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