Detect if code is running as a service

After much searching through intellisense, the debugger, and documentation we weren't able to find anything strictly reliable. It may be possible to get the current process Id and try to find out if that process is registered with the SCM, but while .NET provides a way to get a collection of all the services, their process Ids are not among the information available. Comparing the process name to service names is possible but not necessarily reliable.

However, there are two things that are relatively easy to check and may suffice for the distinction you need, if not exactly "Is this code running as a service?"

System.Environment.UserInteractive : (as Stephen Martin noted) If this is true, it can't be a service. Most processes which are not a service (nor a device driver) will say true. Some console apps may say false when run in non-interactive circumstances such as part of a build process.

System.Diagnostics.Process.GetCurrentProcess().SessionId : (which I think is the same thing Pierre was getting at) If this is not 0, it was not started as a service. Most normal applications will not be in session 0 (with some not-so-normal exceptions as noted by Pierre and Stephen). The biggest question is how this behaves under an older OS such as XP or before. XP and Windows 2000 apparently have services running in session 0, but normal applications will be in session 0 as well. Some configurations of XP (eg. not in a domain) allow multiple user sessions at the same time and they each get a different session id, but the first one gets session 0. So it's not as effective a check prior to Vista.

So, depending on what you actually need to distinguish, one or both of these checks might work for you.

There isn't really any way to tell if your library is running in the context of a service or not though you can use Environment.UserInteractive to make a guess.

But generally a library should never depend on its application context. A library should provide services to an application and if it requires different parameters depending on how it is called it should require the application to provide those parameters.

Your library probably does not act differently strictly based on whether or not it is hosted within a service but rather there is some information about the service environment or user that your library needs to be informed of. The application should inform the library of the necessary conditions or information, the library should not guess on its own.

EDIT: I'd upvote the comments on your question if I could. Use overloaded methods if necessary and/or simply fail if all the information necessary is not provided.

You should probably check that you are running in session zero (at least if you are targeting Vista). You can use WTSRegisterSessionNotification, like in this sample:

  [DllImport("kernel32.dll")]
  private static extern int WTSGetActiveConsoleSessionId();