model.cc

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