qt exec

int QApplication::exec()
{
#ifndef QT_NO_ACCESSIBILITY
    QAccessible::setRootObject(qApp);
#endif
    return QCoreApplication::exec();
}

int QCoreApplication::exec()
{
    if (!QCoreApplicationPrivate::checkInstance("exec"))
        return -1;

    QThreadData *threadData = self->d_func()->threadData;
    if (threadData != QThreadData::current()) {
        qWarning("%s::exec: Must be called from the main thread", self->metaObject()->className());
        return -1;
    }
    if (!threadData->eventLoops.isEmpty()) {
        qWarning("QCoreApplication::exec: The event loop is already running");
        return -1;
    }

    threadData->quitNow = false;
    QEventLoop eventLoop;
    self->d_func()->in_exec = true;
    self->d_func()->aboutToQuitEmitted = false;
    int returnCode = eventLoop.exec();
    threadData->quitNow = false;
    if (self) {
        self->d_func()->in_exec = false;
        if (!self->d_func()->aboutToQuitEmitted)
            emit self->aboutToQuit();
        self->d_func()->aboutToQuitEmitted = true;
        sendPostedEvents(0, QEvent::DeferredDelete);
    }

    return returnCode;
}

eventLoop.exec();------》

while (!d->exit)
    processEvents(flags | WaitForMoreEvents | EventLoopExec);

bool QEventLoop::processEvents(ProcessEventsFlags flags)
{
    Q_D(QEventLoop);
    if (!d->threadData->eventDispatcher)
        return false;
    if (flags & DeferredDeletion)
        QCoreApplication::sendPostedEvents(0, QEvent::DeferredDelete);
    return d->threadData->eventDispatcher->processEvents(flags);
}

进一步：这将调用平台相关的函数，比如：

bool QEventDispatcherQWS::processEvents(QEventLoop::ProcessEventsFlags flags)    bool QGuiEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)

int QApplication::qwsProcessEvent(QWSEvent* event)