在线程中从内存中同时调用 Graphics.Draw 和 new Bitmap 需要很长时间

Question

Example1

public partial class Form1 : Form
{

    public Form1()
    {

        InitializeComponent();
        pro = new Thread(new ThreadStart(Producer));
        con = new Thread(new ThreadStart(Consumer));
    }
    private AutoResetEvent m_DataAvailableEvent = new AutoResetEvent(false);
    Queue<Bitmap> queue = new Queue<Bitmap>();
    Thread pro;
    Thread con;

    public void Producer()
    {
        MemoryStream[] ms = new MemoryStream[3];
        for (int y = 0; y < 3; y++)
        {
            StreamReader reader = new StreamReader("image" + (y + 1) + ".JPG");
            BinaryReader breader = new BinaryReader(reader.BaseStream);

            byte[] buffer = new byte[reader.BaseStream.Length];
            breader.Read(buffer, 0, buffer.Length);
            ms[y] = new MemoryStream(buffer);
        }
        while (true)
        {
            for (int x = 0; x < 3; x++)
            {
                Bitmap bmp = new Bitmap(ms[x]);
                queue.Enqueue(bmp);

                m_DataAvailableEvent.Set();
                Thread.Sleep(6);
            }
        }
    }
    public void Consumer()
    {
        Graphics g = pictureBox1.CreateGraphics();
        while (true)
        {
            m_DataAvailableEvent.WaitOne();
            Bitmap bmp = queue.Dequeue();
            if (bmp != null)
            {
                //  Bitmap bmp = new Bitmap(ms);
                g.DrawImage(bmp, new Point(0, 0));
                bmp.Dispose();

            }
        }

    }
    private void pictureBox1_Click(object sender, EventArgs e)
    {

        con.Start();
        pro.Start();

    }
}

When creating bitmap and drawing to picture box are in seperate thread then Bitmap bmp = new Bitmap(ms[x]) takes 45.591 millisecond and g.DrawImage(bmp,new Point(0,0)) takes 41.430 milisecond.

When I make a bitmap from memoryStream and draw it to picture box in one thread then Bitmap bmp = new Bitmap(ms[x]) takes 29.619 and g.DrawImage(bmp,new Point(0,0)) takes 35.540.

The code is for Example 2 is

public Form1()
{

    InitializeComponent();
    pro = new Thread(new ThreadStart(Producer));
    con = new Thread(new ThreadStart(Consumer));
}

private AutoResetEvent m_DataAvailableEvent = new AutoResetEvent(false);
Queue<MemoryStream> queue = new Queue<MemoryStream>();
Thread pro;
Thread con;

public void Producer()
{
    MemoryStream[] ms = new MemoryStream[3];
    for (int y = 0; y < 3; y++)
    {
        StreamReader reader = new StreamReader("image" + (y + 1) + ".JPG");
        BinaryReader breader = new BinaryReader(reader.BaseStream);

        byte[] buffer = new byte[reader.BaseStream.Length];
        breader.Read(buffer, 0, buffer.Length);
        ms[y] = new MemoryStream(buffer);
    }
    while (true)
    {
        for (int x = 0; x < 3; x++)
        {
            // Bitmap bmp = new Bitmap(ms[x]);
            queue.Enqueue(ms[x]);

            m_DataAvailableEvent.Set();
            Thread.Sleep(6);
        }
    }
}

public void Consumer()
{
    Graphics g = pictureBox1.CreateGraphics();
    while (true)
    {
        m_DataAvailableEvent.WaitOne();
        //Bitmap bmp = queue.Dequeue();
        MemoryStream ms = queue.Dequeue();
        if (ms != null)
        {
            Bitmap bmp = new Bitmap(ms);
            g.DrawImage(bmp, new Point(0, 0));
            bmp.Dispose();

        }
    }

}

private void pictureBox1_Click(object sender, EventArgs e)
{

    con.Start();
    pro.Start();

}

Why does it take more time to draw and create a bitmap in seperate thread and how to reduce the time when processing in seperate thread ? I am using ANTS performance profiler 4.3

Answer 1

All UI operations should take place on the same thread. In fact if you want your system to be stable they must all take place on the same thread. I guess that what you're seeing with the slower performance on the multithreaded code is evidence of that instability.

By all means load the images in separate threads, but update the UI in the main thread.

If you search for questions tagged [multithreading] [c#] here on Stack Overflow you'll see many other questions along the same lines as yours.

See here and here for example.