Merge branch 'norris'
[c11tester.git] / model.cc
1 #include <stdio.h>
2 #include <algorithm>
3
4 #include "model.h"
5 #include "action.h"
6 #include "nodestack.h"
7 #include "schedule.h"
8 #include "snapshot-interface.h"
9 #include "common.h"
10 #include "clockvector.h"
11 #include "cyclegraph.h"
12 #include "promise.h"
13 #include "datarace.h"
14
15 #define INITIAL_THREAD_ID       0
16
17 ModelChecker *model;
18
19 /** @brief Constructor */
20 ModelChecker::ModelChecker(struct model_params params) :
21         /* Initialize default scheduler */
22         scheduler(new Scheduler()),
23         num_executions(0),
24         num_feasible_executions(0),
25         params(params),
26         diverge(NULL),
27         action_trace(new action_list_t()),
28         thread_map(new HashTable<int, Thread *, int>()),
29         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
30         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
31         promises(new std::vector<Promise *>()),
32         futurevalues(new std::vector<struct PendingFutureValue>()),
33         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
34         thrd_last_action(new std::vector<ModelAction *>(1)),
35         node_stack(new NodeStack()),
36         mo_graph(new CycleGraph()),
37         failed_promise(false),
38         too_many_reads(false),
39         asserted(false)
40 {
41         /* Allocate this "size" on the snapshotting heap */
42         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
43         /* First thread created will have id INITIAL_THREAD_ID */
44         priv->next_thread_id = INITIAL_THREAD_ID;
45
46         lazy_sync_size = &priv->lazy_sync_size;
47 }
48
49 /** @brief Destructor */
50 ModelChecker::~ModelChecker()
51 {
52         for (int i = 0; i < get_num_threads(); i++)
53                 delete thread_map->get(i);
54         delete thread_map;
55
56         delete obj_thrd_map;
57         delete obj_map;
58         delete action_trace;
59
60         for (unsigned int i = 0; i < promises->size(); i++)
61                 delete (*promises)[i];
62         delete promises;
63
64         delete lazy_sync_with_release;
65
66         delete thrd_last_action;
67         delete node_stack;
68         delete scheduler;
69         delete mo_graph;
70 }
71
72 /**
73  * Restores user program to initial state and resets all model-checker data
74  * structures.
75  */
76 void ModelChecker::reset_to_initial_state()
77 {
78         DEBUG("+++ Resetting to initial state +++\n");
79         node_stack->reset_execution();
80         failed_promise = false;
81         too_many_reads = false;
82         reset_asserted();
83         snapshotObject->backTrackBeforeStep(0);
84 }
85
86 /** @returns a thread ID for a new Thread */
87 thread_id_t ModelChecker::get_next_id()
88 {
89         return priv->next_thread_id++;
90 }
91
92 /** @returns the number of user threads created during this execution */
93 int ModelChecker::get_num_threads()
94 {
95         return priv->next_thread_id;
96 }
97
98 /** @returns a sequence number for a new ModelAction */
99 modelclock_t ModelChecker::get_next_seq_num()
100 {
101         return ++priv->used_sequence_numbers;
102 }
103
104 /**
105  * @brief Choose the next thread to execute.
106  *
107  * This function chooses the next thread that should execute. It can force the
108  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
109  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
110  * The model-checker may have no preference regarding the next thread (i.e.,
111  * when exploring a new execution ordering), in which case this will return
112  * NULL.
113  * @param curr The current ModelAction. This action might guide the choice of
114  * next thread.
115  * @return The next thread to run. If the model-checker has no preference, NULL.
116  */
117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
118 {
119         thread_id_t tid;
120
121         /* Do not split atomic actions. */
122         if (curr->is_rmwr())
123                 return thread_current();
124         /* The THREAD_CREATE action points to the created Thread */
125         else if (curr->get_type() == THREAD_CREATE)
126                 return (Thread *)curr->get_location();
127
128         /* Have we completed exploring the preselected path? */
129         if (diverge == NULL)
130                 return NULL;
131
132         /* Else, we are trying to replay an execution */
133         ModelAction *next = node_stack->get_next()->get_action();
134
135         if (next == diverge) {
136                 Node *nextnode = next->get_node();
137                 /* Reached divergence point */
138                 if (nextnode->increment_promise()) {
139                         /* The next node will try to satisfy a different set of promises. */
140                         tid = next->get_tid();
141                         node_stack->pop_restofstack(2);
142                 } else if (nextnode->increment_read_from()) {
143                         /* The next node will read from a different value. */
144                         tid = next->get_tid();
145                         node_stack->pop_restofstack(2);
146                 } else if (nextnode->increment_future_value()) {
147                         /* The next node will try to read from a different future value. */
148                         tid = next->get_tid();
149                         node_stack->pop_restofstack(2);
150                 } else {
151                         /* Make a different thread execute for next step */
152                         Node *node = nextnode->get_parent();
153                         tid = node->get_next_backtrack();
154                         node_stack->pop_restofstack(1);
155                 }
156                 DEBUG("*** Divergence point ***\n");
157                 diverge = NULL;
158         } else {
159                 tid = next->get_tid();
160         }
161         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
162         ASSERT(tid != THREAD_ID_T_NONE);
163         return thread_map->get(id_to_int(tid));
164 }
165
166 /**
167  * Queries the model-checker for more executions to explore and, if one
168  * exists, resets the model-checker state to execute a new execution.
169  *
170  * @return If there are more executions to explore, return true. Otherwise,
171  * return false.
172  */
173 bool ModelChecker::next_execution()
174 {
175         DBG();
176
177         num_executions++;
178         if (isfinalfeasible())
179                 num_feasible_executions++;
180
181         if (isfinalfeasible() || DBG_ENABLED())
182                 print_summary();
183
184         if ((diverge = get_next_backtrack()) == NULL)
185                 return false;
186
187         if (DBG_ENABLED()) {
188                 printf("Next execution will diverge at:\n");
189                 diverge->print();
190         }
191
192         reset_to_initial_state();
193         return true;
194 }
195
196 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
197 {
198         action_type type = act->get_type();
199
200         switch (type) {
201                 case ATOMIC_READ:
202                 case ATOMIC_WRITE:
203                 case ATOMIC_RMW:
204                         break;
205                 default:
206                         return NULL;
207         }
208         /* linear search: from most recent to oldest */
209         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
210         action_list_t::reverse_iterator rit;
211         for (rit = list->rbegin(); rit != list->rend(); rit++) {
212                 ModelAction *prev = *rit;
213                 if (act->is_synchronizing(prev))
214                         return prev;
215         }
216         return NULL;
217 }
218
219 void ModelChecker::set_backtracking(ModelAction *act)
220 {
221         ModelAction *prev;
222         Node *node;
223         Thread *t = get_thread(act);
224
225         prev = get_last_conflict(act);
226         if (prev == NULL)
227                 return;
228
229         node = prev->get_node()->get_parent();
230
231         while (!node->is_enabled(t))
232                 t = t->get_parent();
233
234         /* Check if this has been explored already */
235         if (node->has_been_explored(t->get_id()))
236                 return;
237
238         /* Cache the latest backtracking point */
239         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
240                 priv->next_backtrack = prev;
241
242         /* If this is a new backtracking point, mark the tree */
243         if (!node->set_backtrack(t->get_id()))
244                 return;
245         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
246                         prev->get_tid(), t->get_id());
247         if (DBG_ENABLED()) {
248                 prev->print();
249                 act->print();
250         }
251 }
252
253 /**
254  * Returns last backtracking point. The model checker will explore a different
255  * path for this point in the next execution.
256  * @return The ModelAction at which the next execution should diverge.
257  */
258 ModelAction * ModelChecker::get_next_backtrack()
259 {
260         ModelAction *next = priv->next_backtrack;
261         priv->next_backtrack = NULL;
262         return next;
263 }
264
265 /**
266  * Processes a read or rmw model action.
267  * @param curr is the read model action to process.
268  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
269  * @return True if processing this read updates the mo_graph.
270  */
271 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
272 {
273         uint64_t value;
274         bool updated = false;
275         while (true) {
276                 const ModelAction *reads_from = curr->get_node()->get_read_from();
277                 if (reads_from != NULL) {
278                         mo_graph->startChanges();
279
280                         value = reads_from->get_value();
281                         bool r_status = false;
282
283                         if (!second_part_of_rmw) {
284                                 check_recency(curr,false);
285                                 r_status = r_modification_order(curr, reads_from);
286                         }
287
288
289                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
290                                 mo_graph->rollbackChanges();
291                                 too_many_reads = false;
292                                 continue;
293                         }
294
295                         curr->read_from(reads_from);
296                         mo_graph->commitChanges();
297                         updated |= r_status;
298                 } else if (!second_part_of_rmw) {
299                         /* Read from future value */
300                         value = curr->get_node()->get_future_value();
301                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
302                         curr->read_from(NULL);
303                         Promise *valuepromise = new Promise(curr, value, expiration);
304                         promises->push_back(valuepromise);
305                 }
306                 get_thread(curr)->set_return_value(value);
307                 return updated;
308         }
309 }
310
311 /**
312  * Process a write ModelAction
313  * @param curr The ModelAction to process
314  * @return True if the mo_graph was updated or promises were resolved
315  */
316 bool ModelChecker::process_write(ModelAction *curr)
317 {
318         bool updated_mod_order = w_modification_order(curr);
319         bool updated_promises = resolve_promises(curr);
320
321         if (promises->size() == 0) {
322                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
323                         struct PendingFutureValue pfv = (*futurevalues)[i];
324                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
325                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
326                                 priv->next_backtrack = pfv.act;
327                 }
328                 futurevalues->resize(0);
329         }
330
331         mo_graph->commitChanges();
332         get_thread(curr)->set_return_value(VALUE_NONE);
333         return updated_mod_order || updated_promises;
334 }
335
336 /**
337  * This is the heart of the model checker routine. It performs model-checking
338  * actions corresponding to a given "current action." Among other processes, it
339  * calculates reads-from relationships, updates synchronization clock vectors,
340  * forms a memory_order constraints graph, and handles replay/backtrack
341  * execution when running permutations of previously-observed executions.
342  *
343  * @param curr The current action to process
344  * @return The next Thread that must be executed. May be NULL if ModelChecker
345  * makes no choice (e.g., according to replay execution, combining RMW actions,
346  * etc.)
347  */
348 Thread * ModelChecker::check_current_action(ModelAction *curr)
349 {
350         bool second_part_of_rmw = false;
351
352         ASSERT(curr);
353
354         if (curr->is_rmwc() || curr->is_rmw()) {
355                 ModelAction *tmp = process_rmw(curr);
356                 second_part_of_rmw = true;
357                 delete curr;
358                 curr = tmp;
359                 compute_promises(curr);
360         } else {
361                 ModelAction *tmp = node_stack->explore_action(curr);
362                 if (tmp) {
363                         /* Discard duplicate ModelAction; use action from NodeStack */
364                         /* First restore type and order in case of RMW operation */
365                         if (curr->is_rmwr())
366                                 tmp->copy_typeandorder(curr);
367
368                         /* If we have diverged, we need to reset the clock vector. */
369                         if (diverge == NULL)
370                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
371
372                         delete curr;
373                         curr = tmp;
374                 } else {
375                         /*
376                          * Perform one-time actions when pushing new ModelAction onto
377                          * NodeStack
378                          */
379                         curr->create_cv(get_parent_action(curr->get_tid()));
380                         /* Build may_read_from set */
381                         if (curr->is_read())
382                                 build_reads_from_past(curr);
383                         if (curr->is_write())
384                                 compute_promises(curr);
385                 }
386         }
387
388         /* Thread specific actions */
389         switch (curr->get_type()) {
390         case THREAD_CREATE: {
391                 Thread *th = (Thread *)curr->get_location();
392                 th->set_creation(curr);
393                 break;
394         }
395         case THREAD_JOIN: {
396                 Thread *waiting, *blocking;
397                 waiting = get_thread(curr);
398                 blocking = (Thread *)curr->get_location();
399                 if (!blocking->is_complete()) {
400                         blocking->push_wait_list(curr);
401                         scheduler->sleep(waiting);
402                 }
403                 break;
404         }
405         case THREAD_FINISH: {
406                 Thread *th = get_thread(curr);
407                 while (!th->wait_list_empty()) {
408                         ModelAction *act = th->pop_wait_list();
409                         Thread *wake = get_thread(act);
410                         scheduler->wake(wake);
411                 }
412                 th->complete();
413                 break;
414         }
415         case THREAD_START: {
416                 check_promises(NULL, curr->get_cv());
417                 break;
418         }
419         default:
420                 break;
421         }
422
423         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
424
425         while (!work_queue.empty()) {
426                 WorkQueueEntry work = work_queue.front();
427                 work_queue.pop_front();
428
429                 switch (work.type) {
430                 case WORK_CHECK_CURR_ACTION: {
431                         ModelAction *act = work.action;
432                         bool updated = false;
433                         if (act->is_read() && process_read(act, second_part_of_rmw))
434                                 updated = true;
435
436                         if (act->is_write() && process_write(act))
437                                 updated = true;
438
439                         if (updated)
440                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
441                         break;
442                 }
443                 case WORK_CHECK_RELEASE_SEQ:
444                         resolve_release_sequences(work.location, &work_queue);
445                         break;
446                 case WORK_CHECK_MO_EDGES:
447                         /** @todo Perform follow-up mo_graph checks */
448                 default:
449                         ASSERT(false);
450                         break;
451                 }
452         }
453
454         /* Add action to list.  */
455         if (!second_part_of_rmw)
456                 add_action_to_lists(curr);
457
458         check_curr_backtracking(curr);
459
460         set_backtracking(curr);
461
462         return get_next_thread(curr);
463 }
464
465 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
466         Node *currnode = curr->get_node();
467         Node *parnode = currnode->get_parent();
468
469         if ((!parnode->backtrack_empty() ||
470                          !currnode->read_from_empty() ||
471                          !currnode->future_value_empty() ||
472                          !currnode->promise_empty())
473                         && (!priv->next_backtrack ||
474                                         *curr > *priv->next_backtrack)) {
475                 priv->next_backtrack = curr;
476         }
477 }
478
479 bool ModelChecker::promises_expired() {
480         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
481                 Promise *promise = (*promises)[promise_index];
482                 if (promise->get_expiration()<priv->used_sequence_numbers) {
483                         return true;
484                 }
485         }
486         return false;
487 }
488
489 /** @returns whether the current partial trace must be a prefix of a
490  * feasible trace. */
491 bool ModelChecker::isfeasibleprefix() {
492         return promises->size() == 0 && *lazy_sync_size == 0;
493 }
494
495 /** @returns whether the current partial trace is feasible. */
496 bool ModelChecker::isfeasible() {
497         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
498 }
499
500 /** @returns whether the current partial trace is feasible other than
501  * multiple RMW reading from the same store. */
502 bool ModelChecker::isfeasibleotherthanRMW() {
503         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
504 }
505
506 /** Returns whether the current completed trace is feasible. */
507 bool ModelChecker::isfinalfeasible() {
508         return isfeasible() && promises->size() == 0;
509 }
510
511 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
512 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
513         int tid = id_to_int(act->get_tid());
514         ModelAction *lastread = get_last_action(tid);
515         lastread->process_rmw(act);
516         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
517                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
518                 mo_graph->commitChanges();
519         }
520         return lastread;
521 }
522
523 /**
524  * Checks whether a thread has read from the same write for too many times
525  * without seeing the effects of a later write.
526  *
527  * Basic idea:
528  * 1) there must a different write that we could read from that would satisfy the modification order,
529  * 2) we must have read from the same value in excess of maxreads times, and
530  * 3) that other write must have been in the reads_from set for maxreads times.
531  *
532  * If so, we decide that the execution is no longer feasible.
533  */
534 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
535         if (params.maxreads != 0) {
536                 if (curr->get_node()->get_read_from_size() <= 1)
537                         return;
538
539                 //Must make sure that execution is currently feasible...  We could
540                 //accidentally clear by rolling back
541                 if (!isfeasible())
542                         return;
543
544                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
545                 int tid = id_to_int(curr->get_tid());
546
547                 /* Skip checks */
548                 if ((int)thrd_lists->size() <= tid)
549                         return;
550
551                 action_list_t *list = &(*thrd_lists)[tid];
552
553                 action_list_t::reverse_iterator rit = list->rbegin();
554                 /* Skip past curr */
555                 if (already_added) {
556                         for (; (*rit) != curr; rit++)
557                                 ;
558                         /* go past curr now */
559                         rit++;
560                 }
561
562                 action_list_t::reverse_iterator ritcopy = rit;
563                 //See if we have enough reads from the same value
564                 int count = 0;
565                 for (; count < params.maxreads; rit++,count++) {
566                         if (rit==list->rend())
567                                 return;
568                         ModelAction *act = *rit;
569                         if (!act->is_read())
570                                 return;
571                         if (act->get_reads_from() != curr->get_reads_from())
572                                 return;
573                         if (act->get_node()->get_read_from_size() <= 1)
574                                 return;
575                 }
576
577                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
578                         //Get write
579                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
580                         //Need a different write
581                         if (write==curr->get_reads_from())
582                                 continue;
583
584                         /* Test to see whether this is a feasible write to read from*/
585                         mo_graph->startChanges();
586                         r_modification_order(curr, write);
587                         bool feasiblereadfrom = isfeasible();
588                         mo_graph->rollbackChanges();
589
590                         if (!feasiblereadfrom)
591                                 continue;
592                         rit = ritcopy;
593
594                         bool feasiblewrite = true;
595                         //new we need to see if this write works for everyone
596
597                         for (int loop = count; loop>0; loop--,rit++) {
598                                 ModelAction *act=*rit;
599                                 bool foundvalue = false;
600                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
601                                         if (act->get_node()->get_read_from_at(i)==write) {
602                                                 foundvalue = true;
603                                                 break;
604                                         }
605                                 }
606                                 if (!foundvalue) {
607                                         feasiblewrite = false;
608                                         break;
609                                 }
610                         }
611                         if (feasiblewrite) {
612                                 too_many_reads = true;
613                                 return;
614                         }
615                 }
616         }
617 }
618
619 /**
620  * Updates the mo_graph with the constraints imposed from the current
621  * read.  
622  *
623  * Basic idea is the following: Go through each other thread and find
624  * the lastest action that happened before our read.  Two cases:
625  *
626  * (1) The action is a write => that write must either occur before
627  * the write we read from or be the write we read from.
628  *
629  * (2) The action is a read => the write that that action read from
630  * must occur before the write we read from or be the same write.
631  *
632  * @param curr The current action. Must be a read.
633  * @param rf The action that curr reads from. Must be a write.
634  * @return True if modification order edges were added; false otherwise
635  */
636 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
637 {
638         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
639         unsigned int i;
640         bool added = false;
641         ASSERT(curr->is_read());
642
643         /* Iterate over all threads */
644         for (i = 0; i < thrd_lists->size(); i++) {
645                 /* Iterate over actions in thread, starting from most recent */
646                 action_list_t *list = &(*thrd_lists)[i];
647                 action_list_t::reverse_iterator rit;
648                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
649                         ModelAction *act = *rit;
650
651                         /* Include at most one act per-thread that "happens before" curr */
652                         if (act->happens_before(curr)) {
653                                 if (act->is_write()) {
654                                         if (rf != act && act != curr) {
655                                                 mo_graph->addEdge(act, rf);
656                                                 added = true;
657                                         }
658                                 } else {
659                                         const ModelAction *prevreadfrom = act->get_reads_from();
660                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
661                                                 mo_graph->addEdge(prevreadfrom, rf);
662                                                 added = true;
663                                         }
664                                 }
665
666                                 break;
667                         }
668                 }
669         }
670
671         return added;
672 }
673
674 /** This method fixes up the modification order when we resolve a
675  *  promises.  The basic problem is that actions that occur after the
676  *  read curr could not property add items to the modification order
677  *  for our read.
678  *  
679  *  So for each thread, we find the earliest item that happens after
680  *  the read curr.  This is the item we have to fix up with additional
681  *  constraints.  If that action is write, we add a MO edge between
682  *  the Action rf and that action.  If the action is a read, we add a
683  *  MO edge between the Action rf, and whatever the read accessed.
684  *
685  * @param curr is the read ModelAction that we are fixing up MO edges for.
686  * @param rf is the write ModelAction that curr reads from.
687  *
688  */
689
690 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
691 {
692         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
693         unsigned int i;
694         ASSERT(curr->is_read());
695
696         /* Iterate over all threads */
697         for (i = 0; i < thrd_lists->size(); i++) {
698                 /* Iterate over actions in thread, starting from most recent */
699                 action_list_t *list = &(*thrd_lists)[i];
700                 action_list_t::reverse_iterator rit;
701                 ModelAction *lastact = NULL;
702
703                 /* Find last action that happens after curr */
704                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
705                         ModelAction *act = *rit;
706                         if (curr->happens_before(act)) {
707                                 lastact = act;
708                         } else
709                                 break;
710                 }
711
712                         /* Include at most one act per-thread that "happens before" curr */
713                 if (lastact != NULL) {
714                         if (lastact->is_read()) {
715                                 const ModelAction *postreadfrom = lastact->get_reads_from();
716                                 if (postreadfrom != NULL&&rf != postreadfrom)
717                                         mo_graph->addEdge(rf, postreadfrom);
718                         } else if (rf != lastact) {
719                                 mo_graph->addEdge(rf, lastact);
720                         }
721                         break;
722                 }
723         }
724 }
725
726 /**
727  * Updates the mo_graph with the constraints imposed from the current write.
728  *
729  * Basic idea is the following: Go through each other thread and find
730  * the lastest action that happened before our write.  Two cases:
731  *
732  * (1) The action is a write => that write must occur before
733  * the current write
734  *
735  * (2) The action is a read => the write that that action read from
736  * must occur before the current write.
737  *
738  * This method also handles two other issues:
739  *
740  * (I) Sequential Consistency: Making sure that if the current write is
741  * seq_cst, that it occurs after the previous seq_cst write.
742  *
743  * (II) Sending the write back to non-synchronizing reads.
744  *
745  * @param curr The current action. Must be a write.
746  * @return True if modification order edges were added; false otherwise
747  */
748 bool ModelChecker::w_modification_order(ModelAction *curr)
749 {
750         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
751         unsigned int i;
752         bool added = false;
753         ASSERT(curr->is_write());
754
755         if (curr->is_seqcst()) {
756                 /* We have to at least see the last sequentially consistent write,
757                          so we are initialized. */
758                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
759                 if (last_seq_cst != NULL) {
760                         mo_graph->addEdge(last_seq_cst, curr);
761                         added = true;
762                 }
763         }
764
765         /* Iterate over all threads */
766         for (i = 0; i < thrd_lists->size(); i++) {
767                 /* Iterate over actions in thread, starting from most recent */
768                 action_list_t *list = &(*thrd_lists)[i];
769                 action_list_t::reverse_iterator rit;
770                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
771                         ModelAction *act = *rit;
772
773                         /* Include at most one act per-thread that "happens before" curr */
774                         if (act->happens_before(curr)) {
775                                 /*
776                                  * Note: if act is RMW, just add edge:
777                                  *   act --mo--> curr
778                                  * The following edge should be handled elsewhere:
779                                  *   readfrom(act) --mo--> act
780                                  */
781                                 if (act->is_write()) {
782                                         //RMW shouldn't have an edge to themselves
783                                         if (act!=curr)
784                                                 mo_graph->addEdge(act, curr);
785                                 } else if (act->is_read() && act->get_reads_from() != NULL)
786                                         mo_graph->addEdge(act->get_reads_from(), curr);
787                                 added = true;
788                                 break;
789                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
790                                                      !act->same_thread(curr)) {
791                                 /* We have an action that:
792                                    (1) did not happen before us
793                                    (2) is a read and we are a write
794                                    (3) cannot synchronize with us
795                                    (4) is in a different thread
796                                    =>
797                                    that read could potentially read from our write.
798                                  */
799                                 if (thin_air_constraint_may_allow(curr, act)) {
800                                         if (isfeasible() ||
801                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
802                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
803                                                 futurevalues->push_back(pfv);
804                                         }
805                                 }
806                         }
807                 }
808         }
809
810         return added;
811 }
812
813 /** Arbitrary reads from the future are not allowed.  Section 29.3
814  * part 9 places some constraints.  This method checks one result of constraint
815  * constraint.  Others require compiler support. */
816
817 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
818         if (!writer->is_rmw())
819                 return true;
820
821         if (!reader->is_rmw())
822                 return true;
823
824         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
825                 if (search==reader)
826                         return false;
827                 if (search->get_tid() == reader->get_tid() &&
828                                 search->happens_before(reader))
829                         break;
830         }
831
832         return true;
833 }
834
835 /**
836  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
837  * The ModelAction under consideration is expected to be taking part in
838  * release/acquire synchronization as an object of the "reads from" relation.
839  * Note that this can only provide release sequence support for RMW chains
840  * which do not read from the future, as those actions cannot be traced until
841  * their "promise" is fulfilled. Similarly, we may not even establish the
842  * presence of a release sequence with certainty, as some modification order
843  * constraints may be decided further in the future. Thus, this function
844  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
845  * and a boolean representing certainty.
846  *
847  * @todo Finish lazy updating, when promises are fulfilled in the future
848  * @param rf The action that might be part of a release sequence. Must be a
849  * write.
850  * @param release_heads A pass-by-reference style return parameter.  After
851  * execution of this function, release_heads will contain the heads of all the
852  * relevant release sequences, if any exists
853  * @return true, if the ModelChecker is certain that release_heads is complete;
854  * false otherwise
855  */
856 bool ModelChecker::release_seq_head(const ModelAction *rf,
857                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
858 {
859         if (!rf) {
860                 /* read from future: need to settle this later */
861                 return false; /* incomplete */
862         }
863
864         ASSERT(rf->is_write());
865
866         if (rf->is_release())
867                 release_heads->push_back(rf);
868         if (rf->is_rmw()) {
869                 /* We need a RMW action that is both an acquire and release to stop */
870                 /** @todo Need to be smarter here...  In the linux lock
871                  * example, this will run to the beginning of the program for
872                  * every acquire. */
873                 if (rf->is_acquire() && rf->is_release())
874                         return true; /* complete */
875                 return release_seq_head(rf->get_reads_from(), release_heads);
876         }
877         if (rf->is_release())
878                 return true; /* complete */
879
880         /* else relaxed write; check modification order for contiguous subsequence
881          * -> rf must be same thread as release */
882         int tid = id_to_int(rf->get_tid());
883         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
884         action_list_t *list = &(*thrd_lists)[tid];
885         action_list_t::const_reverse_iterator rit;
886
887         /* Find rf in the thread list */
888         rit = std::find(list->rbegin(), list->rend(), rf);
889         ASSERT(rit != list->rend());
890
891         /* Find the last write/release */
892         for (; rit != list->rend(); rit++)
893                 if ((*rit)->is_release())
894                         break;
895         if (rit == list->rend()) {
896                 /* No write-release in this thread */
897                 return true; /* complete */
898         }
899         ModelAction *release = *rit;
900
901         ASSERT(rf->same_thread(release));
902
903         bool certain = true;
904         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
905                 if (id_to_int(rf->get_tid()) == (int)i)
906                         continue;
907                 list = &(*thrd_lists)[i];
908
909                 /* Can we ensure no future writes from this thread may break
910                  * the release seq? */
911                 bool future_ordered = false;
912
913                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
914                         const ModelAction *act = *rit;
915                         if (!act->is_write())
916                                 continue;
917                         /* Reach synchronization -> this thread is complete */
918                         if (act->happens_before(release))
919                                 break;
920                         if (rf->happens_before(act)) {
921                                 future_ordered = true;
922                                 continue;
923                         }
924
925                         /* Check modification order */
926                         if (mo_graph->checkReachable(rf, act)) {
927                                 /* rf --mo--> act */
928                                 future_ordered = true;
929                                 continue;
930                         }
931                         if (mo_graph->checkReachable(act, release))
932                                 /* act --mo--> release */
933                                 break;
934                         if (mo_graph->checkReachable(release, act) &&
935                                       mo_graph->checkReachable(act, rf)) {
936                                 /* release --mo-> act --mo--> rf */
937                                 return true; /* complete */
938                         }
939                         certain = false;
940                 }
941                 if (!future_ordered)
942                         return false; /* This thread is uncertain */
943         }
944
945         if (certain)
946                 release_heads->push_back(release);
947         return certain;
948 }
949
950 /**
951  * A public interface for getting the release sequence head(s) with which a
952  * given ModelAction must synchronize. This function only returns a non-empty
953  * result when it can locate a release sequence head with certainty. Otherwise,
954  * it may mark the internal state of the ModelChecker so that it will handle
955  * the release sequence at a later time, causing @a act to update its
956  * synchronization at some later point in execution.
957  * @param act The 'acquire' action that may read from a release sequence
958  * @param release_heads A pass-by-reference return parameter. Will be filled
959  * with the head(s) of the release sequence(s), if they exists with certainty.
960  * @see ModelChecker::release_seq_head
961  */
962 void ModelChecker::get_release_seq_heads(ModelAction *act,
963                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
964 {
965         const ModelAction *rf = act->get_reads_from();
966         bool complete;
967         complete = release_seq_head(rf, release_heads);
968         if (!complete) {
969                 /* add act to 'lazy checking' list */
970                 std::list<ModelAction *> *list;
971                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
972                 list->push_back(act);
973                 (*lazy_sync_size)++;
974         }
975 }
976
977 /**
978  * Attempt to resolve all stashed operations that might synchronize with a
979  * release sequence for a given location. This implements the "lazy" portion of
980  * determining whether or not a release sequence was contiguous, since not all
981  * modification order information is present at the time an action occurs.
982  *
983  * @param location The location/object that should be checked for release
984  * sequence resolutions
985  * @param work_queue The work queue to which to add work items as they are
986  * generated
987  * @return True if any updates occurred (new synchronization, new mo_graph
988  * edges)
989  */
990 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
991 {
992         std::list<ModelAction *> *list;
993         list = lazy_sync_with_release->getptr(location);
994         if (!list)
995                 return false;
996
997         bool updated = false;
998         std::list<ModelAction *>::iterator it = list->begin();
999         while (it != list->end()) {
1000                 ModelAction *act = *it;
1001                 const ModelAction *rf = act->get_reads_from();
1002                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1003                 bool complete;
1004                 complete = release_seq_head(rf, &release_heads);
1005                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1006                         if (!act->has_synchronized_with(release_heads[i])) {
1007                                 updated = true;
1008                                 act->synchronize_with(release_heads[i]);
1009                         }
1010                 }
1011
1012                 if (updated) {
1013                         /* Re-check act for mo_graph edges */
1014                         work_queue->push_back(MOEdgeWorkEntry(act));
1015
1016                         /* propagate synchronization to later actions */
1017                         action_list_t::reverse_iterator it = action_trace->rbegin();
1018                         while ((*it) != act) {
1019                                 ModelAction *propagate = *it;
1020                                 if (act->happens_before(propagate)) {
1021                                         propagate->synchronize_with(act);
1022                                         /* Re-check 'propagate' for mo_graph edges */
1023                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1024                                 }
1025                         }
1026                 }
1027                 if (complete) {
1028                         it = list->erase(it);
1029                         (*lazy_sync_size)--;
1030                 } else
1031                         it++;
1032         }
1033
1034         // If we resolved promises or data races, see if we have realized a data race.
1035         if (checkDataRaces()) {
1036                 set_assert();
1037         }
1038
1039         return updated;
1040 }
1041
1042 /**
1043  * Performs various bookkeeping operations for the current ModelAction. For
1044  * instance, adds action to the per-object, per-thread action vector and to the
1045  * action trace list of all thread actions.
1046  *
1047  * @param act is the ModelAction to add.
1048  */
1049 void ModelChecker::add_action_to_lists(ModelAction *act)
1050 {
1051         int tid = id_to_int(act->get_tid());
1052         action_trace->push_back(act);
1053
1054         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1055
1056         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1057         if (tid >= (int)vec->size())
1058                 vec->resize(priv->next_thread_id);
1059         (*vec)[tid].push_back(act);
1060
1061         if ((int)thrd_last_action->size() <= tid)
1062                 thrd_last_action->resize(get_num_threads());
1063         (*thrd_last_action)[tid] = act;
1064 }
1065
1066 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1067 {
1068         int nthreads = get_num_threads();
1069         if ((int)thrd_last_action->size() < nthreads)
1070                 thrd_last_action->resize(nthreads);
1071         return (*thrd_last_action)[id_to_int(tid)];
1072 }
1073
1074 /**
1075  * Gets the last memory_order_seq_cst action (in the total global sequence)
1076  * performed on a particular object (i.e., memory location).
1077  * @param location The object location to check
1078  * @return The last seq_cst action performed
1079  */
1080 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1081 {
1082         action_list_t *list = obj_map->get_safe_ptr(location);
1083         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1084         action_list_t::reverse_iterator rit;
1085         for (rit = list->rbegin(); rit != list->rend(); rit++)
1086                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1087                         return *rit;
1088         return NULL;
1089 }
1090
1091 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1092 {
1093         ModelAction *parent = get_last_action(tid);
1094         if (!parent)
1095                 parent = get_thread(tid)->get_creation();
1096         return parent;
1097 }
1098
1099 /**
1100  * Returns the clock vector for a given thread.
1101  * @param tid The thread whose clock vector we want
1102  * @return Desired clock vector
1103  */
1104 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1105 {
1106         return get_parent_action(tid)->get_cv();
1107 }
1108
1109 /**
1110  * Resolve a set of Promises with a current write. The set is provided in the
1111  * Node corresponding to @a write.
1112  * @param write The ModelAction that is fulfilling Promises
1113  * @return True if promises were resolved; false otherwise
1114  */
1115 bool ModelChecker::resolve_promises(ModelAction *write)
1116 {
1117         bool resolved = false;
1118
1119         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1120                 Promise *promise = (*promises)[promise_index];
1121                 if (write->get_node()->get_promise(i)) {
1122                         ModelAction *read = promise->get_action();
1123                         read->read_from(write);
1124                         if (read->is_rmw()) {
1125                                 mo_graph->addRMWEdge(write, read);
1126                         }
1127                         //First fix up the modification order for actions that happened
1128                         //before the read
1129                         r_modification_order(read, write);
1130                         //Next fix up the modification order for actions that happened
1131                         //after the read.
1132                         post_r_modification_order(read, write);
1133                         promises->erase(promises->begin() + promise_index);
1134                         resolved = true;
1135                 } else
1136                         promise_index++;
1137         }
1138         return resolved;
1139 }
1140
1141 /**
1142  * Compute the set of promises that could potentially be satisfied by this
1143  * action. Note that the set computation actually appears in the Node, not in
1144  * ModelChecker.
1145  * @param curr The ModelAction that may satisfy promises
1146  */
1147 void ModelChecker::compute_promises(ModelAction *curr)
1148 {
1149         for (unsigned int i = 0; i < promises->size(); i++) {
1150                 Promise *promise = (*promises)[i];
1151                 const ModelAction *act = promise->get_action();
1152                 if (!act->happens_before(curr) &&
1153                                 act->is_read() &&
1154                                 !act->is_synchronizing(curr) &&
1155                                 !act->same_thread(curr) &&
1156                                 promise->get_value() == curr->get_value()) {
1157                         curr->get_node()->set_promise(i);
1158                 }
1159         }
1160 }
1161
1162 /** Checks promises in response to change in ClockVector Threads. */
1163 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1164 {
1165         for (unsigned int i = 0; i < promises->size(); i++) {
1166                 Promise *promise = (*promises)[i];
1167                 const ModelAction *act = promise->get_action();
1168                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1169                                 merge_cv->synchronized_since(act)) {
1170                         //This thread is no longer able to send values back to satisfy the promise
1171                         int num_synchronized_threads = promise->increment_threads();
1172                         if (num_synchronized_threads == get_num_threads()) {
1173                                 //Promise has failed
1174                                 failed_promise = true;
1175                                 return;
1176                         }
1177                 }
1178         }
1179 }
1180
1181 /**
1182  * Build up an initial set of all past writes that this 'read' action may read
1183  * from. This set is determined by the clock vector's "happens before"
1184  * relationship.
1185  * @param curr is the current ModelAction that we are exploring; it must be a
1186  * 'read' operation.
1187  */
1188 void ModelChecker::build_reads_from_past(ModelAction *curr)
1189 {
1190         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1191         unsigned int i;
1192         ASSERT(curr->is_read());
1193
1194         ModelAction *last_seq_cst = NULL;
1195
1196         /* Track whether this object has been initialized */
1197         bool initialized = false;
1198
1199         if (curr->is_seqcst()) {
1200                 last_seq_cst = get_last_seq_cst(curr->get_location());
1201                 /* We have to at least see the last sequentially consistent write,
1202                          so we are initialized. */
1203                 if (last_seq_cst != NULL)
1204                         initialized = true;
1205         }
1206
1207         /* Iterate over all threads */
1208         for (i = 0; i < thrd_lists->size(); i++) {
1209                 /* Iterate over actions in thread, starting from most recent */
1210                 action_list_t *list = &(*thrd_lists)[i];
1211                 action_list_t::reverse_iterator rit;
1212                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1213                         ModelAction *act = *rit;
1214
1215                         /* Only consider 'write' actions */
1216                         if (!act->is_write())
1217                                 continue;
1218
1219                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1220                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1221                                 DEBUG("Adding action to may_read_from:\n");
1222                                 if (DBG_ENABLED()) {
1223                                         act->print();
1224                                         curr->print();
1225                                 }
1226                                 curr->get_node()->add_read_from(act);
1227                         }
1228
1229                         /* Include at most one act per-thread that "happens before" curr */
1230                         if (act->happens_before(curr)) {
1231                                 initialized = true;
1232                                 break;
1233                         }
1234                 }
1235         }
1236
1237         if (!initialized) {
1238                 /** @todo Need a more informative way of reporting errors. */
1239                 printf("ERROR: may read from uninitialized atomic\n");
1240         }
1241
1242         if (DBG_ENABLED() || !initialized) {
1243                 printf("Reached read action:\n");
1244                 curr->print();
1245                 printf("Printing may_read_from\n");
1246                 curr->get_node()->print_may_read_from();
1247                 printf("End printing may_read_from\n");
1248         }
1249
1250         ASSERT(initialized);
1251 }
1252
1253 static void print_list(action_list_t *list)
1254 {
1255         action_list_t::iterator it;
1256
1257         printf("---------------------------------------------------------------------\n");
1258         printf("Trace:\n");
1259
1260         for (it = list->begin(); it != list->end(); it++) {
1261                 (*it)->print();
1262         }
1263         printf("---------------------------------------------------------------------\n");
1264 }
1265
1266 void ModelChecker::print_summary()
1267 {
1268         printf("\n");
1269         printf("Number of executions: %d\n", num_executions);
1270         printf("Number of feasible executions: %d\n", num_feasible_executions);
1271         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1272
1273 #if SUPPORT_MOD_ORDER_DUMP
1274         scheduler->print();
1275         char buffername[100];
1276         sprintf(buffername, "exec%u",num_executions);
1277         mo_graph->dumpGraphToFile(buffername);
1278 #endif
1279
1280         if (!isfinalfeasible())
1281                 printf("INFEASIBLE EXECUTION!\n");
1282         print_list(action_trace);
1283         printf("\n");
1284 }
1285
1286 /**
1287  * Add a Thread to the system for the first time. Should only be called once
1288  * per thread.
1289  * @param t The Thread to add
1290  */
1291 void ModelChecker::add_thread(Thread *t)
1292 {
1293         thread_map->put(id_to_int(t->get_id()), t);
1294         scheduler->add_thread(t);
1295 }
1296
1297 void ModelChecker::remove_thread(Thread *t)
1298 {
1299         scheduler->remove_thread(t);
1300 }
1301
1302 /**
1303  * Switch from a user-context to the "master thread" context (a.k.a. system
1304  * context). This switch is made with the intention of exploring a particular
1305  * model-checking action (described by a ModelAction object). Must be called
1306  * from a user-thread context.
1307  * @param act The current action that will be explored. Must not be NULL.
1308  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1309  */
1310 int ModelChecker::switch_to_master(ModelAction *act)
1311 {
1312         DBG();
1313         Thread *old = thread_current();
1314         set_current_action(act);
1315         old->set_state(THREAD_READY);
1316         return Thread::swap(old, &system_context);
1317 }
1318
1319 /**
1320  * Takes the next step in the execution, if possible.
1321  * @return Returns true (success) if a step was taken and false otherwise.
1322  */
1323 bool ModelChecker::take_step() {
1324         Thread *curr, *next;
1325
1326         if (has_asserted())
1327                 return false;
1328
1329         curr = thread_current();
1330         if (curr) {
1331                 if (curr->get_state() == THREAD_READY) {
1332                         ASSERT(priv->current_action);
1333
1334                         priv->nextThread = check_current_action(priv->current_action);
1335                         priv->current_action = NULL;
1336                         if (!curr->is_blocked() && !curr->is_complete())
1337                                 scheduler->add_thread(curr);
1338                 } else {
1339                         ASSERT(false);
1340                 }
1341         }
1342         next = scheduler->next_thread(priv->nextThread);
1343
1344         /* Infeasible -> don't take any more steps */
1345         if (!isfeasible())
1346                 return false;
1347
1348         if (next)
1349                 next->set_state(THREAD_RUNNING);
1350         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1351
1352         /* next == NULL -> don't take any more steps */
1353         if (!next)
1354                 return false;
1355         /* Return false only if swap fails with an error */
1356         return (Thread::swap(&system_context, next) == 0);
1357 }
1358
1359 /** Runs the current execution until threre are no more steps to take. */
1360 void ModelChecker::finish_execution() {
1361         DBG();
1362
1363         while (take_step());
1364 }