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;
262 * Processes a read or rmw model action.
263 * @param curr is the read model action to process.
264 * @param th is the thread
265 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
266 * @return True if processing this read updates the mo_graph.
269 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
273 const ModelAction *reads_from = curr->get_node()->get_read_from();
274 if (reads_from != NULL) {
275 value = reads_from->get_value();
276 /* Assign reads_from, perform release/acquire synchronization */
277 curr->read_from(reads_from);
278 if (!second_part_of_rmw) {
279 check_recency(curr,false);
282 bool r_status=r_modification_order(curr,reads_from);
284 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
285 mo_graph->rollbackChanges();
286 too_many_reads=false;
290 mo_graph->commitChanges();
293 /* Read from future value */
294 value = curr->get_node()->get_future_value();
295 curr->read_from(NULL);
296 Promise *valuepromise = new Promise(curr, value);
297 promises->push_back(valuepromise);
299 th->set_return_value(value);
305 * This is the heart of the model checker routine. It performs model-checking
306 * actions corresponding to a given "current action." Among other processes, it
307 * calculates reads-from relationships, updates synchronization clock vectors,
308 * forms a memory_order constraints graph, and handles replay/backtrack
309 * execution when running permutations of previously-observed executions.
311 * @param curr The current action to process
312 * @return The next Thread that must be executed. May be NULL if ModelChecker
313 * makes no choice (e.g., according to replay execution, combining RMW actions,
316 Thread * ModelChecker::check_current_action(ModelAction *curr)
318 bool second_part_of_rmw = false;
322 if (curr->is_rmwc() || curr->is_rmw()) {
323 ModelAction *tmp = process_rmw(curr);
324 second_part_of_rmw = true;
328 ModelAction *tmp = node_stack->explore_action(curr);
330 /* Discard duplicate ModelAction; use action from NodeStack */
331 /* First restore type and order in case of RMW operation */
333 tmp->copy_typeandorder(curr);
335 /* If we have diverged, we need to reset the clock vector. */
337 tmp->create_cv(get_parent_action(tmp->get_tid()));
343 * Perform one-time actions when pushing new ModelAction onto
346 curr->create_cv(get_parent_action(curr->get_tid()));
347 /* Build may_read_from set */
349 build_reads_from_past(curr);
350 if (curr->is_write())
351 compute_promises(curr);
355 /* Thread specific actions */
356 switch(curr->get_type()) {
357 case THREAD_CREATE: {
358 Thread *th = (Thread *)curr->get_location();
359 th->set_creation(curr);
364 wait = get_thread(curr);
365 join = (Thread *)curr->get_location();
366 if (!join->is_complete())
367 scheduler->wait(wait, join);
370 case THREAD_FINISH: {
371 Thread *th = get_thread(curr);
372 while (!th->wait_list_empty()) {
373 Thread *wake = th->pop_wait_list();
374 scheduler->wake(wake);
380 check_promises(NULL, curr->get_cv());
387 Thread *th = get_thread(curr);
389 bool updated = false;
390 if (curr->is_read()) {
391 updated=process_read(curr, th, second_part_of_rmw);
394 if (curr->is_write()) {
395 bool updated_mod_order=w_modification_order(curr);
396 bool updated_promises=resolve_promises(curr);
397 updated=updated_mod_order|updated_promises;
399 mo_graph->commitChanges();
400 th->set_return_value(VALUE_NONE);
404 resolve_release_sequences(curr->get_location());
406 /* Add action to list. */
407 if (!second_part_of_rmw)
408 add_action_to_lists(curr);
410 Node *currnode = curr->get_node();
411 Node *parnode = currnode->get_parent();
413 if ((!parnode->backtrack_empty() ||
414 !currnode->read_from_empty() ||
415 !currnode->future_value_empty() ||
416 !currnode->promise_empty())
417 && (!priv->next_backtrack ||
418 *curr > *priv->next_backtrack)) {
419 priv->next_backtrack = curr;
422 set_backtracking(curr);
424 return get_next_thread(curr);
427 /** @returns whether the current partial trace must be a prefix of a
429 bool ModelChecker::isfeasibleprefix() {
430 return promises->size() == 0 && *lazy_sync_size == 0;
433 /** @returns whether the current partial trace is feasible. */
434 bool ModelChecker::isfeasible() {
435 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
438 /** Returns whether the current completed trace is feasible. */
439 bool ModelChecker::isfinalfeasible() {
440 return isfeasible() && promises->size() == 0;
443 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
444 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
445 int tid = id_to_int(act->get_tid());
446 ModelAction *lastread = get_last_action(tid);
447 lastread->process_rmw(act);
449 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
454 * Checks whether a thread has read from the same write for too many times
455 * without seeing the effects of a later write.
458 * 1) there must a different write that we could read from that would satisfy the modification order,
459 * 2) we must have read from the same value in excess of maxreads times, and
460 * 3) that other write must have been in the reads_from set for maxreads times.
462 * If so, we decide that the execution is no longer feasible.
464 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
465 if (params.maxreads != 0) {
466 if (curr->get_node()->get_read_from_size() <= 1)
469 //Must make sure that execution is currently feasible... We could
470 //accidentally clear by rolling back
474 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
475 int tid = id_to_int(curr->get_tid());
478 if ((int)thrd_lists->size() <= tid)
481 action_list_t *list = &(*thrd_lists)[tid];
483 action_list_t::reverse_iterator rit = list->rbegin();
485 if (!already_added) {
486 for (; (*rit) != curr; rit++)
488 /* go past curr now */
492 action_list_t::reverse_iterator ritcopy=rit;
493 //See if we have enough reads from the same value
495 for (; count < params.maxreads; rit++,count++) {
496 if (rit==list->rend())
498 ModelAction *act = *rit;
501 if (act->get_reads_from() != curr->get_reads_from())
503 if (act->get_node()->get_read_from_size() <= 1)
507 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
509 const ModelAction * write=curr->get_node()->get_read_from_at(i);
510 //Need a different write
511 if (write==curr->get_reads_from())
514 /* Test to see whether this is a feasible write to read from*/
515 r_modification_order(curr, write);
516 bool feasiblereadfrom=isfeasible();
517 mo_graph->rollbackChanges();
519 if (!feasiblereadfrom)
523 bool feasiblewrite=true;
524 //new we need to see if this write works for everyone
526 for (int loop=count;loop>0;loop--,rit++) {
527 ModelAction *act=*rit;
528 bool foundvalue=false;
529 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
530 if (act->get_node()->get_read_from_at(i)==write) {
541 too_many_reads = true;
549 * Updates the mo_graph with the constraints imposed from the current read.
550 * @param curr The current action. Must be a read.
551 * @param rf The action that curr reads from. Must be a write.
552 * @return True if modification order edges were added; false otherwise
554 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
556 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
559 ASSERT(curr->is_read());
561 /* Iterate over all threads */
562 for (i = 0; i < thrd_lists->size(); i++) {
563 /* Iterate over actions in thread, starting from most recent */
564 action_list_t *list = &(*thrd_lists)[i];
565 action_list_t::reverse_iterator rit;
566 for (rit = list->rbegin(); rit != list->rend(); rit++) {
567 ModelAction *act = *rit;
569 /* Include at most one act per-thread that "happens before" curr */
570 if (act->happens_before(curr)) {
571 if (act->is_read()) {
572 const ModelAction *prevreadfrom = act->get_reads_from();
573 if (prevreadfrom != NULL && rf != prevreadfrom) {
574 mo_graph->addEdge(prevreadfrom, rf);
577 } else if (rf != act) {
578 mo_graph->addEdge(act, rf);
589 /** Updates the mo_graph with the constraints imposed from the current read. */
590 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
592 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
594 ASSERT(curr->is_read());
596 /* Iterate over all threads */
597 for (i = 0; i < thrd_lists->size(); i++) {
598 /* Iterate over actions in thread, starting from most recent */
599 action_list_t *list = &(*thrd_lists)[i];
600 action_list_t::reverse_iterator rit;
601 ModelAction *lastact = NULL;
603 /* Find last action that happens after curr */
604 for (rit = list->rbegin(); rit != list->rend(); rit++) {
605 ModelAction *act = *rit;
606 if (curr->happens_before(act)) {
612 /* Include at most one act per-thread that "happens before" curr */
613 if (lastact != NULL) {
614 if (lastact->is_read()) {
615 const ModelAction *postreadfrom = lastact->get_reads_from();
616 if (postreadfrom != NULL&&rf != postreadfrom)
617 mo_graph->addEdge(rf, postreadfrom);
618 } else if (rf != lastact) {
619 mo_graph->addEdge(rf, lastact);
627 * Updates the mo_graph with the constraints imposed from the current write.
628 * @param curr The current action. Must be a write.
629 * @return True if modification order edges were added; false otherwise
631 bool ModelChecker::w_modification_order(ModelAction *curr)
633 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
636 ASSERT(curr->is_write());
638 if (curr->is_seqcst()) {
639 /* We have to at least see the last sequentially consistent write,
640 so we are initialized. */
641 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
642 if (last_seq_cst != NULL) {
643 mo_graph->addEdge(last_seq_cst, curr);
648 /* Iterate over all threads */
649 for (i = 0; i < thrd_lists->size(); i++) {
650 /* Iterate over actions in thread, starting from most recent */
651 action_list_t *list = &(*thrd_lists)[i];
652 action_list_t::reverse_iterator rit;
653 for (rit = list->rbegin(); rit != list->rend(); rit++) {
654 ModelAction *act = *rit;
656 /* Include at most one act per-thread that "happens before" curr */
657 if (act->happens_before(curr)) {
659 * Note: if act is RMW, just add edge:
661 * The following edge should be handled elsewhere:
662 * readfrom(act) --mo--> act
665 mo_graph->addEdge(act, curr);
666 else if (act->is_read() && act->get_reads_from() != NULL)
667 mo_graph->addEdge(act->get_reads_from(), curr);
670 } else if (act->is_read() && !act->is_synchronizing(curr) &&
671 !act->same_thread(curr)) {
672 /* We have an action that:
673 (1) did not happen before us
674 (2) is a read and we are a write
675 (3) cannot synchronize with us
676 (4) is in a different thread
678 that read could potentially read from our write.
680 if (act->get_node()->add_future_value(curr->get_value()) &&
681 (!priv->next_backtrack || *act > *priv->next_backtrack))
682 priv->next_backtrack = act;
691 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
692 * The ModelAction under consideration is expected to be taking part in
693 * release/acquire synchronization as an object of the "reads from" relation.
694 * Note that this can only provide release sequence support for RMW chains
695 * which do not read from the future, as those actions cannot be traced until
696 * their "promise" is fulfilled. Similarly, we may not even establish the
697 * presence of a release sequence with certainty, as some modification order
698 * constraints may be decided further in the future. Thus, this function
699 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
700 * and a boolean representing certainty.
702 * @todo Finish lazy updating, when promises are fulfilled in the future
703 * @param rf The action that might be part of a release sequence. Must be a
705 * @param release_heads A pass-by-reference style return parameter. After
706 * execution of this function, release_heads will contain the heads of all the
707 * relevant release sequences, if any exists
708 * @return true, if the ModelChecker is certain that release_heads is complete;
711 bool ModelChecker::release_seq_head(const ModelAction *rf,
712 std::vector<const ModelAction *> *release_heads) const
714 ASSERT(rf->is_write());
716 /* read from future: need to settle this later */
717 return false; /* incomplete */
719 if (rf->is_release())
720 release_heads->push_back(rf);
722 /* We need a RMW action that is both an acquire and release to stop */
723 /** @todo Need to be smarter here... In the linux lock
724 * example, this will run to the beginning of the program for
726 if (rf->is_acquire() && rf->is_release())
727 return true; /* complete */
728 return release_seq_head(rf->get_reads_from(), release_heads);
730 if (rf->is_release())
731 return true; /* complete */
733 /* else relaxed write; check modification order for contiguous subsequence
734 * -> rf must be same thread as release */
735 int tid = id_to_int(rf->get_tid());
736 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
737 action_list_t *list = &(*thrd_lists)[tid];
738 action_list_t::const_reverse_iterator rit;
740 /* Find rf in the thread list */
741 rit = std::find(list->rbegin(), list->rend(), rf);
742 ASSERT(rit != list->rend());
744 /* Find the last write/release */
745 for (; rit != list->rend(); rit++)
746 if ((*rit)->is_release())
748 if (rit == list->rend()) {
749 /* No write-release in this thread */
750 return true; /* complete */
752 ModelAction *release = *rit;
754 ASSERT(rf->same_thread(release));
757 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
758 if (id_to_int(rf->get_tid()) == (int)i)
760 list = &(*thrd_lists)[i];
762 /* Can we ensure no future writes from this thread may break
763 * the release seq? */
764 bool future_ordered = false;
766 for (rit = list->rbegin(); rit != list->rend(); rit++) {
767 const ModelAction *act = *rit;
768 if (!act->is_write())
770 /* Reach synchronization -> this thread is complete */
771 if (act->happens_before(release))
773 if (rf->happens_before(act)) {
774 future_ordered = true;
778 /* Check modification order */
779 if (mo_graph->checkReachable(rf, act)) {
781 future_ordered = true;
784 if (mo_graph->checkReachable(act, release))
785 /* act --mo--> release */
787 if (mo_graph->checkReachable(release, act) &&
788 mo_graph->checkReachable(act, rf)) {
789 /* release --mo-> act --mo--> rf */
790 return true; /* complete */
795 return false; /* This thread is uncertain */
799 release_heads->push_back(release);
804 * A public interface for getting the release sequence head(s) with which a
805 * given ModelAction must synchronize. This function only returns a non-empty
806 * result when it can locate a release sequence head with certainty. Otherwise,
807 * it may mark the internal state of the ModelChecker so that it will handle
808 * the release sequence at a later time, causing @a act to update its
809 * synchronization at some later point in execution.
810 * @param act The 'acquire' action that may read from a release sequence
811 * @param release_heads A pass-by-reference return parameter. Will be filled
812 * with the head(s) of the release sequence(s), if they exists with certainty.
813 * @see ModelChecker::release_seq_head
815 void ModelChecker::get_release_seq_heads(ModelAction *act,
816 std::vector<const ModelAction *> *release_heads)
818 const ModelAction *rf = act->get_reads_from();
820 complete = release_seq_head(rf, release_heads);
822 /* add act to 'lazy checking' list */
823 std::list<ModelAction *> *list;
824 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
825 list->push_back(act);
831 * Attempt to resolve all stashed operations that might synchronize with a
832 * release sequence for a given location. This implements the "lazy" portion of
833 * determining whether or not a release sequence was contiguous, since not all
834 * modification order information is present at the time an action occurs.
836 * @param location The location/object that should be checked for release
837 * sequence resolutions
838 * @return True if any updates occurred (new synchronization, new mo_graph edges)
840 bool ModelChecker::resolve_release_sequences(void *location)
842 std::list<ModelAction *> *list;
843 list = lazy_sync_with_release->getptr(location);
847 bool updated = false;
848 std::list<ModelAction *>::iterator it = list->begin();
849 while (it != list->end()) {
850 ModelAction *act = *it;
851 const ModelAction *rf = act->get_reads_from();
852 std::vector<const ModelAction *> release_heads;
854 complete = release_seq_head(rf, &release_heads);
855 for (unsigned int i = 0; i < release_heads.size(); i++) {
856 if (!act->has_synchronized_with(release_heads[i])) {
858 act->synchronize_with(release_heads[i]);
863 /* propagate synchronization to later actions */
864 action_list_t::reverse_iterator it = action_trace->rbegin();
865 while ((*it) != act) {
866 ModelAction *propagate = *it;
867 if (act->happens_before(propagate))
868 /** @todo new mo_graph edges along with
869 * this synchronization? */
870 propagate->synchronize_with(act);
874 it = list->erase(it);
880 // If we resolved promises or data races, see if we have realized a data race.
881 if (checkDataRaces()) {
889 * Performs various bookkeeping operations for the current ModelAction. For
890 * instance, adds action to the per-object, per-thread action vector and to the
891 * action trace list of all thread actions.
893 * @param act is the ModelAction to add.
895 void ModelChecker::add_action_to_lists(ModelAction *act)
897 int tid = id_to_int(act->get_tid());
898 action_trace->push_back(act);
900 obj_map->get_safe_ptr(act->get_location())->push_back(act);
902 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
903 if (tid >= (int)vec->size())
904 vec->resize(priv->next_thread_id);
905 (*vec)[tid].push_back(act);
907 if ((int)thrd_last_action->size() <= tid)
908 thrd_last_action->resize(get_num_threads());
909 (*thrd_last_action)[tid] = act;
912 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
914 int nthreads = get_num_threads();
915 if ((int)thrd_last_action->size() < nthreads)
916 thrd_last_action->resize(nthreads);
917 return (*thrd_last_action)[id_to_int(tid)];
921 * Gets the last memory_order_seq_cst action (in the total global sequence)
922 * performed on a particular object (i.e., memory location).
923 * @param location The object location to check
924 * @return The last seq_cst action performed
926 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
928 action_list_t *list = obj_map->get_safe_ptr(location);
929 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
930 action_list_t::reverse_iterator rit;
931 for (rit = list->rbegin(); rit != list->rend(); rit++)
932 if ((*rit)->is_write() && (*rit)->is_seqcst())
937 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
939 ModelAction *parent = get_last_action(tid);
941 parent = get_thread(tid)->get_creation();
946 * Returns the clock vector for a given thread.
947 * @param tid The thread whose clock vector we want
948 * @return Desired clock vector
950 ClockVector * ModelChecker::get_cv(thread_id_t tid)
952 return get_parent_action(tid)->get_cv();
956 * Resolve a set of Promises with a current write. The set is provided in the
957 * Node corresponding to @a write.
958 * @param write The ModelAction that is fulfilling Promises
959 * @return True if promises were resolved; false otherwise
961 bool ModelChecker::resolve_promises(ModelAction *write)
963 bool resolved = false;
964 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
965 Promise *promise = (*promises)[promise_index];
966 if (write->get_node()->get_promise(i)) {
967 ModelAction *read = promise->get_action();
968 read->read_from(write);
969 r_modification_order(read, write);
970 post_r_modification_order(read, write);
971 promises->erase(promises->begin() + promise_index);
981 * Compute the set of promises that could potentially be satisfied by this
982 * action. Note that the set computation actually appears in the Node, not in
984 * @param curr The ModelAction that may satisfy promises
986 void ModelChecker::compute_promises(ModelAction *curr)
988 for (unsigned int i = 0; i < promises->size(); i++) {
989 Promise *promise = (*promises)[i];
990 const ModelAction *act = promise->get_action();
991 if (!act->happens_before(curr) &&
993 !act->is_synchronizing(curr) &&
994 !act->same_thread(curr) &&
995 promise->get_value() == curr->get_value()) {
996 curr->get_node()->set_promise(i);
1001 /** Checks promises in response to change in ClockVector Threads. */
1002 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1004 for (unsigned int i = 0; i < promises->size(); i++) {
1005 Promise *promise = (*promises)[i];
1006 const ModelAction *act = promise->get_action();
1007 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1008 merge_cv->synchronized_since(act)) {
1009 //This thread is no longer able to send values back to satisfy the promise
1010 int num_synchronized_threads = promise->increment_threads();
1011 if (num_synchronized_threads == get_num_threads()) {
1012 //Promise has failed
1013 failed_promise = true;
1021 * Build up an initial set of all past writes that this 'read' action may read
1022 * from. This set is determined by the clock vector's "happens before"
1024 * @param curr is the current ModelAction that we are exploring; it must be a
1027 void ModelChecker::build_reads_from_past(ModelAction *curr)
1029 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1031 ASSERT(curr->is_read());
1033 ModelAction *last_seq_cst = NULL;
1035 /* Track whether this object has been initialized */
1036 bool initialized = false;
1038 if (curr->is_seqcst()) {
1039 last_seq_cst = get_last_seq_cst(curr->get_location());
1040 /* We have to at least see the last sequentially consistent write,
1041 so we are initialized. */
1042 if (last_seq_cst != NULL)
1046 /* Iterate over all threads */
1047 for (i = 0; i < thrd_lists->size(); i++) {
1048 /* Iterate over actions in thread, starting from most recent */
1049 action_list_t *list = &(*thrd_lists)[i];
1050 action_list_t::reverse_iterator rit;
1051 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1052 ModelAction *act = *rit;
1054 /* Only consider 'write' actions */
1055 if (!act->is_write())
1058 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1059 if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
1060 DEBUG("Adding action to may_read_from:\n");
1061 if (DBG_ENABLED()) {
1065 curr->get_node()->add_read_from(act);
1068 /* Include at most one act per-thread that "happens before" curr */
1069 if (act->happens_before(curr)) {
1077 /** @todo Need a more informative way of reporting errors. */
1078 printf("ERROR: may read from uninitialized atomic\n");
1081 if (DBG_ENABLED() || !initialized) {
1082 printf("Reached read action:\n");
1084 printf("Printing may_read_from\n");
1085 curr->get_node()->print_may_read_from();
1086 printf("End printing may_read_from\n");
1089 ASSERT(initialized);
1092 static void print_list(action_list_t *list)
1094 action_list_t::iterator it;
1096 printf("---------------------------------------------------------------------\n");
1099 for (it = list->begin(); it != list->end(); it++) {
1102 printf("---------------------------------------------------------------------\n");
1105 void ModelChecker::print_summary()
1108 printf("Number of executions: %d\n", num_executions);
1109 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1113 if (!isfinalfeasible())
1114 printf("INFEASIBLE EXECUTION!\n");
1115 print_list(action_trace);
1120 * Add a Thread to the system for the first time. Should only be called once
1122 * @param t The Thread to add
1124 void ModelChecker::add_thread(Thread *t)
1126 thread_map->put(id_to_int(t->get_id()), t);
1127 scheduler->add_thread(t);
1130 void ModelChecker::remove_thread(Thread *t)
1132 scheduler->remove_thread(t);
1136 * Switch from a user-context to the "master thread" context (a.k.a. system
1137 * context). This switch is made with the intention of exploring a particular
1138 * model-checking action (described by a ModelAction object). Must be called
1139 * from a user-thread context.
1140 * @param act The current action that will be explored. Must not be NULL.
1141 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1143 int ModelChecker::switch_to_master(ModelAction *act)
1146 Thread *old = thread_current();
1147 set_current_action(act);
1148 old->set_state(THREAD_READY);
1149 return Thread::swap(old, &system_context);
1153 * Takes the next step in the execution, if possible.
1154 * @return Returns true (success) if a step was taken and false otherwise.
1156 bool ModelChecker::take_step() {
1157 Thread *curr, *next;
1162 curr = thread_current();
1164 if (curr->get_state() == THREAD_READY) {
1165 ASSERT(priv->current_action);
1166 priv->nextThread = check_current_action(priv->current_action);
1167 priv->current_action = NULL;
1168 if (!curr->is_blocked() && !curr->is_complete())
1169 scheduler->add_thread(curr);
1174 next = scheduler->next_thread(priv->nextThread);
1176 /* Infeasible -> don't take any more steps */
1181 next->set_state(THREAD_RUNNING);
1182 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1184 /* next == NULL -> don't take any more steps */
1187 /* Return false only if swap fails with an error */
1188 return (Thread::swap(&system_context, next) == 0);
1191 /** Runs the current execution until threre are no more steps to take. */
1192 void ModelChecker::finish_execution() {
1195 while (take_step());