9 #include "snapshot-interface.h"
11 #include "clockvector.h"
12 #include "cyclegraph.h"
15 #include "threads-model.h"
18 #define INITIAL_THREAD_ID 0
23 bug_message(const char *str) {
24 const char *fmt = " [BUG] %s\n";
25 msg = (char *)snapshot_malloc(strlen(fmt) + strlen(str));
26 sprintf(msg, fmt, str);
28 ~bug_message() { if (msg) snapshot_free(msg); }
31 void print() { model_print("%s", msg); }
37 * Structure for holding small ModelChecker members that should be snapshotted
39 struct model_snapshot_members {
40 model_snapshot_members() :
42 /* First thread created will have id INITIAL_THREAD_ID */
43 next_thread_id(INITIAL_THREAD_ID),
44 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;
65 ModelAction *next_backtrack;
66 std::vector< bug_message *, SnapshotAlloc<bug_message *> > bugs;
67 struct execution_stats stats;
70 /** @brief Incorrectly-ordered synchronization was made */
71 bool bad_synchronization;
77 /** @brief Constructor */
78 ModelChecker::ModelChecker(struct model_params params) :
79 /* Initialize default scheduler */
81 scheduler(new Scheduler()),
83 earliest_diverge(NULL),
84 action_trace(new action_list_t()),
85 thread_map(new HashTable<int, Thread *, int>()),
86 obj_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
87 lock_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
88 condvar_waiters_map(new HashTable<const void *, action_list_t *, uintptr_t, 4>()),
89 obj_thrd_map(new HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4 >()),
90 promises(new std::vector< Promise *, SnapshotAlloc<Promise *> >()),
91 futurevalues(new std::vector< struct PendingFutureValue, SnapshotAlloc<struct PendingFutureValue> >()),
92 pending_rel_seqs(new std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >()),
93 thrd_last_action(new std::vector< ModelAction *, SnapshotAlloc<ModelAction *> >(1)),
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;
129 static action_list_t * get_safe_ptr_action(HashTable<const void *, action_list_t *, uintptr_t, 4> * hash, void * ptr) {
130 action_list_t * tmp=hash->get(ptr);
132 tmp=new action_list_t();
138 static std::vector<action_list_t> * get_safe_ptr_vect_action(HashTable<void *, std::vector<action_list_t> *, uintptr_t, 4> * hash, void * ptr) {
139 std::vector<action_list_t> * tmp=hash->get(ptr);
141 tmp=new std::vector<action_list_t>();
148 * Restores user program to initial state and resets all model-checker data
151 void ModelChecker::reset_to_initial_state()
153 DEBUG("+++ Resetting to initial state +++\n");
154 node_stack->reset_execution();
156 /* Print all model-checker output before rollback */
159 snapshotObject->backTrackBeforeStep(0);
162 /** @return a thread ID for a new Thread */
163 thread_id_t ModelChecker::get_next_id()
165 return priv->next_thread_id++;
168 /** @return the number of user threads created during this execution */
169 unsigned int ModelChecker::get_num_threads() const
171 return priv->next_thread_id;
174 /** @return The currently executing Thread. */
175 Thread * ModelChecker::get_current_thread()
177 return scheduler->get_current_thread();
180 /** @return a sequence number for a new ModelAction */
181 modelclock_t ModelChecker::get_next_seq_num()
183 return ++priv->used_sequence_numbers;
186 Node * ModelChecker::get_curr_node() {
187 return node_stack->get_head();
191 * @brief Choose the next thread to execute.
193 * This function chooses the next thread that should execute. It can force the
194 * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
195 * followed by a THREAD_START, or it can enforce execution replay/backtracking.
196 * The model-checker may have no preference regarding the next thread (i.e.,
197 * when exploring a new execution ordering), in which case this will return
199 * @param curr The current ModelAction. This action might guide the choice of
201 * @return The next thread to run. If the model-checker has no preference, NULL.
203 Thread * ModelChecker::get_next_thread(ModelAction *curr)
208 /* Do not split atomic actions. */
210 return thread_current();
211 /* The THREAD_CREATE action points to the created Thread */
212 else if (curr->get_type() == THREAD_CREATE)
213 return (Thread *)curr->get_location();
216 /* Have we completed exploring the preselected path? */
220 /* Else, we are trying to replay an execution */
221 ModelAction *next = node_stack->get_next()->get_action();
223 if (next == diverge) {
224 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
225 earliest_diverge=diverge;
227 Node *nextnode = next->get_node();
228 Node *prevnode = nextnode->get_parent();
229 scheduler->update_sleep_set(prevnode);
231 /* Reached divergence point */
232 if (nextnode->increment_misc()) {
233 /* The next node will try to satisfy a different misc_index values. */
234 tid = next->get_tid();
235 node_stack->pop_restofstack(2);
236 } else if (nextnode->increment_promise()) {
237 /* The next node will try to satisfy a different set of promises. */
238 tid = next->get_tid();
239 node_stack->pop_restofstack(2);
240 } else if (nextnode->increment_read_from()) {
241 /* The next node will read from a different value. */
242 tid = next->get_tid();
243 node_stack->pop_restofstack(2);
244 } else if (nextnode->increment_future_value()) {
245 /* The next node will try to read from a different future value. */
246 tid = next->get_tid();
247 node_stack->pop_restofstack(2);
248 } else if (nextnode->increment_relseq_break()) {
249 /* The next node will try to resolve a release sequence differently */
250 tid = next->get_tid();
251 node_stack->pop_restofstack(2);
253 /* Make a different thread execute for next step */
254 scheduler->add_sleep(thread_map->get(id_to_int(next->get_tid())));
255 tid = prevnode->get_next_backtrack();
256 /* Make sure the backtracked thread isn't sleeping. */
257 node_stack->pop_restofstack(1);
258 if (diverge==earliest_diverge) {
259 earliest_diverge=prevnode->get_action();
262 /* The correct sleep set is in the parent node. */
265 DEBUG("*** Divergence point ***\n");
269 tid = next->get_tid();
271 DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
272 ASSERT(tid != THREAD_ID_T_NONE);
273 return thread_map->get(id_to_int(tid));
277 * We need to know what the next actions of all threads in the sleep
278 * set will be. This method computes them and stores the actions at
279 * the corresponding thread object's pending action.
282 void ModelChecker::execute_sleep_set() {
283 for(unsigned int i=0;i<get_num_threads();i++) {
284 thread_id_t tid=int_to_id(i);
285 Thread *thr=get_thread(tid);
286 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET &&
287 thr->get_pending() == NULL ) {
288 thr->set_state(THREAD_RUNNING);
289 scheduler->next_thread(thr);
290 Thread::swap(&system_context, thr);
291 priv->current_action->set_sleep_flag();
292 thr->set_pending(priv->current_action);
295 priv->current_action = NULL;
298 void ModelChecker::wake_up_sleeping_actions(ModelAction * curr) {
299 for(unsigned int i=0;i<get_num_threads();i++) {
300 thread_id_t tid=int_to_id(i);
301 Thread *thr=get_thread(tid);
302 if ( scheduler->get_enabled(thr) == THREAD_SLEEP_SET ) {
303 ModelAction *pending_act=thr->get_pending();
304 if ((!curr->is_rmwr())&&pending_act->could_synchronize_with(curr)) {
305 //Remove this thread from sleep set
306 scheduler->remove_sleep(thr);
312 /** @brief Alert the model-checker that an incorrectly-ordered
313 * synchronization was made */
314 void ModelChecker::set_bad_synchronization()
316 priv->bad_synchronization = true;
319 bool ModelChecker::has_asserted() const
321 return priv->asserted;
324 void ModelChecker::set_assert()
326 priv->asserted = true;
330 * Check if we are in a deadlock. Should only be called at the end of an
331 * execution, although it should not give false positives in the middle of an
332 * execution (there should be some ENABLED thread).
334 * @return True if program is in a deadlock; false otherwise
336 bool ModelChecker::is_deadlocked() const
338 bool blocking_threads = false;
339 for (unsigned int i = 0; i < get_num_threads(); i++) {
340 thread_id_t tid = int_to_id(i);
343 Thread *t = get_thread(tid);
344 if (!t->is_model_thread() && t->get_pending())
345 blocking_threads = true;
347 return blocking_threads;
351 * Check if this is a complete execution. That is, have all thread completed
352 * execution (rather than exiting because sleep sets have forced a redundant
355 * @return True if the execution is complete.
357 bool ModelChecker::is_complete_execution() const
359 for (unsigned int i = 0; i < get_num_threads(); i++)
360 if (is_enabled(int_to_id(i)))
366 * @brief Assert a bug in the executing program.
368 * Use this function to assert any sort of bug in the user program. If the
369 * current trace is feasible (actually, a prefix of some feasible execution),
370 * then this execution will be aborted, printing the appropriate message. If
371 * the current trace is not yet feasible, the error message will be stashed and
372 * printed if the execution ever becomes feasible.
374 * @param msg Descriptive message for the bug (do not include newline char)
375 * @return True if bug is immediately-feasible
377 bool ModelChecker::assert_bug(const char *msg)
379 priv->bugs.push_back(new bug_message(msg));
381 if (isfeasibleprefix()) {
389 * @brief Assert a bug in the executing program, asserted by a user thread
390 * @see ModelChecker::assert_bug
391 * @param msg Descriptive message for the bug (do not include newline char)
393 void ModelChecker::assert_user_bug(const char *msg)
395 /* If feasible bug, bail out now */
397 switch_to_master(NULL);
400 /** @return True, if any bugs have been reported for this execution */
401 bool ModelChecker::have_bug_reports() const
403 return priv->bugs.size() != 0;
406 /** @brief Print bug report listing for this execution (if any bugs exist) */
407 void ModelChecker::print_bugs() const
409 if (have_bug_reports()) {
410 model_print("Bug report: %zu bug%s detected\n",
412 priv->bugs.size() > 1 ? "s" : "");
413 for (unsigned int i = 0; i < priv->bugs.size(); i++)
414 priv->bugs[i]->print();
419 * @brief Record end-of-execution stats
421 * Must be run when exiting an execution. Records various stats.
422 * @see struct execution_stats
424 void ModelChecker::record_stats()
427 if (!isfinalfeasible())
428 stats.num_infeasible++;
429 else if (have_bug_reports())
430 stats.num_buggy_executions++;
431 else if (is_complete_execution())
432 stats.num_complete++;
434 stats.num_redundant++;
437 /** @brief Print execution stats */
438 void ModelChecker::print_stats() const
440 model_print("Number of complete, bug-free executions: %d\n", stats.num_complete);
441 model_print("Number of redundant executions: %d\n", stats.num_redundant);
442 model_print("Number of buggy executions: %d\n", stats.num_buggy_executions);
443 model_print("Number of infeasible executions: %d\n", stats.num_infeasible);
444 model_print("Total executions: %d\n", stats.num_total);
445 model_print("Total nodes created: %d\n", node_stack->get_total_nodes());
449 * @brief End-of-exeuction print
450 * @param printbugs Should any existing bugs be printed?
452 void ModelChecker::print_execution(bool printbugs) const
454 print_program_output();
456 if (DBG_ENABLED() || params.verbose) {
457 model_print("Earliest divergence point since last feasible execution:\n");
458 if (earliest_diverge)
459 earliest_diverge->print();
461 model_print("(Not set)\n");
467 /* Don't print invalid bugs */
476 * Queries the model-checker for more executions to explore and, if one
477 * exists, resets the model-checker state to execute a new execution.
479 * @return If there are more executions to explore, return true. Otherwise,
482 bool ModelChecker::next_execution()
485 /* Is this execution a feasible execution that's worth bug-checking? */
486 bool complete = isfinalfeasible() && (is_complete_execution() ||
489 /* End-of-execution bug checks */
492 assert_bug("Deadlock detected");
500 if (DBG_ENABLED() || params.verbose || have_bug_reports())
501 print_execution(complete);
503 clear_program_output();
506 earliest_diverge = NULL;
508 if ((diverge = get_next_backtrack()) == NULL)
512 model_print("Next execution will diverge at:\n");
516 reset_to_initial_state();
520 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
522 switch (act->get_type()) {
526 /* Optimization: relaxed operations don't need backtracking */
527 if (act->is_relaxed())
529 /* linear search: from most recent to oldest */
530 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
531 action_list_t::reverse_iterator rit;
532 for (rit = list->rbegin(); rit != list->rend(); rit++) {
533 ModelAction *prev = *rit;
534 if (prev->could_synchronize_with(act))
540 case ATOMIC_TRYLOCK: {
541 /* linear search: from most recent to oldest */
542 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
543 action_list_t::reverse_iterator rit;
544 for (rit = list->rbegin(); rit != list->rend(); rit++) {
545 ModelAction *prev = *rit;
546 if (act->is_conflicting_lock(prev))
551 case ATOMIC_UNLOCK: {
552 /* linear search: from most recent to oldest */
553 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
554 action_list_t::reverse_iterator rit;
555 for (rit = list->rbegin(); rit != list->rend(); rit++) {
556 ModelAction *prev = *rit;
557 if (!act->same_thread(prev)&&prev->is_failed_trylock())
563 /* linear search: from most recent to oldest */
564 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
565 action_list_t::reverse_iterator rit;
566 for (rit = list->rbegin(); rit != list->rend(); rit++) {
567 ModelAction *prev = *rit;
568 if (!act->same_thread(prev)&&prev->is_failed_trylock())
570 if (!act->same_thread(prev)&&prev->is_notify())
576 case ATOMIC_NOTIFY_ALL:
577 case ATOMIC_NOTIFY_ONE: {
578 /* linear search: from most recent to oldest */
579 action_list_t *list = get_safe_ptr_action(obj_map, act->get_location());
580 action_list_t::reverse_iterator rit;
581 for (rit = list->rbegin(); rit != list->rend(); rit++) {
582 ModelAction *prev = *rit;
583 if (!act->same_thread(prev)&&prev->is_wait())
594 /** This method finds backtracking points where we should try to
595 * reorder the parameter ModelAction against.
597 * @param the ModelAction to find backtracking points for.
599 void ModelChecker::set_backtracking(ModelAction *act)
601 Thread *t = get_thread(act);
602 ModelAction * prev = get_last_conflict(act);
606 Node * node = prev->get_node()->get_parent();
608 int low_tid, high_tid;
609 if (node->is_enabled(t)) {
610 low_tid = id_to_int(act->get_tid());
611 high_tid = low_tid+1;
614 high_tid = get_num_threads();
617 for(int i = low_tid; i < high_tid; i++) {
618 thread_id_t tid = int_to_id(i);
620 /* Make sure this thread can be enabled here. */
621 if (i >= node->get_num_threads())
624 /* Don't backtrack into a point where the thread is disabled or sleeping. */
625 if (node->enabled_status(tid)!=THREAD_ENABLED)
628 /* Check if this has been explored already */
629 if (node->has_been_explored(tid))
632 /* See if fairness allows */
633 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
635 for(int t=0;t<node->get_num_threads();t++) {
636 thread_id_t tother=int_to_id(t);
637 if (node->is_enabled(tother) && node->has_priority(tother)) {
645 /* Cache the latest backtracking point */
646 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
647 priv->next_backtrack = prev;
649 /* If this is a new backtracking point, mark the tree */
650 if (!node->set_backtrack(tid))
652 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
653 id_to_int(prev->get_tid()),
654 id_to_int(t->get_id()));
663 * Returns last backtracking point. The model checker will explore a different
664 * path for this point in the next execution.
665 * @return The ModelAction at which the next execution should diverge.
667 ModelAction * ModelChecker::get_next_backtrack()
669 ModelAction *next = priv->next_backtrack;
670 priv->next_backtrack = NULL;
675 * Processes a read or rmw model action.
676 * @param curr is the read model action to process.
677 * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
678 * @return True if processing this read updates the mo_graph.
680 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
682 uint64_t value = VALUE_NONE;
683 bool updated = false;
685 const ModelAction *reads_from = curr->get_node()->get_read_from();
686 if (reads_from != NULL) {
687 mo_graph->startChanges();
689 value = reads_from->get_value();
690 bool r_status = false;
692 if (!second_part_of_rmw) {
693 check_recency(curr, reads_from);
694 r_status = r_modification_order(curr, reads_from);
698 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
699 mo_graph->rollbackChanges();
700 priv->too_many_reads = false;
704 curr->read_from(reads_from);
705 mo_graph->commitChanges();
706 mo_check_promises(curr->get_tid(), reads_from);
709 } else if (!second_part_of_rmw) {
710 /* Read from future value */
711 value = curr->get_node()->get_future_value();
712 modelclock_t expiration = curr->get_node()->get_future_value_expiration();
713 curr->read_from(NULL);
714 Promise *valuepromise = new Promise(curr, value, expiration);
715 promises->push_back(valuepromise);
717 get_thread(curr)->set_return_value(value);
723 * Processes a lock, trylock, or unlock model action. @param curr is
724 * the read model action to process.
726 * The try lock operation checks whether the lock is taken. If not,
727 * it falls to the normal lock operation case. If so, it returns
730 * The lock operation has already been checked that it is enabled, so
731 * it just grabs the lock and synchronizes with the previous unlock.
733 * The unlock operation has to re-enable all of the threads that are
734 * waiting on the lock.
736 * @return True if synchronization was updated; false otherwise
738 bool ModelChecker::process_mutex(ModelAction *curr) {
739 std::mutex *mutex=NULL;
740 struct std::mutex_state *state=NULL;
742 if (curr->is_trylock() || curr->is_lock() || curr->is_unlock()) {
743 mutex = (std::mutex *)curr->get_location();
744 state = mutex->get_state();
745 } else if(curr->is_wait()) {
746 mutex = (std::mutex *)curr->get_value();
747 state = mutex->get_state();
750 switch (curr->get_type()) {
751 case ATOMIC_TRYLOCK: {
752 bool success = !state->islocked;
753 curr->set_try_lock(success);
755 get_thread(curr)->set_return_value(0);
758 get_thread(curr)->set_return_value(1);
760 //otherwise fall into the lock case
762 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock)
763 assert_bug("Lock access before initialization");
764 state->islocked = true;
765 ModelAction *unlock = get_last_unlock(curr);
766 //synchronize with the previous unlock statement
767 if (unlock != NULL) {
768 curr->synchronize_with(unlock);
773 case ATOMIC_UNLOCK: {
775 state->islocked = false;
776 //wake up the other threads
777 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, curr->get_location());
778 //activate all the waiting threads
779 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
780 scheduler->wake(get_thread(*rit));
787 state->islocked = false;
788 //wake up the other threads
789 action_list_t *waiters = get_safe_ptr_action(lock_waiters_map, (void *) curr->get_value());
790 //activate all the waiting threads
791 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
792 scheduler->wake(get_thread(*rit));
795 //check whether we should go to sleep or not...simulate spurious failures
796 if (curr->get_node()->get_misc()==0) {
797 get_safe_ptr_action(condvar_waiters_map, curr->get_location())->push_back(curr);
799 scheduler->sleep(get_current_thread());
803 case ATOMIC_NOTIFY_ALL: {
804 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
805 //activate all the waiting threads
806 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
807 scheduler->wake(get_thread(*rit));
812 case ATOMIC_NOTIFY_ONE: {
813 action_list_t *waiters = get_safe_ptr_action(condvar_waiters_map, curr->get_location());
814 int wakeupthread=curr->get_node()->get_misc();
815 action_list_t::iterator it = waiters->begin();
816 advance(it, wakeupthread);
817 scheduler->wake(get_thread(*it));
829 * Process a write ModelAction
830 * @param curr The ModelAction to process
831 * @return True if the mo_graph was updated or promises were resolved
833 bool ModelChecker::process_write(ModelAction *curr)
835 bool updated_mod_order = w_modification_order(curr);
836 bool updated_promises = resolve_promises(curr);
838 if (promises->size() == 0) {
839 for (unsigned int i = 0; i < futurevalues->size(); i++) {
840 struct PendingFutureValue pfv = (*futurevalues)[i];
841 //Do more ambitious checks now that mo is more complete
842 if (mo_may_allow(pfv.writer, pfv.act)&&
843 pfv.act->get_node()->add_future_value(pfv.writer->get_value(), pfv.writer->get_seq_number()+params.maxfuturedelay) &&
844 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
845 priv->next_backtrack = pfv.act;
847 futurevalues->resize(0);
850 mo_graph->commitChanges();
851 mo_check_promises(curr->get_tid(), curr);
853 get_thread(curr)->set_return_value(VALUE_NONE);
854 return updated_mod_order || updated_promises;
858 * @brief Process the current action for thread-related activity
860 * Performs current-action processing for a THREAD_* ModelAction. Proccesses
861 * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
862 * synchronization, etc. This function is a no-op for non-THREAD actions
863 * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
865 * @param curr The current action
866 * @return True if synchronization was updated or a thread completed
868 bool ModelChecker::process_thread_action(ModelAction *curr)
870 bool updated = false;
872 switch (curr->get_type()) {
873 case THREAD_CREATE: {
874 Thread *th = (Thread *)curr->get_location();
875 th->set_creation(curr);
879 Thread *blocking = (Thread *)curr->get_location();
880 ModelAction *act = get_last_action(blocking->get_id());
881 curr->synchronize_with(act);
882 updated = true; /* trigger rel-seq checks */
885 case THREAD_FINISH: {
886 Thread *th = get_thread(curr);
887 while (!th->wait_list_empty()) {
888 ModelAction *act = th->pop_wait_list();
889 scheduler->wake(get_thread(act));
892 updated = true; /* trigger rel-seq checks */
896 check_promises(curr->get_tid(), NULL, curr->get_cv());
907 * @brief Process the current action for release sequence fixup activity
909 * Performs model-checker release sequence fixups for the current action,
910 * forcing a single pending release sequence to break (with a given, potential
911 * "loose" write) or to complete (i.e., synchronize). If a pending release
912 * sequence forms a complete release sequence, then we must perform the fixup
913 * synchronization, mo_graph additions, etc.
915 * @param curr The current action; must be a release sequence fixup action
916 * @param work_queue The work queue to which to add work items as they are
919 void ModelChecker::process_relseq_fixup(ModelAction *curr, work_queue_t *work_queue)
921 const ModelAction *write = curr->get_node()->get_relseq_break();
922 struct release_seq *sequence = pending_rel_seqs->back();
923 pending_rel_seqs->pop_back();
925 ModelAction *acquire = sequence->acquire;
926 const ModelAction *rf = sequence->rf;
927 const ModelAction *release = sequence->release;
931 ASSERT(release->same_thread(rf));
935 * @todo Forcing a synchronization requires that we set
936 * modification order constraints. For instance, we can't allow
937 * a fixup sequence in which two separate read-acquire
938 * operations read from the same sequence, where the first one
939 * synchronizes and the other doesn't. Essentially, we can't
940 * allow any writes to insert themselves between 'release' and
944 /* Must synchronize */
945 if (!acquire->synchronize_with(release)) {
946 set_bad_synchronization();
949 /* Re-check all pending release sequences */
950 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
951 /* Re-check act for mo_graph edges */
952 work_queue->push_back(MOEdgeWorkEntry(acquire));
954 /* propagate synchronization to later actions */
955 action_list_t::reverse_iterator rit = action_trace->rbegin();
956 for (; (*rit) != acquire; rit++) {
957 ModelAction *propagate = *rit;
958 if (acquire->happens_before(propagate)) {
959 propagate->synchronize_with(acquire);
960 /* Re-check 'propagate' for mo_graph edges */
961 work_queue->push_back(MOEdgeWorkEntry(propagate));
965 /* Break release sequence with new edges:
966 * release --mo--> write --mo--> rf */
967 mo_graph->addEdge(release, write);
968 mo_graph->addEdge(write, rf);
971 /* See if we have realized a data race */
976 * Initialize the current action by performing one or more of the following
977 * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
978 * in the NodeStack, manipulating backtracking sets, allocating and
979 * initializing clock vectors, and computing the promises to fulfill.
981 * @param curr The current action, as passed from the user context; may be
982 * freed/invalidated after the execution of this function, with a different
983 * action "returned" its place (pass-by-reference)
984 * @return True if curr is a newly-explored action; false otherwise
986 bool ModelChecker::initialize_curr_action(ModelAction **curr)
988 ModelAction *newcurr;
990 if ((*curr)->is_rmwc() || (*curr)->is_rmw()) {
991 newcurr = process_rmw(*curr);
994 if (newcurr->is_rmw())
995 compute_promises(newcurr);
1001 (*curr)->set_seq_number(get_next_seq_num());
1003 newcurr = node_stack->explore_action(*curr, scheduler->get_enabled());
1005 /* First restore type and order in case of RMW operation */
1006 if ((*curr)->is_rmwr())
1007 newcurr->copy_typeandorder(*curr);
1009 ASSERT((*curr)->get_location() == newcurr->get_location());
1010 newcurr->copy_from_new(*curr);
1012 /* Discard duplicate ModelAction; use action from NodeStack */
1015 /* Always compute new clock vector */
1016 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1019 return false; /* Action was explored previously */
1023 /* Always compute new clock vector */
1024 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
1026 * Perform one-time actions when pushing new ModelAction onto
1029 if (newcurr->is_write())
1030 compute_promises(newcurr);
1031 else if (newcurr->is_relseq_fixup())
1032 compute_relseq_breakwrites(newcurr);
1033 else if (newcurr->is_wait())
1034 newcurr->get_node()->set_misc_max(2);
1035 else if (newcurr->is_notify_one()) {
1036 newcurr->get_node()->set_misc_max(get_safe_ptr_action(condvar_waiters_map, newcurr->get_location())->size());
1038 return true; /* This was a new ModelAction */
1043 * @brief Check whether a model action is enabled.
1045 * Checks whether a lock or join operation would be successful (i.e., is the
1046 * lock already locked, or is the joined thread already complete). If not, put
1047 * the action in a waiter list.
1049 * @param curr is the ModelAction to check whether it is enabled.
1050 * @return a bool that indicates whether the action is enabled.
1052 bool ModelChecker::check_action_enabled(ModelAction *curr) {
1053 if (curr->is_lock()) {
1054 std::mutex * lock = (std::mutex *)curr->get_location();
1055 struct std::mutex_state * state = lock->get_state();
1056 if (state->islocked) {
1057 //Stick the action in the appropriate waiting queue
1058 get_safe_ptr_action(lock_waiters_map, curr->get_location())->push_back(curr);
1061 } else if (curr->get_type() == THREAD_JOIN) {
1062 Thread *blocking = (Thread *)curr->get_location();
1063 if (!blocking->is_complete()) {
1064 blocking->push_wait_list(curr);
1073 * Stores the ModelAction for the current thread action. Call this
1074 * immediately before switching from user- to system-context to pass
1075 * data between them.
1076 * @param act The ModelAction created by the user-thread action
1078 void ModelChecker::set_current_action(ModelAction *act) {
1079 priv->current_action = act;
1083 * This is the heart of the model checker routine. It performs model-checking
1084 * actions corresponding to a given "current action." Among other processes, it
1085 * calculates reads-from relationships, updates synchronization clock vectors,
1086 * forms a memory_order constraints graph, and handles replay/backtrack
1087 * execution when running permutations of previously-observed executions.
1089 * @param curr The current action to process
1090 * @return The next Thread that must be executed. May be NULL if ModelChecker
1091 * makes no choice (e.g., according to replay execution, combining RMW actions,
1094 Thread * ModelChecker::check_current_action(ModelAction *curr)
1097 bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
1099 if (!check_action_enabled(curr)) {
1100 /* Make the execution look like we chose to run this action
1101 * much later, when a lock/join can succeed */
1102 get_current_thread()->set_pending(curr);
1103 scheduler->sleep(get_current_thread());
1104 return get_next_thread(NULL);
1107 bool newly_explored = initialize_curr_action(&curr);
1109 wake_up_sleeping_actions(curr);
1111 /* Add the action to lists before any other model-checking tasks */
1112 if (!second_part_of_rmw)
1113 add_action_to_lists(curr);
1115 /* Build may_read_from set for newly-created actions */
1116 if (newly_explored && curr->is_read())
1117 build_reads_from_past(curr);
1119 /* Initialize work_queue with the "current action" work */
1120 work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
1121 while (!work_queue.empty() && !has_asserted()) {
1122 WorkQueueEntry work = work_queue.front();
1123 work_queue.pop_front();
1125 switch (work.type) {
1126 case WORK_CHECK_CURR_ACTION: {
1127 ModelAction *act = work.action;
1128 bool update = false; /* update this location's release seq's */
1129 bool update_all = false; /* update all release seq's */
1131 if (process_thread_action(curr))
1134 if (act->is_read() && process_read(act, second_part_of_rmw))
1137 if (act->is_write() && process_write(act))
1140 if (act->is_mutex_op() && process_mutex(act))
1143 if (act->is_relseq_fixup())
1144 process_relseq_fixup(curr, &work_queue);
1147 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
1149 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1152 case WORK_CHECK_RELEASE_SEQ:
1153 resolve_release_sequences(work.location, &work_queue);
1155 case WORK_CHECK_MO_EDGES: {
1156 /** @todo Complete verification of work_queue */
1157 ModelAction *act = work.action;
1158 bool updated = false;
1160 if (act->is_read()) {
1161 const ModelAction *rf = act->get_reads_from();
1162 if (rf != NULL && r_modification_order(act, rf))
1165 if (act->is_write()) {
1166 if (w_modification_order(act))
1169 mo_graph->commitChanges();
1172 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
1181 check_curr_backtracking(curr);
1182 set_backtracking(curr);
1183 return get_next_thread(curr);
1186 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
1187 Node *currnode = curr->get_node();
1188 Node *parnode = currnode->get_parent();
1190 if ((!parnode->backtrack_empty() ||
1191 !currnode->misc_empty() ||
1192 !currnode->read_from_empty() ||
1193 !currnode->future_value_empty() ||
1194 !currnode->promise_empty() ||
1195 !currnode->relseq_break_empty())
1196 && (!priv->next_backtrack ||
1197 *curr > *priv->next_backtrack)) {
1198 priv->next_backtrack = curr;
1202 bool ModelChecker::promises_expired() const
1204 for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
1205 Promise *promise = (*promises)[promise_index];
1206 if (promise->get_expiration()<priv->used_sequence_numbers) {
1213 /** @return whether the current partial trace must be a prefix of a
1214 * feasible trace. */
1215 bool ModelChecker::isfeasibleprefix() const
1217 return promises->size() == 0 && pending_rel_seqs->size() == 0 && isfeasible();
1220 /** @return whether the current partial trace is feasible. */
1221 bool ModelChecker::isfeasible() const
1223 if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
1224 DEBUG("Infeasible: RMW violation\n");
1226 return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
1229 /** @return whether the current partial trace is feasible other than
1230 * multiple RMW reading from the same store. */
1231 bool ModelChecker::isfeasibleotherthanRMW() const
1233 if (DBG_ENABLED()) {
1234 if (mo_graph->checkForCycles())
1235 DEBUG("Infeasible: modification order cycles\n");
1236 if (priv->failed_promise)
1237 DEBUG("Infeasible: failed promise\n");
1238 if (priv->too_many_reads)
1239 DEBUG("Infeasible: too many reads\n");
1240 if (priv->bad_synchronization)
1241 DEBUG("Infeasible: bad synchronization ordering\n");
1242 if (promises_expired())
1243 DEBUG("Infeasible: promises expired\n");
1245 return !mo_graph->checkForCycles() && !priv->failed_promise && !priv->too_many_reads && !priv->bad_synchronization && !promises_expired();
1248 /** Returns whether the current completed trace is feasible. */
1249 bool ModelChecker::isfinalfeasible() const
1251 if (DBG_ENABLED() && promises->size() != 0)
1252 DEBUG("Infeasible: unrevolved promises\n");
1254 return isfeasible() && promises->size() == 0;
1257 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
1258 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
1259 ModelAction *lastread = get_last_action(act->get_tid());
1260 lastread->process_rmw(act);
1261 if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
1262 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
1263 mo_graph->commitChanges();
1269 * Checks whether a thread has read from the same write for too many times
1270 * without seeing the effects of a later write.
1273 * 1) there must a different write that we could read from that would satisfy the modification order,
1274 * 2) we must have read from the same value in excess of maxreads times, and
1275 * 3) that other write must have been in the reads_from set for maxreads times.
1277 * If so, we decide that the execution is no longer feasible.
1279 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
1280 if (params.maxreads != 0) {
1282 if (curr->get_node()->get_read_from_size() <= 1)
1284 //Must make sure that execution is currently feasible... We could
1285 //accidentally clear by rolling back
1288 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1289 int tid = id_to_int(curr->get_tid());
1292 if ((int)thrd_lists->size() <= tid)
1294 action_list_t *list = &(*thrd_lists)[tid];
1296 action_list_t::reverse_iterator rit = list->rbegin();
1297 /* Skip past curr */
1298 for (; (*rit) != curr; rit++)
1300 /* go past curr now */
1303 action_list_t::reverse_iterator ritcopy = rit;
1304 //See if we have enough reads from the same value
1306 for (; count < params.maxreads; rit++,count++) {
1307 if (rit==list->rend())
1309 ModelAction *act = *rit;
1310 if (!act->is_read())
1313 if (act->get_reads_from() != rf)
1315 if (act->get_node()->get_read_from_size() <= 1)
1318 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
1320 const ModelAction * write = curr->get_node()->get_read_from_at(i);
1322 //Need a different write
1326 /* Test to see whether this is a feasible write to read from*/
1327 mo_graph->startChanges();
1328 r_modification_order(curr, write);
1329 bool feasiblereadfrom = isfeasible();
1330 mo_graph->rollbackChanges();
1332 if (!feasiblereadfrom)
1336 bool feasiblewrite = true;
1337 //new we need to see if this write works for everyone
1339 for (int loop = count; loop>0; loop--,rit++) {
1340 ModelAction *act=*rit;
1341 bool foundvalue = false;
1342 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
1343 if (act->get_node()->get_read_from_at(j)==write) {
1349 feasiblewrite = false;
1353 if (feasiblewrite) {
1354 priv->too_many_reads = true;
1362 * Updates the mo_graph with the constraints imposed from the current
1365 * Basic idea is the following: Go through each other thread and find
1366 * the lastest action that happened before our read. Two cases:
1368 * (1) The action is a write => that write must either occur before
1369 * the write we read from or be the write we read from.
1371 * (2) The action is a read => the write that that action read from
1372 * must occur before the write we read from or be the same write.
1374 * @param curr The current action. Must be a read.
1375 * @param rf The action that curr reads from. Must be a write.
1376 * @return True if modification order edges were added; false otherwise
1378 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
1380 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1383 ASSERT(curr->is_read());
1385 /* Iterate over all threads */
1386 for (i = 0; i < thrd_lists->size(); i++) {
1387 /* Iterate over actions in thread, starting from most recent */
1388 action_list_t *list = &(*thrd_lists)[i];
1389 action_list_t::reverse_iterator rit;
1390 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1391 ModelAction *act = *rit;
1394 * Include at most one act per-thread that "happens
1395 * before" curr. Don't consider reflexively.
1397 if (act->happens_before(curr) && act != curr) {
1398 if (act->is_write()) {
1400 mo_graph->addEdge(act, rf);
1404 const ModelAction *prevreadfrom = act->get_reads_from();
1405 //if the previous read is unresolved, keep going...
1406 if (prevreadfrom == NULL)
1409 if (rf != prevreadfrom) {
1410 mo_graph->addEdge(prevreadfrom, rf);
1422 /** This method fixes up the modification order when we resolve a
1423 * promises. The basic problem is that actions that occur after the
1424 * read curr could not property add items to the modification order
1427 * So for each thread, we find the earliest item that happens after
1428 * the read curr. This is the item we have to fix up with additional
1429 * constraints. If that action is write, we add a MO edge between
1430 * the Action rf and that action. If the action is a read, we add a
1431 * MO edge between the Action rf, and whatever the read accessed.
1433 * @param curr is the read ModelAction that we are fixing up MO edges for.
1434 * @param rf is the write ModelAction that curr reads from.
1437 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
1439 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1441 ASSERT(curr->is_read());
1443 /* Iterate over all threads */
1444 for (i = 0; i < thrd_lists->size(); i++) {
1445 /* Iterate over actions in thread, starting from most recent */
1446 action_list_t *list = &(*thrd_lists)[i];
1447 action_list_t::reverse_iterator rit;
1448 ModelAction *lastact = NULL;
1450 /* Find last action that happens after curr that is either not curr or a rmw */
1451 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1452 ModelAction *act = *rit;
1453 if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
1459 /* Include at most one act per-thread that "happens before" curr */
1460 if (lastact != NULL) {
1461 if (lastact==curr) {
1462 //Case 1: The resolved read is a RMW, and we need to make sure
1463 //that the write portion of the RMW mod order after rf
1465 mo_graph->addEdge(rf, lastact);
1466 } else if (lastact->is_read()) {
1467 //Case 2: The resolved read is a normal read and the next
1468 //operation is a read, and we need to make sure the value read
1469 //is mod ordered after rf
1471 const ModelAction *postreadfrom = lastact->get_reads_from();
1472 if (postreadfrom != NULL&&rf != postreadfrom)
1473 mo_graph->addEdge(rf, postreadfrom);
1475 //Case 3: The resolved read is a normal read and the next
1476 //operation is a write, and we need to make sure that the
1477 //write is mod ordered after rf
1479 mo_graph->addEdge(rf, lastact);
1487 * Updates the mo_graph with the constraints imposed from the current write.
1489 * Basic idea is the following: Go through each other thread and find
1490 * the lastest action that happened before our write. Two cases:
1492 * (1) The action is a write => that write must occur before
1495 * (2) The action is a read => the write that that action read from
1496 * must occur before the current write.
1498 * This method also handles two other issues:
1500 * (I) Sequential Consistency: Making sure that if the current write is
1501 * seq_cst, that it occurs after the previous seq_cst write.
1503 * (II) Sending the write back to non-synchronizing reads.
1505 * @param curr The current action. Must be a write.
1506 * @return True if modification order edges were added; false otherwise
1508 bool ModelChecker::w_modification_order(ModelAction *curr)
1510 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
1513 ASSERT(curr->is_write());
1515 if (curr->is_seqcst()) {
1516 /* We have to at least see the last sequentially consistent write,
1517 so we are initialized. */
1518 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1519 if (last_seq_cst != NULL) {
1520 mo_graph->addEdge(last_seq_cst, curr);
1525 /* Iterate over all threads */
1526 for (i = 0; i < thrd_lists->size(); i++) {
1527 /* Iterate over actions in thread, starting from most recent */
1528 action_list_t *list = &(*thrd_lists)[i];
1529 action_list_t::reverse_iterator rit;
1530 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1531 ModelAction *act = *rit;
1534 * 1) If RMW and it actually read from something, then we
1535 * already have all relevant edges, so just skip to next
1538 * 2) If RMW and it didn't read from anything, we should
1539 * whatever edge we can get to speed up convergence.
1541 * 3) If normal write, we need to look at earlier actions, so
1542 * continue processing list.
1544 if (curr->is_rmw()) {
1545 if (curr->get_reads_from()!=NULL)
1554 * Include at most one act per-thread that "happens
1557 if (act->happens_before(curr)) {
1559 * Note: if act is RMW, just add edge:
1561 * The following edge should be handled elsewhere:
1562 * readfrom(act) --mo--> act
1564 if (act->is_write())
1565 mo_graph->addEdge(act, curr);
1566 else if (act->is_read()) {
1567 //if previous read accessed a null, just keep going
1568 if (act->get_reads_from() == NULL)
1570 mo_graph->addEdge(act->get_reads_from(), curr);
1574 } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1575 !act->same_thread(curr)) {
1576 /* We have an action that:
1577 (1) did not happen before us
1578 (2) is a read and we are a write
1579 (3) cannot synchronize with us
1580 (4) is in a different thread
1582 that read could potentially read from our write. Note that
1583 these checks are overly conservative at this point, we'll
1584 do more checks before actually removing the
1588 if (thin_air_constraint_may_allow(curr, act)) {
1590 (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1591 struct PendingFutureValue pfv = {curr,act};
1592 futurevalues->push_back(pfv);
1602 /** Arbitrary reads from the future are not allowed. Section 29.3
1603 * part 9 places some constraints. This method checks one result of constraint
1604 * constraint. Others require compiler support. */
1605 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1606 if (!writer->is_rmw())
1609 if (!reader->is_rmw())
1612 for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1613 if (search == reader)
1615 if (search->get_tid() == reader->get_tid() &&
1616 search->happens_before(reader))
1624 * Arbitrary reads from the future are not allowed. Section 29.3 part 9 places
1625 * some constraints. This method checks one the following constraint (others
1626 * require compiler support):
1628 * If X --hb-> Y --mo-> Z, then X should not read from Z.
1630 bool ModelChecker::mo_may_allow(const ModelAction *writer, const ModelAction *reader)
1632 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, reader->get_location());
1634 /* Iterate over all threads */
1635 for (i = 0; i < thrd_lists->size(); i++) {
1636 const ModelAction *write_after_read = NULL;
1638 /* Iterate over actions in thread, starting from most recent */
1639 action_list_t *list = &(*thrd_lists)[i];
1640 action_list_t::reverse_iterator rit;
1641 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1642 ModelAction *act = *rit;
1644 if (!reader->happens_before(act))
1646 else if (act->is_write())
1647 write_after_read = act;
1648 else if (act->is_read() && act->get_reads_from() != NULL && act != reader) {
1649 write_after_read = act->get_reads_from();
1653 if (write_after_read && write_after_read!=writer && mo_graph->checkReachable(write_after_read, writer))
1660 * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1661 * The ModelAction under consideration is expected to be taking part in
1662 * release/acquire synchronization as an object of the "reads from" relation.
1663 * Note that this can only provide release sequence support for RMW chains
1664 * which do not read from the future, as those actions cannot be traced until
1665 * their "promise" is fulfilled. Similarly, we may not even establish the
1666 * presence of a release sequence with certainty, as some modification order
1667 * constraints may be decided further in the future. Thus, this function
1668 * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1669 * and a boolean representing certainty.
1671 * @param rf The action that might be part of a release sequence. Must be a
1673 * @param release_heads A pass-by-reference style return parameter. After
1674 * execution of this function, release_heads will contain the heads of all the
1675 * relevant release sequences, if any exists with certainty
1676 * @param pending A pass-by-reference style return parameter which is only used
1677 * when returning false (i.e., uncertain). Returns most information regarding
1678 * an uncertain release sequence, including any write operations that might
1679 * break the sequence.
1680 * @return true, if the ModelChecker is certain that release_heads is complete;
1683 bool ModelChecker::release_seq_heads(const ModelAction *rf,
1684 rel_heads_list_t *release_heads,
1685 struct release_seq *pending) const
1687 /* Only check for release sequences if there are no cycles */
1688 if (mo_graph->checkForCycles())
1692 ASSERT(rf->is_write());
1694 if (rf->is_release())
1695 release_heads->push_back(rf);
1697 break; /* End of RMW chain */
1699 /** @todo Need to be smarter here... In the linux lock
1700 * example, this will run to the beginning of the program for
1702 /** @todo The way to be smarter here is to keep going until 1
1703 * thread has a release preceded by an acquire and you've seen
1706 /* acq_rel RMW is a sufficient stopping condition */
1707 if (rf->is_acquire() && rf->is_release())
1708 return true; /* complete */
1710 rf = rf->get_reads_from();
1713 /* read from future: need to settle this later */
1715 return false; /* incomplete */
1718 if (rf->is_release())
1719 return true; /* complete */
1721 /* else relaxed write; check modification order for contiguous subsequence
1722 * -> rf must be same thread as release */
1723 int tid = id_to_int(rf->get_tid());
1724 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, rf->get_location());
1725 action_list_t *list = &(*thrd_lists)[tid];
1726 action_list_t::const_reverse_iterator rit;
1728 /* Find rf in the thread list */
1729 rit = std::find(list->rbegin(), list->rend(), rf);
1730 ASSERT(rit != list->rend());
1732 /* Find the last write/release */
1733 for (; rit != list->rend(); rit++)
1734 if ((*rit)->is_release())
1736 if (rit == list->rend()) {
1737 /* No write-release in this thread */
1738 return true; /* complete */
1740 ModelAction *release = *rit;
1742 ASSERT(rf->same_thread(release));
1744 pending->writes.clear();
1746 bool certain = true;
1747 for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1748 if (id_to_int(rf->get_tid()) == (int)i)
1750 list = &(*thrd_lists)[i];
1752 /* Can we ensure no future writes from this thread may break
1753 * the release seq? */
1754 bool future_ordered = false;
1756 ModelAction *last = get_last_action(int_to_id(i));
1757 Thread *th = get_thread(int_to_id(i));
1758 if ((last && rf->happens_before(last)) ||
1761 future_ordered = true;
1763 ASSERT(!th->is_model_thread() || future_ordered);
1765 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1766 const ModelAction *act = *rit;
1767 /* Reach synchronization -> this thread is complete */
1768 if (act->happens_before(release))
1770 if (rf->happens_before(act)) {
1771 future_ordered = true;
1775 /* Only non-RMW writes can break release sequences */
1776 if (!act->is_write() || act->is_rmw())
1779 /* Check modification order */
1780 if (mo_graph->checkReachable(rf, act)) {
1781 /* rf --mo--> act */
1782 future_ordered = true;
1785 if (mo_graph->checkReachable(act, release))
1786 /* act --mo--> release */
1788 if (mo_graph->checkReachable(release, act) &&
1789 mo_graph->checkReachable(act, rf)) {
1790 /* release --mo-> act --mo--> rf */
1791 return true; /* complete */
1793 /* act may break release sequence */
1794 pending->writes.push_back(act);
1797 if (!future_ordered)
1798 certain = false; /* This thread is uncertain */
1802 release_heads->push_back(release);
1803 pending->writes.clear();
1805 pending->release = release;
1812 * A public interface for getting the release sequence head(s) with which a
1813 * given ModelAction must synchronize. This function only returns a non-empty
1814 * result when it can locate a release sequence head with certainty. Otherwise,
1815 * it may mark the internal state of the ModelChecker so that it will handle
1816 * the release sequence at a later time, causing @a act to update its
1817 * synchronization at some later point in execution.
1818 * @param act The 'acquire' action that may read from a release sequence
1819 * @param release_heads A pass-by-reference return parameter. Will be filled
1820 * with the head(s) of the release sequence(s), if they exists with certainty.
1821 * @see ModelChecker::release_seq_heads
1823 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1825 const ModelAction *rf = act->get_reads_from();
1826 struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
1827 sequence->acquire = act;
1829 if (!release_seq_heads(rf, release_heads, sequence)) {
1830 /* add act to 'lazy checking' list */
1831 pending_rel_seqs->push_back(sequence);
1833 snapshot_free(sequence);
1838 * Attempt to resolve all stashed operations that might synchronize with a
1839 * release sequence for a given location. This implements the "lazy" portion of
1840 * determining whether or not a release sequence was contiguous, since not all
1841 * modification order information is present at the time an action occurs.
1843 * @param location The location/object that should be checked for release
1844 * sequence resolutions. A NULL value means to check all locations.
1845 * @param work_queue The work queue to which to add work items as they are
1847 * @return True if any updates occurred (new synchronization, new mo_graph
1850 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1852 bool updated = false;
1853 std::vector< struct release_seq *, SnapshotAlloc<struct release_seq *> >::iterator it = pending_rel_seqs->begin();
1854 while (it != pending_rel_seqs->end()) {
1855 struct release_seq *pending = *it;
1856 ModelAction *act = pending->acquire;
1858 /* Only resolve sequences on the given location, if provided */
1859 if (location && act->get_location() != location) {
1864 const ModelAction *rf = act->get_reads_from();
1865 rel_heads_list_t release_heads;
1867 complete = release_seq_heads(rf, &release_heads, pending);
1868 for (unsigned int i = 0; i < release_heads.size(); i++) {
1869 if (!act->has_synchronized_with(release_heads[i])) {
1870 if (act->synchronize_with(release_heads[i]))
1873 set_bad_synchronization();
1878 /* Re-check all pending release sequences */
1879 work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1880 /* Re-check act for mo_graph edges */
1881 work_queue->push_back(MOEdgeWorkEntry(act));
1883 /* propagate synchronization to later actions */
1884 action_list_t::reverse_iterator rit = action_trace->rbegin();
1885 for (; (*rit) != act; rit++) {
1886 ModelAction *propagate = *rit;
1887 if (act->happens_before(propagate)) {
1888 propagate->synchronize_with(act);
1889 /* Re-check 'propagate' for mo_graph edges */
1890 work_queue->push_back(MOEdgeWorkEntry(propagate));
1895 it = pending_rel_seqs->erase(it);
1896 snapshot_free(pending);
1902 // If we resolved promises or data races, see if we have realized a data race.
1909 * Performs various bookkeeping operations for the current ModelAction. For
1910 * instance, adds action to the per-object, per-thread action vector and to the
1911 * action trace list of all thread actions.
1913 * @param act is the ModelAction to add.
1915 void ModelChecker::add_action_to_lists(ModelAction *act)
1917 int tid = id_to_int(act->get_tid());
1918 action_trace->push_back(act);
1920 get_safe_ptr_action(obj_map, act->get_location())->push_back(act);
1922 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, act->get_location());
1923 if (tid >= (int)vec->size())
1924 vec->resize(priv->next_thread_id);
1925 (*vec)[tid].push_back(act);
1927 if ((int)thrd_last_action->size() <= tid)
1928 thrd_last_action->resize(get_num_threads());
1929 (*thrd_last_action)[tid] = act;
1931 if (act->is_wait()) {
1932 void *mutex_loc=(void *) act->get_value();
1933 get_safe_ptr_action(obj_map, mutex_loc)->push_back(act);
1935 std::vector<action_list_t> *vec = get_safe_ptr_vect_action(obj_thrd_map, mutex_loc);
1936 if (tid >= (int)vec->size())
1937 vec->resize(priv->next_thread_id);
1938 (*vec)[tid].push_back(act);
1940 if ((int)thrd_last_action->size() <= tid)
1941 thrd_last_action->resize(get_num_threads());
1942 (*thrd_last_action)[tid] = act;
1947 * @brief Get the last action performed by a particular Thread
1948 * @param tid The thread ID of the Thread in question
1949 * @return The last action in the thread
1951 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1953 int threadid = id_to_int(tid);
1954 if (threadid < (int)thrd_last_action->size())
1955 return (*thrd_last_action)[id_to_int(tid)];
1961 * Gets the last memory_order_seq_cst write (in the total global sequence)
1962 * performed on a particular object (i.e., memory location), not including the
1964 * @param curr The current ModelAction; also denotes the object location to
1966 * @return The last seq_cst write
1968 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1970 void *location = curr->get_location();
1971 action_list_t *list = get_safe_ptr_action(obj_map, location);
1972 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1973 action_list_t::reverse_iterator rit;
1974 for (rit = list->rbegin(); rit != list->rend(); rit++)
1975 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1981 * Gets the last unlock operation performed on a particular mutex (i.e., memory
1982 * location). This function identifies the mutex according to the current
1983 * action, which is presumed to perform on the same mutex.
1984 * @param curr The current ModelAction; also denotes the object location to
1986 * @return The last unlock operation
1988 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1990 void *location = curr->get_location();
1991 action_list_t *list = get_safe_ptr_action(obj_map, location);
1992 /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1993 action_list_t::reverse_iterator rit;
1994 for (rit = list->rbegin(); rit != list->rend(); rit++)
1995 if ((*rit)->is_unlock() || (*rit)->is_wait())
2000 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
2002 ModelAction *parent = get_last_action(tid);
2004 parent = get_thread(tid)->get_creation();
2009 * Returns the clock vector for a given thread.
2010 * @param tid The thread whose clock vector we want
2011 * @return Desired clock vector
2013 ClockVector * ModelChecker::get_cv(thread_id_t tid)
2015 return get_parent_action(tid)->get_cv();
2019 * Resolve a set of Promises with a current write. The set is provided in the
2020 * Node corresponding to @a write.
2021 * @param write The ModelAction that is fulfilling Promises
2022 * @return True if promises were resolved; false otherwise
2024 bool ModelChecker::resolve_promises(ModelAction *write)
2026 bool resolved = false;
2027 std::vector< thread_id_t, ModelAlloc<thread_id_t> > threads_to_check;
2029 for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
2030 Promise *promise = (*promises)[promise_index];
2031 if (write->get_node()->get_promise(i)) {
2032 ModelAction *read = promise->get_action();
2033 if (read->is_rmw()) {
2034 mo_graph->addRMWEdge(write, read);
2036 read->read_from(write);
2037 //First fix up the modification order for actions that happened
2039 r_modification_order(read, write);
2040 //Next fix up the modification order for actions that happened
2042 post_r_modification_order(read, write);
2043 //Make sure the promise's value matches the write's value
2044 ASSERT(promise->get_value() == write->get_value());
2047 promises->erase(promises->begin() + promise_index);
2048 threads_to_check.push_back(read->get_tid());
2055 //Check whether reading these writes has made threads unable to
2058 for(unsigned int i=0;i<threads_to_check.size();i++)
2059 mo_check_promises(threads_to_check[i], write);
2065 * Compute the set of promises that could potentially be satisfied by this
2066 * action. Note that the set computation actually appears in the Node, not in
2068 * @param curr The ModelAction that may satisfy promises
2070 void ModelChecker::compute_promises(ModelAction *curr)
2072 for (unsigned int i = 0; i < promises->size(); i++) {
2073 Promise *promise = (*promises)[i];
2074 const ModelAction *act = promise->get_action();
2075 if (!act->happens_before(curr) &&
2077 !act->could_synchronize_with(curr) &&
2078 !act->same_thread(curr) &&
2079 act->get_location() == curr->get_location() &&
2080 promise->get_value() == curr->get_value()) {
2081 curr->get_node()->set_promise(i, act->is_rmw());
2086 /** Checks promises in response to change in ClockVector Threads. */
2087 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
2089 for (unsigned int i = 0; i < promises->size(); i++) {
2090 Promise *promise = (*promises)[i];
2091 const ModelAction *act = promise->get_action();
2092 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
2093 merge_cv->synchronized_since(act)) {
2094 if (promise->increment_threads(tid)) {
2095 //Promise has failed
2096 priv->failed_promise = true;
2103 void ModelChecker::check_promises_thread_disabled() {
2104 for (unsigned int i = 0; i < promises->size(); i++) {
2105 Promise *promise = (*promises)[i];
2106 if (promise->check_promise()) {
2107 priv->failed_promise = true;
2113 /** Checks promises in response to addition to modification order for threads.
2115 * pthread is the thread that performed the read that created the promise
2117 * pread is the read that created the promise
2119 * pwrite is either the first write to same location as pread by
2120 * pthread that is sequenced after pread or the value read by the
2121 * first read to the same lcoation as pread by pthread that is
2122 * sequenced after pread..
2124 * 1. If tid=pthread, then we check what other threads are reachable
2125 * through the mode order starting with pwrite. Those threads cannot
2126 * perform a write that will resolve the promise due to modification
2127 * order constraints.
2129 * 2. If the tid is not pthread, we check whether pwrite can reach the
2130 * action write through the modification order. If so, that thread
2131 * cannot perform a future write that will resolve the promise due to
2132 * modificatin order constraints.
2134 * @parem tid The thread that either read from the model action
2135 * write, or actually did the model action write.
2137 * @parem write The ModelAction representing the relevant write.
2140 void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write) {
2141 void * location = write->get_location();
2142 for (unsigned int i = 0; i < promises->size(); i++) {
2143 Promise *promise = (*promises)[i];
2144 const ModelAction *act = promise->get_action();
2146 //Is this promise on the same location?
2147 if ( act->get_location() != location )
2150 //same thread as the promise
2151 if ( act->get_tid()==tid ) {
2153 //do we have a pwrite for the promise, if not, set it
2154 if (promise->get_write() == NULL ) {
2155 promise->set_write(write);
2156 //The pwrite cannot happen before the promise
2157 if (write->happens_before(act) && (write != act)) {
2158 priv->failed_promise = true;
2162 if (mo_graph->checkPromise(write, promise)) {
2163 priv->failed_promise = true;
2168 //Don't do any lookups twice for the same thread
2169 if (promise->has_sync_thread(tid))
2172 if (promise->get_write()&&mo_graph->checkReachable(promise->get_write(), write)) {
2173 if (promise->increment_threads(tid)) {
2174 priv->failed_promise = true;
2182 * Compute the set of writes that may break the current pending release
2183 * sequence. This information is extracted from previou release sequence
2186 * @param curr The current ModelAction. Must be a release sequence fixup
2189 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
2191 if (pending_rel_seqs->empty())
2194 struct release_seq *pending = pending_rel_seqs->back();
2195 for (unsigned int i = 0; i < pending->writes.size(); i++) {
2196 const ModelAction *write = pending->writes[i];
2197 curr->get_node()->add_relseq_break(write);
2200 /* NULL means don't break the sequence; just synchronize */
2201 curr->get_node()->add_relseq_break(NULL);
2205 * Build up an initial set of all past writes that this 'read' action may read
2206 * from. This set is determined by the clock vector's "happens before"
2208 * @param curr is the current ModelAction that we are exploring; it must be a
2211 void ModelChecker::build_reads_from_past(ModelAction *curr)
2213 std::vector<action_list_t> *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location());
2215 ASSERT(curr->is_read());
2217 ModelAction *last_seq_cst = NULL;
2219 /* Track whether this object has been initialized */
2220 bool initialized = false;
2222 if (curr->is_seqcst()) {
2223 last_seq_cst = get_last_seq_cst(curr);
2224 /* We have to at least see the last sequentially consistent write,
2225 so we are initialized. */
2226 if (last_seq_cst != NULL)
2230 /* Iterate over all threads */
2231 for (i = 0; i < thrd_lists->size(); i++) {
2232 /* Iterate over actions in thread, starting from most recent */
2233 action_list_t *list = &(*thrd_lists)[i];
2234 action_list_t::reverse_iterator rit;
2235 for (rit = list->rbegin(); rit != list->rend(); rit++) {
2236 ModelAction *act = *rit;
2238 /* Only consider 'write' actions */
2239 if (!act->is_write() || act == curr)
2242 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
2243 if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
2244 if (!curr->get_sleep_flag() || curr->is_seqcst() || sleep_can_read_from(curr, act)) {
2245 DEBUG("Adding action to may_read_from:\n");
2246 if (DBG_ENABLED()) {
2250 curr->get_node()->add_read_from(act);
2254 /* Include at most one act per-thread that "happens before" curr */
2255 if (act->happens_before(curr)) {
2263 assert_bug("May read from uninitialized atomic");
2265 if (DBG_ENABLED() || !initialized) {
2266 model_print("Reached read action:\n");
2268 model_print("Printing may_read_from\n");
2269 curr->get_node()->print_may_read_from();
2270 model_print("End printing may_read_from\n");
2274 bool ModelChecker::sleep_can_read_from(ModelAction * curr, const ModelAction *write) {
2276 Node *prevnode=write->get_node()->get_parent();
2278 bool thread_sleep=prevnode->enabled_status(curr->get_tid())==THREAD_SLEEP_SET;
2279 if (write->is_release()&&thread_sleep)
2281 if (!write->is_rmw()) {
2284 if (write->get_reads_from()==NULL)
2286 write=write->get_reads_from();
2290 static void print_list(action_list_t *list, int exec_num = -1)
2292 action_list_t::iterator it;
2294 model_print("---------------------------------------------------------------------\n");
2296 model_print("Execution %d:\n", exec_num);
2298 unsigned int hash=0;
2300 for (it = list->begin(); it != list->end(); it++) {
2302 hash=hash^(hash<<3)^((*it)->hash());
2304 model_print("HASH %u\n", hash);
2305 model_print("---------------------------------------------------------------------\n");
2308 #if SUPPORT_MOD_ORDER_DUMP
2309 void ModelChecker::dumpGraph(char *filename) {
2311 sprintf(buffer, "%s.dot",filename);
2312 FILE *file=fopen(buffer, "w");
2313 fprintf(file, "digraph %s {\n",filename);
2314 mo_graph->dumpNodes(file);
2315 ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
2317 for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
2318 ModelAction *action=*it;
2319 if (action->is_read()) {
2320 fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
2321 if (action->get_reads_from()!=NULL)
2322 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
2324 if (thread_array[action->get_tid()] != NULL) {
2325 fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
2328 thread_array[action->get_tid()]=action;
2330 fprintf(file,"}\n");
2331 model_free(thread_array);
2336 /** @brief Prints an execution trace summary. */
2337 void ModelChecker::print_summary() const
2339 #if SUPPORT_MOD_ORDER_DUMP
2341 char buffername[100];
2342 sprintf(buffername, "exec%04u", stats.num_total);
2343 mo_graph->dumpGraphToFile(buffername);
2344 sprintf(buffername, "graph%04u", stats.num_total);
2345 dumpGraph(buffername);
2348 if (!isfinalfeasible())
2349 model_print("INFEASIBLE EXECUTION!\n");
2350 print_list(action_trace, stats.num_total);
2355 * Add a Thread to the system for the first time. Should only be called once
2357 * @param t The Thread to add
2359 void ModelChecker::add_thread(Thread *t)
2361 thread_map->put(id_to_int(t->get_id()), t);
2362 scheduler->add_thread(t);
2366 * Removes a thread from the scheduler.
2367 * @param the thread to remove.
2369 void ModelChecker::remove_thread(Thread *t)
2371 scheduler->remove_thread(t);
2375 * @brief Get a Thread reference by its ID
2376 * @param tid The Thread's ID
2377 * @return A Thread reference
2379 Thread * ModelChecker::get_thread(thread_id_t tid) const
2381 return thread_map->get(id_to_int(tid));
2385 * @brief Get a reference to the Thread in which a ModelAction was executed
2386 * @param act The ModelAction
2387 * @return A Thread reference
2389 Thread * ModelChecker::get_thread(ModelAction *act) const
2391 return get_thread(act->get_tid());
2395 * @brief Check if a Thread is currently enabled
2396 * @param t The Thread to check
2397 * @return True if the Thread is currently enabled
2399 bool ModelChecker::is_enabled(Thread *t) const
2401 return scheduler->is_enabled(t);
2405 * @brief Check if a Thread is currently enabled
2406 * @param tid The ID of the Thread to check
2407 * @return True if the Thread is currently enabled
2409 bool ModelChecker::is_enabled(thread_id_t tid) const
2411 return scheduler->is_enabled(tid);
2415 * Switch from a user-context to the "master thread" context (a.k.a. system
2416 * context). This switch is made with the intention of exploring a particular
2417 * model-checking action (described by a ModelAction object). Must be called
2418 * from a user-thread context.
2420 * @param act The current action that will be explored. May be NULL only if
2421 * trace is exiting via an assertion (see ModelChecker::set_assert and
2422 * ModelChecker::has_asserted).
2423 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
2425 int ModelChecker::switch_to_master(ModelAction *act)
2428 Thread *old = thread_current();
2429 set_current_action(act);
2430 old->set_state(THREAD_READY);
2431 return Thread::swap(old, &system_context);
2435 * Takes the next step in the execution, if possible.
2436 * @return Returns true (success) if a step was taken and false otherwise.
2438 bool ModelChecker::take_step() {
2442 Thread *curr = priv->current_action ? get_thread(priv->current_action) : NULL;
2444 if (curr->get_state() == THREAD_READY) {
2445 ASSERT(priv->current_action);
2447 priv->nextThread = check_current_action(priv->current_action);
2448 priv->current_action = NULL;
2450 if (curr->is_blocked() || curr->is_complete())
2451 scheduler->remove_thread(curr);
2456 Thread *next = scheduler->next_thread(priv->nextThread);
2458 /* Infeasible -> don't take any more steps */
2461 else if (isfeasibleprefix() && have_bug_reports()) {
2466 if (params.bound != 0) {
2467 if (priv->used_sequence_numbers > params.bound) {
2472 DEBUG("(%d, %d)\n", curr ? id_to_int(curr->get_id()) : -1,
2473 next ? id_to_int(next->get_id()) : -1);
2476 * Launch end-of-execution release sequence fixups only when there are:
2478 * (1) no more user threads to run (or when execution replay chooses
2479 * the 'model_thread')
2480 * (2) pending release sequences
2481 * (3) pending assertions (i.e., data races)
2482 * (4) no pending promises
2484 if (!pending_rel_seqs->empty() && (!next || next->is_model_thread()) &&
2485 isfinalfeasible() && !unrealizedraces.empty()) {
2486 model_print("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n",
2487 pending_rel_seqs->size());
2488 ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
2489 std::memory_order_seq_cst, NULL, VALUE_NONE,
2491 set_current_action(fixup);
2495 /* next == NULL -> don't take any more steps */
2499 next->set_state(THREAD_RUNNING);
2501 if (next->get_pending() != NULL) {
2502 /* restart a pending action */
2503 set_current_action(next->get_pending());
2504 next->set_pending(NULL);
2505 next->set_state(THREAD_READY);
2509 /* Return false only if swap fails with an error */
2510 return (Thread::swap(&system_context, next) == 0);
2513 /** Runs the current execution until threre are no more steps to take. */
2514 void ModelChecker::finish_execution() {
2517 while (take_step());