__gmp_allocate_func and garbage collection
tg at gmplib.org
Tue May 5 10:41:49 CEST 2009
Marc Glisse <marc.glisse at normalesup.org> writes:
some garbage collectors (take the one by Boehm-Demers-Weiser) provide
2 malloc variants, one for pure "data", and one for stuff that may
include pointers to garbage collected memory (the GC 0-initializes
memory in this case).
On some private mailing list, someone asked about using a garbage
collector with gmp. I was thus wondering whether it was safe to use
mp_set_memory_functions with the first ("pure data") variant of
malloc, or whether we had to use the safe general variant.
Scanning through the GMP sources, and excluding tune/, tests/ and
tal-debug, I found only one problematic file (I may have missed
others, obviously). In randlc2x.c, __gmp_allocate_func is used to
allocate a structure that contains several mpz_t.
So it looks like if you don't use random numbers, it is safe to use
the fast allocation routine. It would be nice to have some more formal
guarantees though. I understand this message would be more convincing
with benchmarks, but now is not the best time, I just wanted to get
the idea out before I forgot.
Are you saying that a struct that contains a pointer is the rub? So,
any time we malloc an mpz_t (not just declare it) these garbage
collectors will become unhappy?
I really don't know where this happens in GMP, but it should be quite
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