[GHC] #11760: runST with lazy blackholing breaks referential transparency

[GHC]

#11760: runST with lazy blackholing breaks referential transparency
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        Reporter:  Yuras             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * cc: simonmar, rnewton (added)


Comment:

 This looks bad.  Do you have a more detailed theory?   Our thinking about
 lazy blackholing is that if two threads start to evaluate the same thunk,
 they may waste work but shoudl still get the same value.  But that is not
 happening here and I'd like to understand why.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11760#comment:1>
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