From: Brian Candler <b.candler@...>
Date: 2011-08-02T16:36:14+09:00
Subject: Re: system stack error in ObjectSpace.each_object

luke gruber wrote in post #1014312:
> 1) For the container idea, how would you go about doing this?

Others have answered this already. (There's weakref if you really need a 
container which doesn't prevent garbage collection, but I've never had 
to use it)

> 2) As for ObjectSpace returning dead objects, is there a way to force GC
> during runtime?

You can force garbage collection, but the issue is rather that the 
garbage collector is conservative; any bit of junk sitting on the stack 
which looks like it *might* be a reference to an object is treated as if 
it is, just to be on the safe side. This means that some objects which 
really could be garbage-collected, aren't.

You can write some simple test programs using ObjectSpace to count the 
number of objects of each class, create some and drop the refs, then run 
GC.start, then count them again. It's not unusual to see one or two 
objects left in a particular class, even though there are no live refs.

> Also, does taking all variables that point to an object
> and pointing them to nil effectively dangle an object like this?

Explicitly destroying all references to an object will normally make it 
eligible for garbage collection: it's a mark-and-sweep collector, so the 
object won't be found during the mark phase. But as I say, a few objects 
may be considered live when technically they aren't.

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