private:
QString hostName;
quint16 port;
QMutex mutex;
QWaitCondition cond;
bool quit;
public:
FortuneThread(QObject *parent = 0);
~FortuneThread();

void requestNewFortune(const QString &hostName, qint16 port);
void run() override;

signals:
void newFortune(const QString &fortune);
void error(int socketError, const QString &message);
};

and this is my .cpp file:
#include <QtCore>
#include <QtNetwork>

#include "FortuneThread.h"

using namespace Qt;
FortuneThread::FortuneThread(QObject *parent): QThread(parent), quit(false)
{
}

FortuneThread::~FortuneThread()
{
mutex.lock();
quit = true;
cond.wakeOne();
mutex.unlock();
wait();
}

void FortuneThread::requestNewFortune(const QString &hostName, qint16 port)
{
QMutexLocker locker(&mutex);
this->hostName = hostName;
this->port = port;
if (!isRunning())
start();
else
cond.wakeOne();
}

void FortuneThread::run()
{
mutex.lock();
QString serverName = hostName;
qint16 serverPort = port;
mutex.unlock();

while (!quit)
{
	const int Timeout = 5 * 1000;
	QTcpSocket socket;
	socket.connectToHost(serverName, serverPort);

	if (!socket.waitForConnected(Timeout))
	{
		emit error(socket.error(), socket.errorString());
		return;
	}

	QDataStream in(&socket);
	in.setVersion(QDataStream::Qt_4_0);
	QString fortune;

	do
	{
		if (!socket.waitForReadyRead(Timeout))
		{
			emit error(socket.error(), socket.errorString());
			return;
		}
		in.startTransaction();
		in >> fortune;
	} while (!in.commitTransaction());

	mutex.lock();
	emit newFortune(fortune);

	cond.wait(&mutex);
	serverName = hostName;
	serverPort = port;
	mutex.unlock();
}

}

you know, when I define QMutex or QmutexLocker, I get this error ??