[GHC] #4001: Implement an atomic readMVar

[GHC]

#4001: Implement an atomic readMVar
----------------------------+----------------------------------------------
        Reporter:           |            Owner:  ezyang
  simonmar                  |           Status:  new
            Type:  task     |        Milestone:  7.6.2
        Priority:  low      |          Version:  6.12.2
       Component:  Runtime  |         Keywords:
  System                    |     Architecture:  Unknown/Multiple
      Resolution:           |       Difficulty:  Moderate (less than a day)
Operating System:           |       Blocked By:
  Unknown/Multiple          |  Related Tickets:
 Type of failure:           |
  None/Unknown              |
       Test Case:           |
        Blocking:           |
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Comment (by ezyang):

 Performance impact of the new patch:

 {{{
 --------------------------------------------------------------------------------
         Program           Size    Allocs   Runtime   Elapsed  TotalMem
 --------------------------------------------------------------------------------
     callback001          +0.1%     +0.0%     +1.4%     +1.6%     +0.0%
     callback002          +0.1%     +0.0%     -1.0%     -1.0%     +0.0%
            chan          +0.1%     +0.0%     +0.0%     +0.2%     -2.0%
           sieve          +0.1%     +0.0%     -1.0%     -1.5%     -8.0%
      threads001          +0.1%     +0.0%     -0.4%     -0.3%     +0.0%
      threads003          +0.1%     -0.0%     -0.2%     -0.6%     +0.0%
      threads006          +0.1%     +0.0%     +0.6%     +0.6%     +0.0%
      threads007          +0.1%     +0.0%     +0.4%     +0.1%     +0.2%
 --------------------------------------------------------------------------------
             Min          +0.1%     -0.0%     -1.0%     -1.5%     -8.0%
             Max          +0.1%     +0.0%     +1.4%     +1.6%     +0.2%
  Geometric Mean          +0.1%     -0.0%     -0.0%     -0.1%     -1.3%
 }}}

 Looks pretty good to me :)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4001#comment:17>
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