[libnice] Sending packets uses a static, global lock?

[Miguel París Díaz]

Good point Lorenzo!!!

This change was added in this commit:

commit 2faa76a4840100bebd9532bd47a2755874c5b3a0
Author: Youness Alaoui <youness.alaoui at collabora.co.uk>
Date:   Tue Jun 16 20:40:33 2009 -0400

    Use a global mutex for all nice agents and use g_source_is_destroyed to
avoid the race condition of a source being destroyed while we wait for the
mutex

And then the RecMutex was changed by a Mutex in:

commit 2faa76a4840100bebd9532bd47a2755874c5b3a0
Author: Youness Alaoui <youness.alaoui at collabora.co.uk>
Date:   Tue Jun 16 20:40:33 2009 -0400

    Use a global mutex for all nice agents and use g_source_is_destroyed to
avoid the race condition of a source being destroyed while we wait for the
mutex

It would be interesting rethink a solution using an unique mutex per agent
;).



2016-10-05 11:45 GMT+02:00 Lorenzo Miniero <lminiero at gmail.com>:

> Hi all,
>
> we've been working on some stress tests of our Janus WebRTC server, which
> uses libnice for all the ICE related stuff. While it works great in
> general, we reach a wall much sooner than we expect, and performance start
> to degrade quite a bit. By doing some digging and diagnostic in the code we
> wrote and the one we use, we found out something we thought was weird.
>
> Specifically, we noticed that the internal method that is used to send
> packets, nice_agent_send_messages_nonblocking (which nice_agent_send
> itself uses internally) has a lot of code wrapped in an
> agent_lock()/agent_unlock(), which locks/unlocks a global mutex, and this
> includes the process of physiclly sending the packet. This means that the
> whole library is locked until that code is called, which seems overkill. I
> guess the same happens in other parts of the code as well. I'd understand
> locking the specific agent if the purpose is thread-safety, but why lock
> ALL agents at the same time for each packet you send? I tried searching the
> archives for some info on that, but couldn't find any discussion related to
> this choice.
>
> Since I'm already handling thread-safety for most stuff in my own code, is
> there any way for preventing this from happening? I guess that one possible
> way could be to retrieve the file descriptor from the agent object and send
> the packet manually myself, but while this may work in simple
> (host/prflx/srflx) connectivity, this would definitely not be the case
> when, for instance, TURN is involved, as that's one of the things the
> library would take care of for me.
>
> Looking forward to your thoughts, thanks!
> Lorenzo
>
> _______________________________________________
> nice mailing list
> nice at lists.freedesktop.org
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>
>


-- 
Miguel París Díaz
------------------------------------------------------------------------
Computer/Software engineer.
Researcher and architect in http://www.kurento.org
http://twitter.com/mparisdiaz
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