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_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)
1327 act->set_read_from(rf);
1328 if (rf != NULL && act->is_acquire()) {
1329 rel_heads_list_t release_heads;
1330 get_release_seq_heads(act, act, &release_heads);
1331 int num_heads = release_heads.size();
1332 for (unsigned int i = 0; i < release_heads.size(); i++)
1333 if (!act->synchronize_with(release_heads[i])) {
1334 set_bad_synchronization();
1337 return num_heads > 0;
1343 * Check promises and eliminate potentially-satisfying threads when a thread is
1344 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1345 * no longer satisfy a promise generated from that thread.
1347 * @param blocker The thread on which a thread is waiting
1348 * @param waiting The waiting thread
1350 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1352 for (unsigned int i = 0; i < promises->size(); i++) {
1353 Promise *promise = (*promises)[i];
1354 if (!promise->thread_is_available(waiting->get_id()))
1356 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1357 ModelAction *reader = promise->get_reader(j);
1358 if (reader->get_tid() != blocker->get_id())
1360 if (promise->eliminate_thread(waiting->get_id())) {
1361 /* Promise has failed */
1362 priv->failed_promise = true;
1364 /* Only eliminate the 'waiting' thread once */
1372 * @brief Check whether a model action is enabled.
1374 * Checks whether a lock or join operation would be successful (i.e., is the
1375 * lock already locked, or is the joined thread already complete). If not, put
1376 * the action in a waiter list.
1378 * @param curr is the ModelAction to check whether it is enabled.
1379 * @return a bool that indicates whether the action is enabled.
1381 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1382 if (curr->is_lock()) {
1383 std::mutex *lock = (std::mutex *)curr->get_location();
1384 struct std::mutex_state *state = lock->get_state();
1385 if (state->islocked) {
1386 //Stick the action in the appropriate waiting queue
1387 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1390 } else if (curr->get_type() == THREAD_JOIN) {
1391 Thread *blocking = (Thread *)curr->get_location();
1392 if (!blocking->is_complete()) {
1393 blocking->push_wait_list(curr);
1394 thread_blocking_check_promises(blocking, get_thread(curr));
1403 * This is the heart of the model checker routine. It performs model-checking
1404 * actions corresponding to a given "current action." Among other processes, it
1405 * calculates reads-from relationships, updates synchronization clock vectors,
1406 * forms a memory_order constraints graph, and handles replay/backtrack
1407 * execution when running permutations of previously-observed executions.
1409 * @param curr The current action to process
1410 * @return The ModelAction that is actually executed; may be different than
1411 * curr; may be NULL, if the current action is not enabled to run
1413 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1416 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1418 if (!check_action_enabled(curr)) {
1419 /* Make the execution look like we chose to run this action
1420 * much later, when a lock/join can succeed */
1421 get_thread(curr)->set_pending(curr);
1422 scheduler->sleep(get_thread(curr));
1426 bool newly_explored = initialize_curr_action(&curr);
1432 wake_up_sleeping_actions(curr);
1434 /* Add the action to lists before any other model-checking tasks */
1435 if (!second_part_of_rmw)
1436 add_action_to_lists(curr);
1438 /* Build may_read_from set for newly-created actions */
1439 if (newly_explored && curr->is_read())
1440 build_may_read_from(curr);
1442 /* Initialize work_queue with the "current action" work */
1443 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1444 while (!work_queue.empty() && !has_asserted()) {
1445 WorkQueueEntry work = work_queue.front();
1446 work_queue.pop_front();
1448 switch (work.type) {
1449 case WORK_CHECK_CURR_ACTION: {
1450 ModelAction *act = work.action;
1451 bool update = false; /* update this location's release seq's */
1452 bool update_all = false; /* update all release seq's */
1454 if (process_thread_action(curr))
1457 if (act->is_read() && !second_part_of_rmw && process_read(act))
1460 if (act->is_write() && process_write(act))
1463 if (act->is_fence() && process_fence(act))
1466 if (act->is_mutex_op() && process_mutex(act))
1469 if (act->is_relseq_fixup())
1470 process_relseq_fixup(curr, &work_queue);
1473 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1475 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1478 case WORK_CHECK_RELEASE_SEQ:
1479 resolve_release_sequences(work.location, &work_queue);
1481 case WORK_CHECK_MO_EDGES: {
1482 /** @todo Complete verification of work_queue */
1483 ModelAction *act = work.action;
1484 bool updated = false;
1486 if (act->is_read()) {
1487 const ModelAction *rf = act->get_reads_from();
1488 const Promise *promise = act->get_reads_from_promise();
1490 if (r_modification_order(act, rf))
1492 } else if (promise) {
1493 if (r_modification_order(act, promise))
1497 if (act->is_write()) {
1498 if (w_modification_order(act))
1501 mo_graph->commitChanges();
1504 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1513 check_curr_backtracking(curr);
1514 set_backtracking(curr);
1518 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1520 Node *currnode = curr->get_node();
1521 Node *parnode = currnode->get_parent();
1523 if ((parnode && !parnode->backtrack_empty()) ||
1524 !currnode->misc_empty() ||
1525 !currnode->read_from_empty() ||
1526 !currnode->promise_empty() ||
1527 !currnode->relseq_break_empty()) {
1528 set_latest_backtrack(curr);
1532 bool ModelChecker::promises_expired() const
1534 for (unsigned int i = 0; i < promises->size(); i++) {
1535 Promise *promise = (*promises)[i];
1536 if (promise->get_expiration() < priv->used_sequence_numbers)
1543 * This is the strongest feasibility check available.
1544 * @return whether the current trace (partial or complete) must be a prefix of
1547 bool ModelChecker::isfeasibleprefix() const
1549 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1553 * Print disagnostic information about an infeasible execution
1554 * @param prefix A string to prefix the output with; if NULL, then a default
1555 * message prefix will be provided
1557 void ModelChecker::print_infeasibility(const char *prefix) const
1561 if (mo_graph->checkForCycles())
1562 ptr += sprintf(ptr, "[mo cycle]");
1563 if (priv->failed_promise)
1564 ptr += sprintf(ptr, "[failed promise]");
1565 if (priv->too_many_reads)
1566 ptr += sprintf(ptr, "[too many reads]");
1567 if (priv->no_valid_reads)
1568 ptr += sprintf(ptr, "[no valid reads-from]");
1569 if (priv->bad_synchronization)
1570 ptr += sprintf(ptr, "[bad sw ordering]");
1571 if (promises_expired())
1572 ptr += sprintf(ptr, "[promise expired]");
1573 if (promises->size() != 0)
1574 ptr += sprintf(ptr, "[unresolved promise]");
1576 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1580 * Returns whether the current completed trace is feasible, except for pending
1581 * release sequences.
1583 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1585 return !is_infeasible() && promises->size() == 0;
1589 * Check if the current partial trace is infeasible. Does not check any
1590 * end-of-execution flags, which might rule out the execution. Thus, this is
1591 * useful only for ruling an execution as infeasible.
1592 * @return whether the current partial trace is infeasible.
1594 bool ModelChecker::is_infeasible() const
1596 return mo_graph->checkForCycles() ||
1597 priv->no_valid_reads ||
1598 priv->failed_promise ||
1599 priv->too_many_reads ||
1600 priv->bad_synchronization ||
1604 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1605 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1606 ModelAction *lastread = get_last_action(act->get_tid());
1607 lastread->process_rmw(act);
1608 if (act->is_rmw()) {
1609 if (lastread->get_reads_from())
1610 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1612 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1613 mo_graph->commitChanges();
1619 * Checks whether a thread has read from the same write for too many times
1620 * without seeing the effects of a later write.
1623 * 1) there must a different write that we could read from that would satisfy the modification order,
1624 * 2) we must have read from the same value in excess of maxreads times, and
1625 * 3) that other write must have been in the reads_from set for maxreads times.
1627 * If so, we decide that the execution is no longer feasible.
1629 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf)
1631 if (params.maxreads != 0) {
1632 if (curr->get_node()->get_read_from_past_size() <= 1)
1634 //Must make sure that execution is currently feasible... We could
1635 //accidentally clear by rolling back
1636 if (is_infeasible())
1638 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1639 int tid = id_to_int(curr->get_tid());
1642 if ((int)thrd_lists->size() <= tid)
1644 action_list_t *list = &(*thrd_lists)[tid];
1646 action_list_t::reverse_iterator rit = list->rbegin();
1647 /* Skip past curr */
1648 for (; (*rit) != curr; rit++)
1650 /* go past curr now */
1653 action_list_t::reverse_iterator ritcopy = rit;
1654 //See if we have enough reads from the same value
1656 for (; count < params.maxreads; rit++, count++) {
1657 if (rit == list->rend())
1659 ModelAction *act = *rit;
1660 if (!act->is_read())
1663 if (act->get_reads_from() != rf)
1665 if (act->get_node()->get_read_from_past_size() <= 1)
1668 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1670 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1672 /* Need a different write */
1676 /* Test to see whether this is a feasible write to read from */
1677 /** NOTE: all members of read-from set should be
1678 * feasible, so we no longer check it here **/
1682 bool feasiblewrite = true;
1683 //new we need to see if this write works for everyone
1685 for (int loop = count; loop > 0; loop--, rit++) {
1686 ModelAction *act = *rit;
1687 bool foundvalue = false;
1688 for (int j = 0; j < act->get_node()->get_read_from_past_size(); j++) {
1689 if (act->get_node()->get_read_from_past(j) == write) {
1695 feasiblewrite = false;
1699 if (feasiblewrite) {
1700 priv->too_many_reads = true;
1708 * Updates the mo_graph with the constraints imposed from the current
1711 * Basic idea is the following: Go through each other thread and find
1712 * the last action that happened before our read. Two cases:
1714 * (1) The action is a write => that write must either occur before
1715 * the write we read from or be the write we read from.
1717 * (2) The action is a read => the write that that action read from
1718 * must occur before the write we read from or be the same write.
1720 * @param curr The current action. Must be a read.
1721 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1722 * @return True if modification order edges were added; false otherwise
1724 template <typename rf_type>
1725 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1727 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1730 ASSERT(curr->is_read());
1732 /* Last SC fence in the current thread */
1733 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1735 /* Iterate over all threads */
1736 for (i = 0; i < thrd_lists->size(); i++) {
1737 /* Last SC fence in thread i */
1738 ModelAction *last_sc_fence_thread_local = NULL;
1739 if (int_to_id((int)i) != curr->get_tid())
1740 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1742 /* Last SC fence in thread i, before last SC fence in current thread */
1743 ModelAction *last_sc_fence_thread_before = NULL;
1744 if (last_sc_fence_local)
1745 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1747 /* Iterate over actions in thread, starting from most recent */
1748 action_list_t *list = &(*thrd_lists)[i];
1749 action_list_t::reverse_iterator rit;
1750 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1751 ModelAction *act = *rit;
1753 if (act->is_write() && !act->equals(rf) && act != curr) {
1754 /* C++, Section 29.3 statement 5 */
1755 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1756 *act < *last_sc_fence_thread_local) {
1757 added = mo_graph->addEdge(act, rf) || added;
1760 /* C++, Section 29.3 statement 4 */
1761 else if (act->is_seqcst() && last_sc_fence_local &&
1762 *act < *last_sc_fence_local) {
1763 added = mo_graph->addEdge(act, rf) || added;
1766 /* C++, Section 29.3 statement 6 */
1767 else if (last_sc_fence_thread_before &&
1768 *act < *last_sc_fence_thread_before) {
1769 added = mo_graph->addEdge(act, rf) || added;
1775 * Include at most one act per-thread that "happens
1776 * before" curr. Don't consider reflexively.
1778 if (act->happens_before(curr) && act != curr) {
1779 if (act->is_write()) {
1780 if (!act->equals(rf)) {
1781 added = mo_graph->addEdge(act, rf) || added;
1784 const ModelAction *prevrf = act->get_reads_from();
1785 const Promise *prevrf_promise = act->get_reads_from_promise();
1787 if (!prevrf->equals(rf))
1788 added = mo_graph->addEdge(prevrf, rf) || added;
1789 } else if (!prevrf_promise->equals(rf)) {
1790 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1799 * All compatible, thread-exclusive promises must be ordered after any
1800 * concrete loads from the same thread
1802 for (unsigned int i = 0; i < promises->size(); i++)
1803 if ((*promises)[i]->is_compatible_exclusive(curr))
1804 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1810 * Updates the mo_graph with the constraints imposed from the current write.
1812 * Basic idea is the following: Go through each other thread and find
1813 * the lastest action that happened before our write. Two cases:
1815 * (1) The action is a write => that write must occur before
1818 * (2) The action is a read => the write that that action read from
1819 * must occur before the current write.
1821 * This method also handles two other issues:
1823 * (I) Sequential Consistency: Making sure that if the current write is
1824 * seq_cst, that it occurs after the previous seq_cst write.
1826 * (II) Sending the write back to non-synchronizing reads.
1828 * @param curr The current action. Must be a write.
1829 * @return True if modification order edges were added; false otherwise
1831 bool ModelChecker::w_modification_order(ModelAction *curr)
1833 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1836 ASSERT(curr->is_write());
1838 if (curr->is_seqcst()) {
1839 /* We have to at least see the last sequentially consistent write,
1840 so we are initialized. */
1841 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1842 if (last_seq_cst != NULL) {
1843 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1847 /* Last SC fence in the current thread */
1848 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1850 /* Iterate over all threads */
1851 for (i = 0; i < thrd_lists->size(); i++) {
1852 /* Last SC fence in thread i, before last SC fence in current thread */
1853 ModelAction *last_sc_fence_thread_before = NULL;
1854 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1855 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1857 /* Iterate over actions in thread, starting from most recent */
1858 action_list_t *list = &(*thrd_lists)[i];
1859 action_list_t::reverse_iterator rit;
1860 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1861 ModelAction *act = *rit;
1864 * 1) If RMW and it actually read from something, then we
1865 * already have all relevant edges, so just skip to next
1868 * 2) If RMW and it didn't read from anything, we should
1869 * whatever edge we can get to speed up convergence.
1871 * 3) If normal write, we need to look at earlier actions, so
1872 * continue processing list.
1874 if (curr->is_rmw()) {
1875 if (curr->get_reads_from() != NULL)
1883 /* C++, Section 29.3 statement 7 */
1884 if (last_sc_fence_thread_before && act->is_write() &&
1885 *act < *last_sc_fence_thread_before) {
1886 added = mo_graph->addEdge(act, curr) || added;
1891 * Include at most one act per-thread that "happens
1894 if (act->happens_before(curr)) {
1896 * Note: if act is RMW, just add edge:
1898 * The following edge should be handled elsewhere:
1899 * readfrom(act) --mo--> act
1901 if (act->is_write())
1902 added = mo_graph->addEdge(act, curr) || added;
1903 else if (act->is_read()) {
1904 //if previous read accessed a null, just keep going
1905 if (act->get_reads_from() == NULL)
1907 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1910 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1911 !act->same_thread(curr)) {
1912 /* We have an action that:
1913 (1) did not happen before us
1914 (2) is a read and we are a write
1915 (3) cannot synchronize with us
1916 (4) is in a different thread
1918 that read could potentially read from our write. Note that
1919 these checks are overly conservative at this point, we'll
1920 do more checks before actually removing the
1924 if (thin_air_constraint_may_allow(curr, act)) {
1925 if (!is_infeasible())
1926 futurevalues->push_back(PendingFutureValue(curr, act));
1927 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1928 add_future_value(curr, act);
1935 * All compatible, thread-exclusive promises must be ordered after any
1936 * concrete stores to the same thread, or else they can be merged with
1939 for (unsigned int i = 0; i < promises->size(); i++)
1940 if ((*promises)[i]->is_compatible_exclusive(curr))
1941 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1946 /** Arbitrary reads from the future are not allowed. Section 29.3
1947 * part 9 places some constraints. This method checks one result of constraint
1948 * constraint. Others require compiler support. */
1949 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1951 if (!writer->is_rmw())
1954 if (!reader->is_rmw())
1957 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1958 if (search == reader)
1960 if (search->get_tid() == reader->get_tid() &&
1961 search->happens_before(reader))
1969 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1970 * some constraints. This method checks one the following constraint (others
1971 * require compiler support):
1973 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1975 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1977 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1979 /* Iterate over all threads */
1980 for (i = 0; i < thrd_lists->size(); i++) {
1981 const ModelAction *write_after_read = NULL;
1983 /* Iterate over actions in thread, starting from most recent */
1984 action_list_t *list = &(*thrd_lists)[i];
1985 action_list_t::reverse_iterator rit;
1986 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1987 ModelAction *act = *rit;
1989 /* Don't disallow due to act == reader */
1990 if (!reader->happens_before(act) || reader == act)
1992 else if (act->is_write())
1993 write_after_read = act;
1994 else if (act->is_read() && act->get_reads_from() != NULL)
1995 write_after_read = act->get_reads_from();
1998 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2005 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2006 * The ModelAction under consideration is expected to be taking part in
2007 * release/acquire synchronization as an object of the "reads from" relation.
2008 * Note that this can only provide release sequence support for RMW chains
2009 * which do not read from the future, as those actions cannot be traced until
2010 * their "promise" is fulfilled. Similarly, we may not even establish the
2011 * presence of a release sequence with certainty, as some modification order
2012 * constraints may be decided further in the future. Thus, this function
2013 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2014 * and a boolean representing certainty.
2016 * @param rf The action that might be part of a release sequence. Must be a
2018 * @param release_heads A pass-by-reference style return parameter. After
2019 * execution of this function, release_heads will contain the heads of all the
2020 * relevant release sequences, if any exists with certainty
2021 * @param pending A pass-by-reference style return parameter which is only used
2022 * when returning false (i.e., uncertain). Returns most information regarding
2023 * an uncertain release sequence, including any write operations that might
2024 * break the sequence.
2025 * @return true, if the ModelChecker is certain that release_heads is complete;
2028 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2029 rel_heads_list_t *release_heads,
2030 struct release_seq *pending) const
2032 /* Only check for release sequences if there are no cycles */
2033 if (mo_graph->checkForCycles())
2036 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2037 ASSERT(rf->is_write());
2039 if (rf->is_release())
2040 release_heads->push_back(rf);
2041 else if (rf->get_last_fence_release())
2042 release_heads->push_back(rf->get_last_fence_release());
2044 break; /* End of RMW chain */
2046 /** @todo Need to be smarter here... In the linux lock
2047 * example, this will run to the beginning of the program for
2049 /** @todo The way to be smarter here is to keep going until 1
2050 * thread has a release preceded by an acquire and you've seen
2053 /* acq_rel RMW is a sufficient stopping condition */
2054 if (rf->is_acquire() && rf->is_release())
2055 return true; /* complete */
2058 /* read from future: need to settle this later */
2060 return false; /* incomplete */
2063 if (rf->is_release())
2064 return true; /* complete */
2066 /* else relaxed write
2067 * - check for fence-release in the same thread (29.8, stmt. 3)
2068 * - check modification order for contiguous subsequence
2069 * -> rf must be same thread as release */
2071 const ModelAction *fence_release = rf->get_last_fence_release();
2072 /* Synchronize with a fence-release unconditionally; we don't need to
2073 * find any more "contiguous subsequence..." for it */
2075 release_heads->push_back(fence_release);
2077 int tid = id_to_int(rf->get_tid());
2078 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2079 action_list_t *list = &(*thrd_lists)[tid];
2080 action_list_t::const_reverse_iterator rit;
2082 /* Find rf in the thread list */
2083 rit = std::find(list->rbegin(), list->rend(), rf);
2084 ASSERT(rit != list->rend());
2086 /* Find the last {write,fence}-release */
2087 for (; rit != list->rend(); rit++) {
2088 if (fence_release && *(*rit) < *fence_release)
2090 if ((*rit)->is_release())
2093 if (rit == list->rend()) {
2094 /* No write-release in this thread */
2095 return true; /* complete */
2096 } else if (fence_release && *(*rit) < *fence_release) {
2097 /* The fence-release is more recent (and so, "stronger") than
2098 * the most recent write-release */
2099 return true; /* complete */
2100 } /* else, need to establish contiguous release sequence */
2101 ModelAction *release = *rit;
2103 ASSERT(rf->same_thread(release));
2105 pending->writes.clear();
2107 bool certain = true;
2108 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2109 if (id_to_int(rf->get_tid()) == (int)i)
2111 list = &(*thrd_lists)[i];
2113 /* Can we ensure no future writes from this thread may break
2114 * the release seq? */
2115 bool future_ordered = false;
2117 ModelAction *last = get_last_action(int_to_id(i));
2118 Thread *th = get_thread(int_to_id(i));
2119 if ((last && rf->happens_before(last)) ||
2122 future_ordered = true;
2124 ASSERT(!th->is_model_thread() || future_ordered);
2126 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2127 const ModelAction *act = *rit;
2128 /* Reach synchronization -> this thread is complete */
2129 if (act->happens_before(release))
2131 if (rf->happens_before(act)) {
2132 future_ordered = true;
2136 /* Only non-RMW writes can break release sequences */
2137 if (!act->is_write() || act->is_rmw())
2140 /* Check modification order */
2141 if (mo_graph->checkReachable(rf, act)) {
2142 /* rf --mo--> act */
2143 future_ordered = true;
2146 if (mo_graph->checkReachable(act, release))
2147 /* act --mo--> release */
2149 if (mo_graph->checkReachable(release, act) &&
2150 mo_graph->checkReachable(act, rf)) {
2151 /* release --mo-> act --mo--> rf */
2152 return true; /* complete */
2154 /* act may break release sequence */
2155 pending->writes.push_back(act);
2158 if (!future_ordered)
2159 certain = false; /* This thread is uncertain */
2163 release_heads->push_back(release);
2164 pending->writes.clear();
2166 pending->release = release;
2173 * An interface for getting the release sequence head(s) with which a
2174 * given ModelAction must synchronize. This function only returns a non-empty
2175 * result when it can locate a release sequence head with certainty. Otherwise,
2176 * it may mark the internal state of the ModelChecker so that it will handle
2177 * the release sequence at a later time, causing @a acquire to update its
2178 * synchronization at some later point in execution.
2180 * @param acquire The 'acquire' action that may synchronize with a release
2182 * @param read The read action that may read from a release sequence; this may
2183 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2184 * when 'acquire' is a fence-acquire)
2185 * @param release_heads A pass-by-reference return parameter. Will be filled
2186 * with the head(s) of the release sequence(s), if they exists with certainty.
2187 * @see ModelChecker::release_seq_heads
2189 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2190 ModelAction *read, rel_heads_list_t *release_heads)
2192 const ModelAction *rf = read->get_reads_from();
2193 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2194 sequence->acquire = acquire;
2195 sequence->read = read;
2197 if (!release_seq_heads(rf, release_heads, sequence)) {
2198 /* add act to 'lazy checking' list */
2199 pending_rel_seqs->push_back(sequence);
2201 snapshot_free(sequence);
2206 * Attempt to resolve all stashed operations that might synchronize with a
2207 * release sequence for a given location. This implements the "lazy" portion of
2208 * determining whether or not a release sequence was contiguous, since not all
2209 * modification order information is present at the time an action occurs.
2211 * @param location The location/object that should be checked for release
2212 * sequence resolutions. A NULL value means to check all locations.
2213 * @param work_queue The work queue to which to add work items as they are
2215 * @return True if any updates occurred (new synchronization, new mo_graph
2218 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2220 bool updated = false;
2221 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2222 while (it != pending_rel_seqs->end()) {
2223 struct release_seq *pending = *it;
2224 ModelAction *acquire = pending->acquire;
2225 const ModelAction *read = pending->read;
2227 /* Only resolve sequences on the given location, if provided */
2228 if (location && read->get_location() != location) {
2233 const ModelAction *rf = read->get_reads_from();
2234 rel_heads_list_t release_heads;
2236 complete = release_seq_heads(rf, &release_heads, pending);
2237 for (unsigned int i = 0; i < release_heads.size(); i++) {
2238 if (!acquire->has_synchronized_with(release_heads[i])) {
2239 if (acquire->synchronize_with(release_heads[i]))
2242 set_bad_synchronization();
2247 /* Re-check all pending release sequences */
2248 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2249 /* Re-check read-acquire for mo_graph edges */
2250 if (acquire->is_read())
2251 work_queue->push_back(MOEdgeWorkEntry(acquire));
2253 /* propagate synchronization to later actions */
2254 action_list_t::reverse_iterator rit = action_trace->rbegin();
2255 for (; (*rit) != acquire; rit++) {
2256 ModelAction *propagate = *rit;
2257 if (acquire->happens_before(propagate)) {
2258 propagate->synchronize_with(acquire);
2259 /* Re-check 'propagate' for mo_graph edges */
2260 work_queue->push_back(MOEdgeWorkEntry(propagate));
2265 it = pending_rel_seqs->erase(it);
2266 snapshot_free(pending);
2272 // If we resolved promises or data races, see if we have realized a data race.
2279 * Performs various bookkeeping operations for the current ModelAction. For
2280 * instance, adds action to the per-object, per-thread action vector and to the
2281 * action trace list of all thread actions.
2283 * @param act is the ModelAction to add.
2285 void ModelChecker::add_action_to_lists(ModelAction *act)
2287 int tid = id_to_int(act->get_tid());
2288 ModelAction *uninit = NULL;
2290 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2291 if (list->empty() && act->is_atomic_var()) {
2292 uninit = new_uninitialized_action(act->get_location());
2293 uninit_id = id_to_int(uninit->get_tid());
2294 list->push_back(uninit);
2296 list->push_back(act);
2298 action_trace->push_back(act);
2300 action_trace->push_front(uninit);
2302 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2303 if (tid >= (int)vec->size())
2304 vec->resize(priv->next_thread_id);
2305 (*vec)[tid].push_back(act);
2307 (*vec)[uninit_id].push_front(uninit);
2309 if ((int)thrd_last_action->size() <= tid)
2310 thrd_last_action->resize(get_num_threads());
2311 (*thrd_last_action)[tid] = act;
2313 (*thrd_last_action)[uninit_id] = uninit;
2315 if (act->is_fence() && act->is_release()) {
2316 if ((int)thrd_last_fence_release->size() <= tid)
2317 thrd_last_fence_release->resize(get_num_threads());
2318 (*thrd_last_fence_release)[tid] = act;
2321 if (act->is_wait()) {
2322 void *mutex_loc = (void *) act->get_value();
2323 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2325 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2326 if (tid >= (int)vec->size())
2327 vec->resize(priv->next_thread_id);
2328 (*vec)[tid].push_back(act);
2333 * @brief Get the last action performed by a particular Thread
2334 * @param tid The thread ID of the Thread in question
2335 * @return The last action in the thread
2337 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2339 int threadid = id_to_int(tid);
2340 if (threadid < (int)thrd_last_action->size())
2341 return (*thrd_last_action)[id_to_int(tid)];
2347 * @brief Get the last fence release performed by a particular Thread
2348 * @param tid The thread ID of the Thread in question
2349 * @return The last fence release in the thread, if one exists; NULL otherwise
2351 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2353 int threadid = id_to_int(tid);
2354 if (threadid < (int)thrd_last_fence_release->size())
2355 return (*thrd_last_fence_release)[id_to_int(tid)];
2361 * Gets the last memory_order_seq_cst write (in the total global sequence)
2362 * performed on a particular object (i.e., memory location), not including the
2364 * @param curr The current ModelAction; also denotes the object location to
2366 * @return The last seq_cst write
2368 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2370 void *location = curr->get_location();
2371 action_list_t *list = get_safe_ptr_action(obj_map, location);
2372 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2373 action_list_t::reverse_iterator rit;
2374 for (rit = list->rbegin(); rit != list->rend(); rit++)
2375 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2381 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2382 * performed in a particular thread, prior to a particular fence.
2383 * @param tid The ID of the thread to check
2384 * @param before_fence The fence from which to begin the search; if NULL, then
2385 * search for the most recent fence in the thread.
2386 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2388 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2390 /* All fences should have NULL location */
2391 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2392 action_list_t::reverse_iterator rit = list->rbegin();
2395 for (; rit != list->rend(); rit++)
2396 if (*rit == before_fence)
2399 ASSERT(*rit == before_fence);
2403 for (; rit != list->rend(); rit++)
2404 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2410 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2411 * location). This function identifies the mutex according to the current
2412 * action, which is presumed to perform on the same mutex.
2413 * @param curr The current ModelAction; also denotes the object location to
2415 * @return The last unlock operation
2417 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2419 void *location = curr->get_location();
2420 action_list_t *list = get_safe_ptr_action(obj_map, location);
2421 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2422 action_list_t::reverse_iterator rit;
2423 for (rit = list->rbegin(); rit != list->rend(); rit++)
2424 if ((*rit)->is_unlock() || (*rit)->is_wait())
2429 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2431 ModelAction *parent = get_last_action(tid);
2433 parent = get_thread(tid)->get_creation();
2438 * Returns the clock vector for a given thread.
2439 * @param tid The thread whose clock vector we want
2440 * @return Desired clock vector
2442 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2444 return get_parent_action(tid)->get_cv();
2448 * Resolve a set of Promises with a current write. The set is provided in the
2449 * Node corresponding to @a write.
2450 * @param write The ModelAction that is fulfilling Promises
2451 * @return True if promises were resolved; false otherwise
2453 bool ModelChecker::resolve_promises(ModelAction *write)
2455 bool haveResolved = false;
2456 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2457 promise_list_t mustResolve, resolved;
2459 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
2460 Promise *promise = (*promises)[promise_index];
2461 if (write->get_node()->get_promise(i)) {
2462 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2463 ModelAction *read = promise->get_reader(j);
2464 read_from(read, write);
2465 actions_to_check.push_back(read);
2467 //Make sure the promise's value matches the write's value
2468 ASSERT(promise->is_compatible(write));
2469 mo_graph->resolvePromise(promise, write, &mustResolve);
2471 resolved.push_back(promise);
2472 promises->erase(promises->begin() + promise_index);
2474 haveResolved = true;
2479 for (unsigned int i = 0; i < mustResolve.size(); i++) {
2480 if (std::find(resolved.begin(), resolved.end(), mustResolve[i])
2482 priv->failed_promise = true;
2484 for (unsigned int i = 0; i < resolved.size(); i++)
2486 //Check whether reading these writes has made threads unable to
2489 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2490 ModelAction *read = actions_to_check[i];
2491 mo_check_promises(read, true);
2494 return haveResolved;
2498 * Compute the set of promises that could potentially be satisfied by this
2499 * action. Note that the set computation actually appears in the Node, not in
2501 * @param curr The ModelAction that may satisfy promises
2503 void ModelChecker::compute_promises(ModelAction *curr)
2505 for (unsigned int i = 0; i < promises->size(); i++) {
2506 Promise *promise = (*promises)[i];
2507 if (!promise->is_compatible(curr) || promise->get_value() != curr->get_value())
2510 bool satisfy = true;
2511 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2512 const ModelAction *act = promise->get_reader(j);
2513 if (act->happens_before(curr) ||
2514 act->could_synchronize_with(curr)) {
2520 curr->get_node()->set_promise(i);
2524 /** Checks promises in response to change in ClockVector Threads. */
2525 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2527 for (unsigned int i = 0; i < promises->size(); i++) {
2528 Promise *promise = (*promises)[i];
2529 if (!promise->thread_is_available(tid))
2531 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2532 const ModelAction *act = promise->get_reader(j);
2533 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2534 merge_cv->synchronized_since(act)) {
2535 if (promise->eliminate_thread(tid)) {
2536 /* Promise has failed */
2537 priv->failed_promise = true;
2545 void ModelChecker::check_promises_thread_disabled()
2547 for (unsigned int i = 0; i < promises->size(); i++) {
2548 Promise *promise = (*promises)[i];
2549 if (promise->has_failed()) {
2550 priv->failed_promise = true;
2557 * @brief Checks promises in response to addition to modification order for
2560 * We test whether threads are still available for satisfying promises after an
2561 * addition to our modification order constraints. Those that are unavailable
2562 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2563 * that promise has failed.
2565 * @param act The ModelAction which updated the modification order
2566 * @param is_read_check Should be true if act is a read and we must check for
2567 * updates to the store from which it read (there is a distinction here for
2568 * RMW's, which are both a load and a store)
2570 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2572 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2574 for (unsigned int i = 0; i < promises->size(); i++) {
2575 Promise *promise = (*promises)[i];
2577 // Is this promise on the same location?
2578 if (promise->get_value() != write->get_value())
2581 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2582 const ModelAction *pread = promise->get_reader(j);
2583 if (!pread->happens_before(act))
2585 if (mo_graph->checkPromise(write, promise)) {
2586 priv->failed_promise = true;
2592 // Don't do any lookups twice for the same thread
2593 if (!promise->thread_is_available(act->get_tid()))
2596 if (mo_graph->checkReachable(promise, write)) {
2597 if (mo_graph->checkPromise(write, promise)) {
2598 priv->failed_promise = true;
2606 * Compute the set of writes that may break the current pending release
2607 * sequence. This information is extracted from previou release sequence
2610 * @param curr The current ModelAction. Must be a release sequence fixup
2613 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2615 if (pending_rel_seqs->empty())
2618 struct release_seq *pending = pending_rel_seqs->back();
2619 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2620 const ModelAction *write = pending->writes[i];
2621 curr->get_node()->add_relseq_break(write);
2624 /* NULL means don't break the sequence; just synchronize */
2625 curr->get_node()->add_relseq_break(NULL);
2629 * Build up an initial set of all past writes that this 'read' action may read
2630 * from, as well as any previously-observed future values that must still be valid.
2632 * @param curr is the current ModelAction that we are exploring; it must be a
2635 void ModelChecker::build_may_read_from(ModelAction *curr)
2637 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2639 ASSERT(curr->is_read());
2641 ModelAction *last_sc_write = NULL;
2643 if (curr->is_seqcst())
2644 last_sc_write = get_last_seq_cst_write(curr);
2646 /* Iterate over all threads */
2647 for (i = 0; i < thrd_lists->size(); i++) {
2648 /* Iterate over actions in thread, starting from most recent */
2649 action_list_t *list = &(*thrd_lists)[i];
2650 action_list_t::reverse_iterator rit;
2651 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2652 ModelAction *act = *rit;
2654 /* Only consider 'write' actions */
2655 if (!act->is_write() || act == curr)
2658 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2659 bool allow_read = true;
2661 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2663 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2667 /* Only add feasible reads */
2668 mo_graph->startChanges();
2669 r_modification_order(curr, act);
2670 if (!is_infeasible())
2671 curr->get_node()->add_read_from_past(act);
2672 mo_graph->rollbackChanges();
2675 /* Include at most one act per-thread that "happens before" curr */
2676 if (act->happens_before(curr))
2681 /* Inherit existing, promised future values */
2682 for (i = 0; i < promises->size(); i++) {
2683 const Promise *promise = (*promises)[i];
2684 const ModelAction *promise_read = promise->get_reader(0);
2685 if (promise_read->same_var(curr)) {
2686 /* Only add feasible future-values */
2687 mo_graph->startChanges();
2688 r_modification_order(curr, promise);
2689 if (!is_infeasible())
2690 curr->get_node()->add_read_from_promise(promise_read);
2691 mo_graph->rollbackChanges();
2695 /* We may find no valid may-read-from only if the execution is doomed */
2696 if (!curr->get_node()->read_from_size()) {
2697 priv->no_valid_reads = true;
2701 if (DBG_ENABLED()) {
2702 model_print("Reached read action:\n");
2704 model_print("Printing read_from_past\n");
2705 curr->get_node()->print_read_from_past();
2706 model_print("End printing read_from_past\n");
2710 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2712 for ( ; write != NULL; write = write->get_reads_from()) {
2713 /* UNINIT actions don't have a Node, and they never sleep */
2714 if (write->is_uninitialized())
2716 Node *prevnode = write->get_node()->get_parent();
2718 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2719 if (write->is_release() && thread_sleep)
2721 if (!write->is_rmw())
2728 * @brief Create a new action representing an uninitialized atomic
2729 * @param location The memory location of the atomic object
2730 * @return A pointer to a new ModelAction
2732 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2734 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2735 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2736 act->create_cv(NULL);
2740 static void print_list(action_list_t *list)
2742 action_list_t::iterator it;
2744 model_print("---------------------------------------------------------------------\n");
2746 unsigned int hash = 0;
2748 for (it = list->begin(); it != list->end(); it++) {
2750 hash = hash^(hash<<3)^((*it)->hash());
2752 model_print("HASH %u\n", hash);
2753 model_print("---------------------------------------------------------------------\n");
2756 #if SUPPORT_MOD_ORDER_DUMP
2757 void ModelChecker::dumpGraph(char *filename) const
2760 sprintf(buffer, "%s.dot", filename);
2761 FILE *file = fopen(buffer, "w");
2762 fprintf(file, "digraph %s {\n", filename);
2763 mo_graph->dumpNodes(file);
2764 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2766 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2767 ModelAction *action = *it;
2768 if (action->is_read()) {
2769 fprintf(file, "N%u [label=\"N%u, T%u\"];\n", action->get_seq_number(), action->get_seq_number(), action->get_tid());
2770 if (action->get_reads_from() != NULL)
2771 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
2773 if (thread_array[action->get_tid()] != NULL) {
2774 fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
2777 thread_array[action->get_tid()] = action;
2779 fprintf(file, "}\n");
2780 model_free(thread_array);
2785 /** @brief Prints an execution trace summary. */
2786 void ModelChecker::print_summary() const
2788 #if SUPPORT_MOD_ORDER_DUMP
2789 char buffername[100];
2790 sprintf(buffername, "exec%04u", stats.num_total);
2791 mo_graph->dumpGraphToFile(buffername);
2792 sprintf(buffername, "graph%04u", stats.num_total);
2793 dumpGraph(buffername);
2796 model_print("Execution %d:", stats.num_total);
2797 if (isfeasibleprefix()) {
2798 if (scheduler->all_threads_sleeping())
2799 model_print(" SLEEP-SET REDUNDANT");
2802 print_infeasibility(" INFEASIBLE");
2803 print_list(action_trace);
2808 * Add a Thread to the system for the first time. Should only be called once
2810 * @param t The Thread to add
2812 void ModelChecker::add_thread(Thread *t)
2814 thread_map->put(id_to_int(t->get_id()), t);
2815 scheduler->add_thread(t);
2819 * Removes a thread from the scheduler.
2820 * @param the thread to remove.
2822 void ModelChecker::remove_thread(Thread *t)
2824 scheduler->remove_thread(t);
2828 * @brief Get a Thread reference by its ID
2829 * @param tid The Thread's ID
2830 * @return A Thread reference
2832 Thread * ModelChecker::get_thread(thread_id_t tid) const
2834 return thread_map->get(id_to_int(tid));
2838 * @brief Get a reference to the Thread in which a ModelAction was executed
2839 * @param act The ModelAction
2840 * @return A Thread reference
2842 Thread * ModelChecker::get_thread(const ModelAction *act) const
2844 return get_thread(act->get_tid());
2848 * @brief Get a Promise's "promise number"
2850 * A "promise number" is an index number that is unique to a promise, valid
2851 * only for a specific snapshot of an execution trace. Promises may come and go
2852 * as they are generated an resolved, so an index only retains meaning for the
2855 * @param promise The Promise to check
2856 * @return The promise index, if the promise still is valid; otherwise -1
2858 int ModelChecker::get_promise_number(const Promise *promise) const
2860 for (unsigned int i = 0; i < promises->size(); i++)
2861 if ((*promises)[i] == promise)
2868 * @brief Check if a Thread is currently enabled
2869 * @param t The Thread to check
2870 * @return True if the Thread is currently enabled
2872 bool ModelChecker::is_enabled(Thread *t) const
2874 return scheduler->is_enabled(t);
2878 * @brief Check if a Thread is currently enabled
2879 * @param tid The ID of the Thread to check
2880 * @return True if the Thread is currently enabled
2882 bool ModelChecker::is_enabled(thread_id_t tid) const
2884 return scheduler->is_enabled(tid);
2888 * Switch from a model-checker context to a user-thread context. This is the
2889 * complement of ModelChecker::switch_to_master and must be called from the
2890 * model-checker context
2892 * @param thread The user-thread to switch to
2894 void ModelChecker::switch_from_master(Thread *thread)
2896 scheduler->set_current_thread(thread);
2897 Thread::swap(&system_context, thread);
2901 * Switch from a user-context to the "master thread" context (a.k.a. system
2902 * context). This switch is made with the intention of exploring a particular
2903 * model-checking action (described by a ModelAction object). Must be called
2904 * from a user-thread context.
2906 * @param act The current action that will be explored. May be NULL only if
2907 * trace is exiting via an assertion (see ModelChecker::set_assert and
2908 * ModelChecker::has_asserted).
2909 * @return Return the value returned by the current action
2911 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2914 Thread *old = thread_current();
2915 ASSERT(!old->get_pending());
2916 old->set_pending(act);
2917 if (Thread::swap(old, &system_context) < 0) {
2918 perror("swap threads");
2921 return old->get_return_value();
2925 * Takes the next step in the execution, if possible.
2926 * @param curr The current step to take
2927 * @return Returns the next Thread to run, if any; NULL if this execution
2930 Thread * ModelChecker::take_step(ModelAction *curr)
2932 Thread *curr_thrd = get_thread(curr);
2933 ASSERT(curr_thrd->get_state() == THREAD_READY);
2935 curr = check_current_action(curr);
2937 /* Infeasible -> don't take any more steps */
2938 if (is_infeasible())
2940 else if (isfeasibleprefix() && have_bug_reports()) {
2945 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
2948 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2949 scheduler->remove_thread(curr_thrd);
2951 Thread *next_thrd = get_next_thread(curr);
2953 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
2954 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
2959 /** Wrapper to run the user's main function, with appropriate arguments */
2960 void user_main_wrapper(void *)
2962 user_main(model->params.argc, model->params.argv);
2965 /** @brief Run ModelChecker for the user program */
2966 void ModelChecker::run()
2970 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
2975 * Stash next pending action(s) for thread(s). There
2976 * should only need to stash one thread's action--the
2977 * thread which just took a step--plus the first step
2978 * for any newly-created thread
2980 for (unsigned int i = 0; i < get_num_threads(); i++) {
2981 thread_id_t tid = int_to_id(i);
2982 Thread *thr = get_thread(tid);
2983 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
2984 switch_from_master(thr);
2988 /* Catch assertions from prior take_step or from
2989 * between-ModelAction bugs (e.g., data races) */
2993 /* Consume the next action for a Thread */
2994 ModelAction *curr = t->get_pending();
2995 t->set_pending(NULL);
2996 t = take_step(curr);
2997 } while (t && !t->is_model_thread());
3000 * Launch end-of-execution release sequence fixups only when
3001 * the execution is otherwise feasible AND there are:
3003 * (1) pending release sequences
3004 * (2) pending assertions that could be invalidated by a change
3005 * in clock vectors (i.e., data races)
3006 * (3) no pending promises
3008 while (!pending_rel_seqs->empty() &&
3009 is_feasible_prefix_ignore_relseq() &&
3010 !unrealizedraces.empty()) {
3011 model_print("*** WARNING: release sequence fixup action "
3012 "(%zu pending release seuqence(s)) ***\n",
3013 pending_rel_seqs->size());
3014 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3015 std::memory_order_seq_cst, NULL, VALUE_NONE,
3019 } while (next_execution());
3021 model_print("******* Model-checking complete: *******\n");