QtQuick animation freezing on list and open serial ports

Question

I wrote a C++ method to find all serial ports, open, write and close and use to Q_INVOKABLE to call this method from a QML. At QML, first I push a LoadingPage.qml to StackView and then I call the find() Serial Ports, inside the onClicked: Button slot.

The problem: It is a freezing on push a LoadingPage.qml to StackView if there are many serial ports connected, the animation start and then immediately freezes, when the function find finish the animation start again. [SerialPort.qml] How is it the better way to solve that?

//SerialPort.qml
Button {
    text: qsTr("start")
    onClicked: {
        stackView.push(Qt.resolvedUrl("LoadingPage.qml"))
        module.find()
    }
}


QVector<QString> Physical::find()
{
    m_ports.clear();

    foreach (const QSerialPortInfo &info, QSerialPortInfo::availablePorts()) {
        bool hasError = false;

        QSerialPort port;
        port.setPort(info);

        if (port.open(QIODevice::ReadWrite)) {
            if (!hasError && !port.setBaudRate(serial::baudRate)) {
                emit error(tr("Can't set baud to %1, error %2")
                           .arg(port.portName())
                           .arg(port.error()));
                hasError |= true;
            }
            if (!hasError && !port.setDataBits(serial::dataBits)) {
                emit error(tr("Can't set data bits to %1, error %2")
                           .arg(port.portName())
                           .arg(port.error()));
                hasError |= true;
            }

            if (!hasError && !port.setParity(serial::parity)) {
                emit error(tr("Can't set parity to %1, error %2")
                           .arg(port.portName())
                           .arg(port.error()));
                hasError |= true;
            }
            if (!hasError && !port.setStopBits(serial::stopBits)) {
                emit error(tr("Can't set stop bits to %1, error %2")
                           .arg(port.portName())
                           .arg(port.error()));
                hasError |= true;
            }
            if (!hasError && !port.setFlowControl(serial::flowCtrl)) {
                emit error(tr("Can't set flow control to %1, error %2")
                           .arg(port.portName())
                           .arg(port.error()));
                hasError |= true;
            }
            if (!hasError) {
                m_ports.append(port.portName());
            }

            QByteArray data;
            data.resize(1);
            data[0] = ID_READ;

            port.write(data);
            port.close();
        }
    }

    return m_ports;
}

I understand why you test if each port supports your requested parameters; but I don't understand why you send some data to each of the ports and do not test anything after doing so (you already stored the port in your internal list...). Do you want to scan for some type of device by testing the behavior? — leemes, Feb 20 '14 at 15:06

score 4 · Accepted Answer · edited Jun 07 '18 at 12:15

Your code runs in the GUI thread, and since it blocks the GUI thread, the user interaction is stopped as well.

You need to perform the scan in a separate thread. The Qt Concurrent framework is perfect for this, since you're performing a self-contained action that can be done in any thread. Your find() method can be turned into a stand-alone function or a static method (since that's what it really is). You could also capture this in a lambda.

You'd then run it as follows:

class Physical {
  QFuture<QStringList> m_future;
  QFutureWatcher<QStringList> m_futureWatcher;
  // A string list is a simpler type to type :)
  static QStringList doFindPorts() {
    ...
  }
  Q_SLOT void findPortsFinished() {
    QStringList ports(m_future);
    // use the list of ports
  }

public:
  Physical() {
    connect(&m_futureWatcher, SIGNAL(finished()), SLOT(findPortsFinished()));
    ...
  }
  Q_SLOT void findPorts() {
    if (m_future.isRunning()) return;
    m_future = QtConcurrent::run(doFindPorts);
    m_futureWatcher.setFuture(m_future);
  }
};

score 0 · Answer 2 · edited Jun 07 '18 at 11:46

0

The right interface to set a future is setFuture and called after starting the thread

m_future = QtConcurrent::run(doFindPorts);
m_futureWatcher.setFuture(m_future);

edited Jun 07 '18 at 11:46

vonaka

913
1
11
23

answered Jun 07 '18 at 11:32

ymorvan

3
5

QtQuick animation freezing on list and open serial ports

2 Answers2

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