Creating a QTcpSocket or a QTcpServer in a thread other than the main thread.

[jan]

where have you read that?

In Qt4 you can either:
* work with blocking I/O (not in the gui thread, as otherwise your app freezes til the I/O is over)
* work with non-blocking I/O: you need a QEventLoop running in your thread - you may use the main (i.e. gui) thread, but you do not have to.

HTH

Here is a sample code to illustrate the problem I have encountered. I made it as brief as possible. Hence, it is not going with the best practice. Please forgive me for that.

#include <QtNetwork/QTcpServer>
#include <QtCore/QThread>
#include <QtCore/QCoreApplication>
#include <iostream>
#include <assert.h>
 
class ServerThread : public QThread
{
	Q_OBJECT
 
public:
	ServerThread(QObject *ipParent)
		: QThread(ipParent)
		, mpServer(0)
	{}
 
	void run ()
	{
		mpServer = new QTcpServer();
		bool lbOk(connect(mpServer, SIGNAL(newConnection()),
				this, SLOT(onNewConnection())));
		assert(lbOk);
		mpServer->listen(QHostAddress::Any, 8888);
	}
 
private:
	QTcpServer* mpServer;
 
protected slots:
	void onNewConnection()
	{
		std::cout << "new connection!" << std::endl;
	}
};
 
int main(int argc, char *argv[])
{
	QCoreApplication a(argc, argv);
	ServerThread lrThread(0);
//	lrThread.start();
	lrThread.run();
	return a.exec();
}

#include <QtNetwork/QTcpServer>
#include <QtCore/QThread>
#include <QtCore/QCoreApplication>
#include <iostream>
#include <assert.h>

class ServerThread : public QThread
{
	Q_OBJECT

public:
	ServerThread(QObject *ipParent)
		: QThread(ipParent)
		, mpServer(0)
	{}

	void run ()
	{
		mpServer = new QTcpServer();
		bool lbOk(connect(mpServer, SIGNAL(newConnection()),
				this, SLOT(onNewConnection())));
		assert(lbOk);
		mpServer->listen(QHostAddress::Any, 8888);
	}

private:
	QTcpServer* mpServer;

protected slots:
	void onNewConnection()
	{
		std::cout << "new connection!" << std::endl;
	}
};

int main(int argc, char *argv[])
{
	QCoreApplication a(argc, argv);
	ServerThread lrThread(0);
//	lrThread.start();
	lrThread.run();
	return a.exec();
}

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It runs fine with expected outcome which print a message every time a connection is made.

However, if the line 40 is uncommented and line 41 commented, the ServerThread::onNewConnection() method is never called with connections made.

It stops working while the QTcpServer is not created on the main thread.