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                         delete curr;
 385                         curr = tmp;
 386                 } else {
 387                         /*
 388                          * Perform one-time actions when pushing new ModelAction onto
 389                          * NodeStack
 390                          */
 391                         curr->create_cv(get_parent_action(curr->get_tid()));
 392                         /* Build may_read_from set */
 393                         if (curr->is_read())
 394                                 build_reads_from_past(curr);
 395                         if (curr->is_write())
 396                                 compute_promises(curr);
 397                 }
 398         }
 399
 400         /* Thread specific actions */
 401         switch (curr->get_type()) {
 402         case THREAD_CREATE: {
 403                 Thread *th = (Thread *)curr->get_location();
 404                 th->set_creation(curr);
 405                 break;
 406         }
 407         case THREAD_JOIN: {
 408                 Thread *waiting, *blocking;
 409                 waiting = get_thread(curr);
 410                 blocking = (Thread *)curr->get_location();
 411                 if (!blocking->is_complete()) {
 412                         blocking->push_wait_list(curr);
 413                         scheduler->sleep(waiting);
 414                 }
 415                 break;
 416         }
 417         case THREAD_FINISH: {
 418                 Thread *th = get_thread(curr);
 419                 while (!th->wait_list_empty()) {
 420                         ModelAction *act = th->pop_wait_list();
 421                         Thread *wake = get_thread(act);
 422                         scheduler->wake(wake);
 423                 }
 424                 th->complete();
 425                 break;
 426         }
 427         case THREAD_START: {
 428                 check_promises(NULL, curr->get_cv());
 429                 break;
 430         }
 431         default:
 432                 break;
 433         }
 434
 435         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 436
 437         while (!work_queue.empty()) {
 438                 WorkQueueEntry work = work_queue.front();
 439                 work_queue.pop_front();
 440
 441                 switch (work.type) {
 442                 case WORK_CHECK_CURR_ACTION: {
 443                         ModelAction *act = work.action;
 444                         bool updated = false;
 445                         if (act->is_read() && process_read(act, second_part_of_rmw))
 446                                 updated = true;
 447
 448                         if (act->is_write() && process_write(act))
 449                                 updated = true;
 450
 451                         if (updated)
 452                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 453                         break;
 454                 }
 455                 case WORK_CHECK_RELEASE_SEQ:
 456                         resolve_release_sequences(work.location, &work_queue);
 457                         break;
 458                 case WORK_CHECK_MO_EDGES:
 459                         /** @todo Perform follow-up mo_graph checks */
 460                 default:
 461                         ASSERT(false);
 462                         break;
 463                 }
 464         }
 465
 466         /* Add action to list.  */
 467         if (!second_part_of_rmw)
 468                 add_action_to_lists(curr);
 469
 470         check_curr_backtracking(curr);
 471
 472         set_backtracking(curr);
 473
 474         return get_next_thread(curr);
 475 }
 476
 477 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 478         Node *currnode = curr->get_node();
 479         Node *parnode = currnode->get_parent();
 480
 481         if ((!parnode->backtrack_empty() ||
 482                          !currnode->read_from_empty() ||
 483                          !currnode->future_value_empty() ||
 484                          !currnode->promise_empty())
 485                         && (!priv->next_backtrack ||
 486                                         *curr > *priv->next_backtrack)) {
 487                 priv->next_backtrack = curr;
 488         }
 489 }
 490
 491 bool ModelChecker::promises_expired() {
 492         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 493                 Promise *promise = (*promises)[promise_index];
 494                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 495                         return true;
 496                 }
 497         }
 498         return false;
 499 }
 500
 501 /** @returns whether the current partial trace must be a prefix of a
 502  * feasible trace. */
 503 bool ModelChecker::isfeasibleprefix() {
 504         return promises->size() == 0 && *lazy_sync_size == 0;
 505 }
 506
 507 /** @returns whether the current partial trace is feasible. */
 508 bool ModelChecker::isfeasible() {
 509         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 510 }
 511
 512 /** @returns whether the current partial trace is feasible other than
 513  * multiple RMW reading from the same store. */
 514 bool ModelChecker::isfeasibleotherthanRMW() {
 515         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 516 }
 517
 518 /** Returns whether the current completed trace is feasible. */
 519 bool ModelChecker::isfinalfeasible() {
 520         return isfeasible() && promises->size() == 0;
 521 }
 522
 523 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 524 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 525         int tid = id_to_int(act->get_tid());
 526         ModelAction *lastread = get_last_action(tid);
 527         lastread->process_rmw(act);
 528         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 529                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 530                 mo_graph->commitChanges();
 531         }
 532         return lastread;
 533 }
 534
 535 /**
 536  * Checks whether a thread has read from the same write for too many times
 537  * without seeing the effects of a later write.
 538  *
 539  * Basic idea:
 540  * 1) there must a different write that we could read from that would satisfy the modification order,
 541  * 2) we must have read from the same value in excess of maxreads times, and
 542  * 3) that other write must have been in the reads_from set for maxreads times.
 543  *
 544  * If so, we decide that the execution is no longer feasible.
 545  */
 546 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 547         if (params.maxreads != 0) {
 548                 if (curr->get_node()->get_read_from_size() <= 1)
 549                         return;
 550
 551                 //Must make sure that execution is currently feasible...  We could
 552                 //accidentally clear by rolling back
 553                 if (!isfeasible())
 554                         return;
 555
 556                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 557                 int tid = id_to_int(curr->get_tid());
 558
 559                 /* Skip checks */
 560                 if ((int)thrd_lists->size() <= tid)
 561                         return;
 562
 563                 action_list_t *list = &(*thrd_lists)[tid];
 564
 565                 action_list_t::reverse_iterator rit = list->rbegin();
 566                 /* Skip past curr */
 567                 if (already_added) {
 568                         for (; (*rit) != curr; rit++)
 569                                 ;
 570                         /* go past curr now */
 571                         rit++;
 572                 }
 573
 574                 action_list_t::reverse_iterator ritcopy = rit;
 575                 //See if we have enough reads from the same value
 576                 int count = 0;
 577                 for (; count < params.maxreads; rit++,count++) {
 578                         if (rit==list->rend())
 579                                 return;
 580                         ModelAction *act = *rit;
 581                         if (!act->is_read())
 582                                 return;
 583                         if (act->get_reads_from() != curr->get_reads_from())
 584                                 return;
 585                         if (act->get_node()->get_read_from_size() <= 1)
 586                                 return;
 587                 }
 588
 589                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 590                         //Get write
 591                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 592                         //Need a different write
 593                         if (write==curr->get_reads_from())
 594                                 continue;
 595
 596                         /* Test to see whether this is a feasible write to read from*/
 597                         mo_graph->startChanges();
 598                         r_modification_order(curr, write);
 599                         bool feasiblereadfrom = isfeasible();
 600                         mo_graph->rollbackChanges();
 601
 602                         if (!feasiblereadfrom)
 603                                 continue;
 604                         rit = ritcopy;
 605
 606                         bool feasiblewrite = true;
 607                         //new we need to see if this write works for everyone
 608
 609                         for (int loop = count; loop>0; loop--,rit++) {
 610                                 ModelAction *act=*rit;
 611                                 bool foundvalue = false;
 612                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 613                                         if (act->get_node()->get_read_from_at(i)==write) {
 614                                                 foundvalue = true;
 615                                                 break;
 616                                         }
 617                                 }
 618                                 if (!foundvalue) {
 619                                         feasiblewrite = false;
 620                                         break;
 621                                 }
 622                         }
 623                         if (feasiblewrite) {
 624                                 too_many_reads = true;
 625                                 return;
 626                         }
 627                 }
 628         }
 629 }
 630
 631 /**
 632  * Updates the mo_graph with the constraints imposed from the current
 633  * read.
 634  *
 635  * Basic idea is the following: Go through each other thread and find
 636  * the lastest action that happened before our read.  Two cases:
 637  *
 638  * (1) The action is a write => that write must either occur before
 639  * the write we read from or be the write we read from.
 640  *
 641  * (2) The action is a read => the write that that action read from
 642  * must occur before the write we read from or be the same write.
 643  *
 644  * @param curr The current action. Must be a read.
 645  * @param rf The action that curr reads from. Must be a write.
 646  * @return True if modification order edges were added; false otherwise
 647  */
 648 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 649 {
 650         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 651         unsigned int i;
 652         bool added = false;
 653         ASSERT(curr->is_read());
 654
 655         /* Iterate over all threads */
 656         for (i = 0; i < thrd_lists->size(); i++) {
 657                 /* Iterate over actions in thread, starting from most recent */
 658                 action_list_t *list = &(*thrd_lists)[i];
 659                 action_list_t::reverse_iterator rit;
 660                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 661                         ModelAction *act = *rit;
 662
 663                         /* Include at most one act per-thread that "happens before" curr */
 664                         if (act->happens_before(curr)) {
 665                                 if (act->is_write()) {
 666                                         if (rf != act && act != curr) {
 667                                                 mo_graph->addEdge(act, rf);
 668                                                 added = true;
 669                                         }
 670                                 } else {
 671                                         const ModelAction *prevreadfrom = act->get_reads_from();
 672                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 673                                                 mo_graph->addEdge(prevreadfrom, rf);
 674                                                 added = true;
 675                                         }
 676                                 }
 677
 678                                 break;
 679                         }
 680                 }
 681         }
 682
 683         return added;
 684 }
 685
 686 /** This method fixes up the modification order when we resolve a
 687  *  promises.  The basic problem is that actions that occur after the
 688  *  read curr could not property add items to the modification order
 689  *  for our read.
 690  *
 691  *  So for each thread, we find the earliest item that happens after
 692  *  the read curr.  This is the item we have to fix up with additional
 693  *  constraints.  If that action is write, we add a MO edge between
 694  *  the Action rf and that action.  If the action is a read, we add a
 695  *  MO edge between the Action rf, and whatever the read accessed.
 696  *
 697  * @param curr is the read ModelAction that we are fixing up MO edges for.
 698  * @param rf is the write ModelAction that curr reads from.
 699  *
 700  */
 701
 702 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 703 {
 704         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 705         unsigned int i;
 706         ASSERT(curr->is_read());
 707
 708         /* Iterate over all threads */
 709         for (i = 0; i < thrd_lists->size(); i++) {
 710                 /* Iterate over actions in thread, starting from most recent */
 711                 action_list_t *list = &(*thrd_lists)[i];
 712                 action_list_t::reverse_iterator rit;
 713                 ModelAction *lastact = NULL;
 714
 715                 /* Find last action that happens after curr */
 716                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 717                         ModelAction *act = *rit;
 718                         if (curr->happens_before(act)) {
 719                                 lastact = act;
 720                         } else
 721                                 break;
 722                 }
 723
 724                         /* Include at most one act per-thread that "happens before" curr */
 725                 if (lastact != NULL) {
 726                         if (lastact->is_read()) {
 727                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 728                                 if (postreadfrom != NULL&&rf != postreadfrom)
 729                                         mo_graph->addEdge(rf, postreadfrom);
 730                         } else if (rf != lastact) {
 731                                 mo_graph->addEdge(rf, lastact);
 732                         }
 733                         break;
 734                 }
 735         }
 736 }
 737
 738 /**
 739  * Updates the mo_graph with the constraints imposed from the current write.
 740  *
 741  * Basic idea is the following: Go through each other thread and find
 742  * the lastest action that happened before our write.  Two cases:
 743  *
 744  * (1) The action is a write => that write must occur before
 745  * the current write
 746  *
 747  * (2) The action is a read => the write that that action read from
 748  * must occur before the current write.
 749  *
 750  * This method also handles two other issues:
 751  *
 752  * (I) Sequential Consistency: Making sure that if the current write is
 753  * seq_cst, that it occurs after the previous seq_cst write.
 754  *
 755  * (II) Sending the write back to non-synchronizing reads.
 756  *
 757  * @param curr The current action. Must be a write.
 758  * @return True if modification order edges were added; false otherwise
 759  */
 760 bool ModelChecker::w_modification_order(ModelAction *curr)
 761 {
 762         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 763         unsigned int i;
 764         bool added = false;
 765         ASSERT(curr->is_write());
 766
 767         if (curr->is_seqcst()) {
 768                 /* We have to at least see the last sequentially consistent write,
 769                          so we are initialized. */
 770                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 771                 if (last_seq_cst != NULL) {
 772                         mo_graph->addEdge(last_seq_cst, curr);
 773                         added = true;
 774                 }
 775         }
 776
 777         /* Iterate over all threads */
 778         for (i = 0; i < thrd_lists->size(); i++) {
 779                 /* Iterate over actions in thread, starting from most recent */
 780                 action_list_t *list = &(*thrd_lists)[i];
 781                 action_list_t::reverse_iterator rit;
 782                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 783                         ModelAction *act = *rit;
 784
 785                         /* Include at most one act per-thread that "happens before" curr */
 786                         if (act->happens_before(curr)) {
 787                                 /*
 788                                  * Note: if act is RMW, just add edge:
 789                                  *   act --mo--> curr
 790                                  * The following edge should be handled elsewhere:
 791                                  *   readfrom(act) --mo--> act
 792                                  */
 793                                 if (act->is_write()) {
 794                                         //RMW shouldn't have an edge to themselves
 795                                         if (act!=curr)
 796                                                 mo_graph->addEdge(act, curr);
 797                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 798                                         mo_graph->addEdge(act->get_reads_from(), curr);
 799                                 added = true;
 800                                 break;
 801                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 802                                                      !act->same_thread(curr)) {
 803                                 /* We have an action that:
 804                                    (1) did not happen before us
 805                                    (2) is a read and we are a write
 806                                    (3) cannot synchronize with us
 807                                    (4) is in a different thread
 808                                    =>
 809                                    that read could potentially read from our write.
 810                                  */
 811                                 if (thin_air_constraint_may_allow(curr, act)) {
 812                                         if (isfeasible() ||
 813                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 814                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 815                                                 futurevalues->push_back(pfv);
 816                                         }
 817                                 }
 818                         }
 819                 }
 820         }
 821
 822         return added;
 823 }
 824
 825 /** Arbitrary reads from the future are not allowed.  Section 29.3
 826  * part 9 places some constraints.  This method checks one result of constraint
 827  * constraint.  Others require compiler support. */
 828
 829 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 830         if (!writer->is_rmw())
 831                 return true;
 832
 833         if (!reader->is_rmw())
 834                 return true;
 835
 836         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 837                 if (search==reader)
 838                         return false;
 839                 if (search->get_tid() == reader->get_tid() &&
 840                                 search->happens_before(reader))
 841                         break;
 842         }
 843
 844         return true;
 845 }
 846
 847 /**
 848  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 849  * The ModelAction under consideration is expected to be taking part in
 850  * release/acquire synchronization as an object of the "reads from" relation.
 851  * Note that this can only provide release sequence support for RMW chains
 852  * which do not read from the future, as those actions cannot be traced until
 853  * their "promise" is fulfilled. Similarly, we may not even establish the
 854  * presence of a release sequence with certainty, as some modification order
 855  * constraints may be decided further in the future. Thus, this function
 856  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 857  * and a boolean representing certainty.
 858  *
 859  * @todo Finish lazy updating, when promises are fulfilled in the future
 860  * @param rf The action that might be part of a release sequence. Must be a
 861  * write.
 862  * @param release_heads A pass-by-reference style return parameter.  After
 863  * execution of this function, release_heads will contain the heads of all the
 864  * relevant release sequences, if any exists
 865  * @return true, if the ModelChecker is certain that release_heads is complete;
 866  * false otherwise
 867  */
 868 bool ModelChecker::release_seq_head(const ModelAction *rf,
 869                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 870 {
 871         if (!rf) {
 872                 /* read from future: need to settle this later */
 873                 return false; /* incomplete */
 874         }
 875
 876         ASSERT(rf->is_write());
 877
 878         if (rf->is_release())
 879                 release_heads->push_back(rf);
 880         if (rf->is_rmw()) {
 881                 /* We need a RMW action that is both an acquire and release to stop */
 882                 /** @todo Need to be smarter here...  In the linux lock
 883                  * example, this will run to the beginning of the program for
 884                  * every acquire. */
 885                 if (rf->is_acquire() && rf->is_release())
 886                         return true; /* complete */
 887                 return release_seq_head(rf->get_reads_from(), release_heads);
 888         }
 889         if (rf->is_release())
 890                 return true; /* complete */
 891
 892         /* else relaxed write; check modification order for contiguous subsequence
 893          * -> rf must be same thread as release */
 894         int tid = id_to_int(rf->get_tid());
 895         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 896         action_list_t *list = &(*thrd_lists)[tid];
 897         action_list_t::const_reverse_iterator rit;
 898
 899         /* Find rf in the thread list */
 900         rit = std::find(list->rbegin(), list->rend(), rf);
 901         ASSERT(rit != list->rend());
 902
 903         /* Find the last write/release */
 904         for (; rit != list->rend(); rit++)
 905                 if ((*rit)->is_release())
 906                         break;
 907         if (rit == list->rend()) {
 908                 /* No write-release in this thread */
 909                 return true; /* complete */
 910         }
 911         ModelAction *release = *rit;
 912
 913         ASSERT(rf->same_thread(release));
 914
 915         bool certain = true;
 916         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 917                 if (id_to_int(rf->get_tid()) == (int)i)
 918                         continue;
 919                 list = &(*thrd_lists)[i];
 920
 921                 /* Can we ensure no future writes from this thread may break
 922                  * the release seq? */
 923                 bool future_ordered = false;
 924
 925                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 926                         const ModelAction *act = *rit;
 927                         if (!act->is_write())
 928                                 continue;
 929                         /* Reach synchronization -> this thread is complete */
 930                         if (act->happens_before(release))
 931                                 break;
 932                         if (rf->happens_before(act)) {
 933                                 future_ordered = true;
 934                                 continue;
 935                         }
 936
 937                         /* Check modification order */
 938                         if (mo_graph->checkReachable(rf, act)) {
 939                                 /* rf --mo--> act */
 940                                 future_ordered = true;
 941                                 continue;
 942                         }
 943                         if (mo_graph->checkReachable(act, release))
 944                                 /* act --mo--> release */
 945                                 break;
 946                         if (mo_graph->checkReachable(release, act) &&
 947                                       mo_graph->checkReachable(act, rf)) {
 948                                 /* release --mo-> act --mo--> rf */
 949                                 return true; /* complete */
 950                         }
 951                         certain = false;
 952                 }
 953                 if (!future_ordered)
 954                         return false; /* This thread is uncertain */
 955         }
 956
 957         if (certain)
 958                 release_heads->push_back(release);
 959         return certain;
 960 }
 961
 962 /**
 963  * A public interface for getting the release sequence head(s) with which a
 964  * given ModelAction must synchronize. This function only returns a non-empty
 965  * result when it can locate a release sequence head with certainty. Otherwise,
 966  * it may mark the internal state of the ModelChecker so that it will handle
 967  * the release sequence at a later time, causing @a act to update its
 968  * synchronization at some later point in execution.
 969  * @param act The 'acquire' action that may read from a release sequence
 970  * @param release_heads A pass-by-reference return parameter. Will be filled
 971  * with the head(s) of the release sequence(s), if they exists with certainty.
 972  * @see ModelChecker::release_seq_head
 973  */
 974 void ModelChecker::get_release_seq_heads(ModelAction *act,
 975                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 976 {
 977         const ModelAction *rf = act->get_reads_from();
 978         bool complete;
 979         complete = release_seq_head(rf, release_heads);
 980         if (!complete) {
 981                 /* add act to 'lazy checking' list */
 982                 std::list<ModelAction *> *list;
 983                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 984                 list->push_back(act);
 985                 (*lazy_sync_size)++;
 986         }
 987 }
 988
 989 /**
 990  * Attempt to resolve all stashed operations that might synchronize with a
 991  * release sequence for a given location. This implements the "lazy" portion of
 992  * determining whether or not a release sequence was contiguous, since not all
 993  * modification order information is present at the time an action occurs.
 994  *
 995  * @param location The location/object that should be checked for release
 996  * sequence resolutions
 997  * @param work_queue The work queue to which to add work items as they are
 998  * generated
 999  * @return True if any updates occurred (new synchronization, new mo_graph
1000  * edges)
1001  */
1002 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1003 {
1004         std::list<ModelAction *> *list;
1005         list = lazy_sync_with_release->getptr(location);
1006         if (!list)
1007                 return false;
1008
1009         bool updated = false;
1010         std::list<ModelAction *>::iterator it = list->begin();
1011         while (it != list->end()) {
1012                 ModelAction *act = *it;
1013                 const ModelAction *rf = act->get_reads_from();
1014                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1015                 bool complete;
1016                 complete = release_seq_head(rf, &release_heads);
1017                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1018                         if (!act->has_synchronized_with(release_heads[i])) {
1019                                 updated = true;
1020                                 act->synchronize_with(release_heads[i]);
1021                         }
1022                 }
1023
1024                 if (updated) {
1025                         /* Re-check act for mo_graph edges */
1026                         work_queue->push_back(MOEdgeWorkEntry(act));
1027
1028                         /* propagate synchronization to later actions */
1029                         action_list_t::reverse_iterator it = action_trace->rbegin();
1030                         while ((*it) != act) {
1031                                 ModelAction *propagate = *it;
1032                                 if (act->happens_before(propagate)) {
1033                                         propagate->synchronize_with(act);
1034                                         /* Re-check 'propagate' for mo_graph edges */
1035                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1036                                 }
1037                         }
1038                 }
1039                 if (complete) {
1040                         it = list->erase(it);
1041                         (*lazy_sync_size)--;
1042                 } else
1043                         it++;
1044         }
1045
1046         // If we resolved promises or data races, see if we have realized a data race.
1047         if (checkDataRaces()) {
1048                 set_assert();
1049         }
1050
1051         return updated;
1052 }
1053
1054 /**
1055  * Performs various bookkeeping operations for the current ModelAction. For
1056  * instance, adds action to the per-object, per-thread action vector and to the
1057  * action trace list of all thread actions.
1058  *
1059  * @param act is the ModelAction to add.
1060  */
1061 void ModelChecker::add_action_to_lists(ModelAction *act)
1062 {
1063         int tid = id_to_int(act->get_tid());
1064         action_trace->push_back(act);
1065
1066         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1067
1068         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1069         if (tid >= (int)vec->size())
1070                 vec->resize(priv->next_thread_id);
1071         (*vec)[tid].push_back(act);
1072
1073         if ((int)thrd_last_action->size() <= tid)
1074                 thrd_last_action->resize(get_num_threads());
1075         (*thrd_last_action)[tid] = act;
1076 }
1077
1078 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1079 {
1080         int nthreads = get_num_threads();
1081         if ((int)thrd_last_action->size() < nthreads)
1082                 thrd_last_action->resize(nthreads);
1083         return (*thrd_last_action)[id_to_int(tid)];
1084 }
1085
1086 /**
1087  * Gets the last memory_order_seq_cst action (in the total global sequence)
1088  * performed on a particular object (i.e., memory location).
1089  * @param location The object location to check
1090  * @return The last seq_cst action performed
1091  */
1092 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1093 {
1094         action_list_t *list = obj_map->get_safe_ptr(location);
1095         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1096         action_list_t::reverse_iterator rit;
1097         for (rit = list->rbegin(); rit != list->rend(); rit++)
1098                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1099                         return *rit;
1100         return NULL;
1101 }
1102
1103 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1104 {
1105         ModelAction *parent = get_last_action(tid);
1106         if (!parent)
1107                 parent = get_thread(tid)->get_creation();
1108         return parent;
1109 }
1110
1111 /**
1112  * Returns the clock vector for a given thread.
1113  * @param tid The thread whose clock vector we want
1114  * @return Desired clock vector
1115  */
1116 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1117 {
1118         return get_parent_action(tid)->get_cv();
1119 }
1120
1121 /**
1122  * Resolve a set of Promises with a current write. The set is provided in the
1123  * Node corresponding to @a write.
1124  * @param write The ModelAction that is fulfilling Promises
1125  * @return True if promises were resolved; false otherwise
1126  */
1127 bool ModelChecker::resolve_promises(ModelAction *write)
1128 {
1129         bool resolved = false;
1130
1131         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1132                 Promise *promise = (*promises)[promise_index];
1133                 if (write->get_node()->get_promise(i)) {
1134                         ModelAction *read = promise->get_action();
1135                         read->read_from(write);
1136                         if (read->is_rmw()) {
1137                                 mo_graph->addRMWEdge(write, read);
1138                         }
1139                         //First fix up the modification order for actions that happened
1140                         //before the read
1141                         r_modification_order(read, write);
1142                         //Next fix up the modification order for actions that happened
1143                         //after the read.
1144                         post_r_modification_order(read, write);
1145                         promises->erase(promises->begin() + promise_index);
1146                         resolved = true;
1147                 } else
1148                         promise_index++;
1149         }
1150         return resolved;
1151 }
1152
1153 /**
1154  * Compute the set of promises that could potentially be satisfied by this
1155  * action. Note that the set computation actually appears in the Node, not in
1156  * ModelChecker.
1157  * @param curr The ModelAction that may satisfy promises
1158  */
1159 void ModelChecker::compute_promises(ModelAction *curr)
1160 {
1161         for (unsigned int i = 0; i < promises->size(); i++) {
1162                 Promise *promise = (*promises)[i];
1163                 const ModelAction *act = promise->get_action();
1164                 if (!act->happens_before(curr) &&
1165                                 act->is_read() &&
1166                                 !act->is_synchronizing(curr) &&
1167                                 !act->same_thread(curr) &&
1168                                 promise->get_value() == curr->get_value()) {
1169                         curr->get_node()->set_promise(i);
1170                 }
1171         }
1172 }
1173
1174 /** Checks promises in response to change in ClockVector Threads. */
1175 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1176 {
1177         for (unsigned int i = 0; i < promises->size(); i++) {
1178                 Promise *promise = (*promises)[i];
1179                 const ModelAction *act = promise->get_action();
1180                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1181                                 merge_cv->synchronized_since(act)) {
1182                         //This thread is no longer able to send values back to satisfy the promise
1183                         int num_synchronized_threads = promise->increment_threads();
1184                         if (num_synchronized_threads == get_num_threads()) {
1185                                 //Promise has failed
1186                                 failed_promise = true;
1187                                 return;
1188                         }
1189                 }
1190         }
1191 }
1192
1193 /**
1194  * Build up an initial set of all past writes that this 'read' action may read
1195  * from. This set is determined by the clock vector's "happens before"
1196  * relationship.
1197  * @param curr is the current ModelAction that we are exploring; it must be a
1198  * 'read' operation.
1199  */
1200 void ModelChecker::build_reads_from_past(ModelAction *curr)
1201 {
1202         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1203         unsigned int i;
1204         ASSERT(curr->is_read());
1205
1206         ModelAction *last_seq_cst = NULL;
1207
1208         /* Track whether this object has been initialized */
1209         bool initialized = false;
1210
1211         if (curr->is_seqcst()) {
1212                 last_seq_cst = get_last_seq_cst(curr->get_location());
1213                 /* We have to at least see the last sequentially consistent write,
1214                          so we are initialized. */
1215                 if (last_seq_cst != NULL)
1216                         initialized = true;
1217         }
1218
1219         /* Iterate over all threads */
1220         for (i = 0; i < thrd_lists->size(); i++) {
1221                 /* Iterate over actions in thread, starting from most recent */
1222                 action_list_t *list = &(*thrd_lists)[i];
1223                 action_list_t::reverse_iterator rit;
1224                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1225                         ModelAction *act = *rit;
1226
1227                         /* Only consider 'write' actions */
1228                         if (!act->is_write())
1229                                 continue;
1230
1231                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1232                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1233                                 DEBUG("Adding action to may_read_from:\n");
1234                                 if (DBG_ENABLED()) {
1235                                         act->print();
1236                                         curr->print();
1237                                 }
1238                                 curr->get_node()->add_read_from(act);
1239                         }
1240
1241                         /* Include at most one act per-thread that "happens before" curr */
1242                         if (act->happens_before(curr)) {
1243                                 initialized = true;
1244                                 break;
1245                         }
1246                 }
1247         }
1248
1249         if (!initialized) {
1250                 /** @todo Need a more informative way of reporting errors. */
1251                 printf("ERROR: may read from uninitialized atomic\n");
1252         }
1253
1254         if (DBG_ENABLED() || !initialized) {
1255                 printf("Reached read action:\n");
1256                 curr->print();
1257                 printf("Printing may_read_from\n");
1258                 curr->get_node()->print_may_read_from();
1259                 printf("End printing may_read_from\n");
1260         }
1261
1262         ASSERT(initialized);
1263 }
1264
1265 static void print_list(action_list_t *list)
1266 {
1267         action_list_t::iterator it;
1268
1269         printf("---------------------------------------------------------------------\n");
1270         printf("Trace:\n");
1271
1272         for (it = list->begin(); it != list->end(); it++) {
1273                 (*it)->print();
1274         }
1275         printf("---------------------------------------------------------------------\n");
1276 }
1277
1278 void ModelChecker::print_summary()
1279 {
1280         printf("\n");
1281         printf("Number of executions: %d\n", num_executions);
1282         printf("Number of feasible executions: %d\n", num_feasible_executions);
1283         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1284
1285 #if SUPPORT_MOD_ORDER_DUMP
1286         scheduler->print();
1287         char buffername[100];
1288         sprintf(buffername, "exec%u",num_executions);
1289         mo_graph->dumpGraphToFile(buffername);
1290 #endif
1291
1292         if (!isfinalfeasible())
1293                 printf("INFEASIBLE EXECUTION!\n");
1294         print_list(action_trace);
1295         printf("\n");
1296 }
1297
1298 /**
1299  * Add a Thread to the system for the first time. Should only be called once
1300  * per thread.
1301  * @param t The Thread to add
1302  */
1303 void ModelChecker::add_thread(Thread *t)
1304 {
1305         thread_map->put(id_to_int(t->get_id()), t);
1306         scheduler->add_thread(t);
1307 }
1308
1309 void ModelChecker::remove_thread(Thread *t)
1310 {
1311         scheduler->remove_thread(t);
1312 }
1313
1314 /**
1315  * Switch from a user-context to the "master thread" context (a.k.a. system
1316  * context). This switch is made with the intention of exploring a particular
1317  * model-checking action (described by a ModelAction object). Must be called
1318  * from a user-thread context.
1319  * @param act The current action that will be explored. Must not be NULL.
1320  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1321  */
1322 int ModelChecker::switch_to_master(ModelAction *act)
1323 {
1324         DBG();
1325         Thread *old = thread_current();
1326         set_current_action(act);
1327         old->set_state(THREAD_READY);
1328         return Thread::swap(old, &system_context);
1329 }
1330
1331 /**
1332  * Takes the next step in the execution, if possible.
1333  * @return Returns true (success) if a step was taken and false otherwise.
1334  */
1335 bool ModelChecker::take_step() {
1336         if (has_asserted())
1337                 return false;
1338
1339         Thread * curr = thread_current();
1340         if (curr) {
1341                 if (curr->get_state() == THREAD_READY) {
1342                         ASSERT(priv->current_action);
1343
1344                         priv->nextThread = check_current_action(priv->current_action);
1345                         priv->current_action = NULL;
1346                         if (curr->is_blocked() || curr->is_complete())
1347                                 scheduler->remove_thread(curr);
1348                 } else {
1349                         ASSERT(false);
1350                 }
1351         }
1352         Thread * next = scheduler->next_thread(priv->nextThread);
1353
1354         /* Infeasible -> don't take any more steps */
1355         if (!isfeasible())
1356                 return false;
1357
1358         if (next)
1359                 next->set_state(THREAD_RUNNING);
1360         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1361
1362         /* next == NULL -> don't take any more steps */
1363         if (!next)
1364                 return false;
1365         /* Return false only if swap fails with an error */
1366         return (Thread::swap(&system_context, next) == 0);
1367 }
1368
1369 /** Runs the current execution until threre are no more steps to take. */
1370 void ModelChecker::finish_execution() {
1371         DBG();
1372
1373         while (take_step());
1374 }