history.cc

   1 #include <inttypes.h>
   2 #include "history.h"
   3 #include "action.h"
   4 #include "funcnode.h"
   5 #include "funcinst.h"
   6 #include "common.h"
   7 #include "concretepredicate.h"
   8 #include "waitobj.h"
   9
  10 #include "model.h"
  11 #include "execution.h"
  12 #include "newfuzzer.h"
  13
  14 /** @brief Constructor */
  15 ModelHistory::ModelHistory() :
  16         func_counter(1),        /* function id starts with 1 */
  17         func_map(),
  18         func_map_rev(),
  19         func_nodes()
  20 {
  21         /* The following are snapshot data structures */
  22         write_history = new HashTable<void *, value_set_t *, uintptr_t, 0>();
  23         loc_rd_func_nodes_map = new HashTable<void *, SnapVector<FuncNode *> *, uintptr_t, 0>();
  24         loc_wr_func_nodes_map = new HashTable<void *, SnapVector<FuncNode *> *, uintptr_t, 0>();
  25         loc_waiting_writes_map = new HashTable<void *, SnapVector<ConcretePredicate *> *, uintptr_t, 0>();
  26         thrd_waiting_write = new SnapVector<ConcretePredicate *>();
  27         thrd_wait_obj = new SnapVector<WaitObj *>();
  28         func_inst_act_maps = new HashTable<uint32_t, SnapVector<inst_act_map_t *> *, int, 0>(128);
  29 }
  30
  31 ModelHistory::~ModelHistory()
  32 {
  33         // TODO: complete deconstructor; maybe not needed
  34         for (uint i = 0; i < thrd_wait_obj->size(); i++)
  35                 delete (*thrd_wait_obj)[i];
  36 }
  37
  38 void ModelHistory::enter_function(const uint32_t func_id, thread_id_t tid)
  39 {
  40         //model_print("thread %d entering func %d\n", tid, func_id);
  41         ModelExecution * execution = model->get_execution();
  42         uint id = id_to_int(tid);
  43
  44         SnapVector<func_id_list_t> * thrd_func_list = execution->get_thrd_func_list();
  45         SnapVector< SnapList<action_list_t *> *> *
  46                 thrd_func_act_lists = execution->get_thrd_func_act_lists();
  47         SnapVector<uint32_t> * thrd_last_entered_func = execution->get_thrd_last_entered_func();
  48
  49         if ( thrd_func_list->size() <= id ) {
  50                 uint oldsize = thrd_func_list->size();
  51                 thrd_func_list->resize( id + 1 );
  52                 thrd_func_act_lists->resize( id + 1 );
  53
  54                 for (uint i = oldsize; i < id + 1; i++) {
  55                         // push 0 as a dummy function id to a void seg fault
  56                         new (&(*thrd_func_list)[i]) func_id_list_t();
  57                         (*thrd_func_list)[i].push_back(0);
  58
  59                         (*thrd_func_act_lists)[i] = new SnapList<action_list_t *>();
  60                         thrd_last_entered_func->push_back(0);
  61                 }
  62         }
  63
  64         SnapList<action_list_t *> * func_act_lists = (*thrd_func_act_lists)[id];
  65         func_act_lists->push_back( new action_list_t() );
  66
  67         uint32_t last_entered_func_id = (*thrd_last_entered_func)[id];
  68         (*thrd_last_entered_func)[id] = func_id;
  69         (*thrd_func_list)[id].push_back(func_id);
  70
  71         if ( func_nodes.size() <= func_id )
  72                 resize_func_nodes( func_id + 1 );
  73
  74         FuncNode * func_node = func_nodes[func_id];
  75         func_node->init_predicate_tree_position(tid);
  76         func_node->init_inst_act_map(tid);
  77
  78         /* Add edges between FuncNodes */
  79         if (last_entered_func_id != 0) {
  80                 FuncNode * last_func_node = func_nodes[last_entered_func_id];
  81                 last_func_node->add_out_edge(func_node);
  82         }
  83
  84         /* Monitor the statuses of threads waiting for tid */
  85         monitor_waiting_thread(func_id, tid);
  86 }
  87
  88 /* @param func_id a non-zero value */
  89 void ModelHistory::exit_function(const uint32_t func_id, thread_id_t tid)
  90 {
  91         ModelExecution * execution = model->get_execution();
  92         uint32_t id = id_to_int(tid);
  93         SnapVector<func_id_list_t> * thrd_func_list = execution->get_thrd_func_list();
  94         SnapVector< SnapList<action_list_t *> *> *
  95                 thrd_func_act_lists = execution->get_thrd_func_act_lists();
  96
  97         SnapList<action_list_t *> * func_act_lists = (*thrd_func_act_lists)[id];
  98         uint32_t last_func_id = (*thrd_func_list)[id].back();
  99
 100         if (last_func_id == func_id) {
 101                 FuncNode * func_node = func_nodes[func_id];
 102                 func_node->set_predicate_tree_position(tid, NULL);
 103                 func_node->reset_inst_act_map(tid);
 104
 105                 action_list_t * curr_act_list = func_act_lists->back();
 106
 107                 /* defer the processing of curr_act_list until the function has exits a few times
 108                  * (currently twice) so that more information can be gathered to infer nullity predicates.
 109                  */
 110                 func_node->incr_exit_count();
 111                 if (func_node->get_exit_count() >= 2) {
 112                         SnapList<action_list_t *> * action_list_buffer = func_node->get_action_list_buffer();
 113                         while (action_list_buffer->size() > 0) {
 114                                 action_list_t * act_list = action_list_buffer->back();
 115                                 action_list_buffer->pop_back();
 116                                 func_node->update_tree(act_list);
 117                         }
 118
 119                         func_node->update_tree(curr_act_list);
 120                 } else
 121                         func_node->get_action_list_buffer()->push_front(curr_act_list);
 122
 123                 (*thrd_func_list)[id].pop_back();
 124                 func_act_lists->pop_back();
 125         } else {
 126                 model_print("trying to exit with a wrong function id\n");
 127                 model_print("--- last_func: %d, func_id: %d\n", last_func_id, func_id);
 128         }
 129         //model_print("thread %d exiting func %d\n", tid, func_id);
 130 }
 131
 132 void ModelHistory::resize_func_nodes(uint32_t new_size)
 133 {
 134         uint32_t old_size = func_nodes.size();
 135
 136         if ( old_size < new_size )
 137                 func_nodes.resize(new_size);
 138
 139         for (uint32_t id = old_size; id < new_size; id++) {
 140                 const char * func_name = func_map_rev[id];
 141                 FuncNode * func_node = new FuncNode(this);
 142                 func_node->set_func_id(id);
 143                 func_node->set_func_name(func_name);
 144                 func_nodes[id] = func_node;
 145         }
 146 }
 147
 148 void ModelHistory::process_action(ModelAction *act, thread_id_t tid)
 149 {
 150         ModelExecution * execution = model->get_execution();
 151         SnapVector<func_id_list_t> * thrd_func_list = execution->get_thrd_func_list();
 152         SnapVector< SnapList<action_list_t *> *> *
 153                 thrd_func_act_lists = execution->get_thrd_func_act_lists();
 154
 155         uint32_t thread_id = id_to_int(tid);
 156         /* Return if thread tid has not entered any function that contains atomics */
 157         if ( thrd_func_list->size() <= thread_id )
 158                 return;
 159
 160         /* Monitor the statuses of threads waiting for tid */
 161         monitor_waiting_thread_counter(tid);
 162
 163         /* Every write action should be processed, including
 164          * nonatomic writes (which have no position) */
 165         if (act->is_write()) {
 166                 void * location = act->get_location();
 167                 uint64_t value = act->get_write_value();
 168                 update_write_history(location, value);
 169
 170                 /* Notify FuncNodes that may read from this location */
 171                 SnapVector<FuncNode *> * func_node_list = getRdFuncNodes(location);
 172                 for (uint i = 0; i < func_node_list->size(); i++) {
 173                         FuncNode * func_node = (*func_node_list)[i];
 174                         func_node->add_to_val_loc_map(value, location);
 175                 }
 176
 177                 check_waiting_write(act);
 178         }
 179
 180         uint32_t func_id = (*thrd_func_list)[thread_id].back();
 181
 182         /* The following does not care about actions that are not inside
 183          * any function that contains atomics or actions without a position */
 184         if (func_id == 0 || act->get_position() == NULL)
 185                 return;
 186
 187         SnapList<action_list_t *> * func_act_lists = (*thrd_func_act_lists)[thread_id];
 188
 189         /* The list of actions that thread tid has taken in its current function */
 190         action_list_t * curr_act_list = func_act_lists->back();
 191
 192         if (skip_action(act, curr_act_list))
 193                 return;
 194
 195         /* Add to curr_inst_list */
 196         curr_act_list->push_back(act);
 197
 198         FuncNode * func_node = func_nodes[func_id];
 199         func_node->add_inst(act);
 200
 201         if (act->is_read()) {
 202                 func_node->update_inst_act_map(tid, act);
 203         }
 204 }
 205
 206 /* Return the FuncNode given its func_id  */
 207 FuncNode * ModelHistory::get_func_node(uint32_t func_id)
 208 {
 209         if (func_id == 0)
 210                 return NULL;
 211
 212         // This node has not been added to func_nodes
 213         if (func_nodes.size() <= func_id)
 214                 return NULL;
 215
 216         return func_nodes[func_id];
 217 }
 218
 219 /* Return the current FuncNode when given a thread id */
 220 FuncNode * ModelHistory::get_curr_func_node(thread_id_t tid)
 221 {
 222         int thread_id = id_to_int(tid);
 223         SnapVector<func_id_list_t> * thrd_func_list =  model->get_execution()->get_thrd_func_list();
 224         uint32_t func_id = (*thrd_func_list)[thread_id].back();
 225
 226         if (func_id != 0) {
 227                 return func_nodes[func_id];
 228         }
 229
 230         return NULL;
 231 }
 232
 233 void ModelHistory::update_write_history(void * location, uint64_t write_val)
 234 {
 235         value_set_t * write_set = write_history->get(location);
 236
 237         if (write_set == NULL) {
 238                 write_set = new value_set_t();
 239                 write_history->put(location, write_set);
 240         }
 241
 242         write_set->add(write_val);
 243 }
 244
 245 void ModelHistory::update_loc_rd_func_nodes_map(void * location, FuncNode * node)
 246 {
 247         SnapVector<FuncNode *> * func_node_list = getRdFuncNodes(location);
 248         func_node_list->push_back(node);
 249 }
 250
 251 void ModelHistory::update_loc_wr_func_nodes_map(void * location, FuncNode * node)
 252 {
 253         SnapVector<FuncNode *> * func_node_list = getWrFuncNodes(location);
 254         func_node_list->push_back(node);
 255 }
 256
 257 SnapVector<FuncNode *> * ModelHistory::getRdFuncNodes(void * location)
 258 {
 259         SnapVector<FuncNode *> * func_node_list = loc_rd_func_nodes_map->get(location);
 260         if (func_node_list == NULL) {
 261                 func_node_list = new SnapVector<FuncNode *>();
 262                 loc_rd_func_nodes_map->put(location, func_node_list);
 263         }
 264
 265         return func_node_list;
 266 }
 267
 268 SnapVector<FuncNode *> * ModelHistory::getWrFuncNodes(void * location)
 269 {
 270         SnapVector<FuncNode *> * func_node_list = loc_wr_func_nodes_map->get(location);
 271         if (func_node_list == NULL) {
 272                 func_node_list = new SnapVector<FuncNode *>();
 273                 loc_wr_func_nodes_map->put(location, func_node_list);
 274         }
 275
 276         return func_node_list;
 277 }
 278
 279 /* When a thread is paused by Fuzzer, keep track of the condition it is waiting for */
 280 void ModelHistory::add_waiting_write(ConcretePredicate * concrete)
 281 {
 282         void * location = concrete->get_location();
 283         SnapVector<ConcretePredicate *> * waiting_conditions = loc_waiting_writes_map->get(location);
 284         if (waiting_conditions == NULL) {
 285                 waiting_conditions = new SnapVector<ConcretePredicate *>();
 286                 loc_waiting_writes_map->put(location, waiting_conditions);
 287         }
 288
 289         /* waiting_conditions should not have duplications */
 290         waiting_conditions->push_back(concrete);
 291
 292         int thread_id = id_to_int(concrete->get_tid());
 293         if (thrd_waiting_write->size() <= (uint) thread_id) {
 294                 thrd_waiting_write->resize(thread_id + 1);
 295         }
 296
 297         (*thrd_waiting_write)[thread_id] = concrete;
 298 }
 299
 300 void ModelHistory::remove_waiting_write(thread_id_t tid)
 301 {
 302         ConcretePredicate * concrete = (*thrd_waiting_write)[ id_to_int(tid) ];
 303         void * location = concrete->get_location();
 304         SnapVector<ConcretePredicate *> * concrete_preds = loc_waiting_writes_map->get(location);
 305
 306         /* Linear search should be fine because presumably not many ConcretePredicates
 307          * are at the same memory location */
 308         for (uint i = 0; i < concrete_preds->size(); i++) {
 309                 ConcretePredicate * current = (*concrete_preds)[i];
 310                 if (concrete == current) {
 311                         (*concrete_preds)[i] = concrete_preds->back();
 312                         concrete_preds->pop_back();
 313                         break;
 314                 }
 315         }
 316
 317         int thread_id = id_to_int( concrete->get_tid() );
 318         (*thrd_waiting_write)[thread_id] = NULL;
 319         delete concrete;
 320 }
 321
 322 /* Check if any other thread is waiting for this write action. If so, "notify" them */
 323 void ModelHistory::check_waiting_write(ModelAction * write_act)
 324 {
 325         void * location = write_act->get_location();
 326         uint64_t value = write_act->get_write_value();
 327         SnapVector<ConcretePredicate *> * concrete_preds = loc_waiting_writes_map->get(location);
 328         if (concrete_preds == NULL)
 329                 return;
 330
 331         uint index = 0;
 332         while (index < concrete_preds->size()) {
 333                 ConcretePredicate * concrete_pred = (*concrete_preds)[index];
 334                 SnapVector<struct concrete_pred_expr> * concrete_exprs = concrete_pred->getExpressions();
 335                 bool satisfy_predicate = true;
 336                 /* Check if the written value satisfies every predicate expression */
 337                 for (uint i = 0; i < concrete_exprs->size(); i++) {
 338                         struct concrete_pred_expr concrete = (*concrete_exprs)[i];
 339                         bool equality = false;
 340                         switch (concrete.token) {
 341                                 case EQUALITY:
 342                                         equality = (value == concrete.value);
 343                                         break;
 344                                 case NULLITY:
 345                                         equality = ((void*)value == NULL);
 346                                         break;
 347                                 default:
 348                                         model_print("unknown predicate token");
 349                                         break;
 350                         }
 351
 352                         if (equality != concrete.equality) {
 353                                 satisfy_predicate = false;
 354                                 break;
 355                         }
 356                 }
 357
 358                 if (satisfy_predicate) {
 359                         /* Wake up threads */
 360                         thread_id_t tid = concrete_pred->get_tid();
 361                         Thread * thread = model->get_thread(tid);
 362
 363                         //model_print("** thread %d is woken up\n", thread->get_id());
 364                         model->get_execution()->getFuzzer()->notify_paused_thread(thread);
 365                 }
 366
 367                 index++;
 368         }
 369 }
 370
 371 WaitObj * ModelHistory::getWaitObj(thread_id_t tid)
 372 {
 373         int thread_id = id_to_int(tid);
 374         int old_size = thrd_wait_obj->size();
 375         if (old_size <= thread_id) {
 376                 thrd_wait_obj->resize(thread_id + 1);
 377                 for (int i = old_size; i < thread_id + 1; i++) {
 378                         (*thrd_wait_obj)[i] = new WaitObj( int_to_id(i) );
 379                 }
 380         }
 381
 382         return (*thrd_wait_obj)[thread_id];
 383 }
 384
 385 void ModelHistory::add_waiting_thread(thread_id_t self_id,
 386         thread_id_t waiting_for_id, FuncNode * target_node, int dist)
 387 {
 388         WaitObj * self_wait_obj = getWaitObj(self_id);
 389         self_wait_obj->add_waiting_for(waiting_for_id, target_node, dist);
 390
 391         /* Update waited-by relation */
 392         WaitObj * other_wait_obj = getWaitObj(waiting_for_id);
 393         other_wait_obj->add_waited_by(self_id);
 394 }
 395
 396 /* Thread tid is woken up (or notified), so it is not waiting for others anymore */
 397 void ModelHistory::remove_waiting_thread(thread_id_t tid)
 398 {
 399         WaitObj * self_wait_obj = getWaitObj(tid);
 400         thrd_id_set_t * waiting_for = self_wait_obj->getWaitingFor();
 401
 402         /* Remove tid from waited_by's */
 403         thrd_id_set_iter * iter = waiting_for->iterator();
 404         while (iter->hasNext()) {
 405                 thread_id_t other_id = iter->next();
 406                 WaitObj * other_wait_obj = getWaitObj(other_id);
 407                 other_wait_obj->remove_waited_by(tid);
 408         }
 409
 410         self_wait_obj->clear_waiting_for();
 411 }
 412
 413 void ModelHistory::stop_waiting_for_node(thread_id_t self_id,
 414         thread_id_t waiting_for_id, FuncNode * target_node)
 415 {
 416         WaitObj * self_wait_obj = getWaitObj(self_id);
 417         bool thread_removed = self_wait_obj->remove_waiting_for_node(waiting_for_id, target_node);
 418
 419         // model_print("\t%d gives up %d on node %d\n", self_id, waiting_for_id, target_node->get_func_id());
 420
 421         /* If thread self_id is not waiting for waiting_for_id anymore */
 422         if (thread_removed) {
 423                 WaitObj * other_wait_obj = getWaitObj(waiting_for_id);
 424                 other_wait_obj->remove_waited_by(self_id);
 425
 426                 thrd_id_set_t * self_waiting_for = self_wait_obj->getWaitingFor();
 427                 if ( self_waiting_for->isEmpty() ) {
 428                         // model_print("\tthread %d waits for nobody, wake up\n", self_id);
 429                         ModelExecution * execution = model->get_execution();
 430                         Thread * thread = execution->get_thread(self_id);
 431                         execution->getFuzzer()->notify_paused_thread(thread);
 432                 }
 433         }
 434 }
 435
 436 SnapVector<inst_act_map_t *> * ModelHistory::getThrdInstActMap(uint32_t func_id)
 437 {
 438         ASSERT(func_id != 0);
 439
 440         SnapVector<inst_act_map_t *> * maps = func_inst_act_maps->get(func_id);
 441         if (maps == NULL) {
 442                 maps = new SnapVector<inst_act_map_t *>();
 443                 func_inst_act_maps->put(func_id, maps);
 444         }
 445
 446         return maps;
 447 }
 448
 449 bool ModelHistory::skip_action(ModelAction * act, SnapList<ModelAction *> * curr_act_list)
 450 {
 451         ASSERT(curr_act_list != NULL);
 452
 453         bool second_part_of_rmw = act->is_rmwc() || act->is_rmw();
 454         modelclock_t curr_seq_number = act->get_seq_number();
 455
 456         /* Skip actions that are second part of a read modify write */
 457         if (second_part_of_rmw)
 458                 return true;
 459
 460         /* Skip actions with the same sequence number */
 461         if (curr_act_list->size() != 0) {
 462                 ModelAction * last_act = curr_act_list->back();
 463                 if (last_act->get_seq_number() == curr_seq_number)
 464                         return true;
 465         }
 466
 467         /* Skip actions that are paused by fuzzer (sequence number is 0) */
 468         if (curr_seq_number == 0)
 469                 return true;
 470
 471         return false;
 472 }
 473
 474 /* Monitor thread tid and decide whether other threads (that are waiting for tid)
 475  * should keep waiting for this thread or not. Shall only be called when a thread
 476  * enters a function.
 477  *
 478  * Heuristics: If the distance from the current FuncNode to some target node
 479  * ever increases, stop waiting for this thread on this target node.
 480  */
 481 void ModelHistory::monitor_waiting_thread(uint32_t func_id, thread_id_t tid)
 482 {
 483         WaitObj * wait_obj = getWaitObj(tid);
 484         thrd_id_set_t * waited_by = wait_obj->getWaitedBy();
 485         FuncNode * curr_node = func_nodes[func_id];
 486
 487         /* For each thread waiting for tid */
 488         thrd_id_set_iter * tid_iter = waited_by->iterator();
 489         while (tid_iter->hasNext()) {
 490                 thread_id_t waited_by_id = tid_iter->next();
 491                 WaitObj * other_wait_obj = getWaitObj(waited_by_id);
 492
 493                 node_set_t * target_nodes = other_wait_obj->getTargetNodes(tid);
 494                 node_set_iter * node_iter = target_nodes->iterator();
 495                 while (node_iter->hasNext()) {
 496                         FuncNode * target = node_iter->next();
 497                         int old_dist = other_wait_obj->lookup_dist(tid, target);
 498                         int new_dist = curr_node->compute_distance(target, old_dist);
 499
 500                         if (new_dist == -1) {
 501                                 stop_waiting_for_node(waited_by_id, tid, target);
 502                         }
 503                 }
 504         }
 505 }
 506
 507 void ModelHistory::monitor_waiting_thread_counter(thread_id_t tid)
 508 {
 509         WaitObj * wait_obj = getWaitObj(tid);
 510         thrd_id_set_t * waited_by = wait_obj->getWaitedBy();
 511
 512         // Thread tid has taken an action, update the counter for threads waiting for tid
 513         thrd_id_set_iter * tid_iter = waited_by->iterator();
 514         while (tid_iter->hasNext()) {
 515                 thread_id_t waited_by_id = tid_iter->next();
 516                 WaitObj * other_wait_obj = getWaitObj(waited_by_id);
 517
 518                 bool expire = other_wait_obj->incr_counter(tid);
 519                 if (expire) {
 520 //                      model_print("thread %d stops waiting for thread %d\n", waited_by_id, tid);
 521                         wait_obj->remove_waited_by(waited_by_id);
 522                         other_wait_obj->remove_waiting_for(tid);
 523
 524                         thrd_id_set_t * other_waiting_for = other_wait_obj->getWaitingFor();
 525                         if ( other_waiting_for->isEmpty() ) {
 526                                 // model_print("\tthread %d waits for nobody, wake up\n", self_id);
 527                                 ModelExecution * execution = model->get_execution();
 528                                 Thread * thread = execution->get_thread(waited_by_id);
 529                                 execution->getFuzzer()->notify_paused_thread(thread);
 530                         }
 531                 }
 532         }
 533 }
 534
 535 /* Reallocate some snapshotted memories when new executions start */
 536 void ModelHistory::set_new_exec_flag()
 537 {
 538         for (uint i = 1; i < func_nodes.size(); i++) {
 539                 FuncNode * func_node = func_nodes[i];
 540                 func_node->set_new_exec_flag();
 541         }
 542 }
 543
 544 void ModelHistory::dump_func_node_graph()
 545 {
 546         model_print("digraph func_node_graph {\n");
 547         for (uint i = 1; i < func_nodes.size(); i++) {
 548                 FuncNode * node = func_nodes[i];
 549                 ModelList<FuncNode *> * out_edges = node->get_out_edges();
 550
 551                 model_print("\"%p\" [label=\"%s\"]\n", node, node->get_func_name());
 552                 mllnode<FuncNode *> * it;
 553                 for (it = out_edges->begin(); it != NULL; it = it->getNext()) {
 554                         FuncNode * other = it->getVal();
 555                         model_print("\"%p\" -> \"%p\"\n", node, other);
 556                 }
 557         }
 558         model_print("}\n");
 559 }
 560
 561 void ModelHistory::print_func_node()
 562 {
 563         /* function id starts with 1 */
 564         for (uint32_t i = 1; i < func_nodes.size(); i++) {
 565                 FuncNode * func_node = func_nodes[i];
 566
 567                 func_node->print_predicate_tree();
 568 /*
 569                 func_inst_list_mt * entry_insts = func_node->get_entry_insts();
 570                 model_print("function %s has entry actions\n", func_node->get_func_name());
 571
 572                 mllnode<FuncInst*>* it;
 573                 for (it = entry_insts->begin();it != NULL;it=it->getNext()) {
 574                         FuncInst *inst = it->getVal();
 575                         model_print("type: %d, at: %s\n", inst->get_type(), inst->get_position());
 576                 }
 577                 */
 578         }
 579 }
 580
 581 void ModelHistory::print_waiting_threads()
 582 {
 583         ModelExecution * execution = model->get_execution();
 584         for (unsigned int i = 0; i < execution->get_num_threads();i++) {
 585                 thread_id_t tid = int_to_id(i);
 586                 WaitObj * wait_obj = getWaitObj(tid);
 587                 wait_obj->print_waiting_for();
 588         }
 589
 590         for (unsigned int i = 0; i < execution->get_num_threads();i++) {
 591                 thread_id_t tid = int_to_id(i);
 592                 WaitObj * wait_obj = getWaitObj(tid);
 593                 wait_obj->print_waited_by();
 594         }
 595 }