Question

I am trying to make a simple windows service that maintains a queue of integers and accepts new integers from other applications via a WCF call. My current implementation seems to maintain separate queues for each application which communicates with it, which is not what I want.

I started by following the instructions at from Microsoft on How to: Host a WCF Service in a Managed Windows Service.

My WindowsService class looks like this:

public class MyWindowsService : ServiceBase{
    public ServiceHost serviceHost = null;

    public MyWindowsService(){
        ServiceName = "AdHocReportService";
    }
    public static void Main(){
        ServiceBase.Run(new MyWindowsService());
    }

    protected override void OnStart(string[] args){
        if (serviceHost != null)
            serviceHost.Close();

        serviceHost = new ServiceHost(typeof(MyService));
        serviceHost.Open();
    }
    protected override void OnStop(){
        if (serviceHost != null){
            serviceHost.Close();
            serviceHost = null;
        }
    }
}

In my Service class I have a queue and an Add method. The add method returns the count of items in the queue after the add. The code looks like this:

public class MyService : IMyService
{
    private Queue<int> myQueue= new Queue<int>();

    public int Add(int reportId)
    {
        myQueue.Enqueue(reportId);
        return myQueue.Count;
    }
}

Lastly, I test my service using the following code in a ConsoleApp:

MyServiceClient client = new MyServiceClient();
int count = client.Add(10);
Console.WriteLine(count);  //prints 1
count = client.Add(25);
Console.WriteLine(count);  //prints 2
Console.ReadLine();

I would expect this to print 1 and 2 the first time my test is run, then 3 and 4 the second time, and then 5 and 6 the third and so on. However, it simply returns 1 and 2 each time, as if the Console App is instantiating the object itself and not operating on the object inside the Windows Service. What am I not understanding?

Answer 1

I think you want a singleton WCF service. See here.

By default, the instance mode for a WCF service is per-call. So an instance of your service is being created by the host for each call you make.

Note: When using a singleton service, your operations need to be thread safe. So I suggest switching from a Queue to a ConcurrentQueue, so you can handle multiple concurrent clients.

Alternative: Use a MSMQ binding. This will ensure you that all of your incoming messages are queued out of process, therefore persisted between restarts too.