QTcpSocket/QTcpServer on a heavy load server

[Eumcoz]

Hello, I am designing and making a server that should be able to handle about 100+ hits per second. The information I am getting from the server is just the HTTP header. Based on the information from the header, it will query a database(different thread) for some information and send the final information back to the QTcpServer which create an output string, and send back a HTTP Response. I am having a big problem with this that I cannot debug. My code look similar to this:

TCPInterface::TCPInterface(QObject *parent): QTcpServer(parent)
{
    //start listening for tcp traffic on port 80
    listen(QHostAddress::Any, 80);
 
    connect(this,SIGNAL(sendInfo(QTcpSocket*, QString *)), databaseThread, SLOT(recieveInfo(QTcpSocket*, QString*)));
    connect(databaseThread, SIGNAL(sendToTCPSend(QTcpSocket *, QString *)), this, SLOT(TCPSend(QTcpSocket*, QString*)));
 
}

TCPInterface::TCPInterface(QObject *parent): QTcpServer(parent)
{
    //start listening for tcp traffic on port 80
    listen(QHostAddress::Any, 80);

    connect(this,SIGNAL(sendInfo(QTcpSocket*, QString *)), databaseThread, SLOT(recieveInfo(QTcpSocket*, QString*)));
    connect(databaseThread, SIGNAL(sendToTCPSend(QTcpSocket *, QString *)), this, SLOT(TCPSend(QTcpSocket*, QString*)));

}

To copy to clipboard, switch view to plain text mode 

void TCPInterface::incomingConnection(int socket)
{
    QTcpSocket *s = new QTcpSocket(this);
 
    connect(s, SIGNAL(readyRead()), this, SLOT(readClient()));
//    connect(s, SIGNAL(disconnected()), this, SLOT(discardClient()));
 
    s->setSocketDescriptor(socket);
}

void TCPInterface::incomingConnection(int socket)
{
    QTcpSocket *s = new QTcpSocket(this);

    connect(s, SIGNAL(readyRead()), this, SLOT(readClient()));
//    connect(s, SIGNAL(disconnected()), this, SLOT(discardClient()));

    s->setSocketDescriptor(socket);
}

To copy to clipboard, switch view to plain text mode 

//void TCPInterface::discardClient()
//{
//    QTcpSocket* socket = (QTcpSocket*)sender();
//    socket->deleteLater();
//}

//void TCPInterface::discardClient()
//{
//    QTcpSocket* socket = (QTcpSocket*)sender();
//    socket->deleteLater();
//}

To copy to clipboard, switch view to plain text mode 

void TCPInterface::readClient()
{
    QTcpSocket* socket = (QTcpSocket*)sender();
 
    QString header;
    while(socket->canReadLine())
    {
        header += socket->readLine();
    }
 
    emit sendInfo(socket, headerInfo);
}

void TCPInterface::readClient()
{
    QTcpSocket* socket = (QTcpSocket*)sender();

    QString header;
    while(socket->canReadLine())
    {
        header += socket->readLine();
    }

    emit sendInfo(socket, headerInfo);
}

To copy to clipboard, switch view to plain text mode 

void databaseThread::recieveInfo(QTcpSocket* socket, QString* headerInfo)
{
   QString*outputInfo = getDatabaseInfo(headerInfo);
   emit sendToTCPSend(socket, outputInfo);
}

void databaseThread::recieveInfo(QTcpSocket* socket, QString* headerInfo)
{
   QString*outputInfo = getDatabaseInfo(headerInfo);
   emit sendToTCPSend(socket, outputInfo);
}

To copy to clipboard, switch view to plain text mode 

void TCPInterface::TCPSend(QTcpSocket* socket, QString* outputInfo);
{
    QString response = "HTTP/1.0 200 Ok\r\n";
    response += "Content-Type: text/html; charset=\"utf-8\"\r\n";
    response += "\r\n" + *outputInfo + "\n";
 
    if(socket->isWritable() && socket->isOpen())
    {
         socket->write(response.toAscii());
    }
    //socket->disconnectFromHost();
    socket->close();
    delete headerInfo;
}

void TCPInterface::TCPSend(QTcpSocket* socket, QString* outputInfo);
{
    QString response = "HTTP/1.0 200 Ok\r\n";
    response += "Content-Type: text/html; charset=\"utf-8\"\r\n";
    response += "\r\n" + *outputInfo + "\n";
    
    if(socket->isWritable() && socket->isOpen())
    {
         socket->write(response.toAscii());
    }
    //socket->disconnectFromHost();
    socket->close();
    delete headerInfo;
}

To copy to clipboard, switch view to plain text mode 

I having one main problem which I have an idea what it is, but cannot find a solution to fix it.

My problem is my memory is constantly increasing as I get more hits. I am sure the cause of this is my QTcpSockets are never being deleted, since I am just closing them. However when I don't use close, and use disconnectFromHost and disconnected/discardClient slot/signal my server will crash with heavy traffic(no message or anything so I am not sure of the exact reason of the crash). Has anyone run into this problem before? Any ideas at all.

[StrikeByte]

I think the problem is that you try to delete the socket when it is not ready sending/receiving data
connect to the signal disconnected() of the QTcpSocket use disconnectFromHost() to initiate the disconnect.
then when the signal is fired disconnect the signal and kill the QTcpSocket

[spirit]

Side note to StrikeByte's. Kill them using QObject::deleteLater.

[Eumcoz]

Sorry, I think I made everything kind of confusing. I have tried using deleteLater.

I have tried:

void TCPInterface::discardClient()
{
   QTcpSocket* socket = (QTcpSocket*)sender();
   socket->deleteLater();
}

void TCPInterface::discardClient()
{
   QTcpSocket* socket = (QTcpSocket*)sender();
   socket->deleteLater();
}

To copy to clipboard, switch view to plain text mode 

Which is connected to the signal disconnected. And when doing this I call disconnectFromHost() instead of close() in my last function.

When using this method, my program will crash. So i am assuming something weird is happening when I delete the socket, but I have no clue as to what it is.

Also another note. It does not crash every time on delete. I am stress testing my server with a script that is constantly sending me get requests, and It will crash anywhere between the 2nd and 200th packet. When I see a lower amount of traffic going into the server, I have no problem with the server staying up. Any ideas what the cause of this problem could be?

[spirit]

As I understand, you call "deleteLater" then "disconnectFromHost"? You should try to call "disconnectFromHost" and then "deleteLater".