model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14
  15 #define INITIAL_THREAD_ID       0
  16
  17 ModelChecker *model;
  18
  19 /** @brief Constructor */
  20 ModelChecker::ModelChecker(struct model_params params) :
  21         /* Initialize default scheduler */
  22         scheduler(new Scheduler()),
  23         num_executions(0),
  24         num_feasible_executions(0),
  25         params(params),
  26         diverge(NULL),
  27         action_trace(new action_list_t()),
  28         thread_map(new HashTable<int, Thread *, int>()),
  29         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  30         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  31         promises(new std::vector<Promise *>()),
  32         futurevalues(new std::vector<struct PendingFutureValue>()),
  33         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  34         thrd_last_action(new std::vector<ModelAction *>(1)),
  35         node_stack(new NodeStack()),
  36         is_enabled(NULL),
  37         mo_graph(new CycleGraph()),
  38         failed_promise(false),
  39         too_many_reads(false),
  40         asserted(false)
  41 {
  42         /* Allocate this "size" on the snapshotting heap */
  43         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  44         /* First thread created will have id INITIAL_THREAD_ID */
  45         priv->next_thread_id = INITIAL_THREAD_ID;
  46
  47         lazy_sync_size = &priv->lazy_sync_size;
  48 }
  49
  50 /** @brief Destructor */
  51 ModelChecker::~ModelChecker()
  52 {
  53         for (int i = 0; i < get_num_threads(); i++)
  54                 delete thread_map->get(i);
  55         delete thread_map;
  56         if (is_enabled)
  57                 free(is_enabled);
  58
  59         delete obj_thrd_map;
  60         delete obj_map;
  61         delete action_trace;
  62
  63         for (unsigned int i = 0; i < promises->size(); i++)
  64                 delete (*promises)[i];
  65         delete promises;
  66
  67         delete lazy_sync_with_release;
  68
  69         delete thrd_last_action;
  70         delete node_stack;
  71         delete scheduler;
  72         delete mo_graph;
  73 }
  74
  75 /**
  76  * Restores user program to initial state and resets all model-checker data
  77  * structures.
  78  */
  79 void ModelChecker::reset_to_initial_state()
  80 {
  81         DEBUG("+++ Resetting to initial state +++\n");
  82         node_stack->reset_execution();
  83         failed_promise = false;
  84         too_many_reads = false;
  85         reset_asserted();
  86         snapshotObject->backTrackBeforeStep(0);
  87 }
  88
  89 /** @returns a thread ID for a new Thread */
  90 thread_id_t ModelChecker::get_next_id()
  91 {
  92         thread_id_t newid=priv->next_thread_id++;
  93         bool * tmp=(bool *) malloc((newid+1)*sizeof(bool));
  94         memcpy(tmp, is_enabled, newid*sizeof(bool));
  95         tmp[newid]=true;
  96         free(is_enabled);
  97         is_enabled=tmp;
  98         return newid;
  99 }
 100
 101 /** @returns the number of user threads created during this execution */
 102 int ModelChecker::get_num_threads()
 103 {
 104         return priv->next_thread_id;
 105 }
 106
 107 /** @returns a sequence number for a new ModelAction */
 108 modelclock_t ModelChecker::get_next_seq_num()
 109 {
 110         return ++priv->used_sequence_numbers;
 111 }
 112
 113 /**
 114  * @brief Choose the next thread to execute.
 115  *
 116  * This function chooses the next thread that should execute. It can force the
 117  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 118  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 119  * The model-checker may have no preference regarding the next thread (i.e.,
 120  * when exploring a new execution ordering), in which case this will return
 121  * NULL.
 122  * @param curr The current ModelAction. This action might guide the choice of
 123  * next thread.
 124  * @return The next thread to run. If the model-checker has no preference, NULL.
 125  */
 126 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 127 {
 128         thread_id_t tid;
 129
 130         /* Do not split atomic actions. */
 131         if (curr->is_rmwr())
 132                 return thread_current();
 133         /* The THREAD_CREATE action points to the created Thread */
 134         else if (curr->get_type() == THREAD_CREATE)
 135                 return (Thread *)curr->get_location();
 136
 137         /* Have we completed exploring the preselected path? */
 138         if (diverge == NULL)
 139                 return NULL;
 140
 141         /* Else, we are trying to replay an execution */
 142         ModelAction *next = node_stack->get_next()->get_action();
 143
 144         if (next == diverge) {
 145                 Node *nextnode = next->get_node();
 146                 /* Reached divergence point */
 147                 if (nextnode->increment_promise()) {
 148                         /* The next node will try to satisfy a different set of promises. */
 149                         tid = next->get_tid();
 150                         node_stack->pop_restofstack(2);
 151                 } else if (nextnode->increment_read_from()) {
 152                         /* The next node will read from a different value. */
 153                         tid = next->get_tid();
 154                         node_stack->pop_restofstack(2);
 155                 } else if (nextnode->increment_future_value()) {
 156                         /* The next node will try to read from a different future value. */
 157                         tid = next->get_tid();
 158                         node_stack->pop_restofstack(2);
 159                 } else {
 160                         /* Make a different thread execute for next step */
 161                         Node *node = nextnode->get_parent();
 162                         tid = node->get_next_backtrack();
 163                         node_stack->pop_restofstack(1);
 164                 }
 165                 DEBUG("*** Divergence point ***\n");
 166                 diverge = NULL;
 167         } else {
 168                 tid = next->get_tid();
 169         }
 170         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 171         ASSERT(tid != THREAD_ID_T_NONE);
 172         return thread_map->get(id_to_int(tid));
 173 }
 174
 175 /**
 176  * Queries the model-checker for more executions to explore and, if one
 177  * exists, resets the model-checker state to execute a new execution.
 178  *
 179  * @return If there are more executions to explore, return true. Otherwise,
 180  * return false.
 181  */
 182 bool ModelChecker::next_execution()
 183 {
 184         DBG();
 185
 186         num_executions++;
 187         if (isfinalfeasible())
 188                 num_feasible_executions++;
 189
 190         if (isfinalfeasible() || DBG_ENABLED())
 191                 print_summary();
 192
 193         if ((diverge = get_next_backtrack()) == NULL)
 194                 return false;
 195
 196         if (DBG_ENABLED()) {
 197                 printf("Next execution will diverge at:\n");
 198                 diverge->print();
 199         }
 200
 201         reset_to_initial_state();
 202         return true;
 203 }
 204
 205 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 206 {
 207         action_type type = act->get_type();
 208
 209         if (type==ATOMIC_READ||type==ATOMIC_WRITE||type==ATOMIC_RMW) {
 210                 /* linear search: from most recent to oldest */
 211                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 212                 action_list_t::reverse_iterator rit;
 213                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 214                         ModelAction *prev = *rit;
 215                         if (act->is_synchronizing(prev))
 216                                 return prev;
 217                 }
 218         } else if (type==ATOMIC_LOCK||type==ATOMIC_TRYLOCK) {
 219                 /* linear search: from most recent to oldest */
 220                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 221                 action_list_t::reverse_iterator rit;
 222                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 223                         ModelAction *prev = *rit;
 224                         if (prev->is_success_lock())
 225                                 return prev;
 226                 }
 227         } else if (type==ATOMIC_UNLOCK) {
 228                 /* linear search: from most recent to oldest */
 229                 action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 230                 action_list_t::reverse_iterator rit;
 231                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 232                         ModelAction *prev = *rit;
 233                         if (prev->is_failed_trylock())
 234                                 return prev;
 235                 }
 236         }
 237         return NULL;
 238 }
 239
 240 void ModelChecker::set_backtracking(ModelAction *act)
 241 {
 242         ModelAction *prev;
 243         Node *node;
 244         Thread *t = get_thread(act);
 245
 246         prev = get_last_conflict(act);
 247         if (prev == NULL)
 248                 return;
 249
 250         node = prev->get_node()->get_parent();
 251
 252         while (!node->is_enabled(t))
 253                 t = t->get_parent();
 254
 255         /* Check if this has been explored already */
 256         if (node->has_been_explored(t->get_id()))
 257                 return;
 258
 259         /* Cache the latest backtracking point */
 260         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 261                 priv->next_backtrack = prev;
 262
 263         /* If this is a new backtracking point, mark the tree */
 264         if (!node->set_backtrack(t->get_id()))
 265                 return;
 266         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 267                         prev->get_tid(), t->get_id());
 268         if (DBG_ENABLED()) {
 269                 prev->print();
 270                 act->print();
 271         }
 272 }
 273
 274 /**
 275  * Returns last backtracking point. The model checker will explore a different
 276  * path for this point in the next execution.
 277  * @return The ModelAction at which the next execution should diverge.
 278  */
 279 ModelAction * ModelChecker::get_next_backtrack()
 280 {
 281         ModelAction *next = priv->next_backtrack;
 282         priv->next_backtrack = NULL;
 283         return next;
 284 }
 285
 286 /**
 287  * Processes a read or rmw model action.
 288  * @param curr is the read model action to process.
 289  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 290  * @return True if processing this read updates the mo_graph.
 291  */
 292 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 293 {
 294         uint64_t value;
 295         bool updated = false;
 296         while (true) {
 297                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 298                 if (reads_from != NULL) {
 299                         mo_graph->startChanges();
 300
 301                         value = reads_from->get_value();
 302                         bool r_status = false;
 303
 304                         if (!second_part_of_rmw) {
 305                                 check_recency(curr,false);
 306                                 r_status = r_modification_order(curr, reads_from);
 307                         }
 308
 309
 310                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 311                                 mo_graph->rollbackChanges();
 312                                 too_many_reads = false;
 313                                 continue;
 314                         }
 315
 316                         curr->read_from(reads_from);
 317                         mo_graph->commitChanges();
 318                         updated |= r_status;
 319                 } else if (!second_part_of_rmw) {
 320                         /* Read from future value */
 321                         value = curr->get_node()->get_future_value();
 322                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 323                         curr->read_from(NULL);
 324                         Promise *valuepromise = new Promise(curr, value, expiration);
 325                         promises->push_back(valuepromise);
 326                 }
 327                 get_thread(curr)->set_return_value(value);
 328                 return updated;
 329         }
 330 }
 331
 332 /**
 333  * Process a write ModelAction
 334  * @param curr The ModelAction to process
 335  * @return True if the mo_graph was updated or promises were resolved
 336  */
 337 bool ModelChecker::process_write(ModelAction *curr)
 338 {
 339         bool updated_mod_order = w_modification_order(curr);
 340         bool updated_promises = resolve_promises(curr);
 341
 342         if (promises->size() == 0) {
 343                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 344                         struct PendingFutureValue pfv = (*futurevalues)[i];
 345                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 346                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 347                                 priv->next_backtrack = pfv.act;
 348                 }
 349                 futurevalues->resize(0);
 350         }
 351
 352         mo_graph->commitChanges();
 353         get_thread(curr)->set_return_value(VALUE_NONE);
 354         return updated_mod_order || updated_promises;
 355 }
 356
 357 /**
 358  * This is the heart of the model checker routine. It performs model-checking
 359  * actions corresponding to a given "current action." Among other processes, it
 360  * calculates reads-from relationships, updates synchronization clock vectors,
 361  * forms a memory_order constraints graph, and handles replay/backtrack
 362  * execution when running permutations of previously-observed executions.
 363  *
 364  * @param curr The current action to process
 365  * @return The next Thread that must be executed. May be NULL if ModelChecker
 366  * makes no choice (e.g., according to replay execution, combining RMW actions,
 367  * etc.)
 368  */
 369 Thread * ModelChecker::check_current_action(ModelAction *curr)
 370 {
 371         bool second_part_of_rmw = false;
 372
 373         ASSERT(curr);
 374
 375         if (curr->is_rmwc() || curr->is_rmw()) {
 376                 ModelAction *tmp = process_rmw(curr);
 377                 second_part_of_rmw = true;
 378                 delete curr;
 379                 curr = tmp;
 380                 compute_promises(curr);
 381         } else {
 382                 ModelAction *tmp = node_stack->explore_action(curr, NULL);
 383                 if (tmp) {
 384                         /* Discard duplicate ModelAction; use action from NodeStack */
 385                         /* First restore type and order in case of RMW operation */
 386                         if (curr->is_rmwr())
 387                                 tmp->copy_typeandorder(curr);
 388
 389                         /* If we have diverged, we need to reset the clock vector. */
 390                         if (diverge == NULL)
 391                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 392
 393                         delete curr;
 394                         curr = tmp;
 395                 } else {
 396                         /*
 397                          * Perform one-time actions when pushing new ModelAction onto
 398                          * NodeStack
 399                          */
 400                         curr->create_cv(get_parent_action(curr->get_tid()));
 401                         /* Build may_read_from set */
 402                         if (curr->is_read())
 403                                 build_reads_from_past(curr);
 404                         if (curr->is_write())
 405                                 compute_promises(curr);
 406                 }
 407         }
 408
 409         /* Thread specific actions */
 410         switch (curr->get_type()) {
 411         case THREAD_CREATE: {
 412                 Thread *th = (Thread *)curr->get_location();
 413                 th->set_creation(curr);
 414                 break;
 415         }
 416         case THREAD_JOIN: {
 417                 Thread *waiting, *blocking;
 418                 waiting = get_thread(curr);
 419                 blocking = (Thread *)curr->get_location();
 420                 if (!blocking->is_complete()) {
 421                         blocking->push_wait_list(curr);
 422                         scheduler->sleep(waiting);
 423                 }
 424                 break;
 425         }
 426         case THREAD_FINISH: {
 427                 Thread *th = get_thread(curr);
 428                 while (!th->wait_list_empty()) {
 429                         ModelAction *act = th->pop_wait_list();
 430                         Thread *wake = get_thread(act);
 431                         scheduler->wake(wake);
 432                 }
 433                 th->complete();
 434                 break;
 435         }
 436         case THREAD_START: {
 437                 check_promises(NULL, curr->get_cv());
 438                 break;
 439         }
 440         default:
 441                 break;
 442         }
 443
 444         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 445
 446         while (!work_queue.empty()) {
 447                 WorkQueueEntry work = work_queue.front();
 448                 work_queue.pop_front();
 449
 450                 switch (work.type) {
 451                 case WORK_CHECK_CURR_ACTION: {
 452                         ModelAction *act = work.action;
 453                         bool updated = false;
 454                         if (act->is_read() && process_read(act, second_part_of_rmw))
 455                                 updated = true;
 456
 457                         if (act->is_write() && process_write(act))
 458                                 updated = true;
 459
 460                         if (updated)
 461                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 462                         break;
 463                 }
 464                 case WORK_CHECK_RELEASE_SEQ:
 465                         resolve_release_sequences(work.location, &work_queue);
 466                         break;
 467                 case WORK_CHECK_MO_EDGES:
 468                         /** @todo Perform follow-up mo_graph checks */
 469                 default:
 470                         ASSERT(false);
 471                         break;
 472                 }
 473         }
 474
 475         /* Add action to list.  */
 476         if (!second_part_of_rmw)
 477                 add_action_to_lists(curr);
 478
 479         check_curr_backtracking(curr);
 480
 481         set_backtracking(curr);
 482
 483         return get_next_thread(curr);
 484 }
 485
 486 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 487         Node *currnode = curr->get_node();
 488         Node *parnode = currnode->get_parent();
 489
 490         if ((!parnode->backtrack_empty() ||
 491                          !currnode->read_from_empty() ||
 492                          !currnode->future_value_empty() ||
 493                          !currnode->promise_empty())
 494                         && (!priv->next_backtrack ||
 495                                         *curr > *priv->next_backtrack)) {
 496                 priv->next_backtrack = curr;
 497         }
 498 }
 499
 500 bool ModelChecker::promises_expired() {
 501         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 502                 Promise *promise = (*promises)[promise_index];
 503                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 504                         return true;
 505                 }
 506         }
 507         return false;
 508 }
 509
 510 /** @returns whether the current partial trace must be a prefix of a
 511  * feasible trace. */
 512 bool ModelChecker::isfeasibleprefix() {
 513         return promises->size() == 0 && *lazy_sync_size == 0;
 514 }
 515
 516 /** @returns whether the current partial trace is feasible. */
 517 bool ModelChecker::isfeasible() {
 518         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 519 }
 520
 521 /** @returns whether the current partial trace is feasible other than
 522  * multiple RMW reading from the same store. */
 523 bool ModelChecker::isfeasibleotherthanRMW() {
 524         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 525 }
 526
 527 /** Returns whether the current completed trace is feasible. */
 528 bool ModelChecker::isfinalfeasible() {
 529         return isfeasible() && promises->size() == 0;
 530 }
 531
 532 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 533 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 534         int tid = id_to_int(act->get_tid());
 535         ModelAction *lastread = get_last_action(tid);
 536         lastread->process_rmw(act);
 537         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 538                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 539                 mo_graph->commitChanges();
 540         }
 541         return lastread;
 542 }
 543
 544 /**
 545  * Checks whether a thread has read from the same write for too many times
 546  * without seeing the effects of a later write.
 547  *
 548  * Basic idea:
 549  * 1) there must a different write that we could read from that would satisfy the modification order,
 550  * 2) we must have read from the same value in excess of maxreads times, and
 551  * 3) that other write must have been in the reads_from set for maxreads times.
 552  *
 553  * If so, we decide that the execution is no longer feasible.
 554  */
 555 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 556         if (params.maxreads != 0) {
 557                 if (curr->get_node()->get_read_from_size() <= 1)
 558                         return;
 559
 560                 //Must make sure that execution is currently feasible...  We could
 561                 //accidentally clear by rolling back
 562                 if (!isfeasible())
 563                         return;
 564
 565                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 566                 int tid = id_to_int(curr->get_tid());
 567
 568                 /* Skip checks */
 569                 if ((int)thrd_lists->size() <= tid)
 570                         return;
 571
 572                 action_list_t *list = &(*thrd_lists)[tid];
 573
 574                 action_list_t::reverse_iterator rit = list->rbegin();
 575                 /* Skip past curr */
 576                 if (already_added) {
 577                         for (; (*rit) != curr; rit++)
 578                                 ;
 579                         /* go past curr now */
 580                         rit++;
 581                 }
 582
 583                 action_list_t::reverse_iterator ritcopy = rit;
 584                 //See if we have enough reads from the same value
 585                 int count = 0;
 586                 for (; count < params.maxreads; rit++,count++) {
 587                         if (rit==list->rend())
 588                                 return;
 589                         ModelAction *act = *rit;
 590                         if (!act->is_read())
 591                                 return;
 592                         if (act->get_reads_from() != curr->get_reads_from())
 593                                 return;
 594                         if (act->get_node()->get_read_from_size() <= 1)
 595                                 return;
 596                 }
 597
 598                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 599                         //Get write
 600                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 601                         //Need a different write
 602                         if (write==curr->get_reads_from())
 603                                 continue;
 604
 605                         /* Test to see whether this is a feasible write to read from*/
 606                         mo_graph->startChanges();
 607                         r_modification_order(curr, write);
 608                         bool feasiblereadfrom = isfeasible();
 609                         mo_graph->rollbackChanges();
 610
 611                         if (!feasiblereadfrom)
 612                                 continue;
 613                         rit = ritcopy;
 614
 615                         bool feasiblewrite = true;
 616                         //new we need to see if this write works for everyone
 617
 618                         for (int loop = count; loop>0; loop--,rit++) {
 619                                 ModelAction *act=*rit;
 620                                 bool foundvalue = false;
 621                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 622                                         if (act->get_node()->get_read_from_at(i)==write) {
 623                                                 foundvalue = true;
 624                                                 break;
 625                                         }
 626                                 }
 627                                 if (!foundvalue) {
 628                                         feasiblewrite = false;
 629                                         break;
 630                                 }
 631                         }
 632                         if (feasiblewrite) {
 633                                 too_many_reads = true;
 634                                 return;
 635                         }
 636                 }
 637         }
 638 }
 639
 640 /**
 641  * Updates the mo_graph with the constraints imposed from the current
 642  * read.
 643  *
 644  * Basic idea is the following: Go through each other thread and find
 645  * the lastest action that happened before our read.  Two cases:
 646  *
 647  * (1) The action is a write => that write must either occur before
 648  * the write we read from or be the write we read from.
 649  *
 650  * (2) The action is a read => the write that that action read from
 651  * must occur before the write we read from or be the same write.
 652  *
 653  * @param curr The current action. Must be a read.
 654  * @param rf The action that curr reads from. Must be a write.
 655  * @return True if modification order edges were added; false otherwise
 656  */
 657 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 658 {
 659         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 660         unsigned int i;
 661         bool added = false;
 662         ASSERT(curr->is_read());
 663
 664         /* Iterate over all threads */
 665         for (i = 0; i < thrd_lists->size(); i++) {
 666                 /* Iterate over actions in thread, starting from most recent */
 667                 action_list_t *list = &(*thrd_lists)[i];
 668                 action_list_t::reverse_iterator rit;
 669                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 670                         ModelAction *act = *rit;
 671
 672                         /* Include at most one act per-thread that "happens before" curr */
 673                         if (act->happens_before(curr)) {
 674                                 if (act->is_write()) {
 675                                         if (rf != act && act != curr) {
 676                                                 mo_graph->addEdge(act, rf);
 677                                                 added = true;
 678                                         }
 679                                 } else {
 680                                         const ModelAction *prevreadfrom = act->get_reads_from();
 681                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 682                                                 mo_graph->addEdge(prevreadfrom, rf);
 683                                                 added = true;
 684                                         }
 685                                 }
 686
 687                                 break;
 688                         }
 689                 }
 690         }
 691
 692         return added;
 693 }
 694
 695 /** This method fixes up the modification order when we resolve a
 696  *  promises.  The basic problem is that actions that occur after the
 697  *  read curr could not property add items to the modification order
 698  *  for our read.
 699  *
 700  *  So for each thread, we find the earliest item that happens after
 701  *  the read curr.  This is the item we have to fix up with additional
 702  *  constraints.  If that action is write, we add a MO edge between
 703  *  the Action rf and that action.  If the action is a read, we add a
 704  *  MO edge between the Action rf, and whatever the read accessed.
 705  *
 706  * @param curr is the read ModelAction that we are fixing up MO edges for.
 707  * @param rf is the write ModelAction that curr reads from.
 708  *
 709  */
 710
 711 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 712 {
 713         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 714         unsigned int i;
 715         ASSERT(curr->is_read());
 716
 717         /* Iterate over all threads */
 718         for (i = 0; i < thrd_lists->size(); i++) {
 719                 /* Iterate over actions in thread, starting from most recent */
 720                 action_list_t *list = &(*thrd_lists)[i];
 721                 action_list_t::reverse_iterator rit;
 722                 ModelAction *lastact = NULL;
 723
 724                 /* Find last action that happens after curr */
 725                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 726                         ModelAction *act = *rit;
 727                         if (curr->happens_before(act)) {
 728                                 lastact = act;
 729                         } else
 730                                 break;
 731                 }
 732
 733                         /* Include at most one act per-thread that "happens before" curr */
 734                 if (lastact != NULL) {
 735                         if (lastact->is_read()) {
 736                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 737                                 if (postreadfrom != NULL&&rf != postreadfrom)
 738                                         mo_graph->addEdge(rf, postreadfrom);
 739                         } else if (rf != lastact) {
 740                                 mo_graph->addEdge(rf, lastact);
 741                         }
 742                         break;
 743                 }
 744         }
 745 }
 746
 747 /**
 748  * Updates the mo_graph with the constraints imposed from the current write.
 749  *
 750  * Basic idea is the following: Go through each other thread and find
 751  * the lastest action that happened before our write.  Two cases:
 752  *
 753  * (1) The action is a write => that write must occur before
 754  * the current write
 755  *
 756  * (2) The action is a read => the write that that action read from
 757  * must occur before the current write.
 758  *
 759  * This method also handles two other issues:
 760  *
 761  * (I) Sequential Consistency: Making sure that if the current write is
 762  * seq_cst, that it occurs after the previous seq_cst write.
 763  *
 764  * (II) Sending the write back to non-synchronizing reads.
 765  *
 766  * @param curr The current action. Must be a write.
 767  * @return True if modification order edges were added; false otherwise
 768  */
 769 bool ModelChecker::w_modification_order(ModelAction *curr)
 770 {
 771         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 772         unsigned int i;
 773         bool added = false;
 774         ASSERT(curr->is_write());
 775
 776         if (curr->is_seqcst()) {
 777                 /* We have to at least see the last sequentially consistent write,
 778                          so we are initialized. */
 779                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 780                 if (last_seq_cst != NULL) {
 781                         mo_graph->addEdge(last_seq_cst, curr);
 782                         added = true;
 783                 }
 784         }
 785
 786         /* Iterate over all threads */
 787         for (i = 0; i < thrd_lists->size(); i++) {
 788                 /* Iterate over actions in thread, starting from most recent */
 789                 action_list_t *list = &(*thrd_lists)[i];
 790                 action_list_t::reverse_iterator rit;
 791                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 792                         ModelAction *act = *rit;
 793
 794                         /* Include at most one act per-thread that "happens before" curr */
 795                         if (act->happens_before(curr)) {
 796                                 /*
 797                                  * Note: if act is RMW, just add edge:
 798                                  *   act --mo--> curr
 799                                  * The following edge should be handled elsewhere:
 800                                  *   readfrom(act) --mo--> act
 801                                  */
 802                                 if (act->is_write()) {
 803                                         //RMW shouldn't have an edge to themselves
 804                                         if (act!=curr)
 805                                                 mo_graph->addEdge(act, curr);
 806                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 807                                         mo_graph->addEdge(act->get_reads_from(), curr);
 808                                 added = true;
 809                                 break;
 810                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 811                                                      !act->same_thread(curr)) {
 812                                 /* We have an action that:
 813                                    (1) did not happen before us
 814                                    (2) is a read and we are a write
 815                                    (3) cannot synchronize with us
 816                                    (4) is in a different thread
 817                                    =>
 818                                    that read could potentially read from our write.
 819                                  */
 820                                 if (thin_air_constraint_may_allow(curr, act)) {
 821                                         if (isfeasible() ||
 822                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 823                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 824                                                 futurevalues->push_back(pfv);
 825                                         }
 826                                 }
 827                         }
 828                 }
 829         }
 830
 831         return added;
 832 }
 833
 834 /** Arbitrary reads from the future are not allowed.  Section 29.3
 835  * part 9 places some constraints.  This method checks one result of constraint
 836  * constraint.  Others require compiler support. */
 837
 838 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 839         if (!writer->is_rmw())
 840                 return true;
 841
 842         if (!reader->is_rmw())
 843                 return true;
 844
 845         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 846                 if (search==reader)
 847                         return false;
 848                 if (search->get_tid() == reader->get_tid() &&
 849                                 search->happens_before(reader))
 850                         break;
 851         }
 852
 853         return true;
 854 }
 855
 856 /**
 857  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 858  * The ModelAction under consideration is expected to be taking part in
 859  * release/acquire synchronization as an object of the "reads from" relation.
 860  * Note that this can only provide release sequence support for RMW chains
 861  * which do not read from the future, as those actions cannot be traced until
 862  * their "promise" is fulfilled. Similarly, we may not even establish the
 863  * presence of a release sequence with certainty, as some modification order
 864  * constraints may be decided further in the future. Thus, this function
 865  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 866  * and a boolean representing certainty.
 867  *
 868  * @todo Finish lazy updating, when promises are fulfilled in the future
 869  * @param rf The action that might be part of a release sequence. Must be a
 870  * write.
 871  * @param release_heads A pass-by-reference style return parameter.  After
 872  * execution of this function, release_heads will contain the heads of all the
 873  * relevant release sequences, if any exists
 874  * @return true, if the ModelChecker is certain that release_heads is complete;
 875  * false otherwise
 876  */
 877 bool ModelChecker::release_seq_head(const ModelAction *rf,
 878                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 879 {
 880         if (!rf) {
 881                 /* read from future: need to settle this later */
 882                 return false; /* incomplete */
 883         }
 884
 885         ASSERT(rf->is_write());
 886
 887         if (rf->is_release())
 888                 release_heads->push_back(rf);
 889         if (rf->is_rmw()) {
 890                 /* We need a RMW action that is both an acquire and release to stop */
 891                 /** @todo Need to be smarter here...  In the linux lock
 892                  * example, this will run to the beginning of the program for
 893                  * every acquire. */
 894                 if (rf->is_acquire() && rf->is_release())
 895                         return true; /* complete */
 896                 return release_seq_head(rf->get_reads_from(), release_heads);
 897         }
 898         if (rf->is_release())
 899                 return true; /* complete */
 900
 901         /* else relaxed write; check modification order for contiguous subsequence
 902          * -> rf must be same thread as release */
 903         int tid = id_to_int(rf->get_tid());
 904         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 905         action_list_t *list = &(*thrd_lists)[tid];
 906         action_list_t::const_reverse_iterator rit;
 907
 908         /* Find rf in the thread list */
 909         rit = std::find(list->rbegin(), list->rend(), rf);
 910         ASSERT(rit != list->rend());
 911
 912         /* Find the last write/release */
 913         for (; rit != list->rend(); rit++)
 914                 if ((*rit)->is_release())
 915                         break;
 916         if (rit == list->rend()) {
 917                 /* No write-release in this thread */
 918                 return true; /* complete */
 919         }
 920         ModelAction *release = *rit;
 921
 922         ASSERT(rf->same_thread(release));
 923
 924         bool certain = true;
 925         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 926                 if (id_to_int(rf->get_tid()) == (int)i)
 927                         continue;
 928                 list = &(*thrd_lists)[i];
 929
 930                 /* Can we ensure no future writes from this thread may break
 931                  * the release seq? */
 932                 bool future_ordered = false;
 933
 934                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 935                         const ModelAction *act = *rit;
 936                         if (!act->is_write())
 937                                 continue;
 938                         /* Reach synchronization -> this thread is complete */
 939                         if (act->happens_before(release))
 940                                 break;
 941                         if (rf->happens_before(act)) {
 942                                 future_ordered = true;
 943                                 continue;
 944                         }
 945
 946                         /* Check modification order */
 947                         if (mo_graph->checkReachable(rf, act)) {
 948                                 /* rf --mo--> act */
 949                                 future_ordered = true;
 950                                 continue;
 951                         }
 952                         if (mo_graph->checkReachable(act, release))
 953                                 /* act --mo--> release */
 954                                 break;
 955                         if (mo_graph->checkReachable(release, act) &&
 956                                       mo_graph->checkReachable(act, rf)) {
 957                                 /* release --mo-> act --mo--> rf */
 958                                 return true; /* complete */
 959                         }
 960                         certain = false;
 961                 }
 962                 if (!future_ordered)
 963                         return false; /* This thread is uncertain */
 964         }
 965
 966         if (certain)
 967                 release_heads->push_back(release);
 968         return certain;
 969 }
 970
 971 /**
 972  * A public interface for getting the release sequence head(s) with which a
 973  * given ModelAction must synchronize. This function only returns a non-empty
 974  * result when it can locate a release sequence head with certainty. Otherwise,
 975  * it may mark the internal state of the ModelChecker so that it will handle
 976  * the release sequence at a later time, causing @a act to update its
 977  * synchronization at some later point in execution.
 978  * @param act The 'acquire' action that may read from a release sequence
 979  * @param release_heads A pass-by-reference return parameter. Will be filled
 980  * with the head(s) of the release sequence(s), if they exists with certainty.
 981  * @see ModelChecker::release_seq_head
 982  */
 983 void ModelChecker::get_release_seq_heads(ModelAction *act,
 984                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 985 {
 986         const ModelAction *rf = act->get_reads_from();
 987         bool complete;
 988         complete = release_seq_head(rf, release_heads);
 989         if (!complete) {
 990                 /* add act to 'lazy checking' list */
 991                 std::list<ModelAction *> *list;
 992                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 993                 list->push_back(act);
 994                 (*lazy_sync_size)++;
 995         }
 996 }
 997
 998 /**
 999  * Attempt to resolve all stashed operations that might synchronize with a
1000  * release sequence for a given location. This implements the "lazy" portion of
1001  * determining whether or not a release sequence was contiguous, since not all
1002  * modification order information is present at the time an action occurs.
1003  *
1004  * @param location The location/object that should be checked for release
1005  * sequence resolutions
1006  * @param work_queue The work queue to which to add work items as they are
1007  * generated
1008  * @return True if any updates occurred (new synchronization, new mo_graph
1009  * edges)
1010  */
1011 bool ModelChecker::resolve_release_sequences(void *location, work_queue_t *work_queue)
1012 {
1013         std::list<ModelAction *> *list;
1014         list = lazy_sync_with_release->getptr(location);
1015         if (!list)
1016                 return false;
1017
1018         bool updated = false;
1019         std::list<ModelAction *>::iterator it = list->begin();
1020         while (it != list->end()) {
1021                 ModelAction *act = *it;
1022                 const ModelAction *rf = act->get_reads_from();
1023                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
1024                 bool complete;
1025                 complete = release_seq_head(rf, &release_heads);
1026                 for (unsigned int i = 0; i < release_heads.size(); i++) {
1027                         if (!act->has_synchronized_with(release_heads[i])) {
1028                                 updated = true;
1029                                 act->synchronize_with(release_heads[i]);
1030                         }
1031                 }
1032
1033                 if (updated) {
1034                         /* Re-check act for mo_graph edges */
1035                         work_queue->push_back(MOEdgeWorkEntry(act));
1036
1037                         /* propagate synchronization to later actions */
1038                         action_list_t::reverse_iterator it = action_trace->rbegin();
1039                         while ((*it) != act) {
1040                                 ModelAction *propagate = *it;
1041                                 if (act->happens_before(propagate)) {
1042                                         propagate->synchronize_with(act);
1043                                         /* Re-check 'propagate' for mo_graph edges */
1044                                         work_queue->push_back(MOEdgeWorkEntry(propagate));
1045                                 }
1046                         }
1047                 }
1048                 if (complete) {
1049                         it = list->erase(it);
1050                         (*lazy_sync_size)--;
1051                 } else
1052                         it++;
1053         }
1054
1055         // If we resolved promises or data races, see if we have realized a data race.
1056         if (checkDataRaces()) {
1057                 set_assert();
1058         }
1059
1060         return updated;
1061 }
1062
1063 /**
1064  * Performs various bookkeeping operations for the current ModelAction. For
1065  * instance, adds action to the per-object, per-thread action vector and to the
1066  * action trace list of all thread actions.
1067  *
1068  * @param act is the ModelAction to add.
1069  */
1070 void ModelChecker::add_action_to_lists(ModelAction *act)
1071 {
1072         int tid = id_to_int(act->get_tid());
1073         action_trace->push_back(act);
1074
1075         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1076
1077         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1078         if (tid >= (int)vec->size())
1079                 vec->resize(priv->next_thread_id);
1080         (*vec)[tid].push_back(act);
1081
1082         if ((int)thrd_last_action->size() <= tid)
1083                 thrd_last_action->resize(get_num_threads());
1084         (*thrd_last_action)[tid] = act;
1085 }
1086
1087 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1088 {
1089         int nthreads = get_num_threads();
1090         if ((int)thrd_last_action->size() < nthreads)
1091                 thrd_last_action->resize(nthreads);
1092         return (*thrd_last_action)[id_to_int(tid)];
1093 }
1094
1095 /**
1096  * Gets the last memory_order_seq_cst action (in the total global sequence)
1097  * performed on a particular object (i.e., memory location).
1098  * @param location The object location to check
1099  * @return The last seq_cst action performed
1100  */
1101 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1102 {
1103         action_list_t *list = obj_map->get_safe_ptr(location);
1104         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1105         action_list_t::reverse_iterator rit;
1106         for (rit = list->rbegin(); rit != list->rend(); rit++)
1107                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1108                         return *rit;
1109         return NULL;
1110 }
1111
1112 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1113 {
1114         ModelAction *parent = get_last_action(tid);
1115         if (!parent)
1116                 parent = get_thread(tid)->get_creation();
1117         return parent;
1118 }
1119
1120 /**
1121  * Returns the clock vector for a given thread.
1122  * @param tid The thread whose clock vector we want
1123  * @return Desired clock vector
1124  */
1125 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1126 {
1127         return get_parent_action(tid)->get_cv();
1128 }
1129
1130 /**
1131  * Resolve a set of Promises with a current write. The set is provided in the
1132  * Node corresponding to @a write.
1133  * @param write The ModelAction that is fulfilling Promises
1134  * @return True if promises were resolved; false otherwise
1135  */
1136 bool ModelChecker::resolve_promises(ModelAction *write)
1137 {
1138         bool resolved = false;
1139
1140         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1141                 Promise *promise = (*promises)[promise_index];
1142                 if (write->get_node()->get_promise(i)) {
1143                         ModelAction *read = promise->get_action();
1144                         read->read_from(write);
1145                         if (read->is_rmw()) {
1146                                 mo_graph->addRMWEdge(write, read);
1147                         }
1148                         //First fix up the modification order for actions that happened
1149                         //before the read
1150                         r_modification_order(read, write);
1151                         //Next fix up the modification order for actions that happened
1152                         //after the read.
1153                         post_r_modification_order(read, write);
1154                         promises->erase(promises->begin() + promise_index);
1155                         resolved = true;
1156                 } else
1157                         promise_index++;
1158         }
1159         return resolved;
1160 }
1161
1162 /**
1163  * Compute the set of promises that could potentially be satisfied by this
1164  * action. Note that the set computation actually appears in the Node, not in
1165  * ModelChecker.
1166  * @param curr The ModelAction that may satisfy promises
1167  */
1168 void ModelChecker::compute_promises(ModelAction *curr)
1169 {
1170         for (unsigned int i = 0; i < promises->size(); i++) {
1171                 Promise *promise = (*promises)[i];
1172                 const ModelAction *act = promise->get_action();
1173                 if (!act->happens_before(curr) &&
1174                                 act->is_read() &&
1175                                 !act->is_synchronizing(curr) &&
1176                                 !act->same_thread(curr) &&
1177                                 promise->get_value() == curr->get_value()) {
1178                         curr->get_node()->set_promise(i);
1179                 }
1180         }
1181 }
1182
1183 /** Checks promises in response to change in ClockVector Threads. */
1184 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1185 {
1186         for (unsigned int i = 0; i < promises->size(); i++) {
1187                 Promise *promise = (*promises)[i];
1188                 const ModelAction *act = promise->get_action();
1189                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1190                                 merge_cv->synchronized_since(act)) {
1191                         //This thread is no longer able to send values back to satisfy the promise
1192                         int num_synchronized_threads = promise->increment_threads();
1193                         if (num_synchronized_threads == get_num_threads()) {
1194                                 //Promise has failed
1195                                 failed_promise = true;
1196                                 return;
1197                         }
1198                 }
1199         }
1200 }
1201
1202 /**
1203  * Build up an initial set of all past writes that this 'read' action may read
1204  * from. This set is determined by the clock vector's "happens before"
1205  * relationship.
1206  * @param curr is the current ModelAction that we are exploring; it must be a
1207  * 'read' operation.
1208  */
1209 void ModelChecker::build_reads_from_past(ModelAction *curr)
1210 {
1211         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1212         unsigned int i;
1213         ASSERT(curr->is_read());
1214
1215         ModelAction *last_seq_cst = NULL;
1216
1217         /* Track whether this object has been initialized */
1218         bool initialized = false;
1219
1220         if (curr->is_seqcst()) {
1221                 last_seq_cst = get_last_seq_cst(curr->get_location());
1222                 /* We have to at least see the last sequentially consistent write,
1223                          so we are initialized. */
1224                 if (last_seq_cst != NULL)
1225                         initialized = true;
1226         }
1227
1228         /* Iterate over all threads */
1229         for (i = 0; i < thrd_lists->size(); i++) {
1230                 /* Iterate over actions in thread, starting from most recent */
1231                 action_list_t *list = &(*thrd_lists)[i];
1232                 action_list_t::reverse_iterator rit;
1233                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1234                         ModelAction *act = *rit;
1235
1236                         /* Only consider 'write' actions */
1237                         if (!act->is_write())
1238                                 continue;
1239
1240                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1241                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1242                                 DEBUG("Adding action to may_read_from:\n");
1243                                 if (DBG_ENABLED()) {
1244                                         act->print();
1245                                         curr->print();
1246                                 }
1247                                 curr->get_node()->add_read_from(act);
1248                         }
1249
1250                         /* Include at most one act per-thread that "happens before" curr */
1251                         if (act->happens_before(curr)) {
1252                                 initialized = true;
1253                                 break;
1254                         }
1255                 }
1256         }
1257
1258         if (!initialized) {
1259                 /** @todo Need a more informative way of reporting errors. */
1260                 printf("ERROR: may read from uninitialized atomic\n");
1261         }
1262
1263         if (DBG_ENABLED() || !initialized) {
1264                 printf("Reached read action:\n");
1265                 curr->print();
1266                 printf("Printing may_read_from\n");
1267                 curr->get_node()->print_may_read_from();
1268                 printf("End printing may_read_from\n");
1269         }
1270
1271         ASSERT(initialized);
1272 }
1273
1274 static void print_list(action_list_t *list)
1275 {
1276         action_list_t::iterator it;
1277
1278         printf("---------------------------------------------------------------------\n");
1279         printf("Trace:\n");
1280
1281         for (it = list->begin(); it != list->end(); it++) {
1282                 (*it)->print();
1283         }
1284         printf("---------------------------------------------------------------------\n");
1285 }
1286
1287 void ModelChecker::print_summary()
1288 {
1289         printf("\n");
1290         printf("Number of executions: %d\n", num_executions);
1291         printf("Number of feasible executions: %d\n", num_feasible_executions);
1292         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1293
1294 #if SUPPORT_MOD_ORDER_DUMP
1295         scheduler->print();
1296         char buffername[100];
1297         sprintf(buffername, "exec%u",num_executions);
1298         mo_graph->dumpGraphToFile(buffername);
1299 #endif
1300
1301         if (!isfinalfeasible())
1302                 printf("INFEASIBLE EXECUTION!\n");
1303         print_list(action_trace);
1304         printf("\n");
1305 }
1306
1307 /**
1308  * Add a Thread to the system for the first time. Should only be called once
1309  * per thread.
1310  * @param t The Thread to add
1311  */
1312 void ModelChecker::add_thread(Thread *t)
1313 {
1314         thread_map->put(id_to_int(t->get_id()), t);
1315         scheduler->add_thread(t);
1316 }
1317
1318 void ModelChecker::remove_thread(Thread *t)
1319 {
1320         scheduler->remove_thread(t);
1321 }
1322
1323 /**
1324  * Switch from a user-context to the "master thread" context (a.k.a. system
1325  * context). This switch is made with the intention of exploring a particular
1326  * model-checking action (described by a ModelAction object). Must be called
1327  * from a user-thread context.
1328  * @param act The current action that will be explored. Must not be NULL.
1329  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1330  */
1331 int ModelChecker::switch_to_master(ModelAction *act)
1332 {
1333         DBG();
1334         Thread *old = thread_current();
1335         set_current_action(act);
1336         old->set_state(THREAD_READY);
1337         return Thread::swap(old, &system_context);
1338 }
1339
1340 /**
1341  * Takes the next step in the execution, if possible.
1342  * @return Returns true (success) if a step was taken and false otherwise.
1343  */
1344 bool ModelChecker::take_step() {
1345         Thread *curr, *next;
1346
1347         if (has_asserted())
1348                 return false;
1349
1350         curr = thread_current();
1351         if (curr) {
1352                 if (curr->get_state() == THREAD_READY) {
1353                         ASSERT(priv->current_action);
1354
1355                         priv->nextThread = check_current_action(priv->current_action);
1356                         priv->current_action = NULL;
1357                         if (!curr->is_blocked() && !curr->is_complete())
1358                                 scheduler->add_thread(curr);
1359                 } else {
1360                         ASSERT(false);
1361                 }
1362         }
1363         next = scheduler->next_thread(priv->nextThread);
1364
1365         /* Infeasible -> don't take any more steps */
1366         if (!isfeasible())
1367                 return false;
1368
1369         if (next)
1370                 next->set_state(THREAD_RUNNING);
1371         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1372
1373         /* next == NULL -> don't take any more steps */
1374         if (!next)
1375                 return false;
1376         /* Return false only if swap fails with an error */
1377         return (Thread::swap(&system_context, next) == 0);
1378 }
1379
1380 /** Runs the current execution until threre are no more steps to take. */
1381 void ModelChecker::finish_execution() {
1382         DBG();
1383
1384         while (take_step());
1385 }