| 1 | /****************************************************************************
|
|---|
| 2 | **
|
|---|
| 3 | ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
|
|---|
| 4 | ** All rights reserved.
|
|---|
| 5 | ** Contact: Nokia Corporation ([email protected])
|
|---|
| 6 | **
|
|---|
| 7 | ** This file is part of the documentation of the Qt Toolkit.
|
|---|
| 8 | **
|
|---|
| 9 | ** $QT_BEGIN_LICENSE:FDL$
|
|---|
| 10 | ** Commercial Usage
|
|---|
| 11 | ** Licensees holding valid Qt Commercial licenses may use this file in
|
|---|
| 12 | ** accordance with the Qt Commercial License Agreement provided with the
|
|---|
| 13 | ** Software or, alternatively, in accordance with the terms contained in a
|
|---|
| 14 | ** written agreement between you and Nokia.
|
|---|
| 15 | **
|
|---|
| 16 | ** GNU Free Documentation License
|
|---|
| 17 | ** Alternatively, this file may be used under the terms of the GNU Free
|
|---|
| 18 | ** Documentation License version 1.3 as published by the Free Software
|
|---|
| 19 | ** Foundation and appearing in the file included in the packaging of this
|
|---|
| 20 | ** file.
|
|---|
| 21 | **
|
|---|
| 22 | ** If you have questions regarding the use of this file, please contact
|
|---|
| 23 | ** Nokia at [email protected].
|
|---|
| 24 | ** $QT_END_LICENSE$
|
|---|
| 25 | **
|
|---|
| 26 | ****************************************************************************/
|
|---|
| 27 |
|
|---|
| 28 | /*!
|
|---|
| 29 | \page atomic-operations.html
|
|---|
| 30 | \title Implementing Atomic Operations
|
|---|
| 31 | \brief A guide to implementing atomic operations on new architectures.
|
|---|
| 32 |
|
|---|
| 33 | \ingroup best-practices
|
|---|
| 34 | \ingroup qt-embedded-linux
|
|---|
| 35 |
|
|---|
| 36 | Qt uses an optimization called \l {Implicitly Shared
|
|---|
| 37 | Classes}{implicit sharing} for many of its value classes.
|
|---|
| 38 |
|
|---|
| 39 | Starting with Qt 4, all of Qt's implicitly shared classes can
|
|---|
| 40 | safely be copied across threads like any other value classes,
|
|---|
| 41 | i.e., they are fully \l {Reentrancy and Thread-Safety}{reentrant}.
|
|---|
| 42 | This is accomplished by implementing reference counting
|
|---|
| 43 | operations using atomic hardware instructions on all the
|
|---|
| 44 | different platforms supported by Qt.
|
|---|
| 45 |
|
|---|
| 46 | To support a new architecture, it is important to ensure that
|
|---|
| 47 | these platform-specific atomic operations are implemented in a
|
|---|
| 48 | corresponding header file (\c qatomic_ARCH.h), and that this file
|
|---|
| 49 | is located in Qt's \c src/corelib/arch directory. For example, the
|
|---|
| 50 | Intel 80386 implementation is located in \c
|
|---|
| 51 | src/corelib/arch/qatomic_i386.h.
|
|---|
| 52 |
|
|---|
| 53 | Currently, Qt provides two classes providing several atomic
|
|---|
| 54 | operations, QAtomicInt and QAtomicPointer. These classes inherit
|
|---|
| 55 | from QBasicAtomicInt and QBasicAtomicPointer, respectively.
|
|---|
| 56 |
|
|---|
| 57 | When porting Qt to a new architecture, the QBasicAtomicInt and
|
|---|
| 58 | QBasicAtomicPointer classes must be implemented, \e not QAtomicInt
|
|---|
| 59 | and QAtomicPointer. The former classes do not have constructors,
|
|---|
| 60 | which makes them POD (plain-old-data). Both classes only have a
|
|---|
| 61 | single member variable called \c _q_value, which stores the
|
|---|
| 62 | value. This is the value that all of the atomic operations read
|
|---|
| 63 | and modify.
|
|---|
| 64 |
|
|---|
| 65 | All of the member functions mentioned in the QAtomicInt and
|
|---|
| 66 | QAtomicPointer API documentation must be implemented. Note that
|
|---|
| 67 | these the implementations of the atomic operations in these
|
|---|
| 68 | classes must be atomic with respect to both interrupts and
|
|---|
| 69 | multiple processors.
|
|---|
| 70 |
|
|---|
| 71 | \warning The QBasicAtomicInt and QBasicAtomicPointer classes
|
|---|
| 72 | mentioned in this document are used internally by Qt and are not
|
|---|
| 73 | part of the public API. They may change in future versions of
|
|---|
| 74 | Qt. The purpose of this document is to aid people interested in
|
|---|
| 75 | porting Qt to a new architecture.
|
|---|
| 76 | */
|
|---|
