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In the following code (compiled with compiled with ghc --make -fffi -fvia-c Test.hs) the finalizer never gets called, even after replacing printf with something else:

Test.hs:

module Main where

import Foreign.Ptr
import Foreign.ForeignPtr
import Foreign.Marshal.Utils

foreign import ccall safe "ctest.h &ctest" ctestPtr :: FunPtr (Ptr Int -> IO ())

test :: Int -> IO ()
test i = with i test'
    where
        test' ptr = do fptr <- newForeignPtr ctestPtr ptr
                       putStrLn "test"

main = do putStrLn "before test..."
          test 33
          putStrLn "after test..."

ctest.h:

#include <stdio.h>

static inline void ctest( int *i )
{
    printf( "finalizer called with: %d\n", *i );
}

I've asked about this on IRC and the Haskell Cafe mailing list and received confirmation that in GHC there is no guarantee that finalizers will run before the program exits:

http://www.haskell.org/pipermail/haskell-cafe/2007-May/025458.html

The FFI addendum to the Haskell 98 report states in section 5.5 that "The only guarantee [for finalizers] is that the finalizer runs before the program terminates".

The same statement is made in GHC documentation for newForeignPtr.

This could be a bug or merely a documentation issue but something should probably be done about it. I suspect it's a bug considering the guarantee specified in the FFI addendum isn't met.

Trac metadata

Trac field	Value
Version	6.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
BlockedBy
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Blocking
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Operating system	Unknown
Architecture	Unknown