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