QLocalSocket Named pipe

king558

Hello all,

I am using QLocalSocket and QLocalServer for named pipe in MainWindows as member variables. QLocalSocket for multiple client put into QVector<QLocalSocket*>, it works great. But I still have problem with disconnection. I am using a slot void disconnect and a MainWindow::closeEvent. Is this code below correct? I need the slot disconnect, if other part close the connection. And CloseEvent is my part to close the connection. I got crash in slot disconnect.

QVector<QLocalSocket*> clients;

void MainWindow::disconnected() {
    for ( auto& client: this->clients ) {
        if ( client->state() == QLocalSocket::UnconnectedState ) {
            client->deleteLater();
        }
    }
}

void MainWindow::closeEvent( QCloseEvent *event ) {
    for ( auto& client: this->clients ) {
        if ( client->isValid() ) {
            client->disconnectFromServer();
        }
    }

    event->accept();
}

JonB

@king558
Run it to crash in the debugger, and look at the stack trace to verify precisely which line of your code it dies from. I assume that if you comment out the client->deleteLater(); it does not crash?

kshegunov

At a glance, you don't remove the client from the list so after disconnecting one client you're left with a dangling pointer.

king558

@JonB said in QLocalSocket Named pipe:

@king558
Run it to crash in the debugger, and look at the stack trace to verify precisely which line of your code it dies from. I assume that if you comment out the client->deleteLater(); it does not crash?

Thx for your help

@kshegunov said in QLocalSocket Named pipe:

At a glance, you don't remove the client from the list so after disconnecting one client you're left with a dangling pointer.

Thx also for your help.

Currently I have a workaround like that. But the design of QLocalSocket slot is bad, if there are not another proper solution available.

this->index = -1;

void MainWindow::disconnected() {
    if ( this->index >= 0 ) {
        const auto& client = this->clients[ this->index ];
        if ( client->state() == QLocalSocket::UnconnectedState ) {
            client->deleteLater();
        }
    } else {
        for ( const auto& client: this->clients  ) {
            if ( client->state() == QLocalSocket::UnconnectedState ) {
                client->deleteLater();
            }
        }
    }
}

void MainWindow::closeEvent( QCloseEvent *event ) {
    for ( const auto& client = this->clients ) {
        this->index++;
        if ( client->isValid() ) {
            client->disconnectFromServer();
        }
    }

    event->accept();
}

I watched many times in stack windows. in closeEvent is a loop and in slot disconnect, that means disconnectFromServer would cause slot disconnect have been called. client->deleteLater(); would be called multiple times, each client two times. Why do disconnected not have a parameter, it would indicate which client object has send the signal?

kshegunov

@king558 said in QLocalSocket Named pipe:

Why do disconnected not have a parameter, it would indicate which client object has send the signal?

Usually it isn't needed. However there's an easy solution:

void MainWindow::disconnected(QLocalSocket * socket)
{
    // Remove from list and deleteLater()
}

// Where you create the socket:
QLocalSocket * socket;
// Init socket etc.
QObject::connect(socket, &QLocalSocket::disconnected, mainWindow, std::bind(&MainWindow::disconnected, mainWindow, socket));