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 /**
 263  * Processes a read or rmw model action.
 264  * @param curr is the read model action to process.
 265  * @param th is the thread
 266  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 267  * @return True if processing this read updates the mo_graph.
 268  */
 269
 270 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
 271         uint64_t value;
 272         bool updated=false;
 273         while(true) {
 274                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 275                 if (reads_from != NULL) {
 276                         mo_graph->startChanges();
 277
 278                         value = reads_from->get_value();
 279
 280                         if (!second_part_of_rmw) {
 281                                 check_recency(curr,false);
 282                         }
 283
 284                         bool r_status=r_modification_order(curr,reads_from);
 285
 286                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
 287                                 mo_graph->rollbackChanges();
 288                                 too_many_reads=false;
 289                                 continue;
 290                         }
 291
 292                         curr->read_from(reads_from);
 293                         mo_graph->commitChanges();
 294                         updated |= r_status;
 295                 } else if (!second_part_of_rmw) {
 296                         /* Read from future value */
 297                         value = curr->get_node()->get_future_value();
 298                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 299                         curr->read_from(NULL);
 300                         Promise *valuepromise = new Promise(curr, value, expiration);
 301                         promises->push_back(valuepromise);
 302                 }
 303                 th->set_return_value(value);
 304                 return updated;
 305         }
 306 }
 307
 308 /**
 309  * This is the heart of the model checker routine. It performs model-checking
 310  * actions corresponding to a given "current action." Among other processes, it
 311  * calculates reads-from relationships, updates synchronization clock vectors,
 312  * forms a memory_order constraints graph, and handles replay/backtrack
 313  * execution when running permutations of previously-observed executions.
 314  *
 315  * @param curr The current action to process
 316  * @return The next Thread that must be executed. May be NULL if ModelChecker
 317  * makes no choice (e.g., according to replay execution, combining RMW actions,
 318  * etc.)
 319  */
 320 Thread * ModelChecker::check_current_action(ModelAction *curr)
 321 {
 322         bool second_part_of_rmw = false;
 323
 324         ASSERT(curr);
 325
 326         if (curr->is_rmwc() || curr->is_rmw()) {
 327                 ModelAction *tmp = process_rmw(curr);
 328                 second_part_of_rmw = true;
 329                 delete curr;
 330                 curr = tmp;
 331                 compute_promises(curr);
 332         } else {
 333                 ModelAction *tmp = node_stack->explore_action(curr);
 334                 if (tmp) {
 335                         /* Discard duplicate ModelAction; use action from NodeStack */
 336                         /* First restore type and order in case of RMW operation */
 337                         if (curr->is_rmwr())
 338                                 tmp->copy_typeandorder(curr);
 339
 340                         /* If we have diverged, we need to reset the clock vector. */
 341                         if (diverge == NULL)
 342                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 343
 344                         delete curr;
 345                         curr = tmp;
 346                 } else {
 347                         /*
 348                          * Perform one-time actions when pushing new ModelAction onto
 349                          * NodeStack
 350                          */
 351                         curr->create_cv(get_parent_action(curr->get_tid()));
 352                         /* Build may_read_from set */
 353                         if (curr->is_read())
 354                                 build_reads_from_past(curr);
 355                         if (curr->is_write())
 356                                 compute_promises(curr);
 357                 }
 358         }
 359
 360         /* Thread specific actions */
 361         switch(curr->get_type()) {
 362         case THREAD_CREATE: {
 363                 Thread *th = (Thread *)curr->get_location();
 364                 th->set_creation(curr);
 365                 break;
 366         }
 367         case THREAD_JOIN: {
 368                 Thread *waiting, *blocking;
 369                 waiting = get_thread(curr);
 370                 blocking = (Thread *)curr->get_location();
 371                 if (!blocking->is_complete()) {
 372                         blocking->push_wait_list(curr);
 373                         scheduler->sleep(waiting);
 374                 }
 375                 break;
 376         }
 377         case THREAD_FINISH: {
 378                 Thread *th = get_thread(curr);
 379                 while (!th->wait_list_empty()) {
 380                         ModelAction *act = th->pop_wait_list();
 381                         Thread *wake = get_thread(act);
 382                         scheduler->wake(wake);
 383                 }
 384                 th->complete();
 385                 break;
 386         }
 387         case THREAD_START: {
 388                 check_promises(NULL, curr->get_cv());
 389                 break;
 390         }
 391         default:
 392                 break;
 393         }
 394
 395         Thread *th = get_thread(curr);
 396
 397         bool updated = false;
 398         if (curr->is_read()) {
 399                 updated=process_read(curr, th, second_part_of_rmw);
 400         }
 401
 402         if (curr->is_write()) {
 403                 bool updated_mod_order=w_modification_order(curr);
 404                 bool updated_promises=resolve_promises(curr);
 405                 updated=updated_mod_order|updated_promises;
 406
 407                 mo_graph->commitChanges();
 408                 th->set_return_value(VALUE_NONE);
 409         }
 410
 411         if (updated)
 412                 resolve_release_sequences(curr->get_location());
 413
 414         /* Add action to list.  */
 415         if (!second_part_of_rmw)
 416                 add_action_to_lists(curr);
 417
 418         check_curr_backtracking(curr);
 419
 420         set_backtracking(curr);
 421
 422         return get_next_thread(curr);
 423 }
 424
 425 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 426         Node *currnode = curr->get_node();
 427         Node *parnode = currnode->get_parent();
 428
 429         if ((!parnode->backtrack_empty() ||
 430                          !currnode->read_from_empty() ||
 431                          !currnode->future_value_empty() ||
 432                          !currnode->promise_empty())
 433                         && (!priv->next_backtrack ||
 434                                         *curr > *priv->next_backtrack)) {
 435                 priv->next_backtrack = curr;
 436         }
 437 }
 438
 439
 440 bool ModelChecker::promises_expired() {
 441         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 442                 Promise *promise = (*promises)[promise_index];
 443                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 444                         return true;
 445                 }
 446         }
 447         return false;
 448 }
 449
 450 /** @returns whether the current partial trace must be a prefix of a
 451  * feasible trace. */
 452 bool ModelChecker::isfeasibleprefix() {
 453         return promises->size() == 0 && *lazy_sync_size == 0;
 454 }
 455
 456 /** @returns whether the current partial trace is feasible. */
 457 bool ModelChecker::isfeasible() {
 458         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 459 }
 460
 461 /** @returns whether the current partial trace is feasible other than
 462  * multiple RMW reading from the same store. */
 463 bool ModelChecker::isfeasibleotherthanRMW() {
 464         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 465 }
 466
 467 /** Returns whether the current completed trace is feasible. */
 468 bool ModelChecker::isfinalfeasible() {
 469         return isfeasible() && promises->size() == 0;
 470 }
 471
 472 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 473 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 474         int tid = id_to_int(act->get_tid());
 475         ModelAction *lastread = get_last_action(tid);
 476         lastread->process_rmw(act);
 477         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 478                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 479                 mo_graph->commitChanges();
 480         }
 481         return lastread;
 482 }
 483
 484 /**
 485  * Checks whether a thread has read from the same write for too many times
 486  * without seeing the effects of a later write.
 487  *
 488  * Basic idea:
 489  * 1) there must a different write that we could read from that would satisfy the modification order,
 490  * 2) we must have read from the same value in excess of maxreads times, and
 491  * 3) that other write must have been in the reads_from set for maxreads times.
 492  *
 493  * If so, we decide that the execution is no longer feasible.
 494  */
 495 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 496         if (params.maxreads != 0) {
 497                 if (curr->get_node()->get_read_from_size() <= 1)
 498                         return;
 499
 500                 //Must make sure that execution is currently feasible...  We could
 501                 //accidentally clear by rolling back
 502                 if (!isfeasible())
 503                         return;
 504
 505                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 506                 int tid = id_to_int(curr->get_tid());
 507
 508                 /* Skip checks */
 509                 if ((int)thrd_lists->size() <= tid)
 510                         return;
 511
 512                 action_list_t *list = &(*thrd_lists)[tid];
 513
 514                 action_list_t::reverse_iterator rit = list->rbegin();
 515                 /* Skip past curr */
 516                 if (already_added) {
 517                         for (; (*rit) != curr; rit++)
 518                                 ;
 519                         /* go past curr now */
 520                         rit++;
 521                 }
 522
 523                 action_list_t::reverse_iterator ritcopy=rit;
 524                 //See if we have enough reads from the same value
 525                 int count=0;
 526                 for (; count < params.maxreads; rit++,count++) {
 527                         if (rit==list->rend())
 528                                 return;
 529                         ModelAction *act = *rit;
 530                         if (!act->is_read())
 531                                 return;
 532                         if (act->get_reads_from() != curr->get_reads_from())
 533                                 return;
 534                         if (act->get_node()->get_read_from_size() <= 1)
 535                                 return;
 536                 }
 537
 538                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 539                         //Get write
 540                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 541                         //Need a different write
 542                         if (write==curr->get_reads_from())
 543                                 continue;
 544
 545                         /* Test to see whether this is a feasible write to read from*/
 546                         mo_graph->startChanges();
 547                         r_modification_order(curr, write);
 548                         bool feasiblereadfrom=isfeasible();
 549                         mo_graph->rollbackChanges();
 550
 551                         if (!feasiblereadfrom)
 552                                 continue;
 553                         rit=ritcopy;
 554
 555                         bool feasiblewrite=true;
 556                         //new we need to see if this write works for everyone
 557
 558                         for (int loop=count;loop>0;loop--,rit++) {
 559                                 ModelAction *act=*rit;
 560                                 bool foundvalue=false;
 561                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 562                                         if (act->get_node()->get_read_from_at(i)==write) {
 563                                                 foundvalue=true;
 564                                                 break;
 565                                         }
 566                                 }
 567                                 if (!foundvalue) {
 568                                         feasiblewrite=false;
 569                                         break;
 570                                 }
 571                         }
 572                         if (feasiblewrite) {
 573                                 too_many_reads = true;
 574                                 return;
 575                         }
 576                 }
 577         }
 578 }
 579
 580 /**
 581  * Updates the mo_graph with the constraints imposed from the current read.
 582  * @param curr The current action. Must be a read.
 583  * @param rf The action that curr reads from. Must be a write.
 584  * @return True if modification order edges were added; false otherwise
 585  */
 586 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 587 {
 588         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 589         unsigned int i;
 590         bool added = false;
 591         ASSERT(curr->is_read());
 592
 593         /* Iterate over all threads */
 594         for (i = 0; i < thrd_lists->size(); i++) {
 595                 /* Iterate over actions in thread, starting from most recent */
 596                 action_list_t *list = &(*thrd_lists)[i];
 597                 action_list_t::reverse_iterator rit;
 598                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 599                         ModelAction *act = *rit;
 600
 601                         /* Include at most one act per-thread that "happens before" curr */
 602                         if (act->happens_before(curr)) {
 603                                 if (act->is_read()) {
 604                                         const ModelAction *prevreadfrom = act->get_reads_from();
 605                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 606                                                 mo_graph->addEdge(prevreadfrom, rf);
 607                                                 added = true;
 608                                         }
 609                                 } else if (rf != act) {
 610                                         mo_graph->addEdge(act, rf);
 611                                         added = true;
 612                                 }
 613                                 break;
 614                         }
 615                 }
 616         }
 617
 618         return added;
 619 }
 620
 621 /** Updates the mo_graph with the constraints imposed from the current read. */
 622 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 623 {
 624         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 625         unsigned int i;
 626         ASSERT(curr->is_read());
 627
 628         /* Iterate over all threads */
 629         for (i = 0; i < thrd_lists->size(); i++) {
 630                 /* Iterate over actions in thread, starting from most recent */
 631                 action_list_t *list = &(*thrd_lists)[i];
 632                 action_list_t::reverse_iterator rit;
 633                 ModelAction *lastact = NULL;
 634
 635                 /* Find last action that happens after curr */
 636                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 637                         ModelAction *act = *rit;
 638                         if (curr->happens_before(act)) {
 639                                 lastact = act;
 640                         } else
 641                                 break;
 642                 }
 643
 644                         /* Include at most one act per-thread that "happens before" curr */
 645                 if (lastact != NULL) {
 646                         if (lastact->is_read()) {
 647                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 648                                 if (postreadfrom != NULL&&rf != postreadfrom)
 649                                         mo_graph->addEdge(rf, postreadfrom);
 650                         } else if (rf != lastact) {
 651                                 mo_graph->addEdge(rf, lastact);
 652                         }
 653                         break;
 654                 }
 655         }
 656 }
 657
 658 /**
 659  * Updates the mo_graph with the constraints imposed from the current write.
 660  * @param curr The current action. Must be a write.
 661  * @return True if modification order edges were added; false otherwise
 662  */
 663 bool ModelChecker::w_modification_order(ModelAction *curr)
 664 {
 665         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 666         unsigned int i;
 667         bool added = false;
 668         ASSERT(curr->is_write());
 669
 670         if (curr->is_seqcst()) {
 671                 /* We have to at least see the last sequentially consistent write,
 672                          so we are initialized. */
 673                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 674                 if (last_seq_cst != NULL) {
 675                         mo_graph->addEdge(last_seq_cst, curr);
 676                         added = true;
 677                 }
 678         }
 679
 680         /* Iterate over all threads */
 681         for (i = 0; i < thrd_lists->size(); i++) {
 682                 /* Iterate over actions in thread, starting from most recent */
 683                 action_list_t *list = &(*thrd_lists)[i];
 684                 action_list_t::reverse_iterator rit;
 685                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 686                         ModelAction *act = *rit;
 687
 688                         /* Include at most one act per-thread that "happens before" curr */
 689                         if (act->happens_before(curr)) {
 690                                 /*
 691                                  * Note: if act is RMW, just add edge:
 692                                  *   act --mo--> curr
 693                                  * The following edge should be handled elsewhere:
 694                                  *   readfrom(act) --mo--> act
 695                                  */
 696                                 if (act->is_write()) {
 697                                         //RMW shouldn't have an edge to themselves
 698                                         if (act!=curr)
 699                                                 mo_graph->addEdge(act, curr);
 700                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 701                                         mo_graph->addEdge(act->get_reads_from(), curr);
 702                                 added = true;
 703                                 break;
 704                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 705                                                      !act->same_thread(curr)) {
 706                                 /* We have an action that:
 707                                    (1) did not happen before us
 708                                    (2) is a read and we are a write
 709                                    (3) cannot synchronize with us
 710                                    (4) is in a different thread
 711                                    =>
 712                                    that read could potentially read from our write.
 713                                  */
 714                                 if (thin_air_constraint_may_allow(curr, act)) {
 715                                         if (isfeasible() ||
 716                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 717                                                 if (act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
 718                                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 719                                                         priv->next_backtrack = act;
 720                                         }
 721                                 }
 722                         }
 723                 }
 724         }
 725
 726         return added;
 727 }
 728
 729 /** Arbitrary reads from the future are not allowed.  Section 29.3
 730  * part 9 places some constraints.  This method checks one result of constraint
 731  * constraint.  Others require compiler support. */
 732
 733 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 734         if (!writer->is_rmw())
 735                 return true;
 736
 737         if (!reader->is_rmw())
 738                 return true;
 739
 740         for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
 741                 if (search==reader)
 742                         return false;
 743                 if (search->get_tid()==reader->get_tid()&&
 744                                 search->happens_before(reader))
 745                         break;
 746         }
 747
 748         return true;
 749 }
 750
 751
 752 /**
 753  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 754  * The ModelAction under consideration is expected to be taking part in
 755  * release/acquire synchronization as an object of the "reads from" relation.
 756  * Note that this can only provide release sequence support for RMW chains
 757  * which do not read from the future, as those actions cannot be traced until
 758  * their "promise" is fulfilled. Similarly, we may not even establish the
 759  * presence of a release sequence with certainty, as some modification order
 760  * constraints may be decided further in the future. Thus, this function
 761  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 762  * and a boolean representing certainty.
 763  *
 764  * @todo Finish lazy updating, when promises are fulfilled in the future
 765  * @param rf The action that might be part of a release sequence. Must be a
 766  * write.
 767  * @param release_heads A pass-by-reference style return parameter.  After
 768  * execution of this function, release_heads will contain the heads of all the
 769  * relevant release sequences, if any exists
 770  * @return true, if the ModelChecker is certain that release_heads is complete;
 771  * false otherwise
 772  */
 773 bool ModelChecker::release_seq_head(const ModelAction *rf,
 774                 std::vector<const ModelAction *> *release_heads) const
 775 {
 776         ASSERT(rf->is_write());
 777         if (!rf) {
 778                 /* read from future: need to settle this later */
 779                 return false; /* incomplete */
 780         }
 781         if (rf->is_release())
 782                 release_heads->push_back(rf);
 783         if (rf->is_rmw()) {
 784                 /* We need a RMW action that is both an acquire and release to stop */
 785                 /** @todo Need to be smarter here...  In the linux lock
 786                  * example, this will run to the beginning of the program for
 787                  * every acquire. */
 788                 if (rf->is_acquire() && rf->is_release())
 789                         return true; /* complete */
 790                 return release_seq_head(rf->get_reads_from(), release_heads);
 791         }
 792         if (rf->is_release())
 793                 return true; /* complete */
 794
 795         /* else relaxed write; check modification order for contiguous subsequence
 796          * -> rf must be same thread as release */
 797         int tid = id_to_int(rf->get_tid());
 798         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 799         action_list_t *list = &(*thrd_lists)[tid];
 800         action_list_t::const_reverse_iterator rit;
 801
 802         /* Find rf in the thread list */
 803         rit = std::find(list->rbegin(), list->rend(), rf);
 804         ASSERT(rit != list->rend());
 805
 806         /* Find the last write/release */
 807         for (; rit != list->rend(); rit++)
 808                 if ((*rit)->is_release())
 809                         break;
 810         if (rit == list->rend()) {
 811                 /* No write-release in this thread */
 812                 return true; /* complete */
 813         }
 814         ModelAction *release = *rit;
 815
 816         ASSERT(rf->same_thread(release));
 817
 818         bool certain = true;
 819         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 820                 if (id_to_int(rf->get_tid()) == (int)i)
 821                         continue;
 822                 list = &(*thrd_lists)[i];
 823
 824                 /* Can we ensure no future writes from this thread may break
 825                  * the release seq? */
 826                 bool future_ordered = false;
 827
 828                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 829                         const ModelAction *act = *rit;
 830                         if (!act->is_write())
 831                                 continue;
 832                         /* Reach synchronization -> this thread is complete */
 833                         if (act->happens_before(release))
 834                                 break;
 835                         if (rf->happens_before(act)) {
 836                                 future_ordered = true;
 837                                 continue;
 838                         }
 839
 840                         /* Check modification order */
 841                         if (mo_graph->checkReachable(rf, act)) {
 842                                 /* rf --mo--> act */
 843                                 future_ordered = true;
 844                                 continue;
 845                         }
 846                         if (mo_graph->checkReachable(act, release))
 847                                 /* act --mo--> release */
 848                                 break;
 849                         if (mo_graph->checkReachable(release, act) &&
 850                                       mo_graph->checkReachable(act, rf)) {
 851                                 /* release --mo-> act --mo--> rf */
 852                                 return true; /* complete */
 853                         }
 854                         certain = false;
 855                 }
 856                 if (!future_ordered)
 857                         return false; /* This thread is uncertain */
 858         }
 859
 860         if (certain)
 861                 release_heads->push_back(release);
 862         return certain;
 863 }
 864
 865 /**
 866  * A public interface for getting the release sequence head(s) with which a
 867  * given ModelAction must synchronize. This function only returns a non-empty
 868  * result when it can locate a release sequence head with certainty. Otherwise,
 869  * it may mark the internal state of the ModelChecker so that it will handle
 870  * the release sequence at a later time, causing @a act to update its
 871  * synchronization at some later point in execution.
 872  * @param act The 'acquire' action that may read from a release sequence
 873  * @param release_heads A pass-by-reference return parameter. Will be filled
 874  * with the head(s) of the release sequence(s), if they exists with certainty.
 875  * @see ModelChecker::release_seq_head
 876  */
 877 void ModelChecker::get_release_seq_heads(ModelAction *act,
 878                 std::vector<const ModelAction *> *release_heads)
 879 {
 880         const ModelAction *rf = act->get_reads_from();
 881         bool complete;
 882         complete = release_seq_head(rf, release_heads);
 883         if (!complete) {
 884                 /* add act to 'lazy checking' list */
 885                 std::list<ModelAction *> *list;
 886                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 887                 list->push_back(act);
 888                 (*lazy_sync_size)++;
 889         }
 890 }
 891
 892 /**
 893  * Attempt to resolve all stashed operations that might synchronize with a
 894  * release sequence for a given location. This implements the "lazy" portion of
 895  * determining whether or not a release sequence was contiguous, since not all
 896  * modification order information is present at the time an action occurs.
 897  *
 898  * @param location The location/object that should be checked for release
 899  * sequence resolutions
 900  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 901  */
 902 bool ModelChecker::resolve_release_sequences(void *location)
 903 {
 904         std::list<ModelAction *> *list;
 905         list = lazy_sync_with_release->getptr(location);
 906         if (!list)
 907                 return false;
 908
 909         bool updated = false;
 910         std::list<ModelAction *>::iterator it = list->begin();
 911         while (it != list->end()) {
 912                 ModelAction *act = *it;
 913                 const ModelAction *rf = act->get_reads_from();
 914                 std::vector<const ModelAction *> release_heads;
 915                 bool complete;
 916                 complete = release_seq_head(rf, &release_heads);
 917                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 918                         if (!act->has_synchronized_with(release_heads[i])) {
 919                                 updated = true;
 920                                 act->synchronize_with(release_heads[i]);
 921                         }
 922                 }
 923
 924                 if (updated) {
 925                         /* propagate synchronization to later actions */
 926                         action_list_t::reverse_iterator it = action_trace->rbegin();
 927                         while ((*it) != act) {
 928                                 ModelAction *propagate = *it;
 929                                 if (act->happens_before(propagate))
 930                                         /** @todo new mo_graph edges along with
 931                                          * this synchronization? */
 932                                         propagate->synchronize_with(act);
 933                         }
 934                 }
 935                 if (complete) {
 936                         it = list->erase(it);
 937                         (*lazy_sync_size)--;
 938                 } else
 939                         it++;
 940         }
 941
 942         // If we resolved promises or data races, see if we have realized a data race.
 943         if (checkDataRaces()) {
 944                 set_assert();
 945         }
 946
 947         return updated;
 948 }
 949
 950 /**
 951  * Performs various bookkeeping operations for the current ModelAction. For
 952  * instance, adds action to the per-object, per-thread action vector and to the
 953  * action trace list of all thread actions.
 954  *
 955  * @param act is the ModelAction to add.
 956  */
 957 void ModelChecker::add_action_to_lists(ModelAction *act)
 958 {
 959         int tid = id_to_int(act->get_tid());
 960         action_trace->push_back(act);
 961
 962         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 963
 964         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 965         if (tid >= (int)vec->size())
 966                 vec->resize(priv->next_thread_id);
 967         (*vec)[tid].push_back(act);
 968
 969         if ((int)thrd_last_action->size() <= tid)
 970                 thrd_last_action->resize(get_num_threads());
 971         (*thrd_last_action)[tid] = act;
 972 }
 973
 974 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 975 {
 976         int nthreads = get_num_threads();
 977         if ((int)thrd_last_action->size() < nthreads)
 978                 thrd_last_action->resize(nthreads);
 979         return (*thrd_last_action)[id_to_int(tid)];
 980 }
 981
 982 /**
 983  * Gets the last memory_order_seq_cst action (in the total global sequence)
 984  * performed on a particular object (i.e., memory location).
 985  * @param location The object location to check
 986  * @return The last seq_cst action performed
 987  */
 988 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 989 {
 990         action_list_t *list = obj_map->get_safe_ptr(location);
 991         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 992         action_list_t::reverse_iterator rit;
 993         for (rit = list->rbegin(); rit != list->rend(); rit++)
 994                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 995                         return *rit;
 996         return NULL;
 997 }
 998
 999 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1000 {
1001         ModelAction *parent = get_last_action(tid);
1002         if (!parent)
1003                 parent = get_thread(tid)->get_creation();
1004         return parent;
1005 }
1006
1007 /**
1008  * Returns the clock vector for a given thread.
1009  * @param tid The thread whose clock vector we want
1010  * @return Desired clock vector
1011  */
1012 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1013 {
1014         return get_parent_action(tid)->get_cv();
1015 }
1016
1017 /**
1018  * Resolve a set of Promises with a current write. The set is provided in the
1019  * Node corresponding to @a write.
1020  * @param write The ModelAction that is fulfilling Promises
1021  * @return True if promises were resolved; false otherwise
1022  */
1023 bool ModelChecker::resolve_promises(ModelAction *write)
1024 {
1025         bool resolved = false;
1026
1027         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1028                 Promise *promise = (*promises)[promise_index];
1029                 if (write->get_node()->get_promise(i)) {
1030                         ModelAction *read = promise->get_action();
1031                         read->read_from(write);
1032                         if (read->is_rmw()) {
1033                                 mo_graph->addRMWEdge(write, read);
1034                         }
1035                         r_modification_order(read, write);
1036                         post_r_modification_order(read, write);
1037                         promises->erase(promises->begin() + promise_index);
1038                         resolved = true;
1039                 } else
1040                         promise_index++;
1041         }
1042         return resolved;
1043 }
1044
1045
1046
1047 /**
1048  * Compute the set of promises that could potentially be satisfied by this
1049  * action. Note that the set computation actually appears in the Node, not in
1050  * ModelChecker.
1051  * @param curr The ModelAction that may satisfy promises
1052  */
1053 void ModelChecker::compute_promises(ModelAction *curr)
1054 {
1055         for (unsigned int i = 0; i < promises->size(); i++) {
1056                 Promise *promise = (*promises)[i];
1057                 const ModelAction *act = promise->get_action();
1058                 if (!act->happens_before(curr) &&
1059                                 act->is_read() &&
1060                                 !act->is_synchronizing(curr) &&
1061                                 !act->same_thread(curr) &&
1062                                 promise->get_value() == curr->get_value()) {
1063                         curr->get_node()->set_promise(i);
1064                 }
1065         }
1066 }
1067
1068 /** Checks promises in response to change in ClockVector Threads. */
1069 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1070 {
1071         for (unsigned int i = 0; i < promises->size(); i++) {
1072                 Promise *promise = (*promises)[i];
1073                 const ModelAction *act = promise->get_action();
1074                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1075                                 merge_cv->synchronized_since(act)) {
1076                         //This thread is no longer able to send values back to satisfy the promise
1077                         int num_synchronized_threads = promise->increment_threads();
1078                         if (num_synchronized_threads == get_num_threads()) {
1079                                 //Promise has failed
1080                                 failed_promise = true;
1081                                 return;
1082                         }
1083                 }
1084         }
1085 }
1086
1087 /**
1088  * Build up an initial set of all past writes that this 'read' action may read
1089  * from. This set is determined by the clock vector's "happens before"
1090  * relationship.
1091  * @param curr is the current ModelAction that we are exploring; it must be a
1092  * 'read' operation.
1093  */
1094 void ModelChecker::build_reads_from_past(ModelAction *curr)
1095 {
1096         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1097         unsigned int i;
1098         ASSERT(curr->is_read());
1099
1100         ModelAction *last_seq_cst = NULL;
1101
1102         /* Track whether this object has been initialized */
1103         bool initialized = false;
1104
1105         if (curr->is_seqcst()) {
1106                 last_seq_cst = get_last_seq_cst(curr->get_location());
1107                 /* We have to at least see the last sequentially consistent write,
1108                          so we are initialized. */
1109                 if (last_seq_cst != NULL)
1110                         initialized = true;
1111         }
1112
1113         /* Iterate over all threads */
1114         for (i = 0; i < thrd_lists->size(); i++) {
1115                 /* Iterate over actions in thread, starting from most recent */
1116                 action_list_t *list = &(*thrd_lists)[i];
1117                 action_list_t::reverse_iterator rit;
1118                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1119                         ModelAction *act = *rit;
1120
1121                         /* Only consider 'write' actions */
1122                         if (!act->is_write())
1123                                 continue;
1124
1125                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1126                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1127                                 DEBUG("Adding action to may_read_from:\n");
1128                                 if (DBG_ENABLED()) {
1129                                         act->print();
1130                                         curr->print();
1131                                 }
1132                                 curr->get_node()->add_read_from(act);
1133                         }
1134
1135                         /* Include at most one act per-thread that "happens before" curr */
1136                         if (act->happens_before(curr)) {
1137                                 initialized = true;
1138                                 break;
1139                         }
1140                 }
1141         }
1142
1143         if (!initialized) {
1144                 /** @todo Need a more informative way of reporting errors. */
1145                 printf("ERROR: may read from uninitialized atomic\n");
1146         }
1147
1148         if (DBG_ENABLED() || !initialized) {
1149                 printf("Reached read action:\n");
1150                 curr->print();
1151                 printf("Printing may_read_from\n");
1152                 curr->get_node()->print_may_read_from();
1153                 printf("End printing may_read_from\n");
1154         }
1155
1156         ASSERT(initialized);
1157 }
1158
1159 static void print_list(action_list_t *list)
1160 {
1161         action_list_t::iterator it;
1162
1163         printf("---------------------------------------------------------------------\n");
1164         printf("Trace:\n");
1165
1166         for (it = list->begin(); it != list->end(); it++) {
1167                 (*it)->print();
1168         }
1169         printf("---------------------------------------------------------------------\n");
1170 }
1171
1172 void ModelChecker::print_summary()
1173 {
1174         printf("\n");
1175         printf("Number of executions: %d\n", num_executions);
1176         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1177
1178         scheduler->print();
1179
1180         if (!isfinalfeasible())
1181                 printf("INFEASIBLE EXECUTION!\n");
1182         print_list(action_trace);
1183         printf("\n");
1184 }
1185
1186 /**
1187  * Add a Thread to the system for the first time. Should only be called once
1188  * per thread.
1189  * @param t The Thread to add
1190  */
1191 void ModelChecker::add_thread(Thread *t)
1192 {
1193         thread_map->put(id_to_int(t->get_id()), t);
1194         scheduler->add_thread(t);
1195 }
1196
1197 void ModelChecker::remove_thread(Thread *t)
1198 {
1199         scheduler->remove_thread(t);
1200 }
1201
1202 /**
1203  * Switch from a user-context to the "master thread" context (a.k.a. system
1204  * context). This switch is made with the intention of exploring a particular
1205  * model-checking action (described by a ModelAction object). Must be called
1206  * from a user-thread context.
1207  * @param act The current action that will be explored. Must not be NULL.
1208  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1209  */
1210 int ModelChecker::switch_to_master(ModelAction *act)
1211 {
1212         DBG();
1213         Thread *old = thread_current();
1214         set_current_action(act);
1215         old->set_state(THREAD_READY);
1216         return Thread::swap(old, &system_context);
1217 }
1218
1219 /**
1220  * Takes the next step in the execution, if possible.
1221  * @return Returns true (success) if a step was taken and false otherwise.
1222  */
1223 bool ModelChecker::take_step() {
1224         Thread *curr, *next;
1225
1226         if (has_asserted())
1227                 return false;
1228
1229         curr = thread_current();
1230         if (curr) {
1231                 if (curr->get_state() == THREAD_READY) {
1232                         ASSERT(priv->current_action);
1233
1234                         priv->nextThread = check_current_action(priv->current_action);
1235                         priv->current_action = NULL;
1236                         if (!curr->is_blocked() && !curr->is_complete())
1237                                 scheduler->add_thread(curr);
1238                 } else {
1239                         ASSERT(false);
1240                 }
1241         }
1242         next = scheduler->next_thread(priv->nextThread);
1243
1244         /* Infeasible -> don't take any more steps */
1245         if (!isfeasible())
1246                 return false;
1247
1248         if (next)
1249                 next->set_state(THREAD_RUNNING);
1250         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1251
1252         /* next == NULL -> don't take any more steps */
1253         if (!next)
1254                 return false;
1255         /* Return false only if swap fails with an error */
1256         return (Thread::swap(&system_context, next) == 0);
1257 }
1258
1259 /** Runs the current execution until threre are no more steps to take. */
1260 void ModelChecker::finish_execution() {
1261         DBG();
1262
1263         while (take_step());
1264 }