source: vendor/trolltech/current/src/kernel/qtimer.cpp

/****************************************************************************
** $Id: qtimer.cpp 2 2005-11-16 15:49:26Z dmik $
**
** Implementation of QTimer class
**
** Created : 931111
**
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** Foundation and appearing in the file LICENSE.GPL included in the
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**********************************************************************/

#include "qtimer.h"
#include "qsignal.h"
#include "qobjectlist.h"

/*!
    \class QTimer qtimer.h
    \brief The QTimer class provides timer signals and single-shot timers.

    \ingroup time
    \ingroup events
    \mainclass

    It uses \link QTimerEvent timer events\endlink internally to
    provide a more versatile timer. QTimer is very easy to use:
    create a QTimer, call start() to start it and connect its
    timeout() to the appropriate slots. When the time is up it will
    emit the timeout() signal.

    Note that a QTimer object is destroyed automatically when its
    parent object is destroyed.

    Example:
    \code
        QTimer *timer = new QTimer( myObject );
        connect( timer, SIGNAL(timeout()), myObject, SLOT(timerDone()) );
        timer->start( 2000, TRUE ); // 2 seconds single-shot timer
    \endcode

    You can also use the static singleShot() function to create a
    single shot timer.

    As a special case, a QTimer with timeout 0 times out as soon as
    all the events in the window system's event queue have been
    processed.

    This can be used to do heavy work while providing a snappy
    user interface:
    \code
        QTimer *t = new QTimer( myObject );
        connect( t, SIGNAL(timeout()), SLOT(processOneThing()) );
        t->start( 0, FALSE );
    \endcode

    myObject->processOneThing() will be called repeatedly and should
    return quickly (typically after processing one data item) so that
    Qt can deliver events to widgets and stop the timer as soon as it
    has done all its work. This is the traditional way of
    implementing heavy work in GUI applications; multi-threading is
    now becoming available on more and more platforms, and we expect
    that null events will eventually be replaced by threading.

    Note that QTimer's accuracy depends on the underlying operating
    system and hardware. Most platforms support an accuracy of 20ms;
    some provide more. If Qt is unable to deliver the requested
    number of timer clicks, it will silently discard some.

    An alternative to using QTimer is to call QObject::startTimer()
    for your object and reimplement the QObject::timerEvent() event
    handler in your class (which must, of course, inherit QObject).
    The disadvantage is that timerEvent() does not support such
    high-level features as single-shot timers or signals.

    Some operating systems limit the number of timers that may be
    used; Qt tries to work around these limitations.
*/


static const int INV_TIMER = -1;                // invalid timer id


/*!
    Constructs a timer called \a name, with the parent \a parent.

    Note that the parent object's destructor will destroy this timer
    object.
*/

QTimer::QTimer( QObject *parent, const char *name )
    : QObject( parent, name ), id(INV_TIMER), single(0), nulltimer(0)
{
}

/*!
    Destroys the timer.
*/

QTimer::~QTimer()
{
    if ( id != INV_TIMER )                      // stop running timer
        stop();
}


/*!
    \fn void QTimer::timeout()

    This signal is emitted when the timer is activated.
*/

/*!
    \fn bool QTimer::isActive() const

    Returns TRUE if the timer is running (pending); otherwise returns
    FALSE.
*/

/*!
    \fn int QTimer::timerId() const

    Returns the ID of the timer if the timer is running; otherwise returns
    -1.
*/


/*!
    Starts the timer with a \a msec milliseconds timeout, and returns
    the ID of the timer, or zero when starting the timer failed.

    If \a sshot is TRUE, the timer will be activated only once;
    otherwise it will continue until it is stopped.

    Any pending timer will be stopped.

    \sa singleShot() stop(), changeInterval(), isActive()
*/

int QTimer::start( int msec, bool sshot )
{
    if ( id >=0 && nulltimer && !msec && sshot )
        return id;
    if ( id != INV_TIMER )                      // stop running timer
        stop();
    single = sshot;
    nulltimer = ( !msec && sshot );
    return id = startTimer( msec );
}


/*!
    Changes the timeout interval to \a msec milliseconds.

    If the timer signal is pending, it will be stopped and restarted;
    otherwise it will be started.

    \sa start(), isActive()
*/

void QTimer::changeInterval( int msec )
{
    if ( id == INV_TIMER ) {                    // create new timer
        start( msec );
    } else {
        killTimer( id );                        // restart timer
        id = startTimer( msec );
    }
}

/*!
    Stops the timer.

    \sa start()
*/

void QTimer::stop()
{
    if ( id != INV_TIMER ) {
        killTimer( id );
        id = INV_TIMER;
    }
}


/*!
    \reimp
*/
bool QTimer::event( QEvent *e )
{
    if ( e->type() != QEvent::Timer )           // ignore all other events
        return FALSE;
    if ( single )                               // stop single shot timer
        stop();
    emit timeout();                             // emit timeout signal
    return TRUE;
}


/*
  The QSingleShotTimer class is an internal class for implementing
  QTimer::singleShot(). It starts a timer and emits the signal
  and kills itself when it gets the timeout.
*/

static QObjectList *sst_list = 0;               // list of single shot timers

static void sst_cleanup()
{
    if ( sst_list ) {
        sst_list->setAutoDelete( TRUE );
        delete sst_list;
        sst_list = 0;
    }
}

static void sst_init()
{
    if ( !sst_list ) {
        sst_list = new QObjectList;
        Q_CHECK_PTR( sst_list );
        qAddPostRoutine( sst_cleanup );
    }
}


class QSingleShotTimer : public QObject
{
public:
    bool    start( int msec, QObject *r, const char * m );
    bool    isActive() const { return timerId > 0; }
protected:
    bool    event( QEvent * );
private:
    QSignal signal;
    int     timerId;
};

extern int  qStartTimer( int interval, QObject *obj ); // implemented in qapp_xxx.cpp
extern bool qKillTimer( int id );

bool QSingleShotTimer::start( int msec, QObject *r, const char *m )
{
    timerId = 0;
    if ( signal.connect(r, m) )
        timerId = qStartTimer( msec, (QObject *)this );
    return timerId != 0;
}

bool QSingleShotTimer::event( QEvent * )
{
    qKillTimer( timerId );                      // no more timeouts
    signal.activate();                          // emit the signal
    signal.disconnect( 0, 0 );
    timerId = 0;                                // mark as inactive
    return TRUE;
}


/*!
    This static function calls a slot after a given time interval.

    It is very convenient to use this function because you do not need
    to bother with a \link QObject::timerEvent() timerEvent\endlink or
    to create a local QTimer object.

    Example:
    \code
        #include <qapplication.h>
        #include <qtimer.h>

        int main( int argc, char **argv )
        {
            QApplication a( argc, argv );
            QTimer::singleShot( 10*60*1000, &a, SLOT(quit()) );
                ... // create and show your widgets
            return a.exec();
        }
    \endcode

    This sample program automatically terminates after 10 minutes (i.e.
    600000 milliseconds).

    The \a receiver is the receiving object and the \a member is the
    slot. The time interval is \a msec.
*/

void QTimer::singleShot( int msec, QObject *receiver, const char *member )
{
    if ( !sst_list )
        sst_init();
    // search the list for a free ss timer we could reuse
    QSingleShotTimer *sst = (QSingleShotTimer*)sst_list->first();
    while ( sst && sst->isActive() )
        sst = (QSingleShotTimer*)sst_list->next();
    // create a new one if not successful
    if ( !sst ) {
        sst = new QSingleShotTimer;
        sst_list->append( sst );
    }
    sst->start(msec, receiver, member);
}