Re: Help me grok addFinalizer
> I haven't checked, but ...
I checked, and your solution works. In the context of a larger program,
getting NOLINE pragmas in all the right places would be challenging,
wouldn't it?
I found a bug report on the GHC Trac [1] in which Simon explains the
importance of evaluating the thunk before calling addFinalizer. (Otherwise
the finalizer is added to the thunk.) This works:
newThing :: IO Thing
newThing = do
x <- Thing `fmap` newIORef True
return $ unsafePerformIO ( do
x' <- evaluate x
addFinalizer x' $ putStrLn "running finalizer" ) `seq` x
If anyone can show me how to get rid of unsafePerformIO in there, that'd be
great. Tried a few things to no avail.
> Finalizers are tricky things, especially when combined with some of
> GHC's optimisations.
No kidding!
[1] http://hackage.haskell.org/trac/ghc/ticket/5365
Mike Craig
On Thu, Feb 16, 2012 at 4:15 PM, Ian Lynagh wrote:
> On Thu, Feb 16, 2012 at 02:55:13PM -0600, Austin Seipp wrote:
> > 64-bit GHC on OS X gives me this:
> >
> > $ ghc -fforce-recomp -threaded finalizer
> > [1 of 1] Compiling Main ( finalizer.hs, finalizer.o )
> > Linking finalizer ...
> > $ ./finalizer
> > waiting ...
> > done!
> > waiting ...
> > running finalizer
> > done!
> >
> > However, it's a different story when `-O2` is specified:
> >
> > $ ghc -O2 -fforce-recomp -threaded finalizer
> > [1 of 1] Compiling Main ( finalizer.hs, finalizer.o )
> > Linking finalizer ...
> > $ ./finalizer
> > waiting ...
> > running finalizer
> > done!
> > waiting ...
> > done!
> >
> > This smells like a bug. The stranger thing is that the GC will run the
> > finalizer, but it doesn't reclaim the object? I'd think `readIORef`
> > going after an invalidated pointer the GC reclaimed would almost
> > certainly crash.
>
> The finalizer is attached to the Thing, not the IORef. I haven't
> checked, but I assume that ioref gets inlined, so effectively (ioref x)
> is evaluated early. If you change it to
>
>readIORef (ioref' x) >>= \ix -> ix `seq` return ()
>
> and define
>
>{-# NOINLINE ioref' #-}
>ioref' :: Thing -> IORef Bool
>ioref' = ioref
>
> then you'll get the sort of output you expect.
>
> Finalizers are tricky things, especially when combined with some of
> GHC's optimisations.
>
>
> Thanks
> Ian
>
>
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>
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Re: Help me grok addFinalizer
> This seems to be an explanation of why a finalizer might run later than expected (or not run at all). But his paste shows that it runs *earlier* than what he expected. What he said. > 64-bit GHC on OS X gives me this: > > ... > > However, it's a different story when `-O2` is specified: > > ... You're right. I was compiling with cabal and had -O turned on without knowing it. So this looks like an optimization bug? Mike Craig On Thu, Feb 16, 2012 at 3:55 PM, Austin Seipp wrote: > 64-bit GHC on OS X gives me this: > > $ ghc -fforce-recomp -threaded finalizer > [1 of 1] Compiling Main ( finalizer.hs, finalizer.o ) > Linking finalizer ... > $ ./finalizer > waiting ... > done! > waiting ... > running finalizer > done! > > However, it's a different story when `-O2` is specified: > > $ ghc -O2 -fforce-recomp -threaded finalizer > [1 of 1] Compiling Main ( finalizer.hs, finalizer.o ) > Linking finalizer ... > $ ./finalizer > waiting ... > running finalizer > done! > waiting ... > done! > > This smells like a bug. The stranger thing is that the GC will run the > finalizer, but it doesn't reclaim the object? I'd think `readIORef` > going after an invalidated pointer the GC reclaimed would almost > certainly crash. > > On Thu, Feb 16, 2012 at 2:04 PM, Michael Craig wrote: > > When I read the docs for System.Mem.Weak, it all seems to make sense. But > > then this code doesn't run as I expect it to when I turn on > > -threaded: http://hpaste.org/63832 (Expected/actual output are listed > in the > > paste.) > > > > I've tried this on 7.4.1 and 7.0.4 with the same results. Can someone > > enlighten me? > > > > Cheers, > > Mike Craig > > > > > > ___ > > Glasgow-haskell-users mailing list > > Glasgow-haskell-users@haskell.org > > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > > > > > > -- > Regards, > Austin > ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Help me grok addFinalizer
When I read the docs for System.Mem.Weak, it all seems to make sense. But then this code doesn't run as I expect it to when I turn on -threaded: http://hpaste.org/63832 (Expected/actual output are listed in the paste.) I've tried this on 7.4.1 and 7.0.4 with the same results. Can someone enlighten me? Cheers, Mike Craig ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
