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/*!

    \page atomic-operations.html

    \title Implementing Atomic Operations

    \brief A guide to implementing atomic operations on new architectures.

    \ingroup best-practices

    \ingroup qt-embedded-linux

    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 {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.

*/