[erlang-questions] NIFs and lists of resources

[Sverker Eriksson]

Each call to enif_alloc_resource() returns ONE resource object.
enif_make_resource expects a pointer returned from enif_alloc_resource(),
and only your &templates [0] is such a pointer.
So, you probable want to call enif_alloc_resource one time for every resource in
your array/list.
/Sverker
On ons, 2018-09-19 at 13:32 -0500, Jordan Day wrote:
> Apologies that this is more of a C question than an Erlang question…
> 
> I’m working on a NIF accessing a vendor’s C API and wondering what the correct
> approach is to handling a function from which I’d like to return a list of
> resources. While my functions handling individual resources seem to be working
> as expected (calling the destructors when the item is GC’d on the erlang
> side), I’m not seeing that happen with a function where I’m returning a list
> of resources.
> 
> In code where I’d normally do something like
> vendor_template templates[num_templates];
> fill_templates(templates);
> ...
> return templates;
> 
> 
> I’d like each vendor_template struct to become a resource I can pass around
> and have GC’d when I’m done with them, on a per-item basis. I presumed I could
> do the normal resource-related calls and then return an erlang list, but I’m
> not seeing the destructor function called when the list should be getting GC’d
> on the erlang side.
> 
> Example:
> 
> vendor_template *templates = enif_alloc_resource(TEMPLATE_TYPE,
> sizeof(vendor_template) * num_templates);
> ERL_NIF_TERM template_res[num_templates];
> fill_templates(templates);
> for (int i = 0; i < num_templates; i++) {
>   template_res[i] = enif_make_resource(env, &(templates[i]));
>   enif_release_resource(&(templates[i]));
> }
> 
> ERL_NIF_TERM template_list = enif_make_list_from_array(env, template_res,
> num_templates);
> return template_list;
> 
> The returned list of resources seem to be correct, as I can use their
> individual references in subsequent NIF calls, but when the returned list is
> discarded, I never see the destructor function called.
> 
> Any tips on what I might be doing wrong? Does the enif_make_list_from_array/2
> call “break” this? If so, how can I return my list of resources?
> 
> Regards,
> Jordan
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@REDACTED
> http://erlang.org/mailman/listinfo/erlang-questions
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://erlang.org/pipermail/erlang-questions/attachments/20180919/156142ce/attachment.htm>