model.cc

   1 #include <stdio.h>
   2 #include <algorithm>
   3
   4 #include "model.h"
   5 #include "action.h"
   6 #include "nodestack.h"
   7 #include "schedule.h"
   8 #include "snapshot-interface.h"
   9 #include "common.h"
  10 #include "clockvector.h"
  11 #include "cyclegraph.h"
  12 #include "promise.h"
  13 #include "datarace.h"
  14
  15 #define INITIAL_THREAD_ID       0
  16
  17 ModelChecker *model;
  18
  19 /** @brief Constructor */
  20 ModelChecker::ModelChecker(struct model_params params) :
  21         /* Initialize default scheduler */
  22         scheduler(new Scheduler()),
  23         num_executions(0),
  24         params(params),
  25         diverge(NULL),
  26         action_trace(new action_list_t()),
  27         thread_map(new HashTable<int, Thread *, int>()),
  28         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  29         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  30         promises(new std::vector<Promise *>()),
  31         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  32         thrd_last_action(new std::vector<ModelAction *>(1)),
  33         node_stack(new NodeStack()),
  34         mo_graph(new CycleGraph()),
  35         failed_promise(false),
  36         too_many_reads(false),
  37         asserted(false)
  38 {
  39         /* Allocate this "size" on the snapshotting heap */
  40         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  41         /* First thread created will have id INITIAL_THREAD_ID */
  42         priv->next_thread_id = INITIAL_THREAD_ID;
  43
  44         lazy_sync_size = &priv->lazy_sync_size;
  45 }
  46
  47 /** @brief Destructor */
  48 ModelChecker::~ModelChecker()
  49 {
  50         for (int i = 0; i < get_num_threads(); i++)
  51                 delete thread_map->get(i);
  52         delete thread_map;
  53
  54         delete obj_thrd_map;
  55         delete obj_map;
  56         delete action_trace;
  57
  58         for (unsigned int i = 0; i < promises->size(); i++)
  59                 delete (*promises)[i];
  60         delete promises;
  61
  62         delete lazy_sync_with_release;
  63
  64         delete thrd_last_action;
  65         delete node_stack;
  66         delete scheduler;
  67         delete mo_graph;
  68 }
  69
  70 /**
  71  * Restores user program to initial state and resets all model-checker data
  72  * structures.
  73  */
  74 void ModelChecker::reset_to_initial_state()
  75 {
  76         DEBUG("+++ Resetting to initial state +++\n");
  77         node_stack->reset_execution();
  78         failed_promise = false;
  79         too_many_reads = false;
  80         reset_asserted();
  81         snapshotObject->backTrackBeforeStep(0);
  82 }
  83
  84 /** @returns a thread ID for a new Thread */
  85 thread_id_t ModelChecker::get_next_id()
  86 {
  87         return priv->next_thread_id++;
  88 }
  89
  90 /** @returns the number of user threads created during this execution */
  91 int ModelChecker::get_num_threads()
  92 {
  93         return priv->next_thread_id;
  94 }
  95
  96 /** @returns a sequence number for a new ModelAction */
  97 modelclock_t ModelChecker::get_next_seq_num()
  98 {
  99         return ++priv->used_sequence_numbers;
 100 }
 101
 102 /**
 103  * Choose the next thread in the replay sequence.
 104  *
 105  * If the replay sequence has reached the 'diverge' point, returns a thread
 106  * from the backtracking set. Otherwise, simply returns the next thread in the
 107  * sequence that is being replayed.
 108  */
 109 Thread * ModelChecker::get_next_replay_thread()
 110 {
 111         thread_id_t tid;
 112
 113         /* Have we completed exploring the preselected path? */
 114         if (diverge == NULL)
 115                 return NULL;
 116
 117         /* Else, we are trying to replay an execution */
 118         ModelAction *next = node_stack->get_next()->get_action();
 119
 120         if (next == diverge) {
 121                 Node *nextnode = next->get_node();
 122                 /* Reached divergence point */
 123                 if (nextnode->increment_promise()) {
 124                         /* The next node will try to satisfy a different set of promises. */
 125                         tid = next->get_tid();
 126                         node_stack->pop_restofstack(2);
 127                 } else if (nextnode->increment_read_from()) {
 128                         /* The next node will read from a different value. */
 129                         tid = next->get_tid();
 130                         node_stack->pop_restofstack(2);
 131                 } else if (nextnode->increment_future_value()) {
 132                         /* The next node will try to read from a different future value. */
 133                         tid = next->get_tid();
 134                         node_stack->pop_restofstack(2);
 135                 } else {
 136                         /* Make a different thread execute for next step */
 137                         Node *node = nextnode->get_parent();
 138                         tid = node->get_next_backtrack();
 139                         node_stack->pop_restofstack(1);
 140                 }
 141                 DEBUG("*** Divergence point ***\n");
 142                 diverge = NULL;
 143         } else {
 144                 tid = next->get_tid();
 145         }
 146         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 147         ASSERT(tid != THREAD_ID_T_NONE);
 148         return thread_map->get(id_to_int(tid));
 149 }
 150
 151 /**
 152  * Queries the model-checker for more executions to explore and, if one
 153  * exists, resets the model-checker state to execute a new execution.
 154  *
 155  * @return If there are more executions to explore, return true. Otherwise,
 156  * return false.
 157  */
 158 bool ModelChecker::next_execution()
 159 {
 160         DBG();
 161
 162         num_executions++;
 163
 164         if (isfinalfeasible() || DBG_ENABLED())
 165                 print_summary();
 166
 167         if ((diverge = get_next_backtrack()) == NULL)
 168                 return false;
 169
 170         if (DBG_ENABLED()) {
 171                 printf("Next execution will diverge at:\n");
 172                 diverge->print();
 173         }
 174
 175         reset_to_initial_state();
 176         return true;
 177 }
 178
 179 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 180 {
 181         action_type type = act->get_type();
 182
 183         switch (type) {
 184                 case ATOMIC_READ:
 185                 case ATOMIC_WRITE:
 186                 case ATOMIC_RMW:
 187                         break;
 188                 default:
 189                         return NULL;
 190         }
 191         /* linear search: from most recent to oldest */
 192         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 193         action_list_t::reverse_iterator rit;
 194         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 195                 ModelAction *prev = *rit;
 196                 if (act->is_synchronizing(prev))
 197                         return prev;
 198         }
 199         return NULL;
 200 }
 201
 202 void ModelChecker::set_backtracking(ModelAction *act)
 203 {
 204         ModelAction *prev;
 205         Node *node;
 206         Thread *t = get_thread(act->get_tid());
 207
 208         prev = get_last_conflict(act);
 209         if (prev == NULL)
 210                 return;
 211
 212         node = prev->get_node()->get_parent();
 213
 214         while (!node->is_enabled(t))
 215                 t = t->get_parent();
 216
 217         /* Check if this has been explored already */
 218         if (node->has_been_explored(t->get_id()))
 219                 return;
 220
 221         /* Cache the latest backtracking point */
 222         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 223                 priv->next_backtrack = prev;
 224
 225         /* If this is a new backtracking point, mark the tree */
 226         if (!node->set_backtrack(t->get_id()))
 227                 return;
 228         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 229                         prev->get_tid(), t->get_id());
 230         if (DBG_ENABLED()) {
 231                 prev->print();
 232                 act->print();
 233         }
 234 }
 235
 236 /**
 237  * Returns last backtracking point. The model checker will explore a different
 238  * path for this point in the next execution.
 239  * @return The ModelAction at which the next execution should diverge.
 240  */
 241 ModelAction * ModelChecker::get_next_backtrack()
 242 {
 243         ModelAction *next = priv->next_backtrack;
 244         priv->next_backtrack = NULL;
 245         return next;
 246 }
 247
 248 /**
 249  * Processes a read or rmw model action.
 250  * @param curr is the read model action to process.
 251  * @param th is the thread
 252  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 253  * @return True if processing this read updates the mo_graph.
 254  */
 255
 256 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
 257         uint64_t value;
 258         bool updated=false;
 259         while(true) {
 260                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 261                 if (reads_from != NULL) {
 262                         value = reads_from->get_value();
 263                                 /* Assign reads_from, perform release/acquire synchronization */
 264                         curr->read_from(reads_from);
 265                         if (!second_part_of_rmw) {
 266                                 check_recency(curr,false);
 267                         }
 268
 269                         bool r_status=r_modification_order(curr,reads_from);
 270
 271                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||!curr->get_node()->future_value_empty())) {
 272                                 mo_graph->rollbackChanges();
 273                                 too_many_reads=false;
 274                                 continue;
 275                         }
 276
 277                         mo_graph->commitChanges();
 278                         updated |= r_status;
 279                 } else {
 280                         /* Read from future value */
 281                         value = curr->get_node()->get_future_value();
 282                         curr->read_from(NULL);
 283                         Promise *valuepromise = new Promise(curr, value);
 284                         promises->push_back(valuepromise);
 285                 }
 286                 th->set_return_value(value);
 287                 return updated;
 288         }
 289 }
 290
 291 /**
 292  * This is the heart of the model checker routine. It performs model-checking
 293  * actions corresponding to a given "current action." Among other processes, it
 294  * calculates reads-from relationships, updates synchronization clock vectors,
 295  * forms a memory_order constraints graph, and handles replay/backtrack
 296  * execution when running permutations of previously-observed executions.
 297  *
 298  * @param curr The current action to process
 299  * @return The next Thread that must be executed. May be NULL if ModelChecker
 300  * makes no choice (e.g., according to replay execution, combining RMW actions,
 301  * etc.)
 302  */
 303 Thread * ModelChecker::check_current_action(ModelAction *curr)
 304 {
 305         bool second_part_of_rmw = false;
 306
 307         ASSERT(curr);
 308
 309         if (curr->is_rmwc() || curr->is_rmw()) {
 310                 ModelAction *tmp = process_rmw(curr);
 311                 second_part_of_rmw = true;
 312                 delete curr;
 313                 curr = tmp;
 314         } else {
 315                 ModelAction *tmp = node_stack->explore_action(curr);
 316                 if (tmp) {
 317                         /* Discard duplicate ModelAction; use action from NodeStack */
 318                         /* First restore type and order in case of RMW operation */
 319                         if (curr->is_rmwr())
 320                                 tmp->copy_typeandorder(curr);
 321
 322                         /* If we have diverged, we need to reset the clock vector. */
 323                         if (diverge == NULL)
 324                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 325
 326                         delete curr;
 327                         curr = tmp;
 328                 } else {
 329                         /*
 330                          * Perform one-time actions when pushing new ModelAction onto
 331                          * NodeStack
 332                          */
 333                         curr->create_cv(get_parent_action(curr->get_tid()));
 334                         /* Build may_read_from set */
 335                         if (curr->is_read())
 336                                 build_reads_from_past(curr);
 337                         if (curr->is_write())
 338                                 compute_promises(curr);
 339                 }
 340         }
 341
 342         /* Assign 'creation' parent */
 343         if (curr->get_type() == THREAD_CREATE) {
 344                 Thread *th = (Thread *)curr->get_location();
 345                 th->set_creation(curr);
 346         } else if (curr->get_type() == THREAD_JOIN) {
 347                 Thread *wait, *join;
 348                 wait = get_thread(curr->get_tid());
 349                 join = (Thread *)curr->get_location();
 350                 if (!join->is_complete())
 351                         scheduler->wait(wait, join);
 352         } else if (curr->get_type() == THREAD_FINISH) {
 353                 Thread *th = get_thread(curr->get_tid());
 354                 while (!th->wait_list_empty()) {
 355                         Thread *wake = th->pop_wait_list();
 356                         scheduler->wake(wake);
 357                 }
 358                 th->complete();
 359         }
 360
 361         /* Deal with new thread */
 362         if (curr->get_type() == THREAD_START)
 363                 check_promises(NULL, curr->get_cv());
 364
 365         Thread *th = get_thread(curr->get_tid());
 366
 367         bool updated = false;
 368         if (curr->is_read()) {
 369                 updated=process_read(curr, th, second_part_of_rmw);
 370         }
 371
 372         if (curr->is_write()) {
 373                 bool updated_mod_order=w_modification_order(curr);
 374                 bool updated_promises=resolve_promises(curr);
 375                 updated=updated_mod_order|updated_promises;
 376
 377                 mo_graph->commitChanges();
 378                 th->set_return_value(VALUE_NONE);
 379         }
 380
 381         if (updated)
 382                 resolve_release_sequences(curr->get_location());
 383
 384         /* Add action to list.  */
 385         if (!second_part_of_rmw)
 386                 add_action_to_lists(curr);
 387
 388         Node *currnode = curr->get_node();
 389         Node *parnode = currnode->get_parent();
 390
 391         if ((!parnode->backtrack_empty() ||
 392                         !currnode->read_from_empty() ||
 393                         !currnode->future_value_empty() ||
 394                         !currnode->promise_empty())
 395                     && (!priv->next_backtrack ||
 396                         *curr > *priv->next_backtrack)) {
 397                 priv->next_backtrack = curr;
 398         }
 399
 400         set_backtracking(curr);
 401
 402         /* Do not split atomic actions. */
 403         if (curr->is_rmwr())
 404                 return thread_current();
 405         /* The THREAD_CREATE action points to the created Thread */
 406         else if (curr->get_type() == THREAD_CREATE)
 407                 return (Thread *)curr->get_location();
 408         else
 409                 return get_next_replay_thread();
 410 }
 411
 412 /** @returns whether the current partial trace must be a prefix of a
 413  * feasible trace. */
 414 bool ModelChecker::isfeasibleprefix() {
 415         return promises->size() == 0 && *lazy_sync_size == 0;
 416 }
 417
 418 /** @returns whether the current partial trace is feasible. */
 419 bool ModelChecker::isfeasible() {
 420         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads;
 421 }
 422
 423 /** Returns whether the current completed trace is feasible. */
 424 bool ModelChecker::isfinalfeasible() {
 425         return isfeasible() && promises->size() == 0;
 426 }
 427
 428 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 429 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 430         int tid = id_to_int(act->get_tid());
 431         ModelAction *lastread = get_last_action(tid);
 432         lastread->process_rmw(act);
 433         if (act->is_rmw())
 434                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 435         return lastread;
 436 }
 437
 438 /**
 439  * Checks whether a thread has read from the same write for too many times
 440  * without seeing the effects of a later write.
 441  *
 442  * Basic idea:
 443  * 1) there must a different write that we could read from that would satisfy the modification order,
 444  * 2) we must have read from the same value in excess of maxreads times, and
 445  * 3) that other write must have been in the reads_from set for maxreads times.
 446  *
 447  * If so, we decide that the execution is no longer feasible.
 448  */
 449 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 450         if (params.maxreads != 0) {
 451                 if (curr->get_node()->get_read_from_size() <= 1)
 452                         return;
 453
 454                 //Must make sure that execution is currently feasible...  We could
 455                 //accidentally clear by rolling back
 456                 if (!isfeasible())
 457                         return;
 458
 459                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 460                 int tid = id_to_int(curr->get_tid());
 461
 462                 /* Skip checks */
 463                 if ((int)thrd_lists->size() <= tid)
 464                         return;
 465
 466                 action_list_t *list = &(*thrd_lists)[tid];
 467
 468                 action_list_t::reverse_iterator rit = list->rbegin();
 469                 /* Skip past curr */
 470                 if (!already_added) {
 471                         for (; (*rit) != curr; rit++)
 472                                 ;
 473                         /* go past curr now */
 474                         rit++;
 475                 }
 476
 477                 action_list_t::reverse_iterator ritcopy=rit;
 478                 //See if we have enough reads from the same value
 479                 int count=0;
 480                 for (; count < params.maxreads; rit++,count++) {
 481                         if (rit==list->rend())
 482                                 return;
 483                         ModelAction *act = *rit;
 484                         if (!act->is_read())
 485                                 return;
 486                         if (act->get_reads_from() != curr->get_reads_from())
 487                                 return;
 488                         if (act->get_node()->get_read_from_size() <= 1)
 489                                 return;
 490                 }
 491
 492                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 493                         //Get write
 494                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 495                         //Need a different write
 496                         if (write==curr->get_reads_from())
 497                                 continue;
 498
 499                         /* Test to see whether this is a feasible write to read from*/
 500                         r_modification_order(curr, write);
 501                         bool feasiblereadfrom=isfeasible();
 502                         mo_graph->rollbackChanges();
 503
 504                         if (!feasiblereadfrom)
 505                                 continue;
 506                         rit=ritcopy;
 507
 508                         bool feasiblewrite=true;
 509                         //new we need to see if this write works for everyone
 510
 511                         for (int loop=count;loop>0;loop--,rit++) {
 512                                 ModelAction *act=*rit;
 513                                 bool foundvalue=false;
 514                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 515                                         if (act->get_node()->get_read_from_at(i)==write) {
 516                                                 foundvalue=true;
 517                                                 break;
 518                                         }
 519                                 }
 520                                 if (!foundvalue) {
 521                                         feasiblewrite=false;
 522                                         break;
 523                                 }
 524                         }
 525                         if (feasiblewrite) {
 526                                 too_many_reads = true;
 527                                 return;
 528                         }
 529                 }
 530         }
 531 }
 532
 533 /**
 534  * Updates the mo_graph with the constraints imposed from the current read.
 535  * @param curr The current action. Must be a read.
 536  * @param rf The action that curr reads from. Must be a write.
 537  * @return True if modification order edges were added; false otherwise
 538  */
 539 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 540 {
 541         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 542         unsigned int i;
 543         bool added = false;
 544         ASSERT(curr->is_read());
 545
 546         /* Iterate over all threads */
 547         for (i = 0; i < thrd_lists->size(); i++) {
 548                 /* Iterate over actions in thread, starting from most recent */
 549                 action_list_t *list = &(*thrd_lists)[i];
 550                 action_list_t::reverse_iterator rit;
 551                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 552                         ModelAction *act = *rit;
 553
 554                         /* Include at most one act per-thread that "happens before" curr */
 555                         if (act->happens_before(curr)) {
 556                                 if (act->is_read()) {
 557                                         const ModelAction *prevreadfrom = act->get_reads_from();
 558                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 559                                                 mo_graph->addEdge(prevreadfrom, rf);
 560                                                 added = true;
 561                                         }
 562                                 } else if (rf != act) {
 563                                         mo_graph->addEdge(act, rf);
 564                                         added = true;
 565                                 }
 566                                 break;
 567                         }
 568                 }
 569         }
 570
 571         return added;
 572 }
 573
 574 /** Updates the mo_graph with the constraints imposed from the current read. */
 575 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 576 {
 577         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 578         unsigned int i;
 579         ASSERT(curr->is_read());
 580
 581         /* Iterate over all threads */
 582         for (i = 0; i < thrd_lists->size(); i++) {
 583                 /* Iterate over actions in thread, starting from most recent */
 584                 action_list_t *list = &(*thrd_lists)[i];
 585                 action_list_t::reverse_iterator rit;
 586                 ModelAction *lastact = NULL;
 587
 588                 /* Find last action that happens after curr */
 589                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 590                         ModelAction *act = *rit;
 591                         if (curr->happens_before(act)) {
 592                                 lastact = act;
 593                         } else
 594                                 break;
 595                 }
 596
 597                         /* Include at most one act per-thread that "happens before" curr */
 598                 if (lastact != NULL) {
 599                         if (lastact->is_read()) {
 600                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 601                                 if (postreadfrom != NULL&&rf != postreadfrom)
 602                                         mo_graph->addEdge(rf, postreadfrom);
 603                         } else if (rf != lastact) {
 604                                 mo_graph->addEdge(rf, lastact);
 605                         }
 606                         break;
 607                 }
 608         }
 609 }
 610
 611 /**
 612  * Updates the mo_graph with the constraints imposed from the current write.
 613  * @param curr The current action. Must be a write.
 614  * @return True if modification order edges were added; false otherwise
 615  */
 616 bool ModelChecker::w_modification_order(ModelAction *curr)
 617 {
 618         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 619         unsigned int i;
 620         bool added = false;
 621         ASSERT(curr->is_write());
 622
 623         if (curr->is_seqcst()) {
 624                 /* We have to at least see the last sequentially consistent write,
 625                          so we are initialized. */
 626                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 627                 if (last_seq_cst != NULL) {
 628                         mo_graph->addEdge(last_seq_cst, curr);
 629                         added = true;
 630                 }
 631         }
 632
 633         /* Iterate over all threads */
 634         for (i = 0; i < thrd_lists->size(); i++) {
 635                 /* Iterate over actions in thread, starting from most recent */
 636                 action_list_t *list = &(*thrd_lists)[i];
 637                 action_list_t::reverse_iterator rit;
 638                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 639                         ModelAction *act = *rit;
 640
 641                         /* Include at most one act per-thread that "happens before" curr */
 642                         if (act->happens_before(curr)) {
 643                                 /*
 644                                  * Note: if act is RMW, just add edge:
 645                                  *   act --mo--> curr
 646                                  * The following edge should be handled elsewhere:
 647                                  *   readfrom(act) --mo--> act
 648                                  */
 649                                 if (act->is_write())
 650                                         mo_graph->addEdge(act, curr);
 651                                 else if (act->is_read() && act->get_reads_from() != NULL)
 652                                         mo_graph->addEdge(act->get_reads_from(), curr);
 653                                 added = true;
 654                                 break;
 655                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 656                                                      !act->same_thread(curr)) {
 657                                 /* We have an action that:
 658                                    (1) did not happen before us
 659                                    (2) is a read and we are a write
 660                                    (3) cannot synchronize with us
 661                                    (4) is in a different thread
 662                                    =>
 663                                    that read could potentially read from our write.
 664                                  */
 665                                 if (act->get_node()->add_future_value(curr->get_value()) &&
 666                                                 (!priv->next_backtrack || *act > *priv->next_backtrack))
 667                                         priv->next_backtrack = act;
 668                         }
 669                 }
 670         }
 671
 672         return added;
 673 }
 674
 675 /**
 676  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 677  * The ModelAction under consideration is expected to be taking part in
 678  * release/acquire synchronization as an object of the "reads from" relation.
 679  * Note that this can only provide release sequence support for RMW chains
 680  * which do not read from the future, as those actions cannot be traced until
 681  * their "promise" is fulfilled. Similarly, we may not even establish the
 682  * presence of a release sequence with certainty, as some modification order
 683  * constraints may be decided further in the future. Thus, this function
 684  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 685  * and a boolean representing certainty.
 686  *
 687  * @todo Finish lazy updating, when promises are fulfilled in the future
 688  * @param rf The action that might be part of a release sequence. Must be a
 689  * write.
 690  * @param release_heads A pass-by-reference style return parameter.  After
 691  * execution of this function, release_heads will contain the heads of all the
 692  * relevant release sequences, if any exists
 693  * @return true, if the ModelChecker is certain that release_heads is complete;
 694  * false otherwise
 695  */
 696 bool ModelChecker::release_seq_head(const ModelAction *rf,
 697                 std::vector<const ModelAction *> *release_heads) const
 698 {
 699         ASSERT(rf->is_write());
 700         if (!rf) {
 701                 /* read from future: need to settle this later */
 702                 return false; /* incomplete */
 703         }
 704         if (rf->is_release())
 705                 release_heads->push_back(rf);
 706         if (rf->is_rmw()) {
 707                 /* We need a RMW action that is both an acquire and release to stop */
 708                 /** @todo Need to be smarter here...  In the linux lock
 709                  * example, this will run to the beginning of the program for
 710                  * every acquire. */
 711                 if (rf->is_acquire() && rf->is_release())
 712                         return true; /* complete */
 713                 return release_seq_head(rf->get_reads_from(), release_heads);
 714         }
 715         if (rf->is_release())
 716                 return true; /* complete */
 717
 718         /* else relaxed write; check modification order for contiguous subsequence
 719          * -> rf must be same thread as release */
 720         int tid = id_to_int(rf->get_tid());
 721         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 722         action_list_t *list = &(*thrd_lists)[tid];
 723         action_list_t::const_reverse_iterator rit;
 724
 725         /* Find rf in the thread list */
 726         rit = std::find(list->rbegin(), list->rend(), rf);
 727         ASSERT(rit != list->rend());
 728
 729         /* Find the last write/release */
 730         for (; rit != list->rend(); rit++)
 731                 if ((*rit)->is_release())
 732                         break;
 733         if (rit == list->rend()) {
 734                 /* No write-release in this thread */
 735                 return true; /* complete */
 736         }
 737         ModelAction *release = *rit;
 738
 739         ASSERT(rf->same_thread(release));
 740
 741         bool certain = true;
 742         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 743                 if (id_to_int(rf->get_tid()) == (int)i)
 744                         continue;
 745                 list = &(*thrd_lists)[i];
 746
 747                 /* Can we ensure no future writes from this thread may break
 748                  * the release seq? */
 749                 bool future_ordered = false;
 750
 751                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 752                         const ModelAction *act = *rit;
 753                         if (!act->is_write())
 754                                 continue;
 755                         /* Reach synchronization -> this thread is complete */
 756                         if (act->happens_before(release))
 757                                 break;
 758                         if (rf->happens_before(act)) {
 759                                 future_ordered = true;
 760                                 continue;
 761                         }
 762
 763                         /* Check modification order */
 764                         if (mo_graph->checkReachable(rf, act)) {
 765                                 /* rf --mo--> act */
 766                                 future_ordered = true;
 767                                 continue;
 768                         }
 769                         if (mo_graph->checkReachable(act, release))
 770                                 /* act --mo--> release */
 771                                 break;
 772                         if (mo_graph->checkReachable(release, act) &&
 773                                       mo_graph->checkReachable(act, rf)) {
 774                                 /* release --mo-> act --mo--> rf */
 775                                 return true; /* complete */
 776                         }
 777                         certain = false;
 778                 }
 779                 if (!future_ordered)
 780                         return false; /* This thread is uncertain */
 781         }
 782
 783         if (certain)
 784                 release_heads->push_back(release);
 785         return certain;
 786 }
 787
 788 /**
 789  * A public interface for getting the release sequence head(s) with which a
 790  * given ModelAction must synchronize. This function only returns a non-empty
 791  * result when it can locate a release sequence head with certainty. Otherwise,
 792  * it may mark the internal state of the ModelChecker so that it will handle
 793  * the release sequence at a later time, causing @a act to update its
 794  * synchronization at some later point in execution.
 795  * @param act The 'acquire' action that may read from a release sequence
 796  * @param release_heads A pass-by-reference return parameter. Will be filled
 797  * with the head(s) of the release sequence(s), if they exists with certainty.
 798  * @see ModelChecker::release_seq_head
 799  */
 800 void ModelChecker::get_release_seq_heads(ModelAction *act,
 801                 std::vector<const ModelAction *> *release_heads)
 802 {
 803         const ModelAction *rf = act->get_reads_from();
 804         bool complete;
 805         complete = release_seq_head(rf, release_heads);
 806         if (!complete) {
 807                 /* add act to 'lazy checking' list */
 808                 std::list<ModelAction *> *list;
 809                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 810                 list->push_back(act);
 811                 (*lazy_sync_size)++;
 812         }
 813 }
 814
 815 /**
 816  * Attempt to resolve all stashed operations that might synchronize with a
 817  * release sequence for a given location. This implements the "lazy" portion of
 818  * determining whether or not a release sequence was contiguous, since not all
 819  * modification order information is present at the time an action occurs.
 820  *
 821  * @param location The location/object that should be checked for release
 822  * sequence resolutions
 823  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 824  */
 825 bool ModelChecker::resolve_release_sequences(void *location)
 826 {
 827         std::list<ModelAction *> *list;
 828         list = lazy_sync_with_release->getptr(location);
 829         if (!list)
 830                 return false;
 831
 832         bool updated = false;
 833         std::list<ModelAction *>::iterator it = list->begin();
 834         while (it != list->end()) {
 835                 ModelAction *act = *it;
 836                 const ModelAction *rf = act->get_reads_from();
 837                 std::vector<const ModelAction *> release_heads;
 838                 bool complete;
 839                 complete = release_seq_head(rf, &release_heads);
 840                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 841                         if (!act->has_synchronized_with(release_heads[i])) {
 842                                 updated = true;
 843                                 act->synchronize_with(release_heads[i]);
 844                         }
 845                 }
 846
 847                 if (updated) {
 848                         /* propagate synchronization to later actions */
 849                         action_list_t::reverse_iterator it = action_trace->rbegin();
 850                         while ((*it) != act) {
 851                                 ModelAction *propagate = *it;
 852                                 if (act->happens_before(propagate))
 853                                         /** @todo new mo_graph edges along with
 854                                          * this synchronization? */
 855                                         propagate->synchronize_with(act);
 856                         }
 857                 }
 858                 if (complete) {
 859                         it = list->erase(it);
 860                         (*lazy_sync_size)--;
 861                 } else
 862                         it++;
 863         }
 864
 865         // If we resolved promises or data races, see if we have realized a data race.
 866         if (checkDataRaces()) {
 867                 set_assert();
 868         }
 869
 870         return updated;
 871 }
 872
 873 /**
 874  * Performs various bookkeeping operations for the current ModelAction. For
 875  * instance, adds action to the per-object, per-thread action vector and to the
 876  * action trace list of all thread actions.
 877  *
 878  * @param act is the ModelAction to add.
 879  */
 880 void ModelChecker::add_action_to_lists(ModelAction *act)
 881 {
 882         int tid = id_to_int(act->get_tid());
 883         action_trace->push_back(act);
 884
 885         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 886
 887         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 888         if (tid >= (int)vec->size())
 889                 vec->resize(priv->next_thread_id);
 890         (*vec)[tid].push_back(act);
 891
 892         if ((int)thrd_last_action->size() <= tid)
 893                 thrd_last_action->resize(get_num_threads());
 894         (*thrd_last_action)[tid] = act;
 895 }
 896
 897 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 898 {
 899         int nthreads = get_num_threads();
 900         if ((int)thrd_last_action->size() < nthreads)
 901                 thrd_last_action->resize(nthreads);
 902         return (*thrd_last_action)[id_to_int(tid)];
 903 }
 904
 905 /**
 906  * Gets the last memory_order_seq_cst action (in the total global sequence)
 907  * performed on a particular object (i.e., memory location).
 908  * @param location The object location to check
 909  * @return The last seq_cst action performed
 910  */
 911 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 912 {
 913         action_list_t *list = obj_map->get_safe_ptr(location);
 914         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 915         action_list_t::reverse_iterator rit;
 916         for (rit = list->rbegin(); rit != list->rend(); rit++)
 917                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 918                         return *rit;
 919         return NULL;
 920 }
 921
 922 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 923 {
 924         ModelAction *parent = get_last_action(tid);
 925         if (!parent)
 926                 parent = get_thread(tid)->get_creation();
 927         return parent;
 928 }
 929
 930 /**
 931  * Returns the clock vector for a given thread.
 932  * @param tid The thread whose clock vector we want
 933  * @return Desired clock vector
 934  */
 935 ClockVector * ModelChecker::get_cv(thread_id_t tid)
 936 {
 937         return get_parent_action(tid)->get_cv();
 938 }
 939
 940 /**
 941  * Resolve a set of Promises with a current write. The set is provided in the
 942  * Node corresponding to @a write.
 943  * @param write The ModelAction that is fulfilling Promises
 944  * @return True if promises were resolved; false otherwise
 945  */
 946 bool ModelChecker::resolve_promises(ModelAction *write)
 947 {
 948         bool resolved = false;
 949         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
 950                 Promise *promise = (*promises)[promise_index];
 951                 if (write->get_node()->get_promise(i)) {
 952                         ModelAction *read = promise->get_action();
 953                         read->read_from(write);
 954                         r_modification_order(read, write);
 955                         post_r_modification_order(read, write);
 956                         promises->erase(promises->begin() + promise_index);
 957                         resolved = true;
 958                 } else
 959                         promise_index++;
 960         }
 961
 962         return resolved;
 963 }
 964
 965 /**
 966  * Compute the set of promises that could potentially be satisfied by this
 967  * action. Note that the set computation actually appears in the Node, not in
 968  * ModelChecker.
 969  * @param curr The ModelAction that may satisfy promises
 970  */
 971 void ModelChecker::compute_promises(ModelAction *curr)
 972 {
 973         for (unsigned int i = 0; i < promises->size(); i++) {
 974                 Promise *promise = (*promises)[i];
 975                 const ModelAction *act = promise->get_action();
 976                 if (!act->happens_before(curr) &&
 977                                 act->is_read() &&
 978                                 !act->is_synchronizing(curr) &&
 979                                 !act->same_thread(curr) &&
 980                                 promise->get_value() == curr->get_value()) {
 981                         curr->get_node()->set_promise(i);
 982                 }
 983         }
 984 }
 985
 986 /** Checks promises in response to change in ClockVector Threads. */
 987 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
 988 {
 989         for (unsigned int i = 0; i < promises->size(); i++) {
 990                 Promise *promise = (*promises)[i];
 991                 const ModelAction *act = promise->get_action();
 992                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
 993                                 merge_cv->synchronized_since(act)) {
 994                         //This thread is no longer able to send values back to satisfy the promise
 995                         int num_synchronized_threads = promise->increment_threads();
 996                         if (num_synchronized_threads == get_num_threads()) {
 997                                 //Promise has failed
 998                                 failed_promise = true;
 999                                 return;
1000                         }
1001                 }
1002         }
1003 }
1004
1005 /**
1006  * Build up an initial set of all past writes that this 'read' action may read
1007  * from. This set is determined by the clock vector's "happens before"
1008  * relationship.
1009  * @param curr is the current ModelAction that we are exploring; it must be a
1010  * 'read' operation.
1011  */
1012 void ModelChecker::build_reads_from_past(ModelAction *curr)
1013 {
1014         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1015         unsigned int i;
1016         ASSERT(curr->is_read());
1017
1018         ModelAction *last_seq_cst = NULL;
1019
1020         /* Track whether this object has been initialized */
1021         bool initialized = false;
1022
1023         if (curr->is_seqcst()) {
1024                 last_seq_cst = get_last_seq_cst(curr->get_location());
1025                 /* We have to at least see the last sequentially consistent write,
1026                          so we are initialized. */
1027                 if (last_seq_cst != NULL)
1028                         initialized = true;
1029         }
1030
1031         /* Iterate over all threads */
1032         for (i = 0; i < thrd_lists->size(); i++) {
1033                 /* Iterate over actions in thread, starting from most recent */
1034                 action_list_t *list = &(*thrd_lists)[i];
1035                 action_list_t::reverse_iterator rit;
1036                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1037                         ModelAction *act = *rit;
1038
1039                         /* Only consider 'write' actions */
1040                         if (!act->is_write())
1041                                 continue;
1042
1043                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1044                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
1045                                 DEBUG("Adding action to may_read_from:\n");
1046                                 if (DBG_ENABLED()) {
1047                                         act->print();
1048                                         curr->print();
1049                                 }
1050                                 curr->get_node()->add_read_from(act);
1051                         }
1052
1053                         /* Include at most one act per-thread that "happens before" curr */
1054                         if (act->happens_before(curr)) {
1055                                 initialized = true;
1056                                 break;
1057                         }
1058                 }
1059         }
1060
1061         if (!initialized) {
1062                 /** @todo Need a more informative way of reporting errors. */
1063                 printf("ERROR: may read from uninitialized atomic\n");
1064         }
1065
1066         if (DBG_ENABLED() || !initialized) {
1067                 printf("Reached read action:\n");
1068                 curr->print();
1069                 printf("Printing may_read_from\n");
1070                 curr->get_node()->print_may_read_from();
1071                 printf("End printing may_read_from\n");
1072         }
1073
1074         ASSERT(initialized);
1075 }
1076
1077 static void print_list(action_list_t *list)
1078 {
1079         action_list_t::iterator it;
1080
1081         printf("---------------------------------------------------------------------\n");
1082         printf("Trace:\n");
1083
1084         for (it = list->begin(); it != list->end(); it++) {
1085                 (*it)->print();
1086         }
1087         printf("---------------------------------------------------------------------\n");
1088 }
1089
1090 void ModelChecker::print_summary()
1091 {
1092         printf("\n");
1093         printf("Number of executions: %d\n", num_executions);
1094         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1095
1096         scheduler->print();
1097
1098         if (!isfinalfeasible())
1099                 printf("INFEASIBLE EXECUTION!\n");
1100         print_list(action_trace);
1101         printf("\n");
1102 }
1103
1104 /**
1105  * Add a Thread to the system for the first time. Should only be called once
1106  * per thread.
1107  * @param t The Thread to add
1108  */
1109 void ModelChecker::add_thread(Thread *t)
1110 {
1111         thread_map->put(id_to_int(t->get_id()), t);
1112         scheduler->add_thread(t);
1113 }
1114
1115 void ModelChecker::remove_thread(Thread *t)
1116 {
1117         scheduler->remove_thread(t);
1118 }
1119
1120 /**
1121  * Switch from a user-context to the "master thread" context (a.k.a. system
1122  * context). This switch is made with the intention of exploring a particular
1123  * model-checking action (described by a ModelAction object). Must be called
1124  * from a user-thread context.
1125  * @param act The current action that will be explored. Must not be NULL.
1126  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1127  */
1128 int ModelChecker::switch_to_master(ModelAction *act)
1129 {
1130         DBG();
1131         Thread *old = thread_current();
1132         set_current_action(act);
1133         old->set_state(THREAD_READY);
1134         return Thread::swap(old, &system_context);
1135 }
1136
1137 /**
1138  * Takes the next step in the execution, if possible.
1139  * @return Returns true (success) if a step was taken and false otherwise.
1140  */
1141 bool ModelChecker::take_step() {
1142         Thread *curr, *next;
1143
1144         if (has_asserted())
1145                 return false;
1146
1147         curr = thread_current();
1148         if (curr) {
1149                 if (curr->get_state() == THREAD_READY) {
1150                         ASSERT(priv->current_action);
1151                         priv->nextThread = check_current_action(priv->current_action);
1152                         priv->current_action = NULL;
1153                         if (!curr->is_blocked() && !curr->is_complete())
1154                                 scheduler->add_thread(curr);
1155                 } else {
1156                         ASSERT(false);
1157                 }
1158         }
1159         next = scheduler->next_thread(priv->nextThread);
1160
1161         /* Infeasible -> don't take any more steps */
1162         if (!isfeasible())
1163                 return false;
1164
1165         if (next)
1166                 next->set_state(THREAD_RUNNING);
1167         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1168
1169         /* next == NULL -> don't take any more steps */
1170         if (!next)
1171                 return false;
1172         /* Return false only if swap fails with an error */
1173         return (Thread::swap(&system_context, next) == 0);
1174 }
1175
1176 /** Runs the current execution until threre are no more steps to take. */
1177 void ModelChecker::finish_execution() {
1178         DBG();
1179
1180         while (take_step());
1181 }