model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14
  15 #define INITIAL_THREAD_ID       0
  16
  17 ModelChecker *model;
  18
  19 /** @brief Constructor */
  20 ModelChecker::ModelChecker(struct model_params params) :
  21         /* Initialize default scheduler */
  22         scheduler(new Scheduler()),
  23         num_executions(0),
  24         num_feasible_executions(0),
  25         params(params),
  26         diverge(NULL),
  27         action_trace(new action_list_t()),
  28         thread_map(new HashTable<int, Thread *, int>()),
  29         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  30         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  31         promises(new std::vector<Promise *>()),
  32         futurevalues(new std::vector<struct PendingFutureValue>()),
  33         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  34         thrd_last_action(new std::vector<ModelAction *>(1)),
  35         node_stack(new NodeStack()),
  36         mo_graph(new CycleGraph()),
  37         failed_promise(false),
  38         too_many_reads(false),
  39         asserted(false)
  40 {
  41         /* Allocate this "size" on the snapshotting heap */
  42         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  43         /* First thread created will have id INITIAL_THREAD_ID */
  44         priv->next_thread_id = INITIAL_THREAD_ID;
  45
  46         lazy_sync_size = &priv->lazy_sync_size;
  47 }
  48
  49 /** @brief Destructor */
  50 ModelChecker::~ModelChecker()
  51 {
  52         for (int i = 0; i < get_num_threads(); i++)
  53                 delete thread_map->get(i);
  54         delete thread_map;
  55
  56         delete obj_thrd_map;
  57         delete obj_map;
  58         delete action_trace;
  59
  60         for (unsigned int i = 0; i < promises->size(); i++)
  61                 delete (*promises)[i];
  62         delete promises;
  63
  64         delete lazy_sync_with_release;
  65
  66         delete thrd_last_action;
  67         delete node_stack;
  68         delete scheduler;
  69         delete mo_graph;
  70 }
  71
  72 /**
  73  * Restores user program to initial state and resets all model-checker data
  74  * structures.
  75  */
  76 void ModelChecker::reset_to_initial_state()
  77 {
  78         DEBUG("+++ Resetting to initial state +++\n");
  79         node_stack->reset_execution();
  80         failed_promise = false;
  81         too_many_reads = false;
  82         reset_asserted();
  83         snapshotObject->backTrackBeforeStep(0);
  84 }
  85
  86 /** @returns a thread ID for a new Thread */
  87 thread_id_t ModelChecker::get_next_id()
  88 {
  89         return priv->next_thread_id++;
  90 }
  91
  92 /** @returns the number of user threads created during this execution */
  93 int ModelChecker::get_num_threads()
  94 {
  95         return priv->next_thread_id;
  96 }
  97
  98 /** @returns a sequence number for a new ModelAction */
  99 modelclock_t ModelChecker::get_next_seq_num()
 100 {
 101         return ++priv->used_sequence_numbers;
 102 }
 103
 104 /**
 105  * @brief Choose the next thread to execute.
 106  *
 107  * This function chooses the next thread that should execute. It can force the
 108  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 109  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 110  * The model-checker may have no preference regarding the next thread (i.e.,
 111  * when exploring a new execution ordering), in which case this will return
 112  * NULL.
 113  * @param curr The current ModelAction. This action might guide the choice of
 114  * next thread.
 115  * @return The next thread to run. If the model-checker has no preference, NULL.
 116  */
 117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 118 {
 119         thread_id_t tid;
 120
 121         /* Do not split atomic actions. */
 122         if (curr->is_rmwr())
 123                 return thread_current();
 124         /* The THREAD_CREATE action points to the created Thread */
 125         else if (curr->get_type() == THREAD_CREATE)
 126                 return (Thread *)curr->get_location();
 127
 128         /* Have we completed exploring the preselected path? */
 129         if (diverge == NULL)
 130                 return NULL;
 131
 132         /* Else, we are trying to replay an execution */
 133         ModelAction *next = node_stack->get_next()->get_action();
 134
 135         if (next == diverge) {
 136                 Node *nextnode = next->get_node();
 137                 /* Reached divergence point */
 138                 if (nextnode->increment_promise()) {
 139                         /* The next node will try to satisfy a different set of promises. */
 140                         tid = next->get_tid();
 141                         node_stack->pop_restofstack(2);
 142                 } else if (nextnode->increment_read_from()) {
 143                         /* The next node will read from a different value. */
 144                         tid = next->get_tid();
 145                         node_stack->pop_restofstack(2);
 146                 } else if (nextnode->increment_future_value()) {
 147                         /* The next node will try to read from a different future value. */
 148                         tid = next->get_tid();
 149                         node_stack->pop_restofstack(2);
 150                 } else {
 151                         /* Make a different thread execute for next step */
 152                         Node *node = nextnode->get_parent();
 153                         tid = node->get_next_backtrack();
 154                         node_stack->pop_restofstack(1);
 155                 }
 156                 DEBUG("*** Divergence point ***\n");
 157                 diverge = NULL;
 158         } else {
 159                 tid = next->get_tid();
 160         }
 161         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 162         ASSERT(tid != THREAD_ID_T_NONE);
 163         return thread_map->get(id_to_int(tid));
 164 }
 165
 166 /**
 167  * Queries the model-checker for more executions to explore and, if one
 168  * exists, resets the model-checker state to execute a new execution.
 169  *
 170  * @return If there are more executions to explore, return true. Otherwise,
 171  * return false.
 172  */
 173 bool ModelChecker::next_execution()
 174 {
 175         DBG();
 176
 177         num_executions++;
 178         if (isfinalfeasible())
 179                 num_feasible_executions++;
 180
 181         if (isfinalfeasible() || DBG_ENABLED())
 182                 print_summary();
 183
 184         if ((diverge = get_next_backtrack()) == NULL)
 185                 return false;
 186
 187         if (DBG_ENABLED()) {
 188                 printf("Next execution will diverge at:\n");
 189                 diverge->print();
 190         }
 191
 192         reset_to_initial_state();
 193         return true;
 194 }
 195
 196 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 197 {
 198         action_type type = act->get_type();
 199
 200         if (type==ATOMIC_READ||type==ATOMIC_WRITE||type==ATOMIC_RMW) {
 201                 /* linear search: from most recent to oldest */
 202                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 203                 action_list_t::reverse_iterator rit;
 204                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 205                         ModelAction *prev = *rit;
 206                         if (act->is_synchronizing(prev))
 207                                 return prev;
 208                 }
 209         } else if (type==ATOMIC_LOCK||type==ATOMIC_TRYLOCK) {
 210                 /* linear search: from most recent to oldest */
 211                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 212                 action_list_t::reverse_iterator rit;
 213                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 214                         ModelAction *prev = *rit;
 215                         if (prev->is_success_lock())
 216                                 return prev;
 217                 }
 218         } else if (type==ATOMIC_UNLOCK) {
 219                 /* linear search: from most recent to oldest */
 220                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 221                 action_list_t::reverse_iterator rit;
 222                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 223                         ModelAction *prev = *rit;
 224                         if (prev->is_failed_trylock())
 225                                 return prev;
 226                 }
 227         }
 228         return NULL;
 229 }
 230
 231 void ModelChecker::set_backtracking(ModelAction *act)
 232 {
 233         ModelAction *prev;
 234         Node *node;
 235         Thread *t = get_thread(act);
 236
 237         prev = get_last_conflict(act);
 238         if (prev == NULL)
 239                 return;
 240
 241         node = prev->get_node()->get_parent();
 242
 243         while (!node->is_enabled(t))
 244                 t = t->get_parent();
 245
 246         /* Check if this has been explored already */
 247         if (node->has_been_explored(t->get_id()))
 248                 return;
 249
 250         /* Cache the latest backtracking point */
 251         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 252                 priv->next_backtrack = prev;
 253
 254         /* If this is a new backtracking point, mark the tree */
 255         if (!node->set_backtrack(t->get_id()))
 256                 return;
 257         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 258                         prev->get_tid(), t->get_id());
 259         if (DBG_ENABLED()) {
 260                 prev->print();
 261                 act->print();
 262         }
 263 }
 264
 265 /**
 266  * Returns last backtracking point. The model checker will explore a different
 267  * path for this point in the next execution.
 268  * @return The ModelAction at which the next execution should diverge.
 269  */
 270 ModelAction * ModelChecker::get_next_backtrack()
 271 {
 272         ModelAction *next = priv->next_backtrack;
 273         priv->next_backtrack = NULL;
 274         return next;
 275 }
 276
 277 /**
 278  * Processes a read or rmw model action.
 279  * @param curr is the read model action to process.
 280  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 281  * @return True if processing this read updates the mo_graph.
 282  */
 283 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 284 {
 285         uint64_t value;
 286         bool updated = false;
 287         while (true) {
 288                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 289                 if (reads_from != NULL) {
 290                         mo_graph->startChanges();
 291
 292                         value = reads_from->get_value();
 293                         bool r_status = false;
 294
 295                         if (!second_part_of_rmw) {
 296                                 check_recency(curr,false);
 297                                 r_status = r_modification_order(curr, reads_from);
 298                         }
 299
 300
 301                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 302                                 mo_graph->rollbackChanges();
 303                                 too_many_reads = false;
 304                                 continue;
 305                         }
 306
 307                         curr->read_from(reads_from);
 308                         mo_graph->commitChanges();
 309                         updated |= r_status;
 310                 } else if (!second_part_of_rmw) {
 311                         /* Read from future value */
 312                         value = curr->get_node()->get_future_value();
 313                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 314                         curr->read_from(NULL);
 315                         Promise *valuepromise = new Promise(curr, value, expiration);
 316                         promises->push_back(valuepromise);
 317                 }
 318                 get_thread(curr)->set_return_value(value);
 319                 return updated;
 320         }
 321 }
 322
 323 /**
 324  * Process a write ModelAction
 325  * @param curr The ModelAction to process
 326  * @return True if the mo_graph was updated or promises were resolved
 327  */
 328 bool ModelChecker::process_write(ModelAction *curr)
 329 {
 330         bool updated_mod_order = w_modification_order(curr);
 331         bool updated_promises = resolve_promises(curr);
 332
 333         if (promises->size() == 0) {
 334                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 335                         struct PendingFutureValue pfv = (*futurevalues)[i];
 336                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 337                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 338                                 priv->next_backtrack = pfv.act;
 339                 }
 340                 futurevalues->resize(0);
 341         }
 342
 343         mo_graph->commitChanges();
 344         get_thread(curr)->set_return_value(VALUE_NONE);
 345         return updated_mod_order || updated_promises;
 346 }
 347
 348 /**
 349  * This is the heart of the model checker routine. It performs model-checking
 350  * actions corresponding to a given "current action." Among other processes, it
 351  * calculates reads-from relationships, updates synchronization clock vectors,
 352  * forms a memory_order constraints graph, and handles replay/backtrack
 353  * execution when running permutations of previously-observed executions.
 354  *
 355  * @param curr The current action to process
 356  * @return The next Thread that must be executed. May be NULL if ModelChecker
 357  * makes no choice (e.g., according to replay execution, combining RMW actions,
 358  * etc.)
 359  */
 360 Thread * ModelChecker::check_current_action(ModelAction *curr)
 361 {
 362         bool second_part_of_rmw = false;
 363
 364         ASSERT(curr);
 365
 366         if (curr->is_rmwc() || curr->is_rmw()) {
 367                 ModelAction *tmp = process_rmw(curr);
 368                 second_part_of_rmw = true;
 369                 delete curr;
 370                 curr = tmp;
 371                 compute_promises(curr);
 372         } else {
 373                 ModelAction *tmp = node_stack->explore_action(curr, scheduler->get_enabled());
 374                 if (tmp) {
 375                         /* Discard duplicate ModelAction; use action from NodeStack */
 376                         /* First restore type and order in case of RMW operation */
 377                         if (curr->is_rmwr())
 378                                 tmp->copy_typeandorder(curr);
 379
 380                         /* If we have diverged, we need to reset the clock vector. */
 381                         if (diverge == NULL)
 382                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 383
 384                         ASSERT(curr->get_location()==tmp->get_location());
 385
 386                         delete curr;
 387                         curr = tmp;
 388                 } else {
 389                         /*
 390                          * Perform one-time actions when pushing new ModelAction onto
 391                          * NodeStack
 392                          */
 393                         curr->create_cv(get_parent_action(curr->get_tid()));
 394                         /* Build may_read_from set */
 395                         if (curr->is_read())
 396                                 build_reads_from_past(curr);
 397                         if (curr->is_write())
 398                                 compute_promises(curr);
 399                 }
 400         }
 401
 402         /* Thread specific actions */
 403         switch (curr->get_type()) {
 404         case THREAD_CREATE: {
 405                 Thread *th = (Thread *)curr->get_location();
 406                 th->set_creation(curr);
 407                 break;
 408         }
 409         case THREAD_JOIN: {
 410                 Thread *waiting, *blocking;
 411                 waiting = get_thread(curr);
 412                 blocking = (Thread *)curr->get_location();
 413                 if (!blocking->is_complete()) {
 414                         blocking->push_wait_list(curr);
 415                         scheduler->sleep(waiting);
 416                 }
 417                 break;
 418         }
 419         case THREAD_FINISH: {
 420                 Thread *th = get_thread(curr);
 421                 while (!th->wait_list_empty()) {
 422                         ModelAction *act = th->pop_wait_list();
 423                         Thread *wake = get_thread(act);
 424                         scheduler->wake(wake);
 425                 }
 426                 th->complete();
 427                 break;
 428         }
 429         case THREAD_START: {
 430                 check_promises(NULL, curr->get_cv());
 431                 break;
 432         }
 433         default:
 434                 break;
 435         }
 436
 437         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 438
 439         while (!work_queue.empty()) {
 440                 WorkQueueEntry work = work_queue.front();
 441                 work_queue.pop_front();
 442
 443                 switch (work.type) {
 444                 case WORK_CHECK_CURR_ACTION: {
 445                         ModelAction *act = work.action;
 446                         bool updated = false;
 447                         if (act->is_read() && process_read(act, second_part_of_rmw))
 448                                 updated = true;
 449
 450                         if (act->is_write() && process_write(act))
 451                                 updated = true;
 452
 453                         if (updated)
 454                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 455                         break;
 456                 }
 457                 case WORK_CHECK_RELEASE_SEQ:
 458                         resolve_release_sequences(work.location, &work_queue);
 459                         break;
 460                 case WORK_CHECK_MO_EDGES:
 461                         /** @todo Perform follow-up mo_graph checks */
 462                 default:
 463                         ASSERT(false);
 464                         break;
 465                 }
 466         }
 467
 468         /* Add action to list.  */
 469         if (!second_part_of_rmw)
 470                 add_action_to_lists(curr);
 471
 472         check_curr_backtracking(curr);
 473
 474         set_backtracking(curr);
 475
 476         return get_next_thread(curr);
 477 }
 478
 479 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 480         Node *currnode = curr->get_node();
 481         Node *parnode = currnode->get_parent();
 482
 483         if ((!parnode->backtrack_empty() ||
 484                          !currnode->read_from_empty() ||
 485                          !currnode->future_value_empty() ||
 486                          !currnode->promise_empty())
 487                         && (!priv->next_backtrack ||
 488                                         *curr > *priv->next_backtrack)) {
 489                 priv->next_backtrack = curr;
 490         }
 491 }
 492
 493 bool ModelChecker::promises_expired() {
 494         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 495                 Promise *promise = (*promises)[promise_index];
 496                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 497                         return true;
 498                 }
 499         }
 500         return false;
 501 }
 502
 503 /** @returns whether the current partial trace must be a prefix of a
 504  * feasible trace. */
 505 bool ModelChecker::isfeasibleprefix() {
 506         return promises->size() == 0 && *lazy_sync_size == 0;
 507 }
 508
 509 /** @returns whether the current partial trace is feasible. */
 510 bool ModelChecker::isfeasible() {
 511         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 512 }
 513
 514 /** @returns whether the current partial trace is feasible other than
 515  * multiple RMW reading from the same store. */
 516 bool ModelChecker::isfeasibleotherthanRMW() {
 517         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 518 }
 519
 520 /** Returns whether the current completed trace is feasible. */
 521 bool ModelChecker::isfinalfeasible() {
 522         return isfeasible() && promises->size() == 0;
 523 }
 524
 525 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 526 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 527         int tid = id_to_int(act->get_tid());
 528         ModelAction *lastread = get_last_action(tid);
 529         lastread->process_rmw(act);
 530         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 531                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 532                 mo_graph->commitChanges();
 533         }
 534         return lastread;
 535 }
 536
 537 /**
 538  * Checks whether a thread has read from the same write for too many times
 539  * without seeing the effects of a later write.
 540  *
 541  * Basic idea:
 542  * 1) there must a different write that we could read from that would satisfy the modification order,
 543  * 2) we must have read from the same value in excess of maxreads times, and
 544  * 3) that other write must have been in the reads_from set for maxreads times.
 545  *
 546  * If so, we decide that the execution is no longer feasible.
 547  */
 548 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 549         if (params.maxreads != 0) {
 550                 if (curr->get_node()->get_read_from_size() <= 1)
 551                         return;
 552
 553                 //Must make sure that execution is currently feasible...  We could
 554                 //accidentally clear by rolling back
 555                 if (!isfeasible())
 556                         return;
 557
 558                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 559                 int tid = id_to_int(curr->get_tid());
 560
 561                 /* Skip checks */
 562                 if ((int)thrd_lists->size() <= tid)
 563                         return;
 564
 565                 action_list_t *list = &(*thrd_lists)[tid];
 566
 567                 action_list_t::reverse_iterator rit = list->rbegin();
 568                 /* Skip past curr */
 569                 if (already_added) {
 570                         for (; (*rit) != curr; rit++)
 571                                 ;
 572                         /* go past curr now */
 573                         rit++;
 574                 }
 575
 576                 action_list_t::reverse_iterator ritcopy = rit;
 577                 //See if we have enough reads from the same value
 578                 int count = 0;
 579                 for (; count < params.maxreads; rit++,count++) {
 580                         if (rit==list->rend())
 581                                 return;
 582                         ModelAction *act = *rit;
 583                         if (!act->is_read())
 584                                 return;
 585                         if (act->get_reads_from() != curr->get_reads_from())
 586                                 return;
 587                         if (act->get_node()->get_read_from_size() <= 1)
 588                                 return;
 589                 }
 590
 591                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 592                         //Get write
 593                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 594                         //Need a different write
 595                         if (write==curr->get_reads_from())
 596                                 continue;
 597
 598                         /* Test to see whether this is a feasible write to read from*/
 599                         mo_graph->startChanges();
 600                         r_modification_order(curr, write);
 601                         bool feasiblereadfrom = isfeasible();
 602                         mo_graph->rollbackChanges();
 603
 604                         if (!feasiblereadfrom)
 605                                 continue;
 606                         rit = ritcopy;
 607
 608                         bool feasiblewrite = true;
 609                         //new we need to see if this write works for everyone
 610
 611                         for (int loop = count; loop>0; loop--,rit++) {
 612                                 ModelAction *act=*rit;
 613                                 bool foundvalue = false;
 614                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 615                                         if (act->get_node()->get_read_from_at(i)==write) {
 616                                                 foundvalue = true;
 617                                                 break;
 618                                         }
 619                                 }
 620                                 if (!foundvalue) {
 621                                         feasiblewrite = false;
 622                                         break;
 623                                 }
 624                         }
 625                         if (feasiblewrite) {
 626                                 too_many_reads = true;
 627                                 return;
 628                         }
 629                 }
 630         }
 631 }
 632
 633 /**
 634  * Updates the mo_graph with the constraints imposed from the current
 635  * read.
 636  *
 637  * Basic idea is the following: Go through each other thread and find
 638  * the lastest action that happened before our read.  Two cases:
 639  *
 640  * (1) The action is a write => that write must either occur before
 641  * the write we read from or be the write we read from.
 642  *
 643  * (2) The action is a read => the write that that action read from
 644  * must occur before the write we read from or be the same write.
 645  *
 646  * @param curr The current action. Must be a read.
 647  * @param rf The action that curr reads from. Must be a write.
 648  * @return True if modification order edges were added; false otherwise
 649  */
 650 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 651 {
 652         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 653         unsigned int i;
 654         bool added = false;
 655         ASSERT(curr->is_read());
 656
 657         /* Iterate over all threads */
 658         for (i = 0; i < thrd_lists->size(); i++) {
 659                 /* Iterate over actions in thread, starting from most recent */
 660                 action_list_t *list = &(*thrd_lists)[i];
 661                 action_list_t::reverse_iterator rit;
 662                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 663                         ModelAction *act = *rit;
 664
 665                         /* Include at most one act per-thread that "happens before" curr */
 666                         if (act->happens_before(curr)) {
 667                                 if (act->is_write()) {
 668                                         if (rf != act && act != curr) {
 669                                                 mo_graph->addEdge(act, rf);
 670                                                 added = true;
 671                                         }
 672                                 } else {
 673                                         const ModelAction *prevreadfrom = act->get_reads_from();
 674                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 675                                                 mo_graph->addEdge(prevreadfrom, rf);
 676                                                 added = true;
 677                                         }
 678                                 }
 679
 680                                 break;
 681                         }
 682                 }
 683         }
 684
 685         return added;
 686 }
 687
 688 /** This method fixes up the modification order when we resolve a
 689  *  promises.  The basic problem is that actions that occur after the
 690  *  read curr could not property add items to the modification order
 691  *  for our read.
 692  *
 693  *  So for each thread, we find the earliest item that happens after
 694  *  the read curr.  This is the item we have to fix up with additional
 695  *  constraints.  If that action is write, we add a MO edge between
 696  *  the Action rf and that action.  If the action is a read, we add a
 697  *  MO edge between the Action rf, and whatever the read accessed.
 698  *
 699  * @param curr is the read ModelAction that we are fixing up MO edges for.
 700  * @param rf is the write ModelAction that curr reads from.
 701  *
 702  */
 703
 704 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 705 {
 706         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 707         unsigned int i;
 708         ASSERT(curr->is_read());
 709
 710         /* Iterate over all threads */
 711         for (i = 0; i < thrd_lists->size(); i++) {
 712                 /* Iterate over actions in thread, starting from most recent */
 713                 action_list_t *list = &(*thrd_lists)[i];
 714                 action_list_t::reverse_iterator rit;
 715                 ModelAction *lastact = NULL;
 716
 717                 /* Find last action that happens after curr */
 718                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 719                         ModelAction *act = *rit;
 720                         if (curr->happens_before(act)) {
 721                                 lastact = act;
 722                         } else
 723                                 break;
 724                 }
 725
 726                         /* Include at most one act per-thread that "happens before" curr */
 727                 if (lastact != NULL) {
 728                         if (lastact->is_read()) {
 729                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 730                                 if (postreadfrom != NULL&&rf != postreadfrom)
 731                                         mo_graph->addEdge(rf, postreadfrom);
 732                         } else if (rf != lastact) {
 733                                 mo_graph->addEdge(rf, lastact);
 734                         }
 735                         break;
 736                 }
 737         }
 738 }
 739
 740 /**
 741  * Updates the mo_graph with the constraints imposed from the current write.
 742  *
 743  * Basic idea is the following: Go through each other thread and find
 744  * the lastest action that happened before our write.  Two cases:
 745  *
 746  * (1) The action is a write => that write must occur before
 747  * the current write
 748  *
 749  * (2) The action is a read => the write that that action read from
 750  * must occur before the current write.
 751  *
 752  * This method also handles two other issues:
 753  *
 754  * (I) Sequential Consistency: Making sure that if the current write is
 755  * seq_cst, that it occurs after the previous seq_cst write.
 756  *
 757  * (II) Sending the write back to non-synchronizing reads.
 758  *
 759  * @param curr The current action. Must be a write.
 760  * @return True if modification order edges were added; false otherwise
 761  */
 762 bool ModelChecker::w_modification_order(ModelAction *curr)
 763 {
 764         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 765         unsigned int i;
 766         bool added = false;
 767         ASSERT(curr->is_write());
 768
 769         if (curr->is_seqcst()) {
 770                 /* We have to at least see the last sequentially consistent write,
 771                          so we are initialized. */
 772                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 773                 if (last_seq_cst != NULL) {
 774                         mo_graph->addEdge(last_seq_cst, curr);
 775                         added = true;
 776                 }
 777         }
 778
 779         /* Iterate over all threads */
 780         for (i = 0; i < thrd_lists->size(); i++) {
 781                 /* Iterate over actions in thread, starting from most recent */
 782                 action_list_t *list = &(*thrd_lists)[i];
 783                 action_list_t::reverse_iterator rit;
 784                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 785                         ModelAction *act = *rit;
 786
 787                         /* Include at most one act per-thread that "happens before" curr */
 788                         if (act->happens_before(curr)) {
 789                                 /*
 790                                  * Note: if act is RMW, just add edge:
 791                                  *   act --mo--> curr
 792                                  * The following edge should be handled elsewhere:
 793                                  *   readfrom(act) --mo--> act
 794                                  */
 795                                 if (act->is_write()) {
 796                                         //RMW shouldn't have an edge to themselves
 797                                         if (act!=curr)
 798                                                 mo_graph->addEdge(act, curr);
 799                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 800                                         mo_graph->addEdge(act->get_reads_from(), curr);
 801                                 added = true;
 802                                 break;
 803                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 804                                                      !act->same_thread(curr)) {
 805                                 /* We have an action that:
 806                                    (1) did not happen before us
 807                                    (2) is a read and we are a write
 808                                    (3) cannot synchronize with us
 809                                    (4) is in a different thread
 810                                    =>
 811                                    that read could potentially read from our write.
 812                                  */
 813                                 if (thin_air_constraint_may_allow(curr, act)) {
 814                                         if (isfeasible() ||
 815                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 816                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 817                                                 futurevalues->push_back(pfv);
 818                                         }
 819                                 }
 820                         }
 821                 }
 822         }
 823
 824         return added;
 825 }
 826
 827 /** Arbitrary reads from the future are not allowed.  Section 29.3
 828  * part 9 places some constraints.  This method checks one result of constraint
 829  * constraint.  Others require compiler support. */
 830
 831 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 832         if (!writer->is_rmw())
 833                 return true;
 834
 835         if (!reader->is_rmw())
 836                 return true;
 837
 838         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 839                 if (search==reader)
 840                         return false;
 841                 if (search->get_tid() == reader->get_tid() &&
 842                                 search->happens_before(reader))
 843                         break;
 844         }
 845
 846         return true;
 847 }
 848
 849 /**
 850  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 851  * The ModelAction under consideration is expected to be taking part in
 852  * release/acquire synchronization as an object of the "reads from" relation.
 853  * Note that this can only provide release sequence support for RMW chains
 854  * which do not read from the future, as those actions cannot be traced until
 855  * their "promise" is fulfilled. Similarly, we may not even establish the
 856  * presence of a release sequence with certainty, as some modification order
 857  * constraints may be decided further in the future. Thus, this function
 858  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 859  * and a boolean representing certainty.
 860  *
 861  * @todo Finish lazy updating, when promises are fulfilled in the future
 862  * @param rf The action that might be part of a release sequence. Must be a
 863  * write.
 864  * @param release_heads A pass-by-reference style return parameter.  After
 865  * execution of this function, release_heads will contain the heads of all the
 866  * relevant release sequences, if any exists
 867  * @return true, if the ModelChecker is certain that release_heads is complete;
 868  * false otherwise
 869  */
 870 bool ModelChecker::release_seq_head(const ModelAction *rf,
 871                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 872 {
 873         if (!rf) {
 874                 /* read from future: need to settle this later */
 875                 return false; /* incomplete */
 876         }
 877
 878         ASSERT(rf->is_write());
 879
 880         if (rf->is_release())
 881                 release_heads->push_back(rf);
 882         if (rf->is_rmw()) {
 883                 /* We need a RMW action that is both an acquire and release to stop */
 884                 /** @todo Need to be smarter here...  In the linux lock
 885                  * example, this will run to the beginning of the program for
 886                  * every acquire. */
 887                 if (rf->is_acquire() && rf->is_release())
 888                         return true; /* complete */
 889                 return release_seq_head(rf->get_reads_from(), release_heads);
 890         }
 891         if (rf->is_release())
 892                 return true; /* complete */
 893
 894         /* else relaxed write; check modification order for contiguous subsequence
 895          * -> rf must be same thread as release */
 896         int tid = id_to_int(rf->get_tid());
 897         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 898         action_list_t *list = &(*thrd_lists)[tid];
 899         action_list_t::const_reverse_iterator rit;
 900
 901         /* Find rf in the thread list */
 902         rit = std::find(list->rbegin(), list->rend(), rf);
 903         ASSERT(rit != list->rend());
 904
 905         /* Find the last write/release */
 906         for (; rit != list->rend(); rit++)
 907                 if ((*rit)->is_release())
 908                         break;
 909         if (rit == list->rend()) {
 910                 /* No write-release in this thread */
 911                 return true; /* complete */
 912         }
 913         ModelAction *release = *rit;
 914
 915         ASSERT(rf->same_thread(release));
 916
 917         bool certain = true;
 918         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 919                 if (id_to_int(rf->get_tid()) == (int)i)
 920                         continue;
 921                 list = &(*thrd_lists)[i];
 922
 923                 /* Can we ensure no future writes from this thread may break
 924                  * the release seq? */
 925                 bool future_ordered = false;
 926
 927                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 928                         const ModelAction *act = *rit;
 929                         if (!act->is_write())
 930                                 continue;
 931                         /* Reach synchronization -> this thread is complete */
 932                         if (act->happens_before(release))
 933                                 break;
 934                         if (rf->happens_before(act)) {
 935                                 future_ordered = true;
 936                                 continue;
 937                         }
 938
 939                         /* Check modification order */
 940                         if (mo_graph->checkReachable(rf, act)) {
 941                                 /* rf --mo--> act */
 942                                 future_ordered = true;
 943                                 continue;
 944                         }
 945                         if (mo_graph->checkReachable(act, release))
 946                                 /* act --mo--> release */
 947                                 break;
 948                         if (mo_graph->checkReachable(release, act) &&
 949                                       mo_graph->checkReachable(act, rf)) {
 950                                 /* release --mo-> act --mo--> rf */
 951                                 return true; /* complete */
 952                         }
 953                         certain = false;
 954                 }
 955                 if (!future_ordered)
 956                         return false; /* This thread is uncertain */
 957         }
 958
 959         if (certain)
 960                 release_heads->push_back(release);
 961         return certain;
 962 }
 963
 964 /**
 965  * A public interface for getting the release sequence head(s) with which a
 966  * given ModelAction must synchronize. This function only returns a non-empty
 967  * result when it can locate a release sequence head with certainty. Otherwise,
 968  * it may mark the internal state of the ModelChecker so that it will handle
 969  * the release sequence at a later time, causing @a act to update its
 970  * synchronization at some later point in execution.
 971  * @param act The 'acquire' action that may read from a release sequence
 972  * @param release_heads A pass-by-reference return parameter. Will be filled
 973  * with the head(s) of the release sequence(s), if they exists with certainty.
 974  * @see ModelChecker::release_seq_head
 975  */
 976 void ModelChecker::get_release_seq_heads(ModelAction *act,
 977                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 978 {
 979         const ModelAction *rf = act->get_reads_from();
 980         bool complete;
 981         complete = release_seq_head(rf, release_heads);
 982         if (!complete) {
 983                 /* add act to 'lazy checking' list */
 984                 std::list<ModelAction *> *list;
 985                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 986                 list->push_back(act);
 987                 (*lazy_sync_size)++;
 988         }
 989 }
 990
 991 /**
 992  * Attempt to resolve all stashed operations that might synchronize with a
 993  * release sequence for a given location. This implements the "lazy" portion of
 994  * determining whether or not a release sequence was contiguous, since not all
 995  * modification order information is present at the time an action occurs.
 996  *
 997  * @param location The location/object that should be checked for release
 998  * sequence resolutions
 999  * @param work_queue The work queue to which to add work items as they are
1000  * generated
1001  * @return True if any updates occurred (new synchronization, new mo_graph
1002  * edges)
1003  */
1004 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1005 {
1006         std::list<ModelAction *> *list;
1007         list = lazy_sync_with_release->getptr(location);
1008         if (!list)
1009                 return false;
1010
1011         bool updated = false;
1012         std::list<ModelAction *>::iterator it = list->begin();
1013         while (it != list->end()) {
1014                 ModelAction *act = *it;
1015                 const ModelAction *rf = act->get_reads_from();
1016                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1017                 bool complete;
1018                 complete = release_seq_head(rf, &release_heads);
1019                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1020                         if (!act->has_synchronized_with(release_heads[i])) {
1021                                 updated = true;
1022                                 act->synchronize_with(release_heads[i]);
1023                         }
1024                 }
1025
1026                 if (updated) {
1027                         /* Re-check act for mo_graph edges */
1028                         work_queue->push_back(MOEdgeWorkEntry(act));
1029
1030                         /* propagate synchronization to later actions */
1031                         action_list_t::reverse_iterator it = action_trace->rbegin();
1032                         while ((*it) != act) {
1033                                 ModelAction *propagate = *it;
1034                                 if (act->happens_before(propagate)) {
1035                                         propagate->synchronize_with(act);
1036                                         /* Re-check 'propagate' for mo_graph edges */
1037                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1038                                 }
1039                         }
1040                 }
1041                 if (complete) {
1042                         it = list->erase(it);
1043                         (*lazy_sync_size)--;
1044                 } else
1045                         it++;
1046         }
1047
1048         // If we resolved promises or data races, see if we have realized a data race.
1049         if (checkDataRaces()) {
1050                 set_assert();
1051         }
1052
1053         return updated;
1054 }
1055
1056 /**
1057  * Performs various bookkeeping operations for the current ModelAction. For
1058  * instance, adds action to the per-object, per-thread action vector and to the
1059  * action trace list of all thread actions.
1060  *
1061  * @param act is the ModelAction to add.
1062  */
1063 void ModelChecker::add_action_to_lists(ModelAction *act)
1064 {
1065         int tid = id_to_int(act->get_tid());
1066         action_trace->push_back(act);
1067
1068         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1069
1070         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1071         if (tid >= (int)vec->size())
1072                 vec->resize(priv->next_thread_id);
1073         (*vec)[tid].push_back(act);
1074
1075         if ((int)thrd_last_action->size() <= tid)
1076                 thrd_last_action->resize(get_num_threads());
1077         (*thrd_last_action)[tid] = act;
1078 }
1079
1080 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1081 {
1082         int threadid=id_to_int(tid);
1083         if (threadid<(int)thrd_last_action->size())
1084                 return (*thrd_last_action)[id_to_int(tid)];
1085         else
1086                 return NULL;
1087 }
1088
1089 /**
1090  * Gets the last memory_order_seq_cst action (in the total global sequence)
1091  * performed on a particular object (i.e., memory location).
1092  * @param location The object location to check
1093  * @return The last seq_cst action performed
1094  */
1095 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1096 {
1097         action_list_t *list = obj_map->get_safe_ptr(location);
1098         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1099         action_list_t::reverse_iterator rit;
1100         for (rit = list->rbegin(); rit != list->rend(); rit++)
1101                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1102                         return *rit;
1103         return NULL;
1104 }
1105
1106 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1107 {
1108         ModelAction *parent = get_last_action(tid);
1109         if (!parent)
1110                 parent = get_thread(tid)->get_creation();
1111         return parent;
1112 }
1113
1114 /**
1115  * Returns the clock vector for a given thread.
1116  * @param tid The thread whose clock vector we want
1117  * @return Desired clock vector
1118  */
1119 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1120 {
1121         return get_parent_action(tid)->get_cv();
1122 }
1123
1124 /**
1125  * Resolve a set of Promises with a current write. The set is provided in the
1126  * Node corresponding to @a write.
1127  * @param write The ModelAction that is fulfilling Promises
1128  * @return True if promises were resolved; false otherwise
1129  */
1130 bool ModelChecker::resolve_promises(ModelAction *write)
1131 {
1132         bool resolved = false;
1133
1134         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1135                 Promise *promise = (*promises)[promise_index];
1136                 if (write->get_node()->get_promise(i)) {
1137                         ModelAction *read = promise->get_action();
1138                         read->read_from(write);
1139                         if (read->is_rmw()) {
1140                                 mo_graph->addRMWEdge(write, read);
1141                         }
1142                         //First fix up the modification order for actions that happened
1143                         //before the read
1144                         r_modification_order(read, write);
1145                         //Next fix up the modification order for actions that happened
1146                         //after the read.
1147                         post_r_modification_order(read, write);
1148                         promises->erase(promises->begin() + promise_index);
1149                         resolved = true;
1150                 } else
1151                         promise_index++;
1152         }
1153         return resolved;
1154 }
1155
1156 /**
1157  * Compute the set of promises that could potentially be satisfied by this
1158  * action. Note that the set computation actually appears in the Node, not in
1159  * ModelChecker.
1160  * @param curr The ModelAction that may satisfy promises
1161  */
1162 void ModelChecker::compute_promises(ModelAction *curr)
1163 {
1164         for (unsigned int i = 0; i < promises->size(); i++) {
1165                 Promise *promise = (*promises)[i];
1166                 const ModelAction *act = promise->get_action();
1167                 if (!act->happens_before(curr) &&
1168                                 act->is_read() &&
1169                                 !act->is_synchronizing(curr) &&
1170                                 !act->same_thread(curr) &&
1171                                 promise->get_value() == curr->get_value()) {
1172                         curr->get_node()->set_promise(i);
1173                 }
1174         }
1175 }
1176
1177 /** Checks promises in response to change in ClockVector Threads. */
1178 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1179 {
1180         for (unsigned int i = 0; i < promises->size(); i++) {
1181                 Promise *promise = (*promises)[i];
1182                 const ModelAction *act = promise->get_action();
1183                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1184                                 merge_cv->synchronized_since(act)) {
1185                         //This thread is no longer able to send values back to satisfy the promise
1186                         int num_synchronized_threads = promise->increment_threads();
1187                         if (num_synchronized_threads == get_num_threads()) {
1188                                 //Promise has failed
1189                                 failed_promise = true;
1190                                 return;
1191                         }
1192                 }
1193         }
1194 }
1195
1196 /**
1197  * Build up an initial set of all past writes that this 'read' action may read
1198  * from. This set is determined by the clock vector's "happens before"
1199  * relationship.
1200  * @param curr is the current ModelAction that we are exploring; it must be a
1201  * 'read' operation.
1202  */
1203 void ModelChecker::build_reads_from_past(ModelAction *curr)
1204 {
1205         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1206         unsigned int i;
1207         ASSERT(curr->is_read());
1208
1209         ModelAction *last_seq_cst = NULL;
1210
1211         /* Track whether this object has been initialized */
1212         bool initialized = false;
1213
1214         if (curr->is_seqcst()) {
1215                 last_seq_cst = get_last_seq_cst(curr->get_location());
1216                 /* We have to at least see the last sequentially consistent write,
1217                          so we are initialized. */
1218                 if (last_seq_cst != NULL)
1219                         initialized = true;
1220         }
1221
1222         /* Iterate over all threads */
1223         for (i = 0; i < thrd_lists->size(); i++) {
1224                 /* Iterate over actions in thread, starting from most recent */
1225                 action_list_t *list = &(*thrd_lists)[i];
1226                 action_list_t::reverse_iterator rit;
1227                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1228                         ModelAction *act = *rit;
1229
1230                         /* Only consider 'write' actions */
1231                         if (!act->is_write())
1232                                 continue;
1233
1234                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1235                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1236                                 DEBUG("Adding action to may_read_from:\n");
1237                                 if (DBG_ENABLED()) {
1238                                         act->print();
1239                                         curr->print();
1240                                 }
1241                                 curr->get_node()->add_read_from(act);
1242                         }
1243
1244                         /* Include at most one act per-thread that "happens before" curr */
1245                         if (act->happens_before(curr)) {
1246                                 initialized = true;
1247                                 break;
1248                         }
1249                 }
1250         }
1251
1252         if (!initialized) {
1253                 /** @todo Need a more informative way of reporting errors. */
1254                 printf("ERROR: may read from uninitialized atomic\n");
1255         }
1256
1257         if (DBG_ENABLED() || !initialized) {
1258                 printf("Reached read action:\n");
1259                 curr->print();
1260                 printf("Printing may_read_from\n");
1261                 curr->get_node()->print_may_read_from();
1262                 printf("End printing may_read_from\n");
1263         }
1264
1265         ASSERT(initialized);
1266 }
1267
1268 static void print_list(action_list_t *list)
1269 {
1270         action_list_t::iterator it;
1271
1272         printf("---------------------------------------------------------------------\n");
1273         printf("Trace:\n");
1274
1275         for (it = list->begin(); it != list->end(); it++) {
1276                 (*it)->print();
1277         }
1278         printf("---------------------------------------------------------------------\n");
1279 }
1280
1281 void ModelChecker::print_summary()
1282 {
1283         printf("\n");
1284         printf("Number of executions: %d\n", num_executions);
1285         printf("Number of feasible executions: %d\n", num_feasible_executions);
1286         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1287
1288 #if SUPPORT_MOD_ORDER_DUMP
1289         scheduler->print();
1290         char buffername[100];
1291         sprintf(buffername, "exec%u",num_executions);
1292         mo_graph->dumpGraphToFile(buffername);
1293 #endif
1294
1295         if (!isfinalfeasible())
1296                 printf("INFEASIBLE EXECUTION!\n");
1297         print_list(action_trace);
1298         printf("\n");
1299 }
1300
1301 /**
1302  * Add a Thread to the system for the first time. Should only be called once
1303  * per thread.
1304  * @param t The Thread to add
1305  */
1306 void ModelChecker::add_thread(Thread *t)
1307 {
1308         thread_map->put(id_to_int(t->get_id()), t);
1309         scheduler->add_thread(t);
1310 }
1311
1312 void ModelChecker::remove_thread(Thread *t)
1313 {
1314         scheduler->remove_thread(t);
1315 }
1316
1317 /**
1318  * Switch from a user-context to the "master thread" context (a.k.a. system
1319  * context). This switch is made with the intention of exploring a particular
1320  * model-checking action (described by a ModelAction object). Must be called
1321  * from a user-thread context.
1322  * @param act The current action that will be explored. Must not be NULL.
1323  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1324  */
1325 int ModelChecker::switch_to_master(ModelAction *act)
1326 {
1327         DBG();
1328         Thread *old = thread_current();
1329         set_current_action(act);
1330         old->set_state(THREAD_READY);
1331         return Thread::swap(old, &system_context);
1332 }
1333
1334 /**
1335  * Takes the next step in the execution, if possible.
1336  * @return Returns true (success) if a step was taken and false otherwise.
1337  */
1338 bool ModelChecker::take_step() {
1339         if (has_asserted())
1340                 return false;
1341
1342         Thread * curr = thread_current();
1343         if (curr) {
1344                 if (curr->get_state() == THREAD_READY) {
1345                         ASSERT(priv->current_action);
1346
1347                         priv->nextThread = check_current_action(priv->current_action);
1348                         priv->current_action = NULL;
1349                         if (curr->is_blocked() || curr->is_complete())
1350                                 scheduler->remove_thread(curr);
1351                 } else {
1352                         ASSERT(false);
1353                 }
1354         }
1355         Thread * next = scheduler->next_thread(priv->nextThread);
1356
1357         /* Infeasible -> don't take any more steps */
1358         if (!isfeasible())
1359                 return false;
1360
1361         if (next)
1362                 next->set_state(THREAD_RUNNING);
1363         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1364
1365         /* next == NULL -> don't take any more steps */
1366         if (!next)
1367                 return false;
1368         /* Return false only if swap fails with an error */
1369         return (Thread::swap(&system_context, next) == 0);
1370 }
1371
1372 /** Runs the current execution until threre are no more steps to take. */
1373 void ModelChecker::finish_execution() {
1374         DBG();
1375
1376         while (take_step());
1377 }