Enterprise Integration Zone is brought to you in partnership with:

Mike Hadlow is a Brighton, UK based developer, blogger and author of a number of open source frameworks and applications. Mike is a DZone MVB and is not an employee of DZone and has posted 87 posts at DZone. You can read more from them at their website. View Full User Profile

An Action Cache

01.02.2013
| 1633 views |
  • submit to reddit
Do you ever find yourself in a loop calling a method that expects an Action or a Func as an argument? Here’s an example from an EasyNetQ test method where I’m doing just that:
[Test, Explicit("Needs a Rabbit instance on localhost to work")]
public void Should_be_able_to_do_simple_request_response_lots()
{
    for (int i = 0; i < 1000; i++)
    {
        var request = new TestRequestMessage { Text = "Hello from the client! " + i.ToString() };
        bus.Request<TestRequestMessage, TestResponseMessage>(request, response =>
            Console.WriteLine("Got response: '{0}'", response.Text));
    }

    Thread.Sleep(1000);
}

My initial naive implementation of IBus.Request set up a new response subscription each time Request was called. Obviously this is inefficient. It would be much nicer if I could identify when Request is called more than once with the same callback and re-use the subscription.

The question I had was: how can I uniquely identify each callback? It turns out that action.Method.GetHashcode() reliably identifies a unique action. I can demonstrate this with the following code:

public class UniquelyIdentifyDelegate
{
readonly IDictionary<int, Action> actionCache = new Dictionary<int, Action>();

public void DemonstrateActionCache()
{
for (var i=0; i < 3; i++)
{
RunAction(() => Console.Out.WriteLine("Hello from A {0}", i));
RunAction(() => Console.Out.WriteLine("Hello from B {0}", i));

Console.Out.WriteLine("");
}
}

public void RunAction(Action action)
{
Console.Out.WriteLine("Mehod = {0}, Cache Size = {1}", action.Method.GetHashCode(), actionCache.Count);
if (!actionCache.ContainsKey(action.Method.GetHashCode()))
{
actionCache.Add(action.Method.GetHashCode(), action);
}

var actionFromCache = actionCache[action.Method.GetHashCode()];

actionFromCache();
}
}

Here, I’m creating an action cache keyed on the action method’s hashcode. Then I’m calling RunAction a few times with two distinct action delegates. Note that they also close over a variable, i, from the outer scope.

Running DemonstrateActionCache() outputs the expected result:

Mehod = 59022676, Cache Size = 0
Hello from A 0
Mehod = 62968415, Cache Size = 1
Hello from B 0

Mehod = 59022676, Cache Size = 2
Hello from A 1
Mehod = 62968415, Cache Size = 2
Hello from B 1

Mehod = 59022676, Cache Size = 2
Hello from A 2
Mehod = 62968415, Cache Size = 2
Hello from B 2

Rather nice I think :)


Published at DZone with permission of Mike Hadlow, author and DZone MVB. (source)

(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)