[GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar

[GHC]

#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
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    Reporter:  ChrisKuklewicz    |        Owner:                  
        Type:  bug               |       Status:  new             
    Priority:  normal            |    Milestone:                  
   Component:  libraries/base    |      Version:  6.10.2          
    Severity:  major             |   Resolution:                  
    Keywords:                    |   Difficulty:  Unknown         
    Testcase:                    |           Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |  
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Comment (by simonmar):

 I think rather than trying to get things right with `modifyMVar` and
 `withMVar`, we should try using STM for these abstractions.  I suspect
 that the overhead of `modifyMVar` and co is comparable to the overhead of
 using STM (we measured this result for Chan in the original Haskell STM
 paper), and the STM version is much easier to get right.  It would let us
 supply composable versions of the operations, too.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3160#comment:3>
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