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;
}

Answer 1

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);
  }
};

Answer 2

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);