与 QThread 的通信不适用于信号/插槽答案

【问题标题】：Communication with QThread not working with Signals / Slots与 QThread 的通信不适用于信号/插槽
【发布时间】：2014-05-08 21:32:05
【问题描述】：

我为QThreads 关注了本教程： http://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

我遇到的唯一问题是杀死QThread。我在工作对象的process() 循环中有一个标志，我将它推入我的QThread 实例，称为m_ShouldSendFrames。如果该标志被翻转为 false，那么我的处理循环会中断，并且工作对象会发出 finished() 信号。

我遇到的问题是我似乎无法让QThread 中的工作对象从主线程接收我的stopSendingFrames() 信号。我像这样连接它（并且连接返回 'true' ）：

connect(this, SIGNAL(stopSendingFrames()), m_UdpWorkerBlended, SLOT(stopFrames()),Qt::QueuedConnection); // Stop broadcasting

在我的killUdpThread 函数中，我想发出stopSendingFrames() 信号并让m_UdpWorker 对象得到它。但它永远不会！我可以更改该标志的唯一方法是在 killUdpThread 中执行此操作：

m_UdpWorkerBlended->stopFrames();

然而，这是不安全的并且随机崩溃，因为它不是从工作人员正在运行的QThread 调用的。

我也尝试过 invokeMethod 方式 - 但它也不会触发插槽：

QMetaObject::invokeMethod(m_UdpWorkerBlended,"stopFrames",Qt::QueuedConnection);

有人可以帮我理解为什么我不能调用invokeMethod 或使用信号来触发我在QThread 的worker 对象中运行的插槽，但我可以直接调用它（不安全）？谢谢！

启动线程函数：

int UdpThreadController::startUdpThread(int frameType, int port, QString ip) {

    #if SINGLETON_CAMERA_UDP_DEBUG
    qDebug() << "Starting Thread! Frame type is: " << frameType;
    #endif

    // Check for type of frame to emit
    if ( frameType == 0 ) {

        #if SINGLETON_CAMERA_UDP_DEBUG
        qDebug() << "Frames are vl";
        #endif

        // Delete any existing threads / workers
        killUdpThread(0);

        // New objects
        m_UdpThreadBlended = new QThread();
        m_UdpWorkerBlended = new UdpWorker();

        // Assign Port and IP and Frame Type
        m_UdpWorkerBlended->m_ShouldSendFrames = true;
        m_UdpWorkerBlended->m_Port = port;
        m_UdpWorkerBlended->m_AddressToUse = ip;
        m_UdpWorkerBlended->m_FrameType = frameType;

        // Push into thread
        m_UdpWorkerBlended->moveToThread(m_UdpThreadBlended);

        // Connect signals
        connect(this, SIGNAL(stopSendingFrames()), m_UdpWorkerBlended, SLOT(stopFrames()),Qt::QueuedConnection); // Stop broadcasting
        connect(m_UdpThreadBlended, SIGNAL(started()), m_UdpWorkerBlended, SLOT(process()));
        connect(m_UdpWorkerBlended, SIGNAL(finished()), m_UdpThreadBlended, SLOT(quit()));
        connect(m_UdpWorkerBlended, SIGNAL(finished()), m_UdpWorkerBlended, SLOT(deleteLater()));
        connect(m_UdpThreadBlended, SIGNAL(finished()), m_UdpThreadBlended, SLOT(deleteLater()));
        m_UdpThreadBlended->start();

        // All done
        return 0;

杀死线程函数：

int UdpThreadController::killUdpThread(int frameType) {

    #if SINGLETON_CAMERA_UDP_DEBUG
    qDebug() << "Killing Thread! Frame type is: " << frameType;
    #endif

    // Check for type of frame to emit
    if ( frameType == 0 ) {

        // Delete any existing threads / workers
        if ( m_UdpWorkerBlended ) {

            #if SINGLETON_CAMERA_UDP_DEBUG
            qDebug() << "Emit signal to kill thread...";
            #endif

            // Stop broadcasting
            m_UdpWorkerBlended->stopFrames();

        }

        #if SINGLETON_CAMERA_UDP_DEBUG
        qDebug() << "Success ending UDP...";
        #endif

        // All done
        return 0;

    }

【问题讨论】：

你能分享你发出stopSendingFrames信号的代码吗？
嗨，所以在清单末尾的 killUdpThread 函数中，我尝试发出信号 stopSendingFrames 来代替 m_UdpWorkerBlended->stopFrames()。我将清单中的行替换为：“emit stopSendingFrames()”。工作对象从未收到信号。
当您尝试发出信号时，工作线程“忙”吗？只有在线程空闲时才能传递信号。另外，您是否考虑过使用<QtConcurrentRun> 代替线程？我发现它更方便。
您的UdpWorker 中不会碰巧有某种无限循环吗？

标签： c++ qt signals-slots qthread qobject

【解决方案1】：

感谢您的意见。我通过一个单例解决了这个问题，该单例具有一个标志，即 QThread 中我的工作对象中的处理循环读取每个循环迭代。它受到 QReadWrite 锁的保护。

int UdpThreadController::killUdpThread(int frameType) {

    #if SINGLETON_CAMERA_UDP_DEBUG
    qDebug() << "Killing Thread! Frame type is: " << frameType;
    #endif

    // Check for type of frame to emit
    if ( frameType == 0 ) {

        // Delete any existing threads / workers
        if ( m_UdpWorkerBlended ) {

            #if SINGLETON_CAMERA_UDP_DEBUG
            qDebug() << "Setting flag to kill thread...";
            #endif

            // Stop broadcasting
            m_Lock.lockForWrite();
            m_ShouldSendFramesBlended = false;
            m_Lock.unlock();

        }

        #if SINGLETON_CAMERA_UDP_DEBUG
        qDebug() << "Success ending Blended UDP...";
        #endif

        // All done
        return 0;

bool UdpThreadController::shouldContinueSendingFrames(int frameType) {

    #if SINGLETON_CAMERA_UDP_DEBUG
    qDebug() << "Checking if we should continue processing: " << frameType;
    #endif

    // Check for type of frame to emit
    if ( frameType == 0 ) {

        m_Lock.lockForRead();
        #if SINGLETON_CAMERA_UDP_DEBUG
        qDebug() << "Should continue Blended: " << m_ShouldSendFramesBlended;
        #endif
        bool shouldBroadcast = m_ShouldSendFramesBlended;
        m_Lock.unlock();

        // All done
        return shouldBroadcast;

    }

【讨论】：