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_thrd_map(new std::map<void *, std::vector<action_list_t> >()),
  31         thrd_last_action(new std::vector<ModelAction *>(1)),
  32         node_stack(new NodeStack()),
  33         next_backtrack(NULL)
  34 {
  35 }
  36
  37 /** @brief Destructor */
  38 ModelChecker::~ModelChecker()
  39 {
  40         std::map<int, Thread *>::iterator it;
  41         for (it = thread_map->begin(); it != thread_map->end(); it++)
  42                 delete (*it).second;
  43         delete thread_map;
  44
  45         delete obj_thrd_map;
  46         delete action_trace;
  47         delete thrd_last_action;
  48         delete node_stack;
  49         delete scheduler;
  50 }
  51
  52 /**
  53  * Restores user program to initial state and resets all model-checker data
  54  * structures.
  55  */
  56 void ModelChecker::reset_to_initial_state()
  57 {
  58         DEBUG("+++ Resetting to initial state +++\n");
  59         node_stack->reset_execution();
  60         current_action = NULL;
  61         next_thread_id = INITIAL_THREAD_ID;
  62         used_sequence_numbers = 0;
  63         nextThread = 0;
  64         next_backtrack = NULL;
  65         snapshotObject->backTrackBeforeStep(0);
  66 }
  67
  68 /** @returns a thread ID for a new Thread */
  69 thread_id_t ModelChecker::get_next_id()
  70 {
  71         return next_thread_id++;
  72 }
  73
  74 /** @returns the number of user threads created during this execution */
  75 int ModelChecker::get_num_threads()
  76 {
  77         return next_thread_id;
  78 }
  79
  80 /** @returns a sequence number for a new ModelAction */
  81 modelclock_t ModelChecker::get_next_seq_num()
  82 {
  83         return ++used_sequence_numbers;
  84 }
  85
  86 /**
  87  * Performs the "scheduling" for the model-checker. That is, it checks if the
  88  * model-checker has selected a "next thread to run" and returns it, if
  89  * available. This function should be called from the Scheduler routine, where
  90  * the Scheduler falls back to a default scheduling routine if needed.
  91  *
  92  * @return The next thread chosen by the model-checker. If the model-checker
  93  * makes no selection, retuns NULL.
  94  */
  95 Thread * ModelChecker::schedule_next_thread()
  96 {
  97         Thread *t;
  98         if (nextThread == THREAD_ID_T_NONE)
  99                 return NULL;
 100         t = (*thread_map)[id_to_int(nextThread)];
 101
 102         ASSERT(t != NULL);
 103
 104         return t;
 105 }
 106
 107 /**
 108  * Choose the next thread in the replay sequence.
 109  *
 110  * If the replay sequence has reached the 'diverge' point, returns a thread
 111  * from the backtracking set. Otherwise, simply returns the next thread in the
 112  * sequence that is being replayed.
 113  */
 114 thread_id_t ModelChecker::get_next_replay_thread()
 115 {
 116         ModelAction *next;
 117         thread_id_t tid;
 118
 119         /* Have we completed exploring the preselected path? */
 120         if (diverge == NULL)
 121                 return THREAD_ID_T_NONE;
 122
 123         /* Else, we are trying to replay an execution */
 124         next = node_stack->get_next()->get_action();
 125
 126         if (next == diverge) {
 127                 Node *node = next->get_node()->get_parent();
 128
 129                 /* Reached divergence point */
 130                 DEBUG("*** Divergence point ***\n");
 131                 tid = node->get_next_backtrack();
 132                 diverge = NULL;
 133         } else {
 134                 tid = next->get_tid();
 135         }
 136         DEBUG("*** ModelChecker chose next thread = %d ***\n", tid);
 137         return tid;
 138 }
 139
 140 /**
 141  * Queries the model-checker for more executions to explore and, if one
 142  * exists, resets the model-checker state to execute a new execution.
 143  *
 144  * @return If there are more executions to explore, return true. Otherwise,
 145  * return false.
 146  */
 147 bool ModelChecker::next_execution()
 148 {
 149         DBG();
 150
 151         num_executions++;
 152         print_summary();
 153         if ((diverge = model->get_next_backtrack()) == NULL)
 154                 return false;
 155
 156         if (DBG_ENABLED()) {
 157                 printf("Next execution will diverge at:\n");
 158                 diverge->print();
 159         }
 160
 161         model->reset_to_initial_state();
 162         return true;
 163 }
 164
 165 ModelAction * ModelChecker::get_last_conflict(ModelAction *act)
 166 {
 167         action_type type = act->get_type();
 168
 169         switch (type) {
 170                 case THREAD_CREATE:
 171                 case THREAD_YIELD:
 172                 case THREAD_JOIN:
 173                         return NULL;
 174                 case ATOMIC_READ:
 175                 case ATOMIC_WRITE:
 176                 default:
 177                         break;
 178         }
 179         /* linear search: from most recent to oldest */
 180         action_list_t::reverse_iterator rit;
 181         for (rit = action_trace->rbegin(); rit != action_trace->rend(); rit++) {
 182                 ModelAction *prev = *rit;
 183                 if (act->is_synchronizing(prev))
 184                         return prev;
 185         }
 186         return NULL;
 187 }
 188
 189 void ModelChecker::set_backtracking(ModelAction *act)
 190 {
 191         ModelAction *prev;
 192         Node *node;
 193         Thread *t = get_thread(act->get_tid());
 194
 195         prev = get_last_conflict(act);
 196         if (prev == NULL)
 197                 return;
 198
 199         node = prev->get_node()->get_parent();
 200
 201         while (!node->is_enabled(t))
 202                 t = t->get_parent();
 203
 204         /* Check if this has been explored already */
 205         if (node->has_been_explored(t->get_id()))
 206                 return;
 207
 208         /* Cache the latest backtracking point */
 209         if (!next_backtrack || *prev > *next_backtrack)
 210                 next_backtrack = prev;
 211
 212         /* If this is a new backtracking point, mark the tree */
 213         if (!node->set_backtrack(t->get_id()))
 214                 return;
 215         DEBUG("Setting backtrack: conflict = %d, instead tid = %d\n",
 216                         prev->get_tid(), t->get_id());
 217         if (DBG_ENABLED()) {
 218                 prev->print();
 219                 act->print();
 220         }
 221 }
 222
 223 ModelAction * ModelChecker::get_next_backtrack()
 224 {
 225         ModelAction *next = next_backtrack;
 226         next_backtrack = NULL;
 227         return next;
 228 }
 229
 230 void ModelChecker::check_current_action(void)
 231 {
 232         Node *currnode;
 233
 234         ModelAction *curr = this->current_action;
 235         ModelAction *tmp;
 236         current_action = NULL;
 237         if (!curr) {
 238                 DEBUG("trying to push NULL action...\n");
 239                 return;
 240         }
 241
 242         tmp = node_stack->explore_action(curr);
 243         if (tmp) {
 244                 /* Discard duplicate ModelAction; use action from NodeStack */
 245                 delete curr;
 246                 curr = tmp;
 247         } else {
 248                 /*
 249                  * Perform one-time actions when pushing new ModelAction onto
 250                  * NodeStack
 251                  */
 252                 curr->create_cv(get_parent_action(curr->get_tid()));
 253                 /* Build may_read_from set */
 254                 if (curr->is_read())
 255                         build_reads_from_past(curr);
 256         }
 257
 258         /* Assign 'creation' parent */
 259         if (curr->get_type() == THREAD_CREATE) {
 260                 Thread *th = (Thread *)curr->get_location();
 261                 th->set_creation(curr);
 262         }
 263
 264         nextThread = get_next_replay_thread();
 265
 266         currnode = curr->get_node()->get_parent();
 267
 268         if (!currnode->backtrack_empty())
 269                 if (!next_backtrack || *curr > *next_backtrack)
 270                         next_backtrack = curr;
 271
 272         set_backtracking(curr);
 273
 274         add_action_to_lists(curr);
 275 }
 276
 277 /**
 278  * Performs various bookkeeping operations for the current ModelAction. For
 279  * instance, adds action to the per-object, per-thread action vector and to the
 280  * action trace list of all thread actions.
 281  *
 282  * @param act is the ModelAction to add.
 283  */
 284 void ModelChecker::add_action_to_lists(ModelAction *act)
 285 {
 286         int tid = id_to_int(act->get_tid());
 287         action_trace->push_back(act);
 288
 289         std::vector<action_list_t> *vec = &(*obj_thrd_map)[act->get_location()];
 290         if (tid >= (int)vec->size())
 291                 vec->resize(next_thread_id);
 292         (*vec)[tid].push_back(act);
 293
 294         (*thrd_last_action)[tid] = act;
 295 }
 296
 297 ModelAction * ModelChecker::get_last_action(thread_id_t tid)
 298 {
 299         int nthreads = get_num_threads();
 300         if ((int)thrd_last_action->size() < nthreads)
 301                 thrd_last_action->resize(nthreads);
 302         return (*thrd_last_action)[id_to_int(tid)];
 303 }
 304
 305 ModelAction * ModelChecker::get_parent_action(thread_id_t tid)
 306 {
 307         ModelAction *parent = get_last_action(tid);
 308         if (!parent)
 309                 parent = get_thread(tid)->get_creation();
 310         return parent;
 311 }
 312
 313 ClockVector * ModelChecker::get_cv(thread_id_t tid) {
 314         return get_parent_action(tid)->get_cv();
 315 }
 316
 317 /**
 318  * Build up an initial set of all past writes that this 'read' action may read
 319  * from. This set is determined by the clock vector's "happens before"
 320  * relationship.
 321  * @param curr is the current ModelAction that we are exploring; it must be a
 322  * 'read' operation.
 323  */
 324 void ModelChecker::build_reads_from_past(ModelAction *curr)
 325 {
 326         std::vector<action_list_t> *thrd_lists = &(*obj_thrd_map)[curr->get_location()];
 327         unsigned int i;
 328
 329         ASSERT(curr->is_read());
 330
 331         /* Track whether this object has been initialized */
 332         bool initialized = false;
 333
 334         for (i = 0; i < thrd_lists->size(); i++) {
 335                 action_list_t *list = &(*thrd_lists)[i];
 336                 action_list_t::reverse_iterator rit;
 337                 for (rit = list->rbegin(); rit != list->rend(); rit++) {
 338                         ModelAction *act = *rit;
 339
 340                         /* Only consider 'write' actions */
 341                         if (!act->is_write())
 342                                 continue;
 343
 344                         DEBUG("Adding action to may_read_from:\n");
 345                         if (DBG_ENABLED()) {
 346                                 act->print();
 347                                 curr->print();
 348                         }
 349                         curr->get_node()->add_read_from(act);
 350
 351                         /* Include at most one act per-thread that "happens before" curr */
 352                         if (act->happens_before(curr)) {
 353                                 initialized = true;
 354                                 break;
 355                         }
 356                 }
 357         }
 358
 359         if (!initialized) {
 360                 /* TODO: need a more informative way of reporting errors */
 361                 printf("ERROR: may read from uninitialized atomic\n");
 362         }
 363
 364         if (DBG_ENABLED() || !initialized) {
 365                 printf("Reached read action:\n");
 366                 curr->print();
 367                 printf("Printing may_read_from\n");
 368                 curr->get_node()->print_may_read_from();
 369                 printf("End printing may_read_from\n");
 370         }
 371
 372         ASSERT(initialized);
 373 }
 374
 375 static void print_list(action_list_t *list)
 376 {
 377         action_list_t::iterator it;
 378
 379         printf("---------------------------------------------------------------------\n");
 380         printf("Trace:\n");
 381
 382         for (it = list->begin(); it != list->end(); it++) {
 383                 (*it)->print();
 384         }
 385         printf("---------------------------------------------------------------------\n");
 386 }
 387
 388 void ModelChecker::print_summary(void)
 389 {
 390         printf("\n");
 391         printf("Number of executions: %d\n", num_executions);
 392         printf("Total nodes created: %d\n", node_stack->get_total_nodes());
 393
 394         scheduler->print();
 395
 396         print_list(action_trace);
 397         printf("\n");
 398 }
 399
 400 int ModelChecker::add_thread(Thread *t)
 401 {
 402         (*thread_map)[id_to_int(t->get_id())] = t;
 403         scheduler->add_thread(t);
 404         return 0;
 405 }
 406
 407 void ModelChecker::remove_thread(Thread *t)
 408 {
 409         scheduler->remove_thread(t);
 410 }
 411
 412 int ModelChecker::switch_to_master(ModelAction *act)
 413 {
 414         Thread *old;
 415
 416         DBG();
 417         old = thread_current();
 418         set_current_action(act);
 419         old->set_state(THREAD_READY);
 420         return Thread::swap(old, get_system_context());
 421 }