BIND 10 #2205: introduce a "data source configurator" thread in auth

[BIND 10 Development]

#2205: introduce a "data source configurator" thread in auth
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                   Reporter:         |                 Owner:
  jinmei                             |                Status:  new
                       Type:  task   |             Milestone:
                   Priority:         |            Resolution:
  medium                             |             Sensitive:  0
                  Component:         |           Sub-Project:  DNS
  b10-auth                           |  Estimated Difficulty:  5
                   Keywords:         |           Total Hours:  0
            Defect Severity:  N/A    |
Feature Depending on Ticket:         |
  background zone loading            |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Description changed by jinmei:

Old description:

> A subtask of #2201.
>
> First, fully consider how to test these without creating threads.
>
> In this task, we let auth spawn a separate thread with a
> synchronization mechanism with the main auth thread.  The main and
> configurator thread work as the producer and the consumer: the main
> thread (producer) passes general form of command in the form of
> `ConstElementPtr` and the configurator thread (consumer) accepts each
> command and execute it.
>
> Choose an appropriate synchronization mechanism for the concept and
> implement it.  One way is to let both threads share
> `vector<ConstElementPtr>` with a conditional variable to get access to
> it.
>
> In this task, we only support "shutdown" command.  On auth's shutdown,
> the main thread sends this command to configurator, and waits for it
> to die by join().  The configurator simply exits if it gets this
> command.
>
> Same open question as in #2202 applies.  We use the consistent policy
> on this.

New description:

 A subtask of #2201.

 First, fully consider how to test these without creating threads.

 In this task, we let auth spawn a separate thread with a
 synchronization mechanism with the main auth thread.  The main and
 configurator thread work as the producer and the consumer: the main
 thread (producer) passes general form of command in the form of
 `ConstElementPtr` and the configurator thread (consumer) accepts each
 command and execute it.

 Choose an appropriate synchronization mechanism for the concept and
 implement it.  One way is to let both threads share
 `vector<ConstElementPtr>` with a conditional variable to get access to
 it.

 In this task, we only support "shutdown" command.  On auth's shutdown,
 the main thread sends this command to configurator, and waits for it
 to die by join().  The configurator simply exits if it gets this
 command.

 Same open question as in #2202 applies.  We use the consistent policy
 on this.

 This ticket depends on #2332 if we use condition variables.

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Ticket URL: <http://bind10.isc.org/ticket/2205#comment:9>
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