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[fraunhofer.lists.frees...]

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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[mrene_lists at avgs.ca]

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@avgs.ca




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