[GHC] #8818: Add withMVarMasked

[GHC]

#8818: Add withMVarMasked
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       Reporter:  hvr               |             Owner:  hvr
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:  7.10.1
      Component:  libraries/base    |           Version:
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 We already have `modifyMVarMasked` and `modifyMVarMasked_`, and so
 I propose to add

 {{{#!haskell
 {-|
   Like 'withMVar', but the @IO@ action in the second argument is executed
   with asynchronous exceptions masked.

   /Since: 4.7.0.0/
 -}
 {-# INLINE withMVarMasked_ #-}
 withMVarMasked :: MVar a -> (a -> IO b) -> IO b
 withMVarMasked m io =
   mask_ $ do
     a <- takeMVar m
     b <- io a `onException` putMVar m a
     putMVar m a
     return b
 }}}

 any arguments against this addition?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8818>
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