haiku/docs/user/app/MessageQueue.dox

/*
 * Copyright 2007, Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Niels Sascha Reedijk, niels.reedijk@gmail.com
 *
 * Corresponds to:
 *		/trunk/headers/os/app/MessageQueue.h  rev 19956
 *		/trunk/src/kits/app/MessageQueue.cpp  rev 19956
 */

/*!
	\file MessageQueue.h
	\ingroup app
	\ingroup libroot
	\brief Provides the BMessageQueue class.
*/


/*!
	\class BMessageQueue
	\ingroup app
	\ingroup libroot
	\brief A container that maintains a queue of messages.

	This class is used by BLooper to maintain a queue of messages that need to
	be processed. This class has been designed as a first in, first out
	container.

	The default message handling of a BLooper probably suffices for most uses,
	but if you want more control, you can perform operations using the methods
	of this class. Use BLooper::MessageQueue() to retrieve the specific
	BMessageQueue instance. 

	Note that you are encouraged to make sure that whichever operation you
	perform, that you only do this after the object has been locked (see
	Lock()). The most important method, NextMessage() will fail if you have not
	complied with this requirement.
*/


/*!
	\fn BMessageQueue::BMessageQueue()
	\brief Constructs an empty message queue.
*/


/*!
	\fn BMessageQueue::~BMessageQueue()
	\brief Destruct the BMessageQueue. It iterates over any messages left on
		the queue and deletes them.

	The implementation is careful not to release the lock when the
	BMessageQueue is deconstructed.  If the lock is released, it is
	possible another thread will start an AddMessage() operation before
	the BLocker is deleted.  The safe thing to do is not to unlock the
	BLocker from the destructor once it is acquired. That way, any thread
	waiting to do a AddMessage() will fail to acquire the lock since the
	BLocker will be deleted before they can acquire it.
*/


/*!
	\fn void BMessageQueue::AddMessage(BMessage* message)
	\brief Add a \a message to the end of the queue.

	The message has to be allocated on the heap with \c new, because the queue
	claims ownership of the message. Messages that were constructed on the
	stack will corrupt the queue.

	Because a BMessageQueue claims ownership of the \a message, it is important
	that the message does not belong to another BMessageQueue.
*/


/*!
	\fn void BMessageQueue::RemoveMessage(BMessage* message)
	\brief Remove a \a message from the queue.

	If the \a message is indeed associated with this queue, it is removed from
	it. This effectively means that you regain ownership of the message.
*/


/*!
	\fn int32 BMessageQueue::CountMessages() const
	\brief Return the number of messages waiting in the queue.
*/


/*!
	\fn bool BMessageQueue::IsEmpty() const
	\brief Check if there are messages waiting in the queue.
*/


/*!
	\fn BMessage *BMessageQueue::FindMessage(int32 index) const
	\brief Retrieve the message at the \a index of this queue.

	\param index A zero-based index of the message you want to retrieve.

	\return A pointer to a message, or \c NULL if the \a index is out of
		bounds.
	\see FindMessage(uint32, int32) for a variant that takes a specific \c what
		identifier.
*/


/*!
	\fn BMessage *BMessageQueue::FindMessage(uint32 what, int32 index) const
	\brief Retrieve the message at the \a index of this queue, but only if it
	 	has a specific \a what constant.

	\param index A zero-based index of the message you want to retrieve.
	\param what The \a what code of the message.

	\return A pointer to a message, or \c NULL if there is no message at the
		\a index with that \a what constant, or if the \a index is out of
		bounds.
*/


/*!
	\fn bool BMessageQueue::Lock()
	\brief Lock the queue so no other thread can perform operations on it.

	\see Unlock()
*/


/*!
	\fn void BMessageQueue::Unlock()
	\brief Unlock the queue after a Lock() request.

	\see Lock()
*/


/*!
	\fn bool BMessageQueue::IsLocked() const
	\brief Check if the queue is locked.

	\see Lock() and Unlock()
*/


/*!
	\fn BMessage *BMessageQueue::NextMessage()
	\brief Remove the first BMessage on the queue and return it to the caller.

	After calling this method, you get the ownership of the message, so make
	sure it is deleted after you are done.

	\return A pointer to a message, or \c NULL if the queue is empty, or the
		object has not been properly locked.
	\see Lock()
	\see IsNextMessage()
*/


/*!
	\fn bool BMessageQueue::IsNextMessage(const BMessage* message) const
	\brief Check if the pointer to a \a message points at the next message on
		the queue.
*/