model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14
  15 #define INITIAL_THREAD_ID       0
  16
  17 ModelChecker *model;
  18
  19 /** @brief Constructor */
  20 ModelChecker::ModelChecker(struct model_params params) :
  21         /* Initialize default scheduler */
  22         scheduler(new Scheduler()),
  23         num_executions(0),
  24         params(params),
  25         diverge(NULL),
  26         action_trace(new action_list_t()),
  27         thread_map(new HashTable<int, Thread *, int>()),
  28         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  29         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  30         promises(new std::vector<Promise *>()),
  31         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  32         thrd_last_action(new std::vector<ModelAction *>(1)),
  33         node_stack(new NodeStack()),
  34         mo_graph(new CycleGraph()),
  35         failed_promise(false),
  36         too_many_reads(false),
  37         asserted(false)
  38 {
  39         /* Allocate this "size" on the snapshotting heap */
  40         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  41         /* First thread created will have id INITIAL_THREAD_ID */
  42         priv->next_thread_id = INITIAL_THREAD_ID;
  43
  44         lazy_sync_size = &priv->lazy_sync_size;
  45 }
  46
  47 /** @brief Destructor */
  48 ModelChecker::~ModelChecker()
  49 {
  50         for (int i = 0; i < get_num_threads(); i++)
  51                 delete thread_map->get(i);
  52         delete thread_map;
  53
  54         delete obj_thrd_map;
  55         delete obj_map;
  56         delete action_trace;
  57
  58         for (unsigned int i = 0; i < promises->size(); i++)
  59                 delete (*promises)[i];
  60         delete promises;
  61
  62         delete lazy_sync_with_release;
  63
  64         delete thrd_last_action;
  65         delete node_stack;
  66         delete scheduler;
  67         delete mo_graph;
  68 }
  69
  70 /**
  71  * Restores user program to initial state and resets all model-checker data
  72  * structures.
  73  */
  74 void ModelChecker::reset_to_initial_state()
  75 {
  76         DEBUG("+++ Resetting to initial state +++\n");
  77         node_stack->reset_execution();
  78         failed_promise = false;
  79         too_many_reads = false;
  80         reset_asserted();
  81         snapshotObject->backTrackBeforeStep(0);
  82 }
  83
  84 /** @returns a thread ID for a new Thread */
  85 thread_id_t ModelChecker::get_next_id()
  86 {
  87         return priv->next_thread_id++;
  88 }
  89
  90 /** @returns the number of user threads created during this execution */
  91 int ModelChecker::get_num_threads()
  92 {
  93         return priv->next_thread_id;
  94 }
  95
  96 /** @returns a sequence number for a new ModelAction */
  97 modelclock_t ModelChecker::get_next_seq_num()
  98 {
  99         return ++priv->used_sequence_numbers;
 100 }
 101
 102 /**
 103  * Choose the next thread in the replay sequence.
 104  *
 105  * If the replay sequence has reached the 'diverge' point, returns a thread
 106  * from the backtracking set. Otherwise, simply returns the next thread in the
 107  * sequence that is being replayed.
 108  */
 109 Thread * ModelChecker::get_next_replay_thread()
 110 {
 111         thread_id_t tid;
 112
 113         /* Have we completed exploring the preselected path? */
 114         if (diverge == NULL)
 115                 return NULL;
 116
 117         /* Else, we are trying to replay an execution */
 118         ModelAction *next = node_stack->get_next()->get_action();
 119
 120         if (next == diverge) {
 121                 Node *nextnode = next->get_node();
 122                 /* Reached divergence point */
 123                 if (nextnode->increment_promise()) {
 124                         /* The next node will try to satisfy a different set of promises. */
 125                         tid = next->get_tid();
 126                         node_stack->pop_restofstack(2);
 127                 } else if (nextnode->increment_read_from()) {
 128                         /* The next node will read from a different value. */
 129                         tid = next->get_tid();
 130                         node_stack->pop_restofstack(2);
 131                 } else if (nextnode->increment_future_value()) {
 132                         /* The next node will try to read from a different future value. */
 133                         tid = next->get_tid();
 134                         node_stack->pop_restofstack(2);
 135                 } else {
 136                         /* Make a different thread execute for next step */
 137                         Node *node = nextnode->get_parent();
 138                         tid = node->get_next_backtrack();
 139                         node_stack->pop_restofstack(1);
 140                 }
 141                 DEBUG("*** Divergence point ***\n");
 142                 diverge = NULL;
 143         } else {
 144                 tid = next->get_tid();
 145         }
 146         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 147         ASSERT(tid != THREAD_ID_T_NONE);
 148         return thread_map->get(id_to_int(tid));
 149 }
 150
 151 /**
 152  * Queries the model-checker for more executions to explore and, if one
 153  * exists, resets the model-checker state to execute a new execution.
 154  *
 155  * @return If there are more executions to explore, return true. Otherwise,
 156  * return false.
 157  */
 158 bool ModelChecker::next_execution()
 159 {
 160         DBG();
 161
 162         num_executions++;
 163
 164         if (isfinalfeasible() || DBG_ENABLED())
 165                 print_summary();
 166
 167         if ((diverge = get_next_backtrack()) == NULL)
 168                 return false;
 169
 170         if (DBG_ENABLED()) {
 171                 printf("Next execution will diverge at:\n");
 172                 diverge->print();
 173         }
 174
 175         reset_to_initial_state();
 176         return true;
 177 }
 178
 179 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 180 {
 181         action_type type = act->get_type();
 182
 183         switch (type) {
 184                 case ATOMIC_READ:
 185                 case ATOMIC_WRITE:
 186                 case ATOMIC_RMW:
 187                         break;
 188                 default:
 189                         return NULL;
 190         }
 191         /* linear search: from most recent to oldest */
 192         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 193         action_list_t::reverse_iterator rit;
 194         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 195                 ModelAction *prev = *rit;
 196                 if (act->is_synchronizing(prev))
 197                         return prev;
 198         }
 199         return NULL;
 200 }
 201
 202 void ModelChecker::set_backtracking(ModelAction *act)
 203 {
 204         ModelAction *prev;
 205         Node *node;
 206         Thread *t = get_thread(act->get_tid());
 207
 208         prev = get_last_conflict(act);
 209         if (prev == NULL)
 210                 return;
 211
 212         node = prev->get_node()->get_parent();
 213
 214         while (!node->is_enabled(t))
 215                 t = t->get_parent();
 216
 217         /* Check if this has been explored already */
 218         if (node->has_been_explored(t->get_id()))
 219                 return;
 220
 221         /* Cache the latest backtracking point */
 222         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 223                 priv->next_backtrack = prev;
 224
 225         /* If this is a new backtracking point, mark the tree */
 226         if (!node->set_backtrack(t->get_id()))
 227                 return;
 228         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 229                         prev->get_tid(), t->get_id());
 230         if (DBG_ENABLED()) {
 231                 prev->print();
 232                 act->print();
 233         }
 234 }
 235
 236 /**
 237  * Returns last backtracking point. The model checker will explore a different
 238  * path for this point in the next execution.
 239  * @return The ModelAction at which the next execution should diverge.
 240  */
 241 ModelAction * ModelChecker::get_next_backtrack()
 242 {
 243         ModelAction *next = priv->next_backtrack;
 244         priv->next_backtrack = NULL;
 245         return next;
 246 }
 247
 248 /**
 249  * This is the heart of the model checker routine. It performs model-checking
 250  * actions corresponding to a given "current action." Among other processes, it
 251  * calculates reads-from relationships, updates synchronization clock vectors,
 252  * forms a memory_order constraints graph, and handles replay/backtrack
 253  * execution when running permutations of previously-observed executions.
 254  *
 255  * @param curr The current action to process
 256  * @return The next Thread that must be executed. May be NULL if ModelChecker
 257  * makes no choice (e.g., according to replay execution, combining RMW actions,
 258  * etc.)
 259  */
 260 Thread * ModelChecker::check_current_action(ModelAction *curr)
 261 {
 262         bool second_part_of_rmw = false;
 263
 264         ASSERT(curr);
 265
 266         if (curr->is_rmwc() || curr->is_rmw()) {
 267                 ModelAction *tmp = process_rmw(curr);
 268                 second_part_of_rmw = true;
 269                 delete curr;
 270                 curr = tmp;
 271         } else {
 272                 ModelAction *tmp = node_stack->explore_action(curr);
 273                 if (tmp) {
 274                         /* Discard duplicate ModelAction; use action from NodeStack */
 275                         /* First restore type and order in case of RMW operation */
 276                         if (curr->is_rmwr())
 277                                 tmp->copy_typeandorder(curr);
 278
 279                         /* If we have diverged, we need to reset the clock vector. */
 280                         if (diverge == NULL)
 281                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 282
 283                         delete curr;
 284                         curr = tmp;
 285                 } else {
 286                         /*
 287                          * Perform one-time actions when pushing new ModelAction onto
 288                          * NodeStack
 289                          */
 290                         curr->create_cv(get_parent_action(curr->get_tid()));
 291                         /* Build may_read_from set */
 292                         if (curr->is_read())
 293                                 build_reads_from_past(curr);
 294                         if (curr->is_write())
 295                                 compute_promises(curr);
 296                 }
 297         }
 298
 299         /* Assign 'creation' parent */
 300         if (curr->get_type() == THREAD_CREATE) {
 301                 Thread *th = (Thread *)curr->get_location();
 302                 th->set_creation(curr);
 303         } else if (curr->get_type() == THREAD_JOIN) {
 304                 Thread *wait, *join;
 305                 wait = get_thread(curr->get_tid());
 306                 join = (Thread *)curr->get_location();
 307                 if (!join->is_complete())
 308                         scheduler->wait(wait, join);
 309         } else if (curr->get_type() == THREAD_FINISH) {
 310                 Thread *th = get_thread(curr->get_tid());
 311                 while (!th->wait_list_empty()) {
 312                         Thread *wake = th->pop_wait_list();
 313                         scheduler->wake(wake);
 314                 }
 315                 th->complete();
 316         }
 317
 318         /* Deal with new thread */
 319         if (curr->get_type() == THREAD_START)
 320                 check_promises(NULL, curr->get_cv());
 321
 322         /* Assign reads_from values */
 323         Thread *th = get_thread(curr->get_tid());
 324         uint64_t value = VALUE_NONE;
 325         bool updated = false;
 326         if (curr->is_read()) {
 327                 while(true) {
 328                         const ModelAction *reads_from = curr->get_node()->get_read_from();
 329                         if (reads_from != NULL) {
 330                                 value = reads_from->get_value();
 331                                 /* Assign reads_from, perform release/acquire synchronization */
 332                                 curr->read_from(reads_from);
 333                                 if (!second_part_of_rmw)
 334                                         check_recency(curr,false);
 335
 336                                 bool r_status=r_modification_order(curr,reads_from);
 337
 338                                 if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
 339                                         mo_graph->rollbackChanges();
 340                                         too_many_reads=false;
 341                                         continue;
 342                                 }
 343
 344                                 mo_graph->commitChanges();
 345                                 updated |= r_status;
 346                         } else {
 347                                 /* Read from future value */
 348                                 value = curr->get_node()->get_future_value();
 349                                 curr->read_from(NULL);
 350                                 Promise *valuepromise = new Promise(curr, value);
 351                                 promises->push_back(valuepromise);
 352                         }
 353                         break;
 354                 }
 355         } else if (curr->is_write()) {
 356                 if (w_modification_order(curr))
 357                         updated = true;
 358                 if (resolve_promises(curr))
 359                         updated = true;
 360                 mo_graph->commitChanges();
 361         }
 362
 363         if (updated)
 364                 resolve_release_sequences(curr->get_location());
 365
 366         th->set_return_value(value);
 367
 368         /* Add action to list.  */
 369         if (!second_part_of_rmw)
 370                 add_action_to_lists(curr);
 371
 372         Node *currnode = curr->get_node();
 373         Node *parnode = currnode->get_parent();
 374
 375         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 376                   !currnode->future_value_empty() || !currnode->promise_empty())
 377                 if (!priv->next_backtrack || *curr > *priv->next_backtrack)
 378                         priv->next_backtrack = curr;
 379
 380         set_backtracking(curr);
 381
 382         /* Do not split atomic actions. */
 383         if (curr->is_rmwr())
 384                 return thread_current();
 385         /* The THREAD_CREATE action points to the created Thread */
 386         else if (curr->get_type() == THREAD_CREATE)
 387                 return (Thread *)curr->get_location();
 388         else
 389                 return get_next_replay_thread();
 390 }
 391
 392 /** @returns whether the current partial trace must be a prefix of a
 393  * feasible trace. */
 394 bool ModelChecker::isfeasibleprefix() {
 395         return promises->size() == 0 && *lazy_sync_size == 0;
 396 }
 397
 398 /** @returns whether the current partial trace is feasible. */
 399 bool ModelChecker::isfeasible() {
 400         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
 401 }
 402
 403 /** Returns whether the current completed trace is feasible. */
 404 bool ModelChecker::isfinalfeasible() {
 405         return isfeasible() && promises->size() == 0;
 406 }
 407
 408 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 409 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 410         int tid = id_to_int(act->get_tid());
 411         ModelAction *lastread = get_last_action(tid);
 412         lastread->process_rmw(act);
 413         if (act->is_rmw())
 414                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 415         return lastread;
 416 }
 417
 418 /**
 419  * Checks whether a thread has read from the same write for too many times.
 420  * @todo This may be more subtle than this code segment addresses at this
 421  * point...  Potential problems to ponder and fix:
 422  * (1) What if the reads_from set keeps changing such that there is no common
 423  * write?
 424  * (2) What if the problem is that the other writes would break modification
 425  * order.
 426  */
 427 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 428         if (params.maxreads != 0) {
 429                 if (curr->get_node()->get_read_from_size() <= 1)
 430                         return;
 431
 432                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 433                 int tid = id_to_int(curr->get_tid());
 434
 435                 /* Skip checks */
 436                 if ((int)thrd_lists->size() <= tid)
 437                         return;
 438
 439                 action_list_t *list = &(*thrd_lists)[tid];
 440
 441                 action_list_t::reverse_iterator rit = list->rbegin();
 442                 /* Skip past curr */
 443                 if (!already_added) {
 444                         for (; (*rit) != curr; rit++)
 445                                 ;
 446                         /* go past curr now */
 447                         rit++;
 448                 }
 449
 450                 int count=0;
 451                 for (; rit != list->rend(); rit++) {
 452                         ModelAction *act = *rit;
 453                         if (!act->is_read())
 454                                 return;
 455                         if (act->get_reads_from() != curr->get_reads_from())
 456                                 return;
 457                         if (act->get_node()->get_read_from_size() <= 1)
 458                                 return;
 459                         count++;
 460                         if (count >= params.maxreads) {
 461                                 /* We've read from the same write for too many times */
 462                                 too_many_reads = true;
 463                         }
 464                 }
 465         }
 466 }
 467
 468 /**
 469  * Updates the mo_graph with the constraints imposed from the current read.
 470  * @param curr The current action. Must be a read.
 471  * @param rf The action that curr reads from. Must be a write.
 472  * @return True if modification order edges were added; false otherwise
 473  */
 474 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 475 {
 476         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 477         unsigned int i;
 478         bool added = false;
 479         ASSERT(curr->is_read());
 480
 481         /* Iterate over all threads */
 482         for (i = 0; i < thrd_lists->size(); i++) {
 483                 /* Iterate over actions in thread, starting from most recent */
 484                 action_list_t *list = &(*thrd_lists)[i];
 485                 action_list_t::reverse_iterator rit;
 486                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 487                         ModelAction *act = *rit;
 488
 489                         /* Include at most one act per-thread that "happens before" curr */
 490                         if (act->happens_before(curr)) {
 491                                 if (act->is_read()) {
 492                                         const ModelAction *prevreadfrom = act->get_reads_from();
 493                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 494                                                 mo_graph->addEdge(prevreadfrom, rf);
 495                                                 added = true;
 496                                         }
 497                                 } else if (rf != act) {
 498                                         mo_graph->addEdge(act, rf);
 499                                         added = true;
 500                                 }
 501                                 break;
 502                         }
 503                 }
 504         }
 505
 506         return added;
 507 }
 508
 509 /** Updates the mo_graph with the constraints imposed from the current read. */
 510 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 511 {
 512         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 513         unsigned int i;
 514         ASSERT(curr->is_read());
 515
 516         /* Iterate over all threads */
 517         for (i = 0; i < thrd_lists->size(); i++) {
 518                 /* Iterate over actions in thread, starting from most recent */
 519                 action_list_t *list = &(*thrd_lists)[i];
 520                 action_list_t::reverse_iterator rit;
 521                 ModelAction *lastact = NULL;
 522
 523                 /* Find last action that happens after curr */
 524                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 525                         ModelAction *act = *rit;
 526                         if (curr->happens_before(act)) {
 527                                 lastact = act;
 528                         } else
 529                                 break;
 530                 }
 531
 532                         /* Include at most one act per-thread that "happens before" curr */
 533                 if (lastact != NULL) {
 534                         if (lastact->is_read()) {
 535                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 536                                 if (postreadfrom != NULL&&rf != postreadfrom)
 537                                         mo_graph->addEdge(rf, postreadfrom);
 538                         } else if (rf != lastact) {
 539                                 mo_graph->addEdge(rf, lastact);
 540                         }
 541                         break;
 542                 }
 543         }
 544 }
 545
 546 /**
 547  * Updates the mo_graph with the constraints imposed from the current write.
 548  * @param curr The current action. Must be a write.
 549  * @return True if modification order edges were added; false otherwise
 550  */
 551 bool ModelChecker::w_modification_order(ModelAction *curr)
 552 {
 553         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 554         unsigned int i;
 555         bool added = false;
 556         ASSERT(curr->is_write());
 557
 558         if (curr->is_seqcst()) {
 559                 /* We have to at least see the last sequentially consistent write,
 560                          so we are initialized. */
 561                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 562                 if (last_seq_cst != NULL) {
 563                         mo_graph->addEdge(last_seq_cst, curr);
 564                         added = true;
 565                 }
 566         }
 567
 568         /* Iterate over all threads */
 569         for (i = 0; i < thrd_lists->size(); i++) {
 570                 /* Iterate over actions in thread, starting from most recent */
 571                 action_list_t *list = &(*thrd_lists)[i];
 572                 action_list_t::reverse_iterator rit;
 573                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 574                         ModelAction *act = *rit;
 575
 576                         /* Include at most one act per-thread that "happens before" curr */
 577                         if (act->happens_before(curr)) {
 578                                 if (act->is_read())
 579                                         mo_graph->addEdge(act->get_reads_from(), curr);
 580                                 else
 581                                         mo_graph->addEdge(act, curr);
 582                                 added = true;
 583                                 break;
 584                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 585                                                      !act->same_thread(curr)) {
 586                                 /* We have an action that:
 587                                    (1) did not happen before us
 588                                    (2) is a read and we are a write
 589                                    (3) cannot synchronize with us
 590                                    (4) is in a different thread
 591                                    =>
 592                                    that read could potentially read from our write.
 593                                  */
 594                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 595                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 596                                         priv->next_backtrack = act;
 597                         }
 598                 }
 599         }
 600
 601         return added;
 602 }
 603
 604 /**
 605  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 606  * The ModelAction under consideration is expected to be taking part in
 607  * release/acquire synchronization as an object of the "reads from" relation.
 608  * Note that this can only provide release sequence support for RMW chains
 609  * which do not read from the future, as those actions cannot be traced until
 610  * their "promise" is fulfilled. Similarly, we may not even establish the
 611  * presence of a release sequence with certainty, as some modification order
 612  * constraints may be decided further in the future. Thus, this function
 613  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 614  * and a boolean representing certainty.
 615  *
 616  * @todo Finish lazy updating, when promises are fulfilled in the future
 617  * @param rf The action that might be part of a release sequence. Must be a
 618  * write.
 619  * @param release_heads A pass-by-reference style return parameter.  After
 620  * execution of this function, release_heads will contain the heads of all the
 621  * relevant release sequences, if any exists
 622  * @return true, if the ModelChecker is certain that release_heads is complete;
 623  * false otherwise
 624  */
 625 bool ModelChecker::release_seq_head(const ModelAction *rf,
 626                 std::vector<const ModelAction *> *release_heads) const
 627 {
 628         ASSERT(rf->is_write());
 629         if (!rf) {
 630                 /* read from future: need to settle this later */
 631                 return false; /* incomplete */
 632         }
 633         if (rf->is_release())
 634                 release_heads->push_back(rf);
 635         if (rf->is_rmw()) {
 636                 /* We need a RMW action that is both an acquire and release to stop */
 637                 /** @todo Need to be smarter here...  In the linux lock
 638                  * example, this will run to the beginning of the program for
 639                  * every acquire. */
 640                 if (rf->is_acquire() && rf->is_release())
 641                         return true; /* complete */
 642                 return release_seq_head(rf->get_reads_from(), release_heads);
 643         }
 644         if (rf->is_release())
 645                 return true; /* complete */
 646
 647         /* else relaxed write; check modification order for contiguous subsequence
 648          * -> rf must be same thread as release */
 649         int tid = id_to_int(rf->get_tid());
 650         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 651         action_list_t *list = &(*thrd_lists)[tid];
 652         action_list_t::const_reverse_iterator rit;
 653
 654         /* Find rf in the thread list */
 655         rit = std::find(list->rbegin(), list->rend(), rf);
 656         ASSERT(rit != list->rend());
 657
 658         /* Find the last write/release */
 659         for (; rit != list->rend(); rit++)
 660                 if ((*rit)->is_release())
 661                         break;
 662         if (rit == list->rend()) {
 663                 /* No write-release in this thread */
 664                 return true; /* complete */
 665         }
 666         ModelAction *release = *rit;
 667
 668         ASSERT(rf->same_thread(release));
 669
 670         bool certain = true;
 671         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 672                 if (id_to_int(rf->get_tid()) == (int)i)
 673                         continue;
 674                 list = &(*thrd_lists)[i];
 675
 676                 /* Can we ensure no future writes from this thread may break
 677                  * the release seq? */
 678                 bool future_ordered = false;
 679
 680                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 681                         const ModelAction *act = *rit;
 682                         if (!act->is_write())
 683                                 continue;
 684                         /* Reach synchronization -> this thread is complete */
 685                         if (act->happens_before(release))
 686                                 break;
 687                         if (rf->happens_before(act)) {
 688                                 future_ordered = true;
 689                                 continue;
 690                         }
 691
 692                         /* Check modification order */
 693                         if (mo_graph->checkReachable(rf, act)) {
 694                                 /* rf --mo--> act */
 695                                 future_ordered = true;
 696                                 continue;
 697                         }
 698                         if (mo_graph->checkReachable(act, release))
 699                                 /* act --mo--> release */
 700                                 break;
 701                         if (mo_graph->checkReachable(release, act) &&
 702                                       mo_graph->checkReachable(act, rf)) {
 703                                 /* release --mo-> act --mo--> rf */
 704                                 return true; /* complete */
 705                         }
 706                         certain = false;
 707                 }
 708                 if (!future_ordered)
 709                         return false; /* This thread is uncertain */
 710         }
 711
 712         if (certain)
 713                 release_heads->push_back(release);
 714         return certain;
 715 }
 716
 717 /**
 718  * A public interface for getting the release sequence head(s) with which a
 719  * given ModelAction must synchronize. This function only returns a non-empty
 720  * result when it can locate a release sequence head with certainty. Otherwise,
 721  * it may mark the internal state of the ModelChecker so that it will handle
 722  * the release sequence at a later time, causing @a act to update its
 723  * synchronization at some later point in execution.
 724  * @param act The 'acquire' action that may read from a release sequence
 725  * @param release_heads A pass-by-reference return parameter. Will be filled
 726  * with the head(s) of the release sequence(s), if they exists with certainty.
 727  * @see ModelChecker::release_seq_head
 728  */
 729 void ModelChecker::get_release_seq_heads(ModelAction *act,
 730                 std::vector<const ModelAction *> *release_heads)
 731 {
 732         const ModelAction *rf = act->get_reads_from();
 733         bool complete;
 734         complete = release_seq_head(rf, release_heads);
 735         if (!complete) {
 736                 /* add act to 'lazy checking' list */
 737                 std::list<ModelAction *> *list;
 738                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 739                 list->push_back(act);
 740                 (*lazy_sync_size)++;
 741         }
 742 }
 743
 744 /**
 745  * Attempt to resolve all stashed operations that might synchronize with a
 746  * release sequence for a given location. This implements the "lazy" portion of
 747  * determining whether or not a release sequence was contiguous, since not all
 748  * modification order information is present at the time an action occurs.
 749  *
 750  * @param location The location/object that should be checked for release
 751  * sequence resolutions
 752  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 753  */
 754 bool ModelChecker::resolve_release_sequences(void *location)
 755 {
 756         std::list<ModelAction *> *list;
 757         list = lazy_sync_with_release->getptr(location);
 758         if (!list)
 759                 return false;
 760
 761         bool updated = false;
 762         std::list<ModelAction *>::iterator it = list->begin();
 763         while (it != list->end()) {
 764                 ModelAction *act = *it;
 765                 const ModelAction *rf = act->get_reads_from();
 766                 std::vector<const ModelAction *> release_heads;
 767                 bool complete;
 768                 complete = release_seq_head(rf, &release_heads);
 769                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 770                         if (!act->has_synchronized_with(release_heads[i])) {
 771                                 updated = true;
 772                                 act->synchronize_with(release_heads[i]);
 773                         }
 774                 }
 775
 776                 if (updated) {
 777                         /* propagate synchronization to later actions */
 778                         action_list_t::reverse_iterator it = action_trace->rbegin();
 779                         while ((*it) != act) {
 780                                 ModelAction *propagate = *it;
 781                                 if (act->happens_before(propagate))
 782                                         /** @todo new mo_graph edges along with
 783                                          * this synchronization? */
 784                                         propagate->synchronize_with(act);
 785                         }
 786                 }
 787                 if (complete) {
 788                         it = list->erase(it);
 789                         (*lazy_sync_size)--;
 790                 } else
 791                         it++;
 792         }
 793
 794         // If we resolved promises or data races, see if we have realized a data race.
 795         if (checkDataRaces()) {
 796                 set_assert();
 797         }
 798
 799         return updated;
 800 }
 801
 802 /**
 803  * Performs various bookkeeping operations for the current ModelAction. For
 804  * instance, adds action to the per-object, per-thread action vector and to the
 805  * action trace list of all thread actions.
 806  *
 807  * @param act is the ModelAction to add.
 808  */
 809 void ModelChecker::add_action_to_lists(ModelAction *act)
 810 {
 811         int tid = id_to_int(act->get_tid());
 812         action_trace->push_back(act);
 813
 814         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 815
 816         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 817         if (tid >= (int)vec->size())
 818                 vec->resize(priv->next_thread_id);
 819         (*vec)[tid].push_back(act);
 820
 821         if ((int)thrd_last_action->size() <= tid)
 822                 thrd_last_action->resize(get_num_threads());
 823         (*thrd_last_action)[tid] = act;
 824 }
 825
 826 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 827 {
 828         int nthreads = get_num_threads();
 829         if ((int)thrd_last_action->size() < nthreads)
 830                 thrd_last_action->resize(nthreads);
 831         return (*thrd_last_action)[id_to_int(tid)];
 832 }
 833
 834 /**
 835  * Gets the last memory_order_seq_cst action (in the total global sequence)
 836  * performed on a particular object (i.e., memory location).
 837  * @param location The object location to check
 838  * @return The last seq_cst action performed
 839  */
 840 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 841 {
 842         action_list_t *list = obj_map->get_safe_ptr(location);
 843         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 844         action_list_t::reverse_iterator rit;
 845         for (rit = list->rbegin(); rit != list->rend(); rit++)
 846                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 847                         return *rit;
 848         return NULL;
 849 }
 850
 851 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 852 {
 853         ModelAction *parent = get_last_action(tid);
 854         if (!parent)
 855                 parent = get_thread(tid)->get_creation();
 856         return parent;
 857 }
 858
 859 /**
 860  * Returns the clock vector for a given thread.
 861  * @param tid The thread whose clock vector we want
 862  * @return Desired clock vector
 863  */
 864 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 865 {
 866         return get_parent_action(tid)->get_cv();
 867 }
 868
 869 /**
 870  * Resolve a set of Promises with a current write. The set is provided in the
 871  * Node corresponding to @a write.
 872  * @param write The ModelAction that is fulfilling Promises
 873  * @return True if promises were resolved; false otherwise
 874  */
 875 bool ModelChecker::resolve_promises(ModelAction *write)
 876 {
 877         bool resolved = false;
 878         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 879                 Promise *promise = (*promises)[promise_index];
 880                 if (write->get_node()->get_promise(i)) {
 881                         ModelAction *read = promise->get_action();
 882                         read->read_from(write);
 883                         r_modification_order(read, write);
 884                         post_r_modification_order(read, write);
 885                         promises->erase(promises->begin() + promise_index);
 886                         resolved = true;
 887                 } else
 888                         promise_index++;
 889         }
 890
 891         return resolved;
 892 }
 893
 894 /**
 895  * Compute the set of promises that could potentially be satisfied by this
 896  * action. Note that the set computation actually appears in the Node, not in
 897  * ModelChecker.
 898  * @param curr The ModelAction that may satisfy promises
 899  */
 900 void ModelChecker::compute_promises(ModelAction *curr)
 901 {
 902         for (unsigned int i = 0; i < promises->size(); i++) {
 903                 Promise *promise = (*promises)[i];
 904                 const ModelAction *act = promise->get_action();
 905                 if (!act->happens_before(curr) &&
 906                                 act->is_read() &&
 907                                 !act->is_synchronizing(curr) &&
 908                                 !act->same_thread(curr) &&
 909                                 promise->get_value() == curr->get_value()) {
 910                         curr->get_node()->set_promise(i);
 911                 }
 912         }
 913 }
 914
 915 /** Checks promises in response to change in ClockVector Threads. */
 916 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 917 {
 918         for (unsigned int i = 0; i < promises->size(); i++) {
 919                 Promise *promise = (*promises)[i];
 920                 const ModelAction *act = promise->get_action();
 921                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 922                                 merge_cv->synchronized_since(act)) {
 923                         //This thread is no longer able to send values back to satisfy the promise
 924                         int num_synchronized_threads = promise->increment_threads();
 925                         if (num_synchronized_threads == get_num_threads()) {
 926                                 //Promise has failed
 927                                 failed_promise = true;
 928                                 return;
 929                         }
 930                 }
 931         }
 932 }
 933
 934 /**
 935  * Build up an initial set of all past writes that this 'read' action may read
 936  * from. This set is determined by the clock vector's "happens before"
 937  * relationship.
 938  * @param curr is the current ModelAction that we are exploring; it must be a
 939  * 'read' operation.
 940  */
 941 void ModelChecker::build_reads_from_past(ModelAction *curr)
 942 {
 943         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 944         unsigned int i;
 945         ASSERT(curr->is_read());
 946
 947         ModelAction *last_seq_cst = NULL;
 948
 949         /* Track whether this object has been initialized */
 950         bool initialized = false;
 951
 952         if (curr->is_seqcst()) {
 953                 last_seq_cst = get_last_seq_cst(curr->get_location());
 954                 /* We have to at least see the last sequentially consistent write,
 955                          so we are initialized. */
 956                 if (last_seq_cst != NULL)
 957                         initialized = true;
 958         }
 959
 960         /* Iterate over all threads */
 961         for (i = 0; i < thrd_lists->size(); i++) {
 962                 /* Iterate over actions in thread, starting from most recent */
 963                 action_list_t *list = &(*thrd_lists)[i];
 964                 action_list_t::reverse_iterator rit;
 965                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 966                         ModelAction *act = *rit;
 967
 968                         /* Only consider 'write' actions */
 969                         if (!act->is_write())
 970                                 continue;
 971
 972                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 973                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 974                                 DEBUG("Adding action to may_read_from:\n");
 975                                 if (DBG_ENABLED()) {
 976                                         act->print();
 977                                         curr->print();
 978                                 }
 979                                 curr->get_node()->add_read_from(act);
 980                         }
 981
 982                         /* Include at most one act per-thread that "happens before" curr */
 983                         if (act->happens_before(curr)) {
 984                                 initialized = true;
 985                                 break;
 986                         }
 987                 }
 988         }
 989
 990         if (!initialized) {
 991                 /** @todo Need a more informative way of reporting errors. */
 992                 printf("ERROR: may read from uninitialized atomic\n");
 993         }
 994
 995         if (DBG_ENABLED() || !initialized) {
 996                 printf("Reached read action:\n");
 997                 curr->print();
 998                 printf("Printing may_read_from\n");
 999                 curr->get_node()->print_may_read_from();
1000                 printf("End printing may_read_from\n");
1001         }
1002
1003         ASSERT(initialized);
1004 }
1005
1006 static void print_list(action_list_t *list)
1007 {
1008         action_list_t::iterator it;
1009
1010         printf("---------------------------------------------------------------------\n");
1011         printf("Trace:\n");
1012
1013         for (it = list->begin(); it != list->end(); it++) {
1014                 (*it)->print();
1015         }
1016         printf("---------------------------------------------------------------------\n");
1017 }
1018
1019 void ModelChecker::print_summary()
1020 {
1021         printf("\n");
1022         printf("Number of executions: %d\n", num_executions);
1023         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1024
1025         scheduler->print();
1026
1027         if (!isfinalfeasible())
1028                 printf("INFEASIBLE EXECUTION!\n");
1029         print_list(action_trace);
1030         printf("\n");
1031 }
1032
1033 /**
1034  * Add a Thread to the system for the first time. Should only be called once
1035  * per thread.
1036  * @param t The Thread to add
1037  */
1038 void ModelChecker::add_thread(Thread *t)
1039 {
1040         thread_map->put(id_to_int(t->get_id()), t);
1041         scheduler->add_thread(t);
1042 }
1043
1044 void ModelChecker::remove_thread(Thread *t)
1045 {
1046         scheduler->remove_thread(t);
1047 }
1048
1049 /**
1050  * Switch from a user-context to the "master thread" context (a.k.a. system
1051  * context). This switch is made with the intention of exploring a particular
1052  * model-checking action (described by a ModelAction object). Must be called
1053  * from a user-thread context.
1054  * @param act The current action that will be explored. Must not be NULL.
1055  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1056  */
1057 int ModelChecker::switch_to_master(ModelAction *act)
1058 {
1059         DBG();
1060         Thread *old = thread_current();
1061         set_current_action(act);
1062         old->set_state(THREAD_READY);
1063         return Thread::swap(old, &system_context);
1064 }
1065
1066 /**
1067  * Takes the next step in the execution, if possible.
1068  * @return Returns true (success) if a step was taken and false otherwise.
1069  */
1070 bool ModelChecker::take_step() {
1071         Thread *curr, *next;
1072
1073         if (has_asserted())
1074                 return false;
1075
1076         curr = thread_current();
1077         if (curr) {
1078                 if (curr->get_state() == THREAD_READY) {
1079                         ASSERT(priv->current_action);
1080                         priv->nextThread = check_current_action(priv->current_action);
1081                         priv->current_action = NULL;
1082                         if (!curr->is_blocked() && !curr->is_complete())
1083                                 scheduler->add_thread(curr);
1084                 } else {
1085                         ASSERT(false);
1086                 }
1087         }
1088         next = scheduler->next_thread(priv->nextThread);
1089
1090         /* Infeasible -> don't take any more steps */
1091         if (!isfeasible())
1092                 return false;
1093
1094         if (next)
1095                 next->set_state(THREAD_RUNNING);
1096         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1097
1098         /* next == NULL -> don't take any more steps */
1099         if (!next)
1100                 return false;
1101         /* Return false only if swap fails with an error */
1102         return (Thread::swap(&system_context, next) == 0);
1103 }
1104
1105 /** Runs the current execution until threre are no more steps to take. */
1106 void ModelChecker::finish_execution() {
1107         DBG();
1108
1109         while (take_step());
1110 }