[pulseaudio-discuss] [PATCH v2] pacat: Write to stream in frame-sized chunks

[Ahmed S. Darwish]

On Tue, Dec 20, 2016 at 03:20:00PM +0530, Arun Raghavan wrote:
> 
> On Tue, 20 Dec 2016, at 03:14 PM, Ahmed S. Darwish wrote:
> > Hi Tanu,
> > 
> > On Sun, Dec 18, 2016 at 08:59:58PM +0200, Tanu Kaskinen wrote:
> > >
> > > On Sat, 2016-12-17 at 01:43 +0200, Ahmed S. Darwish wrote:
> > > > # Note: Documentation of `pa_stream_begin_write(stream, &buf, &nbytes)'
> > > > # suggests to pass nbytes = -1. Doing so though lends to a huge returned
> > > > # nbytes values. Calling a pa_stream_write() with such values chokes the
> > > > # stream: making it go silent and not produce any further write-callback
> > > > # events.
> > > > #
> > > > # Is this a problem in usage pattern, or a bug?
> > > 
> > > Sounds like a bug. Trying to write more than buffer_attr.maxlength
> > > bytes at once would be expected to cause some kind of problems, but I
> > > don't think that's the case here. The returned nbytes value is 64k,
> > > isn't it? pacat uses the default maxlength, and the default maxlength
> > > is 4M, so nbytes is nowhere near that limit. As long as maxlength isn't
> > > exceeded, any "extra" audio should just get buffered in the stream
> > > buffer at the server side.
> > >
> > 
> > Yeah; sounds like a bug in the write stream indeed.
> > 
> > In the command below, (second pacat):
> > 
> >   ./src/pacat -r --latency-msec=4 | ./src/pacat --latency-msec=4
> > 
> > When using "writable" values from pa_stream_writable_size(), we
> > get the following, valid, sequence:
> > 
> >   ++ STDIN callback: mute! stream writable = 0
> >   @@ WRITE callback: Re-enable STDIN events
> >   <-- Small writable val; appropriate for requested small latency -->  
> >   @@ STDIN callback: stream writable size = 192
> >   ** Writing 192 bytes; frame len = 4
> > 
> >   ++ STDIN callback: mute! writable = 0
> >   @@ WRITE callback: Re-enable STDIN events
> >   <-- Small writable val; appropriate for requested small latency -->  
> >   @@ STDIN callback: stream writable size = 192
> >   ** Writing 192 bytes; frame len = 4
> > 
> >   ... Sequence endlessly repeated ...
> > 
> > BUT when using "writable" values from pa_stream_begin_read(), with
> > "writable = (size_t)-1" as the documentation recommends, we get
> > that sequence instead:
> > 
> >   @@ WRITE callback: Re-enable STDIN events
> >   @@ STDIN callback: stream writable size = 65472   <== 64K indeed
> >   ** Writing 2112 bytes; frame len = 4
> >   ++ STDIN callback: mute! writable = 0
> > 
> >   <-- COMPLETE silence! - no more stream write callback events -->
> > 
> > Hopefully not a new blocker, but if you agree with the assessment
> > above, I'll submit a bug to be tracked for v11.
> 
> Is that a regression?
>

Didn't try this on earlier versions of pulse to know for sure;
will invesitgate further..