CODEWITHSUNDEEP
scalaakka
matanox
matanox

Reputation: 13686

Can an actor return an object to a future waiting on an ask?

I would like to use an actor to synchronize access to a pool of objects. The actor would manage the objects in the pool including their state (busy v.s. free to allocate). When asked by non-actor code, it would return an object from the pool once available. Thus the calling code has an abstraction for obtaining an object to work with.

To get this kind of abstraction, I need the actor to be able to respond to its message senders' ask messages with the object the actor is allocating to them. Can this be accomplished and would it be resource intensive to pass a whole object via a message?

Upvotes: 2

Views: 256

Answers (1)

Eugene Loy
Eugene Loy

Reputation: 12416

There is nothing wrong in returning future that will be completed later, by actor.

Keep an eye on this matter, however: will you complete the future with some mutable internal actor state or not?

If the answer is no - it is ok and there is nothing you should worry about.

If the answer is yes - you'll have to take care of synchronization, since actor/external code may mutate this state in different threads (which, kind of defeats the purpose of using actors).

Otherwise it is legit.

BTW, this is not something that is specific to futures only. You have to follow this for any message you send from actor.

UPDATE: extending my answer to address OP's comment.

Question was primarily about returning an object that's not an actor, from an actor, not just about the scenario... not sure if this answer relates to just that... an object can be much heavier than just a "regular" message... unless Akka passes a message in a way equivalent to a reference / interning.

There is no special requirements about "heaviness" of the message in akka and in general it can be any object (you can infer this from the fact that Any is used for the type of the message instead of some akka-defined message class/trait with set of defined limitations).

Of course, you have to treat specially situations when messages should be persisted or sent to remote host, but this is kind of special case. In this scenario you have to ensure that serialization is handled properly.

Anyway, if the message (object) does not leave boundaries of the same jvm - it is ok for object to hold any amount of state.

Upvotes: 2

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