QSocketNotifier: Can only be used with threads started with QThread error

Question

I'm trying to use QLocalServer as an ipc solution. The version of qt is 4.6

This is my main.cpp:

int main(int argc, const char*argv[]) {  
  QServer test();

  while (true) {
  }
}

This is my QServer class:

class QServer : public QObject
{
 Q_OBJECT

public :
 QServer ();

  virtual ~QServer();

private :  
  QLocalServer* m_server;
  QLocalSocket* m_connection;


private slots:
  void socket_new_connection();
};

QServer::QServer()
{
  m_server = new QLocalServer(this);
  if (!m_server->listen("DLSERVER")) {
    qDebug() << "Testing";
    qDebug() << "Not able to start the server";
    qDebug() << m_server->errorString();
    qDebug() << "Server is " << m_server->isListening();
  }

  connect(m_server, SIGNAL(newConnection()),
          this, SLOT(socket_new_connection()));
}

void
QServer::socket_new_connection()
{
  m_connection = m_server->nextPendingConnection();

  connect(clientConnection, SIGNAL(readyRead()),
          this, SLOT(newData(clientConnection)));
}

This all compiles, however at runtime, when I try to connect newConnection(), I get a QSocketNotifier: Can only be used with threads started with QThread error.

I have tried wrapping this whole thing in a QThread, but I still got the same error.

Can anybody explain what I'm doing wrong or why there's even a thread involved?

Answer 1

The error message is misleading. You need a Qt event loop in order to use QSocketNotifier. The appropriate way to do that in your application is to create a QApplication (or if you don't want any graphical stuff, a QCoreApplication). Your main should look like:

int main(int argc, char** argv)
{
    QCoreApplication app(argc, argv);
    QServer test();
    app.exec();
    return 0;
}

QCoreApplication::exec() starts the event loop (which replaces your while (true) {} loop).