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

[David Henningsson]

2012-11-03 17:19, Colin Guthrie skrev:
> 'Twas brillig, and Tanu Kaskinen at 05/10/12 13:58 did gyre and gimble:
>> 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.
> This discussion seemed to stagnate. Is this worth fixing/documenting for
> the 3.0 release?
>
> Col
>
>
Returning NULL seems to be the right thing to do here, even if 
gnome-control-center does not handle that very well IIRC. So we might 
need an additional patch in g-c-c.
So assuming I commit a patch doing that. If somebody else wants to add 
logic to figure out how large the hole is, that could be discussed 
separately.
Any objections?

-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic