Create object in another object

[jsulm]

@Damian7546 said in Create object in another object:

In my example using thread it is a mistake ?

You should avoid threads if they are not needed as it is easy to do mistakes and the code becomes more complex. As I wrote: Qt is an asynchronous framework, that means you usually do not need threads. QSerialPort is also asynchronous - you can use it without threads and it will still not block your main thread. Threads are usually used to move heavy calculations to other threads, but I don't see any heavy calculations in your code.

[Christian Ehrlicher]

@Damian7546 said in Create object in another object:

This project is for learning programming purposes only

Then start with writing clean code without threads. Write a good handler class to handle your incoming data. Once this is done this class can be easily moved into a separate thread if really needed.

[Damian7546]

anyway, can anyone demonstrate why the above code doesn't work when created from the constructor? but works with the main.cpp one?

[jsulm]

@Damian7546 If your application crashes then the first thing to do is: use the debugger.
So, please run your app in debugger and post the stack trace after the crash here...

[Christian Ehrlicher]

Your code crashes in the dtor of RfidSerialWorker (if doWork() would reach it's end), also it's using a blocking approach instead signals and slots to wait for data, the strange while(1) - loop does never exits and at last ít's accessing outFrameQueue from two different threads without proper locking mechanisms (and before you ask - read and understand at least https://doc.qt.io/qt-6/threads-synchronizing.html before fiddling around with threads for no reason).

[Damian7546]

@Christian-Ehrlicher so I will do like you propose.

[Damian7546]

I think that no a problem with thread.

I remove thread and create my object like below:

  QQueue<RfidFrame*> outFrameQueue;
    RfidSerialWorker *rfidSerialWorker = new RfidSerialWorker(&outFrameQueue);
    RfidFrameProcessor *rfidFrameProcessor = new RfidFrameProcessor(&outFrameQueue);

    connect(rfidSerialWorker, SIGNAL(frameReceived(RfidFrame*)), rfidFrameProcessor, SLOT(FrameIncoming(RfidFrame*)));
    connect(rfidFrameProcessor, SIGNAL(frameSend()), rfidSerialWorker, SLOT(frameToSend()));
    rfidSerialWorker->initSerialPort();

    //tests - try send frame cyclically
    QTimer *timer = new QTimer(this);
    QObject::connect(timer, SIGNAL(timeout()), rfidFrameProcessor , SLOT(update_power_ind()));
    timer->start(2000);

Function which one try send frame is below:

void RfidFrameProcessor::update_power_ind()
{
    readSourceRSx(1,9);
}
void RfidFrameProcessor::readSourceRSx(quint8 addr, quint8 source)
{

    QByteArray data;
    data.append(source);
    RfidFrame *frameToSend = new RfidFrame(addr, C_ReadSourceRSx, data);
    qDebug() << "Get lenght from frameToSend: " << frameToSend->GetDataLength();
    m_outFrameQueue->enqueue(frameToSend);
    emit frameSend();

}

and problem is in the same step:
m_outFrameQueue->enqueue(frameToSend); despite the fact that in frameToSend I have data like you can see in below in Application Output.

[jsulm]

@Damian7546 said in Create object in another object:

and problem is in the same step

And again: is m_outFrameQueue a valid pointer?

[Damian7546]

@jsulm In my opinion yes, but I am beginner.... Please explain me.
.h

class RfidFrameProcessor : public QObject
{
    Q_OBJECT
public:
    explicit RfidFrameProcessor(QQueue<RfidFrame*> *outFrameQueue, QObject *parent = nullptr);
private:
    QQueue<RfidFrame*> *m_outFrameQueue;
}

.cpp

RfidFrameProcessor::RfidFrameProcessor(QQueue<RfidFrame*> *outFrameQueue,QObject *parent)
    : QObject(parent)
{
    m_outFrameQueue = outFrameQueue;
}

[jsulm]

@Damian7546 said in Create object in another object:

m_outFrameQueue = outFrameQueue;

I laready asked that before: is outFrameQueue a valid pointer?

[Damian7546]

Ok,
I create in this way:

 QQueue<RfidFrame*> outFrameQueue;
    RfidSerialWorker *rfidSerialWorker = new RfidSerialWorker(&outFrameQueue);
    RfidFrameProcessor *rfidFrameProcessor = new RfidFrameProcessor(&outFrameQueue);

But in class

   Q_OBJECT
public:
    explicit RfidFrameProcessor(QQueue<RfidFrame*> *outFrameQueue, QObject *parent = nullptr);
private:
    QQueue<RfidFrame*> *m_outFrameQueue;

[JonB]

@Damian7546 said in Create object in another object:

QQueue<RfidFrame*> outFrameQueue;
RfidSerialWorker *rfidSerialWorker = new RfidSerialWorker(&outFrameQueue);
RfidFrameProcessor *rfidFrameProcessor = new RfidFrameProcessor(&outFrameQueue);
...
timer->start(2000);

If I understand your code right. QQueue<RfidFrame*> outFrameQueue is a local variable in some method? But once you have set off the timer you exit that method, right? So the QQueue<RfidFrame*> outFrameQueue goes out of scope and gets destroyed at that point. Yet you have passed that queue as a parameter to RfidSerialWorker/RfidFrameProcessor, they have set a m_outFrameQueue to point to that queue passed in, it is no longer valid, but they still use it => disaster. Is my analysis correct for your code?

I'm not sure, but it sounds like your QQueue<RfidFrame*> outFrameQueue; should not be local variable in a method but rather a persistent member variable?

[Damian7546]

Thanks QQueue<RfidFrame*> outFrameQueue i wolud like to pass frame to send beetwen RfidSerialWorker and RfidFrameProcessor.

@JonB said in Create object in another object:

I'm not sure, but it sounds like your QQueue<RfidFrame*> outFrameQueue; should not be local variable in a method but rather a persistent member variable?

Exactly. But how do this ?

[jsulm]

@Damian7546 said in Create object in another object:

But how do this ?

Make outFrameQueue member variable instead of local variable.

[Damian7546]

sure!! Thank you !