Could we benefit from an abstract/opaque Finalizer type here? I know we don't have those yet but it may address the general problem. -- Matthias
On Aug 16, 2014, at 8:55 AM, Neil Toronto wrote: > Short version: the contract system doesn't allow `register-finalizer` to be > used in Typed Racket. > > Long version: consider the following Typed Racket program, in which instances > of `os-resource-wrapper` represent an operating system resource > `os-resource`, which itself is just a counter. It attempts to register a > finalizer for allocated wrappers, which decrements the counter. > > > #lang typed/racket > > (require/typed > ffi/unsafe > [register-finalizer (All (A) (-> A (-> A Any) Void))]) > > (: os-resource Integer) > (define os-resource 0) > > (struct os-resource-wrapper ()) > > (: alloc-os-resource (-> os-resource-wrapper)) > (define (alloc-os-resource) > (set! os-resource (add1 os-resource)) > (define w (os-resource-wrapper)) > (register-finalizer w (λ (w) (set! os-resource (sub1 os-resource)))) > w) > > (define w (alloc-os-resource)) > (printf "os-resource = ~v~n" os-resource) > (collect-garbage) > (sleep 1) ; give finalizers a chance to run > (printf "os-resource = ~v~n" os-resource) > > > I get this output: > > os-resource = 1 > os-resource = 0 > > The finalizer is being run while the program still has a pointer to the > wrapper object. I think it's because the wrapper object is being impersonated > when it's sent across the contract barrier, and the *impersonator* is getting > the finalizer. (Or it's a chaperone, or an impostor, or a charlatan, or > whatever. Let's go with impersonator.) > > In my specific case, the OS resources are OpenGL objects; e.g. vertex object > arrays. The call to `register-finalizer` *must* be in Typed Racket code > because the wrapper contains an (Instance GL-Context<%>), which can't have a > contract put on it, so it can't pass from untyped to typed code. > > Is there any reason for `register-finalizer` to behave this way? Does it ever > make sense to register a finalizer on an impersonator? > > Neil ⊥ > _________________________ > Racket Developers list: > http://lists.racket-lang.org/dev _________________________ Racket Developers list: http://lists.racket-lang.org/dev
