Semaphore and multithread

Montanaro

I wrote the code without ui and it works. Then I wrote ui->label->setText("il valore della distanza in mm è: " + QString::number(distance)); into my code and code works with time of 1 second (its resultes are correct) and code doesnt work with time of 500 ms (its results are bad)

I dont understant why.

Senior suggest me that the resource is occuped by the other process

@jsulm I think you are right.
If with ui.label or without ui.label, I Always have ui in my code. But I'm not the boss and I have task :D

J.Hilk

@Montanaro
ok, just to make sure, so that I'm not going crazy:

unsigned char MainWindow::poll()
{
    unsigned short distance;
    qDebug() << " Polling started";

    check_for_interrupt(ADDR, &distance); 
        
    qDebug() << "valore distanza:" << distance;
 
    //ui->label->setText("il valore della distanza in mm è: " + QString::number(distance));
}

Results in the correct read of
120 distance
150 distance
180 distance

but

unsigned char MainWindow::poll()
{
    unsigned short distance;
    qDebug() << " Polling started";

    check_for_interrupt(ADDR, &distance); 
        
    qDebug() << "valore distanza:" << distance;
 
    ui->label->setText("il valore della distanza in mm è: " + QString::number(distance));
}

results in
3000 distance
3000 distance
3000 distance

?

JonB

@Montanaro
First, please answer @J-Hilk's latest question.

There must be more going on in your code somewhere than you show... And for my part at least, I don't understand what the "resource" you refer to is....

I suggest you briefly test one more case. Try having:

    qDebug() << "valore distanza:" << QString::number(distance);  // <- this is changed, it uses `QString::number`
 
    // next line is still commented out
    //ui->label->setText("il valore della distanza in mm è: " + QString::number(distance));

Does this produce right or wrong output? If by any chance this also produces wrong output, it suggests that any call to a Qt method is causing a problem, not the label->setText() itself.

Montanaro

@J.Hilk

Yes. your summary is right

@JonB thanks. I try your suggest (In check_interrupt, I use ioctl to read i2c from dev/usb/myDevice)

JonB

@Montanaro
Depending on your call to ioctl, it could be a blocking or non-blocking call, which is what we have asked you about with success....