[Openmcl-devel] sharing data between fortran and OpenMCL
ch-openmcl at bobobeach.com
Fri Oct 29 12:08:39 PDT 2004
On Oct 29, 2004, at 1:37 AM, Gary Byers wrote:
> It's admittedly a little hard to tell, but I think that I was being
> facetious. If you were to (hypothetically) try to combine:
> - a fully relocating GC
> - preemptively-scheduled threads, which make it difficult to predict
> when a GC might happen
> - the ability to pass the (fleeting, transitory) address of some lisp
> object(s) to foreign code
> you'd likely find that things worked fine a high percentage of the time
> and would fail (possibly with bizarre symptoms, possibly with
> symptoms) some small percentage of the time.
I get all of this, yet I still think I want the ability to pass the
address of some lisp object to foreign code. Forgive me if I'm
repeating myself and please forgive my general cluelessness on lisp
> [The point of the FOO example is that it and the practice of passing
> the address of relocatable lisp objects to foreign code can both
> lead to memory-corruption scenarios that're very hard to debug.]
Yeah, but it's not like the relocatable lisp objects are necessary for
memory-corruption scenarios that are very hard to debug. Sure, the may
make the problem more likely, but this, is part of life. I agree that
trying to minimize these scenarios is a good thing.
> Saying "I'll implement this, but someone else gets to debug the
> that it'll cause" is intended to mean "it wouldn't be a good idea to
> implement this, and I'm glad that it isn't implemented because
> those problems is often virtually impossible."
Hmm... Ok, I'm willing to consider alternatives. For better or worse,
I'm attempting to try to port matlisp, which is basically a wrapper
around the BLAS and LAPACK, and maybe a few other, fortran libraries. I
don't really want to re-implement all of this nice matrix math stuff in
lisp. Clearly, there are off-the-shelf packages like MATLAB to build
their own high level language around this stuff, but I, for hopefully
obvious reasons, would like to use lisp as that higher-level
(higher-level than Fortran) language. The matlisp guys have made this
work for sbcl, cmucl, acl, etc... And I think I'd like to make this
work for openmcl.
There is another approach, which is a copy from lisp to/from non-lisp
data structures on every round trip to the fortran code. This would
presumably avoid (or minimize) the problems we've been discussing, but
I think this would incur a big performance overhead.
I hate to keep flogging this same horse, but I really would like some
nice matrix package to use from OpenMCL and I get the feeling that the
one I've cobbled together on my own is suboptimal.
> If you remember the bouncer-in-the-diner analogy, the compaction
> algorithm (the bouncer shoving diner customers around to make all free
> space contiguous) is simple and linear in the number of active
> customers, and it makes subsequent seating (allocation) trivial.
> Partial compaction/relocation algorithms are certainly possible (see
> the traditional MacOS memory manager), but they're generally slower,
> more complicated, less effective, and complicate allocation (see the
> traditional MacOS memory manager.)
> I think that the schemes that would work better are:
> - inside a certain syntactic construct , it'd be legal to use some
> primitive to obtain the address of (at least certain types of) lisp
> objects and to pass those addresses to foreign code, with the
> understanding that those addresses have "dynamic extent" and cease
> to be valid when the construct exits.
Sounds like what I need.
> - (harder, but more general): provide for the allocation of lisp
> objects in one or more "static" memory areas. In general (there
> may be room for exceptions), the GC might reclaim the memory used
> by a statically-allocated object, but it would never move such
> objects around (and it'd be legal/safe for foreign code to point
> at static objects, and doing so wouldn't constrain the GC from
> doing whatever it wants to do with "dynamic" objects.)
I like this approach. Does it entail a ton of work?
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