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