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++;
487 stats.num_redundant++;
490 * @todo We can violate this ASSERT() when fairness/sleep sets
491 * conflict to cause an execution to terminate, e.g. with:
492 * Scheduler: [0: disabled][1: disabled][2: sleep][3: current, enabled]
494 //ASSERT(scheduler->all_threads_sleeping());
498 /** @brief Print execution stats */
499 void ModelChecker::print_stats() const
501 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
502 model_print("Number of redundant executions: %d\n", stats.num_redundant);
503 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
504 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
505 model_print("Total executions: %d\n", stats.num_total);
506 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
510 * @brief End-of-exeuction print
511 * @param printbugs Should any existing bugs be printed?
513 void ModelChecker::print_execution(bool printbugs) const
515 print_program_output();
517 if (DBG_ENABLED() || params.verbose) {
518 model_print("Earliest divergence point since last feasible execution:\n");
519 if (earliest_diverge)
520 earliest_diverge->print();
522 model_print("(Not set)\n");
528 /* Don't print invalid bugs */
537 * Queries the model-checker for more executions to explore and, if one
538 * exists, resets the model-checker state to execute a new execution.
540 * @return If there are more executions to explore, return true. Otherwise,
543 bool ModelChecker::next_execution()
546 /* Is this execution a feasible execution that's worth bug-checking? */
547 bool complete = isfeasibleprefix() && (is_complete_execution() ||
550 /* End-of-execution bug checks */
553 assert_bug("Deadlock detected");
561 if (DBG_ENABLED() || params.verbose || (complete && have_bug_reports()))
562 print_execution(complete);
564 clear_program_output();
567 earliest_diverge = NULL;
569 if ((diverge = get_next_backtrack()) == NULL)
573 model_print("Next execution will diverge at:\n");
577 reset_to_initial_state();
582 * @brief Find the last fence-related backtracking conflict for a ModelAction
584 * This function performs the search for the most recent conflicting action
585 * against which we should perform backtracking, as affected by fence
586 * operations. This includes pairs of potentially-synchronizing actions which
587 * occur due to fence-acquire or fence-release, and hence should be explored in
588 * the opposite execution order.
590 * @param act The current action
591 * @return The most recent action which conflicts with act due to fences
593 ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const
595 /* Only perform release/acquire fence backtracking for stores */
596 if (!act->is_write())
599 /* Find a fence-release (or, act is a release) */
600 ModelAction *last_release;
601 if (act->is_release())
604 last_release = get_last_fence_release(act->get_tid());
608 /* Skip past the release */
609 action_list_t *list = action_trace;
610 action_list_t::reverse_iterator rit;
611 for (rit = list->rbegin(); rit != list->rend(); rit++)
612 if (*rit == last_release)
614 ASSERT(rit != list->rend());
619 * load --sb-> fence-acquire */
620 std::vector< ModelAction *, ModelAlloc<ModelAction *> > acquire_fences(get_num_threads(), NULL);
621 std::vector< ModelAction *, ModelAlloc<ModelAction *> > prior_loads(get_num_threads(), NULL);
622 bool found_acquire_fences = false;
623 for ( ; rit != list->rend(); rit++) {
624 ModelAction *prev = *rit;
625 if (act->same_thread(prev))
628 int tid = id_to_int(prev->get_tid());
630 if (prev->is_read() && act->same_var(prev)) {
631 if (prev->is_acquire()) {
632 /* Found most recent load-acquire, don't need
633 * to search for more fences */
634 if (!found_acquire_fences)
637 prior_loads[tid] = prev;
640 if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) {
641 found_acquire_fences = true;
642 acquire_fences[tid] = prev;
646 ModelAction *latest_backtrack = NULL;
647 for (unsigned int i = 0; i < acquire_fences.size(); i++)
648 if (acquire_fences[i] && prior_loads[i])
649 if (!latest_backtrack || *latest_backtrack < *acquire_fences[i])
650 latest_backtrack = acquire_fences[i];
651 return latest_backtrack;
655 * @brief Find the last backtracking conflict for a ModelAction
657 * This function performs the search for the most recent conflicting action
658 * against which we should perform backtracking. This primary includes pairs of
659 * synchronizing actions which should be explored in the opposite execution
662 * @param act The current action
663 * @return The most recent action which conflicts with act
665 ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const
667 switch (act->get_type()) {
668 /* case ATOMIC_FENCE: fences don't directly cause backtracking */
672 ModelAction *ret = NULL;
674 /* linear search: from most recent to oldest */
675 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
676 action_list_t::reverse_iterator rit;
677 for (rit = list->rbegin(); rit != list->rend(); rit++) {
678 ModelAction *prev = *rit;
679 if (prev->could_synchronize_with(act)) {
685 ModelAction *ret2 = get_last_fence_conflict(act);
695 case ATOMIC_TRYLOCK: {
696 /* linear search: from most recent to oldest */
697 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
698 action_list_t::reverse_iterator rit;
699 for (rit = list->rbegin(); rit != list->rend(); rit++) {
700 ModelAction *prev = *rit;
701 if (act->is_conflicting_lock(prev))
706 case ATOMIC_UNLOCK: {
707 /* linear search: from most recent to oldest */
708 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
709 action_list_t::reverse_iterator rit;
710 for (rit = list->rbegin(); rit != list->rend(); rit++) {
711 ModelAction *prev = *rit;
712 if (!act->same_thread(prev) && prev->is_failed_trylock())
718 /* linear search: from most recent to oldest */
719 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
720 action_list_t::reverse_iterator rit;
721 for (rit = list->rbegin(); rit != list->rend(); rit++) {
722 ModelAction *prev = *rit;
723 if (!act->same_thread(prev) && prev->is_failed_trylock())
725 if (!act->same_thread(prev) && prev->is_notify())
731 case ATOMIC_NOTIFY_ALL:
732 case ATOMIC_NOTIFY_ONE: {
733 /* linear search: from most recent to oldest */
734 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
735 action_list_t::reverse_iterator rit;
736 for (rit = list->rbegin(); rit != list->rend(); rit++) {
737 ModelAction *prev = *rit;
738 if (!act->same_thread(prev) && prev->is_wait())
749 /** This method finds backtracking points where we should try to
750 * reorder the parameter ModelAction against.
752 * @param the ModelAction to find backtracking points for.
754 void ModelChecker::set_backtracking(ModelAction *act)
756 Thread *t = get_thread(act);
757 ModelAction *prev = get_last_conflict(act);
761 Node *node = prev->get_node()->get_parent();
763 int low_tid, high_tid;
764 if (node->enabled_status(t->get_id()) == THREAD_ENABLED) {
765 low_tid = id_to_int(act->get_tid());
766 high_tid = low_tid + 1;
769 high_tid = get_num_threads();
772 for (int i = low_tid; i < high_tid; i++) {
773 thread_id_t tid = int_to_id(i);
775 /* Make sure this thread can be enabled here. */
776 if (i >= node->get_num_threads())
779 /* Don't backtrack into a point where the thread is disabled or sleeping. */
780 if (node->enabled_status(tid) != THREAD_ENABLED)
783 /* Check if this has been explored already */
784 if (node->has_been_explored(tid))
787 /* See if fairness allows */
788 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
790 for (int t = 0; t < node->get_num_threads(); t++) {
791 thread_id_t tother = int_to_id(t);
792 if (node->is_enabled(tother) && node->has_priority(tother)) {
800 /* Cache the latest backtracking point */
801 set_latest_backtrack(prev);
803 /* If this is a new backtracking point, mark the tree */
804 if (!node->set_backtrack(tid))
806 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
807 id_to_int(prev->get_tid()),
808 id_to_int(t->get_id()));
817 * @brief Cache the a backtracking point as the "most recent", if eligible
819 * Note that this does not prepare the NodeStack for this backtracking
820 * operation, it only caches the action on a per-execution basis
822 * @param act The operation at which we should explore a different next action
823 * (i.e., backtracking point)
824 * @return True, if this action is now the most recent backtracking point;
827 bool ModelChecker::set_latest_backtrack(ModelAction *act)
829 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
830 priv->next_backtrack = act;
837 * Returns last backtracking point. The model checker will explore a different
838 * path for this point in the next execution.
839 * @return The ModelAction at which the next execution should diverge.
841 ModelAction * ModelChecker::get_next_backtrack()
843 ModelAction *next = priv->next_backtrack;
844 priv->next_backtrack = NULL;
849 * Processes a read model action.
850 * @param curr is the read model action to process.
851 * @return True if processing this read updates the mo_graph.
853 bool ModelChecker::process_read(ModelAction *curr)
855 Node *node = curr->get_node();
856 uint64_t value = VALUE_NONE;
857 bool updated = false;
859 switch (node->get_read_from_status()) {
860 case READ_FROM_PAST: {
861 const ModelAction *rf = node->get_read_from_past();
864 mo_graph->startChanges();
865 value = rf->get_value();
866 check_recency(curr, rf);
867 bool r_status = r_modification_order(curr, rf);
869 if (is_infeasible() && node->increment_read_from()) {
870 mo_graph->rollbackChanges();
871 priv->too_many_reads = false;
876 mo_graph->commitChanges();
877 mo_check_promises(curr, true);
882 case READ_FROM_PROMISE: {
883 Promise *promise = curr->get_node()->get_read_from_promise();
884 promise->add_reader(curr);
885 value = promise->get_value();
886 curr->set_read_from_promise(promise);
887 mo_graph->startChanges();
888 updated = r_modification_order(curr, promise);
889 mo_graph->commitChanges();
892 case READ_FROM_FUTURE: {
893 /* Read from future value */
894 struct future_value fv = node->get_future_value();
895 Promise *promise = new Promise(curr, fv);
897 curr->set_read_from_promise(promise);
898 promises->push_back(promise);
899 mo_graph->startChanges();
900 updated = r_modification_order(curr, promise);
901 mo_graph->commitChanges();
907 get_thread(curr)->set_return_value(value);
913 * Processes a lock, trylock, or unlock model action. @param curr is
914 * the read model action to process.
916 * The try lock operation checks whether the lock is taken. If not,
917 * it falls to the normal lock operation case. If so, it returns
920 * The lock operation has already been checked that it is enabled, so
921 * it just grabs the lock and synchronizes with the previous unlock.
923 * The unlock operation has to re-enable all of the threads that are
924 * waiting on the lock.
926 * @return True if synchronization was updated; false otherwise
928 bool ModelChecker::process_mutex(ModelAction *curr)
930 std::mutex *mutex = NULL;
931 struct std::mutex_state *state = NULL;
933 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
934 mutex = (std::mutex *)curr->get_location();
935 state = mutex->get_state();
936 } else if (curr->is_wait()) {
937 mutex = (std::mutex *)curr->get_value();
938 state = mutex->get_state();
941 switch (curr->get_type()) {
942 case ATOMIC_TRYLOCK: {
943 bool success = !state->islocked;
944 curr->set_try_lock(success);
946 get_thread(curr)->set_return_value(0);
949 get_thread(curr)->set_return_value(1);
951 //otherwise fall into the lock case
953 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
954 assert_bug("Lock access before initialization");
955 state->islocked = true;
956 ModelAction *unlock = get_last_unlock(curr);
957 //synchronize with the previous unlock statement
958 if (unlock != NULL) {
959 curr->synchronize_with(unlock);
964 case ATOMIC_UNLOCK: {
966 state->islocked = false;
967 //wake up the other threads
968 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
969 //activate all the waiting threads
970 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
971 scheduler->wake(get_thread(*rit));
978 state->islocked = false;
979 //wake up the other threads
980 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
981 //activate all the waiting threads
982 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
983 scheduler->wake(get_thread(*rit));
986 //check whether we should go to sleep or not...simulate spurious failures
987 if (curr->get_node()->get_misc() == 0) {
988 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
990 scheduler->sleep(get_thread(curr));
994 case ATOMIC_NOTIFY_ALL: {
995 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
996 //activate all the waiting threads
997 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
998 scheduler->wake(get_thread(*rit));
1003 case ATOMIC_NOTIFY_ONE: {
1004 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
1005 int wakeupthread = curr->get_node()->get_misc();
1006 action_list_t::iterator it = waiters->begin();
1007 advance(it, wakeupthread);
1008 scheduler->wake(get_thread(*it));
1019 void ModelChecker::add_future_value(const ModelAction *writer, ModelAction *reader)
1021 /* Do more ambitious checks now that mo is more complete */
1022 if (mo_may_allow(writer, reader)) {
1023 Node *node = reader->get_node();
1025 /* Find an ancestor thread which exists at the time of the reader */
1026 Thread *write_thread = get_thread(writer);
1027 while (id_to_int(write_thread->get_id()) >= node->get_num_threads())
1028 write_thread = write_thread->get_parent();
1030 struct future_value fv = {
1031 writer->get_write_value(),
1032 writer->get_seq_number() + params.maxfuturedelay,
1033 write_thread->get_id(),
1035 if (node->add_future_value(fv))
1036 set_latest_backtrack(reader);
1041 * Process a write ModelAction
1042 * @param curr The ModelAction to process
1043 * @return True if the mo_graph was updated or promises were resolved
1045 bool ModelChecker::process_write(ModelAction *curr)
1047 bool updated_mod_order = w_modification_order(curr);
1048 bool updated_promises = resolve_promises(curr);
1050 if (promises->size() == 0) {
1051 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1052 struct PendingFutureValue pfv = (*futurevalues)[i];
1053 add_future_value(pfv.writer, pfv.act);
1055 futurevalues->clear();
1058 mo_graph->commitChanges();
1059 mo_check_promises(curr, false);
1061 get_thread(curr)->set_return_value(VALUE_NONE);
1062 return updated_mod_order || updated_promises;
1066 * Process a fence ModelAction
1067 * @param curr The ModelAction to process
1068 * @return True if synchronization was updated
1070 bool ModelChecker::process_fence(ModelAction *curr)
1073 * fence-relaxed: no-op
1074 * fence-release: only log the occurence (not in this function), for
1075 * use in later synchronization
1076 * fence-acquire (this function): search for hypothetical release
1079 bool updated = false;
1080 if (curr->is_acquire()) {
1081 action_list_t *list = action_trace;
1082 action_list_t::reverse_iterator rit;
1083 /* Find X : is_read(X) && X --sb-> curr */
1084 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1085 ModelAction *act = *rit;
1088 if (act->get_tid() != curr->get_tid())
1090 /* Stop at the beginning of the thread */
1091 if (act->is_thread_start())
1093 /* Stop once we reach a prior fence-acquire */
1094 if (act->is_fence() && act->is_acquire())
1096 if (!act->is_read())
1098 /* read-acquire will find its own release sequences */
1099 if (act->is_acquire())
1102 /* Establish hypothetical release sequences */
1103 rel_heads_list_t release_heads;
1104 get_release_seq_heads(curr, act, &release_heads);
1105 for (unsigned int i = 0; i < release_heads.size(); i++)
1106 if (!curr->synchronize_with(release_heads[i]))
1107 set_bad_synchronization();
1108 if (release_heads.size() != 0)
1116 * @brief Process the current action for thread-related activity
1118 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1119 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1120 * synchronization, etc. This function is a no-op for non-THREAD actions
1121 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1123 * @param curr The current action
1124 * @return True if synchronization was updated or a thread completed
1126 bool ModelChecker::process_thread_action(ModelAction *curr)
1128 bool updated = false;
1130 switch (curr->get_type()) {
1131 case THREAD_CREATE: {
1132 thrd_t *thrd = (thrd_t *)curr->get_location();
1133 struct thread_params *params = (struct thread_params *)curr->get_value();
1134 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1136 th->set_creation(curr);
1137 /* Promises can be satisfied by children */
1138 for (unsigned int i = 0; i < promises->size(); i++) {
1139 Promise *promise = (*promises)[i];
1140 if (promise->thread_is_available(curr->get_tid()))
1141 promise->add_thread(th->get_id());
1146 Thread *blocking = curr->get_thread_operand();
1147 ModelAction *act = get_last_action(blocking->get_id());
1148 curr->synchronize_with(act);
1149 updated = true; /* trigger rel-seq checks */
1152 case THREAD_FINISH: {
1153 Thread *th = get_thread(curr);
1154 while (!th->wait_list_empty()) {
1155 ModelAction *act = th->pop_wait_list();
1156 scheduler->wake(get_thread(act));
1159 /* Completed thread can't satisfy promises */
1160 for (unsigned int i = 0; i < promises->size(); i++) {
1161 Promise *promise = (*promises)[i];
1162 if (promise->thread_is_available(th->get_id()))
1163 if (promise->eliminate_thread(th->get_id()))
1164 priv->failed_promise = true;
1166 updated = true; /* trigger rel-seq checks */
1169 case THREAD_START: {
1170 check_promises(curr->get_tid(), NULL, curr->get_cv());
1181 * @brief Process the current action for release sequence fixup activity
1183 * Performs model-checker release sequence fixups for the current action,
1184 * forcing a single pending release sequence to break (with a given, potential
1185 * "loose" write) or to complete (i.e., synchronize). If a pending release
1186 * sequence forms a complete release sequence, then we must perform the fixup
1187 * synchronization, mo_graph additions, etc.
1189 * @param curr The current action; must be a release sequence fixup action
1190 * @param work_queue The work queue to which to add work items as they are
1193 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1195 const ModelAction *write = curr->get_node()->get_relseq_break();
1196 struct release_seq *sequence = pending_rel_seqs->back();
1197 pending_rel_seqs->pop_back();
1199 ModelAction *acquire = sequence->acquire;
1200 const ModelAction *rf = sequence->rf;
1201 const ModelAction *release = sequence->release;
1205 ASSERT(release->same_thread(rf));
1207 if (write == NULL) {
1209 * @todo Forcing a synchronization requires that we set
1210 * modification order constraints. For instance, we can't allow
1211 * a fixup sequence in which two separate read-acquire
1212 * operations read from the same sequence, where the first one
1213 * synchronizes and the other doesn't. Essentially, we can't
1214 * allow any writes to insert themselves between 'release' and
1218 /* Must synchronize */
1219 if (!acquire->synchronize_with(release)) {
1220 set_bad_synchronization();
1223 /* Re-check all pending release sequences */
1224 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1225 /* Re-check act for mo_graph edges */
1226 work_queue->push_back(MOEdgeWorkEntry(acquire));
1228 /* propagate synchronization to later actions */
1229 action_list_t::reverse_iterator rit = action_trace->rbegin();
1230 for (; (*rit) != acquire; rit++) {
1231 ModelAction *propagate = *rit;
1232 if (acquire->happens_before(propagate)) {
1233 propagate->synchronize_with(acquire);
1234 /* Re-check 'propagate' for mo_graph edges */
1235 work_queue->push_back(MOEdgeWorkEntry(propagate));
1239 /* Break release sequence with new edges:
1240 * release --mo--> write --mo--> rf */
1241 mo_graph->addEdge(release, write);
1242 mo_graph->addEdge(write, rf);
1245 /* See if we have realized a data race */
1250 * Initialize the current action by performing one or more of the following
1251 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1252 * in the NodeStack, manipulating backtracking sets, allocating and
1253 * initializing clock vectors, and computing the promises to fulfill.
1255 * @param curr The current action, as passed from the user context; may be
1256 * freed/invalidated after the execution of this function, with a different
1257 * action "returned" its place (pass-by-reference)
1258 * @return True if curr is a newly-explored action; false otherwise
1260 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1262 ModelAction *newcurr;
1264 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1265 newcurr = process_rmw(*curr);
1268 if (newcurr->is_rmw())
1269 compute_promises(newcurr);
1275 (*curr)->set_seq_number(get_next_seq_num());
1277 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1279 /* First restore type and order in case of RMW operation */
1280 if ((*curr)->is_rmwr())
1281 newcurr->copy_typeandorder(*curr);
1283 ASSERT((*curr)->get_location() == newcurr->get_location());
1284 newcurr->copy_from_new(*curr);
1286 /* Discard duplicate ModelAction; use action from NodeStack */
1289 /* Always compute new clock vector */
1290 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1293 return false; /* Action was explored previously */
1297 /* Always compute new clock vector */
1298 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1300 /* Assign most recent release fence */
1301 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1304 * Perform one-time actions when pushing new ModelAction onto
1307 if (newcurr->is_write())
1308 compute_promises(newcurr);
1309 else if (newcurr->is_relseq_fixup())
1310 compute_relseq_breakwrites(newcurr);
1311 else if (newcurr->is_wait())
1312 newcurr->get_node()->set_misc_max(2);
1313 else if (newcurr->is_notify_one()) {
1314 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1316 return true; /* This was a new ModelAction */
1321 * @brief Establish reads-from relation between two actions
1323 * Perform basic operations involved with establishing a concrete rf relation,
1324 * including setting the ModelAction data and checking for release sequences.
1326 * @param act The action that is reading (must be a read)
1327 * @param rf The action from which we are reading (must be a write)
1329 * @return True if this read established synchronization
1331 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1334 act->set_read_from(rf);
1335 if (act->is_acquire()) {
1336 rel_heads_list_t release_heads;
1337 get_release_seq_heads(act, act, &release_heads);
1338 int num_heads = release_heads.size();
1339 for (unsigned int i = 0; i < release_heads.size(); i++)
1340 if (!act->synchronize_with(release_heads[i])) {
1341 set_bad_synchronization();
1344 return num_heads > 0;
1350 * Check promises and eliminate potentially-satisfying threads when a thread is
1351 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1352 * no longer satisfy a promise generated from that thread.
1354 * @param blocker The thread on which a thread is waiting
1355 * @param waiting The waiting thread
1357 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1359 for (unsigned int i = 0; i < promises->size(); i++) {
1360 Promise *promise = (*promises)[i];
1361 if (!promise->thread_is_available(waiting->get_id()))
1363 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1364 ModelAction *reader = promise->get_reader(j);
1365 if (reader->get_tid() != blocker->get_id())
1367 if (promise->eliminate_thread(waiting->get_id())) {
1368 /* Promise has failed */
1369 priv->failed_promise = true;
1371 /* Only eliminate the 'waiting' thread once */
1379 * @brief Check whether a model action is enabled.
1381 * Checks whether a lock or join operation would be successful (i.e., is the
1382 * lock already locked, or is the joined thread already complete). If not, put
1383 * the action in a waiter list.
1385 * @param curr is the ModelAction to check whether it is enabled.
1386 * @return a bool that indicates whether the action is enabled.
1388 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1389 if (curr->is_lock()) {
1390 std::mutex *lock = (std::mutex *)curr->get_location();
1391 struct std::mutex_state *state = lock->get_state();
1392 if (state->islocked) {
1393 //Stick the action in the appropriate waiting queue
1394 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1397 } else if (curr->get_type() == THREAD_JOIN) {
1398 Thread *blocking = (Thread *)curr->get_location();
1399 if (!blocking->is_complete()) {
1400 blocking->push_wait_list(curr);
1401 thread_blocking_check_promises(blocking, get_thread(curr));
1410 * This is the heart of the model checker routine. It performs model-checking
1411 * actions corresponding to a given "current action." Among other processes, it
1412 * calculates reads-from relationships, updates synchronization clock vectors,
1413 * forms a memory_order constraints graph, and handles replay/backtrack
1414 * execution when running permutations of previously-observed executions.
1416 * @param curr The current action to process
1417 * @return The ModelAction that is actually executed; may be different than
1418 * curr; may be NULL, if the current action is not enabled to run
1420 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1423 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1425 if (!check_action_enabled(curr)) {
1426 /* Make the execution look like we chose to run this action
1427 * much later, when a lock/join can succeed */
1428 get_thread(curr)->set_pending(curr);
1429 scheduler->sleep(get_thread(curr));
1433 bool newly_explored = initialize_curr_action(&curr);
1439 wake_up_sleeping_actions(curr);
1441 /* Add the action to lists before any other model-checking tasks */
1442 if (!second_part_of_rmw)
1443 add_action_to_lists(curr);
1445 /* Build may_read_from set for newly-created actions */
1446 if (newly_explored && curr->is_read())
1447 build_may_read_from(curr);
1449 /* Initialize work_queue with the "current action" work */
1450 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1451 while (!work_queue.empty() && !has_asserted()) {
1452 WorkQueueEntry work = work_queue.front();
1453 work_queue.pop_front();
1455 switch (work.type) {
1456 case WORK_CHECK_CURR_ACTION: {
1457 ModelAction *act = work.action;
1458 bool update = false; /* update this location's release seq's */
1459 bool update_all = false; /* update all release seq's */
1461 if (process_thread_action(curr))
1464 if (act->is_read() && !second_part_of_rmw && process_read(act))
1467 if (act->is_write() && process_write(act))
1470 if (act->is_fence() && process_fence(act))
1473 if (act->is_mutex_op() && process_mutex(act))
1476 if (act->is_relseq_fixup())
1477 process_relseq_fixup(curr, &work_queue);
1480 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1482 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1485 case WORK_CHECK_RELEASE_SEQ:
1486 resolve_release_sequences(work.location, &work_queue);
1488 case WORK_CHECK_MO_EDGES: {
1489 /** @todo Complete verification of work_queue */
1490 ModelAction *act = work.action;
1491 bool updated = false;
1493 if (act->is_read()) {
1494 const ModelAction *rf = act->get_reads_from();
1495 const Promise *promise = act->get_reads_from_promise();
1497 if (r_modification_order(act, rf))
1499 } else if (promise) {
1500 if (r_modification_order(act, promise))
1504 if (act->is_write()) {
1505 if (w_modification_order(act))
1508 mo_graph->commitChanges();
1511 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1520 check_curr_backtracking(curr);
1521 set_backtracking(curr);
1525 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1527 Node *currnode = curr->get_node();
1528 Node *parnode = currnode->get_parent();
1530 if ((parnode && !parnode->backtrack_empty()) ||
1531 !currnode->misc_empty() ||
1532 !currnode->read_from_empty() ||
1533 !currnode->promise_empty() ||
1534 !currnode->relseq_break_empty()) {
1535 set_latest_backtrack(curr);
1539 bool ModelChecker::promises_expired() const
1541 for (unsigned int i = 0; i < promises->size(); i++) {
1542 Promise *promise = (*promises)[i];
1543 if (promise->get_expiration() < priv->used_sequence_numbers)
1550 * This is the strongest feasibility check available.
1551 * @return whether the current trace (partial or complete) must be a prefix of
1554 bool ModelChecker::isfeasibleprefix() const
1556 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1560 * Print disagnostic information about an infeasible execution
1561 * @param prefix A string to prefix the output with; if NULL, then a default
1562 * message prefix will be provided
1564 void ModelChecker::print_infeasibility(const char *prefix) const
1568 if (mo_graph->checkForCycles())
1569 ptr += sprintf(ptr, "[mo cycle]");
1570 if (priv->failed_promise)
1571 ptr += sprintf(ptr, "[failed promise]");
1572 if (priv->too_many_reads)
1573 ptr += sprintf(ptr, "[too many reads]");
1574 if (priv->no_valid_reads)
1575 ptr += sprintf(ptr, "[no valid reads-from]");
1576 if (priv->bad_synchronization)
1577 ptr += sprintf(ptr, "[bad sw ordering]");
1578 if (promises_expired())
1579 ptr += sprintf(ptr, "[promise expired]");
1580 if (promises->size() != 0)
1581 ptr += sprintf(ptr, "[unresolved promise]");
1583 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1587 * Returns whether the current completed trace is feasible, except for pending
1588 * release sequences.
1590 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1592 return !is_infeasible() && promises->size() == 0;
1596 * Check if the current partial trace is infeasible. Does not check any
1597 * end-of-execution flags, which might rule out the execution. Thus, this is
1598 * useful only for ruling an execution as infeasible.
1599 * @return whether the current partial trace is infeasible.
1601 bool ModelChecker::is_infeasible() const
1603 return mo_graph->checkForCycles() ||
1604 priv->no_valid_reads ||
1605 priv->failed_promise ||
1606 priv->too_many_reads ||
1607 priv->bad_synchronization ||
1611 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1612 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1613 ModelAction *lastread = get_last_action(act->get_tid());
1614 lastread->process_rmw(act);
1615 if (act->is_rmw()) {
1616 if (lastread->get_reads_from())
1617 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1619 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1620 mo_graph->commitChanges();
1626 * Checks whether a thread has read from the same write for too many times
1627 * without seeing the effects of a later write.
1630 * 1) there must a different write that we could read from that would satisfy the modification order,
1631 * 2) we must have read from the same value in excess of maxreads times, and
1632 * 3) that other write must have been in the reads_from set for maxreads times.
1634 * If so, we decide that the execution is no longer feasible.
1636 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf)
1638 if (params.maxreads != 0) {
1639 if (curr->get_node()->get_read_from_past_size() <= 1)
1641 //Must make sure that execution is currently feasible... We could
1642 //accidentally clear by rolling back
1643 if (is_infeasible())
1645 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1646 int tid = id_to_int(curr->get_tid());
1649 if ((int)thrd_lists->size() <= tid)
1651 action_list_t *list = &(*thrd_lists)[tid];
1653 action_list_t::reverse_iterator rit = list->rbegin();
1654 /* Skip past curr */
1655 for (; (*rit) != curr; rit++)
1657 /* go past curr now */
1660 action_list_t::reverse_iterator ritcopy = rit;
1661 //See if we have enough reads from the same value
1663 for (; count < params.maxreads; rit++, count++) {
1664 if (rit == list->rend())
1666 ModelAction *act = *rit;
1667 if (!act->is_read())
1670 if (act->get_reads_from() != rf)
1672 if (act->get_node()->get_read_from_past_size() <= 1)
1675 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1677 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1679 /* Need a different write */
1683 /* Test to see whether this is a feasible write to read from */
1684 /** NOTE: all members of read-from set should be
1685 * feasible, so we no longer check it here **/
1689 bool feasiblewrite = true;
1690 //new we need to see if this write works for everyone
1692 for (int loop = count; loop > 0; loop--, rit++) {
1693 ModelAction *act = *rit;
1694 bool foundvalue = false;
1695 for (int j = 0; j < act->get_node()->get_read_from_past_size(); j++) {
1696 if (act->get_node()->get_read_from_past(j) == write) {
1702 feasiblewrite = false;
1706 if (feasiblewrite) {
1707 priv->too_many_reads = true;
1715 * Updates the mo_graph with the constraints imposed from the current
1718 * Basic idea is the following: Go through each other thread and find
1719 * the last action that happened before our read. Two cases:
1721 * (1) The action is a write => that write must either occur before
1722 * the write we read from or be the write we read from.
1724 * (2) The action is a read => the write that that action read from
1725 * must occur before the write we read from or be the same write.
1727 * @param curr The current action. Must be a read.
1728 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1729 * @return True if modification order edges were added; false otherwise
1731 template <typename rf_type>
1732 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1734 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1737 ASSERT(curr->is_read());
1739 /* Last SC fence in the current thread */
1740 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1742 /* Iterate over all threads */
1743 for (i = 0; i < thrd_lists->size(); i++) {
1744 /* Last SC fence in thread i */
1745 ModelAction *last_sc_fence_thread_local = NULL;
1746 if (int_to_id((int)i) != curr->get_tid())
1747 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1749 /* Last SC fence in thread i, before last SC fence in current thread */
1750 ModelAction *last_sc_fence_thread_before = NULL;
1751 if (last_sc_fence_local)
1752 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1754 /* Iterate over actions in thread, starting from most recent */
1755 action_list_t *list = &(*thrd_lists)[i];
1756 action_list_t::reverse_iterator rit;
1757 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1758 ModelAction *act = *rit;
1760 if (act->is_write() && !act->equals(rf) && act != curr) {
1761 /* C++, Section 29.3 statement 5 */
1762 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1763 *act < *last_sc_fence_thread_local) {
1764 added = mo_graph->addEdge(act, rf) || added;
1767 /* C++, Section 29.3 statement 4 */
1768 else if (act->is_seqcst() && last_sc_fence_local &&
1769 *act < *last_sc_fence_local) {
1770 added = mo_graph->addEdge(act, rf) || added;
1773 /* C++, Section 29.3 statement 6 */
1774 else if (last_sc_fence_thread_before &&
1775 *act < *last_sc_fence_thread_before) {
1776 added = mo_graph->addEdge(act, rf) || added;
1782 * Include at most one act per-thread that "happens
1783 * before" curr. Don't consider reflexively.
1785 if (act->happens_before(curr) && act != curr) {
1786 if (act->is_write()) {
1787 if (!act->equals(rf)) {
1788 added = mo_graph->addEdge(act, rf) || added;
1791 const ModelAction *prevrf = act->get_reads_from();
1792 const Promise *prevrf_promise = act->get_reads_from_promise();
1794 if (!prevrf->equals(rf))
1795 added = mo_graph->addEdge(prevrf, rf) || added;
1796 } else if (!prevrf_promise->equals(rf)) {
1797 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1806 * All compatible, thread-exclusive promises must be ordered after any
1807 * concrete loads from the same thread
1809 for (unsigned int i = 0; i < promises->size(); i++)
1810 if ((*promises)[i]->is_compatible_exclusive(curr))
1811 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1817 * Updates the mo_graph with the constraints imposed from the current write.
1819 * Basic idea is the following: Go through each other thread and find
1820 * the lastest action that happened before our write. Two cases:
1822 * (1) The action is a write => that write must occur before
1825 * (2) The action is a read => the write that that action read from
1826 * must occur before the current write.
1828 * This method also handles two other issues:
1830 * (I) Sequential Consistency: Making sure that if the current write is
1831 * seq_cst, that it occurs after the previous seq_cst write.
1833 * (II) Sending the write back to non-synchronizing reads.
1835 * @param curr The current action. Must be a write.
1836 * @return True if modification order edges were added; false otherwise
1838 bool ModelChecker::w_modification_order(ModelAction *curr)
1840 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1843 ASSERT(curr->is_write());
1845 if (curr->is_seqcst()) {
1846 /* We have to at least see the last sequentially consistent write,
1847 so we are initialized. */
1848 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1849 if (last_seq_cst != NULL) {
1850 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1854 /* Last SC fence in the current thread */
1855 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1857 /* Iterate over all threads */
1858 for (i = 0; i < thrd_lists->size(); i++) {
1859 /* Last SC fence in thread i, before last SC fence in current thread */
1860 ModelAction *last_sc_fence_thread_before = NULL;
1861 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1862 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1864 /* Iterate over actions in thread, starting from most recent */
1865 action_list_t *list = &(*thrd_lists)[i];
1866 action_list_t::reverse_iterator rit;
1867 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1868 ModelAction *act = *rit;
1871 * 1) If RMW and it actually read from something, then we
1872 * already have all relevant edges, so just skip to next
1875 * 2) If RMW and it didn't read from anything, we should
1876 * whatever edge we can get to speed up convergence.
1878 * 3) If normal write, we need to look at earlier actions, so
1879 * continue processing list.
1881 if (curr->is_rmw()) {
1882 if (curr->get_reads_from() != NULL)
1890 /* C++, Section 29.3 statement 7 */
1891 if (last_sc_fence_thread_before && act->is_write() &&
1892 *act < *last_sc_fence_thread_before) {
1893 added = mo_graph->addEdge(act, curr) || added;
1898 * Include at most one act per-thread that "happens
1901 if (act->happens_before(curr)) {
1903 * Note: if act is RMW, just add edge:
1905 * The following edge should be handled elsewhere:
1906 * readfrom(act) --mo--> act
1908 if (act->is_write())
1909 added = mo_graph->addEdge(act, curr) || added;
1910 else if (act->is_read()) {
1911 //if previous read accessed a null, just keep going
1912 if (act->get_reads_from() == NULL)
1914 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1917 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1918 !act->same_thread(curr)) {
1919 /* We have an action that:
1920 (1) did not happen before us
1921 (2) is a read and we are a write
1922 (3) cannot synchronize with us
1923 (4) is in a different thread
1925 that read could potentially read from our write. Note that
1926 these checks are overly conservative at this point, we'll
1927 do more checks before actually removing the
1931 if (thin_air_constraint_may_allow(curr, act)) {
1932 if (!is_infeasible())
1933 futurevalues->push_back(PendingFutureValue(curr, act));
1934 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1935 add_future_value(curr, act);
1942 * All compatible, thread-exclusive promises must be ordered after any
1943 * concrete stores to the same thread, or else they can be merged with
1946 for (unsigned int i = 0; i < promises->size(); i++)
1947 if ((*promises)[i]->is_compatible_exclusive(curr))
1948 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1953 /** Arbitrary reads from the future are not allowed. Section 29.3
1954 * part 9 places some constraints. This method checks one result of constraint
1955 * constraint. Others require compiler support. */
1956 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1958 if (!writer->is_rmw())
1961 if (!reader->is_rmw())
1964 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1965 if (search == reader)
1967 if (search->get_tid() == reader->get_tid() &&
1968 search->happens_before(reader))
1976 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1977 * some constraints. This method checks one the following constraint (others
1978 * require compiler support):
1980 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1982 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1984 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1986 /* Iterate over all threads */
1987 for (i = 0; i < thrd_lists->size(); i++) {
1988 const ModelAction *write_after_read = NULL;
1990 /* Iterate over actions in thread, starting from most recent */
1991 action_list_t *list = &(*thrd_lists)[i];
1992 action_list_t::reverse_iterator rit;
1993 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1994 ModelAction *act = *rit;
1996 /* Don't disallow due to act == reader */
1997 if (!reader->happens_before(act) || reader == act)
1999 else if (act->is_write())
2000 write_after_read = act;
2001 else if (act->is_read() && act->get_reads_from() != NULL)
2002 write_after_read = act->get_reads_from();
2005 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2012 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2013 * The ModelAction under consideration is expected to be taking part in
2014 * release/acquire synchronization as an object of the "reads from" relation.
2015 * Note that this can only provide release sequence support for RMW chains
2016 * which do not read from the future, as those actions cannot be traced until
2017 * their "promise" is fulfilled. Similarly, we may not even establish the
2018 * presence of a release sequence with certainty, as some modification order
2019 * constraints may be decided further in the future. Thus, this function
2020 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2021 * and a boolean representing certainty.
2023 * @param rf The action that might be part of a release sequence. Must be a
2025 * @param release_heads A pass-by-reference style return parameter. After
2026 * execution of this function, release_heads will contain the heads of all the
2027 * relevant release sequences, if any exists with certainty
2028 * @param pending A pass-by-reference style return parameter which is only used
2029 * when returning false (i.e., uncertain). Returns most information regarding
2030 * an uncertain release sequence, including any write operations that might
2031 * break the sequence.
2032 * @return true, if the ModelChecker is certain that release_heads is complete;
2035 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2036 rel_heads_list_t *release_heads,
2037 struct release_seq *pending) const
2039 /* Only check for release sequences if there are no cycles */
2040 if (mo_graph->checkForCycles())
2043 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2044 ASSERT(rf->is_write());
2046 if (rf->is_release())
2047 release_heads->push_back(rf);
2048 else if (rf->get_last_fence_release())
2049 release_heads->push_back(rf->get_last_fence_release());
2051 break; /* End of RMW chain */
2053 /** @todo Need to be smarter here... In the linux lock
2054 * example, this will run to the beginning of the program for
2056 /** @todo The way to be smarter here is to keep going until 1
2057 * thread has a release preceded by an acquire and you've seen
2060 /* acq_rel RMW is a sufficient stopping condition */
2061 if (rf->is_acquire() && rf->is_release())
2062 return true; /* complete */
2065 /* read from future: need to settle this later */
2067 return false; /* incomplete */
2070 if (rf->is_release())
2071 return true; /* complete */
2073 /* else relaxed write
2074 * - check for fence-release in the same thread (29.8, stmt. 3)
2075 * - check modification order for contiguous subsequence
2076 * -> rf must be same thread as release */
2078 const ModelAction *fence_release = rf->get_last_fence_release();
2079 /* Synchronize with a fence-release unconditionally; we don't need to
2080 * find any more "contiguous subsequence..." for it */
2082 release_heads->push_back(fence_release);
2084 int tid = id_to_int(rf->get_tid());
2085 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2086 action_list_t *list = &(*thrd_lists)[tid];
2087 action_list_t::const_reverse_iterator rit;
2089 /* Find rf in the thread list */
2090 rit = std::find(list->rbegin(), list->rend(), rf);
2091 ASSERT(rit != list->rend());
2093 /* Find the last {write,fence}-release */
2094 for (; rit != list->rend(); rit++) {
2095 if (fence_release && *(*rit) < *fence_release)
2097 if ((*rit)->is_release())
2100 if (rit == list->rend()) {
2101 /* No write-release in this thread */
2102 return true; /* complete */
2103 } else if (fence_release && *(*rit) < *fence_release) {
2104 /* The fence-release is more recent (and so, "stronger") than
2105 * the most recent write-release */
2106 return true; /* complete */
2107 } /* else, need to establish contiguous release sequence */
2108 ModelAction *release = *rit;
2110 ASSERT(rf->same_thread(release));
2112 pending->writes.clear();
2114 bool certain = true;
2115 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2116 if (id_to_int(rf->get_tid()) == (int)i)
2118 list = &(*thrd_lists)[i];
2120 /* Can we ensure no future writes from this thread may break
2121 * the release seq? */
2122 bool future_ordered = false;
2124 ModelAction *last = get_last_action(int_to_id(i));
2125 Thread *th = get_thread(int_to_id(i));
2126 if ((last && rf->happens_before(last)) ||
2129 future_ordered = true;
2131 ASSERT(!th->is_model_thread() || future_ordered);
2133 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2134 const ModelAction *act = *rit;
2135 /* Reach synchronization -> this thread is complete */
2136 if (act->happens_before(release))
2138 if (rf->happens_before(act)) {
2139 future_ordered = true;
2143 /* Only non-RMW writes can break release sequences */
2144 if (!act->is_write() || act->is_rmw())
2147 /* Check modification order */
2148 if (mo_graph->checkReachable(rf, act)) {
2149 /* rf --mo--> act */
2150 future_ordered = true;
2153 if (mo_graph->checkReachable(act, release))
2154 /* act --mo--> release */
2156 if (mo_graph->checkReachable(release, act) &&
2157 mo_graph->checkReachable(act, rf)) {
2158 /* release --mo-> act --mo--> rf */
2159 return true; /* complete */
2161 /* act may break release sequence */
2162 pending->writes.push_back(act);
2165 if (!future_ordered)
2166 certain = false; /* This thread is uncertain */
2170 release_heads->push_back(release);
2171 pending->writes.clear();
2173 pending->release = release;
2180 * An interface for getting the release sequence head(s) with which a
2181 * given ModelAction must synchronize. This function only returns a non-empty
2182 * result when it can locate a release sequence head with certainty. Otherwise,
2183 * it may mark the internal state of the ModelChecker so that it will handle
2184 * the release sequence at a later time, causing @a acquire to update its
2185 * synchronization at some later point in execution.
2187 * @param acquire The 'acquire' action that may synchronize with a release
2189 * @param read The read action that may read from a release sequence; this may
2190 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2191 * when 'acquire' is a fence-acquire)
2192 * @param release_heads A pass-by-reference return parameter. Will be filled
2193 * with the head(s) of the release sequence(s), if they exists with certainty.
2194 * @see ModelChecker::release_seq_heads
2196 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2197 ModelAction *read, rel_heads_list_t *release_heads)
2199 const ModelAction *rf = read->get_reads_from();
2200 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2201 sequence->acquire = acquire;
2202 sequence->read = read;
2204 if (!release_seq_heads(rf, release_heads, sequence)) {
2205 /* add act to 'lazy checking' list */
2206 pending_rel_seqs->push_back(sequence);
2208 snapshot_free(sequence);
2213 * Attempt to resolve all stashed operations that might synchronize with a
2214 * release sequence for a given location. This implements the "lazy" portion of
2215 * determining whether or not a release sequence was contiguous, since not all
2216 * modification order information is present at the time an action occurs.
2218 * @param location The location/object that should be checked for release
2219 * sequence resolutions. A NULL value means to check all locations.
2220 * @param work_queue The work queue to which to add work items as they are
2222 * @return True if any updates occurred (new synchronization, new mo_graph
2225 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2227 bool updated = false;
2228 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2229 while (it != pending_rel_seqs->end()) {
2230 struct release_seq *pending = *it;
2231 ModelAction *acquire = pending->acquire;
2232 const ModelAction *read = pending->read;
2234 /* Only resolve sequences on the given location, if provided */
2235 if (location && read->get_location() != location) {
2240 const ModelAction *rf = read->get_reads_from();
2241 rel_heads_list_t release_heads;
2243 complete = release_seq_heads(rf, &release_heads, pending);
2244 for (unsigned int i = 0; i < release_heads.size(); i++) {
2245 if (!acquire->has_synchronized_with(release_heads[i])) {
2246 if (acquire->synchronize_with(release_heads[i]))
2249 set_bad_synchronization();
2254 /* Re-check all pending release sequences */
2255 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2256 /* Re-check read-acquire for mo_graph edges */
2257 if (acquire->is_read())
2258 work_queue->push_back(MOEdgeWorkEntry(acquire));
2260 /* propagate synchronization to later actions */
2261 action_list_t::reverse_iterator rit = action_trace->rbegin();
2262 for (; (*rit) != acquire; rit++) {
2263 ModelAction *propagate = *rit;
2264 if (acquire->happens_before(propagate)) {
2265 propagate->synchronize_with(acquire);
2266 /* Re-check 'propagate' for mo_graph edges */
2267 work_queue->push_back(MOEdgeWorkEntry(propagate));
2272 it = pending_rel_seqs->erase(it);
2273 snapshot_free(pending);
2279 // If we resolved promises or data races, see if we have realized a data race.
2286 * Performs various bookkeeping operations for the current ModelAction. For
2287 * instance, adds action to the per-object, per-thread action vector and to the
2288 * action trace list of all thread actions.
2290 * @param act is the ModelAction to add.
2292 void ModelChecker::add_action_to_lists(ModelAction *act)
2294 int tid = id_to_int(act->get_tid());
2295 ModelAction *uninit = NULL;
2297 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2298 if (list->empty() && act->is_atomic_var()) {
2299 uninit = new_uninitialized_action(act->get_location());
2300 uninit_id = id_to_int(uninit->get_tid());
2301 list->push_back(uninit);
2303 list->push_back(act);
2305 action_trace->push_back(act);
2307 action_trace->push_front(uninit);
2309 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2310 if (tid >= (int)vec->size())
2311 vec->resize(priv->next_thread_id);
2312 (*vec)[tid].push_back(act);
2314 (*vec)[uninit_id].push_front(uninit);
2316 if ((int)thrd_last_action->size() <= tid)
2317 thrd_last_action->resize(get_num_threads());
2318 (*thrd_last_action)[tid] = act;
2320 (*thrd_last_action)[uninit_id] = uninit;
2322 if (act->is_fence() && act->is_release()) {
2323 if ((int)thrd_last_fence_release->size() <= tid)
2324 thrd_last_fence_release->resize(get_num_threads());
2325 (*thrd_last_fence_release)[tid] = act;
2328 if (act->is_wait()) {
2329 void *mutex_loc = (void *) act->get_value();
2330 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2332 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2333 if (tid >= (int)vec->size())
2334 vec->resize(priv->next_thread_id);
2335 (*vec)[tid].push_back(act);
2340 * @brief Get the last action performed by a particular Thread
2341 * @param tid The thread ID of the Thread in question
2342 * @return The last action in the thread
2344 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2346 int threadid = id_to_int(tid);
2347 if (threadid < (int)thrd_last_action->size())
2348 return (*thrd_last_action)[id_to_int(tid)];
2354 * @brief Get the last fence release performed by a particular Thread
2355 * @param tid The thread ID of the Thread in question
2356 * @return The last fence release in the thread, if one exists; NULL otherwise
2358 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2360 int threadid = id_to_int(tid);
2361 if (threadid < (int)thrd_last_fence_release->size())
2362 return (*thrd_last_fence_release)[id_to_int(tid)];
2368 * Gets the last memory_order_seq_cst write (in the total global sequence)
2369 * performed on a particular object (i.e., memory location), not including the
2371 * @param curr The current ModelAction; also denotes the object location to
2373 * @return The last seq_cst write
2375 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2377 void *location = curr->get_location();
2378 action_list_t *list = get_safe_ptr_action(obj_map, location);
2379 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2380 action_list_t::reverse_iterator rit;
2381 for (rit = list->rbegin(); rit != list->rend(); rit++)
2382 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2388 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2389 * performed in a particular thread, prior to a particular fence.
2390 * @param tid The ID of the thread to check
2391 * @param before_fence The fence from which to begin the search; if NULL, then
2392 * search for the most recent fence in the thread.
2393 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2395 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2397 /* All fences should have NULL location */
2398 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2399 action_list_t::reverse_iterator rit = list->rbegin();
2402 for (; rit != list->rend(); rit++)
2403 if (*rit == before_fence)
2406 ASSERT(*rit == before_fence);
2410 for (; rit != list->rend(); rit++)
2411 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2417 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2418 * location). This function identifies the mutex according to the current
2419 * action, which is presumed to perform on the same mutex.
2420 * @param curr The current ModelAction; also denotes the object location to
2422 * @return The last unlock operation
2424 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2426 void *location = curr->get_location();
2427 action_list_t *list = get_safe_ptr_action(obj_map, location);
2428 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2429 action_list_t::reverse_iterator rit;
2430 for (rit = list->rbegin(); rit != list->rend(); rit++)
2431 if ((*rit)->is_unlock() || (*rit)->is_wait())
2436 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2438 ModelAction *parent = get_last_action(tid);
2440 parent = get_thread(tid)->get_creation();
2445 * Returns the clock vector for a given thread.
2446 * @param tid The thread whose clock vector we want
2447 * @return Desired clock vector
2449 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2451 return get_parent_action(tid)->get_cv();
2455 * Resolve a set of Promises with a current write. The set is provided in the
2456 * Node corresponding to @a write.
2457 * @param write The ModelAction that is fulfilling Promises
2458 * @return True if promises were resolved; false otherwise
2460 bool ModelChecker::resolve_promises(ModelAction *write)
2462 bool haveResolved = false;
2463 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2464 promise_list_t mustResolve, resolved;
2466 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
2467 Promise *promise = (*promises)[promise_index];
2468 if (write->get_node()->get_promise(i)) {
2469 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2470 ModelAction *read = promise->get_reader(j);
2471 read_from(read, write);
2472 actions_to_check.push_back(read);
2474 //Make sure the promise's value matches the write's value
2475 ASSERT(promise->is_compatible(write));
2476 mo_graph->resolvePromise(promise, write, &mustResolve);
2478 resolved.push_back(promise);
2479 promises->erase(promises->begin() + promise_index);
2481 haveResolved = true;
2486 for (unsigned int i = 0; i < mustResolve.size(); i++) {
2487 if (std::find(resolved.begin(), resolved.end(), mustResolve[i])
2489 priv->failed_promise = true;
2491 for (unsigned int i = 0; i < resolved.size(); i++)
2493 //Check whether reading these writes has made threads unable to
2496 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2497 ModelAction *read = actions_to_check[i];
2498 mo_check_promises(read, true);
2501 return haveResolved;
2505 * Compute the set of promises that could potentially be satisfied by this
2506 * action. Note that the set computation actually appears in the Node, not in
2508 * @param curr The ModelAction that may satisfy promises
2510 void ModelChecker::compute_promises(ModelAction *curr)
2512 for (unsigned int i = 0; i < promises->size(); i++) {
2513 Promise *promise = (*promises)[i];
2514 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2517 bool satisfy = true;
2518 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2519 const ModelAction *act = promise->get_reader(j);
2520 if (act->happens_before(curr) ||
2521 act->could_synchronize_with(curr)) {
2527 curr->get_node()->set_promise(i);
2531 /** Checks promises in response to change in ClockVector Threads. */
2532 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2534 for (unsigned int i = 0; i < promises->size(); i++) {
2535 Promise *promise = (*promises)[i];
2536 if (!promise->thread_is_available(tid))
2538 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2539 const ModelAction *act = promise->get_reader(j);
2540 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2541 merge_cv->synchronized_since(act)) {
2542 if (promise->eliminate_thread(tid)) {
2543 /* Promise has failed */
2544 priv->failed_promise = true;
2552 void ModelChecker::check_promises_thread_disabled()
2554 for (unsigned int i = 0; i < promises->size(); i++) {
2555 Promise *promise = (*promises)[i];
2556 if (promise->has_failed()) {
2557 priv->failed_promise = true;
2564 * @brief Checks promises in response to addition to modification order for
2567 * We test whether threads are still available for satisfying promises after an
2568 * addition to our modification order constraints. Those that are unavailable
2569 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2570 * that promise has failed.
2572 * @param act The ModelAction which updated the modification order
2573 * @param is_read_check Should be true if act is a read and we must check for
2574 * updates to the store from which it read (there is a distinction here for
2575 * RMW's, which are both a load and a store)
2577 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2579 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2581 for (unsigned int i = 0; i < promises->size(); i++) {
2582 Promise *promise = (*promises)[i];
2584 // Is this promise on the same location?
2585 if (!promise->same_location(write))
2588 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2589 const ModelAction *pread = promise->get_reader(j);
2590 if (!pread->happens_before(act))
2592 if (mo_graph->checkPromise(write, promise)) {
2593 priv->failed_promise = true;
2599 // Don't do any lookups twice for the same thread
2600 if (!promise->thread_is_available(act->get_tid()))
2603 if (mo_graph->checkReachable(promise, write)) {
2604 if (mo_graph->checkPromise(write, promise)) {
2605 priv->failed_promise = true;
2613 * Compute the set of writes that may break the current pending release
2614 * sequence. This information is extracted from previou release sequence
2617 * @param curr The current ModelAction. Must be a release sequence fixup
2620 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2622 if (pending_rel_seqs->empty())
2625 struct release_seq *pending = pending_rel_seqs->back();
2626 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2627 const ModelAction *write = pending->writes[i];
2628 curr->get_node()->add_relseq_break(write);
2631 /* NULL means don't break the sequence; just synchronize */
2632 curr->get_node()->add_relseq_break(NULL);
2636 * Build up an initial set of all past writes that this 'read' action may read
2637 * from, as well as any previously-observed future values that must still be valid.
2639 * @param curr is the current ModelAction that we are exploring; it must be a
2642 void ModelChecker::build_may_read_from(ModelAction *curr)
2644 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2646 ASSERT(curr->is_read());
2648 ModelAction *last_sc_write = NULL;
2650 if (curr->is_seqcst())
2651 last_sc_write = get_last_seq_cst_write(curr);
2653 /* Iterate over all threads */
2654 for (i = 0; i < thrd_lists->size(); i++) {
2655 /* Iterate over actions in thread, starting from most recent */
2656 action_list_t *list = &(*thrd_lists)[i];
2657 action_list_t::reverse_iterator rit;
2658 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2659 ModelAction *act = *rit;
2661 /* Only consider 'write' actions */
2662 if (!act->is_write() || act == curr)
2665 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2666 bool allow_read = true;
2668 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2670 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2674 /* Only add feasible reads */
2675 mo_graph->startChanges();
2676 r_modification_order(curr, act);
2677 if (!is_infeasible())
2678 curr->get_node()->add_read_from_past(act);
2679 mo_graph->rollbackChanges();
2682 /* Include at most one act per-thread that "happens before" curr */
2683 if (act->happens_before(curr))
2688 /* Inherit existing, promised future values */
2689 for (i = 0; i < promises->size(); i++) {
2690 const Promise *promise = (*promises)[i];
2691 const ModelAction *promise_read = promise->get_reader(0);
2692 if (promise_read->same_var(curr)) {
2693 /* Only add feasible future-values */
2694 mo_graph->startChanges();
2695 r_modification_order(curr, promise);
2696 if (!is_infeasible())
2697 curr->get_node()->add_read_from_promise(promise_read);
2698 mo_graph->rollbackChanges();
2702 /* We may find no valid may-read-from only if the execution is doomed */
2703 if (!curr->get_node()->read_from_size()) {
2704 priv->no_valid_reads = true;
2708 if (DBG_ENABLED()) {
2709 model_print("Reached read action:\n");
2711 model_print("Printing read_from_past\n");
2712 curr->get_node()->print_read_from_past();
2713 model_print("End printing read_from_past\n");
2717 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2719 for ( ; write != NULL; write = write->get_reads_from()) {
2720 /* UNINIT actions don't have a Node, and they never sleep */
2721 if (write->is_uninitialized())
2723 Node *prevnode = write->get_node()->get_parent();
2725 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2726 if (write->is_release() && thread_sleep)
2728 if (!write->is_rmw())
2735 * @brief Create a new action representing an uninitialized atomic
2736 * @param location The memory location of the atomic object
2737 * @return A pointer to a new ModelAction
2739 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2741 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2742 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2743 act->create_cv(NULL);
2747 static void print_list(action_list_t *list)
2749 action_list_t::iterator it;
2751 model_print("---------------------------------------------------------------------\n");
2753 unsigned int hash = 0;
2755 for (it = list->begin(); it != list->end(); it++) {
2757 hash = hash^(hash<<3)^((*it)->hash());
2759 model_print("HASH %u\n", hash);
2760 model_print("---------------------------------------------------------------------\n");
2763 #if SUPPORT_MOD_ORDER_DUMP
2764 void ModelChecker::dumpGraph(char *filename) const
2767 sprintf(buffer, "%s.dot", filename);
2768 FILE *file = fopen(buffer, "w");
2769 fprintf(file, "digraph %s {\n", filename);
2770 mo_graph->dumpNodes(file);
2771 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2773 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2774 ModelAction *act = *it;
2775 if (act->is_read()) {
2776 mo_graph->dot_print_node(file, act);
2777 if (act->get_reads_from())
2778 mo_graph->dot_print_edge(file,
2779 act->get_reads_from(),
2781 "label=\"rf\", color=red, weight=2");
2783 mo_graph->dot_print_edge(file,
2784 act->get_reads_from_promise(),
2786 "label=\"rf\", color=red");
2788 if (thread_array[act->get_tid()]) {
2789 mo_graph->dot_print_edge(file,
2790 thread_array[id_to_int(act->get_tid())],
2792 "label=\"sb\", color=blue, weight=400");
2795 thread_array[act->get_tid()] = act;
2797 fprintf(file, "}\n");
2798 model_free(thread_array);
2803 /** @brief Prints an execution trace summary. */
2804 void ModelChecker::print_summary() const
2806 #if SUPPORT_MOD_ORDER_DUMP
2807 char buffername[100];
2808 sprintf(buffername, "exec%04u", stats.num_total);
2809 mo_graph->dumpGraphToFile(buffername);
2810 sprintf(buffername, "graph%04u", stats.num_total);
2811 dumpGraph(buffername);
2814 model_print("Execution %d:", stats.num_total);
2815 if (isfeasibleprefix()) {
2816 if (scheduler->all_threads_sleeping())
2817 model_print(" SLEEP-SET REDUNDANT");
2820 print_infeasibility(" INFEASIBLE");
2821 print_list(action_trace);
2826 * Add a Thread to the system for the first time. Should only be called once
2828 * @param t The Thread to add
2830 void ModelChecker::add_thread(Thread *t)
2832 thread_map->put(id_to_int(t->get_id()), t);
2833 scheduler->add_thread(t);
2837 * Removes a thread from the scheduler.
2838 * @param the thread to remove.
2840 void ModelChecker::remove_thread(Thread *t)
2842 scheduler->remove_thread(t);
2846 * @brief Get a Thread reference by its ID
2847 * @param tid The Thread's ID
2848 * @return A Thread reference
2850 Thread * ModelChecker::get_thread(thread_id_t tid) const
2852 return thread_map->get(id_to_int(tid));
2856 * @brief Get a reference to the Thread in which a ModelAction was executed
2857 * @param act The ModelAction
2858 * @return A Thread reference
2860 Thread * ModelChecker::get_thread(const ModelAction *act) const
2862 return get_thread(act->get_tid());
2866 * @brief Get a Promise's "promise number"
2868 * A "promise number" is an index number that is unique to a promise, valid
2869 * only for a specific snapshot of an execution trace. Promises may come and go
2870 * as they are generated an resolved, so an index only retains meaning for the
2873 * @param promise The Promise to check
2874 * @return The promise index, if the promise still is valid; otherwise -1
2876 int ModelChecker::get_promise_number(const Promise *promise) const
2878 for (unsigned int i = 0; i < promises->size(); i++)
2879 if ((*promises)[i] == promise)
2886 * @brief Check if a Thread is currently enabled
2887 * @param t The Thread to check
2888 * @return True if the Thread is currently enabled
2890 bool ModelChecker::is_enabled(Thread *t) const
2892 return scheduler->is_enabled(t);
2896 * @brief Check if a Thread is currently enabled
2897 * @param tid The ID of the Thread to check
2898 * @return True if the Thread is currently enabled
2900 bool ModelChecker::is_enabled(thread_id_t tid) const
2902 return scheduler->is_enabled(tid);
2906 * Switch from a model-checker context to a user-thread context. This is the
2907 * complement of ModelChecker::switch_to_master and must be called from the
2908 * model-checker context
2910 * @param thread The user-thread to switch to
2912 void ModelChecker::switch_from_master(Thread *thread)
2914 scheduler->set_current_thread(thread);
2915 Thread::swap(&system_context, thread);
2919 * Switch from a user-context to the "master thread" context (a.k.a. system
2920 * context). This switch is made with the intention of exploring a particular
2921 * model-checking action (described by a ModelAction object). Must be called
2922 * from a user-thread context.
2924 * @param act The current action that will be explored. May be NULL only if
2925 * trace is exiting via an assertion (see ModelChecker::set_assert and
2926 * ModelChecker::has_asserted).
2927 * @return Return the value returned by the current action
2929 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2932 Thread *old = thread_current();
2933 ASSERT(!old->get_pending());
2934 old->set_pending(act);
2935 if (Thread::swap(old, &system_context) < 0) {
2936 perror("swap threads");
2939 return old->get_return_value();
2943 * Takes the next step in the execution, if possible.
2944 * @param curr The current step to take
2945 * @return Returns the next Thread to run, if any; NULL if this execution
2948 Thread * ModelChecker::take_step(ModelAction *curr)
2950 Thread *curr_thrd = get_thread(curr);
2951 ASSERT(curr_thrd->get_state() == THREAD_READY);
2953 curr = check_current_action(curr);
2955 /* Infeasible -> don't take any more steps */
2956 if (is_infeasible())
2958 else if (isfeasibleprefix() && have_bug_reports()) {
2963 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
2966 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2967 scheduler->remove_thread(curr_thrd);
2969 Thread *next_thrd = get_next_thread(curr);
2971 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
2972 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
2977 /** Wrapper to run the user's main function, with appropriate arguments */
2978 void user_main_wrapper(void *)
2980 user_main(model->params.argc, model->params.argv);
2983 /** @brief Run ModelChecker for the user program */
2984 void ModelChecker::run()
2988 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
2993 * Stash next pending action(s) for thread(s). There
2994 * should only need to stash one thread's action--the
2995 * thread which just took a step--plus the first step
2996 * for any newly-created thread
2998 for (unsigned int i = 0; i < get_num_threads(); i++) {
2999 thread_id_t tid = int_to_id(i);
3000 Thread *thr = get_thread(tid);
3001 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3002 switch_from_master(thr);
3006 /* Catch assertions from prior take_step or from
3007 * between-ModelAction bugs (e.g., data races) */
3011 /* Consume the next action for a Thread */
3012 ModelAction *curr = t->get_pending();
3013 t->set_pending(NULL);
3014 t = take_step(curr);
3015 } while (t && !t->is_model_thread());
3018 * Launch end-of-execution release sequence fixups only when
3019 * the execution is otherwise feasible AND there are:
3021 * (1) pending release sequences
3022 * (2) pending assertions that could be invalidated by a change
3023 * in clock vectors (i.e., data races)
3024 * (3) no pending promises
3026 while (!pending_rel_seqs->empty() &&
3027 is_feasible_prefix_ignore_relseq() &&
3028 !unrealizedraces.empty()) {
3029 model_print("*** WARNING: release sequence fixup action "
3030 "(%zu pending release seuqence(s)) ***\n",
3031 pending_rel_seqs->size());
3032 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3033 std::memory_order_seq_cst, NULL, VALUE_NONE,
3037 } while (next_execution());
3039 model_print("******* Model-checking complete: *******\n");