Florian Weimer wrote: > At least in my experience, in order to get proper resource management > for things like file or database handles, you need both a close > operation and a finalizer registered with the garbage collector. The > former is needed so that you can create resources faster than the > garbage collector freeing them. The latter is a safety net in cases > where proper resource management is not follwoed (perhaps in GHCi). > When the explicit close operation or the finalizer has been invoked, > the object must somehow be disabled, so that further operations on it > fail (otherwise, you might dereference a dangling pointer). > > What's the idom for implementing this in Haskell (or GHC)? It seems > that a ForeignPtr cannot be written to (otherwise I'd change it to a > null pointer when the resource is freed). It's also not possible to > check if the finalizers have been run. > > Can the finalizers hold a reference to the object which in turn holds > the ForeignPtr to be finalized? Or would that prevent the finalizers > from running at all? Is there a way to avoid the extra level of > indirection (or is GHC sufficiently smart to optimize it away)?
You might be interested in Lightweight Monadic Regions http://okmij.org/ftp/Haskell/regions.html#light-weight which solve the problem (IMHO) in a much cleaner way, i.e. w/o explicit closing and also w/o using finalizers. Cheers Ben _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
