model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14 #include "mutex.h"
  15
  16 #define INITIAL_THREAD_ID       0
  17
  18 ModelChecker *model;
  19
  20 /** @brief Constructor */
  21 ModelChecker::ModelChecker(struct model_params params) :
  22         /* Initialize default scheduler */
  23         scheduler(new Scheduler()),
  24         num_executions(0),
  25         num_feasible_executions(0),
  26         params(params),
  27         diverge(NULL),
  28         action_trace(new action_list_t()),
  29         thread_map(new HashTable<int, Thread *, int>()),
  30         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  31         lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         promises(new std::vector<Promise *>()),
  34         futurevalues(new std::vector<struct PendingFutureValue>()),
  35         lazy_sync_with_release(new HashTable<void *, action_list_t, uintptr_t, 4>()),
  36         thrd_last_action(new std::vector<ModelAction *>(1)),
  37         node_stack(new NodeStack()),
  38         mo_graph(new CycleGraph()),
  39         failed_promise(false),
  40         too_many_reads(false),
  41         asserted(false)
  42 {
  43         /* Allocate this "size" on the snapshotting heap */
  44         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  45         /* First thread created will have id INITIAL_THREAD_ID */
  46         priv->next_thread_id = INITIAL_THREAD_ID;
  47
  48         lazy_sync_size = &priv->lazy_sync_size;
  49 }
  50
  51 /** @brief Destructor */
  52 ModelChecker::~ModelChecker()
  53 {
  54         for (int i = 0; i < get_num_threads(); i++)
  55                 delete thread_map->get(i);
  56         delete thread_map;
  57
  58         delete obj_thrd_map;
  59         delete obj_map;
  60         delete lock_waiters_map;
  61         delete action_trace;
  62
  63         for (unsigned int i = 0; i < promises->size(); i++)
  64                 delete (*promises)[i];
  65         delete promises;
  66
  67         delete lazy_sync_with_release;
  68
  69         delete thrd_last_action;
  70         delete node_stack;
  71         delete scheduler;
  72         delete mo_graph;
  73 }
  74
  75 /**
  76  * Restores user program to initial state and resets all model-checker data
  77  * structures.
  78  */
  79 void ModelChecker::reset_to_initial_state()
  80 {
  81         DEBUG("+++ Resetting to initial state +++\n");
  82         node_stack->reset_execution();
  83         failed_promise = false;
  84         too_many_reads = false;
  85         reset_asserted();
  86         snapshotObject->backTrackBeforeStep(0);
  87 }
  88
  89 /** @return a thread ID for a new Thread */
  90 thread_id_t ModelChecker::get_next_id()
  91 {
  92         return priv->next_thread_id++;
  93 }
  94
  95 /** @return the number of user threads created during this execution */
  96 int ModelChecker::get_num_threads()
  97 {
  98         return priv->next_thread_id;
  99 }
 100
 101 /** @return a sequence number for a new ModelAction */
 102 modelclock_t ModelChecker::get_next_seq_num()
 103 {
 104         return ++priv->used_sequence_numbers;
 105 }
 106
 107 /**
 108  * @brief Choose the next thread to execute.
 109  *
 110  * This function chooses the next thread that should execute. It can force the
 111  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 112  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 113  * The model-checker may have no preference regarding the next thread (i.e.,
 114  * when exploring a new execution ordering), in which case this will return
 115  * NULL.
 116  * @param curr The current ModelAction. This action might guide the choice of
 117  * next thread.
 118  * @return The next thread to run. If the model-checker has no preference, NULL.
 119  */
 120 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 121 {
 122         thread_id_t tid;
 123
 124         if (curr!=NULL) {
 125                 /* Do not split atomic actions. */
 126                 if (curr->is_rmwr())
 127                         return thread_current();
 128                 /* The THREAD_CREATE action points to the created Thread */
 129                 else if (curr->get_type() == THREAD_CREATE)
 130                         return (Thread *)curr->get_location();
 131         }
 132
 133         /* Have we completed exploring the preselected path? */
 134         if (diverge == NULL)
 135                 return NULL;
 136
 137         /* Else, we are trying to replay an execution */
 138         ModelAction *next = node_stack->get_next()->get_action();
 139
 140         if (next == diverge) {
 141                 Node *nextnode = next->get_node();
 142                 /* Reached divergence point */
 143                 if (nextnode->increment_promise()) {
 144                         /* The next node will try to satisfy a different set of promises. */
 145                         tid = next->get_tid();
 146                         node_stack->pop_restofstack(2);
 147                 } else if (nextnode->increment_read_from()) {
 148                         /* The next node will read from a different value. */
 149                         tid = next->get_tid();
 150                         node_stack->pop_restofstack(2);
 151                 } else if (nextnode->increment_future_value()) {
 152                         /* The next node will try to read from a different future value. */
 153                         tid = next->get_tid();
 154                         node_stack->pop_restofstack(2);
 155                 } else {
 156                         /* Make a different thread execute for next step */
 157                         Node *node = nextnode->get_parent();
 158                         tid = node->get_next_backtrack();
 159                         node_stack->pop_restofstack(1);
 160                 }
 161                 DEBUG("*** Divergence point ***\n");
 162                 diverge = NULL;
 163         } else {
 164                 tid = next->get_tid();
 165         }
 166         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 167         ASSERT(tid != THREAD_ID_T_NONE);
 168         return thread_map->get(id_to_int(tid));
 169 }
 170
 171 /**
 172  * Queries the model-checker for more executions to explore and, if one
 173  * exists, resets the model-checker state to execute a new execution.
 174  *
 175  * @return If there are more executions to explore, return true. Otherwise,
 176  * return false.
 177  */
 178 bool ModelChecker::next_execution()
 179 {
 180         DBG();
 181
 182         num_executions++;
 183         if (isfinalfeasible())
 184                 num_feasible_executions++;
 185
 186         if (isfinalfeasible() || DBG_ENABLED())
 187                 print_summary();
 188
 189         if ((diverge = get_next_backtrack()) == NULL)
 190                 return false;
 191
 192         if (DBG_ENABLED()) {
 193                 printf("Next execution will diverge at:\n");
 194                 diverge->print();
 195         }
 196
 197         reset_to_initial_state();
 198         return true;
 199 }
 200
 201 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 202 {
 203         switch (act->get_type()) {
 204         case ATOMIC_READ:
 205         case ATOMIC_WRITE:
 206         case ATOMIC_RMW: {
 207                 /* linear search: from most recent to oldest */
 208                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 209                 action_list_t::reverse_iterator rit;
 210                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 211                         ModelAction *prev = *rit;
 212                         if (act->is_synchronizing(prev))
 213                                 return prev;
 214                 }
 215                 break;
 216         }
 217         case ATOMIC_LOCK:
 218         case ATOMIC_TRYLOCK: {
 219                 /* linear search: from most recent to oldest */
 220                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 221                 action_list_t::reverse_iterator rit;
 222                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 223                         ModelAction *prev = *rit;
 224                         if (act->is_conflicting_lock(prev))
 225                                 return prev;
 226                 }
 227                 break;
 228         }
 229         case ATOMIC_UNLOCK: {
 230                 /* linear search: from most recent to oldest */
 231                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 232                 action_list_t::reverse_iterator rit;
 233                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 234                         ModelAction *prev = *rit;
 235                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 236                                 return prev;
 237                 }
 238                 break;
 239         }
 240         default:
 241                 break;
 242         }
 243         return NULL;
 244 }
 245
 246 /** This method find backtracking points where we should try to
 247  * reorder the parameter ModelAction against.
 248  *
 249  * @param the ModelAction to find backtracking points for.
 250  */
 251
 252
 253 void ModelChecker::set_backtracking(ModelAction *act)
 254 {
 255         Thread *t = get_thread(act);
 256         ModelAction * prev = get_last_conflict(act);
 257         if (prev == NULL)
 258                 return;
 259
 260         Node * node = prev->get_node()->get_parent();
 261
 262         int low_tid, high_tid;
 263         if (node->is_enabled(t)) {
 264                 low_tid=id_to_int(act->get_tid());
 265                 high_tid=low_tid+1;
 266         } else {
 267                 low_tid=0;
 268                 high_tid=get_num_threads();
 269         }
 270
 271         for(int i=low_tid;i<high_tid;i++) {
 272                 thread_id_t tid=int_to_id(i);
 273                 if (!node->is_enabled(tid))
 274                         continue;
 275
 276                 /* Check if this has been explored already */
 277                 if (node->has_been_explored(tid))
 278                         continue;
 279
 280                 /* Cache the latest backtracking point */
 281                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 282                         priv->next_backtrack = prev;
 283
 284                 /* If this is a new backtracking point, mark the tree */
 285                 if (!node->set_backtrack(tid))
 286                         continue;
 287                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 288                                         prev->get_tid(), t->get_id());
 289                 if (DBG_ENABLED()) {
 290                         prev->print();
 291                         act->print();
 292                 }
 293         }
 294 }
 295
 296 /**
 297  * Returns last backtracking point. The model checker will explore a different
 298  * path for this point in the next execution.
 299  * @return The ModelAction at which the next execution should diverge.
 300  */
 301 ModelAction * ModelChecker::get_next_backtrack()
 302 {
 303         ModelAction *next = priv->next_backtrack;
 304         priv->next_backtrack = NULL;
 305         return next;
 306 }
 307
 308 /**
 309  * Processes a read or rmw model action.
 310  * @param curr is the read model action to process.
 311  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 312  * @return True if processing this read updates the mo_graph.
 313  */
 314 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 315 {
 316         uint64_t value;
 317         bool updated = false;
 318         while (true) {
 319                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 320                 if (reads_from != NULL) {
 321                         mo_graph->startChanges();
 322
 323                         value = reads_from->get_value();
 324                         bool r_status = false;
 325
 326                         if (!second_part_of_rmw) {
 327                                 check_recency(curr);
 328                                 r_status = r_modification_order(curr, reads_from);
 329                         }
 330
 331
 332                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 333                                 mo_graph->rollbackChanges();
 334                                 too_many_reads = false;
 335                                 continue;
 336                         }
 337
 338                         curr->read_from(reads_from);
 339                         mo_graph->commitChanges();
 340                         updated |= r_status;
 341                 } else if (!second_part_of_rmw) {
 342                         /* Read from future value */
 343                         value = curr->get_node()->get_future_value();
 344                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 345                         curr->read_from(NULL);
 346                         Promise *valuepromise = new Promise(curr, value, expiration);
 347                         promises->push_back(valuepromise);
 348                 }
 349                 get_thread(curr)->set_return_value(value);
 350                 return updated;
 351         }
 352 }
 353
 354 /**
 355  * Processes a lock, trylock, or unlock model action.  @param curr is
 356  * the read model action to process.
 357  *
 358  * The try lock operation checks whether the lock is taken.  If not,
 359  * it falls to the normal lock operation case.  If so, it returns
 360  * fail.
 361  *
 362  * The lock operation has already been checked that it is enabled, so
 363  * it just grabs the lock and synchronizes with the previous unlock.
 364  *
 365  * The unlock operation has to re-enable all of the threads that are
 366  * waiting on the lock.
 367  */
 368
 369 void ModelChecker::process_mutex(ModelAction *curr) {
 370         std::mutex * mutex=(std::mutex *) curr->get_location();
 371         struct std::mutex_state * state=mutex->get_state();
 372         switch(curr->get_type()) {
 373         case ATOMIC_TRYLOCK: {
 374                 bool success=!state->islocked;
 375                 curr->set_try_lock(success);
 376                 if (!success) {
 377                         get_thread(curr)->set_return_value(0);
 378                         break;
 379                 }
 380                 get_thread(curr)->set_return_value(1);
 381         }
 382                 //otherwise fall into the lock case
 383         case ATOMIC_LOCK: {
 384                 if (curr->get_cv()->getClock(state->alloc_tid)<=state->alloc_clock) {
 385                         printf("Lock access before initialization\n");
 386                         set_assert();
 387                 }
 388                 state->islocked=true;
 389                 ModelAction *unlock=get_last_unlock(curr);
 390                 //synchronize with the previous unlock statement
 391                 if ( unlock != NULL )
 392                         curr->synchronize_with(unlock);
 393                 break;
 394         }
 395         case ATOMIC_UNLOCK: {
 396                 //unlock the lock
 397                 state->islocked=false;
 398                 //wake up the other threads
 399                 action_list_t * waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 400                 //activate all the waiting threads
 401                 for(action_list_t::iterator rit = waiters->begin(); rit!=waiters->end(); rit++) {
 402                         scheduler->add_thread(get_thread((*rit)->get_tid()));
 403                 }
 404                 waiters->clear();
 405                 break;
 406         }
 407         default:
 408                 ASSERT(0);
 409         }
 410 }
 411
 412
 413 /**
 414  * Process a write ModelAction
 415  * @param curr The ModelAction to process
 416  * @return True if the mo_graph was updated or promises were resolved
 417  */
 418 bool ModelChecker::process_write(ModelAction *curr)
 419 {
 420         bool updated_mod_order = w_modification_order(curr);
 421         bool updated_promises = resolve_promises(curr);
 422
 423         if (promises->size() == 0) {
 424                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 425                         struct PendingFutureValue pfv = (*futurevalues)[i];
 426                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 427                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 428                                 priv->next_backtrack = pfv.act;
 429                 }
 430                 futurevalues->resize(0);
 431         }
 432
 433         mo_graph->commitChanges();
 434         get_thread(curr)->set_return_value(VALUE_NONE);
 435         return updated_mod_order || updated_promises;
 436 }
 437
 438 /**
 439  * Initialize the current action by performing one or more of the following
 440  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 441  * in the NodeStack, manipulating backtracking sets, allocating and
 442  * initializing clock vectors, and computing the promises to fulfill.
 443  *
 444  * @param curr The current action, as passed from the user context; may be
 445  * freed/invalidated after the execution of this function
 446  * @return The current action, as processed by the ModelChecker. Is only the
 447  * same as the parameter @a curr if this is a newly-explored action.
 448  */
 449 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 450 {
 451         ModelAction *newcurr;
 452
 453         if (curr->is_rmwc() || curr->is_rmw()) {
 454                 newcurr = process_rmw(curr);
 455                 delete curr;
 456                 compute_promises(newcurr);
 457                 return newcurr;
 458         }
 459
 460         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 461         if (newcurr) {
 462                 /* First restore type and order in case of RMW operation */
 463                 if (curr->is_rmwr())
 464                         newcurr->copy_typeandorder(curr);
 465
 466                 ASSERT(curr->get_location()==newcurr->get_location());
 467                 newcurr->copy_from_new(curr);
 468
 469                 /* Discard duplicate ModelAction; use action from NodeStack */
 470                 delete curr;
 471
 472                 /* If we have diverged, we need to reset the clock vector. */
 473                 if (diverge == NULL)
 474                         newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 475         } else {
 476                 newcurr = curr;
 477                 /*
 478                  * Perform one-time actions when pushing new ModelAction onto
 479                  * NodeStack
 480                  */
 481                 curr->create_cv(get_parent_action(curr->get_tid()));
 482                 if (curr->is_write())
 483                         compute_promises(curr);
 484         }
 485         return newcurr;
 486 }
 487
 488 /**
 489  * This method checks whether a model action is enabled at the given point.
 490  * At this point, it checks whether a lock operation would be successful at this point.
 491  * If not, it puts the thread in a waiter list.
 492  * @param curr is the ModelAction to check whether it is enabled.
 493  * @return a bool that indicates whether the action is enabled.
 494  */
 495
 496 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 497         if (curr->is_lock()) {
 498                 std::mutex * lock=(std::mutex *) curr->get_location();
 499                 struct std::mutex_state * state = lock->get_state();
 500                 if (state->islocked) {
 501                         //Stick the action in the appropriate waiting queue
 502                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 503                         return false;
 504                 }
 505         }
 506
 507         return true;
 508 }
 509
 510 /**
 511  * This is the heart of the model checker routine. It performs model-checking
 512  * actions corresponding to a given "current action." Among other processes, it
 513  * calculates reads-from relationships, updates synchronization clock vectors,
 514  * forms a memory_order constraints graph, and handles replay/backtrack
 515  * execution when running permutations of previously-observed executions.
 516  *
 517  * @param curr The current action to process
 518  * @return The next Thread that must be executed. May be NULL if ModelChecker
 519  * makes no choice (e.g., according to replay execution, combining RMW actions,
 520  * etc.)
 521  */
 522 Thread * ModelChecker::check_current_action(ModelAction *curr)
 523 {
 524         ASSERT(curr);
 525
 526         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 527
 528         if (!check_action_enabled(curr)) {
 529                 //we'll make the execution look like we chose to run this action
 530                 //much later...when a lock is actually available to relese
 531                 get_current_thread()->set_pending(curr);
 532                 remove_thread(get_current_thread());
 533                 return get_next_thread(NULL);
 534         }
 535
 536         ModelAction *newcurr = initialize_curr_action(curr);
 537
 538         /* Add the action to lists before any other model-checking tasks */
 539         if (!second_part_of_rmw)
 540                 add_action_to_lists(newcurr);
 541
 542         /* Build may_read_from set for newly-created actions */
 543         if (curr == newcurr && curr->is_read())
 544                 build_reads_from_past(curr);
 545         curr = newcurr;
 546
 547         /* Thread specific actions */
 548         switch (curr->get_type()) {
 549         case THREAD_CREATE: {
 550                 Thread *th = (Thread *)curr->get_location();
 551                 th->set_creation(curr);
 552                 break;
 553         }
 554         case THREAD_JOIN: {
 555                 Thread *waiting, *blocking;
 556                 waiting = get_thread(curr);
 557                 blocking = (Thread *)curr->get_location();
 558                 if (!blocking->is_complete()) {
 559                         blocking->push_wait_list(curr);
 560                         scheduler->sleep(waiting);
 561                 } else {
 562                         do_complete_join(curr);
 563                 }
 564                 break;
 565         }
 566         case THREAD_FINISH: {
 567                 Thread *th = get_thread(curr);
 568                 while (!th->wait_list_empty()) {
 569                         ModelAction *act = th->pop_wait_list();
 570                         Thread *wake = get_thread(act);
 571                         scheduler->wake(wake);
 572                         do_complete_join(act);
 573                 }
 574                 th->complete();
 575                 break;
 576         }
 577         case THREAD_START: {
 578                 check_promises(NULL, curr->get_cv());
 579                 break;
 580         }
 581         default:
 582                 break;
 583         }
 584
 585         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 586
 587         while (!work_queue.empty()) {
 588                 WorkQueueEntry work = work_queue.front();
 589                 work_queue.pop_front();
 590
 591                 switch (work.type) {
 592                 case WORK_CHECK_CURR_ACTION: {
 593                         ModelAction *act = work.action;
 594                         bool updated = false;
 595                         if (act->is_read() && process_read(act, second_part_of_rmw))
 596                                 updated = true;
 597
 598                         if (act->is_write() && process_write(act))
 599                                 updated = true;
 600
 601                         if (act->is_mutex_op())
 602                                 process_mutex(act);
 603
 604                         if (updated)
 605                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 606                         break;
 607                 }
 608                 case WORK_CHECK_RELEASE_SEQ:
 609                         resolve_release_sequences(work.location, &work_queue);
 610                         break;
 611                 case WORK_CHECK_MO_EDGES: {
 612                         /** @todo Complete verification of work_queue */
 613                         ModelAction *act = work.action;
 614                         bool updated = false;
 615
 616                         if (act->is_read()) {
 617                                 if (r_modification_order(act, act->get_reads_from()))
 618                                         updated = true;
 619                         }
 620                         if (act->is_write()) {
 621                                 if (w_modification_order(act))
 622                                         updated = true;
 623                         }
 624
 625                         if (updated)
 626                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 627                         break;
 628                 }
 629                 default:
 630                         ASSERT(false);
 631                         break;
 632                 }
 633         }
 634
 635         check_curr_backtracking(curr);
 636
 637         set_backtracking(curr);
 638
 639         return get_next_thread(curr);
 640 }
 641
 642 /**
 643  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 644  * operation from the Thread it is joining with. Must be called after the
 645  * completion of the Thread in question.
 646  * @param join The THREAD_JOIN action
 647  */
 648 void ModelChecker::do_complete_join(ModelAction *join)
 649 {
 650         Thread *blocking = (Thread *)join->get_location();
 651         ModelAction *act = get_last_action(blocking->get_id());
 652         join->synchronize_with(act);
 653 }
 654
 655 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 656         Node *currnode = curr->get_node();
 657         Node *parnode = currnode->get_parent();
 658
 659         if ((!parnode->backtrack_empty() ||
 660                          !currnode->read_from_empty() ||
 661                          !currnode->future_value_empty() ||
 662                          !currnode->promise_empty())
 663                         && (!priv->next_backtrack ||
 664                                         *curr > *priv->next_backtrack)) {
 665                 priv->next_backtrack = curr;
 666         }
 667 }
 668
 669 bool ModelChecker::promises_expired() {
 670         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 671                 Promise *promise = (*promises)[promise_index];
 672                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 673                         return true;
 674                 }
 675         }
 676         return false;
 677 }
 678
 679 /** @return whether the current partial trace must be a prefix of a
 680  * feasible trace. */
 681 bool ModelChecker::isfeasibleprefix() {
 682         return promises->size() == 0 && *lazy_sync_size == 0;
 683 }
 684
 685 /** @return whether the current partial trace is feasible. */
 686 bool ModelChecker::isfeasible() {
 687         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 688 }
 689
 690 /** @return whether the current partial trace is feasible other than
 691  * multiple RMW reading from the same store. */
 692 bool ModelChecker::isfeasibleotherthanRMW() {
 693         if (DBG_ENABLED()) {
 694                 if (mo_graph->checkForCycles())
 695                         DEBUG("Infeasible: modification order cycles\n");
 696                 if (failed_promise)
 697                         DEBUG("Infeasible: failed promise\n");
 698                 if (too_many_reads)
 699                         DEBUG("Infeasible: too many reads\n");
 700                 if (promises_expired())
 701                         DEBUG("Infeasible: promises expired\n");
 702         }
 703         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 704 }
 705
 706 /** Returns whether the current completed trace is feasible. */
 707 bool ModelChecker::isfinalfeasible() {
 708         if (DBG_ENABLED() && promises->size() != 0)
 709                 DEBUG("Infeasible: unrevolved promises\n");
 710
 711         return isfeasible() && promises->size() == 0;
 712 }
 713
 714 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 715 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 716         int tid = id_to_int(act->get_tid());
 717         ModelAction *lastread = get_last_action(tid);
 718         lastread->process_rmw(act);
 719         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 720                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 721                 mo_graph->commitChanges();
 722         }
 723         return lastread;
 724 }
 725
 726 /**
 727  * Checks whether a thread has read from the same write for too many times
 728  * without seeing the effects of a later write.
 729  *
 730  * Basic idea:
 731  * 1) there must a different write that we could read from that would satisfy the modification order,
 732  * 2) we must have read from the same value in excess of maxreads times, and
 733  * 3) that other write must have been in the reads_from set for maxreads times.
 734  *
 735  * If so, we decide that the execution is no longer feasible.
 736  */
 737 void ModelChecker::check_recency(ModelAction *curr) {
 738         if (params.maxreads != 0) {
 739                 if (curr->get_node()->get_read_from_size() <= 1)
 740                         return;
 741
 742                 //Must make sure that execution is currently feasible...  We could
 743                 //accidentally clear by rolling back
 744                 if (!isfeasible())
 745                         return;
 746
 747                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 748                 int tid = id_to_int(curr->get_tid());
 749
 750                 /* Skip checks */
 751                 if ((int)thrd_lists->size() <= tid)
 752                         return;
 753
 754                 action_list_t *list = &(*thrd_lists)[tid];
 755
 756                 action_list_t::reverse_iterator rit = list->rbegin();
 757                 /* Skip past curr */
 758                 for (; (*rit) != curr; rit++)
 759                         ;
 760                 /* go past curr now */
 761                 rit++;
 762
 763                 action_list_t::reverse_iterator ritcopy = rit;
 764                 //See if we have enough reads from the same value
 765                 int count = 0;
 766                 for (; count < params.maxreads; rit++,count++) {
 767                         if (rit==list->rend())
 768                                 return;
 769                         ModelAction *act = *rit;
 770                         if (!act->is_read())
 771                                 return;
 772                         if (act->get_reads_from() != curr->get_reads_from())
 773                                 return;
 774                         if (act->get_node()->get_read_from_size() <= 1)
 775                                 return;
 776                 }
 777
 778                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 779                         //Get write
 780                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 781                         //Need a different write
 782                         if (write==curr->get_reads_from())
 783                                 continue;
 784
 785                         /* Test to see whether this is a feasible write to read from*/
 786                         mo_graph->startChanges();
 787                         r_modification_order(curr, write);
 788                         bool feasiblereadfrom = isfeasible();
 789                         mo_graph->rollbackChanges();
 790
 791                         if (!feasiblereadfrom)
 792                                 continue;
 793                         rit = ritcopy;
 794
 795                         bool feasiblewrite = true;
 796                         //new we need to see if this write works for everyone
 797
 798                         for (int loop = count; loop>0; loop--,rit++) {
 799                                 ModelAction *act=*rit;
 800                                 bool foundvalue = false;
 801                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 802                                         if (act->get_node()->get_read_from_at(i)==write) {
 803                                                 foundvalue = true;
 804                                                 break;
 805                                         }
 806                                 }
 807                                 if (!foundvalue) {
 808                                         feasiblewrite = false;
 809                                         break;
 810                                 }
 811                         }
 812                         if (feasiblewrite) {
 813                                 too_many_reads = true;
 814                                 return;
 815                         }
 816                 }
 817         }
 818 }
 819
 820 /**
 821  * Updates the mo_graph with the constraints imposed from the current
 822  * read.
 823  *
 824  * Basic idea is the following: Go through each other thread and find
 825  * the lastest action that happened before our read.  Two cases:
 826  *
 827  * (1) The action is a write => that write must either occur before
 828  * the write we read from or be the write we read from.
 829  *
 830  * (2) The action is a read => the write that that action read from
 831  * must occur before the write we read from or be the same write.
 832  *
 833  * @param curr The current action. Must be a read.
 834  * @param rf The action that curr reads from. Must be a write.
 835  * @return True if modification order edges were added; false otherwise
 836  */
 837 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 838 {
 839         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 840         unsigned int i;
 841         bool added = false;
 842         ASSERT(curr->is_read());
 843
 844         /* Iterate over all threads */
 845         for (i = 0; i < thrd_lists->size(); i++) {
 846                 /* Iterate over actions in thread, starting from most recent */
 847                 action_list_t *list = &(*thrd_lists)[i];
 848                 action_list_t::reverse_iterator rit;
 849                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 850                         ModelAction *act = *rit;
 851
 852                         /*
 853                          * Include at most one act per-thread that "happens
 854                          * before" curr. Don't consider reflexively.
 855                          */
 856                         if (act->happens_before(curr) && act != curr) {
 857                                 if (act->is_write()) {
 858                                         if (rf != act) {
 859                                                 mo_graph->addEdge(act, rf);
 860                                                 added = true;
 861                                         }
 862                                 } else {
 863                                         const ModelAction *prevreadfrom = act->get_reads_from();
 864                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 865                                                 mo_graph->addEdge(prevreadfrom, rf);
 866                                                 added = true;
 867                                         }
 868                                 }
 869                                 break;
 870                         }
 871                 }
 872         }
 873
 874         return added;
 875 }
 876
 877 /** This method fixes up the modification order when we resolve a
 878  *  promises.  The basic problem is that actions that occur after the
 879  *  read curr could not property add items to the modification order
 880  *  for our read.
 881  *
 882  *  So for each thread, we find the earliest item that happens after
 883  *  the read curr.  This is the item we have to fix up with additional
 884  *  constraints.  If that action is write, we add a MO edge between
 885  *  the Action rf and that action.  If the action is a read, we add a
 886  *  MO edge between the Action rf, and whatever the read accessed.
 887  *
 888  * @param curr is the read ModelAction that we are fixing up MO edges for.
 889  * @param rf is the write ModelAction that curr reads from.
 890  *
 891  */
 892
 893 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 894 {
 895         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 896         unsigned int i;
 897         ASSERT(curr->is_read());
 898
 899         /* Iterate over all threads */
 900         for (i = 0; i < thrd_lists->size(); i++) {
 901                 /* Iterate over actions in thread, starting from most recent */
 902                 action_list_t *list = &(*thrd_lists)[i];
 903                 action_list_t::reverse_iterator rit;
 904                 ModelAction *lastact = NULL;
 905
 906                 /* Find last action that happens after curr */
 907                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 908                         ModelAction *act = *rit;
 909                         if (curr->happens_before(act)) {
 910                                 lastact = act;
 911                         } else
 912                                 break;
 913                 }
 914
 915                         /* Include at most one act per-thread that "happens before" curr */
 916                 if (lastact != NULL) {
 917                         if (lastact->is_read()) {
 918                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 919                                 if (postreadfrom != NULL&&rf != postreadfrom)
 920                                         mo_graph->addEdge(rf, postreadfrom);
 921                         } else if (rf != lastact) {
 922                                 mo_graph->addEdge(rf, lastact);
 923                         }
 924                         break;
 925                 }
 926         }
 927 }
 928
 929 /**
 930  * Updates the mo_graph with the constraints imposed from the current write.
 931  *
 932  * Basic idea is the following: Go through each other thread and find
 933  * the lastest action that happened before our write.  Two cases:
 934  *
 935  * (1) The action is a write => that write must occur before
 936  * the current write
 937  *
 938  * (2) The action is a read => the write that that action read from
 939  * must occur before the current write.
 940  *
 941  * This method also handles two other issues:
 942  *
 943  * (I) Sequential Consistency: Making sure that if the current write is
 944  * seq_cst, that it occurs after the previous seq_cst write.
 945  *
 946  * (II) Sending the write back to non-synchronizing reads.
 947  *
 948  * @param curr The current action. Must be a write.
 949  * @return True if modification order edges were added; false otherwise
 950  */
 951 bool ModelChecker::w_modification_order(ModelAction *curr)
 952 {
 953         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 954         unsigned int i;
 955         bool added = false;
 956         ASSERT(curr->is_write());
 957
 958         if (curr->is_seqcst()) {
 959                 /* We have to at least see the last sequentially consistent write,
 960                          so we are initialized. */
 961                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
 962                 if (last_seq_cst != NULL) {
 963                         mo_graph->addEdge(last_seq_cst, curr);
 964                         added = true;
 965                 }
 966         }
 967
 968         /* Iterate over all threads */
 969         for (i = 0; i < thrd_lists->size(); i++) {
 970                 /* Iterate over actions in thread, starting from most recent */
 971                 action_list_t *list = &(*thrd_lists)[i];
 972                 action_list_t::reverse_iterator rit;
 973                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 974                         ModelAction *act = *rit;
 975                         if (act == curr) {
 976                                 /*
 977                                  * If RMW, we already have all relevant edges,
 978                                  * so just skip to next thread.
 979                                  * If normal write, we need to look at earlier
 980                                  * actions, so continue processing list.
 981                                  */
 982                                 if (curr->is_rmw())
 983                                         break;
 984                                 else
 985                                         continue;
 986                         }
 987
 988                         /*
 989                          * Include at most one act per-thread that "happens
 990                          * before" curr
 991                          */
 992                         if (act->happens_before(curr)) {
 993                                 /*
 994                                  * Note: if act is RMW, just add edge:
 995                                  *   act --mo--> curr
 996                                  * The following edge should be handled elsewhere:
 997                                  *   readfrom(act) --mo--> act
 998                                  */
 999                                 if (act->is_write())
1000                                         mo_graph->addEdge(act, curr);
1001                                 else if (act->is_read() && act->get_reads_from() != NULL)
1002                                         mo_graph->addEdge(act->get_reads_from(), curr);
1003                                 added = true;
1004                                 break;
1005                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
1006                                                      !act->same_thread(curr)) {
1007                                 /* We have an action that:
1008                                    (1) did not happen before us
1009                                    (2) is a read and we are a write
1010                                    (3) cannot synchronize with us
1011                                    (4) is in a different thread
1012                                    =>
1013                                    that read could potentially read from our write.
1014                                  */
1015                                 if (thin_air_constraint_may_allow(curr, act)) {
1016                                         if (isfeasible() ||
1017                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
1018                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1019                                                 futurevalues->push_back(pfv);
1020                                         }
1021                                 }
1022                         }
1023                 }
1024         }
1025
1026         return added;
1027 }
1028
1029 /** Arbitrary reads from the future are not allowed.  Section 29.3
1030  * part 9 places some constraints.  This method checks one result of constraint
1031  * constraint.  Others require compiler support. */
1032
1033 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1034         if (!writer->is_rmw())
1035                 return true;
1036
1037         if (!reader->is_rmw())
1038                 return true;
1039
1040         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1041                 if (search==reader)
1042                         return false;
1043                 if (search->get_tid() == reader->get_tid() &&
1044                                 search->happens_before(reader))
1045                         break;
1046         }
1047
1048         return true;
1049 }
1050
1051 /**
1052  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1053  * The ModelAction under consideration is expected to be taking part in
1054  * release/acquire synchronization as an object of the "reads from" relation.
1055  * Note that this can only provide release sequence support for RMW chains
1056  * which do not read from the future, as those actions cannot be traced until
1057  * their "promise" is fulfilled. Similarly, we may not even establish the
1058  * presence of a release sequence with certainty, as some modification order
1059  * constraints may be decided further in the future. Thus, this function
1060  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1061  * and a boolean representing certainty.
1062  *
1063  * @todo Finish lazy updating, when promises are fulfilled in the future
1064  * @param rf The action that might be part of a release sequence. Must be a
1065  * write.
1066  * @param release_heads A pass-by-reference style return parameter.  After
1067  * execution of this function, release_heads will contain the heads of all the
1068  * relevant release sequences, if any exists
1069  * @return true, if the ModelChecker is certain that release_heads is complete;
1070  * false otherwise
1071  */
1072 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1073 {
1074         if (!rf) {
1075                 /* read from future: need to settle this later */
1076                 return false; /* incomplete */
1077         }
1078
1079         ASSERT(rf->is_write());
1080
1081         if (rf->is_release())
1082                 release_heads->push_back(rf);
1083         if (rf->is_rmw()) {
1084                 /* We need a RMW action that is both an acquire and release to stop */
1085                 /** @todo Need to be smarter here...  In the linux lock
1086                  * example, this will run to the beginning of the program for
1087                  * every acquire. */
1088                 if (rf->is_acquire() && rf->is_release())
1089                         return true; /* complete */
1090                 return release_seq_head(rf->get_reads_from(), release_heads);
1091         }
1092         if (rf->is_release())
1093                 return true; /* complete */
1094
1095         /* else relaxed write; check modification order for contiguous subsequence
1096          * -> rf must be same thread as release */
1097         int tid = id_to_int(rf->get_tid());
1098         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1099         action_list_t *list = &(*thrd_lists)[tid];
1100         action_list_t::const_reverse_iterator rit;
1101
1102         /* Find rf in the thread list */
1103         rit = std::find(list->rbegin(), list->rend(), rf);
1104         ASSERT(rit != list->rend());
1105
1106         /* Find the last write/release */
1107         for (; rit != list->rend(); rit++)
1108                 if ((*rit)->is_release())
1109                         break;
1110         if (rit == list->rend()) {
1111                 /* No write-release in this thread */
1112                 return true; /* complete */
1113         }
1114         ModelAction *release = *rit;
1115
1116         ASSERT(rf->same_thread(release));
1117
1118         bool certain = true;
1119         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1120                 if (id_to_int(rf->get_tid()) == (int)i)
1121                         continue;
1122                 list = &(*thrd_lists)[i];
1123
1124                 /* Can we ensure no future writes from this thread may break
1125                  * the release seq? */
1126                 bool future_ordered = false;
1127
1128                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1129                         const ModelAction *act = *rit;
1130                         if (!act->is_write())
1131                                 continue;
1132                         /* Reach synchronization -> this thread is complete */
1133                         if (act->happens_before(release))
1134                                 break;
1135                         if (rf->happens_before(act)) {
1136                                 future_ordered = true;
1137                                 continue;
1138                         }
1139
1140                         /* Check modification order */
1141                         if (mo_graph->checkReachable(rf, act)) {
1142                                 /* rf --mo--> act */
1143                                 future_ordered = true;
1144                                 continue;
1145                         }
1146                         if (mo_graph->checkReachable(act, release))
1147                                 /* act --mo--> release */
1148                                 break;
1149                         if (mo_graph->checkReachable(release, act) &&
1150                                       mo_graph->checkReachable(act, rf)) {
1151                                 /* release --mo-> act --mo--> rf */
1152                                 return true; /* complete */
1153                         }
1154                         certain = false;
1155                 }
1156                 if (!future_ordered)
1157                         return false; /* This thread is uncertain */
1158         }
1159
1160         if (certain)
1161                 release_heads->push_back(release);
1162         return certain;
1163 }
1164
1165 /**
1166  * A public interface for getting the release sequence head(s) with which a
1167  * given ModelAction must synchronize. This function only returns a non-empty
1168  * result when it can locate a release sequence head with certainty. Otherwise,
1169  * it may mark the internal state of the ModelChecker so that it will handle
1170  * the release sequence at a later time, causing @a act to update its
1171  * synchronization at some later point in execution.
1172  * @param act The 'acquire' action that may read from a release sequence
1173  * @param release_heads A pass-by-reference return parameter. Will be filled
1174  * with the head(s) of the release sequence(s), if they exists with certainty.
1175  * @see ModelChecker::release_seq_head
1176  */
1177 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1178 {
1179         const ModelAction *rf = act->get_reads_from();
1180         bool complete;
1181         complete = release_seq_head(rf, release_heads);
1182         if (!complete) {
1183                 /* add act to 'lazy checking' list */
1184                 action_list_t *list;
1185                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1186                 list->push_back(act);
1187                 (*lazy_sync_size)++;
1188         }
1189 }
1190
1191 /**
1192  * Attempt to resolve all stashed operations that might synchronize with a
1193  * release sequence for a given location. This implements the "lazy" portion of
1194  * determining whether or not a release sequence was contiguous, since not all
1195  * modification order information is present at the time an action occurs.
1196  *
1197  * @param location The location/object that should be checked for release
1198  * sequence resolutions
1199  * @param work_queue The work queue to which to add work items as they are
1200  * generated
1201  * @return True if any updates occurred (new synchronization, new mo_graph
1202  * edges)
1203  */
1204 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1205 {
1206         action_list_t *list;
1207         list = lazy_sync_with_release->getptr(location);
1208         if (!list)
1209                 return false;
1210
1211         bool updated = false;
1212         action_list_t::iterator it = list->begin();
1213         while (it != list->end()) {
1214                 ModelAction *act = *it;
1215                 const ModelAction *rf = act->get_reads_from();
1216                 rel_heads_list_t release_heads;
1217                 bool complete;
1218                 complete = release_seq_head(rf, &release_heads);
1219                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1220                         if (!act->has_synchronized_with(release_heads[i])) {
1221                                 updated = true;
1222                                 act->synchronize_with(release_heads[i]);
1223                         }
1224                 }
1225
1226                 if (updated) {
1227                         /* Re-check act for mo_graph edges */
1228                         work_queue->push_back(MOEdgeWorkEntry(act));
1229
1230                         /* propagate synchronization to later actions */
1231                         action_list_t::reverse_iterator it = action_trace->rbegin();
1232                         while ((*it) != act) {
1233                                 ModelAction *propagate = *it;
1234                                 if (act->happens_before(propagate)) {
1235                                         propagate->synchronize_with(act);
1236                                         /* Re-check 'propagate' for mo_graph edges */
1237                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1238                                 }
1239                         }
1240                 }
1241                 if (complete) {
1242                         it = list->erase(it);
1243                         (*lazy_sync_size)--;
1244                 } else
1245                         it++;
1246         }
1247
1248         // If we resolved promises or data races, see if we have realized a data race.
1249         if (checkDataRaces()) {
1250                 set_assert();
1251         }
1252
1253         return updated;
1254 }
1255
1256 /**
1257  * Performs various bookkeeping operations for the current ModelAction. For
1258  * instance, adds action to the per-object, per-thread action vector and to the
1259  * action trace list of all thread actions.
1260  *
1261  * @param act is the ModelAction to add.
1262  */
1263 void ModelChecker::add_action_to_lists(ModelAction *act)
1264 {
1265         int tid = id_to_int(act->get_tid());
1266         action_trace->push_back(act);
1267
1268         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1269
1270         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1271         if (tid >= (int)vec->size())
1272                 vec->resize(priv->next_thread_id);
1273         (*vec)[tid].push_back(act);
1274
1275         if ((int)thrd_last_action->size() <= tid)
1276                 thrd_last_action->resize(get_num_threads());
1277         (*thrd_last_action)[tid] = act;
1278 }
1279
1280 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1281 {
1282         int threadid=id_to_int(tid);
1283         if (threadid<(int)thrd_last_action->size())
1284                 return (*thrd_last_action)[id_to_int(tid)];
1285         else
1286                 return NULL;
1287 }
1288
1289 /**
1290  * Gets the last memory_order_seq_cst write (in the total global sequence)
1291  * performed on a particular object (i.e., memory location), not including the
1292  * current action.
1293  * @param curr The current ModelAction; also denotes the object location to
1294  * check
1295  * @return The last seq_cst write
1296  */
1297 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr)
1298 {
1299         void *location = curr->get_location();
1300         action_list_t *list = obj_map->get_safe_ptr(location);
1301         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1302         action_list_t::reverse_iterator rit;
1303         for (rit = list->rbegin(); rit != list->rend(); rit++)
1304                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1305                         return *rit;
1306         return NULL;
1307 }
1308
1309 /**
1310  * Gets the last unlock operation
1311  * performed on a particular mutex (i.e., memory location).
1312  * @param curr The current ModelAction; also denotes the object location to
1313  * check
1314  * @return The last unlock operation
1315  */
1316
1317 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr)
1318 {
1319         void *location = curr->get_location();
1320         action_list_t *list = obj_map->get_safe_ptr(location);
1321         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1322         action_list_t::reverse_iterator rit;
1323         for (rit = list->rbegin(); rit != list->rend(); rit++)
1324                 if ((*rit)->is_unlock())
1325                         return *rit;
1326         return NULL;
1327 }
1328
1329 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1330 {
1331         ModelAction *parent = get_last_action(tid);
1332         if (!parent)
1333                 parent = get_thread(tid)->get_creation();
1334         return parent;
1335 }
1336
1337 /**
1338  * Returns the clock vector for a given thread.
1339  * @param tid The thread whose clock vector we want
1340  * @return Desired clock vector
1341  */
1342 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1343 {
1344         return get_parent_action(tid)->get_cv();
1345 }
1346
1347 /**
1348  * Resolve a set of Promises with a current write. The set is provided in the
1349  * Node corresponding to @a write.
1350  * @param write The ModelAction that is fulfilling Promises
1351  * @return True if promises were resolved; false otherwise
1352  */
1353 bool ModelChecker::resolve_promises(ModelAction *write)
1354 {
1355         bool resolved = false;
1356
1357         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1358                 Promise *promise = (*promises)[promise_index];
1359                 if (write->get_node()->get_promise(i)) {
1360                         ModelAction *read = promise->get_action();
1361                         read->read_from(write);
1362                         if (read->is_rmw()) {
1363                                 mo_graph->addRMWEdge(write, read);
1364                         }
1365                         //First fix up the modification order for actions that happened
1366                         //before the read
1367                         r_modification_order(read, write);
1368                         //Next fix up the modification order for actions that happened
1369                         //after the read.
1370                         post_r_modification_order(read, write);
1371                         promises->erase(promises->begin() + promise_index);
1372                         resolved = true;
1373                 } else
1374                         promise_index++;
1375         }
1376         return resolved;
1377 }
1378
1379 /**
1380  * Compute the set of promises that could potentially be satisfied by this
1381  * action. Note that the set computation actually appears in the Node, not in
1382  * ModelChecker.
1383  * @param curr The ModelAction that may satisfy promises
1384  */
1385 void ModelChecker::compute_promises(ModelAction *curr)
1386 {
1387         for (unsigned int i = 0; i < promises->size(); i++) {
1388                 Promise *promise = (*promises)[i];
1389                 const ModelAction *act = promise->get_action();
1390                 if (!act->happens_before(curr) &&
1391                                 act->is_read() &&
1392                                 !act->is_synchronizing(curr) &&
1393                                 !act->same_thread(curr) &&
1394                                 promise->get_value() == curr->get_value()) {
1395                         curr->get_node()->set_promise(i);
1396                 }
1397         }
1398 }
1399
1400 /** Checks promises in response to change in ClockVector Threads. */
1401 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1402 {
1403         for (unsigned int i = 0; i < promises->size(); i++) {
1404                 Promise *promise = (*promises)[i];
1405                 const ModelAction *act = promise->get_action();
1406                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1407                                 merge_cv->synchronized_since(act)) {
1408                         //This thread is no longer able to send values back to satisfy the promise
1409                         int num_synchronized_threads = promise->increment_threads();
1410                         if (num_synchronized_threads == get_num_threads()) {
1411                                 //Promise has failed
1412                                 failed_promise = true;
1413                                 return;
1414                         }
1415                 }
1416         }
1417 }
1418
1419 /**
1420  * Build up an initial set of all past writes that this 'read' action may read
1421  * from. This set is determined by the clock vector's "happens before"
1422  * relationship.
1423  * @param curr is the current ModelAction that we are exploring; it must be a
1424  * 'read' operation.
1425  */
1426 void ModelChecker::build_reads_from_past(ModelAction *curr)
1427 {
1428         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1429         unsigned int i;
1430         ASSERT(curr->is_read());
1431
1432         ModelAction *last_seq_cst = NULL;
1433
1434         /* Track whether this object has been initialized */
1435         bool initialized = false;
1436
1437         if (curr->is_seqcst()) {
1438                 last_seq_cst = get_last_seq_cst(curr);
1439                 /* We have to at least see the last sequentially consistent write,
1440                          so we are initialized. */
1441                 if (last_seq_cst != NULL)
1442                         initialized = true;
1443         }
1444
1445         /* Iterate over all threads */
1446         for (i = 0; i < thrd_lists->size(); i++) {
1447                 /* Iterate over actions in thread, starting from most recent */
1448                 action_list_t *list = &(*thrd_lists)[i];
1449                 action_list_t::reverse_iterator rit;
1450                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1451                         ModelAction *act = *rit;
1452
1453                         /* Only consider 'write' actions */
1454                         if (!act->is_write() || act == curr)
1455                                 continue;
1456
1457                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1458                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1459                                 DEBUG("Adding action to may_read_from:\n");
1460                                 if (DBG_ENABLED()) {
1461                                         act->print();
1462                                         curr->print();
1463                                 }
1464                                 curr->get_node()->add_read_from(act);
1465                         }
1466
1467                         /* Include at most one act per-thread that "happens before" curr */
1468                         if (act->happens_before(curr)) {
1469                                 initialized = true;
1470                                 break;
1471                         }
1472                 }
1473         }
1474
1475         if (!initialized) {
1476                 /** @todo Need a more informative way of reporting errors. */
1477                 printf("ERROR: may read from uninitialized atomic\n");
1478         }
1479
1480         if (DBG_ENABLED() || !initialized) {
1481                 printf("Reached read action:\n");
1482                 curr->print();
1483                 printf("Printing may_read_from\n");
1484                 curr->get_node()->print_may_read_from();
1485                 printf("End printing may_read_from\n");
1486         }
1487
1488         ASSERT(initialized);
1489 }
1490
1491 static void print_list(action_list_t *list)
1492 {
1493         action_list_t::iterator it;
1494
1495         printf("---------------------------------------------------------------------\n");
1496         printf("Trace:\n");
1497
1498         for (it = list->begin(); it != list->end(); it++) {
1499                 (*it)->print();
1500         }
1501         printf("---------------------------------------------------------------------\n");
1502 }
1503
1504 void ModelChecker::print_summary()
1505 {
1506         printf("\n");
1507         printf("Number of executions: %d\n", num_executions);
1508         printf("Number of feasible executions: %d\n", num_feasible_executions);
1509         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1510
1511 #if SUPPORT_MOD_ORDER_DUMP
1512         scheduler->print();
1513         char buffername[100];
1514         sprintf(buffername, "exec%u",num_executions);
1515         mo_graph->dumpGraphToFile(buffername);
1516 #endif
1517
1518         if (!isfinalfeasible())
1519                 printf("INFEASIBLE EXECUTION!\n");
1520         print_list(action_trace);
1521         printf("\n");
1522 }
1523
1524 /**
1525  * Add a Thread to the system for the first time. Should only be called once
1526  * per thread.
1527  * @param t The Thread to add
1528  */
1529 void ModelChecker::add_thread(Thread *t)
1530 {
1531         thread_map->put(id_to_int(t->get_id()), t);
1532         scheduler->add_thread(t);
1533 }
1534
1535 /**
1536  * Removes a thread from the scheduler.
1537  * @param the thread to remove.
1538  */
1539
1540 void ModelChecker::remove_thread(Thread *t)
1541 {
1542         scheduler->remove_thread(t);
1543 }
1544
1545 /**
1546  * Switch from a user-context to the "master thread" context (a.k.a. system
1547  * context). This switch is made with the intention of exploring a particular
1548  * model-checking action (described by a ModelAction object). Must be called
1549  * from a user-thread context.
1550  * @param act The current action that will be explored. Must not be NULL.
1551  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1552  */
1553 int ModelChecker::switch_to_master(ModelAction *act)
1554 {
1555         DBG();
1556         Thread *old = thread_current();
1557         set_current_action(act);
1558         old->set_state(THREAD_READY);
1559         return Thread::swap(old, &system_context);
1560 }
1561
1562 /**
1563  * Takes the next step in the execution, if possible.
1564  * @return Returns true (success) if a step was taken and false otherwise.
1565  */
1566 bool ModelChecker::take_step() {
1567         if (has_asserted())
1568                 return false;
1569
1570         Thread * curr = thread_current();
1571         if (curr) {
1572                 if (curr->get_state() == THREAD_READY) {
1573                         ASSERT(priv->current_action);
1574
1575                         priv->nextThread = check_current_action(priv->current_action);
1576                         priv->current_action = NULL;
1577                         if (curr->is_blocked() || curr->is_complete())
1578                                 scheduler->remove_thread(curr);
1579                 } else {
1580                         ASSERT(false);
1581                 }
1582         }
1583         Thread * next = scheduler->next_thread(priv->nextThread);
1584
1585         /* Infeasible -> don't take any more steps */
1586         if (!isfeasible())
1587                 return false;
1588
1589         if (next)
1590                 next->set_state(THREAD_RUNNING);
1591         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1592
1593         /* next == NULL -> don't take any more steps */
1594         if (!next)
1595                 return false;
1596
1597         if ( next->get_pending() != NULL ) {
1598                 //restart a pending action
1599                 set_current_action(next->get_pending());
1600                 next->set_pending(NULL);
1601                 next->set_state(THREAD_READY);
1602                 return true;
1603         }
1604
1605         /* Return false only if swap fails with an error */
1606         return (Thread::swap(&system_context, next) == 0);
1607 }
1608
1609 /** Runs the current execution until threre are no more steps to take. */
1610 void ModelChecker::finish_execution() {
1611         DBG();
1612
1613         while (take_step());
1614 }