BIND 10 #2853: Python wrapper of data source extensions

[BIND 10 Development]

#2853: Python wrapper of data source extensions
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            Reporter:  jinmei        |                        Owner:  muks
                Type:  task          |                       Status:
            Priority:  medium        |  reviewing
           Component:  data source   |                    Milestone:
            Keywords:                |  Sprint-20130611
           Sensitive:  0             |                   Resolution:
         Sub-Project:  DNS           |                 CVSS Scoring:
Estimated Difficulty:  5             |              Defect Severity:  N/A
         Total Hours:  0             |  Feature Depending on Ticket:
                                     |  shared memory data source
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by jinmei):

 One more thing: I suspect the attached patch will still cause a crash
 even with the fix at b3befd1 (it does for me).  So the real issue
 is not returning None correctly itself, but `ZoneWriter` is used after
 the `ConfigurableClientList` that created the writer is destroyed
 (in case of unexpected exception due the Python unit test module keeps
 tested objects alive, seemingly.  On the other hand, clist is
 destroyed in tearDown()).

 Basically, `ZoneWriter` is expected to be ephemeral and at least
 shouldn't live beyond the lifetime of the creating
 `ConfigurableClientList` (if it's not documented, it should).
 So one way to address is to just make sure it's documented.
 But in the case of Python this level of crash may still seem
 too harsh.  So we might want to hold a reference to
 `ConfigurableClientList` in the wrapper object.  I'm not confident
 which is the best.  Please consider.

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Ticket URL: <http://bind10.isc.org/ticket/2853#comment:9>
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