Why do we put GMP allocations on GHC heaps?

Edward Z. Yang ezyang at MIT.EDU
Tue Oct 22 23:36:45 UTC 2013

Hey Gergeley,

> (obviously we would have to call mpz_free here and there, but that
> seems doable).

Actually, this is precisely the problem.  When is a GMP integer freed?
It can have pointers to it from objects on the heap, so this free should
only occur when the integer is dead, with no references from the heap.
How can that be arranged?  Well, the garbage collector is responsible
for figuring this out.  So why shouldn't they just live on the heap, and
then smoothly integrate with the existing garbage collector.

The alternate strategy is to arrange that some sort of "callback" gets
invoked when an object dies.  You can achieve this using our finalizer
support, but you pay an efficiency penalty and cannot guarantee that
the integers will get freed in a timely manner at all.

> More concretely: openssl BN uses the openssl_malloc function can only be
> overridden openssl wide.  But if we link statically, than this override
> won't affect external openssl library bindings, because the openssl
> symbols in our object files won't even be exported, right?

Only if literally two copies of OpenSSL are linked.  This seems unlikely to
work the way you want it to.


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