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 #include "mutex.h"
  15
  16 #define INITIAL_THREAD_ID       0
  17
  18 ModelChecker *model;
  19
  20 /** @brief Constructor */
  21 ModelChecker::ModelChecker(struct model_params params) :
  22         /* Initialize default scheduler */
  23         params(params),
  24         scheduler(new Scheduler()),
  25         num_executions(0),
  26         num_feasible_executions(0),
  27         diverge(NULL),
  28         action_trace(new action_list_t()),
  29         thread_map(new HashTable<int, Thread *, int>()),
  30         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  31         lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         promises(new std::vector<Promise *>()),
  34         futurevalues(new std::vector<struct PendingFutureValue>()),
  35         pending_acq_rel_seq(new std::vector<ModelAction *>()),
  36         thrd_last_action(new std::vector<ModelAction *>(1)),
  37         node_stack(new NodeStack()),
  38         mo_graph(new CycleGraph()),
  39         failed_promise(false),
  40         too_many_reads(false),
  41         asserted(false),
  42         bad_synchronization(false)
  43 {
  44         /* Allocate this "size" on the snapshotting heap */
  45         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  46         /* First thread created will have id INITIAL_THREAD_ID */
  47         priv->next_thread_id = INITIAL_THREAD_ID;
  48 }
  49
  50 /** @brief Destructor */
  51 ModelChecker::~ModelChecker()
  52 {
  53         for (int i = 0; i < get_num_threads(); i++)
  54                 delete thread_map->get(i);
  55         delete thread_map;
  56
  57         delete obj_thrd_map;
  58         delete obj_map;
  59         delete lock_waiters_map;
  60         delete action_trace;
  61
  62         for (unsigned int i = 0; i < promises->size(); i++)
  63                 delete (*promises)[i];
  64         delete promises;
  65
  66         delete pending_acq_rel_seq;
  67
  68         delete thrd_last_action;
  69         delete node_stack;
  70         delete scheduler;
  71         delete mo_graph;
  72 }
  73
  74 /**
  75  * Restores user program to initial state and resets all model-checker data
  76  * structures.
  77  */
  78 void ModelChecker::reset_to_initial_state()
  79 {
  80         DEBUG("+++ Resetting to initial state +++\n");
  81         node_stack->reset_execution();
  82         failed_promise = false;
  83         too_many_reads = false;
  84         bad_synchronization = false;
  85         reset_asserted();
  86         snapshotObject->backTrackBeforeStep(0);
  87 }
  88
  89 /** @return a thread ID for a new Thread */
  90 thread_id_t ModelChecker::get_next_id()
  91 {
  92         return priv->next_thread_id++;
  93 }
  94
  95 /** @return the number of user threads created during this execution */
  96 int ModelChecker::get_num_threads()
  97 {
  98         return priv->next_thread_id;
  99 }
 100
 101 /** @return a sequence number for a new ModelAction */
 102 modelclock_t ModelChecker::get_next_seq_num()
 103 {
 104         return ++priv->used_sequence_numbers;
 105 }
 106
 107 /**
 108  * @brief Choose the next thread to execute.
 109  *
 110  * This function chooses the next thread that should execute. It can force the
 111  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 112  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 113  * The model-checker may have no preference regarding the next thread (i.e.,
 114  * when exploring a new execution ordering), in which case this will return
 115  * NULL.
 116  * @param curr The current ModelAction. This action might guide the choice of
 117  * next thread.
 118  * @return The next thread to run. If the model-checker has no preference, NULL.
 119  */
 120 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 121 {
 122         thread_id_t tid;
 123
 124         if (curr!=NULL) {
 125                 /* Do not split atomic actions. */
 126                 if (curr->is_rmwr())
 127                         return thread_current();
 128                 /* The THREAD_CREATE action points to the created Thread */
 129                 else if (curr->get_type() == THREAD_CREATE)
 130                         return (Thread *)curr->get_location();
 131         }
 132
 133         /* Have we completed exploring the preselected path? */
 134         if (diverge == NULL)
 135                 return NULL;
 136
 137         /* Else, we are trying to replay an execution */
 138         ModelAction *next = node_stack->get_next()->get_action();
 139
 140         if (next == diverge) {
 141                 Node *nextnode = next->get_node();
 142                 /* Reached divergence point */
 143                 if (nextnode->increment_promise()) {
 144                         /* The next node will try to satisfy a different set of promises. */
 145                         tid = next->get_tid();
 146                         node_stack->pop_restofstack(2);
 147                 } else if (nextnode->increment_read_from()) {
 148                         /* The next node will read from a different value. */
 149                         tid = next->get_tid();
 150                         node_stack->pop_restofstack(2);
 151                 } else if (nextnode->increment_future_value()) {
 152                         /* The next node will try to read from a different future value. */
 153                         tid = next->get_tid();
 154                         node_stack->pop_restofstack(2);
 155                 } else {
 156                         /* Make a different thread execute for next step */
 157                         Node *node = nextnode->get_parent();
 158                         tid = node->get_next_backtrack();
 159                         node_stack->pop_restofstack(1);
 160                 }
 161                 DEBUG("*** Divergence point ***\n");
 162                 diverge = NULL;
 163         } else {
 164                 tid = next->get_tid();
 165         }
 166         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 167         ASSERT(tid != THREAD_ID_T_NONE);
 168         return thread_map->get(id_to_int(tid));
 169 }
 170
 171 /**
 172  * Queries the model-checker for more executions to explore and, if one
 173  * exists, resets the model-checker state to execute a new execution.
 174  *
 175  * @return If there are more executions to explore, return true. Otherwise,
 176  * return false.
 177  */
 178 bool ModelChecker::next_execution()
 179 {
 180         DBG();
 181
 182         num_executions++;
 183         if (isfinalfeasible())
 184                 num_feasible_executions++;
 185
 186         if (isfinalfeasible() || DBG_ENABLED())
 187                 print_summary();
 188
 189         if ((diverge = get_next_backtrack()) == NULL)
 190                 return false;
 191
 192         if (DBG_ENABLED()) {
 193                 printf("Next execution will diverge at:\n");
 194                 diverge->print();
 195         }
 196
 197         reset_to_initial_state();
 198         return true;
 199 }
 200
 201 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 202 {
 203         switch (act->get_type()) {
 204         case ATOMIC_READ:
 205         case ATOMIC_WRITE:
 206         case ATOMIC_RMW: {
 207                 /* linear search: from most recent to oldest */
 208                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 209                 action_list_t::reverse_iterator rit;
 210                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 211                         ModelAction *prev = *rit;
 212                         if (act->is_synchronizing(prev))
 213                                 return prev;
 214                 }
 215                 break;
 216         }
 217         case ATOMIC_LOCK:
 218         case ATOMIC_TRYLOCK: {
 219                 /* linear search: from most recent to oldest */
 220                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 221                 action_list_t::reverse_iterator rit;
 222                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 223                         ModelAction *prev = *rit;
 224                         if (act->is_conflicting_lock(prev))
 225                                 return prev;
 226                 }
 227                 break;
 228         }
 229         case ATOMIC_UNLOCK: {
 230                 /* linear search: from most recent to oldest */
 231                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 232                 action_list_t::reverse_iterator rit;
 233                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 234                         ModelAction *prev = *rit;
 235                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 236                                 return prev;
 237                 }
 238                 break;
 239         }
 240         default:
 241                 break;
 242         }
 243         return NULL;
 244 }
 245
 246 /** This method find backtracking points where we should try to
 247  * reorder the parameter ModelAction against.
 248  *
 249  * @param the ModelAction to find backtracking points for.
 250  */
 251 void ModelChecker::set_backtracking(ModelAction *act)
 252 {
 253         Thread *t = get_thread(act);
 254         ModelAction * prev = get_last_conflict(act);
 255         if (prev == NULL)
 256                 return;
 257
 258         Node * node = prev->get_node()->get_parent();
 259
 260         int low_tid, high_tid;
 261         if (node->is_enabled(t)) {
 262                 low_tid = id_to_int(act->get_tid());
 263                 high_tid = low_tid+1;
 264         } else {
 265                 low_tid = 0;
 266                 high_tid = get_num_threads();
 267         }
 268
 269         for(int i = low_tid; i < high_tid; i++) {
 270                 thread_id_t tid = int_to_id(i);
 271                 if (!node->is_enabled(tid))
 272                         continue;
 273
 274                 /* Check if this has been explored already */
 275                 if (node->has_been_explored(tid))
 276                         continue;
 277
 278                 /* See if fairness allows */
 279                 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
 280                         bool unfair=false;
 281                         for(int t=0;t<node->get_num_threads();t++) {
 282                                 thread_id_t tother=int_to_id(t);
 283                                 if (node->is_enabled(tother) && node->has_priority(tother)) {
 284                                         unfair=true;
 285                                         break;
 286                                 }
 287                         }
 288                         if (unfair)
 289                                 continue;
 290                 }
 291
 292                 /* Cache the latest backtracking point */
 293                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 294                         priv->next_backtrack = prev;
 295
 296                 /* If this is a new backtracking point, mark the tree */
 297                 if (!node->set_backtrack(tid))
 298                         continue;
 299                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 300                                         prev->get_tid(), t->get_id());
 301                 if (DBG_ENABLED()) {
 302                         prev->print();
 303                         act->print();
 304                 }
 305         }
 306 }
 307
 308 /**
 309  * Returns last backtracking point. The model checker will explore a different
 310  * path for this point in the next execution.
 311  * @return The ModelAction at which the next execution should diverge.
 312  */
 313 ModelAction * ModelChecker::get_next_backtrack()
 314 {
 315         ModelAction *next = priv->next_backtrack;
 316         priv->next_backtrack = NULL;
 317         return next;
 318 }
 319
 320 /**
 321  * Processes a read or rmw model action.
 322  * @param curr is the read model action to process.
 323  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 324  * @return True if processing this read updates the mo_graph.
 325  */
 326 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 327 {
 328         uint64_t value;
 329         bool updated = false;
 330         while (true) {
 331                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 332                 if (reads_from != NULL) {
 333                         mo_graph->startChanges();
 334
 335                         value = reads_from->get_value();
 336                         bool r_status = false;
 337
 338                         if (!second_part_of_rmw) {
 339                                 check_recency(curr, reads_from);
 340                                 r_status = r_modification_order(curr, reads_from);
 341                         }
 342
 343
 344                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 345                                 mo_graph->rollbackChanges();
 346                                 too_many_reads = false;
 347                                 continue;
 348                         }
 349
 350                         curr->read_from(reads_from);
 351                         mo_graph->commitChanges();
 352                         updated |= r_status;
 353                 } else if (!second_part_of_rmw) {
 354                         /* Read from future value */
 355                         value = curr->get_node()->get_future_value();
 356                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 357                         curr->read_from(NULL);
 358                         Promise *valuepromise = new Promise(curr, value, expiration);
 359                         promises->push_back(valuepromise);
 360                 }
 361                 get_thread(curr)->set_return_value(value);
 362                 return updated;
 363         }
 364 }
 365
 366 /**
 367  * Processes a lock, trylock, or unlock model action.  @param curr is
 368  * the read model action to process.
 369  *
 370  * The try lock operation checks whether the lock is taken.  If not,
 371  * it falls to the normal lock operation case.  If so, it returns
 372  * fail.
 373  *
 374  * The lock operation has already been checked that it is enabled, so
 375  * it just grabs the lock and synchronizes with the previous unlock.
 376  *
 377  * The unlock operation has to re-enable all of the threads that are
 378  * waiting on the lock.
 379  *
 380  * @return True if synchronization was updated; false otherwise
 381  */
 382 bool ModelChecker::process_mutex(ModelAction *curr) {
 383         std::mutex *mutex = (std::mutex *)curr->get_location();
 384         struct std::mutex_state *state = mutex->get_state();
 385         switch (curr->get_type()) {
 386         case ATOMIC_TRYLOCK: {
 387                 bool success = !state->islocked;
 388                 curr->set_try_lock(success);
 389                 if (!success) {
 390                         get_thread(curr)->set_return_value(0);
 391                         break;
 392                 }
 393                 get_thread(curr)->set_return_value(1);
 394         }
 395                 //otherwise fall into the lock case
 396         case ATOMIC_LOCK: {
 397                 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
 398                         printf("Lock access before initialization\n");
 399                         set_assert();
 400                 }
 401                 state->islocked = true;
 402                 ModelAction *unlock = get_last_unlock(curr);
 403                 //synchronize with the previous unlock statement
 404                 if (unlock != NULL) {
 405                         curr->synchronize_with(unlock);
 406                         return true;
 407                 }
 408                 break;
 409         }
 410         case ATOMIC_UNLOCK: {
 411                 //unlock the lock
 412                 state->islocked = false;
 413                 //wake up the other threads
 414                 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 415                 //activate all the waiting threads
 416                 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
 417                         scheduler->add_thread(get_thread((*rit)->get_tid()));
 418                 }
 419                 waiters->clear();
 420                 break;
 421         }
 422         default:
 423                 ASSERT(0);
 424         }
 425         return false;
 426 }
 427
 428 /**
 429  * Process a write ModelAction
 430  * @param curr The ModelAction to process
 431  * @return True if the mo_graph was updated or promises were resolved
 432  */
 433 bool ModelChecker::process_write(ModelAction *curr)
 434 {
 435         bool updated_mod_order = w_modification_order(curr);
 436         bool updated_promises = resolve_promises(curr);
 437
 438         if (promises->size() == 0) {
 439                 for (unsigned int i = 0; i < futurevalues->size(); i++) {
 440                         struct PendingFutureValue pfv = (*futurevalues)[i];
 441                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 442                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 443                                 priv->next_backtrack = pfv.act;
 444                 }
 445                 futurevalues->resize(0);
 446         }
 447
 448         mo_graph->commitChanges();
 449         get_thread(curr)->set_return_value(VALUE_NONE);
 450         return updated_mod_order || updated_promises;
 451 }
 452
 453 /**
 454  * @brief Process the current action for thread-related activity
 455  *
 456  * Performs current-action processing for a THREAD_* ModelAction. Proccesses
 457  * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
 458  * synchronization, etc.  This function is a no-op for non-THREAD actions
 459  * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
 460  *
 461  * @param curr The current action
 462  * @return True if synchronization was updated
 463  */
 464 bool ModelChecker::process_thread_action(ModelAction *curr)
 465 {
 466         bool synchronized = false;
 467
 468         switch (curr->get_type()) {
 469         case THREAD_CREATE: {
 470                 Thread *th = (Thread *)curr->get_location();
 471                 th->set_creation(curr);
 472                 break;
 473         }
 474         case THREAD_JOIN: {
 475                 Thread *waiting, *blocking;
 476                 waiting = get_thread(curr);
 477                 blocking = (Thread *)curr->get_location();
 478                 if (!blocking->is_complete()) {
 479                         blocking->push_wait_list(curr);
 480                         scheduler->sleep(waiting);
 481                 } else {
 482                         do_complete_join(curr);
 483                         synchronized = true;
 484                 }
 485                 break;
 486         }
 487         case THREAD_FINISH: {
 488                 Thread *th = get_thread(curr);
 489                 while (!th->wait_list_empty()) {
 490                         ModelAction *act = th->pop_wait_list();
 491                         Thread *wake = get_thread(act);
 492                         scheduler->wake(wake);
 493                         do_complete_join(act);
 494                         synchronized = true;
 495                 }
 496                 th->complete();
 497                 break;
 498         }
 499         case THREAD_START: {
 500                 check_promises(NULL, curr->get_cv());
 501                 break;
 502         }
 503         default:
 504                 break;
 505         }
 506
 507         return synchronized;
 508 }
 509
 510 /**
 511  * Initialize the current action by performing one or more of the following
 512  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 513  * in the NodeStack, manipulating backtracking sets, allocating and
 514  * initializing clock vectors, and computing the promises to fulfill.
 515  *
 516  * @param curr The current action, as passed from the user context; may be
 517  * freed/invalidated after the execution of this function
 518  * @return The current action, as processed by the ModelChecker. Is only the
 519  * same as the parameter @a curr if this is a newly-explored action.
 520  */
 521 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 522 {
 523         ModelAction *newcurr;
 524
 525         if (curr->is_rmwc() || curr->is_rmw()) {
 526                 newcurr = process_rmw(curr);
 527                 delete curr;
 528                 compute_promises(newcurr);
 529                 return newcurr;
 530         }
 531
 532         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 533         if (newcurr) {
 534                 /* First restore type and order in case of RMW operation */
 535                 if (curr->is_rmwr())
 536                         newcurr->copy_typeandorder(curr);
 537
 538                 ASSERT(curr->get_location() == newcurr->get_location());
 539                 newcurr->copy_from_new(curr);
 540
 541                 /* Discard duplicate ModelAction; use action from NodeStack */
 542                 delete curr;
 543
 544                 /* If we have diverged, we need to reset the clock vector. */
 545                 if (diverge == NULL)
 546                         newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 547         } else {
 548                 newcurr = curr;
 549                 /*
 550                  * Perform one-time actions when pushing new ModelAction onto
 551                  * NodeStack
 552                  */
 553                 curr->create_cv(get_parent_action(curr->get_tid()));
 554                 if (curr->is_write())
 555                         compute_promises(curr);
 556         }
 557         return newcurr;
 558 }
 559
 560 /**
 561  * This method checks whether a model action is enabled at the given point.
 562  * At this point, it checks whether a lock operation would be successful at this point.
 563  * If not, it puts the thread in a waiter list.
 564  * @param curr is the ModelAction to check whether it is enabled.
 565  * @return a bool that indicates whether the action is enabled.
 566  */
 567 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 568         if (curr->is_lock()) {
 569                 std::mutex * lock = (std::mutex *)curr->get_location();
 570                 struct std::mutex_state * state = lock->get_state();
 571                 if (state->islocked) {
 572                         //Stick the action in the appropriate waiting queue
 573                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 574                         return false;
 575                 }
 576         }
 577
 578         return true;
 579 }
 580
 581 /**
 582  * This is the heart of the model checker routine. It performs model-checking
 583  * actions corresponding to a given "current action." Among other processes, it
 584  * calculates reads-from relationships, updates synchronization clock vectors,
 585  * forms a memory_order constraints graph, and handles replay/backtrack
 586  * execution when running permutations of previously-observed executions.
 587  *
 588  * @param curr The current action to process
 589  * @return The next Thread that must be executed. May be NULL if ModelChecker
 590  * makes no choice (e.g., according to replay execution, combining RMW actions,
 591  * etc.)
 592  */
 593 Thread * ModelChecker::check_current_action(ModelAction *curr)
 594 {
 595         ASSERT(curr);
 596
 597         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 598
 599         if (!check_action_enabled(curr)) {
 600                 /* Make the execution look like we chose to run this action
 601                  * much later, when a lock is actually available to release */
 602                 get_current_thread()->set_pending(curr);
 603                 remove_thread(get_current_thread());
 604                 return get_next_thread(NULL);
 605         }
 606
 607         ModelAction *newcurr = initialize_curr_action(curr);
 608
 609         /* Add the action to lists before any other model-checking tasks */
 610         if (!second_part_of_rmw)
 611                 add_action_to_lists(newcurr);
 612
 613         /* Build may_read_from set for newly-created actions */
 614         if (curr == newcurr && curr->is_read())
 615                 build_reads_from_past(curr);
 616         curr = newcurr;
 617
 618         /* Initialize work_queue with the "current action" work */
 619         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 620
 621         while (!work_queue.empty()) {
 622                 WorkQueueEntry work = work_queue.front();
 623                 work_queue.pop_front();
 624
 625                 switch (work.type) {
 626                 case WORK_CHECK_CURR_ACTION: {
 627                         ModelAction *act = work.action;
 628                         bool update = false; /* update this location's release seq's */
 629                         bool update_all = false; /* update all release seq's */
 630
 631                         if (process_thread_action(curr))
 632                                 update_all = true;
 633
 634                         if (act->is_read() && process_read(act, second_part_of_rmw))
 635                                 update = true;
 636
 637                         if (act->is_write() && process_write(act))
 638                                 update = true;
 639
 640                         if (act->is_mutex_op() && process_mutex(act))
 641                                 update_all = true;
 642
 643                         if (update_all)
 644                                 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
 645                         else if (update)
 646                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 647                         break;
 648                 }
 649                 case WORK_CHECK_RELEASE_SEQ:
 650                         resolve_release_sequences(work.location, &work_queue);
 651                         break;
 652                 case WORK_CHECK_MO_EDGES: {
 653                         /** @todo Complete verification of work_queue */
 654                         ModelAction *act = work.action;
 655                         bool updated = false;
 656
 657                         if (act->is_read()) {
 658                                 if (r_modification_order(act, act->get_reads_from()))
 659                                         updated = true;
 660                         }
 661                         if (act->is_write()) {
 662                                 if (w_modification_order(act))
 663                                         updated = true;
 664                         }
 665                         mo_graph->commitChanges();
 666
 667                         if (updated)
 668                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 669                         break;
 670                 }
 671                 default:
 672                         ASSERT(false);
 673                         break;
 674                 }
 675         }
 676
 677         check_curr_backtracking(curr);
 678
 679         set_backtracking(curr);
 680
 681         return get_next_thread(curr);
 682 }
 683
 684 /**
 685  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 686  * operation from the Thread it is joining with. Must be called after the
 687  * completion of the Thread in question.
 688  * @param join The THREAD_JOIN action
 689  */
 690 void ModelChecker::do_complete_join(ModelAction *join)
 691 {
 692         Thread *blocking = (Thread *)join->get_location();
 693         ModelAction *act = get_last_action(blocking->get_id());
 694         join->synchronize_with(act);
 695 }
 696
 697 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 698         Node *currnode = curr->get_node();
 699         Node *parnode = currnode->get_parent();
 700
 701         if ((!parnode->backtrack_empty() ||
 702                          !currnode->read_from_empty() ||
 703                          !currnode->future_value_empty() ||
 704                          !currnode->promise_empty())
 705                         && (!priv->next_backtrack ||
 706                                         *curr > *priv->next_backtrack)) {
 707                 priv->next_backtrack = curr;
 708         }
 709 }
 710
 711 bool ModelChecker::promises_expired() {
 712         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 713                 Promise *promise = (*promises)[promise_index];
 714                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 715                         return true;
 716                 }
 717         }
 718         return false;
 719 }
 720
 721 /** @return whether the current partial trace must be a prefix of a
 722  * feasible trace. */
 723 bool ModelChecker::isfeasibleprefix() {
 724         return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
 725 }
 726
 727 /** @return whether the current partial trace is feasible. */
 728 bool ModelChecker::isfeasible() {
 729         if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
 730                 DEBUG("Infeasible: RMW violation\n");
 731
 732         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 733 }
 734
 735 /** @return whether the current partial trace is feasible other than
 736  * multiple RMW reading from the same store. */
 737 bool ModelChecker::isfeasibleotherthanRMW() {
 738         if (DBG_ENABLED()) {
 739                 if (mo_graph->checkForCycles())
 740                         DEBUG("Infeasible: modification order cycles\n");
 741                 if (failed_promise)
 742                         DEBUG("Infeasible: failed promise\n");
 743                 if (too_many_reads)
 744                         DEBUG("Infeasible: too many reads\n");
 745                 if (bad_synchronization)
 746                         DEBUG("Infeasible: bad synchronization ordering\n");
 747                 if (promises_expired())
 748                         DEBUG("Infeasible: promises expired\n");
 749         }
 750         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
 751 }
 752
 753 /** Returns whether the current completed trace is feasible. */
 754 bool ModelChecker::isfinalfeasible() {
 755         if (DBG_ENABLED() && promises->size() != 0)
 756                 DEBUG("Infeasible: unrevolved promises\n");
 757
 758         return isfeasible() && promises->size() == 0;
 759 }
 760
 761 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 762 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 763         int tid = id_to_int(act->get_tid());
 764         ModelAction *lastread = get_last_action(tid);
 765         lastread->process_rmw(act);
 766         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 767                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 768                 mo_graph->commitChanges();
 769         }
 770         return lastread;
 771 }
 772
 773 /**
 774  * Checks whether a thread has read from the same write for too many times
 775  * without seeing the effects of a later write.
 776  *
 777  * Basic idea:
 778  * 1) there must a different write that we could read from that would satisfy the modification order,
 779  * 2) we must have read from the same value in excess of maxreads times, and
 780  * 3) that other write must have been in the reads_from set for maxreads times.
 781  *
 782  * If so, we decide that the execution is no longer feasible.
 783  */
 784 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
 785         if (params.maxreads != 0) {
 786
 787                 if (curr->get_node()->get_read_from_size() <= 1)
 788                         return;
 789                 //Must make sure that execution is currently feasible...  We could
 790                 //accidentally clear by rolling back
 791                 if (!isfeasible())
 792                         return;
 793                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 794                 int tid = id_to_int(curr->get_tid());
 795
 796                 /* Skip checks */
 797                 if ((int)thrd_lists->size() <= tid)
 798                         return;
 799                 action_list_t *list = &(*thrd_lists)[tid];
 800
 801                 action_list_t::reverse_iterator rit = list->rbegin();
 802                 /* Skip past curr */
 803                 for (; (*rit) != curr; rit++)
 804                         ;
 805                 /* go past curr now */
 806                 rit++;
 807
 808                 action_list_t::reverse_iterator ritcopy = rit;
 809                 //See if we have enough reads from the same value
 810                 int count = 0;
 811                 for (; count < params.maxreads; rit++,count++) {
 812                         if (rit==list->rend())
 813                                 return;
 814                         ModelAction *act = *rit;
 815                         if (!act->is_read())
 816                                 return;
 817
 818                         if (act->get_reads_from() != rf)
 819                                 return;
 820                         if (act->get_node()->get_read_from_size() <= 1)
 821                                 return;
 822                 }
 823                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 824                         //Get write
 825                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 826
 827                         //Need a different write
 828                         if (write==rf)
 829                                 continue;
 830
 831                         /* Test to see whether this is a feasible write to read from*/
 832                         mo_graph->startChanges();
 833                         r_modification_order(curr, write);
 834                         bool feasiblereadfrom = isfeasible();
 835                         mo_graph->rollbackChanges();
 836
 837                         if (!feasiblereadfrom)
 838                                 continue;
 839                         rit = ritcopy;
 840
 841                         bool feasiblewrite = true;
 842                         //new we need to see if this write works for everyone
 843
 844                         for (int loop = count; loop>0; loop--,rit++) {
 845                                 ModelAction *act=*rit;
 846                                 bool foundvalue = false;
 847                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 848                                         if (act->get_node()->get_read_from_at(i)==write) {
 849                                                 foundvalue = true;
 850                                                 break;
 851                                         }
 852                                 }
 853                                 if (!foundvalue) {
 854                                         feasiblewrite = false;
 855                                         break;
 856                                 }
 857                         }
 858                         if (feasiblewrite) {
 859                                 too_many_reads = true;
 860                                 return;
 861                         }
 862                 }
 863         }
 864 }
 865
 866 /**
 867  * Updates the mo_graph with the constraints imposed from the current
 868  * read.
 869  *
 870  * Basic idea is the following: Go through each other thread and find
 871  * the lastest action that happened before our read.  Two cases:
 872  *
 873  * (1) The action is a write => that write must either occur before
 874  * the write we read from or be the write we read from.
 875  *
 876  * (2) The action is a read => the write that that action read from
 877  * must occur before the write we read from or be the same write.
 878  *
 879  * @param curr The current action. Must be a read.
 880  * @param rf The action that curr reads from. Must be a write.
 881  * @return True if modification order edges were added; false otherwise
 882  */
 883 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 884 {
 885         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 886         unsigned int i;
 887         bool added = false;
 888         ASSERT(curr->is_read());
 889
 890         /* Iterate over all threads */
 891         for (i = 0; i < thrd_lists->size(); i++) {
 892                 /* Iterate over actions in thread, starting from most recent */
 893                 action_list_t *list = &(*thrd_lists)[i];
 894                 action_list_t::reverse_iterator rit;
 895                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 896                         ModelAction *act = *rit;
 897
 898                         /*
 899                          * Include at most one act per-thread that "happens
 900                          * before" curr. Don't consider reflexively.
 901                          */
 902                         if (act->happens_before(curr) && act != curr) {
 903                                 if (act->is_write()) {
 904                                         if (rf != act) {
 905                                                 mo_graph->addEdge(act, rf);
 906                                                 added = true;
 907                                         }
 908                                 } else {
 909                                         const ModelAction *prevreadfrom = act->get_reads_from();
 910                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 911                                                 mo_graph->addEdge(prevreadfrom, rf);
 912                                                 added = true;
 913                                         }
 914                                 }
 915                                 break;
 916                         }
 917                 }
 918         }
 919
 920         return added;
 921 }
 922
 923 /** This method fixes up the modification order when we resolve a
 924  *  promises.  The basic problem is that actions that occur after the
 925  *  read curr could not property add items to the modification order
 926  *  for our read.
 927  *
 928  *  So for each thread, we find the earliest item that happens after
 929  *  the read curr.  This is the item we have to fix up with additional
 930  *  constraints.  If that action is write, we add a MO edge between
 931  *  the Action rf and that action.  If the action is a read, we add a
 932  *  MO edge between the Action rf, and whatever the read accessed.
 933  *
 934  * @param curr is the read ModelAction that we are fixing up MO edges for.
 935  * @param rf is the write ModelAction that curr reads from.
 936  *
 937  */
 938 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 939 {
 940         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 941         unsigned int i;
 942         ASSERT(curr->is_read());
 943
 944         /* Iterate over all threads */
 945         for (i = 0; i < thrd_lists->size(); i++) {
 946                 /* Iterate over actions in thread, starting from most recent */
 947                 action_list_t *list = &(*thrd_lists)[i];
 948                 action_list_t::reverse_iterator rit;
 949                 ModelAction *lastact = NULL;
 950
 951                 /* Find last action that happens after curr */
 952                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 953                         ModelAction *act = *rit;
 954                         if (curr->happens_before(act)) {
 955                                 lastact = act;
 956                         } else
 957                                 break;
 958                 }
 959
 960                         /* Include at most one act per-thread that "happens before" curr */
 961                 if (lastact != NULL) {
 962                         if (lastact->is_read()) {
 963                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 964                                 if (postreadfrom != NULL&&rf != postreadfrom)
 965                                         mo_graph->addEdge(rf, postreadfrom);
 966                         } else if (rf != lastact) {
 967                                 mo_graph->addEdge(rf, lastact);
 968                         }
 969                         break;
 970                 }
 971         }
 972 }
 973
 974 /**
 975  * Updates the mo_graph with the constraints imposed from the current write.
 976  *
 977  * Basic idea is the following: Go through each other thread and find
 978  * the lastest action that happened before our write.  Two cases:
 979  *
 980  * (1) The action is a write => that write must occur before
 981  * the current write
 982  *
 983  * (2) The action is a read => the write that that action read from
 984  * must occur before the current write.
 985  *
 986  * This method also handles two other issues:
 987  *
 988  * (I) Sequential Consistency: Making sure that if the current write is
 989  * seq_cst, that it occurs after the previous seq_cst write.
 990  *
 991  * (II) Sending the write back to non-synchronizing reads.
 992  *
 993  * @param curr The current action. Must be a write.
 994  * @return True if modification order edges were added; false otherwise
 995  */
 996 bool ModelChecker::w_modification_order(ModelAction *curr)
 997 {
 998         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 999         unsigned int i;
1000         bool added = false;
1001         ASSERT(curr->is_write());
1002
1003         if (curr->is_seqcst()) {
1004                 /* We have to at least see the last sequentially consistent write,
1005                          so we are initialized. */
1006                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1007                 if (last_seq_cst != NULL) {
1008                         mo_graph->addEdge(last_seq_cst, curr);
1009                         added = true;
1010                 }
1011         }
1012
1013         /* Iterate over all threads */
1014         for (i = 0; i < thrd_lists->size(); i++) {
1015                 /* Iterate over actions in thread, starting from most recent */
1016                 action_list_t *list = &(*thrd_lists)[i];
1017                 action_list_t::reverse_iterator rit;
1018                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1019                         ModelAction *act = *rit;
1020                         if (act == curr) {
1021                                 /*
1022                                  * If RMW, we already have all relevant edges,
1023                                  * so just skip to next thread.
1024                                  * If normal write, we need to look at earlier
1025                                  * actions, so continue processing list.
1026                                  */
1027                                 if (curr->is_rmw())
1028                                         break;
1029                                 else
1030                                         continue;
1031                         }
1032
1033                         /*
1034                          * Include at most one act per-thread that "happens
1035                          * before" curr
1036                          */
1037                         if (act->happens_before(curr)) {
1038                                 /*
1039                                  * Note: if act is RMW, just add edge:
1040                                  *   act --mo--> curr
1041                                  * The following edge should be handled elsewhere:
1042                                  *   readfrom(act) --mo--> act
1043                                  */
1044                                 if (act->is_write())
1045                                         mo_graph->addEdge(act, curr);
1046                                 else if (act->is_read() && act->get_reads_from() != NULL)
1047                                         mo_graph->addEdge(act->get_reads_from(), curr);
1048                                 added = true;
1049                                 break;
1050                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
1051                                                      !act->same_thread(curr)) {
1052                                 /* We have an action that:
1053                                    (1) did not happen before us
1054                                    (2) is a read and we are a write
1055                                    (3) cannot synchronize with us
1056                                    (4) is in a different thread
1057                                    =>
1058                                    that read could potentially read from our write.
1059                                  */
1060                                 if (thin_air_constraint_may_allow(curr, act)) {
1061                                         if (isfeasible() ||
1062                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1063                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1064                                                 futurevalues->push_back(pfv);
1065                                         }
1066                                 }
1067                         }
1068                 }
1069         }
1070
1071         return added;
1072 }
1073
1074 /** Arbitrary reads from the future are not allowed.  Section 29.3
1075  * part 9 places some constraints.  This method checks one result of constraint
1076  * constraint.  Others require compiler support. */
1077 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1078         if (!writer->is_rmw())
1079                 return true;
1080
1081         if (!reader->is_rmw())
1082                 return true;
1083
1084         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1085                 if (search == reader)
1086                         return false;
1087                 if (search->get_tid() == reader->get_tid() &&
1088                                 search->happens_before(reader))
1089                         break;
1090         }
1091
1092         return true;
1093 }
1094
1095 /**
1096  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1097  * The ModelAction under consideration is expected to be taking part in
1098  * release/acquire synchronization as an object of the "reads from" relation.
1099  * Note that this can only provide release sequence support for RMW chains
1100  * which do not read from the future, as those actions cannot be traced until
1101  * their "promise" is fulfilled. Similarly, we may not even establish the
1102  * presence of a release sequence with certainty, as some modification order
1103  * constraints may be decided further in the future. Thus, this function
1104  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1105  * and a boolean representing certainty.
1106  *
1107  * @todo Finish lazy updating, when promises are fulfilled in the future
1108  * @param rf The action that might be part of a release sequence. Must be a
1109  * write.
1110  * @param release_heads A pass-by-reference style return parameter.  After
1111  * execution of this function, release_heads will contain the heads of all the
1112  * relevant release sequences, if any exists
1113  * @return true, if the ModelChecker is certain that release_heads is complete;
1114  * false otherwise
1115  */
1116 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1117 {
1118         /* Only check for release sequences if there are no cycles */
1119         if (mo_graph->checkForCycles())
1120                 return false;
1121
1122         while (rf) {
1123                 ASSERT(rf->is_write());
1124
1125                 if (rf->is_release())
1126                         release_heads->push_back(rf);
1127                 if (!rf->is_rmw())
1128                         break; /* End of RMW chain */
1129
1130                 /** @todo Need to be smarter here...  In the linux lock
1131                  * example, this will run to the beginning of the program for
1132                  * every acquire. */
1133                 /** @todo The way to be smarter here is to keep going until 1
1134                  * thread has a release preceded by an acquire and you've seen
1135                  *       both. */
1136
1137                 /* acq_rel RMW is a sufficient stopping condition */
1138                 if (rf->is_acquire() && rf->is_release())
1139                         return true; /* complete */
1140
1141                 rf = rf->get_reads_from();
1142         };
1143         if (!rf) {
1144                 /* read from future: need to settle this later */
1145                 return false; /* incomplete */
1146         }
1147
1148         if (rf->is_release())
1149                 return true; /* complete */
1150
1151         /* else relaxed write; check modification order for contiguous subsequence
1152          * -> rf must be same thread as release */
1153         int tid = id_to_int(rf->get_tid());
1154         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1155         action_list_t *list = &(*thrd_lists)[tid];
1156         action_list_t::const_reverse_iterator rit;
1157
1158         /* Find rf in the thread list */
1159         rit = std::find(list->rbegin(), list->rend(), rf);
1160         ASSERT(rit != list->rend());
1161
1162         /* Find the last write/release */
1163         for (; rit != list->rend(); rit++)
1164                 if ((*rit)->is_release())
1165                         break;
1166         if (rit == list->rend()) {
1167                 /* No write-release in this thread */
1168                 return true; /* complete */
1169         }
1170         ModelAction *release = *rit;
1171
1172         ASSERT(rf->same_thread(release));
1173
1174         bool certain = true;
1175         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1176                 if (id_to_int(rf->get_tid()) == (int)i)
1177                         continue;
1178                 list = &(*thrd_lists)[i];
1179
1180                 /* Can we ensure no future writes from this thread may break
1181                  * the release seq? */
1182                 bool future_ordered = false;
1183
1184                 ModelAction *last = get_last_action(int_to_id(i));
1185                 if (last && (rf->happens_before(last) ||
1186                                 last->get_type() == THREAD_FINISH))
1187                         future_ordered = true;
1188
1189                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1190                         const ModelAction *act = *rit;
1191                         /* Reach synchronization -> this thread is complete */
1192                         if (act->happens_before(release))
1193                                 break;
1194                         if (rf->happens_before(act)) {
1195                                 future_ordered = true;
1196                                 continue;
1197                         }
1198
1199                         /* Only writes can break release sequences */
1200                         if (!act->is_write())
1201                                 continue;
1202
1203                         /* Check modification order */
1204                         if (mo_graph->checkReachable(rf, act)) {
1205                                 /* rf --mo--> act */
1206                                 future_ordered = true;
1207                                 continue;
1208                         }
1209                         if (mo_graph->checkReachable(act, release))
1210                                 /* act --mo--> release */
1211                                 break;
1212                         if (mo_graph->checkReachable(release, act) &&
1213                                       mo_graph->checkReachable(act, rf)) {
1214                                 /* release --mo-> act --mo--> rf */
1215                                 return true; /* complete */
1216                         }
1217                         certain = false;
1218                 }
1219                 if (!future_ordered)
1220                         return false; /* This thread is uncertain */
1221         }
1222
1223         if (certain)
1224                 release_heads->push_back(release);
1225         return certain;
1226 }
1227
1228 /**
1229  * A public interface for getting the release sequence head(s) with which a
1230  * given ModelAction must synchronize. This function only returns a non-empty
1231  * result when it can locate a release sequence head with certainty. Otherwise,
1232  * it may mark the internal state of the ModelChecker so that it will handle
1233  * the release sequence at a later time, causing @a act to update its
1234  * synchronization at some later point in execution.
1235  * @param act The 'acquire' action that may read from a release sequence
1236  * @param release_heads A pass-by-reference return parameter. Will be filled
1237  * with the head(s) of the release sequence(s), if they exists with certainty.
1238  * @see ModelChecker::release_seq_head
1239  */
1240 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1241 {
1242         const ModelAction *rf = act->get_reads_from();
1243         bool complete;
1244         complete = release_seq_head(rf, release_heads);
1245         if (!complete) {
1246                 /* add act to 'lazy checking' list */
1247                 pending_acq_rel_seq->push_back(act);
1248         }
1249 }
1250
1251 /**
1252  * Attempt to resolve all stashed operations that might synchronize with a
1253  * release sequence for a given location. This implements the "lazy" portion of
1254  * determining whether or not a release sequence was contiguous, since not all
1255  * modification order information is present at the time an action occurs.
1256  *
1257  * @param location The location/object that should be checked for release
1258  * sequence resolutions. A NULL value means to check all locations.
1259  * @param work_queue The work queue to which to add work items as they are
1260  * generated
1261  * @return True if any updates occurred (new synchronization, new mo_graph
1262  * edges)
1263  */
1264 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1265 {
1266         bool updated = false;
1267         std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
1268         while (it != pending_acq_rel_seq->end()) {
1269                 ModelAction *act = *it;
1270
1271                 /* Only resolve sequences on the given location, if provided */
1272                 if (location && act->get_location() != location) {
1273                         it++;
1274                         continue;
1275                 }
1276
1277                 const ModelAction *rf = act->get_reads_from();
1278                 rel_heads_list_t release_heads;
1279                 bool complete;
1280                 complete = release_seq_head(rf, &release_heads);
1281                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1282                         if (!act->has_synchronized_with(release_heads[i])) {
1283                                 if (act->synchronize_with(release_heads[i]))
1284                                         updated = true;
1285                                 else
1286                                         set_bad_synchronization();
1287                         }
1288                 }
1289
1290                 if (updated) {
1291                         /* Re-check act for mo_graph edges */
1292                         work_queue->push_back(MOEdgeWorkEntry(act));
1293
1294                         /* propagate synchronization to later actions */
1295                         action_list_t::reverse_iterator rit = action_trace->rbegin();
1296                         for (; (*rit) != act; rit++) {
1297                                 ModelAction *propagate = *rit;
1298                                 if (act->happens_before(propagate)) {
1299                                         propagate->synchronize_with(act);
1300                                         /* Re-check 'propagate' for mo_graph edges */
1301                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1302                                 }
1303                         }
1304                 }
1305                 if (complete)
1306                         it = pending_acq_rel_seq->erase(it);
1307                 else
1308                         it++;
1309         }
1310
1311         // If we resolved promises or data races, see if we have realized a data race.
1312         if (checkDataRaces()) {
1313                 set_assert();
1314         }
1315
1316         return updated;
1317 }
1318
1319 /**
1320  * Performs various bookkeeping operations for the current ModelAction. For
1321  * instance, adds action to the per-object, per-thread action vector and to the
1322  * action trace list of all thread actions.
1323  *
1324  * @param act is the ModelAction to add.
1325  */
1326 void ModelChecker::add_action_to_lists(ModelAction *act)
1327 {
1328         int tid = id_to_int(act->get_tid());
1329         action_trace->push_back(act);
1330
1331         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1332
1333         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1334         if (tid >= (int)vec->size())
1335                 vec->resize(priv->next_thread_id);
1336         (*vec)[tid].push_back(act);
1337
1338         if ((int)thrd_last_action->size() <= tid)
1339                 thrd_last_action->resize(get_num_threads());
1340         (*thrd_last_action)[tid] = act;
1341 }
1342
1343 /**
1344  * @brief Get the last action performed by a particular Thread
1345  * @param tid The thread ID of the Thread in question
1346  * @return The last action in the thread
1347  */
1348 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1349 {
1350         int threadid = id_to_int(tid);
1351         if (threadid < (int)thrd_last_action->size())
1352                 return (*thrd_last_action)[id_to_int(tid)];
1353         else
1354                 return NULL;
1355 }
1356
1357 /**
1358  * Gets the last memory_order_seq_cst write (in the total global sequence)
1359  * performed on a particular object (i.e., memory location), not including the
1360  * current action.
1361  * @param curr The current ModelAction; also denotes the object location to
1362  * check
1363  * @return The last seq_cst write
1364  */
1365 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1366 {
1367         void *location = curr->get_location();
1368         action_list_t *list = obj_map->get_safe_ptr(location);
1369         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1370         action_list_t::reverse_iterator rit;
1371         for (rit = list->rbegin(); rit != list->rend(); rit++)
1372                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1373                         return *rit;
1374         return NULL;
1375 }
1376
1377 /**
1378  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1379  * location). This function identifies the mutex according to the current
1380  * action, which is presumed to perform on the same mutex.
1381  * @param curr The current ModelAction; also denotes the object location to
1382  * check
1383  * @return The last unlock operation
1384  */
1385 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1386 {
1387         void *location = curr->get_location();
1388         action_list_t *list = obj_map->get_safe_ptr(location);
1389         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1390         action_list_t::reverse_iterator rit;
1391         for (rit = list->rbegin(); rit != list->rend(); rit++)
1392                 if ((*rit)->is_unlock())
1393                         return *rit;
1394         return NULL;
1395 }
1396
1397 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1398 {
1399         ModelAction *parent = get_last_action(tid);
1400         if (!parent)
1401                 parent = get_thread(tid)->get_creation();
1402         return parent;
1403 }
1404
1405 /**
1406  * Returns the clock vector for a given thread.
1407  * @param tid The thread whose clock vector we want
1408  * @return Desired clock vector
1409  */
1410 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1411 {
1412         return get_parent_action(tid)->get_cv();
1413 }
1414
1415 /**
1416  * Resolve a set of Promises with a current write. The set is provided in the
1417  * Node corresponding to @a write.
1418  * @param write The ModelAction that is fulfilling Promises
1419  * @return True if promises were resolved; false otherwise
1420  */
1421 bool ModelChecker::resolve_promises(ModelAction *write)
1422 {
1423         bool resolved = false;
1424
1425         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1426                 Promise *promise = (*promises)[promise_index];
1427                 if (write->get_node()->get_promise(i)) {
1428                         ModelAction *read = promise->get_action();
1429                         if (read->is_rmw()) {
1430                                 mo_graph->addRMWEdge(write, read);
1431                         }
1432                         read->read_from(write);
1433                         //First fix up the modification order for actions that happened
1434                         //before the read
1435                         r_modification_order(read, write);
1436                         //Next fix up the modification order for actions that happened
1437                         //after the read.
1438                         post_r_modification_order(read, write);
1439
1440                         promises->erase(promises->begin() + promise_index);
1441                         resolved = true;
1442                 } else
1443                         promise_index++;
1444         }
1445         return resolved;
1446 }
1447
1448 /**
1449  * Compute the set of promises that could potentially be satisfied by this
1450  * action. Note that the set computation actually appears in the Node, not in
1451  * ModelChecker.
1452  * @param curr The ModelAction that may satisfy promises
1453  */
1454 void ModelChecker::compute_promises(ModelAction *curr)
1455 {
1456         for (unsigned int i = 0; i < promises->size(); i++) {
1457                 Promise *promise = (*promises)[i];
1458                 const ModelAction *act = promise->get_action();
1459                 if (!act->happens_before(curr) &&
1460                                 act->is_read() &&
1461                                 !act->is_synchronizing(curr) &&
1462                                 !act->same_thread(curr) &&
1463                                 promise->get_value() == curr->get_value()) {
1464                         curr->get_node()->set_promise(i);
1465                 }
1466         }
1467 }
1468
1469 /** Checks promises in response to change in ClockVector Threads. */
1470 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1471 {
1472         for (unsigned int i = 0; i < promises->size(); i++) {
1473                 Promise *promise = (*promises)[i];
1474                 const ModelAction *act = promise->get_action();
1475                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1476                                 merge_cv->synchronized_since(act)) {
1477                         //This thread is no longer able to send values back to satisfy the promise
1478                         int num_synchronized_threads = promise->increment_threads();
1479                         if (num_synchronized_threads == get_num_threads()) {
1480                                 //Promise has failed
1481                                 failed_promise = true;
1482                                 return;
1483                         }
1484                 }
1485         }
1486 }
1487
1488 /**
1489  * Build up an initial set of all past writes that this 'read' action may read
1490  * from. This set is determined by the clock vector's "happens before"
1491  * relationship.
1492  * @param curr is the current ModelAction that we are exploring; it must be a
1493  * 'read' operation.
1494  */
1495 void ModelChecker::build_reads_from_past(ModelAction *curr)
1496 {
1497         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1498         unsigned int i;
1499         ASSERT(curr->is_read());
1500
1501         ModelAction *last_seq_cst = NULL;
1502
1503         /* Track whether this object has been initialized */
1504         bool initialized = false;
1505
1506         if (curr->is_seqcst()) {
1507                 last_seq_cst = get_last_seq_cst(curr);
1508                 /* We have to at least see the last sequentially consistent write,
1509                          so we are initialized. */
1510                 if (last_seq_cst != NULL)
1511                         initialized = true;
1512         }
1513
1514         /* Iterate over all threads */
1515         for (i = 0; i < thrd_lists->size(); i++) {
1516                 /* Iterate over actions in thread, starting from most recent */
1517                 action_list_t *list = &(*thrd_lists)[i];
1518                 action_list_t::reverse_iterator rit;
1519                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1520                         ModelAction *act = *rit;
1521
1522                         /* Only consider 'write' actions */
1523                         if (!act->is_write() || act == curr)
1524                                 continue;
1525
1526                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1527                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1528                                 DEBUG("Adding action to may_read_from:\n");
1529                                 if (DBG_ENABLED()) {
1530                                         act->print();
1531                                         curr->print();
1532                                 }
1533                                 curr->get_node()->add_read_from(act);
1534                         }
1535
1536                         /* Include at most one act per-thread that "happens before" curr */
1537                         if (act->happens_before(curr)) {
1538                                 initialized = true;
1539                                 break;
1540                         }
1541                 }
1542         }
1543
1544         if (!initialized) {
1545                 /** @todo Need a more informative way of reporting errors. */
1546                 printf("ERROR: may read from uninitialized atomic\n");
1547         }
1548
1549         if (DBG_ENABLED() || !initialized) {
1550                 printf("Reached read action:\n");
1551                 curr->print();
1552                 printf("Printing may_read_from\n");
1553                 curr->get_node()->print_may_read_from();
1554                 printf("End printing may_read_from\n");
1555         }
1556
1557         ASSERT(initialized);
1558 }
1559
1560 static void print_list(action_list_t *list)
1561 {
1562         action_list_t::iterator it;
1563
1564         printf("---------------------------------------------------------------------\n");
1565         printf("Trace:\n");
1566
1567         for (it = list->begin(); it != list->end(); it++) {
1568                 (*it)->print();
1569         }
1570         printf("---------------------------------------------------------------------\n");
1571 }
1572
1573 void ModelChecker::print_summary()
1574 {
1575         printf("\n");
1576         printf("Number of executions: %d\n", num_executions);
1577         printf("Number of feasible executions: %d\n", num_feasible_executions);
1578         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1579
1580 #if SUPPORT_MOD_ORDER_DUMP
1581         scheduler->print();
1582         char buffername[100];
1583         sprintf(buffername, "exec%04u", num_executions);
1584         mo_graph->dumpGraphToFile(buffername);
1585 #endif
1586
1587         if (!isfinalfeasible())
1588                 printf("INFEASIBLE EXECUTION!\n");
1589         print_list(action_trace);
1590         printf("\n");
1591 }
1592
1593 /**
1594  * Add a Thread to the system for the first time. Should only be called once
1595  * per thread.
1596  * @param t The Thread to add
1597  */
1598 void ModelChecker::add_thread(Thread *t)
1599 {
1600         thread_map->put(id_to_int(t->get_id()), t);
1601         scheduler->add_thread(t);
1602 }
1603
1604 /**
1605  * Removes a thread from the scheduler.
1606  * @param the thread to remove.
1607  */
1608 void ModelChecker::remove_thread(Thread *t)
1609 {
1610         scheduler->remove_thread(t);
1611 }
1612
1613 /**
1614  * Switch from a user-context to the "master thread" context (a.k.a. system
1615  * context). This switch is made with the intention of exploring a particular
1616  * model-checking action (described by a ModelAction object). Must be called
1617  * from a user-thread context.
1618  * @param act The current action that will be explored. Must not be NULL.
1619  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1620  */
1621 int ModelChecker::switch_to_master(ModelAction *act)
1622 {
1623         DBG();
1624         Thread *old = thread_current();
1625         set_current_action(act);
1626         old->set_state(THREAD_READY);
1627         return Thread::swap(old, &system_context);
1628 }
1629
1630 /**
1631  * Takes the next step in the execution, if possible.
1632  * @return Returns true (success) if a step was taken and false otherwise.
1633  */
1634 bool ModelChecker::take_step() {
1635         if (has_asserted())
1636                 return false;
1637
1638         Thread * curr = thread_current();
1639         if (curr) {
1640                 if (curr->get_state() == THREAD_READY) {
1641                         ASSERT(priv->current_action);
1642
1643                         priv->nextThread = check_current_action(priv->current_action);
1644                         priv->current_action = NULL;
1645                         if (curr->is_blocked() || curr->is_complete())
1646                                 scheduler->remove_thread(curr);
1647                 } else {
1648                         ASSERT(false);
1649                 }
1650         }
1651         Thread * next = scheduler->next_thread(priv->nextThread);
1652
1653         /* Infeasible -> don't take any more steps */
1654         if (!isfeasible())
1655                 return false;
1656
1657         if (next)
1658                 next->set_state(THREAD_RUNNING);
1659         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1660
1661         /* next == NULL -> don't take any more steps */
1662         if (!next)
1663                 return false;
1664
1665         if ( next->get_pending() != NULL ) {
1666                 //restart a pending action
1667                 set_current_action(next->get_pending());
1668                 next->set_pending(NULL);
1669                 next->set_state(THREAD_READY);
1670                 return true;
1671         }
1672
1673         /* Return false only if swap fails with an error */
1674         return (Thread::swap(&system_context, next) == 0);
1675 }
1676
1677 /** Runs the current execution until threre are no more steps to take. */
1678 void ModelChecker::finish_execution() {
1679         DBG();
1680
1681         while (take_step());
1682 }