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;
336 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
338 if (curr->is_rmwc() || curr->is_rmw()) {
339 ModelAction *tmp = process_rmw(curr);
342 compute_promises(curr);
344 ModelAction *tmp = node_stack->explore_action(curr);
346 /* Discard duplicate ModelAction; use action from NodeStack */
347 /* First restore type and order in case of RMW operation */
349 tmp->copy_typeandorder(curr);
351 /* If we have diverged, we need to reset the clock vector. */
353 tmp->create_cv(get_parent_action(tmp->get_tid()));
359 * Perform one-time actions when pushing new ModelAction onto
362 curr->create_cv(get_parent_action(curr->get_tid()));
363 /* Build may_read_from set */
365 build_reads_from_past(curr);
366 if (curr->is_write())
367 compute_promises(curr);
374 * This is the heart of the model checker routine. It performs model-checking
375 * actions corresponding to a given "current action." Among other processes, it
376 * calculates reads-from relationships, updates synchronization clock vectors,
377 * forms a memory_order constraints graph, and handles replay/backtrack
378 * execution when running permutations of previously-observed executions.
380 * @param curr The current action to process
381 * @return The next Thread that must be executed. May be NULL if ModelChecker
382 * makes no choice (e.g., according to replay execution, combining RMW actions,
385 Thread * ModelChecker::check_current_action(ModelAction *curr)
389 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
391 curr = initialize_curr_action(curr);
393 /* Thread specific actions */
394 switch (curr->get_type()) {
395 case THREAD_CREATE: {
396 Thread *th = (Thread *)curr->get_location();
397 th->set_creation(curr);
401 Thread *waiting, *blocking;
402 waiting = get_thread(curr);
403 blocking = (Thread *)curr->get_location();
404 if (!blocking->is_complete()) {
405 blocking->push_wait_list(curr);
406 scheduler->sleep(waiting);
410 case THREAD_FINISH: {
411 Thread *th = get_thread(curr);
412 while (!th->wait_list_empty()) {
413 ModelAction *act = th->pop_wait_list();
414 Thread *wake = get_thread(act);
415 scheduler->wake(wake);
421 check_promises(NULL, curr->get_cv());
428 /* Add current action to lists before work_queue loop */
429 if (!second_part_of_rmw)
430 add_action_to_lists(curr);
432 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
434 while (!work_queue.empty()) {
435 WorkQueueEntry work = work_queue.front();
436 work_queue.pop_front();
439 case WORK_CHECK_CURR_ACTION: {
440 ModelAction *act = work.action;
441 bool updated = false;
442 if (act->is_read() && process_read(act, second_part_of_rmw))
445 if (act->is_write() && process_write(act))
449 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
452 case WORK_CHECK_RELEASE_SEQ:
453 resolve_release_sequences(work.location, &work_queue);
455 case WORK_CHECK_MO_EDGES: {
456 /** @todo Complete verification of work_queue */
457 ModelAction *act = work.action;
458 bool updated = false;
460 if (act->is_read()) {
461 if (r_modification_order(act, act->get_reads_from()))
464 if (act->is_write()) {
465 if (w_modification_order(act))
470 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
479 check_curr_backtracking(curr);
481 set_backtracking(curr);
483 return get_next_thread(curr);
486 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
487 Node *currnode = curr->get_node();
488 Node *parnode = currnode->get_parent();
490 if ((!parnode->backtrack_empty() ||
491 !currnode->read_from_empty() ||
492 !currnode->future_value_empty() ||
493 !currnode->promise_empty())
494 && (!priv->next_backtrack ||
495 *curr > *priv->next_backtrack)) {
496 priv->next_backtrack = curr;
500 bool ModelChecker::promises_expired() {
501 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
502 Promise *promise = (*promises)[promise_index];
503 if (promise->get_expiration()<priv->used_sequence_numbers) {
510 /** @returns whether the current partial trace must be a prefix of a
512 bool ModelChecker::isfeasibleprefix() {
513 return promises->size() == 0 && *lazy_sync_size == 0;
516 /** @returns whether the current partial trace is feasible. */
517 bool ModelChecker::isfeasible() {
518 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
521 /** @returns whether the current partial trace is feasible other than
522 * multiple RMW reading from the same store. */
523 bool ModelChecker::isfeasibleotherthanRMW() {
525 if (mo_graph->checkForCycles())
526 DEBUG("Infeasible: modification order cycles\n");
528 DEBUG("Infeasible: failed promise\n");
530 DEBUG("Infeasible: too many reads\n");
531 if (promises_expired())
532 DEBUG("Infeasible: promises expired\n");
534 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
537 /** Returns whether the current completed trace is feasible. */
538 bool ModelChecker::isfinalfeasible() {
539 if (DBG_ENABLED() && promises->size() != 0)
540 DEBUG("Infeasible: unrevolved promises\n");
542 return isfeasible() && promises->size() == 0;
545 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
546 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
547 int tid = id_to_int(act->get_tid());
548 ModelAction *lastread = get_last_action(tid);
549 lastread->process_rmw(act);
550 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
551 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
552 mo_graph->commitChanges();
558 * Checks whether a thread has read from the same write for too many times
559 * without seeing the effects of a later write.
562 * 1) there must a different write that we could read from that would satisfy the modification order,
563 * 2) we must have read from the same value in excess of maxreads times, and
564 * 3) that other write must have been in the reads_from set for maxreads times.
566 * If so, we decide that the execution is no longer feasible.
568 void ModelChecker::check_recency(ModelAction *curr) {
569 if (params.maxreads != 0) {
570 if (curr->get_node()->get_read_from_size() <= 1)
573 //Must make sure that execution is currently feasible... We could
574 //accidentally clear by rolling back
578 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
579 int tid = id_to_int(curr->get_tid());
582 if ((int)thrd_lists->size() <= tid)
585 action_list_t *list = &(*thrd_lists)[tid];
587 action_list_t::reverse_iterator rit = list->rbegin();
589 for (; (*rit) != curr; rit++)
591 /* go past curr now */
594 action_list_t::reverse_iterator ritcopy = rit;
595 //See if we have enough reads from the same value
597 for (; count < params.maxreads; rit++,count++) {
598 if (rit==list->rend())
600 ModelAction *act = *rit;
603 if (act->get_reads_from() != curr->get_reads_from())
605 if (act->get_node()->get_read_from_size() <= 1)
609 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
611 const ModelAction * write = curr->get_node()->get_read_from_at(i);
612 //Need a different write
613 if (write==curr->get_reads_from())
616 /* Test to see whether this is a feasible write to read from*/
617 mo_graph->startChanges();
618 r_modification_order(curr, write);
619 bool feasiblereadfrom = isfeasible();
620 mo_graph->rollbackChanges();
622 if (!feasiblereadfrom)
626 bool feasiblewrite = true;
627 //new we need to see if this write works for everyone
629 for (int loop = count; loop>0; loop--,rit++) {
630 ModelAction *act=*rit;
631 bool foundvalue = false;
632 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
633 if (act->get_node()->get_read_from_at(i)==write) {
639 feasiblewrite = false;
644 too_many_reads = true;
652 * Updates the mo_graph with the constraints imposed from the current
655 * Basic idea is the following: Go through each other thread and find
656 * the lastest action that happened before our read. Two cases:
658 * (1) The action is a write => that write must either occur before
659 * the write we read from or be the write we read from.
661 * (2) The action is a read => the write that that action read from
662 * must occur before the write we read from or be the same write.
664 * @param curr The current action. Must be a read.
665 * @param rf The action that curr reads from. Must be a write.
666 * @return True if modification order edges were added; false otherwise
668 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
670 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
673 ASSERT(curr->is_read());
675 /* Iterate over all threads */
676 for (i = 0; i < thrd_lists->size(); i++) {
677 /* Iterate over actions in thread, starting from most recent */
678 action_list_t *list = &(*thrd_lists)[i];
679 action_list_t::reverse_iterator rit;
680 for (rit = list->rbegin(); rit != list->rend(); rit++) {
681 ModelAction *act = *rit;
684 * Include at most one act per-thread that "happens
685 * before" curr. Don't consider reflexively.
687 if (act->happens_before(curr) && act != curr) {
688 if (act->is_write()) {
690 mo_graph->addEdge(act, rf);
694 const ModelAction *prevreadfrom = act->get_reads_from();
695 if (prevreadfrom != NULL && rf != prevreadfrom) {
696 mo_graph->addEdge(prevreadfrom, rf);
708 /** This method fixes up the modification order when we resolve a
709 * promises. The basic problem is that actions that occur after the
710 * read curr could not property add items to the modification order
713 * So for each thread, we find the earliest item that happens after
714 * the read curr. This is the item we have to fix up with additional
715 * constraints. If that action is write, we add a MO edge between
716 * the Action rf and that action. If the action is a read, we add a
717 * MO edge between the Action rf, and whatever the read accessed.
719 * @param curr is the read ModelAction that we are fixing up MO edges for.
720 * @param rf is the write ModelAction that curr reads from.
724 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
726 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
728 ASSERT(curr->is_read());
730 /* Iterate over all threads */
731 for (i = 0; i < thrd_lists->size(); i++) {
732 /* Iterate over actions in thread, starting from most recent */
733 action_list_t *list = &(*thrd_lists)[i];
734 action_list_t::reverse_iterator rit;
735 ModelAction *lastact = NULL;
737 /* Find last action that happens after curr */
738 for (rit = list->rbegin(); rit != list->rend(); rit++) {
739 ModelAction *act = *rit;
740 if (curr->happens_before(act)) {
746 /* Include at most one act per-thread that "happens before" curr */
747 if (lastact != NULL) {
748 if (lastact->is_read()) {
749 const ModelAction *postreadfrom = lastact->get_reads_from();
750 if (postreadfrom != NULL&&rf != postreadfrom)
751 mo_graph->addEdge(rf, postreadfrom);
752 } else if (rf != lastact) {
753 mo_graph->addEdge(rf, lastact);
761 * Updates the mo_graph with the constraints imposed from the current write.
763 * Basic idea is the following: Go through each other thread and find
764 * the lastest action that happened before our write. Two cases:
766 * (1) The action is a write => that write must occur before
769 * (2) The action is a read => the write that that action read from
770 * must occur before the current write.
772 * This method also handles two other issues:
774 * (I) Sequential Consistency: Making sure that if the current write is
775 * seq_cst, that it occurs after the previous seq_cst write.
777 * (II) Sending the write back to non-synchronizing reads.
779 * @param curr The current action. Must be a write.
780 * @return True if modification order edges were added; false otherwise
782 bool ModelChecker::w_modification_order(ModelAction *curr)
784 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
787 ASSERT(curr->is_write());
789 if (curr->is_seqcst()) {
790 /* We have to at least see the last sequentially consistent write,
791 so we are initialized. */
792 ModelAction *last_seq_cst = get_last_seq_cst(curr);
793 if (last_seq_cst != NULL) {
794 mo_graph->addEdge(last_seq_cst, curr);
799 /* Iterate over all threads */
800 for (i = 0; i < thrd_lists->size(); i++) {
801 /* Iterate over actions in thread, starting from most recent */
802 action_list_t *list = &(*thrd_lists)[i];
803 action_list_t::reverse_iterator rit;
804 for (rit = list->rbegin(); rit != list->rend(); rit++) {
805 ModelAction *act = *rit;
808 * If RMW, we already have all relevant edges,
809 * so just skip to next thread.
810 * If normal write, we need to look at earlier
811 * actions, so continue processing list.
820 * Include at most one act per-thread that "happens
823 if (act->happens_before(curr)) {
825 * Note: if act is RMW, just add edge:
827 * The following edge should be handled elsewhere:
828 * readfrom(act) --mo--> act
831 mo_graph->addEdge(act, curr);
832 else if (act->is_read() && act->get_reads_from() != NULL)
833 mo_graph->addEdge(act->get_reads_from(), curr);
836 } else if (act->is_read() && !act->is_synchronizing(curr) &&
837 !act->same_thread(curr)) {
838 /* We have an action that:
839 (1) did not happen before us
840 (2) is a read and we are a write
841 (3) cannot synchronize with us
842 (4) is in a different thread
844 that read could potentially read from our write.
846 if (thin_air_constraint_may_allow(curr, act)) {
848 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
849 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
850 futurevalues->push_back(pfv);
860 /** Arbitrary reads from the future are not allowed. Section 29.3
861 * part 9 places some constraints. This method checks one result of constraint
862 * constraint. Others require compiler support. */
864 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
865 if (!writer->is_rmw())
868 if (!reader->is_rmw())
871 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
874 if (search->get_tid() == reader->get_tid() &&
875 search->happens_before(reader))
883 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
884 * The ModelAction under consideration is expected to be taking part in
885 * release/acquire synchronization as an object of the "reads from" relation.
886 * Note that this can only provide release sequence support for RMW chains
887 * which do not read from the future, as those actions cannot be traced until
888 * their "promise" is fulfilled. Similarly, we may not even establish the
889 * presence of a release sequence with certainty, as some modification order
890 * constraints may be decided further in the future. Thus, this function
891 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
892 * and a boolean representing certainty.
894 * @todo Finish lazy updating, when promises are fulfilled in the future
895 * @param rf The action that might be part of a release sequence. Must be a
897 * @param release_heads A pass-by-reference style return parameter. After
898 * execution of this function, release_heads will contain the heads of all the
899 * relevant release sequences, if any exists
900 * @return true, if the ModelChecker is certain that release_heads is complete;
903 bool ModelChecker::release_seq_head(const ModelAction *rf,
904 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
907 /* read from future: need to settle this later */
908 return false; /* incomplete */
911 ASSERT(rf->is_write());
913 if (rf->is_release())
914 release_heads->push_back(rf);
916 /* We need a RMW action that is both an acquire and release to stop */
917 /** @todo Need to be smarter here... In the linux lock
918 * example, this will run to the beginning of the program for
920 if (rf->is_acquire() && rf->is_release())
921 return true; /* complete */
922 return release_seq_head(rf->get_reads_from(), release_heads);
924 if (rf->is_release())
925 return true; /* complete */
927 /* else relaxed write; check modification order for contiguous subsequence
928 * -> rf must be same thread as release */
929 int tid = id_to_int(rf->get_tid());
930 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
931 action_list_t *list = &(*thrd_lists)[tid];
932 action_list_t::const_reverse_iterator rit;
934 /* Find rf in the thread list */
935 rit = std::find(list->rbegin(), list->rend(), rf);
936 ASSERT(rit != list->rend());
938 /* Find the last write/release */
939 for (; rit != list->rend(); rit++)
940 if ((*rit)->is_release())
942 if (rit == list->rend()) {
943 /* No write-release in this thread */
944 return true; /* complete */
946 ModelAction *release = *rit;
948 ASSERT(rf->same_thread(release));
951 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
952 if (id_to_int(rf->get_tid()) == (int)i)
954 list = &(*thrd_lists)[i];
956 /* Can we ensure no future writes from this thread may break
957 * the release seq? */
958 bool future_ordered = false;
960 for (rit = list->rbegin(); rit != list->rend(); rit++) {
961 const ModelAction *act = *rit;
962 if (!act->is_write())
964 /* Reach synchronization -> this thread is complete */
965 if (act->happens_before(release))
967 if (rf->happens_before(act)) {
968 future_ordered = true;
972 /* Check modification order */
973 if (mo_graph->checkReachable(rf, act)) {
975 future_ordered = true;
978 if (mo_graph->checkReachable(act, release))
979 /* act --mo--> release */
981 if (mo_graph->checkReachable(release, act) &&
982 mo_graph->checkReachable(act, rf)) {
983 /* release --mo-> act --mo--> rf */
984 return true; /* complete */
989 return false; /* This thread is uncertain */
993 release_heads->push_back(release);
998 * A public interface for getting the release sequence head(s) with which a
999 * given ModelAction must synchronize. This function only returns a non-empty
1000 * result when it can locate a release sequence head with certainty. Otherwise,
1001 * it may mark the internal state of the ModelChecker so that it will handle
1002 * the release sequence at a later time, causing @a act to update its
1003 * synchronization at some later point in execution.
1004 * @param act The 'acquire' action that may read from a release sequence
1005 * @param release_heads A pass-by-reference return parameter. Will be filled
1006 * with the head(s) of the release sequence(s), if they exists with certainty.
1007 * @see ModelChecker::release_seq_head
1009 void ModelChecker::get_release_seq_heads(ModelAction *act,
1010 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
1012 const ModelAction *rf = act->get_reads_from();
1014 complete = release_seq_head(rf, release_heads);
1016 /* add act to 'lazy checking' list */
1017 std::list<ModelAction *> *list;
1018 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1019 list->push_back(act);
1020 (*lazy_sync_size)++;
1025 * Attempt to resolve all stashed operations that might synchronize with a
1026 * release sequence for a given location. This implements the "lazy" portion of
1027 * determining whether or not a release sequence was contiguous, since not all
1028 * modification order information is present at the time an action occurs.
1030 * @param location The location/object that should be checked for release
1031 * sequence resolutions
1032 * @param work_queue The work queue to which to add work items as they are
1034 * @return True if any updates occurred (new synchronization, new mo_graph
1037 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1039 std::list<ModelAction *> *list;
1040 list = lazy_sync_with_release->getptr(location);
1044 bool updated = false;
1045 std::list<ModelAction *>::iterator it = list->begin();
1046 while (it != list->end()) {
1047 ModelAction *act = *it;
1048 const ModelAction *rf = act->get_reads_from();
1049 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1051 complete = release_seq_head(rf, &release_heads);
1052 for (unsigned int i = 0; i < release_heads.size(); i++) {
1053 if (!act->has_synchronized_with(release_heads[i])) {
1055 act->synchronize_with(release_heads[i]);
1060 /* Re-check act for mo_graph edges */
1061 work_queue->push_back(MOEdgeWorkEntry(act));
1063 /* propagate synchronization to later actions */
1064 action_list_t::reverse_iterator it = action_trace->rbegin();
1065 while ((*it) != act) {
1066 ModelAction *propagate = *it;
1067 if (act->happens_before(propagate)) {
1068 propagate->synchronize_with(act);
1069 /* Re-check 'propagate' for mo_graph edges */
1070 work_queue->push_back(MOEdgeWorkEntry(propagate));
1075 it = list->erase(it);
1076 (*lazy_sync_size)--;
1081 // If we resolved promises or data races, see if we have realized a data race.
1082 if (checkDataRaces()) {
1090 * Performs various bookkeeping operations for the current ModelAction. For
1091 * instance, adds action to the per-object, per-thread action vector and to the
1092 * action trace list of all thread actions.
1094 * @param act is the ModelAction to add.
1096 void ModelChecker::add_action_to_lists(ModelAction *act)
1098 int tid = id_to_int(act->get_tid());
1099 action_trace->push_back(act);
1101 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1103 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1104 if (tid >= (int)vec->size())
1105 vec->resize(priv->next_thread_id);
1106 (*vec)[tid].push_back(act);
1108 if ((int)thrd_last_action->size() <= tid)
1109 thrd_last_action->resize(get_num_threads());
1110 (*thrd_last_action)[tid] = act;
1113 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1115 int nthreads = get_num_threads();
1116 if ((int)thrd_last_action->size() < nthreads)
1117 thrd_last_action->resize(nthreads);
1118 return (*thrd_last_action)[id_to_int(tid)];
1122 * Gets the last memory_order_seq_cst write (in the total global sequence)
1123 * performed on a particular object (i.e., memory location), not including the
1125 * @param curr The current ModelAction; also denotes the object location to
1127 * @return The last seq_cst write
1129 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1131 void *location = curr->get_location();
1132 action_list_t *list = obj_map->get_safe_ptr(location);
1133 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1134 action_list_t::reverse_iterator rit;
1135 for (rit = list->rbegin(); rit != list->rend(); rit++)
1136 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1141 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1143 ModelAction *parent = get_last_action(tid);
1145 parent = get_thread(tid)->get_creation();
1150 * Returns the clock vector for a given thread.
1151 * @param tid The thread whose clock vector we want
1152 * @return Desired clock vector
1154 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1156 return get_parent_action(tid)->get_cv();
1160 * Resolve a set of Promises with a current write. The set is provided in the
1161 * Node corresponding to @a write.
1162 * @param write The ModelAction that is fulfilling Promises
1163 * @return True if promises were resolved; false otherwise
1165 bool ModelChecker::resolve_promises(ModelAction *write)
1167 bool resolved = false;
1169 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1170 Promise *promise = (*promises)[promise_index];
1171 if (write->get_node()->get_promise(i)) {
1172 ModelAction *read = promise->get_action();
1173 read->read_from(write);
1174 if (read->is_rmw()) {
1175 mo_graph->addRMWEdge(write, read);
1177 //First fix up the modification order for actions that happened
1179 r_modification_order(read, write);
1180 //Next fix up the modification order for actions that happened
1182 post_r_modification_order(read, write);
1183 promises->erase(promises->begin() + promise_index);
1192 * Compute the set of promises that could potentially be satisfied by this
1193 * action. Note that the set computation actually appears in the Node, not in
1195 * @param curr The ModelAction that may satisfy promises
1197 void ModelChecker::compute_promises(ModelAction *curr)
1199 for (unsigned int i = 0; i < promises->size(); i++) {
1200 Promise *promise = (*promises)[i];
1201 const ModelAction *act = promise->get_action();
1202 if (!act->happens_before(curr) &&
1204 !act->is_synchronizing(curr) &&
1205 !act->same_thread(curr) &&
1206 promise->get_value() == curr->get_value()) {
1207 curr->get_node()->set_promise(i);
1212 /** Checks promises in response to change in ClockVector Threads. */
1213 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1215 for (unsigned int i = 0; i < promises->size(); i++) {
1216 Promise *promise = (*promises)[i];
1217 const ModelAction *act = promise->get_action();
1218 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1219 merge_cv->synchronized_since(act)) {
1220 //This thread is no longer able to send values back to satisfy the promise
1221 int num_synchronized_threads = promise->increment_threads();
1222 if (num_synchronized_threads == get_num_threads()) {
1223 //Promise has failed
1224 failed_promise = true;
1232 * Build up an initial set of all past writes that this 'read' action may read
1233 * from. This set is determined by the clock vector's "happens before"
1235 * @param curr is the current ModelAction that we are exploring; it must be a
1238 void ModelChecker::build_reads_from_past(ModelAction *curr)
1240 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1242 ASSERT(curr->is_read());
1244 ModelAction *last_seq_cst = NULL;
1246 /* Track whether this object has been initialized */
1247 bool initialized = false;
1249 if (curr->is_seqcst()) {
1250 last_seq_cst = get_last_seq_cst(curr);
1251 /* We have to at least see the last sequentially consistent write,
1252 so we are initialized. */
1253 if (last_seq_cst != NULL)
1257 /* Iterate over all threads */
1258 for (i = 0; i < thrd_lists->size(); i++) {
1259 /* Iterate over actions in thread, starting from most recent */
1260 action_list_t *list = &(*thrd_lists)[i];
1261 action_list_t::reverse_iterator rit;
1262 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1263 ModelAction *act = *rit;
1265 /* Only consider 'write' actions */
1266 if (!act->is_write())
1269 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1270 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1271 DEBUG("Adding action to may_read_from:\n");
1272 if (DBG_ENABLED()) {
1276 curr->get_node()->add_read_from(act);
1279 /* Include at most one act per-thread that "happens before" curr */
1280 if (act->happens_before(curr)) {
1288 /** @todo Need a more informative way of reporting errors. */
1289 printf("ERROR: may read from uninitialized atomic\n");
1292 if (DBG_ENABLED() || !initialized) {
1293 printf("Reached read action:\n");
1295 printf("Printing may_read_from\n");
1296 curr->get_node()->print_may_read_from();
1297 printf("End printing may_read_from\n");
1300 ASSERT(initialized);
1303 static void print_list(action_list_t *list)
1305 action_list_t::iterator it;
1307 printf("---------------------------------------------------------------------\n");
1310 for (it = list->begin(); it != list->end(); it++) {
1313 printf("---------------------------------------------------------------------\n");
1316 void ModelChecker::print_summary()
1319 printf("Number of executions: %d\n", num_executions);
1320 printf("Number of feasible executions: %d\n", num_feasible_executions);
1321 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1323 #if SUPPORT_MOD_ORDER_DUMP
1325 char buffername[100];
1326 sprintf(buffername, "exec%u",num_executions);
1327 mo_graph->dumpGraphToFile(buffername);
1330 if (!isfinalfeasible())
1331 printf("INFEASIBLE EXECUTION!\n");
1332 print_list(action_trace);
1337 * Add a Thread to the system for the first time. Should only be called once
1339 * @param t The Thread to add
1341 void ModelChecker::add_thread(Thread *t)
1343 thread_map->put(id_to_int(t->get_id()), t);
1344 scheduler->add_thread(t);
1347 void ModelChecker::remove_thread(Thread *t)
1349 scheduler->remove_thread(t);
1353 * Switch from a user-context to the "master thread" context (a.k.a. system
1354 * context). This switch is made with the intention of exploring a particular
1355 * model-checking action (described by a ModelAction object). Must be called
1356 * from a user-thread context.
1357 * @param act The current action that will be explored. Must not be NULL.
1358 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1360 int ModelChecker::switch_to_master(ModelAction *act)
1363 Thread *old = thread_current();
1364 set_current_action(act);
1365 old->set_state(THREAD_READY);
1366 return Thread::swap(old, &system_context);
1370 * Takes the next step in the execution, if possible.
1371 * @return Returns true (success) if a step was taken and false otherwise.
1373 bool ModelChecker::take_step() {
1374 Thread *curr, *next;
1379 curr = thread_current();
1381 if (curr->get_state() == THREAD_READY) {
1382 ASSERT(priv->current_action);
1384 priv->nextThread = check_current_action(priv->current_action);
1385 priv->current_action = NULL;
1386 if (!curr->is_blocked() && !curr->is_complete())
1387 scheduler->add_thread(curr);
1392 next = scheduler->next_thread(priv->nextThread);
1394 /* Infeasible -> don't take any more steps */
1399 next->set_state(THREAD_RUNNING);
1400 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1402 /* next == NULL -> don't take any more steps */
1405 /* Return false only if swap fails with an error */
1406 return (Thread::swap(&system_context, next) == 0);
1409 /** Runs the current execution until threre are no more steps to take. */
1410 void ModelChecker::finish_execution() {
1413 while (take_step());