model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14
  15 #define INITIAL_THREAD_ID       0
  16
  17 ModelChecker *model;
  18
  19 /** @brief Constructor */
  20 ModelChecker::ModelChecker(struct model_params params) :
  21         /* Initialize default scheduler */
  22         scheduler(new Scheduler()),
  23         num_executions(0),
  24         params(params),
  25         diverge(NULL),
  26         action_trace(new action_list_t()),
  27         thread_map(new HashTable<int, Thread *, int>()),
  28         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  29         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  30         promises(new std::vector<Promise *>()),
  31         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  32         thrd_last_action(new std::vector<ModelAction *>(1)),
  33         node_stack(new NodeStack()),
  34         mo_graph(new CycleGraph()),
  35         failed_promise(false),
  36         too_many_reads(false),
  37         asserted(false)
  38 {
  39         /* Allocate this "size" on the snapshotting heap */
  40         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  41         /* First thread created will have id INITIAL_THREAD_ID */
  42         priv->next_thread_id = INITIAL_THREAD_ID;
  43
  44         lazy_sync_size = &priv->lazy_sync_size;
  45 }
  46
  47 /** @brief Destructor */
  48 ModelChecker::~ModelChecker()
  49 {
  50         for (int i = 0; i < get_num_threads(); i++)
  51                 delete thread_map->get(i);
  52         delete thread_map;
  53
  54         delete obj_thrd_map;
  55         delete obj_map;
  56         delete action_trace;
  57
  58         for (unsigned int i = 0; i < promises->size(); i++)
  59                 delete (*promises)[i];
  60         delete promises;
  61
  62         delete lazy_sync_with_release;
  63
  64         delete thrd_last_action;
  65         delete node_stack;
  66         delete scheduler;
  67         delete mo_graph;
  68 }
  69
  70 /**
  71  * Restores user program to initial state and resets all model-checker data
  72  * structures.
  73  */
  74 void ModelChecker::reset_to_initial_state()
  75 {
  76         DEBUG("+++ Resetting to initial state +++\n");
  77         node_stack->reset_execution();
  78         failed_promise = false;
  79         too_many_reads = false;
  80         reset_asserted();
  81         snapshotObject->backTrackBeforeStep(0);
  82 }
  83
  84 /** @returns a thread ID for a new Thread */
  85 thread_id_t ModelChecker::get_next_id()
  86 {
  87         return priv->next_thread_id++;
  88 }
  89
  90 /** @returns the number of user threads created during this execution */
  91 int ModelChecker::get_num_threads()
  92 {
  93         return priv->next_thread_id;
  94 }
  95
  96 /** @returns a sequence number for a new ModelAction */
  97 modelclock_t ModelChecker::get_next_seq_num()
  98 {
  99         return ++priv->used_sequence_numbers;
 100 }
 101
 102 /**
 103  * @brief Choose the next thread to execute.
 104  *
 105  * This function chooses the next thread that should execute. It can force the
 106  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 107  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 108  * The model-checker may have no preference regarding the next thread (i.e.,
 109  * when exploring a new execution ordering), in which case this will return
 110  * NULL.
 111  * @param curr The current ModelAction. This action might guide the choice of
 112  * next thread.
 113  * @return The next thread to run. If the model-checker has no preference, NULL.
 114  */
 115 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 116 {
 117         thread_id_t tid;
 118
 119         /* Do not split atomic actions. */
 120         if (curr->is_rmwr())
 121                 return thread_current();
 122         /* The THREAD_CREATE action points to the created Thread */
 123         else if (curr->get_type() == THREAD_CREATE)
 124                 return (Thread *)curr->get_location();
 125
 126         /* Have we completed exploring the preselected path? */
 127         if (diverge == NULL)
 128                 return NULL;
 129
 130         /* Else, we are trying to replay an execution */
 131         ModelAction *next = node_stack->get_next()->get_action();
 132
 133         if (next == diverge) {
 134                 Node *nextnode = next->get_node();
 135                 /* Reached divergence point */
 136                 if (nextnode->increment_promise()) {
 137                         /* The next node will try to satisfy a different set of promises. */
 138                         tid = next->get_tid();
 139                         node_stack->pop_restofstack(2);
 140                 } else if (nextnode->increment_read_from()) {
 141                         /* The next node will read from a different value. */
 142                         tid = next->get_tid();
 143                         node_stack->pop_restofstack(2);
 144                 } else if (nextnode->increment_future_value()) {
 145                         /* The next node will try to read from a different future value. */
 146                         tid = next->get_tid();
 147                         node_stack->pop_restofstack(2);
 148                 } else {
 149                         /* Make a different thread execute for next step */
 150                         Node *node = nextnode->get_parent();
 151                         tid = node->get_next_backtrack();
 152                         node_stack->pop_restofstack(1);
 153                 }
 154                 DEBUG("*** Divergence point ***\n");
 155                 diverge = NULL;
 156         } else {
 157                 tid = next->get_tid();
 158         }
 159         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 160         ASSERT(tid != THREAD_ID_T_NONE);
 161         return thread_map->get(id_to_int(tid));
 162 }
 163
 164 /**
 165  * Queries the model-checker for more executions to explore and, if one
 166  * exists, resets the model-checker state to execute a new execution.
 167  *
 168  * @return If there are more executions to explore, return true. Otherwise,
 169  * return false.
 170  */
 171 bool ModelChecker::next_execution()
 172 {
 173         DBG();
 174
 175         num_executions++;
 176
 177         if (isfinalfeasible() || DBG_ENABLED())
 178                 print_summary();
 179
 180         if ((diverge = get_next_backtrack()) == NULL)
 181                 return false;
 182
 183         if (DBG_ENABLED()) {
 184                 printf("Next execution will diverge at:\n");
 185                 diverge->print();
 186         }
 187
 188         reset_to_initial_state();
 189         return true;
 190 }
 191
 192 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 193 {
 194         action_type type = act->get_type();
 195
 196         switch (type) {
 197                 case ATOMIC_READ:
 198                 case ATOMIC_WRITE:
 199                 case ATOMIC_RMW:
 200                         break;
 201                 default:
 202                         return NULL;
 203         }
 204         /* linear search: from most recent to oldest */
 205         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 206         action_list_t::reverse_iterator rit;
 207         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 208                 ModelAction *prev = *rit;
 209                 if (act->is_synchronizing(prev))
 210                         return prev;
 211         }
 212         return NULL;
 213 }
 214
 215 void ModelChecker::set_backtracking(ModelAction *act)
 216 {
 217         ModelAction *prev;
 218         Node *node;
 219         Thread *t = get_thread(act);
 220
 221         prev = get_last_conflict(act);
 222         if (prev == NULL)
 223                 return;
 224
 225         node = prev->get_node()->get_parent();
 226
 227         while (!node->is_enabled(t))
 228                 t = t->get_parent();
 229
 230         /* Check if this has been explored already */
 231         if (node->has_been_explored(t->get_id()))
 232                 return;
 233
 234         /* Cache the latest backtracking point */
 235         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 236                 priv->next_backtrack = prev;
 237
 238         /* If this is a new backtracking point, mark the tree */
 239         if (!node->set_backtrack(t->get_id()))
 240                 return;
 241         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 242                         prev->get_tid(), t->get_id());
 243         if (DBG_ENABLED()) {
 244                 prev->print();
 245                 act->print();
 246         }
 247 }
 248
 249 /**
 250  * Returns last backtracking point. The model checker will explore a different
 251  * path for this point in the next execution.
 252  * @return The ModelAction at which the next execution should diverge.
 253  */
 254 ModelAction * ModelChecker::get_next_backtrack()
 255 {
 256         ModelAction *next = priv->next_backtrack;
 257         priv->next_backtrack = NULL;
 258         return next;
 259 }
 260
 261 /**
 262  * Processes a read or rmw model action.
 263  * @param curr is the read model action to process.
 264  * @param th is the thread
 265  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 266  * @return True if processing this read updates the mo_graph.
 267  */
 268
 269 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
 270         uint64_t value;
 271         bool updated=false;
 272         while(true) {
 273                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 274                 if (reads_from != NULL) {
 275                         mo_graph->startChanges();
 276
 277                         value = reads_from->get_value();
 278                                 /* Assign reads_from, perform release/acquire synchronization */
 279                         curr->read_from(reads_from);
 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                         mo_graph->commitChanges();
 293                         updated |= r_status;
 294                 } else if (!second_part_of_rmw) {
 295                         /* Read from future value */
 296                         value = curr->get_node()->get_future_value();
 297                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 298                         curr->read_from(NULL);
 299                         Promise *valuepromise = new Promise(curr, value, expiration);
 300                         promises->push_back(valuepromise);
 301                 }
 302                 th->set_return_value(value);
 303                 return updated;
 304         }
 305 }
 306
 307 /**
 308  * This is the heart of the model checker routine. It performs model-checking
 309  * actions corresponding to a given "current action." Among other processes, it
 310  * calculates reads-from relationships, updates synchronization clock vectors,
 311  * forms a memory_order constraints graph, and handles replay/backtrack
 312  * execution when running permutations of previously-observed executions.
 313  *
 314  * @param curr The current action to process
 315  * @return The next Thread that must be executed. May be NULL if ModelChecker
 316  * makes no choice (e.g., according to replay execution, combining RMW actions,
 317  * etc.)
 318  */
 319 Thread * ModelChecker::check_current_action(ModelAction *curr)
 320 {
 321         bool second_part_of_rmw = false;
 322
 323         ASSERT(curr);
 324
 325         if (curr->is_rmwc() || curr->is_rmw()) {
 326                 ModelAction *tmp = process_rmw(curr);
 327                 second_part_of_rmw = true;
 328                 delete curr;
 329                 curr = tmp;
 330                 compute_promises(curr);
 331         } else {
 332                 ModelAction *tmp = node_stack->explore_action(curr);
 333                 if (tmp) {
 334                         /* Discard duplicate ModelAction; use action from NodeStack */
 335                         /* First restore type and order in case of RMW operation */
 336                         if (curr->is_rmwr())
 337                                 tmp->copy_typeandorder(curr);
 338
 339                         /* If we have diverged, we need to reset the clock vector. */
 340                         if (diverge == NULL)
 341                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 342
 343                         delete curr;
 344                         curr = tmp;
 345                 } else {
 346                         /*
 347                          * Perform one-time actions when pushing new ModelAction onto
 348                          * NodeStack
 349                          */
 350                         curr->create_cv(get_parent_action(curr->get_tid()));
 351                         /* Build may_read_from set */
 352                         if (curr->is_read())
 353                                 build_reads_from_past(curr);
 354                         if (curr->is_write())
 355                                 compute_promises(curr);
 356                 }
 357         }
 358
 359         /* Thread specific actions */
 360         switch(curr->get_type()) {
 361         case THREAD_CREATE: {
 362                 Thread *th = (Thread *)curr->get_location();
 363                 th->set_creation(curr);
 364                 break;
 365         }
 366         case THREAD_JOIN: {
 367                 Thread *waiting, *blocking;
 368                 waiting = get_thread(curr);
 369                 blocking = (Thread *)curr->get_location();
 370                 if (!blocking->is_complete()) {
 371                         blocking->push_wait_list(curr);
 372                         scheduler->sleep(waiting);
 373                 }
 374                 break;
 375         }
 376         case THREAD_FINISH: {
 377                 Thread *th = get_thread(curr);
 378                 while (!th->wait_list_empty()) {
 379                         ModelAction *act = th->pop_wait_list();
 380                         Thread *wake = get_thread(act);
 381                         scheduler->wake(wake);
 382                 }
 383                 th->complete();
 384                 break;
 385         }
 386         case THREAD_START: {
 387                 check_promises(NULL, curr->get_cv());
 388                 break;
 389         }
 390         default:
 391                 break;
 392         }
 393
 394         Thread *th = get_thread(curr);
 395
 396         bool updated = false;
 397         if (curr->is_read()) {
 398                 updated=process_read(curr, th, second_part_of_rmw);
 399         }
 400
 401         if (curr->is_write()) {
 402                 bool updated_mod_order=w_modification_order(curr);
 403                 bool updated_promises=resolve_promises(curr);
 404                 updated=updated_mod_order|updated_promises;
 405
 406                 mo_graph->commitChanges();
 407                 th->set_return_value(VALUE_NONE);
 408         }
 409
 410         if (updated)
 411                 resolve_release_sequences(curr->get_location());
 412
 413         /* Add action to list.  */
 414         if (!second_part_of_rmw)
 415                 add_action_to_lists(curr);
 416
 417         check_curr_backtracking(curr);
 418
 419         set_backtracking(curr);
 420
 421         return get_next_thread(curr);
 422 }
 423
 424 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 425         Node *currnode = curr->get_node();
 426         Node *parnode = currnode->get_parent();
 427
 428         if ((!parnode->backtrack_empty() ||
 429                          !currnode->read_from_empty() ||
 430                          !currnode->future_value_empty() ||
 431                          !currnode->promise_empty())
 432                         && (!priv->next_backtrack ||
 433                                         *curr > *priv->next_backtrack)) {
 434                 priv->next_backtrack = curr;
 435         }
 436 }
 437
 438
 439 bool ModelChecker::promises_expired() {
 440         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 441                 Promise *promise = (*promises)[promise_index];
 442                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 443                         return true;
 444                 }
 445         }
 446         return false;
 447 }
 448
 449 /** @returns whether the current partial trace must be a prefix of a
 450  * feasible trace. */
 451 bool ModelChecker::isfeasibleprefix() {
 452         return promises->size() == 0 && *lazy_sync_size == 0;
 453 }
 454
 455 /** @returns whether the current partial trace is feasible. */
 456 bool ModelChecker::isfeasible() {
 457         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 458 }
 459
 460 /** @returns whether the current partial trace is feasible. */
 461 bool ModelChecker::isfeasibleotherthanRMW() {
 462         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 463 }
 464
 465 /** Returns whether the current completed trace is feasible. */
 466 bool ModelChecker::isfinalfeasible() {
 467         return isfeasible() && promises->size() == 0;
 468 }
 469
 470 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 471 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 472         int tid = id_to_int(act->get_tid());
 473         ModelAction *lastread = get_last_action(tid);
 474         lastread->process_rmw(act);
 475         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 476                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 477                 mo_graph->commitChanges();
 478         }
 479         return lastread;
 480 }
 481
 482 /**
 483  * Checks whether a thread has read from the same write for too many times
 484  * without seeing the effects of a later write.
 485  *
 486  * Basic idea:
 487  * 1) there must a different write that we could read from that would satisfy the modification order,
 488  * 2) we must have read from the same value in excess of maxreads times, and
 489  * 3) that other write must have been in the reads_from set for maxreads times.
 490  *
 491  * If so, we decide that the execution is no longer feasible.
 492  */
 493 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 494         if (params.maxreads != 0) {
 495                 if (curr->get_node()->get_read_from_size() <= 1)
 496                         return;
 497
 498                 //Must make sure that execution is currently feasible...  We could
 499                 //accidentally clear by rolling back
 500                 if (!isfeasible())
 501                         return;
 502
 503                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 504                 int tid = id_to_int(curr->get_tid());
 505
 506                 /* Skip checks */
 507                 if ((int)thrd_lists->size() <= tid)
 508                         return;
 509
 510                 action_list_t *list = &(*thrd_lists)[tid];
 511
 512                 action_list_t::reverse_iterator rit = list->rbegin();
 513                 /* Skip past curr */
 514                 if (already_added) {
 515                         for (; (*rit) != curr; rit++)
 516                                 ;
 517                         /* go past curr now */
 518                         rit++;
 519                 }
 520
 521                 action_list_t::reverse_iterator ritcopy=rit;
 522                 //See if we have enough reads from the same value
 523                 int count=0;
 524                 for (; count < params.maxreads; rit++,count++) {
 525                         if (rit==list->rend())
 526                                 return;
 527                         ModelAction *act = *rit;
 528                         if (!act->is_read())
 529                                 return;
 530                         if (act->get_reads_from() != curr->get_reads_from())
 531                                 return;
 532                         if (act->get_node()->get_read_from_size() <= 1)
 533                                 return;
 534                 }
 535
 536                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 537                         //Get write
 538                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 539                         //Need a different write
 540                         if (write==curr->get_reads_from())
 541                                 continue;
 542
 543                         /* Test to see whether this is a feasible write to read from*/
 544                         mo_graph->startChanges();
 545                         r_modification_order(curr, write);
 546                         bool feasiblereadfrom=isfeasible();
 547                         mo_graph->rollbackChanges();
 548
 549                         if (!feasiblereadfrom)
 550                                 continue;
 551                         rit=ritcopy;
 552
 553                         bool feasiblewrite=true;
 554                         //new we need to see if this write works for everyone
 555
 556                         for (int loop=count;loop>0;loop--,rit++) {
 557                                 ModelAction *act=*rit;
 558                                 bool foundvalue=false;
 559                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 560                                         if (act->get_node()->get_read_from_at(i)==write) {
 561                                                 foundvalue=true;
 562                                                 break;
 563                                         }
 564                                 }
 565                                 if (!foundvalue) {
 566                                         feasiblewrite=false;
 567                                         break;
 568                                 }
 569                         }
 570                         if (feasiblewrite) {
 571                                 too_many_reads = true;
 572                                 return;
 573                         }
 574                 }
 575         }
 576 }
 577
 578 /**
 579  * Updates the mo_graph with the constraints imposed from the current read.
 580  * @param curr The current action. Must be a read.
 581  * @param rf The action that curr reads from. Must be a write.
 582  * @return True if modification order edges were added; false otherwise
 583  */
 584 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 585 {
 586         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 587         unsigned int i;
 588         bool added = false;
 589         ASSERT(curr->is_read());
 590
 591         /* Iterate over all threads */
 592         for (i = 0; i < thrd_lists->size(); i++) {
 593                 /* Iterate over actions in thread, starting from most recent */
 594                 action_list_t *list = &(*thrd_lists)[i];
 595                 action_list_t::reverse_iterator rit;
 596                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 597                         ModelAction *act = *rit;
 598
 599                         /* Include at most one act per-thread that "happens before" curr */
 600                         if (act->happens_before(curr)) {
 601                                 if (act->is_read()) {
 602                                         const ModelAction *prevreadfrom = act->get_reads_from();
 603                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 604                                                 mo_graph->addEdge(prevreadfrom, rf);
 605                                                 added = true;
 606                                         }
 607                                 } else if (rf != act) {
 608                                         mo_graph->addEdge(act, rf);
 609                                         added = true;
 610                                 }
 611                                 break;
 612                         }
 613                 }
 614         }
 615
 616         return added;
 617 }
 618
 619 /** Updates the mo_graph with the constraints imposed from the current read. */
 620 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 621 {
 622         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 623         unsigned int i;
 624         ASSERT(curr->is_read());
 625
 626         /* Iterate over all threads */
 627         for (i = 0; i < thrd_lists->size(); i++) {
 628                 /* Iterate over actions in thread, starting from most recent */
 629                 action_list_t *list = &(*thrd_lists)[i];
 630                 action_list_t::reverse_iterator rit;
 631                 ModelAction *lastact = NULL;
 632
 633                 /* Find last action that happens after curr */
 634                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 635                         ModelAction *act = *rit;
 636                         if (curr->happens_before(act)) {
 637                                 lastact = act;
 638                         } else
 639                                 break;
 640                 }
 641
 642                         /* Include at most one act per-thread that "happens before" curr */
 643                 if (lastact != NULL) {
 644                         if (lastact->is_read()) {
 645                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 646                                 if (postreadfrom != NULL&&rf != postreadfrom)
 647                                         mo_graph->addEdge(rf, postreadfrom);
 648                         } else if (rf != lastact) {
 649                                 mo_graph->addEdge(rf, lastact);
 650                         }
 651                         break;
 652                 }
 653         }
 654 }
 655
 656 /**
 657  * Updates the mo_graph with the constraints imposed from the current write.
 658  * @param curr The current action. Must be a write.
 659  * @return True if modification order edges were added; false otherwise
 660  */
 661 bool ModelChecker::w_modification_order(ModelAction *curr)
 662 {
 663         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 664         unsigned int i;
 665         bool added = false;
 666         ASSERT(curr->is_write());
 667
 668         if (curr->is_seqcst()) {
 669                 /* We have to at least see the last sequentially consistent write,
 670                          so we are initialized. */
 671                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 672                 if (last_seq_cst != NULL) {
 673                         mo_graph->addEdge(last_seq_cst, curr);
 674                         added = true;
 675                 }
 676         }
 677
 678         /* Iterate over all threads */
 679         for (i = 0; i < thrd_lists->size(); i++) {
 680                 /* Iterate over actions in thread, starting from most recent */
 681                 action_list_t *list = &(*thrd_lists)[i];
 682                 action_list_t::reverse_iterator rit;
 683                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 684                         ModelAction *act = *rit;
 685
 686                         /* Include at most one act per-thread that "happens before" curr */
 687                         if (act->happens_before(curr)) {
 688                                 /*
 689                                  * Note: if act is RMW, just add edge:
 690                                  *   act --mo--> curr
 691                                  * The following edge should be handled elsewhere:
 692                                  *   readfrom(act) --mo--> act
 693                                  */
 694                                 if (act->is_write()) {
 695                                         //RMW shouldn't have an edge to themselves
 696                                         if (act!=curr)
 697                                                 mo_graph->addEdge(act, curr);
 698                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 699                                         mo_graph->addEdge(act->get_reads_from(), curr);
 700                                 added = true;
 701                                 break;
 702                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 703                                                      !act->same_thread(curr)) {
 704                                 /* We have an action that:
 705                                    (1) did not happen before us
 706                                    (2) is a read and we are a write
 707                                    (3) cannot synchronize with us
 708                                    (4) is in a different thread
 709                                    =>
 710                                    that read could potentially read from our write.
 711                                  */
 712                                 if (thin_air_constraint_may_allow(curr, act)) {
 713                                         if (isfeasible() ||
 714                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 715                                                 if (act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
 716                                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 717                                                         priv->next_backtrack = act;
 718                                         }
 719                                 }
 720                         }
 721                 }
 722         }
 723
 724         return added;
 725 }
 726
 727 /** Arbitrary reads from the future are not allowed.  Section 29.3
 728  * part 9 places some constraints.  This method checks one result of constraint
 729  * constraint.  Others require compiler support. */
 730
 731 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 732         if (!writer->is_rmw())
 733                 return true;
 734
 735         if (!reader->is_rmw())
 736                 return true;
 737
 738         for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
 739                 if (search==reader)
 740                         return false;
 741                 if (search->get_tid()==reader->get_tid()&&
 742                                 search->happens_before(reader))
 743                         break;
 744         }
 745
 746         return true;
 747 }
 748
 749
 750 /**
 751  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 752  * The ModelAction under consideration is expected to be taking part in
 753  * release/acquire synchronization as an object of the "reads from" relation.
 754  * Note that this can only provide release sequence support for RMW chains
 755  * which do not read from the future, as those actions cannot be traced until
 756  * their "promise" is fulfilled. Similarly, we may not even establish the
 757  * presence of a release sequence with certainty, as some modification order
 758  * constraints may be decided further in the future. Thus, this function
 759  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 760  * and a boolean representing certainty.
 761  *
 762  * @todo Finish lazy updating, when promises are fulfilled in the future
 763  * @param rf The action that might be part of a release sequence. Must be a
 764  * write.
 765  * @param release_heads A pass-by-reference style return parameter.  After
 766  * execution of this function, release_heads will contain the heads of all the
 767  * relevant release sequences, if any exists
 768  * @return true, if the ModelChecker is certain that release_heads is complete;
 769  * false otherwise
 770  */
 771 bool ModelChecker::release_seq_head(const ModelAction *rf,
 772                 std::vector<const ModelAction *> *release_heads) const
 773 {
 774         ASSERT(rf->is_write());
 775         if (!rf) {
 776                 /* read from future: need to settle this later */
 777                 return false; /* incomplete */
 778         }
 779         if (rf->is_release())
 780                 release_heads->push_back(rf);
 781         if (rf->is_rmw()) {
 782                 /* We need a RMW action that is both an acquire and release to stop */
 783                 /** @todo Need to be smarter here...  In the linux lock
 784                  * example, this will run to the beginning of the program for
 785                  * every acquire. */
 786                 if (rf->is_acquire() && rf->is_release())
 787                         return true; /* complete */
 788                 return release_seq_head(rf->get_reads_from(), release_heads);
 789         }
 790         if (rf->is_release())
 791                 return true; /* complete */
 792
 793         /* else relaxed write; check modification order for contiguous subsequence
 794          * -> rf must be same thread as release */
 795         int tid = id_to_int(rf->get_tid());
 796         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 797         action_list_t *list = &(*thrd_lists)[tid];
 798         action_list_t::const_reverse_iterator rit;
 799
 800         /* Find rf in the thread list */
 801         rit = std::find(list->rbegin(), list->rend(), rf);
 802         ASSERT(rit != list->rend());
 803
 804         /* Find the last write/release */
 805         for (; rit != list->rend(); rit++)
 806                 if ((*rit)->is_release())
 807                         break;
 808         if (rit == list->rend()) {
 809                 /* No write-release in this thread */
 810                 return true; /* complete */
 811         }
 812         ModelAction *release = *rit;
 813
 814         ASSERT(rf->same_thread(release));
 815
 816         bool certain = true;
 817         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 818                 if (id_to_int(rf->get_tid()) == (int)i)
 819                         continue;
 820                 list = &(*thrd_lists)[i];
 821
 822                 /* Can we ensure no future writes from this thread may break
 823                  * the release seq? */
 824                 bool future_ordered = false;
 825
 826                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 827                         const ModelAction *act = *rit;
 828                         if (!act->is_write())
 829                                 continue;
 830                         /* Reach synchronization -> this thread is complete */
 831                         if (act->happens_before(release))
 832                                 break;
 833                         if (rf->happens_before(act)) {
 834                                 future_ordered = true;
 835                                 continue;
 836                         }
 837
 838                         /* Check modification order */
 839                         if (mo_graph->checkReachable(rf, act)) {
 840                                 /* rf --mo--> act */
 841                                 future_ordered = true;
 842                                 continue;
 843                         }
 844                         if (mo_graph->checkReachable(act, release))
 845                                 /* act --mo--> release */
 846                                 break;
 847                         if (mo_graph->checkReachable(release, act) &&
 848                                       mo_graph->checkReachable(act, rf)) {
 849                                 /* release --mo-> act --mo--> rf */
 850                                 return true; /* complete */
 851                         }
 852                         certain = false;
 853                 }
 854                 if (!future_ordered)
 855                         return false; /* This thread is uncertain */
 856         }
 857
 858         if (certain)
 859                 release_heads->push_back(release);
 860         return certain;
 861 }
 862
 863 /**
 864  * A public interface for getting the release sequence head(s) with which a
 865  * given ModelAction must synchronize. This function only returns a non-empty
 866  * result when it can locate a release sequence head with certainty. Otherwise,
 867  * it may mark the internal state of the ModelChecker so that it will handle
 868  * the release sequence at a later time, causing @a act to update its
 869  * synchronization at some later point in execution.
 870  * @param act The 'acquire' action that may read from a release sequence
 871  * @param release_heads A pass-by-reference return parameter. Will be filled
 872  * with the head(s) of the release sequence(s), if they exists with certainty.
 873  * @see ModelChecker::release_seq_head
 874  */
 875 void ModelChecker::get_release_seq_heads(ModelAction *act,
 876                 std::vector<const ModelAction *> *release_heads)
 877 {
 878         const ModelAction *rf = act->get_reads_from();
 879         bool complete;
 880         complete = release_seq_head(rf, release_heads);
 881         if (!complete) {
 882                 /* add act to 'lazy checking' list */
 883                 std::list<ModelAction *> *list;
 884                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 885                 list->push_back(act);
 886                 (*lazy_sync_size)++;
 887         }
 888 }
 889
 890 /**
 891  * Attempt to resolve all stashed operations that might synchronize with a
 892  * release sequence for a given location. This implements the "lazy" portion of
 893  * determining whether or not a release sequence was contiguous, since not all
 894  * modification order information is present at the time an action occurs.
 895  *
 896  * @param location The location/object that should be checked for release
 897  * sequence resolutions
 898  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 899  */
 900 bool ModelChecker::resolve_release_sequences(void *location)
 901 {
 902         std::list<ModelAction *> *list;
 903         list = lazy_sync_with_release->getptr(location);
 904         if (!list)
 905                 return false;
 906
 907         bool updated = false;
 908         std::list<ModelAction *>::iterator it = list->begin();
 909         while (it != list->end()) {
 910                 ModelAction *act = *it;
 911                 const ModelAction *rf = act->get_reads_from();
 912                 std::vector<const ModelAction *> release_heads;
 913                 bool complete;
 914                 complete = release_seq_head(rf, &release_heads);
 915                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 916                         if (!act->has_synchronized_with(release_heads[i])) {
 917                                 updated = true;
 918                                 act->synchronize_with(release_heads[i]);
 919                         }
 920                 }
 921
 922                 if (updated) {
 923                         /* propagate synchronization to later actions */
 924                         action_list_t::reverse_iterator it = action_trace->rbegin();
 925                         while ((*it) != act) {
 926                                 ModelAction *propagate = *it;
 927                                 if (act->happens_before(propagate))
 928                                         /** @todo new mo_graph edges along with
 929                                          * this synchronization? */
 930                                         propagate->synchronize_with(act);
 931                         }
 932                 }
 933                 if (complete) {
 934                         it = list->erase(it);
 935                         (*lazy_sync_size)--;
 936                 } else
 937                         it++;
 938         }
 939
 940         // If we resolved promises or data races, see if we have realized a data race.
 941         if (checkDataRaces()) {
 942                 set_assert();
 943         }
 944
 945         return updated;
 946 }
 947
 948 /**
 949  * Performs various bookkeeping operations for the current ModelAction. For
 950  * instance, adds action to the per-object, per-thread action vector and to the
 951  * action trace list of all thread actions.
 952  *
 953  * @param act is the ModelAction to add.
 954  */
 955 void ModelChecker::add_action_to_lists(ModelAction *act)
 956 {
 957         int tid = id_to_int(act->get_tid());
 958         action_trace->push_back(act);
 959
 960         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 961
 962         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 963         if (tid >= (int)vec->size())
 964                 vec->resize(priv->next_thread_id);
 965         (*vec)[tid].push_back(act);
 966
 967         if ((int)thrd_last_action->size() <= tid)
 968                 thrd_last_action->resize(get_num_threads());
 969         (*thrd_last_action)[tid] = act;
 970 }
 971
 972 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 973 {
 974         int nthreads = get_num_threads();
 975         if ((int)thrd_last_action->size() < nthreads)
 976                 thrd_last_action->resize(nthreads);
 977         return (*thrd_last_action)[id_to_int(tid)];
 978 }
 979
 980 /**
 981  * Gets the last memory_order_seq_cst action (in the total global sequence)
 982  * performed on a particular object (i.e., memory location).
 983  * @param location The object location to check
 984  * @return The last seq_cst action performed
 985  */
 986 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 987 {
 988         action_list_t *list = obj_map->get_safe_ptr(location);
 989         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 990         action_list_t::reverse_iterator rit;
 991         for (rit = list->rbegin(); rit != list->rend(); rit++)
 992                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 993                         return *rit;
 994         return NULL;
 995 }
 996
 997 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 998 {
 999         ModelAction *parent = get_last_action(tid);
1000         if (!parent)
1001                 parent = get_thread(tid)->get_creation();
1002         return parent;
1003 }
1004
1005 /**
1006  * Returns the clock vector for a given thread.
1007  * @param tid The thread whose clock vector we want
1008  * @return Desired clock vector
1009  */
1010 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1011 {
1012         return get_parent_action(tid)->get_cv();
1013 }
1014
1015 /**
1016  * Resolve a set of Promises with a current write. The set is provided in the
1017  * Node corresponding to @a write.
1018  * @param write The ModelAction that is fulfilling Promises
1019  * @return True if promises were resolved; false otherwise
1020  */
1021 bool ModelChecker::resolve_promises(ModelAction *write)
1022 {
1023         bool resolved = false;
1024
1025         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1026                 Promise *promise = (*promises)[promise_index];
1027                 if (write->get_node()->get_promise(i)) {
1028                         ModelAction *read = promise->get_action();
1029                         read->read_from(write);
1030                         if (read->is_rmw()) {
1031                                 mo_graph->addRMWEdge(write, read);
1032                         }
1033                         r_modification_order(read, write);
1034                         post_r_modification_order(read, write);
1035                         promises->erase(promises->begin() + promise_index);
1036                         resolved = true;
1037                 } else
1038                         promise_index++;
1039         }
1040         return resolved;
1041 }
1042
1043 /**
1044  * Compute the set of promises that could potentially be satisfied by this
1045  * action. Note that the set computation actually appears in the Node, not in
1046  * ModelChecker.
1047  * @param curr The ModelAction that may satisfy promises
1048  */
1049 void ModelChecker::compute_promises(ModelAction *curr)
1050 {
1051         for (unsigned int i = 0; i < promises->size(); i++) {
1052                 Promise *promise = (*promises)[i];
1053                 const ModelAction *act = promise->get_action();
1054                 if (!act->happens_before(curr) &&
1055                                 act->is_read() &&
1056                                 !act->is_synchronizing(curr) &&
1057                                 !act->same_thread(curr) &&
1058                                 promise->get_value() == curr->get_value()) {
1059                         curr->get_node()->set_promise(i);
1060                 }
1061         }
1062 }
1063
1064 /** Checks promises in response to change in ClockVector Threads. */
1065 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1066 {
1067         for (unsigned int i = 0; i < promises->size(); i++) {
1068                 Promise *promise = (*promises)[i];
1069                 const ModelAction *act = promise->get_action();
1070                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1071                                 merge_cv->synchronized_since(act)) {
1072                         //This thread is no longer able to send values back to satisfy the promise
1073                         int num_synchronized_threads = promise->increment_threads();
1074                         if (num_synchronized_threads == get_num_threads()) {
1075                                 //Promise has failed
1076                                 failed_promise = true;
1077                                 return;
1078                         }
1079                 }
1080         }
1081 }
1082
1083 /**
1084  * Build up an initial set of all past writes that this 'read' action may read
1085  * from. This set is determined by the clock vector's "happens before"
1086  * relationship.
1087  * @param curr is the current ModelAction that we are exploring; it must be a
1088  * 'read' operation.
1089  */
1090 void ModelChecker::build_reads_from_past(ModelAction *curr)
1091 {
1092         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1093         unsigned int i;
1094         ASSERT(curr->is_read());
1095
1096         ModelAction *last_seq_cst = NULL;
1097
1098         /* Track whether this object has been initialized */
1099         bool initialized = false;
1100
1101         if (curr->is_seqcst()) {
1102                 last_seq_cst = get_last_seq_cst(curr->get_location());
1103                 /* We have to at least see the last sequentially consistent write,
1104                          so we are initialized. */
1105                 if (last_seq_cst != NULL)
1106                         initialized = true;
1107         }
1108
1109         /* Iterate over all threads */
1110         for (i = 0; i < thrd_lists->size(); i++) {
1111                 /* Iterate over actions in thread, starting from most recent */
1112                 action_list_t *list = &(*thrd_lists)[i];
1113                 action_list_t::reverse_iterator rit;
1114                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1115                         ModelAction *act = *rit;
1116
1117                         /* Only consider 'write' actions */
1118                         if (!act->is_write())
1119                                 continue;
1120
1121                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1122                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1123                                 DEBUG("Adding action to may_read_from:\n");
1124                                 if (DBG_ENABLED()) {
1125                                         act->print();
1126                                         curr->print();
1127                                 }
1128                                 curr->get_node()->add_read_from(act);
1129                         }
1130
1131                         /* Include at most one act per-thread that "happens before" curr */
1132                         if (act->happens_before(curr)) {
1133                                 initialized = true;
1134                                 break;
1135                         }
1136                 }
1137         }
1138
1139         if (!initialized) {
1140                 /** @todo Need a more informative way of reporting errors. */
1141                 printf("ERROR: may read from uninitialized atomic\n");
1142         }
1143
1144         if (DBG_ENABLED() || !initialized) {
1145                 printf("Reached read action:\n");
1146                 curr->print();
1147                 printf("Printing may_read_from\n");
1148                 curr->get_node()->print_may_read_from();
1149                 printf("End printing may_read_from\n");
1150         }
1151
1152         ASSERT(initialized);
1153 }
1154
1155 static void print_list(action_list_t *list)
1156 {
1157         action_list_t::iterator it;
1158
1159         printf("---------------------------------------------------------------------\n");
1160         printf("Trace:\n");
1161
1162         for (it = list->begin(); it != list->end(); it++) {
1163                 (*it)->print();
1164         }
1165         printf("---------------------------------------------------------------------\n");
1166 }
1167
1168 void ModelChecker::print_summary()
1169 {
1170         printf("\n");
1171         printf("Number of executions: %d\n", num_executions);
1172         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1173
1174         scheduler->print();
1175
1176         if (!isfinalfeasible())
1177                 printf("INFEASIBLE EXECUTION!\n");
1178         print_list(action_trace);
1179         printf("\n");
1180 }
1181
1182 /**
1183  * Add a Thread to the system for the first time. Should only be called once
1184  * per thread.
1185  * @param t The Thread to add
1186  */
1187 void ModelChecker::add_thread(Thread *t)
1188 {
1189         thread_map->put(id_to_int(t->get_id()), t);
1190         scheduler->add_thread(t);
1191 }
1192
1193 void ModelChecker::remove_thread(Thread *t)
1194 {
1195         scheduler->remove_thread(t);
1196 }
1197
1198 /**
1199  * Switch from a user-context to the "master thread" context (a.k.a. system
1200  * context). This switch is made with the intention of exploring a particular
1201  * model-checking action (described by a ModelAction object). Must be called
1202  * from a user-thread context.
1203  * @param act The current action that will be explored. Must not be NULL.
1204  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1205  */
1206 int ModelChecker::switch_to_master(ModelAction *act)
1207 {
1208         DBG();
1209         Thread *old = thread_current();
1210         set_current_action(act);
1211         old->set_state(THREAD_READY);
1212         return Thread::swap(old, &system_context);
1213 }
1214
1215 /**
1216  * Takes the next step in the execution, if possible.
1217  * @return Returns true (success) if a step was taken and false otherwise.
1218  */
1219 bool ModelChecker::take_step() {
1220         Thread *curr, *next;
1221
1222         if (has_asserted())
1223                 return false;
1224
1225         curr = thread_current();
1226         if (curr) {
1227                 if (curr->get_state() == THREAD_READY) {
1228                         ASSERT(priv->current_action);
1229
1230                         priv->nextThread = check_current_action(priv->current_action);
1231                         priv->current_action = NULL;
1232                         if (!curr->is_blocked() && !curr->is_complete())
1233                                 scheduler->add_thread(curr);
1234                 } else {
1235                         ASSERT(false);
1236                 }
1237         }
1238         next = scheduler->next_thread(priv->nextThread);
1239
1240         /* Infeasible -> don't take any more steps */
1241         if (!isfeasible())
1242                 return false;
1243
1244         if (next)
1245                 next->set_state(THREAD_RUNNING);
1246         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1247
1248         /* next == NULL -> don't take any more steps */
1249         if (!next)
1250                 return false;
1251         /* Return false only if swap fails with an error */
1252         return (Thread::swap(&system_context, next) == 0);
1253 }
1254
1255 /** Runs the current execution until threre are no more steps to take. */
1256 void ModelChecker::finish_execution() {
1257         DBG();
1258
1259         while (take_step());
1260 }