Re: [Caml-list] Thread-private data in C stubs

[Andre Nathan <andre@digirati.com.br>]

On Mon, 2012-08-27 at 16:41 -0300, Andre Nathan wrote:
> Hello
> 
> I'm writing stubs to a C library uses pthreads and exposes two functions
> to get and set thread-private data, getpriv(ctx) and setpriv(ctx, p)
> where ctx is some opaque context object, and p is a void* pointer.
> 
> What's the best way to deal with this from the stub code, ie., how do I
> avoid the thread-private data to be garbage collected when the OCaml
> variable goes out of scope?
> 
> Since the library in question uses threads internally, this needs to be
> a thread-safe solution.

For the record, with help from #ocaml, I got it to work like this:

struct priv {
  value v;
};

CAMLprim value
caml_setpriv(value ctx_val, value priv_val)
{
    CAMLparam2(ctx_val, priv_val);
    context *ctx = (context *)ctx_val;
    struct priv *p;
   
    p = getpriv(ctx);
    if (p != NULL) {
        caml_remove_global_root(&(p->v));
        caml_stat_free(p);
    }

    p = caml_stat_alloc(sizeof(*p));
    p->v = priv_val;
    ret = setpriv(ctx, p);
    caml_register_global_root(&(p->v));

    CAMLreturn(Val_unit);
}