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         ModelAction *newcurr;
 339
 340         if (curr->is_rmwc() || curr->is_rmw()) {
 341                 newcurr = process_rmw(curr);
 342                 delete curr;
 343                 compute_promises(newcurr);
 344                 return newcurr;
 345         }
 346
 347         newcurr = node_stack->explore_action(curr);
 348         if (newcurr) {
 349                 /* First restore type and order in case of RMW operation */
 350                 if (curr->is_rmwr())
 351                         newcurr->copy_typeandorder(curr);
 352
 353                 /* Discard duplicate ModelAction; use action from NodeStack */
 354                 delete curr;
 355
 356                 /* If we have diverged, we need to reset the clock vector. */
 357                 if (diverge == NULL)
 358                         newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 359         } else {
 360                 newcurr = curr;
 361                 /*
 362                  * Perform one-time actions when pushing new ModelAction onto
 363                  * NodeStack
 364                  */
 365                 curr->create_cv(get_parent_action(curr->get_tid()));
 366                 if (curr->is_write())
 367                         compute_promises(curr);
 368         }
 369         return newcurr;
 370 }
 371
 372 /**
 373  * This is the heart of the model checker routine. It performs model-checking
 374  * actions corresponding to a given "current action." Among other processes, it
 375  * calculates reads-from relationships, updates synchronization clock vectors,
 376  * forms a memory_order constraints graph, and handles replay/backtrack
 377  * execution when running permutations of previously-observed executions.
 378  *
 379  * @param curr The current action to process
 380  * @return The next Thread that must be executed. May be NULL if ModelChecker
 381  * makes no choice (e.g., according to replay execution, combining RMW actions,
 382  * etc.)
 383  */
 384 Thread * ModelChecker::check_current_action(ModelAction *curr)
 385 {
 386         ASSERT(curr);
 387
 388         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 389
 390         ModelAction *newcurr = initialize_curr_action(curr);
 391
 392         /* Build may_read_from set for newly-created actions */
 393         if (curr == newcurr && curr->is_read())
 394                 build_reads_from_past(curr);
 395         curr = newcurr;
 396
 397         /* Thread specific actions */
 398         switch (curr->get_type()) {
 399         case THREAD_CREATE: {
 400                 Thread *th = (Thread *)curr->get_location();
 401                 th->set_creation(curr);
 402                 break;
 403         }
 404         case THREAD_JOIN: {
 405                 Thread *waiting, *blocking;
 406                 waiting = get_thread(curr);
 407                 blocking = (Thread *)curr->get_location();
 408                 if (!blocking->is_complete()) {
 409                         blocking->push_wait_list(curr);
 410                         scheduler->sleep(waiting);
 411                 }
 412                 break;
 413         }
 414         case THREAD_FINISH: {
 415                 Thread *th = get_thread(curr);
 416                 while (!th->wait_list_empty()) {
 417                         ModelAction *act = th->pop_wait_list();
 418                         Thread *wake = get_thread(act);
 419                         scheduler->wake(wake);
 420                 }
 421                 th->complete();
 422                 break;
 423         }
 424         case THREAD_START: {
 425                 check_promises(NULL, curr->get_cv());
 426                 break;
 427         }
 428         default:
 429                 break;
 430         }
 431
 432         /* Add current action to lists before work_queue loop */
 433         if (!second_part_of_rmw)
 434                 add_action_to_lists(curr);
 435
 436         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 437
 438         while (!work_queue.empty()) {
 439                 WorkQueueEntry work = work_queue.front();
 440                 work_queue.pop_front();
 441
 442                 switch (work.type) {
 443                 case WORK_CHECK_CURR_ACTION: {
 444                         ModelAction *act = work.action;
 445                         bool updated = false;
 446                         if (act->is_read() && process_read(act, second_part_of_rmw))
 447                                 updated = true;
 448
 449                         if (act->is_write() && process_write(act))
 450                                 updated = true;
 451
 452                         if (updated)
 453                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 454                         break;
 455                 }
 456                 case WORK_CHECK_RELEASE_SEQ:
 457                         resolve_release_sequences(work.location, &work_queue);
 458                         break;
 459                 case WORK_CHECK_MO_EDGES: {
 460                         /** @todo Complete verification of work_queue */
 461                         ModelAction *act = work.action;
 462                         bool updated = false;
 463
 464                         if (act->is_read()) {
 465                                 if (r_modification_order(act, act->get_reads_from()))
 466                                         updated = true;
 467                         }
 468                         if (act->is_write()) {
 469                                 if (w_modification_order(act))
 470                                         updated = true;
 471                         }
 472
 473                         if (updated)
 474                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 475                         break;
 476                 }
 477                 default:
 478                         ASSERT(false);
 479                         break;
 480                 }
 481         }
 482
 483         check_curr_backtracking(curr);
 484
 485         set_backtracking(curr);
 486
 487         return get_next_thread(curr);
 488 }
 489
 490 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 491         Node *currnode = curr->get_node();
 492         Node *parnode = currnode->get_parent();
 493
 494         if ((!parnode->backtrack_empty() ||
 495                          !currnode->read_from_empty() ||
 496                          !currnode->future_value_empty() ||
 497                          !currnode->promise_empty())
 498                         && (!priv->next_backtrack ||
 499                                         *curr > *priv->next_backtrack)) {
 500                 priv->next_backtrack = curr;
 501         }
 502 }
 503
 504 bool ModelChecker::promises_expired() {
 505         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 506                 Promise *promise = (*promises)[promise_index];
 507                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 508                         return true;
 509                 }
 510         }
 511         return false;
 512 }
 513
 514 /** @returns whether the current partial trace must be a prefix of a
 515  * feasible trace. */
 516 bool ModelChecker::isfeasibleprefix() {
 517         return promises->size() == 0 && *lazy_sync_size == 0;
 518 }
 519
 520 /** @returns whether the current partial trace is feasible. */
 521 bool ModelChecker::isfeasible() {
 522         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 523 }
 524
 525 /** @returns whether the current partial trace is feasible other than
 526  * multiple RMW reading from the same store. */
 527 bool ModelChecker::isfeasibleotherthanRMW() {
 528         if (DBG_ENABLED()) {
 529                 if (mo_graph->checkForCycles())
 530                         DEBUG("Infeasible: modification order cycles\n");
 531                 if (failed_promise)
 532                         DEBUG("Infeasible: failed promise\n");
 533                 if (too_many_reads)
 534                         DEBUG("Infeasible: too many reads\n");
 535                 if (promises_expired())
 536                         DEBUG("Infeasible: promises expired\n");
 537         }
 538         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 539 }
 540
 541 /** Returns whether the current completed trace is feasible. */
 542 bool ModelChecker::isfinalfeasible() {
 543         if (DBG_ENABLED() && promises->size() != 0)
 544                 DEBUG("Infeasible: unrevolved promises\n");
 545
 546         return isfeasible() && promises->size() == 0;
 547 }
 548
 549 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 550 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 551         int tid = id_to_int(act->get_tid());
 552         ModelAction *lastread = get_last_action(tid);
 553         lastread->process_rmw(act);
 554         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 555                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 556                 mo_graph->commitChanges();
 557         }
 558         return lastread;
 559 }
 560
 561 /**
 562  * Checks whether a thread has read from the same write for too many times
 563  * without seeing the effects of a later write.
 564  *
 565  * Basic idea:
 566  * 1) there must a different write that we could read from that would satisfy the modification order,
 567  * 2) we must have read from the same value in excess of maxreads times, and
 568  * 3) that other write must have been in the reads_from set for maxreads times.
 569  *
 570  * If so, we decide that the execution is no longer feasible.
 571  */
 572 void ModelChecker::check_recency(ModelAction *curr) {
 573         if (params.maxreads != 0) {
 574                 if (curr->get_node()->get_read_from_size() <= 1)
 575                         return;
 576
 577                 //Must make sure that execution is currently feasible...  We could
 578                 //accidentally clear by rolling back
 579                 if (!isfeasible())
 580                         return;
 581
 582                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 583                 int tid = id_to_int(curr->get_tid());
 584
 585                 /* Skip checks */
 586                 if ((int)thrd_lists->size() <= tid)
 587                         return;
 588
 589                 action_list_t *list = &(*thrd_lists)[tid];
 590
 591                 action_list_t::reverse_iterator rit = list->rbegin();
 592                 /* Skip past curr */
 593                 for (; (*rit) != curr; rit++)
 594                         ;
 595                 /* go past curr now */
 596                 rit++;
 597
 598                 action_list_t::reverse_iterator ritcopy = rit;
 599                 //See if we have enough reads from the same value
 600                 int count = 0;
 601                 for (; count < params.maxreads; rit++,count++) {
 602                         if (rit==list->rend())
 603                                 return;
 604                         ModelAction *act = *rit;
 605                         if (!act->is_read())
 606                                 return;
 607                         if (act->get_reads_from() != curr->get_reads_from())
 608                                 return;
 609                         if (act->get_node()->get_read_from_size() <= 1)
 610                                 return;
 611                 }
 612
 613                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 614                         //Get write
 615                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 616                         //Need a different write
 617                         if (write==curr->get_reads_from())
 618                                 continue;
 619
 620                         /* Test to see whether this is a feasible write to read from*/
 621                         mo_graph->startChanges();
 622                         r_modification_order(curr, write);
 623                         bool feasiblereadfrom = isfeasible();
 624                         mo_graph->rollbackChanges();
 625
 626                         if (!feasiblereadfrom)
 627                                 continue;
 628                         rit = ritcopy;
 629
 630                         bool feasiblewrite = true;
 631                         //new we need to see if this write works for everyone
 632
 633                         for (int loop = count; loop>0; loop--,rit++) {
 634                                 ModelAction *act=*rit;
 635                                 bool foundvalue = false;
 636                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 637                                         if (act->get_node()->get_read_from_at(i)==write) {
 638                                                 foundvalue = true;
 639                                                 break;
 640                                         }
 641                                 }
 642                                 if (!foundvalue) {
 643                                         feasiblewrite = false;
 644                                         break;
 645                                 }
 646                         }
 647                         if (feasiblewrite) {
 648                                 too_many_reads = true;
 649                                 return;
 650                         }
 651                 }
 652         }
 653 }
 654
 655 /**
 656  * Updates the mo_graph with the constraints imposed from the current
 657  * read.
 658  *
 659  * Basic idea is the following: Go through each other thread and find
 660  * the lastest action that happened before our read.  Two cases:
 661  *
 662  * (1) The action is a write => that write must either occur before
 663  * the write we read from or be the write we read from.
 664  *
 665  * (2) The action is a read => the write that that action read from
 666  * must occur before the write we read from or be the same write.
 667  *
 668  * @param curr The current action. Must be a read.
 669  * @param rf The action that curr reads from. Must be a write.
 670  * @return True if modification order edges were added; false otherwise
 671  */
 672 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 673 {
 674         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 675         unsigned int i;
 676         bool added = false;
 677         ASSERT(curr->is_read());
 678
 679         /* Iterate over all threads */
 680         for (i = 0; i < thrd_lists->size(); i++) {
 681                 /* Iterate over actions in thread, starting from most recent */
 682                 action_list_t *list = &(*thrd_lists)[i];
 683                 action_list_t::reverse_iterator rit;
 684                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 685                         ModelAction *act = *rit;
 686
 687                         /*
 688                          * Include at most one act per-thread that "happens
 689                          * before" curr. Don't consider reflexively.
 690                          */
 691                         if (act->happens_before(curr) && act != curr) {
 692                                 if (act->is_write()) {
 693                                         if (rf != act) {
 694                                                 mo_graph->addEdge(act, rf);
 695                                                 added = true;
 696                                         }
 697                                 } else {
 698                                         const ModelAction *prevreadfrom = act->get_reads_from();
 699                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 700                                                 mo_graph->addEdge(prevreadfrom, rf);
 701                                                 added = true;
 702                                         }
 703                                 }
 704                                 break;
 705                         }
 706                 }
 707         }
 708
 709         return added;
 710 }
 711
 712 /** This method fixes up the modification order when we resolve a
 713  *  promises.  The basic problem is that actions that occur after the
 714  *  read curr could not property add items to the modification order
 715  *  for our read.
 716  *
 717  *  So for each thread, we find the earliest item that happens after
 718  *  the read curr.  This is the item we have to fix up with additional
 719  *  constraints.  If that action is write, we add a MO edge between
 720  *  the Action rf and that action.  If the action is a read, we add a
 721  *  MO edge between the Action rf, and whatever the read accessed.
 722  *
 723  * @param curr is the read ModelAction that we are fixing up MO edges for.
 724  * @param rf is the write ModelAction that curr reads from.
 725  *
 726  */
 727
 728 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 729 {
 730         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 731         unsigned int i;
 732         ASSERT(curr->is_read());
 733
 734         /* Iterate over all threads */
 735         for (i = 0; i < thrd_lists->size(); i++) {
 736                 /* Iterate over actions in thread, starting from most recent */
 737                 action_list_t *list = &(*thrd_lists)[i];
 738                 action_list_t::reverse_iterator rit;
 739                 ModelAction *lastact = NULL;
 740
 741                 /* Find last action that happens after curr */
 742                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 743                         ModelAction *act = *rit;
 744                         if (curr->happens_before(act)) {
 745                                 lastact = act;
 746                         } else
 747                                 break;
 748                 }
 749
 750                         /* Include at most one act per-thread that "happens before" curr */
 751                 if (lastact != NULL) {
 752                         if (lastact->is_read()) {
 753                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 754                                 if (postreadfrom != NULL&&rf != postreadfrom)
 755                                         mo_graph->addEdge(rf, postreadfrom);
 756                         } else if (rf != lastact) {
 757                                 mo_graph->addEdge(rf, lastact);
 758                         }
 759                         break;
 760                 }
 761         }
 762 }
 763
 764 /**
 765  * Updates the mo_graph with the constraints imposed from the current write.
 766  *
 767  * Basic idea is the following: Go through each other thread and find
 768  * the lastest action that happened before our write.  Two cases:
 769  *
 770  * (1) The action is a write => that write must occur before
 771  * the current write
 772  *
 773  * (2) The action is a read => the write that that action read from
 774  * must occur before the current write.
 775  *
 776  * This method also handles two other issues:
 777  *
 778  * (I) Sequential Consistency: Making sure that if the current write is
 779  * seq_cst, that it occurs after the previous seq_cst write.
 780  *
 781  * (II) Sending the write back to non-synchronizing reads.
 782  *
 783  * @param curr The current action. Must be a write.
 784  * @return True if modification order edges were added; false otherwise
 785  */
 786 bool ModelChecker::w_modification_order(ModelAction *curr)
 787 {
 788         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 789         unsigned int i;
 790         bool added = false;
 791         ASSERT(curr->is_write());
 792
 793         if (curr->is_seqcst()) {
 794                 /* We have to at least see the last sequentially consistent write,
 795                          so we are initialized. */
 796                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
 797                 if (last_seq_cst != NULL) {
 798                         mo_graph->addEdge(last_seq_cst, curr);
 799                         added = true;
 800                 }
 801         }
 802
 803         /* Iterate over all threads */
 804         for (i = 0; i < thrd_lists->size(); i++) {
 805                 /* Iterate over actions in thread, starting from most recent */
 806                 action_list_t *list = &(*thrd_lists)[i];
 807                 action_list_t::reverse_iterator rit;
 808                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 809                         ModelAction *act = *rit;
 810                         if (act == curr) {
 811                                 /*
 812                                  * If RMW, we already have all relevant edges,
 813                                  * so just skip to next thread.
 814                                  * If normal write, we need to look at earlier
 815                                  * actions, so continue processing list.
 816                                  */
 817                                 if (curr->is_rmw())
 818                                         break;
 819                                 else
 820                                         continue;
 821                         }
 822
 823                         /*
 824                          * Include at most one act per-thread that "happens
 825                          * before" curr
 826                          */
 827                         if (act->happens_before(curr)) {
 828                                 /*
 829                                  * Note: if act is RMW, just add edge:
 830                                  *   act --mo--> curr
 831                                  * The following edge should be handled elsewhere:
 832                                  *   readfrom(act) --mo--> act
 833                                  */
 834                                 if (act->is_write())
 835                                         mo_graph->addEdge(act, curr);
 836                                 else if (act->is_read() && act->get_reads_from() != NULL)
 837                                         mo_graph->addEdge(act->get_reads_from(), curr);
 838                                 added = true;
 839                                 break;
 840                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 841                                                      !act->same_thread(curr)) {
 842                                 /* We have an action that:
 843                                    (1) did not happen before us
 844                                    (2) is a read and we are a write
 845                                    (3) cannot synchronize with us
 846                                    (4) is in a different thread
 847                                    =>
 848                                    that read could potentially read from our write.
 849                                  */
 850                                 if (thin_air_constraint_may_allow(curr, act)) {
 851                                         if (isfeasible() ||
 852                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 853                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 854                                                 futurevalues->push_back(pfv);
 855                                         }
 856                                 }
 857                         }
 858                 }
 859         }
 860
 861         return added;
 862 }
 863
 864 /** Arbitrary reads from the future are not allowed.  Section 29.3
 865  * part 9 places some constraints.  This method checks one result of constraint
 866  * constraint.  Others require compiler support. */
 867
 868 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 869         if (!writer->is_rmw())
 870                 return true;
 871
 872         if (!reader->is_rmw())
 873                 return true;
 874
 875         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 876                 if (search==reader)
 877                         return false;
 878                 if (search->get_tid() == reader->get_tid() &&
 879                                 search->happens_before(reader))
 880                         break;
 881         }
 882
 883         return true;
 884 }
 885
 886 /**
 887  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 888  * The ModelAction under consideration is expected to be taking part in
 889  * release/acquire synchronization as an object of the "reads from" relation.
 890  * Note that this can only provide release sequence support for RMW chains
 891  * which do not read from the future, as those actions cannot be traced until
 892  * their "promise" is fulfilled. Similarly, we may not even establish the
 893  * presence of a release sequence with certainty, as some modification order
 894  * constraints may be decided further in the future. Thus, this function
 895  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 896  * and a boolean representing certainty.
 897  *
 898  * @todo Finish lazy updating, when promises are fulfilled in the future
 899  * @param rf The action that might be part of a release sequence. Must be a
 900  * write.
 901  * @param release_heads A pass-by-reference style return parameter.  After
 902  * execution of this function, release_heads will contain the heads of all the
 903  * relevant release sequences, if any exists
 904  * @return true, if the ModelChecker is certain that release_heads is complete;
 905  * false otherwise
 906  */
 907 bool ModelChecker::release_seq_head(const ModelAction *rf,
 908                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 909 {
 910         if (!rf) {
 911                 /* read from future: need to settle this later */
 912                 return false; /* incomplete */
 913         }
 914
 915         ASSERT(rf->is_write());
 916
 917         if (rf->is_release())
 918                 release_heads->push_back(rf);
 919         if (rf->is_rmw()) {
 920                 /* We need a RMW action that is both an acquire and release to stop */
 921                 /** @todo Need to be smarter here...  In the linux lock
 922                  * example, this will run to the beginning of the program for
 923                  * every acquire. */
 924                 if (rf->is_acquire() && rf->is_release())
 925                         return true; /* complete */
 926                 return release_seq_head(rf->get_reads_from(), release_heads);
 927         }
 928         if (rf->is_release())
 929                 return true; /* complete */
 930
 931         /* else relaxed write; check modification order for contiguous subsequence
 932          * -> rf must be same thread as release */
 933         int tid = id_to_int(rf->get_tid());
 934         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 935         action_list_t *list = &(*thrd_lists)[tid];
 936         action_list_t::const_reverse_iterator rit;
 937
 938         /* Find rf in the thread list */
 939         rit = std::find(list->rbegin(), list->rend(), rf);
 940         ASSERT(rit != list->rend());
 941
 942         /* Find the last write/release */
 943         for (; rit != list->rend(); rit++)
 944                 if ((*rit)->is_release())
 945                         break;
 946         if (rit == list->rend()) {
 947                 /* No write-release in this thread */
 948                 return true; /* complete */
 949         }
 950         ModelAction *release = *rit;
 951
 952         ASSERT(rf->same_thread(release));
 953
 954         bool certain = true;
 955         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 956                 if (id_to_int(rf->get_tid()) == (int)i)
 957                         continue;
 958                 list = &(*thrd_lists)[i];
 959
 960                 /* Can we ensure no future writes from this thread may break
 961                  * the release seq? */
 962                 bool future_ordered = false;
 963
 964                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 965                         const ModelAction *act = *rit;
 966                         if (!act->is_write())
 967                                 continue;
 968                         /* Reach synchronization -> this thread is complete */
 969                         if (act->happens_before(release))
 970                                 break;
 971                         if (rf->happens_before(act)) {
 972                                 future_ordered = true;
 973                                 continue;
 974                         }
 975
 976                         /* Check modification order */
 977                         if (mo_graph->checkReachable(rf, act)) {
 978                                 /* rf --mo--> act */
 979                                 future_ordered = true;
 980                                 continue;
 981                         }
 982                         if (mo_graph->checkReachable(act, release))
 983                                 /* act --mo--> release */
 984                                 break;
 985                         if (mo_graph->checkReachable(release, act) &&
 986                                       mo_graph->checkReachable(act, rf)) {
 987                                 /* release --mo-> act --mo--> rf */
 988                                 return true; /* complete */
 989                         }
 990                         certain = false;
 991                 }
 992                 if (!future_ordered)
 993                         return false; /* This thread is uncertain */
 994         }
 995
 996         if (certain)
 997                 release_heads->push_back(release);
 998         return certain;
 999 }
1000
1001 /**
1002  * A public interface for getting the release sequence head(s) with which a
1003  * given ModelAction must synchronize. This function only returns a non-empty
1004  * result when it can locate a release sequence head with certainty. Otherwise,
1005  * it may mark the internal state of the ModelChecker so that it will handle
1006  * the release sequence at a later time, causing @a act to update its
1007  * synchronization at some later point in execution.
1008  * @param act The 'acquire' action that may read from a release sequence
1009  * @param release_heads A pass-by-reference return parameter. Will be filled
1010  * with the head(s) of the release sequence(s), if they exists with certainty.
1011  * @see ModelChecker::release_seq_head
1012  */
1013 void ModelChecker::get_release_seq_heads(ModelAction *act,
1014                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
1015 {
1016         const ModelAction *rf = act->get_reads_from();
1017         bool complete;
1018         complete = release_seq_head(rf, release_heads);
1019         if (!complete) {
1020                 /* add act to 'lazy checking' list */
1021                 std::list<ModelAction *> *list;
1022                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1023                 list->push_back(act);
1024                 (*lazy_sync_size)++;
1025         }
1026 }
1027
1028 /**
1029  * Attempt to resolve all stashed operations that might synchronize with a
1030  * release sequence for a given location. This implements the "lazy" portion of
1031  * determining whether or not a release sequence was contiguous, since not all
1032  * modification order information is present at the time an action occurs.
1033  *
1034  * @param location The location/object that should be checked for release
1035  * sequence resolutions
1036  * @param work_queue The work queue to which to add work items as they are
1037  * generated
1038  * @return True if any updates occurred (new synchronization, new mo_graph
1039  * edges)
1040  */
1041 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1042 {
1043         std::list<ModelAction *> *list;
1044         list = lazy_sync_with_release->getptr(location);
1045         if (!list)
1046                 return false;
1047
1048         bool updated = false;
1049         std::list<ModelAction *>::iterator it = list->begin();
1050         while (it != list->end()) {
1051                 ModelAction *act = *it;
1052                 const ModelAction *rf = act->get_reads_from();
1053                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1054                 bool complete;
1055                 complete = release_seq_head(rf, &release_heads);
1056                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1057                         if (!act->has_synchronized_with(release_heads[i])) {
1058                                 updated = true;
1059                                 act->synchronize_with(release_heads[i]);
1060                         }
1061                 }
1062
1063                 if (updated) {
1064                         /* Re-check act for mo_graph edges */
1065                         work_queue->push_back(MOEdgeWorkEntry(act));
1066
1067                         /* propagate synchronization to later actions */
1068                         action_list_t::reverse_iterator it = action_trace->rbegin();
1069                         while ((*it) != act) {
1070                                 ModelAction *propagate = *it;
1071                                 if (act->happens_before(propagate)) {
1072                                         propagate->synchronize_with(act);
1073                                         /* Re-check 'propagate' for mo_graph edges */
1074                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1075                                 }
1076                         }
1077                 }
1078                 if (complete) {
1079                         it = list->erase(it);
1080                         (*lazy_sync_size)--;
1081                 } else
1082                         it++;
1083         }
1084
1085         // If we resolved promises or data races, see if we have realized a data race.
1086         if (checkDataRaces()) {
1087                 set_assert();
1088         }
1089
1090         return updated;
1091 }
1092
1093 /**
1094  * Performs various bookkeeping operations for the current ModelAction. For
1095  * instance, adds action to the per-object, per-thread action vector and to the
1096  * action trace list of all thread actions.
1097  *
1098  * @param act is the ModelAction to add.
1099  */
1100 void ModelChecker::add_action_to_lists(ModelAction *act)
1101 {
1102         int tid = id_to_int(act->get_tid());
1103         action_trace->push_back(act);
1104
1105         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1106
1107         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1108         if (tid >= (int)vec->size())
1109                 vec->resize(priv->next_thread_id);
1110         (*vec)[tid].push_back(act);
1111
1112         if ((int)thrd_last_action->size() <= tid)
1113                 thrd_last_action->resize(get_num_threads());
1114         (*thrd_last_action)[tid] = act;
1115 }
1116
1117 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1118 {
1119         int nthreads = get_num_threads();
1120         if ((int)thrd_last_action->size() < nthreads)
1121                 thrd_last_action->resize(nthreads);
1122         return (*thrd_last_action)[id_to_int(tid)];
1123 }
1124
1125 /**
1126  * Gets the last memory_order_seq_cst write (in the total global sequence)
1127  * performed on a particular object (i.e., memory location), not including the
1128  * current action.
1129  * @param curr The current ModelAction; also denotes the object location to
1130  * check
1131  * @return The last seq_cst write
1132  */
1133 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1134 {
1135         void *location = curr->get_location();
1136         action_list_t *list = obj_map->get_safe_ptr(location);
1137         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1138         action_list_t::reverse_iterator rit;
1139         for (rit = list->rbegin(); rit != list->rend(); rit++)
1140                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1141                         return *rit;
1142         return NULL;
1143 }
1144
1145 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1146 {
1147         ModelAction *parent = get_last_action(tid);
1148         if (!parent)
1149                 parent = get_thread(tid)->get_creation();
1150         return parent;
1151 }
1152
1153 /**
1154  * Returns the clock vector for a given thread.
1155  * @param tid The thread whose clock vector we want
1156  * @return Desired clock vector
1157  */
1158 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1159 {
1160         return get_parent_action(tid)->get_cv();
1161 }
1162
1163 /**
1164  * Resolve a set of Promises with a current write. The set is provided in the
1165  * Node corresponding to @a write.
1166  * @param write The ModelAction that is fulfilling Promises
1167  * @return True if promises were resolved; false otherwise
1168  */
1169 bool ModelChecker::resolve_promises(ModelAction *write)
1170 {
1171         bool resolved = false;
1172
1173         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1174                 Promise *promise = (*promises)[promise_index];
1175                 if (write->get_node()->get_promise(i)) {
1176                         ModelAction *read = promise->get_action();
1177                         read->read_from(write);
1178                         if (read->is_rmw()) {
1179                                 mo_graph->addRMWEdge(write, read);
1180                         }
1181                         //First fix up the modification order for actions that happened
1182                         //before the read
1183                         r_modification_order(read, write);
1184                         //Next fix up the modification order for actions that happened
1185                         //after the read.
1186                         post_r_modification_order(read, write);
1187                         promises->erase(promises->begin() + promise_index);
1188                         resolved = true;
1189                 } else
1190                         promise_index++;
1191         }
1192         return resolved;
1193 }
1194
1195 /**
1196  * Compute the set of promises that could potentially be satisfied by this
1197  * action. Note that the set computation actually appears in the Node, not in
1198  * ModelChecker.
1199  * @param curr The ModelAction that may satisfy promises
1200  */
1201 void ModelChecker::compute_promises(ModelAction *curr)
1202 {
1203         for (unsigned int i = 0; i < promises->size(); i++) {
1204                 Promise *promise = (*promises)[i];
1205                 const ModelAction *act = promise->get_action();
1206                 if (!act->happens_before(curr) &&
1207                                 act->is_read() &&
1208                                 !act->is_synchronizing(curr) &&
1209                                 !act->same_thread(curr) &&
1210                                 promise->get_value() == curr->get_value()) {
1211                         curr->get_node()->set_promise(i);
1212                 }
1213         }
1214 }
1215
1216 /** Checks promises in response to change in ClockVector Threads. */
1217 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1218 {
1219         for (unsigned int i = 0; i < promises->size(); i++) {
1220                 Promise *promise = (*promises)[i];
1221                 const ModelAction *act = promise->get_action();
1222                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1223                                 merge_cv->synchronized_since(act)) {
1224                         //This thread is no longer able to send values back to satisfy the promise
1225                         int num_synchronized_threads = promise->increment_threads();
1226                         if (num_synchronized_threads == get_num_threads()) {
1227                                 //Promise has failed
1228                                 failed_promise = true;
1229                                 return;
1230                         }
1231                 }
1232         }
1233 }
1234
1235 /**
1236  * Build up an initial set of all past writes that this 'read' action may read
1237  * from. This set is determined by the clock vector's "happens before"
1238  * relationship.
1239  * @param curr is the current ModelAction that we are exploring; it must be a
1240  * 'read' operation.
1241  */
1242 void ModelChecker::build_reads_from_past(ModelAction *curr)
1243 {
1244         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1245         unsigned int i;
1246         ASSERT(curr->is_read());
1247
1248         ModelAction *last_seq_cst = NULL;
1249
1250         /* Track whether this object has been initialized */
1251         bool initialized = false;
1252
1253         if (curr->is_seqcst()) {
1254                 last_seq_cst = get_last_seq_cst(curr);
1255                 /* We have to at least see the last sequentially consistent write,
1256                          so we are initialized. */
1257                 if (last_seq_cst != NULL)
1258                         initialized = true;
1259         }
1260
1261         /* Iterate over all threads */
1262         for (i = 0; i < thrd_lists->size(); i++) {
1263                 /* Iterate over actions in thread, starting from most recent */
1264                 action_list_t *list = &(*thrd_lists)[i];
1265                 action_list_t::reverse_iterator rit;
1266                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1267                         ModelAction *act = *rit;
1268
1269                         /* Only consider 'write' actions */
1270                         if (!act->is_write() || act == curr)
1271                                 continue;
1272
1273                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1274                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1275                                 DEBUG("Adding action to may_read_from:\n");
1276                                 if (DBG_ENABLED()) {
1277                                         act->print();
1278                                         curr->print();
1279                                 }
1280                                 curr->get_node()->add_read_from(act);
1281                         }
1282
1283                         /* Include at most one act per-thread that "happens before" curr */
1284                         if (act->happens_before(curr)) {
1285                                 initialized = true;
1286                                 break;
1287                         }
1288                 }
1289         }
1290
1291         if (!initialized) {
1292                 /** @todo Need a more informative way of reporting errors. */
1293                 printf("ERROR: may read from uninitialized atomic\n");
1294         }
1295
1296         if (DBG_ENABLED() || !initialized) {
1297                 printf("Reached read action:\n");
1298                 curr->print();
1299                 printf("Printing may_read_from\n");
1300                 curr->get_node()->print_may_read_from();
1301                 printf("End printing may_read_from\n");
1302         }
1303
1304         ASSERT(initialized);
1305 }
1306
1307 static void print_list(action_list_t *list)
1308 {
1309         action_list_t::iterator it;
1310
1311         printf("---------------------------------------------------------------------\n");
1312         printf("Trace:\n");
1313
1314         for (it = list->begin(); it != list->end(); it++) {
1315                 (*it)->print();
1316         }
1317         printf("---------------------------------------------------------------------\n");
1318 }
1319
1320 void ModelChecker::print_summary()
1321 {
1322         printf("\n");
1323         printf("Number of executions: %d\n", num_executions);
1324         printf("Number of feasible executions: %d\n", num_feasible_executions);
1325         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1326
1327 #if SUPPORT_MOD_ORDER_DUMP
1328         scheduler->print();
1329         char buffername[100];
1330         sprintf(buffername, "exec%u",num_executions);
1331         mo_graph->dumpGraphToFile(buffername);
1332 #endif
1333
1334         if (!isfinalfeasible())
1335                 printf("INFEASIBLE EXECUTION!\n");
1336         print_list(action_trace);
1337         printf("\n");
1338 }
1339
1340 /**
1341  * Add a Thread to the system for the first time. Should only be called once
1342  * per thread.
1343  * @param t The Thread to add
1344  */
1345 void ModelChecker::add_thread(Thread *t)
1346 {
1347         thread_map->put(id_to_int(t->get_id()), t);
1348         scheduler->add_thread(t);
1349 }
1350
1351 void ModelChecker::remove_thread(Thread *t)
1352 {
1353         scheduler->remove_thread(t);
1354 }
1355
1356 /**
1357  * Switch from a user-context to the "master thread" context (a.k.a. system
1358  * context). This switch is made with the intention of exploring a particular
1359  * model-checking action (described by a ModelAction object). Must be called
1360  * from a user-thread context.
1361  * @param act The current action that will be explored. Must not be NULL.
1362  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1363  */
1364 int ModelChecker::switch_to_master(ModelAction *act)
1365 {
1366         DBG();
1367         Thread *old = thread_current();
1368         set_current_action(act);
1369         old->set_state(THREAD_READY);
1370         return Thread::swap(old, &system_context);
1371 }
1372
1373 /**
1374  * Takes the next step in the execution, if possible.
1375  * @return Returns true (success) if a step was taken and false otherwise.
1376  */
1377 bool ModelChecker::take_step() {
1378         Thread *curr, *next;
1379
1380         if (has_asserted())
1381                 return false;
1382
1383         curr = thread_current();
1384         if (curr) {
1385                 if (curr->get_state() == THREAD_READY) {
1386                         ASSERT(priv->current_action);
1387
1388                         priv->nextThread = check_current_action(priv->current_action);
1389                         priv->current_action = NULL;
1390                         if (!curr->is_blocked() && !curr->is_complete())
1391                                 scheduler->add_thread(curr);
1392                 } else {
1393                         ASSERT(false);
1394                 }
1395         }
1396         next = scheduler->next_thread(priv->nextThread);
1397
1398         /* Infeasible -> don't take any more steps */
1399         if (!isfeasible())
1400                 return false;
1401
1402         if (next)
1403                 next->set_state(THREAD_RUNNING);
1404         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1405
1406         /* next == NULL -> don't take any more steps */
1407         if (!next)
1408                 return false;
1409         /* Return false only if swap fails with an error */
1410         return (Thread::swap(&system_context, next) == 0);
1411 }
1412
1413 /** Runs the current execution until threre are no more steps to take. */
1414 void ModelChecker::finish_execution() {
1415         DBG();
1416
1417         while (take_step());
1418 }