Problem with QTcpSocket in QThread

[Raistlin]

When I have a QThread which is responsible for handling a connection for a client application, I seem to have a strange problem. When I allocate a QTcpSocket in the constructor of the QThread, I do not succeed to open a connection afterwards in run(). When I do the allocation in run(), no problems arises. Any idea what might cause this ?

Header file :

#ifndef CONNECTIONTHREAD_H
#define CONNECTIONTHREAD_H
 
#include <QThread>
#include <QString>
 
class QTcpSocket;
 
class ConnectionThread : public QThread
{
	Q_OBJECT
 
public:
	ConnectionThread(QObject *parent);
	~ConnectionThread();
 
	bool isConnected() const;
 
signals:
	void connectionEstablished();
 
public slots:
	//void setHostInfo(QString& hostName, int portNumber);
 
private:
	void run();
 
	QTcpSocket* tcpSocket_;
	bool connected_;
	QString hostName_;
	int portNumber_;
 
};
 
#endif // CONNECTIONTHREAD_H

#ifndef CONNECTIONTHREAD_H
#define CONNECTIONTHREAD_H

#include <QThread>
#include <QString>

class QTcpSocket;

class ConnectionThread : public QThread
{
	Q_OBJECT

public:
	ConnectionThread(QObject *parent);
	~ConnectionThread();

	bool isConnected() const;

signals:
	void connectionEstablished();

public slots:
	//void setHostInfo(QString& hostName, int portNumber);

private:
	void run();

	QTcpSocket* tcpSocket_;
	bool connected_;
	QString hostName_;
	int portNumber_;
	
};

#endif // CONNECTIONTHREAD_H

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This works :

#include "connectionthread.h"
#include <QTcpSocket>
 
ConnectionThread::ConnectionThread(QObject *parent)
	: QThread(parent)
{
	connected_ = false;
 
	hostName_ = "localhost";
	portNumber_ = 4974;
 
	connect(this, SIGNAL(connectionEstablished()), parent, SLOT(connectionEstablished()));
}
 
ConnectionThread::~ConnectionThread()
{	
}
 
bool ConnectionThread::isConnected() const
{
	return connected_;
}
 
void ConnectionThread::run()
{
	tcpSocket_ = new QTcpSocket(this);
 
	tcpSocket_->abort();
	tcpSocket_->connectToHost(hostName_, portNumber_);
 
	if (tcpSocket_->waitForConnected(1000))
		emit connectionEstablished();
 
	exec();	
}

#include "connectionthread.h"
#include <QTcpSocket>

ConnectionThread::ConnectionThread(QObject *parent)
	: QThread(parent)
{
	connected_ = false;

	hostName_ = "localhost";
	portNumber_ = 4974;

	connect(this, SIGNAL(connectionEstablished()), parent, SLOT(connectionEstablished()));
}

ConnectionThread::~ConnectionThread()
{	
}

bool ConnectionThread::isConnected() const
{
	return connected_;
}

void ConnectionThread::run()
{
	tcpSocket_ = new QTcpSocket(this);

	tcpSocket_->abort();
	tcpSocket_->connectToHost(hostName_, portNumber_);

	if (tcpSocket_->waitForConnected(1000))
		emit connectionEstablished();

	exec();	
}

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This does not :

#include "connectionthread.h"
#include <QTcpSocket>
 
ConnectionThread::ConnectionThread(QObject *parent)
	: QThread(parent)
{
	connected_ = false;
 
	tcpSocket_ = new QTcpSocket(this);
 
	hostName_ = "localhost";
	portNumber_ = 4974;
 
	connect(this, SIGNAL(connectionEstablished()), parent, SLOT(connectionEstablished()));
}
 
ConnectionThread::~ConnectionThread()
{	
}
 
bool ConnectionThread::isConnected() const
{
	return connected_;
}
 
void ConnectionThread::run()
{
	tcpSocket_->abort();
	tcpSocket_->connectToHost(hostName_, portNumber_);
 
	if (tcpSocket_->waitForConnected(1000))
		emit connectionEstablished();
 
	exec();	
}

#include "connectionthread.h"
#include <QTcpSocket>

ConnectionThread::ConnectionThread(QObject *parent)
	: QThread(parent)
{
	connected_ = false;

	tcpSocket_ = new QTcpSocket(this);

	hostName_ = "localhost";
	portNumber_ = 4974;

	connect(this, SIGNAL(connectionEstablished()), parent, SLOT(connectionEstablished()));
}

ConnectionThread::~ConnectionThread()
{	
}

bool ConnectionThread::isConnected() const
{
	return connected_;
}

void ConnectionThread::run()
{
	tcpSocket_->abort();
	tcpSocket_->connectToHost(hostName_, portNumber_);

	if (tcpSocket_->waitForConnected(1000))
		emit connectionEstablished();

	exec();	
}

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[marcel]

I think the socket is created in the parent thread's context.
Try calling connectionThread->moveToThread(connectionThread) from wherever you start the connection thread, but after it has started.

[jpn]

Are you sure you need a separate thread?

http://www.qtcentre.org/forum/f-qt-p...cket-4242.html

[Raistlin]

Are you sure you need a separate thread?

http://www.qtcentre.org/forum/f-qt-p...cket-4242.html

It might be a similar title, but I did not see the link at first. I think more trivial questions have been asked more than one time in the past

[jpn]

If you would have bothered reading the thread, you would know that

• QThread constructor and QThread::run() are executed in different threads
• QThread object itself lives in the thread where it was created
• You shouldn't pass "this" as parent in QThread::run() because "this" lives in another thread

[marcel]

Kids these days... They don't read anything, just want to give them the code.

[Raistlin]

I did not find the link first, so I was not aware of this. I understood the issue after reading the thread, and did not ask any additional things. So what makes you conclude I do not read the info which is given to me?

Just for the record, I am certainly not a kid, and spent a lot of time resolving other issues in Qt without asking questions. I never asked for any code, I just raised a question about an issue I did not understand.

[jpn]

Looks like it was me who misunderstood your answer. I thought you meant that it was similar but something more trivial that was solved in the linked thread. My apologies for that. No hard feelings.

[Raistlin]

Indeed a misunderstanding, I just meant people ask the same question twice in this forum sometimes, although the issue is easier than this problem.

No hard feelings back .