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         /* Assign 'creation' parent */
 311         if (curr->get_type() == THREAD_CREATE) {
 312                 Thread *th = (Thread *)curr->get_location();
 313                 th->set_creation(curr);
 314         } else if (curr->get_type() == THREAD_JOIN) {
 315                 Thread *wait, *join;
 316                 wait = get_thread(curr->get_tid());
 317                 join = (Thread *)curr->get_location();
 318                 if (!join->is_complete())
 319                         scheduler->wait(wait, join);
 320         } else if (curr->get_type() == THREAD_FINISH) {
 321                 Thread *th = get_thread(curr->get_tid());
 322                 while (!th->wait_list_empty()) {
 323                         Thread *wake = th->pop_wait_list();
 324                         scheduler->wake(wake);
 325                 }
 326                 th->complete();
 327         }
 328
 329         /* Deal with new thread */
 330         if (curr->get_type() == THREAD_START)
 331                 check_promises(NULL, curr->get_cv());
 332
 333         /* Assign reads_from values */
 334         Thread *th = get_thread(curr->get_tid());
 335         uint64_t value = VALUE_NONE;
 336         bool updated = false;
 337         if (curr->is_read()) {
 338                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 339                 if (reads_from != NULL) {
 340                         value = reads_from->get_value();
 341                         /* Assign reads_from, perform release/acquire synchronization */
 342                         curr->read_from(reads_from);
 343                         if (r_modification_order(curr,reads_from))
 344                                 updated = true;
 345                 } else {
 346                         /* Read from future value */
 347                         value = curr->get_node()->get_future_value();
 348                         curr->read_from(NULL);
 349                         Promise *valuepromise = new Promise(curr, value);
 350                         promises->push_back(valuepromise);
 351                 }
 352         } else if (curr->is_write()) {
 353                 if (w_modification_order(curr))
 354                         updated = true;
 355                 if (resolve_promises(curr))
 356                         updated = true;
 357         }
 358
 359         if (updated)
 360                 resolve_release_sequences(curr->get_location());
 361
 362         th->set_return_value(value);
 363
 364         /* Add action to list.  */
 365         if (!already_added)
 366                 add_action_to_lists(curr);
 367
 368         Node *currnode = curr->get_node();
 369         Node *parnode = currnode->get_parent();
 370
 371         if (!parnode->backtrack_empty() || !currnode->read_from_empty() ||
 372                   !currnode->future_value_empty() || !currnode->promise_empty())
 373                 if (!priv->next_backtrack || *curr > *priv->next_backtrack)
 374                         priv->next_backtrack = curr;
 375
 376         set_backtracking(curr);
 377
 378         return get_next_thread(curr);
 379 }
 380
 381 /** @returns whether the current partial trace must be a prefix of a
 382  * feasible trace. */
 383 bool ModelChecker::isfeasibleprefix() {
 384         return promises->size() == 0 && *lazy_sync_size == 0;
 385 }
 386
 387 /** @returns whether the current partial trace is feasible. */
 388 bool ModelChecker::isfeasible() {
 389         return !mo_graph->checkForCycles() && !failed_promise;
 390 }
 391
 392 /** Returns whether the current completed trace is feasible. */
 393 bool ModelChecker::isfinalfeasible() {
 394         return isfeasible() && promises->size() == 0;
 395 }
 396
 397 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 398 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 399         int tid = id_to_int(act->get_tid());
 400         ModelAction *lastread = get_last_action(tid);
 401         lastread->process_rmw(act);
 402         if (act->is_rmw())
 403                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 404         return lastread;
 405 }
 406
 407 /**
 408  * Updates the mo_graph with the constraints imposed from the current read.
 409  * @param curr The current action. Must be a read.
 410  * @param rf The action that curr reads from. Must be a write.
 411  * @return True if modification order edges were added; false otherwise
 412  */
 413 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 414 {
 415         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 416         unsigned int i;
 417         bool added = false;
 418         ASSERT(curr->is_read());
 419
 420         /* Iterate over all threads */
 421         for (i = 0; i < thrd_lists->size(); i++) {
 422                 /* Iterate over actions in thread, starting from most recent */
 423                 action_list_t *list = &(*thrd_lists)[i];
 424                 action_list_t::reverse_iterator rit;
 425                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 426                         ModelAction *act = *rit;
 427
 428                         /* Include at most one act per-thread that "happens before" curr */
 429                         if (act->happens_before(curr)) {
 430                                 if (act->is_read()) {
 431                                         const ModelAction *prevreadfrom = act->get_reads_from();
 432                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 433                                                 mo_graph->addEdge(prevreadfrom, rf);
 434                                                 added = true;
 435                                         }
 436                                 } else if (rf != act) {
 437                                         mo_graph->addEdge(act, rf);
 438                                         added = true;
 439                                 }
 440                                 break;
 441                         }
 442                 }
 443         }
 444
 445         return added;
 446 }
 447
 448 /** Updates the mo_graph with the constraints imposed from the current read. */
 449 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 450 {
 451         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 452         unsigned int i;
 453         ASSERT(curr->is_read());
 454
 455         /* Iterate over all threads */
 456         for (i = 0; i < thrd_lists->size(); i++) {
 457                 /* Iterate over actions in thread, starting from most recent */
 458                 action_list_t *list = &(*thrd_lists)[i];
 459                 action_list_t::reverse_iterator rit;
 460                 ModelAction *lastact = NULL;
 461
 462                 /* Find last action that happens after curr */
 463                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 464                         ModelAction *act = *rit;
 465                         if (curr->happens_before(act)) {
 466                                 lastact = act;
 467                         } else
 468                                 break;
 469                 }
 470
 471                         /* Include at most one act per-thread that "happens before" curr */
 472                 if (lastact != NULL) {
 473                         if (lastact->is_read()) {
 474                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 475                                 if (postreadfrom != NULL&&rf != postreadfrom)
 476                                         mo_graph->addEdge(rf, postreadfrom);
 477                         } else if (rf != lastact) {
 478                                 mo_graph->addEdge(rf, lastact);
 479                         }
 480                         break;
 481                 }
 482         }
 483 }
 484
 485 /**
 486  * Updates the mo_graph with the constraints imposed from the current write.
 487  * @param curr The current action. Must be a write.
 488  * @return True if modification order edges were added; false otherwise
 489  */
 490 bool ModelChecker::w_modification_order(ModelAction *curr)
 491 {
 492         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 493         unsigned int i;
 494         bool added = false;
 495         ASSERT(curr->is_write());
 496
 497         if (curr->is_seqcst()) {
 498                 /* We have to at least see the last sequentially consistent write,
 499                          so we are initialized. */
 500                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 501                 if (last_seq_cst != NULL) {
 502                         mo_graph->addEdge(last_seq_cst, curr);
 503                         added = true;
 504                 }
 505         }
 506
 507         /* Iterate over all threads */
 508         for (i = 0; i < thrd_lists->size(); i++) {
 509                 /* Iterate over actions in thread, starting from most recent */
 510                 action_list_t *list = &(*thrd_lists)[i];
 511                 action_list_t::reverse_iterator rit;
 512                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 513                         ModelAction *act = *rit;
 514
 515                         /* Include at most one act per-thread that "happens before" curr */
 516                         if (act->happens_before(curr)) {
 517                                 if (act->is_read())
 518                                         mo_graph->addEdge(act->get_reads_from(), curr);
 519                                 else
 520                                         mo_graph->addEdge(act, curr);
 521                                 added = true;
 522                                 break;
 523                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 524                                                      !act->same_thread(curr)) {
 525                                 /* We have an action that:
 526                                    (1) did not happen before us
 527                                    (2) is a read and we are a write
 528                                    (3) cannot synchronize with us
 529                                    (4) is in a different thread
 530                                    =>
 531                                    that read could potentially read from our write.
 532                                  */
 533                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 534                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 535                                         priv->next_backtrack = act;
 536                         }
 537                 }
 538         }
 539
 540         return added;
 541 }
 542
 543 /**
 544  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 545  * The ModelAction under consideration is expected to be taking part in
 546  * release/acquire synchronization as an object of the "reads from" relation.
 547  * Note that this can only provide release sequence support for RMW chains
 548  * which do not read from the future, as those actions cannot be traced until
 549  * their "promise" is fulfilled. Similarly, we may not even establish the
 550  * presence of a release sequence with certainty, as some modification order
 551  * constraints may be decided further in the future. Thus, this function
 552  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 553  * and a boolean representing certainty.
 554  *
 555  * @todo Finish lazy updating, when promises are fulfilled in the future
 556  * @param rf The action that might be part of a release sequence. Must be a
 557  * write.
 558  * @param release_heads A pass-by-reference style return parameter.  After
 559  * execution of this function, release_heads will contain the heads of all the
 560  * relevant release sequences, if any exists
 561  * @return true, if the ModelChecker is certain that release_heads is complete;
 562  * false otherwise
 563  */
 564 bool ModelChecker::release_seq_head(const ModelAction *rf,
 565                 std::vector<const ModelAction *> *release_heads) const
 566 {
 567         ASSERT(rf->is_write());
 568         if (!rf) {
 569                 /* read from future: need to settle this later */
 570                 return false; /* incomplete */
 571         }
 572         if (rf->is_release())
 573                 release_heads->push_back(rf);
 574         if (rf->is_rmw()) {
 575                 /* We need a RMW action that is both an acquire and release to stop */
 576                 /** @todo Need to be smarter here...  In the linux lock
 577                  * example, this will run to the beginning of the program for
 578                  * every acquire. */
 579                 if (rf->is_acquire() && rf->is_release())
 580                         return true; /* complete */
 581                 return release_seq_head(rf->get_reads_from(), release_heads);
 582         }
 583         if (rf->is_release())
 584                 return true; /* complete */
 585
 586         /* else relaxed write; check modification order for contiguous subsequence
 587          * -> rf must be same thread as release */
 588         int tid = id_to_int(rf->get_tid());
 589         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 590         action_list_t *list = &(*thrd_lists)[tid];
 591         action_list_t::const_reverse_iterator rit;
 592
 593         /* Find rf in the thread list */
 594         rit = std::find(list->rbegin(), list->rend(), rf);
 595         ASSERT(rit != list->rend());
 596
 597         /* Find the last write/release */
 598         for (; rit != list->rend(); rit++)
 599                 if ((*rit)->is_release())
 600                         break;
 601         if (rit == list->rend()) {
 602                 /* No write-release in this thread */
 603                 return true; /* complete */
 604         }
 605         ModelAction *release = *rit;
 606
 607         ASSERT(rf->same_thread(release));
 608
 609         bool certain = true;
 610         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 611                 if (id_to_int(rf->get_tid()) == (int)i)
 612                         continue;
 613                 list = &(*thrd_lists)[i];
 614
 615                 /* Can we ensure no future writes from this thread may break
 616                  * the release seq? */
 617                 bool future_ordered = false;
 618
 619                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 620                         const ModelAction *act = *rit;
 621                         if (!act->is_write())
 622                                 continue;
 623                         /* Reach synchronization -> this thread is complete */
 624                         if (act->happens_before(release))
 625                                 break;
 626                         if (rf->happens_before(act)) {
 627                                 future_ordered = true;
 628                                 continue;
 629                         }
 630
 631                         /* Check modification order */
 632                         if (mo_graph->checkReachable(rf, act)) {
 633                                 /* rf --mo--> act */
 634                                 future_ordered = true;
 635                                 continue;
 636                         }
 637                         if (mo_graph->checkReachable(act, release))
 638                                 /* act --mo--> release */
 639                                 break;
 640                         if (mo_graph->checkReachable(release, act) &&
 641                                       mo_graph->checkReachable(act, rf)) {
 642                                 /* release --mo-> act --mo--> rf */
 643                                 return true; /* complete */
 644                         }
 645                         certain = false;
 646                 }
 647                 if (!future_ordered)
 648                         return false; /* This thread is uncertain */
 649         }
 650
 651         if (certain)
 652                 release_heads->push_back(release);
 653         return certain;
 654 }
 655
 656 /**
 657  * A public interface for getting the release sequence head(s) with which a
 658  * given ModelAction must synchronize. This function only returns a non-empty
 659  * result when it can locate a release sequence head with certainty. Otherwise,
 660  * it may mark the internal state of the ModelChecker so that it will handle
 661  * the release sequence at a later time, causing @a act to update its
 662  * synchronization at some later point in execution.
 663  * @param act The 'acquire' action that may read from a release sequence
 664  * @param release_heads A pass-by-reference return parameter. Will be filled
 665  * with the head(s) of the release sequence(s), if they exists with certainty.
 666  * @see ModelChecker::release_seq_head
 667  */
 668 void ModelChecker::get_release_seq_heads(ModelAction *act,
 669                 std::vector<const ModelAction *> *release_heads)
 670 {
 671         const ModelAction *rf = act->get_reads_from();
 672         bool complete;
 673         complete = release_seq_head(rf, release_heads);
 674         if (!complete) {
 675                 /* add act to 'lazy checking' list */
 676                 std::list<ModelAction *> *list;
 677                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 678                 list->push_back(act);
 679                 (*lazy_sync_size)++;
 680         }
 681 }
 682
 683 /**
 684  * Attempt to resolve all stashed operations that might synchronize with a
 685  * release sequence for a given location. This implements the "lazy" portion of
 686  * determining whether or not a release sequence was contiguous, since not all
 687  * modification order information is present at the time an action occurs.
 688  *
 689  * @param location The location/object that should be checked for release
 690  * sequence resolutions
 691  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 692  */
 693 bool ModelChecker::resolve_release_sequences(void *location)
 694 {
 695         std::list<ModelAction *> *list;
 696         list = lazy_sync_with_release->getptr(location);
 697         if (!list)
 698                 return false;
 699
 700         bool updated = false;
 701         std::list<ModelAction *>::iterator it = list->begin();
 702         while (it != list->end()) {
 703                 ModelAction *act = *it;
 704                 const ModelAction *rf = act->get_reads_from();
 705                 std::vector<const ModelAction *> release_heads;
 706                 bool complete;
 707                 complete = release_seq_head(rf, &release_heads);
 708                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 709                         if (!act->has_synchronized_with(release_heads[i])) {
 710                                 updated = true;
 711                                 act->synchronize_with(release_heads[i]);
 712                         }
 713                 }
 714
 715                 if (updated) {
 716                         /* propagate synchronization to later actions */
 717                         action_list_t::reverse_iterator it = action_trace->rbegin();
 718                         while ((*it) != act) {
 719                                 ModelAction *propagate = *it;
 720                                 if (act->happens_before(propagate))
 721                                         /** @todo new mo_graph edges along with
 722                                          * this synchronization? */
 723                                         propagate->synchronize_with(act);
 724                         }
 725                 }
 726                 if (complete) {
 727                         it = list->erase(it);
 728                         (*lazy_sync_size)--;
 729                 } else
 730                         it++;
 731         }
 732
 733         // If we resolved promises or data races, see if we have realized a data race.
 734         if (checkDataRaces()) {
 735                 set_assert();
 736         }
 737
 738         return updated;
 739 }
 740
 741 /**
 742  * Performs various bookkeeping operations for the current ModelAction. For
 743  * instance, adds action to the per-object, per-thread action vector and to the
 744  * action trace list of all thread actions.
 745  *
 746  * @param act is the ModelAction to add.
 747  */
 748 void ModelChecker::add_action_to_lists(ModelAction *act)
 749 {
 750         int tid = id_to_int(act->get_tid());
 751         action_trace->push_back(act);
 752
 753         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 754
 755         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 756         if (tid >= (int)vec->size())
 757                 vec->resize(priv->next_thread_id);
 758         (*vec)[tid].push_back(act);
 759
 760         if ((int)thrd_last_action->size() <= tid)
 761                 thrd_last_action->resize(get_num_threads());
 762         (*thrd_last_action)[tid] = act;
 763 }
 764
 765 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 766 {
 767         int nthreads = get_num_threads();
 768         if ((int)thrd_last_action->size() < nthreads)
 769                 thrd_last_action->resize(nthreads);
 770         return (*thrd_last_action)[id_to_int(tid)];
 771 }
 772
 773 /**
 774  * Gets the last memory_order_seq_cst action (in the total global sequence)
 775  * performed on a particular object (i.e., memory location).
 776  * @param location The object location to check
 777  * @return The last seq_cst action performed
 778  */
 779 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 780 {
 781         action_list_t *list = obj_map->get_safe_ptr(location);
 782         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 783         action_list_t::reverse_iterator rit;
 784         for (rit = list->rbegin(); rit != list->rend(); rit++)
 785                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 786                         return *rit;
 787         return NULL;
 788 }
 789
 790 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 791 {
 792         ModelAction *parent = get_last_action(tid);
 793         if (!parent)
 794                 parent = get_thread(tid)->get_creation();
 795         return parent;
 796 }
 797
 798 /**
 799  * Returns the clock vector for a given thread.
 800  * @param tid The thread whose clock vector we want
 801  * @return Desired clock vector
 802  */
 803 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 804 {
 805         return get_parent_action(tid)->get_cv();
 806 }
 807
 808 /**
 809  * Resolve a set of Promises with a current write. The set is provided in the
 810  * Node corresponding to @a write.
 811  * @param write The ModelAction that is fulfilling Promises
 812  * @return True if promises were resolved; false otherwise
 813  */
 814 bool ModelChecker::resolve_promises(ModelAction *write)
 815 {
 816         bool resolved = false;
 817         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 818                 Promise *promise = (*promises)[promise_index];
 819                 if (write->get_node()->get_promise(i)) {
 820                         ModelAction *read = promise->get_action();
 821                         read->read_from(write);
 822                         r_modification_order(read, write);
 823                         post_r_modification_order(read, write);
 824                         promises->erase(promises->begin() + promise_index);
 825                         resolved = true;
 826                 } else
 827                         promise_index++;
 828         }
 829
 830         return resolved;
 831 }
 832
 833 /**
 834  * Compute the set of promises that could potentially be satisfied by this
 835  * action. Note that the set computation actually appears in the Node, not in
 836  * ModelChecker.
 837  * @param curr The ModelAction that may satisfy promises
 838  */
 839 void ModelChecker::compute_promises(ModelAction *curr)
 840 {
 841         for (unsigned int i = 0; i < promises->size(); i++) {
 842                 Promise *promise = (*promises)[i];
 843                 const ModelAction *act = promise->get_action();
 844                 if (!act->happens_before(curr) &&
 845                                 act->is_read() &&
 846                                 !act->is_synchronizing(curr) &&
 847                                 !act->same_thread(curr) &&
 848                                 promise->get_value() == curr->get_value()) {
 849                         curr->get_node()->set_promise(i);
 850                 }
 851         }
 852 }
 853
 854 /** Checks promises in response to change in ClockVector Threads. */
 855 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 856 {
 857         for (unsigned int i = 0; i < promises->size(); i++) {
 858                 Promise *promise = (*promises)[i];
 859                 const ModelAction *act = promise->get_action();
 860                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 861                                 merge_cv->synchronized_since(act)) {
 862                         //This thread is no longer able to send values back to satisfy the promise
 863                         int num_synchronized_threads = promise->increment_threads();
 864                         if (num_synchronized_threads == get_num_threads()) {
 865                                 //Promise has failed
 866                                 failed_promise = true;
 867                                 return;
 868                         }
 869                 }
 870         }
 871 }
 872
 873 /**
 874  * Build up an initial set of all past writes that this 'read' action may read
 875  * from. This set is determined by the clock vector's "happens before"
 876  * relationship.
 877  * @param curr is the current ModelAction that we are exploring; it must be a
 878  * 'read' operation.
 879  */
 880 void ModelChecker::build_reads_from_past(ModelAction *curr)
 881 {
 882         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 883         unsigned int i;
 884         ASSERT(curr->is_read());
 885
 886         ModelAction *last_seq_cst = NULL;
 887
 888         /* Track whether this object has been initialized */
 889         bool initialized = false;
 890
 891         if (curr->is_seqcst()) {
 892                 last_seq_cst = get_last_seq_cst(curr->get_location());
 893                 /* We have to at least see the last sequentially consistent write,
 894                          so we are initialized. */
 895                 if (last_seq_cst != NULL)
 896                         initialized = true;
 897         }
 898
 899         /* Iterate over all threads */
 900         for (i = 0; i < thrd_lists->size(); i++) {
 901                 /* Iterate over actions in thread, starting from most recent */
 902                 action_list_t *list = &(*thrd_lists)[i];
 903                 action_list_t::reverse_iterator rit;
 904                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 905                         ModelAction *act = *rit;
 906
 907                         /* Only consider 'write' actions */
 908                         if (!act->is_write())
 909                                 continue;
 910
 911                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 912                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 913                                 DEBUG("Adding action to may_read_from:\n");
 914                                 if (DBG_ENABLED()) {
 915                                         act->print();
 916                                         curr->print();
 917                                 }
 918                                 curr->get_node()->add_read_from(act);
 919                         }
 920
 921                         /* Include at most one act per-thread that "happens before" curr */
 922                         if (act->happens_before(curr)) {
 923                                 initialized = true;
 924                                 break;
 925                         }
 926                 }
 927         }
 928
 929         if (!initialized) {
 930                 /** @todo Need a more informative way of reporting errors. */
 931                 printf("ERROR: may read from uninitialized atomic\n");
 932         }
 933
 934         if (DBG_ENABLED() || !initialized) {
 935                 printf("Reached read action:\n");
 936                 curr->print();
 937                 printf("Printing may_read_from\n");
 938                 curr->get_node()->print_may_read_from();
 939                 printf("End printing may_read_from\n");
 940         }
 941
 942         ASSERT(initialized);
 943 }
 944
 945 static void print_list(action_list_t *list)
 946 {
 947         action_list_t::iterator it;
 948
 949         printf("---------------------------------------------------------------------\n");
 950         printf("Trace:\n");
 951
 952         for (it = list->begin(); it != list->end(); it++) {
 953                 (*it)->print();
 954         }
 955         printf("---------------------------------------------------------------------\n");
 956 }
 957
 958 void ModelChecker::print_summary()
 959 {
 960         printf("\n");
 961         printf("Number of executions: %d\n", num_executions);
 962         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 963
 964         scheduler->print();
 965
 966         if (!isfinalfeasible())
 967                 printf("INFEASIBLE EXECUTION!\n");
 968         print_list(action_trace);
 969         printf("\n");
 970 }
 971
 972 /**
 973  * Add a Thread to the system for the first time. Should only be called once
 974  * per thread.
 975  * @param t The Thread to add
 976  */
 977 void ModelChecker::add_thread(Thread *t)
 978 {
 979         thread_map->put(id_to_int(t->get_id()), t);
 980         scheduler->add_thread(t);
 981 }
 982
 983 void ModelChecker::remove_thread(Thread *t)
 984 {
 985         scheduler->remove_thread(t);
 986 }
 987
 988 /**
 989  * Switch from a user-context to the "master thread" context (a.k.a. system
 990  * context). This switch is made with the intention of exploring a particular
 991  * model-checking action (described by a ModelAction object). Must be called
 992  * from a user-thread context.
 993  * @param act The current action that will be explored. Must not be NULL.
 994  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 995  */
 996 int ModelChecker::switch_to_master(ModelAction *act)
 997 {
 998         DBG();
 999         Thread *old = thread_current();
1000         set_current_action(act);
1001         old->set_state(THREAD_READY);
1002         return Thread::swap(old, &system_context);
1003 }
1004
1005 /**
1006  * Takes the next step in the execution, if possible.
1007  * @return Returns true (success) if a step was taken and false otherwise.
1008  */
1009 bool ModelChecker::take_step() {
1010         Thread *curr, *next;
1011
1012         if (has_asserted())
1013                 return false;
1014
1015         curr = thread_current();
1016         if (curr) {
1017                 if (curr->get_state() == THREAD_READY) {
1018                         ASSERT(priv->current_action);
1019                         priv->nextThread = check_current_action(priv->current_action);
1020                         priv->current_action = NULL;
1021                         if (!curr->is_blocked() && !curr->is_complete())
1022                                 scheduler->add_thread(curr);
1023                 } else {
1024                         ASSERT(false);
1025                 }
1026         }
1027         next = scheduler->next_thread(priv->nextThread);
1028
1029         /* Infeasible -> don't take any more steps */
1030         if (!isfeasible())
1031                 return false;
1032
1033         if (next)
1034                 next->set_state(THREAD_RUNNING);
1035         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1036
1037         /* next == NULL -> don't take any more steps */
1038         if (!next)
1039                 return false;
1040         /* Return false only if swap fails with an error */
1041         return (Thread::swap(&system_context, next) == 0);
1042 }
1043
1044 /** Runs the current execution until threre are no more steps to take. */
1045 void ModelChecker::finish_execution() {
1046         DBG();
1047
1048         while (take_step());
1049 }