从WCF服务调用基于任务的异步单向回调方法

Question

I have a WCF service which uses a callback contract to notify the clients, similar to this

public interface IClientCallback
{
    [OperationContract(IsOneWay = true)]
    void NotifySomething();
}

and the service code calling it similar to this

void NotifySomething()
{
    try
    {
        this.callback.NotifySomething();
    }
    catch (Exception ex)
    {
        // Log the exception and eat it
    }
}

Note that by design the callback notification is optional , ie nice to have, but not required. That's why it's marked as OneWay and the implementation eats exceptions.

Due to some misunderstanding we were thinking that would be enough for having a non blocking fire and forget method. But of course that wasn't true, so under some circumstances it's blocking for a while, which is causing problems because it's called from inside thread synchronized block. So we decided to make it asynchronous by changing the definition as follows

public interface IClientCallback
{
    [OperationContract(IsOneWay = true)]
    Task NotifySomething();
}

I have no problem with client implementation, my question is how to call it from the service. Here is what I'm thinking to do

async void NotifySomething()
{
    try
    {
        await this.callback.NotifySomething();
    }
    catch (AggregateException ex)
    {
        // Unwrap, log the exception(s) and eat it
    }
    catch (Exception ex)
    {
        // Log the exception and eat it
    }
}

Now, since everyone is saying async void is not a good practice, is it ok to use it here? What other options do I have? What is the recommended way to perform this in the WCF service context?

Answer 1

The way you have written it is pretty safe as it handles the exceptions. You could also write a reusable extension method to do that so that you don't need to repeat it.

Perhaps something like this:

public static class Extensions
{
    public static void FireAndForget(this Task task)
    {
        task.ContinueWith(t => 
        {
            // log exceptions
            t.Exception.Handle((ex) =>
            {
                Console.WriteLine(ex.Message);
                return true;
            });

        }, TaskContinuationOptions.OnlyOnFaulted);
    }
}

public async Task FailingOperation()
{
    await Task.Delay(2000);

    throw new Exception("Error");
}   

void Main()
{
    FailingOperation().FireAndForget();

    Console.ReadLine();
}