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Some improvements suggested by Axel. Thanks.

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docs/user/app/_app_messaging.dox
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One of the foundations of the Haiku API is the messaging system. This One of the foundations of the Haiku API is the messaging system. This
framework is the basis for the efficient multithreaded Haiku applications, framework is the basis for the efficient multithreaded Haiku applications,
because it solves one of the fundamental issues of multithreading: it because it solves one of the fundamental issues of multithreading: it
allows you to easily and securely communicate between threads. But the allows you to easily and securely communicate between threads. The
framework goes even further: it allows inter-application communication! framework allows inter-application messaging as well as
intra-application messaging, and it will always use the most effective
mechanism for the communication automatically.
This page will introduce you to the subject of messaging. It is meant as a 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 broad overview to the classes, rather than a tutorial. If you are looking
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- Zero or more data objects. BMessage is a powerful data container that - Zero or more data objects. BMessage is a powerful data container that
keeps track of different sorts of data. BMessage provides many convenient keeps track of different sorts of data. BMessage provides many convenient
Add*() methods, for example BMessage::AddBool(). With the corresponding Add*() methods, for example BMessage::AddBool(). With the corresponding
Find*() method (in this example, FindBook()) you can retrieve the data. Find*() method (in this example,
\link BMessage::FindBool(const char *, int32, bool *) const FindBool() \endlink)
you can retrieve the data.
BMessage itself is generic, its syntax and semantics are determined by the BMessage itself is generic, its syntax and semantics are determined by the
context. The Haiku API defines several messages and their required data context. The Haiku API defines several messages and their required data
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Objects of the BLooper type are objects that run message loops. Every Objects of the BLooper type are objects that run message loops. Every
object runs in its own thread. The BLooper objects continually check for 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 incoming messages. To process the messages, the looper looks for message
messages within their thread context. Message handling within a thread is handlers that handle the messages within the thread's context. Message
synchronous. handling within a looper is synchronous.
BLooper inherits BHandler, the base class for message handling. However, it BLooper inherits BHandler, the base class for message handling. However, it
is possible to chain additional handlers to the object. For example, if you is possible to chain additional handlers to the object. For example, if you
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If your handler cannot handle the object, it will pass the message on to If your handler cannot handle the object, it will pass the message on to
the parent class. the parent class.
\warning Don't forget to actuall call \warning Don't forget to actuall call the MessageReceived() method of the
<em>baseclass</em>::MessageReceived(). Failing to do this will mean base class. Failing to do this will mean that the message chain will
that the message chain will not completely be followed, which can lead not completely be followed, which can lead to unhandled messages. There
to unhandled messages. There might be some internal system messages might be some internal system messages that the Haiku API classes
that the Haiku API classes handle, and not actually handling these handle, and not actually handling these messages could lead to
messages could lead to inconsistent internal behavior. inconsistent internal behavior.
\subsection app_messaging_overview_bmessenger BMessenger \subsection app_messaging_overview_bmessenger BMessenger
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- BMessageFilter is the base class of the filters. Filters can be applied - BMessageFilter is the base class of the filters. Filters can be applied
to BLoopers to filter all incoming messages, or to BHandlers to filter 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 messages that could be handled by that object. The filter object can be
subclassed and extended by overriding the Filter() method. subclassed and extended by overriding the \link BMessageFilter::Filter()
Filter() \endlink method.
\section app-messaging-receiving Receiving Messages \section app-messaging-receiving Receiving Messages