RPC: real garbage collection notes

[natevw]

It's a bit premature (Chrome still has ESnext stuff behind a flag) but I'm realizing that the coincident of WebRTC and WeakMap support should be pretty likely!

So here's how I think this might work:

serialize — stores object/function in a old-fashioned id:target object mapping. deserialize — creates wrapper object/function and tracks it in weakmap[id] = wrapper. when this is GC'ed the remote should unmap the actual target.

Periodically, the serializer must send Object.keys(exposedObjects) to the deserializer. The deserializer then sends back a list of which weakmap.has(id) return false, which the serializer should remove from its strong mapping.

[This assumes that values in a weakmap can GC and cause the keypair to go away, which I need to check with the actual draft spec.]

[natevw]

Hmmm, current spec says:

If an object that is being used as the key of a WeakMap key/value pair is only reachable by following a chain of references that start within that WeakMap, then that key/value pair is inaccessible and is automatically removed from the WeakMap. WeakMap implementations must detect and remove such key/value pairs and any associated resources.

This doesn't sound nearly as promising as a cursory reading of the strawman. c.f. http://www.nczonline.net/blog/2012/11/06/ecmascript-6-collections-part-3-weakmaps/ for potential clarification.

[natevw]

Also note a primitive value can't be used for weakmap key, so further cleverness might be needed there if that's not already implying that this idea won't work.

I've actually got a sinking feeling that what I'm trying to do (detect the garbage collection of an object) is precisely what WeakMap is designed to prevent.

[natevw]

With WeakMaps alone, garbage collection remains as unobservable as before — http://wiki.ecmascript.org/doku.php?id=harmony:weak_maps