[asterisk-users] Help with semaphores

[Mitch Thompson]

Trevor Peirce wrote:
> Mitch Thompson wrote:
>> [SATX_555_Extensions]
>>
>> exten => 1212,1,System(cat /tmp/{orig_num})  ; ${orig_num} is set at 
>> the beginning of [from-trunk-custom] to the full dialed digits in 
>> ${EXTEN}, before I break it down.
>> exten => 1212,n,Busy(); if the file exists, someone else has already 
>> called this number, return busy
>>
>> exten => 1212,102,System(echo ${UNIQUEID} > /tmp/${orig_num}) ; 
>> basically, create a file in /tmp whose name is the full number from 
>> the beginning.  In this case, the full
>>                                                                                                              
>> ; filename would be /tmp/2105551212.  I don't really care about the 
>> contents, though.
>> exten => 1212,103, Goto(Idle,1) ; from here, we jump to a new 
>> extension called Idle, where we do a Random to decide whether to 
>> simulate no one home (ring no answer) or
>>                                                    ; we send ring for 
>> about 10 seconds, then Answer() and play some .wav files, then 
>> hangup.  The last thing we do in either case is to delete
>>                                                    ; the 
>> /tmp/${orig_num} file.
>>
>> The above code works very well at low call volumes.  However, I'm 
>> running into race conditions at high call volumes where several calls 
>> are getting through the test in priority 1 before the file is created 
>> in priority 102 (n+101).
>>
>
> Here's what I would do...
>
> First, no System calls.  Stay within asterisk.
>
> I doubt this will get rid of all race conditions, but I imagine it 
> would at least reduce them.
>
> exten => 1212,1,GotoIf($["${DB(/tmp/${orig_num})}" != 
> "${UNIQUEID}"]?abort)
> exten => 1212,1,Set(${DB(/tmp/${orig_num})}=${UNIQUEID})
> exten => 1212,n,GotoIf($["${DB(/tmp/${orig_num})}" != 
> "${UNIQUEID}"]?abort)
> exten => 1212,n, Goto(Idle,1)
>
> exten => 1212,n(abort),Busy()
>
> Regards,
> Trevor
Trevor,

Thank you very much for your response.  Yes, I was worried about the 
performance hit of the System() call, but as I said, I tried doing it 
with Global and/or local variables, and just wound up confusing myself.  
I'm not a programmer by trade or nature, so I knew up front it was 
"dirty code".  Your method of staying with Asterisk looks like something 
I can easily switch to in one exchange context and give it a quick try.

Thanks again!

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Mitch Thompson, San Antonio, Texas//WB5UZG
Red Hat Certified Engineer