10 #include "snapshot-interface.h"
12 #include "clockvector.h"
13 #include "cyclegraph.h"
16 #include "threads-model.h"
19 #define INITIAL_THREAD_ID 0
24 bug_message(const char *str) {
25 const char *fmt = " [BUG] %s\n";
26 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
27 sprintf(msg, fmt, str);
29 ~bug_message() { if (msg) snapshot_free(msg); }
32 void print() { model_print("%s", msg); }
38 * Structure for holding small ModelChecker members that should be snapshotted
40 struct model_snapshot_members {
41 model_snapshot_members() :
42 /* First thread created will have id INITIAL_THREAD_ID */
43 next_thread_id(INITIAL_THREAD_ID),
44 used_sequence_numbers(0),
48 failed_promise(false),
49 too_many_reads(false),
50 no_valid_reads(false),
51 bad_synchronization(false),
55 ~model_snapshot_members() {
56 for (unsigned int i = 0; i < bugs.size(); i++)
61 unsigned int next_thread_id;
62 modelclock_t used_sequence_numbers;
63 ModelAction *next_backtrack;
64 std::vector< bug_message *, SnapshotAlloc<bug_message *> > bugs;
65 struct execution_stats stats;
69 /** @brief Incorrectly-ordered synchronization was made */
70 bool bad_synchronization;
76 /** @brief Constructor */
77 ModelChecker::ModelChecker(struct model_params params) :
78 /* Initialize default scheduler */
80 scheduler(new Scheduler()),
82 earliest_diverge(NULL),
83 action_trace(new action_list_t()),
84 thread_map(new HashTable<int, Thread *, int>()),
85 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
86 lock_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
87 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 obj_thrd_map(new HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
90 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
91 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
92 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
93 thrd_last_fence_release(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >()),
94 node_stack(new NodeStack()),
95 priv(new struct model_snapshot_members()),
96 mo_graph(new CycleGraph())
98 /* Initialize a model-checker thread, for special ModelActions */
99 model_thread = new Thread(get_next_id());
100 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
103 /** @brief Destructor */
104 ModelChecker::~ModelChecker()
106 for (unsigned int i = 0; i < get_num_threads(); i++)
107 delete thread_map->get(i);
112 delete lock_waiters_map;
113 delete condvar_waiters_map;
116 for (unsigned int i = 0; i < promises->size(); i++)
117 delete (*promises)[i];
120 delete pending_rel_seqs;
122 delete thrd_last_action;
123 delete thrd_last_fence_release;
130 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
132 action_list_t *tmp = hash->get(ptr);
134 tmp = new action_list_t();
140 static std::vector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
142 std::vector<action_list_t> *tmp = hash->get(ptr);
144 tmp = new std::vector<action_list_t>();
151 * Restores user program to initial state and resets all model-checker data
154 void ModelChecker::reset_to_initial_state()
156 DEBUG("+++ Resetting to initial state +++\n");
157 node_stack->reset_execution();
159 /* Print all model-checker output before rollback */
163 * FIXME: if we utilize partial rollback, we will need to free only
164 * those pending actions which were NOT pending before the rollback
167 for (unsigned int i = 0; i < get_num_threads(); i++)
168 delete get_thread(int_to_id(i))->get_pending();
170 snapshot_backtrack_before(0);
173 /** @return a thread ID for a new Thread */
174 thread_id_t ModelChecker::get_next_id()
176 return priv->next_thread_id++;
179 /** @return the number of user threads created during this execution */
180 unsigned int ModelChecker::get_num_threads() const
182 return priv->next_thread_id;
186 * Must be called from user-thread context (e.g., through the global
187 * thread_current() interface)
189 * @return The currently executing Thread.
191 Thread * ModelChecker::get_current_thread() const
193 return scheduler->get_current_thread();
196 /** @return a sequence number for a new ModelAction */
197 modelclock_t ModelChecker::get_next_seq_num()
199 return ++priv->used_sequence_numbers;
202 Node * ModelChecker::get_curr_node() const
204 return node_stack->get_head();
208 * @brief Choose the next thread to execute.
210 * This function chooses the next thread that should execute. It can force the
211 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
212 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
213 * The model-checker may have no preference regarding the next thread (i.e.,
214 * when exploring a new execution ordering), in which case we defer to the
217 * @param curr Optional: The current ModelAction. Only used if non-NULL and it
218 * might guide the choice of next thread (i.e., THREAD_CREATE should be
219 * followed by THREAD_START, or ATOMIC_RMWR followed by ATOMIC_{RMW,RMWC})
220 * @return The next chosen thread to run, if any exist. Or else if no threads
221 * remain to be executed, return NULL.
223 Thread * ModelChecker::get_next_thread(ModelAction *curr)
228 /* Do not split atomic actions. */
230 return get_thread(curr);
231 else if (curr->get_type() == THREAD_CREATE)
232 return curr->get_thread_operand();
236 * Have we completed exploring the preselected path? Then let the
240 return scheduler->select_next_thread();
242 /* Else, we are trying to replay an execution */
243 ModelAction *next = node_stack->get_next()->get_action();
245 if (next == diverge) {
246 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
247 earliest_diverge = diverge;
249 Node *nextnode = next->get_node();
250 Node *prevnode = nextnode->get_parent();
251 scheduler->update_sleep_set(prevnode);
253 /* Reached divergence point */
254 if (nextnode->increment_misc()) {
255 /* The next node will try to satisfy a different misc_index values. */
256 tid = next->get_tid();
257 node_stack->pop_restofstack(2);
258 } else if (nextnode->increment_promise()) {
259 /* The next node will try to satisfy a different set of promises. */
260 tid = next->get_tid();
261 node_stack->pop_restofstack(2);
262 } else if (nextnode->increment_read_from()) {
263 /* The next node will read from a different value. */
264 tid = next->get_tid();
265 node_stack->pop_restofstack(2);
266 } else if (nextnode->increment_relseq_break()) {
267 /* The next node will try to resolve a release sequence differently */
268 tid = next->get_tid();
269 node_stack->pop_restofstack(2);
272 /* Make a different thread execute for next step */
273 scheduler->add_sleep(get_thread(next->get_tid()));
274 tid = prevnode->get_next_backtrack();
275 /* Make sure the backtracked thread isn't sleeping. */
276 node_stack->pop_restofstack(1);
277 if (diverge == earliest_diverge) {
278 earliest_diverge = prevnode->get_action();
281 /* Start the round robin scheduler from this thread id */
282 scheduler->set_scheduler_thread(tid);
283 /* The correct sleep set is in the parent node. */
286 DEBUG("*** Divergence point ***\n");
290 tid = next->get_tid();
292 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
293 ASSERT(tid != THREAD_ID_T_NONE);
294 return thread_map->get(id_to_int(tid));
298 * We need to know what the next actions of all threads in the sleep
299 * set will be. This method computes them and stores the actions at
300 * the corresponding thread object's pending action.
303 void ModelChecker::execute_sleep_set()
305 for (unsigned int i = 0; i < get_num_threads(); i++) {
306 thread_id_t tid = int_to_id(i);
307 Thread *thr = get_thread(tid);
308 if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
309 thr->get_pending()->set_sleep_flag();
315 * @brief Should the current action wake up a given thread?
317 * @param curr The current action
318 * @param thread The thread that we might wake up
319 * @return True, if we should wake up the sleeping thread; false otherwise
321 bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const
323 const ModelAction *asleep = thread->get_pending();
324 /* Don't allow partial RMW to wake anyone up */
327 /* Synchronizing actions may have been backtracked */
328 if (asleep->could_synchronize_with(curr))
330 /* All acquire/release fences and fence-acquire/store-release */
331 if (asleep->is_fence() && asleep->is_acquire() && curr->is_release())
333 /* Fence-release + store can awake load-acquire on the same location */
334 if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) {
335 ModelAction *fence_release = get_last_fence_release(curr->get_tid());
336 if (fence_release && *(get_last_action(thread->get_id())) < *fence_release)
342 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
344 for (unsigned int i = 0; i < get_num_threads(); i++) {
345 Thread *thr = get_thread(int_to_id(i));
346 if (scheduler->is_sleep_set(thr)) {
347 if (should_wake_up(curr, thr))
348 /* Remove this thread from sleep set */
349 scheduler->remove_sleep(thr);
354 /** @brief Alert the model-checker that an incorrectly-ordered
355 * synchronization was made */
356 void ModelChecker::set_bad_synchronization()
358 priv->bad_synchronization = true;
362 * Check whether the current trace has triggered an assertion which should halt
365 * @return True, if the execution should be aborted; false otherwise
367 bool ModelChecker::has_asserted() const
369 return priv->asserted;
373 * Trigger a trace assertion which should cause this execution to be halted.
374 * This can be due to a detected bug or due to an infeasibility that should
377 void ModelChecker::set_assert()
379 priv->asserted = true;
383 * Check if we are in a deadlock. Should only be called at the end of an
384 * execution, although it should not give false positives in the middle of an
385 * execution (there should be some ENABLED thread).
387 * @return True if program is in a deadlock; false otherwise
389 bool ModelChecker::is_deadlocked() const
391 bool blocking_threads = false;
392 for (unsigned int i = 0; i < get_num_threads(); i++) {
393 thread_id_t tid = int_to_id(i);
396 Thread *t = get_thread(tid);
397 if (!t->is_model_thread() && t->get_pending())
398 blocking_threads = true;
400 return blocking_threads;
404 * Check if this is a complete execution. That is, have all thread completed
405 * execution (rather than exiting because sleep sets have forced a redundant
408 * @return True if the execution is complete.
410 bool ModelChecker::is_complete_execution() const
412 for (unsigned int i = 0; i < get_num_threads(); i++)
413 if (is_enabled(int_to_id(i)))
419 * @brief Assert a bug in the executing program.
421 * Use this function to assert any sort of bug in the user program. If the
422 * current trace is feasible (actually, a prefix of some feasible execution),
423 * then this execution will be aborted, printing the appropriate message. If
424 * the current trace is not yet feasible, the error message will be stashed and
425 * printed if the execution ever becomes feasible.
427 * @param msg Descriptive message for the bug (do not include newline char)
428 * @return True if bug is immediately-feasible
430 bool ModelChecker::assert_bug(const char *msg)
432 priv->bugs.push_back(new bug_message(msg));
434 if (isfeasibleprefix()) {
442 * @brief Assert a bug in the executing program, asserted by a user thread
443 * @see ModelChecker::assert_bug
444 * @param msg Descriptive message for the bug (do not include newline char)
446 void ModelChecker::assert_user_bug(const char *msg)
448 /* If feasible bug, bail out now */
450 switch_to_master(NULL);
453 /** @return True, if any bugs have been reported for this execution */
454 bool ModelChecker::have_bug_reports() const
456 return priv->bugs.size() != 0;
459 /** @brief Print bug report listing for this execution (if any bugs exist) */
460 void ModelChecker::print_bugs() const
462 if (have_bug_reports()) {
463 model_print("Bug report: %zu bug%s detected\n",
465 priv->bugs.size() > 1 ? "s" : "");
466 for (unsigned int i = 0; i < priv->bugs.size(); i++)
467 priv->bugs[i]->print();
472 * @brief Record end-of-execution stats
474 * Must be run when exiting an execution. Records various stats.
475 * @see struct execution_stats
477 void ModelChecker::record_stats()
480 if (!isfeasibleprefix())
481 stats.num_infeasible++;
482 else if (have_bug_reports())
483 stats.num_buggy_executions++;
484 else if (is_complete_execution())
485 stats.num_complete++;
486 else if (scheduler->all_threads_sleeping())
487 stats.num_redundant++;
492 /** @brief Print execution stats */
493 void ModelChecker::print_stats() const
495 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
496 model_print("Number of redundant executions: %d\n", stats.num_redundant);
497 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
498 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
499 model_print("Total executions: %d\n", stats.num_total);
500 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
504 * @brief End-of-exeuction print
505 * @param printbugs Should any existing bugs be printed?
507 void ModelChecker::print_execution(bool printbugs) const
509 print_program_output();
511 if (DBG_ENABLED() || params.verbose) {
512 model_print("Earliest divergence point since last feasible execution:\n");
513 if (earliest_diverge)
514 earliest_diverge->print();
516 model_print("(Not set)\n");
522 /* Don't print invalid bugs */
531 * Queries the model-checker for more executions to explore and, if one
532 * exists, resets the model-checker state to execute a new execution.
534 * @return If there are more executions to explore, return true. Otherwise,
537 bool ModelChecker::next_execution()
540 /* Is this execution a feasible execution that's worth bug-checking? */
541 bool complete = isfeasibleprefix() && (is_complete_execution() ||
544 /* End-of-execution bug checks */
547 assert_bug("Deadlock detected");
555 if (DBG_ENABLED() || params.verbose || (complete && have_bug_reports()))
556 print_execution(complete);
558 clear_program_output();
561 earliest_diverge = NULL;
563 if ((diverge = get_next_backtrack()) == NULL)
567 model_print("Next execution will diverge at:\n");
571 reset_to_initial_state();
576 * @brief Find the last fence-related backtracking conflict for a ModelAction
578 * This function performs the search for the most recent conflicting action
579 * against which we should perform backtracking, as affected by fence
580 * operations. This includes pairs of potentially-synchronizing actions which
581 * occur due to fence-acquire or fence-release, and hence should be explored in
582 * the opposite execution order.
584 * @param act The current action
585 * @return The most recent action which conflicts with act due to fences
587 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
589 /* Only perform release/acquire fence backtracking for stores */
590 if (!act->is_write())
593 /* Find a fence-release (or, act is a release) */
594 ModelAction *last_release;
595 if (act->is_release())
598 last_release = get_last_fence_release(act->get_tid());
602 /* Skip past the release */
603 action_list_t *list = action_trace;
604 action_list_t::reverse_iterator rit;
605 for (rit = list->rbegin(); rit != list->rend(); rit++)
606 if (*rit == last_release)
608 ASSERT(rit != list->rend());
613 * load --sb-> fence-acquire */
614 std::vector< ModelAction *, ModelAlloc<ModelAction *> > acquire_fences(get_num_threads(), NULL);
615 std::vector< ModelAction *, ModelAlloc<ModelAction *> > prior_loads(get_num_threads(), NULL);
616 bool found_acquire_fences = false;
617 for ( ; rit != list->rend(); rit++) {
618 ModelAction *prev = *rit;
619 if (act->same_thread(prev))
622 int tid = id_to_int(prev->get_tid());
624 if (prev->is_read() && act->same_var(prev)) {
625 if (prev->is_acquire()) {
626 /* Found most recent load-acquire, don't need
627 * to search for more fences */
628 if (!found_acquire_fences)
631 prior_loads[tid] = prev;
634 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
635 found_acquire_fences = true;
636 acquire_fences[tid] = prev;
640 ModelAction *latest_backtrack = NULL;
641 for (unsigned int i = 0; i < acquire_fences.size(); i++)
642 if (acquire_fences[i] && prior_loads[i])
643 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
644 latest_backtrack = acquire_fences[i];
645 return latest_backtrack;
649 * @brief Find the last backtracking conflict for a ModelAction
651 * This function performs the search for the most recent conflicting action
652 * against which we should perform backtracking. This primary includes pairs of
653 * synchronizing actions which should be explored in the opposite execution
656 * @param act The current action
657 * @return The most recent action which conflicts with act
659 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
661 switch (act->get_type()) {
662 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
666 ModelAction *ret = NULL;
668 /* linear search: from most recent to oldest */
669 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
670 action_list_t::reverse_iterator rit;
671 for (rit = list->rbegin(); rit != list->rend(); rit++) {
672 ModelAction *prev = *rit;
673 if (prev->could_synchronize_with(act)) {
679 ModelAction *ret2 = get_last_fence_conflict(act);
689 case ATOMIC_TRYLOCK: {
690 /* linear search: from most recent to oldest */
691 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
692 action_list_t::reverse_iterator rit;
693 for (rit = list->rbegin(); rit != list->rend(); rit++) {
694 ModelAction *prev = *rit;
695 if (act->is_conflicting_lock(prev))
700 case ATOMIC_UNLOCK: {
701 /* linear search: from most recent to oldest */
702 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
703 action_list_t::reverse_iterator rit;
704 for (rit = list->rbegin(); rit != list->rend(); rit++) {
705 ModelAction *prev = *rit;
706 if (!act->same_thread(prev) && prev->is_failed_trylock())
712 /* linear search: from most recent to oldest */
713 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
714 action_list_t::reverse_iterator rit;
715 for (rit = list->rbegin(); rit != list->rend(); rit++) {
716 ModelAction *prev = *rit;
717 if (!act->same_thread(prev) && prev->is_failed_trylock())
719 if (!act->same_thread(prev) && prev->is_notify())
725 case ATOMIC_NOTIFY_ALL:
726 case ATOMIC_NOTIFY_ONE: {
727 /* linear search: from most recent to oldest */
728 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
729 action_list_t::reverse_iterator rit;
730 for (rit = list->rbegin(); rit != list->rend(); rit++) {
731 ModelAction *prev = *rit;
732 if (!act->same_thread(prev) && prev->is_wait())
743 /** This method finds backtracking points where we should try to
744 * reorder the parameter ModelAction against.
746 * @param the ModelAction to find backtracking points for.
748 void ModelChecker::set_backtracking(ModelAction *act)
750 Thread *t = get_thread(act);
751 ModelAction *prev = get_last_conflict(act);
755 Node *node = prev->get_node()->get_parent();
757 int low_tid, high_tid;
758 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
759 low_tid = id_to_int(act->get_tid());
760 high_tid = low_tid + 1;
763 high_tid = get_num_threads();
766 for (int i = low_tid; i < high_tid; i++) {
767 thread_id_t tid = int_to_id(i);
769 /* Make sure this thread can be enabled here. */
770 if (i >= node->get_num_threads())
773 /* Don't backtrack into a point where the thread is disabled or sleeping. */
774 if (node->enabled_status(tid) != THREAD_ENABLED)
777 /* Check if this has been explored already */
778 if (node->has_been_explored(tid))
781 /* See if fairness allows */
782 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
784 for (int t = 0; t < node->get_num_threads(); t++) {
785 thread_id_t tother = int_to_id(t);
786 if (node->is_enabled(tother) && node->has_priority(tother)) {
794 /* Cache the latest backtracking point */
795 set_latest_backtrack(prev);
797 /* If this is a new backtracking point, mark the tree */
798 if (!node->set_backtrack(tid))
800 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
801 id_to_int(prev->get_tid()),
802 id_to_int(t->get_id()));
811 * @brief Cache the a backtracking point as the "most recent", if eligible
813 * Note that this does not prepare the NodeStack for this backtracking
814 * operation, it only caches the action on a per-execution basis
816 * @param act The operation at which we should explore a different next action
817 * (i.e., backtracking point)
818 * @return True, if this action is now the most recent backtracking point;
821 bool ModelChecker::set_latest_backtrack(ModelAction *act)
823 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
824 priv->next_backtrack = act;
831 * Returns last backtracking point. The model checker will explore a different
832 * path for this point in the next execution.
833 * @return The ModelAction at which the next execution should diverge.
835 ModelAction * ModelChecker::get_next_backtrack()
837 ModelAction *next = priv->next_backtrack;
838 priv->next_backtrack = NULL;
843 * Processes a read model action.
844 * @param curr is the read model action to process.
845 * @return True if processing this read updates the mo_graph.
847 bool ModelChecker::process_read(ModelAction *curr)
849 Node *node = curr->get_node();
850 uint64_t value = VALUE_NONE;
851 bool updated = false;
853 switch (node->get_read_from_status()) {
854 case READ_FROM_PAST: {
855 const ModelAction *rf = node->get_read_from_past();
858 mo_graph->startChanges();
859 value = rf->get_value();
860 check_recency(curr, rf);
861 bool r_status = r_modification_order(curr, rf);
863 if (is_infeasible() && node->increment_read_from()) {
864 mo_graph->rollbackChanges();
865 priv->too_many_reads = false;
870 mo_graph->commitChanges();
871 mo_check_promises(curr, true);
876 case READ_FROM_PROMISE: {
877 Promise *promise = curr->get_node()->get_read_from_promise();
878 promise->add_reader(curr);
879 value = promise->get_value();
880 curr->set_read_from_promise(promise);
881 mo_graph->startChanges();
882 updated = r_modification_order(curr, promise);
883 mo_graph->commitChanges();
886 case READ_FROM_FUTURE: {
887 /* Read from future value */
888 struct future_value fv = node->get_future_value();
889 Promise *promise = new Promise(curr, fv);
891 curr->set_read_from_promise(promise);
892 promises->push_back(promise);
893 mo_graph->startChanges();
894 updated = r_modification_order(curr, promise);
895 mo_graph->commitChanges();
901 get_thread(curr)->set_return_value(value);
907 * Processes a lock, trylock, or unlock model action. @param curr is
908 * the read model action to process.
910 * The try lock operation checks whether the lock is taken. If not,
911 * it falls to the normal lock operation case. If so, it returns
914 * The lock operation has already been checked that it is enabled, so
915 * it just grabs the lock and synchronizes with the previous unlock.
917 * The unlock operation has to re-enable all of the threads that are
918 * waiting on the lock.
920 * @return True if synchronization was updated; false otherwise
922 bool ModelChecker::process_mutex(ModelAction *curr)
924 std::mutex *mutex = NULL;
925 struct std::mutex_state *state = NULL;
927 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
928 mutex = (std::mutex *)curr->get_location();
929 state = mutex->get_state();
930 } else if (curr->is_wait()) {
931 mutex = (std::mutex *)curr->get_value();
932 state = mutex->get_state();
935 switch (curr->get_type()) {
936 case ATOMIC_TRYLOCK: {
937 bool success = !state->islocked;
938 curr->set_try_lock(success);
940 get_thread(curr)->set_return_value(0);
943 get_thread(curr)->set_return_value(1);
945 //otherwise fall into the lock case
947 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
948 assert_bug("Lock access before initialization");
949 state->islocked = true;
950 ModelAction *unlock = get_last_unlock(curr);
951 //synchronize with the previous unlock statement
952 if (unlock != NULL) {
953 curr->synchronize_with(unlock);
958 case ATOMIC_UNLOCK: {
960 state->islocked = false;
961 //wake up the other threads
962 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
963 //activate all the waiting threads
964 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
965 scheduler->wake(get_thread(*rit));
972 state->islocked = false;
973 //wake up the other threads
974 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
975 //activate all the waiting threads
976 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
977 scheduler->wake(get_thread(*rit));
980 //check whether we should go to sleep or not...simulate spurious failures
981 if (curr->get_node()->get_misc() == 0) {
982 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
984 scheduler->sleep(get_thread(curr));
988 case ATOMIC_NOTIFY_ALL: {
989 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
990 //activate all the waiting threads
991 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
992 scheduler->wake(get_thread(*rit));
997 case ATOMIC_NOTIFY_ONE: {
998 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
999 int wakeupthread = curr->get_node()->get_misc();
1000 action_list_t::iterator it = waiters->begin();
1001 advance(it, wakeupthread);
1002 scheduler->wake(get_thread(*it));
1013 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1015 /* Do more ambitious checks now that mo is more complete */
1016 if (mo_may_allow(writer, reader)) {
1017 Node *node = reader->get_node();
1019 /* Find an ancestor thread which exists at the time of the reader */
1020 Thread *write_thread = get_thread(writer);
1021 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1022 write_thread = write_thread->get_parent();
1024 struct future_value fv = {
1025 writer->get_write_value(),
1026 writer->get_seq_number() + params.maxfuturedelay,
1027 write_thread->get_id(),
1029 if (node->add_future_value(fv))
1030 set_latest_backtrack(reader);
1035 * Process a write ModelAction
1036 * @param curr The ModelAction to process
1037 * @return True if the mo_graph was updated or promises were resolved
1039 bool ModelChecker::process_write(ModelAction *curr)
1041 bool updated_mod_order = w_modification_order(curr);
1042 bool updated_promises = resolve_promises(curr);
1044 if (promises->size() == 0) {
1045 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1046 struct PendingFutureValue pfv = (*futurevalues)[i];
1047 add_future_value(pfv.writer, pfv.act);
1049 futurevalues->clear();
1052 mo_graph->commitChanges();
1053 mo_check_promises(curr, false);
1055 get_thread(curr)->set_return_value(VALUE_NONE);
1056 return updated_mod_order || updated_promises;
1060 * Process a fence ModelAction
1061 * @param curr The ModelAction to process
1062 * @return True if synchronization was updated
1064 bool ModelChecker::process_fence(ModelAction *curr)
1067 * fence-relaxed: no-op
1068 * fence-release: only log the occurence (not in this function), for
1069 * use in later synchronization
1070 * fence-acquire (this function): search for hypothetical release
1073 bool updated = false;
1074 if (curr->is_acquire()) {
1075 action_list_t *list = action_trace;
1076 action_list_t::reverse_iterator rit;
1077 /* Find X : is_read(X) && X --sb-> curr */
1078 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1079 ModelAction *act = *rit;
1082 if (act->get_tid() != curr->get_tid())
1084 /* Stop at the beginning of the thread */
1085 if (act->is_thread_start())
1087 /* Stop once we reach a prior fence-acquire */
1088 if (act->is_fence() && act->is_acquire())
1090 if (!act->is_read())
1092 /* read-acquire will find its own release sequences */
1093 if (act->is_acquire())
1096 /* Establish hypothetical release sequences */
1097 rel_heads_list_t release_heads;
1098 get_release_seq_heads(curr, act, &release_heads);
1099 for (unsigned int i = 0; i < release_heads.size(); i++)
1100 if (!curr->synchronize_with(release_heads[i]))
1101 set_bad_synchronization();
1102 if (release_heads.size() != 0)
1110 * @brief Process the current action for thread-related activity
1112 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1113 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1114 * synchronization, etc. This function is a no-op for non-THREAD actions
1115 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1117 * @param curr The current action
1118 * @return True if synchronization was updated or a thread completed
1120 bool ModelChecker::process_thread_action(ModelAction *curr)
1122 bool updated = false;
1124 switch (curr->get_type()) {
1125 case THREAD_CREATE: {
1126 thrd_t *thrd = (thrd_t *)curr->get_location();
1127 struct thread_params *params = (struct thread_params *)curr->get_value();
1128 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1130 th->set_creation(curr);
1131 /* Promises can be satisfied by children */
1132 for (unsigned int i = 0; i < promises->size(); i++) {
1133 Promise *promise = (*promises)[i];
1134 if (promise->thread_is_available(curr->get_tid()))
1135 promise->add_thread(th->get_id());
1140 Thread *blocking = curr->get_thread_operand();
1141 ModelAction *act = get_last_action(blocking->get_id());
1142 curr->synchronize_with(act);
1143 updated = true; /* trigger rel-seq checks */
1146 case THREAD_FINISH: {
1147 Thread *th = get_thread(curr);
1148 while (!th->wait_list_empty()) {
1149 ModelAction *act = th->pop_wait_list();
1150 scheduler->wake(get_thread(act));
1153 /* Completed thread can't satisfy promises */
1154 for (unsigned int i = 0; i < promises->size(); i++) {
1155 Promise *promise = (*promises)[i];
1156 if (promise->thread_is_available(th->get_id()))
1157 if (promise->eliminate_thread(th->get_id()))
1158 priv->failed_promise = true;
1160 updated = true; /* trigger rel-seq checks */
1163 case THREAD_START: {
1164 check_promises(curr->get_tid(), NULL, curr->get_cv());
1175 * @brief Process the current action for release sequence fixup activity
1177 * Performs model-checker release sequence fixups for the current action,
1178 * forcing a single pending release sequence to break (with a given, potential
1179 * "loose" write) or to complete (i.e., synchronize). If a pending release
1180 * sequence forms a complete release sequence, then we must perform the fixup
1181 * synchronization, mo_graph additions, etc.
1183 * @param curr The current action; must be a release sequence fixup action
1184 * @param work_queue The work queue to which to add work items as they are
1187 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1189 const ModelAction *write = curr->get_node()->get_relseq_break();
1190 struct release_seq *sequence = pending_rel_seqs->back();
1191 pending_rel_seqs->pop_back();
1193 ModelAction *acquire = sequence->acquire;
1194 const ModelAction *rf = sequence->rf;
1195 const ModelAction *release = sequence->release;
1199 ASSERT(release->same_thread(rf));
1201 if (write == NULL) {
1203 * @todo Forcing a synchronization requires that we set
1204 * modification order constraints. For instance, we can't allow
1205 * a fixup sequence in which two separate read-acquire
1206 * operations read from the same sequence, where the first one
1207 * synchronizes and the other doesn't. Essentially, we can't
1208 * allow any writes to insert themselves between 'release' and
1212 /* Must synchronize */
1213 if (!acquire->synchronize_with(release)) {
1214 set_bad_synchronization();
1217 /* Re-check all pending release sequences */
1218 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1219 /* Re-check act for mo_graph edges */
1220 work_queue->push_back(MOEdgeWorkEntry(acquire));
1222 /* propagate synchronization to later actions */
1223 action_list_t::reverse_iterator rit = action_trace->rbegin();
1224 for (; (*rit) != acquire; rit++) {
1225 ModelAction *propagate = *rit;
1226 if (acquire->happens_before(propagate)) {
1227 propagate->synchronize_with(acquire);
1228 /* Re-check 'propagate' for mo_graph edges */
1229 work_queue->push_back(MOEdgeWorkEntry(propagate));
1233 /* Break release sequence with new edges:
1234 * release --mo--> write --mo--> rf */
1235 mo_graph->addEdge(release, write);
1236 mo_graph->addEdge(write, rf);
1239 /* See if we have realized a data race */
1244 * Initialize the current action by performing one or more of the following
1245 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1246 * in the NodeStack, manipulating backtracking sets, allocating and
1247 * initializing clock vectors, and computing the promises to fulfill.
1249 * @param curr The current action, as passed from the user context; may be
1250 * freed/invalidated after the execution of this function, with a different
1251 * action "returned" its place (pass-by-reference)
1252 * @return True if curr is a newly-explored action; false otherwise
1254 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1256 ModelAction *newcurr;
1258 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1259 newcurr = process_rmw(*curr);
1262 if (newcurr->is_rmw())
1263 compute_promises(newcurr);
1269 (*curr)->set_seq_number(get_next_seq_num());
1271 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1273 /* First restore type and order in case of RMW operation */
1274 if ((*curr)->is_rmwr())
1275 newcurr->copy_typeandorder(*curr);
1277 ASSERT((*curr)->get_location() == newcurr->get_location());
1278 newcurr->copy_from_new(*curr);
1280 /* Discard duplicate ModelAction; use action from NodeStack */
1283 /* Always compute new clock vector */
1284 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1287 return false; /* Action was explored previously */
1291 /* Always compute new clock vector */
1292 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1294 /* Assign most recent release fence */
1295 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1298 * Perform one-time actions when pushing new ModelAction onto
1301 if (newcurr->is_write())
1302 compute_promises(newcurr);
1303 else if (newcurr->is_relseq_fixup())
1304 compute_relseq_breakwrites(newcurr);
1305 else if (newcurr->is_wait())
1306 newcurr->get_node()->set_misc_max(2);
1307 else if (newcurr->is_notify_one()) {
1308 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1310 return true; /* This was a new ModelAction */
1315 * @brief Establish reads-from relation between two actions
1317 * Perform basic operations involved with establishing a concrete rf relation,
1318 * including setting the ModelAction data and checking for release sequences.
1320 * @param act The action that is reading (must be a read)
1321 * @param rf The action from which we are reading (must be a write)
1323 * @return True if this read established synchronization
1325 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1328 act->set_read_from(rf);
1329 if (act->is_acquire()) {
1330 rel_heads_list_t release_heads;
1331 get_release_seq_heads(act, act, &release_heads);
1332 int num_heads = release_heads.size();
1333 for (unsigned int i = 0; i < release_heads.size(); i++)
1334 if (!act->synchronize_with(release_heads[i])) {
1335 set_bad_synchronization();
1338 return num_heads > 0;
1344 * Check promises and eliminate potentially-satisfying threads when a thread is
1345 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1346 * no longer satisfy a promise generated from that thread.
1348 * @param blocker The thread on which a thread is waiting
1349 * @param waiting The waiting thread
1351 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1353 for (unsigned int i = 0; i < promises->size(); i++) {
1354 Promise *promise = (*promises)[i];
1355 if (!promise->thread_is_available(waiting->get_id()))
1357 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1358 ModelAction *reader = promise->get_reader(j);
1359 if (reader->get_tid() != blocker->get_id())
1361 if (promise->eliminate_thread(waiting->get_id())) {
1362 /* Promise has failed */
1363 priv->failed_promise = true;
1365 /* Only eliminate the 'waiting' thread once */
1373 * @brief Check whether a model action is enabled.
1375 * Checks whether a lock or join operation would be successful (i.e., is the
1376 * lock already locked, or is the joined thread already complete). If not, put
1377 * the action in a waiter list.
1379 * @param curr is the ModelAction to check whether it is enabled.
1380 * @return a bool that indicates whether the action is enabled.
1382 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1383 if (curr->is_lock()) {
1384 std::mutex *lock = (std::mutex *)curr->get_location();
1385 struct std::mutex_state *state = lock->get_state();
1386 if (state->islocked) {
1387 //Stick the action in the appropriate waiting queue
1388 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1391 } else if (curr->get_type() == THREAD_JOIN) {
1392 Thread *blocking = (Thread *)curr->get_location();
1393 if (!blocking->is_complete()) {
1394 blocking->push_wait_list(curr);
1395 thread_blocking_check_promises(blocking, get_thread(curr));
1404 * This is the heart of the model checker routine. It performs model-checking
1405 * actions corresponding to a given "current action." Among other processes, it
1406 * calculates reads-from relationships, updates synchronization clock vectors,
1407 * forms a memory_order constraints graph, and handles replay/backtrack
1408 * execution when running permutations of previously-observed executions.
1410 * @param curr The current action to process
1411 * @return The ModelAction that is actually executed; may be different than
1412 * curr; may be NULL, if the current action is not enabled to run
1414 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1417 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1419 if (!check_action_enabled(curr)) {
1420 /* Make the execution look like we chose to run this action
1421 * much later, when a lock/join can succeed */
1422 get_thread(curr)->set_pending(curr);
1423 scheduler->sleep(get_thread(curr));
1427 bool newly_explored = initialize_curr_action(&curr);
1433 wake_up_sleeping_actions(curr);
1435 /* Add the action to lists before any other model-checking tasks */
1436 if (!second_part_of_rmw)
1437 add_action_to_lists(curr);
1439 /* Build may_read_from set for newly-created actions */
1440 if (newly_explored && curr->is_read())
1441 build_may_read_from(curr);
1443 /* Initialize work_queue with the "current action" work */
1444 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1445 while (!work_queue.empty() && !has_asserted()) {
1446 WorkQueueEntry work = work_queue.front();
1447 work_queue.pop_front();
1449 switch (work.type) {
1450 case WORK_CHECK_CURR_ACTION: {
1451 ModelAction *act = work.action;
1452 bool update = false; /* update this location's release seq's */
1453 bool update_all = false; /* update all release seq's */
1455 if (process_thread_action(curr))
1458 if (act->is_read() && !second_part_of_rmw && process_read(act))
1461 if (act->is_write() && process_write(act))
1464 if (act->is_fence() && process_fence(act))
1467 if (act->is_mutex_op() && process_mutex(act))
1470 if (act->is_relseq_fixup())
1471 process_relseq_fixup(curr, &work_queue);
1474 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1476 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1479 case WORK_CHECK_RELEASE_SEQ:
1480 resolve_release_sequences(work.location, &work_queue);
1482 case WORK_CHECK_MO_EDGES: {
1483 /** @todo Complete verification of work_queue */
1484 ModelAction *act = work.action;
1485 bool updated = false;
1487 if (act->is_read()) {
1488 const ModelAction *rf = act->get_reads_from();
1489 const Promise *promise = act->get_reads_from_promise();
1491 if (r_modification_order(act, rf))
1493 } else if (promise) {
1494 if (r_modification_order(act, promise))
1498 if (act->is_write()) {
1499 if (w_modification_order(act))
1502 mo_graph->commitChanges();
1505 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1514 check_curr_backtracking(curr);
1515 set_backtracking(curr);
1519 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1521 Node *currnode = curr->get_node();
1522 Node *parnode = currnode->get_parent();
1524 if ((parnode && !parnode->backtrack_empty()) ||
1525 !currnode->misc_empty() ||
1526 !currnode->read_from_empty() ||
1527 !currnode->promise_empty() ||
1528 !currnode->relseq_break_empty()) {
1529 set_latest_backtrack(curr);
1533 bool ModelChecker::promises_expired() const
1535 for (unsigned int i = 0; i < promises->size(); i++) {
1536 Promise *promise = (*promises)[i];
1537 if (promise->get_expiration() < priv->used_sequence_numbers)
1544 * This is the strongest feasibility check available.
1545 * @return whether the current trace (partial or complete) must be a prefix of
1548 bool ModelChecker::isfeasibleprefix() const
1550 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1554 * Print disagnostic information about an infeasible execution
1555 * @param prefix A string to prefix the output with; if NULL, then a default
1556 * message prefix will be provided
1558 void ModelChecker::print_infeasibility(const char *prefix) const
1562 if (mo_graph->checkForCycles())
1563 ptr += sprintf(ptr, "[mo cycle]");
1564 if (priv->failed_promise)
1565 ptr += sprintf(ptr, "[failed promise]");
1566 if (priv->too_many_reads)
1567 ptr += sprintf(ptr, "[too many reads]");
1568 if (priv->no_valid_reads)
1569 ptr += sprintf(ptr, "[no valid reads-from]");
1570 if (priv->bad_synchronization)
1571 ptr += sprintf(ptr, "[bad sw ordering]");
1572 if (promises_expired())
1573 ptr += sprintf(ptr, "[promise expired]");
1574 if (promises->size() != 0)
1575 ptr += sprintf(ptr, "[unresolved promise]");
1577 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1581 * Returns whether the current completed trace is feasible, except for pending
1582 * release sequences.
1584 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1586 return !is_infeasible() && promises->size() == 0;
1590 * Check if the current partial trace is infeasible. Does not check any
1591 * end-of-execution flags, which might rule out the execution. Thus, this is
1592 * useful only for ruling an execution as infeasible.
1593 * @return whether the current partial trace is infeasible.
1595 bool ModelChecker::is_infeasible() const
1597 return mo_graph->checkForCycles() ||
1598 priv->no_valid_reads ||
1599 priv->failed_promise ||
1600 priv->too_many_reads ||
1601 priv->bad_synchronization ||
1605 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1606 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1607 ModelAction *lastread = get_last_action(act->get_tid());
1608 lastread->process_rmw(act);
1609 if (act->is_rmw()) {
1610 if (lastread->get_reads_from())
1611 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1613 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1614 mo_graph->commitChanges();
1620 * Checks whether a thread has read from the same write for too many times
1621 * without seeing the effects of a later write.
1624 * 1) there must a different write that we could read from that would satisfy the modification order,
1625 * 2) we must have read from the same value in excess of maxreads times, and
1626 * 3) that other write must have been in the reads_from set for maxreads times.
1628 * If so, we decide that the execution is no longer feasible.
1630 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf)
1632 if (params.maxreads != 0) {
1633 if (curr->get_node()->get_read_from_past_size() <= 1)
1635 //Must make sure that execution is currently feasible... We could
1636 //accidentally clear by rolling back
1637 if (is_infeasible())
1639 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1640 int tid = id_to_int(curr->get_tid());
1643 if ((int)thrd_lists->size() <= tid)
1645 action_list_t *list = &(*thrd_lists)[tid];
1647 action_list_t::reverse_iterator rit = list->rbegin();
1648 /* Skip past curr */
1649 for (; (*rit) != curr; rit++)
1651 /* go past curr now */
1654 action_list_t::reverse_iterator ritcopy = rit;
1655 //See if we have enough reads from the same value
1657 for (; count < params.maxreads; rit++, count++) {
1658 if (rit == list->rend())
1660 ModelAction *act = *rit;
1661 if (!act->is_read())
1664 if (act->get_reads_from() != rf)
1666 if (act->get_node()->get_read_from_past_size() <= 1)
1669 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1671 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1673 /* Need a different write */
1677 /* Test to see whether this is a feasible write to read from */
1678 /** NOTE: all members of read-from set should be
1679 * feasible, so we no longer check it here **/
1683 bool feasiblewrite = true;
1684 //new we need to see if this write works for everyone
1686 for (int loop = count; loop > 0; loop--, rit++) {
1687 ModelAction *act = *rit;
1688 bool foundvalue = false;
1689 for (int j = 0; j < act->get_node()->get_read_from_past_size(); j++) {
1690 if (act->get_node()->get_read_from_past(j) == write) {
1696 feasiblewrite = false;
1700 if (feasiblewrite) {
1701 priv->too_many_reads = true;
1709 * Updates the mo_graph with the constraints imposed from the current
1712 * Basic idea is the following: Go through each other thread and find
1713 * the last action that happened before our read. Two cases:
1715 * (1) The action is a write => that write must either occur before
1716 * the write we read from or be the write we read from.
1718 * (2) The action is a read => the write that that action read from
1719 * must occur before the write we read from or be the same write.
1721 * @param curr The current action. Must be a read.
1722 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1723 * @return True if modification order edges were added; false otherwise
1725 template <typename rf_type>
1726 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1728 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1731 ASSERT(curr->is_read());
1733 /* Last SC fence in the current thread */
1734 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1736 /* Iterate over all threads */
1737 for (i = 0; i < thrd_lists->size(); i++) {
1738 /* Last SC fence in thread i */
1739 ModelAction *last_sc_fence_thread_local = NULL;
1740 if (int_to_id((int)i) != curr->get_tid())
1741 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1743 /* Last SC fence in thread i, before last SC fence in current thread */
1744 ModelAction *last_sc_fence_thread_before = NULL;
1745 if (last_sc_fence_local)
1746 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1748 /* Iterate over actions in thread, starting from most recent */
1749 action_list_t *list = &(*thrd_lists)[i];
1750 action_list_t::reverse_iterator rit;
1751 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1752 ModelAction *act = *rit;
1754 if (act->is_write() && !act->equals(rf) && act != curr) {
1755 /* C++, Section 29.3 statement 5 */
1756 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1757 *act < *last_sc_fence_thread_local) {
1758 added = mo_graph->addEdge(act, rf) || added;
1761 /* C++, Section 29.3 statement 4 */
1762 else if (act->is_seqcst() && last_sc_fence_local &&
1763 *act < *last_sc_fence_local) {
1764 added = mo_graph->addEdge(act, rf) || added;
1767 /* C++, Section 29.3 statement 6 */
1768 else if (last_sc_fence_thread_before &&
1769 *act < *last_sc_fence_thread_before) {
1770 added = mo_graph->addEdge(act, rf) || added;
1776 * Include at most one act per-thread that "happens
1777 * before" curr. Don't consider reflexively.
1779 if (act->happens_before(curr) && act != curr) {
1780 if (act->is_write()) {
1781 if (!act->equals(rf)) {
1782 added = mo_graph->addEdge(act, rf) || added;
1785 const ModelAction *prevrf = act->get_reads_from();
1786 const Promise *prevrf_promise = act->get_reads_from_promise();
1788 if (!prevrf->equals(rf))
1789 added = mo_graph->addEdge(prevrf, rf) || added;
1790 } else if (!prevrf_promise->equals(rf)) {
1791 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1800 * All compatible, thread-exclusive promises must be ordered after any
1801 * concrete loads from the same thread
1803 for (unsigned int i = 0; i < promises->size(); i++)
1804 if ((*promises)[i]->is_compatible_exclusive(curr))
1805 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1811 * Updates the mo_graph with the constraints imposed from the current write.
1813 * Basic idea is the following: Go through each other thread and find
1814 * the lastest action that happened before our write. Two cases:
1816 * (1) The action is a write => that write must occur before
1819 * (2) The action is a read => the write that that action read from
1820 * must occur before the current write.
1822 * This method also handles two other issues:
1824 * (I) Sequential Consistency: Making sure that if the current write is
1825 * seq_cst, that it occurs after the previous seq_cst write.
1827 * (II) Sending the write back to non-synchronizing reads.
1829 * @param curr The current action. Must be a write.
1830 * @return True if modification order edges were added; false otherwise
1832 bool ModelChecker::w_modification_order(ModelAction *curr)
1834 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1837 ASSERT(curr->is_write());
1839 if (curr->is_seqcst()) {
1840 /* We have to at least see the last sequentially consistent write,
1841 so we are initialized. */
1842 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1843 if (last_seq_cst != NULL) {
1844 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1848 /* Last SC fence in the current thread */
1849 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1851 /* Iterate over all threads */
1852 for (i = 0; i < thrd_lists->size(); i++) {
1853 /* Last SC fence in thread i, before last SC fence in current thread */
1854 ModelAction *last_sc_fence_thread_before = NULL;
1855 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1856 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1858 /* Iterate over actions in thread, starting from most recent */
1859 action_list_t *list = &(*thrd_lists)[i];
1860 action_list_t::reverse_iterator rit;
1861 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1862 ModelAction *act = *rit;
1865 * 1) If RMW and it actually read from something, then we
1866 * already have all relevant edges, so just skip to next
1869 * 2) If RMW and it didn't read from anything, we should
1870 * whatever edge we can get to speed up convergence.
1872 * 3) If normal write, we need to look at earlier actions, so
1873 * continue processing list.
1875 if (curr->is_rmw()) {
1876 if (curr->get_reads_from() != NULL)
1884 /* C++, Section 29.3 statement 7 */
1885 if (last_sc_fence_thread_before && act->is_write() &&
1886 *act < *last_sc_fence_thread_before) {
1887 added = mo_graph->addEdge(act, curr) || added;
1892 * Include at most one act per-thread that "happens
1895 if (act->happens_before(curr)) {
1897 * Note: if act is RMW, just add edge:
1899 * The following edge should be handled elsewhere:
1900 * readfrom(act) --mo--> act
1902 if (act->is_write())
1903 added = mo_graph->addEdge(act, curr) || added;
1904 else if (act->is_read()) {
1905 //if previous read accessed a null, just keep going
1906 if (act->get_reads_from() == NULL)
1908 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1911 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1912 !act->same_thread(curr)) {
1913 /* We have an action that:
1914 (1) did not happen before us
1915 (2) is a read and we are a write
1916 (3) cannot synchronize with us
1917 (4) is in a different thread
1919 that read could potentially read from our write. Note that
1920 these checks are overly conservative at this point, we'll
1921 do more checks before actually removing the
1925 if (thin_air_constraint_may_allow(curr, act)) {
1926 if (!is_infeasible())
1927 futurevalues->push_back(PendingFutureValue(curr, act));
1928 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1929 add_future_value(curr, act);
1936 * All compatible, thread-exclusive promises must be ordered after any
1937 * concrete stores to the same thread, or else they can be merged with
1940 for (unsigned int i = 0; i < promises->size(); i++)
1941 if ((*promises)[i]->is_compatible_exclusive(curr))
1942 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1947 /** Arbitrary reads from the future are not allowed. Section 29.3
1948 * part 9 places some constraints. This method checks one result of constraint
1949 * constraint. Others require compiler support. */
1950 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1952 if (!writer->is_rmw())
1955 if (!reader->is_rmw())
1958 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1959 if (search == reader)
1961 if (search->get_tid() == reader->get_tid() &&
1962 search->happens_before(reader))
1970 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1971 * some constraints. This method checks one the following constraint (others
1972 * require compiler support):
1974 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1976 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1978 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1980 /* Iterate over all threads */
1981 for (i = 0; i < thrd_lists->size(); i++) {
1982 const ModelAction *write_after_read = NULL;
1984 /* Iterate over actions in thread, starting from most recent */
1985 action_list_t *list = &(*thrd_lists)[i];
1986 action_list_t::reverse_iterator rit;
1987 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1988 ModelAction *act = *rit;
1990 /* Don't disallow due to act == reader */
1991 if (!reader->happens_before(act) || reader == act)
1993 else if (act->is_write())
1994 write_after_read = act;
1995 else if (act->is_read() && act->get_reads_from() != NULL)
1996 write_after_read = act->get_reads_from();
1999 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2006 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2007 * The ModelAction under consideration is expected to be taking part in
2008 * release/acquire synchronization as an object of the "reads from" relation.
2009 * Note that this can only provide release sequence support for RMW chains
2010 * which do not read from the future, as those actions cannot be traced until
2011 * their "promise" is fulfilled. Similarly, we may not even establish the
2012 * presence of a release sequence with certainty, as some modification order
2013 * constraints may be decided further in the future. Thus, this function
2014 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2015 * and a boolean representing certainty.
2017 * @param rf The action that might be part of a release sequence. Must be a
2019 * @param release_heads A pass-by-reference style return parameter. After
2020 * execution of this function, release_heads will contain the heads of all the
2021 * relevant release sequences, if any exists with certainty
2022 * @param pending A pass-by-reference style return parameter which is only used
2023 * when returning false (i.e., uncertain). Returns most information regarding
2024 * an uncertain release sequence, including any write operations that might
2025 * break the sequence.
2026 * @return true, if the ModelChecker is certain that release_heads is complete;
2029 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2030 rel_heads_list_t *release_heads,
2031 struct release_seq *pending) const
2033 /* Only check for release sequences if there are no cycles */
2034 if (mo_graph->checkForCycles())
2037 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2038 ASSERT(rf->is_write());
2040 if (rf->is_release())
2041 release_heads->push_back(rf);
2042 else if (rf->get_last_fence_release())
2043 release_heads->push_back(rf->get_last_fence_release());
2045 break; /* End of RMW chain */
2047 /** @todo Need to be smarter here... In the linux lock
2048 * example, this will run to the beginning of the program for
2050 /** @todo The way to be smarter here is to keep going until 1
2051 * thread has a release preceded by an acquire and you've seen
2054 /* acq_rel RMW is a sufficient stopping condition */
2055 if (rf->is_acquire() && rf->is_release())
2056 return true; /* complete */
2059 /* read from future: need to settle this later */
2061 return false; /* incomplete */
2064 if (rf->is_release())
2065 return true; /* complete */
2067 /* else relaxed write
2068 * - check for fence-release in the same thread (29.8, stmt. 3)
2069 * - check modification order for contiguous subsequence
2070 * -> rf must be same thread as release */
2072 const ModelAction *fence_release = rf->get_last_fence_release();
2073 /* Synchronize with a fence-release unconditionally; we don't need to
2074 * find any more "contiguous subsequence..." for it */
2076 release_heads->push_back(fence_release);
2078 int tid = id_to_int(rf->get_tid());
2079 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2080 action_list_t *list = &(*thrd_lists)[tid];
2081 action_list_t::const_reverse_iterator rit;
2083 /* Find rf in the thread list */
2084 rit = std::find(list->rbegin(), list->rend(), rf);
2085 ASSERT(rit != list->rend());
2087 /* Find the last {write,fence}-release */
2088 for (; rit != list->rend(); rit++) {
2089 if (fence_release && *(*rit) < *fence_release)
2091 if ((*rit)->is_release())
2094 if (rit == list->rend()) {
2095 /* No write-release in this thread */
2096 return true; /* complete */
2097 } else if (fence_release && *(*rit) < *fence_release) {
2098 /* The fence-release is more recent (and so, "stronger") than
2099 * the most recent write-release */
2100 return true; /* complete */
2101 } /* else, need to establish contiguous release sequence */
2102 ModelAction *release = *rit;
2104 ASSERT(rf->same_thread(release));
2106 pending->writes.clear();
2108 bool certain = true;
2109 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2110 if (id_to_int(rf->get_tid()) == (int)i)
2112 list = &(*thrd_lists)[i];
2114 /* Can we ensure no future writes from this thread may break
2115 * the release seq? */
2116 bool future_ordered = false;
2118 ModelAction *last = get_last_action(int_to_id(i));
2119 Thread *th = get_thread(int_to_id(i));
2120 if ((last && rf->happens_before(last)) ||
2123 future_ordered = true;
2125 ASSERT(!th->is_model_thread() || future_ordered);
2127 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2128 const ModelAction *act = *rit;
2129 /* Reach synchronization -> this thread is complete */
2130 if (act->happens_before(release))
2132 if (rf->happens_before(act)) {
2133 future_ordered = true;
2137 /* Only non-RMW writes can break release sequences */
2138 if (!act->is_write() || act->is_rmw())
2141 /* Check modification order */
2142 if (mo_graph->checkReachable(rf, act)) {
2143 /* rf --mo--> act */
2144 future_ordered = true;
2147 if (mo_graph->checkReachable(act, release))
2148 /* act --mo--> release */
2150 if (mo_graph->checkReachable(release, act) &&
2151 mo_graph->checkReachable(act, rf)) {
2152 /* release --mo-> act --mo--> rf */
2153 return true; /* complete */
2155 /* act may break release sequence */
2156 pending->writes.push_back(act);
2159 if (!future_ordered)
2160 certain = false; /* This thread is uncertain */
2164 release_heads->push_back(release);
2165 pending->writes.clear();
2167 pending->release = release;
2174 * An interface for getting the release sequence head(s) with which a
2175 * given ModelAction must synchronize. This function only returns a non-empty
2176 * result when it can locate a release sequence head with certainty. Otherwise,
2177 * it may mark the internal state of the ModelChecker so that it will handle
2178 * the release sequence at a later time, causing @a acquire to update its
2179 * synchronization at some later point in execution.
2181 * @param acquire The 'acquire' action that may synchronize with a release
2183 * @param read The read action that may read from a release sequence; this may
2184 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2185 * when 'acquire' is a fence-acquire)
2186 * @param release_heads A pass-by-reference return parameter. Will be filled
2187 * with the head(s) of the release sequence(s), if they exists with certainty.
2188 * @see ModelChecker::release_seq_heads
2190 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2191 ModelAction *read, rel_heads_list_t *release_heads)
2193 const ModelAction *rf = read->get_reads_from();
2194 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2195 sequence->acquire = acquire;
2196 sequence->read = read;
2198 if (!release_seq_heads(rf, release_heads, sequence)) {
2199 /* add act to 'lazy checking' list */
2200 pending_rel_seqs->push_back(sequence);
2202 snapshot_free(sequence);
2207 * Attempt to resolve all stashed operations that might synchronize with a
2208 * release sequence for a given location. This implements the "lazy" portion of
2209 * determining whether or not a release sequence was contiguous, since not all
2210 * modification order information is present at the time an action occurs.
2212 * @param location The location/object that should be checked for release
2213 * sequence resolutions. A NULL value means to check all locations.
2214 * @param work_queue The work queue to which to add work items as they are
2216 * @return True if any updates occurred (new synchronization, new mo_graph
2219 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2221 bool updated = false;
2222 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2223 while (it != pending_rel_seqs->end()) {
2224 struct release_seq *pending = *it;
2225 ModelAction *acquire = pending->acquire;
2226 const ModelAction *read = pending->read;
2228 /* Only resolve sequences on the given location, if provided */
2229 if (location && read->get_location() != location) {
2234 const ModelAction *rf = read->get_reads_from();
2235 rel_heads_list_t release_heads;
2237 complete = release_seq_heads(rf, &release_heads, pending);
2238 for (unsigned int i = 0; i < release_heads.size(); i++) {
2239 if (!acquire->has_synchronized_with(release_heads[i])) {
2240 if (acquire->synchronize_with(release_heads[i]))
2243 set_bad_synchronization();
2248 /* Re-check all pending release sequences */
2249 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2250 /* Re-check read-acquire for mo_graph edges */
2251 if (acquire->is_read())
2252 work_queue->push_back(MOEdgeWorkEntry(acquire));
2254 /* propagate synchronization to later actions */
2255 action_list_t::reverse_iterator rit = action_trace->rbegin();
2256 for (; (*rit) != acquire; rit++) {
2257 ModelAction *propagate = *rit;
2258 if (acquire->happens_before(propagate)) {
2259 propagate->synchronize_with(acquire);
2260 /* Re-check 'propagate' for mo_graph edges */
2261 work_queue->push_back(MOEdgeWorkEntry(propagate));
2266 it = pending_rel_seqs->erase(it);
2267 snapshot_free(pending);
2273 // If we resolved promises or data races, see if we have realized a data race.
2280 * Performs various bookkeeping operations for the current ModelAction. For
2281 * instance, adds action to the per-object, per-thread action vector and to the
2282 * action trace list of all thread actions.
2284 * @param act is the ModelAction to add.
2286 void ModelChecker::add_action_to_lists(ModelAction *act)
2288 int tid = id_to_int(act->get_tid());
2289 ModelAction *uninit = NULL;
2291 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2292 if (list->empty() && act->is_atomic_var()) {
2293 uninit = new_uninitialized_action(act->get_location());
2294 uninit_id = id_to_int(uninit->get_tid());
2295 list->push_back(uninit);
2297 list->push_back(act);
2299 action_trace->push_back(act);
2301 action_trace->push_front(uninit);
2303 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2304 if (tid >= (int)vec->size())
2305 vec->resize(priv->next_thread_id);
2306 (*vec)[tid].push_back(act);
2308 (*vec)[uninit_id].push_front(uninit);
2310 if ((int)thrd_last_action->size() <= tid)
2311 thrd_last_action->resize(get_num_threads());
2312 (*thrd_last_action)[tid] = act;
2314 (*thrd_last_action)[uninit_id] = uninit;
2316 if (act->is_fence() && act->is_release()) {
2317 if ((int)thrd_last_fence_release->size() <= tid)
2318 thrd_last_fence_release->resize(get_num_threads());
2319 (*thrd_last_fence_release)[tid] = act;
2322 if (act->is_wait()) {
2323 void *mutex_loc = (void *) act->get_value();
2324 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2326 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2327 if (tid >= (int)vec->size())
2328 vec->resize(priv->next_thread_id);
2329 (*vec)[tid].push_back(act);
2334 * @brief Get the last action performed by a particular Thread
2335 * @param tid The thread ID of the Thread in question
2336 * @return The last action in the thread
2338 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2340 int threadid = id_to_int(tid);
2341 if (threadid < (int)thrd_last_action->size())
2342 return (*thrd_last_action)[id_to_int(tid)];
2348 * @brief Get the last fence release performed by a particular Thread
2349 * @param tid The thread ID of the Thread in question
2350 * @return The last fence release in the thread, if one exists; NULL otherwise
2352 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2354 int threadid = id_to_int(tid);
2355 if (threadid < (int)thrd_last_fence_release->size())
2356 return (*thrd_last_fence_release)[id_to_int(tid)];
2362 * Gets the last memory_order_seq_cst write (in the total global sequence)
2363 * performed on a particular object (i.e., memory location), not including the
2365 * @param curr The current ModelAction; also denotes the object location to
2367 * @return The last seq_cst write
2369 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2371 void *location = curr->get_location();
2372 action_list_t *list = get_safe_ptr_action(obj_map, location);
2373 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2374 action_list_t::reverse_iterator rit;
2375 for (rit = list->rbegin(); rit != list->rend(); rit++)
2376 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2382 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2383 * performed in a particular thread, prior to a particular fence.
2384 * @param tid The ID of the thread to check
2385 * @param before_fence The fence from which to begin the search; if NULL, then
2386 * search for the most recent fence in the thread.
2387 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2389 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2391 /* All fences should have NULL location */
2392 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2393 action_list_t::reverse_iterator rit = list->rbegin();
2396 for (; rit != list->rend(); rit++)
2397 if (*rit == before_fence)
2400 ASSERT(*rit == before_fence);
2404 for (; rit != list->rend(); rit++)
2405 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2411 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2412 * location). This function identifies the mutex according to the current
2413 * action, which is presumed to perform on the same mutex.
2414 * @param curr The current ModelAction; also denotes the object location to
2416 * @return The last unlock operation
2418 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2420 void *location = curr->get_location();
2421 action_list_t *list = get_safe_ptr_action(obj_map, location);
2422 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2423 action_list_t::reverse_iterator rit;
2424 for (rit = list->rbegin(); rit != list->rend(); rit++)
2425 if ((*rit)->is_unlock() || (*rit)->is_wait())
2430 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2432 ModelAction *parent = get_last_action(tid);
2434 parent = get_thread(tid)->get_creation();
2439 * Returns the clock vector for a given thread.
2440 * @param tid The thread whose clock vector we want
2441 * @return Desired clock vector
2443 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2445 return get_parent_action(tid)->get_cv();
2449 * Resolve a set of Promises with a current write. The set is provided in the
2450 * Node corresponding to @a write.
2451 * @param write The ModelAction that is fulfilling Promises
2452 * @return True if promises were resolved; false otherwise
2454 bool ModelChecker::resolve_promises(ModelAction *write)
2456 bool haveResolved = false;
2457 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2458 promise_list_t mustResolve, resolved;
2460 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
2461 Promise *promise = (*promises)[promise_index];
2462 if (write->get_node()->get_promise(i)) {
2463 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2464 ModelAction *read = promise->get_reader(j);
2465 read_from(read, write);
2466 actions_to_check.push_back(read);
2468 //Make sure the promise's value matches the write's value
2469 ASSERT(promise->is_compatible(write));
2470 mo_graph->resolvePromise(promise, write, &mustResolve);
2472 resolved.push_back(promise);
2473 promises->erase(promises->begin() + promise_index);
2475 haveResolved = true;
2480 for (unsigned int i = 0; i < mustResolve.size(); i++) {
2481 if (std::find(resolved.begin(), resolved.end(), mustResolve[i])
2483 priv->failed_promise = true;
2485 for (unsigned int i = 0; i < resolved.size(); i++)
2487 //Check whether reading these writes has made threads unable to
2490 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2491 ModelAction *read = actions_to_check[i];
2492 mo_check_promises(read, true);
2495 return haveResolved;
2499 * Compute the set of promises that could potentially be satisfied by this
2500 * action. Note that the set computation actually appears in the Node, not in
2502 * @param curr The ModelAction that may satisfy promises
2504 void ModelChecker::compute_promises(ModelAction *curr)
2506 for (unsigned int i = 0; i < promises->size(); i++) {
2507 Promise *promise = (*promises)[i];
2508 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2511 bool satisfy = true;
2512 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2513 const ModelAction *act = promise->get_reader(j);
2514 if (act->happens_before(curr) ||
2515 act->could_synchronize_with(curr)) {
2521 curr->get_node()->set_promise(i);
2525 /** Checks promises in response to change in ClockVector Threads. */
2526 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2528 for (unsigned int i = 0; i < promises->size(); i++) {
2529 Promise *promise = (*promises)[i];
2530 if (!promise->thread_is_available(tid))
2532 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2533 const ModelAction *act = promise->get_reader(j);
2534 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2535 merge_cv->synchronized_since(act)) {
2536 if (promise->eliminate_thread(tid)) {
2537 /* Promise has failed */
2538 priv->failed_promise = true;
2546 void ModelChecker::check_promises_thread_disabled()
2548 for (unsigned int i = 0; i < promises->size(); i++) {
2549 Promise *promise = (*promises)[i];
2550 if (promise->has_failed()) {
2551 priv->failed_promise = true;
2558 * @brief Checks promises in response to addition to modification order for
2561 * We test whether threads are still available for satisfying promises after an
2562 * addition to our modification order constraints. Those that are unavailable
2563 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2564 * that promise has failed.
2566 * @param act The ModelAction which updated the modification order
2567 * @param is_read_check Should be true if act is a read and we must check for
2568 * updates to the store from which it read (there is a distinction here for
2569 * RMW's, which are both a load and a store)
2571 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2573 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2575 for (unsigned int i = 0; i < promises->size(); i++) {
2576 Promise *promise = (*promises)[i];
2578 // Is this promise on the same location?
2579 if (!promise->same_location(write))
2582 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2583 const ModelAction *pread = promise->get_reader(j);
2584 if (!pread->happens_before(act))
2586 if (mo_graph->checkPromise(write, promise)) {
2587 priv->failed_promise = true;
2593 // Don't do any lookups twice for the same thread
2594 if (!promise->thread_is_available(act->get_tid()))
2597 if (mo_graph->checkReachable(promise, write)) {
2598 if (mo_graph->checkPromise(write, promise)) {
2599 priv->failed_promise = true;
2607 * Compute the set of writes that may break the current pending release
2608 * sequence. This information is extracted from previou release sequence
2611 * @param curr The current ModelAction. Must be a release sequence fixup
2614 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2616 if (pending_rel_seqs->empty())
2619 struct release_seq *pending = pending_rel_seqs->back();
2620 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2621 const ModelAction *write = pending->writes[i];
2622 curr->get_node()->add_relseq_break(write);
2625 /* NULL means don't break the sequence; just synchronize */
2626 curr->get_node()->add_relseq_break(NULL);
2630 * Build up an initial set of all past writes that this 'read' action may read
2631 * from, as well as any previously-observed future values that must still be valid.
2633 * @param curr is the current ModelAction that we are exploring; it must be a
2636 void ModelChecker::build_may_read_from(ModelAction *curr)
2638 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2640 ASSERT(curr->is_read());
2642 ModelAction *last_sc_write = NULL;
2644 if (curr->is_seqcst())
2645 last_sc_write = get_last_seq_cst_write(curr);
2647 /* Iterate over all threads */
2648 for (i = 0; i < thrd_lists->size(); i++) {
2649 /* Iterate over actions in thread, starting from most recent */
2650 action_list_t *list = &(*thrd_lists)[i];
2651 action_list_t::reverse_iterator rit;
2652 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2653 ModelAction *act = *rit;
2655 /* Only consider 'write' actions */
2656 if (!act->is_write() || act == curr)
2659 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2660 bool allow_read = true;
2662 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2664 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2668 /* Only add feasible reads */
2669 mo_graph->startChanges();
2670 r_modification_order(curr, act);
2671 if (!is_infeasible())
2672 curr->get_node()->add_read_from_past(act);
2673 mo_graph->rollbackChanges();
2676 /* Include at most one act per-thread that "happens before" curr */
2677 if (act->happens_before(curr))
2682 /* Inherit existing, promised future values */
2683 for (i = 0; i < promises->size(); i++) {
2684 const Promise *promise = (*promises)[i];
2685 const ModelAction *promise_read = promise->get_reader(0);
2686 if (promise_read->same_var(curr)) {
2687 /* Only add feasible future-values */
2688 mo_graph->startChanges();
2689 r_modification_order(curr, promise);
2690 if (!is_infeasible())
2691 curr->get_node()->add_read_from_promise(promise_read);
2692 mo_graph->rollbackChanges();
2696 /* We may find no valid may-read-from only if the execution is doomed */
2697 if (!curr->get_node()->read_from_size()) {
2698 priv->no_valid_reads = true;
2702 if (DBG_ENABLED()) {
2703 model_print("Reached read action:\n");
2705 model_print("Printing read_from_past\n");
2706 curr->get_node()->print_read_from_past();
2707 model_print("End printing read_from_past\n");
2711 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2713 for ( ; write != NULL; write = write->get_reads_from()) {
2714 /* UNINIT actions don't have a Node, and they never sleep */
2715 if (write->is_uninitialized())
2717 Node *prevnode = write->get_node()->get_parent();
2719 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2720 if (write->is_release() && thread_sleep)
2722 if (!write->is_rmw())
2729 * @brief Create a new action representing an uninitialized atomic
2730 * @param location The memory location of the atomic object
2731 * @return A pointer to a new ModelAction
2733 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2735 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2736 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2737 act->create_cv(NULL);
2741 static void print_list(action_list_t *list)
2743 action_list_t::iterator it;
2745 model_print("---------------------------------------------------------------------\n");
2747 unsigned int hash = 0;
2749 for (it = list->begin(); it != list->end(); it++) {
2751 hash = hash^(hash<<3)^((*it)->hash());
2753 model_print("HASH %u\n", hash);
2754 model_print("---------------------------------------------------------------------\n");
2757 #if SUPPORT_MOD_ORDER_DUMP
2758 void ModelChecker::dumpGraph(char *filename) const
2761 sprintf(buffer, "%s.dot", filename);
2762 FILE *file = fopen(buffer, "w");
2763 fprintf(file, "digraph %s {\n", filename);
2764 mo_graph->dumpNodes(file);
2765 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2767 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2768 ModelAction *act = *it;
2769 if (act->is_read()) {
2770 mo_graph->dot_print_node(file, act);
2771 if (act->get_reads_from())
2772 mo_graph->dot_print_edge(file,
2773 act->get_reads_from(),
2775 "label=\"rf\", color=red, weight=2");
2777 mo_graph->dot_print_edge(file,
2778 act->get_reads_from_promise(),
2780 "label=\"rf\", color=red");
2782 if (thread_array[act->get_tid()]) {
2783 mo_graph->dot_print_edge(file,
2784 thread_array[id_to_int(act->get_tid())],
2786 "label=\"sb\", color=blue, weight=400");
2789 thread_array[act->get_tid()] = act;
2791 fprintf(file, "}\n");
2792 model_free(thread_array);
2797 /** @brief Prints an execution trace summary. */
2798 void ModelChecker::print_summary() const
2800 #if SUPPORT_MOD_ORDER_DUMP
2801 char buffername[100];
2802 sprintf(buffername, "exec%04u", stats.num_total);
2803 mo_graph->dumpGraphToFile(buffername);
2804 sprintf(buffername, "graph%04u", stats.num_total);
2805 dumpGraph(buffername);
2808 model_print("Execution %d:", stats.num_total);
2809 if (isfeasibleprefix()) {
2810 if (scheduler->all_threads_sleeping())
2811 model_print(" SLEEP-SET REDUNDANT");
2814 print_infeasibility(" INFEASIBLE");
2815 print_list(action_trace);
2820 * Add a Thread to the system for the first time. Should only be called once
2822 * @param t The Thread to add
2824 void ModelChecker::add_thread(Thread *t)
2826 thread_map->put(id_to_int(t->get_id()), t);
2827 scheduler->add_thread(t);
2831 * Removes a thread from the scheduler.
2832 * @param the thread to remove.
2834 void ModelChecker::remove_thread(Thread *t)
2836 scheduler->remove_thread(t);
2840 * @brief Get a Thread reference by its ID
2841 * @param tid The Thread's ID
2842 * @return A Thread reference
2844 Thread * ModelChecker::get_thread(thread_id_t tid) const
2846 return thread_map->get(id_to_int(tid));
2850 * @brief Get a reference to the Thread in which a ModelAction was executed
2851 * @param act The ModelAction
2852 * @return A Thread reference
2854 Thread * ModelChecker::get_thread(const ModelAction *act) const
2856 return get_thread(act->get_tid());
2860 * @brief Get a Promise's "promise number"
2862 * A "promise number" is an index number that is unique to a promise, valid
2863 * only for a specific snapshot of an execution trace. Promises may come and go
2864 * as they are generated an resolved, so an index only retains meaning for the
2867 * @param promise The Promise to check
2868 * @return The promise index, if the promise still is valid; otherwise -1
2870 int ModelChecker::get_promise_number(const Promise *promise) const
2872 for (unsigned int i = 0; i < promises->size(); i++)
2873 if ((*promises)[i] == promise)
2880 * @brief Check if a Thread is currently enabled
2881 * @param t The Thread to check
2882 * @return True if the Thread is currently enabled
2884 bool ModelChecker::is_enabled(Thread *t) const
2886 return scheduler->is_enabled(t);
2890 * @brief Check if a Thread is currently enabled
2891 * @param tid The ID of the Thread to check
2892 * @return True if the Thread is currently enabled
2894 bool ModelChecker::is_enabled(thread_id_t tid) const
2896 return scheduler->is_enabled(tid);
2900 * Switch from a model-checker context to a user-thread context. This is the
2901 * complement of ModelChecker::switch_to_master and must be called from the
2902 * model-checker context
2904 * @param thread The user-thread to switch to
2906 void ModelChecker::switch_from_master(Thread *thread)
2908 scheduler->set_current_thread(thread);
2909 Thread::swap(&system_context, thread);
2913 * Switch from a user-context to the "master thread" context (a.k.a. system
2914 * context). This switch is made with the intention of exploring a particular
2915 * model-checking action (described by a ModelAction object). Must be called
2916 * from a user-thread context.
2918 * @param act The current action that will be explored. May be NULL only if
2919 * trace is exiting via an assertion (see ModelChecker::set_assert and
2920 * ModelChecker::has_asserted).
2921 * @return Return the value returned by the current action
2923 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2926 Thread *old = thread_current();
2927 ASSERT(!old->get_pending());
2928 old->set_pending(act);
2929 if (Thread::swap(old, &system_context) < 0) {
2930 perror("swap threads");
2933 return old->get_return_value();
2937 * Takes the next step in the execution, if possible.
2938 * @param curr The current step to take
2939 * @return Returns the next Thread to run, if any; NULL if this execution
2942 Thread * ModelChecker::take_step(ModelAction *curr)
2944 Thread *curr_thrd = get_thread(curr);
2945 ASSERT(curr_thrd->get_state() == THREAD_READY);
2947 curr = check_current_action(curr);
2949 /* Infeasible -> don't take any more steps */
2950 if (is_infeasible())
2952 else if (isfeasibleprefix() && have_bug_reports()) {
2957 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
2960 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2961 scheduler->remove_thread(curr_thrd);
2963 Thread *next_thrd = get_next_thread(curr);
2965 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
2966 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
2971 /** Wrapper to run the user's main function, with appropriate arguments */
2972 void user_main_wrapper(void *)
2974 user_main(model->params.argc, model->params.argv);
2977 /** @brief Run ModelChecker for the user program */
2978 void ModelChecker::run()
2982 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
2987 * Stash next pending action(s) for thread(s). There
2988 * should only need to stash one thread's action--the
2989 * thread which just took a step--plus the first step
2990 * for any newly-created thread
2992 for (unsigned int i = 0; i < get_num_threads(); i++) {
2993 thread_id_t tid = int_to_id(i);
2994 Thread *thr = get_thread(tid);
2995 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
2996 switch_from_master(thr);
3000 /* Catch assertions from prior take_step or from
3001 * between-ModelAction bugs (e.g., data races) */
3005 /* Consume the next action for a Thread */
3006 ModelAction *curr = t->get_pending();
3007 t->set_pending(NULL);
3008 t = take_step(curr);
3009 } while (t && !t->is_model_thread());
3012 * Launch end-of-execution release sequence fixups only when
3013 * the execution is otherwise feasible AND there are:
3015 * (1) pending release sequences
3016 * (2) pending assertions that could be invalidated by a change
3017 * in clock vectors (i.e., data races)
3018 * (3) no pending promises
3020 while (!pending_rel_seqs->empty() &&
3021 is_feasible_prefix_ignore_relseq() &&
3022 !unrealizedraces.empty()) {
3023 model_print("*** WARNING: release sequence fixup action "
3024 "(%zu pending release seuqence(s)) ***\n",
3025 pending_rel_seqs->size());
3026 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3027 std::memory_order_seq_cst, NULL, VALUE_NONE,
3031 } while (next_execution());
3033 model_print("******* Model-checking complete: *******\n");