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         earliest_diverge(NULL),
  29         action_trace(new action_list_t()),
  30         thread_map(new HashTable<int, Thread *, int>()),
  31         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  33         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  34         promises(new std::vector<Promise *>()),
  35         futurevalues(new std::vector<struct PendingFutureValue>()),
  36         pending_acq_rel_seq(new std::vector<ModelAction *>()),
  37         thrd_last_action(new std::vector<ModelAction *>(1)),
  38         node_stack(new NodeStack()),
  39         mo_graph(new CycleGraph()),
  40         failed_promise(false),
  41         too_many_reads(false),
  42         asserted(false),
  43         bad_synchronization(false)
  44 {
  45         /* Allocate this "size" on the snapshotting heap */
  46         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  47         /* First thread created will have id INITIAL_THREAD_ID */
  48         priv->next_thread_id = INITIAL_THREAD_ID;
  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 pending_acq_rel_seq;
  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         bad_synchronization = false;
  86         reset_asserted();
  87         snapshotObject->backTrackBeforeStep(0);
  88 }
  89
  90 /** @return a thread ID for a new Thread */
  91 thread_id_t ModelChecker::get_next_id()
  92 {
  93         return priv->next_thread_id++;
  94 }
  95
  96 /** @return the number of user threads created during this execution */
  97 int ModelChecker::get_num_threads()
  98 {
  99         return priv->next_thread_id;
 100 }
 101
 102 /** @return a sequence number for a new ModelAction */
 103 modelclock_t ModelChecker::get_next_seq_num()
 104 {
 105         return ++priv->used_sequence_numbers;
 106 }
 107
 108 /**
 109  * @brief Choose the next thread to execute.
 110  *
 111  * This function chooses the next thread that should execute. It can force the
 112  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 113  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 114  * The model-checker may have no preference regarding the next thread (i.e.,
 115  * when exploring a new execution ordering), in which case this will return
 116  * NULL.
 117  * @param curr The current ModelAction. This action might guide the choice of
 118  * next thread.
 119  * @return The next thread to run. If the model-checker has no preference, NULL.
 120  */
 121 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 122 {
 123         thread_id_t tid;
 124
 125         if (curr!=NULL) {
 126                 /* Do not split atomic actions. */
 127                 if (curr->is_rmwr())
 128                         return thread_current();
 129                 /* The THREAD_CREATE action points to the created Thread */
 130                 else if (curr->get_type() == THREAD_CREATE)
 131                         return (Thread *)curr->get_location();
 132         }
 133
 134         /* Have we completed exploring the preselected path? */
 135         if (diverge == NULL)
 136                 return NULL;
 137
 138         /* Else, we are trying to replay an execution */
 139         ModelAction *next = node_stack->get_next()->get_action();
 140
 141         if (next == diverge) {
 142                 if (earliest_diverge == NULL || *diverge < *earliest_diverge)
 143                         earliest_diverge=diverge;
 144
 145                 Node *nextnode = next->get_node();
 146                 /* Reached divergence point */
 147                 if (nextnode->increment_promise()) {
 148                         /* The next node will try to satisfy a different set of promises. */
 149                         tid = next->get_tid();
 150                         node_stack->pop_restofstack(2);
 151                 } else if (nextnode->increment_read_from()) {
 152                         /* The next node will read from a different value. */
 153                         tid = next->get_tid();
 154                         node_stack->pop_restofstack(2);
 155                 } else if (nextnode->increment_future_value()) {
 156                         /* The next node will try to read from a different future value. */
 157                         tid = next->get_tid();
 158                         node_stack->pop_restofstack(2);
 159                 } else {
 160                         /* Make a different thread execute for next step */
 161                         Node *node = nextnode->get_parent();
 162                         tid = node->get_next_backtrack();
 163                         node_stack->pop_restofstack(1);
 164                         if (diverge==earliest_diverge) {
 165                                 earliest_diverge=node->get_action();
 166                         }
 167                 }
 168                 DEBUG("*** Divergence point ***\n");
 169
 170                 diverge = NULL;
 171         } else {
 172                 tid = next->get_tid();
 173         }
 174         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 175         ASSERT(tid != THREAD_ID_T_NONE);
 176         return thread_map->get(id_to_int(tid));
 177 }
 178
 179 /**
 180  * Queries the model-checker for more executions to explore and, if one
 181  * exists, resets the model-checker state to execute a new execution.
 182  *
 183  * @return If there are more executions to explore, return true. Otherwise,
 184  * return false.
 185  */
 186 bool ModelChecker::next_execution()
 187 {
 188         DBG();
 189
 190         num_executions++;
 191
 192         if (isfinalfeasible()) {
 193                 printf("Earliest divergence point since last feasible execution:\n");
 194                 if (earliest_diverge)
 195                         earliest_diverge->print(false);
 196                 else
 197                         printf("(Not set)\n");
 198
 199                 earliest_diverge = NULL;
 200                 num_feasible_executions++;
 201         }
 202
 203         DEBUG("Number of acquires waiting on pending release sequences: %lu\n",
 204                         pending_acq_rel_seq->size());
 205
 206         if (isfinalfeasible() || DBG_ENABLED())
 207                 print_summary();
 208
 209         if ((diverge = get_next_backtrack()) == NULL)
 210                 return false;
 211
 212         if (DBG_ENABLED()) {
 213                 printf("Next execution will diverge at:\n");
 214                 diverge->print();
 215         }
 216
 217         reset_to_initial_state();
 218         return true;
 219 }
 220
 221 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 222 {
 223         switch (act->get_type()) {
 224         case ATOMIC_READ:
 225         case ATOMIC_WRITE:
 226         case ATOMIC_RMW: {
 227                 /* linear search: from most recent to oldest */
 228                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 229                 action_list_t::reverse_iterator rit;
 230                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 231                         ModelAction *prev = *rit;
 232                         if (act->is_synchronizing(prev))
 233                                 return prev;
 234                 }
 235                 break;
 236         }
 237         case ATOMIC_LOCK:
 238         case ATOMIC_TRYLOCK: {
 239                 /* linear search: from most recent to oldest */
 240                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 241                 action_list_t::reverse_iterator rit;
 242                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 243                         ModelAction *prev = *rit;
 244                         if (act->is_conflicting_lock(prev))
 245                                 return prev;
 246                 }
 247                 break;
 248         }
 249         case ATOMIC_UNLOCK: {
 250                 /* linear search: from most recent to oldest */
 251                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 252                 action_list_t::reverse_iterator rit;
 253                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 254                         ModelAction *prev = *rit;
 255                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 256                                 return prev;
 257                 }
 258                 break;
 259         }
 260         default:
 261                 break;
 262         }
 263         return NULL;
 264 }
 265
 266 /** This method find backtracking points where we should try to
 267  * reorder the parameter ModelAction against.
 268  *
 269  * @param the ModelAction to find backtracking points for.
 270  */
 271 void ModelChecker::set_backtracking(ModelAction *act)
 272 {
 273         Thread *t = get_thread(act);
 274         ModelAction * prev = get_last_conflict(act);
 275         if (prev == NULL)
 276                 return;
 277
 278         Node * node = prev->get_node()->get_parent();
 279
 280         int low_tid, high_tid;
 281         if (node->is_enabled(t)) {
 282                 low_tid = id_to_int(act->get_tid());
 283                 high_tid = low_tid+1;
 284         } else {
 285                 low_tid = 0;
 286                 high_tid = get_num_threads();
 287         }
 288
 289         for(int i = low_tid; i < high_tid; i++) {
 290                 thread_id_t tid = int_to_id(i);
 291                 if (!node->is_enabled(tid))
 292                         continue;
 293
 294                 /* Check if this has been explored already */
 295                 if (node->has_been_explored(tid))
 296                         continue;
 297
 298                 /* See if fairness allows */
 299                 if (model->params.fairwindow != 0 && !node->has_priority(tid)) {
 300                         bool unfair=false;
 301                         for(int t=0;t<node->get_num_threads();t++) {
 302                                 thread_id_t tother=int_to_id(t);
 303                                 if (node->is_enabled(tother) && node->has_priority(tother)) {
 304                                         unfair=true;
 305                                         break;
 306                                 }
 307                         }
 308                         if (unfair)
 309                                 continue;
 310                 }
 311
 312                 /* Cache the latest backtracking point */
 313                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 314                         priv->next_backtrack = prev;
 315
 316                 /* If this is a new backtracking point, mark the tree */
 317                 if (!node->set_backtrack(tid))
 318                         continue;
 319                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 320                                         prev->get_tid(), t->get_id());
 321                 if (DBG_ENABLED()) {
 322                         prev->print();
 323                         act->print();
 324                 }
 325         }
 326 }
 327
 328 /**
 329  * Returns last backtracking point. The model checker will explore a different
 330  * path for this point in the next execution.
 331  * @return The ModelAction at which the next execution should diverge.
 332  */
 333 ModelAction * ModelChecker::get_next_backtrack()
 334 {
 335         ModelAction *next = priv->next_backtrack;
 336         priv->next_backtrack = NULL;
 337         return next;
 338 }
 339
 340 /**
 341  * Processes a read or rmw model action.
 342  * @param curr is the read model action to process.
 343  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 344  * @return True if processing this read updates the mo_graph.
 345  */
 346 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 347 {
 348         uint64_t value;
 349         bool updated = false;
 350         while (true) {
 351                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 352                 if (reads_from != NULL) {
 353                         mo_graph->startChanges();
 354
 355                         value = reads_from->get_value();
 356                         bool r_status = false;
 357
 358                         if (!second_part_of_rmw) {
 359                                 check_recency(curr, reads_from);
 360                                 r_status = r_modification_order(curr, reads_from);
 361                         }
 362
 363
 364                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 365                                 mo_graph->rollbackChanges();
 366                                 too_many_reads = false;
 367                                 continue;
 368                         }
 369
 370                         curr->read_from(reads_from);
 371                         mo_graph->commitChanges();
 372                         updated |= r_status;
 373                 } else if (!second_part_of_rmw) {
 374                         /* Read from future value */
 375                         value = curr->get_node()->get_future_value();
 376                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 377                         curr->read_from(NULL);
 378                         Promise *valuepromise = new Promise(curr, value, expiration);
 379                         promises->push_back(valuepromise);
 380                 }
 381                 get_thread(curr)->set_return_value(value);
 382                 return updated;
 383         }
 384 }
 385
 386 /**
 387  * Processes a lock, trylock, or unlock model action.  @param curr is
 388  * the read model action to process.
 389  *
 390  * The try lock operation checks whether the lock is taken.  If not,
 391  * it falls to the normal lock operation case.  If so, it returns
 392  * fail.
 393  *
 394  * The lock operation has already been checked that it is enabled, so
 395  * it just grabs the lock and synchronizes with the previous unlock.
 396  *
 397  * The unlock operation has to re-enable all of the threads that are
 398  * waiting on the lock.
 399  *
 400  * @return True if synchronization was updated; false otherwise
 401  */
 402 bool ModelChecker::process_mutex(ModelAction *curr) {
 403         std::mutex *mutex = (std::mutex *)curr->get_location();
 404         struct std::mutex_state *state = mutex->get_state();
 405         switch (curr->get_type()) {
 406         case ATOMIC_TRYLOCK: {
 407                 bool success = !state->islocked;
 408                 curr->set_try_lock(success);
 409                 if (!success) {
 410                         get_thread(curr)->set_return_value(0);
 411                         break;
 412                 }
 413                 get_thread(curr)->set_return_value(1);
 414         }
 415                 //otherwise fall into the lock case
 416         case ATOMIC_LOCK: {
 417                 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
 418                         printf("Lock access before initialization\n");
 419                         set_assert();
 420                 }
 421                 state->islocked = true;
 422                 ModelAction *unlock = get_last_unlock(curr);
 423                 //synchronize with the previous unlock statement
 424                 if (unlock != NULL) {
 425                         curr->synchronize_with(unlock);
 426                         return true;
 427                 }
 428                 break;
 429         }
 430         case ATOMIC_UNLOCK: {
 431                 //unlock the lock
 432                 state->islocked = false;
 433                 //wake up the other threads
 434                 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 435                 //activate all the waiting threads
 436                 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
 437                         scheduler->wake(get_thread(*rit));
 438                 }
 439                 waiters->clear();
 440                 break;
 441         }
 442         default:
 443                 ASSERT(0);
 444         }
 445         return false;
 446 }
 447
 448 /**
 449  * Process a write ModelAction
 450  * @param curr The ModelAction to process
 451  * @return True if the mo_graph was updated or promises were resolved
 452  */
 453 bool ModelChecker::process_write(ModelAction *curr)
 454 {
 455         bool updated_mod_order = w_modification_order(curr);
 456         bool updated_promises = resolve_promises(curr);
 457
 458         if (promises->size() == 0) {
 459                 for (unsigned int i = 0; i < futurevalues->size(); i++) {
 460                         struct PendingFutureValue pfv = (*futurevalues)[i];
 461                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 462                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 463                                 priv->next_backtrack = pfv.act;
 464                 }
 465                 futurevalues->resize(0);
 466         }
 467
 468         mo_graph->commitChanges();
 469         get_thread(curr)->set_return_value(VALUE_NONE);
 470         return updated_mod_order || updated_promises;
 471 }
 472
 473 /**
 474  * @brief Process the current action for thread-related activity
 475  *
 476  * Performs current-action processing for a THREAD_* ModelAction. Proccesses
 477  * may include setting Thread status, completing THREAD_FINISH/THREAD_JOIN
 478  * synchronization, etc.  This function is a no-op for non-THREAD actions
 479  * (e.g., ATOMIC_{READ,WRITE,RMW,LOCK}, etc.)
 480  *
 481  * @param curr The current action
 482  * @return True if synchronization was updated or a thread completed
 483  */
 484 bool ModelChecker::process_thread_action(ModelAction *curr)
 485 {
 486         bool updated = false;
 487
 488         switch (curr->get_type()) {
 489         case THREAD_CREATE: {
 490                 Thread *th = (Thread *)curr->get_location();
 491                 th->set_creation(curr);
 492                 break;
 493         }
 494         case THREAD_JOIN: {
 495                 Thread *waiting, *blocking;
 496                 waiting = get_thread(curr);
 497                 blocking = (Thread *)curr->get_location();
 498                 if (!blocking->is_complete()) {
 499                         blocking->push_wait_list(curr);
 500                         scheduler->sleep(waiting);
 501                 } else {
 502                         do_complete_join(curr);
 503                         updated = true; /* trigger rel-seq checks */
 504                 }
 505                 break;
 506         }
 507         case THREAD_FINISH: {
 508                 Thread *th = get_thread(curr);
 509                 while (!th->wait_list_empty()) {
 510                         ModelAction *act = th->pop_wait_list();
 511                         Thread *wake = get_thread(act);
 512                         scheduler->wake(wake);
 513                         do_complete_join(act);
 514                         updated = true; /* trigger rel-seq checks */
 515                 }
 516                 th->complete();
 517                 updated = true; /* trigger rel-seq checks */
 518                 break;
 519         }
 520         case THREAD_START: {
 521                 check_promises(NULL, curr->get_cv());
 522                 break;
 523         }
 524         default:
 525                 break;
 526         }
 527
 528         return updated;
 529 }
 530
 531 /**
 532  * Initialize the current action by performing one or more of the following
 533  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 534  * in the NodeStack, manipulating backtracking sets, allocating and
 535  * initializing clock vectors, and computing the promises to fulfill.
 536  *
 537  * @param curr The current action, as passed from the user context; may be
 538  * freed/invalidated after the execution of this function
 539  * @return The current action, as processed by the ModelChecker. Is only the
 540  * same as the parameter @a curr if this is a newly-explored action.
 541  */
 542 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 543 {
 544         ModelAction *newcurr;
 545
 546         if (curr->is_rmwc() || curr->is_rmw()) {
 547                 newcurr = process_rmw(curr);
 548                 delete curr;
 549
 550                 if (newcurr->is_rmw())
 551                         compute_promises(newcurr);
 552                 return newcurr;
 553         }
 554
 555         curr->set_seq_number(get_next_seq_num());
 556
 557         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 558         if (newcurr) {
 559                 /* First restore type and order in case of RMW operation */
 560                 if (curr->is_rmwr())
 561                         newcurr->copy_typeandorder(curr);
 562
 563                 ASSERT(curr->get_location() == newcurr->get_location());
 564                 newcurr->copy_from_new(curr);
 565
 566                 /* Discard duplicate ModelAction; use action from NodeStack */
 567                 delete curr;
 568
 569                 /* Always compute new clock vector */
 570                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 571         } else {
 572                 newcurr = curr;
 573
 574                 /* Always compute new clock vector */
 575                 newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 576                 /*
 577                  * Perform one-time actions when pushing new ModelAction onto
 578                  * NodeStack
 579                  */
 580                 if (newcurr->is_write())
 581                         compute_promises(newcurr);
 582         }
 583         return newcurr;
 584 }
 585
 586 /**
 587  * This method checks whether a model action is enabled at the given point.
 588  * At this point, it checks whether a lock operation would be successful at this point.
 589  * If not, it puts the thread in a waiter list.
 590  * @param curr is the ModelAction to check whether it is enabled.
 591  * @return a bool that indicates whether the action is enabled.
 592  */
 593 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 594         if (curr->is_lock()) {
 595                 std::mutex * lock = (std::mutex *)curr->get_location();
 596                 struct std::mutex_state * state = lock->get_state();
 597                 if (state->islocked) {
 598                         //Stick the action in the appropriate waiting queue
 599                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 600                         return false;
 601                 }
 602         }
 603
 604         return true;
 605 }
 606
 607 /**
 608  * This is the heart of the model checker routine. It performs model-checking
 609  * actions corresponding to a given "current action." Among other processes, it
 610  * calculates reads-from relationships, updates synchronization clock vectors,
 611  * forms a memory_order constraints graph, and handles replay/backtrack
 612  * execution when running permutations of previously-observed executions.
 613  *
 614  * @param curr The current action to process
 615  * @return The next Thread that must be executed. May be NULL if ModelChecker
 616  * makes no choice (e.g., according to replay execution, combining RMW actions,
 617  * etc.)
 618  */
 619 Thread * ModelChecker::check_current_action(ModelAction *curr)
 620 {
 621         ASSERT(curr);
 622
 623         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 624
 625         if (!check_action_enabled(curr)) {
 626                 /* Make the execution look like we chose to run this action
 627                  * much later, when a lock is actually available to release */
 628                 get_current_thread()->set_pending(curr);
 629                 scheduler->sleep(get_current_thread());
 630                 return get_next_thread(NULL);
 631         }
 632
 633         ModelAction *newcurr = initialize_curr_action(curr);
 634
 635         /* Add the action to lists before any other model-checking tasks */
 636         if (!second_part_of_rmw)
 637                 add_action_to_lists(newcurr);
 638
 639         /* Build may_read_from set for newly-created actions */
 640         if (curr == newcurr && curr->is_read())
 641                 build_reads_from_past(curr);
 642         curr = newcurr;
 643
 644         /* Initialize work_queue with the "current action" work */
 645         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 646
 647         while (!work_queue.empty()) {
 648                 WorkQueueEntry work = work_queue.front();
 649                 work_queue.pop_front();
 650
 651                 switch (work.type) {
 652                 case WORK_CHECK_CURR_ACTION: {
 653                         ModelAction *act = work.action;
 654                         bool update = false; /* update this location's release seq's */
 655                         bool update_all = false; /* update all release seq's */
 656
 657                         if (process_thread_action(curr))
 658                                 update_all = true;
 659
 660                         if (act->is_read() && process_read(act, second_part_of_rmw))
 661                                 update = true;
 662
 663                         if (act->is_write() && process_write(act))
 664                                 update = true;
 665
 666                         if (act->is_mutex_op() && process_mutex(act))
 667                                 update_all = true;
 668
 669                         if (update_all)
 670                                 work_queue.push_back(CheckRelSeqWorkEntry(NULL));
 671                         else if (update)
 672                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 673                         break;
 674                 }
 675                 case WORK_CHECK_RELEASE_SEQ:
 676                         resolve_release_sequences(work.location, &work_queue);
 677                         break;
 678                 case WORK_CHECK_MO_EDGES: {
 679                         /** @todo Complete verification of work_queue */
 680                         ModelAction *act = work.action;
 681                         bool updated = false;
 682
 683                         if (act->is_read()) {
 684                                 const ModelAction *rf = act->get_reads_from();
 685                                 if (rf != NULL && r_modification_order(act, rf))
 686                                         updated = true;
 687                         }
 688                         if (act->is_write()) {
 689                                 if (w_modification_order(act))
 690                                         updated = true;
 691                         }
 692                         mo_graph->commitChanges();
 693
 694                         if (updated)
 695                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 696                         break;
 697                 }
 698                 default:
 699                         ASSERT(false);
 700                         break;
 701                 }
 702         }
 703
 704         check_curr_backtracking(curr);
 705
 706         set_backtracking(curr);
 707
 708         return get_next_thread(curr);
 709 }
 710
 711 /**
 712  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 713  * operation from the Thread it is joining with. Must be called after the
 714  * completion of the Thread in question.
 715  * @param join The THREAD_JOIN action
 716  */
 717 void ModelChecker::do_complete_join(ModelAction *join)
 718 {
 719         Thread *blocking = (Thread *)join->get_location();
 720         ModelAction *act = get_last_action(blocking->get_id());
 721         join->synchronize_with(act);
 722 }
 723
 724 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 725         Node *currnode = curr->get_node();
 726         Node *parnode = currnode->get_parent();
 727
 728         if ((!parnode->backtrack_empty() ||
 729                          !currnode->read_from_empty() ||
 730                          !currnode->future_value_empty() ||
 731                          !currnode->promise_empty())
 732                         && (!priv->next_backtrack ||
 733                                         *curr > *priv->next_backtrack)) {
 734                 priv->next_backtrack = curr;
 735         }
 736 }
 737
 738 bool ModelChecker::promises_expired() {
 739         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 740                 Promise *promise = (*promises)[promise_index];
 741                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 742                         return true;
 743                 }
 744         }
 745         return false;
 746 }
 747
 748 /** @return whether the current partial trace must be a prefix of a
 749  * feasible trace. */
 750 bool ModelChecker::isfeasibleprefix() {
 751         return promises->size() == 0 && pending_acq_rel_seq->size() == 0;
 752 }
 753
 754 /** @return whether the current partial trace is feasible. */
 755 bool ModelChecker::isfeasible() {
 756         if (DBG_ENABLED() && mo_graph->checkForRMWViolation())
 757                 DEBUG("Infeasible: RMW violation\n");
 758
 759         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 760 }
 761
 762 /** @return whether the current partial trace is feasible other than
 763  * multiple RMW reading from the same store. */
 764 bool ModelChecker::isfeasibleotherthanRMW() {
 765         if (DBG_ENABLED()) {
 766                 if (mo_graph->checkForCycles())
 767                         DEBUG("Infeasible: modification order cycles\n");
 768                 if (failed_promise)
 769                         DEBUG("Infeasible: failed promise\n");
 770                 if (too_many_reads)
 771                         DEBUG("Infeasible: too many reads\n");
 772                 if (bad_synchronization)
 773                         DEBUG("Infeasible: bad synchronization ordering\n");
 774                 if (promises_expired())
 775                         DEBUG("Infeasible: promises expired\n");
 776         }
 777         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !bad_synchronization && !promises_expired();
 778 }
 779
 780 /** Returns whether the current completed trace is feasible. */
 781 bool ModelChecker::isfinalfeasible() {
 782         if (DBG_ENABLED() && promises->size() != 0)
 783                 DEBUG("Infeasible: unrevolved promises\n");
 784
 785         return isfeasible() && promises->size() == 0;
 786 }
 787
 788 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 789 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 790         int tid = id_to_int(act->get_tid());
 791         ModelAction *lastread = get_last_action(tid);
 792         lastread->process_rmw(act);
 793         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 794                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 795                 mo_graph->commitChanges();
 796         }
 797         return lastread;
 798 }
 799
 800 /**
 801  * Checks whether a thread has read from the same write for too many times
 802  * without seeing the effects of a later write.
 803  *
 804  * Basic idea:
 805  * 1) there must a different write that we could read from that would satisfy the modification order,
 806  * 2) we must have read from the same value in excess of maxreads times, and
 807  * 3) that other write must have been in the reads_from set for maxreads times.
 808  *
 809  * If so, we decide that the execution is no longer feasible.
 810  */
 811 void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) {
 812         if (params.maxreads != 0) {
 813
 814                 if (curr->get_node()->get_read_from_size() <= 1)
 815                         return;
 816                 //Must make sure that execution is currently feasible...  We could
 817                 //accidentally clear by rolling back
 818                 if (!isfeasible())
 819                         return;
 820                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 821                 int tid = id_to_int(curr->get_tid());
 822
 823                 /* Skip checks */
 824                 if ((int)thrd_lists->size() <= tid)
 825                         return;
 826                 action_list_t *list = &(*thrd_lists)[tid];
 827
 828                 action_list_t::reverse_iterator rit = list->rbegin();
 829                 /* Skip past curr */
 830                 for (; (*rit) != curr; rit++)
 831                         ;
 832                 /* go past curr now */
 833                 rit++;
 834
 835                 action_list_t::reverse_iterator ritcopy = rit;
 836                 //See if we have enough reads from the same value
 837                 int count = 0;
 838                 for (; count < params.maxreads; rit++,count++) {
 839                         if (rit==list->rend())
 840                                 return;
 841                         ModelAction *act = *rit;
 842                         if (!act->is_read())
 843                                 return;
 844
 845                         if (act->get_reads_from() != rf)
 846                                 return;
 847                         if (act->get_node()->get_read_from_size() <= 1)
 848                                 return;
 849                 }
 850                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 851                         //Get write
 852                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 853
 854                         //Need a different write
 855                         if (write==rf)
 856                                 continue;
 857
 858                         /* Test to see whether this is a feasible write to read from*/
 859                         mo_graph->startChanges();
 860                         r_modification_order(curr, write);
 861                         bool feasiblereadfrom = isfeasible();
 862                         mo_graph->rollbackChanges();
 863
 864                         if (!feasiblereadfrom)
 865                                 continue;
 866                         rit = ritcopy;
 867
 868                         bool feasiblewrite = true;
 869                         //new we need to see if this write works for everyone
 870
 871                         for (int loop = count; loop>0; loop--,rit++) {
 872                                 ModelAction *act=*rit;
 873                                 bool foundvalue = false;
 874                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 875                                         if (act->get_node()->get_read_from_at(i)==write) {
 876                                                 foundvalue = true;
 877                                                 break;
 878                                         }
 879                                 }
 880                                 if (!foundvalue) {
 881                                         feasiblewrite = false;
 882                                         break;
 883                                 }
 884                         }
 885                         if (feasiblewrite) {
 886                                 too_many_reads = true;
 887                                 return;
 888                         }
 889                 }
 890         }
 891 }
 892
 893 /**
 894  * Updates the mo_graph with the constraints imposed from the current
 895  * read.
 896  *
 897  * Basic idea is the following: Go through each other thread and find
 898  * the lastest action that happened before our read.  Two cases:
 899  *
 900  * (1) The action is a write => that write must either occur before
 901  * the write we read from or be the write we read from.
 902  *
 903  * (2) The action is a read => the write that that action read from
 904  * must occur before the write we read from or be the same write.
 905  *
 906  * @param curr The current action. Must be a read.
 907  * @param rf The action that curr reads from. Must be a write.
 908  * @return True if modification order edges were added; false otherwise
 909  */
 910 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 911 {
 912         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 913         unsigned int i;
 914         bool added = false;
 915         ASSERT(curr->is_read());
 916
 917         /* Iterate over all threads */
 918         for (i = 0; i < thrd_lists->size(); i++) {
 919                 /* Iterate over actions in thread, starting from most recent */
 920                 action_list_t *list = &(*thrd_lists)[i];
 921                 action_list_t::reverse_iterator rit;
 922                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 923                         ModelAction *act = *rit;
 924
 925                         /*
 926                          * Include at most one act per-thread that "happens
 927                          * before" curr. Don't consider reflexively.
 928                          */
 929                         if (act->happens_before(curr) && act != curr) {
 930                                 if (act->is_write()) {
 931                                         if (rf != act) {
 932                                                 mo_graph->addEdge(act, rf);
 933                                                 added = true;
 934                                         }
 935                                 } else {
 936                                         const ModelAction *prevreadfrom = act->get_reads_from();
 937                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 938                                                 mo_graph->addEdge(prevreadfrom, rf);
 939                                                 added = true;
 940                                         }
 941                                 }
 942                                 break;
 943                         }
 944                 }
 945         }
 946
 947         return added;
 948 }
 949
 950 /** This method fixes up the modification order when we resolve a
 951  *  promises.  The basic problem is that actions that occur after the
 952  *  read curr could not property add items to the modification order
 953  *  for our read.
 954  *
 955  *  So for each thread, we find the earliest item that happens after
 956  *  the read curr.  This is the item we have to fix up with additional
 957  *  constraints.  If that action is write, we add a MO edge between
 958  *  the Action rf and that action.  If the action is a read, we add a
 959  *  MO edge between the Action rf, and whatever the read accessed.
 960  *
 961  * @param curr is the read ModelAction that we are fixing up MO edges for.
 962  * @param rf is the write ModelAction that curr reads from.
 963  *
 964  */
 965 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 966 {
 967         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 968         unsigned int i;
 969         ASSERT(curr->is_read());
 970
 971         /* Iterate over all threads */
 972         for (i = 0; i < thrd_lists->size(); i++) {
 973                 /* Iterate over actions in thread, starting from most recent */
 974                 action_list_t *list = &(*thrd_lists)[i];
 975                 action_list_t::reverse_iterator rit;
 976                 ModelAction *lastact = NULL;
 977
 978                 /* Find last action that happens after curr that is either not curr or a rmw */
 979                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 980                         ModelAction *act = *rit;
 981                         if (curr->happens_before(act) && (curr != act || curr->is_rmw())) {
 982                                 lastact = act;
 983                         } else
 984                                 break;
 985                 }
 986
 987                         /* Include at most one act per-thread that "happens before" curr */
 988                 if (lastact != NULL) {
 989                         if (lastact==curr) {
 990                                 //Case 1: The resolved read is a RMW, and we need to make sure
 991                                 //that the write portion of the RMW mod order after rf
 992
 993                                 mo_graph->addEdge(rf, lastact);
 994                         } else if (lastact->is_read()) {
 995                                 //Case 2: The resolved read is a normal read and the next
 996                                 //operation is a read, and we need to make sure the value read
 997                                 //is mod ordered after rf
 998
 999                                 const ModelAction *postreadfrom = lastact->get_reads_from();
1000                                 if (postreadfrom != NULL&&rf != postreadfrom)
1001                                         mo_graph->addEdge(rf, postreadfrom);
1002                         } else {
1003                                 //Case 3: The resolved read is a normal read and the next
1004                                 //operation is a write, and we need to make sure that the
1005                                 //write is mod ordered after rf
1006                                 if (lastact!=rf)
1007                                         mo_graph->addEdge(rf, lastact);
1008                         }
1009                         break;
1010                 }
1011         }
1012 }
1013
1014 /**
1015  * Updates the mo_graph with the constraints imposed from the current write.
1016  *
1017  * Basic idea is the following: Go through each other thread and find
1018  * the lastest action that happened before our write.  Two cases:
1019  *
1020  * (1) The action is a write => that write must occur before
1021  * the current write
1022  *
1023  * (2) The action is a read => the write that that action read from
1024  * must occur before the current write.
1025  *
1026  * This method also handles two other issues:
1027  *
1028  * (I) Sequential Consistency: Making sure that if the current write is
1029  * seq_cst, that it occurs after the previous seq_cst write.
1030  *
1031  * (II) Sending the write back to non-synchronizing reads.
1032  *
1033  * @param curr The current action. Must be a write.
1034  * @return True if modification order edges were added; false otherwise
1035  */
1036 bool ModelChecker::w_modification_order(ModelAction *curr)
1037 {
1038         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1039         unsigned int i;
1040         bool added = false;
1041         ASSERT(curr->is_write());
1042
1043         if (curr->is_seqcst()) {
1044                 /* We have to at least see the last sequentially consistent write,
1045                          so we are initialized. */
1046                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
1047                 if (last_seq_cst != NULL) {
1048                         mo_graph->addEdge(last_seq_cst, curr);
1049                         added = true;
1050                 }
1051         }
1052
1053         /* Iterate over all threads */
1054         for (i = 0; i < thrd_lists->size(); i++) {
1055                 /* Iterate over actions in thread, starting from most recent */
1056                 action_list_t *list = &(*thrd_lists)[i];
1057                 action_list_t::reverse_iterator rit;
1058                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1059                         ModelAction *act = *rit;
1060                         if (act == curr) {
1061                                 /*
1062                                  * If RMW, we already have all relevant edges,
1063                                  * so just skip to next thread.
1064                                  * If normal write, we need to look at earlier
1065                                  * actions, so continue processing list.
1066                                  */
1067                                 if (curr->is_rmw())
1068                                         break;
1069                                 else
1070                                         continue;
1071                         }
1072
1073                         /*
1074                          * Include at most one act per-thread that "happens
1075                          * before" curr
1076                          */
1077                         if (act->happens_before(curr)) {
1078                                 /*
1079                                  * Note: if act is RMW, just add edge:
1080                                  *   act --mo--> curr
1081                                  * The following edge should be handled elsewhere:
1082                                  *   readfrom(act) --mo--> act
1083                                  */
1084                                 if (act->is_write())
1085                                         mo_graph->addEdge(act, curr);
1086                                 else if (act->is_read() && act->get_reads_from() != NULL)
1087                                         mo_graph->addEdge(act->get_reads_from(), curr);
1088                                 added = true;
1089                                 break;
1090                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
1091                                                      !act->same_thread(curr)) {
1092                                 /* We have an action that:
1093                                    (1) did not happen before us
1094                                    (2) is a read and we are a write
1095                                    (3) cannot synchronize with us
1096                                    (4) is in a different thread
1097                                    =>
1098                                    that read could potentially read from our write.
1099                                  */
1100                                 if (thin_air_constraint_may_allow(curr, act)) {
1101                                         if (isfeasible() ||
1102                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1103                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1104                                                 futurevalues->push_back(pfv);
1105                                         }
1106                                 }
1107                         }
1108                 }
1109         }
1110
1111         return added;
1112 }
1113
1114 /** Arbitrary reads from the future are not allowed.  Section 29.3
1115  * part 9 places some constraints.  This method checks one result of constraint
1116  * constraint.  Others require compiler support. */
1117 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1118         if (!writer->is_rmw())
1119                 return true;
1120
1121         if (!reader->is_rmw())
1122                 return true;
1123
1124         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1125                 if (search == reader)
1126                         return false;
1127                 if (search->get_tid() == reader->get_tid() &&
1128                                 search->happens_before(reader))
1129                         break;
1130         }
1131
1132         return true;
1133 }
1134
1135 /**
1136  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1137  * The ModelAction under consideration is expected to be taking part in
1138  * release/acquire synchronization as an object of the "reads from" relation.
1139  * Note that this can only provide release sequence support for RMW chains
1140  * which do not read from the future, as those actions cannot be traced until
1141  * their "promise" is fulfilled. Similarly, we may not even establish the
1142  * presence of a release sequence with certainty, as some modification order
1143  * constraints may be decided further in the future. Thus, this function
1144  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1145  * and a boolean representing certainty.
1146  *
1147  * @todo Finish lazy updating, when promises are fulfilled in the future
1148  * @param rf The action that might be part of a release sequence. Must be a
1149  * write.
1150  * @param release_heads A pass-by-reference style return parameter.  After
1151  * execution of this function, release_heads will contain the heads of all the
1152  * relevant release sequences, if any exists
1153  * @return true, if the ModelChecker is certain that release_heads is complete;
1154  * false otherwise
1155  */
1156 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1157 {
1158         /* Only check for release sequences if there are no cycles */
1159         if (mo_graph->checkForCycles())
1160                 return false;
1161
1162         while (rf) {
1163                 ASSERT(rf->is_write());
1164
1165                 if (rf->is_release())
1166                         release_heads->push_back(rf);
1167                 if (!rf->is_rmw())
1168                         break; /* End of RMW chain */
1169
1170                 /** @todo Need to be smarter here...  In the linux lock
1171                  * example, this will run to the beginning of the program for
1172                  * every acquire. */
1173                 /** @todo The way to be smarter here is to keep going until 1
1174                  * thread has a release preceded by an acquire and you've seen
1175                  *       both. */
1176
1177                 /* acq_rel RMW is a sufficient stopping condition */
1178                 if (rf->is_acquire() && rf->is_release())
1179                         return true; /* complete */
1180
1181                 rf = rf->get_reads_from();
1182         };
1183         if (!rf) {
1184                 /* read from future: need to settle this later */
1185                 return false; /* incomplete */
1186         }
1187
1188         if (rf->is_release())
1189                 return true; /* complete */
1190
1191         /* else relaxed write; check modification order for contiguous subsequence
1192          * -> rf must be same thread as release */
1193         int tid = id_to_int(rf->get_tid());
1194         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1195         action_list_t *list = &(*thrd_lists)[tid];
1196         action_list_t::const_reverse_iterator rit;
1197
1198         /* Find rf in the thread list */
1199         rit = std::find(list->rbegin(), list->rend(), rf);
1200         ASSERT(rit != list->rend());
1201
1202         /* Find the last write/release */
1203         for (; rit != list->rend(); rit++)
1204                 if ((*rit)->is_release())
1205                         break;
1206         if (rit == list->rend()) {
1207                 /* No write-release in this thread */
1208                 return true; /* complete */
1209         }
1210         ModelAction *release = *rit;
1211
1212         ASSERT(rf->same_thread(release));
1213
1214         bool certain = true;
1215         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1216                 if (id_to_int(rf->get_tid()) == (int)i)
1217                         continue;
1218                 list = &(*thrd_lists)[i];
1219
1220                 /* Can we ensure no future writes from this thread may break
1221                  * the release seq? */
1222                 bool future_ordered = false;
1223
1224                 ModelAction *last = get_last_action(int_to_id(i));
1225                 if (last && (rf->happens_before(last) ||
1226                                 last->get_type() == THREAD_FINISH))
1227                         future_ordered = true;
1228
1229                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1230                         const ModelAction *act = *rit;
1231                         /* Reach synchronization -> this thread is complete */
1232                         if (act->happens_before(release))
1233                                 break;
1234                         if (rf->happens_before(act)) {
1235                                 future_ordered = true;
1236                                 continue;
1237                         }
1238
1239                         /* Only writes can break release sequences */
1240                         if (!act->is_write())
1241                                 continue;
1242
1243                         /* Check modification order */
1244                         if (mo_graph->checkReachable(rf, act)) {
1245                                 /* rf --mo--> act */
1246                                 future_ordered = true;
1247                                 continue;
1248                         }
1249                         if (mo_graph->checkReachable(act, release))
1250                                 /* act --mo--> release */
1251                                 break;
1252                         if (mo_graph->checkReachable(release, act) &&
1253                                       mo_graph->checkReachable(act, rf)) {
1254                                 /* release --mo-> act --mo--> rf */
1255                                 return true; /* complete */
1256                         }
1257                         certain = false;
1258                 }
1259                 if (!future_ordered)
1260                         return false; /* This thread is uncertain */
1261         }
1262
1263         if (certain)
1264                 release_heads->push_back(release);
1265         return certain;
1266 }
1267
1268 /**
1269  * A public interface for getting the release sequence head(s) with which a
1270  * given ModelAction must synchronize. This function only returns a non-empty
1271  * result when it can locate a release sequence head with certainty. Otherwise,
1272  * it may mark the internal state of the ModelChecker so that it will handle
1273  * the release sequence at a later time, causing @a act to update its
1274  * synchronization at some later point in execution.
1275  * @param act The 'acquire' action that may read from a release sequence
1276  * @param release_heads A pass-by-reference return parameter. Will be filled
1277  * with the head(s) of the release sequence(s), if they exists with certainty.
1278  * @see ModelChecker::release_seq_head
1279  */
1280 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1281 {
1282         const ModelAction *rf = act->get_reads_from();
1283         bool complete;
1284         complete = release_seq_head(rf, release_heads);
1285         if (!complete) {
1286                 /* add act to 'lazy checking' list */
1287                 pending_acq_rel_seq->push_back(act);
1288         }
1289 }
1290
1291 /**
1292  * Attempt to resolve all stashed operations that might synchronize with a
1293  * release sequence for a given location. This implements the "lazy" portion of
1294  * determining whether or not a release sequence was contiguous, since not all
1295  * modification order information is present at the time an action occurs.
1296  *
1297  * @param location The location/object that should be checked for release
1298  * sequence resolutions. A NULL value means to check all locations.
1299  * @param work_queue The work queue to which to add work items as they are
1300  * generated
1301  * @return True if any updates occurred (new synchronization, new mo_graph
1302  * edges)
1303  */
1304 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1305 {
1306         bool updated = false;
1307         std::vector<ModelAction *>::iterator it = pending_acq_rel_seq->begin();
1308         while (it != pending_acq_rel_seq->end()) {
1309                 ModelAction *act = *it;
1310
1311                 /* Only resolve sequences on the given location, if provided */
1312                 if (location && act->get_location() != location) {
1313                         it++;
1314                         continue;
1315                 }
1316
1317                 const ModelAction *rf = act->get_reads_from();
1318                 rel_heads_list_t release_heads;
1319                 bool complete;
1320                 complete = release_seq_head(rf, &release_heads);
1321                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1322                         if (!act->has_synchronized_with(release_heads[i])) {
1323                                 if (act->synchronize_with(release_heads[i]))
1324                                         updated = true;
1325                                 else
1326                                         set_bad_synchronization();
1327                         }
1328                 }
1329
1330                 if (updated) {
1331                         /* Re-check all pending release sequences */
1332                         work_queue->push_back(CheckRelSeqWorkEntry(NULL));
1333                         /* Re-check act for mo_graph edges */
1334                         work_queue->push_back(MOEdgeWorkEntry(act));
1335
1336                         /* propagate synchronization to later actions */
1337                         action_list_t::reverse_iterator rit = action_trace->rbegin();
1338                         for (; (*rit) != act; rit++) {
1339                                 ModelAction *propagate = *rit;
1340                                 if (act->happens_before(propagate)) {
1341                                         propagate->synchronize_with(act);
1342                                         /* Re-check 'propagate' for mo_graph edges */
1343                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1344                                 }
1345                         }
1346                 }
1347                 if (complete)
1348                         it = pending_acq_rel_seq->erase(it);
1349                 else
1350                         it++;
1351         }
1352
1353         // If we resolved promises or data races, see if we have realized a data race.
1354         if (checkDataRaces()) {
1355                 set_assert();
1356         }
1357
1358         return updated;
1359 }
1360
1361 /**
1362  * Performs various bookkeeping operations for the current ModelAction. For
1363  * instance, adds action to the per-object, per-thread action vector and to the
1364  * action trace list of all thread actions.
1365  *
1366  * @param act is the ModelAction to add.
1367  */
1368 void ModelChecker::add_action_to_lists(ModelAction *act)
1369 {
1370         int tid = id_to_int(act->get_tid());
1371         action_trace->push_back(act);
1372
1373         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1374
1375         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1376         if (tid >= (int)vec->size())
1377                 vec->resize(priv->next_thread_id);
1378         (*vec)[tid].push_back(act);
1379
1380         if ((int)thrd_last_action->size() <= tid)
1381                 thrd_last_action->resize(get_num_threads());
1382         (*thrd_last_action)[tid] = act;
1383 }
1384
1385 /**
1386  * @brief Get the last action performed by a particular Thread
1387  * @param tid The thread ID of the Thread in question
1388  * @return The last action in the thread
1389  */
1390 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1391 {
1392         int threadid = id_to_int(tid);
1393         if (threadid < (int)thrd_last_action->size())
1394                 return (*thrd_last_action)[id_to_int(tid)];
1395         else
1396                 return NULL;
1397 }
1398
1399 /**
1400  * Gets the last memory_order_seq_cst write (in the total global sequence)
1401  * performed on a particular object (i.e., memory location), not including the
1402  * current action.
1403  * @param curr The current ModelAction; also denotes the object location to
1404  * check
1405  * @return The last seq_cst write
1406  */
1407 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1408 {
1409         void *location = curr->get_location();
1410         action_list_t *list = obj_map->get_safe_ptr(location);
1411         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1412         action_list_t::reverse_iterator rit;
1413         for (rit = list->rbegin(); rit != list->rend(); rit++)
1414                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1415                         return *rit;
1416         return NULL;
1417 }
1418
1419 /**
1420  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1421  * location). This function identifies the mutex according to the current
1422  * action, which is presumed to perform on the same mutex.
1423  * @param curr The current ModelAction; also denotes the object location to
1424  * check
1425  * @return The last unlock operation
1426  */
1427 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1428 {
1429         void *location = curr->get_location();
1430         action_list_t *list = obj_map->get_safe_ptr(location);
1431         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1432         action_list_t::reverse_iterator rit;
1433         for (rit = list->rbegin(); rit != list->rend(); rit++)
1434                 if ((*rit)->is_unlock())
1435                         return *rit;
1436         return NULL;
1437 }
1438
1439 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1440 {
1441         ModelAction *parent = get_last_action(tid);
1442         if (!parent)
1443                 parent = get_thread(tid)->get_creation();
1444         return parent;
1445 }
1446
1447 /**
1448  * Returns the clock vector for a given thread.
1449  * @param tid The thread whose clock vector we want
1450  * @return Desired clock vector
1451  */
1452 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1453 {
1454         return get_parent_action(tid)->get_cv();
1455 }
1456
1457 /**
1458  * Resolve a set of Promises with a current write. The set is provided in the
1459  * Node corresponding to @a write.
1460  * @param write The ModelAction that is fulfilling Promises
1461  * @return True if promises were resolved; false otherwise
1462  */
1463 bool ModelChecker::resolve_promises(ModelAction *write)
1464 {
1465         bool resolved = false;
1466
1467         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1468                 Promise *promise = (*promises)[promise_index];
1469                 if (write->get_node()->get_promise(i)) {
1470                         ModelAction *read = promise->get_action();
1471                         if (read->is_rmw()) {
1472                                 mo_graph->addRMWEdge(write, read);
1473                         }
1474                         read->read_from(write);
1475                         //First fix up the modification order for actions that happened
1476                         //before the read
1477                         r_modification_order(read, write);
1478                         //Next fix up the modification order for actions that happened
1479                         //after the read.
1480                         post_r_modification_order(read, write);
1481                         //Make sure the promise's value matches the write's value
1482                         ASSERT(promise->get_value() == write->get_value());
1483
1484                         promises->erase(promises->begin() + promise_index);
1485                         resolved = true;
1486                 } else
1487                         promise_index++;
1488         }
1489         return resolved;
1490 }
1491
1492 /**
1493  * Compute the set of promises that could potentially be satisfied by this
1494  * action. Note that the set computation actually appears in the Node, not in
1495  * ModelChecker.
1496  * @param curr The ModelAction that may satisfy promises
1497  */
1498 void ModelChecker::compute_promises(ModelAction *curr)
1499 {
1500         for (unsigned int i = 0; i < promises->size(); i++) {
1501                 Promise *promise = (*promises)[i];
1502                 const ModelAction *act = promise->get_action();
1503                 if (!act->happens_before(curr) &&
1504                                 act->is_read() &&
1505                                 !act->is_synchronizing(curr) &&
1506                                 !act->same_thread(curr) &&
1507                                 promise->get_value() == curr->get_value()) {
1508                         curr->get_node()->set_promise(i);
1509                 }
1510         }
1511 }
1512
1513 /** Checks promises in response to change in ClockVector Threads. */
1514 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1515 {
1516         for (unsigned int i = 0; i < promises->size(); i++) {
1517                 Promise *promise = (*promises)[i];
1518                 const ModelAction *act = promise->get_action();
1519                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1520                                 merge_cv->synchronized_since(act)) {
1521                         //This thread is no longer able to send values back to satisfy the promise
1522                         int num_synchronized_threads = promise->increment_threads();
1523                         if (num_synchronized_threads == get_num_threads()) {
1524                                 //Promise has failed
1525                                 failed_promise = true;
1526                                 return;
1527                         }
1528                 }
1529         }
1530 }
1531
1532 /**
1533  * Build up an initial set of all past writes that this 'read' action may read
1534  * from. This set is determined by the clock vector's "happens before"
1535  * relationship.
1536  * @param curr is the current ModelAction that we are exploring; it must be a
1537  * 'read' operation.
1538  */
1539 void ModelChecker::build_reads_from_past(ModelAction *curr)
1540 {
1541         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1542         unsigned int i;
1543         ASSERT(curr->is_read());
1544
1545         ModelAction *last_seq_cst = NULL;
1546
1547         /* Track whether this object has been initialized */
1548         bool initialized = false;
1549
1550         if (curr->is_seqcst()) {
1551                 last_seq_cst = get_last_seq_cst(curr);
1552                 /* We have to at least see the last sequentially consistent write,
1553                          so we are initialized. */
1554                 if (last_seq_cst != NULL)
1555                         initialized = true;
1556         }
1557
1558         /* Iterate over all threads */
1559         for (i = 0; i < thrd_lists->size(); i++) {
1560                 /* Iterate over actions in thread, starting from most recent */
1561                 action_list_t *list = &(*thrd_lists)[i];
1562                 action_list_t::reverse_iterator rit;
1563                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1564                         ModelAction *act = *rit;
1565
1566                         /* Only consider 'write' actions */
1567                         if (!act->is_write() || act == curr)
1568                                 continue;
1569
1570                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1571                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1572                                 DEBUG("Adding action to may_read_from:\n");
1573                                 if (DBG_ENABLED()) {
1574                                         act->print();
1575                                         curr->print();
1576                                 }
1577                                 curr->get_node()->add_read_from(act);
1578                         }
1579
1580                         /* Include at most one act per-thread that "happens before" curr */
1581                         if (act->happens_before(curr)) {
1582                                 initialized = true;
1583                                 break;
1584                         }
1585                 }
1586         }
1587
1588         if (!initialized) {
1589                 /** @todo Need a more informative way of reporting errors. */
1590                 printf("ERROR: may read from uninitialized atomic\n");
1591         }
1592
1593         if (DBG_ENABLED() || !initialized) {
1594                 printf("Reached read action:\n");
1595                 curr->print();
1596                 printf("Printing may_read_from\n");
1597                 curr->get_node()->print_may_read_from();
1598                 printf("End printing may_read_from\n");
1599         }
1600
1601         ASSERT(initialized);
1602 }
1603
1604 static void print_list(action_list_t *list)
1605 {
1606         action_list_t::iterator it;
1607
1608         printf("---------------------------------------------------------------------\n");
1609         printf("Trace:\n");
1610
1611         for (it = list->begin(); it != list->end(); it++) {
1612                 (*it)->print();
1613         }
1614         printf("---------------------------------------------------------------------\n");
1615 }
1616
1617 #if SUPPORT_MOD_ORDER_DUMP
1618 void ModelChecker::dumpGraph(char *filename) {
1619         char buffer[200];
1620   sprintf(buffer, "%s.dot",filename);
1621   FILE *file=fopen(buffer, "w");
1622   fprintf(file, "digraph %s {\n",filename);
1623         mo_graph->dumpNodes(file);
1624         ModelAction ** thread_array=(ModelAction **)model_calloc(1, sizeof(ModelAction *)*get_num_threads());
1625
1626         for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) {
1627                 ModelAction *action=*it;
1628                 if (action->is_read()) {
1629                         fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(),action->get_seq_number(), action->get_tid());
1630                         fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number());
1631                 }
1632                 if (thread_array[action->get_tid()] != NULL) {
1633                         fprintf(file, "N%u -> N%u[label=\"sb\", color=blue];\n", thread_array[action->get_tid()]->get_seq_number(), action->get_seq_number());
1634                 }
1635
1636                 thread_array[action->get_tid()]=action;
1637         }
1638   fprintf(file,"}\n");
1639         model_free(thread_array);
1640   fclose(file);
1641 }
1642 #endif
1643
1644 void ModelChecker::print_summary()
1645 {
1646         printf("\n");
1647         printf("Number of executions: %d\n", num_executions);
1648         printf("Number of feasible executions: %d\n", num_feasible_executions);
1649         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1650
1651 #if SUPPORT_MOD_ORDER_DUMP
1652         scheduler->print();
1653         char buffername[100];
1654         sprintf(buffername, "exec%04u", num_executions);
1655         mo_graph->dumpGraphToFile(buffername);
1656         sprintf(buffername, "graph%04u", num_executions);
1657   dumpGraph(buffername);
1658 #endif
1659
1660         if (!isfinalfeasible())
1661                 printf("INFEASIBLE EXECUTION!\n");
1662         print_list(action_trace);
1663         printf("\n");
1664 }
1665
1666 /**
1667  * Add a Thread to the system for the first time. Should only be called once
1668  * per thread.
1669  * @param t The Thread to add
1670  */
1671 void ModelChecker::add_thread(Thread *t)
1672 {
1673         thread_map->put(id_to_int(t->get_id()), t);
1674         scheduler->add_thread(t);
1675 }
1676
1677 /**
1678  * Removes a thread from the scheduler.
1679  * @param the thread to remove.
1680  */
1681 void ModelChecker::remove_thread(Thread *t)
1682 {
1683         scheduler->remove_thread(t);
1684 }
1685
1686 /**
1687  * Switch from a user-context to the "master thread" context (a.k.a. system
1688  * context). This switch is made with the intention of exploring a particular
1689  * model-checking action (described by a ModelAction object). Must be called
1690  * from a user-thread context.
1691  * @param act The current action that will be explored. Must not be NULL.
1692  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1693  */
1694 int ModelChecker::switch_to_master(ModelAction *act)
1695 {
1696         DBG();
1697         Thread *old = thread_current();
1698         set_current_action(act);
1699         old->set_state(THREAD_READY);
1700         return Thread::swap(old, &system_context);
1701 }
1702
1703 /**
1704  * Takes the next step in the execution, if possible.
1705  * @return Returns true (success) if a step was taken and false otherwise.
1706  */
1707 bool ModelChecker::take_step() {
1708         if (has_asserted())
1709                 return false;
1710
1711         Thread * curr = thread_current();
1712         if (curr) {
1713                 if (curr->get_state() == THREAD_READY) {
1714                         ASSERT(priv->current_action);
1715
1716                         priv->nextThread = check_current_action(priv->current_action);
1717                         priv->current_action = NULL;
1718
1719                         if (curr->is_blocked() || curr->is_complete())
1720                                 scheduler->remove_thread(curr);
1721                 } else {
1722                         ASSERT(false);
1723                 }
1724         }
1725         Thread * next = scheduler->next_thread(priv->nextThread);
1726
1727         /* Infeasible -> don't take any more steps */
1728         if (!isfeasible())
1729                 return false;
1730
1731         if (next)
1732                 next->set_state(THREAD_RUNNING);
1733         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1734
1735         /* next == NULL -> don't take any more steps */
1736         if (!next)
1737                 return false;
1738
1739         if ( next->get_pending() != NULL ) {
1740                 //restart a pending action
1741                 set_current_action(next->get_pending());
1742                 next->set_pending(NULL);
1743                 next->set_state(THREAD_READY);
1744                 return true;
1745         }
1746
1747         /* Return false only if swap fails with an error */
1748         return (Thread::swap(&system_context, next) == 0);
1749 }
1750
1751 /** Runs the current execution until threre are no more steps to take. */
1752 void ModelChecker::finish_execution() {
1753         DBG();
1754
1755         while (take_step());
1756 }