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 second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 266  * @return True if processing this read updates the mo_graph.
 267  */
 268 bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw)
 269 {
 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                 get_thread(curr)->set_return_value(value);
 304                 return updated;
 305         }
 306 }
 307
 308 /**
 309  * Process a write ModelAction
 310  * @param curr The ModelAction to process
 311  * @return True if the mo_graph was updated or promises were resolved
 312  */
 313 bool ModelChecker::process_write(ModelAction *curr)
 314 {
 315         bool updated_mod_order = w_modification_order(curr);
 316         bool updated_promises = resolve_promises(curr);
 317
 318         if (promises->size() == 0) {
 319                 for (unsigned int i = 0; i<futurevalues->size(); i++) {
 320                         struct PendingFutureValue pfv = (*futurevalues)[i];
 321                         if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 322                                         (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 323                                 priv->next_backtrack = pfv.act;
 324                 }
 325                 futurevalues->resize(0);
 326         }
 327
 328         mo_graph->commitChanges();
 329         get_thread(curr)->set_return_value(VALUE_NONE);
 330         return updated_mod_order || updated_promises;
 331 }
 332
 333 /**
 334  * This is the heart of the model checker routine. It performs model-checking
 335  * actions corresponding to a given "current action." Among other processes, it
 336  * calculates reads-from relationships, updates synchronization clock vectors,
 337  * forms a memory_order constraints graph, and handles replay/backtrack
 338  * execution when running permutations of previously-observed executions.
 339  *
 340  * @param curr The current action to process
 341  * @return The next Thread that must be executed. May be NULL if ModelChecker
 342  * makes no choice (e.g., according to replay execution, combining RMW actions,
 343  * etc.)
 344  */
 345 Thread * ModelChecker::check_current_action(ModelAction *curr)
 346 {
 347         bool second_part_of_rmw = false;
 348
 349         ASSERT(curr);
 350
 351         if (curr->is_rmwc() || curr->is_rmw()) {
 352                 ModelAction *tmp = process_rmw(curr);
 353                 second_part_of_rmw = true;
 354                 delete curr;
 355                 curr = tmp;
 356                 compute_promises(curr);
 357         } else {
 358                 ModelAction *tmp = node_stack->explore_action(curr);
 359                 if (tmp) {
 360                         /* Discard duplicate ModelAction; use action from NodeStack */
 361                         /* First restore type and order in case of RMW operation */
 362                         if (curr->is_rmwr())
 363                                 tmp->copy_typeandorder(curr);
 364
 365                         /* If we have diverged, we need to reset the clock vector. */
 366                         if (diverge == NULL)
 367                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 368
 369                         delete curr;
 370                         curr = tmp;
 371                 } else {
 372                         /*
 373                          * Perform one-time actions when pushing new ModelAction onto
 374                          * NodeStack
 375                          */
 376                         curr->create_cv(get_parent_action(curr->get_tid()));
 377                         /* Build may_read_from set */
 378                         if (curr->is_read())
 379                                 build_reads_from_past(curr);
 380                         if (curr->is_write())
 381                                 compute_promises(curr);
 382                 }
 383         }
 384
 385         /* Thread specific actions */
 386         switch (curr->get_type()) {
 387         case THREAD_CREATE: {
 388                 Thread *th = (Thread *)curr->get_location();
 389                 th->set_creation(curr);
 390                 break;
 391         }
 392         case THREAD_JOIN: {
 393                 Thread *waiting, *blocking;
 394                 waiting = get_thread(curr);
 395                 blocking = (Thread *)curr->get_location();
 396                 if (!blocking->is_complete()) {
 397                         blocking->push_wait_list(curr);
 398                         scheduler->sleep(waiting);
 399                 }
 400                 break;
 401         }
 402         case THREAD_FINISH: {
 403                 Thread *th = get_thread(curr);
 404                 while (!th->wait_list_empty()) {
 405                         ModelAction *act = th->pop_wait_list();
 406                         Thread *wake = get_thread(act);
 407                         scheduler->wake(wake);
 408                 }
 409                 th->complete();
 410                 break;
 411         }
 412         case THREAD_START: {
 413                 check_promises(NULL, curr->get_cv());
 414                 break;
 415         }
 416         default:
 417                 break;
 418         }
 419
 420         bool updated = false;
 421
 422         if (curr->is_read() && process_read(curr, second_part_of_rmw))
 423                 updated = true;
 424
 425         if (curr->is_write() && process_write(curr))
 426                 updated = true;
 427
 428         if (updated)
 429                 resolve_release_sequences(curr->get_location());
 430
 431         /* Add action to list.  */
 432         if (!second_part_of_rmw)
 433                 add_action_to_lists(curr);
 434
 435         check_curr_backtracking(curr);
 436
 437         set_backtracking(curr);
 438
 439         return get_next_thread(curr);
 440 }
 441
 442 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 443         Node *currnode = curr->get_node();
 444         Node *parnode = currnode->get_parent();
 445
 446         if ((!parnode->backtrack_empty() ||
 447                          !currnode->read_from_empty() ||
 448                          !currnode->future_value_empty() ||
 449                          !currnode->promise_empty())
 450                         && (!priv->next_backtrack ||
 451                                         *curr > *priv->next_backtrack)) {
 452                 priv->next_backtrack = curr;
 453         }
 454 }
 455
 456 bool ModelChecker::promises_expired() {
 457         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 458                 Promise *promise = (*promises)[promise_index];
 459                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 460                         return true;
 461                 }
 462         }
 463         return false;
 464 }
 465
 466 /** @returns whether the current partial trace must be a prefix of a
 467  * feasible trace. */
 468 bool ModelChecker::isfeasibleprefix() {
 469         return promises->size() == 0 && *lazy_sync_size == 0;
 470 }
 471
 472 /** @returns whether the current partial trace is feasible. */
 473 bool ModelChecker::isfeasible() {
 474         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 475 }
 476
 477 /** @returns whether the current partial trace is feasible other than
 478  * multiple RMW reading from the same store. */
 479 bool ModelChecker::isfeasibleotherthanRMW() {
 480         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 481 }
 482
 483 /** Returns whether the current completed trace is feasible. */
 484 bool ModelChecker::isfinalfeasible() {
 485         return isfeasible() && promises->size() == 0;
 486 }
 487
 488 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 489 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 490         int tid = id_to_int(act->get_tid());
 491         ModelAction *lastread = get_last_action(tid);
 492         lastread->process_rmw(act);
 493         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 494                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 495                 mo_graph->commitChanges();
 496         }
 497         return lastread;
 498 }
 499
 500 /**
 501  * Checks whether a thread has read from the same write for too many times
 502  * without seeing the effects of a later write.
 503  *
 504  * Basic idea:
 505  * 1) there must a different write that we could read from that would satisfy the modification order,
 506  * 2) we must have read from the same value in excess of maxreads times, and
 507  * 3) that other write must have been in the reads_from set for maxreads times.
 508  *
 509  * If so, we decide that the execution is no longer feasible.
 510  */
 511 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 512         if (params.maxreads != 0) {
 513                 if (curr->get_node()->get_read_from_size() <= 1)
 514                         return;
 515
 516                 //Must make sure that execution is currently feasible...  We could
 517                 //accidentally clear by rolling back
 518                 if (!isfeasible())
 519                         return;
 520
 521                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 522                 int tid = id_to_int(curr->get_tid());
 523
 524                 /* Skip checks */
 525                 if ((int)thrd_lists->size() <= tid)
 526                         return;
 527
 528                 action_list_t *list = &(*thrd_lists)[tid];
 529
 530                 action_list_t::reverse_iterator rit = list->rbegin();
 531                 /* Skip past curr */
 532                 if (already_added) {
 533                         for (; (*rit) != curr; rit++)
 534                                 ;
 535                         /* go past curr now */
 536                         rit++;
 537                 }
 538
 539                 action_list_t::reverse_iterator ritcopy = rit;
 540                 //See if we have enough reads from the same value
 541                 int count = 0;
 542                 for (; count < params.maxreads; rit++,count++) {
 543                         if (rit==list->rend())
 544                                 return;
 545                         ModelAction *act = *rit;
 546                         if (!act->is_read())
 547                                 return;
 548                         if (act->get_reads_from() != curr->get_reads_from())
 549                                 return;
 550                         if (act->get_node()->get_read_from_size() <= 1)
 551                                 return;
 552                 }
 553
 554                 for (int i = 0; i<curr->get_node()->get_read_from_size(); i++) {
 555                         //Get write
 556                         const ModelAction * write = curr->get_node()->get_read_from_at(i);
 557                         //Need a different write
 558                         if (write==curr->get_reads_from())
 559                                 continue;
 560
 561                         /* Test to see whether this is a feasible write to read from*/
 562                         mo_graph->startChanges();
 563                         r_modification_order(curr, write);
 564                         bool feasiblereadfrom = isfeasible();
 565                         mo_graph->rollbackChanges();
 566
 567                         if (!feasiblereadfrom)
 568                                 continue;
 569                         rit = ritcopy;
 570
 571                         bool feasiblewrite = true;
 572                         //new we need to see if this write works for everyone
 573
 574                         for (int loop = count; loop>0; loop--,rit++) {
 575                                 ModelAction *act=*rit;
 576                                 bool foundvalue = false;
 577                                 for (int j = 0; j<act->get_node()->get_read_from_size(); j++) {
 578                                         if (act->get_node()->get_read_from_at(i)==write) {
 579                                                 foundvalue = true;
 580                                                 break;
 581                                         }
 582                                 }
 583                                 if (!foundvalue) {
 584                                         feasiblewrite = false;
 585                                         break;
 586                                 }
 587                         }
 588                         if (feasiblewrite) {
 589                                 too_many_reads = true;
 590                                 return;
 591                         }
 592                 }
 593         }
 594 }
 595
 596 /**
 597  * Updates the mo_graph with the constraints imposed from the current read.
 598  * @param curr The current action. Must be a read.
 599  * @param rf The action that curr reads from. Must be a write.
 600  * @return True if modification order edges were added; false otherwise
 601  */
 602 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 603 {
 604         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 605         unsigned int i;
 606         bool added = false;
 607         ASSERT(curr->is_read());
 608
 609         /* Iterate over all threads */
 610         for (i = 0; i < thrd_lists->size(); i++) {
 611                 /* Iterate over actions in thread, starting from most recent */
 612                 action_list_t *list = &(*thrd_lists)[i];
 613                 action_list_t::reverse_iterator rit;
 614                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 615                         ModelAction *act = *rit;
 616
 617                         /* Include at most one act per-thread that "happens before" curr */
 618                         if (act->happens_before(curr)) {
 619                                 if (act->is_write()) {
 620                                         if (rf != act && act != curr) {
 621                                                 mo_graph->addEdge(act, rf);
 622                                                 added = true;
 623                                         }
 624                                 } else {
 625                                         const ModelAction *prevreadfrom = act->get_reads_from();
 626                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 627                                                 mo_graph->addEdge(prevreadfrom, rf);
 628                                                 added = true;
 629                                         }
 630                                 }
 631
 632                                 break;
 633                         }
 634                 }
 635         }
 636
 637         return added;
 638 }
 639
 640 /** Updates the mo_graph with the constraints imposed from the current read. */
 641 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 642 {
 643         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 644         unsigned int i;
 645         ASSERT(curr->is_read());
 646
 647         /* Iterate over all threads */
 648         for (i = 0; i < thrd_lists->size(); i++) {
 649                 /* Iterate over actions in thread, starting from most recent */
 650                 action_list_t *list = &(*thrd_lists)[i];
 651                 action_list_t::reverse_iterator rit;
 652                 ModelAction *lastact = NULL;
 653
 654                 /* Find last action that happens after curr */
 655                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 656                         ModelAction *act = *rit;
 657                         if (curr->happens_before(act)) {
 658                                 lastact = act;
 659                         } else
 660                                 break;
 661                 }
 662
 663                         /* Include at most one act per-thread that "happens before" curr */
 664                 if (lastact != NULL) {
 665                         if (lastact->is_read()) {
 666                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 667                                 if (postreadfrom != NULL&&rf != postreadfrom)
 668                                         mo_graph->addEdge(rf, postreadfrom);
 669                         } else if (rf != lastact) {
 670                                 mo_graph->addEdge(rf, lastact);
 671                         }
 672                         break;
 673                 }
 674         }
 675 }
 676
 677 /**
 678  * Updates the mo_graph with the constraints imposed from the current write.
 679  * @param curr The current action. Must be a write.
 680  * @return True if modification order edges were added; false otherwise
 681  */
 682 bool ModelChecker::w_modification_order(ModelAction *curr)
 683 {
 684         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 685         unsigned int i;
 686         bool added = false;
 687         ASSERT(curr->is_write());
 688
 689         if (curr->is_seqcst()) {
 690                 /* We have to at least see the last sequentially consistent write,
 691                          so we are initialized. */
 692                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 693                 if (last_seq_cst != NULL) {
 694                         mo_graph->addEdge(last_seq_cst, curr);
 695                         added = true;
 696                 }
 697         }
 698
 699         /* Iterate over all threads */
 700         for (i = 0; i < thrd_lists->size(); i++) {
 701                 /* Iterate over actions in thread, starting from most recent */
 702                 action_list_t *list = &(*thrd_lists)[i];
 703                 action_list_t::reverse_iterator rit;
 704                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 705                         ModelAction *act = *rit;
 706
 707                         /* Include at most one act per-thread that "happens before" curr */
 708                         if (act->happens_before(curr)) {
 709                                 /*
 710                                  * Note: if act is RMW, just add edge:
 711                                  *   act --mo--> curr
 712                                  * The following edge should be handled elsewhere:
 713                                  *   readfrom(act) --mo--> act
 714                                  */
 715                                 if (act->is_write()) {
 716                                         //RMW shouldn't have an edge to themselves
 717                                         if (act!=curr)
 718                                                 mo_graph->addEdge(act, curr);
 719                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 720                                         mo_graph->addEdge(act->get_reads_from(), curr);
 721                                 added = true;
 722                                 break;
 723                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 724                                                      !act->same_thread(curr)) {
 725                                 /* We have an action that:
 726                                    (1) did not happen before us
 727                                    (2) is a read and we are a write
 728                                    (3) cannot synchronize with us
 729                                    (4) is in a different thread
 730                                    =>
 731                                    that read could potentially read from our write.
 732                                  */
 733                                 if (thin_air_constraint_may_allow(curr, act)) {
 734                                         if (isfeasible() ||
 735                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 736                                                 struct PendingFutureValue pfv = {curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 737                                                 futurevalues->push_back(pfv);
 738                                         }
 739                                 }
 740                         }
 741                 }
 742         }
 743
 744         return added;
 745 }
 746
 747 /** Arbitrary reads from the future are not allowed.  Section 29.3
 748  * part 9 places some constraints.  This method checks one result of constraint
 749  * constraint.  Others require compiler support. */
 750
 751 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 752         if (!writer->is_rmw())
 753                 return true;
 754
 755         if (!reader->is_rmw())
 756                 return true;
 757
 758         for (const ModelAction *search = writer->get_reads_from(); search != NULL; search = search->get_reads_from()) {
 759                 if (search==reader)
 760                         return false;
 761                 if (search->get_tid() == reader->get_tid() &&
 762                                 search->happens_before(reader))
 763                         break;
 764         }
 765
 766         return true;
 767 }
 768
 769 /**
 770  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 771  * The ModelAction under consideration is expected to be taking part in
 772  * release/acquire synchronization as an object of the "reads from" relation.
 773  * Note that this can only provide release sequence support for RMW chains
 774  * which do not read from the future, as those actions cannot be traced until
 775  * their "promise" is fulfilled. Similarly, we may not even establish the
 776  * presence of a release sequence with certainty, as some modification order
 777  * constraints may be decided further in the future. Thus, this function
 778  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 779  * and a boolean representing certainty.
 780  *
 781  * @todo Finish lazy updating, when promises are fulfilled in the future
 782  * @param rf The action that might be part of a release sequence. Must be a
 783  * write.
 784  * @param release_heads A pass-by-reference style return parameter.  After
 785  * execution of this function, release_heads will contain the heads of all the
 786  * relevant release sequences, if any exists
 787  * @return true, if the ModelChecker is certain that release_heads is complete;
 788  * false otherwise
 789  */
 790 bool ModelChecker::release_seq_head(const ModelAction *rf,
 791                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads) const
 792 {
 793         if (!rf) {
 794                 /* read from future: need to settle this later */
 795                 return false; /* incomplete */
 796         }
 797
 798         ASSERT(rf->is_write());
 799
 800         if (rf->is_release())
 801                 release_heads->push_back(rf);
 802         if (rf->is_rmw()) {
 803                 /* We need a RMW action that is both an acquire and release to stop */
 804                 /** @todo Need to be smarter here...  In the linux lock
 805                  * example, this will run to the beginning of the program for
 806                  * every acquire. */
 807                 if (rf->is_acquire() && rf->is_release())
 808                         return true; /* complete */
 809                 return release_seq_head(rf->get_reads_from(), release_heads);
 810         }
 811         if (rf->is_release())
 812                 return true; /* complete */
 813
 814         /* else relaxed write; check modification order for contiguous subsequence
 815          * -> rf must be same thread as release */
 816         int tid = id_to_int(rf->get_tid());
 817         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 818         action_list_t *list = &(*thrd_lists)[tid];
 819         action_list_t::const_reverse_iterator rit;
 820
 821         /* Find rf in the thread list */
 822         rit = std::find(list->rbegin(), list->rend(), rf);
 823         ASSERT(rit != list->rend());
 824
 825         /* Find the last write/release */
 826         for (; rit != list->rend(); rit++)
 827                 if ((*rit)->is_release())
 828                         break;
 829         if (rit == list->rend()) {
 830                 /* No write-release in this thread */
 831                 return true; /* complete */
 832         }
 833         ModelAction *release = *rit;
 834
 835         ASSERT(rf->same_thread(release));
 836
 837         bool certain = true;
 838         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 839                 if (id_to_int(rf->get_tid()) == (int)i)
 840                         continue;
 841                 list = &(*thrd_lists)[i];
 842
 843                 /* Can we ensure no future writes from this thread may break
 844                  * the release seq? */
 845                 bool future_ordered = false;
 846
 847                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 848                         const ModelAction *act = *rit;
 849                         if (!act->is_write())
 850                                 continue;
 851                         /* Reach synchronization -> this thread is complete */
 852                         if (act->happens_before(release))
 853                                 break;
 854                         if (rf->happens_before(act)) {
 855                                 future_ordered = true;
 856                                 continue;
 857                         }
 858
 859                         /* Check modification order */
 860                         if (mo_graph->checkReachable(rf, act)) {
 861                                 /* rf --mo--> act */
 862                                 future_ordered = true;
 863                                 continue;
 864                         }
 865                         if (mo_graph->checkReachable(act, release))
 866                                 /* act --mo--> release */
 867                                 break;
 868                         if (mo_graph->checkReachable(release, act) &&
 869                                       mo_graph->checkReachable(act, rf)) {
 870                                 /* release --mo-> act --mo--> rf */
 871                                 return true; /* complete */
 872                         }
 873                         certain = false;
 874                 }
 875                 if (!future_ordered)
 876                         return false; /* This thread is uncertain */
 877         }
 878
 879         if (certain)
 880                 release_heads->push_back(release);
 881         return certain;
 882 }
 883
 884 /**
 885  * A public interface for getting the release sequence head(s) with which a
 886  * given ModelAction must synchronize. This function only returns a non-empty
 887  * result when it can locate a release sequence head with certainty. Otherwise,
 888  * it may mark the internal state of the ModelChecker so that it will handle
 889  * the release sequence at a later time, causing @a act to update its
 890  * synchronization at some later point in execution.
 891  * @param act The 'acquire' action that may read from a release sequence
 892  * @param release_heads A pass-by-reference return parameter. Will be filled
 893  * with the head(s) of the release sequence(s), if they exists with certainty.
 894  * @see ModelChecker::release_seq_head
 895  */
 896 void ModelChecker::get_release_seq_heads(ModelAction *act,
 897                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > *release_heads)
 898 {
 899         const ModelAction *rf = act->get_reads_from();
 900         bool complete;
 901         complete = release_seq_head(rf, release_heads);
 902         if (!complete) {
 903                 /* add act to 'lazy checking' list */
 904                 std::list<ModelAction *> *list;
 905                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 906                 list->push_back(act);
 907                 (*lazy_sync_size)++;
 908         }
 909 }
 910
 911 /**
 912  * Attempt to resolve all stashed operations that might synchronize with a
 913  * release sequence for a given location. This implements the "lazy" portion of
 914  * determining whether or not a release sequence was contiguous, since not all
 915  * modification order information is present at the time an action occurs.
 916  *
 917  * @param location The location/object that should be checked for release
 918  * sequence resolutions
 919  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 920  */
 921 bool ModelChecker::resolve_release_sequences(void *location)
 922 {
 923         std::list<ModelAction *> *list;
 924         list = lazy_sync_with_release->getptr(location);
 925         if (!list)
 926                 return false;
 927
 928         bool updated = false;
 929         std::list<ModelAction *>::iterator it = list->begin();
 930         while (it != list->end()) {
 931                 ModelAction *act = *it;
 932                 const ModelAction *rf = act->get_reads_from();
 933                 std::vector< const ModelAction *, MyAlloc<const ModelAction *> > release_heads;
 934                 bool complete;
 935                 complete = release_seq_head(rf, &release_heads);
 936                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 937                         if (!act->has_synchronized_with(release_heads[i])) {
 938                                 updated = true;
 939                                 act->synchronize_with(release_heads[i]);
 940                         }
 941                 }
 942
 943                 if (updated) {
 944                         /* propagate synchronization to later actions */
 945                         action_list_t::reverse_iterator it = action_trace->rbegin();
 946                         while ((*it) != act) {
 947                                 ModelAction *propagate = *it;
 948                                 if (act->happens_before(propagate))
 949                                         /** @todo new mo_graph edges along with
 950                                          * this synchronization? */
 951                                         propagate->synchronize_with(act);
 952                         }
 953                 }
 954                 if (complete) {
 955                         it = list->erase(it);
 956                         (*lazy_sync_size)--;
 957                 } else
 958                         it++;
 959         }
 960
 961         // If we resolved promises or data races, see if we have realized a data race.
 962         if (checkDataRaces()) {
 963                 set_assert();
 964         }
 965
 966         return updated;
 967 }
 968
 969 /**
 970  * Performs various bookkeeping operations for the current ModelAction. For
 971  * instance, adds action to the per-object, per-thread action vector and to the
 972  * action trace list of all thread actions.
 973  *
 974  * @param act is the ModelAction to add.
 975  */
 976 void ModelChecker::add_action_to_lists(ModelAction *act)
 977 {
 978         int tid = id_to_int(act->get_tid());
 979         action_trace->push_back(act);
 980
 981         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 982
 983         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 984         if (tid >= (int)vec->size())
 985                 vec->resize(priv->next_thread_id);
 986         (*vec)[tid].push_back(act);
 987
 988         if ((int)thrd_last_action->size() <= tid)
 989                 thrd_last_action->resize(get_num_threads());
 990         (*thrd_last_action)[tid] = act;
 991 }
 992
 993 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 994 {
 995         int nthreads = get_num_threads();
 996         if ((int)thrd_last_action->size() < nthreads)
 997                 thrd_last_action->resize(nthreads);
 998         return (*thrd_last_action)[id_to_int(tid)];
 999 }
1000
1001 /**
1002  * Gets the last memory_order_seq_cst action (in the total global sequence)
1003  * performed on a particular object (i.e., memory location).
1004  * @param location The object location to check
1005  * @return The last seq_cst action performed
1006  */
1007 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1008 {
1009         action_list_t *list = obj_map->get_safe_ptr(location);
1010         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1011         action_list_t::reverse_iterator rit;
1012         for (rit = list->rbegin(); rit != list->rend(); rit++)
1013                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1014                         return *rit;
1015         return NULL;
1016 }
1017
1018 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1019 {
1020         ModelAction *parent = get_last_action(tid);
1021         if (!parent)
1022                 parent = get_thread(tid)->get_creation();
1023         return parent;
1024 }
1025
1026 /**
1027  * Returns the clock vector for a given thread.
1028  * @param tid The thread whose clock vector we want
1029  * @return Desired clock vector
1030  */
1031 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1032 {
1033         return get_parent_action(tid)->get_cv();
1034 }
1035
1036 /**
1037  * Resolve a set of Promises with a current write. The set is provided in the
1038  * Node corresponding to @a write.
1039  * @param write The ModelAction that is fulfilling Promises
1040  * @return True if promises were resolved; false otherwise
1041  */
1042 bool ModelChecker::resolve_promises(ModelAction *write)
1043 {
1044         bool resolved = false;
1045
1046         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1047                 Promise *promise = (*promises)[promise_index];
1048                 if (write->get_node()->get_promise(i)) {
1049                         ModelAction *read = promise->get_action();
1050                         read->read_from(write);
1051                         if (read->is_rmw()) {
1052                                 mo_graph->addRMWEdge(write, read);
1053                         }
1054                         r_modification_order(read, write);
1055                         post_r_modification_order(read, write);
1056                         promises->erase(promises->begin() + promise_index);
1057                         resolved = true;
1058                 } else
1059                         promise_index++;
1060         }
1061         return resolved;
1062 }
1063
1064 /**
1065  * Compute the set of promises that could potentially be satisfied by this
1066  * action. Note that the set computation actually appears in the Node, not in
1067  * ModelChecker.
1068  * @param curr The ModelAction that may satisfy promises
1069  */
1070 void ModelChecker::compute_promises(ModelAction *curr)
1071 {
1072         for (unsigned int i = 0; i < promises->size(); i++) {
1073                 Promise *promise = (*promises)[i];
1074                 const ModelAction *act = promise->get_action();
1075                 if (!act->happens_before(curr) &&
1076                                 act->is_read() &&
1077                                 !act->is_synchronizing(curr) &&
1078                                 !act->same_thread(curr) &&
1079                                 promise->get_value() == curr->get_value()) {
1080                         curr->get_node()->set_promise(i);
1081                 }
1082         }
1083 }
1084
1085 /** Checks promises in response to change in ClockVector Threads. */
1086 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1087 {
1088         for (unsigned int i = 0; i < promises->size(); i++) {
1089                 Promise *promise = (*promises)[i];
1090                 const ModelAction *act = promise->get_action();
1091                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1092                                 merge_cv->synchronized_since(act)) {
1093                         //This thread is no longer able to send values back to satisfy the promise
1094                         int num_synchronized_threads = promise->increment_threads();
1095                         if (num_synchronized_threads == get_num_threads()) {
1096                                 //Promise has failed
1097                                 failed_promise = true;
1098                                 return;
1099                         }
1100                 }
1101         }
1102 }
1103
1104 /**
1105  * Build up an initial set of all past writes that this 'read' action may read
1106  * from. This set is determined by the clock vector's "happens before"
1107  * relationship.
1108  * @param curr is the current ModelAction that we are exploring; it must be a
1109  * 'read' operation.
1110  */
1111 void ModelChecker::build_reads_from_past(ModelAction *curr)
1112 {
1113         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1114         unsigned int i;
1115         ASSERT(curr->is_read());
1116
1117         ModelAction *last_seq_cst = NULL;
1118
1119         /* Track whether this object has been initialized */
1120         bool initialized = false;
1121
1122         if (curr->is_seqcst()) {
1123                 last_seq_cst = get_last_seq_cst(curr->get_location());
1124                 /* We have to at least see the last sequentially consistent write,
1125                          so we are initialized. */
1126                 if (last_seq_cst != NULL)
1127                         initialized = true;
1128         }
1129
1130         /* Iterate over all threads */
1131         for (i = 0; i < thrd_lists->size(); i++) {
1132                 /* Iterate over actions in thread, starting from most recent */
1133                 action_list_t *list = &(*thrd_lists)[i];
1134                 action_list_t::reverse_iterator rit;
1135                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1136                         ModelAction *act = *rit;
1137
1138                         /* Only consider 'write' actions */
1139                         if (!act->is_write())
1140                                 continue;
1141
1142                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1143                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1144                                 DEBUG("Adding action to may_read_from:\n");
1145                                 if (DBG_ENABLED()) {
1146                                         act->print();
1147                                         curr->print();
1148                                 }
1149                                 curr->get_node()->add_read_from(act);
1150                         }
1151
1152                         /* Include at most one act per-thread that "happens before" curr */
1153                         if (act->happens_before(curr)) {
1154                                 initialized = true;
1155                                 break;
1156                         }
1157                 }
1158         }
1159
1160         if (!initialized) {
1161                 /** @todo Need a more informative way of reporting errors. */
1162                 printf("ERROR: may read from uninitialized atomic\n");
1163         }
1164
1165         if (DBG_ENABLED() || !initialized) {
1166                 printf("Reached read action:\n");
1167                 curr->print();
1168                 printf("Printing may_read_from\n");
1169                 curr->get_node()->print_may_read_from();
1170                 printf("End printing may_read_from\n");
1171         }
1172
1173         ASSERT(initialized);
1174 }
1175
1176 static void print_list(action_list_t *list)
1177 {
1178         action_list_t::iterator it;
1179
1180         printf("---------------------------------------------------------------------\n");
1181         printf("Trace:\n");
1182
1183         for (it = list->begin(); it != list->end(); it++) {
1184                 (*it)->print();
1185         }
1186         printf("---------------------------------------------------------------------\n");
1187 }
1188
1189 void ModelChecker::print_summary()
1190 {
1191         printf("\n");
1192         printf("Number of executions: %d\n", num_executions);
1193         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1194
1195         scheduler->print();
1196
1197         if (!isfinalfeasible())
1198                 printf("INFEASIBLE EXECUTION!\n");
1199         print_list(action_trace);
1200         printf("\n");
1201 }
1202
1203 /**
1204  * Add a Thread to the system for the first time. Should only be called once
1205  * per thread.
1206  * @param t The Thread to add
1207  */
1208 void ModelChecker::add_thread(Thread *t)
1209 {
1210         thread_map->put(id_to_int(t->get_id()), t);
1211         scheduler->add_thread(t);
1212 }
1213
1214 void ModelChecker::remove_thread(Thread *t)
1215 {
1216         scheduler->remove_thread(t);
1217 }
1218
1219 /**
1220  * Switch from a user-context to the "master thread" context (a.k.a. system
1221  * context). This switch is made with the intention of exploring a particular
1222  * model-checking action (described by a ModelAction object). Must be called
1223  * from a user-thread context.
1224  * @param act The current action that will be explored. Must not be NULL.
1225  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1226  */
1227 int ModelChecker::switch_to_master(ModelAction *act)
1228 {
1229         DBG();
1230         Thread *old = thread_current();
1231         set_current_action(act);
1232         old->set_state(THREAD_READY);
1233         return Thread::swap(old, &system_context);
1234 }
1235
1236 /**
1237  * Takes the next step in the execution, if possible.
1238  * @return Returns true (success) if a step was taken and false otherwise.
1239  */
1240 bool ModelChecker::take_step() {
1241         Thread *curr, *next;
1242
1243         if (has_asserted())
1244                 return false;
1245
1246         curr = thread_current();
1247         if (curr) {
1248                 if (curr->get_state() == THREAD_READY) {
1249                         ASSERT(priv->current_action);
1250
1251                         priv->nextThread = check_current_action(priv->current_action);
1252                         priv->current_action = NULL;
1253                         if (!curr->is_blocked() && !curr->is_complete())
1254                                 scheduler->add_thread(curr);
1255                 } else {
1256                         ASSERT(false);
1257                 }
1258         }
1259         next = scheduler->next_thread(priv->nextThread);
1260
1261         /* Infeasible -> don't take any more steps */
1262         if (!isfeasible())
1263                 return false;
1264
1265         if (next)
1266                 next->set_state(THREAD_RUNNING);
1267         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1268
1269         /* next == NULL -> don't take any more steps */
1270         if (!next)
1271                 return false;
1272         /* Return false only if swap fails with an error */
1273         return (Thread::swap(&system_context, next) == 0);
1274 }
1275
1276 /** Runs the current execution until threre are no more steps to take. */
1277 void ModelChecker::finish_execution() {
1278         DBG();
1279
1280         while (take_step());
1281 }