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                 node_stack->pop_restofstack();
 136         } else {
 137                 tid = next->get_tid();
 138         }
 139         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 140         return tid;
 141 }
 142
 143 /**
 144  * Queries the model-checker for more executions to explore and, if one
 145  * exists, resets the model-checker state to execute a new execution.
 146  *
 147  * @return If there are more executions to explore, return true. Otherwise,
 148  * return false.
 149  */
 150 bool ModelChecker::next_execution()
 151 {
 152         DBG();
 153
 154         num_executions++;
 155         print_summary();
 156         if ((diverge = model->get_next_backtrack()) == NULL)
 157                 return false;
 158
 159         if (DBG_ENABLED()) {
 160                 printf("Next execution will diverge at:\n");
 161                 diverge->print();
 162         }
 163
 164         model->reset_to_initial_state();
 165         return true;
 166 }
 167
 168 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 169 {
 170         action_type type = act->get_type();
 171
 172         switch (type) {
 173                 case ATOMIC_READ:
 174                 case ATOMIC_WRITE:
 175                 case ATOMIC_RMW:
 176                         break;
 177                 default:
 178                         return NULL;
 179         }
 180         /* linear search: from most recent to oldest */
 181         action_list_t *list = &(*obj_map)[act->get_location()];
 182         action_list_t::reverse_iterator rit;
 183         for (rit = list->rbegin(); rit != list->rend(); rit++) {
 184                 ModelAction *prev = *rit;
 185                 if (act->is_synchronizing(prev))
 186                         return prev;
 187         }
 188         return NULL;
 189 }
 190
 191 void ModelChecker::set_backtracking(ModelAction *act)
 192 {
 193         ModelAction *prev;
 194         Node *node;
 195         Thread *t = get_thread(act->get_tid());
 196
 197         prev = get_last_conflict(act);
 198         if (prev == NULL)
 199                 return;
 200
 201         node = prev->get_node()->get_parent();
 202
 203         while (!node->is_enabled(t))
 204                 t = t->get_parent();
 205
 206         /* Check if this has been explored already */
 207         if (node->has_been_explored(t->get_id()))
 208                 return;
 209
 210         /* Cache the latest backtracking point */
 211         if (!next_backtrack || *prev > *next_backtrack)
 212                 next_backtrack = prev;
 213
 214         /* If this is a new backtracking point, mark the tree */
 215         if (!node->set_backtrack(t->get_id()))
 216                 return;
 217         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 218                         prev->get_tid(), t->get_id());
 219         if (DBG_ENABLED()) {
 220                 prev->print();
 221                 act->print();
 222         }
 223 }
 224
 225 ModelAction * ModelChecker::get_next_backtrack()
 226 {
 227         ModelAction *next = next_backtrack;
 228         next_backtrack = NULL;
 229         return next;
 230 }
 231
 232 void ModelChecker::check_current_action(void)
 233 {
 234         Node *currnode;
 235
 236         ModelAction *curr = this->current_action;
 237         ModelAction *tmp;
 238         current_action = NULL;
 239         if (!curr) {
 240                 DEBUG("trying to push NULL action...\n");
 241                 return;
 242         }
 243
 244         tmp = node_stack->explore_action(curr);
 245         if (tmp) {
 246                 /* Discard duplicate ModelAction; use action from NodeStack */
 247                 delete curr;
 248                 curr = tmp;
 249         } else {
 250                 /*
 251                  * Perform one-time actions when pushing new ModelAction onto
 252                  * NodeStack
 253                  */
 254                 curr->create_cv(get_parent_action(curr->get_tid()));
 255                 /* Build may_read_from set */
 256                 if (curr->is_read())
 257                         build_reads_from_past(curr);
 258         }
 259
 260         /* Assign 'creation' parent */
 261         if (curr->get_type() == THREAD_CREATE) {
 262                 Thread *th = (Thread *)curr->get_location();
 263                 th->set_creation(curr);
 264         }
 265
 266         nextThread = get_next_replay_thread();
 267
 268         currnode = curr->get_node()->get_parent();
 269
 270         if (!currnode->backtrack_empty())
 271                 if (!next_backtrack || *curr > *next_backtrack)
 272                         next_backtrack = curr;
 273
 274         set_backtracking(curr);
 275
 276         add_action_to_lists(curr);
 277
 278         /* Assign reads_from values */
 279         /* TODO: perform release/acquire synchronization here; include
 280          * reads_from as ModelAction member? */
 281         Thread *th = get_thread(curr->get_tid());
 282         uint64_t value = VALUE_NONE;
 283         if (curr->is_read()) {
 284                 const ModelAction *reads_from = curr->get_node()->get_next_read_from();
 285                 value = reads_from->get_value();
 286                 /* Assign reads_from, perform release/acquire synchronization */
 287                 curr->read_from(reads_from);
 288         }
 289         th->set_return_value(value);
 290 }
 291
 292 /**
 293  * Performs various bookkeeping operations for the current ModelAction. For
 294  * instance, adds action to the per-object, per-thread action vector and to the
 295  * action trace list of all thread actions.
 296  *
 297  * @param act is the ModelAction to add.
 298  */
 299 void ModelChecker::add_action_to_lists(ModelAction *act)
 300 {
 301         int tid = id_to_int(act->get_tid());
 302         action_trace->push_back(act);
 303
 304         (*obj_map)[act->get_location()].push_back(act);
 305
 306         std::vector<action_list_t> *vec = &(*obj_thrd_map)[act->get_location()];
 307         if (tid >= (int)vec->size())
 308                 vec->resize(next_thread_id);
 309         (*vec)[tid].push_back(act);
 310
 311         if ((int)thrd_last_action->size() <= tid)
 312                 thrd_last_action->resize(get_num_threads());
 313         (*thrd_last_action)[tid] = act;
 314 }
 315
 316 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 317 {
 318         int nthreads = get_num_threads();
 319         if ((int)thrd_last_action->size() < nthreads)
 320                 thrd_last_action->resize(nthreads);
 321         return (*thrd_last_action)[id_to_int(tid)];
 322 }
 323
 324 /**
 325  * Gets the last memory_order_seq_cst action (in the total global sequence)
 326  * performed on a particular object (i.e., memory location).
 327  * @param location The object location to check
 328  * @return The last seq_cst action performed
 329  */
 330 ModelAction * ModelChecker::get_last_seq_cst(const void *location)
 331 {
 332         action_list_t *list = &(*obj_map)[location];
 333         /* Find: max({i in dom(S) | seq_cst(t_i) && isWrite(t_i) && samevar(t_i, t)}) */
 334         action_list_t::reverse_iterator rit;
 335         for (rit = list->rbegin(); rit != list->rend(); rit++)
 336                 if ((*rit)->is_write() && (*rit)->is_seqcst())
 337                         return *rit;
 338         return NULL;
 339 }
 340
 341 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 342 {
 343         ModelAction *parent = get_last_action(tid);
 344         if (!parent)
 345                 parent = get_thread(tid)->get_creation();
 346         return parent;
 347 }
 348
 349 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
 350         return get_parent_action(tid)->get_cv();
 351 }
 352
 353 /**
 354  * Build up an initial set of all past writes that this 'read' action may read
 355  * from. This set is determined by the clock vector's "happens before"
 356  * relationship.
 357  * @param curr is the current ModelAction that we are exploring; it must be a
 358  * 'read' operation.
 359  */
 360 void ModelChecker::build_reads_from_past(ModelAction *curr)
 361 {
 362         std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
 363         unsigned int i;
 364
 365         ASSERT(curr->is_read());
 366
 367         ModelAction *last_seq_cst = NULL;
 368
 369         /* Track whether this object has been initialized */
 370         bool initialized = false;
 371
 372         if (curr->is_seqcst()) {
 373                 last_seq_cst = get_last_seq_cst(curr->get_location());
 374                 /* We have to at least see the last sequentially consistent write,
 375                          so we are initialized. */
 376                 if (last_seq_cst != NULL)
 377                         initialized = true;
 378         }
 379
 380         /* Iterate over all threads */
 381         for (i = 0; i < thrd_lists->size(); i++) {
 382                 /* Iterate over actions in thread, starting from most recent */
 383                 action_list_t *list = &(*thrd_lists)[i];
 384                 action_list_t::reverse_iterator rit;
 385                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 386                         ModelAction *act = *rit;
 387
 388                         /* Only consider 'write' actions */
 389                         if (!act->is_write())
 390                                 continue;
 391
 392                         /* Don't consider more than one seq_cst write */
 393                         if (!act->is_seqcst() || act == last_seq_cst) {
 394                                 DEBUG("Adding action to may_read_from:\n");
 395                                 if (DBG_ENABLED()) {
 396                                         act->print();
 397                                         curr->print();
 398                                 }
 399                                 curr->get_node()->add_read_from(act);
 400                         }
 401
 402                         /* Include at most one act per-thread that "happens before" curr */
 403                         if (act->happens_before(curr)) {
 404                                 initialized = true;
 405                                 break;
 406                         }
 407                 }
 408         }
 409
 410         if (!initialized) {
 411                 /* TODO: need a more informative way of reporting errors */
 412                 printf("ERROR: may read from uninitialized atomic\n");
 413         }
 414
 415         if (DBG_ENABLED() || !initialized) {
 416                 printf("Reached read action:\n");
 417                 curr->print();
 418                 printf("Printing may_read_from\n");
 419                 curr->get_node()->print_may_read_from();
 420                 printf("End printing may_read_from\n");
 421         }
 422
 423         ASSERT(initialized);
 424 }
 425
 426 static void print_list(action_list_t *list)
 427 {
 428         action_list_t::iterator it;
 429
 430         printf("---------------------------------------------------------------------\n");
 431         printf("Trace:\n");
 432
 433         for (it = list->begin(); it != list->end(); it++) {
 434                 (*it)->print();
 435         }
 436         printf("---------------------------------------------------------------------\n");
 437 }
 438
 439 void ModelChecker::print_summary(void)
 440 {
 441         printf("\n");
 442         printf("Number of executions: %d\n", num_executions);
 443         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 444
 445         scheduler->print();
 446
 447         print_list(action_trace);
 448         printf("\n");
 449 }
 450
 451 int ModelChecker::add_thread(Thread *t)
 452 {
 453         (*thread_map)[id_to_int(t->get_id())] = t;
 454         scheduler->add_thread(t);
 455         return 0;
 456 }
 457
 458 void ModelChecker::remove_thread(Thread *t)
 459 {
 460         scheduler->remove_thread(t);
 461 }
 462
 463 /**
 464  * Switch from a user-context to the "master thread" context (a.k.a. system
 465  * context). This switch is made with the intention of exploring a particular
 466  * model-checking action (described by a ModelAction object). Must be called
 467  * from a user-thread context.
 468  * @param act The current action that will be explored. May be NULL, although
 469  * there is little reason to switch to the model-checker without an action to
 470  * explore (note: act == NULL is sometimes used as a hack to allow a thread to
 471  * yield control without performing any progress; see thrd_join()).
 472  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
 473  */
 474 int ModelChecker::switch_to_master(ModelAction *act)
 475 {
 476         Thread *old;
 477
 478         DBG();
 479         old = thread_current();
 480         set_current_action(act);
 481         old->set_state(THREAD_READY);
 482         return Thread::swap(old, get_system_context());
 483 }