Buffer destruction at sink

[Iván Aponte]

thanks for your prompt answer.

On Sun, Mar 20, 2016 at 5:10 AM Sebastian Dröge <sebastian at centricular.com>
wrote:

> On So, 2016-03-20 at 01:53 +0000, Iván Aponte wrote:
> > Hello,
> >
> > I am programming  a sink plugin which basically gets the memory from
> > a buffer, maps it to the gpu (since we have zerocopy available) and
> > executes a cuda kernel. I am using the basesink class as a base for
> > my sink.   I have some questions:
> >
> > Should I unref the buffer at the end of the render function or is it
> > automatically unreffed when the render function returns ?
>
> render() only gives you a reference for the scope of the function call
> and will unref it afterwards. If you need to keep another reference
> around, you need to ref() it.
>
> > Why  gst_buffer_ref is potentially a memory copy operation? is this
> > true even if it is in the render function of basesink ? I just don't
> > want the memory to get freed.
>
> ref() is not going to copy the buffer, where did it say that it might
> copy? What can happen though is that ref() causes a copy elsewhere.
>
> Reason for that is that only a buffer with a reference count of exactly
> one is considered writable. If something wants to write to a buffer
> with a higher reference count, a copy would have to be done first.
> gst_buffer_make_writable() would do that.
>
> In case of your sink you wouldn't really have to worry about that.
>
> > Is the memory in GstMapInfo is contiguous?
>
> It's contiguous virtual memory, not necessarily physically contiguous.
> It's behaving like a memory area returned by malloc().
>
> >  Does gst_buffer_map implies a   memory copy operation  ?
>
> It might, depending of the underlying memory and if the buffer has 1 or
> multiple GstMemory stored inside it.
>
> In many cases it is doing nothing other than giving you a pointer. If
> it is backed by normal system memory and there is exactly one GstMemory
> in the buffer.
>
> But for example memory based on GL textures might involve downloading
> data from the GPU and then uploading it again on unmap. (which might be
> async, or not, the implementation decides that).
>
> --
> Sebastian Dröge, Centricular Ltd · http://www.centricular.com
>
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-- 
Iván Aponte
+58 412 2774713
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