如何退订WCF服务

Question

I've managed to get my WCF service with callbacks working. The client simply "subscribes" to the service and the service starts a timer. This timer determines when to call the callback function(s).

Now my question is how to unsubscribe the client because simply closing the client causes an CommunicationException .

Is my implementation of Unsubscribe() with disabling the timer correct or should I perform additional steps?

Here's my service class:

[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant, InstanceContextMode = InstanceContextMode.PerSession)]
internal class HostFunctions : IHostFunctions
{
    private static ILog _log = LogManager.GetLogger(typeof(HostFunctions));
    private IHostFunctionsCallback _callback;
    private Timer _timer;

    #region Implementation of IHostFunctions

    public void Subscribe()
    {
        _callback = OperationContext.Current.GetCallbackChannel<IHostFunctionsCallback>();
        _timer = new Timer(1000);
        _timer.Elapsed += OnTimerElapsed;
        _timer.Enabled = true;
    }

    public void Unsubscribe()
    {
        _timer.Enabled = false;
    }

    private void OnTimerElapsed(object sender, ElapsedEventArgs e)
    {
        if (_callback == null) return;
        try
        {
            _callback.OnCallback();
        }
        catch (CommunicationException comEx)
        {
            // Log: Client was closed or has crashed
            _timer.Enabled = false;
        }
    }

    #endregion
}

Answer 1

In your case, you don't need to perform additional steps. Because your clients each get their own service instance the callback channel will go out of scope when the client channel closes. (Note: this is the case because the service instance mode is Per Session)

So you only need to call Close() on the client channel from the client and everything will go out of scope on the service end. Don't forget to close the channel in the correct way:

try
{
    channel.Close();
}
catch
{
    channel.Abort();
    throw;
}

Either that or wait for the service receive timeout to be exceeded and then the session will end and the channel will go out of scope. This is slightly wasteful however as the service will remain in memory on the server for longer.

Note, it is not necessary to call Close/Dispose on the callback channel from the service end.