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 #include "threads.h"
  16
  17 #define INITIAL_THREAD_ID       0
  18
  19 ModelChecker *model;
  20
  21 /** @brief Constructor */
  22 ModelChecker::ModelChecker(struct model_params params) :
  23         /* Initialize default scheduler */
  24         params(params),
  25         scheduler(new Scheduler()),
  26         num_executions(0),
  27         num_feasible_executions(0),
  28         diverge(NULL),
  29         earliest_diverge(NULL),
  30         action_trace(new action_list_t()),
  31         thread_map(new HashTable<int, Thread *, int>()),
  32         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  33         lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  34         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  35         promises(new std::vector<Promise *>()),
  36         futurevalues(new std::vector<struct PendingFutureValue>()),
  37         pending_rel_seqs(new std::vector<struct release_seq *>()),
  38         thrd_last_action(new std::vector<ModelAction *>(1)),
  39         node_stack(new NodeStack()),
  40         mo_graph(new CycleGraph()),
  41         failed_promise(false),
  42         too_many_reads(false),
  43         asserted(false),
  44         bad_synchronization(false)
  45 {
  46         /* Allocate this "size" on the snapshotting heap */
  47         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  48         /* First thread created will have id INITIAL_THREAD_ID */
  49         priv->next_thread_id = INITIAL_THREAD_ID;
  50 }
  51
  52 /** @brief Destructor */
  53 ModelChecker::~ModelChecker()
  54 {
  55         for (unsigned int i = 0; i < get_num_threads(); i++)
  56                 delete thread_map->get(i);
  57         delete thread_map;
  58
  59         delete obj_thrd_map;
  60         delete obj_map;
  61         delete lock_waiters_map;
  62         delete action_trace;
  63
  64         for (unsigned int i = 0; i < promises->size(); i++)
  65                 delete (*promises)[i];
  66         delete promises;
  67
  68         delete pending_rel_seqs;
  69
  70         delete thrd_last_action;
  71         delete node_stack;
  72         delete scheduler;
  73         delete mo_graph;
  74 }
  75
  76 /**
  77  * Restores user program to initial state and resets all model-checker data
  78  * structures.
  79  */
  80 void ModelChecker::reset_to_initial_state()
  81 {
  82         DEBUG("+++ Resetting to initial state +++\n");
  83         node_stack->reset_execution();
  84         failed_promise = false;
  85         too_many_reads = false;
  86         bad_synchronization = false;
  87         reset_asserted();
  88         snapshotObject->backTrackBeforeStep(0);
  89 }
  90
  91 /** @return a thread ID for a new Thread */
  92 thread_id_t ModelChecker::get_next_id()
  93 {
  94         return priv->next_thread_id++;
  95 }
  96
  97 /** @return the number of user threads created during this execution */
  98 unsigned int ModelChecker::get_num_threads()
  99 {
 100         return priv->next_thread_id;
 101 }
 102
 103 /** @return The currently executing Thread. */
 104 Thread * ModelChecker::get_current_thread()
 105 {
 106         return scheduler->get_current_thread();
 107 }
 108
 109 /** @return a sequence number for a new ModelAction */
 110 modelclock_t ModelChecker::get_next_seq_num()
 111 {
 112         return ++priv->used_sequence_numbers;
 113 }
 114
 115 /**
 116  * @brief Choose the next thread to execute.
 117  *
 118  * This function chooses the next thread that should execute. It can force the
 119  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 120  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 121  * The model-checker may have no preference regarding the next thread (i.e.,
 122  * when exploring a new execution ordering), in which case this will return
 123  * NULL.
 124  * @param curr The current ModelAction. This action might guide the choice of
 125  * next thread.
 126  * @return The next thread to run. If the model-checker has no preference, NULL.
 127  */
 128 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 129 {
 130         thread_id_t tid;
 131
 132         if (curr!=NULL) {
 133                 /* Do not split atomic actions. */
 134                 if (curr->is_rmwr())
 135                         return thread_current();
 136                 /* The THREAD_CREATE action points to the created Thread */
 137                 else if (curr->get_type() == THREAD_CREATE)
 138                         return (Thread *)curr->get_location();
 139         }
 140
 141         /* Have we completed exploring the preselected path? */
 142         if (diverge == NULL)
 143                 return NULL;
 144
 145         /* Else, we are trying to replay an execution */
 146         ModelAction *next = node_stack->get_next()->get_action();
 147
 148         if (next == diverge) {
 149                 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
 150                         earliest_diverge=diverge;
 151
 152                 Node *nextnode = next->get_node();
 153                 /* Reached divergence point */
 154                 if (nextnode->increment_promise()) {
 155                         /* The next node will try to satisfy a different set of promises. */
 156                         tid = next->get_tid();
 157                         node_stack->pop_restofstack(2);
 158                 } else if (nextnode->increment_read_from()) {
 159                         /* The next node will read from a different value. */
 160                         tid = next->get_tid();
 161                         node_stack->pop_restofstack(2);
 162                 } else if (nextnode->increment_future_value()) {
 163                         /* The next node will try to read from a different future value. */
 164                         tid = next->get_tid();
 165                         node_stack->pop_restofstack(2);
 166                 } else if (nextnode->increment_relseq_break()) {
 167                         /* The next node will try to resolve a release sequence differently */
 168                         tid = next->get_tid();
 169                         node_stack->pop_restofstack(2);
 170                 } else {
 171                         /* Make a different thread execute for next step */
 172                         Node *node = nextnode->get_parent();
 173                         tid = node->get_next_backtrack();
 174                         node_stack->pop_restofstack(1);
 175                         if (diverge==earliest_diverge) {
 176                                 earliest_diverge=node->get_action();
 177                         }
 178                 }
 179                 DEBUG("*** Divergence point ***\n");
 180
 181                 diverge = NULL;
 182         } else {
 183                 tid = next->get_tid();
 184         }
 185         DEBUG("*** ModelChecker chose next thread = %d ***\n", id_to_int(tid));
 186         ASSERT(tid != THREAD_ID_T_NONE);
 187         return thread_map->get(id_to_int(tid));
 188 }
 189
 190 /**
 191  * Queries the model-checker for more executions to explore and, if one
 192  * exists, resets the model-checker state to execute a new execution.
 193  *
 194  * @return If there are more executions to explore, return true. Otherwise,
 195  * return false.
 196  */
 197 bool ModelChecker::next_execution()
 198 {
 199         DBG();
 200
 201         num_executions++;
 202
 203         if (isfinalfeasible()) {
 204                 printf("Earliest divergence point since last feasible execution:\n");
 205                 if (earliest_diverge)
 206                         earliest_diverge->print();
 207                 else
 208                         printf("(Not set)\n");
 209
 210                 earliest_diverge = NULL;
 211                 num_feasible_executions++;
 212         }
 213
 214         DEBUG("Number of acquires waiting on pending release sequences: %zu\n",
 215                         pending_rel_seqs->size());
 216
 217         if (isfinalfeasible() || DBG_ENABLED())
 218                 print_summary();
 219
 220         if ((diverge = get_next_backtrack()) == NULL)
 221                 return false;
 222
 223         if (DBG_ENABLED()) {
 224                 printf("Next execution will diverge at:\n");
 225                 diverge->print();
 226         }
 227
 228         reset_to_initial_state();
 229         return true;
 230 }
 231
 232 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 233 {
 234         switch (act->get_type()) {
 235         case ATOMIC_READ:
 236         case ATOMIC_WRITE:
 237         case ATOMIC_RMW: {
 238                 /* linear search: from most recent to oldest */
 239                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 240                 action_list_t::reverse_iterator rit;
 241                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 242                         ModelAction *prev = *rit;
 243                         if (prev->could_synchronize_with(act))
 244                                 return prev;
 245                 }
 246                 break;
 247         }
 248         case ATOMIC_LOCK:
 249         case ATOMIC_TRYLOCK: {
 250                 /* linear search: from most recent to oldest */
 251                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 252                 action_list_t::reverse_iterator rit;
 253                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 254                         ModelAction *prev = *rit;
 255                         if (act->is_conflicting_lock(prev))
 256                                 return prev;
 257                 }
 258                 break;
 259         }
 260         case ATOMIC_UNLOCK: {
 261                 /* linear search: from most recent to oldest */
 262                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 263                 action_list_t::reverse_iterator rit;
 264                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 265                         ModelAction *prev = *rit;
 266                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 267                                 return prev;
 268                 }
 269                 break;
 270         }
 271         default:
 272                 break;
 273         }
 274         return NULL;
 275 }
 276
 277 /** This method find backtracking points where we should try to
 278  * reorder the parameter ModelAction against.
 279  *
 280  * @param the ModelAction to find backtracking points for.
 281  */
 282 void ModelChecker::set_backtracking(ModelAction *act)
 283 {
 284         Thread *t = get_thread(act);
 285         ModelAction * prev = get_last_conflict(act);
 286         if (prev == NULL)
 287                 return;
 288
 289         Node * node = prev->get_node()->get_parent();
 290
 291         int low_tid, high_tid;
 292         if (node->is_enabled(t)) {
 293                 low_tid = id_to_int(act->get_tid());
 294                 high_tid = low_tid+1;
 295         } else {
 296                 low_tid = 0;
 297                 high_tid = get_num_threads();
 298         }
 299
 300         for(int i = low_tid; i < high_tid; i++) {
 301                 thread_id_t tid = int_to_id(i);
 302                 if (!node->is_enabled(tid))
 303                         continue;
 304
 305                 /* Check if this has been explored already */
 306                 if (node->has_been_explored(tid))
 307                         continue;
 308
 309                 /* See if fairness allows */
 310                 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
 311                         bool unfair=false;
 312                         for(int t=0;t<node->get_num_threads();t++) {
 313                                 thread_id_t tother=int_to_id(t);
 314                                 if (node->is_enabled(tother) && node->has_priority(tother)) {
 315                                         unfair=true;
 316                                         break;
 317                                 }
 318                         }
 319                         if (unfair)
 320                                 continue;
 321                 }
 322
 323                 /* Cache the latest backtracking point */
 324                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 325                         priv->next_backtrack = prev;
 326
 327                 /* If this is a new backtracking point, mark the tree */
 328                 if (!node->set_backtrack(tid))
 329                         continue;
 330                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 331                                         id_to_int(prev->get_tid()),
 332                                         id_to_int(t->get_id()));
 333                 if (DBG_ENABLED()) {
 334                         prev->print();
 335                         act->print();
 336                 }
 337         }
 338 }
 339
 340 /**
 341  * Returns last backtracking point. The model checker will explore a different
 342  * path for this point in the next execution.
 343  * @return The ModelAction at which the next execution should diverge.
 344  */
 345 ModelAction * ModelChecker::get_next_backtrack()
 346 {
 347         ModelAction *next = priv->next_backtrack;
 348         priv->next_backtrack = NULL;
 349         return next;
 350 }
 351
 352 /**
 353  * Processes a read or rmw model action.
 354  * @param curr is the read model action to process.
 355  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 356  * @return True if processing this read updates the mo_graph.
 357  */
 358 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 359 {
 360         uint64_t value;
 361         bool updated = false;
 362         while (true) {
 363                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 364                 if (reads_from != NULL) {
 365                         mo_graph->startChanges();
 366
 367                         value = reads_from->get_value();
 368                         bool r_status = false;
 369
 370                         if (!second_part_of_rmw) {
 371                                 check_recency(curr, reads_from);
 372                                 r_status = r_modification_order(curr, reads_from);
 373                         }
 374
 375
 376                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 377                                 mo_graph->rollbackChanges();
 378                                 too_many_reads = false;
 379                                 continue;
 380                         }
 381
 382                         curr->read_from(reads_from);
 383                         mo_graph->commitChanges();
 384                         mo_check_promises(curr->get_tid(), reads_from);
 385
 386                         updated |= r_status;
 387                 } else if (!second_part_of_rmw) {
 388                         /* Read from future value */
 389                         value = curr->get_node()->get_future_value();
 390                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 391                         curr->read_from(NULL);
 392                         Promise *valuepromise = new Promise(curr, value, expiration);
 393                         promises->push_back(valuepromise);
 394                 }
 395                 get_thread(curr)->set_return_value(value);
 396                 return updated;
 397         }
 398 }
 399
 400 /**
 401  * Processes a lock, trylock, or unlock model action.  @param curr is
 402  * the read model action to process.
 403  *
 404  * The try lock operation checks whether the lock is taken.  If not,
 405  * it falls to the normal lock operation case.  If so, it returns
 406  * fail.
 407  *
 408  * The lock operation has already been checked that it is enabled, so
 409  * it just grabs the lock and synchronizes with the previous unlock.
 410  *
 411  * The unlock operation has to re-enable all of the threads that are
 412  * waiting on the lock.
 413  *
 414  * @return True if synchronization was updated; false otherwise
 415  */
 416 bool ModelChecker::process_mutex(ModelAction *curr) {
 417         std::mutex *mutex = (std::mutex *)curr->get_location();
 418         struct std::mutex_state *state = mutex->get_state();
 419         switch (curr->get_type()) {
 420         case ATOMIC_TRYLOCK: {
 421                 bool success = !state->islocked;
 422                 curr->set_try_lock(success);
 423                 if (!success) {
 424                         get_thread(curr)->set_return_value(0);
 425                         break;
 426                 }
 427                 get_thread(curr)->set_return_value(1);
 428         }
 429                 //otherwise fall into the lock case
 430         case ATOMIC_LOCK: {
 431                 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
 432                         printf("Lock access before initialization\n");
 433                         set_assert();
 434                 }
 435                 state->islocked = true;
 436                 ModelAction *unlock = get_last_unlock(curr);
 437                 //synchronize with the previous unlock statement
 438                 if (unlock != NULL) {
 439                         curr->synchronize_with(unlock);
 440                         return true;
 441                 }
 442                 break;
 443         }
 444         case ATOMIC_UNLOCK: {
 445                 //unlock the lock
 446                 state->islocked = false;
 447                 //wake up the other threads
 448                 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 449                 //activate all the waiting threads
 450                 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
 451                         scheduler->wake(get_thread(*rit));
 452                 }
 453                 waiters->clear();
 454                 break;
 455         }
 456         default:
 457                 ASSERT(0);
 458         }
 459         return false;
 460 }
 461
 462 /**
 463  * Process a write ModelAction
 464  * @param curr The ModelAction to process
 465  * @return True if the mo_graph was updated or promises were resolved
 466  */
 467 bool ModelChecker::process_write(ModelAction *curr)
 468 {
 469         bool updated_mod_order = w_modification_order(curr);
 470         bool updated_promises = resolve_promises(curr);
 471
 472         if (promises->size() == 0) {
 473                 for (unsigned int i = 0; i < futurevalues->size(); i++) {
 474                         struct PendingFutureValue pfv = (*futurevalues)[i];
 475                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 476                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 477                                 priv->next_backtrack = pfv.act;
 478                 }
 479                 futurevalues->resize(0);
 480         }
 481
 482         mo_graph->commitChanges();
 483         mo_check_promises(curr->get_tid(), curr);
 484
 485         get_thread(curr)->set_return_value(VALUE_NONE);
 486         return updated_mod_order || updated_promises;
 487 }
 488
 489 /**
 490  * @brief Process the current action for thread-related activity
 491  *
 492  * Performs current-action processing for a THREAD_* ModelAction. Proccesses
 493  * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
 494  * synchronization, etc.  This function is a no-op for non-THREAD actions
 495  * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
 496  *
 497  * @param curr The current action
 498  * @return True if synchronization was updated or a thread completed
 499  */
 500 bool ModelChecker::process_thread_action(ModelAction *curr)
 501 {
 502         bool updated = false;
 503
 504         switch (curr->get_type()) {
 505         case THREAD_CREATE: {
 506                 Thread *th = (Thread *)curr->get_location();
 507                 th->set_creation(curr);
 508                 break;
 509         }
 510         case THREAD_JOIN: {
 511                 Thread *waiting, *blocking;
 512                 waiting = get_thread(curr);
 513                 blocking = (Thread *)curr->get_location();
 514                 if (!blocking->is_complete()) {
 515                         blocking->push_wait_list(curr);
 516                         scheduler->sleep(waiting);
 517                 } else {
 518                         do_complete_join(curr);
 519                         updated = true; /* trigger rel-seq checks */
 520                 }
 521                 break;
 522         }
 523         case THREAD_FINISH: {
 524                 Thread *th = get_thread(curr);
 525                 while (!th->wait_list_empty()) {
 526                         ModelAction *act = th->pop_wait_list();
 527                         Thread *wake = get_thread(act);
 528                         scheduler->wake(wake);
 529                         do_complete_join(act);
 530                         updated = true; /* trigger rel-seq checks */
 531                 }
 532                 th->complete();
 533                 updated = true; /* trigger rel-seq checks */
 534                 break;
 535         }
 536         case THREAD_START: {
 537                 check_promises(curr->get_tid(), NULL, curr->get_cv());
 538                 break;
 539         }
 540         default:
 541                 break;
 542         }
 543
 544         return updated;
 545 }
 546
 547 /**
 548  * Initialize the current action by performing one or more of the following
 549  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 550  * in the NodeStack, manipulating backtracking sets, allocating and
 551  * initializing clock vectors, and computing the promises to fulfill.
 552  *
 553  * @param curr The current action, as passed from the user context; may be
 554  * freed/invalidated after the execution of this function
 555  * @return The current action, as processed by the ModelChecker. Is only the
 556  * same as the parameter @a curr if this is a newly-explored action.
 557  */
 558 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 559 {
 560         ModelAction *newcurr;
 561
 562         if (curr->is_rmwc() || curr->is_rmw()) {
 563                 newcurr = process_rmw(curr);
 564                 delete curr;
 565
 566                 if (newcurr->is_rmw())
 567                         compute_promises(newcurr);
 568                 return newcurr;
 569         }
 570
 571         curr->set_seq_number(get_next_seq_num());
 572
 573         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 574         if (newcurr) {
 575                 /* First restore type and order in case of RMW operation */
 576                 if (curr->is_rmwr())
 577                         newcurr->copy_typeandorder(curr);
 578
 579                 ASSERT(curr->get_location() == newcurr->get_location());
 580                 newcurr->copy_from_new(curr);
 581
 582                 /* Discard duplicate ModelAction; use action from NodeStack */
 583                 delete curr;
 584
 585                 /* Always compute new clock vector */
 586                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 587         } else {
 588                 newcurr = curr;
 589
 590                 /* Always compute new clock vector */
 591                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 592                 /*
 593                  * Perform one-time actions when pushing new ModelAction onto
 594                  * NodeStack
 595                  */
 596                 if (newcurr->is_write())
 597                         compute_promises(newcurr);
 598                 else if (newcurr->is_relseq_fixup())
 599                         compute_relseq_breakwrites(newcurr);
 600         }
 601         return newcurr;
 602 }
 603
 604 /**
 605  * This method checks whether a model action is enabled at the given point.
 606  * At this point, it checks whether a lock operation would be successful at this point.
 607  * If not, it puts the thread in a waiter list.
 608  * @param curr is the ModelAction to check whether it is enabled.
 609  * @return a bool that indicates whether the action is enabled.
 610  */
 611 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 612         if (curr->is_lock()) {
 613                 std::mutex * lock = (std::mutex *)curr->get_location();
 614                 struct std::mutex_state * state = lock->get_state();
 615                 if (state->islocked) {
 616                         //Stick the action in the appropriate waiting queue
 617                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 618                         return false;
 619                 }
 620         }
 621
 622         return true;
 623 }
 624
 625 /**
 626  * This is the heart of the model checker routine. It performs model-checking
 627  * actions corresponding to a given "current action." Among other processes, it
 628  * calculates reads-from relationships, updates synchronization clock vectors,
 629  * forms a memory_order constraints graph, and handles replay/backtrack
 630  * execution when running permutations of previously-observed executions.
 631  *
 632  * @param curr The current action to process
 633  * @return The next Thread that must be executed. May be NULL if ModelChecker
 634  * makes no choice (e.g., according to replay execution, combining RMW actions,
 635  * etc.)
 636  */
 637 Thread * ModelChecker::check_current_action(ModelAction *curr)
 638 {
 639         ASSERT(curr);
 640
 641         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 642
 643         if (!check_action_enabled(curr)) {
 644                 /* Make the execution look like we chose to run this action
 645                  * much later, when a lock is actually available to release */
 646                 get_current_thread()->set_pending(curr);
 647                 scheduler->sleep(get_current_thread());
 648                 return get_next_thread(NULL);
 649         }
 650
 651         ModelAction *newcurr = initialize_curr_action(curr);
 652
 653         /* Add the action to lists before any other model-checking tasks */
 654         if (!second_part_of_rmw)
 655                 add_action_to_lists(newcurr);
 656
 657         /* Build may_read_from set for newly-created actions */
 658         if (curr == newcurr && curr->is_read())
 659                 build_reads_from_past(curr);
 660         curr = newcurr;
 661
 662         /* Initialize work_queue with the "current action" work */
 663         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 664
 665         while (!work_queue.empty()) {
 666                 WorkQueueEntry work = work_queue.front();
 667                 work_queue.pop_front();
 668
 669                 switch (work.type) {
 670                 case WORK_CHECK_CURR_ACTION: {
 671                         ModelAction *act = work.action;
 672                         bool update = false; /* update this location's release seq's */
 673                         bool update_all = false; /* update all release seq's */
 674
 675                         if (process_thread_action(curr))
 676                                 update_all = true;
 677
 678                         if (act->is_read() && process_read(act, second_part_of_rmw))
 679                                 update = true;
 680
 681                         if (act->is_write() && process_write(act))
 682                                 update = true;
 683
 684                         if (act->is_mutex_op() && process_mutex(act))
 685                                 update_all = true;
 686
 687                         if (update_all)
 688                                 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
 689                         else if (update)
 690                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 691                         break;
 692                 }
 693                 case WORK_CHECK_RELEASE_SEQ:
 694                         resolve_release_sequences(work.location, &work_queue);
 695                         break;
 696                 case WORK_CHECK_MO_EDGES: {
 697                         /** @todo Complete verification of work_queue */
 698                         ModelAction *act = work.action;
 699                         bool updated = false;
 700
 701                         if (act->is_read()) {
 702                                 const ModelAction *rf = act->get_reads_from();
 703                                 if (rf != NULL && r_modification_order(act, rf))
 704                                         updated = true;
 705                         }
 706                         if (act->is_write()) {
 707                                 if (w_modification_order(act))
 708                                         updated = true;
 709                         }
 710                         mo_graph->commitChanges();
 711
 712                         if (updated)
 713                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 714                         break;
 715                 }
 716                 default:
 717                         ASSERT(false);
 718                         break;
 719                 }
 720         }
 721
 722         check_curr_backtracking(curr);
 723
 724         set_backtracking(curr);
 725
 726         return get_next_thread(curr);
 727 }
 728
 729 /**
 730  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 731  * operation from the Thread it is joining with. Must be called after the
 732  * completion of the Thread in question.
 733  * @param join The THREAD_JOIN action
 734  */
 735 void ModelChecker::do_complete_join(ModelAction *join)
 736 {
 737         Thread *blocking = (Thread *)join->get_location();
 738         ModelAction *act = get_last_action(blocking->get_id());
 739         join->synchronize_with(act);
 740 }
 741
 742 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 743         Node *currnode = curr->get_node();
 744         Node *parnode = currnode->get_parent();
 745
 746         if ((!parnode->backtrack_empty() ||
 747                          !currnode->read_from_empty() ||
 748                          !currnode->future_value_empty() ||
 749                          !currnode->promise_empty() ||
 750                          !currnode->relseq_break_empty())
 751                         && (!priv->next_backtrack ||
 752                                         *curr > *priv->next_backtrack)) {
 753                 priv->next_backtrack = curr;
 754         }
 755 }
 756
 757 bool ModelChecker::promises_expired() {
 758         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 759                 Promise *promise = (*promises)[promise_index];
 760                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 761                         return true;
 762                 }
 763         }
 764         return false;
 765 }
 766
 767 /** @return whether the current partial trace must be a prefix of a
 768  * feasible trace. */
 769 bool ModelChecker::isfeasibleprefix() {
 770         return promises->size() == 0 && pending_rel_seqs->size() == 0;
 771 }
 772
 773 /** @return whether the current partial trace is feasible. */
 774 bool ModelChecker::isfeasible() {
 775         if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
 776                 DEBUG("Infeasible: RMW violation\n");
 777
 778         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 779 }
 780
 781 /** @return whether the current partial trace is feasible other than
 782  * multiple RMW reading from the same store. */
 783 bool ModelChecker::isfeasibleotherthanRMW() {
 784         if (DBG_ENABLED()) {
 785                 if (mo_graph->checkForCycles())
 786                         DEBUG("Infeasible: modification order cycles\n");
 787                 if (failed_promise)
 788                         DEBUG("Infeasible: failed promise\n");
 789                 if (too_many_reads)
 790                         DEBUG("Infeasible: too many reads\n");
 791                 if (bad_synchronization)
 792                         DEBUG("Infeasible: bad synchronization ordering\n");
 793                 if (promises_expired())
 794                         DEBUG("Infeasible: promises expired\n");
 795         }
 796         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
 797 }
 798
 799 /** Returns whether the current completed trace is feasible. */
 800 bool ModelChecker::isfinalfeasible() {
 801         if (DBG_ENABLED() && promises->size() != 0)
 802                 DEBUG("Infeasible: unrevolved promises\n");
 803
 804         return isfeasible() && promises->size() == 0;
 805 }
 806
 807 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 808 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 809         ModelAction *lastread = get_last_action(act->get_tid());
 810         lastread->process_rmw(act);
 811         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 812                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 813                 mo_graph->commitChanges();
 814         }
 815         return lastread;
 816 }
 817
 818 /**
 819  * Checks whether a thread has read from the same write for too many times
 820  * without seeing the effects of a later write.
 821  *
 822  * Basic idea:
 823  * 1) there must a different write that we could read from that would satisfy the modification order,
 824  * 2) we must have read from the same value in excess of maxreads times, and
 825  * 3) that other write must have been in the reads_from set for maxreads times.
 826  *
 827  * If so, we decide that the execution is no longer feasible.
 828  */
 829 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
 830         if (params.maxreads != 0) {
 831
 832                 if (curr->get_node()->get_read_from_size() <= 1)
 833                         return;
 834                 //Must make sure that execution is currently feasible...  We could
 835                 //accidentally clear by rolling back
 836                 if (!isfeasible())
 837                         return;
 838                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 839                 int tid = id_to_int(curr->get_tid());
 840
 841                 /* Skip checks */
 842                 if ((int)thrd_lists->size() <= tid)
 843                         return;
 844                 action_list_t *list = &(*thrd_lists)[tid];
 845
 846                 action_list_t::reverse_iterator rit = list->rbegin();
 847                 /* Skip past curr */
 848                 for (; (*rit) != curr; rit++)
 849                         ;
 850                 /* go past curr now */
 851                 rit++;
 852
 853                 action_list_t::reverse_iterator ritcopy = rit;
 854                 //See if we have enough reads from the same value
 855                 int count = 0;
 856                 for (; count < params.maxreads; rit++,count++) {
 857                         if (rit==list->rend())
 858                                 return;
 859                         ModelAction *act = *rit;
 860                         if (!act->is_read())
 861                                 return;
 862
 863                         if (act->get_reads_from() != rf)
 864                                 return;
 865                         if (act->get_node()->get_read_from_size() <= 1)
 866                                 return;
 867                 }
 868                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 869                         //Get write
 870                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 871
 872                         //Need a different write
 873                         if (write==rf)
 874                                 continue;
 875
 876                         /* Test to see whether this is a feasible write to read from*/
 877                         mo_graph->startChanges();
 878                         r_modification_order(curr, write);
 879                         bool feasiblereadfrom = isfeasible();
 880                         mo_graph->rollbackChanges();
 881
 882                         if (!feasiblereadfrom)
 883                                 continue;
 884                         rit = ritcopy;
 885
 886                         bool feasiblewrite = true;
 887                         //new we need to see if this write works for everyone
 888
 889                         for (int loop = count; loop>0; loop--,rit++) {
 890                                 ModelAction *act=*rit;
 891                                 bool foundvalue = false;
 892                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 893                                         if (act->get_node()->get_read_from_at(i)==write) {
 894                                                 foundvalue = true;
 895                                                 break;
 896                                         }
 897                                 }
 898                                 if (!foundvalue) {
 899                                         feasiblewrite = false;
 900                                         break;
 901                                 }
 902                         }
 903                         if (feasiblewrite) {
 904                                 too_many_reads = true;
 905                                 return;
 906                         }
 907                 }
 908         }
 909 }
 910
 911 /**
 912  * Updates the mo_graph with the constraints imposed from the current
 913  * read.
 914  *
 915  * Basic idea is the following: Go through each other thread and find
 916  * the lastest action that happened before our read.  Two cases:
 917  *
 918  * (1) The action is a write => that write must either occur before
 919  * the write we read from or be the write we read from.
 920  *
 921  * (2) The action is a read => the write that that action read from
 922  * must occur before the write we read from or be the same write.
 923  *
 924  * @param curr The current action. Must be a read.
 925  * @param rf The action that curr reads from. Must be a write.
 926  * @return True if modification order edges were added; false otherwise
 927  */
 928 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 929 {
 930         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 931         unsigned int i;
 932         bool added = false;
 933         ASSERT(curr->is_read());
 934
 935         /* Iterate over all threads */
 936         for (i = 0; i < thrd_lists->size(); i++) {
 937                 /* Iterate over actions in thread, starting from most recent */
 938                 action_list_t *list = &(*thrd_lists)[i];
 939                 action_list_t::reverse_iterator rit;
 940                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 941                         ModelAction *act = *rit;
 942
 943                         /*
 944                          * Include at most one act per-thread that "happens
 945                          * before" curr. Don't consider reflexively.
 946                          */
 947                         if (act->happens_before(curr) && act != curr) {
 948                                 if (act->is_write()) {
 949                                         if (rf != act) {
 950                                                 mo_graph->addEdge(act, rf);
 951                                                 added = true;
 952                                         }
 953                                 } else {
 954                                         const ModelAction *prevreadfrom = act->get_reads_from();
 955                                         //if the previous read is unresolved, keep going...
 956                                         if (prevreadfrom == NULL)
 957                                                 continue;
 958
 959                                         if (rf != prevreadfrom) {
 960                                                 mo_graph->addEdge(prevreadfrom, rf);
 961                                                 added = true;
 962                                         }
 963                                 }
 964                                 break;
 965                         }
 966                 }
 967         }
 968
 969         return added;
 970 }
 971
 972 /** This method fixes up the modification order when we resolve a
 973  *  promises.  The basic problem is that actions that occur after the
 974  *  read curr could not property add items to the modification order
 975  *  for our read.
 976  *
 977  *  So for each thread, we find the earliest item that happens after
 978  *  the read curr.  This is the item we have to fix up with additional
 979  *  constraints.  If that action is write, we add a MO edge between
 980  *  the Action rf and that action.  If the action is a read, we add a
 981  *  MO edge between the Action rf, and whatever the read accessed.
 982  *
 983  * @param curr is the read ModelAction that we are fixing up MO edges for.
 984  * @param rf is the write ModelAction that curr reads from.
 985  *
 986  */
 987 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 988 {
 989         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 990         unsigned int i;
 991         ASSERT(curr->is_read());
 992
 993         /* Iterate over all threads */
 994         for (i = 0; i < thrd_lists->size(); i++) {
 995                 /* Iterate over actions in thread, starting from most recent */
 996                 action_list_t *list = &(*thrd_lists)[i];
 997                 action_list_t::reverse_iterator rit;
 998                 ModelAction *lastact = NULL;
 999
1000                 /* Find last action that happens after curr that is either not curr or a rmw */
1001                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1002                         ModelAction *act = *rit;
1003                         if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
1004                                 lastact = act;
1005                         } else
1006                                 break;
1007                 }
1008
1009                         /* Include at most one act per-thread that "happens before" curr */
1010                 if (lastact != NULL) {
1011                         if (lastact==curr) {
1012                                 //Case 1: The resolved read is a RMW, and we need to make sure
1013                                 //that the write portion of the RMW mod order after rf
1014
1015                                 mo_graph->addEdge(rf, lastact);
1016                         } else if (lastact->is_read()) {
1017                                 //Case 2: The resolved read is a normal read and the next
1018                                 //operation is a read, and we need to make sure the value read
1019                                 //is mod ordered after rf
1020
1021                                 const ModelAction *postreadfrom = lastact->get_reads_from();
1022                                 if (postreadfrom != NULL&&rf != postreadfrom)
1023                                         mo_graph->addEdge(rf, postreadfrom);
1024                         } else {
1025                                 //Case 3: The resolved read is a normal read and the next
1026                                 //operation is a write, and we need to make sure that the
1027                                 //write is mod ordered after rf
1028                                 if (lastact!=rf)
1029                                         mo_graph->addEdge(rf, lastact);
1030                         }
1031                         break;
1032                 }
1033         }
1034 }
1035
1036 /**
1037  * Updates the mo_graph with the constraints imposed from the current write.
1038  *
1039  * Basic idea is the following: Go through each other thread and find
1040  * the lastest action that happened before our write.  Two cases:
1041  *
1042  * (1) The action is a write => that write must occur before
1043  * the current write
1044  *
1045  * (2) The action is a read => the write that that action read from
1046  * must occur before the current write.
1047  *
1048  * This method also handles two other issues:
1049  *
1050  * (I) Sequential Consistency: Making sure that if the current write is
1051  * seq_cst, that it occurs after the previous seq_cst write.
1052  *
1053  * (II) Sending the write back to non-synchronizing reads.
1054  *
1055  * @param curr The current action. Must be a write.
1056  * @return True if modification order edges were added; false otherwise
1057  */
1058 bool ModelChecker::w_modification_order(ModelAction *curr)
1059 {
1060         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1061         unsigned int i;
1062         bool added = false;
1063         ASSERT(curr->is_write());
1064
1065         if (curr->is_seqcst()) {
1066                 /* We have to at least see the last sequentially consistent write,
1067                          so we are initialized. */
1068                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1069                 if (last_seq_cst != NULL) {
1070                         mo_graph->addEdge(last_seq_cst, curr);
1071                         added = true;
1072                 }
1073         }
1074
1075         /* Iterate over all threads */
1076         for (i = 0; i < thrd_lists->size(); i++) {
1077                 /* Iterate over actions in thread, starting from most recent */
1078                 action_list_t *list = &(*thrd_lists)[i];
1079                 action_list_t::reverse_iterator rit;
1080                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1081                         ModelAction *act = *rit;
1082                         if (act == curr) {
1083                                 /*
1084                                  * 1) If RMW and it actually read from something, then we
1085                                  * already have all relevant edges, so just skip to next
1086                                  * thread.
1087                                  *
1088                                  * 2) If RMW and it didn't read from anything, we should
1089                                  * whatever edge we can get to speed up convergence.
1090                                  *
1091                                  * 3) If normal write, we need to look at earlier actions, so
1092                                  * continue processing list.
1093                                  */
1094                                 if (curr->is_rmw()) {
1095                                         if (curr->get_reads_from()!=NULL)
1096                                                 break;
1097                                         else
1098                                                 continue;
1099                                 } else
1100                                         continue;
1101                         }
1102
1103                         /*
1104                          * Include at most one act per-thread that "happens
1105                          * before" curr
1106                          */
1107                         if (act->happens_before(curr)) {
1108                                 /*
1109                                  * Note: if act is RMW, just add edge:
1110                                  *   act --mo--> curr
1111                                  * The following edge should be handled elsewhere:
1112                                  *   readfrom(act) --mo--> act
1113                                  */
1114                                 if (act->is_write())
1115                                         mo_graph->addEdge(act, curr);
1116                                 else if (act->is_read()) {
1117                                         //if previous read accessed a null, just keep going
1118                                         if (act->get_reads_from() == NULL)
1119                                                 continue;
1120                                         mo_graph->addEdge(act->get_reads_from(), curr);
1121                                 }
1122                                 added = true;
1123                                 break;
1124                         } else if (act->is_read() && !act->could_synchronize_with(curr) &&
1125                                                      !act->same_thread(curr)) {
1126                                 /* We have an action that:
1127                                    (1) did not happen before us
1128                                    (2) is a read and we are a write
1129                                    (3) cannot synchronize with us
1130                                    (4) is in a different thread
1131                                    =>
1132                                    that read could potentially read from our write.
1133                                  */
1134                                 if (thin_air_constraint_may_allow(curr, act)) {
1135                                         if (isfeasible() ||
1136                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1137                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1138                                                 futurevalues->push_back(pfv);
1139                                         }
1140                                 }
1141                         }
1142                 }
1143         }
1144
1145         return added;
1146 }
1147
1148 /** Arbitrary reads from the future are not allowed.  Section 29.3
1149  * part 9 places some constraints.  This method checks one result of constraint
1150  * constraint.  Others require compiler support. */
1151 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1152         if (!writer->is_rmw())
1153                 return true;
1154
1155         if (!reader->is_rmw())
1156                 return true;
1157
1158         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1159                 if (search == reader)
1160                         return false;
1161                 if (search->get_tid() == reader->get_tid() &&
1162                                 search->happens_before(reader))
1163                         break;
1164         }
1165
1166         return true;
1167 }
1168
1169 /**
1170  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1171  * The ModelAction under consideration is expected to be taking part in
1172  * release/acquire synchronization as an object of the "reads from" relation.
1173  * Note that this can only provide release sequence support for RMW chains
1174  * which do not read from the future, as those actions cannot be traced until
1175  * their "promise" is fulfilled. Similarly, we may not even establish the
1176  * presence of a release sequence with certainty, as some modification order
1177  * constraints may be decided further in the future. Thus, this function
1178  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1179  * and a boolean representing certainty.
1180  *
1181  * @todo Finish lazy updating, when promises are fulfilled in the future
1182  * @param rf The action that might be part of a release sequence. Must be a
1183  * write.
1184  * @param release_heads A pass-by-reference style return parameter. After
1185  * execution of this function, release_heads will contain the heads of all the
1186  * relevant release sequences, if any exists with certainty
1187  * @param pending A pass-by-reference style return parameter which is only used
1188  * when returning false (i.e., uncertain). Returns most information regarding
1189  * an uncertain release sequence, including any write operations that might
1190  * break the sequence.
1191  * @return true, if the ModelChecker is certain that release_heads is complete;
1192  * false otherwise
1193  */
1194 bool ModelChecker::release_seq_heads(const ModelAction *rf,
1195                 rel_heads_list_t *release_heads,
1196                 struct release_seq *pending) const
1197 {
1198         /* Only check for release sequences if there are no cycles */
1199         if (mo_graph->checkForCycles())
1200                 return false;
1201
1202         while (rf) {
1203                 ASSERT(rf->is_write());
1204
1205                 if (rf->is_release())
1206                         release_heads->push_back(rf);
1207                 if (!rf->is_rmw())
1208                         break; /* End of RMW chain */
1209
1210                 /** @todo Need to be smarter here...  In the linux lock
1211                  * example, this will run to the beginning of the program for
1212                  * every acquire. */
1213                 /** @todo The way to be smarter here is to keep going until 1
1214                  * thread has a release preceded by an acquire and you've seen
1215                  *       both. */
1216
1217                 /* acq_rel RMW is a sufficient stopping condition */
1218                 if (rf->is_acquire() && rf->is_release())
1219                         return true; /* complete */
1220
1221                 rf = rf->get_reads_from();
1222         };
1223         if (!rf) {
1224                 /* read from future: need to settle this later */
1225                 pending->rf = NULL;
1226                 return false; /* incomplete */
1227         }
1228
1229         if (rf->is_release())
1230                 return true; /* complete */
1231
1232         /* else relaxed write; check modification order for contiguous subsequence
1233          * -> rf must be same thread as release */
1234         int tid = id_to_int(rf->get_tid());
1235         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1236         action_list_t *list = &(*thrd_lists)[tid];
1237         action_list_t::const_reverse_iterator rit;
1238
1239         /* Find rf in the thread list */
1240         rit = std::find(list->rbegin(), list->rend(), rf);
1241         ASSERT(rit != list->rend());
1242
1243         /* Find the last write/release */
1244         for (; rit != list->rend(); rit++)
1245                 if ((*rit)->is_release())
1246                         break;
1247         if (rit == list->rend()) {
1248                 /* No write-release in this thread */
1249                 return true; /* complete */
1250         }
1251         ModelAction *release = *rit;
1252
1253         ASSERT(rf->same_thread(release));
1254
1255         pending->writes.clear();
1256
1257         bool certain = true;
1258         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1259                 if (id_to_int(rf->get_tid()) == (int)i)
1260                         continue;
1261                 list = &(*thrd_lists)[i];
1262
1263                 /* Can we ensure no future writes from this thread may break
1264                  * the release seq? */
1265                 bool future_ordered = false;
1266
1267                 ModelAction *last = get_last_action(int_to_id(i));
1268                 Thread *th = get_thread(int_to_id(i));
1269                 if ((last && rf->happens_before(last)) ||
1270                                 !scheduler->is_enabled(th) ||
1271                                 th->is_complete())
1272                         future_ordered = true;
1273
1274                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1275                         const ModelAction *act = *rit;
1276                         /* Reach synchronization -> this thread is complete */
1277                         if (act->happens_before(release))
1278                                 break;
1279                         if (rf->happens_before(act)) {
1280                                 future_ordered = true;
1281                                 continue;
1282                         }
1283
1284                         /* Only writes can break release sequences */
1285                         if (!act->is_write())
1286                                 continue;
1287
1288                         /* Check modification order */
1289                         if (mo_graph->checkReachable(rf, act)) {
1290                                 /* rf --mo--> act */
1291                                 future_ordered = true;
1292                                 continue;
1293                         }
1294                         if (mo_graph->checkReachable(act, release))
1295                                 /* act --mo--> release */
1296                                 break;
1297                         if (mo_graph->checkReachable(release, act) &&
1298                                       mo_graph->checkReachable(act, rf)) {
1299                                 /* release --mo-> act --mo--> rf */
1300                                 return true; /* complete */
1301                         }
1302                         /* act may break release sequence */
1303                         pending->writes.push_back(act);
1304                         certain = false;
1305                 }
1306                 if (!future_ordered)
1307                         certain = false; /* This thread is uncertain */
1308         }
1309
1310         if (certain) {
1311                 release_heads->push_back(release);
1312                 pending->writes.clear();
1313         } else {
1314                 pending->release = release;
1315                 pending->rf = rf;
1316         }
1317         return certain;
1318 }
1319
1320 /**
1321  * A public interface for getting the release sequence head(s) with which a
1322  * given ModelAction must synchronize. This function only returns a non-empty
1323  * result when it can locate a release sequence head with certainty. Otherwise,
1324  * it may mark the internal state of the ModelChecker so that it will handle
1325  * the release sequence at a later time, causing @a act to update its
1326  * synchronization at some later point in execution.
1327  * @param act The 'acquire' action that may read from a release sequence
1328  * @param release_heads A pass-by-reference return parameter. Will be filled
1329  * with the head(s) of the release sequence(s), if they exists with certainty.
1330  * @see ModelChecker::release_seq_heads
1331  */
1332 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1333 {
1334         const ModelAction *rf = act->get_reads_from();
1335         struct release_seq *sequence = (struct release_seq *)snapshot_calloc(1, sizeof(struct release_seq));
1336         sequence->acquire = act;
1337
1338         if (!release_seq_heads(rf, release_heads, sequence)) {
1339                 /* add act to 'lazy checking' list */
1340                 pending_rel_seqs->push_back(sequence);
1341         } else {
1342                 snapshot_free(sequence);
1343         }
1344 }
1345
1346 /**
1347  * Attempt to resolve all stashed operations that might synchronize with a
1348  * release sequence for a given location. This implements the "lazy" portion of
1349  * determining whether or not a release sequence was contiguous, since not all
1350  * modification order information is present at the time an action occurs.
1351  *
1352  * @param location The location/object that should be checked for release
1353  * sequence resolutions. A NULL value means to check all locations.
1354  * @param work_queue The work queue to which to add work items as they are
1355  * generated
1356  * @return True if any updates occurred (new synchronization, new mo_graph
1357  * edges)
1358  */
1359 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1360 {
1361         bool updated = false;
1362         std::vector<struct release_seq *>::iterator it = pending_rel_seqs->begin();
1363         while (it != pending_rel_seqs->end()) {
1364                 struct release_seq *pending = *it;
1365                 ModelAction *act = pending->acquire;
1366
1367                 /* Only resolve sequences on the given location, if provided */
1368                 if (location && act->get_location() != location) {
1369                         it++;
1370                         continue;
1371                 }
1372
1373                 const ModelAction *rf = act->get_reads_from();
1374                 rel_heads_list_t release_heads;
1375                 bool complete;
1376                 complete = release_seq_heads(rf, &release_heads, pending);
1377                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1378                         if (!act->has_synchronized_with(release_heads[i])) {
1379                                 if (act->synchronize_with(release_heads[i]))
1380                                         updated = true;
1381                                 else
1382                                         set_bad_synchronization();
1383                         }
1384                 }
1385
1386                 if (updated) {
1387                         /* Re-check all pending release sequences */
1388                         work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1389                         /* Re-check act for mo_graph edges */
1390                         work_queue->push_back(MOEdgeWorkEntry(act));
1391
1392                         /* propagate synchronization to later actions */
1393                         action_list_t::reverse_iterator rit = action_trace->rbegin();
1394                         for (; (*rit) != act; rit++) {
1395                                 ModelAction *propagate = *rit;
1396                                 if (act->happens_before(propagate)) {
1397                                         propagate->synchronize_with(act);
1398                                         /* Re-check 'propagate' for mo_graph edges */
1399                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1400                                 }
1401                         }
1402                 }
1403                 if (complete) {
1404                         it = pending_rel_seqs->erase(it);
1405                         snapshot_free(pending);
1406                 } else {
1407                         it++;
1408                 }
1409         }
1410
1411         // If we resolved promises or data races, see if we have realized a data race.
1412         if (checkDataRaces()) {
1413                 set_assert();
1414         }
1415
1416         return updated;
1417 }
1418
1419 /**
1420  * Performs various bookkeeping operations for the current ModelAction. For
1421  * instance, adds action to the per-object, per-thread action vector and to the
1422  * action trace list of all thread actions.
1423  *
1424  * @param act is the ModelAction to add.
1425  */
1426 void ModelChecker::add_action_to_lists(ModelAction *act)
1427 {
1428         int tid = id_to_int(act->get_tid());
1429         action_trace->push_back(act);
1430
1431         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1432
1433         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1434         if (tid >= (int)vec->size())
1435                 vec->resize(priv->next_thread_id);
1436         (*vec)[tid].push_back(act);
1437
1438         if ((int)thrd_last_action->size() <= tid)
1439                 thrd_last_action->resize(get_num_threads());
1440         (*thrd_last_action)[tid] = act;
1441 }
1442
1443 /**
1444  * @brief Get the last action performed by a particular Thread
1445  * @param tid The thread ID of the Thread in question
1446  * @return The last action in the thread
1447  */
1448 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1449 {
1450         int threadid = id_to_int(tid);
1451         if (threadid < (int)thrd_last_action->size())
1452                 return (*thrd_last_action)[id_to_int(tid)];
1453         else
1454                 return NULL;
1455 }
1456
1457 /**
1458  * Gets the last memory_order_seq_cst write (in the total global sequence)
1459  * performed on a particular object (i.e., memory location), not including the
1460  * current action.
1461  * @param curr The current ModelAction; also denotes the object location to
1462  * check
1463  * @return The last seq_cst write
1464  */
1465 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1466 {
1467         void *location = curr->get_location();
1468         action_list_t *list = obj_map->get_safe_ptr(location);
1469         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1470         action_list_t::reverse_iterator rit;
1471         for (rit = list->rbegin(); rit != list->rend(); rit++)
1472                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1473                         return *rit;
1474         return NULL;
1475 }
1476
1477 /**
1478  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1479  * location). This function identifies the mutex according to the current
1480  * action, which is presumed to perform on the same mutex.
1481  * @param curr The current ModelAction; also denotes the object location to
1482  * check
1483  * @return The last unlock operation
1484  */
1485 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1486 {
1487         void *location = curr->get_location();
1488         action_list_t *list = obj_map->get_safe_ptr(location);
1489         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1490         action_list_t::reverse_iterator rit;
1491         for (rit = list->rbegin(); rit != list->rend(); rit++)
1492                 if ((*rit)->is_unlock())
1493                         return *rit;
1494         return NULL;
1495 }
1496
1497 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1498 {
1499         ModelAction *parent = get_last_action(tid);
1500         if (!parent)
1501                 parent = get_thread(tid)->get_creation();
1502         return parent;
1503 }
1504
1505 /**
1506  * Returns the clock vector for a given thread.
1507  * @param tid The thread whose clock vector we want
1508  * @return Desired clock vector
1509  */
1510 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1511 {
1512         return get_parent_action(tid)->get_cv();
1513 }
1514
1515 /**
1516  * Resolve a set of Promises with a current write. The set is provided in the
1517  * Node corresponding to @a write.
1518  * @param write The ModelAction that is fulfilling Promises
1519  * @return True if promises were resolved; false otherwise
1520  */
1521 bool ModelChecker::resolve_promises(ModelAction *write)
1522 {
1523         bool resolved = false;
1524   std::vector<thread_id_t> threads_to_check;
1525
1526         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1527                 Promise *promise = (*promises)[promise_index];
1528                 if (write->get_node()->get_promise(i)) {
1529                         ModelAction *read = promise->get_action();
1530                         if (read->is_rmw()) {
1531                                 mo_graph->addRMWEdge(write, read);
1532                         }
1533                         read->read_from(write);
1534                         //First fix up the modification order for actions that happened
1535                         //before the read
1536                         r_modification_order(read, write);
1537                         //Next fix up the modification order for actions that happened
1538                         //after the read.
1539                         post_r_modification_order(read, write);
1540                         //Make sure the promise's value matches the write's value
1541                         ASSERT(promise->get_value() == write->get_value());
1542                         delete(promise);
1543
1544                         promises->erase(promises->begin() + promise_index);
1545                         threads_to_check.push_back(read->get_tid());
1546
1547                         resolved = true;
1548                 } else
1549                         promise_index++;
1550         }
1551
1552         //Check whether reading these writes has made threads unable to
1553         //resolve promises
1554
1555         for(unsigned int i=0;i<threads_to_check.size();i++)
1556                 mo_check_promises(threads_to_check[i], write);
1557
1558         return resolved;
1559 }
1560
1561 /**
1562  * Compute the set of promises that could potentially be satisfied by this
1563  * action. Note that the set computation actually appears in the Node, not in
1564  * ModelChecker.
1565  * @param curr The ModelAction that may satisfy promises
1566  */
1567 void ModelChecker::compute_promises(ModelAction *curr)
1568 {
1569         for (unsigned int i = 0; i < promises->size(); i++) {
1570                 Promise *promise = (*promises)[i];
1571                 const ModelAction *act = promise->get_action();
1572                 if (!act->happens_before(curr) &&
1573                                 act->is_read() &&
1574                                 !act->could_synchronize_with(curr) &&
1575                                 !act->same_thread(curr) &&
1576                                 promise->get_value() == curr->get_value()) {
1577                         curr->get_node()->set_promise(i);
1578                 }
1579         }
1580 }
1581
1582 /** Checks promises in response to change in ClockVector Threads. */
1583 void ModelChecker::check_promises(thread_id_t tid, ClockVector *old_cv, ClockVector *merge_cv)
1584 {
1585         for (unsigned int i = 0; i < promises->size(); i++) {
1586                 Promise *promise = (*promises)[i];
1587                 const ModelAction *act = promise->get_action();
1588                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1589                                 merge_cv->synchronized_since(act)) {
1590                         if (promise->increment_threads(tid)) {
1591                                 //Promise has failed
1592                                 failed_promise = true;
1593                                 return;
1594                         }
1595                 }
1596         }
1597 }
1598
1599 /** Checks promises in response to addition to modification order for threads.
1600  * Definitions:
1601  * pthread is the thread that performed the read that created the promise
1602  *
1603  * pread is the read that created the promise
1604  *
1605  * pwrite is either the first write to same location as pread by
1606  * pthread that is sequenced after pread or the value read by the
1607  * first read to the same lcoation as pread by pthread that is
1608  * sequenced after pread..
1609  *
1610  *      1. If tid=pthread, then we check what other threads are reachable
1611  * through the mode order starting with pwrite.  Those threads cannot
1612  * perform a write that will resolve the promise due to modification
1613  * order constraints.
1614  *
1615  * 2. If the tid is not pthread, we check whether pwrite can reach the
1616  * action write through the modification order.  If so, that thread
1617  * cannot perform a future write that will resolve the promise due to
1618  * modificatin order constraints.
1619  *
1620  *      @parem tid The thread that either read from the model action
1621  *      write, or actually did the model action write.
1622  *
1623  *      @parem write The ModelAction representing the relevant write.
1624  */
1625
1626 void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write) {
1627         void * location = write->get_location();
1628         for (unsigned int i = 0; i < promises->size(); i++) {
1629                 Promise *promise = (*promises)[i];
1630                 const ModelAction *act = promise->get_action();
1631
1632                 //Is this promise on the same location?
1633                 if ( act->get_location() != location )
1634                         continue;
1635
1636                 //same thread as the promise
1637                 if ( act->get_tid()==tid ) {
1638
1639                         //do we have a pwrite for the promise, if not, set it
1640                         if (promise->get_write() == NULL ) {
1641                                 promise->set_write(write);
1642                         }
1643                         if (mo_graph->checkPromise(write, promise)) {
1644                                 failed_promise = true;
1645                                 return;
1646                         }
1647                 }
1648
1649                 //Don't do any lookups twice for the same thread
1650                 if (promise->has_sync_thread(tid))
1651                         continue;
1652
1653                 if (mo_graph->checkReachable(promise->get_write(), write)) {
1654                         if (promise->increment_threads(tid)) {
1655                                 failed_promise = true;
1656                                 return;
1657                         }
1658                 }
1659         }
1660 }
1661
1662 /**
1663  * Compute the set of writes that may break the current pending release
1664  * sequence. This information is extracted from previou release sequence
1665  * calculations.
1666  *
1667  * @param curr The current ModelAction. Must be a release sequence fixup
1668  * action.
1669  */
1670 void ModelChecker::compute_relseq_breakwrites(ModelAction *curr)
1671 {
1672         if (pending_rel_seqs->empty())
1673                 return;
1674
1675         struct release_seq *pending = pending_rel_seqs->back();
1676         for (unsigned int i = 0; i < pending->writes.size(); i++) {
1677                 const ModelAction *write = pending->writes[i];
1678                 curr->get_node()->add_relseq_break(write);
1679         }
1680
1681         /* NULL means don't break the sequence; just synchronize */
1682         curr->get_node()->add_relseq_break(NULL);
1683 }
1684
1685 /**
1686  * Build up an initial set of all past writes that this 'read' action may read
1687  * from. This set is determined by the clock vector's "happens before"
1688  * relationship.
1689  * @param curr is the current ModelAction that we are exploring; it must be a
1690  * 'read' operation.
1691  */
1692 void ModelChecker::build_reads_from_past(ModelAction *curr)
1693 {
1694         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1695         unsigned int i;
1696         ASSERT(curr->is_read());
1697
1698         ModelAction *last_seq_cst = NULL;
1699
1700         /* Track whether this object has been initialized */
1701         bool initialized = false;
1702
1703         if (curr->is_seqcst()) {
1704                 last_seq_cst = get_last_seq_cst(curr);
1705                 /* We have to at least see the last sequentially consistent write,
1706                          so we are initialized. */
1707                 if (last_seq_cst != NULL)
1708                         initialized = true;
1709         }
1710
1711         /* Iterate over all threads */
1712         for (i = 0; i < thrd_lists->size(); i++) {
1713                 /* Iterate over actions in thread, starting from most recent */
1714                 action_list_t *list = &(*thrd_lists)[i];
1715                 action_list_t::reverse_iterator rit;
1716                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1717                         ModelAction *act = *rit;
1718
1719                         /* Only consider 'write' actions */
1720                         if (!act->is_write() || act == curr)
1721                                 continue;
1722
1723                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1724                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1725                                 DEBUG("Adding action to may_read_from:\n");
1726                                 if (DBG_ENABLED()) {
1727                                         act->print();
1728                                         curr->print();
1729                                 }
1730                                 curr->get_node()->add_read_from(act);
1731                         }
1732
1733                         /* Include at most one act per-thread that "happens before" curr */
1734                         if (act->happens_before(curr)) {
1735                                 initialized = true;
1736                                 break;
1737                         }
1738                 }
1739         }
1740
1741         if (!initialized) {
1742                 /** @todo Need a more informative way of reporting errors. */
1743                 printf("ERROR: may read from uninitialized atomic\n");
1744         }
1745
1746         if (DBG_ENABLED() || !initialized) {
1747                 printf("Reached read action:\n");
1748                 curr->print();
1749                 printf("Printing may_read_from\n");
1750                 curr->get_node()->print_may_read_from();
1751                 printf("End printing may_read_from\n");
1752         }
1753
1754         ASSERT(initialized);
1755 }
1756
1757 static void print_list(action_list_t *list)
1758 {
1759         action_list_t::iterator it;
1760
1761         printf("---------------------------------------------------------------------\n");
1762         printf("Trace:\n");
1763
1764         for (it = list->begin(); it != list->end(); it++) {
1765                 (*it)->print();
1766         }
1767         printf("---------------------------------------------------------------------\n");
1768 }
1769
1770 #if SUPPORT_MOD_ORDER_DUMP
1771 void ModelChecker::dumpGraph(char *filename) {
1772         char buffer[200];
1773   sprintf(buffer, "%s.dot",filename);
1774   FILE *file=fopen(buffer, "w");
1775   fprintf(file, "digraph %s {\n",filename);
1776         mo_graph->dumpNodes(file);
1777         ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
1778
1779         for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
1780                 ModelAction *action=*it;
1781                 if (action->is_read()) {
1782                         fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
1783                         if (action->get_reads_from()!=NULL)
1784                                 fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
1785                 }
1786                 if (thread_array[action->get_tid()] != NULL) {
1787                         fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
1788                 }
1789
1790                 thread_array[action->get_tid()]=action;
1791         }
1792   fprintf(file,"}\n");
1793         model_free(thread_array);
1794   fclose(file);
1795 }
1796 #endif
1797
1798 void ModelChecker::print_summary()
1799 {
1800         printf("\n");
1801         printf("Number of executions: %d\n", num_executions);
1802         printf("Number of feasible executions: %d\n", num_feasible_executions);
1803         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1804
1805 #if SUPPORT_MOD_ORDER_DUMP
1806         scheduler->print();
1807         char buffername[100];
1808         sprintf(buffername, "exec%04u", num_executions);
1809         mo_graph->dumpGraphToFile(buffername);
1810         sprintf(buffername, "graph%04u", num_executions);
1811   dumpGraph(buffername);
1812 #endif
1813
1814         if (!isfinalfeasible())
1815                 printf("INFEASIBLE EXECUTION!\n");
1816         print_list(action_trace);
1817         printf("\n");
1818 }
1819
1820 /**
1821  * Add a Thread to the system for the first time. Should only be called once
1822  * per thread.
1823  * @param t The Thread to add
1824  */
1825 void ModelChecker::add_thread(Thread *t)
1826 {
1827         thread_map->put(id_to_int(t->get_id()), t);
1828         scheduler->add_thread(t);
1829 }
1830
1831 /**
1832  * Removes a thread from the scheduler.
1833  * @param the thread to remove.
1834  */
1835 void ModelChecker::remove_thread(Thread *t)
1836 {
1837         scheduler->remove_thread(t);
1838 }
1839
1840 /**
1841  * @brief Get a Thread reference by its ID
1842  * @param tid The Thread's ID
1843  * @return A Thread reference
1844  */
1845 Thread * ModelChecker::get_thread(thread_id_t tid) const
1846 {
1847         return thread_map->get(id_to_int(tid));
1848 }
1849
1850 /**
1851  * @brief Get a reference to the Thread in which a ModelAction was executed
1852  * @param act The ModelAction
1853  * @return A Thread reference
1854  */
1855 Thread * ModelChecker::get_thread(ModelAction *act) const
1856 {
1857         return get_thread(act->get_tid());
1858 }
1859
1860 /**
1861  * Switch from a user-context to the "master thread" context (a.k.a. system
1862  * context). This switch is made with the intention of exploring a particular
1863  * model-checking action (described by a ModelAction object). Must be called
1864  * from a user-thread context.
1865  *
1866  * @param act The current action that will be explored. May be NULL only if
1867  * trace is exiting via an assertion (see ModelChecker::set_assert and
1868  * ModelChecker::has_asserted).
1869  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1870  */
1871 int ModelChecker::switch_to_master(ModelAction *act)
1872 {
1873         DBG();
1874         Thread *old = thread_current();
1875         set_current_action(act);
1876         old->set_state(THREAD_READY);
1877         return Thread::swap(old, &system_context);
1878 }
1879
1880 /**
1881  * Takes the next step in the execution, if possible.
1882  * @return Returns true (success) if a step was taken and false otherwise.
1883  */
1884 bool ModelChecker::take_step() {
1885         if (has_asserted())
1886                 return false;
1887
1888         Thread *curr = thread_current();
1889         if (curr) {
1890                 if (curr->get_state() == THREAD_READY) {
1891                         ASSERT(priv->current_action);
1892
1893                         priv->nextThread = check_current_action(priv->current_action);
1894                         priv->current_action = NULL;
1895
1896                         if (curr->is_blocked() || curr->is_complete())
1897                                 scheduler->remove_thread(curr);
1898                 } else {
1899                         ASSERT(false);
1900                 }
1901         }
1902         Thread *next = scheduler->next_thread(priv->nextThread);
1903
1904         /* Infeasible -> don't take any more steps */
1905         if (!isfeasible())
1906                 return false;
1907
1908         DEBUG("(%d, %d)\n", curr ? id_to_int(curr->get_id()) : -1,
1909                         next ? id_to_int(next->get_id()) : -1);
1910
1911         /* next == NULL -> don't take any more steps */
1912         if (!next)
1913                 return false;
1914
1915         next->set_state(THREAD_RUNNING);
1916
1917         if (next->get_pending() != NULL) {
1918                 /* restart a pending action */
1919                 set_current_action(next->get_pending());
1920                 next->set_pending(NULL);
1921                 next->set_state(THREAD_READY);
1922                 return true;
1923         }
1924
1925         /* Return false only if swap fails with an error */
1926         return (Thread::swap(&system_context, next) == 0);
1927 }
1928
1929 /** Runs the current execution until threre are no more steps to take. */
1930 void ModelChecker::finish_execution() {
1931         DBG();
1932
1933         while (take_step());
1934 }