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