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         too_many_reads(false),
  37         asserted(false)
  38 {
  39         /* Allocate this "size" on the snapshotting heap */
  40         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  41         /* First thread created will have id INITIAL_THREAD_ID */
  42         priv->next_thread_id = INITIAL_THREAD_ID;
  43
  44         lazy_sync_size = &priv->lazy_sync_size;
  45 }
  46
  47 /** @brief Destructor */
  48 ModelChecker::~ModelChecker()
  49 {
  50         for (int i = 0; i < get_num_threads(); i++)
  51                 delete thread_map->get(i);
  52         delete thread_map;
  53
  54         delete obj_thrd_map;
  55         delete obj_map;
  56         delete action_trace;
  57
  58         for (unsigned int i = 0; i < promises->size(); i++)
  59                 delete (*promises)[i];
  60         delete promises;
  61
  62         delete lazy_sync_with_release;
  63
  64         delete thrd_last_action;
  65         delete node_stack;
  66         delete scheduler;
  67         delete mo_graph;
  68 }
  69
  70 /**
  71  * Restores user program to initial state and resets all model-checker data
  72  * structures.
  73  */
  74 void ModelChecker::reset_to_initial_state()
  75 {
  76         DEBUG("+++ Resetting to initial state +++\n");
  77         node_stack->reset_execution();
  78         failed_promise = false;
  79         too_many_reads = false;
  80         reset_asserted();
  81         snapshotObject->backTrackBeforeStep(0);
  82 }
  83
  84 /** @returns a thread ID for a new Thread */
  85 thread_id_t ModelChecker::get_next_id()
  86 {
  87         return priv->next_thread_id++;
  88 }
  89
  90 /** @returns the number of user threads created during this execution */
  91 int ModelChecker::get_num_threads()
  92 {
  93         return priv->next_thread_id;
  94 }
  95
  96 /** @returns a sequence number for a new ModelAction */
  97 modelclock_t ModelChecker::get_next_seq_num()
  98 {
  99         return ++priv->used_sequence_numbers;
 100 }
 101
 102 /**
 103  * Choose the next thread in the replay sequence.
 104  *
 105  * If the replay sequence has reached the 'diverge' point, returns a thread
 106  * from the backtracking set. Otherwise, simply returns the next thread in the
 107  * sequence that is being replayed.
 108  */
 109 Thread * ModelChecker::get_next_replay_thread()
 110 {
 111         thread_id_t tid;
 112
 113         /* Have we completed exploring the preselected path? */
 114         if (diverge == NULL)
 115                 return NULL;
 116
 117         /* Else, we are trying to replay an execution */
 118         ModelAction *next = node_stack->get_next()->get_action();
 119
 120         if (next == diverge) {
 121                 Node *nextnode = next->get_node();
 122                 /* Reached divergence point */
 123                 if (nextnode->increment_promise()) {
 124                         /* The next node will try to satisfy a different set of promises. */
 125                         tid = next->get_tid();
 126                         node_stack->pop_restofstack(2);
 127                 } else if (nextnode->increment_read_from()) {
 128                         /* The next node will read from a different value. */
 129                         tid = next->get_tid();
 130                         node_stack->pop_restofstack(2);
 131                 } else if (nextnode->increment_future_value()) {
 132                         /* The next node will try to read from a different future value. */
 133                         tid = next->get_tid();
 134                         node_stack->pop_restofstack(2);
 135                 } else {
 136                         /* Make a different thread execute for next step */
 137                         Node *node = nextnode->get_parent();
 138                         tid = node->get_next_backtrack();
 139                         node_stack->pop_restofstack(1);
 140                 }
 141                 DEBUG("*** Divergence point ***\n");
 142                 diverge = NULL;
 143         } else {
 144                 tid = next->get_tid();
 145         }
 146         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 147         ASSERT(tid != THREAD_ID_T_NONE);
 148         return thread_map->get(id_to_int(tid));
 149 }
 150
 151 /**
 152  * Queries the model-checker for more executions to explore and, if one
 153  * exists, resets the model-checker state to execute a new execution.
 154  *
 155  * @return If there are more executions to explore, return true. Otherwise,
 156  * return false.
 157  */
 158 bool ModelChecker::next_execution()
 159 {
 160         DBG();
 161
 162         num_executions++;
 163
 164         if (isfinalfeasible() || DBG_ENABLED())
 165                 print_summary();
 166
 167         if ((diverge = get_next_backtrack()) == NULL)
 168                 return false;
 169
 170         if (DBG_ENABLED()) {
 171                 printf("Next execution will diverge at:\n");
 172                 diverge->print();
 173         }
 174
 175         reset_to_initial_state();
 176         return true;
 177 }
 178
 179 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 180 {
 181         action_type type = act->get_type();
 182
 183         switch (type) {
 184                 case ATOMIC_READ:
 185                 case ATOMIC_WRITE:
 186                 case ATOMIC_RMW:
 187                         break;
 188                 default:
 189                         return NULL;
 190         }
 191         /* linear search: from most recent to oldest */
 192         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 193         action_list_t::reverse_iterator rit;
 194         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 195                 ModelAction *prev = *rit;
 196                 if (act->is_synchronizing(prev))
 197                         return prev;
 198         }
 199         return NULL;
 200 }
 201
 202 void ModelChecker::set_backtracking(ModelAction *act)
 203 {
 204         ModelAction *prev;
 205         Node *node;
 206         Thread *t = get_thread(act->get_tid());
 207
 208         prev = get_last_conflict(act);
 209         if (prev == NULL)
 210                 return;
 211
 212         node = prev->get_node()->get_parent();
 213
 214         while (!node->is_enabled(t))
 215                 t = t->get_parent();
 216
 217         /* Check if this has been explored already */
 218         if (node->has_been_explored(t->get_id()))
 219                 return;
 220
 221         /* Cache the latest backtracking point */
 222         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 223                 priv->next_backtrack = prev;
 224
 225         /* If this is a new backtracking point, mark the tree */
 226         if (!node->set_backtrack(t->get_id()))
 227                 return;
 228         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 229                         prev->get_tid(), t->get_id());
 230         if (DBG_ENABLED()) {
 231                 prev->print();
 232                 act->print();
 233         }
 234 }
 235
 236 /**
 237  * Returns last backtracking point. The model checker will explore a different
 238  * path for this point in the next execution.
 239  * @return The ModelAction at which the next execution should diverge.
 240  */
 241 ModelAction * ModelChecker::get_next_backtrack()
 242 {
 243         ModelAction *next = priv->next_backtrack;
 244         priv->next_backtrack = NULL;
 245         return next;
 246 }
 247
 248 /**
 249  * This is the heart of the model checker routine. It performs model-checking
 250  * actions corresponding to a given "current action." Among other processes, it
 251  * calculates reads-from relationships, updates synchronization clock vectors,
 252  * forms a memory_order constraints graph, and handles replay/backtrack
 253  * execution when running permutations of previously-observed executions.
 254  *
 255  * @param curr The current action to process
 256  * @return The next Thread that must be executed. May be NULL if ModelChecker
 257  * makes no choice (e.g., according to replay execution, combining RMW actions,
 258  * etc.)
 259  */
 260 Thread * ModelChecker::check_current_action(ModelAction *curr)
 261 {
 262         bool already_added = false;
 263
 264         ASSERT(curr);
 265
 266         if (curr->is_rmwc() || curr->is_rmw()) {
 267                 ModelAction *tmp = process_rmw(curr);
 268                 already_added = true;
 269                 delete curr;
 270                 curr = tmp;
 271         } else {
 272                 ModelAction *tmp = node_stack->explore_action(curr);
 273                 if (tmp) {
 274                         /* Discard duplicate ModelAction; use action from NodeStack */
 275                         /* First restore type and order in case of RMW operation */
 276                         if (curr->is_rmwr())
 277                                 tmp->copy_typeandorder(curr);
 278
 279                         /* If we have diverged, we need to reset the clock vector. */
 280                         if (diverge == NULL)
 281                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 282
 283                         delete curr;
 284                         curr = tmp;
 285                 } else {
 286                         /*
 287                          * Perform one-time actions when pushing new ModelAction onto
 288                          * NodeStack
 289                          */
 290                         curr->create_cv(get_parent_action(curr->get_tid()));
 291                         /* Build may_read_from set */
 292                         if (curr->is_read())
 293                                 build_reads_from_past(curr);
 294                         if (curr->is_write())
 295                                 compute_promises(curr);
 296                 }
 297         }
 298
 299         /* Assign 'creation' parent */
 300         if (curr->get_type() == THREAD_CREATE) {
 301                 Thread *th = (Thread *)curr->get_location();
 302                 th->set_creation(curr);
 303         } else if (curr->get_type() == THREAD_JOIN) {
 304                 Thread *wait, *join;
 305                 wait = get_thread(curr->get_tid());
 306                 join = (Thread *)curr->get_location();
 307                 if (!join->is_complete())
 308                         scheduler->wait(wait, join);
 309         } else if (curr->get_type() == THREAD_FINISH) {
 310                 Thread *th = get_thread(curr->get_tid());
 311                 while (!th->wait_list_empty()) {
 312                         Thread *wake = th->pop_wait_list();
 313                         scheduler->wake(wake);
 314                 }
 315                 th->complete();
 316         }
 317
 318         /* Deal with new thread */
 319         if (curr->get_type() == THREAD_START)
 320                 check_promises(NULL, curr->get_cv());
 321
 322         /* Assign reads_from values */
 323         Thread *th = get_thread(curr->get_tid());
 324         uint64_t value = VALUE_NONE;
 325         bool updated = false;
 326         if (curr->is_read()) {
 327                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 328                 if (reads_from != NULL) {
 329                         value = reads_from->get_value();
 330                         /* Assign reads_from, perform release/acquire synchronization */
 331                         curr->read_from(reads_from);
 332                         check_recency(curr, already_added);
 333
 334                         if (r_modification_order(curr,reads_from))
 335                                 updated = true;
 336                 } else {
 337                         /* Read from future value */
 338                         value = curr->get_node()->get_future_value();
 339                         curr->read_from(NULL);
 340                         Promise *valuepromise = new Promise(curr, value);
 341                         promises->push_back(valuepromise);
 342                 }
 343         } else if (curr->is_write()) {
 344                 if (w_modification_order(curr))
 345                         updated = true;
 346                 if (resolve_promises(curr))
 347                         updated = true;
 348         }
 349
 350         if (updated)
 351                 resolve_release_sequences(curr->get_location());
 352
 353         th->set_return_value(value);
 354
 355         /* Add action to list.  */
 356         if (!already_added)
 357                 add_action_to_lists(curr);
 358
 359         Node *currnode = curr->get_node();
 360         Node *parnode = currnode->get_parent();
 361
 362         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 363                   !currnode->future_value_empty() || !currnode->promise_empty())
 364                 if (!priv->next_backtrack || *curr > *priv->next_backtrack)
 365                         priv->next_backtrack = curr;
 366
 367         set_backtracking(curr);
 368
 369         /* Do not split atomic actions. */
 370         if (curr->is_rmwr())
 371                 return thread_current();
 372         /* The THREAD_CREATE action points to the created Thread */
 373         else if (curr->get_type() == THREAD_CREATE)
 374                 return (Thread *)curr->get_location();
 375         else
 376                 return get_next_replay_thread();
 377 }
 378
 379 /** @returns whether the current partial trace must be a prefix of a
 380  * feasible trace. */
 381 bool ModelChecker::isfeasibleprefix() {
 382         return promises->size() == 0 && *lazy_sync_size == 0;
 383 }
 384
 385 /** @returns whether the current partial trace is feasible. */
 386 bool ModelChecker::isfeasible() {
 387         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
 388 }
 389
 390 /** Returns whether the current completed trace is feasible. */
 391 bool ModelChecker::isfinalfeasible() {
 392         return isfeasible() && promises->size() == 0;
 393 }
 394
 395 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 396 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 397         int tid = id_to_int(act->get_tid());
 398         ModelAction *lastread = get_last_action(tid);
 399         lastread->process_rmw(act);
 400         if (act->is_rmw())
 401                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 402         return lastread;
 403 }
 404
 405 /**
 406  * Checks whether a thread has read from the same write for too many times.
 407  * @todo This may be more subtle than this code segment addresses at this
 408  * point...  Potential problems to ponder and fix:
 409  * (1) What if the reads_from set keeps changing such that there is no common
 410  * write?
 411  * (2) What if the problem is that the other writes would break modification
 412  * order.
 413  */
 414 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 415         if (params.maxreads != 0) {
 416                 if (curr->get_node()->get_read_from_size() <= 1)
 417                         return;
 418
 419                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 420                 int tid = id_to_int(curr->get_tid());
 421
 422                 /* Skip checks */
 423                 if ((int)thrd_lists->size() <= tid)
 424                         return;
 425
 426                 action_list_t *list = &(*thrd_lists)[tid];
 427
 428                 action_list_t::reverse_iterator rit = list->rbegin();
 429                 /* Skip past curr */
 430                 if (!already_added) {
 431                         for (; (*rit) != curr; rit++)
 432                                 ;
 433                         /* go past curr now */
 434                         rit++;
 435                 }
 436
 437                 int count=0;
 438                 for (; rit != list->rend(); rit++) {
 439                         ModelAction *act = *rit;
 440                         if (!act->is_read())
 441                                 return;
 442                         if (act->get_reads_from() != curr->get_reads_from())
 443                                 return;
 444                         if (act->get_node()->get_read_from_size() <= 1)
 445                                 return;
 446                         count++;
 447                         if (count >= params.maxreads) {
 448                                 /* We've read from the same write for too many times */
 449                                 too_many_reads = true;
 450                         }
 451                 }
 452         }
 453 }
 454
 455 /**
 456  * Updates the mo_graph with the constraints imposed from the current read.
 457  * @param curr The current action. Must be a read.
 458  * @param rf The action that curr reads from. Must be a write.
 459  * @return True if modification order edges were added; false otherwise
 460  */
 461 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 462 {
 463         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 464         unsigned int i;
 465         bool added = false;
 466         ASSERT(curr->is_read());
 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                                         const ModelAction *prevreadfrom = act->get_reads_from();
 480                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 481                                                 mo_graph->addEdge(prevreadfrom, rf);
 482                                                 added = true;
 483                                         }
 484                                 } else if (rf != act) {
 485                                         mo_graph->addEdge(act, rf);
 486                                         added = true;
 487                                 }
 488                                 break;
 489                         }
 490                 }
 491         }
 492
 493         return added;
 494 }
 495
 496 /** Updates the mo_graph with the constraints imposed from the current read. */
 497 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 498 {
 499         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 500         unsigned int i;
 501         ASSERT(curr->is_read());
 502
 503         /* Iterate over all threads */
 504         for (i = 0; i < thrd_lists->size(); i++) {
 505                 /* Iterate over actions in thread, starting from most recent */
 506                 action_list_t *list = &(*thrd_lists)[i];
 507                 action_list_t::reverse_iterator rit;
 508                 ModelAction *lastact = NULL;
 509
 510                 /* Find last action that happens after curr */
 511                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 512                         ModelAction *act = *rit;
 513                         if (curr->happens_before(act)) {
 514                                 lastact = act;
 515                         } else
 516                                 break;
 517                 }
 518
 519                         /* Include at most one act per-thread that "happens before" curr */
 520                 if (lastact != NULL) {
 521                         if (lastact->is_read()) {
 522                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 523                                 if (postreadfrom != NULL&&rf != postreadfrom)
 524                                         mo_graph->addEdge(rf, postreadfrom);
 525                         } else if (rf != lastact) {
 526                                 mo_graph->addEdge(rf, lastact);
 527                         }
 528                         break;
 529                 }
 530         }
 531 }
 532
 533 /**
 534  * Updates the mo_graph with the constraints imposed from the current write.
 535  * @param curr The current action. Must be a write.
 536  * @return True if modification order edges were added; false otherwise
 537  */
 538 bool ModelChecker::w_modification_order(ModelAction *curr)
 539 {
 540         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 541         unsigned int i;
 542         bool added = false;
 543         ASSERT(curr->is_write());
 544
 545         if (curr->is_seqcst()) {
 546                 /* We have to at least see the last sequentially consistent write,
 547                          so we are initialized. */
 548                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 549                 if (last_seq_cst != NULL) {
 550                         mo_graph->addEdge(last_seq_cst, curr);
 551                         added = true;
 552                 }
 553         }
 554
 555         /* Iterate over all threads */
 556         for (i = 0; i < thrd_lists->size(); i++) {
 557                 /* Iterate over actions in thread, starting from most recent */
 558                 action_list_t *list = &(*thrd_lists)[i];
 559                 action_list_t::reverse_iterator rit;
 560                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 561                         ModelAction *act = *rit;
 562
 563                         /* Include at most one act per-thread that "happens before" curr */
 564                         if (act->happens_before(curr)) {
 565                                 if (act->is_read())
 566                                         mo_graph->addEdge(act->get_reads_from(), curr);
 567                                 else
 568                                         mo_graph->addEdge(act, curr);
 569                                 added = true;
 570                                 break;
 571                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 572                                                      !act->same_thread(curr)) {
 573                                 /* We have an action that:
 574                                    (1) did not happen before us
 575                                    (2) is a read and we are a write
 576                                    (3) cannot synchronize with us
 577                                    (4) is in a different thread
 578                                    =>
 579                                    that read could potentially read from our write.
 580                                  */
 581                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 582                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 583                                         priv->next_backtrack = act;
 584                         }
 585                 }
 586         }
 587
 588         return added;
 589 }
 590
 591 /**
 592  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 593  * The ModelAction under consideration is expected to be taking part in
 594  * release/acquire synchronization as an object of the "reads from" relation.
 595  * Note that this can only provide release sequence support for RMW chains
 596  * which do not read from the future, as those actions cannot be traced until
 597  * their "promise" is fulfilled. Similarly, we may not even establish the
 598  * presence of a release sequence with certainty, as some modification order
 599  * constraints may be decided further in the future. Thus, this function
 600  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 601  * and a boolean representing certainty.
 602  *
 603  * @todo Finish lazy updating, when promises are fulfilled in the future
 604  * @param rf The action that might be part of a release sequence. Must be a
 605  * write.
 606  * @param release_heads A pass-by-reference style return parameter.  After
 607  * execution of this function, release_heads will contain the heads of all the
 608  * relevant release sequences, if any exists
 609  * @return true, if the ModelChecker is certain that release_heads is complete;
 610  * false otherwise
 611  */
 612 bool ModelChecker::release_seq_head(const ModelAction *rf,
 613                 std::vector<const ModelAction *> *release_heads) const
 614 {
 615         ASSERT(rf->is_write());
 616         if (!rf) {
 617                 /* read from future: need to settle this later */
 618                 return false; /* incomplete */
 619         }
 620         if (rf->is_release())
 621                 release_heads->push_back(rf);
 622         if (rf->is_rmw()) {
 623                 /* We need a RMW action that is both an acquire and release to stop */
 624                 /** @todo Need to be smarter here...  In the linux lock
 625                  * example, this will run to the beginning of the program for
 626                  * every acquire. */
 627                 if (rf->is_acquire() && rf->is_release())
 628                         return true; /* complete */
 629                 return release_seq_head(rf->get_reads_from(), release_heads);
 630         }
 631         if (rf->is_release())
 632                 return true; /* complete */
 633
 634         /* else relaxed write; check modification order for contiguous subsequence
 635          * -> rf must be same thread as release */
 636         int tid = id_to_int(rf->get_tid());
 637         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 638         action_list_t *list = &(*thrd_lists)[tid];
 639         action_list_t::const_reverse_iterator rit;
 640
 641         /* Find rf in the thread list */
 642         rit = std::find(list->rbegin(), list->rend(), rf);
 643         ASSERT(rit != list->rend());
 644
 645         /* Find the last write/release */
 646         for (; rit != list->rend(); rit++)
 647                 if ((*rit)->is_release())
 648                         break;
 649         if (rit == list->rend()) {
 650                 /* No write-release in this thread */
 651                 return true; /* complete */
 652         }
 653         ModelAction *release = *rit;
 654
 655         ASSERT(rf->same_thread(release));
 656
 657         bool certain = true;
 658         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 659                 if (id_to_int(rf->get_tid()) == (int)i)
 660                         continue;
 661                 list = &(*thrd_lists)[i];
 662
 663                 /* Can we ensure no future writes from this thread may break
 664                  * the release seq? */
 665                 bool future_ordered = false;
 666
 667                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 668                         const ModelAction *act = *rit;
 669                         if (!act->is_write())
 670                                 continue;
 671                         /* Reach synchronization -> this thread is complete */
 672                         if (act->happens_before(release))
 673                                 break;
 674                         if (rf->happens_before(act)) {
 675                                 future_ordered = true;
 676                                 continue;
 677                         }
 678
 679                         /* Check modification order */
 680                         if (mo_graph->checkReachable(rf, act)) {
 681                                 /* rf --mo--> act */
 682                                 future_ordered = true;
 683                                 continue;
 684                         }
 685                         if (mo_graph->checkReachable(act, release))
 686                                 /* act --mo--> release */
 687                                 break;
 688                         if (mo_graph->checkReachable(release, act) &&
 689                                       mo_graph->checkReachable(act, rf)) {
 690                                 /* release --mo-> act --mo--> rf */
 691                                 return true; /* complete */
 692                         }
 693                         certain = false;
 694                 }
 695                 if (!future_ordered)
 696                         return false; /* This thread is uncertain */
 697         }
 698
 699         if (certain)
 700                 release_heads->push_back(release);
 701         return certain;
 702 }
 703
 704 /**
 705  * A public interface for getting the release sequence head(s) with which a
 706  * given ModelAction must synchronize. This function only returns a non-empty
 707  * result when it can locate a release sequence head with certainty. Otherwise,
 708  * it may mark the internal state of the ModelChecker so that it will handle
 709  * the release sequence at a later time, causing @a act to update its
 710  * synchronization at some later point in execution.
 711  * @param act The 'acquire' action that may read from a release sequence
 712  * @param release_heads A pass-by-reference return parameter. Will be filled
 713  * with the head(s) of the release sequence(s), if they exists with certainty.
 714  * @see ModelChecker::release_seq_head
 715  */
 716 void ModelChecker::get_release_seq_heads(ModelAction *act,
 717                 std::vector<const ModelAction *> *release_heads)
 718 {
 719         const ModelAction *rf = act->get_reads_from();
 720         bool complete;
 721         complete = release_seq_head(rf, release_heads);
 722         if (!complete) {
 723                 /* add act to 'lazy checking' list */
 724                 std::list<ModelAction *> *list;
 725                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 726                 list->push_back(act);
 727                 (*lazy_sync_size)++;
 728         }
 729 }
 730
 731 /**
 732  * Attempt to resolve all stashed operations that might synchronize with a
 733  * release sequence for a given location. This implements the "lazy" portion of
 734  * determining whether or not a release sequence was contiguous, since not all
 735  * modification order information is present at the time an action occurs.
 736  *
 737  * @param location The location/object that should be checked for release
 738  * sequence resolutions
 739  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 740  */
 741 bool ModelChecker::resolve_release_sequences(void *location)
 742 {
 743         std::list<ModelAction *> *list;
 744         list = lazy_sync_with_release->getptr(location);
 745         if (!list)
 746                 return false;
 747
 748         bool updated = false;
 749         std::list<ModelAction *>::iterator it = list->begin();
 750         while (it != list->end()) {
 751                 ModelAction *act = *it;
 752                 const ModelAction *rf = act->get_reads_from();
 753                 std::vector<const ModelAction *> release_heads;
 754                 bool complete;
 755                 complete = release_seq_head(rf, &release_heads);
 756                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 757                         if (!act->has_synchronized_with(release_heads[i])) {
 758                                 updated = true;
 759                                 act->synchronize_with(release_heads[i]);
 760                         }
 761                 }
 762
 763                 if (updated) {
 764                         /* propagate synchronization to later actions */
 765                         action_list_t::reverse_iterator it = action_trace->rbegin();
 766                         while ((*it) != act) {
 767                                 ModelAction *propagate = *it;
 768                                 if (act->happens_before(propagate))
 769                                         /** @todo new mo_graph edges along with
 770                                          * this synchronization? */
 771                                         propagate->synchronize_with(act);
 772                         }
 773                 }
 774                 if (complete) {
 775                         it = list->erase(it);
 776                         (*lazy_sync_size)--;
 777                 } else
 778                         it++;
 779         }
 780
 781         // If we resolved promises or data races, see if we have realized a data race.
 782         if (checkDataRaces()) {
 783                 set_assert();
 784         }
 785
 786         return updated;
 787 }
 788
 789 /**
 790  * Performs various bookkeeping operations for the current ModelAction. For
 791  * instance, adds action to the per-object, per-thread action vector and to the
 792  * action trace list of all thread actions.
 793  *
 794  * @param act is the ModelAction to add.
 795  */
 796 void ModelChecker::add_action_to_lists(ModelAction *act)
 797 {
 798         int tid = id_to_int(act->get_tid());
 799         action_trace->push_back(act);
 800
 801         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 802
 803         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 804         if (tid >= (int)vec->size())
 805                 vec->resize(priv->next_thread_id);
 806         (*vec)[tid].push_back(act);
 807
 808         if ((int)thrd_last_action->size() <= tid)
 809                 thrd_last_action->resize(get_num_threads());
 810         (*thrd_last_action)[tid] = act;
 811 }
 812
 813 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 814 {
 815         int nthreads = get_num_threads();
 816         if ((int)thrd_last_action->size() < nthreads)
 817                 thrd_last_action->resize(nthreads);
 818         return (*thrd_last_action)[id_to_int(tid)];
 819 }
 820
 821 /**
 822  * Gets the last memory_order_seq_cst action (in the total global sequence)
 823  * performed on a particular object (i.e., memory location).
 824  * @param location The object location to check
 825  * @return The last seq_cst action performed
 826  */
 827 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 828 {
 829         action_list_t *list = obj_map->get_safe_ptr(location);
 830         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 831         action_list_t::reverse_iterator rit;
 832         for (rit = list->rbegin(); rit != list->rend(); rit++)
 833                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 834                         return *rit;
 835         return NULL;
 836 }
 837
 838 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 839 {
 840         ModelAction *parent = get_last_action(tid);
 841         if (!parent)
 842                 parent = get_thread(tid)->get_creation();
 843         return parent;
 844 }
 845
 846 /**
 847  * Returns the clock vector for a given thread.
 848  * @param tid The thread whose clock vector we want
 849  * @return Desired clock vector
 850  */
 851 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 852 {
 853         return get_parent_action(tid)->get_cv();
 854 }
 855
 856 /**
 857  * Resolve a set of Promises with a current write. The set is provided in the
 858  * Node corresponding to @a write.
 859  * @param write The ModelAction that is fulfilling Promises
 860  * @return True if promises were resolved; false otherwise
 861  */
 862 bool ModelChecker::resolve_promises(ModelAction *write)
 863 {
 864         bool resolved = false;
 865         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 866                 Promise *promise = (*promises)[promise_index];
 867                 if (write->get_node()->get_promise(i)) {
 868                         ModelAction *read = promise->get_action();
 869                         read->read_from(write);
 870                         r_modification_order(read, write);
 871                         post_r_modification_order(read, write);
 872                         promises->erase(promises->begin() + promise_index);
 873                         resolved = true;
 874                 } else
 875                         promise_index++;
 876         }
 877
 878         return resolved;
 879 }
 880
 881 /**
 882  * Compute the set of promises that could potentially be satisfied by this
 883  * action. Note that the set computation actually appears in the Node, not in
 884  * ModelChecker.
 885  * @param curr The ModelAction that may satisfy promises
 886  */
 887 void ModelChecker::compute_promises(ModelAction *curr)
 888 {
 889         for (unsigned int i = 0; i < promises->size(); i++) {
 890                 Promise *promise = (*promises)[i];
 891                 const ModelAction *act = promise->get_action();
 892                 if (!act->happens_before(curr) &&
 893                                 act->is_read() &&
 894                                 !act->is_synchronizing(curr) &&
 895                                 !act->same_thread(curr) &&
 896                                 promise->get_value() == curr->get_value()) {
 897                         curr->get_node()->set_promise(i);
 898                 }
 899         }
 900 }
 901
 902 /** Checks promises in response to change in ClockVector Threads. */
 903 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 904 {
 905         for (unsigned int i = 0; i < promises->size(); i++) {
 906                 Promise *promise = (*promises)[i];
 907                 const ModelAction *act = promise->get_action();
 908                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 909                                 merge_cv->synchronized_since(act)) {
 910                         //This thread is no longer able to send values back to satisfy the promise
 911                         int num_synchronized_threads = promise->increment_threads();
 912                         if (num_synchronized_threads == get_num_threads()) {
 913                                 //Promise has failed
 914                                 failed_promise = true;
 915                                 return;
 916                         }
 917                 }
 918         }
 919 }
 920
 921 /**
 922  * Build up an initial set of all past writes that this 'read' action may read
 923  * from. This set is determined by the clock vector's "happens before"
 924  * relationship.
 925  * @param curr is the current ModelAction that we are exploring; it must be a
 926  * 'read' operation.
 927  */
 928 void ModelChecker::build_reads_from_past(ModelAction *curr)
 929 {
 930         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 931         unsigned int i;
 932         ASSERT(curr->is_read());
 933
 934         ModelAction *last_seq_cst = NULL;
 935
 936         /* Track whether this object has been initialized */
 937         bool initialized = false;
 938
 939         if (curr->is_seqcst()) {
 940                 last_seq_cst = get_last_seq_cst(curr->get_location());
 941                 /* We have to at least see the last sequentially consistent write,
 942                          so we are initialized. */
 943                 if (last_seq_cst != NULL)
 944                         initialized = true;
 945         }
 946
 947         /* Iterate over all threads */
 948         for (i = 0; i < thrd_lists->size(); i++) {
 949                 /* Iterate over actions in thread, starting from most recent */
 950                 action_list_t *list = &(*thrd_lists)[i];
 951                 action_list_t::reverse_iterator rit;
 952                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 953                         ModelAction *act = *rit;
 954
 955                         /* Only consider 'write' actions */
 956                         if (!act->is_write())
 957                                 continue;
 958
 959                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 960                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 961                                 DEBUG("Adding action to may_read_from:\n");
 962                                 if (DBG_ENABLED()) {
 963                                         act->print();
 964                                         curr->print();
 965                                 }
 966                                 curr->get_node()->add_read_from(act);
 967                         }
 968
 969                         /* Include at most one act per-thread that "happens before" curr */
 970                         if (act->happens_before(curr)) {
 971                                 initialized = true;
 972                                 break;
 973                         }
 974                 }
 975         }
 976
 977         if (!initialized) {
 978                 /** @todo Need a more informative way of reporting errors. */
 979                 printf("ERROR: may read from uninitialized atomic\n");
 980         }
 981
 982         if (DBG_ENABLED() || !initialized) {
 983                 printf("Reached read action:\n");
 984                 curr->print();
 985                 printf("Printing may_read_from\n");
 986                 curr->get_node()->print_may_read_from();
 987                 printf("End printing may_read_from\n");
 988         }
 989
 990         ASSERT(initialized);
 991 }
 992
 993 static void print_list(action_list_t *list)
 994 {
 995         action_list_t::iterator it;
 996
 997         printf("---------------------------------------------------------------------\n");
 998         printf("Trace:\n");
 999
1000         for (it = list->begin(); it != list->end(); it++) {
1001                 (*it)->print();
1002         }
1003         printf("---------------------------------------------------------------------\n");
1004 }
1005
1006 void ModelChecker::print_summary()
1007 {
1008         printf("\n");
1009         printf("Number of executions: %d\n", num_executions);
1010         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1011
1012         scheduler->print();
1013
1014         if (!isfinalfeasible())
1015                 printf("INFEASIBLE EXECUTION!\n");
1016         print_list(action_trace);
1017         printf("\n");
1018 }
1019
1020 /**
1021  * Add a Thread to the system for the first time. Should only be called once
1022  * per thread.
1023  * @param t The Thread to add
1024  */
1025 void ModelChecker::add_thread(Thread *t)
1026 {
1027         thread_map->put(id_to_int(t->get_id()), t);
1028         scheduler->add_thread(t);
1029 }
1030
1031 void ModelChecker::remove_thread(Thread *t)
1032 {
1033         scheduler->remove_thread(t);
1034 }
1035
1036 /**
1037  * Switch from a user-context to the "master thread" context (a.k.a. system
1038  * context). This switch is made with the intention of exploring a particular
1039  * model-checking action (described by a ModelAction object). Must be called
1040  * from a user-thread context.
1041  * @param act The current action that will be explored. Must not be NULL.
1042  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1043  */
1044 int ModelChecker::switch_to_master(ModelAction *act)
1045 {
1046         DBG();
1047         Thread *old = thread_current();
1048         set_current_action(act);
1049         old->set_state(THREAD_READY);
1050         return Thread::swap(old, &system_context);
1051 }
1052
1053 /**
1054  * Takes the next step in the execution, if possible.
1055  * @return Returns true (success) if a step was taken and false otherwise.
1056  */
1057 bool ModelChecker::take_step() {
1058         Thread *curr, *next;
1059
1060         if (has_asserted())
1061                 return false;
1062
1063         curr = thread_current();
1064         if (curr) {
1065                 if (curr->get_state() == THREAD_READY) {
1066                         ASSERT(priv->current_action);
1067                         priv->nextThread = check_current_action(priv->current_action);
1068                         priv->current_action = NULL;
1069                         if (!curr->is_blocked() && !curr->is_complete())
1070                                 scheduler->add_thread(curr);
1071                 } else {
1072                         ASSERT(false);
1073                 }
1074         }
1075         next = scheduler->next_thread(priv->nextThread);
1076
1077         /* Infeasible -> don't take any more steps */
1078         if (!isfeasible())
1079                 return false;
1080
1081         if (next)
1082                 next->set_state(THREAD_RUNNING);
1083         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1084
1085         /* next == NULL -> don't take any more steps */
1086         if (!next)
1087                 return false;
1088         /* Return false only if swap fails with an error */
1089         return (Thread::swap(&system_context, next) == 0);
1090 }
1091
1092 /** Runs the current execution until threre are no more steps to take. */
1093 void ModelChecker::finish_execution() {
1094         DBG();
1095
1096         while (take_step());
1097 }