在winforms应用程序中缓存GDI +对象：是否值得，如何正确执行？

Question

For some of my winforms applications I need to create a whole bunch of GDI+ objects (brushes, pens, fonts, etc) and use them over and over again. I created a ghetto caching singleton to accomplish what I need, but the code smell is overwhelming...

public sealed class GraphicsPalette
{
    public static readonly GraphicsPalette Instance = new GraphicsPalette();

    static GraphicsPalette()
    {
    }

    private Dictionary<Color, Brush> solidBrushes;

    //multithreading
    private object brushLock;

    private GraphicsPalette()
    {
        solidBrushes = new Dictionary<Color, Brush>();

        brushLock = new object();
    }

    public Brush GetSolidBrush(Color color, int alpha)
    {
        return GetSolidBrush(Color.FromArgb(alpha, color));
    }

    public Brush GetSolidBrush(Color color)
    {
        if (!solidBrushes.ContainsKey(color))
        {
            lock (brushLock)
            {
                if (!solidBrushes.ContainsKey(color))
                {
                    Brush brush = new SolidBrush(color);
                    solidBrushes.Add(color, brush);
                    return brush;
                }
            }
        }
        return solidBrushes[color];
    }
}

1. Is there a better way for me to reuse these GDI+ objects, as opposed to instantiating them all over again every time OnPaint() etc gets called?
2. Will the GDI+ objects cause an unmanaged memory leak once the program terminates, or will the finalizer for each Brush object get called which will in turn release any unmanaged resources?

I apologize if this is a repeat, but I didn't find any similar questions.

Answer 1

There will not be memory leak but it's better to release GDI+ objects when it makes sense for you. There are a limited amount of them in the operating system, so you might cause rendering issues in your and others applications. Another thing to be mentioned is inability of GDI+ objects (fonts, etc.) to be used by 2+ threads the same time (some difficult to reproduce exceptions might be thrown). You might be interested in some measurements of actual GDI+ objects creation time vs. possible exclusive locking delays. "premature optimization is the root of all evil" © Donald Knuth

Actually it works for me to do some GDI+ objects caching: per painting cycle. Client code might look like this:

class Visual 
{
    public void Draw() 
    {
        using (new GraphicsPalette()) {
            DrawHeader();
            DrawFooter();
        }
    }

    private void DrawHeader() {
        var brush = GraphicsPalette.GetSolidBrush(Color.Green);
        ...   
    }

    public void DrawFooter() { 
        using (new GraphicsPalette()) { // ensures palette existence; does nothing if there is a palette on the stack
            var brush = GraphicsPalette.GetSolidBrush(Color.Green); // returns the same brush as in DrawHeader
            ...
        }
    }
}

So we need GraphicsPalette to ignore nested construction and return the same brush for a given thread. The suggested solution:

public class GraphicsPalette : IDisposable 
{
    [ThreadStatic]
    private static GraphicsPalette _current = null;
    private readonly Dictionary<Color, SolidBrush> _solidBrushes = new Dictionary<Color, SolidBrush>();

    public GraphicsPalette() 
    {
        if (_current == null)
            _current = this;
    }

    public void Dispose() 
    {
        if (_current == this)
            _current = null;

        foreach (var solidBrush in _solidBrushes.Values)
            solidBrush.Dispose();            
    }

    public static SolidBrush GetSolidBrush(Color color) 
    {
        if (!_current._solidBrushes.ContainsKey(color))
            _current._solidBrushes[color] = new SolidBrush(color);

        return _current._solidBrushes[color];
    }
}

Answer 2

Based on my experience with VG.net, I do not believe caching GDI+ objects is usually worth the trouble, except for large things like Bitmaps. Of course it is easy to measure.