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