise *promise = (*promises)[i];
1416 if (!promise->thread_is_available(waiting->get_id()))
1418 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1419 ModelAction *reader = promise->get_reader(j);
1420 if (reader->get_tid() != blocker->get_id())
1422 if (promise->eliminate_thread(waiting->get_id())) {
1423 /* Promise has failed */
1424 priv->failed_promise = true;
1426 /* Only eliminate the 'waiting' thread once */
1434 * @brief Check whether a model action is enabled.
1436 * Checks whether a lock or join operation would be successful (i.e., is the
1437 * lock already locked, or is the joined thread already complete). If not, put
1438 * the action in a waiter list.
1440 * @param curr is the ModelAction to check whether it is enabled.
1441 * @return a bool that indicates whether the action is enabled.
1443 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1444 if (curr->is_lock()) {
1445 std::mutex *lock = (std::mutex *)curr->get_location();
1446 struct std::mutex_state *state = lock->get_state();
1447 if (state->locked) {
1448 //Stick the action in the appropriate waiting queue
1449 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1452 } else if (curr->get_type() == THREAD_JOIN) {
1453 Thread *blocking = (Thread *)curr->get_location();
1454 if (!blocking->is_complete()) {
1455 blocking->push_wait_list(curr);
1456 thread_blocking_check_promises(blocking, get_thread(curr));
1465 * This is the heart of the model checker routine. It performs model-checking
1466 * actions corresponding to a given "current action." Among other processes, it
1467 * calculates reads-from relationships, updates synchronization clock vectors,
1468 * forms a memory_order constraints graph, and handles replay/backtrack
1469 * execution when running permutations of previously-observed executions.
1471 * @param curr The current action to process
1472 * @return The ModelAction that is actually executed; may be different than
1473 * curr; may be NULL, if the current action is not enabled to run
1475 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1478 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1480 if (!check_action_enabled(curr)) {
1481 /* Make the execution look like we chose to run this action
1482 * much later, when a lock/join can succeed */
1483 get_thread(curr)->set_pending(curr);
1484 scheduler->sleep(get_thread(curr));
1488 bool newly_explored = initialize_curr_action(&curr);
1494 wake_up_sleeping_actions(curr);
1496 /* Compute fairness information for CHESS yield algorithm */
1497 if (model->params.yieldon) {
1498 curr->get_node()->update_yield(scheduler);
1501 /* Add the action to lists before any other model-checking tasks */
1502 if (!second_part_of_rmw)
1503 add_action_to_lists(curr);
1505 /* Build may_read_from set for newly-created actions */
1506 if (newly_explored && curr->is_read())
1507 build_may_read_from(curr);
1509 /* Initialize work_queue with the "current action" work */
1510 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1511 while (!work_queue.empty() && !has_asserted()) {
1512 WorkQueueEntry work = work_queue.front();
1513 work_queue.pop_front();
1515 switch (work.type) {
1516 case WORK_CHECK_CURR_ACTION: {
1517 ModelAction *act = work.action;
1518 bool update = false; /* update this location's release seq's */
1519 bool update_all = false; /* update all release seq's */
1521 if (process_thread_action(curr))
1524 if (act->is_read() && !second_part_of_rmw && process_read(act))
1527 if (act->is_write() && process_write(act))
1530 if (act->is_fence() && process_fence(act))
1533 if (act->is_mutex_op() && process_mutex(act))
1536 if (act->is_relseq_fixup())
1537 process_relseq_fixup(curr, &work_queue);
1540 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1542 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1545 case WORK_CHECK_RELEASE_SEQ:
1546 resolve_release_sequences(work.location, &work_queue);
1548 case WORK_CHECK_MO_EDGES: {
1549 /** @todo Complete verification of work_queue */
1550 ModelAction *act = work.action;
1551 bool updated = false;
1553 if (act->is_read()) {
1554 const ModelAction *rf = act->get_reads_from();
1555 const Promise *promise = act->get_reads_from_promise();
1557 if (r_modification_order(act, rf))
1559 } else if (promise) {
1560 if (r_modification_order(act, promise))
1564 if (act->is_write()) {
1565 if (w_modification_order(act, NULL))
1568 mo_graph->commitChanges();
1571 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1580 check_curr_backtracking(curr);
1581 set_backtracking(curr);
1585 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1587 Node *currnode = curr->get_node();
1588 Node *parnode = currnode->get_parent();
1590 if ((parnode && !parnode->backtrack_empty()) ||
1591 !currnode->misc_empty() ||
1592 !currnode->read_from_empty() ||
1593 !currnode->promise_empty() ||
1594 !currnode->relseq_break_empty()) {
1595 set_latest_backtrack(curr);
1599 bool ModelChecker::promises_expired() const
1601 for (unsigned int i = 0; i < promises->size(); i++) {
1602 Promise *promise = (*promises)[i];
1603 if (promise->get_expiration() < priv->used_sequence_numbers)
1610 * This is the strongest feasibility check available.
1611 * @return whether the current trace (partial or complete) must be a prefix of
1614 bool ModelChecker::isfeasibleprefix() const
1616 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1620 * Print disagnostic information about an infeasible execution
1621 * @param prefix A string to prefix the output with; if NULL, then a default
1622 * message prefix will be provided
1624 void ModelChecker::print_infeasibility(const char *prefix) const
1628 if (mo_graph->checkForCycles())
1629 ptr += sprintf(ptr, "[mo cycle]");
1630 if (priv->failed_promise)
1631 ptr += sprintf(ptr, "[failed promise]");
1632 if (priv->too_many_reads)
1633 ptr += sprintf(ptr, "[too many reads]");
1634 if (priv->no_valid_reads)
1635 ptr += sprintf(ptr, "[no valid reads-from]");
1636 if (priv->bad_synchronization)
1637 ptr += sprintf(ptr, "[bad sw ordering]");
1638 if (promises_expired())
1639 ptr += sprintf(ptr, "[promise expired]");
1640 if (promises->size() != 0)
1641 ptr += sprintf(ptr, "[unresolved promise]");
1643 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1647 * Returns whether the current completed trace is feasible, except for pending
1648 * release sequences.
1650 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1652 return !is_infeasible() && promises->size() == 0;
1656 * Check if the current partial trace is infeasible. Does not check any
1657 * end-of-execution flags, which might rule out the execution. Thus, this is
1658 * useful only for ruling an execution as infeasible.
1659 * @return whether the current partial trace is infeasible.
1661 bool ModelChecker::is_infeasible() const
1663 return mo_graph->checkForCycles() ||
1664 priv->no_valid_reads ||
1665 priv->failed_promise ||
1666 priv->too_many_reads ||
1667 priv->bad_synchronization ||
1671 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1672 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1673 ModelAction *lastread = get_last_action(act->get_tid());
1674 lastread->process_rmw(act);
1675 if (act->is_rmw()) {
1676 if (lastread->get_reads_from())
1677 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1679 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1680 mo_graph->commitChanges();
1686 * A helper function for ModelChecker::check_recency, to check if the current
1687 * thread is able to read from a different write/promise for 'params.maxreads'
1688 * number of steps and if that write/promise should become visible (i.e., is
1689 * ordered later in the modification order). This helps model memory liveness.
1691 * @param curr The current action. Must be a read.
1692 * @param rf The write/promise from which we plan to read
1693 * @param other_rf The write/promise from which we may read
1694 * @return True if we were able to read from other_rf for params.maxreads steps
1696 template <typename T, typename U>
1697 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1699 /* Need a different write/promise */
1700 if (other_rf->equals(rf))
1703 /* Only look for "newer" writes/promises */
1704 if (!mo_graph->checkReachable(rf, other_rf))
1707 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1708 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1709 action_list_t::reverse_iterator rit = list->rbegin();
1710 ASSERT((*rit) == curr);
1711 /* Skip past curr */
1714 /* Does this write/promise work for everyone? */
1715 for (int i = 0; i < params.maxreads; i++, rit++) {
1716 ModelAction *act = *rit;
1717 if (!act->may_read_from(other_rf))
1724 * Checks whether a thread has read from the same write or Promise for too many
1725 * times without seeing the effects of a later write/Promise.
1728 * 1) there must a different write/promise that we could read from,
1729 * 2) we must have read from the same write/promise in excess of maxreads times,
1730 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1731 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1733 * If so, we decide that the execution is no longer feasible.
1735 * @param curr The current action. Must be a read.
1736 * @param rf The ModelAction/Promise from which we might read.
1737 * @return True if the read should succeed; false otherwise
1739 template <typename T>
1740 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1742 if (!params.maxreads)
1745 //NOTE: Next check is just optimization, not really necessary....
1746 if (curr->get_node()->get_read_from_past_size() +
1747 curr->get_node()->get_read_from_promise_size() <= 1)
1750 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1751 int tid = id_to_int(curr->get_tid());
1752 ASSERT(tid < (int)thrd_lists->size());
1753 action_list_t *list = &(*thrd_lists)[tid];
1754 action_list_t::reverse_iterator rit = list->rbegin();
1755 ASSERT((*rit) == curr);
1756 /* Skip past curr */
1759 action_list_t::reverse_iterator ritcopy = rit;
1760 /* See if we have enough reads from the same value */
1761 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1762 if (ritcopy == list->rend())
1764 ModelAction *act = *ritcopy;
1765 if (!act->is_read())
1767 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1769 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1771 if (act->get_node()->get_read_from_past_size() +
1772 act->get_node()->get_read_from_promise_size() <= 1)
1775 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1776 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1777 if (should_read_instead(curr, rf, write))
1778 return false; /* liveness failure */
1780 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1781 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1782 if (should_read_instead(curr, rf, promise))
1783 return false; /* liveness failure */
1789 * Updates the mo_graph with the constraints imposed from the current
1792 * Basic idea is the following: Go through each other thread and find
1793 * the last action that happened before our read. Two cases:
1795 * (1) The action is a write => that write must either occur before
1796 * the write we read from or be the write we read from.
1798 * (2) The action is a read => the write that that action read from
1799 * must occur before the write we read from or be the same write.
1801 * @param curr The current action. Must be a read.
1802 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1803 * @return True if modification order edges were added; false otherwise
1805 template <typename rf_type>
1806 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1808 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1811 ASSERT(curr->is_read());
1813 /* Last SC fence in the current thread */
1814 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1816 /* Iterate over all threads */
1817 for (i = 0; i < thrd_lists->size(); i++) {
1818 /* Last SC fence in thread i */
1819 ModelAction *last_sc_fence_thread_local = NULL;
1820 if (int_to_id((int)i) != curr->get_tid())
1821 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1823 /* Last SC fence in thread i, before last SC fence in current thread */
1824 ModelAction *last_sc_fence_thread_before = NULL;
1825 if (last_sc_fence_local)
1826 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1828 /* Iterate over actions in thread, starting from most recent */
1829 action_list_t *list = &(*thrd_lists)[i];
1830 action_list_t::reverse_iterator rit;
1831 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1832 ModelAction *act = *rit;
1837 /* Don't want to add reflexive edges on 'rf' */
1838 if (act->equals(rf)) {
1839 if (act->happens_before(curr))
1845 if (act->is_write()) {
1846 /* C++, Section 29.3 statement 5 */
1847 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1848 *act < *last_sc_fence_thread_local) {
1849 added = mo_graph->addEdge(act, rf) || added;
1852 /* C++, Section 29.3 statement 4 */
1853 else if (act->is_seqcst() && last_sc_fence_local &&
1854 *act < *last_sc_fence_local) {
1855 added = mo_graph->addEdge(act, rf) || added;
1858 /* C++, Section 29.3 statement 6 */
1859 else if (last_sc_fence_thread_before &&
1860 *act < *last_sc_fence_thread_before) {
1861 added = mo_graph->addEdge(act, rf) || added;
1867 * Include at most one act per-thread that "happens
1870 if (act->happens_before(curr)) {
1871 if (act->is_write()) {
1872 added = mo_graph->addEdge(act, rf) || added;
1874 const ModelAction *prevrf = act->get_reads_from();
1875 const Promise *prevrf_promise = act->get_reads_from_promise();
1877 if (!prevrf->equals(rf))
1878 added = mo_graph->addEdge(prevrf, rf) || added;
1879 } else if (!prevrf_promise->equals(rf)) {
1880 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1889 * All compatible, thread-exclusive promises must be ordered after any
1890 * concrete loads from the same thread
1892 for (unsigned int i = 0; i < promises->size(); i++)
1893 if ((*promises)[i]->is_compatible_exclusive(curr))
1894 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1900 * Updates the mo_graph with the constraints imposed from the current write.
1902 * Basic idea is the following: Go through each other thread and find
1903 * the lastest action that happened before our write. Two cases:
1905 * (1) The action is a write => that write must occur before
1908 * (2) The action is a read => the write that that action read from
1909 * must occur before the current write.
1911 * This method also handles two other issues:
1913 * (I) Sequential Consistency: Making sure that if the current write is
1914 * seq_cst, that it occurs after the previous seq_cst write.
1916 * (II) Sending the write back to non-synchronizing reads.
1918 * @param curr The current action. Must be a write.
1919 * @param send_fv A vector for stashing reads to which we may pass our future
1920 * value. If NULL, then don't record any future values.
1921 * @return True if modification order edges were added; false otherwise
1923 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1925 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1928 ASSERT(curr->is_write());
1930 if (curr->is_seqcst()) {
1931 /* We have to at least see the last sequentially consistent write,
1932 so we are initialized. */
1933 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1934 if (last_seq_cst != NULL) {
1935 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1939 /* Last SC fence in the current thread */
1940 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1942 /* Iterate over all threads */
1943 for (i = 0; i < thrd_lists->size(); i++) {
1944 /* Last SC fence in thread i, before last SC fence in current thread */
1945 ModelAction *last_sc_fence_thread_before = NULL;
1946 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1947 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1949 /* Iterate over actions in thread, starting from most recent */
1950 action_list_t *list = &(*thrd_lists)[i];
1951 action_list_t::reverse_iterator rit;
1952 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1953 ModelAction *act = *rit;
1956 * 1) If RMW and it actually read from something, then we
1957 * already have all relevant edges, so just skip to next
1960 * 2) If RMW and it didn't read from anything, we should
1961 * whatever edge we can get to speed up convergence.
1963 * 3) If normal write, we need to look at earlier actions, so
1964 * continue processing list.
1966 if (curr->is_rmw()) {
1967 if (curr->get_reads_from() != NULL)
1975 /* C++, Section 29.3 statement 7 */
1976 if (last_sc_fence_thread_before && act->is_write() &&
1977 *act < *last_sc_fence_thread_before) {
1978 added = mo_graph->addEdge(act, curr) || added;
1983 * Include at most one act per-thread that "happens
1986 if (act->happens_before(curr)) {
1988 * Note: if act is RMW, just add edge:
1990 * The following edge should be handled elsewhere:
1991 * readfrom(act) --mo--> act
1993 if (act->is_write())
1994 added = mo_graph->addEdge(act, curr) || added;
1995 else if (act->is_read()) {
1996 //if previous read accessed a null, just keep going
1997 if (act->get_reads_from() == NULL)
1999 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2002 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2003 !act->same_thread(curr)) {
2004 /* We have an action that:
2005 (1) did not happen before us
2006 (2) is a read and we are a write
2007 (3) cannot synchronize with us
2008 (4) is in a different thread
2010 that read could potentially read from our write. Note that
2011 these checks are overly conservative at this point, we'll
2012 do more checks before actually removing the
2016 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2017 if (!is_infeasible())
2018 send_fv->push_back(act);
2019 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2020 add_future_value(curr, act);
2027 * All compatible, thread-exclusive promises must be ordered after any
2028 * concrete stores to the same thread, or else they can be merged with
2031 for (unsigned int i = 0; i < promises->size(); i++)
2032 if ((*promises)[i]->is_compatible_exclusive(curr))
2033 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2038 /** Arbitrary reads from the future are not allowed. Section 29.3
2039 * part 9 places some constraints. This method checks one result of constraint
2040 * constraint. Others require compiler support. */
2041 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
2043 if (!writer->is_rmw())
2046 if (!reader->is_rmw())
2049 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2050 if (search == reader)
2052 if (search->get_tid() == reader->get_tid() &&
2053 search->happens_before(reader))
2061 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2062 * some constraints. This method checks one the following constraint (others
2063 * require compiler support):
2065 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2067 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2069 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2071 /* Iterate over all threads */
2072 for (i = 0; i < thrd_lists->size(); i++) {
2073 const ModelAction *write_after_read = NULL;
2075 /* Iterate over actions in thread, starting from most recent */
2076 action_list_t *list = &(*thrd_lists)[i];
2077 action_list_t::reverse_iterator rit;
2078 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2079 ModelAction *act = *rit;
2081 /* Don't disallow due to act == reader */
2082 if (!reader->happens_before(act) || reader == act)
2084 else if (act->is_write())
2085 write_after_read = act;
2086 else if (act->is_read() && act->get_reads_from() != NULL)
2087 write_after_read = act->get_reads_from();
2090 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2097 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2098 * The ModelAction under consideration is expected to be taking part in
2099 * release/acquire synchronization as an object of the "reads from" relation.
2100 * Note that this can only provide release sequence support for RMW chains
2101 * which do not read from the future, as those actions cannot be traced until
2102 * their "promise" is fulfilled. Similarly, we may not even establish the
2103 * presence of a release sequence with certainty, as some modification order
2104 * constraints may be decided further in the future. Thus, this function
2105 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2106 * and a boolean representing certainty.
2108 * @param rf The action that might be part of a release sequence. Must be a
2110 * @param release_heads A pass-by-reference style return parameter. After
2111 * execution of this function, release_heads will contain the heads of all the
2112 * relevant release sequences, if any exists with certainty
2113 * @param pending A pass-by-reference style return parameter which is only used
2114 * when returning false (i.e., uncertain). Returns most information regarding
2115 * an uncertain release sequence, including any write operations that might
2116 * break the sequence.
2117 * @return true, if the ModelChecker is certain that release_heads is complete;
2120 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2121 rel_heads_list_t *release_heads,
2122 struct release_seq *pending) const
2124 /* Only check for release sequences if there are no cycles */
2125 if (mo_graph->checkForCycles())
2128 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2129 ASSERT(rf->is_write());
2131 if (rf->is_release())
2132 release_heads->push_back(rf);
2133 else if (rf->get_last_fence_release())
2134 release_heads->push_back(rf->get_last_fence_release());
2136 break; /* End of RMW chain */
2138 /** @todo Need to be smarter here... In the linux lock
2139 * example, this will run to the beginning of the program for
2141 /** @todo The way to be smarter here is to keep going until 1
2142 * thread has a release preceded by an acquire and you've seen
2145 /* acq_rel RMW is a sufficient stopping condition */
2146 if (rf->is_acquire() && rf->is_release())
2147 return true; /* complete */
2150 /* read from future: need to settle this later */
2152 return false; /* incomplete */
2155 if (rf->is_release())
2156 return true; /* complete */
2158 /* else relaxed write
2159 * - check for fence-release in the same thread (29.8, stmt. 3)
2160 * - check modification order for contiguous subsequence
2161 * -> rf must be same thread as release */
2163 const ModelAction *fence_release = rf->get_last_fence_release();
2164 /* Synchronize with a fence-release unconditionally; we don't need to
2165 * find any more "contiguous subsequence..." for it */
2167 release_heads->push_back(fence_release);
2169 int tid = id_to_int(rf->get_tid());
2170 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2171 action_list_t *list = &(*thrd_lists)[tid];
2172 action_list_t::const_reverse_iterator rit;
2174 /* Find rf in the thread list */
2175 rit = std::find(list->rbegin(), list->rend(), rf);
2176 ASSERT(rit != list->rend());
2178 /* Find the last {write,fence}-release */
2179 for (; rit != list->rend(); rit++) {
2180 if (fence_release && *(*rit) < *fence_release)
2182 if ((*rit)->is_release())
2185 if (rit == list->rend()) {
2186 /* No write-release in this thread */
2187 return true; /* complete */
2188 } else if (fence_release && *(*rit) < *fence_release) {
2189 /* The fence-release is more recent (and so, "stronger") than
2190 * the most recent write-release */
2191 return true; /* complete */
2192 } /* else, need to establish contiguous release sequence */
2193 ModelAction *release = *rit;
2195 ASSERT(rf->same_thread(release));
2197 pending->writes.clear();
2199 bool certain = true;
2200 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2201 if (id_to_int(rf->get_tid()) == (int)i)
2203 list = &(*thrd_lists)[i];
2205 /* Can we ensure no future writes from this thread may break
2206 * the release seq? */
2207 bool future_ordered = false;
2209 ModelAction *last = get_last_action(int_to_id(i));
2210 Thread *th = get_thread(int_to_id(i));
2211 if ((last && rf->happens_before(last)) ||
2214 future_ordered = true;
2216 ASSERT(!th->is_model_thread() || future_ordered);
2218 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2219 const ModelAction *act = *rit;
2220 /* Reach synchronization -> this thread is complete */
2221 if (act->happens_before(release))
2223 if (rf->happens_before(act)) {
2224 future_ordered = true;
2228 /* Only non-RMW writes can break release sequences */
2229 if (!act->is_write() || act->is_rmw())
2232 /* Check modification order */
2233 if (mo_graph->checkReachable(rf, act)) {
2234 /* rf --mo--> act */
2235 future_ordered = true;
2238 if (mo_graph->checkReachable(act, release))
2239 /* act --mo--> release */
2241 if (mo_graph->checkReachable(release, act) &&
2242 mo_graph->checkReachable(act, rf)) {
2243 /* release --mo-> act --mo--> rf */
2244 return true; /* complete */
2246 /* act may break release sequence */
2247 pending->writes.push_back(act);
2250 if (!future_ordered)
2251 certain = false; /* This thread is uncertain */
2255 release_heads->push_back(release);
2256 pending->writes.clear();
2258 pending->release = release;
2265 * An interface for getting the release sequence head(s) with which a
2266 * given ModelAction must synchronize. This function only returns a non-empty
2267 * result when it can locate a release sequence head with certainty. Otherwise,
2268 * it may mark the internal state of the ModelChecker so that it will handle
2269 * the release sequence at a later time, causing @a acquire to update its
2270 * synchronization at some later point in execution.
2272 * @param acquire The 'acquire' action that may synchronize with a release
2274 * @param read The read action that may read from a release sequence; this may
2275 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2276 * when 'acquire' is a fence-acquire)
2277 * @param release_heads A pass-by-reference return parameter. Will be filled
2278 * with the head(s) of the release sequence(s), if they exists with certainty.
2279 * @see ModelChecker::release_seq_heads
2281 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2282 ModelAction *read, rel_heads_list_t *release_heads)
2284 const ModelAction *rf = read->get_reads_from();
2285 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2286 sequence->acquire = acquire;
2287 sequence->read = read;
2289 if (!release_seq_heads(rf, release_heads, sequence)) {
2290 /* add act to 'lazy checking' list */
2291 pending_rel_seqs->push_back(sequence);
2293 snapshot_free(sequence);
2298 * Attempt to resolve all stashed operations that might synchronize with a
2299 * release sequence for a given location. This implements the "lazy" portion of
2300 * determining whether or not a release sequence was contiguous, since not all
2301 * modification order information is present at the time an action occurs.
2303 * @param location The location/object that should be checked for release
2304 * sequence resolutions. A NULL value means to check all locations.
2305 * @param work_queue The work queue to which to add work items as they are
2307 * @return True if any updates occurred (new synchronization, new mo_graph
2310 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2312 bool updated = false;
2313 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2314 while (it != pending_rel_seqs->end()) {
2315 struct release_seq *pending = *it;
2316 ModelAction *acquire = pending->acquire;
2317 const ModelAction *read = pending->read;
2319 /* Only resolve sequences on the given location, if provided */
2320 if (location && read->get_location() != location) {
2325 const ModelAction *rf = read->get_reads_from();
2326 rel_heads_list_t release_heads;
2328 complete = release_seq_heads(rf, &release_heads, pending);
2329 for (unsigned int i = 0; i < release_heads.size(); i++) {
2330 if (!acquire->has_synchronized_with(release_heads[i])) {
2331 if (acquire->synchronize_with(release_heads[i]))
2334 set_bad_synchronization();
2339 /* Re-check all pending release sequences */
2340 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2341 /* Re-check read-acquire for mo_graph edges */
2342 if (acquire->is_read())
2343 work_queue->push_back(MOEdgeWorkEntry(acquire));
2345 /* propagate synchronization to later actions */
2346 action_list_t::reverse_iterator rit = action_trace->rbegin();
2347 for (; (*rit) != acquire; rit++) {
2348 ModelAction *propagate = *rit;
2349 if (acquire->happens_before(propagate)) {
2350 propagate->synchronize_with(acquire);
2351 /* Re-check 'propagate' for mo_graph edges */
2352 work_queue->push_back(MOEdgeWorkEntry(propagate));
2357 it = pending_rel_seqs->erase(it);
2358 snapshot_free(pending);
2364 // If we resolved promises or data races, see if we have realized a data race.
2371 * Performs various bookkeeping operations for the current ModelAction. For
2372 * instance, adds action to the per-object, per-thread action vector and to the
2373 * action trace list of all thread actions.
2375 * @param act is the ModelAction to add.
2377 void ModelChecker::add_action_to_lists(ModelAction *act)
2379 int tid = id_to_int(act->get_tid());
2380 ModelAction *uninit = NULL;
2382 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2383 if (list->empty() && act->is_atomic_var()) {
2384 uninit = get_uninitialized_action(act);
2385 uninit_id = id_to_int(uninit->get_tid());
2386 list->push_front(uninit);
2388 list->push_back(act);
2390 action_trace->push_back(act);
2392 action_trace->push_front(uninit);
2394 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2395 if (tid >= (int)vec->size())
2396 vec->resize(priv->next_thread_id);
2397 (*vec)[tid].push_back(act);
2399 (*vec)[uninit_id].push_front(uninit);
2401 if ((int)thrd_last_action->size() <= tid)
2402 thrd_last_action->resize(get_num_threads());
2403 (*thrd_last_action)[tid] = act;
2405 (*thrd_last_action)[uninit_id] = uninit;
2407 if (act->is_fence() && act->is_release()) {
2408 if ((int)thrd_last_fence_release->size() <= tid)
2409 thrd_last_fence_release->resize(get_num_threads());
2410 (*thrd_last_fence_release)[tid] = act;
2413 if (act->is_wait()) {
2414 void *mutex_loc = (void *) act->get_value();
2415 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2417 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2418 if (tid >= (int)vec->size())
2419 vec->resize(priv->next_thread_id);
2420 (*vec)[tid].push_back(act);
2425 * @brief Get the last action performed by a particular Thread
2426 * @param tid The thread ID of the Thread in question
2427 * @return The last action in the thread
2429 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2431 int threadid = id_to_int(tid);
2432 if (threadid < (int)thrd_last_action->size())
2433 return (*thrd_last_action)[id_to_int(tid)];
2439 * @brief Get the last fence release performed by a particular Thread
2440 * @param tid The thread ID of the Thread in question
2441 * @return The last fence release in the thread, if one exists; NULL otherwise
2443 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2445 int threadid = id_to_int(tid);
2446 if (threadid < (int)thrd_last_fence_release->size())
2447 return (*thrd_last_fence_release)[id_to_int(tid)];
2453 * Gets the last memory_order_seq_cst write (in the total global sequence)
2454 * performed on a particular object (i.e., memory location), not including the
2456 * @param curr The current ModelAction; also denotes the object location to
2458 * @return The last seq_cst write
2460 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2462 void *location = curr->get_location();
2463 action_list_t *list = get_safe_ptr_action(obj_map, location);
2464 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2465 action_list_t::reverse_iterator rit;
2466 for (rit = list->rbegin(); rit != list->rend(); rit++)
2467 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2473 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2474 * performed in a particular thread, prior to a particular fence.
2475 * @param tid The ID of the thread to check
2476 * @param before_fence The fence from which to begin the search; if NULL, then
2477 * search for the most recent fence in the thread.
2478 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2480 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2482 /* All fences should have NULL location */
2483 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2484 action_list_t::reverse_iterator rit = list->rbegin();
2487 for (; rit != list->rend(); rit++)
2488 if (*rit == before_fence)
2491 ASSERT(*rit == before_fence);
2495 for (; rit != list->rend(); rit++)
2496 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2502 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2503 * location). This function identifies the mutex according to the current
2504 * action, which is presumed to perform on the same mutex.
2505 * @param curr The current ModelAction; also denotes the object location to
2507 * @return The last unlock operation
2509 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2511 void *location = curr->get_location();
2512 action_list_t *list = get_safe_ptr_action(obj_map, location);
2513 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2514 action_list_t::reverse_iterator rit;
2515 for (rit = list->rbegin(); rit != list->rend(); rit++)
2516 if ((*rit)->is_unlock() || (*rit)->is_wait())
2521 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2523 ModelAction *parent = get_last_action(tid);
2525 parent = get_thread(tid)->get_creation();
2530 * Returns the clock vector for a given thread.
2531 * @param tid The thread whose clock vector we want
2532 * @return Desired clock vector
2534 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2536 return get_parent_action(tid)->get_cv();
2540 * @brief Find the promise, if any to resolve for the current action
2541 * @param curr The current ModelAction. Should be a write.
2542 * @return The (non-negative) index for the Promise to resolve, if any;
2545 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2547 for (unsigned int i = 0; i < promises->size(); i++)
2548 if (curr->get_node()->get_promise(i))
2554 * Resolve a Promise with a current write.
2555 * @param write The ModelAction that is fulfilling Promises
2556 * @param promise_idx The index corresponding to the promise
2557 * @return True if the Promise was successfully resolved; false otherwise
2559 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2561 ModelVector<ModelAction *> actions_to_check;
2562 Promise *promise = (*promises)[promise_idx];
2564 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2565 ModelAction *read = promise->get_reader(i);
2566 read_from(read, write);
2567 actions_to_check.push_back(read);
2569 /* Make sure the promise's value matches the write's value */
2570 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2571 if (!mo_graph->resolvePromise(promise, write))
2572 priv->failed_promise = true;
2574 promises->erase(promises->begin() + promise_idx);
2576 * @todo It is possible to end up in an inconsistent state, where a
2577 * "resolved" promise may still be referenced if
2578 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2580 * Note that the inconsistency only matters when dumping mo_graph to
2586 //Check whether reading these writes has made threads unable to
2588 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2589 ModelAction *read = actions_to_check[i];
2590 mo_check_promises(read, true);
2597 * Compute the set of promises that could potentially be satisfied by this
2598 * action. Note that the set computation actually appears in the Node, not in
2600 * @param curr The ModelAction that may satisfy promises
2602 void ModelChecker::compute_promises(ModelAction *curr)
2604 for (unsigned int i = 0; i < promises->size(); i++) {
2605 Promise *promise = (*promises)[i];
2606 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2609 bool satisfy = true;
2610 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2611 const ModelAction *act = promise->get_reader(j);
2612 if (act->happens_before(curr) ||
2613 act->could_synchronize_with(curr)) {
2619 curr->get_node()->set_promise(i);
2623 /** Checks promises in response to change in ClockVector Threads. */
2624 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2626 for (unsigned int i = 0; i < promises->size(); i++) {
2627 Promise *promise = (*promises)[i];
2628 if (!promise->thread_is_available(tid))
2630 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2631 const ModelAction *act = promise->get_reader(j);
2632 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2633 merge_cv->synchronized_since(act)) {
2634 if (promise->eliminate_thread(tid)) {
2635 /* Promise has failed */
2636 priv->failed_promise = true;
2644 void ModelChecker::check_promises_thread_disabled()
2646 for (unsigned int i = 0; i < promises->size(); i++) {
2647 Promise *promise = (*promises)[i];
2648 if (promise->has_failed()) {
2649 priv->failed_promise = true;
2656 * @brief Checks promises in response to addition to modification order for
2659 * We test whether threads are still available for satisfying promises after an
2660 * addition to our modification order constraints. Those that are unavailable
2661 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2662 * that promise has failed.
2664 * @param act The ModelAction which updated the modification order
2665 * @param is_read_check Should be true if act is a read and we must check for
2666 * updates to the store from which it read (there is a distinction here for
2667 * RMW's, which are both a load and a store)
2669 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2671 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2673 for (unsigned int i = 0; i < promises->size(); i++) {
2674 Promise *promise = (*promises)[i];
2676 // Is this promise on the same location?
2677 if (!promise->same_location(write))
2680 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2681 const ModelAction *pread = promise->get_reader(j);
2682 if (!pread->happens_before(act))
2684 if (mo_graph->checkPromise(write, promise)) {
2685 priv->failed_promise = true;
2691 // Don't do any lookups twice for the same thread
2692 if (!promise->thread_is_available(act->get_tid()))
2695 if (mo_graph->checkReachable(promise, write)) {
2696 if (mo_graph->checkPromise(write, promise)) {
2697 priv->failed_promise = true;
2705 * Compute the set of writes that may break the current pending release
2706 * sequence. This information is extracted from previou release sequence
2709 * @param curr The current ModelAction. Must be a release sequence fixup
2712 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2714 if (pending_rel_seqs->empty())
2717 struct release_seq *pending = pending_rel_seqs->back();
2718 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2719 const ModelAction *write = pending->writes[i];
2720 curr->get_node()->add_relseq_break(write);
2723 /* NULL means don't break the sequence; just synchronize */
2724 curr->get_node()->add_relseq_break(NULL);
2728 * Build up an initial set of all past writes that this 'read' action may read
2729 * from, as well as any previously-observed future values that must still be valid.
2731 * @param curr is the current ModelAction that we are exploring; it must be a
2734 void ModelChecker::build_may_read_from(ModelAction *curr)
2736 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2738 ASSERT(curr->is_read());
2740 ModelAction *last_sc_write = NULL;
2742 if (curr->is_seqcst())
2743 last_sc_write = get_last_seq_cst_write(curr);
2745 /* Iterate over all threads */
2746 for (i = 0; i < thrd_lists->size(); i++) {
2747 /* Iterate over actions in thread, starting from most recent */
2748 action_list_t *list = &(*thrd_lists)[i];
2749 action_list_t::reverse_iterator rit;
2750 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2751 ModelAction *act = *rit;
2753 /* Only consider 'write' actions */
2754 if (!act->is_write() || act == curr)
2757 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2758 bool allow_read = true;
2760 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2762 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2766 /* Only add feasible reads */
2767 mo_graph->startChanges();
2768 r_modification_order(curr, act);
2769 if (!is_infeasible())
2770 curr->get_node()->add_read_from_past(act);
2771 mo_graph->rollbackChanges();
2774 /* Include at most one act per-thread that "happens before" curr */
2775 if (act->happens_before(curr))
2780 /* Inherit existing, promised future values */
2781 for (i = 0; i < promises->size(); i++) {
2782 const Promise *promise = (*promises)[i];
2783 const ModelAction *promise_read = promise->get_reader(0);
2784 if (promise_read->same_var(curr)) {
2785 /* Only add feasible future-values */
2786 mo_graph->startChanges();
2787 r_modification_order(curr, promise);
2788 if (!is_infeasible())
2789 curr->get_node()->add_read_from_promise(promise_read);
2790 mo_graph->rollbackChanges();
2794 /* We may find no valid may-read-from only if the execution is doomed */
2795 if (!curr->get_node()->read_from_size()) {
2796 priv->no_valid_reads = true;
2800 if (DBG_ENABLED()) {
2801 model_print("Reached read action:\n");
2803 model_print("Printing read_from_past\n");
2804 curr->get_node()->print_read_from_past();
2805 model_print("End printing read_from_past\n");
2809 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2811 for ( ; write != NULL; write = write->get_reads_from()) {
2812 /* UNINIT actions don't have a Node, and they never sleep */
2813 if (write->is_uninitialized())
2815 Node *prevnode = write->get_node()->get_parent();
2817 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2818 if (write->is_release() && thread_sleep)
2820 if (!write->is_rmw())
2827 * @brief Get an action representing an uninitialized atomic
2829 * This function may create a new one or try to retrieve one from the NodeStack
2831 * @param curr The current action, which prompts the creation of an UNINIT action
2832 * @return A pointer to the UNINIT ModelAction
2834 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2836 Node *node = curr->get_node();
2837 ModelAction *act = node->get_uninit_action();
2839 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2840 node->set_uninit_action(act);
2842 act->create_cv(NULL);
2846 static void print_list(action_list_t *list)
2848 action_list_t::iterator it;
2850 model_print("---------------------------------------------------------------------\n");
2852 unsigned int hash = 0;
2854 for (it = list->begin(); it != list->end(); it++) {
2855 const ModelAction *act = *it;
2856 if (act->get_seq_number() > 0)
2858 hash = hash^(hash<<3)^((*it)->hash());
2860 model_print("HASH %u\n", hash);
2861 model_print("---------------------------------------------------------------------\n");
2864 #if SUPPORT_MOD_ORDER_DUMP
2865 void ModelChecker::dumpGraph(char *filename) const
2868 sprintf(buffer, "%s.dot", filename);
2869 FILE *file = fopen(buffer, "w");
2870 fprintf(file, "digraph %s {\n", filename);
2871 mo_graph->dumpNodes(file);
2872 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2874 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2875 ModelAction *act = *it;
2876 if (act->is_read()) {
2877 mo_graph->dot_print_node(file, act);
2878 if (act->get_reads_from())
2879 mo_graph->dot_print_edge(file,
2880 act->get_reads_from(),
2882 "label=\"rf\", color=red, weight=2");
2884 mo_graph->dot_print_edge(file,
2885 act->get_reads_from_promise(),
2887 "label=\"rf\", color=red");
2889 if (thread_array[act->get_tid()]) {
2890 mo_graph->dot_print_edge(file,
2891 thread_array[id_to_int(act->get_tid())],
2893 "label=\"sb\", color=blue, weight=400");
2896 thread_array[act->get_tid()] = act;
2898 fprintf(file, "}\n");
2899 model_free(thread_array);
2904 /** @brief Prints an execution trace summary. */
2905 void ModelChecker::print_summary() const
2907 #if SUPPORT_MOD_ORDER_DUMP
2908 char buffername[100];
2909 sprintf(buffername, "exec%04u", stats.num_total);
2910 mo_graph->dumpGraphToFile(buffername);
2911 sprintf(buffername, "graph%04u", stats.num_total);
2912 dumpGraph(buffername);
2915 model_print("Execution %d:", stats.num_total);
2916 if (isfeasibleprefix()) {
2917 if (scheduler->all_threads_sleeping())
2918 model_print(" SLEEP-SET REDUNDANT");
2921 print_infeasibility(" INFEASIBLE");
2922 print_list(action_trace);
2924 if (!promises->empty()) {
2925 model_print("Pending promises:\n");
2926 for (unsigned int i = 0; i < promises->size(); i++) {
2927 model_print(" [P%u] ", i);
2928 (*promises)[i]->print();
2935 * Add a Thread to the system for the first time. Should only be called once
2937 * @param t The Thread to add
2939 void ModelChecker::add_thread(Thread *t)
2941 thread_map->put(id_to_int(t->get_id()), t);
2942 scheduler->add_thread(t);
2946 * @brief Get a Thread reference by its ID
2947 * @param tid The Thread's ID
2948 * @return A Thread reference
2950 Thread * ModelChecker::get_thread(thread_id_t tid) const
2952 return thread_map->get(id_to_int(tid));
2956 * @brief Get a reference to the Thread in which a ModelAction was executed
2957 * @param act The ModelAction
2958 * @return A Thread reference
2960 Thread * ModelChecker::get_thread(const ModelAction *act) const
2962 return get_thread(act->get_tid());
2966 * @brief Get a Promise's "promise number"
2968 * A "promise number" is an index number that is unique to a promise, valid
2969 * only for a specific snapshot of an execution trace. Promises may come and go
2970 * as they are generated an resolved, so an index only retains meaning for the
2973 * @param promise The Promise to check
2974 * @return The promise index, if the promise still is valid; otherwise -1
2976 int ModelChecker::get_promise_number(const Promise *promise) const
2978 for (unsigned int i = 0; i < promises->size(); i++)
2979 if ((*promises)[i] == promise)
2986 * @brief Check if a Thread is currently enabled
2987 * @param t The Thread to check
2988 * @return True if the Thread is currently enabled
2990 bool ModelChecker::is_enabled(Thread *t) const
2992 return scheduler->is_enabled(t);
2996 * @brief Check if a Thread is currently enabled
2997 * @param tid The ID of the Thread to check
2998 * @return True if the Thread is currently enabled
3000 bool ModelChecker::is_enabled(thread_id_t tid) const
3002 return scheduler->is_enabled(tid);
3006 * Switch from a model-checker context to a user-thread context. This is the
3007 * complement of ModelChecker::switch_to_master and must be called from the
3008 * model-checker context
3010 * @param thread The user-thread to switch to
3012 void ModelChecker::switch_from_master(Thread *thread)
3014 scheduler->set_current_thread(thread);
3015 Thread::swap(&system_context, thread);
3019 * Switch from a user-context to the "master thread" context (a.k.a. system
3020 * context). This switch is made with the intention of exploring a particular
3021 * model-checking action (described by a ModelAction object). Must be called
3022 * from a user-thread context.
3024 * @param act The current action that will be explored. May be NULL only if
3025 * trace is exiting via an assertion (see ModelChecker::set_assert and
3026 * ModelChecker::has_asserted).
3027 * @return Return the value returned by the current action
3029 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3032 Thread *old = thread_current();
3033 scheduler->set_current_thread(NULL);
3034 ASSERT(!old->get_pending());
3035 old->set_pending(act);
3036 if (Thread::swap(old, &system_context) < 0) {
3037 perror("swap threads");
3040 return old->get_return_value();
3044 * Takes the next step in the execution, if possible.
3045 * @param curr The current step to take
3046 * @return Returns the next Thread to run, if any; NULL if this execution
3049 Thread * ModelChecker::take_step(ModelAction *curr)
3051 Thread *curr_thrd = get_thread(curr);
3052 ASSERT(curr_thrd->get_state() == THREAD_READY);
3054 curr = check_current_action(curr);
3056 /* Infeasible -> don't take any more steps */
3057 if (is_infeasible())
3059 else if (isfeasibleprefix() && have_bug_reports()) {
3064 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3067 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3068 scheduler->remove_thread(curr_thrd);
3070 Thread *next_thrd = NULL;
3072 next_thrd = action_select_next_thread(curr);
3074 next_thrd = get_next_thread();
3076 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3077 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3082 /** Wrapper to run the user's main function, with appropriate arguments */
3083 void user_main_wrapper(void *)
3085 user_main(model->params.argc, model->params.argv);
3088 /** @brief Run ModelChecker for the user program */
3089 void ModelChecker::run()
3093 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3098 * Stash next pending action(s) for thread(s). There
3099 * should only need to stash one thread's action--the
3100 * thread which just took a step--plus the first step
3101 * for any newly-created thread
3103 for (unsigned int i = 0; i < get_num_threads(); i++) {
3104 thread_id_t tid = int_to_id(i);
3105 Thread *thr = get_thread(tid);
3106 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3107 switch_from_master(thr);
3108 if (is_circular_wait(thr))
3109 assert_bug("Deadlock detected");
3113 /* Catch assertions from prior take_step or from
3114 * between-ModelAction bugs (e.g., data races) */
3118 /* Consume the next action for a Thread */
3119 ModelAction *curr = t->get_pending();
3120 t->set_pending(NULL);
3121 t = take_step(curr);
3122 } while (t && !t->is_model_thread());
3125 * Launch end-of-execution release sequence fixups only when
3126 * the execution is otherwise feasible AND there are:
3128 * (1) pending release sequences
3129 * (2) pending assertions that could be invalidated by a change
3130 * in clock vectors (i.e., data races)
3131 * (3) no pending promises
3133 while (!pending_rel_seqs->empty() &&
3134 is_feasible_prefix_ignore_relseq() &&
3135 !unrealizedraces.empty()) {
3136 model_print("*** WARNING: release sequence fixup action "
3137 "(%zu pending release seuqence(s)) ***\n",
3138 pending_rel_seqs->size());
3139 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3140 std::memory_order_seq_cst, NULL, VALUE_NONE,
3144 } while (next_execution());
3146 model_print("******* Model-checking complete: *******\n");