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) {
271 bool updated = false;
273 const ModelAction *reads_from = curr->get_node()->get_read_from();
274 if (reads_from != NULL) {
275 mo_graph->startChanges();
277 value = reads_from->get_value();
278 bool r_status = false;
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 bool updated = false;
397 if (curr->is_read()) {
398 updated = process_read(curr, get_thread(curr), second_part_of_rmw);
401 if (curr->is_write()) {
402 bool updated_mod_order = w_modification_order(curr);
403 bool updated_promises = resolve_promises(curr);
404 updated = updated || updated_mod_order || updated_promises;
406 if (promises->size()==0) {
407 for (unsigned int i = 0; i<futurevalues->size(); i++) {
408 struct PendingFutureValue pfv=(*futurevalues)[i];
409 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
410 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
411 priv->next_backtrack = pfv.act;
413 futurevalues->resize(0);
416 mo_graph->commitChanges();
417 get_thread(curr)->set_return_value(VALUE_NONE);
421 resolve_release_sequences(curr->get_location());
423 /* Add action to list. */
424 if (!second_part_of_rmw)
425 add_action_to_lists(curr);
427 check_curr_backtracking(curr);
429 set_backtracking(curr);
431 return get_next_thread(curr);
434 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
435 Node *currnode = curr->get_node();
436 Node *parnode = currnode->get_parent();
438 if ((!parnode->backtrack_empty() ||
439 !currnode->read_from_empty() ||
440 !currnode->future_value_empty() ||
441 !currnode->promise_empty())
442 && (!priv->next_backtrack ||
443 *curr > *priv->next_backtrack)) {
444 priv->next_backtrack = curr;
448 bool ModelChecker::promises_expired() {
449 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
450 Promise *promise = (*promises)[promise_index];
451 if (promise->get_expiration()<priv->used_sequence_numbers) {
458 /** @returns whether the current partial trace must be a prefix of a
460 bool ModelChecker::isfeasibleprefix() {
461 return promises->size() == 0 && *lazy_sync_size == 0;
464 /** @returns whether the current partial trace is feasible. */
465 bool ModelChecker::isfeasible() {
466 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
469 /** @returns whether the current partial trace is feasible other than
470 * multiple RMW reading from the same store. */
471 bool ModelChecker::isfeasibleotherthanRMW() {
472 return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
475 /** Returns whether the current completed trace is feasible. */
476 bool ModelChecker::isfinalfeasible() {
477 return isfeasible() && promises->size() == 0;
480 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
481 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
482 int tid = id_to_int(act->get_tid());
483 ModelAction *lastread = get_last_action(tid);
484 lastread->process_rmw(act);
485 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
486 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
487 mo_graph->commitChanges();
493 * Checks whether a thread has read from the same write for too many times
494 * without seeing the effects of a later write.
497 * 1) there must a different write that we could read from that would satisfy the modification order,
498 * 2) we must have read from the same value in excess of maxreads times, and
499 * 3) that other write must have been in the reads_from set for maxreads times.
501 * If so, we decide that the execution is no longer feasible.
503 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
504 if (params.maxreads != 0) {
505 if (curr->get_node()->get_read_from_size() <= 1)
508 //Must make sure that execution is currently feasible... We could
509 //accidentally clear by rolling back
513 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
514 int tid = id_to_int(curr->get_tid());
517 if ((int)thrd_lists->size() <= tid)
520 action_list_t *list = &(*thrd_lists)[tid];
522 action_list_t::reverse_iterator rit = list->rbegin();
525 for (; (*rit) != curr; rit++)
527 /* go past curr now */
531 action_list_t::reverse_iterator ritcopy = rit;
532 //See if we have enough reads from the same value
534 for (; count < params.maxreads; rit++,count++) {
535 if (rit==list->rend())
537 ModelAction *act = *rit;
540 if (act->get_reads_from() != curr->get_reads_from())
542 if (act->get_node()->get_read_from_size() <= 1)
546 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
548 const ModelAction * write = curr->get_node()->get_read_from_at(i);
549 //Need a different write
550 if (write==curr->get_reads_from())
553 /* Test to see whether this is a feasible write to read from*/
554 mo_graph->startChanges();
555 r_modification_order(curr, write);
556 bool feasiblereadfrom = isfeasible();
557 mo_graph->rollbackChanges();
559 if (!feasiblereadfrom)
563 bool feasiblewrite = true;
564 //new we need to see if this write works for everyone
566 for (int loop = count; loop>0; loop--,rit++) {
567 ModelAction *act=*rit;
568 bool foundvalue = false;
569 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
570 if (act->get_node()->get_read_from_at(i)==write) {
576 feasiblewrite = false;
581 too_many_reads = true;
589 * Updates the mo_graph with the constraints imposed from the current read.
590 * @param curr The current action. Must be a read.
591 * @param rf The action that curr reads from. Must be a write.
592 * @return True if modification order edges were added; false otherwise
594 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
596 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
599 ASSERT(curr->is_read());
601 /* Iterate over all threads */
602 for (i = 0; i < thrd_lists->size(); i++) {
603 /* Iterate over actions in thread, starting from most recent */
604 action_list_t *list = &(*thrd_lists)[i];
605 action_list_t::reverse_iterator rit;
606 for (rit = list->rbegin(); rit != list->rend(); rit++) {
607 ModelAction *act = *rit;
609 /* Include at most one act per-thread that "happens before" curr */
610 if (act->happens_before(curr)) {
611 if (act->is_write()) {
612 if (rf != act && act != curr) {
613 mo_graph->addEdge(act, rf);
617 const ModelAction *prevreadfrom = act->get_reads_from();
618 if (prevreadfrom != NULL && rf != prevreadfrom) {
619 mo_graph->addEdge(prevreadfrom, rf);
632 /** Updates the mo_graph with the constraints imposed from the current read. */
633 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
635 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
637 ASSERT(curr->is_read());
639 /* Iterate over all threads */
640 for (i = 0; i < thrd_lists->size(); i++) {
641 /* Iterate over actions in thread, starting from most recent */
642 action_list_t *list = &(*thrd_lists)[i];
643 action_list_t::reverse_iterator rit;
644 ModelAction *lastact = NULL;
646 /* Find last action that happens after curr */
647 for (rit = list->rbegin(); rit != list->rend(); rit++) {
648 ModelAction *act = *rit;
649 if (curr->happens_before(act)) {
655 /* Include at most one act per-thread that "happens before" curr */
656 if (lastact != NULL) {
657 if (lastact->is_read()) {
658 const ModelAction *postreadfrom = lastact->get_reads_from();
659 if (postreadfrom != NULL&&rf != postreadfrom)
660 mo_graph->addEdge(rf, postreadfrom);
661 } else if (rf != lastact) {
662 mo_graph->addEdge(rf, lastact);
670 * Updates the mo_graph with the constraints imposed from the current write.
671 * @param curr The current action. Must be a write.
672 * @return True if modification order edges were added; false otherwise
674 bool ModelChecker::w_modification_order(ModelAction *curr)
676 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
679 ASSERT(curr->is_write());
681 if (curr->is_seqcst()) {
682 /* We have to at least see the last sequentially consistent write,
683 so we are initialized. */
684 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
685 if (last_seq_cst != NULL) {
686 mo_graph->addEdge(last_seq_cst, curr);
691 /* Iterate over all threads */
692 for (i = 0; i < thrd_lists->size(); i++) {
693 /* Iterate over actions in thread, starting from most recent */
694 action_list_t *list = &(*thrd_lists)[i];
695 action_list_t::reverse_iterator rit;
696 for (rit = list->rbegin(); rit != list->rend(); rit++) {
697 ModelAction *act = *rit;
699 /* Include at most one act per-thread that "happens before" curr */
700 if (act->happens_before(curr)) {
702 * Note: if act is RMW, just add edge:
704 * The following edge should be handled elsewhere:
705 * readfrom(act) --mo--> act
707 if (act->is_write()) {
708 //RMW shouldn't have an edge to themselves
710 mo_graph->addEdge(act, curr);
711 } else if (act->is_read() && act->get_reads_from() != NULL)
712 mo_graph->addEdge(act->get_reads_from(), curr);
715 } else if (act->is_read() && !act->is_synchronizing(curr) &&
716 !act->same_thread(curr)) {
717 /* We have an action that:
718 (1) did not happen before us
719 (2) is a read and we are a write
720 (3) cannot synchronize with us
721 (4) is in a different thread
723 that read could potentially read from our write.
725 if (thin_air_constraint_may_allow(curr, act)) {
727 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
728 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
729 futurevalues->push_back(pfv);
739 /** Arbitrary reads from the future are not allowed. Section 29.3
740 * part 9 places some constraints. This method checks one result of constraint
741 * constraint. Others require compiler support. */
743 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
744 if (!writer->is_rmw())
747 if (!reader->is_rmw())
750 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
753 if (search->get_tid() == reader->get_tid() &&
754 search->happens_before(reader))
762 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
763 * The ModelAction under consideration is expected to be taking part in
764 * release/acquire synchronization as an object of the "reads from" relation.
765 * Note that this can only provide release sequence support for RMW chains
766 * which do not read from the future, as those actions cannot be traced until
767 * their "promise" is fulfilled. Similarly, we may not even establish the
768 * presence of a release sequence with certainty, as some modification order
769 * constraints may be decided further in the future. Thus, this function
770 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
771 * and a boolean representing certainty.
773 * @todo Finish lazy updating, when promises are fulfilled in the future
774 * @param rf The action that might be part of a release sequence. Must be a
776 * @param release_heads A pass-by-reference style return parameter. After
777 * execution of this function, release_heads will contain the heads of all the
778 * relevant release sequences, if any exists
779 * @return true, if the ModelChecker is certain that release_heads is complete;
782 bool ModelChecker::release_seq_head(const ModelAction *rf,
783 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
786 /* read from future: need to settle this later */
787 return false; /* incomplete */
790 ASSERT(rf->is_write());
792 if (rf->is_release())
793 release_heads->push_back(rf);
795 /* We need a RMW action that is both an acquire and release to stop */
796 /** @todo Need to be smarter here... In the linux lock
797 * example, this will run to the beginning of the program for
799 if (rf->is_acquire() && rf->is_release())
800 return true; /* complete */
801 return release_seq_head(rf->get_reads_from(), release_heads);
803 if (rf->is_release())
804 return true; /* complete */
806 /* else relaxed write; check modification order for contiguous subsequence
807 * -> rf must be same thread as release */
808 int tid = id_to_int(rf->get_tid());
809 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
810 action_list_t *list = &(*thrd_lists)[tid];
811 action_list_t::const_reverse_iterator rit;
813 /* Find rf in the thread list */
814 rit = std::find(list->rbegin(), list->rend(), rf);
815 ASSERT(rit != list->rend());
817 /* Find the last write/release */
818 for (; rit != list->rend(); rit++)
819 if ((*rit)->is_release())
821 if (rit == list->rend()) {
822 /* No write-release in this thread */
823 return true; /* complete */
825 ModelAction *release = *rit;
827 ASSERT(rf->same_thread(release));
830 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
831 if (id_to_int(rf->get_tid()) == (int)i)
833 list = &(*thrd_lists)[i];
835 /* Can we ensure no future writes from this thread may break
836 * the release seq? */
837 bool future_ordered = false;
839 for (rit = list->rbegin(); rit != list->rend(); rit++) {
840 const ModelAction *act = *rit;
841 if (!act->is_write())
843 /* Reach synchronization -> this thread is complete */
844 if (act->happens_before(release))
846 if (rf->happens_before(act)) {
847 future_ordered = true;
851 /* Check modification order */
852 if (mo_graph->checkReachable(rf, act)) {
854 future_ordered = true;
857 if (mo_graph->checkReachable(act, release))
858 /* act --mo--> release */
860 if (mo_graph->checkReachable(release, act) &&
861 mo_graph->checkReachable(act, rf)) {
862 /* release --mo-> act --mo--> rf */
863 return true; /* complete */
868 return false; /* This thread is uncertain */
872 release_heads->push_back(release);
877 * A public interface for getting the release sequence head(s) with which a
878 * given ModelAction must synchronize. This function only returns a non-empty
879 * result when it can locate a release sequence head with certainty. Otherwise,
880 * it may mark the internal state of the ModelChecker so that it will handle
881 * the release sequence at a later time, causing @a act to update its
882 * synchronization at some later point in execution.
883 * @param act The 'acquire' action that may read from a release sequence
884 * @param release_heads A pass-by-reference return parameter. Will be filled
885 * with the head(s) of the release sequence(s), if they exists with certainty.
886 * @see ModelChecker::release_seq_head
888 void ModelChecker::get_release_seq_heads(ModelAction *act,
889 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
891 const ModelAction *rf = act->get_reads_from();
893 complete = release_seq_head(rf, release_heads);
895 /* add act to 'lazy checking' list */
896 std::list<ModelAction *> *list;
897 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
898 list->push_back(act);
904 * Attempt to resolve all stashed operations that might synchronize with a
905 * release sequence for a given location. This implements the "lazy" portion of
906 * determining whether or not a release sequence was contiguous, since not all
907 * modification order information is present at the time an action occurs.
909 * @param location The location/object that should be checked for release
910 * sequence resolutions
911 * @return True if any updates occurred (new synchronization, new mo_graph edges)
913 bool ModelChecker::resolve_release_sequences(void *location)
915 std::list<ModelAction *> *list;
916 list = lazy_sync_with_release->getptr(location);
920 bool updated = false;
921 std::list<ModelAction *>::iterator it = list->begin();
922 while (it != list->end()) {
923 ModelAction *act = *it;
924 const ModelAction *rf = act->get_reads_from();
925 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
927 complete = release_seq_head(rf, &release_heads);
928 for (unsigned int i = 0; i < release_heads.size(); i++) {
929 if (!act->has_synchronized_with(release_heads[i])) {
931 act->synchronize_with(release_heads[i]);
936 /* propagate synchronization to later actions */
937 action_list_t::reverse_iterator it = action_trace->rbegin();
938 while ((*it) != act) {
939 ModelAction *propagate = *it;
940 if (act->happens_before(propagate))
941 /** @todo new mo_graph edges along with
942 * this synchronization? */
943 propagate->synchronize_with(act);
947 it = list->erase(it);
953 // If we resolved promises or data races, see if we have realized a data race.
954 if (checkDataRaces()) {
962 * Performs various bookkeeping operations for the current ModelAction. For
963 * instance, adds action to the per-object, per-thread action vector and to the
964 * action trace list of all thread actions.
966 * @param act is the ModelAction to add.
968 void ModelChecker::add_action_to_lists(ModelAction *act)
970 int tid = id_to_int(act->get_tid());
971 action_trace->push_back(act);
973 obj_map->get_safe_ptr(act->get_location())->push_back(act);
975 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
976 if (tid >= (int)vec->size())
977 vec->resize(priv->next_thread_id);
978 (*vec)[tid].push_back(act);
980 if ((int)thrd_last_action->size() <= tid)
981 thrd_last_action->resize(get_num_threads());
982 (*thrd_last_action)[tid] = act;
985 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
987 int nthreads = get_num_threads();
988 if ((int)thrd_last_action->size() < nthreads)
989 thrd_last_action->resize(nthreads);
990 return (*thrd_last_action)[id_to_int(tid)];
994 * Gets the last memory_order_seq_cst action (in the total global sequence)
995 * performed on a particular object (i.e., memory location).
996 * @param location The object location to check
997 * @return The last seq_cst action performed
999 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1001 action_list_t *list = obj_map->get_safe_ptr(location);
1002 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1003 action_list_t::reverse_iterator rit;
1004 for (rit = list->rbegin(); rit != list->rend(); rit++)
1005 if ((*rit)->is_write() && (*rit)->is_seqcst())
1010 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1012 ModelAction *parent = get_last_action(tid);
1014 parent = get_thread(tid)->get_creation();
1019 * Returns the clock vector for a given thread.
1020 * @param tid The thread whose clock vector we want
1021 * @return Desired clock vector
1023 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1025 return get_parent_action(tid)->get_cv();
1029 * Resolve a set of Promises with a current write. The set is provided in the
1030 * Node corresponding to @a write.
1031 * @param write The ModelAction that is fulfilling Promises
1032 * @return True if promises were resolved; false otherwise
1034 bool ModelChecker::resolve_promises(ModelAction *write)
1036 bool resolved = false;
1038 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1039 Promise *promise = (*promises)[promise_index];
1040 if (write->get_node()->get_promise(i)) {
1041 ModelAction *read = promise->get_action();
1042 read->read_from(write);
1043 if (read->is_rmw()) {
1044 mo_graph->addRMWEdge(write, read);
1046 r_modification_order(read, write);
1047 post_r_modification_order(read, write);
1048 promises->erase(promises->begin() + promise_index);
1057 * Compute the set of promises that could potentially be satisfied by this
1058 * action. Note that the set computation actually appears in the Node, not in
1060 * @param curr The ModelAction that may satisfy promises
1062 void ModelChecker::compute_promises(ModelAction *curr)
1064 for (unsigned int i = 0; i < promises->size(); i++) {
1065 Promise *promise = (*promises)[i];
1066 const ModelAction *act = promise->get_action();
1067 if (!act->happens_before(curr) &&
1069 !act->is_synchronizing(curr) &&
1070 !act->same_thread(curr) &&
1071 promise->get_value() == curr->get_value()) {
1072 curr->get_node()->set_promise(i);
1077 /** Checks promises in response to change in ClockVector Threads. */
1078 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1080 for (unsigned int i = 0; i < promises->size(); i++) {
1081 Promise *promise = (*promises)[i];
1082 const ModelAction *act = promise->get_action();
1083 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1084 merge_cv->synchronized_since(act)) {
1085 //This thread is no longer able to send values back to satisfy the promise
1086 int num_synchronized_threads = promise->increment_threads();
1087 if (num_synchronized_threads == get_num_threads()) {
1088 //Promise has failed
1089 failed_promise = true;
1097 * Build up an initial set of all past writes that this 'read' action may read
1098 * from. This set is determined by the clock vector's "happens before"
1100 * @param curr is the current ModelAction that we are exploring; it must be a
1103 void ModelChecker::build_reads_from_past(ModelAction *curr)
1105 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1107 ASSERT(curr->is_read());
1109 ModelAction *last_seq_cst = NULL;
1111 /* Track whether this object has been initialized */
1112 bool initialized = false;
1114 if (curr->is_seqcst()) {
1115 last_seq_cst = get_last_seq_cst(curr->get_location());
1116 /* We have to at least see the last sequentially consistent write,
1117 so we are initialized. */
1118 if (last_seq_cst != NULL)
1122 /* Iterate over all threads */
1123 for (i = 0; i < thrd_lists->size(); i++) {
1124 /* Iterate over actions in thread, starting from most recent */
1125 action_list_t *list = &(*thrd_lists)[i];
1126 action_list_t::reverse_iterator rit;
1127 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1128 ModelAction *act = *rit;
1130 /* Only consider 'write' actions */
1131 if (!act->is_write())
1134 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1135 if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1136 DEBUG("Adding action to may_read_from:\n");
1137 if (DBG_ENABLED()) {
1141 curr->get_node()->add_read_from(act);
1144 /* Include at most one act per-thread that "happens before" curr */
1145 if (act->happens_before(curr)) {
1153 /** @todo Need a more informative way of reporting errors. */
1154 printf("ERROR: may read from uninitialized atomic\n");
1157 if (DBG_ENABLED() || !initialized) {
1158 printf("Reached read action:\n");
1160 printf("Printing may_read_from\n");
1161 curr->get_node()->print_may_read_from();
1162 printf("End printing may_read_from\n");
1165 ASSERT(initialized);
1168 static void print_list(action_list_t *list)
1170 action_list_t::iterator it;
1172 printf("---------------------------------------------------------------------\n");
1175 for (it = list->begin(); it != list->end(); it++) {
1178 printf("---------------------------------------------------------------------\n");
1181 void ModelChecker::print_summary()
1184 printf("Number of executions: %d\n", num_executions);
1185 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1189 if (!isfinalfeasible())
1190 printf("INFEASIBLE EXECUTION!\n");
1191 print_list(action_trace);
1196 * Add a Thread to the system for the first time. Should only be called once
1198 * @param t The Thread to add
1200 void ModelChecker::add_thread(Thread *t)
1202 thread_map->put(id_to_int(t->get_id()), t);
1203 scheduler->add_thread(t);
1206 void ModelChecker::remove_thread(Thread *t)
1208 scheduler->remove_thread(t);
1212 * Switch from a user-context to the "master thread" context (a.k.a. system
1213 * context). This switch is made with the intention of exploring a particular
1214 * model-checking action (described by a ModelAction object). Must be called
1215 * from a user-thread context.
1216 * @param act The current action that will be explored. Must not be NULL.
1217 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1219 int ModelChecker::switch_to_master(ModelAction *act)
1222 Thread *old = thread_current();
1223 set_current_action(act);
1224 old->set_state(THREAD_READY);
1225 return Thread::swap(old, &system_context);
1229 * Takes the next step in the execution, if possible.
1230 * @return Returns true (success) if a step was taken and false otherwise.
1232 bool ModelChecker::take_step() {
1233 Thread *curr, *next;
1238 curr = thread_current();
1240 if (curr->get_state() == THREAD_READY) {
1241 ASSERT(priv->current_action);
1243 priv->nextThread = check_current_action(priv->current_action);
1244 priv->current_action = NULL;
1245 if (!curr->is_blocked() && !curr->is_complete())
1246 scheduler->add_thread(curr);
1251 next = scheduler->next_thread(priv->nextThread);
1253 /* Infeasible -> don't take any more steps */
1258 next->set_state(THREAD_RUNNING);
1259 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1261 /* next == NULL -> don't take any more steps */
1264 /* Return false only if swap fails with an error */
1265 return (Thread::swap(&system_context, next) == 0);
1268 /** Runs the current execution until threre are no more steps to take. */
1269 void ModelChecker::finish_execution() {
1272 while (take_step());