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

rktech

I have this code:
pool.h

#ifndef POOL_H
#define POOL_H
#include<QObject>
#include<QThread>
#include<QTcpSocket>
#include<QDateTime>
#include<QElapsedTimer>
class Pool : public QThread
{
    Q_OBJECT

protected:
    void run();
private:
    struct conn{
        QTcpSocket *s;
        QTime qdt;
    };
    QList<conn> x;
public:
    void add(QTcpSocket *s, QTime qdt);
};
#endif // POOL_H

pool.cpp

#include "pool.h"
#include <QElapsedTimer>
void Pool::run()
{
QElapsedTimer qet;
qet.start();
while (true) {
    if(qet.elapsed()>=5000){
        foreach (conn y, x) {
            y.s->write("test");
            y.s->flush();
        }
        qet.restart();
    }
}
}
void Pool::add(QTcpSocket *s, QTime qdt){
conn c;
c.s=s;
c.qdt=qdt;
x.append(c);
}

part of myserver.h:

#include "myserver.h"
Pool p;
MyServer::MyServer(QObject *parent) :
    QObject(parent)
{
    server = new QTcpServer(this);
    p.start();
    connect(server, SIGNAL(newConnection()), this, SLOT(newConnection()));

    if(!server->listen(QHostAddress::Any, 1234))
    {
        qDebug() << "Server could not start!";
    }
    else
    {
        qDebug() << "Server started!";
    }
}

void MyServer::newConnection()
{
    QTcpSocket *socket = server->nextPendingConnection();
    connect(socket, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
    socket->write("hello client\r\n");
    socket->flush();
    socket->waitForBytesWritten(3000);
    QDateTime qdt;
    p.add(socket, qdt.time());
}

And I get this error:
QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread
The code itself works, but I don't know, why I am getting this error/warning.

SGaist

Hi,

Based on your code, you are moving socket between threads which you should not.

See the threaded fortune server example.

rktech

I have read that, but I don't know how to fix it. Is it only possible to remove this warning?

jsulm

@rktech said in QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread:

Is it only possible to remove this warning?

You should fix the issue instead of removing the warning!
Did you check the example @SGaist gave you?

rktech

@jsulm As I have written, I have read it, but I don't know, how to fix my code.

Christian Ehrlicher

@rktech said in QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread:

but I don't know, how to fix my code.

As shown in the example pass the socket fd instead the object to your thread. You have to override incomingConnection() as shown there.

rktech

@Christian-Ehrlicher I have read the example like three-times, but I still don't know how to fix it. Can you help me?

Christian Ehrlicher

@rktech said in QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread:

but I still don't know how to fix it.

You have to override incomingConnection() as shown there.

rktech

@Christian-Ehrlicher said in QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread:

@rktech said in QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread:

but I still don't know how to fix it.

You have to override incomingConnection() as shown there.

I have tried, but I don't know how to implement that into my code.

SGaist

What exactly have you tried ?

rktech

@SGaist To add override to my code, but I don't know where should I place it...

rktech

@SGaist How can I send the connection from incomingConnection() to Pool?

rktech

@SGaist I have successfully overrided the incomingconnection(), but I don't know, how to pass it to the Pool.

SGaist

You'll have to redesign your pool a bit to ensure that your sockets are created in the context of the run method of your QThread subclass.

rktech

@SGaist I know, but how?

SGaist

You have to transfer the descriptor to your pool and there in your run method create new sockets when descriptors are added.

rktech

@SGaist Should I add this part of code to my Pool::add() method? (Of course with editing it)

QTcpSocket tcpSocket;

    if (!tcpSocket.setSocketDescriptor(socketDescriptor)) {
        emit error(tcpSocket.error());
        return;
    }

rktech

@SGaist I have (probably) successfully rewritten the Pool add method, but I have another problem. When I add this:

protected:
    void incomingConnection(qintptr socketDescriptor) override;

to myserver.h I get this error:

...\myserver.h:35: Chyba: only virtual member functions can be marked 'override'

(Chyba is Error in my local)
What I am doing wrong?

mrjj

Hi
well it is virtual https://doc.qt.io/qt-5/qtcpserver.html#incomingConnection
so does Pool inherit QTcpServer ?
The error you get says "Hey, i dont see that funtion in base class, so you cant use override"

rktech

@mrjj No, the server is build under the myserver class