[asterisk-dev] masquerade() Education

[Steve Murphy]

I think this letter, if I were to write to only one person, would be 
Josh Colp.

But I know that Josh would appreciate my asking in this forum, so all 
could enjoy the question and its answer.

My Question is this: A decade (or more) ago, I had high  hopes of 
masquerade() being obsolesced in Asterisk, with the introduction of 
channel bridging. But, I see in rel 20, that masquerade still exists, 
and is used in parking, queues, and looking thru the ChangeLog, a lot of 
work has been done to correct problems, and work around masqueraded 
channels. I saw this comment:

<from 2017-03-15> (Richard Mudgett)

    "Dereferencing struct ast_autochan.chan without first calling
      ast_autochan_channel_lock() is unsafe because the pointer could 
change at
      any time due to a masquerade. Unfortunately, 
ast_autochan_channel_lock()
      itself uses struct ast_autochan.chan unsafely and can result in a 
deadlock
      if the original channel happens to get destroyed after a 
masquerade in
      addition to the pointer getting changed."

     "The problem is more likely to happen with v11 and earlier because
       masquerades are used to optimize out local channels on those versions
       However, it could still happen on newer versions if the channel is
       executing a dialplan application when the channel is transferred or
       redirected. In this situation a masquerade still must be used."

While my work revolves largely around asterisk, this issue comes up over 
and over, especially when it's time to upgrade to a new version of 
Asterisk. I keep intending to ask about it, but finally, I have this 
chance. Why exactly is masquerade() still necessary? I am asking more 
out of curiosity than condemnation or other negative reasons!  I would 
love to understand the issues, perhaps at some point in time, I may be 
able to help.

murf