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 /**
 264  * Processes a read or rmw model action.
 265  * @param curr is the read model action to process.
 266  * @param th is the thread
 267  * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw.
 268  * @return True if processing this read updates the mo_graph.
 269  */
 270
 271 bool ModelChecker::process_read(ModelAction *curr, Thread * th, bool second_part_of_rmw) {
 272         uint64_t value;
 273         bool updated=false;
 274         while(true) {
 275                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 276                 if (reads_from != NULL) {
 277                         mo_graph->startChanges();
 278
 279                         value = reads_from->get_value();
 280                         bool r_status=false;
 281
 282                         if (!second_part_of_rmw) {
 283                                 check_recency(curr,false);
 284                                 r_status=r_modification_order(curr, reads_from);
 285                         }
 286
 287
 288                         if (!second_part_of_rmw&&!isfeasible()&&(curr->get_node()->increment_read_from()||curr->get_node()->increment_future_value())) {
 289                                 mo_graph->rollbackChanges();
 290                                 too_many_reads=false;
 291                                 continue;
 292                         }
 293
 294                         curr->read_from(reads_from);
 295                         mo_graph->commitChanges();
 296                         updated |= r_status;
 297                 } else if (!second_part_of_rmw) {
 298                         /* Read from future value */
 299                         value = curr->get_node()->get_future_value();
 300                         modelclock_t expiration = curr->get_node()->get_future_value_expiration();
 301                         curr->read_from(NULL);
 302                         Promise *valuepromise = new Promise(curr, value, expiration);
 303                         promises->push_back(valuepromise);
 304                 }
 305                 th->set_return_value(value);
 306                 return updated;
 307         }
 308 }
 309
 310 /**
 311  * This is the heart of the model checker routine. It performs model-checking
 312  * actions corresponding to a given "current action." Among other processes, it
 313  * calculates reads-from relationships, updates synchronization clock vectors,
 314  * forms a memory_order constraints graph, and handles replay/backtrack
 315  * execution when running permutations of previously-observed executions.
 316  *
 317  * @param curr The current action to process
 318  * @return The next Thread that must be executed. May be NULL if ModelChecker
 319  * makes no choice (e.g., according to replay execution, combining RMW actions,
 320  * etc.)
 321  */
 322 Thread * ModelChecker::check_current_action(ModelAction *curr)
 323 {
 324         bool second_part_of_rmw = false;
 325
 326         ASSERT(curr);
 327
 328         if (curr->is_rmwc() || curr->is_rmw()) {
 329                 ModelAction *tmp = process_rmw(curr);
 330                 second_part_of_rmw = true;
 331                 delete curr;
 332                 curr = tmp;
 333                 compute_promises(curr);
 334         } else {
 335                 ModelAction *tmp = node_stack->explore_action(curr);
 336                 if (tmp) {
 337                         /* Discard duplicate ModelAction; use action from NodeStack */
 338                         /* First restore type and order in case of RMW operation */
 339                         if (curr->is_rmwr())
 340                                 tmp->copy_typeandorder(curr);
 341
 342                         /* If we have diverged, we need to reset the clock vector. */
 343                         if (diverge == NULL)
 344                                 tmp->create_cv(get_parent_action(tmp->get_tid()));
 345
 346                         delete curr;
 347                         curr = tmp;
 348                 } else {
 349                         /*
 350                          * Perform one-time actions when pushing new ModelAction onto
 351                          * NodeStack
 352                          */
 353                         curr->create_cv(get_parent_action(curr->get_tid()));
 354                         /* Build may_read_from set */
 355                         if (curr->is_read())
 356                                 build_reads_from_past(curr);
 357                         if (curr->is_write())
 358                                 compute_promises(curr);
 359                 }
 360         }
 361
 362         /* Thread specific actions */
 363         switch(curr->get_type()) {
 364         case THREAD_CREATE: {
 365                 Thread *th = (Thread *)curr->get_location();
 366                 th->set_creation(curr);
 367                 break;
 368         }
 369         case THREAD_JOIN: {
 370                 Thread *waiting, *blocking;
 371                 waiting = get_thread(curr);
 372                 blocking = (Thread *)curr->get_location();
 373                 if (!blocking->is_complete()) {
 374                         blocking->push_wait_list(curr);
 375                         scheduler->sleep(waiting);
 376                 }
 377                 break;
 378         }
 379         case THREAD_FINISH: {
 380                 Thread *th = get_thread(curr);
 381                 while (!th->wait_list_empty()) {
 382                         ModelAction *act = th->pop_wait_list();
 383                         Thread *wake = get_thread(act);
 384                         scheduler->wake(wake);
 385                 }
 386                 th->complete();
 387                 break;
 388         }
 389         case THREAD_START: {
 390                 check_promises(NULL, curr->get_cv());
 391                 break;
 392         }
 393         default:
 394                 break;
 395         }
 396
 397         Thread *th = get_thread(curr);
 398
 399         bool updated = false;
 400         if (curr->is_read()) {
 401                 updated=process_read(curr, th, second_part_of_rmw);
 402         }
 403
 404         if (curr->is_write()) {
 405                 bool updated_mod_order=w_modification_order(curr);
 406                 bool updated_promises=resolve_promises(curr);
 407                 updated=updated_mod_order|updated_promises;
 408
 409                 if (promises->size()==0) {
 410                         for(unsigned int i=0;i<futurevalues->size();i++) {
 411                                 struct PendingFutureValue pfv=(*futurevalues)[i];
 412                                 if (pfv.act->get_node()->add_future_value(pfv.value, pfv.expiration) &&
 413                                                 (!priv->next_backtrack || *pfv.act > *priv->next_backtrack))
 414                                         priv->next_backtrack = pfv.act;
 415                         }
 416                         futurevalues->resize(0);
 417                 }
 418
 419                 mo_graph->commitChanges();
 420                 th->set_return_value(VALUE_NONE);
 421         }
 422
 423         if (updated)
 424                 resolve_release_sequences(curr->get_location());
 425
 426         /* Add action to list.  */
 427         if (!second_part_of_rmw)
 428                 add_action_to_lists(curr);
 429
 430         check_curr_backtracking(curr);
 431
 432         set_backtracking(curr);
 433
 434         return get_next_thread(curr);
 435 }
 436
 437 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 438         Node *currnode = curr->get_node();
 439         Node *parnode = currnode->get_parent();
 440
 441         if ((!parnode->backtrack_empty() ||
 442                          !currnode->read_from_empty() ||
 443                          !currnode->future_value_empty() ||
 444                          !currnode->promise_empty())
 445                         && (!priv->next_backtrack ||
 446                                         *curr > *priv->next_backtrack)) {
 447                 priv->next_backtrack = curr;
 448         }
 449 }
 450
 451
 452 bool ModelChecker::promises_expired() {
 453         for (unsigned int promise_index = 0; promise_index < promises->size(); promise_index++) {
 454                 Promise *promise = (*promises)[promise_index];
 455                 if (promise->get_expiration()<priv->used_sequence_numbers) {
 456                         return true;
 457                 }
 458         }
 459         return false;
 460 }
 461
 462 /** @returns whether the current partial trace must be a prefix of a
 463  * feasible trace. */
 464 bool ModelChecker::isfeasibleprefix() {
 465         return promises->size() == 0 && *lazy_sync_size == 0;
 466 }
 467
 468 /** @returns whether the current partial trace is feasible. */
 469 bool ModelChecker::isfeasible() {
 470         return !mo_graph->checkForRMWViolation() && isfeasibleotherthanRMW();
 471 }
 472
 473 /** @returns whether the current partial trace is feasible other than
 474  * multiple RMW reading from the same store. */
 475 bool ModelChecker::isfeasibleotherthanRMW() {
 476         return !mo_graph->checkForCycles() && !failed_promise && !too_many_reads && !promises_expired();
 477 }
 478
 479 /** Returns whether the current completed trace is feasible. */
 480 bool ModelChecker::isfinalfeasible() {
 481         return isfeasible() && promises->size() == 0;
 482 }
 483
 484 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 485 ModelAction * ModelChecker::process_rmw(ModelAction *act) {
 486         int tid = id_to_int(act->get_tid());
 487         ModelAction *lastread = get_last_action(tid);
 488         lastread->process_rmw(act);
 489         if (act->is_rmw() && lastread->get_reads_from()!=NULL) {
 490                 mo_graph->addRMWEdge(lastread->get_reads_from(), lastread);
 491                 mo_graph->commitChanges();
 492         }
 493         return lastread;
 494 }
 495
 496 /**
 497  * Checks whether a thread has read from the same write for too many times
 498  * without seeing the effects of a later write.
 499  *
 500  * Basic idea:
 501  * 1) there must a different write that we could read from that would satisfy the modification order,
 502  * 2) we must have read from the same value in excess of maxreads times, and
 503  * 3) that other write must have been in the reads_from set for maxreads times.
 504  *
 505  * If so, we decide that the execution is no longer feasible.
 506  */
 507 void ModelChecker::check_recency(ModelAction *curr, bool already_added) {
 508         if (params.maxreads != 0) {
 509                 if (curr->get_node()->get_read_from_size() <= 1)
 510                         return;
 511
 512                 //Must make sure that execution is currently feasible...  We could
 513                 //accidentally clear by rolling back
 514                 if (!isfeasible())
 515                         return;
 516
 517                 std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 518                 int tid = id_to_int(curr->get_tid());
 519
 520                 /* Skip checks */
 521                 if ((int)thrd_lists->size() <= tid)
 522                         return;
 523
 524                 action_list_t *list = &(*thrd_lists)[tid];
 525
 526                 action_list_t::reverse_iterator rit = list->rbegin();
 527                 /* Skip past curr */
 528                 if (already_added) {
 529                         for (; (*rit) != curr; rit++)
 530                                 ;
 531                         /* go past curr now */
 532                         rit++;
 533                 }
 534
 535                 action_list_t::reverse_iterator ritcopy=rit;
 536                 //See if we have enough reads from the same value
 537                 int count=0;
 538                 for (; count < params.maxreads; rit++,count++) {
 539                         if (rit==list->rend())
 540                                 return;
 541                         ModelAction *act = *rit;
 542                         if (!act->is_read())
 543                                 return;
 544                         if (act->get_reads_from() != curr->get_reads_from())
 545                                 return;
 546                         if (act->get_node()->get_read_from_size() <= 1)
 547                                 return;
 548                 }
 549
 550                 for (int i=0;i<curr->get_node()->get_read_from_size();i++) {
 551                         //Get write
 552                         const ModelAction * write=curr->get_node()->get_read_from_at(i);
 553                         //Need a different write
 554                         if (write==curr->get_reads_from())
 555                                 continue;
 556
 557                         /* Test to see whether this is a feasible write to read from*/
 558                         mo_graph->startChanges();
 559                         r_modification_order(curr, write);
 560                         bool feasiblereadfrom=isfeasible();
 561                         mo_graph->rollbackChanges();
 562
 563                         if (!feasiblereadfrom)
 564                                 continue;
 565                         rit=ritcopy;
 566
 567                         bool feasiblewrite=true;
 568                         //new we need to see if this write works for everyone
 569
 570                         for (int loop=count;loop>0;loop--,rit++) {
 571                                 ModelAction *act=*rit;
 572                                 bool foundvalue=false;
 573                                 for(int j=0;j<act->get_node()->get_read_from_size();j++) {
 574                                         if (act->get_node()->get_read_from_at(i)==write) {
 575                                                 foundvalue=true;
 576                                                 break;
 577                                         }
 578                                 }
 579                                 if (!foundvalue) {
 580                                         feasiblewrite=false;
 581                                         break;
 582                                 }
 583                         }
 584                         if (feasiblewrite) {
 585                                 too_many_reads = true;
 586                                 return;
 587                         }
 588                 }
 589         }
 590 }
 591
 592 /**
 593  * Updates the mo_graph with the constraints imposed from the current read.
 594  * @param curr The current action. Must be a read.
 595  * @param rf The action that curr reads from. Must be a write.
 596  * @return True if modification order edges were added; false otherwise
 597  */
 598 bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf)
 599 {
 600         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 601         unsigned int i;
 602         bool added = false;
 603         ASSERT(curr->is_read());
 604
 605         /* Iterate over all threads */
 606         for (i = 0; i < thrd_lists->size(); i++) {
 607                 /* Iterate over actions in thread, starting from most recent */
 608                 action_list_t *list = &(*thrd_lists)[i];
 609                 action_list_t::reverse_iterator rit;
 610                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 611                         ModelAction *act = *rit;
 612
 613                         /* Include at most one act per-thread that "happens before" curr */
 614                         if (act->happens_before(curr)) {
 615                                 if (act->is_write()) {
 616                                         if (rf != act && act != curr) {
 617                                                 mo_graph->addEdge(act, rf);
 618                                                 added = true;
 619                                         }
 620                                 } else {
 621                                         const ModelAction *prevreadfrom = act->get_reads_from();
 622                                         if (prevreadfrom != NULL && rf != prevreadfrom) {
 623                                                 mo_graph->addEdge(prevreadfrom, rf);
 624                                                 added = true;
 625                                         }
 626                                 }
 627
 628                                 break;
 629                         }
 630                 }
 631         }
 632
 633         return added;
 634 }
 635
 636 /** Updates the mo_graph with the constraints imposed from the current read. */
 637 void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf)
 638 {
 639         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 640         unsigned int i;
 641         ASSERT(curr->is_read());
 642
 643         /* Iterate over all threads */
 644         for (i = 0; i < thrd_lists->size(); i++) {
 645                 /* Iterate over actions in thread, starting from most recent */
 646                 action_list_t *list = &(*thrd_lists)[i];
 647                 action_list_t::reverse_iterator rit;
 648                 ModelAction *lastact = NULL;
 649
 650                 /* Find last action that happens after curr */
 651                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 652                         ModelAction *act = *rit;
 653                         if (curr->happens_before(act)) {
 654                                 lastact = act;
 655                         } else
 656                                 break;
 657                 }
 658
 659                         /* Include at most one act per-thread that "happens before" curr */
 660                 if (lastact != NULL) {
 661                         if (lastact->is_read()) {
 662                                 const ModelAction *postreadfrom = lastact->get_reads_from();
 663                                 if (postreadfrom != NULL&&rf != postreadfrom)
 664                                         mo_graph->addEdge(rf, postreadfrom);
 665                         } else if (rf != lastact) {
 666                                 mo_graph->addEdge(rf, lastact);
 667                         }
 668                         break;
 669                 }
 670         }
 671 }
 672
 673 /**
 674  * Updates the mo_graph with the constraints imposed from the current write.
 675  * @param curr The current action. Must be a write.
 676  * @return True if modification order edges were added; false otherwise
 677  */
 678 bool ModelChecker::w_modification_order(ModelAction *curr)
 679 {
 680         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
 681         unsigned int i;
 682         bool added = false;
 683         ASSERT(curr->is_write());
 684
 685         if (curr->is_seqcst()) {
 686                 /* We have to at least see the last sequentially consistent write,
 687                          so we are initialized. */
 688                 ModelAction *last_seq_cst = get_last_seq_cst(curr->get_location());
 689                 if (last_seq_cst != NULL) {
 690                         mo_graph->addEdge(last_seq_cst, curr);
 691                         added = true;
 692                 }
 693         }
 694
 695         /* Iterate over all threads */
 696         for (i = 0; i < thrd_lists->size(); i++) {
 697                 /* Iterate over actions in thread, starting from most recent */
 698                 action_list_t *list = &(*thrd_lists)[i];
 699                 action_list_t::reverse_iterator rit;
 700                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 701                         ModelAction *act = *rit;
 702
 703                         /* Include at most one act per-thread that "happens before" curr */
 704                         if (act->happens_before(curr)) {
 705                                 /*
 706                                  * Note: if act is RMW, just add edge:
 707                                  *   act --mo--> curr
 708                                  * The following edge should be handled elsewhere:
 709                                  *   readfrom(act) --mo--> act
 710                                  */
 711                                 if (act->is_write()) {
 712                                         //RMW shouldn't have an edge to themselves
 713                                         if (act!=curr)
 714                                                 mo_graph->addEdge(act, curr);
 715                                 } else if (act->is_read() && act->get_reads_from() != NULL)
 716                                         mo_graph->addEdge(act->get_reads_from(), curr);
 717                                 added = true;
 718                                 break;
 719                         } else if (act->is_read() && !act->is_synchronizing(curr) &&
 720                                                      !act->same_thread(curr)) {
 721                                 /* We have an action that:
 722                                    (1) did not happen before us
 723                                    (2) is a read and we are a write
 724                                    (3) cannot synchronize with us
 725                                    (4) is in a different thread
 726                                    =>
 727                                    that read could potentially read from our write.
 728                                  */
 729                                 if (thin_air_constraint_may_allow(curr, act)) {
 730                                         if (isfeasible() ||
 731                                                         (curr->is_rmw() && act->is_rmw() && curr->get_reads_from()==act->get_reads_from() && isfeasibleotherthanRMW())) {
 732                                                 struct PendingFutureValue pfv={curr->get_value(),curr->get_seq_number()+params.maxfuturedelay,act};
 733                                                 futurevalues->push_back(pfv);
 734                                         }
 735                                 }
 736                         }
 737                 }
 738         }
 739
 740         return added;
 741 }
 742
 743 /** Arbitrary reads from the future are not allowed.  Section 29.3
 744  * part 9 places some constraints.  This method checks one result of constraint
 745  * constraint.  Others require compiler support. */
 746
 747 bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, const ModelAction *reader) {
 748         if (!writer->is_rmw())
 749                 return true;
 750
 751         if (!reader->is_rmw())
 752                 return true;
 753
 754         for(const ModelAction *search=writer->get_reads_from();search!=NULL;search=search->get_reads_from()) {
 755                 if (search==reader)
 756                         return false;
 757                 if (search->get_tid()==reader->get_tid()&&
 758                                 search->happens_before(reader))
 759                         break;
 760         }
 761
 762         return true;
 763 }
 764
 765
 766 /**
 767  * Finds the head(s) of the release sequence(s) containing a given ModelAction.
 768  * The ModelAction under consideration is expected to be taking part in
 769  * release/acquire synchronization as an object of the "reads from" relation.
 770  * Note that this can only provide release sequence support for RMW chains
 771  * which do not read from the future, as those actions cannot be traced until
 772  * their "promise" is fulfilled. Similarly, we may not even establish the
 773  * presence of a release sequence with certainty, as some modification order
 774  * constraints may be decided further in the future. Thus, this function
 775  * "returns" two pieces of data: a pass-by-reference vector of @a release_heads
 776  * and a boolean representing certainty.
 777  *
 778  * @todo Finish lazy updating, when promises are fulfilled in the future
 779  * @param rf The action that might be part of a release sequence. Must be a
 780  * write.
 781  * @param release_heads A pass-by-reference style return parameter.  After
 782  * execution of this function, release_heads will contain the heads of all the
 783  * relevant release sequences, if any exists
 784  * @return true, if the ModelChecker is certain that release_heads is complete;
 785  * false otherwise
 786  */
 787 bool ModelChecker::release_seq_head(const ModelAction *rf,
 788                 std::vector<const ModelAction *> *release_heads) const
 789 {
 790         ASSERT(rf->is_write());
 791         if (!rf) {
 792                 /* read from future: need to settle this later */
 793                 return false; /* incomplete */
 794         }
 795         if (rf->is_release())
 796                 release_heads->push_back(rf);
 797         if (rf->is_rmw()) {
 798                 /* We need a RMW action that is both an acquire and release to stop */
 799                 /** @todo Need to be smarter here...  In the linux lock
 800                  * example, this will run to the beginning of the program for
 801                  * every acquire. */
 802                 if (rf->is_acquire() && rf->is_release())
 803                         return true; /* complete */
 804                 return release_seq_head(rf->get_reads_from(), release_heads);
 805         }
 806         if (rf->is_release())
 807                 return true; /* complete */
 808
 809         /* else relaxed write; check modification order for contiguous subsequence
 810          * -> rf must be same thread as release */
 811         int tid = id_to_int(rf->get_tid());
 812         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(rf->get_location());
 813         action_list_t *list = &(*thrd_lists)[tid];
 814         action_list_t::const_reverse_iterator rit;
 815
 816         /* Find rf in the thread list */
 817         rit = std::find(list->rbegin(), list->rend(), rf);
 818         ASSERT(rit != list->rend());
 819
 820         /* Find the last write/release */
 821         for (; rit != list->rend(); rit++)
 822                 if ((*rit)->is_release())
 823                         break;
 824         if (rit == list->rend()) {
 825                 /* No write-release in this thread */
 826                 return true; /* complete */
 827         }
 828         ModelAction *release = *rit;
 829
 830         ASSERT(rf->same_thread(release));
 831
 832         bool certain = true;
 833         for (unsigned int i = 0; i < thrd_lists->size(); i++) {
 834                 if (id_to_int(rf->get_tid()) == (int)i)
 835                         continue;
 836                 list = &(*thrd_lists)[i];
 837
 838                 /* Can we ensure no future writes from this thread may break
 839                  * the release seq? */
 840                 bool future_ordered = false;
 841
 842                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 843                         const ModelAction *act = *rit;
 844                         if (!act->is_write())
 845                                 continue;
 846                         /* Reach synchronization -> this thread is complete */
 847                         if (act->happens_before(release))
 848                                 break;
 849                         if (rf->happens_before(act)) {
 850                                 future_ordered = true;
 851                                 continue;
 852                         }
 853
 854                         /* Check modification order */
 855                         if (mo_graph->checkReachable(rf, act)) {
 856                                 /* rf --mo--> act */
 857                                 future_ordered = true;
 858                                 continue;
 859                         }
 860                         if (mo_graph->checkReachable(act, release))
 861                                 /* act --mo--> release */
 862                                 break;
 863                         if (mo_graph->checkReachable(release, act) &&
 864                                       mo_graph->checkReachable(act, rf)) {
 865                                 /* release --mo-> act --mo--> rf */
 866                                 return true; /* complete */
 867                         }
 868                         certain = false;
 869                 }
 870                 if (!future_ordered)
 871                         return false; /* This thread is uncertain */
 872         }
 873
 874         if (certain)
 875                 release_heads->push_back(release);
 876         return certain;
 877 }
 878
 879 /**
 880  * A public interface for getting the release sequence head(s) with which a
 881  * given ModelAction must synchronize. This function only returns a non-empty
 882  * result when it can locate a release sequence head with certainty. Otherwise,
 883  * it may mark the internal state of the ModelChecker so that it will handle
 884  * the release sequence at a later time, causing @a act to update its
 885  * synchronization at some later point in execution.
 886  * @param act The 'acquire' action that may read from a release sequence
 887  * @param release_heads A pass-by-reference return parameter. Will be filled
 888  * with the head(s) of the release sequence(s), if they exists with certainty.
 889  * @see ModelChecker::release_seq_head
 890  */
 891 void ModelChecker::get_release_seq_heads(ModelAction *act,
 892                 std::vector<const ModelAction *> *release_heads)
 893 {
 894         const ModelAction *rf = act->get_reads_from();
 895         bool complete;
 896         complete = release_seq_head(rf, release_heads);
 897         if (!complete) {
 898                 /* add act to 'lazy checking' list */
 899                 std::list<ModelAction *> *list;
 900                 list = lazy_sync_with_release->get_safe_ptr(act->get_location());
 901                 list->push_back(act);
 902                 (*lazy_sync_size)++;
 903         }
 904 }
 905
 906 /**
 907  * Attempt to resolve all stashed operations that might synchronize with a
 908  * release sequence for a given location. This implements the "lazy" portion of
 909  * determining whether or not a release sequence was contiguous, since not all
 910  * modification order information is present at the time an action occurs.
 911  *
 912  * @param location The location/object that should be checked for release
 913  * sequence resolutions
 914  * @return True if any updates occurred (new synchronization, new mo_graph edges)
 915  */
 916 bool ModelChecker::resolve_release_sequences(void *location)
 917 {
 918         std::list<ModelAction *> *list;
 919         list = lazy_sync_with_release->getptr(location);
 920         if (!list)
 921                 return false;
 922
 923         bool updated = false;
 924         std::list<ModelAction *>::iterator it = list->begin();
 925         while (it != list->end()) {
 926                 ModelAction *act = *it;
 927                 const ModelAction *rf = act->get_reads_from();
 928                 std::vector<const ModelAction *> release_heads;
 929                 bool complete;
 930                 complete = release_seq_head(rf, &release_heads);
 931                 for (unsigned int i = 0; i < release_heads.size(); i++) {
 932                         if (!act->has_synchronized_with(release_heads[i])) {
 933                                 updated = true;
 934                                 act->synchronize_with(release_heads[i]);
 935                         }
 936                 }
 937
 938                 if (updated) {
 939                         /* propagate synchronization to later actions */
 940                         action_list_t::reverse_iterator it = action_trace->rbegin();
 941                         while ((*it) != act) {
 942                                 ModelAction *propagate = *it;
 943                                 if (act->happens_before(propagate))
 944                                         /** @todo new mo_graph edges along with
 945                                          * this synchronization? */
 946                                         propagate->synchronize_with(act);
 947                         }
 948                 }
 949                 if (complete) {
 950                         it = list->erase(it);
 951                         (*lazy_sync_size)--;
 952                 } else
 953                         it++;
 954         }
 955
 956         // If we resolved promises or data races, see if we have realized a data race.
 957         if (checkDataRaces()) {
 958                 set_assert();
 959         }
 960
 961         return updated;
 962 }
 963
 964 /**
 965  * Performs various bookkeeping operations for the current ModelAction. For
 966  * instance, adds action to the per-object, per-thread action vector and to the
 967  * action trace list of all thread actions.
 968  *
 969  * @param act is the ModelAction to add.
 970  */
 971 void ModelChecker::add_action_to_lists(ModelAction *act)
 972 {
 973         int tid = id_to_int(act->get_tid());
 974         action_trace->push_back(act);
 975
 976         obj_map->get_safe_ptr(act->get_location())->push_back(act);
 977
 978         std::vector<action_list_t> *vec = obj_thrd_map->get_safe_ptr(act->get_location());
 979         if (tid >= (int)vec->size())
 980                 vec->resize(priv->next_thread_id);
 981         (*vec)[tid].push_back(act);
 982
 983         if ((int)thrd_last_action->size() <= tid)
 984                 thrd_last_action->resize(get_num_threads());
 985         (*thrd_last_action)[tid] = act;
 986 }
 987
 988 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 989 {
 990         int nthreads = get_num_threads();
 991         if ((int)thrd_last_action->size() < nthreads)
 992                 thrd_last_action->resize(nthreads);
 993         return (*thrd_last_action)[id_to_int(tid)];
 994 }
 995
 996 /**
 997  * Gets the last memory_order_seq_cst action (in the total global sequence)
 998  * performed on a particular object (i.e., memory location).
 999  * @param location The object location to check
1000  * @return The last seq_cst action performed
1001  */
1002 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
1003 {
1004         action_list_t *list = obj_map->get_safe_ptr(location);
1005         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
1006         action_list_t::reverse_iterator rit;
1007         for (rit = list->rbegin(); rit != list->rend(); rit++)
1008                 if ((*rit)->is_write() && (*rit)->is_seqcst())
1009                         return *rit;
1010         return NULL;
1011 }
1012
1013 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
1014 {
1015         ModelAction *parent = get_last_action(tid);
1016         if (!parent)
1017                 parent = get_thread(tid)->get_creation();
1018         return parent;
1019 }
1020
1021 /**
1022  * Returns the clock vector for a given thread.
1023  * @param tid The thread whose clock vector we want
1024  * @return Desired clock vector
1025  */
1026 ClockVector * ModelChecker::get_cv(thread_id_t tid)
1027 {
1028         return get_parent_action(tid)->get_cv();
1029 }
1030
1031 /**
1032  * Resolve a set of Promises with a current write. The set is provided in the
1033  * Node corresponding to @a write.
1034  * @param write The ModelAction that is fulfilling Promises
1035  * @return True if promises were resolved; false otherwise
1036  */
1037 bool ModelChecker::resolve_promises(ModelAction *write)
1038 {
1039         bool resolved = false;
1040
1041         for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) {
1042                 Promise *promise = (*promises)[promise_index];
1043                 if (write->get_node()->get_promise(i)) {
1044                         ModelAction *read = promise->get_action();
1045                         read->read_from(write);
1046                         if (read->is_rmw()) {
1047                                 mo_graph->addRMWEdge(write, read);
1048                         }
1049                         r_modification_order(read, write);
1050                         post_r_modification_order(read, write);
1051                         promises->erase(promises->begin() + promise_index);
1052                         resolved = true;
1053                 } else
1054                         promise_index++;
1055         }
1056         return resolved;
1057 }
1058
1059
1060
1061 /**
1062  * Compute the set of promises that could potentially be satisfied by this
1063  * action. Note that the set computation actually appears in the Node, not in
1064  * ModelChecker.
1065  * @param curr The ModelAction that may satisfy promises
1066  */
1067 void ModelChecker::compute_promises(ModelAction *curr)
1068 {
1069         for (unsigned int i = 0; i < promises->size(); i++) {
1070                 Promise *promise = (*promises)[i];
1071                 const ModelAction *act = promise->get_action();
1072                 if (!act->happens_before(curr) &&
1073                                 act->is_read() &&
1074                                 !act->is_synchronizing(curr) &&
1075                                 !act->same_thread(curr) &&
1076                                 promise->get_value() == curr->get_value()) {
1077                         curr->get_node()->set_promise(i);
1078                 }
1079         }
1080 }
1081
1082 /** Checks promises in response to change in ClockVector Threads. */
1083 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector *merge_cv)
1084 {
1085         for (unsigned int i = 0; i < promises->size(); i++) {
1086                 Promise *promise = (*promises)[i];
1087                 const ModelAction *act = promise->get_action();
1088                 if ((old_cv == NULL || !old_cv->synchronized_since(act)) &&
1089                                 merge_cv->synchronized_since(act)) {
1090                         //This thread is no longer able to send values back to satisfy the promise
1091                         int num_synchronized_threads = promise->increment_threads();
1092                         if (num_synchronized_threads == get_num_threads()) {
1093                                 //Promise has failed
1094                                 failed_promise = true;
1095                                 return;
1096                         }
1097                 }
1098         }
1099 }
1100
1101 /**
1102  * Build up an initial set of all past writes that this 'read' action may read
1103  * from. This set is determined by the clock vector's "happens before"
1104  * relationship.
1105  * @param curr is the current ModelAction that we are exploring; it must be a
1106  * 'read' operation.
1107  */
1108 void ModelChecker::build_reads_from_past(ModelAction *curr)
1109 {
1110         std::vector<action_list_t> *thrd_lists = obj_thrd_map->get_safe_ptr(curr->get_location());
1111         unsigned int i;
1112         ASSERT(curr->is_read());
1113
1114         ModelAction *last_seq_cst = NULL;
1115
1116         /* Track whether this object has been initialized */
1117         bool initialized = false;
1118
1119         if (curr->is_seqcst()) {
1120                 last_seq_cst = get_last_seq_cst(curr->get_location());
1121                 /* We have to at least see the last sequentially consistent write,
1122                          so we are initialized. */
1123                 if (last_seq_cst != NULL)
1124                         initialized = true;
1125         }
1126
1127         /* Iterate over all threads */
1128         for (i = 0; i < thrd_lists->size(); i++) {
1129                 /* Iterate over actions in thread, starting from most recent */
1130                 action_list_t *list = &(*thrd_lists)[i];
1131                 action_list_t::reverse_iterator rit;
1132                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
1133                         ModelAction *act = *rit;
1134
1135                         /* Only consider 'write' actions */
1136                         if (!act->is_write())
1137                                 continue;
1138
1139                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
1140                         if (!curr->is_seqcst()|| (!act->is_seqcst() && (last_seq_cst==NULL||!act->happens_before(last_seq_cst))) || act == last_seq_cst) {
1141                                 DEBUG("Adding action to may_read_from:\n");
1142                                 if (DBG_ENABLED()) {
1143                                         act->print();
1144                                         curr->print();
1145                                 }
1146                                 curr->get_node()->add_read_from(act);
1147                         }
1148
1149                         /* Include at most one act per-thread that "happens before" curr */
1150                         if (act->happens_before(curr)) {
1151                                 initialized = true;
1152                                 break;
1153                         }
1154                 }
1155         }
1156
1157         if (!initialized) {
1158                 /** @todo Need a more informative way of reporting errors. */
1159                 printf("ERROR: may read from uninitialized atomic\n");
1160         }
1161
1162         if (DBG_ENABLED() || !initialized) {
1163                 printf("Reached read action:\n");
1164                 curr->print();
1165                 printf("Printing may_read_from\n");
1166                 curr->get_node()->print_may_read_from();
1167                 printf("End printing may_read_from\n");
1168         }
1169
1170         ASSERT(initialized);
1171 }
1172
1173 static void print_list(action_list_t *list)
1174 {
1175         action_list_t::iterator it;
1176
1177         printf("---------------------------------------------------------------------\n");
1178         printf("Trace:\n");
1179
1180         for (it = list->begin(); it != list->end(); it++) {
1181                 (*it)->print();
1182         }
1183         printf("---------------------------------------------------------------------\n");
1184 }
1185
1186 void ModelChecker::print_summary()
1187 {
1188         printf("\n");
1189         printf("Number of executions: %d\n", num_executions);
1190         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
1191
1192         scheduler->print();
1193
1194         if (!isfinalfeasible())
1195                 printf("INFEASIBLE EXECUTION!\n");
1196         print_list(action_trace);
1197         printf("\n");
1198 }
1199
1200 /**
1201  * Add a Thread to the system for the first time. Should only be called once
1202  * per thread.
1203  * @param t The Thread to add
1204  */
1205 void ModelChecker::add_thread(Thread *t)
1206 {
1207         thread_map->put(id_to_int(t->get_id()), t);
1208         scheduler->add_thread(t);
1209 }
1210
1211 void ModelChecker::remove_thread(Thread *t)
1212 {
1213         scheduler->remove_thread(t);
1214 }
1215
1216 /**
1217  * Switch from a user-context to the "master thread" context (a.k.a. system
1218  * context). This switch is made with the intention of exploring a particular
1219  * model-checking action (described by a ModelAction object). Must be called
1220  * from a user-thread context.
1221  * @param act The current action that will be explored. Must not be NULL.
1222  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
1223  */
1224 int ModelChecker::switch_to_master(ModelAction *act)
1225 {
1226         DBG();
1227         Thread *old = thread_current();
1228         set_current_action(act);
1229         old->set_state(THREAD_READY);
1230         return Thread::swap(old, &system_context);
1231 }
1232
1233 /**
1234  * Takes the next step in the execution, if possible.
1235  * @return Returns true (success) if a step was taken and false otherwise.
1236  */
1237 bool ModelChecker::take_step() {
1238         Thread *curr, *next;
1239
1240         if (has_asserted())
1241                 return false;
1242
1243         curr = thread_current();
1244         if (curr) {
1245                 if (curr->get_state() == THREAD_READY) {
1246                         ASSERT(priv->current_action);
1247
1248                         priv->nextThread = check_current_action(priv->current_action);
1249                         priv->current_action = NULL;
1250                         if (!curr->is_blocked() && !curr->is_complete())
1251                                 scheduler->add_thread(curr);
1252                 } else {
1253                         ASSERT(false);
1254                 }
1255         }
1256         next = scheduler->next_thread(priv->nextThread);
1257
1258         /* Infeasible -> don't take any more steps */
1259         if (!isfeasible())
1260                 return false;
1261
1262         if (next)
1263                 next->set_state(THREAD_RUNNING);
1264         DEBUG("(%d, %d)\n", curr ? curr->get_id() : -1, next ? next->get_id() : -1);
1265
1266         /* next == NULL -> don't take any more steps */
1267         if (!next)
1268                 return false;
1269         /* Return false only if swap fails with an error */
1270         return (Thread::swap(&system_context, next) == 0);
1271 }
1272
1273 /** Runs the current execution until threre are no more steps to take. */
1274 void ModelChecker::finish_execution() {
1275         DBG();
1276
1277         while (take_step());
1278 }