Add CompletableFuture async RPC to channel

[acogoluegnes]

Add CompletableFuture<Command> asyncCompletableRpc(Method method) to Channel. This is foundation to react to asynchronous AMQP methods (most of the resource management methods). Right now, the RPC calls are serialized at the channel level, but this could be improved in the future by using a queue for the outstanding RPC calls.

Fixes #215

[michaelklishin]

@acogoluegnes is this ready for QA? It was submitted in March but there is no "DO NOT MERGE" in the title.

[acogoluegnes]

@michaelklishin Yes, it's ready for QA.

[michaelklishin]

This turned out to be more straightforward than I expected but there's a couple of small things that need addressing.

[michaelklishin]

We should wait for a confirm here, otherwise there can be a race condition between a message send by the channel to the queue master process and handling of the basic.consume below.

[michaelklishin]

Since this is a public method, I'd like to clarify the name. How about exceptionWrappingAsyncRpc?

[michaelklishin]

I now see we already have a "non-async" method with a similar name from way back. Disregard the above.

[michaelklishin]

I added publisher confirms to the test.

[ofavre]

This asyncRpc facility does not permit sending Commands, that is Methods with body.
How can I perform an asyncBasicPublic() then?

[acogoluegnes]

@ofavre If you mean publishing a message asynchronously, basic.publish is already asynchronous.

Please move the discussion to rabbitmq-users if you have further questions.

[michaelklishin]

None of this code is meant to be used directly. Use the Channel API. Publishing is so asynchronous there is no response for it in the protocol (so Publisher Confirms had to be introduced).