qwineventnotifier.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qwineventnotifier_p.h"
 
#include "qcoreapplication.h"
#include "qthread.h"
#include <QPointer>
 
QT_BEGIN_NAMESPACE
 
QWinEventNotifier::QWinEventNotifier(QObject *parent)
  : QObject(*new QWinEventNotifierPrivate, parent)
{}
 
QWinEventNotifier::QWinEventNotifier(HANDLE hEvent, QObject *parent)
 : QObject(*new QWinEventNotifierPrivate(hEvent, false), parent)
{
    setEnabled(true);
}
 
QWinEventNotifier::~QWinEventNotifier()
{
    setEnabled(false);
}
 
void QWinEventNotifier::setHandle(HANDLE hEvent)
{
    Q_D(QWinEventNotifier);
    setEnabled(false);
    d->handleToEvent = hEvent;
}
 
HANDLE  QWinEventNotifier::handle() const
{
    Q_D(const QWinEventNotifier);
    return d->handleToEvent;
}
 
bool QWinEventNotifier::isEnabled() const
{
    Q_D(const QWinEventNotifier);
    return d->enabled;
}
 
void QWinEventNotifier::setEnabled(bool enable)
{
    Q_D(QWinEventNotifier);
    if (d->enabled == enable)                        // no change
        return;
    d->enabled = enable;
 
    if (Q_UNLIKELY(thread() != QThread::currentThread())) {
        qWarning("QWinEventNotifier: Event notifiers cannot be enabled or disabled from another thread");
        return;
    }
 
    if (enable) {
        // It is possible that the notifier was disabled after an event was already
        // posted. In that case we set a state that indicates that such an obsolete
        // event shall be ignored.
        d->winEventActPosted.testAndSetRelaxed(QWinEventNotifierPrivate::Posted,
                                               QWinEventNotifierPrivate::IgnorePosted);
        // The notifier can't be registered, if 'enabled' flag was false.
        // The code in the else branch ensures that.
        Q_ASSERT(!d->registered);
        SetThreadpoolWait(d->waitObject, d->handleToEvent, NULL);
        d->registered = true;
    } else if (d->registered) {
        // Stop waiting for an event. However, there may be a callback queued
        // already after the call.
        SetThreadpoolWait(d->waitObject, NULL, NULL);
        // So, to avoid a race condition after a possible call to
        // setEnabled(true), wait for a possibly outstanding callback
        // to complete.
        WaitForThreadpoolWaitCallbacks(d->waitObject, TRUE);
        d->registered = false;
    }
}
 
bool QWinEventNotifier::event(QEvent * e)
{
    Q_D(QWinEventNotifier);
 
    switch (e->type()) {
    case QEvent::ThreadChange:
        if (d->enabled) {
            QMetaObject::invokeMethod(this, "setEnabled", Qt::QueuedConnection,
                                      Q_ARG(bool, true));
            setEnabled(false);
        }
        break;
    case QEvent::WinEventAct:
        // Emit notification, but only if the event has not been invalidated
        // since by the notifier being disabled, even if it was re-enabled
        // again.
        if (d->winEventActPosted.fetchAndStoreRelaxed(QWinEventNotifierPrivate::NotPosted)
            == QWinEventNotifierPrivate::Posted && d->enabled) {
            // Clear the flag, as the wait object is implicitly unregistered
            // when the callback is queued.
            d->registered = false;
 
            QPointer<QWinEventNotifier> alive(this);
            emit activated(d->handleToEvent, QPrivateSignal());
 
            if (alive && d->enabled && !d->registered) {
                SetThreadpoolWait(d->waitObject, d->handleToEvent, NULL);
                d->registered = true;
            }
        }
        return true;
    default:
        break;
    }
    return QObject::event(e);
}
 
QWinEventNotifierPrivate::QWinEventNotifierPrivate(HANDLE h, bool e)
    : handleToEvent(h), enabled(e), registered(false)
{
    waitObject = CreateThreadpoolWait(waitCallback, this, NULL);
    if (waitObject == NULL)
        qErrnoWarning("QWinEventNotifier:: CreateThreadpollWait failed.");
}
 
QWinEventNotifierPrivate::~QWinEventNotifierPrivate()
{
    CloseThreadpoolWait(waitObject);
}
 
void QWinEventNotifierPrivate::waitCallback(PTP_CALLBACK_INSTANCE instance, PVOID context,
                                            PTP_WAIT wait, TP_WAIT_RESULT waitResult)
{
    Q_UNUSED(instance);
    Q_UNUSED(wait);
    Q_UNUSED(waitResult);
    QWinEventNotifierPrivate *nd = reinterpret_cast<QWinEventNotifierPrivate *>(context);
 
    // Do not post an event, if an event is already in the message queue. Note
    // that an event that was previously invalidated will be reactivated.
    if (nd->winEventActPosted.fetchAndStoreRelaxed(QWinEventNotifierPrivate::Posted)
        == QWinEventNotifierPrivate::NotPosted) {
        QCoreApplication::postEvent(nd->q_func(), new QEvent(QEvent::WinEventAct));
    }
}
 
QT_END_NAMESPACE
 
#include "moc_qwineventnotifier.cpp"