@Override
    public void handleReply(Reply reply) {
        if (destroyed.get()) {
            reply.discard();
            return;
        }
        long seqId = (Long)reply.getContext(); // non-sequenced messages do not enter here
        if (reply.getTrace().shouldTrace(TraceLevel.COMPONENT)) {
            reply.getTrace().trace(TraceLevel.COMPONENT,
                                   "Sequencer received reply with sequence id '" + seqId + "'.");
        }
        sendNextInSequence(seqId);
        ReplyHandler handler = reply.popHandler();
        handler.handleReply(reply);
    }
Lookup the sequencing id of an incoming reply to pop the front of the corresponding queue, and then send the next
message in line, if any.

@param reply The reply received.
messagebus/src/main/java/com/yahoo/messagebus/Sequencer.java