.NET Framework 4.5 contains a very cool new feature called Multi-Core JIT. You can think of it as a profile-guided JIT prefetcher for application startup, and can read about it in a few places …

• MSDN’s documentation for the System.Runtime.ProfileOptimization class.
• Ashwin Kamath’s article, An Overview of Performance Improvements in .NET 4.5, at MSDN Magazine.
• Brandon Bray’s blog post, Improving Launch Performance for Your Desktop Applications.

I’ve been using .NET 4.0 to develop Paint.NET 4.0 for the past few years. Now that .NET 4.5 is out, I’ve been upgrading Paint.NET to require it. However, due to a circumstance beyond my control at this moment, I can’t actually use anything in .NET 4.5 (see below for why). So Paint.NET is compiled for .NET 4.0 and can’t use .NET 4.5’s features at compile time, but as it turns out they are still there at runtime.

I decided to see if it was possible to use the ProfileOptimization class via reflection even if I compiled for .NET 4.0. The answer: yes! You may ask why you’d want to do this at all instead of biting the bullet and requiring .NET 4.5. Well, you may need to keep your project on .NET 4.0 in order to maintain maximum compatibility with your customers who aren’t yet ready (or willing ) to install .NET 4.5. Maybe you’d like to use the ProfileOptimization class in your next “dot release” (e.g. v1.0.1) as a free performance boost for those who’ve upgraded to .NET 4.5, but without displacing those who haven’t.

So, here’s the code, which I’ve verified as working just fine if you compile for .NET 4.0 but run with .NET 4.5 installed:

using System.Reflection;

Type systemRuntimeProfileOptimizationType = Type.GetType("System.Runtime.ProfileOptimization", false);
if (systemRuntimeProfileOptimizationType != null)
{
    MethodInfo setProfileRootMethod = systemRuntimeProfileOptimizationType.GetMethod("SetProfileRoot", BindingFlags.Static | BindingFlags.Public, null, new Type[] { typeof(string) }, null);
    MethodInfo startProfileMethod = systemRuntimeProfileOptimizationType.GetMethod("StartProfile", BindingFlags.Static | BindingFlags.Public, null, new Type[] { typeof(string) }, null);

    if (setProfileRootMethod != null && startProfileMethod != null)
    {
        try
        {
            // Figure out where to put the profile (go ahead and customize this for your application)
            // This code will end up using something like, C:\Users\UserName\AppData\Local\YourAppName\StartupProfile\
            string localSettingsDir = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
            string localAppSettingsDir = Path.Combine(localSettingsDir, "YourAppName");
            string profileDir = Path.Combine(localAppSettingsDir, "ProfileOptimization");
            Directory.CreateDirectory(profileDir);

            setProfileRootMethod.Invoke(null, new object[] { profileDir });
            startProfileMethod.Invoke(null, new object[] { "Startup.profile" }); // don’t need to be too clever here
        }

        catch (Exception)
        {
            // discard errors. good faith effort only.
        }
    }
}

I’m not sure I’ll be using this in Paint.NET 4.0 since it uses NGEN already, but it’s nice to have this code snippet around.

So, why can’t I use .NET 4.5? Well, they removed support for Setup projects (*.vdproj) in Visual Studio 2012, and I don’t yet have the time or energy to convert Paint.NET’s MSI to be built using WiX. I’m not willing to push back Paint.NET 4.0 any further because of this. Instead, I will continue using Visual Studio 2010 and compiling for .NET 4.0 (or maybe I’ll find a better approach). However, at install time and application startup, it will check for and require .NET 4.5. The installer will get it installed if necessary. Also, there’s a serialization bug in .NET 4.0 which has dire consequences for images saved in the native .PDN file format, but it’s fixed in .NET 4.5 (and for .NET 4.0 apps if 4.5 just happens to be what’s installed).