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         switch (type) {
 201                 case ATOMIC_READ:
 202                 case ATOMIC_WRITE:
 203                 case ATOMIC_RMW:
 204                         break;
 205                 default:
 206                         return NULL;
 207         }
 208         /* linear search: from most recent to oldest */
 209         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 210         action_list_t::reverse_iterator rit;
 211         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 212                 ModelAction *prev = *rit;
 213                 if (act->is_synchronizing(prev))
 214                         return prev;
 215         }
 216         return NULL;
 217 }
 218
 219 void ModelChecker::set_backtracking(ModelAction *act)
 220 {
 221         ModelAction *prev;
 222         Node *node;
 223         Thread *t = get_thread(act);
 224
 225         prev = get_last_conflict(act);
 226         if (prev == NULL)
 227                 return;
 228
 229         node = prev->get_node()->get_parent();
 230
 231         while (!node->is_enabled(t))
 232                 t = t->get_parent();
 233
 234         /* Check if this has been explored already */
 235         if (node->has_been_explored(t->get_id()))
 236                 return;
 237
 238         /* Cache the latest backtracking point */
 239         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 240                 priv->next_backtrack = prev;
 241
 242         /* If this is a new backtracking point, mark the tree */
 243         if (!node->set_backtrack(t->get_id()))
 244                 return;
 245         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 246                         prev->get_tid(), t->get_id());
 247         if (DBG_ENABLED()) {
 248                 prev->print();
 249                 act->print();
 250         }
 251 }
 252
 253 /**
 254  * Returns last backtracking point. The model checker will explore a different
 255  * path for this point in the next execution.
 256  * @return The ModelAction at which the next execution should diverge.
 257  */
 258 ModelAction * ModelChecker::get_next_backtrack()
 259 {
 260         ModelAction *next = priv->next_backtrack;
 261         priv->next_backtrack = NULL;
 262         return next;
 263 }
 264
 265 /**
 266  * Processes a read or rmw model action.
 267  * @param curr is the read model action to process.
 268  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 269  * @return True if processing this read updates the mo_graph.
 270  */
 271 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 272 {
 273         uint64_t value;
 274         bool updated = false;
 275         while (true) {
 276                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 277                 if (reads_from != NULL) {
 278                         mo_graph->startChanges();
 279
 280                         value = reads_from->get_value();
 281                         bool r_status = false;
 282
 283                         if (!second_part_of_rmw) {
 284                                 check_recency(curr);
 285                                 r_status = r_modification_order(curr, reads_from);
 286                         }
 287
 288
 289                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 290                                 mo_graph->rollbackChanges();
 291                                 too_many_reads = false;
 292                                 continue;
 293                         }
 294
 295                         curr->read_from(reads_from);
 296                         mo_graph->commitChanges();
 297                         updated |= r_status;
 298                 } else if (!second_part_of_rmw) {
 299                         /* Read from future value */
 300                         value = curr->get_node()->get_future_value();
 301                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 302                         curr->read_from(NULL);
 303                         Promise *valuepromise = new Promise(curr, value, expiration);
 304                         promises->push_back(valuepromise);
 305                 }
 306                 get_thread(curr)->set_return_value(value);
 307                 return updated;
 308         }
 309 }
 310
 311 /**
 312  * Process a write ModelAction
 313  * @param curr The ModelAction to process
 314  * @return True if the mo_graph was updated or promises were resolved
 315  */
 316 bool ModelChecker::process_write(ModelAction *curr)
 317 {
 318         bool updated_mod_order = w_modification_order(curr);
 319         bool updated_promises = resolve_promises(curr);
 320
 321         if (promises->size() == 0) {
 322                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 323                         struct PendingFutureValue pfv = (*futurevalues)[i];
 324                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 325                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 326                                 priv->next_backtrack = pfv.act;
 327                 }
 328                 futurevalues->resize(0);
 329         }
 330
 331         mo_graph->commitChanges();
 332         get_thread(curr)->set_return_value(VALUE_NONE);
 333         return updated_mod_order || updated_promises;
 334 }
 335
 336 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 337 {
 338         if (curr->is_rmwc() || curr->is_rmw()) {
 339                 ModelAction *tmp = process_rmw(curr);
 340                 delete curr;
 341                 curr = tmp;
 342                 compute_promises(curr);
 343         } else {
 344                 ModelAction *tmp = node_stack->explore_action(curr);
 345                 if (tmp) {
 346                         /* Discard duplicate ModelAction; use action from NodeStack */
 347                         /* First restore type and order in case of RMW operation */
 348                         if (curr->is_rmwr())
 349                                 tmp->copy_typeandorder(curr);
 350
 351                         /* If we have diverged, we need to reset the clock vector. */
 352                         if (diverge == NULL)
 353                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 354
 355                         delete curr;
 356                         curr = tmp;
 357                 } else {
 358                         /*
 359                          * Perform one-time actions when pushing new ModelAction onto
 360                          * NodeStack
 361                          */
 362                         curr->create_cv(get_parent_action(curr->get_tid()));
 363                         /* Build may_read_from set */
 364                         if (curr->is_read())
 365                                 build_reads_from_past(curr);
 366                         if (curr->is_write())
 367                                 compute_promises(curr);
 368                 }
 369         }
 370         return curr;
 371 }
 372
 373 /**
 374  * This is the heart of the model checker routine. It performs model-checking
 375  * actions corresponding to a given "current action." Among other processes, it
 376  * calculates reads-from relationships, updates synchronization clock vectors,
 377  * forms a memory_order constraints graph, and handles replay/backtrack
 378  * execution when running permutations of previously-observed executions.
 379  *
 380  * @param curr The current action to process
 381  * @return The next Thread that must be executed. May be NULL if ModelChecker
 382  * makes no choice (e.g., according to replay execution, combining RMW actions,
 383  * etc.)
 384  */
 385 Thread * ModelChecker::check_current_action(ModelAction *curr)
 386 {
 387         ASSERT(curr);
 388
 389         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 390
 391         curr = initialize_curr_action(curr);
 392
 393         /* Thread specific actions */
 394         switch (curr->get_type()) {
 395         case THREAD_CREATE: {
 396                 Thread *th = (Thread *)curr->get_location();
 397                 th->set_creation(curr);
 398                 break;
 399         }
 400         case THREAD_JOIN: {
 401                 Thread *waiting, *blocking;
 402                 waiting = get_thread(curr);
 403                 blocking = (Thread *)curr->get_location();
 404                 if (!blocking->is_complete()) {
 405                         blocking->push_wait_list(curr);
 406                         scheduler->sleep(waiting);
 407                 }
 408                 break;
 409         }
 410         case THREAD_FINISH: {
 411                 Thread *th = get_thread(curr);
 412                 while (!th->wait_list_empty()) {
 413                         ModelAction *act = th->pop_wait_list();
 414                         Thread *wake = get_thread(act);
 415                         scheduler->wake(wake);
 416                 }
 417                 th->complete();
 418                 break;
 419         }
 420         case THREAD_START: {
 421                 check_promises(NULL, curr->get_cv());
 422                 break;
 423         }
 424         default:
 425                 break;
 426         }
 427
 428         /* Add current action to lists before work_queue loop */
 429         if (!second_part_of_rmw)
 430                 add_action_to_lists(curr);
 431
 432         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 433
 434         while (!work_queue.empty()) {
 435                 WorkQueueEntry work = work_queue.front();
 436                 work_queue.pop_front();
 437
 438                 switch (work.type) {
 439                 case WORK_CHECK_CURR_ACTION: {
 440                         ModelAction *act = work.action;
 441                         bool updated = false;
 442                         if (act->is_read() && process_read(act, second_part_of_rmw))
 443                                 updated = true;
 444
 445                         if (act->is_write() && process_write(act))
 446                                 updated = true;
 447
 448                         if (updated)
 449                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 450                         break;
 451                 }
 452                 case WORK_CHECK_RELEASE_SEQ:
 453                         resolve_release_sequences(work.location, &work_queue);
 454                         break;
 455                 case WORK_CHECK_MO_EDGES: {
 456                         /** @todo Complete verification of work_queue */
 457                         ModelAction *act = work.action;
 458                         bool updated = false;
 459
 460                         if (act->is_read()) {
 461                                 if (r_modification_order(act, act->get_reads_from()))
 462                                         updated = true;
 463                         }
 464                         if (act->is_write()) {
 465                                 if (w_modification_order(act))
 466                                         updated = true;
 467                         }
 468
 469                         if (updated)
 470                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 471                         break;
 472                 }
 473                 default:
 474                         ASSERT(false);
 475                         break;
 476                 }
 477         }
 478
 479         check_curr_backtracking(curr);
 480
 481         set_backtracking(curr);
 482
 483         return get_next_thread(curr);
 484 }
 485
 486 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 487         Node *currnode = curr->get_node();
 488         Node *parnode = currnode->get_parent();
 489
 490         if ((!parnode->backtrack_empty() ||
 491                          !currnode->read_from_empty() ||
 492                          !currnode->future_value_empty() ||
 493                          !currnode->promise_empty())
 494                         && (!priv->next_backtrack ||
 495                                         *curr > *priv->next_backtrack)) {
 496                 priv->next_backtrack = curr;
 497         }
 498 }
 499
 500 bool ModelChecker::promises_expired() {
 501         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 502                 Promise *promise = (*promises)[promise_index];
 503                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 504                         return true;
 505                 }
 506         }
 507         return false;
 508 }
 509
 510 /** @returns whether the current partial trace must be a prefix of a
 511  * feasible trace. */
 512 bool ModelChecker::isfeasibleprefix() {
 513         return promises->size() == 0 && *lazy_sync_size == 0;
 514 }
 515
 516 /** @returns whether the current partial trace is feasible. */
 517 bool ModelChecker::isfeasible() {
 518         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 519 }
 520
 521 /** @returns whether the current partial trace is feasible other than
 522  * multiple RMW reading from the same store. */
 523 bool ModelChecker::isfeasibleotherthanRMW() {
 524         if (DBG_ENABLED()) {
 525                 if (mo_graph->checkForCycles())
 526                         DEBUG("Infeasible: modification order cycles\n");
 527                 if (failed_promise)
 528                         DEBUG("Infeasible: failed promise\n");
 529                 if (too_many_reads)
 530                         DEBUG("Infeasible: too many reads\n");
 531                 if (promises_expired())
 532                         DEBUG("Infeasible: promises expired\n");
 533         }
 534         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 535 }
 536
 537 /** Returns whether the current completed trace is feasible. */
 538 bool ModelChecker::isfinalfeasible() {
 539         if (DBG_ENABLED() && promises->size() != 0)
 540                 DEBUG("Infeasible: unrevolved promises\n");
 541
 542         return isfeasible() && promises->size() == 0;
 543 }
 544
 545 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 546 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 547         int tid = id_to_int(act->get_tid());
 548         ModelAction *lastread = get_last_action(tid);
 549         lastread->process_rmw(act);
 550         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 551                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 552                 mo_graph->commitChanges();
 553         }
 554         return lastread;
 555 }
 556
 557 /**
 558  * Checks whether a thread has read from the same write for too many times
 559  * without seeing the effects of a later write.
 560  *
 561  * Basic idea:
 562  * 1) there must a different write that we could read from that would satisfy the modification order,
 563  * 2) we must have read from the same value in excess of maxreads times, and
 564  * 3) that other write must have been in the reads_from set for maxreads times.
 565  *
 566  * If so, we decide that the execution is no longer feasible.
 567  */
 568 void ModelChecker::check_recency(ModelAction *curr) {
 569         if (params.maxreads != 0) {
 570                 if (curr->get_node()->get_read_from_size() <= 1)
 571                         return;
 572
 573                 //Must make sure that execution is currently feasible...  We could
 574                 //accidentally clear by rolling back
 575                 if (!isfeasible())
 576                         return;
 577
 578                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 579                 int tid = id_to_int(curr->get_tid());
 580
 581                 /* Skip checks */
 582                 if ((int)thrd_lists->size() <= tid)
 583                         return;
 584
 585                 action_list_t *list = &(*thrd_lists)[tid];
 586
 587                 action_list_t::reverse_iterator rit = list->rbegin();
 588                 /* Skip past curr */
 589                 for (; (*rit) != curr; rit++)
 590                         ;
 591                 /* go past curr now */
 592                 rit++;
 593
 594                 action_list_t::reverse_iterator ritcopy = rit;
 595                 //See if we have enough reads from the same value
 596                 int count = 0;
 597                 for (; count < params.maxreads; rit++,count++) {
 598                         if (rit==list->rend())
 599                                 return;
 600                         ModelAction *act = *rit;
 601                         if (!act->is_read())
 602                                 return;
 603                         if (act->get_reads_from() != curr->get_reads_from())
 604                                 return;
 605                         if (act->get_node()->get_read_from_size() <= 1)
 606                                 return;
 607                 }
 608
 609                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 610                         //Get write
 611                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 612                         //Need a different write
 613                         if (write==curr->get_reads_from())
 614                                 continue;
 615
 616                         /* Test to see whether this is a feasible write to read from*/
 617                         mo_graph->startChanges();
 618                         r_modification_order(curr, write);
 619                         bool feasiblereadfrom = isfeasible();
 620                         mo_graph->rollbackChanges();
 621
 622                         if (!feasiblereadfrom)
 623                                 continue;
 624                         rit = ritcopy;
 625
 626                         bool feasiblewrite = true;
 627                         //new we need to see if this write works for everyone
 628
 629                         for (int loop = count; loop>0; loop--,rit++) {
 630                                 ModelAction *act=*rit;
 631                                 bool foundvalue = false;
 632                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 633                                         if (act->get_node()->get_read_from_at(i)==write) {
 634                                                 foundvalue = true;
 635                                                 break;
 636                                         }
 637                                 }
 638                                 if (!foundvalue) {
 639                                         feasiblewrite = false;
 640                                         break;
 641                                 }
 642                         }
 643                         if (feasiblewrite) {
 644                                 too_many_reads = true;
 645                                 return;
 646                         }
 647                 }
 648         }
 649 }
 650
 651 /**
 652  * Updates the mo_graph with the constraints imposed from the current
 653  * read.
 654  *
 655  * Basic idea is the following: Go through each other thread and find
 656  * the lastest action that happened before our read.  Two cases:
 657  *
 658  * (1) The action is a write => that write must either occur before
 659  * the write we read from or be the write we read from.
 660  *
 661  * (2) The action is a read => the write that that action read from
 662  * must occur before the write we read from or be the same write.
 663  *
 664  * @param curr The current action. Must be a read.
 665  * @param rf The action that curr reads from. Must be a write.
 666  * @return True if modification order edges were added; false otherwise
 667  */
 668 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 669 {
 670         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 671         unsigned int i;
 672         bool added = false;
 673         ASSERT(curr->is_read());
 674
 675         /* Iterate over all threads */
 676         for (i = 0; i < thrd_lists->size(); i++) {
 677                 /* Iterate over actions in thread, starting from most recent */
 678                 action_list_t *list = &(*thrd_lists)[i];
 679                 action_list_t::reverse_iterator rit;
 680                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 681                         ModelAction *act = *rit;
 682
 683                         /*
 684                          * Include at most one act per-thread that "happens
 685                          * before" curr. Don't consider reflexively.
 686                          */
 687                         if (act->happens_before(curr) && act != curr) {
 688                                 if (act->is_write()) {
 689                                         if (rf != act) {
 690                                                 mo_graph->addEdge(act, rf);
 691                                                 added = true;
 692                                         }
 693                                 } else {
 694                                         const ModelAction *prevreadfrom = act->get_reads_from();
 695                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 696                                                 mo_graph->addEdge(prevreadfrom, rf);
 697                                                 added = true;
 698                                         }
 699                                 }
 700                                 break;
 701                         }
 702                 }
 703         }
 704
 705         return added;
 706 }
 707
 708 /** This method fixes up the modification order when we resolve a
 709  *  promises.  The basic problem is that actions that occur after the
 710  *  read curr could not property add items to the modification order
 711  *  for our read.
 712  *
 713  *  So for each thread, we find the earliest item that happens after
 714  *  the read curr.  This is the item we have to fix up with additional
 715  *  constraints.  If that action is write, we add a MO edge between
 716  *  the Action rf and that action.  If the action is a read, we add a
 717  *  MO edge between the Action rf, and whatever the read accessed.
 718  *
 719  * @param curr is the read ModelAction that we are fixing up MO edges for.
 720  * @param rf is the write ModelAction that curr reads from.
 721  *
 722  */
 723
 724 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 725 {
 726         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 727         unsigned int i;
 728         ASSERT(curr->is_read());
 729
 730         /* Iterate over all threads */
 731         for (i = 0; i < thrd_lists->size(); i++) {
 732                 /* Iterate over actions in thread, starting from most recent */
 733                 action_list_t *list = &(*thrd_lists)[i];
 734                 action_list_t::reverse_iterator rit;
 735                 ModelAction *lastact = NULL;
 736
 737                 /* Find last action that happens after curr */
 738                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 739                         ModelAction *act = *rit;
 740                         if (curr->happens_before(act)) {
 741                                 lastact = act;
 742                         } else
 743                                 break;
 744                 }
 745
 746                         /* Include at most one act per-thread that "happens before" curr */
 747                 if (lastact != NULL) {
 748                         if (lastact->is_read()) {
 749                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 750                                 if (postreadfrom != NULL&&rf != postreadfrom)
 751                                         mo_graph->addEdge(rf, postreadfrom);
 752                         } else if (rf != lastact) {
 753                                 mo_graph->addEdge(rf, lastact);
 754                         }
 755                         break;
 756                 }
 757         }
 758 }
 759
 760 /**
 761  * Updates the mo_graph with the constraints imposed from the current write.
 762  *
 763  * Basic idea is the following: Go through each other thread and find
 764  * the lastest action that happened before our write.  Two cases:
 765  *
 766  * (1) The action is a write => that write must occur before
 767  * the current write
 768  *
 769  * (2) The action is a read => the write that that action read from
 770  * must occur before the current write.
 771  *
 772  * This method also handles two other issues:
 773  *
 774  * (I) Sequential Consistency: Making sure that if the current write is
 775  * seq_cst, that it occurs after the previous seq_cst write.
 776  *
 777  * (II) Sending the write back to non-synchronizing reads.
 778  *
 779  * @param curr The current action. Must be a write.
 780  * @return True if modification order edges were added; false otherwise
 781  */
 782 bool ModelChecker::w_modification_order(ModelAction *curr)
 783 {
 784         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 785         unsigned int i;
 786         bool added = false;
 787         ASSERT(curr->is_write());
 788
 789         if (curr->is_seqcst()) {
 790                 /* We have to at least see the last sequentially consistent write,
 791                          so we are initialized. */
 792                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
 793                 if (last_seq_cst != NULL) {
 794                         mo_graph->addEdge(last_seq_cst, curr);
 795                         added = true;
 796                 }
 797         }
 798
 799         /* Iterate over all threads */
 800         for (i = 0; i < thrd_lists->size(); i++) {
 801                 /* Iterate over actions in thread, starting from most recent */
 802                 action_list_t *list = &(*thrd_lists)[i];
 803                 action_list_t::reverse_iterator rit;
 804                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 805                         ModelAction *act = *rit;
 806                         if (act == curr) {
 807                                 /*
 808                                  * If RMW, we already have all relevant edges,
 809                                  * so just skip to next thread.
 810                                  * If normal write, we need to look at earlier
 811                                  * actions, so continue processing list.
 812                                  */
 813                                 if (curr->is_rmw())
 814                                         break;
 815                                 else
 816                                         continue;
 817                         }
 818
 819                         /*
 820                          * Include at most one act per-thread that "happens
 821                          * before" curr
 822                          */
 823                         if (act->happens_before(curr)) {
 824                                 /*
 825                                  * Note: if act is RMW, just add edge:
 826                                  *   act --mo--> curr
 827                                  * The following edge should be handled elsewhere:
 828                                  *   readfrom(act) --mo--> act
 829                                  */
 830                                 if (act->is_write())
 831                                         mo_graph->addEdge(act, curr);
 832                                 else if (act->is_read() && act->get_reads_from() != NULL)
 833                                         mo_graph->addEdge(act->get_reads_from(), curr);
 834                                 added = true;
 835                                 break;
 836                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 837                                                      !act->same_thread(curr)) {
 838                                 /* We have an action that:
 839                                    (1) did not happen before us
 840                                    (2) is a read and we are a write
 841                                    (3) cannot synchronize with us
 842                                    (4) is in a different thread
 843                                    =>
 844                                    that read could potentially read from our write.
 845                                  */
 846                                 if (thin_air_constraint_may_allow(curr, act)) {
 847                                         if (isfeasible() ||
 848                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 849                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 850                                                 futurevalues->push_back(pfv);
 851                                         }
 852                                 }
 853                         }
 854                 }
 855         }
 856
 857         return added;
 858 }
 859
 860 /** Arbitrary reads from the future are not allowed.  Section 29.3
 861  * part 9 places some constraints.  This method checks one result of constraint
 862  * constraint.  Others require compiler support. */
 863
 864 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 865         if (!writer->is_rmw())
 866                 return true;
 867
 868         if (!reader->is_rmw())
 869                 return true;
 870
 871         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 872                 if (search==reader)
 873                         return false;
 874                 if (search->get_tid() == reader->get_tid() &&
 875                                 search->happens_before(reader))
 876                         break;
 877         }
 878
 879         return true;
 880 }
 881
 882 /**
 883  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 884  * The ModelAction under consideration is expected to be taking part in
 885  * release/acquire synchronization as an object of the "reads from" relation.
 886  * Note that this can only provide release sequence support for RMW chains
 887  * which do not read from the future, as those actions cannot be traced until
 888  * their "promise" is fulfilled. Similarly, we may not even establish the
 889  * presence of a release sequence with certainty, as some modification order
 890  * constraints may be decided further in the future. Thus, this function
 891  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 892  * and a boolean representing certainty.
 893  *
 894  * @todo Finish lazy updating, when promises are fulfilled in the future
 895  * @param rf The action that might be part of a release sequence. Must be a
 896  * write.
 897  * @param release_heads A pass-by-reference style return parameter.  After
 898  * execution of this function, release_heads will contain the heads of all the
 899  * relevant release sequences, if any exists
 900  * @return true, if the ModelChecker is certain that release_heads is complete;
 901  * false otherwise
 902  */
 903 bool ModelChecker::release_seq_head(const ModelAction *rf,
 904                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 905 {
 906         if (!rf) {
 907                 /* read from future: need to settle this later */
 908                 return false; /* incomplete */
 909         }
 910
 911         ASSERT(rf->is_write());
 912
 913         if (rf->is_release())
 914                 release_heads->push_back(rf);
 915         if (rf->is_rmw()) {
 916                 /* We need a RMW action that is both an acquire and release to stop */
 917                 /** @todo Need to be smarter here...  In the linux lock
 918                  * example, this will run to the beginning of the program for
 919                  * every acquire. */
 920                 if (rf->is_acquire() && rf->is_release())
 921                         return true; /* complete */
 922                 return release_seq_head(rf->get_reads_from(), release_heads);
 923         }
 924         if (rf->is_release())
 925                 return true; /* complete */
 926
 927         /* else relaxed write; check modification order for contiguous subsequence
 928          * -> rf must be same thread as release */
 929         int tid = id_to_int(rf->get_tid());
 930         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 931         action_list_t *list = &(*thrd_lists)[tid];
 932         action_list_t::const_reverse_iterator rit;
 933
 934         /* Find rf in the thread list */
 935         rit = std::find(list->rbegin(), list->rend(), rf);
 936         ASSERT(rit != list->rend());
 937
 938         /* Find the last write/release */
 939         for (; rit != list->rend(); rit++)
 940                 if ((*rit)->is_release())
 941                         break;
 942         if (rit == list->rend()) {
 943                 /* No write-release in this thread */
 944                 return true; /* complete */
 945         }
 946         ModelAction *release = *rit;
 947
 948         ASSERT(rf->same_thread(release));
 949
 950         bool certain = true;
 951         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 952                 if (id_to_int(rf->get_tid()) == (int)i)
 953                         continue;
 954                 list = &(*thrd_lists)[i];
 955
 956                 /* Can we ensure no future writes from this thread may break
 957                  * the release seq? */
 958                 bool future_ordered = false;
 959
 960                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 961                         const ModelAction *act = *rit;
 962                         if (!act->is_write())
 963                                 continue;
 964                         /* Reach synchronization -> this thread is complete */
 965                         if (act->happens_before(release))
 966                                 break;
 967                         if (rf->happens_before(act)) {
 968                                 future_ordered = true;
 969                                 continue;
 970                         }
 971
 972                         /* Check modification order */
 973                         if (mo_graph->checkReachable(rf, act)) {
 974                                 /* rf --mo--> act */
 975                                 future_ordered = true;
 976                                 continue;
 977                         }
 978                         if (mo_graph->checkReachable(act, release))
 979                                 /* act --mo--> release */
 980                                 break;
 981                         if (mo_graph->checkReachable(release, act) &&
 982                                       mo_graph->checkReachable(act, rf)) {
 983                                 /* release --mo-> act --mo--> rf */
 984                                 return true; /* complete */
 985                         }
 986                         certain = false;
 987                 }
 988                 if (!future_ordered)
 989                         return false; /* This thread is uncertain */
 990         }
 991
 992         if (certain)
 993                 release_heads->push_back(release);
 994         return certain;
 995 }
 996
 997 /**
 998  * A public interface for getting the release sequence head(s) with which a
 999  * given ModelAction must synchronize. This function only returns a non-empty
1000  * result when it can locate a release sequence head with certainty. Otherwise,
1001  * it may mark the internal state of the ModelChecker so that it will handle
1002  * the release sequence at a later time, causing @a act to update its
1003  * synchronization at some later point in execution.
1004  * @param act The 'acquire' action that may read from a release sequence
1005  * @param release_heads A pass-by-reference return parameter. Will be filled
1006  * with the head(s) of the release sequence(s), if they exists with certainty.
1007  * @see ModelChecker::release_seq_head
1008  */
1009 void ModelChecker::get_release_seq_heads(ModelAction *act,
1010                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
1011 {
1012         const ModelAction *rf = act->get_reads_from();
1013         bool complete;
1014         complete = release_seq_head(rf, release_heads);
1015         if (!complete) {
1016                 /* add act to 'lazy checking' list */
1017                 std::list<ModelAction *> *list;
1018                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1019                 list->push_back(act);
1020                 (*lazy_sync_size)++;
1021         }
1022 }
1023
1024 /**
1025  * Attempt to resolve all stashed operations that might synchronize with a
1026  * release sequence for a given location. This implements the "lazy" portion of
1027  * determining whether or not a release sequence was contiguous, since not all
1028  * modification order information is present at the time an action occurs.
1029  *
1030  * @param location The location/object that should be checked for release
1031  * sequence resolutions
1032  * @param work_queue The work queue to which to add work items as they are
1033  * generated
1034  * @return True if any updates occurred (new synchronization, new mo_graph
1035  * edges)
1036  */
1037 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1038 {
1039         std::list<ModelAction *> *list;
1040         list = lazy_sync_with_release->getptr(location);
1041         if (!list)
1042                 return false;
1043
1044         bool updated = false;
1045         std::list<ModelAction *>::iterator it = list->begin();
1046         while (it != list->end()) {
1047                 ModelAction *act = *it;
1048                 const ModelAction *rf = act->get_reads_from();
1049                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1050                 bool complete;
1051                 complete = release_seq_head(rf, &release_heads);
1052                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1053                         if (!act->has_synchronized_with(release_heads[i])) {
1054                                 updated = true;
1055                                 act->synchronize_with(release_heads[i]);
1056                         }
1057                 }
1058
1059                 if (updated) {
1060                         /* Re-check act for mo_graph edges */
1061                         work_queue->push_back(MOEdgeWorkEntry(act));
1062
1063                         /* propagate synchronization to later actions */
1064                         action_list_t::reverse_iterator it = action_trace->rbegin();
1065                         while ((*it) != act) {
1066                                 ModelAction *propagate = *it;
1067                                 if (act->happens_before(propagate)) {
1068                                         propagate->synchronize_with(act);
1069                                         /* Re-check 'propagate' for mo_graph edges */
1070                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1071                                 }
1072                         }
1073                 }
1074                 if (complete) {
1075                         it = list->erase(it);
1076                         (*lazy_sync_size)--;
1077                 } else
1078                         it++;
1079         }
1080
1081         // If we resolved promises or data races, see if we have realized a data race.
1082         if (checkDataRaces()) {
1083                 set_assert();
1084         }
1085
1086         return updated;
1087 }
1088
1089 /**
1090  * Performs various bookkeeping operations for the current ModelAction. For
1091  * instance, adds action to the per-object, per-thread action vector and to the
1092  * action trace list of all thread actions.
1093  *
1094  * @param act is the ModelAction to add.
1095  */
1096 void ModelChecker::add_action_to_lists(ModelAction *act)
1097 {
1098         int tid = id_to_int(act->get_tid());
1099         action_trace->push_back(act);
1100
1101         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1102
1103         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1104         if (tid >= (int)vec->size())
1105                 vec->resize(priv->next_thread_id);
1106         (*vec)[tid].push_back(act);
1107
1108         if ((int)thrd_last_action->size() <= tid)
1109                 thrd_last_action->resize(get_num_threads());
1110         (*thrd_last_action)[tid] = act;
1111 }
1112
1113 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1114 {
1115         int nthreads = get_num_threads();
1116         if ((int)thrd_last_action->size() < nthreads)
1117                 thrd_last_action->resize(nthreads);
1118         return (*thrd_last_action)[id_to_int(tid)];
1119 }
1120
1121 /**
1122  * Gets the last memory_order_seq_cst write (in the total global sequence)
1123  * performed on a particular object (i.e., memory location), not including the
1124  * current action.
1125  * @param curr The current ModelAction; also denotes the object location to
1126  * check
1127  * @return The last seq_cst write
1128  */
1129 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1130 {
1131         void *location = curr->get_location();
1132         action_list_t *list = obj_map->get_safe_ptr(location);
1133         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1134         action_list_t::reverse_iterator rit;
1135         for (rit = list->rbegin(); rit != list->rend(); rit++)
1136                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1137                         return *rit;
1138         return NULL;
1139 }
1140
1141 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1142 {
1143         ModelAction *parent = get_last_action(tid);
1144         if (!parent)
1145                 parent = get_thread(tid)->get_creation();
1146         return parent;
1147 }
1148
1149 /**
1150  * Returns the clock vector for a given thread.
1151  * @param tid The thread whose clock vector we want
1152  * @return Desired clock vector
1153  */
1154 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1155 {
1156         return get_parent_action(tid)->get_cv();
1157 }
1158
1159 /**
1160  * Resolve a set of Promises with a current write. The set is provided in the
1161  * Node corresponding to @a write.
1162  * @param write The ModelAction that is fulfilling Promises
1163  * @return True if promises were resolved; false otherwise
1164  */
1165 bool ModelChecker::resolve_promises(ModelAction *write)
1166 {
1167         bool resolved = false;
1168
1169         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1170                 Promise *promise = (*promises)[promise_index];
1171                 if (write->get_node()->get_promise(i)) {
1172                         ModelAction *read = promise->get_action();
1173                         read->read_from(write);
1174                         if (read->is_rmw()) {
1175                                 mo_graph->addRMWEdge(write, read);
1176                         }
1177                         //First fix up the modification order for actions that happened
1178                         //before the read
1179                         r_modification_order(read, write);
1180                         //Next fix up the modification order for actions that happened
1181                         //after the read.
1182                         post_r_modification_order(read, write);
1183                         promises->erase(promises->begin() + promise_index);
1184                         resolved = true;
1185                 } else
1186                         promise_index++;
1187         }
1188         return resolved;
1189 }
1190
1191 /**
1192  * Compute the set of promises that could potentially be satisfied by this
1193  * action. Note that the set computation actually appears in the Node, not in
1194  * ModelChecker.
1195  * @param curr The ModelAction that may satisfy promises
1196  */
1197 void ModelChecker::compute_promises(ModelAction *curr)
1198 {
1199         for (unsigned int i = 0; i < promises->size(); i++) {
1200                 Promise *promise = (*promises)[i];
1201                 const ModelAction *act = promise->get_action();
1202                 if (!act->happens_before(curr) &&
1203                                 act->is_read() &&
1204                                 !act->is_synchronizing(curr) &&
1205                                 !act->same_thread(curr) &&
1206                                 promise->get_value() == curr->get_value()) {
1207                         curr->get_node()->set_promise(i);
1208                 }
1209         }
1210 }
1211
1212 /** Checks promises in response to change in ClockVector Threads. */
1213 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1214 {
1215         for (unsigned int i = 0; i < promises->size(); i++) {
1216                 Promise *promise = (*promises)[i];
1217                 const ModelAction *act = promise->get_action();
1218                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1219                                 merge_cv->synchronized_since(act)) {
1220                         //This thread is no longer able to send values back to satisfy the promise
1221                         int num_synchronized_threads = promise->increment_threads();
1222                         if (num_synchronized_threads == get_num_threads()) {
1223                                 //Promise has failed
1224                                 failed_promise = true;
1225                                 return;
1226                         }
1227                 }
1228         }
1229 }
1230
1231 /**
1232  * Build up an initial set of all past writes that this 'read' action may read
1233  * from. This set is determined by the clock vector's "happens before"
1234  * relationship.
1235  * @param curr is the current ModelAction that we are exploring; it must be a
1236  * 'read' operation.
1237  */
1238 void ModelChecker::build_reads_from_past(ModelAction *curr)
1239 {
1240         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1241         unsigned int i;
1242         ASSERT(curr->is_read());
1243
1244         ModelAction *last_seq_cst = NULL;
1245
1246         /* Track whether this object has been initialized */
1247         bool initialized = false;
1248
1249         if (curr->is_seqcst()) {
1250                 last_seq_cst = get_last_seq_cst(curr);
1251                 /* We have to at least see the last sequentially consistent write,
1252                          so we are initialized. */
1253                 if (last_seq_cst != NULL)
1254                         initialized = true;
1255         }
1256
1257         /* Iterate over all threads */
1258         for (i = 0; i < thrd_lists->size(); i++) {
1259                 /* Iterate over actions in thread, starting from most recent */
1260                 action_list_t *list = &(*thrd_lists)[i];
1261                 action_list_t::reverse_iterator rit;
1262                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1263                         ModelAction *act = *rit;
1264
1265                         /* Only consider 'write' actions */
1266                         if (!act->is_write())
1267                                 continue;
1268
1269                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1270                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1271                                 DEBUG("Adding action to may_read_from:\n");
1272                                 if (DBG_ENABLED()) {
1273                                         act->print();
1274                                         curr->print();
1275                                 }
1276                                 curr->get_node()->add_read_from(act);
1277                         }
1278
1279                         /* Include at most one act per-thread that "happens before" curr */
1280                         if (act->happens_before(curr)) {
1281                                 initialized = true;
1282                                 break;
1283                         }
1284                 }
1285         }
1286
1287         if (!initialized) {
1288                 /** @todo Need a more informative way of reporting errors. */
1289                 printf("ERROR: may read from uninitialized atomic\n");
1290         }
1291
1292         if (DBG_ENABLED() || !initialized) {
1293                 printf("Reached read action:\n");
1294                 curr->print();
1295                 printf("Printing may_read_from\n");
1296                 curr->get_node()->print_may_read_from();
1297                 printf("End printing may_read_from\n");
1298         }
1299
1300         ASSERT(initialized);
1301 }
1302
1303 static void print_list(action_list_t *list)
1304 {
1305         action_list_t::iterator it;
1306
1307         printf("---------------------------------------------------------------------\n");
1308         printf("Trace:\n");
1309
1310         for (it = list->begin(); it != list->end(); it++) {
1311                 (*it)->print();
1312         }
1313         printf("---------------------------------------------------------------------\n");
1314 }
1315
1316 void ModelChecker::print_summary()
1317 {
1318         printf("\n");
1319         printf("Number of executions: %d\n", num_executions);
1320         printf("Number of feasible executions: %d\n", num_feasible_executions);
1321         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1322
1323 #if SUPPORT_MOD_ORDER_DUMP
1324         scheduler->print();
1325         char buffername[100];
1326         sprintf(buffername, "exec%u",num_executions);
1327         mo_graph->dumpGraphToFile(buffername);
1328 #endif
1329
1330         if (!isfinalfeasible())
1331                 printf("INFEASIBLE EXECUTION!\n");
1332         print_list(action_trace);
1333         printf("\n");
1334 }
1335
1336 /**
1337  * Add a Thread to the system for the first time. Should only be called once
1338  * per thread.
1339  * @param t The Thread to add
1340  */
1341 void ModelChecker::add_thread(Thread *t)
1342 {
1343         thread_map->put(id_to_int(t->get_id()), t);
1344         scheduler->add_thread(t);
1345 }
1346
1347 void ModelChecker::remove_thread(Thread *t)
1348 {
1349         scheduler->remove_thread(t);
1350 }
1351
1352 /**
1353  * Switch from a user-context to the "master thread" context (a.k.a. system
1354  * context). This switch is made with the intention of exploring a particular
1355  * model-checking action (described by a ModelAction object). Must be called
1356  * from a user-thread context.
1357  * @param act The current action that will be explored. Must not be NULL.
1358  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1359  */
1360 int ModelChecker::switch_to_master(ModelAction *act)
1361 {
1362         DBG();
1363         Thread *old = thread_current();
1364         set_current_action(act);
1365         old->set_state(THREAD_READY);
1366         return Thread::swap(old, &system_context);
1367 }
1368
1369 /**
1370  * Takes the next step in the execution, if possible.
1371  * @return Returns true (success) if a step was taken and false otherwise.
1372  */
1373 bool ModelChecker::take_step() {
1374         Thread *curr, *next;
1375
1376         if (has_asserted())
1377                 return false;
1378
1379         curr = thread_current();
1380         if (curr) {
1381                 if (curr->get_state() == THREAD_READY) {
1382                         ASSERT(priv->current_action);
1383
1384                         priv->nextThread = check_current_action(priv->current_action);
1385                         priv->current_action = NULL;
1386                         if (!curr->is_blocked() && !curr->is_complete())
1387                                 scheduler->add_thread(curr);
1388                 } else {
1389                         ASSERT(false);
1390                 }
1391         }
1392         next = scheduler->next_thread(priv->nextThread);
1393
1394         /* Infeasible -> don't take any more steps */
1395         if (!isfeasible())
1396                 return false;
1397
1398         if (next)
1399                 next->set_state(THREAD_RUNNING);
1400         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1401
1402         /* next == NULL -> don't take any more steps */
1403         if (!next)
1404                 return false;
1405         /* Return false only if swap fails with an error */
1406         return (Thread::swap(&system_context, next) == 0);
1407 }
1408
1409 /** Runs the current execution until threre are no more steps to take. */
1410 void ModelChecker::finish_execution() {
1411         DBG();
1412
1413         while (take_step());
1414 }