c++ - 为什么我的信号在没有 Qt::DirectConnection 的情况下不能触发插槽？

Question

我有一个主类启动一个执行单个操作的线程。我正试图捕捉线程操作何时完成。

主类:

// .h
class MainClass : public QObject
{
    Q_OBJECT
public:
    QThread thread;
// ...
public slots:
    void onFinish();
}

// .cpp
void MainClass::startThread()
{
    thread = new QThread();
    worker = new Worker();
    worker->moveToThread(thread);

    connect(thread, SIGNAL(started()), worker, SLOT(process()));
    connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
    connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));

    connect(worker, SIGNAL(finished()), this, SLOT(onFinish()));
    // connect(worker, SIGNAL(finished()), this, SLOT(onFinish()), Qt::DirectConnection);
}

void MainClass::onFinish()
{
    std::cout << "Finished!" << std::endl << std::flush;
}

线程的 Worker 类:

// .h
class Worker : public QObject
{
    Q_OBJECT
public:
    explicit Worker(QObject *parent = 0);
    ~Worker();
public slots:
    void process();
signals:
    void finished();
}

// .cpp
void Worker::process()
{
    // ...Do stuff...

    emit finished();
}

执行 startThread 不会打印“Finished!”。为什么？

我注意到，如果我将 Qt::DirectConnection 添加到连接到 onFinish() 的行(如在注释行中)，则会打印消息。但是如果想在主类的线程中执行onFinish() Action 怎么办呢？

编辑1

此外，似乎 finished() -> quit() 连接也不起作用，因为如果我调用 thread->isFinished( ) 或 thread->isRunning()，在主线程休眠以确保线程任务完成后，我得到 false 和 分别为 true。

编辑2

因为它也可能是相关的，这里是 main.cpp:

int _tmain(int argc, _TCHAR* argv[])
{
    QCoreApplication a(argc, argv);

    std::unique_ptr <MainClass> mc = std::make_unique <MainClass>();

    mc->startThread();
    mc->thread->wait();

    return a.exec();
}

Answer 1

乍一看，我会说连接的顺序很重要。 deleteLater() 槽应该始终是最后的方法。

connect(thread, SIGNAL(started()), worker, SLOT(process()));
connect(worker, SIGNAL(finished()), this, SLOT(onFinish()));
connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));

站点节点 - QRunnable您可能会考虑使用 QRunnable相反，它专为短期运行的任务/工作而设计。您可以将它们与 QObject 或 QFuture/QFutureWatcher 结合使用，以便在它们完成后立即得到通知。

更新1

您的主事件循环永远不会开始，看起来您想在任务完成时退出应用程序。我不认为这是一个很好的实现，但这些修改应该适合你:

int _tmain(int argc, _TCHAR* argv[])
{
    QCoreApplication a(argc, argv);

    std::unique_ptr<MainClass> mc = std::make_unique<MainClass>();
    mc->startThread();

    // do not wait!
    // let the main-event-loop handle events -> a.exec()
    // and quit() application by signal/slot

    return a.exec();
}

void MainClass::startThread()
{
    thread = new QThread();
    worker = new Worker();
    worker->moveToThread(thread);

    connect(thread, SIGNAL(started()), worker, SLOT(process()));
    connect(worker, SIGNAL(finished()), this, SLOT(onFinish()));
    connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
    connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), qApp, SLOT(quit()));
}