8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
15 #define INITIAL_THREAD_ID 0
19 /** @brief Constructor */
20 ModelChecker::ModelChecker(struct model_params params) :
21 /* Initialize default scheduler */
22 scheduler(new Scheduler()),
26 action_trace(new action_list_t()),
27 thread_map(new HashTable<int, Thread *, int>()),
28 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
29 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
30 promises(new std::vector<Promise *>()),
31 lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
32 thrd_last_action(new std::vector<ModelAction *>(1)),
33 node_stack(new NodeStack()),
34 mo_graph(new CycleGraph()),
35 failed_promise(false),
36 too_many_reads(false),
39 /* Allocate this "size" on the snapshotting heap */
40 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
41 /* First thread created will have id INITIAL_THREAD_ID */
42 priv->next_thread_id = INITIAL_THREAD_ID;
44 lazy_sync_size = &priv->lazy_sync_size;
47 /** @brief Destructor */
48 ModelChecker::~ModelChecker()
50 for (int i = 0; i < get_num_threads(); i++)
51 delete thread_map->get(i);
58 for (unsigned int i = 0; i < promises->size(); i++)
59 delete (*promises)[i];
62 delete lazy_sync_with_release;
64 delete thrd_last_action;
71 * Restores user program to initial state and resets all model-checker data
74 void ModelChecker::reset_to_initial_state()
76 DEBUG("+++ Resetting to initial state +++\n");
77 node_stack->reset_execution();
78 failed_promise = false;
79 too_many_reads = false;
81 snapshotObject->backTrackBeforeStep(0);
84 /** @returns a thread ID for a new Thread */
85 thread_id_t ModelChecker::get_next_id()
87 return priv->next_thread_id++;
90 /** @returns the number of user threads created during this execution */
91 int ModelChecker::get_num_threads()
93 return priv->next_thread_id;
96 /** @returns a sequence number for a new ModelAction */
97 modelclock_t ModelChecker::get_next_seq_num()
99 return ++priv->used_sequence_numbers;
103 * @brief Choose the next thread to execute.
105 * This function chooses the next thread that should execute. It can force the
106 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
107 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
108 * The model-checker may have no preference regarding the next thread (i.e.,
109 * when exploring a new execution ordering), in which case this will return
111 * @param curr The current ModelAction. This action might guide the choice of
113 * @return The next thread to run. If the model-checker has no preference, NULL.
115 Thread * ModelChecker::get_next_thread(ModelAction *curr)
119 /* Do not split atomic actions. */
121 return thread_current();
122 /* The THREAD_CREATE action points to the created Thread */
123 else if (curr->get_type() == THREAD_CREATE)
124 return (Thread *)curr->get_location();
126 /* Have we completed exploring the preselected path? */
130 /* Else, we are trying to replay an execution */
131 ModelAction *next = node_stack->get_next()->get_action();
133 if (next == diverge) {
134 Node *nextnode = next->get_node();
135 /* Reached divergence point */
136 if (nextnode->increment_promise()) {
137 /* The next node will try to satisfy a different set of promises. */
138 tid = next->get_tid();
139 node_stack->pop_restofstack(2);
140 } else if (nextnode->increment_read_from()) {
141 /* The next node will read from a different value. */
142 tid = next->get_tid();
143 node_stack->pop_restofstack(2);
144 } else if (nextnode->increment_future_value()) {
145 /* The next node will try to read from a different future value. */
146 tid = next->get_tid();
147 node_stack->pop_restofstack(2);
149 /* Make a different thread execute for next step */
150 Node *node = nextnode->get_parent();
151 tid = node->get_next_backtrack();
152 node_stack->pop_restofstack(1);
154 DEBUG("*** Divergence point ***\n");
157 tid = next->get_tid();
159 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
160 ASSERT(tid != THREAD_ID_T_NONE);
161 return thread_map->get(id_to_int(tid));
165 * Queries the model-checker for more executions to explore and, if one
166 * exists, resets the model-checker state to execute a new execution.
168 * @return If there are more executions to explore, return true. Otherwise,
171 bool ModelChecker::next_execution()
177 if (isfinalfeasible() || DBG_ENABLED())
180 if ((diverge = get_next_backtrack()) == NULL)
184 printf("Next execution will diverge at:\n");
188 reset_to_initial_state();
192 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
194 action_type type = act->get_type();
204 /* linear search: from most recent to oldest */
205 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
206 action_list_t::reverse_iterator rit;
207 for (rit = list->rbegin(); rit != list->rend(); rit++) {
208 ModelAction *prev = *rit;
209 if (act->is_synchronizing(prev))
215 void ModelChecker::set_backtracking(ModelAction *act)
219 Thread *t = get_thread(act);
221 prev = get_last_conflict(act);
225 node = prev->get_node()->get_parent();
227 while (!node->is_enabled(t))
230 /* Check if this has been explored already */
231 if (node->has_been_explored(t->get_id()))
234 /* Cache the latest backtracking point */
235 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
236 priv->next_backtrack = prev;
238 /* If this is a new backtracking point, mark the tree */
239 if (!node->set_backtrack(t->get_id()))
241 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
242 prev->get_tid(), t->get_id());
250 * Returns last backtracking point. The model checker will explore a different
251 * path for this point in the next execution.
252 * @return The ModelAction at which the next execution should diverge.
254 ModelAction * ModelChecker::get_next_backtrack()
256 ModelAction *next = priv->next_backtrack;
257 priv->next_backtrack = NULL;
262 * Processes a read or rmw model action.
263 * @param curr is the read model action to process.
264 * @param th is the thread
265 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
266 * @return True if processing this read updates the mo_graph.
269 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
273 const ModelAction *reads_from = curr->get_node()->get_read_from();
274 if (reads_from != NULL) {
275 mo_graph->startChanges();
277 value = reads_from->get_value();
278 /* Assign reads_from, perform release/acquire synchronization */
279 curr->read_from(reads_from);
280 if (!second_part_of_rmw) {
281 check_recency(curr,false);
284 bool r_status=r_modification_order(curr,reads_from);
286 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
287 mo_graph->rollbackChanges();
288 too_many_reads=false;
292 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 mo_graph->commitChanges();
407 th->set_return_value(VALUE_NONE);
411 resolve_release_sequences(curr->get_location());
413 /* Add action to list. */
414 if (!second_part_of_rmw)
415 add_action_to_lists(curr);
417 check_curr_backtracking(curr);
419 set_backtracking(curr);
421 return get_next_thread(curr);
424 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
425 Node *currnode = curr->get_node();
426 Node *parnode = currnode->get_parent();
428 if ((!parnode->backtrack_empty() ||
429 !currnode->read_from_empty() ||
430 !currnode->future_value_empty() ||
431 !currnode->promise_empty())
432 && (!priv->next_backtrack ||
433 *curr > *priv->next_backtrack)) {
434 priv->next_backtrack = curr;
439 bool ModelChecker::promises_expired() {
440 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
441 Promise *promise = (*promises)[promise_index];
442 if (promise->get_expiration()<priv->used_sequence_numbers) {
449 /** @returns whether the current partial trace must be a prefix of a
451 bool ModelChecker::isfeasibleprefix() {
452 return promises->size() == 0 && *lazy_sync_size == 0;
455 /** @returns whether the current partial trace is feasible. */
456 bool ModelChecker::isfeasible() {
457 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
460 /** @returns whether the current partial trace is feasible. */
461 bool ModelChecker::isfeasibleotherthanRMW() {
462 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
465 /** Returns whether the current completed trace is feasible. */
466 bool ModelChecker::isfinalfeasible() {
467 return isfeasible() && promises->size() == 0;
470 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
471 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
472 int tid = id_to_int(act->get_tid());
473 ModelAction *lastread = get_last_action(tid);
474 lastread->process_rmw(act);
475 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
476 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
477 mo_graph->commitChanges();
483 * Checks whether a thread has read from the same write for too many times
484 * without seeing the effects of a later write.
487 * 1) there must a different write that we could read from that would satisfy the modification order,
488 * 2) we must have read from the same value in excess of maxreads times, and
489 * 3) that other write must have been in the reads_from set for maxreads times.
491 * If so, we decide that the execution is no longer feasible.
493 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
494 if (params.maxreads != 0) {
495 if (curr->get_node()->get_read_from_size() <= 1)
498 //Must make sure that execution is currently feasible... We could
499 //accidentally clear by rolling back
503 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
504 int tid = id_to_int(curr->get_tid());
507 if ((int)thrd_lists->size() <= tid)
510 action_list_t *list = &(*thrd_lists)[tid];
512 action_list_t::reverse_iterator rit = list->rbegin();
515 for (; (*rit) != curr; rit++)
517 /* go past curr now */
521 action_list_t::reverse_iterator ritcopy=rit;
522 //See if we have enough reads from the same value
524 for (; count < params.maxreads; rit++,count++) {
525 if (rit==list->rend())
527 ModelAction *act = *rit;
530 if (act->get_reads_from() != curr->get_reads_from())
532 if (act->get_node()->get_read_from_size() <= 1)
536 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
538 const ModelAction * write=curr->get_node()->get_read_from_at(i);
539 //Need a different write
540 if (write==curr->get_reads_from())
543 /* Test to see whether this is a feasible write to read from*/
544 mo_graph->startChanges();
545 r_modification_order(curr, write);
546 bool feasiblereadfrom=isfeasible();
547 mo_graph->rollbackChanges();
549 if (!feasiblereadfrom)
553 bool feasiblewrite=true;
554 //new we need to see if this write works for everyone
556 for (int loop=count;loop>0;loop--,rit++) {
557 ModelAction *act=*rit;
558 bool foundvalue=false;
559 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
560 if (act->get_node()->get_read_from_at(i)==write) {
571 too_many_reads = true;
579 * Updates the mo_graph with the constraints imposed from the current read.
580 * @param curr The current action. Must be a read.
581 * @param rf The action that curr reads from. Must be a write.
582 * @return True if modification order edges were added; false otherwise
584 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
586 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
589 ASSERT(curr->is_read());
591 /* Iterate over all threads */
592 for (i = 0; i < thrd_lists->size(); i++) {
593 /* Iterate over actions in thread, starting from most recent */
594 action_list_t *list = &(*thrd_lists)[i];
595 action_list_t::reverse_iterator rit;
596 for (rit = list->rbegin(); rit != list->rend(); rit++) {
597 ModelAction *act = *rit;
599 /* Include at most one act per-thread that "happens before" curr */
600 if (act->happens_before(curr)) {
601 if (act->is_read()) {
602 const ModelAction *prevreadfrom = act->get_reads_from();
603 if (prevreadfrom != NULL && rf != prevreadfrom) {
604 mo_graph->addEdge(prevreadfrom, rf);
607 } else if (rf != act) {
608 mo_graph->addEdge(act, rf);
619 /** Updates the mo_graph with the constraints imposed from the current read. */
620 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
622 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
624 ASSERT(curr->is_read());
626 /* Iterate over all threads */
627 for (i = 0; i < thrd_lists->size(); i++) {
628 /* Iterate over actions in thread, starting from most recent */
629 action_list_t *list = &(*thrd_lists)[i];
630 action_list_t::reverse_iterator rit;
631 ModelAction *lastact = NULL;
633 /* Find last action that happens after curr */
634 for (rit = list->rbegin(); rit != list->rend(); rit++) {
635 ModelAction *act = *rit;
636 if (curr->happens_before(act)) {
642 /* Include at most one act per-thread that "happens before" curr */
643 if (lastact != NULL) {
644 if (lastact->is_read()) {
645 const ModelAction *postreadfrom = lastact->get_reads_from();
646 if (postreadfrom != NULL&&rf != postreadfrom)
647 mo_graph->addEdge(rf, postreadfrom);
648 } else if (rf != lastact) {
649 mo_graph->addEdge(rf, lastact);
657 * Updates the mo_graph with the constraints imposed from the current write.
658 * @param curr The current action. Must be a write.
659 * @return True if modification order edges were added; false otherwise
661 bool ModelChecker::w_modification_order(ModelAction *curr)
663 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
666 ASSERT(curr->is_write());
668 if (curr->is_seqcst()) {
669 /* We have to at least see the last sequentially consistent write,
670 so we are initialized. */
671 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
672 if (last_seq_cst != NULL) {
673 mo_graph->addEdge(last_seq_cst, curr);
678 /* Iterate over all threads */
679 for (i = 0; i < thrd_lists->size(); i++) {
680 /* Iterate over actions in thread, starting from most recent */
681 action_list_t *list = &(*thrd_lists)[i];
682 action_list_t::reverse_iterator rit;
683 for (rit = list->rbegin(); rit != list->rend(); rit++) {
684 ModelAction *act = *rit;
686 /* Include at most one act per-thread that "happens before" curr */
687 if (act->happens_before(curr)) {
689 * Note: if act is RMW, just add edge:
691 * The following edge should be handled elsewhere:
692 * readfrom(act) --mo--> act
694 if (act->is_write()) {
695 //RMW shouldn't have an edge to themselves
697 mo_graph->addEdge(act, curr);
698 } else if (act->is_read() && act->get_reads_from() != NULL)
699 mo_graph->addEdge(act->get_reads_from(), curr);
702 } else if (act->is_read() && !act->is_synchronizing(curr) &&
703 !act->same_thread(curr)) {
704 /* We have an action that:
705 (1) did not happen before us
706 (2) is a read and we are a write
707 (3) cannot synchronize with us
708 (4) is in a different thread
710 that read could potentially read from our write.
712 if (thin_air_constraint_may_allow(curr, act)) {
714 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
715 if (act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
716 (!priv->next_backtrack || *act > *priv->next_backtrack))
717 priv->next_backtrack = act;
727 /** Arbitrary reads from the future are not allowed. Section 29.3
728 * part 9 places some constraints. This method checks one result of constraint
729 * constraint. Others require compiler support. */
731 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
732 if (!writer->is_rmw())
735 if (!reader->is_rmw())
738 for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
741 if (search->get_tid()==reader->get_tid()&&
742 search->happens_before(reader))
751 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
752 * The ModelAction under consideration is expected to be taking part in
753 * release/acquire synchronization as an object of the "reads from" relation.
754 * Note that this can only provide release sequence support for RMW chains
755 * which do not read from the future, as those actions cannot be traced until
756 * their "promise" is fulfilled. Similarly, we may not even establish the
757 * presence of a release sequence with certainty, as some modification order
758 * constraints may be decided further in the future. Thus, this function
759 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
760 * and a boolean representing certainty.
762 * @todo Finish lazy updating, when promises are fulfilled in the future
763 * @param rf The action that might be part of a release sequence. Must be a
765 * @param release_heads A pass-by-reference style return parameter. After
766 * execution of this function, release_heads will contain the heads of all the
767 * relevant release sequences, if any exists
768 * @return true, if the ModelChecker is certain that release_heads is complete;
771 bool ModelChecker::release_seq_head(const ModelAction *rf,
772 std::vector<const ModelAction *> *release_heads) const
774 ASSERT(rf->is_write());
776 /* read from future: need to settle this later */
777 return false; /* incomplete */
779 if (rf->is_release())
780 release_heads->push_back(rf);
782 /* We need a RMW action that is both an acquire and release to stop */
783 /** @todo Need to be smarter here... In the linux lock
784 * example, this will run to the beginning of the program for
786 if (rf->is_acquire() && rf->is_release())
787 return true; /* complete */
788 return release_seq_head(rf->get_reads_from(), release_heads);
790 if (rf->is_release())
791 return true; /* complete */
793 /* else relaxed write; check modification order for contiguous subsequence
794 * -> rf must be same thread as release */
795 int tid = id_to_int(rf->get_tid());
796 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
797 action_list_t *list = &(*thrd_lists)[tid];
798 action_list_t::const_reverse_iterator rit;
800 /* Find rf in the thread list */
801 rit = std::find(list->rbegin(), list->rend(), rf);
802 ASSERT(rit != list->rend());
804 /* Find the last write/release */
805 for (; rit != list->rend(); rit++)
806 if ((*rit)->is_release())
808 if (rit == list->rend()) {
809 /* No write-release in this thread */
810 return true; /* complete */
812 ModelAction *release = *rit;
814 ASSERT(rf->same_thread(release));
817 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
818 if (id_to_int(rf->get_tid()) == (int)i)
820 list = &(*thrd_lists)[i];
822 /* Can we ensure no future writes from this thread may break
823 * the release seq? */
824 bool future_ordered = false;
826 for (rit = list->rbegin(); rit != list->rend(); rit++) {
827 const ModelAction *act = *rit;
828 if (!act->is_write())
830 /* Reach synchronization -> this thread is complete */
831 if (act->happens_before(release))
833 if (rf->happens_before(act)) {
834 future_ordered = true;
838 /* Check modification order */
839 if (mo_graph->checkReachable(rf, act)) {
841 future_ordered = true;
844 if (mo_graph->checkReachable(act, release))
845 /* act --mo--> release */
847 if (mo_graph->checkReachable(release, act) &&
848 mo_graph->checkReachable(act, rf)) {
849 /* release --mo-> act --mo--> rf */
850 return true; /* complete */
855 return false; /* This thread is uncertain */
859 release_heads->push_back(release);
864 * A public interface for getting the release sequence head(s) with which a
865 * given ModelAction must synchronize. This function only returns a non-empty
866 * result when it can locate a release sequence head with certainty. Otherwise,
867 * it may mark the internal state of the ModelChecker so that it will handle
868 * the release sequence at a later time, causing @a act to update its
869 * synchronization at some later point in execution.
870 * @param act The 'acquire' action that may read from a release sequence
871 * @param release_heads A pass-by-reference return parameter. Will be filled
872 * with the head(s) of the release sequence(s), if they exists with certainty.
873 * @see ModelChecker::release_seq_head
875 void ModelChecker::get_release_seq_heads(ModelAction *act,
876 std::vector<const ModelAction *> *release_heads)
878 const ModelAction *rf = act->get_reads_from();
880 complete = release_seq_head(rf, release_heads);
882 /* add act to 'lazy checking' list */
883 std::list<ModelAction *> *list;
884 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
885 list->push_back(act);
891 * Attempt to resolve all stashed operations that might synchronize with a
892 * release sequence for a given location. This implements the "lazy" portion of
893 * determining whether or not a release sequence was contiguous, since not all
894 * modification order information is present at the time an action occurs.
896 * @param location The location/object that should be checked for release
897 * sequence resolutions
898 * @return True if any updates occurred (new synchronization, new mo_graph edges)
900 bool ModelChecker::resolve_release_sequences(void *location)
902 std::list<ModelAction *> *list;
903 list = lazy_sync_with_release->getptr(location);
907 bool updated = false;
908 std::list<ModelAction *>::iterator it = list->begin();
909 while (it != list->end()) {
910 ModelAction *act = *it;
911 const ModelAction *rf = act->get_reads_from();
912 std::vector<const ModelAction *> release_heads;
914 complete = release_seq_head(rf, &release_heads);
915 for (unsigned int i = 0; i < release_heads.size(); i++) {
916 if (!act->has_synchronized_with(release_heads[i])) {
918 act->synchronize_with(release_heads[i]);
923 /* propagate synchronization to later actions */
924 action_list_t::reverse_iterator it = action_trace->rbegin();
925 while ((*it) != act) {
926 ModelAction *propagate = *it;
927 if (act->happens_before(propagate))
928 /** @todo new mo_graph edges along with
929 * this synchronization? */
930 propagate->synchronize_with(act);
934 it = list->erase(it);
940 // If we resolved promises or data races, see if we have realized a data race.
941 if (checkDataRaces()) {
949 * Performs various bookkeeping operations for the current ModelAction. For
950 * instance, adds action to the per-object, per-thread action vector and to the
951 * action trace list of all thread actions.
953 * @param act is the ModelAction to add.
955 void ModelChecker::add_action_to_lists(ModelAction *act)
957 int tid = id_to_int(act->get_tid());
958 action_trace->push_back(act);
960 obj_map->get_safe_ptr(act->get_location())->push_back(act);
962 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
963 if (tid >= (int)vec->size())
964 vec->resize(priv->next_thread_id);
965 (*vec)[tid].push_back(act);
967 if ((int)thrd_last_action->size() <= tid)
968 thrd_last_action->resize(get_num_threads());
969 (*thrd_last_action)[tid] = act;
972 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
974 int nthreads = get_num_threads();
975 if ((int)thrd_last_action->size() < nthreads)
976 thrd_last_action->resize(nthreads);
977 return (*thrd_last_action)[id_to_int(tid)];
981 * Gets the last memory_order_seq_cst action (in the total global sequence)
982 * performed on a particular object (i.e., memory location).
983 * @param location The object location to check
984 * @return The last seq_cst action performed
986 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
988 action_list_t *list = obj_map->get_safe_ptr(location);
989 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
990 action_list_t::reverse_iterator rit;
991 for (rit = list->rbegin(); rit != list->rend(); rit++)
992 if ((*rit)->is_write() && (*rit)->is_seqcst())
997 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
999 ModelAction *parent = get_last_action(tid);
1001 parent = get_thread(tid)->get_creation();
1006 * Returns the clock vector for a given thread.
1007 * @param tid The thread whose clock vector we want
1008 * @return Desired clock vector
1010 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1012 return get_parent_action(tid)->get_cv();
1016 * Resolve a set of Promises with a current write. The set is provided in the
1017 * Node corresponding to @a write.
1018 * @param write The ModelAction that is fulfilling Promises
1019 * @return True if promises were resolved; false otherwise
1021 bool ModelChecker::resolve_promises(ModelAction *write)
1023 bool resolved = false;
1025 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1026 Promise *promise = (*promises)[promise_index];
1027 if (write->get_node()->get_promise(i)) {
1028 ModelAction *read = promise->get_action();
1029 read->read_from(write);
1030 if (read->is_rmw()) {
1031 mo_graph->addRMWEdge(write, read);
1033 r_modification_order(read, write);
1034 post_r_modification_order(read, write);
1035 promises->erase(promises->begin() + promise_index);
1044 * Compute the set of promises that could potentially be satisfied by this
1045 * action. Note that the set computation actually appears in the Node, not in
1047 * @param curr The ModelAction that may satisfy promises
1049 void ModelChecker::compute_promises(ModelAction *curr)
1051 for (unsigned int i = 0; i < promises->size(); i++) {
1052 Promise *promise = (*promises)[i];
1053 const ModelAction *act = promise->get_action();
1054 if (!act->happens_before(curr) &&
1056 !act->is_synchronizing(curr) &&
1057 !act->same_thread(curr) &&
1058 promise->get_value() == curr->get_value()) {
1059 curr->get_node()->set_promise(i);
1064 /** Checks promises in response to change in ClockVector Threads. */
1065 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1067 for (unsigned int i = 0; i < promises->size(); i++) {
1068 Promise *promise = (*promises)[i];
1069 const ModelAction *act = promise->get_action();
1070 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1071 merge_cv->synchronized_since(act)) {
1072 //This thread is no longer able to send values back to satisfy the promise
1073 int num_synchronized_threads = promise->increment_threads();
1074 if (num_synchronized_threads == get_num_threads()) {
1075 //Promise has failed
1076 failed_promise = true;
1084 * Build up an initial set of all past writes that this 'read' action may read
1085 * from. This set is determined by the clock vector's "happens before"
1087 * @param curr is the current ModelAction that we are exploring; it must be a
1090 void ModelChecker::build_reads_from_past(ModelAction *curr)
1092 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1094 ASSERT(curr->is_read());
1096 ModelAction *last_seq_cst = NULL;
1098 /* Track whether this object has been initialized */
1099 bool initialized = false;
1101 if (curr->is_seqcst()) {
1102 last_seq_cst = get_last_seq_cst(curr->get_location());
1103 /* We have to at least see the last sequentially consistent write,
1104 so we are initialized. */
1105 if (last_seq_cst != NULL)
1109 /* Iterate over all threads */
1110 for (i = 0; i < thrd_lists->size(); i++) {
1111 /* Iterate over actions in thread, starting from most recent */
1112 action_list_t *list = &(*thrd_lists)[i];
1113 action_list_t::reverse_iterator rit;
1114 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1115 ModelAction *act = *rit;
1117 /* Only consider 'write' actions */
1118 if (!act->is_write())
1121 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1122 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1123 DEBUG("Adding action to may_read_from:\n");
1124 if (DBG_ENABLED()) {
1128 curr->get_node()->add_read_from(act);
1131 /* Include at most one act per-thread that "happens before" curr */
1132 if (act->happens_before(curr)) {
1140 /** @todo Need a more informative way of reporting errors. */
1141 printf("ERROR: may read from uninitialized atomic\n");
1144 if (DBG_ENABLED() || !initialized) {
1145 printf("Reached read action:\n");
1147 printf("Printing may_read_from\n");
1148 curr->get_node()->print_may_read_from();
1149 printf("End printing may_read_from\n");
1152 ASSERT(initialized);
1155 static void print_list(action_list_t *list)
1157 action_list_t::iterator it;
1159 printf("---------------------------------------------------------------------\n");
1162 for (it = list->begin(); it != list->end(); it++) {
1165 printf("---------------------------------------------------------------------\n");
1168 void ModelChecker::print_summary()
1171 printf("Number of executions: %d\n", num_executions);
1172 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1176 if (!isfinalfeasible())
1177 printf("INFEASIBLE EXECUTION!\n");
1178 print_list(action_trace);
1183 * Add a Thread to the system for the first time. Should only be called once
1185 * @param t The Thread to add
1187 void ModelChecker::add_thread(Thread *t)
1189 thread_map->put(id_to_int(t->get_id()), t);
1190 scheduler->add_thread(t);
1193 void ModelChecker::remove_thread(Thread *t)
1195 scheduler->remove_thread(t);
1199 * Switch from a user-context to the "master thread" context (a.k.a. system
1200 * context). This switch is made with the intention of exploring a particular
1201 * model-checking action (described by a ModelAction object). Must be called
1202 * from a user-thread context.
1203 * @param act The current action that will be explored. Must not be NULL.
1204 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1206 int ModelChecker::switch_to_master(ModelAction *act)
1209 Thread *old = thread_current();
1210 set_current_action(act);
1211 old->set_state(THREAD_READY);
1212 return Thread::swap(old, &system_context);
1216 * Takes the next step in the execution, if possible.
1217 * @return Returns true (success) if a step was taken and false otherwise.
1219 bool ModelChecker::take_step() {
1220 Thread *curr, *next;
1225 curr = thread_current();
1227 if (curr->get_state() == THREAD_READY) {
1228 ASSERT(priv->current_action);
1230 priv->nextThread = check_current_action(priv->current_action);
1231 priv->current_action = NULL;
1232 if (!curr->is_blocked() && !curr->is_complete())
1233 scheduler->add_thread(curr);
1238 next = scheduler->next_thread(priv->nextThread);
1240 /* Infeasible -> don't take any more steps */
1245 next->set_state(THREAD_RUNNING);
1246 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1248 /* next == NULL -> don't take any more steps */
1251 /* Return false only if swap fails with an error */
1252 return (Thread::swap(&system_context, next) == 0);
1255 /** Runs the current execution until threre are no more steps to take. */
1256 void ModelChecker::finish_execution() {
1259 while (take_step());