void
JvmtiEnvBase::set_event_callbacks(const jvmtiEventCallbacks* callbacks,
                                               jint size_of_callbacks) {

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(), "sanity check");

  {- -------------------------------------------
  (1) (変数宣言など)
      ---------------------------------------- -}

      size_t byte_cnt = sizeof(jvmtiEventCallbacks);

  {- -------------------------------------------
  (1) 最初に _event_callbacks フィールドを 0 クリアしておく.
      ---------------------------------------- -}

      // clear in either case to be sure we got any gap between sizes
      memset(&_event_callbacks, 0, byte_cnt);

  {- -------------------------------------------
  (1) memcpy() を呼んで, callbacks 引数で指定された関数ポインタを _event_callbacks フィールドに書き込む.

      (ただし, callbacks 引数が NULL であれば何もしない)
      (また, この JVMTI environment が既に破棄されている場合も (= JvmtiEnvBase::is_valid() が false) 何もしない 
       (See: JvmtiEnvBase::dispose())).
      ---------------------------------------- -}

      // Now that JvmtiThreadState_lock is held, prevent a possible race condition where events
      // are re-enabled by a call to set event callbacks where the DisposeEnvironment
      // occurs after the boiler-plate environment check and before the lock is acquired.
      if (callbacks != NULL && is_valid()) {
        if (size_of_callbacks < (jint)byte_cnt) {
          byte_cnt = size_of_callbacks;
        }
        memcpy(&_event_callbacks, callbacks, byte_cnt);
      }
    }