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         futurevalues(new std::vector<struct PendingFutureValue>()),
  32         lazy_sync_with_release(new HashTable<void *, std::list<ModelAction *>, uintptr_t, 4>()),
  33         thrd_last_action(new std::vector<ModelAction *>(1)),
  34         node_stack(new NodeStack()),
  35         mo_graph(new CycleGraph()),
  36         failed_promise(false),
  37         too_many_reads(false),
  38         asserted(false)
  39 {
  40         /* Allocate this "size" on the snapshotting heap */
  41         priv = (struct model_snapshot_members *)calloc(1, sizeof(*priv));
  42         /* First thread created will have id INITIAL_THREAD_ID */
  43         priv->next_thread_id = INITIAL_THREAD_ID;
  44
  45         lazy_sync_size = &priv->lazy_sync_size;
  46 }
  47
  48 /** @brief Destructor */
  49 ModelChecker::~ModelChecker()
  50 {
  51         for (int i = 0; i < get_num_threads(); i++)
  52                 delete thread_map->get(i);
  53         delete thread_map;
  54
  55         delete obj_thrd_map;
  56         delete obj_map;
  57         delete action_trace;
  58
  59         for (unsigned int i = 0; i < promises->size(); i++)
  60                 delete (*promises)[i];
  61         delete promises;
  62
  63         delete lazy_sync_with_release;
  64
  65         delete thrd_last_action;
  66         delete node_stack;
  67         delete scheduler;
  68         delete mo_graph;
  69 }
  70
  71 /**
  72  * Restores user program to initial state and resets all model-checker data
  73  * structures.
  74  */
  75 void ModelChecker::reset_to_initial_state()
  76 {
  77         DEBUG("+++ Resetting to initial state +++\n");
  78         node_stack->reset_execution();
  79         failed_promise = false;
  80         too_many_reads = false;
  81         reset_asserted();
  82         snapshotObject->backTrackBeforeStep(0);
  83 }
  84
  85 /** @returns a thread ID for a new Thread */
  86 thread_id_t ModelChecker::get_next_id()
  87 {
  88         return priv->next_thread_id++;
  89 }
  90
  91 /** @returns the number of user threads created during this execution */
  92 int ModelChecker::get_num_threads()
  93 {
  94         return priv->next_thread_id;
  95 }
  96
  97 /** @returns a sequence number for a new ModelAction */
  98 modelclock_t ModelChecker::get_next_seq_num()
  99 {
 100         return ++priv->used_sequence_numbers;
 101 }
 102
 103 /**
 104  * @brief Choose the next thread to execute.
 105  *
 106  * This function chooses the next thread that should execute. It can force the
 107  * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
 108  * followed by a THREAD_START, or it can enforce execution replay/backtracking.
 109  * The model-checker may have no preference regarding the next thread (i.e.,
 110  * when exploring a new execution ordering), in which case this will return
 111  * NULL.
 112  * @param curr The current ModelAction. This action might guide the choice of
 113  * next thread.
 114  * @return The next thread to run. If the model-checker has no preference, NULL.
 115  */
 116 Thread * ModelChecker::get_next_thread(ModelAction *curr)
 117 {
 118         thread_id_t tid;
 119
 120         /* Do not split atomic actions. */
 121         if (curr->is_rmwr())
 122                 return thread_current();
 123         /* The THREAD_CREATE action points to the created Thread */
 124         else if (curr->get_type() == THREAD_CREATE)
 125                 return (Thread *)curr->get_location();
 126
 127         /* Have we completed exploring the preselected path? */
 128         if (diverge == NULL)
 129                 return NULL;
 130
 131         /* Else, we are trying to replay an execution */
 132         ModelAction *next = node_stack->get_next()->get_action();
 133
 134         if (next == diverge) {
 135                 Node *nextnode = next->get_node();
 136                 /* Reached divergence point */
 137                 if (nextnode->increment_promise()) {
 138                         /* The next node will try to satisfy a different set of promises. */
 139                         tid = next->get_tid();
 140                         node_stack->pop_restofstack(2);
 141                 } else if (nextnode->increment_read_from()) {
 142                         /* The next node will read from a different value. */
 143                         tid = next->get_tid();
 144                         node_stack->pop_restofstack(2);
 145                 } else if (nextnode->increment_future_value()) {
 146                         /* The next node will try to read from a different future value. */
 147                         tid = next->get_tid();
 148                         node_stack->pop_restofstack(2);
 149                 } else {
 150                         /* Make a different thread execute for next step */
 151                         Node *node = nextnode->get_parent();
 152                         tid = node->get_next_backtrack();
 153                         node_stack->pop_restofstack(1);
 154                 }
 155                 DEBUG("*** Divergence point ***\n");
 156                 diverge = NULL;
 157         } else {
 158                 tid = next->get_tid();
 159         }
 160         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 161         ASSERT(tid != THREAD_ID_T_NONE);
 162         return thread_map->get(id_to_int(tid));
 163 }
 164
 165 /**
 166  * Queries the model-checker for more executions to explore and, if one
 167  * exists, resets the model-checker state to execute a new execution.
 168  *
 169  * @return If there are more executions to explore, return true. Otherwise,
 170  * return false.
 171  */
 172 bool ModelChecker::next_execution()
 173 {
 174         DBG();
 175
 176         num_executions++;
 177
 178         if (isfinalfeasible() || DBG_ENABLED())
 179                 print_summary();
 180
 181         if ((diverge = get_next_backtrack()) == NULL)
 182                 return false;
 183
 184         if (DBG_ENABLED()) {
 185                 printf("Next execution will diverge at:\n");
 186                 diverge->print();
 187         }
 188
 189         reset_to_initial_state();
 190         return true;
 191 }
 192
 193 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 194 {
 195         action_type type = act->get_type();
 196
 197         switch (type) {
 198                 case ATOMIC_READ:
 199                 case ATOMIC_WRITE:
 200                 case ATOMIC_RMW:
 201                         break;
 202                 default:
 203                         return NULL;
 204         }
 205         /* linear search: from most recent to oldest */
 206         action_list_t *list = obj_map->get_safe_ptr(act->get_location());
 207         action_list_t::reverse_iterator rit;
 208         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 209                 ModelAction *prev = *rit;
 210                 if (act->is_synchronizing(prev))
 211                         return prev;
 212         }
 213         return NULL;
 214 }
 215
 216 void ModelChecker::set_backtracking(ModelAction *act)
 217 {
 218         ModelAction *prev;
 219         Node *node;
 220         Thread *t = get_thread(act);
 221
 222         prev = get_last_conflict(act);
 223         if (prev == NULL)
 224                 return;
 225
 226         node = prev->get_node()->get_parent();
 227
 228         while (!node->is_enabled(t))
 229                 t = t->get_parent();
 230
 231         /* Check if this has been explored already */
 232         if (node->has_been_explored(t->get_id()))
 233                 return;
 234
 235         /* Cache the latest backtracking point */
 236         if (!priv->next_backtrack || *prev > *priv->next_backtrack)
 237                 priv->next_backtrack = prev;
 238
 239         /* If this is a new backtracking point, mark the tree */
 240         if (!node->set_backtrack(t->get_id()))
 241                 return;
 242         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 243                         prev->get_tid(), t->get_id());
 244         if (DBG_ENABLED()) {
 245                 prev->print();
 246                 act->print();
 247         }
 248 }
 249
 250 /**
 251  * Returns last backtracking point. The model checker will explore a different
 252  * path for this point in the next execution.
 253  * @return The ModelAction at which the next execution should diverge.
 254  */
 255 ModelAction * ModelChecker::get_next_backtrack()
 256 {
 257         ModelAction *next = priv->next_backtrack;
 258         priv->next_backtrack = NULL;
 259         return next;
 260 }
 261
 262 /**
 263  * Processes a read or rmw model action.
 264  * @param curr is the read model action to process.
 265  * @param th is the thread
 266  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 267  * @return True if processing this read updates the mo_graph.
 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                         mo_graph->startChanges();
 276
 277                         value = reads_from->get_value();
 278                         bool r_status = false;
 279
 280                         if (!second_part_of_rmw) {
 281                                 check_recency(curr,false);
 282                                 r_status = r_modification_order(curr, reads_from);
 283                         }
 284
 285
 286                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 287                                 mo_graph->rollbackChanges();
 288                                 too_many_reads = false;
 289                                 continue;
 290                         }
 291
 292                         curr->read_from(reads_from);
 293                         mo_graph->commitChanges();
 294                         updated |= r_status;
 295                 } else if (!second_part_of_rmw) {
 296                         /* Read from future value */
 297                         value = curr->get_node()->get_future_value();
 298                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 299                         curr->read_from(NULL);
 300                         Promise *valuepromise = new Promise(curr, value, expiration);
 301                         promises->push_back(valuepromise);
 302                 }
 303                 th->set_return_value(value);
 304                 return updated;
 305         }
 306 }
 307
 308 /**
 309  * This is the heart of the model checker routine. It performs model-checking
 310  * actions corresponding to a given "current action." Among other processes, it
 311  * calculates reads-from relationships, updates synchronization clock vectors,
 312  * forms a memory_order constraints graph, and handles replay/backtrack
 313  * execution when running permutations of previously-observed executions.
 314  *
 315  * @param curr The current action to process
 316  * @return The next Thread that must be executed. May be NULL if ModelChecker
 317  * makes no choice (e.g., according to replay execution, combining RMW actions,
 318  * etc.)
 319  */
 320 Thread * ModelChecker::check_current_action(ModelAction *curr)
 321 {
 322         bool second_part_of_rmw = false;
 323
 324         ASSERT(curr);
 325
 326         if (curr->is_rmwc() || curr->is_rmw()) {
 327                 ModelAction *tmp = process_rmw(curr);
 328                 second_part_of_rmw = true;
 329                 delete curr;
 330                 curr = tmp;
 331                 compute_promises(curr);
 332         } else {
 333                 ModelAction *tmp = node_stack->explore_action(curr);
 334                 if (tmp) {
 335                         /* Discard duplicate ModelAction; use action from NodeStack */
 336                         /* First restore type and order in case of RMW operation */
 337                         if (curr->is_rmwr())
 338                                 tmp->copy_typeandorder(curr);
 339
 340                         /* If we have diverged, we need to reset the clock vector. */
 341                         if (diverge == NULL)
 342                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 343
 344                         delete curr;
 345                         curr = tmp;
 346                 } else {
 347                         /*
 348                          * Perform one-time actions when pushing new ModelAction onto
 349                          * NodeStack
 350                          */
 351                         curr->create_cv(get_parent_action(curr->get_tid()));
 352                         /* Build may_read_from set */
 353                         if (curr->is_read())
 354                                 build_reads_from_past(curr);
 355                         if (curr->is_write())
 356                                 compute_promises(curr);
 357                 }
 358         }
 359
 360         /* Thread specific actions */
 361         switch (curr->get_type()) {
 362         case THREAD_CREATE: {
 363                 Thread *th = (Thread *)curr->get_location();
 364                 th->set_creation(curr);
 365                 break;
 366         }
 367         case THREAD_JOIN: {
 368                 Thread *waiting, *blocking;
 369                 waiting = get_thread(curr);
 370                 blocking = (Thread *)curr->get_location();
 371                 if (!blocking->is_complete()) {
 372                         blocking->push_wait_list(curr);
 373                         scheduler->sleep(waiting);
 374                 }
 375                 break;
 376         }
 377         case THREAD_FINISH: {
 378                 Thread *th = get_thread(curr);
 379                 while (!th->wait_list_empty()) {
 380                         ModelAction *act = th->pop_wait_list();
 381                         Thread *wake = get_thread(act);
 382                         scheduler->wake(wake);
 383                 }
 384                 th->complete();
 385                 break;
 386         }
 387         case THREAD_START: {
 388                 check_promises(NULL, curr->get_cv());
 389                 break;
 390         }
 391         default:
 392                 break;
 393         }
 394
 395         bool updated = false;
 396
 397         if (curr->is_read()) {
 398                 updated = process_read(curr, get_thread(curr), second_part_of_rmw);
 399         }
 400
 401         if (curr->is_write()) {
 402                 bool updated_mod_order = w_modification_order(curr);
 403                 bool updated_promises = resolve_promises(curr);
 404                 updated = updated || updated_mod_order || updated_promises;
 405
 406                 if (promises->size()==0) {
 407                         for (unsigned int i = 0; i<futurevalues->size(); i++) {
 408                                 struct PendingFutureValue pfv=(*futurevalues)[i];
 409                                 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 410                                                 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 411                                         priv->next_backtrack = pfv.act;
 412                         }
 413                         futurevalues->resize(0);
 414                 }
 415
 416                 mo_graph->commitChanges();
 417                 get_thread(curr)->set_return_value(VALUE_NONE);
 418         }
 419
 420         if (updated)
 421                 resolve_release_sequences(curr->get_location());
 422
 423         /* Add action to list.  */
 424         if (!second_part_of_rmw)
 425                 add_action_to_lists(curr);
 426
 427         check_curr_backtracking(curr);
 428
 429         set_backtracking(curr);
 430
 431         return get_next_thread(curr);
 432 }
 433
 434 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 435         Node *currnode = curr->get_node();
 436         Node *parnode = currnode->get_parent();
 437
 438         if ((!parnode->backtrack_empty() ||
 439                          !currnode->read_from_empty() ||
 440                          !currnode->future_value_empty() ||
 441                          !currnode->promise_empty())
 442                         && (!priv->next_backtrack ||
 443                                         *curr > *priv->next_backtrack)) {
 444                 priv->next_backtrack = curr;
 445         }
 446 }
 447
 448 bool ModelChecker::promises_expired() {
 449         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 450                 Promise *promise = (*promises)[promise_index];
 451                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 452                         return true;
 453                 }
 454         }
 455         return false;
 456 }
 457
 458 /** @returns whether the current partial trace must be a prefix of a
 459  * feasible trace. */
 460 bool ModelChecker::isfeasibleprefix() {
 461         return promises->size() == 0 && *lazy_sync_size == 0;
 462 }
 463
 464 /** @returns whether the current partial trace is feasible. */
 465 bool ModelChecker::isfeasible() {
 466         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 467 }
 468
 469 /** @returns whether the current partial trace is feasible other than
 470  * multiple RMW reading from the same store. */
 471 bool ModelChecker::isfeasibleotherthanRMW() {
 472         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 473 }
 474
 475 /** Returns whether the current completed trace is feasible. */
 476 bool ModelChecker::isfinalfeasible() {
 477         return isfeasible() && promises->size() == 0;
 478 }
 479
 480 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 481 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 482         int tid = id_to_int(act->get_tid());
 483         ModelAction *lastread = get_last_action(tid);
 484         lastread->process_rmw(act);
 485         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 486                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 487                 mo_graph->commitChanges();
 488         }
 489         return lastread;
 490 }
 491
 492 /**
 493  * Checks whether a thread has read from the same write for too many times
 494  * without seeing the effects of a later write.
 495  *
 496  * Basic idea:
 497  * 1) there must a different write that we could read from that would satisfy the modification order,
 498  * 2) we must have read from the same value in excess of maxreads times, and
 499  * 3) that other write must have been in the reads_from set for maxreads times.
 500  *
 501  * If so, we decide that the execution is no longer feasible.
 502  */
 503 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 504         if (params.maxreads != 0) {
 505                 if (curr->get_node()->get_read_from_size() <= 1)
 506                         return;
 507
 508                 //Must make sure that execution is currently feasible...  We could
 509                 //accidentally clear by rolling back
 510                 if (!isfeasible())
 511                         return;
 512
 513                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 514                 int tid = id_to_int(curr->get_tid());
 515
 516                 /* Skip checks */
 517                 if ((int)thrd_lists->size() <= tid)
 518                         return;
 519
 520                 action_list_t *list = &(*thrd_lists)[tid];
 521
 522                 action_list_t::reverse_iterator rit = list->rbegin();
 523                 /* Skip past curr */
 524                 if (already_added) {
 525                         for (; (*rit) != curr; rit++)
 526                                 ;
 527                         /* go past curr now */
 528                         rit++;
 529                 }
 530
 531                 action_list_t::reverse_iterator ritcopy = rit;
 532                 //See if we have enough reads from the same value
 533                 int count = 0;
 534                 for (; count < params.maxreads; rit++,count++) {
 535                         if (rit==list->rend())
 536                                 return;
 537                         ModelAction *act = *rit;
 538                         if (!act->is_read())
 539                                 return;
 540                         if (act->get_reads_from() != curr->get_reads_from())
 541                                 return;
 542                         if (act->get_node()->get_read_from_size() <= 1)
 543                                 return;
 544                 }
 545
 546                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 547                         //Get write
 548                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 549                         //Need a different write
 550                         if (write==curr->get_reads_from())
 551                                 continue;
 552
 553                         /* Test to see whether this is a feasible write to read from*/
 554                         mo_graph->startChanges();
 555                         r_modification_order(curr, write);
 556                         bool feasiblereadfrom = isfeasible();
 557                         mo_graph->rollbackChanges();
 558
 559                         if (!feasiblereadfrom)
 560                                 continue;
 561                         rit = ritcopy;
 562
 563                         bool feasiblewrite = true;
 564                         //new we need to see if this write works for everyone
 565
 566                         for (int loop = count; loop>0; loop--,rit++) {
 567                                 ModelAction *act=*rit;
 568                                 bool foundvalue = false;
 569                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 570                                         if (act->get_node()->get_read_from_at(i)==write) {
 571                                                 foundvalue = true;
 572                                                 break;
 573                                         }
 574                                 }
 575                                 if (!foundvalue) {
 576                                         feasiblewrite = false;
 577                                         break;
 578                                 }
 579                         }
 580                         if (feasiblewrite) {
 581                                 too_many_reads = true;
 582                                 return;
 583                         }
 584                 }
 585         }
 586 }
 587
 588 /**
 589  * Updates the mo_graph with the constraints imposed from the current
 590  * read.
 591  *
 592  * Basic idea is the following: Go through each other thread and find
 593  * the lastest action that happened before our read.  Two cases:
 594  *
 595  * (1) The action is a write => that write must either occur before
 596  * the write we read from or be the write we read from.
 597  *
 598  * (2) The action is a read => the write that that action read from
 599  * must occur before the write we read from or be the same write.
 600  *
 601  * @param curr The current action. Must be a read.
 602  * @param rf The action that curr reads from. Must be a write.
 603  * @return True if modification order edges were added; false otherwise
 604  */
 605 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 606 {
 607         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 608         unsigned int i;
 609         bool added = false;
 610         ASSERT(curr->is_read());
 611
 612         /* Iterate over all threads */
 613         for (i = 0; i < thrd_lists->size(); i++) {
 614                 /* Iterate over actions in thread, starting from most recent */
 615                 action_list_t *list = &(*thrd_lists)[i];
 616                 action_list_t::reverse_iterator rit;
 617                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 618                         ModelAction *act = *rit;
 619
 620                         /* Include at most one act per-thread that "happens before" curr */
 621                         if (act->happens_before(curr)) {
 622                                 if (act->is_write()) {
 623                                         if (rf != act && act != curr) {
 624                                                 mo_graph->addEdge(act, rf);
 625                                                 added = true;
 626                                         }
 627                                 } else {
 628                                         const ModelAction *prevreadfrom = act->get_reads_from();
 629                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 630                                                 mo_graph->addEdge(prevreadfrom, rf);
 631                                                 added = true;
 632                                         }
 633                                 }
 634
 635                                 break;
 636                         }
 637                 }
 638         }
 639
 640         return added;
 641 }
 642
 643 /** This method fixes up the modification order when we resolve a
 644  *  promises.  The basic problem is that actions that occur after the
 645  *  read curr could not property add items to the modification order
 646  *  for our read.
 647  *
 648  *  So for each thread, we find the earliest item that happens after
 649  *  the read curr.  This is the item we have to fix up with additional
 650  *  constraints.  If that action is write, we add a MO edge between
 651  *  the Action rf and that action.  If the action is a read, we add a
 652  *  MO edge between the Action rf, and whatever the read accessed.
 653  *
 654  * @param curr is the read ModelAction that we are fixing up MO edges for.
 655  * @param rf is the write ModelAction that curr reads from.
 656  *
 657  */
 658
 659 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 660 {
 661         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 662         unsigned int i;
 663         ASSERT(curr->is_read());
 664
 665         /* Iterate over all threads */
 666         for (i = 0; i < thrd_lists->size(); i++) {
 667                 /* Iterate over actions in thread, starting from most recent */
 668                 action_list_t *list = &(*thrd_lists)[i];
 669                 action_list_t::reverse_iterator rit;
 670                 ModelAction *lastact = NULL;
 671
 672                 /* Find last action that happens after curr */
 673                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 674                         ModelAction *act = *rit;
 675                         if (curr->happens_before(act)) {
 676                                 lastact = act;
 677                         } else
 678                                 break;
 679                 }
 680
 681                         /* Include at most one act per-thread that "happens before" curr */
 682                 if (lastact != NULL) {
 683                         if (lastact->is_read()) {
 684                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 685                                 if (postreadfrom != NULL&&rf != postreadfrom)
 686                                         mo_graph->addEdge(rf, postreadfrom);
 687                         } else if (rf != lastact) {
 688                                 mo_graph->addEdge(rf, lastact);
 689                         }
 690                         break;
 691                 }
 692         }
 693 }
 694
 695 /**
 696  * Updates the mo_graph with the constraints imposed from the current write.
 697  *
 698  * Basic idea is the following: Go through each other thread and find
 699  * the lastest action that happened before our write.  Two cases:
 700  *
 701  * (1) The action is a write => that write must occur before
 702  * the current write
 703  *
 704  * (2) The action is a read => the write that that action read from
 705  * must occur before the current write.
 706  *
 707  * This method also handles two other issues:
 708  *
 709  * (I) Sequential Consistency: Making sure that if the current write is
 710  * seq_cst, that it occurs after the previous seq_cst write.
 711  *
 712  * (II) Sending the write back to non-synchronizing reads.
 713  *
 714  * @param curr The current action. Must be a write.
 715  * @return True if modification order edges were added; false otherwise
 716  */
 717 bool ModelChecker::w_modification_order(ModelAction *curr)
 718 {
 719         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 720         unsigned int i;
 721         bool added = false;
 722         ASSERT(curr->is_write());
 723
 724         if (curr->is_seqcst()) {
 725                 /* We have to at least see the last sequentially consistent write,
 726                          so we are initialized. */
 727                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 728                 if (last_seq_cst != NULL) {
 729                         mo_graph->addEdge(last_seq_cst, curr);
 730                         added = true;
 731                 }
 732         }
 733
 734         /* Iterate over all threads */
 735         for (i = 0; i < thrd_lists->size(); i++) {
 736                 /* Iterate over actions in thread, starting from most recent */
 737                 action_list_t *list = &(*thrd_lists)[i];
 738                 action_list_t::reverse_iterator rit;
 739                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 740                         ModelAction *act = *rit;
 741
 742                         /* Include at most one act per-thread that "happens before" curr */
 743                         if (act->happens_before(curr)) {
 744                                 /*
 745                                  * Note: if act is RMW, just add edge:
 746                                  *   act --mo--> curr
 747                                  * The following edge should be handled elsewhere:
 748                                  *   readfrom(act) --mo--> act
 749                                  */
 750                                 if (act->is_write()) {
 751                                         //RMW shouldn't have an edge to themselves
 752                                         if (act!=curr)
 753                                                 mo_graph->addEdge(act, curr);
 754                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 755                                         mo_graph->addEdge(act->get_reads_from(), curr);
 756                                 added = true;
 757                                 break;
 758                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 759                                                      !act->same_thread(curr)) {
 760                                 /* We have an action that:
 761                                    (1) did not happen before us
 762                                    (2) is a read and we are a write
 763                                    (3) cannot synchronize with us
 764                                    (4) is in a different thread
 765                                    =>
 766                                    that read could potentially read from our write.
 767                                  */
 768                                 if (thin_air_constraint_may_allow(curr, act)) {
 769                                         if (isfeasible() ||
 770                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 771                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 772                                                 futurevalues->push_back(pfv);
 773                                         }
 774                                 }
 775                         }
 776                 }
 777         }
 778
 779         return added;
 780 }
 781
 782 /** Arbitrary reads from the future are not allowed.  Section 29.3
 783  * part 9 places some constraints.  This method checks one result of constraint
 784  * constraint.  Others require compiler support. */
 785
 786 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 787         if (!writer->is_rmw())
 788                 return true;
 789
 790         if (!reader->is_rmw())
 791                 return true;
 792
 793         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 794                 if (search==reader)
 795                         return false;
 796                 if (search->get_tid() == reader->get_tid() &&
 797                                 search->happens_before(reader))
 798                         break;
 799         }
 800
 801         return true;
 802 }
 803
 804 /**
 805  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 806  * The ModelAction under consideration is expected to be taking part in
 807  * release/acquire synchronization as an object of the "reads from" relation.
 808  * Note that this can only provide release sequence support for RMW chains
 809  * which do not read from the future, as those actions cannot be traced until
 810  * their "promise" is fulfilled. Similarly, we may not even establish the
 811  * presence of a release sequence with certainty, as some modification order
 812  * constraints may be decided further in the future. Thus, this function
 813  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 814  * and a boolean representing certainty.
 815  *
 816  * @todo Finish lazy updating, when promises are fulfilled in the future
 817  * @param rf The action that might be part of a release sequence. Must be a
 818  * write.
 819  * @param release_heads A pass-by-reference style return parameter.  After
 820  * execution of this function, release_heads will contain the heads of all the
 821  * relevant release sequences, if any exists
 822  * @return true, if the ModelChecker is certain that release_heads is complete;
 823  * false otherwise
 824  */
 825 bool ModelChecker::release_seq_head(const ModelAction *rf,
 826                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 827 {
 828         if (!rf) {
 829                 /* read from future: need to settle this later */
 830                 return false; /* incomplete */
 831         }
 832
 833         ASSERT(rf->is_write());
 834
 835         if (rf->is_release())
 836                 release_heads->push_back(rf);
 837         if (rf->is_rmw()) {
 838                 /* We need a RMW action that is both an acquire and release to stop */
 839                 /** @todo Need to be smarter here...  In the linux lock
 840                  * example, this will run to the beginning of the program for
 841                  * every acquire. */
 842                 if (rf->is_acquire() && rf->is_release())
 843                         return true; /* complete */
 844                 return release_seq_head(rf->get_reads_from(), release_heads);
 845         }
 846         if (rf->is_release())
 847                 return true; /* complete */
 848
 849         /* else relaxed write; check modification order for contiguous subsequence
 850          * -> rf must be same thread as release */
 851         int tid = id_to_int(rf->get_tid());
 852         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 853         action_list_t *list = &(*thrd_lists)[tid];
 854         action_list_t::const_reverse_iterator rit;
 855
 856         /* Find rf in the thread list */
 857         rit = std::find(list->rbegin(), list->rend(), rf);
 858         ASSERT(rit != list->rend());
 859
 860         /* Find the last write/release */
 861         for (; rit != list->rend(); rit++)
 862                 if ((*rit)->is_release())
 863                         break;
 864         if (rit == list->rend()) {
 865                 /* No write-release in this thread */
 866                 return true; /* complete */
 867         }
 868         ModelAction *release = *rit;
 869
 870         ASSERT(rf->same_thread(release));
 871
 872         bool certain = true;
 873         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 874                 if (id_to_int(rf->get_tid()) == (int)i)
 875                         continue;
 876                 list = &(*thrd_lists)[i];
 877
 878                 /* Can we ensure no future writes from this thread may break
 879                  * the release seq? */
 880                 bool future_ordered = false;
 881
 882                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 883                         const ModelAction *act = *rit;
 884                         if (!act->is_write())
 885                                 continue;
 886                         /* Reach synchronization -> this thread is complete */
 887                         if (act->happens_before(release))
 888                                 break;
 889                         if (rf->happens_before(act)) {
 890                                 future_ordered = true;
 891                                 continue;
 892                         }
 893
 894                         /* Check modification order */
 895                         if (mo_graph->checkReachable(rf, act)) {
 896                                 /* rf --mo--> act */
 897                                 future_ordered = true;
 898                                 continue;
 899                         }
 900                         if (mo_graph->checkReachable(act, release))
 901                                 /* act --mo--> release */
 902                                 break;
 903                         if (mo_graph->checkReachable(release, act) &&
 904                                       mo_graph->checkReachable(act, rf)) {
 905                                 /* release --mo-> act --mo--> rf */
 906                                 return true; /* complete */
 907                         }
 908                         certain = false;
 909                 }
 910                 if (!future_ordered)
 911                         return false; /* This thread is uncertain */
 912         }
 913
 914         if (certain)
 915                 release_heads->push_back(release);
 916         return certain;
 917 }
 918
 919 /**
 920  * A public interface for getting the release sequence head(s) with which a
 921  * given ModelAction must synchronize. This function only returns a non-empty
 922  * result when it can locate a release sequence head with certainty. Otherwise,
 923  * it may mark the internal state of the ModelChecker so that it will handle
 924  * the release sequence at a later time, causing @a act to update its
 925  * synchronization at some later point in execution.
 926  * @param act The 'acquire' action that may read from a release sequence
 927  * @param release_heads A pass-by-reference return parameter. Will be filled
 928  * with the head(s) of the release sequence(s), if they exists with certainty.
 929  * @see ModelChecker::release_seq_head
 930  */
 931 void ModelChecker::get_release_seq_heads(ModelAction *act,
 932                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 933 {
 934         const ModelAction *rf = act->get_reads_from();
 935         bool complete;
 936         complete = release_seq_head(rf, release_heads);
 937         if (!complete) {
 938                 /* add act to 'lazy checking' list */
 939                 std::list<ModelAction *> *list;
 940                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 941                 list->push_back(act);
 942                 (*lazy_sync_size)++;
 943         }
 944 }
 945
 946 /**
 947  * Attempt to resolve all stashed operations that might synchronize with a
 948  * release sequence for a given location. This implements the "lazy" portion of
 949  * determining whether or not a release sequence was contiguous, since not all
 950  * modification order information is present at the time an action occurs.
 951  *
 952  * @param location The location/object that should be checked for release
 953  * sequence resolutions
 954  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 955  */
 956 bool ModelChecker::resolve_release_sequences(void *location)
 957 {
 958         std::list<ModelAction *> *list;
 959         list = lazy_sync_with_release->getptr(location);
 960         if (!list)
 961                 return false;
 962
 963         bool updated = false;
 964         std::list<ModelAction *>::iterator it = list->begin();
 965         while (it != list->end()) {
 966                 ModelAction *act = *it;
 967                 const ModelAction *rf = act->get_reads_from();
 968                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
 969                 bool complete;
 970                 complete = release_seq_head(rf, &release_heads);
 971                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 972                         if (!act->has_synchronized_with(release_heads[i])) {
 973                                 updated = true;
 974                                 act->synchronize_with(release_heads[i]);
 975                         }
 976                 }
 977
 978                 if (updated) {
 979                         /* propagate synchronization to later actions */
 980                         action_list_t::reverse_iterator it = action_trace->rbegin();
 981                         while ((*it) != act) {
 982                                 ModelAction *propagate = *it;
 983                                 if (act->happens_before(propagate))
 984                                         /** @todo new mo_graph edges along with
 985                                          * this synchronization? */
 986                                         propagate->synchronize_with(act);
 987                         }
 988                 }
 989                 if (complete) {
 990                         it = list->erase(it);
 991                         (*lazy_sync_size)--;
 992                 } else
 993                         it++;
 994         }
 995
 996         // If we resolved promises or data races, see if we have realized a data race.
 997         if (checkDataRaces()) {
 998                 set_assert();
 999         }
1000
1001         return updated;
1002 }
1003
1004 /**
1005  * Performs various bookkeeping operations for the current ModelAction. For
1006  * instance, adds action to the per-object, per-thread action vector and to the
1007  * action trace list of all thread actions.
1008  *
1009  * @param act is the ModelAction to add.
1010  */
1011 void ModelChecker::add_action_to_lists(ModelAction *act)
1012 {
1013         int tid = id_to_int(act->get_tid());
1014         action_trace->push_back(act);
1015
1016         obj_map->get_safe_ptr(act->get_location())->push_back(act);
1017
1018         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
1019         if (tid >= (int)vec->size())
1020                 vec->resize(priv->next_thread_id);
1021         (*vec)[tid].push_back(act);
1022
1023         if ((int)thrd_last_action->size() <= tid)
1024                 thrd_last_action->resize(get_num_threads());
1025         (*thrd_last_action)[tid] = act;
1026 }
1027
1028 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
1029 {
1030         int nthreads = get_num_threads();
1031         if ((int)thrd_last_action->size() < nthreads)
1032                 thrd_last_action->resize(nthreads);
1033         return (*thrd_last_action)[id_to_int(tid)];
1034 }
1035
1036 /**
1037  * Gets the last memory_order_seq_cst action (in the total global sequence)
1038  * performed on a particular object (i.e., memory location).
1039  * @param location The object location to check
1040  * @return The last seq_cst action performed
1041  */
1042 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1043 {
1044         action_list_t *list = obj_map->get_safe_ptr(location);
1045         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1046         action_list_t::reverse_iterator rit;
1047         for (rit = list->rbegin(); rit != list->rend(); rit++)
1048                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1049                         return *rit;
1050         return NULL;
1051 }
1052
1053 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1054 {
1055         ModelAction *parent = get_last_action(tid);
1056         if (!parent)
1057                 parent = get_thread(tid)->get_creation();
1058         return parent;
1059 }
1060
1061 /**
1062  * Returns the clock vector for a given thread.
1063  * @param tid The thread whose clock vector we want
1064  * @return Desired clock vector
1065  */
1066 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1067 {
1068         return get_parent_action(tid)->get_cv();
1069 }
1070
1071 /**
1072  * Resolve a set of Promises with a current write. The set is provided in the
1073  * Node corresponding to @a write.
1074  * @param write The ModelAction that is fulfilling Promises
1075  * @return True if promises were resolved; false otherwise
1076  */
1077 bool ModelChecker::resolve_promises(ModelAction *write)
1078 {
1079         bool resolved = false;
1080
1081         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1082                 Promise *promise = (*promises)[promise_index];
1083                 if (write->get_node()->get_promise(i)) {
1084                         ModelAction *read = promise->get_action();
1085                         read->read_from(write);
1086                         if (read->is_rmw()) {
1087                                 mo_graph->addRMWEdge(write, read);
1088                         }
1089                         //First fix up the modification order for actions that happened
1090                         //before the read
1091                         r_modification_order(read, write);
1092                         //Next fix up the modification order for actions that happened
1093                         //after the read.
1094                         post_r_modification_order(read, write);
1095                         promises->erase(promises->begin() + promise_index);
1096                         resolved = true;
1097                 } else
1098                         promise_index++;
1099         }
1100         return resolved;
1101 }
1102
1103 /**
1104  * Compute the set of promises that could potentially be satisfied by this
1105  * action. Note that the set computation actually appears in the Node, not in
1106  * ModelChecker.
1107  * @param curr The ModelAction that may satisfy promises
1108  */
1109 void ModelChecker::compute_promises(ModelAction *curr)
1110 {
1111         for (unsigned int i = 0; i < promises->size(); i++) {
1112                 Promise *promise = (*promises)[i];
1113                 const ModelAction *act = promise->get_action();
1114                 if (!act->happens_before(curr) &&
1115                                 act->is_read() &&
1116                                 !act->is_synchronizing(curr) &&
1117                                 !act->same_thread(curr) &&
1118                                 promise->get_value() == curr->get_value()) {
1119                         curr->get_node()->set_promise(i);
1120                 }
1121         }
1122 }
1123
1124 /** Checks promises in response to change in ClockVector Threads. */
1125 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1126 {
1127         for (unsigned int i = 0; i < promises->size(); i++) {
1128                 Promise *promise = (*promises)[i];
1129                 const ModelAction *act = promise->get_action();
1130                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1131                                 merge_cv->synchronized_since(act)) {
1132                         //This thread is no longer able to send values back to satisfy the promise
1133                         int num_synchronized_threads = promise->increment_threads();
1134                         if (num_synchronized_threads == get_num_threads()) {
1135                                 //Promise has failed
1136                                 failed_promise = true;
1137                                 return;
1138                         }
1139                 }
1140         }
1141 }
1142
1143 /**
1144  * Build up an initial set of all past writes that this 'read' action may read
1145  * from. This set is determined by the clock vector's "happens before"
1146  * relationship.
1147  * @param curr is the current ModelAction that we are exploring; it must be a
1148  * 'read' operation.
1149  */
1150 void ModelChecker::build_reads_from_past(ModelAction *curr)
1151 {
1152         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1153         unsigned int i;
1154         ASSERT(curr->is_read());
1155
1156         ModelAction *last_seq_cst = NULL;
1157
1158         /* Track whether this object has been initialized */
1159         bool initialized = false;
1160
1161         if (curr->is_seqcst()) {
1162                 last_seq_cst = get_last_seq_cst(curr->get_location());
1163                 /* We have to at least see the last sequentially consistent write,
1164                          so we are initialized. */
1165                 if (last_seq_cst != NULL)
1166                         initialized = true;
1167         }
1168
1169         /* Iterate over all threads */
1170         for (i = 0; i < thrd_lists->size(); i++) {
1171                 /* Iterate over actions in thread, starting from most recent */
1172                 action_list_t *list = &(*thrd_lists)[i];
1173                 action_list_t::reverse_iterator rit;
1174                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1175                         ModelAction *act = *rit;
1176
1177                         /* Only consider 'write' actions */
1178                         if (!act->is_write())
1179                                 continue;
1180
1181                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1182                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1183                                 DEBUG("Adding action to may_read_from:\n");
1184                                 if (DBG_ENABLED()) {
1185                                         act->print();
1186                                         curr->print();
1187                                 }
1188                                 curr->get_node()->add_read_from(act);
1189                         }
1190
1191                         /* Include at most one act per-thread that "happens before" curr */
1192                         if (act->happens_before(curr)) {
1193                                 initialized = true;
1194                                 break;
1195                         }
1196                 }
1197         }
1198
1199         if (!initialized) {
1200                 /** @todo Need a more informative way of reporting errors. */
1201                 printf("ERROR: may read from uninitialized atomic\n");
1202         }
1203
1204         if (DBG_ENABLED() || !initialized) {
1205                 printf("Reached read action:\n");
1206                 curr->print();
1207                 printf("Printing may_read_from\n");
1208                 curr->get_node()->print_may_read_from();
1209                 printf("End printing may_read_from\n");
1210         }
1211
1212         ASSERT(initialized);
1213 }
1214
1215 static void print_list(action_list_t *list)
1216 {
1217         action_list_t::iterator it;
1218
1219         printf("---------------------------------------------------------------------\n");
1220         printf("Trace:\n");
1221
1222         for (it = list->begin(); it != list->end(); it++) {
1223                 (*it)->print();
1224         }
1225         printf("---------------------------------------------------------------------\n");
1226 }
1227
1228 void ModelChecker::print_summary()
1229 {
1230         printf("\n");
1231         printf("Number of executions: %d\n", num_executions);
1232         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1233
1234 #if SUPPORT_MOD_ORDER_DUMP
1235         scheduler->print();
1236         char buffername[100];
1237         sprintf(buffername, "exec%u",num_executions);
1238         mo_graph->dumpGraphToFile(buffername);
1239 #endif
1240
1241         if (!isfinalfeasible())
1242                 printf("INFEASIBLE EXECUTION!\n");
1243         print_list(action_trace);
1244         printf("\n");
1245 }
1246
1247 /**
1248  * Add a Thread to the system for the first time. Should only be called once
1249  * per thread.
1250  * @param t The Thread to add
1251  */
1252 void ModelChecker::add_thread(Thread *t)
1253 {
1254         thread_map->put(id_to_int(t->get_id()), t);
1255         scheduler->add_thread(t);
1256 }
1257
1258 void ModelChecker::remove_thread(Thread *t)
1259 {
1260         scheduler->remove_thread(t);
1261 }
1262
1263 /**
1264  * Switch from a user-context to the "master thread" context (a.k.a. system
1265  * context). This switch is made with the intention of exploring a particular
1266  * model-checking action (described by a ModelAction object). Must be called
1267  * from a user-thread context.
1268  * @param act The current action that will be explored. Must not be NULL.
1269  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1270  */
1271 int ModelChecker::switch_to_master(ModelAction *act)
1272 {
1273         DBG();
1274         Thread *old = thread_current();
1275         set_current_action(act);
1276         old->set_state(THREAD_READY);
1277         return Thread::swap(old, &system_context);
1278 }
1279
1280 /**
1281  * Takes the next step in the execution, if possible.
1282  * @return Returns true (success) if a step was taken and false otherwise.
1283  */
1284 bool ModelChecker::take_step() {
1285         Thread *curr, *next;
1286
1287         if (has_asserted())
1288                 return false;
1289
1290         curr = thread_current();
1291         if (curr) {
1292                 if (curr->get_state() == THREAD_READY) {
1293                         ASSERT(priv->current_action);
1294
1295                         priv->nextThread = check_current_action(priv->current_action);
1296                         priv->current_action = NULL;
1297                         if (!curr->is_blocked() && !curr->is_complete())
1298                                 scheduler->add_thread(curr);
1299                 } else {
1300                         ASSERT(false);
1301                 }
1302         }
1303         next = scheduler->next_thread(priv->nextThread);
1304
1305         /* Infeasible -> don't take any more steps */
1306         if (!isfeasible())
1307                 return false;
1308
1309         if (next)
1310                 next->set_state(THREAD_RUNNING);
1311         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1312
1313         /* next == NULL -> don't take any more steps */
1314         if (!next)
1315                 return false;
1316         /* Return false only if swap fails with an error */
1317         return (Thread::swap(&system_context, next) == 0);
1318 }
1319
1320 /** Runs the current execution until threre are no more steps to take. */
1321 void ModelChecker::finish_execution() {
1322         DBG();
1323
1324         while (take_step());
1325 }