model.cc

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