BIND 10 #2874: Test the Coroutines/RCU approach for resolver multi-threading

[BIND 10 Development]

#2874: Test the Coroutines/RCU approach for resolver multi-threading
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                   Reporter:  vorner    |                 Owner:
                       Type:  task      |                Status:  new
                   Priority:  medium    |             Milestone:  New Tasks
                  Component:  resolver  |              Keywords:
               CVSS Scoring:            |             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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 On top of #2871 implement the coroutines/RCU approach and measure its
 performance.

 Each query is a separate coroutine with its own stack, multiple coroutines
 live in a single thread (and they don't move from one thread to another).
 If a query waits for something external (eg. network IO), it yields and
 other coroutine can be run (if there's any other waiting). As many things
 that can be are thread-private, so they don't have to be locked (we can,
 for example, have own copy of the network sockets, logging, L1 cache).

 Things that need to be locked are locked by mutexes the usual way. The
 only exception is the cache, that would be done by RCU. Read accesses are
 without locking, only the updates need lock. Test whether we need multiple
 locks for parts of the cache or one is enough.

 Also, check if we need to „recycle“ used coroutines.

 It was suggested to try out the boost.Coroutine library for the
 experiment, as we already use boost.

 More detail can be found in
 https://lists.isc.org/pipermail/bind10-dev/2013-March/004493.html.

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Ticket URL: <http://bind10.isc.org/ticket/2874>
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