C++ PlaceholderEntry类代码示例

void PlaceholderTable::classes_do(KlassClosure* f) {
  for (int index = 0; index < table_size(); index++) {
    for (PlaceholderEntry* probe = bucket(index);
                           probe != NULL;
                           probe = probe->next()) {
      probe->classes_do(f);
    }
  }
}

// do all entries in the placeholder table
void PlaceholderTable::entries_do(void f(Symbol*)) {
  for (int index = 0; index < table_size(); index++) {
    for (PlaceholderEntry* probe = bucket(index);
                           probe != NULL;
                           probe = probe->next()) {
      f(probe->klassname());
    }
  }
}

// do all entries in the placeholder table
void PlaceholderTable::entries_do(void f(symbolOop, oop)) {
  for (int index = 0; index < table_size(); index++) {
    for (PlaceholderEntry* probe = bucket(index);
                           probe != NULL;
                           probe = probe->next()) {
      f(probe->klass(), probe->loader());
    }
  }
}

// placeholder used to track class loading internal states
// placeholder existence now for loading superclass/superinterface
// superthreadQ tracks class circularity, while loading superclass/superinterface
// loadInstanceThreadQ tracks load_instance_class calls
// definer() tracks the single thread that owns define token
// defineThreadQ tracks waiters on defining thread's results
// 1st claimant creates placeholder
// find_and_add adds SeenThread entry for appropriate queue
// All claimants remove SeenThread after completing action
// On removal: if definer and all queues empty, remove entry
// Note: you can be in both placeholders and systemDictionary
// see parse_stream for redefine classes
// Therefore - must always check SD first
// Ignores the case where entry is not found
void PlaceholderTable::find_and_remove(int index, unsigned int hash,
                       symbolHandle name, Handle loader, Thread* thread) {
    assert_locked_or_safepoint(SystemDictionary_lock);
    PlaceholderEntry *probe = get_entry(index, hash, name, loader);
    if (probe != NULL) {
       // No other threads using this entry
       if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL)
          && (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)) {
         remove_entry(index, hash, name, loader);
       }
    }
  }

void PlaceholderTable::print() {
  for (int pindex = 0; pindex < table_size(); pindex++) {
    for (PlaceholderEntry* probe = bucket(pindex);
                           probe != NULL;
                           probe = probe->next()) {
      if (Verbose) tty->print("%4d: ", pindex);
      tty->print(" place holder ");

      probe->print();
      tty->cr();
    }
  }
}

void PlaceholderTable::verify() {
  int element_count = 0;
  for (int pindex = 0; pindex < table_size(); pindex++) {
    for (PlaceholderEntry* probe = bucket(pindex);
                           probe != NULL;
                           probe = probe->next()) {
      probe->verify();
      element_count++;  // both klasses and place holders count
    }
  }
  guarantee(number_of_entries() == element_count,
            "Verify of system dictionary failed");
}

  // find_and_add returns probe pointer - old or new
  // If no entry exists, add a placeholder entry
  // If entry exists, reuse entry
  // For both, push SeenThread for classloadAction
  // if havesupername: this is used for circularity for instanceklass loading
PlaceholderEntry* PlaceholderTable::find_and_add(int index, unsigned int hash, symbolHandle name, Handle loader, classloadAction action, symbolHandle supername, Thread* thread) {
  PlaceholderEntry* probe = get_entry(index, hash, name, loader);
  if (probe == NULL) {
    // Nothing found, add place holder
    add_entry(index, hash, name, loader, (action == LOAD_SUPER), supername);
    probe = get_entry(index, hash, name, loader);
  } else {
    if (action == LOAD_SUPER) {
      probe->set_havesupername(true);
      probe->set_supername(supername());
    }
  }
  if (probe) probe->add_seen_thread(thread, action);
  return probe;
}

// Remove a placeholder object.
void PlaceholderTable::remove_entry(int index, unsigned int hash,
                                    Symbol* class_name,
                                    ClassLoaderData* loader_data) {
  assert_locked_or_safepoint(SystemDictionary_lock);
  PlaceholderEntry** p = bucket_addr(index);
  while (*p) {
    PlaceholderEntry *probe = *p;
    if (probe->hash() == hash && probe->equals(class_name, loader_data)) {
      // Delete entry
      *p = probe->next();
      free_entry(probe);
      return;
    }
    p = probe->next_addr();
  }
}

PlaceholderEntry* PlaceholderTable::new_entry(int hash, symbolOop name,
                                              oop loader, bool havesupername,
                                              symbolOop supername) {
  PlaceholderEntry* entry = (PlaceholderEntry*)Hashtable::new_entry(hash, name);
  entry->set_loader(loader);
  entry->set_havesupername(havesupername);
  entry->set_supername(supername);
  entry->set_superThreadQ(NULL);
  entry->set_loadInstanceThreadQ(NULL);
  entry->set_defineThreadQ(NULL);
  entry->set_definer(NULL);
  entry->set_instanceKlass(NULL);
  return entry;
}

PlaceholderEntry* PlaceholderTable::new_entry(int hash, Symbol* name,
                                              ClassLoaderData* loader_data,
                                              bool havesupername,
                                              Symbol* supername) {
  PlaceholderEntry* entry = (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::new_entry(hash, name);
  // Hashtable with Symbol* literal must increment and decrement refcount.
  name->increment_refcount();
  entry->set_loader_data(loader_data);
  entry->set_havesupername(havesupername);
  entry->set_supername(supername);
  entry->set_superThreadQ(NULL);
  entry->set_loadInstanceThreadQ(NULL);
  entry->set_defineThreadQ(NULL);
  entry->set_definer(NULL);
  entry->set_instance_klass(NULL);
  return entry;
}

Symbol* PlaceholderTable::find_entry(int index, unsigned int hash,
                                       Symbol* class_name,
                                       ClassLoaderData* loader_data) {
  PlaceholderEntry* probe = get_entry(index, hash, class_name, loader_data);
  return (probe? probe->klassname(): (Symbol*)NULL);
}