[Ffmpeg-devel] alsa input / output

[matthieu castet]

Reimar D?ffinger wrote:
> Hello,
> On Sun, Mar 25, 2007 at 05:26:16AM +0200, Michael Niedermayer wrote:
>>> I should also note that such a lock-free implementation depends on
>>> volatile keyword working "well enough" and pointer reads and writes being
>>> atomic on the architecture...
>> could you show one example where volatile makes a difference in practice?
> 
> In practice maybe not, but in theory you could do
> while (av_fifo_size(f) <= 0) sleep();
> and the compiler might inline av_fifo_size (not gcc though unless we
> move it into fifo.h one time) and without volatile that could be converted to
> if (av_fifo_size(f) <= 0) while (1) sleep();
> Actually a compiler could do this even without inlining as long as it
> can find out that av_fifo_size has no side effects (it does not modify
> anything besides its return value) and does not depend on volatile data.
Do you have a better example, because AFAIK pointer are considered as 
volatile data ?


Matthieu