C# WCF closing channels and using functions Func<T>

This is the point, I have a WCF service, it is working now. So I begin to work on the client side. And when the application was running, then an exception showed up: timeout. So I began to read, there are many examples about how to keep the connection alive, but, also I found that the best way, is create channel, 开发者_如何学JAVAuse it, and dispose it. And honestly, I liked that. So, now reading about the best way to close the channel, there are two links that could be useful to anybody who needs them:

1. Clean up clients, the right way

2. Using Func

In the first link, this is the example:

    IIdentityService _identitySvc;
...
if (_identitySvc != null)
 {
     ((IClientChannel)_identitySvc).Close();
     ((IDisposable)_identitySvc).Dispose();
     _identitySvc = null;
 }

So, if the channel is not null, then is closed, disposed, and assign null. But I have a little question. In this example the channel has a .Close() method, but, in my case, intellisense is not showing a Close() method. It only exists in the factory object. So I believe I have to write it. But, in the interface that has the contracts or the class that implemets it??. And, what should be doing this method??.

Now, the next link, this has something I haven't try before. Func<T>. And after reading the goal, it's quite interesting. It creates a funcion that with lambdas creates the channel, uses it, closes it, and dipose it. This example implements that function like a Using() statement. It's really good, and a excellent improvement. But, I need a little help, to be honest, I can't understand the function, so, a little explanatino from an expert will be very useful. This is the function:

TReturn UseService<TChannel, TReturn>(Func<TChannel, TReturn> code)
{
    var chanFactory = GetCachedFactory<TChannel>();
    TChannel channel = chanFactory.CreateChannel();
    bool error = true; 
    try {
        TReturn result = code(channel); 
        ((IClientChannel)channel).Close();
        error = false; 
        return result; 
    }
    finally {
        if (error) {
            ((IClientChannel)channel).Abort();
        }
    }
}

And this is how is being used:

int a = 1; 
int b = 2; 
int sum = UseService((ICalculator calc) => calc.Add(a, b)); 
Console.WriteLine(sum);

Yep, I think is really, really good, I'd like to understand it to use it in the project I have.

And, like always, I hope this could be helpful to a lot of people.

---

the UseService method accepts a delegate, which uses the channel to send request. The delegate has a parameter and a return value. You can put the call to WCF service in the delegate.

And in the UseService, it creates the channel and pass the channel to the delegate, which should be provided by you. After finishing the call, it closes the channel.

---

The proxy object implements more than just your contract - it also implements IClientChannel which allows control of the proxy lifetime

The code in the first example is not reliable - it will leak if the channel is already busted (e.g. the service has gone down in a session based interaction). As you can see in the second version, in the case of an error it calls Abort on the proxy which still cleans up the client side

You can also do this with an extension method as follows:

 enum OnError
 {
     Throw,
     DontThrow
 }

 static class ProxyExtensions
 {
     public static void CleanUp(this IClientChannel proxy, OnError errorBehavior)
     {
         try
         {
             proxy.Close();
         }
         catch
         {
             proxy.Abort();

             if (errorBehavior == OnError.Throw)
             {
                 throw;
             }
         }
     }
 }

However, the usage of this is a little cumbersome

 ((IClientChannel)proxy).CleanUp(OnError.DontThrow);

But you can make this more elegant if you make your own proxy interface that extends both your contract and IClientChannel

interface IPingProxy : IPing, IClientChannel
{

}

---

To answer the question left in the comment in Jason's answer, a simple example of GetCachedFactory may look like the below. The example looks up the endpoint to create by finding the endpoint in the config file with the "Contract" attribute equal to the ConfigurationName of the service the factory is to create.

ChannelFactory<T> GetCachedFactory<T>()
{
    var endPointName = EndPointNameLookUp<T>();
    return new ChannelFactory<T>(endPointName);
}

// Determines the name of the endpoint the factory will create by finding the endpoint in the config file which is the same as the type of the service the factory is to create
string EndPointNameLookUp<T>()
{
    var contractName = LookUpContractName<T>();
    foreach (ChannelEndpointElement serviceElement in ConfigFileEndPoints)
    {
        if (serviceElement.Contract == contractName) return serviceElement.Name;
    }
    return string.Empty;
}

// Retrieves the list of endpoints in the config file
ChannelEndpointElementCollection ConfigFileEndPoints
{
    get
    {
        return ServiceModelSectionGroup.GetSectionGroup(
            ConfigurationManager.OpenExeConfiguration(
                ConfigurationUserLevel.None)).Client.Endpoints;
    }
}

// Retrieves the ConfigurationName of the service being created by the factory
string LookUpContractName<T>()
{
    var attributeNamedArguments = typeof (T).GetCustomAttributesData()
        .Select(x => x.NamedArguments.SingleOrDefault(ConfigurationNameQuery));

    var contractName = attributeNamedArguments.Single(ConfigurationNameQuery).TypedValue.Value.ToString();
    return contractName;
}

Func<CustomAttributeNamedArgument, bool> ConfigurationNameQuery
{
    get { return x => x.MemberInfo != null && x.MemberInfo.Name == "ConfigurationName"; }
}

A better solution though is to let an IoC container manage the creation of the client for you. For example, using autofac it would like the following. First you need to register the service like so:

var builder = new ContainerBuilder();

builder.Register(c => new ChannelFactory<ICalculator>("WSHttpBinding_ICalculator"))
  .SingleInstance();
builder.Register(c => c.Resolve<ChannelFactory<ICalculator>>().CreateChannel())
  .UseWcfSafeRelease();

container = builder.Build();

Where "WSHttpBinding_ICalculator" is the name of the endpoint in the config file. Then later you can use the service like so:

using (var lifetime = container.BeginLifetimeScope())
{
    var calc = lifetime.Resolve<IContentService>();
    var sum = calc.Add(a, b);
    Console.WriteLine(sum);
}