8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
15 #define INITIAL_THREAD_ID 0
19 /** @brief Constructor */
20 ModelChecker::ModelChecker(struct model_params params) :
21 /* Initialize default scheduler */
22 scheduler(new Scheduler()),
24 num_feasible_executions(0),
27 action_trace(new action_list_t()),
28 thread_map(new HashTable<int, Thread *, int>()),
29 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
30 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
31 promises(new std::vector<Promise *>()),
32 futurevalues(new std::vector<struct PendingFutureValue>()),
33 lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
34 thrd_last_action(new std::vector<ModelAction *>(1)),
35 node_stack(new NodeStack()),
36 mo_graph(new CycleGraph()),
37 failed_promise(false),
38 too_many_reads(false),
41 /* Allocate this "size" on the snapshotting heap */
42 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
43 /* First thread created will have id INITIAL_THREAD_ID */
44 priv->next_thread_id = INITIAL_THREAD_ID;
46 lazy_sync_size = &priv->lazy_sync_size;
49 /** @brief Destructor */
50 ModelChecker::~ModelChecker()
52 for (int i = 0; i < get_num_threads(); i++)
53 delete thread_map->get(i);
60 for (unsigned int i = 0; i < promises->size(); i++)
61 delete (*promises)[i];
64 delete lazy_sync_with_release;
66 delete thrd_last_action;
73 * Restores user program to initial state and resets all model-checker data
76 void ModelChecker::reset_to_initial_state()
78 DEBUG("+++ Resetting to initial state +++\n");
79 node_stack->reset_execution();
80 failed_promise = false;
81 too_many_reads = false;
83 snapshotObject->backTrackBeforeStep(0);
86 /** @returns a thread ID for a new Thread */
87 thread_id_t ModelChecker::get_next_id()
89 return priv->next_thread_id++;
92 /** @returns the number of user threads created during this execution */
93 int ModelChecker::get_num_threads()
95 return priv->next_thread_id;
98 /** @returns a sequence number for a new ModelAction */
99 modelclock_t ModelChecker::get_next_seq_num()
101 return ++priv->used_sequence_numbers;
105 * @brief Choose the next thread to execute.
107 * This function chooses the next thread that should execute. It can force the
108 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
109 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
110 * The model-checker may have no preference regarding the next thread (i.e.,
111 * when exploring a new execution ordering), in which case this will return
113 * @param curr The current ModelAction. This action might guide the choice of
115 * @return The next thread to run. If the model-checker has no preference, NULL.
117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
121 /* Do not split atomic actions. */
123 return thread_current();
124 /* The THREAD_CREATE action points to the created Thread */
125 else if (curr->get_type() == THREAD_CREATE)
126 return (Thread *)curr->get_location();
128 /* Have we completed exploring the preselected path? */
132 /* Else, we are trying to replay an execution */
133 ModelAction *next = node_stack->get_next()->get_action();
135 if (next == diverge) {
136 Node *nextnode = next->get_node();
137 /* Reached divergence point */
138 if (nextnode->increment_promise()) {
139 /* The next node will try to satisfy a different set of promises. */
140 tid = next->get_tid();
141 node_stack->pop_restofstack(2);
142 } else if (nextnode->increment_read_from()) {
143 /* The next node will read from a different value. */
144 tid = next->get_tid();
145 node_stack->pop_restofstack(2);
146 } else if (nextnode->increment_future_value()) {
147 /* The next node will try to read from a different future value. */
148 tid = next->get_tid();
149 node_stack->pop_restofstack(2);
151 /* Make a different thread execute for next step */
152 Node *node = nextnode->get_parent();
153 tid = node->get_next_backtrack();
154 node_stack->pop_restofstack(1);
156 DEBUG("*** Divergence point ***\n");
159 tid = next->get_tid();
161 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
162 ASSERT(tid != THREAD_ID_T_NONE);
163 return thread_map->get(id_to_int(tid));
167 * Queries the model-checker for more executions to explore and, if one
168 * exists, resets the model-checker state to execute a new execution.
170 * @return If there are more executions to explore, return true. Otherwise,
173 bool ModelChecker::next_execution()
178 if (isfinalfeasible())
179 num_feasible_executions++;
181 if (isfinalfeasible() || DBG_ENABLED())
184 if ((diverge = get_next_backtrack()) == NULL)
188 printf("Next execution will diverge at:\n");
192 reset_to_initial_state();
196 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
198 action_type type = act->get_type();
208 /* linear search: from most recent to oldest */
209 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
210 action_list_t::reverse_iterator rit;
211 for (rit = list->rbegin(); rit != list->rend(); rit++) {
212 ModelAction *prev = *rit;
213 if (act->is_synchronizing(prev))
219 void ModelChecker::set_backtracking(ModelAction *act)
223 Thread *t = get_thread(act);
225 prev = get_last_conflict(act);
229 node = prev->get_node()->get_parent();
231 while (!node->is_enabled(t))
234 /* Check if this has been explored already */
235 if (node->has_been_explored(t->get_id()))
238 /* Cache the latest backtracking point */
239 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
240 priv->next_backtrack = prev;
242 /* If this is a new backtracking point, mark the tree */
243 if (!node->set_backtrack(t->get_id()))
245 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
246 prev->get_tid(), t->get_id());
254 * Returns last backtracking point. The model checker will explore a different
255 * path for this point in the next execution.
256 * @return The ModelAction at which the next execution should diverge.
258 ModelAction * ModelChecker::get_next_backtrack()
260 ModelAction *next = priv->next_backtrack;
261 priv->next_backtrack = NULL;
266 * Processes a read or rmw model action.
267 * @param curr is the read model action to process.
268 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
269 * @return True if processing this read updates the mo_graph.
271 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
274 bool updated = false;
276 const ModelAction *reads_from = curr->get_node()->get_read_from();
277 if (reads_from != NULL) {
278 mo_graph->startChanges();
280 value = reads_from->get_value();
281 bool r_status = false;
283 if (!second_part_of_rmw) {
285 r_status = r_modification_order(curr, reads_from);
289 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
290 mo_graph->rollbackChanges();
291 too_many_reads = false;
295 curr->read_from(reads_from);
296 mo_graph->commitChanges();
298 } else if (!second_part_of_rmw) {
299 /* Read from future value */
300 value = curr->get_node()->get_future_value();
301 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
302 curr->read_from(NULL);
303 Promise *valuepromise = new Promise(curr, value, expiration);
304 promises->push_back(valuepromise);
306 get_thread(curr)->set_return_value(value);
312 * Process a write ModelAction
313 * @param curr The ModelAction to process
314 * @return True if the mo_graph was updated or promises were resolved
316 bool ModelChecker::process_write(ModelAction *curr)
318 bool updated_mod_order = w_modification_order(curr);
319 bool updated_promises = resolve_promises(curr);
321 if (promises->size() == 0) {
322 for (unsigned int i = 0; i<futurevalues->size(); i++) {
323 struct PendingFutureValue pfv = (*futurevalues)[i];
324 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
325 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
326 priv->next_backtrack = pfv.act;
328 futurevalues->resize(0);
331 mo_graph->commitChanges();
332 get_thread(curr)->set_return_value(VALUE_NONE);
333 return updated_mod_order || updated_promises;
337 * This is the heart of the model checker routine. It performs model-checking
338 * actions corresponding to a given "current action." Among other processes, it
339 * calculates reads-from relationships, updates synchronization clock vectors,
340 * forms a memory_order constraints graph, and handles replay/backtrack
341 * execution when running permutations of previously-observed executions.
343 * @param curr The current action to process
344 * @return The next Thread that must be executed. May be NULL if ModelChecker
345 * makes no choice (e.g., according to replay execution, combining RMW actions,
348 Thread * ModelChecker::check_current_action(ModelAction *curr)
350 bool second_part_of_rmw = false;
354 if (curr->is_rmwc() || curr->is_rmw()) {
355 ModelAction *tmp = process_rmw(curr);
356 second_part_of_rmw = true;
359 compute_promises(curr);
361 ModelAction *tmp = node_stack->explore_action(curr);
363 /* Discard duplicate ModelAction; use action from NodeStack */
364 /* First restore type and order in case of RMW operation */
366 tmp->copy_typeandorder(curr);
368 /* If we have diverged, we need to reset the clock vector. */
370 tmp->create_cv(get_parent_action(tmp->get_tid()));
376 * Perform one-time actions when pushing new ModelAction onto
379 curr->create_cv(get_parent_action(curr->get_tid()));
380 /* Build may_read_from set */
382 build_reads_from_past(curr);
383 if (curr->is_write())
384 compute_promises(curr);
388 /* Thread specific actions */
389 switch (curr->get_type()) {
390 case THREAD_CREATE: {
391 Thread *th = (Thread *)curr->get_location();
392 th->set_creation(curr);
396 Thread *waiting, *blocking;
397 waiting = get_thread(curr);
398 blocking = (Thread *)curr->get_location();
399 if (!blocking->is_complete()) {
400 blocking->push_wait_list(curr);
401 scheduler->sleep(waiting);
405 case THREAD_FINISH: {
406 Thread *th = get_thread(curr);
407 while (!th->wait_list_empty()) {
408 ModelAction *act = th->pop_wait_list();
409 Thread *wake = get_thread(act);
410 scheduler->wake(wake);
416 check_promises(NULL, curr->get_cv());
423 /* Add current action to lists before work_queue loop */
424 if (!second_part_of_rmw)
425 add_action_to_lists(curr);
427 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
429 while (!work_queue.empty()) {
430 WorkQueueEntry work = work_queue.front();
431 work_queue.pop_front();
434 case WORK_CHECK_CURR_ACTION: {
435 ModelAction *act = work.action;
436 bool updated = false;
437 if (act->is_read() && process_read(act, second_part_of_rmw))
440 if (act->is_write() && process_write(act))
444 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
447 case WORK_CHECK_RELEASE_SEQ:
448 resolve_release_sequences(work.location, &work_queue);
450 case WORK_CHECK_MO_EDGES: {
451 /** @todo Complete verification of work_queue */
452 ModelAction *act = work.action;
453 bool updated = false;
455 if (act->is_read()) {
456 if (r_modification_order(act, act->get_reads_from()))
459 if (act->is_write()) {
460 if (w_modification_order(act))
465 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
474 check_curr_backtracking(curr);
476 set_backtracking(curr);
478 return get_next_thread(curr);
481 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
482 Node *currnode = curr->get_node();
483 Node *parnode = currnode->get_parent();
485 if ((!parnode->backtrack_empty() ||
486 !currnode->read_from_empty() ||
487 !currnode->future_value_empty() ||
488 !currnode->promise_empty())
489 && (!priv->next_backtrack ||
490 *curr > *priv->next_backtrack)) {
491 priv->next_backtrack = curr;
495 bool ModelChecker::promises_expired() {
496 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
497 Promise *promise = (*promises)[promise_index];
498 if (promise->get_expiration()<priv->used_sequence_numbers) {
505 /** @returns whether the current partial trace must be a prefix of a
507 bool ModelChecker::isfeasibleprefix() {
508 return promises->size() == 0 && *lazy_sync_size == 0;
511 /** @returns whether the current partial trace is feasible. */
512 bool ModelChecker::isfeasible() {
513 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
516 /** @returns whether the current partial trace is feasible other than
517 * multiple RMW reading from the same store. */
518 bool ModelChecker::isfeasibleotherthanRMW() {
520 if (mo_graph->checkForCycles())
521 DEBUG("Infeasible: modification order cycles\n");
523 DEBUG("Infeasible: failed promise\n");
525 DEBUG("Infeasible: too many reads\n");
526 if (promises_expired())
527 DEBUG("Infeasible: promises expired\n");
529 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
532 /** Returns whether the current completed trace is feasible. */
533 bool ModelChecker::isfinalfeasible() {
534 if (DBG_ENABLED() && promises->size() != 0)
535 DEBUG("Infeasible: unrevolved promises\n");
537 return isfeasible() && promises->size() == 0;
540 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
541 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
542 int tid = id_to_int(act->get_tid());
543 ModelAction *lastread = get_last_action(tid);
544 lastread->process_rmw(act);
545 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
546 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
547 mo_graph->commitChanges();
553 * Checks whether a thread has read from the same write for too many times
554 * without seeing the effects of a later write.
557 * 1) there must a different write that we could read from that would satisfy the modification order,
558 * 2) we must have read from the same value in excess of maxreads times, and
559 * 3) that other write must have been in the reads_from set for maxreads times.
561 * If so, we decide that the execution is no longer feasible.
563 void ModelChecker::check_recency(ModelAction *curr) {
564 if (params.maxreads != 0) {
565 if (curr->get_node()->get_read_from_size() <= 1)
568 //Must make sure that execution is currently feasible... We could
569 //accidentally clear by rolling back
573 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
574 int tid = id_to_int(curr->get_tid());
577 if ((int)thrd_lists->size() <= tid)
580 action_list_t *list = &(*thrd_lists)[tid];
582 action_list_t::reverse_iterator rit = list->rbegin();
584 for (; (*rit) != curr; rit++)
586 /* go past curr now */
589 action_list_t::reverse_iterator ritcopy = rit;
590 //See if we have enough reads from the same value
592 for (; count < params.maxreads; rit++,count++) {
593 if (rit==list->rend())
595 ModelAction *act = *rit;
598 if (act->get_reads_from() != curr->get_reads_from())
600 if (act->get_node()->get_read_from_size() <= 1)
604 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
606 const ModelAction * write = curr->get_node()->get_read_from_at(i);
607 //Need a different write
608 if (write==curr->get_reads_from())
611 /* Test to see whether this is a feasible write to read from*/
612 mo_graph->startChanges();
613 r_modification_order(curr, write);
614 bool feasiblereadfrom = isfeasible();
615 mo_graph->rollbackChanges();
617 if (!feasiblereadfrom)
621 bool feasiblewrite = true;
622 //new we need to see if this write works for everyone
624 for (int loop = count; loop>0; loop--,rit++) {
625 ModelAction *act=*rit;
626 bool foundvalue = false;
627 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
628 if (act->get_node()->get_read_from_at(i)==write) {
634 feasiblewrite = false;
639 too_many_reads = true;
647 * Updates the mo_graph with the constraints imposed from the current
650 * Basic idea is the following: Go through each other thread and find
651 * the lastest action that happened before our read. Two cases:
653 * (1) The action is a write => that write must either occur before
654 * the write we read from or be the write we read from.
656 * (2) The action is a read => the write that that action read from
657 * must occur before the write we read from or be the same write.
659 * @param curr The current action. Must be a read.
660 * @param rf The action that curr reads from. Must be a write.
661 * @return True if modification order edges were added; false otherwise
663 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
665 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
668 ASSERT(curr->is_read());
670 /* Iterate over all threads */
671 for (i = 0; i < thrd_lists->size(); i++) {
672 /* Iterate over actions in thread, starting from most recent */
673 action_list_t *list = &(*thrd_lists)[i];
674 action_list_t::reverse_iterator rit;
675 for (rit = list->rbegin(); rit != list->rend(); rit++) {
676 ModelAction *act = *rit;
679 * Include at most one act per-thread that "happens
680 * before" curr. Don't consider reflexively.
682 if (act->happens_before(curr) && act != curr) {
683 if (act->is_write()) {
685 mo_graph->addEdge(act, rf);
689 const ModelAction *prevreadfrom = act->get_reads_from();
690 if (prevreadfrom != NULL && rf != prevreadfrom) {
691 mo_graph->addEdge(prevreadfrom, rf);
703 /** This method fixes up the modification order when we resolve a
704 * promises. The basic problem is that actions that occur after the
705 * read curr could not property add items to the modification order
708 * So for each thread, we find the earliest item that happens after
709 * the read curr. This is the item we have to fix up with additional
710 * constraints. If that action is write, we add a MO edge between
711 * the Action rf and that action. If the action is a read, we add a
712 * MO edge between the Action rf, and whatever the read accessed.
714 * @param curr is the read ModelAction that we are fixing up MO edges for.
715 * @param rf is the write ModelAction that curr reads from.
719 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
721 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
723 ASSERT(curr->is_read());
725 /* Iterate over all threads */
726 for (i = 0; i < thrd_lists->size(); i++) {
727 /* Iterate over actions in thread, starting from most recent */
728 action_list_t *list = &(*thrd_lists)[i];
729 action_list_t::reverse_iterator rit;
730 ModelAction *lastact = NULL;
732 /* Find last action that happens after curr */
733 for (rit = list->rbegin(); rit != list->rend(); rit++) {
734 ModelAction *act = *rit;
735 if (curr->happens_before(act)) {
741 /* Include at most one act per-thread that "happens before" curr */
742 if (lastact != NULL) {
743 if (lastact->is_read()) {
744 const ModelAction *postreadfrom = lastact->get_reads_from();
745 if (postreadfrom != NULL&&rf != postreadfrom)
746 mo_graph->addEdge(rf, postreadfrom);
747 } else if (rf != lastact) {
748 mo_graph->addEdge(rf, lastact);
756 * Updates the mo_graph with the constraints imposed from the current write.
758 * Basic idea is the following: Go through each other thread and find
759 * the lastest action that happened before our write. Two cases:
761 * (1) The action is a write => that write must occur before
764 * (2) The action is a read => the write that that action read from
765 * must occur before the current write.
767 * This method also handles two other issues:
769 * (I) Sequential Consistency: Making sure that if the current write is
770 * seq_cst, that it occurs after the previous seq_cst write.
772 * (II) Sending the write back to non-synchronizing reads.
774 * @param curr The current action. Must be a write.
775 * @return True if modification order edges were added; false otherwise
777 bool ModelChecker::w_modification_order(ModelAction *curr)
779 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
782 ASSERT(curr->is_write());
784 if (curr->is_seqcst()) {
785 /* We have to at least see the last sequentially consistent write,
786 so we are initialized. */
787 ModelAction *last_seq_cst = get_last_seq_cst(curr);
788 if (last_seq_cst != NULL) {
789 mo_graph->addEdge(last_seq_cst, curr);
794 /* Iterate over all threads */
795 for (i = 0; i < thrd_lists->size(); i++) {
796 /* Iterate over actions in thread, starting from most recent */
797 action_list_t *list = &(*thrd_lists)[i];
798 action_list_t::reverse_iterator rit;
799 for (rit = list->rbegin(); rit != list->rend(); rit++) {
800 ModelAction *act = *rit;
803 * If RMW, we already have all relevant edges,
804 * so just skip to next thread.
805 * If normal write, we need to look at earlier
806 * actions, so continue processing list.
815 * Include at most one act per-thread that "happens
818 if (act->happens_before(curr)) {
820 * Note: if act is RMW, just add edge:
822 * The following edge should be handled elsewhere:
823 * readfrom(act) --mo--> act
826 mo_graph->addEdge(act, curr);
827 else if (act->is_read() && act->get_reads_from() != NULL)
828 mo_graph->addEdge(act->get_reads_from(), curr);
831 } else if (act->is_read() && !act->is_synchronizing(curr) &&
832 !act->same_thread(curr)) {
833 /* We have an action that:
834 (1) did not happen before us
835 (2) is a read and we are a write
836 (3) cannot synchronize with us
837 (4) is in a different thread
839 that read could potentially read from our write.
841 if (thin_air_constraint_may_allow(curr, act)) {
843 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
844 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
845 futurevalues->push_back(pfv);
855 /** Arbitrary reads from the future are not allowed. Section 29.3
856 * part 9 places some constraints. This method checks one result of constraint
857 * constraint. Others require compiler support. */
859 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
860 if (!writer->is_rmw())
863 if (!reader->is_rmw())
866 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
869 if (search->get_tid() == reader->get_tid() &&
870 search->happens_before(reader))
878 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
879 * The ModelAction under consideration is expected to be taking part in
880 * release/acquire synchronization as an object of the "reads from" relation.
881 * Note that this can only provide release sequence support for RMW chains
882 * which do not read from the future, as those actions cannot be traced until
883 * their "promise" is fulfilled. Similarly, we may not even establish the
884 * presence of a release sequence with certainty, as some modification order
885 * constraints may be decided further in the future. Thus, this function
886 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
887 * and a boolean representing certainty.
889 * @todo Finish lazy updating, when promises are fulfilled in the future
890 * @param rf The action that might be part of a release sequence. Must be a
892 * @param release_heads A pass-by-reference style return parameter. After
893 * execution of this function, release_heads will contain the heads of all the
894 * relevant release sequences, if any exists
895 * @return true, if the ModelChecker is certain that release_heads is complete;
898 bool ModelChecker::release_seq_head(const ModelAction *rf,
899 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
902 /* read from future: need to settle this later */
903 return false; /* incomplete */
906 ASSERT(rf->is_write());
908 if (rf->is_release())
909 release_heads->push_back(rf);
911 /* We need a RMW action that is both an acquire and release to stop */
912 /** @todo Need to be smarter here... In the linux lock
913 * example, this will run to the beginning of the program for
915 if (rf->is_acquire() && rf->is_release())
916 return true; /* complete */
917 return release_seq_head(rf->get_reads_from(), release_heads);
919 if (rf->is_release())
920 return true; /* complete */
922 /* else relaxed write; check modification order for contiguous subsequence
923 * -> rf must be same thread as release */
924 int tid = id_to_int(rf->get_tid());
925 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
926 action_list_t *list = &(*thrd_lists)[tid];
927 action_list_t::const_reverse_iterator rit;
929 /* Find rf in the thread list */
930 rit = std::find(list->rbegin(), list->rend(), rf);
931 ASSERT(rit != list->rend());
933 /* Find the last write/release */
934 for (; rit != list->rend(); rit++)
935 if ((*rit)->is_release())
937 if (rit == list->rend()) {
938 /* No write-release in this thread */
939 return true; /* complete */
941 ModelAction *release = *rit;
943 ASSERT(rf->same_thread(release));
946 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
947 if (id_to_int(rf->get_tid()) == (int)i)
949 list = &(*thrd_lists)[i];
951 /* Can we ensure no future writes from this thread may break
952 * the release seq? */
953 bool future_ordered = false;
955 for (rit = list->rbegin(); rit != list->rend(); rit++) {
956 const ModelAction *act = *rit;
957 if (!act->is_write())
959 /* Reach synchronization -> this thread is complete */
960 if (act->happens_before(release))
962 if (rf->happens_before(act)) {
963 future_ordered = true;
967 /* Check modification order */
968 if (mo_graph->checkReachable(rf, act)) {
970 future_ordered = true;
973 if (mo_graph->checkReachable(act, release))
974 /* act --mo--> release */
976 if (mo_graph->checkReachable(release, act) &&
977 mo_graph->checkReachable(act, rf)) {
978 /* release --mo-> act --mo--> rf */
979 return true; /* complete */
984 return false; /* This thread is uncertain */
988 release_heads->push_back(release);
993 * A public interface for getting the release sequence head(s) with which a
994 * given ModelAction must synchronize. This function only returns a non-empty
995 * result when it can locate a release sequence head with certainty. Otherwise,
996 * it may mark the internal state of the ModelChecker so that it will handle
997 * the release sequence at a later time, causing @a act to update its
998 * synchronization at some later point in execution.
999 * @param act The 'acquire' action that may read from a release sequence
1000 * @param release_heads A pass-by-reference return parameter. Will be filled
1001 * with the head(s) of the release sequence(s), if they exists with certainty.
1002 * @see ModelChecker::release_seq_head
1004 void ModelChecker::get_release_seq_heads(ModelAction *act,
1005 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
1007 const ModelAction *rf = act->get_reads_from();
1009 complete = release_seq_head(rf, release_heads);
1011 /* add act to 'lazy checking' list */
1012 std::list<ModelAction *> *list;
1013 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1014 list->push_back(act);
1015 (*lazy_sync_size)++;
1020 * Attempt to resolve all stashed operations that might synchronize with a
1021 * release sequence for a given location. This implements the "lazy" portion of
1022 * determining whether or not a release sequence was contiguous, since not all
1023 * modification order information is present at the time an action occurs.
1025 * @param location The location/object that should be checked for release
1026 * sequence resolutions
1027 * @param work_queue The work queue to which to add work items as they are
1029 * @return True if any updates occurred (new synchronization, new mo_graph
1032 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1034 std::list<ModelAction *> *list;
1035 list = lazy_sync_with_release->getptr(location);
1039 bool updated = false;
1040 std::list<ModelAction *>::iterator it = list->begin();
1041 while (it != list->end()) {
1042 ModelAction *act = *it;
1043 const ModelAction *rf = act->get_reads_from();
1044 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1046 complete = release_seq_head(rf, &release_heads);
1047 for (unsigned int i = 0; i < release_heads.size(); i++) {
1048 if (!act->has_synchronized_with(release_heads[i])) {
1050 act->synchronize_with(release_heads[i]);
1055 /* Re-check act for mo_graph edges */
1056 work_queue->push_back(MOEdgeWorkEntry(act));
1058 /* propagate synchronization to later actions */
1059 action_list_t::reverse_iterator it = action_trace->rbegin();
1060 while ((*it) != act) {
1061 ModelAction *propagate = *it;
1062 if (act->happens_before(propagate)) {
1063 propagate->synchronize_with(act);
1064 /* Re-check 'propagate' for mo_graph edges */
1065 work_queue->push_back(MOEdgeWorkEntry(propagate));
1070 it = list->erase(it);
1071 (*lazy_sync_size)--;
1076 // If we resolved promises or data races, see if we have realized a data race.
1077 if (checkDataRaces()) {
1085 * Performs various bookkeeping operations for the current ModelAction. For
1086 * instance, adds action to the per-object, per-thread action vector and to the
1087 * action trace list of all thread actions.
1089 * @param act is the ModelAction to add.
1091 void ModelChecker::add_action_to_lists(ModelAction *act)
1093 int tid = id_to_int(act->get_tid());
1094 action_trace->push_back(act);
1096 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1098 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1099 if (tid >= (int)vec->size())
1100 vec->resize(priv->next_thread_id);
1101 (*vec)[tid].push_back(act);
1103 if ((int)thrd_last_action->size() <= tid)
1104 thrd_last_action->resize(get_num_threads());
1105 (*thrd_last_action)[tid] = act;
1108 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1110 int nthreads = get_num_threads();
1111 if ((int)thrd_last_action->size() < nthreads)
1112 thrd_last_action->resize(nthreads);
1113 return (*thrd_last_action)[id_to_int(tid)];
1117 * Gets the last memory_order_seq_cst write (in the total global sequence)
1118 * performed on a particular object (i.e., memory location), not including the
1120 * @param curr The current ModelAction; also denotes the object location to
1122 * @return The last seq_cst write
1124 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1126 void *location = curr->get_location();
1127 action_list_t *list = obj_map->get_safe_ptr(location);
1128 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1129 action_list_t::reverse_iterator rit;
1130 for (rit = list->rbegin(); rit != list->rend(); rit++)
1131 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1136 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1138 ModelAction *parent = get_last_action(tid);
1140 parent = get_thread(tid)->get_creation();
1145 * Returns the clock vector for a given thread.
1146 * @param tid The thread whose clock vector we want
1147 * @return Desired clock vector
1149 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1151 return get_parent_action(tid)->get_cv();
1155 * Resolve a set of Promises with a current write. The set is provided in the
1156 * Node corresponding to @a write.
1157 * @param write The ModelAction that is fulfilling Promises
1158 * @return True if promises were resolved; false otherwise
1160 bool ModelChecker::resolve_promises(ModelAction *write)
1162 bool resolved = false;
1164 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1165 Promise *promise = (*promises)[promise_index];
1166 if (write->get_node()->get_promise(i)) {
1167 ModelAction *read = promise->get_action();
1168 read->read_from(write);
1169 if (read->is_rmw()) {
1170 mo_graph->addRMWEdge(write, read);
1172 //First fix up the modification order for actions that happened
1174 r_modification_order(read, write);
1175 //Next fix up the modification order for actions that happened
1177 post_r_modification_order(read, write);
1178 promises->erase(promises->begin() + promise_index);
1187 * Compute the set of promises that could potentially be satisfied by this
1188 * action. Note that the set computation actually appears in the Node, not in
1190 * @param curr The ModelAction that may satisfy promises
1192 void ModelChecker::compute_promises(ModelAction *curr)
1194 for (unsigned int i = 0; i < promises->size(); i++) {
1195 Promise *promise = (*promises)[i];
1196 const ModelAction *act = promise->get_action();
1197 if (!act->happens_before(curr) &&
1199 !act->is_synchronizing(curr) &&
1200 !act->same_thread(curr) &&
1201 promise->get_value() == curr->get_value()) {
1202 curr->get_node()->set_promise(i);
1207 /** Checks promises in response to change in ClockVector Threads. */
1208 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1210 for (unsigned int i = 0; i < promises->size(); i++) {
1211 Promise *promise = (*promises)[i];
1212 const ModelAction *act = promise->get_action();
1213 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1214 merge_cv->synchronized_since(act)) {
1215 //This thread is no longer able to send values back to satisfy the promise
1216 int num_synchronized_threads = promise->increment_threads();
1217 if (num_synchronized_threads == get_num_threads()) {
1218 //Promise has failed
1219 failed_promise = true;
1227 * Build up an initial set of all past writes that this 'read' action may read
1228 * from. This set is determined by the clock vector's "happens before"
1230 * @param curr is the current ModelAction that we are exploring; it must be a
1233 void ModelChecker::build_reads_from_past(ModelAction *curr)
1235 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1237 ASSERT(curr->is_read());
1239 ModelAction *last_seq_cst = NULL;
1241 /* Track whether this object has been initialized */
1242 bool initialized = false;
1244 if (curr->is_seqcst()) {
1245 last_seq_cst = get_last_seq_cst(curr);
1246 /* We have to at least see the last sequentially consistent write,
1247 so we are initialized. */
1248 if (last_seq_cst != NULL)
1252 /* Iterate over all threads */
1253 for (i = 0; i < thrd_lists->size(); i++) {
1254 /* Iterate over actions in thread, starting from most recent */
1255 action_list_t *list = &(*thrd_lists)[i];
1256 action_list_t::reverse_iterator rit;
1257 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1258 ModelAction *act = *rit;
1260 /* Only consider 'write' actions */
1261 if (!act->is_write())
1264 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1265 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1266 DEBUG("Adding action to may_read_from:\n");
1267 if (DBG_ENABLED()) {
1271 curr->get_node()->add_read_from(act);
1274 /* Include at most one act per-thread that "happens before" curr */
1275 if (act->happens_before(curr)) {
1283 /** @todo Need a more informative way of reporting errors. */
1284 printf("ERROR: may read from uninitialized atomic\n");
1287 if (DBG_ENABLED() || !initialized) {
1288 printf("Reached read action:\n");
1290 printf("Printing may_read_from\n");
1291 curr->get_node()->print_may_read_from();
1292 printf("End printing may_read_from\n");
1295 ASSERT(initialized);
1298 static void print_list(action_list_t *list)
1300 action_list_t::iterator it;
1302 printf("---------------------------------------------------------------------\n");
1305 for (it = list->begin(); it != list->end(); it++) {
1308 printf("---------------------------------------------------------------------\n");
1311 void ModelChecker::print_summary()
1314 printf("Number of executions: %d\n", num_executions);
1315 printf("Number of feasible executions: %d\n", num_feasible_executions);
1316 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1318 #if SUPPORT_MOD_ORDER_DUMP
1320 char buffername[100];
1321 sprintf(buffername, "exec%u",num_executions);
1322 mo_graph->dumpGraphToFile(buffername);
1325 if (!isfinalfeasible())
1326 printf("INFEASIBLE EXECUTION!\n");
1327 print_list(action_trace);
1332 * Add a Thread to the system for the first time. Should only be called once
1334 * @param t The Thread to add
1336 void ModelChecker::add_thread(Thread *t)
1338 thread_map->put(id_to_int(t->get_id()), t);
1339 scheduler->add_thread(t);
1342 void ModelChecker::remove_thread(Thread *t)
1344 scheduler->remove_thread(t);
1348 * Switch from a user-context to the "master thread" context (a.k.a. system
1349 * context). This switch is made with the intention of exploring a particular
1350 * model-checking action (described by a ModelAction object). Must be called
1351 * from a user-thread context.
1352 * @param act The current action that will be explored. Must not be NULL.
1353 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1355 int ModelChecker::switch_to_master(ModelAction *act)
1358 Thread *old = thread_current();
1359 set_current_action(act);
1360 old->set_state(THREAD_READY);
1361 return Thread::swap(old, &system_context);
1365 * Takes the next step in the execution, if possible.
1366 * @return Returns true (success) if a step was taken and false otherwise.
1368 bool ModelChecker::take_step() {
1369 Thread *curr, *next;
1374 curr = thread_current();
1376 if (curr->get_state() == THREAD_READY) {
1377 ASSERT(priv->current_action);
1379 priv->nextThread = check_current_action(priv->current_action);
1380 priv->current_action = NULL;
1381 if (!curr->is_blocked() && !curr->is_complete())
1382 scheduler->add_thread(curr);
1387 next = scheduler->next_thread(priv->nextThread);
1389 /* Infeasible -> don't take any more steps */
1394 next->set_state(THREAD_RUNNING);
1395 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1397 /* next == NULL -> don't take any more steps */
1400 /* Return false only if swap fails with an error */
1401 return (Thread::swap(&system_context, next) == 0);
1404 /** Runs the current execution until threre are no more steps to take. */
1405 void ModelChecker::finish_execution() {
1408 while (take_step());