Ticket #7032: 7032.patch

File 7032.patch, 2.6 KB (added by pcapriotti, 3 years ago)
  • System/Posix/Unistd.hsc

    From ba7961f118f42ba9db7e5fba017270a257852ff3 Mon Sep 17 00:00:00 2001
    From: Paolo Capriotti <[email protected]>
    Date: Mon, 2 Jul 2012 11:52:39 +0100
    Subject: [PATCH] Add a WARNING for sleep, and expand documentation.
    
    sleep doesn't really work on GHC because it is always immediately
    interrupted by SIGVTALRM used in the RTS.
    
    I explained the problem in a comment and added a WARNING pragma.
    
    usleep and nanosleep have a similar problem, but, since they have better
    precision, they can be restarted, so they are not as unusable as sleep.
    ---
     System/Posix/Unistd.hsc |   15 +++++++++++++--
     1 file changed, 13 insertions(+), 2 deletions(-)
    
    diff --git a/System/Posix/Unistd.hsc b/System/Posix/Unistd.hsc
    index 7312dae..dfd2673 100644
    a b foreign import ccall unsafe "uname" 
    9595-- | Sleep for the specified duration (in seconds).  Returns the time remaining
    9696-- (if the sleep was interrupted by a signal, for example).
    9797--
    98 -- GHC Note: the comment for 'usleep' also applies here.
     98-- /GHC Note/: 'Control.Concurrent.threadDelay' is a better choice.  Since GHC
     99-- uses signals for its internal clock, a call to 'sleep' will usually be
     100-- interrupted immediately.  That makes 'sleep' unusable in a program compiled
     101-- with GHC, unless the RTS timer is disabled (with @+RTS -V0@).  Furthermore,
     102-- without the @-threaded@ option, 'sleep' will block all other user threads.
     103-- Even with the @-threaded@ option, 'sleep' requires a full OS thread to
     104-- itself.  'Control.Concurrent.threadDelay' has none of these shortcomings.
    99105--
    100106sleep :: Int -> IO Int
    101107sleep 0 = return 0
    102108sleep secs = do r <- c_sleep (fromIntegral secs); return (fromIntegral r)
    103109
     110#ifdef __GLASGOW_HASKELL__
     111{-# WARNING sleep "This function has several shortcomings (see documentation). Please consider using Control.Concurrent.threadDelay instead." #-}
     112#endif
     113
    104114foreign import ccall safe "sleep"
    105115  c_sleep :: CUInt -> IO CUInt
    106116
    107117-- | Sleep for the specified duration (in microseconds).
    108118--
    109 -- GHC Note: 'Control.Concurrent.threadDelay' is a better choice.
     119-- /GHC Note/: 'Control.Concurrent.threadDelay' is a better choice.
    110120-- Without the @-threaded@ option, 'usleep' will block all other user
    111121-- threads.  Even with the @-threaded@ option, 'usleep' requires a
    112122-- full OS thread to itself.  'Control.Concurrent.threadDelay' has
    foreign import ccall safe "usleep" 
    134144
    135145-- | Sleep for the specified duration (in nanoseconds)
    136146--
     147-- /GHC Note/: the comment for 'usleep' also applies here.
    137148nanosleep :: Integer -> IO ()
    138149#ifndef HAVE_NANOSLEEP
    139150nanosleep = error "nanosleep: not available on this platform"