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