[tor-bugs] #19858 [Core Tor/Tor]: Move guard state out of globals per new guard plan

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#19858: Move guard state out of globals per new guard plan
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     Reporter:  andrea        |      Owner:  andrea
         Type:  task          |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.2.9.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: unspecified
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:  3             |   Reviewer:
      Sponsor:  SponsorU      |
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 New guard plan summarized here at https://lists.torproject.org/pipermail
 /tor-dev/2016-July/011234.html

 1) Create main guard selection state data structure (instead of using
 global variables)
  - Ideally there should be no global variables, so that in the future we
 can have multiple parallel guardsets (e.g. prop247)
  - Thoughtworks: guard_selection_t

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19858>
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