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