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

[rktech]

This post is deleted!

[rktech]

@mrjj the header of server look like:

#ifndef MYSERVER_H
#define MYSERVER_H

#include <QObject>
#include <QDebug>
#include <QTcpServer>
#include <QTcpSocket>
#include <QString>
#include <QFile>
#include <QStandardPaths>
#include <QThread>
#include <QElapsedTimer>
#include <pool.h>
#include <QDateTime>
class MyServer : public QObject
{
    Q_OBJECT
public:
    explicit MyServer(QObject *parent = nullptr);

signals:

public slots:
    void newConnection();
    void onReadyRead();

private:
    QTcpServer *server;
    QList<QTcpSocket*>  _sockets;
    QString a;
    QString com;
    QTcpSocket *socket;
    QList<QTcpSocket*> sl;
/*protected:
    void incomingConnection(qintptr socketDescriptor) override;*/
};

#endif // MYSERVER_H

[Christian Ehrlicher]

Sorry but please learn C++ first. If you want to override a function from a class you should inherit from this class. So inherit from QTcpServer, override the function and do whatever you want to. This is basic c++ stuff...

[rktech]

@Christian-Ehrlicher That's the thing, that I didn't notice. Thanks

[rktech]

@Christian-Ehrlicher But I don't know, how to edit it.

[rktech]

I have rewritten half of my project to solve the problem:
myserver.h

#ifndef MYSERVER_H
#define MYSERVER_H
#include <QStringList>
#include <QTcpServer>
#include <QDateTime>
class MyServer : public QTcpServer
{
    Q_OBJECT

public:
    MyServer(QObject *parent = nullptr);

protected:
    void incomingConnection(qintptr socketDescriptor) override;

private:
    QStringList fortunes;
};

#endif // MYSERVER_H

myserver.cpp

#include "myserver.h"
#include "pool.h"
Pool p;

MyServer::MyServer(QObject *parent)
    : QTcpServer(parent)
{
    p.start();
}

void MyServer::incomingConnection(qintptr socketDescriptor)
{
QDateTime qdt;
p.add(socketDescriptor,qdt.time());
}

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(int socketDescriptor, 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) {
            if(y.s==nullptr){
                qDebug()<<"empty";
                continue;
            }
            y.s->write("test");
            y.s->flush();
        }
        qet.restart();
    }
}
}
void Pool::add(int socketDescriptor, QTime qdt){
QTcpSocket* s = new QTcpSocket;
s->setSocketDescriptor(socketDescriptor);
s->write("1\n");
conn c;
c.s=s;
c.qdt=qdt;
x.append(c);
}

But I have still the same error:

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

What's wrong?

[SGaist]

Because your add method is called in the thread of the tcp server.

As I already told you, the socket creation must happen in the run function.

[rktech]

@SGaist I have solved it. I am creating a list of descriptors in add() method and then rewriting it like this:
pool.cpp

void Pool::run()
{
QElapsedTimer qet;
qet.start();
while (true) {
    if(!d.empty()){
        qDebug()<<"rewriting";
        for (int i = 0; i<d.size();i++) {
            desc des = d[i];
            conn con;
            QTcpSocket* soc = new QTcpSocket;
            soc->setSocketDescriptor(des.descriptor);
            con.s=soc;
            con.qdt=des.qt;
            d.removeAt(i);
            x.append(con);
        }
        qDebug()<<"done";
    }
    if(qet.elapsed()>=5000){
        foreach (conn y, x) {
            if(!y.s->isOpen()){
                qDebug()<<"empty";
                continue;
            }
            y.s->write("test");
            qDebug()<<"l";
            y.s->flush();
        }
        qet.restart();
    }
}
}
void Pool::add(int socketDescriptor, QTime qdt){
desc de;
de.descriptor=socketDescriptor;
de.qt=qdt;
d.append(de);
}

definitions of structs and lists in pool.h:

  struct conn{
        QTcpSocket *s;
        QTime qdt;
    };
    struct desc{
        qintptr descriptor;
        QTime qt;
    };
    QList<conn> x;
    QList<desc> d;

[SGaist]

You are missing one important thing: you are accessing a resource from two different threads. You should protect its access accordingly.

[rktech]

@SGaist In my last code it is fixed, right? If no, how to protect it correctly?

[SGaist]

When using a new technology it's always a good idea to start by reading the documentation.

[rktech]

@SGaist I have read it, but I didn't catch what should I edit in my code.

[SGaist]

Did you read the Synchronizing Threads chapter linked in it ?