Re: [Libevent-users] deadlock in libevent-2.0.5-beta

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Sat, Jul 3, 2010 at 2:10 AM, Zhou Li <echou327@xxxxxxxxx> wrote:
> I met such deadlock too. It happened under very high load just as you said.
> I think the cause is that the call write(th_notify_fd[1]) got blocked (
> sorry I didn't remember the exact position of this call to write
> th_notify_fd).
> In event.c line 2597:
>     /*
>       This can't be right, can it?  We want writes to this socket to
>       just succeed.
>       evutil_make_socket_nonblocking(base->th_notify_fd[1]);
>     */
> When I uncommented this block of code, the deadlock disappeared.
>

This change isn't correct, though.  th_notify_fd[1] is used to tell
the main thread (the one running event_base_loop) to wake up.  The
code that writes to it doesn't check for EAGAIN, so  making that
socket nonblocking means that some attempts to wake up the main thread
will just get lost.
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