model.cc

   1 #include <stdio.h>
   2
   3 #include "model.h"
   4 #include "action.h"
   5 #include "nodestack.h"
   6 #include "schedule.h"
   7 #include "snapshot-interface.h"
   8 #include "common.h"
   9 #include "clockvector.h"
  10 #include "cyclegraph.h"
  11
  12 #define INITIAL_THREAD_ID       0
  13
  14 ModelChecker *model;
  15
  16 /** @brief Constructor */
  17 ModelChecker::ModelChecker()
  18         :
  19         /* Initialize default scheduler */
  20         scheduler(new Scheduler()),
  21         /* First thread created will have id INITIAL_THREAD_ID */
  22         next_thread_id(INITIAL_THREAD_ID),
  23         used_sequence_numbers(0),
  24
  25         num_executions(0),
  26         current_action(NULL),
  27         diverge(NULL),
  28         nextThread(THREAD_ID_T_NONE),
  29         action_trace(new action_list_t()),
  30         thread_map(new HashTable<int, Thread *, int>()),
  31         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  32         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  33         thrd_last_action(new std::vector<ModelAction *>(1)),
  34         node_stack(new NodeStack()),
  35         next_backtrack(NULL),
  36         cyclegraph(new CycleGraph())
  37 {
  38 }
  39
  40 /** @brief Destructor */
  41 ModelChecker::~ModelChecker()
  42 {
  43         /*      std::map<int, Thread *>::iterator it;
  44         for (it = thread_map->begin(); it != thread_map->end(); it++)
  45         delete (*it).second;*/
  46         delete thread_map;
  47
  48         delete obj_thrd_map;
  49         delete obj_map;
  50         delete action_trace;
  51         delete thrd_last_action;
  52         delete node_stack;
  53         delete scheduler;
  54         delete cyclegraph;
  55 }
  56
  57 /**
  58  * Restores user program to initial state and resets all model-checker data
  59  * structures.
  60  */
  61 void ModelChecker::reset_to_initial_state()
  62 {
  63         DEBUG("+++ Resetting to initial state +++\n");
  64         node_stack->reset_execution();
  65         current_action = NULL;
  66         next_thread_id = INITIAL_THREAD_ID;
  67         used_sequence_numbers = 0;
  68         nextThread = 0;
  69         next_backtrack = NULL;
  70         snapshotObject->backTrackBeforeStep(0);
  71 }
  72
  73 /** @returns a thread ID for a new Thread */
  74 thread_id_t ModelChecker::get_next_id()
  75 {
  76         return next_thread_id++;
  77 }
  78
  79 /** @returns the number of user threads created during this execution */
  80 int ModelChecker::get_num_threads()
  81 {
  82         return next_thread_id;
  83 }
  84
  85 /** @returns a sequence number for a new ModelAction */
  86 modelclock_t ModelChecker::get_next_seq_num()
  87 {
  88         return ++used_sequence_numbers;
  89 }
  90
  91 /**
  92  * Performs the "scheduling" for the model-checker. That is, it checks if the
  93  * model-checker has selected a "next thread to run" and returns it, if
  94  * available. This function should be called from the Scheduler routine, where
  95  * the Scheduler falls back to a default scheduling routine if needed.
  96  *
  97  * @return The next thread chosen by the model-checker. If the model-checker
  98  * makes no selection, retuns NULL.
  99  */
 100 Thread * ModelChecker::schedule_next_thread()
 101 {
 102         Thread *t;
 103         if (nextThread == THREAD_ID_T_NONE)
 104                 return NULL;
 105         t = thread_map->get(id_to_int(nextThread));
 106
 107         ASSERT(t != NULL);
 108
 109         return t;
 110 }
 111
 112 /**
 113  * Choose the next thread in the replay sequence.
 114  *
 115  * If the replay sequence has reached the 'diverge' point, returns a thread
 116  * from the backtracking set. Otherwise, simply returns the next thread in the
 117  * sequence that is being replayed.
 118  */
 119 thread_id_t ModelChecker::get_next_replay_thread()
 120 {
 121         thread_id_t tid;
 122
 123         /* Have we completed exploring the preselected path? */
 124         if (diverge == NULL)
 125                 return THREAD_ID_T_NONE;
 126
 127         /* Else, we are trying to replay an execution */
 128         ModelAction * next = node_stack->get_next()->get_action();
 129
 130         if (next == diverge) {
 131                 Node *nextnode = next->get_node();
 132                 /* Reached divergence point */
 133                 if (nextnode->increment_read_from()) {
 134                         /* The next node will read from a different value */
 135                         tid = next->get_tid();
 136                         node_stack->pop_restofstack(2);
 137                 } else {
 138                         /* Make a different thread execute for next step */
 139                         Node *node = nextnode->get_parent();
 140                         tid = node->get_next_backtrack();
 141                         node_stack->pop_restofstack(1);
 142                 }
 143                 DEBUG("*** Divergence point ***\n");
 144                 diverge = NULL;
 145         } else {
 146                 tid = next->get_tid();
 147         }
 148         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 149         return tid;
 150 }
 151
 152 /**
 153  * Queries the model-checker for more executions to explore and, if one
 154  * exists, resets the model-checker state to execute a new execution.
 155  *
 156  * @return If there are more executions to explore, return true. Otherwise,
 157  * return false.
 158  */
 159 bool ModelChecker::next_execution()
 160 {
 161         DBG();
 162
 163         num_executions++;
 164
 165         if (isfeasible() || DBG_ENABLED())
 166                 print_summary();
 167
 168         if ((diverge = model->get_next_backtrack()) == NULL)
 169                 return false;
 170
 171         if (DBG_ENABLED()) {
 172                 printf("Next execution will diverge at:\n");
 173                 diverge->print();
 174         }
 175
 176         model->reset_to_initial_state();
 177         return true;
 178 }
 179
 180 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 181 {
 182         action_type type = act->get_type();
 183
 184         switch (type) {
 185                 case ATOMIC_READ:
 186                 case ATOMIC_WRITE:
 187                 case ATOMIC_RMW:
 188                         break;
 189                 default:
 190                         return NULL;
 191         }
 192         /* linear search: from most recent to oldest */
 193         action_list_t *list = obj_map->ensureptr(act->get_location());
 194         action_list_t::reverse_iterator rit;
 195         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 196                 ModelAction *prev = *rit;
 197                 if (act->is_synchronizing(prev))
 198                         return prev;
 199         }
 200         return NULL;
 201 }
 202
 203 void ModelChecker::set_backtracking(ModelAction *act)
 204 {
 205         ModelAction *prev;
 206         Node *node;
 207         Thread *t = get_thread(act->get_tid());
 208
 209         prev = get_last_conflict(act);
 210         if (prev == NULL)
 211                 return;
 212
 213         node = prev->get_node()->get_parent();
 214
 215         while (!node->is_enabled(t))
 216                 t = t->get_parent();
 217
 218         /* Check if this has been explored already */
 219         if (node->has_been_explored(t->get_id()))
 220                 return;
 221
 222         /* Cache the latest backtracking point */
 223         if (!next_backtrack || *prev > *next_backtrack)
 224                 next_backtrack = prev;
 225
 226         /* If this is a new backtracking point, mark the tree */
 227         if (!node->set_backtrack(t->get_id()))
 228                 return;
 229         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 230                         prev->get_tid(), t->get_id());
 231         if (DBG_ENABLED()) {
 232                 prev->print();
 233                 act->print();
 234         }
 235 }
 236
 237 /**
 238  * Returns last backtracking point. The model checker will explore a different
 239  * path for this point in the next execution.
 240  * @return The ModelAction at which the next execution should diverge.
 241  */
 242 ModelAction * ModelChecker::get_next_backtrack()
 243 {
 244         ModelAction *next = next_backtrack;
 245         next_backtrack = NULL;
 246         return next;
 247 }
 248
 249 void ModelChecker::check_current_action(void)
 250 {
 251         ModelAction *curr = this->current_action;
 252         bool already_added = false;
 253         this->current_action = NULL;
 254         if (!curr) {
 255                 DEBUG("trying to push NULL action...\n");
 256                 return;
 257         }
 258
 259         if (curr->is_rmwc()||curr->is_rmw()) {
 260                 ModelAction *tmp=process_rmw(curr);
 261                 already_added = true;
 262                 delete curr;
 263                 curr=tmp;
 264         } else {
 265                 ModelAction * tmp = node_stack->explore_action(curr);
 266                 if (tmp) {
 267                         /* Discard duplicate ModelAction; use action from NodeStack */
 268                         /* First restore type and order in case of RMW operation */
 269                         if (curr->is_rmwr())
 270                                 tmp->copy_typeandorder(curr);
 271                         delete curr;
 272                         curr = tmp;
 273                 } else {
 274                         /*
 275                          * Perform one-time actions when pushing new ModelAction onto
 276                          * NodeStack
 277                          */
 278                         curr->create_cv(get_parent_action(curr->get_tid()));
 279                         /* Build may_read_from set */
 280                         if (curr->is_read())
 281                                 build_reads_from_past(curr);
 282                 }
 283         }
 284
 285         /* Assign 'creation' parent */
 286         if (curr->get_type() == THREAD_CREATE) {
 287                 Thread *th = (Thread *)curr->get_location();
 288                 th->set_creation(curr);
 289         }
 290
 291         /* Assign reads_from values */
 292         Thread *th = get_thread(curr->get_tid());
 293         uint64_t value = VALUE_NONE;
 294         if (curr->is_read()) {
 295                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 296                 value = reads_from->get_value();
 297                 /* Assign reads_from, perform release/acquire synchronization */
 298                 curr->read_from(reads_from);
 299                 r_modification_order(curr,reads_from);
 300         } else if (curr->is_write()) {
 301                 w_modification_order(curr);
 302         }
 303
 304         th->set_return_value(value);
 305
 306         /* Add action to list.  */
 307         if (!already_added)
 308                 add_action_to_lists(curr);
 309
 310         /* Is there a better interface for setting the next thread rather
 311                  than this field/convoluted approach?  Perhaps like just returning
 312                  it or something? */
 313
 314         /* Do not split atomic actions. */
 315         if (curr->is_rmwr()) {
 316                 nextThread = thread_current()->get_id();
 317         } else {
 318                 nextThread = get_next_replay_thread();
 319         }
 320
 321         Node *currnode = curr->get_node();
 322         Node *parnode = currnode->get_parent();
 323
 324         if (!parnode->backtrack_empty()||!currnode->readsfrom_empty())
 325                 if (!next_backtrack || *curr > *next_backtrack)
 326                         next_backtrack = curr;
 327
 328         set_backtracking(curr);
 329 }
 330
 331 /** @returns whether the current trace is feasible. */
 332 bool ModelChecker::isfeasible() {
 333         return !cyclegraph->checkForCycles();
 334 }
 335
 336 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 337 ModelAction * ModelChecker::process_rmw(ModelAction * act) {
 338         int tid = id_to_int(act->get_tid());
 339         ModelAction *lastread=get_last_action(tid);
 340         lastread->process_rmw(act);
 341         if (act->is_rmw())
 342                 cyclegraph->addRMWEdge(lastread, lastread->get_reads_from());
 343         return lastread;
 344 }
 345
 346 /**
 347  * Updates the cyclegraph with the constraints imposed from the current read.
 348  * @param curr The current action. Must be a read.
 349  * @param rf The action that curr reads from. Must be a write.
 350  */
 351 void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
 352         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 353         unsigned int i;
 354         ASSERT(curr->is_read());
 355
 356         /* Iterate over all threads */
 357         for (i = 0; i < thrd_lists->size(); i++) {
 358                 /* Iterate over actions in thread, starting from most recent */
 359                 action_list_t *list = &(*thrd_lists)[i];
 360                 action_list_t::reverse_iterator rit;
 361                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 362                         ModelAction *act = *rit;
 363
 364                         /* Include at most one act per-thread that "happens before" curr */
 365                         if (act->happens_before(curr)) {
 366                                 if (act->is_read()) {
 367                                         const ModelAction * prevreadfrom=act->get_reads_from();
 368                                         if (rf!=prevreadfrom)
 369                                                 cyclegraph->addEdge(rf, prevreadfrom);
 370                                 } else if (rf!=act) {
 371                                         cyclegraph->addEdge(rf, act);
 372                                 }
 373                                 break;
 374                         }
 375                 }
 376         }
 377 }
 378
 379 /**
 380  * Updates the cyclegraph with the constraints imposed from the current write.
 381  * @param curr The current action. Must be a write.
 382  */
 383 void ModelChecker::w_modification_order(ModelAction * curr) {
 384         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 385         unsigned int i;
 386         ASSERT(curr->is_write());
 387
 388         if (curr->is_seqcst()) {
 389                 /* We have to at least see the last sequentially consistent write,
 390                          so we are initialized. */
 391                 ModelAction * last_seq_cst=get_last_seq_cst(curr->get_location());
 392                 if (last_seq_cst!=NULL)
 393                         cyclegraph->addEdge(curr, last_seq_cst);
 394         }
 395
 396         /* Iterate over all threads */
 397         for (i = 0; i < thrd_lists->size(); i++) {
 398                 /* Iterate over actions in thread, starting from most recent */
 399                 action_list_t *list = &(*thrd_lists)[i];
 400                 action_list_t::reverse_iterator rit;
 401                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 402                         ModelAction *act = *rit;
 403
 404                         /* Include at most one act per-thread that "happens before" curr */
 405                         if (act->happens_before(curr)) {
 406                                 if (act->is_read()) {
 407                                         cyclegraph->addEdge(curr, act->get_reads_from());
 408                                 } else
 409                                         cyclegraph->addEdge(curr, act);
 410                                 break;
 411                         }
 412                 }
 413         }
 414 }
 415
 416 /**
 417  * Performs various bookkeeping operations for the current ModelAction. For
 418  * instance, adds action to the per-object, per-thread action vector and to the
 419  * action trace list of all thread actions.
 420  *
 421  * @param act is the ModelAction to add.
 422  */
 423 void ModelChecker::add_action_to_lists(ModelAction *act)
 424 {
 425         int tid = id_to_int(act->get_tid());
 426         action_trace->push_back(act);
 427
 428         obj_map->ensureptr(act->get_location())->push_back(act);
 429
 430         std::vector<action_list_t> *vec = obj_thrd_map->ensureptr(act->get_location());
 431         if (tid >= (int)vec->size())
 432                 vec->resize(next_thread_id);
 433         (*vec)[tid].push_back(act);
 434
 435         if ((int)thrd_last_action->size() <= tid)
 436                 thrd_last_action->resize(get_num_threads());
 437         (*thrd_last_action)[tid] = act;
 438 }
 439
 440 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 441 {
 442         int nthreads = get_num_threads();
 443         if ((int)thrd_last_action->size() < nthreads)
 444                 thrd_last_action->resize(nthreads);
 445         return (*thrd_last_action)[id_to_int(tid)];
 446 }
 447
 448 /**
 449  * Gets the last memory_order_seq_cst action (in the total global sequence)
 450  * performed on a particular object (i.e., memory location).
 451  * @param location The object location to check
 452  * @return The last seq_cst action performed
 453  */
 454 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 455 {
 456         action_list_t *list = obj_map->ensureptr(location);
 457         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 458         action_list_t::reverse_iterator rit;
 459         for (rit = list->rbegin(); rit != list->rend(); rit++)
 460                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 461                         return *rit;
 462         return NULL;
 463 }
 464
 465 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 466 {
 467         ModelAction *parent = get_last_action(tid);
 468         if (!parent)
 469                 parent = get_thread(tid)->get_creation();
 470         return parent;
 471 }
 472
 473 /**
 474  * Returns the clock vector for a given thread.
 475  * @param tid The thread whose clock vector we want
 476  * @return Desired clock vector
 477  */
 478 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
 479         return get_parent_action(tid)->get_cv();
 480 }
 481
 482 /**
 483  * Build up an initial set of all past writes that this 'read' action may read
 484  * from. This set is determined by the clock vector's "happens before"
 485  * relationship.
 486  * @param curr is the current ModelAction that we are exploring; it must be a
 487  * 'read' operation.
 488  */
 489 void ModelChecker::build_reads_from_past(ModelAction *curr)
 490 {
 491         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 492         unsigned int i;
 493         ASSERT(curr->is_read());
 494
 495         ModelAction *last_seq_cst = NULL;
 496
 497         /* Track whether this object has been initialized */
 498         bool initialized = false;
 499
 500         if (curr->is_seqcst()) {
 501                 last_seq_cst = get_last_seq_cst(curr->get_location());
 502                 /* We have to at least see the last sequentially consistent write,
 503                          so we are initialized. */
 504                 if (last_seq_cst != NULL)
 505                         initialized = true;
 506         }
 507
 508         /* Iterate over all threads */
 509         for (i = 0; i < thrd_lists->size(); i++) {
 510                 /* Iterate over actions in thread, starting from most recent */
 511                 action_list_t *list = &(*thrd_lists)[i];
 512                 action_list_t::reverse_iterator rit;
 513                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 514                         ModelAction *act = *rit;
 515
 516                         /* Only consider 'write' actions */
 517                         if (!act->is_write())
 518                                 continue;
 519
 520                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 521                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 522                                 DEBUG("Adding action to may_read_from:\n");
 523                                 if (DBG_ENABLED()) {
 524                                         act->print();
 525                                         curr->print();
 526                                 }
 527                                 curr->get_node()->add_read_from(act);
 528                         }
 529
 530                         /* Include at most one act per-thread that "happens before" curr */
 531                         if (act->happens_before(curr)) {
 532                                 initialized = true;
 533                                 break;
 534                         }
 535                 }
 536         }
 537
 538         if (!initialized) {
 539                 /** @todo Need a more informative way of reporting errors. */
 540                 printf("ERROR: may read from uninitialized atomic\n");
 541         }
 542
 543         if (DBG_ENABLED() || !initialized) {
 544                 printf("Reached read action:\n");
 545                 curr->print();
 546                 printf("Printing may_read_from\n");
 547                 curr->get_node()->print_may_read_from();
 548                 printf("End printing may_read_from\n");
 549         }
 550
 551         ASSERT(initialized);
 552 }
 553
 554 static void print_list(action_list_t *list)
 555 {
 556         action_list_t::iterator it;
 557
 558         printf("---------------------------------------------------------------------\n");
 559         printf("Trace:\n");
 560
 561         for (it = list->begin(); it != list->end(); it++) {
 562                 (*it)->print();
 563         }
 564         printf("---------------------------------------------------------------------\n");
 565 }
 566
 567 void ModelChecker::print_summary(void)
 568 {
 569         printf("\n");
 570         printf("Number of executions: %d\n", num_executions);
 571         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 572
 573         scheduler->print();
 574
 575         if (!isfeasible())
 576                 printf("INFEASIBLE EXECUTION!\n");
 577         print_list(action_trace);
 578         printf("\n");
 579 }
 580
 581 int ModelChecker::add_thread(Thread *t)
 582 {
 583         thread_map->put(id_to_int(t->get_id()), t);
 584         scheduler->add_thread(t);
 585         return 0;
 586 }
 587
 588 void ModelChecker::remove_thread(Thread *t)
 589 {
 590         scheduler->remove_thread(t);
 591 }
 592
 593 /**
 594  * Switch from a user-context to the "master thread" context (a.k.a. system
 595  * context). This switch is made with the intention of exploring a particular
 596  * model-checking action (described by a ModelAction object). Must be called
 597  * from a user-thread context.
 598  * @param act The current action that will be explored. May be NULL, although
 599  * there is little reason to switch to the model-checker without an action to
 600  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 601  * yield control without performing any progress; see thrd_join()).
 602  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 603  */
 604 int ModelChecker::switch_to_master(ModelAction *act)
 605 {
 606         DBG();
 607         Thread * old = thread_current();
 608         set_current_action(act);
 609         old->set_state(THREAD_READY);
 610         return Thread::swap(old, get_system_context());
 611 }