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

[Dooham]

Hello,
I am having this trouble since two days ago and I am not sure how solve this error.
I made a code for a server that can handle multiple connections, my goal is to read in the server messages from a device in the serialPort, send this messages to all the clients connected to my server and, from the clients can send message to the device. To do this, I saw that I need programming a Thread that can handle the multiple connections.
I made this code:

myserver.cpp

#include "myserver.h"

MyServer::MyServer(QObject *parent) : QTcpServer (parent)
{

}

void MyServer::startServer()
{
    if(!this->listen(QHostAddress::Any, 9999)){
qDebug()<<"Server not started";
    }else {
qDebug()<<"Server listening";
    }
}

void MyServer::startSerialPort()
{
   mipuerto2 = new MySerialPort;
   connect(mipuerto2, SIGNAL(msgChanged()), this, SLOT(getMens()));
   mipuerto2->openSerialPort();
}

void MyServer::getMens()
{
    arr2=mipuerto2->getMensaje();

    emit mensChanged(&arr2);
}

void MyServer::sendMens(QByteArray *arraySend)
{
mipuerto2->writeMsg(*arraySend);
}


void MyServer::incomingConnection(int socketDescriptor)
{

qDebug()<<socketDescriptor<<"Connecting... ";
MyThread *thread=new MyThread(socketDescriptor, this);
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(this, SIGNAL(mensChanged(QByteArray * )), thread, SLOT(getMsg(QByteArray *)));
connect(thread, SIGNAL(mensajeEnviar(QByteArray * )), this,SLOT(sendMens(QByteArray * )));
thread->start();

}

mythread.cpp

#include "mythread.h"

MyThread::MyThread(int ID, QObject *parent) : QThread(parent)
{
    this->socketDescriptor=ID;

}

void MyThread::run()
{
//thread start here
    qDebug()<<socketDescriptor<< " Starting thread";
    socket = new QTcpSocket();
    if(!socket->setSocketDescriptor(this->socketDescriptor)){
        emit error(socket->error());

    }

    connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()), Qt::DirectConnection);
    connect(socket, SIGNAL(disconnected()), this, SLOT(disconnected()), Qt::DirectConnection);

    qDebug() << socketDescriptor<< " Client Connect";



    exec();
}

void MyThread::readyRead()
{

    msgSend="";
   // socket->waitForReadyRead(100);
    msgSend=socket->readAll();

        qDebug()<<msgSend.toHex();
emit mensajeEnviar(&msgSend);
}

void MyThread::disconnected()
{
    qDebug() << socketDescriptor<< " Disconnected";

    socket->deleteLater();

    exit(0);
}

void MyThread::getMsg(QByteArray * array)
{

    socket->write(*array);
    socket->waitForBytesWritten(3000);

}

So everytime that, the serial port read a new group of messages, emit a signal to send them.
With this code, I can read the messages from the client and send message (I haven't probe with more connections yet), but when I read I get this error in the server console:

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

This error appears every time that a new messages arrives to the server from the serial port. Does anyone know what I can do to solve it?
Thanks.

[Dooham]

@Dooham I also have this error: QObject: Cannot create children for a parent that is in a different thread.
(Parent is QNativeSocketEngine(0x52fbc8), parent's thread is MyThread(0x5322f0), current thread is QThread(0x514de0)

[CP71]

@Dooham

Check where you create objects in your thread, beware they are created in run slot.

See
https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

[Dooham]

@CP71 Thaks for your answer. I thing that all the QObects that I created are in the run slot. I just created the QTCPSocket and it is in the reun slot in the third line. When I read this article, I tried to use the movetoThread(this) but I didnt work.

[CP71]

@Dooham
You are welcome!
Where do you declare and use QNativeSocketEngine object?
I think I don’t see it in your code?

[Dooham]

@CP71 To be honest, I dont know where is declare. First of all I dont know what is exactly it. I got an example of multithreatings server and adapte it to my trouble. Now, I am trying to change the QTcpSocket from a declare variable to a local variable (I have read that this could solve the problem), but I not sure about how to adapt the function getMsg to read my socket.

[CP71]

@Dooham
sorry!
I believe is a my stupid question :(
i think it is created when you create a socket

https://code.woboq.org/kde/qt4/src/network/socket/qnativesocketengine.cpp.html#_ZN19QNativeSocketEngineD1Ev

[Dooham]

@CP71 Yeah, seeing that socumntation, I think you are right, but I dont understand why appears that error. I wrote the same code that the example that I saw, and that worked , but when I adapted to my case it failed.

[CP71]

@Dooham
I have a dubt.
Maybe I’m beeing wrong but I think that your server musn't create TcpSocket but it should waiting a new connection:

In your server
QObject::connect( this, SIGNAL(newConnection()), this, SLOT(newConnection()) );

In newConnection:

//////////////////////////////////////////////////////////////////////////////////////
///
void MyServer::newConnection()
{
QTcpSocket *socket = server->nextPendingConnection();
if ( socket )
{
… doing your procedure
}
}

I don’t see where incomingConnection is called.

But maybe it is already so.

[Dooham]

@CP71 I think that is not neccesary,because of the function incomingConnection. When I see this Code I had a similar doubt, but this function is a virtual function of QtcpServer that is called when a newConnection Signal appears. In this code,I just edit the function a bit.
Maybe the trouble would be that I didnt called the write function from the run, and this could be problematic. In a while, I will try to rewrite the code un order to call the function that write the message from the run

[SGaist]

Hi,

Are you trying to implement a threaded server ? If so, you can take a look at the threaded fortune server example.

[Dooham]

@SGaist Thanks you, I think this example support my idea, that the trouble is that I dont call the function that write the message from the run function but from a external slot that, in theory dont interact with this routine. Am I right?
On the other hand, do you know any method to initialize the serial port from the thread just one time (at the begginning of the program)? I have been thinking during the last hour but I dont archive any progress
Thanks again

[SGaist]

What is your exact use of QSerialPort ?

[Dooham]

@SGaist I read the continuous message that a device (a Pixhawk). Every thing that I receive a package of message ( the serial port send me package of message) in form of QByteArray I send it to a client that can decode them

[Dooham]

@Dooham That didn't work, I dont know what is the trouble, I have seen that there are two different QThread ID, and that is probably the cause of the issue:

As you can see, I got the adress of the Thread that I generate with the incomingConnection but, in some point I create an Object that its parent is other QThread.
I dont know what to do.

[CP71]

@Dooham
I think you don't call addPendingConnection or it seems so

[Dooham]

@Dooham @CP71 @SGaist Finally I could "solve" the trouble that I had. I had to create other class that has the QTcpSocket, and create that class inside the run function of the thread as a local variable. However I found some trouble with the write method, I dont know how to solve it. The trouble is that dont read the client (with the previous code I could read, the messaged from the client). This is my code:

myserver.cpp

MyServer::MyServer(QObject *parent) : QTcpServer (parent)
{

}

void MyServer::startServer()
{
    if(!this->listen(QHostAddress::Any, 9999)){
qDebug()<<"Server not started";
    }else {
qDebug()<<"Server listening";
    }
}

void MyServer::startSerialPort()
{
   mipuerto2 = new MySerialPort;
  connect(mipuerto2, SIGNAL(msgChanged(QByteArray*)), this, SLOT(getMens(QByteArray*)));
   mipuerto2->openSerialPort();
}

void MyServer::getMens(QByteArray*array)
{



    emit mensChanged(array);
}

void MyServer::sendMens(QByteArray *arraySend)
{
mipuerto2->writeMsg(*arraySend);
}


void MyServer::incomingConnection(int socketDescriptor)
{

qDebug()<<socketDescriptor<<"Connecting... ";
MyThread *thread=new MyThread(socketDescriptor, this);

qDebug()<<thread;
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(this, SIGNAL(mensChanged(QByteArray * )), thread, SLOT(getMsg(QByteArray *)));
connect(thread, SIGNAL(mensajeEnviar(QByteArray * )), this,SLOT(sendMens(QByteArray * )));



thread->start();

}

myserialport.cpp

#include "myserialport.h"
#include <QObject>
#include <QtSerialPort/QSerialPort>
#include <QDebug>


MySerialPort::MySerialPort()
{
    serial = new QSerialPort(this);
    data= "";

    connect(serial, SIGNAL(readyRead()), this, SLOT(readData()));
    openSerialPort();

}

void MySerialPort::openSerialPort()
{
    serial->setPortName("COM4");
    //serial->setBaudRate(QSerialPort::Baud9600);
    serial->setBaudRate(QSerialPort::Baud115200);
    serial->setDataBits(QSerialPort::Data8);
    serial->setParity(QSerialPort::NoParity);
    serial->setStopBits(QSerialPort::OneStop);
    serial->setFlowControl(QSerialPort::NoFlowControl);
    serial->open(QIODevice::ReadWrite);


}

void MySerialPort::closeSerialPort()
{
    if(serial->isOpen()){
        serial->close();
    }
}

void MySerialPort::readData()
{

   data = serial->readAll();
    dataAux=data.toHex();
    emit msgChanged(&data);

}

QByteArray MySerialPort::getMensaje()
{
    return data;
}

void MySerialPort::writeMsg(QByteArray datos)
{

    serial->write(datos);

}

mythread.cpp

#include "mythread.h"
#include "mysocket.h"
MyThread::MyThread(int ID, QObject *parent) : QThread(parent)
{
    this->socketDescriptor=ID;


}

void MyThread::run()
{
    qDebug()<<socketDescriptor<< " Starting thread";
    MySocket socket2(this->socketDescriptor);
    //Revisar mas tarde
    /*if(!socket2.setSocketDescriptor(this->socketDescriptor)){
        emit error(socket->error());

    }*/

    /*connect(socket2, SIGNAL(readyRead()), this, SLOT(readyRead()), Qt::DirectConnection);*/


    connect(this, SIGNAL(mensajeRecibido(QByteArray*)), &socket2, SLOT(getMsg(QByteArray*)));
    connect(&socket2, SIGNAL(disconnected()), this, SLOT(disconnected()));
    connect(&socket2, SIGNAL(mensajeEnviarSocket(QByteArray*)), this, SLOT(readyRead(QByteArray*)));
    qDebug() << socketDescriptor<< " Client Connect";



    exec();
}

void MyThread::readyRead(QByteArray*arraySent)
{


    qDebug()<<arraySent->toHex();
    emit mensajeEnviar(arraySent);
}

void MyThread::disconnected()
{
    qDebug() << socketDescriptor<< " Disconnected";

    //socket->deleteLater();

    exit(0);
}

void MyThread::getMsg(QByteArray * array)
{
    emit mensajeRecibido(array);


}

mysocket.cpp (This is the new class)

#include "mysocket.h"

MySocket::MySocket(int socketDescriptor)
{
socket= new QTcpSocket;
socket->setSocketDescriptor(socketDescriptor);
connect(this, SIGNAL(disconnected()), this, SLOT(desconexion()));
connect(this, SIGNAL(readyRead()), this, SLOT(leerMsg()));
qDebug()<<"Hola";
}

void MySocket::leerMsg()
{
    msgSend="";
    // socket->waitForReadyRead(100);
    msgSend=socket->readAll();

    qDebug()<<msgSend.toHex();
    emit mensajeEnviarSocket(&msgSend);
}

void MySocket::desconexion()
{
   socket->deleteLater();
}

void MySocket::getMsg(QByteArray *array)
{

    arr=*array;
    //qDebug()<<arr;
   // qDebug()<<"server a thread";
    socket->write(arr);
    socket->flush();
    socket->waitForBytesWritten(3000);
}

mysocket.h

#ifndef MYSOCKET_H
#define MYSOCKET_H

#include <QObject>
#include <QTcpSocket>

class MySocket:public QTcpSocket
{
    Q_OBJECT
public:
    MySocket(int socketDescriptor);
signals:
    void mensajeEnviarSocket(QByteArray *arraySend);

public slots:
    void leerMsg();
    void desconexion();
    void getMsg(QByteArray *array);
private:
    QTcpSocket *socket;
    QByteArray arr;
    QByteArray msgSend;
};

#endif // MYSOCKET_H

With this code, I can read the serial port and sending to the client without troubles (I also tried with the telnet command and two connections, and this could with them). But I can read the messages sent. Another trouble that I saw, is that, when I disconect the client, in the server appears the following error: QAbstractSocket::waitForBytesWritten() is not allowed in UnconnectedState

Does anyone knows how I can solve this issues?
Thanks for your help.

[Dooham]

@Dooham I have solved the trouble with waitforBytesWritten with the function: waitforConnected() that return true if is connected so, I just read if the socket is connected. But I cant read yet.

[CP71]

@Dooham
Hi,
I quickly watch your code.
I see a thing that is a bit dangerous or I think so, you emit a pointer and not a copy of data without thread synchronization, don’t you?

[CP71]

@Dooham
And more,
I think you must call addPendingConnection in your incomingConnection

void MyServer::incomingConnection(int socketDescriptor)
{

…

addPendingConnection( thread→GetQTcpSocketPointer() )

thread->start();

}