CODEWITHSUNDEEP
c++qttcp
Eumcoz
Eumcoz

Reputation: 2458

QTcpSocket / QTcpServer memory management / server crash

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*)));
}

`

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

`

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

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

   emit sendInfo(socket, headerInfo);
}

`

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

`

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;
 }

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.

Upvotes: 3

Views: 3208

Answers (2)

Gilco
Gilco

Reputation: 1336

I have the same problem!

close() suppose to be as de-constructor of the object. (QT manual QTcpSocket::~QTcpSocket()) There for I suggest to do an experiment: close a socket, and try to re open it. If it fails, it means the socket Object was destroyed, if not means the object should be deletelater()..

In my case the connection is closed by the client, and there for disconnect() SIGNAL is invoked and it trigger the correspond method to your discardClient() SLOT, where I deletelater() the socket. When I stress test it, it usually crash when I bombard it with 600-800 connection simultaneously on an I5 laptop dual core. it crash every 5 times on average.

Other wise it doesn't.

Happy to discuss it further.

Gil

Upvotes: 2

scai
scai

Reputation: 21509

You should call deleteLater() on your client socket:

connect(socket, SIGNAL(disconnected()),
        socket, SLOT(deleteLater()));

Upvotes: 1

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