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 /**
 248  * This is the heart of the model checker routine. It performs model-checking
 249  * actions corresponding to a given "current action." Among other processes, it
 250  * calculates reads-from relationships, updates synchronization clock vectors,
 251  * forms a memory_order constraints graph, and handles replay/backtrack
 252  * execution when running permutations of previously-observed executions.
 253  *
 254  * @param curr The current action to process
 255  * @return The next Thread that must be executed. May be NULL if ModelChecker
 256  * makes no choice (e.g., according to replay execution, combining RMW actions,
 257  * etc.)
 258  */
 259 Thread * ModelChecker::check_current_action(ModelAction *curr)
 260 {
 261         bool already_added = false;
 262
 263         ASSERT(curr);
 264
 265         if (curr->is_rmwc() || curr->is_rmw()) {
 266                 ModelAction *tmp = process_rmw(curr);
 267                 already_added = true;
 268                 delete curr;
 269                 curr = tmp;
 270         } else {
 271                 ModelAction *tmp = node_stack->explore_action(curr);
 272                 if (tmp) {
 273                         /* Discard duplicate ModelAction; use action from NodeStack */
 274                         /* First restore type and order in case of RMW operation */
 275                         if (curr->is_rmwr())
 276                                 tmp->copy_typeandorder(curr);
 277
 278                         /* If we have diverged, we need to reset the clock vector. */
 279                         if (diverge == NULL)
 280                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 281
 282                         delete curr;
 283                         curr = tmp;
 284                 } else {
 285                         /*
 286                          * Perform one-time actions when pushing new ModelAction onto
 287                          * NodeStack
 288                          */
 289                         curr->create_cv(get_parent_action(curr->get_tid()));
 290                         /* Build may_read_from set */
 291                         if (curr->is_read())
 292                                 build_reads_from_past(curr);
 293                         if (curr->is_write())
 294                                 compute_promises(curr);
 295                 }
 296         }
 297
 298         /* Assign 'creation' parent */
 299         if (curr->get_type() == THREAD_CREATE) {
 300                 Thread *th = (Thread *)curr->get_location();
 301                 th->set_creation(curr);
 302         } else if (curr->get_type() == THREAD_JOIN) {
 303                 Thread *wait, *join;
 304                 wait = get_thread(curr->get_tid());
 305                 join = (Thread *)curr->get_location();
 306                 if (!join->is_complete())
 307                         scheduler->wait(wait, join);
 308         } else if (curr->get_type() == THREAD_FINISH) {
 309                 Thread *th = get_thread(curr->get_tid());
 310                 while (!th->wait_list_empty()) {
 311                         Thread *wake = th->pop_wait_list();
 312                         scheduler->wake(wake);
 313                 }
 314         }
 315
 316         /* Deal with new thread */
 317         if (curr->get_type() == THREAD_START)
 318                 check_promises(NULL, curr->get_cv());
 319
 320         /* Assign reads_from values */
 321         Thread *th = get_thread(curr->get_tid());
 322         uint64_t value = VALUE_NONE;
 323         bool updated = false;
 324         if (curr->is_read()) {
 325                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 326                 if (reads_from != NULL) {
 327                         value = reads_from->get_value();
 328                         /* Assign reads_from, perform release/acquire synchronization */
 329                         curr->read_from(reads_from);
 330                         if (r_modification_order(curr,reads_from))
 331                                 updated = true;
 332                 } else {
 333                         /* Read from future value */
 334                         value = curr->get_node()->get_future_value();
 335                         curr->read_from(NULL);
 336                         Promise *valuepromise = new Promise(curr, value);
 337                         promises->push_back(valuepromise);
 338                 }
 339         } else if (curr->is_write()) {
 340                 if (w_modification_order(curr))
 341                         updated = true;;
 342                 if (resolve_promises(curr))
 343                         updated = true;
 344         }
 345
 346         if (updated)
 347                 resolve_release_sequences(curr->get_location());
 348
 349         th->set_return_value(value);
 350
 351         /* Add action to list.  */
 352         if (!already_added)
 353                 add_action_to_lists(curr);
 354
 355         Node *currnode = curr->get_node();
 356         Node *parnode = currnode->get_parent();
 357
 358         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 359                   !currnode->future_value_empty() || !currnode->promise_empty())
 360                 if (!next_backtrack || *curr > *next_backtrack)
 361                         next_backtrack = curr;
 362
 363         set_backtracking(curr);
 364
 365         /* Do not split atomic actions. */
 366         if (curr->is_rmwr())
 367                 return thread_current();
 368         else
 369                 return get_next_replay_thread();
 370 }
 371
 372 /** @returns whether the current partial trace is feasible. */
 373 bool ModelChecker::isfeasible() {
 374         return !mo_graph->checkForCycles() && !failed_promise;
 375 }
 376
 377 /** Returns whether the current completed trace is feasible. */
 378 bool ModelChecker::isfinalfeasible() {
 379         return isfeasible() && promises->size() == 0;
 380 }
 381
 382 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 383 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 384         int tid = id_to_int(act->get_tid());
 385         ModelAction *lastread = get_last_action(tid);
 386         lastread->process_rmw(act);
 387         if (act->is_rmw())
 388                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 389         return lastread;
 390 }
 391
 392 /**
 393  * Updates the mo_graph with the constraints imposed from the current read.
 394  * @param curr The current action. Must be a read.
 395  * @param rf The action that curr reads from. Must be a write.
 396  * @return True if modification order edges were added; false otherwise
 397  */
 398 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 399 {
 400         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 401         unsigned int i;
 402         bool added = false;
 403         ASSERT(curr->is_read());
 404
 405         /* Iterate over all threads */
 406         for (i = 0; i < thrd_lists->size(); i++) {
 407                 /* Iterate over actions in thread, starting from most recent */
 408                 action_list_t *list = &(*thrd_lists)[i];
 409                 action_list_t::reverse_iterator rit;
 410                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 411                         ModelAction *act = *rit;
 412
 413                         /* Include at most one act per-thread that "happens before" curr */
 414                         if (act->happens_before(curr)) {
 415                                 if (act->is_read()) {
 416                                         const ModelAction *prevreadfrom = act->get_reads_from();
 417                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 418                                                 mo_graph->addEdge(prevreadfrom, rf);
 419                                                 added = true;
 420                                         }
 421                                 } else if (rf != act) {
 422                                         mo_graph->addEdge(act, rf);
 423                                         added = true;
 424                                 }
 425                                 break;
 426                         }
 427                 }
 428         }
 429
 430         return added;
 431 }
 432
 433 /** Updates the mo_graph with the constraints imposed from the current read. */
 434 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 435 {
 436         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 437         unsigned int i;
 438         ASSERT(curr->is_read());
 439
 440         /* Iterate over all threads */
 441         for (i = 0; i < thrd_lists->size(); i++) {
 442                 /* Iterate over actions in thread, starting from most recent */
 443                 action_list_t *list = &(*thrd_lists)[i];
 444                 action_list_t::reverse_iterator rit;
 445                 ModelAction *lastact = NULL;
 446
 447                 /* Find last action that happens after curr */
 448                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 449                         ModelAction *act = *rit;
 450                         if (curr->happens_before(act)) {
 451                                 lastact = act;
 452                         } else
 453                                 break;
 454                 }
 455
 456                         /* Include at most one act per-thread that "happens before" curr */
 457                 if (lastact != NULL) {
 458                         if (lastact->is_read()) {
 459                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 460                                 if (postreadfrom != NULL&&rf != postreadfrom)
 461                                         mo_graph->addEdge(rf, postreadfrom);
 462                         } else if (rf != lastact) {
 463                                 mo_graph->addEdge(rf, lastact);
 464                         }
 465                         break;
 466                 }
 467         }
 468 }
 469
 470 /**
 471  * Updates the mo_graph with the constraints imposed from the current write.
 472  * @param curr The current action. Must be a write.
 473  * @return True if modification order edges were added; false otherwise
 474  */
 475 bool ModelChecker::w_modification_order(ModelAction *curr)
 476 {
 477         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 478         unsigned int i;
 479         bool added = false;
 480         ASSERT(curr->is_write());
 481
 482         if (curr->is_seqcst()) {
 483                 /* We have to at least see the last sequentially consistent write,
 484                          so we are initialized. */
 485                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 486                 if (last_seq_cst != NULL) {
 487                         mo_graph->addEdge(last_seq_cst, curr);
 488                         added = true;
 489                 }
 490         }
 491
 492         /* Iterate over all threads */
 493         for (i = 0; i < thrd_lists->size(); i++) {
 494                 /* Iterate over actions in thread, starting from most recent */
 495                 action_list_t *list = &(*thrd_lists)[i];
 496                 action_list_t::reverse_iterator rit;
 497                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 498                         ModelAction *act = *rit;
 499
 500                         /* Include at most one act per-thread that "happens before" curr */
 501                         if (act->happens_before(curr)) {
 502                                 if (act->is_read())
 503                                         mo_graph->addEdge(act->get_reads_from(), curr);
 504                                 else
 505                                         mo_graph->addEdge(act, curr);
 506                                 added = true;
 507                                 break;
 508                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 509                                                      !act->same_thread(curr)) {
 510                                 /* We have an action that:
 511                                    (1) did not happen before us
 512                                    (2) is a read and we are a write
 513                                    (3) cannot synchronize with us
 514                                    (4) is in a different thread
 515                                    =>
 516                                    that read could potentially read from our write.
 517                                  */
 518                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 519                                                 (!next_backtrack || *act > *next_backtrack))
 520                                         next_backtrack = act;
 521                         }
 522                 }
 523         }
 524
 525         return added;
 526 }
 527
 528 /**
 529  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 530  * The ModelAction under consideration is expected to be taking part in
 531  * release/acquire synchronization as an object of the "reads from" relation.
 532  * Note that this can only provide release sequence support for RMW chains
 533  * which do not read from the future, as those actions cannot be traced until
 534  * their "promise" is fulfilled. Similarly, we may not even establish the
 535  * presence of a release sequence with certainty, as some modification order
 536  * constraints may be decided further in the future. Thus, this function
 537  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 538  * and a boolean representing certainty.
 539  *
 540  * @todo Finish lazy updating, when promises are fulfilled in the future
 541  * @param rf The action that might be part of a release sequence. Must be a
 542  * write.
 543  * @param release_heads A pass-by-reference style return parameter.  After
 544  * execution of this function, release_heads will contain the heads of all the
 545  * relevant release sequences, if any exists
 546  * @return true, if the ModelChecker is certain that release_heads is complete;
 547  * false otherwise
 548  */
 549 bool ModelChecker::release_seq_head(const ModelAction *rf,
 550                 std::vector<const ModelAction *> *release_heads) const
 551 {
 552         ASSERT(rf->is_write());
 553         if (!rf) {
 554                 /* read from future: need to settle this later */
 555                 return false; /* incomplete */
 556         }
 557         if (rf->is_release())
 558                 release_heads->push_back(rf);
 559         if (rf->is_rmw()) {
 560                 if (rf->is_acquire())
 561                         return true; /* complete */
 562                 return release_seq_head(rf->get_reads_from(), release_heads);
 563         }
 564         if (rf->is_release())
 565                 return true; /* complete */
 566
 567         /* else relaxed write; check modification order for contiguous subsequence
 568          * -> rf must be same thread as release */
 569         int tid = id_to_int(rf->get_tid());
 570         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 571         action_list_t *list = &(*thrd_lists)[tid];
 572         action_list_t::const_reverse_iterator rit;
 573
 574         /* Find rf in the thread list */
 575         for (rit = list->rbegin(); rit != list->rend(); rit++)
 576                 if (*rit == rf)
 577                         break;
 578
 579         /* Find the last write/release */
 580         for (; rit != list->rend(); rit++)
 581                 if ((*rit)->is_release())
 582                         break;
 583         if (rit == list->rend()) {
 584                 /* No write-release in this thread */
 585                 return true; /* complete */
 586         }
 587         ModelAction *release = *rit;
 588
 589         ASSERT(rf->same_thread(release));
 590
 591         bool certain = true;
 592         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 593                 if (id_to_int(rf->get_tid()) == (int)i)
 594                         continue;
 595                 list = &(*thrd_lists)[i];
 596                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 597                         const ModelAction *act = *rit;
 598                         if (!act->is_write())
 599                                 continue;
 600                         /* Reach synchronization -> this thread is complete */
 601                         if (act->happens_before(release))
 602                                 break;
 603                         if (rf->happens_before(act))
 604                                 continue;
 605
 606                         /* Check modification order */
 607                         if (mo_graph->checkReachable(rf, act))
 608                                 /* rf --mo--> act */
 609                                 continue;
 610                         if (mo_graph->checkReachable(act, release))
 611                                 /* act --mo--> release */
 612                                 break;
 613                         if (mo_graph->checkReachable(release, act) &&
 614                                       mo_graph->checkReachable(act, rf)) {
 615                                 /* release --mo-> act --mo--> rf */
 616                                 return true; /* complete */
 617                         }
 618                         certain = false;
 619                 }
 620         }
 621
 622         if (certain)
 623                 release_heads->push_back(release);
 624         return certain;
 625 }
 626
 627 /**
 628  * A public interface for getting the release sequence head(s) with which a
 629  * given ModelAction must synchronize. This function only returns a non-empty
 630  * result when it can locate a release sequence head with certainty. Otherwise,
 631  * it may mark the internal state of the ModelChecker so that it will handle
 632  * the release sequence at a later time, causing @a act to update its
 633  * synchronization at some later point in execution.
 634  * @param act The 'acquire' action that may read from a release sequence
 635  * @param release_heads A pass-by-reference return parameter. Will be filled
 636  * with the head(s) of the release sequence(s), if they exists with certainty.
 637  * @see ModelChecker::release_seq_head
 638  */
 639 void ModelChecker::get_release_seq_heads(ModelAction *act,
 640                 std::vector<const ModelAction *> *release_heads)
 641 {
 642         const ModelAction *rf = act->get_reads_from();
 643         bool complete;
 644         complete = release_seq_head(rf, release_heads);
 645         if (!complete) {
 646                 /* add act to 'lazy checking' list */
 647                 std::list<ModelAction *> *list;
 648                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 649                 list->push_back(act);
 650         }
 651 }
 652
 653 /**
 654  * Attempt to resolve all stashed operations that might synchronize with a
 655  * release sequence for a given location. This implements the "lazy" portion of
 656  * determining whether or not a release sequence was contiguous, since not all
 657  * modification order information is present at the time an action occurs.
 658  *
 659  * @param location The location/object that should be checked for release
 660  * sequence resolutions
 661  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 662  */
 663 bool ModelChecker::resolve_release_sequences(void *location)
 664 {
 665         std::list<ModelAction *> *list;
 666         list = lazy_sync_with_release->getptr(location);
 667         if (!list)
 668                 return false;
 669
 670         bool updated = false;
 671         std::list<ModelAction *>::iterator it = list->begin();
 672         while (it != list->end()) {
 673                 ModelAction *act = *it;
 674                 const ModelAction *rf = act->get_reads_from();
 675                 std::vector<const ModelAction *> release_heads;
 676                 bool complete;
 677                 complete = release_seq_head(rf, &release_heads);
 678                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 679                         if (!act->has_synchronized_with(release_heads[i])) {
 680                                 updated = true;
 681                                 act->synchronize_with(release_heads[i]);
 682                         }
 683                 }
 684
 685                 if (updated) {
 686                         /* propagate synchronization to later actions */
 687                         action_list_t::reverse_iterator it = action_trace->rbegin();
 688                         while ((*it) != act) {
 689                                 ModelAction *propagate = *it;
 690                                 if (act->happens_before(propagate))
 691                                         /** @todo new mo_graph edges along with
 692                                          * this synchronization? */
 693                                         propagate->synchronize_with(act);
 694                         }
 695                 }
 696                 if (complete)
 697                         it = list->erase(it);
 698                 else
 699                         it++;
 700         }
 701
 702         return updated;
 703 }
 704
 705 /**
 706  * Performs various bookkeeping operations for the current ModelAction. For
 707  * instance, adds action to the per-object, per-thread action vector and to the
 708  * action trace list of all thread actions.
 709  *
 710  * @param act is the ModelAction to add.
 711  */
 712 void ModelChecker::add_action_to_lists(ModelAction *act)
 713 {
 714         int tid = id_to_int(act->get_tid());
 715         action_trace->push_back(act);
 716
 717         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 718
 719         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 720         if (tid >= (int)vec->size())
 721                 vec->resize(next_thread_id);
 722         (*vec)[tid].push_back(act);
 723
 724         if ((int)thrd_last_action->size() <= tid)
 725                 thrd_last_action->resize(get_num_threads());
 726         (*thrd_last_action)[tid] = act;
 727 }
 728
 729 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 730 {
 731         int nthreads = get_num_threads();
 732         if ((int)thrd_last_action->size() < nthreads)
 733                 thrd_last_action->resize(nthreads);
 734         return (*thrd_last_action)[id_to_int(tid)];
 735 }
 736
 737 /**
 738  * Gets the last memory_order_seq_cst action (in the total global sequence)
 739  * performed on a particular object (i.e., memory location).
 740  * @param location The object location to check
 741  * @return The last seq_cst action performed
 742  */
 743 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 744 {
 745         action_list_t *list = obj_map->get_safe_ptr(location);
 746         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 747         action_list_t::reverse_iterator rit;
 748         for (rit = list->rbegin(); rit != list->rend(); rit++)
 749                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 750                         return *rit;
 751         return NULL;
 752 }
 753
 754 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 755 {
 756         ModelAction *parent = get_last_action(tid);
 757         if (!parent)
 758                 parent = get_thread(tid)->get_creation();
 759         return parent;
 760 }
 761
 762 /**
 763  * Returns the clock vector for a given thread.
 764  * @param tid The thread whose clock vector we want
 765  * @return Desired clock vector
 766  */
 767 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 768 {
 769         return get_parent_action(tid)->get_cv();
 770 }
 771
 772 /**
 773  * Resolve a set of Promises with a current write. The set is provided in the
 774  * Node corresponding to @a write.
 775  * @param write The ModelAction that is fulfilling Promises
 776  * @return True if promises were resolved; false otherwise
 777  */
 778 bool ModelChecker::resolve_promises(ModelAction *write)
 779 {
 780         bool resolved = false;
 781         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 782                 Promise *promise = (*promises)[promise_index];
 783                 if (write->get_node()->get_promise(i)) {
 784                         ModelAction *read = promise->get_action();
 785                         read->read_from(write);
 786                         r_modification_order(read, write);
 787                         post_r_modification_order(read, write);
 788                         promises->erase(promises->begin() + promise_index);
 789                         resolved = true;
 790                 } else
 791                         promise_index++;
 792         }
 793         return resolved;
 794 }
 795
 796 /**
 797  * Compute the set of promises that could potentially be satisfied by this
 798  * action. Note that the set computation actually appears in the Node, not in
 799  * ModelChecker.
 800  * @param curr The ModelAction that may satisfy promises
 801  */
 802 void ModelChecker::compute_promises(ModelAction *curr)
 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 (!act->happens_before(curr) &&
 808                                 act->is_read() &&
 809                                 !act->is_synchronizing(curr) &&
 810                                 !act->same_thread(curr) &&
 811                                 promise->get_value() == curr->get_value()) {
 812                         curr->get_node()->set_promise(i);
 813                 }
 814         }
 815 }
 816
 817 /** Checks promises in response to change in ClockVector Threads. */
 818 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 819 {
 820         for (unsigned int i = 0; i < promises->size(); i++) {
 821                 Promise *promise = (*promises)[i];
 822                 const ModelAction *act = promise->get_action();
 823                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 824                                 merge_cv->synchronized_since(act)) {
 825                         //This thread is no longer able to send values back to satisfy the promise
 826                         int num_synchronized_threads = promise->increment_threads();
 827                         if (num_synchronized_threads == model->get_num_threads()) {
 828                                 //Promise has failed
 829                                 failed_promise = true;
 830                                 return;
 831                         }
 832                 }
 833         }
 834 }
 835
 836 /**
 837  * Build up an initial set of all past writes that this 'read' action may read
 838  * from. This set is determined by the clock vector's "happens before"
 839  * relationship.
 840  * @param curr is the current ModelAction that we are exploring; it must be a
 841  * 'read' operation.
 842  */
 843 void ModelChecker::build_reads_from_past(ModelAction *curr)
 844 {
 845         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 846         unsigned int i;
 847         ASSERT(curr->is_read());
 848
 849         ModelAction *last_seq_cst = NULL;
 850
 851         /* Track whether this object has been initialized */
 852         bool initialized = false;
 853
 854         if (curr->is_seqcst()) {
 855                 last_seq_cst = get_last_seq_cst(curr->get_location());
 856                 /* We have to at least see the last sequentially consistent write,
 857                          so we are initialized. */
 858                 if (last_seq_cst != NULL)
 859                         initialized = true;
 860         }
 861
 862         /* Iterate over all threads */
 863         for (i = 0; i < thrd_lists->size(); i++) {
 864                 /* Iterate over actions in thread, starting from most recent */
 865                 action_list_t *list = &(*thrd_lists)[i];
 866                 action_list_t::reverse_iterator rit;
 867                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 868                         ModelAction *act = *rit;
 869
 870                         /* Only consider 'write' actions */
 871                         if (!act->is_write())
 872                                 continue;
 873
 874                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 875                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 876                                 DEBUG("Adding action to may_read_from:\n");
 877                                 if (DBG_ENABLED()) {
 878                                         act->print();
 879                                         curr->print();
 880                                 }
 881                                 curr->get_node()->add_read_from(act);
 882                         }
 883
 884                         /* Include at most one act per-thread that "happens before" curr */
 885                         if (act->happens_before(curr)) {
 886                                 initialized = true;
 887                                 break;
 888                         }
 889                 }
 890         }
 891
 892         if (!initialized) {
 893                 /** @todo Need a more informative way of reporting errors. */
 894                 printf("ERROR: may read from uninitialized atomic\n");
 895         }
 896
 897         if (DBG_ENABLED() || !initialized) {
 898                 printf("Reached read action:\n");
 899                 curr->print();
 900                 printf("Printing may_read_from\n");
 901                 curr->get_node()->print_may_read_from();
 902                 printf("End printing may_read_from\n");
 903         }
 904
 905         ASSERT(initialized);
 906 }
 907
 908 static void print_list(action_list_t *list)
 909 {
 910         action_list_t::iterator it;
 911
 912         printf("---------------------------------------------------------------------\n");
 913         printf("Trace:\n");
 914
 915         for (it = list->begin(); it != list->end(); it++) {
 916                 (*it)->print();
 917         }
 918         printf("---------------------------------------------------------------------\n");
 919 }
 920
 921 void ModelChecker::print_summary()
 922 {
 923         printf("\n");
 924         printf("Number of executions: %d\n", num_executions);
 925         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 926
 927         scheduler->print();
 928
 929         if (!isfinalfeasible())
 930                 printf("INFEASIBLE EXECUTION!\n");
 931         print_list(action_trace);
 932         printf("\n");
 933 }
 934
 935 /**
 936  * Add a Thread to the system for the first time. Should only be called once
 937  * per thread.
 938  * @param t The Thread to add
 939  */
 940 void ModelChecker::add_thread(Thread *t)
 941 {
 942         thread_map->put(id_to_int(t->get_id()), t);
 943         scheduler->add_thread(t);
 944 }
 945
 946 void ModelChecker::remove_thread(Thread *t)
 947 {
 948         scheduler->remove_thread(t);
 949 }
 950
 951 /**
 952  * Switch from a user-context to the "master thread" context (a.k.a. system
 953  * context). This switch is made with the intention of exploring a particular
 954  * model-checking action (described by a ModelAction object). Must be called
 955  * from a user-thread context.
 956  * @param act The current action that will be explored. May be NULL, although
 957  * there is little reason to switch to the model-checker without an action to
 958  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 959  * yield control without performing any progress; see thrd_join()).
 960  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 961  */
 962 int ModelChecker::switch_to_master(ModelAction *act)
 963 {
 964         DBG();
 965         Thread *old = thread_current();
 966         set_current_action(act);
 967         old->set_state(THREAD_READY);
 968         return Thread::swap(old, &system_context);
 969 }
 970
 971 /**
 972  * Takes the next step in the execution, if possible.
 973  * @return Returns true (success) if a step was taken and false otherwise.
 974  */
 975 bool ModelChecker::take_step() {
 976         Thread *curr, *next;
 977
 978         curr = thread_current();
 979         if (curr) {
 980                 if (curr->get_state() == THREAD_READY) {
 981                         if (current_action) {
 982                                 nextThread = check_current_action(current_action);
 983                                 current_action = NULL;
 984                         }
 985                         if (!curr->is_blocked())
 986                                 scheduler->add_thread(curr);
 987                 } else if (curr->get_state() == THREAD_RUNNING) {
 988                         /* Stopped while running; i.e., completed */
 989                         curr->complete();
 990                 } else {
 991                         ASSERT(false);
 992                 }
 993         }
 994         next = scheduler->next_thread(nextThread);
 995
 996         /* Infeasible -> don't take any more steps */
 997         if (!isfeasible())
 998                 return false;
 999
1000         if (next)
1001                 next->set_state(THREAD_RUNNING);
1002         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1003
1004         /* next == NULL -> don't take any more steps */
1005         if (!next)
1006                 return false;
1007         /* Return false only if swap fails with an error */
1008         return (Thread::swap(&system_context, next) == 0);
1009 }
1010
1011 /** Runs the current execution until threre are no more steps to take. */
1012 void ModelChecker::finish_execution() {
1013         DBG();
1014
1015         while (take_step());
1016 }