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 is ordered after the latest Promise creation
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 return promises->empty() ||
1072 *(promises->back()->get_reader(0)) < *reader;
1076 * @brief Add a future value to a reader
1078 * This function performs a few additional checks to ensure that the future
1079 * value can be feasibly observed by the reader
1081 * @param writer The operation whose value is sent. Must be a write.
1082 * @param reader The read operation which may read the future value. Must be a read.
1084 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1086 /* Do more ambitious checks now that mo is more complete */
1087 if (!mo_may_allow(writer, reader))
1090 Node *node = reader->get_node();
1092 /* Find an ancestor thread which exists at the time of the reader */
1093 Thread *write_thread = get_thread(writer);
1094 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1095 write_thread = write_thread->get_parent();
1097 struct future_value fv = {
1098 writer->get_write_value(),
1099 writer->get_seq_number() + params.maxfuturedelay,
1100 write_thread->get_id(),
1102 if (node->add_future_value(fv))
1103 set_latest_backtrack(reader);
1107 * Process a write ModelAction
1108 * @param curr The ModelAction to process
1109 * @return True if the mo_graph was updated or promises were resolved
1111 bool ModelChecker::process_write(ModelAction *curr)
1113 /* Readers to which we may send our future value */
1114 ModelVector<ModelAction *> send_fv;
1116 const ModelAction *earliest_promise_reader;
1117 bool updated_promises = false;
1119 bool updated_mod_order = w_modification_order(curr, &send_fv);
1120 Promise *promise = pop_promise_to_resolve(curr);
1123 earliest_promise_reader = promise->get_reader(0);
1124 updated_promises = resolve_promise(curr, promise);
1126 earliest_promise_reader = NULL;
1128 for (unsigned int i = 0; i < send_fv.size(); i++) {
1129 ModelAction *read = send_fv[i];
1131 /* Don't send future values to reads after the Promise we resolve */
1132 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
1133 /* Check if future value can be sent immediately */
1134 if (promises_may_allow(curr, read)) {
1135 add_future_value(curr, read);
1137 futurevalues->push_back(PendingFutureValue(curr, read));
1142 /* Check the pending future values */
1143 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
1144 struct PendingFutureValue pfv = (*futurevalues)[i];
1145 if (promises_may_allow(pfv.writer, pfv.reader)) {
1146 add_future_value(pfv.writer, pfv.reader);
1147 futurevalues->erase(futurevalues->begin() + i);
1151 mo_graph->commitChanges();
1152 mo_check_promises(curr, false);
1154 get_thread(curr)->set_return_value(VALUE_NONE);
1155 return updated_mod_order || updated_promises;
1159 * Process a fence ModelAction
1160 * @param curr The ModelAction to process
1161 * @return True if synchronization was updated
1163 bool ModelChecker::process_fence(ModelAction *curr)
1166 * fence-relaxed: no-op
1167 * fence-release: only log the occurence (not in this function), for
1168 * use in later synchronization
1169 * fence-acquire (this function): search for hypothetical release
1171 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1173 bool updated = false;
1174 if (curr->is_acquire()) {
1175 action_list_t *list = action_trace;
1176 action_list_t::reverse_iterator rit;
1177 /* Find X : is_read(X) && X --sb-> curr */
1178 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1179 ModelAction *act = *rit;
1182 if (act->get_tid() != curr->get_tid())
1184 /* Stop at the beginning of the thread */
1185 if (act->is_thread_start())
1187 /* Stop once we reach a prior fence-acquire */
1188 if (act->is_fence() && act->is_acquire())
1190 if (!act->is_read())
1192 /* read-acquire will find its own release sequences */
1193 if (act->is_acquire())
1196 /* Establish hypothetical release sequences */
1197 rel_heads_list_t release_heads;
1198 get_release_seq_heads(curr, act, &release_heads);
1199 for (unsigned int i = 0; i < release_heads.size(); i++)
1200 if (!curr->synchronize_with(release_heads[i]))
1201 set_bad_synchronization();
1202 if (release_heads.size() != 0)
1210 * @brief Process the current action for thread-related activity
1212 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1213 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1214 * synchronization, etc. This function is a no-op for non-THREAD actions
1215 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1217 * @param curr The current action
1218 * @return True if synchronization was updated or a thread completed
1220 bool ModelChecker::process_thread_action(ModelAction *curr)
1222 bool updated = false;
1224 switch (curr->get_type()) {
1225 case THREAD_CREATE: {
1226 thrd_t *thrd = (thrd_t *)curr->get_location();
1227 struct thread_params *params = (struct thread_params *)curr->get_value();
1228 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1230 th->set_creation(curr);
1231 /* Promises can be satisfied by children */
1232 for (unsigned int i = 0; i < promises->size(); i++) {
1233 Promise *promise = (*promises)[i];
1234 if (promise->thread_is_available(curr->get_tid()))
1235 promise->add_thread(th->get_id());
1240 Thread *blocking = curr->get_thread_operand();
1241 ModelAction *act = get_last_action(blocking->get_id());
1242 curr->synchronize_with(act);
1243 updated = true; /* trigger rel-seq checks */
1246 case THREAD_FINISH: {
1247 Thread *th = get_thread(curr);
1248 while (!th->wait_list_empty()) {
1249 ModelAction *act = th->pop_wait_list();
1250 scheduler->wake(get_thread(act));
1253 /* Completed thread can't satisfy promises */
1254 for (unsigned int i = 0; i < promises->size(); i++) {
1255 Promise *promise = (*promises)[i];
1256 if (promise->thread_is_available(th->get_id()))
1257 if (promise->eliminate_thread(th->get_id()))
1258 priv->failed_promise = true;
1260 updated = true; /* trigger rel-seq checks */
1263 case THREAD_START: {
1264 check_promises(curr->get_tid(), NULL, curr->get_cv());
1275 * @brief Process the current action for release sequence fixup activity
1277 * Performs model-checker release sequence fixups for the current action,
1278 * forcing a single pending release sequence to break (with a given, potential
1279 * "loose" write) or to complete (i.e., synchronize). If a pending release
1280 * sequence forms a complete release sequence, then we must perform the fixup
1281 * synchronization, mo_graph additions, etc.
1283 * @param curr The current action; must be a release sequence fixup action
1284 * @param work_queue The work queue to which to add work items as they are
1287 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1289 const ModelAction *write = curr->get_node()->get_relseq_break();
1290 struct release_seq *sequence = pending_rel_seqs->back();
1291 pending_rel_seqs->pop_back();
1293 ModelAction *acquire = sequence->acquire;
1294 const ModelAction *rf = sequence->rf;
1295 const ModelAction *release = sequence->release;
1299 ASSERT(release->same_thread(rf));
1301 if (write == NULL) {
1303 * @todo Forcing a synchronization requires that we set
1304 * modification order constraints. For instance, we can't allow
1305 * a fixup sequence in which two separate read-acquire
1306 * operations read from the same sequence, where the first one
1307 * synchronizes and the other doesn't. Essentially, we can't
1308 * allow any writes to insert themselves between 'release' and
1312 /* Must synchronize */
1313 if (!acquire->synchronize_with(release)) {
1314 set_bad_synchronization();
1317 /* Re-check all pending release sequences */
1318 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1319 /* Re-check act for mo_graph edges */
1320 work_queue->push_back(MOEdgeWorkEntry(acquire));
1322 /* propagate synchronization to later actions */
1323 action_list_t::reverse_iterator rit = action_trace->rbegin();
1324 for (; (*rit) != acquire; rit++) {
1325 ModelAction *propagate = *rit;
1326 if (acquire->happens_before(propagate)) {
1327 propagate->synchronize_with(acquire);
1328 /* Re-check 'propagate' for mo_graph edges */
1329 work_queue->push_back(MOEdgeWorkEntry(propagate));
1333 /* Break release sequence with new edges:
1334 * release --mo--> write --mo--> rf */
1335 mo_graph->addEdge(release, write);
1336 mo_graph->addEdge(write, rf);
1339 /* See if we have realized a data race */
1344 * Initialize the current action by performing one or more of the following
1345 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1346 * in the NodeStack, manipulating backtracking sets, allocating and
1347 * initializing clock vectors, and computing the promises to fulfill.
1349 * @param curr The current action, as passed from the user context; may be
1350 * freed/invalidated after the execution of this function, with a different
1351 * action "returned" its place (pass-by-reference)
1352 * @return True if curr is a newly-explored action; false otherwise
1354 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1356 ModelAction *newcurr;
1358 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1359 newcurr = process_rmw(*curr);
1362 if (newcurr->is_rmw())
1363 compute_promises(newcurr);
1369 (*curr)->set_seq_number(get_next_seq_num());
1371 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1373 /* First restore type and order in case of RMW operation */
1374 if ((*curr)->is_rmwr())
1375 newcurr->copy_typeandorder(*curr);
1377 ASSERT((*curr)->get_location() == newcurr->get_location());
1378 newcurr->copy_from_new(*curr);
1380 /* Discard duplicate ModelAction; use action from NodeStack */
1383 /* Always compute new clock vector */
1384 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1387 return false; /* Action was explored previously */
1391 /* Always compute new clock vector */
1392 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1394 /* Assign most recent release fence */
1395 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1398 * Perform one-time actions when pushing new ModelAction onto
1401 if (newcurr->is_write())
1402 compute_promises(newcurr);
1403 else if (newcurr->is_relseq_fixup())
1404 compute_relseq_breakwrites(newcurr);
1405 else if (newcurr->is_wait())
1406 newcurr->get_node()->set_misc_max(2);
1407 else if (newcurr->is_notify_one()) {
1408 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1410 return true; /* This was a new ModelAction */
1415 * @brief Establish reads-from relation between two actions
1417 * Perform basic operations involved with establishing a concrete rf relation,
1418 * including setting the ModelAction data and checking for release sequences.
1420 * @param act The action that is reading (must be a read)
1421 * @param rf The action from which we are reading (must be a write)
1423 * @return True if this read established synchronization
1425 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1428 ASSERT(rf->is_write());
1430 act->set_read_from(rf);
1431 if (act->is_acquire()) {
1432 rel_heads_list_t release_heads;
1433 get_release_seq_heads(act, act, &release_heads);
1434 int num_heads = release_heads.size();
1435 for (unsigned int i = 0; i < release_heads.size(); i++)
1436 if (!act->synchronize_with(release_heads[i])) {
1437 set_bad_synchronization();
1440 return num_heads > 0;
1446 * Check promises and eliminate potentially-satisfying threads when a thread is
1447 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1448 * no longer satisfy a promise generated from that thread.
1450 * @param blocker The thread on which a thread is waiting
1451 * @param waiting The waiting thread
1453 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1455 for (unsigned int i = 0; i < promises->size(); i++) {
1456 Promise *promise = (*promises)[i];
1457 if (!promise->thread_is_available(waiting->get_id()))
1459 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1460 ModelAction *reader = promise->get_reader(j);
1461 if (reader->get_tid() != blocker->get_id())
1463 if (promise->eliminate_thread(waiting->get_id())) {
1464 /* Promise has failed */
1465 priv->failed_promise = true;
1467 /* Only eliminate the 'waiting' thread once */
1475 * @brief Check whether a model action is enabled.
1477 * Checks whether a lock or join operation would be successful (i.e., is the
1478 * lock already locked, or is the joined thread already complete). If not, put
1479 * the action in a waiter list.
1481 * @param curr is the ModelAction to check whether it is enabled.
1482 * @return a bool that indicates whether the action is enabled.
1484 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1485 if (curr->is_lock()) {
1486 std::mutex *lock = (std::mutex *)curr->get_location();
1487 struct std::mutex_state *state = lock->get_state();
1488 if (state->locked) {
1489 //Stick the action in the appropriate waiting queue
1490 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1493 } else if (curr->get_type() == THREAD_JOIN) {
1494 Thread *blocking = (Thread *)curr->get_location();
1495 if (!blocking->is_complete()) {
1496 blocking->push_wait_list(curr);
1497 thread_blocking_check_promises(blocking, get_thread(curr));
1506 * This is the heart of the model checker routine. It performs model-checking
1507 * actions corresponding to a given "current action." Among other processes, it
1508 * calculates reads-from relationships, updates synchronization clock vectors,
1509 * forms a memory_order constraints graph, and handles replay/backtrack
1510 * execution when running permutations of previously-observed executions.
1512 * @param curr The current action to process
1513 * @return The ModelAction that is actually executed; may be different than
1514 * curr; may be NULL, if the current action is not enabled to run
1516 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1519 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1521 if (!check_action_enabled(curr)) {
1522 /* Make the execution look like we chose to run this action
1523 * much later, when a lock/join can succeed */
1524 get_thread(curr)->set_pending(curr);
1525 scheduler->sleep(get_thread(curr));
1529 bool newly_explored = initialize_curr_action(&curr);
1535 wake_up_sleeping_actions(curr);
1537 /* Compute fairness information for CHESS yield algorithm */
1538 if (model->params.yieldon) {
1539 curr->get_node()->update_yield(scheduler);
1542 /* Add the action to lists before any other model-checking tasks */
1543 if (!second_part_of_rmw)
1544 add_action_to_lists(curr);
1546 /* Build may_read_from set for newly-created actions */
1547 if (newly_explored && curr->is_read())
1548 build_may_read_from(curr);
1550 /* Initialize work_queue with the "current action" work */
1551 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1552 while (!work_queue.empty() && !has_asserted()) {
1553 WorkQueueEntry work = work_queue.front();
1554 work_queue.pop_front();
1556 switch (work.type) {
1557 case WORK_CHECK_CURR_ACTION: {
1558 ModelAction *act = work.action;
1559 bool update = false; /* update this location's release seq's */
1560 bool update_all = false; /* update all release seq's */
1562 if (process_thread_action(curr))
1565 if (act->is_read() && !second_part_of_rmw && process_read(act))
1568 if (act->is_write() && process_write(act))
1571 if (act->is_fence() && process_fence(act))
1574 if (act->is_mutex_op() && process_mutex(act))
1577 if (act->is_relseq_fixup())
1578 process_relseq_fixup(curr, &work_queue);
1581 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1583 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1586 case WORK_CHECK_RELEASE_SEQ:
1587 resolve_release_sequences(work.location, &work_queue);
1589 case WORK_CHECK_MO_EDGES: {
1590 /** @todo Complete verification of work_queue */
1591 ModelAction *act = work.action;
1592 bool updated = false;
1594 if (act->is_read()) {
1595 const ModelAction *rf = act->get_reads_from();
1596 const Promise *promise = act->get_reads_from_promise();
1598 if (r_modification_order(act, rf))
1600 } else if (promise) {
1601 if (r_modification_order(act, promise))
1605 if (act->is_write()) {
1606 if (w_modification_order(act, NULL))
1609 mo_graph->commitChanges();
1612 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1621 check_curr_backtracking(curr);
1622 set_backtracking(curr);
1626 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1628 Node *currnode = curr->get_node();
1629 Node *parnode = currnode->get_parent();
1631 if ((parnode && !parnode->backtrack_empty()) ||
1632 !currnode->misc_empty() ||
1633 !currnode->read_from_empty() ||
1634 !currnode->promise_empty() ||
1635 !currnode->relseq_break_empty()) {
1636 set_latest_backtrack(curr);
1640 bool ModelChecker::promises_expired() const
1642 for (unsigned int i = 0; i < promises->size(); i++) {
1643 Promise *promise = (*promises)[i];
1644 if (promise->get_expiration() < priv->used_sequence_numbers)
1651 * This is the strongest feasibility check available.
1652 * @return whether the current trace (partial or complete) must be a prefix of
1655 bool ModelChecker::isfeasibleprefix() const
1657 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1661 * Print disagnostic information about an infeasible execution
1662 * @param prefix A string to prefix the output with; if NULL, then a default
1663 * message prefix will be provided
1665 void ModelChecker::print_infeasibility(const char *prefix) const
1669 if (mo_graph->checkForCycles())
1670 ptr += sprintf(ptr, "[mo cycle]");
1671 if (priv->failed_promise)
1672 ptr += sprintf(ptr, "[failed promise]");
1673 if (priv->too_many_reads)
1674 ptr += sprintf(ptr, "[too many reads]");
1675 if (priv->no_valid_reads)
1676 ptr += sprintf(ptr, "[no valid reads-from]");
1677 if (priv->bad_synchronization)
1678 ptr += sprintf(ptr, "[bad sw ordering]");
1679 if (promises_expired())
1680 ptr += sprintf(ptr, "[promise expired]");
1681 if (promises->size() != 0)
1682 ptr += sprintf(ptr, "[unresolved promise]");
1684 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1688 * Returns whether the current completed trace is feasible, except for pending
1689 * release sequences.
1691 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1693 return !is_infeasible() && promises->size() == 0;
1697 * Check if the current partial trace is infeasible. Does not check any
1698 * end-of-execution flags, which might rule out the execution. Thus, this is
1699 * useful only for ruling an execution as infeasible.
1700 * @return whether the current partial trace is infeasible.
1702 bool ModelChecker::is_infeasible() const
1704 return mo_graph->checkForCycles() ||
1705 priv->no_valid_reads ||
1706 priv->failed_promise ||
1707 priv->too_many_reads ||
1708 priv->bad_synchronization ||
1712 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1713 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1714 ModelAction *lastread = get_last_action(act->get_tid());
1715 lastread->process_rmw(act);
1716 if (act->is_rmw()) {
1717 if (lastread->get_reads_from())
1718 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1720 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1721 mo_graph->commitChanges();
1727 * A helper function for ModelChecker::check_recency, to check if the current
1728 * thread is able to read from a different write/promise for 'params.maxreads'
1729 * number of steps and if that write/promise should become visible (i.e., is
1730 * ordered later in the modification order). This helps model memory liveness.
1732 * @param curr The current action. Must be a read.
1733 * @param rf The write/promise from which we plan to read
1734 * @param other_rf The write/promise from which we may read
1735 * @return True if we were able to read from other_rf for params.maxreads steps
1737 template <typename T, typename U>
1738 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1740 /* Need a different write/promise */
1741 if (other_rf->equals(rf))
1744 /* Only look for "newer" writes/promises */
1745 if (!mo_graph->checkReachable(rf, other_rf))
1748 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1749 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1750 action_list_t::reverse_iterator rit = list->rbegin();
1751 ASSERT((*rit) == curr);
1752 /* Skip past curr */
1755 /* Does this write/promise work for everyone? */
1756 for (int i = 0; i < params.maxreads; i++, rit++) {
1757 ModelAction *act = *rit;
1758 if (!act->may_read_from(other_rf))
1765 * Checks whether a thread has read from the same write or Promise for too many
1766 * times without seeing the effects of a later write/Promise.
1769 * 1) there must a different write/promise that we could read from,
1770 * 2) we must have read from the same write/promise in excess of maxreads times,
1771 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1772 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1774 * If so, we decide that the execution is no longer feasible.
1776 * @param curr The current action. Must be a read.
1777 * @param rf The ModelAction/Promise from which we might read.
1778 * @return True if the read should succeed; false otherwise
1780 template <typename T>
1781 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1783 if (!params.maxreads)
1786 //NOTE: Next check is just optimization, not really necessary....
1787 if (curr->get_node()->get_read_from_past_size() +
1788 curr->get_node()->get_read_from_promise_size() <= 1)
1791 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1792 int tid = id_to_int(curr->get_tid());
1793 ASSERT(tid < (int)thrd_lists->size());
1794 action_list_t *list = &(*thrd_lists)[tid];
1795 action_list_t::reverse_iterator rit = list->rbegin();
1796 ASSERT((*rit) == curr);
1797 /* Skip past curr */
1800 action_list_t::reverse_iterator ritcopy = rit;
1801 /* See if we have enough reads from the same value */
1802 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1803 if (ritcopy == list->rend())
1805 ModelAction *act = *ritcopy;
1806 if (!act->is_read())
1808 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1810 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1812 if (act->get_node()->get_read_from_past_size() +
1813 act->get_node()->get_read_from_promise_size() <= 1)
1816 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1817 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1818 if (should_read_instead(curr, rf, write))
1819 return false; /* liveness failure */
1821 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1822 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1823 if (should_read_instead(curr, rf, promise))
1824 return false; /* liveness failure */
1830 * Updates the mo_graph with the constraints imposed from the current
1833 * Basic idea is the following: Go through each other thread and find
1834 * the last action that happened before our read. Two cases:
1836 * (1) The action is a write => that write must either occur before
1837 * the write we read from or be the write we read from.
1839 * (2) The action is a read => the write that that action read from
1840 * must occur before the write we read from or be the same write.
1842 * @param curr The current action. Must be a read.
1843 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1844 * @return True if modification order edges were added; false otherwise
1846 template <typename rf_type>
1847 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1849 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1852 ASSERT(curr->is_read());
1854 /* Last SC fence in the current thread */
1855 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1856 ModelAction *last_sc_write = NULL;
1857 if (curr->is_seqcst())
1858 last_sc_write = get_last_seq_cst_write(curr);
1860 /* Iterate over all threads */
1861 for (i = 0; i < thrd_lists->size(); i++) {
1862 /* Last SC fence in thread i */
1863 ModelAction *last_sc_fence_thread_local = NULL;
1864 if (int_to_id((int)i) != curr->get_tid())
1865 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1867 /* Last SC fence in thread i, before last SC fence in current thread */
1868 ModelAction *last_sc_fence_thread_before = NULL;
1869 if (last_sc_fence_local)
1870 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1872 /* Iterate over actions in thread, starting from most recent */
1873 action_list_t *list = &(*thrd_lists)[i];
1874 action_list_t::reverse_iterator rit;
1875 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1876 ModelAction *act = *rit;
1881 /* Don't want to add reflexive edges on 'rf' */
1882 if (act->equals(rf)) {
1883 if (act->happens_before(curr))
1889 if (act->is_write()) {
1890 /* C++, Section 29.3 statement 5 */
1891 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1892 *act < *last_sc_fence_thread_local) {
1893 added = mo_graph->addEdge(act, rf) || added;
1896 /* C++, Section 29.3 statement 4 */
1897 else if (act->is_seqcst() && last_sc_fence_local &&
1898 *act < *last_sc_fence_local) {
1899 added = mo_graph->addEdge(act, rf) || added;
1902 /* C++, Section 29.3 statement 6 */
1903 else if (last_sc_fence_thread_before &&
1904 *act < *last_sc_fence_thread_before) {
1905 added = mo_graph->addEdge(act, rf) || added;
1910 /* C++, Section 29.3 statement 3 (second subpoint) */
1911 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1912 added = mo_graph->addEdge(act, rf) || added;
1917 * Include at most one act per-thread that "happens
1920 if (act->happens_before(curr)) {
1921 if (act->is_write()) {
1922 added = mo_graph->addEdge(act, rf) || added;
1924 const ModelAction *prevrf = act->get_reads_from();
1925 const Promise *prevrf_promise = act->get_reads_from_promise();
1927 if (!prevrf->equals(rf))
1928 added = mo_graph->addEdge(prevrf, rf) || added;
1929 } else if (!prevrf_promise->equals(rf)) {
1930 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1939 * All compatible, thread-exclusive promises must be ordered after any
1940 * concrete loads from the same thread
1942 for (unsigned int i = 0; i < promises->size(); i++)
1943 if ((*promises)[i]->is_compatible_exclusive(curr))
1944 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1950 * Updates the mo_graph with the constraints imposed from the current write.
1952 * Basic idea is the following: Go through each other thread and find
1953 * the lastest action that happened before our write. Two cases:
1955 * (1) The action is a write => that write must occur before
1958 * (2) The action is a read => the write that that action read from
1959 * must occur before the current write.
1961 * This method also handles two other issues:
1963 * (I) Sequential Consistency: Making sure that if the current write is
1964 * seq_cst, that it occurs after the previous seq_cst write.
1966 * (II) Sending the write back to non-synchronizing reads.
1968 * @param curr The current action. Must be a write.
1969 * @param send_fv A vector for stashing reads to which we may pass our future
1970 * value. If NULL, then don't record any future values.
1971 * @return True if modification order edges were added; false otherwise
1973 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1975 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1978 ASSERT(curr->is_write());
1980 if (curr->is_seqcst()) {
1981 /* We have to at least see the last sequentially consistent write,
1982 so we are initialized. */
1983 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1984 if (last_seq_cst != NULL) {
1985 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1989 /* Last SC fence in the current thread */
1990 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1992 /* Iterate over all threads */
1993 for (i = 0; i < thrd_lists->size(); i++) {
1994 /* Last SC fence in thread i, before last SC fence in current thread */
1995 ModelAction *last_sc_fence_thread_before = NULL;
1996 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1997 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1999 /* Iterate over actions in thread, starting from most recent */
2000 action_list_t *list = &(*thrd_lists)[i];
2001 action_list_t::reverse_iterator rit;
2002 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2003 ModelAction *act = *rit;
2006 * 1) If RMW and it actually read from something, then we
2007 * already have all relevant edges, so just skip to next
2010 * 2) If RMW and it didn't read from anything, we should
2011 * whatever edge we can get to speed up convergence.
2013 * 3) If normal write, we need to look at earlier actions, so
2014 * continue processing list.
2016 if (curr->is_rmw()) {
2017 if (curr->get_reads_from() != NULL)
2025 /* C++, Section 29.3 statement 7 */
2026 if (last_sc_fence_thread_before && act->is_write() &&
2027 *act < *last_sc_fence_thread_before) {
2028 added = mo_graph->addEdge(act, curr) || added;
2033 * Include at most one act per-thread that "happens
2036 if (act->happens_before(curr)) {
2038 * Note: if act is RMW, just add edge:
2040 * The following edge should be handled elsewhere:
2041 * readfrom(act) --mo--> act
2043 if (act->is_write())
2044 added = mo_graph->addEdge(act, curr) || added;
2045 else if (act->is_read()) {
2046 //if previous read accessed a null, just keep going
2047 if (act->get_reads_from() == NULL)
2049 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2052 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2053 !act->same_thread(curr)) {
2054 /* We have an action that:
2055 (1) did not happen before us
2056 (2) is a read and we are a write
2057 (3) cannot synchronize with us
2058 (4) is in a different thread
2060 that read could potentially read from our write. Note that
2061 these checks are overly conservative at this point, we'll
2062 do more checks before actually removing the
2066 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2067 if (!is_infeasible())
2068 send_fv->push_back(act);
2069 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2070 add_future_value(curr, act);
2077 * All compatible, thread-exclusive promises must be ordered after any
2078 * concrete stores to the same thread, or else they can be merged with
2081 for (unsigned int i = 0; i < promises->size(); i++)
2082 if ((*promises)[i]->is_compatible_exclusive(curr))
2083 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2088 /** Arbitrary reads from the future are not allowed. Section 29.3
2089 * part 9 places some constraints. This method checks one result of constraint
2090 * constraint. Others require compiler support. */
2091 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2093 if (!writer->is_rmw())
2096 if (!reader->is_rmw())
2099 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2100 if (search == reader)
2102 if (search->get_tid() == reader->get_tid() &&
2103 search->happens_before(reader))
2111 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2112 * some constraints. This method checks one the following constraint (others
2113 * require compiler support):
2115 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2117 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2119 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2121 /* Iterate over all threads */
2122 for (i = 0; i < thrd_lists->size(); i++) {
2123 const ModelAction *write_after_read = NULL;
2125 /* Iterate over actions in thread, starting from most recent */
2126 action_list_t *list = &(*thrd_lists)[i];
2127 action_list_t::reverse_iterator rit;
2128 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2129 ModelAction *act = *rit;
2131 /* Don't disallow due to act == reader */
2132 if (!reader->happens_before(act) || reader == act)
2134 else if (act->is_write())
2135 write_after_read = act;
2136 else if (act->is_read() && act->get_reads_from() != NULL)
2137 write_after_read = act->get_reads_from();
2140 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2147 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2148 * The ModelAction under consideration is expected to be taking part in
2149 * release/acquire synchronization as an object of the "reads from" relation.
2150 * Note that this can only provide release sequence support for RMW chains
2151 * which do not read from the future, as those actions cannot be traced until
2152 * their "promise" is fulfilled. Similarly, we may not even establish the
2153 * presence of a release sequence with certainty, as some modification order
2154 * constraints may be decided further in the future. Thus, this function
2155 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2156 * and a boolean representing certainty.
2158 * @param rf The action that might be part of a release sequence. Must be a
2160 * @param release_heads A pass-by-reference style return parameter. After
2161 * execution of this function, release_heads will contain the heads of all the
2162 * relevant release sequences, if any exists with certainty
2163 * @param pending A pass-by-reference style return parameter which is only used
2164 * when returning false (i.e., uncertain). Returns most information regarding
2165 * an uncertain release sequence, including any write operations that might
2166 * break the sequence.
2167 * @return true, if the ModelChecker is certain that release_heads is complete;
2170 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2171 rel_heads_list_t *release_heads,
2172 struct release_seq *pending) const
2174 /* Only check for release sequences if there are no cycles */
2175 if (mo_graph->checkForCycles())
2178 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2179 ASSERT(rf->is_write());
2181 if (rf->is_release())
2182 release_heads->push_back(rf);
2183 else if (rf->get_last_fence_release())
2184 release_heads->push_back(rf->get_last_fence_release());
2186 break; /* End of RMW chain */
2188 /** @todo Need to be smarter here... In the linux lock
2189 * example, this will run to the beginning of the program for
2191 /** @todo The way to be smarter here is to keep going until 1
2192 * thread has a release preceded by an acquire and you've seen
2195 /* acq_rel RMW is a sufficient stopping condition */
2196 if (rf->is_acquire() && rf->is_release())
2197 return true; /* complete */
2200 /* read from future: need to settle this later */
2202 return false; /* incomplete */
2205 if (rf->is_release())
2206 return true; /* complete */
2208 /* else relaxed write
2209 * - check for fence-release in the same thread (29.8, stmt. 3)
2210 * - check modification order for contiguous subsequence
2211 * -> rf must be same thread as release */
2213 const ModelAction *fence_release = rf->get_last_fence_release();
2214 /* Synchronize with a fence-release unconditionally; we don't need to
2215 * find any more "contiguous subsequence..." for it */
2217 release_heads->push_back(fence_release);
2219 int tid = id_to_int(rf->get_tid());
2220 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2221 action_list_t *list = &(*thrd_lists)[tid];
2222 action_list_t::const_reverse_iterator rit;
2224 /* Find rf in the thread list */
2225 rit = std::find(list->rbegin(), list->rend(), rf);
2226 ASSERT(rit != list->rend());
2228 /* Find the last {write,fence}-release */
2229 for (; rit != list->rend(); rit++) {
2230 if (fence_release && *(*rit) < *fence_release)
2232 if ((*rit)->is_release())
2235 if (rit == list->rend()) {
2236 /* No write-release in this thread */
2237 return true; /* complete */
2238 } else if (fence_release && *(*rit) < *fence_release) {
2239 /* The fence-release is more recent (and so, "stronger") than
2240 * the most recent write-release */
2241 return true; /* complete */
2242 } /* else, need to establish contiguous release sequence */
2243 ModelAction *release = *rit;
2245 ASSERT(rf->same_thread(release));
2247 pending->writes.clear();
2249 bool certain = true;
2250 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2251 if (id_to_int(rf->get_tid()) == (int)i)
2253 list = &(*thrd_lists)[i];
2255 /* Can we ensure no future writes from this thread may break
2256 * the release seq? */
2257 bool future_ordered = false;
2259 ModelAction *last = get_last_action(int_to_id(i));
2260 Thread *th = get_thread(int_to_id(i));
2261 if ((last && rf->happens_before(last)) ||
2264 future_ordered = true;
2266 ASSERT(!th->is_model_thread() || future_ordered);
2268 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2269 const ModelAction *act = *rit;
2270 /* Reach synchronization -> this thread is complete */
2271 if (act->happens_before(release))
2273 if (rf->happens_before(act)) {
2274 future_ordered = true;
2278 /* Only non-RMW writes can break release sequences */
2279 if (!act->is_write() || act->is_rmw())
2282 /* Check modification order */
2283 if (mo_graph->checkReachable(rf, act)) {
2284 /* rf --mo--> act */
2285 future_ordered = true;
2288 if (mo_graph->checkReachable(act, release))
2289 /* act --mo--> release */
2291 if (mo_graph->checkReachable(release, act) &&
2292 mo_graph->checkReachable(act, rf)) {
2293 /* release --mo-> act --mo--> rf */
2294 return true; /* complete */
2296 /* act may break release sequence */
2297 pending->writes.push_back(act);
2300 if (!future_ordered)
2301 certain = false; /* This thread is uncertain */
2305 release_heads->push_back(release);
2306 pending->writes.clear();
2308 pending->release = release;
2315 * An interface for getting the release sequence head(s) with which a
2316 * given ModelAction must synchronize. This function only returns a non-empty
2317 * result when it can locate a release sequence head with certainty. Otherwise,
2318 * it may mark the internal state of the ModelChecker so that it will handle
2319 * the release sequence at a later time, causing @a acquire to update its
2320 * synchronization at some later point in execution.
2322 * @param acquire The 'acquire' action that may synchronize with a release
2324 * @param read The read action that may read from a release sequence; this may
2325 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2326 * when 'acquire' is a fence-acquire)
2327 * @param release_heads A pass-by-reference return parameter. Will be filled
2328 * with the head(s) of the release sequence(s), if they exists with certainty.
2329 * @see ModelChecker::release_seq_heads
2331 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2332 ModelAction *read, rel_heads_list_t *release_heads)
2334 const ModelAction *rf = read->get_reads_from();
2335 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2336 sequence->acquire = acquire;
2337 sequence->read = read;
2339 if (!release_seq_heads(rf, release_heads, sequence)) {
2340 /* add act to 'lazy checking' list */
2341 pending_rel_seqs->push_back(sequence);
2343 snapshot_free(sequence);
2348 * Attempt to resolve all stashed operations that might synchronize with a
2349 * release sequence for a given location. This implements the "lazy" portion of
2350 * determining whether or not a release sequence was contiguous, since not all
2351 * modification order information is present at the time an action occurs.
2353 * @param location The location/object that should be checked for release
2354 * sequence resolutions. A NULL value means to check all locations.
2355 * @param work_queue The work queue to which to add work items as they are
2357 * @return True if any updates occurred (new synchronization, new mo_graph
2360 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2362 bool updated = false;
2363 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2364 while (it != pending_rel_seqs->end()) {
2365 struct release_seq *pending = *it;
2366 ModelAction *acquire = pending->acquire;
2367 const ModelAction *read = pending->read;
2369 /* Only resolve sequences on the given location, if provided */
2370 if (location && read->get_location() != location) {
2375 const ModelAction *rf = read->get_reads_from();
2376 rel_heads_list_t release_heads;
2378 complete = release_seq_heads(rf, &release_heads, pending);
2379 for (unsigned int i = 0; i < release_heads.size(); i++) {
2380 if (!acquire->has_synchronized_with(release_heads[i])) {
2381 if (acquire->synchronize_with(release_heads[i]))
2384 set_bad_synchronization();
2389 /* Re-check all pending release sequences */
2390 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2391 /* Re-check read-acquire for mo_graph edges */
2392 if (acquire->is_read())
2393 work_queue->push_back(MOEdgeWorkEntry(acquire));
2395 /* propagate synchronization to later actions */
2396 action_list_t::reverse_iterator rit = action_trace->rbegin();
2397 for (; (*rit) != acquire; rit++) {
2398 ModelAction *propagate = *rit;
2399 if (acquire->happens_before(propagate)) {
2400 propagate->synchronize_with(acquire);
2401 /* Re-check 'propagate' for mo_graph edges */
2402 work_queue->push_back(MOEdgeWorkEntry(propagate));
2407 it = pending_rel_seqs->erase(it);
2408 snapshot_free(pending);
2414 // If we resolved promises or data races, see if we have realized a data race.
2421 * Performs various bookkeeping operations for the current ModelAction. For
2422 * instance, adds action to the per-object, per-thread action vector and to the
2423 * action trace list of all thread actions.
2425 * @param act is the ModelAction to add.
2427 void ModelChecker::add_action_to_lists(ModelAction *act)
2429 int tid = id_to_int(act->get_tid());
2430 ModelAction *uninit = NULL;
2432 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2433 if (list->empty() && act->is_atomic_var()) {
2434 uninit = get_uninitialized_action(act);
2435 uninit_id = id_to_int(uninit->get_tid());
2436 list->push_front(uninit);
2438 list->push_back(act);
2440 action_trace->push_back(act);
2442 action_trace->push_front(uninit);
2444 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2445 if (tid >= (int)vec->size())
2446 vec->resize(priv->next_thread_id);
2447 (*vec)[tid].push_back(act);
2449 (*vec)[uninit_id].push_front(uninit);
2451 if ((int)thrd_last_action->size() <= tid)
2452 thrd_last_action->resize(get_num_threads());
2453 (*thrd_last_action)[tid] = act;
2455 (*thrd_last_action)[uninit_id] = uninit;
2457 if (act->is_fence() && act->is_release()) {
2458 if ((int)thrd_last_fence_release->size() <= tid)
2459 thrd_last_fence_release->resize(get_num_threads());
2460 (*thrd_last_fence_release)[tid] = act;
2463 if (act->is_wait()) {
2464 void *mutex_loc = (void *) act->get_value();
2465 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2467 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2468 if (tid >= (int)vec->size())
2469 vec->resize(priv->next_thread_id);
2470 (*vec)[tid].push_back(act);
2475 * @brief Get the last action performed by a particular Thread
2476 * @param tid The thread ID of the Thread in question
2477 * @return The last action in the thread
2479 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2481 int threadid = id_to_int(tid);
2482 if (threadid < (int)thrd_last_action->size())
2483 return (*thrd_last_action)[id_to_int(tid)];
2489 * @brief Get the last fence release performed by a particular Thread
2490 * @param tid The thread ID of the Thread in question
2491 * @return The last fence release in the thread, if one exists; NULL otherwise
2493 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2495 int threadid = id_to_int(tid);
2496 if (threadid < (int)thrd_last_fence_release->size())
2497 return (*thrd_last_fence_release)[id_to_int(tid)];
2503 * Gets the last memory_order_seq_cst write (in the total global sequence)
2504 * performed on a particular object (i.e., memory location), not including the
2506 * @param curr The current ModelAction; also denotes the object location to
2508 * @return The last seq_cst write
2510 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2512 void *location = curr->get_location();
2513 action_list_t *list = get_safe_ptr_action(obj_map, location);
2514 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2515 action_list_t::reverse_iterator rit;
2516 for (rit = list->rbegin(); (*rit) != curr; rit++)
2518 rit++; /* Skip past curr */
2519 for ( ; rit != list->rend(); rit++)
2520 if ((*rit)->is_write() && (*rit)->is_seqcst())
2526 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2527 * performed in a particular thread, prior to a particular fence.
2528 * @param tid The ID of the thread to check
2529 * @param before_fence The fence from which to begin the search; if NULL, then
2530 * search for the most recent fence in the thread.
2531 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2533 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2535 /* All fences should have NULL location */
2536 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2537 action_list_t::reverse_iterator rit = list->rbegin();
2540 for (; rit != list->rend(); rit++)
2541 if (*rit == before_fence)
2544 ASSERT(*rit == before_fence);
2548 for (; rit != list->rend(); rit++)
2549 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2555 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2556 * location). This function identifies the mutex according to the current
2557 * action, which is presumed to perform on the same mutex.
2558 * @param curr The current ModelAction; also denotes the object location to
2560 * @return The last unlock operation
2562 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2564 void *location = curr->get_location();
2565 action_list_t *list = get_safe_ptr_action(obj_map, location);
2566 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2567 action_list_t::reverse_iterator rit;
2568 for (rit = list->rbegin(); rit != list->rend(); rit++)
2569 if ((*rit)->is_unlock() || (*rit)->is_wait())
2574 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2576 ModelAction *parent = get_last_action(tid);
2578 parent = get_thread(tid)->get_creation();
2583 * Returns the clock vector for a given thread.
2584 * @param tid The thread whose clock vector we want
2585 * @return Desired clock vector
2587 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2589 return get_parent_action(tid)->get_cv();
2593 * @brief Find the promise (if any) to resolve for the current action and
2594 * remove it from the pending promise vector
2595 * @param curr The current ModelAction. Should be a write.
2596 * @return The Promise to resolve, if any; otherwise NULL
2598 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2600 for (unsigned int i = 0; i < promises->size(); i++)
2601 if (curr->get_node()->get_promise(i)) {
2602 Promise *ret = (*promises)[i];
2603 promises->erase(promises->begin() + i);
2610 * Resolve a Promise with a current write.
2611 * @param write The ModelAction that is fulfilling Promises
2612 * @param promise The Promise to resolve
2613 * @return True if the Promise was successfully resolved; false otherwise
2615 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2617 ModelVector<ModelAction *> actions_to_check;
2619 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2620 ModelAction *read = promise->get_reader(i);
2621 read_from(read, write);
2622 actions_to_check.push_back(read);
2624 /* Make sure the promise's value matches the write's value */
2625 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2626 if (!mo_graph->resolvePromise(promise, write))
2627 priv->failed_promise = true;
2630 * @todo It is possible to end up in an inconsistent state, where a
2631 * "resolved" promise may still be referenced if
2632 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2634 * Note that the inconsistency only matters when dumping mo_graph to
2640 //Check whether reading these writes has made threads unable to
2642 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2643 ModelAction *read = actions_to_check[i];
2644 mo_check_promises(read, true);
2651 * Compute the set of promises that could potentially be satisfied by this
2652 * action. Note that the set computation actually appears in the Node, not in
2654 * @param curr The ModelAction that may satisfy promises
2656 void ModelChecker::compute_promises(ModelAction *curr)
2658 for (unsigned int i = 0; i < promises->size(); i++) {
2659 Promise *promise = (*promises)[i];
2660 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2663 bool satisfy = true;
2664 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2665 const ModelAction *act = promise->get_reader(j);
2666 if (act->happens_before(curr) ||
2667 act->could_synchronize_with(curr)) {
2673 curr->get_node()->set_promise(i);
2677 /** Checks promises in response to change in ClockVector Threads. */
2678 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2680 for (unsigned int i = 0; i < promises->size(); i++) {
2681 Promise *promise = (*promises)[i];
2682 if (!promise->thread_is_available(tid))
2684 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2685 const ModelAction *act = promise->get_reader(j);
2686 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2687 merge_cv->synchronized_since(act)) {
2688 if (promise->eliminate_thread(tid)) {
2689 /* Promise has failed */
2690 priv->failed_promise = true;
2698 void ModelChecker::check_promises_thread_disabled()
2700 for (unsigned int i = 0; i < promises->size(); i++) {
2701 Promise *promise = (*promises)[i];
2702 if (promise->has_failed()) {
2703 priv->failed_promise = true;
2710 * @brief Checks promises in response to addition to modification order for
2713 * We test whether threads are still available for satisfying promises after an
2714 * addition to our modification order constraints. Those that are unavailable
2715 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2716 * that promise has failed.
2718 * @param act The ModelAction which updated the modification order
2719 * @param is_read_check Should be true if act is a read and we must check for
2720 * updates to the store from which it read (there is a distinction here for
2721 * RMW's, which are both a load and a store)
2723 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2725 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2727 for (unsigned int i = 0; i < promises->size(); i++) {
2728 Promise *promise = (*promises)[i];
2730 // Is this promise on the same location?
2731 if (!promise->same_location(write))
2734 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2735 const ModelAction *pread = promise->get_reader(j);
2736 if (!pread->happens_before(act))
2738 if (mo_graph->checkPromise(write, promise)) {
2739 priv->failed_promise = true;
2745 // Don't do any lookups twice for the same thread
2746 if (!promise->thread_is_available(act->get_tid()))
2749 if (mo_graph->checkReachable(promise, write)) {
2750 if (mo_graph->checkPromise(write, promise)) {
2751 priv->failed_promise = true;
2759 * Compute the set of writes that may break the current pending release
2760 * sequence. This information is extracted from previou release sequence
2763 * @param curr The current ModelAction. Must be a release sequence fixup
2766 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2768 if (pending_rel_seqs->empty())
2771 struct release_seq *pending = pending_rel_seqs->back();
2772 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2773 const ModelAction *write = pending->writes[i];
2774 curr->get_node()->add_relseq_break(write);
2777 /* NULL means don't break the sequence; just synchronize */
2778 curr->get_node()->add_relseq_break(NULL);
2782 * Build up an initial set of all past writes that this 'read' action may read
2783 * from, as well as any previously-observed future values that must still be valid.
2785 * @param curr is the current ModelAction that we are exploring; it must be a
2788 void ModelChecker::build_may_read_from(ModelAction *curr)
2790 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2792 ASSERT(curr->is_read());
2794 ModelAction *last_sc_write = NULL;
2796 if (curr->is_seqcst())
2797 last_sc_write = get_last_seq_cst_write(curr);
2799 /* Iterate over all threads */
2800 for (i = 0; i < thrd_lists->size(); i++) {
2801 /* Iterate over actions in thread, starting from most recent */
2802 action_list_t *list = &(*thrd_lists)[i];
2803 action_list_t::reverse_iterator rit;
2804 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2805 ModelAction *act = *rit;
2807 /* Only consider 'write' actions */
2808 if (!act->is_write() || act == curr)
2811 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2812 bool allow_read = true;
2814 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2816 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2820 /* Only add feasible reads */
2821 mo_graph->startChanges();
2822 r_modification_order(curr, act);
2823 if (!is_infeasible())
2824 curr->get_node()->add_read_from_past(act);
2825 mo_graph->rollbackChanges();
2828 /* Include at most one act per-thread that "happens before" curr */
2829 if (act->happens_before(curr))
2834 /* Inherit existing, promised future values */
2835 for (i = 0; i < promises->size(); i++) {
2836 const Promise *promise = (*promises)[i];
2837 const ModelAction *promise_read = promise->get_reader(0);
2838 if (promise_read->same_var(curr)) {
2839 /* Only add feasible future-values */
2840 mo_graph->startChanges();
2841 r_modification_order(curr, promise);
2842 if (!is_infeasible())
2843 curr->get_node()->add_read_from_promise(promise_read);
2844 mo_graph->rollbackChanges();
2848 /* We may find no valid may-read-from only if the execution is doomed */
2849 if (!curr->get_node()->read_from_size()) {
2850 priv->no_valid_reads = true;
2854 if (DBG_ENABLED()) {
2855 model_print("Reached read action:\n");
2857 model_print("Printing read_from_past\n");
2858 curr->get_node()->print_read_from_past();
2859 model_print("End printing read_from_past\n");
2863 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2865 for ( ; write != NULL; write = write->get_reads_from()) {
2866 /* UNINIT actions don't have a Node, and they never sleep */
2867 if (write->is_uninitialized())
2869 Node *prevnode = write->get_node()->get_parent();
2871 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2872 if (write->is_release() && thread_sleep)
2874 if (!write->is_rmw())
2881 * @brief Get an action representing an uninitialized atomic
2883 * This function may create a new one or try to retrieve one from the NodeStack
2885 * @param curr The current action, which prompts the creation of an UNINIT action
2886 * @return A pointer to the UNINIT ModelAction
2888 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2890 Node *node = curr->get_node();
2891 ModelAction *act = node->get_uninit_action();
2893 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2894 node->set_uninit_action(act);
2896 act->create_cv(NULL);
2900 static void print_list(action_list_t *list)
2902 action_list_t::iterator it;
2904 model_print("---------------------------------------------------------------------\n");
2906 unsigned int hash = 0;
2908 for (it = list->begin(); it != list->end(); it++) {
2909 const ModelAction *act = *it;
2910 if (act->get_seq_number() > 0)
2912 hash = hash^(hash<<3)^((*it)->hash());
2914 model_print("HASH %u\n", hash);
2915 model_print("---------------------------------------------------------------------\n");
2918 #if SUPPORT_MOD_ORDER_DUMP
2919 void ModelChecker::dumpGraph(char *filename) const
2922 sprintf(buffer, "%s.dot", filename);
2923 FILE *file = fopen(buffer, "w");
2924 fprintf(file, "digraph %s {\n", filename);
2925 mo_graph->dumpNodes(file);
2926 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2928 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2929 ModelAction *act = *it;
2930 if (act->is_read()) {
2931 mo_graph->dot_print_node(file, act);
2932 if (act->get_reads_from())
2933 mo_graph->dot_print_edge(file,
2934 act->get_reads_from(),
2936 "label=\"rf\", color=red, weight=2");
2938 mo_graph->dot_print_edge(file,
2939 act->get_reads_from_promise(),
2941 "label=\"rf\", color=red");
2943 if (thread_array[act->get_tid()]) {
2944 mo_graph->dot_print_edge(file,
2945 thread_array[id_to_int(act->get_tid())],
2947 "label=\"sb\", color=blue, weight=400");
2950 thread_array[act->get_tid()] = act;
2952 fprintf(file, "}\n");
2953 model_free(thread_array);
2958 /** @brief Prints an execution trace summary. */
2959 void ModelChecker::print_summary() const
2961 #if SUPPORT_MOD_ORDER_DUMP
2962 char buffername[100];
2963 sprintf(buffername, "exec%04u", stats.num_total);
2964 mo_graph->dumpGraphToFile(buffername);
2965 sprintf(buffername, "graph%04u", stats.num_total);
2966 dumpGraph(buffername);
2969 model_print("Execution %d:", stats.num_total);
2970 if (isfeasibleprefix()) {
2971 if (scheduler->all_threads_sleeping())
2972 model_print(" SLEEP-SET REDUNDANT");
2975 print_infeasibility(" INFEASIBLE");
2976 print_list(action_trace);
2978 if (!promises->empty()) {
2979 model_print("Pending promises:\n");
2980 for (unsigned int i = 0; i < promises->size(); i++) {
2981 model_print(" [P%u] ", i);
2982 (*promises)[i]->print();
2989 * Add a Thread to the system for the first time. Should only be called once
2991 * @param t The Thread to add
2993 void ModelChecker::add_thread(Thread *t)
2995 thread_map->put(id_to_int(t->get_id()), t);
2996 scheduler->add_thread(t);
3000 * @brief Get a Thread reference by its ID
3001 * @param tid The Thread's ID
3002 * @return A Thread reference
3004 Thread * ModelChecker::get_thread(thread_id_t tid) const
3006 return thread_map->get(id_to_int(tid));
3010 * @brief Get a reference to the Thread in which a ModelAction was executed
3011 * @param act The ModelAction
3012 * @return A Thread reference
3014 Thread * ModelChecker::get_thread(const ModelAction *act) const
3016 return get_thread(act->get_tid());
3020 * @brief Get a Promise's "promise number"
3022 * A "promise number" is an index number that is unique to a promise, valid
3023 * only for a specific snapshot of an execution trace. Promises may come and go
3024 * as they are generated an resolved, so an index only retains meaning for the
3027 * @param promise The Promise to check
3028 * @return The promise index, if the promise still is valid; otherwise -1
3030 int ModelChecker::get_promise_number(const Promise *promise) const
3032 for (unsigned int i = 0; i < promises->size(); i++)
3033 if ((*promises)[i] == promise)
3040 * @brief Check if a Thread is currently enabled
3041 * @param t The Thread to check
3042 * @return True if the Thread is currently enabled
3044 bool ModelChecker::is_enabled(Thread *t) const
3046 return scheduler->is_enabled(t);
3050 * @brief Check if a Thread is currently enabled
3051 * @param tid The ID of the Thread to check
3052 * @return True if the Thread is currently enabled
3054 bool ModelChecker::is_enabled(thread_id_t tid) const
3056 return scheduler->is_enabled(tid);
3060 * Switch from a model-checker context to a user-thread context. This is the
3061 * complement of ModelChecker::switch_to_master and must be called from the
3062 * model-checker context
3064 * @param thread The user-thread to switch to
3066 void ModelChecker::switch_from_master(Thread *thread)
3068 scheduler->set_current_thread(thread);
3069 Thread::swap(&system_context, thread);
3073 * Switch from a user-context to the "master thread" context (a.k.a. system
3074 * context). This switch is made with the intention of exploring a particular
3075 * model-checking action (described by a ModelAction object). Must be called
3076 * from a user-thread context.
3078 * @param act The current action that will be explored. May be NULL only if
3079 * trace is exiting via an assertion (see ModelChecker::set_assert and
3080 * ModelChecker::has_asserted).
3081 * @return Return the value returned by the current action
3083 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3086 Thread *old = thread_current();
3087 scheduler->set_current_thread(NULL);
3088 ASSERT(!old->get_pending());
3089 old->set_pending(act);
3090 if (Thread::swap(old, &system_context) < 0) {
3091 perror("swap threads");
3094 return old->get_return_value();
3098 * Takes the next step in the execution, if possible.
3099 * @param curr The current step to take
3100 * @return Returns the next Thread to run, if any; NULL if this execution
3103 Thread * ModelChecker::take_step(ModelAction *curr)
3105 Thread *curr_thrd = get_thread(curr);
3106 ASSERT(curr_thrd->get_state() == THREAD_READY);
3108 curr = check_current_action(curr);
3110 /* Infeasible -> don't take any more steps */
3111 if (is_infeasible())
3113 else if (isfeasibleprefix() && have_bug_reports()) {
3118 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3121 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3122 scheduler->remove_thread(curr_thrd);
3124 Thread *next_thrd = NULL;
3126 next_thrd = action_select_next_thread(curr);
3128 next_thrd = get_next_thread();
3130 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3131 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3136 /** Wrapper to run the user's main function, with appropriate arguments */
3137 void user_main_wrapper(void *)
3139 user_main(model->params.argc, model->params.argv);
3142 /** @brief Run ModelChecker for the user program */
3143 void ModelChecker::run()
3147 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3152 * Stash next pending action(s) for thread(s). There
3153 * should only need to stash one thread's action--the
3154 * thread which just took a step--plus the first step
3155 * for any newly-created thread
3157 for (unsigned int i = 0; i < get_num_threads(); i++) {
3158 thread_id_t tid = int_to_id(i);
3159 Thread *thr = get_thread(tid);
3160 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3161 switch_from_master(thr);
3162 if (is_circular_wait(thr))
3163 assert_bug("Deadlock detected");
3167 /* Catch assertions from prior take_step or from
3168 * between-ModelAction bugs (e.g., data races) */
3172 /* Consume the next action for a Thread */
3173 ModelAction *curr = t->get_pending();
3174 t->set_pending(NULL);
3175 t = take_step(curr);
3176 } while (t && !t->is_model_thread());
3179 * Launch end-of-execution release sequence fixups only when
3180 * the execution is otherwise feasible AND there are:
3182 * (1) pending release sequences
3183 * (2) pending assertions that could be invalidated by a change
3184 * in clock vectors (i.e., data races)
3185 * (3) no pending promises
3187 while (!pending_rel_seqs->empty() &&
3188 is_feasible_prefix_ignore_relseq() &&
3189 !unrealizedraces.empty()) {
3190 model_print("*** WARNING: release sequence fixup action "
3191 "(%zu pending release seuqence(s)) ***\n",
3192 pending_rel_seqs->size());
3193 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3194 std::memory_order_seq_cst, NULL, VALUE_NONE,
3198 } while (next_execution());
3200 model_print("******* Model-checking complete: *******\n");