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 const ModelAction *earliest_promise_reader;
1086 bool updated_promises = false;
1088 bool updated_mod_order = w_modification_order(curr, &send_fv);
1089 Promise *promise = pop_promise_to_resolve(curr);
1092 earliest_promise_reader = promise->get_reader(0);
1093 updated_promises = resolve_promise(curr, promise);
1095 earliest_promise_reader = NULL;
1097 /* Don't send future values to reads after the Promise we resolve */
1098 for (unsigned int i = 0; i < send_fv.size(); i++) {
1099 ModelAction *read = send_fv[i];
1100 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1101 futurevalues->push_back(PendingFutureValue(curr, read));
1104 if (promises->empty()) {
1105 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1106 struct PendingFutureValue pfv = (*futurevalues)[i];
1107 add_future_value(pfv.writer, pfv.act);
1109 futurevalues->clear();
1112 mo_graph->commitChanges();
1113 mo_check_promises(curr, false);
1115 get_thread(curr)->set_return_value(VALUE_NONE);
1116 return updated_mod_order || updated_promises;
1120 * Process a fence ModelAction
1121 * @param curr The ModelAction to process
1122 * @return True if synchronization was updated
1124 bool ModelChecker::process_fence(ModelAction *curr)
1127 * fence-relaxed: no-op
1128 * fence-release: only log the occurence (not in this function), for
1129 * use in later synchronization
1130 * fence-acquire (this function): search for hypothetical release
1132 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1134 bool updated = false;
1135 if (curr->is_acquire()) {
1136 action_list_t *list = action_trace;
1137 action_list_t::reverse_iterator rit;
1138 /* Find X : is_read(X) && X --sb-> curr */
1139 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1140 ModelAction *act = *rit;
1143 if (act->get_tid() != curr->get_tid())
1145 /* Stop at the beginning of the thread */
1146 if (act->is_thread_start())
1148 /* Stop once we reach a prior fence-acquire */
1149 if (act->is_fence() && act->is_acquire())
1151 if (!act->is_read())
1153 /* read-acquire will find its own release sequences */
1154 if (act->is_acquire())
1157 /* Establish hypothetical release sequences */
1158 rel_heads_list_t release_heads;
1159 get_release_seq_heads(curr, act, &release_heads);
1160 for (unsigned int i = 0; i < release_heads.size(); i++)
1161 if (!curr->synchronize_with(release_heads[i]))
1162 set_bad_synchronization();
1163 if (release_heads.size() != 0)
1171 * @brief Process the current action for thread-related activity
1173 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1174 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1175 * synchronization, etc. This function is a no-op for non-THREAD actions
1176 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1178 * @param curr The current action
1179 * @return True if synchronization was updated or a thread completed
1181 bool ModelChecker::process_thread_action(ModelAction *curr)
1183 bool updated = false;
1185 switch (curr->get_type()) {
1186 case THREAD_CREATE: {
1187 thrd_t *thrd = (thrd_t *)curr->get_location();
1188 struct thread_params *params = (struct thread_params *)curr->get_value();
1189 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1191 th->set_creation(curr);
1192 /* Promises can be satisfied by children */
1193 for (unsigned int i = 0; i < promises->size(); i++) {
1194 Promise *promise = (*promises)[i];
1195 if (promise->thread_is_available(curr->get_tid()))
1196 promise->add_thread(th->get_id());
1201 Thread *blocking = curr->get_thread_operand();
1202 ModelAction *act = get_last_action(blocking->get_id());
1203 curr->synchronize_with(act);
1204 updated = true; /* trigger rel-seq checks */
1207 case THREAD_FINISH: {
1208 Thread *th = get_thread(curr);
1209 while (!th->wait_list_empty()) {
1210 ModelAction *act = th->pop_wait_list();
1211 scheduler->wake(get_thread(act));
1214 /* Completed thread can't satisfy promises */
1215 for (unsigned int i = 0; i < promises->size(); i++) {
1216 Promise *promise = (*promises)[i];
1217 if (promise->thread_is_available(th->get_id()))
1218 if (promise->eliminate_thread(th->get_id()))
1219 priv->failed_promise = true;
1221 updated = true; /* trigger rel-seq checks */
1224 case THREAD_START: {
1225 check_promises(curr->get_tid(), NULL, curr->get_cv());
1236 * @brief Process the current action for release sequence fixup activity
1238 * Performs model-checker release sequence fixups for the current action,
1239 * forcing a single pending release sequence to break (with a given, potential
1240 * "loose" write) or to complete (i.e., synchronize). If a pending release
1241 * sequence forms a complete release sequence, then we must perform the fixup
1242 * synchronization, mo_graph additions, etc.
1244 * @param curr The current action; must be a release sequence fixup action
1245 * @param work_queue The work queue to which to add work items as they are
1248 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1250 const ModelAction *write = curr->get_node()->get_relseq_break();
1251 struct release_seq *sequence = pending_rel_seqs->back();
1252 pending_rel_seqs->pop_back();
1254 ModelAction *acquire = sequence->acquire;
1255 const ModelAction *rf = sequence->rf;
1256 const ModelAction *release = sequence->release;
1260 ASSERT(release->same_thread(rf));
1262 if (write == NULL) {
1264 * @todo Forcing a synchronization requires that we set
1265 * modification order constraints. For instance, we can't allow
1266 * a fixup sequence in which two separate read-acquire
1267 * operations read from the same sequence, where the first one
1268 * synchronizes and the other doesn't. Essentially, we can't
1269 * allow any writes to insert themselves between 'release' and
1273 /* Must synchronize */
1274 if (!acquire->synchronize_with(release)) {
1275 set_bad_synchronization();
1278 /* Re-check all pending release sequences */
1279 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1280 /* Re-check act for mo_graph edges */
1281 work_queue->push_back(MOEdgeWorkEntry(acquire));
1283 /* propagate synchronization to later actions */
1284 action_list_t::reverse_iterator rit = action_trace->rbegin();
1285 for (; (*rit) != acquire; rit++) {
1286 ModelAction *propagate = *rit;
1287 if (acquire->happens_before(propagate)) {
1288 propagate->synchronize_with(acquire);
1289 /* Re-check 'propagate' for mo_graph edges */
1290 work_queue->push_back(MOEdgeWorkEntry(propagate));
1294 /* Break release sequence with new edges:
1295 * release --mo--> write --mo--> rf */
1296 mo_graph->addEdge(release, write);
1297 mo_graph->addEdge(write, rf);
1300 /* See if we have realized a data race */
1305 * Initialize the current action by performing one or more of the following
1306 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1307 * in the NodeStack, manipulating backtracking sets, allocating and
1308 * initializing clock vectors, and computing the promises to fulfill.
1310 * @param curr The current action, as passed from the user context; may be
1311 * freed/invalidated after the execution of this function, with a different
1312 * action "returned" its place (pass-by-reference)
1313 * @return True if curr is a newly-explored action; false otherwise
1315 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1317 ModelAction *newcurr;
1319 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1320 newcurr = process_rmw(*curr);
1323 if (newcurr->is_rmw())
1324 compute_promises(newcurr);
1330 (*curr)->set_seq_number(get_next_seq_num());
1332 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1334 /* First restore type and order in case of RMW operation */
1335 if ((*curr)->is_rmwr())
1336 newcurr->copy_typeandorder(*curr);
1338 ASSERT((*curr)->get_location() == newcurr->get_location());
1339 newcurr->copy_from_new(*curr);
1341 /* Discard duplicate ModelAction; use action from NodeStack */
1344 /* Always compute new clock vector */
1345 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1348 return false; /* Action was explored previously */
1352 /* Always compute new clock vector */
1353 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1355 /* Assign most recent release fence */
1356 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1359 * Perform one-time actions when pushing new ModelAction onto
1362 if (newcurr->is_write())
1363 compute_promises(newcurr);
1364 else if (newcurr->is_relseq_fixup())
1365 compute_relseq_breakwrites(newcurr);
1366 else if (newcurr->is_wait())
1367 newcurr->get_node()->set_misc_max(2);
1368 else if (newcurr->is_notify_one()) {
1369 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1371 return true; /* This was a new ModelAction */
1376 * @brief Establish reads-from relation between two actions
1378 * Perform basic operations involved with establishing a concrete rf relation,
1379 * including setting the ModelAction data and checking for release sequences.
1381 * @param act The action that is reading (must be a read)
1382 * @param rf The action from which we are reading (must be a write)
1384 * @return True if this read established synchronization
1386 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1389 ASSERT(rf->is_write());
1391 act->set_read_from(rf);
1392 if (act->is_acquire()) {
1393 rel_heads_list_t release_heads;
1394 get_release_seq_heads(act, act, &release_heads);
1395 int num_heads = release_heads.size();
1396 for (unsigned int i = 0; i < release_heads.size(); i++)
1397 if (!act->synchronize_with(release_heads[i])) {
1398 set_bad_synchronization();
1401 return num_heads > 0;
1407 * Check promises and eliminate potentially-satisfying threads when a thread is
1408 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1409 * no longer satisfy a promise generated from that thread.
1411 * @param blocker The thread on which a thread is waiting
1412 * @param waiting The waiting thread
1414 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1416 for (unsigned int i = 0; i < promises->size(); i++) {
1417 Promise *promise = (*promises)[i];
1418 if (!promise->thread_is_available(waiting->get_id()))
1420 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1421 ModelAction *reader = promise->get_reader(j);
1422 if (reader->get_tid() != blocker->get_id())
1424 if (promise->eliminate_thread(waiting->get_id())) {
1425 /* Promise has failed */
1426 priv->failed_promise = true;
1428 /* Only eliminate the 'waiting' thread once */
1436 * @brief Check whether a model action is enabled.
1438 * Checks whether a lock or join operation would be successful (i.e., is the
1439 * lock already locked, or is the joined thread already complete). If not, put
1440 * the action in a waiter list.
1442 * @param curr is the ModelAction to check whether it is enabled.
1443 * @return a bool that indicates whether the action is enabled.
1445 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1446 if (curr->is_lock()) {
1447 std::mutex *lock = (std::mutex *)curr->get_location();
1448 struct std::mutex_state *state = lock->get_state();
1449 if (state->locked) {
1450 //Stick the action in the appropriate waiting queue
1451 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1454 } else if (curr->get_type() == THREAD_JOIN) {
1455 Thread *blocking = (Thread *)curr->get_location();
1456 if (!blocking->is_complete()) {
1457 blocking->push_wait_list(curr);
1458 thread_blocking_check_promises(blocking, get_thread(curr));
1467 * This is the heart of the model checker routine. It performs model-checking
1468 * actions corresponding to a given "current action." Among other processes, it
1469 * calculates reads-from relationships, updates synchronization clock vectors,
1470 * forms a memory_order constraints graph, and handles replay/backtrack
1471 * execution when running permutations of previously-observed executions.
1473 * @param curr The current action to process
1474 * @return The ModelAction that is actually executed; may be different than
1475 * curr; may be NULL, if the current action is not enabled to run
1477 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1480 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1482 if (!check_action_enabled(curr)) {
1483 /* Make the execution look like we chose to run this action
1484 * much later, when a lock/join can succeed */
1485 get_thread(curr)->set_pending(curr);
1486 scheduler->sleep(get_thread(curr));
1490 bool newly_explored = initialize_curr_action(&curr);
1496 wake_up_sleeping_actions(curr);
1498 /* Compute fairness information for CHESS yield algorithm */
1499 if (model->params.yieldon) {
1500 curr->get_node()->update_yield(scheduler);
1503 /* Add the action to lists before any other model-checking tasks */
1504 if (!second_part_of_rmw)
1505 add_action_to_lists(curr);
1507 /* Build may_read_from set for newly-created actions */
1508 if (newly_explored && curr->is_read())
1509 build_may_read_from(curr);
1511 /* Initialize work_queue with the "current action" work */
1512 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1513 while (!work_queue.empty() && !has_asserted()) {
1514 WorkQueueEntry work = work_queue.front();
1515 work_queue.pop_front();
1517 switch (work.type) {
1518 case WORK_CHECK_CURR_ACTION: {
1519 ModelAction *act = work.action;
1520 bool update = false; /* update this location's release seq's */
1521 bool update_all = false; /* update all release seq's */
1523 if (process_thread_action(curr))
1526 if (act->is_read() && !second_part_of_rmw && process_read(act))
1529 if (act->is_write() && process_write(act))
1532 if (act->is_fence() && process_fence(act))
1535 if (act->is_mutex_op() && process_mutex(act))
1538 if (act->is_relseq_fixup())
1539 process_relseq_fixup(curr, &work_queue);
1542 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1544 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1547 case WORK_CHECK_RELEASE_SEQ:
1548 resolve_release_sequences(work.location, &work_queue);
1550 case WORK_CHECK_MO_EDGES: {
1551 /** @todo Complete verification of work_queue */
1552 ModelAction *act = work.action;
1553 bool updated = false;
1555 if (act->is_read()) {
1556 const ModelAction *rf = act->get_reads_from();
1557 const Promise *promise = act->get_reads_from_promise();
1559 if (r_modification_order(act, rf))
1561 } else if (promise) {
1562 if (r_modification_order(act, promise))
1566 if (act->is_write()) {
1567 if (w_modification_order(act, NULL))
1570 mo_graph->commitChanges();
1573 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1582 check_curr_backtracking(curr);
1583 set_backtracking(curr);
1587 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1589 Node *currnode = curr->get_node();
1590 Node *parnode = currnode->get_parent();
1592 if ((parnode && !parnode->backtrack_empty()) ||
1593 !currnode->misc_empty() ||
1594 !currnode->read_from_empty() ||
1595 !currnode->promise_empty() ||
1596 !currnode->relseq_break_empty()) {
1597 set_latest_backtrack(curr);
1601 bool ModelChecker::promises_expired() const
1603 for (unsigned int i = 0; i < promises->size(); i++) {
1604 Promise *promise = (*promises)[i];
1605 if (promise->get_expiration() < priv->used_sequence_numbers)
1612 * This is the strongest feasibility check available.
1613 * @return whether the current trace (partial or complete) must be a prefix of
1616 bool ModelChecker::isfeasibleprefix() const
1618 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1622 * Print disagnostic information about an infeasible execution
1623 * @param prefix A string to prefix the output with; if NULL, then a default
1624 * message prefix will be provided
1626 void ModelChecker::print_infeasibility(const char *prefix) const
1630 if (mo_graph->checkForCycles())
1631 ptr += sprintf(ptr, "[mo cycle]");
1632 if (priv->failed_promise)
1633 ptr += sprintf(ptr, "[failed promise]");
1634 if (priv->too_many_reads)
1635 ptr += sprintf(ptr, "[too many reads]");
1636 if (priv->no_valid_reads)
1637 ptr += sprintf(ptr, "[no valid reads-from]");
1638 if (priv->bad_synchronization)
1639 ptr += sprintf(ptr, "[bad sw ordering]");
1640 if (promises_expired())
1641 ptr += sprintf(ptr, "[promise expired]");
1642 if (promises->size() != 0)
1643 ptr += sprintf(ptr, "[unresolved promise]");
1645 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1649 * Returns whether the current completed trace is feasible, except for pending
1650 * release sequences.
1652 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1654 return !is_infeasible() && promises->size() == 0;
1658 * Check if the current partial trace is infeasible. Does not check any
1659 * end-of-execution flags, which might rule out the execution. Thus, this is
1660 * useful only for ruling an execution as infeasible.
1661 * @return whether the current partial trace is infeasible.
1663 bool ModelChecker::is_infeasible() const
1665 return mo_graph->checkForCycles() ||
1666 priv->no_valid_reads ||
1667 priv->failed_promise ||
1668 priv->too_many_reads ||
1669 priv->bad_synchronization ||
1673 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1674 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1675 ModelAction *lastread = get_last_action(act->get_tid());
1676 lastread->process_rmw(act);
1677 if (act->is_rmw()) {
1678 if (lastread->get_reads_from())
1679 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1681 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1682 mo_graph->commitChanges();
1688 * A helper function for ModelChecker::check_recency, to check if the current
1689 * thread is able to read from a different write/promise for 'params.maxreads'
1690 * number of steps and if that write/promise should become visible (i.e., is
1691 * ordered later in the modification order). This helps model memory liveness.
1693 * @param curr The current action. Must be a read.
1694 * @param rf The write/promise from which we plan to read
1695 * @param other_rf The write/promise from which we may read
1696 * @return True if we were able to read from other_rf for params.maxreads steps
1698 template <typename T, typename U>
1699 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1701 /* Need a different write/promise */
1702 if (other_rf->equals(rf))
1705 /* Only look for "newer" writes/promises */
1706 if (!mo_graph->checkReachable(rf, other_rf))
1709 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1710 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1711 action_list_t::reverse_iterator rit = list->rbegin();
1712 ASSERT((*rit) == curr);
1713 /* Skip past curr */
1716 /* Does this write/promise work for everyone? */
1717 for (int i = 0; i < params.maxreads; i++, rit++) {
1718 ModelAction *act = *rit;
1719 if (!act->may_read_from(other_rf))
1726 * Checks whether a thread has read from the same write or Promise for too many
1727 * times without seeing the effects of a later write/Promise.
1730 * 1) there must a different write/promise that we could read from,
1731 * 2) we must have read from the same write/promise in excess of maxreads times,
1732 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1733 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1735 * If so, we decide that the execution is no longer feasible.
1737 * @param curr The current action. Must be a read.
1738 * @param rf The ModelAction/Promise from which we might read.
1739 * @return True if the read should succeed; false otherwise
1741 template <typename T>
1742 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1744 if (!params.maxreads)
1747 //NOTE: Next check is just optimization, not really necessary....
1748 if (curr->get_node()->get_read_from_past_size() +
1749 curr->get_node()->get_read_from_promise_size() <= 1)
1752 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1753 int tid = id_to_int(curr->get_tid());
1754 ASSERT(tid < (int)thrd_lists->size());
1755 action_list_t *list = &(*thrd_lists)[tid];
1756 action_list_t::reverse_iterator rit = list->rbegin();
1757 ASSERT((*rit) == curr);
1758 /* Skip past curr */
1761 action_list_t::reverse_iterator ritcopy = rit;
1762 /* See if we have enough reads from the same value */
1763 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1764 if (ritcopy == list->rend())
1766 ModelAction *act = *ritcopy;
1767 if (!act->is_read())
1769 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1771 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1773 if (act->get_node()->get_read_from_past_size() +
1774 act->get_node()->get_read_from_promise_size() <= 1)
1777 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1778 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1779 if (should_read_instead(curr, rf, write))
1780 return false; /* liveness failure */
1782 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1783 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1784 if (should_read_instead(curr, rf, promise))
1785 return false; /* liveness failure */
1791 * Updates the mo_graph with the constraints imposed from the current
1794 * Basic idea is the following: Go through each other thread and find
1795 * the last action that happened before our read. Two cases:
1797 * (1) The action is a write => that write must either occur before
1798 * the write we read from or be the write we read from.
1800 * (2) The action is a read => the write that that action read from
1801 * must occur before the write we read from or be the same write.
1803 * @param curr The current action. Must be a read.
1804 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1805 * @return True if modification order edges were added; false otherwise
1807 template <typename rf_type>
1808 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1810 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1813 ASSERT(curr->is_read());
1815 /* Last SC fence in the current thread */
1816 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1817 ModelAction *last_sc_write = NULL;
1818 if (curr->is_seqcst())
1819 last_sc_write = get_last_seq_cst_write(curr);
1821 /* Iterate over all threads */
1822 for (i = 0; i < thrd_lists->size(); i++) {
1823 /* Last SC fence in thread i */
1824 ModelAction *last_sc_fence_thread_local = NULL;
1825 if (int_to_id((int)i) != curr->get_tid())
1826 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1828 /* Last SC fence in thread i, before last SC fence in current thread */
1829 ModelAction *last_sc_fence_thread_before = NULL;
1830 if (last_sc_fence_local)
1831 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1833 /* Iterate over actions in thread, starting from most recent */
1834 action_list_t *list = &(*thrd_lists)[i];
1835 action_list_t::reverse_iterator rit;
1836 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1837 ModelAction *act = *rit;
1842 /* Don't want to add reflexive edges on 'rf' */
1843 if (act->equals(rf)) {
1844 if (act->happens_before(curr))
1850 if (act->is_write()) {
1851 /* C++, Section 29.3 statement 5 */
1852 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1853 *act < *last_sc_fence_thread_local) {
1854 added = mo_graph->addEdge(act, rf) || added;
1857 /* C++, Section 29.3 statement 4 */
1858 else if (act->is_seqcst() && last_sc_fence_local &&
1859 *act < *last_sc_fence_local) {
1860 added = mo_graph->addEdge(act, rf) || added;
1863 /* C++, Section 29.3 statement 6 */
1864 else if (last_sc_fence_thread_before &&
1865 *act < *last_sc_fence_thread_before) {
1866 added = mo_graph->addEdge(act, rf) || added;
1871 /* C++, Section 29.3 statement 3 (second subpoint) */
1872 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1873 added = mo_graph->addEdge(act, rf) || added;
1878 * Include at most one act per-thread that "happens
1881 if (act->happens_before(curr)) {
1882 if (act->is_write()) {
1883 added = mo_graph->addEdge(act, rf) || added;
1885 const ModelAction *prevrf = act->get_reads_from();
1886 const Promise *prevrf_promise = act->get_reads_from_promise();
1888 if (!prevrf->equals(rf))
1889 added = mo_graph->addEdge(prevrf, rf) || added;
1890 } else if (!prevrf_promise->equals(rf)) {
1891 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1900 * All compatible, thread-exclusive promises must be ordered after any
1901 * concrete loads from the same thread
1903 for (unsigned int i = 0; i < promises->size(); i++)
1904 if ((*promises)[i]->is_compatible_exclusive(curr))
1905 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1911 * Updates the mo_graph with the constraints imposed from the current write.
1913 * Basic idea is the following: Go through each other thread and find
1914 * the lastest action that happened before our write. Two cases:
1916 * (1) The action is a write => that write must occur before
1919 * (2) The action is a read => the write that that action read from
1920 * must occur before the current write.
1922 * This method also handles two other issues:
1924 * (I) Sequential Consistency: Making sure that if the current write is
1925 * seq_cst, that it occurs after the previous seq_cst write.
1927 * (II) Sending the write back to non-synchronizing reads.
1929 * @param curr The current action. Must be a write.
1930 * @param send_fv A vector for stashing reads to which we may pass our future
1931 * value. If NULL, then don't record any future values.
1932 * @return True if modification order edges were added; false otherwise
1934 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1936 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1939 ASSERT(curr->is_write());
1941 if (curr->is_seqcst()) {
1942 /* We have to at least see the last sequentially consistent write,
1943 so we are initialized. */
1944 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1945 if (last_seq_cst != NULL) {
1946 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1950 /* Last SC fence in the current thread */
1951 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1953 /* Iterate over all threads */
1954 for (i = 0; i < thrd_lists->size(); i++) {
1955 /* Last SC fence in thread i, before last SC fence in current thread */
1956 ModelAction *last_sc_fence_thread_before = NULL;
1957 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1958 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1960 /* Iterate over actions in thread, starting from most recent */
1961 action_list_t *list = &(*thrd_lists)[i];
1962 action_list_t::reverse_iterator rit;
1963 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1964 ModelAction *act = *rit;
1967 * 1) If RMW and it actually read from something, then we
1968 * already have all relevant edges, so just skip to next
1971 * 2) If RMW and it didn't read from anything, we should
1972 * whatever edge we can get to speed up convergence.
1974 * 3) If normal write, we need to look at earlier actions, so
1975 * continue processing list.
1977 if (curr->is_rmw()) {
1978 if (curr->get_reads_from() != NULL)
1986 /* C++, Section 29.3 statement 7 */
1987 if (last_sc_fence_thread_before && act->is_write() &&
1988 *act < *last_sc_fence_thread_before) {
1989 added = mo_graph->addEdge(act, curr) || added;
1994 * Include at most one act per-thread that "happens
1997 if (act->happens_before(curr)) {
1999 * Note: if act is RMW, just add edge:
2001 * The following edge should be handled elsewhere:
2002 * readfrom(act) --mo--> act
2004 if (act->is_write())
2005 added = mo_graph->addEdge(act, curr) || added;
2006 else if (act->is_read()) {
2007 //if previous read accessed a null, just keep going
2008 if (act->get_reads_from() == NULL)
2010 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2013 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2014 !act->same_thread(curr)) {
2015 /* We have an action that:
2016 (1) did not happen before us
2017 (2) is a read and we are a write
2018 (3) cannot synchronize with us
2019 (4) is in a different thread
2021 that read could potentially read from our write. Note that
2022 these checks are overly conservative at this point, we'll
2023 do more checks before actually removing the
2027 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2028 if (!is_infeasible())
2029 send_fv->push_back(act);
2030 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2031 add_future_value(curr, act);
2038 * All compatible, thread-exclusive promises must be ordered after any
2039 * concrete stores to the same thread, or else they can be merged with
2042 for (unsigned int i = 0; i < promises->size(); i++)
2043 if ((*promises)[i]->is_compatible_exclusive(curr))
2044 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2049 /** Arbitrary reads from the future are not allowed. Section 29.3
2050 * part 9 places some constraints. This method checks one result of constraint
2051 * constraint. Others require compiler support. */
2052 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
2054 if (!writer->is_rmw())
2057 if (!reader->is_rmw())
2060 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2061 if (search == reader)
2063 if (search->get_tid() == reader->get_tid() &&
2064 search->happens_before(reader))
2072 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2073 * some constraints. This method checks one the following constraint (others
2074 * require compiler support):
2076 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2078 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2080 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2082 /* Iterate over all threads */
2083 for (i = 0; i < thrd_lists->size(); i++) {
2084 const ModelAction *write_after_read = NULL;
2086 /* Iterate over actions in thread, starting from most recent */
2087 action_list_t *list = &(*thrd_lists)[i];
2088 action_list_t::reverse_iterator rit;
2089 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2090 ModelAction *act = *rit;
2092 /* Don't disallow due to act == reader */
2093 if (!reader->happens_before(act) || reader == act)
2095 else if (act->is_write())
2096 write_after_read = act;
2097 else if (act->is_read() && act->get_reads_from() != NULL)
2098 write_after_read = act->get_reads_from();
2101 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2108 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2109 * The ModelAction under consideration is expected to be taking part in
2110 * release/acquire synchronization as an object of the "reads from" relation.
2111 * Note that this can only provide release sequence support for RMW chains
2112 * which do not read from the future, as those actions cannot be traced until
2113 * their "promise" is fulfilled. Similarly, we may not even establish the
2114 * presence of a release sequence with certainty, as some modification order
2115 * constraints may be decided further in the future. Thus, this function
2116 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2117 * and a boolean representing certainty.
2119 * @param rf The action that might be part of a release sequence. Must be a
2121 * @param release_heads A pass-by-reference style return parameter. After
2122 * execution of this function, release_heads will contain the heads of all the
2123 * relevant release sequences, if any exists with certainty
2124 * @param pending A pass-by-reference style return parameter which is only used
2125 * when returning false (i.e., uncertain). Returns most information regarding
2126 * an uncertain release sequence, including any write operations that might
2127 * break the sequence.
2128 * @return true, if the ModelChecker is certain that release_heads is complete;
2131 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2132 rel_heads_list_t *release_heads,
2133 struct release_seq *pending) const
2135 /* Only check for release sequences if there are no cycles */
2136 if (mo_graph->checkForCycles())
2139 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2140 ASSERT(rf->is_write());
2142 if (rf->is_release())
2143 release_heads->push_back(rf);
2144 else if (rf->get_last_fence_release())
2145 release_heads->push_back(rf->get_last_fence_release());
2147 break; /* End of RMW chain */
2149 /** @todo Need to be smarter here... In the linux lock
2150 * example, this will run to the beginning of the program for
2152 /** @todo The way to be smarter here is to keep going until 1
2153 * thread has a release preceded by an acquire and you've seen
2156 /* acq_rel RMW is a sufficient stopping condition */
2157 if (rf->is_acquire() && rf->is_release())
2158 return true; /* complete */
2161 /* read from future: need to settle this later */
2163 return false; /* incomplete */
2166 if (rf->is_release())
2167 return true; /* complete */
2169 /* else relaxed write
2170 * - check for fence-release in the same thread (29.8, stmt. 3)
2171 * - check modification order for contiguous subsequence
2172 * -> rf must be same thread as release */
2174 const ModelAction *fence_release = rf->get_last_fence_release();
2175 /* Synchronize with a fence-release unconditionally; we don't need to
2176 * find any more "contiguous subsequence..." for it */
2178 release_heads->push_back(fence_release);
2180 int tid = id_to_int(rf->get_tid());
2181 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2182 action_list_t *list = &(*thrd_lists)[tid];
2183 action_list_t::const_reverse_iterator rit;
2185 /* Find rf in the thread list */
2186 rit = std::find(list->rbegin(), list->rend(), rf);
2187 ASSERT(rit != list->rend());
2189 /* Find the last {write,fence}-release */
2190 for (; rit != list->rend(); rit++) {
2191 if (fence_release && *(*rit) < *fence_release)
2193 if ((*rit)->is_release())
2196 if (rit == list->rend()) {
2197 /* No write-release in this thread */
2198 return true; /* complete */
2199 } else if (fence_release && *(*rit) < *fence_release) {
2200 /* The fence-release is more recent (and so, "stronger") than
2201 * the most recent write-release */
2202 return true; /* complete */
2203 } /* else, need to establish contiguous release sequence */
2204 ModelAction *release = *rit;
2206 ASSERT(rf->same_thread(release));
2208 pending->writes.clear();
2210 bool certain = true;
2211 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2212 if (id_to_int(rf->get_tid()) == (int)i)
2214 list = &(*thrd_lists)[i];
2216 /* Can we ensure no future writes from this thread may break
2217 * the release seq? */
2218 bool future_ordered = false;
2220 ModelAction *last = get_last_action(int_to_id(i));
2221 Thread *th = get_thread(int_to_id(i));
2222 if ((last && rf->happens_before(last)) ||
2225 future_ordered = true;
2227 ASSERT(!th->is_model_thread() || future_ordered);
2229 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2230 const ModelAction *act = *rit;
2231 /* Reach synchronization -> this thread is complete */
2232 if (act->happens_before(release))
2234 if (rf->happens_before(act)) {
2235 future_ordered = true;
2239 /* Only non-RMW writes can break release sequences */
2240 if (!act->is_write() || act->is_rmw())
2243 /* Check modification order */
2244 if (mo_graph->checkReachable(rf, act)) {
2245 /* rf --mo--> act */
2246 future_ordered = true;
2249 if (mo_graph->checkReachable(act, release))
2250 /* act --mo--> release */
2252 if (mo_graph->checkReachable(release, act) &&
2253 mo_graph->checkReachable(act, rf)) {
2254 /* release --mo-> act --mo--> rf */
2255 return true; /* complete */
2257 /* act may break release sequence */
2258 pending->writes.push_back(act);
2261 if (!future_ordered)
2262 certain = false; /* This thread is uncertain */
2266 release_heads->push_back(release);
2267 pending->writes.clear();
2269 pending->release = release;
2276 * An interface for getting the release sequence head(s) with which a
2277 * given ModelAction must synchronize. This function only returns a non-empty
2278 * result when it can locate a release sequence head with certainty. Otherwise,
2279 * it may mark the internal state of the ModelChecker so that it will handle
2280 * the release sequence at a later time, causing @a acquire to update its
2281 * synchronization at some later point in execution.
2283 * @param acquire The 'acquire' action that may synchronize with a release
2285 * @param read The read action that may read from a release sequence; this may
2286 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2287 * when 'acquire' is a fence-acquire)
2288 * @param release_heads A pass-by-reference return parameter. Will be filled
2289 * with the head(s) of the release sequence(s), if they exists with certainty.
2290 * @see ModelChecker::release_seq_heads
2292 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2293 ModelAction *read, rel_heads_list_t *release_heads)
2295 const ModelAction *rf = read->get_reads_from();
2296 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2297 sequence->acquire = acquire;
2298 sequence->read = read;
2300 if (!release_seq_heads(rf, release_heads, sequence)) {
2301 /* add act to 'lazy checking' list */
2302 pending_rel_seqs->push_back(sequence);
2304 snapshot_free(sequence);
2309 * Attempt to resolve all stashed operations that might synchronize with a
2310 * release sequence for a given location. This implements the "lazy" portion of
2311 * determining whether or not a release sequence was contiguous, since not all
2312 * modification order information is present at the time an action occurs.
2314 * @param location The location/object that should be checked for release
2315 * sequence resolutions. A NULL value means to check all locations.
2316 * @param work_queue The work queue to which to add work items as they are
2318 * @return True if any updates occurred (new synchronization, new mo_graph
2321 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2323 bool updated = false;
2324 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2325 while (it != pending_rel_seqs->end()) {
2326 struct release_seq *pending = *it;
2327 ModelAction *acquire = pending->acquire;
2328 const ModelAction *read = pending->read;
2330 /* Only resolve sequences on the given location, if provided */
2331 if (location && read->get_location() != location) {
2336 const ModelAction *rf = read->get_reads_from();
2337 rel_heads_list_t release_heads;
2339 complete = release_seq_heads(rf, &release_heads, pending);
2340 for (unsigned int i = 0; i < release_heads.size(); i++) {
2341 if (!acquire->has_synchronized_with(release_heads[i])) {
2342 if (acquire->synchronize_with(release_heads[i]))
2345 set_bad_synchronization();
2350 /* Re-check all pending release sequences */
2351 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2352 /* Re-check read-acquire for mo_graph edges */
2353 if (acquire->is_read())
2354 work_queue->push_back(MOEdgeWorkEntry(acquire));
2356 /* propagate synchronization to later actions */
2357 action_list_t::reverse_iterator rit = action_trace->rbegin();
2358 for (; (*rit) != acquire; rit++) {
2359 ModelAction *propagate = *rit;
2360 if (acquire->happens_before(propagate)) {
2361 propagate->synchronize_with(acquire);
2362 /* Re-check 'propagate' for mo_graph edges */
2363 work_queue->push_back(MOEdgeWorkEntry(propagate));
2368 it = pending_rel_seqs->erase(it);
2369 snapshot_free(pending);
2375 // If we resolved promises or data races, see if we have realized a data race.
2382 * Performs various bookkeeping operations for the current ModelAction. For
2383 * instance, adds action to the per-object, per-thread action vector and to the
2384 * action trace list of all thread actions.
2386 * @param act is the ModelAction to add.
2388 void ModelChecker::add_action_to_lists(ModelAction *act)
2390 int tid = id_to_int(act->get_tid());
2391 ModelAction *uninit = NULL;
2393 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2394 if (list->empty() && act->is_atomic_var()) {
2395 uninit = get_uninitialized_action(act);
2396 uninit_id = id_to_int(uninit->get_tid());
2397 list->push_front(uninit);
2399 list->push_back(act);
2401 action_trace->push_back(act);
2403 action_trace->push_front(uninit);
2405 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2406 if (tid >= (int)vec->size())
2407 vec->resize(priv->next_thread_id);
2408 (*vec)[tid].push_back(act);
2410 (*vec)[uninit_id].push_front(uninit);
2412 if ((int)thrd_last_action->size() <= tid)
2413 thrd_last_action->resize(get_num_threads());
2414 (*thrd_last_action)[tid] = act;
2416 (*thrd_last_action)[uninit_id] = uninit;
2418 if (act->is_fence() && act->is_release()) {
2419 if ((int)thrd_last_fence_release->size() <= tid)
2420 thrd_last_fence_release->resize(get_num_threads());
2421 (*thrd_last_fence_release)[tid] = act;
2424 if (act->is_wait()) {
2425 void *mutex_loc = (void *) act->get_value();
2426 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2428 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2429 if (tid >= (int)vec->size())
2430 vec->resize(priv->next_thread_id);
2431 (*vec)[tid].push_back(act);
2436 * @brief Get the last action performed by a particular Thread
2437 * @param tid The thread ID of the Thread in question
2438 * @return The last action in the thread
2440 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2442 int threadid = id_to_int(tid);
2443 if (threadid < (int)thrd_last_action->size())
2444 return (*thrd_last_action)[id_to_int(tid)];
2450 * @brief Get the last fence release performed by a particular Thread
2451 * @param tid The thread ID of the Thread in question
2452 * @return The last fence release in the thread, if one exists; NULL otherwise
2454 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2456 int threadid = id_to_int(tid);
2457 if (threadid < (int)thrd_last_fence_release->size())
2458 return (*thrd_last_fence_release)[id_to_int(tid)];
2464 * Gets the last memory_order_seq_cst write (in the total global sequence)
2465 * performed on a particular object (i.e., memory location), not including the
2467 * @param curr The current ModelAction; also denotes the object location to
2469 * @return The last seq_cst write
2471 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2473 void *location = curr->get_location();
2474 action_list_t *list = get_safe_ptr_action(obj_map, location);
2475 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2476 action_list_t::reverse_iterator rit;
2477 for (rit = list->rbegin(); (*rit) != curr; rit++)
2479 rit++; /* Skip past curr */
2480 for ( ; rit != list->rend(); rit++)
2481 if ((*rit)->is_write() && (*rit)->is_seqcst())
2487 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2488 * performed in a particular thread, prior to a particular fence.
2489 * @param tid The ID of the thread to check
2490 * @param before_fence The fence from which to begin the search; if NULL, then
2491 * search for the most recent fence in the thread.
2492 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2494 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2496 /* All fences should have NULL location */
2497 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2498 action_list_t::reverse_iterator rit = list->rbegin();
2501 for (; rit != list->rend(); rit++)
2502 if (*rit == before_fence)
2505 ASSERT(*rit == before_fence);
2509 for (; rit != list->rend(); rit++)
2510 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2516 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2517 * location). This function identifies the mutex according to the current
2518 * action, which is presumed to perform on the same mutex.
2519 * @param curr The current ModelAction; also denotes the object location to
2521 * @return The last unlock operation
2523 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2525 void *location = curr->get_location();
2526 action_list_t *list = get_safe_ptr_action(obj_map, location);
2527 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2528 action_list_t::reverse_iterator rit;
2529 for (rit = list->rbegin(); rit != list->rend(); rit++)
2530 if ((*rit)->is_unlock() || (*rit)->is_wait())
2535 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2537 ModelAction *parent = get_last_action(tid);
2539 parent = get_thread(tid)->get_creation();
2544 * Returns the clock vector for a given thread.
2545 * @param tid The thread whose clock vector we want
2546 * @return Desired clock vector
2548 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2550 return get_parent_action(tid)->get_cv();
2554 * @brief Find the promise (if any) to resolve for the current action and
2555 * remove it from the pending promise vector
2556 * @param curr The current ModelAction. Should be a write.
2557 * @return The Promise to resolve, if any; otherwise NULL
2559 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2561 for (unsigned int i = 0; i < promises->size(); i++)
2562 if (curr->get_node()->get_promise(i)) {
2563 Promise *ret = (*promises)[i];
2564 promises->erase(promises->begin() + i);
2571 * Resolve a Promise with a current write.
2572 * @param write The ModelAction that is fulfilling Promises
2573 * @param promise The Promise to resolve
2574 * @return True if the Promise was successfully resolved; false otherwise
2576 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2578 ModelVector<ModelAction *> actions_to_check;
2580 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2581 ModelAction *read = promise->get_reader(i);
2582 read_from(read, write);
2583 actions_to_check.push_back(read);
2585 /* Make sure the promise's value matches the write's value */
2586 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2587 if (!mo_graph->resolvePromise(promise, write))
2588 priv->failed_promise = true;
2591 * @todo It is possible to end up in an inconsistent state, where a
2592 * "resolved" promise may still be referenced if
2593 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2595 * Note that the inconsistency only matters when dumping mo_graph to
2601 //Check whether reading these writes has made threads unable to
2603 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2604 ModelAction *read = actions_to_check[i];
2605 mo_check_promises(read, true);
2612 * Compute the set of promises that could potentially be satisfied by this
2613 * action. Note that the set computation actually appears in the Node, not in
2615 * @param curr The ModelAction that may satisfy promises
2617 void ModelChecker::compute_promises(ModelAction *curr)
2619 for (unsigned int i = 0; i < promises->size(); i++) {
2620 Promise *promise = (*promises)[i];
2621 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2624 bool satisfy = true;
2625 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2626 const ModelAction *act = promise->get_reader(j);
2627 if (act->happens_before(curr) ||
2628 act->could_synchronize_with(curr)) {
2634 curr->get_node()->set_promise(i);
2638 /** Checks promises in response to change in ClockVector Threads. */
2639 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2641 for (unsigned int i = 0; i < promises->size(); i++) {
2642 Promise *promise = (*promises)[i];
2643 if (!promise->thread_is_available(tid))
2645 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2646 const ModelAction *act = promise->get_reader(j);
2647 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2648 merge_cv->synchronized_since(act)) {
2649 if (promise->eliminate_thread(tid)) {
2650 /* Promise has failed */
2651 priv->failed_promise = true;
2659 void ModelChecker::check_promises_thread_disabled()
2661 for (unsigned int i = 0; i < promises->size(); i++) {
2662 Promise *promise = (*promises)[i];
2663 if (promise->has_failed()) {
2664 priv->failed_promise = true;
2671 * @brief Checks promises in response to addition to modification order for
2674 * We test whether threads are still available for satisfying promises after an
2675 * addition to our modification order constraints. Those that are unavailable
2676 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2677 * that promise has failed.
2679 * @param act The ModelAction which updated the modification order
2680 * @param is_read_check Should be true if act is a read and we must check for
2681 * updates to the store from which it read (there is a distinction here for
2682 * RMW's, which are both a load and a store)
2684 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2686 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2688 for (unsigned int i = 0; i < promises->size(); i++) {
2689 Promise *promise = (*promises)[i];
2691 // Is this promise on the same location?
2692 if (!promise->same_location(write))
2695 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2696 const ModelAction *pread = promise->get_reader(j);
2697 if (!pread->happens_before(act))
2699 if (mo_graph->checkPromise(write, promise)) {
2700 priv->failed_promise = true;
2706 // Don't do any lookups twice for the same thread
2707 if (!promise->thread_is_available(act->get_tid()))
2710 if (mo_graph->checkReachable(promise, write)) {
2711 if (mo_graph->checkPromise(write, promise)) {
2712 priv->failed_promise = true;
2720 * Compute the set of writes that may break the current pending release
2721 * sequence. This information is extracted from previou release sequence
2724 * @param curr The current ModelAction. Must be a release sequence fixup
2727 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2729 if (pending_rel_seqs->empty())
2732 struct release_seq *pending = pending_rel_seqs->back();
2733 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2734 const ModelAction *write = pending->writes[i];
2735 curr->get_node()->add_relseq_break(write);
2738 /* NULL means don't break the sequence; just synchronize */
2739 curr->get_node()->add_relseq_break(NULL);
2743 * Build up an initial set of all past writes that this 'read' action may read
2744 * from, as well as any previously-observed future values that must still be valid.
2746 * @param curr is the current ModelAction that we are exploring; it must be a
2749 void ModelChecker::build_may_read_from(ModelAction *curr)
2751 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2753 ASSERT(curr->is_read());
2755 ModelAction *last_sc_write = NULL;
2757 if (curr->is_seqcst())
2758 last_sc_write = get_last_seq_cst_write(curr);
2760 /* Iterate over all threads */
2761 for (i = 0; i < thrd_lists->size(); i++) {
2762 /* Iterate over actions in thread, starting from most recent */
2763 action_list_t *list = &(*thrd_lists)[i];
2764 action_list_t::reverse_iterator rit;
2765 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2766 ModelAction *act = *rit;
2768 /* Only consider 'write' actions */
2769 if (!act->is_write() || act == curr)
2772 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2773 bool allow_read = true;
2775 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2777 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2781 /* Only add feasible reads */
2782 mo_graph->startChanges();
2783 r_modification_order(curr, act);
2784 if (!is_infeasible())
2785 curr->get_node()->add_read_from_past(act);
2786 mo_graph->rollbackChanges();
2789 /* Include at most one act per-thread that "happens before" curr */
2790 if (act->happens_before(curr))
2795 /* Inherit existing, promised future values */
2796 for (i = 0; i < promises->size(); i++) {
2797 const Promise *promise = (*promises)[i];
2798 const ModelAction *promise_read = promise->get_reader(0);
2799 if (promise_read->same_var(curr)) {
2800 /* Only add feasible future-values */
2801 mo_graph->startChanges();
2802 r_modification_order(curr, promise);
2803 if (!is_infeasible())
2804 curr->get_node()->add_read_from_promise(promise_read);
2805 mo_graph->rollbackChanges();
2809 /* We may find no valid may-read-from only if the execution is doomed */
2810 if (!curr->get_node()->read_from_size()) {
2811 priv->no_valid_reads = true;
2815 if (DBG_ENABLED()) {
2816 model_print("Reached read action:\n");
2818 model_print("Printing read_from_past\n");
2819 curr->get_node()->print_read_from_past();
2820 model_print("End printing read_from_past\n");
2824 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2826 for ( ; write != NULL; write = write->get_reads_from()) {
2827 /* UNINIT actions don't have a Node, and they never sleep */
2828 if (write->is_uninitialized())
2830 Node *prevnode = write->get_node()->get_parent();
2832 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2833 if (write->is_release() && thread_sleep)
2835 if (!write->is_rmw())
2842 * @brief Get an action representing an uninitialized atomic
2844 * This function may create a new one or try to retrieve one from the NodeStack
2846 * @param curr The current action, which prompts the creation of an UNINIT action
2847 * @return A pointer to the UNINIT ModelAction
2849 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2851 Node *node = curr->get_node();
2852 ModelAction *act = node->get_uninit_action();
2854 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2855 node->set_uninit_action(act);
2857 act->create_cv(NULL);
2861 static void print_list(action_list_t *list)
2863 action_list_t::iterator it;
2865 model_print("---------------------------------------------------------------------\n");
2867 unsigned int hash = 0;
2869 for (it = list->begin(); it != list->end(); it++) {
2870 const ModelAction *act = *it;
2871 if (act->get_seq_number() > 0)
2873 hash = hash^(hash<<3)^((*it)->hash());
2875 model_print("HASH %u\n", hash);
2876 model_print("---------------------------------------------------------------------\n");
2879 #if SUPPORT_MOD_ORDER_DUMP
2880 void ModelChecker::dumpGraph(char *filename) const
2883 sprintf(buffer, "%s.dot", filename);
2884 FILE *file = fopen(buffer, "w");
2885 fprintf(file, "digraph %s {\n", filename);
2886 mo_graph->dumpNodes(file);
2887 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2889 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2890 ModelAction *act = *it;
2891 if (act->is_read()) {
2892 mo_graph->dot_print_node(file, act);
2893 if (act->get_reads_from())
2894 mo_graph->dot_print_edge(file,
2895 act->get_reads_from(),
2897 "label=\"rf\", color=red, weight=2");
2899 mo_graph->dot_print_edge(file,
2900 act->get_reads_from_promise(),
2902 "label=\"rf\", color=red");
2904 if (thread_array[act->get_tid()]) {
2905 mo_graph->dot_print_edge(file,
2906 thread_array[id_to_int(act->get_tid())],
2908 "label=\"sb\", color=blue, weight=400");
2911 thread_array[act->get_tid()] = act;
2913 fprintf(file, "}\n");
2914 model_free(thread_array);
2919 /** @brief Prints an execution trace summary. */
2920 void ModelChecker::print_summary() const
2922 #if SUPPORT_MOD_ORDER_DUMP
2923 char buffername[100];
2924 sprintf(buffername, "exec%04u", stats.num_total);
2925 mo_graph->dumpGraphToFile(buffername);
2926 sprintf(buffername, "graph%04u", stats.num_total);
2927 dumpGraph(buffername);
2930 model_print("Execution %d:", stats.num_total);
2931 if (isfeasibleprefix()) {
2932 if (scheduler->all_threads_sleeping())
2933 model_print(" SLEEP-SET REDUNDANT");
2936 print_infeasibility(" INFEASIBLE");
2937 print_list(action_trace);
2939 if (!promises->empty()) {
2940 model_print("Pending promises:\n");
2941 for (unsigned int i = 0; i < promises->size(); i++) {
2942 model_print(" [P%u] ", i);
2943 (*promises)[i]->print();
2950 * Add a Thread to the system for the first time. Should only be called once
2952 * @param t The Thread to add
2954 void ModelChecker::add_thread(Thread *t)
2956 thread_map->put(id_to_int(t->get_id()), t);
2957 scheduler->add_thread(t);
2961 * @brief Get a Thread reference by its ID
2962 * @param tid The Thread's ID
2963 * @return A Thread reference
2965 Thread * ModelChecker::get_thread(thread_id_t tid) const
2967 return thread_map->get(id_to_int(tid));
2971 * @brief Get a reference to the Thread in which a ModelAction was executed
2972 * @param act The ModelAction
2973 * @return A Thread reference
2975 Thread * ModelChecker::get_thread(const ModelAction *act) const
2977 return get_thread(act->get_tid());
2981 * @brief Get a Promise's "promise number"
2983 * A "promise number" is an index number that is unique to a promise, valid
2984 * only for a specific snapshot of an execution trace. Promises may come and go
2985 * as they are generated an resolved, so an index only retains meaning for the
2988 * @param promise The Promise to check
2989 * @return The promise index, if the promise still is valid; otherwise -1
2991 int ModelChecker::get_promise_number(const Promise *promise) const
2993 for (unsigned int i = 0; i < promises->size(); i++)
2994 if ((*promises)[i] == promise)
3001 * @brief Check if a Thread is currently enabled
3002 * @param t The Thread to check
3003 * @return True if the Thread is currently enabled
3005 bool ModelChecker::is_enabled(Thread *t) const
3007 return scheduler->is_enabled(t);
3011 * @brief Check if a Thread is currently enabled
3012 * @param tid The ID of the Thread to check
3013 * @return True if the Thread is currently enabled
3015 bool ModelChecker::is_enabled(thread_id_t tid) const
3017 return scheduler->is_enabled(tid);
3021 * Switch from a model-checker context to a user-thread context. This is the
3022 * complement of ModelChecker::switch_to_master and must be called from the
3023 * model-checker context
3025 * @param thread The user-thread to switch to
3027 void ModelChecker::switch_from_master(Thread *thread)
3029 scheduler->set_current_thread(thread);
3030 Thread::swap(&system_context, thread);
3034 * Switch from a user-context to the "master thread" context (a.k.a. system
3035 * context). This switch is made with the intention of exploring a particular
3036 * model-checking action (described by a ModelAction object). Must be called
3037 * from a user-thread context.
3039 * @param act The current action that will be explored. May be NULL only if
3040 * trace is exiting via an assertion (see ModelChecker::set_assert and
3041 * ModelChecker::has_asserted).
3042 * @return Return the value returned by the current action
3044 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3047 Thread *old = thread_current();
3048 scheduler->set_current_thread(NULL);
3049 ASSERT(!old->get_pending());
3050 old->set_pending(act);
3051 if (Thread::swap(old, &system_context) < 0) {
3052 perror("swap threads");
3055 return old->get_return_value();
3059 * Takes the next step in the execution, if possible.
3060 * @param curr The current step to take
3061 * @return Returns the next Thread to run, if any; NULL if this execution
3064 Thread * ModelChecker::take_step(ModelAction *curr)
3066 Thread *curr_thrd = get_thread(curr);
3067 ASSERT(curr_thrd->get_state() == THREAD_READY);
3069 curr = check_current_action(curr);
3071 /* Infeasible -> don't take any more steps */
3072 if (is_infeasible())
3074 else if (isfeasibleprefix() && have_bug_reports()) {
3079 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3082 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3083 scheduler->remove_thread(curr_thrd);
3085 Thread *next_thrd = NULL;
3087 next_thrd = action_select_next_thread(curr);
3089 next_thrd = get_next_thread();
3091 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3092 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3097 /** Wrapper to run the user's main function, with appropriate arguments */
3098 void user_main_wrapper(void *)
3100 user_main(model->params.argc, model->params.argv);
3103 /** @brief Run ModelChecker for the user program */
3104 void ModelChecker::run()
3108 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3113 * Stash next pending action(s) for thread(s). There
3114 * should only need to stash one thread's action--the
3115 * thread which just took a step--plus the first step
3116 * for any newly-created thread
3118 for (unsigned int i = 0; i < get_num_threads(); i++) {
3119 thread_id_t tid = int_to_id(i);
3120 Thread *thr = get_thread(tid);
3121 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3122 switch_from_master(thr);
3123 if (is_circular_wait(thr))
3124 assert_bug("Deadlock detected");
3128 /* Catch assertions from prior take_step or from
3129 * between-ModelAction bugs (e.g., data races) */
3133 /* Consume the next action for a Thread */
3134 ModelAction *curr = t->get_pending();
3135 t->set_pending(NULL);
3136 t = take_step(curr);
3137 } while (t && !t->is_model_thread());
3140 * Launch end-of-execution release sequence fixups only when
3141 * the execution is otherwise feasible AND there are:
3143 * (1) pending release sequences
3144 * (2) pending assertions that could be invalidated by a change
3145 * in clock vectors (i.e., data races)
3146 * (3) no pending promises
3148 while (!pending_rel_seqs->empty() &&
3149 is_feasible_prefix_ignore_relseq() &&
3150 !unrealizedraces.empty()) {
3151 model_print("*** WARNING: release sequence fixup action "
3152 "(%zu pending release seuqence(s)) ***\n",
3153 pending_rel_seqs->size());
3154 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3155 std::memory_order_seq_cst, NULL, VALUE_NONE,
3159 } while (next_execution());
3161 model_print("******* Model-checking complete: *******\n");