Re: Unrecovered memory leak thoughts.

On 11/8/07, Roger Pack <[e-mail]> wrote:
> So it seems from my trivial analysis that there are instances when
> Ruby's GC doesn't recover recoverable memory.
...
> Anyway, I had a few thoughts with regard to the ominous 'ruby doesn't
> recover all available memory for recovery'
>
> Questions:
> when it walks the stack does it perhaps go over sections that are
> 'unused' of the stack, that contain old references to things?  Are
> there varmaps perhaps in there that need to be cleaned, as you go out
> of scope?  Or locals? Or parameters that should be cleared as you go
> out of scope, perhaps?
> Pointers to varmaps or scope objects that were passed as parameters,
> maybe, that need to be set to 0?

Well, most (all?) garbage collection approaches don't guarantee that
they reclaim space from all unreachable objects, or if they do that
they do it quickly.  There are trade-offs between the bookkeeping
require to do this and overall performance.

The key thing that a GC HAS to ensure is that it doesn't reclaim space
for objects which are still alive!

...

> Anyway good luck to all.  Seems almost like it would be easier to just
> write a reference counting GC than find this bug, should it be a bug
> :)  I'd be willing to offer someone $100 US to build a reference
> counting GC for 1.9 :)

Reference counting has a couple of unfortunate 'features'.

First, it's pretty inefficient in that it imposes an overhead on every
variable assignment to adjust reference counts.  Second, it can easily
leave permanently noncollectable constellations of  unreachable
objects which form reference cycles.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/