[FFmpeg-devel] [PATCH] Yield on AVERROR(EAGAIN).

[Nicolas George]

Hi.

Le quintidi 15 vent?se, an CCXVIII, M?ns Rullg?rd a ?crit?:
>			  On a modern Linux system it will merely invoke
> the scheduler, which will notice that nothing else wants to run and
> put this thread back on the CPU immediately.

It will also do that if there are plenty of other process who want to run
but they have a lower priority.

> The correct solution is to make the devices somehow notify when input
> is available so the process can sleep properly while waiting.  On Unix
> systems this is typically done with select() on a file descriptor.

Unfortunately, select will not always do the trick: AFAIK, there are devices
who relie on ioctls rather than plain reads, or libraries who do not expose
the underlying file descriptor.

A more generic solution is to use threads: each possibly-blocking device
runs in its own thread, where it can block all it wants without delaying the
other devices or the encoding. The packets read from the devices is queued
in memory, and the main loop just takes the packets from the queue.

If AVFormatContext gets a new field "AVThreadInfo *thread_info", then the
basic feature can probably be implemented with minor changes to
av_read_packet and av_close_input_stream, and later extended without the
need for a version bump.

Regards,

-- 
  Nicolas George
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