model.cc

   1 #include <stdio.h>
   2
   3 #include "model.h"
   4 #include "action.h"
   5 #include "nodestack.h"
   6 #include "schedule.h"
   7 #include "snapshot-interface.h"
   8 #include "common.h"
   9 #include "clockvector.h"
  10 #include "cyclegraph.h"
  11 #include "promise.h"
  12
  13 #define INITIAL_THREAD_ID       0
  14
  15 ModelChecker *model;
  16
  17 /** @brief Constructor */
  18 ModelChecker::ModelChecker(struct model_params params) :
  19         /* Initialize default scheduler */
  20         scheduler(new Scheduler()),
  21         /* First thread created will have id INITIAL_THREAD_ID */
  22         next_thread_id(INITIAL_THREAD_ID),
  23         used_sequence_numbers(0),
  24         num_executions(0),
  25         params(params),
  26         current_action(NULL),
  27         diverge(NULL),
  28         nextThread(NULL),
  29         action_trace(new action_list_t()),
  30         thread_map(new HashTable<int, Thread *, int>()),
  31         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         promises(new std::vector<Promise *>()),
  34         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  35         thrd_last_action(new std::vector<ModelAction *>(1)),
  36         node_stack(new NodeStack()),
  37         next_backtrack(NULL),
  38         mo_graph(new CycleGraph()),
  39         failed_promise(false)
  40 {
  41 }
  42
  43 /** @brief Destructor */
  44 ModelChecker::~ModelChecker()
  45 {
  46         for (int i = 0; i < get_num_threads(); i++)
  47                 delete thread_map->get(i);
  48         delete thread_map;
  49
  50         delete obj_thrd_map;
  51         delete obj_map;
  52         delete action_trace;
  53
  54         for (unsigned int i = 0; i < promises->size(); i++)
  55                 delete (*promises)[i];
  56         delete promises;
  57
  58         delete lazy_sync_with_release;
  59
  60         delete thrd_last_action;
  61         delete node_stack;
  62         delete scheduler;
  63         delete mo_graph;
  64 }
  65
  66 /**
  67  * Restores user program to initial state and resets all model-checker data
  68  * structures.
  69  */
  70 void ModelChecker::reset_to_initial_state()
  71 {
  72         DEBUG("+++ Resetting to initial state +++\n");
  73         node_stack->reset_execution();
  74         current_action = NULL;
  75         next_thread_id = INITIAL_THREAD_ID;
  76         used_sequence_numbers = 0;
  77         nextThread = NULL;
  78         next_backtrack = NULL;
  79         failed_promise = false;
  80         snapshotObject->backTrackBeforeStep(0);
  81 }
  82
  83 /** @returns a thread ID for a new Thread */
  84 thread_id_t ModelChecker::get_next_id()
  85 {
  86         return next_thread_id++;
  87 }
  88
  89 /** @returns the number of user threads created during this execution */
  90 int ModelChecker::get_num_threads()
  91 {
  92         return next_thread_id;
  93 }
  94
  95 /** @returns a sequence number for a new ModelAction */
  96 modelclock_t ModelChecker::get_next_seq_num()
  97 {
  98         return ++used_sequence_numbers;
  99 }
 100
 101 /**
 102  * Choose the next thread in the replay sequence.
 103  *
 104  * If the replay sequence has reached the 'diverge' point, returns a thread
 105  * from the backtracking set. Otherwise, simply returns the next thread in the
 106  * sequence that is being replayed.
 107  */
 108 Thread * ModelChecker::get_next_replay_thread()
 109 {
 110         thread_id_t tid;
 111
 112         /* Have we completed exploring the preselected path? */
 113         if (diverge == NULL)
 114                 return NULL;
 115
 116         /* Else, we are trying to replay an execution */
 117         ModelAction *next = node_stack->get_next()->get_action();
 118
 119         if (next == diverge) {
 120                 Node *nextnode = next->get_node();
 121                 /* Reached divergence point */
 122                 if (nextnode->increment_promise()) {
 123                         /* The next node will try to satisfy a different set of promises. */
 124                         tid = next->get_tid();
 125                         node_stack->pop_restofstack(2);
 126                 } else if (nextnode->increment_read_from()) {
 127                         /* The next node will read from a different value. */
 128                         tid = next->get_tid();
 129                         node_stack->pop_restofstack(2);
 130                 } else if (nextnode->increment_future_value()) {
 131                         /* The next node will try to read from a different future value. */
 132                         tid = next->get_tid();
 133                         node_stack->pop_restofstack(2);
 134                 } else {
 135                         /* Make a different thread execute for next step */
 136                         Node *node = nextnode->get_parent();
 137                         tid = node->get_next_backtrack();
 138                         node_stack->pop_restofstack(1);
 139                 }
 140                 DEBUG("*** Divergence point ***\n");
 141                 diverge = NULL;
 142         } else {
 143                 tid = next->get_tid();
 144         }
 145         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 146         ASSERT(tid != THREAD_ID_T_NONE);
 147         return thread_map->get(id_to_int(tid));
 148 }
 149
 150 /**
 151  * Queries the model-checker for more executions to explore and, if one
 152  * exists, resets the model-checker state to execute a new execution.
 153  *
 154  * @return If there are more executions to explore, return true. Otherwise,
 155  * return false.
 156  */
 157 bool ModelChecker::next_execution()
 158 {
 159         DBG();
 160
 161         num_executions++;
 162
 163         if (isfinalfeasible() || DBG_ENABLED())
 164                 print_summary();
 165
 166         if ((diverge = model->get_next_backtrack()) == NULL)
 167                 return false;
 168
 169         if (DBG_ENABLED()) {
 170                 printf("Next execution will diverge at:\n");
 171                 diverge->print();
 172         }
 173
 174         model->reset_to_initial_state();
 175         return true;
 176 }
 177
 178 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 179 {
 180         action_type type = act->get_type();
 181
 182         switch (type) {
 183                 case ATOMIC_READ:
 184                 case ATOMIC_WRITE:
 185                 case ATOMIC_RMW:
 186                         break;
 187                 default:
 188                         return NULL;
 189         }
 190         /* linear search: from most recent to oldest */
 191         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 192         action_list_t::reverse_iterator rit;
 193         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 194                 ModelAction *prev = *rit;
 195                 if (act->is_synchronizing(prev))
 196                         return prev;
 197         }
 198         return NULL;
 199 }
 200
 201 void ModelChecker::set_backtracking(ModelAction *act)
 202 {
 203         ModelAction *prev;
 204         Node *node;
 205         Thread *t = get_thread(act->get_tid());
 206
 207         prev = get_last_conflict(act);
 208         if (prev == NULL)
 209                 return;
 210
 211         node = prev->get_node()->get_parent();
 212
 213         while (!node->is_enabled(t))
 214                 t = t->get_parent();
 215
 216         /* Check if this has been explored already */
 217         if (node->has_been_explored(t->get_id()))
 218                 return;
 219
 220         /* Cache the latest backtracking point */
 221         if (!next_backtrack || *prev > *next_backtrack)
 222                 next_backtrack = prev;
 223
 224         /* If this is a new backtracking point, mark the tree */
 225         if (!node->set_backtrack(t->get_id()))
 226                 return;
 227         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 228                         prev->get_tid(), t->get_id());
 229         if (DBG_ENABLED()) {
 230                 prev->print();
 231                 act->print();
 232         }
 233 }
 234
 235 /**
 236  * Returns last backtracking point. The model checker will explore a different
 237  * path for this point in the next execution.
 238  * @return The ModelAction at which the next execution should diverge.
 239  */
 240 ModelAction * ModelChecker::get_next_backtrack()
 241 {
 242         ModelAction *next = next_backtrack;
 243         next_backtrack = NULL;
 244         return next;
 245 }
 246
 247 /**
 248  * This is the heart of the model checker routine. It performs model-checking
 249  * actions corresponding to a given "current action." Among other processes, it
 250  * calculates reads-from relationships, updates synchronization clock vectors,
 251  * forms a memory_order constraints graph, and handles replay/backtrack
 252  * execution when running permutations of previously-observed executions.
 253  *
 254  * @param curr The current action to process
 255  * @return The next Thread that must be executed. May be NULL if ModelChecker
 256  * makes no choice (e.g., according to replay execution, combining RMW actions,
 257  * etc.)
 258  */
 259 Thread * ModelChecker::check_current_action(ModelAction *curr)
 260 {
 261         bool already_added = false;
 262
 263         ASSERT(curr);
 264
 265         if (curr->is_rmwc() || curr->is_rmw()) {
 266                 ModelAction *tmp = process_rmw(curr);
 267                 already_added = true;
 268                 delete curr;
 269                 curr = tmp;
 270         } else {
 271                 ModelAction *tmp = node_stack->explore_action(curr);
 272                 if (tmp) {
 273                         /* Discard duplicate ModelAction; use action from NodeStack */
 274                         /* First restore type and order in case of RMW operation */
 275                         if (curr->is_rmwr())
 276                                 tmp->copy_typeandorder(curr);
 277
 278                         /* If we have diverged, we need to reset the clock vector. */
 279                         if (diverge == NULL)
 280                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 281
 282                         delete curr;
 283                         curr = tmp;
 284                 } else {
 285                         /*
 286                          * Perform one-time actions when pushing new ModelAction onto
 287                          * NodeStack
 288                          */
 289                         curr->create_cv(get_parent_action(curr->get_tid()));
 290                         /* Build may_read_from set */
 291                         if (curr->is_read())
 292                                 build_reads_from_past(curr);
 293                         if (curr->is_write())
 294                                 compute_promises(curr);
 295                 }
 296         }
 297
 298         /* Assign 'creation' parent */
 299         if (curr->get_type() == THREAD_CREATE) {
 300                 Thread *th = (Thread *)curr->get_location();
 301                 th->set_creation(curr);
 302         }
 303
 304         /* Deal with new thread */
 305         if (curr->get_type() == THREAD_START)
 306                 check_promises(NULL, curr->get_cv());
 307
 308         /* Assign reads_from values */
 309         Thread *th = get_thread(curr->get_tid());
 310         uint64_t value = VALUE_NONE;
 311         bool updated = false;
 312         if (curr->is_read()) {
 313                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 314                 if (reads_from != NULL) {
 315                         value = reads_from->get_value();
 316                         /* Assign reads_from, perform release/acquire synchronization */
 317                         curr->read_from(reads_from);
 318                         if (r_modification_order(curr,reads_from))
 319                                 updated = true;
 320                 } else {
 321                         /* Read from future value */
 322                         value = curr->get_node()->get_future_value();
 323                         curr->read_from(NULL);
 324                         Promise *valuepromise = new Promise(curr, value);
 325                         promises->push_back(valuepromise);
 326                 }
 327         } else if (curr->is_write()) {
 328                 if (w_modification_order(curr))
 329                         updated = true;;
 330                 if (resolve_promises(curr))
 331                         updated = true;
 332         }
 333
 334         if (updated)
 335                 resolve_release_sequences(curr->get_location());
 336
 337         th->set_return_value(value);
 338
 339         /* Add action to list.  */
 340         if (!already_added)
 341                 add_action_to_lists(curr);
 342
 343         Node *currnode = curr->get_node();
 344         Node *parnode = currnode->get_parent();
 345
 346         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 347                   !currnode->future_value_empty() || !currnode->promise_empty())
 348                 if (!next_backtrack || *curr > *next_backtrack)
 349                         next_backtrack = curr;
 350
 351         set_backtracking(curr);
 352
 353         /* Do not split atomic actions. */
 354         if (curr->is_rmwr())
 355                 return thread_current();
 356         else
 357                 return get_next_replay_thread();
 358 }
 359
 360 /** @returns whether the current partial trace is feasible. */
 361 bool ModelChecker::isfeasible() {
 362         return !mo_graph->checkForCycles() && !failed_promise;
 363 }
 364
 365 /** Returns whether the current completed trace is feasible. */
 366 bool ModelChecker::isfinalfeasible() {
 367         return isfeasible() && promises->size() == 0;
 368 }
 369
 370 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 371 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 372         int tid = id_to_int(act->get_tid());
 373         ModelAction *lastread = get_last_action(tid);
 374         lastread->process_rmw(act);
 375         if (act->is_rmw())
 376                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 377         return lastread;
 378 }
 379
 380 /**
 381  * Updates the mo_graph with the constraints imposed from the current read.
 382  * @param curr The current action. Must be a read.
 383  * @param rf The action that curr reads from. Must be a write.
 384  * @return True if modification order edges were added; false otherwise
 385  */
 386 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 387 {
 388         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 389         unsigned int i;
 390         bool added = false;
 391         ASSERT(curr->is_read());
 392
 393         /* Iterate over all threads */
 394         for (i = 0; i < thrd_lists->size(); i++) {
 395                 /* Iterate over actions in thread, starting from most recent */
 396                 action_list_t *list = &(*thrd_lists)[i];
 397                 action_list_t::reverse_iterator rit;
 398                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 399                         ModelAction *act = *rit;
 400
 401                         /* Include at most one act per-thread that "happens before" curr */
 402                         if (act->happens_before(curr)) {
 403                                 if (act->is_read()) {
 404                                         const ModelAction *prevreadfrom = act->get_reads_from();
 405                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 406                                                 mo_graph->addEdge(prevreadfrom, rf);
 407                                                 added = true;
 408                                         }
 409                                 } else if (rf != act) {
 410                                         mo_graph->addEdge(act, rf);
 411                                         added = true;
 412                                 }
 413                                 break;
 414                         }
 415                 }
 416         }
 417
 418         return added;
 419 }
 420
 421 /** Updates the mo_graph with the constraints imposed from the current read. */
 422 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 423 {
 424         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 425         unsigned int i;
 426         ASSERT(curr->is_read());
 427
 428         /* Iterate over all threads */
 429         for (i = 0; i < thrd_lists->size(); i++) {
 430                 /* Iterate over actions in thread, starting from most recent */
 431                 action_list_t *list = &(*thrd_lists)[i];
 432                 action_list_t::reverse_iterator rit;
 433                 ModelAction *lastact = NULL;
 434
 435                 /* Find last action that happens after curr */
 436                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 437                         ModelAction *act = *rit;
 438                         if (curr->happens_before(act)) {
 439                                 lastact = act;
 440                         } else
 441                                 break;
 442                 }
 443
 444                         /* Include at most one act per-thread that "happens before" curr */
 445                 if (lastact != NULL) {
 446                         if (lastact->is_read()) {
 447                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 448                                 if (postreadfrom != NULL&&rf != postreadfrom)
 449                                         mo_graph->addEdge(rf, postreadfrom);
 450                         } else if (rf != lastact) {
 451                                 mo_graph->addEdge(rf, lastact);
 452                         }
 453                         break;
 454                 }
 455         }
 456 }
 457
 458 /**
 459  * Updates the mo_graph with the constraints imposed from the current write.
 460  * @param curr The current action. Must be a write.
 461  * @return True if modification order edges were added; false otherwise
 462  */
 463 bool ModelChecker::w_modification_order(ModelAction *curr)
 464 {
 465         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 466         unsigned int i;
 467         bool added = false;
 468         ASSERT(curr->is_write());
 469
 470         if (curr->is_seqcst()) {
 471                 /* We have to at least see the last sequentially consistent write,
 472                          so we are initialized. */
 473                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 474                 if (last_seq_cst != NULL) {
 475                         mo_graph->addEdge(last_seq_cst, curr);
 476                         added = true;
 477                 }
 478         }
 479
 480         /* Iterate over all threads */
 481         for (i = 0; i < thrd_lists->size(); i++) {
 482                 /* Iterate over actions in thread, starting from most recent */
 483                 action_list_t *list = &(*thrd_lists)[i];
 484                 action_list_t::reverse_iterator rit;
 485                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 486                         ModelAction *act = *rit;
 487
 488                         /* Include at most one act per-thread that "happens before" curr */
 489                         if (act->happens_before(curr)) {
 490                                 if (act->is_read())
 491                                         mo_graph->addEdge(act->get_reads_from(), curr);
 492                                 else
 493                                         mo_graph->addEdge(act, curr);
 494                                 added = true;
 495                                 break;
 496                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 497                                                      !act->same_thread(curr)) {
 498                                 /* We have an action that:
 499                                    (1) did not happen before us
 500                                    (2) is a read and we are a write
 501                                    (3) cannot synchronize with us
 502                                    (4) is in a different thread
 503                                    =>
 504                                    that read could potentially read from our write.
 505                                  */
 506                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 507                                                 (!next_backtrack || *act > *next_backtrack))
 508                                         next_backtrack = act;
 509                         }
 510                 }
 511         }
 512
 513         return added;
 514 }
 515
 516 /**
 517  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 518  * The ModelAction under consideration is expected to be taking part in
 519  * release/acquire synchronization as an object of the "reads from" relation.
 520  * Note that this can only provide release sequence support for RMW chains
 521  * which do not read from the future, as those actions cannot be traced until
 522  * their "promise" is fulfilled. Similarly, we may not even establish the
 523  * presence of a release sequence with certainty, as some modification order
 524  * constraints may be decided further in the future. Thus, this function
 525  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 526  * and a boolean representing certainty.
 527  *
 528  * @todo Finish lazy updating, when promises are fulfilled in the future
 529  * @param rf The action that might be part of a release sequence. Must be a
 530  * write.
 531  * @param release_heads A pass-by-reference style return parameter.  After
 532  * execution of this function, release_heads will contain the heads of all the
 533  * relevant release sequences, if any exists
 534  * @return true, if the ModelChecker is certain that release_heads is complete;
 535  * false otherwise
 536  */
 537 bool ModelChecker::release_seq_head(const ModelAction *rf,
 538                 std::vector<const ModelAction *> *release_heads) const
 539 {
 540         ASSERT(rf->is_write());
 541         if (!rf) {
 542                 /* read from future: need to settle this later */
 543                 return false; /* incomplete */
 544         }
 545         if (rf->is_release())
 546                 release_heads->push_back(rf);
 547         if (rf->is_rmw()) {
 548                 if (rf->is_acquire())
 549                         return true; /* complete */
 550                 return release_seq_head(rf->get_reads_from(), release_heads);
 551         }
 552         if (rf->is_release())
 553                 return true; /* complete */
 554
 555         /* else relaxed write; check modification order for contiguous subsequence
 556          * -> rf must be same thread as release */
 557         int tid = id_to_int(rf->get_tid());
 558         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 559         action_list_t *list = &(*thrd_lists)[tid];
 560         action_list_t::const_reverse_iterator rit;
 561
 562         /* Find rf in the thread list */
 563         for (rit = list->rbegin(); rit != list->rend(); rit++)
 564                 if (*rit == rf)
 565                         break;
 566
 567         /* Find the last write/release */
 568         for (; rit != list->rend(); rit++)
 569                 if ((*rit)->is_release())
 570                         break;
 571         if (rit == list->rend()) {
 572                 /* No write-release in this thread */
 573                 return true; /* complete */
 574         }
 575         ModelAction *release = *rit;
 576
 577         ASSERT(rf->same_thread(release));
 578
 579         bool certain = true;
 580         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 581                 if (id_to_int(rf->get_tid()) == (int)i)
 582                         continue;
 583                 list = &(*thrd_lists)[i];
 584                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 585                         const ModelAction *act = *rit;
 586                         if (!act->is_write())
 587                                 continue;
 588                         /* Reach synchronization -> this thread is complete */
 589                         if (act->happens_before(release))
 590                                 break;
 591                         if (rf->happens_before(act))
 592                                 continue;
 593
 594                         /* Check modification order */
 595                         if (mo_graph->checkReachable(rf, act))
 596                                 /* rf --mo--> act */
 597                                 continue;
 598                         if (mo_graph->checkReachable(act, release))
 599                                 /* act --mo--> release */
 600                                 break;
 601                         if (mo_graph->checkReachable(release, act) &&
 602                                       mo_graph->checkReachable(act, rf)) {
 603                                 /* release --mo-> act --mo--> rf */
 604                                 return true; /* complete */
 605                         }
 606                         certain = false;
 607                 }
 608         }
 609
 610         if (certain)
 611                 release_heads->push_back(release);
 612         return certain;
 613 }
 614
 615 /**
 616  * A public interface for getting the release sequence head(s) with which a
 617  * given ModelAction must synchronize. This function only returns a non-empty
 618  * result when it can locate a release sequence head with certainty. Otherwise,
 619  * it may mark the internal state of the ModelChecker so that it will handle
 620  * the release sequence at a later time, causing @a act to update its
 621  * synchronization at some later point in execution.
 622  * @param act The 'acquire' action that may read from a release sequence
 623  * @param release_heads A pass-by-reference return parameter. Will be filled
 624  * with the head(s) of the release sequence(s), if they exists with certainty.
 625  * @see ModelChecker::release_seq_head
 626  */
 627 void ModelChecker::get_release_seq_heads(ModelAction *act,
 628                 std::vector<const ModelAction *> *release_heads)
 629 {
 630         const ModelAction *rf = act->get_reads_from();
 631         bool complete;
 632         complete = release_seq_head(rf, release_heads);
 633         if (!complete) {
 634                 /* add act to 'lazy checking' list */
 635                 std::list<ModelAction *> *list;
 636                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 637                 list->push_back(act);
 638         }
 639 }
 640
 641 /**
 642  * Attempt to resolve all stashed operations that might synchronize with a
 643  * release sequence for a given location. This implements the "lazy" portion of
 644  * determining whether or not a release sequence was contiguous, since not all
 645  * modification order information is present at the time an action occurs.
 646  *
 647  * @param location The location/object that should be checked for release
 648  * sequence resolutions
 649  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 650  */
 651 bool ModelChecker::resolve_release_sequences(void *location)
 652 {
 653         std::list<ModelAction *> *list;
 654         list = lazy_sync_with_release->getptr(location);
 655         if (!list)
 656                 return false;
 657
 658         bool updated = false;
 659         std::list<ModelAction *>::iterator it = list->begin();
 660         while (it != list->end()) {
 661                 ModelAction *act = *it;
 662                 const ModelAction *rf = act->get_reads_from();
 663                 std::vector<const ModelAction *> release_heads;
 664                 bool complete;
 665                 complete = release_seq_head(rf, &release_heads);
 666                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 667                         if (!act->has_synchronized_with(release_heads[i])) {
 668                                 updated = true;
 669                                 act->synchronize_with(release_heads[i]);
 670                         }
 671                 }
 672
 673                 if (updated) {
 674                         /* propagate synchronization to later actions */
 675                         action_list_t::reverse_iterator it = action_trace->rbegin();
 676                         while ((*it) != act) {
 677                                 ModelAction *propagate = *it;
 678                                 if (act->happens_before(propagate))
 679                                         /** @todo new mo_graph edges along with
 680                                          * this synchronization? */
 681                                         propagate->synchronize_with(act);
 682                         }
 683                 }
 684                 if (complete)
 685                         it = list->erase(it);
 686                 else
 687                         it++;
 688         }
 689
 690         return updated;
 691 }
 692
 693 /**
 694  * Performs various bookkeeping operations for the current ModelAction. For
 695  * instance, adds action to the per-object, per-thread action vector and to the
 696  * action trace list of all thread actions.
 697  *
 698  * @param act is the ModelAction to add.
 699  */
 700 void ModelChecker::add_action_to_lists(ModelAction *act)
 701 {
 702         int tid = id_to_int(act->get_tid());
 703         action_trace->push_back(act);
 704
 705         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 706
 707         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 708         if (tid >= (int)vec->size())
 709                 vec->resize(next_thread_id);
 710         (*vec)[tid].push_back(act);
 711
 712         if ((int)thrd_last_action->size() <= tid)
 713                 thrd_last_action->resize(get_num_threads());
 714         (*thrd_last_action)[tid] = act;
 715 }
 716
 717 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 718 {
 719         int nthreads = get_num_threads();
 720         if ((int)thrd_last_action->size() < nthreads)
 721                 thrd_last_action->resize(nthreads);
 722         return (*thrd_last_action)[id_to_int(tid)];
 723 }
 724
 725 /**
 726  * Gets the last memory_order_seq_cst action (in the total global sequence)
 727  * performed on a particular object (i.e., memory location).
 728  * @param location The object location to check
 729  * @return The last seq_cst action performed
 730  */
 731 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 732 {
 733         action_list_t *list = obj_map->get_safe_ptr(location);
 734         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 735         action_list_t::reverse_iterator rit;
 736         for (rit = list->rbegin(); rit != list->rend(); rit++)
 737                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 738                         return *rit;
 739         return NULL;
 740 }
 741
 742 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 743 {
 744         ModelAction *parent = get_last_action(tid);
 745         if (!parent)
 746                 parent = get_thread(tid)->get_creation();
 747         return parent;
 748 }
 749
 750 /**
 751  * Returns the clock vector for a given thread.
 752  * @param tid The thread whose clock vector we want
 753  * @return Desired clock vector
 754  */
 755 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 756 {
 757         return get_parent_action(tid)->get_cv();
 758 }
 759
 760 /**
 761  * Resolve a set of Promises with a current write. The set is provided in the
 762  * Node corresponding to @a write.
 763  * @param write The ModelAction that is fulfilling Promises
 764  * @return True if promises were resolved; false otherwise
 765  */
 766 bool ModelChecker::resolve_promises(ModelAction *write)
 767 {
 768         bool resolved = false;
 769         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 770                 Promise *promise = (*promises)[promise_index];
 771                 if (write->get_node()->get_promise(i)) {
 772                         ModelAction *read = promise->get_action();
 773                         read->read_from(write);
 774                         r_modification_order(read, write);
 775                         post_r_modification_order(read, write);
 776                         promises->erase(promises->begin() + promise_index);
 777                         resolved = true;
 778                 } else
 779                         promise_index++;
 780         }
 781         return resolved;
 782 }
 783
 784 /**
 785  * Compute the set of promises that could potentially be satisfied by this
 786  * action. Note that the set computation actually appears in the Node, not in
 787  * ModelChecker.
 788  * @param curr The ModelAction that may satisfy promises
 789  */
 790 void ModelChecker::compute_promises(ModelAction *curr)
 791 {
 792         for (unsigned int i = 0; i < promises->size(); i++) {
 793                 Promise *promise = (*promises)[i];
 794                 const ModelAction *act = promise->get_action();
 795                 if (!act->happens_before(curr) &&
 796                                 act->is_read() &&
 797                                 !act->is_synchronizing(curr) &&
 798                                 !act->same_thread(curr) &&
 799                                 promise->get_value() == curr->get_value()) {
 800                         curr->get_node()->set_promise(i);
 801                 }
 802         }
 803 }
 804
 805 /** Checks promises in response to change in ClockVector Threads. */
 806 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 807 {
 808         for (unsigned int i = 0; i < promises->size(); i++) {
 809                 Promise *promise = (*promises)[i];
 810                 const ModelAction *act = promise->get_action();
 811                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 812                                 merge_cv->synchronized_since(act)) {
 813                         //This thread is no longer able to send values back to satisfy the promise
 814                         int num_synchronized_threads = promise->increment_threads();
 815                         if (num_synchronized_threads == model->get_num_threads()) {
 816                                 //Promise has failed
 817                                 failed_promise = true;
 818                                 return;
 819                         }
 820                 }
 821         }
 822 }
 823
 824 /**
 825  * Build up an initial set of all past writes that this 'read' action may read
 826  * from. This set is determined by the clock vector's "happens before"
 827  * relationship.
 828  * @param curr is the current ModelAction that we are exploring; it must be a
 829  * 'read' operation.
 830  */
 831 void ModelChecker::build_reads_from_past(ModelAction *curr)
 832 {
 833         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 834         unsigned int i;
 835         ASSERT(curr->is_read());
 836
 837         ModelAction *last_seq_cst = NULL;
 838
 839         /* Track whether this object has been initialized */
 840         bool initialized = false;
 841
 842         if (curr->is_seqcst()) {
 843                 last_seq_cst = get_last_seq_cst(curr->get_location());
 844                 /* We have to at least see the last sequentially consistent write,
 845                          so we are initialized. */
 846                 if (last_seq_cst != NULL)
 847                         initialized = true;
 848         }
 849
 850         /* Iterate over all threads */
 851         for (i = 0; i < thrd_lists->size(); i++) {
 852                 /* Iterate over actions in thread, starting from most recent */
 853                 action_list_t *list = &(*thrd_lists)[i];
 854                 action_list_t::reverse_iterator rit;
 855                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 856                         ModelAction *act = *rit;
 857
 858                         /* Only consider 'write' actions */
 859                         if (!act->is_write())
 860                                 continue;
 861
 862                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 863                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 864                                 DEBUG("Adding action to may_read_from:\n");
 865                                 if (DBG_ENABLED()) {
 866                                         act->print();
 867                                         curr->print();
 868                                 }
 869                                 curr->get_node()->add_read_from(act);
 870                         }
 871
 872                         /* Include at most one act per-thread that "happens before" curr */
 873                         if (act->happens_before(curr)) {
 874                                 initialized = true;
 875                                 break;
 876                         }
 877                 }
 878         }
 879
 880         if (!initialized) {
 881                 /** @todo Need a more informative way of reporting errors. */
 882                 printf("ERROR: may read from uninitialized atomic\n");
 883         }
 884
 885         if (DBG_ENABLED() || !initialized) {
 886                 printf("Reached read action:\n");
 887                 curr->print();
 888                 printf("Printing may_read_from\n");
 889                 curr->get_node()->print_may_read_from();
 890                 printf("End printing may_read_from\n");
 891         }
 892
 893         ASSERT(initialized);
 894 }
 895
 896 static void print_list(action_list_t *list)
 897 {
 898         action_list_t::iterator it;
 899
 900         printf("---------------------------------------------------------------------\n");
 901         printf("Trace:\n");
 902
 903         for (it = list->begin(); it != list->end(); it++) {
 904                 (*it)->print();
 905         }
 906         printf("---------------------------------------------------------------------\n");
 907 }
 908
 909 void ModelChecker::print_summary()
 910 {
 911         printf("\n");
 912         printf("Number of executions: %d\n", num_executions);
 913         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 914
 915         scheduler->print();
 916
 917         if (!isfinalfeasible())
 918                 printf("INFEASIBLE EXECUTION!\n");
 919         print_list(action_trace);
 920         printf("\n");
 921 }
 922
 923 /**
 924  * Add a Thread to the system for the first time. Should only be called once
 925  * per thread.
 926  * @param t The Thread to add
 927  */
 928 void ModelChecker::add_thread(Thread *t)
 929 {
 930         thread_map->put(id_to_int(t->get_id()), t);
 931         scheduler->add_thread(t);
 932 }
 933
 934 void ModelChecker::remove_thread(Thread *t)
 935 {
 936         scheduler->remove_thread(t);
 937 }
 938
 939 /**
 940  * Switch from a user-context to the "master thread" context (a.k.a. system
 941  * context). This switch is made with the intention of exploring a particular
 942  * model-checking action (described by a ModelAction object). Must be called
 943  * from a user-thread context.
 944  * @param act The current action that will be explored. May be NULL, although
 945  * there is little reason to switch to the model-checker without an action to
 946  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 947  * yield control without performing any progress; see thrd_join()).
 948  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 949  */
 950 int ModelChecker::switch_to_master(ModelAction *act)
 951 {
 952         DBG();
 953         Thread *old = thread_current();
 954         set_current_action(act);
 955         old->set_state(THREAD_READY);
 956         return Thread::swap(old, &system_context);
 957 }
 958
 959 /**
 960  * Takes the next step in the execution, if possible.
 961  * @return Returns true (success) if a step was taken and false otherwise.
 962  */
 963 bool ModelChecker::take_step() {
 964         Thread *curr, *next;
 965
 966         curr = thread_current();
 967         if (curr) {
 968                 if (curr->get_state() == THREAD_READY) {
 969                         if (current_action) {
 970                                 nextThread = check_current_action(current_action);
 971                                 current_action = NULL;
 972                         }
 973                         scheduler->add_thread(curr);
 974                 } else if (curr->get_state() == THREAD_RUNNING) {
 975                         /* Stopped while running; i.e., completed */
 976                         curr->complete();
 977                 } else {
 978                         ASSERT(false);
 979                 }
 980         }
 981         next = scheduler->next_thread(nextThread);
 982
 983         /* Infeasible -> don't take any more steps */
 984         if (!isfeasible())
 985                 return false;
 986
 987         if (next)
 988                 next->set_state(THREAD_RUNNING);
 989         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
 990
 991         /* next == NULL -> don't take any more steps */
 992         if (!next)
 993                 return false;
 994         /* Return false only if swap fails with an error */
 995         return (Thread::swap(&system_context, next) == 0);
 996 }
 997
 998 /** Runs the current execution until threre are no more steps to take. */
 999 void ModelChecker::finish_execution() {
1000         DBG();
1001
1002         while (take_step());
1003 }