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