[GHC] #8684: hWaitForInput cannot be interrupted by async exceptions on unix

[GHC]

#8684: hWaitForInput cannot be interrupted by async exceptions on unix
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       Reporter:  nh2               |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  libraries/base    |           Version:  7.6.3
       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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 http://hackage.haskell.org/package/base-4.6.0.1/docs/System-Timeout.html

 claims that {{{timeout}}} can interrupt {{{hWaitForInput}}}, but in fact
 that's false (e.g. mentioned in
 https://ghc.haskell.org/trac/ghc/ticket/7353#comment:4).

 {{{
 -- import Control.Concurrent
 import System.IO
 import System.Timeout

 main = timeout (1 * 1000000) $ hWaitForInput stdin (5 * 1000)
 }}}

 will not be killed after 1 second, but instead wait for the full 5 seconds
 timeout passed to {{{hWaitForInput}}}.

 The implementation is {{{ready}}} at
 http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-IO-
 FD.html, where we have two foreign calls: {{{safe fdReady}}} and {{{unsafe
 unsafe_fdReady}}}.

 The actual C implementation is at https://github.com/haskell-
 suite/base/blob/master/cbits/inputReady.c#L16. It uses {{{select}}} on
 Unix, and does check for {{{EINTR}}}, so I believe that according to
 http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/ffi.html#ffi-
 interruptible both foreign calls can be replaced by a single
 {{{interruptible}}} one.

 Is that true?

 If not, it's a documentation bug in {{{timeout}}} at least.

 Also, does {{{interruptible}}}, apart from allowing the function to be
 interrupted, behave more like {{{safe}}} or {{{unsafe}}}?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8684>
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