Hello On Tuesday 23 Dec 2003 9:27 am, Simon Marlow wrote: > > Assuming the weak pointers solution is the way to go, I've been > > re-aquainting myself with System.Mem.Weak and now I'm now wondering > > what is an appropriate key for each ForeignPtr. > > Before we go down that route, I want to be sure that it's actually > necessary to use weak pointers. It sounds like your application has the > following properties: > > - there is a library that can allocate some resources, where > each resource is represented by a ForeignPtr
Basically, but there are also some hardware resources (other than memory) which are claimed just as a result of library initialisation (before any library objects have been created). > - a resource needs to be released when it is no longer referenced Yes, that's right. > - at some point, we would like to free *all* outstanding resources > (either at the end of the program, or when the library is no > longer required). I want to free all heap space used by library objects, then free whatever other hardware resources have been claimed by the library (by calling the appropriate shutdown routine). > If this is the case, I'd do it something like this: > > - keep a global list of the pointers still to be released, probably > a doubly-linked list. Lock the whole thing with an MVar. Elements > are Ptrs, not ForeignPtrs. > > - the finaliser on each ForeignPtr removes the corresponding Ptr from > the list. > > - the final cleanup routine explicitly releases all the remaining > Ptrs in the list, holding the MVar lock as it does so to avoid > race conditions with finalisers. > > Weak pointers aren't required, AFAICT. Maybe, I'd forgotten that I could get at the Ptr inside each ForeignPtr. I guess I've still got to think about the consequences of ForeignPtr finalisers being run after the "final" shutdown. (Making each List cell an IORef (Maybe something) would do that I think). The other complication I can see is that ForeignPtr finalisers can't be Haskell. So I have to call the Haskell finalisation from C. Is that safe? I'm afraid I still don't fully understand why Haskell finalisers are unsafe or why (if) calling Haskell from a C finaliser (which then called C land again) would be any safer. Thanks for the idea though. I'll play about with a few implementations of these ideas after christmas and see what problems I encounter. Regards -- Adrian Hey _______________________________________________ Glasgow-haskell-users mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
