[Mono-gc-list] My arguments

Fergus Henderson fjh@cs.mu.OZ.AU
Wed, 13 Aug 2003 19:22:28 +1000


On 13-Aug-2003, Fernando Diaz <fdiaz@igalia.com> wrote:
> > I'm not familiar enough with exactly how libgc works to know whether
> > this is the case or not, however, I'll take your word for it.
> 
> At the last version of Mono (0.25), lihgc is working with the metadata
> of the objects as the libgc works with GJC (GNU Java Compiler). This is
> and advantage because makes the collector less conservative and more
> accuracy. In spite of the fact, libgc isn't a good collector for Mono,
> because it can take advantage of the complete metadata that Mono
> provides, it only uses a piece of metadata.

I think you meant to say it _can't_ take advantage. 
That's right, the C stack is still scanned conservatively.

> My initial question refers to a simply "stop-the-world" collector. In
> your opinion, which would be better,a copying or a Mark-Compact 
> collector?

I would go for a copying collector to start with, just because it is a
bit simpler.

> In theory, a copying one needs more space (the double than Mark-Compact)
> and less time (only needs to travel through the heap once, instead of
> Mark-Compact that needs to travel through at least twice) than a
> Mark-Compact collector. But in practice, I have read that they are very
> similar (http://www.hpl.hp.com/personal/Hans_Boehm/gc/complexity.html,
> this site talks about a Mark-Sweep collector, but the complexity of
> Mark-Compact it will be very similar to a Mark-Compact one).

Huh?  Did you mean to say that the complexity of Mark-Sweep will be
similar to the complexity of Mark-Compact?

> Personally, i think that a Mark-Compact will be better because we can
> made Mono more compatible with .NET (.NET uses a Mark-Compact collector)
> in this subject.

It will only be "more compatible" in the sense that the performance
characteristics might be a bit more similar.  I think that is a very
low-priority goal.

-- 
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.