unsync function , QSocketNotifier & Cannot move to target thread

__d4ve__

Hi ,

Here is the flow of tray Icon app syncing with server and the problem.

Client* client = Client::instance();  // Singleton instance of Client

Client instance created on main()

QAction::connect(actionSync, &QAction::triggered, clickHandler, &MenuClickHandler::syncApplication);

actionSync triggers MenuClickHandler::syncApplication
syncApplication()
initSync() runs and connects to the server

The notification i get is :

QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread

void MenuClickHandler::syncApplication()
{

    QThread* thread  = new QThread(this);
    Client::instance()->moveToThread(thread);

    if(Client::instance()->sync)
    {
        thread->quit();
        Client::instance()->disconnectSync();
        return;
    }

    connect(thread, &QThread::started, [=](){
        qDebug() << "Thread started - syncApplication";
        //Client client;
        Client::instance()->initSync();

        while (Client::instance()->sync == true) {
            qDebug() << "Data Receiving loop.";
            qDebug() << "Client->sync = " << Client::instance()->sync;
            Client::instance()->DataReceived();
        }

        // Emit a finished signal to allow thread cleanup
        thread->quit();
    });

    connect(thread, &QThread::finished, thread, &QThread::deleteLater);

    thread->start();
}

Here is some output :

From main()

Client thread: QThread(0x19f82244350)
Current thread: QThread(0x19f82244350)

From syncAppliaction()

Thread started - syncApplication

From initSync()

sync request sent.
QObject: Cannot create children for a parent that is in a different thread.
(Parent is QTcpSocket(0x19f82251780), parent's thread is QThread(0x19f82244350), current thread is QThread(0x19f822c4660)

everything works but with this notifications/errors

I can't figure out how I should troubleshot that ?

Christian Ehrlicher

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

I use socket->waitForReadyRead(1000);

Again: do not block the event loop, use signals and slots.

Christian Ehrlicher

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

can't figure out how I should troubleshot that ?

Don't use a global static, don't use threads at all because they are not needed here.

__d4ve__

GUI will be unresponsive other wise , why not using global static ?

Christian Ehrlicher

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

GUI will be unresponsive other wise

Use signals and slots and a/or a QTimer. No need to block anything.
Globlals, especially QObject one are bad design.

__d4ve__

Ok ,
signals and slots ,
I have Client variable that supposed to be global variable and used in another classes

__d4ve__

Used QTimer , makes GUI freeze :

void MenuClickHandler::syncApplication()
{
    if(Client::instance()->sync)
    {
        Client::instance()->disconnectSync();
        return;
    }

    QTimer* timer = new QTimer(this);  // Use a timer instead of a new thread

    connect(timer, &QTimer::timeout, [=](){

        Client::instance()->initSync();

        while (Client::instance()->sync == true) {
            qDebug() << "Data Receiving loop.";
            qDebug() << "Client->sync = " << Client::instance()->sync;
            Client::instance()->DataReceived();
        }

        });
        timer->start(1000);
}

I can see that something wrong with the design but as far as i know Qt usage , Qthreads or instance() I would like to hear what other options there , if i Initiate object on main() , what's the right way to connect it ?

I have QAction on main()

QAction::connect(actionSync, &QAction::triggered, clickHandler, &MenuClickHandler::syncApplication);

that changes it label to 'unsync' after successful syncing another click should unsync it .
this scenario may confuse so what should be done with signal slot ?

first click syncs
the second unsyncs ( on successful synced client only )
recommended not using Qthreads , Client instance()

Christian Ehrlicher

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

while (Client::instance()->sync == true) {

I mean -what do you expect when you block the event loop... let Client emit a signal when the data was received.

__d4ve__

Changed the code but the GUI still not responsive :

void MenuClickHandler::syncApplication()
{
    qDebug() << Client::instance()->socket->isOpen() ;
    if(Client::instance()->sync && Client::instance()->socket->isOpen() )
    {
        Client::instance()->disconnectSync();
        return;
    }

    QTimer* timer = new QTimer(this);  // Use a timer instead of a new thread

    connect(timer, &QTimer::timeout, [=](){

        Client::instance()->initSync();

        while (Client::instance()->sync == true) {
            qDebug() << "Data Receiving loop.";
            qDebug() << "Client->sync = " << Client::instance()->sync;
            Client::instance()->DataReceived();
        }

        });
        timer->start(1000);
}

Syncs successfully but not responsive afterwards

Pl45m4

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

connect(timer, &QTimer::timeout, ={

    Client::instance()->initSync();

    while (Client::instance()->sync == true) {
        qDebug() << "Data Receiving loop.";
        qDebug() << "Client->sync = " << Client::instance()->sync;
        Client::instance()->DataReceived();
    }

    });
    timer->start(1000);

I think the while loop is still blocking.

So better something like

QTimer::singleShot(0, this, ()[=]{

// sync here

});

__d4ve__

The problem with SingleShot function is that its good as written for 'single shot' what makes the app not responsive as desired in period of times.

I changed program design and currently sync loop runs on SingleShot but I need alternative
not using QThreads and while loop leaves me with maybe connect on some terms

I have :

sync(): init connection

connection_loop() : maintains connection

receiveData() : receives data from server

Christian Ehrlicher

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

connection_loop() : maintains connection

What does this mean? What has to be done in there? A keep-alive every n seconds? Use a QTimer.

receiveData() : receives data from server

Use the readyRead() signal and process your data.

__d4ve__

I use socket->waitForReadyRead(1000); instead readyRead() and yes connection_loop() does keep-alive every n seconds but I look for something more responsive

Christian Ehrlicher

@__d4ve__ said in unsync function , QSocketNotifier & Cannot move to target thread:

I use socket->waitForReadyRead(1000);

Again: do not block the event loop, use signals and slots.