From: MenTaLguY <mental@...>
Date: 2008-01-09T08:45:34+09:00
Subject: Re: Manual Memory Management

On Tue, 8 Jan 2008 14:35:28 +0900, Marcin Raczkowski <mailing.mr@gmail.com> wrote:
> I had idea of reference counting GC for a moment, I'm not sure how hard
> it would be to implement and if it's actually usable.

Perl has a reference-counting GC without cycle-detection (except on thread
termination), as does TCL (though it isn't really possible to create real GC
cycles in TCL anyway).  Python has a reference-counting GC with cycle detection.
Microsoft's JScript (JavaScript) is also purely reference-counted.  So it's
certainly done in practice.

However, more mature garbage-collected languages (i.e. smalltalk, lisp dialects,
java, other JavaScript implementations, etc.) with garbage collection almost
universally use some variant of mark-and-sweep instead.  There are a lot of
reasons for this, including nice handling of reference cycles (Microsoft's
JavaScript implementation is notorious for memory leaks) and minimal overhead
for common reference operations.  Generally the amortized cost of mark-and-sweep
is lower too.

I think the real problem that needs to be addressed is that Ruby's mark-and-sweep
implementation is not actually very good, in terms of heap sizing/reclaimation
and collection heuristics.

-mental