Can you say more about what the API for what you're imagining is? Sam
On Sun, Aug 17, 2014 at 3:41 PM, Matthias Felleisen <matth...@ccs.neu.edu> wrote: > > I am imagining that the type compilation of type Finalizer and such things > would be parameterized over programmer code which would yield a 'trusted' > 'thing' in this case except that this would open the door for other such > things. > > > > > On Aug 17, 2014, at 3:39 PM, Sam Tobin-Hochstadt wrote: > >> How would that change things here? The issue is about >> finalizer-for-what, and that chaperones/impersonators affect object >> identity. >> >> Sam >> >> On Sun, Aug 17, 2014 at 3:37 PM, Matthias Felleisen >> <matth...@ccs.neu.edu> wrote: >>> >>> 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 > _________________________ Racket Developers list: http://lists.racket-lang.org/dev
