Typed actor supervisor hierarchies (in Java)

[Josh]

Is it possible to create a supervisor hierarchy consisting of typed actors in Java? The docs imply that it is possible:

http://doc.akka.io/docs/akka/2.0.1/java/typed-actors.html

"Since you can obtain a contextual Typed Actor Extension by passing in an ActorContext you can create child Typed Actors by invoking typedActorOf(..) on that."

But there doesn't appear to be a typedActorOf method on ActorContext. How do I create a supervisor hierarchy of typed actors?

Followup question - when an exception occurs in an actor where the supervisor is a typed actor, and the exception is escalated, where does the exception go?

Cheers,

Josh

[√iktor Ҡlang]

defget (context: ActorContext): TypedActorFactory

Returns a contextual TypedActorFactory of this extension, this means that any TypedActors created by this TypedActorExtension will be children to the specified context, this allows for creating hierarchies of TypedActors.

http://doc.akka.io/api/akka/2.0.1/#akka.actor.TypedActor$

It's also described here: http://doc.akka.io/docs/akka/2.0.1/java/typed-actors.html

1. //Returns a contextual instance of the Typed Actor Extension
2. //this means that if you create other Typed Actors with this,
3. //they will become children to the current Typed Actor.
4. TypedActor.get(TypedActor.context());

Cheers,

√

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Viktor Klang

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Typesafe - The software stack for applications that scale

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[Jonas Bonér]

We should add an example of how to create a supervisor hierarchy with typed actors. Current docs are close to non existant.

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Jonas Bonér

[√iktor Ҡlang]

On Thu, May 24, 2012 at 11:42 PM, Jonas Bonér <jo...@jonasboner.com> wrote:

We should add an example of how to create a supervisor hierarchy with typed actors. Current docs are close to non existant.

Yeah, definitely, I'll do that. Always tricky to know what people will understand from a description and what needs an example.

[√iktor Ҡlang]

Done

[Josh]

Working good - thanks.

The second thing I was wondering about: Are failures intended to be handled ONLY by one of the pre-defined Directives? Is there any way for a caller (typed actor)/message sender (untyped actor) to learn of a failure, or for a supervisor to learn of a failure, and attempt to handle it?

Cheers,

Josh

On Thursday, May 24, 2012 2:25:46 PM UTC-7, √ wrote:

defget (context: ActorContext): TypedActorFactory

Returns a contextual TypedActorFactory of this extension, this means that any TypedActors created by this TypedActorExtension will be children to the specified context, this allows for creating hierarchies of TypedActors.

http://doc.akka.io/api/akka/2.0.1/#akka.actor.TypedActor$

It's also described here: http://doc.akka.io/docs/akka/2.0.1/java/typed-actors.html

1. //Returns a contextual instance of the Typed Actor Extension
2. //this means that if you create other Typed Actors with this,
3. //they will become children to the current Typed Actor.
4. TypedActor.get(TypedActor.context());

Cheers,

√

On Thu, May 24, 2012 at 11:17 PM, Josh <paces...@gmail.com> wrote:

Is it possible to create a supervisor hierarchy consisting of typed actors in Java? The docs imply that it is possible:

http://doc.akka.io/docs/akka/2.0.1/java/typed-actors.html

"Since you can obtain a contextual Typed Actor Extension by passing in an ActorContext you can create child Typed Actors by invoking typedActorOf(..) on that."

But there doesn't appear to be a typedActorOf method on ActorContext. How do I create a supervisor hierarchy of typed actors?

Followup question - when an exception occurs in an actor where the supervisor is a typed actor, and the exception is escalated, where does the exception go?

Cheers,

Josh

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[√iktor Ҡlang]

Hi Josh,

On Fri, May 25, 2012 at 1:01 AM, Josh <paces...@gmail.com> wrote:

Working good - thanks.

Excellent!

 

The second thing I was wondering about: Are failures intended to be handled ONLY by one of the pre-defined Directives?

Yes

 

Is there any way for a caller (typed actor)/message sender (untyped actor) to learn of a failure,

Yes, please read the docs: http://doc.akka.io/docs/akka/2.0.1/scala/typed-actors.html#Method_dispatch_semantics

 

or for a supervisor to learn of a failure, and attempt to handle it?

Yes, that is the job description of a supervisor, to learn of failures and attempt to handle them.

Cheers,

√

 

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[Josh]

Thanks for the response.

From the docs and a bit of experimenting, it looks like exceptions only get thrown back to the caller/sender for typed actors? For typed actors that do result in exceptions being thrown back to the caller, is it recommended to handle those via supervision instead of try/catch in the caller?

Cheers,

Josh

[Roland Kuhn]

Hi Josh,

TypedActors really should be called something else, because they are not really actors in the model sense. Please have a look at this blog (http://letitcrash.com/post/19074284309/when-to-use-typedactors) for a recommendation on when to use them.

To highlight what I think is the core of the problem: POJOs and actors are two ways of doing object oriented programming (which is not at all about inheritance, mind you), and these ways differ fundamentally. POJOs are poked arbitrarily at the whim of anybody who happens to have a reference while actors consume messages at their own convenience, which is why I think that actors offer better encapsulation—the core feature of OO. Keeping this in mind should help understanding why trying to wrap an actor in POJO clothes will never yield a completely consistent picture.

This ties back into your problem because supervision is a feature only offered by real actors, and it leaks when forcing the POJO looks onto the crew.

Regards,

Roland

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Typesafe – The software stack for applications that scale.
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[Jonas Boner]

Another big difference is the dynamic nature in "real" actors and
static nature of typed-actors.

This means that in the real actors are much more loosely coupled and
we can easily do things like changing the protocol/interface/impl of
the actor at runtime through 'become', very easily do things like
supervision, location transparency, dynamic proxying through routers
etc. These things are much harder in the static typed-actor world.

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[Josh]

Good stuff. Thanks for the responses all.

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