[metrics-bugs] #26963 [Metrics/Onionoo]: regression in host_name field introduced in v6.1

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#26963: regression in host_name field introduced in v6.1
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 Reporter:  nusenu           |          Owner:  irl
     Type:  defect           |         Status:  accepted
 Priority:  High             |      Milestone:
Component:  Metrics/Onionoo  |        Version:
 Severity:  Normal           |     Resolution:
 Keywords:                   |  Actual Points:
Parent ID:                   |         Points:
 Reviewer:                   |        Sponsor:
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Comment (by irl):

 Please review commit
 [[https://gitweb.torproject.org/user/irl/onionoo.git/commit/?h=task/26963&id=6e6a279e8337dd05119477295e8f5d74a05ff3f8|6e6a279
 on my branch task/26963]].

 In the implementation of more accurate DNS resolution, the DirContext used
 by JNDI lookups was shared in a utility class. It turns out that
 InitialDirContext, the implementation we used, is very not thread-safe and
 so as a result lookups would often fail to complete.

 This commit creates a new DirContext for every lookup. The overhead in
 doing so is minimal and ensures that we do not have thread safety issues.

 This commit also increases RDNS_LOOKUP_WORKERS_NUM to 30 (from 5). The
 majority of time in these threads is spent waiting for replies and so
 there are gains to be had in increasing the number of requests in flight.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26963#comment:4>
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