[GHC] #12419: Scheduling bug with forkOS + MVar

[GHC]

#12419: Scheduling bug with forkOS + MVar
-------------------------------------+-------------------------------------
        Reporter:  luisgabriel       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  8.0.1
      Resolution:                    |             Keywords:  forkOS;
                                     |  scheduler
Operating System:  Linux             |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2430
       Wiki Page:                    |
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Changes (by simonmar):

 * differential:   => Phab:D2430


Comment:

 I found one bug, see Phab:D2430.  However, even after the patch the
 threadscope profiles don't look identical.  I don't think there is an
 actual problem, just that the program itself isn't very parallel - if you
 zoom in, there's lots of time in each thread where no work is being done.
 The difference in scheduling is due to the way that `forkOS` has to hand-
 shake with the new thread to get its `ThreadId`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12419#comment:3>
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