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         /* First thread created will have id INITIAL_THREAD_ID */
  24         next_thread_id(INITIAL_THREAD_ID),
  25         used_sequence_numbers(0),
  26         num_executions(0),
  27         params(params),
  28         current_action(NULL),
  29         diverge(NULL),
  30         nextThread(NULL),
  31         action_trace(new action_list_t()),
  32         thread_map(new HashTable<int, Thread *, int>()),
  33         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  34         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  35         promises(new std::vector<Promise *>()),
  36         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  37         thrd_last_action(new std::vector<ModelAction *>(1)),
  38         node_stack(new NodeStack()),
  39         next_backtrack(NULL),
  40         mo_graph(new CycleGraph()),
  41         failed_promise(false),
  42         asserted(false)
  43 {
  44 }
  45
  46 /** @brief Destructor */
  47 ModelChecker::~ModelChecker()
  48 {
  49         for (int i = 0; i < get_num_threads(); i++)
  50                 delete thread_map->get(i);
  51         delete thread_map;
  52
  53         delete obj_thrd_map;
  54         delete obj_map;
  55         delete action_trace;
  56
  57         for (unsigned int i = 0; i < promises->size(); i++)
  58                 delete (*promises)[i];
  59         delete promises;
  60
  61         delete lazy_sync_with_release;
  62
  63         delete thrd_last_action;
  64         delete node_stack;
  65         delete scheduler;
  66         delete mo_graph;
  67 }
  68
  69 /**
  70  * Restores user program to initial state and resets all model-checker data
  71  * structures.
  72  */
  73 void ModelChecker::reset_to_initial_state()
  74 {
  75         DEBUG("+++ Resetting to initial state +++\n");
  76         node_stack->reset_execution();
  77         current_action = NULL;
  78         next_thread_id = INITIAL_THREAD_ID;
  79         used_sequence_numbers = 0;
  80         nextThread = NULL;
  81         next_backtrack = NULL;
  82         failed_promise = false;
  83         reset_asserted();
  84         snapshotObject->backTrackBeforeStep(0);
  85 }
  86
  87 /** @returns a thread ID for a new Thread */
  88 thread_id_t ModelChecker::get_next_id()
  89 {
  90         return next_thread_id++;
  91 }
  92
  93 /** @returns the number of user threads created during this execution */
  94 int ModelChecker::get_num_threads()
  95 {
  96         return next_thread_id;
  97 }
  98
  99 /** @returns a sequence number for a new ModelAction */
 100 modelclock_t ModelChecker::get_next_seq_num()
 101 {
 102         return ++used_sequence_numbers;
 103 }
 104
 105 /**
 106  * Choose the next thread in the replay sequence.
 107  *
 108  * If the replay sequence has reached the 'diverge' point, returns a thread
 109  * from the backtracking set. Otherwise, simply returns the next thread in the
 110  * sequence that is being replayed.
 111  */
 112 Thread * ModelChecker::get_next_replay_thread()
 113 {
 114         thread_id_t tid;
 115
 116         /* Have we completed exploring the preselected path? */
 117         if (diverge == NULL)
 118                 return NULL;
 119
 120         /* Else, we are trying to replay an execution */
 121         ModelAction *next = node_stack->get_next()->get_action();
 122
 123         if (next == diverge) {
 124                 Node *nextnode = next->get_node();
 125                 /* Reached divergence point */
 126                 if (nextnode->increment_promise()) {
 127                         /* The next node will try to satisfy a different set of promises. */
 128                         tid = next->get_tid();
 129                         node_stack->pop_restofstack(2);
 130                 } else if (nextnode->increment_read_from()) {
 131                         /* The next node will read from a different value. */
 132                         tid = next->get_tid();
 133                         node_stack->pop_restofstack(2);
 134                 } else if (nextnode->increment_future_value()) {
 135                         /* The next node will try to read from a different future value. */
 136                         tid = next->get_tid();
 137                         node_stack->pop_restofstack(2);
 138                 } else {
 139                         /* Make a different thread execute for next step */
 140                         Node *node = nextnode->get_parent();
 141                         tid = node->get_next_backtrack();
 142                         node_stack->pop_restofstack(1);
 143                 }
 144                 DEBUG("*** Divergence point ***\n");
 145                 diverge = NULL;
 146         } else {
 147                 tid = next->get_tid();
 148         }
 149         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 150         ASSERT(tid != THREAD_ID_T_NONE);
 151         return thread_map->get(id_to_int(tid));
 152 }
 153
 154 /**
 155  * Queries the model-checker for more executions to explore and, if one
 156  * exists, resets the model-checker state to execute a new execution.
 157  *
 158  * @return If there are more executions to explore, return true. Otherwise,
 159  * return false.
 160  */
 161 bool ModelChecker::next_execution()
 162 {
 163         DBG();
 164
 165         num_executions++;
 166
 167         if (isfinalfeasible() || DBG_ENABLED())
 168                 print_summary();
 169
 170         if ((diverge = get_next_backtrack()) == NULL)
 171                 return false;
 172
 173         if (DBG_ENABLED()) {
 174                 printf("Next execution will diverge at:\n");
 175                 diverge->print();
 176         }
 177
 178         reset_to_initial_state();
 179         return true;
 180 }
 181
 182 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 183 {
 184         action_type type = act->get_type();
 185
 186         switch (type) {
 187                 case ATOMIC_READ:
 188                 case ATOMIC_WRITE:
 189                 case ATOMIC_RMW:
 190                         break;
 191                 default:
 192                         return NULL;
 193         }
 194         /* linear search: from most recent to oldest */
 195         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 196         action_list_t::reverse_iterator rit;
 197         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 198                 ModelAction *prev = *rit;
 199                 if (act->is_synchronizing(prev))
 200                         return prev;
 201         }
 202         return NULL;
 203 }
 204
 205 void ModelChecker::set_backtracking(ModelAction *act)
 206 {
 207         ModelAction *prev;
 208         Node *node;
 209         Thread *t = get_thread(act->get_tid());
 210
 211         prev = get_last_conflict(act);
 212         if (prev == NULL)
 213                 return;
 214
 215         node = prev->get_node()->get_parent();
 216
 217         while (!node->is_enabled(t))
 218                 t = t->get_parent();
 219
 220         /* Check if this has been explored already */
 221         if (node->has_been_explored(t->get_id()))
 222                 return;
 223
 224         /* Cache the latest backtracking point */
 225         if (!next_backtrack || *prev > *next_backtrack)
 226                 next_backtrack = prev;
 227
 228         /* If this is a new backtracking point, mark the tree */
 229         if (!node->set_backtrack(t->get_id()))
 230                 return;
 231         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 232                         prev->get_tid(), t->get_id());
 233         if (DBG_ENABLED()) {
 234                 prev->print();
 235                 act->print();
 236         }
 237 }
 238
 239 /**
 240  * Returns last backtracking point. The model checker will explore a different
 241  * path for this point in the next execution.
 242  * @return The ModelAction at which the next execution should diverge.
 243  */
 244 ModelAction * ModelChecker::get_next_backtrack()
 245 {
 246         ModelAction *next = next_backtrack;
 247         next_backtrack = NULL;
 248         return next;
 249 }
 250
 251 /**
 252  * This is the heart of the model checker routine. It performs model-checking
 253  * actions corresponding to a given "current action." Among other processes, it
 254  * calculates reads-from relationships, updates synchronization clock vectors,
 255  * forms a memory_order constraints graph, and handles replay/backtrack
 256  * execution when running permutations of previously-observed executions.
 257  *
 258  * @param curr The current action to process
 259  * @return The next Thread that must be executed. May be NULL if ModelChecker
 260  * makes no choice (e.g., according to replay execution, combining RMW actions,
 261  * etc.)
 262  */
 263 Thread * ModelChecker::check_current_action(ModelAction *curr)
 264 {
 265         bool already_added = false;
 266
 267         ASSERT(curr);
 268
 269         if (curr->is_rmwc() || curr->is_rmw()) {
 270                 ModelAction *tmp = process_rmw(curr);
 271                 already_added = true;
 272                 delete curr;
 273                 curr = tmp;
 274         } else {
 275                 ModelAction *tmp = node_stack->explore_action(curr);
 276                 if (tmp) {
 277                         /* Discard duplicate ModelAction; use action from NodeStack */
 278                         /* First restore type and order in case of RMW operation */
 279                         if (curr->is_rmwr())
 280                                 tmp->copy_typeandorder(curr);
 281
 282                         /* If we have diverged, we need to reset the clock vector. */
 283                         if (diverge == NULL)
 284                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 285
 286                         delete curr;
 287                         curr = tmp;
 288                 } else {
 289                         /*
 290                          * Perform one-time actions when pushing new ModelAction onto
 291                          * NodeStack
 292                          */
 293                         curr->create_cv(get_parent_action(curr->get_tid()));
 294                         /* Build may_read_from set */
 295                         if (curr->is_read())
 296                                 build_reads_from_past(curr);
 297                         if (curr->is_write())
 298                                 compute_promises(curr);
 299                 }
 300         }
 301
 302         /* Assign 'creation' parent */
 303         if (curr->get_type() == THREAD_CREATE) {
 304                 Thread *th = (Thread *)curr->get_location();
 305                 th->set_creation(curr);
 306         } else if (curr->get_type() == THREAD_JOIN) {
 307                 Thread *wait, *join;
 308                 wait = get_thread(curr->get_tid());
 309                 join = (Thread *)curr->get_location();
 310                 if (!join->is_complete())
 311                         scheduler->wait(wait, join);
 312         } else if (curr->get_type() == THREAD_FINISH) {
 313                 Thread *th = get_thread(curr->get_tid());
 314                 while (!th->wait_list_empty()) {
 315                         Thread *wake = th->pop_wait_list();
 316                         scheduler->wake(wake);
 317                 }
 318                 th->complete();
 319         }
 320
 321         /* Deal with new thread */
 322         if (curr->get_type() == THREAD_START)
 323                 check_promises(NULL, curr->get_cv());
 324
 325         /* Assign reads_from values */
 326         Thread *th = get_thread(curr->get_tid());
 327         uint64_t value = VALUE_NONE;
 328         bool updated = false;
 329         if (curr->is_read()) {
 330                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 331                 if (reads_from != NULL) {
 332                         value = reads_from->get_value();
 333                         /* Assign reads_from, perform release/acquire synchronization */
 334                         curr->read_from(reads_from);
 335                         if (r_modification_order(curr,reads_from))
 336                                 updated = true;
 337                 } else {
 338                         /* Read from future value */
 339                         value = curr->get_node()->get_future_value();
 340                         curr->read_from(NULL);
 341                         Promise *valuepromise = new Promise(curr, value);
 342                         promises->push_back(valuepromise);
 343                 }
 344         } else if (curr->is_write()) {
 345                 if (w_modification_order(curr))
 346                         updated = true;
 347                 if (resolve_promises(curr))
 348                         updated = true;
 349         }
 350
 351         if (updated)
 352                 resolve_release_sequences(curr->get_location());
 353
 354         th->set_return_value(value);
 355
 356         /* Add action to list.  */
 357         if (!already_added)
 358                 add_action_to_lists(curr);
 359
 360         Node *currnode = curr->get_node();
 361         Node *parnode = currnode->get_parent();
 362
 363         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 364                   !currnode->future_value_empty() || !currnode->promise_empty())
 365                 if (!next_backtrack || *curr > *next_backtrack)
 366                         next_backtrack = curr;
 367
 368         set_backtracking(curr);
 369
 370         /* Do not split atomic actions. */
 371         if (curr->is_rmwr())
 372                 return thread_current();
 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
 380 bool ModelChecker::isfeasibleprefix() {
 381         return promises->size()==0;
 382 }
 383
 384 /** @returns whether the current partial trace is feasible. */
 385 bool ModelChecker::isfeasible() {
 386         return !mo_graph->checkForCycles() && !failed_promise;
 387 }
 388
 389 /** Returns whether the current completed trace is feasible. */
 390 bool ModelChecker::isfinalfeasible() {
 391         return isfeasible() && promises->size() == 0;
 392 }
 393
 394 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 395 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 396         int tid = id_to_int(act->get_tid());
 397         ModelAction *lastread = get_last_action(tid);
 398         lastread->process_rmw(act);
 399         if (act->is_rmw())
 400                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 401         return lastread;
 402 }
 403
 404 /**
 405  * Updates the mo_graph with the constraints imposed from the current read.
 406  * @param curr The current action. Must be a read.
 407  * @param rf The action that curr reads from. Must be a write.
 408  * @return True if modification order edges were added; false otherwise
 409  */
 410 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 411 {
 412         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 413         unsigned int i;
 414         bool added = false;
 415         ASSERT(curr->is_read());
 416
 417         /* Iterate over all threads */
 418         for (i = 0; i < thrd_lists->size(); i++) {
 419                 /* Iterate over actions in thread, starting from most recent */
 420                 action_list_t *list = &(*thrd_lists)[i];
 421                 action_list_t::reverse_iterator rit;
 422                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 423                         ModelAction *act = *rit;
 424
 425                         /* Include at most one act per-thread that "happens before" curr */
 426                         if (act->happens_before(curr)) {
 427                                 if (act->is_read()) {
 428                                         const ModelAction *prevreadfrom = act->get_reads_from();
 429                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 430                                                 mo_graph->addEdge(prevreadfrom, rf);
 431                                                 added = true;
 432                                         }
 433                                 } else if (rf != act) {
 434                                         mo_graph->addEdge(act, rf);
 435                                         added = true;
 436                                 }
 437                                 break;
 438                         }
 439                 }
 440         }
 441
 442         return added;
 443 }
 444
 445 /** Updates the mo_graph with the constraints imposed from the current read. */
 446 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 447 {
 448         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 449         unsigned int i;
 450         ASSERT(curr->is_read());
 451
 452         /* Iterate over all threads */
 453         for (i = 0; i < thrd_lists->size(); i++) {
 454                 /* Iterate over actions in thread, starting from most recent */
 455                 action_list_t *list = &(*thrd_lists)[i];
 456                 action_list_t::reverse_iterator rit;
 457                 ModelAction *lastact = NULL;
 458
 459                 /* Find last action that happens after curr */
 460                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 461                         ModelAction *act = *rit;
 462                         if (curr->happens_before(act)) {
 463                                 lastact = act;
 464                         } else
 465                                 break;
 466                 }
 467
 468                         /* Include at most one act per-thread that "happens before" curr */
 469                 if (lastact != NULL) {
 470                         if (lastact->is_read()) {
 471                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 472                                 if (postreadfrom != NULL&&rf != postreadfrom)
 473                                         mo_graph->addEdge(rf, postreadfrom);
 474                         } else if (rf != lastact) {
 475                                 mo_graph->addEdge(rf, lastact);
 476                         }
 477                         break;
 478                 }
 479         }
 480 }
 481
 482 /**
 483  * Updates the mo_graph with the constraints imposed from the current write.
 484  * @param curr The current action. Must be a write.
 485  * @return True if modification order edges were added; false otherwise
 486  */
 487 bool ModelChecker::w_modification_order(ModelAction *curr)
 488 {
 489         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 490         unsigned int i;
 491         bool added = false;
 492         ASSERT(curr->is_write());
 493
 494         if (curr->is_seqcst()) {
 495                 /* We have to at least see the last sequentially consistent write,
 496                          so we are initialized. */
 497                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 498                 if (last_seq_cst != NULL) {
 499                         mo_graph->addEdge(last_seq_cst, curr);
 500                         added = true;
 501                 }
 502         }
 503
 504         /* Iterate over all threads */
 505         for (i = 0; i < thrd_lists->size(); i++) {
 506                 /* Iterate over actions in thread, starting from most recent */
 507                 action_list_t *list = &(*thrd_lists)[i];
 508                 action_list_t::reverse_iterator rit;
 509                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 510                         ModelAction *act = *rit;
 511
 512                         /* Include at most one act per-thread that "happens before" curr */
 513                         if (act->happens_before(curr)) {
 514                                 if (act->is_read())
 515                                         mo_graph->addEdge(act->get_reads_from(), curr);
 516                                 else
 517                                         mo_graph->addEdge(act, curr);
 518                                 added = true;
 519                                 break;
 520                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 521                                                      !act->same_thread(curr)) {
 522                                 /* We have an action that:
 523                                    (1) did not happen before us
 524                                    (2) is a read and we are a write
 525                                    (3) cannot synchronize with us
 526                                    (4) is in a different thread
 527                                    =>
 528                                    that read could potentially read from our write.
 529                                  */
 530                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 531                                                 (!next_backtrack || *act > *next_backtrack))
 532                                         next_backtrack = act;
 533                         }
 534                 }
 535         }
 536
 537         return added;
 538 }
 539
 540 /**
 541  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 542  * The ModelAction under consideration is expected to be taking part in
 543  * release/acquire synchronization as an object of the "reads from" relation.
 544  * Note that this can only provide release sequence support for RMW chains
 545  * which do not read from the future, as those actions cannot be traced until
 546  * their "promise" is fulfilled. Similarly, we may not even establish the
 547  * presence of a release sequence with certainty, as some modification order
 548  * constraints may be decided further in the future. Thus, this function
 549  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 550  * and a boolean representing certainty.
 551  *
 552  * @todo Finish lazy updating, when promises are fulfilled in the future
 553  * @param rf The action that might be part of a release sequence. Must be a
 554  * write.
 555  * @param release_heads A pass-by-reference style return parameter.  After
 556  * execution of this function, release_heads will contain the heads of all the
 557  * relevant release sequences, if any exists
 558  * @return true, if the ModelChecker is certain that release_heads is complete;
 559  * false otherwise
 560  */
 561 bool ModelChecker::release_seq_head(const ModelAction *rf,
 562                 std::vector<const ModelAction *> *release_heads) const
 563 {
 564         ASSERT(rf->is_write());
 565         if (!rf) {
 566                 /* read from future: need to settle this later */
 567                 return false; /* incomplete */
 568         }
 569         if (rf->is_release())
 570                 release_heads->push_back(rf);
 571         if (rf->is_rmw()) {
 572                 if (rf->is_acquire())
 573                         return true; /* complete */
 574                 return release_seq_head(rf->get_reads_from(), release_heads);
 575         }
 576         if (rf->is_release())
 577                 return true; /* complete */
 578
 579         /* else relaxed write; check modification order for contiguous subsequence
 580          * -> rf must be same thread as release */
 581         int tid = id_to_int(rf->get_tid());
 582         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 583         action_list_t *list = &(*thrd_lists)[tid];
 584         action_list_t::const_reverse_iterator rit;
 585
 586         /* Find rf in the thread list */
 587         rit = std::find(list->rbegin(), list->rend(), rf);
 588         ASSERT(rit != list->rend());
 589
 590         /* Find the last write/release */
 591         for (; rit != list->rend(); rit++)
 592                 if ((*rit)->is_release())
 593                         break;
 594         if (rit == list->rend()) {
 595                 /* No write-release in this thread */
 596                 return true; /* complete */
 597         }
 598         ModelAction *release = *rit;
 599
 600         ASSERT(rf->same_thread(release));
 601
 602         bool certain = true;
 603         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 604                 if (id_to_int(rf->get_tid()) == (int)i)
 605                         continue;
 606                 list = &(*thrd_lists)[i];
 607
 608                 /* Can we ensure no future writes from this thread may break
 609                  * the release seq? */
 610                 bool future_ordered = false;
 611
 612                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 613                         const ModelAction *act = *rit;
 614                         if (!act->is_write())
 615                                 continue;
 616                         /* Reach synchronization -> this thread is complete */
 617                         if (act->happens_before(release))
 618                                 break;
 619                         if (rf->happens_before(act)) {
 620                                 future_ordered = true;
 621                                 continue;
 622                         }
 623
 624                         /* Check modification order */
 625                         if (mo_graph->checkReachable(rf, act)) {
 626                                 /* rf --mo--> act */
 627                                 future_ordered = true;
 628                                 continue;
 629                         }
 630                         if (mo_graph->checkReachable(act, release))
 631                                 /* act --mo--> release */
 632                                 break;
 633                         if (mo_graph->checkReachable(release, act) &&
 634                                       mo_graph->checkReachable(act, rf)) {
 635                                 /* release --mo-> act --mo--> rf */
 636                                 return true; /* complete */
 637                         }
 638                         certain = false;
 639                 }
 640                 if (!future_ordered)
 641                         return false; /* This thread is uncertain */
 642         }
 643
 644         if (certain)
 645                 release_heads->push_back(release);
 646         return certain;
 647 }
 648
 649 /**
 650  * A public interface for getting the release sequence head(s) with which a
 651  * given ModelAction must synchronize. This function only returns a non-empty
 652  * result when it can locate a release sequence head with certainty. Otherwise,
 653  * it may mark the internal state of the ModelChecker so that it will handle
 654  * the release sequence at a later time, causing @a act to update its
 655  * synchronization at some later point in execution.
 656  * @param act The 'acquire' action that may read from a release sequence
 657  * @param release_heads A pass-by-reference return parameter. Will be filled
 658  * with the head(s) of the release sequence(s), if they exists with certainty.
 659  * @see ModelChecker::release_seq_head
 660  */
 661 void ModelChecker::get_release_seq_heads(ModelAction *act,
 662                 std::vector<const ModelAction *> *release_heads)
 663 {
 664         const ModelAction *rf = act->get_reads_from();
 665         bool complete;
 666         complete = release_seq_head(rf, release_heads);
 667         if (!complete) {
 668                 /* add act to 'lazy checking' list */
 669                 std::list<ModelAction *> *list;
 670                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 671                 list->push_back(act);
 672         }
 673 }
 674
 675 /**
 676  * Attempt to resolve all stashed operations that might synchronize with a
 677  * release sequence for a given location. This implements the "lazy" portion of
 678  * determining whether or not a release sequence was contiguous, since not all
 679  * modification order information is present at the time an action occurs.
 680  *
 681  * @param location The location/object that should be checked for release
 682  * sequence resolutions
 683  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 684  */
 685 bool ModelChecker::resolve_release_sequences(void *location)
 686 {
 687         std::list<ModelAction *> *list;
 688         list = lazy_sync_with_release->getptr(location);
 689         if (!list)
 690                 return false;
 691
 692         bool updated = false;
 693         std::list<ModelAction *>::iterator it = list->begin();
 694         while (it != list->end()) {
 695                 ModelAction *act = *it;
 696                 const ModelAction *rf = act->get_reads_from();
 697                 std::vector<const ModelAction *> release_heads;
 698                 bool complete;
 699                 complete = release_seq_head(rf, &release_heads);
 700                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 701                         if (!act->has_synchronized_with(release_heads[i])) {
 702                                 updated = true;
 703                                 act->synchronize_with(release_heads[i]);
 704                         }
 705                 }
 706
 707                 if (updated) {
 708                         /* propagate synchronization to later actions */
 709                         action_list_t::reverse_iterator it = action_trace->rbegin();
 710                         while ((*it) != act) {
 711                                 ModelAction *propagate = *it;
 712                                 if (act->happens_before(propagate))
 713                                         /** @todo new mo_graph edges along with
 714                                          * this synchronization? */
 715                                         propagate->synchronize_with(act);
 716                         }
 717                 }
 718                 if (complete)
 719                         it = list->erase(it);
 720                 else
 721                         it++;
 722         }
 723
 724         // If we resolved promises or data races, see if we have realized a data race.
 725         if (checkDataRaces()) {
 726                 set_assert();
 727         }
 728
 729         return updated;
 730 }
 731
 732 /**
 733  * Performs various bookkeeping operations for the current ModelAction. For
 734  * instance, adds action to the per-object, per-thread action vector and to the
 735  * action trace list of all thread actions.
 736  *
 737  * @param act is the ModelAction to add.
 738  */
 739 void ModelChecker::add_action_to_lists(ModelAction *act)
 740 {
 741         int tid = id_to_int(act->get_tid());
 742         action_trace->push_back(act);
 743
 744         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 745
 746         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 747         if (tid >= (int)vec->size())
 748                 vec->resize(next_thread_id);
 749         (*vec)[tid].push_back(act);
 750
 751         if ((int)thrd_last_action->size() <= tid)
 752                 thrd_last_action->resize(get_num_threads());
 753         (*thrd_last_action)[tid] = act;
 754 }
 755
 756 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 757 {
 758         int nthreads = get_num_threads();
 759         if ((int)thrd_last_action->size() < nthreads)
 760                 thrd_last_action->resize(nthreads);
 761         return (*thrd_last_action)[id_to_int(tid)];
 762 }
 763
 764 /**
 765  * Gets the last memory_order_seq_cst action (in the total global sequence)
 766  * performed on a particular object (i.e., memory location).
 767  * @param location The object location to check
 768  * @return The last seq_cst action performed
 769  */
 770 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 771 {
 772         action_list_t *list = obj_map->get_safe_ptr(location);
 773         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 774         action_list_t::reverse_iterator rit;
 775         for (rit = list->rbegin(); rit != list->rend(); rit++)
 776                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 777                         return *rit;
 778         return NULL;
 779 }
 780
 781 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 782 {
 783         ModelAction *parent = get_last_action(tid);
 784         if (!parent)
 785                 parent = get_thread(tid)->get_creation();
 786         return parent;
 787 }
 788
 789 /**
 790  * Returns the clock vector for a given thread.
 791  * @param tid The thread whose clock vector we want
 792  * @return Desired clock vector
 793  */
 794 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 795 {
 796         return get_parent_action(tid)->get_cv();
 797 }
 798
 799 /**
 800  * Resolve a set of Promises with a current write. The set is provided in the
 801  * Node corresponding to @a write.
 802  * @param write The ModelAction that is fulfilling Promises
 803  * @return True if promises were resolved; false otherwise
 804  */
 805 bool ModelChecker::resolve_promises(ModelAction *write)
 806 {
 807         bool resolved = false;
 808         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 809                 Promise *promise = (*promises)[promise_index];
 810                 if (write->get_node()->get_promise(i)) {
 811                         ModelAction *read = promise->get_action();
 812                         read->read_from(write);
 813                         r_modification_order(read, write);
 814                         post_r_modification_order(read, write);
 815                         promises->erase(promises->begin() + promise_index);
 816                         resolved = true;
 817                 } else
 818                         promise_index++;
 819         }
 820
 821         return resolved;
 822 }
 823
 824 /**
 825  * Compute the set of promises that could potentially be satisfied by this
 826  * action. Note that the set computation actually appears in the Node, not in
 827  * ModelChecker.
 828  * @param curr The ModelAction that may satisfy promises
 829  */
 830 void ModelChecker::compute_promises(ModelAction *curr)
 831 {
 832         for (unsigned int i = 0; i < promises->size(); i++) {
 833                 Promise *promise = (*promises)[i];
 834                 const ModelAction *act = promise->get_action();
 835                 if (!act->happens_before(curr) &&
 836                                 act->is_read() &&
 837                                 !act->is_synchronizing(curr) &&
 838                                 !act->same_thread(curr) &&
 839                                 promise->get_value() == curr->get_value()) {
 840                         curr->get_node()->set_promise(i);
 841                 }
 842         }
 843 }
 844
 845 /** Checks promises in response to change in ClockVector Threads. */
 846 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 847 {
 848         for (unsigned int i = 0; i < promises->size(); i++) {
 849                 Promise *promise = (*promises)[i];
 850                 const ModelAction *act = promise->get_action();
 851                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 852                                 merge_cv->synchronized_since(act)) {
 853                         //This thread is no longer able to send values back to satisfy the promise
 854                         int num_synchronized_threads = promise->increment_threads();
 855                         if (num_synchronized_threads == get_num_threads()) {
 856                                 //Promise has failed
 857                                 failed_promise = true;
 858                                 return;
 859                         }
 860                 }
 861         }
 862 }
 863
 864 /**
 865  * Build up an initial set of all past writes that this 'read' action may read
 866  * from. This set is determined by the clock vector's "happens before"
 867  * relationship.
 868  * @param curr is the current ModelAction that we are exploring; it must be a
 869  * 'read' operation.
 870  */
 871 void ModelChecker::build_reads_from_past(ModelAction *curr)
 872 {
 873         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 874         unsigned int i;
 875         ASSERT(curr->is_read());
 876
 877         ModelAction *last_seq_cst = NULL;
 878
 879         /* Track whether this object has been initialized */
 880         bool initialized = false;
 881
 882         if (curr->is_seqcst()) {
 883                 last_seq_cst = get_last_seq_cst(curr->get_location());
 884                 /* We have to at least see the last sequentially consistent write,
 885                          so we are initialized. */
 886                 if (last_seq_cst != NULL)
 887                         initialized = true;
 888         }
 889
 890         /* Iterate over all threads */
 891         for (i = 0; i < thrd_lists->size(); i++) {
 892                 /* Iterate over actions in thread, starting from most recent */
 893                 action_list_t *list = &(*thrd_lists)[i];
 894                 action_list_t::reverse_iterator rit;
 895                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 896                         ModelAction *act = *rit;
 897
 898                         /* Only consider 'write' actions */
 899                         if (!act->is_write())
 900                                 continue;
 901
 902                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 903                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 904                                 DEBUG("Adding action to may_read_from:\n");
 905                                 if (DBG_ENABLED()) {
 906                                         act->print();
 907                                         curr->print();
 908                                 }
 909                                 curr->get_node()->add_read_from(act);
 910                         }
 911
 912                         /* Include at most one act per-thread that "happens before" curr */
 913                         if (act->happens_before(curr)) {
 914                                 initialized = true;
 915                                 break;
 916                         }
 917                 }
 918         }
 919
 920         if (!initialized) {
 921                 /** @todo Need a more informative way of reporting errors. */
 922                 printf("ERROR: may read from uninitialized atomic\n");
 923         }
 924
 925         if (DBG_ENABLED() || !initialized) {
 926                 printf("Reached read action:\n");
 927                 curr->print();
 928                 printf("Printing may_read_from\n");
 929                 curr->get_node()->print_may_read_from();
 930                 printf("End printing may_read_from\n");
 931         }
 932
 933         ASSERT(initialized);
 934 }
 935
 936 static void print_list(action_list_t *list)
 937 {
 938         action_list_t::iterator it;
 939
 940         printf("---------------------------------------------------------------------\n");
 941         printf("Trace:\n");
 942
 943         for (it = list->begin(); it != list->end(); it++) {
 944                 (*it)->print();
 945         }
 946         printf("---------------------------------------------------------------------\n");
 947 }
 948
 949 void ModelChecker::print_summary()
 950 {
 951         printf("\n");
 952         printf("Number of executions: %d\n", num_executions);
 953         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 954
 955         scheduler->print();
 956
 957         if (!isfinalfeasible())
 958                 printf("INFEASIBLE EXECUTION!\n");
 959         print_list(action_trace);
 960         printf("\n");
 961 }
 962
 963 /**
 964  * Add a Thread to the system for the first time. Should only be called once
 965  * per thread.
 966  * @param t The Thread to add
 967  */
 968 void ModelChecker::add_thread(Thread *t)
 969 {
 970         thread_map->put(id_to_int(t->get_id()), t);
 971         scheduler->add_thread(t);
 972 }
 973
 974 void ModelChecker::remove_thread(Thread *t)
 975 {
 976         scheduler->remove_thread(t);
 977 }
 978
 979 /**
 980  * Switch from a user-context to the "master thread" context (a.k.a. system
 981  * context). This switch is made with the intention of exploring a particular
 982  * model-checking action (described by a ModelAction object). Must be called
 983  * from a user-thread context.
 984  * @param act The current action that will be explored. Must not be NULL.
 985  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 986  */
 987 int ModelChecker::switch_to_master(ModelAction *act)
 988 {
 989         DBG();
 990         Thread *old = thread_current();
 991         set_current_action(act);
 992         old->set_state(THREAD_READY);
 993         return Thread::swap(old, &system_context);
 994 }
 995
 996 /**
 997  * Takes the next step in the execution, if possible.
 998  * @return Returns true (success) if a step was taken and false otherwise.
 999  */
1000 bool ModelChecker::take_step() {
1001         Thread *curr, *next;
1002
1003         if (has_asserted())
1004                 return false;
1005
1006         curr = thread_current();
1007         if (curr) {
1008                 if (curr->get_state() == THREAD_READY) {
1009                         ASSERT(current_action);
1010                         nextThread = check_current_action(current_action);
1011                         current_action = NULL;
1012                         if (!curr->is_blocked() && !curr->is_complete())
1013                                 scheduler->add_thread(curr);
1014                 } else {
1015                         ASSERT(false);
1016                 }
1017         }
1018         next = scheduler->next_thread(nextThread);
1019
1020         /* Infeasible -> don't take any more steps */
1021         if (!isfeasible())
1022                 return false;
1023
1024         if (next)
1025                 next->set_state(THREAD_RUNNING);
1026         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1027
1028         /* next == NULL -> don't take any more steps */
1029         if (!next)
1030                 return false;
1031         /* Return false only if swap fails with an error */
1032         return (Thread::swap(&system_context, next) == 0);
1033 }
1034
1035 /** Runs the current execution until threre are no more steps to take. */
1036 void ModelChecker::finish_execution() {
1037         DBG();
1038
1039         while (take_step());
1040 }