Akka Extension dependencies

[Andrey Kuznetsov]

Is there any way of controlling Akka Extensions order?

I found out that Akka loads extension B in parallel with extension A even if extension B follows A in `akka.extensions` config value.

I can explicitly call A.apply from B.apply, but maybe there is (o there SHOULD) be more convenient way for controlling it?

[Viktor Klang]

Hi Andrey,

Akka doesn't load them in parallel:

private def loadExtensions() {
  immutableSeq(settings.config.getStringList("akka.extensions")) foreach { fqcn ⇒
    dynamicAccess.getObjectFor[AnyRef](fqcn) recoverWith { case _ ⇒ dynamicAccess.createInstanceFor[AnyRef](fqcn, Nil) } match {
      case Success(p: ExtensionIdProvider) ⇒ registerExtension(p.lookup())
      case Success(p: ExtensionId[_])      ⇒ registerExtension(p)
      case Success(other)                  ⇒ log.error("[{}] is not an 'ExtensionIdProvider' or 'ExtensionId', skipping...", fqcn)
      case Failure(problem)                ⇒ log.error(problem, "While trying to load extension [{}], skipping...", fqcn)
    }
  }
}

However, extensions are loaded on demand so an extension might trigger the loading of another extension or some other piece of logic running on a separate thread could trigger the loading of an extension.

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Cheers,

√

[Andrey Kuznetsov]

I see, thanks. But why such logic should be in a separate thread?

[Viktor Klang]

On Sun, Nov 1, 2015 at 9:11 PM, Andrey Kuznetsov <fe...@loathing.in> wrote:

I see, thanks. But why such logic should be in a separate thread?

An Actor that is spawned that accesses an Extension, for instance

--

Cheers,

√

[Andrey Kuznetsov]

Did I get it right, an actor can't trigger extension loading directly, and it should trigger extension loading in the other thread?

 

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Andrey Kuznetsov

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[Viktor Klang]

No.

I'm saying that Akka loads the extensions listed in the config sequentially, but extensions can trigger the loading of other extensions, both in the thread loaing the extension, but allso on other threads, for instance if an extension triggers the load of other extensions from within an actor it has spawned or otherwise.