model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14 #include "mutex.h"
  15
  16 #define INITIAL_THREAD_ID       0
  17
  18 ModelChecker *model;
  19
  20 /** @brief Constructor */
  21 ModelChecker::ModelChecker(struct model_params params) :
  22         /* Initialize default scheduler */
  23         scheduler(new Scheduler()),
  24         num_executions(0),
  25         num_feasible_executions(0),
  26         params(params),
  27         diverge(NULL),
  28         action_trace(new action_list_t()),
  29         thread_map(new HashTable<int, Thread *, int>()),
  30         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  31         lock_waiters_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         promises(new std::vector<Promise *>()),
  34         futurevalues(new std::vector<struct PendingFutureValue>()),
  35         lazy_sync_with_release(new HashTable<void *, action_list_t, uintptr_t, 4>()),
  36         thrd_last_action(new std::vector<ModelAction *>(1)),
  37         node_stack(new NodeStack()),
  38         mo_graph(new CycleGraph()),
  39         failed_promise(false),
  40         too_many_reads(false),
  41         asserted(false)
  42 {
  43         /* Allocate this "size" on the snapshotting heap */
  44         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  45         /* First thread created will have id INITIAL_THREAD_ID */
  46         priv->next_thread_id = INITIAL_THREAD_ID;
  47
  48         lazy_sync_size = &priv->lazy_sync_size;
  49 }
  50
  51 /** @brief Destructor */
  52 ModelChecker::~ModelChecker()
  53 {
  54         for (int i = 0; i < get_num_threads(); i++)
  55                 delete thread_map->get(i);
  56         delete thread_map;
  57
  58         delete obj_thrd_map;
  59         delete obj_map;
  60         delete lock_waiters_map;
  61         delete action_trace;
  62
  63         for (unsigned int i = 0; i < promises->size(); i++)
  64                 delete (*promises)[i];
  65         delete promises;
  66
  67         delete lazy_sync_with_release;
  68
  69         delete thrd_last_action;
  70         delete node_stack;
  71         delete scheduler;
  72         delete mo_graph;
  73 }
  74
  75 /**
  76  * Restores user program to initial state and resets all model-checker data
  77  * structures.
  78  */
  79 void ModelChecker::reset_to_initial_state()
  80 {
  81         DEBUG("+++ Resetting to initial state +++\n");
  82         node_stack->reset_execution();
  83         failed_promise = false;
  84         too_many_reads = false;
  85         reset_asserted();
  86         snapshotObject->backTrackBeforeStep(0);
  87 }
  88
  89 /** @return a thread ID for a new Thread */
  90 thread_id_t ModelChecker::get_next_id()
  91 {
  92         return priv->next_thread_id++;
  93 }
  94
  95 /** @return the number of user threads created during this execution */
  96 int ModelChecker::get_num_threads()
  97 {
  98         return priv->next_thread_id;
  99 }
 100
 101 /** @return a sequence number for a new ModelAction */
 102 modelclock_t ModelChecker::get_next_seq_num()
 103 {
 104         return ++priv->used_sequence_numbers;
 105 }
 106
 107 /**
 108  * @brief Choose the next thread to execute.
 109  *
 110  * This function chooses the next thread that should execute. It can force the
 111  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 112  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 113  * The model-checker may have no preference regarding the next thread (i.e.,
 114  * when exploring a new execution ordering), in which case this will return
 115  * NULL.
 116  * @param curr The current ModelAction. This action might guide the choice of
 117  * next thread.
 118  * @return The next thread to run. If the model-checker has no preference, NULL.
 119  */
 120 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 121 {
 122         thread_id_t tid;
 123
 124         if (curr!=NULL) {
 125                 /* Do not split atomic actions. */
 126                 if (curr->is_rmwr())
 127                         return thread_current();
 128                 /* The THREAD_CREATE action points to the created Thread */
 129                 else if (curr->get_type() == THREAD_CREATE)
 130                         return (Thread *)curr->get_location();
 131         }
 132
 133         /* Have we completed exploring the preselected path? */
 134         if (diverge == NULL)
 135                 return NULL;
 136
 137         /* Else, we are trying to replay an execution */
 138         ModelAction *next = node_stack->get_next()->get_action();
 139
 140         if (next == diverge) {
 141                 Node *nextnode = next->get_node();
 142                 /* Reached divergence point */
 143                 if (nextnode->increment_promise()) {
 144                         /* The next node will try to satisfy a different set of promises. */
 145                         tid = next->get_tid();
 146                         node_stack->pop_restofstack(2);
 147                 } else if (nextnode->increment_read_from()) {
 148                         /* The next node will read from a different value. */
 149                         tid = next->get_tid();
 150                         node_stack->pop_restofstack(2);
 151                 } else if (nextnode->increment_future_value()) {
 152                         /* The next node will try to read from a different future value. */
 153                         tid = next->get_tid();
 154                         node_stack->pop_restofstack(2);
 155                 } else {
 156                         /* Make a different thread execute for next step */
 157                         Node *node = nextnode->get_parent();
 158                         tid = node->get_next_backtrack();
 159                         node_stack->pop_restofstack(1);
 160                 }
 161                 DEBUG("*** Divergence point ***\n");
 162                 diverge = NULL;
 163         } else {
 164                 tid = next->get_tid();
 165         }
 166         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 167         ASSERT(tid != THREAD_ID_T_NONE);
 168         return thread_map->get(id_to_int(tid));
 169 }
 170
 171 /**
 172  * Queries the model-checker for more executions to explore and, if one
 173  * exists, resets the model-checker state to execute a new execution.
 174  *
 175  * @return If there are more executions to explore, return true. Otherwise,
 176  * return false.
 177  */
 178 bool ModelChecker::next_execution()
 179 {
 180         DBG();
 181
 182         num_executions++;
 183         if (isfinalfeasible())
 184                 num_feasible_executions++;
 185
 186         if (isfinalfeasible() || DBG_ENABLED())
 187                 print_summary();
 188
 189         if ((diverge = get_next_backtrack()) == NULL)
 190                 return false;
 191
 192         if (DBG_ENABLED()) {
 193                 printf("Next execution will diverge at:\n");
 194                 diverge->print();
 195         }
 196
 197         reset_to_initial_state();
 198         return true;
 199 }
 200
 201 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 202 {
 203         switch (act->get_type()) {
 204         case ATOMIC_READ:
 205         case ATOMIC_WRITE:
 206         case ATOMIC_RMW: {
 207                 /* linear search: from most recent to oldest */
 208                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 209                 action_list_t::reverse_iterator rit;
 210                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 211                         ModelAction *prev = *rit;
 212                         if (act->is_synchronizing(prev))
 213                                 return prev;
 214                 }
 215                 break;
 216         }
 217         case ATOMIC_LOCK:
 218         case ATOMIC_TRYLOCK: {
 219                 /* linear search: from most recent to oldest */
 220                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 221                 action_list_t::reverse_iterator rit;
 222                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 223                         ModelAction *prev = *rit;
 224                         if (act->is_conflicting_lock(prev))
 225                                 return prev;
 226                 }
 227                 break;
 228         }
 229         case ATOMIC_UNLOCK: {
 230                 /* linear search: from most recent to oldest */
 231                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 232                 action_list_t::reverse_iterator rit;
 233                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 234                         ModelAction *prev = *rit;
 235                         if (!act->same_thread(prev)&&prev->is_failed_trylock())
 236                                 return prev;
 237                 }
 238                 break;
 239         }
 240         default:
 241                 break;
 242         }
 243         return NULL;
 244 }
 245
 246 void ModelChecker::set_backtracking(ModelAction *act)
 247 {
 248         Thread *t = get_thread(act);
 249         ModelAction * prev = get_last_conflict(act);
 250         if (prev == NULL)
 251                 return;
 252
 253         Node * node = prev->get_node()->get_parent();
 254
 255         int low_tid, high_tid;
 256         if (node->is_enabled(t)) {
 257                 low_tid = id_to_int(act->get_tid());
 258                 high_tid = low_tid+1;
 259         } else {
 260                 low_tid = 0;
 261                 high_tid = get_num_threads();
 262         }
 263
 264         for(int i = low_tid; i < high_tid; i++) {
 265                 thread_id_t tid = int_to_id(i);
 266                 if (!node->is_enabled(tid))
 267                         continue;
 268
 269                 /* Check if this has been explored already */
 270                 if (node->has_been_explored(tid))
 271                         continue;
 272
 273                 /* Cache the latest backtracking point */
 274                 if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 275                         priv->next_backtrack = prev;
 276
 277                 /* If this is a new backtracking point, mark the tree */
 278                 if (!node->set_backtrack(tid))
 279                         continue;
 280                 DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 281                                         prev->get_tid(), t->get_id());
 282                 if (DBG_ENABLED()) {
 283                         prev->print();
 284                         act->print();
 285                 }
 286         }
 287 }
 288
 289 /**
 290  * Returns last backtracking point. The model checker will explore a different
 291  * path for this point in the next execution.
 292  * @return The ModelAction at which the next execution should diverge.
 293  */
 294 ModelAction * ModelChecker::get_next_backtrack()
 295 {
 296         ModelAction *next = priv->next_backtrack;
 297         priv->next_backtrack = NULL;
 298         return next;
 299 }
 300
 301 /**
 302  * Processes a read or rmw model action.
 303  * @param curr is the read model action to process.
 304  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 305  * @return True if processing this read updates the mo_graph.
 306  */
 307 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 308 {
 309         uint64_t value;
 310         bool updated = false;
 311         while (true) {
 312                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 313                 if (reads_from != NULL) {
 314                         mo_graph->startChanges();
 315
 316                         value = reads_from->get_value();
 317                         bool r_status = false;
 318
 319                         if (!second_part_of_rmw) {
 320                                 check_recency(curr);
 321                                 r_status = r_modification_order(curr, reads_from);
 322                         }
 323
 324
 325                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 326                                 mo_graph->rollbackChanges();
 327                                 too_many_reads = false;
 328                                 continue;
 329                         }
 330
 331                         curr->read_from(reads_from);
 332                         mo_graph->commitChanges();
 333                         updated |= r_status;
 334                 } else if (!second_part_of_rmw) {
 335                         /* Read from future value */
 336                         value = curr->get_node()->get_future_value();
 337                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 338                         curr->read_from(NULL);
 339                         Promise *valuepromise = new Promise(curr, value, expiration);
 340                         promises->push_back(valuepromise);
 341                 }
 342                 get_thread(curr)->set_return_value(value);
 343                 return updated;
 344         }
 345 }
 346
 347 /**
 348  * Processes a lock, trylock, or unlock model action.  @param curr is
 349  * the read model action to process.
 350  *
 351  * The try lock operation checks whether the lock is taken.  If not,
 352  * it falls to the normal lock operation case.  If so, it returns
 353  * fail.
 354  *
 355  * The lock operation has already been checked that it is enabled, so
 356  * it just grabs the lock and synchronizes with the previous unlock.
 357  *
 358  * The unlock operation has to re-enable all of the threads that are
 359  * waiting on the lock.
 360  */
 361 void ModelChecker::process_mutex(ModelAction *curr) {
 362         std::mutex *mutex = (std::mutex *)curr->get_location();
 363         struct std::mutex_state *state = mutex->get_state();
 364         switch (curr->get_type()) {
 365         case ATOMIC_TRYLOCK: {
 366                 bool success = !state->islocked;
 367                 curr->set_try_lock(success);
 368                 if (!success) {
 369                         get_thread(curr)->set_return_value(0);
 370                         break;
 371                 }
 372                 get_thread(curr)->set_return_value(1);
 373         }
 374                 //otherwise fall into the lock case
 375         case ATOMIC_LOCK: {
 376                 if (curr->get_cv()->getClock(state->alloc_tid) <= state->alloc_clock) {
 377                         printf("Lock access before initialization\n");
 378                         set_assert();
 379                 }
 380                 state->islocked = true;
 381                 ModelAction *unlock = get_last_unlock(curr);
 382                 //synchronize with the previous unlock statement
 383                 if (unlock != NULL)
 384                         curr->synchronize_with(unlock);
 385                 break;
 386         }
 387         case ATOMIC_UNLOCK: {
 388                 //unlock the lock
 389                 state->islocked = false;
 390                 //wake up the other threads
 391                 action_list_t *waiters = lock_waiters_map->get_safe_ptr(curr->get_location());
 392                 //activate all the waiting threads
 393                 for (action_list_t::iterator rit = waiters->begin(); rit != waiters->end(); rit++) {
 394                         scheduler->add_thread(get_thread((*rit)->get_tid()));
 395                 }
 396                 waiters->clear();
 397                 break;
 398         }
 399         default:
 400                 ASSERT(0);
 401         }
 402 }
 403
 404 /**
 405  * Process a write ModelAction
 406  * @param curr The ModelAction to process
 407  * @return True if the mo_graph was updated or promises were resolved
 408  */
 409 bool ModelChecker::process_write(ModelAction *curr)
 410 {
 411         bool updated_mod_order = w_modification_order(curr);
 412         bool updated_promises = resolve_promises(curr);
 413
 414         if (promises->size() == 0) {
 415                 for (unsigned int i = 0; i < futurevalues->size(); i++) {
 416                         struct PendingFutureValue pfv = (*futurevalues)[i];
 417                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 418                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 419                                 priv->next_backtrack = pfv.act;
 420                 }
 421                 futurevalues->resize(0);
 422         }
 423
 424         mo_graph->commitChanges();
 425         get_thread(curr)->set_return_value(VALUE_NONE);
 426         return updated_mod_order || updated_promises;
 427 }
 428
 429 /**
 430  * Initialize the current action by performing one or more of the following
 431  * actions, as appropriate: merging RMWR and RMWC/RMW actions, stepping forward
 432  * in the NodeStack, manipulating backtracking sets, allocating and
 433  * initializing clock vectors, and computing the promises to fulfill.
 434  *
 435  * @param curr The current action, as passed from the user context; may be
 436  * freed/invalidated after the execution of this function
 437  * @return The current action, as processed by the ModelChecker. Is only the
 438  * same as the parameter @a curr if this is a newly-explored action.
 439  */
 440 ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 441 {
 442         ModelAction *newcurr;
 443
 444         if (curr->is_rmwc() || curr->is_rmw()) {
 445                 newcurr = process_rmw(curr);
 446                 delete curr;
 447                 compute_promises(newcurr);
 448                 return newcurr;
 449         }
 450
 451         newcurr = node_stack->explore_action(curr, scheduler->get_enabled());
 452         if (newcurr) {
 453                 /* First restore type and order in case of RMW operation */
 454                 if (curr->is_rmwr())
 455                         newcurr->copy_typeandorder(curr);
 456
 457                 ASSERT(curr->get_location() == newcurr->get_location());
 458                 newcurr->copy_from_new(curr);
 459
 460                 /* Discard duplicate ModelAction; use action from NodeStack */
 461                 delete curr;
 462
 463                 /* If we have diverged, we need to reset the clock vector. */
 464                 if (diverge == NULL)
 465                         newcurr->create_cv(get_parent_action(newcurr->get_tid()));
 466         } else {
 467                 newcurr = curr;
 468                 /*
 469                  * Perform one-time actions when pushing new ModelAction onto
 470                  * NodeStack
 471                  */
 472                 curr->create_cv(get_parent_action(curr->get_tid()));
 473                 if (curr->is_write())
 474                         compute_promises(curr);
 475         }
 476         return newcurr;
 477 }
 478
 479 /**
 480  * This method checks whether a model action is enabled at the given point.
 481  * At this point, it checks whether a lock operation would be successful at this point.
 482  * If not, it puts the thread in a waiter list.
 483  * @param curr is the ModelAction to check whether it is enabled.
 484  * @return a bool that indicates whether the action is enabled.
 485  */
 486
 487 bool ModelChecker::check_action_enabled(ModelAction *curr) {
 488         if (curr->is_lock()) {
 489                 std::mutex * lock = (std::mutex *)curr->get_location();
 490                 struct std::mutex_state * state = lock->get_state();
 491                 if (state->islocked) {
 492                         //Stick the action in the appropriate waiting queue
 493                         lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 494                         return false;
 495                 }
 496         }
 497
 498         return true;
 499 }
 500
 501 /**
 502  * This is the heart of the model checker routine. It performs model-checking
 503  * actions corresponding to a given "current action." Among other processes, it
 504  * calculates reads-from relationships, updates synchronization clock vectors,
 505  * forms a memory_order constraints graph, and handles replay/backtrack
 506  * execution when running permutations of previously-observed executions.
 507  *
 508  * @param curr The current action to process
 509  * @return The next Thread that must be executed. May be NULL if ModelChecker
 510  * makes no choice (e.g., according to replay execution, combining RMW actions,
 511  * etc.)
 512  */
 513 Thread * ModelChecker::check_current_action(ModelAction *curr)
 514 {
 515         ASSERT(curr);
 516
 517         bool second_part_of_rmw = curr->is_rmwc() || curr->is_rmw();
 518
 519         if (!check_action_enabled(curr)) {
 520                 //we'll make the execution look like we chose to run this action
 521                 //much later...when a lock is actually available to relese
 522                 get_current_thread()->set_pending(curr);
 523                 remove_thread(get_current_thread());
 524                 return get_next_thread(NULL);
 525         }
 526
 527         ModelAction *newcurr = initialize_curr_action(curr);
 528
 529         /* Add the action to lists before any other model-checking tasks */
 530         if (!second_part_of_rmw)
 531                 add_action_to_lists(newcurr);
 532
 533         /* Build may_read_from set for newly-created actions */
 534         if (curr == newcurr && curr->is_read())
 535                 build_reads_from_past(curr);
 536         curr = newcurr;
 537
 538         /* Thread specific actions */
 539         switch (curr->get_type()) {
 540         case THREAD_CREATE: {
 541                 Thread *th = (Thread *)curr->get_location();
 542                 th->set_creation(curr);
 543                 break;
 544         }
 545         case THREAD_JOIN: {
 546                 Thread *waiting, *blocking;
 547                 waiting = get_thread(curr);
 548                 blocking = (Thread *)curr->get_location();
 549                 if (!blocking->is_complete()) {
 550                         blocking->push_wait_list(curr);
 551                         scheduler->sleep(waiting);
 552                 } else {
 553                         do_complete_join(curr);
 554                 }
 555                 break;
 556         }
 557         case THREAD_FINISH: {
 558                 Thread *th = get_thread(curr);
 559                 while (!th->wait_list_empty()) {
 560                         ModelAction *act = th->pop_wait_list();
 561                         Thread *wake = get_thread(act);
 562                         scheduler->wake(wake);
 563                         do_complete_join(act);
 564                 }
 565                 th->complete();
 566                 break;
 567         }
 568         case THREAD_START: {
 569                 check_promises(NULL, curr->get_cv());
 570                 break;
 571         }
 572         default:
 573                 break;
 574         }
 575
 576         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 577
 578         while (!work_queue.empty()) {
 579                 WorkQueueEntry work = work_queue.front();
 580                 work_queue.pop_front();
 581
 582                 switch (work.type) {
 583                 case WORK_CHECK_CURR_ACTION: {
 584                         ModelAction *act = work.action;
 585                         bool updated = false;
 586                         if (act->is_read() && process_read(act, second_part_of_rmw))
 587                                 updated = true;
 588
 589                         if (act->is_write() && process_write(act))
 590                                 updated = true;
 591
 592                         if (act->is_mutex_op())
 593                                 process_mutex(act);
 594
 595                         if (updated)
 596                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 597                         break;
 598                 }
 599                 case WORK_CHECK_RELEASE_SEQ:
 600                         resolve_release_sequences(work.location, &work_queue);
 601                         break;
 602                 case WORK_CHECK_MO_EDGES: {
 603                         /** @todo Complete verification of work_queue */
 604                         ModelAction *act = work.action;
 605                         bool updated = false;
 606
 607                         if (act->is_read()) {
 608                                 if (r_modification_order(act, act->get_reads_from()))
 609                                         updated = true;
 610                         }
 611                         if (act->is_write()) {
 612                                 if (w_modification_order(act))
 613                                         updated = true;
 614                         }
 615
 616                         if (updated)
 617                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 618                         break;
 619                 }
 620                 default:
 621                         ASSERT(false);
 622                         break;
 623                 }
 624         }
 625
 626         check_curr_backtracking(curr);
 627
 628         set_backtracking(curr);
 629
 630         return get_next_thread(curr);
 631 }
 632
 633 /**
 634  * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
 635  * operation from the Thread it is joining with. Must be called after the
 636  * completion of the Thread in question.
 637  * @param join The THREAD_JOIN action
 638  */
 639 void ModelChecker::do_complete_join(ModelAction *join)
 640 {
 641         Thread *blocking = (Thread *)join->get_location();
 642         ModelAction *act = get_last_action(blocking->get_id());
 643         join->synchronize_with(act);
 644 }
 645
 646 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 647         Node *currnode = curr->get_node();
 648         Node *parnode = currnode->get_parent();
 649
 650         if ((!parnode->backtrack_empty() ||
 651                          !currnode->read_from_empty() ||
 652                          !currnode->future_value_empty() ||
 653                          !currnode->promise_empty())
 654                         && (!priv->next_backtrack ||
 655                                         *curr > *priv->next_backtrack)) {
 656                 priv->next_backtrack = curr;
 657         }
 658 }
 659
 660 bool ModelChecker::promises_expired() {
 661         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 662                 Promise *promise = (*promises)[promise_index];
 663                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 664                         return true;
 665                 }
 666         }
 667         return false;
 668 }
 669
 670 /** @return whether the current partial trace must be a prefix of a
 671  * feasible trace. */
 672 bool ModelChecker::isfeasibleprefix() {
 673         return promises->size() == 0 && *lazy_sync_size == 0;
 674 }
 675
 676 /** @return whether the current partial trace is feasible. */
 677 bool ModelChecker::isfeasible() {
 678         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 679 }
 680
 681 /** @return whether the current partial trace is feasible other than
 682  * multiple RMW reading from the same store. */
 683 bool ModelChecker::isfeasibleotherthanRMW() {
 684         if (DBG_ENABLED()) {
 685                 if (mo_graph->checkForCycles())
 686                         DEBUG("Infeasible: modification order cycles\n");
 687                 if (failed_promise)
 688                         DEBUG("Infeasible: failed promise\n");
 689                 if (too_many_reads)
 690                         DEBUG("Infeasible: too many reads\n");
 691                 if (promises_expired())
 692                         DEBUG("Infeasible: promises expired\n");
 693         }
 694         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 695 }
 696
 697 /** Returns whether the current completed trace is feasible. */
 698 bool ModelChecker::isfinalfeasible() {
 699         if (DBG_ENABLED() && promises->size() != 0)
 700                 DEBUG("Infeasible: unrevolved promises\n");
 701
 702         return isfeasible() && promises->size() == 0;
 703 }
 704
 705 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 706 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 707         int tid = id_to_int(act->get_tid());
 708         ModelAction *lastread = get_last_action(tid);
 709         lastread->process_rmw(act);
 710         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 711                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 712                 mo_graph->commitChanges();
 713         }
 714         return lastread;
 715 }
 716
 717 /**
 718  * Checks whether a thread has read from the same write for too many times
 719  * without seeing the effects of a later write.
 720  *
 721  * Basic idea:
 722  * 1) there must a different write that we could read from that would satisfy the modification order,
 723  * 2) we must have read from the same value in excess of maxreads times, and
 724  * 3) that other write must have been in the reads_from set for maxreads times.
 725  *
 726  * If so, we decide that the execution is no longer feasible.
 727  */
 728 void ModelChecker::check_recency(ModelAction *curr) {
 729         if (params.maxreads != 0) {
 730                 if (curr->get_node()->get_read_from_size() <= 1)
 731                         return;
 732
 733                 //Must make sure that execution is currently feasible...  We could
 734                 //accidentally clear by rolling back
 735                 if (!isfeasible())
 736                         return;
 737
 738                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 739                 int tid = id_to_int(curr->get_tid());
 740
 741                 /* Skip checks */
 742                 if ((int)thrd_lists->size() <= tid)
 743                         return;
 744
 745                 action_list_t *list = &(*thrd_lists)[tid];
 746
 747                 action_list_t::reverse_iterator rit = list->rbegin();
 748                 /* Skip past curr */
 749                 for (; (*rit) != curr; rit++)
 750                         ;
 751                 /* go past curr now */
 752                 rit++;
 753
 754                 action_list_t::reverse_iterator ritcopy = rit;
 755                 //See if we have enough reads from the same value
 756                 int count = 0;
 757                 for (; count < params.maxreads; rit++,count++) {
 758                         if (rit==list->rend())
 759                                 return;
 760                         ModelAction *act = *rit;
 761                         if (!act->is_read())
 762                                 return;
 763                         if (act->get_reads_from() != curr->get_reads_from())
 764                                 return;
 765                         if (act->get_node()->get_read_from_size() <= 1)
 766                                 return;
 767                 }
 768
 769                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 770                         //Get write
 771                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 772                         //Need a different write
 773                         if (write==curr->get_reads_from())
 774                                 continue;
 775
 776                         /* Test to see whether this is a feasible write to read from*/
 777                         mo_graph->startChanges();
 778                         r_modification_order(curr, write);
 779                         bool feasiblereadfrom = isfeasible();
 780                         mo_graph->rollbackChanges();
 781
 782                         if (!feasiblereadfrom)
 783                                 continue;
 784                         rit = ritcopy;
 785
 786                         bool feasiblewrite = true;
 787                         //new we need to see if this write works for everyone
 788
 789                         for (int loop = count; loop>0; loop--,rit++) {
 790                                 ModelAction *act=*rit;
 791                                 bool foundvalue = false;
 792                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 793                                         if (act->get_node()->get_read_from_at(i)==write) {
 794                                                 foundvalue = true;
 795                                                 break;
 796                                         }
 797                                 }
 798                                 if (!foundvalue) {
 799                                         feasiblewrite = false;
 800                                         break;
 801                                 }
 802                         }
 803                         if (feasiblewrite) {
 804                                 too_many_reads = true;
 805                                 return;
 806                         }
 807                 }
 808         }
 809 }
 810
 811 /**
 812  * Updates the mo_graph with the constraints imposed from the current
 813  * read.
 814  *
 815  * Basic idea is the following: Go through each other thread and find
 816  * the lastest action that happened before our read.  Two cases:
 817  *
 818  * (1) The action is a write => that write must either occur before
 819  * the write we read from or be the write we read from.
 820  *
 821  * (2) The action is a read => the write that that action read from
 822  * must occur before the write we read from or be the same write.
 823  *
 824  * @param curr The current action. Must be a read.
 825  * @param rf The action that curr reads from. Must be a write.
 826  * @return True if modification order edges were added; false otherwise
 827  */
 828 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 829 {
 830         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 831         unsigned int i;
 832         bool added = false;
 833         ASSERT(curr->is_read());
 834
 835         /* Iterate over all threads */
 836         for (i = 0; i < thrd_lists->size(); i++) {
 837                 /* Iterate over actions in thread, starting from most recent */
 838                 action_list_t *list = &(*thrd_lists)[i];
 839                 action_list_t::reverse_iterator rit;
 840                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 841                         ModelAction *act = *rit;
 842
 843                         /*
 844                          * Include at most one act per-thread that "happens
 845                          * before" curr. Don't consider reflexively.
 846                          */
 847                         if (act->happens_before(curr) && act != curr) {
 848                                 if (act->is_write()) {
 849                                         if (rf != act) {
 850                                                 mo_graph->addEdge(act, rf);
 851                                                 added = true;
 852                                         }
 853                                 } else {
 854                                         const ModelAction *prevreadfrom = act->get_reads_from();
 855                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 856                                                 mo_graph->addEdge(prevreadfrom, rf);
 857                                                 added = true;
 858                                         }
 859                                 }
 860                                 break;
 861                         }
 862                 }
 863         }
 864
 865         return added;
 866 }
 867
 868 /** This method fixes up the modification order when we resolve a
 869  *  promises.  The basic problem is that actions that occur after the
 870  *  read curr could not property add items to the modification order
 871  *  for our read.
 872  *
 873  *  So for each thread, we find the earliest item that happens after
 874  *  the read curr.  This is the item we have to fix up with additional
 875  *  constraints.  If that action is write, we add a MO edge between
 876  *  the Action rf and that action.  If the action is a read, we add a
 877  *  MO edge between the Action rf, and whatever the read accessed.
 878  *
 879  * @param curr is the read ModelAction that we are fixing up MO edges for.
 880  * @param rf is the write ModelAction that curr reads from.
 881  *
 882  */
 883
 884 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 885 {
 886         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 887         unsigned int i;
 888         ASSERT(curr->is_read());
 889
 890         /* Iterate over all threads */
 891         for (i = 0; i < thrd_lists->size(); i++) {
 892                 /* Iterate over actions in thread, starting from most recent */
 893                 action_list_t *list = &(*thrd_lists)[i];
 894                 action_list_t::reverse_iterator rit;
 895                 ModelAction *lastact = NULL;
 896
 897                 /* Find last action that happens after curr */
 898                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 899                         ModelAction *act = *rit;
 900                         if (curr->happens_before(act)) {
 901                                 lastact = act;
 902                         } else
 903                                 break;
 904                 }
 905
 906                         /* Include at most one act per-thread that "happens before" curr */
 907                 if (lastact != NULL) {
 908                         if (lastact->is_read()) {
 909                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 910                                 if (postreadfrom != NULL&&rf != postreadfrom)
 911                                         mo_graph->addEdge(rf, postreadfrom);
 912                         } else if (rf != lastact) {
 913                                 mo_graph->addEdge(rf, lastact);
 914                         }
 915                         break;
 916                 }
 917         }
 918 }
 919
 920 /**
 921  * Updates the mo_graph with the constraints imposed from the current write.
 922  *
 923  * Basic idea is the following: Go through each other thread and find
 924  * the lastest action that happened before our write.  Two cases:
 925  *
 926  * (1) The action is a write => that write must occur before
 927  * the current write
 928  *
 929  * (2) The action is a read => the write that that action read from
 930  * must occur before the current write.
 931  *
 932  * This method also handles two other issues:
 933  *
 934  * (I) Sequential Consistency: Making sure that if the current write is
 935  * seq_cst, that it occurs after the previous seq_cst write.
 936  *
 937  * (II) Sending the write back to non-synchronizing reads.
 938  *
 939  * @param curr The current action. Must be a write.
 940  * @return True if modification order edges were added; false otherwise
 941  */
 942 bool ModelChecker::w_modification_order(ModelAction *curr)
 943 {
 944         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 945         unsigned int i;
 946         bool added = false;
 947         ASSERT(curr->is_write());
 948
 949         if (curr->is_seqcst()) {
 950                 /* We have to at least see the last sequentially consistent write,
 951                          so we are initialized. */
 952                 ModelAction *last_seq_cst = get_last_seq_cst(curr);
 953                 if (last_seq_cst != NULL) {
 954                         mo_graph->addEdge(last_seq_cst, curr);
 955                         added = true;
 956                 }
 957         }
 958
 959         /* Iterate over all threads */
 960         for (i = 0; i < thrd_lists->size(); i++) {
 961                 /* Iterate over actions in thread, starting from most recent */
 962                 action_list_t *list = &(*thrd_lists)[i];
 963                 action_list_t::reverse_iterator rit;
 964                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 965                         ModelAction *act = *rit;
 966                         if (act == curr) {
 967                                 /*
 968                                  * If RMW, we already have all relevant edges,
 969                                  * so just skip to next thread.
 970                                  * If normal write, we need to look at earlier
 971                                  * actions, so continue processing list.
 972                                  */
 973                                 if (curr->is_rmw())
 974                                         break;
 975                                 else
 976                                         continue;
 977                         }
 978
 979                         /*
 980                          * Include at most one act per-thread that "happens
 981                          * before" curr
 982                          */
 983                         if (act->happens_before(curr)) {
 984                                 /*
 985                                  * Note: if act is RMW, just add edge:
 986                                  *   act --mo--> curr
 987                                  * The following edge should be handled elsewhere:
 988                                  *   readfrom(act) --mo--> act
 989                                  */
 990                                 if (act->is_write())
 991                                         mo_graph->addEdge(act, curr);
 992                                 else if (act->is_read() && act->get_reads_from() != NULL)
 993                                         mo_graph->addEdge(act->get_reads_from(), curr);
 994                                 added = true;
 995                                 break;
 996                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 997                                                      !act->same_thread(curr)) {
 998                                 /* We have an action that:
 999                                    (1) did not happen before us
1000                                    (2) is a read and we are a write
1001                                    (3) cannot synchronize with us
1002                                    (4) is in a different thread
1003                                    =>
1004                                    that read could potentially read from our write.
1005                                  */
1006                                 if (thin_air_constraint_may_allow(curr, act)) {
1007                                         if (isfeasible() ||
1008                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && isfeasibleotherthanRMW())) {
1009                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
1010                                                 futurevalues->push_back(pfv);
1011                                         }
1012                                 }
1013                         }
1014                 }
1015         }
1016
1017         return added;
1018 }
1019
1020 /** Arbitrary reads from the future are not allowed.  Section 29.3
1021  * part 9 places some constraints.  This method checks one result of constraint
1022  * constraint.  Others require compiler support. */
1023
1024 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
1025         if (!writer->is_rmw())
1026                 return true;
1027
1028         if (!reader->is_rmw())
1029                 return true;
1030
1031         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
1032                 if (search == reader)
1033                         return false;
1034                 if (search->get_tid() == reader->get_tid() &&
1035                                 search->happens_before(reader))
1036                         break;
1037         }
1038
1039         return true;
1040 }
1041
1042 /**
1043  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
1044  * The ModelAction under consideration is expected to be taking part in
1045  * release/acquire synchronization as an object of the "reads from" relation.
1046  * Note that this can only provide release sequence support for RMW chains
1047  * which do not read from the future, as those actions cannot be traced until
1048  * their "promise" is fulfilled. Similarly, we may not even establish the
1049  * presence of a release sequence with certainty, as some modification order
1050  * constraints may be decided further in the future. Thus, this function
1051  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
1052  * and a boolean representing certainty.
1053  *
1054  * @todo Finish lazy updating, when promises are fulfilled in the future
1055  * @param rf The action that might be part of a release sequence. Must be a
1056  * write.
1057  * @param release_heads A pass-by-reference style return parameter.  After
1058  * execution of this function, release_heads will contain the heads of all the
1059  * relevant release sequences, if any exists
1060  * @return true, if the ModelChecker is certain that release_heads is complete;
1061  * false otherwise
1062  */
1063 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
1064 {
1065         if (!rf) {
1066                 /* read from future: need to settle this later */
1067                 return false; /* incomplete */
1068         }
1069
1070         ASSERT(rf->is_write());
1071
1072         if (rf->is_release())
1073                 release_heads->push_back(rf);
1074         if (rf->is_rmw()) {
1075                 /* We need a RMW action that is both an acquire and release to stop */
1076                 /** @todo Need to be smarter here...  In the linux lock
1077                  * example, this will run to the beginning of the program for
1078                  * every acquire. */
1079                 if (rf->is_acquire() && rf->is_release())
1080                         return true; /* complete */
1081                 return release_seq_head(rf->get_reads_from(), release_heads);
1082         }
1083         if (rf->is_release())
1084                 return true; /* complete */
1085
1086         /* else relaxed write; check modification order for contiguous subsequence
1087          * -> rf must be same thread as release */
1088         int tid = id_to_int(rf->get_tid());
1089         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
1090         action_list_t *list = &(*thrd_lists)[tid];
1091         action_list_t::const_reverse_iterator rit;
1092
1093         /* Find rf in the thread list */
1094         rit = std::find(list->rbegin(), list->rend(), rf);
1095         ASSERT(rit != list->rend());
1096
1097         /* Find the last write/release */
1098         for (; rit != list->rend(); rit++)
1099                 if ((*rit)->is_release())
1100                         break;
1101         if (rit == list->rend()) {
1102                 /* No write-release in this thread */
1103                 return true; /* complete */
1104         }
1105         ModelAction *release = *rit;
1106
1107         ASSERT(rf->same_thread(release));
1108
1109         bool certain = true;
1110         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
1111                 if (id_to_int(rf->get_tid()) == (int)i)
1112                         continue;
1113                 list = &(*thrd_lists)[i];
1114
1115                 /* Can we ensure no future writes from this thread may break
1116                  * the release seq? */
1117                 bool future_ordered = false;
1118
1119                 ModelAction *last = get_last_action(int_to_id(i));
1120                 if (last && rf->happens_before(last))
1121                         future_ordered = true;
1122
1123                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1124                         const ModelAction *act = *rit;
1125                         /* Reach synchronization -> this thread is complete */
1126                         if (act->happens_before(release))
1127                                 break;
1128                         if (rf->happens_before(act)) {
1129                                 future_ordered = true;
1130                                 continue;
1131                         }
1132
1133                         /* Only writes can break release sequences */
1134                         if (!act->is_write())
1135                                 continue;
1136
1137                         /* Check modification order */
1138                         if (mo_graph->checkReachable(rf, act)) {
1139                                 /* rf --mo--> act */
1140                                 future_ordered = true;
1141                                 continue;
1142                         }
1143                         if (mo_graph->checkReachable(act, release))
1144                                 /* act --mo--> release */
1145                                 break;
1146                         if (mo_graph->checkReachable(release, act) &&
1147                                       mo_graph->checkReachable(act, rf)) {
1148                                 /* release --mo-> act --mo--> rf */
1149                                 return true; /* complete */
1150                         }
1151                         certain = false;
1152                 }
1153                 if (!future_ordered)
1154                         return false; /* This thread is uncertain */
1155         }
1156
1157         if (certain)
1158                 release_heads->push_back(release);
1159         return certain;
1160 }
1161
1162 /**
1163  * A public interface for getting the release sequence head(s) with which a
1164  * given ModelAction must synchronize. This function only returns a non-empty
1165  * result when it can locate a release sequence head with certainty. Otherwise,
1166  * it may mark the internal state of the ModelChecker so that it will handle
1167  * the release sequence at a later time, causing @a act to update its
1168  * synchronization at some later point in execution.
1169  * @param act The 'acquire' action that may read from a release sequence
1170  * @param release_heads A pass-by-reference return parameter. Will be filled
1171  * with the head(s) of the release sequence(s), if they exists with certainty.
1172  * @see ModelChecker::release_seq_head
1173  */
1174 void ModelChecker::get_release_seq_heads(ModelAction *act, rel_heads_list_t *release_heads)
1175 {
1176         const ModelAction *rf = act->get_reads_from();
1177         bool complete;
1178         complete = release_seq_head(rf, release_heads);
1179         if (!complete) {
1180                 /* add act to 'lazy checking' list */
1181                 action_list_t *list;
1182                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
1183                 list->push_back(act);
1184                 (*lazy_sync_size)++;
1185         }
1186 }
1187
1188 /**
1189  * Attempt to resolve all stashed operations that might synchronize with a
1190  * release sequence for a given location. This implements the "lazy" portion of
1191  * determining whether or not a release sequence was contiguous, since not all
1192  * modification order information is present at the time an action occurs.
1193  *
1194  * @param location The location/object that should be checked for release
1195  * sequence resolutions
1196  * @param work_queue The work queue to which to add work items as they are
1197  * generated
1198  * @return True if any updates occurred (new synchronization, new mo_graph
1199  * edges)
1200  */
1201 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1202 {
1203         action_list_t *list;
1204         list = lazy_sync_with_release->getptr(location);
1205         if (!list)
1206                 return false;
1207
1208         bool updated = false;
1209         action_list_t::iterator it = list->begin();
1210         while (it != list->end()) {
1211                 ModelAction *act = *it;
1212                 const ModelAction *rf = act->get_reads_from();
1213                 rel_heads_list_t release_heads;
1214                 bool complete;
1215                 complete = release_seq_head(rf, &release_heads);
1216                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1217                         if (!act->has_synchronized_with(release_heads[i])) {
1218                                 updated = true;
1219                                 act->synchronize_with(release_heads[i]);
1220                         }
1221                 }
1222
1223                 if (updated) {
1224                         /* Re-check act for mo_graph edges */
1225                         work_queue->push_back(MOEdgeWorkEntry(act));
1226
1227                         /* propagate synchronization to later actions */
1228                         action_list_t::reverse_iterator it = action_trace->rbegin();
1229                         while ((*it) != act) {
1230                                 ModelAction *propagate = *it;
1231                                 if (act->happens_before(propagate)) {
1232                                         propagate->synchronize_with(act);
1233                                         /* Re-check 'propagate' for mo_graph edges */
1234                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1235                                 }
1236                         }
1237                 }
1238                 if (complete) {
1239                         it = list->erase(it);
1240                         (*lazy_sync_size)--;
1241                 } else
1242                         it++;
1243         }
1244
1245         // If we resolved promises or data races, see if we have realized a data race.
1246         if (checkDataRaces()) {
1247                 set_assert();
1248         }
1249
1250         return updated;
1251 }
1252
1253 /**
1254  * Performs various bookkeeping operations for the current ModelAction. For
1255  * instance, adds action to the per-object, per-thread action vector and to the
1256  * action trace list of all thread actions.
1257  *
1258  * @param act is the ModelAction to add.
1259  */
1260 void ModelChecker::add_action_to_lists(ModelAction *act)
1261 {
1262         int tid = id_to_int(act->get_tid());
1263         action_trace->push_back(act);
1264
1265         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1266
1267         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1268         if (tid >= (int)vec->size())
1269                 vec->resize(priv->next_thread_id);
1270         (*vec)[tid].push_back(act);
1271
1272         if ((int)thrd_last_action->size() <= tid)
1273                 thrd_last_action->resize(get_num_threads());
1274         (*thrd_last_action)[tid] = act;
1275 }
1276
1277 /**
1278  * @brief Get the last action performed by a particular Thread
1279  * @param tid The thread ID of the Thread in question
1280  * @return The last action in the thread
1281  */
1282 ModelAction * ModelChecker::get_last_action(thread_id_t tid) const
1283 {
1284         int threadid = id_to_int(tid);
1285         if (threadid < (int)thrd_last_action->size())
1286                 return (*thrd_last_action)[id_to_int(tid)];
1287         else
1288                 return NULL;
1289 }
1290
1291 /**
1292  * Gets the last memory_order_seq_cst write (in the total global sequence)
1293  * performed on a particular object (i.e., memory location), not including the
1294  * current action.
1295  * @param curr The current ModelAction; also denotes the object location to
1296  * check
1297  * @return The last seq_cst write
1298  */
1299 ModelAction * ModelChecker::get_last_seq_cst(ModelAction *curr) const
1300 {
1301         void *location = curr->get_location();
1302         action_list_t *list = obj_map->get_safe_ptr(location);
1303         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1304         action_list_t::reverse_iterator rit;
1305         for (rit = list->rbegin(); rit != list->rend(); rit++)
1306                 if ((*rit)->is_write() && (*rit)->is_seqcst() && (*rit) != curr)
1307                         return *rit;
1308         return NULL;
1309 }
1310
1311 /**
1312  * Gets the last unlock operation performed on a particular mutex (i.e., memory
1313  * location). This function identifies the mutex according to the current
1314  * action, which is presumed to perform on the same mutex.
1315  * @param curr The current ModelAction; also denotes the object location to
1316  * check
1317  * @return The last unlock operation
1318  */
1319 ModelAction * ModelChecker::get_last_unlock(ModelAction *curr) const
1320 {
1321         void *location = curr->get_location();
1322         action_list_t *list = obj_map->get_safe_ptr(location);
1323         /* Find: max({i in dom(S) | isUnlock(t_i) && samevar(t_i, t)}) */
1324         action_list_t::reverse_iterator rit;
1325         for (rit = list->rbegin(); rit != list->rend(); rit++)
1326                 if ((*rit)->is_unlock())
1327                         return *rit;
1328         return NULL;
1329 }
1330
1331 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1332 {
1333         ModelAction *parent = get_last_action(tid);
1334         if (!parent)
1335                 parent = get_thread(tid)->get_creation();
1336         return parent;
1337 }
1338
1339 /**
1340  * Returns the clock vector for a given thread.
1341  * @param tid The thread whose clock vector we want
1342  * @return Desired clock vector
1343  */
1344 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1345 {
1346         return get_parent_action(tid)->get_cv();
1347 }
1348
1349 /**
1350  * Resolve a set of Promises with a current write. The set is provided in the
1351  * Node corresponding to @a write.
1352  * @param write The ModelAction that is fulfilling Promises
1353  * @return True if promises were resolved; false otherwise
1354  */
1355 bool ModelChecker::resolve_promises(ModelAction *write)
1356 {
1357         bool resolved = false;
1358
1359         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1360                 Promise *promise = (*promises)[promise_index];
1361                 if (write->get_node()->get_promise(i)) {
1362                         ModelAction *read = promise->get_action();
1363                         read->read_from(write);
1364                         if (read->is_rmw()) {
1365                                 mo_graph->addRMWEdge(write, read);
1366                         }
1367                         //First fix up the modification order for actions that happened
1368                         //before the read
1369                         r_modification_order(read, write);
1370                         //Next fix up the modification order for actions that happened
1371                         //after the read.
1372                         post_r_modification_order(read, write);
1373                         promises->erase(promises->begin() + promise_index);
1374                         resolved = true;
1375                 } else
1376                         promise_index++;
1377         }
1378         return resolved;
1379 }
1380
1381 /**
1382  * Compute the set of promises that could potentially be satisfied by this
1383  * action. Note that the set computation actually appears in the Node, not in
1384  * ModelChecker.
1385  * @param curr The ModelAction that may satisfy promises
1386  */
1387 void ModelChecker::compute_promises(ModelAction *curr)
1388 {
1389         for (unsigned int i = 0; i < promises->size(); i++) {
1390                 Promise *promise = (*promises)[i];
1391                 const ModelAction *act = promise->get_action();
1392                 if (!act->happens_before(curr) &&
1393                                 act->is_read() &&
1394                                 !act->is_synchronizing(curr) &&
1395                                 !act->same_thread(curr) &&
1396                                 promise->get_value() == curr->get_value()) {
1397                         curr->get_node()->set_promise(i);
1398                 }
1399         }
1400 }
1401
1402 /** Checks promises in response to change in ClockVector Threads. */
1403 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1404 {
1405         for (unsigned int i = 0; i < promises->size(); i++) {
1406                 Promise *promise = (*promises)[i];
1407                 const ModelAction *act = promise->get_action();
1408                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1409                                 merge_cv->synchronized_since(act)) {
1410                         //This thread is no longer able to send values back to satisfy the promise
1411                         int num_synchronized_threads = promise->increment_threads();
1412                         if (num_synchronized_threads == get_num_threads()) {
1413                                 //Promise has failed
1414                                 failed_promise = true;
1415                                 return;
1416                         }
1417                 }
1418         }
1419 }
1420
1421 /**
1422  * Build up an initial set of all past writes that this 'read' action may read
1423  * from. This set is determined by the clock vector's "happens before"
1424  * relationship.
1425  * @param curr is the current ModelAction that we are exploring; it must be a
1426  * 'read' operation.
1427  */
1428 void ModelChecker::build_reads_from_past(ModelAction *curr)
1429 {
1430         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1431         unsigned int i;
1432         ASSERT(curr->is_read());
1433
1434         ModelAction *last_seq_cst = NULL;
1435
1436         /* Track whether this object has been initialized */
1437         bool initialized = false;
1438
1439         if (curr->is_seqcst()) {
1440                 last_seq_cst = get_last_seq_cst(curr);
1441                 /* We have to at least see the last sequentially consistent write,
1442                          so we are initialized. */
1443                 if (last_seq_cst != NULL)
1444                         initialized = true;
1445         }
1446
1447         /* Iterate over all threads */
1448         for (i = 0; i < thrd_lists->size(); i++) {
1449                 /* Iterate over actions in thread, starting from most recent */
1450                 action_list_t *list = &(*thrd_lists)[i];
1451                 action_list_t::reverse_iterator rit;
1452                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1453                         ModelAction *act = *rit;
1454
1455                         /* Only consider 'write' actions */
1456                         if (!act->is_write() || act == curr)
1457                                 continue;
1458
1459                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1460                         if (!curr->is_seqcst() || (!act->is_seqcst() && (last_seq_cst == NULL || !act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1461                                 DEBUG("Adding action to may_read_from:\n");
1462                                 if (DBG_ENABLED()) {
1463                                         act->print();
1464                                         curr->print();
1465                                 }
1466                                 curr->get_node()->add_read_from(act);
1467                         }
1468
1469                         /* Include at most one act per-thread that "happens before" curr */
1470                         if (act->happens_before(curr)) {
1471                                 initialized = true;
1472                                 break;
1473                         }
1474                 }
1475         }
1476
1477         if (!initialized) {
1478                 /** @todo Need a more informative way of reporting errors. */
1479                 printf("ERROR: may read from uninitialized atomic\n");
1480         }
1481
1482         if (DBG_ENABLED() || !initialized) {
1483                 printf("Reached read action:\n");
1484                 curr->print();
1485                 printf("Printing may_read_from\n");
1486                 curr->get_node()->print_may_read_from();
1487                 printf("End printing may_read_from\n");
1488         }
1489
1490         ASSERT(initialized);
1491 }
1492
1493 static void print_list(action_list_t *list)
1494 {
1495         action_list_t::iterator it;
1496
1497         printf("---------------------------------------------------------------------\n");
1498         printf("Trace:\n");
1499
1500         for (it = list->begin(); it != list->end(); it++) {
1501                 (*it)->print();
1502         }
1503         printf("---------------------------------------------------------------------\n");
1504 }
1505
1506 void ModelChecker::print_summary()
1507 {
1508         printf("\n");
1509         printf("Number of executions: %d\n", num_executions);
1510         printf("Number of feasible executions: %d\n", num_feasible_executions);
1511         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1512
1513 #if SUPPORT_MOD_ORDER_DUMP
1514         scheduler->print();
1515         char buffername[100];
1516         sprintf(buffername, "exec%04u", num_executions);
1517         mo_graph->dumpGraphToFile(buffername);
1518 #endif
1519
1520         if (!isfinalfeasible())
1521                 printf("INFEASIBLE EXECUTION!\n");
1522         print_list(action_trace);
1523         printf("\n");
1524 }
1525
1526 /**
1527  * Add a Thread to the system for the first time. Should only be called once
1528  * per thread.
1529  * @param t The Thread to add
1530  */
1531 void ModelChecker::add_thread(Thread *t)
1532 {
1533         thread_map->put(id_to_int(t->get_id()), t);
1534         scheduler->add_thread(t);
1535 }
1536
1537 void ModelChecker::remove_thread(Thread *t)
1538 {
1539         scheduler->remove_thread(t);
1540 }
1541
1542 /**
1543  * Switch from a user-context to the "master thread" context (a.k.a. system
1544  * context). This switch is made with the intention of exploring a particular
1545  * model-checking action (described by a ModelAction object). Must be called
1546  * from a user-thread context.
1547  * @param act The current action that will be explored. Must not be NULL.
1548  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1549  */
1550 int ModelChecker::switch_to_master(ModelAction *act)
1551 {
1552         DBG();
1553         Thread *old = thread_current();
1554         set_current_action(act);
1555         old->set_state(THREAD_READY);
1556         return Thread::swap(old, &system_context);
1557 }
1558
1559 /**
1560  * Takes the next step in the execution, if possible.
1561  * @return Returns true (success) if a step was taken and false otherwise.
1562  */
1563 bool ModelChecker::take_step() {
1564         if (has_asserted())
1565                 return false;
1566
1567         Thread * curr = thread_current();
1568         if (curr) {
1569                 if (curr->get_state() == THREAD_READY) {
1570                         ASSERT(priv->current_action);
1571
1572                         priv->nextThread = check_current_action(priv->current_action);
1573                         priv->current_action = NULL;
1574                         if (curr->is_blocked() || curr->is_complete())
1575                                 scheduler->remove_thread(curr);
1576                 } else {
1577                         ASSERT(false);
1578                 }
1579         }
1580         Thread * next = scheduler->next_thread(priv->nextThread);
1581
1582         /* Infeasible -> don't take any more steps */
1583         if (!isfeasible())
1584                 return false;
1585
1586         if (next)
1587                 next->set_state(THREAD_RUNNING);
1588         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1589
1590         /* next == NULL -> don't take any more steps */
1591         if (!next)
1592                 return false;
1593
1594         if ( next->get_pending() != NULL ) {
1595                 //restart a pending action
1596                 set_current_action(next->get_pending());
1597                 next->set_pending(NULL);
1598                 next->set_state(THREAD_READY);
1599                 return true;
1600         }
1601
1602         /* Return false only if swap fails with an error */
1603         return (Thread::swap(&system_context, next) == 0);
1604 }
1605
1606 /** Runs the current execution until threre are no more steps to take. */
1607 void ModelChecker::finish_execution() {
1608         DBG();
1609
1610         while (take_step());
1611 }