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         /* The THREAD_CREATE action points to the created Thread */
 374         else if (curr->get_type() == THREAD_CREATE)
 375                 return (Thread *)curr->get_location();
 376         else
 377                 return get_next_replay_thread();
 378 }
 379
 380 /** @returns whether the current partial trace must be a prefix of a
 381  * feasible trace. */
 382
 383 bool ModelChecker::isfeasibleprefix() {
 384         return promises->size()==0;
 385 }
 386
 387 /** @returns whether the current partial trace is feasible. */
 388 bool ModelChecker::isfeasible() {
 389         return !mo_graph->checkForCycles() && !failed_promise;
 390 }
 391
 392 /** Returns whether the current completed trace is feasible. */
 393 bool ModelChecker::isfinalfeasible() {
 394         return isfeasible() && promises->size() == 0;
 395 }
 396
 397 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 398 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 399         int tid = id_to_int(act->get_tid());
 400         ModelAction *lastread = get_last_action(tid);
 401         lastread->process_rmw(act);
 402         if (act->is_rmw())
 403                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 404         return lastread;
 405 }
 406
 407 /**
 408  * Updates the mo_graph with the constraints imposed from the current read.
 409  * @param curr The current action. Must be a read.
 410  * @param rf The action that curr reads from. Must be a write.
 411  * @return True if modification order edges were added; false otherwise
 412  */
 413 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 414 {
 415         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 416         unsigned int i;
 417         bool added = false;
 418         ASSERT(curr->is_read());
 419
 420         /* Iterate over all threads */
 421         for (i = 0; i < thrd_lists->size(); i++) {
 422                 /* Iterate over actions in thread, starting from most recent */
 423                 action_list_t *list = &(*thrd_lists)[i];
 424                 action_list_t::reverse_iterator rit;
 425                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 426                         ModelAction *act = *rit;
 427
 428                         /* Include at most one act per-thread that "happens before" curr */
 429                         if (act->happens_before(curr)) {
 430                                 if (act->is_read()) {
 431                                         const ModelAction *prevreadfrom = act->get_reads_from();
 432                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 433                                                 mo_graph->addEdge(prevreadfrom, rf);
 434                                                 added = true;
 435                                         }
 436                                 } else if (rf != act) {
 437                                         mo_graph->addEdge(act, rf);
 438                                         added = true;
 439                                 }
 440                                 break;
 441                         }
 442                 }
 443         }
 444
 445         return added;
 446 }
 447
 448 /** Updates the mo_graph with the constraints imposed from the current read. */
 449 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 450 {
 451         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 452         unsigned int i;
 453         ASSERT(curr->is_read());
 454
 455         /* Iterate over all threads */
 456         for (i = 0; i < thrd_lists->size(); i++) {
 457                 /* Iterate over actions in thread, starting from most recent */
 458                 action_list_t *list = &(*thrd_lists)[i];
 459                 action_list_t::reverse_iterator rit;
 460                 ModelAction *lastact = NULL;
 461
 462                 /* Find last action that happens after curr */
 463                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 464                         ModelAction *act = *rit;
 465                         if (curr->happens_before(act)) {
 466                                 lastact = act;
 467                         } else
 468                                 break;
 469                 }
 470
 471                         /* Include at most one act per-thread that "happens before" curr */
 472                 if (lastact != NULL) {
 473                         if (lastact->is_read()) {
 474                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 475                                 if (postreadfrom != NULL&&rf != postreadfrom)
 476                                         mo_graph->addEdge(rf, postreadfrom);
 477                         } else if (rf != lastact) {
 478                                 mo_graph->addEdge(rf, lastact);
 479                         }
 480                         break;
 481                 }
 482         }
 483 }
 484
 485 /**
 486  * Updates the mo_graph with the constraints imposed from the current write.
 487  * @param curr The current action. Must be a write.
 488  * @return True if modification order edges were added; false otherwise
 489  */
 490 bool ModelChecker::w_modification_order(ModelAction *curr)
 491 {
 492         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 493         unsigned int i;
 494         bool added = false;
 495         ASSERT(curr->is_write());
 496
 497         if (curr->is_seqcst()) {
 498                 /* We have to at least see the last sequentially consistent write,
 499                          so we are initialized. */
 500                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 501                 if (last_seq_cst != NULL) {
 502                         mo_graph->addEdge(last_seq_cst, curr);
 503                         added = true;
 504                 }
 505         }
 506
 507         /* Iterate over all threads */
 508         for (i = 0; i < thrd_lists->size(); i++) {
 509                 /* Iterate over actions in thread, starting from most recent */
 510                 action_list_t *list = &(*thrd_lists)[i];
 511                 action_list_t::reverse_iterator rit;
 512                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 513                         ModelAction *act = *rit;
 514
 515                         /* Include at most one act per-thread that "happens before" curr */
 516                         if (act->happens_before(curr)) {
 517                                 if (act->is_read())
 518                                         mo_graph->addEdge(act->get_reads_from(), curr);
 519                                 else
 520                                         mo_graph->addEdge(act, curr);
 521                                 added = true;
 522                                 break;
 523                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 524                                                      !act->same_thread(curr)) {
 525                                 /* We have an action that:
 526                                    (1) did not happen before us
 527                                    (2) is a read and we are a write
 528                                    (3) cannot synchronize with us
 529                                    (4) is in a different thread
 530                                    =>
 531                                    that read could potentially read from our write.
 532                                  */
 533                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 534                                                 (!next_backtrack || *act > *next_backtrack))
 535                                         next_backtrack = act;
 536                         }
 537                 }
 538         }
 539
 540         return added;
 541 }
 542
 543 /**
 544  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 545  * The ModelAction under consideration is expected to be taking part in
 546  * release/acquire synchronization as an object of the "reads from" relation.
 547  * Note that this can only provide release sequence support for RMW chains
 548  * which do not read from the future, as those actions cannot be traced until
 549  * their "promise" is fulfilled. Similarly, we may not even establish the
 550  * presence of a release sequence with certainty, as some modification order
 551  * constraints may be decided further in the future. Thus, this function
 552  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 553  * and a boolean representing certainty.
 554  *
 555  * @todo Finish lazy updating, when promises are fulfilled in the future
 556  * @param rf The action that might be part of a release sequence. Must be a
 557  * write.
 558  * @param release_heads A pass-by-reference style return parameter.  After
 559  * execution of this function, release_heads will contain the heads of all the
 560  * relevant release sequences, if any exists
 561  * @return true, if the ModelChecker is certain that release_heads is complete;
 562  * false otherwise
 563  */
 564 bool ModelChecker::release_seq_head(const ModelAction *rf,
 565                 std::vector<const ModelAction *> *release_heads) const
 566 {
 567         ASSERT(rf->is_write());
 568         if (!rf) {
 569                 /* read from future: need to settle this later */
 570                 return false; /* incomplete */
 571         }
 572         if (rf->is_release())
 573                 release_heads->push_back(rf);
 574         if (rf->is_rmw()) {
 575                 if (rf->is_acquire())
 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         }
 676 }
 677
 678 /**
 679  * Attempt to resolve all stashed operations that might synchronize with a
 680  * release sequence for a given location. This implements the "lazy" portion of
 681  * determining whether or not a release sequence was contiguous, since not all
 682  * modification order information is present at the time an action occurs.
 683  *
 684  * @param location The location/object that should be checked for release
 685  * sequence resolutions
 686  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 687  */
 688 bool ModelChecker::resolve_release_sequences(void *location)
 689 {
 690         std::list<ModelAction *> *list;
 691         list = lazy_sync_with_release->getptr(location);
 692         if (!list)
 693                 return false;
 694
 695         bool updated = false;
 696         std::list<ModelAction *>::iterator it = list->begin();
 697         while (it != list->end()) {
 698                 ModelAction *act = *it;
 699                 const ModelAction *rf = act->get_reads_from();
 700                 std::vector<const ModelAction *> release_heads;
 701                 bool complete;
 702                 complete = release_seq_head(rf, &release_heads);
 703                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 704                         if (!act->has_synchronized_with(release_heads[i])) {
 705                                 updated = true;
 706                                 act->synchronize_with(release_heads[i]);
 707                         }
 708                 }
 709
 710                 if (updated) {
 711                         /* propagate synchronization to later actions */
 712                         action_list_t::reverse_iterator it = action_trace->rbegin();
 713                         while ((*it) != act) {
 714                                 ModelAction *propagate = *it;
 715                                 if (act->happens_before(propagate))
 716                                         /** @todo new mo_graph edges along with
 717                                          * this synchronization? */
 718                                         propagate->synchronize_with(act);
 719                         }
 720                 }
 721                 if (complete)
 722                         it = list->erase(it);
 723                 else
 724                         it++;
 725         }
 726
 727         // If we resolved promises or data races, see if we have realized a data race.
 728         if (checkDataRaces()) {
 729                 set_assert();
 730         }
 731
 732         return updated;
 733 }
 734
 735 /**
 736  * Performs various bookkeeping operations for the current ModelAction. For
 737  * instance, adds action to the per-object, per-thread action vector and to the
 738  * action trace list of all thread actions.
 739  *
 740  * @param act is the ModelAction to add.
 741  */
 742 void ModelChecker::add_action_to_lists(ModelAction *act)
 743 {
 744         int tid = id_to_int(act->get_tid());
 745         action_trace->push_back(act);
 746
 747         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 748
 749         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 750         if (tid >= (int)vec->size())
 751                 vec->resize(next_thread_id);
 752         (*vec)[tid].push_back(act);
 753
 754         if ((int)thrd_last_action->size() <= tid)
 755                 thrd_last_action->resize(get_num_threads());
 756         (*thrd_last_action)[tid] = act;
 757 }
 758
 759 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 760 {
 761         int nthreads = get_num_threads();
 762         if ((int)thrd_last_action->size() < nthreads)
 763                 thrd_last_action->resize(nthreads);
 764         return (*thrd_last_action)[id_to_int(tid)];
 765 }
 766
 767 /**
 768  * Gets the last memory_order_seq_cst action (in the total global sequence)
 769  * performed on a particular object (i.e., memory location).
 770  * @param location The object location to check
 771  * @return The last seq_cst action performed
 772  */
 773 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 774 {
 775         action_list_t *list = obj_map->get_safe_ptr(location);
 776         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 777         action_list_t::reverse_iterator rit;
 778         for (rit = list->rbegin(); rit != list->rend(); rit++)
 779                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 780                         return *rit;
 781         return NULL;
 782 }
 783
 784 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 785 {
 786         ModelAction *parent = get_last_action(tid);
 787         if (!parent)
 788                 parent = get_thread(tid)->get_creation();
 789         return parent;
 790 }
 791
 792 /**
 793  * Returns the clock vector for a given thread.
 794  * @param tid The thread whose clock vector we want
 795  * @return Desired clock vector
 796  */
 797 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 798 {
 799         return get_parent_action(tid)->get_cv();
 800 }
 801
 802 /**
 803  * Resolve a set of Promises with a current write. The set is provided in the
 804  * Node corresponding to @a write.
 805  * @param write The ModelAction that is fulfilling Promises
 806  * @return True if promises were resolved; false otherwise
 807  */
 808 bool ModelChecker::resolve_promises(ModelAction *write)
 809 {
 810         bool resolved = false;
 811         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 812                 Promise *promise = (*promises)[promise_index];
 813                 if (write->get_node()->get_promise(i)) {
 814                         ModelAction *read = promise->get_action();
 815                         read->read_from(write);
 816                         r_modification_order(read, write);
 817                         post_r_modification_order(read, write);
 818                         promises->erase(promises->begin() + promise_index);
 819                         resolved = true;
 820                 } else
 821                         promise_index++;
 822         }
 823
 824         return resolved;
 825 }
 826
 827 /**
 828  * Compute the set of promises that could potentially be satisfied by this
 829  * action. Note that the set computation actually appears in the Node, not in
 830  * ModelChecker.
 831  * @param curr The ModelAction that may satisfy promises
 832  */
 833 void ModelChecker::compute_promises(ModelAction *curr)
 834 {
 835         for (unsigned int i = 0; i < promises->size(); i++) {
 836                 Promise *promise = (*promises)[i];
 837                 const ModelAction *act = promise->get_action();
 838                 if (!act->happens_before(curr) &&
 839                                 act->is_read() &&
 840                                 !act->is_synchronizing(curr) &&
 841                                 !act->same_thread(curr) &&
 842                                 promise->get_value() == curr->get_value()) {
 843                         curr->get_node()->set_promise(i);
 844                 }
 845         }
 846 }
 847
 848 /** Checks promises in response to change in ClockVector Threads. */
 849 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 850 {
 851         for (unsigned int i = 0; i < promises->size(); i++) {
 852                 Promise *promise = (*promises)[i];
 853                 const ModelAction *act = promise->get_action();
 854                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 855                                 merge_cv->synchronized_since(act)) {
 856                         //This thread is no longer able to send values back to satisfy the promise
 857                         int num_synchronized_threads = promise->increment_threads();
 858                         if (num_synchronized_threads == get_num_threads()) {
 859                                 //Promise has failed
 860                                 failed_promise = true;
 861                                 return;
 862                         }
 863                 }
 864         }
 865 }
 866
 867 /**
 868  * Build up an initial set of all past writes that this 'read' action may read
 869  * from. This set is determined by the clock vector's "happens before"
 870  * relationship.
 871  * @param curr is the current ModelAction that we are exploring; it must be a
 872  * 'read' operation.
 873  */
 874 void ModelChecker::build_reads_from_past(ModelAction *curr)
 875 {
 876         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 877         unsigned int i;
 878         ASSERT(curr->is_read());
 879
 880         ModelAction *last_seq_cst = NULL;
 881
 882         /* Track whether this object has been initialized */
 883         bool initialized = false;
 884
 885         if (curr->is_seqcst()) {
 886                 last_seq_cst = get_last_seq_cst(curr->get_location());
 887                 /* We have to at least see the last sequentially consistent write,
 888                          so we are initialized. */
 889                 if (last_seq_cst != NULL)
 890                         initialized = true;
 891         }
 892
 893         /* Iterate over all threads */
 894         for (i = 0; i < thrd_lists->size(); i++) {
 895                 /* Iterate over actions in thread, starting from most recent */
 896                 action_list_t *list = &(*thrd_lists)[i];
 897                 action_list_t::reverse_iterator rit;
 898                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 899                         ModelAction *act = *rit;
 900
 901                         /* Only consider 'write' actions */
 902                         if (!act->is_write())
 903                                 continue;
 904
 905                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 906                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 907                                 DEBUG("Adding action to may_read_from:\n");
 908                                 if (DBG_ENABLED()) {
 909                                         act->print();
 910                                         curr->print();
 911                                 }
 912                                 curr->get_node()->add_read_from(act);
 913                         }
 914
 915                         /* Include at most one act per-thread that "happens before" curr */
 916                         if (act->happens_before(curr)) {
 917                                 initialized = true;
 918                                 break;
 919                         }
 920                 }
 921         }
 922
 923         if (!initialized) {
 924                 /** @todo Need a more informative way of reporting errors. */
 925                 printf("ERROR: may read from uninitialized atomic\n");
 926         }
 927
 928         if (DBG_ENABLED() || !initialized) {
 929                 printf("Reached read action:\n");
 930                 curr->print();
 931                 printf("Printing may_read_from\n");
 932                 curr->get_node()->print_may_read_from();
 933                 printf("End printing may_read_from\n");
 934         }
 935
 936         ASSERT(initialized);
 937 }
 938
 939 static void print_list(action_list_t *list)
 940 {
 941         action_list_t::iterator it;
 942
 943         printf("---------------------------------------------------------------------\n");
 944         printf("Trace:\n");
 945
 946         for (it = list->begin(); it != list->end(); it++) {
 947                 (*it)->print();
 948         }
 949         printf("---------------------------------------------------------------------\n");
 950 }
 951
 952 void ModelChecker::print_summary()
 953 {
 954         printf("\n");
 955         printf("Number of executions: %d\n", num_executions);
 956         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 957
 958         scheduler->print();
 959
 960         if (!isfinalfeasible())
 961                 printf("INFEASIBLE EXECUTION!\n");
 962         print_list(action_trace);
 963         printf("\n");
 964 }
 965
 966 /**
 967  * Add a Thread to the system for the first time. Should only be called once
 968  * per thread.
 969  * @param t The Thread to add
 970  */
 971 void ModelChecker::add_thread(Thread *t)
 972 {
 973         thread_map->put(id_to_int(t->get_id()), t);
 974         scheduler->add_thread(t);
 975 }
 976
 977 void ModelChecker::remove_thread(Thread *t)
 978 {
 979         scheduler->remove_thread(t);
 980 }
 981
 982 /**
 983  * Switch from a user-context to the "master thread" context (a.k.a. system
 984  * context). This switch is made with the intention of exploring a particular
 985  * model-checking action (described by a ModelAction object). Must be called
 986  * from a user-thread context.
 987  * @param act The current action that will be explored. Must not be NULL.
 988  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 989  */
 990 int ModelChecker::switch_to_master(ModelAction *act)
 991 {
 992         DBG();
 993         Thread *old = thread_current();
 994         set_current_action(act);
 995         old->set_state(THREAD_READY);
 996         return Thread::swap(old, &system_context);
 997 }
 998
 999 /**
1000  * Takes the next step in the execution, if possible.
1001  * @return Returns true (success) if a step was taken and false otherwise.
1002  */
1003 bool ModelChecker::take_step() {
1004         Thread *curr, *next;
1005
1006         if (has_asserted())
1007                 return false;
1008
1009         curr = thread_current();
1010         if (curr) {
1011                 if (curr->get_state() == THREAD_READY) {
1012                         ASSERT(current_action);
1013                         nextThread = check_current_action(current_action);
1014                         current_action = NULL;
1015                         if (!curr->is_blocked() && !curr->is_complete())
1016                                 scheduler->add_thread(curr);
1017                 } else {
1018                         ASSERT(false);
1019                 }
1020         }
1021         next = scheduler->next_thread(nextThread);
1022
1023         /* Infeasible -> don't take any more steps */
1024         if (!isfeasible())
1025                 return false;
1026
1027         if (next)
1028                 next->set_state(THREAD_RUNNING);
1029         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1030
1031         /* next == NULL -> don't take any more steps */
1032         if (!next)
1033                 return false;
1034         /* Return false only if swap fails with an error */
1035         return (Thread::swap(&system_context, next) == 0);
1036 }
1037
1038 /** Runs the current execution until threre are no more steps to take. */
1039 void ModelChecker::finish_execution() {
1040         DBG();
1041
1042         while (take_step());
1043 }