Ah, I was missing your point, I've heard something called copy-on-write, which wasn't what you describe (or I also misunderstood it when I heard it before).
I see. But how would one manage these handles? What's to keep me from accidentally copying a handle? It sounds like it'd require explicit memory management, in order to avoid ever copying a handle, if I were to implment this myself. Or are you suggesting that if the simons implemented a copy-on-write scheme in ghc's RTS, then I'd be all set? In short, managing the reader count is exactly the problem that sounds hard, and I still don't have any idea how one would go about it. David On Thu, Mar 08, 2007 at 01:31:19PM -0800, Dan Weston wrote: > I might be missing the point, but I think you are missing mine. > > The copy-on-write I am talking about means that it's no longer "your > data", so you don't need any knowledge of who has access to it because > you don't own it or have a pointer to it. It is owned by some broker > from which you request a read-only or write access handle as needed. > Requested changes to underlying data already shared by others triggers a > copy and reassignment of pointers to it for your handle alone. > > The copy cost appears only when there is more than one handle to the > same data and one of them changes it. > > All this can be wrapped up and hidden away. If you want to escape this > broker business and steal back your data, just ask: the broker will > duplicate shared data needed by others, change their pointers to it, > then disown the pointer it returns to you. > > This is copying without writing (unnecessarily). Or am I missing something? > > Dan > > David Roundy wrote: > >I'm thinking you're missing the point. The point is to copy without > >writing, and that requires some knowledge (whether static or runtime) of > >whether anyone else has a reference to my data--which copy-on-write won't > >give me. > > > >David > > > >On Thu, Mar 08, 2007 at 11:15:25AM -0800, Dan Weston wrote: > >>Or possibly more generally copy-on-write, which requires one more level > >>of indirection (handle instead of ptr). Since you are talking about > >>using ForeignPtr, this is already within your power to prototype, I > >>should think. > >> > >>Dan > >> > >>Dan Piponi wrote: > >>>On 3/8/07, David Roundy <[EMAIL PROTECTED]> wrote: > >>> > >>>>I started wondering whether there's a solution that would allow us to > >>>>write pretty high-level pure functional code, while the RTS can realize > >>>>at run-time that we have the only reference to the input argument and > >>>>that it is therefore safe to consume it destructively. > >>>I think you're talking about uniqueness typing which is supported by > >>>the programming language Clean. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
