Re: [Libevent-users] evconnlistener blocks "other stuff"

[Azat Khuzhin <a3at.mail@xxxxxxxxx>]

On Fri, Jan 15, 2016 at 12:37:54PM +0100, Christian Stieber wrote:
> I recently looked into the problem that spamming my server with
> connections would even prevent it from responding to the CTRL-C signal.
> First thing I did was to add priorities to my events, with signals getting
> the highest and sockets getting the lowest prio. Much to my surprise, that
> didn't change anything at all.
> 
> After some headscratching, and since I'm using EVLOOP_ONCE anyway to
> implement a delayed disposal of objects, I threw some
> event_base_loopbreak() calls into the code to see if that would help.
> Again, it still didn't get my Ctrl-C until I stopped spamming connections
> at the server.
> 
> More reading got me to the "complicated event base", and the
> event_config_set_max_dispatch_interval() option. Needless to say, it
> didn't improve things.
> 
> I was already concerned that the evconnlistener didn't support priorities,
> but even at default priority it should be lower than the signal priority
> as I have 4 priority levels. So, I started to dig into the libevent code
> itself.
> 
> Turns out, the evconnlistener (listener.c) accepts connections until it
> gets an error, apparently (I can't say I went through all the libevent
> code)
> without checking for things like event_config_set_max_dispatch_interval.
> My build now applies a patch to the libevent build that just breaks the
> loop after 10 accepts, and that finally got my signals noticed.
> 
> I've attached the patch for purely informal reasons; a real change should
> not break the loop after 10 tries but use the parameters that libevent
> already has. For now, I just needed something that works, and doesn't
> require me to spend days researching how libevent is supposed to work
> internally.

Hi Christian,

Thanks for reporting this!

You can take a look at:
- https://github.com/azat/libevent/commit/cee579654f3dafe

In the meantime I will try to come with a normal solution (maybe some
flag LEV_OPT_ONCE or some threshold).

Thanks,
Azat.
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