model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14 #include "mutex.h"
  15
  16 #define INITIAL_THREAD_ID       0
  17
  18 ModelChecker *model;
  19
  20 /** @brief Constructor */
  21 ModelChecker::ModelChecker(struct model_params params) :
  22         /* Initialize default scheduler */
  23         params(params),
  24         scheduler(new Scheduler()),
  25         num_executions(0),
  26         num_feasible_executions(0),
  27         diverge(NULL),
  28         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         pending_acq_rel_seq(new std::vector<ModelAction *>()),
  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
  49 /** @brief Destructor */
  50 ModelChecker::~ModelChecker()
  51 {
  52         for (int i = 0; i < get_num_threads(); i++)
  53                 delete thread_map->get(i);
  54         delete thread_map;
  55
  56         delete obj_thrd_map;
  57         delete obj_map;
  58         delete lock_waiters_map;
  59         delete action_trace;
  60
  61         for (unsigned int i = 0; i < promises->size(); i++)
  62                 delete (*promises)[i];
  63         delete promises;
  64
  65         delete pending_acq_rel_seq;
  66
  67         delete thrd_last_action;
  68         delete node_stack;
  69         delete scheduler;
  70         delete mo_graph;
  71 }
  72
  73 /**
  74  * Restores user program to initial state and resets all model-checker data
  75  * structures.
  76  */
  77 void ModelChecker::reset_to_initial_state()
  78 {
  79         DEBUG("+++ Resetting to initial state +++\n");
  80         node_stack->reset_execution();
  81         failed_promise = false;
  82         too_many_reads = false;
  83         reset_asserted();
  84         snapshotObject->backTrackBeforeStep(0);
  85 }
  86
  87 /** @return a thread ID for a new Thread */
  88 thread_id_t ModelChecker::get_next_id()
  89 {
  90         return priv->next_thread_id++;
  91 }
  92
  93 /** @return the number of user threads created during this execution */
  94 int ModelChecker::get_num_threads()
  95 {
  96         return priv->next_thread_id;
  97 }
  98
  99 /** @return a sequence number for a new ModelAction */
 100 modelclock_t ModelChecker::get_next_seq_num()
 101 {
 102         return ++priv->used_sequence_numbers;
 103 }
 104
 105 /**
 106  * @brief Choose the next thread to execute.
 107  *
 108  * This function chooses the next thread that should execute. It can force the
 109  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 110  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 111  * The model-checker may have no preference regarding the next thread (i.e.,
 112  * when exploring a new execution ordering), in which case this will return
 113  * NULL.
 114  * @param curr The current ModelAction. This action might guide the choice of
 115  * next thread.
 116  * @return The next thread to run. If the model-checker has no preference, NULL.
 117  */
 118 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 119 {
 120         thread_id_t tid;
 121
 122         if (curr!=NULL) {
 123                 /* Do not split atomic actions. */
 124                 if (curr->is_rmwr())
 125                         return thread_current();
 126                 /* The THREAD_CREATE action points to the created Thread */
 127                 else if (curr->get_type() == THREAD_CREATE)
 128                         return (Thread *)curr->get_location();
 129         }
 130
 131         /* Have we completed exploring the preselected path? */
 132         if (diverge == NULL)
 133                 return NULL;
 134
 135         /* Else, we are trying to replay an execution */
 136         ModelAction *next = node_stack->get_next()->get_action();
 137
 138         if (next == diverge) {
 139                 Node *nextnode = next->get_node();
 140                 /* Reached divergence point */
 141                 if (nextnode->increment_promise()) {
 142                         /* The next node will try to satisfy a different set of promises. */
 143                         tid = next->get_tid();
 144                         node_stack->pop_restofstack(2);
 145                 } else if (nextnode->increment_read_from()) {
 146                         /* The next node will read from a different value. */
 147                         tid = next->get_tid();
 148                         node_stack->pop_restofstack(2);
 149                 } else if (nextnode->increment_future_value()) {
 150                         /* The next node will try to read from a different future value. */
 151                         tid = next->get_tid();
 152                         node_stack->pop_restofstack(2);
 153                 } else {
 154                         /* Make a different thread execute for next step */
 155                         Node *node = nextnode->get_parent();
 156                         tid = node->get_next_backtrack();
 157                         node_stack->pop_restofstack(1);
 158                 }
 159                 DEBUG("*** Divergence point ***\n");
 160                 diverge = NULL;
 161         } else {
 162                 tid = next->get_tid();
 163         }
 164         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 165         ASSERT(tid != THREAD_ID_T_NONE);
 166         return thread_map->get(id_to_int(tid));
 167 }
 168
 169 /**
 170  * Queries the model-checker for more executions to explore and, if one
 171  * exists, resets the model-checker state to execute a new execution.
 172  *
 173  * @return If there are more executions to explore, return true. Otherwise,
 174  * return false.
 175  */
 176 bool ModelChecker::next_execution()
 177 {
 178         DBG();
 179
 180         num_executions++;
 181         if (isfinalfeasible())
 182                 num_feasible_executions++;
 183
 184         if (isfinalfeasible() || DBG_ENABLED())
 185                 print_summary();
 186
 187         if ((diverge = get_next_backtrack()) == NULL)
 188                 return false;
 189
 190         if (DBG_ENABLED()) {
 191                 printf("Next execution will diverge at:\n");
 192                 diverge->print();
 193         }
 194
 195         reset_to_initial_state();
 196         return true;
 197 }
 198
 199 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 200 {
 201         switch (act->get_type()) {
 202         case ATOMIC_READ:
 203         case ATOMIC_WRITE:
 204         case ATOMIC_RMW: {
 205                 /* linear search: from most recent to oldest */
 206                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 207                 action_list_t::reverse_iterator rit;
 208                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 209                         ModelAction *prev = *rit;
 210                         if (act->is_synchronizing(prev))
 211                                 return prev;
 212                 }
 213                 break;
 214         }
 215         case ATOMIC_LOCK:
 216         case ATOMIC_TRYLOCK: {
 217                 /* linear search: from most recent to oldest */
 218                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 219                 action_list_t::reverse_iterator rit;
 220                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 221                         ModelAction *prev = *rit;
 222                         if (act->is_conflicting_lock(prev))
 223                                 return prev;
 224                 }
 225                 break;
 226         }
 227         case ATOMIC_UNLOCK: {
 228                 /* linear search: from most recent to oldest */
 229                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 230                 action_list_t::reverse_iterator rit;
 231                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 232                         ModelAction *prev = *rit;
 233                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 234                                 return prev;
 235                 }
 236                 break;
 237         }
 238         default:
 239                 break;
 240         }
 241         return NULL;
 242 }
 243
 244 /** This method find backtracking points where we should try to
 245  * reorder the parameter ModelAction against.
 246  *
 247  * @param the ModelAction to find backtracking points for.
 248  */
 249 void ModelChecker::set_backtracking(ModelAction *act)
 250 {
 251         Thread *t = get_thread(act);
 252         ModelAction * prev = get_last_conflict(act);
 253         if (prev == NULL)
 254                 return;
 255
 256         Node * node = prev->get_node()->get_parent();
 257
 258         int low_tid, high_tid;
 259         if (node->is_enabled(t)) {
 260                 low_tid = id_to_int(act->get_tid());
 261                 high_tid = low_tid+1;
 262         } else {
 263                 low_tid = 0;
 264                 high_tid = get_num_threads();
 265         }
 266
 267         for(int i = low_tid; i < high_tid; i++) {
 268                 thread_id_t tid = int_to_id(i);
 269                 if (!node->is_enabled(tid))
 270                         continue;
 271
 272                 /* Check if this has been explored already */
 273                 if (node->has_been_explored(tid))
 274                         continue;
 275
 276                 /* See if fairness allows */
 277                 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
 278                         bool unfair=false;
 279                         for(int t=0;t<node->get_num_threads();t++) {
 280                                 thread_id_t tother=int_to_id(t);
 281                                 if (node->is_enabled(tother) && node->has_priority(tother)) {
 282                                         unfair=true;
 283                                         break;
 284                                 }
 285                         }
 286                         if (unfair)
 287                                 continue;
 288                 }
 289
 290                 /* Cache the latest backtracking point */
 291                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 292                         priv->next_backtrack = prev;
 293
 294                 /* If this is a new backtracking point, mark the tree */
 295                 if (!node->set_backtrack(tid))
 296                         continue;
 297                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 298                                         prev->get_tid(), t->get_id());
 299                 if (DBG_ENABLED()) {
 300                         prev->print();
 301                         act->print();
 302                 }
 303         }
 304 }
 305
 306 /**
 307  * Returns last backtracking point. The model checker will explore a different
 308  * path for this point in the next execution.
 309  * @return The ModelAction at which the next execution should diverge.
 310  */
 311 ModelAction * ModelChecker::get_next_backtrack()
 312 {
 313         ModelAction *next = priv->next_backtrack;
 314         priv->next_backtrack = NULL;
 315         return next;
 316 }
 317
 318 /**
 319  * Processes a read or rmw model action.
 320  * @param curr is the read model action to process.
 321  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 322  * @return True if processing this read updates the mo_graph.
 323  */
 324 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 325 {
 326         uint64_t value;
 327         bool updated = false;
 328         while (true) {
 329                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 330                 if (reads_from != NULL) {
 331                         mo_graph->startChanges();
 332
 333                         value = reads_from->get_value();
 334                         bool r_status = false;
 335
 336                         if (!second_part_of_rmw) {
 337                                 check_recency(curr);
 338                                 r_status = r_modification_order(curr, reads_from);
 339                         }
 340
 341
 342                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 343                                 mo_graph->rollbackChanges();
 344                                 too_many_reads = false;
 345                                 continue;
 346                         }
 347
 348                         curr->read_from(reads_from);
 349                         mo_graph->commitChanges();
 350                         updated |= r_status;
 351                 } else if (!second_part_of_rmw) {
 352                         /* Read from future value */
 353                         value = curr->get_node()->get_future_value();
 354                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 355                         curr->read_from(NULL);
 356                         Promise *valuepromise = new Promise(curr, value, expiration);
 357                         promises->push_back(valuepromise);
 358                 }
 359                 get_thread(curr)->set_return_value(value);
 360                 return updated;
 361         }
 362 }
 363
 364 /**
 365  * Processes a lock, trylock, or unlock model action.  @param curr is
 366  * the read model action to process.
 367  *
 368  * The try lock operation checks whether the lock is taken.  If not,
 369  * it falls to the normal lock operation case.  If so, it returns
 370  * fail.
 371  *
 372  * The lock operation has already been checked that it is enabled, so
 373  * it just grabs the lock and synchronizes with the previous unlock.
 374  *
 375  * The unlock operation has to re-enable all of the threads that are
 376  * waiting on the lock.
 377  *
 378  * @return True if synchronization was updated; false otherwise
 379  */
 380 bool ModelChecker::process_mutex(ModelAction *curr) {
 381         std::mutex *mutex = (std::mutex *)curr->get_location();
 382         struct std::mutex_state *state = mutex->get_state();
 383         switch (curr->get_type()) {
 384         case ATOMIC_TRYLOCK: {
 385                 bool success = !state->islocked;
 386                 curr->set_try_lock(success);
 387                 if (!success) {
 388                         get_thread(curr)->set_return_value(0);
 389                         break;
 390                 }
 391                 get_thread(curr)->set_return_value(1);
 392         }
 393                 //otherwise fall into the lock case
 394         case ATOMIC_LOCK: {
 395                 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
 396                         printf("Lock access before initialization\n");
 397                         set_assert();
 398                 }
 399                 state->islocked = true;
 400                 ModelAction *unlock = get_last_unlock(curr);
 401                 //synchronize with the previous unlock statement
 402                 if (unlock != NULL) {
 403                         curr->synchronize_with(unlock);
 404                         return true;
 405                 }
 406                 break;
 407         }
 408         case ATOMIC_UNLOCK: {
 409                 //unlock the lock
 410                 state->islocked = false;
 411                 //wake up the other threads
 412                 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 413                 //activate all the waiting threads
 414                 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
 415                         scheduler->add_thread(get_thread((*rit)->get_tid()));
 416                 }
 417                 waiters->clear();
 418                 break;
 419         }
 420         default:
 421                 ASSERT(0);
 422         }
 423         return false;
 424 }
 425
 426 /**
 427  * Process a write ModelAction
 428  * @param curr The ModelAction to process
 429  * @return True if the mo_graph was updated or promises were resolved
 430  */
 431 bool ModelChecker::process_write(ModelAction *curr)
 432 {
 433         bool updated_mod_order = w_modification_order(curr);
 434         bool updated_promises = resolve_promises(curr);
 435
 436         if (promises->size() == 0) {
 437                 for (unsigned int i = 0; i < futurevalues->size(); i++) {
 438                         struct PendingFutureValue pfv = (*futurevalues)[i];
 439                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 440                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 441                                 priv->next_backtrack = pfv.act;
 442                 }
 443                 futurevalues->resize(0);
 444         }
 445
 446         mo_graph->commitChanges();
 447         get_thread(curr)->set_return_value(VALUE_NONE);
 448         return updated_mod_order || updated_promises;
 449 }
 450
 451 /**
 452  * @brief Process the current action for thread-related activity
 453  *
 454  * Performs current-action processing for a THREAD_* ModelAction. Proccesses
 455  * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
 456  * synchronization, etc.  This function is a no-op for non-THREAD actions
 457  * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
 458  *
 459  * @param curr The current action
 460  * @return True if synchronization was updated
 461  */
 462 bool ModelChecker::process_thread_action(ModelAction *curr)
 463 {
 464         bool synchronized = false;
 465
 466         switch (curr->get_type()) {
 467         case THREAD_CREATE: {
 468                 Thread *th = (Thread *)curr->get_location();
 469                 th->set_creation(curr);
 470                 break;
 471         }
 472         case THREAD_JOIN: {
 473                 Thread *waiting, *blocking;
 474                 waiting = get_thread(curr);
 475                 blocking = (Thread *)curr->get_location();
 476                 if (!blocking->is_complete()) {
 477                         blocking->push_wait_list(curr);
 478                         scheduler->sleep(waiting);
 479                 } else {
 480                         do_complete_join(curr);
 481                         synchronized = true;
 482                 }
 483                 break;
 484         }
 485         case THREAD_FINISH: {
 486                 Thread *th = get_thread(curr);
 487                 while (!th->wait_list_empty()) {
 488                         ModelAction *act = th->pop_wait_list();
 489                         Thread *wake = get_thread(act);
 490                         scheduler->wake(wake);
 491                         do_complete_join(act);
 492                         synchronized = true;
 493                 }
 494                 th->complete();
 495                 break;
 496         }
 497         case THREAD_START: {
 498                 check_promises(NULL, curr->get_cv());
 499                 break;
 500         }
 501         default:
 502                 break;
 503         }
 504
 505         return synchronized;
 506 }
 507
 508 /**
 509  * Initialize the current action by performing one or more of the following
 510  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 511  * in the NodeStack, manipulating backtracking sets, allocating and
 512  * initializing clock vectors, and computing the promises to fulfill.
 513  *
 514  * @param curr The current action, as passed from the user context; may be
 515  * freed/invalidated after the execution of this function
 516  * @return The current action, as processed by the ModelChecker. Is only the
 517  * same as the parameter @a curr if this is a newly-explored action.
 518  */
 519 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 520 {
 521         ModelAction *newcurr;
 522
 523         if (curr->is_rmwc() || curr->is_rmw()) {
 524                 newcurr = process_rmw(curr);
 525                 delete curr;
 526                 compute_promises(newcurr);
 527                 return newcurr;
 528         }
 529
 530         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 531         if (newcurr) {
 532                 /* First restore type and order in case of RMW operation */
 533                 if (curr->is_rmwr())
 534                         newcurr->copy_typeandorder(curr);
 535
 536                 ASSERT(curr->get_location() == newcurr->get_location());
 537                 newcurr->copy_from_new(curr);
 538
 539                 /* Discard duplicate ModelAction; use action from NodeStack */
 540                 delete curr;
 541
 542                 /* If we have diverged, we need to reset the clock vector. */
 543                 if (diverge == NULL)
 544                         newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 545         } else {
 546                 newcurr = curr;
 547                 /*
 548                  * Perform one-time actions when pushing new ModelAction onto
 549                  * NodeStack
 550                  */
 551                 curr->create_cv(get_parent_action(curr->get_tid()));
 552                 if (curr->is_write())
 553                         compute_promises(curr);
 554         }
 555         return newcurr;
 556 }
 557
 558 /**
 559  * This method checks whether a model action is enabled at the given point.
 560  * At this point, it checks whether a lock operation would be successful at this point.
 561  * If not, it puts the thread in a waiter list.
 562  * @param curr is the ModelAction to check whether it is enabled.
 563  * @return a bool that indicates whether the action is enabled.
 564  */
 565 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 566         if (curr->is_lock()) {
 567                 std::mutex * lock = (std::mutex *)curr->get_location();
 568                 struct std::mutex_state * state = lock->get_state();
 569                 if (state->islocked) {
 570                         //Stick the action in the appropriate waiting queue
 571                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 572                         return false;
 573                 }
 574         }
 575
 576         return true;
 577 }
 578
 579 /**
 580  * This is the heart of the model checker routine. It performs model-checking
 581  * actions corresponding to a given "current action." Among other processes, it
 582  * calculates reads-from relationships, updates synchronization clock vectors,
 583  * forms a memory_order constraints graph, and handles replay/backtrack
 584  * execution when running permutations of previously-observed executions.
 585  *
 586  * @param curr The current action to process
 587  * @return The next Thread that must be executed. May be NULL if ModelChecker
 588  * makes no choice (e.g., according to replay execution, combining RMW actions,
 589  * etc.)
 590  */
 591 Thread * ModelChecker::check_current_action(ModelAction *curr)
 592 {
 593         ASSERT(curr);
 594
 595         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 596
 597         if (!check_action_enabled(curr)) {
 598                 /* Make the execution look like we chose to run this action
 599                  * much later, when a lock is actually available to release */
 600                 get_current_thread()->set_pending(curr);
 601                 remove_thread(get_current_thread());
 602                 return get_next_thread(NULL);
 603         }
 604
 605         ModelAction *newcurr = initialize_curr_action(curr);
 606
 607         /* Add the action to lists before any other model-checking tasks */
 608         if (!second_part_of_rmw)
 609                 add_action_to_lists(newcurr);
 610
 611         /* Build may_read_from set for newly-created actions */
 612         if (curr == newcurr && curr->is_read())
 613                 build_reads_from_past(curr);
 614         curr = newcurr;
 615
 616         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 617
 618         while (!work_queue.empty()) {
 619                 WorkQueueEntry work = work_queue.front();
 620                 work_queue.pop_front();
 621
 622                 switch (work.type) {
 623                 case WORK_CHECK_CURR_ACTION: {
 624                         ModelAction *act = work.action;
 625                         bool update = false; /* update this location's release seq's */
 626                         bool update_all = false; /* update all release seq's */
 627
 628                         process_thread_action(curr);
 629
 630                         if (act->is_read() && process_read(act, second_part_of_rmw))
 631                                 update = true;
 632
 633                         if (act->is_write() && process_write(act))
 634                                 update = true;
 635
 636                         if (act->is_mutex_op() && process_mutex(act))
 637                                 update_all = true;
 638
 639                         if (update_all)
 640                                 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
 641                         else if (update)
 642                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 643                         break;
 644                 }
 645                 case WORK_CHECK_RELEASE_SEQ:
 646                         resolve_release_sequences(work.location, &work_queue);
 647                         break;
 648                 case WORK_CHECK_MO_EDGES: {
 649                         /** @todo Complete verification of work_queue */
 650                         ModelAction *act = work.action;
 651                         bool updated = false;
 652
 653                         if (act->is_read()) {
 654                                 if (r_modification_order(act, act->get_reads_from()))
 655                                         updated = true;
 656                         }
 657                         if (act->is_write()) {
 658                                 if (w_modification_order(act))
 659                                         updated = true;
 660                         }
 661
 662                         if (updated)
 663                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 664                         break;
 665                 }
 666                 default:
 667                         ASSERT(false);
 668                         break;
 669                 }
 670         }
 671
 672         check_curr_backtracking(curr);
 673
 674         set_backtracking(curr);
 675
 676         return get_next_thread(curr);
 677 }
 678
 679 /**
 680  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 681  * operation from the Thread it is joining with. Must be called after the
 682  * completion of the Thread in question.
 683  * @param join The THREAD_JOIN action
 684  */
 685 void ModelChecker::do_complete_join(ModelAction *join)
 686 {
 687         Thread *blocking = (Thread *)join->get_location();
 688         ModelAction *act = get_last_action(blocking->get_id());
 689         join->synchronize_with(act);
 690 }
 691
 692 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 693         Node *currnode = curr->get_node();
 694         Node *parnode = currnode->get_parent();
 695
 696         if ((!parnode->backtrack_empty() ||
 697                          !currnode->read_from_empty() ||
 698                          !currnode->future_value_empty() ||
 699                          !currnode->promise_empty())
 700                         && (!priv->next_backtrack ||
 701                                         *curr > *priv->next_backtrack)) {
 702                 priv->next_backtrack = curr;
 703         }
 704 }
 705
 706 bool ModelChecker::promises_expired() {
 707         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 708                 Promise *promise = (*promises)[promise_index];
 709                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 710                         return true;
 711                 }
 712         }
 713         return false;
 714 }
 715
 716 /** @return whether the current partial trace must be a prefix of a
 717  * feasible trace. */
 718 bool ModelChecker::isfeasibleprefix() {
 719         return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
 720 }
 721
 722 /** @return whether the current partial trace is feasible. */
 723 bool ModelChecker::isfeasible() {
 724         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 725 }
 726
 727 /** @return whether the current partial trace is feasible other than
 728  * multiple RMW reading from the same store. */
 729 bool ModelChecker::isfeasibleotherthanRMW() {
 730         if (DBG_ENABLED()) {
 731                 if (mo_graph->checkForCycles())
 732                         DEBUG("Infeasible: modification order cycles\n");
 733                 if (failed_promise)
 734                         DEBUG("Infeasible: failed promise\n");
 735                 if (too_many_reads)
 736                         DEBUG("Infeasible: too many reads\n");
 737                 if (promises_expired())
 738                         DEBUG("Infeasible: promises expired\n");
 739         }
 740         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 741 }
 742
 743 /** Returns whether the current completed trace is feasible. */
 744 bool ModelChecker::isfinalfeasible() {
 745         if (DBG_ENABLED() && promises->size() != 0)
 746                 DEBUG("Infeasible: unrevolved promises\n");
 747
 748         return isfeasible() && promises->size() == 0;
 749 }
 750
 751 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 752 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 753         int tid = id_to_int(act->get_tid());
 754         ModelAction *lastread = get_last_action(tid);
 755         lastread->process_rmw(act);
 756         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 757                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 758                 mo_graph->commitChanges();
 759         }
 760         return lastread;
 761 }
 762
 763 /**
 764  * Checks whether a thread has read from the same write for too many times
 765  * without seeing the effects of a later write.
 766  *
 767  * Basic idea:
 768  * 1) there must a different write that we could read from that would satisfy the modification order,
 769  * 2) we must have read from the same value in excess of maxreads times, and
 770  * 3) that other write must have been in the reads_from set for maxreads times.
 771  *
 772  * If so, we decide that the execution is no longer feasible.
 773  */
 774 void ModelChecker::check_recency(ModelAction *curr) {
 775         if (params.maxreads != 0) {
 776                 if (curr->get_node()->get_read_from_size() <= 1)
 777                         return;
 778
 779                 //Must make sure that execution is currently feasible...  We could
 780                 //accidentally clear by rolling back
 781                 if (!isfeasible())
 782                         return;
 783
 784                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 785                 int tid = id_to_int(curr->get_tid());
 786
 787                 /* Skip checks */
 788                 if ((int)thrd_lists->size() <= tid)
 789                         return;
 790
 791                 action_list_t *list = &(*thrd_lists)[tid];
 792
 793                 action_list_t::reverse_iterator rit = list->rbegin();
 794                 /* Skip past curr */
 795                 for (; (*rit) != curr; rit++)
 796                         ;
 797                 /* go past curr now */
 798                 rit++;
 799
 800                 action_list_t::reverse_iterator ritcopy = rit;
 801                 //See if we have enough reads from the same value
 802                 int count = 0;
 803                 for (; count < params.maxreads; rit++,count++) {
 804                         if (rit==list->rend())
 805                                 return;
 806                         ModelAction *act = *rit;
 807                         if (!act->is_read())
 808                                 return;
 809                         if (act->get_reads_from() != curr->get_reads_from())
 810                                 return;
 811                         if (act->get_node()->get_read_from_size() <= 1)
 812                                 return;
 813                 }
 814
 815                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 816                         //Get write
 817                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 818                         //Need a different write
 819                         if (write==curr->get_reads_from())
 820                                 continue;
 821
 822                         /* Test to see whether this is a feasible write to read from*/
 823                         mo_graph->startChanges();
 824                         r_modification_order(curr, write);
 825                         bool feasiblereadfrom = isfeasible();
 826                         mo_graph->rollbackChanges();
 827
 828                         if (!feasiblereadfrom)
 829                                 continue;
 830                         rit = ritcopy;
 831
 832                         bool feasiblewrite = true;
 833                         //new we need to see if this write works for everyone
 834
 835                         for (int loop = count; loop>0; loop--,rit++) {
 836                                 ModelAction *act=*rit;
 837                                 bool foundvalue = false;
 838                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 839                                         if (act->get_node()->get_read_from_at(i)==write) {
 840                                                 foundvalue = true;
 841                                                 break;
 842                                         }
 843                                 }
 844                                 if (!foundvalue) {
 845                                         feasiblewrite = false;
 846                                         break;
 847                                 }
 848                         }
 849                         if (feasiblewrite) {
 850                                 too_many_reads = true;
 851                                 return;
 852                         }
 853                 }
 854         }
 855 }
 856
 857 /**
 858  * Updates the mo_graph with the constraints imposed from the current
 859  * read.
 860  *
 861  * Basic idea is the following: Go through each other thread and find
 862  * the lastest action that happened before our read.  Two cases:
 863  *
 864  * (1) The action is a write => that write must either occur before
 865  * the write we read from or be the write we read from.
 866  *
 867  * (2) The action is a read => the write that that action read from
 868  * must occur before the write we read from or be the same write.
 869  *
 870  * @param curr The current action. Must be a read.
 871  * @param rf The action that curr reads from. Must be a write.
 872  * @return True if modification order edges were added; false otherwise
 873  */
 874 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 875 {
 876         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 877         unsigned int i;
 878         bool added = false;
 879         ASSERT(curr->is_read());
 880
 881         /* Iterate over all threads */
 882         for (i = 0; i < thrd_lists->size(); i++) {
 883                 /* Iterate over actions in thread, starting from most recent */
 884                 action_list_t *list = &(*thrd_lists)[i];
 885                 action_list_t::reverse_iterator rit;
 886                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 887                         ModelAction *act = *rit;
 888
 889                         /*
 890                          * Include at most one act per-thread that "happens
 891                          * before" curr. Don't consider reflexively.
 892                          */
 893                         if (act->happens_before(curr) && act != curr) {
 894                                 if (act->is_write()) {
 895                                         if (rf != act) {
 896                                                 mo_graph->addEdge(act, rf);
 897                                                 added = true;
 898                                         }
 899                                 } else {
 900                                         const ModelAction *prevreadfrom = act->get_reads_from();
 901                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 902                                                 mo_graph->addEdge(prevreadfrom, rf);
 903                                                 added = true;
 904                                         }
 905                                 }
 906                                 break;
 907                         }
 908                 }
 909         }
 910
 911         return added;
 912 }
 913
 914 /** This method fixes up the modification order when we resolve a
 915  *  promises.  The basic problem is that actions that occur after the
 916  *  read curr could not property add items to the modification order
 917  *  for our read.
 918  *
 919  *  So for each thread, we find the earliest item that happens after
 920  *  the read curr.  This is the item we have to fix up with additional
 921  *  constraints.  If that action is write, we add a MO edge between
 922  *  the Action rf and that action.  If the action is a read, we add a
 923  *  MO edge between the Action rf, and whatever the read accessed.
 924  *
 925  * @param curr is the read ModelAction that we are fixing up MO edges for.
 926  * @param rf is the write ModelAction that curr reads from.
 927  *
 928  */
 929 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 930 {
 931         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 932         unsigned int i;
 933         ASSERT(curr->is_read());
 934
 935         /* Iterate over all threads */
 936         for (i = 0; i < thrd_lists->size(); i++) {
 937                 /* Iterate over actions in thread, starting from most recent */
 938                 action_list_t *list = &(*thrd_lists)[i];
 939                 action_list_t::reverse_iterator rit;
 940                 ModelAction *lastact = NULL;
 941
 942                 /* Find last action that happens after curr */
 943                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 944                         ModelAction *act = *rit;
 945                         if (curr->happens_before(act)) {
 946                                 lastact = act;
 947                         } else
 948                                 break;
 949                 }
 950
 951                         /* Include at most one act per-thread that "happens before" curr */
 952                 if (lastact != NULL) {
 953                         if (lastact->is_read()) {
 954                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 955                                 if (postreadfrom != NULL&&rf != postreadfrom)
 956                                         mo_graph->addEdge(rf, postreadfrom);
 957                         } else if (rf != lastact) {
 958                                 mo_graph->addEdge(rf, lastact);
 959                         }
 960                         break;
 961                 }
 962         }
 963 }
 964
 965 /**
 966  * Updates the mo_graph with the constraints imposed from the current write.
 967  *
 968  * Basic idea is the following: Go through each other thread and find
 969  * the lastest action that happened before our write.  Two cases:
 970  *
 971  * (1) The action is a write => that write must occur before
 972  * the current write
 973  *
 974  * (2) The action is a read => the write that that action read from
 975  * must occur before the current write.
 976  *
 977  * This method also handles two other issues:
 978  *
 979  * (I) Sequential Consistency: Making sure that if the current write is
 980  * seq_cst, that it occurs after the previous seq_cst write.
 981  *
 982  * (II) Sending the write back to non-synchronizing reads.
 983  *
 984  * @param curr The current action. Must be a write.
 985  * @return True if modification order edges were added; false otherwise
 986  */
 987 bool ModelChecker::w_modification_order(ModelAction *curr)
 988 {
 989         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 990         unsigned int i;
 991         bool added = false;
 992         ASSERT(curr->is_write());
 993
 994         if (curr->is_seqcst()) {
 995                 /* We have to at least see the last sequentially consistent write,
 996                          so we are initialized. */
 997                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
 998                 if (last_seq_cst != NULL) {
 999                         mo_graph->addEdge(last_seq_cst, curr);
1000                         added = true;
1001                 }
1002         }
1003
1004         /* Iterate over all threads */
1005         for (i = 0; i < thrd_lists->size(); i++) {
1006                 /* Iterate over actions in thread, starting from most recent */
1007                 action_list_t *list = &(*thrd_lists)[i];
1008                 action_list_t::reverse_iterator rit;
1009                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1010                         ModelAction *act = *rit;
1011                         if (act == curr) {
1012                                 /*
1013                                  * If RMW, we already have all relevant edges,
1014                                  * so just skip to next thread.
1015                                  * If normal write, we need to look at earlier
1016                                  * actions, so continue processing list.
1017                                  */
1018                                 if (curr->is_rmw())
1019                                         break;
1020                                 else
1021                                         continue;
1022                         }
1023
1024                         /*
1025                          * Include at most one act per-thread that "happens
1026                          * before" curr
1027                          */
1028                         if (act->happens_before(curr)) {
1029                                 /*
1030                                  * Note: if act is RMW, just add edge:
1031                                  *   act --mo--> curr
1032                                  * The following edge should be handled elsewhere:
1033                                  *   readfrom(act) --mo--> act
1034                                  */
1035                                 if (act->is_write())
1036                                         mo_graph->addEdge(act, curr);
1037                                 else if (act->is_read() && act->get_reads_from() != NULL)
1038                                         mo_graph->addEdge(act->get_reads_from(), curr);
1039                                 added = true;
1040                                 break;
1041                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
1042                                                      !act->same_thread(curr)) {
1043                                 /* We have an action that:
1044                                    (1) did not happen before us
1045                                    (2) is a read and we are a write
1046                                    (3) cannot synchronize with us
1047                                    (4) is in a different thread
1048                                    =>
1049                                    that read could potentially read from our write.
1050                                  */
1051                                 if (thin_air_constraint_may_allow(curr, act)) {
1052                                         if (isfeasible() ||
1053                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1054                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1055                                                 futurevalues->push_back(pfv);
1056                                         }
1057                                 }
1058                         }
1059                 }
1060         }
1061
1062         return added;
1063 }
1064
1065 /** Arbitrary reads from the future are not allowed.  Section 29.3
1066  * part 9 places some constraints.  This method checks one result of constraint
1067  * constraint.  Others require compiler support. */
1068 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1069         if (!writer->is_rmw())
1070                 return true;
1071
1072         if (!reader->is_rmw())
1073                 return true;
1074
1075         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1076                 if (search == reader)
1077                         return false;
1078                 if (search->get_tid() == reader->get_tid() &&
1079                                 search->happens_before(reader))
1080                         break;
1081         }
1082
1083         return true;
1084 }
1085
1086 /**
1087  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1088  * The ModelAction under consideration is expected to be taking part in
1089  * release/acquire synchronization as an object of the "reads from" relation.
1090  * Note that this can only provide release sequence support for RMW chains
1091  * which do not read from the future, as those actions cannot be traced until
1092  * their "promise" is fulfilled. Similarly, we may not even establish the
1093  * presence of a release sequence with certainty, as some modification order
1094  * constraints may be decided further in the future. Thus, this function
1095  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1096  * and a boolean representing certainty.
1097  *
1098  * @todo Finish lazy updating, when promises are fulfilled in the future
1099  * @param rf The action that might be part of a release sequence. Must be a
1100  * write.
1101  * @param release_heads A pass-by-reference style return parameter.  After
1102  * execution of this function, release_heads will contain the heads of all the
1103  * relevant release sequences, if any exists
1104  * @return true, if the ModelChecker is certain that release_heads is complete;
1105  * false otherwise
1106  */
1107 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1108 {
1109         while (rf) {
1110                 ASSERT(rf->is_write());
1111
1112                 if (rf->is_release())
1113                         release_heads->push_back(rf);
1114                 if (!rf->is_rmw())
1115                         break; /* End of RMW chain */
1116
1117                 /** @todo Need to be smarter here...  In the linux lock
1118                  * example, this will run to the beginning of the program for
1119                  * every acquire. */
1120                 /** @todo The way to be smarter here is to keep going until 1
1121                  * thread has a release preceded by an acquire and you've seen
1122                  *       both. */
1123
1124                 /* acq_rel RMW is a sufficient stopping condition */
1125                 if (rf->is_acquire() && rf->is_release())
1126                         return true; /* complete */
1127
1128                 rf = rf->get_reads_from();
1129         };
1130         if (!rf) {
1131                 /* read from future: need to settle this later */
1132                 return false; /* incomplete */
1133         }
1134
1135         if (rf->is_release())
1136                 return true; /* complete */
1137
1138         /* else relaxed write; check modification order for contiguous subsequence
1139          * -> rf must be same thread as release */
1140         int tid = id_to_int(rf->get_tid());
1141         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1142         action_list_t *list = &(*thrd_lists)[tid];
1143         action_list_t::const_reverse_iterator rit;
1144
1145         /* Find rf in the thread list */
1146         rit = std::find(list->rbegin(), list->rend(), rf);
1147         ASSERT(rit != list->rend());
1148
1149         /* Find the last write/release */
1150         for (; rit != list->rend(); rit++)
1151                 if ((*rit)->is_release())
1152                         break;
1153         if (rit == list->rend()) {
1154                 /* No write-release in this thread */
1155                 return true; /* complete */
1156         }
1157         ModelAction *release = *rit;
1158
1159         ASSERT(rf->same_thread(release));
1160
1161         bool certain = true;
1162         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1163                 if (id_to_int(rf->get_tid()) == (int)i)
1164                         continue;
1165                 list = &(*thrd_lists)[i];
1166
1167                 /* Can we ensure no future writes from this thread may break
1168                  * the release seq? */
1169                 bool future_ordered = false;
1170
1171                 ModelAction *last = get_last_action(int_to_id(i));
1172                 if (last && (rf->happens_before(last) ||
1173                                 last->get_type() == THREAD_FINISH))
1174                         future_ordered = true;
1175
1176                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1177                         const ModelAction *act = *rit;
1178                         /* Reach synchronization -> this thread is complete */
1179                         if (act->happens_before(release))
1180                                 break;
1181                         if (rf->happens_before(act)) {
1182                                 future_ordered = true;
1183                                 continue;
1184                         }
1185
1186                         /* Only writes can break release sequences */
1187                         if (!act->is_write())
1188                                 continue;
1189
1190                         /* Check modification order */
1191                         if (mo_graph->checkReachable(rf, act)) {
1192                                 /* rf --mo--> act */
1193                                 future_ordered = true;
1194                                 continue;
1195                         }
1196                         if (mo_graph->checkReachable(act, release))
1197                                 /* act --mo--> release */
1198                                 break;
1199                         if (mo_graph->checkReachable(release, act) &&
1200                                       mo_graph->checkReachable(act, rf)) {
1201                                 /* release --mo-> act --mo--> rf */
1202                                 return true; /* complete */
1203                         }
1204                         certain = false;
1205                 }
1206                 if (!future_ordered)
1207                         return false; /* This thread is uncertain */
1208         }
1209
1210         if (certain)
1211                 release_heads->push_back(release);
1212         return certain;
1213 }
1214
1215 /**
1216  * A public interface for getting the release sequence head(s) with which a
1217  * given ModelAction must synchronize. This function only returns a non-empty
1218  * result when it can locate a release sequence head with certainty. Otherwise,
1219  * it may mark the internal state of the ModelChecker so that it will handle
1220  * the release sequence at a later time, causing @a act to update its
1221  * synchronization at some later point in execution.
1222  * @param act The 'acquire' action that may read from a release sequence
1223  * @param release_heads A pass-by-reference return parameter. Will be filled
1224  * with the head(s) of the release sequence(s), if they exists with certainty.
1225  * @see ModelChecker::release_seq_head
1226  */
1227 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1228 {
1229         const ModelAction *rf = act->get_reads_from();
1230         bool complete;
1231         complete = release_seq_head(rf, release_heads);
1232         if (!complete) {
1233                 /* add act to 'lazy checking' list */
1234                 pending_acq_rel_seq->push_back(act);
1235         }
1236 }
1237
1238 /**
1239  * Attempt to resolve all stashed operations that might synchronize with a
1240  * release sequence for a given location. This implements the "lazy" portion of
1241  * determining whether or not a release sequence was contiguous, since not all
1242  * modification order information is present at the time an action occurs.
1243  *
1244  * @param location The location/object that should be checked for release
1245  * sequence resolutions. A NULL value means to check all locations.
1246  * @param work_queue The work queue to which to add work items as they are
1247  * generated
1248  * @return True if any updates occurred (new synchronization, new mo_graph
1249  * edges)
1250  */
1251 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1252 {
1253         bool updated = false;
1254         std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
1255         while (it != pending_acq_rel_seq->end()) {
1256                 ModelAction *act = *it;
1257
1258                 /* Only resolve sequences on the given location, if provided */
1259                 if (location && act->get_location() != location) {
1260                         it++;
1261                         continue;
1262                 }
1263
1264                 const ModelAction *rf = act->get_reads_from();
1265                 rel_heads_list_t release_heads;
1266                 bool complete;
1267                 complete = release_seq_head(rf, &release_heads);
1268                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1269                         if (!act->has_synchronized_with(release_heads[i])) {
1270                                 updated = true;
1271                                 act->synchronize_with(release_heads[i]);
1272                         }
1273                 }
1274
1275                 if (updated) {
1276                         /* Re-check act for mo_graph edges */
1277                         work_queue->push_back(MOEdgeWorkEntry(act));
1278
1279                         /* propagate synchronization to later actions */
1280                         action_list_t::reverse_iterator it = action_trace->rbegin();
1281                         for (; (*it) != act; it++) {
1282                                 ModelAction *propagate = *it;
1283                                 if (act->happens_before(propagate)) {
1284                                         propagate->synchronize_with(act);
1285                                         /* Re-check 'propagate' for mo_graph edges */
1286                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1287                                 }
1288                         }
1289                 }
1290                 if (complete)
1291                         it = pending_acq_rel_seq->erase(it);
1292                 else
1293                         it++;
1294         }
1295
1296         // If we resolved promises or data races, see if we have realized a data race.
1297         if (checkDataRaces()) {
1298                 set_assert();
1299         }
1300
1301         return updated;
1302 }
1303
1304 /**
1305  * Performs various bookkeeping operations for the current ModelAction. For
1306  * instance, adds action to the per-object, per-thread action vector and to the
1307  * action trace list of all thread actions.
1308  *
1309  * @param act is the ModelAction to add.
1310  */
1311 void ModelChecker::add_action_to_lists(ModelAction *act)
1312 {
1313         int tid = id_to_int(act->get_tid());
1314         action_trace->push_back(act);
1315
1316         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1317
1318         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1319         if (tid >= (int)vec->size())
1320                 vec->resize(priv->next_thread_id);
1321         (*vec)[tid].push_back(act);
1322
1323         if ((int)thrd_last_action->size() <= tid)
1324                 thrd_last_action->resize(get_num_threads());
1325         (*thrd_last_action)[tid] = act;
1326 }
1327
1328 /**
1329  * @brief Get the last action performed by a particular Thread
1330  * @param tid The thread ID of the Thread in question
1331  * @return The last action in the thread
1332  */
1333 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1334 {
1335         int threadid = id_to_int(tid);
1336         if (threadid < (int)thrd_last_action->size())
1337                 return (*thrd_last_action)[id_to_int(tid)];
1338         else
1339                 return NULL;
1340 }
1341
1342 /**
1343  * Gets the last memory_order_seq_cst write (in the total global sequence)
1344  * performed on a particular object (i.e., memory location), not including the
1345  * current action.
1346  * @param curr The current ModelAction; also denotes the object location to
1347  * check
1348  * @return The last seq_cst write
1349  */
1350 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1351 {
1352         void *location = curr->get_location();
1353         action_list_t *list = obj_map->get_safe_ptr(location);
1354         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1355         action_list_t::reverse_iterator rit;
1356         for (rit = list->rbegin(); rit != list->rend(); rit++)
1357                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1358                         return *rit;
1359         return NULL;
1360 }
1361
1362 /**
1363  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1364  * location). This function identifies the mutex according to the current
1365  * action, which is presumed to perform on the same mutex.
1366  * @param curr The current ModelAction; also denotes the object location to
1367  * check
1368  * @return The last unlock operation
1369  */
1370 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1371 {
1372         void *location = curr->get_location();
1373         action_list_t *list = obj_map->get_safe_ptr(location);
1374         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1375         action_list_t::reverse_iterator rit;
1376         for (rit = list->rbegin(); rit != list->rend(); rit++)
1377                 if ((*rit)->is_unlock())
1378                         return *rit;
1379         return NULL;
1380 }
1381
1382 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1383 {
1384         ModelAction *parent = get_last_action(tid);
1385         if (!parent)
1386                 parent = get_thread(tid)->get_creation();
1387         return parent;
1388 }
1389
1390 /**
1391  * Returns the clock vector for a given thread.
1392  * @param tid The thread whose clock vector we want
1393  * @return Desired clock vector
1394  */
1395 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1396 {
1397         return get_parent_action(tid)->get_cv();
1398 }
1399
1400 /**
1401  * Resolve a set of Promises with a current write. The set is provided in the
1402  * Node corresponding to @a write.
1403  * @param write The ModelAction that is fulfilling Promises
1404  * @return True if promises were resolved; false otherwise
1405  */
1406 bool ModelChecker::resolve_promises(ModelAction *write)
1407 {
1408         bool resolved = false;
1409
1410         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1411                 Promise *promise = (*promises)[promise_index];
1412                 if (write->get_node()->get_promise(i)) {
1413                         ModelAction *read = promise->get_action();
1414                         read->read_from(write);
1415                         if (read->is_rmw()) {
1416                                 mo_graph->addRMWEdge(write, read);
1417                         }
1418                         //First fix up the modification order for actions that happened
1419                         //before the read
1420                         r_modification_order(read, write);
1421                         //Next fix up the modification order for actions that happened
1422                         //after the read.
1423                         post_r_modification_order(read, write);
1424                         promises->erase(promises->begin() + promise_index);
1425                         resolved = true;
1426                 } else
1427                         promise_index++;
1428         }
1429         return resolved;
1430 }
1431
1432 /**
1433  * Compute the set of promises that could potentially be satisfied by this
1434  * action. Note that the set computation actually appears in the Node, not in
1435  * ModelChecker.
1436  * @param curr The ModelAction that may satisfy promises
1437  */
1438 void ModelChecker::compute_promises(ModelAction *curr)
1439 {
1440         for (unsigned int i = 0; i < promises->size(); i++) {
1441                 Promise *promise = (*promises)[i];
1442                 const ModelAction *act = promise->get_action();
1443                 if (!act->happens_before(curr) &&
1444                                 act->is_read() &&
1445                                 !act->is_synchronizing(curr) &&
1446                                 !act->same_thread(curr) &&
1447                                 promise->get_value() == curr->get_value()) {
1448                         curr->get_node()->set_promise(i);
1449                 }
1450         }
1451 }
1452
1453 /** Checks promises in response to change in ClockVector Threads. */
1454 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1455 {
1456         for (unsigned int i = 0; i < promises->size(); i++) {
1457                 Promise *promise = (*promises)[i];
1458                 const ModelAction *act = promise->get_action();
1459                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1460                                 merge_cv->synchronized_since(act)) {
1461                         //This thread is no longer able to send values back to satisfy the promise
1462                         int num_synchronized_threads = promise->increment_threads();
1463                         if (num_synchronized_threads == get_num_threads()) {
1464                                 //Promise has failed
1465                                 failed_promise = true;
1466                                 return;
1467                         }
1468                 }
1469         }
1470 }
1471
1472 /**
1473  * Build up an initial set of all past writes that this 'read' action may read
1474  * from. This set is determined by the clock vector's "happens before"
1475  * relationship.
1476  * @param curr is the current ModelAction that we are exploring; it must be a
1477  * 'read' operation.
1478  */
1479 void ModelChecker::build_reads_from_past(ModelAction *curr)
1480 {
1481         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1482         unsigned int i;
1483         ASSERT(curr->is_read());
1484
1485         ModelAction *last_seq_cst = NULL;
1486
1487         /* Track whether this object has been initialized */
1488         bool initialized = false;
1489
1490         if (curr->is_seqcst()) {
1491                 last_seq_cst = get_last_seq_cst(curr);
1492                 /* We have to at least see the last sequentially consistent write,
1493                          so we are initialized. */
1494                 if (last_seq_cst != NULL)
1495                         initialized = true;
1496         }
1497
1498         /* Iterate over all threads */
1499         for (i = 0; i < thrd_lists->size(); i++) {
1500                 /* Iterate over actions in thread, starting from most recent */
1501                 action_list_t *list = &(*thrd_lists)[i];
1502                 action_list_t::reverse_iterator rit;
1503                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1504                         ModelAction *act = *rit;
1505
1506                         /* Only consider 'write' actions */
1507                         if (!act->is_write() || act == curr)
1508                                 continue;
1509
1510                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1511                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1512                                 DEBUG("Adding action to may_read_from:\n");
1513                                 if (DBG_ENABLED()) {
1514                                         act->print();
1515                                         curr->print();
1516                                 }
1517                                 curr->get_node()->add_read_from(act);
1518                         }
1519
1520                         /* Include at most one act per-thread that "happens before" curr */
1521                         if (act->happens_before(curr)) {
1522                                 initialized = true;
1523                                 break;
1524                         }
1525                 }
1526         }
1527
1528         if (!initialized) {
1529                 /** @todo Need a more informative way of reporting errors. */
1530                 printf("ERROR: may read from uninitialized atomic\n");
1531         }
1532
1533         if (DBG_ENABLED() || !initialized) {
1534                 printf("Reached read action:\n");
1535                 curr->print();
1536                 printf("Printing may_read_from\n");
1537                 curr->get_node()->print_may_read_from();
1538                 printf("End printing may_read_from\n");
1539         }
1540
1541         ASSERT(initialized);
1542 }
1543
1544 static void print_list(action_list_t *list)
1545 {
1546         action_list_t::iterator it;
1547
1548         printf("---------------------------------------------------------------------\n");
1549         printf("Trace:\n");
1550
1551         for (it = list->begin(); it != list->end(); it++) {
1552                 (*it)->print();
1553         }
1554         printf("---------------------------------------------------------------------\n");
1555 }
1556
1557 void ModelChecker::print_summary()
1558 {
1559         printf("\n");
1560         printf("Number of executions: %d\n", num_executions);
1561         printf("Number of feasible executions: %d\n", num_feasible_executions);
1562         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1563
1564 #if SUPPORT_MOD_ORDER_DUMP
1565         scheduler->print();
1566         char buffername[100];
1567         sprintf(buffername, "exec%04u", num_executions);
1568         mo_graph->dumpGraphToFile(buffername);
1569 #endif
1570
1571         if (!isfinalfeasible())
1572                 printf("INFEASIBLE EXECUTION!\n");
1573         print_list(action_trace);
1574         printf("\n");
1575 }
1576
1577 /**
1578  * Add a Thread to the system for the first time. Should only be called once
1579  * per thread.
1580  * @param t The Thread to add
1581  */
1582 void ModelChecker::add_thread(Thread *t)
1583 {
1584         thread_map->put(id_to_int(t->get_id()), t);
1585         scheduler->add_thread(t);
1586 }
1587
1588 /**
1589  * Removes a thread from the scheduler.
1590  * @param the thread to remove.
1591  */
1592 void ModelChecker::remove_thread(Thread *t)
1593 {
1594         scheduler->remove_thread(t);
1595 }
1596
1597 /**
1598  * Switch from a user-context to the "master thread" context (a.k.a. system
1599  * context). This switch is made with the intention of exploring a particular
1600  * model-checking action (described by a ModelAction object). Must be called
1601  * from a user-thread context.
1602  * @param act The current action that will be explored. Must not be NULL.
1603  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1604  */
1605 int ModelChecker::switch_to_master(ModelAction *act)
1606 {
1607         DBG();
1608         Thread *old = thread_current();
1609         set_current_action(act);
1610         old->set_state(THREAD_READY);
1611         return Thread::swap(old, &system_context);
1612 }
1613
1614 /**
1615  * Takes the next step in the execution, if possible.
1616  * @return Returns true (success) if a step was taken and false otherwise.
1617  */
1618 bool ModelChecker::take_step() {
1619         if (has_asserted())
1620                 return false;
1621
1622         Thread * curr = thread_current();
1623         if (curr) {
1624                 if (curr->get_state() == THREAD_READY) {
1625                         ASSERT(priv->current_action);
1626
1627                         priv->nextThread = check_current_action(priv->current_action);
1628                         priv->current_action = NULL;
1629                         if (curr->is_blocked() || curr->is_complete())
1630                                 scheduler->remove_thread(curr);
1631                 } else {
1632                         ASSERT(false);
1633                 }
1634         }
1635         Thread * next = scheduler->next_thread(priv->nextThread);
1636
1637         /* Infeasible -> don't take any more steps */
1638         if (!isfeasible())
1639                 return false;
1640
1641         if (next)
1642                 next->set_state(THREAD_RUNNING);
1643         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1644
1645         /* next == NULL -> don't take any more steps */
1646         if (!next)
1647                 return false;
1648
1649         if ( next->get_pending() != NULL ) {
1650                 //restart a pending action
1651                 set_current_action(next->get_pending());
1652                 next->set_pending(NULL);
1653                 next->set_state(THREAD_READY);
1654                 return true;
1655         }
1656
1657         /* Return false only if swap fails with an error */
1658         return (Thread::swap(&system_context, next) == 0);
1659 }
1660
1661 /** Runs the current execution until threre are no more steps to take. */
1662 void ModelChecker::finish_execution() {
1663         DBG();
1664
1665         while (take_step());
1666 }