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         print_summary();
 166         if ((diverge = model->get_next_backtrack()) == NULL)
 167                 return false;
 168
 169         if (DBG_ENABLED()) {
 170                 printf("Next execution will diverge at:\n");
 171                 diverge->print();
 172         }
 173
 174         model->reset_to_initial_state();
 175         return true;
 176 }
 177
 178 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 179 {
 180         action_type type = act->get_type();
 181
 182         switch (type) {
 183                 case ATOMIC_READ:
 184                 case ATOMIC_WRITE:
 185                 case ATOMIC_RMW:
 186                         break;
 187                 default:
 188                         return NULL;
 189         }
 190         /* linear search: from most recent to oldest */
 191         action_list_t *list = &(*obj_map)[act->get_location()];
 192         action_list_t::reverse_iterator rit;
 193         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 194                 ModelAction *prev = *rit;
 195                 if (act->is_synchronizing(prev))
 196                         return prev;
 197         }
 198         return NULL;
 199 }
 200
 201 void ModelChecker::set_backtracking(ModelAction *act)
 202 {
 203         ModelAction *prev;
 204         Node *node;
 205         Thread *t = get_thread(act->get_tid());
 206
 207         prev = get_last_conflict(act);
 208         if (prev == NULL)
 209                 return;
 210
 211         node = prev->get_node()->get_parent();
 212
 213         while (!node->is_enabled(t))
 214                 t = t->get_parent();
 215
 216         /* Check if this has been explored already */
 217         if (node->has_been_explored(t->get_id()))
 218                 return;
 219
 220         /* Cache the latest backtracking point */
 221         if (!next_backtrack || *prev > *next_backtrack)
 222                 next_backtrack = prev;
 223
 224         /* If this is a new backtracking point, mark the tree */
 225         if (!node->set_backtrack(t->get_id()))
 226                 return;
 227         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 228                         prev->get_tid(), t->get_id());
 229         if (DBG_ENABLED()) {
 230                 prev->print();
 231                 act->print();
 232         }
 233 }
 234
 235 ModelAction * ModelChecker::get_next_backtrack()
 236 {
 237         ModelAction *next = next_backtrack;
 238         next_backtrack = NULL;
 239         return next;
 240 }
 241
 242 void ModelChecker::check_current_action(void)
 243 {
 244         ModelAction *curr = this->current_action;
 245         ModelAction *tmp;
 246         current_action = NULL;
 247         if (!curr) {
 248                 DEBUG("trying to push NULL action...\n");
 249                 return;
 250         }
 251
 252         tmp = node_stack->explore_action(curr);
 253         if (tmp) {
 254                 /* Discard duplicate ModelAction; use action from NodeStack */
 255                 delete curr;
 256                 curr = tmp;
 257         } else {
 258                 /*
 259                  * Perform one-time actions when pushing new ModelAction onto
 260                  * NodeStack
 261                  */
 262                 curr->create_cv(get_parent_action(curr->get_tid()));
 263                 /* Build may_read_from set */
 264                 if (curr->is_read())
 265                         build_reads_from_past(curr);
 266         }
 267
 268         /* Assign 'creation' parent */
 269         if (curr->get_type() == THREAD_CREATE) {
 270                 Thread *th = (Thread *)curr->get_location();
 271                 th->set_creation(curr);
 272         }
 273
 274         nextThread = get_next_replay_thread();
 275
 276         Node *currnode = curr->get_node();
 277         Node *parnode = currnode->get_parent();
 278
 279         if (!parnode->backtrack_empty()||!currnode->readsfrom_empty())
 280                 if (!next_backtrack || *curr > *next_backtrack)
 281                         next_backtrack = curr;
 282
 283         set_backtracking(curr);
 284
 285         /* Assign reads_from values */
 286         /* TODO: perform release/acquire synchronization here; include
 287          * reads_from as ModelAction member? */
 288         Thread *th = get_thread(curr->get_tid());
 289         uint64_t value = VALUE_NONE;
 290         if (curr->is_read()) {
 291                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 292                 value = reads_from->get_value();
 293                 /* Assign reads_from, perform release/acquire synchronization */
 294                 curr->read_from(reads_from);
 295                 r_modification_order(curr,reads_from);
 296         } else if (curr->is_write()) {
 297                 w_modification_order(curr);
 298         }
 299
 300         th->set_return_value(value);
 301
 302         /* Add action to list last.  */
 303         add_action_to_lists(curr);
 304 }
 305
 306 bool ModelChecker::isfeasible() {
 307         return !cyclegraph->checkForCycles();
 308 }
 309
 310 void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
 311         std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
 312         unsigned int i;
 313         ASSERT(curr->is_read());
 314
 315         /* Iterate over all threads */
 316         for (i = 0; i < thrd_lists->size(); i++) {
 317                 /* Iterate over actions in thread, starting from most recent */
 318                 action_list_t *list = &(*thrd_lists)[i];
 319                 action_list_t::reverse_iterator rit;
 320                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 321                         ModelAction *act = *rit;
 322
 323                         /* Include at most one act per-thread that "happens before" curr */
 324                         if (act->happens_before(curr)) {
 325                                 if (act->is_read()) {
 326                                         const ModelAction * prevreadfrom=act->get_reads_from();
 327                                         if (rf!=prevreadfrom)
 328                                                 cyclegraph->addEdge(rf, prevreadfrom);
 329                                 } else if (rf!=act) {
 330                                         cyclegraph->addEdge(rf, act);
 331                                 }
 332                                 break;
 333                         }
 334                 }
 335         }
 336 }
 337
 338 void ModelChecker::w_modification_order(ModelAction * curr) {
 339         std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
 340         unsigned int i;
 341         ASSERT(curr->is_write());
 342
 343         if (curr->is_seqcst()) {
 344                 /* We have to at least see the last sequentially consistent write,
 345                          so we are initialized. */
 346                 ModelAction * last_seq_cst=get_last_seq_cst(curr->get_location());
 347                 if (last_seq_cst!=NULL)
 348                         cyclegraph->addEdge(curr, last_seq_cst);
 349         }
 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                                         cyclegraph->addEdge(curr, act->get_reads_from());
 363                                 } else
 364                                         cyclegraph->addEdge(curr, act);
 365                                 break;
 366                         }
 367                 }
 368         }
 369 }
 370
 371 /**
 372  * Performs various bookkeeping operations for the current ModelAction. For
 373  * instance, adds action to the per-object, per-thread action vector and to the
 374  * action trace list of all thread actions.
 375  *
 376  * @param act is the ModelAction to add.
 377  */
 378 void ModelChecker::add_action_to_lists(ModelAction *act)
 379 {
 380         int tid = id_to_int(act->get_tid());
 381         action_trace->push_back(act);
 382
 383         (*obj_map)[act->get_location()].push_back(act);
 384
 385         std::vector<action_list_t> *vec = &(*obj_thrd_map)[act->get_location()];
 386         if (tid >= (int)vec->size())
 387                 vec->resize(next_thread_id);
 388         (*vec)[tid].push_back(act);
 389
 390         if ((int)thrd_last_action->size() <= tid)
 391                 thrd_last_action->resize(get_num_threads());
 392         (*thrd_last_action)[tid] = act;
 393 }
 394
 395 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 396 {
 397         int nthreads = get_num_threads();
 398         if ((int)thrd_last_action->size() < nthreads)
 399                 thrd_last_action->resize(nthreads);
 400         return (*thrd_last_action)[id_to_int(tid)];
 401 }
 402
 403 /**
 404  * Gets the last memory_order_seq_cst action (in the total global sequence)
 405  * performed on a particular object (i.e., memory location).
 406  * @param location The object location to check
 407  * @return The last seq_cst action performed
 408  */
 409 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 410 {
 411         action_list_t *list = &(*obj_map)[location];
 412         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 413         action_list_t::reverse_iterator rit;
 414         for (rit = list->rbegin(); rit != list->rend(); rit++)
 415                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 416                         return *rit;
 417         return NULL;
 418 }
 419
 420 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 421 {
 422         ModelAction *parent = get_last_action(tid);
 423         if (!parent)
 424                 parent = get_thread(tid)->get_creation();
 425         return parent;
 426 }
 427
 428 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
 429         return get_parent_action(tid)->get_cv();
 430 }
 431
 432 /**
 433  * Build up an initial set of all past writes that this 'read' action may read
 434  * from. This set is determined by the clock vector's "happens before"
 435  * relationship.
 436  * @param curr is the current ModelAction that we are exploring; it must be a
 437  * 'read' operation.
 438  */
 439 void ModelChecker::build_reads_from_past(ModelAction *curr)
 440 {
 441         std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
 442         unsigned int i;
 443         ASSERT(curr->is_read());
 444
 445         ModelAction *last_seq_cst = NULL;
 446
 447         /* Track whether this object has been initialized */
 448         bool initialized = false;
 449
 450         if (curr->is_seqcst()) {
 451                 last_seq_cst = get_last_seq_cst(curr->get_location());
 452                 /* We have to at least see the last sequentially consistent write,
 453                          so we are initialized. */
 454                 if (last_seq_cst != NULL)
 455                         initialized = true;
 456         }
 457
 458         /* Iterate over all threads */
 459         for (i = 0; i < thrd_lists->size(); i++) {
 460                 /* Iterate over actions in thread, starting from most recent */
 461                 action_list_t *list = &(*thrd_lists)[i];
 462                 action_list_t::reverse_iterator rit;
 463                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 464                         ModelAction *act = *rit;
 465
 466                         /* Only consider 'write' actions */
 467                         if (!act->is_write())
 468                                 continue;
 469
 470                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 471                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 472                                 DEBUG("Adding action to may_read_from:\n");
 473                                 if (DBG_ENABLED()) {
 474                                         act->print();
 475                                         curr->print();
 476                                 }
 477                                 curr->get_node()->add_read_from(act);
 478                         }
 479
 480                         /* Include at most one act per-thread that "happens before" curr */
 481                         if (act->happens_before(curr)) {
 482                                 initialized = true;
 483                                 break;
 484                         }
 485                 }
 486         }
 487
 488         if (!initialized) {
 489                 /* TODO: need a more informative way of reporting errors */
 490                 printf("ERROR: may read from uninitialized atomic\n");
 491         }
 492
 493         if (DBG_ENABLED() || !initialized) {
 494                 printf("Reached read action:\n");
 495                 curr->print();
 496                 printf("Printing may_read_from\n");
 497                 curr->get_node()->print_may_read_from();
 498                 printf("End printing may_read_from\n");
 499         }
 500
 501         ASSERT(initialized);
 502 }
 503
 504 static void print_list(action_list_t *list)
 505 {
 506         action_list_t::iterator it;
 507
 508         printf("---------------------------------------------------------------------\n");
 509         printf("Trace:\n");
 510
 511         for (it = list->begin(); it != list->end(); it++) {
 512                 (*it)->print();
 513         }
 514         printf("---------------------------------------------------------------------\n");
 515 }
 516
 517 void ModelChecker::print_summary(void)
 518 {
 519         if (!isfeasible()) {
 520                 if (DBG_ENABLED())
 521                         printf("INFEASIBLE EXECUTION!\n");
 522                 else
 523                         return;
 524         }
 525
 526         printf("\n");
 527         printf("Number of executions: %d\n", num_executions);
 528         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 529
 530
 531         scheduler->print();
 532
 533         print_list(action_trace);
 534         printf("\n");
 535 }
 536
 537 int ModelChecker::add_thread(Thread *t)
 538 {
 539         (*thread_map)[id_to_int(t->get_id())] = t;
 540         scheduler->add_thread(t);
 541         return 0;
 542 }
 543
 544 void ModelChecker::remove_thread(Thread *t)
 545 {
 546         scheduler->remove_thread(t);
 547 }
 548
 549 /**
 550  * Switch from a user-context to the "master thread" context (a.k.a. system
 551  * context). This switch is made with the intention of exploring a particular
 552  * model-checking action (described by a ModelAction object). Must be called
 553  * from a user-thread context.
 554  * @param act The current action that will be explored. May be NULL, although
 555  * there is little reason to switch to the model-checker without an action to
 556  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 557  * yield control without performing any progress; see thrd_join()).
 558  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 559  */
 560 int ModelChecker::switch_to_master(ModelAction *act)
 561 {
 562         Thread *old;
 563
 564         DBG();
 565         old = thread_current();
 566         set_current_action(act);
 567         old->set_state(THREAD_READY);
 568         return Thread::swap(old, get_system_context());
 569 }