Improve AerospikeClient async api

[yarosman]

From official documentation https://www.aerospike.com/docs/client/java/usage/async/index.html for using aerospike client in async mode you should define EventLoop in client policy, and after that call directly eventLoops.next()

...
eventLoops = new NioEventLoops(eventPolicy, eventLoopSize);

ClientPolicy clientPolicy = new ClientPolicy();
clientPolicy.eventLoops = eventLoops;

client = new AerospikeClient(clientPolicy, "localhost", 3000);

Key key = new Key("test", "test", keyIndex);
Bin bin = new Bin("bin", keyIndex);
client.put(eventLoops.next(), listener, null, key, bin);

Why under the hood aerospike can't use eventLoops from ClientPolicy ? And I have to do it by myself

[BrianNichols]

The EventLoop argument to async commands exists because there are cases where a group of commands need to be placed on the same eventloop. This is advantageous because shared data between these commands can be accessed without the use of atomics. Forcing round-robin eventloop distribution will not work for this use case.

I'm considering adding the following code to each async command that performs round-robin distribution as a default when the EventLoop argument is null.

if (eventLoop == null) {
    eventLoop = cluster.eventLoops.next();
}

Would that suffice?

[yarosman]

@BrianNichols Yes, I think it will be enought. And what do you mean: "This is advantageous because shared data between these commands can be accessed without the use of atomics."? Can you show examples ?

[BrianNichols]

A simple example is running 3 async commands and then performing an action when all commands complete. The implementation requires a shared counter to count each command completion. That shared counter can use an non-atomic increment (count++) when all 3 async commands are run in the same event loop.

[BrianNichols]

Java client 5.0.3 released.

https://www.aerospike.com/download/client/java/notes.html#5.0.3