model.cc

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