Question

我正在尝试使用单独的线程下载带有QNetworkAccessManager :: get（）的网页，当我运行该程序时，它会随机崩溃（可能是一小时或两小时）。代码示例：

class SpiderThread : public QThread
{   
    Q_OBJECT
public:
    SpiderThread();
    void    run();
private:
    bool    _stopped;
}; 

void SpiderThread::run()
{
    while (!_stopped) {
        DownloadManager downloadManager();
        QUrl u = getOneUrl();
        QString content = downloadManager.getContent(u);
        // some other code
    }
}


QString DownloadManager::getContent(const QUrl &url)
{
    QEventLoop  loop;
    QNetworkAccessManager manager;

    QNetworkRequest request(url);
    request.setRawHeader("User-Agent", _userAgent.toAscii());
    QNetworkReply *reply = manager.get(request);
    connect(reply, SIGNAL(finished()),
            SLOT(replyFinished()));
    connect(reply, SIGNAL(finished()),
            &loop, SLOT(quit()));

    loop.exec();
    if (reply->error() != QNetworkReply::NoError) {
        if (reply->isRunning())
            reply->abort();
        reply->deleteLater();
        return QString();
    }


    int httpCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();

    if (httpCode != 200)
        return QString();
    QByteArray data = reply->readAll();
    reply->deleteLater();
    return QString(data);
}

我正在使用QEventloop来阻止http请求直到它完成，当我运行这些代码时，它总是崩溃并显示错误消息：

    pure virtual method called
    terminate called without an active exception

gdb调试信息：

    (gdb) bt
    #0  0x0000003c0dc30285 in raise () from /lib64/libc.so.6
    #1  0x0000003c0dc31d30 in abort () from /lib64/libc.so.6
    #2  0x0000003d992bed94 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib64/libstdc++.so.6
    #3  0x0000003d992bce46 in ?? () from /usr/lib64/libstdc++.so.6
    #4  0x0000003d992bce73 in std::terminate() () from /usr/lib64/libstdc++.so.6
    #5  0x0000003d992bd3cf in __cxa_pure_virtual () from /usr/lib64/libstdc++.so.6
    #6  0x00002aaaabc3cc35 in QCoreApplication::postEvent(QObject*, QEvent*, int) () 
           from /usr/local/Trolltech/Qt-4.8.2/lib/libQtCore.so.4
    #7  0x00002aaaabc5301d in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () 
           from /usr/local/Trolltech/Qt-4.8.2/lib/libQtCore.so.4
    #8  0x00002aaaab7b81a1 in ?? () from /usr/local/Trolltech/Qt-4.8.2/lib/libQtNetwork.so.4
    #9  0x00002aaaab7ac3ad in ?? () from /usr/local/Trolltech/Qt-4.8.2/lib/libQtNetwork.so.4
    #10 0x00002aaaab7c8d1d in ?? () from /usr/local/Trolltech/Qt-4.8.2/lib/libQtNetwork.so.4
    #11 0x00002aaaab7cadb0 in ?? () from /usr/local/Trolltech/Qt-4.8.2/lib/libQtNetwork.so.4
    #12 0x00002aaaab7a89ce in QNetworkAccessManager::createRequest(QNetworkAccessManager::Operation, QNetworkRequest const&, QIODevice*)               () 
          from /usr/local/Trolltech/Qt-4.8.2/lib/libQtNetwork.so.4
    #13 0x00002aaaab7a5ea4 in QNetworkAccessManager::get(QNetworkRequest const&) ()
                     from /usr/local/Trolltech/Qt-4.8.2/lib/libQtNetwork.so.4
    #14 0x00000000004088fe in DownloadManager::getContent (this=0x409fff40, url=..., toCodec=...)
                         at src/downloadmanager.cpp:55
    #15 0x0000000000415248 in SpiderThread::run (this=0x7fffffffe2b0) at src/spiderthread.cpp:27
    #16 0x00002aaaabb2c3b9 in ?? () from /usr/local/Trolltech/Qt-4.8.2/lib/libQtCore.so.4
    #17 0x0000003c0e40677d in start_thread () from /lib64/libpthread.so.0
    #18 0x0000003c0dcd325d in clone () from /lib64/libc.so.6

请帮助我，我花了很多时间找出错误，但它仍然无效。我犯了一些错误？

Answer 1

你有不必要的复杂事情。 QThread::run()的默认实现已经创建并运行了一个事件循环。不要从QThread派生。将您的功能放入QObject，并在启动线程后调用该对象上的moveToThread(thread)，如有必要！使用信号和插槽完成任务。 QNetworkAccessManager已经使用了工作线程IIRC，因此在另一个专用线程中创建它可能毫无意义。

QNetworkAccessManager :: get（）导致调用纯虚方法

1 个答案: