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 /** @returns a thread ID for a new Thread */
90 thread_id_t ModelChecker::get_next_id()
92 return priv->next_thread_id++;
95 /** @returns the number of user threads created during this execution */
96 int ModelChecker::get_num_threads()
98 return priv->next_thread_id;
101 /** @returns 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 action_type type = act->get_type();
205 if (type==ATOMIC_READ||type==ATOMIC_WRITE||type==ATOMIC_RMW) {
206 /* linear search: from most recent to oldest */
207 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
208 action_list_t::reverse_iterator rit;
209 for (rit = list->rbegin(); rit != list->rend(); rit++) {
210 ModelAction *prev = *rit;
211 if (act->is_synchronizing(prev))
214 } else if (type==ATOMIC_LOCK||type==ATOMIC_TRYLOCK) {
215 /* linear search: from most recent to oldest */
216 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
217 action_list_t::reverse_iterator rit;
218 for (rit = list->rbegin(); rit != list->rend(); rit++) {
219 ModelAction *prev = *rit;
220 if (act->is_conflicting_lock(prev))
223 } else if (type==ATOMIC_UNLOCK) {
224 /* linear search: from most recent to oldest */
225 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
226 action_list_t::reverse_iterator rit;
227 for (rit = list->rbegin(); rit != list->rend(); rit++) {
228 ModelAction *prev = *rit;
229 if (!act->same_thread(prev)&&prev->is_failed_trylock())
236 void ModelChecker::set_backtracking(ModelAction *act)
238 Thread *t = get_thread(act);
239 ModelAction * prev = get_last_conflict(act);
243 Node * node = prev->get_node()->get_parent();
245 int low_tid, high_tid;
246 if (node->is_enabled(t)) {
247 low_tid=id_to_int(act->get_tid());
251 high_tid=get_num_threads();
254 for(int i=low_tid;i<high_tid;i++) {
255 thread_id_t tid=int_to_id(i);
256 if (!node->is_enabled(tid))
259 /* Check if this has been explored already */
260 if (node->has_been_explored(tid))
263 /* Cache the latest backtracking point */
264 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
265 priv->next_backtrack = prev;
267 /* If this is a new backtracking point, mark the tree */
268 if (!node->set_backtrack(tid))
270 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
271 prev->get_tid(), t->get_id());
280 * Returns last backtracking point. The model checker will explore a different
281 * path for this point in the next execution.
282 * @return The ModelAction at which the next execution should diverge.
284 ModelAction * ModelChecker::get_next_backtrack()
286 ModelAction *next = priv->next_backtrack;
287 priv->next_backtrack = NULL;
292 * Processes a read or rmw model action.
293 * @param curr is the read model action to process.
294 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
295 * @return True if processing this read updates the mo_graph.
297 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
300 bool updated = false;
302 const ModelAction *reads_from = curr->get_node()->get_read_from();
303 if (reads_from != NULL) {
304 mo_graph->startChanges();
306 value = reads_from->get_value();
307 bool r_status = false;
309 if (!second_part_of_rmw) {
311 r_status = r_modification_order(curr, reads_from);
315 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
316 mo_graph->rollbackChanges();
317 too_many_reads = false;
321 curr->read_from(reads_from);
322 mo_graph->commitChanges();
324 } else if (!second_part_of_rmw) {
325 /* Read from future value */
326 value = curr->get_node()->get_future_value();
327 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
328 curr->read_from(NULL);
329 Promise *valuepromise = new Promise(curr, value, expiration);
330 promises->push_back(valuepromise);
332 get_thread(curr)->set_return_value(value);
337 void ModelChecker::process_mutex(ModelAction *curr) {
338 std::mutex * mutex=(std::mutex *) curr->get_location();
339 struct std::mutex_state * state=mutex->get_state();
340 switch(curr->get_type()) {
341 case ATOMIC_TRYLOCK: {
342 bool success=!state->islocked;
343 curr->set_try_lock(success);
345 get_thread(curr)->set_return_value(0);
348 get_thread(curr)->set_return_value(1);
350 //otherwise fall into the lock case
352 if (curr->get_cv()->getClock(state->alloc_tid)<=state->alloc_clock) {
353 printf("Lock access before initialization\n");
356 state->islocked=true;
357 ModelAction *unlock=get_last_unlock(curr);
358 //synchronize with the previous unlock statement
359 if ( unlock != NULL )
360 curr->synchronize_with(unlock);
363 case ATOMIC_UNLOCK: {
365 state->islocked=false;
366 //wake up the other threads
367 action_list_t * waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
368 //activate all the waiting threads
369 for(action_list_t::iterator rit = waiters->begin(); rit!=waiters->end(); rit++) {
370 add_thread(get_thread((*rit)->get_tid()));
382 * Process a write ModelAction
383 * @param curr The ModelAction to process
384 * @return True if the mo_graph was updated or promises were resolved
386 bool ModelChecker::process_write(ModelAction *curr)
388 bool updated_mod_order = w_modification_order(curr);
389 bool updated_promises = resolve_promises(curr);
391 if (promises->size() == 0) {
392 for (unsigned int i = 0; i<futurevalues->size(); i++) {
393 struct PendingFutureValue pfv = (*futurevalues)[i];
394 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
395 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
396 priv->next_backtrack = pfv.act;
398 futurevalues->resize(0);
401 mo_graph->commitChanges();
402 get_thread(curr)->set_return_value(VALUE_NONE);
403 return updated_mod_order || updated_promises;
407 * Initialize the current action by performing one or more of the following
408 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
409 * in the NodeStack, manipulating backtracking sets, allocating and
410 * initializing clock vectors, and computing the promises to fulfill.
412 * @param curr The current action, as passed from the user context; may be
413 * freed/invalidated after the execution of this function
414 * @return The current action, as processed by the ModelChecker. Is only the
415 * same as the parameter @a curr if this is a newly-explored action.
417 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
419 ModelAction *newcurr;
421 if (curr->is_rmwc() || curr->is_rmw()) {
422 newcurr = process_rmw(curr);
424 compute_promises(newcurr);
428 newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
430 /* First restore type and order in case of RMW operation */
432 newcurr->copy_typeandorder(curr);
434 ASSERT(curr->get_location()==newcurr->get_location());
435 newcurr->copy_from_new(curr);
437 /* Discard duplicate ModelAction; use action from NodeStack */
440 /* If we have diverged, we need to reset the clock vector. */
442 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
446 * Perform one-time actions when pushing new ModelAction onto
449 curr->create_cv(get_parent_action(curr->get_tid()));
450 if (curr->is_write())
451 compute_promises(curr);
456 bool ModelChecker::check_action_enabled(ModelAction *curr) {
457 if (curr->is_lock()) {
458 std::mutex * lock=(std::mutex *) curr->get_location();
459 struct std::mutex_state * state = lock->get_state();
460 if (state->islocked) {
461 //Stick the action in the appropriate waiting queue
462 lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
471 * This is the heart of the model checker routine. It performs model-checking
472 * actions corresponding to a given "current action." Among other processes, it
473 * calculates reads-from relationships, updates synchronization clock vectors,
474 * forms a memory_order constraints graph, and handles replay/backtrack
475 * execution when running permutations of previously-observed executions.
477 * @param curr The current action to process
478 * @return The next Thread that must be executed. May be NULL if ModelChecker
479 * makes no choice (e.g., according to replay execution, combining RMW actions,
482 Thread * ModelChecker::check_current_action(ModelAction *curr)
486 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
488 if (!check_action_enabled(curr)) {
489 //we'll make the execution look like we chose to run this action
490 //much later...when a lock is actually available to relese
491 get_current_thread()->set_pending(curr);
492 remove_thread(get_current_thread());
493 return get_next_thread(NULL);
496 ModelAction *newcurr = initialize_curr_action(curr);
498 /* Add the action to lists before any other model-checking tasks */
499 if (!second_part_of_rmw)
500 add_action_to_lists(newcurr);
502 /* Build may_read_from set for newly-created actions */
503 if (curr == newcurr && curr->is_read())
504 build_reads_from_past(curr);
507 /* Thread specific actions */
508 switch (curr->get_type()) {
509 case THREAD_CREATE: {
510 Thread *th = (Thread *)curr->get_location();
511 th->set_creation(curr);
515 Thread *waiting, *blocking;
516 waiting = get_thread(curr);
517 blocking = (Thread *)curr->get_location();
518 if (!blocking->is_complete()) {
519 blocking->push_wait_list(curr);
520 scheduler->sleep(waiting);
522 do_complete_join(curr);
526 case THREAD_FINISH: {
527 Thread *th = get_thread(curr);
528 while (!th->wait_list_empty()) {
529 ModelAction *act = th->pop_wait_list();
530 Thread *wake = get_thread(act);
531 scheduler->wake(wake);
532 do_complete_join(act);
538 check_promises(NULL, curr->get_cv());
545 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
547 while (!work_queue.empty()) {
548 WorkQueueEntry work = work_queue.front();
549 work_queue.pop_front();
552 case WORK_CHECK_CURR_ACTION: {
553 ModelAction *act = work.action;
554 bool updated = false;
555 if (act->is_read() && process_read(act, second_part_of_rmw))
558 if (act->is_write() && process_write(act))
561 if (act->is_mutex_op())
565 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
568 case WORK_CHECK_RELEASE_SEQ:
569 resolve_release_sequences(work.location, &work_queue);
571 case WORK_CHECK_MO_EDGES: {
572 /** @todo Complete verification of work_queue */
573 ModelAction *act = work.action;
574 bool updated = false;
576 if (act->is_read()) {
577 if (r_modification_order(act, act->get_reads_from()))
580 if (act->is_write()) {
581 if (w_modification_order(act))
586 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
595 check_curr_backtracking(curr);
597 set_backtracking(curr);
599 return get_next_thread(curr);
603 * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
604 * operation from the Thread it is joining with. Must be called after the
605 * completion of the Thread in question.
606 * @param join The THREAD_JOIN action
608 void ModelChecker::do_complete_join(ModelAction *join)
610 Thread *blocking = (Thread *)join->get_location();
611 ModelAction *act = get_last_action(blocking->get_id());
612 join->synchronize_with(act);
615 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
616 Node *currnode = curr->get_node();
617 Node *parnode = currnode->get_parent();
619 if ((!parnode->backtrack_empty() ||
620 !currnode->read_from_empty() ||
621 !currnode->future_value_empty() ||
622 !currnode->promise_empty())
623 && (!priv->next_backtrack ||
624 *curr > *priv->next_backtrack)) {
625 priv->next_backtrack = curr;
629 bool ModelChecker::promises_expired() {
630 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
631 Promise *promise = (*promises)[promise_index];
632 if (promise->get_expiration()<priv->used_sequence_numbers) {
639 /** @returns whether the current partial trace must be a prefix of a
641 bool ModelChecker::isfeasibleprefix() {
642 return promises->size() == 0 && *lazy_sync_size == 0;
645 /** @returns whether the current partial trace is feasible. */
646 bool ModelChecker::isfeasible() {
647 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
650 /** @returns whether the current partial trace is feasible other than
651 * multiple RMW reading from the same store. */
652 bool ModelChecker::isfeasibleotherthanRMW() {
654 if (mo_graph->checkForCycles())
655 DEBUG("Infeasible: modification order cycles\n");
657 DEBUG("Infeasible: failed promise\n");
659 DEBUG("Infeasible: too many reads\n");
660 if (promises_expired())
661 DEBUG("Infeasible: promises expired\n");
663 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
666 /** Returns whether the current completed trace is feasible. */
667 bool ModelChecker::isfinalfeasible() {
668 if (DBG_ENABLED() && promises->size() != 0)
669 DEBUG("Infeasible: unrevolved promises\n");
671 return isfeasible() && promises->size() == 0;
674 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
675 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
676 int tid = id_to_int(act->get_tid());
677 ModelAction *lastread = get_last_action(tid);
678 lastread->process_rmw(act);
679 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
680 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
681 mo_graph->commitChanges();
687 * Checks whether a thread has read from the same write for too many times
688 * without seeing the effects of a later write.
691 * 1) there must a different write that we could read from that would satisfy the modification order,
692 * 2) we must have read from the same value in excess of maxreads times, and
693 * 3) that other write must have been in the reads_from set for maxreads times.
695 * If so, we decide that the execution is no longer feasible.
697 void ModelChecker::check_recency(ModelAction *curr) {
698 if (params.maxreads != 0) {
699 if (curr->get_node()->get_read_from_size() <= 1)
702 //Must make sure that execution is currently feasible... We could
703 //accidentally clear by rolling back
707 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
708 int tid = id_to_int(curr->get_tid());
711 if ((int)thrd_lists->size() <= tid)
714 action_list_t *list = &(*thrd_lists)[tid];
716 action_list_t::reverse_iterator rit = list->rbegin();
718 for (; (*rit) != curr; rit++)
720 /* go past curr now */
723 action_list_t::reverse_iterator ritcopy = rit;
724 //See if we have enough reads from the same value
726 for (; count < params.maxreads; rit++,count++) {
727 if (rit==list->rend())
729 ModelAction *act = *rit;
732 if (act->get_reads_from() != curr->get_reads_from())
734 if (act->get_node()->get_read_from_size() <= 1)
738 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
740 const ModelAction * write = curr->get_node()->get_read_from_at(i);
741 //Need a different write
742 if (write==curr->get_reads_from())
745 /* Test to see whether this is a feasible write to read from*/
746 mo_graph->startChanges();
747 r_modification_order(curr, write);
748 bool feasiblereadfrom = isfeasible();
749 mo_graph->rollbackChanges();
751 if (!feasiblereadfrom)
755 bool feasiblewrite = true;
756 //new we need to see if this write works for everyone
758 for (int loop = count; loop>0; loop--,rit++) {
759 ModelAction *act=*rit;
760 bool foundvalue = false;
761 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
762 if (act->get_node()->get_read_from_at(i)==write) {
768 feasiblewrite = false;
773 too_many_reads = true;
781 * Updates the mo_graph with the constraints imposed from the current
784 * Basic idea is the following: Go through each other thread and find
785 * the lastest action that happened before our read. Two cases:
787 * (1) The action is a write => that write must either occur before
788 * the write we read from or be the write we read from.
790 * (2) The action is a read => the write that that action read from
791 * must occur before the write we read from or be the same write.
793 * @param curr The current action. Must be a read.
794 * @param rf The action that curr reads from. Must be a write.
795 * @return True if modification order edges were added; false otherwise
797 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
799 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
802 ASSERT(curr->is_read());
804 /* Iterate over all threads */
805 for (i = 0; i < thrd_lists->size(); i++) {
806 /* Iterate over actions in thread, starting from most recent */
807 action_list_t *list = &(*thrd_lists)[i];
808 action_list_t::reverse_iterator rit;
809 for (rit = list->rbegin(); rit != list->rend(); rit++) {
810 ModelAction *act = *rit;
813 * Include at most one act per-thread that "happens
814 * before" curr. Don't consider reflexively.
816 if (act->happens_before(curr) && act != curr) {
817 if (act->is_write()) {
819 mo_graph->addEdge(act, rf);
823 const ModelAction *prevreadfrom = act->get_reads_from();
824 if (prevreadfrom != NULL && rf != prevreadfrom) {
825 mo_graph->addEdge(prevreadfrom, rf);
837 /** This method fixes up the modification order when we resolve a
838 * promises. The basic problem is that actions that occur after the
839 * read curr could not property add items to the modification order
842 * So for each thread, we find the earliest item that happens after
843 * the read curr. This is the item we have to fix up with additional
844 * constraints. If that action is write, we add a MO edge between
845 * the Action rf and that action. If the action is a read, we add a
846 * MO edge between the Action rf, and whatever the read accessed.
848 * @param curr is the read ModelAction that we are fixing up MO edges for.
849 * @param rf is the write ModelAction that curr reads from.
853 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
855 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
857 ASSERT(curr->is_read());
859 /* Iterate over all threads */
860 for (i = 0; i < thrd_lists->size(); i++) {
861 /* Iterate over actions in thread, starting from most recent */
862 action_list_t *list = &(*thrd_lists)[i];
863 action_list_t::reverse_iterator rit;
864 ModelAction *lastact = NULL;
866 /* Find last action that happens after curr */
867 for (rit = list->rbegin(); rit != list->rend(); rit++) {
868 ModelAction *act = *rit;
869 if (curr->happens_before(act)) {
875 /* Include at most one act per-thread that "happens before" curr */
876 if (lastact != NULL) {
877 if (lastact->is_read()) {
878 const ModelAction *postreadfrom = lastact->get_reads_from();
879 if (postreadfrom != NULL&&rf != postreadfrom)
880 mo_graph->addEdge(rf, postreadfrom);
881 } else if (rf != lastact) {
882 mo_graph->addEdge(rf, lastact);
890 * Updates the mo_graph with the constraints imposed from the current write.
892 * Basic idea is the following: Go through each other thread and find
893 * the lastest action that happened before our write. Two cases:
895 * (1) The action is a write => that write must occur before
898 * (2) The action is a read => the write that that action read from
899 * must occur before the current write.
901 * This method also handles two other issues:
903 * (I) Sequential Consistency: Making sure that if the current write is
904 * seq_cst, that it occurs after the previous seq_cst write.
906 * (II) Sending the write back to non-synchronizing reads.
908 * @param curr The current action. Must be a write.
909 * @return True if modification order edges were added; false otherwise
911 bool ModelChecker::w_modification_order(ModelAction *curr)
913 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
916 ASSERT(curr->is_write());
918 if (curr->is_seqcst()) {
919 /* We have to at least see the last sequentially consistent write,
920 so we are initialized. */
921 ModelAction *last_seq_cst = get_last_seq_cst(curr);
922 if (last_seq_cst != NULL) {
923 mo_graph->addEdge(last_seq_cst, curr);
928 /* Iterate over all threads */
929 for (i = 0; i < thrd_lists->size(); i++) {
930 /* Iterate over actions in thread, starting from most recent */
931 action_list_t *list = &(*thrd_lists)[i];
932 action_list_t::reverse_iterator rit;
933 for (rit = list->rbegin(); rit != list->rend(); rit++) {
934 ModelAction *act = *rit;
937 * If RMW, we already have all relevant edges,
938 * so just skip to next thread.
939 * If normal write, we need to look at earlier
940 * actions, so continue processing list.
949 * Include at most one act per-thread that "happens
952 if (act->happens_before(curr)) {
954 * Note: if act is RMW, just add edge:
956 * The following edge should be handled elsewhere:
957 * readfrom(act) --mo--> act
960 mo_graph->addEdge(act, curr);
961 else if (act->is_read() && act->get_reads_from() != NULL)
962 mo_graph->addEdge(act->get_reads_from(), curr);
965 } else if (act->is_read() && !act->is_synchronizing(curr) &&
966 !act->same_thread(curr)) {
967 /* We have an action that:
968 (1) did not happen before us
969 (2) is a read and we are a write
970 (3) cannot synchronize with us
971 (4) is in a different thread
973 that read could potentially read from our write.
975 if (thin_air_constraint_may_allow(curr, act)) {
977 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
978 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
979 futurevalues->push_back(pfv);
989 /** Arbitrary reads from the future are not allowed. Section 29.3
990 * part 9 places some constraints. This method checks one result of constraint
991 * constraint. Others require compiler support. */
993 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
994 if (!writer->is_rmw())
997 if (!reader->is_rmw())
1000 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1003 if (search->get_tid() == reader->get_tid() &&
1004 search->happens_before(reader))
1012 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1013 * The ModelAction under consideration is expected to be taking part in
1014 * release/acquire synchronization as an object of the "reads from" relation.
1015 * Note that this can only provide release sequence support for RMW chains
1016 * which do not read from the future, as those actions cannot be traced until
1017 * their "promise" is fulfilled. Similarly, we may not even establish the
1018 * presence of a release sequence with certainty, as some modification order
1019 * constraints may be decided further in the future. Thus, this function
1020 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1021 * and a boolean representing certainty.
1023 * @todo Finish lazy updating, when promises are fulfilled in the future
1024 * @param rf The action that might be part of a release sequence. Must be a
1026 * @param release_heads A pass-by-reference style return parameter. After
1027 * execution of this function, release_heads will contain the heads of all the
1028 * relevant release sequences, if any exists
1029 * @return true, if the ModelChecker is certain that release_heads is complete;
1032 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1035 /* read from future: need to settle this later */
1036 return false; /* incomplete */
1039 ASSERT(rf->is_write());
1041 if (rf->is_release())
1042 release_heads->push_back(rf);
1044 /* We need a RMW action that is both an acquire and release to stop */
1045 /** @todo Need to be smarter here... In the linux lock
1046 * example, this will run to the beginning of the program for
1048 if (rf->is_acquire() && rf->is_release())
1049 return true; /* complete */
1050 return release_seq_head(rf->get_reads_from(), release_heads);
1052 if (rf->is_release())
1053 return true; /* complete */
1055 /* else relaxed write; check modification order for contiguous subsequence
1056 * -> rf must be same thread as release */
1057 int tid = id_to_int(rf->get_tid());
1058 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1059 action_list_t *list = &(*thrd_lists)[tid];
1060 action_list_t::const_reverse_iterator rit;
1062 /* Find rf in the thread list */
1063 rit = std::find(list->rbegin(), list->rend(), rf);
1064 ASSERT(rit != list->rend());
1066 /* Find the last write/release */
1067 for (; rit != list->rend(); rit++)
1068 if ((*rit)->is_release())
1070 if (rit == list->rend()) {
1071 /* No write-release in this thread */
1072 return true; /* complete */
1074 ModelAction *release = *rit;
1076 ASSERT(rf->same_thread(release));
1078 bool certain = true;
1079 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1080 if (id_to_int(rf->get_tid()) == (int)i)
1082 list = &(*thrd_lists)[i];
1084 /* Can we ensure no future writes from this thread may break
1085 * the release seq? */
1086 bool future_ordered = false;
1088 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1089 const ModelAction *act = *rit;
1090 if (!act->is_write())
1092 /* Reach synchronization -> this thread is complete */
1093 if (act->happens_before(release))
1095 if (rf->happens_before(act)) {
1096 future_ordered = true;
1100 /* Check modification order */
1101 if (mo_graph->checkReachable(rf, act)) {
1102 /* rf --mo--> act */
1103 future_ordered = true;
1106 if (mo_graph->checkReachable(act, release))
1107 /* act --mo--> release */
1109 if (mo_graph->checkReachable(release, act) &&
1110 mo_graph->checkReachable(act, rf)) {
1111 /* release --mo-> act --mo--> rf */
1112 return true; /* complete */
1116 if (!future_ordered)
1117 return false; /* This thread is uncertain */
1121 release_heads->push_back(release);
1126 * A public interface for getting the release sequence head(s) with which a
1127 * given ModelAction must synchronize. This function only returns a non-empty
1128 * result when it can locate a release sequence head with certainty. Otherwise,
1129 * it may mark the internal state of the ModelChecker so that it will handle
1130 * the release sequence at a later time, causing @a act to update its
1131 * synchronization at some later point in execution.
1132 * @param act The 'acquire' action that may read from a release sequence
1133 * @param release_heads A pass-by-reference return parameter. Will be filled
1134 * with the head(s) of the release sequence(s), if they exists with certainty.
1135 * @see ModelChecker::release_seq_head
1137 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1139 const ModelAction *rf = act->get_reads_from();
1141 complete = release_seq_head(rf, release_heads);
1143 /* add act to 'lazy checking' list */
1144 action_list_t *list;
1145 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1146 list->push_back(act);
1147 (*lazy_sync_size)++;
1152 * Attempt to resolve all stashed operations that might synchronize with a
1153 * release sequence for a given location. This implements the "lazy" portion of
1154 * determining whether or not a release sequence was contiguous, since not all
1155 * modification order information is present at the time an action occurs.
1157 * @param location The location/object that should be checked for release
1158 * sequence resolutions
1159 * @param work_queue The work queue to which to add work items as they are
1161 * @return True if any updates occurred (new synchronization, new mo_graph
1164 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1166 action_list_t *list;
1167 list = lazy_sync_with_release->getptr(location);
1171 bool updated = false;
1172 action_list_t::iterator it = list->begin();
1173 while (it != list->end()) {
1174 ModelAction *act = *it;
1175 const ModelAction *rf = act->get_reads_from();
1176 rel_heads_list_t release_heads;
1178 complete = release_seq_head(rf, &release_heads);
1179 for (unsigned int i = 0; i < release_heads.size(); i++) {
1180 if (!act->has_synchronized_with(release_heads[i])) {
1182 act->synchronize_with(release_heads[i]);
1187 /* Re-check act for mo_graph edges */
1188 work_queue->push_back(MOEdgeWorkEntry(act));
1190 /* propagate synchronization to later actions */
1191 action_list_t::reverse_iterator it = action_trace->rbegin();
1192 while ((*it) != act) {
1193 ModelAction *propagate = *it;
1194 if (act->happens_before(propagate)) {
1195 propagate->synchronize_with(act);
1196 /* Re-check 'propagate' for mo_graph edges */
1197 work_queue->push_back(MOEdgeWorkEntry(propagate));
1202 it = list->erase(it);
1203 (*lazy_sync_size)--;
1208 // If we resolved promises or data races, see if we have realized a data race.
1209 if (checkDataRaces()) {
1217 * Performs various bookkeeping operations for the current ModelAction. For
1218 * instance, adds action to the per-object, per-thread action vector and to the
1219 * action trace list of all thread actions.
1221 * @param act is the ModelAction to add.
1223 void ModelChecker::add_action_to_lists(ModelAction *act)
1225 int tid = id_to_int(act->get_tid());
1226 action_trace->push_back(act);
1228 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1230 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1231 if (tid >= (int)vec->size())
1232 vec->resize(priv->next_thread_id);
1233 (*vec)[tid].push_back(act);
1235 if ((int)thrd_last_action->size() <= tid)
1236 thrd_last_action->resize(get_num_threads());
1237 (*thrd_last_action)[tid] = act;
1240 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1242 int threadid=id_to_int(tid);
1243 if (threadid<(int)thrd_last_action->size())
1244 return (*thrd_last_action)[id_to_int(tid)];
1250 * Gets the last memory_order_seq_cst write (in the total global sequence)
1251 * performed on a particular object (i.e., memory location), not including the
1253 * @param curr The current ModelAction; also denotes the object location to
1255 * @return The last seq_cst write
1257 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1259 void *location = curr->get_location();
1260 action_list_t *list = obj_map->get_safe_ptr(location);
1261 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1262 action_list_t::reverse_iterator rit;
1263 for (rit = list->rbegin(); rit != list->rend(); rit++)
1264 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1269 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr)
1271 void *location = curr->get_location();
1272 action_list_t *list = obj_map->get_safe_ptr(location);
1273 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1274 action_list_t::reverse_iterator rit;
1275 for (rit = list->rbegin(); rit != list->rend(); rit++)
1276 if ((*rit)->is_unlock())
1281 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1283 ModelAction *parent = get_last_action(tid);
1285 parent = get_thread(tid)->get_creation();
1290 * Returns the clock vector for a given thread.
1291 * @param tid The thread whose clock vector we want
1292 * @return Desired clock vector
1294 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1296 return get_parent_action(tid)->get_cv();
1300 * Resolve a set of Promises with a current write. The set is provided in the
1301 * Node corresponding to @a write.
1302 * @param write The ModelAction that is fulfilling Promises
1303 * @return True if promises were resolved; false otherwise
1305 bool ModelChecker::resolve_promises(ModelAction *write)
1307 bool resolved = false;
1309 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1310 Promise *promise = (*promises)[promise_index];
1311 if (write->get_node()->get_promise(i)) {
1312 ModelAction *read = promise->get_action();
1313 read->read_from(write);
1314 if (read->is_rmw()) {
1315 mo_graph->addRMWEdge(write, read);
1317 //First fix up the modification order for actions that happened
1319 r_modification_order(read, write);
1320 //Next fix up the modification order for actions that happened
1322 post_r_modification_order(read, write);
1323 promises->erase(promises->begin() + promise_index);
1332 * Compute the set of promises that could potentially be satisfied by this
1333 * action. Note that the set computation actually appears in the Node, not in
1335 * @param curr The ModelAction that may satisfy promises
1337 void ModelChecker::compute_promises(ModelAction *curr)
1339 for (unsigned int i = 0; i < promises->size(); i++) {
1340 Promise *promise = (*promises)[i];
1341 const ModelAction *act = promise->get_action();
1342 if (!act->happens_before(curr) &&
1344 !act->is_synchronizing(curr) &&
1345 !act->same_thread(curr) &&
1346 promise->get_value() == curr->get_value()) {
1347 curr->get_node()->set_promise(i);
1352 /** Checks promises in response to change in ClockVector Threads. */
1353 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1355 for (unsigned int i = 0; i < promises->size(); i++) {
1356 Promise *promise = (*promises)[i];
1357 const ModelAction *act = promise->get_action();
1358 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1359 merge_cv->synchronized_since(act)) {
1360 //This thread is no longer able to send values back to satisfy the promise
1361 int num_synchronized_threads = promise->increment_threads();
1362 if (num_synchronized_threads == get_num_threads()) {
1363 //Promise has failed
1364 failed_promise = true;
1372 * Build up an initial set of all past writes that this 'read' action may read
1373 * from. This set is determined by the clock vector's "happens before"
1375 * @param curr is the current ModelAction that we are exploring; it must be a
1378 void ModelChecker::build_reads_from_past(ModelAction *curr)
1380 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1382 ASSERT(curr->is_read());
1384 ModelAction *last_seq_cst = NULL;
1386 /* Track whether this object has been initialized */
1387 bool initialized = false;
1389 if (curr->is_seqcst()) {
1390 last_seq_cst = get_last_seq_cst(curr);
1391 /* We have to at least see the last sequentially consistent write,
1392 so we are initialized. */
1393 if (last_seq_cst != NULL)
1397 /* Iterate over all threads */
1398 for (i = 0; i < thrd_lists->size(); i++) {
1399 /* Iterate over actions in thread, starting from most recent */
1400 action_list_t *list = &(*thrd_lists)[i];
1401 action_list_t::reverse_iterator rit;
1402 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1403 ModelAction *act = *rit;
1405 /* Only consider 'write' actions */
1406 if (!act->is_write() || act == curr)
1409 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1410 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1411 DEBUG("Adding action to may_read_from:\n");
1412 if (DBG_ENABLED()) {
1416 curr->get_node()->add_read_from(act);
1419 /* Include at most one act per-thread that "happens before" curr */
1420 if (act->happens_before(curr)) {
1428 /** @todo Need a more informative way of reporting errors. */
1429 printf("ERROR: may read from uninitialized atomic\n");
1432 if (DBG_ENABLED() || !initialized) {
1433 printf("Reached read action:\n");
1435 printf("Printing may_read_from\n");
1436 curr->get_node()->print_may_read_from();
1437 printf("End printing may_read_from\n");
1440 ASSERT(initialized);
1443 static void print_list(action_list_t *list)
1445 action_list_t::iterator it;
1447 printf("---------------------------------------------------------------------\n");
1450 for (it = list->begin(); it != list->end(); it++) {
1453 printf("---------------------------------------------------------------------\n");
1456 void ModelChecker::print_summary()
1459 printf("Number of executions: %d\n", num_executions);
1460 printf("Number of feasible executions: %d\n", num_feasible_executions);
1461 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1463 #if SUPPORT_MOD_ORDER_DUMP
1465 char buffername[100];
1466 sprintf(buffername, "exec%u",num_executions);
1467 mo_graph->dumpGraphToFile(buffername);
1470 if (!isfinalfeasible())
1471 printf("INFEASIBLE EXECUTION!\n");
1472 print_list(action_trace);
1477 * Add a Thread to the system for the first time. Should only be called once
1479 * @param t The Thread to add
1481 void ModelChecker::add_thread(Thread *t)
1483 thread_map->put(id_to_int(t->get_id()), t);
1484 scheduler->add_thread(t);
1487 void ModelChecker::remove_thread(Thread *t)
1489 scheduler->remove_thread(t);
1493 * Switch from a user-context to the "master thread" context (a.k.a. system
1494 * context). This switch is made with the intention of exploring a particular
1495 * model-checking action (described by a ModelAction object). Must be called
1496 * from a user-thread context.
1497 * @param act The current action that will be explored. Must not be NULL.
1498 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1500 int ModelChecker::switch_to_master(ModelAction *act)
1503 Thread *old = thread_current();
1504 set_current_action(act);
1505 old->set_state(THREAD_READY);
1506 return Thread::swap(old, &system_context);
1510 * Takes the next step in the execution, if possible.
1511 * @return Returns true (success) if a step was taken and false otherwise.
1513 bool ModelChecker::take_step() {
1517 Thread * curr = thread_current();
1519 if (curr->get_state() == THREAD_READY) {
1520 ASSERT(priv->current_action);
1522 priv->nextThread = check_current_action(priv->current_action);
1523 priv->current_action = NULL;
1524 if (curr->is_blocked() || curr->is_complete())
1525 scheduler->remove_thread(curr);
1530 Thread * next = scheduler->next_thread(priv->nextThread);
1532 /* Infeasible -> don't take any more steps */
1537 next->set_state(THREAD_RUNNING);
1538 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1540 /* next == NULL -> don't take any more steps */
1544 if ( next->get_pending() != NULL ) {
1545 //restart a pending action
1546 set_current_action(next->get_pending());
1547 next->set_pending(NULL);
1548 next->set_state(THREAD_READY);
1552 /* Return false only if swap fails with an error */
1553 return (Thread::swap(&system_context, next) == 0);
1556 /** Runs the current execution until threre are no more steps to take. */
1557 void ModelChecker::finish_execution() {
1560 while (take_step());