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