[asterisk-users] global variables and updates

[Lee Jenkins]

Watkins, Bradley wrote:
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> 
>> From: asterisk-users-bounces at lists.digium.com 
>> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of 
>> Julian Lyndon-Smith
>> Sent: Saturday, July 28, 2007 5:18 AM
>> To: asterisk-users at lists.digium.com
>> Subject: [asterisk-users] global variables and updates
>>
>> 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 ?
>>
> 
> The changing of variables is not atomic as would hope, but there is a
> solution for you.  Look the application MacroExclusive.  Put your Set to
> increment the global variable inside of a macro and call it using this,
> and you will get the behavior you desire.  One caveat, however, is that
> you will want as little logic as possible inside of this macro.
> MacroExclusive will block all other calls to this macro until the first
> one exits.  But this is not an issue if all you are doing is a quick
> var++ and then leaving.
> 

That's a very nice feature.  A quick Google search on the wiki didn't 
turn up any topics.  Does it queue subsequent calls or just block them 
and then logic in the dialplan must be used against a return value?

---
Warm Regards,

Lee