Re: [Libevent-users] Re: libevent2 stuck in Linux, CPU 100%

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Sat, Jul 20, 2013 at 2:12 AM, Oleg Moskalenko <mom040267@xxxxxxxxx> wrote:
> I drilled down, eventually, to  the bottom of this problem.
>
> When some kind of socket problem is reported on a UDP socket, then the
> EV_READ is generated but  there is no data is available. So it will go in
> indefinite cycle with libevent.
>
> The solution is to use recvmsg on a socket in this condition, with flag
> MSG_ERRQUEUE. It will read the error message and restore the socket
> condition.
>
> BSD-compatible systems do not do that, this is obviously a Linux
> lesser-known extension.
>
> I am working on including this workaround into the TURN server code, but my
> pilot code tests shows that it works perfectly and this is the right
> solution.

Thanks for sharing this, Oleg!

Is there any reasonable place in the Libevent documentation for us to
mention this?  (I guess that a UDP-based bufferevent-like thing could
wrap this naturally and hide the detail form the user, but we don't
have one of those yet.)

-- 
Nick
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