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                         if (r_modification_order(curr,reads_from))
 333                                 updated = true;
 334                 } else {
 335                         /* Read from future value */
 336                         value = curr->get_node()->get_future_value();
 337                         curr->read_from(NULL);
 338                         Promise *valuepromise = new Promise(curr, value);
 339                         promises->push_back(valuepromise);
 340                 }
 341         } else if (curr->is_write()) {
 342                 if (w_modification_order(curr))
 343                         updated = true;
 344                 if (resolve_promises(curr))
 345                         updated = true;
 346         }
 347
 348         if (updated)
 349                 resolve_release_sequences(curr->get_location());
 350
 351         th->set_return_value(value);
 352
 353         /* Add action to list.  */
 354         if (!already_added)
 355                 add_action_to_lists(curr);
 356
 357         Node *currnode = curr->get_node();
 358         Node *parnode = currnode->get_parent();
 359
 360         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 361                   !currnode->future_value_empty() || !currnode->promise_empty())
 362                 if (!priv->next_backtrack || *curr > *priv->next_backtrack)
 363                         priv->next_backtrack = curr;
 364
 365         set_backtracking(curr);
 366
 367         /* Do not split atomic actions. */
 368         if (curr->is_rmwr())
 369                 return thread_current();
 370         /* The THREAD_CREATE action points to the created Thread */
 371         else if (curr->get_type() == THREAD_CREATE)
 372                 return (Thread *)curr->get_location();
 373         else
 374                 return get_next_replay_thread();
 375 }
 376
 377 /** @returns whether the current partial trace must be a prefix of a
 378  * feasible trace. */
 379 bool ModelChecker::isfeasibleprefix() {
 380         return promises->size() == 0 && *lazy_sync_size == 0;
 381 }
 382
 383 /** @returns whether the current partial trace is feasible. */
 384 bool ModelChecker::isfeasible() {
 385         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
 386 }
 387
 388 /** Returns whether the current completed trace is feasible. */
 389 bool ModelChecker::isfinalfeasible() {
 390         return isfeasible() && promises->size() == 0;
 391 }
 392
 393 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 394 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 395         int tid = id_to_int(act->get_tid());
 396         ModelAction *lastread = get_last_action(tid);
 397         lastread->process_rmw(act);
 398         if (act->is_rmw())
 399                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 400         return lastread;
 401 }
 402
 403 /**
 404  * Updates the mo_graph with the constraints imposed from the current read.
 405  * @param curr The current action. Must be a read.
 406  * @param rf The action that curr reads from. Must be a write.
 407  * @return True if modification order edges were added; false otherwise
 408  */
 409 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 410 {
 411         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 412         unsigned int i;
 413         bool added = false;
 414         ASSERT(curr->is_read());
 415
 416         /* Iterate over all threads */
 417         for (i = 0; i < thrd_lists->size(); i++) {
 418                 /* Iterate over actions in thread, starting from most recent */
 419                 action_list_t *list = &(*thrd_lists)[i];
 420                 action_list_t::reverse_iterator rit;
 421                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 422                         ModelAction *act = *rit;
 423
 424                         /* Include at most one act per-thread that "happens before" curr */
 425                         if (act->happens_before(curr)) {
 426                                 if (act->is_read()) {
 427                                         const ModelAction *prevreadfrom = act->get_reads_from();
 428                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 429                                                 mo_graph->addEdge(prevreadfrom, rf);
 430                                                 added = true;
 431                                         }
 432                                 } else if (rf != act) {
 433                                         mo_graph->addEdge(act, rf);
 434                                         added = true;
 435                                 }
 436                                 break;
 437                         }
 438                 }
 439         }
 440
 441         return added;
 442 }
 443
 444 /** Updates the mo_graph with the constraints imposed from the current read. */
 445 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 446 {
 447         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 448         unsigned int i;
 449         ASSERT(curr->is_read());
 450
 451         /* Iterate over all threads */
 452         for (i = 0; i < thrd_lists->size(); i++) {
 453                 /* Iterate over actions in thread, starting from most recent */
 454                 action_list_t *list = &(*thrd_lists)[i];
 455                 action_list_t::reverse_iterator rit;
 456                 ModelAction *lastact = NULL;
 457
 458                 /* Find last action that happens after curr */
 459                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 460                         ModelAction *act = *rit;
 461                         if (curr->happens_before(act)) {
 462                                 lastact = act;
 463                         } else
 464                                 break;
 465                 }
 466
 467                         /* Include at most one act per-thread that "happens before" curr */
 468                 if (lastact != NULL) {
 469                         if (lastact->is_read()) {
 470                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 471                                 if (postreadfrom != NULL&&rf != postreadfrom)
 472                                         mo_graph->addEdge(rf, postreadfrom);
 473                         } else if (rf != lastact) {
 474                                 mo_graph->addEdge(rf, lastact);
 475                         }
 476                         break;
 477                 }
 478         }
 479 }
 480
 481 /**
 482  * Updates the mo_graph with the constraints imposed from the current write.
 483  * @param curr The current action. Must be a write.
 484  * @return True if modification order edges were added; false otherwise
 485  */
 486 bool ModelChecker::w_modification_order(ModelAction *curr)
 487 {
 488         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 489         unsigned int i;
 490         bool added = false;
 491         ASSERT(curr->is_write());
 492
 493         if (curr->is_seqcst()) {
 494                 /* We have to at least see the last sequentially consistent write,
 495                          so we are initialized. */
 496                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 497                 if (last_seq_cst != NULL) {
 498                         mo_graph->addEdge(last_seq_cst, curr);
 499                         added = true;
 500                 }
 501         }
 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                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 509                         ModelAction *act = *rit;
 510
 511                         /* Include at most one act per-thread that "happens before" curr */
 512                         if (act->happens_before(curr)) {
 513                                 if (act->is_read())
 514                                         mo_graph->addEdge(act->get_reads_from(), curr);
 515                                 else
 516                                         mo_graph->addEdge(act, curr);
 517                                 added = true;
 518                                 break;
 519                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 520                                                      !act->same_thread(curr)) {
 521                                 /* We have an action that:
 522                                    (1) did not happen before us
 523                                    (2) is a read and we are a write
 524                                    (3) cannot synchronize with us
 525                                    (4) is in a different thread
 526                                    =>
 527                                    that read could potentially read from our write.
 528                                  */
 529                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 530                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 531                                         priv->next_backtrack = act;
 532                         }
 533                 }
 534         }
 535
 536         return added;
 537 }
 538
 539 /**
 540  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 541  * The ModelAction under consideration is expected to be taking part in
 542  * release/acquire synchronization as an object of the "reads from" relation.
 543  * Note that this can only provide release sequence support for RMW chains
 544  * which do not read from the future, as those actions cannot be traced until
 545  * their "promise" is fulfilled. Similarly, we may not even establish the
 546  * presence of a release sequence with certainty, as some modification order
 547  * constraints may be decided further in the future. Thus, this function
 548  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 549  * and a boolean representing certainty.
 550  *
 551  * @todo Finish lazy updating, when promises are fulfilled in the future
 552  * @param rf The action that might be part of a release sequence. Must be a
 553  * write.
 554  * @param release_heads A pass-by-reference style return parameter.  After
 555  * execution of this function, release_heads will contain the heads of all the
 556  * relevant release sequences, if any exists
 557  * @return true, if the ModelChecker is certain that release_heads is complete;
 558  * false otherwise
 559  */
 560 bool ModelChecker::release_seq_head(const ModelAction *rf,
 561                 std::vector<const ModelAction *> *release_heads) const
 562 {
 563         ASSERT(rf->is_write());
 564         if (!rf) {
 565                 /* read from future: need to settle this later */
 566                 return false; /* incomplete */
 567         }
 568         if (rf->is_release())
 569                 release_heads->push_back(rf);
 570         if (rf->is_rmw()) {
 571                 /* We need a RMW action that is both an acquire and release to stop */
 572                 /** @todo Need to be smarter here...  In the linux lock
 573                  * example, this will run to the beginning of the program for
 574                  * every acquire. */
 575                 if (rf->is_acquire() && rf->is_release())
 576                         return true; /* complete */
 577                 return release_seq_head(rf->get_reads_from(), release_heads);
 578         }
 579         if (rf->is_release())
 580                 return true; /* complete */
 581
 582         /* else relaxed write; check modification order for contiguous subsequence
 583          * -> rf must be same thread as release */
 584         int tid = id_to_int(rf->get_tid());
 585         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 586         action_list_t *list = &(*thrd_lists)[tid];
 587         action_list_t::const_reverse_iterator rit;
 588
 589         /* Find rf in the thread list */
 590         rit = std::find(list->rbegin(), list->rend(), rf);
 591         ASSERT(rit != list->rend());
 592
 593         /* Find the last write/release */
 594         for (; rit != list->rend(); rit++)
 595                 if ((*rit)->is_release())
 596                         break;
 597         if (rit == list->rend()) {
 598                 /* No write-release in this thread */
 599                 return true; /* complete */
 600         }
 601         ModelAction *release = *rit;
 602
 603         ASSERT(rf->same_thread(release));
 604
 605         bool certain = true;
 606         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 607                 if (id_to_int(rf->get_tid()) == (int)i)
 608                         continue;
 609                 list = &(*thrd_lists)[i];
 610
 611                 /* Can we ensure no future writes from this thread may break
 612                  * the release seq? */
 613                 bool future_ordered = false;
 614
 615                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 616                         const ModelAction *act = *rit;
 617                         if (!act->is_write())
 618                                 continue;
 619                         /* Reach synchronization -> this thread is complete */
 620                         if (act->happens_before(release))
 621                                 break;
 622                         if (rf->happens_before(act)) {
 623                                 future_ordered = true;
 624                                 continue;
 625                         }
 626
 627                         /* Check modification order */
 628                         if (mo_graph->checkReachable(rf, act)) {
 629                                 /* rf --mo--> act */
 630                                 future_ordered = true;
 631                                 continue;
 632                         }
 633                         if (mo_graph->checkReachable(act, release))
 634                                 /* act --mo--> release */
 635                                 break;
 636                         if (mo_graph->checkReachable(release, act) &&
 637                                       mo_graph->checkReachable(act, rf)) {
 638                                 /* release --mo-> act --mo--> rf */
 639                                 return true; /* complete */
 640                         }
 641                         certain = false;
 642                 }
 643                 if (!future_ordered)
 644                         return false; /* This thread is uncertain */
 645         }
 646
 647         if (certain)
 648                 release_heads->push_back(release);
 649         return certain;
 650 }
 651
 652 /**
 653  * A public interface for getting the release sequence head(s) with which a
 654  * given ModelAction must synchronize. This function only returns a non-empty
 655  * result when it can locate a release sequence head with certainty. Otherwise,
 656  * it may mark the internal state of the ModelChecker so that it will handle
 657  * the release sequence at a later time, causing @a act to update its
 658  * synchronization at some later point in execution.
 659  * @param act The 'acquire' action that may read from a release sequence
 660  * @param release_heads A pass-by-reference return parameter. Will be filled
 661  * with the head(s) of the release sequence(s), if they exists with certainty.
 662  * @see ModelChecker::release_seq_head
 663  */
 664 void ModelChecker::get_release_seq_heads(ModelAction *act,
 665                 std::vector<const ModelAction *> *release_heads)
 666 {
 667         const ModelAction *rf = act->get_reads_from();
 668         bool complete;
 669         complete = release_seq_head(rf, release_heads);
 670         if (!complete) {
 671                 /* add act to 'lazy checking' list */
 672                 std::list<ModelAction *> *list;
 673                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 674                 list->push_back(act);
 675                 (*lazy_sync_size)++;
 676         }
 677 }
 678
 679 /**
 680  * Attempt to resolve all stashed operations that might synchronize with a
 681  * release sequence for a given location. This implements the "lazy" portion of
 682  * determining whether or not a release sequence was contiguous, since not all
 683  * modification order information is present at the time an action occurs.
 684  *
 685  * @param location The location/object that should be checked for release
 686  * sequence resolutions
 687  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 688  */
 689 bool ModelChecker::resolve_release_sequences(void *location)
 690 {
 691         std::list<ModelAction *> *list;
 692         list = lazy_sync_with_release->getptr(location);
 693         if (!list)
 694                 return false;
 695
 696         bool updated = false;
 697         std::list<ModelAction *>::iterator it = list->begin();
 698         while (it != list->end()) {
 699                 ModelAction *act = *it;
 700                 const ModelAction *rf = act->get_reads_from();
 701                 std::vector<const ModelAction *> release_heads;
 702                 bool complete;
 703                 complete = release_seq_head(rf, &release_heads);
 704                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 705                         if (!act->has_synchronized_with(release_heads[i])) {
 706                                 updated = true;
 707                                 act->synchronize_with(release_heads[i]);
 708                         }
 709                 }
 710
 711                 if (updated) {
 712                         /* propagate synchronization to later actions */
 713                         action_list_t::reverse_iterator it = action_trace->rbegin();
 714                         while ((*it) != act) {
 715                                 ModelAction *propagate = *it;
 716                                 if (act->happens_before(propagate))
 717                                         /** @todo new mo_graph edges along with
 718                                          * this synchronization? */
 719                                         propagate->synchronize_with(act);
 720                         }
 721                 }
 722                 if (complete) {
 723                         it = list->erase(it);
 724                         (*lazy_sync_size)--;
 725                 } else
 726                         it++;
 727         }
 728
 729         // If we resolved promises or data races, see if we have realized a data race.
 730         if (checkDataRaces()) {
 731                 set_assert();
 732         }
 733
 734         return updated;
 735 }
 736
 737 /**
 738  * Performs various bookkeeping operations for the current ModelAction. For
 739  * instance, adds action to the per-object, per-thread action vector and to the
 740  * action trace list of all thread actions.
 741  *
 742  * @param act is the ModelAction to add.
 743  */
 744 void ModelChecker::add_action_to_lists(ModelAction *act)
 745 {
 746         int tid = id_to_int(act->get_tid());
 747         action_trace->push_back(act);
 748
 749         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 750
 751         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 752         if (tid >= (int)vec->size())
 753                 vec->resize(priv->next_thread_id);
 754         (*vec)[tid].push_back(act);
 755
 756         if ((int)thrd_last_action->size() <= tid)
 757                 thrd_last_action->resize(get_num_threads());
 758         (*thrd_last_action)[tid] = act;
 759 }
 760
 761 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 762 {
 763         int nthreads = get_num_threads();
 764         if ((int)thrd_last_action->size() < nthreads)
 765                 thrd_last_action->resize(nthreads);
 766         return (*thrd_last_action)[id_to_int(tid)];
 767 }
 768
 769 /**
 770  * Gets the last memory_order_seq_cst action (in the total global sequence)
 771  * performed on a particular object (i.e., memory location).
 772  * @param location The object location to check
 773  * @return The last seq_cst action performed
 774  */
 775 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 776 {
 777         action_list_t *list = obj_map->get_safe_ptr(location);
 778         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 779         action_list_t::reverse_iterator rit;
 780         for (rit = list->rbegin(); rit != list->rend(); rit++)
 781                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 782                         return *rit;
 783         return NULL;
 784 }
 785
 786 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 787 {
 788         ModelAction *parent = get_last_action(tid);
 789         if (!parent)
 790                 parent = get_thread(tid)->get_creation();
 791         return parent;
 792 }
 793
 794 /**
 795  * Returns the clock vector for a given thread.
 796  * @param tid The thread whose clock vector we want
 797  * @return Desired clock vector
 798  */
 799 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 800 {
 801         return get_parent_action(tid)->get_cv();
 802 }
 803
 804 /**
 805  * Resolve a set of Promises with a current write. The set is provided in the
 806  * Node corresponding to @a write.
 807  * @param write The ModelAction that is fulfilling Promises
 808  * @return True if promises were resolved; false otherwise
 809  */
 810 bool ModelChecker::resolve_promises(ModelAction *write)
 811 {
 812         bool resolved = false;
 813         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 814                 Promise *promise = (*promises)[promise_index];
 815                 if (write->get_node()->get_promise(i)) {
 816                         ModelAction *read = promise->get_action();
 817                         read->read_from(write);
 818                         r_modification_order(read, write);
 819                         post_r_modification_order(read, write);
 820                         promises->erase(promises->begin() + promise_index);
 821                         resolved = true;
 822                 } else
 823                         promise_index++;
 824         }
 825
 826         return resolved;
 827 }
 828
 829 /**
 830  * Compute the set of promises that could potentially be satisfied by this
 831  * action. Note that the set computation actually appears in the Node, not in
 832  * ModelChecker.
 833  * @param curr The ModelAction that may satisfy promises
 834  */
 835 void ModelChecker::compute_promises(ModelAction *curr)
 836 {
 837         for (unsigned int i = 0; i < promises->size(); i++) {
 838                 Promise *promise = (*promises)[i];
 839                 const ModelAction *act = promise->get_action();
 840                 if (!act->happens_before(curr) &&
 841                                 act->is_read() &&
 842                                 !act->is_synchronizing(curr) &&
 843                                 !act->same_thread(curr) &&
 844                                 promise->get_value() == curr->get_value()) {
 845                         curr->get_node()->set_promise(i);
 846                 }
 847         }
 848 }
 849
 850 /** Checks promises in response to change in ClockVector Threads. */
 851 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 852 {
 853         for (unsigned int i = 0; i < promises->size(); i++) {
 854                 Promise *promise = (*promises)[i];
 855                 const ModelAction *act = promise->get_action();
 856                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 857                                 merge_cv->synchronized_since(act)) {
 858                         //This thread is no longer able to send values back to satisfy the promise
 859                         int num_synchronized_threads = promise->increment_threads();
 860                         if (num_synchronized_threads == get_num_threads()) {
 861                                 //Promise has failed
 862                                 failed_promise = true;
 863                                 return;
 864                         }
 865                 }
 866         }
 867 }
 868
 869 /**
 870  * Build up an initial set of all past writes that this 'read' action may read
 871  * from. This set is determined by the clock vector's "happens before"
 872  * relationship.
 873  * @param curr is the current ModelAction that we are exploring; it must be a
 874  * 'read' operation.
 875  */
 876 void ModelChecker::build_reads_from_past(ModelAction *curr)
 877 {
 878         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 879         unsigned int i;
 880         ASSERT(curr->is_read());
 881
 882         ModelAction *last_seq_cst = NULL;
 883
 884         /* Track whether this object has been initialized */
 885         bool initialized = false;
 886
 887         if (curr->is_seqcst()) {
 888                 last_seq_cst = get_last_seq_cst(curr->get_location());
 889                 /* We have to at least see the last sequentially consistent write,
 890                          so we are initialized. */
 891                 if (last_seq_cst != NULL)
 892                         initialized = true;
 893         }
 894
 895         /* Iterate over all threads */
 896         for (i = 0; i < thrd_lists->size(); i++) {
 897                 /* Iterate over actions in thread, starting from most recent */
 898                 action_list_t *list = &(*thrd_lists)[i];
 899                 action_list_t::reverse_iterator rit;
 900                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 901                         ModelAction *act = *rit;
 902
 903                         /* Only consider 'write' actions */
 904                         if (!act->is_write())
 905                                 continue;
 906
 907                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 908                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 909                                 DEBUG("Adding action to may_read_from:\n");
 910                                 if (DBG_ENABLED()) {
 911                                         act->print();
 912                                         curr->print();
 913                                 }
 914                                 curr->get_node()->add_read_from(act);
 915                         }
 916
 917                         /* Include at most one act per-thread that "happens before" curr */
 918                         if (act->happens_before(curr)) {
 919                                 initialized = true;
 920                                 break;
 921                         }
 922                 }
 923         }
 924
 925         if (!initialized) {
 926                 /** @todo Need a more informative way of reporting errors. */
 927                 printf("ERROR: may read from uninitialized atomic\n");
 928         }
 929
 930         if (DBG_ENABLED() || !initialized) {
 931                 printf("Reached read action:\n");
 932                 curr->print();
 933                 printf("Printing may_read_from\n");
 934                 curr->get_node()->print_may_read_from();
 935                 printf("End printing may_read_from\n");
 936         }
 937
 938         ASSERT(initialized);
 939 }
 940
 941 static void print_list(action_list_t *list)
 942 {
 943         action_list_t::iterator it;
 944
 945         printf("---------------------------------------------------------------------\n");
 946         printf("Trace:\n");
 947
 948         for (it = list->begin(); it != list->end(); it++) {
 949                 (*it)->print();
 950         }
 951         printf("---------------------------------------------------------------------\n");
 952 }
 953
 954 void ModelChecker::print_summary()
 955 {
 956         printf("\n");
 957         printf("Number of executions: %d\n", num_executions);
 958         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 959
 960         scheduler->print();
 961
 962         if (!isfinalfeasible())
 963                 printf("INFEASIBLE EXECUTION!\n");
 964         print_list(action_trace);
 965         printf("\n");
 966 }
 967
 968 /**
 969  * Add a Thread to the system for the first time. Should only be called once
 970  * per thread.
 971  * @param t The Thread to add
 972  */
 973 void ModelChecker::add_thread(Thread *t)
 974 {
 975         thread_map->put(id_to_int(t->get_id()), t);
 976         scheduler->add_thread(t);
 977 }
 978
 979 void ModelChecker::remove_thread(Thread *t)
 980 {
 981         scheduler->remove_thread(t);
 982 }
 983
 984 /**
 985  * Switch from a user-context to the "master thread" context (a.k.a. system
 986  * context). This switch is made with the intention of exploring a particular
 987  * model-checking action (described by a ModelAction object). Must be called
 988  * from a user-thread context.
 989  * @param act The current action that will be explored. Must not be NULL.
 990  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 991  */
 992 int ModelChecker::switch_to_master(ModelAction *act)
 993 {
 994         DBG();
 995         Thread *old = thread_current();
 996         set_current_action(act);
 997         old->set_state(THREAD_READY);
 998         return Thread::swap(old, &system_context);
 999 }
1000
1001 /**
1002  * Takes the next step in the execution, if possible.
1003  * @return Returns true (success) if a step was taken and false otherwise.
1004  */
1005 bool ModelChecker::take_step() {
1006         Thread *curr, *next;
1007
1008         if (has_asserted())
1009                 return false;
1010
1011         curr = thread_current();
1012         if (curr) {
1013                 if (curr->get_state() == THREAD_READY) {
1014                         ASSERT(priv->current_action);
1015                         priv->nextThread = check_current_action(priv->current_action);
1016                         priv->current_action = NULL;
1017                         if (!curr->is_blocked() && !curr->is_complete())
1018                                 scheduler->add_thread(curr);
1019                 } else {
1020                         ASSERT(false);
1021                 }
1022         }
1023         next = scheduler->next_thread(priv->nextThread);
1024
1025         /* Infeasible -> don't take any more steps */
1026         if (!isfeasible())
1027                 return false;
1028
1029         if (next)
1030                 next->set_state(THREAD_RUNNING);
1031         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1032
1033         /* next == NULL -> don't take any more steps */
1034         if (!next)
1035                 return false;
1036         /* Return false only if swap fails with an error */
1037         return (Thread::swap(&system_context, next) == 0);
1038 }
1039
1040 /** Runs the current execution until threre are no more steps to take. */
1041 void ModelChecker::finish_execution() {
1042         DBG();
1043
1044         while (take_step());
1045 }