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() :
  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         current_action(NULL),
  26         diverge(NULL),
  27         nextThread(THREAD_ID_T_NONE),
  28         action_trace(new action_list_t()),
  29         thread_map(new HashTable<int, Thread *, int>()),
  30         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  31         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  32         promises(new std::vector<Promise *>()),
  33         thrd_last_action(new std::vector<ModelAction *>(1)),
  34         node_stack(new NodeStack()),
  35         next_backtrack(NULL),
  36         cyclegraph(new CycleGraph()),
  37         failed_promise(false)
  38 {
  39 }
  40
  41 /** @brief Destructor */
  42 ModelChecker::~ModelChecker()
  43 {
  44         for (int i = 0; i < get_num_threads(); i++)
  45                 delete thread_map->get(i);
  46         delete thread_map;
  47
  48         delete obj_thrd_map;
  49         delete obj_map;
  50         delete action_trace;
  51         delete thrd_last_action;
  52         delete node_stack;
  53         delete scheduler;
  54         delete cyclegraph;
  55 }
  56
  57 /**
  58  * Restores user program to initial state and resets all model-checker data
  59  * structures.
  60  */
  61 void ModelChecker::reset_to_initial_state()
  62 {
  63         DEBUG("+++ Resetting to initial state +++\n");
  64         node_stack->reset_execution();
  65         current_action = NULL;
  66         next_thread_id = INITIAL_THREAD_ID;
  67         used_sequence_numbers = 0;
  68         nextThread = 0;
  69         next_backtrack = NULL;
  70         failed_promise = false;
  71         snapshotObject->backTrackBeforeStep(0);
  72 }
  73
  74 /** @returns a thread ID for a new Thread */
  75 thread_id_t ModelChecker::get_next_id()
  76 {
  77         return next_thread_id++;
  78 }
  79
  80 /** @returns the number of user threads created during this execution */
  81 int ModelChecker::get_num_threads()
  82 {
  83         return next_thread_id;
  84 }
  85
  86 /** @returns a sequence number for a new ModelAction */
  87 modelclock_t ModelChecker::get_next_seq_num()
  88 {
  89         return ++used_sequence_numbers;
  90 }
  91
  92 /**
  93  * Performs the "scheduling" for the model-checker. That is, it checks if the
  94  * model-checker has selected a "next thread to run" and returns it, if
  95  * available. This function should be called from the Scheduler routine, where
  96  * the Scheduler falls back to a default scheduling routine if needed.
  97  *
  98  * @return The next thread chosen by the model-checker. If the model-checker
  99  * makes no selection, retuns NULL.
 100  */
 101 Thread * ModelChecker::schedule_next_thread()
 102 {
 103         Thread *t;
 104         if (nextThread == THREAD_ID_T_NONE)
 105                 return NULL;
 106         t = thread_map->get(id_to_int(nextThread));
 107
 108         ASSERT(t != NULL);
 109
 110         return t;
 111 }
 112
 113 /**
 114  * Choose the next thread in the replay sequence.
 115  *
 116  * If the replay sequence has reached the 'diverge' point, returns a thread
 117  * from the backtracking set. Otherwise, simply returns the next thread in the
 118  * sequence that is being replayed.
 119  */
 120 thread_id_t ModelChecker::get_next_replay_thread()
 121 {
 122         thread_id_t tid;
 123
 124         /* Have we completed exploring the preselected path? */
 125         if (diverge == NULL)
 126                 return THREAD_ID_T_NONE;
 127
 128         /* Else, we are trying to replay an execution */
 129         ModelAction * next = node_stack->get_next()->get_action();
 130
 131         if (next == diverge) {
 132                 Node *nextnode = next->get_node();
 133                 /* Reached divergence point */
 134                 if (nextnode->increment_promise()) {
 135                         /* The next node will try to satisfy a different set of promises. */
 136                         tid = next->get_tid();
 137                         node_stack->pop_restofstack(2);
 138                 } else if (nextnode->increment_read_from()) {
 139                         /* The next node will read from a different value. */
 140                         tid = next->get_tid();
 141                         node_stack->pop_restofstack(2);
 142                 } else if (nextnode->increment_future_value()) {
 143                         /* The next node will try to read from a different future value. */
 144                         tid = next->get_tid();
 145                         node_stack->pop_restofstack(2);
 146                 } else {
 147                         /* Make a different thread execute for next step */
 148                         Node *node = nextnode->get_parent();
 149                         tid = node->get_next_backtrack();
 150                         node_stack->pop_restofstack(1);
 151                 }
 152                 DEBUG("*** Divergence point ***\n");
 153                 diverge = NULL;
 154         } else {
 155                 tid = next->get_tid();
 156         }
 157         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 158         return tid;
 159 }
 160
 161 /**
 162  * Queries the model-checker for more executions to explore and, if one
 163  * exists, resets the model-checker state to execute a new execution.
 164  *
 165  * @return If there are more executions to explore, return true. Otherwise,
 166  * return false.
 167  */
 168 bool ModelChecker::next_execution()
 169 {
 170         DBG();
 171
 172         num_executions++;
 173
 174         bool feasible = isfinalfeasible();
 175         if (feasible || DBG_ENABLED())
 176                 print_summary(feasible);
 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->ensureptr(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
 287                         delete curr;
 288                         curr = tmp;
 289                 } else {
 290                         /*
 291                          * Perform one-time actions when pushing new ModelAction onto
 292                          * NodeStack
 293                          */
 294                         curr->create_cv(get_parent_action(curr->get_tid()));
 295                         /* Build may_read_from set */
 296                         if (curr->is_read())
 297                                 build_reads_from_past(curr);
 298                         if (curr->is_write())
 299                                 compute_promises(curr);
 300                 }
 301         }
 302
 303         /* Assign 'creation' parent */
 304         if (curr->get_type() == THREAD_CREATE) {
 305                 Thread *th = (Thread *)curr->get_location();
 306                 th->set_creation(curr);
 307         }
 308
 309         /* Deal with new thread */
 310         if (curr->get_type() == THREAD_START) {
 311                 check_promises(NULL, curr->get_cv());
 312         }
 313
 314         /* Assign reads_from values */
 315         Thread *th = get_thread(curr->get_tid());
 316         uint64_t value = VALUE_NONE;
 317         if (curr->is_read()) {
 318                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 319                 if (reads_from!=NULL) {
 320                         value = reads_from->get_value();
 321                         /* Assign reads_from, perform release/acquire synchronization */
 322                         curr->read_from(reads_from);
 323                         r_modification_order(curr,reads_from);
 324                 } else {
 325                         /* Read from future value */
 326                         value = curr->get_node()->get_future_value();
 327                         curr->read_from(NULL);
 328                         Promise * valuepromise=new Promise(curr, value);
 329                         promises->push_back(valuepromise);
 330                 }
 331         } else if (curr->is_write()) {
 332                 w_modification_order(curr);
 333                 resolve_promises(curr);
 334         }
 335
 336         th->set_return_value(value);
 337
 338         /* Add action to list.  */
 339         if (!already_added)
 340                 add_action_to_lists(curr);
 341
 342         /* Is there a better interface for setting the next thread rather
 343                  than this field/convoluted approach?  Perhaps like just returning
 344                  it or something? */
 345
 346         /* Do not split atomic actions. */
 347         if (curr->is_rmwr()) {
 348                 nextThread = thread_current()->get_id();
 349         } else {
 350                 nextThread = get_next_replay_thread();
 351         }
 352
 353         Node *currnode = curr->get_node();
 354         Node *parnode = currnode->get_parent();
 355
 356         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 357                   !currnode->future_value_empty() || !currnode->promise_empty())
 358                 if (!next_backtrack || *curr > *next_backtrack)
 359                         next_backtrack = curr;
 360
 361         set_backtracking(curr);
 362 }
 363
 364 /** @returns whether the current partial trace is feasible. */
 365 bool ModelChecker::isfeasible() {
 366         return !cyclegraph->checkForCycles() && !failed_promise;
 367 }
 368
 369 /** Returns whether the current completed trace is feasible. */
 370 bool ModelChecker::isfinalfeasible() {
 371         return isfeasible() && promises->size()==0;
 372 }
 373
 374 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 375 ModelAction * ModelChecker::process_rmw(ModelAction * act) {
 376         int tid = id_to_int(act->get_tid());
 377         ModelAction *lastread=get_last_action(tid);
 378         lastread->process_rmw(act);
 379         if (act->is_rmw())
 380                 cyclegraph->addRMWEdge(lastread, lastread->get_reads_from());
 381         return lastread;
 382 }
 383
 384 /**
 385  * Updates the cyclegraph with the constraints imposed from the current read.
 386  * @param curr The current action. Must be a read.
 387  * @param rf The action that curr reads from. Must be a write.
 388  */
 389 void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
 390         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 391         unsigned int i;
 392         ASSERT(curr->is_read());
 393
 394         /* Iterate over all threads */
 395         for (i = 0; i < thrd_lists->size(); i++) {
 396                 /* Iterate over actions in thread, starting from most recent */
 397                 action_list_t *list = &(*thrd_lists)[i];
 398                 action_list_t::reverse_iterator rit;
 399                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 400                         ModelAction *act = *rit;
 401
 402                         /* Include at most one act per-thread that "happens before" curr */
 403                         if (act->happens_before(curr)) {
 404                                 if (act->is_read()) {
 405                                         const ModelAction * prevreadfrom=act->get_reads_from();
 406                                         if (prevreadfrom!=NULL&&rf!=prevreadfrom)
 407                                                 cyclegraph->addEdge(rf, prevreadfrom);
 408                                 } else if (rf!=act) {
 409                                         cyclegraph->addEdge(rf, act);
 410                                 }
 411                                 break;
 412                         }
 413                 }
 414         }
 415 }
 416
 417 /** Updates the cyclegraph with the constraints imposed from the
 418  *  current read. */
 419 void ModelChecker::post_r_modification_order(ModelAction * curr, const ModelAction *rf) {
 420         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 421         unsigned int i;
 422         ASSERT(curr->is_read());
 423
 424         /* Iterate over all threads */
 425         for (i = 0; i < thrd_lists->size(); i++) {
 426                 /* Iterate over actions in thread, starting from most recent */
 427                 action_list_t *list = &(*thrd_lists)[i];
 428                 action_list_t::reverse_iterator rit;
 429                 ModelAction *lastact=NULL;
 430
 431                 /* Find last action that happens after curr */
 432                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 433                         ModelAction *act = *rit;
 434                         if (curr->happens_before(act)) {
 435                                 lastact=act;
 436                         } else
 437                                 break;
 438                 }
 439
 440                         /* Include at most one act per-thread that "happens before" curr */
 441                 if (lastact!=NULL) {
 442                         if (lastact->is_read()) {
 443                                 const ModelAction * postreadfrom=lastact->get_reads_from();
 444                                 if (postreadfrom!=NULL&&rf!=postreadfrom)
 445                                         cyclegraph->addEdge(postreadfrom, rf);
 446                         } else if (rf!=lastact) {
 447                                 cyclegraph->addEdge(lastact, rf);
 448                         }
 449                         break;
 450                 }
 451         }
 452 }
 453
 454 /**
 455  * Updates the cyclegraph with the constraints imposed from the current write.
 456  * @param curr The current action. Must be a write.
 457  */
 458 void ModelChecker::w_modification_order(ModelAction * curr) {
 459         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 460         unsigned int i;
 461         ASSERT(curr->is_write());
 462
 463         if (curr->is_seqcst()) {
 464                 /* We have to at least see the last sequentially consistent write,
 465                          so we are initialized. */
 466                 ModelAction * last_seq_cst=get_last_seq_cst(curr->get_location());
 467                 if (last_seq_cst!=NULL)
 468                         cyclegraph->addEdge(curr, last_seq_cst);
 469         }
 470
 471         /* Iterate over all threads */
 472         for (i = 0; i < thrd_lists->size(); i++) {
 473                 /* Iterate over actions in thread, starting from most recent */
 474                 action_list_t *list = &(*thrd_lists)[i];
 475                 action_list_t::reverse_iterator rit;
 476                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 477                         ModelAction *act = *rit;
 478
 479                         /* Include at most one act per-thread that "happens before" curr */
 480                         if (act->happens_before(curr)) {
 481                                 if (act->is_read()) {
 482                                         cyclegraph->addEdge(curr, act->get_reads_from());
 483                                 } else
 484                                         cyclegraph->addEdge(curr, act);
 485                                 break;
 486                         } else {
 487                                 if (act->is_read()&&!act->is_synchronizing(curr)&&!act->same_thread(curr)) {
 488                                         /* We have an action that:
 489                                                  (1) did not happen before us
 490                                                  (2) is a read and we are a write
 491                                                  (3) cannot synchronize with us
 492                                                  (4) is in a different thread
 493                                                  =>
 494                                                  that read could potentially read from our write.
 495                                         */
 496                                         if (act->get_node()->add_future_value(curr->get_value())&&
 497                                                         (!next_backtrack || *act > * next_backtrack))
 498                                                 next_backtrack = act;
 499                                 }
 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->ensureptr(act->get_location())->push_back(act);
 518
 519         std::vector<action_list_t> *vec = obj_thrd_map->ensureptr(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->ensureptr(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->ensureptr(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(bool feasible)
 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 (!feasible)
 718                 printf("INFEASIBLE EXECUTION!\n");
 719         print_list(action_trace);
 720         printf("\n");
 721 }
 722
 723 int ModelChecker::add_thread(Thread *t)
 724 {
 725         thread_map->put(id_to_int(t->get_id()), t);
 726         scheduler->add_thread(t);
 727         return 0;
 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, get_system_context());
 753 }