Make Celluloid.new link by default if possible.

[cararemixed]

I've added an experimental change that makes new link by default if called within an actor's context. spawn remains unlinked by default and the new_link method will still require an actor context to link to, unlike new.

I've also added some minimal spec coverage but we might want to clean that up if we can decide on a clearer style to write these specs with proper actor cleanup.

[tarcieri]

Some useful background on this is how Akka works:

http://doc.akka.io/docs/akka/snapshot/general/supervision.html

Akka implements a specific form called “parental supervision”. Actors can only be created by other actors—where the top-level actor is provided by the library—and each created actor is supervised by its parent. This restriction makes the formation of actor supervision hierarchies implicit and encourages sound design decisions. It should be noted that this also guarantees that actors cannot be orphaned or attached to supervisors from the outside, which might otherwise catch them unawares. In addition, this yields a natural and clean shutdown procedure for (sub-trees of) actor applications.

Seems like a good idea to me.

[cararemixed]

I should probably expand on the documentation if Akka is the sort of example we want to follow.

[tarcieri]

Seems good to me ;)

[fujin]

Yeah, this is cool. I like. I wasn't aware of how Akka works, but we'd been building stuff like this into nearly all of our actor supervision trees anyway. 👍

[PragTob]

I like it 👍

[cararemixed]

I've tried to provide some comments as guidance for the three behaviors. We can probably update the wiki to reflect this once merged and released if everything looks fine.

[benlangfeld]

I like this. I would, though, urge caution in releasing it (RC with sufficient time for testing) since it may have unexpected consequences in existing apps.

[cararemixed]

We could probably add logging to warns when implicit links and redundant links are added. The question might then be if that should be released separately first or if we simply should make it configurable with the intent to deprecate the old behavior.

[cararemixed]

It also seems like Travis is reporting errors that my build doesn't show locally. The test suite might have some timing bugs. Can anyone else reproduce the problems?

[tarcieri]

@strmpnk I'm definitely able to reproduce this sporadically on both JRuby and rbx. Here's the failure:

Failures:

  1) Celluloid::SyncCall aborts with ArgumentError when a method is called with too many arguments
     Failure/Error: actor.should be_alive
       expected alive? to return true, got false

As you presume, the existing tests may make some assumptions about ordering that you're changing. Let me take a look...

[halorgium]

I would be tempted to not split up the #new and #spawn methods.

Would it be better to consider this change along with supervision? See #148.
For me, I would really like a simple way to do supervision and linking as one thing.

[halorgium]

I started a discussion about this at https://groups.google.com/d/msg/celluloid-ruby/Rd2AurcPNpo/xejk2OT3zwEJ