[GHC] #12728: setnumcapabilities001 sometimes fails on Windows

[GHC]

#12728: setnumcapabilities001 sometimes fails on Windows
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           Reporter:  bgamari         |             Owner:
               Type:  bug             |            Status:  new
           Priority:  high            |         Milestone:  8.2.1
          Component:  Runtime System  |           Version:  8.0.1
           Keywords:                  |  Operating System:  Windows
       Architecture:  x86_64 (amd64)  |   Type of failure:  Runtime crash
          Test Case:                  |        Blocked By:
           Blocking:                  |   Related Tickets:
Differential Rev(s):                  |         Wiki Page:
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 I have seen the `setnumcapabilities001` test fail at least once on Windows
 ([[https://phabricator.haskell.org/harbormaster/build/14178/?l=0]]). It
 seems that the assertion `ASSERT(n_idle == 0);` in `Schedule.scheduleDoGC`
 is to blame in this particular case.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12728>
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