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Write a Better Windows Service
Writing a Windows service is significantly more involved than many authors would have you believe. Here are the tools you need to create a Windows service robust enough for the real world.
by Alek Davis

August 26, 2005

Technology Toolbox: C#, Windows Services

Most programmers know that you typically implement Windows services as executable programs. What many developers don't realize is that a single executable can contain more than one service. For example, the standard Windows intetinfo.exe process hosts several services, including IIS Admin, World Wide Web Publishing, and Simple Mail Transfer Protocol (SMTP).

All services hosted by one executable and configured to use the same Log On account run in the same process. The first service to start launches the executable, and the last service to stop causes the process to exit. If you configure the services using different Log On properties—say, service X runs as John, service Y runs as Mary, and both services are implemented in the same executable—you end up starting a separate process for each user identity of the launched services.

A single process can contain more than one Windows service, and each service can perform several tasks (see Figure 1). For example, an online shop can use a service to send notifications about shipped products, payment collections, and weekly promotions. You can implement these operations as different services, or you can run them as different threads of the same service. A common approach is to implement logically related tasks as multiple threads of a single service and non-related tasks as different services.

If you read a typical article explaining how to write a Windows service in C# or Visual Basic .NET, you get the impression that building Windows services is easy. Simply pick the Windows Service project template, follow the instructions provided in the MSDN documentation or online tutorials, add code to implement the application logic, and voilà, the service is ready. Unfortunately, many developers discover only after the fact that the Windows services they create using this approach are hard to manage.

For one, you can't debug your service by pressing the F5 key from the Visual Studio .NET IDE. After you figure out how to launch the service executable from command line, debug messages won't appear if you try to display them by calling Console.Write or MessageBox.Show. You also get an error if you install the service using a Windows installer (MSI) package and then attempt to deploy a hot fix by executing an updated MSI file in repair mode. Finally, if your service performs multiple tasks running at scheduled times or timed intervals, you need to design all aspects of your solution, including the timing and multithreading. Faced with these issues, many developers turn to the Web and newsgroups to slog through the issues one-by-one. That brute-force method can work, after a fashion, but a far better solution is to avoid all these problems in the first place.

This article comes with two code samples written in C#. The first sample contains a project to build a library (My.Utilities.dll), which provides classes for implementing easy-to-use Windows services. The SampleService project illustrates how you can incorporate this library in a project that implements several Windows services, each performing multiple tasks. There is also a sample setup project (SampleSetup), which shows how to implement the Windows service installer.