Add explicit reply dispatch queue to XPCConnection so that it is not …

…primarily dependent on dispatch_get_current_queue() (This is a partial solution to issue #1)

XPCKit/XPCConnection.h

@@ -26,6 +26,7 @@
     XPCEventHandler _eventHandler;
     xpc_connection_t _connection;
 	dispatch_queue_t _dispatchQueue;
+	dispatch_queue_t _replyDispatchQueue;
 }
 
 - (id)initWithServiceName:(NSString *)serviceName;
@@ -36,6 +37,11 @@
 @property (nonatomic, readonly)   xpc_connection_t connection;
 @property (nonatomic, assign)     dispatch_queue_t dispatchQueue;
 
+/**
+ * Reply and error handler will be submitted to this queue
+ */
+@property (nonatomic, assign)     dispatch_queue_t replyDispatchQueue;
+
 // connection properties
 @property (nonatomic, readonly) NSString *connectionName;
 @property (nonatomic, readonly) NSNumber *connectionEUID;
@@ -45,10 +51,20 @@
 
 -(void)sendMessage:(XPCMessage *)message;
 
-// Sends a message to the associated connection in the XPC service and invokes the reply handler
-// on the dispatch queue of self once the associated connection sends a reply.
-// Logs an error message to the console if the connection does not reply for whatever reasons.
 
+/*!
+ * @abstract
+ * Sends a message to the associated connection in the XPC service and invokes the reply handler
+ * on the replyDispatchQueue of self once the associated connection sends a reply.
+ * Logs an error message to the console if the connection does not reply for whatever reasons.
+ *
+ * @discussion
+ * If replyDispatchQueue is nil then dispatch_get_current_queue() will be used for backward compatibility.
+ * Be aware that this behavior will be removed in a future release.
+ *
+ * @param replyHandler
+ * Reply handler to be queued on replyDispatchQueue of self after message was executed by XPC service
+ */
 -(void)sendMessage:(XPCMessage *)message withReply:(XPCReplyHandler)replyHandler;
 
 // Sends a message to the associated connection in the XPC service and invokes the reply handler
@@ -59,7 +75,7 @@
 
 // Sends a selector and a target and an optional object argument to the associated connection in the XPC service
 // which will invoke the selector on the (copied) target with the optional (copied) argument. Invokes the
-// return value handler on the dispatch queue of self with the (copied) return value and possibly
+// return value handler on the reply dispatch queue of self with the (copied) return value and possibly
 // a (copied) error object supplied.
 
 -(void)sendSelector:(SEL)inSelector withTarget:(id)inTarget object:(id)inObject returnValueHandler:(XPCReturnValueHandler)inReturnHandler;

XPCKit/XPCConnection.m

@@ -29,7 +29,7 @@
 
 @implementation XPCConnection
 
-@synthesize eventHandler=_eventHandler, dispatchQueue=_dispatchQueue, connection=_connection;
+@synthesize eventHandler=_eventHandler, dispatchQueue=_dispatchQueue, replyDispatchQueue=_replyDispatchQueue, connection=_connection;
 
 - (id)initWithServiceName:(NSString *)serviceName{
 	xpc_connection_t connection = xpc_connection_create([serviceName cStringUsingEncoding:NSUTF8StringEncoding], NULL);
@@ -88,6 +88,17 @@ -(void)setDispatchQueue:(dispatch_queue_t)dispatchQueue{
 	xpc_connection_set_target_queue(self.connection, self.dispatchQueue);
 }
 
+-(void)setReplyDispatchQueue:(dispatch_queue_t)dispatchQueue{
+	if(dispatchQueue){
+		dispatch_retain(dispatchQueue);
+	}
+
+	if(_replyDispatchQueue){
+		dispatch_release(_replyDispatchQueue);
+	}
+	_replyDispatchQueue = dispatchQueue;
+}
+
 -(void)receiveConnection:(xpc_connection_t)connection
 {
 //    __block XPCConnection *this = self;
@@ -172,14 +183,14 @@ -(void)sendMessage:(XPCMessage *)inMessage
         // Need to tell message that we want a direct reply
         [inMessage setNeedsDirectReply:YES];
 
-        dispatch_queue_t currentQueue = dispatch_get_current_queue();
-        dispatch_retain(currentQueue);
+        dispatch_queue_t replyQueue = self.replyDispatchQueue ? self.replyDispatchQueue : dispatch_get_current_queue();
+        dispatch_retain(replyQueue);
 
 		XPCReplyHandler replyHandler = [inReplyHandler copy];
 		XPCErrorHandler errorHandler = [inErrorHandler copy];
 
         dispatch_async(self.dispatchQueue, ^{
-            xpc_connection_send_message_with_reply(_connection, inMessage.XPCDictionary, currentQueue, ^(xpc_object_t event){
+            xpc_connection_send_message_with_reply(_connection, inMessage.XPCDictionary, replyQueue, ^(xpc_object_t event){
                 xpc_type_t type = xpc_get_type(event);
 
                 if (type == XPC_TYPE_ERROR)
@@ -207,7 +218,7 @@ -(void)sendMessage:(XPCMessage *)inMessage
 
 				[replyHandler release];
 				[errorHandler release];
-                dispatch_release(currentQueue);
+                dispatch_release(replyQueue);
             });
         });
     }