[asterisk-dev] [Code Review]: PreDial - Ability to run dialplan on callee channel and caller channel right before actual Dial

[kobaz]

> On Nov. 5, 2011, 4:03 p.m., rmudgett wrote:
> > Does this new b() option run on all forked channels: Dial(SIP/abc&SIP/def,,b(predial,n,1))?
> 
> kobaz wrote:
>     Yeap. It does.
>     
>     The code for the b option is done in the loop that goes through the newly created channels.
>     
>     In this part:
>     /* loop through the list of dial destinations */
>     2143	rest = args.peers;
>     2144	while ((cur = strsep(&rest, "&")) ) {
>     2145		struct chanlist *tmp;
> 
> kobaz wrote:
>     I did notice my xml documentation is wrong, I have the docs on the options flipped.  So, 'b' is on the callee side and 'B' is the caller side
>     
>     SIP/foo is calling SIP/bar
>     SIP/foo is the caller,
>     SIP/bar is the callee,
>     SIP/baz is another callee,
>     
>     example 1:
>     <SIP/foo-123> Dial(SIP/bar,,B(predial,s,1))
>     <SIP/foo-123> Executing predial,s,1
>     <SIP/foo-123> calling SIP/bar-124
>     
>     example 2:
>     <SIP/foo-123> Dial(SIP/bar,,b(predial,s,1))
>     <SIP/bar-124> Executing predial,s,1
>     <SIP/foo-123> calling SIP/bar-124
>     
>     example 3:
>     <SIP/foo-123> Dial(SIP/bar&SIP/baz,,b(predial,s,1))
>     <SIP/bar-124> Executing predial,s,1
>     <SIP/baz-125> Executing predial,s,1
>     <SIP/foo-123> calling SIP/bar-124
>     <SIP/foo-123> calling SIP/baz-125
>
> 
> schmidts wrote:
>     i have found this review by searching for a possibility to set different sip headers for different forked channels and this might be a solution. But by thinking of this i see a major problem which could happen here. If the gosub which is called before the dial tooks too long it might happen that one channel is allready ringing while the other one is still in the gosub and when the ringing one is answered you have a deadlock problem cause chan is locked during the gosub.
>     i dont know if there is a big chance that this might happen but imho it could be possible.

Have you run into this deadlock or is this just based on looking at the code?  I would be interested in a dialplan example, but I'll try to create that and test that situation.


- kobaz


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On Nov. 5, 2011, 10:22 a.m., kobaz wrote:
> 
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> 
> (Updated Nov. 5, 2011, 10:22 a.m.)
> 
> 
> Review request for Asterisk Developers.
> 
> 
> Summary
> -------
> 
> PreDial
>   
>   Say SIP/abc is calling SIP/def
>   You have: Dial(SIP/def)
>   SIP/def-123234 is created.  But how can you tell that from dialplan?
> 
>   You can use a pickup macro: M or U options to Dial(), but you have to wait till pickup to know.
>   'PreDial' new option 'b' to Dial(), will let you run dialplan on the newly created channel before it is connected to the end-device.
> 
>   New way:
>   Dial(SIP/def,,b(predial,s,1))
>   Dialplan will run on SIP/def-123234 and allow you to know right away what channel will be used, and you can set specific variables on that channel.
> 
> You can also run dialplan on the caller channel (option 'B') right before the dial, which is a great place to do a last microsecond UNLOCK to ensure good channel behavior.
> Example:  LOCK(foo)
>           do stuff
>           UNLOCK(foo)
>           Dial(SIP/abc)
> 
> With this above example, say SIP/123 and SIP/234 are running this dialplan.
> 
> SIP/123 locks foo
> SIP/123 unlocks foo
> due to some cpu load issue, SIP/123 takes its time getting to Dial(SIP/abc) and doesn't do it right away
> 
> Meanwhile... SIP/234 zips right by, lock 'foo' is already unlocked, it grabs the lock, does its thing and it gets to Dial(SIP/abc).  SIP/123 wakes up and finally gets to the Dial().  Now you have two channels dialing SIP/abc when there was supposed to be one.
> 
> If your intention is to ensure that Dial(SIP/abc) is only done one at a time, you may have unexpected behavior lurking.
> 
> New way:
>   LOCK(foo)
>   do stuff
>   Dial(SIP/abc,,B(unlock,s,1))
> 
> context unlock {
>   s => {
>     UNLOCK(foo);
>   }
> }
> 
> Now, under no circumstances can this dialplan be run through and execute the Dial unless lock 'foo' is released.
> 
> Obviously this doesn't ensure that you're not calling SIP/abc more than once (you would need more dialplan logic for that), but it will allow a dialplan coder to also put the Dial in the locked section to ensure tighter control.
> 
> 
> Diffs
> -----
> 
>   trunk/apps/app_dial.c 343488 
>   trunk/include/asterisk/pbx.h 343488 
>   trunk/main/pbx.c 343488 
> 
> Diff: https://reviewboard.asterisk.org/r/1229/diff
> 
> 
> Testing
> -------
> 
> context predial {
>   s => {
>     NoOp(I'm Here!);
>   }
> }
> 
>  Dial(SIP/def,,I(predial,s,1))
>    run predial on callee channel
> 
>  Dial(SIP/def&SIP/ghi&SIP/qrx,,I(predial,s,1))
>   runs predial on all three callee channels
> 
>  Dial(SIP/def,,B(predial,s,1))
>    runs predial on caller channel
> 
>  Dial(SIP/def,,B(predial,s,1)I(predial,s,1))
>    runs predial on callee channel and caller channel
> 
> 
> Thanks,
> 
> kobaz
> 
>

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