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