Qt Console Application: while loop blocks event loop

Hello,

Im making a console application where Im getting user input with std::getline() (in a while loop). Im also using QextSerialPort (inherits QIODevice) and readyRead() signal. Thus I need an event loop so I'm using QCoreApplication and calling a.exec().

The problem is getline() blocks event loop and, while it's blocked, I can't receive anything from serial port. I tried to use QCoreApplication::processEvents() in the while(1){getline()} loop, but found that's not a good solution. Then, I tried to call QCoreApplication::processEvents() in a QThread but it didn't work.

Here's the code Im using:

Code:

---

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
 
    Base *base = new Base();
    Commander *commander = new Commander(base);
 
    QObject::connect(commander, SIGNAL(end()), &a, SLOT(quit()));
    QTimer::singleShot(0, commander, SLOT(run()));
 
    return a.exec();
}

---

Code:

---

void Commander::askToConnect()
{
    if(base->connect() == false){
        cout << "Failed to open port." << endl;
    }
}
 
void Commander::run{
    string inputline;
 
    askToConnect();
 
    while(1){
       QCoreApplication::processEvents();  // ???
 
       cout << endl << "> ";
       getline(cin, inputline);
 
       // ...
    }
}

---

Even if I have while(1); the event loop is blocked and I can't read data from serial port.

So, how can I get user input without blocking event loop?

Thanks!

This is drawback of using standard console. There is no easey solution.

Blocking input routines such as getline() block the thread which runs them. I see two options:
1. Move all the input on stdin to a dedicated thread that will send each read line to the main thread (e.g. using signals and slots). Tip: if you need to exit the application, I guess you can close stdin to make the thread return from the blocking call.
2. Use non-blocking input on stdin. This will be trickier and highly platform-dependant. Libraries such as ncurses might help you here.

I would recommend using solution 1.

Use a QSocketNotifier on stdin and query input only when there is something to read.

Quote:

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Originally Posted by yeye_olive

Blocking input routines such as getline() block the thread which runs them. I see two options:
1. Move all the input on stdin to a dedicated thread that will send each read line to the main thread (e.g. using signals and slots). Tip: if you need to exit the application, I guess you can close stdin to make the thread return from the blocking call.
2. Use non-blocking input on stdin. This will be trickier and highly platform-dependant. Libraries such as ncurses might help you here.

I would recommend using solution 1.

---

yeye_olive, I sticked with the first option. getline() is now in a dedicated thread and I send the "inputline" through a signal. It's working!

Thank you all for your help!