[FFmpeg-devel] Network IO in FFmpeg (was: abstractable threading api)

LANGLOIS Olivier PIS -EXT olivier.pis.langlois at transport.alstom.com
Tue Apr 8 20:49:38 CEST 2014

> This thread has caught my attention and I went to see how
> pthread_cancel() was used in libavformat/udp.c and I might have spotted a
> race condition in it.
> cancellation points are implemented inside glibc not in the kernel. That
> means that once the cancellation point check is done and the thread is
> blocked inside the kernel, cancelling the thread will have no effect.
> In order to have the code behave as designed,
> pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
> should be used. asynchronous cancels are implemented with RT signals.
> For that reason only async cancels can interrupt and cancel a thread that is
> already inside a system call.

My mistake. Ignore this whole post. Half of it is true. The other half is that inside cancellation point functions, async cancel type if flipped on/off around the syscall. ie:

      int oldstate = LIBC_CANCEL_ASYNC ();

      r = INTERNAL_SYSCALL (clock_nanosleep, err, 4, clock_id, flags, req,

      LIBC_CANCEL_RESET (oldstate);

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