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 if (promises->empty()) {
1143 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1144 struct PendingFutureValue pfv = (*futurevalues)[i];
1145 add_future_value(pfv.writer, pfv.reader);
1147 futurevalues->clear();
1150 mo_graph->commitChanges();
1151 mo_check_promises(curr, false);
1153 get_thread(curr)->set_return_value(VALUE_NONE);
1154 return updated_mod_order || updated_promises;
1158 * Process a fence ModelAction
1159 * @param curr The ModelAction to process
1160 * @return True if synchronization was updated
1162 bool ModelChecker::process_fence(ModelAction *curr)
1165 * fence-relaxed: no-op
1166 * fence-release: only log the occurence (not in this function), for
1167 * use in later synchronization
1168 * fence-acquire (this function): search for hypothetical release
1170 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1172 bool updated = false;
1173 if (curr->is_acquire()) {
1174 action_list_t *list = action_trace;
1175 action_list_t::reverse_iterator rit;
1176 /* Find X : is_read(X) && X --sb-> curr */
1177 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1178 ModelAction *act = *rit;
1181 if (act->get_tid() != curr->get_tid())
1183 /* Stop at the beginning of the thread */
1184 if (act->is_thread_start())
1186 /* Stop once we reach a prior fence-acquire */
1187 if (act->is_fence() && act->is_acquire())
1189 if (!act->is_read())
1191 /* read-acquire will find its own release sequences */
1192 if (act->is_acquire())
1195 /* Establish hypothetical release sequences */
1196 rel_heads_list_t release_heads;
1197 get_release_seq_heads(curr, act, &release_heads);
1198 for (unsigned int i = 0; i < release_heads.size(); i++)
1199 if (!curr->synchronize_with(release_heads[i]))
1200 set_bad_synchronization();
1201 if (release_heads.size() != 0)
1209 * @brief Process the current action for thread-related activity
1211 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1212 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1213 * synchronization, etc. This function is a no-op for non-THREAD actions
1214 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1216 * @param curr The current action
1217 * @return True if synchronization was updated or a thread completed
1219 bool ModelChecker::process_thread_action(ModelAction *curr)
1221 bool updated = false;
1223 switch (curr->get_type()) {
1224 case THREAD_CREATE: {
1225 thrd_t *thrd = (thrd_t *)curr->get_location();
1226 struct thread_params *params = (struct thread_params *)curr->get_value();
1227 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1229 th->set_creation(curr);
1230 /* Promises can be satisfied by children */
1231 for (unsigned int i = 0; i < promises->size(); i++) {
1232 Promise *promise = (*promises)[i];
1233 if (promise->thread_is_available(curr->get_tid()))
1234 promise->add_thread(th->get_id());
1239 Thread *blocking = curr->get_thread_operand();
1240 ModelAction *act = get_last_action(blocking->get_id());
1241 curr->synchronize_with(act);
1242 updated = true; /* trigger rel-seq checks */
1245 case THREAD_FINISH: {
1246 Thread *th = get_thread(curr);
1247 while (!th->wait_list_empty()) {
1248 ModelAction *act = th->pop_wait_list();
1249 scheduler->wake(get_thread(act));
1252 /* Completed thread can't satisfy promises */
1253 for (unsigned int i = 0; i < promises->size(); i++) {
1254 Promise *promise = (*promises)[i];
1255 if (promise->thread_is_available(th->get_id()))
1256 if (promise->eliminate_thread(th->get_id()))
1257 priv->failed_promise = true;
1259 updated = true; /* trigger rel-seq checks */
1262 case THREAD_START: {
1263 check_promises(curr->get_tid(), NULL, curr->get_cv());
1274 * @brief Process the current action for release sequence fixup activity
1276 * Performs model-checker release sequence fixups for the current action,
1277 * forcing a single pending release sequence to break (with a given, potential
1278 * "loose" write) or to complete (i.e., synchronize). If a pending release
1279 * sequence forms a complete release sequence, then we must perform the fixup
1280 * synchronization, mo_graph additions, etc.
1282 * @param curr The current action; must be a release sequence fixup action
1283 * @param work_queue The work queue to which to add work items as they are
1286 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1288 const ModelAction *write = curr->get_node()->get_relseq_break();
1289 struct release_seq *sequence = pending_rel_seqs->back();
1290 pending_rel_seqs->pop_back();
1292 ModelAction *acquire = sequence->acquire;
1293 const ModelAction *rf = sequence->rf;
1294 const ModelAction *release = sequence->release;
1298 ASSERT(release->same_thread(rf));
1300 if (write == NULL) {
1302 * @todo Forcing a synchronization requires that we set
1303 * modification order constraints. For instance, we can't allow
1304 * a fixup sequence in which two separate read-acquire
1305 * operations read from the same sequence, where the first one
1306 * synchronizes and the other doesn't. Essentially, we can't
1307 * allow any writes to insert themselves between 'release' and
1311 /* Must synchronize */
1312 if (!acquire->synchronize_with(release)) {
1313 set_bad_synchronization();
1316 /* Re-check all pending release sequences */
1317 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1318 /* Re-check act for mo_graph edges */
1319 work_queue->push_back(MOEdgeWorkEntry(acquire));
1321 /* propagate synchronization to later actions */
1322 action_list_t::reverse_iterator rit = action_trace->rbegin();
1323 for (; (*rit) != acquire; rit++) {
1324 ModelAction *propagate = *rit;
1325 if (acquire->happens_before(propagate)) {
1326 propagate->synchronize_with(acquire);
1327 /* Re-check 'propagate' for mo_graph edges */
1328 work_queue->push_back(MOEdgeWorkEntry(propagate));
1332 /* Break release sequence with new edges:
1333 * release --mo--> write --mo--> rf */
1334 mo_graph->addEdge(release, write);
1335 mo_graph->addEdge(write, rf);
1338 /* See if we have realized a data race */
1343 * Initialize the current action by performing one or more of the following
1344 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1345 * in the NodeStack, manipulating backtracking sets, allocating and
1346 * initializing clock vectors, and computing the promises to fulfill.
1348 * @param curr The current action, as passed from the user context; may be
1349 * freed/invalidated after the execution of this function, with a different
1350 * action "returned" its place (pass-by-reference)
1351 * @return True if curr is a newly-explored action; false otherwise
1353 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1355 ModelAction *newcurr;
1357 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1358 newcurr = process_rmw(*curr);
1361 if (newcurr->is_rmw())
1362 compute_promises(newcurr);
1368 (*curr)->set_seq_number(get_next_seq_num());
1370 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1372 /* First restore type and order in case of RMW operation */
1373 if ((*curr)->is_rmwr())
1374 newcurr->copy_typeandorder(*curr);
1376 ASSERT((*curr)->get_location() == newcurr->get_location());
1377 newcurr->copy_from_new(*curr);
1379 /* Discard duplicate ModelAction; use action from NodeStack */
1382 /* Always compute new clock vector */
1383 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1386 return false; /* Action was explored previously */
1390 /* Always compute new clock vector */
1391 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1393 /* Assign most recent release fence */
1394 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1397 * Perform one-time actions when pushing new ModelAction onto
1400 if (newcurr->is_write())
1401 compute_promises(newcurr);
1402 else if (newcurr->is_relseq_fixup())
1403 compute_relseq_breakwrites(newcurr);
1404 else if (newcurr->is_wait())
1405 newcurr->get_node()->set_misc_max(2);
1406 else if (newcurr->is_notify_one()) {
1407 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1409 return true; /* This was a new ModelAction */
1414 * @brief Establish reads-from relation between two actions
1416 * Perform basic operations involved with establishing a concrete rf relation,
1417 * including setting the ModelAction data and checking for release sequences.
1419 * @param act The action that is reading (must be a read)
1420 * @param rf The action from which we are reading (must be a write)
1422 * @return True if this read established synchronization
1424 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1427 ASSERT(rf->is_write());
1429 act->set_read_from(rf);
1430 if (act->is_acquire()) {
1431 rel_heads_list_t release_heads;
1432 get_release_seq_heads(act, act, &release_heads);
1433 int num_heads = release_heads.size();
1434 for (unsigned int i = 0; i < release_heads.size(); i++)
1435 if (!act->synchronize_with(release_heads[i])) {
1436 set_bad_synchronization();
1439 return num_heads > 0;
1445 * Check promises and eliminate potentially-satisfying threads when a thread is
1446 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1447 * no longer satisfy a promise generated from that thread.
1449 * @param blocker The thread on which a thread is waiting
1450 * @param waiting The waiting thread
1452 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1454 for (unsigned int i = 0; i < promises->size(); i++) {
1455 Promise *promise = (*promises)[i];
1456 if (!promise->thread_is_available(waiting->get_id()))
1458 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1459 ModelAction *reader = promise->get_reader(j);
1460 if (reader->get_tid() != blocker->get_id())
1462 if (promise->eliminate_thread(waiting->get_id())) {
1463 /* Promise has failed */
1464 priv->failed_promise = true;
1466 /* Only eliminate the 'waiting' thread once */
1474 * @brief Check whether a model action is enabled.
1476 * Checks whether a lock or join operation would be successful (i.e., is the
1477 * lock already locked, or is the joined thread already complete). If not, put
1478 * the action in a waiter list.
1480 * @param curr is the ModelAction to check whether it is enabled.
1481 * @return a bool that indicates whether the action is enabled.
1483 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1484 if (curr->is_lock()) {
1485 std::mutex *lock = (std::mutex *)curr->get_location();
1486 struct std::mutex_state *state = lock->get_state();
1487 if (state->locked) {
1488 //Stick the action in the appropriate waiting queue
1489 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1492 } else if (curr->get_type() == THREAD_JOIN) {
1493 Thread *blocking = (Thread *)curr->get_location();
1494 if (!blocking->is_complete()) {
1495 blocking->push_wait_list(curr);
1496 thread_blocking_check_promises(blocking, get_thread(curr));
1505 * This is the heart of the model checker routine. It performs model-checking
1506 * actions corresponding to a given "current action." Among other processes, it
1507 * calculates reads-from relationships, updates synchronization clock vectors,
1508 * forms a memory_order constraints graph, and handles replay/backtrack
1509 * execution when running permutations of previously-observed executions.
1511 * @param curr The current action to process
1512 * @return The ModelAction that is actually executed; may be different than
1513 * curr; may be NULL, if the current action is not enabled to run
1515 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1518 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1520 if (!check_action_enabled(curr)) {
1521 /* Make the execution look like we chose to run this action
1522 * much later, when a lock/join can succeed */
1523 get_thread(curr)->set_pending(curr);
1524 scheduler->sleep(get_thread(curr));
1528 bool newly_explored = initialize_curr_action(&curr);
1534 wake_up_sleeping_actions(curr);
1536 /* Compute fairness information for CHESS yield algorithm */
1537 if (model->params.yieldon) {
1538 curr->get_node()->update_yield(scheduler);
1541 /* Add the action to lists before any other model-checking tasks */
1542 if (!second_part_of_rmw)
1543 add_action_to_lists(curr);
1545 /* Build may_read_from set for newly-created actions */
1546 if (newly_explored && curr->is_read())
1547 build_may_read_from(curr);
1549 /* Initialize work_queue with the "current action" work */
1550 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1551 while (!work_queue.empty() && !has_asserted()) {
1552 WorkQueueEntry work = work_queue.front();
1553 work_queue.pop_front();
1555 switch (work.type) {
1556 case WORK_CHECK_CURR_ACTION: {
1557 ModelAction *act = work.action;
1558 bool update = false; /* update this location's release seq's */
1559 bool update_all = false; /* update all release seq's */
1561 if (process_thread_action(curr))
1564 if (act->is_read() && !second_part_of_rmw && process_read(act))
1567 if (act->is_write() && process_write(act))
1570 if (act->is_fence() && process_fence(act))
1573 if (act->is_mutex_op() && process_mutex(act))
1576 if (act->is_relseq_fixup())
1577 process_relseq_fixup(curr, &work_queue);
1580 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1582 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1585 case WORK_CHECK_RELEASE_SEQ:
1586 resolve_release_sequences(work.location, &work_queue);
1588 case WORK_CHECK_MO_EDGES: {
1589 /** @todo Complete verification of work_queue */
1590 ModelAction *act = work.action;
1591 bool updated = false;
1593 if (act->is_read()) {
1594 const ModelAction *rf = act->get_reads_from();
1595 const Promise *promise = act->get_reads_from_promise();
1597 if (r_modification_order(act, rf))
1599 } else if (promise) {
1600 if (r_modification_order(act, promise))
1604 if (act->is_write()) {
1605 if (w_modification_order(act, NULL))
1608 mo_graph->commitChanges();
1611 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1620 check_curr_backtracking(curr);
1621 set_backtracking(curr);
1625 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1627 Node *currnode = curr->get_node();
1628 Node *parnode = currnode->get_parent();
1630 if ((parnode && !parnode->backtrack_empty()) ||
1631 !currnode->misc_empty() ||
1632 !currnode->read_from_empty() ||
1633 !currnode->promise_empty() ||
1634 !currnode->relseq_break_empty()) {
1635 set_latest_backtrack(curr);
1639 bool ModelChecker::promises_expired() const
1641 for (unsigned int i = 0; i < promises->size(); i++) {
1642 Promise *promise = (*promises)[i];
1643 if (promise->get_expiration() < priv->used_sequence_numbers)
1650 * This is the strongest feasibility check available.
1651 * @return whether the current trace (partial or complete) must be a prefix of
1654 bool ModelChecker::isfeasibleprefix() const
1656 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1660 * Print disagnostic information about an infeasible execution
1661 * @param prefix A string to prefix the output with; if NULL, then a default
1662 * message prefix will be provided
1664 void ModelChecker::print_infeasibility(const char *prefix) const
1668 if (mo_graph->checkForCycles())
1669 ptr += sprintf(ptr, "[mo cycle]");
1670 if (priv->failed_promise)
1671 ptr += sprintf(ptr, "[failed promise]");
1672 if (priv->too_many_reads)
1673 ptr += sprintf(ptr, "[too many reads]");
1674 if (priv->no_valid_reads)
1675 ptr += sprintf(ptr, "[no valid reads-from]");
1676 if (priv->bad_synchronization)
1677 ptr += sprintf(ptr, "[bad sw ordering]");
1678 if (promises_expired())
1679 ptr += sprintf(ptr, "[promise expired]");
1680 if (promises->size() != 0)
1681 ptr += sprintf(ptr, "[unresolved promise]");
1683 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1687 * Returns whether the current completed trace is feasible, except for pending
1688 * release sequences.
1690 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1692 return !is_infeasible() && promises->size() == 0;
1696 * Check if the current partial trace is infeasible. Does not check any
1697 * end-of-execution flags, which might rule out the execution. Thus, this is
1698 * useful only for ruling an execution as infeasible.
1699 * @return whether the current partial trace is infeasible.
1701 bool ModelChecker::is_infeasible() const
1703 return mo_graph->checkForCycles() ||
1704 priv->no_valid_reads ||
1705 priv->failed_promise ||
1706 priv->too_many_reads ||
1707 priv->bad_synchronization ||
1711 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1712 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1713 ModelAction *lastread = get_last_action(act->get_tid());
1714 lastread->process_rmw(act);
1715 if (act->is_rmw()) {
1716 if (lastread->get_reads_from())
1717 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1719 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1720 mo_graph->commitChanges();
1726 * A helper function for ModelChecker::check_recency, to check if the current
1727 * thread is able to read from a different write/promise for 'params.maxreads'
1728 * number of steps and if that write/promise should become visible (i.e., is
1729 * ordered later in the modification order). This helps model memory liveness.
1731 * @param curr The current action. Must be a read.
1732 * @param rf The write/promise from which we plan to read
1733 * @param other_rf The write/promise from which we may read
1734 * @return True if we were able to read from other_rf for params.maxreads steps
1736 template <typename T, typename U>
1737 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1739 /* Need a different write/promise */
1740 if (other_rf->equals(rf))
1743 /* Only look for "newer" writes/promises */
1744 if (!mo_graph->checkReachable(rf, other_rf))
1747 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1748 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1749 action_list_t::reverse_iterator rit = list->rbegin();
1750 ASSERT((*rit) == curr);
1751 /* Skip past curr */
1754 /* Does this write/promise work for everyone? */
1755 for (int i = 0; i < params.maxreads; i++, rit++) {
1756 ModelAction *act = *rit;
1757 if (!act->may_read_from(other_rf))
1764 * Checks whether a thread has read from the same write or Promise for too many
1765 * times without seeing the effects of a later write/Promise.
1768 * 1) there must a different write/promise that we could read from,
1769 * 2) we must have read from the same write/promise in excess of maxreads times,
1770 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1771 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1773 * If so, we decide that the execution is no longer feasible.
1775 * @param curr The current action. Must be a read.
1776 * @param rf The ModelAction/Promise from which we might read.
1777 * @return True if the read should succeed; false otherwise
1779 template <typename T>
1780 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1782 if (!params.maxreads)
1785 //NOTE: Next check is just optimization, not really necessary....
1786 if (curr->get_node()->get_read_from_past_size() +
1787 curr->get_node()->get_read_from_promise_size() <= 1)
1790 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1791 int tid = id_to_int(curr->get_tid());
1792 ASSERT(tid < (int)thrd_lists->size());
1793 action_list_t *list = &(*thrd_lists)[tid];
1794 action_list_t::reverse_iterator rit = list->rbegin();
1795 ASSERT((*rit) == curr);
1796 /* Skip past curr */
1799 action_list_t::reverse_iterator ritcopy = rit;
1800 /* See if we have enough reads from the same value */
1801 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1802 if (ritcopy == list->rend())
1804 ModelAction *act = *ritcopy;
1805 if (!act->is_read())
1807 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1809 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1811 if (act->get_node()->get_read_from_past_size() +
1812 act->get_node()->get_read_from_promise_size() <= 1)
1815 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1816 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1817 if (should_read_instead(curr, rf, write))
1818 return false; /* liveness failure */
1820 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1821 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1822 if (should_read_instead(curr, rf, promise))
1823 return false; /* liveness failure */
1829 * Updates the mo_graph with the constraints imposed from the current
1832 * Basic idea is the following: Go through each other thread and find
1833 * the last action that happened before our read. Two cases:
1835 * (1) The action is a write => that write must either occur before
1836 * the write we read from or be the write we read from.
1838 * (2) The action is a read => the write that that action read from
1839 * must occur before the write we read from or be the same write.
1841 * @param curr The current action. Must be a read.
1842 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1843 * @return True if modification order edges were added; false otherwise
1845 template <typename rf_type>
1846 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1848 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1851 ASSERT(curr->is_read());
1853 /* Last SC fence in the current thread */
1854 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1855 ModelAction *last_sc_write = NULL;
1856 if (curr->is_seqcst())
1857 last_sc_write = get_last_seq_cst_write(curr);
1859 /* Iterate over all threads */
1860 for (i = 0; i < thrd_lists->size(); i++) {
1861 /* Last SC fence in thread i */
1862 ModelAction *last_sc_fence_thread_local = NULL;
1863 if (int_to_id((int)i) != curr->get_tid())
1864 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1866 /* Last SC fence in thread i, before last SC fence in current thread */
1867 ModelAction *last_sc_fence_thread_before = NULL;
1868 if (last_sc_fence_local)
1869 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1871 /* Iterate over actions in thread, starting from most recent */
1872 action_list_t *list = &(*thrd_lists)[i];
1873 action_list_t::reverse_iterator rit;
1874 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1875 ModelAction *act = *rit;
1880 /* Don't want to add reflexive edges on 'rf' */
1881 if (act->equals(rf)) {
1882 if (act->happens_before(curr))
1888 if (act->is_write()) {
1889 /* C++, Section 29.3 statement 5 */
1890 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1891 *act < *last_sc_fence_thread_local) {
1892 added = mo_graph->addEdge(act, rf) || added;
1895 /* C++, Section 29.3 statement 4 */
1896 else if (act->is_seqcst() && last_sc_fence_local &&
1897 *act < *last_sc_fence_local) {
1898 added = mo_graph->addEdge(act, rf) || added;
1901 /* C++, Section 29.3 statement 6 */
1902 else if (last_sc_fence_thread_before &&
1903 *act < *last_sc_fence_thread_before) {
1904 added = mo_graph->addEdge(act, rf) || added;
1909 /* C++, Section 29.3 statement 3 (second subpoint) */
1910 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1911 added = mo_graph->addEdge(act, rf) || added;
1916 * Include at most one act per-thread that "happens
1919 if (act->happens_before(curr)) {
1920 if (act->is_write()) {
1921 added = mo_graph->addEdge(act, rf) || added;
1923 const ModelAction *prevrf = act->get_reads_from();
1924 const Promise *prevrf_promise = act->get_reads_from_promise();
1926 if (!prevrf->equals(rf))
1927 added = mo_graph->addEdge(prevrf, rf) || added;
1928 } else if (!prevrf_promise->equals(rf)) {
1929 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1938 * All compatible, thread-exclusive promises must be ordered after any
1939 * concrete loads from the same thread
1941 for (unsigned int i = 0; i < promises->size(); i++)
1942 if ((*promises)[i]->is_compatible_exclusive(curr))
1943 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1949 * Updates the mo_graph with the constraints imposed from the current write.
1951 * Basic idea is the following: Go through each other thread and find
1952 * the lastest action that happened before our write. Two cases:
1954 * (1) The action is a write => that write must occur before
1957 * (2) The action is a read => the write that that action read from
1958 * must occur before the current write.
1960 * This method also handles two other issues:
1962 * (I) Sequential Consistency: Making sure that if the current write is
1963 * seq_cst, that it occurs after the previous seq_cst write.
1965 * (II) Sending the write back to non-synchronizing reads.
1967 * @param curr The current action. Must be a write.
1968 * @param send_fv A vector for stashing reads to which we may pass our future
1969 * value. If NULL, then don't record any future values.
1970 * @return True if modification order edges were added; false otherwise
1972 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1974 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1977 ASSERT(curr->is_write());
1979 if (curr->is_seqcst()) {
1980 /* We have to at least see the last sequentially consistent write,
1981 so we are initialized. */
1982 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1983 if (last_seq_cst != NULL) {
1984 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1988 /* Last SC fence in the current thread */
1989 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1991 /* Iterate over all threads */
1992 for (i = 0; i < thrd_lists->size(); i++) {
1993 /* Last SC fence in thread i, before last SC fence in current thread */
1994 ModelAction *last_sc_fence_thread_before = NULL;
1995 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1996 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1998 /* Iterate over actions in thread, starting from most recent */
1999 action_list_t *list = &(*thrd_lists)[i];
2000 action_list_t::reverse_iterator rit;
2001 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2002 ModelAction *act = *rit;
2005 * 1) If RMW and it actually read from something, then we
2006 * already have all relevant edges, so just skip to next
2009 * 2) If RMW and it didn't read from anything, we should
2010 * whatever edge we can get to speed up convergence.
2012 * 3) If normal write, we need to look at earlier actions, so
2013 * continue processing list.
2015 if (curr->is_rmw()) {
2016 if (curr->get_reads_from() != NULL)
2024 /* C++, Section 29.3 statement 7 */
2025 if (last_sc_fence_thread_before && act->is_write() &&
2026 *act < *last_sc_fence_thread_before) {
2027 added = mo_graph->addEdge(act, curr) || added;
2032 * Include at most one act per-thread that "happens
2035 if (act->happens_before(curr)) {
2037 * Note: if act is RMW, just add edge:
2039 * The following edge should be handled elsewhere:
2040 * readfrom(act) --mo--> act
2042 if (act->is_write())
2043 added = mo_graph->addEdge(act, curr) || added;
2044 else if (act->is_read()) {
2045 //if previous read accessed a null, just keep going
2046 if (act->get_reads_from() == NULL)
2048 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2051 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2052 !act->same_thread(curr)) {
2053 /* We have an action that:
2054 (1) did not happen before us
2055 (2) is a read and we are a write
2056 (3) cannot synchronize with us
2057 (4) is in a different thread
2059 that read could potentially read from our write. Note that
2060 these checks are overly conservative at this point, we'll
2061 do more checks before actually removing the
2065 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2066 if (!is_infeasible())
2067 send_fv->push_back(act);
2068 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2069 add_future_value(curr, act);
2076 * All compatible, thread-exclusive promises must be ordered after any
2077 * concrete stores to the same thread, or else they can be merged with
2080 for (unsigned int i = 0; i < promises->size(); i++)
2081 if ((*promises)[i]->is_compatible_exclusive(curr))
2082 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2087 /** Arbitrary reads from the future are not allowed. Section 29.3
2088 * part 9 places some constraints. This method checks one result of constraint
2089 * constraint. Others require compiler support. */
2090 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2092 if (!writer->is_rmw())
2095 if (!reader->is_rmw())
2098 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2099 if (search == reader)
2101 if (search->get_tid() == reader->get_tid() &&
2102 search->happens_before(reader))
2110 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2111 * some constraints. This method checks one the following constraint (others
2112 * require compiler support):
2114 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2116 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2118 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2120 /* Iterate over all threads */
2121 for (i = 0; i < thrd_lists->size(); i++) {
2122 const ModelAction *write_after_read = NULL;
2124 /* Iterate over actions in thread, starting from most recent */
2125 action_list_t *list = &(*thrd_lists)[i];
2126 action_list_t::reverse_iterator rit;
2127 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2128 ModelAction *act = *rit;
2130 /* Don't disallow due to act == reader */
2131 if (!reader->happens_before(act) || reader == act)
2133 else if (act->is_write())
2134 write_after_read = act;
2135 else if (act->is_read() && act->get_reads_from() != NULL)
2136 write_after_read = act->get_reads_from();
2139 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2146 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2147 * The ModelAction under consideration is expected to be taking part in
2148 * release/acquire synchronization as an object of the "reads from" relation.
2149 * Note that this can only provide release sequence support for RMW chains
2150 * which do not read from the future, as those actions cannot be traced until
2151 * their "promise" is fulfilled. Similarly, we may not even establish the
2152 * presence of a release sequence with certainty, as some modification order
2153 * constraints may be decided further in the future. Thus, this function
2154 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2155 * and a boolean representing certainty.
2157 * @param rf The action that might be part of a release sequence. Must be a
2159 * @param release_heads A pass-by-reference style return parameter. After
2160 * execution of this function, release_heads will contain the heads of all the
2161 * relevant release sequences, if any exists with certainty
2162 * @param pending A pass-by-reference style return parameter which is only used
2163 * when returning false (i.e., uncertain). Returns most information regarding
2164 * an uncertain release sequence, including any write operations that might
2165 * break the sequence.
2166 * @return true, if the ModelChecker is certain that release_heads is complete;
2169 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2170 rel_heads_list_t *release_heads,
2171 struct release_seq *pending) const
2173 /* Only check for release sequences if there are no cycles */
2174 if (mo_graph->checkForCycles())
2177 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2178 ASSERT(rf->is_write());
2180 if (rf->is_release())
2181 release_heads->push_back(rf);
2182 else if (rf->get_last_fence_release())
2183 release_heads->push_back(rf->get_last_fence_release());
2185 break; /* End of RMW chain */
2187 /** @todo Need to be smarter here... In the linux lock
2188 * example, this will run to the beginning of the program for
2190 /** @todo The way to be smarter here is to keep going until 1
2191 * thread has a release preceded by an acquire and you've seen
2194 /* acq_rel RMW is a sufficient stopping condition */
2195 if (rf->is_acquire() && rf->is_release())
2196 return true; /* complete */
2199 /* read from future: need to settle this later */
2201 return false; /* incomplete */
2204 if (rf->is_release())
2205 return true; /* complete */
2207 /* else relaxed write
2208 * - check for fence-release in the same thread (29.8, stmt. 3)
2209 * - check modification order for contiguous subsequence
2210 * -> rf must be same thread as release */
2212 const ModelAction *fence_release = rf->get_last_fence_release();
2213 /* Synchronize with a fence-release unconditionally; we don't need to
2214 * find any more "contiguous subsequence..." for it */
2216 release_heads->push_back(fence_release);
2218 int tid = id_to_int(rf->get_tid());
2219 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2220 action_list_t *list = &(*thrd_lists)[tid];
2221 action_list_t::const_reverse_iterator rit;
2223 /* Find rf in the thread list */
2224 rit = std::find(list->rbegin(), list->rend(), rf);
2225 ASSERT(rit != list->rend());
2227 /* Find the last {write,fence}-release */
2228 for (; rit != list->rend(); rit++) {
2229 if (fence_release && *(*rit) < *fence_release)
2231 if ((*rit)->is_release())
2234 if (rit == list->rend()) {
2235 /* No write-release in this thread */
2236 return true; /* complete */
2237 } else if (fence_release && *(*rit) < *fence_release) {
2238 /* The fence-release is more recent (and so, "stronger") than
2239 * the most recent write-release */
2240 return true; /* complete */
2241 } /* else, need to establish contiguous release sequence */
2242 ModelAction *release = *rit;
2244 ASSERT(rf->same_thread(release));
2246 pending->writes.clear();
2248 bool certain = true;
2249 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2250 if (id_to_int(rf->get_tid()) == (int)i)
2252 list = &(*thrd_lists)[i];
2254 /* Can we ensure no future writes from this thread may break
2255 * the release seq? */
2256 bool future_ordered = false;
2258 ModelAction *last = get_last_action(int_to_id(i));
2259 Thread *th = get_thread(int_to_id(i));
2260 if ((last && rf->happens_before(last)) ||
2263 future_ordered = true;
2265 ASSERT(!th->is_model_thread() || future_ordered);
2267 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2268 const ModelAction *act = *rit;
2269 /* Reach synchronization -> this thread is complete */
2270 if (act->happens_before(release))
2272 if (rf->happens_before(act)) {
2273 future_ordered = true;
2277 /* Only non-RMW writes can break release sequences */
2278 if (!act->is_write() || act->is_rmw())
2281 /* Check modification order */
2282 if (mo_graph->checkReachable(rf, act)) {
2283 /* rf --mo--> act */
2284 future_ordered = true;
2287 if (mo_graph->checkReachable(act, release))
2288 /* act --mo--> release */
2290 if (mo_graph->checkReachable(release, act) &&
2291 mo_graph->checkReachable(act, rf)) {
2292 /* release --mo-> act --mo--> rf */
2293 return true; /* complete */
2295 /* act may break release sequence */
2296 pending->writes.push_back(act);
2299 if (!future_ordered)
2300 certain = false; /* This thread is uncertain */
2304 release_heads->push_back(release);
2305 pending->writes.clear();
2307 pending->release = release;
2314 * An interface for getting the release sequence head(s) with which a
2315 * given ModelAction must synchronize. This function only returns a non-empty
2316 * result when it can locate a release sequence head with certainty. Otherwise,
2317 * it may mark the internal state of the ModelChecker so that it will handle
2318 * the release sequence at a later time, causing @a acquire to update its
2319 * synchronization at some later point in execution.
2321 * @param acquire The 'acquire' action that may synchronize with a release
2323 * @param read The read action that may read from a release sequence; this may
2324 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2325 * when 'acquire' is a fence-acquire)
2326 * @param release_heads A pass-by-reference return parameter. Will be filled
2327 * with the head(s) of the release sequence(s), if they exists with certainty.
2328 * @see ModelChecker::release_seq_heads
2330 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2331 ModelAction *read, rel_heads_list_t *release_heads)
2333 const ModelAction *rf = read->get_reads_from();
2334 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2335 sequence->acquire = acquire;
2336 sequence->read = read;
2338 if (!release_seq_heads(rf, release_heads, sequence)) {
2339 /* add act to 'lazy checking' list */
2340 pending_rel_seqs->push_back(sequence);
2342 snapshot_free(sequence);
2347 * Attempt to resolve all stashed operations that might synchronize with a
2348 * release sequence for a given location. This implements the "lazy" portion of
2349 * determining whether or not a release sequence was contiguous, since not all
2350 * modification order information is present at the time an action occurs.
2352 * @param location The location/object that should be checked for release
2353 * sequence resolutions. A NULL value means to check all locations.
2354 * @param work_queue The work queue to which to add work items as they are
2356 * @return True if any updates occurred (new synchronization, new mo_graph
2359 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2361 bool updated = false;
2362 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2363 while (it != pending_rel_seqs->end()) {
2364 struct release_seq *pending = *it;
2365 ModelAction *acquire = pending->acquire;
2366 const ModelAction *read = pending->read;
2368 /* Only resolve sequences on the given location, if provided */
2369 if (location && read->get_location() != location) {
2374 const ModelAction *rf = read->get_reads_from();
2375 rel_heads_list_t release_heads;
2377 complete = release_seq_heads(rf, &release_heads, pending);
2378 for (unsigned int i = 0; i < release_heads.size(); i++) {
2379 if (!acquire->has_synchronized_with(release_heads[i])) {
2380 if (acquire->synchronize_with(release_heads[i]))
2383 set_bad_synchronization();
2388 /* Re-check all pending release sequences */
2389 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2390 /* Re-check read-acquire for mo_graph edges */
2391 if (acquire->is_read())
2392 work_queue->push_back(MOEdgeWorkEntry(acquire));
2394 /* propagate synchronization to later actions */
2395 action_list_t::reverse_iterator rit = action_trace->rbegin();
2396 for (; (*rit) != acquire; rit++) {
2397 ModelAction *propagate = *rit;
2398 if (acquire->happens_before(propagate)) {
2399 propagate->synchronize_with(acquire);
2400 /* Re-check 'propagate' for mo_graph edges */
2401 work_queue->push_back(MOEdgeWorkEntry(propagate));
2406 it = pending_rel_seqs->erase(it);
2407 snapshot_free(pending);
2413 // If we resolved promises or data races, see if we have realized a data race.
2420 * Performs various bookkeeping operations for the current ModelAction. For
2421 * instance, adds action to the per-object, per-thread action vector and to the
2422 * action trace list of all thread actions.
2424 * @param act is the ModelAction to add.
2426 void ModelChecker::add_action_to_lists(ModelAction *act)
2428 int tid = id_to_int(act->get_tid());
2429 ModelAction *uninit = NULL;
2431 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2432 if (list->empty() && act->is_atomic_var()) {
2433 uninit = get_uninitialized_action(act);
2434 uninit_id = id_to_int(uninit->get_tid());
2435 list->push_front(uninit);
2437 list->push_back(act);
2439 action_trace->push_back(act);
2441 action_trace->push_front(uninit);
2443 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2444 if (tid >= (int)vec->size())
2445 vec->resize(priv->next_thread_id);
2446 (*vec)[tid].push_back(act);
2448 (*vec)[uninit_id].push_front(uninit);
2450 if ((int)thrd_last_action->size() <= tid)
2451 thrd_last_action->resize(get_num_threads());
2452 (*thrd_last_action)[tid] = act;
2454 (*thrd_last_action)[uninit_id] = uninit;
2456 if (act->is_fence() && act->is_release()) {
2457 if ((int)thrd_last_fence_release->size() <= tid)
2458 thrd_last_fence_release->resize(get_num_threads());
2459 (*thrd_last_fence_release)[tid] = act;
2462 if (act->is_wait()) {
2463 void *mutex_loc = (void *) act->get_value();
2464 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2466 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2467 if (tid >= (int)vec->size())
2468 vec->resize(priv->next_thread_id);
2469 (*vec)[tid].push_back(act);
2474 * @brief Get the last action performed by a particular Thread
2475 * @param tid The thread ID of the Thread in question
2476 * @return The last action in the thread
2478 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2480 int threadid = id_to_int(tid);
2481 if (threadid < (int)thrd_last_action->size())
2482 return (*thrd_last_action)[id_to_int(tid)];
2488 * @brief Get the last fence release performed by a particular Thread
2489 * @param tid The thread ID of the Thread in question
2490 * @return The last fence release in the thread, if one exists; NULL otherwise
2492 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2494 int threadid = id_to_int(tid);
2495 if (threadid < (int)thrd_last_fence_release->size())
2496 return (*thrd_last_fence_release)[id_to_int(tid)];
2502 * Gets the last memory_order_seq_cst write (in the total global sequence)
2503 * performed on a particular object (i.e., memory location), not including the
2505 * @param curr The current ModelAction; also denotes the object location to
2507 * @return The last seq_cst write
2509 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2511 void *location = curr->get_location();
2512 action_list_t *list = get_safe_ptr_action(obj_map, location);
2513 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2514 action_list_t::reverse_iterator rit;
2515 for (rit = list->rbegin(); (*rit) != curr; rit++)
2517 rit++; /* Skip past curr */
2518 for ( ; rit != list->rend(); rit++)
2519 if ((*rit)->is_write() && (*rit)->is_seqcst())
2525 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2526 * performed in a particular thread, prior to a particular fence.
2527 * @param tid The ID of the thread to check
2528 * @param before_fence The fence from which to begin the search; if NULL, then
2529 * search for the most recent fence in the thread.
2530 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2532 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2534 /* All fences should have NULL location */
2535 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2536 action_list_t::reverse_iterator rit = list->rbegin();
2539 for (; rit != list->rend(); rit++)
2540 if (*rit == before_fence)
2543 ASSERT(*rit == before_fence);
2547 for (; rit != list->rend(); rit++)
2548 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2554 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2555 * location). This function identifies the mutex according to the current
2556 * action, which is presumed to perform on the same mutex.
2557 * @param curr The current ModelAction; also denotes the object location to
2559 * @return The last unlock operation
2561 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2563 void *location = curr->get_location();
2564 action_list_t *list = get_safe_ptr_action(obj_map, location);
2565 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2566 action_list_t::reverse_iterator rit;
2567 for (rit = list->rbegin(); rit != list->rend(); rit++)
2568 if ((*rit)->is_unlock() || (*rit)->is_wait())
2573 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2575 ModelAction *parent = get_last_action(tid);
2577 parent = get_thread(tid)->get_creation();
2582 * Returns the clock vector for a given thread.
2583 * @param tid The thread whose clock vector we want
2584 * @return Desired clock vector
2586 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2588 return get_parent_action(tid)->get_cv();
2592 * @brief Find the promise (if any) to resolve for the current action and
2593 * remove it from the pending promise vector
2594 * @param curr The current ModelAction. Should be a write.
2595 * @return The Promise to resolve, if any; otherwise NULL
2597 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2599 for (unsigned int i = 0; i < promises->size(); i++)
2600 if (curr->get_node()->get_promise(i)) {
2601 Promise *ret = (*promises)[i];
2602 promises->erase(promises->begin() + i);
2609 * Resolve a Promise with a current write.
2610 * @param write The ModelAction that is fulfilling Promises
2611 * @param promise The Promise to resolve
2612 * @return True if the Promise was successfully resolved; false otherwise
2614 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2616 ModelVector<ModelAction *> actions_to_check;
2618 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2619 ModelAction *read = promise->get_reader(i);
2620 read_from(read, write);
2621 actions_to_check.push_back(read);
2623 /* Make sure the promise's value matches the write's value */
2624 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2625 if (!mo_graph->resolvePromise(promise, write))
2626 priv->failed_promise = true;
2629 * @todo It is possible to end up in an inconsistent state, where a
2630 * "resolved" promise may still be referenced if
2631 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2633 * Note that the inconsistency only matters when dumping mo_graph to
2639 //Check whether reading these writes has made threads unable to
2641 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2642 ModelAction *read = actions_to_check[i];
2643 mo_check_promises(read, true);
2650 * Compute the set of promises that could potentially be satisfied by this
2651 * action. Note that the set computation actually appears in the Node, not in
2653 * @param curr The ModelAction that may satisfy promises
2655 void ModelChecker::compute_promises(ModelAction *curr)
2657 for (unsigned int i = 0; i < promises->size(); i++) {
2658 Promise *promise = (*promises)[i];
2659 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2662 bool satisfy = true;
2663 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2664 const ModelAction *act = promise->get_reader(j);
2665 if (act->happens_before(curr) ||
2666 act->could_synchronize_with(curr)) {
2672 curr->get_node()->set_promise(i);
2676 /** Checks promises in response to change in ClockVector Threads. */
2677 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2679 for (unsigned int i = 0; i < promises->size(); i++) {
2680 Promise *promise = (*promises)[i];
2681 if (!promise->thread_is_available(tid))
2683 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2684 const ModelAction *act = promise->get_reader(j);
2685 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2686 merge_cv->synchronized_since(act)) {
2687 if (promise->eliminate_thread(tid)) {
2688 /* Promise has failed */
2689 priv->failed_promise = true;
2697 void ModelChecker::check_promises_thread_disabled()
2699 for (unsigned int i = 0; i < promises->size(); i++) {
2700 Promise *promise = (*promises)[i];
2701 if (promise->has_failed()) {
2702 priv->failed_promise = true;
2709 * @brief Checks promises in response to addition to modification order for
2712 * We test whether threads are still available for satisfying promises after an
2713 * addition to our modification order constraints. Those that are unavailable
2714 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2715 * that promise has failed.
2717 * @param act The ModelAction which updated the modification order
2718 * @param is_read_check Should be true if act is a read and we must check for
2719 * updates to the store from which it read (there is a distinction here for
2720 * RMW's, which are both a load and a store)
2722 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2724 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2726 for (unsigned int i = 0; i < promises->size(); i++) {
2727 Promise *promise = (*promises)[i];
2729 // Is this promise on the same location?
2730 if (!promise->same_location(write))
2733 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2734 const ModelAction *pread = promise->get_reader(j);
2735 if (!pread->happens_before(act))
2737 if (mo_graph->checkPromise(write, promise)) {
2738 priv->failed_promise = true;
2744 // Don't do any lookups twice for the same thread
2745 if (!promise->thread_is_available(act->get_tid()))
2748 if (mo_graph->checkReachable(promise, write)) {
2749 if (mo_graph->checkPromise(write, promise)) {
2750 priv->failed_promise = true;
2758 * Compute the set of writes that may break the current pending release
2759 * sequence. This information is extracted from previou release sequence
2762 * @param curr The current ModelAction. Must be a release sequence fixup
2765 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2767 if (pending_rel_seqs->empty())
2770 struct release_seq *pending = pending_rel_seqs->back();
2771 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2772 const ModelAction *write = pending->writes[i];
2773 curr->get_node()->add_relseq_break(write);
2776 /* NULL means don't break the sequence; just synchronize */
2777 curr->get_node()->add_relseq_break(NULL);
2781 * Build up an initial set of all past writes that this 'read' action may read
2782 * from, as well as any previously-observed future values that must still be valid.
2784 * @param curr is the current ModelAction that we are exploring; it must be a
2787 void ModelChecker::build_may_read_from(ModelAction *curr)
2789 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2791 ASSERT(curr->is_read());
2793 ModelAction *last_sc_write = NULL;
2795 if (curr->is_seqcst())
2796 last_sc_write = get_last_seq_cst_write(curr);
2798 /* Iterate over all threads */
2799 for (i = 0; i < thrd_lists->size(); i++) {
2800 /* Iterate over actions in thread, starting from most recent */
2801 action_list_t *list = &(*thrd_lists)[i];
2802 action_list_t::reverse_iterator rit;
2803 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2804 ModelAction *act = *rit;
2806 /* Only consider 'write' actions */
2807 if (!act->is_write() || act == curr)
2810 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2811 bool allow_read = true;
2813 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2815 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2819 /* Only add feasible reads */
2820 mo_graph->startChanges();
2821 r_modification_order(curr, act);
2822 if (!is_infeasible())
2823 curr->get_node()->add_read_from_past(act);
2824 mo_graph->rollbackChanges();
2827 /* Include at most one act per-thread that "happens before" curr */
2828 if (act->happens_before(curr))
2833 /* Inherit existing, promised future values */
2834 for (i = 0; i < promises->size(); i++) {
2835 const Promise *promise = (*promises)[i];
2836 const ModelAction *promise_read = promise->get_reader(0);
2837 if (promise_read->same_var(curr)) {
2838 /* Only add feasible future-values */
2839 mo_graph->startChanges();
2840 r_modification_order(curr, promise);
2841 if (!is_infeasible())
2842 curr->get_node()->add_read_from_promise(promise_read);
2843 mo_graph->rollbackChanges();
2847 /* We may find no valid may-read-from only if the execution is doomed */
2848 if (!curr->get_node()->read_from_size()) {
2849 priv->no_valid_reads = true;
2853 if (DBG_ENABLED()) {
2854 model_print("Reached read action:\n");
2856 model_print("Printing read_from_past\n");
2857 curr->get_node()->print_read_from_past();
2858 model_print("End printing read_from_past\n");
2862 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2864 for ( ; write != NULL; write = write->get_reads_from()) {
2865 /* UNINIT actions don't have a Node, and they never sleep */
2866 if (write->is_uninitialized())
2868 Node *prevnode = write->get_node()->get_parent();
2870 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2871 if (write->is_release() && thread_sleep)
2873 if (!write->is_rmw())
2880 * @brief Get an action representing an uninitialized atomic
2882 * This function may create a new one or try to retrieve one from the NodeStack
2884 * @param curr The current action, which prompts the creation of an UNINIT action
2885 * @return A pointer to the UNINIT ModelAction
2887 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2889 Node *node = curr->get_node();
2890 ModelAction *act = node->get_uninit_action();
2892 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2893 node->set_uninit_action(act);
2895 act->create_cv(NULL);
2899 static void print_list(action_list_t *list)
2901 action_list_t::iterator it;
2903 model_print("---------------------------------------------------------------------\n");
2905 unsigned int hash = 0;
2907 for (it = list->begin(); it != list->end(); it++) {
2908 const ModelAction *act = *it;
2909 if (act->get_seq_number() > 0)
2911 hash = hash^(hash<<3)^((*it)->hash());
2913 model_print("HASH %u\n", hash);
2914 model_print("---------------------------------------------------------------------\n");
2917 #if SUPPORT_MOD_ORDER_DUMP
2918 void ModelChecker::dumpGraph(char *filename) const
2921 sprintf(buffer, "%s.dot", filename);
2922 FILE *file = fopen(buffer, "w");
2923 fprintf(file, "digraph %s {\n", filename);
2924 mo_graph->dumpNodes(file);
2925 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2927 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2928 ModelAction *act = *it;
2929 if (act->is_read()) {
2930 mo_graph->dot_print_node(file, act);
2931 if (act->get_reads_from())
2932 mo_graph->dot_print_edge(file,
2933 act->get_reads_from(),
2935 "label=\"rf\", color=red, weight=2");
2937 mo_graph->dot_print_edge(file,
2938 act->get_reads_from_promise(),
2940 "label=\"rf\", color=red");
2942 if (thread_array[act->get_tid()]) {
2943 mo_graph->dot_print_edge(file,
2944 thread_array[id_to_int(act->get_tid())],
2946 "label=\"sb\", color=blue, weight=400");
2949 thread_array[act->get_tid()] = act;
2951 fprintf(file, "}\n");
2952 model_free(thread_array);
2957 /** @brief Prints an execution trace summary. */
2958 void ModelChecker::print_summary() const
2960 #if SUPPORT_MOD_ORDER_DUMP
2961 char buffername[100];
2962 sprintf(buffername, "exec%04u", stats.num_total);
2963 mo_graph->dumpGraphToFile(buffername);
2964 sprintf(buffername, "graph%04u", stats.num_total);
2965 dumpGraph(buffername);
2968 model_print("Execution %d:", stats.num_total);
2969 if (isfeasibleprefix()) {
2970 if (scheduler->all_threads_sleeping())
2971 model_print(" SLEEP-SET REDUNDANT");
2974 print_infeasibility(" INFEASIBLE");
2975 print_list(action_trace);
2977 if (!promises->empty()) {
2978 model_print("Pending promises:\n");
2979 for (unsigned int i = 0; i < promises->size(); i++) {
2980 model_print(" [P%u] ", i);
2981 (*promises)[i]->print();
2988 * Add a Thread to the system for the first time. Should only be called once
2990 * @param t The Thread to add
2992 void ModelChecker::add_thread(Thread *t)
2994 thread_map->put(id_to_int(t->get_id()), t);
2995 scheduler->add_thread(t);
2999 * @brief Get a Thread reference by its ID
3000 * @param tid The Thread's ID
3001 * @return A Thread reference
3003 Thread * ModelChecker::get_thread(thread_id_t tid) const
3005 return thread_map->get(id_to_int(tid));
3009 * @brief Get a reference to the Thread in which a ModelAction was executed
3010 * @param act The ModelAction
3011 * @return A Thread reference
3013 Thread * ModelChecker::get_thread(const ModelAction *act) const
3015 return get_thread(act->get_tid());
3019 * @brief Get a Promise's "promise number"
3021 * A "promise number" is an index number that is unique to a promise, valid
3022 * only for a specific snapshot of an execution trace. Promises may come and go
3023 * as they are generated an resolved, so an index only retains meaning for the
3026 * @param promise The Promise to check
3027 * @return The promise index, if the promise still is valid; otherwise -1
3029 int ModelChecker::get_promise_number(const Promise *promise) const
3031 for (unsigned int i = 0; i < promises->size(); i++)
3032 if ((*promises)[i] == promise)
3039 * @brief Check if a Thread is currently enabled
3040 * @param t The Thread to check
3041 * @return True if the Thread is currently enabled
3043 bool ModelChecker::is_enabled(Thread *t) const
3045 return scheduler->is_enabled(t);
3049 * @brief Check if a Thread is currently enabled
3050 * @param tid The ID of the Thread to check
3051 * @return True if the Thread is currently enabled
3053 bool ModelChecker::is_enabled(thread_id_t tid) const
3055 return scheduler->is_enabled(tid);
3059 * Switch from a model-checker context to a user-thread context. This is the
3060 * complement of ModelChecker::switch_to_master and must be called from the
3061 * model-checker context
3063 * @param thread The user-thread to switch to
3065 void ModelChecker::switch_from_master(Thread *thread)
3067 scheduler->set_current_thread(thread);
3068 Thread::swap(&system_context, thread);
3072 * Switch from a user-context to the "master thread" context (a.k.a. system
3073 * context). This switch is made with the intention of exploring a particular
3074 * model-checking action (described by a ModelAction object). Must be called
3075 * from a user-thread context.
3077 * @param act The current action that will be explored. May be NULL only if
3078 * trace is exiting via an assertion (see ModelChecker::set_assert and
3079 * ModelChecker::has_asserted).
3080 * @return Return the value returned by the current action
3082 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3085 Thread *old = thread_current();
3086 scheduler->set_current_thread(NULL);
3087 ASSERT(!old->get_pending());
3088 old->set_pending(act);
3089 if (Thread::swap(old, &system_context) < 0) {
3090 perror("swap threads");
3093 return old->get_return_value();
3097 * Takes the next step in the execution, if possible.
3098 * @param curr The current step to take
3099 * @return Returns the next Thread to run, if any; NULL if this execution
3102 Thread * ModelChecker::take_step(ModelAction *curr)
3104 Thread *curr_thrd = get_thread(curr);
3105 ASSERT(curr_thrd->get_state() == THREAD_READY);
3107 curr = check_current_action(curr);
3109 /* Infeasible -> don't take any more steps */
3110 if (is_infeasible())
3112 else if (isfeasibleprefix() && have_bug_reports()) {
3117 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3120 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3121 scheduler->remove_thread(curr_thrd);
3123 Thread *next_thrd = NULL;
3125 next_thrd = action_select_next_thread(curr);
3127 next_thrd = get_next_thread();
3129 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3130 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3135 /** Wrapper to run the user's main function, with appropriate arguments */
3136 void user_main_wrapper(void *)
3138 user_main(model->params.argc, model->params.argv);
3141 /** @brief Run ModelChecker for the user program */
3142 void ModelChecker::run()
3146 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3151 * Stash next pending action(s) for thread(s). There
3152 * should only need to stash one thread's action--the
3153 * thread which just took a step--plus the first step
3154 * for any newly-created thread
3156 for (unsigned int i = 0; i < get_num_threads(); i++) {
3157 thread_id_t tid = int_to_id(i);
3158 Thread *thr = get_thread(tid);
3159 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3160 switch_from_master(thr);
3161 if (is_circular_wait(thr))
3162 assert_bug("Deadlock detected");
3166 /* Catch assertions from prior take_step or from
3167 * between-ModelAction bugs (e.g., data races) */
3171 /* Consume the next action for a Thread */
3172 ModelAction *curr = t->get_pending();
3173 t->set_pending(NULL);
3174 t = take_step(curr);
3175 } while (t && !t->is_model_thread());
3178 * Launch end-of-execution release sequence fixups only when
3179 * the execution is otherwise feasible AND there are:
3181 * (1) pending release sequences
3182 * (2) pending assertions that could be invalidated by a change
3183 * in clock vectors (i.e., data races)
3184 * (3) no pending promises
3186 while (!pending_rel_seqs->empty() &&
3187 is_feasible_prefix_ignore_relseq() &&
3188 !unrealizedraces.empty()) {
3189 model_print("*** WARNING: release sequence fixup action "
3190 "(%zu pending release seuqence(s)) ***\n",
3191 pending_rel_seqs->size());
3192 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3193 std::memory_order_seq_cst, NULL, VALUE_NONE,
3197 } while (next_execution());
3199 model_print("******* Model-checking complete: *******\n");