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 *waiting, *blocking;
 488                 waiting = get_thread(curr);
 489                 blocking = (Thread *)curr->get_location();
 490                 if (!blocking->is_complete()) {
 491                         blocking->push_wait_list(curr);
 492                         scheduler->sleep(waiting);
 493                 } else {
 494                         do_complete_join(curr);
 495                         synchronized = true;
 496                 }
 497                 break;
 498         }
 499         case THREAD_FINISH: {
 500                 Thread *th = get_thread(curr);
 501                 while (!th->wait_list_empty()) {
 502                         ModelAction *act = th->pop_wait_list();
 503                         Thread *wake = get_thread(act);
 504                         scheduler->wake(wake);
 505                         do_complete_join(act);
 506                         synchronized = true;
 507                 }
 508                 th->complete();
 509                 break;
 510         }
 511         case THREAD_START: {
 512                 check_promises(NULL, curr->get_cv());
 513                 break;
 514         }
 515         default:
 516                 break;
 517         }
 518
 519         return synchronized;
 520 }
 521
 522 /**
 523  * Initialize the current action by performing one or more of the following
 524  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 525  * in the NodeStack, manipulating backtracking sets, allocating and
 526  * initializing clock vectors, and computing the promises to fulfill.
 527  *
 528  * @param curr The current action, as passed from the user context; may be
 529  * freed/invalidated after the execution of this function
 530  * @return The current action, as processed by the ModelChecker. Is only the
 531  * same as the parameter @a curr if this is a newly-explored action.
 532  */
 533 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 534 {
 535         ModelAction *newcurr;
 536
 537         if (curr->is_rmwc() || curr->is_rmw()) {
 538                 newcurr = process_rmw(curr);
 539                 delete curr;
 540
 541                 if (newcurr->is_rmw())
 542                         compute_promises(newcurr);
 543                 return newcurr;
 544         }
 545
 546         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 547         if (newcurr) {
 548                 /* First restore type and order in case of RMW operation */
 549                 if (curr->is_rmwr())
 550                         newcurr->copy_typeandorder(curr);
 551
 552                 ASSERT(curr->get_location() == newcurr->get_location());
 553                 newcurr->copy_from_new(curr);
 554
 555                 /* Discard duplicate ModelAction; use action from NodeStack */
 556                 delete curr;
 557
 558                 /* Always compute new clock vector */
 559                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 560         } else {
 561                 newcurr = curr;
 562
 563                 /* Always compute new clock vector */
 564                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 565                 /*
 566                  * Perform one-time actions when pushing new ModelAction onto
 567                  * NodeStack
 568                  */
 569                 if (newcurr->is_write())
 570                         compute_promises(newcurr);
 571         }
 572         return newcurr;
 573 }
 574
 575 /**
 576  * This method checks whether a model action is enabled at the given point.
 577  * At this point, it checks whether a lock operation would be successful at this point.
 578  * If not, it puts the thread in a waiter list.
 579  * @param curr is the ModelAction to check whether it is enabled.
 580  * @return a bool that indicates whether the action is enabled.
 581  */
 582 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 583         if (curr->is_lock()) {
 584                 std::mutex * lock = (std::mutex *)curr->get_location();
 585                 struct std::mutex_state * state = lock->get_state();
 586                 if (state->islocked) {
 587                         //Stick the action in the appropriate waiting queue
 588                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(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 is actually available to release */
 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 /**
 701  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 702  * operation from the Thread it is joining with. Must be called after the
 703  * completion of the Thread in question.
 704  * @param join The THREAD_JOIN action
 705  */
 706 void ModelChecker::do_complete_join(ModelAction *join)
 707 {
 708         Thread *blocking = (Thread *)join->get_location();
 709         ModelAction *act = get_last_action(blocking->get_id());
 710         join->synchronize_with(act);
 711 }
 712
 713 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 714         Node *currnode = curr->get_node();
 715         Node *parnode = currnode->get_parent();
 716
 717         if ((!parnode->backtrack_empty() ||
 718                          !currnode->read_from_empty() ||
 719                          !currnode->future_value_empty() ||
 720                          !currnode->promise_empty())
 721                         && (!priv->next_backtrack ||
 722                                         *curr > *priv->next_backtrack)) {
 723                 priv->next_backtrack = curr;
 724         }
 725 }
 726
 727 bool ModelChecker::promises_expired() {
 728         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 729                 Promise *promise = (*promises)[promise_index];
 730                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 731                         return true;
 732                 }
 733         }
 734         return false;
 735 }
 736
 737 /** @return whether the current partial trace must be a prefix of a
 738  * feasible trace. */
 739 bool ModelChecker::isfeasibleprefix() {
 740         return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
 741 }
 742
 743 /** @return whether the current partial trace is feasible. */
 744 bool ModelChecker::isfeasible() {
 745         if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
 746                 DEBUG("Infeasible: RMW violation\n");
 747
 748         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 749 }
 750
 751 /** @return whether the current partial trace is feasible other than
 752  * multiple RMW reading from the same store. */
 753 bool ModelChecker::isfeasibleotherthanRMW() {
 754         if (DBG_ENABLED()) {
 755                 if (mo_graph->checkForCycles())
 756                         DEBUG("Infeasible: modification order cycles\n");
 757                 if (failed_promise)
 758                         DEBUG("Infeasible: failed promise\n");
 759                 if (too_many_reads)
 760                         DEBUG("Infeasible: too many reads\n");
 761                 if (bad_synchronization)
 762                         DEBUG("Infeasible: bad synchronization ordering\n");
 763                 if (promises_expired())
 764                         DEBUG("Infeasible: promises expired\n");
 765         }
 766         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
 767 }
 768
 769 /** Returns whether the current completed trace is feasible. */
 770 bool ModelChecker::isfinalfeasible() {
 771         if (DBG_ENABLED() && promises->size() != 0)
 772                 DEBUG("Infeasible: unrevolved promises\n");
 773
 774         return isfeasible() && promises->size() == 0;
 775 }
 776
 777 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 778 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 779         int tid = id_to_int(act->get_tid());
 780         ModelAction *lastread = get_last_action(tid);
 781         lastread->process_rmw(act);
 782         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 783                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 784                 mo_graph->commitChanges();
 785         }
 786         return lastread;
 787 }
 788
 789 /**
 790  * Checks whether a thread has read from the same write for too many times
 791  * without seeing the effects of a later write.
 792  *
 793  * Basic idea:
 794  * 1) there must a different write that we could read from that would satisfy the modification order,
 795  * 2) we must have read from the same value in excess of maxreads times, and
 796  * 3) that other write must have been in the reads_from set for maxreads times.
 797  *
 798  * If so, we decide that the execution is no longer feasible.
 799  */
 800 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
 801         if (params.maxreads != 0) {
 802
 803                 if (curr->get_node()->get_read_from_size() <= 1)
 804                         return;
 805                 //Must make sure that execution is currently feasible...  We could
 806                 //accidentally clear by rolling back
 807                 if (!isfeasible())
 808                         return;
 809                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 810                 int tid = id_to_int(curr->get_tid());
 811
 812                 /* Skip checks */
 813                 if ((int)thrd_lists->size() <= tid)
 814                         return;
 815                 action_list_t *list = &(*thrd_lists)[tid];
 816
 817                 action_list_t::reverse_iterator rit = list->rbegin();
 818                 /* Skip past curr */
 819                 for (; (*rit) != curr; rit++)
 820                         ;
 821                 /* go past curr now */
 822                 rit++;
 823
 824                 action_list_t::reverse_iterator ritcopy = rit;
 825                 //See if we have enough reads from the same value
 826                 int count = 0;
 827                 for (; count < params.maxreads; rit++,count++) {
 828                         if (rit==list->rend())
 829                                 return;
 830                         ModelAction *act = *rit;
 831                         if (!act->is_read())
 832                                 return;
 833
 834                         if (act->get_reads_from() != rf)
 835                                 return;
 836                         if (act->get_node()->get_read_from_size() <= 1)
 837                                 return;
 838                 }
 839                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 840                         //Get write
 841                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 842
 843                         //Need a different write
 844                         if (write==rf)
 845                                 continue;
 846
 847                         /* Test to see whether this is a feasible write to read from*/
 848                         mo_graph->startChanges();
 849                         r_modification_order(curr, write);
 850                         bool feasiblereadfrom = isfeasible();
 851                         mo_graph->rollbackChanges();
 852
 853                         if (!feasiblereadfrom)
 854                                 continue;
 855                         rit = ritcopy;
 856
 857                         bool feasiblewrite = true;
 858                         //new we need to see if this write works for everyone
 859
 860                         for (int loop = count; loop>0; loop--,rit++) {
 861                                 ModelAction *act=*rit;
 862                                 bool foundvalue = false;
 863                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 864                                         if (act->get_node()->get_read_from_at(i)==write) {
 865                                                 foundvalue = true;
 866                                                 break;
 867                                         }
 868                                 }
 869                                 if (!foundvalue) {
 870                                         feasiblewrite = false;
 871                                         break;
 872                                 }
 873                         }
 874                         if (feasiblewrite) {
 875                                 too_many_reads = true;
 876                                 return;
 877                         }
 878                 }
 879         }
 880 }
 881
 882 /**
 883  * Updates the mo_graph with the constraints imposed from the current
 884  * read.
 885  *
 886  * Basic idea is the following: Go through each other thread and find
 887  * the lastest action that happened before our read.  Two cases:
 888  *
 889  * (1) The action is a write => that write must either occur before
 890  * the write we read from or be the write we read from.
 891  *
 892  * (2) The action is a read => the write that that action read from
 893  * must occur before the write we read from or be the same write.
 894  *
 895  * @param curr The current action. Must be a read.
 896  * @param rf The action that curr reads from. Must be a write.
 897  * @return True if modification order edges were added; false otherwise
 898  */
 899 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 900 {
 901         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 902         unsigned int i;
 903         bool added = false;
 904         ASSERT(curr->is_read());
 905
 906         /* Iterate over all threads */
 907         for (i = 0; i < thrd_lists->size(); i++) {
 908                 /* Iterate over actions in thread, starting from most recent */
 909                 action_list_t *list = &(*thrd_lists)[i];
 910                 action_list_t::reverse_iterator rit;
 911                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 912                         ModelAction *act = *rit;
 913
 914                         /*
 915                          * Include at most one act per-thread that "happens
 916                          * before" curr. Don't consider reflexively.
 917                          */
 918                         if (act->happens_before(curr) && act != curr) {
 919                                 if (act->is_write()) {
 920                                         if (rf != act) {
 921                                                 mo_graph->addEdge(act, rf);
 922                                                 added = true;
 923                                         }
 924                                 } else {
 925                                         const ModelAction *prevreadfrom = act->get_reads_from();
 926                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 927                                                 mo_graph->addEdge(prevreadfrom, rf);
 928                                                 added = true;
 929                                         }
 930                                 }
 931                                 break;
 932                         }
 933                 }
 934         }
 935
 936         return added;
 937 }
 938
 939 /** This method fixes up the modification order when we resolve a
 940  *  promises.  The basic problem is that actions that occur after the
 941  *  read curr could not property add items to the modification order
 942  *  for our read.
 943  *
 944  *  So for each thread, we find the earliest item that happens after
 945  *  the read curr.  This is the item we have to fix up with additional
 946  *  constraints.  If that action is write, we add a MO edge between
 947  *  the Action rf and that action.  If the action is a read, we add a
 948  *  MO edge between the Action rf, and whatever the read accessed.
 949  *
 950  * @param curr is the read ModelAction that we are fixing up MO edges for.
 951  * @param rf is the write ModelAction that curr reads from.
 952  *
 953  */
 954 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 955 {
 956         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 957         unsigned int i;
 958         ASSERT(curr->is_read());
 959
 960         /* Iterate over all threads */
 961         for (i = 0; i < thrd_lists->size(); i++) {
 962                 /* Iterate over actions in thread, starting from most recent */
 963                 action_list_t *list = &(*thrd_lists)[i];
 964                 action_list_t::reverse_iterator rit;
 965                 ModelAction *lastact = NULL;
 966
 967                 /* Find last action that happens after curr that is either not curr or a rmw */
 968                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 969                         ModelAction *act = *rit;
 970                         if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
 971                                 lastact = act;
 972                         } else
 973                                 break;
 974                 }
 975
 976                         /* Include at most one act per-thread that "happens before" curr */
 977                 if (lastact != NULL) {
 978                         if (lastact==curr) {
 979                                 //Case 1: The resolved read is a RMW, and we need to make sure
 980                                 //that the write portion of the RMW mod order after rf
 981
 982                                 mo_graph->addEdge(rf, lastact);
 983                         } else if (lastact->is_read()) {
 984                                 //Case 2: The resolved read is a normal read and the next
 985                                 //operation is a read, and we need to make sure the value read
 986                                 //is mod ordered after rf
 987
 988                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 989                                 if (postreadfrom != NULL&&rf != postreadfrom)
 990                                         mo_graph->addEdge(rf, postreadfrom);
 991                         } else {
 992                                 //Case 3: The resolved read is a normal read and the next
 993                                 //operation is a write, and we need to make sure that the
 994                                 //write is mod ordered after rf
 995                                 if (lastact!=rf)
 996                                         mo_graph->addEdge(rf, lastact);
 997                         }
 998                         break;
 999                 }
1000         }
1001 }
1002
1003 /**
1004  * Updates the mo_graph with the constraints imposed from the current write.
1005  *
1006  * Basic idea is the following: Go through each other thread and find
1007  * the lastest action that happened before our write.  Two cases:
1008  *
1009  * (1) The action is a write => that write must occur before
1010  * the current write
1011  *
1012  * (2) The action is a read => the write that that action read from
1013  * must occur before the current write.
1014  *
1015  * This method also handles two other issues:
1016  *
1017  * (I) Sequential Consistency: Making sure that if the current write is
1018  * seq_cst, that it occurs after the previous seq_cst write.
1019  *
1020  * (II) Sending the write back to non-synchronizing reads.
1021  *
1022  * @param curr The current action. Must be a write.
1023  * @return True if modification order edges were added; false otherwise
1024  */
1025 bool ModelChecker::w_modification_order(ModelAction *curr)
1026 {
1027         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1028         unsigned int i;
1029         bool added = false;
1030         ASSERT(curr->is_write());
1031
1032         if (curr->is_seqcst()) {
1033                 /* We have to at least see the last sequentially consistent write,
1034                          so we are initialized. */
1035                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1036                 if (last_seq_cst != NULL) {
1037                         mo_graph->addEdge(last_seq_cst, curr);
1038                         added = true;
1039                 }
1040         }
1041
1042         /* Iterate over all threads */
1043         for (i = 0; i < thrd_lists->size(); i++) {
1044                 /* Iterate over actions in thread, starting from most recent */
1045                 action_list_t *list = &(*thrd_lists)[i];
1046                 action_list_t::reverse_iterator rit;
1047                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1048                         ModelAction *act = *rit;
1049                         if (act == curr) {
1050                                 /*
1051                                  * If RMW, we already have all relevant edges,
1052                                  * so just skip to next thread.
1053                                  * If normal write, we need to look at earlier
1054                                  * actions, so continue processing list.
1055                                  */
1056                                 if (curr->is_rmw())
1057                                         break;
1058                                 else
1059                                         continue;
1060                         }
1061
1062                         /*
1063                          * Include at most one act per-thread that "happens
1064                          * before" curr
1065                          */
1066                         if (act->happens_before(curr)) {
1067                                 /*
1068                                  * Note: if act is RMW, just add edge:
1069                                  *   act --mo--> curr
1070                                  * The following edge should be handled elsewhere:
1071                                  *   readfrom(act) --mo--> act
1072                                  */
1073                                 if (act->is_write())
1074                                         mo_graph->addEdge(act, curr);
1075                                 else if (act->is_read() && act->get_reads_from() != NULL)
1076                                         mo_graph->addEdge(act->get_reads_from(), curr);
1077                                 added = true;
1078                                 break;
1079                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
1080                                                      !act->same_thread(curr)) {
1081                                 /* We have an action that:
1082                                    (1) did not happen before us
1083                                    (2) is a read and we are a write
1084                                    (3) cannot synchronize with us
1085                                    (4) is in a different thread
1086                                    =>
1087                                    that read could potentially read from our write.
1088                                  */
1089                                 if (thin_air_constraint_may_allow(curr, act)) {
1090                                         if (isfeasible() ||
1091                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1092                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1093                                                 futurevalues->push_back(pfv);
1094                                         }
1095                                 }
1096                         }
1097                 }
1098         }
1099
1100         return added;
1101 }
1102
1103 /** Arbitrary reads from the future are not allowed.  Section 29.3
1104  * part 9 places some constraints.  This method checks one result of constraint
1105  * constraint.  Others require compiler support. */
1106 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1107         if (!writer->is_rmw())
1108                 return true;
1109
1110         if (!reader->is_rmw())
1111                 return true;
1112
1113         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1114                 if (search == reader)
1115                         return false;
1116                 if (search->get_tid() == reader->get_tid() &&
1117                                 search->happens_before(reader))
1118                         break;
1119         }
1120
1121         return true;
1122 }
1123
1124 /**
1125  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1126  * The ModelAction under consideration is expected to be taking part in
1127  * release/acquire synchronization as an object of the "reads from" relation.
1128  * Note that this can only provide release sequence support for RMW chains
1129  * which do not read from the future, as those actions cannot be traced until
1130  * their "promise" is fulfilled. Similarly, we may not even establish the
1131  * presence of a release sequence with certainty, as some modification order
1132  * constraints may be decided further in the future. Thus, this function
1133  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1134  * and a boolean representing certainty.
1135  *
1136  * @todo Finish lazy updating, when promises are fulfilled in the future
1137  * @param rf The action that might be part of a release sequence. Must be a
1138  * write.
1139  * @param release_heads A pass-by-reference style return parameter.  After
1140  * execution of this function, release_heads will contain the heads of all the
1141  * relevant release sequences, if any exists
1142  * @return true, if the ModelChecker is certain that release_heads is complete;
1143  * false otherwise
1144  */
1145 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1146 {
1147         /* Only check for release sequences if there are no cycles */
1148         if (mo_graph->checkForCycles())
1149                 return false;
1150
1151         while (rf) {
1152                 ASSERT(rf->is_write());
1153
1154                 if (rf->is_release())
1155                         release_heads->push_back(rf);
1156                 if (!rf->is_rmw())
1157                         break; /* End of RMW chain */
1158
1159                 /** @todo Need to be smarter here...  In the linux lock
1160                  * example, this will run to the beginning of the program for
1161                  * every acquire. */
1162                 /** @todo The way to be smarter here is to keep going until 1
1163                  * thread has a release preceded by an acquire and you've seen
1164                  *       both. */
1165
1166                 /* acq_rel RMW is a sufficient stopping condition */
1167                 if (rf->is_acquire() && rf->is_release())
1168                         return true; /* complete */
1169
1170                 rf = rf->get_reads_from();
1171         };
1172         if (!rf) {
1173                 /* read from future: need to settle this later */
1174                 return false; /* incomplete */
1175         }
1176
1177         if (rf->is_release())
1178                 return true; /* complete */
1179
1180         /* else relaxed write; check modification order for contiguous subsequence
1181          * -> rf must be same thread as release */
1182         int tid = id_to_int(rf->get_tid());
1183         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1184         action_list_t *list = &(*thrd_lists)[tid];
1185         action_list_t::const_reverse_iterator rit;
1186
1187         /* Find rf in the thread list */
1188         rit = std::find(list->rbegin(), list->rend(), rf);
1189         ASSERT(rit != list->rend());
1190
1191         /* Find the last write/release */
1192         for (; rit != list->rend(); rit++)
1193                 if ((*rit)->is_release())
1194                         break;
1195         if (rit == list->rend()) {
1196                 /* No write-release in this thread */
1197                 return true; /* complete */
1198         }
1199         ModelAction *release = *rit;
1200
1201         ASSERT(rf->same_thread(release));
1202
1203         bool certain = true;
1204         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1205                 if (id_to_int(rf->get_tid()) == (int)i)
1206                         continue;
1207                 list = &(*thrd_lists)[i];
1208
1209                 /* Can we ensure no future writes from this thread may break
1210                  * the release seq? */
1211                 bool future_ordered = false;
1212
1213                 ModelAction *last = get_last_action(int_to_id(i));
1214                 if (last && (rf->happens_before(last) ||
1215                                 last->get_type() == THREAD_FINISH))
1216                         future_ordered = true;
1217
1218                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1219                         const ModelAction *act = *rit;
1220                         /* Reach synchronization -> this thread is complete */
1221                         if (act->happens_before(release))
1222                                 break;
1223                         if (rf->happens_before(act)) {
1224                                 future_ordered = true;
1225                                 continue;
1226                         }
1227
1228                         /* Only writes can break release sequences */
1229                         if (!act->is_write())
1230                                 continue;
1231
1232                         /* Check modification order */
1233                         if (mo_graph->checkReachable(rf, act)) {
1234                                 /* rf --mo--> act */
1235                                 future_ordered = true;
1236                                 continue;
1237                         }
1238                         if (mo_graph->checkReachable(act, release))
1239                                 /* act --mo--> release */
1240                                 break;
1241                         if (mo_graph->checkReachable(release, act) &&
1242                                       mo_graph->checkReachable(act, rf)) {
1243                                 /* release --mo-> act --mo--> rf */
1244                                 return true; /* complete */
1245                         }
1246                         certain = false;
1247                 }
1248                 if (!future_ordered)
1249                         return false; /* This thread is uncertain */
1250         }
1251
1252         if (certain)
1253                 release_heads->push_back(release);
1254         return certain;
1255 }
1256
1257 /**
1258  * A public interface for getting the release sequence head(s) with which a
1259  * given ModelAction must synchronize. This function only returns a non-empty
1260  * result when it can locate a release sequence head with certainty. Otherwise,
1261  * it may mark the internal state of the ModelChecker so that it will handle
1262  * the release sequence at a later time, causing @a act to update its
1263  * synchronization at some later point in execution.
1264  * @param act The 'acquire' action that may read from a release sequence
1265  * @param release_heads A pass-by-reference return parameter. Will be filled
1266  * with the head(s) of the release sequence(s), if they exists with certainty.
1267  * @see ModelChecker::release_seq_head
1268  */
1269 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1270 {
1271         const ModelAction *rf = act->get_reads_from();
1272         bool complete;
1273         complete = release_seq_head(rf, release_heads);
1274         if (!complete) {
1275                 /* add act to 'lazy checking' list */
1276                 pending_acq_rel_seq->push_back(act);
1277         }
1278 }
1279
1280 /**
1281  * Attempt to resolve all stashed operations that might synchronize with a
1282  * release sequence for a given location. This implements the "lazy" portion of
1283  * determining whether or not a release sequence was contiguous, since not all
1284  * modification order information is present at the time an action occurs.
1285  *
1286  * @param location The location/object that should be checked for release
1287  * sequence resolutions. A NULL value means to check all locations.
1288  * @param work_queue The work queue to which to add work items as they are
1289  * generated
1290  * @return True if any updates occurred (new synchronization, new mo_graph
1291  * edges)
1292  */
1293 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1294 {
1295         bool updated = false;
1296         std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
1297         while (it != pending_acq_rel_seq->end()) {
1298                 ModelAction *act = *it;
1299
1300                 /* Only resolve sequences on the given location, if provided */
1301                 if (location && act->get_location() != location) {
1302                         it++;
1303                         continue;
1304                 }
1305
1306                 const ModelAction *rf = act->get_reads_from();
1307                 rel_heads_list_t release_heads;
1308                 bool complete;
1309                 complete = release_seq_head(rf, &release_heads);
1310                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1311                         if (!act->has_synchronized_with(release_heads[i])) {
1312                                 if (act->synchronize_with(release_heads[i]))
1313                                         updated = true;
1314                                 else
1315                                         set_bad_synchronization();
1316                         }
1317                 }
1318
1319                 if (updated) {
1320                         /* Re-check act for mo_graph edges */
1321                         work_queue->push_back(MOEdgeWorkEntry(act));
1322
1323                         /* propagate synchronization to later actions */
1324                         action_list_t::reverse_iterator rit = action_trace->rbegin();
1325                         for (; (*rit) != act; rit++) {
1326                                 ModelAction *propagate = *rit;
1327                                 if (act->happens_before(propagate)) {
1328                                         propagate->synchronize_with(act);
1329                                         /* Re-check 'propagate' for mo_graph edges */
1330                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1331                                 }
1332                         }
1333                 }
1334                 if (complete)
1335                         it = pending_acq_rel_seq->erase(it);
1336                 else
1337                         it++;
1338         }
1339
1340         // If we resolved promises or data races, see if we have realized a data race.
1341         if (checkDataRaces()) {
1342                 set_assert();
1343         }
1344
1345         return updated;
1346 }
1347
1348 /**
1349  * Performs various bookkeeping operations for the current ModelAction. For
1350  * instance, adds action to the per-object, per-thread action vector and to the
1351  * action trace list of all thread actions.
1352  *
1353  * @param act is the ModelAction to add.
1354  */
1355 void ModelChecker::add_action_to_lists(ModelAction *act)
1356 {
1357         int tid = id_to_int(act->get_tid());
1358         action_trace->push_back(act);
1359
1360         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1361
1362         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1363         if (tid >= (int)vec->size())
1364                 vec->resize(priv->next_thread_id);
1365         (*vec)[tid].push_back(act);
1366
1367         if ((int)thrd_last_action->size() <= tid)
1368                 thrd_last_action->resize(get_num_threads());
1369         (*thrd_last_action)[tid] = act;
1370 }
1371
1372 /**
1373  * @brief Get the last action performed by a particular Thread
1374  * @param tid The thread ID of the Thread in question
1375  * @return The last action in the thread
1376  */
1377 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1378 {
1379         int threadid = id_to_int(tid);
1380         if (threadid < (int)thrd_last_action->size())
1381                 return (*thrd_last_action)[id_to_int(tid)];
1382         else
1383                 return NULL;
1384 }
1385
1386 /**
1387  * Gets the last memory_order_seq_cst write (in the total global sequence)
1388  * performed on a particular object (i.e., memory location), not including the
1389  * current action.
1390  * @param curr The current ModelAction; also denotes the object location to
1391  * check
1392  * @return The last seq_cst write
1393  */
1394 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1395 {
1396         void *location = curr->get_location();
1397         action_list_t *list = obj_map->get_safe_ptr(location);
1398         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1399         action_list_t::reverse_iterator rit;
1400         for (rit = list->rbegin(); rit != list->rend(); rit++)
1401                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1402                         return *rit;
1403         return NULL;
1404 }
1405
1406 /**
1407  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1408  * location). This function identifies the mutex according to the current
1409  * action, which is presumed to perform on the same mutex.
1410  * @param curr The current ModelAction; also denotes the object location to
1411  * check
1412  * @return The last unlock operation
1413  */
1414 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1415 {
1416         void *location = curr->get_location();
1417         action_list_t *list = obj_map->get_safe_ptr(location);
1418         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1419         action_list_t::reverse_iterator rit;
1420         for (rit = list->rbegin(); rit != list->rend(); rit++)
1421                 if ((*rit)->is_unlock())
1422                         return *rit;
1423         return NULL;
1424 }
1425
1426 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1427 {
1428         ModelAction *parent = get_last_action(tid);
1429         if (!parent)
1430                 parent = get_thread(tid)->get_creation();
1431         return parent;
1432 }
1433
1434 /**
1435  * Returns the clock vector for a given thread.
1436  * @param tid The thread whose clock vector we want
1437  * @return Desired clock vector
1438  */
1439 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1440 {
1441         return get_parent_action(tid)->get_cv();
1442 }
1443
1444 /**
1445  * Resolve a set of Promises with a current write. The set is provided in the
1446  * Node corresponding to @a write.
1447  * @param write The ModelAction that is fulfilling Promises
1448  * @return True if promises were resolved; false otherwise
1449  */
1450 bool ModelChecker::resolve_promises(ModelAction *write)
1451 {
1452         bool resolved = false;
1453
1454         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1455                 Promise *promise = (*promises)[promise_index];
1456                 if (write->get_node()->get_promise(i)) {
1457                         ModelAction *read = promise->get_action();
1458                         if (read->is_rmw()) {
1459                                 mo_graph->addRMWEdge(write, read);
1460                         }
1461                         read->read_from(write);
1462                         //First fix up the modification order for actions that happened
1463                         //before the read
1464                         r_modification_order(read, write);
1465                         //Next fix up the modification order for actions that happened
1466                         //after the read.
1467                         post_r_modification_order(read, write);
1468                         //Make sure the promise's value matches the write's value
1469                         ASSERT(promise->get_value() == write->get_value());
1470
1471                         promises->erase(promises->begin() + promise_index);
1472                         resolved = true;
1473                 } else
1474                         promise_index++;
1475         }
1476         return resolved;
1477 }
1478
1479 /**
1480  * Compute the set of promises that could potentially be satisfied by this
1481  * action. Note that the set computation actually appears in the Node, not in
1482  * ModelChecker.
1483  * @param curr The ModelAction that may satisfy promises
1484  */
1485 void ModelChecker::compute_promises(ModelAction *curr)
1486 {
1487         for (unsigned int i = 0; i < promises->size(); i++) {
1488                 Promise *promise = (*promises)[i];
1489                 const ModelAction *act = promise->get_action();
1490                 if (!act->happens_before(curr) &&
1491                                 act->is_read() &&
1492                                 !act->is_synchronizing(curr) &&
1493                                 !act->same_thread(curr) &&
1494                                 promise->get_value() == curr->get_value()) {
1495                         curr->get_node()->set_promise(i);
1496                 }
1497         }
1498 }
1499
1500 /** Checks promises in response to change in ClockVector Threads. */
1501 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1502 {
1503         for (unsigned int i = 0; i < promises->size(); i++) {
1504                 Promise *promise = (*promises)[i];
1505                 const ModelAction *act = promise->get_action();
1506                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1507                                 merge_cv->synchronized_since(act)) {
1508                         //This thread is no longer able to send values back to satisfy the promise
1509                         int num_synchronized_threads = promise->increment_threads();
1510                         if (num_synchronized_threads == get_num_threads()) {
1511                                 //Promise has failed
1512                                 failed_promise = true;
1513                                 return;
1514                         }
1515                 }
1516         }
1517 }
1518
1519 /**
1520  * Build up an initial set of all past writes that this 'read' action may read
1521  * from. This set is determined by the clock vector's "happens before"
1522  * relationship.
1523  * @param curr is the current ModelAction that we are exploring; it must be a
1524  * 'read' operation.
1525  */
1526 void ModelChecker::build_reads_from_past(ModelAction *curr)
1527 {
1528         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1529         unsigned int i;
1530         ASSERT(curr->is_read());
1531
1532         ModelAction *last_seq_cst = NULL;
1533
1534         /* Track whether this object has been initialized */
1535         bool initialized = false;
1536
1537         if (curr->is_seqcst()) {
1538                 last_seq_cst = get_last_seq_cst(curr);
1539                 /* We have to at least see the last sequentially consistent write,
1540                          so we are initialized. */
1541                 if (last_seq_cst != NULL)
1542                         initialized = true;
1543         }
1544
1545         /* Iterate over all threads */
1546         for (i = 0; i < thrd_lists->size(); i++) {
1547                 /* Iterate over actions in thread, starting from most recent */
1548                 action_list_t *list = &(*thrd_lists)[i];
1549                 action_list_t::reverse_iterator rit;
1550                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1551                         ModelAction *act = *rit;
1552
1553                         /* Only consider 'write' actions */
1554                         if (!act->is_write() || act == curr)
1555                                 continue;
1556
1557                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1558                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1559                                 DEBUG("Adding action to may_read_from:\n");
1560                                 if (DBG_ENABLED()) {
1561                                         act->print();
1562                                         curr->print();
1563                                 }
1564                                 curr->get_node()->add_read_from(act);
1565                         }
1566
1567                         /* Include at most one act per-thread that "happens before" curr */
1568                         if (act->happens_before(curr)) {
1569                                 initialized = true;
1570                                 break;
1571                         }
1572                 }
1573         }
1574
1575         if (!initialized) {
1576                 /** @todo Need a more informative way of reporting errors. */
1577                 printf("ERROR: may read from uninitialized atomic\n");
1578         }
1579
1580         if (DBG_ENABLED() || !initialized) {
1581                 printf("Reached read action:\n");
1582                 curr->print();
1583                 printf("Printing may_read_from\n");
1584                 curr->get_node()->print_may_read_from();
1585                 printf("End printing may_read_from\n");
1586         }
1587
1588         ASSERT(initialized);
1589 }
1590
1591 static void print_list(action_list_t *list)
1592 {
1593         action_list_t::iterator it;
1594
1595         printf("---------------------------------------------------------------------\n");
1596         printf("Trace:\n");
1597
1598         for (it = list->begin(); it != list->end(); it++) {
1599                 (*it)->print();
1600         }
1601         printf("---------------------------------------------------------------------\n");
1602 }
1603
1604 #if SUPPORT_MOD_ORDER_DUMP
1605 void ModelChecker::dumpGraph(char *filename) {
1606         char buffer[200];
1607   sprintf(buffer, "%s.dot",filename);
1608   FILE *file=fopen(buffer, "w");
1609   fprintf(file, "digraph %s {\n",filename);
1610         mo_graph->dumpNodes(file);
1611         ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
1612
1613         for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
1614                 ModelAction *action=*it;
1615                 if (action->is_read()) {
1616                         fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
1617                         fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
1618                 }
1619                 if (thread_array[action->get_tid()] != NULL) {
1620                         fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
1621                 }
1622
1623                 thread_array[action->get_tid()]=action;
1624         }
1625   fprintf(file,"}\n");
1626         model_free(thread_array);
1627   fclose(file);
1628 }
1629 #endif
1630
1631 void ModelChecker::print_summary()
1632 {
1633         printf("\n");
1634         printf("Number of executions: %d\n", num_executions);
1635         printf("Number of feasible executions: %d\n", num_feasible_executions);
1636         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1637
1638 #if SUPPORT_MOD_ORDER_DUMP
1639         scheduler->print();
1640         char buffername[100];
1641         sprintf(buffername, "exec%04u", num_executions);
1642         mo_graph->dumpGraphToFile(buffername);
1643         sprintf(buffername, "graph%04u", num_executions);
1644   dumpGraph(buffername);
1645 #endif
1646
1647         if (!isfinalfeasible())
1648                 printf("INFEASIBLE EXECUTION!\n");
1649         print_list(action_trace);
1650         printf("\n");
1651 }
1652
1653 /**
1654  * Add a Thread to the system for the first time. Should only be called once
1655  * per thread.
1656  * @param t The Thread to add
1657  */
1658 void ModelChecker::add_thread(Thread *t)
1659 {
1660         thread_map->put(id_to_int(t->get_id()), t);
1661         scheduler->add_thread(t);
1662 }
1663
1664 /**
1665  * Removes a thread from the scheduler.
1666  * @param the thread to remove.
1667  */
1668 void ModelChecker::remove_thread(Thread *t)
1669 {
1670         scheduler->remove_thread(t);
1671 }
1672
1673 /**
1674  * Switch from a user-context to the "master thread" context (a.k.a. system
1675  * context). This switch is made with the intention of exploring a particular
1676  * model-checking action (described by a ModelAction object). Must be called
1677  * from a user-thread context.
1678  * @param act The current action that will be explored. Must not be NULL.
1679  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1680  */
1681 int ModelChecker::switch_to_master(ModelAction *act)
1682 {
1683         DBG();
1684         Thread *old = thread_current();
1685         set_current_action(act);
1686         old->set_state(THREAD_READY);
1687         return Thread::swap(old, &system_context);
1688 }
1689
1690 /**
1691  * Takes the next step in the execution, if possible.
1692  * @return Returns true (success) if a step was taken and false otherwise.
1693  */
1694 bool ModelChecker::take_step() {
1695         if (has_asserted())
1696                 return false;
1697
1698         Thread * curr = thread_current();
1699         if (curr) {
1700                 if (curr->get_state() == THREAD_READY) {
1701                         ASSERT(priv->current_action);
1702
1703                         priv->nextThread = check_current_action(priv->current_action);
1704                         priv->current_action = NULL;
1705
1706                         if (curr->is_blocked() || curr->is_complete())
1707                                 scheduler->remove_thread(curr);
1708                 } else {
1709                         ASSERT(false);
1710                 }
1711         }
1712         Thread * next = scheduler->next_thread(priv->nextThread);
1713
1714         /* Infeasible -> don't take any more steps */
1715         if (!isfeasible())
1716                 return false;
1717
1718         if (next)
1719                 next->set_state(THREAD_RUNNING);
1720         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1721
1722         /* next == NULL -> don't take any more steps */
1723         if (!next)
1724                 return false;
1725
1726         if ( next->get_pending() != NULL ) {
1727                 //restart a pending action
1728                 set_current_action(next->get_pending());
1729                 next->set_pending(NULL);
1730                 next->set_state(THREAD_READY);
1731                 return true;
1732         }
1733
1734         /* Return false only if swap fails with an error */
1735         return (Thread::swap(&system_context, next) == 0);
1736 }
1737
1738 /** Runs the current execution until threre are no more steps to take. */
1739 void ModelChecker::finish_execution() {
1740         DBG();
1741
1742         while (take_step());
1743 }