Bug in touchForeignPtr?

Benjamin Franksen benjamin.franksen at bessy.de
Tue Nov 30 11:39:14 EST 2004

[re-sending because I got no response yet]

On Tuesday 23 November 2004 13:06, Simon Marlow wrote:
> On 22 November 2004 17:28, Benjamin Franksen wrote:
> > However, what I don't understand is why touchForeignPtr is not
> > honored in my example program: Note that the output text lines from
> > the finalizers appear *before* the last action in the program (which
> > is a second getChar). The finalizers *are* called by the GC, and
> > still the order is wrong.
> Note that the GC only starts the finaliser thread.  The program can
> still terminate before this thread has run to completion

I repeat: the program is not yet even near termination when the finalizers get 
executed (in teh wrng order).

Here is the example program again (with 3 lines added to the end of main to 
illustrate the point):

import Foreign hiding (newForeignPtr)
import Foreign.Concurrent
import System.Mem (performGC)

type A = ForeignPtr Int

type B = ForeignPtr Bool

newA :: IO A
newA = do
  (pa::Ptr Int) <- malloc
  newForeignPtr pa $ do
    putStrLn "before finalizing A"
    free pa
    putStrLn "after finalizing A"
newB :: A -> IO B
newB fpa =
  withForeignPtr fpa $ \pa -> do
    (pb::Ptr Bool) <- malloc
    newForeignPtr pb $ do
      putStrLn "before finalizing B"
      free pb
      putStrLn "after finalizing B"
      touchForeignPtr fpa

main = do
  a <- newA
  b <- newB a
  putStrLn "Program still not terminated, please hit <enter> again!"
  putStrLn "Program termination will now be initiated."

And this is the output:

franksen at linux: .../foreigntouchbug > ./a.out 
before finalizing A
after finalizing A
before finalizing B
after finalizing B
Program still not terminated, please hit <enter> again!
Program termination will now be initiated.


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