I have some Alien objects that I'd like to have finalized. Here's
some example code.
(use-package :ALIEN)
(use-package :C-CALL)
(def-alien-type attr-t unsigned-long)
(defun foo ()
(let ((an-attr (make-alien attr-t)))
(do-something-to (deref an-attr))
an-attr))
(defun bar (attr)
(declare (type (alien (* attr-t)) attr))
(do-something-different-to (deref attr)))
(bar (foo))
Now with all this I'd like to add a finalizer inside BAR which will
clean up ATTR by calling FREE-ALIEN on it. Something like this:
(defun bar (attr)
(declare (type (alien (* attr-t)) attr))
(unwind-protect
(do-something-different-to (deref attr))
(ext:finalize attr #'finalize-attr-t)))
For EXT:FINALIZE I need a function that knows what to do, so I thought
I'd write one like:
(defun finalize-attr-t (attr)
(declare (type (alien (* attr-t)) attr))
(free-alien (deref attr)))
But reading in the user manual (cmu-user.dvi) section '2.5.3
Finalization' I see
"/function/ is called with no arguments when /object/ is reclaimed.
Normally /function/ will be a closure over the underlying state that
needs to be freed, e.g. the unix file descriptor in the fd-stream
case."
So the Obvious Solution is right out. I can't just expect to be
passed the object (or a reference to it) into my finalization
function. How exactly am I supposed to make a closure over 'the
underlying state'? And how am I supposed to get at this 'underlying
state' without maintaining a reference to the object itself? I'm
confused.
On a related note, why can't the FUNCTION argument to EXT:FINALIZE
take one argument that is the object (or a reference to it) being
finalized? Is this impossible? It would make it much easier for the
programmer (or for me at least)...
'james
--
James A. Crippen <[EMAIL PROTECTED]> ,-./-. Anchorage, Alaska,
Lambda Unlimited: Recursion 'R' Us | |/ | USA, 61.20939N, -149.767W
Y = \f.(\x.f(xx)) (\x.f(xx)) | |\ | Earth, Sol System,
Y(F) = F(Y(F)) \_,-_/ Milky Way.
