[GHC] #10867: Primop types should not mention ()

[GHC]

#10867: Primop types should not mention ()
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        Reporter:  simonpj           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by fryguybob):

 For the broader question of the STM data invariant feature, it is slightly
 broken (#7930) and may be a significant amount of work to keep around if
 we use an implementation that keeps an approximate read-set for
 performance gains.  I have asked around before and never found any users
 of the feature or code in the wild that uses the feature.  Its usefulness
 for discovering problems in user code is limited in highly concurrent
 settings.  The implementation takes a lock on every `TVar` when the
 transaction has touched an invariant meaning it simply will not see some
 interleavings that might be the exact ones that violate the invariant.
 Perhaps a better approach in the space is to extend Déjà Fu from Michael
 Walker and Colin Runciman to cover the same territory but include all the
 most significant interleavings.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10867#comment:6>
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