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-Concurren...)
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-ForeignPt...)
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-ForeignPt...)
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