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    <p>I think this should be quite simple using some Java NIO framework like e.g. <a href="http://www.jboss.org/netty" rel="nofollow">netty</a>. Haven't used an Actor framework so no idea if that wouldn't be a better fit though.</p> <p>Basically you create one class that handles the whole communication and stores the necessary information - the framework handles the whole threading in the background you just provide a method for e.g. messageReceived and handle it there.</p> <p>The downside is, that you have to basically write your own state machine which may not be that simple - but it's certainly the easiest way to use NIO.</p> <p>Example: </p> <pre><code>enum State { S0, S1 } private State state = State.S0; public void messageReceived( ChannelHandlerContext ctx, MessageEvent e) { switch(state) { case S0: // read object from channel and write appropriate response e.getChannel().write("HELO"); // writes are asynchronous state = State.S1; break; case S1: // same as S0 e.getChannel().write("DONE"); break; } } </code></pre> <p>Note that reading the netty tutorial is still absolutely necessary, because there are things about NIO that aren't self explaining (at least they weren't for me). But there are several examples that are easy to work through which should teach you the basics.</p>
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    1. POHow can I implement a request-response protocol without blocking while awaiting response?
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    1. COThank you. I have neither heard of nor used Netty before. I will definitely look into it. (When it comes to Java NIO frameworks I have only used [Apache MINA](http://mina.apache.org/). Maybe they are similar?) By writing my own state machine I am assuming that it would handle logic in a matter similar to: `if(state == AwaitingResponseForA && response.is("OK")) { /* Perform next step and change state */ }` Are there any available frameworks for helping with this sort of thing? (This is basically where I was hoping that Actor frameworks might be handy.)
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    2. COI just noticed your edit. Thank you! That is very helpful and I am almost certainly going to proceed with such a solution, however I would very much like to find a framework for assisting in making this state machine since it might become very big and unmaintainable otherwise.
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    3. CO@Jiddo Yes they're probably similar. I've only used netty based on some posts here on SO where the basic agreement was that netty is the fastest and rather simple framework (I've not comparison but it's certainly not complicated). I'm not aware of any help with writing state machines (yield statements/coroutines could be useful here), but I imagine you'd still have to come up with all states and transitions anyhow in which case you've already done most of the hard work - just creating the switch and enum is a solely mechanic task. Maybe I've done just too much hardware stuff though ;-)
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