model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14
  15 #define INITIAL_THREAD_ID       0
  16
  17 ModelChecker *model;
  18
  19 /** @brief Constructor */
  20 ModelChecker::ModelChecker(struct model_params params) :
  21         /* Initialize default scheduler */
  22         scheduler(new Scheduler()),
  23         num_executions(0),
  24         params(params),
  25         diverge(NULL),
  26         action_trace(new action_list_t()),
  27         thread_map(new HashTable<int, Thread *, int>()),
  28         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  29         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  30         promises(new std::vector<Promise *>()),
  31         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  32         thrd_last_action(new std::vector<ModelAction *>(1)),
  33         node_stack(new NodeStack()),
  34         mo_graph(new CycleGraph()),
  35         failed_promise(false),
  36         asserted(false)
  37 {
  38         /* Allocate this "size" on the snapshotting heap */
  39         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  40         /* First thread created will have id INITIAL_THREAD_ID */
  41         priv->next_thread_id = INITIAL_THREAD_ID;
  42
  43         lazy_sync_size = &priv->lazy_sync_size;
  44 }
  45
  46 /** @brief Destructor */
  47 ModelChecker::~ModelChecker()
  48 {
  49         for (int i = 0; i < get_num_threads(); i++)
  50                 delete thread_map->get(i);
  51         delete thread_map;
  52
  53         delete obj_thrd_map;
  54         delete obj_map;
  55         delete action_trace;
  56
  57         for (unsigned int i = 0; i < promises->size(); i++)
  58                 delete (*promises)[i];
  59         delete promises;
  60
  61         delete lazy_sync_with_release;
  62
  63         delete thrd_last_action;
  64         delete node_stack;
  65         delete scheduler;
  66         delete mo_graph;
  67 }
  68
  69 /**
  70  * Restores user program to initial state and resets all model-checker data
  71  * structures.
  72  */
  73 void ModelChecker::reset_to_initial_state()
  74 {
  75         DEBUG("+++ Resetting to initial state +++\n");
  76         node_stack->reset_execution();
  77         failed_promise = false;
  78         reset_asserted();
  79         snapshotObject->backTrackBeforeStep(0);
  80 }
  81
  82 /** @returns a thread ID for a new Thread */
  83 thread_id_t ModelChecker::get_next_id()
  84 {
  85         return priv->next_thread_id++;
  86 }
  87
  88 /** @returns the number of user threads created during this execution */
  89 int ModelChecker::get_num_threads()
  90 {
  91         return priv->next_thread_id;
  92 }
  93
  94 /** @returns a sequence number for a new ModelAction */
  95 modelclock_t ModelChecker::get_next_seq_num()
  96 {
  97         return ++priv->used_sequence_numbers;
  98 }
  99
 100 /**
 101  * Choose the next thread in the replay sequence.
 102  *
 103  * If the replay sequence has reached the 'diverge' point, returns a thread
 104  * from the backtracking set. Otherwise, simply returns the next thread in the
 105  * sequence that is being replayed.
 106  */
 107 Thread * ModelChecker::get_next_replay_thread()
 108 {
 109         thread_id_t tid;
 110
 111         /* Have we completed exploring the preselected path? */
 112         if (diverge == NULL)
 113                 return NULL;
 114
 115         /* Else, we are trying to replay an execution */
 116         ModelAction *next = node_stack->get_next()->get_action();
 117
 118         if (next == diverge) {
 119                 Node *nextnode = next->get_node();
 120                 /* Reached divergence point */
 121                 if (nextnode->increment_promise()) {
 122                         /* The next node will try to satisfy a different set of promises. */
 123                         tid = next->get_tid();
 124                         node_stack->pop_restofstack(2);
 125                 } else if (nextnode->increment_read_from()) {
 126                         /* The next node will read from a different value. */
 127                         tid = next->get_tid();
 128                         node_stack->pop_restofstack(2);
 129                 } else if (nextnode->increment_future_value()) {
 130                         /* The next node will try to read from a different future value. */
 131                         tid = next->get_tid();
 132                         node_stack->pop_restofstack(2);
 133                 } else {
 134                         /* Make a different thread execute for next step */
 135                         Node *node = nextnode->get_parent();
 136                         tid = node->get_next_backtrack();
 137                         node_stack->pop_restofstack(1);
 138                 }
 139                 DEBUG("*** Divergence point ***\n");
 140                 diverge = NULL;
 141         } else {
 142                 tid = next->get_tid();
 143         }
 144         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 145         ASSERT(tid != THREAD_ID_T_NONE);
 146         return thread_map->get(id_to_int(tid));
 147 }
 148
 149 /**
 150  * Queries the model-checker for more executions to explore and, if one
 151  * exists, resets the model-checker state to execute a new execution.
 152  *
 153  * @return If there are more executions to explore, return true. Otherwise,
 154  * return false.
 155  */
 156 bool ModelChecker::next_execution()
 157 {
 158         DBG();
 159
 160         num_executions++;
 161
 162         if (isfinalfeasible() || DBG_ENABLED())
 163                 print_summary();
 164
 165         if ((diverge = get_next_backtrack()) == NULL)
 166                 return false;
 167
 168         if (DBG_ENABLED()) {
 169                 printf("Next execution will diverge at:\n");
 170                 diverge->print();
 171         }
 172
 173         reset_to_initial_state();
 174         return true;
 175 }
 176
 177 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 178 {
 179         action_type type = act->get_type();
 180
 181         switch (type) {
 182                 case ATOMIC_READ:
 183                 case ATOMIC_WRITE:
 184                 case ATOMIC_RMW:
 185                         break;
 186                 default:
 187                         return NULL;
 188         }
 189         /* linear search: from most recent to oldest */
 190         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 191         action_list_t::reverse_iterator rit;
 192         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 193                 ModelAction *prev = *rit;
 194                 if (act->is_synchronizing(prev))
 195                         return prev;
 196         }
 197         return NULL;
 198 }
 199
 200 void ModelChecker::set_backtracking(ModelAction *act)
 201 {
 202         ModelAction *prev;
 203         Node *node;
 204         Thread *t = get_thread(act->get_tid());
 205
 206         prev = get_last_conflict(act);
 207         if (prev == NULL)
 208                 return;
 209
 210         node = prev->get_node()->get_parent();
 211
 212         while (!node->is_enabled(t))
 213                 t = t->get_parent();
 214
 215         /* Check if this has been explored already */
 216         if (node->has_been_explored(t->get_id()))
 217                 return;
 218
 219         /* Cache the latest backtracking point */
 220         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 221                 priv->next_backtrack = prev;
 222
 223         /* If this is a new backtracking point, mark the tree */
 224         if (!node->set_backtrack(t->get_id()))
 225                 return;
 226         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 227                         prev->get_tid(), t->get_id());
 228         if (DBG_ENABLED()) {
 229                 prev->print();
 230                 act->print();
 231         }
 232 }
 233
 234 /**
 235  * Returns last backtracking point. The model checker will explore a different
 236  * path for this point in the next execution.
 237  * @return The ModelAction at which the next execution should diverge.
 238  */
 239 ModelAction * ModelChecker::get_next_backtrack()
 240 {
 241         ModelAction *next = priv->next_backtrack;
 242         priv->next_backtrack = NULL;
 243         return next;
 244 }
 245
 246 /**
 247  * This is the heart of the model checker routine. It performs model-checking
 248  * actions corresponding to a given "current action." Among other processes, it
 249  * calculates reads-from relationships, updates synchronization clock vectors,
 250  * forms a memory_order constraints graph, and handles replay/backtrack
 251  * execution when running permutations of previously-observed executions.
 252  *
 253  * @param curr The current action to process
 254  * @return The next Thread that must be executed. May be NULL if ModelChecker
 255  * makes no choice (e.g., according to replay execution, combining RMW actions,
 256  * etc.)
 257  */
 258 Thread * ModelChecker::check_current_action(ModelAction *curr)
 259 {
 260         bool already_added = false;
 261
 262         ASSERT(curr);
 263
 264         if (curr->is_rmwc() || curr->is_rmw()) {
 265                 ModelAction *tmp = process_rmw(curr);
 266                 already_added = true;
 267                 delete curr;
 268                 curr = tmp;
 269         } else {
 270                 ModelAction *tmp = node_stack->explore_action(curr);
 271                 if (tmp) {
 272                         /* Discard duplicate ModelAction; use action from NodeStack */
 273                         /* First restore type and order in case of RMW operation */
 274                         if (curr->is_rmwr())
 275                                 tmp->copy_typeandorder(curr);
 276
 277                         /* If we have diverged, we need to reset the clock vector. */
 278                         if (diverge == NULL)
 279                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 280
 281                         delete curr;
 282                         curr = tmp;
 283                 } else {
 284                         /*
 285                          * Perform one-time actions when pushing new ModelAction onto
 286                          * NodeStack
 287                          */
 288                         curr->create_cv(get_parent_action(curr->get_tid()));
 289                         /* Build may_read_from set */
 290                         if (curr->is_read())
 291                                 build_reads_from_past(curr);
 292                         if (curr->is_write())
 293                                 compute_promises(curr);
 294                 }
 295         }
 296
 297         /* Assign 'creation' parent */
 298         if (curr->get_type() == THREAD_CREATE) {
 299                 Thread *th = (Thread *)curr->get_location();
 300                 th->set_creation(curr);
 301         } else if (curr->get_type() == THREAD_JOIN) {
 302                 Thread *wait, *join;
 303                 wait = get_thread(curr->get_tid());
 304                 join = (Thread *)curr->get_location();
 305                 if (!join->is_complete())
 306                         scheduler->wait(wait, join);
 307         } else if (curr->get_type() == THREAD_FINISH) {
 308                 Thread *th = get_thread(curr->get_tid());
 309                 while (!th->wait_list_empty()) {
 310                         Thread *wake = th->pop_wait_list();
 311                         scheduler->wake(wake);
 312                 }
 313                 th->complete();
 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         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 (!priv->next_backtrack || *curr > *priv->next_backtrack)
 361                         priv->next_backtrack = curr;
 362
 363         set_backtracking(curr);
 364
 365         /* Do not split atomic actions. */
 366         if (curr->is_rmwr())
 367                 return thread_current();
 368         /* The THREAD_CREATE action points to the created Thread */
 369         else if (curr->get_type() == THREAD_CREATE)
 370                 return (Thread *)curr->get_location();
 371         else
 372                 return get_next_replay_thread();
 373 }
 374
 375 /** @returns whether the current partial trace must be a prefix of a
 376  * feasible trace. */
 377 bool ModelChecker::isfeasibleprefix() {
 378         return promises->size() == 0 && *lazy_sync_size == 0;
 379 }
 380
 381 /** @returns whether the current partial trace is feasible. */
 382 bool ModelChecker::isfeasible() {
 383         return !mo_graph->checkForCycles() && !failed_promise;
 384 }
 385
 386 /** Returns whether the current completed trace is feasible. */
 387 bool ModelChecker::isfinalfeasible() {
 388         return isfeasible() && promises->size() == 0;
 389 }
 390
 391 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 392 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 393         int tid = id_to_int(act->get_tid());
 394         ModelAction *lastread = get_last_action(tid);
 395         lastread->process_rmw(act);
 396         if (act->is_rmw())
 397                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 398         return lastread;
 399 }
 400
 401 /**
 402  * Updates the mo_graph with the constraints imposed from the current read.
 403  * @param curr The current action. Must be a read.
 404  * @param rf The action that curr reads from. Must be a write.
 405  * @return True if modification order edges were added; false otherwise
 406  */
 407 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 408 {
 409         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 410         unsigned int i;
 411         bool added = false;
 412         ASSERT(curr->is_read());
 413
 414         /* Iterate over all threads */
 415         for (i = 0; i < thrd_lists->size(); i++) {
 416                 /* Iterate over actions in thread, starting from most recent */
 417                 action_list_t *list = &(*thrd_lists)[i];
 418                 action_list_t::reverse_iterator rit;
 419                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 420                         ModelAction *act = *rit;
 421
 422                         /* Include at most one act per-thread that "happens before" curr */
 423                         if (act->happens_before(curr)) {
 424                                 if (act->is_read()) {
 425                                         const ModelAction *prevreadfrom = act->get_reads_from();
 426                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 427                                                 mo_graph->addEdge(prevreadfrom, rf);
 428                                                 added = true;
 429                                         }
 430                                 } else if (rf != act) {
 431                                         mo_graph->addEdge(act, rf);
 432                                         added = true;
 433                                 }
 434                                 break;
 435                         }
 436                 }
 437         }
 438
 439         return added;
 440 }
 441
 442 /** Updates the mo_graph with the constraints imposed from the current read. */
 443 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 444 {
 445         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 446         unsigned int i;
 447         ASSERT(curr->is_read());
 448
 449         /* Iterate over all threads */
 450         for (i = 0; i < thrd_lists->size(); i++) {
 451                 /* Iterate over actions in thread, starting from most recent */
 452                 action_list_t *list = &(*thrd_lists)[i];
 453                 action_list_t::reverse_iterator rit;
 454                 ModelAction *lastact = NULL;
 455
 456                 /* Find last action that happens after curr */
 457                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 458                         ModelAction *act = *rit;
 459                         if (curr->happens_before(act)) {
 460                                 lastact = act;
 461                         } else
 462                                 break;
 463                 }
 464
 465                         /* Include at most one act per-thread that "happens before" curr */
 466                 if (lastact != NULL) {
 467                         if (lastact->is_read()) {
 468                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 469                                 if (postreadfrom != NULL&&rf != postreadfrom)
 470                                         mo_graph->addEdge(rf, postreadfrom);
 471                         } else if (rf != lastact) {
 472                                 mo_graph->addEdge(rf, lastact);
 473                         }
 474                         break;
 475                 }
 476         }
 477 }
 478
 479 /**
 480  * Updates the mo_graph with the constraints imposed from the current write.
 481  * @param curr The current action. Must be a write.
 482  * @return True if modification order edges were added; false otherwise
 483  */
 484 bool ModelChecker::w_modification_order(ModelAction *curr)
 485 {
 486         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 487         unsigned int i;
 488         bool added = false;
 489         ASSERT(curr->is_write());
 490
 491         if (curr->is_seqcst()) {
 492                 /* We have to at least see the last sequentially consistent write,
 493                          so we are initialized. */
 494                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 495                 if (last_seq_cst != NULL) {
 496                         mo_graph->addEdge(last_seq_cst, curr);
 497                         added = true;
 498                 }
 499         }
 500
 501         /* Iterate over all threads */
 502         for (i = 0; i < thrd_lists->size(); i++) {
 503                 /* Iterate over actions in thread, starting from most recent */
 504                 action_list_t *list = &(*thrd_lists)[i];
 505                 action_list_t::reverse_iterator rit;
 506                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 507                         ModelAction *act = *rit;
 508
 509                         /* Include at most one act per-thread that "happens before" curr */
 510                         if (act->happens_before(curr)) {
 511                                 if (act->is_read())
 512                                         mo_graph->addEdge(act->get_reads_from(), curr);
 513                                 else
 514                                         mo_graph->addEdge(act, curr);
 515                                 added = true;
 516                                 break;
 517                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 518                                                      !act->same_thread(curr)) {
 519                                 /* We have an action that:
 520                                    (1) did not happen before us
 521                                    (2) is a read and we are a write
 522                                    (3) cannot synchronize with us
 523                                    (4) is in a different thread
 524                                    =>
 525                                    that read could potentially read from our write.
 526                                  */
 527                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 528                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 529                                         priv->next_backtrack = act;
 530                         }
 531                 }
 532         }
 533
 534         return added;
 535 }
 536
 537 /**
 538  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 539  * The ModelAction under consideration is expected to be taking part in
 540  * release/acquire synchronization as an object of the "reads from" relation.
 541  * Note that this can only provide release sequence support for RMW chains
 542  * which do not read from the future, as those actions cannot be traced until
 543  * their "promise" is fulfilled. Similarly, we may not even establish the
 544  * presence of a release sequence with certainty, as some modification order
 545  * constraints may be decided further in the future. Thus, this function
 546  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 547  * and a boolean representing certainty.
 548  *
 549  * @todo Finish lazy updating, when promises are fulfilled in the future
 550  * @param rf The action that might be part of a release sequence. Must be a
 551  * write.
 552  * @param release_heads A pass-by-reference style return parameter.  After
 553  * execution of this function, release_heads will contain the heads of all the
 554  * relevant release sequences, if any exists
 555  * @return true, if the ModelChecker is certain that release_heads is complete;
 556  * false otherwise
 557  */
 558 bool ModelChecker::release_seq_head(const ModelAction *rf,
 559                 std::vector<const ModelAction *> *release_heads) const
 560 {
 561         ASSERT(rf->is_write());
 562         if (!rf) {
 563                 /* read from future: need to settle this later */
 564                 return false; /* incomplete */
 565         }
 566         if (rf->is_release())
 567                 release_heads->push_back(rf);
 568         if (rf->is_rmw()) {
 569                 if (rf->is_acquire())
 570                         return true; /* complete */
 571                 return release_seq_head(rf->get_reads_from(), release_heads);
 572         }
 573         if (rf->is_release())
 574                 return true; /* complete */
 575
 576         /* else relaxed write; check modification order for contiguous subsequence
 577          * -> rf must be same thread as release */
 578         int tid = id_to_int(rf->get_tid());
 579         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 580         action_list_t *list = &(*thrd_lists)[tid];
 581         action_list_t::const_reverse_iterator rit;
 582
 583         /* Find rf in the thread list */
 584         rit = std::find(list->rbegin(), list->rend(), rf);
 585         ASSERT(rit != list->rend());
 586
 587         /* Find the last write/release */
 588         for (; rit != list->rend(); rit++)
 589                 if ((*rit)->is_release())
 590                         break;
 591         if (rit == list->rend()) {
 592                 /* No write-release in this thread */
 593                 return true; /* complete */
 594         }
 595         ModelAction *release = *rit;
 596
 597         ASSERT(rf->same_thread(release));
 598
 599         bool certain = true;
 600         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 601                 if (id_to_int(rf->get_tid()) == (int)i)
 602                         continue;
 603                 list = &(*thrd_lists)[i];
 604
 605                 /* Can we ensure no future writes from this thread may break
 606                  * the release seq? */
 607                 bool future_ordered = false;
 608
 609                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 610                         const ModelAction *act = *rit;
 611                         if (!act->is_write())
 612                                 continue;
 613                         /* Reach synchronization -> this thread is complete */
 614                         if (act->happens_before(release))
 615                                 break;
 616                         if (rf->happens_before(act)) {
 617                                 future_ordered = true;
 618                                 continue;
 619                         }
 620
 621                         /* Check modification order */
 622                         if (mo_graph->checkReachable(rf, act)) {
 623                                 /* rf --mo--> act */
 624                                 future_ordered = true;
 625                                 continue;
 626                         }
 627                         if (mo_graph->checkReachable(act, release))
 628                                 /* act --mo--> release */
 629                                 break;
 630                         if (mo_graph->checkReachable(release, act) &&
 631                                       mo_graph->checkReachable(act, rf)) {
 632                                 /* release --mo-> act --mo--> rf */
 633                                 return true; /* complete */
 634                         }
 635                         certain = false;
 636                 }
 637                 if (!future_ordered)
 638                         return false; /* This thread is uncertain */
 639         }
 640
 641         if (certain)
 642                 release_heads->push_back(release);
 643         return certain;
 644 }
 645
 646 /**
 647  * A public interface for getting the release sequence head(s) with which a
 648  * given ModelAction must synchronize. This function only returns a non-empty
 649  * result when it can locate a release sequence head with certainty. Otherwise,
 650  * it may mark the internal state of the ModelChecker so that it will handle
 651  * the release sequence at a later time, causing @a act to update its
 652  * synchronization at some later point in execution.
 653  * @param act The 'acquire' action that may read from a release sequence
 654  * @param release_heads A pass-by-reference return parameter. Will be filled
 655  * with the head(s) of the release sequence(s), if they exists with certainty.
 656  * @see ModelChecker::release_seq_head
 657  */
 658 void ModelChecker::get_release_seq_heads(ModelAction *act,
 659                 std::vector<const ModelAction *> *release_heads)
 660 {
 661         const ModelAction *rf = act->get_reads_from();
 662         bool complete;
 663         complete = release_seq_head(rf, release_heads);
 664         if (!complete) {
 665                 /* add act to 'lazy checking' list */
 666                 std::list<ModelAction *> *list;
 667                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 668                 list->push_back(act);
 669                 (*lazy_sync_size)++;
 670         }
 671 }
 672
 673 /**
 674  * Attempt to resolve all stashed operations that might synchronize with a
 675  * release sequence for a given location. This implements the "lazy" portion of
 676  * determining whether or not a release sequence was contiguous, since not all
 677  * modification order information is present at the time an action occurs.
 678  *
 679  * @param location The location/object that should be checked for release
 680  * sequence resolutions
 681  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 682  */
 683 bool ModelChecker::resolve_release_sequences(void *location)
 684 {
 685         std::list<ModelAction *> *list;
 686         list = lazy_sync_with_release->getptr(location);
 687         if (!list)
 688                 return false;
 689
 690         bool updated = false;
 691         std::list<ModelAction *>::iterator it = list->begin();
 692         while (it != list->end()) {
 693                 ModelAction *act = *it;
 694                 const ModelAction *rf = act->get_reads_from();
 695                 std::vector<const ModelAction *> release_heads;
 696                 bool complete;
 697                 complete = release_seq_head(rf, &release_heads);
 698                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 699                         if (!act->has_synchronized_with(release_heads[i])) {
 700                                 updated = true;
 701                                 act->synchronize_with(release_heads[i]);
 702                         }
 703                 }
 704
 705                 if (updated) {
 706                         /* propagate synchronization to later actions */
 707                         action_list_t::reverse_iterator it = action_trace->rbegin();
 708                         while ((*it) != act) {
 709                                 ModelAction *propagate = *it;
 710                                 if (act->happens_before(propagate))
 711                                         /** @todo new mo_graph edges along with
 712                                          * this synchronization? */
 713                                         propagate->synchronize_with(act);
 714                         }
 715                 }
 716                 if (complete) {
 717                         it = list->erase(it);
 718                         (*lazy_sync_size)--;
 719                 } else
 720                         it++;
 721         }
 722
 723         // If we resolved promises or data races, see if we have realized a data race.
 724         if (checkDataRaces()) {
 725                 set_assert();
 726         }
 727
 728         return updated;
 729 }
 730
 731 /**
 732  * Performs various bookkeeping operations for the current ModelAction. For
 733  * instance, adds action to the per-object, per-thread action vector and to the
 734  * action trace list of all thread actions.
 735  *
 736  * @param act is the ModelAction to add.
 737  */
 738 void ModelChecker::add_action_to_lists(ModelAction *act)
 739 {
 740         int tid = id_to_int(act->get_tid());
 741         action_trace->push_back(act);
 742
 743         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 744
 745         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 746         if (tid >= (int)vec->size())
 747                 vec->resize(priv->next_thread_id);
 748         (*vec)[tid].push_back(act);
 749
 750         if ((int)thrd_last_action->size() <= tid)
 751                 thrd_last_action->resize(get_num_threads());
 752         (*thrd_last_action)[tid] = act;
 753 }
 754
 755 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 756 {
 757         int nthreads = get_num_threads();
 758         if ((int)thrd_last_action->size() < nthreads)
 759                 thrd_last_action->resize(nthreads);
 760         return (*thrd_last_action)[id_to_int(tid)];
 761 }
 762
 763 /**
 764  * Gets the last memory_order_seq_cst action (in the total global sequence)
 765  * performed on a particular object (i.e., memory location).
 766  * @param location The object location to check
 767  * @return The last seq_cst action performed
 768  */
 769 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 770 {
 771         action_list_t *list = obj_map->get_safe_ptr(location);
 772         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 773         action_list_t::reverse_iterator rit;
 774         for (rit = list->rbegin(); rit != list->rend(); rit++)
 775                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 776                         return *rit;
 777         return NULL;
 778 }
 779
 780 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 781 {
 782         ModelAction *parent = get_last_action(tid);
 783         if (!parent)
 784                 parent = get_thread(tid)->get_creation();
 785         return parent;
 786 }
 787
 788 /**
 789  * Returns the clock vector for a given thread.
 790  * @param tid The thread whose clock vector we want
 791  * @return Desired clock vector
 792  */
 793 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 794 {
 795         return get_parent_action(tid)->get_cv();
 796 }
 797
 798 /**
 799  * Resolve a set of Promises with a current write. The set is provided in the
 800  * Node corresponding to @a write.
 801  * @param write The ModelAction that is fulfilling Promises
 802  * @return True if promises were resolved; false otherwise
 803  */
 804 bool ModelChecker::resolve_promises(ModelAction *write)
 805 {
 806         bool resolved = false;
 807         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 808                 Promise *promise = (*promises)[promise_index];
 809                 if (write->get_node()->get_promise(i)) {
 810                         ModelAction *read = promise->get_action();
 811                         read->read_from(write);
 812                         r_modification_order(read, write);
 813                         post_r_modification_order(read, write);
 814                         promises->erase(promises->begin() + promise_index);
 815                         resolved = true;
 816                 } else
 817                         promise_index++;
 818         }
 819
 820         return resolved;
 821 }
 822
 823 /**
 824  * Compute the set of promises that could potentially be satisfied by this
 825  * action. Note that the set computation actually appears in the Node, not in
 826  * ModelChecker.
 827  * @param curr The ModelAction that may satisfy promises
 828  */
 829 void ModelChecker::compute_promises(ModelAction *curr)
 830 {
 831         for (unsigned int i = 0; i < promises->size(); i++) {
 832                 Promise *promise = (*promises)[i];
 833                 const ModelAction *act = promise->get_action();
 834                 if (!act->happens_before(curr) &&
 835                                 act->is_read() &&
 836                                 !act->is_synchronizing(curr) &&
 837                                 !act->same_thread(curr) &&
 838                                 promise->get_value() == curr->get_value()) {
 839                         curr->get_node()->set_promise(i);
 840                 }
 841         }
 842 }
 843
 844 /** Checks promises in response to change in ClockVector Threads. */
 845 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 846 {
 847         for (unsigned int i = 0; i < promises->size(); i++) {
 848                 Promise *promise = (*promises)[i];
 849                 const ModelAction *act = promise->get_action();
 850                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 851                                 merge_cv->synchronized_since(act)) {
 852                         //This thread is no longer able to send values back to satisfy the promise
 853                         int num_synchronized_threads = promise->increment_threads();
 854                         if (num_synchronized_threads == get_num_threads()) {
 855                                 //Promise has failed
 856                                 failed_promise = true;
 857                                 return;
 858                         }
 859                 }
 860         }
 861 }
 862
 863 /**
 864  * Build up an initial set of all past writes that this 'read' action may read
 865  * from. This set is determined by the clock vector's "happens before"
 866  * relationship.
 867  * @param curr is the current ModelAction that we are exploring; it must be a
 868  * 'read' operation.
 869  */
 870 void ModelChecker::build_reads_from_past(ModelAction *curr)
 871 {
 872         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 873         unsigned int i;
 874         ASSERT(curr->is_read());
 875
 876         ModelAction *last_seq_cst = NULL;
 877
 878         /* Track whether this object has been initialized */
 879         bool initialized = false;
 880
 881         if (curr->is_seqcst()) {
 882                 last_seq_cst = get_last_seq_cst(curr->get_location());
 883                 /* We have to at least see the last sequentially consistent write,
 884                          so we are initialized. */
 885                 if (last_seq_cst != NULL)
 886                         initialized = true;
 887         }
 888
 889         /* Iterate over all threads */
 890         for (i = 0; i < thrd_lists->size(); i++) {
 891                 /* Iterate over actions in thread, starting from most recent */
 892                 action_list_t *list = &(*thrd_lists)[i];
 893                 action_list_t::reverse_iterator rit;
 894                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 895                         ModelAction *act = *rit;
 896
 897                         /* Only consider 'write' actions */
 898                         if (!act->is_write())
 899                                 continue;
 900
 901                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 902                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 903                                 DEBUG("Adding action to may_read_from:\n");
 904                                 if (DBG_ENABLED()) {
 905                                         act->print();
 906                                         curr->print();
 907                                 }
 908                                 curr->get_node()->add_read_from(act);
 909                         }
 910
 911                         /* Include at most one act per-thread that "happens before" curr */
 912                         if (act->happens_before(curr)) {
 913                                 initialized = true;
 914                                 break;
 915                         }
 916                 }
 917         }
 918
 919         if (!initialized) {
 920                 /** @todo Need a more informative way of reporting errors. */
 921                 printf("ERROR: may read from uninitialized atomic\n");
 922         }
 923
 924         if (DBG_ENABLED() || !initialized) {
 925                 printf("Reached read action:\n");
 926                 curr->print();
 927                 printf("Printing may_read_from\n");
 928                 curr->get_node()->print_may_read_from();
 929                 printf("End printing may_read_from\n");
 930         }
 931
 932         ASSERT(initialized);
 933 }
 934
 935 static void print_list(action_list_t *list)
 936 {
 937         action_list_t::iterator it;
 938
 939         printf("---------------------------------------------------------------------\n");
 940         printf("Trace:\n");
 941
 942         for (it = list->begin(); it != list->end(); it++) {
 943                 (*it)->print();
 944         }
 945         printf("---------------------------------------------------------------------\n");
 946 }
 947
 948 void ModelChecker::print_summary()
 949 {
 950         printf("\n");
 951         printf("Number of executions: %d\n", num_executions);
 952         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 953
 954         scheduler->print();
 955
 956         if (!isfinalfeasible())
 957                 printf("INFEASIBLE EXECUTION!\n");
 958         print_list(action_trace);
 959         printf("\n");
 960 }
 961
 962 /**
 963  * Add a Thread to the system for the first time. Should only be called once
 964  * per thread.
 965  * @param t The Thread to add
 966  */
 967 void ModelChecker::add_thread(Thread *t)
 968 {
 969         thread_map->put(id_to_int(t->get_id()), t);
 970         scheduler->add_thread(t);
 971 }
 972
 973 void ModelChecker::remove_thread(Thread *t)
 974 {
 975         scheduler->remove_thread(t);
 976 }
 977
 978 /**
 979  * Switch from a user-context to the "master thread" context (a.k.a. system
 980  * context). This switch is made with the intention of exploring a particular
 981  * model-checking action (described by a ModelAction object). Must be called
 982  * from a user-thread context.
 983  * @param act The current action that will be explored. Must not be NULL.
 984  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 985  */
 986 int ModelChecker::switch_to_master(ModelAction *act)
 987 {
 988         DBG();
 989         Thread *old = thread_current();
 990         set_current_action(act);
 991         old->set_state(THREAD_READY);
 992         return Thread::swap(old, &system_context);
 993 }
 994
 995 /**
 996  * Takes the next step in the execution, if possible.
 997  * @return Returns true (success) if a step was taken and false otherwise.
 998  */
 999 bool ModelChecker::take_step() {
1000         Thread *curr, *next;
1001
1002         if (has_asserted())
1003                 return false;
1004
1005         curr = thread_current();
1006         if (curr) {
1007                 if (curr->get_state() == THREAD_READY) {
1008                         ASSERT(priv->current_action);
1009                         priv->nextThread = check_current_action(priv->current_action);
1010                         priv->current_action = NULL;
1011                         if (!curr->is_blocked() && !curr->is_complete())
1012                                 scheduler->add_thread(curr);
1013                 } else {
1014                         ASSERT(false);
1015                 }
1016         }
1017         next = scheduler->next_thread(priv->nextThread);
1018
1019         /* Infeasible -> don't take any more steps */
1020         if (!isfeasible())
1021                 return false;
1022
1023         if (next)
1024                 next->set_state(THREAD_RUNNING);
1025         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1026
1027         /* next == NULL -> don't take any more steps */
1028         if (!next)
1029                 return false;
1030         /* Return false only if swap fails with an error */
1031         return (Thread::swap(&system_context, next) == 0);
1032 }
1033
1034 /** Runs the current execution until threre are no more steps to take. */
1035 void ModelChecker::finish_execution() {
1036         DBG();
1037
1038         while (take_step());
1039 }