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         num_feasible_executions(0),
  25         params(params),
  26         diverge(NULL),
  27         action_trace(new action_list_t()),
  28         thread_map(new HashTable<int, Thread *, int>()),
  29         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  30         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  31         promises(new std::vector<Promise *>()),
  32         futurevalues(new std::vector<struct PendingFutureValue>()),
  33         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  34         thrd_last_action(new std::vector<ModelAction *>(1)),
  35         node_stack(new NodeStack()),
  36         mo_graph(new CycleGraph()),
  37         failed_promise(false),
  38         too_many_reads(false),
  39         asserted(false)
  40 {
  41         /* Allocate this "size" on the snapshotting heap */
  42         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  43         /* First thread created will have id INITIAL_THREAD_ID */
  44         priv->next_thread_id = INITIAL_THREAD_ID;
  45
  46         lazy_sync_size = &priv->lazy_sync_size;
  47 }
  48
  49 /** @brief Destructor */
  50 ModelChecker::~ModelChecker()
  51 {
  52         for (int i = 0; i < get_num_threads(); i++)
  53                 delete thread_map->get(i);
  54         delete thread_map;
  55
  56         delete obj_thrd_map;
  57         delete obj_map;
  58         delete action_trace;
  59
  60         for (unsigned int i = 0; i < promises->size(); i++)
  61                 delete (*promises)[i];
  62         delete promises;
  63
  64         delete lazy_sync_with_release;
  65
  66         delete thrd_last_action;
  67         delete node_stack;
  68         delete scheduler;
  69         delete mo_graph;
  70 }
  71
  72 /**
  73  * Restores user program to initial state and resets all model-checker data
  74  * structures.
  75  */
  76 void ModelChecker::reset_to_initial_state()
  77 {
  78         DEBUG("+++ Resetting to initial state +++\n");
  79         node_stack->reset_execution();
  80         failed_promise = false;
  81         too_many_reads = false;
  82         reset_asserted();
  83         snapshotObject->backTrackBeforeStep(0);
  84 }
  85
  86 /** @returns a thread ID for a new Thread */
  87 thread_id_t ModelChecker::get_next_id()
  88 {
  89         return priv->next_thread_id++;
  90 }
  91
  92 /** @returns the number of user threads created during this execution */
  93 int ModelChecker::get_num_threads()
  94 {
  95         return priv->next_thread_id;
  96 }
  97
  98 /** @returns a sequence number for a new ModelAction */
  99 modelclock_t ModelChecker::get_next_seq_num()
 100 {
 101         return ++priv->used_sequence_numbers;
 102 }
 103
 104 /**
 105  * @brief Choose the next thread to execute.
 106  *
 107  * This function chooses the next thread that should execute. It can force the
 108  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 109  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 110  * The model-checker may have no preference regarding the next thread (i.e.,
 111  * when exploring a new execution ordering), in which case this will return
 112  * NULL.
 113  * @param curr The current ModelAction. This action might guide the choice of
 114  * next thread.
 115  * @return The next thread to run. If the model-checker has no preference, NULL.
 116  */
 117 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 118 {
 119         thread_id_t tid;
 120
 121         /* Do not split atomic actions. */
 122         if (curr->is_rmwr())
 123                 return thread_current();
 124         /* The THREAD_CREATE action points to the created Thread */
 125         else if (curr->get_type() == THREAD_CREATE)
 126                 return (Thread *)curr->get_location();
 127
 128         /* Have we completed exploring the preselected path? */
 129         if (diverge == NULL)
 130                 return NULL;
 131
 132         /* Else, we are trying to replay an execution */
 133         ModelAction *next = node_stack->get_next()->get_action();
 134
 135         if (next == diverge) {
 136                 Node *nextnode = next->get_node();
 137                 /* Reached divergence point */
 138                 if (nextnode->increment_promise()) {
 139                         /* The next node will try to satisfy a different set of promises. */
 140                         tid = next->get_tid();
 141                         node_stack->pop_restofstack(2);
 142                 } else if (nextnode->increment_read_from()) {
 143                         /* The next node will read from a different value. */
 144                         tid = next->get_tid();
 145                         node_stack->pop_restofstack(2);
 146                 } else if (nextnode->increment_future_value()) {
 147                         /* The next node will try to read from a different future value. */
 148                         tid = next->get_tid();
 149                         node_stack->pop_restofstack(2);
 150                 } else {
 151                         /* Make a different thread execute for next step */
 152                         Node *node = nextnode->get_parent();
 153                         tid = node->get_next_backtrack();
 154                         node_stack->pop_restofstack(1);
 155                 }
 156                 DEBUG("*** Divergence point ***\n");
 157                 diverge = NULL;
 158         } else {
 159                 tid = next->get_tid();
 160         }
 161         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 162         ASSERT(tid != THREAD_ID_T_NONE);
 163         return thread_map->get(id_to_int(tid));
 164 }
 165
 166 /**
 167  * Queries the model-checker for more executions to explore and, if one
 168  * exists, resets the model-checker state to execute a new execution.
 169  *
 170  * @return If there are more executions to explore, return true. Otherwise,
 171  * return false.
 172  */
 173 bool ModelChecker::next_execution()
 174 {
 175         DBG();
 176
 177         num_executions++;
 178         if (isfinalfeasible())
 179                 num_feasible_executions++;
 180
 181         if (isfinalfeasible() || DBG_ENABLED())
 182                 print_summary();
 183
 184         if ((diverge = get_next_backtrack()) == NULL)
 185                 return false;
 186
 187         if (DBG_ENABLED()) {
 188                 printf("Next execution will diverge at:\n");
 189                 diverge->print();
 190         }
 191
 192         reset_to_initial_state();
 193         return true;
 194 }
 195
 196 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 197 {
 198         action_type type = act->get_type();
 199
 200         switch (type) {
 201                 case ATOMIC_READ:
 202                 case ATOMIC_WRITE:
 203                 case ATOMIC_RMW:
 204                         break;
 205                 default:
 206                         return NULL;
 207         }
 208         /* linear search: from most recent to oldest */
 209         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 210         action_list_t::reverse_iterator rit;
 211         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 212                 ModelAction *prev = *rit;
 213                 if (act->is_synchronizing(prev))
 214                         return prev;
 215         }
 216         return NULL;
 217 }
 218
 219 void ModelChecker::set_backtracking(ModelAction *act)
 220 {
 221         ModelAction *prev;
 222         Node *node;
 223         Thread *t = get_thread(act);
 224
 225         prev = get_last_conflict(act);
 226         if (prev == NULL)
 227                 return;
 228
 229         node = prev->get_node()->get_parent();
 230
 231         while (!node->is_enabled(t))
 232                 t = t->get_parent();
 233
 234         /* Check if this has been explored already */
 235         if (node->has_been_explored(t->get_id()))
 236                 return;
 237
 238         /* Cache the latest backtracking point */
 239         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 240                 priv->next_backtrack = prev;
 241
 242         /* If this is a new backtracking point, mark the tree */
 243         if (!node->set_backtrack(t->get_id()))
 244                 return;
 245         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 246                         prev->get_tid(), t->get_id());
 247         if (DBG_ENABLED()) {
 248                 prev->print();
 249                 act->print();
 250         }
 251 }
 252
 253 /**
 254  * Returns last backtracking point. The model checker will explore a different
 255  * path for this point in the next execution.
 256  * @return The ModelAction at which the next execution should diverge.
 257  */
 258 ModelAction * ModelChecker::get_next_backtrack()
 259 {
 260         ModelAction *next = priv->next_backtrack;
 261         priv->next_backtrack = NULL;
 262         return next;
 263 }
 264
 265 /**
 266  * Processes a read or rmw model action.
 267  * @param curr is the read model action to process.
 268  * @param th is the thread
 269  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 270  * @return True if processing this read updates the mo_graph.
 271  */
 272 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
 273         uint64_t value;
 274         bool updated = false;
 275         while (true) {
 276                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 277                 if (reads_from != NULL) {
 278                         mo_graph->startChanges();
 279
 280                         value = reads_from->get_value();
 281                         bool r_status = false;
 282
 283                         if (!second_part_of_rmw) {
 284                                 check_recency(curr,false);
 285                                 r_status = r_modification_order(curr, reads_from);
 286                         }
 287
 288
 289                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 290                                 mo_graph->rollbackChanges();
 291                                 too_many_reads = false;
 292                                 continue;
 293                         }
 294
 295                         curr->read_from(reads_from);
 296                         mo_graph->commitChanges();
 297                         updated |= r_status;
 298                 } else if (!second_part_of_rmw) {
 299                         /* Read from future value */
 300                         value = curr->get_node()->get_future_value();
 301                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 302                         curr->read_from(NULL);
 303                         Promise *valuepromise = new Promise(curr, value, expiration);
 304                         promises->push_back(valuepromise);
 305                 }
 306                 th->set_return_value(value);
 307                 return updated;
 308         }
 309 }
 310
 311 /**
 312  * This is the heart of the model checker routine. It performs model-checking
 313  * actions corresponding to a given "current action." Among other processes, it
 314  * calculates reads-from relationships, updates synchronization clock vectors,
 315  * forms a memory_order constraints graph, and handles replay/backtrack
 316  * execution when running permutations of previously-observed executions.
 317  *
 318  * @param curr The current action to process
 319  * @return The next Thread that must be executed. May be NULL if ModelChecker
 320  * makes no choice (e.g., according to replay execution, combining RMW actions,
 321  * etc.)
 322  */
 323 Thread * ModelChecker::check_current_action(ModelAction *curr)
 324 {
 325         bool second_part_of_rmw = false;
 326
 327         ASSERT(curr);
 328
 329         if (curr->is_rmwc() || curr->is_rmw()) {
 330                 ModelAction *tmp = process_rmw(curr);
 331                 second_part_of_rmw = true;
 332                 delete curr;
 333                 curr = tmp;
 334                 compute_promises(curr);
 335         } else {
 336                 ModelAction *tmp = node_stack->explore_action(curr);
 337                 if (tmp) {
 338                         /* Discard duplicate ModelAction; use action from NodeStack */
 339                         /* First restore type and order in case of RMW operation */
 340                         if (curr->is_rmwr())
 341                                 tmp->copy_typeandorder(curr);
 342
 343                         /* If we have diverged, we need to reset the clock vector. */
 344                         if (diverge == NULL)
 345                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 346
 347                         delete curr;
 348                         curr = tmp;
 349                 } else {
 350                         /*
 351                          * Perform one-time actions when pushing new ModelAction onto
 352                          * NodeStack
 353                          */
 354                         curr->create_cv(get_parent_action(curr->get_tid()));
 355                         /* Build may_read_from set */
 356                         if (curr->is_read())
 357                                 build_reads_from_past(curr);
 358                         if (curr->is_write())
 359                                 compute_promises(curr);
 360                 }
 361         }
 362
 363         /* Thread specific actions */
 364         switch (curr->get_type()) {
 365         case THREAD_CREATE: {
 366                 Thread *th = (Thread *)curr->get_location();
 367                 th->set_creation(curr);
 368                 break;
 369         }
 370         case THREAD_JOIN: {
 371                 Thread *waiting, *blocking;
 372                 waiting = get_thread(curr);
 373                 blocking = (Thread *)curr->get_location();
 374                 if (!blocking->is_complete()) {
 375                         blocking->push_wait_list(curr);
 376                         scheduler->sleep(waiting);
 377                 }
 378                 break;
 379         }
 380         case THREAD_FINISH: {
 381                 Thread *th = get_thread(curr);
 382                 while (!th->wait_list_empty()) {
 383                         ModelAction *act = th->pop_wait_list();
 384                         Thread *wake = get_thread(act);
 385                         scheduler->wake(wake);
 386                 }
 387                 th->complete();
 388                 break;
 389         }
 390         case THREAD_START: {
 391                 check_promises(NULL, curr->get_cv());
 392                 break;
 393         }
 394         default:
 395                 break;
 396         }
 397
 398         bool updated = false;
 399
 400         if (curr->is_read()) {
 401                 updated = process_read(curr, get_thread(curr), second_part_of_rmw);
 402         }
 403
 404         if (curr->is_write()) {
 405                 bool updated_mod_order = w_modification_order(curr);
 406                 bool updated_promises = resolve_promises(curr);
 407                 updated = updated || updated_mod_order || updated_promises;
 408
 409                 if (promises->size()==0) {
 410                         for (unsigned int i = 0; i<futurevalues->size(); i++) {
 411                                 struct PendingFutureValue pfv=(*futurevalues)[i];
 412                                 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 413                                                 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 414                                         priv->next_backtrack = pfv.act;
 415                         }
 416                         futurevalues->resize(0);
 417                 }
 418
 419                 mo_graph->commitChanges();
 420                 get_thread(curr)->set_return_value(VALUE_NONE);
 421         }
 422
 423         if (updated)
 424                 resolve_release_sequences(curr->get_location());
 425
 426         /* Add action to list.  */
 427         if (!second_part_of_rmw)
 428                 add_action_to_lists(curr);
 429
 430         check_curr_backtracking(curr);
 431
 432         set_backtracking(curr);
 433
 434         return get_next_thread(curr);
 435 }
 436
 437 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 438         Node *currnode = curr->get_node();
 439         Node *parnode = currnode->get_parent();
 440
 441         if ((!parnode->backtrack_empty() ||
 442                          !currnode->read_from_empty() ||
 443                          !currnode->future_value_empty() ||
 444                          !currnode->promise_empty())
 445                         && (!priv->next_backtrack ||
 446                                         *curr > *priv->next_backtrack)) {
 447                 priv->next_backtrack = curr;
 448         }
 449 }
 450
 451 bool ModelChecker::promises_expired() {
 452         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 453                 Promise *promise = (*promises)[promise_index];
 454                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 455                         return true;
 456                 }
 457         }
 458         return false;
 459 }
 460
 461 /** @returns whether the current partial trace must be a prefix of a
 462  * feasible trace. */
 463 bool ModelChecker::isfeasibleprefix() {
 464         return promises->size() == 0 && *lazy_sync_size == 0;
 465 }
 466
 467 /** @returns whether the current partial trace is feasible. */
 468 bool ModelChecker::isfeasible() {
 469         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 470 }
 471
 472 /** @returns whether the current partial trace is feasible other than
 473  * multiple RMW reading from the same store. */
 474 bool ModelChecker::isfeasibleotherthanRMW() {
 475         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 476 }
 477
 478 /** Returns whether the current completed trace is feasible. */
 479 bool ModelChecker::isfinalfeasible() {
 480         return isfeasible() && promises->size() == 0;
 481 }
 482
 483 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 484 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 485         int tid = id_to_int(act->get_tid());
 486         ModelAction *lastread = get_last_action(tid);
 487         lastread->process_rmw(act);
 488         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 489                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 490                 mo_graph->commitChanges();
 491         }
 492         return lastread;
 493 }
 494
 495 /**
 496  * Checks whether a thread has read from the same write for too many times
 497  * without seeing the effects of a later write.
 498  *
 499  * Basic idea:
 500  * 1) there must a different write that we could read from that would satisfy the modification order,
 501  * 2) we must have read from the same value in excess of maxreads times, and
 502  * 3) that other write must have been in the reads_from set for maxreads times.
 503  *
 504  * If so, we decide that the execution is no longer feasible.
 505  */
 506 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 507         if (params.maxreads != 0) {
 508                 if (curr->get_node()->get_read_from_size() <= 1)
 509                         return;
 510
 511                 //Must make sure that execution is currently feasible...  We could
 512                 //accidentally clear by rolling back
 513                 if (!isfeasible())
 514                         return;
 515
 516                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 517                 int tid = id_to_int(curr->get_tid());
 518
 519                 /* Skip checks */
 520                 if ((int)thrd_lists->size() <= tid)
 521                         return;
 522
 523                 action_list_t *list = &(*thrd_lists)[tid];
 524
 525                 action_list_t::reverse_iterator rit = list->rbegin();
 526                 /* Skip past curr */
 527                 if (already_added) {
 528                         for (; (*rit) != curr; rit++)
 529                                 ;
 530                         /* go past curr now */
 531                         rit++;
 532                 }
 533
 534                 action_list_t::reverse_iterator ritcopy = rit;
 535                 //See if we have enough reads from the same value
 536                 int count = 0;
 537                 for (; count < params.maxreads; rit++,count++) {
 538                         if (rit==list->rend())
 539                                 return;
 540                         ModelAction *act = *rit;
 541                         if (!act->is_read())
 542                                 return;
 543                         if (act->get_reads_from() != curr->get_reads_from())
 544                                 return;
 545                         if (act->get_node()->get_read_from_size() <= 1)
 546                                 return;
 547                 }
 548
 549                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 550                         //Get write
 551                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 552                         //Need a different write
 553                         if (write==curr->get_reads_from())
 554                                 continue;
 555
 556                         /* Test to see whether this is a feasible write to read from*/
 557                         mo_graph->startChanges();
 558                         r_modification_order(curr, write);
 559                         bool feasiblereadfrom = isfeasible();
 560                         mo_graph->rollbackChanges();
 561
 562                         if (!feasiblereadfrom)
 563                                 continue;
 564                         rit = ritcopy;
 565
 566                         bool feasiblewrite = true;
 567                         //new we need to see if this write works for everyone
 568
 569                         for (int loop = count; loop>0; loop--,rit++) {
 570                                 ModelAction *act=*rit;
 571                                 bool foundvalue = false;
 572                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 573                                         if (act->get_node()->get_read_from_at(i)==write) {
 574                                                 foundvalue = true;
 575                                                 break;
 576                                         }
 577                                 }
 578                                 if (!foundvalue) {
 579                                         feasiblewrite = false;
 580                                         break;
 581                                 }
 582                         }
 583                         if (feasiblewrite) {
 584                                 too_many_reads = true;
 585                                 return;
 586                         }
 587                 }
 588         }
 589 }
 590
 591 /**
 592  * Updates the mo_graph with the constraints imposed from the current
 593  * read.
 594  *
 595  * Basic idea is the following: Go through each other thread and find
 596  * the lastest action that happened before our read.  Two cases:
 597  *
 598  * (1) The action is a write => that write must either occur before
 599  * the write we read from or be the write we read from.
 600  *
 601  * (2) The action is a read => the write that that action read from
 602  * must occur before the write we read from or be the same write.
 603  *
 604  * @param curr The current action. Must be a read.
 605  * @param rf The action that curr reads from. Must be a write.
 606  * @return True if modification order edges were added; false otherwise
 607  */
 608 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 609 {
 610         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 611         unsigned int i;
 612         bool added = false;
 613         ASSERT(curr->is_read());
 614
 615         /* Iterate over all threads */
 616         for (i = 0; i < thrd_lists->size(); i++) {
 617                 /* Iterate over actions in thread, starting from most recent */
 618                 action_list_t *list = &(*thrd_lists)[i];
 619                 action_list_t::reverse_iterator rit;
 620                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 621                         ModelAction *act = *rit;
 622
 623                         /* Include at most one act per-thread that "happens before" curr */
 624                         if (act->happens_before(curr)) {
 625                                 if (act->is_write()) {
 626                                         if (rf != act && act != curr) {
 627                                                 mo_graph->addEdge(act, rf);
 628                                                 added = true;
 629                                         }
 630                                 } else {
 631                                         const ModelAction *prevreadfrom = act->get_reads_from();
 632                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 633                                                 mo_graph->addEdge(prevreadfrom, rf);
 634                                                 added = true;
 635                                         }
 636                                 }
 637
 638                                 break;
 639                         }
 640                 }
 641         }
 642
 643         return added;
 644 }
 645
 646 /** This method fixes up the modification order when we resolve a
 647  *  promises.  The basic problem is that actions that occur after the
 648  *  read curr could not property add items to the modification order
 649  *  for our read.
 650  *
 651  *  So for each thread, we find the earliest item that happens after
 652  *  the read curr.  This is the item we have to fix up with additional
 653  *  constraints.  If that action is write, we add a MO edge between
 654  *  the Action rf and that action.  If the action is a read, we add a
 655  *  MO edge between the Action rf, and whatever the read accessed.
 656  *
 657  * @param curr is the read ModelAction that we are fixing up MO edges for.
 658  * @param rf is the write ModelAction that curr reads from.
 659  *
 660  */
 661
 662 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 663 {
 664         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 665         unsigned int i;
 666         ASSERT(curr->is_read());
 667
 668         /* Iterate over all threads */
 669         for (i = 0; i < thrd_lists->size(); i++) {
 670                 /* Iterate over actions in thread, starting from most recent */
 671                 action_list_t *list = &(*thrd_lists)[i];
 672                 action_list_t::reverse_iterator rit;
 673                 ModelAction *lastact = NULL;
 674
 675                 /* Find last action that happens after curr */
 676                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 677                         ModelAction *act = *rit;
 678                         if (curr->happens_before(act)) {
 679                                 lastact = act;
 680                         } else
 681                                 break;
 682                 }
 683
 684                         /* Include at most one act per-thread that "happens before" curr */
 685                 if (lastact != NULL) {
 686                         if (lastact->is_read()) {
 687                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 688                                 if (postreadfrom != NULL&&rf != postreadfrom)
 689                                         mo_graph->addEdge(rf, postreadfrom);
 690                         } else if (rf != lastact) {
 691                                 mo_graph->addEdge(rf, lastact);
 692                         }
 693                         break;
 694                 }
 695         }
 696 }
 697
 698 /**
 699  * Updates the mo_graph with the constraints imposed from the current write.
 700  *
 701  * Basic idea is the following: Go through each other thread and find
 702  * the lastest action that happened before our write.  Two cases:
 703  *
 704  * (1) The action is a write => that write must occur before
 705  * the current write
 706  *
 707  * (2) The action is a read => the write that that action read from
 708  * must occur before the current write.
 709  *
 710  * This method also handles two other issues:
 711  *
 712  * (I) Sequential Consistency: Making sure that if the current write is
 713  * seq_cst, that it occurs after the previous seq_cst write.
 714  *
 715  * (II) Sending the write back to non-synchronizing reads.
 716  *
 717  * @param curr The current action. Must be a write.
 718  * @return True if modification order edges were added; false otherwise
 719  */
 720 bool ModelChecker::w_modification_order(ModelAction *curr)
 721 {
 722         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 723         unsigned int i;
 724         bool added = false;
 725         ASSERT(curr->is_write());
 726
 727         if (curr->is_seqcst()) {
 728                 /* We have to at least see the last sequentially consistent write,
 729                          so we are initialized. */
 730                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 731                 if (last_seq_cst != NULL) {
 732                         mo_graph->addEdge(last_seq_cst, curr);
 733                         added = true;
 734                 }
 735         }
 736
 737         /* Iterate over all threads */
 738         for (i = 0; i < thrd_lists->size(); i++) {
 739                 /* Iterate over actions in thread, starting from most recent */
 740                 action_list_t *list = &(*thrd_lists)[i];
 741                 action_list_t::reverse_iterator rit;
 742                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 743                         ModelAction *act = *rit;
 744
 745                         /* Include at most one act per-thread that "happens before" curr */
 746                         if (act->happens_before(curr)) {
 747                                 /*
 748                                  * Note: if act is RMW, just add edge:
 749                                  *   act --mo--> curr
 750                                  * The following edge should be handled elsewhere:
 751                                  *   readfrom(act) --mo--> act
 752                                  */
 753                                 if (act->is_write()) {
 754                                         //RMW shouldn't have an edge to themselves
 755                                         if (act!=curr)
 756                                                 mo_graph->addEdge(act, curr);
 757                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 758                                         mo_graph->addEdge(act->get_reads_from(), curr);
 759                                 added = true;
 760                                 break;
 761                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 762                                                      !act->same_thread(curr)) {
 763                                 /* We have an action that:
 764                                    (1) did not happen before us
 765                                    (2) is a read and we are a write
 766                                    (3) cannot synchronize with us
 767                                    (4) is in a different thread
 768                                    =>
 769                                    that read could potentially read from our write.
 770                                  */
 771                                 if (thin_air_constraint_may_allow(curr, act)) {
 772                                         if (isfeasible() ||
 773                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 774                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 775                                                 futurevalues->push_back(pfv);
 776                                         }
 777                                 }
 778                         }
 779                 }
 780         }
 781
 782         return added;
 783 }
 784
 785 /** Arbitrary reads from the future are not allowed.  Section 29.3
 786  * part 9 places some constraints.  This method checks one result of constraint
 787  * constraint.  Others require compiler support. */
 788
 789 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 790         if (!writer->is_rmw())
 791                 return true;
 792
 793         if (!reader->is_rmw())
 794                 return true;
 795
 796         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 797                 if (search==reader)
 798                         return false;
 799                 if (search->get_tid() == reader->get_tid() &&
 800                                 search->happens_before(reader))
 801                         break;
 802         }
 803
 804         return true;
 805 }
 806
 807 /**
 808  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 809  * The ModelAction under consideration is expected to be taking part in
 810  * release/acquire synchronization as an object of the "reads from" relation.
 811  * Note that this can only provide release sequence support for RMW chains
 812  * which do not read from the future, as those actions cannot be traced until
 813  * their "promise" is fulfilled. Similarly, we may not even establish the
 814  * presence of a release sequence with certainty, as some modification order
 815  * constraints may be decided further in the future. Thus, this function
 816  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 817  * and a boolean representing certainty.
 818  *
 819  * @todo Finish lazy updating, when promises are fulfilled in the future
 820  * @param rf The action that might be part of a release sequence. Must be a
 821  * write.
 822  * @param release_heads A pass-by-reference style return parameter.  After
 823  * execution of this function, release_heads will contain the heads of all the
 824  * relevant release sequences, if any exists
 825  * @return true, if the ModelChecker is certain that release_heads is complete;
 826  * false otherwise
 827  */
 828 bool ModelChecker::release_seq_head(const ModelAction *rf,
 829                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 830 {
 831         if (!rf) {
 832                 /* read from future: need to settle this later */
 833                 return false; /* incomplete */
 834         }
 835
 836         ASSERT(rf->is_write());
 837
 838         if (rf->is_release())
 839                 release_heads->push_back(rf);
 840         if (rf->is_rmw()) {
 841                 /* We need a RMW action that is both an acquire and release to stop */
 842                 /** @todo Need to be smarter here...  In the linux lock
 843                  * example, this will run to the beginning of the program for
 844                  * every acquire. */
 845                 if (rf->is_acquire() && rf->is_release())
 846                         return true; /* complete */
 847                 return release_seq_head(rf->get_reads_from(), release_heads);
 848         }
 849         if (rf->is_release())
 850                 return true; /* complete */
 851
 852         /* else relaxed write; check modification order for contiguous subsequence
 853          * -> rf must be same thread as release */
 854         int tid = id_to_int(rf->get_tid());
 855         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 856         action_list_t *list = &(*thrd_lists)[tid];
 857         action_list_t::const_reverse_iterator rit;
 858
 859         /* Find rf in the thread list */
 860         rit = std::find(list->rbegin(), list->rend(), rf);
 861         ASSERT(rit != list->rend());
 862
 863         /* Find the last write/release */
 864         for (; rit != list->rend(); rit++)
 865                 if ((*rit)->is_release())
 866                         break;
 867         if (rit == list->rend()) {
 868                 /* No write-release in this thread */
 869                 return true; /* complete */
 870         }
 871         ModelAction *release = *rit;
 872
 873         ASSERT(rf->same_thread(release));
 874
 875         bool certain = true;
 876         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 877                 if (id_to_int(rf->get_tid()) == (int)i)
 878                         continue;
 879                 list = &(*thrd_lists)[i];
 880
 881                 /* Can we ensure no future writes from this thread may break
 882                  * the release seq? */
 883                 bool future_ordered = false;
 884
 885                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 886                         const ModelAction *act = *rit;
 887                         if (!act->is_write())
 888                                 continue;
 889                         /* Reach synchronization -> this thread is complete */
 890                         if (act->happens_before(release))
 891                                 break;
 892                         if (rf->happens_before(act)) {
 893                                 future_ordered = true;
 894                                 continue;
 895                         }
 896
 897                         /* Check modification order */
 898                         if (mo_graph->checkReachable(rf, act)) {
 899                                 /* rf --mo--> act */
 900                                 future_ordered = true;
 901                                 continue;
 902                         }
 903                         if (mo_graph->checkReachable(act, release))
 904                                 /* act --mo--> release */
 905                                 break;
 906                         if (mo_graph->checkReachable(release, act) &&
 907                                       mo_graph->checkReachable(act, rf)) {
 908                                 /* release --mo-> act --mo--> rf */
 909                                 return true; /* complete */
 910                         }
 911                         certain = false;
 912                 }
 913                 if (!future_ordered)
 914                         return false; /* This thread is uncertain */
 915         }
 916
 917         if (certain)
 918                 release_heads->push_back(release);
 919         return certain;
 920 }
 921
 922 /**
 923  * A public interface for getting the release sequence head(s) with which a
 924  * given ModelAction must synchronize. This function only returns a non-empty
 925  * result when it can locate a release sequence head with certainty. Otherwise,
 926  * it may mark the internal state of the ModelChecker so that it will handle
 927  * the release sequence at a later time, causing @a act to update its
 928  * synchronization at some later point in execution.
 929  * @param act The 'acquire' action that may read from a release sequence
 930  * @param release_heads A pass-by-reference return parameter. Will be filled
 931  * with the head(s) of the release sequence(s), if they exists with certainty.
 932  * @see ModelChecker::release_seq_head
 933  */
 934 void ModelChecker::get_release_seq_heads(ModelAction *act,
 935                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 936 {
 937         const ModelAction *rf = act->get_reads_from();
 938         bool complete;
 939         complete = release_seq_head(rf, release_heads);
 940         if (!complete) {
 941                 /* add act to 'lazy checking' list */
 942                 std::list<ModelAction *> *list;
 943                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 944                 list->push_back(act);
 945                 (*lazy_sync_size)++;
 946         }
 947 }
 948
 949 /**
 950  * Attempt to resolve all stashed operations that might synchronize with a
 951  * release sequence for a given location. This implements the "lazy" portion of
 952  * determining whether or not a release sequence was contiguous, since not all
 953  * modification order information is present at the time an action occurs.
 954  *
 955  * @param location The location/object that should be checked for release
 956  * sequence resolutions
 957  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 958  */
 959 bool ModelChecker::resolve_release_sequences(void *location)
 960 {
 961         std::list<ModelAction *> *list;
 962         list = lazy_sync_with_release->getptr(location);
 963         if (!list)
 964                 return false;
 965
 966         bool updated = false;
 967         std::list<ModelAction *>::iterator it = list->begin();
 968         while (it != list->end()) {
 969                 ModelAction *act = *it;
 970                 const ModelAction *rf = act->get_reads_from();
 971                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
 972                 bool complete;
 973                 complete = release_seq_head(rf, &release_heads);
 974                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 975                         if (!act->has_synchronized_with(release_heads[i])) {
 976                                 updated = true;
 977                                 act->synchronize_with(release_heads[i]);
 978                         }
 979                 }
 980
 981                 if (updated) {
 982                         /* propagate synchronization to later actions */
 983                         action_list_t::reverse_iterator it = action_trace->rbegin();
 984                         while ((*it) != act) {
 985                                 ModelAction *propagate = *it;
 986                                 if (act->happens_before(propagate))
 987                                         /** @todo new mo_graph edges along with
 988                                          * this synchronization? */
 989                                         propagate->synchronize_with(act);
 990                         }
 991                 }
 992                 if (complete) {
 993                         it = list->erase(it);
 994                         (*lazy_sync_size)--;
 995                 } else
 996                         it++;
 997         }
 998
 999         // If we resolved promises or data races, see if we have realized a data race.
1000         if (checkDataRaces()) {
1001                 set_assert();
1002         }
1003
1004         return updated;
1005 }
1006
1007 /**
1008  * Performs various bookkeeping operations for the current ModelAction. For
1009  * instance, adds action to the per-object, per-thread action vector and to the
1010  * action trace list of all thread actions.
1011  *
1012  * @param act is the ModelAction to add.
1013  */
1014 void ModelChecker::add_action_to_lists(ModelAction *act)
1015 {
1016         int tid = id_to_int(act->get_tid());
1017         action_trace->push_back(act);
1018
1019         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1020
1021         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1022         if (tid >= (int)vec->size())
1023                 vec->resize(priv->next_thread_id);
1024         (*vec)[tid].push_back(act);
1025
1026         if ((int)thrd_last_action->size() <= tid)
1027                 thrd_last_action->resize(get_num_threads());
1028         (*thrd_last_action)[tid] = act;
1029 }
1030
1031 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1032 {
1033         int nthreads = get_num_threads();
1034         if ((int)thrd_last_action->size() < nthreads)
1035                 thrd_last_action->resize(nthreads);
1036         return (*thrd_last_action)[id_to_int(tid)];
1037 }
1038
1039 /**
1040  * Gets the last memory_order_seq_cst action (in the total global sequence)
1041  * performed on a particular object (i.e., memory location).
1042  * @param location The object location to check
1043  * @return The last seq_cst action performed
1044  */
1045 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1046 {
1047         action_list_t *list = obj_map->get_safe_ptr(location);
1048         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1049         action_list_t::reverse_iterator rit;
1050         for (rit = list->rbegin(); rit != list->rend(); rit++)
1051                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1052                         return *rit;
1053         return NULL;
1054 }
1055
1056 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1057 {
1058         ModelAction *parent = get_last_action(tid);
1059         if (!parent)
1060                 parent = get_thread(tid)->get_creation();
1061         return parent;
1062 }
1063
1064 /**
1065  * Returns the clock vector for a given thread.
1066  * @param tid The thread whose clock vector we want
1067  * @return Desired clock vector
1068  */
1069 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1070 {
1071         return get_parent_action(tid)->get_cv();
1072 }
1073
1074 /**
1075  * Resolve a set of Promises with a current write. The set is provided in the
1076  * Node corresponding to @a write.
1077  * @param write The ModelAction that is fulfilling Promises
1078  * @return True if promises were resolved; false otherwise
1079  */
1080 bool ModelChecker::resolve_promises(ModelAction *write)
1081 {
1082         bool resolved = false;
1083
1084         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1085                 Promise *promise = (*promises)[promise_index];
1086                 if (write->get_node()->get_promise(i)) {
1087                         ModelAction *read = promise->get_action();
1088                         read->read_from(write);
1089                         if (read->is_rmw()) {
1090                                 mo_graph->addRMWEdge(write, read);
1091                         }
1092                         //First fix up the modification order for actions that happened
1093                         //before the read
1094                         r_modification_order(read, write);
1095                         //Next fix up the modification order for actions that happened
1096                         //after the read.
1097                         post_r_modification_order(read, write);
1098                         promises->erase(promises->begin() + promise_index);
1099                         resolved = true;
1100                 } else
1101                         promise_index++;
1102         }
1103         return resolved;
1104 }
1105
1106 /**
1107  * Compute the set of promises that could potentially be satisfied by this
1108  * action. Note that the set computation actually appears in the Node, not in
1109  * ModelChecker.
1110  * @param curr The ModelAction that may satisfy promises
1111  */
1112 void ModelChecker::compute_promises(ModelAction *curr)
1113 {
1114         for (unsigned int i = 0; i < promises->size(); i++) {
1115                 Promise *promise = (*promises)[i];
1116                 const ModelAction *act = promise->get_action();
1117                 if (!act->happens_before(curr) &&
1118                                 act->is_read() &&
1119                                 !act->is_synchronizing(curr) &&
1120                                 !act->same_thread(curr) &&
1121                                 promise->get_value() == curr->get_value()) {
1122                         curr->get_node()->set_promise(i);
1123                 }
1124         }
1125 }
1126
1127 /** Checks promises in response to change in ClockVector Threads. */
1128 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1129 {
1130         for (unsigned int i = 0; i < promises->size(); i++) {
1131                 Promise *promise = (*promises)[i];
1132                 const ModelAction *act = promise->get_action();
1133                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1134                                 merge_cv->synchronized_since(act)) {
1135                         //This thread is no longer able to send values back to satisfy the promise
1136                         int num_synchronized_threads = promise->increment_threads();
1137                         if (num_synchronized_threads == get_num_threads()) {
1138                                 //Promise has failed
1139                                 failed_promise = true;
1140                                 return;
1141                         }
1142                 }
1143         }
1144 }
1145
1146 /**
1147  * Build up an initial set of all past writes that this 'read' action may read
1148  * from. This set is determined by the clock vector's "happens before"
1149  * relationship.
1150  * @param curr is the current ModelAction that we are exploring; it must be a
1151  * 'read' operation.
1152  */
1153 void ModelChecker::build_reads_from_past(ModelAction *curr)
1154 {
1155         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1156         unsigned int i;
1157         ASSERT(curr->is_read());
1158
1159         ModelAction *last_seq_cst = NULL;
1160
1161         /* Track whether this object has been initialized */
1162         bool initialized = false;
1163
1164         if (curr->is_seqcst()) {
1165                 last_seq_cst = get_last_seq_cst(curr->get_location());
1166                 /* We have to at least see the last sequentially consistent write,
1167                          so we are initialized. */
1168                 if (last_seq_cst != NULL)
1169                         initialized = true;
1170         }
1171
1172         /* Iterate over all threads */
1173         for (i = 0; i < thrd_lists->size(); i++) {
1174                 /* Iterate over actions in thread, starting from most recent */
1175                 action_list_t *list = &(*thrd_lists)[i];
1176                 action_list_t::reverse_iterator rit;
1177                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1178                         ModelAction *act = *rit;
1179
1180                         /* Only consider 'write' actions */
1181                         if (!act->is_write())
1182                                 continue;
1183
1184                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1185                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1186                                 DEBUG("Adding action to may_read_from:\n");
1187                                 if (DBG_ENABLED()) {
1188                                         act->print();
1189                                         curr->print();
1190                                 }
1191                                 curr->get_node()->add_read_from(act);
1192                         }
1193
1194                         /* Include at most one act per-thread that "happens before" curr */
1195                         if (act->happens_before(curr)) {
1196                                 initialized = true;
1197                                 break;
1198                         }
1199                 }
1200         }
1201
1202         if (!initialized) {
1203                 /** @todo Need a more informative way of reporting errors. */
1204                 printf("ERROR: may read from uninitialized atomic\n");
1205         }
1206
1207         if (DBG_ENABLED() || !initialized) {
1208                 printf("Reached read action:\n");
1209                 curr->print();
1210                 printf("Printing may_read_from\n");
1211                 curr->get_node()->print_may_read_from();
1212                 printf("End printing may_read_from\n");
1213         }
1214
1215         ASSERT(initialized);
1216 }
1217
1218 static void print_list(action_list_t *list)
1219 {
1220         action_list_t::iterator it;
1221
1222         printf("---------------------------------------------------------------------\n");
1223         printf("Trace:\n");
1224
1225         for (it = list->begin(); it != list->end(); it++) {
1226                 (*it)->print();
1227         }
1228         printf("---------------------------------------------------------------------\n");
1229 }
1230
1231 void ModelChecker::print_summary()
1232 {
1233         printf("\n");
1234         printf("Number of executions: %d\n", num_executions);
1235         printf("Number of feasible executions: %d\n", num_feasible_executions);
1236         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1237
1238 #if SUPPORT_MOD_ORDER_DUMP
1239         scheduler->print();
1240         char buffername[100];
1241         sprintf(buffername, "exec%u",num_executions);
1242         mo_graph->dumpGraphToFile(buffername);
1243 #endif
1244
1245         if (!isfinalfeasible())
1246                 printf("INFEASIBLE EXECUTION!\n");
1247         print_list(action_trace);
1248         printf("\n");
1249 }
1250
1251 /**
1252  * Add a Thread to the system for the first time. Should only be called once
1253  * per thread.
1254  * @param t The Thread to add
1255  */
1256 void ModelChecker::add_thread(Thread *t)
1257 {
1258         thread_map->put(id_to_int(t->get_id()), t);
1259         scheduler->add_thread(t);
1260 }
1261
1262 void ModelChecker::remove_thread(Thread *t)
1263 {
1264         scheduler->remove_thread(t);
1265 }
1266
1267 /**
1268  * Switch from a user-context to the "master thread" context (a.k.a. system
1269  * context). This switch is made with the intention of exploring a particular
1270  * model-checking action (described by a ModelAction object). Must be called
1271  * from a user-thread context.
1272  * @param act The current action that will be explored. Must not be NULL.
1273  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1274  */
1275 int ModelChecker::switch_to_master(ModelAction *act)
1276 {
1277         DBG();
1278         Thread *old = thread_current();
1279         set_current_action(act);
1280         old->set_state(THREAD_READY);
1281         return Thread::swap(old, &system_context);
1282 }
1283
1284 /**
1285  * Takes the next step in the execution, if possible.
1286  * @return Returns true (success) if a step was taken and false otherwise.
1287  */
1288 bool ModelChecker::take_step() {
1289         Thread *curr, *next;
1290
1291         if (has_asserted())
1292                 return false;
1293
1294         curr = thread_current();
1295         if (curr) {
1296                 if (curr->get_state() == THREAD_READY) {
1297                         ASSERT(priv->current_action);
1298
1299                         priv->nextThread = check_current_action(priv->current_action);
1300                         priv->current_action = NULL;
1301                         if (!curr->is_blocked() && !curr->is_complete())
1302                                 scheduler->add_thread(curr);
1303                 } else {
1304                         ASSERT(false);
1305                 }
1306         }
1307         next = scheduler->next_thread(priv->nextThread);
1308
1309         /* Infeasible -> don't take any more steps */
1310         if (!isfeasible())
1311                 return false;
1312
1313         if (next)
1314                 next->set_state(THREAD_RUNNING);
1315         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1316
1317         /* next == NULL -> don't take any more steps */
1318         if (!next)
1319                 return false;
1320         /* Return false only if swap fails with an error */
1321         return (Thread::swap(&system_context, next) == 0);
1322 }
1323
1324 /** Runs the current execution until threre are no more steps to take. */
1325 void ModelChecker::finish_execution() {
1326         DBG();
1327
1328         while (take_step());
1329 }