8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
15 #define INITIAL_THREAD_ID 0
19 /** @brief Constructor */
20 ModelChecker::ModelChecker(struct model_params params) :
21 /* Initialize default scheduler */
22 scheduler(new Scheduler()),
24 num_feasible_executions(0),
27 action_trace(new action_list_t()),
28 thread_map(new HashTable<int, Thread *, int>()),
29 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
30 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
31 promises(new std::vector<Promise *>()),
32 futurevalues(new std::vector<struct PendingFutureValue>()),
33 lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
34 thrd_last_action(new std::vector<ModelAction *>(1)),
35 node_stack(new NodeStack()),
36 mo_graph(new CycleGraph()),
37 failed_promise(false),
38 too_many_reads(false),
41 /* Allocate this "size" on the snapshotting heap */
42 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
43 /* First thread created will have id INITIAL_THREAD_ID */
44 priv->next_thread_id = INITIAL_THREAD_ID;
46 lazy_sync_size = &priv->lazy_sync_size;
49 /** @brief Destructor */
50 ModelChecker::~ModelChecker()
52 for (int i = 0; i < get_num_threads(); i++)
53 delete thread_map->get(i);
60 for (unsigned int i = 0; i < promises->size(); i++)
61 delete (*promises)[i];
64 delete lazy_sync_with_release;
66 delete thrd_last_action;
73 * Restores user program to initial state and resets all model-checker data
76 void ModelChecker::reset_to_initial_state()
78 DEBUG("+++ Resetting to initial state +++\n");
79 node_stack->reset_execution();
80 failed_promise = false;
81 too_many_reads = false;
83 snapshotObject->backTrackBeforeStep(0);
86 /** @returns a thread ID for a new Thread */
87 thread_id_t ModelChecker::get_next_id()
89 return priv->next_thread_id++;
92 /** @returns the number of user threads created during this execution */
93 int ModelChecker::get_num_threads()
95 return priv->next_thread_id;
98 /** @returns a sequence number for a new ModelAction */
99 modelclock_t ModelChecker::get_next_seq_num()
101 return ++priv->used_sequence_numbers;
105 * @brief Choose the next thread to execute.
107 * This function chooses the next thread that should execute. It can force the
108 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
109 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
110 * The model-checker may have no preference regarding the next thread (i.e.,
111 * when exploring a new execution ordering), in which case this will return
113 * @param curr The current ModelAction. This action might guide the choice of
115 * @return The next thread to run. If the model-checker has no preference, NULL.
117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
121 /* Do not split atomic actions. */
123 return thread_current();
124 /* The THREAD_CREATE action points to the created Thread */
125 else if (curr->get_type() == THREAD_CREATE)
126 return (Thread *)curr->get_location();
128 /* Have we completed exploring the preselected path? */
132 /* Else, we are trying to replay an execution */
133 ModelAction *next = node_stack->get_next()->get_action();
135 if (next == diverge) {
136 Node *nextnode = next->get_node();
137 /* Reached divergence point */
138 if (nextnode->increment_promise()) {
139 /* The next node will try to satisfy a different set of promises. */
140 tid = next->get_tid();
141 node_stack->pop_restofstack(2);
142 } else if (nextnode->increment_read_from()) {
143 /* The next node will read from a different value. */
144 tid = next->get_tid();
145 node_stack->pop_restofstack(2);
146 } else if (nextnode->increment_future_value()) {
147 /* The next node will try to read from a different future value. */
148 tid = next->get_tid();
149 node_stack->pop_restofstack(2);
151 /* Make a different thread execute for next step */
152 Node *node = nextnode->get_parent();
153 tid = node->get_next_backtrack();
154 node_stack->pop_restofstack(1);
156 DEBUG("*** Divergence point ***\n");
159 tid = next->get_tid();
161 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
162 ASSERT(tid != THREAD_ID_T_NONE);
163 return thread_map->get(id_to_int(tid));
167 * Queries the model-checker for more executions to explore and, if one
168 * exists, resets the model-checker state to execute a new execution.
170 * @return If there are more executions to explore, return true. Otherwise,
173 bool ModelChecker::next_execution()
178 if (isfinalfeasible())
179 num_feasible_executions++;
181 if (isfinalfeasible() || DBG_ENABLED())
184 if ((diverge = get_next_backtrack()) == NULL)
188 printf("Next execution will diverge at:\n");
192 reset_to_initial_state();
196 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
198 action_type type = act->get_type();
208 /* linear search: from most recent to oldest */
209 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
210 action_list_t::reverse_iterator rit;
211 for (rit = list->rbegin(); rit != list->rend(); rit++) {
212 ModelAction *prev = *rit;
213 if (act->is_synchronizing(prev))
219 void ModelChecker::set_backtracking(ModelAction *act)
223 Thread *t = get_thread(act);
225 prev = get_last_conflict(act);
229 node = prev->get_node()->get_parent();
231 while (!node->is_enabled(t))
234 /* Check if this has been explored already */
235 if (node->has_been_explored(t->get_id()))
238 /* Cache the latest backtracking point */
239 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
240 priv->next_backtrack = prev;
242 /* If this is a new backtracking point, mark the tree */
243 if (!node->set_backtrack(t->get_id()))
245 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
246 prev->get_tid(), t->get_id());
254 * Returns last backtracking point. The model checker will explore a different
255 * path for this point in the next execution.
256 * @return The ModelAction at which the next execution should diverge.
258 ModelAction * ModelChecker::get_next_backtrack()
260 ModelAction *next = priv->next_backtrack;
261 priv->next_backtrack = NULL;
266 * Processes a read or rmw model action.
267 * @param curr is the read model action to process.
268 * @param th is the thread
269 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
270 * @return True if processing this read updates the mo_graph.
272 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
274 bool updated = false;
276 const ModelAction *reads_from = curr->get_node()->get_read_from();
277 if (reads_from != NULL) {
278 mo_graph->startChanges();
280 value = reads_from->get_value();
281 bool r_status = false;
283 if (!second_part_of_rmw) {
284 check_recency(curr,false);
285 r_status = r_modification_order(curr, reads_from);
289 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
290 mo_graph->rollbackChanges();
291 too_many_reads = false;
295 curr->read_from(reads_from);
296 mo_graph->commitChanges();
298 } else if (!second_part_of_rmw) {
299 /* Read from future value */
300 value = curr->get_node()->get_future_value();
301 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
302 curr->read_from(NULL);
303 Promise *valuepromise = new Promise(curr, value, expiration);
304 promises->push_back(valuepromise);
306 th->set_return_value(value);
312 * This is the heart of the model checker routine. It performs model-checking
313 * actions corresponding to a given "current action." Among other processes, it
314 * calculates reads-from relationships, updates synchronization clock vectors,
315 * forms a memory_order constraints graph, and handles replay/backtrack
316 * execution when running permutations of previously-observed executions.
318 * @param curr The current action to process
319 * @return The next Thread that must be executed. May be NULL if ModelChecker
320 * makes no choice (e.g., according to replay execution, combining RMW actions,
323 Thread * ModelChecker::check_current_action(ModelAction *curr)
325 bool second_part_of_rmw = false;
329 if (curr->is_rmwc() || curr->is_rmw()) {
330 ModelAction *tmp = process_rmw(curr);
331 second_part_of_rmw = true;
334 compute_promises(curr);
336 ModelAction *tmp = node_stack->explore_action(curr);
338 /* Discard duplicate ModelAction; use action from NodeStack */
339 /* First restore type and order in case of RMW operation */
341 tmp->copy_typeandorder(curr);
343 /* If we have diverged, we need to reset the clock vector. */
345 tmp->create_cv(get_parent_action(tmp->get_tid()));
351 * Perform one-time actions when pushing new ModelAction onto
354 curr->create_cv(get_parent_action(curr->get_tid()));
355 /* Build may_read_from set */
357 build_reads_from_past(curr);
358 if (curr->is_write())
359 compute_promises(curr);
363 /* Thread specific actions */
364 switch (curr->get_type()) {
365 case THREAD_CREATE: {
366 Thread *th = (Thread *)curr->get_location();
367 th->set_creation(curr);
371 Thread *waiting, *blocking;
372 waiting = get_thread(curr);
373 blocking = (Thread *)curr->get_location();
374 if (!blocking->is_complete()) {
375 blocking->push_wait_list(curr);
376 scheduler->sleep(waiting);
380 case THREAD_FINISH: {
381 Thread *th = get_thread(curr);
382 while (!th->wait_list_empty()) {
383 ModelAction *act = th->pop_wait_list();
384 Thread *wake = get_thread(act);
385 scheduler->wake(wake);
391 check_promises(NULL, curr->get_cv());
398 bool updated = false;
400 if (curr->is_read()) {
401 updated = process_read(curr, get_thread(curr), second_part_of_rmw);
404 if (curr->is_write()) {
405 bool updated_mod_order = w_modification_order(curr);
406 bool updated_promises = resolve_promises(curr);
407 updated = updated || updated_mod_order || updated_promises;
409 if (promises->size()==0) {
410 for (unsigned int i = 0; i<futurevalues->size(); i++) {
411 struct PendingFutureValue pfv=(*futurevalues)[i];
412 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
413 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
414 priv->next_backtrack = pfv.act;
416 futurevalues->resize(0);
419 mo_graph->commitChanges();
420 get_thread(curr)->set_return_value(VALUE_NONE);
424 resolve_release_sequences(curr->get_location());
426 /* Add action to list. */
427 if (!second_part_of_rmw)
428 add_action_to_lists(curr);
430 check_curr_backtracking(curr);
432 set_backtracking(curr);
434 return get_next_thread(curr);
437 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
438 Node *currnode = curr->get_node();
439 Node *parnode = currnode->get_parent();
441 if ((!parnode->backtrack_empty() ||
442 !currnode->read_from_empty() ||
443 !currnode->future_value_empty() ||
444 !currnode->promise_empty())
445 && (!priv->next_backtrack ||
446 *curr > *priv->next_backtrack)) {
447 priv->next_backtrack = curr;
451 bool ModelChecker::promises_expired() {
452 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
453 Promise *promise = (*promises)[promise_index];
454 if (promise->get_expiration()<priv->used_sequence_numbers) {
461 /** @returns whether the current partial trace must be a prefix of a
463 bool ModelChecker::isfeasibleprefix() {
464 return promises->size() == 0 && *lazy_sync_size == 0;
467 /** @returns whether the current partial trace is feasible. */
468 bool ModelChecker::isfeasible() {
469 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
472 /** @returns whether the current partial trace is feasible other than
473 * multiple RMW reading from the same store. */
474 bool ModelChecker::isfeasibleotherthanRMW() {
475 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
478 /** Returns whether the current completed trace is feasible. */
479 bool ModelChecker::isfinalfeasible() {
480 return isfeasible() && promises->size() == 0;
483 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
484 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
485 int tid = id_to_int(act->get_tid());
486 ModelAction *lastread = get_last_action(tid);
487 lastread->process_rmw(act);
488 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
489 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
490 mo_graph->commitChanges();
496 * Checks whether a thread has read from the same write for too many times
497 * without seeing the effects of a later write.
500 * 1) there must a different write that we could read from that would satisfy the modification order,
501 * 2) we must have read from the same value in excess of maxreads times, and
502 * 3) that other write must have been in the reads_from set for maxreads times.
504 * If so, we decide that the execution is no longer feasible.
506 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
507 if (params.maxreads != 0) {
508 if (curr->get_node()->get_read_from_size() <= 1)
511 //Must make sure that execution is currently feasible... We could
512 //accidentally clear by rolling back
516 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
517 int tid = id_to_int(curr->get_tid());
520 if ((int)thrd_lists->size() <= tid)
523 action_list_t *list = &(*thrd_lists)[tid];
525 action_list_t::reverse_iterator rit = list->rbegin();
528 for (; (*rit) != curr; rit++)
530 /* go past curr now */
534 action_list_t::reverse_iterator ritcopy = rit;
535 //See if we have enough reads from the same value
537 for (; count < params.maxreads; rit++,count++) {
538 if (rit==list->rend())
540 ModelAction *act = *rit;
543 if (act->get_reads_from() != curr->get_reads_from())
545 if (act->get_node()->get_read_from_size() <= 1)
549 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
551 const ModelAction * write = curr->get_node()->get_read_from_at(i);
552 //Need a different write
553 if (write==curr->get_reads_from())
556 /* Test to see whether this is a feasible write to read from*/
557 mo_graph->startChanges();
558 r_modification_order(curr, write);
559 bool feasiblereadfrom = isfeasible();
560 mo_graph->rollbackChanges();
562 if (!feasiblereadfrom)
566 bool feasiblewrite = true;
567 //new we need to see if this write works for everyone
569 for (int loop = count; loop>0; loop--,rit++) {
570 ModelAction *act=*rit;
571 bool foundvalue = false;
572 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
573 if (act->get_node()->get_read_from_at(i)==write) {
579 feasiblewrite = false;
584 too_many_reads = true;
592 * Updates the mo_graph with the constraints imposed from the current
595 * Basic idea is the following: Go through each other thread and find
596 * the lastest action that happened before our read. Two cases:
598 * (1) The action is a write => that write must either occur before
599 * the write we read from or be the write we read from.
601 * (2) The action is a read => the write that that action read from
602 * must occur before the write we read from or be the same write.
604 * @param curr The current action. Must be a read.
605 * @param rf The action that curr reads from. Must be a write.
606 * @return True if modification order edges were added; false otherwise
608 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
610 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
613 ASSERT(curr->is_read());
615 /* Iterate over all threads */
616 for (i = 0; i < thrd_lists->size(); i++) {
617 /* Iterate over actions in thread, starting from most recent */
618 action_list_t *list = &(*thrd_lists)[i];
619 action_list_t::reverse_iterator rit;
620 for (rit = list->rbegin(); rit != list->rend(); rit++) {
621 ModelAction *act = *rit;
623 /* Include at most one act per-thread that "happens before" curr */
624 if (act->happens_before(curr)) {
625 if (act->is_write()) {
626 if (rf != act && act != curr) {
627 mo_graph->addEdge(act, rf);
631 const ModelAction *prevreadfrom = act->get_reads_from();
632 if (prevreadfrom != NULL && rf != prevreadfrom) {
633 mo_graph->addEdge(prevreadfrom, rf);
646 /** This method fixes up the modification order when we resolve a
647 * promises. The basic problem is that actions that occur after the
648 * read curr could not property add items to the modification order
651 * So for each thread, we find the earliest item that happens after
652 * the read curr. This is the item we have to fix up with additional
653 * constraints. If that action is write, we add a MO edge between
654 * the Action rf and that action. If the action is a read, we add a
655 * MO edge between the Action rf, and whatever the read accessed.
657 * @param curr is the read ModelAction that we are fixing up MO edges for.
658 * @param rf is the write ModelAction that curr reads from.
662 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
664 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
666 ASSERT(curr->is_read());
668 /* Iterate over all threads */
669 for (i = 0; i < thrd_lists->size(); i++) {
670 /* Iterate over actions in thread, starting from most recent */
671 action_list_t *list = &(*thrd_lists)[i];
672 action_list_t::reverse_iterator rit;
673 ModelAction *lastact = NULL;
675 /* Find last action that happens after curr */
676 for (rit = list->rbegin(); rit != list->rend(); rit++) {
677 ModelAction *act = *rit;
678 if (curr->happens_before(act)) {
684 /* Include at most one act per-thread that "happens before" curr */
685 if (lastact != NULL) {
686 if (lastact->is_read()) {
687 const ModelAction *postreadfrom = lastact->get_reads_from();
688 if (postreadfrom != NULL&&rf != postreadfrom)
689 mo_graph->addEdge(rf, postreadfrom);
690 } else if (rf != lastact) {
691 mo_graph->addEdge(rf, lastact);
699 * Updates the mo_graph with the constraints imposed from the current write.
701 * Basic idea is the following: Go through each other thread and find
702 * the lastest action that happened before our write. Two cases:
704 * (1) The action is a write => that write must occur before
707 * (2) The action is a read => the write that that action read from
708 * must occur before the current write.
710 * This method also handles two other issues:
712 * (I) Sequential Consistency: Making sure that if the current write is
713 * seq_cst, that it occurs after the previous seq_cst write.
715 * (II) Sending the write back to non-synchronizing reads.
717 * @param curr The current action. Must be a write.
718 * @return True if modification order edges were added; false otherwise
720 bool ModelChecker::w_modification_order(ModelAction *curr)
722 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
725 ASSERT(curr->is_write());
727 if (curr->is_seqcst()) {
728 /* We have to at least see the last sequentially consistent write,
729 so we are initialized. */
730 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
731 if (last_seq_cst != NULL) {
732 mo_graph->addEdge(last_seq_cst, curr);
737 /* Iterate over all threads */
738 for (i = 0; i < thrd_lists->size(); i++) {
739 /* Iterate over actions in thread, starting from most recent */
740 action_list_t *list = &(*thrd_lists)[i];
741 action_list_t::reverse_iterator rit;
742 for (rit = list->rbegin(); rit != list->rend(); rit++) {
743 ModelAction *act = *rit;
745 /* Include at most one act per-thread that "happens before" curr */
746 if (act->happens_before(curr)) {
748 * Note: if act is RMW, just add edge:
750 * The following edge should be handled elsewhere:
751 * readfrom(act) --mo--> act
753 if (act->is_write()) {
754 //RMW shouldn't have an edge to themselves
756 mo_graph->addEdge(act, curr);
757 } else if (act->is_read() && act->get_reads_from() != NULL)
758 mo_graph->addEdge(act->get_reads_from(), curr);
761 } else if (act->is_read() && !act->is_synchronizing(curr) &&
762 !act->same_thread(curr)) {
763 /* We have an action that:
764 (1) did not happen before us
765 (2) is a read and we are a write
766 (3) cannot synchronize with us
767 (4) is in a different thread
769 that read could potentially read from our write.
771 if (thin_air_constraint_may_allow(curr, act)) {
773 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
774 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
775 futurevalues->push_back(pfv);
785 /** Arbitrary reads from the future are not allowed. Section 29.3
786 * part 9 places some constraints. This method checks one result of constraint
787 * constraint. Others require compiler support. */
789 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
790 if (!writer->is_rmw())
793 if (!reader->is_rmw())
796 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
799 if (search->get_tid() == reader->get_tid() &&
800 search->happens_before(reader))
808 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
809 * The ModelAction under consideration is expected to be taking part in
810 * release/acquire synchronization as an object of the "reads from" relation.
811 * Note that this can only provide release sequence support for RMW chains
812 * which do not read from the future, as those actions cannot be traced until
813 * their "promise" is fulfilled. Similarly, we may not even establish the
814 * presence of a release sequence with certainty, as some modification order
815 * constraints may be decided further in the future. Thus, this function
816 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
817 * and a boolean representing certainty.
819 * @todo Finish lazy updating, when promises are fulfilled in the future
820 * @param rf The action that might be part of a release sequence. Must be a
822 * @param release_heads A pass-by-reference style return parameter. After
823 * execution of this function, release_heads will contain the heads of all the
824 * relevant release sequences, if any exists
825 * @return true, if the ModelChecker is certain that release_heads is complete;
828 bool ModelChecker::release_seq_head(const ModelAction *rf,
829 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
832 /* read from future: need to settle this later */
833 return false; /* incomplete */
836 ASSERT(rf->is_write());
838 if (rf->is_release())
839 release_heads->push_back(rf);
841 /* We need a RMW action that is both an acquire and release to stop */
842 /** @todo Need to be smarter here... In the linux lock
843 * example, this will run to the beginning of the program for
845 if (rf->is_acquire() && rf->is_release())
846 return true; /* complete */
847 return release_seq_head(rf->get_reads_from(), release_heads);
849 if (rf->is_release())
850 return true; /* complete */
852 /* else relaxed write; check modification order for contiguous subsequence
853 * -> rf must be same thread as release */
854 int tid = id_to_int(rf->get_tid());
855 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
856 action_list_t *list = &(*thrd_lists)[tid];
857 action_list_t::const_reverse_iterator rit;
859 /* Find rf in the thread list */
860 rit = std::find(list->rbegin(), list->rend(), rf);
861 ASSERT(rit != list->rend());
863 /* Find the last write/release */
864 for (; rit != list->rend(); rit++)
865 if ((*rit)->is_release())
867 if (rit == list->rend()) {
868 /* No write-release in this thread */
869 return true; /* complete */
871 ModelAction *release = *rit;
873 ASSERT(rf->same_thread(release));
876 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
877 if (id_to_int(rf->get_tid()) == (int)i)
879 list = &(*thrd_lists)[i];
881 /* Can we ensure no future writes from this thread may break
882 * the release seq? */
883 bool future_ordered = false;
885 for (rit = list->rbegin(); rit != list->rend(); rit++) {
886 const ModelAction *act = *rit;
887 if (!act->is_write())
889 /* Reach synchronization -> this thread is complete */
890 if (act->happens_before(release))
892 if (rf->happens_before(act)) {
893 future_ordered = true;
897 /* Check modification order */
898 if (mo_graph->checkReachable(rf, act)) {
900 future_ordered = true;
903 if (mo_graph->checkReachable(act, release))
904 /* act --mo--> release */
906 if (mo_graph->checkReachable(release, act) &&
907 mo_graph->checkReachable(act, rf)) {
908 /* release --mo-> act --mo--> rf */
909 return true; /* complete */
914 return false; /* This thread is uncertain */
918 release_heads->push_back(release);
923 * A public interface for getting the release sequence head(s) with which a
924 * given ModelAction must synchronize. This function only returns a non-empty
925 * result when it can locate a release sequence head with certainty. Otherwise,
926 * it may mark the internal state of the ModelChecker so that it will handle
927 * the release sequence at a later time, causing @a act to update its
928 * synchronization at some later point in execution.
929 * @param act The 'acquire' action that may read from a release sequence
930 * @param release_heads A pass-by-reference return parameter. Will be filled
931 * with the head(s) of the release sequence(s), if they exists with certainty.
932 * @see ModelChecker::release_seq_head
934 void ModelChecker::get_release_seq_heads(ModelAction *act,
935 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
937 const ModelAction *rf = act->get_reads_from();
939 complete = release_seq_head(rf, release_heads);
941 /* add act to 'lazy checking' list */
942 std::list<ModelAction *> *list;
943 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
944 list->push_back(act);
950 * Attempt to resolve all stashed operations that might synchronize with a
951 * release sequence for a given location. This implements the "lazy" portion of
952 * determining whether or not a release sequence was contiguous, since not all
953 * modification order information is present at the time an action occurs.
955 * @param location The location/object that should be checked for release
956 * sequence resolutions
957 * @return True if any updates occurred (new synchronization, new mo_graph edges)
959 bool ModelChecker::resolve_release_sequences(void *location)
961 std::list<ModelAction *> *list;
962 list = lazy_sync_with_release->getptr(location);
966 bool updated = false;
967 std::list<ModelAction *>::iterator it = list->begin();
968 while (it != list->end()) {
969 ModelAction *act = *it;
970 const ModelAction *rf = act->get_reads_from();
971 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
973 complete = release_seq_head(rf, &release_heads);
974 for (unsigned int i = 0; i < release_heads.size(); i++) {
975 if (!act->has_synchronized_with(release_heads[i])) {
977 act->synchronize_with(release_heads[i]);
982 /* propagate synchronization to later actions */
983 action_list_t::reverse_iterator it = action_trace->rbegin();
984 while ((*it) != act) {
985 ModelAction *propagate = *it;
986 if (act->happens_before(propagate))
987 /** @todo new mo_graph edges along with
988 * this synchronization? */
989 propagate->synchronize_with(act);
993 it = list->erase(it);
999 // If we resolved promises or data races, see if we have realized a data race.
1000 if (checkDataRaces()) {
1008 * Performs various bookkeeping operations for the current ModelAction. For
1009 * instance, adds action to the per-object, per-thread action vector and to the
1010 * action trace list of all thread actions.
1012 * @param act is the ModelAction to add.
1014 void ModelChecker::add_action_to_lists(ModelAction *act)
1016 int tid = id_to_int(act->get_tid());
1017 action_trace->push_back(act);
1019 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1021 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1022 if (tid >= (int)vec->size())
1023 vec->resize(priv->next_thread_id);
1024 (*vec)[tid].push_back(act);
1026 if ((int)thrd_last_action->size() <= tid)
1027 thrd_last_action->resize(get_num_threads());
1028 (*thrd_last_action)[tid] = act;
1031 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1033 int nthreads = get_num_threads();
1034 if ((int)thrd_last_action->size() < nthreads)
1035 thrd_last_action->resize(nthreads);
1036 return (*thrd_last_action)[id_to_int(tid)];
1040 * Gets the last memory_order_seq_cst action (in the total global sequence)
1041 * performed on a particular object (i.e., memory location).
1042 * @param location The object location to check
1043 * @return The last seq_cst action performed
1045 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1047 action_list_t *list = obj_map->get_safe_ptr(location);
1048 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1049 action_list_t::reverse_iterator rit;
1050 for (rit = list->rbegin(); rit != list->rend(); rit++)
1051 if ((*rit)->is_write() && (*rit)->is_seqcst())
1056 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1058 ModelAction *parent = get_last_action(tid);
1060 parent = get_thread(tid)->get_creation();
1065 * Returns the clock vector for a given thread.
1066 * @param tid The thread whose clock vector we want
1067 * @return Desired clock vector
1069 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1071 return get_parent_action(tid)->get_cv();
1075 * Resolve a set of Promises with a current write. The set is provided in the
1076 * Node corresponding to @a write.
1077 * @param write The ModelAction that is fulfilling Promises
1078 * @return True if promises were resolved; false otherwise
1080 bool ModelChecker::resolve_promises(ModelAction *write)
1082 bool resolved = false;
1084 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1085 Promise *promise = (*promises)[promise_index];
1086 if (write->get_node()->get_promise(i)) {
1087 ModelAction *read = promise->get_action();
1088 read->read_from(write);
1089 if (read->is_rmw()) {
1090 mo_graph->addRMWEdge(write, read);
1092 //First fix up the modification order for actions that happened
1094 r_modification_order(read, write);
1095 //Next fix up the modification order for actions that happened
1097 post_r_modification_order(read, write);
1098 promises->erase(promises->begin() + promise_index);
1107 * Compute the set of promises that could potentially be satisfied by this
1108 * action. Note that the set computation actually appears in the Node, not in
1110 * @param curr The ModelAction that may satisfy promises
1112 void ModelChecker::compute_promises(ModelAction *curr)
1114 for (unsigned int i = 0; i < promises->size(); i++) {
1115 Promise *promise = (*promises)[i];
1116 const ModelAction *act = promise->get_action();
1117 if (!act->happens_before(curr) &&
1119 !act->is_synchronizing(curr) &&
1120 !act->same_thread(curr) &&
1121 promise->get_value() == curr->get_value()) {
1122 curr->get_node()->set_promise(i);
1127 /** Checks promises in response to change in ClockVector Threads. */
1128 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1130 for (unsigned int i = 0; i < promises->size(); i++) {
1131 Promise *promise = (*promises)[i];
1132 const ModelAction *act = promise->get_action();
1133 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1134 merge_cv->synchronized_since(act)) {
1135 //This thread is no longer able to send values back to satisfy the promise
1136 int num_synchronized_threads = promise->increment_threads();
1137 if (num_synchronized_threads == get_num_threads()) {
1138 //Promise has failed
1139 failed_promise = true;
1147 * Build up an initial set of all past writes that this 'read' action may read
1148 * from. This set is determined by the clock vector's "happens before"
1150 * @param curr is the current ModelAction that we are exploring; it must be a
1153 void ModelChecker::build_reads_from_past(ModelAction *curr)
1155 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1157 ASSERT(curr->is_read());
1159 ModelAction *last_seq_cst = NULL;
1161 /* Track whether this object has been initialized */
1162 bool initialized = false;
1164 if (curr->is_seqcst()) {
1165 last_seq_cst = get_last_seq_cst(curr->get_location());
1166 /* We have to at least see the last sequentially consistent write,
1167 so we are initialized. */
1168 if (last_seq_cst != NULL)
1172 /* Iterate over all threads */
1173 for (i = 0; i < thrd_lists->size(); i++) {
1174 /* Iterate over actions in thread, starting from most recent */
1175 action_list_t *list = &(*thrd_lists)[i];
1176 action_list_t::reverse_iterator rit;
1177 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1178 ModelAction *act = *rit;
1180 /* Only consider 'write' actions */
1181 if (!act->is_write())
1184 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1185 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1186 DEBUG("Adding action to may_read_from:\n");
1187 if (DBG_ENABLED()) {
1191 curr->get_node()->add_read_from(act);
1194 /* Include at most one act per-thread that "happens before" curr */
1195 if (act->happens_before(curr)) {
1203 /** @todo Need a more informative way of reporting errors. */
1204 printf("ERROR: may read from uninitialized atomic\n");
1207 if (DBG_ENABLED() || !initialized) {
1208 printf("Reached read action:\n");
1210 printf("Printing may_read_from\n");
1211 curr->get_node()->print_may_read_from();
1212 printf("End printing may_read_from\n");
1215 ASSERT(initialized);
1218 static void print_list(action_list_t *list)
1220 action_list_t::iterator it;
1222 printf("---------------------------------------------------------------------\n");
1225 for (it = list->begin(); it != list->end(); it++) {
1228 printf("---------------------------------------------------------------------\n");
1231 void ModelChecker::print_summary()
1234 printf("Number of executions: %d\n", num_executions);
1235 printf("Number of feasible executions: %d\n", num_feasible_executions);
1236 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1238 #if SUPPORT_MOD_ORDER_DUMP
1240 char buffername[100];
1241 sprintf(buffername, "exec%u",num_executions);
1242 mo_graph->dumpGraphToFile(buffername);
1245 if (!isfinalfeasible())
1246 printf("INFEASIBLE EXECUTION!\n");
1247 print_list(action_trace);
1252 * Add a Thread to the system for the first time. Should only be called once
1254 * @param t The Thread to add
1256 void ModelChecker::add_thread(Thread *t)
1258 thread_map->put(id_to_int(t->get_id()), t);
1259 scheduler->add_thread(t);
1262 void ModelChecker::remove_thread(Thread *t)
1264 scheduler->remove_thread(t);
1268 * Switch from a user-context to the "master thread" context (a.k.a. system
1269 * context). This switch is made with the intention of exploring a particular
1270 * model-checking action (described by a ModelAction object). Must be called
1271 * from a user-thread context.
1272 * @param act The current action that will be explored. Must not be NULL.
1273 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1275 int ModelChecker::switch_to_master(ModelAction *act)
1278 Thread *old = thread_current();
1279 set_current_action(act);
1280 old->set_state(THREAD_READY);
1281 return Thread::swap(old, &system_context);
1285 * Takes the next step in the execution, if possible.
1286 * @return Returns true (success) if a step was taken and false otherwise.
1288 bool ModelChecker::take_step() {
1289 Thread *curr, *next;
1294 curr = thread_current();
1296 if (curr->get_state() == THREAD_READY) {
1297 ASSERT(priv->current_action);
1299 priv->nextThread = check_current_action(priv->current_action);
1300 priv->current_action = NULL;
1301 if (!curr->is_blocked() && !curr->is_complete())
1302 scheduler->add_thread(curr);
1307 next = scheduler->next_thread(priv->nextThread);
1309 /* Infeasible -> don't take any more steps */
1314 next->set_state(THREAD_RUNNING);
1315 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1317 /* next == NULL -> don't take any more steps */
1320 /* Return false only if swap fails with an error */
1321 return (Thread::swap(&system_context, next) == 0);
1324 /** Runs the current execution until threre are no more steps to take. */
1325 void ModelChecker::finish_execution() {
1328 while (take_step());