[pulseaudio-discuss] [PATCH] stream: Return error in case a client peeks to early

[Tanu Kaskinen]

On Wed, 2012-10-03 at 08:50 +0200, David Henningsson wrote:
> On 10/02/2012 10:38 PM, Tanu Kaskinen wrote:
> > On Mon, 2012-10-01 at 17:06 +0200, David Henningsson wrote:
> >> If there is no silence memblock and no data, pa_memblockq_peek can
> >> return NULL. In this case, do not crash on an assertion in
> >> pa_memblock_acquire, but instead return a proper error to the client.
> >
> > If there is no data in the buffer, pa_stream_peek() is supposed to
> > return NULL according to the documentation. And it does that: if there's
> > no data, pa_memblock_peek() will return a negative value, causing
> > pa_stream_peek() to return NULL.
> >
> > The problem is the case where the buffer does contain data, but not at
> > the read index. That is, there is a hole in the buffer. The client
> > documentation doesn't have any warnings about holes, so the only safe
> > way to handle holes is to return silence. Fixing this should be a simple
> > matter of giving a silence memchunk when creating record_memblockq.
> 
> I'm not so sure. Silence, as in all zeroes, might work for S16 audio 
> data, but what about other formats? Compressed audio? Peak audio (which 
> I think is the case here)? Etc.

Good point. Regarding PCM, if pa_memchunk_silence() is used, the
function will take care of filling the memory with appropriate content.
But that doesn't work with compressed audio.

> Also maybe it could also be valuable for the client to distinguish 
> between no data available, and valid zero data.
> 
> How about returning NULL and adding to the documentation something like:
> 
> -If no data is available this will return a NULL pointer.
> +If no data is available (at the current read position), this will 
> return a NULL pointer.

An addition: the client probably wants to know how large the hole is. It
might be possible to figure that out somehow from the read index, but I
think it would make sense to return the hole size in the length
parameter.

-- 
Tanu