Reader getReader() {
      currentReader = (currentReader + 1) % readers.length;
      return readers[currentReader];
    }
Updating the readSelector while it's being used is not thread-safe, so the connection must
be queued. The reader will drain the queue and update its readSelector before performing
the next select
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/SimpleRpcServer.java