Crash of the Server Application

Hi,

When I connect with the Server Application I receive the Crash Error on the line:

Code:

---

if( !socket->setSocketDescriptor( m_descriptor ) )

---

Please run the project "ServerTimer" than run "ViewerServerTimer" and click the button "Connect"

ServerTimer.pro

Code:

---

QT       += core
QT       += network
QT       -= gui
 
TARGET = ServerTimer
CONFIG   += console
CONFIG   -= app_bundle
 
TEMPLATE = app
 
 
SOURCES += main.cpp \
    server.cpp \
    serverthread.cpp
 
HEADERS += \
    server.h \
    serverthread.h

---

server.h

Code:

---

#ifndef SERVER_H
#define SERVER_H
 
#include <QTcpServer>
#include "serverthread.h"
 
class Server : public QTcpServer
{
public:
    Server();
 
protected:
    void incomingConnection(int descriptor);
 
private:
    ServerThread *thread;
};
 
#endif // SERVER_H

---

server.cpp

Code:

---

#include "server.h"
 
Server::Server() : QTcpServer()
{
}
 
void Server::incomingConnection( int descriptor )
{
    thread = new ServerThread( descriptor, this );
 
    connect( thread, SIGNAL(finished()), thread, SLOT(deleteLater()) );
    thread->start();
}

---

serverthread.h

Code:

---

#ifndef SERVERTHREAD_H
#define SERVERTHREAD_H
 
#include <QThread>
#include <QTimer>
#include <QTcpSocket>
 
class ServerThread : public QThread
{
public:
    ServerThread( int descriptor, QObject *parent );
 
    void run();
 
public slots:
    void sendData();
 
private:
    int m_descriptor;
 
private:
    QTimer *timer;
    QTcpSocket *socket;
};
 
#endif // SERVERTHREAD_H

---

serverthread.cpp

Code:

---

#include "serverthread.h"
 
ServerThread::ServerThread( int descriptor, QObject *parent ) : QThread( parent )
{
    m_descriptor = descriptor;
}
 
void ServerThread::run()
{
    if( !socket->setSocketDescriptor( m_descriptor ) )
    {
        qDebug( "Socket error!" );
        return;
    }
 
    timer = new QTimer;
    connect(timer, SIGNAL(timeout()), this, SLOT(sendData()));
    timer->start(1000);
}
 
void ServerThread::sendData() {
    //socket->write( "data" );
}

---

main.cpp

Code:

---

#include <QCoreApplication>
#include "server.h"
 
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
 
    Server server;
    if( !server.listen( QHostAddress::Any, 1234 ) )
    {
        qCritical( "Cannot listen to port 1234." );
        return 1;
    }
 
    return a.exec();
}

---

Thank you

Please, download and run my application. It's very important for me. Please, help me. I don't know where the mistake.

The member variable 'socket' is never initialised to point a QTcpSocket allocated in free store. It is an invalid pointer when you try to use it in run().


Can I suggest you develop the habit of always initialising pointer member variables to 0 or a valid pointer in the class constructor initialisation list or body. A zero value in a pointer is immediately obvious on your debugger where the random value that might otherwise be there is not.

Something like:

Code:

---

ServerThread::ServerThread( int descriptor, QObject *parent ):
    QThread( parent ),  m_descriptor( descriptor ), timer( 0 ), socket( 0 )
{
}

---

or

Code:

---

ServerThread::ServerThread( int descriptor, QObject *parent ):
    QThread( parent )
{
    m_descriptor = descriptor;
    timer = 0;
    socket = 0;
}

---

You do not need threads in this example.

Thank you!

I wrote it:

Code:

---

void ServerThread::run()
{
    socket = new QTcpSocket;
    ....
}

---

Quote:

---

You do not need threads in this example.

---

I will have the many clients.

Output:

Quote:

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QObject: Cannot create children for a parent that is in a different thread.
(Parent is QThread(0x547258), parent's thread is QThread(0x5416a8), current thre
ad is QThread(0x547258)
Object::connect: No such slot QThread::sendData() in ../ServerTimer/serverthread
.cpp:20

---

Quote:

---

I will have the many clients.

---

That still does not require threads. If the typical response to a connection is short then adding threads probably complicate matters for no benefit.

Quote:

---

QObject: Cannot create children for a parent that is in a different thread.
(Parent is QThread(0x547258), parent's thread is QThread(0x5416a8), current thread is QThread(0x547258)
Object::connect: No such slot QThread::sendData() in ../ServerTimer/serverthread.cpp:20

---

This is one of those complications.

Consult the Fortune Server Example and the Threaded Fortune Server examples in Assistant.

Quote:

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Originally Posted by ChrisW67

Consult the Fortune Server Example and the Threaded Fortune Server examples in Assistant.

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Thank you. I need to study about threads:
- You’re doing it wrong…
- QThreads General Usage

I found the solution for my task: C++ Qt 70 Advanced Asynchronous QTcpServer with QThreadPool