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 int promise_idx = get_promise_to_resolve(curr);
1049 bool updated_promises = false;
1051 if (promise_idx >= 0)
1052 updated_promises = resolve_promise(curr, promise_idx);
1054 if (promises->size() == 0) {
1055 for (unsigned int i = 0; i < futurevalues->size(); i++) {
1056 struct PendingFutureValue pfv = (*futurevalues)[i];
1057 add_future_value(pfv.writer, pfv.act);
1059 futurevalues->clear();
1062 mo_graph->commitChanges();
1063 mo_check_promises(curr, false);
1065 get_thread(curr)->set_return_value(VALUE_NONE);
1066 return updated_mod_order || updated_promises;
1070 * Process a fence ModelAction
1071 * @param curr The ModelAction to process
1072 * @return True if synchronization was updated
1074 bool ModelChecker::process_fence(ModelAction *curr)
1077 * fence-relaxed: no-op
1078 * fence-release: only log the occurence (not in this function), for
1079 * use in later synchronization
1080 * fence-acquire (this function): search for hypothetical release
1083 bool updated = false;
1084 if (curr->is_acquire()) {
1085 action_list_t *list = action_trace;
1086 action_list_t::reverse_iterator rit;
1087 /* Find X : is_read(X) && X --sb-> curr */
1088 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1089 ModelAction *act = *rit;
1092 if (act->get_tid() != curr->get_tid())
1094 /* Stop at the beginning of the thread */
1095 if (act->is_thread_start())
1097 /* Stop once we reach a prior fence-acquire */
1098 if (act->is_fence() && act->is_acquire())
1100 if (!act->is_read())
1102 /* read-acquire will find its own release sequences */
1103 if (act->is_acquire())
1106 /* Establish hypothetical release sequences */
1107 rel_heads_list_t release_heads;
1108 get_release_seq_heads(curr, act, &release_heads);
1109 for (unsigned int i = 0; i < release_heads.size(); i++)
1110 if (!curr->synchronize_with(release_heads[i]))
1111 set_bad_synchronization();
1112 if (release_heads.size() != 0)
1120 * @brief Process the current action for thread-related activity
1122 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
1123 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
1124 * synchronization, etc. This function is a no-op for non-THREAD actions
1125 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
1127 * @param curr The current action
1128 * @return True if synchronization was updated or a thread completed
1130 bool ModelChecker::process_thread_action(ModelAction *curr)
1132 bool updated = false;
1134 switch (curr->get_type()) {
1135 case THREAD_CREATE: {
1136 thrd_t *thrd = (thrd_t *)curr->get_location();
1137 struct thread_params *params = (struct thread_params *)curr->get_value();
1138 Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr));
1140 th->set_creation(curr);
1141 /* Promises can be satisfied by children */
1142 for (unsigned int i = 0; i < promises->size(); i++) {
1143 Promise *promise = (*promises)[i];
1144 if (promise->thread_is_available(curr->get_tid()))
1145 promise->add_thread(th->get_id());
1150 Thread *blocking = curr->get_thread_operand();
1151 ModelAction *act = get_last_action(blocking->get_id());
1152 curr->synchronize_with(act);
1153 updated = true; /* trigger rel-seq checks */
1156 case THREAD_FINISH: {
1157 Thread *th = get_thread(curr);
1158 while (!th->wait_list_empty()) {
1159 ModelAction *act = th->pop_wait_list();
1160 scheduler->wake(get_thread(act));
1163 /* Completed thread can't satisfy promises */
1164 for (unsigned int i = 0; i < promises->size(); i++) {
1165 Promise *promise = (*promises)[i];
1166 if (promise->thread_is_available(th->get_id()))
1167 if (promise->eliminate_thread(th->get_id()))
1168 priv->failed_promise = true;
1170 updated = true; /* trigger rel-seq checks */
1173 case THREAD_START: {
1174 check_promises(curr->get_tid(), NULL, curr->get_cv());
1185 * @brief Process the current action for release sequence fixup activity
1187 * Performs model-checker release sequence fixups for the current action,
1188 * forcing a single pending release sequence to break (with a given, potential
1189 * "loose" write) or to complete (i.e., synchronize). If a pending release
1190 * sequence forms a complete release sequence, then we must perform the fixup
1191 * synchronization, mo_graph additions, etc.
1193 * @param curr The current action; must be a release sequence fixup action
1194 * @param work_queue The work queue to which to add work items as they are
1197 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
1199 const ModelAction *write = curr->get_node()->get_relseq_break();
1200 struct release_seq *sequence = pending_rel_seqs->back();
1201 pending_rel_seqs->pop_back();
1203 ModelAction *acquire = sequence->acquire;
1204 const ModelAction *rf = sequence->rf;
1205 const ModelAction *release = sequence->release;
1209 ASSERT(release->same_thread(rf));
1211 if (write == NULL) {
1213 * @todo Forcing a synchronization requires that we set
1214 * modification order constraints. For instance, we can't allow
1215 * a fixup sequence in which two separate read-acquire
1216 * operations read from the same sequence, where the first one
1217 * synchronizes and the other doesn't. Essentially, we can't
1218 * allow any writes to insert themselves between 'release' and
1222 /* Must synchronize */
1223 if (!acquire->synchronize_with(release)) {
1224 set_bad_synchronization();
1227 /* Re-check all pending release sequences */
1228 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1229 /* Re-check act for mo_graph edges */
1230 work_queue->push_back(MOEdgeWorkEntry(acquire));
1232 /* propagate synchronization to later actions */
1233 action_list_t::reverse_iterator rit = action_trace->rbegin();
1234 for (; (*rit) != acquire; rit++) {
1235 ModelAction *propagate = *rit;
1236 if (acquire->happens_before(propagate)) {
1237 propagate->synchronize_with(acquire);
1238 /* Re-check 'propagate' for mo_graph edges */
1239 work_queue->push_back(MOEdgeWorkEntry(propagate));
1243 /* Break release sequence with new edges:
1244 * release --mo--> write --mo--> rf */
1245 mo_graph->addEdge(release, write);
1246 mo_graph->addEdge(write, rf);
1249 /* See if we have realized a data race */
1254 * Initialize the current action by performing one or more of the following
1255 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1256 * in the NodeStack, manipulating backtracking sets, allocating and
1257 * initializing clock vectors, and computing the promises to fulfill.
1259 * @param curr The current action, as passed from the user context; may be
1260 * freed/invalidated after the execution of this function, with a different
1261 * action "returned" its place (pass-by-reference)
1262 * @return True if curr is a newly-explored action; false otherwise
1264 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1266 ModelAction *newcurr;
1268 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1269 newcurr = process_rmw(*curr);
1272 if (newcurr->is_rmw())
1273 compute_promises(newcurr);
1279 (*curr)->set_seq_number(get_next_seq_num());
1281 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1283 /* First restore type and order in case of RMW operation */
1284 if ((*curr)->is_rmwr())
1285 newcurr->copy_typeandorder(*curr);
1287 ASSERT((*curr)->get_location() == newcurr->get_location());
1288 newcurr->copy_from_new(*curr);
1290 /* Discard duplicate ModelAction; use action from NodeStack */
1293 /* Always compute new clock vector */
1294 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1297 return false; /* Action was explored previously */
1301 /* Always compute new clock vector */
1302 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1304 /* Assign most recent release fence */
1305 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1308 * Perform one-time actions when pushing new ModelAction onto
1311 if (newcurr->is_write())
1312 compute_promises(newcurr);
1313 else if (newcurr->is_relseq_fixup())
1314 compute_relseq_breakwrites(newcurr);
1315 else if (newcurr->is_wait())
1316 newcurr->get_node()->set_misc_max(2);
1317 else if (newcurr->is_notify_one()) {
1318 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1320 return true; /* This was a new ModelAction */
1325 * @brief Establish reads-from relation between two actions
1327 * Perform basic operations involved with establishing a concrete rf relation,
1328 * including setting the ModelAction data and checking for release sequences.
1330 * @param act The action that is reading (must be a read)
1331 * @param rf The action from which we are reading (must be a write)
1333 * @return True if this read established synchronization
1335 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1338 act->set_read_from(rf);
1339 if (act->is_acquire()) {
1340 rel_heads_list_t release_heads;
1341 get_release_seq_heads(act, act, &release_heads);
1342 int num_heads = release_heads.size();
1343 for (unsigned int i = 0; i < release_heads.size(); i++)
1344 if (!act->synchronize_with(release_heads[i])) {
1345 set_bad_synchronization();
1348 return num_heads > 0;
1354 * Check promises and eliminate potentially-satisfying threads when a thread is
1355 * blocked (e.g., join, lock). A thread which is waiting on another thread can
1356 * no longer satisfy a promise generated from that thread.
1358 * @param blocker The thread on which a thread is waiting
1359 * @param waiting The waiting thread
1361 void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting)
1363 for (unsigned int i = 0; i < promises->size(); i++) {
1364 Promise *promise = (*promises)[i];
1365 if (!promise->thread_is_available(waiting->get_id()))
1367 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
1368 ModelAction *reader = promise->get_reader(j);
1369 if (reader->get_tid() != blocker->get_id())
1371 if (promise->eliminate_thread(waiting->get_id())) {
1372 /* Promise has failed */
1373 priv->failed_promise = true;
1375 /* Only eliminate the 'waiting' thread once */
1383 * @brief Check whether a model action is enabled.
1385 * Checks whether a lock or join operation would be successful (i.e., is the
1386 * lock already locked, or is the joined thread already complete). If not, put
1387 * the action in a waiter list.
1389 * @param curr is the ModelAction to check whether it is enabled.
1390 * @return a bool that indicates whether the action is enabled.
1392 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1393 if (curr->is_lock()) {
1394 std::mutex *lock = (std::mutex *)curr->get_location();
1395 struct std::mutex_state *state = lock->get_state();
1396 if (state->islocked) {
1397 //Stick the action in the appropriate waiting queue
1398 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1401 } else if (curr->get_type() == THREAD_JOIN) {
1402 Thread *blocking = (Thread *)curr->get_location();
1403 if (!blocking->is_complete()) {
1404 blocking->push_wait_list(curr);
1405 thread_blocking_check_promises(blocking, get_thread(curr));
1414 * This is the heart of the model checker routine. It performs model-checking
1415 * actions corresponding to a given "current action." Among other processes, it
1416 * calculates reads-from relationships, updates synchronization clock vectors,
1417 * forms a memory_order constraints graph, and handles replay/backtrack
1418 * execution when running permutations of previously-observed executions.
1420 * @param curr The current action to process
1421 * @return The ModelAction that is actually executed; may be different than
1422 * curr; may be NULL, if the current action is not enabled to run
1424 ModelAction * ModelChecker::check_current_action(ModelAction *curr)
1427 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1429 if (!check_action_enabled(curr)) {
1430 /* Make the execution look like we chose to run this action
1431 * much later, when a lock/join can succeed */
1432 get_thread(curr)->set_pending(curr);
1433 scheduler->sleep(get_thread(curr));
1437 bool newly_explored = initialize_curr_action(&curr);
1443 wake_up_sleeping_actions(curr);
1445 /* Add the action to lists before any other model-checking tasks */
1446 if (!second_part_of_rmw)
1447 add_action_to_lists(curr);
1449 /* Build may_read_from set for newly-created actions */
1450 if (newly_explored && curr->is_read())
1451 build_may_read_from(curr);
1453 /* Initialize work_queue with the "current action" work */
1454 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1455 while (!work_queue.empty() && !has_asserted()) {
1456 WorkQueueEntry work = work_queue.front();
1457 work_queue.pop_front();
1459 switch (work.type) {
1460 case WORK_CHECK_CURR_ACTION: {
1461 ModelAction *act = work.action;
1462 bool update = false; /* update this location's release seq's */
1463 bool update_all = false; /* update all release seq's */
1465 if (process_thread_action(curr))
1468 if (act->is_read() && !second_part_of_rmw && process_read(act))
1471 if (act->is_write() && process_write(act))
1474 if (act->is_fence() && process_fence(act))
1477 if (act->is_mutex_op() && process_mutex(act))
1480 if (act->is_relseq_fixup())
1481 process_relseq_fixup(curr, &work_queue);
1484 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1486 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1489 case WORK_CHECK_RELEASE_SEQ:
1490 resolve_release_sequences(work.location, &work_queue);
1492 case WORK_CHECK_MO_EDGES: {
1493 /** @todo Complete verification of work_queue */
1494 ModelAction *act = work.action;
1495 bool updated = false;
1497 if (act->is_read()) {
1498 const ModelAction *rf = act->get_reads_from();
1499 const Promise *promise = act->get_reads_from_promise();
1501 if (r_modification_order(act, rf))
1503 } else if (promise) {
1504 if (r_modification_order(act, promise))
1508 if (act->is_write()) {
1509 if (w_modification_order(act))
1512 mo_graph->commitChanges();
1515 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1524 check_curr_backtracking(curr);
1525 set_backtracking(curr);
1529 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1531 Node *currnode = curr->get_node();
1532 Node *parnode = currnode->get_parent();
1534 if ((parnode && !parnode->backtrack_empty()) ||
1535 !currnode->misc_empty() ||
1536 !currnode->read_from_empty() ||
1537 !currnode->promise_empty() ||
1538 !currnode->relseq_break_empty()) {
1539 set_latest_backtrack(curr);
1543 bool ModelChecker::promises_expired() const
1545 for (unsigned int i = 0; i < promises->size(); i++) {
1546 Promise *promise = (*promises)[i];
1547 if (promise->get_expiration() < priv->used_sequence_numbers)
1554 * This is the strongest feasibility check available.
1555 * @return whether the current trace (partial or complete) must be a prefix of
1558 bool ModelChecker::isfeasibleprefix() const
1560 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1564 * Print disagnostic information about an infeasible execution
1565 * @param prefix A string to prefix the output with; if NULL, then a default
1566 * message prefix will be provided
1568 void ModelChecker::print_infeasibility(const char *prefix) const
1572 if (mo_graph->checkForCycles())
1573 ptr += sprintf(ptr, "[mo cycle]");
1574 if (priv->failed_promise)
1575 ptr += sprintf(ptr, "[failed promise]");
1576 if (priv->too_many_reads)
1577 ptr += sprintf(ptr, "[too many reads]");
1578 if (priv->no_valid_reads)
1579 ptr += sprintf(ptr, "[no valid reads-from]");
1580 if (priv->bad_synchronization)
1581 ptr += sprintf(ptr, "[bad sw ordering]");
1582 if (promises_expired())
1583 ptr += sprintf(ptr, "[promise expired]");
1584 if (promises->size() != 0)
1585 ptr += sprintf(ptr, "[unresolved promise]");
1587 model_print("%s: %s\n", prefix ? prefix : "Infeasible", buf);
1591 * Returns whether the current completed trace is feasible, except for pending
1592 * release sequences.
1594 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1596 return !is_infeasible() && promises->size() == 0;
1600 * Check if the current partial trace is infeasible. Does not check any
1601 * end-of-execution flags, which might rule out the execution. Thus, this is
1602 * useful only for ruling an execution as infeasible.
1603 * @return whether the current partial trace is infeasible.
1605 bool ModelChecker::is_infeasible() const
1607 return mo_graph->checkForCycles() ||
1608 priv->no_valid_reads ||
1609 priv->failed_promise ||
1610 priv->too_many_reads ||
1611 priv->bad_synchronization ||
1615 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1616 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1617 ModelAction *lastread = get_last_action(act->get_tid());
1618 lastread->process_rmw(act);
1619 if (act->is_rmw()) {
1620 if (lastread->get_reads_from())
1621 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1623 mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread);
1624 mo_graph->commitChanges();
1630 * Checks whether a thread has read from the same write for too many times
1631 * without seeing the effects of a later write.
1634 * 1) there must a different write that we could read from that would satisfy the modification order,
1635 * 2) we must have read from the same value in excess of maxreads times, and
1636 * 3) that other write must have been in the reads_from set for maxreads times.
1638 * If so, we decide that the execution is no longer feasible.
1640 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf)
1642 if (params.maxreads != 0) {
1643 if (curr->get_node()->get_read_from_past_size() <= 1)
1645 //Must make sure that execution is currently feasible... We could
1646 //accidentally clear by rolling back
1647 if (is_infeasible())
1649 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1650 int tid = id_to_int(curr->get_tid());
1653 if ((int)thrd_lists->size() <= tid)
1655 action_list_t *list = &(*thrd_lists)[tid];
1657 action_list_t::reverse_iterator rit = list->rbegin();
1658 /* Skip past curr */
1659 for (; (*rit) != curr; rit++)
1661 /* go past curr now */
1664 action_list_t::reverse_iterator ritcopy = rit;
1665 //See if we have enough reads from the same value
1667 for (; count < params.maxreads; rit++, count++) {
1668 if (rit == list->rend())
1670 ModelAction *act = *rit;
1671 if (!act->is_read())
1674 if (act->get_reads_from() != rf)
1676 if (act->get_node()->get_read_from_past_size() <= 1)
1679 for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) {
1681 const ModelAction *write = curr->get_node()->get_read_from_past(i);
1683 /* Need a different write */
1687 /* Test to see whether this is a feasible write to read from */
1688 /** NOTE: all members of read-from set should be
1689 * feasible, so we no longer check it here **/
1693 bool feasiblewrite = true;
1694 //new we need to see if this write works for everyone
1696 for (int loop = count; loop > 0; loop--, rit++) {
1697 ModelAction *act = *rit;
1698 bool foundvalue = false;
1699 for (int j = 0; j < act->get_node()->get_read_from_past_size(); j++) {
1700 if (act->get_node()->get_read_from_past(j) == write) {
1706 feasiblewrite = false;
1710 if (feasiblewrite) {
1711 priv->too_many_reads = true;
1719 * Updates the mo_graph with the constraints imposed from the current
1722 * Basic idea is the following: Go through each other thread and find
1723 * the last action that happened before our read. Two cases:
1725 * (1) The action is a write => that write must either occur before
1726 * the write we read from or be the write we read from.
1728 * (2) The action is a read => the write that that action read from
1729 * must occur before the write we read from or be the same write.
1731 * @param curr The current action. Must be a read.
1732 * @param rf The ModelAction or Promise that curr reads from. Must be a write.
1733 * @return True if modification order edges were added; false otherwise
1735 template <typename rf_type>
1736 bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf)
1738 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1741 ASSERT(curr->is_read());
1743 /* Last SC fence in the current thread */
1744 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1746 /* Iterate over all threads */
1747 for (i = 0; i < thrd_lists->size(); i++) {
1748 /* Last SC fence in thread i */
1749 ModelAction *last_sc_fence_thread_local = NULL;
1750 if (int_to_id((int)i) != curr->get_tid())
1751 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1753 /* Last SC fence in thread i, before last SC fence in current thread */
1754 ModelAction *last_sc_fence_thread_before = NULL;
1755 if (last_sc_fence_local)
1756 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1758 /* Iterate over actions in thread, starting from most recent */
1759 action_list_t *list = &(*thrd_lists)[i];
1760 action_list_t::reverse_iterator rit;
1761 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1762 ModelAction *act = *rit;
1764 if (act->is_write() && !act->equals(rf) && act != curr) {
1765 /* C++, Section 29.3 statement 5 */
1766 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1767 *act < *last_sc_fence_thread_local) {
1768 added = mo_graph->addEdge(act, rf) || added;
1771 /* C++, Section 29.3 statement 4 */
1772 else if (act->is_seqcst() && last_sc_fence_local &&
1773 *act < *last_sc_fence_local) {
1774 added = mo_graph->addEdge(act, rf) || added;
1777 /* C++, Section 29.3 statement 6 */
1778 else if (last_sc_fence_thread_before &&
1779 *act < *last_sc_fence_thread_before) {
1780 added = mo_graph->addEdge(act, rf) || added;
1786 * Include at most one act per-thread that "happens
1787 * before" curr. Don't consider reflexively.
1789 if (act->happens_before(curr) && act != curr) {
1790 if (act->is_write()) {
1791 if (!act->equals(rf)) {
1792 added = mo_graph->addEdge(act, rf) || added;
1795 const ModelAction *prevrf = act->get_reads_from();
1796 const Promise *prevrf_promise = act->get_reads_from_promise();
1798 if (!prevrf->equals(rf))
1799 added = mo_graph->addEdge(prevrf, rf) || added;
1800 } else if (!prevrf_promise->equals(rf)) {
1801 added = mo_graph->addEdge(prevrf_promise, rf) || added;
1810 * All compatible, thread-exclusive promises must be ordered after any
1811 * concrete loads from the same thread
1813 for (unsigned int i = 0; i < promises->size(); i++)
1814 if ((*promises)[i]->is_compatible_exclusive(curr))
1815 added = mo_graph->addEdge(rf, (*promises)[i]) || added;
1821 * Updates the mo_graph with the constraints imposed from the current write.
1823 * Basic idea is the following: Go through each other thread and find
1824 * the lastest action that happened before our write. Two cases:
1826 * (1) The action is a write => that write must occur before
1829 * (2) The action is a read => the write that that action read from
1830 * must occur before the current write.
1832 * This method also handles two other issues:
1834 * (I) Sequential Consistency: Making sure that if the current write is
1835 * seq_cst, that it occurs after the previous seq_cst write.
1837 * (II) Sending the write back to non-synchronizing reads.
1839 * @param curr The current action. Must be a write.
1840 * @return True if modification order edges were added; false otherwise
1842 bool ModelChecker::w_modification_order(ModelAction *curr)
1844 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1847 ASSERT(curr->is_write());
1849 if (curr->is_seqcst()) {
1850 /* We have to at least see the last sequentially consistent write,
1851 so we are initialized. */
1852 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1853 if (last_seq_cst != NULL) {
1854 added = mo_graph->addEdge(last_seq_cst, curr) || added;
1858 /* Last SC fence in the current thread */
1859 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1861 /* Iterate over all threads */
1862 for (i = 0; i < thrd_lists->size(); i++) {
1863 /* Last SC fence in thread i, before last SC fence in current thread */
1864 ModelAction *last_sc_fence_thread_before = NULL;
1865 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1866 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1868 /* Iterate over actions in thread, starting from most recent */
1869 action_list_t *list = &(*thrd_lists)[i];
1870 action_list_t::reverse_iterator rit;
1871 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1872 ModelAction *act = *rit;
1875 * 1) If RMW and it actually read from something, then we
1876 * already have all relevant edges, so just skip to next
1879 * 2) If RMW and it didn't read from anything, we should
1880 * whatever edge we can get to speed up convergence.
1882 * 3) If normal write, we need to look at earlier actions, so
1883 * continue processing list.
1885 if (curr->is_rmw()) {
1886 if (curr->get_reads_from() != NULL)
1894 /* C++, Section 29.3 statement 7 */
1895 if (last_sc_fence_thread_before && act->is_write() &&
1896 *act < *last_sc_fence_thread_before) {
1897 added = mo_graph->addEdge(act, curr) || added;
1902 * Include at most one act per-thread that "happens
1905 if (act->happens_before(curr)) {
1907 * Note: if act is RMW, just add edge:
1909 * The following edge should be handled elsewhere:
1910 * readfrom(act) --mo--> act
1912 if (act->is_write())
1913 added = mo_graph->addEdge(act, curr) || added;
1914 else if (act->is_read()) {
1915 //if previous read accessed a null, just keep going
1916 if (act->get_reads_from() == NULL)
1918 added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
1921 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1922 !act->same_thread(curr)) {
1923 /* We have an action that:
1924 (1) did not happen before us
1925 (2) is a read and we are a write
1926 (3) cannot synchronize with us
1927 (4) is in a different thread
1929 that read could potentially read from our write. Note that
1930 these checks are overly conservative at this point, we'll
1931 do more checks before actually removing the
1935 if (thin_air_constraint_may_allow(curr, act)) {
1936 if (!is_infeasible())
1937 futurevalues->push_back(PendingFutureValue(curr, act));
1938 else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from())
1939 add_future_value(curr, act);
1946 * All compatible, thread-exclusive promises must be ordered after any
1947 * concrete stores to the same thread, or else they can be merged with
1950 for (unsigned int i = 0; i < promises->size(); i++)
1951 if ((*promises)[i]->is_compatible_exclusive(curr))
1952 added = mo_graph->addEdge(curr, (*promises)[i]) || added;
1957 /** Arbitrary reads from the future are not allowed. Section 29.3
1958 * part 9 places some constraints. This method checks one result of constraint
1959 * constraint. Others require compiler support. */
1960 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1962 if (!writer->is_rmw())
1965 if (!reader->is_rmw())
1968 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1969 if (search == reader)
1971 if (search->get_tid() == reader->get_tid() &&
1972 search->happens_before(reader))
1980 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1981 * some constraints. This method checks one the following constraint (others
1982 * require compiler support):
1984 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1986 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1988 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1990 /* Iterate over all threads */
1991 for (i = 0; i < thrd_lists->size(); i++) {
1992 const ModelAction *write_after_read = NULL;
1994 /* Iterate over actions in thread, starting from most recent */
1995 action_list_t *list = &(*thrd_lists)[i];
1996 action_list_t::reverse_iterator rit;
1997 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1998 ModelAction *act = *rit;
2000 /* Don't disallow due to act == reader */
2001 if (!reader->happens_before(act) || reader == act)
2003 else if (act->is_write())
2004 write_after_read = act;
2005 else if (act->is_read() && act->get_reads_from() != NULL)
2006 write_after_read = act->get_reads_from();
2009 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
2016 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
2017 * The ModelAction under consideration is expected to be taking part in
2018 * release/acquire synchronization as an object of the "reads from" relation.
2019 * Note that this can only provide release sequence support for RMW chains
2020 * which do not read from the future, as those actions cannot be traced until
2021 * their "promise" is fulfilled. Similarly, we may not even establish the
2022 * presence of a release sequence with certainty, as some modification order
2023 * constraints may be decided further in the future. Thus, this function
2024 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
2025 * and a boolean representing certainty.
2027 * @param rf The action that might be part of a release sequence. Must be a
2029 * @param release_heads A pass-by-reference style return parameter. After
2030 * execution of this function, release_heads will contain the heads of all the
2031 * relevant release sequences, if any exists with certainty
2032 * @param pending A pass-by-reference style return parameter which is only used
2033 * when returning false (i.e., uncertain). Returns most information regarding
2034 * an uncertain release sequence, including any write operations that might
2035 * break the sequence.
2036 * @return true, if the ModelChecker is certain that release_heads is complete;
2039 bool ModelChecker::release_seq_heads(const ModelAction *rf,
2040 rel_heads_list_t *release_heads,
2041 struct release_seq *pending) const
2043 /* Only check for release sequences if there are no cycles */
2044 if (mo_graph->checkForCycles())
2047 for ( ; rf != NULL; rf = rf->get_reads_from()) {
2048 ASSERT(rf->is_write());
2050 if (rf->is_release())
2051 release_heads->push_back(rf);
2052 else if (rf->get_last_fence_release())
2053 release_heads->push_back(rf->get_last_fence_release());
2055 break; /* End of RMW chain */
2057 /** @todo Need to be smarter here... In the linux lock
2058 * example, this will run to the beginning of the program for
2060 /** @todo The way to be smarter here is to keep going until 1
2061 * thread has a release preceded by an acquire and you've seen
2064 /* acq_rel RMW is a sufficient stopping condition */
2065 if (rf->is_acquire() && rf->is_release())
2066 return true; /* complete */
2069 /* read from future: need to settle this later */
2071 return false; /* incomplete */
2074 if (rf->is_release())
2075 return true; /* complete */
2077 /* else relaxed write
2078 * - check for fence-release in the same thread (29.8, stmt. 3)
2079 * - check modification order for contiguous subsequence
2080 * -> rf must be same thread as release */
2082 const ModelAction *fence_release = rf->get_last_fence_release();
2083 /* Synchronize with a fence-release unconditionally; we don't need to
2084 * find any more "contiguous subsequence..." for it */
2086 release_heads->push_back(fence_release);
2088 int tid = id_to_int(rf->get_tid());
2089 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
2090 action_list_t *list = &(*thrd_lists)[tid];
2091 action_list_t::const_reverse_iterator rit;
2093 /* Find rf in the thread list */
2094 rit = std::find(list->rbegin(), list->rend(), rf);
2095 ASSERT(rit != list->rend());
2097 /* Find the last {write,fence}-release */
2098 for (; rit != list->rend(); rit++) {
2099 if (fence_release && *(*rit) < *fence_release)
2101 if ((*rit)->is_release())
2104 if (rit == list->rend()) {
2105 /* No write-release in this thread */
2106 return true; /* complete */
2107 } else if (fence_release && *(*rit) < *fence_release) {
2108 /* The fence-release is more recent (and so, "stronger") than
2109 * the most recent write-release */
2110 return true; /* complete */
2111 } /* else, need to establish contiguous release sequence */
2112 ModelAction *release = *rit;
2114 ASSERT(rf->same_thread(release));
2116 pending->writes.clear();
2118 bool certain = true;
2119 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
2120 if (id_to_int(rf->get_tid()) == (int)i)
2122 list = &(*thrd_lists)[i];
2124 /* Can we ensure no future writes from this thread may break
2125 * the release seq? */
2126 bool future_ordered = false;
2128 ModelAction *last = get_last_action(int_to_id(i));
2129 Thread *th = get_thread(int_to_id(i));
2130 if ((last && rf->happens_before(last)) ||
2133 future_ordered = true;
2135 ASSERT(!th->is_model_thread() || future_ordered);
2137 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2138 const ModelAction *act = *rit;
2139 /* Reach synchronization -> this thread is complete */
2140 if (act->happens_before(release))
2142 if (rf->happens_before(act)) {
2143 future_ordered = true;
2147 /* Only non-RMW writes can break release sequences */
2148 if (!act->is_write() || act->is_rmw())
2151 /* Check modification order */
2152 if (mo_graph->checkReachable(rf, act)) {
2153 /* rf --mo--> act */
2154 future_ordered = true;
2157 if (mo_graph->checkReachable(act, release))
2158 /* act --mo--> release */
2160 if (mo_graph->checkReachable(release, act) &&
2161 mo_graph->checkReachable(act, rf)) {
2162 /* release --mo-> act --mo--> rf */
2163 return true; /* complete */
2165 /* act may break release sequence */
2166 pending->writes.push_back(act);
2169 if (!future_ordered)
2170 certain = false; /* This thread is uncertain */
2174 release_heads->push_back(release);
2175 pending->writes.clear();
2177 pending->release = release;
2184 * An interface for getting the release sequence head(s) with which a
2185 * given ModelAction must synchronize. This function only returns a non-empty
2186 * result when it can locate a release sequence head with certainty. Otherwise,
2187 * it may mark the internal state of the ModelChecker so that it will handle
2188 * the release sequence at a later time, causing @a acquire to update its
2189 * synchronization at some later point in execution.
2191 * @param acquire The 'acquire' action that may synchronize with a release
2193 * @param read The read action that may read from a release sequence; this may
2194 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2195 * when 'acquire' is a fence-acquire)
2196 * @param release_heads A pass-by-reference return parameter. Will be filled
2197 * with the head(s) of the release sequence(s), if they exists with certainty.
2198 * @see ModelChecker::release_seq_heads
2200 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2201 ModelAction *read, rel_heads_list_t *release_heads)
2203 const ModelAction *rf = read->get_reads_from();
2204 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2205 sequence->acquire = acquire;
2206 sequence->read = read;
2208 if (!release_seq_heads(rf, release_heads, sequence)) {
2209 /* add act to 'lazy checking' list */
2210 pending_rel_seqs->push_back(sequence);
2212 snapshot_free(sequence);
2217 * Attempt to resolve all stashed operations that might synchronize with a
2218 * release sequence for a given location. This implements the "lazy" portion of
2219 * determining whether or not a release sequence was contiguous, since not all
2220 * modification order information is present at the time an action occurs.
2222 * @param location The location/object that should be checked for release
2223 * sequence resolutions. A NULL value means to check all locations.
2224 * @param work_queue The work queue to which to add work items as they are
2226 * @return True if any updates occurred (new synchronization, new mo_graph
2229 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2231 bool updated = false;
2232 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2233 while (it != pending_rel_seqs->end()) {
2234 struct release_seq *pending = *it;
2235 ModelAction *acquire = pending->acquire;
2236 const ModelAction *read = pending->read;
2238 /* Only resolve sequences on the given location, if provided */
2239 if (location && read->get_location() != location) {
2244 const ModelAction *rf = read->get_reads_from();
2245 rel_heads_list_t release_heads;
2247 complete = release_seq_heads(rf, &release_heads, pending);
2248 for (unsigned int i = 0; i < release_heads.size(); i++) {
2249 if (!acquire->has_synchronized_with(release_heads[i])) {
2250 if (acquire->synchronize_with(release_heads[i]))
2253 set_bad_synchronization();
2258 /* Re-check all pending release sequences */
2259 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2260 /* Re-check read-acquire for mo_graph edges */
2261 if (acquire->is_read())
2262 work_queue->push_back(MOEdgeWorkEntry(acquire));
2264 /* propagate synchronization to later actions */
2265 action_list_t::reverse_iterator rit = action_trace->rbegin();
2266 for (; (*rit) != acquire; rit++) {
2267 ModelAction *propagate = *rit;
2268 if (acquire->happens_before(propagate)) {
2269 propagate->synchronize_with(acquire);
2270 /* Re-check 'propagate' for mo_graph edges */
2271 work_queue->push_back(MOEdgeWorkEntry(propagate));
2276 it = pending_rel_seqs->erase(it);
2277 snapshot_free(pending);
2283 // If we resolved promises or data races, see if we have realized a data race.
2290 * Performs various bookkeeping operations for the current ModelAction. For
2291 * instance, adds action to the per-object, per-thread action vector and to the
2292 * action trace list of all thread actions.
2294 * @param act is the ModelAction to add.
2296 void ModelChecker::add_action_to_lists(ModelAction *act)
2298 int tid = id_to_int(act->get_tid());
2299 ModelAction *uninit = NULL;
2301 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2302 if (list->empty() && act->is_atomic_var()) {
2303 uninit = new_uninitialized_action(act->get_location());
2304 uninit_id = id_to_int(uninit->get_tid());
2305 list->push_back(uninit);
2307 list->push_back(act);
2309 action_trace->push_back(act);
2311 action_trace->push_front(uninit);
2313 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2314 if (tid >= (int)vec->size())
2315 vec->resize(priv->next_thread_id);
2316 (*vec)[tid].push_back(act);
2318 (*vec)[uninit_id].push_front(uninit);
2320 if ((int)thrd_last_action->size() <= tid)
2321 thrd_last_action->resize(get_num_threads());
2322 (*thrd_last_action)[tid] = act;
2324 (*thrd_last_action)[uninit_id] = uninit;
2326 if (act->is_fence() && act->is_release()) {
2327 if ((int)thrd_last_fence_release->size() <= tid)
2328 thrd_last_fence_release->resize(get_num_threads());
2329 (*thrd_last_fence_release)[tid] = act;
2332 if (act->is_wait()) {
2333 void *mutex_loc = (void *) act->get_value();
2334 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2336 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2337 if (tid >= (int)vec->size())
2338 vec->resize(priv->next_thread_id);
2339 (*vec)[tid].push_back(act);
2344 * @brief Get the last action performed by a particular Thread
2345 * @param tid The thread ID of the Thread in question
2346 * @return The last action in the thread
2348 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2350 int threadid = id_to_int(tid);
2351 if (threadid < (int)thrd_last_action->size())
2352 return (*thrd_last_action)[id_to_int(tid)];
2358 * @brief Get the last fence release performed by a particular Thread
2359 * @param tid The thread ID of the Thread in question
2360 * @return The last fence release in the thread, if one exists; NULL otherwise
2362 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2364 int threadid = id_to_int(tid);
2365 if (threadid < (int)thrd_last_fence_release->size())
2366 return (*thrd_last_fence_release)[id_to_int(tid)];
2372 * Gets the last memory_order_seq_cst write (in the total global sequence)
2373 * performed on a particular object (i.e., memory location), not including the
2375 * @param curr The current ModelAction; also denotes the object location to
2377 * @return The last seq_cst write
2379 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2381 void *location = curr->get_location();
2382 action_list_t *list = get_safe_ptr_action(obj_map, location);
2383 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2384 action_list_t::reverse_iterator rit;
2385 for (rit = list->rbegin(); rit != list->rend(); rit++)
2386 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2392 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2393 * performed in a particular thread, prior to a particular fence.
2394 * @param tid The ID of the thread to check
2395 * @param before_fence The fence from which to begin the search; if NULL, then
2396 * search for the most recent fence in the thread.
2397 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2399 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2401 /* All fences should have NULL location */
2402 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2403 action_list_t::reverse_iterator rit = list->rbegin();
2406 for (; rit != list->rend(); rit++)
2407 if (*rit == before_fence)
2410 ASSERT(*rit == before_fence);
2414 for (; rit != list->rend(); rit++)
2415 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2421 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2422 * location). This function identifies the mutex according to the current
2423 * action, which is presumed to perform on the same mutex.
2424 * @param curr The current ModelAction; also denotes the object location to
2426 * @return The last unlock operation
2428 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2430 void *location = curr->get_location();
2431 action_list_t *list = get_safe_ptr_action(obj_map, location);
2432 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2433 action_list_t::reverse_iterator rit;
2434 for (rit = list->rbegin(); rit != list->rend(); rit++)
2435 if ((*rit)->is_unlock() || (*rit)->is_wait())
2440 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2442 ModelAction *parent = get_last_action(tid);
2444 parent = get_thread(tid)->get_creation();
2449 * Returns the clock vector for a given thread.
2450 * @param tid The thread whose clock vector we want
2451 * @return Desired clock vector
2453 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2455 return get_parent_action(tid)->get_cv();
2459 * @brief Find the promise, if any to resolve for the current action
2460 * @param curr The current ModelAction. Should be a write.
2461 * @return The (non-negative) index for the Promise to resolve, if any;
2464 int ModelChecker::get_promise_to_resolve(const ModelAction *curr) const
2466 for (unsigned int i = 0; i < promises->size(); i++)
2467 if (curr->get_node()->get_promise(i))
2473 * Resolve a Promise with a current write.
2474 * @param write The ModelAction that is fulfilling Promises
2475 * @param promise_idx The index corresponding to the promise
2476 * @return True if the Promise was successfully resolved; false otherwise
2478 bool ModelChecker::resolve_promise(ModelAction *write, unsigned int promise_idx)
2480 std::vector< ModelAction *, ModelAlloc<ModelAction *> > actions_to_check;
2481 promise_list_t mustResolve;
2482 Promise *promise = (*promises)[promise_idx];
2484 for (unsigned int i = 0; i < promise->get_num_readers(); i++) {
2485 ModelAction *read = promise->get_reader(i);
2486 read_from(read, write);
2487 actions_to_check.push_back(read);
2489 /* Make sure the promise's value matches the write's value */
2490 ASSERT(promise->is_compatible(write) && promise->same_value(write));
2491 mo_graph->resolvePromise(promise, write, &mustResolve);
2493 promises->erase(promises->begin() + promise_idx);
2495 /** @todo simplify the 'mustResolve' stuff */
2496 ASSERT(mustResolve.size() <= 1);
2498 if (!mustResolve.empty() && mustResolve[0] != promise)
2499 priv->failed_promise = true;
2502 //Check whether reading these writes has made threads unable to
2505 for (unsigned int i = 0; i < actions_to_check.size(); i++) {
2506 ModelAction *read = actions_to_check[i];
2507 mo_check_promises(read, true);
2514 * Compute the set of promises that could potentially be satisfied by this
2515 * action. Note that the set computation actually appears in the Node, not in
2517 * @param curr The ModelAction that may satisfy promises
2519 void ModelChecker::compute_promises(ModelAction *curr)
2521 for (unsigned int i = 0; i < promises->size(); i++) {
2522 Promise *promise = (*promises)[i];
2523 if (!promise->is_compatible(curr) || !promise->same_value(curr))
2526 bool satisfy = true;
2527 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2528 const ModelAction *act = promise->get_reader(j);
2529 if (act->happens_before(curr) ||
2530 act->could_synchronize_with(curr)) {
2536 curr->get_node()->set_promise(i);
2540 /** Checks promises in response to change in ClockVector Threads. */
2541 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2543 for (unsigned int i = 0; i < promises->size(); i++) {
2544 Promise *promise = (*promises)[i];
2545 if (!promise->thread_is_available(tid))
2547 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2548 const ModelAction *act = promise->get_reader(j);
2549 if ((!old_cv || !old_cv->synchronized_since(act)) &&
2550 merge_cv->synchronized_since(act)) {
2551 if (promise->eliminate_thread(tid)) {
2552 /* Promise has failed */
2553 priv->failed_promise = true;
2561 void ModelChecker::check_promises_thread_disabled()
2563 for (unsigned int i = 0; i < promises->size(); i++) {
2564 Promise *promise = (*promises)[i];
2565 if (promise->has_failed()) {
2566 priv->failed_promise = true;
2573 * @brief Checks promises in response to addition to modification order for
2576 * We test whether threads are still available for satisfying promises after an
2577 * addition to our modification order constraints. Those that are unavailable
2578 * are "eliminated". Once all threads are eliminated from satisfying a promise,
2579 * that promise has failed.
2581 * @param act The ModelAction which updated the modification order
2582 * @param is_read_check Should be true if act is a read and we must check for
2583 * updates to the store from which it read (there is a distinction here for
2584 * RMW's, which are both a load and a store)
2586 void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check)
2588 const ModelAction *write = is_read_check ? act->get_reads_from() : act;
2590 for (unsigned int i = 0; i < promises->size(); i++) {
2591 Promise *promise = (*promises)[i];
2593 // Is this promise on the same location?
2594 if (!promise->same_location(write))
2597 for (unsigned int j = 0; j < promise->get_num_readers(); j++) {
2598 const ModelAction *pread = promise->get_reader(j);
2599 if (!pread->happens_before(act))
2601 if (mo_graph->checkPromise(write, promise)) {
2602 priv->failed_promise = true;
2608 // Don't do any lookups twice for the same thread
2609 if (!promise->thread_is_available(act->get_tid()))
2612 if (mo_graph->checkReachable(promise, write)) {
2613 if (mo_graph->checkPromise(write, promise)) {
2614 priv->failed_promise = true;
2622 * Compute the set of writes that may break the current pending release
2623 * sequence. This information is extracted from previou release sequence
2626 * @param curr The current ModelAction. Must be a release sequence fixup
2629 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2631 if (pending_rel_seqs->empty())
2634 struct release_seq *pending = pending_rel_seqs->back();
2635 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2636 const ModelAction *write = pending->writes[i];
2637 curr->get_node()->add_relseq_break(write);
2640 /* NULL means don't break the sequence; just synchronize */
2641 curr->get_node()->add_relseq_break(NULL);
2645 * Build up an initial set of all past writes that this 'read' action may read
2646 * from, as well as any previously-observed future values that must still be valid.
2648 * @param curr is the current ModelAction that we are exploring; it must be a
2651 void ModelChecker::build_may_read_from(ModelAction *curr)
2653 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2655 ASSERT(curr->is_read());
2657 ModelAction *last_sc_write = NULL;
2659 if (curr->is_seqcst())
2660 last_sc_write = get_last_seq_cst_write(curr);
2662 /* Iterate over all threads */
2663 for (i = 0; i < thrd_lists->size(); i++) {
2664 /* Iterate over actions in thread, starting from most recent */
2665 action_list_t *list = &(*thrd_lists)[i];
2666 action_list_t::reverse_iterator rit;
2667 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2668 ModelAction *act = *rit;
2670 /* Only consider 'write' actions */
2671 if (!act->is_write() || act == curr)
2674 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2675 bool allow_read = true;
2677 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2679 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2683 /* Only add feasible reads */
2684 mo_graph->startChanges();
2685 r_modification_order(curr, act);
2686 if (!is_infeasible())
2687 curr->get_node()->add_read_from_past(act);
2688 mo_graph->rollbackChanges();
2691 /* Include at most one act per-thread that "happens before" curr */
2692 if (act->happens_before(curr))
2697 /* Inherit existing, promised future values */
2698 for (i = 0; i < promises->size(); i++) {
2699 const Promise *promise = (*promises)[i];
2700 const ModelAction *promise_read = promise->get_reader(0);
2701 if (promise_read->same_var(curr)) {
2702 /* Only add feasible future-values */
2703 mo_graph->startChanges();
2704 r_modification_order(curr, promise);
2705 if (!is_infeasible())
2706 curr->get_node()->add_read_from_promise(promise_read);
2707 mo_graph->rollbackChanges();
2711 /* We may find no valid may-read-from only if the execution is doomed */
2712 if (!curr->get_node()->read_from_size()) {
2713 priv->no_valid_reads = true;
2717 if (DBG_ENABLED()) {
2718 model_print("Reached read action:\n");
2720 model_print("Printing read_from_past\n");
2721 curr->get_node()->print_read_from_past();
2722 model_print("End printing read_from_past\n");
2726 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2728 for ( ; write != NULL; write = write->get_reads_from()) {
2729 /* UNINIT actions don't have a Node, and they never sleep */
2730 if (write->is_uninitialized())
2732 Node *prevnode = write->get_node()->get_parent();
2734 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2735 if (write->is_release() && thread_sleep)
2737 if (!write->is_rmw())
2744 * @brief Create a new action representing an uninitialized atomic
2745 * @param location The memory location of the atomic object
2746 * @return A pointer to a new ModelAction
2748 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2750 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2751 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2752 act->create_cv(NULL);
2756 static void print_list(action_list_t *list)
2758 action_list_t::iterator it;
2760 model_print("---------------------------------------------------------------------\n");
2762 unsigned int hash = 0;
2764 for (it = list->begin(); it != list->end(); it++) {
2766 hash = hash^(hash<<3)^((*it)->hash());
2768 model_print("HASH %u\n", hash);
2769 model_print("---------------------------------------------------------------------\n");
2772 #if SUPPORT_MOD_ORDER_DUMP
2773 void ModelChecker::dumpGraph(char *filename) const
2776 sprintf(buffer, "%s.dot", filename);
2777 FILE *file = fopen(buffer, "w");
2778 fprintf(file, "digraph %s {\n", filename);
2779 mo_graph->dumpNodes(file);
2780 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2782 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2783 ModelAction *act = *it;
2784 if (act->is_read()) {
2785 mo_graph->dot_print_node(file, act);
2786 if (act->get_reads_from())
2787 mo_graph->dot_print_edge(file,
2788 act->get_reads_from(),
2790 "label=\"rf\", color=red, weight=2");
2792 mo_graph->dot_print_edge(file,
2793 act->get_reads_from_promise(),
2795 "label=\"rf\", color=red");
2797 if (thread_array[act->get_tid()]) {
2798 mo_graph->dot_print_edge(file,
2799 thread_array[id_to_int(act->get_tid())],
2801 "label=\"sb\", color=blue, weight=400");
2804 thread_array[act->get_tid()] = act;
2806 fprintf(file, "}\n");
2807 model_free(thread_array);
2812 /** @brief Prints an execution trace summary. */
2813 void ModelChecker::print_summary() const
2815 #if SUPPORT_MOD_ORDER_DUMP
2816 char buffername[100];
2817 sprintf(buffername, "exec%04u", stats.num_total);
2818 mo_graph->dumpGraphToFile(buffername);
2819 sprintf(buffername, "graph%04u", stats.num_total);
2820 dumpGraph(buffername);
2823 model_print("Execution %d:", stats.num_total);
2824 if (isfeasibleprefix()) {
2825 if (scheduler->all_threads_sleeping())
2826 model_print(" SLEEP-SET REDUNDANT");
2829 print_infeasibility(" INFEASIBLE");
2830 print_list(action_trace);
2835 * Add a Thread to the system for the first time. Should only be called once
2837 * @param t The Thread to add
2839 void ModelChecker::add_thread(Thread *t)
2841 thread_map->put(id_to_int(t->get_id()), t);
2842 scheduler->add_thread(t);
2846 * Removes a thread from the scheduler.
2847 * @param the thread to remove.
2849 void ModelChecker::remove_thread(Thread *t)
2851 scheduler->remove_thread(t);
2855 * @brief Get a Thread reference by its ID
2856 * @param tid The Thread's ID
2857 * @return A Thread reference
2859 Thread * ModelChecker::get_thread(thread_id_t tid) const
2861 return thread_map->get(id_to_int(tid));
2865 * @brief Get a reference to the Thread in which a ModelAction was executed
2866 * @param act The ModelAction
2867 * @return A Thread reference
2869 Thread * ModelChecker::get_thread(const ModelAction *act) const
2871 return get_thread(act->get_tid());
2875 * @brief Get a Promise's "promise number"
2877 * A "promise number" is an index number that is unique to a promise, valid
2878 * only for a specific snapshot of an execution trace. Promises may come and go
2879 * as they are generated an resolved, so an index only retains meaning for the
2882 * @param promise The Promise to check
2883 * @return The promise index, if the promise still is valid; otherwise -1
2885 int ModelChecker::get_promise_number(const Promise *promise) const
2887 for (unsigned int i = 0; i < promises->size(); i++)
2888 if ((*promises)[i] == promise)
2895 * @brief Check if a Thread is currently enabled
2896 * @param t The Thread to check
2897 * @return True if the Thread is currently enabled
2899 bool ModelChecker::is_enabled(Thread *t) const
2901 return scheduler->is_enabled(t);
2905 * @brief Check if a Thread is currently enabled
2906 * @param tid The ID of the Thread to check
2907 * @return True if the Thread is currently enabled
2909 bool ModelChecker::is_enabled(thread_id_t tid) const
2911 return scheduler->is_enabled(tid);
2915 * Switch from a model-checker context to a user-thread context. This is the
2916 * complement of ModelChecker::switch_to_master and must be called from the
2917 * model-checker context
2919 * @param thread The user-thread to switch to
2921 void ModelChecker::switch_from_master(Thread *thread)
2923 scheduler->set_current_thread(thread);
2924 Thread::swap(&system_context, thread);
2928 * Switch from a user-context to the "master thread" context (a.k.a. system
2929 * context). This switch is made with the intention of exploring a particular
2930 * model-checking action (described by a ModelAction object). Must be called
2931 * from a user-thread context.
2933 * @param act The current action that will be explored. May be NULL only if
2934 * trace is exiting via an assertion (see ModelChecker::set_assert and
2935 * ModelChecker::has_asserted).
2936 * @return Return the value returned by the current action
2938 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2941 Thread *old = thread_current();
2942 ASSERT(!old->get_pending());
2943 old->set_pending(act);
2944 if (Thread::swap(old, &system_context) < 0) {
2945 perror("swap threads");
2948 return old->get_return_value();
2952 * Takes the next step in the execution, if possible.
2953 * @param curr The current step to take
2954 * @return Returns the next Thread to run, if any; NULL if this execution
2957 Thread * ModelChecker::take_step(ModelAction *curr)
2959 Thread *curr_thrd = get_thread(curr);
2960 ASSERT(curr_thrd->get_state() == THREAD_READY);
2962 curr = check_current_action(curr);
2964 /* Infeasible -> don't take any more steps */
2965 if (is_infeasible())
2967 else if (isfeasibleprefix() && have_bug_reports()) {
2972 if (params.bound != 0 && priv->used_sequence_numbers > params.bound)
2975 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2976 scheduler->remove_thread(curr_thrd);
2978 Thread *next_thrd = get_next_thread(curr);
2980 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
2981 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
2986 /** Wrapper to run the user's main function, with appropriate arguments */
2987 void user_main_wrapper(void *)
2989 user_main(model->params.argc, model->params.argv);
2992 /** @brief Run ModelChecker for the user program */
2993 void ModelChecker::run()
2997 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL);
3002 * Stash next pending action(s) for thread(s). There
3003 * should only need to stash one thread's action--the
3004 * thread which just took a step--plus the first step
3005 * for any newly-created thread
3007 for (unsigned int i = 0; i < get_num_threads(); i++) {
3008 thread_id_t tid = int_to_id(i);
3009 Thread *thr = get_thread(tid);
3010 if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
3011 switch_from_master(thr);
3015 /* Catch assertions from prior take_step or from
3016 * between-ModelAction bugs (e.g., data races) */
3020 /* Consume the next action for a Thread */
3021 ModelAction *curr = t->get_pending();
3022 t->set_pending(NULL);
3023 t = take_step(curr);
3024 } while (t && !t->is_model_thread());
3027 * Launch end-of-execution release sequence fixups only when
3028 * the execution is otherwise feasible AND there are:
3030 * (1) pending release sequences
3031 * (2) pending assertions that could be invalidated by a change
3032 * in clock vectors (i.e., data races)
3033 * (3) no pending promises
3035 while (!pending_rel_seqs->empty() &&
3036 is_feasible_prefix_ignore_relseq() &&
3037 !unrealizedraces.empty()) {
3038 model_print("*** WARNING: release sequence fixup action "
3039 "(%zu pending release seuqence(s)) ***\n",
3040 pending_rel_seqs->size());
3041 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
3042 std::memory_order_seq_cst, NULL, VALUE_NONE,
3046 } while (next_execution());
3048 model_print("******* Model-checking complete: *******\n");