[GHC] #5902: Cannot tell from an exception handler whether the exception was asynchronous

[GHC]

#5902: Cannot tell from an exception handler whether the exception was
asynchronous
-------------------------------------+------------------------------------
        Reporter:  simonmar          |            Owner:  simonmar
            Type:  bug               |           Status:  new
        Priority:  high              |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.4.1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by exbb2):

 Replying to [comment:19 simonmar]:
 > > Every innocuous catch or try anywhere at any time in any library can
 make a thread unintentionally uncancelable
 > I'm not sure what you mean here.  The issue in this ticket only arises
 when using `unsafePerformIO`.

 {{{
 tryNTimes n
  | n <= 0 = return ()
  | otherwise =
   forever (return ())
    `catch` \(_::SomeException) -> tryNTimes (n - 1)
 }}}
 or
 {{{
 try something :: IO (Either SomeException x)
 }}}
 Catching SomeException is sometimes reasonable, but it's unreasonable not
 to provide ability to discriminate against irrelevant asynchronous
 exceptions which do not directly follow from handled code.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5902#comment:20>
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