Guarantees regarding finalizers

[Simon Marlow]

On 26/11/2009 12:41, Mietek Bąk wrote:

> I'm writing a binding to a C library, which requires an explicit
> cleanup call before program termination.  While looking for a way to
> automatize this, I noticed a discrepancy in the standard library
> documentation.
>
> The Foreign.Concurrent documentation states:
> "The only guarantee is that the finalizer runs before the program terminates."
> (http://www.haskell.org/ghc/docs/latest/html/libraries/base/Foreign-Concurrent.html)
>
> On the other hand, the Foreign.ForeignPtr documentation states:
> "Indeed, there is no guarantee that the finalizer is executed at all;
> a program may exit with finalizers outstanding."
> (http://www.haskell.org/ghc/docs/latest/html/libraries/base/Foreign-ForeignPtr.html)
>
> Note that Foreign.Concurrent.newForeignPtr is implemented in GHC as
> GHC.ForeignPtr.newConcForeignPtr.  The newConcForeignPtr comments also
> state:
> "There is no guarantee of promptness, and in fact there is no
> guarantee that the finalizer will eventually run at all."
> (http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-ForeignPtr.html)
>
> As much as I would like the Foreign.Concurrent guarantee to be true,
> this seems to me like a documentation bug.

The docs are rather backward.  Foreign.ForeignPtr finalizers are 
guaranteed to run, Foreign.Concurrent finalizers are not.  I'll fix the 
docs, thanks for the report.

Cheers,
	Simon