Dynamic retry proxy

Question

Consider the below, which works:

public interface IService
{
    void DoSomething(object arg);
    void DoSomethingElse(object arg, bool anotherArg);
    bool AndDoYetMoreStuff(object arg, object[] moreArgs);
}

public class Service : IService
{
    public void DoSomething(object arg){}

    public void DoSomethingElse(object arg, bool anotherArg){}

    public bool AndDoYetMoreStuff(object arg, object[] moreArgs)
    {
        return true;
    }
}

public class ServiceRetryProxy : IService
{
    const int retryLimit = 3;
    private readonly IService _service;

    public ServiceRetryProxy(IService service)
    {
        _service = service;
    }

    private void RetryOnException(Action<IService> ctx)
    {
        ReconnectOnException(service =>
        {
            ctx(service);
            return new object();
        });
    }

    private T RetryOnException<T>(Func<IService, T> ctx)
    {
        var counter = 0;
        Exception lastException = null;
        while (counter < retryLimit)
        {
            try
            {
                return ctx(_service);
            }
            catch (Exception ex)
            {
                lastException = ex;
                counter++;
            }
        }

        throw lastException;
    }

    public void DoSomething(object arg)
    {
        ReconnectOnException(x => x.DoSomething(arg));
    }

    public void DoSomethingElse(object arg, bool anotherArg)
    {
        ReconnectOnException(x => x.DoSomethingElse(arg, anotherArg));
    }

    public bool AndDoYetMoreStuff(object arg, object[] moreArgs)
    {
        return ReconnectOnException(x => x.AndDoYetMoreStuff(arg, moreArgs));
    }
}

The problem with this is that I have to write a proxy method for every method of the interface. I would like a more 'dynamic' solution so that I can apply the RetryOnException (or any other logic) to every method on any given interface. I'm currently looking at Castle DynamicProxy, but what if any are the other options?

Peter Zajic · Answer 1 · 2012-04-28T16:52:28.120

Castle dynamic proxy is certainly one option.

But I would personally go for postsharp: http://www.sharpcrafters.com/

I already used it for similar scenario. I created RetryOnexceptionAspect where you could specify type of exception, number of retries and apply it on any method:

[Serializable]
public class RetryOnExceptionAspect : MethodInterceptionAspect
{
    private readonly int maxRetries;

    private readonly Type exceptionType;

    public RetryOnExceptionAspect(int maxRetries, Type exceptionType)
    {
        this.maxRetries = maxRetries;
        this.exceptionType = exceptionType;
    }

    public override void OnInvoke(MethodInterceptionArgs args)
    {
        for (int i = 0; i < maxRetries + 1; i++)
        {
            try
            {
                args.Proceed();
            }
            catch (Exception e)
            {
                if (e.GetType() == exceptionType && i < maxRetries)
                {
                    continue;
                }

                throw;
            }

            break;
        }
    }
}

Usage like:

public class Service : IService
{
    [RetryOnExceptionAspect(5, typeof(TimeoutException)]
    public void DoSomething()
    {
    }
}

Dynamic retry proxy

1 Answers1