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