8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
16 #define INITIAL_THREAD_ID 0
20 /** @brief Constructor */
21 ModelChecker::ModelChecker(struct model_params params) :
22 /* Initialize default scheduler */
23 scheduler(new Scheduler()),
25 num_feasible_executions(0),
28 action_trace(new action_list_t()),
29 thread_map(new HashTable<int, Thread *, int>()),
30 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
31 lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
32 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
33 promises(new std::vector<Promise *>()),
34 futurevalues(new std::vector<struct PendingFutureValue>()),
35 lazy_sync_with_release(new HashTable<void *, action_list_t, uintptr_t, 4>()),
36 thrd_last_action(new std::vector<ModelAction *>(1)),
37 node_stack(new NodeStack()),
38 mo_graph(new CycleGraph()),
39 failed_promise(false),
40 too_many_reads(false),
43 /* Allocate this "size" on the snapshotting heap */
44 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
45 /* First thread created will have id INITIAL_THREAD_ID */
46 priv->next_thread_id = INITIAL_THREAD_ID;
48 lazy_sync_size = &priv->lazy_sync_size;
51 /** @brief Destructor */
52 ModelChecker::~ModelChecker()
54 for (int i = 0; i < get_num_threads(); i++)
55 delete thread_map->get(i);
60 delete lock_waiters_map;
63 for (unsigned int i = 0; i < promises->size(); i++)
64 delete (*promises)[i];
67 delete lazy_sync_with_release;
69 delete thrd_last_action;
76 * Restores user program to initial state and resets all model-checker data
79 void ModelChecker::reset_to_initial_state()
81 DEBUG("+++ Resetting to initial state +++\n");
82 node_stack->reset_execution();
83 failed_promise = false;
84 too_many_reads = false;
86 snapshotObject->backTrackBeforeStep(0);
89 /** @return a thread ID for a new Thread */
90 thread_id_t ModelChecker::get_next_id()
92 return priv->next_thread_id++;
95 /** @return the number of user threads created during this execution */
96 int ModelChecker::get_num_threads()
98 return priv->next_thread_id;
101 /** @return a sequence number for a new ModelAction */
102 modelclock_t ModelChecker::get_next_seq_num()
104 return ++priv->used_sequence_numbers;
108 * @brief Choose the next thread to execute.
110 * This function chooses the next thread that should execute. It can force the
111 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
112 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
113 * The model-checker may have no preference regarding the next thread (i.e.,
114 * when exploring a new execution ordering), in which case this will return
116 * @param curr The current ModelAction. This action might guide the choice of
118 * @return The next thread to run. If the model-checker has no preference, NULL.
120 Thread * ModelChecker::get_next_thread(ModelAction *curr)
125 /* Do not split atomic actions. */
127 return thread_current();
128 /* The THREAD_CREATE action points to the created Thread */
129 else if (curr->get_type() == THREAD_CREATE)
130 return (Thread *)curr->get_location();
133 /* Have we completed exploring the preselected path? */
137 /* Else, we are trying to replay an execution */
138 ModelAction *next = node_stack->get_next()->get_action();
140 if (next == diverge) {
141 Node *nextnode = next->get_node();
142 /* Reached divergence point */
143 if (nextnode->increment_promise()) {
144 /* The next node will try to satisfy a different set of promises. */
145 tid = next->get_tid();
146 node_stack->pop_restofstack(2);
147 } else if (nextnode->increment_read_from()) {
148 /* The next node will read from a different value. */
149 tid = next->get_tid();
150 node_stack->pop_restofstack(2);
151 } else if (nextnode->increment_future_value()) {
152 /* The next node will try to read from a different future value. */
153 tid = next->get_tid();
154 node_stack->pop_restofstack(2);
156 /* Make a different thread execute for next step */
157 Node *node = nextnode->get_parent();
158 tid = node->get_next_backtrack();
159 node_stack->pop_restofstack(1);
161 DEBUG("*** Divergence point ***\n");
164 tid = next->get_tid();
166 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
167 ASSERT(tid != THREAD_ID_T_NONE);
168 return thread_map->get(id_to_int(tid));
172 * Queries the model-checker for more executions to explore and, if one
173 * exists, resets the model-checker state to execute a new execution.
175 * @return If there are more executions to explore, return true. Otherwise,
178 bool ModelChecker::next_execution()
183 if (isfinalfeasible())
184 num_feasible_executions++;
186 if (isfinalfeasible() || DBG_ENABLED())
189 if ((diverge = get_next_backtrack()) == NULL)
193 printf("Next execution will diverge at:\n");
197 reset_to_initial_state();
201 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
203 switch (act->get_type()) {
207 /* linear search: from most recent to oldest */
208 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
209 action_list_t::reverse_iterator rit;
210 for (rit = list->rbegin(); rit != list->rend(); rit++) {
211 ModelAction *prev = *rit;
212 if (act->is_synchronizing(prev))
218 case ATOMIC_TRYLOCK: {
219 /* linear search: from most recent to oldest */
220 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
221 action_list_t::reverse_iterator rit;
222 for (rit = list->rbegin(); rit != list->rend(); rit++) {
223 ModelAction *prev = *rit;
224 if (act->is_conflicting_lock(prev))
229 case ATOMIC_UNLOCK: {
230 /* linear search: from most recent to oldest */
231 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
232 action_list_t::reverse_iterator rit;
233 for (rit = list->rbegin(); rit != list->rend(); rit++) {
234 ModelAction *prev = *rit;
235 if (!act->same_thread(prev)&&prev->is_failed_trylock())
246 /** This method find backtracking points where we should try to
247 * reorder the parameter ModelAction against.
249 * @param the ModelAction to find backtracking points for.
253 void ModelChecker::set_backtracking(ModelAction *act)
255 Thread *t = get_thread(act);
256 ModelAction * prev = get_last_conflict(act);
260 Node * node = prev->get_node()->get_parent();
262 int low_tid, high_tid;
263 if (node->is_enabled(t)) {
264 low_tid = id_to_int(act->get_tid());
265 high_tid = low_tid+1;
268 high_tid = get_num_threads();
271 for(int i = low_tid; i < high_tid; i++) {
272 thread_id_t tid = int_to_id(i);
273 if (!node->is_enabled(tid))
276 /* Check if this has been explored already */
277 if (node->has_been_explored(tid))
280 /* Cache the latest backtracking point */
281 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
282 priv->next_backtrack = prev;
284 /* If this is a new backtracking point, mark the tree */
285 if (!node->set_backtrack(tid))
287 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
288 prev->get_tid(), t->get_id());
297 * Returns last backtracking point. The model checker will explore a different
298 * path for this point in the next execution.
299 * @return The ModelAction at which the next execution should diverge.
301 ModelAction * ModelChecker::get_next_backtrack()
303 ModelAction *next = priv->next_backtrack;
304 priv->next_backtrack = NULL;
309 * Processes a read or rmw model action.
310 * @param curr is the read model action to process.
311 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
312 * @return True if processing this read updates the mo_graph.
314 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
317 bool updated = false;
319 const ModelAction *reads_from = curr->get_node()->get_read_from();
320 if (reads_from != NULL) {
321 mo_graph->startChanges();
323 value = reads_from->get_value();
324 bool r_status = false;
326 if (!second_part_of_rmw) {
328 r_status = r_modification_order(curr, reads_from);
332 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
333 mo_graph->rollbackChanges();
334 too_many_reads = false;
338 curr->read_from(reads_from);
339 mo_graph->commitChanges();
341 } else if (!second_part_of_rmw) {
342 /* Read from future value */
343 value = curr->get_node()->get_future_value();
344 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
345 curr->read_from(NULL);
346 Promise *valuepromise = new Promise(curr, value, expiration);
347 promises->push_back(valuepromise);
349 get_thread(curr)->set_return_value(value);
355 * Processes a lock, trylock, or unlock model action. @param curr is
356 * the read model action to process.
358 * The try lock operation checks whether the lock is taken. If not,
359 * it falls to the normal lock operation case. If so, it returns
362 * The lock operation has already been checked that it is enabled, so
363 * it just grabs the lock and synchronizes with the previous unlock.
365 * The unlock operation has to re-enable all of the threads that are
366 * waiting on the lock.
368 void ModelChecker::process_mutex(ModelAction *curr) {
369 std::mutex *mutex = (std::mutex *)curr->get_location();
370 struct std::mutex_state *state = mutex->get_state();
371 switch (curr->get_type()) {
372 case ATOMIC_TRYLOCK: {
373 bool success = !state->islocked;
374 curr->set_try_lock(success);
376 get_thread(curr)->set_return_value(0);
379 get_thread(curr)->set_return_value(1);
381 //otherwise fall into the lock case
383 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
384 printf("Lock access before initialization\n");
387 state->islocked = true;
388 ModelAction *unlock = get_last_unlock(curr);
389 //synchronize with the previous unlock statement
391 curr->synchronize_with(unlock);
394 case ATOMIC_UNLOCK: {
396 state->islocked = false;
397 //wake up the other threads
398 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
399 //activate all the waiting threads
400 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
401 scheduler->add_thread(get_thread((*rit)->get_tid()));
412 * Process a write ModelAction
413 * @param curr The ModelAction to process
414 * @return True if the mo_graph was updated or promises were resolved
416 bool ModelChecker::process_write(ModelAction *curr)
418 bool updated_mod_order = w_modification_order(curr);
419 bool updated_promises = resolve_promises(curr);
421 if (promises->size() == 0) {
422 for (unsigned int i = 0; i < futurevalues->size(); i++) {
423 struct PendingFutureValue pfv = (*futurevalues)[i];
424 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
425 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
426 priv->next_backtrack = pfv.act;
428 futurevalues->resize(0);
431 mo_graph->commitChanges();
432 get_thread(curr)->set_return_value(VALUE_NONE);
433 return updated_mod_order || updated_promises;
437 * Initialize the current action by performing one or more of the following
438 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
439 * in the NodeStack, manipulating backtracking sets, allocating and
440 * initializing clock vectors, and computing the promises to fulfill.
442 * @param curr The current action, as passed from the user context; may be
443 * freed/invalidated after the execution of this function
444 * @return The current action, as processed by the ModelChecker. Is only the
445 * same as the parameter @a curr if this is a newly-explored action.
447 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
449 ModelAction *newcurr;
451 if (curr->is_rmwc() || curr->is_rmw()) {
452 newcurr = process_rmw(curr);
454 compute_promises(newcurr);
458 newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
460 /* First restore type and order in case of RMW operation */
462 newcurr->copy_typeandorder(curr);
464 ASSERT(curr->get_location() == newcurr->get_location());
465 newcurr->copy_from_new(curr);
467 /* Discard duplicate ModelAction; use action from NodeStack */
470 /* If we have diverged, we need to reset the clock vector. */
472 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
476 * Perform one-time actions when pushing new ModelAction onto
479 curr->create_cv(get_parent_action(curr->get_tid()));
480 if (curr->is_write())
481 compute_promises(curr);
487 * This method checks whether a model action is enabled at the given point.
488 * At this point, it checks whether a lock operation would be successful at this point.
489 * If not, it puts the thread in a waiter list.
490 * @param curr is the ModelAction to check whether it is enabled.
491 * @return a bool that indicates whether the action is enabled.
494 bool ModelChecker::check_action_enabled(ModelAction *curr) {
495 if (curr->is_lock()) {
496 std::mutex * lock = (std::mutex *)curr->get_location();
497 struct std::mutex_state * state = lock->get_state();
498 if (state->islocked) {
499 //Stick the action in the appropriate waiting queue
500 lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
509 * This is the heart of the model checker routine. It performs model-checking
510 * actions corresponding to a given "current action." Among other processes, it
511 * calculates reads-from relationships, updates synchronization clock vectors,
512 * forms a memory_order constraints graph, and handles replay/backtrack
513 * execution when running permutations of previously-observed executions.
515 * @param curr The current action to process
516 * @return The next Thread that must be executed. May be NULL if ModelChecker
517 * makes no choice (e.g., according to replay execution, combining RMW actions,
520 Thread * ModelChecker::check_current_action(ModelAction *curr)
524 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
526 if (!check_action_enabled(curr)) {
527 //we'll make the execution look like we chose to run this action
528 //much later...when a lock is actually available to relese
529 get_current_thread()->set_pending(curr);
530 remove_thread(get_current_thread());
531 return get_next_thread(NULL);
534 ModelAction *newcurr = initialize_curr_action(curr);
536 /* Add the action to lists before any other model-checking tasks */
537 if (!second_part_of_rmw)
538 add_action_to_lists(newcurr);
540 /* Build may_read_from set for newly-created actions */
541 if (curr == newcurr && curr->is_read())
542 build_reads_from_past(curr);
545 /* Thread specific actions */
546 switch (curr->get_type()) {
547 case THREAD_CREATE: {
548 Thread *th = (Thread *)curr->get_location();
549 th->set_creation(curr);
553 Thread *waiting, *blocking;
554 waiting = get_thread(curr);
555 blocking = (Thread *)curr->get_location();
556 if (!blocking->is_complete()) {
557 blocking->push_wait_list(curr);
558 scheduler->sleep(waiting);
560 do_complete_join(curr);
564 case THREAD_FINISH: {
565 Thread *th = get_thread(curr);
566 while (!th->wait_list_empty()) {
567 ModelAction *act = th->pop_wait_list();
568 Thread *wake = get_thread(act);
569 scheduler->wake(wake);
570 do_complete_join(act);
576 check_promises(NULL, curr->get_cv());
583 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
585 while (!work_queue.empty()) {
586 WorkQueueEntry work = work_queue.front();
587 work_queue.pop_front();
590 case WORK_CHECK_CURR_ACTION: {
591 ModelAction *act = work.action;
592 bool updated = false;
593 if (act->is_read() && process_read(act, second_part_of_rmw))
596 if (act->is_write() && process_write(act))
599 if (act->is_mutex_op())
603 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
606 case WORK_CHECK_RELEASE_SEQ:
607 resolve_release_sequences(work.location, &work_queue);
609 case WORK_CHECK_MO_EDGES: {
610 /** @todo Complete verification of work_queue */
611 ModelAction *act = work.action;
612 bool updated = false;
614 if (act->is_read()) {
615 if (r_modification_order(act, act->get_reads_from()))
618 if (act->is_write()) {
619 if (w_modification_order(act))
624 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
633 check_curr_backtracking(curr);
635 set_backtracking(curr);
637 return get_next_thread(curr);
641 * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
642 * operation from the Thread it is joining with. Must be called after the
643 * completion of the Thread in question.
644 * @param join The THREAD_JOIN action
646 void ModelChecker::do_complete_join(ModelAction *join)
648 Thread *blocking = (Thread *)join->get_location();
649 ModelAction *act = get_last_action(blocking->get_id());
650 join->synchronize_with(act);
653 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
654 Node *currnode = curr->get_node();
655 Node *parnode = currnode->get_parent();
657 if ((!parnode->backtrack_empty() ||
658 !currnode->read_from_empty() ||
659 !currnode->future_value_empty() ||
660 !currnode->promise_empty())
661 && (!priv->next_backtrack ||
662 *curr > *priv->next_backtrack)) {
663 priv->next_backtrack = curr;
667 bool ModelChecker::promises_expired() {
668 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
669 Promise *promise = (*promises)[promise_index];
670 if (promise->get_expiration()<priv->used_sequence_numbers) {
677 /** @return whether the current partial trace must be a prefix of a
679 bool ModelChecker::isfeasibleprefix() {
680 return promises->size() == 0 && *lazy_sync_size == 0;
683 /** @return whether the current partial trace is feasible. */
684 bool ModelChecker::isfeasible() {
685 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
688 /** @return whether the current partial trace is feasible other than
689 * multiple RMW reading from the same store. */
690 bool ModelChecker::isfeasibleotherthanRMW() {
692 if (mo_graph->checkForCycles())
693 DEBUG("Infeasible: modification order cycles\n");
695 DEBUG("Infeasible: failed promise\n");
697 DEBUG("Infeasible: too many reads\n");
698 if (promises_expired())
699 DEBUG("Infeasible: promises expired\n");
701 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
704 /** Returns whether the current completed trace is feasible. */
705 bool ModelChecker::isfinalfeasible() {
706 if (DBG_ENABLED() && promises->size() != 0)
707 DEBUG("Infeasible: unrevolved promises\n");
709 return isfeasible() && promises->size() == 0;
712 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
713 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
714 int tid = id_to_int(act->get_tid());
715 ModelAction *lastread = get_last_action(tid);
716 lastread->process_rmw(act);
717 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
718 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
719 mo_graph->commitChanges();
725 * Checks whether a thread has read from the same write for too many times
726 * without seeing the effects of a later write.
729 * 1) there must a different write that we could read from that would satisfy the modification order,
730 * 2) we must have read from the same value in excess of maxreads times, and
731 * 3) that other write must have been in the reads_from set for maxreads times.
733 * If so, we decide that the execution is no longer feasible.
735 void ModelChecker::check_recency(ModelAction *curr) {
736 if (params.maxreads != 0) {
737 if (curr->get_node()->get_read_from_size() <= 1)
740 //Must make sure that execution is currently feasible... We could
741 //accidentally clear by rolling back
745 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
746 int tid = id_to_int(curr->get_tid());
749 if ((int)thrd_lists->size() <= tid)
752 action_list_t *list = &(*thrd_lists)[tid];
754 action_list_t::reverse_iterator rit = list->rbegin();
756 for (; (*rit) != curr; rit++)
758 /* go past curr now */
761 action_list_t::reverse_iterator ritcopy = rit;
762 //See if we have enough reads from the same value
764 for (; count < params.maxreads; rit++,count++) {
765 if (rit==list->rend())
767 ModelAction *act = *rit;
770 if (act->get_reads_from() != curr->get_reads_from())
772 if (act->get_node()->get_read_from_size() <= 1)
776 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
778 const ModelAction * write = curr->get_node()->get_read_from_at(i);
779 //Need a different write
780 if (write==curr->get_reads_from())
783 /* Test to see whether this is a feasible write to read from*/
784 mo_graph->startChanges();
785 r_modification_order(curr, write);
786 bool feasiblereadfrom = isfeasible();
787 mo_graph->rollbackChanges();
789 if (!feasiblereadfrom)
793 bool feasiblewrite = true;
794 //new we need to see if this write works for everyone
796 for (int loop = count; loop>0; loop--,rit++) {
797 ModelAction *act=*rit;
798 bool foundvalue = false;
799 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
800 if (act->get_node()->get_read_from_at(i)==write) {
806 feasiblewrite = false;
811 too_many_reads = true;
819 * Updates the mo_graph with the constraints imposed from the current
822 * Basic idea is the following: Go through each other thread and find
823 * the lastest action that happened before our read. Two cases:
825 * (1) The action is a write => that write must either occur before
826 * the write we read from or be the write we read from.
828 * (2) The action is a read => the write that that action read from
829 * must occur before the write we read from or be the same write.
831 * @param curr The current action. Must be a read.
832 * @param rf The action that curr reads from. Must be a write.
833 * @return True if modification order edges were added; false otherwise
835 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
837 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
840 ASSERT(curr->is_read());
842 /* Iterate over all threads */
843 for (i = 0; i < thrd_lists->size(); i++) {
844 /* Iterate over actions in thread, starting from most recent */
845 action_list_t *list = &(*thrd_lists)[i];
846 action_list_t::reverse_iterator rit;
847 for (rit = list->rbegin(); rit != list->rend(); rit++) {
848 ModelAction *act = *rit;
851 * Include at most one act per-thread that "happens
852 * before" curr. Don't consider reflexively.
854 if (act->happens_before(curr) && act != curr) {
855 if (act->is_write()) {
857 mo_graph->addEdge(act, rf);
861 const ModelAction *prevreadfrom = act->get_reads_from();
862 if (prevreadfrom != NULL && rf != prevreadfrom) {
863 mo_graph->addEdge(prevreadfrom, rf);
875 /** This method fixes up the modification order when we resolve a
876 * promises. The basic problem is that actions that occur after the
877 * read curr could not property add items to the modification order
880 * So for each thread, we find the earliest item that happens after
881 * the read curr. This is the item we have to fix up with additional
882 * constraints. If that action is write, we add a MO edge between
883 * the Action rf and that action. If the action is a read, we add a
884 * MO edge between the Action rf, and whatever the read accessed.
886 * @param curr is the read ModelAction that we are fixing up MO edges for.
887 * @param rf is the write ModelAction that curr reads from.
891 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
893 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
895 ASSERT(curr->is_read());
897 /* Iterate over all threads */
898 for (i = 0; i < thrd_lists->size(); i++) {
899 /* Iterate over actions in thread, starting from most recent */
900 action_list_t *list = &(*thrd_lists)[i];
901 action_list_t::reverse_iterator rit;
902 ModelAction *lastact = NULL;
904 /* Find last action that happens after curr */
905 for (rit = list->rbegin(); rit != list->rend(); rit++) {
906 ModelAction *act = *rit;
907 if (curr->happens_before(act)) {
913 /* Include at most one act per-thread that "happens before" curr */
914 if (lastact != NULL) {
915 if (lastact->is_read()) {
916 const ModelAction *postreadfrom = lastact->get_reads_from();
917 if (postreadfrom != NULL&&rf != postreadfrom)
918 mo_graph->addEdge(rf, postreadfrom);
919 } else if (rf != lastact) {
920 mo_graph->addEdge(rf, lastact);
928 * Updates the mo_graph with the constraints imposed from the current write.
930 * Basic idea is the following: Go through each other thread and find
931 * the lastest action that happened before our write. Two cases:
933 * (1) The action is a write => that write must occur before
936 * (2) The action is a read => the write that that action read from
937 * must occur before the current write.
939 * This method also handles two other issues:
941 * (I) Sequential Consistency: Making sure that if the current write is
942 * seq_cst, that it occurs after the previous seq_cst write.
944 * (II) Sending the write back to non-synchronizing reads.
946 * @param curr The current action. Must be a write.
947 * @return True if modification order edges were added; false otherwise
949 bool ModelChecker::w_modification_order(ModelAction *curr)
951 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
954 ASSERT(curr->is_write());
956 if (curr->is_seqcst()) {
957 /* We have to at least see the last sequentially consistent write,
958 so we are initialized. */
959 ModelAction *last_seq_cst = get_last_seq_cst(curr);
960 if (last_seq_cst != NULL) {
961 mo_graph->addEdge(last_seq_cst, curr);
966 /* Iterate over all threads */
967 for (i = 0; i < thrd_lists->size(); i++) {
968 /* Iterate over actions in thread, starting from most recent */
969 action_list_t *list = &(*thrd_lists)[i];
970 action_list_t::reverse_iterator rit;
971 for (rit = list->rbegin(); rit != list->rend(); rit++) {
972 ModelAction *act = *rit;
975 * If RMW, we already have all relevant edges,
976 * so just skip to next thread.
977 * If normal write, we need to look at earlier
978 * actions, so continue processing list.
987 * Include at most one act per-thread that "happens
990 if (act->happens_before(curr)) {
992 * Note: if act is RMW, just add edge:
994 * The following edge should be handled elsewhere:
995 * readfrom(act) --mo--> act
998 mo_graph->addEdge(act, curr);
999 else if (act->is_read() && act->get_reads_from() != NULL)
1000 mo_graph->addEdge(act->get_reads_from(), curr);
1003 } else if (act->is_read() && !act->is_synchronizing(curr) &&
1004 !act->same_thread(curr)) {
1005 /* We have an action that:
1006 (1) did not happen before us
1007 (2) is a read and we are a write
1008 (3) cannot synchronize with us
1009 (4) is in a different thread
1011 that read could potentially read from our write.
1013 if (thin_air_constraint_may_allow(curr, act)) {
1015 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1016 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1017 futurevalues->push_back(pfv);
1027 /** Arbitrary reads from the future are not allowed. Section 29.3
1028 * part 9 places some constraints. This method checks one result of constraint
1029 * constraint. Others require compiler support. */
1031 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1032 if (!writer->is_rmw())
1035 if (!reader->is_rmw())
1038 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1039 if (search == reader)
1041 if (search->get_tid() == reader->get_tid() &&
1042 search->happens_before(reader))
1050 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1051 * The ModelAction under consideration is expected to be taking part in
1052 * release/acquire synchronization as an object of the "reads from" relation.
1053 * Note that this can only provide release sequence support for RMW chains
1054 * which do not read from the future, as those actions cannot be traced until
1055 * their "promise" is fulfilled. Similarly, we may not even establish the
1056 * presence of a release sequence with certainty, as some modification order
1057 * constraints may be decided further in the future. Thus, this function
1058 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1059 * and a boolean representing certainty.
1061 * @todo Finish lazy updating, when promises are fulfilled in the future
1062 * @param rf The action that might be part of a release sequence. Must be a
1064 * @param release_heads A pass-by-reference style return parameter. After
1065 * execution of this function, release_heads will contain the heads of all the
1066 * relevant release sequences, if any exists
1067 * @return true, if the ModelChecker is certain that release_heads is complete;
1070 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1073 /* read from future: need to settle this later */
1074 return false; /* incomplete */
1077 ASSERT(rf->is_write());
1079 if (rf->is_release())
1080 release_heads->push_back(rf);
1082 /* We need a RMW action that is both an acquire and release to stop */
1083 /** @todo Need to be smarter here... In the linux lock
1084 * example, this will run to the beginning of the program for
1086 if (rf->is_acquire() && rf->is_release())
1087 return true; /* complete */
1088 return release_seq_head(rf->get_reads_from(), release_heads);
1090 if (rf->is_release())
1091 return true; /* complete */
1093 /* else relaxed write; check modification order for contiguous subsequence
1094 * -> rf must be same thread as release */
1095 int tid = id_to_int(rf->get_tid());
1096 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1097 action_list_t *list = &(*thrd_lists)[tid];
1098 action_list_t::const_reverse_iterator rit;
1100 /* Find rf in the thread list */
1101 rit = std::find(list->rbegin(), list->rend(), rf);
1102 ASSERT(rit != list->rend());
1104 /* Find the last write/release */
1105 for (; rit != list->rend(); rit++)
1106 if ((*rit)->is_release())
1108 if (rit == list->rend()) {
1109 /* No write-release in this thread */
1110 return true; /* complete */
1112 ModelAction *release = *rit;
1114 ASSERT(rf->same_thread(release));
1116 bool certain = true;
1117 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1118 if (id_to_int(rf->get_tid()) == (int)i)
1120 list = &(*thrd_lists)[i];
1122 /* Can we ensure no future writes from this thread may break
1123 * the release seq? */
1124 bool future_ordered = false;
1126 ModelAction *last = get_last_action(int_to_id(i));
1127 if (last && rf->happens_before(last))
1128 future_ordered = true;
1130 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1131 const ModelAction *act = *rit;
1132 /* Reach synchronization -> this thread is complete */
1133 if (act->happens_before(release))
1135 if (rf->happens_before(act)) {
1136 future_ordered = true;
1140 /* Only writes can break release sequences */
1141 if (!act->is_write())
1144 /* Check modification order */
1145 if (mo_graph->checkReachable(rf, act)) {
1146 /* rf --mo--> act */
1147 future_ordered = true;
1150 if (mo_graph->checkReachable(act, release))
1151 /* act --mo--> release */
1153 if (mo_graph->checkReachable(release, act) &&
1154 mo_graph->checkReachable(act, rf)) {
1155 /* release --mo-> act --mo--> rf */
1156 return true; /* complete */
1160 if (!future_ordered)
1161 return false; /* This thread is uncertain */
1165 release_heads->push_back(release);
1170 * A public interface for getting the release sequence head(s) with which a
1171 * given ModelAction must synchronize. This function only returns a non-empty
1172 * result when it can locate a release sequence head with certainty. Otherwise,
1173 * it may mark the internal state of the ModelChecker so that it will handle
1174 * the release sequence at a later time, causing @a act to update its
1175 * synchronization at some later point in execution.
1176 * @param act The 'acquire' action that may read from a release sequence
1177 * @param release_heads A pass-by-reference return parameter. Will be filled
1178 * with the head(s) of the release sequence(s), if they exists with certainty.
1179 * @see ModelChecker::release_seq_head
1181 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1183 const ModelAction *rf = act->get_reads_from();
1185 complete = release_seq_head(rf, release_heads);
1187 /* add act to 'lazy checking' list */
1188 action_list_t *list;
1189 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1190 list->push_back(act);
1191 (*lazy_sync_size)++;
1196 * Attempt to resolve all stashed operations that might synchronize with a
1197 * release sequence for a given location. This implements the "lazy" portion of
1198 * determining whether or not a release sequence was contiguous, since not all
1199 * modification order information is present at the time an action occurs.
1201 * @param location The location/object that should be checked for release
1202 * sequence resolutions
1203 * @param work_queue The work queue to which to add work items as they are
1205 * @return True if any updates occurred (new synchronization, new mo_graph
1208 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1210 action_list_t *list;
1211 list = lazy_sync_with_release->getptr(location);
1215 bool updated = false;
1216 action_list_t::iterator it = list->begin();
1217 while (it != list->end()) {
1218 ModelAction *act = *it;
1219 const ModelAction *rf = act->get_reads_from();
1220 rel_heads_list_t release_heads;
1222 complete = release_seq_head(rf, &release_heads);
1223 for (unsigned int i = 0; i < release_heads.size(); i++) {
1224 if (!act->has_synchronized_with(release_heads[i])) {
1226 act->synchronize_with(release_heads[i]);
1231 /* Re-check act for mo_graph edges */
1232 work_queue->push_back(MOEdgeWorkEntry(act));
1234 /* propagate synchronization to later actions */
1235 action_list_t::reverse_iterator it = action_trace->rbegin();
1236 for (; (*it) != act; it++) {
1237 ModelAction *propagate = *it;
1238 if (act->happens_before(propagate)) {
1239 propagate->synchronize_with(act);
1240 /* Re-check 'propagate' for mo_graph edges */
1241 work_queue->push_back(MOEdgeWorkEntry(propagate));
1246 it = list->erase(it);
1247 (*lazy_sync_size)--;
1252 // If we resolved promises or data races, see if we have realized a data race.
1253 if (checkDataRaces()) {
1261 * Performs various bookkeeping operations for the current ModelAction. For
1262 * instance, adds action to the per-object, per-thread action vector and to the
1263 * action trace list of all thread actions.
1265 * @param act is the ModelAction to add.
1267 void ModelChecker::add_action_to_lists(ModelAction *act)
1269 int tid = id_to_int(act->get_tid());
1270 action_trace->push_back(act);
1272 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1274 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1275 if (tid >= (int)vec->size())
1276 vec->resize(priv->next_thread_id);
1277 (*vec)[tid].push_back(act);
1279 if ((int)thrd_last_action->size() <= tid)
1280 thrd_last_action->resize(get_num_threads());
1281 (*thrd_last_action)[tid] = act;
1285 * @brief Get the last action performed by a particular Thread
1286 * @param tid The thread ID of the Thread in question
1287 * @return The last action in the thread
1289 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1291 int threadid = id_to_int(tid);
1292 if (threadid < (int)thrd_last_action->size())
1293 return (*thrd_last_action)[id_to_int(tid)];
1299 * Gets the last memory_order_seq_cst write (in the total global sequence)
1300 * performed on a particular object (i.e., memory location), not including the
1302 * @param curr The current ModelAction; also denotes the object location to
1304 * @return The last seq_cst write
1306 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1308 void *location = curr->get_location();
1309 action_list_t *list = obj_map->get_safe_ptr(location);
1310 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1311 action_list_t::reverse_iterator rit;
1312 for (rit = list->rbegin(); rit != list->rend(); rit++)
1313 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1319 * Gets the last unlock operation performed on a particular mutex (i.e., memory
1320 * location). This function identifies the mutex according to the current
1321 * action, which is presumed to perform on the same mutex.
1322 * @param curr The current ModelAction; also denotes the object location to
1324 * @return The last unlock operation
1326 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1328 void *location = curr->get_location();
1329 action_list_t *list = obj_map->get_safe_ptr(location);
1330 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1331 action_list_t::reverse_iterator rit;
1332 for (rit = list->rbegin(); rit != list->rend(); rit++)
1333 if ((*rit)->is_unlock())
1338 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1340 ModelAction *parent = get_last_action(tid);
1342 parent = get_thread(tid)->get_creation();
1347 * Returns the clock vector for a given thread.
1348 * @param tid The thread whose clock vector we want
1349 * @return Desired clock vector
1351 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1353 return get_parent_action(tid)->get_cv();
1357 * Resolve a set of Promises with a current write. The set is provided in the
1358 * Node corresponding to @a write.
1359 * @param write The ModelAction that is fulfilling Promises
1360 * @return True if promises were resolved; false otherwise
1362 bool ModelChecker::resolve_promises(ModelAction *write)
1364 bool resolved = false;
1366 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1367 Promise *promise = (*promises)[promise_index];
1368 if (write->get_node()->get_promise(i)) {
1369 ModelAction *read = promise->get_action();
1370 read->read_from(write);
1371 if (read->is_rmw()) {
1372 mo_graph->addRMWEdge(write, read);
1374 //First fix up the modification order for actions that happened
1376 r_modification_order(read, write);
1377 //Next fix up the modification order for actions that happened
1379 post_r_modification_order(read, write);
1380 promises->erase(promises->begin() + promise_index);
1389 * Compute the set of promises that could potentially be satisfied by this
1390 * action. Note that the set computation actually appears in the Node, not in
1392 * @param curr The ModelAction that may satisfy promises
1394 void ModelChecker::compute_promises(ModelAction *curr)
1396 for (unsigned int i = 0; i < promises->size(); i++) {
1397 Promise *promise = (*promises)[i];
1398 const ModelAction *act = promise->get_action();
1399 if (!act->happens_before(curr) &&
1401 !act->is_synchronizing(curr) &&
1402 !act->same_thread(curr) &&
1403 promise->get_value() == curr->get_value()) {
1404 curr->get_node()->set_promise(i);
1409 /** Checks promises in response to change in ClockVector Threads. */
1410 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1412 for (unsigned int i = 0; i < promises->size(); i++) {
1413 Promise *promise = (*promises)[i];
1414 const ModelAction *act = promise->get_action();
1415 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1416 merge_cv->synchronized_since(act)) {
1417 //This thread is no longer able to send values back to satisfy the promise
1418 int num_synchronized_threads = promise->increment_threads();
1419 if (num_synchronized_threads == get_num_threads()) {
1420 //Promise has failed
1421 failed_promise = true;
1429 * Build up an initial set of all past writes that this 'read' action may read
1430 * from. This set is determined by the clock vector's "happens before"
1432 * @param curr is the current ModelAction that we are exploring; it must be a
1435 void ModelChecker::build_reads_from_past(ModelAction *curr)
1437 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1439 ASSERT(curr->is_read());
1441 ModelAction *last_seq_cst = NULL;
1443 /* Track whether this object has been initialized */
1444 bool initialized = false;
1446 if (curr->is_seqcst()) {
1447 last_seq_cst = get_last_seq_cst(curr);
1448 /* We have to at least see the last sequentially consistent write,
1449 so we are initialized. */
1450 if (last_seq_cst != NULL)
1454 /* Iterate over all threads */
1455 for (i = 0; i < thrd_lists->size(); i++) {
1456 /* Iterate over actions in thread, starting from most recent */
1457 action_list_t *list = &(*thrd_lists)[i];
1458 action_list_t::reverse_iterator rit;
1459 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1460 ModelAction *act = *rit;
1462 /* Only consider 'write' actions */
1463 if (!act->is_write() || act == curr)
1466 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1467 if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1468 DEBUG("Adding action to may_read_from:\n");
1469 if (DBG_ENABLED()) {
1473 curr->get_node()->add_read_from(act);
1476 /* Include at most one act per-thread that "happens before" curr */
1477 if (act->happens_before(curr)) {
1485 /** @todo Need a more informative way of reporting errors. */
1486 printf("ERROR: may read from uninitialized atomic\n");
1489 if (DBG_ENABLED() || !initialized) {
1490 printf("Reached read action:\n");
1492 printf("Printing may_read_from\n");
1493 curr->get_node()->print_may_read_from();
1494 printf("End printing may_read_from\n");
1497 ASSERT(initialized);
1500 static void print_list(action_list_t *list)
1502 action_list_t::iterator it;
1504 printf("---------------------------------------------------------------------\n");
1507 for (it = list->begin(); it != list->end(); it++) {
1510 printf("---------------------------------------------------------------------\n");
1513 void ModelChecker::print_summary()
1516 printf("Number of executions: %d\n", num_executions);
1517 printf("Number of feasible executions: %d\n", num_feasible_executions);
1518 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1520 #if SUPPORT_MOD_ORDER_DUMP
1522 char buffername[100];
1523 sprintf(buffername, "exec%04u", num_executions);
1524 mo_graph->dumpGraphToFile(buffername);
1527 if (!isfinalfeasible())
1528 printf("INFEASIBLE EXECUTION!\n");
1529 print_list(action_trace);
1534 * Add a Thread to the system for the first time. Should only be called once
1536 * @param t The Thread to add
1538 void ModelChecker::add_thread(Thread *t)
1540 thread_map->put(id_to_int(t->get_id()), t);
1541 scheduler->add_thread(t);
1545 * Removes a thread from the scheduler.
1546 * @param the thread to remove.
1549 void ModelChecker::remove_thread(Thread *t)
1551 scheduler->remove_thread(t);
1555 * Switch from a user-context to the "master thread" context (a.k.a. system
1556 * context). This switch is made with the intention of exploring a particular
1557 * model-checking action (described by a ModelAction object). Must be called
1558 * from a user-thread context.
1559 * @param act The current action that will be explored. Must not be NULL.
1560 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1562 int ModelChecker::switch_to_master(ModelAction *act)
1565 Thread *old = thread_current();
1566 set_current_action(act);
1567 old->set_state(THREAD_READY);
1568 return Thread::swap(old, &system_context);
1572 * Takes the next step in the execution, if possible.
1573 * @return Returns true (success) if a step was taken and false otherwise.
1575 bool ModelChecker::take_step() {
1579 Thread * curr = thread_current();
1581 if (curr->get_state() == THREAD_READY) {
1582 ASSERT(priv->current_action);
1584 priv->nextThread = check_current_action(priv->current_action);
1585 priv->current_action = NULL;
1586 if (curr->is_blocked() || curr->is_complete())
1587 scheduler->remove_thread(curr);
1592 Thread * next = scheduler->next_thread(priv->nextThread);
1594 /* Infeasible -> don't take any more steps */
1599 next->set_state(THREAD_RUNNING);
1600 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1602 /* next == NULL -> don't take any more steps */
1606 if ( next->get_pending() != NULL ) {
1607 //restart a pending action
1608 set_current_action(next->get_pending());
1609 next->set_pending(NULL);
1610 next->set_state(THREAD_READY);
1614 /* Return false only if swap fails with an error */
1615 return (Thread::swap(&system_context, next) == 0);
1618 /** Runs the current execution until threre are no more steps to take. */
1619 void ModelChecker::finish_execution() {
1622 while (take_step());