GC performance - was Re: [gclist] GC topics

[Darius Blasband]

> 
> Darius Blasband, you wrote:
> > 
> > In any case, I think we agree on the fact that precise GC is far easier,
> > and globally more reliable and faster than conservative GC's...
> 
> I definitely disagree about precise GC being easier.
>
Let's say that it is surely easier to implement (from scratch), since
it requires almost no knowlegde about the internals of the machine,
memory mapping of the compiler, etc...


> Plugging in Hans Boehm's conservative garbage collector to our
> Mercury implementation was very easy.  It took a couple of days at most.
Well, I guess that plugging in a GC is indeed easier than writing
one's own, but is this the issue ?

> 
> Writing our own precise GC has so far consumed the work of one honours
> thesis and two summer studentships (i.e. about 6 man-months of work),
> and it still isn't complete.
> 
I simply do not understand: it does not match my experience at all, and from
what I know of Mercury (purely logic typed language, generates intermediate 
C, am I right ?) there is nothing which should explain why it is so
difficult. Maybe the simple fact that it is being implemented on an existing
system, instead of being part of the original design. I don't know. My
experience about implementing a precise GC tells exactly the opposite.
Any clue on the reason for this ? Anything too specific about Mercury ?

Cheers...

Darius