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, 4>();
  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         uint32_t func_id = (*thrd_func_list)[thread_id].back();
 157
 158         /* Return if thread tid has not entered any function that contains atomics */
 159         if ( thrd_func_list->size() <= thread_id )
 160                 return;
 161
 162         /* Monitor the statuses of threads waiting for tid */
 163         monitor_waiting_thread_counter(tid);
 164
 165         /* Every write action should be processed, including
 166          * nonatomic writes (which have no position) */
 167         if (act->is_write()) {
 168                 void * location = act->get_location();
 169                 uint64_t value = act->get_write_value();
 170                 update_write_history(location, value);
 171
 172                 /* Notify FuncNodes that may read from this location */
 173                 SnapVector<FuncNode *> * func_node_list = getRdFuncNodes(location);
 174                 for (uint i = 0; i < func_node_list->size(); i++) {
 175                         FuncNode * func_node = (*func_node_list)[i];
 176                         func_node->add_to_val_loc_map(value, location);
 177                 }
 178
 179                 check_waiting_write(act);
 180         }
 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         /* The list of actions that thread tid has taken in its current function */
 189         action_list_t * curr_act_list = func_act_lists->back();
 190         ASSERT(curr_act_list != NULL);
 191
 192         if (skip_action(act, curr_act_list))
 193                 return;
 194
 195         FuncNode * func_node = func_nodes[func_id];
 196
 197         /* Add to curr_inst_list */
 198         curr_act_list->push_back(act);
 199         func_node->add_inst(act);
 200
 201         if (act->is_read()) {
 202                 func_node->update_inst_act_map(tid, act);
 203
 204                 // Update predicate tree position
 205                 Fuzzer * fuzzer = execution->getFuzzer();
 206                 Predicate * selected_branch = fuzzer->get_selected_child_branch(tid);
 207                 func_node->set_predicate_tree_position(tid, selected_branch);
 208         }
 209 }
 210
 211 /* Return the FuncNode given its func_id  */
 212 FuncNode * ModelHistory::get_func_node(uint32_t func_id)
 213 {
 214         if (func_id == 0)
 215                 return NULL;
 216
 217         // This node has not been added to func_nodes
 218         if (func_nodes.size() <= func_id)
 219                 return NULL;
 220
 221         return func_nodes[func_id];
 222 }
 223
 224 /* Return the current FuncNode when given a thread id */
 225 FuncNode * ModelHistory::get_curr_func_node(thread_id_t tid)
 226 {
 227         int thread_id = id_to_int(tid);
 228         SnapVector<func_id_list_t> * thrd_func_list =  model->get_execution()->get_thrd_func_list();
 229         uint32_t func_id = (*thrd_func_list)[thread_id].back();
 230
 231         if (func_id != 0) {
 232                 return func_nodes[func_id];
 233         }
 234
 235         return NULL;
 236 }
 237
 238 void ModelHistory::update_write_history(void * location, uint64_t write_val)
 239 {
 240         value_set_t * write_set = write_history->get(location);
 241
 242         if (write_set == NULL) {
 243                 write_set = new value_set_t();
 244                 write_history->put(location, write_set);
 245         }
 246
 247         write_set->add(write_val);
 248 }
 249
 250 void ModelHistory::update_loc_rd_func_nodes_map(void * location, FuncNode * node)
 251 {
 252         SnapVector<FuncNode *> * func_node_list = getRdFuncNodes(location);
 253         func_node_list->push_back(node);
 254 }
 255
 256 void ModelHistory::update_loc_wr_func_nodes_map(void * location, FuncNode * node)
 257 {
 258         SnapVector<FuncNode *> * func_node_list = getWrFuncNodes(location);
 259         func_node_list->push_back(node);
 260 }
 261
 262 SnapVector<FuncNode *> * ModelHistory::getRdFuncNodes(void * location)
 263 {
 264         SnapVector<FuncNode *> * func_node_list = loc_rd_func_nodes_map->get(location);
 265         if (func_node_list == NULL) {
 266                 func_node_list = new SnapVector<FuncNode *>();
 267                 loc_rd_func_nodes_map->put(location, func_node_list);
 268         }
 269
 270         return func_node_list;
 271 }
 272
 273 SnapVector<FuncNode *> * ModelHistory::getWrFuncNodes(void * location)
 274 {
 275         SnapVector<FuncNode *> * func_node_list = loc_wr_func_nodes_map->get(location);
 276         if (func_node_list == NULL) {
 277                 func_node_list = new SnapVector<FuncNode *>();
 278                 loc_wr_func_nodes_map->put(location, func_node_list);
 279         }
 280
 281         return func_node_list;
 282 }
 283
 284 /* When a thread is paused by Fuzzer, keep track of the condition it is waiting for */
 285 void ModelHistory::add_waiting_write(ConcretePredicate * concrete)
 286 {
 287         void * location = concrete->get_location();
 288         SnapVector<ConcretePredicate *> * waiting_conditions = loc_waiting_writes_map->get(location);
 289         if (waiting_conditions == NULL) {
 290                 waiting_conditions = new SnapVector<ConcretePredicate *>();
 291                 loc_waiting_writes_map->put(location, waiting_conditions);
 292         }
 293
 294         /* waiting_conditions should not have duplications */
 295         waiting_conditions->push_back(concrete);
 296
 297         int thread_id = id_to_int(concrete->get_tid());
 298         if (thrd_waiting_write->size() <= (uint) thread_id) {
 299                 thrd_waiting_write->resize(thread_id + 1);
 300         }
 301
 302         (*thrd_waiting_write)[thread_id] = concrete;
 303 }
 304
 305 void ModelHistory::remove_waiting_write(thread_id_t tid)
 306 {
 307         ConcretePredicate * concrete = (*thrd_waiting_write)[ id_to_int(tid) ];
 308         void * location = concrete->get_location();
 309         SnapVector<ConcretePredicate *> * concrete_preds = loc_waiting_writes_map->get(location);
 310
 311         /* Linear search should be fine because presumably not many ConcretePredicates
 312          * are at the same memory location */
 313         for (uint i = 0; i < concrete_preds->size(); i++) {
 314                 ConcretePredicate * current = (*concrete_preds)[i];
 315                 if (concrete == current) {
 316                         (*concrete_preds)[i] = concrete_preds->back();
 317                         concrete_preds->pop_back();
 318                         break;
 319                 }
 320         }
 321
 322         int thread_id = id_to_int( concrete->get_tid() );
 323         (*thrd_waiting_write)[thread_id] = NULL;
 324         delete concrete;
 325 }
 326
 327 /* Check if any other thread is waiting for this write action. If so, "notify" them */
 328 void ModelHistory::check_waiting_write(ModelAction * write_act)
 329 {
 330         void * location = write_act->get_location();
 331         uint64_t value = write_act->get_write_value();
 332         SnapVector<ConcretePredicate *> * concrete_preds = loc_waiting_writes_map->get(location);
 333         SnapVector<ConcretePredicate *> to_remove = SnapVector<ConcretePredicate *>();
 334         if (concrete_preds == NULL)
 335                 return;
 336
 337         uint index = 0;
 338         while (index < concrete_preds->size()) {
 339                 ConcretePredicate * concrete_pred = (*concrete_preds)[index];
 340                 SnapVector<struct concrete_pred_expr> * concrete_exprs = concrete_pred->getExpressions();
 341                 bool satisfy_predicate = true;
 342                 /* Check if the written value satisfies every predicate expression */
 343                 for (uint i = 0; i < concrete_exprs->size(); i++) {
 344                         struct concrete_pred_expr concrete = (*concrete_exprs)[i];
 345                         bool equality;
 346                         switch (concrete.token) {
 347                                 case EQUALITY:
 348                                         equality = (value == concrete.value);
 349                                         break;
 350                                 case NULLITY:
 351                                         equality = ((void*)value == NULL);
 352                                         break;
 353                                 default:
 354                                         model_print("unknown predicate token");
 355                                         break;
 356                         }
 357
 358                         if (equality != concrete.equality) {
 359                                 satisfy_predicate = false;
 360                                 break;
 361                         }
 362                 }
 363
 364                 if (satisfy_predicate) {
 365                         to_remove.push_back(concrete_pred);
 366                 }
 367
 368                 index++;
 369         }
 370
 371         for (uint i = 0; i < to_remove.size(); i++) {
 372                 ConcretePredicate * concrete_pred = to_remove[i];
 373
 374                 /* Wake up threads */
 375                 thread_id_t tid = concrete_pred->get_tid();
 376                 Thread * thread = model->get_thread(tid);
 377
 378                 model_print("** thread %d is woken up\n", thread->get_id());
 379                 model->get_execution()->getFuzzer()->notify_paused_thread(thread);
 380         }
 381 }
 382
 383 WaitObj * ModelHistory::getWaitObj(thread_id_t tid)
 384 {
 385         int thread_id = id_to_int(tid);
 386         int old_size = thrd_wait_obj->size();
 387         if (old_size <= thread_id) {
 388                 thrd_wait_obj->resize(thread_id + 1);
 389                 for (int i = old_size; i < thread_id + 1; i++) {
 390                         (*thrd_wait_obj)[i] = new WaitObj( int_to_id(i) );
 391                 }
 392         }
 393
 394         return (*thrd_wait_obj)[thread_id];
 395 }
 396
 397 void ModelHistory::add_waiting_thread(thread_id_t self_id,
 398         thread_id_t waiting_for_id, FuncNode * target_node, int dist)
 399 {
 400         WaitObj * self_wait_obj = getWaitObj(self_id);
 401         self_wait_obj->add_waiting_for(waiting_for_id, target_node, dist);
 402
 403         /* Update waited-by relation */
 404         WaitObj * other_wait_obj = getWaitObj(waiting_for_id);
 405         other_wait_obj->add_waited_by(self_id);
 406 }
 407
 408 /* Thread tid is woken up (or notified), so it is not waiting for others anymore */
 409 void ModelHistory::remove_waiting_thread(thread_id_t tid)
 410 {
 411         WaitObj * self_wait_obj = getWaitObj(tid);
 412         thrd_id_set_t * waiting_for = self_wait_obj->getWaitingFor();
 413
 414         /* Remove tid from waited_by's */
 415         thrd_id_set_iter * iter = waiting_for->iterator();
 416         while (iter->hasNext()) {
 417                 thread_id_t other_id = iter->next();
 418                 WaitObj * other_wait_obj = getWaitObj(other_id);
 419                 other_wait_obj->remove_waited_by(tid);
 420         }
 421
 422         self_wait_obj->clear_waiting_for();
 423 }
 424
 425 void ModelHistory::stop_waiting_for_node(thread_id_t self_id,
 426         thread_id_t waiting_for_id, FuncNode * target_node)
 427 {
 428         WaitObj * self_wait_obj = getWaitObj(self_id);
 429         bool thread_removed = self_wait_obj->remove_waiting_for_node(waiting_for_id, target_node);
 430
 431         // model_print("\t%d gives up %d on node %d\n", self_id, waiting_for_id, target_node->get_func_id());
 432
 433         /* If thread self_id is not waiting for waiting_for_id anymore */
 434         if (thread_removed) {
 435                 WaitObj * other_wait_obj = getWaitObj(waiting_for_id);
 436                 other_wait_obj->remove_waited_by(self_id);
 437
 438                 thrd_id_set_t * self_waiting_for = self_wait_obj->getWaitingFor();
 439                 if ( self_waiting_for->isEmpty() ) {
 440                         // model_print("\tthread %d waits for nobody, wake up\n", self_id);
 441                         ModelExecution * execution = model->get_execution();
 442                         Thread * thread = execution->get_thread(self_id);
 443                         execution->getFuzzer()->notify_paused_thread(thread);
 444                 }
 445         }
 446 }
 447
 448 SnapVector<inst_act_map_t *> * ModelHistory::getThrdInstActMap(uint32_t func_id)
 449 {
 450         ASSERT(func_id != 0);
 451
 452         SnapVector<inst_act_map_t *> * maps = func_inst_act_maps->get(func_id);
 453         if (maps == NULL) {
 454                 maps = new SnapVector<inst_act_map_t *>();
 455                 func_inst_act_maps->put(func_id, maps);
 456         }
 457
 458         return maps;
 459 }
 460
 461 bool ModelHistory::skip_action(ModelAction * act, SnapList<ModelAction *> * curr_act_list)
 462 {
 463         bool second_part_of_rmw = act->is_rmwc() || act->is_rmw();
 464         modelclock_t curr_seq_number = act->get_seq_number();
 465
 466         /* Skip actions that are second part of a read modify write */
 467         if (second_part_of_rmw)
 468                 return true;
 469
 470         /* Skip actions with the same sequence number */
 471         if (curr_act_list->size() != 0) {
 472                 ModelAction * last_act = curr_act_list->back();
 473                 if (last_act->get_seq_number() == curr_seq_number)
 474                         return true;
 475         }
 476
 477         /* Skip actions that are paused by fuzzer (sequence number is 0) */
 478         if (curr_seq_number == 0)
 479                 return true;
 480
 481         return false;
 482 }
 483
 484 /* Monitor thread tid and decide whether other threads (that are waiting for tid)
 485  * should keep waiting for this thread or not. Shall only be called when a thread
 486  * enters a function.
 487  *
 488  * Heuristics: If the distance from the current FuncNode to some target node
 489  * ever increases, stop waiting for this thread on this target node.
 490  */
 491 void ModelHistory::monitor_waiting_thread(uint32_t func_id, thread_id_t tid)
 492 {
 493         WaitObj * wait_obj = getWaitObj(tid);
 494         thrd_id_set_t * waited_by = wait_obj->getWaitedBy();
 495         FuncNode * curr_node = func_nodes[func_id];
 496
 497         /* For each thread waiting for tid */
 498         thrd_id_set_iter * tid_iter = waited_by->iterator();
 499         while (tid_iter->hasNext()) {
 500                 thread_id_t waited_by_id = tid_iter->next();
 501                 WaitObj * other_wait_obj = getWaitObj(waited_by_id);
 502
 503                 node_set_t * target_nodes = other_wait_obj->getTargetNodes(tid);
 504                 node_set_iter * node_iter = target_nodes->iterator();
 505                 while (node_iter->hasNext()) {
 506                         FuncNode * target = node_iter->next();
 507                         int old_dist = other_wait_obj->lookup_dist(tid, target);
 508                         int new_dist = curr_node->compute_distance(target, old_dist);
 509
 510                         if (new_dist == -1) {
 511                                 stop_waiting_for_node(waited_by_id, tid, target);
 512                         }
 513                 }
 514         }
 515 }
 516
 517 void monitor_waiting_thread_counter(thread_id_t tid)
 518 {
 519         WaitObj * wait_obj = getWaitObj(tid);
 520         thrd_id_set_t * waited_by = wait_obj->getWaitedBy();
 521         SnapVector<thread_id_t> expire_threads;
 522
 523         // Thread tid has taken an action, update the counter for threads waiting for tid
 524         thrd_id_set_iter * tid_iter = waited_by->iterator();
 525         while (tid_iter->hasNext()) {
 526                 thread_id_t waited_by_id = tid_iter->next();
 527                 WaitObj * other_wait_obj = getWaitObj(waited_by_id);
 528
 529                 bool expire = other_wait_obj->incr_counter(tid);
 530                 if (expire) {
 531                         // TODO: complete
 532                         expire_threads.push_back(tid);
 533                 }
 534         }
 535 }
 536
 537 /* Reallocate some snapshotted memories when new executions start */
 538 void ModelHistory::set_new_exec_flag()
 539 {
 540         for (uint i = 1; i < func_nodes.size(); i++) {
 541                 FuncNode * func_node = func_nodes[i];
 542                 func_node->set_new_exec_flag();
 543         }
 544 }
 545
 546 void ModelHistory::dump_func_node_graph()
 547 {
 548         model_print("digraph func_node_graph {\n");
 549         for (uint i = 1; i < func_nodes.size(); i++) {
 550                 FuncNode * node = func_nodes[i];
 551                 ModelList<FuncNode *> * out_edges = node->get_out_edges();
 552
 553                 model_print("\"%p\" [label=\"%s\"]\n", node, node->get_func_name());
 554                 mllnode<FuncNode *> * it;
 555                 for (it = out_edges->begin(); it != NULL; it = it->getNext()) {
 556                         FuncNode * other = it->getVal();
 557                         model_print("\"%p\" -> \"%p\"\n", node, other);
 558                 }
 559         }
 560         model_print("}\n");
 561 }
 562
 563 void ModelHistory::print_func_node()
 564 {
 565         /* function id starts with 1 */
 566         for (uint32_t i = 1; i < func_nodes.size(); i++) {
 567                 FuncNode * func_node = func_nodes[i];
 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 void ModelHistory::print_waiting_threads()
 581 {
 582         ModelExecution * execution = model->get_execution();
 583         for (unsigned int i = 0; i < execution->get_num_threads();i++) {
 584                 thread_id_t tid = int_to_id(i);
 585                 WaitObj * wait_obj = getWaitObj(tid);
 586                 wait_obj->print_waiting_for();
 587         }
 588
 589         for (unsigned int i = 0; i < execution->get_num_threads();i++) {
 590                 thread_id_t tid = int_to_id(i);
 591                 WaitObj * wait_obj = getWaitObj(tid);
 592                 wait_obj->print_waited_by();
 593         }
 594 }