8 #include "snapshot-interface.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
16 #define INITIAL_THREAD_ID 0
20 /** @brief Constructor */
21 ModelChecker::ModelChecker(struct model_params params) :
22 /* Initialize default scheduler */
24 scheduler(new Scheduler()),
26 num_feasible_executions(0),
28 action_trace(new action_list_t()),
29 thread_map(new HashTable<int, Thread *, int>()),
30 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
31 lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
32 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
33 promises(new std::vector<Promise *>()),
34 futurevalues(new std::vector<struct PendingFutureValue>()),
35 pending_acq_rel_seq(new std::vector<ModelAction *>()),
36 thrd_last_action(new std::vector<ModelAction *>(1)),
37 node_stack(new NodeStack()),
38 mo_graph(new CycleGraph()),
39 failed_promise(false),
40 too_many_reads(false),
43 /* Allocate this "size" on the snapshotting heap */
44 priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
45 /* First thread created will have id INITIAL_THREAD_ID */
46 priv->next_thread_id = INITIAL_THREAD_ID;
49 /** @brief Destructor */
50 ModelChecker::~ModelChecker()
52 for (int i = 0; i < get_num_threads(); i++)
53 delete thread_map->get(i);
58 delete lock_waiters_map;
61 for (unsigned int i = 0; i < promises->size(); i++)
62 delete (*promises)[i];
65 delete pending_acq_rel_seq;
67 delete thrd_last_action;
74 * Restores user program to initial state and resets all model-checker data
77 void ModelChecker::reset_to_initial_state()
79 DEBUG("+++ Resetting to initial state +++\n");
80 node_stack->reset_execution();
81 failed_promise = false;
82 too_many_reads = false;
84 snapshotObject->backTrackBeforeStep(0);
87 /** @return a thread ID for a new Thread */
88 thread_id_t ModelChecker::get_next_id()
90 return priv->next_thread_id++;
93 /** @return the number of user threads created during this execution */
94 int ModelChecker::get_num_threads()
96 return priv->next_thread_id;
99 /** @return a sequence number for a new ModelAction */
100 modelclock_t ModelChecker::get_next_seq_num()
102 return ++priv->used_sequence_numbers;
106 * @brief Choose the next thread to execute.
108 * This function chooses the next thread that should execute. It can force the
109 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
110 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
111 * The model-checker may have no preference regarding the next thread (i.e.,
112 * when exploring a new execution ordering), in which case this will return
114 * @param curr The current ModelAction. This action might guide the choice of
116 * @return The next thread to run. If the model-checker has no preference, NULL.
118 Thread * ModelChecker::get_next_thread(ModelAction *curr)
123 /* Do not split atomic actions. */
125 return thread_current();
126 /* The THREAD_CREATE action points to the created Thread */
127 else if (curr->get_type() == THREAD_CREATE)
128 return (Thread *)curr->get_location();
131 /* Have we completed exploring the preselected path? */
135 /* Else, we are trying to replay an execution */
136 ModelAction *next = node_stack->get_next()->get_action();
138 if (next == diverge) {
139 Node *nextnode = next->get_node();
140 /* Reached divergence point */
141 if (nextnode->increment_promise()) {
142 /* The next node will try to satisfy a different set of promises. */
143 tid = next->get_tid();
144 node_stack->pop_restofstack(2);
145 } else if (nextnode->increment_read_from()) {
146 /* The next node will read from a different value. */
147 tid = next->get_tid();
148 node_stack->pop_restofstack(2);
149 } else if (nextnode->increment_future_value()) {
150 /* The next node will try to read from a different future value. */
151 tid = next->get_tid();
152 node_stack->pop_restofstack(2);
154 /* Make a different thread execute for next step */
155 Node *node = nextnode->get_parent();
156 tid = node->get_next_backtrack();
157 node_stack->pop_restofstack(1);
159 DEBUG("*** Divergence point ***\n");
162 tid = next->get_tid();
164 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
165 ASSERT(tid != THREAD_ID_T_NONE);
166 return thread_map->get(id_to_int(tid));
170 * Queries the model-checker for more executions to explore and, if one
171 * exists, resets the model-checker state to execute a new execution.
173 * @return If there are more executions to explore, return true. Otherwise,
176 bool ModelChecker::next_execution()
181 if (isfinalfeasible())
182 num_feasible_executions++;
184 if (isfinalfeasible() || DBG_ENABLED())
187 if ((diverge = get_next_backtrack()) == NULL)
191 printf("Next execution will diverge at:\n");
195 reset_to_initial_state();
199 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
201 switch (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 case ATOMIC_TRYLOCK: {
217 /* linear search: from most recent to oldest */
218 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
219 action_list_t::reverse_iterator rit;
220 for (rit = list->rbegin(); rit != list->rend(); rit++) {
221 ModelAction *prev = *rit;
222 if (act->is_conflicting_lock(prev))
227 case ATOMIC_UNLOCK: {
228 /* linear search: from most recent to oldest */
229 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
230 action_list_t::reverse_iterator rit;
231 for (rit = list->rbegin(); rit != list->rend(); rit++) {
232 ModelAction *prev = *rit;
233 if (!act->same_thread(prev)&&prev->is_failed_trylock())
244 /** This method find backtracking points where we should try to
245 * reorder the parameter ModelAction against.
247 * @param the ModelAction to find backtracking points for.
249 void ModelChecker::set_backtracking(ModelAction *act)
251 Thread *t = get_thread(act);
252 ModelAction * prev = get_last_conflict(act);
256 Node * node = prev->get_node()->get_parent();
258 int low_tid, high_tid;
259 if (node->is_enabled(t)) {
260 low_tid = id_to_int(act->get_tid());
261 high_tid = low_tid+1;
264 high_tid = get_num_threads();
267 for(int i = low_tid; i < high_tid; i++) {
268 thread_id_t tid = int_to_id(i);
269 if (!node->is_enabled(tid))
272 /* Check if this has been explored already */
273 if (node->has_been_explored(tid))
276 /* See if fairness allows */
277 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
279 for(int t=0;t<node->get_num_threads();t++) {
280 thread_id_t tother=int_to_id(t);
281 if (node->is_enabled(tother) && node->has_priority(tother)) {
290 /* Cache the latest backtracking point */
291 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
292 priv->next_backtrack = prev;
294 /* If this is a new backtracking point, mark the tree */
295 if (!node->set_backtrack(tid))
297 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
298 prev->get_tid(), t->get_id());
307 * Returns last backtracking point. The model checker will explore a different
308 * path for this point in the next execution.
309 * @return The ModelAction at which the next execution should diverge.
311 ModelAction * ModelChecker::get_next_backtrack()
313 ModelAction *next = priv->next_backtrack;
314 priv->next_backtrack = NULL;
319 * Processes a read or rmw model action.
320 * @param curr is the read model action to process.
321 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
322 * @return True if processing this read updates the mo_graph.
324 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
327 bool updated = false;
329 const ModelAction *reads_from = curr->get_node()->get_read_from();
330 if (reads_from != NULL) {
331 mo_graph->startChanges();
333 value = reads_from->get_value();
334 bool r_status = false;
336 if (!second_part_of_rmw) {
338 r_status = r_modification_order(curr, reads_from);
342 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
343 mo_graph->rollbackChanges();
344 too_many_reads = false;
348 curr->read_from(reads_from);
349 mo_graph->commitChanges();
351 } else if (!second_part_of_rmw) {
352 /* Read from future value */
353 value = curr->get_node()->get_future_value();
354 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
355 curr->read_from(NULL);
356 Promise *valuepromise = new Promise(curr, value, expiration);
357 promises->push_back(valuepromise);
359 get_thread(curr)->set_return_value(value);
365 * Processes a lock, trylock, or unlock model action. @param curr is
366 * the read model action to process.
368 * The try lock operation checks whether the lock is taken. If not,
369 * it falls to the normal lock operation case. If so, it returns
372 * The lock operation has already been checked that it is enabled, so
373 * it just grabs the lock and synchronizes with the previous unlock.
375 * The unlock operation has to re-enable all of the threads that are
376 * waiting on the lock.
378 void ModelChecker::process_mutex(ModelAction *curr) {
379 std::mutex *mutex = (std::mutex *)curr->get_location();
380 struct std::mutex_state *state = mutex->get_state();
381 switch (curr->get_type()) {
382 case ATOMIC_TRYLOCK: {
383 bool success = !state->islocked;
384 curr->set_try_lock(success);
386 get_thread(curr)->set_return_value(0);
389 get_thread(curr)->set_return_value(1);
391 //otherwise fall into the lock case
393 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
394 printf("Lock access before initialization\n");
397 state->islocked = true;
398 ModelAction *unlock = get_last_unlock(curr);
399 //synchronize with the previous unlock statement
401 curr->synchronize_with(unlock);
404 case ATOMIC_UNLOCK: {
406 state->islocked = false;
407 //wake up the other threads
408 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
409 //activate all the waiting threads
410 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
411 scheduler->add_thread(get_thread((*rit)->get_tid()));
422 * Process a write ModelAction
423 * @param curr The ModelAction to process
424 * @return True if the mo_graph was updated or promises were resolved
426 bool ModelChecker::process_write(ModelAction *curr)
428 bool updated_mod_order = w_modification_order(curr);
429 bool updated_promises = resolve_promises(curr);
431 if (promises->size() == 0) {
432 for (unsigned int i = 0; i < futurevalues->size(); i++) {
433 struct PendingFutureValue pfv = (*futurevalues)[i];
434 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
435 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
436 priv->next_backtrack = pfv.act;
438 futurevalues->resize(0);
441 mo_graph->commitChanges();
442 get_thread(curr)->set_return_value(VALUE_NONE);
443 return updated_mod_order || updated_promises;
447 * @brief Process the current action for thread-related activity
449 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
450 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
451 * synchronization, etc. This function is a no-op for non-THREAD actions
452 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
454 * @param curr The current action
455 * @return True if synchronization was updated
457 bool ModelChecker::process_thread_action(ModelAction *curr)
459 bool synchronized = false;
461 switch (curr->get_type()) {
462 case THREAD_CREATE: {
463 Thread *th = (Thread *)curr->get_location();
464 th->set_creation(curr);
468 Thread *waiting, *blocking;
469 waiting = get_thread(curr);
470 blocking = (Thread *)curr->get_location();
471 if (!blocking->is_complete()) {
472 blocking->push_wait_list(curr);
473 scheduler->sleep(waiting);
475 do_complete_join(curr);
480 case THREAD_FINISH: {
481 Thread *th = get_thread(curr);
482 while (!th->wait_list_empty()) {
483 ModelAction *act = th->pop_wait_list();
484 Thread *wake = get_thread(act);
485 scheduler->wake(wake);
486 do_complete_join(act);
493 check_promises(NULL, curr->get_cv());
504 * Initialize the current action by performing one or more of the following
505 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
506 * in the NodeStack, manipulating backtracking sets, allocating and
507 * initializing clock vectors, and computing the promises to fulfill.
509 * @param curr The current action, as passed from the user context; may be
510 * freed/invalidated after the execution of this function
511 * @return The current action, as processed by the ModelChecker. Is only the
512 * same as the parameter @a curr if this is a newly-explored action.
514 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
516 ModelAction *newcurr;
518 if (curr->is_rmwc() || curr->is_rmw()) {
519 newcurr = process_rmw(curr);
521 compute_promises(newcurr);
525 newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
527 /* First restore type and order in case of RMW operation */
529 newcurr->copy_typeandorder(curr);
531 ASSERT(curr->get_location() == newcurr->get_location());
532 newcurr->copy_from_new(curr);
534 /* Discard duplicate ModelAction; use action from NodeStack */
537 /* If we have diverged, we need to reset the clock vector. */
539 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
543 * Perform one-time actions when pushing new ModelAction onto
546 curr->create_cv(get_parent_action(curr->get_tid()));
547 if (curr->is_write())
548 compute_promises(curr);
554 * This method checks whether a model action is enabled at the given point.
555 * At this point, it checks whether a lock operation would be successful at this point.
556 * If not, it puts the thread in a waiter list.
557 * @param curr is the ModelAction to check whether it is enabled.
558 * @return a bool that indicates whether the action is enabled.
560 bool ModelChecker::check_action_enabled(ModelAction *curr) {
561 if (curr->is_lock()) {
562 std::mutex * lock = (std::mutex *)curr->get_location();
563 struct std::mutex_state * state = lock->get_state();
564 if (state->islocked) {
565 //Stick the action in the appropriate waiting queue
566 lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
575 * This is the heart of the model checker routine. It performs model-checking
576 * actions corresponding to a given "current action." Among other processes, it
577 * calculates reads-from relationships, updates synchronization clock vectors,
578 * forms a memory_order constraints graph, and handles replay/backtrack
579 * execution when running permutations of previously-observed executions.
581 * @param curr The current action to process
582 * @return The next Thread that must be executed. May be NULL if ModelChecker
583 * makes no choice (e.g., according to replay execution, combining RMW actions,
586 Thread * ModelChecker::check_current_action(ModelAction *curr)
590 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
592 if (!check_action_enabled(curr)) {
593 /* Make the execution look like we chose to run this action
594 * much later, when a lock is actually available to release */
595 get_current_thread()->set_pending(curr);
596 remove_thread(get_current_thread());
597 return get_next_thread(NULL);
600 ModelAction *newcurr = initialize_curr_action(curr);
602 /* Add the action to lists before any other model-checking tasks */
603 if (!second_part_of_rmw)
604 add_action_to_lists(newcurr);
606 /* Build may_read_from set for newly-created actions */
607 if (curr == newcurr && curr->is_read())
608 build_reads_from_past(curr);
611 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
613 while (!work_queue.empty()) {
614 WorkQueueEntry work = work_queue.front();
615 work_queue.pop_front();
618 case WORK_CHECK_CURR_ACTION: {
619 ModelAction *act = work.action;
620 bool updated = false;
622 process_thread_action(curr);
624 if (act->is_read() && process_read(act, second_part_of_rmw))
627 if (act->is_write() && process_write(act))
630 if (act->is_mutex_op())
634 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
637 case WORK_CHECK_RELEASE_SEQ:
638 resolve_release_sequences(work.location, &work_queue);
640 case WORK_CHECK_MO_EDGES: {
641 /** @todo Complete verification of work_queue */
642 ModelAction *act = work.action;
643 bool updated = false;
645 if (act->is_read()) {
646 if (r_modification_order(act, act->get_reads_from()))
649 if (act->is_write()) {
650 if (w_modification_order(act))
655 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
664 check_curr_backtracking(curr);
666 set_backtracking(curr);
668 return get_next_thread(curr);
672 * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
673 * operation from the Thread it is joining with. Must be called after the
674 * completion of the Thread in question.
675 * @param join The THREAD_JOIN action
677 void ModelChecker::do_complete_join(ModelAction *join)
679 Thread *blocking = (Thread *)join->get_location();
680 ModelAction *act = get_last_action(blocking->get_id());
681 join->synchronize_with(act);
684 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
685 Node *currnode = curr->get_node();
686 Node *parnode = currnode->get_parent();
688 if ((!parnode->backtrack_empty() ||
689 !currnode->read_from_empty() ||
690 !currnode->future_value_empty() ||
691 !currnode->promise_empty())
692 && (!priv->next_backtrack ||
693 *curr > *priv->next_backtrack)) {
694 priv->next_backtrack = curr;
698 bool ModelChecker::promises_expired() {
699 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
700 Promise *promise = (*promises)[promise_index];
701 if (promise->get_expiration()<priv->used_sequence_numbers) {
708 /** @return whether the current partial trace must be a prefix of a
710 bool ModelChecker::isfeasibleprefix() {
711 return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
714 /** @return whether the current partial trace is feasible. */
715 bool ModelChecker::isfeasible() {
716 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
719 /** @return whether the current partial trace is feasible other than
720 * multiple RMW reading from the same store. */
721 bool ModelChecker::isfeasibleotherthanRMW() {
723 if (mo_graph->checkForCycles())
724 DEBUG("Infeasible: modification order cycles\n");
726 DEBUG("Infeasible: failed promise\n");
728 DEBUG("Infeasible: too many reads\n");
729 if (promises_expired())
730 DEBUG("Infeasible: promises expired\n");
732 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
735 /** Returns whether the current completed trace is feasible. */
736 bool ModelChecker::isfinalfeasible() {
737 if (DBG_ENABLED() && promises->size() != 0)
738 DEBUG("Infeasible: unrevolved promises\n");
740 return isfeasible() && promises->size() == 0;
743 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
744 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
745 int tid = id_to_int(act->get_tid());
746 ModelAction *lastread = get_last_action(tid);
747 lastread->process_rmw(act);
748 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
749 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
750 mo_graph->commitChanges();
756 * Checks whether a thread has read from the same write for too many times
757 * without seeing the effects of a later write.
760 * 1) there must a different write that we could read from that would satisfy the modification order,
761 * 2) we must have read from the same value in excess of maxreads times, and
762 * 3) that other write must have been in the reads_from set for maxreads times.
764 * If so, we decide that the execution is no longer feasible.
766 void ModelChecker::check_recency(ModelAction *curr) {
767 if (params.maxreads != 0) {
768 if (curr->get_node()->get_read_from_size() <= 1)
771 //Must make sure that execution is currently feasible... We could
772 //accidentally clear by rolling back
776 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
777 int tid = id_to_int(curr->get_tid());
780 if ((int)thrd_lists->size() <= tid)
783 action_list_t *list = &(*thrd_lists)[tid];
785 action_list_t::reverse_iterator rit = list->rbegin();
787 for (; (*rit) != curr; rit++)
789 /* go past curr now */
792 action_list_t::reverse_iterator ritcopy = rit;
793 //See if we have enough reads from the same value
795 for (; count < params.maxreads; rit++,count++) {
796 if (rit==list->rend())
798 ModelAction *act = *rit;
801 if (act->get_reads_from() != curr->get_reads_from())
803 if (act->get_node()->get_read_from_size() <= 1)
807 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
809 const ModelAction * write = curr->get_node()->get_read_from_at(i);
810 //Need a different write
811 if (write==curr->get_reads_from())
814 /* Test to see whether this is a feasible write to read from*/
815 mo_graph->startChanges();
816 r_modification_order(curr, write);
817 bool feasiblereadfrom = isfeasible();
818 mo_graph->rollbackChanges();
820 if (!feasiblereadfrom)
824 bool feasiblewrite = true;
825 //new we need to see if this write works for everyone
827 for (int loop = count; loop>0; loop--,rit++) {
828 ModelAction *act=*rit;
829 bool foundvalue = false;
830 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
831 if (act->get_node()->get_read_from_at(i)==write) {
837 feasiblewrite = false;
842 too_many_reads = true;
850 * Updates the mo_graph with the constraints imposed from the current
853 * Basic idea is the following: Go through each other thread and find
854 * the lastest action that happened before our read. Two cases:
856 * (1) The action is a write => that write must either occur before
857 * the write we read from or be the write we read from.
859 * (2) The action is a read => the write that that action read from
860 * must occur before the write we read from or be the same write.
862 * @param curr The current action. Must be a read.
863 * @param rf The action that curr reads from. Must be a write.
864 * @return True if modification order edges were added; false otherwise
866 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
868 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
871 ASSERT(curr->is_read());
873 /* Iterate over all threads */
874 for (i = 0; i < thrd_lists->size(); i++) {
875 /* Iterate over actions in thread, starting from most recent */
876 action_list_t *list = &(*thrd_lists)[i];
877 action_list_t::reverse_iterator rit;
878 for (rit = list->rbegin(); rit != list->rend(); rit++) {
879 ModelAction *act = *rit;
882 * Include at most one act per-thread that "happens
883 * before" curr. Don't consider reflexively.
885 if (act->happens_before(curr) && act != curr) {
886 if (act->is_write()) {
888 mo_graph->addEdge(act, rf);
892 const ModelAction *prevreadfrom = act->get_reads_from();
893 if (prevreadfrom != NULL && rf != prevreadfrom) {
894 mo_graph->addEdge(prevreadfrom, rf);
906 /** This method fixes up the modification order when we resolve a
907 * promises. The basic problem is that actions that occur after the
908 * read curr could not property add items to the modification order
911 * So for each thread, we find the earliest item that happens after
912 * the read curr. This is the item we have to fix up with additional
913 * constraints. If that action is write, we add a MO edge between
914 * the Action rf and that action. If the action is a read, we add a
915 * MO edge between the Action rf, and whatever the read accessed.
917 * @param curr is the read ModelAction that we are fixing up MO edges for.
918 * @param rf is the write ModelAction that curr reads from.
921 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
923 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
925 ASSERT(curr->is_read());
927 /* Iterate over all threads */
928 for (i = 0; i < thrd_lists->size(); i++) {
929 /* Iterate over actions in thread, starting from most recent */
930 action_list_t *list = &(*thrd_lists)[i];
931 action_list_t::reverse_iterator rit;
932 ModelAction *lastact = NULL;
934 /* Find last action that happens after curr */
935 for (rit = list->rbegin(); rit != list->rend(); rit++) {
936 ModelAction *act = *rit;
937 if (curr->happens_before(act)) {
943 /* Include at most one act per-thread that "happens before" curr */
944 if (lastact != NULL) {
945 if (lastact->is_read()) {
946 const ModelAction *postreadfrom = lastact->get_reads_from();
947 if (postreadfrom != NULL&&rf != postreadfrom)
948 mo_graph->addEdge(rf, postreadfrom);
949 } else if (rf != lastact) {
950 mo_graph->addEdge(rf, lastact);
958 * Updates the mo_graph with the constraints imposed from the current write.
960 * Basic idea is the following: Go through each other thread and find
961 * the lastest action that happened before our write. Two cases:
963 * (1) The action is a write => that write must occur before
966 * (2) The action is a read => the write that that action read from
967 * must occur before the current write.
969 * This method also handles two other issues:
971 * (I) Sequential Consistency: Making sure that if the current write is
972 * seq_cst, that it occurs after the previous seq_cst write.
974 * (II) Sending the write back to non-synchronizing reads.
976 * @param curr The current action. Must be a write.
977 * @return True if modification order edges were added; false otherwise
979 bool ModelChecker::w_modification_order(ModelAction *curr)
981 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
984 ASSERT(curr->is_write());
986 if (curr->is_seqcst()) {
987 /* We have to at least see the last sequentially consistent write,
988 so we are initialized. */
989 ModelAction *last_seq_cst = get_last_seq_cst(curr);
990 if (last_seq_cst != NULL) {
991 mo_graph->addEdge(last_seq_cst, curr);
996 /* Iterate over all threads */
997 for (i = 0; i < thrd_lists->size(); i++) {
998 /* Iterate over actions in thread, starting from most recent */
999 action_list_t *list = &(*thrd_lists)[i];
1000 action_list_t::reverse_iterator rit;
1001 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1002 ModelAction *act = *rit;
1005 * If RMW, we already have all relevant edges,
1006 * so just skip to next thread.
1007 * If normal write, we need to look at earlier
1008 * actions, so continue processing list.
1017 * Include at most one act per-thread that "happens
1020 if (act->happens_before(curr)) {
1022 * Note: if act is RMW, just add edge:
1024 * The following edge should be handled elsewhere:
1025 * readfrom(act) --mo--> act
1027 if (act->is_write())
1028 mo_graph->addEdge(act, curr);
1029 else if (act->is_read() && act->get_reads_from() != NULL)
1030 mo_graph->addEdge(act->get_reads_from(), curr);
1033 } else if (act->is_read() && !act->is_synchronizing(curr) &&
1034 !act->same_thread(curr)) {
1035 /* We have an action that:
1036 (1) did not happen before us
1037 (2) is a read and we are a write
1038 (3) cannot synchronize with us
1039 (4) is in a different thread
1041 that read could potentially read from our write.
1043 if (thin_air_constraint_may_allow(curr, act)) {
1045 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1046 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1047 futurevalues->push_back(pfv);
1057 /** Arbitrary reads from the future are not allowed. Section 29.3
1058 * part 9 places some constraints. This method checks one result of constraint
1059 * constraint. Others require compiler support. */
1060 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1061 if (!writer->is_rmw())
1064 if (!reader->is_rmw())
1067 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1068 if (search == reader)
1070 if (search->get_tid() == reader->get_tid() &&
1071 search->happens_before(reader))
1079 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1080 * The ModelAction under consideration is expected to be taking part in
1081 * release/acquire synchronization as an object of the "reads from" relation.
1082 * Note that this can only provide release sequence support for RMW chains
1083 * which do not read from the future, as those actions cannot be traced until
1084 * their "promise" is fulfilled. Similarly, we may not even establish the
1085 * presence of a release sequence with certainty, as some modification order
1086 * constraints may be decided further in the future. Thus, this function
1087 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1088 * and a boolean representing certainty.
1090 * @todo Finish lazy updating, when promises are fulfilled in the future
1091 * @param rf The action that might be part of a release sequence. Must be a
1093 * @param release_heads A pass-by-reference style return parameter. After
1094 * execution of this function, release_heads will contain the heads of all the
1095 * relevant release sequences, if any exists
1096 * @return true, if the ModelChecker is certain that release_heads is complete;
1099 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1102 ASSERT(rf->is_write());
1104 if (rf->is_release())
1105 release_heads->push_back(rf);
1107 break; /* End of RMW chain */
1109 /** @todo Need to be smarter here... In the linux lock
1110 * example, this will run to the beginning of the program for
1112 /** @todo The way to be smarter here is to keep going until 1
1113 * thread has a release preceded by an acquire and you've seen
1116 /* acq_rel RMW is a sufficient stopping condition */
1117 if (rf->is_acquire() && rf->is_release())
1118 return true; /* complete */
1120 rf = rf->get_reads_from();
1123 /* read from future: need to settle this later */
1124 return false; /* incomplete */
1127 if (rf->is_release())
1128 return true; /* complete */
1130 /* else relaxed write; check modification order for contiguous subsequence
1131 * -> rf must be same thread as release */
1132 int tid = id_to_int(rf->get_tid());
1133 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1134 action_list_t *list = &(*thrd_lists)[tid];
1135 action_list_t::const_reverse_iterator rit;
1137 /* Find rf in the thread list */
1138 rit = std::find(list->rbegin(), list->rend(), rf);
1139 ASSERT(rit != list->rend());
1141 /* Find the last write/release */
1142 for (; rit != list->rend(); rit++)
1143 if ((*rit)->is_release())
1145 if (rit == list->rend()) {
1146 /* No write-release in this thread */
1147 return true; /* complete */
1149 ModelAction *release = *rit;
1151 ASSERT(rf->same_thread(release));
1153 bool certain = true;
1154 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1155 if (id_to_int(rf->get_tid()) == (int)i)
1157 list = &(*thrd_lists)[i];
1159 /* Can we ensure no future writes from this thread may break
1160 * the release seq? */
1161 bool future_ordered = false;
1163 ModelAction *last = get_last_action(int_to_id(i));
1164 if (last && (rf->happens_before(last) ||
1165 last->get_type() == THREAD_FINISH))
1166 future_ordered = true;
1168 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1169 const ModelAction *act = *rit;
1170 /* Reach synchronization -> this thread is complete */
1171 if (act->happens_before(release))
1173 if (rf->happens_before(act)) {
1174 future_ordered = true;
1178 /* Only writes can break release sequences */
1179 if (!act->is_write())
1182 /* Check modification order */
1183 if (mo_graph->checkReachable(rf, act)) {
1184 /* rf --mo--> act */
1185 future_ordered = true;
1188 if (mo_graph->checkReachable(act, release))
1189 /* act --mo--> release */
1191 if (mo_graph->checkReachable(release, act) &&
1192 mo_graph->checkReachable(act, rf)) {
1193 /* release --mo-> act --mo--> rf */
1194 return true; /* complete */
1198 if (!future_ordered)
1199 return false; /* This thread is uncertain */
1203 release_heads->push_back(release);
1208 * A public interface for getting the release sequence head(s) with which a
1209 * given ModelAction must synchronize. This function only returns a non-empty
1210 * result when it can locate a release sequence head with certainty. Otherwise,
1211 * it may mark the internal state of the ModelChecker so that it will handle
1212 * the release sequence at a later time, causing @a act to update its
1213 * synchronization at some later point in execution.
1214 * @param act The 'acquire' action that may read from a release sequence
1215 * @param release_heads A pass-by-reference return parameter. Will be filled
1216 * with the head(s) of the release sequence(s), if they exists with certainty.
1217 * @see ModelChecker::release_seq_head
1219 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1221 const ModelAction *rf = act->get_reads_from();
1223 complete = release_seq_head(rf, release_heads);
1225 /* add act to 'lazy checking' list */
1226 pending_acq_rel_seq->push_back(act);
1231 * Attempt to resolve all stashed operations that might synchronize with a
1232 * release sequence for a given location. This implements the "lazy" portion of
1233 * determining whether or not a release sequence was contiguous, since not all
1234 * modification order information is present at the time an action occurs.
1236 * @param location The location/object that should be checked for release
1237 * sequence resolutions. A NULL value means to check all locations.
1238 * @param work_queue The work queue to which to add work items as they are
1240 * @return True if any updates occurred (new synchronization, new mo_graph
1243 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1245 bool updated = false;
1246 std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
1247 while (it != pending_acq_rel_seq->end()) {
1248 ModelAction *act = *it;
1250 /* Only resolve sequences on the given location, if provided */
1251 if (location && act->get_location() != location) {
1256 const ModelAction *rf = act->get_reads_from();
1257 rel_heads_list_t release_heads;
1259 complete = release_seq_head(rf, &release_heads);
1260 for (unsigned int i = 0; i < release_heads.size(); i++) {
1261 if (!act->has_synchronized_with(release_heads[i])) {
1263 act->synchronize_with(release_heads[i]);
1268 /* Re-check act for mo_graph edges */
1269 work_queue->push_back(MOEdgeWorkEntry(act));
1271 /* propagate synchronization to later actions */
1272 action_list_t::reverse_iterator it = action_trace->rbegin();
1273 for (; (*it) != act; it++) {
1274 ModelAction *propagate = *it;
1275 if (act->happens_before(propagate)) {
1276 propagate->synchronize_with(act);
1277 /* Re-check 'propagate' for mo_graph edges */
1278 work_queue->push_back(MOEdgeWorkEntry(propagate));
1283 it = pending_acq_rel_seq->erase(it);
1288 // If we resolved promises or data races, see if we have realized a data race.
1289 if (checkDataRaces()) {
1297 * Performs various bookkeeping operations for the current ModelAction. For
1298 * instance, adds action to the per-object, per-thread action vector and to the
1299 * action trace list of all thread actions.
1301 * @param act is the ModelAction to add.
1303 void ModelChecker::add_action_to_lists(ModelAction *act)
1305 int tid = id_to_int(act->get_tid());
1306 action_trace->push_back(act);
1308 obj_map->get_safe_ptr(act->get_location())->push_back(act);
1310 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1311 if (tid >= (int)vec->size())
1312 vec->resize(priv->next_thread_id);
1313 (*vec)[tid].push_back(act);
1315 if ((int)thrd_last_action->size() <= tid)
1316 thrd_last_action->resize(get_num_threads());
1317 (*thrd_last_action)[tid] = act;
1321 * @brief Get the last action performed by a particular Thread
1322 * @param tid The thread ID of the Thread in question
1323 * @return The last action in the thread
1325 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1327 int threadid = id_to_int(tid);
1328 if (threadid < (int)thrd_last_action->size())
1329 return (*thrd_last_action)[id_to_int(tid)];
1335 * Gets the last memory_order_seq_cst write (in the total global sequence)
1336 * performed on a particular object (i.e., memory location), not including the
1338 * @param curr The current ModelAction; also denotes the object location to
1340 * @return The last seq_cst write
1342 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1344 void *location = curr->get_location();
1345 action_list_t *list = obj_map->get_safe_ptr(location);
1346 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1347 action_list_t::reverse_iterator rit;
1348 for (rit = list->rbegin(); rit != list->rend(); rit++)
1349 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1355 * Gets the last unlock operation performed on a particular mutex (i.e., memory
1356 * location). This function identifies the mutex according to the current
1357 * action, which is presumed to perform on the same mutex.
1358 * @param curr The current ModelAction; also denotes the object location to
1360 * @return The last unlock operation
1362 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1364 void *location = curr->get_location();
1365 action_list_t *list = obj_map->get_safe_ptr(location);
1366 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1367 action_list_t::reverse_iterator rit;
1368 for (rit = list->rbegin(); rit != list->rend(); rit++)
1369 if ((*rit)->is_unlock())
1374 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1376 ModelAction *parent = get_last_action(tid);
1378 parent = get_thread(tid)->get_creation();
1383 * Returns the clock vector for a given thread.
1384 * @param tid The thread whose clock vector we want
1385 * @return Desired clock vector
1387 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1389 return get_parent_action(tid)->get_cv();
1393 * Resolve a set of Promises with a current write. The set is provided in the
1394 * Node corresponding to @a write.
1395 * @param write The ModelAction that is fulfilling Promises
1396 * @return True if promises were resolved; false otherwise
1398 bool ModelChecker::resolve_promises(ModelAction *write)
1400 bool resolved = false;
1402 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1403 Promise *promise = (*promises)[promise_index];
1404 if (write->get_node()->get_promise(i)) {
1405 ModelAction *read = promise->get_action();
1406 read->read_from(write);
1407 if (read->is_rmw()) {
1408 mo_graph->addRMWEdge(write, read);
1410 //First fix up the modification order for actions that happened
1412 r_modification_order(read, write);
1413 //Next fix up the modification order for actions that happened
1415 post_r_modification_order(read, write);
1416 promises->erase(promises->begin() + promise_index);
1425 * Compute the set of promises that could potentially be satisfied by this
1426 * action. Note that the set computation actually appears in the Node, not in
1428 * @param curr The ModelAction that may satisfy promises
1430 void ModelChecker::compute_promises(ModelAction *curr)
1432 for (unsigned int i = 0; i < promises->size(); i++) {
1433 Promise *promise = (*promises)[i];
1434 const ModelAction *act = promise->get_action();
1435 if (!act->happens_before(curr) &&
1437 !act->is_synchronizing(curr) &&
1438 !act->same_thread(curr) &&
1439 promise->get_value() == curr->get_value()) {
1440 curr->get_node()->set_promise(i);
1445 /** Checks promises in response to change in ClockVector Threads. */
1446 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1448 for (unsigned int i = 0; i < promises->size(); i++) {
1449 Promise *promise = (*promises)[i];
1450 const ModelAction *act = promise->get_action();
1451 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1452 merge_cv->synchronized_since(act)) {
1453 //This thread is no longer able to send values back to satisfy the promise
1454 int num_synchronized_threads = promise->increment_threads();
1455 if (num_synchronized_threads == get_num_threads()) {
1456 //Promise has failed
1457 failed_promise = true;
1465 * Build up an initial set of all past writes that this 'read' action may read
1466 * from. This set is determined by the clock vector's "happens before"
1468 * @param curr is the current ModelAction that we are exploring; it must be a
1471 void ModelChecker::build_reads_from_past(ModelAction *curr)
1473 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1475 ASSERT(curr->is_read());
1477 ModelAction *last_seq_cst = NULL;
1479 /* Track whether this object has been initialized */
1480 bool initialized = false;
1482 if (curr->is_seqcst()) {
1483 last_seq_cst = get_last_seq_cst(curr);
1484 /* We have to at least see the last sequentially consistent write,
1485 so we are initialized. */
1486 if (last_seq_cst != NULL)
1490 /* Iterate over all threads */
1491 for (i = 0; i < thrd_lists->size(); i++) {
1492 /* Iterate over actions in thread, starting from most recent */
1493 action_list_t *list = &(*thrd_lists)[i];
1494 action_list_t::reverse_iterator rit;
1495 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1496 ModelAction *act = *rit;
1498 /* Only consider 'write' actions */
1499 if (!act->is_write() || act == curr)
1502 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1503 if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1504 DEBUG("Adding action to may_read_from:\n");
1505 if (DBG_ENABLED()) {
1509 curr->get_node()->add_read_from(act);
1512 /* Include at most one act per-thread that "happens before" curr */
1513 if (act->happens_before(curr)) {
1521 /** @todo Need a more informative way of reporting errors. */
1522 printf("ERROR: may read from uninitialized atomic\n");
1525 if (DBG_ENABLED() || !initialized) {
1526 printf("Reached read action:\n");
1528 printf("Printing may_read_from\n");
1529 curr->get_node()->print_may_read_from();
1530 printf("End printing may_read_from\n");
1533 ASSERT(initialized);
1536 static void print_list(action_list_t *list)
1538 action_list_t::iterator it;
1540 printf("---------------------------------------------------------------------\n");
1543 for (it = list->begin(); it != list->end(); it++) {
1546 printf("---------------------------------------------------------------------\n");
1549 void ModelChecker::print_summary()
1552 printf("Number of executions: %d\n", num_executions);
1553 printf("Number of feasible executions: %d\n", num_feasible_executions);
1554 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1556 #if SUPPORT_MOD_ORDER_DUMP
1558 char buffername[100];
1559 sprintf(buffername, "exec%04u", num_executions);
1560 mo_graph->dumpGraphToFile(buffername);
1563 if (!isfinalfeasible())
1564 printf("INFEASIBLE EXECUTION!\n");
1565 print_list(action_trace);
1570 * Add a Thread to the system for the first time. Should only be called once
1572 * @param t The Thread to add
1574 void ModelChecker::add_thread(Thread *t)
1576 thread_map->put(id_to_int(t->get_id()), t);
1577 scheduler->add_thread(t);
1581 * Removes a thread from the scheduler.
1582 * @param the thread to remove.
1584 void ModelChecker::remove_thread(Thread *t)
1586 scheduler->remove_thread(t);
1590 * Switch from a user-context to the "master thread" context (a.k.a. system
1591 * context). This switch is made with the intention of exploring a particular
1592 * model-checking action (described by a ModelAction object). Must be called
1593 * from a user-thread context.
1594 * @param act The current action that will be explored. Must not be NULL.
1595 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1597 int ModelChecker::switch_to_master(ModelAction *act)
1600 Thread *old = thread_current();
1601 set_current_action(act);
1602 old->set_state(THREAD_READY);
1603 return Thread::swap(old, &system_context);
1607 * Takes the next step in the execution, if possible.
1608 * @return Returns true (success) if a step was taken and false otherwise.
1610 bool ModelChecker::take_step() {
1614 Thread * curr = thread_current();
1616 if (curr->get_state() == THREAD_READY) {
1617 ASSERT(priv->current_action);
1619 priv->nextThread = check_current_action(priv->current_action);
1620 priv->current_action = NULL;
1621 if (curr->is_blocked() || curr->is_complete())
1622 scheduler->remove_thread(curr);
1627 Thread * next = scheduler->next_thread(priv->nextThread);
1629 /* Infeasible -> don't take any more steps */
1634 next->set_state(THREAD_RUNNING);
1635 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1637 /* next == NULL -> don't take any more steps */
1641 if ( next->get_pending() != NULL ) {
1642 //restart a pending action
1643 set_current_action(next->get_pending());
1644 next->set_pending(NULL);
1645 next->set_state(THREAD_READY);
1649 /* Return false only if swap fails with an error */
1650 return (Thread::swap(&system_context, next) == 0);
1653 /** Runs the current execution until threre are no more steps to take. */
1654 void ModelChecker::finish_execution() {
1657 while (take_step());