[Freeswitch-users] fscore mutex locking question

[Mathieu Rene]

The only time the session is  write locked is when its about to be  
free'd, to make sure nothing holds a valid pointer.

Mathieu Rene
Avant-Garde Solutions Inc
Office: + 1 (514) 664-1044 x100
Cell: +1 (514) 664-1044 x200
mrene at avgs.ca




On 27-Aug-09, at 10:08 AM, Benedikt Fraunhofer wrote:

> Hello *,
>
> while looking at the code i came across a region of code which is
> unclear to me regarding locking issues.
> One example is switch_ivr_broadcast in switch_ivr_async.c. This should
> be the function called by
> uuid_broadcast() and others.
>
> in line 2341 it tries to queue an event to the bleg if it has to...
> -----
> .   if ((flags & SMF_ECHO_BLEG) && (other_uuid =
> switch_channel_get_variable(channel, SWITCH_SIGNAL_BOND_VARIABLE))
> .   .   && (other_session = switch_core_session_locate(other_uuid))) {
>
> ---
> switch_core_session_locate() does a "readonly trylock" on the channel
> mutex returning NULL if it's unable to
> aquire the lock, which brings up the following question:
> If some other thread is currently holding a writelock on the channel,
> the broadcast is not queued and not retried at a later time at all?
>
> I guess it's pretty easy to cause some unexpected behaviour using some
> endless loop calling "uuid_setvar" or some other race condition where
> the channel-mutex is write-locked while calling uuid_broadcast (eg.
> uuid_media?).
>
> Could this lead to a problem in "real live" scenarios, or are there
> other countermeasures despite "chances are one in a million that you
> hit that small time frame"?
>
> thx in advance
>  Beni.
>
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