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