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()),
26 action_trace(new action_list_t()),
27 thread_map(new HashTable<int, Thread *, int>()),
28 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
29 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
30 promises(new std::vector<Promise *>()),
31 lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
32 thrd_last_action(new std::vector<ModelAction *>(1)),
33 node_stack(new NodeStack()),
34 mo_graph(new CycleGraph()),
35 failed_promise(false),
36 too_many_reads(false),
39 /* Allocate this "size" on the snapshotting heap */
40 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
41 /* First thread created will have id INITIAL_THREAD_ID */
42 priv->next_thread_id = INITIAL_THREAD_ID;
44 lazy_sync_size = &priv->lazy_sync_size;
47 /** @brief Destructor */
48 ModelChecker::~ModelChecker()
50 for (int i = 0; i < get_num_threads(); i++)
51 delete thread_map->get(i);
58 for (unsigned int i = 0; i < promises->size(); i++)
59 delete (*promises)[i];
62 delete lazy_sync_with_release;
64 delete thrd_last_action;
71 * Restores user program to initial state and resets all model-checker data
74 void ModelChecker::reset_to_initial_state()
76 DEBUG("+++ Resetting to initial state +++\n");
77 node_stack->reset_execution();
78 failed_promise = false;
79 too_many_reads = false;
81 snapshotObject->backTrackBeforeStep(0);
84 /** @returns a thread ID for a new Thread */
85 thread_id_t ModelChecker::get_next_id()
87 return priv->next_thread_id++;
90 /** @returns the number of user threads created during this execution */
91 int ModelChecker::get_num_threads()
93 return priv->next_thread_id;
96 /** @returns a sequence number for a new ModelAction */
97 modelclock_t ModelChecker::get_next_seq_num()
99 return ++priv->used_sequence_numbers;
103 * @brief Choose the next thread to execute.
105 * This function chooses the next thread that should execute. It can force the
106 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
107 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
108 * The model-checker may have no preference regarding the next thread (i.e.,
109 * when exploring a new execution ordering), in which case this will return
111 * @param curr The current ModelAction. This action might guide the choice of
113 * @return The next thread to run. If the model-checker has no preference, NULL.
115 Thread * ModelChecker::get_next_thread(ModelAction *curr)
119 /* Do not split atomic actions. */
121 return thread_current();
122 /* The THREAD_CREATE action points to the created Thread */
123 else if (curr->get_type() == THREAD_CREATE)
124 return (Thread *)curr->get_location();
126 /* Have we completed exploring the preselected path? */
130 /* Else, we are trying to replay an execution */
131 ModelAction *next = node_stack->get_next()->get_action();
133 if (next == diverge) {
134 Node *nextnode = next->get_node();
135 /* Reached divergence point */
136 if (nextnode->increment_promise()) {
137 /* The next node will try to satisfy a different set of promises. */
138 tid = next->get_tid();
139 node_stack->pop_restofstack(2);
140 } else if (nextnode->increment_read_from()) {
141 /* The next node will read from a different value. */
142 tid = next->get_tid();
143 node_stack->pop_restofstack(2);
144 } else if (nextnode->increment_future_value()) {
145 /* The next node will try to read from a different future value. */
146 tid = next->get_tid();
147 node_stack->pop_restofstack(2);
149 /* Make a different thread execute for next step */
150 Node *node = nextnode->get_parent();
151 tid = node->get_next_backtrack();
152 node_stack->pop_restofstack(1);
154 DEBUG("*** Divergence point ***\n");
157 tid = next->get_tid();
159 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
160 ASSERT(tid != THREAD_ID_T_NONE);
161 return thread_map->get(id_to_int(tid));
165 * Queries the model-checker for more executions to explore and, if one
166 * exists, resets the model-checker state to execute a new execution.
168 * @return If there are more executions to explore, return true. Otherwise,
171 bool ModelChecker::next_execution()
177 if (isfinalfeasible() || DBG_ENABLED())
180 if ((diverge = get_next_backtrack()) == NULL)
184 printf("Next execution will diverge at:\n");
188 reset_to_initial_state();
192 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
194 action_type type = act->get_type();
204 /* linear search: from most recent to oldest */
205 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
206 action_list_t::reverse_iterator rit;
207 for (rit = list->rbegin(); rit != list->rend(); rit++) {
208 ModelAction *prev = *rit;
209 if (act->is_synchronizing(prev))
215 void ModelChecker::set_backtracking(ModelAction *act)
219 Thread *t = get_thread(act);
221 prev = get_last_conflict(act);
225 node = prev->get_node()->get_parent();
227 while (!node->is_enabled(t))
230 /* Check if this has been explored already */
231 if (node->has_been_explored(t->get_id()))
234 /* Cache the latest backtracking point */
235 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
236 priv->next_backtrack = prev;
238 /* If this is a new backtracking point, mark the tree */
239 if (!node->set_backtrack(t->get_id()))
241 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
242 prev->get_tid(), t->get_id());
250 * Returns last backtracking point. The model checker will explore a different
251 * path for this point in the next execution.
252 * @return The ModelAction at which the next execution should diverge.
254 ModelAction * ModelChecker::get_next_backtrack()
256 ModelAction *next = priv->next_backtrack;
257 priv->next_backtrack = NULL;
263 * Processes a read or rmw model action.
264 * @param curr is the read model action to process.
265 * @param th is the thread
266 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
267 * @return True if processing this read updates the mo_graph.
270 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
274 const ModelAction *reads_from = curr->get_node()->get_read_from();
275 if (reads_from != NULL) {
276 mo_graph->startChanges();
278 value = reads_from->get_value();
280 if (!second_part_of_rmw) {
281 check_recency(curr,false);
284 bool r_status=r_modification_order(curr,reads_from);
286 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
287 mo_graph->rollbackChanges();
288 too_many_reads=false;
292 curr->read_from(reads_from);
293 mo_graph->commitChanges();
295 } else if (!second_part_of_rmw) {
296 /* Read from future value */
297 value = curr->get_node()->get_future_value();
298 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
299 curr->read_from(NULL);
300 Promise *valuepromise = new Promise(curr, value, expiration);
301 promises->push_back(valuepromise);
303 th->set_return_value(value);
309 * This is the heart of the model checker routine. It performs model-checking
310 * actions corresponding to a given "current action." Among other processes, it
311 * calculates reads-from relationships, updates synchronization clock vectors,
312 * forms a memory_order constraints graph, and handles replay/backtrack
313 * execution when running permutations of previously-observed executions.
315 * @param curr The current action to process
316 * @return The next Thread that must be executed. May be NULL if ModelChecker
317 * makes no choice (e.g., according to replay execution, combining RMW actions,
320 Thread * ModelChecker::check_current_action(ModelAction *curr)
322 bool second_part_of_rmw = false;
326 if (curr->is_rmwc() || curr->is_rmw()) {
327 ModelAction *tmp = process_rmw(curr);
328 second_part_of_rmw = true;
331 compute_promises(curr);
333 ModelAction *tmp = node_stack->explore_action(curr);
335 /* Discard duplicate ModelAction; use action from NodeStack */
336 /* First restore type and order in case of RMW operation */
338 tmp->copy_typeandorder(curr);
340 /* If we have diverged, we need to reset the clock vector. */
342 tmp->create_cv(get_parent_action(tmp->get_tid()));
348 * Perform one-time actions when pushing new ModelAction onto
351 curr->create_cv(get_parent_action(curr->get_tid()));
352 /* Build may_read_from set */
354 build_reads_from_past(curr);
355 if (curr->is_write())
356 compute_promises(curr);
360 /* Thread specific actions */
361 switch(curr->get_type()) {
362 case THREAD_CREATE: {
363 Thread *th = (Thread *)curr->get_location();
364 th->set_creation(curr);
368 Thread *waiting, *blocking;
369 waiting = get_thread(curr);
370 blocking = (Thread *)curr->get_location();
371 if (!blocking->is_complete()) {
372 blocking->push_wait_list(curr);
373 scheduler->sleep(waiting);
377 case THREAD_FINISH: {
378 Thread *th = get_thread(curr);
379 while (!th->wait_list_empty()) {
380 ModelAction *act = th->pop_wait_list();
381 Thread *wake = get_thread(act);
382 scheduler->wake(wake);
388 check_promises(NULL, curr->get_cv());
395 Thread *th = get_thread(curr);
397 bool updated = false;
398 if (curr->is_read()) {
399 updated=process_read(curr, th, second_part_of_rmw);
402 if (curr->is_write()) {
403 bool updated_mod_order=w_modification_order(curr);
404 bool updated_promises=resolve_promises(curr);
405 updated=updated_mod_order|updated_promises;
407 mo_graph->commitChanges();
408 th->set_return_value(VALUE_NONE);
412 resolve_release_sequences(curr->get_location());
414 /* Add action to list. */
415 if (!second_part_of_rmw)
416 add_action_to_lists(curr);
418 check_curr_backtracking(curr);
420 set_backtracking(curr);
422 return get_next_thread(curr);
425 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
426 Node *currnode = curr->get_node();
427 Node *parnode = currnode->get_parent();
429 if ((!parnode->backtrack_empty() ||
430 !currnode->read_from_empty() ||
431 !currnode->future_value_empty() ||
432 !currnode->promise_empty())
433 && (!priv->next_backtrack ||
434 *curr > *priv->next_backtrack)) {
435 priv->next_backtrack = curr;
440 bool ModelChecker::promises_expired() {
441 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
442 Promise *promise = (*promises)[promise_index];
443 if (promise->get_expiration()<priv->used_sequence_numbers) {
450 /** @returns whether the current partial trace must be a prefix of a
452 bool ModelChecker::isfeasibleprefix() {
453 return promises->size() == 0 && *lazy_sync_size == 0;
456 /** @returns whether the current partial trace is feasible. */
457 bool ModelChecker::isfeasible() {
458 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
461 /** @returns whether the current partial trace is feasible other than
462 * multiple RMW reading from the same store. */
463 bool ModelChecker::isfeasibleotherthanRMW() {
464 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
467 /** Returns whether the current completed trace is feasible. */
468 bool ModelChecker::isfinalfeasible() {
469 return isfeasible() && promises->size() == 0;
472 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
473 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
474 int tid = id_to_int(act->get_tid());
475 ModelAction *lastread = get_last_action(tid);
476 lastread->process_rmw(act);
477 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
478 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
479 mo_graph->commitChanges();
485 * Checks whether a thread has read from the same write for too many times
486 * without seeing the effects of a later write.
489 * 1) there must a different write that we could read from that would satisfy the modification order,
490 * 2) we must have read from the same value in excess of maxreads times, and
491 * 3) that other write must have been in the reads_from set for maxreads times.
493 * If so, we decide that the execution is no longer feasible.
495 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
496 if (params.maxreads != 0) {
497 if (curr->get_node()->get_read_from_size() <= 1)
500 //Must make sure that execution is currently feasible... We could
501 //accidentally clear by rolling back
505 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
506 int tid = id_to_int(curr->get_tid());
509 if ((int)thrd_lists->size() <= tid)
512 action_list_t *list = &(*thrd_lists)[tid];
514 action_list_t::reverse_iterator rit = list->rbegin();
517 for (; (*rit) != curr; rit++)
519 /* go past curr now */
523 action_list_t::reverse_iterator ritcopy=rit;
524 //See if we have enough reads from the same value
526 for (; count < params.maxreads; rit++,count++) {
527 if (rit==list->rend())
529 ModelAction *act = *rit;
532 if (act->get_reads_from() != curr->get_reads_from())
534 if (act->get_node()->get_read_from_size() <= 1)
538 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
540 const ModelAction * write=curr->get_node()->get_read_from_at(i);
541 //Need a different write
542 if (write==curr->get_reads_from())
545 /* Test to see whether this is a feasible write to read from*/
546 mo_graph->startChanges();
547 r_modification_order(curr, write);
548 bool feasiblereadfrom=isfeasible();
549 mo_graph->rollbackChanges();
551 if (!feasiblereadfrom)
555 bool feasiblewrite=true;
556 //new we need to see if this write works for everyone
558 for (int loop=count;loop>0;loop--,rit++) {
559 ModelAction *act=*rit;
560 bool foundvalue=false;
561 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
562 if (act->get_node()->get_read_from_at(i)==write) {
573 too_many_reads = true;
581 * Updates the mo_graph with the constraints imposed from the current read.
582 * @param curr The current action. Must be a read.
583 * @param rf The action that curr reads from. Must be a write.
584 * @return True if modification order edges were added; false otherwise
586 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
588 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
591 ASSERT(curr->is_read());
593 /* Iterate over all threads */
594 for (i = 0; i < thrd_lists->size(); i++) {
595 /* Iterate over actions in thread, starting from most recent */
596 action_list_t *list = &(*thrd_lists)[i];
597 action_list_t::reverse_iterator rit;
598 for (rit = list->rbegin(); rit != list->rend(); rit++) {
599 ModelAction *act = *rit;
601 /* Include at most one act per-thread that "happens before" curr */
602 if (act->happens_before(curr)) {
603 if (act->is_read()) {
604 const ModelAction *prevreadfrom = act->get_reads_from();
605 if (prevreadfrom != NULL && rf != prevreadfrom) {
606 mo_graph->addEdge(prevreadfrom, rf);
609 } else if (rf != act) {
610 mo_graph->addEdge(act, rf);
621 /** Updates the mo_graph with the constraints imposed from the current read. */
622 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
624 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
626 ASSERT(curr->is_read());
628 /* Iterate over all threads */
629 for (i = 0; i < thrd_lists->size(); i++) {
630 /* Iterate over actions in thread, starting from most recent */
631 action_list_t *list = &(*thrd_lists)[i];
632 action_list_t::reverse_iterator rit;
633 ModelAction *lastact = NULL;
635 /* Find last action that happens after curr */
636 for (rit = list->rbegin(); rit != list->rend(); rit++) {
637 ModelAction *act = *rit;
638 if (curr->happens_before(act)) {
644 /* Include at most one act per-thread that "happens before" curr */
645 if (lastact != NULL) {
646 if (lastact->is_read()) {
647 const ModelAction *postreadfrom = lastact->get_reads_from();
648 if (postreadfrom != NULL&&rf != postreadfrom)
649 mo_graph->addEdge(rf, postreadfrom);
650 } else if (rf != lastact) {
651 mo_graph->addEdge(rf, lastact);
659 * Updates the mo_graph with the constraints imposed from the current write.
660 * @param curr The current action. Must be a write.
661 * @return True if modification order edges were added; false otherwise
663 bool ModelChecker::w_modification_order(ModelAction *curr)
665 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
668 ASSERT(curr->is_write());
670 if (curr->is_seqcst()) {
671 /* We have to at least see the last sequentially consistent write,
672 so we are initialized. */
673 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
674 if (last_seq_cst != NULL) {
675 mo_graph->addEdge(last_seq_cst, curr);
680 /* Iterate over all threads */
681 for (i = 0; i < thrd_lists->size(); i++) {
682 /* Iterate over actions in thread, starting from most recent */
683 action_list_t *list = &(*thrd_lists)[i];
684 action_list_t::reverse_iterator rit;
685 for (rit = list->rbegin(); rit != list->rend(); rit++) {
686 ModelAction *act = *rit;
688 /* Include at most one act per-thread that "happens before" curr */
689 if (act->happens_before(curr)) {
691 * Note: if act is RMW, just add edge:
693 * The following edge should be handled elsewhere:
694 * readfrom(act) --mo--> act
696 if (act->is_write()) {
697 //RMW shouldn't have an edge to themselves
699 mo_graph->addEdge(act, curr);
700 } else if (act->is_read() && act->get_reads_from() != NULL)
701 mo_graph->addEdge(act->get_reads_from(), curr);
704 } else if (act->is_read() && !act->is_synchronizing(curr) &&
705 !act->same_thread(curr)) {
706 /* We have an action that:
707 (1) did not happen before us
708 (2) is a read and we are a write
709 (3) cannot synchronize with us
710 (4) is in a different thread
712 that read could potentially read from our write.
714 if (thin_air_constraint_may_allow(curr, act)) {
716 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
717 if (act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
718 (!priv->next_backtrack || *act > *priv->next_backtrack))
719 priv->next_backtrack = act;
729 /** Arbitrary reads from the future are not allowed. Section 29.3
730 * part 9 places some constraints. This method checks one result of constraint
731 * constraint. Others require compiler support. */
733 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
734 if (!writer->is_rmw())
737 if (!reader->is_rmw())
740 for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
743 if (search->get_tid()==reader->get_tid()&&
744 search->happens_before(reader))
753 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
754 * The ModelAction under consideration is expected to be taking part in
755 * release/acquire synchronization as an object of the "reads from" relation.
756 * Note that this can only provide release sequence support for RMW chains
757 * which do not read from the future, as those actions cannot be traced until
758 * their "promise" is fulfilled. Similarly, we may not even establish the
759 * presence of a release sequence with certainty, as some modification order
760 * constraints may be decided further in the future. Thus, this function
761 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
762 * and a boolean representing certainty.
764 * @todo Finish lazy updating, when promises are fulfilled in the future
765 * @param rf The action that might be part of a release sequence. Must be a
767 * @param release_heads A pass-by-reference style return parameter. After
768 * execution of this function, release_heads will contain the heads of all the
769 * relevant release sequences, if any exists
770 * @return true, if the ModelChecker is certain that release_heads is complete;
773 bool ModelChecker::release_seq_head(const ModelAction *rf,
774 std::vector<const ModelAction *> *release_heads) const
776 ASSERT(rf->is_write());
778 /* read from future: need to settle this later */
779 return false; /* incomplete */
781 if (rf->is_release())
782 release_heads->push_back(rf);
784 /* We need a RMW action that is both an acquire and release to stop */
785 /** @todo Need to be smarter here... In the linux lock
786 * example, this will run to the beginning of the program for
788 if (rf->is_acquire() && rf->is_release())
789 return true; /* complete */
790 return release_seq_head(rf->get_reads_from(), release_heads);
792 if (rf->is_release())
793 return true; /* complete */
795 /* else relaxed write; check modification order for contiguous subsequence
796 * -> rf must be same thread as release */
797 int tid = id_to_int(rf->get_tid());
798 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
799 action_list_t *list = &(*thrd_lists)[tid];
800 action_list_t::const_reverse_iterator rit;
802 /* Find rf in the thread list */
803 rit = std::find(list->rbegin(), list->rend(), rf);
804 ASSERT(rit != list->rend());
806 /* Find the last write/release */
807 for (; rit != list->rend(); rit++)
808 if ((*rit)->is_release())
810 if (rit == list->rend()) {
811 /* No write-release in this thread */
812 return true; /* complete */
814 ModelAction *release = *rit;
816 ASSERT(rf->same_thread(release));
819 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
820 if (id_to_int(rf->get_tid()) == (int)i)
822 list = &(*thrd_lists)[i];
824 /* Can we ensure no future writes from this thread may break
825 * the release seq? */
826 bool future_ordered = false;
828 for (rit = list->rbegin(); rit != list->rend(); rit++) {
829 const ModelAction *act = *rit;
830 if (!act->is_write())
832 /* Reach synchronization -> this thread is complete */
833 if (act->happens_before(release))
835 if (rf->happens_before(act)) {
836 future_ordered = true;
840 /* Check modification order */
841 if (mo_graph->checkReachable(rf, act)) {
843 future_ordered = true;
846 if (mo_graph->checkReachable(act, release))
847 /* act --mo--> release */
849 if (mo_graph->checkReachable(release, act) &&
850 mo_graph->checkReachable(act, rf)) {
851 /* release --mo-> act --mo--> rf */
852 return true; /* complete */
857 return false; /* This thread is uncertain */
861 release_heads->push_back(release);
866 * A public interface for getting the release sequence head(s) with which a
867 * given ModelAction must synchronize. This function only returns a non-empty
868 * result when it can locate a release sequence head with certainty. Otherwise,
869 * it may mark the internal state of the ModelChecker so that it will handle
870 * the release sequence at a later time, causing @a act to update its
871 * synchronization at some later point in execution.
872 * @param act The 'acquire' action that may read from a release sequence
873 * @param release_heads A pass-by-reference return parameter. Will be filled
874 * with the head(s) of the release sequence(s), if they exists with certainty.
875 * @see ModelChecker::release_seq_head
877 void ModelChecker::get_release_seq_heads(ModelAction *act,
878 std::vector<const ModelAction *> *release_heads)
880 const ModelAction *rf = act->get_reads_from();
882 complete = release_seq_head(rf, release_heads);
884 /* add act to 'lazy checking' list */
885 std::list<ModelAction *> *list;
886 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
887 list->push_back(act);
893 * Attempt to resolve all stashed operations that might synchronize with a
894 * release sequence for a given location. This implements the "lazy" portion of
895 * determining whether or not a release sequence was contiguous, since not all
896 * modification order information is present at the time an action occurs.
898 * @param location The location/object that should be checked for release
899 * sequence resolutions
900 * @return True if any updates occurred (new synchronization, new mo_graph edges)
902 bool ModelChecker::resolve_release_sequences(void *location)
904 std::list<ModelAction *> *list;
905 list = lazy_sync_with_release->getptr(location);
909 bool updated = false;
910 std::list<ModelAction *>::iterator it = list->begin();
911 while (it != list->end()) {
912 ModelAction *act = *it;
913 const ModelAction *rf = act->get_reads_from();
914 std::vector<const ModelAction *> release_heads;
916 complete = release_seq_head(rf, &release_heads);
917 for (unsigned int i = 0; i < release_heads.size(); i++) {
918 if (!act->has_synchronized_with(release_heads[i])) {
920 act->synchronize_with(release_heads[i]);
925 /* propagate synchronization to later actions */
926 action_list_t::reverse_iterator it = action_trace->rbegin();
927 while ((*it) != act) {
928 ModelAction *propagate = *it;
929 if (act->happens_before(propagate))
930 /** @todo new mo_graph edges along with
931 * this synchronization? */
932 propagate->synchronize_with(act);
936 it = list->erase(it);
942 // If we resolved promises or data races, see if we have realized a data race.
943 if (checkDataRaces()) {
951 * Performs various bookkeeping operations for the current ModelAction. For
952 * instance, adds action to the per-object, per-thread action vector and to the
953 * action trace list of all thread actions.
955 * @param act is the ModelAction to add.
957 void ModelChecker::add_action_to_lists(ModelAction *act)
959 int tid = id_to_int(act->get_tid());
960 action_trace->push_back(act);
962 obj_map->get_safe_ptr(act->get_location())->push_back(act);
964 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
965 if (tid >= (int)vec->size())
966 vec->resize(priv->next_thread_id);
967 (*vec)[tid].push_back(act);
969 if ((int)thrd_last_action->size() <= tid)
970 thrd_last_action->resize(get_num_threads());
971 (*thrd_last_action)[tid] = act;
974 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
976 int nthreads = get_num_threads();
977 if ((int)thrd_last_action->size() < nthreads)
978 thrd_last_action->resize(nthreads);
979 return (*thrd_last_action)[id_to_int(tid)];
983 * Gets the last memory_order_seq_cst action (in the total global sequence)
984 * performed on a particular object (i.e., memory location).
985 * @param location The object location to check
986 * @return The last seq_cst action performed
988 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
990 action_list_t *list = obj_map->get_safe_ptr(location);
991 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
992 action_list_t::reverse_iterator rit;
993 for (rit = list->rbegin(); rit != list->rend(); rit++)
994 if ((*rit)->is_write() && (*rit)->is_seqcst())
999 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1001 ModelAction *parent = get_last_action(tid);
1003 parent = get_thread(tid)->get_creation();
1008 * Returns the clock vector for a given thread.
1009 * @param tid The thread whose clock vector we want
1010 * @return Desired clock vector
1012 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1014 return get_parent_action(tid)->get_cv();
1018 * Resolve a set of Promises with a current write. The set is provided in the
1019 * Node corresponding to @a write.
1020 * @param write The ModelAction that is fulfilling Promises
1021 * @return True if promises were resolved; false otherwise
1023 bool ModelChecker::resolve_promises(ModelAction *write)
1025 bool resolved = false;
1027 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1028 Promise *promise = (*promises)[promise_index];
1029 if (write->get_node()->get_promise(i)) {
1030 ModelAction *read = promise->get_action();
1031 read->read_from(write);
1032 if (read->is_rmw()) {
1033 mo_graph->addRMWEdge(write, read);
1035 r_modification_order(read, write);
1036 post_r_modification_order(read, write);
1037 promises->erase(promises->begin() + promise_index);
1048 * Compute the set of promises that could potentially be satisfied by this
1049 * action. Note that the set computation actually appears in the Node, not in
1051 * @param curr The ModelAction that may satisfy promises
1053 void ModelChecker::compute_promises(ModelAction *curr)
1055 for (unsigned int i = 0; i < promises->size(); i++) {
1056 Promise *promise = (*promises)[i];
1057 const ModelAction *act = promise->get_action();
1058 if (!act->happens_before(curr) &&
1060 !act->is_synchronizing(curr) &&
1061 !act->same_thread(curr) &&
1062 promise->get_value() == curr->get_value()) {
1063 curr->get_node()->set_promise(i);
1068 /** Checks promises in response to change in ClockVector Threads. */
1069 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1071 for (unsigned int i = 0; i < promises->size(); i++) {
1072 Promise *promise = (*promises)[i];
1073 const ModelAction *act = promise->get_action();
1074 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1075 merge_cv->synchronized_since(act)) {
1076 //This thread is no longer able to send values back to satisfy the promise
1077 int num_synchronized_threads = promise->increment_threads();
1078 if (num_synchronized_threads == get_num_threads()) {
1079 //Promise has failed
1080 failed_promise = true;
1088 * Build up an initial set of all past writes that this 'read' action may read
1089 * from. This set is determined by the clock vector's "happens before"
1091 * @param curr is the current ModelAction that we are exploring; it must be a
1094 void ModelChecker::build_reads_from_past(ModelAction *curr)
1096 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1098 ASSERT(curr->is_read());
1100 ModelAction *last_seq_cst = NULL;
1102 /* Track whether this object has been initialized */
1103 bool initialized = false;
1105 if (curr->is_seqcst()) {
1106 last_seq_cst = get_last_seq_cst(curr->get_location());
1107 /* We have to at least see the last sequentially consistent write,
1108 so we are initialized. */
1109 if (last_seq_cst != NULL)
1113 /* Iterate over all threads */
1114 for (i = 0; i < thrd_lists->size(); i++) {
1115 /* Iterate over actions in thread, starting from most recent */
1116 action_list_t *list = &(*thrd_lists)[i];
1117 action_list_t::reverse_iterator rit;
1118 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1119 ModelAction *act = *rit;
1121 /* Only consider 'write' actions */
1122 if (!act->is_write())
1125 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1126 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1127 DEBUG("Adding action to may_read_from:\n");
1128 if (DBG_ENABLED()) {
1132 curr->get_node()->add_read_from(act);
1135 /* Include at most one act per-thread that "happens before" curr */
1136 if (act->happens_before(curr)) {
1144 /** @todo Need a more informative way of reporting errors. */
1145 printf("ERROR: may read from uninitialized atomic\n");
1148 if (DBG_ENABLED() || !initialized) {
1149 printf("Reached read action:\n");
1151 printf("Printing may_read_from\n");
1152 curr->get_node()->print_may_read_from();
1153 printf("End printing may_read_from\n");
1156 ASSERT(initialized);
1159 static void print_list(action_list_t *list)
1161 action_list_t::iterator it;
1163 printf("---------------------------------------------------------------------\n");
1166 for (it = list->begin(); it != list->end(); it++) {
1169 printf("---------------------------------------------------------------------\n");
1172 void ModelChecker::print_summary()
1175 printf("Number of executions: %d\n", num_executions);
1176 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1180 if (!isfinalfeasible())
1181 printf("INFEASIBLE EXECUTION!\n");
1182 print_list(action_trace);
1187 * Add a Thread to the system for the first time. Should only be called once
1189 * @param t The Thread to add
1191 void ModelChecker::add_thread(Thread *t)
1193 thread_map->put(id_to_int(t->get_id()), t);
1194 scheduler->add_thread(t);
1197 void ModelChecker::remove_thread(Thread *t)
1199 scheduler->remove_thread(t);
1203 * Switch from a user-context to the "master thread" context (a.k.a. system
1204 * context). This switch is made with the intention of exploring a particular
1205 * model-checking action (described by a ModelAction object). Must be called
1206 * from a user-thread context.
1207 * @param act The current action that will be explored. Must not be NULL.
1208 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1210 int ModelChecker::switch_to_master(ModelAction *act)
1213 Thread *old = thread_current();
1214 set_current_action(act);
1215 old->set_state(THREAD_READY);
1216 return Thread::swap(old, &system_context);
1220 * Takes the next step in the execution, if possible.
1221 * @return Returns true (success) if a step was taken and false otherwise.
1223 bool ModelChecker::take_step() {
1224 Thread *curr, *next;
1229 curr = thread_current();
1231 if (curr->get_state() == THREAD_READY) {
1232 ASSERT(priv->current_action);
1234 priv->nextThread = check_current_action(priv->current_action);
1235 priv->current_action = NULL;
1236 if (!curr->is_blocked() && !curr->is_complete())
1237 scheduler->add_thread(curr);
1242 next = scheduler->next_thread(priv->nextThread);
1244 /* Infeasible -> don't take any more steps */
1249 next->set_state(THREAD_RUNNING);
1250 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1252 /* next == NULL -> don't take any more steps */
1255 /* Return false only if swap fails with an error */
1256 return (Thread::swap(&system_context, next) == 0);
1259 /** Runs the current execution until threre are no more steps to take. */
1260 void ModelChecker::finish_execution() {
1263 while (take_step());