[GHC] #13330: forkIO has inconsistent behavior under optimization

[GHC]

#13330: forkIO has inconsistent behavior under optimization
-------------------------------------+-------------------------------------
           Reporter:  dfeuer         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Core           |           Version:  8.1
  Libraries                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Troubleshooting the T4030 failure in SimonPJ's early-inline branch, Reid
 and I discovered that the problem showed up when the argument to `forkIO`
 was obviously bottom. He came up with a tiny test case that fails without
 Simon's changes:

 {{{#!hs
 main = forkIO undefined >> threadDelay 1000000
 }}}

 It looks like the trouble is in the definition of `forkIO`:

 {{{#!hs
 forkIO :: IO () -> IO ThreadId
 forkIO action = IO $ \ s ->
    case (fork# action_plus s) of (# s1, tid #) -> (# s1, ThreadId tid #)
  where
   action_plus = catchException action childHandler
 }}}

 This seems to run into the trouble with `catchException` and strictness
 explained in `GHC.IO`. It would appear that the conservative fix would be
 to replace `catchException` with `catch`. Personally, I find it a bit
 surprising that `forkIO` doesn't force its `IO` argument before forking,
 but changing that behavior could break working code.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13330>
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