sclass DoLater implements AutoCloseable {
  long targetSysTime;
  volatile Runnable action;
  transient ISleeper sleeper;
  transient Executor executor;
  transient bool enabled;
  
  *() {}
  *(long *targetSysTime, Runnable *action) {}
  
  void enable() {
    if (enabled) ret;
    if (sleeper == null) sleeper = defaultSleeper();
    sleeper.doLater(targetSysTime, r {
      runWithExecutor(action, executor);
    });
  }
  
  public void close {
    main close(sleeper);
  }
}