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                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 296                         curr->read_from(NULL);
 297                         Promise *valuepromise = new Promise(curr, value, expiration);
 298                         promises->push_back(valuepromise);
 299                 }
 300                 th->set_return_value(value);
 301                 return updated;
 302         }
 303 }
 304
 305 /**
 306  * This is the heart of the model checker routine. It performs model-checking
 307  * actions corresponding to a given "current action." Among other processes, it
 308  * calculates reads-from relationships, updates synchronization clock vectors,
 309  * forms a memory_order constraints graph, and handles replay/backtrack
 310  * execution when running permutations of previously-observed executions.
 311  *
 312  * @param curr The current action to process
 313  * @return The next Thread that must be executed. May be NULL if ModelChecker
 314  * makes no choice (e.g., according to replay execution, combining RMW actions,
 315  * etc.)
 316  */
 317 Thread * ModelChecker::check_current_action(ModelAction *curr)
 318 {
 319         bool second_part_of_rmw = false;
 320
 321         ASSERT(curr);
 322
 323         if (curr->is_rmwc() || curr->is_rmw()) {
 324                 ModelAction *tmp = process_rmw(curr);
 325                 second_part_of_rmw = true;
 326                 delete curr;
 327                 curr = tmp;
 328                 compute_promises(curr);
 329         } else {
 330                 ModelAction *tmp = node_stack->explore_action(curr);
 331                 if (tmp) {
 332                         /* Discard duplicate ModelAction; use action from NodeStack */
 333                         /* First restore type and order in case of RMW operation */
 334                         if (curr->is_rmwr())
 335                                 tmp->copy_typeandorder(curr);
 336
 337                         /* If we have diverged, we need to reset the clock vector. */
 338                         if (diverge == NULL)
 339                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 340
 341                         delete curr;
 342                         curr = tmp;
 343                 } else {
 344                         /*
 345                          * Perform one-time actions when pushing new ModelAction onto
 346                          * NodeStack
 347                          */
 348                         curr->create_cv(get_parent_action(curr->get_tid()));
 349                         /* Build may_read_from set */
 350                         if (curr->is_read())
 351                                 build_reads_from_past(curr);
 352                         if (curr->is_write())
 353                                 compute_promises(curr);
 354                 }
 355         }
 356
 357         /* Thread specific actions */
 358         switch(curr->get_type()) {
 359         case THREAD_CREATE: {
 360                 Thread *th = (Thread *)curr->get_location();
 361                 th->set_creation(curr);
 362                 break;
 363         }
 364         case THREAD_JOIN: {
 365                 Thread *waiting, *blocking;
 366                 waiting = get_thread(curr);
 367                 blocking = (Thread *)curr->get_location();
 368                 if (!blocking->is_complete()) {
 369                         blocking->push_wait_list(curr);
 370                         scheduler->sleep(waiting);
 371                 }
 372                 break;
 373         }
 374         case THREAD_FINISH: {
 375                 Thread *th = get_thread(curr);
 376                 while (!th->wait_list_empty()) {
 377                         ModelAction *act = th->pop_wait_list();
 378                         Thread *wake = get_thread(act);
 379                         scheduler->wake(wake);
 380                 }
 381                 th->complete();
 382                 break;
 383         }
 384         case THREAD_START: {
 385                 check_promises(NULL, curr->get_cv());
 386                 break;
 387         }
 388         default:
 389                 break;
 390         }
 391
 392         Thread *th = get_thread(curr);
 393
 394         bool updated = false;
 395         if (curr->is_read()) {
 396                 updated=process_read(curr, th, second_part_of_rmw);
 397         }
 398
 399         if (curr->is_write()) {
 400                 bool updated_mod_order=w_modification_order(curr);
 401                 bool updated_promises=resolve_promises(curr);
 402                 updated=updated_mod_order|updated_promises;
 403
 404                 mo_graph->commitChanges();
 405                 th->set_return_value(VALUE_NONE);
 406         }
 407
 408         if (updated)
 409                 resolve_release_sequences(curr->get_location());
 410
 411         /* Add action to list.  */
 412         if (!second_part_of_rmw)
 413                 add_action_to_lists(curr);
 414
 415         Node *currnode = curr->get_node();
 416         Node *parnode = currnode->get_parent();
 417
 418         if ((!parnode->backtrack_empty() ||
 419                         !currnode->read_from_empty() ||
 420                         !currnode->future_value_empty() ||
 421                         !currnode->promise_empty())
 422                     && (!priv->next_backtrack ||
 423                         *curr > *priv->next_backtrack)) {
 424                 priv->next_backtrack = curr;
 425         }
 426
 427         set_backtracking(curr);
 428
 429         return get_next_thread(curr);
 430 }
 431
 432 bool ModelChecker::promises_expired() {
 433         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 434                 Promise *promise = (*promises)[promise_index];
 435                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 436                         return true;
 437                 }
 438         }
 439         return false;
 440 }
 441
 442 /** @returns whether the current partial trace must be a prefix of a
 443  * feasible trace. */
 444 bool ModelChecker::isfeasibleprefix() {
 445         return promises->size() == 0 && *lazy_sync_size == 0;
 446 }
 447
 448 /** @returns whether the current partial trace is feasible. */
 449 bool ModelChecker::isfeasible() {
 450         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 451 }
 452
 453 /** Returns whether the current completed trace is feasible. */
 454 bool ModelChecker::isfinalfeasible() {
 455         return isfeasible() && promises->size() == 0;
 456 }
 457
 458 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 459 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 460         int tid = id_to_int(act->get_tid());
 461         ModelAction *lastread = get_last_action(tid);
 462         lastread->process_rmw(act);
 463         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 464                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 465                 mo_graph->commitChanges();
 466         }
 467         return lastread;
 468 }
 469
 470 /**
 471  * Checks whether a thread has read from the same write for too many times
 472  * without seeing the effects of a later write.
 473  *
 474  * Basic idea:
 475  * 1) there must a different write that we could read from that would satisfy the modification order,
 476  * 2) we must have read from the same value in excess of maxreads times, and
 477  * 3) that other write must have been in the reads_from set for maxreads times.
 478  *
 479  * If so, we decide that the execution is no longer feasible.
 480  */
 481 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 482         if (params.maxreads != 0) {
 483                 if (curr->get_node()->get_read_from_size() <= 1)
 484                         return;
 485
 486                 //Must make sure that execution is currently feasible...  We could
 487                 //accidentally clear by rolling back
 488                 if (!isfeasible())
 489                         return;
 490
 491                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 492                 int tid = id_to_int(curr->get_tid());
 493
 494                 /* Skip checks */
 495                 if ((int)thrd_lists->size() <= tid)
 496                         return;
 497
 498                 action_list_t *list = &(*thrd_lists)[tid];
 499
 500                 action_list_t::reverse_iterator rit = list->rbegin();
 501                 /* Skip past curr */
 502                 if (already_added) {
 503                         for (; (*rit) != curr; rit++)
 504                                 ;
 505                         /* go past curr now */
 506                         rit++;
 507                 }
 508
 509                 action_list_t::reverse_iterator ritcopy=rit;
 510                 //See if we have enough reads from the same value
 511                 int count=0;
 512                 for (; count < params.maxreads; rit++,count++) {
 513                         if (rit==list->rend())
 514                                 return;
 515                         ModelAction *act = *rit;
 516                         if (!act->is_read())
 517                                 return;
 518                         if (act->get_reads_from() != curr->get_reads_from())
 519                                 return;
 520                         if (act->get_node()->get_read_from_size() <= 1)
 521                                 return;
 522                 }
 523
 524                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 525                         //Get write
 526                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 527                         //Need a different write
 528                         if (write==curr->get_reads_from())
 529                                 continue;
 530
 531                         /* Test to see whether this is a feasible write to read from*/
 532                         r_modification_order(curr, write);
 533                         bool feasiblereadfrom=isfeasible();
 534                         mo_graph->rollbackChanges();
 535
 536                         if (!feasiblereadfrom)
 537                                 continue;
 538                         rit=ritcopy;
 539
 540                         bool feasiblewrite=true;
 541                         //new we need to see if this write works for everyone
 542
 543                         for (int loop=count;loop>0;loop--,rit++) {
 544                                 ModelAction *act=*rit;
 545                                 bool foundvalue=false;
 546                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 547                                         if (act->get_node()->get_read_from_at(i)==write) {
 548                                                 foundvalue=true;
 549                                                 break;
 550                                         }
 551                                 }
 552                                 if (!foundvalue) {
 553                                         feasiblewrite=false;
 554                                         break;
 555                                 }
 556                         }
 557                         if (feasiblewrite) {
 558                                 too_many_reads = true;
 559                                 return;
 560                         }
 561                 }
 562         }
 563 }
 564
 565 /**
 566  * Updates the mo_graph with the constraints imposed from the current read.
 567  * @param curr The current action. Must be a read.
 568  * @param rf The action that curr reads from. Must be a write.
 569  * @return True if modification order edges were added; false otherwise
 570  */
 571 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 572 {
 573         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 574         unsigned int i;
 575         bool added = false;
 576         ASSERT(curr->is_read());
 577
 578         /* Iterate over all threads */
 579         for (i = 0; i < thrd_lists->size(); i++) {
 580                 /* Iterate over actions in thread, starting from most recent */
 581                 action_list_t *list = &(*thrd_lists)[i];
 582                 action_list_t::reverse_iterator rit;
 583                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 584                         ModelAction *act = *rit;
 585
 586                         /* Include at most one act per-thread that "happens before" curr */
 587                         if (act->happens_before(curr)) {
 588                                 if (act->is_read()) {
 589                                         const ModelAction *prevreadfrom = act->get_reads_from();
 590                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 591                                                 mo_graph->addEdge(prevreadfrom, rf);
 592                                                 added = true;
 593                                         }
 594                                 } else if (rf != act) {
 595                                         mo_graph->addEdge(act, rf);
 596                                         added = true;
 597                                 }
 598                                 break;
 599                         }
 600                 }
 601         }
 602
 603         return added;
 604 }
 605
 606 /** Updates the mo_graph with the constraints imposed from the current read. */
 607 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 608 {
 609         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 610         unsigned int i;
 611         ASSERT(curr->is_read());
 612
 613         /* Iterate over all threads */
 614         for (i = 0; i < thrd_lists->size(); i++) {
 615                 /* Iterate over actions in thread, starting from most recent */
 616                 action_list_t *list = &(*thrd_lists)[i];
 617                 action_list_t::reverse_iterator rit;
 618                 ModelAction *lastact = NULL;
 619
 620                 /* Find last action that happens after curr */
 621                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 622                         ModelAction *act = *rit;
 623                         if (curr->happens_before(act)) {
 624                                 lastact = act;
 625                         } else
 626                                 break;
 627                 }
 628
 629                         /* Include at most one act per-thread that "happens before" curr */
 630                 if (lastact != NULL) {
 631                         if (lastact->is_read()) {
 632                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 633                                 if (postreadfrom != NULL&&rf != postreadfrom)
 634                                         mo_graph->addEdge(rf, postreadfrom);
 635                         } else if (rf != lastact) {
 636                                 mo_graph->addEdge(rf, lastact);
 637                         }
 638                         break;
 639                 }
 640         }
 641 }
 642
 643 /**
 644  * Updates the mo_graph with the constraints imposed from the current write.
 645  * @param curr The current action. Must be a write.
 646  * @return True if modification order edges were added; false otherwise
 647  */
 648 bool ModelChecker::w_modification_order(ModelAction *curr)
 649 {
 650         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 651         unsigned int i;
 652         bool added = false;
 653         ASSERT(curr->is_write());
 654
 655         if (curr->is_seqcst()) {
 656                 /* We have to at least see the last sequentially consistent write,
 657                          so we are initialized. */
 658                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 659                 if (last_seq_cst != NULL) {
 660                         mo_graph->addEdge(last_seq_cst, curr);
 661                         added = true;
 662                 }
 663         }
 664
 665         /* Iterate over all threads */
 666         for (i = 0; i < thrd_lists->size(); i++) {
 667                 /* Iterate over actions in thread, starting from most recent */
 668                 action_list_t *list = &(*thrd_lists)[i];
 669                 action_list_t::reverse_iterator rit;
 670                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 671                         ModelAction *act = *rit;
 672
 673                         /* Include at most one act per-thread that "happens before" curr */
 674                         if (act->happens_before(curr)) {
 675                                 /*
 676                                  * Note: if act is RMW, just add edge:
 677                                  *   act --mo--> curr
 678                                  * The following edge should be handled elsewhere:
 679                                  *   readfrom(act) --mo--> act
 680                                  */
 681                                 if (act->is_write()) {
 682                                         //RMW shouldn't have an edge to themselves
 683                                         if (act!=curr)
 684                                                 mo_graph->addEdge(act, curr);
 685                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 686                                         mo_graph->addEdge(act->get_reads_from(), curr);
 687                                 added = true;
 688                                 break;
 689                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 690                                                      !act->same_thread(curr)) {
 691                                 /* We have an action that:
 692                                    (1) did not happen before us
 693                                    (2) is a read and we are a write
 694                                    (3) cannot synchronize with us
 695                                    (4) is in a different thread
 696                                    =>
 697                                    that read could potentially read from our write.
 698                                  */
 699                                 if (isfeasible() && act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
 700                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 701                                         priv->next_backtrack = act;
 702                         }
 703                 }
 704         }
 705
 706         return added;
 707 }
 708
 709 /**
 710  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 711  * The ModelAction under consideration is expected to be taking part in
 712  * release/acquire synchronization as an object of the "reads from" relation.
 713  * Note that this can only provide release sequence support for RMW chains
 714  * which do not read from the future, as those actions cannot be traced until
 715  * their "promise" is fulfilled. Similarly, we may not even establish the
 716  * presence of a release sequence with certainty, as some modification order
 717  * constraints may be decided further in the future. Thus, this function
 718  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 719  * and a boolean representing certainty.
 720  *
 721  * @todo Finish lazy updating, when promises are fulfilled in the future
 722  * @param rf The action that might be part of a release sequence. Must be a
 723  * write.
 724  * @param release_heads A pass-by-reference style return parameter.  After
 725  * execution of this function, release_heads will contain the heads of all the
 726  * relevant release sequences, if any exists
 727  * @return true, if the ModelChecker is certain that release_heads is complete;
 728  * false otherwise
 729  */
 730 bool ModelChecker::release_seq_head(const ModelAction *rf,
 731                 std::vector<const ModelAction *> *release_heads) const
 732 {
 733         ASSERT(rf->is_write());
 734         if (!rf) {
 735                 /* read from future: need to settle this later */
 736                 return false; /* incomplete */
 737         }
 738         if (rf->is_release())
 739                 release_heads->push_back(rf);
 740         if (rf->is_rmw()) {
 741                 /* We need a RMW action that is both an acquire and release to stop */
 742                 /** @todo Need to be smarter here...  In the linux lock
 743                  * example, this will run to the beginning of the program for
 744                  * every acquire. */
 745                 if (rf->is_acquire() && rf->is_release())
 746                         return true; /* complete */
 747                 return release_seq_head(rf->get_reads_from(), release_heads);
 748         }
 749         if (rf->is_release())
 750                 return true; /* complete */
 751
 752         /* else relaxed write; check modification order for contiguous subsequence
 753          * -> rf must be same thread as release */
 754         int tid = id_to_int(rf->get_tid());
 755         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 756         action_list_t *list = &(*thrd_lists)[tid];
 757         action_list_t::const_reverse_iterator rit;
 758
 759         /* Find rf in the thread list */
 760         rit = std::find(list->rbegin(), list->rend(), rf);
 761         ASSERT(rit != list->rend());
 762
 763         /* Find the last write/release */
 764         for (; rit != list->rend(); rit++)
 765                 if ((*rit)->is_release())
 766                         break;
 767         if (rit == list->rend()) {
 768                 /* No write-release in this thread */
 769                 return true; /* complete */
 770         }
 771         ModelAction *release = *rit;
 772
 773         ASSERT(rf->same_thread(release));
 774
 775         bool certain = true;
 776         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 777                 if (id_to_int(rf->get_tid()) == (int)i)
 778                         continue;
 779                 list = &(*thrd_lists)[i];
 780
 781                 /* Can we ensure no future writes from this thread may break
 782                  * the release seq? */
 783                 bool future_ordered = false;
 784
 785                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 786                         const ModelAction *act = *rit;
 787                         if (!act->is_write())
 788                                 continue;
 789                         /* Reach synchronization -> this thread is complete */
 790                         if (act->happens_before(release))
 791                                 break;
 792                         if (rf->happens_before(act)) {
 793                                 future_ordered = true;
 794                                 continue;
 795                         }
 796
 797                         /* Check modification order */
 798                         if (mo_graph->checkReachable(rf, act)) {
 799                                 /* rf --mo--> act */
 800                                 future_ordered = true;
 801                                 continue;
 802                         }
 803                         if (mo_graph->checkReachable(act, release))
 804                                 /* act --mo--> release */
 805                                 break;
 806                         if (mo_graph->checkReachable(release, act) &&
 807                                       mo_graph->checkReachable(act, rf)) {
 808                                 /* release --mo-> act --mo--> rf */
 809                                 return true; /* complete */
 810                         }
 811                         certain = false;
 812                 }
 813                 if (!future_ordered)
 814                         return false; /* This thread is uncertain */
 815         }
 816
 817         if (certain)
 818                 release_heads->push_back(release);
 819         return certain;
 820 }
 821
 822 /**
 823  * A public interface for getting the release sequence head(s) with which a
 824  * given ModelAction must synchronize. This function only returns a non-empty
 825  * result when it can locate a release sequence head with certainty. Otherwise,
 826  * it may mark the internal state of the ModelChecker so that it will handle
 827  * the release sequence at a later time, causing @a act to update its
 828  * synchronization at some later point in execution.
 829  * @param act The 'acquire' action that may read from a release sequence
 830  * @param release_heads A pass-by-reference return parameter. Will be filled
 831  * with the head(s) of the release sequence(s), if they exists with certainty.
 832  * @see ModelChecker::release_seq_head
 833  */
 834 void ModelChecker::get_release_seq_heads(ModelAction *act,
 835                 std::vector<const ModelAction *> *release_heads)
 836 {
 837         const ModelAction *rf = act->get_reads_from();
 838         bool complete;
 839         complete = release_seq_head(rf, release_heads);
 840         if (!complete) {
 841                 /* add act to 'lazy checking' list */
 842                 std::list<ModelAction *> *list;
 843                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 844                 list->push_back(act);
 845                 (*lazy_sync_size)++;
 846         }
 847 }
 848
 849 /**
 850  * Attempt to resolve all stashed operations that might synchronize with a
 851  * release sequence for a given location. This implements the "lazy" portion of
 852  * determining whether or not a release sequence was contiguous, since not all
 853  * modification order information is present at the time an action occurs.
 854  *
 855  * @param location The location/object that should be checked for release
 856  * sequence resolutions
 857  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 858  */
 859 bool ModelChecker::resolve_release_sequences(void *location)
 860 {
 861         std::list<ModelAction *> *list;
 862         list = lazy_sync_with_release->getptr(location);
 863         if (!list)
 864                 return false;
 865
 866         bool updated = false;
 867         std::list<ModelAction *>::iterator it = list->begin();
 868         while (it != list->end()) {
 869                 ModelAction *act = *it;
 870                 const ModelAction *rf = act->get_reads_from();
 871                 std::vector<const ModelAction *> release_heads;
 872                 bool complete;
 873                 complete = release_seq_head(rf, &release_heads);
 874                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 875                         if (!act->has_synchronized_with(release_heads[i])) {
 876                                 updated = true;
 877                                 act->synchronize_with(release_heads[i]);
 878                         }
 879                 }
 880
 881                 if (updated) {
 882                         /* propagate synchronization to later actions */
 883                         action_list_t::reverse_iterator it = action_trace->rbegin();
 884                         while ((*it) != act) {
 885                                 ModelAction *propagate = *it;
 886                                 if (act->happens_before(propagate))
 887                                         /** @todo new mo_graph edges along with
 888                                          * this synchronization? */
 889                                         propagate->synchronize_with(act);
 890                         }
 891                 }
 892                 if (complete) {
 893                         it = list->erase(it);
 894                         (*lazy_sync_size)--;
 895                 } else
 896                         it++;
 897         }
 898
 899         // If we resolved promises or data races, see if we have realized a data race.
 900         if (checkDataRaces()) {
 901                 set_assert();
 902         }
 903
 904         return updated;
 905 }
 906
 907 /**
 908  * Performs various bookkeeping operations for the current ModelAction. For
 909  * instance, adds action to the per-object, per-thread action vector and to the
 910  * action trace list of all thread actions.
 911  *
 912  * @param act is the ModelAction to add.
 913  */
 914 void ModelChecker::add_action_to_lists(ModelAction *act)
 915 {
 916         int tid = id_to_int(act->get_tid());
 917         action_trace->push_back(act);
 918
 919         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 920
 921         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 922         if (tid >= (int)vec->size())
 923                 vec->resize(priv->next_thread_id);
 924         (*vec)[tid].push_back(act);
 925
 926         if ((int)thrd_last_action->size() <= tid)
 927                 thrd_last_action->resize(get_num_threads());
 928         (*thrd_last_action)[tid] = act;
 929 }
 930
 931 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 932 {
 933         int nthreads = get_num_threads();
 934         if ((int)thrd_last_action->size() < nthreads)
 935                 thrd_last_action->resize(nthreads);
 936         return (*thrd_last_action)[id_to_int(tid)];
 937 }
 938
 939 /**
 940  * Gets the last memory_order_seq_cst action (in the total global sequence)
 941  * performed on a particular object (i.e., memory location).
 942  * @param location The object location to check
 943  * @return The last seq_cst action performed
 944  */
 945 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 946 {
 947         action_list_t *list = obj_map->get_safe_ptr(location);
 948         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 949         action_list_t::reverse_iterator rit;
 950         for (rit = list->rbegin(); rit != list->rend(); rit++)
 951                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 952                         return *rit;
 953         return NULL;
 954 }
 955
 956 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 957 {
 958         ModelAction *parent = get_last_action(tid);
 959         if (!parent)
 960                 parent = get_thread(tid)->get_creation();
 961         return parent;
 962 }
 963
 964 /**
 965  * Returns the clock vector for a given thread.
 966  * @param tid The thread whose clock vector we want
 967  * @return Desired clock vector
 968  */
 969 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 970 {
 971         return get_parent_action(tid)->get_cv();
 972 }
 973
 974 /**
 975  * Resolve a set of Promises with a current write. The set is provided in the
 976  * Node corresponding to @a write.
 977  * @param write The ModelAction that is fulfilling Promises
 978  * @return True if promises were resolved; false otherwise
 979  */
 980 bool ModelChecker::resolve_promises(ModelAction *write)
 981 {
 982         bool resolved = false;
 983         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 984                 Promise *promise = (*promises)[promise_index];
 985                 if (write->get_node()->get_promise(i)) {
 986                         ModelAction *read = promise->get_action();
 987                         read->read_from(write);
 988                         if (read->is_rmw()) {
 989                                 mo_graph->addRMWEdge(write, read);
 990                         }
 991                         r_modification_order(read, write);
 992                         post_r_modification_order(read, write);
 993                         promises->erase(promises->begin() + promise_index);
 994                         resolved = true;
 995                 } else
 996                         promise_index++;
 997         }
 998
 999         return resolved;
1000 }
1001
1002 /**
1003  * Compute the set of promises that could potentially be satisfied by this
1004  * action. Note that the set computation actually appears in the Node, not in
1005  * ModelChecker.
1006  * @param curr The ModelAction that may satisfy promises
1007  */
1008 void ModelChecker::compute_promises(ModelAction *curr)
1009 {
1010         for (unsigned int i = 0; i < promises->size(); i++) {
1011                 Promise *promise = (*promises)[i];
1012                 const ModelAction *act = promise->get_action();
1013                 if (!act->happens_before(curr) &&
1014                                 act->is_read() &&
1015                                 !act->is_synchronizing(curr) &&
1016                                 !act->same_thread(curr) &&
1017                                 promise->get_value() == curr->get_value()) {
1018                         curr->get_node()->set_promise(i);
1019                 }
1020         }
1021 }
1022
1023 /** Checks promises in response to change in ClockVector Threads. */
1024 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1025 {
1026         for (unsigned int i = 0; i < promises->size(); i++) {
1027                 Promise *promise = (*promises)[i];
1028                 const ModelAction *act = promise->get_action();
1029                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1030                                 merge_cv->synchronized_since(act)) {
1031                         //This thread is no longer able to send values back to satisfy the promise
1032                         int num_synchronized_threads = promise->increment_threads();
1033                         if (num_synchronized_threads == get_num_threads()) {
1034                                 //Promise has failed
1035                                 failed_promise = true;
1036                                 return;
1037                         }
1038                 }
1039         }
1040 }
1041
1042 /**
1043  * Build up an initial set of all past writes that this 'read' action may read
1044  * from. This set is determined by the clock vector's "happens before"
1045  * relationship.
1046  * @param curr is the current ModelAction that we are exploring; it must be a
1047  * 'read' operation.
1048  */
1049 void ModelChecker::build_reads_from_past(ModelAction *curr)
1050 {
1051         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1052         unsigned int i;
1053         ASSERT(curr->is_read());
1054
1055         ModelAction *last_seq_cst = NULL;
1056
1057         /* Track whether this object has been initialized */
1058         bool initialized = false;
1059
1060         if (curr->is_seqcst()) {
1061                 last_seq_cst = get_last_seq_cst(curr->get_location());
1062                 /* We have to at least see the last sequentially consistent write,
1063                          so we are initialized. */
1064                 if (last_seq_cst != NULL)
1065                         initialized = true;
1066         }
1067
1068         /* Iterate over all threads */
1069         for (i = 0; i < thrd_lists->size(); i++) {
1070                 /* Iterate over actions in thread, starting from most recent */
1071                 action_list_t *list = &(*thrd_lists)[i];
1072                 action_list_t::reverse_iterator rit;
1073                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1074                         ModelAction *act = *rit;
1075
1076                         /* Only consider 'write' actions */
1077                         if (!act->is_write())
1078                                 continue;
1079
1080                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1081                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1082                                 DEBUG("Adding action to may_read_from:\n");
1083                                 if (DBG_ENABLED()) {
1084                                         act->print();
1085                                         curr->print();
1086                                 }
1087                                 curr->get_node()->add_read_from(act);
1088                         }
1089
1090                         /* Include at most one act per-thread that "happens before" curr */
1091                         if (act->happens_before(curr)) {
1092                                 initialized = true;
1093                                 break;
1094                         }
1095                 }
1096         }
1097
1098         if (!initialized) {
1099                 /** @todo Need a more informative way of reporting errors. */
1100                 printf("ERROR: may read from uninitialized atomic\n");
1101         }
1102
1103         if (DBG_ENABLED() || !initialized) {
1104                 printf("Reached read action:\n");
1105                 curr->print();
1106                 printf("Printing may_read_from\n");
1107                 curr->get_node()->print_may_read_from();
1108                 printf("End printing may_read_from\n");
1109         }
1110
1111         ASSERT(initialized);
1112 }
1113
1114 static void print_list(action_list_t *list)
1115 {
1116         action_list_t::iterator it;
1117
1118         printf("---------------------------------------------------------------------\n");
1119         printf("Trace:\n");
1120
1121         for (it = list->begin(); it != list->end(); it++) {
1122                 (*it)->print();
1123         }
1124         printf("---------------------------------------------------------------------\n");
1125 }
1126
1127 void ModelChecker::print_summary()
1128 {
1129         printf("\n");
1130         printf("Number of executions: %d\n", num_executions);
1131         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1132
1133         scheduler->print();
1134
1135         if (!isfinalfeasible())
1136                 printf("INFEASIBLE EXECUTION!\n");
1137         print_list(action_trace);
1138         printf("\n");
1139 }
1140
1141 /**
1142  * Add a Thread to the system for the first time. Should only be called once
1143  * per thread.
1144  * @param t The Thread to add
1145  */
1146 void ModelChecker::add_thread(Thread *t)
1147 {
1148         thread_map->put(id_to_int(t->get_id()), t);
1149         scheduler->add_thread(t);
1150 }
1151
1152 void ModelChecker::remove_thread(Thread *t)
1153 {
1154         scheduler->remove_thread(t);
1155 }
1156
1157 /**
1158  * Switch from a user-context to the "master thread" context (a.k.a. system
1159  * context). This switch is made with the intention of exploring a particular
1160  * model-checking action (described by a ModelAction object). Must be called
1161  * from a user-thread context.
1162  * @param act The current action that will be explored. Must not be NULL.
1163  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1164  */
1165 int ModelChecker::switch_to_master(ModelAction *act)
1166 {
1167         DBG();
1168         Thread *old = thread_current();
1169         set_current_action(act);
1170         old->set_state(THREAD_READY);
1171         return Thread::swap(old, &system_context);
1172 }
1173
1174 /**
1175  * Takes the next step in the execution, if possible.
1176  * @return Returns true (success) if a step was taken and false otherwise.
1177  */
1178 bool ModelChecker::take_step() {
1179         Thread *curr, *next;
1180
1181         if (has_asserted())
1182                 return false;
1183
1184         curr = thread_current();
1185         if (curr) {
1186                 if (curr->get_state() == THREAD_READY) {
1187                         ASSERT(priv->current_action);
1188                         priv->nextThread = check_current_action(priv->current_action);
1189                         priv->current_action = NULL;
1190                         if (!curr->is_blocked() && !curr->is_complete())
1191                                 scheduler->add_thread(curr);
1192                 } else {
1193                         ASSERT(false);
1194                 }
1195         }
1196         next = scheduler->next_thread(priv->nextThread);
1197
1198         /* Infeasible -> don't take any more steps */
1199         if (!isfeasible())
1200                 return false;
1201
1202         if (next)
1203                 next->set_state(THREAD_RUNNING);
1204         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1205
1206         /* next == NULL -> don't take any more steps */
1207         if (!next)
1208                 return false;
1209         /* Return false only if swap fails with an error */
1210         return (Thread::swap(&system_context, next) == 0);
1211 }
1212
1213 /** Runs the current execution until threre are no more steps to take. */
1214 void ModelChecker::finish_execution() {
1215         DBG();
1216
1217         while (take_step());
1218 }