model.cc

   1 #include <stdio.h>
   2
   3 #include "model.h"
   4 #include "action.h"
   5 #include "nodestack.h"
   6 #include "schedule.h"
   7 #include "snapshot-interface.h"
   8 #include "common.h"
   9 #include "clockvector.h"
  10 #include "cyclegraph.h"
  11 #include "promise.h"
  12
  13 #define INITIAL_THREAD_ID       0
  14
  15 ModelChecker *model;
  16
  17 /** @brief Constructor */
  18 ModelChecker::ModelChecker(struct model_params params) :
  19         /* Initialize default scheduler */
  20         scheduler(new Scheduler()),
  21         /* First thread created will have id INITIAL_THREAD_ID */
  22         next_thread_id(INITIAL_THREAD_ID),
  23         used_sequence_numbers(0),
  24         num_executions(0),
  25         params(params),
  26         current_action(NULL),
  27         diverge(NULL),
  28         nextThread(NULL),
  29         action_trace(new action_list_t()),
  30         thread_map(new HashTable<int, Thread *, int>()),
  31         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         promises(new std::vector<Promise *>()),
  34         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  35         thrd_last_action(new std::vector<ModelAction *>(1)),
  36         node_stack(new NodeStack()),
  37         next_backtrack(NULL),
  38         mo_graph(new CycleGraph()),
  39         failed_promise(false)
  40 {
  41 }
  42
  43 /** @brief Destructor */
  44 ModelChecker::~ModelChecker()
  45 {
  46         for (int i = 0; i < get_num_threads(); i++)
  47                 delete thread_map->get(i);
  48         delete thread_map;
  49
  50         delete obj_thrd_map;
  51         delete obj_map;
  52         delete action_trace;
  53
  54         for (unsigned int i = 0; i < promises->size(); i++)
  55                 delete (*promises)[i];
  56         delete promises;
  57
  58         delete lazy_sync_with_release;
  59
  60         delete thrd_last_action;
  61         delete node_stack;
  62         delete scheduler;
  63         delete mo_graph;
  64 }
  65
  66 /**
  67  * Restores user program to initial state and resets all model-checker data
  68  * structures.
  69  */
  70 void ModelChecker::reset_to_initial_state()
  71 {
  72         DEBUG("+++ Resetting to initial state +++\n");
  73         node_stack->reset_execution();
  74         current_action = NULL;
  75         next_thread_id = INITIAL_THREAD_ID;
  76         used_sequence_numbers = 0;
  77         nextThread = NULL;
  78         next_backtrack = NULL;
  79         failed_promise = false;
  80         snapshotObject->backTrackBeforeStep(0);
  81 }
  82
  83 /** @returns a thread ID for a new Thread */
  84 thread_id_t ModelChecker::get_next_id()
  85 {
  86         return next_thread_id++;
  87 }
  88
  89 /** @returns the number of user threads created during this execution */
  90 int ModelChecker::get_num_threads()
  91 {
  92         return next_thread_id;
  93 }
  94
  95 /** @returns a sequence number for a new ModelAction */
  96 modelclock_t ModelChecker::get_next_seq_num()
  97 {
  98         return ++used_sequence_numbers;
  99 }
 100
 101 /**
 102  * Choose the next thread in the replay sequence.
 103  *
 104  * If the replay sequence has reached the 'diverge' point, returns a thread
 105  * from the backtracking set. Otherwise, simply returns the next thread in the
 106  * sequence that is being replayed.
 107  */
 108 Thread * ModelChecker::get_next_replay_thread()
 109 {
 110         thread_id_t tid;
 111
 112         /* Have we completed exploring the preselected path? */
 113         if (diverge == NULL)
 114                 return NULL;
 115
 116         /* Else, we are trying to replay an execution */
 117         ModelAction *next = node_stack->get_next()->get_action();
 118
 119         if (next == diverge) {
 120                 Node *nextnode = next->get_node();
 121                 /* Reached divergence point */
 122                 if (nextnode->increment_promise()) {
 123                         /* The next node will try to satisfy a different set of promises. */
 124                         tid = next->get_tid();
 125                         node_stack->pop_restofstack(2);
 126                 } else if (nextnode->increment_read_from()) {
 127                         /* The next node will read from a different value. */
 128                         tid = next->get_tid();
 129                         node_stack->pop_restofstack(2);
 130                 } else if (nextnode->increment_future_value()) {
 131                         /* The next node will try to read from a different future value. */
 132                         tid = next->get_tid();
 133                         node_stack->pop_restofstack(2);
 134                 } else {
 135                         /* Make a different thread execute for next step */
 136                         Node *node = nextnode->get_parent();
 137                         tid = node->get_next_backtrack();
 138                         node_stack->pop_restofstack(1);
 139                 }
 140                 DEBUG("*** Divergence point ***\n");
 141                 diverge = NULL;
 142         } else {
 143                 tid = next->get_tid();
 144         }
 145         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 146         ASSERT(tid != THREAD_ID_T_NONE);
 147         return thread_map->get(id_to_int(tid));
 148 }
 149
 150 /**
 151  * Queries the model-checker for more executions to explore and, if one
 152  * exists, resets the model-checker state to execute a new execution.
 153  *
 154  * @return If there are more executions to explore, return true. Otherwise,
 155  * return false.
 156  */
 157 bool ModelChecker::next_execution()
 158 {
 159         DBG();
 160
 161         num_executions++;
 162
 163         if (isfinalfeasible() || DBG_ENABLED())
 164                 print_summary();
 165
 166         if ((diverge = model->get_next_backtrack()) == NULL)
 167                 return false;
 168
 169         if (DBG_ENABLED()) {
 170                 printf("Next execution will diverge at:\n");
 171                 diverge->print();
 172         }
 173
 174         model->reset_to_initial_state();
 175         return true;
 176 }
 177
 178 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 179 {
 180         action_type type = act->get_type();
 181
 182         switch (type) {
 183                 case ATOMIC_READ:
 184                 case ATOMIC_WRITE:
 185                 case ATOMIC_RMW:
 186                         break;
 187                 default:
 188                         return NULL;
 189         }
 190         /* linear search: from most recent to oldest */
 191         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 192         action_list_t::reverse_iterator rit;
 193         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 194                 ModelAction *prev = *rit;
 195                 if (act->is_synchronizing(prev))
 196                         return prev;
 197         }
 198         return NULL;
 199 }
 200
 201 void ModelChecker::set_backtracking(ModelAction *act)
 202 {
 203         ModelAction *prev;
 204         Node *node;
 205         Thread *t = get_thread(act->get_tid());
 206
 207         prev = get_last_conflict(act);
 208         if (prev == NULL)
 209                 return;
 210
 211         node = prev->get_node()->get_parent();
 212
 213         while (!node->is_enabled(t))
 214                 t = t->get_parent();
 215
 216         /* Check if this has been explored already */
 217         if (node->has_been_explored(t->get_id()))
 218                 return;
 219
 220         /* Cache the latest backtracking point */
 221         if (!next_backtrack || *prev > *next_backtrack)
 222                 next_backtrack = prev;
 223
 224         /* If this is a new backtracking point, mark the tree */
 225         if (!node->set_backtrack(t->get_id()))
 226                 return;
 227         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 228                         prev->get_tid(), t->get_id());
 229         if (DBG_ENABLED()) {
 230                 prev->print();
 231                 act->print();
 232         }
 233 }
 234
 235 /**
 236  * Returns last backtracking point. The model checker will explore a different
 237  * path for this point in the next execution.
 238  * @return The ModelAction at which the next execution should diverge.
 239  */
 240 ModelAction * ModelChecker::get_next_backtrack()
 241 {
 242         ModelAction *next = next_backtrack;
 243         next_backtrack = NULL;
 244         return next;
 245 }
 246
 247 void ModelChecker::check_current_action(void)
 248 {
 249         ModelAction *curr = this->current_action;
 250         bool already_added = false;
 251         this->current_action = NULL;
 252         if (!curr) {
 253                 DEBUG("trying to push NULL action...\n");
 254                 return;
 255         }
 256
 257         if (curr->is_rmwc() || curr->is_rmw()) {
 258                 ModelAction *tmp = process_rmw(curr);
 259                 already_added = true;
 260                 delete curr;
 261                 curr = tmp;
 262         } else {
 263                 ModelAction *tmp = node_stack->explore_action(curr);
 264                 if (tmp) {
 265                         /* Discard duplicate ModelAction; use action from NodeStack */
 266                         /* First restore type and order in case of RMW operation */
 267                         if (curr->is_rmwr())
 268                                 tmp->copy_typeandorder(curr);
 269
 270                         /* If we have diverged, we need to reset the clock vector. */
 271                         if (diverge == NULL)
 272                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 273
 274                         delete curr;
 275                         curr = tmp;
 276                 } else {
 277                         /*
 278                          * Perform one-time actions when pushing new ModelAction onto
 279                          * NodeStack
 280                          */
 281                         curr->create_cv(get_parent_action(curr->get_tid()));
 282                         /* Build may_read_from set */
 283                         if (curr->is_read())
 284                                 build_reads_from_past(curr);
 285                         if (curr->is_write())
 286                                 compute_promises(curr);
 287                 }
 288         }
 289
 290         /* Assign 'creation' parent */
 291         if (curr->get_type() == THREAD_CREATE) {
 292                 Thread *th = (Thread *)curr->get_location();
 293                 th->set_creation(curr);
 294         }
 295
 296         /* Deal with new thread */
 297         if (curr->get_type() == THREAD_START)
 298                 check_promises(NULL, curr->get_cv());
 299
 300         /* Assign reads_from values */
 301         Thread *th = get_thread(curr->get_tid());
 302         uint64_t value = VALUE_NONE;
 303         bool updated = false;
 304         if (curr->is_read()) {
 305                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 306                 if (reads_from != NULL) {
 307                         value = reads_from->get_value();
 308                         /* Assign reads_from, perform release/acquire synchronization */
 309                         curr->read_from(reads_from);
 310                         if (r_modification_order(curr,reads_from))
 311                                 updated = true;
 312                 } else {
 313                         /* Read from future value */
 314                         value = curr->get_node()->get_future_value();
 315                         curr->read_from(NULL);
 316                         Promise *valuepromise = new Promise(curr, value);
 317                         promises->push_back(valuepromise);
 318                 }
 319         } else if (curr->is_write()) {
 320                 if (w_modification_order(curr))
 321                         updated = true;;
 322                 if (resolve_promises(curr))
 323                         updated = true;
 324         }
 325
 326         if (updated)
 327                 resolve_release_sequences(curr->get_location());
 328
 329         th->set_return_value(value);
 330
 331         /* Add action to list.  */
 332         if (!already_added)
 333                 add_action_to_lists(curr);
 334
 335         /** @todo Is there a better interface for setting the next thread rather
 336                  than this field/convoluted approach?  Perhaps like just returning
 337                  it or something? */
 338
 339         /* Do not split atomic actions. */
 340         if (curr->is_rmwr())
 341                 nextThread = thread_current();
 342         else
 343                 nextThread = get_next_replay_thread();
 344
 345         Node *currnode = curr->get_node();
 346         Node *parnode = currnode->get_parent();
 347
 348         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 349                   !currnode->future_value_empty() || !currnode->promise_empty())
 350                 if (!next_backtrack || *curr > *next_backtrack)
 351                         next_backtrack = curr;
 352
 353         set_backtracking(curr);
 354 }
 355
 356 /** @returns whether the current partial trace is feasible. */
 357 bool ModelChecker::isfeasible() {
 358         return !mo_graph->checkForCycles() && !failed_promise;
 359 }
 360
 361 /** Returns whether the current completed trace is feasible. */
 362 bool ModelChecker::isfinalfeasible() {
 363         return isfeasible() && promises->size() == 0;
 364 }
 365
 366 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 367 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 368         int tid = id_to_int(act->get_tid());
 369         ModelAction *lastread = get_last_action(tid);
 370         lastread->process_rmw(act);
 371         if (act->is_rmw())
 372                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 373         return lastread;
 374 }
 375
 376 /**
 377  * Updates the mo_graph with the constraints imposed from the current read.
 378  * @param curr The current action. Must be a read.
 379  * @param rf The action that curr reads from. Must be a write.
 380  * @return True if modification order edges were added; false otherwise
 381  */
 382 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 383 {
 384         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 385         unsigned int i;
 386         bool added = false;
 387         ASSERT(curr->is_read());
 388
 389         /* Iterate over all threads */
 390         for (i = 0; i < thrd_lists->size(); i++) {
 391                 /* Iterate over actions in thread, starting from most recent */
 392                 action_list_t *list = &(*thrd_lists)[i];
 393                 action_list_t::reverse_iterator rit;
 394                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 395                         ModelAction *act = *rit;
 396
 397                         /* Include at most one act per-thread that "happens before" curr */
 398                         if (act->happens_before(curr)) {
 399                                 if (act->is_read()) {
 400                                         const ModelAction *prevreadfrom = act->get_reads_from();
 401                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 402                                                 mo_graph->addEdge(prevreadfrom, rf);
 403                                                 added = true;
 404                                         }
 405                                 } else if (rf != act) {
 406                                         mo_graph->addEdge(act, rf);
 407                                         added = true;
 408                                 }
 409                                 break;
 410                         }
 411                 }
 412         }
 413
 414         return added;
 415 }
 416
 417 /** Updates the mo_graph with the constraints imposed from the current read. */
 418 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 419 {
 420         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 421         unsigned int i;
 422         ASSERT(curr->is_read());
 423
 424         /* Iterate over all threads */
 425         for (i = 0; i < thrd_lists->size(); i++) {
 426                 /* Iterate over actions in thread, starting from most recent */
 427                 action_list_t *list = &(*thrd_lists)[i];
 428                 action_list_t::reverse_iterator rit;
 429                 ModelAction *lastact = NULL;
 430
 431                 /* Find last action that happens after curr */
 432                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 433                         ModelAction *act = *rit;
 434                         if (curr->happens_before(act)) {
 435                                 lastact = act;
 436                         } else
 437                                 break;
 438                 }
 439
 440                         /* Include at most one act per-thread that "happens before" curr */
 441                 if (lastact != NULL) {
 442                         if (lastact->is_read()) {
 443                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 444                                 if (postreadfrom != NULL&&rf != postreadfrom)
 445                                         mo_graph->addEdge(rf, postreadfrom);
 446                         } else if (rf != lastact) {
 447                                 mo_graph->addEdge(rf, lastact);
 448                         }
 449                         break;
 450                 }
 451         }
 452 }
 453
 454 /**
 455  * Updates the mo_graph with the constraints imposed from the current write.
 456  * @param curr The current action. Must be a write.
 457  * @return True if modification order edges were added; false otherwise
 458  */
 459 bool ModelChecker::w_modification_order(ModelAction *curr)
 460 {
 461         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 462         unsigned int i;
 463         bool added = false;
 464         ASSERT(curr->is_write());
 465
 466         if (curr->is_seqcst()) {
 467                 /* We have to at least see the last sequentially consistent write,
 468                          so we are initialized. */
 469                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 470                 if (last_seq_cst != NULL) {
 471                         mo_graph->addEdge(last_seq_cst, curr);
 472                         added = true;
 473                 }
 474         }
 475
 476         /* Iterate over all threads */
 477         for (i = 0; i < thrd_lists->size(); i++) {
 478                 /* Iterate over actions in thread, starting from most recent */
 479                 action_list_t *list = &(*thrd_lists)[i];
 480                 action_list_t::reverse_iterator rit;
 481                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 482                         ModelAction *act = *rit;
 483
 484                         /* Include at most one act per-thread that "happens before" curr */
 485                         if (act->happens_before(curr)) {
 486                                 if (act->is_read())
 487                                         mo_graph->addEdge(act->get_reads_from(), curr);
 488                                 else
 489                                         mo_graph->addEdge(act, curr);
 490                                 added = true;
 491                                 break;
 492                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 493                                                      !act->same_thread(curr)) {
 494                                 /* We have an action that:
 495                                    (1) did not happen before us
 496                                    (2) is a read and we are a write
 497                                    (3) cannot synchronize with us
 498                                    (4) is in a different thread
 499                                    =>
 500                                    that read could potentially read from our write.
 501                                  */
 502                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 503                                                 (!next_backtrack || *act > *next_backtrack))
 504                                         next_backtrack = act;
 505                         }
 506                 }
 507         }
 508
 509         return added;
 510 }
 511
 512 /**
 513  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 514  * The ModelAction under consideration is expected to be taking part in
 515  * release/acquire synchronization as an object of the "reads from" relation.
 516  * Note that this can only provide release sequence support for RMW chains
 517  * which do not read from the future, as those actions cannot be traced until
 518  * their "promise" is fulfilled. Similarly, we may not even establish the
 519  * presence of a release sequence with certainty, as some modification order
 520  * constraints may be decided further in the future. Thus, this function
 521  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 522  * and a boolean representing certainty.
 523  *
 524  * @todo Finish lazy updating, when promises are fulfilled in the future
 525  * @param rf The action that might be part of a release sequence. Must be a
 526  * write.
 527  * @param release_heads A pass-by-reference style return parameter.  After
 528  * execution of this function, release_heads will contain the heads of all the
 529  * relevant release sequences, if any exists
 530  * @return true, if the ModelChecker is certain that release_heads is complete;
 531  * false otherwise
 532  */
 533 bool ModelChecker::release_seq_head(const ModelAction *rf,
 534                 std::vector<const ModelAction *> *release_heads) const
 535 {
 536         ASSERT(rf->is_write());
 537         if (!rf) {
 538                 /* read from future: need to settle this later */
 539                 return false; /* incomplete */
 540         }
 541         if (rf->is_release())
 542                 release_heads->push_back(rf);
 543         if (rf->is_rmw()) {
 544                 if (rf->is_acquire())
 545                         return true; /* complete */
 546                 return release_seq_head(rf->get_reads_from(), release_heads);
 547         }
 548         if (rf->is_release())
 549                 return true; /* complete */
 550
 551         /* else relaxed write; check modification order for contiguous subsequence
 552          * -> rf must be same thread as release */
 553         int tid = id_to_int(rf->get_tid());
 554         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 555         action_list_t *list = &(*thrd_lists)[tid];
 556         action_list_t::const_reverse_iterator rit;
 557
 558         /* Find rf in the thread list */
 559         for (rit = list->rbegin(); rit != list->rend(); rit++)
 560                 if (*rit == rf)
 561                         break;
 562
 563         /* Find the last write/release */
 564         for (; rit != list->rend(); rit++)
 565                 if ((*rit)->is_release())
 566                         break;
 567         if (rit == list->rend()) {
 568                 /* No write-release in this thread */
 569                 return true; /* complete */
 570         }
 571         ModelAction *release = *rit;
 572
 573         ASSERT(rf->same_thread(release));
 574
 575         bool certain = true;
 576         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 577                 if (id_to_int(rf->get_tid()) == (int)i)
 578                         continue;
 579                 list = &(*thrd_lists)[i];
 580                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 581                         const ModelAction *act = *rit;
 582                         if (!act->is_write())
 583                                 continue;
 584                         /* Reach synchronization -> this thread is complete */
 585                         if (act->happens_before(release))
 586                                 break;
 587                         if (rf->happens_before(act))
 588                                 continue;
 589
 590                         /* Check modification order */
 591                         if (mo_graph->checkReachable(rf, act))
 592                                 /* rf --mo--> act */
 593                                 continue;
 594                         if (mo_graph->checkReachable(act, release))
 595                                 /* act --mo--> release */
 596                                 break;
 597                         if (mo_graph->checkReachable(release, act) &&
 598                                       mo_graph->checkReachable(act, rf)) {
 599                                 /* release --mo-> act --mo--> rf */
 600                                 return true; /* complete */
 601                         }
 602                         certain = false;
 603                 }
 604         }
 605
 606         if (certain)
 607                 release_heads->push_back(release);
 608         return certain;
 609 }
 610
 611 /**
 612  * A public interface for getting the release sequence head(s) with which a
 613  * given ModelAction must synchronize. This function only returns a non-empty
 614  * result when it can locate a release sequence head with certainty. Otherwise,
 615  * it may mark the internal state of the ModelChecker so that it will handle
 616  * the release sequence at a later time, causing @a act to update its
 617  * synchronization at some later point in execution.
 618  * @param act The 'acquire' action that may read from a release sequence
 619  * @param release_heads A pass-by-reference return parameter. Will be filled
 620  * with the head(s) of the release sequence(s), if they exists with certainty.
 621  * @see ModelChecker::release_seq_head
 622  */
 623 void ModelChecker::get_release_seq_heads(ModelAction *act,
 624                 std::vector<const ModelAction *> *release_heads)
 625 {
 626         const ModelAction *rf = act->get_reads_from();
 627         bool complete;
 628         complete = release_seq_head(rf, release_heads);
 629         if (!complete) {
 630                 /* add act to 'lazy checking' list */
 631                 std::list<ModelAction *> *list;
 632                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 633                 list->push_back(act);
 634         }
 635 }
 636
 637 /**
 638  * Attempt to resolve all stashed operations that might synchronize with a
 639  * release sequence for a given location. This implements the "lazy" portion of
 640  * determining whether or not a release sequence was contiguous, since not all
 641  * modification order information is present at the time an action occurs.
 642  *
 643  * @param location The location/object that should be checked for release
 644  * sequence resolutions
 645  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 646  */
 647 bool ModelChecker::resolve_release_sequences(void *location)
 648 {
 649         std::list<ModelAction *> *list;
 650         list = lazy_sync_with_release->getptr(location);
 651         if (!list)
 652                 return false;
 653
 654         bool updated = false;
 655         std::list<ModelAction *>::iterator it = list->begin();
 656         while (it != list->end()) {
 657                 ModelAction *act = *it;
 658                 const ModelAction *rf = act->get_reads_from();
 659                 std::vector<const ModelAction *> release_heads;
 660                 bool complete;
 661                 complete = release_seq_head(rf, &release_heads);
 662                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 663                         if (!act->has_synchronized_with(release_heads[i])) {
 664                                 updated = true;
 665                                 act->synchronize_with(release_heads[i]);
 666                         }
 667                 }
 668
 669                 if (updated) {
 670                         /* propagate synchronization to later actions */
 671                         action_list_t::reverse_iterator it = action_trace->rbegin();
 672                         while ((*it) != act) {
 673                                 ModelAction *propagate = *it;
 674                                 if (act->happens_before(propagate))
 675                                         /** @todo new mo_graph edges along with
 676                                          * this synchronization? */
 677                                         propagate->synchronize_with(act);
 678                         }
 679                 }
 680                 if (complete)
 681                         it = list->erase(it);
 682                 else
 683                         it++;
 684         }
 685
 686         return updated;
 687 }
 688
 689 /**
 690  * Performs various bookkeeping operations for the current ModelAction. For
 691  * instance, adds action to the per-object, per-thread action vector and to the
 692  * action trace list of all thread actions.
 693  *
 694  * @param act is the ModelAction to add.
 695  */
 696 void ModelChecker::add_action_to_lists(ModelAction *act)
 697 {
 698         int tid = id_to_int(act->get_tid());
 699         action_trace->push_back(act);
 700
 701         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 702
 703         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 704         if (tid >= (int)vec->size())
 705                 vec->resize(next_thread_id);
 706         (*vec)[tid].push_back(act);
 707
 708         if ((int)thrd_last_action->size() <= tid)
 709                 thrd_last_action->resize(get_num_threads());
 710         (*thrd_last_action)[tid] = act;
 711 }
 712
 713 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 714 {
 715         int nthreads = get_num_threads();
 716         if ((int)thrd_last_action->size() < nthreads)
 717                 thrd_last_action->resize(nthreads);
 718         return (*thrd_last_action)[id_to_int(tid)];
 719 }
 720
 721 /**
 722  * Gets the last memory_order_seq_cst action (in the total global sequence)
 723  * performed on a particular object (i.e., memory location).
 724  * @param location The object location to check
 725  * @return The last seq_cst action performed
 726  */
 727 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 728 {
 729         action_list_t *list = obj_map->get_safe_ptr(location);
 730         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 731         action_list_t::reverse_iterator rit;
 732         for (rit = list->rbegin(); rit != list->rend(); rit++)
 733                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 734                         return *rit;
 735         return NULL;
 736 }
 737
 738 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 739 {
 740         ModelAction *parent = get_last_action(tid);
 741         if (!parent)
 742                 parent = get_thread(tid)->get_creation();
 743         return parent;
 744 }
 745
 746 /**
 747  * Returns the clock vector for a given thread.
 748  * @param tid The thread whose clock vector we want
 749  * @return Desired clock vector
 750  */
 751 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 752 {
 753         return get_parent_action(tid)->get_cv();
 754 }
 755
 756 /**
 757  * Resolve a set of Promises with a current write. The set is provided in the
 758  * Node corresponding to @a write.
 759  * @param write The ModelAction that is fulfilling Promises
 760  * @return True if promises were resolved; false otherwise
 761  */
 762 bool ModelChecker::resolve_promises(ModelAction *write)
 763 {
 764         bool resolved = false;
 765         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 766                 Promise *promise = (*promises)[promise_index];
 767                 if (write->get_node()->get_promise(i)) {
 768                         ModelAction *read = promise->get_action();
 769                         read->read_from(write);
 770                         r_modification_order(read, write);
 771                         post_r_modification_order(read, write);
 772                         promises->erase(promises->begin() + promise_index);
 773                         resolved = true;
 774                 } else
 775                         promise_index++;
 776         }
 777         return resolved;
 778 }
 779
 780 /**
 781  * Compute the set of promises that could potentially be satisfied by this
 782  * action. Note that the set computation actually appears in the Node, not in
 783  * ModelChecker.
 784  * @param curr The ModelAction that may satisfy promises
 785  */
 786 void ModelChecker::compute_promises(ModelAction *curr)
 787 {
 788         for (unsigned int i = 0; i < promises->size(); i++) {
 789                 Promise *promise = (*promises)[i];
 790                 const ModelAction *act = promise->get_action();
 791                 if (!act->happens_before(curr) &&
 792                                 act->is_read() &&
 793                                 !act->is_synchronizing(curr) &&
 794                                 !act->same_thread(curr) &&
 795                                 promise->get_value() == curr->get_value()) {
 796                         curr->get_node()->set_promise(i);
 797                 }
 798         }
 799 }
 800
 801 /** Checks promises in response to change in ClockVector Threads. */
 802 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 803 {
 804         for (unsigned int i = 0; i < promises->size(); i++) {
 805                 Promise *promise = (*promises)[i];
 806                 const ModelAction *act = promise->get_action();
 807                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 808                                 merge_cv->synchronized_since(act)) {
 809                         //This thread is no longer able to send values back to satisfy the promise
 810                         int num_synchronized_threads = promise->increment_threads();
 811                         if (num_synchronized_threads == model->get_num_threads()) {
 812                                 //Promise has failed
 813                                 failed_promise = true;
 814                                 return;
 815                         }
 816                 }
 817         }
 818 }
 819
 820 /**
 821  * Build up an initial set of all past writes that this 'read' action may read
 822  * from. This set is determined by the clock vector's "happens before"
 823  * relationship.
 824  * @param curr is the current ModelAction that we are exploring; it must be a
 825  * 'read' operation.
 826  */
 827 void ModelChecker::build_reads_from_past(ModelAction *curr)
 828 {
 829         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 830         unsigned int i;
 831         ASSERT(curr->is_read());
 832
 833         ModelAction *last_seq_cst = NULL;
 834
 835         /* Track whether this object has been initialized */
 836         bool initialized = false;
 837
 838         if (curr->is_seqcst()) {
 839                 last_seq_cst = get_last_seq_cst(curr->get_location());
 840                 /* We have to at least see the last sequentially consistent write,
 841                          so we are initialized. */
 842                 if (last_seq_cst != NULL)
 843                         initialized = true;
 844         }
 845
 846         /* Iterate over all threads */
 847         for (i = 0; i < thrd_lists->size(); i++) {
 848                 /* Iterate over actions in thread, starting from most recent */
 849                 action_list_t *list = &(*thrd_lists)[i];
 850                 action_list_t::reverse_iterator rit;
 851                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 852                         ModelAction *act = *rit;
 853
 854                         /* Only consider 'write' actions */
 855                         if (!act->is_write())
 856                                 continue;
 857
 858                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 859                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 860                                 DEBUG("Adding action to may_read_from:\n");
 861                                 if (DBG_ENABLED()) {
 862                                         act->print();
 863                                         curr->print();
 864                                 }
 865                                 curr->get_node()->add_read_from(act);
 866                         }
 867
 868                         /* Include at most one act per-thread that "happens before" curr */
 869                         if (act->happens_before(curr)) {
 870                                 initialized = true;
 871                                 break;
 872                         }
 873                 }
 874         }
 875
 876         if (!initialized) {
 877                 /** @todo Need a more informative way of reporting errors. */
 878                 printf("ERROR: may read from uninitialized atomic\n");
 879         }
 880
 881         if (DBG_ENABLED() || !initialized) {
 882                 printf("Reached read action:\n");
 883                 curr->print();
 884                 printf("Printing may_read_from\n");
 885                 curr->get_node()->print_may_read_from();
 886                 printf("End printing may_read_from\n");
 887         }
 888
 889         ASSERT(initialized);
 890 }
 891
 892 static void print_list(action_list_t *list)
 893 {
 894         action_list_t::iterator it;
 895
 896         printf("---------------------------------------------------------------------\n");
 897         printf("Trace:\n");
 898
 899         for (it = list->begin(); it != list->end(); it++) {
 900                 (*it)->print();
 901         }
 902         printf("---------------------------------------------------------------------\n");
 903 }
 904
 905 void ModelChecker::print_summary()
 906 {
 907         printf("\n");
 908         printf("Number of executions: %d\n", num_executions);
 909         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 910
 911         scheduler->print();
 912
 913         if (!isfinalfeasible())
 914                 printf("INFEASIBLE EXECUTION!\n");
 915         print_list(action_trace);
 916         printf("\n");
 917 }
 918
 919 /**
 920  * Add a Thread to the system for the first time. Should only be called once
 921  * per thread.
 922  * @param t The Thread to add
 923  */
 924 void ModelChecker::add_thread(Thread *t)
 925 {
 926         thread_map->put(id_to_int(t->get_id()), t);
 927         scheduler->add_thread(t);
 928 }
 929
 930 void ModelChecker::remove_thread(Thread *t)
 931 {
 932         scheduler->remove_thread(t);
 933 }
 934
 935 /**
 936  * Switch from a user-context to the "master thread" context (a.k.a. system
 937  * context). This switch is made with the intention of exploring a particular
 938  * model-checking action (described by a ModelAction object). Must be called
 939  * from a user-thread context.
 940  * @param act The current action that will be explored. May be NULL, although
 941  * there is little reason to switch to the model-checker without an action to
 942  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 943  * yield control without performing any progress; see thrd_join()).
 944  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 945  */
 946 int ModelChecker::switch_to_master(ModelAction *act)
 947 {
 948         DBG();
 949         Thread *old = thread_current();
 950         set_current_action(act);
 951         old->set_state(THREAD_READY);
 952         return Thread::swap(old, &system_context);
 953 }
 954
 955 /**
 956  * Takes the next step in the execution, if possible.
 957  * @return Returns true (success) if a step was taken and false otherwise.
 958  */
 959 bool ModelChecker::take_step() {
 960         Thread *curr, *next;
 961
 962         curr = thread_current();
 963         if (curr) {
 964                 if (curr->get_state() == THREAD_READY) {
 965                         check_current_action();
 966                         scheduler->add_thread(curr);
 967                 } else if (curr->get_state() == THREAD_RUNNING) {
 968                         /* Stopped while running; i.e., completed */
 969                         curr->complete();
 970                 } else {
 971                         ASSERT(false);
 972                 }
 973         }
 974         next = scheduler->next_thread(nextThread);
 975
 976         /* Infeasible -> don't take any more steps */
 977         if (!isfeasible())
 978                 return false;
 979
 980         if (next)
 981                 next->set_state(THREAD_RUNNING);
 982         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
 983
 984         /* next == NULL -> don't take any more steps */
 985         if (!next)
 986                 return false;
 987         /* Return false only if swap fails with an error */
 988         return (Thread::swap(&system_context, next) == 0);
 989 }
 990
 991 /** Runs the current execution until threre are no more steps to take. */
 992 void ModelChecker::finish_execution() {
 993         DBG();
 994
 995         while (take_step());
 996 }