How to solve the QSerialPort::ResourceError on Linux platform?

[jsulm]

This post is deleted!

[SGaist]

Re-reading your issue, I am not sure what you are after. That is a normal behaviour. You remove your device while it's in use. Why would you except your application to stay silent about that ?

[Yash001]

@SGaist said in How to solve the QSerialPort::ResourceError on Linux platform?:

You remove your device while it's in use.

SerialCommunicator::SerialCommunicator(const InstrumentInfo &info, QObject *parent) :
	QObject(parent)
{
	_rawData.reserve(1024*1024);

	_serialThread = new SerialThread(info);

	connect(_serialThread, &SerialThread::NewData, this, &SerialCommunicator::DataArrived, Qt::QueuedConnection);
	connect(this, &SerialCommunicator::SendData, _serialThread, &SerialThread::DataToSend, Qt::QueuedConnection);
}


SerialCommunicator::~SerialCommunicator() {
	if (_serialThread->isRunning()) {
		_serialThread->quit();
		_serialThread->wait();
	}
	_serialThread->deleteLater();
}

I am receiving some initial information from device with help of sub thread. I create objects SerialCommunicator communicator(info) on subthread. and object will delete because of communicator goes out of scope.

Now, if I will get initial information properly then I am creating object of SerialCommunicator on main thread and object will alive until device is connected.

I was thinking it resource error due to threading. So that I modified all code, Now I am creating only one object of SerialCommunicator (for single port) through out application. It will all received information.

But still I am at same page nothing is change. I am getting same error.

few things I would like to mention. It may help.
After this error: QSerialPort::ResourceError

1. _serialPort->isReadable() and _serialPort->isWritable() are return true.
2. if I am trying write data on USB port then I am successfully send it.
3. od -xc < /dev/ttyACM0 give bash: /dev/ttyACM0: Device or resource busy

In addition, If I will put the break point or take some time by writing some dummy statement, then I am able to successful make communication in case 1.

[aha_1980]

@Yash001 do you really need to use threads? Inproper synchronisation can lead to unexplainable behavior. QSerialPort buffrs data in background, so there's rarely a need for threads.

Regards

[Yash001]

@aha_1980 said in How to solve the QSerialPort::ResourceError on Linux platform?:

do you really need to use threads? Inproper synchronisation can lead to unexplainable behavior.

I was thinking same things. So that, I modify the code, and now I am creating only one object of SerialCommunicator for single port in throughout application, and I am creating object from main thread.

If you are talking about this thread SerialThread::run() then yes I need this thread because of I am keeping port open until device is connected to USB port. And just want to information I am calling SerialThread::start() function only single time in application.

[jsulm]

@Yash001 said in How to solve the QSerialPort::ResourceError on Linux platform?:

then yes I need this thread because of I am keeping port open until device is connected to USB port

And why do you think you need a thread for that?

[Yash001]

@jsulm said in How to solve the QSerialPort::ResourceError on Linux platform?:

why do you think you need a thread for that?

So that I can collect the data on different thread. and manipulate data on different thread so that I want that functionalities to be very fast.

In addition,
Today I modify the SerialThread. and remove thread QThread. Here my new SeraulThread.

class SerialThread : public QObject {
	Q_OBJECT

public:
	SerialThread(const InstrumentInfo&);
  InstrumentInfo getInstrumentInfo() { return _info; };
  void waitForBytesWritten() { _serialPort->waitForBytesWritten(1000); };

//protected:

	void run();
    void quit();
signals:
	void NewData(const QByteArray&);

public slots:
	void DataToSend(const QByteArray&);

private slots:
	void DataArrived();
	void ErrorOnSerial(QSerialPort::SerialPortError);

private:
	QSerialPort *_serialPort;
	InstrumentInfo _info;
    
};

SerialThread::SerialThread(const InstrumentInfo &info) :
	_info(info)
{
    //this->moveToThread(this);
    LOG() <<"serail thread is created";
}

// Detect the new instruments and read the data from instruments 
void SerialThread::run() {

	_serialPort = new QSerialPort(this);
     _serialPort->setPortName(_info.port.name);
   _serialPort->setBaudRate(DefaultSerialPortSettings::Baudrate());
   _serialPort->setDataBits(DefaultSerialPortSettings::DataBits());
     _serialPort->setFlowControl(DefaultSerialPortSettings::FlowControl());
    _serialPort->setParity(DefaultSerialPortSettings::Parity());
    _serialPort->setStopBits(DefaultSerialPortSettings::StopBits());

	connect(_serialPort, &QSerialPort::readyRead,
		this, &SerialThread::DataArrived, Qt::QueuedConnection);

    connect(_serialPort, &QSerialPort::errorOccurred,[=](QSerialPort::SerialPortError error){
        LOG() <<"error on serial port" << error;
    });
	//connect(_serialPort, &QSerialPort::errorOccurred, this, &SerialThread::ErrorOnSerial);

	_serialPort->open(QIODevice::ReadWrite);

    //exec();



}

void SerialThread::quit(){
    _serialPort->close();
    _serialPort->deleteLater();
}

// executation is quit if data has error.
void SerialThread::ErrorOnSerial(QSerialPort::SerialPortError error) {
	if (QSerialPort::NoError == error) {
		return;
	}

    //this->quit();
}
// data send to COM port
void SerialThread::DataToSend(const QByteArray &data) {
	if (!_serialPort->isWritable()) {
		return;
	}

	_serialPort->write(data);

}
// if data is safly arived then read from port
void SerialThread::DataArrived() {
    emit NewData(_serialPort->readAll());

}

I am still getting resource error.

[SGaist]

Can you explain the exact logic of your application with regards to selecting the USB port and starting the thread ?

[Yash001]

@SGaist

I have InstrumentEnumerator class. which is inherits from QThread.
InstrumentEnumerator::run() function has while(1) loop. while loop contain QSerialPortInfo::availablePorts();.

If new port is found, and if it is our device then addInstrument signal is emit fromInstrumentEnumerator::run(), with argument as portname.

SIGNALE InstrumentEnumerator::addInstrument connected with MainWindow::addInstrument solt.

MainWindow::addInstrument slot create the object of InstrumentOprator class.

object of InstrumentOprator take port name as arguments, create the object of SerialCommunicator.

object of SerialCommunicator take port name as arguments, create the object of SerialThread.

SerialThread:: run() method is create the object of QSerialPort and keep open port.
(just for testing purpose I changed, earlier it was as run on separate thread.)

SerialThread::run() method is called from SerialCommunicator::start() method;

SerialCommunicator::start() method is called from constructor of InstrumentOprator. So In general, constructor of InstrumentOprator do two things 1) create the object of SerialCommunicator and 2) call SerialCommunicator::start().

Few other detail:

1. I am calling InstrumentEnumerator::start() from constructor of MainWindow class.
2. class Serialthread communicate with only QserialPort.
3. class SerialCommunicator make frame and decode frame, send and received data from Serialthread.
4. class InstrumentOprator is Communicate with MainWindow and SerialCommunicator.

[artwaw]

Hi,
may I suggest two approaches towards narrowing the area of search for a problem (I am sorry if you've been there but I am not able to tell what you already know, just what you've written here):

1. are you completely sure that we can eliminate external issue? Lack of privileges for the user that program runs can cause odd things, depending on the distro;
2. for the sake of dealing with @SGaist suspicions, are you able to modify the program/create a boileplate code that will do the same operations on the port but without deferring to the threads?

Kind Regards,
Artur

[Yash001]

@artwaw said in How to solve the QSerialPort::ResourceError on Linux platform?:

are you completely sure that we can eliminate external issue? Lack of privileges for the user that program runs can cause odd things, depending on the distro;

I install new Ubuntu 18.04 and Qt 5.13.1. After that I add my self to dialout group sudo usermod -a -G dialout $USER. I hope this is enough for making communication with USB Port. did I missing anything?

@artwaw said in How to solve the QSerialPort::ResourceError on Linux platform?:

for the sake of dealing with @SGaist suspicions, are you able to modify the program/create a boileplate code that will do the same operations on the port but without deferring to the threads?

I remove completely thread and eventloop from serial thread class, but still i am getting that issue.

In addition, sometime I am able to generate same error in example/serialport/terminal with baud rate 57600. I am not able to find out certain pattern to regenerate that error.

My device is continuously sending data frame as soon as I connect to usb port. Terminal example is printing that data on console.

I follow this steps with terminal example:

1. open serial port
2. remove usb cable from port.
3. again connect usb cable to usb port.
4. open port (here some data will print and after that sometime I am getting error resource or some time I am not getting.)

[SGaist]

Are you letting the system some oxygen ?
Spamming as fast as possible to find if a new device was added doesn't sound like a good design.

I would rather use something like KDE's Solid framework to get a notification when something changed on the USB side.

[Yash001]

Few place I read, it is generated due to some issue with kernel. So I just update the Ubuntu LTS, and Now it is working with same code.