[GHC] #15616: Bug when using TimerManager/GHC.Event ?

[GHC]

#15616: Bug when using TimerManager/GHC.Event ?
-------------------------------------+-------------------------------------
           Reporter:  ddellacosta    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 It was suggested on #haskell that this is a bug and that I should report
 it here. Hopefully this is the simplest possible example that shows the
 issue. The code sample I got from a StackOverflow answer
 (https://stackoverflow.com/a/25488677) which I found just trying to learn
 how to use GHC.Event properly so presumably, and it seemed to work there,
 so I assume it is still valid code (but let me know if not!).

 Minimal example repo is here: https://github.com/ddellacosta/timermanager-
 bug, please see Main.hs

 I'm on on OS X 10.13.6, and hopefully the shell dump below combined with
 the repo above gives you everything else you need:

 {{{#!bash
 $ cabal new-configure
 Resolving dependencies...
 Build profile: -w ghc-8.4.3 -O1
 In order, the following would be built (use -v for more details):
  - timermanager-bug-0.1.0.0 (exe:timermanager-bug) (first run)
 $ cabal new-build
 Build profile: -w ghc-8.4.3 -O1
 In order, the following will be built (use -v for more details):
  - timermanager-bug-0.1.0.0 (exe:timermanager-bug) (first run)
 Configuring executable 'timermanager-bug' for timermanager-bug-0.1.0.0..
 clang: warning: argument unused during compilation: '-nopie' [-Wunused-
 command-line-argument]
 Preprocessing executable 'timermanager-bug' for timermanager-bug-0.1.0.0..
 Building executable 'timermanager-bug' for timermanager-bug-0.1.0.0..
 [1 of 1] Compiling Main             ( Main.hs, /Users/ddellacosta/code
 /timermanager-bug/dist-newstyle/build/x86_64-osx/ghc-8.4.3/timermanager-
 bug-0.1.0.0/x/timermanager-bug/build/timermanager-bug/timermanager-bug-
 tmp/Main.o )
 Linking /Users/ddellacosta/code/timermanager-bug/dist-
 newstyle/build/x86_64-osx/ghc-8.4.3/timermanager-bug-0.1.0.0/x
 /timermanager-bug/build/timermanager-bug/timermanager-bug ...
 clang: warning: argument unused during compilation: '-nopie' [-Wunused-
 command-line-argument]
 clang: warning: argument unused during compilation: '-nopie' [-Wunused-
 command-line-argument]
 $ cabal new-exec timermanager-bug
 timermanager-bug: user error (Pattern match failure in do expression at
 libraries/base/GHC/Event/Thread.hs:216:3-10)
 $
 }}}

 Let me know if there's any more information I can supply! Apologies if
 this is not actually a bug but something I'm doing wrong! Thanks!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15616>
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