From: Dan Sugalski <dan@...>
Date: 2002-08-24T03:27:58+09:00
Subject: Re: Why Ruby Uses Mark-and-Sweep GC?

At 3:18 AM +0900 8/24/02, Perry E. Metzger wrote:
>Dan Sugalski <dan@sidhe.org> writes:
>>  At 1:18 AM +0900 8/24/02, William Djaja Tjokroaminata wrote:
>>  >I think one of the problems with reference counting is the circular
>>  >reference, which cannot be handled by the gc.
>>
>>  That's one problem. Reference counting is also more expensive over
>>  the long run than more automatic methods. Also more error-prone.
>
>There are, of course, better gc's than mark and sweep -- compacting
>collectors and generational compacting collectors come to
>mind. Writing an implementation that deals with a compacting collector
>can be a royal pain though -- you never know when an object will get
>moved out from under you.

Believe me, I'm well aware of that pain. :(

When dealing with external libraries, a pure copying collector's not 
an option--Oracle, for example, would *really* hate it if you screwed 
around in its internals changing references to things.

The practical alternative is to have moveable and nonmoveable parts 
of objects, and a mechanism to pin objects so they temporarily don't 
move. It's what we've done with Parrot. Not the only solution, but an 
adequate one under the circumstances.
-- 
                                         Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai
dan@sidhe.org                         have teddy bears and even
                                       teddy bears get drunk