What does this qt_GetMessageHook（Qt5.6.3） do？

[Lidada]

Read processEvents() source code in qeventdispatcher_win.cpp, I don't understand the meaning of qt_GetMessageHook(); For example Create a timer (sendPostedEventsWindowsTimerId), I think even without this timer, the peekmessage() in processEvents() in the next cycle can send WM_QT_SENDPOSTEDEVENTS

LRESULT QT_WIN_CALLBACK qt_GetMessageHook(int code, WPARAM wp, LPARAM lp)
{
    QEventDispatcherWin32 *q = qobject_cast<QEventDispatcherWin32 *>(QAbstractEventDispatcher::instance());
    Q_ASSERT(q != 0);

    if (wp == PM_REMOVE) {
        if (q) {
            MSG *msg = (MSG *) lp;
            QEventDispatcherWin32Private *d = q->d_func();
            const int localSerialNumber = d->serialNumber.load();
            static const UINT mask = inputTimerMask();
            if (HIWORD(GetQueueStatus(mask)) == 0) {
                // no more input or timer events in the message queue, we can allow posted events to be sent normally now
                if (d->sendPostedEventsWindowsTimerId != 0) {
                    // stop the timer to send posted events, since we now allow the WM_QT_SENDPOSTEDEVENTS message
                    KillTimer(d->internalHwnd, d->sendPostedEventsWindowsTimerId);
                    d->sendPostedEventsWindowsTimerId = 0;
                }
                (void) d->wakeUps.fetchAndStoreRelease(0);
                if (localSerialNumber != d->lastSerialNumber
                    // if this message IS the one that triggers sendPostedEvents(), no need to post it again
                    && (msg->hwnd != d->internalHwnd
                        || msg->message != WM_QT_SENDPOSTEDEVENTS)) {
                    PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
                }
            } else if (d->sendPostedEventsWindowsTimerId == 0
                       && localSerialNumber != d->lastSerialNumber) {
                // start a special timer to continue delivering posted events while
                // there are still input and timer messages in the message queue
                d->sendPostedEventsWindowsTimerId = SetTimer(d->internalHwnd,
                                                             SendPostedEventsWindowsTimerId,
                                                             0, // we specify zero, but Windows uses USER_TIMER_MINIMUM
                                                             NULL);
                // we don't check the return value of SetTimer()... if creating the timer failed, there's little
                // we can do. we just have to accept that posted events will be starved
            }
        }
    }
#ifdef Q_OS_WINCE
    return 0;
#else
    return q->d_func()->getMessageHook ? CallNextHookEx(0, code, wp, lp) : 0;
#endif
}