F# Windows Service Template

Ok, I certainly love F# but templates are lacking out of the gate for some types of apps with one example being a Windows Service.  Now, I saw a few out there folks have made but they actually make the same mistake IMO as seen in the C# windows service.

When it comes down to it, during debugging, I would prefer to have my Window Service actually run as a Console App when I am debugging and only as a true windows service when it is getting the final finishing touches.

See the code below, and note the last two public methods, “InteractiveStart” and “InteractiveStop”.

type AppHost() as this =
    inherit ServiceBase()

    do
        this.ServiceName <- "Some Cool F# Service"
        this.EventLog.Log <- "Application"

    override this.OnStart(args:String[]) =        
                        
        Console.WriteLine("It is working! Yeah!")
        base.OnStart(args)

    override this.OnStop() = 
        base.OnStop()

    member this.InteractiveStart(args:String[]) = 
        this.OnStart(args)

    member this.InteractiveStop() =
        this.OnStop()

 
Next, let’s be sure to add an installer class so when we do want to run this as a true windows service, it is ready to go.

[<RunInstaller(true)>] 
type MyInstaller() as this = 
    inherit Installer() 
    do 
        let spi = new ServiceProcessInstaller() 
        let si = new ServiceInstaller() 
        spi.Account <- ServiceAccount.NetworkService

        si.DisplayName <- "Computing Service" 
        si.StartType <- ServiceStartMode.Automatic 
        si.ServiceName <- "Computing Service"

        this.Installers.Add(spi) |> ignore 
        this.Installers.Add(si) |> ignore

 
Now we will layout the entry point portion of the program. This code will decide if the app should be started as a console app (InteractiveStart) by looking at the Environment.UserInteractive property. If this is true, then it is intended to be run as a console app as opposed to a windows service. YOu can see below, very simple, and makes life a lot easier during debugging early on. I use this same technique in C# as well and works great.

open System
open System.ServiceProcess

module PROGRAM = 
    [<EntryPoint>] 
    let Main(args:String[]) = 
        
        let host = new AppHost()

        if Environment.UserInteractive then            
            host.InteractiveStart(args)
            Console.ReadLine() |> ignore
            host.InteractiveStop()
            0
        else
           ServiceBase.Run(host) 
           0

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