[Haskell-cafe] Why does sleep not work?

[George Pollard]

On Wed, 2009-02-11 at 00:05 +0100, Manlio Perillo wrote:
> John Ky ha scritto:
> > Hi Haskell Cafe,
> > 
> > I wrote very short program to sleep for 5 seconds compiled with the 
> > -threaded option in ghc on the Mac OS X 1.5.
> > 
> > I am finding that using the sleep function doesn't sleep at all, whereas 
> > using threadDelay does:
> > 
> > [...]
> > main = do
> >       putStrLn "Waiting for 5 seconds."
> >       sleep 5 -- doesn't sleep at all
> >       putStrLn "Done."
> > 
> > Anybody know what's happening?
> > 
> 
> Here is a syscal trace, on Linux:
> http://hpaste.org/fastcgi/hpaste.fcgi/view?id=1332#a1332
> 
> 
> The interesting part:
> write(1, "Waiting for 5 seconds.\n"..., 23) = 23
> rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
> rt_sigaction(SIGCHLD, NULL, {SIG_DFL}, 8) = 0
> rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> nanosleep({5, 0}, 0xbf85f5cc)           = ? ERESTART_RESTARTBLOCK (To be 
> restarted)
> --- SIGVTALRM (Virtual timer expired) @ 0 (0) ---
> sigreturn()                             = ? (mask now [])
> write(1, "5\n"..., 2)                   = 2
> 
> 
> So, it seems nanosleep get interruped by a signal.

This works:

> import System.Posix
> 
> main = do
> 	putStrLn "Waiting for 5 seconds."
> 	blockSignals $ addSignal sigVTALRM emptySignalSet
> 	sleep 5
> 	putStrLn "Done."
> 
So (see my earlier email) `sleep` is lying about what interrupts it :)

- George
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