Re: [PATCH] libobjc __objc_msg_forward2 hook

[Andrew Ruder <andy at aeruder dot net>]

I've attached the latest version of the patch and I got an email earlier
today stating that my fsf copyright assignment has been fully processed.
Thanks, sorry about the copyright assignment delay.

Thanks,

Andy

On Mon, Feb 05, 2007 at 06:37:25PM -0600, Andrew Ruder wrote:
> Hey all,
> 
> The __objc_msg_forward hook is quite handy for handling the forwarding
> in an external library; however, it is often necessary to have a
> receiver available to determine the IMP to return (this is especially
> true for wanting to return a ffi_closure from the forwarding hook).  It
> is impossible to determine the correct signature from the selector alone
> in many circumstances.
> 
> The attached (small) patch adds a __objc_msg_forward2 hook to solve this
> problem.  It leaves the __objc_msg_forward hook intact for backwards
> compatibility reasons; however, the __objc_msg_forward2 hook will be
> queried first for a forwarding implementation (i.e. its result will be
> preferred over that of __objc_msg_forward).
> 
> Questions/comments/criticisms, let me know.
> 
> Thanks,
> Andy

libobjc/ChangeLog:

2007-03-14  Andrew Ruder  <andy@aeruder.net>

	* sendmsg.c: Added __objc_msg_forward2, a hook that allows 
	external libraries to provide a function that returns the real
	forwarding function based on both the selector and the receiver.

	* objc/objc-api.h: Define __objc_msg_forward2


-- 
Andrew Ruder <andy@aeruder.net>
http://www.aeruder.net

Index: libobjc/sendmsg.c
===================================================================
--- libobjc/sendmsg.c	(revision 121799)
+++ libobjc/sendmsg.c	(working copy)
@@ -52,10 +52,15 @@ Boston, MA 02110-1301, USA.  */
 /* The uninstalled dispatch table */
 struct sarray *__objc_uninstalled_dtable = 0;   /* !T:MUTEX */
 
-/* Hook for method forwarding. If it is set, is invoked to return a
-   function that performs the real forwarding. Otherwise the libgcc
-   based functions (__builtin_apply and friends) are used. */
+/* Two hooks for method forwarding. If either is set, it is invoked
+ * to return a function that performs the real forwarding.  If both
+ * are set, the result of __objc_msg_forward2 will be preferred over
+ * that of __objc_msg_forward.  If both return NULL or are unset,
+ * the libgcc based functions (__builtin_apply and friends) are
+ * used.
+ */
 IMP (*__objc_msg_forward) (SEL) = NULL;
+IMP (*__objc_msg_forward2) (id, SEL) = NULL;
 
 /* Send +initialize to class */
 static void __objc_send_initialize (Class);
@@ -87,10 +92,18 @@ id nil_method (id, SEL);
 /* Given a selector, return the proper forwarding implementation. */
 inline
 IMP
-__objc_get_forward_imp (SEL sel)
+__objc_get_forward_imp (id rcv, SEL sel)
 {
   /* If a custom forwarding hook was registered, try getting a forwarding
-   * function from it.  */
+   * function from it. There are two forward routine hooks, one that 
+   * takes the receiver as an argument and one that does not. 
+   */
+  if (__objc_msg_forward2)
+    { 
+      IMP result;
+      if ((result = __objc_msg_forward2 (rcv, sel)) != NULL)
+	return result;
+    }
   if (__objc_msg_forward)
     {
       IMP result;
@@ -168,7 +181,7 @@ get_imp (Class class, SEL sel)
 		 is not in the dispatch table.  So the method just
 		 doesn't exist for the class.  Return the forwarding
 		 implementation. */
-	      res = __objc_get_forward_imp (sel);
+	      res = __objc_get_forward_imp ((id)class, sel);
 	    }
 	}
     }
@@ -237,7 +250,7 @@ objc_msg_lookup (id receiver, SEL op)
 		{
 		  /* If the method still just doesn't exist for the
 		     class, attempt to forward the method. */
-		  result = __objc_get_forward_imp (op);
+		  result = __objc_get_forward_imp (receiver, op);
 		}
 	    }
 	}
Index: libobjc/objc/objc-api.h
===================================================================
--- libobjc/objc/objc-api.h	(revision 121799)
+++ libobjc/objc/objc-api.h	(working copy)
@@ -431,11 +431,14 @@ objc_EXPORT void *(*_objc_calloc)(size_t
 objc_EXPORT void (*_objc_free)(void *);
 
 /*
-**  Hook for method forwarding. This makes it easy to substitute a
+**  Hooks for method forwarding. This makes it easy to substitute a
 **  library, such as ffcall, that implements closures, thereby avoiding
-**  gcc's __builtin_apply problems.
+**  gcc's __builtin_apply problems.  __objc_msg_forward2's result will
+**  be preferred over that of __objc_msg_forward if both are set and
+**  return non-NULL.
 */
 objc_EXPORT IMP (*__objc_msg_forward)(SEL);
+objc_EXPORT IMP (*__objc_msg_forward2)(id, SEL);
 
 Method_t class_get_class_method(MetaClass _class, SEL aSel);