[GHC] #5212: waitForProcess: does not exist (No child processes)

[GHC]

#5212: waitForProcess: does not exist (No child processes)
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        Reporter:  chrisdone                    |            Owner:
            Type:  bug                          |           Status:  closed
        Priority:  normal                       |        Milestone:
       Component:  Runtime System               |          Version:  7.4.2
      Resolution:  invalid                      |         Keywords:
Operating System:  Linux                        |     Architecture:  x86_64
 Type of failure:  Incorrect result at runtime  |  (amd64)
       Test Case:                               |       Difficulty:
        Blocking:                               |  Unknown
                                                |       Blocked By:
                                                |  Related Tickets:
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Changes (by chrisdone):

 * cc: simonmar (added)
 * status:  new => closed
 * resolution:   => invalid


Comment:

 The reason is because XMonad (and presumably some other library I was
 using two years ago) installs signal handlers for SIGCHILD:


 {{{
 import Data.Maybe
 import Control.Monad
 import System.Posix.Signals
 import Control.Monad.Fix
 import Control.Exception
 import Control.Monad.Extra
 import Control.Monad.Trans
 import Control.Concurrent
 import System.Process
 import System.Posix.Process.ByteString

 main = do
   installSignalHandlers
   readProcess "ghc" ["--version"] "" >>= putStrLn

 -- | Ignore SIGPIPE to avoid termination when a pipe is full, and SIGCHLD
 to
 -- avoid zombie processes, and clean up any extant zombie processes.
 installSignalHandlers :: MonadIO m => m ()
 installSignalHandlers = io $ do
     installHandler openEndedPipe Ignore Nothing
     installHandler sigCHLD Ignore Nothing
     (try :: IO a -> IO (Either SomeException a))
       $ fix $ \more -> do
         x <- getAnyProcessStatus False False
         when (isJust x) more
     return ()

 }}}

 This is pretty annoying because it breaks other uses of readProcess. My
 solution was to use a patched version of readProcess which handles
 exceptions thrown on waitForProcess. I guess this ticket can be closed…

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5212#comment:6>
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