source: branches/4.5.1/doc/src/timers.qdoc@ 628

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information ([email protected])
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** 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 [email protected].
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \page timers.html
    \title Timers
    \ingroup architecture
    \brief How to use timers in your application.

    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 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: