First part of the messaging overview

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22240 a95241bf-73f2-0310-859d-f6bbb57e9c96

docs/user/app/_app_intro.dox

@@ -17,15 +17,16 @@
 	documents referenced before going to any other part of the API. 
   
 	We can divide the classes in the application kit up in two categories. The
-	biggest part of the classes are in the 'messaging' classes. The following
+	biggest part of the classes are in the 'messaging' classes. Have a look at
-	are part of it:
+	the \link app_messaging Introduction to Messaging \endlink for more 
+	information. The following classes are part of it:
 	- BHandler
 	- BInvoker
 	- BLooper
 	- BMessage
 	- BMessageFilter
 	- BMessageQueue
-	- BMessageRUnner
+	- BMessageRunner
 	- BMessenger
   
 	The second category is the 'system interaction'  category. These classes

docs/user/app/_app_messaging.dox

@@ -0,0 +1,152 @@
+/*
+ * Copyright 2007, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *		Niels Sascha Reedijk, niels.reedijk@gmail.com
+ */
+
+
+/*!
+	\page app_messaging Messaging Foundations
+	
+	One of the foundations of the Haiku API is the messaging system. This
+	framework is the basis for the efficient multithreaded Haiku applications,
+	because it solves one of the fundamental issues of multithreading: it
+	allows you to easily and securely communicate between threads. But the
+	framework goes even further: it allows inter-application communication!
+	
+	This page will introduce you to the subject of messaging. It is meant as a
+	broad overview to the classes, rather than a tutorial. If you are looking
+	for effective messaging techniques or a tutorial on messaging, have a look
+	at the developer section of the Haiku website.
+	
+	<b>Table of contents</b>
+	- Overview of the Messaging Classes
+	- Receiving and Handling Messages
+	- Sending messages
+	
+	\section app_messaging_overview Overview of the Messaging Classes
+	
+	\subsection app_messaging_overview_bmessage BMessage
+	
+	The BMessage class is the class that is in the center of all the messenger
+	operations, because it represents a message. A message is nothing more than
+	an object that contains:
+	- The \c what member, an \c uint32 that determines the type of message.
+	  Some constants are defined by the Haiku API, for example B_MOUSE_DOWN or
+	  B_QUIT_REQUESTED.
+	- Zero or more data objects. BMessage is a powerful data container that
+	  keeps track of different sorts of data. BMessage provides many convenient
+	  Add*() methods, for example BMessage::AddBool(). With the corresponding
+	  Find*() method (in this example, FindBook()) you can retrieve the data.
+
+	BMessage itself is generic, its syntax and semantics are determined by the
+	context. The Haiku API defines several messages and their required data
+	members. Several applications provide a scripting interface with defined
+	message syntax. You can do the same for your application.
+	
+	\subsection app_messaging_overview_blooper BLooper
+	
+	Objects of the BLooper type are objects that run message loops. Every
+	object runs in its own thread. The BLooper objects continually check for
+	incoming messages, and they try to find a BHandler to actually handle the
+	messages within their thread context. Message handling within a thread is
+	synchronous.
+	
+	BLooper inherits BHandler, the base class for message handling. However, it
+	is possible to chain additional handlers to the object. For example, if you
+	have an application that understands different networking protocols, and
+	you support extensions that understand the base protocol, these extensions
+	can provide handlers that you can chain in your general message parser
+	thread. See AddHandler() and SetPreferredHandler() for information on
+	handlers.
+	
+	Messages can be posted to the looper by using the object's PostMessage()
+	method. This method puts the message in the BMessageQueue of the looper.
+	Since PostMessage() is asynchronous, the message might not be handled
+	immediately. See \link app_messaging_overview_bmessenger BMessenger 
+	\endlink for a synchronous implementation.
+	
+	Loopers can have a generic filter that discards messages based on
+	user-definable characteristics. The BMessageFilter class provides the
+	foundation for the qualifying of messages. See AddCommonFilterList() and
+	SetCommonFilterList() for more information.
+	
+	To get the most out of the functionality of BLooper, it is usually
+	subclassed to create a self-contained event 'machine'. Most of the time,
+	these subclasses also perform the message handling, which is possible
+	due to the fact that it is also a subclass of BHandler.
+	
+	In the Haiku API, there are two major classes that inherit BLooper:
+	the base application class, BApplication, and the window class, BWindow.
+	Because they inherit BLooper, each application and each window has its
+	own message loop. This makes every window quick and responsive. To keep
+	your applications running smoothly, it is advisable to make sure that
+	event handling that requires more processing power, is done within its own
+	BLooper context. Networking usually qualifies as a candidate for its own
+	thread.
+	
+	\section app_messaging_overview_bhandler BHandler
+	
+	Objects of the BHandler type are associated to BLoopers. When they are
+	created, they should be passed to the BLooper::AddHandler() method of the
+	looper they want to handle messages for. They can then either be set as
+	preferred handlers (by chaining them with BLooper::SetPreferredHandler()),
+	or they can be added to other BHandlers with the SetNextHandler() method.
+	
+	The magic of the class happens in the MessageReceived() method. In your
+	subclasses you override this method, to check the incoming BMessage.
+	Usually, you check the \c what member of the message in a switch statement.
+	If your handler cannot handle the object, it will pass the message on to
+	the parent class. 
+	
+	\warning Don't forget to actuall call 
+		<em>baseclass</em>::MessageReceived(). Failing to do this will mean
+		that the message chain will not completely be followed, which can lead
+		to unhandled messages. There might be some internal system messages
+		that the Haiku API classes handle, and not actually handling these
+		messages could lead to inconsistent internal behavior.
+	
+	\section app_messaging-overview-bmessenger BMessenger
+	
+	BMessenger objects can send messages to both local and remote targets. For
+	local targets, a BMessenger provides an advantage over directly calling
+	the BLooper::PostMessage() method: some variants of the 
+	BMessenger::SendMessage() methods allow for synchronous replies. So, the
+	call will actually verify the handling thread processes the message, and
+	reply to the sender.
+	
+	The other feature of BMessenger is that it is able to be constructed with
+	the signature of another application as argument. This allows the messenger
+	to pass messages to other applications. It facilitates inter-application
+	communication.
+	
+	\section app_messaging-overview-other Other messaging classes
+	
+	There are several convenience classes supplied with the application kit,
+	which can make your life easier in some specific cases. 
+	
+	* BInvoker binds together a message and a target. By calling 
+	  BInvoker::Invoke(), the message will be sent. This class is inherited by
+	  the controls in the interface kit, such as BButton.
+	* A BMessageRunner object will send messages to a specified target with
+	  specified intervals in between.
+	* BMessageQueue is a class that is also internally used by BLooper. It
+	  provides a queue of messages, with convenience functions of managing
+	  this queue.
+	* BMessageFilter is the base class of the filters. Filters can be applied
+	  to BLoopers to filter all incoming messages, or to BHandlers to filter
+	  messages that could be handled by that object. The filter object can be
+	  subclassed and extended by overriding the Filter() method.
+
+	\section app-messaging-receiving Receiving Messages
+	
+	To do...
+	
+	\section app-messaging-sending Sending Messages
+	
+	To do...
+	
+*/
+