[Xcb] [PATCH 2/3] fix deadlock with xcb_take_socket/return_socket v3

[Uli Schlachter]

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On 15.05.2013 11:21, Christian König wrote:
> From: Christian König <christian.koenig at amd.com>
> 
> To prevent different threads from stealing the socket from each other the 
> caller of "xcb_take_socket" must hold a lock that is also acquired in 
> "return_socket". Unfortunately xcb tries to prevent calling return_socket 
> from multiple threads and this can lead to a deadlock situation.
> 
> A simple example: - X11 has taken the socket - Thread A has locked the
> display. - Thread B does xcb_no_operation() and thus ends up in libX11's
> return_socket(), waiting for the display lock. - Thread A calls e.g.
> xcb_no_operation(), too, ends up in return_socket() and because
> socket_moving == 1, ends up waiting for thread B => Deadlock
> 
> This patch allows calling return_socket from different threads at the same
> time an so resolves the deadlock situation.
> 
> Partially fixes: https://bugs.freedesktop.org/show_bug.cgi?id=20708
> 
> v2: fixes additional pthread_cond_wait dependencies, rework comments and
> patch description
> 
> v3: separate pthread_cond_wait dependencies and unrelated whitespace change
> into their own patch, use unsigned for socket_seq
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>

After staring at this patch for a while and thinking about weird thread
issues, I come to the conclusion that:

Reviewed-by: Uli Schlachter <psychon at znc.in>

What do others think? If no one objects, this patch could be pushed to master.

Cheers,
Uli

P.S.: I'll stare at patch 3/3 for a little more and try to come up with a
small test program for it. Hopefully that convinces me about it, too.
- -- 
"Why make things difficult, when it is possible to make them cryptic
and totally illogical, with just a little bit more effort?" -- A. P. J.
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