1/* 2 * Copyright 2007, Haiku, Inc. All Rights Reserved. 3 * Distributed under the terms of the MIT License. 4 * 5 * Authors: 6 * Niels Sascha Reedijk, niels.reedijk@gmail.com 7 * 8 * Corresponds to: 9 * /trunk/headers/os/app/MessageQueue.h rev 19956 10 * /trunk/src/kits/app/MessageQueue.cpp rev 19956 11 */ 12 13/*! 14 \file MessageQueue.h 15 \brief Provides the BMessageQueue class. 16*/ 17 18 19/*! 20 \class BMessageQueue 21 \ingroup app 22 \brief A container that maintains a queue of messages. 23 24 This class is used by BLooper to maintain a queue of messages that need to 25 be processed. This class has been designed as a first in, first out 26 container. 27 28 The default message handling of a BLooper probably suffices for most uses, 29 but if you want more control, you can perform operations using the methods 30 of this class. Use BLooper::MessageQueue() to retrieve the specific 31 BMessageQueue instance. 32 33 Note that you are encouraged to make sure that whichever operation you 34 perform, that you only do this after the object has been locked (see 35 Lock()). The most important method, NextMessage() will fail if you have not 36 complied with this requirement. 37*/ 38 39 40/*! 41 \fn BMessageQueue::BMessageQueue() 42 \brief Constructs an empty message queue. 43*/ 44 45 46/*! 47 \fn BMessageQueue::~BMessageQueue() 48 \brief Destruct the BMessageQueue. It iterates over any messages left on 49 the queue and deletes them. 50 51 The implementation is careful not to release the lock when the 52 BMessageQueue is deconstructed. If the lock is released, it is 53 possible another thread will start an AddMessage() operation before 54 the BLocker is deleted. The safe thing to do is not to unlock the 55 BLocker from the destructor once it is acquired. That way, any thread 56 waiting to do a AddMessage() will fail to acquire the lock since the 57 BLocker will be deleted before they can acquire it. 58*/ 59 60 61/*! 62 \fn void BMessageQueue::AddMessage(BMessage* message) 63 \brief Add a \a message to the end of the queue. 64 65 The message has to be allocated on the heap with \c new, because the queue 66 claims ownership of the message. Messages that were constructed on the 67 stack will corrupt the queue. 68 69 Because a BMessageQueue claims ownership of the \a message, it is important 70 that the message does not belong to another BMessageQueue. 71*/ 72 73 74/*! 75 \fn void BMessageQueue::RemoveMessage(BMessage* message) 76 \brief Remove a \a message from the queue. 77 78 If the \a message is indeed associated with this queue, it is removed from 79 it. This effectively means that you regain ownership of the message. 80*/ 81 82 83/*! 84 \fn int32 BMessageQueue::CountMessages() const 85 \brief Return the number of messages waiting in the queue. 86*/ 87 88 89/*! 90 \fn bool BMessageQueue::IsEmpty() const 91 \brief Check if there are messages waiting in the queue. 92*/ 93 94 95/*! 96 \fn BMessage *BMessageQueue::FindMessage(int32 index) const 97 \brief Retrieve the message at the \a index of this queue. 98 99 \param index A zero-based index of the message you want to retrieve. 100 101 \return A pointer to a message, or \c NULL if the \a index is out of 102 bounds. 103 \see FindMessage(uint32, int32) for a variant that takes a specific \c what 104 identifier. 105*/ 106 107 108/*! 109 \fn BMessage *BMessageQueue::FindMessage(uint32 what, int32 index) const 110 \brief Retrieve the message at the \a index of this queue, but only if it 111 has a specific \a what constant. 112 113 \param index A zero-based index of the message you want to retrieve. 114 \param what The \a what code of the message. 115 116 \return A pointer to a message, or \c NULL if there is no message at the 117 \a index with that \a what constant, or if the \a index is out of 118 bounds. 119*/ 120 121 122/*! 123 \fn bool BMessageQueue::Lock() 124 \brief Lock the queue so no other thread can perform operations on it. 125 126 \see Unlock() 127*/ 128 129 130/*! 131 \fn void BMessageQueue::Unlock() 132 \brief Unlock the queue after a Lock() request. 133 134 \see Lock() 135*/ 136 137 138/*! 139 \fn bool BMessageQueue::IsLocked() const 140 \brief Check if the queue is locked. 141 142 \see Lock() and Unlock() 143*/ 144 145 146/*! 147 \fn BMessage *BMessageQueue::NextMessage() 148 \brief Remove the first BMessage on the queue and return it to the caller. 149 150 After calling this method, you get the ownership of the message, so make 151 sure it is deleted after you are done. 152 153 \return A pointer to a message, or \c NULL if the queue is empty, or the 154 object has not been properly locked. 155 \see Lock() 156 \see IsNextMessage() 157*/ 158 159 160/*! 161 \fn bool BMessageQueue::IsNextMessage(const BMessage* message) const 162 \brief Check if the pointer to a \a message points at the next message on 163 the queue. 164*/ 165