[tor-bugs] #7713 [Stem]: Stem should invalidate GETCONF cache

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#7713: Stem should invalidate GETCONF cache
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    Reporter:  atagar  |       Owner:  atagar         
        Type:  defect  |      Status:  closed         
    Priority:  minor   |   Milestone:                 
   Component:  Stem    |     Version:                 
  Resolution:  fixed   |    Keywords:  controller easy
      Parent:          |      Points:                 
Actualpoints:          |  
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Changes (by atagar):

  * status:  needs_revision => closed
  * resolution:  => fixed


Comment:

 > The right way to do this would probably be to, umm, lock a lock when
 CONF_CHANGED occurs and wait for it to be released in the get_conf call.

 Well drats. Thanks for the catch, Ravi!

 We can't really lock and await the CONF_CHANGED event since that is
 happening in a separate loop. The actual issue here seems to be that we're
 using msg() rather than set_conf(). If we used set_conf() then it would be
 updating the cache for us, so we could be sure the following get_conf()
 would be consistent.

 We're probably using msg() on purpose in this test to better simulate what
 it is like to have a second controller attached.

 Actually, now that I think about it more I'm less concerned that
 get_conf() provided the wrong response - if a separate controller makes
 asynchronous SETCONF calls then all bets are off. I am, however, concerned
 that we got this kind of half-way response. We didn't return either ""
 (the old value) or "['abc,xyz,pqrs', 'mno,tuv,wxyz']" (the new value) but
 rather a mix of the two because the get_conf() came *between* events.

 I suspect the best way for us to handle this is the change I made (which
 is to invalidate the cache rather than attempt to update it). If you have
 a better idea then let me know!

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7713#comment:11>
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