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AOP using RealProxy (custom implementation) - Part I (RealProxy)

This days I read a post from MSDN Magazine about RealProxy. Using RealProxy you can control the call itself of a method, alter the result or the input. We could say that this is the door for AOP (Aspect Oriented Programming) without using a specific stack.
The most important method of RealProxy is “Invoke”. This method is called each time when a method from you specific class is called. From it you can access the method name, parameters and call your real method or a fake one.
Before saying “Wooww, it’s so cool!” you should know that this will works only when you use also the interfaces.
Reading the above article I had the idea to see if and how we can implement a duration profiling mechanism that is based on attributes. If a method from your specific implementation had the custom profiling attribute, than automatically, the system will measure how long it takes to make a specific call.
First step is to create a custom attribute, which accept a custom message that will be written when we will write the duration time to the trace.
public class DurationProfillingAttribute : Attribute
{
    public DurationProfillingAttribute(string message)
    {
        Message = message;
    }

    public DurationProfillingAttribute()
    {
        Message = string.Empty;
    }

    public string Message { get; set; }
}
Next we need is a generic class that extends RealProxy and calculate the duration of the call. In the Invoke method we will need to use a Stopwatch that will calculate how long a call takes. At this level we can check if a specific method is decorated with our attribute.
public class DurationProfilingDynamicProxy<T> : RealProxy
{
    private readonly T _decorated;

    public DurationProfilingDynamicProxy(T decorated)
        : base(typeof(T))
    {
        _decorated = decorated;
    }

    public override IMessage Invoke(IMessage msg)
    {
        IMethodCallMessage methodCall = (IMethodCallMessage)msg;
        MethodInfo methodInfo = methodCall.MethodBase as MethodInfo;
        DurationProfillingAttribute profillingAttribute = (DurationProfillingAttribute)methodInfo.GetCustomAttributes(typeof(DurationProfillingAttribute)).FirstOrDefault();

        // Method don't needs to be measured. 
        if (profillingAttribute == null)
        {
            return NormalInvoke(methodInfo, methodCall);
        }

        return ProfiledInvoke(methodInfo, methodCall, profillingAttribute.Message);
    }

    private IMessage ProfiledInvoke(MethodInfo methodInfo, IMethodCallMessage methodCall, string profiledMessage)
    {
        Stopwatch stopWatch = null;
        try
        {
            stopWatch = Stopwatch.StartNew();
            var result = InvokeMethod(methodInfo, methodCall);
            stopWatch.Stop();

            WriteMessage(profiledMessage, methodInfo.DeclaringType.FullName, methodInfo.Name, stopWatch.Elapsed);

            return new ReturnMessage(result, null, 0,
                methodCall.LogicalCallContext, methodCall);
        }
        catch (Exception e)
        {
            if (stopWatch != null
                && stopWatch.IsRunning)
            {
                stopWatch.Stop();
            }
            return new ReturnMessage(e, methodCall);
        }
    }

    private IMessage NormalInvoke(MethodInfo methodInfo, IMethodCallMessage methodCall)
    {
        try
        {
            var result = InvokeMethod(methodInfo, methodCall);

            return new ReturnMessage(result, null, 0,
                methodCall.LogicalCallContext, methodCall);
        }
        catch (Exception e)
        {
            return new ReturnMessage(e, methodCall);
        }
    }

    private object InvokeMethod(MethodInfo methodInfo, IMethodCallMessage methodCall)
    {
        object result = methodInfo.Invoke(_decorated, methodCall.InArgs);
        return result;
    }


    private void WriteMessage(string message, string className, string methodName, TimeSpan elapsedTime)
    {
        Trace.WriteLine(string.Format("Duration Profiling: '{0}' for '{1}.{2}' Duration:'{3}'", message, className,methodName, elapsedTime));
    }
We could have another approach here, calculating the duration for all the methods from the class. You can find below the classes used to test the implementation. Using "GetTransparentProxy" method we can obtain a reference to our interface.
class Program
{
    static void Main(string[] args)
    {
        DurationProfilingDynamicProxy<IFoo> fooDurationProfiling = new DurationProfilingDynamicProxy<IFoo>(new Foo());
        IFoo foo = (IFoo)fooDurationProfiling.GetTransparentProxy();

        foo.GetCurrentTime();
        foo.Concat("A", "B");
        foo.LongRunning();
        foo.NoProfiling();
    }
}

public interface IFoo
{
[DurationProfilling("Some text")]
DateTime GetCurrentTime();

[DurationProfilling]
string Concat(string a, string b);

[DurationProfilling("After 2 seconds")]
void LongRunning();

string NoProfiling();
}

public class Foo : IFoo
{
public DateTime GetCurrentTime()
{
    return DateTime.UtcNow;
}

public string Concat(string a, string b)
{
    return a + b;
}

public void LongRunning()
{
    Thread.Sleep(TimeSpan.FromSeconds(2));
}

public string NoProfiling()
{
    return "NoProfiling";
}

}
In the next post related to RealProxy we will see how we can integrate this with a IoC container to be able to control what part of the system have the duration profiling active.

Comments

  1. Interesting - isn't RealProxy a bit too tied to .Net Remoting?

    ReplyDelete

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