Re: [Libevent-users] questions about bufferevent callbacks in multithreaded code

[Sashan Govender <sashang@xxxxxxxxx>]

So in theory the following scenarios should not deadlock:

This all happens in a single thread:

1) a bufferevent read callback is triggered (lock acquired)

2) the user supplied callback function reads the data and calls bufferevent_write (lock acquired - ok because using a recursive mutex)

and neither should this where 2 threads are involved:

1) a bufferevent read callback is triggered

2) the user supplied callback function does some stuff (callback ends -> lock released by libevent)

3) bufferevent_write is called from another thread

On Thu, May 2, 2013 at 2:12 AM, Nick Mathewson <nickm@xxxxxxxxxxxxx> wrote:

On Wed, May 1, 2013 at 12:07 PM, Sashan Govender <sashang@xxxxxxxxx> wrote:
> Hi
>
> I need to clarify my understanding of how bufferevent objects work with
> mulithreaded code. If a bufferevent triggers a callback (read or write) does
> it hold a lock until that callback completes?

Ordinarily, yes. You can override this with the
BEV_OPT_UNLOCK_CALLBACKS option, as described in
http://www.wangafu.net/~nickm/libevent-book/Ref6_bufferevent.html

> Do the locks use a recursive
> mutex?

Yes.

Yrs,
--
Nick
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