[Freeswitch-dev] Safely Traversing call lists

Ronnie Beck ronybeck at themenz.biz
Tue Sep 15 15:44:00 MSD 2015

Hi All,

I have just a small question about the thread safety of the following code:

switch_console_callback_match_t *callList = switch_core_session_findall();
for( node = callList->head; node; node = node->next )
     switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG, "(%s) 
Checking session '%s'\n", __FUNCTION__,  node->val);

I just want to check some specific channel variables on all the active 
calls on a Freeswitch server.  However it seems to me that while 
traversing the list, it is possible that "node" could be deleted by 
freeswitch while my code is still using it.  Is there some sort of 
protection I should be doing in order to safely traverse the list and 
investigate each session?

I thought I could lock each session as I interrogate the session however 
this doesn't protect against the situation where the "next" node is 
deleted as my code switches to that node.  In C++, if you traverse a 
list with an iterator, changes to the list invalidate the iterator.  So 
one must obtain a new iterator each time the list is changed.   But I 
don't see how to do this with the list provided by 

Any tips?


Ronnie Beck

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