@Override
  public void close() {
    if (resetLastPeeked) {
      returnToQueuePreviouslyPeekedEvents();
      resetLastPeeked = false;
    }
  }
This method does the cleanup of any threads, sockets, connection that are held up by the queue.
Note that this cleanup doesn't clean the data held by the queue.
geode-core/src/main/java/org/apache/geode/internal/cache/wan/parallel/ParallelGatewaySenderQueue.java