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 second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 266  * @return True if processing this read updates the mo_graph.
 267  */
 268 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 269 {
 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                         bool r_status = false;
 279
 280                         if (!second_part_of_rmw) {
 281                                 check_recency(curr,false);
 282                                 r_status = r_modification_order(curr, reads_from);
 283                         }
 284
 285
 286                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 287                                 mo_graph->rollbackChanges();
 288                                 too_many_reads = false;
 289                                 continue;
 290                         }
 291
 292                         curr->read_from(reads_from);
 293                         mo_graph->commitChanges();
 294                         updated |= r_status;
 295                 } else if (!second_part_of_rmw) {
 296                         /* Read from future value */
 297                         value = curr->get_node()->get_future_value();
 298                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 299                         curr->read_from(NULL);
 300                         Promise *valuepromise = new Promise(curr, value, expiration);
 301                         promises->push_back(valuepromise);
 302                 }
 303                 get_thread(curr)->set_return_value(value);
 304                 return updated;
 305         }
 306 }
 307
 308 /**
 309  * Process a write ModelAction
 310  * @param curr The ModelAction to process
 311  * @return True if the mo_graph was updated or promises were resolved
 312  */
 313 bool ModelChecker::process_write(ModelAction *curr)
 314 {
 315         bool updated_mod_order = w_modification_order(curr);
 316         bool updated_promises = resolve_promises(curr);
 317
 318         if (promises->size() == 0) {
 319                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 320                         struct PendingFutureValue pfv = (*futurevalues)[i];
 321                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 322                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 323                                 priv->next_backtrack = pfv.act;
 324                 }
 325                 futurevalues->resize(0);
 326         }
 327
 328         mo_graph->commitChanges();
 329         get_thread(curr)->set_return_value(VALUE_NONE);
 330         return updated_mod_order || updated_promises;
 331 }
 332
 333 /**
 334  * This is the heart of the model checker routine. It performs model-checking
 335  * actions corresponding to a given "current action." Among other processes, it
 336  * calculates reads-from relationships, updates synchronization clock vectors,
 337  * forms a memory_order constraints graph, and handles replay/backtrack
 338  * execution when running permutations of previously-observed executions.
 339  *
 340  * @param curr The current action to process
 341  * @return The next Thread that must be executed. May be NULL if ModelChecker
 342  * makes no choice (e.g., according to replay execution, combining RMW actions,
 343  * etc.)
 344  */
 345 Thread * ModelChecker::check_current_action(ModelAction *curr)
 346 {
 347         bool second_part_of_rmw = false;
 348
 349         ASSERT(curr);
 350
 351         if (curr->is_rmwc() || curr->is_rmw()) {
 352                 ModelAction *tmp = process_rmw(curr);
 353                 second_part_of_rmw = true;
 354                 delete curr;
 355                 curr = tmp;
 356                 compute_promises(curr);
 357         } else {
 358                 ModelAction *tmp = node_stack->explore_action(curr);
 359                 if (tmp) {
 360                         /* Discard duplicate ModelAction; use action from NodeStack */
 361                         /* First restore type and order in case of RMW operation */
 362                         if (curr->is_rmwr())
 363                                 tmp->copy_typeandorder(curr);
 364
 365                         /* If we have diverged, we need to reset the clock vector. */
 366                         if (diverge == NULL)
 367                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 368
 369                         delete curr;
 370                         curr = tmp;
 371                 } else {
 372                         /*
 373                          * Perform one-time actions when pushing new ModelAction onto
 374                          * NodeStack
 375                          */
 376                         curr->create_cv(get_parent_action(curr->get_tid()));
 377                         /* Build may_read_from set */
 378                         if (curr->is_read())
 379                                 build_reads_from_past(curr);
 380                         if (curr->is_write())
 381                                 compute_promises(curr);
 382                 }
 383         }
 384
 385         /* Thread specific actions */
 386         switch (curr->get_type()) {
 387         case THREAD_CREATE: {
 388                 Thread *th = (Thread *)curr->get_location();
 389                 th->set_creation(curr);
 390                 break;
 391         }
 392         case THREAD_JOIN: {
 393                 Thread *waiting, *blocking;
 394                 waiting = get_thread(curr);
 395                 blocking = (Thread *)curr->get_location();
 396                 if (!blocking->is_complete()) {
 397                         blocking->push_wait_list(curr);
 398                         scheduler->sleep(waiting);
 399                 }
 400                 break;
 401         }
 402         case THREAD_FINISH: {
 403                 Thread *th = get_thread(curr);
 404                 while (!th->wait_list_empty()) {
 405                         ModelAction *act = th->pop_wait_list();
 406                         Thread *wake = get_thread(act);
 407                         scheduler->wake(wake);
 408                 }
 409                 th->complete();
 410                 break;
 411         }
 412         case THREAD_START: {
 413                 check_promises(NULL, curr->get_cv());
 414                 break;
 415         }
 416         default:
 417                 break;
 418         }
 419
 420         work_queue_t work_queue(1, CheckCurrWorkEntry(curr));
 421
 422         while (!work_queue.empty()) {
 423                 WorkQueueEntry work = work_queue.front();
 424                 work_queue.pop_front();
 425
 426                 switch (work.type) {
 427                 case WORK_CHECK_CURR_ACTION: {
 428                         ModelAction *act = work.action;
 429                         bool updated = false;
 430                         if (act->is_read() && process_read(act, second_part_of_rmw))
 431                                 updated = true;
 432
 433                         if (act->is_write() && process_write(act))
 434                                 updated = true;
 435
 436                         if (updated)
 437                                 work_queue.push_back(CheckRelSeqWorkEntry(act->get_location()));
 438                         break;
 439                 }
 440                 case WORK_CHECK_RELEASE_SEQ:
 441                         resolve_release_sequences(work.location);
 442                         break;
 443                 case WORK_CHECK_MO_EDGES:
 444                         /** @todo Perform follow-up mo_graph checks */
 445                 default:
 446                         ASSERT(false);
 447                         break;
 448                 }
 449         }
 450
 451         /* Add action to list.  */
 452         if (!second_part_of_rmw)
 453                 add_action_to_lists(curr);
 454
 455         check_curr_backtracking(curr);
 456
 457         set_backtracking(curr);
 458
 459         return get_next_thread(curr);
 460 }
 461
 462 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 463         Node *currnode = curr->get_node();
 464         Node *parnode = currnode->get_parent();
 465
 466         if ((!parnode->backtrack_empty() ||
 467                          !currnode->read_from_empty() ||
 468                          !currnode->future_value_empty() ||
 469                          !currnode->promise_empty())
 470                         && (!priv->next_backtrack ||
 471                                         *curr > *priv->next_backtrack)) {
 472                 priv->next_backtrack = curr;
 473         }
 474 }
 475
 476 bool ModelChecker::promises_expired() {
 477         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 478                 Promise *promise = (*promises)[promise_index];
 479                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 480                         return true;
 481                 }
 482         }
 483         return false;
 484 }
 485
 486 /** @returns whether the current partial trace must be a prefix of a
 487  * feasible trace. */
 488 bool ModelChecker::isfeasibleprefix() {
 489         return promises->size() == 0 && *lazy_sync_size == 0;
 490 }
 491
 492 /** @returns whether the current partial trace is feasible. */
 493 bool ModelChecker::isfeasible() {
 494         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 495 }
 496
 497 /** @returns whether the current partial trace is feasible other than
 498  * multiple RMW reading from the same store. */
 499 bool ModelChecker::isfeasibleotherthanRMW() {
 500         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 501 }
 502
 503 /** Returns whether the current completed trace is feasible. */
 504 bool ModelChecker::isfinalfeasible() {
 505         return isfeasible() && promises->size() == 0;
 506 }
 507
 508 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 509 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 510         int tid = id_to_int(act->get_tid());
 511         ModelAction *lastread = get_last_action(tid);
 512         lastread->process_rmw(act);
 513         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 514                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 515                 mo_graph->commitChanges();
 516         }
 517         return lastread;
 518 }
 519
 520 /**
 521  * Checks whether a thread has read from the same write for too many times
 522  * without seeing the effects of a later write.
 523  *
 524  * Basic idea:
 525  * 1) there must a different write that we could read from that would satisfy the modification order,
 526  * 2) we must have read from the same value in excess of maxreads times, and
 527  * 3) that other write must have been in the reads_from set for maxreads times.
 528  *
 529  * If so, we decide that the execution is no longer feasible.
 530  */
 531 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 532         if (params.maxreads != 0) {
 533                 if (curr->get_node()->get_read_from_size() <= 1)
 534                         return;
 535
 536                 //Must make sure that execution is currently feasible...  We could
 537                 //accidentally clear by rolling back
 538                 if (!isfeasible())
 539                         return;
 540
 541                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 542                 int tid = id_to_int(curr->get_tid());
 543
 544                 /* Skip checks */
 545                 if ((int)thrd_lists->size() <= tid)
 546                         return;
 547
 548                 action_list_t *list = &(*thrd_lists)[tid];
 549
 550                 action_list_t::reverse_iterator rit = list->rbegin();
 551                 /* Skip past curr */
 552                 if (already_added) {
 553                         for (; (*rit) != curr; rit++)
 554                                 ;
 555                         /* go past curr now */
 556                         rit++;
 557                 }
 558
 559                 action_list_t::reverse_iterator ritcopy = rit;
 560                 //See if we have enough reads from the same value
 561                 int count = 0;
 562                 for (; count < params.maxreads; rit++,count++) {
 563                         if (rit==list->rend())
 564                                 return;
 565                         ModelAction *act = *rit;
 566                         if (!act->is_read())
 567                                 return;
 568                         if (act->get_reads_from() != curr->get_reads_from())
 569                                 return;
 570                         if (act->get_node()->get_read_from_size() <= 1)
 571                                 return;
 572                 }
 573
 574                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 575                         //Get write
 576                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 577                         //Need a different write
 578                         if (write==curr->get_reads_from())
 579                                 continue;
 580
 581                         /* Test to see whether this is a feasible write to read from*/
 582                         mo_graph->startChanges();
 583                         r_modification_order(curr, write);
 584                         bool feasiblereadfrom = isfeasible();
 585                         mo_graph->rollbackChanges();
 586
 587                         if (!feasiblereadfrom)
 588                                 continue;
 589                         rit = ritcopy;
 590
 591                         bool feasiblewrite = true;
 592                         //new we need to see if this write works for everyone
 593
 594                         for (int loop = count; loop>0; loop--,rit++) {
 595                                 ModelAction *act=*rit;
 596                                 bool foundvalue = false;
 597                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 598                                         if (act->get_node()->get_read_from_at(i)==write) {
 599                                                 foundvalue = true;
 600                                                 break;
 601                                         }
 602                                 }
 603                                 if (!foundvalue) {
 604                                         feasiblewrite = false;
 605                                         break;
 606                                 }
 607                         }
 608                         if (feasiblewrite) {
 609                                 too_many_reads = true;
 610                                 return;
 611                         }
 612                 }
 613         }
 614 }
 615
 616 /**
 617  * Updates the mo_graph with the constraints imposed from the current read.
 618  * @param curr The current action. Must be a read.
 619  * @param rf The action that curr reads from. Must be a write.
 620  * @return True if modification order edges were added; false otherwise
 621  */
 622 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 623 {
 624         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 625         unsigned int i;
 626         bool added = false;
 627         ASSERT(curr->is_read());
 628
 629         /* Iterate over all threads */
 630         for (i = 0; i < thrd_lists->size(); i++) {
 631                 /* Iterate over actions in thread, starting from most recent */
 632                 action_list_t *list = &(*thrd_lists)[i];
 633                 action_list_t::reverse_iterator rit;
 634                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 635                         ModelAction *act = *rit;
 636
 637                         /* Include at most one act per-thread that "happens before" curr */
 638                         if (act->happens_before(curr)) {
 639                                 if (act->is_write()) {
 640                                         if (rf != act && act != curr) {
 641                                                 mo_graph->addEdge(act, rf);
 642                                                 added = true;
 643                                         }
 644                                 } else {
 645                                         const ModelAction *prevreadfrom = act->get_reads_from();
 646                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 647                                                 mo_graph->addEdge(prevreadfrom, rf);
 648                                                 added = true;
 649                                         }
 650                                 }
 651
 652                                 break;
 653                         }
 654                 }
 655         }
 656
 657         return added;
 658 }
 659
 660 /** Updates the mo_graph with the constraints imposed from the current read. */
 661 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 662 {
 663         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 664         unsigned int i;
 665         ASSERT(curr->is_read());
 666
 667         /* Iterate over all threads */
 668         for (i = 0; i < thrd_lists->size(); i++) {
 669                 /* Iterate over actions in thread, starting from most recent */
 670                 action_list_t *list = &(*thrd_lists)[i];
 671                 action_list_t::reverse_iterator rit;
 672                 ModelAction *lastact = NULL;
 673
 674                 /* Find last action that happens after curr */
 675                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 676                         ModelAction *act = *rit;
 677                         if (curr->happens_before(act)) {
 678                                 lastact = act;
 679                         } else
 680                                 break;
 681                 }
 682
 683                         /* Include at most one act per-thread that "happens before" curr */
 684                 if (lastact != NULL) {
 685                         if (lastact->is_read()) {
 686                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 687                                 if (postreadfrom != NULL&&rf != postreadfrom)
 688                                         mo_graph->addEdge(rf, postreadfrom);
 689                         } else if (rf != lastact) {
 690                                 mo_graph->addEdge(rf, lastact);
 691                         }
 692                         break;
 693                 }
 694         }
 695 }
 696
 697 /**
 698  * Updates the mo_graph with the constraints imposed from the current write.
 699  * @param curr The current action. Must be a write.
 700  * @return True if modification order edges were added; false otherwise
 701  */
 702 bool ModelChecker::w_modification_order(ModelAction *curr)
 703 {
 704         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 705         unsigned int i;
 706         bool added = false;
 707         ASSERT(curr->is_write());
 708
 709         if (curr->is_seqcst()) {
 710                 /* We have to at least see the last sequentially consistent write,
 711                          so we are initialized. */
 712                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 713                 if (last_seq_cst != NULL) {
 714                         mo_graph->addEdge(last_seq_cst, curr);
 715                         added = true;
 716                 }
 717         }
 718
 719         /* Iterate over all threads */
 720         for (i = 0; i < thrd_lists->size(); i++) {
 721                 /* Iterate over actions in thread, starting from most recent */
 722                 action_list_t *list = &(*thrd_lists)[i];
 723                 action_list_t::reverse_iterator rit;
 724                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 725                         ModelAction *act = *rit;
 726
 727                         /* Include at most one act per-thread that "happens before" curr */
 728                         if (act->happens_before(curr)) {
 729                                 /*
 730                                  * Note: if act is RMW, just add edge:
 731                                  *   act --mo--> curr
 732                                  * The following edge should be handled elsewhere:
 733                                  *   readfrom(act) --mo--> act
 734                                  */
 735                                 if (act->is_write()) {
 736                                         //RMW shouldn't have an edge to themselves
 737                                         if (act!=curr)
 738                                                 mo_graph->addEdge(act, curr);
 739                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 740                                         mo_graph->addEdge(act->get_reads_from(), curr);
 741                                 added = true;
 742                                 break;
 743                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 744                                                      !act->same_thread(curr)) {
 745                                 /* We have an action that:
 746                                    (1) did not happen before us
 747                                    (2) is a read and we are a write
 748                                    (3) cannot synchronize with us
 749                                    (4) is in a different thread
 750                                    =>
 751                                    that read could potentially read from our write.
 752                                  */
 753                                 if (thin_air_constraint_may_allow(curr, act)) {
 754                                         if (isfeasible() ||
 755                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 756                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 757                                                 futurevalues->push_back(pfv);
 758                                         }
 759                                 }
 760                         }
 761                 }
 762         }
 763
 764         return added;
 765 }
 766
 767 /** Arbitrary reads from the future are not allowed.  Section 29.3
 768  * part 9 places some constraints.  This method checks one result of constraint
 769  * constraint.  Others require compiler support. */
 770
 771 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 772         if (!writer->is_rmw())
 773                 return true;
 774
 775         if (!reader->is_rmw())
 776                 return true;
 777
 778         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 779                 if (search==reader)
 780                         return false;
 781                 if (search->get_tid() == reader->get_tid() &&
 782                                 search->happens_before(reader))
 783                         break;
 784         }
 785
 786         return true;
 787 }
 788
 789 /**
 790  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 791  * The ModelAction under consideration is expected to be taking part in
 792  * release/acquire synchronization as an object of the "reads from" relation.
 793  * Note that this can only provide release sequence support for RMW chains
 794  * which do not read from the future, as those actions cannot be traced until
 795  * their "promise" is fulfilled. Similarly, we may not even establish the
 796  * presence of a release sequence with certainty, as some modification order
 797  * constraints may be decided further in the future. Thus, this function
 798  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 799  * and a boolean representing certainty.
 800  *
 801  * @todo Finish lazy updating, when promises are fulfilled in the future
 802  * @param rf The action that might be part of a release sequence. Must be a
 803  * write.
 804  * @param release_heads A pass-by-reference style return parameter.  After
 805  * execution of this function, release_heads will contain the heads of all the
 806  * relevant release sequences, if any exists
 807  * @return true, if the ModelChecker is certain that release_heads is complete;
 808  * false otherwise
 809  */
 810 bool ModelChecker::release_seq_head(const ModelAction *rf,
 811                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 812 {
 813         if (!rf) {
 814                 /* read from future: need to settle this later */
 815                 return false; /* incomplete */
 816         }
 817
 818         ASSERT(rf->is_write());
 819
 820         if (rf->is_release())
 821                 release_heads->push_back(rf);
 822         if (rf->is_rmw()) {
 823                 /* We need a RMW action that is both an acquire and release to stop */
 824                 /** @todo Need to be smarter here...  In the linux lock
 825                  * example, this will run to the beginning of the program for
 826                  * every acquire. */
 827                 if (rf->is_acquire() && rf->is_release())
 828                         return true; /* complete */
 829                 return release_seq_head(rf->get_reads_from(), release_heads);
 830         }
 831         if (rf->is_release())
 832                 return true; /* complete */
 833
 834         /* else relaxed write; check modification order for contiguous subsequence
 835          * -> rf must be same thread as release */
 836         int tid = id_to_int(rf->get_tid());
 837         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 838         action_list_t *list = &(*thrd_lists)[tid];
 839         action_list_t::const_reverse_iterator rit;
 840
 841         /* Find rf in the thread list */
 842         rit = std::find(list->rbegin(), list->rend(), rf);
 843         ASSERT(rit != list->rend());
 844
 845         /* Find the last write/release */
 846         for (; rit != list->rend(); rit++)
 847                 if ((*rit)->is_release())
 848                         break;
 849         if (rit == list->rend()) {
 850                 /* No write-release in this thread */
 851                 return true; /* complete */
 852         }
 853         ModelAction *release = *rit;
 854
 855         ASSERT(rf->same_thread(release));
 856
 857         bool certain = true;
 858         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 859                 if (id_to_int(rf->get_tid()) == (int)i)
 860                         continue;
 861                 list = &(*thrd_lists)[i];
 862
 863                 /* Can we ensure no future writes from this thread may break
 864                  * the release seq? */
 865                 bool future_ordered = false;
 866
 867                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 868                         const ModelAction *act = *rit;
 869                         if (!act->is_write())
 870                                 continue;
 871                         /* Reach synchronization -> this thread is complete */
 872                         if (act->happens_before(release))
 873                                 break;
 874                         if (rf->happens_before(act)) {
 875                                 future_ordered = true;
 876                                 continue;
 877                         }
 878
 879                         /* Check modification order */
 880                         if (mo_graph->checkReachable(rf, act)) {
 881                                 /* rf --mo--> act */
 882                                 future_ordered = true;
 883                                 continue;
 884                         }
 885                         if (mo_graph->checkReachable(act, release))
 886                                 /* act --mo--> release */
 887                                 break;
 888                         if (mo_graph->checkReachable(release, act) &&
 889                                       mo_graph->checkReachable(act, rf)) {
 890                                 /* release --mo-> act --mo--> rf */
 891                                 return true; /* complete */
 892                         }
 893                         certain = false;
 894                 }
 895                 if (!future_ordered)
 896                         return false; /* This thread is uncertain */
 897         }
 898
 899         if (certain)
 900                 release_heads->push_back(release);
 901         return certain;
 902 }
 903
 904 /**
 905  * A public interface for getting the release sequence head(s) with which a
 906  * given ModelAction must synchronize. This function only returns a non-empty
 907  * result when it can locate a release sequence head with certainty. Otherwise,
 908  * it may mark the internal state of the ModelChecker so that it will handle
 909  * the release sequence at a later time, causing @a act to update its
 910  * synchronization at some later point in execution.
 911  * @param act The 'acquire' action that may read from a release sequence
 912  * @param release_heads A pass-by-reference return parameter. Will be filled
 913  * with the head(s) of the release sequence(s), if they exists with certainty.
 914  * @see ModelChecker::release_seq_head
 915  */
 916 void ModelChecker::get_release_seq_heads(ModelAction *act,
 917                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 918 {
 919         const ModelAction *rf = act->get_reads_from();
 920         bool complete;
 921         complete = release_seq_head(rf, release_heads);
 922         if (!complete) {
 923                 /* add act to 'lazy checking' list */
 924                 std::list<ModelAction *> *list;
 925                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 926                 list->push_back(act);
 927                 (*lazy_sync_size)++;
 928         }
 929 }
 930
 931 /**
 932  * Attempt to resolve all stashed operations that might synchronize with a
 933  * release sequence for a given location. This implements the "lazy" portion of
 934  * determining whether or not a release sequence was contiguous, since not all
 935  * modification order information is present at the time an action occurs.
 936  *
 937  * @param location The location/object that should be checked for release
 938  * sequence resolutions
 939  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 940  */
 941 bool ModelChecker::resolve_release_sequences(void *location)
 942 {
 943         std::list<ModelAction *> *list;
 944         list = lazy_sync_with_release->getptr(location);
 945         if (!list)
 946                 return false;
 947
 948         bool updated = false;
 949         std::list<ModelAction *>::iterator it = list->begin();
 950         while (it != list->end()) {
 951                 ModelAction *act = *it;
 952                 const ModelAction *rf = act->get_reads_from();
 953                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
 954                 bool complete;
 955                 complete = release_seq_head(rf, &release_heads);
 956                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 957                         if (!act->has_synchronized_with(release_heads[i])) {
 958                                 updated = true;
 959                                 act->synchronize_with(release_heads[i]);
 960                         }
 961                 }
 962
 963                 if (updated) {
 964                         /* propagate synchronization to later actions */
 965                         action_list_t::reverse_iterator it = action_trace->rbegin();
 966                         while ((*it) != act) {
 967                                 ModelAction *propagate = *it;
 968                                 if (act->happens_before(propagate))
 969                                         /** @todo new mo_graph edges along with
 970                                          * this synchronization? */
 971                                         propagate->synchronize_with(act);
 972                         }
 973                 }
 974                 if (complete) {
 975                         it = list->erase(it);
 976                         (*lazy_sync_size)--;
 977                 } else
 978                         it++;
 979         }
 980
 981         // If we resolved promises or data races, see if we have realized a data race.
 982         if (checkDataRaces()) {
 983                 set_assert();
 984         }
 985
 986         return updated;
 987 }
 988
 989 /**
 990  * Performs various bookkeeping operations for the current ModelAction. For
 991  * instance, adds action to the per-object, per-thread action vector and to the
 992  * action trace list of all thread actions.
 993  *
 994  * @param act is the ModelAction to add.
 995  */
 996 void ModelChecker::add_action_to_lists(ModelAction *act)
 997 {
 998         int tid = id_to_int(act->get_tid());
 999         action_trace->push_back(act);
1000
1001         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1002
1003         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1004         if (tid >= (int)vec->size())
1005                 vec->resize(priv->next_thread_id);
1006         (*vec)[tid].push_back(act);
1007
1008         if ((int)thrd_last_action->size() <= tid)
1009                 thrd_last_action->resize(get_num_threads());
1010         (*thrd_last_action)[tid] = act;
1011 }
1012
1013 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1014 {
1015         int nthreads = get_num_threads();
1016         if ((int)thrd_last_action->size() < nthreads)
1017                 thrd_last_action->resize(nthreads);
1018         return (*thrd_last_action)[id_to_int(tid)];
1019 }
1020
1021 /**
1022  * Gets the last memory_order_seq_cst action (in the total global sequence)
1023  * performed on a particular object (i.e., memory location).
1024  * @param location The object location to check
1025  * @return The last seq_cst action performed
1026  */
1027 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1028 {
1029         action_list_t *list = obj_map->get_safe_ptr(location);
1030         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1031         action_list_t::reverse_iterator rit;
1032         for (rit = list->rbegin(); rit != list->rend(); rit++)
1033                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1034                         return *rit;
1035         return NULL;
1036 }
1037
1038 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1039 {
1040         ModelAction *parent = get_last_action(tid);
1041         if (!parent)
1042                 parent = get_thread(tid)->get_creation();
1043         return parent;
1044 }
1045
1046 /**
1047  * Returns the clock vector for a given thread.
1048  * @param tid The thread whose clock vector we want
1049  * @return Desired clock vector
1050  */
1051 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1052 {
1053         return get_parent_action(tid)->get_cv();
1054 }
1055
1056 /**
1057  * Resolve a set of Promises with a current write. The set is provided in the
1058  * Node corresponding to @a write.
1059  * @param write The ModelAction that is fulfilling Promises
1060  * @return True if promises were resolved; false otherwise
1061  */
1062 bool ModelChecker::resolve_promises(ModelAction *write)
1063 {
1064         bool resolved = false;
1065
1066         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1067                 Promise *promise = (*promises)[promise_index];
1068                 if (write->get_node()->get_promise(i)) {
1069                         ModelAction *read = promise->get_action();
1070                         read->read_from(write);
1071                         if (read->is_rmw()) {
1072                                 mo_graph->addRMWEdge(write, read);
1073                         }
1074                         r_modification_order(read, write);
1075                         post_r_modification_order(read, write);
1076                         promises->erase(promises->begin() + promise_index);
1077                         resolved = true;
1078                 } else
1079                         promise_index++;
1080         }
1081         return resolved;
1082 }
1083
1084 /**
1085  * Compute the set of promises that could potentially be satisfied by this
1086  * action. Note that the set computation actually appears in the Node, not in
1087  * ModelChecker.
1088  * @param curr The ModelAction that may satisfy promises
1089  */
1090 void ModelChecker::compute_promises(ModelAction *curr)
1091 {
1092         for (unsigned int i = 0; i < promises->size(); i++) {
1093                 Promise *promise = (*promises)[i];
1094                 const ModelAction *act = promise->get_action();
1095                 if (!act->happens_before(curr) &&
1096                                 act->is_read() &&
1097                                 !act->is_synchronizing(curr) &&
1098                                 !act->same_thread(curr) &&
1099                                 promise->get_value() == curr->get_value()) {
1100                         curr->get_node()->set_promise(i);
1101                 }
1102         }
1103 }
1104
1105 /** Checks promises in response to change in ClockVector Threads. */
1106 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1107 {
1108         for (unsigned int i = 0; i < promises->size(); i++) {
1109                 Promise *promise = (*promises)[i];
1110                 const ModelAction *act = promise->get_action();
1111                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1112                                 merge_cv->synchronized_since(act)) {
1113                         //This thread is no longer able to send values back to satisfy the promise
1114                         int num_synchronized_threads = promise->increment_threads();
1115                         if (num_synchronized_threads == get_num_threads()) {
1116                                 //Promise has failed
1117                                 failed_promise = true;
1118                                 return;
1119                         }
1120                 }
1121         }
1122 }
1123
1124 /**
1125  * Build up an initial set of all past writes that this 'read' action may read
1126  * from. This set is determined by the clock vector's "happens before"
1127  * relationship.
1128  * @param curr is the current ModelAction that we are exploring; it must be a
1129  * 'read' operation.
1130  */
1131 void ModelChecker::build_reads_from_past(ModelAction *curr)
1132 {
1133         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1134         unsigned int i;
1135         ASSERT(curr->is_read());
1136
1137         ModelAction *last_seq_cst = NULL;
1138
1139         /* Track whether this object has been initialized */
1140         bool initialized = false;
1141
1142         if (curr->is_seqcst()) {
1143                 last_seq_cst = get_last_seq_cst(curr->get_location());
1144                 /* We have to at least see the last sequentially consistent write,
1145                          so we are initialized. */
1146                 if (last_seq_cst != NULL)
1147                         initialized = true;
1148         }
1149
1150         /* Iterate over all threads */
1151         for (i = 0; i < thrd_lists->size(); i++) {
1152                 /* Iterate over actions in thread, starting from most recent */
1153                 action_list_t *list = &(*thrd_lists)[i];
1154                 action_list_t::reverse_iterator rit;
1155                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1156                         ModelAction *act = *rit;
1157
1158                         /* Only consider 'write' actions */
1159                         if (!act->is_write())
1160                                 continue;
1161
1162                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1163                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1164                                 DEBUG("Adding action to may_read_from:\n");
1165                                 if (DBG_ENABLED()) {
1166                                         act->print();
1167                                         curr->print();
1168                                 }
1169                                 curr->get_node()->add_read_from(act);
1170                         }
1171
1172                         /* Include at most one act per-thread that "happens before" curr */
1173                         if (act->happens_before(curr)) {
1174                                 initialized = true;
1175                                 break;
1176                         }
1177                 }
1178         }
1179
1180         if (!initialized) {
1181                 /** @todo Need a more informative way of reporting errors. */
1182                 printf("ERROR: may read from uninitialized atomic\n");
1183         }
1184
1185         if (DBG_ENABLED() || !initialized) {
1186                 printf("Reached read action:\n");
1187                 curr->print();
1188                 printf("Printing may_read_from\n");
1189                 curr->get_node()->print_may_read_from();
1190                 printf("End printing may_read_from\n");
1191         }
1192
1193         ASSERT(initialized);
1194 }
1195
1196 static void print_list(action_list_t *list)
1197 {
1198         action_list_t::iterator it;
1199
1200         printf("---------------------------------------------------------------------\n");
1201         printf("Trace:\n");
1202
1203         for (it = list->begin(); it != list->end(); it++) {
1204                 (*it)->print();
1205         }
1206         printf("---------------------------------------------------------------------\n");
1207 }
1208
1209 void ModelChecker::print_summary()
1210 {
1211         printf("\n");
1212         printf("Number of executions: %d\n", num_executions);
1213         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1214
1215         scheduler->print();
1216
1217         if (!isfinalfeasible())
1218                 printf("INFEASIBLE EXECUTION!\n");
1219         print_list(action_trace);
1220         printf("\n");
1221 }
1222
1223 /**
1224  * Add a Thread to the system for the first time. Should only be called once
1225  * per thread.
1226  * @param t The Thread to add
1227  */
1228 void ModelChecker::add_thread(Thread *t)
1229 {
1230         thread_map->put(id_to_int(t->get_id()), t);
1231         scheduler->add_thread(t);
1232 }
1233
1234 void ModelChecker::remove_thread(Thread *t)
1235 {
1236         scheduler->remove_thread(t);
1237 }
1238
1239 /**
1240  * Switch from a user-context to the "master thread" context (a.k.a. system
1241  * context). This switch is made with the intention of exploring a particular
1242  * model-checking action (described by a ModelAction object). Must be called
1243  * from a user-thread context.
1244  * @param act The current action that will be explored. Must not be NULL.
1245  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1246  */
1247 int ModelChecker::switch_to_master(ModelAction *act)
1248 {
1249         DBG();
1250         Thread *old = thread_current();
1251         set_current_action(act);
1252         old->set_state(THREAD_READY);
1253         return Thread::swap(old, &system_context);
1254 }
1255
1256 /**
1257  * Takes the next step in the execution, if possible.
1258  * @return Returns true (success) if a step was taken and false otherwise.
1259  */
1260 bool ModelChecker::take_step() {
1261         Thread *curr, *next;
1262
1263         if (has_asserted())
1264                 return false;
1265
1266         curr = thread_current();
1267         if (curr) {
1268                 if (curr->get_state() == THREAD_READY) {
1269                         ASSERT(priv->current_action);
1270
1271                         priv->nextThread = check_current_action(priv->current_action);
1272                         priv->current_action = NULL;
1273                         if (!curr->is_blocked() && !curr->is_complete())
1274                                 scheduler->add_thread(curr);
1275                 } else {
1276                         ASSERT(false);
1277                 }
1278         }
1279         next = scheduler->next_thread(priv->nextThread);
1280
1281         /* Infeasible -> don't take any more steps */
1282         if (!isfeasible())
1283                 return false;
1284
1285         if (next)
1286                 next->set_state(THREAD_RUNNING);
1287         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1288
1289         /* next == NULL -> don't take any more steps */
1290         if (!next)
1291                 return false;
1292         /* Return false only if swap fails with an error */
1293         return (Thread::swap(&system_context, next) == 0);
1294 }
1295
1296 /** Runs the current execution until threre are no more steps to take. */
1297 void ModelChecker::finish_execution() {
1298         DBG();
1299
1300         while (take_step());
1301 }