X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~mdw/git/clg/blobdiff_plain/7479d92c2e0ee576d0d376bbbbb72a9dcb948e4b..73572c12ccd49c661d06287903bfa725f5fd93a5:/glib/proxy.lisp

diff --git a/glib/proxy.lisp b/glib/proxy.lisp
index b4ff7a3..6ad8b90 100644
--- a/glib/proxy.lisp
+++ b/glib/proxy.lisp
@@ -15,109 +15,204 @@
 ;; License along with this library; if not, write to the Free Software
 ;; Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 
-;; $Id: proxy.lisp,v 1.2 2001-04-30 11:25:25 espen Exp $
+;; $Id: proxy.lisp,v 1.19 2005-02-03 23:09:04 espen Exp $
 
 (in-package "GLIB")
 
-
 ;;;; Superclass for all metaclasses implementing some sort of virtual slots
 
 (eval-when (:compile-toplevel :load-toplevel :execute)
-  (defclass virtual-class (pcl::standard-class))
+  (defclass virtual-slots-class (standard-class) 
+    ())
 
   (defclass direct-virtual-slot-definition (standard-direct-slot-definition)
-    ((location
-      :reader slot-definition-location
-      :initarg :location)))
+    ((setter :reader slot-definition-setter :initarg :setter)
+     (getter :reader slot-definition-getter :initarg :getter)
+     (unbound :reader slot-definition-unbound :initarg :unbound)
+     (boundp :reader slot-definition-boundp :initarg :boundp)))
+  
+  (defclass effective-virtual-slot-definition (standard-effective-slot-definition)
+    ((setter :reader slot-definition-setter :initarg :setter)
+     (getter :reader slot-definition-getter :initarg :getter)
+     (unbound :reader slot-definition-unbound :initarg :unbound)
+     (boundp :reader slot-definition-boundp :initarg :boundp))))
   
-  (defclass effective-virtual-slot-definition
-    (standard-effective-slot-definition)))
+  (defvar *unbound-marker* (gensym "UNBOUND-MARKER-"))
+
+  (defun most-specific-slot-value (instances slot &optional 
+				   (default *unbound-marker*))
+    (let ((object (find-if
+		   #'(lambda (ob)
+		       (and (slot-exists-p ob slot) (slot-boundp ob slot)))
+		   instances)))
+      (if object
+	  (slot-value object slot)
+	  default)));)
+
   
 
-(defmethod direct-slot-definition-class ((class virtual-class) initargs)
+(defmethod direct-slot-definition-class ((class virtual-slots-class) &rest initargs)
   (if (eq (getf initargs :allocation) :virtual)
       (find-class 'direct-virtual-slot-definition)
     (call-next-method)))
 
-
-(defmethod effective-slot-definition-class ((class virtual-class) initargs)
+(defmethod effective-slot-definition-class ((class virtual-slots-class) &rest initargs)
   (if (eq (getf initargs :allocation) :virtual)
       (find-class 'effective-virtual-slot-definition)
     (call-next-method)))
 
 
-(defun %direct-slot-definitions-slot-value (slotds slot &optional default)
-  (let ((slotd
-	 (find-if
-	  #'(lambda (slotd)
-	      (and
-	       (slot-exists-p slotd slot)
-	       (slot-boundp slotd slot)))
-	  slotds)))
-    (if slotd
-	(slot-value slotd slot)
-      default)))
-  
-
-(defgeneric compute-virtual-slot-location (class slotd direct-slotds))
-
-(defmethod compute-virtual-slot-location
-    ((class virtual-class)
-     (slotd effective-virtual-slot-definition)
-     direct-slotds)
-    (let ((location
-	   (%direct-slot-definitions-slot-value direct-slotds 'location)))
-      (if (and location (symbolp location))
-	  (list location `(setf ,location))
-	location)))
-
+(defmethod initialize-internal-slot-functions ((slotd effective-virtual-slot-definition))
+  (if (not (slot-boundp slotd 'getter))
+      (setf
+       (slot-value slotd 'reader-function)
+       #'(lambda (object)
+	   (declare (ignore object))
+	   (error "Can't read slot: ~A" (slot-definition-name slotd)))
+       (slot-value slotd 'boundp-function)
+       #'(lambda (object) (declare (ignore object)) nil))
+
+    (let ((getter-function
+	   (let ((getter (slot-value slotd 'getter)))
+	     (etypecase getter
+	       (function getter)
+	       (symbol 
+		#'(lambda (object)
+		    (funcall getter object)))
+	       (string 
+		(let ((reader nil))
+		  (setf (slot-value slotd 'reader-function)
+			#'(lambda (object)
+			    (unless reader
+			      (setq reader
+			       (mkbinding getter 
+				(slot-definition-type slotd) 'pointer)))
+			    (funcall reader (proxy-location object))))))))))
+
+      (setf 
+       (slot-value slotd 'boundp-function)
+       (cond
+	((slot-boundp slotd 'unbound)
+	 (let ((unbound-value (slot-value slotd 'unbound)))
+	   #'(lambda (object)
+	       (not (eq (funcall getter-function object) unbound-value)))))
+	((slot-boundp slotd 'boundp)
+	 (let ((boundp (slot-value slotd 'boundp)))
+	   (etypecase boundp
+	     (function boundp)
+	     (symbol #'(lambda (object)
+			 (funcall boundp object)))
+	     (string (let ((reader ()))
+		       #'(lambda (object)
+			   (unless reader
+			     (setq reader
+			      (mkbinding boundp
+			       (slot-definition-type slotd) 'pointer)))
+			   (funcall reader (proxy-location object))))))))
+	((multiple-value-bind (unbound-p unbound-value)
+	     (unbound-value (slot-definition-type slotd))
+	   (when unbound-p
+	     #'(lambda (object)
+		 (not (eq (funcall getter-function object) unbound-value))))))
+	(#'(lambda (object) (declare (ignore object)) t))))
 
-(defmethod compute-effective-slot-definition
-    ((class virtual-class) direct-slotds)
-  (let ((slotd (call-next-method)))
-    (when (typep slotd 'effective-virtual-slot-definition)
       (setf
-       (slot-value slotd 'pcl::location)
-       (compute-virtual-slot-location class slotd direct-slotds)))
-    slotd))
+       (slot-value slotd 'reader-function)
+       (cond
+	((slot-boundp slotd 'unbound)
+	 (let ((unbound (slot-value slotd 'unbound))
+	       (slot-name (slot-definition-name slotd)))
+	   #'(lambda (object)
+	       (let ((value (funcall getter-function object)))
+		 (if (eq value unbound)
+		     (slot-unbound (class-of object) object slot-name)
+		   value)))))
+	((slot-boundp slotd 'boundp)
+	 (let ((boundp-function (slot-value slotd 'boundp-function)))
+	   #'(lambda (object)
+	       (and
+		(funcall boundp-function object)
+		(funcall getter-function object)))))
+	((multiple-value-bind (unbound-p unbound-value)
+	     (unbound-value (slot-definition-type slotd))
+	   (let ((slot-name (slot-definition-name slotd)))
+	     (when unbound-p
+	       #'(lambda (object)
+		   (let ((value (funcall getter-function object)))
+		     (if (eq value unbound-value)
+			 (slot-unbound (class-of object) object slot-name)
+			 value)))))))
+	(getter-function)))))
+
+  (setf 
+   (slot-value slotd 'writer-function)
+   (if (not (slot-boundp slotd 'setter))
+       #'(lambda (object)
+	   (declare (ignore object))
+	   (error "Can't set slot: ~A" (slot-definition-name slotd)))
+     (with-slots (setter) slotd
+       (etypecase setter
+	 (function setter)
+	 ((or symbol cons) 
+	  #'(lambda (value object)
+	      (funcall (fdefinition setter) value object)))
+	 (string
+	  (let ((writer ()))
+	    (setf
+	     (slot-value slotd 'writer-function)
+	     #'(lambda (value object)
+		 (unless writer
+		   (setq writer
+		    (mkbinding setter 'nil 'pointer 
+		     (slot-definition-type slotd))))
+		 (funcall writer (proxy-location object) value)))))))))
+
+  (initialize-internal-slot-gfs (slot-definition-name slotd)))
+
+
+
+(defmethod compute-slot-accessor-info ((slotd effective-virtual-slot-definition) type gf)
+  nil)
+
+(defmethod compute-effective-slot-definition-initargs ((class virtual-slots-class) direct-slotds)
+  (if (typep (first direct-slotds) 'direct-virtual-slot-definition)
+      (let ((initargs ()))
+	(let ((getter (most-specific-slot-value direct-slotds 'getter)))
+	  (unless (eq getter *unbound-marker*)
+	    (setf (getf initargs :getter) getter)))
+	(let ((setter (most-specific-slot-value direct-slotds 'setter)))
+	  (unless (eq setter *unbound-marker*)
+	    (setf (getf initargs :setter) setter)))
+	(let ((unbound (most-specific-slot-value direct-slotds 'unbound)))
+	  (unless (eq unbound *unbound-marker*)
+	    (setf (getf initargs :unbound) unbound)))
+	(let ((boundp (most-specific-slot-value direct-slotds 'boundp)))
+	  (unless (eq boundp *unbound-marker*)
+	    (setf (getf initargs :boundp) boundp)))
+	(nconc initargs (call-next-method)))
+    (call-next-method)))
 
 
 (defmethod slot-value-using-class
-    ((class virtual-class) (object standard-object)
+    ((class virtual-slots-class) (object standard-object)
      (slotd effective-virtual-slot-definition))
-  (let ((reader (first (slot-definition-location slotd))))
-    (if reader
-	(funcall reader object)
-      (slot-unbound class object (slot-definition-name slotd)))))
-
+  (if (funcall (slot-value slotd 'boundp-function) object)
+      (funcall (slot-value slotd 'reader-function) object)
+    (slot-unbound class object (slot-definition-name slotd))))
 
 (defmethod slot-boundp-using-class
-    ((class virtual-class) (object standard-object)
+    ((class virtual-slots-class) (object standard-object)
      (slotd effective-virtual-slot-definition))
-   (and (first (slot-definition-location slotd)) t))
-    
-
-
-(defmethod (setf slot-value-using-class)
-    (value (class virtual-class) (object standard-object)
+  (funcall (slot-value slotd 'boundp-function) object))
+  
+(defmethod (setf slot-value-using-class) 
+    (value (class virtual-slots-class) (object standard-object)
      (slotd effective-virtual-slot-definition))
-  (let ((writer (second (slot-definition-location slotd))))
-    (cond
-     ((null writer)
-      (error
-       "Can't set read-only slot ~A in ~A"
-       (slot-definition-name slotd)
-       object))
-     ((or (functionp writer) (symbolp writer))
-      (funcall writer value object)
-      value)
-     (t
-      (funcall (fdefinition writer) value object)
-      value))))
-	
+  (funcall (slot-value slotd 'writer-function) value object))
 
+  
 (defmethod validate-superclass
-    ((class virtual-class) (super pcl::standard-class))
+    ((class virtual-slots-class) (super standard-class))
   t)
 
 
@@ -128,271 +223,313 @@ (defvar *instance-cache* (make-hash-table :test #'eql))
 
 (defun cache-instance (instance)
   (setf
-   (gethash (system:sap-int (proxy-location instance)) *instance-cache*)
-   (ext:make-weak-pointer instance)))
+   (gethash (sap-int (proxy-location instance)) *instance-cache*)
+   (make-weak-pointer instance)))
 
 (defun find-cached-instance (location)
-  (let ((ref (gethash (system:sap-int location) *instance-cache*)))
+  (let ((ref (gethash (sap-int location) *instance-cache*)))
     (when ref
-      (ext:weak-pointer-value ref))))
+      (weak-pointer-value ref))))
+
+(defun instance-cached-p (location)
+  (gethash (sap-int location) *instance-cache*))
 
 (defun remove-cached-instance (location)
-  (remhash (system:sap-int location) *instance-cache*))
+  (remhash (sap-int location) *instance-cache*))
 
+;; For debuging
+(defun cached-instances ()
+  (let ((instances ()))
+    (maphash #'(lambda (location ref)
+		 (declare (ignore location))
+		 (push (weak-pointer-value ref) instances))
+	     *instance-cache*)
+    instances))
+			
 
 
 ;;;; Proxy for alien instances
 
-(eval-when (:compile-toplevel :load-toplevel :execute)
-  (defclass proxy ()
-    ((location
-      :reader proxy-location
-      :type system-area-pointer)))
-
-  (defgeneric initialize-proxy (object &rest initargs))
-  (defgeneric instance-finalizer (object)))
-
+(defclass proxy ()
+  ((location :reader proxy-location :type system-area-pointer)))
 
-(defmethod initialize-instance :after ((instance proxy)
-				       &rest initargs &key)
-  (declare (ignore initargs))
-  (cache-instance instance)
-  (ext:finalize instance (instance-finalizer instance)))
+(defgeneric initialize-proxy (object &rest initargs))
+(defgeneric instance-finalizer (object))
+(defgeneric reference-foreign (class location))
+(defgeneric unreference-foreign (class location))
 
+(defmethod reference-foreign ((name symbol) location)
+  (reference-foreign (find-class name) location))
 
-(defmethod initialize-proxy ((instance proxy)
-			     &rest initargs)
-  (declare (ignore initargs))
-  (cache-instance instance))
+(defmethod unreference-foreign ((name symbol) location)
+  (unreference-foreign (find-class name) location))
 
+(defmethod unreference-foreign :around ((class class) location)
+  (unless (null-pointer-p location)
+;;     (format t "Unreferencing ~A at ~A" (class-name class) location)
+;;     (finish-output *standard-output*)
+    (call-next-method)
+;;     (write-line " done")
+;;     (finish-output *standard-output*)
+    ))
+
+(defmethod print-object ((instance proxy) stream)
+  (print-unreadable-object (instance stream :type t :identity nil)
+    (when (slot-boundp instance 'location)
+      (format stream "at 0x~X" (sap-int (proxy-location instance))))))
+
+(defmethod initialize-instance :around ((instance proxy) &key location)
+  (if location
+      (setf (slot-value instance 'location) location)      
+    (call-next-method))
+  (cache-instance instance)
+  (finalize instance (instance-finalizer instance))
+  instance)
 
 (defmethod instance-finalizer ((instance proxy))
-  (let ((location (proxy-location instance)))
+  (let ((location (proxy-location instance))
+	(class (class-of instance)))    
+;;     (unless (find-method #'unreference-foreign nil (list (class-of class) t) nil)
+;;       (error "No matching method for UNREFERENCE-INSTANCE when called with class ~A" class))
     #'(lambda ()
-	(remove-cached-instance location))))
-
-
-(deftype-method translate-type-spec proxy (type-spec)
-  (declare (ignore type-spec))
-  (translate-type-spec 'pointer))
-
-(deftype-method size-of proxy (type-spec)
-  (declare (ignore type-spec))
-  (size-of 'pointer))
-
-(deftype-method translate-from-alien
-    proxy (type-spec location &optional weak-ref)
-  `(let ((location ,location))
-     (unless (null-pointer-p location)
-       (ensure-proxy-instance ',type-spec location ,weak-ref))))
-
+	(remove-cached-instance location)
+	(unreference-foreign class location))))
 
 
 ;;;; Metaclass used for subclasses of proxy
 
+(defgeneric most-specific-proxy-superclass (class))
+(defgeneric direct-proxy-superclass (class))
+  
+
 (eval-when (:compile-toplevel :load-toplevel :execute)
-  (defclass proxy-class (virtual-class)
-    ((size :reader proxy-class-instance-size)))
+  (defclass proxy-class (virtual-slots-class)
+    ((size :reader proxy-instance-size)))
 
   (defclass direct-alien-slot-definition (direct-virtual-slot-definition)
-    ((allocation
-      :initform :alien)
-     (offset
-      :reader slot-definition-offset
-      :initarg :offset
-      :initform 0)))
+    ((allocation :initform :alien)
+     (offset :reader slot-definition-offset :initarg :offset)))
   
   (defclass effective-alien-slot-definition (effective-virtual-slot-definition)
-    ((offset :reader slot-definition-offset)))
-  
-  (defclass effective-virtual-alien-slot-definition
-    (effective-virtual-slot-definition))
- 
+    ((offset :reader slot-definition-offset :initarg :offset)))
 
   (defmethod most-specific-proxy-superclass ((class proxy-class))
     (find-if
      #'(lambda (class)
 	 (subtypep (class-name class) 'proxy))
-     (cdr (pcl::compute-class-precedence-list class))))
-
+     (cdr (compute-class-precedence-list class))))
 
-  (defmethod shared-initialize ((class proxy-class) names
-				&rest initargs &key size name)
-    (declare (ignore initargs))
+  (defmethod direct-proxy-superclass ((class proxy-class))
+    (find-if
+     #'(lambda (class)
+	 (subtypep (class-name class) 'proxy))
+     (class-direct-superclasses class)))
+  
+  (defmethod shared-initialize ((class proxy-class) names &key size)
     (call-next-method)
-    (when size
-      (setf (slot-value class 'size) (first size))))
-    
-
-  (defmethod shared-initialize :after ((class proxy-class) names
-				       &rest initargs &key)
-    (declare (ignore initargs names))
-    (let* ((super (most-specific-proxy-superclass class))
-	   (actual-size
-	    (if (eq (class-name super) 'proxy)
-		0
-	      (proxy-class-instance-size super))))
-      (dolist (slotd (class-slots class))
-	(when (eq (slot-definition-allocation slotd) :alien)
-	  (with-slots (offset type) slotd
-	    (setq actual-size (max actual-size (+ offset (size-of type)))))))
-      (cond
-       ((not (slot-boundp class 'size))
-	(setf (slot-value class 'size) actual-size))
-       ((> actual-size (slot-value class 'size))
-	(warn "The actual size of class ~A is lager than specified" class)))))
-
-
-  (defmethod direct-slot-definition-class ((class proxy-class) initargs)
+    (cond
+      (size (setf (slot-value class 'size) (first size)))
+      ((slot-boundp class 'size) (slot-makunbound class 'size))))
+  
+  (defmethod direct-slot-definition-class ((class proxy-class) &rest initargs)
     (case (getf initargs :allocation)
       ((nil :alien) (find-class 'direct-alien-slot-definition))
-;      (:instance (error "Allocation :instance not allowed in class ~A" class))
       (t (call-next-method))))
-
-
-  (defmethod effective-slot-definition-class ((class proxy-class) initargs)
+  
+  (defmethod effective-slot-definition-class ((class proxy-class) &rest initargs)
     (case (getf initargs :allocation)
       (:alien (find-class 'effective-alien-slot-definition))
-      (:virtual (find-class 'effective-virtual-alien-slot-definition))
       (t (call-next-method))))
   
   
-  (defmethod compute-virtual-slot-location
-      ((class proxy-class) (slotd effective-alien-slot-definition)
-       direct-slotds)
-    (with-slots (offset type) slotd
-      (setf offset (%direct-slot-definitions-slot-value direct-slotds 'offset))
-      (let ((reader (intern-reader-function type))
-	    (writer (intern-writer-function type))
-	    (destroy (intern-destroy-function type)))
-	(list
-	 #'(lambda (object)
-	     (funcall reader (proxy-location object) offset))
-	 #'(lambda (value object)
-	     (let ((location (proxy-location object)))
-	       (funcall destroy location offset)
-	       (funcall writer value location offset)))))))
-	     
+  (defmethod compute-effective-slot-definition-initargs ((class proxy-class) direct-slotds)
+    (if (eq (most-specific-slot-value direct-slotds 'allocation) :alien)
+	(nconc 
+	 (list :offset (most-specific-slot-value direct-slotds 'offset))
+	 (call-next-method))
+      (call-next-method)))
   
-  (defmethod compute-virtual-slot-location
-      ((class proxy-class)
-       (slotd effective-virtual-alien-slot-definition)
-       direct-slotds)
-    (let ((location (call-next-method))
-	  (class-name (class-name class)))
-      (if (or (stringp location) (consp location))
-	  (destructuring-bind (reader &optional writer) (mklist location)
-	    (with-slots (type) slotd
-              (list
-	       (if (stringp reader)
-		   (mkbinding reader type class-name)
-		 reader)
-	       (if (stringp writer)
-		   (let ((writer (mkbinding writer 'nil class-name type)))
-		     #'(lambda (value object)
-			 (funcall writer object value)))
-		 writer))))
-	location)))
 
+  (defmethod initialize-internal-slot-functions ((slotd effective-alien-slot-definition))
+    (with-slots (offset) slotd
+      (let ((type (slot-definition-type slotd)))
+	(unless (slot-boundp slotd 'getter)
+	  (let ((reader (reader-function type)))
+	    (setf 
+	     (slot-value slotd 'getter)
+	     #'(lambda (object)
+		 (funcall reader (proxy-location object) offset)))))
+
+	(unless (slot-boundp slotd 'setter)
+	  (let ((writer (writer-function type))
+		(destroy (destroy-function type)))
+	    (setf 
+	     (slot-value slotd 'setter)
+	     #'(lambda (value object)
+		 (let ((location (proxy-location object)))
+		   (funcall destroy location offset) ; destroy old value
+		   (funcall writer value location offset))))))))
 
-  (defmethod compute-slots ((class proxy-class))
-    ;; Translating the user supplied relative (to previous slot) offsets
-    ;; to absolute offsets.
-    ;; This code is broken and have to be fixed.
-    (with-slots (direct-slots) class
-      (let* ((super (most-specific-proxy-superclass class))
-	     (slot-offset
-	      (if (eq (class-name super) 'proxy)
-		  0
-		(proxy-class-instance-size super))))
-	(dolist (slotd direct-slots)
-	  (when (eq (slot-definition-allocation slotd) :alien)
-	    (with-slots (offset type) slotd
-	      (setf
-	       offset (+ slot-offset offset)
-	       slot-offset (+ offset (size-of type)))))))
-    
-      ;; Reverse the direct slot definitions so the effective slots
-      ;; will be in correct order.
-      (setf direct-slots (reverse direct-slots))
-      ;; This nreverse caused me so much frustration that I leave it
-      ;; here just as a reminder of what not to do.
-;      (setf direct-slots (nreverse direct-slots))
-      )
     (call-next-method))
+  
 
+  ;; TODO: call some C code to detect this a compile time
+  (defconstant +struct-alignmen+ 4)
 
-  (defmethod validate-superclass ((class proxy-class)
-				  (super pcl::standard-class))
-     (subtypep (class-name super) 'proxy))
-
-  (defgeneric make-proxy-instance (class location weak-ref &rest initargs &key)))
+  (defmethod compute-slots ((class proxy-class))
+    (loop 
+     with offset = (let ((size-of-super-classes
+			  (proxy-instance-size 
+			   (most-specific-proxy-superclass class))))
+		     (+ size-of-super-classes 
+			(mod size-of-super-classes +struct-alignmen+)))
+     with size = offset
+     for slotd in (class-direct-slots class)
+     when (eq (slot-definition-allocation slotd) :alien)
+     do (if (not (slot-boundp slotd 'offset))
+	    (setf (slot-value slotd 'offset) offset)
+	  (setq offset (slot-value slotd 'offset)))
+
+        (incf offset (size-of (slot-definition-type slotd)))
+	(incf offset (mod offset +struct-alignmen+))
+	(setq size (max size offset))
+
+     finally (unless (slot-boundp class 'size)
+	       (setf (slot-value class 'size) size)))
+    (call-next-method))
 
+  
+  (defmethod validate-superclass ((class proxy-class) (super standard-class))
+    (subtypep (class-name super) 'proxy))
+  
+  (defmethod proxy-instance-size (class)
+    (declare (ignore class))
+    0)
 
-(defmethod make-proxy-instance ((class symbol) location weak-ref
-				&rest initargs &key)
-  (apply #'make-proxy-instance (find-class class) location weak-ref initargs))
+  (defmethod proxy-instance-size ((class-name symbol))
+    (proxy-instance-size (find-class class-name)))
+)
+  
+(defmethod alien-type ((class proxy-class) &rest args)
+  (declare (ignore class args))
+  (alien-type 'pointer))
 
-(defmethod make-proxy-instance ((class proxy-class) location weak-ref
-				&rest initargs &key)
-  (let ((instance (allocate-instance class)))
-    (apply
-     #'initialize-proxy
-     instance :location location :weak-ref weak-ref initargs)
-    instance))
+(defmethod size-of ((class proxy-class) &rest args)
+  (declare (ignore class args))
+  (size-of 'pointer))
 
-(defun ensure-proxy-instance (class location weak-ref &rest initargs)
-  (or
-   (find-cached-instance location)
-   (apply #'make-proxy-instance class location weak-ref initargs)))
+(defmethod from-alien-form (location (class proxy-class) &rest args)
+  (declare (ignore args))
+  `(ensure-proxy-instance ',(class-name class) ,location))
+
+(defmethod from-alien-function ((class proxy-class) &rest args)
+  (declare (ignore args))  
+  #'(lambda (location)
+      (ensure-proxy-instance class location)))
+
+(defmethod to-alien-form (instance (class proxy-class) &rest args)
+  (declare (ignore class args))
+  `(proxy-location ,instance))
+
+(defmethod to-alien-function ((class proxy-class) &rest args)
+  (declare (ignore class args))
+  #'proxy-location)
+
+(defmethod copy-from-alien-form (location (class proxy-class) &rest args)
+  (declare (ignore args))
+  (let ((class-name (class-name class)))
+    `(ensure-proxy-instance ',class-name
+      (reference-foreign ',class-name ,location))))
+
+(defmethod copy-from-alien-function ((class proxy-class) &rest args)
+  (declare (ignore args))  
+  #'(lambda (location)
+      (ensure-proxy-instance class (reference-foreign class location))))
+
+(defmethod copy-to-alien-form (instance (class proxy-class) &rest args)
+  (declare (ignore args))
+  `(reference-foreign ',(class-name class) (proxy-location ,instance)))
+
+(defmethod copy-to-alien-function ((class proxy-class) &rest args)
+  (declare (ignore args))
+  #'(lambda (instance)
+      (reference-foreign class (proxy-location instance))))
+
+(defmethod writer-function ((class proxy-class) &rest args)
+  (declare (ignore args))
+  #'(lambda (instance location &optional (offset 0))
+      (assert (null-pointer-p (sap-ref-sap location offset)))
+      (setf 
+       (sap-ref-sap location offset)
+       (reference-foreign class (proxy-location instance)))))
+
+(defmethod reader-function ((class proxy-class) &rest args)
+  (declare (ignore args))
+  #'(lambda (location &optional (offset 0))
+      (let ((instance (sap-ref-sap location offset)))
+	(unless (null-pointer-p instance)
+	  (ensure-proxy-instance class (reference-foreign class instance))))))
+
+(defmethod destroy-function ((class proxy-class) &rest args)
+  (declare (ignore args))
+  #'(lambda (location &optional (offset 0))
+      (unreference-foreign class (sap-ref-sap location offset))))
+
+(defmethod unbound-value ((class proxy-class) &rest args)
+  (declare (ignore args))
+  (values t nil))
+
+(defgeneric ensure-proxy-instance (class location)
+  (:documentation "Returns a proxy object representing the foreign object at the give location."))
+
+(defmethod ensure-proxy-instance :around (class location)
+  (unless (null-pointer-p location)
+    (or 
+     (find-cached-instance location)
+     (call-next-method))))
+  
+(defmethod ensure-proxy-instance ((class symbol) location)
+  (ensure-proxy-instance (find-class class) location))
 
+(defmethod ensure-proxy-instance ((class proxy-class) location)
+  (make-instance class :location location))
 
-;;;; Superclass for wrapping of C structures
 
-(eval-when (:compile-toplevel :load-toplevel :execute)
-  (defclass alien-structure (proxy)
-    ()
-    (:metaclass proxy-class)
-    (:size 0)))
+;;;; Superclasses for wrapping of C structures
 
+(defclass struct (proxy)
+  ()
+  (:metaclass proxy-class))
 
-(defmethod initialize-instance ((structure alien-structure)
-				&rest initargs)
+(defmethod initialize-instance ((struct struct) &rest initargs)
   (declare (ignore initargs))
-  (setf 
-   (slot-value structure 'location)
-   (allocate-memory (proxy-class-instance-size (class-of structure))))
+  (unless (slot-boundp struct 'location)
+    (let ((size (proxy-instance-size (class-of struct))))
+      (if (zerop size)
+	  (error "~A has zero size" (class-of struct))
+	(setf (slot-value struct 'location) (allocate-memory size)))))
   (call-next-method))
 
 
-(defmethod initialize-proxy ((structure alien-structure)
-			     &rest initargs &key location weak-ref)
-  (declare (ignore initargs))
-  (setf
-   (slot-value structure 'location)
-   (if weak-ref
-       (copy-memory location (proxy-class-instance-size (class-of structure)))
-     location))
-  (call-next-method))
+;;;; Metaclasses used for subclasses of struct
 
+(defclass struct-class (proxy-class)
+  ())
 
-(defmethod instance-finalizer ((structure alien-structure))
-  (let ((location (proxy-location structure)))
-    (declare (type system-area-pointer location))
-    #'(lambda ()
-	(deallocate-memory location)
-	(remove-cached-instance location))))
+(defmethod reference-foreign ((class struct-class) location)
+  (copy-memory location (proxy-instance-size class)))
+
+(defmethod unreference-foreign ((class struct-class) location)
+  (deallocate-memory location))
 
 
-(deftype-method translate-to-alien
-     alien-structure (type-spec object &optional weak-ref)
-  (if weak-ref
-      `(proxy-location ,object)
-    `(copy-memory
-      (proxy-location ,object)
-      ,(proxy-class-instance-size (find-class type-spec)))))
+(defclass static-struct-class (struct-class)
+  ())
 
+(defmethod reference-foreign ((class static-struct-class) location)
+  (declare (ignore class))
+  location)
 
-(deftype-method unreference-alien alien-structure (type-spec c-struct)
-  (declare (ignore type-spec))
-  `(deallocate-memory ,c-struct))
+(defmethod unreference-foreign ((class static-struct-class) location)
+  (declare (ignore class location))
+  nil)