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         earliest_diverge(NULL),
  29         action_trace(new action_list_t()),
  30         thread_map(new HashTable<int, Thread *, int>()),
  31         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  33         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  34         promises(new std::vector<Promise *>()),
  35         futurevalues(new std::vector<struct PendingFutureValue>()),
  36         pending_acq_rel_seq(new std::vector<ModelAction *>()),
  37         thrd_last_action(new std::vector<ModelAction *>(1)),
  38         node_stack(new NodeStack()),
  39         mo_graph(new CycleGraph()),
  40         failed_promise(false),
  41         too_many_reads(false),
  42         asserted(false),
  43         bad_synchronization(false)
  44 {
  45         /* Allocate this "size" on the snapshotting heap */
  46         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  47         /* First thread created will have id INITIAL_THREAD_ID */
  48         priv->next_thread_id = INITIAL_THREAD_ID;
  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 pending_acq_rel_seq;
  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         bad_synchronization = false;
  86         reset_asserted();
  87         snapshotObject->backTrackBeforeStep(0);
  88 }
  89
  90 /** @return a thread ID for a new Thread */
  91 thread_id_t ModelChecker::get_next_id()
  92 {
  93         return priv->next_thread_id++;
  94 }
  95
  96 /** @return the number of user threads created during this execution */
  97 int ModelChecker::get_num_threads()
  98 {
  99         return priv->next_thread_id;
 100 }
 101
 102 /** @return a sequence number for a new ModelAction */
 103 modelclock_t ModelChecker::get_next_seq_num()
 104 {
 105         return ++priv->used_sequence_numbers;
 106 }
 107
 108 /**
 109  * @brief Choose the next thread to execute.
 110  *
 111  * This function chooses the next thread that should execute. It can force the
 112  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 113  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 114  * The model-checker may have no preference regarding the next thread (i.e.,
 115  * when exploring a new execution ordering), in which case this will return
 116  * NULL.
 117  * @param curr The current ModelAction. This action might guide the choice of
 118  * next thread.
 119  * @return The next thread to run. If the model-checker has no preference, NULL.
 120  */
 121 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 122 {
 123         thread_id_t tid;
 124
 125         if (curr!=NULL) {
 126                 /* Do not split atomic actions. */
 127                 if (curr->is_rmwr())
 128                         return thread_current();
 129                 /* The THREAD_CREATE action points to the created Thread */
 130                 else if (curr->get_type() == THREAD_CREATE)
 131                         return (Thread *)curr->get_location();
 132         }
 133
 134         /* Have we completed exploring the preselected path? */
 135         if (diverge == NULL)
 136                 return NULL;
 137
 138         /* Else, we are trying to replay an execution */
 139         ModelAction *next = node_stack->get_next()->get_action();
 140
 141         if (next == diverge) {
 142                 Node *nextnode = next->get_node();
 143                 /* Reached divergence point */
 144                 if (nextnode->increment_promise()) {
 145                         /* The next node will try to satisfy a different set of promises. */
 146                         tid = next->get_tid();
 147                         node_stack->pop_restofstack(2);
 148                 } else if (nextnode->increment_read_from()) {
 149                         /* The next node will read from a different value. */
 150                         tid = next->get_tid();
 151                         node_stack->pop_restofstack(2);
 152                 } else if (nextnode->increment_future_value()) {
 153                         /* The next node will try to read from a different future value. */
 154                         tid = next->get_tid();
 155                         node_stack->pop_restofstack(2);
 156                 } else {
 157                         /* Make a different thread execute for next step */
 158                         Node *node = nextnode->get_parent();
 159                         tid = node->get_next_backtrack();
 160                         node_stack->pop_restofstack(1);
 161                 }
 162                 DEBUG("*** Divergence point ***\n");
 163                 diverge = NULL;
 164         } else {
 165                 tid = next->get_tid();
 166         }
 167         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 168         ASSERT(tid != THREAD_ID_T_NONE);
 169         return thread_map->get(id_to_int(tid));
 170 }
 171
 172 /**
 173  * Queries the model-checker for more executions to explore and, if one
 174  * exists, resets the model-checker state to execute a new execution.
 175  *
 176  * @return If there are more executions to explore, return true. Otherwise,
 177  * return false.
 178  */
 179 bool ModelChecker::next_execution()
 180 {
 181         DBG();
 182
 183         num_executions++;
 184         if (isfinalfeasible()) {
 185                 printf("Earliest divergence point since last feasible execution:\n");
 186                 if (earliest_diverge)
 187                         earliest_diverge->print(false);
 188                 else
 189                         printf("(Not set)\n");
 190
 191                 earliest_diverge = NULL;
 192                 num_feasible_executions++;
 193         }
 194
 195         if (isfinalfeasible() || DBG_ENABLED())
 196                 print_summary();
 197
 198         if ((diverge = get_next_backtrack()) == NULL)
 199                 return false;
 200
 201         if (earliest_diverge == NULL || *diverge < *earliest_diverge)
 202                 earliest_diverge=diverge;
 203
 204         if (DBG_ENABLED()) {
 205                 printf("Next execution will diverge at:\n");
 206                 diverge->print();
 207         }
 208
 209         reset_to_initial_state();
 210         return true;
 211 }
 212
 213 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 214 {
 215         switch (act->get_type()) {
 216         case ATOMIC_READ:
 217         case ATOMIC_WRITE:
 218         case ATOMIC_RMW: {
 219                 /* linear search: from most recent to oldest */
 220                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 221                 action_list_t::reverse_iterator rit;
 222                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 223                         ModelAction *prev = *rit;
 224                         if (act->is_synchronizing(prev))
 225                                 return prev;
 226                 }
 227                 break;
 228         }
 229         case ATOMIC_LOCK:
 230         case ATOMIC_TRYLOCK: {
 231                 /* linear search: from most recent to oldest */
 232                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 233                 action_list_t::reverse_iterator rit;
 234                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 235                         ModelAction *prev = *rit;
 236                         if (act->is_conflicting_lock(prev))
 237                                 return prev;
 238                 }
 239                 break;
 240         }
 241         case ATOMIC_UNLOCK: {
 242                 /* linear search: from most recent to oldest */
 243                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 244                 action_list_t::reverse_iterator rit;
 245                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 246                         ModelAction *prev = *rit;
 247                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 248                                 return prev;
 249                 }
 250                 break;
 251         }
 252         default:
 253                 break;
 254         }
 255         return NULL;
 256 }
 257
 258 /** This method find backtracking points where we should try to
 259  * reorder the parameter ModelAction against.
 260  *
 261  * @param the ModelAction to find backtracking points for.
 262  */
 263 void ModelChecker::set_backtracking(ModelAction *act)
 264 {
 265         Thread *t = get_thread(act);
 266         ModelAction * prev = get_last_conflict(act);
 267         if (prev == NULL)
 268                 return;
 269
 270         Node * node = prev->get_node()->get_parent();
 271
 272         int low_tid, high_tid;
 273         if (node->is_enabled(t)) {
 274                 low_tid = id_to_int(act->get_tid());
 275                 high_tid = low_tid+1;
 276         } else {
 277                 low_tid = 0;
 278                 high_tid = get_num_threads();
 279         }
 280
 281         for(int i = low_tid; i < high_tid; i++) {
 282                 thread_id_t tid = int_to_id(i);
 283                 if (!node->is_enabled(tid))
 284                         continue;
 285
 286                 /* Check if this has been explored already */
 287                 if (node->has_been_explored(tid))
 288                         continue;
 289
 290                 /* See if fairness allows */
 291                 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
 292                         bool unfair=false;
 293                         for(int t=0;t<node->get_num_threads();t++) {
 294                                 thread_id_t tother=int_to_id(t);
 295                                 if (node->is_enabled(tother) && node->has_priority(tother)) {
 296                                         unfair=true;
 297                                         break;
 298                                 }
 299                         }
 300                         if (unfair)
 301                                 continue;
 302                 }
 303
 304                 /* Cache the latest backtracking point */
 305                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 306                         priv->next_backtrack = prev;
 307
 308                 /* If this is a new backtracking point, mark the tree */
 309                 if (!node->set_backtrack(tid))
 310                         continue;
 311                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 312                                         prev->get_tid(), t->get_id());
 313                 if (DBG_ENABLED()) {
 314                         prev->print();
 315                         act->print();
 316                 }
 317         }
 318 }
 319
 320 /**
 321  * Returns last backtracking point. The model checker will explore a different
 322  * path for this point in the next execution.
 323  * @return The ModelAction at which the next execution should diverge.
 324  */
 325 ModelAction * ModelChecker::get_next_backtrack()
 326 {
 327         ModelAction *next = priv->next_backtrack;
 328         priv->next_backtrack = NULL;
 329         return next;
 330 }
 331
 332 /**
 333  * Processes a read or rmw model action.
 334  * @param curr is the read model action to process.
 335  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 336  * @return True if processing this read updates the mo_graph.
 337  */
 338 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 339 {
 340         uint64_t value;
 341         bool updated = false;
 342         while (true) {
 343                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 344                 if (reads_from != NULL) {
 345                         mo_graph->startChanges();
 346
 347                         value = reads_from->get_value();
 348                         bool r_status = false;
 349
 350                         if (!second_part_of_rmw) {
 351                                 check_recency(curr, reads_from);
 352                                 r_status = r_modification_order(curr, reads_from);
 353                         }
 354
 355
 356                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 357                                 mo_graph->rollbackChanges();
 358                                 too_many_reads = false;
 359                                 continue;
 360                         }
 361
 362                         curr->read_from(reads_from);
 363                         mo_graph->commitChanges();
 364                         updated |= r_status;
 365                 } else if (!second_part_of_rmw) {
 366                         /* Read from future value */
 367                         value = curr->get_node()->get_future_value();
 368                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 369                         curr->read_from(NULL);
 370                         Promise *valuepromise = new Promise(curr, value, expiration);
 371                         promises->push_back(valuepromise);
 372                 }
 373                 get_thread(curr)->set_return_value(value);
 374                 return updated;
 375         }
 376 }
 377
 378 /**
 379  * Processes a lock, trylock, or unlock model action.  @param curr is
 380  * the read model action to process.
 381  *
 382  * The try lock operation checks whether the lock is taken.  If not,
 383  * it falls to the normal lock operation case.  If so, it returns
 384  * fail.
 385  *
 386  * The lock operation has already been checked that it is enabled, so
 387  * it just grabs the lock and synchronizes with the previous unlock.
 388  *
 389  * The unlock operation has to re-enable all of the threads that are
 390  * waiting on the lock.
 391  *
 392  * @return True if synchronization was updated; false otherwise
 393  */
 394 bool ModelChecker::process_mutex(ModelAction *curr) {
 395         std::mutex *mutex = (std::mutex *)curr->get_location();
 396         struct std::mutex_state *state = mutex->get_state();
 397         switch (curr->get_type()) {
 398         case ATOMIC_TRYLOCK: {
 399                 bool success = !state->islocked;
 400                 curr->set_try_lock(success);
 401                 if (!success) {
 402                         get_thread(curr)->set_return_value(0);
 403                         break;
 404                 }
 405                 get_thread(curr)->set_return_value(1);
 406         }
 407                 //otherwise fall into the lock case
 408         case ATOMIC_LOCK: {
 409                 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
 410                         printf("Lock access before initialization\n");
 411                         set_assert();
 412                 }
 413                 state->islocked = true;
 414                 ModelAction *unlock = get_last_unlock(curr);
 415                 //synchronize with the previous unlock statement
 416                 if (unlock != NULL) {
 417                         curr->synchronize_with(unlock);
 418                         return true;
 419                 }
 420                 break;
 421         }
 422         case ATOMIC_UNLOCK: {
 423                 //unlock the lock
 424                 state->islocked = false;
 425                 //wake up the other threads
 426                 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 427                 //activate all the waiting threads
 428                 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
 429                         scheduler->wake(get_thread(*rit));
 430                 }
 431                 waiters->clear();
 432                 break;
 433         }
 434         default:
 435                 ASSERT(0);
 436         }
 437         return false;
 438 }
 439
 440 /**
 441  * Process a write ModelAction
 442  * @param curr The ModelAction to process
 443  * @return True if the mo_graph was updated or promises were resolved
 444  */
 445 bool ModelChecker::process_write(ModelAction *curr)
 446 {
 447         bool updated_mod_order = w_modification_order(curr);
 448         bool updated_promises = resolve_promises(curr);
 449
 450         if (promises->size() == 0) {
 451                 for (unsigned int i = 0; i < futurevalues->size(); i++) {
 452                         struct PendingFutureValue pfv = (*futurevalues)[i];
 453                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 454                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 455                                 priv->next_backtrack = pfv.act;
 456                 }
 457                 futurevalues->resize(0);
 458         }
 459
 460         mo_graph->commitChanges();
 461         get_thread(curr)->set_return_value(VALUE_NONE);
 462         return updated_mod_order || updated_promises;
 463 }
 464
 465 /**
 466  * @brief Process the current action for thread-related activity
 467  *
 468  * Performs current-action processing for a THREAD_* ModelAction. Proccesses
 469  * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
 470  * synchronization, etc.  This function is a no-op for non-THREAD actions
 471  * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
 472  *
 473  * @param curr The current action
 474  * @return True if synchronization was updated
 475  */
 476 bool ModelChecker::process_thread_action(ModelAction *curr)
 477 {
 478         bool synchronized = false;
 479
 480         switch (curr->get_type()) {
 481         case THREAD_CREATE: {
 482                 Thread *th = (Thread *)curr->get_location();
 483                 th->set_creation(curr);
 484                 break;
 485         }
 486         case THREAD_JOIN: {
 487                 Thread *blocking = (Thread *)curr->get_location();
 488                 ModelAction *act = get_last_action(blocking->get_id());
 489                 curr->synchronize_with(act);
 490                 synchronized = true;
 491                 break;
 492         }
 493         case THREAD_FINISH: {
 494                 Thread *th = get_thread(curr);
 495                 while (!th->wait_list_empty()) {
 496                         ModelAction *act = th->pop_wait_list();
 497                         scheduler->wake(get_thread(act));
 498                 }
 499                 th->complete();
 500                 break;
 501         }
 502         case THREAD_START: {
 503                 check_promises(NULL, curr->get_cv());
 504                 break;
 505         }
 506         default:
 507                 break;
 508         }
 509
 510         return synchronized;
 511 }
 512
 513 /**
 514  * Initialize the current action by performing one or more of the following
 515  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 516  * in the NodeStack, manipulating backtracking sets, allocating and
 517  * initializing clock vectors, and computing the promises to fulfill.
 518  *
 519  * @param curr The current action, as passed from the user context; may be
 520  * freed/invalidated after the execution of this function
 521  * @return The current action, as processed by the ModelChecker. Is only the
 522  * same as the parameter @a curr if this is a newly-explored action.
 523  */
 524 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 525 {
 526         ModelAction *newcurr;
 527
 528         if (curr->is_rmwc() || curr->is_rmw()) {
 529                 newcurr = process_rmw(curr);
 530                 delete curr;
 531
 532                 if (newcurr->is_rmw())
 533                         compute_promises(newcurr);
 534                 return newcurr;
 535         }
 536
 537         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 538         if (newcurr) {
 539                 /* First restore type and order in case of RMW operation */
 540                 if (curr->is_rmwr())
 541                         newcurr->copy_typeandorder(curr);
 542
 543                 ASSERT(curr->get_location() == newcurr->get_location());
 544                 newcurr->copy_from_new(curr);
 545
 546                 /* Discard duplicate ModelAction; use action from NodeStack */
 547                 delete curr;
 548
 549                 /* Always compute new clock vector */
 550                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 551         } else {
 552                 newcurr = curr;
 553
 554                 /* Always compute new clock vector */
 555                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 556                 /*
 557                  * Perform one-time actions when pushing new ModelAction onto
 558                  * NodeStack
 559                  */
 560                 if (newcurr->is_write())
 561                         compute_promises(newcurr);
 562         }
 563         return newcurr;
 564 }
 565
 566 /**
 567  * @brief Check whether a model action is enabled.
 568  *
 569  * Checks whether a lock or join operation would be successful (i.e., is the
 570  * lock already locked, or is the joined thread already complete). If not, put
 571  * the action in a waiter list.
 572  *
 573  * @param curr is the ModelAction to check whether it is enabled.
 574  * @return a bool that indicates whether the action is enabled.
 575  */
 576 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 577         if (curr->is_lock()) {
 578                 std::mutex * lock = (std::mutex *)curr->get_location();
 579                 struct std::mutex_state * state = lock->get_state();
 580                 if (state->islocked) {
 581                         //Stick the action in the appropriate waiting queue
 582                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 583                         return false;
 584                 }
 585         } else if (curr->get_type() == THREAD_JOIN) {
 586                 Thread *blocking = (Thread *)curr->get_location();
 587                 if (!blocking->is_complete()) {
 588                         blocking->push_wait_list(curr);
 589                         return false;
 590                 }
 591         }
 592
 593         return true;
 594 }
 595
 596 /**
 597  * This is the heart of the model checker routine. It performs model-checking
 598  * actions corresponding to a given "current action." Among other processes, it
 599  * calculates reads-from relationships, updates synchronization clock vectors,
 600  * forms a memory_order constraints graph, and handles replay/backtrack
 601  * execution when running permutations of previously-observed executions.
 602  *
 603  * @param curr The current action to process
 604  * @return The next Thread that must be executed. May be NULL if ModelChecker
 605  * makes no choice (e.g., according to replay execution, combining RMW actions,
 606  * etc.)
 607  */
 608 Thread * ModelChecker::check_current_action(ModelAction *curr)
 609 {
 610         ASSERT(curr);
 611
 612         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 613
 614         if (!check_action_enabled(curr)) {
 615                 /* Make the execution look like we chose to run this action
 616                  * much later, when a lock/join can succeed */
 617                 get_current_thread()->set_pending(curr);
 618                 scheduler->sleep(get_current_thread());
 619                 return get_next_thread(NULL);
 620         }
 621
 622         ModelAction *newcurr = initialize_curr_action(curr);
 623
 624         /* Add the action to lists before any other model-checking tasks */
 625         if (!second_part_of_rmw)
 626                 add_action_to_lists(newcurr);
 627
 628         /* Build may_read_from set for newly-created actions */
 629         if (curr == newcurr && curr->is_read())
 630                 build_reads_from_past(curr);
 631         curr = newcurr;
 632
 633         /* Initialize work_queue with the "current action" work */
 634         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 635
 636         while (!work_queue.empty()) {
 637                 WorkQueueEntry work = work_queue.front();
 638                 work_queue.pop_front();
 639
 640                 switch (work.type) {
 641                 case WORK_CHECK_CURR_ACTION: {
 642                         ModelAction *act = work.action;
 643                         bool update = false; /* update this location's release seq's */
 644                         bool update_all = false; /* update all release seq's */
 645
 646                         if (process_thread_action(curr))
 647                                 update_all = true;
 648
 649                         if (act->is_read() && process_read(act, second_part_of_rmw))
 650                                 update = true;
 651
 652                         if (act->is_write() && process_write(act))
 653                                 update = true;
 654
 655                         if (act->is_mutex_op() && process_mutex(act))
 656                                 update_all = true;
 657
 658                         if (update_all)
 659                                 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
 660                         else if (update)
 661                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 662                         break;
 663                 }
 664                 case WORK_CHECK_RELEASE_SEQ:
 665                         resolve_release_sequences(work.location, &work_queue);
 666                         break;
 667                 case WORK_CHECK_MO_EDGES: {
 668                         /** @todo Complete verification of work_queue */
 669                         ModelAction *act = work.action;
 670                         bool updated = false;
 671
 672                         if (act->is_read()) {
 673                                 const ModelAction *rf = act->get_reads_from();
 674                                 if (rf != NULL && r_modification_order(act, rf))
 675                                         updated = true;
 676                         }
 677                         if (act->is_write()) {
 678                                 if (w_modification_order(act))
 679                                         updated = true;
 680                         }
 681                         mo_graph->commitChanges();
 682
 683                         if (updated)
 684                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 685                         break;
 686                 }
 687                 default:
 688                         ASSERT(false);
 689                         break;
 690                 }
 691         }
 692
 693         check_curr_backtracking(curr);
 694
 695         set_backtracking(curr);
 696
 697         return get_next_thread(curr);
 698 }
 699
 700 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 701         Node *currnode = curr->get_node();
 702         Node *parnode = currnode->get_parent();
 703
 704         if ((!parnode->backtrack_empty() ||
 705                          !currnode->read_from_empty() ||
 706                          !currnode->future_value_empty() ||
 707                          !currnode->promise_empty())
 708                         && (!priv->next_backtrack ||
 709                                         *curr > *priv->next_backtrack)) {
 710                 priv->next_backtrack = curr;
 711         }
 712 }
 713
 714 bool ModelChecker::promises_expired() {
 715         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 716                 Promise *promise = (*promises)[promise_index];
 717                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 718                         return true;
 719                 }
 720         }
 721         return false;
 722 }
 723
 724 /** @return whether the current partial trace must be a prefix of a
 725  * feasible trace. */
 726 bool ModelChecker::isfeasibleprefix() {
 727         return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
 728 }
 729
 730 /** @return whether the current partial trace is feasible. */
 731 bool ModelChecker::isfeasible() {
 732         if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
 733                 DEBUG("Infeasible: RMW violation\n");
 734
 735         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 736 }
 737
 738 /** @return whether the current partial trace is feasible other than
 739  * multiple RMW reading from the same store. */
 740 bool ModelChecker::isfeasibleotherthanRMW() {
 741         if (DBG_ENABLED()) {
 742                 if (mo_graph->checkForCycles())
 743                         DEBUG("Infeasible: modification order cycles\n");
 744                 if (failed_promise)
 745                         DEBUG("Infeasible: failed promise\n");
 746                 if (too_many_reads)
 747                         DEBUG("Infeasible: too many reads\n");
 748                 if (bad_synchronization)
 749                         DEBUG("Infeasible: bad synchronization ordering\n");
 750                 if (promises_expired())
 751                         DEBUG("Infeasible: promises expired\n");
 752         }
 753         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
 754 }
 755
 756 /** Returns whether the current completed trace is feasible. */
 757 bool ModelChecker::isfinalfeasible() {
 758         if (DBG_ENABLED() && promises->size() != 0)
 759                 DEBUG("Infeasible: unrevolved promises\n");
 760
 761         return isfeasible() && promises->size() == 0;
 762 }
 763
 764 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 765 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 766         int tid = id_to_int(act->get_tid());
 767         ModelAction *lastread = get_last_action(tid);
 768         lastread->process_rmw(act);
 769         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 770                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 771                 mo_graph->commitChanges();
 772         }
 773         return lastread;
 774 }
 775
 776 /**
 777  * Checks whether a thread has read from the same write for too many times
 778  * without seeing the effects of a later write.
 779  *
 780  * Basic idea:
 781  * 1) there must a different write that we could read from that would satisfy the modification order,
 782  * 2) we must have read from the same value in excess of maxreads times, and
 783  * 3) that other write must have been in the reads_from set for maxreads times.
 784  *
 785  * If so, we decide that the execution is no longer feasible.
 786  */
 787 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
 788         if (params.maxreads != 0) {
 789
 790                 if (curr->get_node()->get_read_from_size() <= 1)
 791                         return;
 792                 //Must make sure that execution is currently feasible...  We could
 793                 //accidentally clear by rolling back
 794                 if (!isfeasible())
 795                         return;
 796                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 797                 int tid = id_to_int(curr->get_tid());
 798
 799                 /* Skip checks */
 800                 if ((int)thrd_lists->size() <= tid)
 801                         return;
 802                 action_list_t *list = &(*thrd_lists)[tid];
 803
 804                 action_list_t::reverse_iterator rit = list->rbegin();
 805                 /* Skip past curr */
 806                 for (; (*rit) != curr; rit++)
 807                         ;
 808                 /* go past curr now */
 809                 rit++;
 810
 811                 action_list_t::reverse_iterator ritcopy = rit;
 812                 //See if we have enough reads from the same value
 813                 int count = 0;
 814                 for (; count < params.maxreads; rit++,count++) {
 815                         if (rit==list->rend())
 816                                 return;
 817                         ModelAction *act = *rit;
 818                         if (!act->is_read())
 819                                 return;
 820
 821                         if (act->get_reads_from() != rf)
 822                                 return;
 823                         if (act->get_node()->get_read_from_size() <= 1)
 824                                 return;
 825                 }
 826                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 827                         //Get write
 828                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 829
 830                         //Need a different write
 831                         if (write==rf)
 832                                 continue;
 833
 834                         /* Test to see whether this is a feasible write to read from*/
 835                         mo_graph->startChanges();
 836                         r_modification_order(curr, write);
 837                         bool feasiblereadfrom = isfeasible();
 838                         mo_graph->rollbackChanges();
 839
 840                         if (!feasiblereadfrom)
 841                                 continue;
 842                         rit = ritcopy;
 843
 844                         bool feasiblewrite = true;
 845                         //new we need to see if this write works for everyone
 846
 847                         for (int loop = count; loop>0; loop--,rit++) {
 848                                 ModelAction *act=*rit;
 849                                 bool foundvalue = false;
 850                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 851                                         if (act->get_node()->get_read_from_at(i)==write) {
 852                                                 foundvalue = true;
 853                                                 break;
 854                                         }
 855                                 }
 856                                 if (!foundvalue) {
 857                                         feasiblewrite = false;
 858                                         break;
 859                                 }
 860                         }
 861                         if (feasiblewrite) {
 862                                 too_many_reads = true;
 863                                 return;
 864                         }
 865                 }
 866         }
 867 }
 868
 869 /**
 870  * Updates the mo_graph with the constraints imposed from the current
 871  * read.
 872  *
 873  * Basic idea is the following: Go through each other thread and find
 874  * the lastest action that happened before our read.  Two cases:
 875  *
 876  * (1) The action is a write => that write must either occur before
 877  * the write we read from or be the write we read from.
 878  *
 879  * (2) The action is a read => the write that that action read from
 880  * must occur before the write we read from or be the same write.
 881  *
 882  * @param curr The current action. Must be a read.
 883  * @param rf The action that curr reads from. Must be a write.
 884  * @return True if modification order edges were added; false otherwise
 885  */
 886 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 887 {
 888         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 889         unsigned int i;
 890         bool added = false;
 891         ASSERT(curr->is_read());
 892
 893         /* Iterate over all threads */
 894         for (i = 0; i < thrd_lists->size(); i++) {
 895                 /* Iterate over actions in thread, starting from most recent */
 896                 action_list_t *list = &(*thrd_lists)[i];
 897                 action_list_t::reverse_iterator rit;
 898                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 899                         ModelAction *act = *rit;
 900
 901                         /*
 902                          * Include at most one act per-thread that "happens
 903                          * before" curr. Don't consider reflexively.
 904                          */
 905                         if (act->happens_before(curr) && act != curr) {
 906                                 if (act->is_write()) {
 907                                         if (rf != act) {
 908                                                 mo_graph->addEdge(act, rf);
 909                                                 added = true;
 910                                         }
 911                                 } else {
 912                                         const ModelAction *prevreadfrom = act->get_reads_from();
 913                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 914                                                 mo_graph->addEdge(prevreadfrom, rf);
 915                                                 added = true;
 916                                         }
 917                                 }
 918                                 break;
 919                         }
 920                 }
 921         }
 922
 923         return added;
 924 }
 925
 926 /** This method fixes up the modification order when we resolve a
 927  *  promises.  The basic problem is that actions that occur after the
 928  *  read curr could not property add items to the modification order
 929  *  for our read.
 930  *
 931  *  So for each thread, we find the earliest item that happens after
 932  *  the read curr.  This is the item we have to fix up with additional
 933  *  constraints.  If that action is write, we add a MO edge between
 934  *  the Action rf and that action.  If the action is a read, we add a
 935  *  MO edge between the Action rf, and whatever the read accessed.
 936  *
 937  * @param curr is the read ModelAction that we are fixing up MO edges for.
 938  * @param rf is the write ModelAction that curr reads from.
 939  *
 940  */
 941 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 942 {
 943         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 944         unsigned int i;
 945         ASSERT(curr->is_read());
 946
 947         /* Iterate over all threads */
 948         for (i = 0; i < thrd_lists->size(); i++) {
 949                 /* Iterate over actions in thread, starting from most recent */
 950                 action_list_t *list = &(*thrd_lists)[i];
 951                 action_list_t::reverse_iterator rit;
 952                 ModelAction *lastact = NULL;
 953
 954                 /* Find last action that happens after curr that is either not curr or a rmw */
 955                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 956                         ModelAction *act = *rit;
 957                         if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
 958                                 lastact = act;
 959                         } else
 960                                 break;
 961                 }
 962
 963                         /* Include at most one act per-thread that "happens before" curr */
 964                 if (lastact != NULL) {
 965                         if (lastact==curr) {
 966                                 //Case 1: The resolved read is a RMW, and we need to make sure
 967                                 //that the write portion of the RMW mod order after rf
 968
 969                                 mo_graph->addEdge(rf, lastact);
 970                         } else if (lastact->is_read()) {
 971                                 //Case 2: The resolved read is a normal read and the next
 972                                 //operation is a read, and we need to make sure the value read
 973                                 //is mod ordered after rf
 974
 975                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 976                                 if (postreadfrom != NULL&&rf != postreadfrom)
 977                                         mo_graph->addEdge(rf, postreadfrom);
 978                         } else {
 979                                 //Case 3: The resolved read is a normal read and the next
 980                                 //operation is a write, and we need to make sure that the
 981                                 //write is mod ordered after rf
 982                                 if (lastact!=rf)
 983                                         mo_graph->addEdge(rf, lastact);
 984                         }
 985                         break;
 986                 }
 987         }
 988 }
 989
 990 /**
 991  * Updates the mo_graph with the constraints imposed from the current write.
 992  *
 993  * Basic idea is the following: Go through each other thread and find
 994  * the lastest action that happened before our write.  Two cases:
 995  *
 996  * (1) The action is a write => that write must occur before
 997  * the current write
 998  *
 999  * (2) The action is a read => the write that that action read from
1000  * must occur before the current write.
1001  *
1002  * This method also handles two other issues:
1003  *
1004  * (I) Sequential Consistency: Making sure that if the current write is
1005  * seq_cst, that it occurs after the previous seq_cst write.
1006  *
1007  * (II) Sending the write back to non-synchronizing reads.
1008  *
1009  * @param curr The current action. Must be a write.
1010  * @return True if modification order edges were added; false otherwise
1011  */
1012 bool ModelChecker::w_modification_order(ModelAction *curr)
1013 {
1014         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1015         unsigned int i;
1016         bool added = false;
1017         ASSERT(curr->is_write());
1018
1019         if (curr->is_seqcst()) {
1020                 /* We have to at least see the last sequentially consistent write,
1021                          so we are initialized. */
1022                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1023                 if (last_seq_cst != NULL) {
1024                         mo_graph->addEdge(last_seq_cst, curr);
1025                         added = true;
1026                 }
1027         }
1028
1029         /* Iterate over all threads */
1030         for (i = 0; i < thrd_lists->size(); i++) {
1031                 /* Iterate over actions in thread, starting from most recent */
1032                 action_list_t *list = &(*thrd_lists)[i];
1033                 action_list_t::reverse_iterator rit;
1034                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1035                         ModelAction *act = *rit;
1036                         if (act == curr) {
1037                                 /*
1038                                  * If RMW, we already have all relevant edges,
1039                                  * so just skip to next thread.
1040                                  * If normal write, we need to look at earlier
1041                                  * actions, so continue processing list.
1042                                  */
1043                                 if (curr->is_rmw())
1044                                         break;
1045                                 else
1046                                         continue;
1047                         }
1048
1049                         /*
1050                          * Include at most one act per-thread that "happens
1051                          * before" curr
1052                          */
1053                         if (act->happens_before(curr)) {
1054                                 /*
1055                                  * Note: if act is RMW, just add edge:
1056                                  *   act --mo--> curr
1057                                  * The following edge should be handled elsewhere:
1058                                  *   readfrom(act) --mo--> act
1059                                  */
1060                                 if (act->is_write())
1061                                         mo_graph->addEdge(act, curr);
1062                                 else if (act->is_read() && act->get_reads_from() != NULL)
1063                                         mo_graph->addEdge(act->get_reads_from(), curr);
1064                                 added = true;
1065                                 break;
1066                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
1067                                                      !act->same_thread(curr)) {
1068                                 /* We have an action that:
1069                                    (1) did not happen before us
1070                                    (2) is a read and we are a write
1071                                    (3) cannot synchronize with us
1072                                    (4) is in a different thread
1073                                    =>
1074                                    that read could potentially read from our write.
1075                                  */
1076                                 if (thin_air_constraint_may_allow(curr, act)) {
1077                                         if (isfeasible() ||
1078                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1079                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1080                                                 futurevalues->push_back(pfv);
1081                                         }
1082                                 }
1083                         }
1084                 }
1085         }
1086
1087         return added;
1088 }
1089
1090 /** Arbitrary reads from the future are not allowed.  Section 29.3
1091  * part 9 places some constraints.  This method checks one result of constraint
1092  * constraint.  Others require compiler support. */
1093 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1094         if (!writer->is_rmw())
1095                 return true;
1096
1097         if (!reader->is_rmw())
1098                 return true;
1099
1100         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1101                 if (search == reader)
1102                         return false;
1103                 if (search->get_tid() == reader->get_tid() &&
1104                                 search->happens_before(reader))
1105                         break;
1106         }
1107
1108         return true;
1109 }
1110
1111 /**
1112  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1113  * The ModelAction under consideration is expected to be taking part in
1114  * release/acquire synchronization as an object of the "reads from" relation.
1115  * Note that this can only provide release sequence support for RMW chains
1116  * which do not read from the future, as those actions cannot be traced until
1117  * their "promise" is fulfilled. Similarly, we may not even establish the
1118  * presence of a release sequence with certainty, as some modification order
1119  * constraints may be decided further in the future. Thus, this function
1120  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1121  * and a boolean representing certainty.
1122  *
1123  * @todo Finish lazy updating, when promises are fulfilled in the future
1124  * @param rf The action that might be part of a release sequence. Must be a
1125  * write.
1126  * @param release_heads A pass-by-reference style return parameter.  After
1127  * execution of this function, release_heads will contain the heads of all the
1128  * relevant release sequences, if any exists
1129  * @return true, if the ModelChecker is certain that release_heads is complete;
1130  * false otherwise
1131  */
1132 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1133 {
1134         /* Only check for release sequences if there are no cycles */
1135         if (mo_graph->checkForCycles())
1136                 return false;
1137
1138         while (rf) {
1139                 ASSERT(rf->is_write());
1140
1141                 if (rf->is_release())
1142                         release_heads->push_back(rf);
1143                 if (!rf->is_rmw())
1144                         break; /* End of RMW chain */
1145
1146                 /** @todo Need to be smarter here...  In the linux lock
1147                  * example, this will run to the beginning of the program for
1148                  * every acquire. */
1149                 /** @todo The way to be smarter here is to keep going until 1
1150                  * thread has a release preceded by an acquire and you've seen
1151                  *       both. */
1152
1153                 /* acq_rel RMW is a sufficient stopping condition */
1154                 if (rf->is_acquire() && rf->is_release())
1155                         return true; /* complete */
1156
1157                 rf = rf->get_reads_from();
1158         };
1159         if (!rf) {
1160                 /* read from future: need to settle this later */
1161                 return false; /* incomplete */
1162         }
1163
1164         if (rf->is_release())
1165                 return true; /* complete */
1166
1167         /* else relaxed write; check modification order for contiguous subsequence
1168          * -> rf must be same thread as release */
1169         int tid = id_to_int(rf->get_tid());
1170         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1171         action_list_t *list = &(*thrd_lists)[tid];
1172         action_list_t::const_reverse_iterator rit;
1173
1174         /* Find rf in the thread list */
1175         rit = std::find(list->rbegin(), list->rend(), rf);
1176         ASSERT(rit != list->rend());
1177
1178         /* Find the last write/release */
1179         for (; rit != list->rend(); rit++)
1180                 if ((*rit)->is_release())
1181                         break;
1182         if (rit == list->rend()) {
1183                 /* No write-release in this thread */
1184                 return true; /* complete */
1185         }
1186         ModelAction *release = *rit;
1187
1188         ASSERT(rf->same_thread(release));
1189
1190         bool certain = true;
1191         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1192                 if (id_to_int(rf->get_tid()) == (int)i)
1193                         continue;
1194                 list = &(*thrd_lists)[i];
1195
1196                 /* Can we ensure no future writes from this thread may break
1197                  * the release seq? */
1198                 bool future_ordered = false;
1199
1200                 ModelAction *last = get_last_action(int_to_id(i));
1201                 if (last && (rf->happens_before(last) ||
1202                                 last->get_type() == THREAD_FINISH))
1203                         future_ordered = true;
1204
1205                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1206                         const ModelAction *act = *rit;
1207                         /* Reach synchronization -> this thread is complete */
1208                         if (act->happens_before(release))
1209                                 break;
1210                         if (rf->happens_before(act)) {
1211                                 future_ordered = true;
1212                                 continue;
1213                         }
1214
1215                         /* Only writes can break release sequences */
1216                         if (!act->is_write())
1217                                 continue;
1218
1219                         /* Check modification order */
1220                         if (mo_graph->checkReachable(rf, act)) {
1221                                 /* rf --mo--> act */
1222                                 future_ordered = true;
1223                                 continue;
1224                         }
1225                         if (mo_graph->checkReachable(act, release))
1226                                 /* act --mo--> release */
1227                                 break;
1228                         if (mo_graph->checkReachable(release, act) &&
1229                                       mo_graph->checkReachable(act, rf)) {
1230                                 /* release --mo-> act --mo--> rf */
1231                                 return true; /* complete */
1232                         }
1233                         certain = false;
1234                 }
1235                 if (!future_ordered)
1236                         return false; /* This thread is uncertain */
1237         }
1238
1239         if (certain)
1240                 release_heads->push_back(release);
1241         return certain;
1242 }
1243
1244 /**
1245  * A public interface for getting the release sequence head(s) with which a
1246  * given ModelAction must synchronize. This function only returns a non-empty
1247  * result when it can locate a release sequence head with certainty. Otherwise,
1248  * it may mark the internal state of the ModelChecker so that it will handle
1249  * the release sequence at a later time, causing @a act to update its
1250  * synchronization at some later point in execution.
1251  * @param act The 'acquire' action that may read from a release sequence
1252  * @param release_heads A pass-by-reference return parameter. Will be filled
1253  * with the head(s) of the release sequence(s), if they exists with certainty.
1254  * @see ModelChecker::release_seq_head
1255  */
1256 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1257 {
1258         const ModelAction *rf = act->get_reads_from();
1259         bool complete;
1260         complete = release_seq_head(rf, release_heads);
1261         if (!complete) {
1262                 /* add act to 'lazy checking' list */
1263                 pending_acq_rel_seq->push_back(act);
1264         }
1265 }
1266
1267 /**
1268  * Attempt to resolve all stashed operations that might synchronize with a
1269  * release sequence for a given location. This implements the "lazy" portion of
1270  * determining whether or not a release sequence was contiguous, since not all
1271  * modification order information is present at the time an action occurs.
1272  *
1273  * @param location The location/object that should be checked for release
1274  * sequence resolutions. A NULL value means to check all locations.
1275  * @param work_queue The work queue to which to add work items as they are
1276  * generated
1277  * @return True if any updates occurred (new synchronization, new mo_graph
1278  * edges)
1279  */
1280 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1281 {
1282         bool updated = false;
1283         std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
1284         while (it != pending_acq_rel_seq->end()) {
1285                 ModelAction *act = *it;
1286
1287                 /* Only resolve sequences on the given location, if provided */
1288                 if (location && act->get_location() != location) {
1289                         it++;
1290                         continue;
1291                 }
1292
1293                 const ModelAction *rf = act->get_reads_from();
1294                 rel_heads_list_t release_heads;
1295                 bool complete;
1296                 complete = release_seq_head(rf, &release_heads);
1297                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1298                         if (!act->has_synchronized_with(release_heads[i])) {
1299                                 if (act->synchronize_with(release_heads[i]))
1300                                         updated = true;
1301                                 else
1302                                         set_bad_synchronization();
1303                         }
1304                 }
1305
1306                 if (updated) {
1307                         /* Re-check act for mo_graph edges */
1308                         work_queue->push_back(MOEdgeWorkEntry(act));
1309
1310                         /* propagate synchronization to later actions */
1311                         action_list_t::reverse_iterator rit = action_trace->rbegin();
1312                         for (; (*rit) != act; rit++) {
1313                                 ModelAction *propagate = *rit;
1314                                 if (act->happens_before(propagate)) {
1315                                         propagate->synchronize_with(act);
1316                                         /* Re-check 'propagate' for mo_graph edges */
1317                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1318                                 }
1319                         }
1320                 }
1321                 if (complete)
1322                         it = pending_acq_rel_seq->erase(it);
1323                 else
1324                         it++;
1325         }
1326
1327         // If we resolved promises or data races, see if we have realized a data race.
1328         if (checkDataRaces()) {
1329                 set_assert();
1330         }
1331
1332         return updated;
1333 }
1334
1335 /**
1336  * Performs various bookkeeping operations for the current ModelAction. For
1337  * instance, adds action to the per-object, per-thread action vector and to the
1338  * action trace list of all thread actions.
1339  *
1340  * @param act is the ModelAction to add.
1341  */
1342 void ModelChecker::add_action_to_lists(ModelAction *act)
1343 {
1344         int tid = id_to_int(act->get_tid());
1345         action_trace->push_back(act);
1346
1347         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1348
1349         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1350         if (tid >= (int)vec->size())
1351                 vec->resize(priv->next_thread_id);
1352         (*vec)[tid].push_back(act);
1353
1354         if ((int)thrd_last_action->size() <= tid)
1355                 thrd_last_action->resize(get_num_threads());
1356         (*thrd_last_action)[tid] = act;
1357 }
1358
1359 /**
1360  * @brief Get the last action performed by a particular Thread
1361  * @param tid The thread ID of the Thread in question
1362  * @return The last action in the thread
1363  */
1364 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1365 {
1366         int threadid = id_to_int(tid);
1367         if (threadid < (int)thrd_last_action->size())
1368                 return (*thrd_last_action)[id_to_int(tid)];
1369         else
1370                 return NULL;
1371 }
1372
1373 /**
1374  * Gets the last memory_order_seq_cst write (in the total global sequence)
1375  * performed on a particular object (i.e., memory location), not including the
1376  * current action.
1377  * @param curr The current ModelAction; also denotes the object location to
1378  * check
1379  * @return The last seq_cst write
1380  */
1381 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1382 {
1383         void *location = curr->get_location();
1384         action_list_t *list = obj_map->get_safe_ptr(location);
1385         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1386         action_list_t::reverse_iterator rit;
1387         for (rit = list->rbegin(); rit != list->rend(); rit++)
1388                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1389                         return *rit;
1390         return NULL;
1391 }
1392
1393 /**
1394  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1395  * location). This function identifies the mutex according to the current
1396  * action, which is presumed to perform on the same mutex.
1397  * @param curr The current ModelAction; also denotes the object location to
1398  * check
1399  * @return The last unlock operation
1400  */
1401 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1402 {
1403         void *location = curr->get_location();
1404         action_list_t *list = obj_map->get_safe_ptr(location);
1405         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1406         action_list_t::reverse_iterator rit;
1407         for (rit = list->rbegin(); rit != list->rend(); rit++)
1408                 if ((*rit)->is_unlock())
1409                         return *rit;
1410         return NULL;
1411 }
1412
1413 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1414 {
1415         ModelAction *parent = get_last_action(tid);
1416         if (!parent)
1417                 parent = get_thread(tid)->get_creation();
1418         return parent;
1419 }
1420
1421 /**
1422  * Returns the clock vector for a given thread.
1423  * @param tid The thread whose clock vector we want
1424  * @return Desired clock vector
1425  */
1426 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1427 {
1428         return get_parent_action(tid)->get_cv();
1429 }
1430
1431 /**
1432  * Resolve a set of Promises with a current write. The set is provided in the
1433  * Node corresponding to @a write.
1434  * @param write The ModelAction that is fulfilling Promises
1435  * @return True if promises were resolved; false otherwise
1436  */
1437 bool ModelChecker::resolve_promises(ModelAction *write)
1438 {
1439         bool resolved = false;
1440
1441         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1442                 Promise *promise = (*promises)[promise_index];
1443                 if (write->get_node()->get_promise(i)) {
1444                         ModelAction *read = promise->get_action();
1445                         if (read->is_rmw()) {
1446                                 mo_graph->addRMWEdge(write, read);
1447                         }
1448                         read->read_from(write);
1449                         //First fix up the modification order for actions that happened
1450                         //before the read
1451                         r_modification_order(read, write);
1452                         //Next fix up the modification order for actions that happened
1453                         //after the read.
1454                         post_r_modification_order(read, write);
1455                         //Make sure the promise's value matches the write's value
1456                         ASSERT(promise->get_value() == write->get_value());
1457
1458                         promises->erase(promises->begin() + promise_index);
1459                         resolved = true;
1460                 } else
1461                         promise_index++;
1462         }
1463         return resolved;
1464 }
1465
1466 /**
1467  * Compute the set of promises that could potentially be satisfied by this
1468  * action. Note that the set computation actually appears in the Node, not in
1469  * ModelChecker.
1470  * @param curr The ModelAction that may satisfy promises
1471  */
1472 void ModelChecker::compute_promises(ModelAction *curr)
1473 {
1474         for (unsigned int i = 0; i < promises->size(); i++) {
1475                 Promise *promise = (*promises)[i];
1476                 const ModelAction *act = promise->get_action();
1477                 if (!act->happens_before(curr) &&
1478                                 act->is_read() &&
1479                                 !act->is_synchronizing(curr) &&
1480                                 !act->same_thread(curr) &&
1481                                 promise->get_value() == curr->get_value()) {
1482                         curr->get_node()->set_promise(i);
1483                 }
1484         }
1485 }
1486
1487 /** Checks promises in response to change in ClockVector Threads. */
1488 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1489 {
1490         for (unsigned int i = 0; i < promises->size(); i++) {
1491                 Promise *promise = (*promises)[i];
1492                 const ModelAction *act = promise->get_action();
1493                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1494                                 merge_cv->synchronized_since(act)) {
1495                         //This thread is no longer able to send values back to satisfy the promise
1496                         int num_synchronized_threads = promise->increment_threads();
1497                         if (num_synchronized_threads == get_num_threads()) {
1498                                 //Promise has failed
1499                                 failed_promise = true;
1500                                 return;
1501                         }
1502                 }
1503         }
1504 }
1505
1506 /**
1507  * Build up an initial set of all past writes that this 'read' action may read
1508  * from. This set is determined by the clock vector's "happens before"
1509  * relationship.
1510  * @param curr is the current ModelAction that we are exploring; it must be a
1511  * 'read' operation.
1512  */
1513 void ModelChecker::build_reads_from_past(ModelAction *curr)
1514 {
1515         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1516         unsigned int i;
1517         ASSERT(curr->is_read());
1518
1519         ModelAction *last_seq_cst = NULL;
1520
1521         /* Track whether this object has been initialized */
1522         bool initialized = false;
1523
1524         if (curr->is_seqcst()) {
1525                 last_seq_cst = get_last_seq_cst(curr);
1526                 /* We have to at least see the last sequentially consistent write,
1527                          so we are initialized. */
1528                 if (last_seq_cst != NULL)
1529                         initialized = true;
1530         }
1531
1532         /* Iterate over all threads */
1533         for (i = 0; i < thrd_lists->size(); i++) {
1534                 /* Iterate over actions in thread, starting from most recent */
1535                 action_list_t *list = &(*thrd_lists)[i];
1536                 action_list_t::reverse_iterator rit;
1537                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1538                         ModelAction *act = *rit;
1539
1540                         /* Only consider 'write' actions */
1541                         if (!act->is_write() || act == curr)
1542                                 continue;
1543
1544                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1545                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1546                                 DEBUG("Adding action to may_read_from:\n");
1547                                 if (DBG_ENABLED()) {
1548                                         act->print();
1549                                         curr->print();
1550                                 }
1551                                 curr->get_node()->add_read_from(act);
1552                         }
1553
1554                         /* Include at most one act per-thread that "happens before" curr */
1555                         if (act->happens_before(curr)) {
1556                                 initialized = true;
1557                                 break;
1558                         }
1559                 }
1560         }
1561
1562         if (!initialized) {
1563                 /** @todo Need a more informative way of reporting errors. */
1564                 printf("ERROR: may read from uninitialized atomic\n");
1565         }
1566
1567         if (DBG_ENABLED() || !initialized) {
1568                 printf("Reached read action:\n");
1569                 curr->print();
1570                 printf("Printing may_read_from\n");
1571                 curr->get_node()->print_may_read_from();
1572                 printf("End printing may_read_from\n");
1573         }
1574
1575         ASSERT(initialized);
1576 }
1577
1578 static void print_list(action_list_t *list)
1579 {
1580         action_list_t::iterator it;
1581
1582         printf("---------------------------------------------------------------------\n");
1583         printf("Trace:\n");
1584
1585         for (it = list->begin(); it != list->end(); it++) {
1586                 (*it)->print();
1587         }
1588         printf("---------------------------------------------------------------------\n");
1589 }
1590
1591 #if SUPPORT_MOD_ORDER_DUMP
1592 void ModelChecker::dumpGraph(char *filename) {
1593         char buffer[200];
1594   sprintf(buffer, "%s.dot",filename);
1595   FILE *file=fopen(buffer, "w");
1596   fprintf(file, "digraph %s {\n",filename);
1597         mo_graph->dumpNodes(file);
1598         ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
1599
1600         for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
1601                 ModelAction *action=*it;
1602                 if (action->is_read()) {
1603                         fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
1604                         fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
1605                 }
1606                 if (thread_array[action->get_tid()] != NULL) {
1607                         fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
1608                 }
1609
1610                 thread_array[action->get_tid()]=action;
1611         }
1612   fprintf(file,"}\n");
1613         model_free(thread_array);
1614   fclose(file);
1615 }
1616 #endif
1617
1618 void ModelChecker::print_summary()
1619 {
1620         printf("\n");
1621         printf("Number of executions: %d\n", num_executions);
1622         printf("Number of feasible executions: %d\n", num_feasible_executions);
1623         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1624
1625 #if SUPPORT_MOD_ORDER_DUMP
1626         scheduler->print();
1627         char buffername[100];
1628         sprintf(buffername, "exec%04u", num_executions);
1629         mo_graph->dumpGraphToFile(buffername);
1630         sprintf(buffername, "graph%04u", num_executions);
1631   dumpGraph(buffername);
1632 #endif
1633
1634         if (!isfinalfeasible())
1635                 printf("INFEASIBLE EXECUTION!\n");
1636         print_list(action_trace);
1637         printf("\n");
1638 }
1639
1640 /**
1641  * Add a Thread to the system for the first time. Should only be called once
1642  * per thread.
1643  * @param t The Thread to add
1644  */
1645 void ModelChecker::add_thread(Thread *t)
1646 {
1647         thread_map->put(id_to_int(t->get_id()), t);
1648         scheduler->add_thread(t);
1649 }
1650
1651 /**
1652  * Removes a thread from the scheduler.
1653  * @param the thread to remove.
1654  */
1655 void ModelChecker::remove_thread(Thread *t)
1656 {
1657         scheduler->remove_thread(t);
1658 }
1659
1660 /**
1661  * Switch from a user-context to the "master thread" context (a.k.a. system
1662  * context). This switch is made with the intention of exploring a particular
1663  * model-checking action (described by a ModelAction object). Must be called
1664  * from a user-thread context.
1665  * @param act The current action that will be explored. Must not be NULL.
1666  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1667  */
1668 int ModelChecker::switch_to_master(ModelAction *act)
1669 {
1670         DBG();
1671         Thread *old = thread_current();
1672         set_current_action(act);
1673         old->set_state(THREAD_READY);
1674         return Thread::swap(old, &system_context);
1675 }
1676
1677 /**
1678  * Takes the next step in the execution, if possible.
1679  * @return Returns true (success) if a step was taken and false otherwise.
1680  */
1681 bool ModelChecker::take_step() {
1682         if (has_asserted())
1683                 return false;
1684
1685         Thread * curr = thread_current();
1686         if (curr) {
1687                 if (curr->get_state() == THREAD_READY) {
1688                         ASSERT(priv->current_action);
1689
1690                         priv->nextThread = check_current_action(priv->current_action);
1691                         priv->current_action = NULL;
1692
1693                         if (curr->is_blocked() || curr->is_complete())
1694                                 scheduler->remove_thread(curr);
1695                 } else {
1696                         ASSERT(false);
1697                 }
1698         }
1699         Thread * next = scheduler->next_thread(priv->nextThread);
1700
1701         /* Infeasible -> don't take any more steps */
1702         if (!isfeasible())
1703                 return false;
1704
1705         if (next)
1706                 next->set_state(THREAD_RUNNING);
1707         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1708
1709         /* next == NULL -> don't take any more steps */
1710         if (!next)
1711                 return false;
1712
1713         if ( next->get_pending() != NULL ) {
1714                 //restart a pending action
1715                 set_current_action(next->get_pending());
1716                 next->set_pending(NULL);
1717                 next->set_state(THREAD_READY);
1718                 return true;
1719         }
1720
1721         /* Return false only if swap fails with an error */
1722         return (Thread::swap(&system_context, next) == 0);
1723 }
1724
1725 /** Runs the current execution until threre are no more steps to take. */
1726 void ModelChecker::finish_execution() {
1727         DBG();
1728
1729         while (take_step());
1730 }