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