Problems use QFtp in QThread

Bruce.Zhang

Hi Guys, I use QFtp in my project, now I faced a strange problem. The codes as follows:

class FtpOutput: public QObject{
private:
QFtp* mQFtpPtr = nullptr;
} 

MyApp::MyApp(QObject *parent) : QObject(parent){
    mFtpThread = new QThread;
    mFtpOutput = new FtpOutput;
    mFtpOutput->setUrlStr("127.0.0.1");
    mFtpOutput->moveToThread(mFtpThread);
    connect(mFtpThread, &QThread::started, mFtpOutput, &FtpOutput::run);
    connect(mFtpThread, &QThread::destroyed, mFtpOutput, &FtpOutput::deleteLater);
    mFtpThread->start();
}

void FtpOutput::run()
{
    static FileDescriptorPtr filePtr;

    if(mQFtpPtr == nullptr) {
        mQFtpPtr = new QFtp(this);
        //![1]
        this->connect(this, &FtpOutput::destroyed, mQFtpPtr, &QFtp::deleteLater);

        this->connect(mQFtpPtr, SIGNAL(commandFinished(int,bool)),
                      this, SLOT(onFtpCommandFinished(int,bool)));
        this->connect(mQFtpPtr, SIGNAL(dataTransferProgress(qint64,qint64)),
                      this, SLOT(onDataTransferProgress(qint64,qint64)));
        this->connect(mQFtpPtr, SIGNAL(stateChanged(int)),
                      this, SLOT(onStatusChange(int)));
        this->connect(mQFtpPtr, SIGNAL(listInfo(QUrlInfo)),
                      this, SLOT(onListInfo(QUrlInfo)));
        //![1]
    }

    QThread::msleep(100);

    int state = mQFtpPtr->state();
    //Step 1 check connection
    if(state == QFtp::Unconnected && mStep == 0) {
        doConnect();
        mStep = 1;
}
}

The problem is when exec the doConnect(), nothing happens, but when I use QFtp directly from GUI( not use QThread), everything goes well.
I tracked that：

int QFtpPrivate::addCommand(QFtpCommand *cmd)
{
    pending.append(cmd);

    if (pending.count() == 1) {
        // don't emit the commandStarted() signal before the ID is returned
        QTimer::singleShot(0, q_func(), SLOT(_q_startNextCommand()));
    } else {
        qDebug()<<"pending count:"<<pending.count();
    }
    return cmd->id;
}

When the code QTimer::singleShot exec,
the _q_startNextCommand slot function not exec. Please help me.

KroMignon

@Bruce-Zhang Your code cannot work QThread::msleep(100); is an "active wait", so the QEventLoop of the thread is locked and all signals are not executed!

I would also recommend you to use new connect syntax to allow signals/slots validity check at compilation.

void FtpOutput::run()
{
    if(mQFtpPtr == nullptr) {
        mQFtpPtr = new QFtp(this);
		// => not needed, because this is parent
        //connect(this, &FtpOutput::destroyed, mQFtpPtr, &QFtp::deleteLater);
        connect(mQFtpPtr, &QFtp::commandFinished, this, &FtpOutput::onFtpCommandFinished);
        connect(mQFtpPtr, &QFtp::dataTransferProgress, this, &FtpOutput::onDataTransferProgress);
        connect(mQFtpPtr, &QFtp::stateChanged, this, &FtpOutput::onStatusChange);
        connect(mQFtpPtr, &QFtp::listInfo, this, &FtpOutput::onListInfo);

		//Step 1 start connection
        doConnect();
        mStep = 1;
    }
}

KroMignon

@Bruce-Zhang Your code cannot work QThread::msleep(100); is an "active wait", so the QEventLoop of the thread is locked and all signals are not executed!

I would also recommend you to use new connect syntax to allow signals/slots validity check at compilation.

void FtpOutput::run()
{
    if(mQFtpPtr == nullptr) {
        mQFtpPtr = new QFtp(this);
		// => not needed, because this is parent
        //connect(this, &FtpOutput::destroyed, mQFtpPtr, &QFtp::deleteLater);
        connect(mQFtpPtr, &QFtp::commandFinished, this, &FtpOutput::onFtpCommandFinished);
        connect(mQFtpPtr, &QFtp::dataTransferProgress, this, &FtpOutput::onDataTransferProgress);
        connect(mQFtpPtr, &QFtp::stateChanged, this, &FtpOutput::onStatusChange);
        connect(mQFtpPtr, &QFtp::listInfo, this, &FtpOutput::onListInfo);

		//Step 1 start connection
        doConnect();
        mStep = 1;
    }
}

Bruce.Zhang

@KroMignon said in Problems use QFtp in QThread:

connect(mQFtpPtr, &QFtp::commandFinished, this, &FtpOutput::onFtpCommandFinished);
connect(mQFtpPtr, &QFtp::dataTransferProgress, this, &FtpOutput::onDataTransferProgress);
connect(mQFtpPtr, &QFtp::stateChanged, this, &FtpOutput::onStatusChange);
connect(mQFtpPtr, &QFtp::listInfo, this, &FtpOutput::onListInfo);

Thanks a lot, really works.

Qt World Summit: Submit your Presentation

Problems use QFtp in QThread