[FFmpeg-devel] [PATCH v4] Add ZeroMQ as protocol option

[Andriy Gelman]

On Thu, 29. Aug 21:01, Marton Balint wrote:
> 
> 
> On Thu, 29 Aug 2019, Andriy Gelman wrote:
> 
> > Changes in v4:
> >  - Use polling instead of non-blocking option for socket
> >    read/write operations.
> >  - Added pkt_size, timeout_send, timeout_recv options.
> >    Updated documentation for new options.
> 
> No, timeout_send and timeout_recv is not needed. The URL context has a
> timeout parameter.
> 
> Please see how unix.c or tcp.c does the polling: They both use a helper
> funciton called ff_network_wait_fd_timeout (implemented in network.c) which
> does polling in a loop with small timeouts in order to be able to check the
> interrupt callback. After successful polling you can call the actual
> transfer function.
> 
> You should do something similar, copy ff_network_wait_fd_timeout, replace
> the file descriptor polling with zmq polling and you should be good to go.

Thanks Marton, I've added these changes. I'll send the updated patch shortly. 

When working on this new version, I first tried to use the AVIO_FLAG_NONBLOCK
flag to decide whether to go into a blocking or non-blocking mode.

My intention was to return AVERROR(EAGAIN) when in the non-blocking mode if
read/write is not available. But avio exits with "Resource temporarily
unavailable" when AVIO_FLAG_NONBLOCK flag is set and AVERROR(EAGAIN) is
returned.  So probably I've misunderstood the meaning of AVIO_FLAG_NONBLOCK.
The updated patch is not using this flag.

Another point: the documentation in url.h says:

" * In non-blocking mode, return AVERROR(EAGAIN) immediately.
 * In blocking mode, wait for data/EOF/error with a short timeout (0.1s),
 * and return AVERROR(EAGAIN) on timeout."

But the function ff_network_wait_fd_timeout returns AVERROR(ETIMEDOUT) on
timeout (causing the code to exit) in blocking mode. It seems to me that either
the documentation or the return value should be updated. Should I submit a
separate patch on this? 

Thanks, 
Andriy