model.cc

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