BIND 10 #1668: redo threaded stats tests with mocksessions

[BIND 10 Development]

#1668: redo threaded stats tests with mocksessions
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                   Reporter:  jelte  |                 Owner:
                       Type:  task   |                Status:  new
                   Priority:  major  |             Milestone:  Year 3 Task
                  Component:         |  Backlog
  statistics                         |            Resolution:
                   Keywords:         |             Sensitive:  0
            Defect Severity:  N/A    |           Sub-Project:  DNS
Feature Depending on Ticket:         |  Estimated Difficulty:  0
        Add Hours to Ticket:  0      |           Total Hours:  0
                  Internal?:  0      |
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Comment (by jelte):

 Replying to [comment:3 naokikambe]:
 > Hello,
 > I'm just curious about the race condition issue found on
 [ticket:640#comment:21]. It was seemed to be discussed only on jabber.
 >

 The problem is partly in ThreadingServerManager from testutils.py; when
 shutdown() is called on it, it forwards that call to whatever server-type
 it is managing. It the join()s the thread for that server, but does so
 with a zero timeout (i.e. it does not wait for it to finish). Since the
 test I needed for 640 does want those threads to do some additional
 processing (it tests cleanup), this often fails.

 However, a lot of the other tests would deadlock here, should one change
 that zero timeout to a blocking one. So the workaround there, for now, is
 to specifically do a blocking join() for that specific test. See commit
 2da5a3de561484f902aa7fb8475551217b9535b9

 You can reproduce the behaviour by changing the call
 self.stats_server.shutdown(True) to self.stats_server.shutdown() in
 b10-stats_test.py. But since it is a race condition, the problem does not
 show on every run (about one in 5 on my system).

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Ticket URL: <http://bind10.isc.org/ticket/1668#comment:5>
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