10 #include "snapshot-interface.h"
12 #include "clockvector.h"
13 #include "cyclegraph.h"
16 #include "threads-model.h"
19 #define INITIAL_THREAD_ID 0
24 bug_message(const char *str) {
25 const char *fmt = " [BUG] %s\n";
26 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
27 sprintf(msg, fmt, str);
29 ~bug_message() { if (msg) snapshot_free(msg); }
32 void print() { model_print("%s", msg); }
38 * Structure for holding small ModelChecker members that should be snapshotted
40 struct model_snapshot_members {
41 model_snapshot_members() :
42 /* First thread created will have id INITIAL_THREAD_ID */
43 next_thread_id(INITIAL_THREAD_ID),
44 used_sequence_numbers(0),
48 failed_promise(false),
49 too_many_reads(false),
50 no_valid_reads(false),
51 bad_synchronization(false),
55 ~model_snapshot_members() {
56 for (unsigned int i = 0; i < bugs.size(); i++)
61 unsigned int next_thread_id;
62 modelclock_t used_sequence_numbers;
63 ModelAction *next_backtrack;
64 SnapVector<bug_message *> bugs;
65 struct execution_stats stats;
69 /** @brief Incorrectly-ordered synchronization was made */
70 bool bad_synchronization;
76 /** @brief Constructor */
77 ModelChecker::ModelChecker(struct model_params params) :
78 /* Initialize default scheduler */
80 scheduler(new Scheduler()),
82 earliest_diverge(NULL),
83 action_trace(new action_list_t()),
84 thread_map(new HashTable<int, Thread *, int>()),
85 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
86 lock_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
87 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new SnapVector<Promise *>()),
90 futurevalues(new SnapVector<struct PendingFutureValue>()),
91 pending_rel_seqs(new SnapVector<struct release_seq *>()),
92 thrd_last_action(new SnapVector<ModelAction *>(1)),
93 thrd_last_fence_release(new SnapVector<ModelAction *>()),
94 node_stack(new NodeStack()),
95 priv(new struct model_snapshot_members()),
96 mo_graph(new CycleGraph())
98 /* Initialize a model-checker thread, for special ModelActions */
99 model_thread = new Thread(get_next_id());
100 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
103 /** @brief Destructor */
104 ModelChecker::~ModelChecker()
106 for (unsigned int i = 0; i < get_num_threads(); i++)
107 delete thread_map->get(i);
112 delete lock_waiters_map;
113 delete condvar_waiters_map;
116 for (unsigned int i = 0; i < promises->size(); i++)
117 delete (*promises)[i];
120 delete pending_rel_seqs;
122 delete thrd_last_action;
123 delete thrd_last_fence_release;
130 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
132 action_list_t *tmp = hash->get(ptr);
134 tmp = new action_list_t();
140 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
142 SnapVector<action_list_t> *tmp = hash->get(ptr);
144 tmp = new SnapVector<action_list_t>();
151 * Restores user program to initial state and resets all model-checker data
154 void ModelChecker::reset_to_initial_state()
156 DEBUG("+++ Resetting to initial state +++\n");
157 node_stack->reset_execution();
159 /* Print all model-checker output before rollback */
163 * FIXME: if we utilize partial rollback, we will need to free only
164 * those pending actions which were NOT pending before the rollback
167 for (unsigned int i = 0; i < get_num_threads(); i++)
168 delete get_thread(int_to_id(i))->get_pending();
170 snapshot_backtrack_before(0);
173 /** @return a thread ID for a new Thread */
174 thread_id_t ModelChecker::get_next_id()
176 return priv->next_thread_id++;
179 /** @return the number of user threads created during this execution */
180 unsigned int ModelChecker::get_num_threads() const
182 return priv->next_thread_id;
186 * Must be called from user-thread context (e.g., through the global
187 * thread_current() interface)
189 * @return The currently executing Thread.
191 Thread * ModelChecker::get_current_thread() const
193 return scheduler->get_current_thread();
196 /** @return a sequence number for a new ModelAction */
197 modelclock_t ModelChecker::get_next_seq_num()
199 return ++priv->used_sequence_numbers;
202 Node * ModelChecker::get_curr_node() const
204 return node_stack->get_head();
208 * @brief Select the next thread to execute based on the curren action
210 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
211 * actions should be followed by the execution of their child thread. In either
212 * case, the current action should determine the next thread schedule.
214 * @param curr The current action
215 * @return The next thread to run, if the current action will determine this
216 * selection; otherwise NULL
218 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
220 /* Do not split atomic RMW */
222 return get_thread(curr);
223 /* Follow CREATE with the created thread */
224 if (curr->get_type() == THREAD_CREATE)
225 return curr->get_thread_operand();
230 * @brief Choose the next thread to execute.
232 * This function chooses the next thread that should execute. It can enforce
233 * execution replay/backtracking or, if the model-checker has no preference
234 * regarding the next thread (i.e., when exploring a new execution ordering),
235 * we defer to the scheduler.
237 * @return The next chosen thread to run, if any exist. Or else if the current
238 * execution should terminate, return NULL.
240 Thread * ModelChecker::get_next_thread()
245 * Have we completed exploring the preselected path? Then let the
249 return scheduler->select_next_thread();
251 /* Else, we are trying to replay an execution */
252 ModelAction *next = node_stack->get_next()->get_action();
254 if (next == diverge) {
255 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
256 earliest_diverge = diverge;
258 Node *nextnode = next->get_node();
259 Node *prevnode = nextnode->get_parent();
260 scheduler->update_sleep_set(prevnode);
262 /* Reached divergence point */
263 if (nextnode->increment_misc()) {
264 /* The next node will try to satisfy a different misc_index values. */
265 tid = next->get_tid();
266 node_stack->pop_restofstack(2);
267 } else if (nextnode->increment_promise()) {
268 /* The next node will try to satisfy a different set of promises. */
269 tid = next->get_tid();
270 node_stack->pop_restofstack(2);
271 } else if (nextnode->increment_read_from()) {
272 /* The next node will read from a different value. */
273 tid = next->get_tid();
274 node_stack->pop_restofstack(2);
275 } else if (nextnode->increment_relseq_break()) {
276 /* The next node will try to resolve a release sequence differently */
277 tid = next->get_tid();
278 node_stack->pop_restofstack(2);
281 /* Make a different thread execute for next step */
282 scheduler->add_sleep(get_thread(next->get_tid()));
283 tid = prevnode->get_next_backtrack();
284 /* Make sure the backtracked thread isn't sleeping. */
285 node_stack->pop_restofstack(1);
286 if (diverge == earliest_diverge) {
287 earliest_diverge = prevnode->get_action();
290 /* Start the round robin scheduler from this thread id */
291 scheduler->set_scheduler_thread(tid);
292 /* The correct sleep set is in the parent node. */
295 DEBUG("*** Divergence point ***\n");
299 tid = next->get_tid();
301 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
302 ASSERT(tid != THREAD_ID_T_NONE);
303 return thread_map->get(id_to_int(tid));
307 * We need to know what the next actions of all threads in the sleep
308 * set will be. This method computes them and stores the actions at
309 * the corresponding thread object's pending action.
312 void ModelChecker::execute_sleep_set()
314 for (unsigned int i = 0; i < get_num_threads(); i++) {
315 thread_id_t tid = int_to_id(i);
316 Thread *thr = get_thread(tid);
317 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
318 thr->get_pending()->set_sleep_flag();
324 * @brief Should the current action wake up a given thread?
326 * @param curr The current action
327 * @param thread The thread that we might wake up
328 * @return True, if we should wake up the sleeping thread; false otherwise
330 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
332 const ModelAction *asleep = thread->get_pending();
333 /* Don't allow partial RMW to wake anyone up */
336 /* Synchronizing actions may have been backtracked */
337 if (asleep->could_synchronize_with(curr))
339 /* All acquire/release fences and fence-acquire/store-release */
340 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
342 /* Fence-release + store can awake load-acquire on the same location */
343 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
344 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
345 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
351 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
353 for (unsigned int i = 0; i < get_num_threads(); i++) {
354 Thread *thr = get_thread(int_to_id(i));
355 if (scheduler->is_sleep_set(thr)) {
356 if (should_wake_up(curr, thr))
357 /* Remove this thread from sleep set */
358 scheduler->remove_sleep(thr);
363 /** @brief Alert the model-checker that an incorrectly-ordered
364 * synchronization was made */
365 void ModelChecker::set_bad_synchronization()
367 priv->bad_synchronization = true;
371 * Check whether the current trace has triggered an assertion which should halt
374 * @return True, if the execution should be aborted; false otherwise
376 bool ModelChecker::has_asserted() const
378 return priv->asserted;
382 * Trigger a trace assertion which should cause this execution to be halted.
383 * This can be due to a detected bug or due to an infeasibility that should
386 void ModelChecker::set_assert()
388 priv->asserted = true;
392 * Check if we are in a deadlock. Should only be called at the end of an
393 * execution, although it should not give false positives in the middle of an
394 * execution (there should be some ENABLED thread).
396 * @return True if program is in a deadlock; false otherwise
398 bool ModelChecker::is_deadlocked() const
400 bool blocking_threads = false;
401 for (unsigned int i = 0; i < get_num_threads(); i++) {
402 thread_id_t tid = int_to_id(i);
405 Thread *t = get_thread(tid);
406 if (!t->is_model_thread() && t->get_pending())
407 blocking_threads = true;
409 return blocking_threads;
413 * Check if a Thread has entered a circular wait deadlock situation. This will
414 * not check other threads for potential deadlock situations, and may miss
415 * deadlocks involving WAIT.
417 * @param t The thread which may have entered a deadlock
418 * @return True if this Thread entered a deadlock; false otherwise
420 bool ModelChecker::is_circular_wait(const Thread *t) const
422 for (Thread *waiting = t->waiting_on() ; waiting != NULL; waiting = waiting->waiting_on())
429 * Check if this is a complete execution. That is, have all thread completed
430 * execution (rather than exiting because sleep sets have forced a redundant
433 * @return True if the execution is complete.
435 bool ModelChecker::is_complete_execution() const
437 for (unsigned int i = 0; i < get_num_threads(); i++)
438 if (is_enabled(int_to_id(i)))
444 * @brief Assert a bug in the executing program.
446 * Use this function to assert any sort of bug in the user program. If the
447 * current trace is feasible (actually, a prefix of some feasible execution),
448 * then this execution will be aborted, printing the appropriate message. If
449 * the current trace is not yet feasible, the error message will be stashed and
450 * printed if the execution ever becomes feasible.
452 * @param msg Descriptive message for the bug (do not include newline char)
453 * @return True if bug is immediately-feasible
455 bool ModelChecker::assert_bug(const char *msg)
457 priv->bugs.push_back(new bug_message(msg));
459 if (isfeasibleprefix()) {
467 * @brief Assert a bug in the executing program, asserted by a user thread
468 * @see ModelChecker::assert_bug
469 * @param msg Descriptive message for the bug (do not include newline char)
471 void ModelChecker::assert_user_bug(const char *msg)
473 /* If feasible bug, bail out now */
475 switch_to_master(NULL);
478 /** @return True, if any bugs have been reported for this execution */
479 bool ModelChecker::have_bug_reports() const
481 return priv->bugs.size() != 0;
484 /** @brief Print bug report listing for this execution (if any bugs exist) */
485 void ModelChecker::print_bugs() const
487 if (have_bug_reports()) {
488 model_print("Bug report: %zu bug%s detected\n",
490 priv->bugs.size() > 1 ? "s" : "");
491 for (unsigned int i = 0; i < priv->bugs.size(); i++)
492 priv->bugs[i]->print();
497 * @brief Record end-of-execution stats
499 * Must be run when exiting an execution. Records various stats.
500 * @see struct execution_stats
502 void ModelChecker::record_stats()
505 if (!isfeasibleprefix())
506 stats.num_infeasible++;
507 else if (have_bug_reports())
508 stats.num_buggy_executions++;
509 else if (is_complete_execution())
510 stats.num_complete++;
512 stats.num_redundant++;
515 * @todo We can violate this ASSERT() when fairness/sleep sets
516 * conflict to cause an execution to terminate, e.g. with:
517 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
519 //ASSERT(scheduler->all_threads_sleeping());
523 /** @brief Print execution stats */
524 void ModelChecker::print_stats() const
526 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
527 model_print("Number of redundant executions: %d\n", stats.num_redundant);
528 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
529 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
530 model_print("Total executions: %d\n", stats.num_total);
531 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
535 * @brief End-of-exeuction print
536 * @param printbugs Should any existing bugs be printed?
538 void ModelChecker::print_execution(bool printbugs) const
540 print_program_output();
542 if (params.verbose) {
543 model_print("Earliest divergence point since last feasible execution:\n");
544 if (earliest_diverge)
545 earliest_diverge->print();
547 model_print("(Not set)\n");
553 /* Don't print invalid bugs */
562 * Queries the model-checker for more executions to explore and, if one
563 * exists, resets the model-checker state to execute a new execution.
565 * @return If there are more executions to explore, return true. Otherwise,
568 bool ModelChecker::next_execution()
571 /* Is this execution a feasible execution that's worth bug-checking? */
572 bool complete = isfeasibleprefix() && (is_complete_execution() ||
575 /* End-of-execution bug checks */
578 assert_bug("Deadlock detected");
586 if (params.verbose || (complete && have_bug_reports()))
587 print_execution(complete);
589 clear_program_output();
592 earliest_diverge = NULL;
594 if ((diverge = get_next_backtrack()) == NULL)
598 model_print("Next execution will diverge at:\n");
602 reset_to_initial_state();
607 * @brief Find the last fence-related backtracking conflict for a ModelAction
609 * This function performs the search for the most recent conflicting action
610 * against which we should perform backtracking, as affected by fence
611 * operations. This includes pairs of potentially-synchronizing actions which
612 * occur due to fence-acquire or fence-release, and hence should be explored in
613 * the opposite execution order.
615 * @param act The current action
616 * @return The most recent action which conflicts with act due to fences
618 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
620 /* Only perform release/acquire fence backtracking for stores */
621 if (!act->is_write())
624 /* Find a fence-release (or, act is a release) */
625 ModelAction *last_release;
626 if (act->is_release())
629 last_release = get_last_fence_release(act->get_tid());
633 /* Skip past the release */
634 action_list_t *list = action_trace;
635 action_list_t::reverse_iterator rit;
636 for (rit = list->rbegin(); rit != list->rend(); rit++)
637 if (*rit == last_release)
639 ASSERT(rit != list->rend());
644 * load --sb-> fence-acquire */
645 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
646 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
647 bool found_acquire_fences = false;
648 for ( ; rit != list->rend(); rit++) {
649 ModelAction *prev = *rit;
650 if (act->same_thread(prev))
653 int tid = id_to_int(prev->get_tid());
655 if (prev->is_read() && act->same_var(prev)) {
656 if (prev->is_acquire()) {
657 /* Found most recent load-acquire, don't need
658 * to search for more fences */
659 if (!found_acquire_fences)
662 prior_loads[tid] = prev;
665 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
666 found_acquire_fences = true;
667 acquire_fences[tid] = prev;
671 ModelAction *latest_backtrack = NULL;
672 for (unsigned int i = 0; i < acquire_fences.size(); i++)
673 if (acquire_fences[i] && prior_loads[i])
674 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
675 latest_backtrack = acquire_fences[i];
676 return latest_backtrack;
680 * @brief Find the last backtracking conflict for a ModelAction
682 * This function performs the search for the most recent conflicting action
683 * against which we should perform backtracking. This primary includes pairs of
684 * synchronizing actions which should be explored in the opposite execution
687 * @param act The current action
688 * @return The most recent action which conflicts with act
690 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
692 switch (act->get_type()) {
693 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
697 ModelAction *ret = NULL;
699 /* linear search: from most recent to oldest */
700 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
701 action_list_t::reverse_iterator rit;
702 for (rit = list->rbegin(); rit != list->rend(); rit++) {
703 ModelAction *prev = *rit;
704 if (prev->could_synchronize_with(act)) {
710 ModelAction *ret2 = get_last_fence_conflict(act);
720 case ATOMIC_TRYLOCK: {
721 /* linear search: from most recent to oldest */
722 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
723 action_list_t::reverse_iterator rit;
724 for (rit = list->rbegin(); rit != list->rend(); rit++) {
725 ModelAction *prev = *rit;
726 if (act->is_conflicting_lock(prev))
731 case ATOMIC_UNLOCK: {
732 /* linear search: from most recent to oldest */
733 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
734 action_list_t::reverse_iterator rit;
735 for (rit = list->rbegin(); rit != list->rend(); rit++) {
736 ModelAction *prev = *rit;
737 if (!act->same_thread(prev) && prev->is_failed_trylock())
743 /* linear search: from most recent to oldest */
744 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
745 action_list_t::reverse_iterator rit;
746 for (rit = list->rbegin(); rit != list->rend(); rit++) {
747 ModelAction *prev = *rit;
748 if (!act->same_thread(prev) && prev->is_failed_trylock())
750 if (!act->same_thread(prev) && prev->is_notify())
756 case ATOMIC_NOTIFY_ALL:
757 case ATOMIC_NOTIFY_ONE: {
758 /* linear search: from most recent to oldest */
759 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
760 action_list_t::reverse_iterator rit;
761 for (rit = list->rbegin(); rit != list->rend(); rit++) {
762 ModelAction *prev = *rit;
763 if (!act->same_thread(prev) && prev->is_wait())
774 /** This method finds backtracking points where we should try to
775 * reorder the parameter ModelAction against.
777 * @param the ModelAction to find backtracking points for.
779 void ModelChecker::set_backtracking(ModelAction *act)
781 Thread *t = get_thread(act);
782 ModelAction *prev = get_last_conflict(act);
786 Node *node = prev->get_node()->get_parent();
788 int low_tid, high_tid;
789 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
790 low_tid = id_to_int(act->get_tid());
791 high_tid = low_tid + 1;
794 high_tid = get_num_threads();
797 for (int i = low_tid; i < high_tid; i++) {
798 thread_id_t tid = int_to_id(i);
800 /* Make sure this thread can be enabled here. */
801 if (i >= node->get_num_threads())
804 /* Don't backtrack into a point where the thread is disabled or sleeping. */
805 if (node->enabled_status(tid) != THREAD_ENABLED)
808 /* Check if this has been explored already */
809 if (node->has_been_explored(tid))
812 /* See if fairness allows */
813 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
815 for (int t = 0; t < node->get_num_threads(); t++) {
816 thread_id_t tother = int_to_id(t);
817 if (node->is_enabled(tother) && node->has_priority(tother)) {
826 /* See if CHESS-like yield fairness allows */
827 if (model->params.yieldon) {
829 for (int t = 0; t < node->get_num_threads(); t++) {
830 thread_id_t tother = int_to_id(t);
831 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
840 /* Cache the latest backtracking point */
841 set_latest_backtrack(prev);
843 /* If this is a new backtracking point, mark the tree */
844 if (!node->set_backtrack(tid))
846 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
847 id_to_int(prev->get_tid()),
848 id_to_int(t->get_id()));
857 * @brief Cache the a backtracking point as the "most recent", if eligible
859 * Note that this does not prepare the NodeStack for this backtracking
860 * operation, it only caches the action on a per-execution basis
862 * @param act The operation at which we should explore a different next action
863 * (i.e., backtracking point)
864 * @return True, if this action is now the most recent backtracking point;
867 bool ModelChecker::set_latest_backtrack(ModelAction *act)
869 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
870 priv->next_backtrack = act;
877 * Returns last backtracking point. The model checker will explore a different
878 * path for this point in the next execution.
879 * @return The ModelAction at which the next execution should diverge.
881 ModelAction * ModelChecker::get_next_backtrack()
883 ModelAction *next = priv->next_backtrack;
884 priv->next_backtrack = NULL;
889 * Processes a read model action.
890 * @param curr is the read model action to process.
891 * @return True if processing this read updates the mo_graph.
893 bool ModelChecker::process_read(ModelAction *curr)
895 Node *node = curr->get_node();
897 bool updated = false;
898 switch (node->get_read_from_status()) {
899 case READ_FROM_PAST: {
900 const ModelAction *rf = node->get_read_from_past();
903 mo_graph->startChanges();
905 ASSERT(!is_infeasible());
906 if (!check_recency(curr, rf)) {
907 if (node->increment_read_from()) {
908 mo_graph->rollbackChanges();
911 priv->too_many_reads = true;
915 updated = r_modification_order(curr, rf);
917 mo_graph->commitChanges();
918 mo_check_promises(curr, true);
921 case READ_FROM_PROMISE: {
922 Promise *promise = curr->get_node()->get_read_from_promise();
923 if (promise->add_reader(curr))
924 priv->failed_promise = true;
925 curr->set_read_from_promise(promise);
926 mo_graph->startChanges();
927 if (!check_recency(curr, promise))
928 priv->too_many_reads = true;
929 updated = r_modification_order(curr, promise);
930 mo_graph->commitChanges();
933 case READ_FROM_FUTURE: {
934 /* Read from future value */
935 struct future_value fv = node->get_future_value();
936 Promise *promise = new Promise(curr, fv);
937 curr->set_read_from_promise(promise);
938 promises->push_back(promise);
939 mo_graph->startChanges();
940 updated = r_modification_order(curr, promise);
941 mo_graph->commitChanges();
947 get_thread(curr)->set_return_value(curr->get_return_value());
953 * Processes a lock, trylock, or unlock model action. @param curr is
954 * the read model action to process.
956 * The try lock operation checks whether the lock is taken. If not,
957 * it falls to the normal lock operation case. If so, it returns
960 * The lock operation has already been checked that it is enabled, so
961 * it just grabs the lock and synchronizes with the previous unlock.
963 * The unlock operation has to re-enable all of the threads that are
964 * waiting on the lock.
966 * @return True if synchronization was updated; false otherwise
968 bool ModelChecker::process_mutex(ModelAction *curr)
970 std::mutex *mutex = curr->get_mutex();
971 struct std::mutex_state *state = NULL;
974 state = mutex->get_state();
976 switch (curr->get_type()) {
977 case ATOMIC_TRYLOCK: {
978 bool success = !state->locked;
979 curr->set_try_lock(success);
981 get_thread(curr)->set_return_value(0);
984 get_thread(curr)->set_return_value(1);
986 //otherwise fall into the lock case
988 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
989 assert_bug("Lock access before initialization");
990 state->locked = get_thread(curr);
991 ModelAction *unlock = get_last_unlock(curr);
992 //synchronize with the previous unlock statement
993 if (unlock != NULL) {
994 curr->synchronize_with(unlock);
999 case ATOMIC_UNLOCK: {
1001 state->locked = NULL;
1002 //wake up the other threads
1003 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
1004 //activate all the waiting threads
1005 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1006 scheduler->wake(get_thread(*rit));
1013 state->locked = NULL;
1014 //wake up the other threads
1015 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
1016 //activate all the waiting threads
1017 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1018 scheduler->wake(get_thread(*rit));
1021 //check whether we should go to sleep or not...simulate spurious failures
1022 if (curr->get_node()->get_misc() == 0) {
1023 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1025 scheduler->sleep(get_thread(curr));
1029 case ATOMIC_NOTIFY_ALL: {
1030 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1031 //activate all the waiting threads
1032 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1033 scheduler->wake(get_thread(*rit));
1038 case ATOMIC_NOTIFY_ONE: {
1039 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1040 int wakeupthread = curr->get_node()->get_misc();
1041 action_list_t::iterator it = waiters->begin();
1042 advance(it, wakeupthread);
1043 scheduler->wake(get_thread(*it));
1055 * @brief Check if the current pending promises allow a future value to be sent
1057 * If one of the following is true:
1058 * (a) there are no pending promises
1059 * (b) the reader and writer do not cross any promises
1060 * Then, it is safe to pass a future value back now.
1062 * Otherwise, we must save the pending future value until (a) or (b) is true
1064 * @param writer The operation which sends the future value. Must be a write.
1065 * @param reader The operation which will observe the value. Must be a read.
1066 * @return True if the future value can be sent now; false if it must wait.
1068 bool ModelChecker::promises_may_allow(const ModelAction *writer,
1069 const ModelAction *reader) const
1071 if (promises->empty())
1073 for(int i=promises->size()-1;i>=0;i--) {
1074 ModelAction *pr=(*promises)[i]->get_reader(0);
1075 //reader is after promise...doesn't cross any promise
1078 //writer is after promise, reader before...bad...
1086 * @brief Add a future value to a reader
1088 * This function performs a few additional checks to ensure that the future
1089 * value can be feasibly observed by the reader
1091 * @param writer The operation whose value is sent. Must be a write.
1092 * @param reader The read operation which may read the future value. Must be a read.
1094 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1096 /* Do more ambitious checks now that mo is more complete */
1097 if (!mo_may_allow(writer, reader))
1100 Node *node = reader->get_node();
1102 /* Find an ancestor thread which exists at the time of the reader */
1103 Thread *write_thread = get_thread(writer);
1104 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1105 write_thread = write_thread->get_parent();
1107 struct future_value fv = {
1108 writer->get_write_value(),
1109 writer->get_seq_number() + params.maxfuturedelay,
1110 write_thread->get_id(),
1112 if (node->add_future_value(fv))
1113 set_latest_backtrack(reader);
1117 * Process a write ModelAction
1118 * @param curr The ModelAction to process
1119 * @return True if the mo_graph was updated or promises were resolved
1121 bool ModelChecker::process_write(ModelAction *curr)
1123 /* Readers to which we may send our future value */
1124 ModelVector<ModelAction *> send_fv;
1126 const ModelAction *earliest_promise_reader;
1127 bool updated_promises = false;
1129 bool updated_mod_order = w_modification_order(curr, &send_fv);
1130 Promise *promise = pop_promise_to_resolve(curr);
1133 earliest_promise_reader = promise->get_reader(0);
1134 updated_promises = resolve_promise(curr, promise);
1136 earliest_promise_reader = NULL;
1138 for (unsigned int i = 0; i < send_fv.size(); i++) {
1139 ModelAction *read = send_fv[i];
1141 /* Don't send future values to reads after the Promise we resolve */
1142 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
1143 /* Check if future value can be sent immediately */
1144 if (promises_may_allow(curr, read)) {
1145 add_future_value(curr, read);
1147 futurevalues->push_back(PendingFutureValue(curr, read));
1152 /* Check the pending future values */
1153 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
1154 struct PendingFutureValue pfv = (*futurevalues)[i];
1155 if (promises_may_allow(pfv.writer, pfv.reader)) {
1156 add_future_value(pfv.writer, pfv.reader);
1157 futurevalues->erase(futurevalues->begin() + i);
1161 mo_graph->commitChanges();
1162 mo_check_promises(curr, false);
1164 get_thread(curr)->set_return_value(VALUE_NONE);
1165 return updated_mod_order || updated_promises;
1169 * Process a fence ModelAction
1170 * @param curr The ModelAction to process
1171 * @return True if synchronization was updated
1173 bool ModelChecker::process_fence(ModelAction *curr)
1176 * fence-relaxed: no-op
1177 * fence-release: only log the occurence (not in this function), for
1178 * use in later synchronization
1179 * fence-acquire (this function): search for hypothetical release
1181 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1183 bool updated = false;
1184 if (curr->is_acquire()) {
1185 action_list_t *list = action_trace;
1186 action_list_t::reverse_iterator rit;
1187 /* Find X : is_read(X) && X --sb-> curr */
1188 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1189 ModelAction *act = *rit;
1192 if (act->get_tid() != curr->get_tid())
1194 /* Stop at the beginning of the thread */
1195 if (act->is_thread_start())
1197 /* Stop once we reach a prior fence-acquire */
1198 if (act->is_fence() && act->is_acquire())
1200 if (!act->is_read())
1202 /* read-acquire will find its own release sequences */
1203 if (act->is_acquire())
1206 /* Establish hypothetical release sequences */
1207 rel_heads_list_t release_heads;
1208 get_release_seq_heads(curr, act, &release_heads);
1209 for (unsigned int i = 0; i < release_heads.size(); i++)
1210 if (!curr->synchronize_with(release_heads[i]))
1211 set_bad_synchronization();
1212 if (release_heads.size() != 0)
1220 * @brief Process the current action for thread-related activity
1222 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1223 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1224 * synchronization, etc. This function is a no-op for non-THREAD actions
1225 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1227 * @param curr The current action
1228 * @return True if synchronization was updated or a thread completed
1230 bool ModelChecker::process_thread_action(ModelAction *curr)
1232 bool updated = false;
1234 switch (curr->get_type()) {
1235 case THREAD_CREATE: {
1236 thrd_t *thrd = (thrd_t *)curr->get_location();
1237 struct thread_params *params = (struct thread_params *)curr->get_value();
1238 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1240 th->set_creation(curr);
1241 /* Promises can be satisfied by children */
1242 for (unsigned int i = 0; i < promises->size(); i++) {
1243 Promise *promise = (*promises)[i];
1244 if (promise->thread_is_available(curr->get_tid()))
1245 promise->add_thread(th->get_id());
1250 Thread *blocking = curr->get_thread_operand();
1251 ModelAction *act = get_last_action(blocking->get_id());
1252 curr->synchronize_with(act);
1253 updated = true; /* trigger rel-seq checks */
1256 case THREAD_FINISH: {
1257 Thread *th = get_thread(curr);
1258 while (!th->wait_list_empty()) {
1259 ModelAction *act = th->pop_wait_list();
1260 scheduler->wake(get_thread(act));
1263 /* Completed thread can't satisfy promises */
1264 for (unsigned int i = 0; i < promises->size(); i++) {
1265 Promise *promise = (*promises)[i];
1266 if (promise->thread_is_available(th->get_id()))
1267 if (promise->eliminate_thread(th->get_id()))
1268 priv->failed_promise = true;
1270 updated = true; /* trigger rel-seq checks */
1273 case THREAD_START: {
1274 check_promises(curr->get_tid(), NULL, curr->get_cv());
1285 * @brief Process the current action for release sequence fixup activity
1287 * Performs model-checker release sequence fixups for the current action,
1288 * forcing a single pending release sequence to break (with a given, potential
1289 * "loose" write) or to complete (i.e., synchronize). If a pending release
1290 * sequence forms a complete release sequence, then we must perform the fixup
1291 * synchronization, mo_graph additions, etc.
1293 * @param curr The current action; must be a release sequence fixup action
1294 * @param work_queue The work queue to which to add work items as they are
1297 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1299 const ModelAction *write = curr->get_node()->get_relseq_break();
1300 struct release_seq *sequence = pending_rel_seqs->back();
1301 pending_rel_seqs->pop_back();
1303 ModelAction *acquire = sequence->acquire;
1304 const ModelAction *rf = sequence->rf;
1305 const ModelAction *release = sequence->release;
1309 ASSERT(release->same_thread(rf));
1311 if (write == NULL) {
1313 * @todo Forcing a synchronization requires that we set
1314 * modification order constraints. For instance, we can't allow
1315 * a fixup sequence in which two separate read-acquire
1316 * operations read from the same sequence, where the first one
1317 * synchronizes and the other doesn't. Essentially, we can't
1318 * allow any writes to insert themselves between 'release' and
1322 /* Must synchronize */
1323 if (!acquire->synchronize_with(release)) {
1324 set_bad_synchronization();
1327 /* Re-check all pending release sequences */
1328 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1329 /* Re-check act for mo_graph edges */
1330 work_queue->push_back(MOEdgeWorkEntry(acquire));
1332 /* propagate synchronization to later actions */
1333 action_list_t::reverse_iterator rit = action_trace->rbegin();
1334 for (; (*rit) != acquire; rit++) {
1335 ModelAction *propagate = *rit;
1336 if (acquire->happens_before(propagate)) {
1337 propagate->synchronize_with(acquire);
1338 /* Re-check 'propagate' for mo_graph edges */
1339 work_queue->push_back(MOEdgeWorkEntry(propagate));
1343 /* Break release sequence with new edges:
1344 * release --mo--> write --mo--> rf */
1345 mo_graph->addEdge(release, write);
1346 mo_graph->addEdge(write, rf);
1349 /* See if we have realized a data race */
1354 * Initialize the current action by performing one or more of the following
1355 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1356 * in the NodeStack, manipulating backtracking sets, allocating and
1357 * initializing clock vectors, and computing the promises to fulfill.
1359 * @param curr The current action, as passed from the user context; may be
1360 * freed/invalidated after the execution of this function, with a different
1361 * action "returned" its place (pass-by-reference)
1362 * @return True if curr is a newly-explored action; false otherwise
1364 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1366 ModelAction *newcurr;
1368 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1369 newcurr = process_rmw(*curr);
1372 if (newcurr->is_rmw())
1373 compute_promises(newcurr);
1379 (*curr)->set_seq_number(get_next_seq_num());
1381 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1383 /* First restore type and order in case of RMW operation */
1384 if ((*curr)->is_rmwr())
1385 newcurr->copy_typeandorder(*curr);
1387 ASSERT((*curr)->get_location() == newcurr->get_location());
1388 newcurr->copy_from_new(*curr);
1390 /* Discard duplicate ModelAction; use action from NodeStack */
1393 /* Always compute new clock vector */
1394 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1397 return false; /* Action was explored previously */
1401 /* Always compute new clock vector */
1402 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1404 /* Assign most recent release fence */
1405 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1408 * Perform one-time actions when pushing new ModelAction onto
1411 if (newcurr->is_write())
1412 compute_promises(newcurr);
1413 else if (newcurr->is_relseq_fixup())
1414 compute_relseq_breakwrites(newcurr);
1415 else if (newcurr->is_wait())
1416 newcurr->get_node()->set_misc_max(2);
1417 else if (newcurr->is_notify_one()) {
1418 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1420 return true; /* This was a new ModelAction */
1425 * @brief Establish reads-from relation between two actions
1427 * Perform basic operations involved with establishing a concrete rf relation,
1428 * including setting the ModelAction data and checking for release sequences.
1430 * @param act The action that is reading (must be a read)
1431 * @param rf The action from which we are reading (must be a write)
1433 * @return True if this read established synchronization
1435 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1438 ASSERT(rf->is_write());
1440 act->set_read_from(rf);
1441 if (act->is_acquire()) {
1442 rel_heads_list_t release_heads;
1443 get_release_seq_heads(act, act, &release_heads);
1444 int num_heads = release_heads.size();
1445 for (unsigned int i = 0; i < release_heads.size(); i++)
1446 if (!act->synchronize_with(release_heads[i])) {
1447 set_bad_synchronization();
1450 return num_heads > 0;
1456 * Check promises and eliminate potentially-satisfying threads when a thread is
1457 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1458 * no longer satisfy a promise generated from that thread.
1460 * @param blocker The thread on which a thread is waiting
1461 * @param waiting The waiting thread
1463 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1465 for (unsigned int i = 0; i < promises->size(); i++) {
1466 Promise *promise = (*promises)[i];
1467 if (!promise->thread_is_available(waiting->get_id()))
1469 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1470 ModelAction *reader = promise->get_reader(j);
1471 if (reader->get_tid() != blocker->get_id())
1473 if (promise->eliminate_thread(waiting->get_id())) {
1474 /* Promise has failed */
1475 priv->failed_promise = true;
1477 /* Only eliminate the 'waiting' thread once */
1485 * @brief Check whether a model action is enabled.
1487 * Checks whether a lock or join operation would be successful (i.e., is the
1488 * lock already locked, or is the joined thread already complete). If not, put
1489 * the action in a waiter list.
1491 * @param curr is the ModelAction to check whether it is enabled.
1492 * @return a bool that indicates whether the action is enabled.
1494 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1495 if (curr->is_lock()) {
1496 std::mutex *lock = (std::mutex *)curr->get_location();
1497 struct std::mutex_state *state = lock->get_state();
1498 if (state->locked) {
1499 //Stick the action in the appropriate waiting queue
1500 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1503 } else if (curr->get_type() == THREAD_JOIN) {
1504 Thread *blocking = (Thread *)curr->get_location();
1505 if (!blocking->is_complete()) {
1506 blocking->push_wait_list(curr);
1507 thread_blocking_check_promises(blocking, get_thread(curr));
1516 * This is the heart of the model checker routine. It performs model-checking
1517 * actions corresponding to a given "current action." Among other processes, it
1518 * calculates reads-from relationships, updates synchronization clock vectors,
1519 * forms a memory_order constraints graph, and handles replay/backtrack
1520 * execution when running permutations of previously-observed executions.
1522 * @param curr The current action to process
1523 * @return The ModelAction that is actually executed; may be different than
1524 * curr; may be NULL, if the current action is not enabled to run
1526 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1529 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1531 if (!check_action_enabled(curr)) {
1532 /* Make the execution look like we chose to run this action
1533 * much later, when a lock/join can succeed */
1534 get_thread(curr)->set_pending(curr);
1535 scheduler->sleep(get_thread(curr));
1539 bool newly_explored = initialize_curr_action(&curr);
1545 wake_up_sleeping_actions(curr);
1547 /* Compute fairness information for CHESS yield algorithm */
1548 if (model->params.yieldon) {
1549 curr->get_node()->update_yield(scheduler);
1552 /* Add the action to lists before any other model-checking tasks */
1553 if (!second_part_of_rmw)
1554 add_action_to_lists(curr);
1556 /* Build may_read_from set for newly-created actions */
1557 if (newly_explored && curr->is_read())
1558 build_may_read_from(curr);
1560 /* Initialize work_queue with the "current action" work */
1561 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1562 while (!work_queue.empty() && !has_asserted()) {
1563 WorkQueueEntry work = work_queue.front();
1564 work_queue.pop_front();
1566 switch (work.type) {
1567 case WORK_CHECK_CURR_ACTION: {
1568 ModelAction *act = work.action;
1569 bool update = false; /* update this location's release seq's */
1570 bool update_all = false; /* update all release seq's */
1572 if (process_thread_action(curr))
1575 if (act->is_read() && !second_part_of_rmw && process_read(act))
1578 if (act->is_write() && process_write(act))
1581 if (act->is_fence() && process_fence(act))
1584 if (act->is_mutex_op() && process_mutex(act))
1587 if (act->is_relseq_fixup())
1588 process_relseq_fixup(curr, &work_queue);
1591 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1593 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1596 case WORK_CHECK_RELEASE_SEQ:
1597 resolve_release_sequences(work.location, &work_queue);
1599 case WORK_CHECK_MO_EDGES: {
1600 /** @todo Complete verification of work_queue */
1601 ModelAction *act = work.action;
1602 bool updated = false;
1604 if (act->is_read()) {
1605 const ModelAction *rf = act->get_reads_from();
1606 const Promise *promise = act->get_reads_from_promise();
1608 if (r_modification_order(act, rf))
1610 } else if (promise) {
1611 if (r_modification_order(act, promise))
1615 if (act->is_write()) {
1616 if (w_modification_order(act, NULL))
1619 mo_graph->commitChanges();
1622 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1631 check_curr_backtracking(curr);
1632 set_backtracking(curr);
1636 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1638 Node *currnode = curr->get_node();
1639 Node *parnode = currnode->get_parent();
1641 if ((parnode && !parnode->backtrack_empty()) ||
1642 !currnode->misc_empty() ||
1643 !currnode->read_from_empty() ||
1644 !currnode->promise_empty() ||
1645 !currnode->relseq_break_empty()) {
1646 set_latest_backtrack(curr);
1650 bool ModelChecker::promises_expired() const
1652 for (unsigned int i = 0; i < promises->size(); i++) {
1653 Promise *promise = (*promises)[i];
1654 if (promise->get_expiration() < priv->used_sequence_numbers)
1661 * This is the strongest feasibility check available.
1662 * @return whether the current trace (partial or complete) must be a prefix of
1665 bool ModelChecker::isfeasibleprefix() const
1667 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1671 * Print disagnostic information about an infeasible execution
1672 * @param prefix A string to prefix the output with; if NULL, then a default
1673 * message prefix will be provided
1675 void ModelChecker::print_infeasibility(const char *prefix) const
1679 if (mo_graph->checkForCycles())
1680 ptr += sprintf(ptr, "[mo cycle]");
1681 if (priv->failed_promise)
1682 ptr += sprintf(ptr, "[failed promise]");
1683 if (priv->too_many_reads)
1684 ptr += sprintf(ptr, "[too many reads]");
1685 if (priv->no_valid_reads)
1686 ptr += sprintf(ptr, "[no valid reads-from]");
1687 if (priv->bad_synchronization)
1688 ptr += sprintf(ptr, "[bad sw ordering]");
1689 if (promises_expired())
1690 ptr += sprintf(ptr, "[promise expired]");
1691 if (promises->size() != 0)
1692 ptr += sprintf(ptr, "[unresolved promise]");
1694 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1698 * Returns whether the current completed trace is feasible, except for pending
1699 * release sequences.
1701 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1703 return !is_infeasible() && promises->size() == 0;
1707 * Check if the current partial trace is infeasible. Does not check any
1708 * end-of-execution flags, which might rule out the execution. Thus, this is
1709 * useful only for ruling an execution as infeasible.
1710 * @return whether the current partial trace is infeasible.
1712 bool ModelChecker::is_infeasible() const
1714 return mo_graph->checkForCycles() ||
1715 priv->no_valid_reads ||
1716 priv->failed_promise ||
1717 priv->too_many_reads ||
1718 priv->bad_synchronization ||
1722 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1723 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1724 ModelAction *lastread = get_last_action(act->get_tid());
1725 lastread->process_rmw(act);
1726 if (act->is_rmw()) {
1727 if (lastread->get_reads_from())
1728 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1730 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1731 mo_graph->commitChanges();
1737 * A helper function for ModelChecker::check_recency, to check if the current
1738 * thread is able to read from a different write/promise for 'params.maxreads'
1739 * number of steps and if that write/promise should become visible (i.e., is
1740 * ordered later in the modification order). This helps model memory liveness.
1742 * @param curr The current action. Must be a read.
1743 * @param rf The write/promise from which we plan to read
1744 * @param other_rf The write/promise from which we may read
1745 * @return True if we were able to read from other_rf for params.maxreads steps
1747 template <typename T, typename U>
1748 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1750 /* Need a different write/promise */
1751 if (other_rf->equals(rf))
1754 /* Only look for "newer" writes/promises */
1755 if (!mo_graph->checkReachable(rf, other_rf))
1758 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1759 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1760 action_list_t::reverse_iterator rit = list->rbegin();
1761 ASSERT((*rit) == curr);
1762 /* Skip past curr */
1765 /* Does this write/promise work for everyone? */
1766 for (int i = 0; i < params.maxreads; i++, rit++) {
1767 ModelAction *act = *rit;
1768 if (!act->may_read_from(other_rf))
1775 * Checks whether a thread has read from the same write or Promise for too many
1776 * times without seeing the effects of a later write/Promise.
1779 * 1) there must a different write/promise that we could read from,
1780 * 2) we must have read from the same write/promise in excess of maxreads times,
1781 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1782 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1784 * If so, we decide that the execution is no longer feasible.
1786 * @param curr The current action. Must be a read.
1787 * @param rf The ModelAction/Promise from which we might read.
1788 * @return True if the read should succeed; false otherwise
1790 template <typename T>
1791 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1793 if (!params.maxreads)
1796 //NOTE: Next check is just optimization, not really necessary....
1797 if (curr->get_node()->get_read_from_past_size() +
1798 curr->get_node()->get_read_from_promise_size() <= 1)
1801 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1802 int tid = id_to_int(curr->get_tid());
1803 ASSERT(tid < (int)thrd_lists->size());
1804 action_list_t *list = &(*thrd_lists)[tid];
1805 action_list_t::reverse_iterator rit = list->rbegin();
1806 ASSERT((*rit) == curr);
1807 /* Skip past curr */
1810 action_list_t::reverse_iterator ritcopy = rit;
1811 /* See if we have enough reads from the same value */
1812 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1813 if (ritcopy == list->rend())
1815 ModelAction *act = *ritcopy;
1816 if (!act->is_read())
1818 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1820 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1822 if (act->get_node()->get_read_from_past_size() +
1823 act->get_node()->get_read_from_promise_size() <= 1)
1826 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1827 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1828 if (should_read_instead(curr, rf, write))
1829 return false; /* liveness failure */
1831 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1832 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1833 if (should_read_instead(curr, rf, promise))
1834 return false; /* liveness failure */
1840 * Updates the mo_graph with the constraints imposed from the current
1843 * Basic idea is the following: Go through each other thread and find
1844 * the last action that happened before our read. Two cases:
1846 * (1) The action is a write => that write must either occur before
1847 * the write we read from or be the write we read from.
1849 * (2) The action is a read => the write that that action read from
1850 * must occur before the write we read from or be the same write.
1852 * @param curr The current action. Must be a read.
1853 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1854 * @return True if modification order edges were added; false otherwise
1856 template <typename rf_type>
1857 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1859 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1862 ASSERT(curr->is_read());
1864 /* Last SC fence in the current thread */
1865 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1866 ModelAction *last_sc_write = NULL;
1867 if (curr->is_seqcst())
1868 last_sc_write = get_last_seq_cst_write(curr);
1870 /* Iterate over all threads */
1871 for (i = 0; i < thrd_lists->size(); i++) {
1872 /* Last SC fence in thread i */
1873 ModelAction *last_sc_fence_thread_local = NULL;
1874 if (int_to_id((int)i) != curr->get_tid())
1875 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1877 /* Last SC fence in thread i, before last SC fence in current thread */
1878 ModelAction *last_sc_fence_thread_before = NULL;
1879 if (last_sc_fence_local)
1880 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1882 /* Iterate over actions in thread, starting from most recent */
1883 action_list_t *list = &(*thrd_lists)[i];
1884 action_list_t::reverse_iterator rit;
1885 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1886 ModelAction *act = *rit;
1891 /* Don't want to add reflexive edges on 'rf' */
1892 if (act->equals(rf)) {
1893 if (act->happens_before(curr))
1899 if (act->is_write()) {
1900 /* C++, Section 29.3 statement 5 */
1901 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1902 *act < *last_sc_fence_thread_local) {
1903 added = mo_graph->addEdge(act, rf) || added;
1906 /* C++, Section 29.3 statement 4 */
1907 else if (act->is_seqcst() && last_sc_fence_local &&
1908 *act < *last_sc_fence_local) {
1909 added = mo_graph->addEdge(act, rf) || added;
1912 /* C++, Section 29.3 statement 6 */
1913 else if (last_sc_fence_thread_before &&
1914 *act < *last_sc_fence_thread_before) {
1915 added = mo_graph->addEdge(act, rf) || added;
1920 /* C++, Section 29.3 statement 3 (second subpoint) */
1921 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1922 added = mo_graph->addEdge(act, rf) || added;
1927 * Include at most one act per-thread that "happens
1930 if (act->happens_before(curr)) {
1931 if (act->is_write()) {
1932 added = mo_graph->addEdge(act, rf) || added;
1934 const ModelAction *prevrf = act->get_reads_from();
1935 const Promise *prevrf_promise = act->get_reads_from_promise();
1937 if (!prevrf->equals(rf))
1938 added = mo_graph->addEdge(prevrf, rf) || added;
1939 } else if (!prevrf_promise->equals(rf)) {
1940 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1949 * All compatible, thread-exclusive promises must be ordered after any
1950 * concrete loads from the same thread
1952 for (unsigned int i = 0; i < promises->size(); i++)
1953 if ((*promises)[i]->is_compatible_exclusive(curr))
1954 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1960 * Updates the mo_graph with the constraints imposed from the current write.
1962 * Basic idea is the following: Go through each other thread and find
1963 * the lastest action that happened before our write. Two cases:
1965 * (1) The action is a write => that write must occur before
1968 * (2) The action is a read => the write that that action read from
1969 * must occur before the current write.
1971 * This method also handles two other issues:
1973 * (I) Sequential Consistency: Making sure that if the current write is
1974 * seq_cst, that it occurs after the previous seq_cst write.
1976 * (II) Sending the write back to non-synchronizing reads.
1978 * @param curr The current action. Must be a write.
1979 * @param send_fv A vector for stashing reads to which we may pass our future
1980 * value. If NULL, then don't record any future values.
1981 * @return True if modification order edges were added; false otherwise
1983 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1985 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1988 ASSERT(curr->is_write());
1990 if (curr->is_seqcst()) {
1991 /* We have to at least see the last sequentially consistent write,
1992 so we are initialized. */
1993 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1994 if (last_seq_cst != NULL) {
1995 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1999 /* Last SC fence in the current thread */
2000 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
2002 /* Iterate over all threads */
2003 for (i = 0; i < thrd_lists->size(); i++) {
2004 /* Last SC fence in thread i, before last SC fence in current thread */
2005 ModelAction *last_sc_fence_thread_before = NULL;
2006 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
2007 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
2009 /* Iterate over actions in thread, starting from most recent */
2010 action_list_t *list = &(*thrd_lists)[i];
2011 action_list_t::reverse_iterator rit;
2012 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2013 ModelAction *act = *rit;
2016 * 1) If RMW and it actually read from something, then we
2017 * already have all relevant edges, so just skip to next
2020 * 2) If RMW and it didn't read from anything, we should
2021 * whatever edge we can get to speed up convergence.
2023 * 3) If normal write, we need to look at earlier actions, so
2024 * continue processing list.
2026 if (curr->is_rmw()) {
2027 if (curr->get_reads_from() != NULL)
2035 /* C++, Section 29.3 statement 7 */
2036 if (last_sc_fence_thread_before && act->is_write() &&
2037 *act < *last_sc_fence_thread_before) {
2038 added = mo_graph->addEdge(act, curr) || added;
2043 * Include at most one act per-thread that "happens
2046 if (act->happens_before(curr)) {
2048 * Note: if act is RMW, just add edge:
2050 * The following edge should be handled elsewhere:
2051 * readfrom(act) --mo--> act
2053 if (act->is_write())
2054 added = mo_graph->addEdge(act, curr) || added;
2055 else if (act->is_read()) {
2056 //if previous read accessed a null, just keep going
2057 if (act->get_reads_from() == NULL)
2059 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2062 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2063 !act->same_thread(curr)) {
2064 /* We have an action that:
2065 (1) did not happen before us
2066 (2) is a read and we are a write
2067 (3) cannot synchronize with us
2068 (4) is in a different thread
2070 that read could potentially read from our write. Note that
2071 these checks are overly conservative at this point, we'll
2072 do more checks before actually removing the
2076 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2077 if (!is_infeasible())
2078 send_fv->push_back(act);
2079 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2080 add_future_value(curr, act);
2087 * All compatible, thread-exclusive promises must be ordered after any
2088 * concrete stores to the same thread, or else they can be merged with
2091 for (unsigned int i = 0; i < promises->size(); i++)
2092 if ((*promises)[i]->is_compatible_exclusive(curr))
2093 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2098 /** Arbitrary reads from the future are not allowed. Section 29.3
2099 * part 9 places some constraints. This method checks one result of constraint
2100 * constraint. Others require compiler support. */
2101 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2103 if (!writer->is_rmw())
2106 if (!reader->is_rmw())
2109 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2110 if (search == reader)
2112 if (search->get_tid() == reader->get_tid() &&
2113 search->happens_before(reader))
2121 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2122 * some constraints. This method checks one the following constraint (others
2123 * require compiler support):
2125 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2127 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2129 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2131 /* Iterate over all threads */
2132 for (i = 0; i < thrd_lists->size(); i++) {
2133 const ModelAction *write_after_read = NULL;
2135 /* Iterate over actions in thread, starting from most recent */
2136 action_list_t *list = &(*thrd_lists)[i];
2137 action_list_t::reverse_iterator rit;
2138 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2139 ModelAction *act = *rit;
2141 /* Don't disallow due to act == reader */
2142 if (!reader->happens_before(act) || reader == act)
2144 else if (act->is_write())
2145 write_after_read = act;
2146 else if (act->is_read() && act->get_reads_from() != NULL)
2147 write_after_read = act->get_reads_from();
2150 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2157 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2158 * The ModelAction under consideration is expected to be taking part in
2159 * release/acquire synchronization as an object of the "reads from" relation.
2160 * Note that this can only provide release sequence support for RMW chains
2161 * which do not read from the future, as those actions cannot be traced until
2162 * their "promise" is fulfilled. Similarly, we may not even establish the
2163 * presence of a release sequence with certainty, as some modification order
2164 * constraints may be decided further in the future. Thus, this function
2165 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2166 * and a boolean representing certainty.
2168 * @param rf The action that might be part of a release sequence. Must be a
2170 * @param release_heads A pass-by-reference style return parameter. After
2171 * execution of this function, release_heads will contain the heads of all the
2172 * relevant release sequences, if any exists with certainty
2173 * @param pending A pass-by-reference style return parameter which is only used
2174 * when returning false (i.e., uncertain). Returns most information regarding
2175 * an uncertain release sequence, including any write operations that might
2176 * break the sequence.
2177 * @return true, if the ModelChecker is certain that release_heads is complete;
2180 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2181 rel_heads_list_t *release_heads,
2182 struct release_seq *pending) const
2184 /* Only check for release sequences if there are no cycles */
2185 if (mo_graph->checkForCycles())
2188 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2189 ASSERT(rf->is_write());
2191 if (rf->is_release())
2192 release_heads->push_back(rf);
2193 else if (rf->get_last_fence_release())
2194 release_heads->push_back(rf->get_last_fence_release());
2196 break; /* End of RMW chain */
2198 /** @todo Need to be smarter here... In the linux lock
2199 * example, this will run to the beginning of the program for
2201 /** @todo The way to be smarter here is to keep going until 1
2202 * thread has a release preceded by an acquire and you've seen
2205 /* acq_rel RMW is a sufficient stopping condition */
2206 if (rf->is_acquire() && rf->is_release())
2207 return true; /* complete */
2210 /* read from future: need to settle this later */
2212 return false; /* incomplete */
2215 if (rf->is_release())
2216 return true; /* complete */
2218 /* else relaxed write
2219 * - check for fence-release in the same thread (29.8, stmt. 3)
2220 * - check modification order for contiguous subsequence
2221 * -> rf must be same thread as release */
2223 const ModelAction *fence_release = rf->get_last_fence_release();
2224 /* Synchronize with a fence-release unconditionally; we don't need to
2225 * find any more "contiguous subsequence..." for it */
2227 release_heads->push_back(fence_release);
2229 int tid = id_to_int(rf->get_tid());
2230 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2231 action_list_t *list = &(*thrd_lists)[tid];
2232 action_list_t::const_reverse_iterator rit;
2234 /* Find rf in the thread list */
2235 rit = std::find(list->rbegin(), list->rend(), rf);
2236 ASSERT(rit != list->rend());
2238 /* Find the last {write,fence}-release */
2239 for (; rit != list->rend(); rit++) {
2240 if (fence_release && *(*rit) < *fence_release)
2242 if ((*rit)->is_release())
2245 if (rit == list->rend()) {
2246 /* No write-release in this thread */
2247 return true; /* complete */
2248 } else if (fence_release && *(*rit) < *fence_release) {
2249 /* The fence-release is more recent (and so, "stronger") than
2250 * the most recent write-release */
2251 return true; /* complete */
2252 } /* else, need to establish contiguous release sequence */
2253 ModelAction *release = *rit;
2255 ASSERT(rf->same_thread(release));
2257 pending->writes.clear();
2259 bool certain = true;
2260 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2261 if (id_to_int(rf->get_tid()) == (int)i)
2263 list = &(*thrd_lists)[i];
2265 /* Can we ensure no future writes from this thread may break
2266 * the release seq? */
2267 bool future_ordered = false;
2269 ModelAction *last = get_last_action(int_to_id(i));
2270 Thread *th = get_thread(int_to_id(i));
2271 if ((last && rf->happens_before(last)) ||
2274 future_ordered = true;
2276 ASSERT(!th->is_model_thread() || future_ordered);
2278 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2279 const ModelAction *act = *rit;
2280 /* Reach synchronization -> this thread is complete */
2281 if (act->happens_before(release))
2283 if (rf->happens_before(act)) {
2284 future_ordered = true;
2288 /* Only non-RMW writes can break release sequences */
2289 if (!act->is_write() || act->is_rmw())
2292 /* Check modification order */
2293 if (mo_graph->checkReachable(rf, act)) {
2294 /* rf --mo--> act */
2295 future_ordered = true;
2298 if (mo_graph->checkReachable(act, release))
2299 /* act --mo--> release */
2301 if (mo_graph->checkReachable(release, act) &&
2302 mo_graph->checkReachable(act, rf)) {
2303 /* release --mo-> act --mo--> rf */
2304 return true; /* complete */
2306 /* act may break release sequence */
2307 pending->writes.push_back(act);
2310 if (!future_ordered)
2311 certain = false; /* This thread is uncertain */
2315 release_heads->push_back(release);
2316 pending->writes.clear();
2318 pending->release = release;
2325 * An interface for getting the release sequence head(s) with which a
2326 * given ModelAction must synchronize. This function only returns a non-empty
2327 * result when it can locate a release sequence head with certainty. Otherwise,
2328 * it may mark the internal state of the ModelChecker so that it will handle
2329 * the release sequence at a later time, causing @a acquire to update its
2330 * synchronization at some later point in execution.
2332 * @param acquire The 'acquire' action that may synchronize with a release
2334 * @param read The read action that may read from a release sequence; this may
2335 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2336 * when 'acquire' is a fence-acquire)
2337 * @param release_heads A pass-by-reference return parameter. Will be filled
2338 * with the head(s) of the release sequence(s), if they exists with certainty.
2339 * @see ModelChecker::release_seq_heads
2341 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2342 ModelAction *read, rel_heads_list_t *release_heads)
2344 const ModelAction *rf = read->get_reads_from();
2345 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2346 sequence->acquire = acquire;
2347 sequence->read = read;
2349 if (!release_seq_heads(rf, release_heads, sequence)) {
2350 /* add act to 'lazy checking' list */
2351 pending_rel_seqs->push_back(sequence);
2353 snapshot_free(sequence);
2358 * Attempt to resolve all stashed operations that might synchronize with a
2359 * release sequence for a given location. This implements the "lazy" portion of
2360 * determining whether or not a release sequence was contiguous, since not all
2361 * modification order information is present at the time an action occurs.
2363 * @param location The location/object that should be checked for release
2364 * sequence resolutions. A NULL value means to check all locations.
2365 * @param work_queue The work queue to which to add work items as they are
2367 * @return True if any updates occurred (new synchronization, new mo_graph
2370 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2372 bool updated = false;
2373 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2374 while (it != pending_rel_seqs->end()) {
2375 struct release_seq *pending = *it;
2376 ModelAction *acquire = pending->acquire;
2377 const ModelAction *read = pending->read;
2379 /* Only resolve sequences on the given location, if provided */
2380 if (location && read->get_location() != location) {
2385 const ModelAction *rf = read->get_reads_from();
2386 rel_heads_list_t release_heads;
2388 complete = release_seq_heads(rf, &release_heads, pending);
2389 for (unsigned int i = 0; i < release_heads.size(); i++) {
2390 if (!acquire->has_synchronized_with(release_heads[i])) {
2391 if (acquire->synchronize_with(release_heads[i]))
2394 set_bad_synchronization();
2399 /* Re-check all pending release sequences */
2400 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2401 /* Re-check read-acquire for mo_graph edges */
2402 if (acquire->is_read())
2403 work_queue->push_back(MOEdgeWorkEntry(acquire));
2405 /* propagate synchronization to later actions */
2406 action_list_t::reverse_iterator rit = action_trace->rbegin();
2407 for (; (*rit) != acquire; rit++) {
2408 ModelAction *propagate = *rit;
2409 if (acquire->happens_before(propagate)) {
2410 propagate->synchronize_with(acquire);
2411 /* Re-check 'propagate' for mo_graph edges */
2412 work_queue->push_back(MOEdgeWorkEntry(propagate));
2417 it = pending_rel_seqs->erase(it);
2418 snapshot_free(pending);
2424 // If we resolved promises or data races, see if we have realized a data race.
2431 * Performs various bookkeeping operations for the current ModelAction. For
2432 * instance, adds action to the per-object, per-thread action vector and to the
2433 * action trace list of all thread actions.
2435 * @param act is the ModelAction to add.
2437 void ModelChecker::add_action_to_lists(ModelAction *act)
2439 int tid = id_to_int(act->get_tid());
2440 ModelAction *uninit = NULL;
2442 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2443 if (list->empty() && act->is_atomic_var()) {
2444 uninit = get_uninitialized_action(act);
2445 uninit_id = id_to_int(uninit->get_tid());
2446 list->push_front(uninit);
2448 list->push_back(act);
2450 action_trace->push_back(act);
2452 action_trace->push_front(uninit);
2454 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2455 if (tid >= (int)vec->size())
2456 vec->resize(priv->next_thread_id);
2457 (*vec)[tid].push_back(act);
2459 (*vec)[uninit_id].push_front(uninit);
2461 if ((int)thrd_last_action->size() <= tid)
2462 thrd_last_action->resize(get_num_threads());
2463 (*thrd_last_action)[tid] = act;
2465 (*thrd_last_action)[uninit_id] = uninit;
2467 if (act->is_fence() && act->is_release()) {
2468 if ((int)thrd_last_fence_release->size() <= tid)
2469 thrd_last_fence_release->resize(get_num_threads());
2470 (*thrd_last_fence_release)[tid] = act;
2473 if (act->is_wait()) {
2474 void *mutex_loc = (void *) act->get_value();
2475 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2477 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2478 if (tid >= (int)vec->size())
2479 vec->resize(priv->next_thread_id);
2480 (*vec)[tid].push_back(act);
2485 * @brief Get the last action performed by a particular Thread
2486 * @param tid The thread ID of the Thread in question
2487 * @return The last action in the thread
2489 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2491 int threadid = id_to_int(tid);
2492 if (threadid < (int)thrd_last_action->size())
2493 return (*thrd_last_action)[id_to_int(tid)];
2499 * @brief Get the last fence release performed by a particular Thread
2500 * @param tid The thread ID of the Thread in question
2501 * @return The last fence release in the thread, if one exists; NULL otherwise
2503 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2505 int threadid = id_to_int(tid);
2506 if (threadid < (int)thrd_last_fence_release->size())
2507 return (*thrd_last_fence_release)[id_to_int(tid)];
2513 * Gets the last memory_order_seq_cst write (in the total global sequence)
2514 * performed on a particular object (i.e., memory location), not including the
2516 * @param curr The current ModelAction; also denotes the object location to
2518 * @return The last seq_cst write
2520 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2522 void *location = curr->get_location();
2523 action_list_t *list = get_safe_ptr_action(obj_map, location);
2524 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2525 action_list_t::reverse_iterator rit;
2526 for (rit = list->rbegin(); (*rit) != curr; rit++)
2528 rit++; /* Skip past curr */
2529 for ( ; rit != list->rend(); rit++)
2530 if ((*rit)->is_write() && (*rit)->is_seqcst())
2536 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2537 * performed in a particular thread, prior to a particular fence.
2538 * @param tid The ID of the thread to check
2539 * @param before_fence The fence from which to begin the search; if NULL, then
2540 * search for the most recent fence in the thread.
2541 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2543 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2545 /* All fences should have NULL location */
2546 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2547 action_list_t::reverse_iterator rit = list->rbegin();
2550 for (; rit != list->rend(); rit++)
2551 if (*rit == before_fence)
2554 ASSERT(*rit == before_fence);
2558 for (; rit != list->rend(); rit++)
2559 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2565 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2566 * location). This function identifies the mutex according to the current
2567 * action, which is presumed to perform on the same mutex.
2568 * @param curr The current ModelAction; also denotes the object location to
2570 * @return The last unlock operation
2572 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2574 void *location = curr->get_location();
2575 action_list_t *list = get_safe_ptr_action(obj_map, location);
2576 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2577 action_list_t::reverse_iterator rit;
2578 for (rit = list->rbegin(); rit != list->rend(); rit++)
2579 if ((*rit)->is_unlock() || (*rit)->is_wait())
2584 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2586 ModelAction *parent = get_last_action(tid);
2588 parent = get_thread(tid)->get_creation();
2593 * Returns the clock vector for a given thread.
2594 * @param tid The thread whose clock vector we want
2595 * @return Desired clock vector
2597 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2599 return get_parent_action(tid)->get_cv();
2603 * @brief Find the promise (if any) to resolve for the current action and
2604 * remove it from the pending promise vector
2605 * @param curr The current ModelAction. Should be a write.
2606 * @return The Promise to resolve, if any; otherwise NULL
2608 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2610 for (unsigned int i = 0; i < promises->size(); i++)
2611 if (curr->get_node()->get_promise(i)) {
2612 Promise *ret = (*promises)[i];
2613 promises->erase(promises->begin() + i);
2620 * Resolve a Promise with a current write.
2621 * @param write The ModelAction that is fulfilling Promises
2622 * @param promise The Promise to resolve
2623 * @return True if the Promise was successfully resolved; false otherwise
2625 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2627 ModelVector<ModelAction *> actions_to_check;
2629 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2630 ModelAction *read = promise->get_reader(i);
2631 read_from(read, write);
2632 actions_to_check.push_back(read);
2634 /* Make sure the promise's value matches the write's value */
2635 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2636 if (!mo_graph->resolvePromise(promise, write))
2637 priv->failed_promise = true;
2640 * @todo It is possible to end up in an inconsistent state, where a
2641 * "resolved" promise may still be referenced if
2642 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2644 * Note that the inconsistency only matters when dumping mo_graph to
2650 //Check whether reading these writes has made threads unable to
2652 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2653 ModelAction *read = actions_to_check[i];
2654 mo_check_promises(read, true);
2661 * Compute the set of promises that could potentially be satisfied by this
2662 * action. Note that the set computation actually appears in the Node, not in
2664 * @param curr The ModelAction that may satisfy promises
2666 void ModelChecker::compute_promises(ModelAction *curr)
2668 for (unsigned int i = 0; i < promises->size(); i++) {
2669 Promise *promise = (*promises)[i];
2670 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2673 bool satisfy = true;
2674 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2675 const ModelAction *act = promise->get_reader(j);
2676 if (act->happens_before(curr) ||
2677 act->could_synchronize_with(curr)) {
2683 curr->get_node()->set_promise(i);
2687 /** Checks promises in response to change in ClockVector Threads. */
2688 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2690 for (unsigned int i = 0; i < promises->size(); i++) {
2691 Promise *promise = (*promises)[i];
2692 if (!promise->thread_is_available(tid))
2694 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2695 const ModelAction *act = promise->get_reader(j);
2696 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2697 merge_cv->synchronized_since(act)) {
2698 if (promise->eliminate_thread(tid)) {
2699 /* Promise has failed */
2700 priv->failed_promise = true;
2708 void ModelChecker::check_promises_thread_disabled()
2710 for (unsigned int i = 0; i < promises->size(); i++) {
2711 Promise *promise = (*promises)[i];
2712 if (promise->has_failed()) {
2713 priv->failed_promise = true;
2720 * @brief Checks promises in response to addition to modification order for
2723 * We test whether threads are still available for satisfying promises after an
2724 * addition to our modification order constraints. Those that are unavailable
2725 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2726 * that promise has failed.
2728 * @param act The ModelAction which updated the modification order
2729 * @param is_read_check Should be true if act is a read and we must check for
2730 * updates to the store from which it read (there is a distinction here for
2731 * RMW's, which are both a load and a store)
2733 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2735 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2737 for (unsigned int i = 0; i < promises->size(); i++) {
2738 Promise *promise = (*promises)[i];
2740 // Is this promise on the same location?
2741 if (!promise->same_location(write))
2744 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2745 const ModelAction *pread = promise->get_reader(j);
2746 if (!pread->happens_before(act))
2748 if (mo_graph->checkPromise(write, promise)) {
2749 priv->failed_promise = true;
2755 // Don't do any lookups twice for the same thread
2756 if (!promise->thread_is_available(act->get_tid()))
2759 if (mo_graph->checkReachable(promise, write)) {
2760 if (mo_graph->checkPromise(write, promise)) {
2761 priv->failed_promise = true;
2769 * Compute the set of writes that may break the current pending release
2770 * sequence. This information is extracted from previou release sequence
2773 * @param curr The current ModelAction. Must be a release sequence fixup
2776 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2778 if (pending_rel_seqs->empty())
2781 struct release_seq *pending = pending_rel_seqs->back();
2782 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2783 const ModelAction *write = pending->writes[i];
2784 curr->get_node()->add_relseq_break(write);
2787 /* NULL means don't break the sequence; just synchronize */
2788 curr->get_node()->add_relseq_break(NULL);
2792 * Build up an initial set of all past writes that this 'read' action may read
2793 * from, as well as any previously-observed future values that must still be valid.
2795 * @param curr is the current ModelAction that we are exploring; it must be a
2798 void ModelChecker::build_may_read_from(ModelAction *curr)
2800 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2802 ASSERT(curr->is_read());
2804 ModelAction *last_sc_write = NULL;
2806 if (curr->is_seqcst())
2807 last_sc_write = get_last_seq_cst_write(curr);
2809 /* Iterate over all threads */
2810 for (i = 0; i < thrd_lists->size(); i++) {
2811 /* Iterate over actions in thread, starting from most recent */
2812 action_list_t *list = &(*thrd_lists)[i];
2813 action_list_t::reverse_iterator rit;
2814 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2815 ModelAction *act = *rit;
2817 /* Only consider 'write' actions */
2818 if (!act->is_write() || act == curr)
2821 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2822 bool allow_read = true;
2824 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2826 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2830 /* Only add feasible reads */
2831 mo_graph->startChanges();
2832 r_modification_order(curr, act);
2833 if (!is_infeasible())
2834 curr->get_node()->add_read_from_past(act);
2835 mo_graph->rollbackChanges();
2838 /* Include at most one act per-thread that "happens before" curr */
2839 if (act->happens_before(curr))
2844 /* Inherit existing, promised future values */
2845 for (i = 0; i < promises->size(); i++) {
2846 const Promise *promise = (*promises)[i];
2847 const ModelAction *promise_read = promise->get_reader(0);
2848 if (promise_read->same_var(curr)) {
2849 /* Only add feasible future-values */
2850 mo_graph->startChanges();
2851 r_modification_order(curr, promise);
2852 if (!is_infeasible())
2853 curr->get_node()->add_read_from_promise(promise_read);
2854 mo_graph->rollbackChanges();
2858 /* We may find no valid may-read-from only if the execution is doomed */
2859 if (!curr->get_node()->read_from_size()) {
2860 priv->no_valid_reads = true;
2864 if (DBG_ENABLED()) {
2865 model_print("Reached read action:\n");
2867 model_print("Printing read_from_past\n");
2868 curr->get_node()->print_read_from_past();
2869 model_print("End printing read_from_past\n");
2873 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2875 for ( ; write != NULL; write = write->get_reads_from()) {
2876 /* UNINIT actions don't have a Node, and they never sleep */
2877 if (write->is_uninitialized())
2879 Node *prevnode = write->get_node()->get_parent();
2881 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2882 if (write->is_release() && thread_sleep)
2884 if (!write->is_rmw())
2891 * @brief Get an action representing an uninitialized atomic
2893 * This function may create a new one or try to retrieve one from the NodeStack
2895 * @param curr The current action, which prompts the creation of an UNINIT action
2896 * @return A pointer to the UNINIT ModelAction
2898 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2900 Node *node = curr->get_node();
2901 ModelAction *act = node->get_uninit_action();
2903 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2904 node->set_uninit_action(act);
2906 act->create_cv(NULL);
2910 static void print_list(action_list_t *list)
2912 action_list_t::iterator it;
2914 model_print("---------------------------------------------------------------------\n");
2916 unsigned int hash = 0;
2918 for (it = list->begin(); it != list->end(); it++) {
2919 const ModelAction *act = *it;
2920 if (act->get_seq_number() > 0)
2922 hash = hash^(hash<<3)^((*it)->hash());
2924 model_print("HASH %u\n", hash);
2925 model_print("---------------------------------------------------------------------\n");
2928 #if SUPPORT_MOD_ORDER_DUMP
2929 void ModelChecker::dumpGraph(char *filename) const
2932 sprintf(buffer, "%s.dot", filename);
2933 FILE *file = fopen(buffer, "w");
2934 fprintf(file, "digraph %s {\n", filename);
2935 mo_graph->dumpNodes(file);
2936 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2938 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2939 ModelAction *act = *it;
2940 if (act->is_read()) {
2941 mo_graph->dot_print_node(file, act);
2942 if (act->get_reads_from())
2943 mo_graph->dot_print_edge(file,
2944 act->get_reads_from(),
2946 "label=\"rf\", color=red, weight=2");
2948 mo_graph->dot_print_edge(file,
2949 act->get_reads_from_promise(),
2951 "label=\"rf\", color=red");
2953 if (thread_array[act->get_tid()]) {
2954 mo_graph->dot_print_edge(file,
2955 thread_array[id_to_int(act->get_tid())],
2957 "label=\"sb\", color=blue, weight=400");
2960 thread_array[act->get_tid()] = act;
2962 fprintf(file, "}\n");
2963 model_free(thread_array);
2968 /** @brief Prints an execution trace summary. */
2969 void ModelChecker::print_summary() const
2971 #if SUPPORT_MOD_ORDER_DUMP
2972 char buffername[100];
2973 sprintf(buffername, "exec%04u", stats.num_total);
2974 mo_graph->dumpGraphToFile(buffername);
2975 sprintf(buffername, "graph%04u", stats.num_total);
2976 dumpGraph(buffername);
2979 model_print("Execution %d:", stats.num_total);
2980 if (isfeasibleprefix()) {
2981 if (scheduler->all_threads_sleeping())
2982 model_print(" SLEEP-SET REDUNDANT");
2985 print_infeasibility(" INFEASIBLE");
2986 print_list(action_trace);
2988 if (!promises->empty()) {
2989 model_print("Pending promises:\n");
2990 for (unsigned int i = 0; i < promises->size(); i++) {
2991 model_print(" [P%u] ", i);
2992 (*promises)[i]->print();
2999 * Add a Thread to the system for the first time. Should only be called once
3001 * @param t The Thread to add
3003 void ModelChecker::add_thread(Thread *t)
3005 thread_map->put(id_to_int(t->get_id()), t);
3006 scheduler->add_thread(t);
3010 * @brief Get a Thread reference by its ID
3011 * @param tid The Thread's ID
3012 * @return A Thread reference
3014 Thread * ModelChecker::get_thread(thread_id_t tid) const
3016 return thread_map->get(id_to_int(tid));
3020 * @brief Get a reference to the Thread in which a ModelAction was executed
3021 * @param act The ModelAction
3022 * @return A Thread reference
3024 Thread * ModelChecker::get_thread(const ModelAction *act) const
3026 return get_thread(act->get_tid());
3030 * @brief Get a Promise's "promise number"
3032 * A "promise number" is an index number that is unique to a promise, valid
3033 * only for a specific snapshot of an execution trace. Promises may come and go
3034 * as they are generated an resolved, so an index only retains meaning for the
3037 * @param promise The Promise to check
3038 * @return The promise index, if the promise still is valid; otherwise -1
3040 int ModelChecker::get_promise_number(const Promise *promise) const
3042 for (unsigned int i = 0; i < promises->size(); i++)
3043 if ((*promises)[i] == promise)
3050 * @brief Check if a Thread is currently enabled
3051 * @param t The Thread to check
3052 * @return True if the Thread is currently enabled
3054 bool ModelChecker::is_enabled(Thread *t) const
3056 return scheduler->is_enabled(t);
3060 * @brief Check if a Thread is currently enabled
3061 * @param tid The ID of the Thread to check
3062 * @return True if the Thread is currently enabled
3064 bool ModelChecker::is_enabled(thread_id_t tid) const
3066 return scheduler->is_enabled(tid);
3070 * Switch from a model-checker context to a user-thread context. This is the
3071 * complement of ModelChecker::switch_to_master and must be called from the
3072 * model-checker context
3074 * @param thread The user-thread to switch to
3076 void ModelChecker::switch_from_master(Thread *thread)
3078 scheduler->set_current_thread(thread);
3079 Thread::swap(&system_context, thread);
3083 * Switch from a user-context to the "master thread" context (a.k.a. system
3084 * context). This switch is made with the intention of exploring a particular
3085 * model-checking action (described by a ModelAction object). Must be called
3086 * from a user-thread context.
3088 * @param act The current action that will be explored. May be NULL only if
3089 * trace is exiting via an assertion (see ModelChecker::set_assert and
3090 * ModelChecker::has_asserted).
3091 * @return Return the value returned by the current action
3093 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3096 Thread *old = thread_current();
3097 scheduler->set_current_thread(NULL);
3098 ASSERT(!old->get_pending());
3099 old->set_pending(act);
3100 if (Thread::swap(old, &system_context) < 0) {
3101 perror("swap threads");
3104 return old->get_return_value();
3108 * Takes the next step in the execution, if possible.
3109 * @param curr The current step to take
3110 * @return Returns the next Thread to run, if any; NULL if this execution
3113 Thread * ModelChecker::take_step(ModelAction *curr)
3115 Thread *curr_thrd = get_thread(curr);
3116 ASSERT(curr_thrd->get_state() == THREAD_READY);
3118 curr = check_current_action(curr);
3120 /* Infeasible -> don't take any more steps */
3121 if (is_infeasible())
3123 else if (isfeasibleprefix() && have_bug_reports()) {
3128 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3131 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3132 scheduler->remove_thread(curr_thrd);
3134 Thread *next_thrd = NULL;
3136 next_thrd = action_select_next_thread(curr);
3138 next_thrd = get_next_thread();
3140 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3141 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3146 /** Wrapper to run the user's main function, with appropriate arguments */
3147 void user_main_wrapper(void *)
3149 user_main(model->params.argc, model->params.argv);
3152 /** @brief Run ModelChecker for the user program */
3153 void ModelChecker::run()
3157 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3162 * Stash next pending action(s) for thread(s). There
3163 * should only need to stash one thread's action--the
3164 * thread which just took a step--plus the first step
3165 * for any newly-created thread
3167 for (unsigned int i = 0; i < get_num_threads(); i++) {
3168 thread_id_t tid = int_to_id(i);
3169 Thread *thr = get_thread(tid);
3170 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3171 switch_from_master(thr);
3172 if (is_circular_wait(thr))
3173 assert_bug("Deadlock detected");
3177 /* Catch assertions from prior take_step or from
3178 * between-ModelAction bugs (e.g., data races) */
3182 /* Consume the next action for a Thread */
3183 ModelAction *curr = t->get_pending();
3184 t->set_pending(NULL);
3185 t = take_step(curr);
3186 } while (t && !t->is_model_thread());
3189 * Launch end-of-execution release sequence fixups only when
3190 * the execution is otherwise feasible AND there are:
3192 * (1) pending release sequences
3193 * (2) pending assertions that could be invalidated by a change
3194 * in clock vectors (i.e., data races)
3195 * (3) no pending promises
3197 while (!pending_rel_seqs->empty() &&
3198 is_feasible_prefix_ignore_relseq() &&
3199 !unrealizedraces.empty()) {
3200 model_print("*** WARNING: release sequence fixup action "
3201 "(%zu pending release seuqence(s)) ***\n",
3202 pending_rel_seqs->size());
3203 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3204 std::memory_order_seq_cst, NULL, VALUE_NONE,
3208 } while (next_execution());
3210 model_print("******* Model-checking complete: *******\n");