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/*!

    \page timers.html

    \title Timers

    \brief How to use timers in your application.

    \ingroup best-practices

    QObject, the base class of all Qt objects, provides the basic

    timer support in Qt. With QObject::startTimer(), you start a

    timer with an interval in milliseconds as argument. The function

    returns a unique integer timer ID. The timer will now fire at

    regular intervals until you explicitly call QObject::killTimer()

    with the timer ID.

    For this mechanism to work, the application must run in an event

    loop. You start an event loop with QApplication::exec(). When a

    timer fires, the application sends a QTimerEvent, and the flow of

    control leaves the event loop until the timer event is processed.

    This implies that a timer cannot fire while your application is

    busy doing something else. In other words: the accuracy of timers

    depends on the granularity of your application.

    In multithreaded applications, you can use the timer mechanism in

    any thread that has an event loop. To start an event loop from a

    non-GUI thread, use QThread::exec(). Qt uses the object's

    \l{QObject::thread()}{thread affinity} to determine which thread

    will deliver the QTimerEvent. Because of this, you must start and

    stop all timers in the object's thread; it is not possible to

    start timers for objects in another thread.

    The upper limit for the interval value is determined by the number

    of milliseconds that can be specified in a signed integer

    (in practice, this is a period of just over 24 days). The accuracy

    depends on the underlying operating system. Windows 98 has 55

    millisecond accuracy; other systems that we have tested can handle

    1 millisecond intervals.

    The main API for the timer functionality is QTimer. That class

    provides regular timers that emit a signal when the timer fires, and

    inherits QObject so that it fits well into the ownership structure

    of most GUI programs. The normal way of using it is like this:

    \snippet doc/src/snippets/timers/timers.cpp 0

    \snippet doc/src/snippets/timers/timers.cpp 1

    \snippet doc/src/snippets/timers/timers.cpp 2

    The QTimer object is made into a child of this widget so that,

    when this widget is deleted, the timer is deleted too.

    Next, its \l{QTimer::}{timeout()} signal is connected to the slot

    that will do the work, it is started with a value of 1000

    milliseconds, indicating that it will time out every second.

    QTimer also provides a static function for single-shot timers.

    For example:

    \snippet doc/src/snippets/timers/timers.cpp 3

    200 milliseconds (0.2 seconds) after this line of code is

    executed, the \c updateCaption() slot will be called.

    For QTimer to work, you must have an event loop in your

    application; that is, you must call QCoreApplication::exec()

    somewhere. Timer events will be delivered only while the event

    loop is running.

    In multithreaded applications, you can use QTimer in any thread

    that has an event loop. To start an event loop from a non-GUI

    thread, use QThread::exec(). Qt uses the timer's

    \l{QObject::thread()}{thread affinity} to determine which thread

    will emit the \l{QTimer::}{timeout()} signal. Because of this, you

    must start and stop the timer in its thread; it is not possible to

    start a timer from another thread.

    The \l{widgets/analogclock}{Analog Clock} example shows how to use

    QTimer to redraw a widget at regular intervals. From \c{AnalogClock}'s

    implementation:

    \snippet examples/widgets/analogclock/analogclock.cpp 0

    \snippet examples/widgets/analogclock/analogclock.cpp 2

    \snippet examples/widgets/analogclock/analogclock.cpp 3

    \snippet examples/widgets/analogclock/analogclock.cpp 4

    \snippet examples/widgets/analogclock/analogclock.cpp 5

    \snippet examples/widgets/analogclock/analogclock.cpp 6

    \dots

    \snippet examples/widgets/analogclock/analogclock.cpp 7

    Every second, QTimer will call the QWidget::update() slot to

    refresh the clock's display.

    If you already have a QObject subclass and want an easy

    optimization, you can use QBasicTimer instead of QTimer. With

    QBasicTimer, you must reimplement

    \l{QObject::timerEvent()}{timerEvent()} in your QObject subclass

    and handle the timeout there. The \l{widgets/wiggly}{Wiggly}

    example shows how to use QBasicTimer.

*/