[GHC] #8591: Concurrent executions of ghc-pkg can cause inconstant package.cache files

[GHC]

#8591: Concurrent executions of ghc-pkg can cause inconstant package.cache files
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              Reporter:  janm        |            Owner:  pgj
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Package     |          Version:  7.6.3
  system                             |         Keywords:  ghc-pkg race
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:  FreeBSD     |       Difficulty:  Unknown
       Type of failure:  Other       |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by thomie):

 Not reading this thread closely, but since there's also a comment that
 says "copied from Cabal's Distribution.Simple.Utils", there might be a
 function in there now that does exactly what you need:
 https://github.com/haskell/cabal/blob/master/Cabal/Distribution/Simple/Utils.hs

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8591#comment:6>
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