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 std::vector< bug_message *, SnapshotAlloc<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 *, std::vector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
90 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
91 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
92 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
93 thrd_last_fence_release(new std::vector< ModelAction *, SnapshotAlloc<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 std::vector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
142 std::vector<action_list_t> *tmp = hash->get(ptr);
144 tmp = new std::vector<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 std::vector< ModelAction *, ModelAlloc<ModelAction *> > acquire_fences(get_num_threads(), NULL);
646 std::vector< ModelAction *, ModelAlloc<ModelAction *> > prior_loads(get_num_threads(), NULL);
647 bool found_acquire_fences = false;
648 for ( ; rit != list->rend(); rit++) {
649 ModelAction *prev = *rit;
650 if (act->same_thread(prev))
653 int tid = id_to_int(prev->get_tid());
655 if (prev->is_read() && act->same_var(prev)) {
656 if (prev->is_acquire()) {
657 /* Found most recent load-acquire, don't need
658 * to search for more fences */
659 if (!found_acquire_fences)
662 prior_loads[tid] = prev;
665 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
666 found_acquire_fences = true;
667 acquire_fences[tid] = prev;
671 ModelAction *latest_backtrack = NULL;
672 for (unsigned int i = 0; i < acquire_fences.size(); i++)
673 if (acquire_fences[i] && prior_loads[i])
674 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
675 latest_backtrack = acquire_fences[i];
676 return latest_backtrack;
680 * @brief Find the last backtracking conflict for a ModelAction
682 * This function performs the search for the most recent conflicting action
683 * against which we should perform backtracking. This primary includes pairs of
684 * synchronizing actions which should be explored in the opposite execution
687 * @param act The current action
688 * @return The most recent action which conflicts with act
690 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
692 switch (act->get_type()) {
693 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
697 ModelAction *ret = NULL;
699 /* linear search: from most recent to oldest */
700 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
701 action_list_t::reverse_iterator rit;
702 for (rit = list->rbegin(); rit != list->rend(); rit++) {
703 ModelAction *prev = *rit;
704 if (prev->could_synchronize_with(act)) {
710 ModelAction *ret2 = get_last_fence_conflict(act);
720 case ATOMIC_TRYLOCK: {
721 /* linear search: from most recent to oldest */
722 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
723 action_list_t::reverse_iterator rit;
724 for (rit = list->rbegin(); rit != list->rend(); rit++) {
725 ModelAction *prev = *rit;
726 if (act->is_conflicting_lock(prev))
731 case ATOMIC_UNLOCK: {
732 /* linear search: from most recent to oldest */
733 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
734 action_list_t::reverse_iterator rit;
735 for (rit = list->rbegin(); rit != list->rend(); rit++) {
736 ModelAction *prev = *rit;
737 if (!act->same_thread(prev) && prev->is_failed_trylock())
743 /* linear search: from most recent to oldest */
744 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
745 action_list_t::reverse_iterator rit;
746 for (rit = list->rbegin(); rit != list->rend(); rit++) {
747 ModelAction *prev = *rit;
748 if (!act->same_thread(prev) && prev->is_failed_trylock())
750 if (!act->same_thread(prev) && prev->is_notify())
756 case ATOMIC_NOTIFY_ALL:
757 case ATOMIC_NOTIFY_ONE: {
758 /* linear search: from most recent to oldest */
759 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
760 action_list_t::reverse_iterator rit;
761 for (rit = list->rbegin(); rit != list->rend(); rit++) {
762 ModelAction *prev = *rit;
763 if (!act->same_thread(prev) && prev->is_wait())
774 /** This method finds backtracking points where we should try to
775 * reorder the parameter ModelAction against.
777 * @param the ModelAction to find backtracking points for.
779 void ModelChecker::set_backtracking(ModelAction *act)
781 Thread *t = get_thread(act);
782 ModelAction *prev = get_last_conflict(act);
786 Node *node = prev->get_node()->get_parent();
788 int low_tid, high_tid;
789 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
790 low_tid = id_to_int(act->get_tid());
791 high_tid = low_tid + 1;
794 high_tid = get_num_threads();
797 for (int i = low_tid; i < high_tid; i++) {
798 thread_id_t tid = int_to_id(i);
800 /* Make sure this thread can be enabled here. */
801 if (i >= node->get_num_threads())
804 /* Don't backtrack into a point where the thread is disabled or sleeping. */
805 if (node->enabled_status(tid) != THREAD_ENABLED)
808 /* Check if this has been explored already */
809 if (node->has_been_explored(tid))
812 /* See if fairness allows */
813 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
815 for (int t = 0; t < node->get_num_threads(); t++) {
816 thread_id_t tother = int_to_id(t);
817 if (node->is_enabled(tother) && node->has_priority(tother)) {
826 /* See if CHESS-like yield fairness allows */
827 if (model->params.yieldon) {
829 for (int t = 0; t < node->get_num_threads(); t++) {
830 thread_id_t tother = int_to_id(t);
831 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
840 /* Cache the latest backtracking point */
841 set_latest_backtrack(prev);
843 /* If this is a new backtracking point, mark the tree */
844 if (!node->set_backtrack(tid))
846 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
847 id_to_int(prev->get_tid()),
848 id_to_int(t->get_id()));
857 * @brief Cache the a backtracking point as the "most recent", if eligible
859 * Note that this does not prepare the NodeStack for this backtracking
860 * operation, it only caches the action on a per-execution basis
862 * @param act The operation at which we should explore a different next action
863 * (i.e., backtracking point)
864 * @return True, if this action is now the most recent backtracking point;
867 bool ModelChecker::set_latest_backtrack(ModelAction *act)
869 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
870 priv->next_backtrack = act;
877 * Returns last backtracking point. The model checker will explore a different
878 * path for this point in the next execution.
879 * @return The ModelAction at which the next execution should diverge.
881 ModelAction * ModelChecker::get_next_backtrack()
883 ModelAction *next = priv->next_backtrack;
884 priv->next_backtrack = NULL;
889 * Processes a read model action.
890 * @param curr is the read model action to process.
891 * @return True if processing this read updates the mo_graph.
893 bool ModelChecker::process_read(ModelAction *curr)
895 Node *node = curr->get_node();
897 bool updated = false;
898 switch (node->get_read_from_status()) {
899 case READ_FROM_PAST: {
900 const ModelAction *rf = node->get_read_from_past();
903 mo_graph->startChanges();
905 ASSERT(!is_infeasible());
906 if (!check_recency(curr, rf)) {
907 if (node->increment_read_from()) {
908 mo_graph->rollbackChanges();
911 priv->too_many_reads = true;
915 updated = r_modification_order(curr, rf);
917 mo_graph->commitChanges();
918 mo_check_promises(curr, true);
921 case READ_FROM_PROMISE: {
922 Promise *promise = curr->get_node()->get_read_from_promise();
923 if (promise->add_reader(curr))
924 priv->failed_promise = true;
925 curr->set_read_from_promise(promise);
926 mo_graph->startChanges();
927 if (!check_recency(curr, promise))
928 priv->too_many_reads = true;
929 updated = r_modification_order(curr, promise);
930 mo_graph->commitChanges();
933 case READ_FROM_FUTURE: {
934 /* Read from future value */
935 struct future_value fv = node->get_future_value();
936 Promise *promise = new Promise(curr, fv);
937 curr->set_read_from_promise(promise);
938 promises->push_back(promise);
939 mo_graph->startChanges();
940 updated = r_modification_order(curr, promise);
941 mo_graph->commitChanges();
947 get_thread(curr)->set_return_value(curr->get_return_value());
953 * Processes a lock, trylock, or unlock model action. @param curr is
954 * the read model action to process.
956 * The try lock operation checks whether the lock is taken. If not,
957 * it falls to the normal lock operation case. If so, it returns
960 * The lock operation has already been checked that it is enabled, so
961 * it just grabs the lock and synchronizes with the previous unlock.
963 * The unlock operation has to re-enable all of the threads that are
964 * waiting on the lock.
966 * @return True if synchronization was updated; false otherwise
968 bool ModelChecker::process_mutex(ModelAction *curr)
970 std::mutex *mutex = curr->get_mutex();
971 struct std::mutex_state *state = NULL;
974 state = mutex->get_state();
976 switch (curr->get_type()) {
977 case ATOMIC_TRYLOCK: {
978 bool success = !state->locked;
979 curr->set_try_lock(success);
981 get_thread(curr)->set_return_value(0);
984 get_thread(curr)->set_return_value(1);
986 //otherwise fall into the lock case
988 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
989 assert_bug("Lock access before initialization");
990 state->locked = get_thread(curr);
991 ModelAction *unlock = get_last_unlock(curr);
992 //synchronize with the previous unlock statement
993 if (unlock != NULL) {
994 curr->synchronize_with(unlock);
999 case ATOMIC_UNLOCK: {
1001 state->locked = NULL;
1002 //wake up the other threads
1003 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
1004 //activate all the waiting threads
1005 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1006 scheduler->wake(get_thread(*rit));
1013 state->locked = NULL;
1014 //wake up the other threads
1015 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
1016 //activate all the waiting threads
1017 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1018 scheduler->wake(get_thread(*rit));
1021 //check whether we should go to sleep or not...simulate spurious failures
1022 if (curr->get_node()->get_misc() == 0) {
1023 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1025 scheduler->sleep(get_thread(curr));
1029 case ATOMIC_NOTIFY_ALL: {
1030 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1031 //activate all the waiting threads
1032 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1033 scheduler->wake(get_thread(*rit));
1038 case ATOMIC_NOTIFY_ONE: {
1039 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1040 int wakeupthread = curr->get_node()->get_misc();
1041 action_list_t::iterator it = waiters->begin();
1042 advance(it, wakeupthread);
1043 scheduler->wake(get_thread(*it));
1054 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1056 /* Do more ambitious checks now that mo is more complete */
1057 if (mo_may_allow(writer, reader)) {
1058 Node *node = reader->get_node();
1060 /* Find an ancestor thread which exists at the time of the reader */
1061 Thread *write_thread = get_thread(writer);
1062 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1063 write_thread = write_thread->get_parent();
1065 struct future_value fv = {
1066 writer->get_write_value(),
1067 writer->get_seq_number() + params.maxfuturedelay,
1068 write_thread->get_id(),
1070 if (node->add_future_value(fv))
1071 set_latest_backtrack(reader);
1076 * Process a write ModelAction
1077 * @param curr The ModelAction to process
1078 * @return True if the mo_graph was updated or promises were resolved
1080 bool ModelChecker::process_write(ModelAction *curr)
1082 /* Readers to which we may send our future value */
1083 std::vector< ModelAction *, ModelAlloc<ModelAction *> > send_fv;
1085 bool updated_mod_order = w_modification_order(curr, &send_fv);
1086 int promise_idx = get_promise_to_resolve(curr);
1087 const ModelAction *earliest_promise_reader;
1088 bool updated_promises = false;
1090 if (promise_idx >= 0) {
1091 earliest_promise_reader = (*promises)[promise_idx]->get_reader(0);
1092 updated_promises = resolve_promise(curr, promise_idx);
1094 earliest_promise_reader = NULL;
1096 /* Don't send future values to reads after the Promise we resolve */
1097 for (unsigned int i = 0; i < send_fv.size(); i++) {
1098 ModelAction *read = send_fv[i];
1099 if (!earliest_promise_reader || *read < *earliest_promise_reader)
1100 futurevalues->push_back(PendingFutureValue(curr, read));
1103 if (promises->size() == 0) {
1104 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1105 struct PendingFutureValue pfv = (*futurevalues)[i];
1106 add_future_value(pfv.writer, pfv.act);
1108 futurevalues->clear();
1111 mo_graph->commitChanges();
1112 mo_check_promises(curr, false);
1114 get_thread(curr)->set_return_value(VALUE_NONE);
1115 return updated_mod_order || updated_promises;
1119 * Process a fence ModelAction
1120 * @param curr The ModelAction to process
1121 * @return True if synchronization was updated
1123 bool ModelChecker::process_fence(ModelAction *curr)
1126 * fence-relaxed: no-op
1127 * fence-release: only log the occurence (not in this function), for
1128 * use in later synchronization
1129 * fence-acquire (this function): search for hypothetical release
1132 bool updated = false;
1133 if (curr->is_acquire()) {
1134 action_list_t *list = action_trace;
1135 action_list_t::reverse_iterator rit;
1136 /* Find X : is_read(X) && X --sb-> curr */
1137 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1138 ModelAction *act = *rit;
1141 if (act->get_tid() != curr->get_tid())
1143 /* Stop at the beginning of the thread */
1144 if (act->is_thread_start())
1146 /* Stop once we reach a prior fence-acquire */
1147 if (act->is_fence() && act->is_acquire())
1149 if (!act->is_read())
1151 /* read-acquire will find its own release sequences */
1152 if (act->is_acquire())
1155 /* Establish hypothetical release sequences */
1156 rel_heads_list_t release_heads;
1157 get_release_seq_heads(curr, act, &release_heads);
1158 for (unsigned int i = 0; i < release_heads.size(); i++)
1159 if (!curr->synchronize_with(release_heads[i]))
1160 set_bad_synchronization();
1161 if (release_heads.size() != 0)
1169 * @brief Process the current action for thread-related activity
1171 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1172 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1173 * synchronization, etc. This function is a no-op for non-THREAD actions
1174 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1176 * @param curr The current action
1177 * @return True if synchronization was updated or a thread completed
1179 bool ModelChecker::process_thread_action(ModelAction *curr)
1181 bool updated = false;
1183 switch (curr->get_type()) {
1184 case THREAD_CREATE: {
1185 thrd_t *thrd = (thrd_t *)curr->get_location();
1186 struct thread_params *params = (struct thread_params *)curr->get_value();
1187 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1189 th->set_creation(curr);
1190 /* Promises can be satisfied by children */
1191 for (unsigned int i = 0; i < promises->size(); i++) {
1192 Promise *promise = (*promises)[i];
1193 if (promise->thread_is_available(curr->get_tid()))
1194 promise->add_thread(th->get_id());
1199 Thread *blocking = curr->get_thread_operand();
1200 ModelAction *act = get_last_action(blocking->get_id());
1201 curr->synchronize_with(act);
1202 updated = true; /* trigger rel-seq checks */
1205 case THREAD_FINISH: {
1206 Thread *th = get_thread(curr);
1207 while (!th->wait_list_empty()) {
1208 ModelAction *act = th->pop_wait_list();
1209 scheduler->wake(get_thread(act));
1212 /* Completed thread can't satisfy promises */
1213 for (unsigned int i = 0; i < promises->size(); i++) {
1214 Promise *promise = (*promises)[i];
1215 if (promise->thread_is_available(th->get_id()))
1216 if (promise->eliminate_thread(th->get_id()))
1217 priv->failed_promise = true;
1219 updated = true; /* trigger rel-seq checks */
1222 case THREAD_START: {
1223 check_promises(curr->get_tid(), NULL, curr->get_cv());
1234 * @brief Process the current action for release sequence fixup activity
1236 * Performs model-checker release sequence fixups for the current action,
1237 * forcing a single pending release sequence to break (with a given, potential
1238 * "loose" write) or to complete (i.e., synchronize). If a pending release
1239 * sequence forms a complete release sequence, then we must perform the fixup
1240 * synchronization, mo_graph additions, etc.
1242 * @param curr The current action; must be a release sequence fixup action
1243 * @param work_queue The work queue to which to add work items as they are
1246 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1248 const ModelAction *write = curr->get_node()->get_relseq_break();
1249 struct release_seq *sequence = pending_rel_seqs->back();
1250 pending_rel_seqs->pop_back();
1252 ModelAction *acquire = sequence->acquire;
1253 const ModelAction *rf = sequence->rf;
1254 const ModelAction *release = sequence->release;
1258 ASSERT(release->same_thread(rf));
1260 if (write == NULL) {
1262 * @todo Forcing a synchronization requires that we set
1263 * modification order constraints. For instance, we can't allow
1264 * a fixup sequence in which two separate read-acquire
1265 * operations read from the same sequence, where the first one
1266 * synchronizes and the other doesn't. Essentially, we can't
1267 * allow any writes to insert themselves between 'release' and
1271 /* Must synchronize */
1272 if (!acquire->synchronize_with(release)) {
1273 set_bad_synchronization();
1276 /* Re-check all pending release sequences */
1277 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1278 /* Re-check act for mo_graph edges */
1279 work_queue->push_back(MOEdgeWorkEntry(acquire));
1281 /* propagate synchronization to later actions */
1282 action_list_t::reverse_iterator rit = action_trace->rbegin();
1283 for (; (*rit) != acquire; rit++) {
1284 ModelAction *propagate = *rit;
1285 if (acquire->happens_before(propagate)) {
1286 propagate->synchronize_with(acquire);
1287 /* Re-check 'propagate' for mo_graph edges */
1288 work_queue->push_back(MOEdgeWorkEntry(propagate));
1292 /* Break release sequence with new edges:
1293 * release --mo--> write --mo--> rf */
1294 mo_graph->addEdge(release, write);
1295 mo_graph->addEdge(write, rf);
1298 /* See if we have realized a data race */
1303 * Initialize the current action by performing one or more of the following
1304 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1305 * in the NodeStack, manipulating backtracking sets, allocating and
1306 * initializing clock vectors, and computing the promises to fulfill.
1308 * @param curr The current action, as passed from the user context; may be
1309 * freed/invalidated after the execution of this function, with a different
1310 * action "returned" its place (pass-by-reference)
1311 * @return True if curr is a newly-explored action; false otherwise
1313 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1315 ModelAction *newcurr;
1317 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1318 newcurr = process_rmw(*curr);
1321 if (newcurr->is_rmw())
1322 compute_promises(newcurr);
1328 (*curr)->set_seq_number(get_next_seq_num());
1330 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1332 /* First restore type and order in case of RMW operation */
1333 if ((*curr)->is_rmwr())
1334 newcurr->copy_typeandorder(*curr);
1336 ASSERT((*curr)->get_location() == newcurr->get_location());
1337 newcurr->copy_from_new(*curr);
1339 /* Discard duplicate ModelAction; use action from NodeStack */
1342 /* Always compute new clock vector */
1343 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1346 return false; /* Action was explored previously */
1350 /* Always compute new clock vector */
1351 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1353 /* Assign most recent release fence */
1354 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1357 * Perform one-time actions when pushing new ModelAction onto
1360 if (newcurr->is_write())
1361 compute_promises(newcurr);
1362 else if (newcurr->is_relseq_fixup())
1363 compute_relseq_breakwrites(newcurr);
1364 else if (newcurr->is_wait())
1365 newcurr->get_node()->set_misc_max(2);
1366 else if (newcurr->is_notify_one()) {
1367 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1369 return true; /* This was a new ModelAction */
1374 * @brief Establish reads-from relation between two actions
1376 * Perform basic operations involved with establishing a concrete rf relation,
1377 * including setting the ModelAction data and checking for release sequences.
1379 * @param act The action that is reading (must be a read)
1380 * @param rf The action from which we are reading (must be a write)
1382 * @return True if this read established synchronization
1384 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1387 act->set_read_from(rf);
1388 if (act->is_acquire()) {
1389 rel_heads_list_t release_heads;
1390 get_release_seq_heads(act, act, &release_heads);
1391 int num_heads = release_heads.size();
1392 for (unsigned int i = 0; i < release_heads.size(); i++)
1393 if (!act->synchronize_with(release_heads[i])) {
1394 set_bad_synchronization();
1397 return num_heads > 0;
1403 * Check promises and eliminate potentially-satisfying threads when a thread is
1404 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1405 * no longer satisfy a promise generated from that thread.
1407 * @param blocker The thread on which a thread is waiting
1408 * @param waiting The waiting thread
1410 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1412 for (unsigned int i = 0; i < promises->size(); i++) {
1413 Promise *promise = (*promises)[i];
1414 if (!promise->thread_is_available(waiting->get_id()))
1416 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1417 ModelAction *reader = promise->get_reader(j);
1418 if (reader->get_tid() != blocker->get_id())
1420 if (promise->eliminate_thread(waiting->get_id())) {
1421 /* Promise has failed */
1422 priv->failed_promise = true;
1424 /* Only eliminate the 'waiting' thread once */
1432 * @brief Check whether a model action is enabled.
1434 * Checks whether a lock or join operation would be successful (i.e., is the
1435 * lock already locked, or is the joined thread already complete). If not, put
1436 * the action in a waiter list.
1438 * @param curr is the ModelAction to check whether it is enabled.
1439 * @return a bool that indicates whether the action is enabled.
1441 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1442 if (curr->is_lock()) {
1443 std::mutex *lock = (std::mutex *)curr->get_location();
1444 struct std::mutex_state *state = lock->get_state();
1445 if (state->locked) {
1446 //Stick the action in the appropriate waiting queue
1447 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1450 } else if (curr->get_type() == THREAD_JOIN) {
1451 Thread *blocking = (Thread *)curr->get_location();
1452 if (!blocking->is_complete()) {
1453 blocking->push_wait_list(curr);
1454 thread_blocking_check_promises(blocking, get_thread(curr));
1463 * This is the heart of the model checker routine. It performs model-checking
1464 * actions corresponding to a given "current action." Among other processes, it
1465 * calculates reads-from relationships, updates synchronization clock vectors,
1466 * forms a memory_order constraints graph, and handles replay/backtrack
1467 * execution when running permutations of previously-observed executions.
1469 * @param curr The current action to process
1470 * @return The ModelAction that is actually executed; may be different than
1471 * curr; may be NULL, if the current action is not enabled to run
1473 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1476 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1478 if (!check_action_enabled(curr)) {
1479 /* Make the execution look like we chose to run this action
1480 * much later, when a lock/join can succeed */
1481 get_thread(curr)->set_pending(curr);
1482 scheduler->sleep(get_thread(curr));
1486 bool newly_explored = initialize_curr_action(&curr);
1492 wake_up_sleeping_actions(curr);
1494 /* Compute fairness information for CHESS yield algorithm */
1495 if (model->params.yieldon) {
1496 curr->get_node()->update_yield(scheduler);
1499 /* Add the action to lists before any other model-checking tasks */
1500 if (!second_part_of_rmw)
1501 add_action_to_lists(curr);
1503 /* Build may_read_from set for newly-created actions */
1504 if (newly_explored && curr->is_read())
1505 build_may_read_from(curr);
1507 /* Initialize work_queue with the "current action" work */
1508 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1509 while (!work_queue.empty() && !has_asserted()) {
1510 WorkQueueEntry work = work_queue.front();
1511 work_queue.pop_front();
1513 switch (work.type) {
1514 case WORK_CHECK_CURR_ACTION: {
1515 ModelAction *act = work.action;
1516 bool update = false; /* update this location's release seq's */
1517 bool update_all = false; /* update all release seq's */
1519 if (process_thread_action(curr))
1522 if (act->is_read() && !second_part_of_rmw && process_read(act))
1525 if (act->is_write() && process_write(act))
1528 if (act->is_fence() && process_fence(act))
1531 if (act->is_mutex_op() && process_mutex(act))
1534 if (act->is_relseq_fixup())
1535 process_relseq_fixup(curr, &work_queue);
1538 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1540 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1543 case WORK_CHECK_RELEASE_SEQ:
1544 resolve_release_sequences(work.location, &work_queue);
1546 case WORK_CHECK_MO_EDGES: {
1547 /** @todo Complete verification of work_queue */
1548 ModelAction *act = work.action;
1549 bool updated = false;
1551 if (act->is_read()) {
1552 const ModelAction *rf = act->get_reads_from();
1553 const Promise *promise = act->get_reads_from_promise();
1555 if (r_modification_order(act, rf))
1557 } else if (promise) {
1558 if (r_modification_order(act, promise))
1562 if (act->is_write()) {
1563 if (w_modification_order(act, NULL))
1566 mo_graph->commitChanges();
1569 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1578 check_curr_backtracking(curr);
1579 set_backtracking(curr);
1583 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1585 Node *currnode = curr->get_node();
1586 Node *parnode = currnode->get_parent();
1588 if ((parnode && !parnode->backtrack_empty()) ||
1589 !currnode->misc_empty() ||
1590 !currnode->read_from_empty() ||
1591 !currnode->promise_empty() ||
1592 !currnode->relseq_break_empty()) {
1593 set_latest_backtrack(curr);
1597 bool ModelChecker::promises_expired() const
1599 for (unsigned int i = 0; i < promises->size(); i++) {
1600 Promise *promise = (*promises)[i];
1601 if (promise->get_expiration() < priv->used_sequence_numbers)
1608 * This is the strongest feasibility check available.
1609 * @return whether the current trace (partial or complete) must be a prefix of
1612 bool ModelChecker::isfeasibleprefix() const
1614 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1618 * Print disagnostic information about an infeasible execution
1619 * @param prefix A string to prefix the output with; if NULL, then a default
1620 * message prefix will be provided
1622 void ModelChecker::print_infeasibility(const char *prefix) const
1626 if (mo_graph->checkForCycles())
1627 ptr += sprintf(ptr, "[mo cycle]");
1628 if (priv->failed_promise)
1629 ptr += sprintf(ptr, "[failed promise]");
1630 if (priv->too_many_reads)
1631 ptr += sprintf(ptr, "[too many reads]");
1632 if (priv->no_valid_reads)
1633 ptr += sprintf(ptr, "[no valid reads-from]");
1634 if (priv->bad_synchronization)
1635 ptr += sprintf(ptr, "[bad sw ordering]");
1636 if (promises_expired())
1637 ptr += sprintf(ptr, "[promise expired]");
1638 if (promises->size() != 0)
1639 ptr += sprintf(ptr, "[unresolved promise]");
1641 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1645 * Returns whether the current completed trace is feasible, except for pending
1646 * release sequences.
1648 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1650 return !is_infeasible() && promises->size() == 0;
1654 * Check if the current partial trace is infeasible. Does not check any
1655 * end-of-execution flags, which might rule out the execution. Thus, this is
1656 * useful only for ruling an execution as infeasible.
1657 * @return whether the current partial trace is infeasible.
1659 bool ModelChecker::is_infeasible() const
1661 return mo_graph->checkForCycles() ||
1662 priv->no_valid_reads ||
1663 priv->failed_promise ||
1664 priv->too_many_reads ||
1665 priv->bad_synchronization ||
1669 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1670 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1671 ModelAction *lastread = get_last_action(act->get_tid());
1672 lastread->process_rmw(act);
1673 if (act->is_rmw()) {
1674 if (lastread->get_reads_from())
1675 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1677 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1678 mo_graph->commitChanges();
1684 * A helper function for ModelChecker::check_recency, to check if the current
1685 * thread is able to read from a different write/promise for 'params.maxreads'
1686 * number of steps and if that write/promise should become visible (i.e., is
1687 * ordered later in the modification order). This helps model memory liveness.
1689 * @param curr The current action. Must be a read.
1690 * @param rf The write/promise from which we plan to read
1691 * @param other_rf The write/promise from which we may read
1692 * @return True if we were able to read from other_rf for params.maxreads steps
1694 template <typename T, typename U>
1695 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1697 /* Need a different write/promise */
1698 if (other_rf->equals(rf))
1701 /* Only look for "newer" writes/promises */
1702 if (!mo_graph->checkReachable(rf, other_rf))
1705 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1706 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1707 action_list_t::reverse_iterator rit = list->rbegin();
1708 ASSERT((*rit) == curr);
1709 /* Skip past curr */
1712 /* Does this write/promise work for everyone? */
1713 for (int i = 0; i < params.maxreads; i++, rit++) {
1714 ModelAction *act = *rit;
1715 if (!act->may_read_from(other_rf))
1722 * Checks whether a thread has read from the same write or Promise for too many
1723 * times without seeing the effects of a later write/Promise.
1726 * 1) there must a different write/promise that we could read from,
1727 * 2) we must have read from the same write/promise in excess of maxreads times,
1728 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1729 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1731 * If so, we decide that the execution is no longer feasible.
1733 * @param curr The current action. Must be a read.
1734 * @param rf The ModelAction/Promise from which we might read.
1735 * @return True if the read should succeed; false otherwise
1737 template <typename T>
1738 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1740 if (!params.maxreads)
1743 //NOTE: Next check is just optimization, not really necessary....
1744 if (curr->get_node()->get_read_from_past_size() +
1745 curr->get_node()->get_read_from_promise_size() <= 1)
1748 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1749 int tid = id_to_int(curr->get_tid());
1750 ASSERT(tid < (int)thrd_lists->size());
1751 action_list_t *list = &(*thrd_lists)[tid];
1752 action_list_t::reverse_iterator rit = list->rbegin();
1753 ASSERT((*rit) == curr);
1754 /* Skip past curr */
1757 action_list_t::reverse_iterator ritcopy = rit;
1758 /* See if we have enough reads from the same value */
1759 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1760 if (ritcopy == list->rend())
1762 ModelAction *act = *ritcopy;
1763 if (!act->is_read())
1765 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1767 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1769 if (act->get_node()->get_read_from_past_size() +
1770 act->get_node()->get_read_from_promise_size() <= 1)
1773 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1774 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1775 if (should_read_instead(curr, rf, write))
1776 return false; /* liveness failure */
1778 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1779 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1780 if (should_read_instead(curr, rf, promise))
1781 return false; /* liveness failure */
1787 * Updates the mo_graph with the constraints imposed from the current
1790 * Basic idea is the following: Go through each other thread and find
1791 * the last action that happened before our read. Two cases:
1793 * (1) The action is a write => that write must either occur before
1794 * the write we read from or be the write we read from.
1796 * (2) The action is a read => the write that that action read from
1797 * must occur before the write we read from or be the same write.
1799 * @param curr The current action. Must be a read.
1800 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1801 * @return True if modification order edges were added; false otherwise
1803 template <typename rf_type>
1804 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1806 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1809 ASSERT(curr->is_read());
1811 /* Last SC fence in the current thread */
1812 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1814 /* Iterate over all threads */
1815 for (i = 0; i < thrd_lists->size(); i++) {
1816 /* Last SC fence in thread i */
1817 ModelAction *last_sc_fence_thread_local = NULL;
1818 if (int_to_id((int)i) != curr->get_tid())
1819 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1821 /* Last SC fence in thread i, before last SC fence in current thread */
1822 ModelAction *last_sc_fence_thread_before = NULL;
1823 if (last_sc_fence_local)
1824 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1826 /* Iterate over actions in thread, starting from most recent */
1827 action_list_t *list = &(*thrd_lists)[i];
1828 action_list_t::reverse_iterator rit;
1829 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1830 ModelAction *act = *rit;
1832 if (act->is_write() && !act->equals(rf) && act != curr) {
1833 /* C++, Section 29.3 statement 5 */
1834 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1835 *act < *last_sc_fence_thread_local) {
1836 added = mo_graph->addEdge(act, rf) || added;
1839 /* C++, Section 29.3 statement 4 */
1840 else if (act->is_seqcst() && last_sc_fence_local &&
1841 *act < *last_sc_fence_local) {
1842 added = mo_graph->addEdge(act, rf) || added;
1845 /* C++, Section 29.3 statement 6 */
1846 else if (last_sc_fence_thread_before &&
1847 *act < *last_sc_fence_thread_before) {
1848 added = mo_graph->addEdge(act, rf) || added;
1854 * Include at most one act per-thread that "happens
1855 * before" curr. Don't consider reflexively.
1857 if (act->happens_before(curr) && act != curr) {
1858 if (act->is_write()) {
1859 if (!act->equals(rf)) {
1860 added = mo_graph->addEdge(act, rf) || added;
1863 const ModelAction *prevrf = act->get_reads_from();
1864 const Promise *prevrf_promise = act->get_reads_from_promise();
1866 if (!prevrf->equals(rf))
1867 added = mo_graph->addEdge(prevrf, rf) || added;
1868 } else if (!prevrf_promise->equals(rf)) {
1869 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1878 * All compatible, thread-exclusive promises must be ordered after any
1879 * concrete loads from the same thread
1881 for (unsigned int i = 0; i < promises->size(); i++)
1882 if ((*promises)[i]->is_compatible_exclusive(curr))
1883 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1889 * Updates the mo_graph with the constraints imposed from the current write.
1891 * Basic idea is the following: Go through each other thread and find
1892 * the lastest action that happened before our write. Two cases:
1894 * (1) The action is a write => that write must occur before
1897 * (2) The action is a read => the write that that action read from
1898 * must occur before the current write.
1900 * This method also handles two other issues:
1902 * (I) Sequential Consistency: Making sure that if the current write is
1903 * seq_cst, that it occurs after the previous seq_cst write.
1905 * (II) Sending the write back to non-synchronizing reads.
1907 * @param curr The current action. Must be a write.
1908 * @param send_fv A vector for stashing reads to which we may pass our future
1909 * value. If NULL, then don't record any future values.
1910 * @return True if modification order edges were added; false otherwise
1912 bool ModelChecker::w_modification_order(ModelAction *curr, std::vector< ModelAction *, ModelAlloc<ModelAction *> > *send_fv)
1914 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1917 ASSERT(curr->is_write());
1919 if (curr->is_seqcst()) {
1920 /* We have to at least see the last sequentially consistent write,
1921 so we are initialized. */
1922 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1923 if (last_seq_cst != NULL) {
1924 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1928 /* Last SC fence in the current thread */
1929 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1931 /* Iterate over all threads */
1932 for (i = 0; i < thrd_lists->size(); i++) {
1933 /* Last SC fence in thread i, before last SC fence in current thread */
1934 ModelAction *last_sc_fence_thread_before = NULL;
1935 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1936 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1938 /* Iterate over actions in thread, starting from most recent */
1939 action_list_t *list = &(*thrd_lists)[i];
1940 action_list_t::reverse_iterator rit;
1941 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1942 ModelAction *act = *rit;
1945 * 1) If RMW and it actually read from something, then we
1946 * already have all relevant edges, so just skip to next
1949 * 2) If RMW and it didn't read from anything, we should
1950 * whatever edge we can get to speed up convergence.
1952 * 3) If normal write, we need to look at earlier actions, so
1953 * continue processing list.
1955 if (curr->is_rmw()) {
1956 if (curr->get_reads_from() != NULL)
1964 /* C++, Section 29.3 statement 7 */
1965 if (last_sc_fence_thread_before && act->is_write() &&
1966 *act < *last_sc_fence_thread_before) {
1967 added = mo_graph->addEdge(act, curr) || added;
1972 * Include at most one act per-thread that "happens
1975 if (act->happens_before(curr)) {
1977 * Note: if act is RMW, just add edge:
1979 * The following edge should be handled elsewhere:
1980 * readfrom(act) --mo--> act
1982 if (act->is_write())
1983 added = mo_graph->addEdge(act, curr) || added;
1984 else if (act->is_read()) {
1985 //if previous read accessed a null, just keep going
1986 if (act->get_reads_from() == NULL)
1988 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1991 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1992 !act->same_thread(curr)) {
1993 /* We have an action that:
1994 (1) did not happen before us
1995 (2) is a read and we are a write
1996 (3) cannot synchronize with us
1997 (4) is in a different thread
1999 that read could potentially read from our write. Note that
2000 these checks are overly conservative at this point, we'll
2001 do more checks before actually removing the
2005 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2006 if (!is_infeasible())
2007 send_fv->push_back(act);
2008 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2009 add_future_value(curr, act);
2016 * All compatible, thread-exclusive promises must be ordered after any
2017 * concrete stores to the same thread, or else they can be merged with
2020 for (unsigned int i = 0; i < promises->size(); i++)
2021 if ((*promises)[i]->is_compatible_exclusive(curr))
2022 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2027 /** Arbitrary reads from the future are not allowed. Section 29.3
2028 * part 9 places some constraints. This method checks one result of constraint
2029 * constraint. Others require compiler support. */
2030 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
2032 if (!writer->is_rmw())
2035 if (!reader->is_rmw())
2038 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2039 if (search == reader)
2041 if (search->get_tid() == reader->get_tid() &&
2042 search->happens_before(reader))
2050 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2051 * some constraints. This method checks one the following constraint (others
2052 * require compiler support):
2054 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2056 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2058 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2060 /* Iterate over all threads */
2061 for (i = 0; i < thrd_lists->size(); i++) {
2062 const ModelAction *write_after_read = NULL;
2064 /* Iterate over actions in thread, starting from most recent */
2065 action_list_t *list = &(*thrd_lists)[i];
2066 action_list_t::reverse_iterator rit;
2067 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2068 ModelAction *act = *rit;
2070 /* Don't disallow due to act == reader */
2071 if (!reader->happens_before(act) || reader == act)
2073 else if (act->is_write())
2074 write_after_read = act;
2075 else if (act->is_read() && act->get_reads_from() != NULL)
2076 write_after_read = act->get_reads_from();
2079 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2086 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2087 * The ModelAction under consideration is expected to be taking part in
2088 * release/acquire synchronization as an object of the "reads from" relation.
2089 * Note that this can only provide release sequence support for RMW chains
2090 * which do not read from the future, as those actions cannot be traced until
2091 * their "promise" is fulfilled. Similarly, we may not even establish the
2092 * presence of a release sequence with certainty, as some modification order
2093 * constraints may be decided further in the future. Thus, this function
2094 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2095 * and a boolean representing certainty.
2097 * @param rf The action that might be part of a release sequence. Must be a
2099 * @param release_heads A pass-by-reference style return parameter. After
2100 * execution of this function, release_heads will contain the heads of all the
2101 * relevant release sequences, if any exists with certainty
2102 * @param pending A pass-by-reference style return parameter which is only used
2103 * when returning false (i.e., uncertain). Returns most information regarding
2104 * an uncertain release sequence, including any write operations that might
2105 * break the sequence.
2106 * @return true, if the ModelChecker is certain that release_heads is complete;
2109 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2110 rel_heads_list_t *release_heads,
2111 struct release_seq *pending) const
2113 /* Only check for release sequences if there are no cycles */
2114 if (mo_graph->checkForCycles())
2117 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2118 ASSERT(rf->is_write());
2120 if (rf->is_release())
2121 release_heads->push_back(rf);
2122 else if (rf->get_last_fence_release())
2123 release_heads->push_back(rf->get_last_fence_release());
2125 break; /* End of RMW chain */
2127 /** @todo Need to be smarter here... In the linux lock
2128 * example, this will run to the beginning of the program for
2130 /** @todo The way to be smarter here is to keep going until 1
2131 * thread has a release preceded by an acquire and you've seen
2134 /* acq_rel RMW is a sufficient stopping condition */
2135 if (rf->is_acquire() && rf->is_release())
2136 return true; /* complete */
2139 /* read from future: need to settle this later */
2141 return false; /* incomplete */
2144 if (rf->is_release())
2145 return true; /* complete */
2147 /* else relaxed write
2148 * - check for fence-release in the same thread (29.8, stmt. 3)
2149 * - check modification order for contiguous subsequence
2150 * -> rf must be same thread as release */
2152 const ModelAction *fence_release = rf->get_last_fence_release();
2153 /* Synchronize with a fence-release unconditionally; we don't need to
2154 * find any more "contiguous subsequence..." for it */
2156 release_heads->push_back(fence_release);
2158 int tid = id_to_int(rf->get_tid());
2159 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2160 action_list_t *list = &(*thrd_lists)[tid];
2161 action_list_t::const_reverse_iterator rit;
2163 /* Find rf in the thread list */
2164 rit = std::find(list->rbegin(), list->rend(), rf);
2165 ASSERT(rit != list->rend());
2167 /* Find the last {write,fence}-release */
2168 for (; rit != list->rend(); rit++) {
2169 if (fence_release && *(*rit) < *fence_release)
2171 if ((*rit)->is_release())
2174 if (rit == list->rend()) {
2175 /* No write-release in this thread */
2176 return true; /* complete */
2177 } else if (fence_release && *(*rit) < *fence_release) {
2178 /* The fence-release is more recent (and so, "stronger") than
2179 * the most recent write-release */
2180 return true; /* complete */
2181 } /* else, need to establish contiguous release sequence */
2182 ModelAction *release = *rit;
2184 ASSERT(rf->same_thread(release));
2186 pending->writes.clear();
2188 bool certain = true;
2189 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2190 if (id_to_int(rf->get_tid()) == (int)i)
2192 list = &(*thrd_lists)[i];
2194 /* Can we ensure no future writes from this thread may break
2195 * the release seq? */
2196 bool future_ordered = false;
2198 ModelAction *last = get_last_action(int_to_id(i));
2199 Thread *th = get_thread(int_to_id(i));
2200 if ((last && rf->happens_before(last)) ||
2203 future_ordered = true;
2205 ASSERT(!th->is_model_thread() || future_ordered);
2207 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2208 const ModelAction *act = *rit;
2209 /* Reach synchronization -> this thread is complete */
2210 if (act->happens_before(release))
2212 if (rf->happens_before(act)) {
2213 future_ordered = true;
2217 /* Only non-RMW writes can break release sequences */
2218 if (!act->is_write() || act->is_rmw())
2221 /* Check modification order */
2222 if (mo_graph->checkReachable(rf, act)) {
2223 /* rf --mo--> act */
2224 future_ordered = true;
2227 if (mo_graph->checkReachable(act, release))
2228 /* act --mo--> release */
2230 if (mo_graph->checkReachable(release, act) &&
2231 mo_graph->checkReachable(act, rf)) {
2232 /* release --mo-> act --mo--> rf */
2233 return true; /* complete */
2235 /* act may break release sequence */
2236 pending->writes.push_back(act);
2239 if (!future_ordered)
2240 certain = false; /* This thread is uncertain */
2244 release_heads->push_back(release);
2245 pending->writes.clear();
2247 pending->release = release;
2254 * An interface for getting the release sequence head(s) with which a
2255 * given ModelAction must synchronize. This function only returns a non-empty
2256 * result when it can locate a release sequence head with certainty. Otherwise,
2257 * it may mark the internal state of the ModelChecker so that it will handle
2258 * the release sequence at a later time, causing @a acquire to update its
2259 * synchronization at some later point in execution.
2261 * @param acquire The 'acquire' action that may synchronize with a release
2263 * @param read The read action that may read from a release sequence; this may
2264 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2265 * when 'acquire' is a fence-acquire)
2266 * @param release_heads A pass-by-reference return parameter. Will be filled
2267 * with the head(s) of the release sequence(s), if they exists with certainty.
2268 * @see ModelChecker::release_seq_heads
2270 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2271 ModelAction *read, rel_heads_list_t *release_heads)
2273 const ModelAction *rf = read->get_reads_from();
2274 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2275 sequence->acquire = acquire;
2276 sequence->read = read;
2278 if (!release_seq_heads(rf, release_heads, sequence)) {
2279 /* add act to 'lazy checking' list */
2280 pending_rel_seqs->push_back(sequence);
2282 snapshot_free(sequence);
2287 * Attempt to resolve all stashed operations that might synchronize with a
2288 * release sequence for a given location. This implements the "lazy" portion of
2289 * determining whether or not a release sequence was contiguous, since not all
2290 * modification order information is present at the time an action occurs.
2292 * @param location The location/object that should be checked for release
2293 * sequence resolutions. A NULL value means to check all locations.
2294 * @param work_queue The work queue to which to add work items as they are
2296 * @return True if any updates occurred (new synchronization, new mo_graph
2299 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2301 bool updated = false;
2302 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2303 while (it != pending_rel_seqs->end()) {
2304 struct release_seq *pending = *it;
2305 ModelAction *acquire = pending->acquire;
2306 const ModelAction *read = pending->read;
2308 /* Only resolve sequences on the given location, if provided */
2309 if (location && read->get_location() != location) {
2314 const ModelAction *rf = read->get_reads_from();
2315 rel_heads_list_t release_heads;
2317 complete = release_seq_heads(rf, &release_heads, pending);
2318 for (unsigned int i = 0; i < release_heads.size(); i++) {
2319 if (!acquire->has_synchronized_with(release_heads[i])) {
2320 if (acquire->synchronize_with(release_heads[i]))
2323 set_bad_synchronization();
2328 /* Re-check all pending release sequences */
2329 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2330 /* Re-check read-acquire for mo_graph edges */
2331 if (acquire->is_read())
2332 work_queue->push_back(MOEdgeWorkEntry(acquire));
2334 /* propagate synchronization to later actions */
2335 action_list_t::reverse_iterator rit = action_trace->rbegin();
2336 for (; (*rit) != acquire; rit++) {
2337 ModelAction *propagate = *rit;
2338 if (acquire->happens_before(propagate)) {
2339 propagate->synchronize_with(acquire);
2340 /* Re-check 'propagate' for mo_graph edges */
2341 work_queue->push_back(MOEdgeWorkEntry(propagate));
2346 it = pending_rel_seqs->erase(it);
2347 snapshot_free(pending);
2353 // If we resolved promises or data races, see if we have realized a data race.
2360 * Performs various bookkeeping operations for the current ModelAction. For
2361 * instance, adds action to the per-object, per-thread action vector and to the
2362 * action trace list of all thread actions.
2364 * @param act is the ModelAction to add.
2366 void ModelChecker::add_action_to_lists(ModelAction *act)
2368 int tid = id_to_int(act->get_tid());
2369 ModelAction *uninit = NULL;
2371 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2372 if (list->empty() && act->is_atomic_var()) {
2373 uninit = new_uninitialized_action(act->get_location());
2374 uninit_id = id_to_int(uninit->get_tid());
2375 list->push_back(uninit);
2377 list->push_back(act);
2379 action_trace->push_back(act);
2381 action_trace->push_front(uninit);
2383 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2384 if (tid >= (int)vec->size())
2385 vec->resize(priv->next_thread_id);
2386 (*vec)[tid].push_back(act);
2388 (*vec)[uninit_id].push_front(uninit);
2390 if ((int)thrd_last_action->size() <= tid)
2391 thrd_last_action->resize(get_num_threads());
2392 (*thrd_last_action)[tid] = act;
2394 (*thrd_last_action)[uninit_id] = uninit;
2396 if (act->is_fence() && act->is_release()) {
2397 if ((int)thrd_last_fence_release->size() <= tid)
2398 thrd_last_fence_release->resize(get_num_threads());
2399 (*thrd_last_fence_release)[tid] = act;
2402 if (act->is_wait()) {
2403 void *mutex_loc = (void *) act->get_value();
2404 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2406 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2407 if (tid >= (int)vec->size())
2408 vec->resize(priv->next_thread_id);
2409 (*vec)[tid].push_back(act);
2414 * @brief Get the last action performed by a particular Thread
2415 * @param tid The thread ID of the Thread in question
2416 * @return The last action in the thread
2418 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2420 int threadid = id_to_int(tid);
2421 if (threadid < (int)thrd_last_action->size())
2422 return (*thrd_last_action)[id_to_int(tid)];
2428 * @brief Get the last fence release performed by a particular Thread
2429 * @param tid The thread ID of the Thread in question
2430 * @return The last fence release in the thread, if one exists; NULL otherwise
2432 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2434 int threadid = id_to_int(tid);
2435 if (threadid < (int)thrd_last_fence_release->size())
2436 return (*thrd_last_fence_release)[id_to_int(tid)];
2442 * Gets the last memory_order_seq_cst write (in the total global sequence)
2443 * performed on a particular object (i.e., memory location), not including the
2445 * @param curr The current ModelAction; also denotes the object location to
2447 * @return The last seq_cst write
2449 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2451 void *location = curr->get_location();
2452 action_list_t *list = get_safe_ptr_action(obj_map, location);
2453 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2454 action_list_t::reverse_iterator rit;
2455 for (rit = list->rbegin(); rit != list->rend(); rit++)
2456 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2462 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2463 * performed in a particular thread, prior to a particular fence.
2464 * @param tid The ID of the thread to check
2465 * @param before_fence The fence from which to begin the search; if NULL, then
2466 * search for the most recent fence in the thread.
2467 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2469 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2471 /* All fences should have NULL location */
2472 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2473 action_list_t::reverse_iterator rit = list->rbegin();
2476 for (; rit != list->rend(); rit++)
2477 if (*rit == before_fence)
2480 ASSERT(*rit == before_fence);
2484 for (; rit != list->rend(); rit++)
2485 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2491 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2492 * location). This function identifies the mutex according to the current
2493 * action, which is presumed to perform on the same mutex.
2494 * @param curr The current ModelAction; also denotes the object location to
2496 * @return The last unlock operation
2498 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2500 void *location = curr->get_location();
2501 action_list_t *list = get_safe_ptr_action(obj_map, location);
2502 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2503 action_list_t::reverse_iterator rit;
2504 for (rit = list->rbegin(); rit != list->rend(); rit++)
2505 if ((*rit)->is_unlock() || (*rit)->is_wait())
2510 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2512 ModelAction *parent = get_last_action(tid);
2514 parent = get_thread(tid)->get_creation();
2519 * Returns the clock vector for a given thread.
2520 * @param tid The thread whose clock vector we want
2521 * @return Desired clock vector
2523 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2525 return get_parent_action(tid)->get_cv();
2529 * @brief Find the promise, if any to resolve for the current action
2530 * @param curr The current ModelAction. Should be a write.
2531 * @return The (non-negative) index for the Promise to resolve, if any;
2534 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2536 for (unsigned int i = 0; i < promises->size(); i++)
2537 if (curr->get_node()->get_promise(i))
2543 * Resolve a Promise with a current write.
2544 * @param write The ModelAction that is fulfilling Promises
2545 * @param promise_idx The index corresponding to the promise
2546 * @return True if the Promise was successfully resolved; false otherwise
2548 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2550 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2551 Promise *promise = (*promises)[promise_idx];
2553 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2554 ModelAction *read = promise->get_reader(i);
2555 read_from(read, write);
2556 actions_to_check.push_back(read);
2558 /* Make sure the promise's value matches the write's value */
2559 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2560 if (!mo_graph->resolvePromise(promise, write))
2561 priv->failed_promise = true;
2563 promises->erase(promises->begin() + promise_idx);
2565 * @todo It is possible to end up in an inconsistent state, where a
2566 * "resolved" promise may still be referenced if
2567 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2569 * Note that the inconsistency only matters when dumping mo_graph to
2575 //Check whether reading these writes has made threads unable to
2577 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2578 ModelAction *read = actions_to_check[i];
2579 mo_check_promises(read, true);
2586 * Compute the set of promises that could potentially be satisfied by this
2587 * action. Note that the set computation actually appears in the Node, not in
2589 * @param curr The ModelAction that may satisfy promises
2591 void ModelChecker::compute_promises(ModelAction *curr)
2593 for (unsigned int i = 0; i < promises->size(); i++) {
2594 Promise *promise = (*promises)[i];
2595 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2598 bool satisfy = true;
2599 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2600 const ModelAction *act = promise->get_reader(j);
2601 if (act->happens_before(curr) ||
2602 act->could_synchronize_with(curr)) {
2608 curr->get_node()->set_promise(i);
2612 /** Checks promises in response to change in ClockVector Threads. */
2613 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2615 for (unsigned int i = 0; i < promises->size(); i++) {
2616 Promise *promise = (*promises)[i];
2617 if (!promise->thread_is_available(tid))
2619 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2620 const ModelAction *act = promise->get_reader(j);
2621 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2622 merge_cv->synchronized_since(act)) {
2623 if (promise->eliminate_thread(tid)) {
2624 /* Promise has failed */
2625 priv->failed_promise = true;
2633 void ModelChecker::check_promises_thread_disabled()
2635 for (unsigned int i = 0; i < promises->size(); i++) {
2636 Promise *promise = (*promises)[i];
2637 if (promise->has_failed()) {
2638 priv->failed_promise = true;
2645 * @brief Checks promises in response to addition to modification order for
2648 * We test whether threads are still available for satisfying promises after an
2649 * addition to our modification order constraints. Those that are unavailable
2650 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2651 * that promise has failed.
2653 * @param act The ModelAction which updated the modification order
2654 * @param is_read_check Should be true if act is a read and we must check for
2655 * updates to the store from which it read (there is a distinction here for
2656 * RMW's, which are both a load and a store)
2658 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2660 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2662 for (unsigned int i = 0; i < promises->size(); i++) {
2663 Promise *promise = (*promises)[i];
2665 // Is this promise on the same location?
2666 if (!promise->same_location(write))
2669 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2670 const ModelAction *pread = promise->get_reader(j);
2671 if (!pread->happens_before(act))
2673 if (mo_graph->checkPromise(write, promise)) {
2674 priv->failed_promise = true;
2680 // Don't do any lookups twice for the same thread
2681 if (!promise->thread_is_available(act->get_tid()))
2684 if (mo_graph->checkReachable(promise, write)) {
2685 if (mo_graph->checkPromise(write, promise)) {
2686 priv->failed_promise = true;
2694 * Compute the set of writes that may break the current pending release
2695 * sequence. This information is extracted from previou release sequence
2698 * @param curr The current ModelAction. Must be a release sequence fixup
2701 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2703 if (pending_rel_seqs->empty())
2706 struct release_seq *pending = pending_rel_seqs->back();
2707 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2708 const ModelAction *write = pending->writes[i];
2709 curr->get_node()->add_relseq_break(write);
2712 /* NULL means don't break the sequence; just synchronize */
2713 curr->get_node()->add_relseq_break(NULL);
2717 * Build up an initial set of all past writes that this 'read' action may read
2718 * from, as well as any previously-observed future values that must still be valid.
2720 * @param curr is the current ModelAction that we are exploring; it must be a
2723 void ModelChecker::build_may_read_from(ModelAction *curr)
2725 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2727 ASSERT(curr->is_read());
2729 ModelAction *last_sc_write = NULL;
2731 if (curr->is_seqcst())
2732 last_sc_write = get_last_seq_cst_write(curr);
2734 /* Iterate over all threads */
2735 for (i = 0; i < thrd_lists->size(); i++) {
2736 /* Iterate over actions in thread, starting from most recent */
2737 action_list_t *list = &(*thrd_lists)[i];
2738 action_list_t::reverse_iterator rit;
2739 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2740 ModelAction *act = *rit;
2742 /* Only consider 'write' actions */
2743 if (!act->is_write() || act == curr)
2746 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2747 bool allow_read = true;
2749 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2751 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2755 /* Only add feasible reads */
2756 mo_graph->startChanges();
2757 r_modification_order(curr, act);
2758 if (!is_infeasible())
2759 curr->get_node()->add_read_from_past(act);
2760 mo_graph->rollbackChanges();
2763 /* Include at most one act per-thread that "happens before" curr */
2764 if (act->happens_before(curr))
2769 /* Inherit existing, promised future values */
2770 for (i = 0; i < promises->size(); i++) {
2771 const Promise *promise = (*promises)[i];
2772 const ModelAction *promise_read = promise->get_reader(0);
2773 if (promise_read->same_var(curr)) {
2774 /* Only add feasible future-values */
2775 mo_graph->startChanges();
2776 r_modification_order(curr, promise);
2777 if (!is_infeasible())
2778 curr->get_node()->add_read_from_promise(promise_read);
2779 mo_graph->rollbackChanges();
2783 /* We may find no valid may-read-from only if the execution is doomed */
2784 if (!curr->get_node()->read_from_size()) {
2785 priv->no_valid_reads = true;
2789 if (DBG_ENABLED()) {
2790 model_print("Reached read action:\n");
2792 model_print("Printing read_from_past\n");
2793 curr->get_node()->print_read_from_past();
2794 model_print("End printing read_from_past\n");
2798 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2800 for ( ; write != NULL; write = write->get_reads_from()) {
2801 /* UNINIT actions don't have a Node, and they never sleep */
2802 if (write->is_uninitialized())
2804 Node *prevnode = write->get_node()->get_parent();
2806 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2807 if (write->is_release() && thread_sleep)
2809 if (!write->is_rmw())
2816 * @brief Create a new action representing an uninitialized atomic
2817 * @param location The memory location of the atomic object
2818 * @return A pointer to a new ModelAction
2820 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2822 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2823 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2824 act->create_cv(NULL);
2828 static void print_list(action_list_t *list)
2830 action_list_t::iterator it;
2832 model_print("---------------------------------------------------------------------\n");
2834 unsigned int hash = 0;
2836 for (it = list->begin(); it != list->end(); it++) {
2838 hash = hash^(hash<<3)^((*it)->hash());
2840 model_print("HASH %u\n", hash);
2841 model_print("---------------------------------------------------------------------\n");
2844 #if SUPPORT_MOD_ORDER_DUMP
2845 void ModelChecker::dumpGraph(char *filename) const
2848 sprintf(buffer, "%s.dot", filename);
2849 FILE *file = fopen(buffer, "w");
2850 fprintf(file, "digraph %s {\n", filename);
2851 mo_graph->dumpNodes(file);
2852 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2854 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2855 ModelAction *act = *it;
2856 if (act->is_read()) {
2857 mo_graph->dot_print_node(file, act);
2858 if (act->get_reads_from())
2859 mo_graph->dot_print_edge(file,
2860 act->get_reads_from(),
2862 "label=\"rf\", color=red, weight=2");
2864 mo_graph->dot_print_edge(file,
2865 act->get_reads_from_promise(),
2867 "label=\"rf\", color=red");
2869 if (thread_array[act->get_tid()]) {
2870 mo_graph->dot_print_edge(file,
2871 thread_array[id_to_int(act->get_tid())],
2873 "label=\"sb\", color=blue, weight=400");
2876 thread_array[act->get_tid()] = act;
2878 fprintf(file, "}\n");
2879 model_free(thread_array);
2884 /** @brief Prints an execution trace summary. */
2885 void ModelChecker::print_summary() const
2887 #if SUPPORT_MOD_ORDER_DUMP
2888 char buffername[100];
2889 sprintf(buffername, "exec%04u", stats.num_total);
2890 mo_graph->dumpGraphToFile(buffername);
2891 sprintf(buffername, "graph%04u", stats.num_total);
2892 dumpGraph(buffername);
2895 model_print("Execution %d:", stats.num_total);
2896 if (isfeasibleprefix()) {
2897 if (scheduler->all_threads_sleeping())
2898 model_print(" SLEEP-SET REDUNDANT");
2901 print_infeasibility(" INFEASIBLE");
2902 print_list(action_trace);
2904 if (!promises->empty()) {
2905 model_print("Pending promises:\n");
2906 for (unsigned int i = 0; i < promises->size(); i++) {
2907 model_print(" [P%u] ", i);
2908 (*promises)[i]->print();
2915 * Add a Thread to the system for the first time. Should only be called once
2917 * @param t The Thread to add
2919 void ModelChecker::add_thread(Thread *t)
2921 thread_map->put(id_to_int(t->get_id()), t);
2922 scheduler->add_thread(t);
2926 * Removes a thread from the scheduler.
2927 * @param the thread to remove.
2929 void ModelChecker::remove_thread(Thread *t)
2931 scheduler->remove_thread(t);
2935 * @brief Get a Thread reference by its ID
2936 * @param tid The Thread's ID
2937 * @return A Thread reference
2939 Thread * ModelChecker::get_thread(thread_id_t tid) const
2941 return thread_map->get(id_to_int(tid));
2945 * @brief Get a reference to the Thread in which a ModelAction was executed
2946 * @param act The ModelAction
2947 * @return A Thread reference
2949 Thread * ModelChecker::get_thread(const ModelAction *act) const
2951 return get_thread(act->get_tid());
2955 * @brief Get a Promise's "promise number"
2957 * A "promise number" is an index number that is unique to a promise, valid
2958 * only for a specific snapshot of an execution trace. Promises may come and go
2959 * as they are generated an resolved, so an index only retains meaning for the
2962 * @param promise The Promise to check
2963 * @return The promise index, if the promise still is valid; otherwise -1
2965 int ModelChecker::get_promise_number(const Promise *promise) const
2967 for (unsigned int i = 0; i < promises->size(); i++)
2968 if ((*promises)[i] == promise)
2975 * @brief Check if a Thread is currently enabled
2976 * @param t The Thread to check
2977 * @return True if the Thread is currently enabled
2979 bool ModelChecker::is_enabled(Thread *t) const
2981 return scheduler->is_enabled(t);
2985 * @brief Check if a Thread is currently enabled
2986 * @param tid The ID of the Thread to check
2987 * @return True if the Thread is currently enabled
2989 bool ModelChecker::is_enabled(thread_id_t tid) const
2991 return scheduler->is_enabled(tid);
2995 * Switch from a model-checker context to a user-thread context. This is the
2996 * complement of ModelChecker::switch_to_master and must be called from the
2997 * model-checker context
2999 * @param thread The user-thread to switch to
3001 void ModelChecker::switch_from_master(Thread *thread)
3003 scheduler->set_current_thread(thread);
3004 Thread::swap(&system_context, thread);
3008 * Switch from a user-context to the "master thread" context (a.k.a. system
3009 * context). This switch is made with the intention of exploring a particular
3010 * model-checking action (described by a ModelAction object). Must be called
3011 * from a user-thread context.
3013 * @param act The current action that will be explored. May be NULL only if
3014 * trace is exiting via an assertion (see ModelChecker::set_assert and
3015 * ModelChecker::has_asserted).
3016 * @return Return the value returned by the current action
3018 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3021 Thread *old = thread_current();
3022 ASSERT(!old->get_pending());
3023 old->set_pending(act);
3024 if (Thread::swap(old, &system_context) < 0) {
3025 perror("swap threads");
3028 return old->get_return_value();
3032 * Takes the next step in the execution, if possible.
3033 * @param curr The current step to take
3034 * @return Returns the next Thread to run, if any; NULL if this execution
3037 Thread * ModelChecker::take_step(ModelAction *curr)
3039 Thread *curr_thrd = get_thread(curr);
3040 ASSERT(curr_thrd->get_state() == THREAD_READY);
3042 curr = check_current_action(curr);
3044 /* Infeasible -> don't take any more steps */
3045 if (is_infeasible())
3047 else if (isfeasibleprefix() && have_bug_reports()) {
3052 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
3055 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3056 scheduler->remove_thread(curr_thrd);
3058 Thread *next_thrd = NULL;
3060 next_thrd = action_select_next_thread(curr);
3062 next_thrd = get_next_thread();
3064 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
3065 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
3070 /** Wrapper to run the user's main function, with appropriate arguments */
3071 void user_main_wrapper(void *)
3073 user_main(model->params.argc, model->params.argv);
3076 /** @brief Run ModelChecker for the user program */
3077 void ModelChecker::run()
3081 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3086 * Stash next pending action(s) for thread(s). There
3087 * should only need to stash one thread's action--the
3088 * thread which just took a step--plus the first step
3089 * for any newly-created thread
3091 for (unsigned int i = 0; i < get_num_threads(); i++) {
3092 thread_id_t tid = int_to_id(i);
3093 Thread *thr = get_thread(tid);
3094 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3095 switch_from_master(thr);
3096 if (is_circular_wait(thr))
3097 assert_bug("Deadlock detected");
3101 /* Catch assertions from prior take_step or from
3102 * between-ModelAction bugs (e.g., data races) */
3106 /* Consume the next action for a Thread */
3107 ModelAction *curr = t->get_pending();
3108 t->set_pending(NULL);
3109 t = take_step(curr);
3110 } while (t && !t->is_model_thread());
3113 * Launch end-of-execution release sequence fixups only when
3114 * the execution is otherwise feasible AND there are:
3116 * (1) pending release sequences
3117 * (2) pending assertions that could be invalidated by a change
3118 * in clock vectors (i.e., data races)
3119 * (3) no pending promises
3121 while (!pending_rel_seqs->empty() &&
3122 is_feasible_prefix_ignore_relseq() &&
3123 !unrealizedraces.empty()) {
3124 model_print("*** WARNING: release sequence fixup action "
3125 "(%zu pending release seuqence(s)) ***\n",
3126 pending_rel_seqs->size());
3127 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3128 std::memory_order_seq_cst, NULL, VALUE_NONE,
3132 } while (next_execution());
3134 model_print("******* Model-checking complete: *******\n");