How can I speed up the performance of the first execution of my .NET app?

Question

Our C# client applications always take a much longer time to load on their first run. I haven't gone so far as to test if it is the first run of any .NET app that is slower, or if the first run of each .NET app is slower, but it remains a problem in any case. How can we eliminate this one-time startup hit?

My initial thoughts are that some sort of service could "warm up" the libraries. Would we need to do this for each of our apps, or just any .NET app? Would the user the service runs as make a difference? Perhaps rather than a Windows service, an application that runs on Windows login could do the dirty work? Again, would the fact that it's a .NET service be enough, or would we have to run each of our programs to eliminate the penalty? We could pass in a command-line parameter that would tell the program to exit immediately, but would that be sufficient, or would we need .NET to load each assembly we'll be using during the normal execution of the application?

---

Re: Some answers, we are deploying release-mode DLLs, and the slowdown is only on the first startup. We are delaying initialization of classes as much as possible.

Answer 1

Other answers have talked about JIT time, but in my experience another very significant factor is the time taken to load the .NET framework itself for the first time after a boot.

Try writing an absolutely trivial program (although preferrably one which at least touches the assemblies your real code uses). Compile it and reboot. Run the trivial program, and then (when it's finished) run your real application - see how that compares with running your real application after a reboot without running the trivial application as well.

Answer 2

Its the JIT (Just In Time compilation) that lets you wait the first time you run your .net apps. This compiles your IL to machine code before running the code. The reason this happens only the first time is that the machine code version is then stored on disk an reused.

You can use NGEN.EXE to pre-jit your application...

This needs to be done on the computer you run the software on, since the JIT will compile and optimize for the CPU it is running on. You could do this as a part of your programs installation...

Answer 3

Read this (Improving Application Startup Time), this (CLR Optimizations In .NET Framework 3.5 SP1) and this (The Performance Benefits of NGen).

Main idea to improve startup time is to use delayed initialization whenever possible. Do not instantiate things that unnecessary immediately after startup. Etc, etc, etc.

Answer 4

I have a feeling the startup delay is in the .NET runtime converting MSIL to native code.

You could possibly ngen your assemblies upon installation, this would compile them to native code and would possibly prevent the startup delay. WiX (http://wix.sourceforge.net) has a custom action that does just that.