model.cc

   1 #include <stdio.h>
   2
   3 #include "model.h"
   4 #include "action.h"
   5 #include "nodestack.h"
   6 #include "schedule.h"
   7 #include "snapshot-interface.h"
   8 #include "common.h"
   9 #include "clockvector.h"
  10 #include "cyclegraph.h"
  11 #include "promise.h"
  12
  13 #define INITIAL_THREAD_ID       0
  14
  15 ModelChecker *model;
  16
  17 /** @brief Constructor */
  18 ModelChecker::ModelChecker(struct model_params params) :
  19         /* Initialize default scheduler */
  20         scheduler(new Scheduler()),
  21         /* First thread created will have id INITIAL_THREAD_ID */
  22         next_thread_id(INITIAL_THREAD_ID),
  23         used_sequence_numbers(0),
  24         num_executions(0),
  25         params(params),
  26         current_action(NULL),
  27         diverge(NULL),
  28         nextThread(NULL),
  29         action_trace(new action_list_t()),
  30         thread_map(new HashTable<int, Thread *, int>()),
  31         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         promises(new std::vector<Promise *>()),
  34         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  35         thrd_last_action(new std::vector<ModelAction *>(1)),
  36         node_stack(new NodeStack()),
  37         next_backtrack(NULL),
  38         mo_graph(new CycleGraph()),
  39         failed_promise(false)
  40 {
  41 }
  42
  43 /** @brief Destructor */
  44 ModelChecker::~ModelChecker()
  45 {
  46         for (int i = 0; i < get_num_threads(); i++)
  47                 delete thread_map->get(i);
  48         delete thread_map;
  49
  50         delete obj_thrd_map;
  51         delete obj_map;
  52         delete action_trace;
  53
  54         for (unsigned int i = 0; i < promises->size(); i++)
  55                 delete (*promises)[i];
  56         delete promises;
  57
  58         delete lazy_sync_with_release;
  59
  60         delete thrd_last_action;
  61         delete node_stack;
  62         delete scheduler;
  63         delete mo_graph;
  64 }
  65
  66 /**
  67  * Restores user program to initial state and resets all model-checker data
  68  * structures.
  69  */
  70 void ModelChecker::reset_to_initial_state()
  71 {
  72         DEBUG("+++ Resetting to initial state +++\n");
  73         node_stack->reset_execution();
  74         current_action = NULL;
  75         next_thread_id = INITIAL_THREAD_ID;
  76         used_sequence_numbers = 0;
  77         nextThread = NULL;
  78         next_backtrack = NULL;
  79         failed_promise = false;
  80         snapshotObject->backTrackBeforeStep(0);
  81 }
  82
  83 /** @returns a thread ID for a new Thread */
  84 thread_id_t ModelChecker::get_next_id()
  85 {
  86         return next_thread_id++;
  87 }
  88
  89 /** @returns the number of user threads created during this execution */
  90 int ModelChecker::get_num_threads()
  91 {
  92         return next_thread_id;
  93 }
  94
  95 /** @returns a sequence number for a new ModelAction */
  96 modelclock_t ModelChecker::get_next_seq_num()
  97 {
  98         return ++used_sequence_numbers;
  99 }
 100
 101 /**
 102  * Choose the next thread in the replay sequence.
 103  *
 104  * If the replay sequence has reached the 'diverge' point, returns a thread
 105  * from the backtracking set. Otherwise, simply returns the next thread in the
 106  * sequence that is being replayed.
 107  */
 108 Thread * ModelChecker::get_next_replay_thread()
 109 {
 110         thread_id_t tid;
 111
 112         /* Have we completed exploring the preselected path? */
 113         if (diverge == NULL)
 114                 return NULL;
 115
 116         /* Else, we are trying to replay an execution */
 117         ModelAction *next = node_stack->get_next()->get_action();
 118
 119         if (next == diverge) {
 120                 Node *nextnode = next->get_node();
 121                 /* Reached divergence point */
 122                 if (nextnode->increment_promise()) {
 123                         /* The next node will try to satisfy a different set of promises. */
 124                         tid = next->get_tid();
 125                         node_stack->pop_restofstack(2);
 126                 } else if (nextnode->increment_read_from()) {
 127                         /* The next node will read from a different value. */
 128                         tid = next->get_tid();
 129                         node_stack->pop_restofstack(2);
 130                 } else if (nextnode->increment_future_value()) {
 131                         /* The next node will try to read from a different future value. */
 132                         tid = next->get_tid();
 133                         node_stack->pop_restofstack(2);
 134                 } else {
 135                         /* Make a different thread execute for next step */
 136                         Node *node = nextnode->get_parent();
 137                         tid = node->get_next_backtrack();
 138                         node_stack->pop_restofstack(1);
 139                 }
 140                 DEBUG("*** Divergence point ***\n");
 141                 diverge = NULL;
 142         } else {
 143                 tid = next->get_tid();
 144         }
 145         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 146         ASSERT(tid != THREAD_ID_T_NONE);
 147         return thread_map->get(id_to_int(tid));
 148 }
 149
 150 /**
 151  * Queries the model-checker for more executions to explore and, if one
 152  * exists, resets the model-checker state to execute a new execution.
 153  *
 154  * @return If there are more executions to explore, return true. Otherwise,
 155  * return false.
 156  */
 157 bool ModelChecker::next_execution()
 158 {
 159         DBG();
 160
 161         num_executions++;
 162
 163         if (isfinalfeasible() || DBG_ENABLED())
 164                 print_summary();
 165
 166         if ((diverge = model->get_next_backtrack()) == NULL)
 167                 return false;
 168
 169         if (DBG_ENABLED()) {
 170                 printf("Next execution will diverge at:\n");
 171                 diverge->print();
 172         }
 173
 174         model->reset_to_initial_state();
 175         return true;
 176 }
 177
 178 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 179 {
 180         action_type type = act->get_type();
 181
 182         switch (type) {
 183                 case ATOMIC_READ:
 184                 case ATOMIC_WRITE:
 185                 case ATOMIC_RMW:
 186                         break;
 187                 default:
 188                         return NULL;
 189         }
 190         /* linear search: from most recent to oldest */
 191         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 192         action_list_t::reverse_iterator rit;
 193         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 194                 ModelAction *prev = *rit;
 195                 if (act->is_synchronizing(prev))
 196                         return prev;
 197         }
 198         return NULL;
 199 }
 200
 201 void ModelChecker::set_backtracking(ModelAction *act)
 202 {
 203         ModelAction *prev;
 204         Node *node;
 205         Thread *t = get_thread(act->get_tid());
 206
 207         prev = get_last_conflict(act);
 208         if (prev == NULL)
 209                 return;
 210
 211         node = prev->get_node()->get_parent();
 212
 213         while (!node->is_enabled(t))
 214                 t = t->get_parent();
 215
 216         /* Check if this has been explored already */
 217         if (node->has_been_explored(t->get_id()))
 218                 return;
 219
 220         /* Cache the latest backtracking point */
 221         if (!next_backtrack || *prev > *next_backtrack)
 222                 next_backtrack = prev;
 223
 224         /* If this is a new backtracking point, mark the tree */
 225         if (!node->set_backtrack(t->get_id()))
 226                 return;
 227         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 228                         prev->get_tid(), t->get_id());
 229         if (DBG_ENABLED()) {
 230                 prev->print();
 231                 act->print();
 232         }
 233 }
 234
 235 /**
 236  * Returns last backtracking point. The model checker will explore a different
 237  * path for this point in the next execution.
 238  * @return The ModelAction at which the next execution should diverge.
 239  */
 240 ModelAction * ModelChecker::get_next_backtrack()
 241 {
 242         ModelAction *next = next_backtrack;
 243         next_backtrack = NULL;
 244         return next;
 245 }
 246
 247 /**
 248  * This is the heart of the model checker routine. It performs model-checking
 249  * actions corresponding to a given "current action." Among other processes, it
 250  * calculates reads-from relationships, updates synchronization clock vectors,
 251  * forms a memory_order constraints graph, and handles replay/backtrack
 252  * execution when running permutations of previously-observed executions.
 253  *
 254  * @param curr The current action to process
 255  * @return The next Thread that must be executed. May be NULL if ModelChecker
 256  * makes no choice (e.g., according to replay execution, combining RMW actions,
 257  * etc.)
 258  */
 259 Thread * ModelChecker::check_current_action(ModelAction *curr)
 260 {
 261         bool already_added = false;
 262
 263         ASSERT(curr);
 264
 265         if (curr->is_rmwc() || curr->is_rmw()) {
 266                 ModelAction *tmp = process_rmw(curr);
 267                 already_added = true;
 268                 delete curr;
 269                 curr = tmp;
 270         } else {
 271                 ModelAction *tmp = node_stack->explore_action(curr);
 272                 if (tmp) {
 273                         /* Discard duplicate ModelAction; use action from NodeStack */
 274                         /* First restore type and order in case of RMW operation */
 275                         if (curr->is_rmwr())
 276                                 tmp->copy_typeandorder(curr);
 277
 278                         /* If we have diverged, we need to reset the clock vector. */
 279                         if (diverge == NULL)
 280                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 281
 282                         delete curr;
 283                         curr = tmp;
 284                 } else {
 285                         /*
 286                          * Perform one-time actions when pushing new ModelAction onto
 287                          * NodeStack
 288                          */
 289                         curr->create_cv(get_parent_action(curr->get_tid()));
 290                         /* Build may_read_from set */
 291                         if (curr->is_read())
 292                                 build_reads_from_past(curr);
 293                         if (curr->is_write())
 294                                 compute_promises(curr);
 295                 }
 296         }
 297
 298         /* Assign 'creation' parent */
 299         if (curr->get_type() == THREAD_CREATE) {
 300                 Thread *th = (Thread *)curr->get_location();
 301                 th->set_creation(curr);
 302         }
 303
 304         /* Deal with new thread */
 305         if (curr->get_type() == THREAD_START)
 306                 check_promises(NULL, curr->get_cv());
 307
 308         /* Assign reads_from values */
 309         Thread *th = get_thread(curr->get_tid());
 310         uint64_t value = VALUE_NONE;
 311         bool updated = false;
 312         if (curr->is_read()) {
 313                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 314                 if (reads_from != NULL) {
 315                         value = reads_from->get_value();
 316                         /* Assign reads_from, perform release/acquire synchronization */
 317                         curr->read_from(reads_from);
 318                         if (r_modification_order(curr,reads_from))
 319                                 updated = true;
 320                 } else {
 321                         /* Read from future value */
 322                         value = curr->get_node()->get_future_value();
 323                         curr->read_from(NULL);
 324                         Promise *valuepromise = new Promise(curr, value);
 325                         promises->push_back(valuepromise);
 326                 }
 327         } else if (curr->is_write()) {
 328                 if (w_modification_order(curr))
 329                         updated = true;;
 330                 if (resolve_promises(curr))
 331                         updated = true;
 332         }
 333
 334         if (updated)
 335                 resolve_release_sequences(curr->get_location());
 336
 337         th->set_return_value(value);
 338
 339         /* Add action to list.  */
 340         if (!already_added)
 341                 add_action_to_lists(curr);
 342
 343         Node *currnode = curr->get_node();
 344         Node *parnode = currnode->get_parent();
 345
 346         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 347                   !currnode->future_value_empty() || !currnode->promise_empty())
 348                 if (!next_backtrack || *curr > *next_backtrack)
 349                         next_backtrack = curr;
 350
 351         set_backtracking(curr);
 352
 353         /* Do not split atomic actions. */
 354         if (curr->is_rmwr())
 355                 return thread_current();
 356         else
 357                 return get_next_replay_thread();
 358 }
 359
 360 /** @returns whether the current partial trace must be a prefix of a
 361  * feasible trace. */
 362
 363 bool ModelChecker::isfeasibleprefix() {
 364 }
 365
 366 /** @returns whether the current partial trace is feasible. */
 367 bool ModelChecker::isfeasible() {
 368         return !mo_graph->checkForCycles() && !failed_promise;
 369 }
 370
 371 /** Returns whether the current completed trace is feasible. */
 372 bool ModelChecker::isfinalfeasible() {
 373         return isfeasible() && promises->size() == 0;
 374 }
 375
 376 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 377 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 378         int tid = id_to_int(act->get_tid());
 379         ModelAction *lastread = get_last_action(tid);
 380         lastread->process_rmw(act);
 381         if (act->is_rmw())
 382                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 383         return lastread;
 384 }
 385
 386 /**
 387  * Updates the mo_graph with the constraints imposed from the current read.
 388  * @param curr The current action. Must be a read.
 389  * @param rf The action that curr reads from. Must be a write.
 390  * @return True if modification order edges were added; false otherwise
 391  */
 392 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 393 {
 394         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 395         unsigned int i;
 396         bool added = false;
 397         ASSERT(curr->is_read());
 398
 399         /* Iterate over all threads */
 400         for (i = 0; i < thrd_lists->size(); i++) {
 401                 /* Iterate over actions in thread, starting from most recent */
 402                 action_list_t *list = &(*thrd_lists)[i];
 403                 action_list_t::reverse_iterator rit;
 404                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 405                         ModelAction *act = *rit;
 406
 407                         /* Include at most one act per-thread that "happens before" curr */
 408                         if (act->happens_before(curr)) {
 409                                 if (act->is_read()) {
 410                                         const ModelAction *prevreadfrom = act->get_reads_from();
 411                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 412                                                 mo_graph->addEdge(prevreadfrom, rf);
 413                                                 added = true;
 414                                         }
 415                                 } else if (rf != act) {
 416                                         mo_graph->addEdge(act, rf);
 417                                         added = true;
 418                                 }
 419                                 break;
 420                         }
 421                 }
 422         }
 423
 424         return added;
 425 }
 426
 427 /** Updates the mo_graph with the constraints imposed from the current read. */
 428 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 429 {
 430         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 431         unsigned int i;
 432         ASSERT(curr->is_read());
 433
 434         /* Iterate over all threads */
 435         for (i = 0; i < thrd_lists->size(); i++) {
 436                 /* Iterate over actions in thread, starting from most recent */
 437                 action_list_t *list = &(*thrd_lists)[i];
 438                 action_list_t::reverse_iterator rit;
 439                 ModelAction *lastact = NULL;
 440
 441                 /* Find last action that happens after curr */
 442                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 443                         ModelAction *act = *rit;
 444                         if (curr->happens_before(act)) {
 445                                 lastact = act;
 446                         } else
 447                                 break;
 448                 }
 449
 450                         /* Include at most one act per-thread that "happens before" curr */
 451                 if (lastact != NULL) {
 452                         if (lastact->is_read()) {
 453                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 454                                 if (postreadfrom != NULL&&rf != postreadfrom)
 455                                         mo_graph->addEdge(rf, postreadfrom);
 456                         } else if (rf != lastact) {
 457                                 mo_graph->addEdge(rf, lastact);
 458                         }
 459                         break;
 460                 }
 461         }
 462 }
 463
 464 /**
 465  * Updates the mo_graph with the constraints imposed from the current write.
 466  * @param curr The current action. Must be a write.
 467  * @return True if modification order edges were added; false otherwise
 468  */
 469 bool ModelChecker::w_modification_order(ModelAction *curr)
 470 {
 471         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 472         unsigned int i;
 473         bool added = false;
 474         ASSERT(curr->is_write());
 475
 476         if (curr->is_seqcst()) {
 477                 /* We have to at least see the last sequentially consistent write,
 478                          so we are initialized. */
 479                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 480                 if (last_seq_cst != NULL) {
 481                         mo_graph->addEdge(last_seq_cst, curr);
 482                         added = true;
 483                 }
 484         }
 485
 486         /* Iterate over all threads */
 487         for (i = 0; i < thrd_lists->size(); i++) {
 488                 /* Iterate over actions in thread, starting from most recent */
 489                 action_list_t *list = &(*thrd_lists)[i];
 490                 action_list_t::reverse_iterator rit;
 491                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 492                         ModelAction *act = *rit;
 493
 494                         /* Include at most one act per-thread that "happens before" curr */
 495                         if (act->happens_before(curr)) {
 496                                 if (act->is_read())
 497                                         mo_graph->addEdge(act->get_reads_from(), curr);
 498                                 else
 499                                         mo_graph->addEdge(act, curr);
 500                                 added = true;
 501                                 break;
 502                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 503                                                      !act->same_thread(curr)) {
 504                                 /* We have an action that:
 505                                    (1) did not happen before us
 506                                    (2) is a read and we are a write
 507                                    (3) cannot synchronize with us
 508                                    (4) is in a different thread
 509                                    =>
 510                                    that read could potentially read from our write.
 511                                  */
 512                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 513                                                 (!next_backtrack || *act > *next_backtrack))
 514                                         next_backtrack = act;
 515                         }
 516                 }
 517         }
 518
 519         return added;
 520 }
 521
 522 /**
 523  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 524  * The ModelAction under consideration is expected to be taking part in
 525  * release/acquire synchronization as an object of the "reads from" relation.
 526  * Note that this can only provide release sequence support for RMW chains
 527  * which do not read from the future, as those actions cannot be traced until
 528  * their "promise" is fulfilled. Similarly, we may not even establish the
 529  * presence of a release sequence with certainty, as some modification order
 530  * constraints may be decided further in the future. Thus, this function
 531  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 532  * and a boolean representing certainty.
 533  *
 534  * @todo Finish lazy updating, when promises are fulfilled in the future
 535  * @param rf The action that might be part of a release sequence. Must be a
 536  * write.
 537  * @param release_heads A pass-by-reference style return parameter.  After
 538  * execution of this function, release_heads will contain the heads of all the
 539  * relevant release sequences, if any exists
 540  * @return true, if the ModelChecker is certain that release_heads is complete;
 541  * false otherwise
 542  */
 543 bool ModelChecker::release_seq_head(const ModelAction *rf,
 544                 std::vector<const ModelAction *> *release_heads) const
 545 {
 546         ASSERT(rf->is_write());
 547         if (!rf) {
 548                 /* read from future: need to settle this later */
 549                 return false; /* incomplete */
 550         }
 551         if (rf->is_release())
 552                 release_heads->push_back(rf);
 553         if (rf->is_rmw()) {
 554                 if (rf->is_acquire())
 555                         return true; /* complete */
 556                 return release_seq_head(rf->get_reads_from(), release_heads);
 557         }
 558         if (rf->is_release())
 559                 return true; /* complete */
 560
 561         /* else relaxed write; check modification order for contiguous subsequence
 562          * -> rf must be same thread as release */
 563         int tid = id_to_int(rf->get_tid());
 564         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 565         action_list_t *list = &(*thrd_lists)[tid];
 566         action_list_t::const_reverse_iterator rit;
 567
 568         /* Find rf in the thread list */
 569         for (rit = list->rbegin(); rit != list->rend(); rit++)
 570                 if (*rit == rf)
 571                         break;
 572
 573         /* Find the last write/release */
 574         for (; rit != list->rend(); rit++)
 575                 if ((*rit)->is_release())
 576                         break;
 577         if (rit == list->rend()) {
 578                 /* No write-release in this thread */
 579                 return true; /* complete */
 580         }
 581         ModelAction *release = *rit;
 582
 583         ASSERT(rf->same_thread(release));
 584
 585         bool certain = true;
 586         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 587                 if (id_to_int(rf->get_tid()) == (int)i)
 588                         continue;
 589                 list = &(*thrd_lists)[i];
 590                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 591                         const ModelAction *act = *rit;
 592                         if (!act->is_write())
 593                                 continue;
 594                         /* Reach synchronization -> this thread is complete */
 595                         if (act->happens_before(release))
 596                                 break;
 597                         if (rf->happens_before(act))
 598                                 continue;
 599
 600                         /* Check modification order */
 601                         if (mo_graph->checkReachable(rf, act))
 602                                 /* rf --mo--> act */
 603                                 continue;
 604                         if (mo_graph->checkReachable(act, release))
 605                                 /* act --mo--> release */
 606                                 break;
 607                         if (mo_graph->checkReachable(release, act) &&
 608                                       mo_graph->checkReachable(act, rf)) {
 609                                 /* release --mo-> act --mo--> rf */
 610                                 return true; /* complete */
 611                         }
 612                         certain = false;
 613                 }
 614         }
 615
 616         if (certain)
 617                 release_heads->push_back(release);
 618         return certain;
 619 }
 620
 621 /**
 622  * A public interface for getting the release sequence head(s) with which a
 623  * given ModelAction must synchronize. This function only returns a non-empty
 624  * result when it can locate a release sequence head with certainty. Otherwise,
 625  * it may mark the internal state of the ModelChecker so that it will handle
 626  * the release sequence at a later time, causing @a act to update its
 627  * synchronization at some later point in execution.
 628  * @param act The 'acquire' action that may read from a release sequence
 629  * @param release_heads A pass-by-reference return parameter. Will be filled
 630  * with the head(s) of the release sequence(s), if they exists with certainty.
 631  * @see ModelChecker::release_seq_head
 632  */
 633 void ModelChecker::get_release_seq_heads(ModelAction *act,
 634                 std::vector<const ModelAction *> *release_heads)
 635 {
 636         const ModelAction *rf = act->get_reads_from();
 637         bool complete;
 638         complete = release_seq_head(rf, release_heads);
 639         if (!complete) {
 640                 /* add act to 'lazy checking' list */
 641                 std::list<ModelAction *> *list;
 642                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 643                 list->push_back(act);
 644         }
 645 }
 646
 647 /**
 648  * Attempt to resolve all stashed operations that might synchronize with a
 649  * release sequence for a given location. This implements the "lazy" portion of
 650  * determining whether or not a release sequence was contiguous, since not all
 651  * modification order information is present at the time an action occurs.
 652  *
 653  * @param location The location/object that should be checked for release
 654  * sequence resolutions
 655  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 656  */
 657 bool ModelChecker::resolve_release_sequences(void *location)
 658 {
 659         std::list<ModelAction *> *list;
 660         list = lazy_sync_with_release->getptr(location);
 661         if (!list)
 662                 return false;
 663
 664         bool updated = false;
 665         std::list<ModelAction *>::iterator it = list->begin();
 666         while (it != list->end()) {
 667                 ModelAction *act = *it;
 668                 const ModelAction *rf = act->get_reads_from();
 669                 std::vector<const ModelAction *> release_heads;
 670                 bool complete;
 671                 complete = release_seq_head(rf, &release_heads);
 672                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 673                         if (!act->has_synchronized_with(release_heads[i])) {
 674                                 updated = true;
 675                                 act->synchronize_with(release_heads[i]);
 676                         }
 677                 }
 678
 679                 if (updated) {
 680                         /* propagate synchronization to later actions */
 681                         action_list_t::reverse_iterator it = action_trace->rbegin();
 682                         while ((*it) != act) {
 683                                 ModelAction *propagate = *it;
 684                                 if (act->happens_before(propagate))
 685                                         /** @todo new mo_graph edges along with
 686                                          * this synchronization? */
 687                                         propagate->synchronize_with(act);
 688                         }
 689                 }
 690                 if (complete)
 691                         it = list->erase(it);
 692                 else
 693                         it++;
 694         }
 695
 696         return updated;
 697 }
 698
 699 /**
 700  * Performs various bookkeeping operations for the current ModelAction. For
 701  * instance, adds action to the per-object, per-thread action vector and to the
 702  * action trace list of all thread actions.
 703  *
 704  * @param act is the ModelAction to add.
 705  */
 706 void ModelChecker::add_action_to_lists(ModelAction *act)
 707 {
 708         int tid = id_to_int(act->get_tid());
 709         action_trace->push_back(act);
 710
 711         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 712
 713         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 714         if (tid >= (int)vec->size())
 715                 vec->resize(next_thread_id);
 716         (*vec)[tid].push_back(act);
 717
 718         if ((int)thrd_last_action->size() <= tid)
 719                 thrd_last_action->resize(get_num_threads());
 720         (*thrd_last_action)[tid] = act;
 721 }
 722
 723 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 724 {
 725         int nthreads = get_num_threads();
 726         if ((int)thrd_last_action->size() < nthreads)
 727                 thrd_last_action->resize(nthreads);
 728         return (*thrd_last_action)[id_to_int(tid)];
 729 }
 730
 731 /**
 732  * Gets the last memory_order_seq_cst action (in the total global sequence)
 733  * performed on a particular object (i.e., memory location).
 734  * @param location The object location to check
 735  * @return The last seq_cst action performed
 736  */
 737 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 738 {
 739         action_list_t *list = obj_map->get_safe_ptr(location);
 740         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 741         action_list_t::reverse_iterator rit;
 742         for (rit = list->rbegin(); rit != list->rend(); rit++)
 743                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 744                         return *rit;
 745         return NULL;
 746 }
 747
 748 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 749 {
 750         ModelAction *parent = get_last_action(tid);
 751         if (!parent)
 752                 parent = get_thread(tid)->get_creation();
 753         return parent;
 754 }
 755
 756 /**
 757  * Returns the clock vector for a given thread.
 758  * @param tid The thread whose clock vector we want
 759  * @return Desired clock vector
 760  */
 761 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 762 {
 763         return get_parent_action(tid)->get_cv();
 764 }
 765
 766 /**
 767  * Resolve a set of Promises with a current write. The set is provided in the
 768  * Node corresponding to @a write.
 769  * @param write The ModelAction that is fulfilling Promises
 770  * @return True if promises were resolved; false otherwise
 771  */
 772 bool ModelChecker::resolve_promises(ModelAction *write)
 773 {
 774         bool resolved = false;
 775         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 776                 Promise *promise = (*promises)[promise_index];
 777                 if (write->get_node()->get_promise(i)) {
 778                         ModelAction *read = promise->get_action();
 779                         read->read_from(write);
 780                         r_modification_order(read, write);
 781                         post_r_modification_order(read, write);
 782                         promises->erase(promises->begin() + promise_index);
 783                         resolved = true;
 784                 } else
 785                         promise_index++;
 786         }
 787         return resolved;
 788 }
 789
 790 /**
 791  * Compute the set of promises that could potentially be satisfied by this
 792  * action. Note that the set computation actually appears in the Node, not in
 793  * ModelChecker.
 794  * @param curr The ModelAction that may satisfy promises
 795  */
 796 void ModelChecker::compute_promises(ModelAction *curr)
 797 {
 798         for (unsigned int i = 0; i < promises->size(); i++) {
 799                 Promise *promise = (*promises)[i];
 800                 const ModelAction *act = promise->get_action();
 801                 if (!act->happens_before(curr) &&
 802                                 act->is_read() &&
 803                                 !act->is_synchronizing(curr) &&
 804                                 !act->same_thread(curr) &&
 805                                 promise->get_value() == curr->get_value()) {
 806                         curr->get_node()->set_promise(i);
 807                 }
 808         }
 809 }
 810
 811 /** Checks promises in response to change in ClockVector Threads. */
 812 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 813 {
 814         for (unsigned int i = 0; i < promises->size(); i++) {
 815                 Promise *promise = (*promises)[i];
 816                 const ModelAction *act = promise->get_action();
 817                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 818                                 merge_cv->synchronized_since(act)) {
 819                         //This thread is no longer able to send values back to satisfy the promise
 820                         int num_synchronized_threads = promise->increment_threads();
 821                         if (num_synchronized_threads == model->get_num_threads()) {
 822                                 //Promise has failed
 823                                 failed_promise = true;
 824                                 return;
 825                         }
 826                 }
 827         }
 828 }
 829
 830 /**
 831  * Build up an initial set of all past writes that this 'read' action may read
 832  * from. This set is determined by the clock vector's "happens before"
 833  * relationship.
 834  * @param curr is the current ModelAction that we are exploring; it must be a
 835  * 'read' operation.
 836  */
 837 void ModelChecker::build_reads_from_past(ModelAction *curr)
 838 {
 839         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 840         unsigned int i;
 841         ASSERT(curr->is_read());
 842
 843         ModelAction *last_seq_cst = NULL;
 844
 845         /* Track whether this object has been initialized */
 846         bool initialized = false;
 847
 848         if (curr->is_seqcst()) {
 849                 last_seq_cst = get_last_seq_cst(curr->get_location());
 850                 /* We have to at least see the last sequentially consistent write,
 851                          so we are initialized. */
 852                 if (last_seq_cst != NULL)
 853                         initialized = true;
 854         }
 855
 856         /* Iterate over all threads */
 857         for (i = 0; i < thrd_lists->size(); i++) {
 858                 /* Iterate over actions in thread, starting from most recent */
 859                 action_list_t *list = &(*thrd_lists)[i];
 860                 action_list_t::reverse_iterator rit;
 861                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 862                         ModelAction *act = *rit;
 863
 864                         /* Only consider 'write' actions */
 865                         if (!act->is_write())
 866                                 continue;
 867
 868                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 869                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 870                                 DEBUG("Adding action to may_read_from:\n");
 871                                 if (DBG_ENABLED()) {
 872                                         act->print();
 873                                         curr->print();
 874                                 }
 875                                 curr->get_node()->add_read_from(act);
 876                         }
 877
 878                         /* Include at most one act per-thread that "happens before" curr */
 879                         if (act->happens_before(curr)) {
 880                                 initialized = true;
 881                                 break;
 882                         }
 883                 }
 884         }
 885
 886         if (!initialized) {
 887                 /** @todo Need a more informative way of reporting errors. */
 888                 printf("ERROR: may read from uninitialized atomic\n");
 889         }
 890
 891         if (DBG_ENABLED() || !initialized) {
 892                 printf("Reached read action:\n");
 893                 curr->print();
 894                 printf("Printing may_read_from\n");
 895                 curr->get_node()->print_may_read_from();
 896                 printf("End printing may_read_from\n");
 897         }
 898
 899         ASSERT(initialized);
 900 }
 901
 902 static void print_list(action_list_t *list)
 903 {
 904         action_list_t::iterator it;
 905
 906         printf("---------------------------------------------------------------------\n");
 907         printf("Trace:\n");
 908
 909         for (it = list->begin(); it != list->end(); it++) {
 910                 (*it)->print();
 911         }
 912         printf("---------------------------------------------------------------------\n");
 913 }
 914
 915 void ModelChecker::print_summary()
 916 {
 917         printf("\n");
 918         printf("Number of executions: %d\n", num_executions);
 919         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 920
 921         scheduler->print();
 922
 923         if (!isfinalfeasible())
 924                 printf("INFEASIBLE EXECUTION!\n");
 925         print_list(action_trace);
 926         printf("\n");
 927 }
 928
 929 /**
 930  * Add a Thread to the system for the first time. Should only be called once
 931  * per thread.
 932  * @param t The Thread to add
 933  */
 934 void ModelChecker::add_thread(Thread *t)
 935 {
 936         thread_map->put(id_to_int(t->get_id()), t);
 937         scheduler->add_thread(t);
 938 }
 939
 940 void ModelChecker::remove_thread(Thread *t)
 941 {
 942         scheduler->remove_thread(t);
 943 }
 944
 945 /**
 946  * Switch from a user-context to the "master thread" context (a.k.a. system
 947  * context). This switch is made with the intention of exploring a particular
 948  * model-checking action (described by a ModelAction object). Must be called
 949  * from a user-thread context.
 950  * @param act The current action that will be explored. May be NULL, although
 951  * there is little reason to switch to the model-checker without an action to
 952  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 953  * yield control without performing any progress; see thrd_join()).
 954  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 955  */
 956 int ModelChecker::switch_to_master(ModelAction *act)
 957 {
 958         DBG();
 959         Thread *old = thread_current();
 960         set_current_action(act);
 961         old->set_state(THREAD_READY);
 962         return Thread::swap(old, &system_context);
 963 }
 964
 965 void ModelChecker::assert_thread() {
 966         DBG();
 967         Thread *old = thread_current();
 968         set_current_action(NULL);
 969         old->set_state(THREAD_ASSERTED);
 970         return Thread::swap(old, &system_context);
 971 }
 972
 973 /**
 974  * Takes the next step in the execution, if possible.
 975  * @return Returns true (success) if a step was taken and false otherwise.
 976  */
 977 bool ModelChecker::take_step() {
 978         Thread *curr, *next;
 979
 980         curr = thread_current();
 981         if (curr) {
 982                 if (curr->get_state() == THREAD_READY) {
 983                         if (current_action) {
 984                                 nextThread = check_current_action(current_action);
 985                                 current_action = NULL;
 986                         }
 987                         scheduler->add_thread(curr);
 988                 } else if (curr->get_state() == THREAD_RUNNING) {
 989                         /* Stopped while running; i.e., completed */
 990                         curr->complete();
 991                 } else if (curr->get_state()==THREAD_ASSERTED) {
 992                         /* Something bad happened.  Stop taking steps. */
 993                         return false;
 994                 } else {
 995                         ASSERT(false);
 996                 }
 997         }
 998         next = scheduler->next_thread(nextThread);
 999
1000         /* Infeasible -> don't take any more steps */
1001         if (!isfeasible())
1002                 return false;
1003
1004         if (next)
1005                 next->set_state(THREAD_RUNNING);
1006         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1007
1008         /* next == NULL -> don't take any more steps */
1009         if (!next)
1010                 return false;
1011         /* Return false only if swap fails with an error */
1012         return (Thread::swap(&system_context, next) == 0);
1013 }
1014
1015 /** Runs the current execution until threre are no more steps to take. */
1016 void ModelChecker::finish_execution() {
1017         DBG();
1018
1019         while (take_step());
1020 }