Implemented direct message passing for local targets; this fixes a deadlock

with PostMessage() in case the message queue is full.
Some notes:
* for synchronous replies, we don't use this mechanism yet, but it could be
  extended to do that as well.
* the code looks so complicated because we need a way to access the looper's
  queue without locking it (to prevent deadlocks); like Dano's solution, I've
  abused BTokenSpace to store a BDirectMessageTarget with a BHandler.
* we also need to decouple the lifetime of a looper's queue from its target,
  as we cannot lock the looper, and therefore, can't guarantee it stays valid
  as long as we're accessing it outside of BLooper.
* init_clipboard() now needs to be done after the global constructors have
  been called - since sending messages now needs gDefaultTokens to be initialized.
  Since this is done per image, it shouldn't cause any troubles, though.
* some minor cleanup, removed unused _msg_cache_cleanup_() and friends.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@19968 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/app/DirectMessageTarget.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2007, Haiku, Inc.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *		Axel Dörfler, [email protected]
+ */
+#ifndef _DIRECT_MESSAGE_TARGET_H
+#define _DIRECT_MESSAGE_TARGET_H
+
+
+#include <MessageQueue.h>
+
+
+namespace BPrivate {
+
+class BDirectMessageTarget {
+	public:
+		BDirectMessageTarget();
+		~BDirectMessageTarget();
+
+		bool AddMessage(BMessage* message);
+
+		void Close();
+		void Acquire();
+		void Release();
+
+		BMessageQueue* Queue() { return &fQueue; }
+
+	private:
+		int32			fReferenceCount;
+		BMessageQueue	fQueue;
+		bool			fClosed;
+};
+
+}	// namespace BPrivate
+
+#endif	// _DIRECT_MESSAGE_TARGET_H