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 futurevalues(new std::vector<struct PendingFutureValue>()),
32 lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
33 thrd_last_action(new std::vector<ModelAction *>(1)),
34 node_stack(new NodeStack()),
35 mo_graph(new CycleGraph()),
36 failed_promise(false),
37 too_many_reads(false),
40 /* Allocate this "size" on the snapshotting heap */
41 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
42 /* First thread created will have id INITIAL_THREAD_ID */
43 priv->next_thread_id = INITIAL_THREAD_ID;
45 lazy_sync_size = &priv->lazy_sync_size;
48 /** @brief Destructor */
49 ModelChecker::~ModelChecker()
51 for (int i = 0; i < get_num_threads(); i++)
52 delete thread_map->get(i);
59 for (unsigned int i = 0; i < promises->size(); i++)
60 delete (*promises)[i];
63 delete lazy_sync_with_release;
65 delete thrd_last_action;
72 * Restores user program to initial state and resets all model-checker data
75 void ModelChecker::reset_to_initial_state()
77 DEBUG("+++ Resetting to initial state +++\n");
78 node_stack->reset_execution();
79 failed_promise = false;
80 too_many_reads = false;
82 snapshotObject->backTrackBeforeStep(0);
85 /** @returns a thread ID for a new Thread */
86 thread_id_t ModelChecker::get_next_id()
88 return priv->next_thread_id++;
91 /** @returns the number of user threads created during this execution */
92 int ModelChecker::get_num_threads()
94 return priv->next_thread_id;
97 /** @returns a sequence number for a new ModelAction */
98 modelclock_t ModelChecker::get_next_seq_num()
100 return ++priv->used_sequence_numbers;
104 * @brief Choose the next thread to execute.
106 * This function chooses the next thread that should execute. It can force the
107 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
108 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
109 * The model-checker may have no preference regarding the next thread (i.e.,
110 * when exploring a new execution ordering), in which case this will return
112 * @param curr The current ModelAction. This action might guide the choice of
114 * @return The next thread to run. If the model-checker has no preference, NULL.
116 Thread * ModelChecker::get_next_thread(ModelAction *curr)
120 /* Do not split atomic actions. */
122 return thread_current();
123 /* The THREAD_CREATE action points to the created Thread */
124 else if (curr->get_type() == THREAD_CREATE)
125 return (Thread *)curr->get_location();
127 /* Have we completed exploring the preselected path? */
131 /* Else, we are trying to replay an execution */
132 ModelAction *next = node_stack->get_next()->get_action();
134 if (next == diverge) {
135 Node *nextnode = next->get_node();
136 /* Reached divergence point */
137 if (nextnode->increment_promise()) {
138 /* The next node will try to satisfy a different set of promises. */
139 tid = next->get_tid();
140 node_stack->pop_restofstack(2);
141 } else if (nextnode->increment_read_from()) {
142 /* The next node will read from a different value. */
143 tid = next->get_tid();
144 node_stack->pop_restofstack(2);
145 } else if (nextnode->increment_future_value()) {
146 /* The next node will try to read from a different future value. */
147 tid = next->get_tid();
148 node_stack->pop_restofstack(2);
150 /* Make a different thread execute for next step */
151 Node *node = nextnode->get_parent();
152 tid = node->get_next_backtrack();
153 node_stack->pop_restofstack(1);
155 DEBUG("*** Divergence point ***\n");
158 tid = next->get_tid();
160 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
161 ASSERT(tid != THREAD_ID_T_NONE);
162 return thread_map->get(id_to_int(tid));
166 * Queries the model-checker for more executions to explore and, if one
167 * exists, resets the model-checker state to execute a new execution.
169 * @return If there are more executions to explore, return true. Otherwise,
172 bool ModelChecker::next_execution()
178 if (isfinalfeasible() || DBG_ENABLED())
181 if ((diverge = get_next_backtrack()) == NULL)
185 printf("Next execution will diverge at:\n");
189 reset_to_initial_state();
193 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
195 action_type type = act->get_type();
205 /* linear search: from most recent to oldest */
206 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
207 action_list_t::reverse_iterator rit;
208 for (rit = list->rbegin(); rit != list->rend(); rit++) {
209 ModelAction *prev = *rit;
210 if (act->is_synchronizing(prev))
216 void ModelChecker::set_backtracking(ModelAction *act)
220 Thread *t = get_thread(act);
222 prev = get_last_conflict(act);
226 node = prev->get_node()->get_parent();
228 while (!node->is_enabled(t))
231 /* Check if this has been explored already */
232 if (node->has_been_explored(t->get_id()))
235 /* Cache the latest backtracking point */
236 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
237 priv->next_backtrack = prev;
239 /* If this is a new backtracking point, mark the tree */
240 if (!node->set_backtrack(t->get_id()))
242 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
243 prev->get_tid(), t->get_id());
251 * Returns last backtracking point. The model checker will explore a different
252 * path for this point in the next execution.
253 * @return The ModelAction at which the next execution should diverge.
255 ModelAction * ModelChecker::get_next_backtrack()
257 ModelAction *next = priv->next_backtrack;
258 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.
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 mo_graph->startChanges();
277 value = reads_from->get_value();
279 if (!second_part_of_rmw) {
280 check_recency(curr,false);
283 bool r_status=r_modification_order(curr,reads_from);
285 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
286 mo_graph->rollbackChanges();
287 too_many_reads=false;
291 curr->read_from(reads_from);
292 mo_graph->commitChanges();
294 } else if (!second_part_of_rmw) {
295 /* Read from future value */
296 value = curr->get_node()->get_future_value();
297 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
298 curr->read_from(NULL);
299 Promise *valuepromise = new Promise(curr, value, expiration);
300 promises->push_back(valuepromise);
302 th->set_return_value(value);
308 * This is the heart of the model checker routine. It performs model-checking
309 * actions corresponding to a given "current action." Among other processes, it
310 * calculates reads-from relationships, updates synchronization clock vectors,
311 * forms a memory_order constraints graph, and handles replay/backtrack
312 * execution when running permutations of previously-observed executions.
314 * @param curr The current action to process
315 * @return The next Thread that must be executed. May be NULL if ModelChecker
316 * makes no choice (e.g., according to replay execution, combining RMW actions,
319 Thread * ModelChecker::check_current_action(ModelAction *curr)
321 bool second_part_of_rmw = false;
325 if (curr->is_rmwc() || curr->is_rmw()) {
326 ModelAction *tmp = process_rmw(curr);
327 second_part_of_rmw = true;
330 compute_promises(curr);
332 ModelAction *tmp = node_stack->explore_action(curr);
334 /* Discard duplicate ModelAction; use action from NodeStack */
335 /* First restore type and order in case of RMW operation */
337 tmp->copy_typeandorder(curr);
339 /* If we have diverged, we need to reset the clock vector. */
341 tmp->create_cv(get_parent_action(tmp->get_tid()));
347 * Perform one-time actions when pushing new ModelAction onto
350 curr->create_cv(get_parent_action(curr->get_tid()));
351 /* Build may_read_from set */
353 build_reads_from_past(curr);
354 if (curr->is_write())
355 compute_promises(curr);
359 /* Thread specific actions */
360 switch(curr->get_type()) {
361 case THREAD_CREATE: {
362 Thread *th = (Thread *)curr->get_location();
363 th->set_creation(curr);
367 Thread *waiting, *blocking;
368 waiting = get_thread(curr);
369 blocking = (Thread *)curr->get_location();
370 if (!blocking->is_complete()) {
371 blocking->push_wait_list(curr);
372 scheduler->sleep(waiting);
376 case THREAD_FINISH: {
377 Thread *th = get_thread(curr);
378 while (!th->wait_list_empty()) {
379 ModelAction *act = th->pop_wait_list();
380 Thread *wake = get_thread(act);
381 scheduler->wake(wake);
387 check_promises(NULL, curr->get_cv());
394 Thread *th = get_thread(curr);
396 bool updated = false;
397 if (curr->is_read()) {
398 updated=process_read(curr, th, second_part_of_rmw);
401 if (curr->is_write()) {
402 bool updated_mod_order=w_modification_order(curr);
403 bool updated_promises=resolve_promises(curr);
404 updated=updated_mod_order|updated_promises;
406 if (promises->size()==0) {
407 for(unsigned int i=0;i<futurevalues->size();i++) {
408 struct PendingFutureValue pfv=(*futurevalues)[i];
409 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
410 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
411 priv->next_backtrack = pfv.act;
413 futurevalues->resize(0);
416 mo_graph->commitChanges();
417 th->set_return_value(VALUE_NONE);
421 resolve_release_sequences(curr->get_location());
423 /* Add action to list. */
424 if (!second_part_of_rmw)
425 add_action_to_lists(curr);
427 check_curr_backtracking(curr);
429 set_backtracking(curr);
431 return get_next_thread(curr);
434 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
435 Node *currnode = curr->get_node();
436 Node *parnode = currnode->get_parent();
438 if ((!parnode->backtrack_empty() ||
439 !currnode->read_from_empty() ||
440 !currnode->future_value_empty() ||
441 !currnode->promise_empty())
442 && (!priv->next_backtrack ||
443 *curr > *priv->next_backtrack)) {
444 priv->next_backtrack = curr;
448 bool ModelChecker::promises_expired() {
449 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
450 Promise *promise = (*promises)[promise_index];
451 if (promise->get_expiration()<priv->used_sequence_numbers) {
458 /** @returns whether the current partial trace must be a prefix of a
460 bool ModelChecker::isfeasibleprefix() {
461 return promises->size() == 0 && *lazy_sync_size == 0;
464 /** @returns whether the current partial trace is feasible. */
465 bool ModelChecker::isfeasible() {
466 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
469 /** @returns whether the current partial trace is feasible other than
470 * multiple RMW reading from the same store. */
471 bool ModelChecker::isfeasibleotherthanRMW() {
472 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
475 /** Returns whether the current completed trace is feasible. */
476 bool ModelChecker::isfinalfeasible() {
477 return isfeasible() && promises->size() == 0;
480 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
481 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
482 int tid = id_to_int(act->get_tid());
483 ModelAction *lastread = get_last_action(tid);
484 lastread->process_rmw(act);
485 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
486 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
487 mo_graph->commitChanges();
493 * Checks whether a thread has read from the same write for too many times
494 * without seeing the effects of a later write.
497 * 1) there must a different write that we could read from that would satisfy the modification order,
498 * 2) we must have read from the same value in excess of maxreads times, and
499 * 3) that other write must have been in the reads_from set for maxreads times.
501 * If so, we decide that the execution is no longer feasible.
503 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
504 if (params.maxreads != 0) {
505 if (curr->get_node()->get_read_from_size() <= 1)
508 //Must make sure that execution is currently feasible... We could
509 //accidentally clear by rolling back
513 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
514 int tid = id_to_int(curr->get_tid());
517 if ((int)thrd_lists->size() <= tid)
520 action_list_t *list = &(*thrd_lists)[tid];
522 action_list_t::reverse_iterator rit = list->rbegin();
525 for (; (*rit) != curr; rit++)
527 /* go past curr now */
531 action_list_t::reverse_iterator ritcopy=rit;
532 //See if we have enough reads from the same value
534 for (; count < params.maxreads; rit++,count++) {
535 if (rit==list->rend())
537 ModelAction *act = *rit;
540 if (act->get_reads_from() != curr->get_reads_from())
542 if (act->get_node()->get_read_from_size() <= 1)
546 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
548 const ModelAction * write=curr->get_node()->get_read_from_at(i);
549 //Need a different write
550 if (write==curr->get_reads_from())
553 /* Test to see whether this is a feasible write to read from*/
554 mo_graph->startChanges();
555 r_modification_order(curr, write);
556 bool feasiblereadfrom=isfeasible();
557 mo_graph->rollbackChanges();
559 if (!feasiblereadfrom)
563 bool feasiblewrite=true;
564 //new we need to see if this write works for everyone
566 for (int loop=count;loop>0;loop--,rit++) {
567 ModelAction *act=*rit;
568 bool foundvalue=false;
569 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
570 if (act->get_node()->get_read_from_at(i)==write) {
581 too_many_reads = true;
589 * Updates the mo_graph with the constraints imposed from the current read.
590 * @param curr The current action. Must be a read.
591 * @param rf The action that curr reads from. Must be a write.
592 * @return True if modification order edges were added; false otherwise
594 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
596 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
599 ASSERT(curr->is_read());
601 /* Iterate over all threads */
602 for (i = 0; i < thrd_lists->size(); i++) {
603 /* Iterate over actions in thread, starting from most recent */
604 action_list_t *list = &(*thrd_lists)[i];
605 action_list_t::reverse_iterator rit;
606 for (rit = list->rbegin(); rit != list->rend(); rit++) {
607 ModelAction *act = *rit;
609 /* Include at most one act per-thread that "happens before" curr */
610 if (act->happens_before(curr)) {
611 if (act->is_read()) {
612 const ModelAction *prevreadfrom = act->get_reads_from();
613 if (prevreadfrom != NULL && rf != prevreadfrom) {
614 mo_graph->addEdge(prevreadfrom, rf);
617 } else if (rf != act) {
618 mo_graph->addEdge(act, rf);
629 /** Updates the mo_graph with the constraints imposed from the current read. */
630 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
632 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
634 ASSERT(curr->is_read());
636 /* Iterate over all threads */
637 for (i = 0; i < thrd_lists->size(); i++) {
638 /* Iterate over actions in thread, starting from most recent */
639 action_list_t *list = &(*thrd_lists)[i];
640 action_list_t::reverse_iterator rit;
641 ModelAction *lastact = NULL;
643 /* Find last action that happens after curr */
644 for (rit = list->rbegin(); rit != list->rend(); rit++) {
645 ModelAction *act = *rit;
646 if (curr->happens_before(act)) {
652 /* Include at most one act per-thread that "happens before" curr */
653 if (lastact != NULL) {
654 if (lastact->is_read()) {
655 const ModelAction *postreadfrom = lastact->get_reads_from();
656 if (postreadfrom != NULL&&rf != postreadfrom)
657 mo_graph->addEdge(rf, postreadfrom);
658 } else if (rf != lastact) {
659 mo_graph->addEdge(rf, lastact);
667 * Updates the mo_graph with the constraints imposed from the current write.
668 * @param curr The current action. Must be a write.
669 * @return True if modification order edges were added; false otherwise
671 bool ModelChecker::w_modification_order(ModelAction *curr)
673 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
676 ASSERT(curr->is_write());
678 if (curr->is_seqcst()) {
679 /* We have to at least see the last sequentially consistent write,
680 so we are initialized. */
681 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
682 if (last_seq_cst != NULL) {
683 mo_graph->addEdge(last_seq_cst, curr);
688 /* Iterate over all threads */
689 for (i = 0; i < thrd_lists->size(); i++) {
690 /* Iterate over actions in thread, starting from most recent */
691 action_list_t *list = &(*thrd_lists)[i];
692 action_list_t::reverse_iterator rit;
693 for (rit = list->rbegin(); rit != list->rend(); rit++) {
694 ModelAction *act = *rit;
696 /* Include at most one act per-thread that "happens before" curr */
697 if (act->happens_before(curr)) {
699 * Note: if act is RMW, just add edge:
701 * The following edge should be handled elsewhere:
702 * readfrom(act) --mo--> act
704 if (act->is_write()) {
705 //RMW shouldn't have an edge to themselves
707 mo_graph->addEdge(act, curr);
708 } else if (act->is_read() && act->get_reads_from() != NULL)
709 mo_graph->addEdge(act->get_reads_from(), curr);
712 } else if (act->is_read() && !act->is_synchronizing(curr) &&
713 !act->same_thread(curr)) {
714 /* We have an action that:
715 (1) did not happen before us
716 (2) is a read and we are a write
717 (3) cannot synchronize with us
718 (4) is in a different thread
720 that read could potentially read from our write.
722 if (thin_air_constraint_may_allow(curr, act)) {
724 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
725 struct PendingFutureValue pfv={curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
726 futurevalues->push_back(pfv);
736 /** Arbitrary reads from the future are not allowed. Section 29.3
737 * part 9 places some constraints. This method checks one result of constraint
738 * constraint. Others require compiler support. */
740 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
741 if (!writer->is_rmw())
744 if (!reader->is_rmw())
747 for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
750 if (search->get_tid()==reader->get_tid()&&
751 search->happens_before(reader))
759 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
760 * The ModelAction under consideration is expected to be taking part in
761 * release/acquire synchronization as an object of the "reads from" relation.
762 * Note that this can only provide release sequence support for RMW chains
763 * which do not read from the future, as those actions cannot be traced until
764 * their "promise" is fulfilled. Similarly, we may not even establish the
765 * presence of a release sequence with certainty, as some modification order
766 * constraints may be decided further in the future. Thus, this function
767 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
768 * and a boolean representing certainty.
770 * @todo Finish lazy updating, when promises are fulfilled in the future
771 * @param rf The action that might be part of a release sequence. Must be a
773 * @param release_heads A pass-by-reference style return parameter. After
774 * execution of this function, release_heads will contain the heads of all the
775 * relevant release sequences, if any exists
776 * @return true, if the ModelChecker is certain that release_heads is complete;
779 bool ModelChecker::release_seq_head(const ModelAction *rf,
780 std::vector<const ModelAction *> *release_heads) const
782 ASSERT(rf->is_write());
784 /* read from future: need to settle this later */
785 return false; /* incomplete */
787 if (rf->is_release())
788 release_heads->push_back(rf);
790 /* We need a RMW action that is both an acquire and release to stop */
791 /** @todo Need to be smarter here... In the linux lock
792 * example, this will run to the beginning of the program for
794 if (rf->is_acquire() && rf->is_release())
795 return true; /* complete */
796 return release_seq_head(rf->get_reads_from(), release_heads);
798 if (rf->is_release())
799 return true; /* complete */
801 /* else relaxed write; check modification order for contiguous subsequence
802 * -> rf must be same thread as release */
803 int tid = id_to_int(rf->get_tid());
804 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
805 action_list_t *list = &(*thrd_lists)[tid];
806 action_list_t::const_reverse_iterator rit;
808 /* Find rf in the thread list */
809 rit = std::find(list->rbegin(), list->rend(), rf);
810 ASSERT(rit != list->rend());
812 /* Find the last write/release */
813 for (; rit != list->rend(); rit++)
814 if ((*rit)->is_release())
816 if (rit == list->rend()) {
817 /* No write-release in this thread */
818 return true; /* complete */
820 ModelAction *release = *rit;
822 ASSERT(rf->same_thread(release));
825 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
826 if (id_to_int(rf->get_tid()) == (int)i)
828 list = &(*thrd_lists)[i];
830 /* Can we ensure no future writes from this thread may break
831 * the release seq? */
832 bool future_ordered = false;
834 for (rit = list->rbegin(); rit != list->rend(); rit++) {
835 const ModelAction *act = *rit;
836 if (!act->is_write())
838 /* Reach synchronization -> this thread is complete */
839 if (act->happens_before(release))
841 if (rf->happens_before(act)) {
842 future_ordered = true;
846 /* Check modification order */
847 if (mo_graph->checkReachable(rf, act)) {
849 future_ordered = true;
852 if (mo_graph->checkReachable(act, release))
853 /* act --mo--> release */
855 if (mo_graph->checkReachable(release, act) &&
856 mo_graph->checkReachable(act, rf)) {
857 /* release --mo-> act --mo--> rf */
858 return true; /* complete */
863 return false; /* This thread is uncertain */
867 release_heads->push_back(release);
872 * A public interface for getting the release sequence head(s) with which a
873 * given ModelAction must synchronize. This function only returns a non-empty
874 * result when it can locate a release sequence head with certainty. Otherwise,
875 * it may mark the internal state of the ModelChecker so that it will handle
876 * the release sequence at a later time, causing @a act to update its
877 * synchronization at some later point in execution.
878 * @param act The 'acquire' action that may read from a release sequence
879 * @param release_heads A pass-by-reference return parameter. Will be filled
880 * with the head(s) of the release sequence(s), if they exists with certainty.
881 * @see ModelChecker::release_seq_head
883 void ModelChecker::get_release_seq_heads(ModelAction *act,
884 std::vector<const ModelAction *> *release_heads)
886 const ModelAction *rf = act->get_reads_from();
888 complete = release_seq_head(rf, release_heads);
890 /* add act to 'lazy checking' list */
891 std::list<ModelAction *> *list;
892 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
893 list->push_back(act);
899 * Attempt to resolve all stashed operations that might synchronize with a
900 * release sequence for a given location. This implements the "lazy" portion of
901 * determining whether or not a release sequence was contiguous, since not all
902 * modification order information is present at the time an action occurs.
904 * @param location The location/object that should be checked for release
905 * sequence resolutions
906 * @return True if any updates occurred (new synchronization, new mo_graph edges)
908 bool ModelChecker::resolve_release_sequences(void *location)
910 std::list<ModelAction *> *list;
911 list = lazy_sync_with_release->getptr(location);
915 bool updated = false;
916 std::list<ModelAction *>::iterator it = list->begin();
917 while (it != list->end()) {
918 ModelAction *act = *it;
919 const ModelAction *rf = act->get_reads_from();
920 std::vector<const ModelAction *> release_heads;
922 complete = release_seq_head(rf, &release_heads);
923 for (unsigned int i = 0; i < release_heads.size(); i++) {
924 if (!act->has_synchronized_with(release_heads[i])) {
926 act->synchronize_with(release_heads[i]);
931 /* propagate synchronization to later actions */
932 action_list_t::reverse_iterator it = action_trace->rbegin();
933 while ((*it) != act) {
934 ModelAction *propagate = *it;
935 if (act->happens_before(propagate))
936 /** @todo new mo_graph edges along with
937 * this synchronization? */
938 propagate->synchronize_with(act);
942 it = list->erase(it);
948 // If we resolved promises or data races, see if we have realized a data race.
949 if (checkDataRaces()) {
957 * Performs various bookkeeping operations for the current ModelAction. For
958 * instance, adds action to the per-object, per-thread action vector and to the
959 * action trace list of all thread actions.
961 * @param act is the ModelAction to add.
963 void ModelChecker::add_action_to_lists(ModelAction *act)
965 int tid = id_to_int(act->get_tid());
966 action_trace->push_back(act);
968 obj_map->get_safe_ptr(act->get_location())->push_back(act);
970 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
971 if (tid >= (int)vec->size())
972 vec->resize(priv->next_thread_id);
973 (*vec)[tid].push_back(act);
975 if ((int)thrd_last_action->size() <= tid)
976 thrd_last_action->resize(get_num_threads());
977 (*thrd_last_action)[tid] = act;
980 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
982 int nthreads = get_num_threads();
983 if ((int)thrd_last_action->size() < nthreads)
984 thrd_last_action->resize(nthreads);
985 return (*thrd_last_action)[id_to_int(tid)];
989 * Gets the last memory_order_seq_cst action (in the total global sequence)
990 * performed on a particular object (i.e., memory location).
991 * @param location The object location to check
992 * @return The last seq_cst action performed
994 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
996 action_list_t *list = obj_map->get_safe_ptr(location);
997 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
998 action_list_t::reverse_iterator rit;
999 for (rit = list->rbegin(); rit != list->rend(); rit++)
1000 if ((*rit)->is_write() && (*rit)->is_seqcst())
1005 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1007 ModelAction *parent = get_last_action(tid);
1009 parent = get_thread(tid)->get_creation();
1014 * Returns the clock vector for a given thread.
1015 * @param tid The thread whose clock vector we want
1016 * @return Desired clock vector
1018 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1020 return get_parent_action(tid)->get_cv();
1024 * Resolve a set of Promises with a current write. The set is provided in the
1025 * Node corresponding to @a write.
1026 * @param write The ModelAction that is fulfilling Promises
1027 * @return True if promises were resolved; false otherwise
1029 bool ModelChecker::resolve_promises(ModelAction *write)
1031 bool resolved = false;
1033 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1034 Promise *promise = (*promises)[promise_index];
1035 if (write->get_node()->get_promise(i)) {
1036 ModelAction *read = promise->get_action();
1037 read->read_from(write);
1038 if (read->is_rmw()) {
1039 mo_graph->addRMWEdge(write, read);
1041 r_modification_order(read, write);
1042 post_r_modification_order(read, write);
1043 promises->erase(promises->begin() + promise_index);
1052 * Compute the set of promises that could potentially be satisfied by this
1053 * action. Note that the set computation actually appears in the Node, not in
1055 * @param curr The ModelAction that may satisfy promises
1057 void ModelChecker::compute_promises(ModelAction *curr)
1059 for (unsigned int i = 0; i < promises->size(); i++) {
1060 Promise *promise = (*promises)[i];
1061 const ModelAction *act = promise->get_action();
1062 if (!act->happens_before(curr) &&
1064 !act->is_synchronizing(curr) &&
1065 !act->same_thread(curr) &&
1066 promise->get_value() == curr->get_value()) {
1067 curr->get_node()->set_promise(i);
1072 /** Checks promises in response to change in ClockVector Threads. */
1073 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1075 for (unsigned int i = 0; i < promises->size(); i++) {
1076 Promise *promise = (*promises)[i];
1077 const ModelAction *act = promise->get_action();
1078 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1079 merge_cv->synchronized_since(act)) {
1080 //This thread is no longer able to send values back to satisfy the promise
1081 int num_synchronized_threads = promise->increment_threads();
1082 if (num_synchronized_threads == get_num_threads()) {
1083 //Promise has failed
1084 failed_promise = true;
1092 * Build up an initial set of all past writes that this 'read' action may read
1093 * from. This set is determined by the clock vector's "happens before"
1095 * @param curr is the current ModelAction that we are exploring; it must be a
1098 void ModelChecker::build_reads_from_past(ModelAction *curr)
1100 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1102 ASSERT(curr->is_read());
1104 ModelAction *last_seq_cst = NULL;
1106 /* Track whether this object has been initialized */
1107 bool initialized = false;
1109 if (curr->is_seqcst()) {
1110 last_seq_cst = get_last_seq_cst(curr->get_location());
1111 /* We have to at least see the last sequentially consistent write,
1112 so we are initialized. */
1113 if (last_seq_cst != NULL)
1117 /* Iterate over all threads */
1118 for (i = 0; i < thrd_lists->size(); i++) {
1119 /* Iterate over actions in thread, starting from most recent */
1120 action_list_t *list = &(*thrd_lists)[i];
1121 action_list_t::reverse_iterator rit;
1122 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1123 ModelAction *act = *rit;
1125 /* Only consider 'write' actions */
1126 if (!act->is_write())
1129 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1130 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1131 DEBUG("Adding action to may_read_from:\n");
1132 if (DBG_ENABLED()) {
1136 curr->get_node()->add_read_from(act);
1139 /* Include at most one act per-thread that "happens before" curr */
1140 if (act->happens_before(curr)) {
1148 /** @todo Need a more informative way of reporting errors. */
1149 printf("ERROR: may read from uninitialized atomic\n");
1152 if (DBG_ENABLED() || !initialized) {
1153 printf("Reached read action:\n");
1155 printf("Printing may_read_from\n");
1156 curr->get_node()->print_may_read_from();
1157 printf("End printing may_read_from\n");
1160 ASSERT(initialized);
1163 static void print_list(action_list_t *list)
1165 action_list_t::iterator it;
1167 printf("---------------------------------------------------------------------\n");
1170 for (it = list->begin(); it != list->end(); it++) {
1173 printf("---------------------------------------------------------------------\n");
1176 void ModelChecker::print_summary()
1179 printf("Number of executions: %d\n", num_executions);
1180 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1184 if (!isfinalfeasible())
1185 printf("INFEASIBLE EXECUTION!\n");
1186 print_list(action_trace);
1191 * Add a Thread to the system for the first time. Should only be called once
1193 * @param t The Thread to add
1195 void ModelChecker::add_thread(Thread *t)
1197 thread_map->put(id_to_int(t->get_id()), t);
1198 scheduler->add_thread(t);
1201 void ModelChecker::remove_thread(Thread *t)
1203 scheduler->remove_thread(t);
1207 * Switch from a user-context to the "master thread" context (a.k.a. system
1208 * context). This switch is made with the intention of exploring a particular
1209 * model-checking action (described by a ModelAction object). Must be called
1210 * from a user-thread context.
1211 * @param act The current action that will be explored. Must not be NULL.
1212 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1214 int ModelChecker::switch_to_master(ModelAction *act)
1217 Thread *old = thread_current();
1218 set_current_action(act);
1219 old->set_state(THREAD_READY);
1220 return Thread::swap(old, &system_context);
1224 * Takes the next step in the execution, if possible.
1225 * @return Returns true (success) if a step was taken and false otherwise.
1227 bool ModelChecker::take_step() {
1228 Thread *curr, *next;
1233 curr = thread_current();
1235 if (curr->get_state() == THREAD_READY) {
1236 ASSERT(priv->current_action);
1238 priv->nextThread = check_current_action(priv->current_action);
1239 priv->current_action = NULL;
1240 if (!curr->is_blocked() && !curr->is_complete())
1241 scheduler->add_thread(curr);
1246 next = scheduler->next_thread(priv->nextThread);
1248 /* Infeasible -> don't take any more steps */
1253 next->set_state(THREAD_RUNNING);
1254 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1256 /* next == NULL -> don't take any more steps */
1259 /* Return false only if swap fails with an error */
1260 return (Thread::swap(&system_context, next) == 0);
1263 /** Runs the current execution until threre are no more steps to take. */
1264 void ModelChecker::finish_execution() {
1267 while (take_step());