model.cc

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