Preloading Assemblies

Question

At work we use DevExpress for the user interface. The first time a form employing a DevExpress control is opened there's a long pause (sometimes 15-20 sec on some clients). In Visual Studio i can see that tons of assemblies are being loaded during that phase. Is there a way to preload that assemblies into the AppDomain in the background on a thread that is spawned for example before the login screen pops up?

Answer 1

Another choice is to force the JIT to load the assemblies asynchronious instead of doing it by hand. The trick is to simply call the constructor of the control, so the Jit knows that it has to start compiling that particular code path. Usually that forces it to load all dependant assemblies. Just make sure to surround the call of the constructor by a try catch.

An example of how to do that at loadtime:

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

        PreJitControls();

        Application.Run(new Form1());
    }

    private static void PreJitControls()
    {           
        ThreadPool.QueueUserWorkItem((t) =>
        {
            Thread.Sleep(1000); // Or whatever reasonable amount of time
            try
            {
                AssemblyPullingControl1 c = new AssemblyPullingControl1();
            }
            catch (Exception) { }

            try
            {
                AssemblyPullingControl2 c = new AssemblyPullingControl2();
            }
            catch (Exception) { }

        });
    }
}

But you could also do something similar in the constructor of the login form, if that is a better time to do the pre-loading. Just move the PreJitControls method to the login form and call it from the constructor.

Answer 2

This will however force your users to always take that hit on start up.

In general this is a bad idea (if you have the hit at least defer it till you really need it). A case where it might help is to trigger the load if there is a strong chance that they are going to use the functionality in the near future but the system is otherwise idle. This can be very hard to do accurately though.

You might see whether any of the loaded assemblies are under your control and in the GAC. If so you could ngen them which may have a significant effect on the start up time of this aspect of your UI.