[asterisk-users] global variables and updates

[Lee Jenkins]

Julian Lyndon-Smith wrote:
> Sorry if this appears twice - I originally sent it nearly 18 hours ago 
> and never saw it ..
> 
> I have a need to have a unique integer number that can be used by a
> dynamic meetme room (I am wanting to redirect a call into a meeting 
> room, and need a unique number to make sure I don't put two people 
> together !)
> 
> I was going to use a global variable ${NEXTMEETME}, and add one every 
> time I redirect.
> 
> Is the changing of a global variable atomic ? That is, if I have two or 
> more channels being redirected at the same time, and they all execute
> 
> exten => _X.,n,Set(NEXTMEETME=${MATH(${NEXTMEETME}+1,i)})
> exten => _X.,n,Set(MYMEETME=${NEXTMEETME})
> 
> if NEXTMEETME is initially 0, would channel A get MYMEETME as 1, channel 
> B get 2 and channel C get 3, even if they execute the dialplan at the 
> same time ?
> 

Someone more knowledgeable about Asterisk than I can correct me, but I 
would look at it from the perspective any development environement:

Global variables are typically bad in a threaded environment without 
some form of queuing/locking/critical section functionality to avoid 
collisions.

If I needed a globally unique, sequential number, I'd push it out to 
AGI/FastAGI so I could use a language with support for locking/queuing.

A DB like MySQL or FirebirdSQL would easily handle this need as you 
know, but then is the overhead of establishing DB connections worth it 
for simply getting a incremented int?

-- 
Warm Regards,

Lee