extends AtomicReference<@Nullable Runnable> implements Runnable {
  static {
    // Prevent rare disastrous classloading in first call to LockSupport.park.
    // See: https://bugs.openjdk.java.net/browse/JDK-8074773
    @SuppressWarnings("unused")
    Class<?> ensureLoaded = LockSupport.class;
  }

  private static final class DoNothingRunnable implements Runnable {
    @Override
    public void run() {}
  }