9 #include "snapshot-interface.h"
11 #include "clockvector.h"
12 #include "cyclegraph.h"
15 #include "threads-model.h"
17 #define INITIAL_THREAD_ID 0
21 /** @brief Constructor */
22 ModelChecker::ModelChecker(struct model_params params) :
23 /* Initialize default scheduler */
25 scheduler(new Scheduler()),
27 num_feasible_executions(0),
29 earliest_diverge(NULL),
30 action_trace(new action_list_t()),
31 thread_map(new HashTable<int, Thread *, int>()),
32 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
33 lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
34 condvar_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
35 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
36 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
37 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
38 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
39 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
40 node_stack(new NodeStack()),
41 mo_graph(new CycleGraph()),
42 failed_promise(false),
43 too_many_reads(false),
45 bad_synchronization(false)
47 /* Allocate this "size" on the snapshotting heap */
48 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
49 /* First thread created will have id INITIAL_THREAD_ID */
50 priv->next_thread_id = INITIAL_THREAD_ID;
52 /* Initialize a model-checker thread, for special ModelActions */
53 model_thread = new Thread(get_next_id());
54 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
57 /** @brief Destructor */
58 ModelChecker::~ModelChecker()
60 for (unsigned int i = 0; i < get_num_threads(); i++)
61 delete thread_map->get(i);
66 delete lock_waiters_map;
67 delete condvar_waiters_map;
70 for (unsigned int i = 0; i < promises->size(); i++)
71 delete (*promises)[i];
74 delete pending_rel_seqs;
76 delete thrd_last_action;
83 * Restores user program to initial state and resets all model-checker data
86 void ModelChecker::reset_to_initial_state()
88 DEBUG("+++ Resetting to initial state +++\n");
89 node_stack->reset_execution();
90 failed_promise = false;
91 too_many_reads = false;
92 bad_synchronization = false;
94 snapshotObject->backTrackBeforeStep(0);
97 /** @return a thread ID for a new Thread */
98 thread_id_t ModelChecker::get_next_id()
100 return priv->next_thread_id++;
103 /** @return the number of user threads created during this execution */
104 unsigned int ModelChecker::get_num_threads()
106 return priv->next_thread_id;
109 /** @return The currently executing Thread. */
110 Thread * ModelChecker::get_current_thread()
112 return scheduler->get_current_thread();
115 /** @return a sequence number for a new ModelAction */
116 modelclock_t ModelChecker::get_next_seq_num()
118 return ++priv->used_sequence_numbers;
121 Node * ModelChecker::get_curr_node() {
122 return node_stack->get_head();
126 * @brief Choose the next thread to execute.
128 * This function chooses the next thread that should execute. It can force the
129 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
130 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
131 * The model-checker may have no preference regarding the next thread (i.e.,
132 * when exploring a new execution ordering), in which case this will return
134 * @param curr The current ModelAction. This action might guide the choice of
136 * @return The next thread to run. If the model-checker has no preference, NULL.
138 Thread * ModelChecker::get_next_thread(ModelAction *curr)
143 /* Do not split atomic actions. */
145 return thread_current();
146 /* The THREAD_CREATE action points to the created Thread */
147 else if (curr->get_type() == THREAD_CREATE)
148 return (Thread *)curr->get_location();
151 /* Have we completed exploring the preselected path? */
155 /* Else, we are trying to replay an execution */
156 ModelAction *next = node_stack->get_next()->get_action();
158 if (next == diverge) {
159 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
160 earliest_diverge=diverge;
162 Node *nextnode = next->get_node();
163 Node *prevnode = nextnode->get_parent();
164 scheduler->update_sleep_set(prevnode);
166 /* Reached divergence point */
167 if (nextnode->increment_misc()) {
168 /* The next node will try to satisfy a different misc_index values. */
169 tid = next->get_tid();
170 node_stack->pop_restofstack(2);
171 } else if (nextnode->increment_promise()) {
172 /* The next node will try to satisfy a different set of promises. */
173 tid = next->get_tid();
174 node_stack->pop_restofstack(2);
175 } else if (nextnode->increment_read_from()) {
176 /* The next node will read from a different value. */
177 tid = next->get_tid();
178 node_stack->pop_restofstack(2);
179 } else if (nextnode->increment_future_value()) {
180 /* The next node will try to read from a different future value. */
181 tid = next->get_tid();
182 node_stack->pop_restofstack(2);
183 } else if (nextnode->increment_relseq_break()) {
184 /* The next node will try to resolve a release sequence differently */
185 tid = next->get_tid();
186 node_stack->pop_restofstack(2);
188 /* Make a different thread execute for next step */
189 scheduler->add_sleep(thread_map->get(id_to_int(next->get_tid())));
190 tid = prevnode->get_next_backtrack();
191 /* Make sure the backtracked thread isn't sleeping. */
192 node_stack->pop_restofstack(1);
193 if (diverge==earliest_diverge) {
194 earliest_diverge=prevnode->get_action();
197 /* The correct sleep set is in the parent node. */
200 DEBUG("*** Divergence point ***\n");
204 tid = next->get_tid();
206 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
207 ASSERT(tid != THREAD_ID_T_NONE);
208 return thread_map->get(id_to_int(tid));
212 * We need to know what the next actions of all threads in the sleep
213 * set will be. This method computes them and stores the actions at
214 * the corresponding thread object's pending action.
217 void ModelChecker::execute_sleep_set() {
218 for(unsigned int i=0;i<get_num_threads();i++) {
219 thread_id_t tid=int_to_id(i);
220 Thread *thr=get_thread(tid);
221 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
222 thr->set_state(THREAD_RUNNING);
223 scheduler->next_thread(thr);
224 Thread::swap(&system_context, thr);
225 priv->current_action->set_sleep_flag();
226 thr->set_pending(priv->current_action);
229 priv->current_action = NULL;
232 void ModelChecker::wake_up_sleeping_actions(ModelAction * curr) {
233 for(unsigned int i=0;i<get_num_threads();i++) {
234 thread_id_t tid=int_to_id(i);
235 Thread *thr=get_thread(tid);
236 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
237 ModelAction *pending_act=thr->get_pending();
238 if ((!curr->is_rmwr())&&pending_act->could_synchronize_with(curr)) {
239 //Remove this thread from sleep set
240 scheduler->remove_sleep(thr);
247 * Queries the model-checker for more executions to explore and, if one
248 * exists, resets the model-checker state to execute a new execution.
250 * @return If there are more executions to explore, return true. Otherwise,
253 bool ModelChecker::next_execution()
259 if (isfinalfeasible()) {
260 printf("Earliest divergence point since last feasible execution:\n");
261 if (earliest_diverge)
262 earliest_diverge->print();
264 printf("(Not set)\n");
266 earliest_diverge = NULL;
267 num_feasible_executions++;
270 DEBUG("Number of acquires waiting on pending release sequences: %zu\n",
271 pending_rel_seqs->size());
274 if (isfinalfeasible() || (params.bound != 0 && priv->used_sequence_numbers > params.bound ) || DBG_ENABLED() )
277 if ((diverge = get_next_backtrack()) == NULL)
281 printf("Next execution will diverge at:\n");
285 reset_to_initial_state();
289 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
291 switch (act->get_type()) {
295 /* linear search: from most recent to oldest */
296 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
297 action_list_t::reverse_iterator rit;
298 for (rit = list->rbegin(); rit != list->rend(); rit++) {
299 ModelAction *prev = *rit;
300 if (prev->could_synchronize_with(act))
306 case ATOMIC_TRYLOCK: {
307 /* linear search: from most recent to oldest */
308 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
309 action_list_t::reverse_iterator rit;
310 for (rit = list->rbegin(); rit != list->rend(); rit++) {
311 ModelAction *prev = *rit;
312 if (act->is_conflicting_lock(prev))
317 case ATOMIC_UNLOCK: {
318 /* linear search: from most recent to oldest */
319 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
320 action_list_t::reverse_iterator rit;
321 for (rit = list->rbegin(); rit != list->rend(); rit++) {
322 ModelAction *prev = *rit;
323 if (!act->same_thread(prev)&&prev->is_failed_trylock())
329 /* linear search: from most recent to oldest */
330 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
331 action_list_t::reverse_iterator rit;
332 for (rit = list->rbegin(); rit != list->rend(); rit++) {
333 ModelAction *prev = *rit;
334 if (!act->same_thread(prev)&&prev->is_failed_trylock())
336 if (!act->same_thread(prev)&&prev->is_notify())
342 case ATOMIC_NOTIFY_ALL:
343 case ATOMIC_NOTIFY_ONE: {
344 /* linear search: from most recent to oldest */
345 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
346 action_list_t::reverse_iterator rit;
347 for (rit = list->rbegin(); rit != list->rend(); rit++) {
348 ModelAction *prev = *rit;
349 if (!act->same_thread(prev)&&prev->is_wait())
360 /** This method finds backtracking points where we should try to
361 * reorder the parameter ModelAction against.
363 * @param the ModelAction to find backtracking points for.
365 void ModelChecker::set_backtracking(ModelAction *act)
367 Thread *t = get_thread(act);
368 ModelAction * prev = get_last_conflict(act);
372 Node * node = prev->get_node()->get_parent();
374 int low_tid, high_tid;
375 if (node->is_enabled(t)) {
376 low_tid = id_to_int(act->get_tid());
377 high_tid = low_tid+1;
380 high_tid = get_num_threads();
383 for(int i = low_tid; i < high_tid; i++) {
384 thread_id_t tid = int_to_id(i);
386 /* Don't backtrack into a point where the thread is disabled or sleeping. */
387 if (node->get_enabled_array()[i]!=THREAD_ENABLED)
390 /* Check if this has been explored already */
391 if (node->has_been_explored(tid))
394 /* See if fairness allows */
395 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
397 for(int t=0;t<node->get_num_threads();t++) {
398 thread_id_t tother=int_to_id(t);
399 if (node->is_enabled(tother) && node->has_priority(tother)) {
407 /* Cache the latest backtracking point */
408 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
409 priv->next_backtrack = prev;
411 /* If this is a new backtracking point, mark the tree */
412 if (!node->set_backtrack(tid))
414 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
415 id_to_int(prev->get_tid()),
416 id_to_int(t->get_id()));
425 * Returns last backtracking point. The model checker will explore a different
426 * path for this point in the next execution.
427 * @return The ModelAction at which the next execution should diverge.
429 ModelAction * ModelChecker::get_next_backtrack()
431 ModelAction *next = priv->next_backtrack;
432 priv->next_backtrack = NULL;
437 * Processes a read or rmw model action.
438 * @param curr is the read model action to process.
439 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
440 * @return True if processing this read updates the mo_graph.
442 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
444 uint64_t value = VALUE_NONE;
445 bool updated = false;
447 const ModelAction *reads_from = curr->get_node()->get_read_from();
448 if (reads_from != NULL) {
449 mo_graph->startChanges();
451 value = reads_from->get_value();
452 bool r_status = false;
454 if (!second_part_of_rmw) {
455 check_recency(curr, reads_from);
456 r_status = r_modification_order(curr, reads_from);
460 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
461 mo_graph->rollbackChanges();
462 too_many_reads = false;
466 curr->read_from(reads_from);
467 mo_graph->commitChanges();
468 mo_check_promises(curr->get_tid(), reads_from);
471 } else if (!second_part_of_rmw) {
472 /* Read from future value */
473 value = curr->get_node()->get_future_value();
474 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
475 curr->read_from(NULL);
476 Promise *valuepromise = new Promise(curr, value, expiration);
477 promises->push_back(valuepromise);
479 get_thread(curr)->set_return_value(value);
485 * Processes a lock, trylock, or unlock model action. @param curr is
486 * the read model action to process.
488 * The try lock operation checks whether the lock is taken. If not,
489 * it falls to the normal lock operation case. If so, it returns
492 * The lock operation has already been checked that it is enabled, so
493 * it just grabs the lock and synchronizes with the previous unlock.
495 * The unlock operation has to re-enable all of the threads that are
496 * waiting on the lock.
498 * @return True if synchronization was updated; false otherwise
500 bool ModelChecker::process_mutex(ModelAction *curr) {
501 std::mutex *mutex=NULL;
502 struct std::mutex_state *state=NULL;
504 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
505 mutex = (std::mutex *)curr->get_location();
506 state = mutex->get_state();
507 } else if(curr->is_wait()) {
508 mutex = (std::mutex *)curr->get_value();
509 state = mutex->get_state();
512 switch (curr->get_type()) {
513 case ATOMIC_TRYLOCK: {
514 bool success = !state->islocked;
515 curr->set_try_lock(success);
517 get_thread(curr)->set_return_value(0);
520 get_thread(curr)->set_return_value(1);
522 //otherwise fall into the lock case
524 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
525 printf("Lock access before initialization\n");
528 state->islocked = true;
529 ModelAction *unlock = get_last_unlock(curr);
530 //synchronize with the previous unlock statement
531 if (unlock != NULL) {
532 curr->synchronize_with(unlock);
537 case ATOMIC_UNLOCK: {
539 state->islocked = false;
540 //wake up the other threads
541 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
542 //activate all the waiting threads
543 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
544 scheduler->wake(get_thread(*rit));
551 state->islocked = false;
552 //wake up the other threads
553 action_list_t *waiters = lock_waiters_map->get_safe_ptr((void *) curr->get_value());
554 //activate all the waiting threads
555 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
556 scheduler->wake(get_thread(*rit));
559 //check whether we should go to sleep or not...simulate spurious failures
560 if (curr->get_node()->get_misc()==0) {
561 condvar_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
563 scheduler->sleep(get_current_thread());
567 case ATOMIC_NOTIFY_ALL: {
568 action_list_t *waiters = condvar_waiters_map->get_safe_ptr(curr->get_location());
569 //activate all the waiting threads
570 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
571 scheduler->wake(get_thread(*rit));
576 case ATOMIC_NOTIFY_ONE: {
577 action_list_t *waiters = condvar_waiters_map->get_safe_ptr(curr->get_location());
578 int wakeupthread=curr->get_node()->get_misc();
579 action_list_t::iterator it = waiters->begin();
580 advance(it, wakeupthread);
581 scheduler->wake(get_thread(*it));
593 * Process a write ModelAction
594 * @param curr The ModelAction to process
595 * @return True if the mo_graph was updated or promises were resolved
597 bool ModelChecker::process_write(ModelAction *curr)
599 bool updated_mod_order = w_modification_order(curr);
600 bool updated_promises = resolve_promises(curr);
602 if (promises->size() == 0) {
603 for (unsigned int i = 0; i < futurevalues->size(); i++) {
604 struct PendingFutureValue pfv = (*futurevalues)[i];
605 //Do more ambitious checks now that mo is more complete
606 if (mo_may_allow(pfv.writer, pfv.act)&&
607 pfv.act->get_node()->add_future_value(pfv.writer->get_value(), pfv.writer->get_seq_number()+params.maxfuturedelay) &&
608 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
609 priv->next_backtrack = pfv.act;
611 futurevalues->resize(0);
614 mo_graph->commitChanges();
615 mo_check_promises(curr->get_tid(), curr);
617 get_thread(curr)->set_return_value(VALUE_NONE);
618 return updated_mod_order || updated_promises;
622 * @brief Process the current action for thread-related activity
624 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
625 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
626 * synchronization, etc. This function is a no-op for non-THREAD actions
627 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
629 * @param curr The current action
630 * @return True if synchronization was updated or a thread completed
632 bool ModelChecker::process_thread_action(ModelAction *curr)
634 bool updated = false;
636 switch (curr->get_type()) {
637 case THREAD_CREATE: {
638 Thread *th = (Thread *)curr->get_location();
639 th->set_creation(curr);
643 Thread *blocking = (Thread *)curr->get_location();
644 ModelAction *act = get_last_action(blocking->get_id());
645 curr->synchronize_with(act);
646 updated = true; /* trigger rel-seq checks */
649 case THREAD_FINISH: {
650 Thread *th = get_thread(curr);
651 while (!th->wait_list_empty()) {
652 ModelAction *act = th->pop_wait_list();
653 scheduler->wake(get_thread(act));
656 updated = true; /* trigger rel-seq checks */
660 check_promises(curr->get_tid(), NULL, curr->get_cv());
671 * @brief Process the current action for release sequence fixup activity
673 * Performs model-checker release sequence fixups for the current action,
674 * forcing a single pending release sequence to break (with a given, potential
675 * "loose" write) or to complete (i.e., synchronize). If a pending release
676 * sequence forms a complete release sequence, then we must perform the fixup
677 * synchronization, mo_graph additions, etc.
679 * @param curr The current action; must be a release sequence fixup action
680 * @param work_queue The work queue to which to add work items as they are
683 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
685 const ModelAction *write = curr->get_node()->get_relseq_break();
686 struct release_seq *sequence = pending_rel_seqs->back();
687 pending_rel_seqs->pop_back();
689 ModelAction *acquire = sequence->acquire;
690 const ModelAction *rf = sequence->rf;
691 const ModelAction *release = sequence->release;
695 ASSERT(release->same_thread(rf));
699 * @todo Forcing a synchronization requires that we set
700 * modification order constraints. For instance, we can't allow
701 * a fixup sequence in which two separate read-acquire
702 * operations read from the same sequence, where the first one
703 * synchronizes and the other doesn't. Essentially, we can't
704 * allow any writes to insert themselves between 'release' and
708 /* Must synchronize */
709 if (!acquire->synchronize_with(release)) {
710 set_bad_synchronization();
713 /* Re-check all pending release sequences */
714 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
715 /* Re-check act for mo_graph edges */
716 work_queue->push_back(MOEdgeWorkEntry(acquire));
718 /* propagate synchronization to later actions */
719 action_list_t::reverse_iterator rit = action_trace->rbegin();
720 for (; (*rit) != acquire; rit++) {
721 ModelAction *propagate = *rit;
722 if (acquire->happens_before(propagate)) {
723 propagate->synchronize_with(acquire);
724 /* Re-check 'propagate' for mo_graph edges */
725 work_queue->push_back(MOEdgeWorkEntry(propagate));
729 /* Break release sequence with new edges:
730 * release --mo--> write --mo--> rf */
731 mo_graph->addEdge(release, write);
732 mo_graph->addEdge(write, rf);
735 /* See if we have realized a data race */
736 if (checkDataRaces())
741 * Initialize the current action by performing one or more of the following
742 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
743 * in the NodeStack, manipulating backtracking sets, allocating and
744 * initializing clock vectors, and computing the promises to fulfill.
746 * @param curr The current action, as passed from the user context; may be
747 * freed/invalidated after the execution of this function, with a different
748 * action "returned" its place (pass-by-reference)
749 * @return True if curr is a newly-explored action; false otherwise
751 bool ModelChecker::initialize_curr_action(ModelAction **curr)
753 ModelAction *newcurr;
755 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
756 newcurr = process_rmw(*curr);
759 if (newcurr->is_rmw())
760 compute_promises(newcurr);
766 (*curr)->set_seq_number(get_next_seq_num());
768 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled());
770 /* First restore type and order in case of RMW operation */
771 if ((*curr)->is_rmwr())
772 newcurr->copy_typeandorder(*curr);
774 ASSERT((*curr)->get_location() == newcurr->get_location());
775 newcurr->copy_from_new(*curr);
777 /* Discard duplicate ModelAction; use action from NodeStack */
780 /* Always compute new clock vector */
781 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
784 return false; /* Action was explored previously */
788 /* Always compute new clock vector */
789 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
791 * Perform one-time actions when pushing new ModelAction onto
794 if (newcurr->is_write())
795 compute_promises(newcurr);
796 else if (newcurr->is_relseq_fixup())
797 compute_relseq_breakwrites(newcurr);
798 else if (newcurr->is_wait())
799 newcurr->get_node()->set_misc_max(2);
800 else if (newcurr->is_notify_one()) {
801 newcurr->get_node()->set_misc_max(condvar_waiters_map->get_safe_ptr(newcurr->get_location())->size());
803 return true; /* This was a new ModelAction */
808 * @brief Check whether a model action is enabled.
810 * Checks whether a lock or join operation would be successful (i.e., is the
811 * lock already locked, or is the joined thread already complete). If not, put
812 * the action in a waiter list.
814 * @param curr is the ModelAction to check whether it is enabled.
815 * @return a bool that indicates whether the action is enabled.
817 bool ModelChecker::check_action_enabled(ModelAction *curr) {
818 if (curr->is_lock()) {
819 std::mutex * lock = (std::mutex *)curr->get_location();
820 struct std::mutex_state * state = lock->get_state();
821 if (state->islocked) {
822 //Stick the action in the appropriate waiting queue
823 lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
826 } else if (curr->get_type() == THREAD_JOIN) {
827 Thread *blocking = (Thread *)curr->get_location();
828 if (!blocking->is_complete()) {
829 blocking->push_wait_list(curr);
838 * This is the heart of the model checker routine. It performs model-checking
839 * actions corresponding to a given "current action." Among other processes, it
840 * calculates reads-from relationships, updates synchronization clock vectors,
841 * forms a memory_order constraints graph, and handles replay/backtrack
842 * execution when running permutations of previously-observed executions.
844 * @param curr The current action to process
845 * @return The next Thread that must be executed. May be NULL if ModelChecker
846 * makes no choice (e.g., according to replay execution, combining RMW actions,
849 Thread * ModelChecker::check_current_action(ModelAction *curr)
852 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
854 if (!check_action_enabled(curr)) {
855 /* Make the execution look like we chose to run this action
856 * much later, when a lock/join can succeed */
857 get_current_thread()->set_pending(curr);
858 scheduler->sleep(get_current_thread());
859 return get_next_thread(NULL);
862 bool newly_explored = initialize_curr_action(&curr);
864 wake_up_sleeping_actions(curr);
866 /* Add the action to lists before any other model-checking tasks */
867 if (!second_part_of_rmw)
868 add_action_to_lists(curr);
870 /* Build may_read_from set for newly-created actions */
871 if (newly_explored && curr->is_read())
872 build_reads_from_past(curr);
874 /* Initialize work_queue with the "current action" work */
875 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
876 while (!work_queue.empty()) {
877 WorkQueueEntry work = work_queue.front();
878 work_queue.pop_front();
881 case WORK_CHECK_CURR_ACTION: {
882 ModelAction *act = work.action;
883 bool update = false; /* update this location's release seq's */
884 bool update_all = false; /* update all release seq's */
886 if (process_thread_action(curr))
889 if (act->is_read() && process_read(act, second_part_of_rmw))
892 if (act->is_write() && process_write(act))
895 if (act->is_mutex_op() && process_mutex(act))
898 if (act->is_relseq_fixup())
899 process_relseq_fixup(curr, &work_queue);
902 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
904 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
907 case WORK_CHECK_RELEASE_SEQ:
908 resolve_release_sequences(work.location, &work_queue);
910 case WORK_CHECK_MO_EDGES: {
911 /** @todo Complete verification of work_queue */
912 ModelAction *act = work.action;
913 bool updated = false;
915 if (act->is_read()) {
916 const ModelAction *rf = act->get_reads_from();
917 if (rf != NULL && r_modification_order(act, rf))
920 if (act->is_write()) {
921 if (w_modification_order(act))
924 mo_graph->commitChanges();
927 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
936 check_curr_backtracking(curr);
937 set_backtracking(curr);
938 return get_next_thread(curr);
941 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
942 Node *currnode = curr->get_node();
943 Node *parnode = currnode->get_parent();
945 if ((!parnode->backtrack_empty() ||
946 !currnode->misc_empty() ||
947 !currnode->read_from_empty() ||
948 !currnode->future_value_empty() ||
949 !currnode->promise_empty() ||
950 !currnode->relseq_break_empty())
951 && (!priv->next_backtrack ||
952 *curr > *priv->next_backtrack)) {
953 priv->next_backtrack = curr;
957 bool ModelChecker::promises_expired() {
958 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
959 Promise *promise = (*promises)[promise_index];
960 if (promise->get_expiration()<priv->used_sequence_numbers) {
967 /** @return whether the current partial trace must be a prefix of a
969 bool ModelChecker::isfeasibleprefix() {
970 return promises->size() == 0 && pending_rel_seqs->size() == 0;
973 /** @return whether the current partial trace is feasible. */
974 bool ModelChecker::isfeasible() {
975 if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
976 DEBUG("Infeasible: RMW violation\n");
978 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
981 /** @return whether the current partial trace is feasible other than
982 * multiple RMW reading from the same store. */
983 bool ModelChecker::isfeasibleotherthanRMW() {
985 if (mo_graph->checkForCycles())
986 DEBUG("Infeasible: modification order cycles\n");
988 DEBUG("Infeasible: failed promise\n");
990 DEBUG("Infeasible: too many reads\n");
991 if (bad_synchronization)
992 DEBUG("Infeasible: bad synchronization ordering\n");
993 if (promises_expired())
994 DEBUG("Infeasible: promises expired\n");
996 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
999 /** Returns whether the current completed trace is feasible. */
1000 bool ModelChecker::isfinalfeasible() {
1001 if (DBG_ENABLED() && promises->size() != 0)
1002 DEBUG("Infeasible: unrevolved promises\n");
1004 return isfeasible() && promises->size() == 0;
1007 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1008 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1009 ModelAction *lastread = get_last_action(act->get_tid());
1010 lastread->process_rmw(act);
1011 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
1012 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1013 mo_graph->commitChanges();
1019 * Checks whether a thread has read from the same write for too many times
1020 * without seeing the effects of a later write.
1023 * 1) there must a different write that we could read from that would satisfy the modification order,
1024 * 2) we must have read from the same value in excess of maxreads times, and
1025 * 3) that other write must have been in the reads_from set for maxreads times.
1027 * If so, we decide that the execution is no longer feasible.
1029 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
1030 if (params.maxreads != 0) {
1032 if (curr->get_node()->get_read_from_size() <= 1)
1034 //Must make sure that execution is currently feasible... We could
1035 //accidentally clear by rolling back
1038 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1039 int tid = id_to_int(curr->get_tid());
1042 if ((int)thrd_lists->size() <= tid)
1044 action_list_t *list = &(*thrd_lists)[tid];
1046 action_list_t::reverse_iterator rit = list->rbegin();
1047 /* Skip past curr */
1048 for (; (*rit) != curr; rit++)
1050 /* go past curr now */
1053 action_list_t::reverse_iterator ritcopy = rit;
1054 //See if we have enough reads from the same value
1056 for (; count < params.maxreads; rit++,count++) {
1057 if (rit==list->rend())
1059 ModelAction *act = *rit;
1060 if (!act->is_read())
1063 if (act->get_reads_from() != rf)
1065 if (act->get_node()->get_read_from_size() <= 1)
1068 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
1070 const ModelAction * write = curr->get_node()->get_read_from_at(i);
1072 //Need a different write
1076 /* Test to see whether this is a feasible write to read from*/
1077 mo_graph->startChanges();
1078 r_modification_order(curr, write);
1079 bool feasiblereadfrom = isfeasible();
1080 mo_graph->rollbackChanges();
1082 if (!feasiblereadfrom)
1086 bool feasiblewrite = true;
1087 //new we need to see if this write works for everyone
1089 for (int loop = count; loop>0; loop--,rit++) {
1090 ModelAction *act=*rit;
1091 bool foundvalue = false;
1092 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
1093 if (act->get_node()->get_read_from_at(i)==write) {
1099 feasiblewrite = false;
1103 if (feasiblewrite) {
1104 too_many_reads = true;
1112 * Updates the mo_graph with the constraints imposed from the current
1115 * Basic idea is the following: Go through each other thread and find
1116 * the lastest action that happened before our read. Two cases:
1118 * (1) The action is a write => that write must either occur before
1119 * the write we read from or be the write we read from.
1121 * (2) The action is a read => the write that that action read from
1122 * must occur before the write we read from or be the same write.
1124 * @param curr The current action. Must be a read.
1125 * @param rf The action that curr reads from. Must be a write.
1126 * @return True if modification order edges were added; false otherwise
1128 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
1130 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1133 ASSERT(curr->is_read());
1135 /* Iterate over all threads */
1136 for (i = 0; i < thrd_lists->size(); i++) {
1137 /* Iterate over actions in thread, starting from most recent */
1138 action_list_t *list = &(*thrd_lists)[i];
1139 action_list_t::reverse_iterator rit;
1140 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1141 ModelAction *act = *rit;
1144 * Include at most one act per-thread that "happens
1145 * before" curr. Don't consider reflexively.
1147 if (act->happens_before(curr) && act != curr) {
1148 if (act->is_write()) {
1150 mo_graph->addEdge(act, rf);
1154 const ModelAction *prevreadfrom = act->get_reads_from();
1155 //if the previous read is unresolved, keep going...
1156 if (prevreadfrom == NULL)
1159 if (rf != prevreadfrom) {
1160 mo_graph->addEdge(prevreadfrom, rf);
1172 /** This method fixes up the modification order when we resolve a
1173 * promises. The basic problem is that actions that occur after the
1174 * read curr could not property add items to the modification order
1177 * So for each thread, we find the earliest item that happens after
1178 * the read curr. This is the item we have to fix up with additional
1179 * constraints. If that action is write, we add a MO edge between
1180 * the Action rf and that action. If the action is a read, we add a
1181 * MO edge between the Action rf, and whatever the read accessed.
1183 * @param curr is the read ModelAction that we are fixing up MO edges for.
1184 * @param rf is the write ModelAction that curr reads from.
1187 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
1189 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1191 ASSERT(curr->is_read());
1193 /* Iterate over all threads */
1194 for (i = 0; i < thrd_lists->size(); i++) {
1195 /* Iterate over actions in thread, starting from most recent */
1196 action_list_t *list = &(*thrd_lists)[i];
1197 action_list_t::reverse_iterator rit;
1198 ModelAction *lastact = NULL;
1200 /* Find last action that happens after curr that is either not curr or a rmw */
1201 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1202 ModelAction *act = *rit;
1203 if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
1209 /* Include at most one act per-thread that "happens before" curr */
1210 if (lastact != NULL) {
1211 if (lastact==curr) {
1212 //Case 1: The resolved read is a RMW, and we need to make sure
1213 //that the write portion of the RMW mod order after rf
1215 mo_graph->addEdge(rf, lastact);
1216 } else if (lastact->is_read()) {
1217 //Case 2: The resolved read is a normal read and the next
1218 //operation is a read, and we need to make sure the value read
1219 //is mod ordered after rf
1221 const ModelAction *postreadfrom = lastact->get_reads_from();
1222 if (postreadfrom != NULL&&rf != postreadfrom)
1223 mo_graph->addEdge(rf, postreadfrom);
1225 //Case 3: The resolved read is a normal read and the next
1226 //operation is a write, and we need to make sure that the
1227 //write is mod ordered after rf
1229 mo_graph->addEdge(rf, lastact);
1237 * Updates the mo_graph with the constraints imposed from the current write.
1239 * Basic idea is the following: Go through each other thread and find
1240 * the lastest action that happened before our write. Two cases:
1242 * (1) The action is a write => that write must occur before
1245 * (2) The action is a read => the write that that action read from
1246 * must occur before the current write.
1248 * This method also handles two other issues:
1250 * (I) Sequential Consistency: Making sure that if the current write is
1251 * seq_cst, that it occurs after the previous seq_cst write.
1253 * (II) Sending the write back to non-synchronizing reads.
1255 * @param curr The current action. Must be a write.
1256 * @return True if modification order edges were added; false otherwise
1258 bool ModelChecker::w_modification_order(ModelAction *curr)
1260 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1263 ASSERT(curr->is_write());
1265 if (curr->is_seqcst()) {
1266 /* We have to at least see the last sequentially consistent write,
1267 so we are initialized. */
1268 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1269 if (last_seq_cst != NULL) {
1270 mo_graph->addEdge(last_seq_cst, curr);
1275 /* Iterate over all threads */
1276 for (i = 0; i < thrd_lists->size(); i++) {
1277 /* Iterate over actions in thread, starting from most recent */
1278 action_list_t *list = &(*thrd_lists)[i];
1279 action_list_t::reverse_iterator rit;
1280 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1281 ModelAction *act = *rit;
1284 * 1) If RMW and it actually read from something, then we
1285 * already have all relevant edges, so just skip to next
1288 * 2) If RMW and it didn't read from anything, we should
1289 * whatever edge we can get to speed up convergence.
1291 * 3) If normal write, we need to look at earlier actions, so
1292 * continue processing list.
1294 if (curr->is_rmw()) {
1295 if (curr->get_reads_from()!=NULL)
1304 * Include at most one act per-thread that "happens
1307 if (act->happens_before(curr)) {
1309 * Note: if act is RMW, just add edge:
1311 * The following edge should be handled elsewhere:
1312 * readfrom(act) --mo--> act
1314 if (act->is_write())
1315 mo_graph->addEdge(act, curr);
1316 else if (act->is_read()) {
1317 //if previous read accessed a null, just keep going
1318 if (act->get_reads_from() == NULL)
1320 mo_graph->addEdge(act->get_reads_from(), curr);
1324 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1325 !act->same_thread(curr)) {
1326 /* We have an action that:
1327 (1) did not happen before us
1328 (2) is a read and we are a write
1329 (3) cannot synchronize with us
1330 (4) is in a different thread
1332 that read could potentially read from our write. Note that
1333 these checks are overly conservative at this point, we'll
1334 do more checks before actually removing the
1338 if (thin_air_constraint_may_allow(curr, act)) {
1340 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1341 struct PendingFutureValue pfv = {curr,act};
1342 futurevalues->push_back(pfv);
1352 /** Arbitrary reads from the future are not allowed. Section 29.3
1353 * part 9 places some constraints. This method checks one result of constraint
1354 * constraint. Others require compiler support. */
1355 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1356 if (!writer->is_rmw())
1359 if (!reader->is_rmw())
1362 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1363 if (search == reader)
1365 if (search->get_tid() == reader->get_tid() &&
1366 search->happens_before(reader))
1374 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1375 * some constraints. This method checks one the following constraint (others
1376 * require compiler support):
1378 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1380 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1382 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(reader->get_location());
1385 /* Iterate over all threads */
1386 for (i = 0; i < thrd_lists->size(); i++) {
1387 ModelAction *write_after_read = NULL;
1389 /* Iterate over actions in thread, starting from most recent */
1390 action_list_t *list = &(*thrd_lists)[i];
1391 action_list_t::reverse_iterator rit;
1392 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1393 ModelAction *act = *rit;
1395 if (!reader->happens_before(act))
1397 else if (act->is_write())
1398 write_after_read = act;
1401 if (write_after_read && mo_graph->checkReachable(write_after_read, writer))
1409 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1410 * The ModelAction under consideration is expected to be taking part in
1411 * release/acquire synchronization as an object of the "reads from" relation.
1412 * Note that this can only provide release sequence support for RMW chains
1413 * which do not read from the future, as those actions cannot be traced until
1414 * their "promise" is fulfilled. Similarly, we may not even establish the
1415 * presence of a release sequence with certainty, as some modification order
1416 * constraints may be decided further in the future. Thus, this function
1417 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1418 * and a boolean representing certainty.
1420 * @param rf The action that might be part of a release sequence. Must be a
1422 * @param release_heads A pass-by-reference style return parameter. After
1423 * execution of this function, release_heads will contain the heads of all the
1424 * relevant release sequences, if any exists with certainty
1425 * @param pending A pass-by-reference style return parameter which is only used
1426 * when returning false (i.e., uncertain). Returns most information regarding
1427 * an uncertain release sequence, including any write operations that might
1428 * break the sequence.
1429 * @return true, if the ModelChecker is certain that release_heads is complete;
1432 bool ModelChecker::release_seq_heads(const ModelAction *rf,
1433 rel_heads_list_t *release_heads,
1434 struct release_seq *pending) const
1436 /* Only check for release sequences if there are no cycles */
1437 if (mo_graph->checkForCycles())
1441 ASSERT(rf->is_write());
1443 if (rf->is_release())
1444 release_heads->push_back(rf);
1446 break; /* End of RMW chain */
1448 /** @todo Need to be smarter here... In the linux lock
1449 * example, this will run to the beginning of the program for
1451 /** @todo The way to be smarter here is to keep going until 1
1452 * thread has a release preceded by an acquire and you've seen
1455 /* acq_rel RMW is a sufficient stopping condition */
1456 if (rf->is_acquire() && rf->is_release())
1457 return true; /* complete */
1459 rf = rf->get_reads_from();
1462 /* read from future: need to settle this later */
1464 return false; /* incomplete */
1467 if (rf->is_release())
1468 return true; /* complete */
1470 /* else relaxed write; check modification order for contiguous subsequence
1471 * -> rf must be same thread as release */
1472 int tid = id_to_int(rf->get_tid());
1473 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1474 action_list_t *list = &(*thrd_lists)[tid];
1475 action_list_t::const_reverse_iterator rit;
1477 /* Find rf in the thread list */
1478 rit = std::find(list->rbegin(), list->rend(), rf);
1479 ASSERT(rit != list->rend());
1481 /* Find the last write/release */
1482 for (; rit != list->rend(); rit++)
1483 if ((*rit)->is_release())
1485 if (rit == list->rend()) {
1486 /* No write-release in this thread */
1487 return true; /* complete */
1489 ModelAction *release = *rit;
1491 ASSERT(rf->same_thread(release));
1493 pending->writes.clear();
1495 bool certain = true;
1496 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1497 if (id_to_int(rf->get_tid()) == (int)i)
1499 list = &(*thrd_lists)[i];
1501 /* Can we ensure no future writes from this thread may break
1502 * the release seq? */
1503 bool future_ordered = false;
1505 ModelAction *last = get_last_action(int_to_id(i));
1506 Thread *th = get_thread(int_to_id(i));
1507 if ((last && rf->happens_before(last)) ||
1508 !scheduler->is_enabled(th) ||
1510 future_ordered = true;
1512 ASSERT(!th->is_model_thread() || future_ordered);
1514 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1515 const ModelAction *act = *rit;
1516 /* Reach synchronization -> this thread is complete */
1517 if (act->happens_before(release))
1519 if (rf->happens_before(act)) {
1520 future_ordered = true;
1524 /* Only non-RMW writes can break release sequences */
1525 if (!act->is_write() || act->is_rmw())
1528 /* Check modification order */
1529 if (mo_graph->checkReachable(rf, act)) {
1530 /* rf --mo--> act */
1531 future_ordered = true;
1534 if (mo_graph->checkReachable(act, release))
1535 /* act --mo--> release */
1537 if (mo_graph->checkReachable(release, act) &&
1538 mo_graph->checkReachable(act, rf)) {
1539 /* release --mo-> act --mo--> rf */
1540 return true; /* complete */
1542 /* act may break release sequence */
1543 pending->writes.push_back(act);
1546 if (!future_ordered)
1547 certain = false; /* This thread is uncertain */
1551 release_heads->push_back(release);
1552 pending->writes.clear();
1554 pending->release = release;
1561 * A public interface for getting the release sequence head(s) with which a
1562 * given ModelAction must synchronize. This function only returns a non-empty
1563 * result when it can locate a release sequence head with certainty. Otherwise,
1564 * it may mark the internal state of the ModelChecker so that it will handle
1565 * the release sequence at a later time, causing @a act to update its
1566 * synchronization at some later point in execution.
1567 * @param act The 'acquire' action that may read from a release sequence
1568 * @param release_heads A pass-by-reference return parameter. Will be filled
1569 * with the head(s) of the release sequence(s), if they exists with certainty.
1570 * @see ModelChecker::release_seq_heads
1572 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1574 const ModelAction *rf = act->get_reads_from();
1575 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
1576 sequence->acquire = act;
1578 if (!release_seq_heads(rf, release_heads, sequence)) {
1579 /* add act to 'lazy checking' list */
1580 pending_rel_seqs->push_back(sequence);
1582 snapshot_free(sequence);
1587 * Attempt to resolve all stashed operations that might synchronize with a
1588 * release sequence for a given location. This implements the "lazy" portion of
1589 * determining whether or not a release sequence was contiguous, since not all
1590 * modification order information is present at the time an action occurs.
1592 * @param location The location/object that should be checked for release
1593 * sequence resolutions. A NULL value means to check all locations.
1594 * @param work_queue The work queue to which to add work items as they are
1596 * @return True if any updates occurred (new synchronization, new mo_graph
1599 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1601 bool updated = false;
1602 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
1603 while (it != pending_rel_seqs->end()) {
1604 struct release_seq *pending = *it;
1605 ModelAction *act = pending->acquire;
1607 /* Only resolve sequences on the given location, if provided */
1608 if (location && act->get_location() != location) {
1613 const ModelAction *rf = act->get_reads_from();
1614 rel_heads_list_t release_heads;
1616 complete = release_seq_heads(rf, &release_heads, pending);
1617 for (unsigned int i = 0; i < release_heads.size(); i++) {
1618 if (!act->has_synchronized_with(release_heads[i])) {
1619 if (act->synchronize_with(release_heads[i]))
1622 set_bad_synchronization();
1627 /* Re-check all pending release sequences */
1628 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1629 /* Re-check act for mo_graph edges */
1630 work_queue->push_back(MOEdgeWorkEntry(act));
1632 /* propagate synchronization to later actions */
1633 action_list_t::reverse_iterator rit = action_trace->rbegin();
1634 for (; (*rit) != act; rit++) {
1635 ModelAction *propagate = *rit;
1636 if (act->happens_before(propagate)) {
1637 propagate->synchronize_with(act);
1638 /* Re-check 'propagate' for mo_graph edges */
1639 work_queue->push_back(MOEdgeWorkEntry(propagate));
1644 it = pending_rel_seqs->erase(it);
1645 snapshot_free(pending);
1651 // If we resolved promises or data races, see if we have realized a data race.
1652 if (checkDataRaces()) {
1660 * Performs various bookkeeping operations for the current ModelAction. For
1661 * instance, adds action to the per-object, per-thread action vector and to the
1662 * action trace list of all thread actions.
1664 * @param act is the ModelAction to add.
1666 void ModelChecker::add_action_to_lists(ModelAction *act)
1668 int tid = id_to_int(act->get_tid());
1669 action_trace->push_back(act);
1671 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1673 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1674 if (tid >= (int)vec->size())
1675 vec->resize(priv->next_thread_id);
1676 (*vec)[tid].push_back(act);
1678 if ((int)thrd_last_action->size() <= tid)
1679 thrd_last_action->resize(get_num_threads());
1680 (*thrd_last_action)[tid] = act;
1682 if (act->is_wait()) {
1683 void *mutex_loc=(void *) act->get_value();
1684 obj_map->get_safe_ptr(mutex_loc)->push_back(act);
1686 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(mutex_loc);
1687 if (tid >= (int)vec->size())
1688 vec->resize(priv->next_thread_id);
1689 (*vec)[tid].push_back(act);
1691 if ((int)thrd_last_action->size() <= tid)
1692 thrd_last_action->resize(get_num_threads());
1693 (*thrd_last_action)[tid] = act;
1698 * @brief Get the last action performed by a particular Thread
1699 * @param tid The thread ID of the Thread in question
1700 * @return The last action in the thread
1702 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1704 int threadid = id_to_int(tid);
1705 if (threadid < (int)thrd_last_action->size())
1706 return (*thrd_last_action)[id_to_int(tid)];
1712 * Gets the last memory_order_seq_cst write (in the total global sequence)
1713 * performed on a particular object (i.e., memory location), not including the
1715 * @param curr The current ModelAction; also denotes the object location to
1717 * @return The last seq_cst write
1719 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1721 void *location = curr->get_location();
1722 action_list_t *list = obj_map->get_safe_ptr(location);
1723 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1724 action_list_t::reverse_iterator rit;
1725 for (rit = list->rbegin(); rit != list->rend(); rit++)
1726 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1732 * Gets the last unlock operation performed on a particular mutex (i.e., memory
1733 * location). This function identifies the mutex according to the current
1734 * action, which is presumed to perform on the same mutex.
1735 * @param curr The current ModelAction; also denotes the object location to
1737 * @return The last unlock operation
1739 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1741 void *location = curr->get_location();
1742 action_list_t *list = obj_map->get_safe_ptr(location);
1743 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1744 action_list_t::reverse_iterator rit;
1745 for (rit = list->rbegin(); rit != list->rend(); rit++)
1746 if ((*rit)->is_unlock() || (*rit)->is_wait())
1751 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1753 ModelAction *parent = get_last_action(tid);
1755 parent = get_thread(tid)->get_creation();
1760 * Returns the clock vector for a given thread.
1761 * @param tid The thread whose clock vector we want
1762 * @return Desired clock vector
1764 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1766 return get_parent_action(tid)->get_cv();
1770 * Resolve a set of Promises with a current write. The set is provided in the
1771 * Node corresponding to @a write.
1772 * @param write The ModelAction that is fulfilling Promises
1773 * @return True if promises were resolved; false otherwise
1775 bool ModelChecker::resolve_promises(ModelAction *write)
1777 bool resolved = false;
1778 std::vector< thread_id_t, ModelAlloc<thread_id_t> > threads_to_check;
1780 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1781 Promise *promise = (*promises)[promise_index];
1782 if (write->get_node()->get_promise(i)) {
1783 ModelAction *read = promise->get_action();
1784 if (read->is_rmw()) {
1785 mo_graph->addRMWEdge(write, read);
1787 read->read_from(write);
1788 //First fix up the modification order for actions that happened
1790 r_modification_order(read, write);
1791 //Next fix up the modification order for actions that happened
1793 post_r_modification_order(read, write);
1794 //Make sure the promise's value matches the write's value
1795 ASSERT(promise->get_value() == write->get_value());
1798 promises->erase(promises->begin() + promise_index);
1799 threads_to_check.push_back(read->get_tid());
1806 //Check whether reading these writes has made threads unable to
1809 for(unsigned int i=0;i<threads_to_check.size();i++)
1810 mo_check_promises(threads_to_check[i], write);
1816 * Compute the set of promises that could potentially be satisfied by this
1817 * action. Note that the set computation actually appears in the Node, not in
1819 * @param curr The ModelAction that may satisfy promises
1821 void ModelChecker::compute_promises(ModelAction *curr)
1823 for (unsigned int i = 0; i < promises->size(); i++) {
1824 Promise *promise = (*promises)[i];
1825 const ModelAction *act = promise->get_action();
1826 if (!act->happens_before(curr) &&
1828 !act->could_synchronize_with(curr) &&
1829 !act->same_thread(curr) &&
1830 act->get_location() == curr->get_location() &&
1831 promise->get_value() == curr->get_value()) {
1832 curr->get_node()->set_promise(i);
1837 /** Checks promises in response to change in ClockVector Threads. */
1838 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
1840 for (unsigned int i = 0; i < promises->size(); i++) {
1841 Promise *promise = (*promises)[i];
1842 const ModelAction *act = promise->get_action();
1843 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1844 merge_cv->synchronized_since(act)) {
1845 if (promise->increment_threads(tid)) {
1846 //Promise has failed
1847 failed_promise = true;
1854 /** Checks promises in response to addition to modification order for threads.
1856 * pthread is the thread that performed the read that created the promise
1858 * pread is the read that created the promise
1860 * pwrite is either the first write to same location as pread by
1861 * pthread that is sequenced after pread or the value read by the
1862 * first read to the same lcoation as pread by pthread that is
1863 * sequenced after pread..
1865 * 1. If tid=pthread, then we check what other threads are reachable
1866 * through the mode order starting with pwrite. Those threads cannot
1867 * perform a write that will resolve the promise due to modification
1868 * order constraints.
1870 * 2. If the tid is not pthread, we check whether pwrite can reach the
1871 * action write through the modification order. If so, that thread
1872 * cannot perform a future write that will resolve the promise due to
1873 * modificatin order constraints.
1875 * @parem tid The thread that either read from the model action
1876 * write, or actually did the model action write.
1878 * @parem write The ModelAction representing the relevant write.
1881 void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write) {
1882 void * location = write->get_location();
1883 for (unsigned int i = 0; i < promises->size(); i++) {
1884 Promise *promise = (*promises)[i];
1885 const ModelAction *act = promise->get_action();
1887 //Is this promise on the same location?
1888 if ( act->get_location() != location )
1891 //same thread as the promise
1892 if ( act->get_tid()==tid ) {
1894 //do we have a pwrite for the promise, if not, set it
1895 if (promise->get_write() == NULL ) {
1896 promise->set_write(write);
1897 //The pwrite cannot happen before the promise
1898 if (write->happens_before(act) && (write != act)) {
1899 failed_promise = true;
1903 if (mo_graph->checkPromise(write, promise)) {
1904 failed_promise = true;
1909 //Don't do any lookups twice for the same thread
1910 if (promise->has_sync_thread(tid))
1913 if (mo_graph->checkReachable(promise->get_write(), write)) {
1914 if (promise->increment_threads(tid)) {
1915 failed_promise = true;
1923 * Compute the set of writes that may break the current pending release
1924 * sequence. This information is extracted from previou release sequence
1927 * @param curr The current ModelAction. Must be a release sequence fixup
1930 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
1932 if (pending_rel_seqs->empty())
1935 struct release_seq *pending = pending_rel_seqs->back();
1936 for (unsigned int i = 0; i < pending->writes.size(); i++) {
1937 const ModelAction *write = pending->writes[i];
1938 curr->get_node()->add_relseq_break(write);
1941 /* NULL means don't break the sequence; just synchronize */
1942 curr->get_node()->add_relseq_break(NULL);
1946 * Build up an initial set of all past writes that this 'read' action may read
1947 * from. This set is determined by the clock vector's "happens before"
1949 * @param curr is the current ModelAction that we are exploring; it must be a
1952 void ModelChecker::build_reads_from_past(ModelAction *curr)
1954 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1956 ASSERT(curr->is_read());
1958 ModelAction *last_seq_cst = NULL;
1960 /* Track whether this object has been initialized */
1961 bool initialized = false;
1963 if (curr->is_seqcst()) {
1964 last_seq_cst = get_last_seq_cst(curr);
1965 /* We have to at least see the last sequentially consistent write,
1966 so we are initialized. */
1967 if (last_seq_cst != NULL)
1971 /* Iterate over all threads */
1972 for (i = 0; i < thrd_lists->size(); i++) {
1973 /* Iterate over actions in thread, starting from most recent */
1974 action_list_t *list = &(*thrd_lists)[i];
1975 action_list_t::reverse_iterator rit;
1976 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1977 ModelAction *act = *rit;
1979 /* Only consider 'write' actions */
1980 if (!act->is_write() || act == curr)
1983 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1984 if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1985 DEBUG("Adding action to may_read_from:\n");
1986 if (DBG_ENABLED()) {
1991 if (curr->get_sleep_flag() && ! curr->is_seqcst()) {
1992 if (sleep_can_read_from(curr, act))
1993 curr->get_node()->add_read_from(act);
1995 curr->get_node()->add_read_from(act);
1998 /* Include at most one act per-thread that "happens before" curr */
1999 if (act->happens_before(curr)) {
2007 /** @todo Need a more informative way of reporting errors. */
2008 printf("ERROR: may read from uninitialized atomic\n");
2012 if (DBG_ENABLED() || !initialized) {
2013 printf("Reached read action:\n");
2015 printf("Printing may_read_from\n");
2016 curr->get_node()->print_may_read_from();
2017 printf("End printing may_read_from\n");
2021 bool ModelChecker::sleep_can_read_from(ModelAction * curr, const ModelAction *write) {
2023 Node *prevnode=write->get_node()->get_parent();
2024 bool thread_sleep=prevnode->get_enabled_array()[id_to_int(curr->get_tid())]==THREAD_SLEEP_SET;
2025 if (write->is_release()&&thread_sleep)
2027 if (!write->is_rmw()) {
2030 if (write->get_reads_from()==NULL)
2032 write=write->get_reads_from();
2036 static void print_list(action_list_t *list)
2038 action_list_t::iterator it;
2040 printf("---------------------------------------------------------------------\n");
2042 unsigned int hash=0;
2044 for (it = list->begin(); it != list->end(); it++) {
2046 hash=hash^(hash<<3)^((*it)->hash());
2048 printf("HASH %u\n", hash);
2049 printf("---------------------------------------------------------------------\n");
2052 #if SUPPORT_MOD_ORDER_DUMP
2053 void ModelChecker::dumpGraph(char *filename) {
2055 sprintf(buffer, "%s.dot",filename);
2056 FILE *file=fopen(buffer, "w");
2057 fprintf(file, "digraph %s {\n",filename);
2058 mo_graph->dumpNodes(file);
2059 ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
2061 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2062 ModelAction *action=*it;
2063 if (action->is_read()) {
2064 fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
2065 if (action->get_reads_from()!=NULL)
2066 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
2068 if (thread_array[action->get_tid()] != NULL) {
2069 fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
2072 thread_array[action->get_tid()]=action;
2074 fprintf(file,"}\n");
2075 model_free(thread_array);
2080 void ModelChecker::print_summary()
2083 printf("Number of executions: %d\n", num_executions);
2084 printf("Number of feasible executions: %d\n", num_feasible_executions);
2085 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
2087 #if SUPPORT_MOD_ORDER_DUMP
2089 char buffername[100];
2090 sprintf(buffername, "exec%04u", num_executions);
2091 mo_graph->dumpGraphToFile(buffername);
2092 sprintf(buffername, "graph%04u", num_executions);
2093 dumpGraph(buffername);
2096 if (!isfinalfeasible())
2097 printf("INFEASIBLE EXECUTION!\n");
2098 print_list(action_trace);
2103 * Add a Thread to the system for the first time. Should only be called once
2105 * @param t The Thread to add
2107 void ModelChecker::add_thread(Thread *t)
2109 thread_map->put(id_to_int(t->get_id()), t);
2110 scheduler->add_thread(t);
2114 * Removes a thread from the scheduler.
2115 * @param the thread to remove.
2117 void ModelChecker::remove_thread(Thread *t)
2119 scheduler->remove_thread(t);
2123 * @brief Get a Thread reference by its ID
2124 * @param tid The Thread's ID
2125 * @return A Thread reference
2127 Thread * ModelChecker::get_thread(thread_id_t tid) const
2129 return thread_map->get(id_to_int(tid));
2133 * @brief Get a reference to the Thread in which a ModelAction was executed
2134 * @param act The ModelAction
2135 * @return A Thread reference
2137 Thread * ModelChecker::get_thread(ModelAction *act) const
2139 return get_thread(act->get_tid());
2143 * Switch from a user-context to the "master thread" context (a.k.a. system
2144 * context). This switch is made with the intention of exploring a particular
2145 * model-checking action (described by a ModelAction object). Must be called
2146 * from a user-thread context.
2148 * @param act The current action that will be explored. May be NULL only if
2149 * trace is exiting via an assertion (see ModelChecker::set_assert and
2150 * ModelChecker::has_asserted).
2151 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
2153 int ModelChecker::switch_to_master(ModelAction *act)
2156 Thread *old = thread_current();
2157 set_current_action(act);
2158 old->set_state(THREAD_READY);
2159 return Thread::swap(old, &system_context);
2163 * Takes the next step in the execution, if possible.
2164 * @return Returns true (success) if a step was taken and false otherwise.
2166 bool ModelChecker::take_step() {
2170 Thread *curr = priv->current_action ? get_thread(priv->current_action) : NULL;
2172 if (curr->get_state() == THREAD_READY) {
2173 ASSERT(priv->current_action);
2175 priv->nextThread = check_current_action(priv->current_action);
2176 priv->current_action = NULL;
2178 if (curr->is_blocked() || curr->is_complete())
2179 scheduler->remove_thread(curr);
2184 Thread *next = scheduler->next_thread(priv->nextThread);
2186 /* Infeasible -> don't take any more steps */
2190 if (params.bound != 0) {
2191 if (priv->used_sequence_numbers > params.bound) {
2196 DEBUG("(%d, %d)\n", curr ? id_to_int(curr->get_id()) : -1,
2197 next ? id_to_int(next->get_id()) : -1);
2200 * Launch end-of-execution release sequence fixups only when there are:
2202 * (1) no more user threads to run (or when execution replay chooses
2203 * the 'model_thread')
2204 * (2) pending release sequences
2205 * (3) pending assertions (i.e., data races)
2206 * (4) no pending promises
2208 if (!pending_rel_seqs->empty() && (!next || next->is_model_thread()) &&
2209 isfinalfeasible() && !unrealizedraces.empty()) {
2210 printf("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
2211 pending_rel_seqs->size());
2212 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2213 std::memory_order_seq_cst, NULL, VALUE_NONE,
2215 set_current_action(fixup);
2219 /* next == NULL -> don't take any more steps */
2223 next->set_state(THREAD_RUNNING);
2225 if (next->get_pending() != NULL) {
2226 /* restart a pending action */
2227 set_current_action(next->get_pending());
2228 next->set_pending(NULL);
2229 next->set_state(THREAD_READY);
2233 /* Return false only if swap fails with an error */
2234 return (Thread::swap(&system_context, next) == 0);
2237 /** Runs the current execution until threre are no more steps to take. */
2238 void ModelChecker::finish_execution() {
2241 while (take_step());