2003-06-22 Havoc Pennington <hp@pobox.com>

	* mono/Message.cs: implement Message.Wrap() that ensures we only
	have a single C# wrapper per DBusMessage, assuming it works which
	it probably doesn't.

	* dbus/dbus-message.c (dbus_message_allocate_data_slot): new
	(dbus_message_free_data_slot): new
	(dbus_message_set_data): new
	(dbus_message_get_data): new

1 files changed, 81 insertions, 5 deletions

diff --git a/mono/Message.cs b/mono/Message.cs
index 84bd12ec..0e41c9ec 100644
--- a/mono/Message.cs
+++ b/mono/Message.cs
@@ -2,12 +2,15 @@ namespace DBus {
   
   using System;
   using System.Runtime.InteropServices;
+  using System.Diagnostics;
   
   public class Message {
 
     public Message (string name,
                     string dest_service) {
+      // the assignment bumps the refcount
       raw = dbus_message_new (name, dest_service);
+      dbus_message_unref (raw);
     }
 
     public string Name {
@@ -15,23 +18,80 @@ namespace DBus {
         return dbus_message_get_name (raw);
       }
     }
-    
-    IntPtr raw;
+
+    public static Message Wrap (IntPtr ptr) {
+      IntPtr gch_ptr;
+      
+      gch_ptr = dbus_message_get_data (ptr, wrapper_slot);
+      if (gch_ptr != (IntPtr) 0) {
+        return (DBus.Message) ((GCHandle)gch_ptr).Target;
+      } else {
+        return new Message (ptr);
+      }
+    }
+
+    // surely there's a convention for this pattern with the property
+    // and the real member
+    IntPtr raw_;
+    IntPtr raw {
+      get {
+        return raw_; 
+      }
+      set {
+        if (value == raw_)
+          return;
+        
+        if (raw_ != (IntPtr) 0) {
+          IntPtr gch_ptr;
+          
+          gch_ptr = dbus_message_get_data (raw_,
+                                           wrapper_slot);
+          Debug.Assert (gch_ptr != (IntPtr) 0);
+
+          dbus_message_set_data (raw_, wrapper_slot,
+                                 (IntPtr) 0, (IntPtr) 0);
+          
+          ((GCHandle) gch_ptr).Free ();
+          
+          dbus_message_unref (raw_);
+        }
+        
+        raw_ = value;
+
+        if (raw_ != (IntPtr) 0) {
+          GCHandle gch;
+
+          dbus_message_ref (raw_);
+
+          // We store a weak reference to the C# object on the C object
+          gch = GCHandle.Alloc (this, GCHandleType.WeakTrackResurrection);
+          
+          dbus_message_set_data (raw_, wrapper_slot,
+                                 (IntPtr) gch, (IntPtr) 0);
+        }
+      }
+    }
 
     ~Message () {
-      dbus_message_unref (raw);
+      raw = (IntPtr) 0; // free the native object
     }
     
     Message (IntPtr r) {
       raw = r;
-      dbus_message_ref (r);
     }
     
     // static constructor runs before any methods 
     static Message () {
+      Debug.Assert (wrapper_slot == -1);
       
+      if (!dbus_message_allocate_data_slot (ref wrapper_slot))
+        throw new OutOfMemoryException ();
+
+      Debug.Assert (wrapper_slot >= 0);
     }
-      
+
+    // slot used to store the C# object on the C object
+    static int wrapper_slot = -1;
     const string libname = "libdbus-1.so.0";
     
     [DllImport (libname, EntryPoint="dbus_message_new")]
@@ -46,5 +106,21 @@ namespace DBus {
 
     [DllImport (libname, EntryPoint="dbus_message_get_name")]
       private extern static string dbus_message_get_name (IntPtr ptr);
+
+    [DllImport (libname, EntryPoint="dbus_message_allocate_data_slot")]
+      private extern static bool dbus_message_allocate_data_slot (ref int slot);
+
+    [DllImport (libname, EntryPoint="dbus_message_free_data_slot")]
+      private extern static void dbus_message_free_data_slot (ref int slot);
+
+    [DllImport (libname, EntryPoint="dbus_message_set_data")]
+      private extern static bool dbus_message_set_data (IntPtr ptr,
+                                                        int    slot,
+                                                        IntPtr data,
+                                                        IntPtr free_data_func);
+
+    [DllImport (libname, EntryPoint="dbus_message_get_data")]
+      private extern static IntPtr dbus_message_get_data (IntPtr ptr,
+                                                          int    slot);
   }
 }