creating WCF ChannelFactory<T>

Question

I'm trying to convert an existing .NET Remoting application to WCF. Both server and client share common interface and all objects are server-activated objects.

In WCF world, this would be similar to creating per-call service and using ChannelFactory<T> to create a proxy. I'm struggling a bit with how to properly create ChannelFactory<T> for an ASP.NET client.

For performance reasons, I want to cache ChannelFactory<T> objects and just create channel every time I call the service. In .NET remoting days, there used to be RemotingConfiguration.GetRegisteredWellknownClientTypes() method to get a collection of client objects that I could then cache. It appears, in WCF world there is no such thing, although I was able to get a collection of endpoints from config file.

Now here is what I think will work. I can create something like this:

public static ProxyHelper
{
    static Dictionary<Type, object> lookup = new Dictionary<string, object>();  

    static public T GetChannel<T>()
    {
        Type type = typeof(T);
        ChannelFactory<T> factory;

        if (!lookup.ContainsKey(type))
        {
            factory = new ChannelFactory<T>();
            lookup.Add(type, factory);
        }
        else
        {
            factory = (ChannelFactory<T>)lookup[type];
        }

        T proxy = factory.CreateChannel();   
        ((IClientChannel)proxy).Open();

        return proxy;
    }    
}

I think the above code will work, but I'm a bit worried about multiple threads trying to add new ChannelFactory<T> objects if it's not in the lookup. Since I'm using .NET 4.0, I was thinking about using ConcurrentDictionary and use GetOrAdd() method or use TryGetValue() method first to check if ChannelFactory<T> exists and it does not exist, then use GetOrAdd() method. Not sure about performance though of ConcurrentDictionary.TryGetValue() and ConcurrentDictionary.GetOrAdd() method.

Another minor question is whether I need to call ChannelFactory.Close() method on channel factory objects after ASP.NET application ends or can I just let .NET framework dispose the channel factory objects on its own. The proxy channel will always be closed after calling service method by using ((IChannel)proxy).Close() method.

Answer 1

Yes, if you want to create something like this - a static class to hold all those ChannelFactory<T> instances - you definitely have to make sure this class is 100% thread-safe and cannot stumble when accessed concurrently. I haven't used .NET 4's features much yet, so I cannot comment on those specifically - but I would definitely recommend to make this as safe as possible.

As for your second (minor) question: the ChannelFactory itself is a static class - so you cannot really call a .Close() method on it. If you meant to ask whether or not to call the .Close() method on the actual IChannel, then again: yes, try your best to be a good citizen and close those channels if you ever can. If you miss one, .NET will take care of it - but don't just toss your unused channels on the floor and go on - clean up after yourself! :-)