10 #include "snapshot-interface.h"
12 #include "clockvector.h"
13 #include "cyclegraph.h"
16 #include "threads-model.h"
19 #define INITIAL_THREAD_ID 0
24 bug_message(const char *str) {
25 const char *fmt = " [BUG] %s\n";
26 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
27 sprintf(msg, fmt, str);
29 ~bug_message() { if (msg) snapshot_free(msg); }
32 void print() { model_print("%s", msg); }
38 * Structure for holding small ModelChecker members that should be snapshotted
40 struct model_snapshot_members {
41 model_snapshot_members() :
43 /* First thread created will have id INITIAL_THREAD_ID */
44 next_thread_id(INITIAL_THREAD_ID),
45 used_sequence_numbers(0),
49 failed_promise(false),
50 too_many_reads(false),
51 bad_synchronization(false),
55 ~model_snapshot_members() {
56 for (unsigned int i = 0; i < bugs.size(); i++)
61 ModelAction *current_action;
62 unsigned int next_thread_id;
63 modelclock_t used_sequence_numbers;
64 ModelAction *next_backtrack;
65 std::vector< bug_message *, SnapshotAlloc<bug_message *> > bugs;
66 struct execution_stats stats;
69 /** @brief Incorrectly-ordered synchronization was made */
70 bool bad_synchronization;
76 /** @brief Constructor */
77 ModelChecker::ModelChecker(struct model_params params) :
78 /* Initialize default scheduler */
80 scheduler(new Scheduler()),
82 earliest_diverge(NULL),
83 action_trace(new action_list_t()),
84 thread_map(new HashTable<int, Thread *, int>()),
85 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
86 lock_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
87 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 obj_thrd_map(new HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4 >()),
89 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
90 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
91 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
92 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
93 thrd_last_fence_release(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >()),
94 node_stack(new NodeStack()),
95 priv(new struct model_snapshot_members()),
96 mo_graph(new CycleGraph())
98 /* Initialize a model-checker thread, for special ModelActions */
99 model_thread = new Thread(get_next_id());
100 thread_map->put(id_to_int(model_thread->get_id()), model_thread);
103 /** @brief Destructor */
104 ModelChecker::~ModelChecker()
106 for (unsigned int i = 0; i < get_num_threads(); i++)
107 delete thread_map->get(i);
112 delete lock_waiters_map;
113 delete condvar_waiters_map;
116 for (unsigned int i = 0; i < promises->size(); i++)
117 delete (*promises)[i];
120 delete pending_rel_seqs;
122 delete thrd_last_action;
123 delete thrd_last_fence_release;
130 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr)
132 action_list_t *tmp = hash->get(ptr);
134 tmp = new action_list_t();
140 static std::vector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4> * hash, void * ptr)
142 std::vector<action_list_t> *tmp = hash->get(ptr);
144 tmp = new std::vector<action_list_t>();
151 * Restores user program to initial state and resets all model-checker data
154 void ModelChecker::reset_to_initial_state()
156 DEBUG("+++ Resetting to initial state +++\n");
157 node_stack->reset_execution();
159 /* Print all model-checker output before rollback */
162 snapshotObject->backTrackBeforeStep(0);
165 /** @return a thread ID for a new Thread */
166 thread_id_t ModelChecker::get_next_id()
168 return priv->next_thread_id++;
171 /** @return the number of user threads created during this execution */
172 unsigned int ModelChecker::get_num_threads() const
174 return priv->next_thread_id;
177 /** @return The currently executing Thread. */
178 Thread * ModelChecker::get_current_thread() const
180 return scheduler->get_current_thread();
183 /** @return a sequence number for a new ModelAction */
184 modelclock_t ModelChecker::get_next_seq_num()
186 return ++priv->used_sequence_numbers;
189 Node * ModelChecker::get_curr_node() const
191 return node_stack->get_head();
195 * @brief Choose the next thread to execute.
197 * This function chooses the next thread that should execute. It can force the
198 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
199 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
200 * The model-checker may have no preference regarding the next thread (i.e.,
201 * when exploring a new execution ordering), in which case this will return
203 * @param curr The current ModelAction. This action might guide the choice of
205 * @return The next thread to run. If the model-checker has no preference, NULL.
207 Thread * ModelChecker::get_next_thread(ModelAction *curr)
212 /* Do not split atomic actions. */
214 return thread_current();
215 /* The THREAD_CREATE action points to the created Thread */
216 else if (curr->get_type() == THREAD_CREATE)
217 return (Thread *)curr->get_location();
220 /* Have we completed exploring the preselected path? */
224 /* Else, we are trying to replay an execution */
225 ModelAction *next = node_stack->get_next()->get_action();
227 if (next == diverge) {
228 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
229 earliest_diverge = diverge;
231 Node *nextnode = next->get_node();
232 Node *prevnode = nextnode->get_parent();
233 scheduler->update_sleep_set(prevnode);
235 /* Reached divergence point */
236 if (nextnode->increment_misc()) {
237 /* The next node will try to satisfy a different misc_index values. */
238 tid = next->get_tid();
239 node_stack->pop_restofstack(2);
240 } else if (nextnode->increment_promise()) {
241 /* The next node will try to satisfy a different set of promises. */
242 tid = next->get_tid();
243 node_stack->pop_restofstack(2);
244 } else if (nextnode->increment_read_from()) {
245 /* The next node will read from a different value. */
246 tid = next->get_tid();
247 node_stack->pop_restofstack(2);
248 } else if (nextnode->increment_future_value()) {
249 /* The next node will try to read from a different future value. */
250 tid = next->get_tid();
251 node_stack->pop_restofstack(2);
252 } else if (nextnode->increment_relseq_break()) {
253 /* The next node will try to resolve a release sequence differently */
254 tid = next->get_tid();
255 node_stack->pop_restofstack(2);
258 /* Make a different thread execute for next step */
259 scheduler->add_sleep(get_thread(next->get_tid()));
260 tid = prevnode->get_next_backtrack();
261 /* Make sure the backtracked thread isn't sleeping. */
262 node_stack->pop_restofstack(1);
263 if (diverge == earliest_diverge) {
264 earliest_diverge = prevnode->get_action();
267 /* The correct sleep set is in the parent node. */
270 DEBUG("*** Divergence point ***\n");
274 tid = next->get_tid();
276 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
277 ASSERT(tid != THREAD_ID_T_NONE);
278 return thread_map->get(id_to_int(tid));
282 * We need to know what the next actions of all threads in the sleep
283 * set will be. This method computes them and stores the actions at
284 * the corresponding thread object's pending action.
287 void ModelChecker::execute_sleep_set()
289 for (unsigned int i = 0; i < get_num_threads(); i++) {
290 thread_id_t tid = int_to_id(i);
291 Thread *thr = get_thread(tid);
292 if (scheduler->is_sleep_set(thr) && thr->get_pending() == NULL) {
293 thr->set_state(THREAD_RUNNING);
294 scheduler->next_thread(thr);
295 Thread::swap(&system_context, thr);
296 priv->current_action->set_sleep_flag();
297 thr->set_pending(priv->current_action);
302 void ModelChecker::wake_up_sleeping_actions(ModelAction *curr)
304 for (unsigned int i = 0; i < get_num_threads(); i++) {
305 Thread *thr = get_thread(int_to_id(i));
306 if (scheduler->is_sleep_set(thr)) {
307 ModelAction *pending_act = thr->get_pending();
308 if ((!curr->is_rmwr()) && pending_act->could_synchronize_with(curr))
309 //Remove this thread from sleep set
310 scheduler->remove_sleep(thr);
315 /** @brief Alert the model-checker that an incorrectly-ordered
316 * synchronization was made */
317 void ModelChecker::set_bad_synchronization()
319 priv->bad_synchronization = true;
322 bool ModelChecker::has_asserted() const
324 return priv->asserted;
327 void ModelChecker::set_assert()
329 priv->asserted = true;
333 * Check if we are in a deadlock. Should only be called at the end of an
334 * execution, although it should not give false positives in the middle of an
335 * execution (there should be some ENABLED thread).
337 * @return True if program is in a deadlock; false otherwise
339 bool ModelChecker::is_deadlocked() const
341 bool blocking_threads = false;
342 for (unsigned int i = 0; i < get_num_threads(); i++) {
343 thread_id_t tid = int_to_id(i);
346 Thread *t = get_thread(tid);
347 if (!t->is_model_thread() && t->get_pending())
348 blocking_threads = true;
350 return blocking_threads;
354 * Check if this is a complete execution. That is, have all thread completed
355 * execution (rather than exiting because sleep sets have forced a redundant
358 * @return True if the execution is complete.
360 bool ModelChecker::is_complete_execution() const
362 for (unsigned int i = 0; i < get_num_threads(); i++)
363 if (is_enabled(int_to_id(i)))
369 * @brief Assert a bug in the executing program.
371 * Use this function to assert any sort of bug in the user program. If the
372 * current trace is feasible (actually, a prefix of some feasible execution),
373 * then this execution will be aborted, printing the appropriate message. If
374 * the current trace is not yet feasible, the error message will be stashed and
375 * printed if the execution ever becomes feasible.
377 * @param msg Descriptive message for the bug (do not include newline char)
378 * @return True if bug is immediately-feasible
380 bool ModelChecker::assert_bug(const char *msg)
382 priv->bugs.push_back(new bug_message(msg));
384 if (isfeasibleprefix()) {
392 * @brief Assert a bug in the executing program, asserted by a user thread
393 * @see ModelChecker::assert_bug
394 * @param msg Descriptive message for the bug (do not include newline char)
396 void ModelChecker::assert_user_bug(const char *msg)
398 /* If feasible bug, bail out now */
400 switch_to_master(NULL);
403 /** @return True, if any bugs have been reported for this execution */
404 bool ModelChecker::have_bug_reports() const
406 return priv->bugs.size() != 0;
409 /** @brief Print bug report listing for this execution (if any bugs exist) */
410 void ModelChecker::print_bugs() const
412 if (have_bug_reports()) {
413 model_print("Bug report: %zu bug%s detected\n",
415 priv->bugs.size() > 1 ? "s" : "");
416 for (unsigned int i = 0; i < priv->bugs.size(); i++)
417 priv->bugs[i]->print();
422 * @brief Record end-of-execution stats
424 * Must be run when exiting an execution. Records various stats.
425 * @see struct execution_stats
427 void ModelChecker::record_stats()
430 if (!isfeasibleprefix())
431 stats.num_infeasible++;
432 else if (have_bug_reports())
433 stats.num_buggy_executions++;
434 else if (is_complete_execution())
435 stats.num_complete++;
437 stats.num_redundant++;
440 /** @brief Print execution stats */
441 void ModelChecker::print_stats() const
443 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
444 model_print("Number of redundant executions: %d\n", stats.num_redundant);
445 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
446 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
447 model_print("Total executions: %d\n", stats.num_total);
448 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
452 * @brief End-of-exeuction print
453 * @param printbugs Should any existing bugs be printed?
455 void ModelChecker::print_execution(bool printbugs) const
457 print_program_output();
459 if (DBG_ENABLED() || params.verbose) {
460 model_print("Earliest divergence point since last feasible execution:\n");
461 if (earliest_diverge)
462 earliest_diverge->print();
464 model_print("(Not set)\n");
470 /* Don't print invalid bugs */
479 * Queries the model-checker for more executions to explore and, if one
480 * exists, resets the model-checker state to execute a new execution.
482 * @return If there are more executions to explore, return true. Otherwise,
485 bool ModelChecker::next_execution()
488 /* Is this execution a feasible execution that's worth bug-checking? */
489 bool complete = isfeasibleprefix() && (is_complete_execution() ||
492 /* End-of-execution bug checks */
495 assert_bug("Deadlock detected");
503 if (DBG_ENABLED() || params.verbose || (complete && have_bug_reports()))
504 print_execution(complete);
506 clear_program_output();
509 earliest_diverge = NULL;
511 if ((diverge = get_next_backtrack()) == NULL)
515 model_print("Next execution will diverge at:\n");
519 reset_to_initial_state();
523 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
525 switch (act->get_type()) {
530 /* Optimization: relaxed operations don't need backtracking */
531 if (act->is_relaxed())
533 /* linear search: from most recent to oldest */
534 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
535 action_list_t::reverse_iterator rit;
536 for (rit = list->rbegin(); rit != list->rend(); rit++) {
537 ModelAction *prev = *rit;
538 if (prev->could_synchronize_with(act))
544 case ATOMIC_TRYLOCK: {
545 /* linear search: from most recent to oldest */
546 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
547 action_list_t::reverse_iterator rit;
548 for (rit = list->rbegin(); rit != list->rend(); rit++) {
549 ModelAction *prev = *rit;
550 if (act->is_conflicting_lock(prev))
555 case ATOMIC_UNLOCK: {
556 /* linear search: from most recent to oldest */
557 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
558 action_list_t::reverse_iterator rit;
559 for (rit = list->rbegin(); rit != list->rend(); rit++) {
560 ModelAction *prev = *rit;
561 if (!act->same_thread(prev) && prev->is_failed_trylock())
567 /* linear search: from most recent to oldest */
568 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
569 action_list_t::reverse_iterator rit;
570 for (rit = list->rbegin(); rit != list->rend(); rit++) {
571 ModelAction *prev = *rit;
572 if (!act->same_thread(prev) && prev->is_failed_trylock())
574 if (!act->same_thread(prev) && prev->is_notify())
580 case ATOMIC_NOTIFY_ALL:
581 case ATOMIC_NOTIFY_ONE: {
582 /* linear search: from most recent to oldest */
583 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
584 action_list_t::reverse_iterator rit;
585 for (rit = list->rbegin(); rit != list->rend(); rit++) {
586 ModelAction *prev = *rit;
587 if (!act->same_thread(prev) && prev->is_wait())
598 /** This method finds backtracking points where we should try to
599 * reorder the parameter ModelAction against.
601 * @param the ModelAction to find backtracking points for.
603 void ModelChecker::set_backtracking(ModelAction *act)
605 Thread *t = get_thread(act);
606 ModelAction *prev = get_last_conflict(act);
610 Node *node = prev->get_node()->get_parent();
612 int low_tid, high_tid;
613 if (node->is_enabled(t)) {
614 low_tid = id_to_int(act->get_tid());
615 high_tid = low_tid + 1;
618 high_tid = get_num_threads();
621 for (int i = low_tid; i < high_tid; i++) {
622 thread_id_t tid = int_to_id(i);
624 /* Make sure this thread can be enabled here. */
625 if (i >= node->get_num_threads())
628 /* Don't backtrack into a point where the thread is disabled or sleeping. */
629 if (node->enabled_status(tid) != THREAD_ENABLED)
632 /* Check if this has been explored already */
633 if (node->has_been_explored(tid))
636 /* See if fairness allows */
637 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
639 for (int t = 0; t < node->get_num_threads(); t++) {
640 thread_id_t tother = int_to_id(t);
641 if (node->is_enabled(tother) && node->has_priority(tother)) {
649 /* Cache the latest backtracking point */
650 set_latest_backtrack(prev);
652 /* If this is a new backtracking point, mark the tree */
653 if (!node->set_backtrack(tid))
655 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
656 id_to_int(prev->get_tid()),
657 id_to_int(t->get_id()));
666 * @brief Cache the a backtracking point as the "most recent", if eligible
668 * Note that this does not prepare the NodeStack for this backtracking
669 * operation, it only caches the action on a per-execution basis
671 * @param act The operation at which we should explore a different next action
672 * (i.e., backtracking point)
673 * @return True, if this action is now the most recent backtracking point;
676 bool ModelChecker::set_latest_backtrack(ModelAction *act)
678 if (!priv->next_backtrack || *act > *priv->next_backtrack) {
679 priv->next_backtrack = act;
686 * Returns last backtracking point. The model checker will explore a different
687 * path for this point in the next execution.
688 * @return The ModelAction at which the next execution should diverge.
690 ModelAction * ModelChecker::get_next_backtrack()
692 ModelAction *next = priv->next_backtrack;
693 priv->next_backtrack = NULL;
698 * Processes a read or rmw model action.
699 * @param curr is the read model action to process.
700 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
701 * @return True if processing this read updates the mo_graph.
703 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
705 uint64_t value = VALUE_NONE;
706 bool updated = false;
708 const ModelAction *reads_from = curr->get_node()->get_read_from();
709 if (reads_from != NULL) {
710 mo_graph->startChanges();
712 value = reads_from->get_value();
713 bool r_status = false;
715 if (!second_part_of_rmw) {
716 check_recency(curr, reads_from);
717 r_status = r_modification_order(curr, reads_from);
721 if (!second_part_of_rmw && is_infeasible() && (curr->get_node()->increment_read_from() || curr->get_node()->increment_future_value())) {
722 mo_graph->rollbackChanges();
723 priv->too_many_reads = false;
727 read_from(curr, reads_from);
728 mo_graph->commitChanges();
729 mo_check_promises(curr->get_tid(), reads_from);
732 } else if (!second_part_of_rmw) {
733 /* Read from future value */
734 value = curr->get_node()->get_future_value();
735 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
736 curr->set_read_from(NULL);
737 Promise *valuepromise = new Promise(curr, value, expiration);
738 promises->push_back(valuepromise);
740 get_thread(curr)->set_return_value(value);
746 * Processes a lock, trylock, or unlock model action. @param curr is
747 * the read model action to process.
749 * The try lock operation checks whether the lock is taken. If not,
750 * it falls to the normal lock operation case. If so, it returns
753 * The lock operation has already been checked that it is enabled, so
754 * it just grabs the lock and synchronizes with the previous unlock.
756 * The unlock operation has to re-enable all of the threads that are
757 * waiting on the lock.
759 * @return True if synchronization was updated; false otherwise
761 bool ModelChecker::process_mutex(ModelAction *curr)
763 std::mutex *mutex = NULL;
764 struct std::mutex_state *state = NULL;
766 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
767 mutex = (std::mutex *)curr->get_location();
768 state = mutex->get_state();
769 } else if (curr->is_wait()) {
770 mutex = (std::mutex *)curr->get_value();
771 state = mutex->get_state();
774 switch (curr->get_type()) {
775 case ATOMIC_TRYLOCK: {
776 bool success = !state->islocked;
777 curr->set_try_lock(success);
779 get_thread(curr)->set_return_value(0);
782 get_thread(curr)->set_return_value(1);
784 //otherwise fall into the lock case
786 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
787 assert_bug("Lock access before initialization");
788 state->islocked = true;
789 ModelAction *unlock = get_last_unlock(curr);
790 //synchronize with the previous unlock statement
791 if (unlock != NULL) {
792 curr->synchronize_with(unlock);
797 case ATOMIC_UNLOCK: {
799 state->islocked = false;
800 //wake up the other threads
801 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
802 //activate all the waiting threads
803 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
804 scheduler->wake(get_thread(*rit));
811 state->islocked = false;
812 //wake up the other threads
813 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
814 //activate all the waiting threads
815 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
816 scheduler->wake(get_thread(*rit));
819 //check whether we should go to sleep or not...simulate spurious failures
820 if (curr->get_node()->get_misc() == 0) {
821 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
823 scheduler->sleep(get_current_thread());
827 case ATOMIC_NOTIFY_ALL: {
828 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
829 //activate all the waiting threads
830 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
831 scheduler->wake(get_thread(*rit));
836 case ATOMIC_NOTIFY_ONE: {
837 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
838 int wakeupthread = curr->get_node()->get_misc();
839 action_list_t::iterator it = waiters->begin();
840 advance(it, wakeupthread);
841 scheduler->wake(get_thread(*it));
853 * Process a write ModelAction
854 * @param curr The ModelAction to process
855 * @return True if the mo_graph was updated or promises were resolved
857 bool ModelChecker::process_write(ModelAction *curr)
859 bool updated_mod_order = w_modification_order(curr);
860 bool updated_promises = resolve_promises(curr);
862 if (promises->size() == 0) {
863 for (unsigned int i = 0; i < futurevalues->size(); i++) {
864 struct PendingFutureValue pfv = (*futurevalues)[i];
865 //Do more ambitious checks now that mo is more complete
866 if (mo_may_allow(pfv.writer, pfv.act) &&
867 pfv.act->get_node()->add_future_value(pfv.writer->get_value(), pfv.writer->get_seq_number() + params.maxfuturedelay))
868 set_latest_backtrack(pfv.act);
870 futurevalues->resize(0);
873 mo_graph->commitChanges();
874 mo_check_promises(curr->get_tid(), curr);
876 get_thread(curr)->set_return_value(VALUE_NONE);
877 return updated_mod_order || updated_promises;
881 * Process a fence ModelAction
882 * @param curr The ModelAction to process
883 * @return True if synchronization was updated
885 bool ModelChecker::process_fence(ModelAction *curr)
888 * fence-relaxed: no-op
889 * fence-release: only log the occurence (not in this function), for
890 * use in later synchronization
891 * fence-acquire (this function): search for hypothetical release
894 bool updated = false;
895 if (curr->is_acquire()) {
896 action_list_t *list = action_trace;
897 action_list_t::reverse_iterator rit;
898 /* Find X : is_read(X) && X --sb-> curr */
899 for (rit = list->rbegin(); rit != list->rend(); rit++) {
900 ModelAction *act = *rit;
903 if (act->get_tid() != curr->get_tid())
905 /* Stop at the beginning of the thread */
906 if (act->is_thread_start())
908 /* Stop once we reach a prior fence-acquire */
909 if (act->is_fence() && act->is_acquire())
913 /* read-acquire will find its own release sequences */
914 if (act->is_acquire())
917 /* Establish hypothetical release sequences */
918 rel_heads_list_t release_heads;
919 get_release_seq_heads(curr, act, &release_heads);
920 for (unsigned int i = 0; i < release_heads.size(); i++)
921 if (!curr->synchronize_with(release_heads[i]))
922 set_bad_synchronization();
923 if (release_heads.size() != 0)
931 * @brief Process the current action for thread-related activity
933 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
934 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
935 * synchronization, etc. This function is a no-op for non-THREAD actions
936 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
938 * @param curr The current action
939 * @return True if synchronization was updated or a thread completed
941 bool ModelChecker::process_thread_action(ModelAction *curr)
943 bool updated = false;
945 switch (curr->get_type()) {
946 case THREAD_CREATE: {
947 Thread *th = (Thread *)curr->get_location();
948 th->set_creation(curr);
952 Thread *blocking = (Thread *)curr->get_location();
953 ModelAction *act = get_last_action(blocking->get_id());
954 curr->synchronize_with(act);
955 updated = true; /* trigger rel-seq checks */
958 case THREAD_FINISH: {
959 Thread *th = get_thread(curr);
960 while (!th->wait_list_empty()) {
961 ModelAction *act = th->pop_wait_list();
962 scheduler->wake(get_thread(act));
965 updated = true; /* trigger rel-seq checks */
969 check_promises(curr->get_tid(), NULL, curr->get_cv());
980 * @brief Process the current action for release sequence fixup activity
982 * Performs model-checker release sequence fixups for the current action,
983 * forcing a single pending release sequence to break (with a given, potential
984 * "loose" write) or to complete (i.e., synchronize). If a pending release
985 * sequence forms a complete release sequence, then we must perform the fixup
986 * synchronization, mo_graph additions, etc.
988 * @param curr The current action; must be a release sequence fixup action
989 * @param work_queue The work queue to which to add work items as they are
992 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
994 const ModelAction *write = curr->get_node()->get_relseq_break();
995 struct release_seq *sequence = pending_rel_seqs->back();
996 pending_rel_seqs->pop_back();
998 ModelAction *acquire = sequence->acquire;
999 const ModelAction *rf = sequence->rf;
1000 const ModelAction *release = sequence->release;
1004 ASSERT(release->same_thread(rf));
1006 if (write == NULL) {
1008 * @todo Forcing a synchronization requires that we set
1009 * modification order constraints. For instance, we can't allow
1010 * a fixup sequence in which two separate read-acquire
1011 * operations read from the same sequence, where the first one
1012 * synchronizes and the other doesn't. Essentially, we can't
1013 * allow any writes to insert themselves between 'release' and
1017 /* Must synchronize */
1018 if (!acquire->synchronize_with(release)) {
1019 set_bad_synchronization();
1022 /* Re-check all pending release sequences */
1023 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1024 /* Re-check act for mo_graph edges */
1025 work_queue->push_back(MOEdgeWorkEntry(acquire));
1027 /* propagate synchronization to later actions */
1028 action_list_t::reverse_iterator rit = action_trace->rbegin();
1029 for (; (*rit) != acquire; rit++) {
1030 ModelAction *propagate = *rit;
1031 if (acquire->happens_before(propagate)) {
1032 propagate->synchronize_with(acquire);
1033 /* Re-check 'propagate' for mo_graph edges */
1034 work_queue->push_back(MOEdgeWorkEntry(propagate));
1038 /* Break release sequence with new edges:
1039 * release --mo--> write --mo--> rf */
1040 mo_graph->addEdge(release, write);
1041 mo_graph->addEdge(write, rf);
1044 /* See if we have realized a data race */
1049 * Initialize the current action by performing one or more of the following
1050 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
1051 * in the NodeStack, manipulating backtracking sets, allocating and
1052 * initializing clock vectors, and computing the promises to fulfill.
1054 * @param curr The current action, as passed from the user context; may be
1055 * freed/invalidated after the execution of this function, with a different
1056 * action "returned" its place (pass-by-reference)
1057 * @return True if curr is a newly-explored action; false otherwise
1059 bool ModelChecker::initialize_curr_action(ModelAction **curr)
1061 ModelAction *newcurr;
1063 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
1064 newcurr = process_rmw(*curr);
1067 if (newcurr->is_rmw())
1068 compute_promises(newcurr);
1074 (*curr)->set_seq_number(get_next_seq_num());
1076 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled_array());
1078 /* First restore type and order in case of RMW operation */
1079 if ((*curr)->is_rmwr())
1080 newcurr->copy_typeandorder(*curr);
1082 ASSERT((*curr)->get_location() == newcurr->get_location());
1083 newcurr->copy_from_new(*curr);
1085 /* Discard duplicate ModelAction; use action from NodeStack */
1088 /* Always compute new clock vector */
1089 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1092 return false; /* Action was explored previously */
1096 /* Always compute new clock vector */
1097 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1099 /* Assign most recent release fence */
1100 newcurr->set_last_fence_release(get_last_fence_release(newcurr->get_tid()));
1103 * Perform one-time actions when pushing new ModelAction onto
1106 if (newcurr->is_write())
1107 compute_promises(newcurr);
1108 else if (newcurr->is_relseq_fixup())
1109 compute_relseq_breakwrites(newcurr);
1110 else if (newcurr->is_wait())
1111 newcurr->get_node()->set_misc_max(2);
1112 else if (newcurr->is_notify_one()) {
1113 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1115 return true; /* This was a new ModelAction */
1120 * @brief Establish reads-from relation between two actions
1122 * Perform basic operations involved with establishing a concrete rf relation,
1123 * including setting the ModelAction data and checking for release sequences.
1125 * @param act The action that is reading (must be a read)
1126 * @param rf The action from which we are reading (must be a write)
1128 * @return True if this read established synchronization
1130 bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf)
1132 act->set_read_from(rf);
1133 if (rf != NULL && act->is_acquire()) {
1134 rel_heads_list_t release_heads;
1135 get_release_seq_heads(act, act, &release_heads);
1136 int num_heads = release_heads.size();
1137 for (unsigned int i = 0; i < release_heads.size(); i++)
1138 if (!act->synchronize_with(release_heads[i])) {
1139 set_bad_synchronization();
1142 return num_heads > 0;
1148 * @brief Check whether a model action is enabled.
1150 * Checks whether a lock or join operation would be successful (i.e., is the
1151 * lock already locked, or is the joined thread already complete). If not, put
1152 * the action in a waiter list.
1154 * @param curr is the ModelAction to check whether it is enabled.
1155 * @return a bool that indicates whether the action is enabled.
1157 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1158 if (curr->is_lock()) {
1159 std::mutex *lock = (std::mutex *)curr->get_location();
1160 struct std::mutex_state *state = lock->get_state();
1161 if (state->islocked) {
1162 //Stick the action in the appropriate waiting queue
1163 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1166 } else if (curr->get_type() == THREAD_JOIN) {
1167 Thread *blocking = (Thread *)curr->get_location();
1168 if (!blocking->is_complete()) {
1169 blocking->push_wait_list(curr);
1178 * Stores the ModelAction for the current thread action. Call this
1179 * immediately before switching from user- to system-context to pass
1180 * data between them.
1181 * @param act The ModelAction created by the user-thread action
1183 void ModelChecker::set_current_action(ModelAction *act) {
1184 priv->current_action = act;
1188 * This is the heart of the model checker routine. It performs model-checking
1189 * actions corresponding to a given "current action." Among other processes, it
1190 * calculates reads-from relationships, updates synchronization clock vectors,
1191 * forms a memory_order constraints graph, and handles replay/backtrack
1192 * execution when running permutations of previously-observed executions.
1194 * @param curr The current action to process
1195 * @return The next Thread that must be executed. May be NULL if ModelChecker
1196 * makes no choice (e.g., according to replay execution, combining RMW actions,
1199 Thread * ModelChecker::check_current_action(ModelAction *curr)
1202 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1204 if (!check_action_enabled(curr)) {
1205 /* Make the execution look like we chose to run this action
1206 * much later, when a lock/join can succeed */
1207 get_current_thread()->set_pending(curr);
1208 scheduler->sleep(get_current_thread());
1209 return get_next_thread(NULL);
1212 bool newly_explored = initialize_curr_action(&curr);
1218 wake_up_sleeping_actions(curr);
1220 /* Add the action to lists before any other model-checking tasks */
1221 if (!second_part_of_rmw)
1222 add_action_to_lists(curr);
1224 /* Build may_read_from set for newly-created actions */
1225 if (newly_explored && curr->is_read())
1226 build_reads_from_past(curr);
1228 /* Initialize work_queue with the "current action" work */
1229 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1230 while (!work_queue.empty() && !has_asserted()) {
1231 WorkQueueEntry work = work_queue.front();
1232 work_queue.pop_front();
1234 switch (work.type) {
1235 case WORK_CHECK_CURR_ACTION: {
1236 ModelAction *act = work.action;
1237 bool update = false; /* update this location's release seq's */
1238 bool update_all = false; /* update all release seq's */
1240 if (process_thread_action(curr))
1243 if (act->is_read() && process_read(act, second_part_of_rmw))
1246 if (act->is_write() && process_write(act))
1249 if (act->is_fence() && process_fence(act))
1252 if (act->is_mutex_op() && process_mutex(act))
1255 if (act->is_relseq_fixup())
1256 process_relseq_fixup(curr, &work_queue);
1259 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1261 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1264 case WORK_CHECK_RELEASE_SEQ:
1265 resolve_release_sequences(work.location, &work_queue);
1267 case WORK_CHECK_MO_EDGES: {
1268 /** @todo Complete verification of work_queue */
1269 ModelAction *act = work.action;
1270 bool updated = false;
1272 if (act->is_read()) {
1273 const ModelAction *rf = act->get_reads_from();
1274 if (rf != NULL && r_modification_order(act, rf))
1277 if (act->is_write()) {
1278 if (w_modification_order(act))
1281 mo_graph->commitChanges();
1284 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1293 check_curr_backtracking(curr);
1294 set_backtracking(curr);
1295 return get_next_thread(curr);
1298 void ModelChecker::check_curr_backtracking(ModelAction *curr)
1300 Node *currnode = curr->get_node();
1301 Node *parnode = currnode->get_parent();
1303 if ((parnode && !parnode->backtrack_empty()) ||
1304 !currnode->misc_empty() ||
1305 !currnode->read_from_empty() ||
1306 !currnode->future_value_empty() ||
1307 !currnode->promise_empty() ||
1308 !currnode->relseq_break_empty()) {
1309 set_latest_backtrack(curr);
1313 bool ModelChecker::promises_expired() const
1315 for (unsigned int i = 0; i < promises->size(); i++) {
1316 Promise *promise = (*promises)[i];
1317 if (promise->get_expiration() < priv->used_sequence_numbers)
1324 * This is the strongest feasibility check available.
1325 * @return whether the current trace (partial or complete) must be a prefix of
1328 bool ModelChecker::isfeasibleprefix() const
1330 return pending_rel_seqs->size() == 0 && is_feasible_prefix_ignore_relseq();
1334 * Returns whether the current completed trace is feasible, except for pending
1335 * release sequences.
1337 bool ModelChecker::is_feasible_prefix_ignore_relseq() const
1339 if (DBG_ENABLED() && promises->size() != 0)
1340 DEBUG("Infeasible: unrevolved promises\n");
1342 return !is_infeasible() && promises->size() == 0;
1346 * Check if the current partial trace is infeasible. Does not check any
1347 * end-of-execution flags, which might rule out the execution. Thus, this is
1348 * useful only for ruling an execution as infeasible.
1349 * @return whether the current partial trace is infeasible.
1351 bool ModelChecker::is_infeasible() const
1353 if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
1354 DEBUG("Infeasible: RMW violation\n");
1356 return mo_graph->checkForRMWViolation() || is_infeasible_ignoreRMW();
1360 * Check If the current partial trace is infeasible, while ignoring
1361 * infeasibility related to 2 RMW's reading from the same store. It does not
1362 * check end-of-execution feasibility.
1363 * @see ModelChecker::is_infeasible
1364 * @return whether the current partial trace is infeasible, ignoring multiple
1365 * RMWs reading from the same store.
1367 bool ModelChecker::is_infeasible_ignoreRMW() const
1369 if (DBG_ENABLED()) {
1370 if (mo_graph->checkForCycles())
1371 DEBUG("Infeasible: modification order cycles\n");
1372 if (priv->failed_promise)
1373 DEBUG("Infeasible: failed promise\n");
1374 if (priv->too_many_reads)
1375 DEBUG("Infeasible: too many reads\n");
1376 if (priv->bad_synchronization)
1377 DEBUG("Infeasible: bad synchronization ordering\n");
1378 if (promises_expired())
1379 DEBUG("Infeasible: promises expired\n");
1381 return mo_graph->checkForCycles() || priv->failed_promise ||
1382 priv->too_many_reads || priv->bad_synchronization ||
1386 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1387 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1388 ModelAction *lastread = get_last_action(act->get_tid());
1389 lastread->process_rmw(act);
1390 if (act->is_rmw() && lastread->get_reads_from() != NULL) {
1391 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1392 mo_graph->commitChanges();
1398 * Checks whether a thread has read from the same write for too many times
1399 * without seeing the effects of a later write.
1402 * 1) there must a different write that we could read from that would satisfy the modification order,
1403 * 2) we must have read from the same value in excess of maxreads times, and
1404 * 3) that other write must have been in the reads_from set for maxreads times.
1406 * If so, we decide that the execution is no longer feasible.
1408 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf)
1410 if (params.maxreads != 0) {
1411 if (curr->get_node()->get_read_from_size() <= 1)
1413 //Must make sure that execution is currently feasible... We could
1414 //accidentally clear by rolling back
1415 if (is_infeasible())
1417 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1418 int tid = id_to_int(curr->get_tid());
1421 if ((int)thrd_lists->size() <= tid)
1423 action_list_t *list = &(*thrd_lists)[tid];
1425 action_list_t::reverse_iterator rit = list->rbegin();
1426 /* Skip past curr */
1427 for (; (*rit) != curr; rit++)
1429 /* go past curr now */
1432 action_list_t::reverse_iterator ritcopy = rit;
1433 //See if we have enough reads from the same value
1435 for (; count < params.maxreads; rit++, count++) {
1436 if (rit == list->rend())
1438 ModelAction *act = *rit;
1439 if (!act->is_read())
1442 if (act->get_reads_from() != rf)
1444 if (act->get_node()->get_read_from_size() <= 1)
1447 for (int i = 0; i < curr->get_node()->get_read_from_size(); i++) {
1449 const ModelAction *write = curr->get_node()->get_read_from_at(i);
1451 /* Need a different write */
1455 /* Test to see whether this is a feasible write to read from */
1456 mo_graph->startChanges();
1457 r_modification_order(curr, write);
1458 bool feasiblereadfrom = !is_infeasible();
1459 mo_graph->rollbackChanges();
1461 if (!feasiblereadfrom)
1465 bool feasiblewrite = true;
1466 //new we need to see if this write works for everyone
1468 for (int loop = count; loop > 0; loop--, rit++) {
1469 ModelAction *act = *rit;
1470 bool foundvalue = false;
1471 for (int j = 0; j < act->get_node()->get_read_from_size(); j++) {
1472 if (act->get_node()->get_read_from_at(j) == write) {
1478 feasiblewrite = false;
1482 if (feasiblewrite) {
1483 priv->too_many_reads = true;
1491 * Updates the mo_graph with the constraints imposed from the current
1494 * Basic idea is the following: Go through each other thread and find
1495 * the lastest action that happened before our read. Two cases:
1497 * (1) The action is a write => that write must either occur before
1498 * the write we read from or be the write we read from.
1500 * (2) The action is a read => the write that that action read from
1501 * must occur before the write we read from or be the same write.
1503 * @param curr The current action. Must be a read.
1504 * @param rf The action that curr reads from. Must be a write.
1505 * @return True if modification order edges were added; false otherwise
1507 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
1509 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1512 ASSERT(curr->is_read());
1514 /* Last SC fence in the current thread */
1515 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1517 /* Iterate over all threads */
1518 for (i = 0; i < thrd_lists->size(); i++) {
1519 /* Last SC fence in thread i */
1520 ModelAction *last_sc_fence_thread_local = NULL;
1521 if (int_to_id((int)i) != curr->get_tid())
1522 last_sc_fence_thread_local = get_last_seq_cst_fence(int_to_id(i), NULL);
1524 /* Last SC fence in thread i, before last SC fence in current thread */
1525 ModelAction *last_sc_fence_thread_before = NULL;
1526 if (last_sc_fence_local)
1527 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1529 /* Iterate over actions in thread, starting from most recent */
1530 action_list_t *list = &(*thrd_lists)[i];
1531 action_list_t::reverse_iterator rit;
1532 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1533 ModelAction *act = *rit;
1535 if (act->is_write() && act != rf && act != curr) {
1536 /* C++, Section 29.3 statement 5 */
1537 if (curr->is_seqcst() && last_sc_fence_thread_local &&
1538 *act < *last_sc_fence_thread_local) {
1539 mo_graph->addEdge(act, rf);
1543 /* C++, Section 29.3 statement 4 */
1544 else if (act->is_seqcst() && last_sc_fence_local &&
1545 *act < *last_sc_fence_local) {
1546 mo_graph->addEdge(act, rf);
1550 /* C++, Section 29.3 statement 6 */
1551 else if (last_sc_fence_thread_before &&
1552 *act < *last_sc_fence_thread_before) {
1553 mo_graph->addEdge(act, rf);
1560 * Include at most one act per-thread that "happens
1561 * before" curr. Don't consider reflexively.
1563 if (act->happens_before(curr) && act != curr) {
1564 if (act->is_write()) {
1566 mo_graph->addEdge(act, rf);
1570 const ModelAction *prevreadfrom = act->get_reads_from();
1571 //if the previous read is unresolved, keep going...
1572 if (prevreadfrom == NULL)
1575 if (rf != prevreadfrom) {
1576 mo_graph->addEdge(prevreadfrom, rf);
1588 /** This method fixes up the modification order when we resolve a
1589 * promises. The basic problem is that actions that occur after the
1590 * read curr could not property add items to the modification order
1593 * So for each thread, we find the earliest item that happens after
1594 * the read curr. This is the item we have to fix up with additional
1595 * constraints. If that action is write, we add a MO edge between
1596 * the Action rf and that action. If the action is a read, we add a
1597 * MO edge between the Action rf, and whatever the read accessed.
1599 * @param curr is the read ModelAction that we are fixing up MO edges for.
1600 * @param rf is the write ModelAction that curr reads from.
1603 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
1605 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1607 ASSERT(curr->is_read());
1609 /* Iterate over all threads */
1610 for (i = 0; i < thrd_lists->size(); i++) {
1611 /* Iterate over actions in thread, starting from most recent */
1612 action_list_t *list = &(*thrd_lists)[i];
1613 action_list_t::reverse_iterator rit;
1614 ModelAction *lastact = NULL;
1616 /* Find last action that happens after curr that is either not curr or a rmw */
1617 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1618 ModelAction *act = *rit;
1619 if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
1625 /* Include at most one act per-thread that "happens before" curr */
1626 if (lastact != NULL) {
1627 if (lastact == curr) {
1628 //Case 1: The resolved read is a RMW, and we need to make sure
1629 //that the write portion of the RMW mod order after rf
1631 mo_graph->addEdge(rf, lastact);
1632 } else if (lastact->is_read()) {
1633 //Case 2: The resolved read is a normal read and the next
1634 //operation is a read, and we need to make sure the value read
1635 //is mod ordered after rf
1637 const ModelAction *postreadfrom = lastact->get_reads_from();
1638 if (postreadfrom != NULL && rf != postreadfrom)
1639 mo_graph->addEdge(rf, postreadfrom);
1641 //Case 3: The resolved read is a normal read and the next
1642 //operation is a write, and we need to make sure that the
1643 //write is mod ordered after rf
1645 mo_graph->addEdge(rf, lastact);
1653 * Updates the mo_graph with the constraints imposed from the current write.
1655 * Basic idea is the following: Go through each other thread and find
1656 * the lastest action that happened before our write. Two cases:
1658 * (1) The action is a write => that write must occur before
1661 * (2) The action is a read => the write that that action read from
1662 * must occur before the current write.
1664 * This method also handles two other issues:
1666 * (I) Sequential Consistency: Making sure that if the current write is
1667 * seq_cst, that it occurs after the previous seq_cst write.
1669 * (II) Sending the write back to non-synchronizing reads.
1671 * @param curr The current action. Must be a write.
1672 * @return True if modification order edges were added; false otherwise
1674 bool ModelChecker::w_modification_order(ModelAction *curr)
1676 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1679 ASSERT(curr->is_write());
1681 if (curr->is_seqcst()) {
1682 /* We have to at least see the last sequentially consistent write,
1683 so we are initialized. */
1684 ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
1685 if (last_seq_cst != NULL) {
1686 mo_graph->addEdge(last_seq_cst, curr);
1691 /* Last SC fence in the current thread */
1692 ModelAction *last_sc_fence_local = get_last_seq_cst_fence(curr->get_tid(), NULL);
1694 /* Iterate over all threads */
1695 for (i = 0; i < thrd_lists->size(); i++) {
1696 /* Last SC fence in thread i, before last SC fence in current thread */
1697 ModelAction *last_sc_fence_thread_before = NULL;
1698 if (last_sc_fence_local && int_to_id((int)i) != curr->get_tid())
1699 last_sc_fence_thread_before = get_last_seq_cst_fence(int_to_id(i), last_sc_fence_local);
1701 /* Iterate over actions in thread, starting from most recent */
1702 action_list_t *list = &(*thrd_lists)[i];
1703 action_list_t::reverse_iterator rit;
1704 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1705 ModelAction *act = *rit;
1708 * 1) If RMW and it actually read from something, then we
1709 * already have all relevant edges, so just skip to next
1712 * 2) If RMW and it didn't read from anything, we should
1713 * whatever edge we can get to speed up convergence.
1715 * 3) If normal write, we need to look at earlier actions, so
1716 * continue processing list.
1718 if (curr->is_rmw()) {
1719 if (curr->get_reads_from() != NULL)
1727 /* C++, Section 29.3 statement 7 */
1728 if (last_sc_fence_thread_before && act->is_write() &&
1729 *act < *last_sc_fence_thread_before) {
1730 mo_graph->addEdge(act, curr);
1736 * Include at most one act per-thread that "happens
1739 if (act->happens_before(curr)) {
1741 * Note: if act is RMW, just add edge:
1743 * The following edge should be handled elsewhere:
1744 * readfrom(act) --mo--> act
1746 if (act->is_write())
1747 mo_graph->addEdge(act, curr);
1748 else if (act->is_read()) {
1749 //if previous read accessed a null, just keep going
1750 if (act->get_reads_from() == NULL)
1752 mo_graph->addEdge(act->get_reads_from(), curr);
1756 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1757 !act->same_thread(curr)) {
1758 /* We have an action that:
1759 (1) did not happen before us
1760 (2) is a read and we are a write
1761 (3) cannot synchronize with us
1762 (4) is in a different thread
1764 that read could potentially read from our write. Note that
1765 these checks are overly conservative at this point, we'll
1766 do more checks before actually removing the
1770 if (thin_air_constraint_may_allow(curr, act)) {
1771 if (!is_infeasible() ||
1772 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && !is_infeasible_ignoreRMW())) {
1773 struct PendingFutureValue pfv = {curr, act};
1774 futurevalues->push_back(pfv);
1784 /** Arbitrary reads from the future are not allowed. Section 29.3
1785 * part 9 places some constraints. This method checks one result of constraint
1786 * constraint. Others require compiler support. */
1787 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction *writer, const ModelAction *reader)
1789 if (!writer->is_rmw())
1792 if (!reader->is_rmw())
1795 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1796 if (search == reader)
1798 if (search->get_tid() == reader->get_tid() &&
1799 search->happens_before(reader))
1807 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1808 * some constraints. This method checks one the following constraint (others
1809 * require compiler support):
1811 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1813 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1815 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1817 /* Iterate over all threads */
1818 for (i = 0; i < thrd_lists->size(); i++) {
1819 const ModelAction *write_after_read = NULL;
1821 /* Iterate over actions in thread, starting from most recent */
1822 action_list_t *list = &(*thrd_lists)[i];
1823 action_list_t::reverse_iterator rit;
1824 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1825 ModelAction *act = *rit;
1827 /* Don't disallow due to act == reader */
1828 if (!reader->happens_before(act) || reader == act)
1830 else if (act->is_write())
1831 write_after_read = act;
1832 else if (act->is_read() && act->get_reads_from() != NULL)
1833 write_after_read = act->get_reads_from();
1836 if (write_after_read && write_after_read != writer && mo_graph->checkReachable(write_after_read, writer))
1843 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1844 * The ModelAction under consideration is expected to be taking part in
1845 * release/acquire synchronization as an object of the "reads from" relation.
1846 * Note that this can only provide release sequence support for RMW chains
1847 * which do not read from the future, as those actions cannot be traced until
1848 * their "promise" is fulfilled. Similarly, we may not even establish the
1849 * presence of a release sequence with certainty, as some modification order
1850 * constraints may be decided further in the future. Thus, this function
1851 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1852 * and a boolean representing certainty.
1854 * @param rf The action that might be part of a release sequence. Must be a
1856 * @param release_heads A pass-by-reference style return parameter. After
1857 * execution of this function, release_heads will contain the heads of all the
1858 * relevant release sequences, if any exists with certainty
1859 * @param pending A pass-by-reference style return parameter which is only used
1860 * when returning false (i.e., uncertain). Returns most information regarding
1861 * an uncertain release sequence, including any write operations that might
1862 * break the sequence.
1863 * @return true, if the ModelChecker is certain that release_heads is complete;
1866 bool ModelChecker::release_seq_heads(const ModelAction *rf,
1867 rel_heads_list_t *release_heads,
1868 struct release_seq *pending) const
1870 /* Only check for release sequences if there are no cycles */
1871 if (mo_graph->checkForCycles())
1875 ASSERT(rf->is_write());
1877 if (rf->is_release())
1878 release_heads->push_back(rf);
1879 else if (rf->get_last_fence_release())
1880 release_heads->push_back(rf->get_last_fence_release());
1882 break; /* End of RMW chain */
1884 /** @todo Need to be smarter here... In the linux lock
1885 * example, this will run to the beginning of the program for
1887 /** @todo The way to be smarter here is to keep going until 1
1888 * thread has a release preceded by an acquire and you've seen
1891 /* acq_rel RMW is a sufficient stopping condition */
1892 if (rf->is_acquire() && rf->is_release())
1893 return true; /* complete */
1895 rf = rf->get_reads_from();
1898 /* read from future: need to settle this later */
1900 return false; /* incomplete */
1903 if (rf->is_release())
1904 return true; /* complete */
1906 /* else relaxed write
1907 * - check for fence-release in the same thread (29.8, stmt. 3)
1908 * - check modification order for contiguous subsequence
1909 * -> rf must be same thread as release */
1911 const ModelAction *fence_release = rf->get_last_fence_release();
1912 /* Synchronize with a fence-release unconditionally; we don't need to
1913 * find any more "contiguous subsequence..." for it */
1915 release_heads->push_back(fence_release);
1917 int tid = id_to_int(rf->get_tid());
1918 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
1919 action_list_t *list = &(*thrd_lists)[tid];
1920 action_list_t::const_reverse_iterator rit;
1922 /* Find rf in the thread list */
1923 rit = std::find(list->rbegin(), list->rend(), rf);
1924 ASSERT(rit != list->rend());
1926 /* Find the last {write,fence}-release */
1927 for (; rit != list->rend(); rit++) {
1928 if (fence_release && *(*rit) < *fence_release)
1930 if ((*rit)->is_release())
1933 if (rit == list->rend()) {
1934 /* No write-release in this thread */
1935 return true; /* complete */
1936 } else if (fence_release && *(*rit) < *fence_release) {
1937 /* The fence-release is more recent (and so, "stronger") than
1938 * the most recent write-release */
1939 return true; /* complete */
1940 } /* else, need to establish contiguous release sequence */
1941 ModelAction *release = *rit;
1943 ASSERT(rf->same_thread(release));
1945 pending->writes.clear();
1947 bool certain = true;
1948 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1949 if (id_to_int(rf->get_tid()) == (int)i)
1951 list = &(*thrd_lists)[i];
1953 /* Can we ensure no future writes from this thread may break
1954 * the release seq? */
1955 bool future_ordered = false;
1957 ModelAction *last = get_last_action(int_to_id(i));
1958 Thread *th = get_thread(int_to_id(i));
1959 if ((last && rf->happens_before(last)) ||
1962 future_ordered = true;
1964 ASSERT(!th->is_model_thread() || future_ordered);
1966 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1967 const ModelAction *act = *rit;
1968 /* Reach synchronization -> this thread is complete */
1969 if (act->happens_before(release))
1971 if (rf->happens_before(act)) {
1972 future_ordered = true;
1976 /* Only non-RMW writes can break release sequences */
1977 if (!act->is_write() || act->is_rmw())
1980 /* Check modification order */
1981 if (mo_graph->checkReachable(rf, act)) {
1982 /* rf --mo--> act */
1983 future_ordered = true;
1986 if (mo_graph->checkReachable(act, release))
1987 /* act --mo--> release */
1989 if (mo_graph->checkReachable(release, act) &&
1990 mo_graph->checkReachable(act, rf)) {
1991 /* release --mo-> act --mo--> rf */
1992 return true; /* complete */
1994 /* act may break release sequence */
1995 pending->writes.push_back(act);
1998 if (!future_ordered)
1999 certain = false; /* This thread is uncertain */
2003 release_heads->push_back(release);
2004 pending->writes.clear();
2006 pending->release = release;
2013 * An interface for getting the release sequence head(s) with which a
2014 * given ModelAction must synchronize. This function only returns a non-empty
2015 * result when it can locate a release sequence head with certainty. Otherwise,
2016 * it may mark the internal state of the ModelChecker so that it will handle
2017 * the release sequence at a later time, causing @a acquire to update its
2018 * synchronization at some later point in execution.
2020 * @param acquire The 'acquire' action that may synchronize with a release
2022 * @param read The read action that may read from a release sequence; this may
2023 * be the same as acquire, or else an earlier action in the same thread (i.e.,
2024 * when 'acquire' is a fence-acquire)
2025 * @param release_heads A pass-by-reference return parameter. Will be filled
2026 * with the head(s) of the release sequence(s), if they exists with certainty.
2027 * @see ModelChecker::release_seq_heads
2029 void ModelChecker::get_release_seq_heads(ModelAction *acquire,
2030 ModelAction *read, rel_heads_list_t *release_heads)
2032 const ModelAction *rf = read->get_reads_from();
2033 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
2034 sequence->acquire = acquire;
2035 sequence->read = read;
2037 if (!release_seq_heads(rf, release_heads, sequence)) {
2038 /* add act to 'lazy checking' list */
2039 pending_rel_seqs->push_back(sequence);
2041 snapshot_free(sequence);
2046 * Attempt to resolve all stashed operations that might synchronize with a
2047 * release sequence for a given location. This implements the "lazy" portion of
2048 * determining whether or not a release sequence was contiguous, since not all
2049 * modification order information is present at the time an action occurs.
2051 * @param location The location/object that should be checked for release
2052 * sequence resolutions. A NULL value means to check all locations.
2053 * @param work_queue The work queue to which to add work items as they are
2055 * @return True if any updates occurred (new synchronization, new mo_graph
2058 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
2060 bool updated = false;
2061 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
2062 while (it != pending_rel_seqs->end()) {
2063 struct release_seq *pending = *it;
2064 ModelAction *acquire = pending->acquire;
2065 const ModelAction *read = pending->read;
2067 /* Only resolve sequences on the given location, if provided */
2068 if (location && read->get_location() != location) {
2073 const ModelAction *rf = read->get_reads_from();
2074 rel_heads_list_t release_heads;
2076 complete = release_seq_heads(rf, &release_heads, pending);
2077 for (unsigned int i = 0; i < release_heads.size(); i++) {
2078 if (!acquire->has_synchronized_with(release_heads[i])) {
2079 if (acquire->synchronize_with(release_heads[i]))
2082 set_bad_synchronization();
2087 /* Re-check all pending release sequences */
2088 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
2089 /* Re-check read-acquire for mo_graph edges */
2090 if (acquire->is_read())
2091 work_queue->push_back(MOEdgeWorkEntry(acquire));
2093 /* propagate synchronization to later actions */
2094 action_list_t::reverse_iterator rit = action_trace->rbegin();
2095 for (; (*rit) != acquire; rit++) {
2096 ModelAction *propagate = *rit;
2097 if (acquire->happens_before(propagate)) {
2098 propagate->synchronize_with(acquire);
2099 /* Re-check 'propagate' for mo_graph edges */
2100 work_queue->push_back(MOEdgeWorkEntry(propagate));
2105 it = pending_rel_seqs->erase(it);
2106 snapshot_free(pending);
2112 // If we resolved promises or data races, see if we have realized a data race.
2119 * Performs various bookkeeping operations for the current ModelAction. For
2120 * instance, adds action to the per-object, per-thread action vector and to the
2121 * action trace list of all thread actions.
2123 * @param act is the ModelAction to add.
2125 void ModelChecker::add_action_to_lists(ModelAction *act)
2127 int tid = id_to_int(act->get_tid());
2128 ModelAction *uninit = NULL;
2130 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
2131 if (list->empty() && act->is_atomic_var()) {
2132 uninit = new_uninitialized_action(act->get_location());
2133 uninit_id = id_to_int(uninit->get_tid());
2134 list->push_back(uninit);
2136 list->push_back(act);
2138 action_trace->push_back(act);
2140 action_trace->push_front(uninit);
2142 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
2143 if (tid >= (int)vec->size())
2144 vec->resize(priv->next_thread_id);
2145 (*vec)[tid].push_back(act);
2147 (*vec)[uninit_id].push_front(uninit);
2149 if ((int)thrd_last_action->size() <= tid)
2150 thrd_last_action->resize(get_num_threads());
2151 (*thrd_last_action)[tid] = act;
2153 (*thrd_last_action)[uninit_id] = uninit;
2155 if (act->is_fence() && act->is_release()) {
2156 if ((int)thrd_last_fence_release->size() <= tid)
2157 thrd_last_fence_release->resize(get_num_threads());
2158 (*thrd_last_fence_release)[tid] = act;
2161 if (act->is_wait()) {
2162 void *mutex_loc = (void *) act->get_value();
2163 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
2165 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
2166 if (tid >= (int)vec->size())
2167 vec->resize(priv->next_thread_id);
2168 (*vec)[tid].push_back(act);
2173 * @brief Get the last action performed by a particular Thread
2174 * @param tid The thread ID of the Thread in question
2175 * @return The last action in the thread
2177 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
2179 int threadid = id_to_int(tid);
2180 if (threadid < (int)thrd_last_action->size())
2181 return (*thrd_last_action)[id_to_int(tid)];
2187 * @brief Get the last fence release performed by a particular Thread
2188 * @param tid The thread ID of the Thread in question
2189 * @return The last fence release in the thread, if one exists; NULL otherwise
2191 ModelAction * ModelChecker::get_last_fence_release(thread_id_t tid) const
2193 int threadid = id_to_int(tid);
2194 if (threadid < (int)thrd_last_fence_release->size())
2195 return (*thrd_last_fence_release)[id_to_int(tid)];
2201 * Gets the last memory_order_seq_cst write (in the total global sequence)
2202 * performed on a particular object (i.e., memory location), not including the
2204 * @param curr The current ModelAction; also denotes the object location to
2206 * @return The last seq_cst write
2208 ModelAction * ModelChecker::get_last_seq_cst_write(ModelAction *curr) const
2210 void *location = curr->get_location();
2211 action_list_t *list = get_safe_ptr_action(obj_map, location);
2212 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
2213 action_list_t::reverse_iterator rit;
2214 for (rit = list->rbegin(); rit != list->rend(); rit++)
2215 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
2221 * Gets the last memory_order_seq_cst fence (in the total global sequence)
2222 * performed in a particular thread, prior to a particular fence.
2223 * @param tid The ID of the thread to check
2224 * @param before_fence The fence from which to begin the search; if NULL, then
2225 * search for the most recent fence in the thread.
2226 * @return The last prior seq_cst fence in the thread, if exists; otherwise, NULL
2228 ModelAction * ModelChecker::get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const
2230 /* All fences should have NULL location */
2231 action_list_t *list = get_safe_ptr_action(obj_map, NULL);
2232 action_list_t::reverse_iterator rit = list->rbegin();
2235 for (; rit != list->rend(); rit++)
2236 if (*rit == before_fence)
2239 ASSERT(*rit == before_fence);
2243 for (; rit != list->rend(); rit++)
2244 if ((*rit)->is_fence() && (tid == (*rit)->get_tid()) && (*rit)->is_seqcst())
2250 * Gets the last unlock operation performed on a particular mutex (i.e., memory
2251 * location). This function identifies the mutex according to the current
2252 * action, which is presumed to perform on the same mutex.
2253 * @param curr The current ModelAction; also denotes the object location to
2255 * @return The last unlock operation
2257 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
2259 void *location = curr->get_location();
2260 action_list_t *list = get_safe_ptr_action(obj_map, location);
2261 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
2262 action_list_t::reverse_iterator rit;
2263 for (rit = list->rbegin(); rit != list->rend(); rit++)
2264 if ((*rit)->is_unlock() || (*rit)->is_wait())
2269 ModelAction * ModelChecker::get_parent_action(thread_id_t tid) const
2271 ModelAction *parent = get_last_action(tid);
2273 parent = get_thread(tid)->get_creation();
2278 * Returns the clock vector for a given thread.
2279 * @param tid The thread whose clock vector we want
2280 * @return Desired clock vector
2282 ClockVector * ModelChecker::get_cv(thread_id_t tid) const
2284 return get_parent_action(tid)->get_cv();
2288 * Resolve a set of Promises with a current write. The set is provided in the
2289 * Node corresponding to @a write.
2290 * @param write The ModelAction that is fulfilling Promises
2291 * @return True if promises were resolved; false otherwise
2293 bool ModelChecker::resolve_promises(ModelAction *write)
2295 bool resolved = false;
2296 std::vector< thread_id_t, ModelAlloc<thread_id_t> > threads_to_check;
2298 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
2299 Promise *promise = (*promises)[promise_index];
2300 if (write->get_node()->get_promise(i)) {
2301 ModelAction *read = promise->get_action();
2302 if (read->is_rmw()) {
2303 mo_graph->addRMWEdge(write, read);
2305 read_from(read, write);
2306 //First fix up the modification order for actions that happened
2308 r_modification_order(read, write);
2309 //Next fix up the modification order for actions that happened
2311 post_r_modification_order(read, write);
2312 //Make sure the promise's value matches the write's value
2313 ASSERT(promise->get_value() == write->get_value());
2316 promises->erase(promises->begin() + promise_index);
2317 threads_to_check.push_back(read->get_tid());
2324 //Check whether reading these writes has made threads unable to
2327 for (unsigned int i = 0; i < threads_to_check.size(); i++)
2328 mo_check_promises(threads_to_check[i], write);
2334 * Compute the set of promises that could potentially be satisfied by this
2335 * action. Note that the set computation actually appears in the Node, not in
2337 * @param curr The ModelAction that may satisfy promises
2339 void ModelChecker::compute_promises(ModelAction *curr)
2341 for (unsigned int i = 0; i < promises->size(); i++) {
2342 Promise *promise = (*promises)[i];
2343 const ModelAction *act = promise->get_action();
2344 if (!act->happens_before(curr) &&
2346 !act->could_synchronize_with(curr) &&
2347 !act->same_thread(curr) &&
2348 act->get_location() == curr->get_location() &&
2349 promise->get_value() == curr->get_value()) {
2350 curr->get_node()->set_promise(i, act->is_rmw());
2355 /** Checks promises in response to change in ClockVector Threads. */
2356 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2358 for (unsigned int i = 0; i < promises->size(); i++) {
2359 Promise *promise = (*promises)[i];
2360 const ModelAction *act = promise->get_action();
2361 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
2362 merge_cv->synchronized_since(act)) {
2363 if (promise->increment_threads(tid)) {
2364 //Promise has failed
2365 priv->failed_promise = true;
2372 void ModelChecker::check_promises_thread_disabled() {
2373 for (unsigned int i = 0; i < promises->size(); i++) {
2374 Promise *promise = (*promises)[i];
2375 if (promise->check_promise()) {
2376 priv->failed_promise = true;
2382 /** Checks promises in response to addition to modification order for threads.
2384 * pthread is the thread that performed the read that created the promise
2386 * pread is the read that created the promise
2388 * pwrite is either the first write to same location as pread by
2389 * pthread that is sequenced after pread or the value read by the
2390 * first read to the same lcoation as pread by pthread that is
2391 * sequenced after pread..
2393 * 1. If tid=pthread, then we check what other threads are reachable
2394 * through the mode order starting with pwrite. Those threads cannot
2395 * perform a write that will resolve the promise due to modification
2396 * order constraints.
2398 * 2. If the tid is not pthread, we check whether pwrite can reach the
2399 * action write through the modification order. If so, that thread
2400 * cannot perform a future write that will resolve the promise due to
2401 * modificatin order constraints.
2403 * @param tid The thread that either read from the model action
2404 * write, or actually did the model action write.
2406 * @param write The ModelAction representing the relevant write.
2408 void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write)
2410 void *location = write->get_location();
2411 for (unsigned int i = 0; i < promises->size(); i++) {
2412 Promise *promise = (*promises)[i];
2413 const ModelAction *act = promise->get_action();
2415 //Is this promise on the same location?
2416 if (act->get_location() != location)
2419 //same thread as the promise
2420 if (act->get_tid() == tid) {
2422 //do we have a pwrite for the promise, if not, set it
2423 if (promise->get_write() == NULL) {
2424 promise->set_write(write);
2425 //The pwrite cannot happen before the promise
2426 if (write->happens_before(act) && (write != act)) {
2427 priv->failed_promise = true;
2431 if (mo_graph->checkPromise(write, promise)) {
2432 priv->failed_promise = true;
2437 //Don't do any lookups twice for the same thread
2438 if (promise->has_sync_thread(tid))
2441 if (promise->get_write() && mo_graph->checkReachable(promise->get_write(), write)) {
2442 if (promise->increment_threads(tid)) {
2443 priv->failed_promise = true;
2451 * Compute the set of writes that may break the current pending release
2452 * sequence. This information is extracted from previou release sequence
2455 * @param curr The current ModelAction. Must be a release sequence fixup
2458 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2460 if (pending_rel_seqs->empty())
2463 struct release_seq *pending = pending_rel_seqs->back();
2464 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2465 const ModelAction *write = pending->writes[i];
2466 curr->get_node()->add_relseq_break(write);
2469 /* NULL means don't break the sequence; just synchronize */
2470 curr->get_node()->add_relseq_break(NULL);
2474 * Build up an initial set of all past writes that this 'read' action may read
2475 * from. This set is determined by the clock vector's "happens before"
2477 * @param curr is the current ModelAction that we are exploring; it must be a
2480 void ModelChecker::build_reads_from_past(ModelAction *curr)
2482 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2484 ASSERT(curr->is_read());
2486 ModelAction *last_sc_write = NULL;
2488 if (curr->is_seqcst())
2489 last_sc_write = get_last_seq_cst_write(curr);
2491 /* Iterate over all threads */
2492 for (i = 0; i < thrd_lists->size(); i++) {
2493 /* Iterate over actions in thread, starting from most recent */
2494 action_list_t *list = &(*thrd_lists)[i];
2495 action_list_t::reverse_iterator rit;
2496 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2497 ModelAction *act = *rit;
2499 /* Only consider 'write' actions */
2500 if (!act->is_write() || act == curr)
2503 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2504 bool allow_read = true;
2506 if (curr->is_seqcst() && (act->is_seqcst() || (last_sc_write != NULL && act->happens_before(last_sc_write))) && act != last_sc_write)
2508 else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act))
2512 curr->get_node()->add_read_from(act);
2514 /* Include at most one act per-thread that "happens before" curr */
2515 if (act->happens_before(curr))
2520 if (DBG_ENABLED()) {
2521 model_print("Reached read action:\n");
2523 model_print("Printing may_read_from\n");
2524 curr->get_node()->print_may_read_from();
2525 model_print("End printing may_read_from\n");
2529 bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write)
2532 /* UNINIT actions don't have a Node, and they never sleep */
2533 if (write->is_uninitialized())
2535 Node *prevnode = write->get_node()->get_parent();
2537 bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET;
2538 if (write->is_release() && thread_sleep)
2540 if (!write->is_rmw()) {
2543 if (write->get_reads_from() == NULL)
2545 write = write->get_reads_from();
2550 * @brief Create a new action representing an uninitialized atomic
2551 * @param location The memory location of the atomic object
2552 * @return A pointer to a new ModelAction
2554 ModelAction * ModelChecker::new_uninitialized_action(void *location) const
2556 ModelAction *act = (ModelAction *)snapshot_malloc(sizeof(class ModelAction));
2557 act = new (act) ModelAction(ATOMIC_UNINIT, std::memory_order_relaxed, location, 0, model_thread);
2558 act->create_cv(NULL);
2562 static void print_list(action_list_t *list, int exec_num = -1)
2564 action_list_t::iterator it;
2566 model_print("---------------------------------------------------------------------\n");
2568 model_print("Execution %d:\n", exec_num);
2570 unsigned int hash = 0;
2572 for (it = list->begin(); it != list->end(); it++) {
2574 hash = hash^(hash<<3)^((*it)->hash());
2576 model_print("HASH %u\n", hash);
2577 model_print("---------------------------------------------------------------------\n");
2580 #if SUPPORT_MOD_ORDER_DUMP
2581 void ModelChecker::dumpGraph(char *filename) const
2584 sprintf(buffer, "%s.dot", filename);
2585 FILE *file = fopen(buffer, "w");
2586 fprintf(file, "digraph %s {\n", filename);
2587 mo_graph->dumpNodes(file);
2588 ModelAction **thread_array = (ModelAction **)model_calloc(1, sizeof(ModelAction *) * get_num_threads());
2590 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2591 ModelAction *action = *it;
2592 if (action->is_read()) {
2593 fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(), action->get_seq_number(), action->get_tid());
2594 if (action->get_reads_from() != NULL)
2595 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
2597 if (thread_array[action->get_tid()] != NULL) {
2598 fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
2601 thread_array[action->get_tid()] = action;
2603 fprintf(file, "}\n");
2604 model_free(thread_array);
2609 /** @brief Prints an execution trace summary. */
2610 void ModelChecker::print_summary() const
2612 #if SUPPORT_MOD_ORDER_DUMP
2614 char buffername[100];
2615 sprintf(buffername, "exec%04u", stats.num_total);
2616 mo_graph->dumpGraphToFile(buffername);
2617 sprintf(buffername, "graph%04u", stats.num_total);
2618 dumpGraph(buffername);
2621 if (!isfeasibleprefix())
2622 model_print("INFEASIBLE EXECUTION!\n");
2623 print_list(action_trace, stats.num_total);
2628 * Add a Thread to the system for the first time. Should only be called once
2630 * @param t The Thread to add
2632 void ModelChecker::add_thread(Thread *t)
2634 thread_map->put(id_to_int(t->get_id()), t);
2635 scheduler->add_thread(t);
2639 * Removes a thread from the scheduler.
2640 * @param the thread to remove.
2642 void ModelChecker::remove_thread(Thread *t)
2644 scheduler->remove_thread(t);
2648 * @brief Get a Thread reference by its ID
2649 * @param tid The Thread's ID
2650 * @return A Thread reference
2652 Thread * ModelChecker::get_thread(thread_id_t tid) const
2654 return thread_map->get(id_to_int(tid));
2658 * @brief Get a reference to the Thread in which a ModelAction was executed
2659 * @param act The ModelAction
2660 * @return A Thread reference
2662 Thread * ModelChecker::get_thread(ModelAction *act) const
2664 return get_thread(act->get_tid());
2668 * @brief Check if a Thread is currently enabled
2669 * @param t The Thread to check
2670 * @return True if the Thread is currently enabled
2672 bool ModelChecker::is_enabled(Thread *t) const
2674 return scheduler->is_enabled(t);
2678 * @brief Check if a Thread is currently enabled
2679 * @param tid The ID of the Thread to check
2680 * @return True if the Thread is currently enabled
2682 bool ModelChecker::is_enabled(thread_id_t tid) const
2684 return scheduler->is_enabled(tid);
2688 * Switch from a user-context to the "master thread" context (a.k.a. system
2689 * context). This switch is made with the intention of exploring a particular
2690 * model-checking action (described by a ModelAction object). Must be called
2691 * from a user-thread context.
2693 * @param act The current action that will be explored. May be NULL only if
2694 * trace is exiting via an assertion (see ModelChecker::set_assert and
2695 * ModelChecker::has_asserted).
2696 * @return Return the value returned by the current action
2698 uint64_t ModelChecker::switch_to_master(ModelAction *act)
2701 Thread *old = thread_current();
2702 set_current_action(act);
2703 old->set_state(THREAD_READY);
2704 if (Thread::swap(old, &system_context) < 0) {
2705 perror("swap threads");
2708 return old->get_return_value();
2712 * Takes the next step in the execution, if possible.
2713 * @param curr The current step to take
2714 * @return Returns true (success) if a step was taken and false otherwise.
2716 bool ModelChecker::take_step(ModelAction *curr)
2721 Thread *curr_thrd = get_thread(curr);
2722 ASSERT(curr_thrd->get_state() == THREAD_READY);
2724 Thread *next_thrd = check_current_action(curr);
2726 if (curr_thrd->is_blocked() || curr_thrd->is_complete())
2727 scheduler->remove_thread(curr_thrd);
2729 next_thrd = scheduler->next_thread(next_thrd);
2731 /* Infeasible -> don't take any more steps */
2732 if (is_infeasible())
2734 else if (isfeasibleprefix() && have_bug_reports()) {
2739 if (params.bound != 0) {
2740 if (priv->used_sequence_numbers > params.bound) {
2745 DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
2746 next_thrd ? id_to_int(next_thrd->get_id()) : -1);
2749 * Launch end-of-execution release sequence fixups only when there are:
2751 * (1) no more user threads to run (or when execution replay chooses
2752 * the 'model_thread')
2753 * (2) pending release sequences
2754 * (3) pending assertions (i.e., data races)
2755 * (4) no pending promises
2757 if (!pending_rel_seqs->empty() && (!next_thrd || next_thrd->is_model_thread()) &&
2758 is_feasible_prefix_ignore_relseq() && !unrealizedraces.empty()) {
2759 model_print("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
2760 pending_rel_seqs->size());
2761 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2762 std::memory_order_seq_cst, NULL, VALUE_NONE,
2764 set_current_action(fixup);
2768 /* next_thrd == NULL -> don't take any more steps */
2772 next_thrd->set_state(THREAD_RUNNING);
2774 if (next_thrd->get_pending() != NULL) {
2775 /* restart a pending action */
2776 set_current_action(next_thrd->get_pending());
2777 next_thrd->set_pending(NULL);
2778 next_thrd->set_state(THREAD_READY);
2782 /* Return false only if swap fails with an error */
2783 return (Thread::swap(&system_context, next_thrd) == 0);
2786 /** Wrapper to run the user's main function, with appropriate arguments */
2787 void user_main_wrapper(void *)
2789 user_main(model->params.argc, model->params.argv);
2792 /** @brief Run ModelChecker for the user program */
2793 void ModelChecker::run()
2797 Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL);
2801 /* Run user thread up to its first action */
2802 scheduler->next_thread(t);
2803 Thread::swap(&system_context, t);
2805 /* Wait for all threads to complete */
2806 while (take_step(priv->current_action));
2807 } while (next_execution());