// SocketServer.java
// ...
  public ScheduledFuture<IOException> startThenStopAfter(long delay, TimeUnit unit) {
    if (stopRequested.get()) {
      return null;
    }
    synchronized (this) {
      start();
      ScheduledFuture<?> existingFuture = this.timeoutFuture;
      if (existingFuture != null) {
        existingFuture.cancel(false);
        this.timeoutFuture = null; // violation here
      }

      return (this.timeoutFuture = TIMEOUTS.schedule(new Callable<IOException>() {
        @SuppressFBWarnings("THROWS_METHOD_THROWS_CLAUSE_BASIC_EXCEPTION")
        @Override
        public IOException call() throws Exception {
          try {
            stop();
            return null;
          } catch (IOException e) {
            return e;
          }
        }
      }, delay, unit));
    }
  }