[Asterisk-Dev] [RFC] Dial plan extension handling change: "snapshot run list"

[Kevin P. Fleming]

I'm working on an enhancement for dial plan handling, and it would 
simplify my work quite a bit if the following change was acceptable to 
the Asterisk community :-)

extensions.conf

exten => 100,1,Wait(2)
exten => 100,2,Answer
exten => 100,3,Playback(foo/bar)
exten => 100,4,Background(foo/menu)
exten => 100,5,Background(foo/menu2)
exten => 1,...
exten => 2,...
exten => 3,...
exten => i,...

Let's assume for the sake of this discussion that "sounds/foo/bar" is a 
10-second audio clip.

As it stands today, if a channel is sent into this context/extension, 
and then extensions.conf is changed/reloaded while the channel is 
processing these steps, it will _not_ continue processing the steps as 
they were when it entered the context/extension, the reload will affect 
the "live" channel.

For example: if the channel is currently in priority 3 playing the audio 
clip, and the reload causes the steps to be moved down one (maybe 
someone added another Wait() at priority 3), then the same audio clip 
will be played again to the channel, because it will now be priority 4.

What I'm proposing is that when a channel enters a context/extension, a 
"snapshot" of all the priorities of that extension is grabbed into a 
"runlist", which the channel uses until it needs to leave the runlist 
(because of a Goto/GotoIfTime, hangup/timeout, etc.).

This will have (at least) two advantages: the live channel's behavior 
will not be affected by a reload, and processing of the extension's 
priorities will be somewhat faster as the list of steps to be run will 
already be determined (as opposed to doing the dialplan search for each 
step).

This will be somewhat complicated to implement, but I believe it can be 
done and I'm willing to do the work to make it happen. This change will 
allow me to implement a "prefix", a set of steps to be run before any 
defined steps for a given extension, because those prefix steps could be 
prepended to the "runlist", as if they had been present in the 
extension's priorities.

Comments?