[Mesa-dev] [PATCH 06/13] mesa: Replace sampler object locks with atomic inc/dec.

[Matt Turner]

On Mon, Aug 10, 2015 at 9:16 AM, Matt Turner <mattst88 at gmail.com> wrote:
> On Fri, Aug 7, 2015 at 10:09 AM, Ian Romanick <idr at freedesktop.org> wrote:
>> I know we've talked about this about 100 times, but something in the
>> back of my mind tells me that we have a pre-existing race.  What happens
>> if the p_atomic_dec_zero happens on thread A while thread B is between
>> the _mesa_lookup_renderbuffer call and the _mesa_reference_renderbuffer
>> call on the same object?  Won't thread A free the memory out from under
>> thread B?
>
> Generally:
>
> RefCount is initialized to 1 (in all cases but renderbuffers... that
> might be a bug -- did you choose renderbuffers in your example for
> this reason?). When Bind is called the first time, RefCount is
> incremented to 2.
>
> When Delete is called, RefCount is decremented -- RefCount only goes
> to 0 only if the object isn't bound anywhere, in which case it's
> actually deleted. If The object is still bound somewhere and RefCount
> is decremented to non-zero, the object cannot be rebound and will be
> deleted when its last reference is unbound.
>
> Commit 42aaa548 changed the renderbuffer code from RefCount = 1 to =
> 0. It seems pretty clearly wrong to me, since a
> glGenRenderbuffers()/glDeleteRenderBuffers() pair would fail to
> actually delete the renderbuffers. Does anyone else read it
> differently?

Ian, does this make sense?

Does it seem like initializing RefCount to 1 for renderbuffers is a bug?