8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
15 #define INITIAL_THREAD_ID 0
19 /** @brief Constructor */
20 ModelChecker::ModelChecker(struct model_params params) :
21 /* Initialize default scheduler */
22 scheduler(new Scheduler()),
24 num_feasible_executions(0),
27 action_trace(new action_list_t()),
28 thread_map(new HashTable<int, Thread *, int>()),
29 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
30 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
31 promises(new std::vector<Promise *>()),
32 futurevalues(new std::vector<struct PendingFutureValue>()),
33 lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
34 thrd_last_action(new std::vector<ModelAction *>(1)),
35 node_stack(new NodeStack()),
36 mo_graph(new CycleGraph()),
37 failed_promise(false),
38 too_many_reads(false),
41 /* Allocate this "size" on the snapshotting heap */
42 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
43 /* First thread created will have id INITIAL_THREAD_ID */
44 priv->next_thread_id = INITIAL_THREAD_ID;
46 lazy_sync_size = &priv->lazy_sync_size;
49 /** @brief Destructor */
50 ModelChecker::~ModelChecker()
52 for (int i = 0; i < get_num_threads(); i++)
53 delete thread_map->get(i);
60 for (unsigned int i = 0; i < promises->size(); i++)
61 delete (*promises)[i];
64 delete lazy_sync_with_release;
66 delete thrd_last_action;
73 * Restores user program to initial state and resets all model-checker data
76 void ModelChecker::reset_to_initial_state()
78 DEBUG("+++ Resetting to initial state +++\n");
79 node_stack->reset_execution();
80 failed_promise = false;
81 too_many_reads = false;
83 snapshotObject->backTrackBeforeStep(0);
86 /** @returns a thread ID for a new Thread */
87 thread_id_t ModelChecker::get_next_id()
89 return priv->next_thread_id++;
92 /** @returns the number of user threads created during this execution */
93 int ModelChecker::get_num_threads()
95 return priv->next_thread_id;
98 /** @returns a sequence number for a new ModelAction */
99 modelclock_t ModelChecker::get_next_seq_num()
101 return ++priv->used_sequence_numbers;
105 * @brief Choose the next thread to execute.
107 * This function chooses the next thread that should execute. It can force the
108 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
109 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
110 * The model-checker may have no preference regarding the next thread (i.e.,
111 * when exploring a new execution ordering), in which case this will return
113 * @param curr The current ModelAction. This action might guide the choice of
115 * @return The next thread to run. If the model-checker has no preference, NULL.
117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
121 /* Do not split atomic actions. */
123 return thread_current();
124 /* The THREAD_CREATE action points to the created Thread */
125 else if (curr->get_type() == THREAD_CREATE)
126 return (Thread *)curr->get_location();
128 /* Have we completed exploring the preselected path? */
132 /* Else, we are trying to replay an execution */
133 ModelAction *next = node_stack->get_next()->get_action();
135 if (next == diverge) {
136 Node *nextnode = next->get_node();
137 /* Reached divergence point */
138 if (nextnode->increment_promise()) {
139 /* The next node will try to satisfy a different set of promises. */
140 tid = next->get_tid();
141 node_stack->pop_restofstack(2);
142 } else if (nextnode->increment_read_from()) {
143 /* The next node will read from a different value. */
144 tid = next->get_tid();
145 node_stack->pop_restofstack(2);
146 } else if (nextnode->increment_future_value()) {
147 /* The next node will try to read from a different future value. */
148 tid = next->get_tid();
149 node_stack->pop_restofstack(2);
151 /* Make a different thread execute for next step */
152 Node *node = nextnode->get_parent();
153 tid = node->get_next_backtrack();
154 node_stack->pop_restofstack(1);
156 DEBUG("*** Divergence point ***\n");
159 tid = next->get_tid();
161 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
162 ASSERT(tid != THREAD_ID_T_NONE);
163 return thread_map->get(id_to_int(tid));
167 * Queries the model-checker for more executions to explore and, if one
168 * exists, resets the model-checker state to execute a new execution.
170 * @return If there are more executions to explore, return true. Otherwise,
173 bool ModelChecker::next_execution()
178 if (isfinalfeasible())
179 num_feasible_executions++;
181 if (isfinalfeasible() || DBG_ENABLED())
184 if ((diverge = get_next_backtrack()) == NULL)
188 printf("Next execution will diverge at:\n");
192 reset_to_initial_state();
196 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
198 action_type type = act->get_type();
208 /* linear search: from most recent to oldest */
209 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
210 action_list_t::reverse_iterator rit;
211 for (rit = list->rbegin(); rit != list->rend(); rit++) {
212 ModelAction *prev = *rit;
213 if (act->is_synchronizing(prev))
219 void ModelChecker::set_backtracking(ModelAction *act)
223 Thread *t = get_thread(act);
225 prev = get_last_conflict(act);
229 node = prev->get_node()->get_parent();
231 while (!node->is_enabled(t))
234 /* Check if this has been explored already */
235 if (node->has_been_explored(t->get_id()))
238 /* Cache the latest backtracking point */
239 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
240 priv->next_backtrack = prev;
242 /* If this is a new backtracking point, mark the tree */
243 if (!node->set_backtrack(t->get_id()))
245 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
246 prev->get_tid(), t->get_id());
254 * Returns last backtracking point. The model checker will explore a different
255 * path for this point in the next execution.
256 * @return The ModelAction at which the next execution should diverge.
258 ModelAction * ModelChecker::get_next_backtrack()
260 ModelAction *next = priv->next_backtrack;
261 priv->next_backtrack = NULL;
266 * Processes a read or rmw model action.
267 * @param curr is the read model action to process.
268 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
269 * @return True if processing this read updates the mo_graph.
271 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
274 bool updated = false;
276 const ModelAction *reads_from = curr->get_node()->get_read_from();
277 if (reads_from != NULL) {
278 mo_graph->startChanges();
280 value = reads_from->get_value();
281 bool r_status = false;
283 if (!second_part_of_rmw) {
285 r_status = r_modification_order(curr, reads_from);
289 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
290 mo_graph->rollbackChanges();
291 too_many_reads = false;
295 curr->read_from(reads_from);
296 mo_graph->commitChanges();
298 } else if (!second_part_of_rmw) {
299 /* Read from future value */
300 value = curr->get_node()->get_future_value();
301 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
302 curr->read_from(NULL);
303 Promise *valuepromise = new Promise(curr, value, expiration);
304 promises->push_back(valuepromise);
306 get_thread(curr)->set_return_value(value);
312 * Process a write ModelAction
313 * @param curr The ModelAction to process
314 * @return True if the mo_graph was updated or promises were resolved
316 bool ModelChecker::process_write(ModelAction *curr)
318 bool updated_mod_order = w_modification_order(curr);
319 bool updated_promises = resolve_promises(curr);
321 if (promises->size() == 0) {
322 for (unsigned int i = 0; i<futurevalues->size(); i++) {
323 struct PendingFutureValue pfv = (*futurevalues)[i];
324 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
325 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
326 priv->next_backtrack = pfv.act;
328 futurevalues->resize(0);
331 mo_graph->commitChanges();
332 get_thread(curr)->set_return_value(VALUE_NONE);
333 return updated_mod_order || updated_promises;
337 * Initialize the current action by performing one or more of the following
338 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
339 * in the NodeStack, manipulating backtracking sets, allocating and
340 * initializing clock vectors, and computing the promises to fulfill.
342 * @param curr The current action, as passed from the user context; may be
343 * freed/invalidated after the execution of this function
344 * @return The current action, as processed by the ModelChecker. Is only the
345 * same as the parameter @a curr if this is a newly-explored action.
347 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
349 ModelAction *newcurr;
351 if (curr->is_rmwc() || curr->is_rmw()) {
352 newcurr = process_rmw(curr);
354 compute_promises(newcurr);
358 newcurr = node_stack->explore_action(curr);
360 /* First restore type and order in case of RMW operation */
362 newcurr->copy_typeandorder(curr);
364 /* Discard duplicate ModelAction; use action from NodeStack */
367 /* If we have diverged, we need to reset the clock vector. */
369 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
373 * Perform one-time actions when pushing new ModelAction onto
376 curr->create_cv(get_parent_action(curr->get_tid()));
377 if (curr->is_write())
378 compute_promises(curr);
384 * This is the heart of the model checker routine. It performs model-checking
385 * actions corresponding to a given "current action." Among other processes, it
386 * calculates reads-from relationships, updates synchronization clock vectors,
387 * forms a memory_order constraints graph, and handles replay/backtrack
388 * execution when running permutations of previously-observed executions.
390 * @param curr The current action to process
391 * @return The next Thread that must be executed. May be NULL if ModelChecker
392 * makes no choice (e.g., according to replay execution, combining RMW actions,
395 Thread * ModelChecker::check_current_action(ModelAction *curr)
399 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
401 ModelAction *newcurr = initialize_curr_action(curr);
403 /* Build may_read_from set for newly-created actions */
404 if (curr == newcurr && curr->is_read())
405 build_reads_from_past(curr);
408 /* Thread specific actions */
409 switch (curr->get_type()) {
410 case THREAD_CREATE: {
411 Thread *th = (Thread *)curr->get_location();
412 th->set_creation(curr);
416 Thread *waiting, *blocking;
417 waiting = get_thread(curr);
418 blocking = (Thread *)curr->get_location();
419 if (!blocking->is_complete()) {
420 blocking->push_wait_list(curr);
421 scheduler->sleep(waiting);
425 case THREAD_FINISH: {
426 Thread *th = get_thread(curr);
427 while (!th->wait_list_empty()) {
428 ModelAction *act = th->pop_wait_list();
429 Thread *wake = get_thread(act);
430 scheduler->wake(wake);
436 check_promises(NULL, curr->get_cv());
443 /* Add current action to lists before work_queue loop */
444 if (!second_part_of_rmw)
445 add_action_to_lists(curr);
447 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
449 while (!work_queue.empty()) {
450 WorkQueueEntry work = work_queue.front();
451 work_queue.pop_front();
454 case WORK_CHECK_CURR_ACTION: {
455 ModelAction *act = work.action;
456 bool updated = false;
457 if (act->is_read() && process_read(act, second_part_of_rmw))
460 if (act->is_write() && process_write(act))
464 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
467 case WORK_CHECK_RELEASE_SEQ:
468 resolve_release_sequences(work.location, &work_queue);
470 case WORK_CHECK_MO_EDGES: {
471 /** @todo Complete verification of work_queue */
472 ModelAction *act = work.action;
473 bool updated = false;
475 if (act->is_read()) {
476 if (r_modification_order(act, act->get_reads_from()))
479 if (act->is_write()) {
480 if (w_modification_order(act))
485 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
494 check_curr_backtracking(curr);
496 set_backtracking(curr);
498 return get_next_thread(curr);
501 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
502 Node *currnode = curr->get_node();
503 Node *parnode = currnode->get_parent();
505 if ((!parnode->backtrack_empty() ||
506 !currnode->read_from_empty() ||
507 !currnode->future_value_empty() ||
508 !currnode->promise_empty())
509 && (!priv->next_backtrack ||
510 *curr > *priv->next_backtrack)) {
511 priv->next_backtrack = curr;
515 bool ModelChecker::promises_expired() {
516 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
517 Promise *promise = (*promises)[promise_index];
518 if (promise->get_expiration()<priv->used_sequence_numbers) {
525 /** @returns whether the current partial trace must be a prefix of a
527 bool ModelChecker::isfeasibleprefix() {
528 return promises->size() == 0 && *lazy_sync_size == 0;
531 /** @returns whether the current partial trace is feasible. */
532 bool ModelChecker::isfeasible() {
533 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
536 /** @returns whether the current partial trace is feasible other than
537 * multiple RMW reading from the same store. */
538 bool ModelChecker::isfeasibleotherthanRMW() {
540 if (mo_graph->checkForCycles())
541 DEBUG("Infeasible: modification order cycles\n");
543 DEBUG("Infeasible: failed promise\n");
545 DEBUG("Infeasible: too many reads\n");
546 if (promises_expired())
547 DEBUG("Infeasible: promises expired\n");
549 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
552 /** Returns whether the current completed trace is feasible. */
553 bool ModelChecker::isfinalfeasible() {
554 if (DBG_ENABLED() && promises->size() != 0)
555 DEBUG("Infeasible: unrevolved promises\n");
557 return isfeasible() && promises->size() == 0;
560 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
561 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
562 int tid = id_to_int(act->get_tid());
563 ModelAction *lastread = get_last_action(tid);
564 lastread->process_rmw(act);
565 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
566 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
567 mo_graph->commitChanges();
573 * Checks whether a thread has read from the same write for too many times
574 * without seeing the effects of a later write.
577 * 1) there must a different write that we could read from that would satisfy the modification order,
578 * 2) we must have read from the same value in excess of maxreads times, and
579 * 3) that other write must have been in the reads_from set for maxreads times.
581 * If so, we decide that the execution is no longer feasible.
583 void ModelChecker::check_recency(ModelAction *curr) {
584 if (params.maxreads != 0) {
585 if (curr->get_node()->get_read_from_size() <= 1)
588 //Must make sure that execution is currently feasible... We could
589 //accidentally clear by rolling back
593 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
594 int tid = id_to_int(curr->get_tid());
597 if ((int)thrd_lists->size() <= tid)
600 action_list_t *list = &(*thrd_lists)[tid];
602 action_list_t::reverse_iterator rit = list->rbegin();
604 for (; (*rit) != curr; rit++)
606 /* go past curr now */
609 action_list_t::reverse_iterator ritcopy = rit;
610 //See if we have enough reads from the same value
612 for (; count < params.maxreads; rit++,count++) {
613 if (rit==list->rend())
615 ModelAction *act = *rit;
618 if (act->get_reads_from() != curr->get_reads_from())
620 if (act->get_node()->get_read_from_size() <= 1)
624 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
626 const ModelAction * write = curr->get_node()->get_read_from_at(i);
627 //Need a different write
628 if (write==curr->get_reads_from())
631 /* Test to see whether this is a feasible write to read from*/
632 mo_graph->startChanges();
633 r_modification_order(curr, write);
634 bool feasiblereadfrom = isfeasible();
635 mo_graph->rollbackChanges();
637 if (!feasiblereadfrom)
641 bool feasiblewrite = true;
642 //new we need to see if this write works for everyone
644 for (int loop = count; loop>0; loop--,rit++) {
645 ModelAction *act=*rit;
646 bool foundvalue = false;
647 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
648 if (act->get_node()->get_read_from_at(i)==write) {
654 feasiblewrite = false;
659 too_many_reads = true;
667 * Updates the mo_graph with the constraints imposed from the current
670 * Basic idea is the following: Go through each other thread and find
671 * the lastest action that happened before our read. Two cases:
673 * (1) The action is a write => that write must either occur before
674 * the write we read from or be the write we read from.
676 * (2) The action is a read => the write that that action read from
677 * must occur before the write we read from or be the same write.
679 * @param curr The current action. Must be a read.
680 * @param rf The action that curr reads from. Must be a write.
681 * @return True if modification order edges were added; false otherwise
683 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
685 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
688 ASSERT(curr->is_read());
690 /* Iterate over all threads */
691 for (i = 0; i < thrd_lists->size(); i++) {
692 /* Iterate over actions in thread, starting from most recent */
693 action_list_t *list = &(*thrd_lists)[i];
694 action_list_t::reverse_iterator rit;
695 for (rit = list->rbegin(); rit != list->rend(); rit++) {
696 ModelAction *act = *rit;
699 * Include at most one act per-thread that "happens
700 * before" curr. Don't consider reflexively.
702 if (act->happens_before(curr) && act != curr) {
703 if (act->is_write()) {
705 mo_graph->addEdge(act, rf);
709 const ModelAction *prevreadfrom = act->get_reads_from();
710 if (prevreadfrom != NULL && rf != prevreadfrom) {
711 mo_graph->addEdge(prevreadfrom, rf);
723 /** This method fixes up the modification order when we resolve a
724 * promises. The basic problem is that actions that occur after the
725 * read curr could not property add items to the modification order
728 * So for each thread, we find the earliest item that happens after
729 * the read curr. This is the item we have to fix up with additional
730 * constraints. If that action is write, we add a MO edge between
731 * the Action rf and that action. If the action is a read, we add a
732 * MO edge between the Action rf, and whatever the read accessed.
734 * @param curr is the read ModelAction that we are fixing up MO edges for.
735 * @param rf is the write ModelAction that curr reads from.
739 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
741 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
743 ASSERT(curr->is_read());
745 /* Iterate over all threads */
746 for (i = 0; i < thrd_lists->size(); i++) {
747 /* Iterate over actions in thread, starting from most recent */
748 action_list_t *list = &(*thrd_lists)[i];
749 action_list_t::reverse_iterator rit;
750 ModelAction *lastact = NULL;
752 /* Find last action that happens after curr */
753 for (rit = list->rbegin(); rit != list->rend(); rit++) {
754 ModelAction *act = *rit;
755 if (curr->happens_before(act)) {
761 /* Include at most one act per-thread that "happens before" curr */
762 if (lastact != NULL) {
763 if (lastact->is_read()) {
764 const ModelAction *postreadfrom = lastact->get_reads_from();
765 if (postreadfrom != NULL&&rf != postreadfrom)
766 mo_graph->addEdge(rf, postreadfrom);
767 } else if (rf != lastact) {
768 mo_graph->addEdge(rf, lastact);
776 * Updates the mo_graph with the constraints imposed from the current write.
778 * Basic idea is the following: Go through each other thread and find
779 * the lastest action that happened before our write. Two cases:
781 * (1) The action is a write => that write must occur before
784 * (2) The action is a read => the write that that action read from
785 * must occur before the current write.
787 * This method also handles two other issues:
789 * (I) Sequential Consistency: Making sure that if the current write is
790 * seq_cst, that it occurs after the previous seq_cst write.
792 * (II) Sending the write back to non-synchronizing reads.
794 * @param curr The current action. Must be a write.
795 * @return True if modification order edges were added; false otherwise
797 bool ModelChecker::w_modification_order(ModelAction *curr)
799 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
802 ASSERT(curr->is_write());
804 if (curr->is_seqcst()) {
805 /* We have to at least see the last sequentially consistent write,
806 so we are initialized. */
807 ModelAction *last_seq_cst = get_last_seq_cst(curr);
808 if (last_seq_cst != NULL) {
809 mo_graph->addEdge(last_seq_cst, curr);
814 /* Iterate over all threads */
815 for (i = 0; i < thrd_lists->size(); i++) {
816 /* Iterate over actions in thread, starting from most recent */
817 action_list_t *list = &(*thrd_lists)[i];
818 action_list_t::reverse_iterator rit;
819 for (rit = list->rbegin(); rit != list->rend(); rit++) {
820 ModelAction *act = *rit;
823 * If RMW, we already have all relevant edges,
824 * so just skip to next thread.
825 * If normal write, we need to look at earlier
826 * actions, so continue processing list.
835 * Include at most one act per-thread that "happens
838 if (act->happens_before(curr)) {
840 * Note: if act is RMW, just add edge:
842 * The following edge should be handled elsewhere:
843 * readfrom(act) --mo--> act
846 mo_graph->addEdge(act, curr);
847 else if (act->is_read() && act->get_reads_from() != NULL)
848 mo_graph->addEdge(act->get_reads_from(), curr);
851 } else if (act->is_read() && !act->is_synchronizing(curr) &&
852 !act->same_thread(curr)) {
853 /* We have an action that:
854 (1) did not happen before us
855 (2) is a read and we are a write
856 (3) cannot synchronize with us
857 (4) is in a different thread
859 that read could potentially read from our write.
861 if (thin_air_constraint_may_allow(curr, act)) {
863 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
864 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
865 futurevalues->push_back(pfv);
875 /** Arbitrary reads from the future are not allowed. Section 29.3
876 * part 9 places some constraints. This method checks one result of constraint
877 * constraint. Others require compiler support. */
879 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
880 if (!writer->is_rmw())
883 if (!reader->is_rmw())
886 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
889 if (search->get_tid() == reader->get_tid() &&
890 search->happens_before(reader))
898 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
899 * The ModelAction under consideration is expected to be taking part in
900 * release/acquire synchronization as an object of the "reads from" relation.
901 * Note that this can only provide release sequence support for RMW chains
902 * which do not read from the future, as those actions cannot be traced until
903 * their "promise" is fulfilled. Similarly, we may not even establish the
904 * presence of a release sequence with certainty, as some modification order
905 * constraints may be decided further in the future. Thus, this function
906 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
907 * and a boolean representing certainty.
909 * @todo Finish lazy updating, when promises are fulfilled in the future
910 * @param rf The action that might be part of a release sequence. Must be a
912 * @param release_heads A pass-by-reference style return parameter. After
913 * execution of this function, release_heads will contain the heads of all the
914 * relevant release sequences, if any exists
915 * @return true, if the ModelChecker is certain that release_heads is complete;
918 bool ModelChecker::release_seq_head(const ModelAction *rf,
919 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
922 /* read from future: need to settle this later */
923 return false; /* incomplete */
926 ASSERT(rf->is_write());
928 if (rf->is_release())
929 release_heads->push_back(rf);
931 /* We need a RMW action that is both an acquire and release to stop */
932 /** @todo Need to be smarter here... In the linux lock
933 * example, this will run to the beginning of the program for
935 if (rf->is_acquire() && rf->is_release())
936 return true; /* complete */
937 return release_seq_head(rf->get_reads_from(), release_heads);
939 if (rf->is_release())
940 return true; /* complete */
942 /* else relaxed write; check modification order for contiguous subsequence
943 * -> rf must be same thread as release */
944 int tid = id_to_int(rf->get_tid());
945 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
946 action_list_t *list = &(*thrd_lists)[tid];
947 action_list_t::const_reverse_iterator rit;
949 /* Find rf in the thread list */
950 rit = std::find(list->rbegin(), list->rend(), rf);
951 ASSERT(rit != list->rend());
953 /* Find the last write/release */
954 for (; rit != list->rend(); rit++)
955 if ((*rit)->is_release())
957 if (rit == list->rend()) {
958 /* No write-release in this thread */
959 return true; /* complete */
961 ModelAction *release = *rit;
963 ASSERT(rf->same_thread(release));
966 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
967 if (id_to_int(rf->get_tid()) == (int)i)
969 list = &(*thrd_lists)[i];
971 /* Can we ensure no future writes from this thread may break
972 * the release seq? */
973 bool future_ordered = false;
975 for (rit = list->rbegin(); rit != list->rend(); rit++) {
976 const ModelAction *act = *rit;
977 if (!act->is_write())
979 /* Reach synchronization -> this thread is complete */
980 if (act->happens_before(release))
982 if (rf->happens_before(act)) {
983 future_ordered = true;
987 /* Check modification order */
988 if (mo_graph->checkReachable(rf, act)) {
990 future_ordered = true;
993 if (mo_graph->checkReachable(act, release))
994 /* act --mo--> release */
996 if (mo_graph->checkReachable(release, act) &&
997 mo_graph->checkReachable(act, rf)) {
998 /* release --mo-> act --mo--> rf */
999 return true; /* complete */
1003 if (!future_ordered)
1004 return false; /* This thread is uncertain */
1008 release_heads->push_back(release);
1013 * A public interface for getting the release sequence head(s) with which a
1014 * given ModelAction must synchronize. This function only returns a non-empty
1015 * result when it can locate a release sequence head with certainty. Otherwise,
1016 * it may mark the internal state of the ModelChecker so that it will handle
1017 * the release sequence at a later time, causing @a act to update its
1018 * synchronization at some later point in execution.
1019 * @param act The 'acquire' action that may read from a release sequence
1020 * @param release_heads A pass-by-reference return parameter. Will be filled
1021 * with the head(s) of the release sequence(s), if they exists with certainty.
1022 * @see ModelChecker::release_seq_head
1024 void ModelChecker::get_release_seq_heads(ModelAction *act,
1025 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
1027 const ModelAction *rf = act->get_reads_from();
1029 complete = release_seq_head(rf, release_heads);
1031 /* add act to 'lazy checking' list */
1032 std::list<ModelAction *> *list;
1033 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1034 list->push_back(act);
1035 (*lazy_sync_size)++;
1040 * Attempt to resolve all stashed operations that might synchronize with a
1041 * release sequence for a given location. This implements the "lazy" portion of
1042 * determining whether or not a release sequence was contiguous, since not all
1043 * modification order information is present at the time an action occurs.
1045 * @param location The location/object that should be checked for release
1046 * sequence resolutions
1047 * @param work_queue The work queue to which to add work items as they are
1049 * @return True if any updates occurred (new synchronization, new mo_graph
1052 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1054 std::list<ModelAction *> *list;
1055 list = lazy_sync_with_release->getptr(location);
1059 bool updated = false;
1060 std::list<ModelAction *>::iterator it = list->begin();
1061 while (it != list->end()) {
1062 ModelAction *act = *it;
1063 const ModelAction *rf = act->get_reads_from();
1064 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1066 complete = release_seq_head(rf, &release_heads);
1067 for (unsigned int i = 0; i < release_heads.size(); i++) {
1068 if (!act->has_synchronized_with(release_heads[i])) {
1070 act->synchronize_with(release_heads[i]);
1075 /* Re-check act for mo_graph edges */
1076 work_queue->push_back(MOEdgeWorkEntry(act));
1078 /* propagate synchronization to later actions */
1079 action_list_t::reverse_iterator it = action_trace->rbegin();
1080 while ((*it) != act) {
1081 ModelAction *propagate = *it;
1082 if (act->happens_before(propagate)) {
1083 propagate->synchronize_with(act);
1084 /* Re-check 'propagate' for mo_graph edges */
1085 work_queue->push_back(MOEdgeWorkEntry(propagate));
1090 it = list->erase(it);
1091 (*lazy_sync_size)--;
1096 // If we resolved promises or data races, see if we have realized a data race.
1097 if (checkDataRaces()) {
1105 * Performs various bookkeeping operations for the current ModelAction. For
1106 * instance, adds action to the per-object, per-thread action vector and to the
1107 * action trace list of all thread actions.
1109 * @param act is the ModelAction to add.
1111 void ModelChecker::add_action_to_lists(ModelAction *act)
1113 int tid = id_to_int(act->get_tid());
1114 action_trace->push_back(act);
1116 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1118 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1119 if (tid >= (int)vec->size())
1120 vec->resize(priv->next_thread_id);
1121 (*vec)[tid].push_back(act);
1123 if ((int)thrd_last_action->size() <= tid)
1124 thrd_last_action->resize(get_num_threads());
1125 (*thrd_last_action)[tid] = act;
1128 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1130 int nthreads = get_num_threads();
1131 if ((int)thrd_last_action->size() < nthreads)
1132 thrd_last_action->resize(nthreads);
1133 return (*thrd_last_action)[id_to_int(tid)];
1137 * Gets the last memory_order_seq_cst write (in the total global sequence)
1138 * performed on a particular object (i.e., memory location), not including the
1140 * @param curr The current ModelAction; also denotes the object location to
1142 * @return The last seq_cst write
1144 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1146 void *location = curr->get_location();
1147 action_list_t *list = obj_map->get_safe_ptr(location);
1148 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1149 action_list_t::reverse_iterator rit;
1150 for (rit = list->rbegin(); rit != list->rend(); rit++)
1151 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1156 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1158 ModelAction *parent = get_last_action(tid);
1160 parent = get_thread(tid)->get_creation();
1165 * Returns the clock vector for a given thread.
1166 * @param tid The thread whose clock vector we want
1167 * @return Desired clock vector
1169 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1171 return get_parent_action(tid)->get_cv();
1175 * Resolve a set of Promises with a current write. The set is provided in the
1176 * Node corresponding to @a write.
1177 * @param write The ModelAction that is fulfilling Promises
1178 * @return True if promises were resolved; false otherwise
1180 bool ModelChecker::resolve_promises(ModelAction *write)
1182 bool resolved = false;
1184 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1185 Promise *promise = (*promises)[promise_index];
1186 if (write->get_node()->get_promise(i)) {
1187 ModelAction *read = promise->get_action();
1188 read->read_from(write);
1189 if (read->is_rmw()) {
1190 mo_graph->addRMWEdge(write, read);
1192 //First fix up the modification order for actions that happened
1194 r_modification_order(read, write);
1195 //Next fix up the modification order for actions that happened
1197 post_r_modification_order(read, write);
1198 promises->erase(promises->begin() + promise_index);
1207 * Compute the set of promises that could potentially be satisfied by this
1208 * action. Note that the set computation actually appears in the Node, not in
1210 * @param curr The ModelAction that may satisfy promises
1212 void ModelChecker::compute_promises(ModelAction *curr)
1214 for (unsigned int i = 0; i < promises->size(); i++) {
1215 Promise *promise = (*promises)[i];
1216 const ModelAction *act = promise->get_action();
1217 if (!act->happens_before(curr) &&
1219 !act->is_synchronizing(curr) &&
1220 !act->same_thread(curr) &&
1221 promise->get_value() == curr->get_value()) {
1222 curr->get_node()->set_promise(i);
1227 /** Checks promises in response to change in ClockVector Threads. */
1228 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1230 for (unsigned int i = 0; i < promises->size(); i++) {
1231 Promise *promise = (*promises)[i];
1232 const ModelAction *act = promise->get_action();
1233 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1234 merge_cv->synchronized_since(act)) {
1235 //This thread is no longer able to send values back to satisfy the promise
1236 int num_synchronized_threads = promise->increment_threads();
1237 if (num_synchronized_threads == get_num_threads()) {
1238 //Promise has failed
1239 failed_promise = true;
1247 * Build up an initial set of all past writes that this 'read' action may read
1248 * from. This set is determined by the clock vector's "happens before"
1250 * @param curr is the current ModelAction that we are exploring; it must be a
1253 void ModelChecker::build_reads_from_past(ModelAction *curr)
1255 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1257 ASSERT(curr->is_read());
1259 ModelAction *last_seq_cst = NULL;
1261 /* Track whether this object has been initialized */
1262 bool initialized = false;
1264 if (curr->is_seqcst()) {
1265 last_seq_cst = get_last_seq_cst(curr);
1266 /* We have to at least see the last sequentially consistent write,
1267 so we are initialized. */
1268 if (last_seq_cst != NULL)
1272 /* Iterate over all threads */
1273 for (i = 0; i < thrd_lists->size(); i++) {
1274 /* Iterate over actions in thread, starting from most recent */
1275 action_list_t *list = &(*thrd_lists)[i];
1276 action_list_t::reverse_iterator rit;
1277 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1278 ModelAction *act = *rit;
1280 /* Only consider 'write' actions */
1281 if (!act->is_write() || act == curr)
1284 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1285 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1286 DEBUG("Adding action to may_read_from:\n");
1287 if (DBG_ENABLED()) {
1291 curr->get_node()->add_read_from(act);
1294 /* Include at most one act per-thread that "happens before" curr */
1295 if (act->happens_before(curr)) {
1303 /** @todo Need a more informative way of reporting errors. */
1304 printf("ERROR: may read from uninitialized atomic\n");
1307 if (DBG_ENABLED() || !initialized) {
1308 printf("Reached read action:\n");
1310 printf("Printing may_read_from\n");
1311 curr->get_node()->print_may_read_from();
1312 printf("End printing may_read_from\n");
1315 ASSERT(initialized);
1318 static void print_list(action_list_t *list)
1320 action_list_t::iterator it;
1322 printf("---------------------------------------------------------------------\n");
1325 for (it = list->begin(); it != list->end(); it++) {
1328 printf("---------------------------------------------------------------------\n");
1331 void ModelChecker::print_summary()
1334 printf("Number of executions: %d\n", num_executions);
1335 printf("Number of feasible executions: %d\n", num_feasible_executions);
1336 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1338 #if SUPPORT_MOD_ORDER_DUMP
1340 char buffername[100];
1341 sprintf(buffername, "exec%u",num_executions);
1342 mo_graph->dumpGraphToFile(buffername);
1345 if (!isfinalfeasible())
1346 printf("INFEASIBLE EXECUTION!\n");
1347 print_list(action_trace);
1352 * Add a Thread to the system for the first time. Should only be called once
1354 * @param t The Thread to add
1356 void ModelChecker::add_thread(Thread *t)
1358 thread_map->put(id_to_int(t->get_id()), t);
1359 scheduler->add_thread(t);
1362 void ModelChecker::remove_thread(Thread *t)
1364 scheduler->remove_thread(t);
1368 * Switch from a user-context to the "master thread" context (a.k.a. system
1369 * context). This switch is made with the intention of exploring a particular
1370 * model-checking action (described by a ModelAction object). Must be called
1371 * from a user-thread context.
1372 * @param act The current action that will be explored. Must not be NULL.
1373 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1375 int ModelChecker::switch_to_master(ModelAction *act)
1378 Thread *old = thread_current();
1379 set_current_action(act);
1380 old->set_state(THREAD_READY);
1381 return Thread::swap(old, &system_context);
1385 * Takes the next step in the execution, if possible.
1386 * @return Returns true (success) if a step was taken and false otherwise.
1388 bool ModelChecker::take_step() {
1389 Thread *curr, *next;
1394 curr = thread_current();
1396 if (curr->get_state() == THREAD_READY) {
1397 ASSERT(priv->current_action);
1399 priv->nextThread = check_current_action(priv->current_action);
1400 priv->current_action = NULL;
1401 if (!curr->is_blocked() && !curr->is_complete())
1402 scheduler->add_thread(curr);
1407 next = scheduler->next_thread(priv->nextThread);
1409 /* Infeasible -> don't take any more steps */
1414 next->set_state(THREAD_RUNNING);
1415 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1417 /* next == NULL -> don't take any more steps */
1420 /* Return false only if swap fails with an error */
1421 return (Thread::swap(&system_context, next) == 0);
1424 /** Runs the current execution until threre are no more steps to take. */
1425 void ModelChecker::finish_execution() {
1428 while (take_step());