[pulseaudio-discuss] pa_stream_readable_size() returns 4294967295

[Lennart Poettering]

On Fri, 11.12.09 03:27, Tanu Kaskinen (tanuk at iki.fi) wrote:

> 
> to, 2009-12-10 kello 21:20 +0100, Mads Kiilerich kirjoitti:
> > With reference to 
> > http://0pointer.de/lennart/projects/pulseaudio/doxygen/stream_8h.html#aa2e5ff19aa36b90471c34badbdfdf345 
> > and using pulseaudio-0.9.15-17.fc11.i586:
> > 
> > My experiments shows that pa_stream_readable_size() sometimes returns 
> > 4294967295 = 0xffffffff. That possibility is not described in the 
> > documentation, AFAICS.
> > 
> > However, I have only seen that happen when not PA_STREAM_READY. Is the 
> > ready state a precondition for calling this function? How should race 
> > conditions be avoided?
> 
> Yes, the READY state is a precondition.
> 
> What kind of race conditions do you mean? Do you mean that how are you
> supposed to know prior to calling pa_stream_readable_size() whether the
> stream is still in READY state? Are you not able to reliably track the
> state with a state change callback (pa_set_state_callback)?

Also, you can just call _readable_size(), and then check if that
failed. Duplicating the state check externally is not necessary.

> I'm not terribly familiar with the client library details, so I'm not
> saying that there are no races. But since the library is
> single-threaded, I believe you can use the state callback to always have
> the same knowledge of the state as the library itself.

That is true. The PA libraries are not generally thread-safe, however
they are threads-aware.

> > It would have matched my expectations better if the type was ssize_t and 
> > the value thus -1.
> 
> Pulseaudio uses ((size_t) -1) in error cases in many places. I guess
> it's at least partially a matter of taste...

Yes, that is true.

> > Are there any other special values?
> 
> I didn't write the code, but I'm quite sure that the answer is no.

Yes, that is correct. The answer is "no".

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4