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                         break;
 337         }
 338                 //otherwise fall into the lock case
 339         case ATOMIC_LOCK: {
 340                 if (curr->get_cv()->getClock(state->alloc_tid)<=state->alloc_clock) {
 341                         printf("Lock access before initialization\n");
 342                         set_assert();
 343                 }
 344                 state->islocked=true;
 345                 ModelAction *unlock=get_last_unlock(curr);
 346                 //synchronize with the previous unlock statement
 347                 curr->synchronize_with(unlock);
 348                 break;
 349         }
 350         case ATOMIC_UNLOCK: {
 351                 //unlock the lock
 352                 state->islocked=false;
 353                 //wake up the other threads
 354                 action_list_t * waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 355                 //activate all the waiting threads
 356                 for(action_list_t::iterator rit = waiters->begin(); rit!=waiters->end(); rit++) {
 357                         add_thread(get_thread((*rit)->get_tid()));
 358                 }
 359                 waiters->clear();
 360                 break;
 361         }
 362         default:
 363                 ASSERT(0);
 364         }
 365 }
 366
 367
 368 /**
 369  * Process a write ModelAction
 370  * @param curr The ModelAction to process
 371  * @return True if the mo_graph was updated or promises were resolved
 372  */
 373 bool ModelChecker::process_write(ModelAction *curr)
 374 {
 375         bool updated_mod_order = w_modification_order(curr);
 376         bool updated_promises = resolve_promises(curr);
 377
 378         if (promises->size() == 0) {
 379                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 380                         struct PendingFutureValue pfv = (*futurevalues)[i];
 381                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 382                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 383                                 priv->next_backtrack = pfv.act;
 384                 }
 385                 futurevalues->resize(0);
 386         }
 387
 388         mo_graph->commitChanges();
 389         get_thread(curr)->set_return_value(VALUE_NONE);
 390         return updated_mod_order || updated_promises;
 391 }
 392
 393 /**
 394  * Initialize the current action by performing one or more of the following
 395  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 396  * in the NodeStack, manipulating backtracking sets, allocating and
 397  * initializing clock vectors, and computing the promises to fulfill.
 398  *
 399  * @param curr The current action, as passed from the user context; may be
 400  * freed/invalidated after the execution of this function
 401  * @return The current action, as processed by the ModelChecker. Is only the
 402  * same as the parameter @a curr if this is a newly-explored action.
 403  */
 404 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 405 {
 406         ModelAction *newcurr;
 407
 408         if (curr->is_rmwc() || curr->is_rmw()) {
 409                 newcurr = process_rmw(curr);
 410                 delete curr;
 411                 compute_promises(newcurr);
 412                 return newcurr;
 413         }
 414
 415         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 416         if (newcurr) {
 417                 /* First restore type and order in case of RMW operation */
 418                 if (curr->is_rmwr())
 419                         newcurr->copy_typeandorder(curr);
 420
 421                 ASSERT(curr->get_location()==newcurr->get_location());
 422                 /* Discard duplicate ModelAction; use action from NodeStack */
 423                 delete curr;
 424
 425                 /* If we have diverged, we need to reset the clock vector. */
 426                 if (diverge == NULL)
 427                         newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 428         } else {
 429                 newcurr = curr;
 430                 /*
 431                  * Perform one-time actions when pushing new ModelAction onto
 432                  * NodeStack
 433                  */
 434                 curr->create_cv(get_parent_action(curr->get_tid()));
 435                 if (curr->is_write())
 436                         compute_promises(curr);
 437         }
 438         return newcurr;
 439 }
 440
 441 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 442         if (curr->is_lock()) {
 443                 std::mutex * lock=(std::mutex *) curr->get_location();
 444                 struct std::mutex_state * state = lock->get_state();
 445                 if (state->islocked) {
 446                         //Stick the action in the appropriate waiting queue
 447                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 448                         return false;
 449                 }
 450         }
 451
 452         return true;
 453 }
 454
 455 /**
 456  * This is the heart of the model checker routine. It performs model-checking
 457  * actions corresponding to a given "current action." Among other processes, it
 458  * calculates reads-from relationships, updates synchronization clock vectors,
 459  * forms a memory_order constraints graph, and handles replay/backtrack
 460  * execution when running permutations of previously-observed executions.
 461  *
 462  * @param curr The current action to process
 463  * @return The next Thread that must be executed. May be NULL if ModelChecker
 464  * makes no choice (e.g., according to replay execution, combining RMW actions,
 465  * etc.)
 466  */
 467 Thread * ModelChecker::check_current_action(ModelAction *curr)
 468 {
 469         ASSERT(curr);
 470
 471         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 472
 473         if (!check_action_enabled(curr)) {
 474                 //we'll make the execution look like we chose to run this action
 475                 //much later...when a lock is actually available to relese
 476                 remove_thread(get_current_thread());
 477                 get_current_thread()->set_pending(curr);
 478                 return get_next_thread(NULL);
 479         }
 480
 481         ModelAction *newcurr = initialize_curr_action(curr);
 482
 483         /* Add the action to lists before any other model-checking tasks */
 484         if (!second_part_of_rmw)
 485                 add_action_to_lists(newcurr);
 486
 487         /* Build may_read_from set for newly-created actions */
 488         if (curr == newcurr && curr->is_read())
 489                 build_reads_from_past(curr);
 490         curr = newcurr;
 491
 492         /* Thread specific actions */
 493         switch (curr->get_type()) {
 494         case THREAD_CREATE: {
 495                 Thread *th = (Thread *)curr->get_location();
 496                 th->set_creation(curr);
 497                 break;
 498         }
 499         case THREAD_JOIN: {
 500                 Thread *waiting, *blocking;
 501                 waiting = get_thread(curr);
 502                 blocking = (Thread *)curr->get_location();
 503                 if (!blocking->is_complete()) {
 504                         blocking->push_wait_list(curr);
 505                         scheduler->sleep(waiting);
 506                 } else {
 507                         do_complete_join(curr);
 508                 }
 509                 break;
 510         }
 511         case THREAD_FINISH: {
 512                 Thread *th = get_thread(curr);
 513                 while (!th->wait_list_empty()) {
 514                         ModelAction *act = th->pop_wait_list();
 515                         Thread *wake = get_thread(act);
 516                         scheduler->wake(wake);
 517                         do_complete_join(act);
 518                 }
 519                 th->complete();
 520                 break;
 521         }
 522         case THREAD_START: {
 523                 check_promises(NULL, curr->get_cv());
 524                 break;
 525         }
 526         default:
 527                 break;
 528         }
 529
 530         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 531
 532         while (!work_queue.empty()) {
 533                 WorkQueueEntry work = work_queue.front();
 534                 work_queue.pop_front();
 535
 536                 switch (work.type) {
 537                 case WORK_CHECK_CURR_ACTION: {
 538                         ModelAction *act = work.action;
 539                         bool updated = false;
 540                         if (act->is_read() && process_read(act, second_part_of_rmw))
 541                                 updated = true;
 542
 543                         if (act->is_write() && process_write(act))
 544                                 updated = true;
 545
 546                         if (act->is_mutex_op())
 547                                 process_mutex(act);
 548
 549                         if (updated)
 550                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 551                         break;
 552                 }
 553                 case WORK_CHECK_RELEASE_SEQ:
 554                         resolve_release_sequences(work.location, &work_queue);
 555                         break;
 556                 case WORK_CHECK_MO_EDGES: {
 557                         /** @todo Complete verification of work_queue */
 558                         ModelAction *act = work.action;
 559                         bool updated = false;
 560
 561                         if (act->is_read()) {
 562                                 if (r_modification_order(act, act->get_reads_from()))
 563                                         updated = true;
 564                         }
 565                         if (act->is_write()) {
 566                                 if (w_modification_order(act))
 567                                         updated = true;
 568                         }
 569
 570                         if (updated)
 571                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 572                         break;
 573                 }
 574                 default:
 575                         ASSERT(false);
 576                         break;
 577                 }
 578         }
 579
 580         check_curr_backtracking(curr);
 581
 582         set_backtracking(curr);
 583
 584         return get_next_thread(curr);
 585 }
 586
 587 /**
 588  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 589  * operation from the Thread it is joining with. Must be called after the
 590  * completion of the Thread in question.
 591  * @param join The THREAD_JOIN action
 592  */
 593 void ModelChecker::do_complete_join(ModelAction *join)
 594 {
 595         Thread *blocking = (Thread *)join->get_location();
 596         ModelAction *act = get_last_action(blocking->get_id());
 597         join->synchronize_with(act);
 598 }
 599
 600 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 601         Node *currnode = curr->get_node();
 602         Node *parnode = currnode->get_parent();
 603
 604         if ((!parnode->backtrack_empty() ||
 605                          !currnode->read_from_empty() ||
 606                          !currnode->future_value_empty() ||
 607                          !currnode->promise_empty())
 608                         && (!priv->next_backtrack ||
 609                                         *curr > *priv->next_backtrack)) {
 610                 priv->next_backtrack = curr;
 611         }
 612 }
 613
 614 bool ModelChecker::promises_expired() {
 615         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 616                 Promise *promise = (*promises)[promise_index];
 617                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 618                         return true;
 619                 }
 620         }
 621         return false;
 622 }
 623
 624 /** @returns whether the current partial trace must be a prefix of a
 625  * feasible trace. */
 626 bool ModelChecker::isfeasibleprefix() {
 627         return promises->size() == 0 && *lazy_sync_size == 0;
 628 }
 629
 630 /** @returns whether the current partial trace is feasible. */
 631 bool ModelChecker::isfeasible() {
 632         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 633 }
 634
 635 /** @returns whether the current partial trace is feasible other than
 636  * multiple RMW reading from the same store. */
 637 bool ModelChecker::isfeasibleotherthanRMW() {
 638         if (DBG_ENABLED()) {
 639                 if (mo_graph->checkForCycles())
 640                         DEBUG("Infeasible: modification order cycles\n");
 641                 if (failed_promise)
 642                         DEBUG("Infeasible: failed promise\n");
 643                 if (too_many_reads)
 644                         DEBUG("Infeasible: too many reads\n");
 645                 if (promises_expired())
 646                         DEBUG("Infeasible: promises expired\n");
 647         }
 648         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 649 }
 650
 651 /** Returns whether the current completed trace is feasible. */
 652 bool ModelChecker::isfinalfeasible() {
 653         if (DBG_ENABLED() && promises->size() != 0)
 654                 DEBUG("Infeasible: unrevolved promises\n");
 655
 656         return isfeasible() && promises->size() == 0;
 657 }
 658
 659 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 660 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 661         int tid = id_to_int(act->get_tid());
 662         ModelAction *lastread = get_last_action(tid);
 663         lastread->process_rmw(act);
 664         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 665                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 666                 mo_graph->commitChanges();
 667         }
 668         return lastread;
 669 }
 670
 671 /**
 672  * Checks whether a thread has read from the same write for too many times
 673  * without seeing the effects of a later write.
 674  *
 675  * Basic idea:
 676  * 1) there must a different write that we could read from that would satisfy the modification order,
 677  * 2) we must have read from the same value in excess of maxreads times, and
 678  * 3) that other write must have been in the reads_from set for maxreads times.
 679  *
 680  * If so, we decide that the execution is no longer feasible.
 681  */
 682 void ModelChecker::check_recency(ModelAction *curr) {
 683         if (params.maxreads != 0) {
 684                 if (curr->get_node()->get_read_from_size() <= 1)
 685                         return;
 686
 687                 //Must make sure that execution is currently feasible...  We could
 688                 //accidentally clear by rolling back
 689                 if (!isfeasible())
 690                         return;
 691
 692                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 693                 int tid = id_to_int(curr->get_tid());
 694
 695                 /* Skip checks */
 696                 if ((int)thrd_lists->size() <= tid)
 697                         return;
 698
 699                 action_list_t *list = &(*thrd_lists)[tid];
 700
 701                 action_list_t::reverse_iterator rit = list->rbegin();
 702                 /* Skip past curr */
 703                 for (; (*rit) != curr; rit++)
 704                         ;
 705                 /* go past curr now */
 706                 rit++;
 707
 708                 action_list_t::reverse_iterator ritcopy = rit;
 709                 //See if we have enough reads from the same value
 710                 int count = 0;
 711                 for (; count < params.maxreads; rit++,count++) {
 712                         if (rit==list->rend())
 713                                 return;
 714                         ModelAction *act = *rit;
 715                         if (!act->is_read())
 716                                 return;
 717                         if (act->get_reads_from() != curr->get_reads_from())
 718                                 return;
 719                         if (act->get_node()->get_read_from_size() <= 1)
 720                                 return;
 721                 }
 722
 723                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 724                         //Get write
 725                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 726                         //Need a different write
 727                         if (write==curr->get_reads_from())
 728                                 continue;
 729
 730                         /* Test to see whether this is a feasible write to read from*/
 731                         mo_graph->startChanges();
 732                         r_modification_order(curr, write);
 733                         bool feasiblereadfrom = isfeasible();
 734                         mo_graph->rollbackChanges();
 735
 736                         if (!feasiblereadfrom)
 737                                 continue;
 738                         rit = ritcopy;
 739
 740                         bool feasiblewrite = true;
 741                         //new we need to see if this write works for everyone
 742
 743                         for (int loop = count; loop>0; loop--,rit++) {
 744                                 ModelAction *act=*rit;
 745                                 bool foundvalue = false;
 746                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 747                                         if (act->get_node()->get_read_from_at(i)==write) {
 748                                                 foundvalue = true;
 749                                                 break;
 750                                         }
 751                                 }
 752                                 if (!foundvalue) {
 753                                         feasiblewrite = false;
 754                                         break;
 755                                 }
 756                         }
 757                         if (feasiblewrite) {
 758                                 too_many_reads = true;
 759                                 return;
 760                         }
 761                 }
 762         }
 763 }
 764
 765 /**
 766  * Updates the mo_graph with the constraints imposed from the current
 767  * read.
 768  *
 769  * Basic idea is the following: Go through each other thread and find
 770  * the lastest action that happened before our read.  Two cases:
 771  *
 772  * (1) The action is a write => that write must either occur before
 773  * the write we read from or be the write we read from.
 774  *
 775  * (2) The action is a read => the write that that action read from
 776  * must occur before the write we read from or be the same write.
 777  *
 778  * @param curr The current action. Must be a read.
 779  * @param rf The action that curr reads from. Must be a write.
 780  * @return True if modification order edges were added; false otherwise
 781  */
 782 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 783 {
 784         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 785         unsigned int i;
 786         bool added = false;
 787         ASSERT(curr->is_read());
 788
 789         /* Iterate over all threads */
 790         for (i = 0; i < thrd_lists->size(); i++) {
 791                 /* Iterate over actions in thread, starting from most recent */
 792                 action_list_t *list = &(*thrd_lists)[i];
 793                 action_list_t::reverse_iterator rit;
 794                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 795                         ModelAction *act = *rit;
 796
 797                         /*
 798                          * Include at most one act per-thread that "happens
 799                          * before" curr. Don't consider reflexively.
 800                          */
 801                         if (act->happens_before(curr) && act != curr) {
 802                                 if (act->is_write()) {
 803                                         if (rf != act) {
 804                                                 mo_graph->addEdge(act, rf);
 805                                                 added = true;
 806                                         }
 807                                 } else {
 808                                         const ModelAction *prevreadfrom = act->get_reads_from();
 809                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 810                                                 mo_graph->addEdge(prevreadfrom, rf);
 811                                                 added = true;
 812                                         }
 813                                 }
 814                                 break;
 815                         }
 816                 }
 817         }
 818
 819         return added;
 820 }
 821
 822 /** This method fixes up the modification order when we resolve a
 823  *  promises.  The basic problem is that actions that occur after the
 824  *  read curr could not property add items to the modification order
 825  *  for our read.
 826  *
 827  *  So for each thread, we find the earliest item that happens after
 828  *  the read curr.  This is the item we have to fix up with additional
 829  *  constraints.  If that action is write, we add a MO edge between
 830  *  the Action rf and that action.  If the action is a read, we add a
 831  *  MO edge between the Action rf, and whatever the read accessed.
 832  *
 833  * @param curr is the read ModelAction that we are fixing up MO edges for.
 834  * @param rf is the write ModelAction that curr reads from.
 835  *
 836  */
 837
 838 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 839 {
 840         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 841         unsigned int i;
 842         ASSERT(curr->is_read());
 843
 844         /* Iterate over all threads */
 845         for (i = 0; i < thrd_lists->size(); i++) {
 846                 /* Iterate over actions in thread, starting from most recent */
 847                 action_list_t *list = &(*thrd_lists)[i];
 848                 action_list_t::reverse_iterator rit;
 849                 ModelAction *lastact = NULL;
 850
 851                 /* Find last action that happens after curr */
 852                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 853                         ModelAction *act = *rit;
 854                         if (curr->happens_before(act)) {
 855                                 lastact = act;
 856                         } else
 857                                 break;
 858                 }
 859
 860                         /* Include at most one act per-thread that "happens before" curr */
 861                 if (lastact != NULL) {
 862                         if (lastact->is_read()) {
 863                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 864                                 if (postreadfrom != NULL&&rf != postreadfrom)
 865                                         mo_graph->addEdge(rf, postreadfrom);
 866                         } else if (rf != lastact) {
 867                                 mo_graph->addEdge(rf, lastact);
 868                         }
 869                         break;
 870                 }
 871         }
 872 }
 873
 874 /**
 875  * Updates the mo_graph with the constraints imposed from the current write.
 876  *
 877  * Basic idea is the following: Go through each other thread and find
 878  * the lastest action that happened before our write.  Two cases:
 879  *
 880  * (1) The action is a write => that write must occur before
 881  * the current write
 882  *
 883  * (2) The action is a read => the write that that action read from
 884  * must occur before the current write.
 885  *
 886  * This method also handles two other issues:
 887  *
 888  * (I) Sequential Consistency: Making sure that if the current write is
 889  * seq_cst, that it occurs after the previous seq_cst write.
 890  *
 891  * (II) Sending the write back to non-synchronizing reads.
 892  *
 893  * @param curr The current action. Must be a write.
 894  * @return True if modification order edges were added; false otherwise
 895  */
 896 bool ModelChecker::w_modification_order(ModelAction *curr)
 897 {
 898         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 899         unsigned int i;
 900         bool added = false;
 901         ASSERT(curr->is_write());
 902
 903         if (curr->is_seqcst()) {
 904                 /* We have to at least see the last sequentially consistent write,
 905                          so we are initialized. */
 906                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
 907                 if (last_seq_cst != NULL) {
 908                         mo_graph->addEdge(last_seq_cst, curr);
 909                         added = true;
 910                 }
 911         }
 912
 913         /* Iterate over all threads */
 914         for (i = 0; i < thrd_lists->size(); i++) {
 915                 /* Iterate over actions in thread, starting from most recent */
 916                 action_list_t *list = &(*thrd_lists)[i];
 917                 action_list_t::reverse_iterator rit;
 918                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 919                         ModelAction *act = *rit;
 920                         if (act == curr) {
 921                                 /*
 922                                  * If RMW, we already have all relevant edges,
 923                                  * so just skip to next thread.
 924                                  * If normal write, we need to look at earlier
 925                                  * actions, so continue processing list.
 926                                  */
 927                                 if (curr->is_rmw())
 928                                         break;
 929                                 else
 930                                         continue;
 931                         }
 932
 933                         /*
 934                          * Include at most one act per-thread that "happens
 935                          * before" curr
 936                          */
 937                         if (act->happens_before(curr)) {
 938                                 /*
 939                                  * Note: if act is RMW, just add edge:
 940                                  *   act --mo--> curr
 941                                  * The following edge should be handled elsewhere:
 942                                  *   readfrom(act) --mo--> act
 943                                  */
 944                                 if (act->is_write())
 945                                         mo_graph->addEdge(act, curr);
 946                                 else if (act->is_read() && act->get_reads_from() != NULL)
 947                                         mo_graph->addEdge(act->get_reads_from(), curr);
 948                                 added = true;
 949                                 break;
 950                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 951                                                      !act->same_thread(curr)) {
 952                                 /* We have an action that:
 953                                    (1) did not happen before us
 954                                    (2) is a read and we are a write
 955                                    (3) cannot synchronize with us
 956                                    (4) is in a different thread
 957                                    =>
 958                                    that read could potentially read from our write.
 959                                  */
 960                                 if (thin_air_constraint_may_allow(curr, act)) {
 961                                         if (isfeasible() ||
 962                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 963                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 964                                                 futurevalues->push_back(pfv);
 965                                         }
 966                                 }
 967                         }
 968                 }
 969         }
 970
 971         return added;
 972 }
 973
 974 /** Arbitrary reads from the future are not allowed.  Section 29.3
 975  * part 9 places some constraints.  This method checks one result of constraint
 976  * constraint.  Others require compiler support. */
 977
 978 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 979         if (!writer->is_rmw())
 980                 return true;
 981
 982         if (!reader->is_rmw())
 983                 return true;
 984
 985         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 986                 if (search==reader)
 987                         return false;
 988                 if (search->get_tid() == reader->get_tid() &&
 989                                 search->happens_before(reader))
 990                         break;
 991         }
 992
 993         return true;
 994 }
 995
 996 /**
 997  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 998  * The ModelAction under consideration is expected to be taking part in
 999  * release/acquire synchronization as an object of the "reads from" relation.
1000  * Note that this can only provide release sequence support for RMW chains
1001  * which do not read from the future, as those actions cannot be traced until
1002  * their "promise" is fulfilled. Similarly, we may not even establish the
1003  * presence of a release sequence with certainty, as some modification order
1004  * constraints may be decided further in the future. Thus, this function
1005  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1006  * and a boolean representing certainty.
1007  *
1008  * @todo Finish lazy updating, when promises are fulfilled in the future
1009  * @param rf The action that might be part of a release sequence. Must be a
1010  * write.
1011  * @param release_heads A pass-by-reference style return parameter.  After
1012  * execution of this function, release_heads will contain the heads of all the
1013  * relevant release sequences, if any exists
1014  * @return true, if the ModelChecker is certain that release_heads is complete;
1015  * false otherwise
1016  */
1017 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1018 {
1019         if (!rf) {
1020                 /* read from future: need to settle this later */
1021                 return false; /* incomplete */
1022         }
1023
1024         ASSERT(rf->is_write());
1025
1026         if (rf->is_release())
1027                 release_heads->push_back(rf);
1028         if (rf->is_rmw()) {
1029                 /* We need a RMW action that is both an acquire and release to stop */
1030                 /** @todo Need to be smarter here...  In the linux lock
1031                  * example, this will run to the beginning of the program for
1032                  * every acquire. */
1033                 if (rf->is_acquire() && rf->is_release())
1034                         return true; /* complete */
1035                 return release_seq_head(rf->get_reads_from(), release_heads);
1036         }
1037         if (rf->is_release())
1038                 return true; /* complete */
1039
1040         /* else relaxed write; check modification order for contiguous subsequence
1041          * -> rf must be same thread as release */
1042         int tid = id_to_int(rf->get_tid());
1043         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1044         action_list_t *list = &(*thrd_lists)[tid];
1045         action_list_t::const_reverse_iterator rit;
1046
1047         /* Find rf in the thread list */
1048         rit = std::find(list->rbegin(), list->rend(), rf);
1049         ASSERT(rit != list->rend());
1050
1051         /* Find the last write/release */
1052         for (; rit != list->rend(); rit++)
1053                 if ((*rit)->is_release())
1054                         break;
1055         if (rit == list->rend()) {
1056                 /* No write-release in this thread */
1057                 return true; /* complete */
1058         }
1059         ModelAction *release = *rit;
1060
1061         ASSERT(rf->same_thread(release));
1062
1063         bool certain = true;
1064         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1065                 if (id_to_int(rf->get_tid()) == (int)i)
1066                         continue;
1067                 list = &(*thrd_lists)[i];
1068
1069                 /* Can we ensure no future writes from this thread may break
1070                  * the release seq? */
1071                 bool future_ordered = false;
1072
1073                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1074                         const ModelAction *act = *rit;
1075                         if (!act->is_write())
1076                                 continue;
1077                         /* Reach synchronization -> this thread is complete */
1078                         if (act->happens_before(release))
1079                                 break;
1080                         if (rf->happens_before(act)) {
1081                                 future_ordered = true;
1082                                 continue;
1083                         }
1084
1085                         /* Check modification order */
1086                         if (mo_graph->checkReachable(rf, act)) {
1087                                 /* rf --mo--> act */
1088                                 future_ordered = true;
1089                                 continue;
1090                         }
1091                         if (mo_graph->checkReachable(act, release))
1092                                 /* act --mo--> release */
1093                                 break;
1094                         if (mo_graph->checkReachable(release, act) &&
1095                                       mo_graph->checkReachable(act, rf)) {
1096                                 /* release --mo-> act --mo--> rf */
1097                                 return true; /* complete */
1098                         }
1099                         certain = false;
1100                 }
1101                 if (!future_ordered)
1102                         return false; /* This thread is uncertain */
1103         }
1104
1105         if (certain)
1106                 release_heads->push_back(release);
1107         return certain;
1108 }
1109
1110 /**
1111  * A public interface for getting the release sequence head(s) with which a
1112  * given ModelAction must synchronize. This function only returns a non-empty
1113  * result when it can locate a release sequence head with certainty. Otherwise,
1114  * it may mark the internal state of the ModelChecker so that it will handle
1115  * the release sequence at a later time, causing @a act to update its
1116  * synchronization at some later point in execution.
1117  * @param act The 'acquire' action that may read from a release sequence
1118  * @param release_heads A pass-by-reference return parameter. Will be filled
1119  * with the head(s) of the release sequence(s), if they exists with certainty.
1120  * @see ModelChecker::release_seq_head
1121  */
1122 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1123 {
1124         const ModelAction *rf = act->get_reads_from();
1125         bool complete;
1126         complete = release_seq_head(rf, release_heads);
1127         if (!complete) {
1128                 /* add act to 'lazy checking' list */
1129                 action_list_t *list;
1130                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1131                 list->push_back(act);
1132                 (*lazy_sync_size)++;
1133         }
1134 }
1135
1136 /**
1137  * Attempt to resolve all stashed operations that might synchronize with a
1138  * release sequence for a given location. This implements the "lazy" portion of
1139  * determining whether or not a release sequence was contiguous, since not all
1140  * modification order information is present at the time an action occurs.
1141  *
1142  * @param location The location/object that should be checked for release
1143  * sequence resolutions
1144  * @param work_queue The work queue to which to add work items as they are
1145  * generated
1146  * @return True if any updates occurred (new synchronization, new mo_graph
1147  * edges)
1148  */
1149 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1150 {
1151         action_list_t *list;
1152         list = lazy_sync_with_release->getptr(location);
1153         if (!list)
1154                 return false;
1155
1156         bool updated = false;
1157         action_list_t::iterator it = list->begin();
1158         while (it != list->end()) {
1159                 ModelAction *act = *it;
1160                 const ModelAction *rf = act->get_reads_from();
1161                 rel_heads_list_t release_heads;
1162                 bool complete;
1163                 complete = release_seq_head(rf, &release_heads);
1164                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1165                         if (!act->has_synchronized_with(release_heads[i])) {
1166                                 updated = true;
1167                                 act->synchronize_with(release_heads[i]);
1168                         }
1169                 }
1170
1171                 if (updated) {
1172                         /* Re-check act for mo_graph edges */
1173                         work_queue->push_back(MOEdgeWorkEntry(act));
1174
1175                         /* propagate synchronization to later actions */
1176                         action_list_t::reverse_iterator it = action_trace->rbegin();
1177                         while ((*it) != act) {
1178                                 ModelAction *propagate = *it;
1179                                 if (act->happens_before(propagate)) {
1180                                         propagate->synchronize_with(act);
1181                                         /* Re-check 'propagate' for mo_graph edges */
1182                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1183                                 }
1184                         }
1185                 }
1186                 if (complete) {
1187                         it = list->erase(it);
1188                         (*lazy_sync_size)--;
1189                 } else
1190                         it++;
1191         }
1192
1193         // If we resolved promises or data races, see if we have realized a data race.
1194         if (checkDataRaces()) {
1195                 set_assert();
1196         }
1197
1198         return updated;
1199 }
1200
1201 /**
1202  * Performs various bookkeeping operations for the current ModelAction. For
1203  * instance, adds action to the per-object, per-thread action vector and to the
1204  * action trace list of all thread actions.
1205  *
1206  * @param act is the ModelAction to add.
1207  */
1208 void ModelChecker::add_action_to_lists(ModelAction *act)
1209 {
1210         int tid = id_to_int(act->get_tid());
1211         action_trace->push_back(act);
1212
1213         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1214
1215         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1216         if (tid >= (int)vec->size())
1217                 vec->resize(priv->next_thread_id);
1218         (*vec)[tid].push_back(act);
1219
1220         if ((int)thrd_last_action->size() <= tid)
1221                 thrd_last_action->resize(get_num_threads());
1222         (*thrd_last_action)[tid] = act;
1223 }
1224
1225 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1226 {
1227         int threadid=id_to_int(tid);
1228         if (threadid<(int)thrd_last_action->size())
1229                 return (*thrd_last_action)[id_to_int(tid)];
1230         else
1231                 return NULL;
1232 }
1233
1234 /**
1235  * Gets the last memory_order_seq_cst write (in the total global sequence)
1236  * performed on a particular object (i.e., memory location), not including the
1237  * current action.
1238  * @param curr The current ModelAction; also denotes the object location to
1239  * check
1240  * @return The last seq_cst write
1241  */
1242 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1243 {
1244         void *location = curr->get_location();
1245         action_list_t *list = obj_map->get_safe_ptr(location);
1246         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1247         action_list_t::reverse_iterator rit;
1248         for (rit = list->rbegin(); rit != list->rend(); rit++)
1249                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1250                         return *rit;
1251         return NULL;
1252 }
1253
1254 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr)
1255 {
1256         void *location = curr->get_location();
1257         action_list_t *list = obj_map->get_safe_ptr(location);
1258         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1259         action_list_t::reverse_iterator rit;
1260         for (rit = list->rbegin(); rit != list->rend(); rit++)
1261                 if ((*rit)->is_unlock())
1262                         return *rit;
1263         return NULL;
1264 }
1265
1266 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1267 {
1268         ModelAction *parent = get_last_action(tid);
1269         if (!parent)
1270                 parent = get_thread(tid)->get_creation();
1271         return parent;
1272 }
1273
1274 /**
1275  * Returns the clock vector for a given thread.
1276  * @param tid The thread whose clock vector we want
1277  * @return Desired clock vector
1278  */
1279 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1280 {
1281         return get_parent_action(tid)->get_cv();
1282 }
1283
1284 /**
1285  * Resolve a set of Promises with a current write. The set is provided in the
1286  * Node corresponding to @a write.
1287  * @param write The ModelAction that is fulfilling Promises
1288  * @return True if promises were resolved; false otherwise
1289  */
1290 bool ModelChecker::resolve_promises(ModelAction *write)
1291 {
1292         bool resolved = false;
1293
1294         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1295                 Promise *promise = (*promises)[promise_index];
1296                 if (write->get_node()->get_promise(i)) {
1297                         ModelAction *read = promise->get_action();
1298                         read->read_from(write);
1299                         if (read->is_rmw()) {
1300                                 mo_graph->addRMWEdge(write, read);
1301                         }
1302                         //First fix up the modification order for actions that happened
1303                         //before the read
1304                         r_modification_order(read, write);
1305                         //Next fix up the modification order for actions that happened
1306                         //after the read.
1307                         post_r_modification_order(read, write);
1308                         promises->erase(promises->begin() + promise_index);
1309                         resolved = true;
1310                 } else
1311                         promise_index++;
1312         }
1313         return resolved;
1314 }
1315
1316 /**
1317  * Compute the set of promises that could potentially be satisfied by this
1318  * action. Note that the set computation actually appears in the Node, not in
1319  * ModelChecker.
1320  * @param curr The ModelAction that may satisfy promises
1321  */
1322 void ModelChecker::compute_promises(ModelAction *curr)
1323 {
1324         for (unsigned int i = 0; i < promises->size(); i++) {
1325                 Promise *promise = (*promises)[i];
1326                 const ModelAction *act = promise->get_action();
1327                 if (!act->happens_before(curr) &&
1328                                 act->is_read() &&
1329                                 !act->is_synchronizing(curr) &&
1330                                 !act->same_thread(curr) &&
1331                                 promise->get_value() == curr->get_value()) {
1332                         curr->get_node()->set_promise(i);
1333                 }
1334         }
1335 }
1336
1337 /** Checks promises in response to change in ClockVector Threads. */
1338 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1339 {
1340         for (unsigned int i = 0; i < promises->size(); i++) {
1341                 Promise *promise = (*promises)[i];
1342                 const ModelAction *act = promise->get_action();
1343                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1344                                 merge_cv->synchronized_since(act)) {
1345                         //This thread is no longer able to send values back to satisfy the promise
1346                         int num_synchronized_threads = promise->increment_threads();
1347                         if (num_synchronized_threads == get_num_threads()) {
1348                                 //Promise has failed
1349                                 failed_promise = true;
1350                                 return;
1351                         }
1352                 }
1353         }
1354 }
1355
1356 /**
1357  * Build up an initial set of all past writes that this 'read' action may read
1358  * from. This set is determined by the clock vector's "happens before"
1359  * relationship.
1360  * @param curr is the current ModelAction that we are exploring; it must be a
1361  * 'read' operation.
1362  */
1363 void ModelChecker::build_reads_from_past(ModelAction *curr)
1364 {
1365         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1366         unsigned int i;
1367         ASSERT(curr->is_read());
1368
1369         ModelAction *last_seq_cst = NULL;
1370
1371         /* Track whether this object has been initialized */
1372         bool initialized = false;
1373
1374         if (curr->is_seqcst()) {
1375                 last_seq_cst = get_last_seq_cst(curr);
1376                 /* We have to at least see the last sequentially consistent write,
1377                          so we are initialized. */
1378                 if (last_seq_cst != NULL)
1379                         initialized = true;
1380         }
1381
1382         /* Iterate over all threads */
1383         for (i = 0; i < thrd_lists->size(); i++) {
1384                 /* Iterate over actions in thread, starting from most recent */
1385                 action_list_t *list = &(*thrd_lists)[i];
1386                 action_list_t::reverse_iterator rit;
1387                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1388                         ModelAction *act = *rit;
1389
1390                         /* Only consider 'write' actions */
1391                         if (!act->is_write() || act == curr)
1392                                 continue;
1393
1394                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1395                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1396                                 DEBUG("Adding action to may_read_from:\n");
1397                                 if (DBG_ENABLED()) {
1398                                         act->print();
1399                                         curr->print();
1400                                 }
1401                                 curr->get_node()->add_read_from(act);
1402                         }
1403
1404                         /* Include at most one act per-thread that "happens before" curr */
1405                         if (act->happens_before(curr)) {
1406                                 initialized = true;
1407                                 break;
1408                         }
1409                 }
1410         }
1411
1412         if (!initialized) {
1413                 /** @todo Need a more informative way of reporting errors. */
1414                 printf("ERROR: may read from uninitialized atomic\n");
1415         }
1416
1417         if (DBG_ENABLED() || !initialized) {
1418                 printf("Reached read action:\n");
1419                 curr->print();
1420                 printf("Printing may_read_from\n");
1421                 curr->get_node()->print_may_read_from();
1422                 printf("End printing may_read_from\n");
1423         }
1424
1425         ASSERT(initialized);
1426 }
1427
1428 static void print_list(action_list_t *list)
1429 {
1430         action_list_t::iterator it;
1431
1432         printf("---------------------------------------------------------------------\n");
1433         printf("Trace:\n");
1434
1435         for (it = list->begin(); it != list->end(); it++) {
1436                 (*it)->print();
1437         }
1438         printf("---------------------------------------------------------------------\n");
1439 }
1440
1441 void ModelChecker::print_summary()
1442 {
1443         printf("\n");
1444         printf("Number of executions: %d\n", num_executions);
1445         printf("Number of feasible executions: %d\n", num_feasible_executions);
1446         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1447
1448 #if SUPPORT_MOD_ORDER_DUMP
1449         scheduler->print();
1450         char buffername[100];
1451         sprintf(buffername, "exec%u",num_executions);
1452         mo_graph->dumpGraphToFile(buffername);
1453 #endif
1454
1455         if (!isfinalfeasible())
1456                 printf("INFEASIBLE EXECUTION!\n");
1457         print_list(action_trace);
1458         printf("\n");
1459 }
1460
1461 /**
1462  * Add a Thread to the system for the first time. Should only be called once
1463  * per thread.
1464  * @param t The Thread to add
1465  */
1466 void ModelChecker::add_thread(Thread *t)
1467 {
1468         thread_map->put(id_to_int(t->get_id()), t);
1469         scheduler->add_thread(t);
1470 }
1471
1472 void ModelChecker::remove_thread(Thread *t)
1473 {
1474         scheduler->remove_thread(t);
1475 }
1476
1477 /**
1478  * Switch from a user-context to the "master thread" context (a.k.a. system
1479  * context). This switch is made with the intention of exploring a particular
1480  * model-checking action (described by a ModelAction object). Must be called
1481  * from a user-thread context.
1482  * @param act The current action that will be explored. Must not be NULL.
1483  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1484  */
1485 int ModelChecker::switch_to_master(ModelAction *act)
1486 {
1487         DBG();
1488         Thread *old = thread_current();
1489         set_current_action(act);
1490         old->set_state(THREAD_READY);
1491         return Thread::swap(old, &system_context);
1492 }
1493
1494 /**
1495  * Takes the next step in the execution, if possible.
1496  * @return Returns true (success) if a step was taken and false otherwise.
1497  */
1498 bool ModelChecker::take_step() {
1499         if (has_asserted())
1500                 return false;
1501
1502         Thread * curr = thread_current();
1503         if (curr) {
1504                 if (curr->get_state() == THREAD_READY) {
1505                         ASSERT(priv->current_action);
1506
1507                         priv->nextThread = check_current_action(priv->current_action);
1508                         priv->current_action = NULL;
1509                         if (curr->is_blocked() || curr->is_complete())
1510                                 scheduler->remove_thread(curr);
1511                 } else {
1512                         ASSERT(false);
1513                 }
1514         }
1515         Thread * next = scheduler->next_thread(priv->nextThread);
1516
1517         /* Infeasible -> don't take any more steps */
1518         if (!isfeasible())
1519                 return false;
1520
1521         if (next)
1522                 next->set_state(THREAD_RUNNING);
1523         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1524
1525         /* next == NULL -> don't take any more steps */
1526         if (!next)
1527                 return false;
1528
1529         if ( next->get_pending() != NULL ) {
1530                 //restart a pending action
1531                 set_current_action(next->get_pending());
1532                 next->set_pending(NULL);
1533                 next->set_state(THREAD_READY);
1534                 return true;
1535         }
1536
1537         /* Return false only if swap fails with an error */
1538         return (Thread::swap(&system_context, next) == 0);
1539 }
1540
1541 /** Runs the current execution until threre are no more steps to take. */
1542 void ModelChecker::finish_execution() {
1543         DBG();
1544
1545         while (take_step());
1546 }