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