source: trunk/doc/src/atomic-operations.qdoc@ 498

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41
42/*!
43 \page atomic-operations.html
44 \title Implementing Atomic Operations
45 \ingroup architecture
46 \ingroup qt-embedded-linux
47 \brief A guide to implementing atomic operations on new architectures.
48
49 Qt uses an optimization called \l {Implicitly Shared
50 Classes}{implicit sharing} for many of its value classes.
51
52 Starting with Qt 4, all of Qt's implicitly shared classes can
53 safely be copied across threads like any other value classes,
54 i.e., they are fully \l {Thread Support in Qt#Reentrancy and
55 Thread-Safety}{reentrant}. This is accomplished by implementing
56 reference counting operations using atomic hardware instructions
57 on all the different platforms supported by Qt.
58
59 To support a new architecture, it is important to ensure that
60 these platform-specific atomic operations are implemented in a
61 corresponding header file (\c qatomic_ARCH.h), and that this file
62 is located in Qt's \c src/corelib/arch directory. For example, the
63 Intel 80386 implementation is located in \c
64 src/corelib/arch/qatomic_i386.h.
65
66 Currently, Qt provides two classes providing several atomic
67 operations, QAtomicInt and QAtomicPointer. These classes inherit
68 from QBasicAtomicInt and QBasicAtomicPointer, respectively.
69
70 When porting Qt to a new architecture, the QBasicAtomicInt and
71 QBasicAtomicPointer classes must be implemented, \e not QAtomicInt
72 and QAtomicPointer. The former classes do not have constructors,
73 which makes them POD (plain-old-data). Both classes only have a
74 single member variable called \c _q_value, which stores the
75 value. This is the value that all of the atomic operations read
76 and modify.
77
78 All of the member functions mentioned in the QAtomicInt and
79 QAtomicPointer API documentation must be implemented. Note that
80 these the implementations of the atomic operations in these
81 classes must be atomic with respect to both interrupts and
82 multiple processors.
83
84 \warning The QBasicAtomicInt and QBasicAtomicPointer classes
85 mentioned in this document are used internally by Qt and are not
86 part of the public API. They may change in future versions of
87 Qt. The purpose of this document is to aid people interested in
88 porting Qt to a new architecture.
89*/
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