unable to update label from another thread

Iam new to Qt programming.Qt 4.7.3 is using for the development.
We are developing a program to read from the multiple file(initially started with two) and display in to the Gui.File reading is doing from one thread and the read value is passing to the label in Gui thread.
Here the code.
fileread.cpp

Code:

#include "fileread.h"
#include "ui_fileread.h"
#include "filethread.h"
#include<QThread>
#include <QtGui>
#include<QLabel>
fileread::fileread(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::fileread)
{
    ui->setupUi(this);
 
}
 
fileread::~fileread()
{
    delete ui;
}
 
 
void fileread::on_pushButton_clicked()
{
 
    QString fname1="E:/QT/test1.txt";
    QString fname2="E:/QT/test3.txt";
 
 
    filethread fthread1(fname1),fthread2(fname2);
 
    QObject::connect(&fthread1, SIGNAL(setlabel(QString)),ui->label_2, SLOT(setText(QString)), Qt::QueuedConnection);
    QObject::connect(&fthread2, SIGNAL(setlabel(QString)),ui->label_3 , SLOT(setText(QString)), Qt::QueuedConnection);
 
    fthread1.start();
    fthread2.start();
 
    fthread1.wait();
    fthread2.wait();
 
}
 
 
filethread.cpp
 
filethread::filethread(QString text) : QThread()
{
 
    fname=text;
}
 
 
QMutex mutex;
void filethread::run()
{
    QFile fp(fname);
    if(fp.open(QIODevice::ReadOnly))
    {
        QDataStream in(&fp);
    }
        QTextStream in(&fp);
 
        QString line = in.readLine();
 
         while (!line.isNull())
        {
 
          mutex.lock();
          emit setlabel(line);
          sleep(1);
          qDebug()<<"Content from the file:"<<line;
          line = in.readLine();
          mutex.unlock();
 
        }
      }

Here what problem Iam facing is only last line from the file is displaying in the label.Other text from the file is not comming in the label.All line from the file should come in the label.File is reading properly,that I understood from qDebug function.I think Gui thread is get blocked because of that it is not comming for all line from file.
Iam in this problem for about three weeks...
Please help me..