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 *, action_list_t, 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();
200 if (type==ATOMIC_READ||type==ATOMIC_WRITE||type==ATOMIC_RMW) {
201 /* linear search: from most recent to oldest */
202 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
203 action_list_t::reverse_iterator rit;
204 for (rit = list->rbegin(); rit != list->rend(); rit++) {
205 ModelAction *prev = *rit;
206 if (act->is_synchronizing(prev))
209 } else if (type==ATOMIC_LOCK||type==ATOMIC_TRYLOCK) {
210 /* linear search: from most recent to oldest */
211 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
212 action_list_t::reverse_iterator rit;
213 for (rit = list->rbegin(); rit != list->rend(); rit++) {
214 ModelAction *prev = *rit;
215 if (prev->is_success_lock())
218 } else if (type==ATOMIC_UNLOCK) {
219 /* linear search: from most recent to oldest */
220 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
221 action_list_t::reverse_iterator rit;
222 for (rit = list->rbegin(); rit != list->rend(); rit++) {
223 ModelAction *prev = *rit;
224 if (prev->is_failed_trylock())
231 void ModelChecker::set_backtracking(ModelAction *act)
235 Thread *t = get_thread(act);
237 prev = get_last_conflict(act);
241 node = prev->get_node()->get_parent();
243 while (!node->is_enabled(t))
246 /* Check if this has been explored already */
247 if (node->has_been_explored(t->get_id()))
250 /* Cache the latest backtracking point */
251 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
252 priv->next_backtrack = prev;
254 /* If this is a new backtracking point, mark the tree */
255 if (!node->set_backtrack(t->get_id()))
257 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
258 prev->get_tid(), t->get_id());
266 * Returns last backtracking point. The model checker will explore a different
267 * path for this point in the next execution.
268 * @return The ModelAction at which the next execution should diverge.
270 ModelAction * ModelChecker::get_next_backtrack()
272 ModelAction *next = priv->next_backtrack;
273 priv->next_backtrack = NULL;
278 * Processes a read or rmw model action.
279 * @param curr is the read model action to process.
280 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
281 * @return True if processing this read updates the mo_graph.
283 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
286 bool updated = false;
288 const ModelAction *reads_from = curr->get_node()->get_read_from();
289 if (reads_from != NULL) {
290 mo_graph->startChanges();
292 value = reads_from->get_value();
293 bool r_status = false;
295 if (!second_part_of_rmw) {
297 r_status = r_modification_order(curr, reads_from);
301 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
302 mo_graph->rollbackChanges();
303 too_many_reads = false;
307 curr->read_from(reads_from);
308 mo_graph->commitChanges();
310 } else if (!second_part_of_rmw) {
311 /* Read from future value */
312 value = curr->get_node()->get_future_value();
313 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
314 curr->read_from(NULL);
315 Promise *valuepromise = new Promise(curr, value, expiration);
316 promises->push_back(valuepromise);
318 get_thread(curr)->set_return_value(value);
324 * Process a write ModelAction
325 * @param curr The ModelAction to process
326 * @return True if the mo_graph was updated or promises were resolved
328 bool ModelChecker::process_write(ModelAction *curr)
330 bool updated_mod_order = w_modification_order(curr);
331 bool updated_promises = resolve_promises(curr);
333 if (promises->size() == 0) {
334 for (unsigned int i = 0; i<futurevalues->size(); i++) {
335 struct PendingFutureValue pfv = (*futurevalues)[i];
336 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
337 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
338 priv->next_backtrack = pfv.act;
340 futurevalues->resize(0);
343 mo_graph->commitChanges();
344 get_thread(curr)->set_return_value(VALUE_NONE);
345 return updated_mod_order || updated_promises;
349 * Initialize the current action by performing one or more of the following
350 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
351 * in the NodeStack, manipulating backtracking sets, allocating and
352 * initializing clock vectors, and computing the promises to fulfill.
354 * @param curr The current action, as passed from the user context; may be
355 * freed/invalidated after the execution of this function
356 * @return The current action, as processed by the ModelChecker. Is only the
357 * same as the parameter @a curr if this is a newly-explored action.
359 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
361 ModelAction *newcurr;
363 if (curr->is_rmwc() || curr->is_rmw()) {
364 newcurr = process_rmw(curr);
366 compute_promises(newcurr);
370 newcurr = node_stack->explore_action(curr);
372 /* First restore type and order in case of RMW operation */
374 newcurr->copy_typeandorder(curr);
376 ASSERT(curr->get_location()==newcurr->get_location());
377 /* Discard duplicate ModelAction; use action from NodeStack */
380 /* If we have diverged, we need to reset the clock vector. */
382 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
386 * Perform one-time actions when pushing new ModelAction onto
389 curr->create_cv(get_parent_action(curr->get_tid()));
390 if (curr->is_write())
391 compute_promises(curr);
397 * This is the heart of the model checker routine. It performs model-checking
398 * actions corresponding to a given "current action." Among other processes, it
399 * calculates reads-from relationships, updates synchronization clock vectors,
400 * forms a memory_order constraints graph, and handles replay/backtrack
401 * execution when running permutations of previously-observed executions.
403 * @param curr The current action to process
404 * @return The next Thread that must be executed. May be NULL if ModelChecker
405 * makes no choice (e.g., according to replay execution, combining RMW actions,
408 Thread * ModelChecker::check_current_action(ModelAction *curr)
412 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
414 ModelAction *newcurr = initialize_curr_action(curr);
416 /* Add the action to lists before any other model-checking tasks */
417 if (!second_part_of_rmw)
418 add_action_to_lists(newcurr);
420 /* Build may_read_from set for newly-created actions */
421 if (curr == newcurr && curr->is_read())
422 build_reads_from_past(curr);
425 /* Thread specific actions */
426 switch (curr->get_type()) {
427 case THREAD_CREATE: {
428 Thread *th = (Thread *)curr->get_location();
429 th->set_creation(curr);
433 Thread *waiting, *blocking;
434 waiting = get_thread(curr);
435 blocking = (Thread *)curr->get_location();
436 if (!blocking->is_complete()) {
437 blocking->push_wait_list(curr);
438 scheduler->sleep(waiting);
440 do_complete_join(curr);
444 case THREAD_FINISH: {
445 Thread *th = get_thread(curr);
446 while (!th->wait_list_empty()) {
447 ModelAction *act = th->pop_wait_list();
448 Thread *wake = get_thread(act);
449 scheduler->wake(wake);
450 do_complete_join(act);
456 check_promises(NULL, curr->get_cv());
463 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
465 while (!work_queue.empty()) {
466 WorkQueueEntry work = work_queue.front();
467 work_queue.pop_front();
470 case WORK_CHECK_CURR_ACTION: {
471 ModelAction *act = work.action;
472 bool updated = false;
473 if (act->is_read() && process_read(act, second_part_of_rmw))
476 if (act->is_write() && process_write(act))
480 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
483 case WORK_CHECK_RELEASE_SEQ:
484 resolve_release_sequences(work.location, &work_queue);
486 case WORK_CHECK_MO_EDGES: {
487 /** @todo Complete verification of work_queue */
488 ModelAction *act = work.action;
489 bool updated = false;
491 if (act->is_read()) {
492 if (r_modification_order(act, act->get_reads_from()))
495 if (act->is_write()) {
496 if (w_modification_order(act))
501 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
510 check_curr_backtracking(curr);
512 set_backtracking(curr);
514 return get_next_thread(curr);
518 * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
519 * operation from the Thread it is joining with. Must be called after the
520 * completion of the Thread in question.
521 * @param join The THREAD_JOIN action
523 void ModelChecker::do_complete_join(ModelAction *join)
525 Thread *blocking = (Thread *)join->get_location();
526 ModelAction *act = get_last_action(blocking->get_id());
527 join->synchronize_with(act);
530 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
531 Node *currnode = curr->get_node();
532 Node *parnode = currnode->get_parent();
534 if ((!parnode->backtrack_empty() ||
535 !currnode->read_from_empty() ||
536 !currnode->future_value_empty() ||
537 !currnode->promise_empty())
538 && (!priv->next_backtrack ||
539 *curr > *priv->next_backtrack)) {
540 priv->next_backtrack = curr;
544 bool ModelChecker::promises_expired() {
545 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
546 Promise *promise = (*promises)[promise_index];
547 if (promise->get_expiration()<priv->used_sequence_numbers) {
554 /** @returns whether the current partial trace must be a prefix of a
556 bool ModelChecker::isfeasibleprefix() {
557 return promises->size() == 0 && *lazy_sync_size == 0;
560 /** @returns whether the current partial trace is feasible. */
561 bool ModelChecker::isfeasible() {
562 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
565 /** @returns whether the current partial trace is feasible other than
566 * multiple RMW reading from the same store. */
567 bool ModelChecker::isfeasibleotherthanRMW() {
569 if (mo_graph->checkForCycles())
570 DEBUG("Infeasible: modification order cycles\n");
572 DEBUG("Infeasible: failed promise\n");
574 DEBUG("Infeasible: too many reads\n");
575 if (promises_expired())
576 DEBUG("Infeasible: promises expired\n");
578 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
581 /** Returns whether the current completed trace is feasible. */
582 bool ModelChecker::isfinalfeasible() {
583 if (DBG_ENABLED() && promises->size() != 0)
584 DEBUG("Infeasible: unrevolved promises\n");
586 return isfeasible() && promises->size() == 0;
589 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
590 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
591 int tid = id_to_int(act->get_tid());
592 ModelAction *lastread = get_last_action(tid);
593 lastread->process_rmw(act);
594 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
595 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
596 mo_graph->commitChanges();
602 * Checks whether a thread has read from the same write for too many times
603 * without seeing the effects of a later write.
606 * 1) there must a different write that we could read from that would satisfy the modification order,
607 * 2) we must have read from the same value in excess of maxreads times, and
608 * 3) that other write must have been in the reads_from set for maxreads times.
610 * If so, we decide that the execution is no longer feasible.
612 void ModelChecker::check_recency(ModelAction *curr) {
613 if (params.maxreads != 0) {
614 if (curr->get_node()->get_read_from_size() <= 1)
617 //Must make sure that execution is currently feasible... We could
618 //accidentally clear by rolling back
622 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
623 int tid = id_to_int(curr->get_tid());
626 if ((int)thrd_lists->size() <= tid)
629 action_list_t *list = &(*thrd_lists)[tid];
631 action_list_t::reverse_iterator rit = list->rbegin();
633 for (; (*rit) != curr; rit++)
635 /* go past curr now */
638 action_list_t::reverse_iterator ritcopy = rit;
639 //See if we have enough reads from the same value
641 for (; count < params.maxreads; rit++,count++) {
642 if (rit==list->rend())
644 ModelAction *act = *rit;
647 if (act->get_reads_from() != curr->get_reads_from())
649 if (act->get_node()->get_read_from_size() <= 1)
653 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
655 const ModelAction * write = curr->get_node()->get_read_from_at(i);
656 //Need a different write
657 if (write==curr->get_reads_from())
660 /* Test to see whether this is a feasible write to read from*/
661 mo_graph->startChanges();
662 r_modification_order(curr, write);
663 bool feasiblereadfrom = isfeasible();
664 mo_graph->rollbackChanges();
666 if (!feasiblereadfrom)
670 bool feasiblewrite = true;
671 //new we need to see if this write works for everyone
673 for (int loop = count; loop>0; loop--,rit++) {
674 ModelAction *act=*rit;
675 bool foundvalue = false;
676 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
677 if (act->get_node()->get_read_from_at(i)==write) {
683 feasiblewrite = false;
688 too_many_reads = true;
696 * Updates the mo_graph with the constraints imposed from the current
699 * Basic idea is the following: Go through each other thread and find
700 * the lastest action that happened before our read. Two cases:
702 * (1) The action is a write => that write must either occur before
703 * the write we read from or be the write we read from.
705 * (2) The action is a read => the write that that action read from
706 * must occur before the write we read from or be the same write.
708 * @param curr The current action. Must be a read.
709 * @param rf The action that curr reads from. Must be a write.
710 * @return True if modification order edges were added; false otherwise
712 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
714 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
717 ASSERT(curr->is_read());
719 /* Iterate over all threads */
720 for (i = 0; i < thrd_lists->size(); i++) {
721 /* Iterate over actions in thread, starting from most recent */
722 action_list_t *list = &(*thrd_lists)[i];
723 action_list_t::reverse_iterator rit;
724 for (rit = list->rbegin(); rit != list->rend(); rit++) {
725 ModelAction *act = *rit;
728 * Include at most one act per-thread that "happens
729 * before" curr. Don't consider reflexively.
731 if (act->happens_before(curr) && act != curr) {
732 if (act->is_write()) {
734 mo_graph->addEdge(act, rf);
738 const ModelAction *prevreadfrom = act->get_reads_from();
739 if (prevreadfrom != NULL && rf != prevreadfrom) {
740 mo_graph->addEdge(prevreadfrom, rf);
752 /** This method fixes up the modification order when we resolve a
753 * promises. The basic problem is that actions that occur after the
754 * read curr could not property add items to the modification order
757 * So for each thread, we find the earliest item that happens after
758 * the read curr. This is the item we have to fix up with additional
759 * constraints. If that action is write, we add a MO edge between
760 * the Action rf and that action. If the action is a read, we add a
761 * MO edge between the Action rf, and whatever the read accessed.
763 * @param curr is the read ModelAction that we are fixing up MO edges for.
764 * @param rf is the write ModelAction that curr reads from.
768 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
770 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
772 ASSERT(curr->is_read());
774 /* Iterate over all threads */
775 for (i = 0; i < thrd_lists->size(); i++) {
776 /* Iterate over actions in thread, starting from most recent */
777 action_list_t *list = &(*thrd_lists)[i];
778 action_list_t::reverse_iterator rit;
779 ModelAction *lastact = NULL;
781 /* Find last action that happens after curr */
782 for (rit = list->rbegin(); rit != list->rend(); rit++) {
783 ModelAction *act = *rit;
784 if (curr->happens_before(act)) {
790 /* Include at most one act per-thread that "happens before" curr */
791 if (lastact != NULL) {
792 if (lastact->is_read()) {
793 const ModelAction *postreadfrom = lastact->get_reads_from();
794 if (postreadfrom != NULL&&rf != postreadfrom)
795 mo_graph->addEdge(rf, postreadfrom);
796 } else if (rf != lastact) {
797 mo_graph->addEdge(rf, lastact);
805 * Updates the mo_graph with the constraints imposed from the current write.
807 * Basic idea is the following: Go through each other thread and find
808 * the lastest action that happened before our write. Two cases:
810 * (1) The action is a write => that write must occur before
813 * (2) The action is a read => the write that that action read from
814 * must occur before the current write.
816 * This method also handles two other issues:
818 * (I) Sequential Consistency: Making sure that if the current write is
819 * seq_cst, that it occurs after the previous seq_cst write.
821 * (II) Sending the write back to non-synchronizing reads.
823 * @param curr The current action. Must be a write.
824 * @return True if modification order edges were added; false otherwise
826 bool ModelChecker::w_modification_order(ModelAction *curr)
828 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
831 ASSERT(curr->is_write());
833 if (curr->is_seqcst()) {
834 /* We have to at least see the last sequentially consistent write,
835 so we are initialized. */
836 ModelAction *last_seq_cst = get_last_seq_cst(curr);
837 if (last_seq_cst != NULL) {
838 mo_graph->addEdge(last_seq_cst, curr);
843 /* Iterate over all threads */
844 for (i = 0; i < thrd_lists->size(); i++) {
845 /* Iterate over actions in thread, starting from most recent */
846 action_list_t *list = &(*thrd_lists)[i];
847 action_list_t::reverse_iterator rit;
848 for (rit = list->rbegin(); rit != list->rend(); rit++) {
849 ModelAction *act = *rit;
852 * If RMW, we already have all relevant edges,
853 * so just skip to next thread.
854 * If normal write, we need to look at earlier
855 * actions, so continue processing list.
864 * Include at most one act per-thread that "happens
867 if (act->happens_before(curr)) {
869 * Note: if act is RMW, just add edge:
871 * The following edge should be handled elsewhere:
872 * readfrom(act) --mo--> act
875 mo_graph->addEdge(act, curr);
876 else if (act->is_read() && act->get_reads_from() != NULL)
877 mo_graph->addEdge(act->get_reads_from(), curr);
880 } else if (act->is_read() && !act->is_synchronizing(curr) &&
881 !act->same_thread(curr)) {
882 /* We have an action that:
883 (1) did not happen before us
884 (2) is a read and we are a write
885 (3) cannot synchronize with us
886 (4) is in a different thread
888 that read could potentially read from our write.
890 if (thin_air_constraint_may_allow(curr, act)) {
892 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
893 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
894 futurevalues->push_back(pfv);
904 /** Arbitrary reads from the future are not allowed. Section 29.3
905 * part 9 places some constraints. This method checks one result of constraint
906 * constraint. Others require compiler support. */
908 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
909 if (!writer->is_rmw())
912 if (!reader->is_rmw())
915 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
918 if (search->get_tid() == reader->get_tid() &&
919 search->happens_before(reader))
927 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
928 * The ModelAction under consideration is expected to be taking part in
929 * release/acquire synchronization as an object of the "reads from" relation.
930 * Note that this can only provide release sequence support for RMW chains
931 * which do not read from the future, as those actions cannot be traced until
932 * their "promise" is fulfilled. Similarly, we may not even establish the
933 * presence of a release sequence with certainty, as some modification order
934 * constraints may be decided further in the future. Thus, this function
935 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
936 * and a boolean representing certainty.
938 * @todo Finish lazy updating, when promises are fulfilled in the future
939 * @param rf The action that might be part of a release sequence. Must be a
941 * @param release_heads A pass-by-reference style return parameter. After
942 * execution of this function, release_heads will contain the heads of all the
943 * relevant release sequences, if any exists
944 * @return true, if the ModelChecker is certain that release_heads is complete;
947 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
950 /* read from future: need to settle this later */
951 return false; /* incomplete */
954 ASSERT(rf->is_write());
956 if (rf->is_release())
957 release_heads->push_back(rf);
959 /* We need a RMW action that is both an acquire and release to stop */
960 /** @todo Need to be smarter here... In the linux lock
961 * example, this will run to the beginning of the program for
963 if (rf->is_acquire() && rf->is_release())
964 return true; /* complete */
965 return release_seq_head(rf->get_reads_from(), release_heads);
967 if (rf->is_release())
968 return true; /* complete */
970 /* else relaxed write; check modification order for contiguous subsequence
971 * -> rf must be same thread as release */
972 int tid = id_to_int(rf->get_tid());
973 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
974 action_list_t *list = &(*thrd_lists)[tid];
975 action_list_t::const_reverse_iterator rit;
977 /* Find rf in the thread list */
978 rit = std::find(list->rbegin(), list->rend(), rf);
979 ASSERT(rit != list->rend());
981 /* Find the last write/release */
982 for (; rit != list->rend(); rit++)
983 if ((*rit)->is_release())
985 if (rit == list->rend()) {
986 /* No write-release in this thread */
987 return true; /* complete */
989 ModelAction *release = *rit;
991 ASSERT(rf->same_thread(release));
994 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
995 if (id_to_int(rf->get_tid()) == (int)i)
997 list = &(*thrd_lists)[i];
999 /* Can we ensure no future writes from this thread may break
1000 * the release seq? */
1001 bool future_ordered = false;
1003 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1004 const ModelAction *act = *rit;
1005 if (!act->is_write())
1007 /* Reach synchronization -> this thread is complete */
1008 if (act->happens_before(release))
1010 if (rf->happens_before(act)) {
1011 future_ordered = true;
1015 /* Check modification order */
1016 if (mo_graph->checkReachable(rf, act)) {
1017 /* rf --mo--> act */
1018 future_ordered = true;
1021 if (mo_graph->checkReachable(act, release))
1022 /* act --mo--> release */
1024 if (mo_graph->checkReachable(release, act) &&
1025 mo_graph->checkReachable(act, rf)) {
1026 /* release --mo-> act --mo--> rf */
1027 return true; /* complete */
1031 if (!future_ordered)
1032 return false; /* This thread is uncertain */
1036 release_heads->push_back(release);
1041 * A public interface for getting the release sequence head(s) with which a
1042 * given ModelAction must synchronize. This function only returns a non-empty
1043 * result when it can locate a release sequence head with certainty. Otherwise,
1044 * it may mark the internal state of the ModelChecker so that it will handle
1045 * the release sequence at a later time, causing @a act to update its
1046 * synchronization at some later point in execution.
1047 * @param act The 'acquire' action that may read from a release sequence
1048 * @param release_heads A pass-by-reference return parameter. Will be filled
1049 * with the head(s) of the release sequence(s), if they exists with certainty.
1050 * @see ModelChecker::release_seq_head
1052 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1054 const ModelAction *rf = act->get_reads_from();
1056 complete = release_seq_head(rf, release_heads);
1058 /* add act to 'lazy checking' list */
1059 action_list_t *list;
1060 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1061 list->push_back(act);
1062 (*lazy_sync_size)++;
1067 * Attempt to resolve all stashed operations that might synchronize with a
1068 * release sequence for a given location. This implements the "lazy" portion of
1069 * determining whether or not a release sequence was contiguous, since not all
1070 * modification order information is present at the time an action occurs.
1072 * @param location The location/object that should be checked for release
1073 * sequence resolutions
1074 * @param work_queue The work queue to which to add work items as they are
1076 * @return True if any updates occurred (new synchronization, new mo_graph
1079 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1081 action_list_t *list;
1082 list = lazy_sync_with_release->getptr(location);
1086 bool updated = false;
1087 action_list_t::iterator it = list->begin();
1088 while (it != list->end()) {
1089 ModelAction *act = *it;
1090 const ModelAction *rf = act->get_reads_from();
1091 rel_heads_list_t release_heads;
1093 complete = release_seq_head(rf, &release_heads);
1094 for (unsigned int i = 0; i < release_heads.size(); i++) {
1095 if (!act->has_synchronized_with(release_heads[i])) {
1097 act->synchronize_with(release_heads[i]);
1102 /* Re-check act for mo_graph edges */
1103 work_queue->push_back(MOEdgeWorkEntry(act));
1105 /* propagate synchronization to later actions */
1106 action_list_t::reverse_iterator it = action_trace->rbegin();
1107 while ((*it) != act) {
1108 ModelAction *propagate = *it;
1109 if (act->happens_before(propagate)) {
1110 propagate->synchronize_with(act);
1111 /* Re-check 'propagate' for mo_graph edges */
1112 work_queue->push_back(MOEdgeWorkEntry(propagate));
1117 it = list->erase(it);
1118 (*lazy_sync_size)--;
1123 // If we resolved promises or data races, see if we have realized a data race.
1124 if (checkDataRaces()) {
1132 * Performs various bookkeeping operations for the current ModelAction. For
1133 * instance, adds action to the per-object, per-thread action vector and to the
1134 * action trace list of all thread actions.
1136 * @param act is the ModelAction to add.
1138 void ModelChecker::add_action_to_lists(ModelAction *act)
1140 int tid = id_to_int(act->get_tid());
1141 action_trace->push_back(act);
1143 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1145 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1146 if (tid >= (int)vec->size())
1147 vec->resize(priv->next_thread_id);
1148 (*vec)[tid].push_back(act);
1150 if ((int)thrd_last_action->size() <= tid)
1151 thrd_last_action->resize(get_num_threads());
1152 (*thrd_last_action)[tid] = act;
1155 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1157 int threadid=id_to_int(tid);
1158 if (threadid<(int)thrd_last_action->size())
1159 return (*thrd_last_action)[id_to_int(tid)];
1165 * Gets the last memory_order_seq_cst write (in the total global sequence)
1166 * performed on a particular object (i.e., memory location), not including the
1168 * @param curr The current ModelAction; also denotes the object location to
1170 * @return The last seq_cst write
1172 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1174 void *location = curr->get_location();
1175 action_list_t *list = obj_map->get_safe_ptr(location);
1176 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1177 action_list_t::reverse_iterator rit;
1178 for (rit = list->rbegin(); rit != list->rend(); rit++)
1179 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1184 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1186 ModelAction *parent = get_last_action(tid);
1188 parent = get_thread(tid)->get_creation();
1193 * Returns the clock vector for a given thread.
1194 * @param tid The thread whose clock vector we want
1195 * @return Desired clock vector
1197 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1199 return get_parent_action(tid)->get_cv();
1203 * Resolve a set of Promises with a current write. The set is provided in the
1204 * Node corresponding to @a write.
1205 * @param write The ModelAction that is fulfilling Promises
1206 * @return True if promises were resolved; false otherwise
1208 bool ModelChecker::resolve_promises(ModelAction *write)
1210 bool resolved = false;
1212 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1213 Promise *promise = (*promises)[promise_index];
1214 if (write->get_node()->get_promise(i)) {
1215 ModelAction *read = promise->get_action();
1216 read->read_from(write);
1217 if (read->is_rmw()) {
1218 mo_graph->addRMWEdge(write, read);
1220 //First fix up the modification order for actions that happened
1222 r_modification_order(read, write);
1223 //Next fix up the modification order for actions that happened
1225 post_r_modification_order(read, write);
1226 promises->erase(promises->begin() + promise_index);
1235 * Compute the set of promises that could potentially be satisfied by this
1236 * action. Note that the set computation actually appears in the Node, not in
1238 * @param curr The ModelAction that may satisfy promises
1240 void ModelChecker::compute_promises(ModelAction *curr)
1242 for (unsigned int i = 0; i < promises->size(); i++) {
1243 Promise *promise = (*promises)[i];
1244 const ModelAction *act = promise->get_action();
1245 if (!act->happens_before(curr) &&
1247 !act->is_synchronizing(curr) &&
1248 !act->same_thread(curr) &&
1249 promise->get_value() == curr->get_value()) {
1250 curr->get_node()->set_promise(i);
1255 /** Checks promises in response to change in ClockVector Threads. */
1256 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1258 for (unsigned int i = 0; i < promises->size(); i++) {
1259 Promise *promise = (*promises)[i];
1260 const ModelAction *act = promise->get_action();
1261 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1262 merge_cv->synchronized_since(act)) {
1263 //This thread is no longer able to send values back to satisfy the promise
1264 int num_synchronized_threads = promise->increment_threads();
1265 if (num_synchronized_threads == get_num_threads()) {
1266 //Promise has failed
1267 failed_promise = true;
1275 * Build up an initial set of all past writes that this 'read' action may read
1276 * from. This set is determined by the clock vector's "happens before"
1278 * @param curr is the current ModelAction that we are exploring; it must be a
1281 void ModelChecker::build_reads_from_past(ModelAction *curr)
1283 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1285 ASSERT(curr->is_read());
1287 ModelAction *last_seq_cst = NULL;
1289 /* Track whether this object has been initialized */
1290 bool initialized = false;
1292 if (curr->is_seqcst()) {
1293 last_seq_cst = get_last_seq_cst(curr);
1294 /* We have to at least see the last sequentially consistent write,
1295 so we are initialized. */
1296 if (last_seq_cst != NULL)
1300 /* Iterate over all threads */
1301 for (i = 0; i < thrd_lists->size(); i++) {
1302 /* Iterate over actions in thread, starting from most recent */
1303 action_list_t *list = &(*thrd_lists)[i];
1304 action_list_t::reverse_iterator rit;
1305 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1306 ModelAction *act = *rit;
1308 /* Only consider 'write' actions */
1309 if (!act->is_write() || act == curr)
1312 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1313 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1314 DEBUG("Adding action to may_read_from:\n");
1315 if (DBG_ENABLED()) {
1319 curr->get_node()->add_read_from(act);
1322 /* Include at most one act per-thread that "happens before" curr */
1323 if (act->happens_before(curr)) {
1331 /** @todo Need a more informative way of reporting errors. */
1332 printf("ERROR: may read from uninitialized atomic\n");
1335 if (DBG_ENABLED() || !initialized) {
1336 printf("Reached read action:\n");
1338 printf("Printing may_read_from\n");
1339 curr->get_node()->print_may_read_from();
1340 printf("End printing may_read_from\n");
1343 ASSERT(initialized);
1346 static void print_list(action_list_t *list)
1348 action_list_t::iterator it;
1350 printf("---------------------------------------------------------------------\n");
1353 for (it = list->begin(); it != list->end(); it++) {
1356 printf("---------------------------------------------------------------------\n");
1359 void ModelChecker::print_summary()
1362 printf("Number of executions: %d\n", num_executions);
1363 printf("Number of feasible executions: %d\n", num_feasible_executions);
1364 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1366 #if SUPPORT_MOD_ORDER_DUMP
1368 char buffername[100];
1369 sprintf(buffername, "exec%u",num_executions);
1370 mo_graph->dumpGraphToFile(buffername);
1373 if (!isfinalfeasible())
1374 printf("INFEASIBLE EXECUTION!\n");
1375 print_list(action_trace);
1380 * Add a Thread to the system for the first time. Should only be called once
1382 * @param t The Thread to add
1384 void ModelChecker::add_thread(Thread *t)
1386 thread_map->put(id_to_int(t->get_id()), t);
1387 scheduler->add_thread(t);
1390 void ModelChecker::remove_thread(Thread *t)
1392 scheduler->remove_thread(t);
1396 * Switch from a user-context to the "master thread" context (a.k.a. system
1397 * context). This switch is made with the intention of exploring a particular
1398 * model-checking action (described by a ModelAction object). Must be called
1399 * from a user-thread context.
1400 * @param act The current action that will be explored. Must not be NULL.
1401 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1403 int ModelChecker::switch_to_master(ModelAction *act)
1406 Thread *old = thread_current();
1407 set_current_action(act);
1408 old->set_state(THREAD_READY);
1409 return Thread::swap(old, &system_context);
1413 * Takes the next step in the execution, if possible.
1414 * @return Returns true (success) if a step was taken and false otherwise.
1416 bool ModelChecker::take_step() {
1420 Thread * curr = thread_current();
1422 if (curr->get_state() == THREAD_READY) {
1423 ASSERT(priv->current_action);
1425 priv->nextThread = check_current_action(priv->current_action);
1426 priv->current_action = NULL;
1427 if (curr->is_blocked() || curr->is_complete())
1428 scheduler->remove_thread(curr);
1433 Thread * next = scheduler->next_thread(priv->nextThread);
1435 /* Infeasible -> don't take any more steps */
1440 next->set_state(THREAD_RUNNING);
1441 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1443 /* next == NULL -> don't take any more steps */
1446 /* Return false only if swap fails with an error */
1447 return (Thread::swap(&system_context, next) == 0);
1450 /** Runs the current execution until threre are no more steps to take. */
1451 void ModelChecker::finish_execution() {
1454 while (take_step());