BLooper: Add DispatchExternalMessage()

* This is primarily a service method for ports of widget tool kits
  that require single-threaded GUI. DispatchExternalMessage() calls
  DispatchMessage(), but also sets fLastMessage, so that
  [Detach]CurrentMessage() work correctly. This allows to detach a
  message in DispatchMessage() when called from the window thread,
  add it to a global queue, and later process the queued messages in
  a different thread that calls DispatchExternalMessage().
* BLooper/BWindow: Make sure fLastMessage is accessed only when locked.

headers/os/app/Looper.h

@@ -52,6 +52,8 @@ public:
 	virtual	void			MessageReceived(BMessage* message);
 			BMessage*		CurrentMessage() const;
 			BMessage*		DetachCurrentMessage();
+			void			DispatchExternalMessage(BMessage* message,
+								BHandler* handler, bool& _detached);
 			BMessageQueue*	MessageQueue() const;
 			bool			IsMessageWaiting() const;
 

src/kits/app/Looper.cpp

@@ -300,6 +300,22 @@ BLooper::DetachCurrentMessage()
 }
 
 
+void
+BLooper::DispatchExternalMessage(BMessage* message, BHandler* handler,
+	bool& _detached)
+{
+	AssertLocked();
+
+	BMessage* previousMessage = fLastMessage;
+	fLastMessage = message;
+
+	DispatchMessage(message, handler);
+
+	_detached = fLastMessage == NULL;
+	fLastMessage = previousMessage;
+}
+
+
 BMessageQueue*
 BLooper::MessageQueue() const
 {
@@ -1115,11 +1131,14 @@ BLooper::task_looper()
 		bool dispatchNextMessage = true;
 		while (!fTerminating && dispatchNextMessage) {
 			PRINT(("LOOPER: inner loop\n"));
-			// Get next message from queue (assign to fLastMessage)
+			// Get next message from queue (assign to fLastMessage after
-			fLastMessage = fDirectTarget->Queue()->NextMessage();
+			// locking)
+			BMessage* message = fDirectTarget->Queue()->NextMessage();
 
 			Lock();
 
+			fLastMessage = message;
+
 			if (!fLastMessage) {
 				// No more messages: Unlock the looper and terminate the
 				// dispatch loop.
@@ -1173,14 +1192,15 @@ BLooper::task_looper()
 				return;
 			}
 
+			message = fLastMessage;
+			fLastMessage = NULL;
+
 			// Unlock the looper
 			Unlock();
 
 			// Delete the current message (fLastMessage)
-			if (fLastMessage) {
+			if (message != NULL)
-				delete fLastMessage;
+				delete message;
-				fLastMessage = NULL;
-			}
 
 			// Are any messages on the port?
 			if (port_count(fMsgPort) > 0) {

src/kits/interface/Window.cpp

@@ -3037,12 +3037,17 @@ BWindow::task_looper()
 
 		bool dispatchNextMessage = true;
 		while (!fTerminating && dispatchNextMessage) {
-			// Get next message from queue (assign to fLastMessage)
+			// Get next message from queue (assign to fLastMessage after
-			fLastMessage = fDirectTarget->Queue()->NextMessage();
+			// locking)
+			BMessage* message = fDirectTarget->Queue()->NextMessage();
 
 			// Lock the looper
-			if (!Lock())
+			if (!Lock()) {
+				delete message;
 				break;
+			}
+
+			fLastMessage = message;
 
 			if (fLastMessage == NULL) {
 				// No more messages: Unlock the looper and terminate the