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