code: private void checkIfLastPacketTimeout() {
       synchronized (ackQueue) {
               if( !ackQueue.isEmpty()  && (
                               System.currentTimeMillis() - lastPacketSentTime > packetTimeout) ) {
                 DFSClient.LOG.warn("Packet " + ackQueue.getLast().seqno +
                               " of " + block + " is timed out");
               }
       }
    }
docs: Check if the last outstanding packet has not received an ack before
  it is timed out.
  If true, for now just log it.
  We will provide a decent solution to this later on.