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         rmw_cycle(false)
  39 {
  40         /* Allocate this "size" on the snapshotting heap */
  41         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  42         /* First thread created will have id INITIAL_THREAD_ID */
  43         priv->next_thread_id = INITIAL_THREAD_ID;
  44
  45         lazy_sync_size = &priv->lazy_sync_size;
  46 }
  47
  48 /** @brief Destructor */
  49 ModelChecker::~ModelChecker()
  50 {
  51         for (int i = 0; i < get_num_threads(); i++)
  52                 delete thread_map->get(i);
  53         delete thread_map;
  54
  55         delete obj_thrd_map;
  56         delete obj_map;
  57         delete action_trace;
  58
  59         for (unsigned int i = 0; i < promises->size(); i++)
  60                 delete (*promises)[i];
  61         delete promises;
  62
  63         delete lazy_sync_with_release;
  64
  65         delete thrd_last_action;
  66         delete node_stack;
  67         delete scheduler;
  68         delete mo_graph;
  69 }
  70
  71 /**
  72  * Restores user program to initial state and resets all model-checker data
  73  * structures.
  74  */
  75 void ModelChecker::reset_to_initial_state()
  76 {
  77         DEBUG("+++ Resetting to initial state +++\n");
  78         node_stack->reset_execution();
  79         failed_promise = false;
  80         too_many_reads = false;
  81         rmw_cycle=false;
  82         reset_asserted();
  83         snapshotObject->backTrackBeforeStep(0);
  84 }
  85
  86 /** @returns a thread ID for a new Thread */
  87 thread_id_t ModelChecker::get_next_id()
  88 {
  89         return priv->next_thread_id++;
  90 }
  91
  92 /** @returns the number of user threads created during this execution */
  93 int ModelChecker::get_num_threads()
  94 {
  95         return priv->next_thread_id;
  96 }
  97
  98 /** @returns a sequence number for a new ModelAction */
  99 modelclock_t ModelChecker::get_next_seq_num()
 100 {
 101         return ++priv->used_sequence_numbers;
 102 }
 103
 104 /**
 105  * @brief Choose the next thread to execute.
 106  *
 107  * This function chooses the next thread that should execute. It can force the
 108  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 109  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 110  * The model-checker may have no preference regarding the next thread (i.e.,
 111  * when exploring a new execution ordering), in which case this will return
 112  * NULL.
 113  * @param curr The current ModelAction. This action might guide the choice of
 114  * next thread.
 115  * @return The next thread to run. If the model-checker has no preference, NULL.
 116  */
 117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 118 {
 119         thread_id_t tid;
 120
 121         /* Do not split atomic actions. */
 122         if (curr->is_rmwr())
 123                 return thread_current();
 124         /* The THREAD_CREATE action points to the created Thread */
 125         else if (curr->get_type() == THREAD_CREATE)
 126                 return (Thread *)curr->get_location();
 127
 128         /* Have we completed exploring the preselected path? */
 129         if (diverge == NULL)
 130                 return NULL;
 131
 132         /* Else, we are trying to replay an execution */
 133         ModelAction *next = node_stack->get_next()->get_action();
 134
 135         if (next == diverge) {
 136                 Node *nextnode = next->get_node();
 137                 /* Reached divergence point */
 138                 if (nextnode->increment_promise()) {
 139                         /* The next node will try to satisfy a different set of promises. */
 140                         tid = next->get_tid();
 141                         node_stack->pop_restofstack(2);
 142                 } else if (nextnode->increment_read_from()) {
 143                         /* The next node will read from a different value. */
 144                         tid = next->get_tid();
 145                         node_stack->pop_restofstack(2);
 146                 } else if (nextnode->increment_future_value()) {
 147                         /* The next node will try to read from a different future value. */
 148                         tid = next->get_tid();
 149                         node_stack->pop_restofstack(2);
 150                 } else {
 151                         /* Make a different thread execute for next step */
 152                         Node *node = nextnode->get_parent();
 153                         tid = node->get_next_backtrack();
 154                         node_stack->pop_restofstack(1);
 155                 }
 156                 DEBUG("*** Divergence point ***\n");
 157                 diverge = NULL;
 158         } else {
 159                 tid = next->get_tid();
 160         }
 161         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 162         ASSERT(tid != THREAD_ID_T_NONE);
 163         return thread_map->get(id_to_int(tid));
 164 }
 165
 166 /**
 167  * Queries the model-checker for more executions to explore and, if one
 168  * exists, resets the model-checker state to execute a new execution.
 169  *
 170  * @return If there are more executions to explore, return true. Otherwise,
 171  * return false.
 172  */
 173 bool ModelChecker::next_execution()
 174 {
 175         DBG();
 176
 177         num_executions++;
 178
 179         if (isfinalfeasible() || DBG_ENABLED())
 180                 print_summary();
 181
 182         if ((diverge = get_next_backtrack()) == NULL)
 183                 return false;
 184
 185         if (DBG_ENABLED()) {
 186                 printf("Next execution will diverge at:\n");
 187                 diverge->print();
 188         }
 189
 190         reset_to_initial_state();
 191         return true;
 192 }
 193
 194 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 195 {
 196         action_type type = act->get_type();
 197
 198         switch (type) {
 199                 case ATOMIC_READ:
 200                 case ATOMIC_WRITE:
 201                 case ATOMIC_RMW:
 202                         break;
 203                 default:
 204                         return NULL;
 205         }
 206         /* linear search: from most recent to oldest */
 207         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 208         action_list_t::reverse_iterator rit;
 209         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 210                 ModelAction *prev = *rit;
 211                 if (act->is_synchronizing(prev))
 212                         return prev;
 213         }
 214         return NULL;
 215 }
 216
 217 void ModelChecker::set_backtracking(ModelAction *act)
 218 {
 219         ModelAction *prev;
 220         Node *node;
 221         Thread *t = get_thread(act);
 222
 223         prev = get_last_conflict(act);
 224         if (prev == NULL)
 225                 return;
 226
 227         node = prev->get_node()->get_parent();
 228
 229         while (!node->is_enabled(t))
 230                 t = t->get_parent();
 231
 232         /* Check if this has been explored already */
 233         if (node->has_been_explored(t->get_id()))
 234                 return;
 235
 236         /* Cache the latest backtracking point */
 237         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 238                 priv->next_backtrack = prev;
 239
 240         /* If this is a new backtracking point, mark the tree */
 241         if (!node->set_backtrack(t->get_id()))
 242                 return;
 243         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 244                         prev->get_tid(), t->get_id());
 245         if (DBG_ENABLED()) {
 246                 prev->print();
 247                 act->print();
 248         }
 249 }
 250
 251 /**
 252  * Returns last backtracking point. The model checker will explore a different
 253  * path for this point in the next execution.
 254  * @return The ModelAction at which the next execution should diverge.
 255  */
 256 ModelAction * ModelChecker::get_next_backtrack()
 257 {
 258         ModelAction *next = priv->next_backtrack;
 259         priv->next_backtrack = NULL;
 260         return next;
 261 }
 262
 263
 264 /** Checks whether making the ModelAction read read_from the
 265                 ModelAction write will introduce a cycle in the reads_from
 266                 relation.
 267
 268 @return true if making it read from will be fine, false otherwise.
 269
 270 */
 271
 272 bool ModelChecker::ensure_rmw_acyclic(const ModelAction * read, const ModelAction *write) {
 273         if (!read->is_rmw())
 274                 return true;
 275         if (!write->is_rmw())
 276                 return true;
 277         while(write!=NULL) {
 278                 if (write==read) {
 279                         rmw_cycle=true;
 280                         return false;
 281                 }
 282                 write=write->get_reads_from();
 283         }
 284         return true;
 285 }
 286
 287 /**
 288  * Processes a read or rmw model action.
 289  * @param curr is the read model action to process.
 290  * @param th is the thread
 291  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 292  * @return True if processing this read updates the mo_graph.
 293  */
 294
 295 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
 296         uint64_t value;
 297         bool updated=false;
 298         while(true) {
 299                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 300                 if (reads_from != NULL) {
 301                         mo_graph->startChanges();
 302
 303                         value = reads_from->get_value();
 304                                 /* Assign reads_from, perform release/acquire synchronization */
 305                         if (ensure_rmw_acyclic(curr, reads_from))
 306                                 curr->read_from(reads_from);
 307                         if (!second_part_of_rmw) {
 308                                 check_recency(curr,false);
 309                         }
 310
 311                         bool r_status=r_modification_order(curr,reads_from);
 312
 313                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
 314                                 mo_graph->rollbackChanges();
 315                                 too_many_reads=false;
 316                                 continue;
 317                         }
 318
 319                         mo_graph->commitChanges();
 320                         updated |= r_status;
 321                 } else if (!second_part_of_rmw) {
 322                         /* Read from future value */
 323                         value = curr->get_node()->get_future_value();
 324                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 325                         curr->read_from(NULL);
 326                         Promise *valuepromise = new Promise(curr, value, expiration);
 327                         promises->push_back(valuepromise);
 328                 }
 329                 th->set_return_value(value);
 330                 return updated;
 331         }
 332 }
 333
 334 /**
 335  * This is the heart of the model checker routine. It performs model-checking
 336  * actions corresponding to a given "current action." Among other processes, it
 337  * calculates reads-from relationships, updates synchronization clock vectors,
 338  * forms a memory_order constraints graph, and handles replay/backtrack
 339  * execution when running permutations of previously-observed executions.
 340  *
 341  * @param curr The current action to process
 342  * @return The next Thread that must be executed. May be NULL if ModelChecker
 343  * makes no choice (e.g., according to replay execution, combining RMW actions,
 344  * etc.)
 345  */
 346 Thread * ModelChecker::check_current_action(ModelAction *curr)
 347 {
 348         bool second_part_of_rmw = false;
 349
 350         ASSERT(curr);
 351
 352         if (curr->is_rmwc() || curr->is_rmw()) {
 353                 ModelAction *tmp = process_rmw(curr);
 354                 second_part_of_rmw = true;
 355                 delete curr;
 356                 curr = tmp;
 357                 compute_promises(curr);
 358         } else {
 359                 ModelAction *tmp = node_stack->explore_action(curr);
 360                 if (tmp) {
 361                         /* Discard duplicate ModelAction; use action from NodeStack */
 362                         /* First restore type and order in case of RMW operation */
 363                         if (curr->is_rmwr())
 364                                 tmp->copy_typeandorder(curr);
 365
 366                         /* If we have diverged, we need to reset the clock vector. */
 367                         if (diverge == NULL)
 368                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 369
 370                         delete curr;
 371                         curr = tmp;
 372                 } else {
 373                         /*
 374                          * Perform one-time actions when pushing new ModelAction onto
 375                          * NodeStack
 376                          */
 377                         curr->create_cv(get_parent_action(curr->get_tid()));
 378                         /* Build may_read_from set */
 379                         if (curr->is_read())
 380                                 build_reads_from_past(curr);
 381                         if (curr->is_write())
 382                                 compute_promises(curr);
 383                 }
 384         }
 385
 386         /* Thread specific actions */
 387         switch(curr->get_type()) {
 388         case THREAD_CREATE: {
 389                 Thread *th = (Thread *)curr->get_location();
 390                 th->set_creation(curr);
 391                 break;
 392         }
 393         case THREAD_JOIN: {
 394                 Thread *waiting, *blocking;
 395                 waiting = get_thread(curr);
 396                 blocking = (Thread *)curr->get_location();
 397                 if (!blocking->is_complete()) {
 398                         blocking->push_wait_list(curr);
 399                         scheduler->sleep(waiting);
 400                 }
 401                 break;
 402         }
 403         case THREAD_FINISH: {
 404                 Thread *th = get_thread(curr);
 405                 while (!th->wait_list_empty()) {
 406                         ModelAction *act = th->pop_wait_list();
 407                         Thread *wake = get_thread(act);
 408                         scheduler->wake(wake);
 409                 }
 410                 th->complete();
 411                 break;
 412         }
 413         case THREAD_START: {
 414                 check_promises(NULL, curr->get_cv());
 415                 break;
 416         }
 417         default:
 418                 break;
 419         }
 420
 421         Thread *th = get_thread(curr);
 422
 423         bool updated = false;
 424         if (curr->is_read()) {
 425                 updated=process_read(curr, th, second_part_of_rmw);
 426         }
 427
 428         if (curr->is_write()) {
 429                 bool updated_mod_order=w_modification_order(curr);
 430                 bool updated_promises=resolve_promises(curr);
 431                 updated=updated_mod_order|updated_promises;
 432
 433                 mo_graph->commitChanges();
 434                 th->set_return_value(VALUE_NONE);
 435         }
 436
 437         if (updated)
 438                 resolve_release_sequences(curr->get_location());
 439
 440         /* Add action to list.  */
 441         if (!second_part_of_rmw)
 442                 add_action_to_lists(curr);
 443
 444         check_curr_backtracking(curr);
 445
 446         set_backtracking(curr);
 447
 448         return get_next_thread(curr);
 449 }
 450
 451 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 452         Node *currnode = curr->get_node();
 453         Node *parnode = currnode->get_parent();
 454
 455         if ((!parnode->backtrack_empty() ||
 456                          !currnode->read_from_empty() ||
 457                          !currnode->future_value_empty() ||
 458                          !currnode->promise_empty())
 459                         && (!priv->next_backtrack ||
 460                                         *curr > *priv->next_backtrack)) {
 461                 priv->next_backtrack = curr;
 462         }
 463 }
 464
 465
 466 bool ModelChecker::promises_expired() {
 467         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 468                 Promise *promise = (*promises)[promise_index];
 469                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 470                         return true;
 471                 }
 472         }
 473         return false;
 474 }
 475
 476 /** @returns whether the current partial trace must be a prefix of a
 477  * feasible trace. */
 478 bool ModelChecker::isfeasibleprefix() {
 479         return promises->size() == 0 && *lazy_sync_size == 0;
 480 }
 481
 482 /** @returns whether the current partial trace is feasible. */
 483 bool ModelChecker::isfeasible() {
 484         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 485 }
 486
 487 /** @returns whether the current partial trace is feasible other than
 488  * multiple RMW reading from the same store. */
 489 bool ModelChecker::isfeasibleotherthanRMW() {
 490         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !rmw_cycle && !promises_expired();
 491 }
 492
 493 /** Returns whether the current completed trace is feasible. */
 494 bool ModelChecker::isfinalfeasible() {
 495         return isfeasible() && promises->size() == 0;
 496 }
 497
 498 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 499 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 500         int tid = id_to_int(act->get_tid());
 501         ModelAction *lastread = get_last_action(tid);
 502         lastread->process_rmw(act);
 503         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 504                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 505                 mo_graph->commitChanges();
 506         }
 507         return lastread;
 508 }
 509
 510 /**
 511  * Checks whether a thread has read from the same write for too many times
 512  * without seeing the effects of a later write.
 513  *
 514  * Basic idea:
 515  * 1) there must a different write that we could read from that would satisfy the modification order,
 516  * 2) we must have read from the same value in excess of maxreads times, and
 517  * 3) that other write must have been in the reads_from set for maxreads times.
 518  *
 519  * If so, we decide that the execution is no longer feasible.
 520  */
 521 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 522         if (params.maxreads != 0) {
 523                 if (curr->get_node()->get_read_from_size() <= 1)
 524                         return;
 525
 526                 //Must make sure that execution is currently feasible...  We could
 527                 //accidentally clear by rolling back
 528                 if (!isfeasible())
 529                         return;
 530
 531                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 532                 int tid = id_to_int(curr->get_tid());
 533
 534                 /* Skip checks */
 535                 if ((int)thrd_lists->size() <= tid)
 536                         return;
 537
 538                 action_list_t *list = &(*thrd_lists)[tid];
 539
 540                 action_list_t::reverse_iterator rit = list->rbegin();
 541                 /* Skip past curr */
 542                 if (already_added) {
 543                         for (; (*rit) != curr; rit++)
 544                                 ;
 545                         /* go past curr now */
 546                         rit++;
 547                 }
 548
 549                 action_list_t::reverse_iterator ritcopy=rit;
 550                 //See if we have enough reads from the same value
 551                 int count=0;
 552                 for (; count < params.maxreads; rit++,count++) {
 553                         if (rit==list->rend())
 554                                 return;
 555                         ModelAction *act = *rit;
 556                         if (!act->is_read())
 557                                 return;
 558                         if (act->get_reads_from() != curr->get_reads_from())
 559                                 return;
 560                         if (act->get_node()->get_read_from_size() <= 1)
 561                                 return;
 562                 }
 563
 564                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 565                         //Get write
 566                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 567                         //Need a different write
 568                         if (write==curr->get_reads_from())
 569                                 continue;
 570
 571                         /* Test to see whether this is a feasible write to read from*/
 572                         mo_graph->startChanges();
 573                         r_modification_order(curr, write);
 574                         bool feasiblereadfrom=isfeasible();
 575                         mo_graph->rollbackChanges();
 576
 577                         if (!feasiblereadfrom)
 578                                 continue;
 579                         rit=ritcopy;
 580
 581                         bool feasiblewrite=true;
 582                         //new we need to see if this write works for everyone
 583
 584                         for (int loop=count;loop>0;loop--,rit++) {
 585                                 ModelAction *act=*rit;
 586                                 bool foundvalue=false;
 587                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 588                                         if (act->get_node()->get_read_from_at(i)==write) {
 589                                                 foundvalue=true;
 590                                                 break;
 591                                         }
 592                                 }
 593                                 if (!foundvalue) {
 594                                         feasiblewrite=false;
 595                                         break;
 596                                 }
 597                         }
 598                         if (feasiblewrite) {
 599                                 too_many_reads = true;
 600                                 return;
 601                         }
 602                 }
 603         }
 604 }
 605
 606 /**
 607  * Updates the mo_graph with the constraints imposed from the current read.
 608  * @param curr The current action. Must be a read.
 609  * @param rf The action that curr reads from. Must be a write.
 610  * @return True if modification order edges were added; false otherwise
 611  */
 612 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 613 {
 614         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 615         unsigned int i;
 616         bool added = false;
 617         ASSERT(curr->is_read());
 618
 619         /* Iterate over all threads */
 620         for (i = 0; i < thrd_lists->size(); i++) {
 621                 /* Iterate over actions in thread, starting from most recent */
 622                 action_list_t *list = &(*thrd_lists)[i];
 623                 action_list_t::reverse_iterator rit;
 624                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 625                         ModelAction *act = *rit;
 626
 627                         /* Include at most one act per-thread that "happens before" curr */
 628                         if (act->happens_before(curr)) {
 629                                 if (act->is_read()) {
 630                                         const ModelAction *prevreadfrom = act->get_reads_from();
 631                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 632                                                 mo_graph->addEdge(prevreadfrom, rf);
 633                                                 added = true;
 634                                         }
 635                                 } else if (rf != act) {
 636                                         mo_graph->addEdge(act, rf);
 637                                         added = true;
 638                                 }
 639                                 break;
 640                         }
 641                 }
 642         }
 643
 644         return added;
 645 }
 646
 647 /** Updates the mo_graph with the constraints imposed from the current read. */
 648 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 649 {
 650         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 651         unsigned int i;
 652         ASSERT(curr->is_read());
 653
 654         /* Iterate over all threads */
 655         for (i = 0; i < thrd_lists->size(); i++) {
 656                 /* Iterate over actions in thread, starting from most recent */
 657                 action_list_t *list = &(*thrd_lists)[i];
 658                 action_list_t::reverse_iterator rit;
 659                 ModelAction *lastact = NULL;
 660
 661                 /* Find last action that happens after curr */
 662                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 663                         ModelAction *act = *rit;
 664                         if (curr->happens_before(act)) {
 665                                 lastact = act;
 666                         } else
 667                                 break;
 668                 }
 669
 670                         /* Include at most one act per-thread that "happens before" curr */
 671                 if (lastact != NULL) {
 672                         if (lastact->is_read()) {
 673                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 674                                 if (postreadfrom != NULL&&rf != postreadfrom)
 675                                         mo_graph->addEdge(rf, postreadfrom);
 676                         } else if (rf != lastact) {
 677                                 mo_graph->addEdge(rf, lastact);
 678                         }
 679                         break;
 680                 }
 681         }
 682 }
 683
 684 /**
 685  * Updates the mo_graph with the constraints imposed from the current write.
 686  * @param curr The current action. Must be a write.
 687  * @return True if modification order edges were added; false otherwise
 688  */
 689 bool ModelChecker::w_modification_order(ModelAction *curr)
 690 {
 691         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 692         unsigned int i;
 693         bool added = false;
 694         ASSERT(curr->is_write());
 695
 696         if (curr->is_seqcst()) {
 697                 /* We have to at least see the last sequentially consistent write,
 698                          so we are initialized. */
 699                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 700                 if (last_seq_cst != NULL) {
 701                         mo_graph->addEdge(last_seq_cst, curr);
 702                         added = true;
 703                 }
 704         }
 705
 706         /* Iterate over all threads */
 707         for (i = 0; i < thrd_lists->size(); i++) {
 708                 /* Iterate over actions in thread, starting from most recent */
 709                 action_list_t *list = &(*thrd_lists)[i];
 710                 action_list_t::reverse_iterator rit;
 711                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 712                         ModelAction *act = *rit;
 713
 714                         /* Include at most one act per-thread that "happens before" curr */
 715                         if (act->happens_before(curr)) {
 716                                 /*
 717                                  * Note: if act is RMW, just add edge:
 718                                  *   act --mo--> curr
 719                                  * The following edge should be handled elsewhere:
 720                                  *   readfrom(act) --mo--> act
 721                                  */
 722                                 if (act->is_write()) {
 723                                         //RMW shouldn't have an edge to themselves
 724                                         if (act!=curr)
 725                                                 mo_graph->addEdge(act, curr);
 726                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 727                                         mo_graph->addEdge(act->get_reads_from(), curr);
 728                                 added = true;
 729                                 break;
 730                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 731                                                      !act->same_thread(curr)) {
 732                                 /* We have an action that:
 733                                    (1) did not happen before us
 734                                    (2) is a read and we are a write
 735                                    (3) cannot synchronize with us
 736                                    (4) is in a different thread
 737                                    =>
 738                                    that read could potentially read from our write.
 739                                  */
 740                                 if (thin_air_constraint_may_allow(curr, act)) {
 741                                         if (isfeasible() ||
 742                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 743                                                 if (act->get_node()->add_future_value(curr->get_value(), curr->get_seq_number()+params.maxfuturedelay) &&
 744                                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 745                                                         priv->next_backtrack = act;
 746                                         }
 747                                 }
 748                         }
 749                 }
 750         }
 751
 752         return added;
 753 }
 754
 755 /** Arbitrary reads from the future are not allowed.  Section 29.3
 756  * part 9 places some constraints.  This method checks one result of constraint
 757  * constraint.  Others require compiler support. */
 758
 759 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 760         if (!writer->is_rmw())
 761                 return true;
 762
 763         if (!reader->is_rmw())
 764                 return true;
 765
 766         for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
 767                 if (search==reader)
 768                         return false;
 769                 if (search->get_tid()==reader->get_tid()&&
 770                                 search->happens_before(reader))
 771                         break;
 772         }
 773
 774         return true;
 775 }
 776
 777
 778 /**
 779  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 780  * The ModelAction under consideration is expected to be taking part in
 781  * release/acquire synchronization as an object of the "reads from" relation.
 782  * Note that this can only provide release sequence support for RMW chains
 783  * which do not read from the future, as those actions cannot be traced until
 784  * their "promise" is fulfilled. Similarly, we may not even establish the
 785  * presence of a release sequence with certainty, as some modification order
 786  * constraints may be decided further in the future. Thus, this function
 787  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 788  * and a boolean representing certainty.
 789  *
 790  * @todo Finish lazy updating, when promises are fulfilled in the future
 791  * @param rf The action that might be part of a release sequence. Must be a
 792  * write.
 793  * @param release_heads A pass-by-reference style return parameter.  After
 794  * execution of this function, release_heads will contain the heads of all the
 795  * relevant release sequences, if any exists
 796  * @return true, if the ModelChecker is certain that release_heads is complete;
 797  * false otherwise
 798  */
 799 bool ModelChecker::release_seq_head(const ModelAction *rf,
 800                 std::vector<const ModelAction *> *release_heads) const
 801 {
 802         ASSERT(rf->is_write());
 803         if (!rf) {
 804                 /* read from future: need to settle this later */
 805                 return false; /* incomplete */
 806         }
 807         if (rf->is_release())
 808                 release_heads->push_back(rf);
 809         if (rf->is_rmw()) {
 810                 /* We need a RMW action that is both an acquire and release to stop */
 811                 /** @todo Need to be smarter here...  In the linux lock
 812                  * example, this will run to the beginning of the program for
 813                  * every acquire. */
 814                 if (rf->is_acquire() && rf->is_release())
 815                         return true; /* complete */
 816                 return release_seq_head(rf->get_reads_from(), release_heads);
 817         }
 818         if (rf->is_release())
 819                 return true; /* complete */
 820
 821         /* else relaxed write; check modification order for contiguous subsequence
 822          * -> rf must be same thread as release */
 823         int tid = id_to_int(rf->get_tid());
 824         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 825         action_list_t *list = &(*thrd_lists)[tid];
 826         action_list_t::const_reverse_iterator rit;
 827
 828         /* Find rf in the thread list */
 829         rit = std::find(list->rbegin(), list->rend(), rf);
 830         ASSERT(rit != list->rend());
 831
 832         /* Find the last write/release */
 833         for (; rit != list->rend(); rit++)
 834                 if ((*rit)->is_release())
 835                         break;
 836         if (rit == list->rend()) {
 837                 /* No write-release in this thread */
 838                 return true; /* complete */
 839         }
 840         ModelAction *release = *rit;
 841
 842         ASSERT(rf->same_thread(release));
 843
 844         bool certain = true;
 845         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 846                 if (id_to_int(rf->get_tid()) == (int)i)
 847                         continue;
 848                 list = &(*thrd_lists)[i];
 849
 850                 /* Can we ensure no future writes from this thread may break
 851                  * the release seq? */
 852                 bool future_ordered = false;
 853
 854                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 855                         const ModelAction *act = *rit;
 856                         if (!act->is_write())
 857                                 continue;
 858                         /* Reach synchronization -> this thread is complete */
 859                         if (act->happens_before(release))
 860                                 break;
 861                         if (rf->happens_before(act)) {
 862                                 future_ordered = true;
 863                                 continue;
 864                         }
 865
 866                         /* Check modification order */
 867                         if (mo_graph->checkReachable(rf, act)) {
 868                                 /* rf --mo--> act */
 869                                 future_ordered = true;
 870                                 continue;
 871                         }
 872                         if (mo_graph->checkReachable(act, release))
 873                                 /* act --mo--> release */
 874                                 break;
 875                         if (mo_graph->checkReachable(release, act) &&
 876                                       mo_graph->checkReachable(act, rf)) {
 877                                 /* release --mo-> act --mo--> rf */
 878                                 return true; /* complete */
 879                         }
 880                         certain = false;
 881                 }
 882                 if (!future_ordered)
 883                         return false; /* This thread is uncertain */
 884         }
 885
 886         if (certain)
 887                 release_heads->push_back(release);
 888         return certain;
 889 }
 890
 891 /**
 892  * A public interface for getting the release sequence head(s) with which a
 893  * given ModelAction must synchronize. This function only returns a non-empty
 894  * result when it can locate a release sequence head with certainty. Otherwise,
 895  * it may mark the internal state of the ModelChecker so that it will handle
 896  * the release sequence at a later time, causing @a act to update its
 897  * synchronization at some later point in execution.
 898  * @param act The 'acquire' action that may read from a release sequence
 899  * @param release_heads A pass-by-reference return parameter. Will be filled
 900  * with the head(s) of the release sequence(s), if they exists with certainty.
 901  * @see ModelChecker::release_seq_head
 902  */
 903 void ModelChecker::get_release_seq_heads(ModelAction *act,
 904                 std::vector<const ModelAction *> *release_heads)
 905 {
 906         const ModelAction *rf = act->get_reads_from();
 907         bool complete;
 908         complete = release_seq_head(rf, release_heads);
 909         if (!complete) {
 910                 /* add act to 'lazy checking' list */
 911                 std::list<ModelAction *> *list;
 912                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 913                 list->push_back(act);
 914                 (*lazy_sync_size)++;
 915         }
 916 }
 917
 918 /**
 919  * Attempt to resolve all stashed operations that might synchronize with a
 920  * release sequence for a given location. This implements the "lazy" portion of
 921  * determining whether or not a release sequence was contiguous, since not all
 922  * modification order information is present at the time an action occurs.
 923  *
 924  * @param location The location/object that should be checked for release
 925  * sequence resolutions
 926  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 927  */
 928 bool ModelChecker::resolve_release_sequences(void *location)
 929 {
 930         std::list<ModelAction *> *list;
 931         list = lazy_sync_with_release->getptr(location);
 932         if (!list)
 933                 return false;
 934
 935         bool updated = false;
 936         std::list<ModelAction *>::iterator it = list->begin();
 937         while (it != list->end()) {
 938                 ModelAction *act = *it;
 939                 const ModelAction *rf = act->get_reads_from();
 940                 std::vector<const ModelAction *> release_heads;
 941                 bool complete;
 942                 complete = release_seq_head(rf, &release_heads);
 943                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 944                         if (!act->has_synchronized_with(release_heads[i])) {
 945                                 updated = true;
 946                                 act->synchronize_with(release_heads[i]);
 947                         }
 948                 }
 949
 950                 if (updated) {
 951                         /* propagate synchronization to later actions */
 952                         action_list_t::reverse_iterator it = action_trace->rbegin();
 953                         while ((*it) != act) {
 954                                 ModelAction *propagate = *it;
 955                                 if (act->happens_before(propagate))
 956                                         /** @todo new mo_graph edges along with
 957                                          * this synchronization? */
 958                                         propagate->synchronize_with(act);
 959                         }
 960                 }
 961                 if (complete) {
 962                         it = list->erase(it);
 963                         (*lazy_sync_size)--;
 964                 } else
 965                         it++;
 966         }
 967
 968         // If we resolved promises or data races, see if we have realized a data race.
 969         if (checkDataRaces()) {
 970                 set_assert();
 971         }
 972
 973         return updated;
 974 }
 975
 976 /**
 977  * Performs various bookkeeping operations for the current ModelAction. For
 978  * instance, adds action to the per-object, per-thread action vector and to the
 979  * action trace list of all thread actions.
 980  *
 981  * @param act is the ModelAction to add.
 982  */
 983 void ModelChecker::add_action_to_lists(ModelAction *act)
 984 {
 985         int tid = id_to_int(act->get_tid());
 986         action_trace->push_back(act);
 987
 988         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 989
 990         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 991         if (tid >= (int)vec->size())
 992                 vec->resize(priv->next_thread_id);
 993         (*vec)[tid].push_back(act);
 994
 995         if ((int)thrd_last_action->size() <= tid)
 996                 thrd_last_action->resize(get_num_threads());
 997         (*thrd_last_action)[tid] = act;
 998 }
 999
1000 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1001 {
1002         int nthreads = get_num_threads();
1003         if ((int)thrd_last_action->size() < nthreads)
1004                 thrd_last_action->resize(nthreads);
1005         return (*thrd_last_action)[id_to_int(tid)];
1006 }
1007
1008 /**
1009  * Gets the last memory_order_seq_cst action (in the total global sequence)
1010  * performed on a particular object (i.e., memory location).
1011  * @param location The object location to check
1012  * @return The last seq_cst action performed
1013  */
1014 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1015 {
1016         action_list_t *list = obj_map->get_safe_ptr(location);
1017         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1018         action_list_t::reverse_iterator rit;
1019         for (rit = list->rbegin(); rit != list->rend(); rit++)
1020                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1021                         return *rit;
1022         return NULL;
1023 }
1024
1025 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1026 {
1027         ModelAction *parent = get_last_action(tid);
1028         if (!parent)
1029                 parent = get_thread(tid)->get_creation();
1030         return parent;
1031 }
1032
1033 /**
1034  * Returns the clock vector for a given thread.
1035  * @param tid The thread whose clock vector we want
1036  * @return Desired clock vector
1037  */
1038 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1039 {
1040         return get_parent_action(tid)->get_cv();
1041 }
1042
1043 /**
1044  * Resolve a set of Promises with a current write. The set is provided in the
1045  * Node corresponding to @a write.
1046  * @param write The ModelAction that is fulfilling Promises
1047  * @return True if promises were resolved; false otherwise
1048  */
1049 bool ModelChecker::resolve_promises(ModelAction *write)
1050 {
1051         bool resolved = false;
1052
1053         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1054                 Promise *promise = (*promises)[promise_index];
1055                 if (write->get_node()->get_promise(i)) {
1056                         ModelAction *read = promise->get_action();
1057                         if (ensure_rmw_acyclic(read, write))
1058                                 read->read_from(write);
1059                         if (read->is_rmw()) {
1060                                 mo_graph->addRMWEdge(write, read);
1061                         }
1062                         r_modification_order(read, write);
1063                         post_r_modification_order(read, write);
1064                         promises->erase(promises->begin() + promise_index);
1065                         resolved = true;
1066                 } else
1067                         promise_index++;
1068         }
1069         return resolved;
1070 }
1071
1072
1073
1074 /**
1075  * Compute the set of promises that could potentially be satisfied by this
1076  * action. Note that the set computation actually appears in the Node, not in
1077  * ModelChecker.
1078  * @param curr The ModelAction that may satisfy promises
1079  */
1080 void ModelChecker::compute_promises(ModelAction *curr)
1081 {
1082         for (unsigned int i = 0; i < promises->size(); i++) {
1083                 Promise *promise = (*promises)[i];
1084                 const ModelAction *act = promise->get_action();
1085                 if (!act->happens_before(curr) &&
1086                                 act->is_read() &&
1087                                 !act->is_synchronizing(curr) &&
1088                                 !act->same_thread(curr) &&
1089                                 promise->get_value() == curr->get_value()) {
1090                         curr->get_node()->set_promise(i);
1091                 }
1092         }
1093 }
1094
1095 /** Checks promises in response to change in ClockVector Threads. */
1096 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1097 {
1098         for (unsigned int i = 0; i < promises->size(); i++) {
1099                 Promise *promise = (*promises)[i];
1100                 const ModelAction *act = promise->get_action();
1101                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1102                                 merge_cv->synchronized_since(act)) {
1103                         //This thread is no longer able to send values back to satisfy the promise
1104                         int num_synchronized_threads = promise->increment_threads();
1105                         if (num_synchronized_threads == get_num_threads()) {
1106                                 //Promise has failed
1107                                 failed_promise = true;
1108                                 return;
1109                         }
1110                 }
1111         }
1112 }
1113
1114 /**
1115  * Build up an initial set of all past writes that this 'read' action may read
1116  * from. This set is determined by the clock vector's "happens before"
1117  * relationship.
1118  * @param curr is the current ModelAction that we are exploring; it must be a
1119  * 'read' operation.
1120  */
1121 void ModelChecker::build_reads_from_past(ModelAction *curr)
1122 {
1123         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1124         unsigned int i;
1125         ASSERT(curr->is_read());
1126
1127         ModelAction *last_seq_cst = NULL;
1128
1129         /* Track whether this object has been initialized */
1130         bool initialized = false;
1131
1132         if (curr->is_seqcst()) {
1133                 last_seq_cst = get_last_seq_cst(curr->get_location());
1134                 /* We have to at least see the last sequentially consistent write,
1135                          so we are initialized. */
1136                 if (last_seq_cst != NULL)
1137                         initialized = true;
1138         }
1139
1140         /* Iterate over all threads */
1141         for (i = 0; i < thrd_lists->size(); i++) {
1142                 /* Iterate over actions in thread, starting from most recent */
1143                 action_list_t *list = &(*thrd_lists)[i];
1144                 action_list_t::reverse_iterator rit;
1145                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1146                         ModelAction *act = *rit;
1147
1148                         /* Only consider 'write' actions */
1149                         if (!act->is_write())
1150                                 continue;
1151
1152                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1153                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1154                                 DEBUG("Adding action to may_read_from:\n");
1155                                 if (DBG_ENABLED()) {
1156                                         act->print();
1157                                         curr->print();
1158                                 }
1159                                 curr->get_node()->add_read_from(act);
1160                         }
1161
1162                         /* Include at most one act per-thread that "happens before" curr */
1163                         if (act->happens_before(curr)) {
1164                                 initialized = true;
1165                                 break;
1166                         }
1167                 }
1168         }
1169
1170         if (!initialized) {
1171                 /** @todo Need a more informative way of reporting errors. */
1172                 printf("ERROR: may read from uninitialized atomic\n");
1173         }
1174
1175         if (DBG_ENABLED() || !initialized) {
1176                 printf("Reached read action:\n");
1177                 curr->print();
1178                 printf("Printing may_read_from\n");
1179                 curr->get_node()->print_may_read_from();
1180                 printf("End printing may_read_from\n");
1181         }
1182
1183         ASSERT(initialized);
1184 }
1185
1186 static void print_list(action_list_t *list)
1187 {
1188         action_list_t::iterator it;
1189
1190         printf("---------------------------------------------------------------------\n");
1191         printf("Trace:\n");
1192
1193         for (it = list->begin(); it != list->end(); it++) {
1194                 (*it)->print();
1195         }
1196         printf("---------------------------------------------------------------------\n");
1197 }
1198
1199 void ModelChecker::print_summary()
1200 {
1201         printf("\n");
1202         printf("Number of executions: %d\n", num_executions);
1203         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1204
1205         scheduler->print();
1206
1207         if (!isfinalfeasible())
1208                 printf("INFEASIBLE EXECUTION!\n");
1209         print_list(action_trace);
1210         printf("\n");
1211 }
1212
1213 /**
1214  * Add a Thread to the system for the first time. Should only be called once
1215  * per thread.
1216  * @param t The Thread to add
1217  */
1218 void ModelChecker::add_thread(Thread *t)
1219 {
1220         thread_map->put(id_to_int(t->get_id()), t);
1221         scheduler->add_thread(t);
1222 }
1223
1224 void ModelChecker::remove_thread(Thread *t)
1225 {
1226         scheduler->remove_thread(t);
1227 }
1228
1229 /**
1230  * Switch from a user-context to the "master thread" context (a.k.a. system
1231  * context). This switch is made with the intention of exploring a particular
1232  * model-checking action (described by a ModelAction object). Must be called
1233  * from a user-thread context.
1234  * @param act The current action that will be explored. Must not be NULL.
1235  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1236  */
1237 int ModelChecker::switch_to_master(ModelAction *act)
1238 {
1239         DBG();
1240         Thread *old = thread_current();
1241         set_current_action(act);
1242         old->set_state(THREAD_READY);
1243         return Thread::swap(old, &system_context);
1244 }
1245
1246 /**
1247  * Takes the next step in the execution, if possible.
1248  * @return Returns true (success) if a step was taken and false otherwise.
1249  */
1250 bool ModelChecker::take_step() {
1251         Thread *curr, *next;
1252
1253         if (has_asserted())
1254                 return false;
1255
1256         curr = thread_current();
1257         if (curr) {
1258                 if (curr->get_state() == THREAD_READY) {
1259                         ASSERT(priv->current_action);
1260
1261                         priv->nextThread = check_current_action(priv->current_action);
1262                         priv->current_action = NULL;
1263                         if (!curr->is_blocked() && !curr->is_complete())
1264                                 scheduler->add_thread(curr);
1265                 } else {
1266                         ASSERT(false);
1267                 }
1268         }
1269         next = scheduler->next_thread(priv->nextThread);
1270
1271         /* Infeasible -> don't take any more steps */
1272         if (!isfeasible())
1273                 return false;
1274
1275         if (next)
1276                 next->set_state(THREAD_RUNNING);
1277         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1278
1279         /* next == NULL -> don't take any more steps */
1280         if (!next)
1281                 return false;
1282         /* Return false only if swap fails with an error */
1283         return (Thread::swap(&system_context, next) == 0);
1284 }
1285
1286 /** Runs the current execution until threre are no more steps to take. */
1287 void ModelChecker::finish_execution() {
1288         DBG();
1289
1290         while (take_step());
1291 }