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 #include "promise.h"
  12
  13 #define INITIAL_THREAD_ID       0
  14
  15 ModelChecker *model;
  16
  17 /** @brief Constructor */
  18 ModelChecker::ModelChecker()
  19         :
  20         /* Initialize default scheduler */
  21         scheduler(new Scheduler()),
  22         /* First thread created will have id INITIAL_THREAD_ID */
  23         next_thread_id(INITIAL_THREAD_ID),
  24         used_sequence_numbers(0),
  25
  26         num_executions(0),
  27         current_action(NULL),
  28         diverge(NULL),
  29         nextThread(THREAD_ID_T_NONE),
  30         action_trace(new action_list_t()),
  31         thread_map(new HashTable<int, Thread *, int>()),
  32         obj_map(new HashTable<const void *, action_list_t, uintptr_t, 4>()),
  33         obj_thrd_map(new HashTable<void *, std::vector<action_list_t>, uintptr_t, 4 >()),
  34         promises(new std::vector<Promise *>()),
  35         thrd_last_action(new std::vector<ModelAction *>(1)),
  36         node_stack(new NodeStack()),
  37         next_backtrack(NULL),
  38         cyclegraph(new CycleGraph()),
  39         failed_promise(false)
  40 {
  41 }
  42
  43 /** @brief Destructor */
  44 ModelChecker::~ModelChecker()
  45 {
  46         /*      std::map<int, Thread *>::iterator it;
  47         for (it = thread_map->begin(); it != thread_map->end(); it++)
  48         delete (*it).second;*/
  49         delete thread_map;
  50
  51         delete obj_thrd_map;
  52         delete obj_map;
  53         delete action_trace;
  54         delete thrd_last_action;
  55         delete node_stack;
  56         delete scheduler;
  57         delete cyclegraph;
  58 }
  59
  60 /**
  61  * Restores user program to initial state and resets all model-checker data
  62  * structures.
  63  */
  64 void ModelChecker::reset_to_initial_state()
  65 {
  66         DEBUG("+++ Resetting to initial state +++\n");
  67         node_stack->reset_execution();
  68         current_action = NULL;
  69         next_thread_id = INITIAL_THREAD_ID;
  70         used_sequence_numbers = 0;
  71         nextThread = 0;
  72         next_backtrack = NULL;
  73         failed_promise = false;
  74         snapshotObject->backTrackBeforeStep(0);
  75 }
  76
  77 /** @returns a thread ID for a new Thread */
  78 thread_id_t ModelChecker::get_next_id()
  79 {
  80         return next_thread_id++;
  81 }
  82
  83 /** @returns the number of user threads created during this execution */
  84 int ModelChecker::get_num_threads()
  85 {
  86         return next_thread_id;
  87 }
  88
  89 /** @returns a sequence number for a new ModelAction */
  90 modelclock_t ModelChecker::get_next_seq_num()
  91 {
  92         return ++used_sequence_numbers;
  93 }
  94
  95 /**
  96  * Performs the "scheduling" for the model-checker. That is, it checks if the
  97  * model-checker has selected a "next thread to run" and returns it, if
  98  * available. This function should be called from the Scheduler routine, where
  99  * the Scheduler falls back to a default scheduling routine if needed.
 100  *
 101  * @return The next thread chosen by the model-checker. If the model-checker
 102  * makes no selection, retuns NULL.
 103  */
 104 Thread * ModelChecker::schedule_next_thread()
 105 {
 106         Thread *t;
 107         if (nextThread == THREAD_ID_T_NONE)
 108                 return NULL;
 109         t = thread_map->get(id_to_int(nextThread));
 110
 111         ASSERT(t != NULL);
 112
 113         return t;
 114 }
 115
 116 /**
 117  * Choose the next thread in the replay sequence.
 118  *
 119  * If the replay sequence has reached the 'diverge' point, returns a thread
 120  * from the backtracking set. Otherwise, simply returns the next thread in the
 121  * sequence that is being replayed.
 122  */
 123 thread_id_t ModelChecker::get_next_replay_thread()
 124 {
 125         thread_id_t tid;
 126
 127         /* Have we completed exploring the preselected path? */
 128         if (diverge == NULL)
 129                 return THREAD_ID_T_NONE;
 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_read_from()) {
 138                         /* The next node will read from a different value. */
 139                         tid = next->get_tid();
 140                         node_stack->pop_restofstack(2);
 141                 } else if (nextnode->increment_future_values()) {
 142                         /* The next node will try to read from a different future value. */
 143                         tid = next->get_tid();
 144                         node_stack->pop_restofstack(2);
 145                 } else {
 146                         /* Make a different thread execute for next step */
 147                         Node *node = nextnode->get_parent();
 148                         tid = node->get_next_backtrack();
 149                         node_stack->pop_restofstack(1);
 150                 }
 151                 DEBUG("*** Divergence point ***\n");
 152                 diverge = NULL;
 153         } else {
 154                 tid = next->get_tid();
 155         }
 156         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 157         return tid;
 158 }
 159
 160 /**
 161  * Queries the model-checker for more executions to explore and, if one
 162  * exists, resets the model-checker state to execute a new execution.
 163  *
 164  * @return If there are more executions to explore, return true. Otherwise,
 165  * return false.
 166  */
 167 bool ModelChecker::next_execution()
 168 {
 169         DBG();
 170
 171         num_executions++;
 172
 173         if (isfeasible() || DBG_ENABLED())
 174                 print_summary();
 175
 176         if ((diverge = model->get_next_backtrack()) == NULL)
 177                 return false;
 178
 179         if (DBG_ENABLED()) {
 180                 printf("Next execution will diverge at:\n");
 181                 diverge->print();
 182         }
 183
 184         model->reset_to_initial_state();
 185         return true;
 186 }
 187
 188 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 189 {
 190         action_type type = act->get_type();
 191
 192         switch (type) {
 193                 case ATOMIC_READ:
 194                 case ATOMIC_WRITE:
 195                 case ATOMIC_RMW:
 196                         break;
 197                 default:
 198                         return NULL;
 199         }
 200         /* linear search: from most recent to oldest */
 201         action_list_t *list = obj_map->ensureptr(act->get_location());
 202         action_list_t::reverse_iterator rit;
 203         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 204                 ModelAction *prev = *rit;
 205                 if (act->is_synchronizing(prev))
 206                         return prev;
 207         }
 208         return NULL;
 209 }
 210
 211 void ModelChecker::set_backtracking(ModelAction *act)
 212 {
 213         ModelAction *prev;
 214         Node *node;
 215         Thread *t = get_thread(act->get_tid());
 216
 217         prev = get_last_conflict(act);
 218         if (prev == NULL)
 219                 return;
 220
 221         node = prev->get_node()->get_parent();
 222
 223         while (!node->is_enabled(t))
 224                 t = t->get_parent();
 225
 226         /* Check if this has been explored already */
 227         if (node->has_been_explored(t->get_id()))
 228                 return;
 229
 230         /* Cache the latest backtracking point */
 231         if (!next_backtrack || *prev > *next_backtrack)
 232                 next_backtrack = prev;
 233
 234         /* If this is a new backtracking point, mark the tree */
 235         if (!node->set_backtrack(t->get_id()))
 236                 return;
 237         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 238                         prev->get_tid(), t->get_id());
 239         if (DBG_ENABLED()) {
 240                 prev->print();
 241                 act->print();
 242         }
 243 }
 244
 245 /**
 246  * Returns last backtracking point. The model checker will explore a different
 247  * path for this point in the next execution.
 248  * @return The ModelAction at which the next execution should diverge.
 249  */
 250 ModelAction * ModelChecker::get_next_backtrack()
 251 {
 252         ModelAction *next = next_backtrack;
 253         next_backtrack = NULL;
 254         return next;
 255 }
 256
 257 void ModelChecker::check_current_action(void)
 258 {
 259         ModelAction *curr = this->current_action;
 260         bool already_added = false;
 261         this->current_action = NULL;
 262         if (!curr) {
 263                 DEBUG("trying to push NULL action...\n");
 264                 return;
 265         }
 266
 267         if (curr->is_rmwc()||curr->is_rmw()) {
 268                 ModelAction *tmp=process_rmw(curr);
 269                 already_added = true;
 270                 delete curr;
 271                 curr=tmp;
 272         } else {
 273                 ModelAction * tmp = node_stack->explore_action(curr);
 274                 if (tmp) {
 275                         /* Discard duplicate ModelAction; use action from NodeStack */
 276                         /* First restore type and order in case of RMW operation */
 277                         if (curr->is_rmwr())
 278                                 tmp->copy_typeandorder(curr);
 279                         delete curr;
 280                         curr = tmp;
 281                 } else {
 282                         /*
 283                          * Perform one-time actions when pushing new ModelAction onto
 284                          * NodeStack
 285                          */
 286                         curr->create_cv(get_parent_action(curr->get_tid()));
 287                         /* Build may_read_from set */
 288                         if (curr->is_read())
 289                                 build_reads_from_past(curr);
 290                 }
 291         }
 292
 293         /* Assign 'creation' parent */
 294         if (curr->get_type() == THREAD_CREATE) {
 295                 Thread *th = (Thread *)curr->get_location();
 296                 th->set_creation(curr);
 297         }
 298
 299         /* Deal with new thread */
 300         if (curr->get_type() == THREAD_START) {
 301                 check_promises(NULL, curr->get_cv());
 302         }
 303
 304         /* Assign reads_from values */
 305         Thread *th = get_thread(curr->get_tid());
 306         uint64_t value = VALUE_NONE;
 307         if (curr->is_read()) {
 308                 const ModelAction *reads_from = curr->get_node()->get_read_from();
 309                 if (reads_from!=NULL) {
 310                         value = reads_from->get_value();
 311                         /* Assign reads_from, perform release/acquire synchronization */
 312                         curr->read_from(reads_from);
 313                         r_modification_order(curr,reads_from);
 314                 } else {
 315                         /* Read from future value */
 316                         value = curr->get_node()->get_future_value();
 317                         curr->read_from(NULL);
 318                         Promise * valuepromise=new Promise(curr, value);
 319                         promises->push_back(valuepromise);
 320                 }
 321         } else if (curr->is_write()) {
 322                 w_modification_order(curr);
 323         }
 324
 325         th->set_return_value(value);
 326
 327         /* Add action to list.  */
 328         if (!already_added)
 329                 add_action_to_lists(curr);
 330
 331         /* Is there a better interface for setting the next thread rather
 332                  than this field/convoluted approach?  Perhaps like just returning
 333                  it or something? */
 334
 335         /* Do not split atomic actions. */
 336         if (curr->is_rmwr()) {
 337                 nextThread = thread_current()->get_id();
 338         } else {
 339                 nextThread = get_next_replay_thread();
 340         }
 341
 342         Node *currnode = curr->get_node();
 343         Node *parnode = currnode->get_parent();
 344
 345         if (!parnode->backtrack_empty()||!currnode->readsfrom_empty()||!currnode->futurevalues_empty())
 346                 if (!next_backtrack || *curr > *next_backtrack)
 347                         next_backtrack = curr;
 348
 349         set_backtracking(curr);
 350 }
 351
 352 /** @returns whether the current trace is feasible. */
 353 bool ModelChecker::isfeasible() {
 354         return !cyclegraph->checkForCycles() && !failed_promise;
 355 }
 356
 357 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
 358 ModelAction * ModelChecker::process_rmw(ModelAction * act) {
 359         int tid = id_to_int(act->get_tid());
 360         ModelAction *lastread=get_last_action(tid);
 361         lastread->process_rmw(act);
 362         if (act->is_rmw())
 363                 cyclegraph->addRMWEdge(lastread, lastread->get_reads_from());
 364         return lastread;
 365 }
 366
 367 /**
 368  * Updates the cyclegraph with the constraints imposed from the current read.
 369  * @param curr The current action. Must be a read.
 370  * @param rf The action that curr reads from. Must be a write.
 371  */
 372 void ModelChecker::r_modification_order(ModelAction * curr, const ModelAction *rf) {
 373         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 374         unsigned int i;
 375         ASSERT(curr->is_read());
 376
 377         /* Iterate over all threads */
 378         for (i = 0; i < thrd_lists->size(); i++) {
 379                 /* Iterate over actions in thread, starting from most recent */
 380                 action_list_t *list = &(*thrd_lists)[i];
 381                 action_list_t::reverse_iterator rit;
 382                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 383                         ModelAction *act = *rit;
 384
 385                         /* Include at most one act per-thread that "happens before" curr */
 386                         if (act->happens_before(curr)) {
 387                                 if (act->is_read()) {
 388                                         const ModelAction * prevreadfrom=act->get_reads_from();
 389                                         if (rf!=prevreadfrom)
 390                                                 cyclegraph->addEdge(rf, prevreadfrom);
 391                                 } else if (rf!=act) {
 392                                         cyclegraph->addEdge(rf, act);
 393                                 }
 394                                 break;
 395                         }
 396                 }
 397         }
 398 }
 399
 400 /**
 401  * Updates the cyclegraph with the constraints imposed from the current write.
 402  * @param curr The current action. Must be a write.
 403  */
 404 void ModelChecker::w_modification_order(ModelAction * curr) {
 405         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 406         unsigned int i;
 407         ASSERT(curr->is_write());
 408
 409         if (curr->is_seqcst()) {
 410                 /* We have to at least see the last sequentially consistent write,
 411                          so we are initialized. */
 412                 ModelAction * last_seq_cst=get_last_seq_cst(curr->get_location());
 413                 if (last_seq_cst!=NULL)
 414                         cyclegraph->addEdge(curr, last_seq_cst);
 415         }
 416
 417         /* Iterate over all threads */
 418         for (i = 0; i < thrd_lists->size(); i++) {
 419                 /* Iterate over actions in thread, starting from most recent */
 420                 action_list_t *list = &(*thrd_lists)[i];
 421                 action_list_t::reverse_iterator rit;
 422                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 423                         ModelAction *act = *rit;
 424
 425                         /* Include at most one act per-thread that "happens before" curr */
 426                         if (act->happens_before(curr)) {
 427                                 if (act->is_read()) {
 428                                         cyclegraph->addEdge(curr, act->get_reads_from());
 429                                 } else
 430                                         cyclegraph->addEdge(curr, act);
 431                                 break;
 432                         } else {
 433                                 if (act->is_read()&&!act->is_synchronizing(curr)&&!act->same_thread(curr)) {
 434                                         /* We have an action that:
 435                                                  (1) did not happen before us
 436                                                  (2) is a read and we are a write
 437                                                  (3) cannot synchronize with us
 438                                                  (4) is in a different thread
 439                                                  =>
 440                                                  that read could potentially read from our write.
 441                                         */
 442
 443                                         if (act->get_node()->add_future_value(curr->get_value())&&
 444                                                         (!next_backtrack || *act > * next_backtrack))
 445                                                 next_backtrack = act;
 446                                 }
 447                         }
 448                 }
 449         }
 450 }
 451
 452 /**
 453  * Performs various bookkeeping operations for the current ModelAction. For
 454  * instance, adds action to the per-object, per-thread action vector and to the
 455  * action trace list of all thread actions.
 456  *
 457  * @param act is the ModelAction to add.
 458  */
 459 void ModelChecker::add_action_to_lists(ModelAction *act)
 460 {
 461         int tid = id_to_int(act->get_tid());
 462         action_trace->push_back(act);
 463
 464         obj_map->ensureptr(act->get_location())->push_back(act);
 465
 466         std::vector<action_list_t> *vec = obj_thrd_map->ensureptr(act->get_location());
 467         if (tid >= (int)vec->size())
 468                 vec->resize(next_thread_id);
 469         (*vec)[tid].push_back(act);
 470
 471         if ((int)thrd_last_action->size() <= tid)
 472                 thrd_last_action->resize(get_num_threads());
 473         (*thrd_last_action)[tid] = act;
 474 }
 475
 476 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 477 {
 478         int nthreads = get_num_threads();
 479         if ((int)thrd_last_action->size() < nthreads)
 480                 thrd_last_action->resize(nthreads);
 481         return (*thrd_last_action)[id_to_int(tid)];
 482 }
 483
 484 /**
 485  * Gets the last memory_order_seq_cst action (in the total global sequence)
 486  * performed on a particular object (i.e., memory location).
 487  * @param location The object location to check
 488  * @return The last seq_cst action performed
 489  */
 490 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 491 {
 492         action_list_t *list = obj_map->ensureptr(location);
 493         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 494         action_list_t::reverse_iterator rit;
 495         for (rit = list->rbegin(); rit != list->rend(); rit++)
 496                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 497                         return *rit;
 498         return NULL;
 499 }
 500
 501 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 502 {
 503         ModelAction *parent = get_last_action(tid);
 504         if (!parent)
 505                 parent = get_thread(tid)->get_creation();
 506         return parent;
 507 }
 508
 509 /**
 510  * Returns the clock vector for a given thread.
 511  * @param tid The thread whose clock vector we want
 512  * @return Desired clock vector
 513  */
 514 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
 515         return get_parent_action(tid)->get_cv();
 516 }
 517
 518 /** Checks promises in response to change in ClockVector Threads. */
 519
 520 void ModelChecker::check_promises(ClockVector *old_cv, ClockVector * merge_cv) {
 521         for(unsigned int i=0;i<promises->size();i++) {
 522                 Promise * promise=(*promises)[i];
 523                 const ModelAction * act=promise->get_action();
 524                 if ((old_cv==NULL||!old_cv->synchronized_since(act))&&
 525                                 merge_cv->synchronized_since(act)) {
 526                         //This thread is no longer able to send values back to satisfy the promise
 527                         int num_synchronized_threads=promise->increment_threads();
 528                         if (num_synchronized_threads==model->get_num_threads()) {
 529                                 //Promise has failed
 530                                 failed_promise = true;
 531                                 return;
 532                         }
 533                 }
 534         }
 535 }
 536
 537 /**
 538  * Build up an initial set of all past writes that this 'read' action may read
 539  * from. This set is determined by the clock vector's "happens before"
 540  * relationship.
 541  * @param curr is the current ModelAction that we are exploring; it must be a
 542  * 'read' operation.
 543  */
 544 void ModelChecker::build_reads_from_past(ModelAction *curr)
 545 {
 546         std::vector<action_list_t> *thrd_lists = obj_thrd_map->ensureptr(curr->get_location());
 547         unsigned int i;
 548         ASSERT(curr->is_read());
 549
 550         ModelAction *last_seq_cst = NULL;
 551
 552         /* Track whether this object has been initialized */
 553         bool initialized = false;
 554
 555         if (curr->is_seqcst()) {
 556                 last_seq_cst = get_last_seq_cst(curr->get_location());
 557                 /* We have to at least see the last sequentially consistent write,
 558                          so we are initialized. */
 559                 if (last_seq_cst != NULL)
 560                         initialized = true;
 561         }
 562
 563         /* Iterate over all threads */
 564         for (i = 0; i < thrd_lists->size(); i++) {
 565                 /* Iterate over actions in thread, starting from most recent */
 566                 action_list_t *list = &(*thrd_lists)[i];
 567                 action_list_t::reverse_iterator rit;
 568                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 569                         ModelAction *act = *rit;
 570
 571                         /* Only consider 'write' actions */
 572                         if (!act->is_write())
 573                                 continue;
 574
 575                         /* Don't consider more than one seq_cst write if we are a seq_cst read. */
 576                         if (!act->is_seqcst() || !curr->is_seqcst() || act == last_seq_cst) {
 577                                 DEBUG("Adding action to may_read_from:\n");
 578                                 if (DBG_ENABLED()) {
 579                                         act->print();
 580                                         curr->print();
 581                                 }
 582                                 curr->get_node()->add_read_from(act);
 583                         }
 584
 585                         /* Include at most one act per-thread that "happens before" curr */
 586                         if (act->happens_before(curr)) {
 587                                 initialized = true;
 588                                 break;
 589                         }
 590                 }
 591         }
 592
 593         if (!initialized) {
 594                 /** @todo Need a more informative way of reporting errors. */
 595                 printf("ERROR: may read from uninitialized atomic\n");
 596         }
 597
 598         if (DBG_ENABLED() || !initialized) {
 599                 printf("Reached read action:\n");
 600                 curr->print();
 601                 printf("Printing may_read_from\n");
 602                 curr->get_node()->print_may_read_from();
 603                 printf("End printing may_read_from\n");
 604         }
 605
 606         ASSERT(initialized);
 607 }
 608
 609 static void print_list(action_list_t *list)
 610 {
 611         action_list_t::iterator it;
 612
 613         printf("---------------------------------------------------------------------\n");
 614         printf("Trace:\n");
 615
 616         for (it = list->begin(); it != list->end(); it++) {
 617                 (*it)->print();
 618         }
 619         printf("---------------------------------------------------------------------\n");
 620 }
 621
 622 void ModelChecker::print_summary(void)
 623 {
 624         printf("\n");
 625         printf("Number of executions: %d\n", num_executions);
 626         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 627
 628         scheduler->print();
 629
 630         if (!isfeasible())
 631                 printf("INFEASIBLE EXECUTION!\n");
 632         print_list(action_trace);
 633         printf("\n");
 634 }
 635
 636 int ModelChecker::add_thread(Thread *t)
 637 {
 638         thread_map->put(id_to_int(t->get_id()), t);
 639         scheduler->add_thread(t);
 640         return 0;
 641 }
 642
 643 void ModelChecker::remove_thread(Thread *t)
 644 {
 645         scheduler->remove_thread(t);
 646 }
 647
 648 /**
 649  * Switch from a user-context to the "master thread" context (a.k.a. system
 650  * context). This switch is made with the intention of exploring a particular
 651  * model-checking action (described by a ModelAction object). Must be called
 652  * from a user-thread context.
 653  * @param act The current action that will be explored. May be NULL, although
 654  * there is little reason to switch to the model-checker without an action to
 655  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 656  * yield control without performing any progress; see thrd_join()).
 657  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 658  */
 659 int ModelChecker::switch_to_master(ModelAction *act)
 660 {
 661         DBG();
 662         Thread * old = thread_current();
 663         set_current_action(act);
 664         old->set_state(THREAD_READY);
 665         return Thread::swap(old, get_system_context());
 666 }