That's clearly the right solution for this particular bug, but it does seem like there's a more general problem here.
Sam On Sat, Aug 16, 2014 at 10:40 AM, Robby Findler <ro...@eecs.northwestern.edu> wrote: > Seems simplest to be to have typed racket know to trust register finalizer > and thus avoid wrapping it with a contract. > > Robby > > > On Saturday, August 16, 2014, Neil Toronto <neil.toro...@gmail.com> 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
