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