11 #include "snapshot-interface.h"
13 #include "clockvector.h"
14 #include "cyclegraph.h"
17 #include "threads-model.h"
19 #include "traceanalysis.h"
21 #define INITIAL_THREAD_ID 0
26 bug_message(const char *str) {
27 const char *fmt = " [BUG] %s\n";
28 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
29 sprintf(msg, fmt, str);
31 ~bug_message() { if (msg) snapshot_free(msg); }
34 void print() { model_print("%s", msg); }
40 * Structure for holding small ModelChecker members that should be snapshotted
42 struct model_snapshot_members {
43 model_snapshot_members() :
44 /* First thread created will have id INITIAL_THREAD_ID */
45 next_thread_id(INITIAL_THREAD_ID),
46 used_sequence_numbers(0),
50 failed_promise(false),
51 too_many_reads(false),
52 no_valid_reads(false),
53 bad_synchronization(false),
57 ~model_snapshot_members() {
58 for (unsigned int i = 0; i < bugs.size(); i++)
63 unsigned int next_thread_id;
64 modelclock_t used_sequence_numbers;
65 ModelAction *next_backtrack;
66 SnapVector<bug_message *> bugs;
67 struct execution_stats stats;
71 /** @brief Incorrectly-ordered synchronization was made */
72 bool bad_synchronization;
78 /** @brief Constructor */
79 ModelChecker::ModelChecker(struct model_params params) :
80 /* Initialize default scheduler */
82 scheduler(new Scheduler()),
84 earliest_diverge(NULL),
85 action_trace(new action_list_t()),
86 thread_map(new HashTable<int, Thread *, int>()),
87 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
89 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
90 promises(new SnapVector<Promise *>()),
91 futurevalues(new SnapVector<struct PendingFutureValue>()),
92 pending_rel_seqs(new SnapVector<struct release_seq *>()),
93 thrd_last_action(new SnapVector<ModelAction *>(1)),
94 thrd_last_fence_release(new SnapVector<ModelAction *>()),
95 node_stack(new NodeStack()),
96 trace_analyses(new ModelVector<Trace_Analysis *>()),
97 priv(new struct model_snapshot_members()),
98 mo_graph(new CycleGraph())
100 /* Initialize a model-checker thread, for special ModelActions */
101 model_thread = new Thread(get_next_id());
102 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
105 /** @brief Destructor */
106 ModelChecker::~ModelChecker()
108 for (unsigned int i = 0; i < get_num_threads(); i++)
109 delete thread_map->get(i);
114 delete condvar_waiters_map;
117 for (unsigned int i = 0; i < promises->size(); i++)
118 delete (*promises)[i];
121 delete pending_rel_seqs;
123 delete thrd_last_action;
124 delete thrd_last_fence_release;
126 for (unsigned int i = 0; i < trace_analyses->size(); i++)
127 delete (*trace_analyses)[i];
128 delete trace_analyses;
134 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
136 action_list_t *tmp = hash->get(ptr);
138 tmp = new action_list_t();
144 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
146 SnapVector<action_list_t> *tmp = hash->get(ptr);
148 tmp = new SnapVector<action_list_t>();
154 action_list_t * ModelChecker::get_actions_on_obj(void * obj, thread_id_t tid) {
155 SnapVector<action_list_t> *wrv=obj_thrd_map->get(obj);
158 unsigned int thread=id_to_int(tid);
159 if (thread < wrv->size())
160 return &(*wrv)[thread];
167 * Restores user program to initial state and resets all model-checker data
170 void ModelChecker::reset_to_initial_state()
172 DEBUG("+++ Resetting to initial state +++\n");
173 node_stack->reset_execution();
176 * FIXME: if we utilize partial rollback, we will need to free only
177 * those pending actions which were NOT pending before the rollback
180 for (unsigned int i = 0; i < get_num_threads(); i++)
181 delete get_thread(int_to_id(i))->get_pending();
183 snapshot_backtrack_before(0);
186 /** @return a thread ID for a new Thread */
187 thread_id_t ModelChecker::get_next_id()
189 return priv->next_thread_id++;
192 /** @return the number of user threads created during this execution */
193 unsigned int ModelChecker::get_num_threads() const
195 return priv->next_thread_id;
199 * Must be called from user-thread context (e.g., through the global
200 * thread_current() interface)
202 * @return The currently executing Thread.
204 Thread * ModelChecker::get_current_thread() const
206 return scheduler->get_current_thread();
209 /** @return a sequence number for a new ModelAction */
210 modelclock_t ModelChecker::get_next_seq_num()
212 return ++priv->used_sequence_numbers;
215 Node * ModelChecker::get_curr_node() const
217 return node_stack->get_head();
221 * @brief Select the next thread to execute based on the curren action
223 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
224 * actions should be followed by the execution of their child thread. In either
225 * case, the current action should determine the next thread schedule.
227 * @param curr The current action
228 * @return The next thread to run, if the current action will determine this
229 * selection; otherwise NULL
231 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
233 /* Do not split atomic RMW */
235 return get_thread(curr);
236 /* Follow CREATE with the created thread */
237 if (curr->get_type() == THREAD_CREATE)
238 return curr->get_thread_operand();
243 * @brief Choose the next thread to execute.
245 * This function chooses the next thread that should execute. It can enforce
246 * execution replay/backtracking or, if the model-checker has no preference
247 * regarding the next thread (i.e., when exploring a new execution ordering),
248 * we defer to the scheduler.
250 * @return The next chosen thread to run, if any exist. Or else if the current
251 * execution should terminate, return NULL.
253 Thread * ModelChecker::get_next_thread()
258 * Have we completed exploring the preselected path? Then let the
262 return scheduler->select_next_thread();
264 /* Else, we are trying to replay an execution */
265 ModelAction *next = node_stack->get_next()->get_action();
267 if (next == diverge) {
268 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
269 earliest_diverge = diverge;
271 Node *nextnode = next->get_node();
272 Node *prevnode = nextnode->get_parent();
273 scheduler->update_sleep_set(prevnode);
275 /* Reached divergence point */
276 if (nextnode->increment_behaviors()) {
277 /* Execute the same thread with a new behavior */
278 tid = next->get_tid();
279 node_stack->pop_restofstack(2);
282 /* Make a different thread execute for next step */
283 scheduler->add_sleep(get_thread(next->get_tid()));
284 tid = prevnode->get_next_backtrack();
285 /* Make sure the backtracked thread isn't sleeping. */
286 node_stack->pop_restofstack(1);
287 if (diverge == earliest_diverge) {
288 earliest_diverge = prevnode->get_action();
291 /* Start the round robin scheduler from this thread id */
292 scheduler->set_scheduler_thread(tid);
293 /* The correct sleep set is in the parent node. */
296 DEBUG("*** Divergence point ***\n");
300 tid = next->get_tid();
302 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
303 ASSERT(tid != THREAD_ID_T_NONE);
304 return get_thread(id_to_int(tid));
308 * We need to know what the next actions of all threads in the sleep
309 * set will be. This method computes them and stores the actions at
310 * the corresponding thread object's pending action.
313 void ModelChecker::execute_sleep_set()
315 for (unsigned int i = 0; i < get_num_threads(); i++) {
316 thread_id_t tid = int_to_id(i);
317 Thread *thr = get_thread(tid);
318 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
319 thr->get_pending()->set_sleep_flag();
325 * @brief Should the current action wake up a given thread?
327 * @param curr The current action
328 * @param thread The thread that we might wake up
329 * @return True, if we should wake up the sleeping thread; false otherwise
331 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
333 const ModelAction *asleep = thread->get_pending();
334 /* Don't allow partial RMW to wake anyone up */
337 /* Synchronizing actions may have been backtracked */
338 if (asleep->could_synchronize_with(curr))
340 /* All acquire/release fences and fence-acquire/store-release */
341 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
343 /* Fence-release + store can awake load-acquire on the same location */
344 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
345 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
346 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
352 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
354 for (unsigned int i = 0; i < get_num_threads(); i++) {
355 Thread *thr = get_thread(int_to_id(i));
356 if (scheduler->is_sleep_set(thr)) {
357 if (should_wake_up(curr, thr))
358 /* Remove this thread from sleep set */
359 scheduler->remove_sleep(thr);
364 /** @brief Alert the model-checker that an incorrectly-ordered
365 * synchronization was made */
366 void ModelChecker::set_bad_synchronization()
368 priv->bad_synchronization = true;
372 * Check whether the current trace has triggered an assertion which should halt
375 * @return True, if the execution should be aborted; false otherwise
377 bool ModelChecker::has_asserted() const
379 return priv->asserted;
383 * Trigger a trace assertion which should cause this execution to be halted.
384 * This can be due to a detected bug or due to an infeasibility that should
387 void ModelChecker::set_assert()
389 priv->asserted = true;
393 * Check if we are in a deadlock. Should only be called at the end of an
394 * execution, although it should not give false positives in the middle of an
395 * execution (there should be some ENABLED thread).
397 * @return True if program is in a deadlock; false otherwise
399 bool ModelChecker::is_deadlocked() const
401 bool blocking_threads = false;
402 for (unsigned int i = 0; i < get_num_threads(); i++) {
403 thread_id_t tid = int_to_id(i);
406 Thread *t = get_thread(tid);
407 if (!t->is_model_thread() && t->get_pending())
408 blocking_threads = true;
410 return blocking_threads;
414 * Check if this is a complete execution. That is, have all thread completed
415 * execution (rather than exiting because sleep sets have forced a redundant
418 * @return True if the execution is complete.
420 bool ModelChecker::is_complete_execution() const
422 for (unsigned int i = 0; i < get_num_threads(); i++)
423 if (is_enabled(int_to_id(i)))
429 * @brief Assert a bug in the executing program.
431 * Use this function to assert any sort of bug in the user program. If the
432 * current trace is feasible (actually, a prefix of some feasible execution),
433 * then this execution will be aborted, printing the appropriate message. If
434 * the current trace is not yet feasible, the error message will be stashed and
435 * printed if the execution ever becomes feasible.
437 * @param msg Descriptive message for the bug (do not include newline char)
438 * @return True if bug is immediately-feasible
440 bool ModelChecker::assert_bug(const char *msg, ...)
446 vsnprintf(str, sizeof(str), msg, ap);
449 priv->bugs.push_back(new bug_message(str));
451 if (isfeasibleprefix()) {
459 * @brief Assert a bug in the executing program, asserted by a user thread
460 * @see ModelChecker::assert_bug
461 * @param msg Descriptive message for the bug (do not include newline char)
463 void ModelChecker::assert_user_bug(const char *msg)
465 /* If feasible bug, bail out now */
467 switch_to_master(NULL);
470 /** @return True, if any bugs have been reported for this execution */
471 bool ModelChecker::have_bug_reports() const
473 return priv->bugs.size() != 0;
476 /** @brief Print bug report listing for this execution (if any bugs exist) */
477 void ModelChecker::print_bugs() const
479 if (have_bug_reports()) {
480 model_print("Bug report: %zu bug%s detected\n",
482 priv->bugs.size() > 1 ? "s" : "");
483 for (unsigned int i = 0; i < priv->bugs.size(); i++)
484 priv->bugs[i]->print();
489 * @brief Record end-of-execution stats
491 * Must be run when exiting an execution. Records various stats.
492 * @see struct execution_stats
494 void ModelChecker::record_stats()
497 if (!isfeasibleprefix())
498 stats.num_infeasible++;
499 else if (have_bug_reports())
500 stats.num_buggy_executions++;
501 else if (is_complete_execution())
502 stats.num_complete++;
504 stats.num_redundant++;
507 * @todo We can violate this ASSERT() when fairness/sleep sets
508 * conflict to cause an execution to terminate, e.g. with:
509 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
511 //ASSERT(scheduler->all_threads_sleeping());
515 /** @brief Print execution stats */
516 void ModelChecker::print_stats() const
518 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
519 model_print("Number of redundant executions: %d\n", stats.num_redundant);
520 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
521 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
522 model_print("Total executions: %d\n", stats.num_total);
523 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
527 * @brief End-of-exeuction print
528 * @param printbugs Should any existing bugs be printed?
530 void ModelChecker::print_execution(bool printbugs) const
532 print_program_output();
534 if (params.verbose) {
535 model_print("Earliest divergence point since last feasible execution:\n");
536 if (earliest_diverge)
537 earliest_diverge->print();
539 model_print("(Not set)\n");
545 /* Don't print invalid bugs */
554 * Queries the model-checker for more executions to explore and, if one
555 * exists, resets the model-checker state to execute a new execution.
557 * @return If there are more executions to explore, return true. Otherwise,
560 bool ModelChecker::next_execution()
563 /* Is this execution a feasible execution that's worth bug-checking? */
564 bool complete = isfeasibleprefix() && (is_complete_execution() ||
567 /* End-of-execution bug checks */
570 assert_bug("Deadlock detected");
573 run_trace_analyses();
579 if (params.verbose || (complete && have_bug_reports()))
580 print_execution(complete);
582 clear_program_output();
585 earliest_diverge = NULL;
587 if ((diverge = get_next_backtrack()) == NULL)
591 model_print("Next execution will diverge at:\n");
595 reset_to_initial_state();
599 /** @brief Run trace analyses on complete trace */
600 void ModelChecker::run_trace_analyses() {
601 for (unsigned int i = 0; i < trace_analyses->size(); i++)
602 (*trace_analyses)[i]->analyze(action_trace);
606 * @brief Find the last fence-related backtracking conflict for a ModelAction
608 * This function performs the search for the most recent conflicting action
609 * against which we should perform backtracking, as affected by fence
610 * operations. This includes pairs of potentially-synchronizing actions which
611 * occur due to fence-acquire or fence-release, and hence should be explored in
612 * the opposite execution order.
614 * @param act The current action
615 * @return The most recent action which conflicts with act due to fences
617 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
619 /* Only perform release/acquire fence backtracking for stores */
620 if (!act->is_write())
623 /* Find a fence-release (or, act is a release) */
624 ModelAction *last_release;
625 if (act->is_release())
628 last_release = get_last_fence_release(act->get_tid());
632 /* Skip past the release */
633 action_list_t *list = action_trace;
634 action_list_t::reverse_iterator rit;
635 for (rit = list->rbegin(); rit != list->rend(); rit++)
636 if (*rit == last_release)
638 ASSERT(rit != list->rend());
643 * load --sb-> fence-acquire */
644 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
645 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
646 bool found_acquire_fences = false;
647 for ( ; rit != list->rend(); rit++) {
648 ModelAction *prev = *rit;
649 if (act->same_thread(prev))
652 int tid = id_to_int(prev->get_tid());
654 if (prev->is_read() && act->same_var(prev)) {
655 if (prev->is_acquire()) {
656 /* Found most recent load-acquire, don't need
657 * to search for more fences */
658 if (!found_acquire_fences)
661 prior_loads[tid] = prev;
664 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
665 found_acquire_fences = true;
666 acquire_fences[tid] = prev;
670 ModelAction *latest_backtrack = NULL;
671 for (unsigned int i = 0; i < acquire_fences.size(); i++)
672 if (acquire_fences[i] && prior_loads[i])
673 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
674 latest_backtrack = acquire_fences[i];
675 return latest_backtrack;
679 * @brief Find the last backtracking conflict for a ModelAction
681 * This function performs the search for the most recent conflicting action
682 * against which we should perform backtracking. This primary includes pairs of
683 * synchronizing actions which should be explored in the opposite execution
686 * @param act The current action
687 * @return The most recent action which conflicts with act
689 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
691 switch (act->get_type()) {
692 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
696 ModelAction *ret = NULL;
698 /* linear search: from most recent to oldest */
699 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
700 action_list_t::reverse_iterator rit;
701 for (rit = list->rbegin(); rit != list->rend(); rit++) {
702 ModelAction *prev = *rit;
703 if (prev->could_synchronize_with(act)) {
709 ModelAction *ret2 = get_last_fence_conflict(act);
719 case ATOMIC_TRYLOCK: {
720 /* linear search: from most recent to oldest */
721 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
722 action_list_t::reverse_iterator rit;
723 for (rit = list->rbegin(); rit != list->rend(); rit++) {
724 ModelAction *prev = *rit;
725 if (act->is_conflicting_lock(prev))
730 case ATOMIC_UNLOCK: {
731 /* linear search: from most recent to oldest */
732 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
733 action_list_t::reverse_iterator rit;
734 for (rit = list->rbegin(); rit != list->rend(); rit++) {
735 ModelAction *prev = *rit;
736 if (!act->same_thread(prev) && prev->is_failed_trylock())
742 /* linear search: from most recent to oldest */
743 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
744 action_list_t::reverse_iterator rit;
745 for (rit = list->rbegin(); rit != list->rend(); rit++) {
746 ModelAction *prev = *rit;
747 if (!act->same_thread(prev) && prev->is_failed_trylock())
749 if (!act->same_thread(prev) && prev->is_notify())
755 case ATOMIC_NOTIFY_ALL:
756 case ATOMIC_NOTIFY_ONE: {
757 /* linear search: from most recent to oldest */
758 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
759 action_list_t::reverse_iterator rit;
760 for (rit = list->rbegin(); rit != list->rend(); rit++) {
761 ModelAction *prev = *rit;
762 if (!act->same_thread(prev) && prev->is_wait())
773 /** This method finds backtracking points where we should try to
774 * reorder the parameter ModelAction against.
776 * @param the ModelAction to find backtracking points for.
778 void ModelChecker::set_backtracking(ModelAction *act)
780 Thread *t = get_thread(act);
781 ModelAction *prev = get_last_conflict(act);
785 Node *node = prev->get_node()->get_parent();
787 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
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 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
805 /* Don't backtrack into a point where the thread is disabled or sleeping. */
806 if (node->enabled_status(tid) != THREAD_ENABLED)
809 /* Check if this has been explored already */
810 if (node->has_been_explored(tid))
813 /* See if fairness allows */
814 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
816 for (int t = 0; t < node->get_num_threads(); t++) {
817 thread_id_t tother = int_to_id(t);
818 if (node->is_enabled(tother) && node->has_priority(tother)) {
827 /* See if CHESS-like yield fairness allows */
828 if (model->params.yieldon) {
830 for (int t = 0; t < node->get_num_threads(); t++) {
831 thread_id_t tother = int_to_id(t);
832 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
841 /* Cache the latest backtracking point */
842 set_latest_backtrack(prev);
844 /* If this is a new backtracking point, mark the tree */
845 if (!node->set_backtrack(tid))
847 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
848 id_to_int(prev->get_tid()),
849 id_to_int(t->get_id()));
858 * @brief Cache the a backtracking point as the "most recent", if eligible
860 * Note that this does not prepare the NodeStack for this backtracking
861 * operation, it only caches the action on a per-execution basis
863 * @param act The operation at which we should explore a different next action
864 * (i.e., backtracking point)
865 * @return True, if this action is now the most recent backtracking point;
868 bool ModelChecker::set_latest_backtrack(ModelAction *act)
870 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
871 priv->next_backtrack = act;
878 * Returns last backtracking point. The model checker will explore a different
879 * path for this point in the next execution.
880 * @return The ModelAction at which the next execution should diverge.
882 ModelAction * ModelChecker::get_next_backtrack()
884 ModelAction *next = priv->next_backtrack;
885 priv->next_backtrack = NULL;
890 * Processes a read model action.
891 * @param curr is the read model action to process.
892 * @return True if processing this read updates the mo_graph.
894 bool ModelChecker::process_read(ModelAction *curr)
896 Node *node = curr->get_node();
898 bool updated = false;
899 switch (node->get_read_from_status()) {
900 case READ_FROM_PAST: {
901 const ModelAction *rf = node->get_read_from_past();
904 mo_graph->startChanges();
906 ASSERT(!is_infeasible());
907 if (!check_recency(curr, rf)) {
908 if (node->increment_read_from()) {
909 mo_graph->rollbackChanges();
912 priv->too_many_reads = true;
916 updated = r_modification_order(curr, rf);
918 mo_graph->commitChanges();
919 mo_check_promises(curr, true);
922 case READ_FROM_PROMISE: {
923 Promise *promise = curr->get_node()->get_read_from_promise();
924 if (promise->add_reader(curr))
925 priv->failed_promise = true;
926 curr->set_read_from_promise(promise);
927 mo_graph->startChanges();
928 if (!check_recency(curr, promise))
929 priv->too_many_reads = true;
930 updated = r_modification_order(curr, promise);
931 mo_graph->commitChanges();
934 case READ_FROM_FUTURE: {
935 /* Read from future value */
936 struct future_value fv = node->get_future_value();
937 Promise *promise = new Promise(curr, fv);
938 curr->set_read_from_promise(promise);
939 promises->push_back(promise);
940 mo_graph->startChanges();
941 updated = r_modification_order(curr, promise);
942 mo_graph->commitChanges();
948 get_thread(curr)->set_return_value(curr->get_return_value());
954 * Processes a lock, trylock, or unlock model action. @param curr is
955 * the read model action to process.
957 * The try lock operation checks whether the lock is taken. If not,
958 * it falls to the normal lock operation case. If so, it returns
961 * The lock operation has already been checked that it is enabled, so
962 * it just grabs the lock and synchronizes with the previous unlock.
964 * The unlock operation has to re-enable all of the threads that are
965 * waiting on the lock.
967 * @return True if synchronization was updated; false otherwise
969 bool ModelChecker::process_mutex(ModelAction *curr)
971 std::mutex *mutex = curr->get_mutex();
972 struct std::mutex_state *state = NULL;
975 state = mutex->get_state();
977 switch (curr->get_type()) {
978 case ATOMIC_TRYLOCK: {
979 bool success = !state->locked;
980 curr->set_try_lock(success);
982 get_thread(curr)->set_return_value(0);
985 get_thread(curr)->set_return_value(1);
987 //otherwise fall into the lock case
989 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
990 assert_bug("Lock access before initialization");
991 state->locked = get_thread(curr);
992 ModelAction *unlock = get_last_unlock(curr);
993 //synchronize with the previous unlock statement
994 if (unlock != NULL) {
995 curr->synchronize_with(unlock);
1001 case ATOMIC_UNLOCK: {
1002 /* wake up the other threads */
1003 for (unsigned int i = 0; i < get_num_threads(); i++) {
1004 Thread *t = get_thread(int_to_id(i));
1005 Thread *curr_thrd = get_thread(curr);
1006 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
1010 /* unlock the lock - after checking who was waiting on it */
1011 state->locked = NULL;
1013 if (!curr->is_wait())
1014 break; /* The rest is only for ATOMIC_WAIT */
1016 /* Should we go to sleep? (simulate spurious failures) */
1017 if (curr->get_node()->get_misc() == 0) {
1018 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1020 scheduler->sleep(get_thread(curr));
1024 case ATOMIC_NOTIFY_ALL: {
1025 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1026 //activate all the waiting threads
1027 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1028 scheduler->wake(get_thread(*rit));
1033 case ATOMIC_NOTIFY_ONE: {
1034 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1035 int wakeupthread = curr->get_node()->get_misc();
1036 action_list_t::iterator it = waiters->begin();
1037 advance(it, wakeupthread);
1038 scheduler->wake(get_thread(*it));
1050 * @brief Check if the current pending promises allow a future value to be sent
1052 * If one of the following is true:
1053 * (a) there are no pending promises
1054 * (b) the reader and writer do not cross any promises
1055 * Then, it is safe to pass a future value back now.
1057 * Otherwise, we must save the pending future value until (a) or (b) is true
1059 * @param writer The operation which sends the future value. Must be a write.
1060 * @param reader The operation which will observe the value. Must be a read.
1061 * @return True if the future value can be sent now; false if it must wait.
1063 bool ModelChecker::promises_may_allow(const ModelAction *writer,
1064 const ModelAction *reader) const
1066 if (promises->empty())
1068 for(int i=promises->size()-1;i>=0;i--) {
1069 ModelAction *pr=(*promises)[i]->get_reader(0);
1070 //reader is after promise...doesn't cross any promise
1073 //writer is after promise, reader before...bad...
1081 * @brief Add a future value to a reader
1083 * This function performs a few additional checks to ensure that the future
1084 * value can be feasibly observed by the reader
1086 * @param writer The operation whose value is sent. Must be a write.
1087 * @param reader The read operation which may read the future value. Must be a read.
1089 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1091 /* Do more ambitious checks now that mo is more complete */
1092 if (!mo_may_allow(writer, reader))
1095 Node *node = reader->get_node();
1097 /* Find an ancestor thread which exists at the time of the reader */
1098 Thread *write_thread = get_thread(writer);
1099 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1100 write_thread = write_thread->get_parent();
1102 struct future_value fv = {
1103 writer->get_write_value(),
1104 writer->get_seq_number() + params.maxfuturedelay,
1105 write_thread->get_id(),
1107 if (node->add_future_value(fv))
1108 set_latest_backtrack(reader);
1112 * Process a write ModelAction
1113 * @param curr The ModelAction to process
1114 * @return True if the mo_graph was updated or promises were resolved
1116 bool ModelChecker::process_write(ModelAction *curr)
1118 /* Readers to which we may send our future value */
1119 ModelVector<ModelAction *> send_fv;
1121 const ModelAction *earliest_promise_reader;
1122 bool updated_promises = false;
1124 bool updated_mod_order = w_modification_order(curr, &send_fv);
1125 Promise *promise = pop_promise_to_resolve(curr);
1128 earliest_promise_reader = promise->get_reader(0);
1129 updated_promises = resolve_promise(curr, promise);
1131 earliest_promise_reader = NULL;
1133 for (unsigned int i = 0; i < send_fv.size(); i++) {
1134 ModelAction *read = send_fv[i];
1136 /* Don't send future values to reads after the Promise we resolve */
1137 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
1138 /* Check if future value can be sent immediately */
1139 if (promises_may_allow(curr, read)) {
1140 add_future_value(curr, read);
1142 futurevalues->push_back(PendingFutureValue(curr, read));
1147 /* Check the pending future values */
1148 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
1149 struct PendingFutureValue pfv = (*futurevalues)[i];
1150 if (promises_may_allow(pfv.writer, pfv.reader)) {
1151 add_future_value(pfv.writer, pfv.reader);
1152 futurevalues->erase(futurevalues->begin() + i);
1156 mo_graph->commitChanges();
1157 mo_check_promises(curr, false);
1159 get_thread(curr)->set_return_value(VALUE_NONE);
1160 return updated_mod_order || updated_promises;
1164 * Process a fence ModelAction
1165 * @param curr The ModelAction to process
1166 * @return True if synchronization was updated
1168 bool ModelChecker::process_fence(ModelAction *curr)
1171 * fence-relaxed: no-op
1172 * fence-release: only log the occurence (not in this function), for
1173 * use in later synchronization
1174 * fence-acquire (this function): search for hypothetical release
1176 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1178 bool updated = false;
1179 if (curr->is_acquire()) {
1180 action_list_t *list = action_trace;
1181 action_list_t::reverse_iterator rit;
1182 /* Find X : is_read(X) && X --sb-> curr */
1183 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1184 ModelAction *act = *rit;
1187 if (act->get_tid() != curr->get_tid())
1189 /* Stop at the beginning of the thread */
1190 if (act->is_thread_start())
1192 /* Stop once we reach a prior fence-acquire */
1193 if (act->is_fence() && act->is_acquire())
1195 if (!act->is_read())
1197 /* read-acquire will find its own release sequences */
1198 if (act->is_acquire())
1201 /* Establish hypothetical release sequences */
1202 rel_heads_list_t release_heads;
1203 get_release_seq_heads(curr, act, &release_heads);
1204 for (unsigned int i = 0; i < release_heads.size(); i++)
1205 if (!curr->synchronize_with(release_heads[i]))
1206 set_bad_synchronization();
1207 if (release_heads.size() != 0)
1215 * @brief Process the current action for thread-related activity
1217 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1218 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1219 * synchronization, etc. This function is a no-op for non-THREAD actions
1220 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1222 * @param curr The current action
1223 * @return True if synchronization was updated or a thread completed
1225 bool ModelChecker::process_thread_action(ModelAction *curr)
1227 bool updated = false;
1229 switch (curr->get_type()) {
1230 case THREAD_CREATE: {
1231 thrd_t *thrd = (thrd_t *)curr->get_location();
1232 struct thread_params *params = (struct thread_params *)curr->get_value();
1233 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1235 th->set_creation(curr);
1236 /* Promises can be satisfied by children */
1237 for (unsigned int i = 0; i < promises->size(); i++) {
1238 Promise *promise = (*promises)[i];
1239 if (promise->thread_is_available(curr->get_tid()))
1240 promise->add_thread(th->get_id());
1245 Thread *blocking = curr->get_thread_operand();
1246 ModelAction *act = get_last_action(blocking->get_id());
1247 curr->synchronize_with(act);
1248 updated = true; /* trigger rel-seq checks */
1251 case THREAD_FINISH: {
1252 Thread *th = get_thread(curr);
1253 /* Wake up any joining threads */
1254 for (unsigned int i = 0; i < get_num_threads(); i++) {
1255 Thread *waiting = get_thread(int_to_id(i));
1256 if (waiting->waiting_on() == th &&
1257 waiting->get_pending()->is_thread_join())
1258 scheduler->wake(waiting);
1261 /* Completed thread can't satisfy promises */
1262 for (unsigned int i = 0; i < promises->size(); i++) {
1263 Promise *promise = (*promises)[i];
1264 if (promise->thread_is_available(th->get_id()))
1265 if (promise->eliminate_thread(th->get_id()))
1266 priv->failed_promise = true;
1268 updated = true; /* trigger rel-seq checks */
1271 case THREAD_START: {
1272 check_promises(curr->get_tid(), NULL, curr->get_cv());
1283 * @brief Process the current action for release sequence fixup activity
1285 * Performs model-checker release sequence fixups for the current action,
1286 * forcing a single pending release sequence to break (with a given, potential
1287 * "loose" write) or to complete (i.e., synchronize). If a pending release
1288 * sequence forms a complete release sequence, then we must perform the fixup
1289 * synchronization, mo_graph additions, etc.
1291 * @param curr The current action; must be a release sequence fixup action
1292 * @param work_queue The work queue to which to add work items as they are
1295 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1297 const ModelAction *write = curr->get_node()->get_relseq_break();
1298 struct release_seq *sequence = pending_rel_seqs->back();
1299 pending_rel_seqs->pop_back();
1301 ModelAction *acquire = sequence->acquire;
1302 const ModelAction *rf = sequence->rf;
1303 const ModelAction *release = sequence->release;
1307 ASSERT(release->same_thread(rf));
1309 if (write == NULL) {
1311 * @todo Forcing a synchronization requires that we set
1312 * modification order constraints. For instance, we can't allow
1313 * a fixup sequence in which two separate read-acquire
1314 * operations read from the same sequence, where the first one
1315 * synchronizes and the other doesn't. Essentially, we can't
1316 * allow any writes to insert themselves between 'release' and
1320 /* Must synchronize */
1321 if (!acquire->synchronize_with(release)) {
1322 set_bad_synchronization();
1325 /* Re-check all pending release sequences */
1326 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1327 /* Re-check act for mo_graph edges */
1328 work_queue->push_back(MOEdgeWorkEntry(acquire));
1330 /* propagate synchronization to later actions */
1331 action_list_t::reverse_iterator rit = action_trace->rbegin();
1332 for (; (*rit) != acquire; rit++) {
1333 ModelAction *propagate = *rit;
1334 if (acquire->happens_before(propagate)) {
1335 propagate->synchronize_with(acquire);
1336 /* Re-check 'propagate' for mo_graph edges */
1337 work_queue->push_back(MOEdgeWorkEntry(propagate));
1341 /* Break release sequence with new edges:
1342 * release --mo--> write --mo--> rf */
1343 mo_graph->addEdge(release, write);
1344 mo_graph->addEdge(write, rf);
1347 /* See if we have realized a data race */
1352 * Initialize the current action by performing one or more of the following
1353 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1354 * in the NodeStack, manipulating backtracking sets, allocating and
1355 * initializing clock vectors, and computing the promises to fulfill.
1357 * @param curr The current action, as passed from the user context; may be
1358 * freed/invalidated after the execution of this function, with a different
1359 * action "returned" its place (pass-by-reference)
1360 * @return True if curr is a newly-explored action; false otherwise
1362 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1364 ModelAction *newcurr;
1366 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1367 newcurr = process_rmw(*curr);
1370 if (newcurr->is_rmw())
1371 compute_promises(newcurr);
1377 (*curr)->set_seq_number(get_next_seq_num());
1379 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1381 /* First restore type and order in case of RMW operation */
1382 if ((*curr)->is_rmwr())
1383 newcurr->copy_typeandorder(*curr);
1385 ASSERT((*curr)->get_location() == newcurr->get_location());
1386 newcurr->copy_from_new(*curr);
1388 /* Discard duplicate ModelAction; use action from NodeStack */
1391 /* Always compute new clock vector */
1392 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1395 return false; /* Action was explored previously */
1399 /* Always compute new clock vector */
1400 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1402 /* Assign most recent release fence */
1403 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1406 * Perform one-time actions when pushing new ModelAction onto
1409 if (newcurr->is_write())
1410 compute_promises(newcurr);
1411 else if (newcurr->is_relseq_fixup())
1412 compute_relseq_breakwrites(newcurr);
1413 else if (newcurr->is_wait())
1414 newcurr->get_node()->set_misc_max(2);
1415 else if (newcurr->is_notify_one()) {
1416 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1418 return true; /* This was a new ModelAction */
1423 * @brief Establish reads-from relation between two actions
1425 * Perform basic operations involved with establishing a concrete rf relation,
1426 * including setting the ModelAction data and checking for release sequences.
1428 * @param act The action that is reading (must be a read)
1429 * @param rf The action from which we are reading (must be a write)
1431 * @return True if this read established synchronization
1433 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1436 ASSERT(rf->is_write());
1438 act->set_read_from(rf);
1439 if (act->is_acquire()) {
1440 rel_heads_list_t release_heads;
1441 get_release_seq_heads(act, act, &release_heads);
1442 int num_heads = release_heads.size();
1443 for (unsigned int i = 0; i < release_heads.size(); i++)
1444 if (!act->synchronize_with(release_heads[i])) {
1445 set_bad_synchronization();
1448 return num_heads > 0;
1454 * Check promises and eliminate potentially-satisfying threads when a thread is
1455 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1456 * no longer satisfy a promise generated from that thread.
1458 * @param blocker The thread on which a thread is waiting
1459 * @param waiting The waiting thread
1461 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1463 for (unsigned int i = 0; i < promises->size(); i++) {
1464 Promise *promise = (*promises)[i];
1465 if (!promise->thread_is_available(waiting->get_id()))
1467 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1468 ModelAction *reader = promise->get_reader(j);
1469 if (reader->get_tid() != blocker->get_id())
1471 if (promise->eliminate_thread(waiting->get_id())) {
1472 /* Promise has failed */
1473 priv->failed_promise = true;
1475 /* Only eliminate the 'waiting' thread once */
1483 * @brief Check whether a model action is enabled.
1485 * Checks whether a lock or join operation would be successful (i.e., is the
1486 * lock already locked, or is the joined thread already complete). If not, put
1487 * the action in a waiter list.
1489 * @param curr is the ModelAction to check whether it is enabled.
1490 * @return a bool that indicates whether the action is enabled.
1492 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1493 if (curr->is_lock()) {
1494 std::mutex *lock = curr->get_mutex();
1495 struct std::mutex_state *state = lock->get_state();
1498 } else if (curr->is_thread_join()) {
1499 Thread *blocking = curr->get_thread_operand();
1500 if (!blocking->is_complete()) {
1501 thread_blocking_check_promises(blocking, get_thread(curr));
1510 * This is the heart of the model checker routine. It performs model-checking
1511 * actions corresponding to a given "current action." Among other processes, it
1512 * calculates reads-from relationships, updates synchronization clock vectors,
1513 * forms a memory_order constraints graph, and handles replay/backtrack
1514 * execution when running permutations of previously-observed executions.
1516 * @param curr The current action to process
1517 * @return The ModelAction that is actually executed; may be different than
1518 * curr; may be NULL, if the current action is not enabled to run
1520 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1523 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1524 bool newly_explored = initialize_curr_action(&curr);
1528 wake_up_sleeping_actions(curr);
1530 /* Compute fairness information for CHESS yield algorithm */
1531 if (model->params.yieldon) {
1532 curr->get_node()->update_yield(scheduler);
1535 /* Add the action to lists before any other model-checking tasks */
1536 if (!second_part_of_rmw)
1537 add_action_to_lists(curr);
1539 /* Build may_read_from set for newly-created actions */
1540 if (newly_explored && curr->is_read())
1541 build_may_read_from(curr);
1543 /* Initialize work_queue with the "current action" work */
1544 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1545 while (!work_queue.empty() && !has_asserted()) {
1546 WorkQueueEntry work = work_queue.front();
1547 work_queue.pop_front();
1549 switch (work.type) {
1550 case WORK_CHECK_CURR_ACTION: {
1551 ModelAction *act = work.action;
1552 bool update = false; /* update this location's release seq's */
1553 bool update_all = false; /* update all release seq's */
1555 if (process_thread_action(curr))
1558 if (act->is_read() && !second_part_of_rmw && process_read(act))
1561 if (act->is_write() && process_write(act))
1564 if (act->is_fence() && process_fence(act))
1567 if (act->is_mutex_op() && process_mutex(act))
1570 if (act->is_relseq_fixup())
1571 process_relseq_fixup(curr, &work_queue);
1574 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1576 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1579 case WORK_CHECK_RELEASE_SEQ:
1580 resolve_release_sequences(work.location, &work_queue);
1582 case WORK_CHECK_MO_EDGES: {
1583 /** @todo Complete verification of work_queue */
1584 ModelAction *act = work.action;
1585 bool updated = false;
1587 if (act->is_read()) {
1588 const ModelAction *rf = act->get_reads_from();
1589 const Promise *promise = act->get_reads_from_promise();
1591 if (r_modification_order(act, rf))
1593 } else if (promise) {
1594 if (r_modification_order(act, promise))
1598 if (act->is_write()) {
1599 if (w_modification_order(act, NULL))
1602 mo_graph->commitChanges();
1605 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1614 check_curr_backtracking(curr);
1615 set_backtracking(curr);
1619 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1621 Node *currnode = curr->get_node();
1622 Node *parnode = currnode->get_parent();
1624 if ((parnode && !parnode->backtrack_empty()) ||
1625 !currnode->misc_empty() ||
1626 !currnode->read_from_empty() ||
1627 !currnode->promise_empty() ||
1628 !currnode->relseq_break_empty()) {
1629 set_latest_backtrack(curr);
1633 bool ModelChecker::promises_expired() const
1635 for (unsigned int i = 0; i < promises->size(); i++) {
1636 Promise *promise = (*promises)[i];
1637 if (promise->get_expiration() < priv->used_sequence_numbers)
1644 * This is the strongest feasibility check available.
1645 * @return whether the current trace (partial or complete) must be a prefix of
1648 bool ModelChecker::isfeasibleprefix() const
1650 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1654 * Print disagnostic information about an infeasible execution
1655 * @param prefix A string to prefix the output with; if NULL, then a default
1656 * message prefix will be provided
1658 void ModelChecker::print_infeasibility(const char *prefix) const
1662 if (mo_graph->checkForCycles())
1663 ptr += sprintf(ptr, "[mo cycle]");
1664 if (priv->failed_promise)
1665 ptr += sprintf(ptr, "[failed promise]");
1666 if (priv->too_many_reads)
1667 ptr += sprintf(ptr, "[too many reads]");
1668 if (priv->no_valid_reads)
1669 ptr += sprintf(ptr, "[no valid reads-from]");
1670 if (priv->bad_synchronization)
1671 ptr += sprintf(ptr, "[bad sw ordering]");
1672 if (promises_expired())
1673 ptr += sprintf(ptr, "[promise expired]");
1674 if (promises->size() != 0)
1675 ptr += sprintf(ptr, "[unresolved promise]");
1677 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1681 * Returns whether the current completed trace is feasible, except for pending
1682 * release sequences.
1684 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1686 return !is_infeasible() && promises->size() == 0;
1690 * Check if the current partial trace is infeasible. Does not check any
1691 * end-of-execution flags, which might rule out the execution. Thus, this is
1692 * useful only for ruling an execution as infeasible.
1693 * @return whether the current partial trace is infeasible.
1695 bool ModelChecker::is_infeasible() const
1697 return mo_graph->checkForCycles() ||
1698 priv->no_valid_reads ||
1699 priv->failed_promise ||
1700 priv->too_many_reads ||
1701 priv->bad_synchronization ||
1705 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1706 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1707 ModelAction *lastread = get_last_action(act->get_tid());
1708 lastread->process_rmw(act);
1709 if (act->is_rmw()) {
1710 if (lastread->get_reads_from())
1711 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1713 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1714 mo_graph->commitChanges();
1720 * A helper function for ModelChecker::check_recency, to check if the current
1721 * thread is able to read from a different write/promise for 'params.maxreads'
1722 * number of steps and if that write/promise should become visible (i.e., is
1723 * ordered later in the modification order). This helps model memory liveness.
1725 * @param curr The current action. Must be a read.
1726 * @param rf The write/promise from which we plan to read
1727 * @param other_rf The write/promise from which we may read
1728 * @return True if we were able to read from other_rf for params.maxreads steps
1730 template <typename T, typename U>
1731 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1733 /* Need a different write/promise */
1734 if (other_rf->equals(rf))
1737 /* Only look for "newer" writes/promises */
1738 if (!mo_graph->checkReachable(rf, other_rf))
1741 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1742 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1743 action_list_t::reverse_iterator rit = list->rbegin();
1744 ASSERT((*rit) == curr);
1745 /* Skip past curr */
1748 /* Does this write/promise work for everyone? */
1749 for (int i = 0; i < params.maxreads; i++, rit++) {
1750 ModelAction *act = *rit;
1751 if (!act->may_read_from(other_rf))
1758 * Checks whether a thread has read from the same write or Promise for too many
1759 * times without seeing the effects of a later write/Promise.
1762 * 1) there must a different write/promise that we could read from,
1763 * 2) we must have read from the same write/promise in excess of maxreads times,
1764 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1765 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1767 * If so, we decide that the execution is no longer feasible.
1769 * @param curr The current action. Must be a read.
1770 * @param rf The ModelAction/Promise from which we might read.
1771 * @return True if the read should succeed; false otherwise
1773 template <typename T>
1774 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1776 if (!params.maxreads)
1779 //NOTE: Next check is just optimization, not really necessary....
1780 if (curr->get_node()->get_read_from_past_size() +
1781 curr->get_node()->get_read_from_promise_size() <= 1)
1784 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1785 int tid = id_to_int(curr->get_tid());
1786 ASSERT(tid < (int)thrd_lists->size());
1787 action_list_t *list = &(*thrd_lists)[tid];
1788 action_list_t::reverse_iterator rit = list->rbegin();
1789 ASSERT((*rit) == curr);
1790 /* Skip past curr */
1793 action_list_t::reverse_iterator ritcopy = rit;
1794 /* See if we have enough reads from the same value */
1795 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1796 if (ritcopy == list->rend())
1798 ModelAction *act = *ritcopy;
1799 if (!act->is_read())
1801 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1803 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1805 if (act->get_node()->get_read_from_past_size() +
1806 act->get_node()->get_read_from_promise_size() <= 1)
1809 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1810 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1811 if (should_read_instead(curr, rf, write))
1812 return false; /* liveness failure */
1814 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1815 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1816 if (should_read_instead(curr, rf, promise))
1817 return false; /* liveness failure */
1823 * @brief Updates the mo_graph with the constraints imposed from the current
1826 * Basic idea is the following: Go through each other thread and find
1827 * the last action that happened before our read. Two cases:
1829 * -# The action is a write: that write must either occur before
1830 * the write we read from or be the write we read from.
1831 * -# The action is a read: the write that that action read from
1832 * must occur before the write we read from or be the same write.
1834 * @param curr The current action. Must be a read.
1835 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1836 * @return True if modification order edges were added; false otherwise
1838 template <typename rf_type>
1839 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1841 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1844 ASSERT(curr->is_read());
1846 /* Last SC fence in the current thread */
1847 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1848 ModelAction *last_sc_write = NULL;
1849 if (curr->is_seqcst())
1850 last_sc_write = get_last_seq_cst_write(curr);
1852 /* Iterate over all threads */
1853 for (i = 0; i < thrd_lists->size(); i++) {
1854 /* Last SC fence in thread i */
1855 ModelAction *last_sc_fence_thread_local = NULL;
1856 if (int_to_id((int)i) != curr->get_tid())
1857 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1859 /* Last SC fence in thread i, before last SC fence in current thread */
1860 ModelAction *last_sc_fence_thread_before = NULL;
1861 if (last_sc_fence_local)
1862 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1864 /* Iterate over actions in thread, starting from most recent */
1865 action_list_t *list = &(*thrd_lists)[i];
1866 action_list_t::reverse_iterator rit;
1867 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1868 ModelAction *act = *rit;
1873 /* Don't want to add reflexive edges on 'rf' */
1874 if (act->equals(rf)) {
1875 if (act->happens_before(curr))
1881 if (act->is_write()) {
1882 /* C++, Section 29.3 statement 5 */
1883 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1884 *act < *last_sc_fence_thread_local) {
1885 added = mo_graph->addEdge(act, rf) || added;
1888 /* C++, Section 29.3 statement 4 */
1889 else if (act->is_seqcst() && last_sc_fence_local &&
1890 *act < *last_sc_fence_local) {
1891 added = mo_graph->addEdge(act, rf) || added;
1894 /* C++, Section 29.3 statement 6 */
1895 else if (last_sc_fence_thread_before &&
1896 *act < *last_sc_fence_thread_before) {
1897 added = mo_graph->addEdge(act, rf) || added;
1902 /* C++, Section 29.3 statement 3 (second subpoint) */
1903 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1904 added = mo_graph->addEdge(act, rf) || added;
1909 * Include at most one act per-thread that "happens
1912 if (act->happens_before(curr)) {
1913 if (act->is_write()) {
1914 added = mo_graph->addEdge(act, rf) || added;
1916 const ModelAction *prevrf = act->get_reads_from();
1917 const Promise *prevrf_promise = act->get_reads_from_promise();
1919 if (!prevrf->equals(rf))
1920 added = mo_graph->addEdge(prevrf, rf) || added;
1921 } else if (!prevrf_promise->equals(rf)) {
1922 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1931 * All compatible, thread-exclusive promises must be ordered after any
1932 * concrete loads from the same thread
1934 for (unsigned int i = 0; i < promises->size(); i++)
1935 if ((*promises)[i]->is_compatible_exclusive(curr))
1936 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1942 * Updates the mo_graph with the constraints imposed from the current write.
1944 * Basic idea is the following: Go through each other thread and find
1945 * the lastest action that happened before our write. Two cases:
1947 * (1) The action is a write => that write must occur before
1950 * (2) The action is a read => the write that that action read from
1951 * must occur before the current write.
1953 * This method also handles two other issues:
1955 * (I) Sequential Consistency: Making sure that if the current write is
1956 * seq_cst, that it occurs after the previous seq_cst write.
1958 * (II) Sending the write back to non-synchronizing reads.
1960 * @param curr The current action. Must be a write.
1961 * @param send_fv A vector for stashing reads to which we may pass our future
1962 * value. If NULL, then don't record any future values.
1963 * @return True if modification order edges were added; false otherwise
1965 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1967 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1970 ASSERT(curr->is_write());
1972 if (curr->is_seqcst()) {
1973 /* We have to at least see the last sequentially consistent write,
1974 so we are initialized. */
1975 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1976 if (last_seq_cst != NULL) {
1977 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1981 /* Last SC fence in the current thread */
1982 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1984 /* Iterate over all threads */
1985 for (i = 0; i < thrd_lists->size(); i++) {
1986 /* Last SC fence in thread i, before last SC fence in current thread */
1987 ModelAction *last_sc_fence_thread_before = NULL;
1988 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1989 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1991 /* Iterate over actions in thread, starting from most recent */
1992 action_list_t *list = &(*thrd_lists)[i];
1993 action_list_t::reverse_iterator rit;
1994 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1995 ModelAction *act = *rit;
1998 * 1) If RMW and it actually read from something, then we
1999 * already have all relevant edges, so just skip to next
2002 * 2) If RMW and it didn't read from anything, we should
2003 * whatever edge we can get to speed up convergence.
2005 * 3) If normal write, we need to look at earlier actions, so
2006 * continue processing list.
2008 if (curr->is_rmw()) {
2009 if (curr->get_reads_from() != NULL)
2017 /* C++, Section 29.3 statement 7 */
2018 if (last_sc_fence_thread_before && act->is_write() &&
2019 *act < *last_sc_fence_thread_before) {
2020 added = mo_graph->addEdge(act, curr) || added;
2025 * Include at most one act per-thread that "happens
2028 if (act->happens_before(curr)) {
2030 * Note: if act is RMW, just add edge:
2032 * The following edge should be handled elsewhere:
2033 * readfrom(act) --mo--> act
2035 if (act->is_write())
2036 added = mo_graph->addEdge(act, curr) || added;
2037 else if (act->is_read()) {
2038 //if previous read accessed a null, just keep going
2039 if (act->get_reads_from() == NULL)
2041 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2044 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2045 !act->same_thread(curr)) {
2046 /* We have an action that:
2047 (1) did not happen before us
2048 (2) is a read and we are a write
2049 (3) cannot synchronize with us
2050 (4) is in a different thread
2052 that read could potentially read from our write. Note that
2053 these checks are overly conservative at this point, we'll
2054 do more checks before actually removing the
2058 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2059 if (!is_infeasible())
2060 send_fv->push_back(act);
2061 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2062 add_future_value(curr, act);
2069 * All compatible, thread-exclusive promises must be ordered after any
2070 * concrete stores to the same thread, or else they can be merged with
2073 for (unsigned int i = 0; i < promises->size(); i++)
2074 if ((*promises)[i]->is_compatible_exclusive(curr))
2075 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2080 /** Arbitrary reads from the future are not allowed. Section 29.3
2081 * part 9 places some constraints. This method checks one result of constraint
2082 * constraint. Others require compiler support. */
2083 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2085 if (!writer->is_rmw())
2088 if (!reader->is_rmw())
2091 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2092 if (search == reader)
2094 if (search->get_tid() == reader->get_tid() &&
2095 search->happens_before(reader))
2103 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2104 * some constraints. This method checks one the following constraint (others
2105 * require compiler support):
2107 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2109 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2111 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2113 /* Iterate over all threads */
2114 for (i = 0; i < thrd_lists->size(); i++) {
2115 const ModelAction *write_after_read = NULL;
2117 /* Iterate over actions in thread, starting from most recent */
2118 action_list_t *list = &(*thrd_lists)[i];
2119 action_list_t::reverse_iterator rit;
2120 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2121 ModelAction *act = *rit;
2123 /* Don't disallow due to act == reader */
2124 if (!reader->happens_before(act) || reader == act)
2126 else if (act->is_write())
2127 write_after_read = act;
2128 else if (act->is_read() && act->get_reads_from() != NULL)
2129 write_after_read = act->get_reads_from();
2132 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2139 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2140 * The ModelAction under consideration is expected to be taking part in
2141 * release/acquire synchronization as an object of the "reads from" relation.
2142 * Note that this can only provide release sequence support for RMW chains
2143 * which do not read from the future, as those actions cannot be traced until
2144 * their "promise" is fulfilled. Similarly, we may not even establish the
2145 * presence of a release sequence with certainty, as some modification order
2146 * constraints may be decided further in the future. Thus, this function
2147 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2148 * and a boolean representing certainty.
2150 * @param rf The action that might be part of a release sequence. Must be a
2152 * @param release_heads A pass-by-reference style return parameter. After
2153 * execution of this function, release_heads will contain the heads of all the
2154 * relevant release sequences, if any exists with certainty
2155 * @param pending A pass-by-reference style return parameter which is only used
2156 * when returning false (i.e., uncertain). Returns most information regarding
2157 * an uncertain release sequence, including any write operations that might
2158 * break the sequence.
2159 * @return true, if the ModelChecker is certain that release_heads is complete;
2162 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2163 rel_heads_list_t *release_heads,
2164 struct release_seq *pending) const
2166 /* Only check for release sequences if there are no cycles */
2167 if (mo_graph->checkForCycles())
2170 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2171 ASSERT(rf->is_write());
2173 if (rf->is_release())
2174 release_heads->push_back(rf);
2175 else if (rf->get_last_fence_release())
2176 release_heads->push_back(rf->get_last_fence_release());
2178 break; /* End of RMW chain */
2180 /** @todo Need to be smarter here... In the linux lock
2181 * example, this will run to the beginning of the program for
2183 /** @todo The way to be smarter here is to keep going until 1
2184 * thread has a release preceded by an acquire and you've seen
2187 /* acq_rel RMW is a sufficient stopping condition */
2188 if (rf->is_acquire() && rf->is_release())
2189 return true; /* complete */
2192 /* read from future: need to settle this later */
2194 return false; /* incomplete */
2197 if (rf->is_release())
2198 return true; /* complete */
2200 /* else relaxed write
2201 * - check for fence-release in the same thread (29.8, stmt. 3)
2202 * - check modification order for contiguous subsequence
2203 * -> rf must be same thread as release */
2205 const ModelAction *fence_release = rf->get_last_fence_release();
2206 /* Synchronize with a fence-release unconditionally; we don't need to
2207 * find any more "contiguous subsequence..." for it */
2209 release_heads->push_back(fence_release);
2211 int tid = id_to_int(rf->get_tid());
2212 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2213 action_list_t *list = &(*thrd_lists)[tid];
2214 action_list_t::const_reverse_iterator rit;
2216 /* Find rf in the thread list */
2217 rit = std::find(list->rbegin(), list->rend(), rf);
2218 ASSERT(rit != list->rend());
2220 /* Find the last {write,fence}-release */
2221 for (; rit != list->rend(); rit++) {
2222 if (fence_release && *(*rit) < *fence_release)
2224 if ((*rit)->is_release())
2227 if (rit == list->rend()) {
2228 /* No write-release in this thread */
2229 return true; /* complete */
2230 } else if (fence_release && *(*rit) < *fence_release) {
2231 /* The fence-release is more recent (and so, "stronger") than
2232 * the most recent write-release */
2233 return true; /* complete */
2234 } /* else, need to establish contiguous release sequence */
2235 ModelAction *release = *rit;
2237 ASSERT(rf->same_thread(release));
2239 pending->writes.clear();
2241 bool certain = true;
2242 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2243 if (id_to_int(rf->get_tid()) == (int)i)
2245 list = &(*thrd_lists)[i];
2247 /* Can we ensure no future writes from this thread may break
2248 * the release seq? */
2249 bool future_ordered = false;
2251 ModelAction *last = get_last_action(int_to_id(i));
2252 Thread *th = get_thread(int_to_id(i));
2253 if ((last && rf->happens_before(last)) ||
2256 future_ordered = true;
2258 ASSERT(!th->is_model_thread() || future_ordered);
2260 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2261 const ModelAction *act = *rit;
2262 /* Reach synchronization -> this thread is complete */
2263 if (act->happens_before(release))
2265 if (rf->happens_before(act)) {
2266 future_ordered = true;
2270 /* Only non-RMW writes can break release sequences */
2271 if (!act->is_write() || act->is_rmw())
2274 /* Check modification order */
2275 if (mo_graph->checkReachable(rf, act)) {
2276 /* rf --mo--> act */
2277 future_ordered = true;
2280 if (mo_graph->checkReachable(act, release))
2281 /* act --mo--> release */
2283 if (mo_graph->checkReachable(release, act) &&
2284 mo_graph->checkReachable(act, rf)) {
2285 /* release --mo-> act --mo--> rf */
2286 return true; /* complete */
2288 /* act may break release sequence */
2289 pending->writes.push_back(act);
2292 if (!future_ordered)
2293 certain = false; /* This thread is uncertain */
2297 release_heads->push_back(release);
2298 pending->writes.clear();
2300 pending->release = release;
2307 * An interface for getting the release sequence head(s) with which a
2308 * given ModelAction must synchronize. This function only returns a non-empty
2309 * result when it can locate a release sequence head with certainty. Otherwise,
2310 * it may mark the internal state of the ModelChecker so that it will handle
2311 * the release sequence at a later time, causing @a acquire to update its
2312 * synchronization at some later point in execution.
2314 * @param acquire The 'acquire' action that may synchronize with a release
2316 * @param read The read action that may read from a release sequence; this may
2317 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2318 * when 'acquire' is a fence-acquire)
2319 * @param release_heads A pass-by-reference return parameter. Will be filled
2320 * with the head(s) of the release sequence(s), if they exists with certainty.
2321 * @see ModelChecker::release_seq_heads
2323 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2324 ModelAction *read, rel_heads_list_t *release_heads)
2326 const ModelAction *rf = read->get_reads_from();
2327 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2328 sequence->acquire = acquire;
2329 sequence->read = read;
2331 if (!release_seq_heads(rf, release_heads, sequence)) {
2332 /* add act to 'lazy checking' list */
2333 pending_rel_seqs->push_back(sequence);
2335 snapshot_free(sequence);
2340 * Attempt to resolve all stashed operations that might synchronize with a
2341 * release sequence for a given location. This implements the "lazy" portion of
2342 * determining whether or not a release sequence was contiguous, since not all
2343 * modification order information is present at the time an action occurs.
2345 * @param location The location/object that should be checked for release
2346 * sequence resolutions. A NULL value means to check all locations.
2347 * @param work_queue The work queue to which to add work items as they are
2349 * @return True if any updates occurred (new synchronization, new mo_graph
2352 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2354 bool updated = false;
2355 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2356 while (it != pending_rel_seqs->end()) {
2357 struct release_seq *pending = *it;
2358 ModelAction *acquire = pending->acquire;
2359 const ModelAction *read = pending->read;
2361 /* Only resolve sequences on the given location, if provided */
2362 if (location && read->get_location() != location) {
2367 const ModelAction *rf = read->get_reads_from();
2368 rel_heads_list_t release_heads;
2370 complete = release_seq_heads(rf, &release_heads, pending);
2371 for (unsigned int i = 0; i < release_heads.size(); i++) {
2372 if (!acquire->has_synchronized_with(release_heads[i])) {
2373 if (acquire->synchronize_with(release_heads[i]))
2376 set_bad_synchronization();
2381 /* Re-check all pending release sequences */
2382 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2383 /* Re-check read-acquire for mo_graph edges */
2384 if (acquire->is_read())
2385 work_queue->push_back(MOEdgeWorkEntry(acquire));
2387 /* propagate synchronization to later actions */
2388 action_list_t::reverse_iterator rit = action_trace->rbegin();
2389 for (; (*rit) != acquire; rit++) {
2390 ModelAction *propagate = *rit;
2391 if (acquire->happens_before(propagate)) {
2392 propagate->synchronize_with(acquire);
2393 /* Re-check 'propagate' for mo_graph edges */
2394 work_queue->push_back(MOEdgeWorkEntry(propagate));
2399 it = pending_rel_seqs->erase(it);
2400 snapshot_free(pending);
2406 // If we resolved promises or data races, see if we have realized a data race.
2413 * Performs various bookkeeping operations for the current ModelAction. For
2414 * instance, adds action to the per-object, per-thread action vector and to the
2415 * action trace list of all thread actions.
2417 * @param act is the ModelAction to add.
2419 void ModelChecker::add_action_to_lists(ModelAction *act)
2421 int tid = id_to_int(act->get_tid());
2422 ModelAction *uninit = NULL;
2424 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2425 if (list->empty() && act->is_atomic_var()) {
2426 uninit = get_uninitialized_action(act);
2427 uninit_id = id_to_int(uninit->get_tid());
2428 list->push_front(uninit);
2430 list->push_back(act);
2432 action_trace->push_back(act);
2434 action_trace->push_front(uninit);
2436 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2437 if (tid >= (int)vec->size())
2438 vec->resize(priv->next_thread_id);
2439 (*vec)[tid].push_back(act);
2441 (*vec)[uninit_id].push_front(uninit);
2443 if ((int)thrd_last_action->size() <= tid)
2444 thrd_last_action->resize(get_num_threads());
2445 (*thrd_last_action)[tid] = act;
2447 (*thrd_last_action)[uninit_id] = uninit;
2449 if (act->is_fence() && act->is_release()) {
2450 if ((int)thrd_last_fence_release->size() <= tid)
2451 thrd_last_fence_release->resize(get_num_threads());
2452 (*thrd_last_fence_release)[tid] = act;
2455 if (act->is_wait()) {
2456 void *mutex_loc = (void *) act->get_value();
2457 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2459 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2460 if (tid >= (int)vec->size())
2461 vec->resize(priv->next_thread_id);
2462 (*vec)[tid].push_back(act);
2467 * @brief Get the last action performed by a particular Thread
2468 * @param tid The thread ID of the Thread in question
2469 * @return The last action in the thread
2471 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2473 int threadid = id_to_int(tid);
2474 if (threadid < (int)thrd_last_action->size())
2475 return (*thrd_last_action)[id_to_int(tid)];
2481 * @brief Get the last fence release performed by a particular Thread
2482 * @param tid The thread ID of the Thread in question
2483 * @return The last fence release in the thread, if one exists; NULL otherwise
2485 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2487 int threadid = id_to_int(tid);
2488 if (threadid < (int)thrd_last_fence_release->size())
2489 return (*thrd_last_fence_release)[id_to_int(tid)];
2495 * Gets the last memory_order_seq_cst write (in the total global sequence)
2496 * performed on a particular object (i.e., memory location), not including the
2498 * @param curr The current ModelAction; also denotes the object location to
2500 * @return The last seq_cst write
2502 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2504 void *location = curr->get_location();
2505 action_list_t *list = get_safe_ptr_action(obj_map, location);
2506 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2507 action_list_t::reverse_iterator rit;
2508 for (rit = list->rbegin(); (*rit) != curr; rit++)
2510 rit++; /* Skip past curr */
2511 for ( ; rit != list->rend(); rit++)
2512 if ((*rit)->is_write() && (*rit)->is_seqcst())
2518 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2519 * performed in a particular thread, prior to a particular fence.
2520 * @param tid The ID of the thread to check
2521 * @param before_fence The fence from which to begin the search; if NULL, then
2522 * search for the most recent fence in the thread.
2523 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2525 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2527 /* All fences should have NULL location */
2528 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2529 action_list_t::reverse_iterator rit = list->rbegin();
2532 for (; rit != list->rend(); rit++)
2533 if (*rit == before_fence)
2536 ASSERT(*rit == before_fence);
2540 for (; rit != list->rend(); rit++)
2541 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2547 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2548 * location). This function identifies the mutex according to the current
2549 * action, which is presumed to perform on the same mutex.
2550 * @param curr The current ModelAction; also denotes the object location to
2552 * @return The last unlock operation
2554 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2556 void *location = curr->get_location();
2557 action_list_t *list = get_safe_ptr_action(obj_map, location);
2558 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2559 action_list_t::reverse_iterator rit;
2560 for (rit = list->rbegin(); rit != list->rend(); rit++)
2561 if ((*rit)->is_unlock() || (*rit)->is_wait())
2566 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2568 ModelAction *parent = get_last_action(tid);
2570 parent = get_thread(tid)->get_creation();
2575 * Returns the clock vector for a given thread.
2576 * @param tid The thread whose clock vector we want
2577 * @return Desired clock vector
2579 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2581 return get_parent_action(tid)->get_cv();
2585 * @brief Find the promise (if any) to resolve for the current action and
2586 * remove it from the pending promise vector
2587 * @param curr The current ModelAction. Should be a write.
2588 * @return The Promise to resolve, if any; otherwise NULL
2590 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2592 for (unsigned int i = 0; i < promises->size(); i++)
2593 if (curr->get_node()->get_promise(i)) {
2594 Promise *ret = (*promises)[i];
2595 promises->erase(promises->begin() + i);
2602 * Resolve a Promise with a current write.
2603 * @param write The ModelAction that is fulfilling Promises
2604 * @param promise The Promise to resolve
2605 * @return True if the Promise was successfully resolved; false otherwise
2607 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2609 ModelVector<ModelAction *> actions_to_check;
2611 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2612 ModelAction *read = promise->get_reader(i);
2613 read_from(read, write);
2614 actions_to_check.push_back(read);
2616 /* Make sure the promise's value matches the write's value */
2617 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2618 if (!mo_graph->resolvePromise(promise, write))
2619 priv->failed_promise = true;
2622 * @todo It is possible to end up in an inconsistent state, where a
2623 * "resolved" promise may still be referenced if
2624 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2626 * Note that the inconsistency only matters when dumping mo_graph to
2632 //Check whether reading these writes has made threads unable to
2634 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2635 ModelAction *read = actions_to_check[i];
2636 mo_check_promises(read, true);
2643 * Compute the set of promises that could potentially be satisfied by this
2644 * action. Note that the set computation actually appears in the Node, not in
2646 * @param curr The ModelAction that may satisfy promises
2648 void ModelChecker::compute_promises(ModelAction *curr)
2650 for (unsigned int i = 0; i < promises->size(); i++) {
2651 Promise *promise = (*promises)[i];
2652 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2655 bool satisfy = true;
2656 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2657 const ModelAction *act = promise->get_reader(j);
2658 if (act->happens_before(curr) ||
2659 act->could_synchronize_with(curr)) {
2665 curr->get_node()->set_promise(i);
2669 /** Checks promises in response to change in ClockVector Threads. */
2670 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2672 for (unsigned int i = 0; i < promises->size(); i++) {
2673 Promise *promise = (*promises)[i];
2674 if (!promise->thread_is_available(tid))
2676 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2677 const ModelAction *act = promise->get_reader(j);
2678 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2679 merge_cv->synchronized_since(act)) {
2680 if (promise->eliminate_thread(tid)) {
2681 /* Promise has failed */
2682 priv->failed_promise = true;
2690 void ModelChecker::check_promises_thread_disabled()
2692 for (unsigned int i = 0; i < promises->size(); i++) {
2693 Promise *promise = (*promises)[i];
2694 if (promise->has_failed()) {
2695 priv->failed_promise = true;
2702 * @brief Checks promises in response to addition to modification order for
2705 * We test whether threads are still available for satisfying promises after an
2706 * addition to our modification order constraints. Those that are unavailable
2707 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2708 * that promise has failed.
2710 * @param act The ModelAction which updated the modification order
2711 * @param is_read_check Should be true if act is a read and we must check for
2712 * updates to the store from which it read (there is a distinction here for
2713 * RMW's, which are both a load and a store)
2715 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2717 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2719 for (unsigned int i = 0; i < promises->size(); i++) {
2720 Promise *promise = (*promises)[i];
2722 // Is this promise on the same location?
2723 if (!promise->same_location(write))
2726 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2727 const ModelAction *pread = promise->get_reader(j);
2728 if (!pread->happens_before(act))
2730 if (mo_graph->checkPromise(write, promise)) {
2731 priv->failed_promise = true;
2737 // Don't do any lookups twice for the same thread
2738 if (!promise->thread_is_available(act->get_tid()))
2741 if (mo_graph->checkReachable(promise, write)) {
2742 if (mo_graph->checkPromise(write, promise)) {
2743 priv->failed_promise = true;
2751 * Compute the set of writes that may break the current pending release
2752 * sequence. This information is extracted from previou release sequence
2755 * @param curr The current ModelAction. Must be a release sequence fixup
2758 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2760 if (pending_rel_seqs->empty())
2763 struct release_seq *pending = pending_rel_seqs->back();
2764 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2765 const ModelAction *write = pending->writes[i];
2766 curr->get_node()->add_relseq_break(write);
2769 /* NULL means don't break the sequence; just synchronize */
2770 curr->get_node()->add_relseq_break(NULL);
2774 * Build up an initial set of all past writes that this 'read' action may read
2775 * from, as well as any previously-observed future values that must still be valid.
2777 * @param curr is the current ModelAction that we are exploring; it must be a
2780 void ModelChecker::build_may_read_from(ModelAction *curr)
2782 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2784 ASSERT(curr->is_read());
2786 ModelAction *last_sc_write = NULL;
2788 if (curr->is_seqcst())
2789 last_sc_write = get_last_seq_cst_write(curr);
2791 /* Iterate over all threads */
2792 for (i = 0; i < thrd_lists->size(); i++) {
2793 /* Iterate over actions in thread, starting from most recent */
2794 action_list_t *list = &(*thrd_lists)[i];
2795 action_list_t::reverse_iterator rit;
2796 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2797 ModelAction *act = *rit;
2799 /* Only consider 'write' actions */
2800 if (!act->is_write() || act == curr)
2803 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2804 bool allow_read = true;
2806 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2808 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2812 /* Only add feasible reads */
2813 mo_graph->startChanges();
2814 r_modification_order(curr, act);
2815 if (!is_infeasible())
2816 curr->get_node()->add_read_from_past(act);
2817 mo_graph->rollbackChanges();
2820 /* Include at most one act per-thread that "happens before" curr */
2821 if (act->happens_before(curr))
2826 /* Inherit existing, promised future values */
2827 for (i = 0; i < promises->size(); i++) {
2828 const Promise *promise = (*promises)[i];
2829 const ModelAction *promise_read = promise->get_reader(0);
2830 if (promise_read->same_var(curr)) {
2831 /* Only add feasible future-values */
2832 mo_graph->startChanges();
2833 r_modification_order(curr, promise);
2834 if (!is_infeasible())
2835 curr->get_node()->add_read_from_promise(promise_read);
2836 mo_graph->rollbackChanges();
2840 /* We may find no valid may-read-from only if the execution is doomed */
2841 if (!curr->get_node()->read_from_size()) {
2842 priv->no_valid_reads = true;
2846 if (DBG_ENABLED()) {
2847 model_print("Reached read action:\n");
2849 model_print("Printing read_from_past\n");
2850 curr->get_node()->print_read_from_past();
2851 model_print("End printing read_from_past\n");
2855 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2857 for ( ; write != NULL; write = write->get_reads_from()) {
2858 /* UNINIT actions don't have a Node, and they never sleep */
2859 if (write->is_uninitialized())
2861 Node *prevnode = write->get_node()->get_parent();
2863 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2864 if (write->is_release() && thread_sleep)
2866 if (!write->is_rmw())
2873 * @brief Get an action representing an uninitialized atomic
2875 * This function may create a new one or try to retrieve one from the NodeStack
2877 * @param curr The current action, which prompts the creation of an UNINIT action
2878 * @return A pointer to the UNINIT ModelAction
2880 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2882 Node *node = curr->get_node();
2883 ModelAction *act = node->get_uninit_action();
2885 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2886 node->set_uninit_action(act);
2888 act->create_cv(NULL);
2892 static void print_list(action_list_t *list)
2894 action_list_t::iterator it;
2896 model_print("---------------------------------------------------------------------\n");
2898 unsigned int hash = 0;
2900 for (it = list->begin(); it != list->end(); it++) {
2901 const ModelAction *act = *it;
2902 if (act->get_seq_number() > 0)
2904 hash = hash^(hash<<3)^((*it)->hash());
2906 model_print("HASH %u\n", hash);
2907 model_print("---------------------------------------------------------------------\n");
2910 #if SUPPORT_MOD_ORDER_DUMP
2911 void ModelChecker::dumpGraph(char *filename) const
2914 sprintf(buffer, "%s.dot", filename);
2915 FILE *file = fopen(buffer, "w");
2916 fprintf(file, "digraph %s {\n", filename);
2917 mo_graph->dumpNodes(file);
2918 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2920 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2921 ModelAction *act = *it;
2922 if (act->is_read()) {
2923 mo_graph->dot_print_node(file, act);
2924 if (act->get_reads_from())
2925 mo_graph->dot_print_edge(file,
2926 act->get_reads_from(),
2928 "label=\"rf\", color=red, weight=2");
2930 mo_graph->dot_print_edge(file,
2931 act->get_reads_from_promise(),
2933 "label=\"rf\", color=red");
2935 if (thread_array[act->get_tid()]) {
2936 mo_graph->dot_print_edge(file,
2937 thread_array[id_to_int(act->get_tid())],
2939 "label=\"sb\", color=blue, weight=400");
2942 thread_array[act->get_tid()] = act;
2944 fprintf(file, "}\n");
2945 model_free(thread_array);
2950 /** @brief Prints an execution trace summary. */
2951 void ModelChecker::print_summary() const
2953 #if SUPPORT_MOD_ORDER_DUMP
2954 char buffername[100];
2955 sprintf(buffername, "exec%04u", stats.num_total);
2956 mo_graph->dumpGraphToFile(buffername);
2957 sprintf(buffername, "graph%04u", stats.num_total);
2958 dumpGraph(buffername);
2961 model_print("Execution %d:", stats.num_total);
2962 if (isfeasibleprefix()) {
2963 if (scheduler->all_threads_sleeping())
2964 model_print(" SLEEP-SET REDUNDANT");
2967 print_infeasibility(" INFEASIBLE");
2968 print_list(action_trace);
2970 if (!promises->empty()) {
2971 model_print("Pending promises:\n");
2972 for (unsigned int i = 0; i < promises->size(); i++) {
2973 model_print(" [P%u] ", i);
2974 (*promises)[i]->print();
2981 * Add a Thread to the system for the first time. Should only be called once
2983 * @param t The Thread to add
2985 void ModelChecker::add_thread(Thread *t)
2987 thread_map->put(id_to_int(t->get_id()), t);
2988 scheduler->add_thread(t);
2992 * @brief Get a Thread reference by its ID
2993 * @param tid The Thread's ID
2994 * @return A Thread reference
2996 Thread * ModelChecker::get_thread(thread_id_t tid) const
2998 return thread_map->get(id_to_int(tid));
3002 * @brief Get a reference to the Thread in which a ModelAction was executed
3003 * @param act The ModelAction
3004 * @return A Thread reference
3006 Thread * ModelChecker::get_thread(const ModelAction *act) const
3008 return get_thread(act->get_tid());
3012 * @brief Get a Promise's "promise number"
3014 * A "promise number" is an index number that is unique to a promise, valid
3015 * only for a specific snapshot of an execution trace. Promises may come and go
3016 * as they are generated an resolved, so an index only retains meaning for the
3019 * @param promise The Promise to check
3020 * @return The promise index, if the promise still is valid; otherwise -1
3022 int ModelChecker::get_promise_number(const Promise *promise) const
3024 for (unsigned int i = 0; i < promises->size(); i++)
3025 if ((*promises)[i] == promise)
3032 * @brief Check if a Thread is currently enabled
3033 * @param t The Thread to check
3034 * @return True if the Thread is currently enabled
3036 bool ModelChecker::is_enabled(Thread *t) const
3038 return scheduler->is_enabled(t);
3042 * @brief Check if a Thread is currently enabled
3043 * @param tid The ID of the Thread to check
3044 * @return True if the Thread is currently enabled
3046 bool ModelChecker::is_enabled(thread_id_t tid) const
3048 return scheduler->is_enabled(tid);
3052 * Switch from a model-checker context to a user-thread context. This is the
3053 * complement of ModelChecker::switch_to_master and must be called from the
3054 * model-checker context
3056 * @param thread The user-thread to switch to
3058 void ModelChecker::switch_from_master(Thread *thread)
3060 scheduler->set_current_thread(thread);
3061 Thread::swap(&system_context, thread);
3065 * Switch from a user-context to the "master thread" context (a.k.a. system
3066 * context). This switch is made with the intention of exploring a particular
3067 * model-checking action (described by a ModelAction object). Must be called
3068 * from a user-thread context.
3070 * @param act The current action that will be explored. May be NULL only if
3071 * trace is exiting via an assertion (see ModelChecker::set_assert and
3072 * ModelChecker::has_asserted).
3073 * @return Return the value returned by the current action
3075 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3078 Thread *old = thread_current();
3079 scheduler->set_current_thread(NULL);
3080 ASSERT(!old->get_pending());
3081 old->set_pending(act);
3082 if (Thread::swap(old, &system_context) < 0) {
3083 perror("swap threads");
3086 return old->get_return_value();
3090 * Takes the next step in the execution, if possible.
3091 * @param curr The current step to take
3092 * @return Returns the next Thread to run, if any; NULL if this execution
3095 Thread * ModelChecker::take_step(ModelAction *curr)
3097 Thread *curr_thrd = get_thread(curr);
3098 ASSERT(curr_thrd->get_state() == THREAD_READY);
3100 ASSERT(check_action_enabled(curr)); /* May have side effects? */
3101 curr = check_current_action(curr);
3104 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3105 scheduler->remove_thread(curr_thrd);
3107 return action_select_next_thread(curr);
3110 /** Wrapper to run the user's main function, with appropriate arguments */
3111 void user_main_wrapper(void *)
3113 user_main(model->params.argc, model->params.argv);
3116 /** @return True if the execution has taken too many steps */
3117 bool ModelChecker::too_many_steps() const
3119 return params.bound != 0 && priv->used_sequence_numbers > params.bound;
3122 bool ModelChecker::should_terminate_execution()
3124 /* Infeasible -> don't take any more steps */
3125 if (is_infeasible())
3127 else if (isfeasibleprefix() && have_bug_reports()) {
3132 if (too_many_steps())
3137 /** @brief Run ModelChecker for the user program */
3138 void ModelChecker::run()
3142 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3147 * Stash next pending action(s) for thread(s). There
3148 * should only need to stash one thread's action--the
3149 * thread which just took a step--plus the first step
3150 * for any newly-created thread
3152 for (unsigned int i = 0; i < get_num_threads(); i++) {
3153 thread_id_t tid = int_to_id(i);
3154 Thread *thr = get_thread(tid);
3155 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3156 switch_from_master(thr);
3157 if (thr->is_waiting_on(thr))
3158 assert_bug("Deadlock detected (thread %u)", i);
3162 /* Don't schedule threads which should be disabled */
3163 for (unsigned int i = 0; i < get_num_threads(); i++) {
3164 Thread *th = get_thread(int_to_id(i));
3165 ModelAction *act = th->get_pending();
3166 if (act && is_enabled(th) && !check_action_enabled(act)) {
3167 scheduler->sleep(th);
3171 /* Catch assertions from prior take_step or from
3172 * between-ModelAction bugs (e.g., data races) */
3177 t = get_next_thread();
3178 if (!t || t->is_model_thread())
3181 /* Consume the next action for a Thread */
3182 ModelAction *curr = t->get_pending();
3183 t->set_pending(NULL);
3184 t = take_step(curr);
3185 } while (!should_terminate_execution());
3188 * Launch end-of-execution release sequence fixups only when
3189 * the execution is otherwise feasible AND there are:
3191 * (1) pending release sequences
3192 * (2) pending assertions that could be invalidated by a change
3193 * in clock vectors (i.e., data races)
3194 * (3) no pending promises
3196 while (!pending_rel_seqs->empty() &&
3197 is_feasible_prefix_ignore_relseq() &&
3198 !unrealizedraces.empty()) {
3199 model_print("*** WARNING: release sequence fixup action "
3200 "(%zu pending release seuqence(s)) ***\n",
3201 pending_rel_seqs->size());
3202 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3203 std::memory_order_seq_cst, NULL, VALUE_NONE,
3207 } while (next_execution());
3209 model_print("******* Model-checking complete: *******\n");