Il giorno mar, 21/09/2021 alle 10.25 -0400, Olivier Dion ha scritto: > On Tue, 21 Sep 2021, adriano <randomloo...@riseup.net> wrote: > > Hi Olivier, > > > > thank you very much for your reply > > > > Il giorno dom, 19/09/2021 alle 14.11 -0400, Olivier Dion ha > > scritto: > > > On Sun, 19 Sep 2021, adriano <randomloo...@riseup.net> wrote: > > > > > > > > > > > > > > > > > > > > It'd be so nice to have an example > > > > > > (define (with-my-resource token proc) > > > (let ((resource #f)) > > > (dynamic-wind > > > (lambda () > > > (set! resource (open-my-resource% token))) > > > > > > (proc resource) > > > > > > (lambda () > > > (when resource > > > (close-my-resource% resource)))))) > > > > > > (with-my-resource "some-internal-token" (lambda ())) > > > > Oh my, thank you for this ! > > > > This should be included in the manual ! > > > > The example that's there currently is totally indequate, in my > > opinion > > > > > > > > > > > > Says you have `open_my_resource()` and `close_my_resource()` in C > > > in > > > library "libfoo.so" where open_my_resource takes a C string and > > > returns > > > an integer for the resource while close_my_resource takes the > > > integer > > > of > > > the resource: > > > > > > (define open-my-resource% > > > (eval-when (eval load compile) > > > (let ((this-lib (load-foreign-library "libfoo"))) > > > (foreign-library-function this-lib "open_my_resource" > > > #:return-type int > > > #:arg-types (list '*)))) > > > > > > (define open-my-resource% > > > (eval-when (eval load compile) > > > (let ((this-lib (load-foreign-library "libfoo"))) > > > (foreign-library-function this-lib "open_my_resource" > > > #:return-type int > > > #:arg-types (list int))))) > > > > Uhmm... I see 2 versions of open-my-resource% > > The only slight difference I see is in the #:arg-types > > > > The first one has > > > > (list '*) > > > > and the second one has > > > > (list int) > > > > > > Maybe you you got confused while editing ? > > You're right. I copy paste the form two times and forget to edit the > second > binding name. I meant `close-my-resource%` for the second define. > > > > > Thank you again > > Just make sure to read what Maxime says about escape continuation. > Dynamic wind are not bullet proof. > > As the manual says: > > If, any time during the execution of THUNK, the dynamic > extent of > the ‘dynamic-wind’ expression is escaped non-locally, > OUT_GUARD is > called. If the dynamic extent of the dynamic-wind is re- > entered, > IN_GUARD is called. Thus IN_GUARD and OUT_GUARD may be > called any > number of times. > > Thus, you could also do a `(set! resource #f)` after freeing it, so > that > the overall dynamic-wind is reentrant and you don't end up with > double > free of resource. >
After seeing your example of usage of dinamic-wind, I understand what IN_GUARD and OUT_GUARD are supposed to be Before that it was quite nebulous Thanks again