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diff --git a/doc/src/atomic-operations.qdoc b/doc/src/atomic-operations.qdoc new file mode 100644 index 0000000..5c0973b --- /dev/null +++ b/doc/src/atomic-operations.qdoc @@ -0,0 +1,89 @@ +/**************************************************************************** +** +** 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. +** +** $QT_BEGIN_LICENSE:LGPL$ +** No Commercial Usage +** This file contains pre-release code and may not be distributed. +** You may use this file in accordance with the terms and conditions +** contained in the either Technology Preview License Agreement or the +** Beta Release License Agreement. +** +** 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. +*/ |