[GHC] #12038: Shutdown interacts badly with requestSync()

[GHC]

#12038: Shutdown interacts badly with requestSync()
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        Reporter:  simonmar          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Runtime System    |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 I've left the test running for several thousand iterations in the
 background and have seen the error mentioned in comment:9 pop up a handful
 of times. On the bright side, this appears to be the only failure mode.

 It seems what is happening here is that the IO manager is trying to wake-
 up a manager thread which has already exited. We could simply add an
 `IORef` to `Control` to indicate that the manager has exited, but it's not
 clear to me whether this would merely be working around some more sinister
 root cause.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12038#comment:10>
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