基于任务的WCF调用应该是OneWay吗？

Question

A WCF contract might look like this:

[ServiceContract]
public interface IService
{
    [OperationContract]
    void DoSomethingFast();

    [OperationContract]
    void DoSomethingSlow();

    [OperationContract]
    int GetSomethingFast();

    [OperationContract]
    int GetSomethingSlow();
}

When a client makes any of these calls, its thread blocks while the server does its thing. For the Fast methods, that's no problem, but for the Slow methods, this blocking is far from ideal. We can add (IsOneWay = true) to the DoSomething methods, but we can't do the same for the GetSomething methods, because they really are two way - we have to wait for the result:

[ServiceContract]
public interface IService
{
    [OperationContract(IsOneWay = true)]
    void DoSomethingFast();

    [OperationContract(IsOneWay = true)]
    void DoSomethingSlow();

    [OperationContract]
    int GetSomething();  

    [OperationContract]
    int GetSomethingSlow();    
}

Enter the Task-based Asynchronous Pattern (TAP). We define the contract to return Task , and WCF (to the best of my knowledge), does some magic behind the scenes and immediately returns a Task which waits for a callback from the WCF service before completing. This eliminates the client-side blocking, allowing the use of await instead:

[ServiceContract]
public interface IService
{
    [OperationContract(IsOneWay = true)]
    Task DoSomethingFastAsync();

    [OperationContract(IsOneWay = true)]
    Task DoSomethingSlowAsync();

    [OperationContract]
    Task<int> GetSomethingAsync();  

    [OperationContract]
    Task<int> GetSomethingSlowAsync();    
}

My question is about how this all works, and whether you still need to include (IsOneWay = true) on the service contract:

• Is the to the best of my knowledge bit above accurate? Does WCF automatically return a Task which completes when the service tells us it's finished?
• Is (IsOneWay = true) necessary for the above magic to happen? If not, does it have any effect at all?
• Given that the callback from the service can be "I'm finished", or "Here's your result" with equal ease, can the DoSomething and GetSomething calls be treated equally? So if (IsOneWay = true) is necessary, can it also be used on the GetSomething methods?

Answer 1

If the service is one way or not has nothing to do with the technology of the client. In C# method semantics, it just means that it's a void returning method.

Now, if the client is implemented in .NET and the user chooses to call it on a blocking way or not, it's her/his choice.

Before the introduction of TAP (Task Asynchronous Patter) , there was APM (Asynchronous Programming Model) and EAP (Event-based Asynchronous Pattern) - if I recall correctly, WCF used EAP.