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 {
 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->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 458 }
 459
 460 /** Returns whether the current completed trace is feasible. */
 461 bool ModelChecker::isfinalfeasible() {
 462         return isfeasible() && promises->size() == 0;
 463 }
 464
 465 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 466 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 467         int tid = id_to_int(act->get_tid());
 468         ModelAction *lastread = get_last_action(tid);
 469         lastread->process_rmw(act);
 470         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 471                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 472                 mo_graph->commitChanges();
 473         }
 474         return lastread;
 475 }
 476
 477 /**
 478  * Checks whether a thread has read from the same write for too many times
 479  * without seeing the effects of a later write.
 480  *
 481  * Basic idea:
 482  * 1) there must a different write that we could read from that would satisfy the modification order,
 483  * 2) we must have read from the same value in excess of maxreads times, and
 484  * 3) that other write must have been in the reads_from set for maxreads times.
 485  *
 486  * If so, we decide that the execution is no longer feasible.
 487  */
 488 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 489         if (params.maxreads != 0) {
 490                 if (curr->get_node()->get_read_from_size() <= 1)
 491                         return;
 492
 493                 //Must make sure that execution is currently feasible...  We could
 494                 //accidentally clear by rolling back
 495                 if (!isfeasible())
 496                         return;
 497
 498                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 499                 int tid = id_to_int(curr->get_tid());
 500
 501                 /* Skip checks */
 502                 if ((int)thrd_lists->size() <= tid)
 503                         return;
 504
 505                 action_list_t *list = &(*thrd_lists)[tid];
 506
 507                 action_list_t::reverse_iterator rit = list->rbegin();
 508                 /* Skip past curr */
 509                 if (already_added) {
 510                         for (; (*rit) != curr; rit++)
 511                                 ;
 512                         /* go past curr now */
 513                         rit++;
 514                 }
 515
 516                 action_list_t::reverse_iterator ritcopy=rit;
 517                 //See if we have enough reads from the same value
 518                 int count=0;
 519                 for (; count < params.maxreads; rit++,count++) {
 520                         if (rit==list->rend())
 521                                 return;
 522                         ModelAction *act = *rit;
 523                         if (!act->is_read())
 524                                 return;
 525                         if (act->get_reads_from() != curr->get_reads_from())
 526                                 return;
 527                         if (act->get_node()->get_read_from_size() <= 1)
 528                                 return;
 529                 }
 530
 531                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 532                         //Get write
 533                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 534                         //Need a different write
 535                         if (write==curr->get_reads_from())
 536                                 continue;
 537
 538                         /* Test to see whether this is a feasible write to read from*/
 539                         mo_graph->startChanges();
 540                         r_modification_order(curr, write);
 541                         bool feasiblereadfrom=isfeasible();
 542                         mo_graph->rollbackChanges();
 543
 544                         if (!feasiblereadfrom)
 545                                 continue;
 546                         rit=ritcopy;
 547
 548                         bool feasiblewrite=true;
 549                         //new we need to see if this write works for everyone
 550
 551                         for (int loop=count;loop>0;loop--,rit++) {
 552                                 ModelAction *act=*rit;
 553                                 bool foundvalue=false;
 554                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 555                                         if (act->get_node()->get_read_from_at(i)==write) {
 556                                                 foundvalue=true;
 557                                                 break;
 558                                         }
 559                                 }
 560                                 if (!foundvalue) {
 561                                         feasiblewrite=false;
 562                                         break;
 563                                 }
 564                         }
 565                         if (feasiblewrite) {
 566                                 too_many_reads = true;
 567                                 return;
 568                         }
 569                 }
 570         }
 571 }
 572
 573 /**
 574  * Updates the mo_graph with the constraints imposed from the current read.
 575  * @param curr The current action. Must be a read.
 576  * @param rf The action that curr reads from. Must be a write.
 577  * @return True if modification order edges were added; false otherwise
 578  */
 579 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 580 {
 581         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 582         unsigned int i;
 583         bool added = false;
 584         ASSERT(curr->is_read());
 585
 586         /* Iterate over all threads */
 587         for (i = 0; i < thrd_lists->size(); i++) {
 588                 /* Iterate over actions in thread, starting from most recent */
 589                 action_list_t *list = &(*thrd_lists)[i];
 590                 action_list_t::reverse_iterator rit;
 591                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 592                         ModelAction *act = *rit;
 593
 594                         /* Include at most one act per-thread that "happens before" curr */
 595                         if (act->happens_before(curr)) {
 596                                 if (act->is_read()) {
 597                                         const ModelAction *prevreadfrom = act->get_reads_from();
 598                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 599                                                 mo_graph->addEdge(prevreadfrom, rf);
 600                                                 added = true;
 601                                         }
 602                                 } else if (rf != act) {
 603                                         mo_graph->addEdge(act, rf);
 604                                         added = true;
 605                                 }
 606                                 break;
 607                         }
 608                 }
 609         }
 610
 611         return added;
 612 }
 613
 614 /** Updates the mo_graph with the constraints imposed from the current read. */
 615 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 616 {
 617         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 618         unsigned int i;
 619         ASSERT(curr->is_read());
 620
 621         /* Iterate over all threads */
 622         for (i = 0; i < thrd_lists->size(); i++) {
 623                 /* Iterate over actions in thread, starting from most recent */
 624                 action_list_t *list = &(*thrd_lists)[i];
 625                 action_list_t::reverse_iterator rit;
 626                 ModelAction *lastact = NULL;
 627
 628                 /* Find last action that happens after curr */
 629                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 630                         ModelAction *act = *rit;
 631                         if (curr->happens_before(act)) {
 632                                 lastact = act;
 633                         } else
 634                                 break;
 635                 }
 636
 637                         /* Include at most one act per-thread that "happens before" curr */
 638                 if (lastact != NULL) {
 639                         if (lastact->is_read()) {
 640                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 641                                 if (postreadfrom != NULL&&rf != postreadfrom)
 642                                         mo_graph->addEdge(rf, postreadfrom);
 643                         } else if (rf != lastact) {
 644                                 mo_graph->addEdge(rf, lastact);
 645                         }
 646                         break;
 647                 }
 648         }
 649 }
 650
 651 /**
 652  * Updates the mo_graph with the constraints imposed from the current write.
 653  * @param curr The current action. Must be a write.
 654  * @return True if modification order edges were added; false otherwise
 655  */
 656 bool ModelChecker::w_modification_order(ModelAction *curr)
 657 {
 658         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 659         unsigned int i;
 660         bool added = false;
 661         ASSERT(curr->is_write());
 662
 663         if (curr->is_seqcst()) {
 664                 /* We have to at least see the last sequentially consistent write,
 665                          so we are initialized. */
 666                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 667                 if (last_seq_cst != NULL) {
 668                         mo_graph->addEdge(last_seq_cst, curr);
 669                         added = true;
 670                 }
 671         }
 672
 673         /* Iterate over all threads */
 674         for (i = 0; i < thrd_lists->size(); i++) {
 675                 /* Iterate over actions in thread, starting from most recent */
 676                 action_list_t *list = &(*thrd_lists)[i];
 677                 action_list_t::reverse_iterator rit;
 678                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 679                         ModelAction *act = *rit;
 680
 681                         /* Include at most one act per-thread that "happens before" curr */
 682                         if (act->happens_before(curr)) {
 683                                 /*
 684                                  * Note: if act is RMW, just add edge:
 685                                  *   act --mo--> curr
 686                                  * The following edge should be handled elsewhere:
 687                                  *   readfrom(act) --mo--> act
 688                                  */
 689                                 if (act->is_write()) {
 690                                         //RMW shouldn't have an edge to themselves
 691                                         if (act!=curr)
 692                                                 mo_graph->addEdge(act, curr);
 693                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 694                                         mo_graph->addEdge(act->get_reads_from(), curr);
 695                                 added = true;
 696                                 break;
 697                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 698                                                      !act->same_thread(curr)) {
 699                                 /* We have an action that:
 700                                    (1) did not happen before us
 701                                    (2) is a read and we are a write
 702                                    (3) cannot synchronize with us
 703                                    (4) is in a different thread
 704                                    =>
 705                                    that read could potentially read from our write.
 706                                  */
 707                                 if (isfeasible() && act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
 708                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 709                                         priv->next_backtrack = act;
 710                         }
 711                 }
 712         }
 713
 714         return added;
 715 }
 716
 717 /**
 718  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 719  * The ModelAction under consideration is expected to be taking part in
 720  * release/acquire synchronization as an object of the "reads from" relation.
 721  * Note that this can only provide release sequence support for RMW chains
 722  * which do not read from the future, as those actions cannot be traced until
 723  * their "promise" is fulfilled. Similarly, we may not even establish the
 724  * presence of a release sequence with certainty, as some modification order
 725  * constraints may be decided further in the future. Thus, this function
 726  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 727  * and a boolean representing certainty.
 728  *
 729  * @todo Finish lazy updating, when promises are fulfilled in the future
 730  * @param rf The action that might be part of a release sequence. Must be a
 731  * write.
 732  * @param release_heads A pass-by-reference style return parameter.  After
 733  * execution of this function, release_heads will contain the heads of all the
 734  * relevant release sequences, if any exists
 735  * @return true, if the ModelChecker is certain that release_heads is complete;
 736  * false otherwise
 737  */
 738 bool ModelChecker::release_seq_head(const ModelAction *rf,
 739                 std::vector<const ModelAction *> *release_heads) const
 740 {
 741         ASSERT(rf->is_write());
 742         if (!rf) {
 743                 /* read from future: need to settle this later */
 744                 return false; /* incomplete */
 745         }
 746         if (rf->is_release())
 747                 release_heads->push_back(rf);
 748         if (rf->is_rmw()) {
 749                 /* We need a RMW action that is both an acquire and release to stop */
 750                 /** @todo Need to be smarter here...  In the linux lock
 751                  * example, this will run to the beginning of the program for
 752                  * every acquire. */
 753                 if (rf->is_acquire() && rf->is_release())
 754                         return true; /* complete */
 755                 return release_seq_head(rf->get_reads_from(), release_heads);
 756         }
 757         if (rf->is_release())
 758                 return true; /* complete */
 759
 760         /* else relaxed write; check modification order for contiguous subsequence
 761          * -> rf must be same thread as release */
 762         int tid = id_to_int(rf->get_tid());
 763         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 764         action_list_t *list = &(*thrd_lists)[tid];
 765         action_list_t::const_reverse_iterator rit;
 766
 767         /* Find rf in the thread list */
 768         rit = std::find(list->rbegin(), list->rend(), rf);
 769         ASSERT(rit != list->rend());
 770
 771         /* Find the last write/release */
 772         for (; rit != list->rend(); rit++)
 773                 if ((*rit)->is_release())
 774                         break;
 775         if (rit == list->rend()) {
 776                 /* No write-release in this thread */
 777                 return true; /* complete */
 778         }
 779         ModelAction *release = *rit;
 780
 781         ASSERT(rf->same_thread(release));
 782
 783         bool certain = true;
 784         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 785                 if (id_to_int(rf->get_tid()) == (int)i)
 786                         continue;
 787                 list = &(*thrd_lists)[i];
 788
 789                 /* Can we ensure no future writes from this thread may break
 790                  * the release seq? */
 791                 bool future_ordered = false;
 792
 793                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 794                         const ModelAction *act = *rit;
 795                         if (!act->is_write())
 796                                 continue;
 797                         /* Reach synchronization -> this thread is complete */
 798                         if (act->happens_before(release))
 799                                 break;
 800                         if (rf->happens_before(act)) {
 801                                 future_ordered = true;
 802                                 continue;
 803                         }
 804
 805                         /* Check modification order */
 806                         if (mo_graph->checkReachable(rf, act)) {
 807                                 /* rf --mo--> act */
 808                                 future_ordered = true;
 809                                 continue;
 810                         }
 811                         if (mo_graph->checkReachable(act, release))
 812                                 /* act --mo--> release */
 813                                 break;
 814                         if (mo_graph->checkReachable(release, act) &&
 815                                       mo_graph->checkReachable(act, rf)) {
 816                                 /* release --mo-> act --mo--> rf */
 817                                 return true; /* complete */
 818                         }
 819                         certain = false;
 820                 }
 821                 if (!future_ordered)
 822                         return false; /* This thread is uncertain */
 823         }
 824
 825         if (certain)
 826                 release_heads->push_back(release);
 827         return certain;
 828 }
 829
 830 /**
 831  * A public interface for getting the release sequence head(s) with which a
 832  * given ModelAction must synchronize. This function only returns a non-empty
 833  * result when it can locate a release sequence head with certainty. Otherwise,
 834  * it may mark the internal state of the ModelChecker so that it will handle
 835  * the release sequence at a later time, causing @a act to update its
 836  * synchronization at some later point in execution.
 837  * @param act The 'acquire' action that may read from a release sequence
 838  * @param release_heads A pass-by-reference return parameter. Will be filled
 839  * with the head(s) of the release sequence(s), if they exists with certainty.
 840  * @see ModelChecker::release_seq_head
 841  */
 842 void ModelChecker::get_release_seq_heads(ModelAction *act,
 843                 std::vector<const ModelAction *> *release_heads)
 844 {
 845         const ModelAction *rf = act->get_reads_from();
 846         bool complete;
 847         complete = release_seq_head(rf, release_heads);
 848         if (!complete) {
 849                 /* add act to 'lazy checking' list */
 850                 std::list<ModelAction *> *list;
 851                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 852                 list->push_back(act);
 853                 (*lazy_sync_size)++;
 854         }
 855 }
 856
 857 /**
 858  * Attempt to resolve all stashed operations that might synchronize with a
 859  * release sequence for a given location. This implements the "lazy" portion of
 860  * determining whether or not a release sequence was contiguous, since not all
 861  * modification order information is present at the time an action occurs.
 862  *
 863  * @param location The location/object that should be checked for release
 864  * sequence resolutions
 865  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 866  */
 867 bool ModelChecker::resolve_release_sequences(void *location)
 868 {
 869         std::list<ModelAction *> *list;
 870         list = lazy_sync_with_release->getptr(location);
 871         if (!list)
 872                 return false;
 873
 874         bool updated = false;
 875         std::list<ModelAction *>::iterator it = list->begin();
 876         while (it != list->end()) {
 877                 ModelAction *act = *it;
 878                 const ModelAction *rf = act->get_reads_from();
 879                 std::vector<const ModelAction *> release_heads;
 880                 bool complete;
 881                 complete = release_seq_head(rf, &release_heads);
 882                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 883                         if (!act->has_synchronized_with(release_heads[i])) {
 884                                 updated = true;
 885                                 act->synchronize_with(release_heads[i]);
 886                         }
 887                 }
 888
 889                 if (updated) {
 890                         /* propagate synchronization to later actions */
 891                         action_list_t::reverse_iterator it = action_trace->rbegin();
 892                         while ((*it) != act) {
 893                                 ModelAction *propagate = *it;
 894                                 if (act->happens_before(propagate))
 895                                         /** @todo new mo_graph edges along with
 896                                          * this synchronization? */
 897                                         propagate->synchronize_with(act);
 898                         }
 899                 }
 900                 if (complete) {
 901                         it = list->erase(it);
 902                         (*lazy_sync_size)--;
 903                 } else
 904                         it++;
 905         }
 906
 907         // If we resolved promises or data races, see if we have realized a data race.
 908         if (checkDataRaces()) {
 909                 set_assert();
 910         }
 911
 912         return updated;
 913 }
 914
 915 /**
 916  * Performs various bookkeeping operations for the current ModelAction. For
 917  * instance, adds action to the per-object, per-thread action vector and to the
 918  * action trace list of all thread actions.
 919  *
 920  * @param act is the ModelAction to add.
 921  */
 922 void ModelChecker::add_action_to_lists(ModelAction *act)
 923 {
 924         int tid = id_to_int(act->get_tid());
 925         action_trace->push_back(act);
 926
 927         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 928
 929         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 930         if (tid >= (int)vec->size())
 931                 vec->resize(priv->next_thread_id);
 932         (*vec)[tid].push_back(act);
 933
 934         if ((int)thrd_last_action->size() <= tid)
 935                 thrd_last_action->resize(get_num_threads());
 936         (*thrd_last_action)[tid] = act;
 937 }
 938
 939 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 940 {
 941         int nthreads = get_num_threads();
 942         if ((int)thrd_last_action->size() < nthreads)
 943                 thrd_last_action->resize(nthreads);
 944         return (*thrd_last_action)[id_to_int(tid)];
 945 }
 946
 947 /**
 948  * Gets the last memory_order_seq_cst action (in the total global sequence)
 949  * performed on a particular object (i.e., memory location).
 950  * @param location The object location to check
 951  * @return The last seq_cst action performed
 952  */
 953 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 954 {
 955         action_list_t *list = obj_map->get_safe_ptr(location);
 956         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 957         action_list_t::reverse_iterator rit;
 958         for (rit = list->rbegin(); rit != list->rend(); rit++)
 959                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 960                         return *rit;
 961         return NULL;
 962 }
 963
 964 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 965 {
 966         ModelAction *parent = get_last_action(tid);
 967         if (!parent)
 968                 parent = get_thread(tid)->get_creation();
 969         return parent;
 970 }
 971
 972 /**
 973  * Returns the clock vector for a given thread.
 974  * @param tid The thread whose clock vector we want
 975  * @return Desired clock vector
 976  */
 977 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 978 {
 979         return get_parent_action(tid)->get_cv();
 980 }
 981
 982 /**
 983  * Resolve a set of Promises with a current write. The set is provided in the
 984  * Node corresponding to @a write.
 985  * @param write The ModelAction that is fulfilling Promises
 986  * @return True if promises were resolved; false otherwise
 987  */
 988 bool ModelChecker::resolve_promises(ModelAction *write)
 989 {
 990         bool resolved = false;
 991         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 992                 Promise *promise = (*promises)[promise_index];
 993                 if (write->get_node()->get_promise(i)) {
 994                         ModelAction *read = promise->get_action();
 995                         read->read_from(write);
 996                         if (read->is_rmw()) {
 997                                 mo_graph->addRMWEdge(write, read);
 998                         }
 999                         r_modification_order(read, write);
1000                         post_r_modification_order(read, write);
1001                         promises->erase(promises->begin() + promise_index);
1002                         resolved = true;
1003                 } else
1004                         promise_index++;
1005         }
1006
1007         return resolved;
1008 }
1009
1010 /**
1011  * Compute the set of promises that could potentially be satisfied by this
1012  * action. Note that the set computation actually appears in the Node, not in
1013  * ModelChecker.
1014  * @param curr The ModelAction that may satisfy promises
1015  */
1016 void ModelChecker::compute_promises(ModelAction *curr)
1017 {
1018         for (unsigned int i = 0; i < promises->size(); i++) {
1019                 Promise *promise = (*promises)[i];
1020                 const ModelAction *act = promise->get_action();
1021                 if (!act->happens_before(curr) &&
1022                                 act->is_read() &&
1023                                 !act->is_synchronizing(curr) &&
1024                                 !act->same_thread(curr) &&
1025                                 promise->get_value() == curr->get_value()) {
1026                         curr->get_node()->set_promise(i);
1027                 }
1028         }
1029 }
1030
1031 /** Checks promises in response to change in ClockVector Threads. */
1032 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1033 {
1034         for (unsigned int i = 0; i < promises->size(); i++) {
1035                 Promise *promise = (*promises)[i];
1036                 const ModelAction *act = promise->get_action();
1037                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1038                                 merge_cv->synchronized_since(act)) {
1039                         //This thread is no longer able to send values back to satisfy the promise
1040                         int num_synchronized_threads = promise->increment_threads();
1041                         if (num_synchronized_threads == get_num_threads()) {
1042                                 //Promise has failed
1043                                 failed_promise = true;
1044                                 return;
1045                         }
1046                 }
1047         }
1048 }
1049
1050 /**
1051  * Build up an initial set of all past writes that this 'read' action may read
1052  * from. This set is determined by the clock vector's "happens before"
1053  * relationship.
1054  * @param curr is the current ModelAction that we are exploring; it must be a
1055  * 'read' operation.
1056  */
1057 void ModelChecker::build_reads_from_past(ModelAction *curr)
1058 {
1059         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1060         unsigned int i;
1061         ASSERT(curr->is_read());
1062
1063         ModelAction *last_seq_cst = NULL;
1064
1065         /* Track whether this object has been initialized */
1066         bool initialized = false;
1067
1068         if (curr->is_seqcst()) {
1069                 last_seq_cst = get_last_seq_cst(curr->get_location());
1070                 /* We have to at least see the last sequentially consistent write,
1071                          so we are initialized. */
1072                 if (last_seq_cst != NULL)
1073                         initialized = true;
1074         }
1075
1076         /* Iterate over all threads */
1077         for (i = 0; i < thrd_lists->size(); i++) {
1078                 /* Iterate over actions in thread, starting from most recent */
1079                 action_list_t *list = &(*thrd_lists)[i];
1080                 action_list_t::reverse_iterator rit;
1081                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1082                         ModelAction *act = *rit;
1083
1084                         /* Only consider 'write' actions */
1085                         if (!act->is_write())
1086                                 continue;
1087
1088                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1089                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1090                                 DEBUG("Adding action to may_read_from:\n");
1091                                 if (DBG_ENABLED()) {
1092                                         act->print();
1093                                         curr->print();
1094                                 }
1095                                 curr->get_node()->add_read_from(act);
1096                         }
1097
1098                         /* Include at most one act per-thread that "happens before" curr */
1099                         if (act->happens_before(curr)) {
1100                                 initialized = true;
1101                                 break;
1102                         }
1103                 }
1104         }
1105
1106         if (!initialized) {
1107                 /** @todo Need a more informative way of reporting errors. */
1108                 printf("ERROR: may read from uninitialized atomic\n");
1109         }
1110
1111         if (DBG_ENABLED() || !initialized) {
1112                 printf("Reached read action:\n");
1113                 curr->print();
1114                 printf("Printing may_read_from\n");
1115                 curr->get_node()->print_may_read_from();
1116                 printf("End printing may_read_from\n");
1117         }
1118
1119         ASSERT(initialized);
1120 }
1121
1122 static void print_list(action_list_t *list)
1123 {
1124         action_list_t::iterator it;
1125
1126         printf("---------------------------------------------------------------------\n");
1127         printf("Trace:\n");
1128
1129         for (it = list->begin(); it != list->end(); it++) {
1130                 (*it)->print();
1131         }
1132         printf("---------------------------------------------------------------------\n");
1133 }
1134
1135 void ModelChecker::print_summary()
1136 {
1137         printf("\n");
1138         printf("Number of executions: %d\n", num_executions);
1139         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1140
1141         scheduler->print();
1142
1143         if (!isfinalfeasible())
1144                 printf("INFEASIBLE EXECUTION!\n");
1145         print_list(action_trace);
1146         printf("\n");
1147 }
1148
1149 /**
1150  * Add a Thread to the system for the first time. Should only be called once
1151  * per thread.
1152  * @param t The Thread to add
1153  */
1154 void ModelChecker::add_thread(Thread *t)
1155 {
1156         thread_map->put(id_to_int(t->get_id()), t);
1157         scheduler->add_thread(t);
1158 }
1159
1160 void ModelChecker::remove_thread(Thread *t)
1161 {
1162         scheduler->remove_thread(t);
1163 }
1164
1165 /**
1166  * Switch from a user-context to the "master thread" context (a.k.a. system
1167  * context). This switch is made with the intention of exploring a particular
1168  * model-checking action (described by a ModelAction object). Must be called
1169  * from a user-thread context.
1170  * @param act The current action that will be explored. Must not be NULL.
1171  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1172  */
1173 int ModelChecker::switch_to_master(ModelAction *act)
1174 {
1175         DBG();
1176         Thread *old = thread_current();
1177         set_current_action(act);
1178         old->set_state(THREAD_READY);
1179         return Thread::swap(old, &system_context);
1180 }
1181
1182 /**
1183  * Takes the next step in the execution, if possible.
1184  * @return Returns true (success) if a step was taken and false otherwise.
1185  */
1186 bool ModelChecker::take_step() {
1187         Thread *curr, *next;
1188
1189         if (has_asserted())
1190                 return false;
1191
1192         curr = thread_current();
1193         if (curr) {
1194                 if (curr->get_state() == THREAD_READY) {
1195                         ASSERT(priv->current_action);
1196                         priv->nextThread = check_current_action(priv->current_action);
1197                         priv->current_action = NULL;
1198                         if (!curr->is_blocked() && !curr->is_complete())
1199                                 scheduler->add_thread(curr);
1200                 } else {
1201                         ASSERT(false);
1202                 }
1203         }
1204         next = scheduler->next_thread(priv->nextThread);
1205
1206         /* Infeasible -> don't take any more steps */
1207         if (!isfeasible())
1208                 return false;
1209
1210         if (next)
1211                 next->set_state(THREAD_RUNNING);
1212         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1213
1214         /* next == NULL -> don't take any more steps */
1215         if (!next)
1216                 return false;
1217         /* Return false only if swap fails with an error */
1218         return (Thread::swap(&system_context, next) == 0);
1219 }
1220
1221 /** Runs the current execution until threre are no more steps to take. */
1222 void ModelChecker::finish_execution() {
1223         DBG();
1224
1225         while (take_step());
1226 }