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