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