/**************************************************************************** ** ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). ** Contact: Qt Software Information (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:LGPL$ ** Commercial Usage ** Licensees holding valid Qt Commercial licenses may use this file in ** accordance with the Qt Commercial License Agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and Nokia. ** ** GNU Lesser General Public License Usage ** Alternatively, this file may be used under the terms of the GNU Lesser ** General Public License version 2.1 as published by the Free Software ** Foundation and appearing in the file LICENSE.LGPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU Lesser General Public License version 2.1 requirements ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. ** ** In addition, as a special exception, Nokia gives you certain ** additional rights. These rights are described in the Nokia Qt LGPL ** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this ** package. ** ** GNU General Public License Usage ** Alternatively, this file may be used under the terms of the GNU ** General Public License version 3.0 as published by the Free Software ** Foundation and appearing in the file LICENSE.GPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU General Public License version 3.0 requirements will be ** met: http://www.gnu.org/copyleft/gpl.html. ** ** If you are unsure which license is appropriate for your use, please ** contact the sales department at qt-sales@nokia.com. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \page atomic-operations.html \title Implementing Atomic Operations \ingroup architecture \ingroup qt-embedded-linux \brief A guide to implementing atomic operations on new architectures. Qt uses an optimization called \l {Implicitly Shared Classes}{implicit sharing} for many of its value classes. Starting with Qt 4, all of Qt's implicitly shared classes can safely be copied across threads like any other value classes, i.e., they are fully \l {Thread Support in Qt#Reentrancy and Thread-Safety}{reentrant}. This is accomplished by implementing reference counting operations using atomic hardware instructions on all the different platforms supported by Qt. To support a new architecture, it is important to ensure that these platform-specific atomic operations are implemented in a corresponding header file (\c qatomic_ARCH.h), and that this file is located in Qt's \c src/corelib/arch directory. For example, the Intel 80386 implementation is located in \c src/corelib/arch/qatomic_i386.h. Currently, Qt provides two classes providing several atomic operations, QAtomicInt and QAtomicPointer. These classes inherit from QBasicAtomicInt and QBasicAtomicPointer, respectively. When porting Qt to a new architecture, the QBasicAtomicInt and QBasicAtomicPointer classes must be implemented, \e not QAtomicInt and QAtomicPointer. The former classes do not have constructors, which makes them POD (plain-old-data). Both classes only have a single member variable called \c _q_value, which stores the value. This is the value that all of the atomic operations read and modify. All of the member functions mentioned in the QAtomicInt and QAtomicPointer API documentation must be implemented. Note that these the implementations of the atomic operations in these classes must be atomic with respect to both interrupts and multiple processors. \warning The QBasicAtomicInt and QBasicAtomicPointer classes mentioned in this document are used internally by Qt and are not part of the public API. They may change in future versions of Qt. The purpose of this document is to aid people interested in porting Qt to a new architecture. */