static ISleeper defaultSleeper() {
  ret new ISleeper {
    java.util.Timer timer;
    
    public void doLater(long targetSysTime, Runnable r) {
      timer = main doLater(max(0, targetSysTime-sysNow()), r);
    }
    
    public void close() {
      cancelTimer(timer);
    }
  };
}