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();
280 if (!second_part_of_rmw) {
281 check_recency(curr,false);
282 r_status=r_modification_order(curr, reads_from);
286 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
287 mo_graph->rollbackChanges();
288 too_many_reads=false;
292 curr->read_from(reads_from);
293 mo_graph->commitChanges();
295 } else if (!second_part_of_rmw) {
296 /* Read from future value */
297 value = curr->get_node()->get_future_value();
298 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
299 curr->read_from(NULL);
300 Promise *valuepromise = new Promise(curr, value, expiration);
301 promises->push_back(valuepromise);
303 th->set_return_value(value);
309 * This is the heart of the model checker routine. It performs model-checking
310 * actions corresponding to a given "current action." Among other processes, it
311 * calculates reads-from relationships, updates synchronization clock vectors,
312 * forms a memory_order constraints graph, and handles replay/backtrack
313 * execution when running permutations of previously-observed executions.
315 * @param curr The current action to process
316 * @return The next Thread that must be executed. May be NULL if ModelChecker
317 * makes no choice (e.g., according to replay execution, combining RMW actions,
320 Thread * ModelChecker::check_current_action(ModelAction *curr)
322 bool second_part_of_rmw = false;
326 if (curr->is_rmwc() || curr->is_rmw()) {
327 ModelAction *tmp = process_rmw(curr);
328 second_part_of_rmw = true;
331 compute_promises(curr);
333 ModelAction *tmp = node_stack->explore_action(curr);
335 /* Discard duplicate ModelAction; use action from NodeStack */
336 /* First restore type and order in case of RMW operation */
338 tmp->copy_typeandorder(curr);
340 /* If we have diverged, we need to reset the clock vector. */
342 tmp->create_cv(get_parent_action(tmp->get_tid()));
348 * Perform one-time actions when pushing new ModelAction onto
351 curr->create_cv(get_parent_action(curr->get_tid()));
352 /* Build may_read_from set */
354 build_reads_from_past(curr);
355 if (curr->is_write())
356 compute_promises(curr);
360 /* Thread specific actions */
361 switch(curr->get_type()) {
362 case THREAD_CREATE: {
363 Thread *th = (Thread *)curr->get_location();
364 th->set_creation(curr);
368 Thread *waiting, *blocking;
369 waiting = get_thread(curr);
370 blocking = (Thread *)curr->get_location();
371 if (!blocking->is_complete()) {
372 blocking->push_wait_list(curr);
373 scheduler->sleep(waiting);
377 case THREAD_FINISH: {
378 Thread *th = get_thread(curr);
379 while (!th->wait_list_empty()) {
380 ModelAction *act = th->pop_wait_list();
381 Thread *wake = get_thread(act);
382 scheduler->wake(wake);
388 check_promises(NULL, curr->get_cv());
395 Thread *th = get_thread(curr);
397 bool updated = false;
398 if (curr->is_read()) {
399 updated=process_read(curr, th, second_part_of_rmw);
402 if (curr->is_write()) {
403 bool updated_mod_order=w_modification_order(curr);
404 bool updated_promises=resolve_promises(curr);
405 updated=updated_mod_order|updated_promises;
407 if (promises->size()==0) {
408 for(unsigned int i=0;i<futurevalues->size();i++) {
409 struct PendingFutureValue pfv=(*futurevalues)[i];
410 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
411 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
412 priv->next_backtrack = pfv.act;
414 futurevalues->resize(0);
417 mo_graph->commitChanges();
418 th->set_return_value(VALUE_NONE);
422 resolve_release_sequences(curr->get_location());
424 /* Add action to list. */
425 if (!second_part_of_rmw)
426 add_action_to_lists(curr);
428 check_curr_backtracking(curr);
430 set_backtracking(curr);
432 return get_next_thread(curr);
435 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
436 Node *currnode = curr->get_node();
437 Node *parnode = currnode->get_parent();
439 if ((!parnode->backtrack_empty() ||
440 !currnode->read_from_empty() ||
441 !currnode->future_value_empty() ||
442 !currnode->promise_empty())
443 && (!priv->next_backtrack ||
444 *curr > *priv->next_backtrack)) {
445 priv->next_backtrack = curr;
449 bool ModelChecker::promises_expired() {
450 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
451 Promise *promise = (*promises)[promise_index];
452 if (promise->get_expiration()<priv->used_sequence_numbers) {
459 /** @returns whether the current partial trace must be a prefix of a
461 bool ModelChecker::isfeasibleprefix() {
462 return promises->size() == 0 && *lazy_sync_size == 0;
465 /** @returns whether the current partial trace is feasible. */
466 bool ModelChecker::isfeasible() {
467 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
470 /** @returns whether the current partial trace is feasible other than
471 * multiple RMW reading from the same store. */
472 bool ModelChecker::isfeasibleotherthanRMW() {
473 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
476 /** Returns whether the current completed trace is feasible. */
477 bool ModelChecker::isfinalfeasible() {
478 return isfeasible() && promises->size() == 0;
481 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
482 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
483 int tid = id_to_int(act->get_tid());
484 ModelAction *lastread = get_last_action(tid);
485 lastread->process_rmw(act);
486 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
487 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
488 mo_graph->commitChanges();
494 * Checks whether a thread has read from the same write for too many times
495 * without seeing the effects of a later write.
498 * 1) there must a different write that we could read from that would satisfy the modification order,
499 * 2) we must have read from the same value in excess of maxreads times, and
500 * 3) that other write must have been in the reads_from set for maxreads times.
502 * If so, we decide that the execution is no longer feasible.
504 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
505 if (params.maxreads != 0) {
506 if (curr->get_node()->get_read_from_size() <= 1)
509 //Must make sure that execution is currently feasible... We could
510 //accidentally clear by rolling back
514 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
515 int tid = id_to_int(curr->get_tid());
518 if ((int)thrd_lists->size() <= tid)
521 action_list_t *list = &(*thrd_lists)[tid];
523 action_list_t::reverse_iterator rit = list->rbegin();
526 for (; (*rit) != curr; rit++)
528 /* go past curr now */
532 action_list_t::reverse_iterator ritcopy=rit;
533 //See if we have enough reads from the same value
535 for (; count < params.maxreads; rit++,count++) {
536 if (rit==list->rend())
538 ModelAction *act = *rit;
541 if (act->get_reads_from() != curr->get_reads_from())
543 if (act->get_node()->get_read_from_size() <= 1)
547 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
549 const ModelAction * write=curr->get_node()->get_read_from_at(i);
550 //Need a different write
551 if (write==curr->get_reads_from())
554 /* Test to see whether this is a feasible write to read from*/
555 mo_graph->startChanges();
556 r_modification_order(curr, write);
557 bool feasiblereadfrom=isfeasible();
558 mo_graph->rollbackChanges();
560 if (!feasiblereadfrom)
564 bool feasiblewrite=true;
565 //new we need to see if this write works for everyone
567 for (int loop=count;loop>0;loop--,rit++) {
568 ModelAction *act=*rit;
569 bool foundvalue=false;
570 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
571 if (act->get_node()->get_read_from_at(i)==write) {
582 too_many_reads = true;
590 * Updates the mo_graph with the constraints imposed from the current read.
591 * @param curr The current action. Must be a read.
592 * @param rf The action that curr reads from. Must be a write.
593 * @return True if modification order edges were added; false otherwise
595 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
597 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
600 ASSERT(curr->is_read());
602 /* Iterate over all threads */
603 for (i = 0; i < thrd_lists->size(); i++) {
604 /* Iterate over actions in thread, starting from most recent */
605 action_list_t *list = &(*thrd_lists)[i];
606 action_list_t::reverse_iterator rit;
607 for (rit = list->rbegin(); rit != list->rend(); rit++) {
608 ModelAction *act = *rit;
610 /* Include at most one act per-thread that "happens before" curr */
611 if (act->happens_before(curr)) {
612 if (act->is_write()) {
613 if (rf != act && act != curr) {
614 mo_graph->addEdge(act, rf);
618 const ModelAction *prevreadfrom = act->get_reads_from();
619 if (prevreadfrom != NULL && rf != prevreadfrom) {
620 mo_graph->addEdge(prevreadfrom, rf);
633 /** Updates the mo_graph with the constraints imposed from the current read. */
634 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
636 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
638 ASSERT(curr->is_read());
640 /* Iterate over all threads */
641 for (i = 0; i < thrd_lists->size(); i++) {
642 /* Iterate over actions in thread, starting from most recent */
643 action_list_t *list = &(*thrd_lists)[i];
644 action_list_t::reverse_iterator rit;
645 ModelAction *lastact = NULL;
647 /* Find last action that happens after curr */
648 for (rit = list->rbegin(); rit != list->rend(); rit++) {
649 ModelAction *act = *rit;
650 if (curr->happens_before(act)) {
656 /* Include at most one act per-thread that "happens before" curr */
657 if (lastact != NULL) {
658 if (lastact->is_read()) {
659 const ModelAction *postreadfrom = lastact->get_reads_from();
660 if (postreadfrom != NULL&&rf != postreadfrom)
661 mo_graph->addEdge(rf, postreadfrom);
662 } else if (rf != lastact) {
663 mo_graph->addEdge(rf, lastact);
671 * Updates the mo_graph with the constraints imposed from the current write.
672 * @param curr The current action. Must be a write.
673 * @return True if modification order edges were added; false otherwise
675 bool ModelChecker::w_modification_order(ModelAction *curr)
677 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
680 ASSERT(curr->is_write());
682 if (curr->is_seqcst()) {
683 /* We have to at least see the last sequentially consistent write,
684 so we are initialized. */
685 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
686 if (last_seq_cst != NULL) {
687 mo_graph->addEdge(last_seq_cst, curr);
692 /* Iterate over all threads */
693 for (i = 0; i < thrd_lists->size(); i++) {
694 /* Iterate over actions in thread, starting from most recent */
695 action_list_t *list = &(*thrd_lists)[i];
696 action_list_t::reverse_iterator rit;
697 for (rit = list->rbegin(); rit != list->rend(); rit++) {
698 ModelAction *act = *rit;
700 /* Include at most one act per-thread that "happens before" curr */
701 if (act->happens_before(curr)) {
703 * Note: if act is RMW, just add edge:
705 * The following edge should be handled elsewhere:
706 * readfrom(act) --mo--> act
708 if (act->is_write()) {
709 //RMW shouldn't have an edge to themselves
711 mo_graph->addEdge(act, curr);
712 } else if (act->is_read() && act->get_reads_from() != NULL)
713 mo_graph->addEdge(act->get_reads_from(), curr);
716 } else if (act->is_read() && !act->is_synchronizing(curr) &&
717 !act->same_thread(curr)) {
718 /* We have an action that:
719 (1) did not happen before us
720 (2) is a read and we are a write
721 (3) cannot synchronize with us
722 (4) is in a different thread
724 that read could potentially read from our write.
726 if (thin_air_constraint_may_allow(curr, act)) {
728 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
729 struct PendingFutureValue pfv={curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
730 futurevalues->push_back(pfv);
740 /** Arbitrary reads from the future are not allowed. Section 29.3
741 * part 9 places some constraints. This method checks one result of constraint
742 * constraint. Others require compiler support. */
744 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
745 if (!writer->is_rmw())
748 if (!reader->is_rmw())
751 for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
754 if (search->get_tid()==reader->get_tid()&&
755 search->happens_before(reader))
763 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
764 * The ModelAction under consideration is expected to be taking part in
765 * release/acquire synchronization as an object of the "reads from" relation.
766 * Note that this can only provide release sequence support for RMW chains
767 * which do not read from the future, as those actions cannot be traced until
768 * their "promise" is fulfilled. Similarly, we may not even establish the
769 * presence of a release sequence with certainty, as some modification order
770 * constraints may be decided further in the future. Thus, this function
771 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
772 * and a boolean representing certainty.
774 * @todo Finish lazy updating, when promises are fulfilled in the future
775 * @param rf The action that might be part of a release sequence. Must be a
777 * @param release_heads A pass-by-reference style return parameter. After
778 * execution of this function, release_heads will contain the heads of all the
779 * relevant release sequences, if any exists
780 * @return true, if the ModelChecker is certain that release_heads is complete;
783 bool ModelChecker::release_seq_head(const ModelAction *rf,
784 std::vector<const ModelAction *> *release_heads) const
786 ASSERT(rf->is_write());
788 /* read from future: need to settle this later */
789 return false; /* incomplete */
791 if (rf->is_release())
792 release_heads->push_back(rf);
794 /* We need a RMW action that is both an acquire and release to stop */
795 /** @todo Need to be smarter here... In the linux lock
796 * example, this will run to the beginning of the program for
798 if (rf->is_acquire() && rf->is_release())
799 return true; /* complete */
800 return release_seq_head(rf->get_reads_from(), release_heads);
802 if (rf->is_release())
803 return true; /* complete */
805 /* else relaxed write; check modification order for contiguous subsequence
806 * -> rf must be same thread as release */
807 int tid = id_to_int(rf->get_tid());
808 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
809 action_list_t *list = &(*thrd_lists)[tid];
810 action_list_t::const_reverse_iterator rit;
812 /* Find rf in the thread list */
813 rit = std::find(list->rbegin(), list->rend(), rf);
814 ASSERT(rit != list->rend());
816 /* Find the last write/release */
817 for (; rit != list->rend(); rit++)
818 if ((*rit)->is_release())
820 if (rit == list->rend()) {
821 /* No write-release in this thread */
822 return true; /* complete */
824 ModelAction *release = *rit;
826 ASSERT(rf->same_thread(release));
829 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
830 if (id_to_int(rf->get_tid()) == (int)i)
832 list = &(*thrd_lists)[i];
834 /* Can we ensure no future writes from this thread may break
835 * the release seq? */
836 bool future_ordered = false;
838 for (rit = list->rbegin(); rit != list->rend(); rit++) {
839 const ModelAction *act = *rit;
840 if (!act->is_write())
842 /* Reach synchronization -> this thread is complete */
843 if (act->happens_before(release))
845 if (rf->happens_before(act)) {
846 future_ordered = true;
850 /* Check modification order */
851 if (mo_graph->checkReachable(rf, act)) {
853 future_ordered = true;
856 if (mo_graph->checkReachable(act, release))
857 /* act --mo--> release */
859 if (mo_graph->checkReachable(release, act) &&
860 mo_graph->checkReachable(act, rf)) {
861 /* release --mo-> act --mo--> rf */
862 return true; /* complete */
867 return false; /* This thread is uncertain */
871 release_heads->push_back(release);
876 * A public interface for getting the release sequence head(s) with which a
877 * given ModelAction must synchronize. This function only returns a non-empty
878 * result when it can locate a release sequence head with certainty. Otherwise,
879 * it may mark the internal state of the ModelChecker so that it will handle
880 * the release sequence at a later time, causing @a act to update its
881 * synchronization at some later point in execution.
882 * @param act The 'acquire' action that may read from a release sequence
883 * @param release_heads A pass-by-reference return parameter. Will be filled
884 * with the head(s) of the release sequence(s), if they exists with certainty.
885 * @see ModelChecker::release_seq_head
887 void ModelChecker::get_release_seq_heads(ModelAction *act,
888 std::vector<const ModelAction *> *release_heads)
890 const ModelAction *rf = act->get_reads_from();
892 complete = release_seq_head(rf, release_heads);
894 /* add act to 'lazy checking' list */
895 std::list<ModelAction *> *list;
896 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
897 list->push_back(act);
903 * Attempt to resolve all stashed operations that might synchronize with a
904 * release sequence for a given location. This implements the "lazy" portion of
905 * determining whether or not a release sequence was contiguous, since not all
906 * modification order information is present at the time an action occurs.
908 * @param location The location/object that should be checked for release
909 * sequence resolutions
910 * @return True if any updates occurred (new synchronization, new mo_graph edges)
912 bool ModelChecker::resolve_release_sequences(void *location)
914 std::list<ModelAction *> *list;
915 list = lazy_sync_with_release->getptr(location);
919 bool updated = false;
920 std::list<ModelAction *>::iterator it = list->begin();
921 while (it != list->end()) {
922 ModelAction *act = *it;
923 const ModelAction *rf = act->get_reads_from();
924 std::vector<const ModelAction *> release_heads;
926 complete = release_seq_head(rf, &release_heads);
927 for (unsigned int i = 0; i < release_heads.size(); i++) {
928 if (!act->has_synchronized_with(release_heads[i])) {
930 act->synchronize_with(release_heads[i]);
935 /* propagate synchronization to later actions */
936 action_list_t::reverse_iterator it = action_trace->rbegin();
937 while ((*it) != act) {
938 ModelAction *propagate = *it;
939 if (act->happens_before(propagate))
940 /** @todo new mo_graph edges along with
941 * this synchronization? */
942 propagate->synchronize_with(act);
946 it = list->erase(it);
952 // If we resolved promises or data races, see if we have realized a data race.
953 if (checkDataRaces()) {
961 * Performs various bookkeeping operations for the current ModelAction. For
962 * instance, adds action to the per-object, per-thread action vector and to the
963 * action trace list of all thread actions.
965 * @param act is the ModelAction to add.
967 void ModelChecker::add_action_to_lists(ModelAction *act)
969 int tid = id_to_int(act->get_tid());
970 action_trace->push_back(act);
972 obj_map->get_safe_ptr(act->get_location())->push_back(act);
974 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
975 if (tid >= (int)vec->size())
976 vec->resize(priv->next_thread_id);
977 (*vec)[tid].push_back(act);
979 if ((int)thrd_last_action->size() <= tid)
980 thrd_last_action->resize(get_num_threads());
981 (*thrd_last_action)[tid] = act;
984 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
986 int nthreads = get_num_threads();
987 if ((int)thrd_last_action->size() < nthreads)
988 thrd_last_action->resize(nthreads);
989 return (*thrd_last_action)[id_to_int(tid)];
993 * Gets the last memory_order_seq_cst action (in the total global sequence)
994 * performed on a particular object (i.e., memory location).
995 * @param location The object location to check
996 * @return The last seq_cst action performed
998 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1000 action_list_t *list = obj_map->get_safe_ptr(location);
1001 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1002 action_list_t::reverse_iterator rit;
1003 for (rit = list->rbegin(); rit != list->rend(); rit++)
1004 if ((*rit)->is_write() && (*rit)->is_seqcst())
1009 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1011 ModelAction *parent = get_last_action(tid);
1013 parent = get_thread(tid)->get_creation();
1018 * Returns the clock vector for a given thread.
1019 * @param tid The thread whose clock vector we want
1020 * @return Desired clock vector
1022 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1024 return get_parent_action(tid)->get_cv();
1028 * Resolve a set of Promises with a current write. The set is provided in the
1029 * Node corresponding to @a write.
1030 * @param write The ModelAction that is fulfilling Promises
1031 * @return True if promises were resolved; false otherwise
1033 bool ModelChecker::resolve_promises(ModelAction *write)
1035 bool resolved = false;
1037 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1038 Promise *promise = (*promises)[promise_index];
1039 if (write->get_node()->get_promise(i)) {
1040 ModelAction *read = promise->get_action();
1041 read->read_from(write);
1042 if (read->is_rmw()) {
1043 mo_graph->addRMWEdge(write, read);
1045 r_modification_order(read, write);
1046 post_r_modification_order(read, write);
1047 promises->erase(promises->begin() + promise_index);
1056 * Compute the set of promises that could potentially be satisfied by this
1057 * action. Note that the set computation actually appears in the Node, not in
1059 * @param curr The ModelAction that may satisfy promises
1061 void ModelChecker::compute_promises(ModelAction *curr)
1063 for (unsigned int i = 0; i < promises->size(); i++) {
1064 Promise *promise = (*promises)[i];
1065 const ModelAction *act = promise->get_action();
1066 if (!act->happens_before(curr) &&
1068 !act->is_synchronizing(curr) &&
1069 !act->same_thread(curr) &&
1070 promise->get_value() == curr->get_value()) {
1071 curr->get_node()->set_promise(i);
1076 /** Checks promises in response to change in ClockVector Threads. */
1077 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1079 for (unsigned int i = 0; i < promises->size(); i++) {
1080 Promise *promise = (*promises)[i];
1081 const ModelAction *act = promise->get_action();
1082 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1083 merge_cv->synchronized_since(act)) {
1084 //This thread is no longer able to send values back to satisfy the promise
1085 int num_synchronized_threads = promise->increment_threads();
1086 if (num_synchronized_threads == get_num_threads()) {
1087 //Promise has failed
1088 failed_promise = true;
1096 * Build up an initial set of all past writes that this 'read' action may read
1097 * from. This set is determined by the clock vector's "happens before"
1099 * @param curr is the current ModelAction that we are exploring; it must be a
1102 void ModelChecker::build_reads_from_past(ModelAction *curr)
1104 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1106 ASSERT(curr->is_read());
1108 ModelAction *last_seq_cst = NULL;
1110 /* Track whether this object has been initialized */
1111 bool initialized = false;
1113 if (curr->is_seqcst()) {
1114 last_seq_cst = get_last_seq_cst(curr->get_location());
1115 /* We have to at least see the last sequentially consistent write,
1116 so we are initialized. */
1117 if (last_seq_cst != NULL)
1121 /* Iterate over all threads */
1122 for (i = 0; i < thrd_lists->size(); i++) {
1123 /* Iterate over actions in thread, starting from most recent */
1124 action_list_t *list = &(*thrd_lists)[i];
1125 action_list_t::reverse_iterator rit;
1126 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1127 ModelAction *act = *rit;
1129 /* Only consider 'write' actions */
1130 if (!act->is_write())
1133 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1134 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1135 DEBUG("Adding action to may_read_from:\n");
1136 if (DBG_ENABLED()) {
1140 curr->get_node()->add_read_from(act);
1143 /* Include at most one act per-thread that "happens before" curr */
1144 if (act->happens_before(curr)) {
1152 /** @todo Need a more informative way of reporting errors. */
1153 printf("ERROR: may read from uninitialized atomic\n");
1156 if (DBG_ENABLED() || !initialized) {
1157 printf("Reached read action:\n");
1159 printf("Printing may_read_from\n");
1160 curr->get_node()->print_may_read_from();
1161 printf("End printing may_read_from\n");
1164 ASSERT(initialized);
1167 static void print_list(action_list_t *list)
1169 action_list_t::iterator it;
1171 printf("---------------------------------------------------------------------\n");
1174 for (it = list->begin(); it != list->end(); it++) {
1177 printf("---------------------------------------------------------------------\n");
1180 void ModelChecker::print_summary()
1183 printf("Number of executions: %d\n", num_executions);
1184 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1188 if (!isfinalfeasible())
1189 printf("INFEASIBLE EXECUTION!\n");
1190 print_list(action_trace);
1195 * Add a Thread to the system for the first time. Should only be called once
1197 * @param t The Thread to add
1199 void ModelChecker::add_thread(Thread *t)
1201 thread_map->put(id_to_int(t->get_id()), t);
1202 scheduler->add_thread(t);
1205 void ModelChecker::remove_thread(Thread *t)
1207 scheduler->remove_thread(t);
1211 * Switch from a user-context to the "master thread" context (a.k.a. system
1212 * context). This switch is made with the intention of exploring a particular
1213 * model-checking action (described by a ModelAction object). Must be called
1214 * from a user-thread context.
1215 * @param act The current action that will be explored. Must not be NULL.
1216 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1218 int ModelChecker::switch_to_master(ModelAction *act)
1221 Thread *old = thread_current();
1222 set_current_action(act);
1223 old->set_state(THREAD_READY);
1224 return Thread::swap(old, &system_context);
1228 * Takes the next step in the execution, if possible.
1229 * @return Returns true (success) if a step was taken and false otherwise.
1231 bool ModelChecker::take_step() {
1232 Thread *curr, *next;
1237 curr = thread_current();
1239 if (curr->get_state() == THREAD_READY) {
1240 ASSERT(priv->current_action);
1242 priv->nextThread = check_current_action(priv->current_action);
1243 priv->current_action = NULL;
1244 if (!curr->is_blocked() && !curr->is_complete())
1245 scheduler->add_thread(curr);
1250 next = scheduler->next_thread(priv->nextThread);
1252 /* Infeasible -> don't take any more steps */
1257 next->set_state(THREAD_RUNNING);
1258 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1260 /* next == NULL -> don't take any more steps */
1263 /* Return false only if swap fails with an error */
1264 return (Thread::swap(&system_context, next) == 0);
1267 /** Runs the current execution until threre are no more steps to take. */
1268 void ModelChecker::finish_execution() {
1271 while (take_step());