Android : display bitmap setImageBitmap

In my application Android, I am trying to receive some image from a server with socket, but I can't display them with setImageBitmap(). I don't have any error, but my screen stay white. Here is my code :

public class CommunicateurAndroid implements Runnable {
    public CommunicateurAndroid(Socket s, ImageView img) {
        _imageV = img;
        try {
            _din = new DataInputStream(s.getInputStream());
            _dout = new DataOutputStream(s.getOutputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }
        new Thread(this).start();
    }

    public void run() {

        int length = 0;
        byte tmp;
        while (true) try {
            length = _din.readInt();
            byte tab[] = new byte[length];
            for (int i = 0; i < length; i++) {
                tmp = _din.readByte();
                tab[i] = tmp;
            }
            _image = BitmapFactory.decodeByteArray(tab, 0, tab.length);
            System.out.println("----------");
            if (_image != null) {
                _imageV.setImageBitmap(_image);
                System.out.println("TEST");
                Thread.sleep(5000);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public Bitmap get_image() {
        return _image;
    }

    private DataInputStream _din;
    private DataOutputStream _dout;
    private Bitmap _image;
    private ImageView _imageV;

}

I call the constructor with this line

new CommunicateurAndroid(_socket, (ImageView) findViewById(R.id.ImageView3_Left));

Can anybody help me?