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 *node = next->get_node()->get_parent();
 130
 131                 /* Reached divergence point */
 132                 DEBUG("*** Divergence point ***\n");
 133                 tid = node->get_next_backtrack();
 134                 diverge = NULL;
 135         } else {
 136                 tid = next->get_tid();
 137         }
 138         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 139         return tid;
 140 }
 141
 142 /**
 143  * Queries the model-checker for more executions to explore and, if one
 144  * exists, resets the model-checker state to execute a new execution.
 145  *
 146  * @return If there are more executions to explore, return true. Otherwise,
 147  * return false.
 148  */
 149 bool ModelChecker::next_execution()
 150 {
 151         DBG();
 152
 153         num_executions++;
 154         print_summary();
 155         if ((diverge = model->get_next_backtrack()) == NULL)
 156                 return false;
 157
 158         if (DBG_ENABLED()) {
 159                 printf("Next execution will diverge at:\n");
 160                 diverge->print();
 161         }
 162
 163         model->reset_to_initial_state();
 164         return true;
 165 }
 166
 167 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 168 {
 169         action_type type = act->get_type();
 170
 171         switch (type) {
 172                 case ATOMIC_READ:
 173                 case ATOMIC_WRITE:
 174                 case ATOMIC_RMW:
 175                         break;
 176                 default:
 177                         return NULL;
 178         }
 179         /* linear search: from most recent to oldest */
 180         action_list_t *list = &(*obj_map)[act->get_location()];
 181         action_list_t::reverse_iterator rit;
 182         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 183                 ModelAction *prev = *rit;
 184                 if (act->is_synchronizing(prev))
 185                         return prev;
 186         }
 187         return NULL;
 188 }
 189
 190 void ModelChecker::set_backtracking(ModelAction *act)
 191 {
 192         ModelAction *prev;
 193         Node *node;
 194         Thread *t = get_thread(act->get_tid());
 195
 196         prev = get_last_conflict(act);
 197         if (prev == NULL)
 198                 return;
 199
 200         node = prev->get_node()->get_parent();
 201
 202         while (!node->is_enabled(t))
 203                 t = t->get_parent();
 204
 205         /* Check if this has been explored already */
 206         if (node->has_been_explored(t->get_id()))
 207                 return;
 208
 209         /* Cache the latest backtracking point */
 210         if (!next_backtrack || *prev > *next_backtrack)
 211                 next_backtrack = prev;
 212
 213         /* If this is a new backtracking point, mark the tree */
 214         if (!node->set_backtrack(t->get_id()))
 215                 return;
 216         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 217                         prev->get_tid(), t->get_id());
 218         if (DBG_ENABLED()) {
 219                 prev->print();
 220                 act->print();
 221         }
 222 }
 223
 224 ModelAction * ModelChecker::get_next_backtrack()
 225 {
 226         ModelAction *next = next_backtrack;
 227         next_backtrack = NULL;
 228         return next;
 229 }
 230
 231 void ModelChecker::check_current_action(void)
 232 {
 233         Node *currnode;
 234
 235         ModelAction *curr = this->current_action;
 236         ModelAction *tmp;
 237         current_action = NULL;
 238         if (!curr) {
 239                 DEBUG("trying to push NULL action...\n");
 240                 return;
 241         }
 242
 243         tmp = node_stack->explore_action(curr);
 244         if (tmp) {
 245                 /* Discard duplicate ModelAction; use action from NodeStack */
 246                 delete curr;
 247                 curr = tmp;
 248         } else {
 249                 /*
 250                  * Perform one-time actions when pushing new ModelAction onto
 251                  * NodeStack
 252                  */
 253                 curr->create_cv(get_parent_action(curr->get_tid()));
 254                 /* Build may_read_from set */
 255                 if (curr->is_read())
 256                         build_reads_from_past(curr);
 257         }
 258
 259         /* Assign 'creation' parent */
 260         if (curr->get_type() == THREAD_CREATE) {
 261                 Thread *th = (Thread *)curr->get_location();
 262                 th->set_creation(curr);
 263         }
 264
 265         nextThread = get_next_replay_thread();
 266
 267         currnode = curr->get_node()->get_parent();
 268
 269         if (!currnode->backtrack_empty())
 270                 if (!next_backtrack || *curr > *next_backtrack)
 271                         next_backtrack = curr;
 272
 273         set_backtracking(curr);
 274
 275         add_action_to_lists(curr);
 276
 277         /* Assign reads_from values */
 278         /* TODO: perform release/acquire synchronization here; include
 279          * reads_from as ModelAction member? */
 280         Thread *th = get_thread(curr->get_tid());
 281         int value = VALUE_NONE;
 282         if (curr->is_read()) {
 283                 const ModelAction *reads_from = curr->get_node()->get_next_read_from();
 284                 value = reads_from->get_value();
 285                 /* Assign reads_from, perform release/acquire synchronization */
 286                 curr->read_from(reads_from);
 287         }
 288         th->set_return_value(value);
 289 }
 290
 291 /**
 292  * Performs various bookkeeping operations for the current ModelAction. For
 293  * instance, adds action to the per-object, per-thread action vector and to the
 294  * action trace list of all thread actions.
 295  *
 296  * @param act is the ModelAction to add.
 297  */
 298 void ModelChecker::add_action_to_lists(ModelAction *act)
 299 {
 300         int tid = id_to_int(act->get_tid());
 301         action_trace->push_back(act);
 302
 303         (*obj_map)[act->get_location()].push_back(act);
 304
 305         std::vector<action_list_t> *vec = &(*obj_thrd_map)[act->get_location()];
 306         if (tid >= (int)vec->size())
 307                 vec->resize(next_thread_id);
 308         (*vec)[tid].push_back(act);
 309
 310         if ((int)thrd_last_action->size() <= tid)
 311                 thrd_last_action->resize(get_num_threads());
 312         (*thrd_last_action)[tid] = act;
 313 }
 314
 315 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 316 {
 317         int nthreads = get_num_threads();
 318         if ((int)thrd_last_action->size() < nthreads)
 319                 thrd_last_action->resize(nthreads);
 320         return (*thrd_last_action)[id_to_int(tid)];
 321 }
 322
 323 /**
 324  * Gets the last memory_order_seq_cst action (in the total global sequence)
 325  * performed on a particular object (i.e., memory location).
 326  * @param location The object location to check
 327  * @return The last seq_cst action performed
 328  */
 329 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 330 {
 331         action_list_t *list = &(*obj_map)[location];
 332         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 333         action_list_t::reverse_iterator rit;
 334         for (rit = list->rbegin(); rit != list->rend(); rit++)
 335                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 336                         return *rit;
 337         return NULL;
 338 }
 339
 340 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 341 {
 342         ModelAction *parent = get_last_action(tid);
 343         if (!parent)
 344                 parent = get_thread(tid)->get_creation();
 345         return parent;
 346 }
 347
 348 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
 349         return get_parent_action(tid)->get_cv();
 350 }
 351
 352 /**
 353  * Build up an initial set of all past writes that this 'read' action may read
 354  * from. This set is determined by the clock vector's "happens before"
 355  * relationship.
 356  * @param curr is the current ModelAction that we are exploring; it must be a
 357  * 'read' operation.
 358  */
 359 void ModelChecker::build_reads_from_past(ModelAction *curr)
 360 {
 361         std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
 362         unsigned int i;
 363
 364         ASSERT(curr->is_read());
 365
 366         ModelAction *last_seq_cst = NULL;
 367
 368         /* Track whether this object has been initialized */
 369         bool initialized = false;
 370
 371         if (curr->is_seqcst()) {
 372                 last_seq_cst = get_last_seq_cst(curr->get_location());
 373                 /* We have to at least see the last sequentially consistent write,
 374                          so we are initialized. */
 375                 if (last_seq_cst != NULL)
 376                         initialized = true;
 377         }
 378
 379         /* Iterate over all threads */
 380         for (i = 0; i < thrd_lists->size(); i++) {
 381                 /* Iterate over actions in thread, starting from most recent */
 382                 action_list_t *list = &(*thrd_lists)[i];
 383                 action_list_t::reverse_iterator rit;
 384                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 385                         ModelAction *act = *rit;
 386
 387                         /* Only consider 'write' actions */
 388                         if (!act->is_write())
 389                                 continue;
 390
 391                         /* Don't consider more than one seq_cst write */
 392                         if (!act->is_seqcst() || act == last_seq_cst) {
 393                                 DEBUG("Adding action to may_read_from:\n");
 394                                 if (DBG_ENABLED()) {
 395                                         act->print();
 396                                         curr->print();
 397                                 }
 398                                 curr->get_node()->add_read_from(act);
 399                         }
 400
 401                         /* Include at most one act per-thread that "happens before" curr */
 402                         if (act->happens_before(curr)) {
 403                                 initialized = true;
 404                                 break;
 405                         }
 406                 }
 407         }
 408
 409         if (!initialized) {
 410                 /* TODO: need a more informative way of reporting errors */
 411                 printf("ERROR: may read from uninitialized atomic\n");
 412         }
 413
 414         if (DBG_ENABLED() || !initialized) {
 415                 printf("Reached read action:\n");
 416                 curr->print();
 417                 printf("Printing may_read_from\n");
 418                 curr->get_node()->print_may_read_from();
 419                 printf("End printing may_read_from\n");
 420         }
 421
 422         ASSERT(initialized);
 423 }
 424
 425 static void print_list(action_list_t *list)
 426 {
 427         action_list_t::iterator it;
 428
 429         printf("---------------------------------------------------------------------\n");
 430         printf("Trace:\n");
 431
 432         for (it = list->begin(); it != list->end(); it++) {
 433                 (*it)->print();
 434         }
 435         printf("---------------------------------------------------------------------\n");
 436 }
 437
 438 void ModelChecker::print_summary(void)
 439 {
 440         printf("\n");
 441         printf("Number of executions: %d\n", num_executions);
 442         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 443
 444         scheduler->print();
 445
 446         print_list(action_trace);
 447         printf("\n");
 448 }
 449
 450 int ModelChecker::add_thread(Thread *t)
 451 {
 452         (*thread_map)[id_to_int(t->get_id())] = t;
 453         scheduler->add_thread(t);
 454         return 0;
 455 }
 456
 457 void ModelChecker::remove_thread(Thread *t)
 458 {
 459         scheduler->remove_thread(t);
 460 }
 461
 462 /**
 463  * Switch from a user-context to the "master thread" context (a.k.a. system
 464  * context). This switch is made with the intention of exploring a particular
 465  * model-checking action (described by a ModelAction object). Must be called
 466  * from a user-thread context.
 467  * @param act The current action that will be explored. May be NULL, although
 468  * there is little reason to switch to the model-checker without an action to
 469  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 470  * yield control without performing any progress; see thrd_join()).
 471  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 472  */
 473 int ModelChecker::switch_to_master(ModelAction *act)
 474 {
 475         Thread *old;
 476
 477         DBG();
 478         old = thread_current();
 479         set_current_action(act);
 480         old->set_state(THREAD_READY);
 481         return Thread::swap(old, get_system_context());
 482 }