Question

I am currently investigating a performance issue in an application and have highlighted the following;

I have a class –

public static class CommonIcons
{
    ...
    public static readonly System.Windows.Media.ImageSource Attributes = typeof(CommonIcons).Assembly.GetImageFromResourcePath("Resources/attributes.png");
    ...
}

As a test harness I then have the following code using this class to show the issue –

for (int loop = 0; loop < 20000; loop++)
{
    // store time before call

    System.Windows.Controls.Image image = new System.Windows.Controls.Image
                    {
                        Source = CommonIcons.Attributes,
                        Width = 16,
                        Height = 16,
                        VerticalAlignment = VerticalAlignment.Center,
                        SnapsToDevicePixels = true
                    };

    // store time after call
    // log time between before and after

}

At the start of the loop the time difference is less than 0.001 seconds, but after 20000 goes this has increased to 0.015 seconds.

If I don’t use the static member and directly refer to my icon, then I do not have the performance hit, i.e.

for (int loop = 0; loop < 20000; loop++)
{
    // store time before call

    System.Windows.Controls.Image image = new System.Windows.Controls.Image
                    {
                        Source = typeof(CommonIcons).Assembly.GetImageFromResourcePath("Resources/attributes.png"),
                        Width = 16,
                        Height = 16,
                        VerticalAlignment = VerticalAlignment.Center,
                        SnapsToDevicePixels = true
                    };

    // store time after call
    // log time between before and after

}

But in my real world program I don’t want to be creating the imagesource on every call (increased memory until a garbage collection), hence why a static member is used. However I also cannot live with the performance hit.

Can someone explain why the original code is creating this performance hit? And also a better solution for what I am trying to do?

Thanks

Answer 1

It smells like something to do with garbage collection. I wonder whether there’s some kind of coupling between the ImageSource and the Image which is causing problems in your first case. Have you looked to see what the memory usage of your test harness looks like in each case?

Out of interest, what happens if you set the Source to null at the end of each iteration? I know this is a bit silly, but then that’s a natural corollary of it being a test harness 🙂 It might be a further indication that it’s a link between the source and the image…