[pjsip] Question about stream.c

Michael Broughton Michael_Broughton at advanis.ca
Thu Feb 14 14:10:47 EST 2008


Benny Prijono wrote:
> I think you're probably right, the callback thread would eventually
> timeout when it tries to call acquire_call(). The scenario would be
> like this:
>
> transport thread:
>  1. on_dtmf callback is called (with ioqueue's key mutex held)
>  2. tries to lock call with acquire_call()
>
> Application thread:
>  3. acquire_call() returns successfully
>  4. close transport, which eventually try to get ioqueue's key mutex
>
> This is a deadlock scenario. But with soft deadlock protection, step
> no 2 above would time out eventually, and everything will run again.
>
> But soft deadlocking is very expensive in term of processing, as
> everything that tries to lock PJSUA-LIB will be blocked while
> PJSUA-LIB tries to acquire (and finally gives up) the locks. This
> would block the application for at least 1 second for the best case, I
> think.
>
>   

What if acquire_call monitored a flag that indicates when the transport 
trying to shutdown? My own solution to ticket 460 sort-of worked that way.

I'm not sure if there is a clean way to implement this...

>
> What about if you only post the destroy request to other thread, and
> handle everything else in the callback? Anyway the deadlock situation
> should only occur when we're trying to destroy the transport, so for
> everything else, it should be safe to process the call (and call
> acquire_call()) in the callback.
>   

Sorry, I think I am leaving out too many details. I already defer any 
call drops to my main loop. I have far too much cleanup work to do after 
a call to do it in a callback.

-- 
Michael Broughton, Advanis

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