7 #include "snapshot-interface.h"
9 #include "clockvector.h"
10 #include "cyclegraph.h"
13 #define INITIAL_THREAD_ID 0
17 /** @brief Constructor */
18 ModelChecker::ModelChecker(struct model_params params) :
19 /* Initialize default scheduler */
20 scheduler(new Scheduler()),
21 /* First thread created will have id INITIAL_THREAD_ID */
22 next_thread_id(INITIAL_THREAD_ID),
23 used_sequence_numbers(0),
28 nextThread(THREAD_ID_T_NONE),
29 action_trace(new action_list_t()),
30 thread_map(new HashTable<int, Thread *, int>()),
31 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
32 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
33 promises(new std::vector<Promise *>()),
34 thrd_last_action(new std::vector<ModelAction *>(1)),
35 node_stack(new NodeStack()),
37 mo_graph(new CycleGraph()),
42 /** @brief Destructor */
43 ModelChecker::~ModelChecker()
45 for (int i = 0; i < get_num_threads(); i++)
46 delete thread_map->get(i);
53 for (unsigned int i = 0; i < promises->size(); i++)
54 delete (*promises)[i];
57 delete thrd_last_action;
64 * Restores user program to initial state and resets all model-checker data
67 void ModelChecker::reset_to_initial_state()
69 DEBUG("+++ Resetting to initial state +++\n");
70 node_stack->reset_execution();
71 current_action = NULL;
72 next_thread_id = INITIAL_THREAD_ID;
73 used_sequence_numbers = 0;
75 next_backtrack = NULL;
76 failed_promise = false;
77 snapshotObject->backTrackBeforeStep(0);
80 /** @returns a thread ID for a new Thread */
81 thread_id_t ModelChecker::get_next_id()
83 return next_thread_id++;
86 /** @returns the number of user threads created during this execution */
87 int ModelChecker::get_num_threads()
89 return next_thread_id;
92 /** @returns a sequence number for a new ModelAction */
93 modelclock_t ModelChecker::get_next_seq_num()
95 return ++used_sequence_numbers;
99 * Performs the "scheduling" for the model-checker. That is, it checks if the
100 * model-checker has selected a "next thread to run" and returns it, if
101 * available. This function should be called from the Scheduler routine, where
102 * the Scheduler falls back to a default scheduling routine if needed.
104 * @return The next thread chosen by the model-checker. If the model-checker
105 * makes no selection, retuns NULL.
107 Thread * ModelChecker::schedule_next_thread()
110 if (nextThread == THREAD_ID_T_NONE)
112 t = thread_map->get(id_to_int(nextThread));
120 * Choose the next thread in the replay sequence.
122 * If the replay sequence has reached the 'diverge' point, returns a thread
123 * from the backtracking set. Otherwise, simply returns the next thread in the
124 * sequence that is being replayed.
126 thread_id_t ModelChecker::get_next_replay_thread()
130 /* Have we completed exploring the preselected path? */
132 return THREAD_ID_T_NONE;
134 /* Else, we are trying to replay an execution */
135 ModelAction * next = node_stack->get_next()->get_action();
137 if (next == diverge) {
138 Node *nextnode = next->get_node();
139 /* Reached divergence point */
140 if (nextnode->increment_promise()) {
141 /* The next node will try to satisfy a different set of promises. */
142 tid = next->get_tid();
143 node_stack->pop_restofstack(2);
144 } else if (nextnode->increment_read_from()) {
145 /* The next node will read from a different value. */
146 tid = next->get_tid();
147 node_stack->pop_restofstack(2);
148 } else if (nextnode->increment_future_value()) {
149 /* The next node will try to read from a different future value. */
150 tid = next->get_tid();
151 node_stack->pop_restofstack(2);
153 /* Make a different thread execute for next step */
154 Node *node = nextnode->get_parent();
155 tid = node->get_next_backtrack();
156 node_stack->pop_restofstack(1);
158 DEBUG("*** Divergence point ***\n");
161 tid = next->get_tid();
163 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
168 * Queries the model-checker for more executions to explore and, if one
169 * exists, resets the model-checker state to execute a new execution.
171 * @return If there are more executions to explore, return true. Otherwise,
174 bool ModelChecker::next_execution()
180 if (isfinalfeasible() || DBG_ENABLED())
183 if ((diverge = model->get_next_backtrack()) == NULL)
187 printf("Next execution will diverge at:\n");
191 model->reset_to_initial_state();
195 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
197 action_type type = act->get_type();
207 /* linear search: from most recent to oldest */
208 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
209 action_list_t::reverse_iterator rit;
210 for (rit = list->rbegin(); rit != list->rend(); rit++) {
211 ModelAction *prev = *rit;
212 if (act->is_synchronizing(prev))
218 void ModelChecker::set_backtracking(ModelAction *act)
222 Thread *t = get_thread(act->get_tid());
224 prev = get_last_conflict(act);
228 node = prev->get_node()->get_parent();
230 while (!node->is_enabled(t))
233 /* Check if this has been explored already */
234 if (node->has_been_explored(t->get_id()))
237 /* Cache the latest backtracking point */
238 if (!next_backtrack || *prev > *next_backtrack)
239 next_backtrack = prev;
241 /* If this is a new backtracking point, mark the tree */
242 if (!node->set_backtrack(t->get_id()))
244 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
245 prev->get_tid(), t->get_id());
253 * Returns last backtracking point. The model checker will explore a different
254 * path for this point in the next execution.
255 * @return The ModelAction at which the next execution should diverge.
257 ModelAction * ModelChecker::get_next_backtrack()
259 ModelAction *next = next_backtrack;
260 next_backtrack = NULL;
264 void ModelChecker::check_current_action(void)
266 ModelAction *curr = this->current_action;
267 bool already_added = false;
268 this->current_action = NULL;
270 DEBUG("trying to push NULL action...\n");
274 if (curr->is_rmwc() || curr->is_rmw()) {
275 ModelAction *tmp = process_rmw(curr);
276 already_added = true;
280 ModelAction * tmp = node_stack->explore_action(curr);
282 /* Discard duplicate ModelAction; use action from NodeStack */
283 /* First restore type and order in case of RMW operation */
285 tmp->copy_typeandorder(curr);
287 /* If we have diverged, we need to reset the clock vector. */
289 tmp->create_cv(get_parent_action(tmp->get_tid()));
295 * Perform one-time actions when pushing new ModelAction onto
298 curr->create_cv(get_parent_action(curr->get_tid()));
299 /* Build may_read_from set */
301 build_reads_from_past(curr);
302 if (curr->is_write())
303 compute_promises(curr);
307 /* Assign 'creation' parent */
308 if (curr->get_type() == THREAD_CREATE) {
309 Thread *th = (Thread *)curr->get_location();
310 th->set_creation(curr);
313 /* Deal with new thread */
314 if (curr->get_type() == THREAD_START)
315 check_promises(NULL, curr->get_cv());
317 /* Assign reads_from values */
318 Thread *th = get_thread(curr->get_tid());
319 uint64_t value = VALUE_NONE;
320 if (curr->is_read()) {
321 const ModelAction *reads_from = curr->get_node()->get_read_from();
322 if (reads_from != NULL) {
323 value = reads_from->get_value();
324 /* Assign reads_from, perform release/acquire synchronization */
325 curr->read_from(reads_from);
326 r_modification_order(curr,reads_from);
328 /* Read from future value */
329 value = curr->get_node()->get_future_value();
330 curr->read_from(NULL);
331 Promise * valuepromise = new Promise(curr, value);
332 promises->push_back(valuepromise);
334 } else if (curr->is_write()) {
335 w_modification_order(curr);
336 resolve_promises(curr);
339 th->set_return_value(value);
341 /* Add action to list. */
343 add_action_to_lists(curr);
345 /** @todo Is there a better interface for setting the next thread rather
346 than this field/convoluted approach? Perhaps like just returning
349 /* Do not split atomic actions. */
351 nextThread = thread_current()->get_id();
353 nextThread = get_next_replay_thread();
355 Node *currnode = curr->get_node();
356 Node *parnode = currnode->get_parent();
358 if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
359 !currnode->future_value_empty() || !currnode->promise_empty())
360 if (!next_backtrack || *curr > *next_backtrack)
361 next_backtrack = curr;
363 set_backtracking(curr);
366 /** @returns whether the current partial trace is feasible. */
367 bool ModelChecker::isfeasible() {
368 return !mo_graph->checkForCycles() && !failed_promise;
371 /** Returns whether the current completed trace is feasible. */
372 bool ModelChecker::isfinalfeasible() {
373 return isfeasible() && promises->size() == 0;
376 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
377 ModelAction * ModelChecker::process_rmw(ModelAction * act) {
378 int tid = id_to_int(act->get_tid());
379 ModelAction *lastread = get_last_action(tid);
380 lastread->process_rmw(act);
382 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
387 * Updates the mo_graph with the constraints imposed from the current read.
388 * @param curr The current action. Must be a read.
389 * @param rf The action that curr reads from. Must be a write.
391 void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
392 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
394 ASSERT(curr->is_read());
396 /* Iterate over all threads */
397 for (i = 0; i < thrd_lists->size(); i++) {
398 /* Iterate over actions in thread, starting from most recent */
399 action_list_t *list = &(*thrd_lists)[i];
400 action_list_t::reverse_iterator rit;
401 for (rit = list->rbegin(); rit != list->rend(); rit++) {
402 ModelAction *act = *rit;
404 /* Include at most one act per-thread that "happens before" curr */
405 if (act->happens_before(curr)) {
406 if (act->is_read()) {
407 const ModelAction * prevreadfrom = act->get_reads_from();
408 if (prevreadfrom != NULL && rf != prevreadfrom)
409 mo_graph->addEdge(prevreadfrom, rf);
410 } else if (rf != act) {
411 mo_graph->addEdge(act, rf);
419 /** Updates the mo_graph with the constraints imposed from the current read. */
420 void ModelChecker::post_r_modification_order(ModelAction * curr, const ModelAction *rf) {
421 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
423 ASSERT(curr->is_read());
425 /* Iterate over all threads */
426 for (i = 0; i < thrd_lists->size(); i++) {
427 /* Iterate over actions in thread, starting from most recent */
428 action_list_t *list = &(*thrd_lists)[i];
429 action_list_t::reverse_iterator rit;
430 ModelAction *lastact = NULL;
432 /* Find last action that happens after curr */
433 for (rit = list->rbegin(); rit != list->rend(); rit++) {
434 ModelAction *act = *rit;
435 if (curr->happens_before(act)) {
441 /* Include at most one act per-thread that "happens before" curr */
442 if (lastact != NULL) {
443 if (lastact->is_read()) {
444 const ModelAction * postreadfrom = lastact->get_reads_from();
445 if (postreadfrom != NULL&&rf != postreadfrom)
446 mo_graph->addEdge(rf, postreadfrom);
447 } else if (rf != lastact) {
448 mo_graph->addEdge(rf, lastact);
456 * Updates the mo_graph with the constraints imposed from the current write.
457 * @param curr The current action. Must be a write.
459 void ModelChecker::w_modification_order(ModelAction * curr) {
460 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
462 ASSERT(curr->is_write());
464 if (curr->is_seqcst()) {
465 /* We have to at least see the last sequentially consistent write,
466 so we are initialized. */
467 ModelAction * last_seq_cst = get_last_seq_cst(curr->get_location());
468 if (last_seq_cst != NULL)
469 mo_graph->addEdge(last_seq_cst, curr);
472 /* Iterate over all threads */
473 for (i = 0; i < thrd_lists->size(); i++) {
474 /* Iterate over actions in thread, starting from most recent */
475 action_list_t *list = &(*thrd_lists)[i];
476 action_list_t::reverse_iterator rit;
477 for (rit = list->rbegin(); rit != list->rend(); rit++) {
478 ModelAction *act = *rit;
480 /* Include at most one act per-thread that "happens before" curr */
481 if (act->happens_before(curr)) {
483 mo_graph->addEdge(act->get_reads_from(), curr);
485 mo_graph->addEdge(act, curr);
487 } else if (act->is_read() && !act->is_synchronizing(curr) &&
488 !act->same_thread(curr)) {
489 /* We have an action that:
490 (1) did not happen before us
491 (2) is a read and we are a write
492 (3) cannot synchronize with us
493 (4) is in a different thread
495 that read could potentially read from our write.
497 if (act->get_node()->add_future_value(curr->get_value()) &&
498 (!next_backtrack || *act > *next_backtrack))
499 next_backtrack = act;
506 * Performs various bookkeeping operations for the current ModelAction. For
507 * instance, adds action to the per-object, per-thread action vector and to the
508 * action trace list of all thread actions.
510 * @param act is the ModelAction to add.
512 void ModelChecker::add_action_to_lists(ModelAction *act)
514 int tid = id_to_int(act->get_tid());
515 action_trace->push_back(act);
517 obj_map->get_safe_ptr(act->get_location())->push_back(act);
519 std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
520 if (tid >= (int)vec->size())
521 vec->resize(next_thread_id);
522 (*vec)[tid].push_back(act);
524 if ((int)thrd_last_action->size() <= tid)
525 thrd_last_action->resize(get_num_threads());
526 (*thrd_last_action)[tid] = act;
529 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
531 int nthreads = get_num_threads();
532 if ((int)thrd_last_action->size() < nthreads)
533 thrd_last_action->resize(nthreads);
534 return (*thrd_last_action)[id_to_int(tid)];
538 * Gets the last memory_order_seq_cst action (in the total global sequence)
539 * performed on a particular object (i.e., memory location).
540 * @param location The object location to check
541 * @return The last seq_cst action performed
543 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
545 action_list_t *list = obj_map->get_safe_ptr(location);
546 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
547 action_list_t::reverse_iterator rit;
548 for (rit = list->rbegin(); rit != list->rend(); rit++)
549 if ((*rit)->is_write() && (*rit)->is_seqcst())
554 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
556 ModelAction *parent = get_last_action(tid);
558 parent = get_thread(tid)->get_creation();
563 * Returns the clock vector for a given thread.
564 * @param tid The thread whose clock vector we want
565 * @return Desired clock vector
567 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
568 return get_parent_action(tid)->get_cv();
572 /** Resolve the given promises. */
574 void ModelChecker::resolve_promises(ModelAction *write) {
575 for (unsigned int i = 0, promise_index = 0;promise_index<promises->size(); i++) {
576 Promise * promise = (*promises)[promise_index];
577 if (write->get_node()->get_promise(i)) {
578 ModelAction * read = promise->get_action();
579 read->read_from(write);
580 r_modification_order(read, write);
581 post_r_modification_order(read, write);
582 promises->erase(promises->begin()+promise_index);
588 /** Compute the set of promises that could potentially be satisfied by
591 void ModelChecker::compute_promises(ModelAction *curr) {
592 for (unsigned int i = 0;i<promises->size();i++) {
593 Promise * promise = (*promises)[i];
594 const ModelAction * act = promise->get_action();
595 if (!act->happens_before(curr)&&
597 !act->is_synchronizing(curr)&&
598 !act->same_thread(curr)&&
599 promise->get_value() == curr->get_value()) {
600 curr->get_node()->set_promise(i);
605 /** Checks promises in response to change in ClockVector Threads. */
607 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector * merge_cv) {
608 for (unsigned int i = 0;i<promises->size();i++) {
609 Promise * promise = (*promises)[i];
610 const ModelAction * act = promise->get_action();
611 if ((old_cv == NULL||!old_cv->synchronized_since(act))&&
612 merge_cv->synchronized_since(act)) {
613 //This thread is no longer able to send values back to satisfy the promise
614 int num_synchronized_threads = promise->increment_threads();
615 if (num_synchronized_threads == model->get_num_threads()) {
617 failed_promise = true;
625 * Build up an initial set of all past writes that this 'read' action may read
626 * from. This set is determined by the clock vector's "happens before"
628 * @param curr is the current ModelAction that we are exploring; it must be a
631 void ModelChecker::build_reads_from_past(ModelAction *curr)
633 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
635 ASSERT(curr->is_read());
637 ModelAction *last_seq_cst = NULL;
639 /* Track whether this object has been initialized */
640 bool initialized = false;
642 if (curr->is_seqcst()) {
643 last_seq_cst = get_last_seq_cst(curr->get_location());
644 /* We have to at least see the last sequentially consistent write,
645 so we are initialized. */
646 if (last_seq_cst != NULL)
650 /* Iterate over all threads */
651 for (i = 0; i < thrd_lists->size(); i++) {
652 /* Iterate over actions in thread, starting from most recent */
653 action_list_t *list = &(*thrd_lists)[i];
654 action_list_t::reverse_iterator rit;
655 for (rit = list->rbegin(); rit != list->rend(); rit++) {
656 ModelAction *act = *rit;
658 /* Only consider 'write' actions */
659 if (!act->is_write())
662 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
663 if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
664 DEBUG("Adding action to may_read_from:\n");
669 curr->get_node()->add_read_from(act);
672 /* Include at most one act per-thread that "happens before" curr */
673 if (act->happens_before(curr)) {
681 /** @todo Need a more informative way of reporting errors. */
682 printf("ERROR: may read from uninitialized atomic\n");
685 if (DBG_ENABLED() || !initialized) {
686 printf("Reached read action:\n");
688 printf("Printing may_read_from\n");
689 curr->get_node()->print_may_read_from();
690 printf("End printing may_read_from\n");
696 static void print_list(action_list_t *list)
698 action_list_t::iterator it;
700 printf("---------------------------------------------------------------------\n");
703 for (it = list->begin(); it != list->end(); it++) {
706 printf("---------------------------------------------------------------------\n");
709 void ModelChecker::print_summary()
712 printf("Number of executions: %d\n", num_executions);
713 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
717 if (!isfinalfeasible())
718 printf("INFEASIBLE EXECUTION!\n");
719 print_list(action_trace);
724 * Add a Thread to the system for the first time. Should only be called once
726 * @param t The Thread to add
728 void ModelChecker::add_thread(Thread *t)
730 thread_map->put(id_to_int(t->get_id()), t);
731 scheduler->add_thread(t);
734 void ModelChecker::remove_thread(Thread *t)
736 scheduler->remove_thread(t);
740 * Switch from a user-context to the "master thread" context (a.k.a. system
741 * context). This switch is made with the intention of exploring a particular
742 * model-checking action (described by a ModelAction object). Must be called
743 * from a user-thread context.
744 * @param act The current action that will be explored. May be NULL, although
745 * there is little reason to switch to the model-checker without an action to
746 * explore (note: act == NULL is sometimes used as a hack to allow a thread to
747 * yield control without performing any progress; see thrd_join()).
748 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
750 int ModelChecker::switch_to_master(ModelAction *act)
753 Thread * old = thread_current();
754 set_current_action(act);
755 old->set_state(THREAD_READY);
756 return Thread::swap(old, &system_context);
760 * Takes the next step in the execution, if possible.
761 * @return Returns true (success) if a step was taken and false otherwise.
763 bool ModelChecker::take_step() {
766 curr = thread_current();
768 if (curr->get_state() == THREAD_READY) {
769 check_current_action();
770 scheduler->add_thread(curr);
771 } else if (curr->get_state() == THREAD_RUNNING) {
772 /* Stopped while running; i.e., completed */
778 next = scheduler->next_thread();
780 /* Infeasible -> don't take any more steps */
785 next->set_state(THREAD_RUNNING);
786 DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
788 /* next == NULL -> don't take any more steps */
791 /* Return false only if swap fails with an error */
792 return (Thread::swap(&system_context, next) == 0);
795 /** Runs the current execution until threre are no more steps to take. */
796 void ModelChecker::finish_execution() {