11 #include "snapshot-interface.h"
13 #include "clockvector.h"
14 #include "cyclegraph.h"
17 #include "threads-model.h"
19 #include "traceanalysis.h"
20 #include "bugmessage.h"
22 #define INITIAL_THREAD_ID 0
27 * Structure for holding small ModelChecker members that should be snapshotted
29 struct model_snapshot_members {
30 model_snapshot_members() :
31 /* First thread created will have id INITIAL_THREAD_ID */
32 next_thread_id(INITIAL_THREAD_ID),
33 used_sequence_numbers(0),
37 failed_promise(false),
38 too_many_reads(false),
39 no_valid_reads(false),
40 bad_synchronization(false),
44 ~model_snapshot_members() {
45 for (unsigned int i = 0; i < bugs.size(); i++)
50 unsigned int next_thread_id;
51 modelclock_t used_sequence_numbers;
52 ModelAction *next_backtrack;
53 SnapVector<bug_message *> bugs;
54 struct execution_stats stats;
58 /** @brief Incorrectly-ordered synchronization was made */
59 bool bad_synchronization;
65 /** @brief Constructor */
66 ModelChecker::ModelChecker(struct model_params params) :
67 /* Initialize default scheduler */
69 scheduler(new Scheduler()),
71 earliest_diverge(NULL),
72 action_trace(new action_list_t()),
73 thread_map(new HashTable<int, Thread *, int>()),
74 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
75 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
76 obj_thrd_map(new HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4 >()),
77 promises(new SnapVector<Promise *>()),
78 futurevalues(new SnapVector<struct PendingFutureValue>()),
79 pending_rel_seqs(new SnapVector<struct release_seq *>()),
80 thrd_last_action(new SnapVector<ModelAction *>(1)),
81 thrd_last_fence_release(new SnapVector<ModelAction *>()),
82 node_stack(new NodeStack()),
83 trace_analyses(new ModelVector<TraceAnalysis *>()),
84 priv(new struct model_snapshot_members()),
85 mo_graph(new CycleGraph())
87 /* Initialize a model-checker thread, for special ModelActions */
88 model_thread = new Thread(get_next_id());
89 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
92 /** @brief Destructor */
93 ModelChecker::~ModelChecker()
95 for (unsigned int i = 0; i < get_num_threads(); i++)
96 delete thread_map->get(i);
101 delete condvar_waiters_map;
104 for (unsigned int i = 0; i < promises->size(); i++)
105 delete (*promises)[i];
108 delete pending_rel_seqs;
110 delete thrd_last_action;
111 delete thrd_last_fence_release;
113 for (unsigned int i = 0; i < trace_analyses->size(); i++)
114 delete (*trace_analyses)[i];
115 delete trace_analyses;
121 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
123 action_list_t *tmp = hash->get(ptr);
125 tmp = new action_list_t();
131 static SnapVector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, SnapVector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
133 SnapVector<action_list_t> *tmp = hash->get(ptr);
135 tmp = new SnapVector<action_list_t>();
141 action_list_t * ModelChecker::get_actions_on_obj(void * obj, thread_id_t tid) {
142 SnapVector<action_list_t> *wrv=obj_thrd_map->get(obj);
145 unsigned int thread=id_to_int(tid);
146 if (thread < wrv->size())
147 return &(*wrv)[thread];
154 * Restores user program to initial state and resets all model-checker data
157 void ModelChecker::reset_to_initial_state()
159 DEBUG("+++ Resetting to initial state +++\n");
160 node_stack->reset_execution();
163 * FIXME: if we utilize partial rollback, we will need to free only
164 * those pending actions which were NOT pending before the rollback
167 for (unsigned int i = 0; i < get_num_threads(); i++)
168 delete get_thread(int_to_id(i))->get_pending();
170 snapshot_backtrack_before(0);
173 /** @return a thread ID for a new Thread */
174 thread_id_t ModelChecker::get_next_id()
176 return priv->next_thread_id++;
179 /** @return the number of user threads created during this execution */
180 unsigned int ModelChecker::get_num_threads() const
182 return priv->next_thread_id;
186 * Must be called from user-thread context (e.g., through the global
187 * thread_current() interface)
189 * @return The currently executing Thread.
191 Thread * ModelChecker::get_current_thread() const
193 return scheduler->get_current_thread();
196 /** @return a sequence number for a new ModelAction */
197 modelclock_t ModelChecker::get_next_seq_num()
199 return ++priv->used_sequence_numbers;
202 Node * ModelChecker::get_curr_node() const
204 return node_stack->get_head();
208 * @brief Select the next thread to execute based on the curren action
210 * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
211 * actions should be followed by the execution of their child thread. In either
212 * case, the current action should determine the next thread schedule.
214 * @param curr The current action
215 * @return The next thread to run, if the current action will determine this
216 * selection; otherwise NULL
218 Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
220 /* Do not split atomic RMW */
222 return get_thread(curr);
223 /* Follow CREATE with the created thread */
224 if (curr->get_type() == THREAD_CREATE)
225 return curr->get_thread_operand();
230 * @brief Choose the next thread to execute.
232 * This function chooses the next thread that should execute. It can enforce
233 * execution replay/backtracking or, if the model-checker has no preference
234 * regarding the next thread (i.e., when exploring a new execution ordering),
235 * we defer to the scheduler.
237 * @return The next chosen thread to run, if any exist. Or else if the current
238 * execution should terminate, return NULL.
240 Thread * ModelChecker::get_next_thread()
245 * Have we completed exploring the preselected path? Then let the
249 return scheduler->select_next_thread();
251 /* Else, we are trying to replay an execution */
252 ModelAction *next = node_stack->get_next()->get_action();
254 if (next == diverge) {
255 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
256 earliest_diverge = diverge;
258 Node *nextnode = next->get_node();
259 Node *prevnode = nextnode->get_parent();
260 scheduler->update_sleep_set(prevnode);
262 /* Reached divergence point */
263 if (nextnode->increment_behaviors()) {
264 /* Execute the same thread with a new behavior */
265 tid = next->get_tid();
266 node_stack->pop_restofstack(2);
269 /* Make a different thread execute for next step */
270 scheduler->add_sleep(get_thread(next->get_tid()));
271 tid = prevnode->get_next_backtrack();
272 /* Make sure the backtracked thread isn't sleeping. */
273 node_stack->pop_restofstack(1);
274 if (diverge == earliest_diverge) {
275 earliest_diverge = prevnode->get_action();
278 /* Start the round robin scheduler from this thread id */
279 scheduler->set_scheduler_thread(tid);
280 /* The correct sleep set is in the parent node. */
283 DEBUG("*** Divergence point ***\n");
287 tid = next->get_tid();
289 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
290 ASSERT(tid != THREAD_ID_T_NONE);
291 return get_thread(id_to_int(tid));
295 * We need to know what the next actions of all threads in the sleep
296 * set will be. This method computes them and stores the actions at
297 * the corresponding thread object's pending action.
300 void ModelChecker::execute_sleep_set()
302 for (unsigned int i = 0; i < get_num_threads(); i++) {
303 thread_id_t tid = int_to_id(i);
304 Thread *thr = get_thread(tid);
305 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
306 thr->get_pending()->set_sleep_flag();
312 * @brief Should the current action wake up a given thread?
314 * @param curr The current action
315 * @param thread The thread that we might wake up
316 * @return True, if we should wake up the sleeping thread; false otherwise
318 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
320 const ModelAction *asleep = thread->get_pending();
321 /* Don't allow partial RMW to wake anyone up */
324 /* Synchronizing actions may have been backtracked */
325 if (asleep->could_synchronize_with(curr))
327 /* All acquire/release fences and fence-acquire/store-release */
328 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
330 /* Fence-release + store can awake load-acquire on the same location */
331 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
332 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
333 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
339 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
341 for (unsigned int i = 0; i < get_num_threads(); i++) {
342 Thread *thr = get_thread(int_to_id(i));
343 if (scheduler->is_sleep_set(thr)) {
344 if (should_wake_up(curr, thr))
345 /* Remove this thread from sleep set */
346 scheduler->remove_sleep(thr);
351 /** @brief Alert the model-checker that an incorrectly-ordered
352 * synchronization was made */
353 void ModelChecker::set_bad_synchronization()
355 priv->bad_synchronization = true;
359 * Check whether the current trace has triggered an assertion which should halt
362 * @return True, if the execution should be aborted; false otherwise
364 bool ModelChecker::has_asserted() const
366 return priv->asserted;
370 * Trigger a trace assertion which should cause this execution to be halted.
371 * This can be due to a detected bug or due to an infeasibility that should
374 void ModelChecker::set_assert()
376 priv->asserted = true;
380 * Check if we are in a deadlock. Should only be called at the end of an
381 * execution, although it should not give false positives in the middle of an
382 * execution (there should be some ENABLED thread).
384 * @return True if program is in a deadlock; false otherwise
386 bool ModelChecker::is_deadlocked() const
388 bool blocking_threads = false;
389 for (unsigned int i = 0; i < get_num_threads(); i++) {
390 thread_id_t tid = int_to_id(i);
393 Thread *t = get_thread(tid);
394 if (!t->is_model_thread() && t->get_pending())
395 blocking_threads = true;
397 return blocking_threads;
401 * Check if this is a complete execution. That is, have all thread completed
402 * execution (rather than exiting because sleep sets have forced a redundant
405 * @return True if the execution is complete.
407 bool ModelChecker::is_complete_execution() const
409 for (unsigned int i = 0; i < get_num_threads(); i++)
410 if (is_enabled(int_to_id(i)))
416 * @brief Assert a bug in the executing program.
418 * Use this function to assert any sort of bug in the user program. If the
419 * current trace is feasible (actually, a prefix of some feasible execution),
420 * then this execution will be aborted, printing the appropriate message. If
421 * the current trace is not yet feasible, the error message will be stashed and
422 * printed if the execution ever becomes feasible.
424 * @param msg Descriptive message for the bug (do not include newline char)
425 * @return True if bug is immediately-feasible
427 bool ModelChecker::assert_bug(const char *msg, ...)
433 vsnprintf(str, sizeof(str), msg, ap);
436 priv->bugs.push_back(new bug_message(str));
438 if (isfeasibleprefix()) {
446 * @brief Assert a bug in the executing program, asserted by a user thread
447 * @see ModelChecker::assert_bug
448 * @param msg Descriptive message for the bug (do not include newline char)
450 void ModelChecker::assert_user_bug(const char *msg)
452 /* If feasible bug, bail out now */
454 switch_to_master(NULL);
457 /** @return True, if any bugs have been reported for this execution */
458 bool ModelChecker::have_bug_reports() const
460 return priv->bugs.size() != 0;
463 /** @brief Print bug report listing for this execution (if any bugs exist) */
464 void ModelChecker::print_bugs() const
466 if (have_bug_reports()) {
467 model_print("Bug report: %zu bug%s detected\n",
469 priv->bugs.size() > 1 ? "s" : "");
470 for (unsigned int i = 0; i < priv->bugs.size(); i++)
471 priv->bugs[i]->print();
476 * @brief Record end-of-execution stats
478 * Must be run when exiting an execution. Records various stats.
479 * @see struct execution_stats
481 void ModelChecker::record_stats()
484 if (!isfeasibleprefix())
485 stats.num_infeasible++;
486 else if (have_bug_reports())
487 stats.num_buggy_executions++;
488 else if (is_complete_execution())
489 stats.num_complete++;
491 stats.num_redundant++;
494 * @todo We can violate this ASSERT() when fairness/sleep sets
495 * conflict to cause an execution to terminate, e.g. with:
496 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
498 //ASSERT(scheduler->all_threads_sleeping());
502 /** @brief Print execution stats */
503 void ModelChecker::print_stats() const
505 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
506 model_print("Number of redundant executions: %d\n", stats.num_redundant);
507 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
508 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
509 model_print("Total executions: %d\n", stats.num_total);
510 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
514 * @brief End-of-exeuction print
515 * @param printbugs Should any existing bugs be printed?
517 void ModelChecker::print_execution(bool printbugs) const
519 print_program_output();
521 if (params.verbose) {
522 model_print("Earliest divergence point since last feasible execution:\n");
523 if (earliest_diverge)
524 earliest_diverge->print();
526 model_print("(Not set)\n");
532 /* Don't print invalid bugs */
541 * Queries the model-checker for more executions to explore and, if one
542 * exists, resets the model-checker state to execute a new execution.
544 * @return If there are more executions to explore, return true. Otherwise,
547 bool ModelChecker::next_execution()
550 /* Is this execution a feasible execution that's worth bug-checking? */
551 bool complete = isfeasibleprefix() && (is_complete_execution() ||
554 /* End-of-execution bug checks */
557 assert_bug("Deadlock detected");
560 run_trace_analyses();
566 if (params.verbose || (complete && have_bug_reports()))
567 print_execution(complete);
569 clear_program_output();
572 earliest_diverge = NULL;
574 if ((diverge = get_next_backtrack()) == NULL)
578 model_print("Next execution will diverge at:\n");
582 reset_to_initial_state();
586 /** @brief Run trace analyses on complete trace */
587 void ModelChecker::run_trace_analyses() {
588 for (unsigned int i = 0; i < trace_analyses->size(); i++)
589 (*trace_analyses)[i]->analyze(action_trace);
593 * @brief Find the last fence-related backtracking conflict for a ModelAction
595 * This function performs the search for the most recent conflicting action
596 * against which we should perform backtracking, as affected by fence
597 * operations. This includes pairs of potentially-synchronizing actions which
598 * occur due to fence-acquire or fence-release, and hence should be explored in
599 * the opposite execution order.
601 * @param act The current action
602 * @return The most recent action which conflicts with act due to fences
604 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
606 /* Only perform release/acquire fence backtracking for stores */
607 if (!act->is_write())
610 /* Find a fence-release (or, act is a release) */
611 ModelAction *last_release;
612 if (act->is_release())
615 last_release = get_last_fence_release(act->get_tid());
619 /* Skip past the release */
620 action_list_t *list = action_trace;
621 action_list_t::reverse_iterator rit;
622 for (rit = list->rbegin(); rit != list->rend(); rit++)
623 if (*rit == last_release)
625 ASSERT(rit != list->rend());
630 * load --sb-> fence-acquire */
631 ModelVector<ModelAction *> acquire_fences(get_num_threads(), NULL);
632 ModelVector<ModelAction *> prior_loads(get_num_threads(), NULL);
633 bool found_acquire_fences = false;
634 for ( ; rit != list->rend(); rit++) {
635 ModelAction *prev = *rit;
636 if (act->same_thread(prev))
639 int tid = id_to_int(prev->get_tid());
641 if (prev->is_read() && act->same_var(prev)) {
642 if (prev->is_acquire()) {
643 /* Found most recent load-acquire, don't need
644 * to search for more fences */
645 if (!found_acquire_fences)
648 prior_loads[tid] = prev;
651 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
652 found_acquire_fences = true;
653 acquire_fences[tid] = prev;
657 ModelAction *latest_backtrack = NULL;
658 for (unsigned int i = 0; i < acquire_fences.size(); i++)
659 if (acquire_fences[i] && prior_loads[i])
660 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
661 latest_backtrack = acquire_fences[i];
662 return latest_backtrack;
666 * @brief Find the last backtracking conflict for a ModelAction
668 * This function performs the search for the most recent conflicting action
669 * against which we should perform backtracking. This primary includes pairs of
670 * synchronizing actions which should be explored in the opposite execution
673 * @param act The current action
674 * @return The most recent action which conflicts with act
676 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
678 switch (act->get_type()) {
679 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
683 ModelAction *ret = NULL;
685 /* linear search: from most recent to oldest */
686 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
687 action_list_t::reverse_iterator rit;
688 for (rit = list->rbegin(); rit != list->rend(); rit++) {
689 ModelAction *prev = *rit;
690 if (prev->could_synchronize_with(act)) {
696 ModelAction *ret2 = get_last_fence_conflict(act);
706 case ATOMIC_TRYLOCK: {
707 /* linear search: from most recent to oldest */
708 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
709 action_list_t::reverse_iterator rit;
710 for (rit = list->rbegin(); rit != list->rend(); rit++) {
711 ModelAction *prev = *rit;
712 if (act->is_conflicting_lock(prev))
717 case ATOMIC_UNLOCK: {
718 /* linear search: from most recent to oldest */
719 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
720 action_list_t::reverse_iterator rit;
721 for (rit = list->rbegin(); rit != list->rend(); rit++) {
722 ModelAction *prev = *rit;
723 if (!act->same_thread(prev) && prev->is_failed_trylock())
729 /* linear search: from most recent to oldest */
730 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
731 action_list_t::reverse_iterator rit;
732 for (rit = list->rbegin(); rit != list->rend(); rit++) {
733 ModelAction *prev = *rit;
734 if (!act->same_thread(prev) && prev->is_failed_trylock())
736 if (!act->same_thread(prev) && prev->is_notify())
742 case ATOMIC_NOTIFY_ALL:
743 case ATOMIC_NOTIFY_ONE: {
744 /* linear search: from most recent to oldest */
745 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
746 action_list_t::reverse_iterator rit;
747 for (rit = list->rbegin(); rit != list->rend(); rit++) {
748 ModelAction *prev = *rit;
749 if (!act->same_thread(prev) && prev->is_wait())
760 /** This method finds backtracking points where we should try to
761 * reorder the parameter ModelAction against.
763 * @param the ModelAction to find backtracking points for.
765 void ModelChecker::set_backtracking(ModelAction *act)
767 Thread *t = get_thread(act);
768 ModelAction *prev = get_last_conflict(act);
772 Node *node = prev->get_node()->get_parent();
774 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
775 int low_tid, high_tid;
776 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
777 low_tid = id_to_int(act->get_tid());
778 high_tid = low_tid + 1;
781 high_tid = get_num_threads();
784 for (int i = low_tid; i < high_tid; i++) {
785 thread_id_t tid = int_to_id(i);
787 /* Make sure this thread can be enabled here. */
788 if (i >= node->get_num_threads())
791 /* See Dynamic Partial Order Reduction (addendum), POPL '05 */
792 /* Don't backtrack into a point where the thread is disabled or sleeping. */
793 if (node->enabled_status(tid) != THREAD_ENABLED)
796 /* Check if this has been explored already */
797 if (node->has_been_explored(tid))
800 /* See if fairness allows */
801 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
803 for (int t = 0; t < node->get_num_threads(); t++) {
804 thread_id_t tother = int_to_id(t);
805 if (node->is_enabled(tother) && node->has_priority(tother)) {
814 /* See if CHESS-like yield fairness allows */
815 if (model->params.yieldon) {
817 for (int t = 0; t < node->get_num_threads(); t++) {
818 thread_id_t tother = int_to_id(t);
819 if (node->is_enabled(tother) && node->has_priority_over(tid, tother)) {
828 /* Cache the latest backtracking point */
829 set_latest_backtrack(prev);
831 /* If this is a new backtracking point, mark the tree */
832 if (!node->set_backtrack(tid))
834 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
835 id_to_int(prev->get_tid()),
836 id_to_int(t->get_id()));
845 * @brief Cache the a backtracking point as the "most recent", if eligible
847 * Note that this does not prepare the NodeStack for this backtracking
848 * operation, it only caches the action on a per-execution basis
850 * @param act The operation at which we should explore a different next action
851 * (i.e., backtracking point)
852 * @return True, if this action is now the most recent backtracking point;
855 bool ModelChecker::set_latest_backtrack(ModelAction *act)
857 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
858 priv->next_backtrack = act;
865 * Returns last backtracking point. The model checker will explore a different
866 * path for this point in the next execution.
867 * @return The ModelAction at which the next execution should diverge.
869 ModelAction * ModelChecker::get_next_backtrack()
871 ModelAction *next = priv->next_backtrack;
872 priv->next_backtrack = NULL;
877 * Processes a read model action.
878 * @param curr is the read model action to process.
879 * @return True if processing this read updates the mo_graph.
881 bool ModelChecker::process_read(ModelAction *curr)
883 Node *node = curr->get_node();
885 bool updated = false;
886 switch (node->get_read_from_status()) {
887 case READ_FROM_PAST: {
888 const ModelAction *rf = node->get_read_from_past();
891 mo_graph->startChanges();
893 ASSERT(!is_infeasible());
894 if (!check_recency(curr, rf)) {
895 if (node->increment_read_from()) {
896 mo_graph->rollbackChanges();
899 priv->too_many_reads = true;
903 updated = r_modification_order(curr, rf);
905 mo_graph->commitChanges();
906 mo_check_promises(curr, true);
909 case READ_FROM_PROMISE: {
910 Promise *promise = curr->get_node()->get_read_from_promise();
911 if (promise->add_reader(curr))
912 priv->failed_promise = true;
913 curr->set_read_from_promise(promise);
914 mo_graph->startChanges();
915 if (!check_recency(curr, promise))
916 priv->too_many_reads = true;
917 updated = r_modification_order(curr, promise);
918 mo_graph->commitChanges();
921 case READ_FROM_FUTURE: {
922 /* Read from future value */
923 struct future_value fv = node->get_future_value();
924 Promise *promise = new Promise(curr, fv);
925 curr->set_read_from_promise(promise);
926 promises->push_back(promise);
927 mo_graph->startChanges();
928 updated = r_modification_order(curr, promise);
929 mo_graph->commitChanges();
935 get_thread(curr)->set_return_value(curr->get_return_value());
941 * Processes a lock, trylock, or unlock model action. @param curr is
942 * the read model action to process.
944 * The try lock operation checks whether the lock is taken. If not,
945 * it falls to the normal lock operation case. If so, it returns
948 * The lock operation has already been checked that it is enabled, so
949 * it just grabs the lock and synchronizes with the previous unlock.
951 * The unlock operation has to re-enable all of the threads that are
952 * waiting on the lock.
954 * @return True if synchronization was updated; false otherwise
956 bool ModelChecker::process_mutex(ModelAction *curr)
958 std::mutex *mutex = curr->get_mutex();
959 struct std::mutex_state *state = NULL;
962 state = mutex->get_state();
964 switch (curr->get_type()) {
965 case ATOMIC_TRYLOCK: {
966 bool success = !state->locked;
967 curr->set_try_lock(success);
969 get_thread(curr)->set_return_value(0);
972 get_thread(curr)->set_return_value(1);
974 //otherwise fall into the lock case
976 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
977 assert_bug("Lock access before initialization");
978 state->locked = get_thread(curr);
979 ModelAction *unlock = get_last_unlock(curr);
980 //synchronize with the previous unlock statement
981 if (unlock != NULL) {
982 synchronize(unlock, curr);
988 case ATOMIC_UNLOCK: {
989 /* wake up the other threads */
990 for (unsigned int i = 0; i < get_num_threads(); i++) {
991 Thread *t = get_thread(int_to_id(i));
992 Thread *curr_thrd = get_thread(curr);
993 if (t->waiting_on() == curr_thrd && t->get_pending()->is_lock())
997 /* unlock the lock - after checking who was waiting on it */
998 state->locked = NULL;
1000 if (!curr->is_wait())
1001 break; /* The rest is only for ATOMIC_WAIT */
1003 /* Should we go to sleep? (simulate spurious failures) */
1004 if (curr->get_node()->get_misc() == 0) {
1005 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
1007 scheduler->sleep(get_thread(curr));
1011 case ATOMIC_NOTIFY_ALL: {
1012 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1013 //activate all the waiting threads
1014 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
1015 scheduler->wake(get_thread(*rit));
1020 case ATOMIC_NOTIFY_ONE: {
1021 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1022 int wakeupthread = curr->get_node()->get_misc();
1023 action_list_t::iterator it = waiters->begin();
1024 advance(it, wakeupthread);
1025 scheduler->wake(get_thread(*it));
1037 * @brief Check if the current pending promises allow a future value to be sent
1039 * If one of the following is true:
1040 * (a) there are no pending promises
1041 * (b) the reader and writer do not cross any promises
1042 * Then, it is safe to pass a future value back now.
1044 * Otherwise, we must save the pending future value until (a) or (b) is true
1046 * @param writer The operation which sends the future value. Must be a write.
1047 * @param reader The operation which will observe the value. Must be a read.
1048 * @return True if the future value can be sent now; false if it must wait.
1050 bool ModelChecker::promises_may_allow(const ModelAction *writer,
1051 const ModelAction *reader) const
1053 if (promises->empty())
1055 for(int i=promises->size()-1;i>=0;i--) {
1056 ModelAction *pr=(*promises)[i]->get_reader(0);
1057 //reader is after promise...doesn't cross any promise
1060 //writer is after promise, reader before...bad...
1068 * @brief Add a future value to a reader
1070 * This function performs a few additional checks to ensure that the future
1071 * value can be feasibly observed by the reader
1073 * @param writer The operation whose value is sent. Must be a write.
1074 * @param reader The read operation which may read the future value. Must be a read.
1076 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1078 /* Do more ambitious checks now that mo is more complete */
1079 if (!mo_may_allow(writer, reader))
1082 Node *node = reader->get_node();
1084 /* Find an ancestor thread which exists at the time of the reader */
1085 Thread *write_thread = get_thread(writer);
1086 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1087 write_thread = write_thread->get_parent();
1089 struct future_value fv = {
1090 writer->get_write_value(),
1091 writer->get_seq_number() + params.maxfuturedelay,
1092 write_thread->get_id(),
1094 if (node->add_future_value(fv))
1095 set_latest_backtrack(reader);
1099 * Process a write ModelAction
1100 * @param curr The ModelAction to process
1101 * @return True if the mo_graph was updated or promises were resolved
1103 bool ModelChecker::process_write(ModelAction *curr)
1105 /* Readers to which we may send our future value */
1106 ModelVector<ModelAction *> send_fv;
1108 const ModelAction *earliest_promise_reader;
1109 bool updated_promises = false;
1111 bool updated_mod_order = w_modification_order(curr, &send_fv);
1112 Promise *promise = pop_promise_to_resolve(curr);
1115 earliest_promise_reader = promise->get_reader(0);
1116 updated_promises = resolve_promise(curr, promise);
1118 earliest_promise_reader = NULL;
1120 for (unsigned int i = 0; i < send_fv.size(); i++) {
1121 ModelAction *read = send_fv[i];
1123 /* Don't send future values to reads after the Promise we resolve */
1124 if (!earliest_promise_reader || *read < *earliest_promise_reader) {
1125 /* Check if future value can be sent immediately */
1126 if (promises_may_allow(curr, read)) {
1127 add_future_value(curr, read);
1129 futurevalues->push_back(PendingFutureValue(curr, read));
1134 /* Check the pending future values */
1135 for (int i = (int)futurevalues->size() - 1; i >= 0; i--) {
1136 struct PendingFutureValue pfv = (*futurevalues)[i];
1137 if (promises_may_allow(pfv.writer, pfv.reader)) {
1138 add_future_value(pfv.writer, pfv.reader);
1139 futurevalues->erase(futurevalues->begin() + i);
1143 mo_graph->commitChanges();
1144 mo_check_promises(curr, false);
1146 get_thread(curr)->set_return_value(VALUE_NONE);
1147 return updated_mod_order || updated_promises;
1151 * Process a fence ModelAction
1152 * @param curr The ModelAction to process
1153 * @return True if synchronization was updated
1155 bool ModelChecker::process_fence(ModelAction *curr)
1158 * fence-relaxed: no-op
1159 * fence-release: only log the occurence (not in this function), for
1160 * use in later synchronization
1161 * fence-acquire (this function): search for hypothetical release
1163 * fence-seq-cst: MO constraints formed in {r,w}_modification_order
1165 bool updated = false;
1166 if (curr->is_acquire()) {
1167 action_list_t *list = action_trace;
1168 action_list_t::reverse_iterator rit;
1169 /* Find X : is_read(X) && X --sb-> curr */
1170 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1171 ModelAction *act = *rit;
1174 if (act->get_tid() != curr->get_tid())
1176 /* Stop at the beginning of the thread */
1177 if (act->is_thread_start())
1179 /* Stop once we reach a prior fence-acquire */
1180 if (act->is_fence() && act->is_acquire())
1182 if (!act->is_read())
1184 /* read-acquire will find its own release sequences */
1185 if (act->is_acquire())
1188 /* Establish hypothetical release sequences */
1189 rel_heads_list_t release_heads;
1190 get_release_seq_heads(curr, act, &release_heads);
1191 for (unsigned int i = 0; i < release_heads.size(); i++)
1192 synchronize(release_heads[i], curr);
1193 if (release_heads.size() != 0)
1201 * @brief Process the current action for thread-related activity
1203 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1204 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1205 * synchronization, etc. This function is a no-op for non-THREAD actions
1206 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1208 * @param curr The current action
1209 * @return True if synchronization was updated or a thread completed
1211 bool ModelChecker::process_thread_action(ModelAction *curr)
1213 bool updated = false;
1215 switch (curr->get_type()) {
1216 case THREAD_CREATE: {
1217 thrd_t *thrd = (thrd_t *)curr->get_location();
1218 struct thread_params *params = (struct thread_params *)curr->get_value();
1219 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1221 th->set_creation(curr);
1222 /* Promises can be satisfied by children */
1223 for (unsigned int i = 0; i < promises->size(); i++) {
1224 Promise *promise = (*promises)[i];
1225 if (promise->thread_is_available(curr->get_tid()))
1226 promise->add_thread(th->get_id());
1231 Thread *blocking = curr->get_thread_operand();
1232 ModelAction *act = get_last_action(blocking->get_id());
1233 synchronize(act, curr);
1234 updated = true; /* trigger rel-seq checks */
1237 case THREAD_FINISH: {
1238 Thread *th = get_thread(curr);
1239 /* Wake up any joining threads */
1240 for (unsigned int i = 0; i < get_num_threads(); i++) {
1241 Thread *waiting = get_thread(int_to_id(i));
1242 if (waiting->waiting_on() == th &&
1243 waiting->get_pending()->is_thread_join())
1244 scheduler->wake(waiting);
1247 /* Completed thread can't satisfy promises */
1248 for (unsigned int i = 0; i < promises->size(); i++) {
1249 Promise *promise = (*promises)[i];
1250 if (promise->thread_is_available(th->get_id()))
1251 if (promise->eliminate_thread(th->get_id()))
1252 priv->failed_promise = true;
1254 updated = true; /* trigger rel-seq checks */
1257 case THREAD_START: {
1258 check_promises(curr->get_tid(), NULL, curr->get_cv());
1269 * @brief Process the current action for release sequence fixup activity
1271 * Performs model-checker release sequence fixups for the current action,
1272 * forcing a single pending release sequence to break (with a given, potential
1273 * "loose" write) or to complete (i.e., synchronize). If a pending release
1274 * sequence forms a complete release sequence, then we must perform the fixup
1275 * synchronization, mo_graph additions, etc.
1277 * @param curr The current action; must be a release sequence fixup action
1278 * @param work_queue The work queue to which to add work items as they are
1281 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1283 const ModelAction *write = curr->get_node()->get_relseq_break();
1284 struct release_seq *sequence = pending_rel_seqs->back();
1285 pending_rel_seqs->pop_back();
1287 ModelAction *acquire = sequence->acquire;
1288 const ModelAction *rf = sequence->rf;
1289 const ModelAction *release = sequence->release;
1293 ASSERT(release->same_thread(rf));
1295 if (write == NULL) {
1297 * @todo Forcing a synchronization requires that we set
1298 * modification order constraints. For instance, we can't allow
1299 * a fixup sequence in which two separate read-acquire
1300 * operations read from the same sequence, where the first one
1301 * synchronizes and the other doesn't. Essentially, we can't
1302 * allow any writes to insert themselves between 'release' and
1306 /* Must synchronize */
1307 if (!synchronize(release, acquire))
1309 /* Re-check all pending release sequences */
1310 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1311 /* Re-check act for mo_graph edges */
1312 work_queue->push_back(MOEdgeWorkEntry(acquire));
1314 /* propagate synchronization to later actions */
1315 action_list_t::reverse_iterator rit = action_trace->rbegin();
1316 for (; (*rit) != acquire; rit++) {
1317 ModelAction *propagate = *rit;
1318 if (acquire->happens_before(propagate)) {
1319 synchronize(acquire, propagate);
1320 /* Re-check 'propagate' for mo_graph edges */
1321 work_queue->push_back(MOEdgeWorkEntry(propagate));
1325 /* Break release sequence with new edges:
1326 * release --mo--> write --mo--> rf */
1327 mo_graph->addEdge(release, write);
1328 mo_graph->addEdge(write, rf);
1331 /* See if we have realized a data race */
1336 * Initialize the current action by performing one or more of the following
1337 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1338 * in the NodeStack, manipulating backtracking sets, allocating and
1339 * initializing clock vectors, and computing the promises to fulfill.
1341 * @param curr The current action, as passed from the user context; may be
1342 * freed/invalidated after the execution of this function, with a different
1343 * action "returned" its place (pass-by-reference)
1344 * @return True if curr is a newly-explored action; false otherwise
1346 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1348 ModelAction *newcurr;
1350 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1351 newcurr = process_rmw(*curr);
1354 if (newcurr->is_rmw())
1355 compute_promises(newcurr);
1361 (*curr)->set_seq_number(get_next_seq_num());
1363 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1365 /* First restore type and order in case of RMW operation */
1366 if ((*curr)->is_rmwr())
1367 newcurr->copy_typeandorder(*curr);
1369 ASSERT((*curr)->get_location() == newcurr->get_location());
1370 newcurr->copy_from_new(*curr);
1372 /* Discard duplicate ModelAction; use action from NodeStack */
1375 /* Always compute new clock vector */
1376 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1379 return false; /* Action was explored previously */
1383 /* Always compute new clock vector */
1384 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1386 /* Assign most recent release fence */
1387 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1390 * Perform one-time actions when pushing new ModelAction onto
1393 if (newcurr->is_write())
1394 compute_promises(newcurr);
1395 else if (newcurr->is_relseq_fixup())
1396 compute_relseq_breakwrites(newcurr);
1397 else if (newcurr->is_wait())
1398 newcurr->get_node()->set_misc_max(2);
1399 else if (newcurr->is_notify_one()) {
1400 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1402 return true; /* This was a new ModelAction */
1407 * @brief Establish reads-from relation between two actions
1409 * Perform basic operations involved with establishing a concrete rf relation,
1410 * including setting the ModelAction data and checking for release sequences.
1412 * @param act The action that is reading (must be a read)
1413 * @param rf The action from which we are reading (must be a write)
1415 * @return True if this read established synchronization
1417 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1420 ASSERT(rf->is_write());
1422 act->set_read_from(rf);
1423 if (act->is_acquire()) {
1424 rel_heads_list_t release_heads;
1425 get_release_seq_heads(act, act, &release_heads);
1426 int num_heads = release_heads.size();
1427 for (unsigned int i = 0; i < release_heads.size(); i++)
1428 if (!synchronize(release_heads[i], act))
1430 return num_heads > 0;
1436 * @brief Synchronizes two actions
1438 * When A synchronizes with B (or A --sw-> B), B inherits A's clock vector.
1439 * This function performs the synchronization as well as providing other hooks
1440 * for other checks along with synchronization.
1442 * @param first The left-hand side of the synchronizes-with relation
1443 * @param second The right-hand side of the synchronizes-with relation
1444 * @return True if the synchronization was successful (i.e., was consistent
1445 * with the execution order); false otherwise
1447 bool ModelChecker::synchronize(const ModelAction *first, ModelAction *second)
1449 if (!second->synchronize_with(first)) {
1450 set_bad_synchronization();
1457 * Check promises and eliminate potentially-satisfying threads when a thread is
1458 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1459 * no longer satisfy a promise generated from that thread.
1461 * @param blocker The thread on which a thread is waiting
1462 * @param waiting The waiting thread
1464 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1466 for (unsigned int i = 0; i < promises->size(); i++) {
1467 Promise *promise = (*promises)[i];
1468 if (!promise->thread_is_available(waiting->get_id()))
1470 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1471 ModelAction *reader = promise->get_reader(j);
1472 if (reader->get_tid() != blocker->get_id())
1474 if (promise->eliminate_thread(waiting->get_id())) {
1475 /* Promise has failed */
1476 priv->failed_promise = true;
1478 /* Only eliminate the 'waiting' thread once */
1486 * @brief Check whether a model action is enabled.
1488 * Checks whether a lock or join operation would be successful (i.e., is the
1489 * lock already locked, or is the joined thread already complete). If not, put
1490 * the action in a waiter list.
1492 * @param curr is the ModelAction to check whether it is enabled.
1493 * @return a bool that indicates whether the action is enabled.
1495 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1496 if (curr->is_lock()) {
1497 std::mutex *lock = curr->get_mutex();
1498 struct std::mutex_state *state = lock->get_state();
1501 } else if (curr->is_thread_join()) {
1502 Thread *blocking = curr->get_thread_operand();
1503 if (!blocking->is_complete()) {
1504 thread_blocking_check_promises(blocking, get_thread(curr));
1513 * This is the heart of the model checker routine. It performs model-checking
1514 * actions corresponding to a given "current action." Among other processes, it
1515 * calculates reads-from relationships, updates synchronization clock vectors,
1516 * forms a memory_order constraints graph, and handles replay/backtrack
1517 * execution when running permutations of previously-observed executions.
1519 * @param curr The current action to process
1520 * @return The ModelAction that is actually executed; may be different than
1521 * curr; may be NULL, if the current action is not enabled to run
1523 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1526 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1527 bool newly_explored = initialize_curr_action(&curr);
1531 wake_up_sleeping_actions(curr);
1533 /* Compute fairness information for CHESS yield algorithm */
1534 if (model->params.yieldon) {
1535 curr->get_node()->update_yield(scheduler);
1538 /* Add the action to lists before any other model-checking tasks */
1539 if (!second_part_of_rmw)
1540 add_action_to_lists(curr);
1542 /* Build may_read_from set for newly-created actions */
1543 if (newly_explored && curr->is_read())
1544 build_may_read_from(curr);
1546 /* Initialize work_queue with the "current action" work */
1547 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1548 while (!work_queue.empty() && !has_asserted()) {
1549 WorkQueueEntry work = work_queue.front();
1550 work_queue.pop_front();
1552 switch (work.type) {
1553 case WORK_CHECK_CURR_ACTION: {
1554 ModelAction *act = work.action;
1555 bool update = false; /* update this location's release seq's */
1556 bool update_all = false; /* update all release seq's */
1558 if (process_thread_action(curr))
1561 if (act->is_read() && !second_part_of_rmw && process_read(act))
1564 if (act->is_write() && process_write(act))
1567 if (act->is_fence() && process_fence(act))
1570 if (act->is_mutex_op() && process_mutex(act))
1573 if (act->is_relseq_fixup())
1574 process_relseq_fixup(curr, &work_queue);
1577 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1579 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1582 case WORK_CHECK_RELEASE_SEQ:
1583 resolve_release_sequences(work.location, &work_queue);
1585 case WORK_CHECK_MO_EDGES: {
1586 /** @todo Complete verification of work_queue */
1587 ModelAction *act = work.action;
1588 bool updated = false;
1590 if (act->is_read()) {
1591 const ModelAction *rf = act->get_reads_from();
1592 const Promise *promise = act->get_reads_from_promise();
1594 if (r_modification_order(act, rf))
1596 } else if (promise) {
1597 if (r_modification_order(act, promise))
1601 if (act->is_write()) {
1602 if (w_modification_order(act, NULL))
1605 mo_graph->commitChanges();
1608 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1617 check_curr_backtracking(curr);
1618 set_backtracking(curr);
1622 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1624 Node *currnode = curr->get_node();
1625 Node *parnode = currnode->get_parent();
1627 if ((parnode && !parnode->backtrack_empty()) ||
1628 !currnode->misc_empty() ||
1629 !currnode->read_from_empty() ||
1630 !currnode->promise_empty() ||
1631 !currnode->relseq_break_empty()) {
1632 set_latest_backtrack(curr);
1636 bool ModelChecker::promises_expired() const
1638 for (unsigned int i = 0; i < promises->size(); i++) {
1639 Promise *promise = (*promises)[i];
1640 if (promise->get_expiration() < priv->used_sequence_numbers)
1647 * This is the strongest feasibility check available.
1648 * @return whether the current trace (partial or complete) must be a prefix of
1651 bool ModelChecker::isfeasibleprefix() const
1653 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1657 * Print disagnostic information about an infeasible execution
1658 * @param prefix A string to prefix the output with; if NULL, then a default
1659 * message prefix will be provided
1661 void ModelChecker::print_infeasibility(const char *prefix) const
1665 if (mo_graph->checkForCycles())
1666 ptr += sprintf(ptr, "[mo cycle]");
1667 if (priv->failed_promise)
1668 ptr += sprintf(ptr, "[failed promise]");
1669 if (priv->too_many_reads)
1670 ptr += sprintf(ptr, "[too many reads]");
1671 if (priv->no_valid_reads)
1672 ptr += sprintf(ptr, "[no valid reads-from]");
1673 if (priv->bad_synchronization)
1674 ptr += sprintf(ptr, "[bad sw ordering]");
1675 if (promises_expired())
1676 ptr += sprintf(ptr, "[promise expired]");
1677 if (promises->size() != 0)
1678 ptr += sprintf(ptr, "[unresolved promise]");
1680 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1684 * Returns whether the current completed trace is feasible, except for pending
1685 * release sequences.
1687 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1689 return !is_infeasible() && promises->size() == 0;
1693 * Check if the current partial trace is infeasible. Does not check any
1694 * end-of-execution flags, which might rule out the execution. Thus, this is
1695 * useful only for ruling an execution as infeasible.
1696 * @return whether the current partial trace is infeasible.
1698 bool ModelChecker::is_infeasible() const
1700 return mo_graph->checkForCycles() ||
1701 priv->no_valid_reads ||
1702 priv->failed_promise ||
1703 priv->too_many_reads ||
1704 priv->bad_synchronization ||
1708 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1709 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1710 ModelAction *lastread = get_last_action(act->get_tid());
1711 lastread->process_rmw(act);
1712 if (act->is_rmw()) {
1713 if (lastread->get_reads_from())
1714 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1716 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1717 mo_graph->commitChanges();
1723 * A helper function for ModelChecker::check_recency, to check if the current
1724 * thread is able to read from a different write/promise for 'params.maxreads'
1725 * number of steps and if that write/promise should become visible (i.e., is
1726 * ordered later in the modification order). This helps model memory liveness.
1728 * @param curr The current action. Must be a read.
1729 * @param rf The write/promise from which we plan to read
1730 * @param other_rf The write/promise from which we may read
1731 * @return True if we were able to read from other_rf for params.maxreads steps
1733 template <typename T, typename U>
1734 bool ModelChecker::should_read_instead(const ModelAction *curr, const T *rf, const U *other_rf) const
1736 /* Need a different write/promise */
1737 if (other_rf->equals(rf))
1740 /* Only look for "newer" writes/promises */
1741 if (!mo_graph->checkReachable(rf, other_rf))
1744 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1745 action_list_t *list = &(*thrd_lists)[id_to_int(curr->get_tid())];
1746 action_list_t::reverse_iterator rit = list->rbegin();
1747 ASSERT((*rit) == curr);
1748 /* Skip past curr */
1751 /* Does this write/promise work for everyone? */
1752 for (int i = 0; i < params.maxreads; i++, rit++) {
1753 ModelAction *act = *rit;
1754 if (!act->may_read_from(other_rf))
1761 * Checks whether a thread has read from the same write or Promise for too many
1762 * times without seeing the effects of a later write/Promise.
1765 * 1) there must a different write/promise that we could read from,
1766 * 2) we must have read from the same write/promise in excess of maxreads times,
1767 * 3) that other write/promise must have been in the reads_from set for maxreads times, and
1768 * 4) that other write/promise must be mod-ordered after the write/promise we are reading.
1770 * If so, we decide that the execution is no longer feasible.
1772 * @param curr The current action. Must be a read.
1773 * @param rf The ModelAction/Promise from which we might read.
1774 * @return True if the read should succeed; false otherwise
1776 template <typename T>
1777 bool ModelChecker::check_recency(ModelAction *curr, const T *rf) const
1779 if (!params.maxreads)
1782 //NOTE: Next check is just optimization, not really necessary....
1783 if (curr->get_node()->get_read_from_past_size() +
1784 curr->get_node()->get_read_from_promise_size() <= 1)
1787 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1788 int tid = id_to_int(curr->get_tid());
1789 ASSERT(tid < (int)thrd_lists->size());
1790 action_list_t *list = &(*thrd_lists)[tid];
1791 action_list_t::reverse_iterator rit = list->rbegin();
1792 ASSERT((*rit) == curr);
1793 /* Skip past curr */
1796 action_list_t::reverse_iterator ritcopy = rit;
1797 /* See if we have enough reads from the same value */
1798 for (int count = 0; count < params.maxreads; ritcopy++, count++) {
1799 if (ritcopy == list->rend())
1801 ModelAction *act = *ritcopy;
1802 if (!act->is_read())
1804 if (act->get_reads_from_promise() && !act->get_reads_from_promise()->equals(rf))
1806 if (act->get_reads_from() && !act->get_reads_from()->equals(rf))
1808 if (act->get_node()->get_read_from_past_size() +
1809 act->get_node()->get_read_from_promise_size() <= 1)
1812 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1813 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1814 if (should_read_instead(curr, rf, write))
1815 return false; /* liveness failure */
1817 for (int i = 0; i < curr->get_node()->get_read_from_promise_size(); i++) {
1818 const Promise *promise = curr->get_node()->get_read_from_promise(i);
1819 if (should_read_instead(curr, rf, promise))
1820 return false; /* liveness failure */
1826 * @brief Updates the mo_graph with the constraints imposed from the current
1829 * Basic idea is the following: Go through each other thread and find
1830 * the last action that happened before our read. Two cases:
1832 * -# The action is a write: that write must either occur before
1833 * the write we read from or be the write we read from.
1834 * -# The action is a read: the write that that action read from
1835 * must occur before the write we read from or be the same write.
1837 * @param curr The current action. Must be a read.
1838 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1839 * @return True if modification order edges were added; false otherwise
1841 template <typename rf_type>
1842 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1844 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1847 ASSERT(curr->is_read());
1849 /* Last SC fence in the current thread */
1850 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1851 ModelAction *last_sc_write = NULL;
1852 if (curr->is_seqcst())
1853 last_sc_write = get_last_seq_cst_write(curr);
1855 /* Iterate over all threads */
1856 for (i = 0; i < thrd_lists->size(); i++) {
1857 /* Last SC fence in thread i */
1858 ModelAction *last_sc_fence_thread_local = NULL;
1859 if (int_to_id((int)i) != curr->get_tid())
1860 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1862 /* Last SC fence in thread i, before last SC fence in current thread */
1863 ModelAction *last_sc_fence_thread_before = NULL;
1864 if (last_sc_fence_local)
1865 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1867 /* Iterate over actions in thread, starting from most recent */
1868 action_list_t *list = &(*thrd_lists)[i];
1869 action_list_t::reverse_iterator rit;
1870 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1871 ModelAction *act = *rit;
1876 /* Don't want to add reflexive edges on 'rf' */
1877 if (act->equals(rf)) {
1878 if (act->happens_before(curr))
1884 if (act->is_write()) {
1885 /* C++, Section 29.3 statement 5 */
1886 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1887 *act < *last_sc_fence_thread_local) {
1888 added = mo_graph->addEdge(act, rf) || added;
1891 /* C++, Section 29.3 statement 4 */
1892 else if (act->is_seqcst() && last_sc_fence_local &&
1893 *act < *last_sc_fence_local) {
1894 added = mo_graph->addEdge(act, rf) || added;
1897 /* C++, Section 29.3 statement 6 */
1898 else if (last_sc_fence_thread_before &&
1899 *act < *last_sc_fence_thread_before) {
1900 added = mo_graph->addEdge(act, rf) || added;
1905 /* C++, Section 29.3 statement 3 (second subpoint) */
1906 if (curr->is_seqcst() && last_sc_write && act == last_sc_write) {
1907 added = mo_graph->addEdge(act, rf) || added;
1912 * Include at most one act per-thread that "happens
1915 if (act->happens_before(curr)) {
1916 if (act->is_write()) {
1917 added = mo_graph->addEdge(act, rf) || added;
1919 const ModelAction *prevrf = act->get_reads_from();
1920 const Promise *prevrf_promise = act->get_reads_from_promise();
1922 if (!prevrf->equals(rf))
1923 added = mo_graph->addEdge(prevrf, rf) || added;
1924 } else if (!prevrf_promise->equals(rf)) {
1925 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1934 * All compatible, thread-exclusive promises must be ordered after any
1935 * concrete loads from the same thread
1937 for (unsigned int i = 0; i < promises->size(); i++)
1938 if ((*promises)[i]->is_compatible_exclusive(curr))
1939 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1945 * Updates the mo_graph with the constraints imposed from the current write.
1947 * Basic idea is the following: Go through each other thread and find
1948 * the lastest action that happened before our write. Two cases:
1950 * (1) The action is a write => that write must occur before
1953 * (2) The action is a read => the write that that action read from
1954 * must occur before the current write.
1956 * This method also handles two other issues:
1958 * (I) Sequential Consistency: Making sure that if the current write is
1959 * seq_cst, that it occurs after the previous seq_cst write.
1961 * (II) Sending the write back to non-synchronizing reads.
1963 * @param curr The current action. Must be a write.
1964 * @param send_fv A vector for stashing reads to which we may pass our future
1965 * value. If NULL, then don't record any future values.
1966 * @return True if modification order edges were added; false otherwise
1968 bool ModelChecker::w_modification_order(ModelAction *curr, ModelVector<ModelAction *> *send_fv)
1970 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1973 ASSERT(curr->is_write());
1975 if (curr->is_seqcst()) {
1976 /* We have to at least see the last sequentially consistent write,
1977 so we are initialized. */
1978 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1979 if (last_seq_cst != NULL) {
1980 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1984 /* Last SC fence in the current thread */
1985 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1987 /* Iterate over all threads */
1988 for (i = 0; i < thrd_lists->size(); i++) {
1989 /* Last SC fence in thread i, before last SC fence in current thread */
1990 ModelAction *last_sc_fence_thread_before = NULL;
1991 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1992 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1994 /* Iterate over actions in thread, starting from most recent */
1995 action_list_t *list = &(*thrd_lists)[i];
1996 action_list_t::reverse_iterator rit;
1997 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1998 ModelAction *act = *rit;
2001 * 1) If RMW and it actually read from something, then we
2002 * already have all relevant edges, so just skip to next
2005 * 2) If RMW and it didn't read from anything, we should
2006 * whatever edge we can get to speed up convergence.
2008 * 3) If normal write, we need to look at earlier actions, so
2009 * continue processing list.
2011 if (curr->is_rmw()) {
2012 if (curr->get_reads_from() != NULL)
2020 /* C++, Section 29.3 statement 7 */
2021 if (last_sc_fence_thread_before && act->is_write() &&
2022 *act < *last_sc_fence_thread_before) {
2023 added = mo_graph->addEdge(act, curr) || added;
2028 * Include at most one act per-thread that "happens
2031 if (act->happens_before(curr)) {
2033 * Note: if act is RMW, just add edge:
2035 * The following edge should be handled elsewhere:
2036 * readfrom(act) --mo--> act
2038 if (act->is_write())
2039 added = mo_graph->addEdge(act, curr) || added;
2040 else if (act->is_read()) {
2041 //if previous read accessed a null, just keep going
2042 if (act->get_reads_from() == NULL)
2044 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
2047 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
2048 !act->same_thread(curr)) {
2049 /* We have an action that:
2050 (1) did not happen before us
2051 (2) is a read and we are a write
2052 (3) cannot synchronize with us
2053 (4) is in a different thread
2055 that read could potentially read from our write. Note that
2056 these checks are overly conservative at this point, we'll
2057 do more checks before actually removing the
2061 if (send_fv && thin_air_constraint_may_allow(curr, act)) {
2062 if (!is_infeasible())
2063 send_fv->push_back(act);
2064 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
2065 add_future_value(curr, act);
2072 * All compatible, thread-exclusive promises must be ordered after any
2073 * concrete stores to the same thread, or else they can be merged with
2076 for (unsigned int i = 0; i < promises->size(); i++)
2077 if ((*promises)[i]->is_compatible_exclusive(curr))
2078 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
2083 /** Arbitrary reads from the future are not allowed. Section 29.3
2084 * part 9 places some constraints. This method checks one result of constraint
2085 * constraint. Others require compiler support. */
2086 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader) const
2088 if (!writer->is_rmw())
2091 if (!reader->is_rmw())
2094 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
2095 if (search == reader)
2097 if (search->get_tid() == reader->get_tid() &&
2098 search->happens_before(reader))
2106 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
2107 * some constraints. This method checks one the following constraint (others
2108 * require compiler support):
2110 * If X --hb-> Y --mo-> Z, then X should not read from Z.
2112 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
2114 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
2116 /* Iterate over all threads */
2117 for (i = 0; i < thrd_lists->size(); i++) {
2118 const ModelAction *write_after_read = NULL;
2120 /* Iterate over actions in thread, starting from most recent */
2121 action_list_t *list = &(*thrd_lists)[i];
2122 action_list_t::reverse_iterator rit;
2123 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2124 ModelAction *act = *rit;
2126 /* Don't disallow due to act == reader */
2127 if (!reader->happens_before(act) || reader == act)
2129 else if (act->is_write())
2130 write_after_read = act;
2131 else if (act->is_read() && act->get_reads_from() != NULL)
2132 write_after_read = act->get_reads_from();
2135 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2142 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2143 * The ModelAction under consideration is expected to be taking part in
2144 * release/acquire synchronization as an object of the "reads from" relation.
2145 * Note that this can only provide release sequence support for RMW chains
2146 * which do not read from the future, as those actions cannot be traced until
2147 * their "promise" is fulfilled. Similarly, we may not even establish the
2148 * presence of a release sequence with certainty, as some modification order
2149 * constraints may be decided further in the future. Thus, this function
2150 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2151 * and a boolean representing certainty.
2153 * @param rf The action that might be part of a release sequence. Must be a
2155 * @param release_heads A pass-by-reference style return parameter. After
2156 * execution of this function, release_heads will contain the heads of all the
2157 * relevant release sequences, if any exists with certainty
2158 * @param pending A pass-by-reference style return parameter which is only used
2159 * when returning false (i.e., uncertain). Returns most information regarding
2160 * an uncertain release sequence, including any write operations that might
2161 * break the sequence.
2162 * @return true, if the ModelChecker is certain that release_heads is complete;
2165 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2166 rel_heads_list_t *release_heads,
2167 struct release_seq *pending) const
2169 /* Only check for release sequences if there are no cycles */
2170 if (mo_graph->checkForCycles())
2173 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2174 ASSERT(rf->is_write());
2176 if (rf->is_release())
2177 release_heads->push_back(rf);
2178 else if (rf->get_last_fence_release())
2179 release_heads->push_back(rf->get_last_fence_release());
2181 break; /* End of RMW chain */
2183 /** @todo Need to be smarter here... In the linux lock
2184 * example, this will run to the beginning of the program for
2186 /** @todo The way to be smarter here is to keep going until 1
2187 * thread has a release preceded by an acquire and you've seen
2190 /* acq_rel RMW is a sufficient stopping condition */
2191 if (rf->is_acquire() && rf->is_release())
2192 return true; /* complete */
2195 /* read from future: need to settle this later */
2197 return false; /* incomplete */
2200 if (rf->is_release())
2201 return true; /* complete */
2203 /* else relaxed write
2204 * - check for fence-release in the same thread (29.8, stmt. 3)
2205 * - check modification order for contiguous subsequence
2206 * -> rf must be same thread as release */
2208 const ModelAction *fence_release = rf->get_last_fence_release();
2209 /* Synchronize with a fence-release unconditionally; we don't need to
2210 * find any more "contiguous subsequence..." for it */
2212 release_heads->push_back(fence_release);
2214 int tid = id_to_int(rf->get_tid());
2215 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2216 action_list_t *list = &(*thrd_lists)[tid];
2217 action_list_t::const_reverse_iterator rit;
2219 /* Find rf in the thread list */
2220 rit = std::find(list->rbegin(), list->rend(), rf);
2221 ASSERT(rit != list->rend());
2223 /* Find the last {write,fence}-release */
2224 for (; rit != list->rend(); rit++) {
2225 if (fence_release && *(*rit) < *fence_release)
2227 if ((*rit)->is_release())
2230 if (rit == list->rend()) {
2231 /* No write-release in this thread */
2232 return true; /* complete */
2233 } else if (fence_release && *(*rit) < *fence_release) {
2234 /* The fence-release is more recent (and so, "stronger") than
2235 * the most recent write-release */
2236 return true; /* complete */
2237 } /* else, need to establish contiguous release sequence */
2238 ModelAction *release = *rit;
2240 ASSERT(rf->same_thread(release));
2242 pending->writes.clear();
2244 bool certain = true;
2245 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2246 if (id_to_int(rf->get_tid()) == (int)i)
2248 list = &(*thrd_lists)[i];
2250 /* Can we ensure no future writes from this thread may break
2251 * the release seq? */
2252 bool future_ordered = false;
2254 ModelAction *last = get_last_action(int_to_id(i));
2255 Thread *th = get_thread(int_to_id(i));
2256 if ((last && rf->happens_before(last)) ||
2259 future_ordered = true;
2261 ASSERT(!th->is_model_thread() || future_ordered);
2263 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2264 const ModelAction *act = *rit;
2265 /* Reach synchronization -> this thread is complete */
2266 if (act->happens_before(release))
2268 if (rf->happens_before(act)) {
2269 future_ordered = true;
2273 /* Only non-RMW writes can break release sequences */
2274 if (!act->is_write() || act->is_rmw())
2277 /* Check modification order */
2278 if (mo_graph->checkReachable(rf, act)) {
2279 /* rf --mo--> act */
2280 future_ordered = true;
2283 if (mo_graph->checkReachable(act, release))
2284 /* act --mo--> release */
2286 if (mo_graph->checkReachable(release, act) &&
2287 mo_graph->checkReachable(act, rf)) {
2288 /* release --mo-> act --mo--> rf */
2289 return true; /* complete */
2291 /* act may break release sequence */
2292 pending->writes.push_back(act);
2295 if (!future_ordered)
2296 certain = false; /* This thread is uncertain */
2300 release_heads->push_back(release);
2301 pending->writes.clear();
2303 pending->release = release;
2310 * An interface for getting the release sequence head(s) with which a
2311 * given ModelAction must synchronize. This function only returns a non-empty
2312 * result when it can locate a release sequence head with certainty. Otherwise,
2313 * it may mark the internal state of the ModelChecker so that it will handle
2314 * the release sequence at a later time, causing @a acquire to update its
2315 * synchronization at some later point in execution.
2317 * @param acquire The 'acquire' action that may synchronize with a release
2319 * @param read The read action that may read from a release sequence; this may
2320 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2321 * when 'acquire' is a fence-acquire)
2322 * @param release_heads A pass-by-reference return parameter. Will be filled
2323 * with the head(s) of the release sequence(s), if they exists with certainty.
2324 * @see ModelChecker::release_seq_heads
2326 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2327 ModelAction *read, rel_heads_list_t *release_heads)
2329 const ModelAction *rf = read->get_reads_from();
2330 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2331 sequence->acquire = acquire;
2332 sequence->read = read;
2334 if (!release_seq_heads(rf, release_heads, sequence)) {
2335 /* add act to 'lazy checking' list */
2336 pending_rel_seqs->push_back(sequence);
2338 snapshot_free(sequence);
2343 * Attempt to resolve all stashed operations that might synchronize with a
2344 * release sequence for a given location. This implements the "lazy" portion of
2345 * determining whether or not a release sequence was contiguous, since not all
2346 * modification order information is present at the time an action occurs.
2348 * @param location The location/object that should be checked for release
2349 * sequence resolutions. A NULL value means to check all locations.
2350 * @param work_queue The work queue to which to add work items as they are
2352 * @return True if any updates occurred (new synchronization, new mo_graph
2355 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2357 bool updated = false;
2358 SnapVector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
2359 while (it != pending_rel_seqs->end()) {
2360 struct release_seq *pending = *it;
2361 ModelAction *acquire = pending->acquire;
2362 const ModelAction *read = pending->read;
2364 /* Only resolve sequences on the given location, if provided */
2365 if (location && read->get_location() != location) {
2370 const ModelAction *rf = read->get_reads_from();
2371 rel_heads_list_t release_heads;
2373 complete = release_seq_heads(rf, &release_heads, pending);
2374 for (unsigned int i = 0; i < release_heads.size(); i++)
2375 if (!acquire->has_synchronized_with(release_heads[i]))
2376 if (synchronize(release_heads[i], acquire))
2380 /* Re-check all pending release sequences */
2381 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2382 /* Re-check read-acquire for mo_graph edges */
2383 if (acquire->is_read())
2384 work_queue->push_back(MOEdgeWorkEntry(acquire));
2386 /* propagate synchronization to later actions */
2387 action_list_t::reverse_iterator rit = action_trace->rbegin();
2388 for (; (*rit) != acquire; rit++) {
2389 ModelAction *propagate = *rit;
2390 if (acquire->happens_before(propagate)) {
2391 synchronize(acquire, propagate);
2392 /* Re-check 'propagate' for mo_graph edges */
2393 work_queue->push_back(MOEdgeWorkEntry(propagate));
2398 it = pending_rel_seqs->erase(it);
2399 snapshot_free(pending);
2405 // If we resolved promises or data races, see if we have realized a data race.
2412 * Performs various bookkeeping operations for the current ModelAction. For
2413 * instance, adds action to the per-object, per-thread action vector and to the
2414 * action trace list of all thread actions.
2416 * @param act is the ModelAction to add.
2418 void ModelChecker::add_action_to_lists(ModelAction *act)
2420 int tid = id_to_int(act->get_tid());
2421 ModelAction *uninit = NULL;
2423 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2424 if (list->empty() && act->is_atomic_var()) {
2425 uninit = get_uninitialized_action(act);
2426 uninit_id = id_to_int(uninit->get_tid());
2427 list->push_front(uninit);
2429 list->push_back(act);
2431 action_trace->push_back(act);
2433 action_trace->push_front(uninit);
2435 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2436 if (tid >= (int)vec->size())
2437 vec->resize(priv->next_thread_id);
2438 (*vec)[tid].push_back(act);
2440 (*vec)[uninit_id].push_front(uninit);
2442 if ((int)thrd_last_action->size() <= tid)
2443 thrd_last_action->resize(get_num_threads());
2444 (*thrd_last_action)[tid] = act;
2446 (*thrd_last_action)[uninit_id] = uninit;
2448 if (act->is_fence() && act->is_release()) {
2449 if ((int)thrd_last_fence_release->size() <= tid)
2450 thrd_last_fence_release->resize(get_num_threads());
2451 (*thrd_last_fence_release)[tid] = act;
2454 if (act->is_wait()) {
2455 void *mutex_loc = (void *) act->get_value();
2456 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2458 SnapVector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2459 if (tid >= (int)vec->size())
2460 vec->resize(priv->next_thread_id);
2461 (*vec)[tid].push_back(act);
2466 * @brief Get the last action performed by a particular Thread
2467 * @param tid The thread ID of the Thread in question
2468 * @return The last action in the thread
2470 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2472 int threadid = id_to_int(tid);
2473 if (threadid < (int)thrd_last_action->size())
2474 return (*thrd_last_action)[id_to_int(tid)];
2480 * @brief Get the last fence release performed by a particular Thread
2481 * @param tid The thread ID of the Thread in question
2482 * @return The last fence release in the thread, if one exists; NULL otherwise
2484 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2486 int threadid = id_to_int(tid);
2487 if (threadid < (int)thrd_last_fence_release->size())
2488 return (*thrd_last_fence_release)[id_to_int(tid)];
2494 * Gets the last memory_order_seq_cst write (in the total global sequence)
2495 * performed on a particular object (i.e., memory location), not including the
2497 * @param curr The current ModelAction; also denotes the object location to
2499 * @return The last seq_cst write
2501 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2503 void *location = curr->get_location();
2504 action_list_t *list = get_safe_ptr_action(obj_map, location);
2505 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2506 action_list_t::reverse_iterator rit;
2507 for (rit = list->rbegin(); (*rit) != curr; rit++)
2509 rit++; /* Skip past curr */
2510 for ( ; rit != list->rend(); rit++)
2511 if ((*rit)->is_write() && (*rit)->is_seqcst())
2517 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2518 * performed in a particular thread, prior to a particular fence.
2519 * @param tid The ID of the thread to check
2520 * @param before_fence The fence from which to begin the search; if NULL, then
2521 * search for the most recent fence in the thread.
2522 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2524 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2526 /* All fences should have NULL location */
2527 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2528 action_list_t::reverse_iterator rit = list->rbegin();
2531 for (; rit != list->rend(); rit++)
2532 if (*rit == before_fence)
2535 ASSERT(*rit == before_fence);
2539 for (; rit != list->rend(); rit++)
2540 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2546 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2547 * location). This function identifies the mutex according to the current
2548 * action, which is presumed to perform on the same mutex.
2549 * @param curr The current ModelAction; also denotes the object location to
2551 * @return The last unlock operation
2553 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2555 void *location = curr->get_location();
2556 action_list_t *list = get_safe_ptr_action(obj_map, location);
2557 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2558 action_list_t::reverse_iterator rit;
2559 for (rit = list->rbegin(); rit != list->rend(); rit++)
2560 if ((*rit)->is_unlock() || (*rit)->is_wait())
2565 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2567 ModelAction *parent = get_last_action(tid);
2569 parent = get_thread(tid)->get_creation();
2574 * Returns the clock vector for a given thread.
2575 * @param tid The thread whose clock vector we want
2576 * @return Desired clock vector
2578 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2580 return get_parent_action(tid)->get_cv();
2584 * @brief Find the promise (if any) to resolve for the current action and
2585 * remove it from the pending promise vector
2586 * @param curr The current ModelAction. Should be a write.
2587 * @return The Promise to resolve, if any; otherwise NULL
2589 Promise * ModelChecker::pop_promise_to_resolve(const ModelAction *curr)
2591 for (unsigned int i = 0; i < promises->size(); i++)
2592 if (curr->get_node()->get_promise(i)) {
2593 Promise *ret = (*promises)[i];
2594 promises->erase(promises->begin() + i);
2601 * Resolve a Promise with a current write.
2602 * @param write The ModelAction that is fulfilling Promises
2603 * @param promise The Promise to resolve
2604 * @return True if the Promise was successfully resolved; false otherwise
2606 bool ModelChecker::resolve_promise(ModelAction *write, Promise *promise)
2608 ModelVector<ModelAction *> actions_to_check;
2610 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2611 ModelAction *read = promise->get_reader(i);
2612 read_from(read, write);
2613 actions_to_check.push_back(read);
2615 /* Make sure the promise's value matches the write's value */
2616 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2617 if (!mo_graph->resolvePromise(promise, write))
2618 priv->failed_promise = true;
2621 * @todo It is possible to end up in an inconsistent state, where a
2622 * "resolved" promise may still be referenced if
2623 * CycleGraph::resolvePromise() failed, so don't delete 'promise'.
2625 * Note that the inconsistency only matters when dumping mo_graph to
2631 //Check whether reading these writes has made threads unable to
2633 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2634 ModelAction *read = actions_to_check[i];
2635 mo_check_promises(read, true);
2642 * Compute the set of promises that could potentially be satisfied by this
2643 * action. Note that the set computation actually appears in the Node, not in
2645 * @param curr The ModelAction that may satisfy promises
2647 void ModelChecker::compute_promises(ModelAction *curr)
2649 for (unsigned int i = 0; i < promises->size(); i++) {
2650 Promise *promise = (*promises)[i];
2651 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2654 bool satisfy = true;
2655 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2656 const ModelAction *act = promise->get_reader(j);
2657 if (act->happens_before(curr) ||
2658 act->could_synchronize_with(curr)) {
2664 curr->get_node()->set_promise(i);
2668 /** Checks promises in response to change in ClockVector Threads. */
2669 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2671 for (unsigned int i = 0; i < promises->size(); i++) {
2672 Promise *promise = (*promises)[i];
2673 if (!promise->thread_is_available(tid))
2675 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2676 const ModelAction *act = promise->get_reader(j);
2677 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2678 merge_cv->synchronized_since(act)) {
2679 if (promise->eliminate_thread(tid)) {
2680 /* Promise has failed */
2681 priv->failed_promise = true;
2689 void ModelChecker::check_promises_thread_disabled()
2691 for (unsigned int i = 0; i < promises->size(); i++) {
2692 Promise *promise = (*promises)[i];
2693 if (promise->has_failed()) {
2694 priv->failed_promise = true;
2701 * @brief Checks promises in response to addition to modification order for
2704 * We test whether threads are still available for satisfying promises after an
2705 * addition to our modification order constraints. Those that are unavailable
2706 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2707 * that promise has failed.
2709 * @param act The ModelAction which updated the modification order
2710 * @param is_read_check Should be true if act is a read and we must check for
2711 * updates to the store from which it read (there is a distinction here for
2712 * RMW's, which are both a load and a store)
2714 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2716 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2718 for (unsigned int i = 0; i < promises->size(); i++) {
2719 Promise *promise = (*promises)[i];
2721 // Is this promise on the same location?
2722 if (!promise->same_location(write))
2725 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2726 const ModelAction *pread = promise->get_reader(j);
2727 if (!pread->happens_before(act))
2729 if (mo_graph->checkPromise(write, promise)) {
2730 priv->failed_promise = true;
2736 // Don't do any lookups twice for the same thread
2737 if (!promise->thread_is_available(act->get_tid()))
2740 if (mo_graph->checkReachable(promise, write)) {
2741 if (mo_graph->checkPromise(write, promise)) {
2742 priv->failed_promise = true;
2750 * Compute the set of writes that may break the current pending release
2751 * sequence. This information is extracted from previou release sequence
2754 * @param curr The current ModelAction. Must be a release sequence fixup
2757 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2759 if (pending_rel_seqs->empty())
2762 struct release_seq *pending = pending_rel_seqs->back();
2763 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2764 const ModelAction *write = pending->writes[i];
2765 curr->get_node()->add_relseq_break(write);
2768 /* NULL means don't break the sequence; just synchronize */
2769 curr->get_node()->add_relseq_break(NULL);
2773 * Build up an initial set of all past writes that this 'read' action may read
2774 * from, as well as any previously-observed future values that must still be valid.
2776 * @param curr is the current ModelAction that we are exploring; it must be a
2779 void ModelChecker::build_may_read_from(ModelAction *curr)
2781 SnapVector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2783 ASSERT(curr->is_read());
2785 ModelAction *last_sc_write = NULL;
2787 if (curr->is_seqcst())
2788 last_sc_write = get_last_seq_cst_write(curr);
2790 /* Iterate over all threads */
2791 for (i = 0; i < thrd_lists->size(); i++) {
2792 /* Iterate over actions in thread, starting from most recent */
2793 action_list_t *list = &(*thrd_lists)[i];
2794 action_list_t::reverse_iterator rit;
2795 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2796 ModelAction *act = *rit;
2798 /* Only consider 'write' actions */
2799 if (!act->is_write() || act == curr)
2802 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2803 bool allow_read = true;
2805 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2807 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2811 /* Only add feasible reads */
2812 mo_graph->startChanges();
2813 r_modification_order(curr, act);
2814 if (!is_infeasible())
2815 curr->get_node()->add_read_from_past(act);
2816 mo_graph->rollbackChanges();
2819 /* Include at most one act per-thread that "happens before" curr */
2820 if (act->happens_before(curr))
2825 /* Inherit existing, promised future values */
2826 for (i = 0; i < promises->size(); i++) {
2827 const Promise *promise = (*promises)[i];
2828 const ModelAction *promise_read = promise->get_reader(0);
2829 if (promise_read->same_var(curr)) {
2830 /* Only add feasible future-values */
2831 mo_graph->startChanges();
2832 r_modification_order(curr, promise);
2833 if (!is_infeasible())
2834 curr->get_node()->add_read_from_promise(promise_read);
2835 mo_graph->rollbackChanges();
2839 /* We may find no valid may-read-from only if the execution is doomed */
2840 if (!curr->get_node()->read_from_size()) {
2841 priv->no_valid_reads = true;
2845 if (DBG_ENABLED()) {
2846 model_print("Reached read action:\n");
2848 model_print("Printing read_from_past\n");
2849 curr->get_node()->print_read_from_past();
2850 model_print("End printing read_from_past\n");
2854 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2856 for ( ; write != NULL; write = write->get_reads_from()) {
2857 /* UNINIT actions don't have a Node, and they never sleep */
2858 if (write->is_uninitialized())
2860 Node *prevnode = write->get_node()->get_parent();
2862 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2863 if (write->is_release() && thread_sleep)
2865 if (!write->is_rmw())
2872 * @brief Get an action representing an uninitialized atomic
2874 * This function may create a new one or try to retrieve one from the NodeStack
2876 * @param curr The current action, which prompts the creation of an UNINIT action
2877 * @return A pointer to the UNINIT ModelAction
2879 ModelAction * ModelChecker::get_uninitialized_action(const ModelAction *curr) const
2881 Node *node = curr->get_node();
2882 ModelAction *act = node->get_uninit_action();
2884 act = new ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, curr->get_location(), model->params.uninitvalue, model_thread);
2885 node->set_uninit_action(act);
2887 act->create_cv(NULL);
2891 static void print_list(action_list_t *list)
2893 action_list_t::iterator it;
2895 model_print("---------------------------------------------------------------------\n");
2897 unsigned int hash = 0;
2899 for (it = list->begin(); it != list->end(); it++) {
2900 const ModelAction *act = *it;
2901 if (act->get_seq_number() > 0)
2903 hash = hash^(hash<<3)^((*it)->hash());
2905 model_print("HASH %u\n", hash);
2906 model_print("---------------------------------------------------------------------\n");
2909 #if SUPPORT_MOD_ORDER_DUMP
2910 void ModelChecker::dumpGraph(char *filename) const
2913 sprintf(buffer, "%s.dot", filename);
2914 FILE *file = fopen(buffer, "w");
2915 fprintf(file, "digraph %s {\n", filename);
2916 mo_graph->dumpNodes(file);
2917 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2919 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2920 ModelAction *act = *it;
2921 if (act->is_read()) {
2922 mo_graph->dot_print_node(file, act);
2923 if (act->get_reads_from())
2924 mo_graph->dot_print_edge(file,
2925 act->get_reads_from(),
2927 "label=\"rf\", color=red, weight=2");
2929 mo_graph->dot_print_edge(file,
2930 act->get_reads_from_promise(),
2932 "label=\"rf\", color=red");
2934 if (thread_array[act->get_tid()]) {
2935 mo_graph->dot_print_edge(file,
2936 thread_array[id_to_int(act->get_tid())],
2938 "label=\"sb\", color=blue, weight=400");
2941 thread_array[act->get_tid()] = act;
2943 fprintf(file, "}\n");
2944 model_free(thread_array);
2949 /** @brief Prints an execution trace summary. */
2950 void ModelChecker::print_summary() const
2952 #if SUPPORT_MOD_ORDER_DUMP
2953 char buffername[100];
2954 sprintf(buffername, "exec%04u", stats.num_total);
2955 mo_graph->dumpGraphToFile(buffername);
2956 sprintf(buffername, "graph%04u", stats.num_total);
2957 dumpGraph(buffername);
2960 model_print("Execution %d:", stats.num_total);
2961 if (isfeasibleprefix()) {
2962 if (scheduler->all_threads_sleeping())
2963 model_print(" SLEEP-SET REDUNDANT");
2966 print_infeasibility(" INFEASIBLE");
2967 print_list(action_trace);
2969 if (!promises->empty()) {
2970 model_print("Pending promises:\n");
2971 for (unsigned int i = 0; i < promises->size(); i++) {
2972 model_print(" [P%u] ", i);
2973 (*promises)[i]->print();
2980 * Add a Thread to the system for the first time. Should only be called once
2982 * @param t The Thread to add
2984 void ModelChecker::add_thread(Thread *t)
2986 thread_map->put(id_to_int(t->get_id()), t);
2987 scheduler->add_thread(t);
2991 * @brief Get a Thread reference by its ID
2992 * @param tid The Thread's ID
2993 * @return A Thread reference
2995 Thread * ModelChecker::get_thread(thread_id_t tid) const
2997 return thread_map->get(id_to_int(tid));
3001 * @brief Get a reference to the Thread in which a ModelAction was executed
3002 * @param act The ModelAction
3003 * @return A Thread reference
3005 Thread * ModelChecker::get_thread(const ModelAction *act) const
3007 return get_thread(act->get_tid());
3011 * @brief Get a Promise's "promise number"
3013 * A "promise number" is an index number that is unique to a promise, valid
3014 * only for a specific snapshot of an execution trace. Promises may come and go
3015 * as they are generated an resolved, so an index only retains meaning for the
3018 * @param promise The Promise to check
3019 * @return The promise index, if the promise still is valid; otherwise -1
3021 int ModelChecker::get_promise_number(const Promise *promise) const
3023 for (unsigned int i = 0; i < promises->size(); i++)
3024 if ((*promises)[i] == promise)
3031 * @brief Check if a Thread is currently enabled
3032 * @param t The Thread to check
3033 * @return True if the Thread is currently enabled
3035 bool ModelChecker::is_enabled(Thread *t) const
3037 return scheduler->is_enabled(t);
3041 * @brief Check if a Thread is currently enabled
3042 * @param tid The ID of the Thread to check
3043 * @return True if the Thread is currently enabled
3045 bool ModelChecker::is_enabled(thread_id_t tid) const
3047 return scheduler->is_enabled(tid);
3051 * Switch from a model-checker context to a user-thread context. This is the
3052 * complement of ModelChecker::switch_to_master and must be called from the
3053 * model-checker context
3055 * @param thread The user-thread to switch to
3057 void ModelChecker::switch_from_master(Thread *thread)
3059 scheduler->set_current_thread(thread);
3060 Thread::swap(&system_context, thread);
3064 * Switch from a user-context to the "master thread" context (a.k.a. system
3065 * context). This switch is made with the intention of exploring a particular
3066 * model-checking action (described by a ModelAction object). Must be called
3067 * from a user-thread context.
3069 * @param act The current action that will be explored. May be NULL only if
3070 * trace is exiting via an assertion (see ModelChecker::set_assert and
3071 * ModelChecker::has_asserted).
3072 * @return Return the value returned by the current action
3074 uint64_t ModelChecker::switch_to_master(ModelAction *act)
3077 Thread *old = thread_current();
3078 scheduler->set_current_thread(NULL);
3079 ASSERT(!old->get_pending());
3080 old->set_pending(act);
3081 if (Thread::swap(old, &system_context) < 0) {
3082 perror("swap threads");
3085 return old->get_return_value();
3089 * Takes the next step in the execution, if possible.
3090 * @param curr The current step to take
3091 * @return Returns the next Thread to run, if any; NULL if this execution
3094 Thread * ModelChecker::take_step(ModelAction *curr)
3096 Thread *curr_thrd = get_thread(curr);
3097 ASSERT(curr_thrd->get_state() == THREAD_READY);
3099 ASSERT(check_action_enabled(curr)); /* May have side effects? */
3100 curr = check_current_action(curr);
3103 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
3104 scheduler->remove_thread(curr_thrd);
3106 return action_select_next_thread(curr);
3109 /** Wrapper to run the user's main function, with appropriate arguments */
3110 void user_main_wrapper(void *)
3112 user_main(model->params.argc, model->params.argv);
3115 /** @return True if the execution has taken too many steps */
3116 bool ModelChecker::too_many_steps() const
3118 return params.bound != 0 && priv->used_sequence_numbers > params.bound;
3121 bool ModelChecker::should_terminate_execution()
3123 /* Infeasible -> don't take any more steps */
3124 if (is_infeasible())
3126 else if (isfeasibleprefix() && have_bug_reports()) {
3131 if (too_many_steps())
3136 /** @brief Run ModelChecker for the user program */
3137 void ModelChecker::run()
3141 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3146 * Stash next pending action(s) for thread(s). There
3147 * should only need to stash one thread's action--the
3148 * thread which just took a step--plus the first step
3149 * for any newly-created thread
3151 for (unsigned int i = 0; i < get_num_threads(); i++) {
3152 thread_id_t tid = int_to_id(i);
3153 Thread *thr = get_thread(tid);
3154 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3155 switch_from_master(thr);
3156 if (thr->is_waiting_on(thr))
3157 assert_bug("Deadlock detected (thread %u)", i);
3161 /* Don't schedule threads which should be disabled */
3162 for (unsigned int i = 0; i < get_num_threads(); i++) {
3163 Thread *th = get_thread(int_to_id(i));
3164 ModelAction *act = th->get_pending();
3165 if (act && is_enabled(th) && !check_action_enabled(act)) {
3166 scheduler->sleep(th);
3170 /* Catch assertions from prior take_step or from
3171 * between-ModelAction bugs (e.g., data races) */
3176 t = get_next_thread();
3177 if (!t || t->is_model_thread())
3180 /* Consume the next action for a Thread */
3181 ModelAction *curr = t->get_pending();
3182 t->set_pending(NULL);
3183 t = take_step(curr);
3184 } while (!should_terminate_execution());
3187 * Launch end-of-execution release sequence fixups only when
3188 * the execution is otherwise feasible AND there are:
3190 * (1) pending release sequences
3191 * (2) pending assertions that could be invalidated by a change
3192 * in clock vectors (i.e., data races)
3193 * (3) no pending promises
3195 while (!pending_rel_seqs->empty() &&
3196 is_feasible_prefix_ignore_relseq() &&
3197 !unrealizedraces.empty()) {
3198 model_print("*** WARNING: release sequence fixup action "
3199 "(%zu pending release seuqence(s)) ***\n",
3200 pending_rel_seqs->size());
3201 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3202 std::memory_order_seq_cst, NULL, VALUE_NONE,
3206 } while (next_execution());
3208 model_print("******* Model-checking complete: *******\n");