BIND 10 #2855: introduce a "zone builder" thread in memory manager

[BIND 10 Development]

#2855: introduce a "zone builder" thread in memory manager
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                   Reporter:         |                 Owner:
  jinmei                             |                Status:  new
                       Type:  task   |             Milestone:  Next-Sprint-
                   Priority:         |  Proposed
  medium                             |              Keywords:
                  Component:  shmem  |             Sensitive:  0
  manager                            |           Sub-Project:  DNS
               CVSS Scoring:         |  Estimated Difficulty:  0
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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 Subtask of #2830.  Depend on #2854.

 Like b10-auth, we'll need to be able to load zones into memory in
 "background"; memmgr doesn't have to answer queries, but it should
 still need to handle commands from other modules while it's loading zones.
 There could be several possible ways, but we should probably use a
 separate thread like b10-auth.

 Assuming that approach, in this task we introduce this thread and
 implement some communication channel between the main thread.  Right
 now the "builder thread" doesn't do anything, except probably a
 "shutdown" operation.

 Consider using some wrapper of thread so it can be tested without
 actually spawning threads.

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Ticket URL: <http://bind10.isc.org/ticket/2855>
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BIND 10 Development