public void abort() {
        if (clientHandler == null) {
            throw new IllegalStateException("No client handler registered");
        }
        clientHandler.handleAbort();
    }
Abort a request. This method may only be called by the RPC
client after an asynchronous method invocation was requested.

@throws IllegalStateException if invoked inappropriately
jrt/src/com/yahoo/jrt/Request.java