[FFmpeg-devel] [PATCH] Non-blocking protocols

[Nicolas George]

Hi.

The attached patches start to implement non-blocking URL protocols, which
are necessary in certain situations, especially with formats that need
several URL contexts at once (RTP for example).

The first patch introduces the URL_FLAG_NONBLOCK and documents it. Its
principle was approved by Michael on 2011-01-17, but I reworded slightly the
documentation.

The second patch implements the necessary code in the wrapper functions
(url_read/url_write).

The third patch add support for non-blocking to TCP sockets.

make test still succeeds and a small test-program against a remote rot13
server works as expected.


I noticed that there is a lot of duplicated code between the wrapper
functions and the member functions of each URLProtocol: handling of short
reads, looping on EINTR, etc. I tried to do each task in only one place;
this allowed me to greatly simplify the code for TCP sockets (cf. the
diffstat).

Here is the summary of the choices I made about who is responsible for what:

- blocking for a short while if blocking: URLProtocol member functions;
- looping on EINTR: avio wrapper;
- looping on EAGAIN if blocking: avio wrapper;
- checking for url_interrupt_cb: avio wrapper;
- looping on short reads and write: avio wrapper;

The code implemented by the second patch thus guarantees that:

- url_read(_complete) and url_write never return AVERROR(EAGAIN) if
  URL_FLAG_NONBLOCK is not set;

- url_read(_complete) and url_write return AVERROR(EINTR) if and only if an
  interrupt callback was triggered.

Regards,

-- 
  Nicolas George
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