model.cc

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