Re: [Caml-list] Save callbacks from OCaml to C

[Jeremy Yallop <yallop@gmail.com>]

On 3 February 2016 at 05:44, David Sheets <sheets@alum.mit.edu> wrote:
> On Wed, Feb 3, 2016 at 12:26 PM, Malcolm Matalka <mmatalka@gmail.com> wrote:
>> Jeremie Dimino <jdimino@janestreet.com> writes:
>>> You need to register [ml_t], [ml_x] and [ml_g
>>> ] as GC roots. Otherwise if the GC runs in caml_ba_alloc for instance,
>>> [ml_t] might ends up containing garbage even before reaching
>>> [caml_callback3]. You can use the normal macros for that:
>>>
>> If one is using ctypes, is all of this taken care of?  I have a library
>> that registers a bunch of Ocaml functions in C code, which the C code
>> calls.  I haven't experienced anything bad happening yet, but that
>> doesn't mean much...
>
> If you use ctypes and pass OCaml closures to C, you *must* retain a
> reference to the closure to avoid it being GCed. If you do not, you
> may experience the exception CallToExpiredClosure sporadically.

Besides David's caveat, the answer is yes: ctypes will take care of
registering arguments as GC roots as necessary.