ThoughtShapes - .NET Delegate Recipes - Comments

Sweet! Thanks!

jay — Wed, 31 Oct 2007 14:34:09 -0400

Sweet! Thanks!

You sure do get it Jay. But

Rjae Easton — Wed, 31 Oct 2007 14:26:52 -0400

You sure do get it Jay. But I kinda already knew that.

I am thrilled that the post was so timely and helped.

I hope you don't mind, but I

Rjae Easton — Wed, 31 Oct 2007 14:25:35 -0400

I hope you don't mind, but I replaced <code> with <pre class="code cs"> to retain your formatting.

sorry for the formatting of

jay — Wed, 31 Oct 2007 13:16:00 -0400

sorry for the formatting of the code.
There were spaces there when I hit post :P

I get it! So I must admit

jay — Wed, 31 Oct 2007 13:14:00 -0400

I get it!
So I must admit that the terms Closure and lexical context threw me off at first. But when I replaced them with Scope and Stack (and happened to be using something like this in a unit test I was writing) it coalesced for me.

My example was this:

[Test]
public SomeWorkRelatedUnitTestIWasWorkingOnThatTestsThreadSafetyOfACertainCall()
{
      // Some Mocking initialization goes here
      //....

      List autos = new List();
      for (int i = 0; i < 1; i++)
      {
          autos.Add(new AutoResetEvent(false));                
            ThreadPool.QueueUserWorkItem(
                delegate
                    {
                        myWorker.InitializeProcessors(true, mySettings);
                        autos[i].Set();
                    });
       }
       WaitHandle.WaitAll(autos.ToArray());
       myMocks.VerifyAllExpectationsHaveBeenMet();
}

When I ran my test I was getting an exception at the autos[i].Set() call. at this point i was 1, when I expected it to be 0. I remember reading this post this morning and hopped on back to see what I was missing.

Rjae's words (once I understood them) were exactly what was happening to me. i was continuing to increment while the work was being done, because the delegate has a view into the scope that i lives at.
When I switched to something like:

[Test]
public SomeWorkRelatedUnitTestIWasWorkingOnThatTestsThreadSafetyOfACertainCall()
{
     List autos = new List();
     for (int i = 0; i < 1; i++)
     {
         int anotherI = i;
         autos.Add(new AutoResetEvent(false));                
           ThreadPool.QueueUserWorkItem(
              delegate
                    {
                        myWorker.InitializeProcessors(true, mySettings);
                        autos[anotherI].Set();
                    });
      }
      WaitHandle.WaitAll(autos.ToArray());
}

It really became clear to me what Rjae was saying. It's almost like a delegate gets it's own "local(ish)" storage.

Thanks Rjae for the timely post!

.NET Delegate Recipes

Rjae Easton — Tue, 30 Oct 2007 23:40:05 -0400

Delegates are ubiquitous throughout .NET development though many developers are not aware of their full range. This stems from the fact that few books or articles do a good job tying together all ways in which delegates may be used. Additionally there are often misconceptions over delegate semantics - how to construct a delegate within a given context. This post seeks to clarify the muddy water around delegates by use of demonstrative tests. Each test is explicitly named for the semantic it demonstrates and internally each test asserts expected behavior. As the title implies, this post is not intended as an introduction to delegates. If you are looking for such material Juval Lowy does a decent job here.