[GHC] #4001: Implement an atomic readMVar

[GHC]

#4001: Implement an atomic readMVar
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    Reporter:  simonmar                    |       Owner:  ezyang          
        Type:  task                        |      Status:  new             
    Priority:  low                         |   Milestone:  7.6.2           
   Component:  Runtime System              |     Version:  6.12.2          
    Keywords:                              |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple            |     Failure:  None/Unknown    
  Difficulty:  Moderate (less than a day)  |    Testcase:                  
   Blockedby:                              |    Blocking:                  
     Related:                              |  
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Comment(by ezyang):

 It occurs to me that there is a problem with the current implementation,
 which is that we may do an unbounded amount of work while the spinlock for
 an MVar is taken out. Probably the right thing to do is arrange for the
 closure to be unlocked before we start spinning up threads.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4001#comment:12>
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