Qt Thread architecture

king558

Hello Qt Gurus,

I have following process scenario. I need receive datas from server A, parse the content and put the datas to server B.

I itend to have two thread, the main thread with gui to communicate with server B and another thread communicate with server A. The following is pseudo-code

class ServerAThread: public QThread {
          QMutex _mutex;
         QString   _data;
         QLocalServer _server;
         void run { QMutexLocker locker( &_mutex );  _server.receive( data ); _data = data;  }
public:
         ServerAThread( QString &data ) : _data( data ) {}
};

class MainWindow : public QMainWindow {
        QString               _data; // shared data between Thread A and Main
        ServerAThread _threadA;

MainWindow() : _threadA( _data ) { _threadA.start(); }
}

Is this architechture great or do you have better idea for this? Do I need a loop to check any change of datas or is better to use emit signal? Do emit Signal block the thread A if the main thread need time to parse the content of data?

SGaist

Hi,

The first question is: why do you think you need threads involved ? Qt as well as its networking classes are asynchronous. Take advantage of that first. If the load is so heavy that it triggers freezing issues in your GUI then, and only then, add a thread in the mix.

king558

@SGaist

Hello, I forgot to mentions about communication with Server A using third libraries, so it need a loop, check in every loop the data is coming in. So there must a thread for the communication with Server A.

SGaist

Well, QLocalServer is also asynchronous. Which 3rd party library do you need to use ? You are showing none in your code sample.

king558

@king558

its a tdlib on github, from its I take datas, it runs with a loop, check its state and give the content to main thread to parse the content and forward to Server B

Christian Ehrlicher

The provided code does nothing - at least what not you expect. It neither shares some data nor is the mutex useful at all. Receive the data, emit a signal and connect it to a slot in your main thread if you need a separate thread at all - your example code does not.

SGaist

tdlib ? Are you writing a client for telegram ? If so, there are Qt based libraries for that which might be simpler to use in your case.

SimonSchroeder

It is not good style (anymore) to override QThread::run(). Have a look at the documentation for QThread how to create a worker thread.

There is an even better approach for your use case. Just create a plain old QThread object and start it. It will run its own event loop. You should probably not run an infinite loop to takes up every CPU cycle of one core. Instead, start a QTimer (with a low timeout) in this thread to call your external library and check for new data.

Also, try to avoid QMutex. Synchronization between threads is slow. Furthermore, in your small code example only a single object has access to the mutex. This means that you don't need it.

king558

@Christian-Ehrlicher

Really? Could you please provide me the name or github link?

SGaist

@king558 where you in fact asking me for a link ?

king558

@SimonSchroeder said in Qt Thread architecture:

It is not good style (anymore) to override QThread::run(). Have a look at the documentation for QThread how to create a worker thread.

There is an even better approach for your use case. Just create a plain old QThread object and start it. It will run its own event loop. You should probably not run an infinite loop to takes up every CPU cycle of one core. Instead, start a QTimer (with a low timeout) in this thread to call your external library and check for new data.

Also, try to avoid QMutex. Synchronization between threads is slow. Furthermore, in your small code example only a single object has access to the mutex. This means that you don't need it.

Thx you, I have a infinite run loop, that need to check the state of the connection and data received. In this case is movetoThread also possible or override QThread::run is best fot fit?

king558

@SGaist said in Qt Thread architecture:

@king558 where you in fact asking me for a link ?

You said, there are qt based library for telegram, so I asked you for the name if it is third party library and where I can find it

SGaist

@king558 said in Qt Thread architecture:

@Christian-Ehrlicher

Really? Could you please provide me the name or github link?

I don't want to nitpick but you literally tagged @Christian-Ehrlicher with that request hence my question.

Anyway, the first hit when searching Qt telegram client brings you this https://github.com/Kaffeine/telegram-qt

king558

@SGaist

Thx you for link, it was my mistake.