Closing over java.util.concurrent.ConcurrentHashMap inside a Future ?

[Soumya Simanta]

I've an actor where I want to store my mutable state inside a map.

Clients can send Get(key:String) and Put(key:String,value:String) messages to this actor. 

I'm considering the following options. 

1. Don't use futures inside the Actor's receive method. In this may have a negative impact on both latency as well as throughput in case I've a large number of gets/puts. because both will be performed in sequence. 

2. Use java.util.concurrent.ConcurrentHashMap and then invoke the gets and puts inside a Future. 

Given that java.util.concurrent.ConcurrentHashMap is thread-safe, I was wondering if it is still a problem to close over the concurrentHashMap inside a Future created for each put and get. 

PS: I'm aware of the fact that it's a really bad idea to close over mutable state inside  a Future inside an Actor but I'm still interested to know if in this particular case it is correct or not? 

[Jeroen Gordijn]

Hi Soumya,

Do agents cover your usecase?
http://doc.akka.io/docs/akka/snapshot/scala/agents.html

Cheers,
Jeroen

[Soumya Simanta]

@Jeroen - Thanks. I've not looked at agents yet. 

[Konrad Malawski]

Hi Soumya,

Why do you have the concurrent hash map in the Actor at all?

When using Actors you can easily have a var with an immutable.Map

which you can update/read from the Actor's receive. If you need to use Futures,

apply the pipeTo pattern to forward the action to self.

Of course, if you actually have benchmarked this and observe that this is not fast enough

(though it should be fast enough for many use-cases) you could drop down to mutable things.

The reason I'd advertise to use vars with immutable datastructures is that you don't

have the problem of accidentally sending a mutable thing over to someone - in case

of the immutable Map you'd send an outdated version, but at least noone can break it.

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Cheers,

Konrad 'ktoso' Malawski

Akka @ Typesafe