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() :
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),
27 nextThread(THREAD_ID_T_NONE),
28 action_trace(new action_list_t()),
29 thread_map(new HashTable<int, Thread *, int>()),
30 obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
31 obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
32 promises(new std::vector<Promise *>()),
33 thrd_last_action(new std::vector<ModelAction *>(1)),
34 node_stack(new NodeStack()),
36 cyclegraph(new CycleGraph()),
41 /** @brief Destructor */
42 ModelChecker::~ModelChecker()
44 for (int i = 0; i < get_num_threads(); i++)
45 delete thread_map->get(i);
51 delete thrd_last_action;
58 * Restores user program to initial state and resets all model-checker data
61 void ModelChecker::reset_to_initial_state()
63 DEBUG("+++ Resetting to initial state +++\n");
64 node_stack->reset_execution();
65 current_action = NULL;
66 next_thread_id = INITIAL_THREAD_ID;
67 used_sequence_numbers = 0;
69 next_backtrack = NULL;
70 failed_promise = false;
71 snapshotObject->backTrackBeforeStep(0);
74 /** @returns a thread ID for a new Thread */
75 thread_id_t ModelChecker::get_next_id()
77 return next_thread_id++;
80 /** @returns the number of user threads created during this execution */
81 int ModelChecker::get_num_threads()
83 return next_thread_id;
86 /** @returns a sequence number for a new ModelAction */
87 modelclock_t ModelChecker::get_next_seq_num()
89 return ++used_sequence_numbers;
93 * Performs the "scheduling" for the model-checker. That is, it checks if the
94 * model-checker has selected a "next thread to run" and returns it, if
95 * available. This function should be called from the Scheduler routine, where
96 * the Scheduler falls back to a default scheduling routine if needed.
98 * @return The next thread chosen by the model-checker. If the model-checker
99 * makes no selection, retuns NULL.
101 Thread * ModelChecker::schedule_next_thread()
104 if (nextThread == THREAD_ID_T_NONE)
106 t = thread_map->get(id_to_int(nextThread));
114 * Choose the next thread in the replay sequence.
116 * If the replay sequence has reached the 'diverge' point, returns a thread
117 * from the backtracking set. Otherwise, simply returns the next thread in the
118 * sequence that is being replayed.
120 thread_id_t ModelChecker::get_next_replay_thread()
124 /* Have we completed exploring the preselected path? */
126 return THREAD_ID_T_NONE;
128 /* Else, we are trying to replay an execution */
129 ModelAction * next = node_stack->get_next()->get_action();
131 if (next == diverge) {
132 Node *nextnode = next->get_node();
133 /* Reached divergence point */
134 if (nextnode->increment_promise()) {
135 /* The next node will try to satisfy a different set of promises. */
136 tid = next->get_tid();
137 node_stack->pop_restofstack(2);
138 } else if (nextnode->increment_read_from()) {
139 /* The next node will read from a different value. */
140 tid = next->get_tid();
141 node_stack->pop_restofstack(2);
142 } else if (nextnode->increment_future_value()) {
143 /* The next node will try to read from a different future value. */
144 tid = next->get_tid();
145 node_stack->pop_restofstack(2);
147 /* Make a different thread execute for next step */
148 Node *node = nextnode->get_parent();
149 tid = node->get_next_backtrack();
150 node_stack->pop_restofstack(1);
152 DEBUG("*** Divergence point ***\n");
155 tid = next->get_tid();
157 DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
162 * Queries the model-checker for more executions to explore and, if one
163 * exists, resets the model-checker state to execute a new execution.
165 * @return If there are more executions to explore, return true. Otherwise,
168 bool ModelChecker::next_execution()
174 if (isfinalfeasible() || DBG_ENABLED())
177 if ((diverge = model->get_next_backtrack()) == NULL)
181 printf("Next execution will diverge at:\n");
185 model->reset_to_initial_state();
189 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
191 action_type type = act->get_type();
201 /* linear search: from most recent to oldest */
202 action_list_t *list = obj_map->ensureptr(act->get_location());
203 action_list_t::reverse_iterator rit;
204 for (rit = list->rbegin(); rit != list->rend(); rit++) {
205 ModelAction *prev = *rit;
206 if (act->is_synchronizing(prev))
212 void ModelChecker::set_backtracking(ModelAction *act)
216 Thread *t = get_thread(act->get_tid());
218 prev = get_last_conflict(act);
222 node = prev->get_node()->get_parent();
224 while (!node->is_enabled(t))
227 /* Check if this has been explored already */
228 if (node->has_been_explored(t->get_id()))
231 /* Cache the latest backtracking point */
232 if (!next_backtrack || *prev > *next_backtrack)
233 next_backtrack = prev;
235 /* If this is a new backtracking point, mark the tree */
236 if (!node->set_backtrack(t->get_id()))
238 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
239 prev->get_tid(), t->get_id());
247 * Returns last backtracking point. The model checker will explore a different
248 * path for this point in the next execution.
249 * @return The ModelAction at which the next execution should diverge.
251 ModelAction * ModelChecker::get_next_backtrack()
253 ModelAction *next = next_backtrack;
254 next_backtrack = NULL;
258 void ModelChecker::check_current_action(void)
260 ModelAction *curr = this->current_action;
261 bool already_added = false;
262 this->current_action = NULL;
264 DEBUG("trying to push NULL action...\n");
268 if (curr->is_rmwc()||curr->is_rmw()) {
269 ModelAction *tmp=process_rmw(curr);
270 already_added = true;
274 ModelAction * tmp = node_stack->explore_action(curr);
276 /* Discard duplicate ModelAction; use action from NodeStack */
277 /* First restore type and order in case of RMW operation */
279 tmp->copy_typeandorder(curr);
281 /* If we have diverged, we need to reset the clock vector. */
283 tmp->create_cv(get_parent_action(tmp->get_tid()));
290 * Perform one-time actions when pushing new ModelAction onto
293 curr->create_cv(get_parent_action(curr->get_tid()));
294 /* Build may_read_from set */
296 build_reads_from_past(curr);
297 if (curr->is_write())
298 compute_promises(curr);
302 /* Assign 'creation' parent */
303 if (curr->get_type() == THREAD_CREATE) {
304 Thread *th = (Thread *)curr->get_location();
305 th->set_creation(curr);
308 /* Deal with new thread */
309 if (curr->get_type() == THREAD_START) {
310 check_promises(NULL, curr->get_cv());
313 /* Assign reads_from values */
314 Thread *th = get_thread(curr->get_tid());
315 uint64_t value = VALUE_NONE;
316 if (curr->is_read()) {
317 const ModelAction *reads_from = curr->get_node()->get_read_from();
318 if (reads_from!=NULL) {
319 value = reads_from->get_value();
320 /* Assign reads_from, perform release/acquire synchronization */
321 curr->read_from(reads_from);
322 r_modification_order(curr,reads_from);
324 /* Read from future value */
325 value = curr->get_node()->get_future_value();
326 curr->read_from(NULL);
327 Promise * valuepromise=new Promise(curr, value);
328 promises->push_back(valuepromise);
330 } else if (curr->is_write()) {
331 w_modification_order(curr);
332 resolve_promises(curr);
335 th->set_return_value(value);
337 /* Add action to list. */
339 add_action_to_lists(curr);
341 /* Is there a better interface for setting the next thread rather
342 than this field/convoluted approach? Perhaps like just returning
345 /* Do not split atomic actions. */
346 if (curr->is_rmwr()) {
347 nextThread = thread_current()->get_id();
349 nextThread = get_next_replay_thread();
352 Node *currnode = curr->get_node();
353 Node *parnode = currnode->get_parent();
355 if (!parnode->backtrack_empty()||!currnode->read_from_empty()||!currnode->future_value_empty()||!currnode->promise_empty())
356 if (!next_backtrack || *curr > *next_backtrack)
357 next_backtrack = curr;
359 set_backtracking(curr);
362 /** @returns whether the current partial trace is feasible. */
363 bool ModelChecker::isfeasible() {
364 return !cyclegraph->checkForCycles() && !failed_promise;
367 /** Returns whether the current completed trace is feasible. */
368 bool ModelChecker::isfinalfeasible() {
369 return isfeasible() && promises->size()==0;
372 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
373 ModelAction * ModelChecker::process_rmw(ModelAction * act) {
374 int tid = id_to_int(act->get_tid());
375 ModelAction *lastread=get_last_action(tid);
376 lastread->process_rmw(act);
378 cyclegraph->addRMWEdge(lastread, lastread->get_reads_from());
383 * Updates the cyclegraph with the constraints imposed from the current read.
384 * @param curr The current action. Must be a read.
385 * @param rf The action that curr reads from. Must be a write.
387 void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
388 std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
390 ASSERT(curr->is_read());
392 /* Iterate over all threads */
393 for (i = 0; i < thrd_lists->size(); i++) {
394 /* Iterate over actions in thread, starting from most recent */
395 action_list_t *list = &(*thrd_lists)[i];
396 action_list_t::reverse_iterator rit;
397 for (rit = list->rbegin(); rit != list->rend(); rit++) {
398 ModelAction *act = *rit;
400 /* Include at most one act per-thread that "happens before" curr */
401 if (act->happens_before(curr)) {
402 if (act->is_read()) {
403 const ModelAction * prevreadfrom=act->get_reads_from();
404 if (prevreadfrom!=NULL&&rf!=prevreadfrom)
405 cyclegraph->addEdge(rf, prevreadfrom);
406 } else if (rf!=act) {
407 cyclegraph->addEdge(rf, act);
415 /** Updates the cyclegraph with the constraints imposed from the
417 void ModelChecker::post_r_modification_order(ModelAction * curr, const ModelAction *rf) {
418 std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
420 ASSERT(curr->is_read());
422 /* Iterate over all threads */
423 for (i = 0; i < thrd_lists->size(); i++) {
424 /* Iterate over actions in thread, starting from most recent */
425 action_list_t *list = &(*thrd_lists)[i];
426 action_list_t::reverse_iterator rit;
427 ModelAction *lastact=NULL;
429 /* Find last action that happens after curr */
430 for (rit = list->rbegin(); rit != list->rend(); rit++) {
431 ModelAction *act = *rit;
432 if (curr->happens_before(act)) {
438 /* Include at most one act per-thread that "happens before" curr */
440 if (lastact->is_read()) {
441 const ModelAction * postreadfrom=lastact->get_reads_from();
442 if (postreadfrom!=NULL&&rf!=postreadfrom)
443 cyclegraph->addEdge(postreadfrom, rf);
444 } else if (rf!=lastact) {
445 cyclegraph->addEdge(lastact, rf);
453 * Updates the cyclegraph with the constraints imposed from the current write.
454 * @param curr The current action. Must be a write.
456 void ModelChecker::w_modification_order(ModelAction * curr) {
457 std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
459 ASSERT(curr->is_write());
461 if (curr->is_seqcst()) {
462 /* We have to at least see the last sequentially consistent write,
463 so we are initialized. */
464 ModelAction * last_seq_cst=get_last_seq_cst(curr->get_location());
465 if (last_seq_cst!=NULL)
466 cyclegraph->addEdge(curr, last_seq_cst);
469 /* Iterate over all threads */
470 for (i = 0; i < thrd_lists->size(); i++) {
471 /* Iterate over actions in thread, starting from most recent */
472 action_list_t *list = &(*thrd_lists)[i];
473 action_list_t::reverse_iterator rit;
474 for (rit = list->rbegin(); rit != list->rend(); rit++) {
475 ModelAction *act = *rit;
477 /* Include at most one act per-thread that "happens before" curr */
478 if (act->happens_before(curr)) {
479 if (act->is_read()) {
480 cyclegraph->addEdge(curr, act->get_reads_from());
482 cyclegraph->addEdge(curr, act);
485 if (act->is_read()&&!act->is_synchronizing(curr)&&!act->same_thread(curr)) {
486 /* We have an action that:
487 (1) did not happen before us
488 (2) is a read and we are a write
489 (3) cannot synchronize with us
490 (4) is in a different thread
492 that read could potentially read from our write.
494 if (act->get_node()->add_future_value(curr->get_value())&&
495 (!next_backtrack || *act > * next_backtrack))
496 next_backtrack = act;
504 * Performs various bookkeeping operations for the current ModelAction. For
505 * instance, adds action to the per-object, per-thread action vector and to the
506 * action trace list of all thread actions.
508 * @param act is the ModelAction to add.
510 void ModelChecker::add_action_to_lists(ModelAction *act)
512 int tid = id_to_int(act->get_tid());
513 action_trace->push_back(act);
515 obj_map->ensureptr(act->get_location())->push_back(act);
517 std::vector<action_list_t> *vec = obj_thrd_map->ensureptr(act->get_location());
518 if (tid >= (int)vec->size())
519 vec->resize(next_thread_id);
520 (*vec)[tid].push_back(act);
522 if ((int)thrd_last_action->size() <= tid)
523 thrd_last_action->resize(get_num_threads());
524 (*thrd_last_action)[tid] = act;
527 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
529 int nthreads = get_num_threads();
530 if ((int)thrd_last_action->size() < nthreads)
531 thrd_last_action->resize(nthreads);
532 return (*thrd_last_action)[id_to_int(tid)];
536 * Gets the last memory_order_seq_cst action (in the total global sequence)
537 * performed on a particular object (i.e., memory location).
538 * @param location The object location to check
539 * @return The last seq_cst action performed
541 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
543 action_list_t *list = obj_map->ensureptr(location);
544 /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
545 action_list_t::reverse_iterator rit;
546 for (rit = list->rbegin(); rit != list->rend(); rit++)
547 if ((*rit)->is_write() && (*rit)->is_seqcst())
552 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
554 ModelAction *parent = get_last_action(tid);
556 parent = get_thread(tid)->get_creation();
561 * Returns the clock vector for a given thread.
562 * @param tid The thread whose clock vector we want
563 * @return Desired clock vector
565 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
566 return get_parent_action(tid)->get_cv();
570 /** Resolve the given promises. */
572 void ModelChecker::resolve_promises(ModelAction *write) {
573 for(unsigned int i=0, promise_index=0;promise_index<promises->size(); i++) {
574 Promise * promise=(*promises)[promise_index];
575 if (write->get_node()->get_promise(i)) {
576 ModelAction * read=promise->get_action();
577 read->read_from(write);
578 r_modification_order(read, write);
579 post_r_modification_order(read, write);
580 promises->erase(promises->begin()+promise_index);
586 /** Compute the set of promises that could potentially be satisfied by
589 void ModelChecker::compute_promises(ModelAction *curr) {
590 for(unsigned int i=0;i<promises->size();i++) {
591 Promise * promise=(*promises)[i];
592 const ModelAction * act=promise->get_action();
593 if (!act->happens_before(curr)&&
595 !act->is_synchronizing(curr)&&
596 !act->same_thread(curr)&&
597 promise->get_value()==curr->get_value()) {
598 curr->get_node()->set_promise(i);
603 /** Checks promises in response to change in ClockVector Threads. */
605 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector * merge_cv) {
606 for(unsigned int i=0;i<promises->size();i++) {
607 Promise * promise=(*promises)[i];
608 const ModelAction * act=promise->get_action();
609 if ((old_cv==NULL||!old_cv->synchronized_since(act))&&
610 merge_cv->synchronized_since(act)) {
611 //This thread is no longer able to send values back to satisfy the promise
612 int num_synchronized_threads=promise->increment_threads();
613 if (num_synchronized_threads==model->get_num_threads()) {
615 failed_promise = true;
623 * Build up an initial set of all past writes that this 'read' action may read
624 * from. This set is determined by the clock vector's "happens before"
626 * @param curr is the current ModelAction that we are exploring; it must be a
629 void ModelChecker::build_reads_from_past(ModelAction *curr)
631 std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
633 ASSERT(curr->is_read());
635 ModelAction *last_seq_cst = NULL;
637 /* Track whether this object has been initialized */
638 bool initialized = false;
640 if (curr->is_seqcst()) {
641 last_seq_cst = get_last_seq_cst(curr->get_location());
642 /* We have to at least see the last sequentially consistent write,
643 so we are initialized. */
644 if (last_seq_cst != NULL)
648 /* Iterate over all threads */
649 for (i = 0; i < thrd_lists->size(); i++) {
650 /* Iterate over actions in thread, starting from most recent */
651 action_list_t *list = &(*thrd_lists)[i];
652 action_list_t::reverse_iterator rit;
653 for (rit = list->rbegin(); rit != list->rend(); rit++) {
654 ModelAction *act = *rit;
656 /* Only consider 'write' actions */
657 if (!act->is_write())
660 /* Don't consider more than one seq_cst write if we are a seq_cst read. */
661 if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
662 DEBUG("Adding action to may_read_from:\n");
667 curr->get_node()->add_read_from(act);
670 /* Include at most one act per-thread that "happens before" curr */
671 if (act->happens_before(curr)) {
679 /** @todo Need a more informative way of reporting errors. */
680 printf("ERROR: may read from uninitialized atomic\n");
683 if (DBG_ENABLED() || !initialized) {
684 printf("Reached read action:\n");
686 printf("Printing may_read_from\n");
687 curr->get_node()->print_may_read_from();
688 printf("End printing may_read_from\n");
694 static void print_list(action_list_t *list)
696 action_list_t::iterator it;
698 printf("---------------------------------------------------------------------\n");
701 for (it = list->begin(); it != list->end(); it++) {
704 printf("---------------------------------------------------------------------\n");
707 void ModelChecker::print_summary(void)
710 printf("Number of executions: %d\n", num_executions);
711 printf("Total nodes created: %d\n", node_stack->get_total_nodes());
715 if (!isfinalfeasible())
716 printf("INFEASIBLE EXECUTION!\n");
717 print_list(action_trace);
721 int ModelChecker::add_thread(Thread *t)
723 thread_map->put(id_to_int(t->get_id()), t);
724 scheduler->add_thread(t);
728 void ModelChecker::remove_thread(Thread *t)
730 scheduler->remove_thread(t);
734 * Switch from a user-context to the "master thread" context (a.k.a. system
735 * context). This switch is made with the intention of exploring a particular
736 * model-checking action (described by a ModelAction object). Must be called
737 * from a user-thread context.
738 * @param act The current action that will be explored. May be NULL, although
739 * there is little reason to switch to the model-checker without an action to
740 * explore (note: act == NULL is sometimes used as a hack to allow a thread to
741 * yield control without performing any progress; see thrd_join()).
742 * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
744 int ModelChecker::switch_to_master(ModelAction *act)
747 Thread * old = thread_current();
748 set_current_action(act);
749 old->set_state(THREAD_READY);
750 return Thread::swap(old, get_system_context());