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;
264 * Processes a read or rmw model action.
265 * @param curr is the read model action to process.
266 * @param th is the thread
267 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
268 * @return True if processing this read updates the mo_graph.
271 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
275 const ModelAction *reads_from = curr->get_node()->get_read_from();
276 if (reads_from != NULL) {
277 mo_graph->startChanges();
279 value = reads_from->get_value();
282 if (!second_part_of_rmw) {
283 check_recency(curr,false);
284 r_status=r_modification_order(curr, reads_from);
288 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
289 mo_graph->rollbackChanges();
290 too_many_reads=false;
294 curr->read_from(reads_from);
295 mo_graph->commitChanges();
297 } else if (!second_part_of_rmw) {
298 /* Read from future value */
299 value = curr->get_node()->get_future_value();
300 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
301 curr->read_from(NULL);
302 Promise *valuepromise = new Promise(curr, value, expiration);
303 promises->push_back(valuepromise);
305 th->set_return_value(value);
311 * This is the heart of the model checker routine. It performs model-checking
312 * actions corresponding to a given "current action." Among other processes, it
313 * calculates reads-from relationships, updates synchronization clock vectors,
314 * forms a memory_order constraints graph, and handles replay/backtrack
315 * execution when running permutations of previously-observed executions.
317 * @param curr The current action to process
318 * @return The next Thread that must be executed. May be NULL if ModelChecker
319 * makes no choice (e.g., according to replay execution, combining RMW actions,
322 Thread * ModelChecker::check_current_action(ModelAction *curr)
324 bool second_part_of_rmw = false;
328 if (curr->is_rmwc() || curr->is_rmw()) {
329 ModelAction *tmp = process_rmw(curr);
330 second_part_of_rmw = true;
333 compute_promises(curr);
335 ModelAction *tmp = node_stack->explore_action(curr);
337 /* Discard duplicate ModelAction; use action from NodeStack */
338 /* First restore type and order in case of RMW operation */
340 tmp->copy_typeandorder(curr);
342 /* If we have diverged, we need to reset the clock vector. */
344 tmp->create_cv(get_parent_action(tmp->get_tid()));
350 * Perform one-time actions when pushing new ModelAction onto
353 curr->create_cv(get_parent_action(curr->get_tid()));
354 /* Build may_read_from set */
356 build_reads_from_past(curr);
357 if (curr->is_write())
358 compute_promises(curr);
362 /* Thread specific actions */
363 switch(curr->get_type()) {
364 case THREAD_CREATE: {
365 Thread *th = (Thread *)curr->get_location();
366 th->set_creation(curr);
370 Thread *waiting, *blocking;
371 waiting = get_thread(curr);
372 blocking = (Thread *)curr->get_location();
373 if (!blocking->is_complete()) {
374 blocking->push_wait_list(curr);
375 scheduler->sleep(waiting);
379 case THREAD_FINISH: {
380 Thread *th = get_thread(curr);
381 while (!th->wait_list_empty()) {
382 ModelAction *act = th->pop_wait_list();
383 Thread *wake = get_thread(act);
384 scheduler->wake(wake);
390 check_promises(NULL, curr->get_cv());
397 Thread *th = get_thread(curr);
399 bool updated = false;
400 if (curr->is_read()) {
401 updated=process_read(curr, th, 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_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 th->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;
452 bool ModelChecker::promises_expired() {
453 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
454 Promise *promise = (*promises)[promise_index];
455 if (promise->get_expiration()<priv->used_sequence_numbers) {
462 /** @returns whether the current partial trace must be a prefix of a
464 bool ModelChecker::isfeasibleprefix() {
465 return promises->size() == 0 && *lazy_sync_size == 0;
468 /** @returns whether the current partial trace is feasible. */
469 bool ModelChecker::isfeasible() {
470 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
473 /** @returns whether the current partial trace is feasible other than
474 * multiple RMW reading from the same store. */
475 bool ModelChecker::isfeasibleotherthanRMW() {
476 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
479 /** Returns whether the current completed trace is feasible. */
480 bool ModelChecker::isfinalfeasible() {
481 return isfeasible() && promises->size() == 0;
484 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
485 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
486 int tid = id_to_int(act->get_tid());
487 ModelAction *lastread = get_last_action(tid);
488 lastread->process_rmw(act);
489 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
490 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
491 mo_graph->commitChanges();
497 * Checks whether a thread has read from the same write for too many times
498 * without seeing the effects of a later write.
501 * 1) there must a different write that we could read from that would satisfy the modification order,
502 * 2) we must have read from the same value in excess of maxreads times, and
503 * 3) that other write must have been in the reads_from set for maxreads times.
505 * If so, we decide that the execution is no longer feasible.
507 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
508 if (params.maxreads != 0) {
509 if (curr->get_node()->get_read_from_size() <= 1)
512 //Must make sure that execution is currently feasible... We could
513 //accidentally clear by rolling back
517 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
518 int tid = id_to_int(curr->get_tid());
521 if ((int)thrd_lists->size() <= tid)
524 action_list_t *list = &(*thrd_lists)[tid];
526 action_list_t::reverse_iterator rit = list->rbegin();
529 for (; (*rit) != curr; rit++)
531 /* go past curr now */
535 action_list_t::reverse_iterator ritcopy=rit;
536 //See if we have enough reads from the same value
538 for (; count < params.maxreads; rit++,count++) {
539 if (rit==list->rend())
541 ModelAction *act = *rit;
544 if (act->get_reads_from() != curr->get_reads_from())
546 if (act->get_node()->get_read_from_size() <= 1)
550 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
552 const ModelAction * write=curr->get_node()->get_read_from_at(i);
553 //Need a different write
554 if (write==curr->get_reads_from())
557 /* Test to see whether this is a feasible write to read from*/
558 mo_graph->startChanges();
559 r_modification_order(curr, write);
560 bool feasiblereadfrom=isfeasible();
561 mo_graph->rollbackChanges();
563 if (!feasiblereadfrom)
567 bool feasiblewrite=true;
568 //new we need to see if this write works for everyone
570 for (int loop=count;loop>0;loop--,rit++) {
571 ModelAction *act=*rit;
572 bool foundvalue=false;
573 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
574 if (act->get_node()->get_read_from_at(i)==write) {
585 too_many_reads = true;
593 * Updates the mo_graph with the constraints imposed from the current read.
594 * @param curr The current action. Must be a read.
595 * @param rf The action that curr reads from. Must be a write.
596 * @return True if modification order edges were added; false otherwise
598 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
600 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
603 ASSERT(curr->is_read());
605 /* Iterate over all threads */
606 for (i = 0; i < thrd_lists->size(); i++) {
607 /* Iterate over actions in thread, starting from most recent */
608 action_list_t *list = &(*thrd_lists)[i];
609 action_list_t::reverse_iterator rit;
610 for (rit = list->rbegin(); rit != list->rend(); rit++) {
611 ModelAction *act = *rit;
613 /* Include at most one act per-thread that "happens before" curr */
614 if (act->happens_before(curr)) {
615 if (act->is_write()) {
616 if (rf != act && act != curr) {
617 mo_graph->addEdge(act, rf);
621 const ModelAction *prevreadfrom = act->get_reads_from();
622 if (prevreadfrom != NULL && rf != prevreadfrom) {
623 mo_graph->addEdge(prevreadfrom, rf);
636 /** Updates the mo_graph with the constraints imposed from the current read. */
637 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
639 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
641 ASSERT(curr->is_read());
643 /* Iterate over all threads */
644 for (i = 0; i < thrd_lists->size(); i++) {
645 /* Iterate over actions in thread, starting from most recent */
646 action_list_t *list = &(*thrd_lists)[i];
647 action_list_t::reverse_iterator rit;
648 ModelAction *lastact = NULL;
650 /* Find last action that happens after curr */
651 for (rit = list->rbegin(); rit != list->rend(); rit++) {
652 ModelAction *act = *rit;
653 if (curr->happens_before(act)) {
659 /* Include at most one act per-thread that "happens before" curr */
660 if (lastact != NULL) {
661 if (lastact->is_read()) {
662 const ModelAction *postreadfrom = lastact->get_reads_from();
663 if (postreadfrom != NULL&&rf != postreadfrom)
664 mo_graph->addEdge(rf, postreadfrom);
665 } else if (rf != lastact) {
666 mo_graph->addEdge(rf, lastact);
674 * Updates the mo_graph with the constraints imposed from the current write.
675 * @param curr The current action. Must be a write.
676 * @return True if modification order edges were added; false otherwise
678 bool ModelChecker::w_modification_order(ModelAction *curr)
680 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
683 ASSERT(curr->is_write());
685 if (curr->is_seqcst()) {
686 /* We have to at least see the last sequentially consistent write,
687 so we are initialized. */
688 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
689 if (last_seq_cst != NULL) {
690 mo_graph->addEdge(last_seq_cst, curr);
695 /* Iterate over all threads */
696 for (i = 0; i < thrd_lists->size(); i++) {
697 /* Iterate over actions in thread, starting from most recent */
698 action_list_t *list = &(*thrd_lists)[i];
699 action_list_t::reverse_iterator rit;
700 for (rit = list->rbegin(); rit != list->rend(); rit++) {
701 ModelAction *act = *rit;
703 /* Include at most one act per-thread that "happens before" curr */
704 if (act->happens_before(curr)) {
706 * Note: if act is RMW, just add edge:
708 * The following edge should be handled elsewhere:
709 * readfrom(act) --mo--> act
711 if (act->is_write()) {
712 //RMW shouldn't have an edge to themselves
714 mo_graph->addEdge(act, curr);
715 } else if (act->is_read() && act->get_reads_from() != NULL)
716 mo_graph->addEdge(act->get_reads_from(), curr);
719 } else if (act->is_read() && !act->is_synchronizing(curr) &&
720 !act->same_thread(curr)) {
721 /* We have an action that:
722 (1) did not happen before us
723 (2) is a read and we are a write
724 (3) cannot synchronize with us
725 (4) is in a different thread
727 that read could potentially read from our write.
729 if (thin_air_constraint_may_allow(curr, act)) {
731 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
732 struct PendingFutureValue pfv={curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
733 futurevalues->push_back(pfv);
743 /** Arbitrary reads from the future are not allowed. Section 29.3
744 * part 9 places some constraints. This method checks one result of constraint
745 * constraint. Others require compiler support. */
747 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
748 if (!writer->is_rmw())
751 if (!reader->is_rmw())
754 for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
757 if (search->get_tid()==reader->get_tid()&&
758 search->happens_before(reader))
767 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
768 * The ModelAction under consideration is expected to be taking part in
769 * release/acquire synchronization as an object of the "reads from" relation.
770 * Note that this can only provide release sequence support for RMW chains
771 * which do not read from the future, as those actions cannot be traced until
772 * their "promise" is fulfilled. Similarly, we may not even establish the
773 * presence of a release sequence with certainty, as some modification order
774 * constraints may be decided further in the future. Thus, this function
775 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
776 * and a boolean representing certainty.
778 * @todo Finish lazy updating, when promises are fulfilled in the future
779 * @param rf The action that might be part of a release sequence. Must be a
781 * @param release_heads A pass-by-reference style return parameter. After
782 * execution of this function, release_heads will contain the heads of all the
783 * relevant release sequences, if any exists
784 * @return true, if the ModelChecker is certain that release_heads is complete;
787 bool ModelChecker::release_seq_head(const ModelAction *rf,
788 std::vector<const ModelAction *> *release_heads) const
790 ASSERT(rf->is_write());
792 /* read from future: need to settle this later */
793 return false; /* incomplete */
795 if (rf->is_release())
796 release_heads->push_back(rf);
798 /* We need a RMW action that is both an acquire and release to stop */
799 /** @todo Need to be smarter here... In the linux lock
800 * example, this will run to the beginning of the program for
802 if (rf->is_acquire() && rf->is_release())
803 return true; /* complete */
804 return release_seq_head(rf->get_reads_from(), release_heads);
806 if (rf->is_release())
807 return true; /* complete */
809 /* else relaxed write; check modification order for contiguous subsequence
810 * -> rf must be same thread as release */
811 int tid = id_to_int(rf->get_tid());
812 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
813 action_list_t *list = &(*thrd_lists)[tid];
814 action_list_t::const_reverse_iterator rit;
816 /* Find rf in the thread list */
817 rit = std::find(list->rbegin(), list->rend(), rf);
818 ASSERT(rit != list->rend());
820 /* Find the last write/release */
821 for (; rit != list->rend(); rit++)
822 if ((*rit)->is_release())
824 if (rit == list->rend()) {
825 /* No write-release in this thread */
826 return true; /* complete */
828 ModelAction *release = *rit;
830 ASSERT(rf->same_thread(release));
833 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
834 if (id_to_int(rf->get_tid()) == (int)i)
836 list = &(*thrd_lists)[i];
838 /* Can we ensure no future writes from this thread may break
839 * the release seq? */
840 bool future_ordered = false;
842 for (rit = list->rbegin(); rit != list->rend(); rit++) {
843 const ModelAction *act = *rit;
844 if (!act->is_write())
846 /* Reach synchronization -> this thread is complete */
847 if (act->happens_before(release))
849 if (rf->happens_before(act)) {
850 future_ordered = true;
854 /* Check modification order */
855 if (mo_graph->checkReachable(rf, act)) {
857 future_ordered = true;
860 if (mo_graph->checkReachable(act, release))
861 /* act --mo--> release */
863 if (mo_graph->checkReachable(release, act) &&
864 mo_graph->checkReachable(act, rf)) {
865 /* release --mo-> act --mo--> rf */
866 return true; /* complete */
871 return false; /* This thread is uncertain */
875 release_heads->push_back(release);
880 * A public interface for getting the release sequence head(s) with which a
881 * given ModelAction must synchronize. This function only returns a non-empty
882 * result when it can locate a release sequence head with certainty. Otherwise,
883 * it may mark the internal state of the ModelChecker so that it will handle
884 * the release sequence at a later time, causing @a act to update its
885 * synchronization at some later point in execution.
886 * @param act The 'acquire' action that may read from a release sequence
887 * @param release_heads A pass-by-reference return parameter. Will be filled
888 * with the head(s) of the release sequence(s), if they exists with certainty.
889 * @see ModelChecker::release_seq_head
891 void ModelChecker::get_release_seq_heads(ModelAction *act,
892 std::vector<const ModelAction *> *release_heads)
894 const ModelAction *rf = act->get_reads_from();
896 complete = release_seq_head(rf, release_heads);
898 /* add act to 'lazy checking' list */
899 std::list<ModelAction *> *list;
900 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
901 list->push_back(act);
907 * Attempt to resolve all stashed operations that might synchronize with a
908 * release sequence for a given location. This implements the "lazy" portion of
909 * determining whether or not a release sequence was contiguous, since not all
910 * modification order information is present at the time an action occurs.
912 * @param location The location/object that should be checked for release
913 * sequence resolutions
914 * @return True if any updates occurred (new synchronization, new mo_graph edges)
916 bool ModelChecker::resolve_release_sequences(void *location)
918 std::list<ModelAction *> *list;
919 list = lazy_sync_with_release->getptr(location);
923 bool updated = false;
924 std::list<ModelAction *>::iterator it = list->begin();
925 while (it != list->end()) {
926 ModelAction *act = *it;
927 const ModelAction *rf = act->get_reads_from();
928 std::vector<const ModelAction *> release_heads;
930 complete = release_seq_head(rf, &release_heads);
931 for (unsigned int i = 0; i < release_heads.size(); i++) {
932 if (!act->has_synchronized_with(release_heads[i])) {
934 act->synchronize_with(release_heads[i]);
939 /* propagate synchronization to later actions */
940 action_list_t::reverse_iterator it = action_trace->rbegin();
941 while ((*it) != act) {
942 ModelAction *propagate = *it;
943 if (act->happens_before(propagate))
944 /** @todo new mo_graph edges along with
945 * this synchronization? */
946 propagate->synchronize_with(act);
950 it = list->erase(it);
956 // If we resolved promises or data races, see if we have realized a data race.
957 if (checkDataRaces()) {
965 * Performs various bookkeeping operations for the current ModelAction. For
966 * instance, adds action to the per-object, per-thread action vector and to the
967 * action trace list of all thread actions.
969 * @param act is the ModelAction to add.
971 void ModelChecker::add_action_to_lists(ModelAction *act)
973 int tid = id_to_int(act->get_tid());
974 action_trace->push_back(act);
976 obj_map->get_safe_ptr(act->get_location())->push_back(act);
978 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
979 if (tid >= (int)vec->size())
980 vec->resize(priv->next_thread_id);
981 (*vec)[tid].push_back(act);
983 if ((int)thrd_last_action->size() <= tid)
984 thrd_last_action->resize(get_num_threads());
985 (*thrd_last_action)[tid] = act;
988 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
990 int nthreads = get_num_threads();
991 if ((int)thrd_last_action->size() < nthreads)
992 thrd_last_action->resize(nthreads);
993 return (*thrd_last_action)[id_to_int(tid)];
997 * Gets the last memory_order_seq_cst action (in the total global sequence)
998 * performed on a particular object (i.e., memory location).
999 * @param location The object location to check
1000 * @return The last seq_cst action performed
1002 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1004 action_list_t *list = obj_map->get_safe_ptr(location);
1005 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1006 action_list_t::reverse_iterator rit;
1007 for (rit = list->rbegin(); rit != list->rend(); rit++)
1008 if ((*rit)->is_write() && (*rit)->is_seqcst())
1013 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1015 ModelAction *parent = get_last_action(tid);
1017 parent = get_thread(tid)->get_creation();
1022 * Returns the clock vector for a given thread.
1023 * @param tid The thread whose clock vector we want
1024 * @return Desired clock vector
1026 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1028 return get_parent_action(tid)->get_cv();
1032 * Resolve a set of Promises with a current write. The set is provided in the
1033 * Node corresponding to @a write.
1034 * @param write The ModelAction that is fulfilling Promises
1035 * @return True if promises were resolved; false otherwise
1037 bool ModelChecker::resolve_promises(ModelAction *write)
1039 bool resolved = false;
1041 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1042 Promise *promise = (*promises)[promise_index];
1043 if (write->get_node()->get_promise(i)) {
1044 ModelAction *read = promise->get_action();
1045 read->read_from(write);
1046 if (read->is_rmw()) {
1047 mo_graph->addRMWEdge(write, read);
1049 r_modification_order(read, write);
1050 post_r_modification_order(read, write);
1051 promises->erase(promises->begin() + promise_index);
1062 * Compute the set of promises that could potentially be satisfied by this
1063 * action. Note that the set computation actually appears in the Node, not in
1065 * @param curr The ModelAction that may satisfy promises
1067 void ModelChecker::compute_promises(ModelAction *curr)
1069 for (unsigned int i = 0; i < promises->size(); i++) {
1070 Promise *promise = (*promises)[i];
1071 const ModelAction *act = promise->get_action();
1072 if (!act->happens_before(curr) &&
1074 !act->is_synchronizing(curr) &&
1075 !act->same_thread(curr) &&
1076 promise->get_value() == curr->get_value()) {
1077 curr->get_node()->set_promise(i);
1082 /** Checks promises in response to change in ClockVector Threads. */
1083 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1085 for (unsigned int i = 0; i < promises->size(); i++) {
1086 Promise *promise = (*promises)[i];
1087 const ModelAction *act = promise->get_action();
1088 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1089 merge_cv->synchronized_since(act)) {
1090 //This thread is no longer able to send values back to satisfy the promise
1091 int num_synchronized_threads = promise->increment_threads();
1092 if (num_synchronized_threads == get_num_threads()) {
1093 //Promise has failed
1094 failed_promise = true;
1102 * Build up an initial set of all past writes that this 'read' action may read
1103 * from. This set is determined by the clock vector's "happens before"
1105 * @param curr is the current ModelAction that we are exploring; it must be a
1108 void ModelChecker::build_reads_from_past(ModelAction *curr)
1110 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1112 ASSERT(curr->is_read());
1114 ModelAction *last_seq_cst = NULL;
1116 /* Track whether this object has been initialized */
1117 bool initialized = false;
1119 if (curr->is_seqcst()) {
1120 last_seq_cst = get_last_seq_cst(curr->get_location());
1121 /* We have to at least see the last sequentially consistent write,
1122 so we are initialized. */
1123 if (last_seq_cst != NULL)
1127 /* Iterate over all threads */
1128 for (i = 0; i < thrd_lists->size(); i++) {
1129 /* Iterate over actions in thread, starting from most recent */
1130 action_list_t *list = &(*thrd_lists)[i];
1131 action_list_t::reverse_iterator rit;
1132 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1133 ModelAction *act = *rit;
1135 /* Only consider 'write' actions */
1136 if (!act->is_write())
1139 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1140 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1141 DEBUG("Adding action to may_read_from:\n");
1142 if (DBG_ENABLED()) {
1146 curr->get_node()->add_read_from(act);
1149 /* Include at most one act per-thread that "happens before" curr */
1150 if (act->happens_before(curr)) {
1158 /** @todo Need a more informative way of reporting errors. */
1159 printf("ERROR: may read from uninitialized atomic\n");
1162 if (DBG_ENABLED() || !initialized) {
1163 printf("Reached read action:\n");
1165 printf("Printing may_read_from\n");
1166 curr->get_node()->print_may_read_from();
1167 printf("End printing may_read_from\n");
1170 ASSERT(initialized);
1173 static void print_list(action_list_t *list)
1175 action_list_t::iterator it;
1177 printf("---------------------------------------------------------------------\n");
1180 for (it = list->begin(); it != list->end(); it++) {
1183 printf("---------------------------------------------------------------------\n");
1186 void ModelChecker::print_summary()
1189 printf("Number of executions: %d\n", num_executions);
1190 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1194 if (!isfinalfeasible())
1195 printf("INFEASIBLE EXECUTION!\n");
1196 print_list(action_trace);
1201 * Add a Thread to the system for the first time. Should only be called once
1203 * @param t The Thread to add
1205 void ModelChecker::add_thread(Thread *t)
1207 thread_map->put(id_to_int(t->get_id()), t);
1208 scheduler->add_thread(t);
1211 void ModelChecker::remove_thread(Thread *t)
1213 scheduler->remove_thread(t);
1217 * Switch from a user-context to the "master thread" context (a.k.a. system
1218 * context). This switch is made with the intention of exploring a particular
1219 * model-checking action (described by a ModelAction object). Must be called
1220 * from a user-thread context.
1221 * @param act The current action that will be explored. Must not be NULL.
1222 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1224 int ModelChecker::switch_to_master(ModelAction *act)
1227 Thread *old = thread_current();
1228 set_current_action(act);
1229 old->set_state(THREAD_READY);
1230 return Thread::swap(old, &system_context);
1234 * Takes the next step in the execution, if possible.
1235 * @return Returns true (success) if a step was taken and false otherwise.
1237 bool ModelChecker::take_step() {
1238 Thread *curr, *next;
1243 curr = thread_current();
1245 if (curr->get_state() == THREAD_READY) {
1246 ASSERT(priv->current_action);
1248 priv->nextThread = check_current_action(priv->current_action);
1249 priv->current_action = NULL;
1250 if (!curr->is_blocked() && !curr->is_complete())
1251 scheduler->add_thread(curr);
1256 next = scheduler->next_thread(priv->nextThread);
1258 /* Infeasible -> don't take any more steps */
1263 next->set_state(THREAD_RUNNING);
1264 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1266 /* next == NULL -> don't take any more steps */
1269 /* Return false only if swap fails with an error */
1270 return (Thread::swap(&system_context, next) == 0);
1273 /** Runs the current execution until threre are no more steps to take. */
1274 void ModelChecker::finish_execution() {
1277 while (take_step());