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POUnexpected poor performance of delegates in C#
 

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  1. POUnexpected poor performance of delegates in C#
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    <p>I posted <a href="https://stackoverflow.com/questions/10613728/run-dynamically-compiled-c-sharp-code-at-native-speed-how">this question</a> earlier about dynamically compiling code in C#, and the answer has lead to another question.</p> <p>One suggestion is that I use delegates, which I tried and they work well. However, they are benching at about 8.4 X slower than direct calls, which makes no sense.</p> <p>What is wrong with this code?</p> <p>My results, .Net 4.0, 64 bit, ran exe directly: 62, 514, 530</p> <pre><code>public static int Execute(int i) { return i * 2; } private void button30_Click(object sender, EventArgs e) { CSharpCodeProvider foo = new CSharpCodeProvider(); var res = foo.CompileAssemblyFromSource( new System.CodeDom.Compiler.CompilerParameters() { GenerateInMemory = true, CompilerOptions = @"/optimize", }, @"public class FooClass { public static int Execute(int i) { return i * 2; }}" ); var type = res.CompiledAssembly.GetType("FooClass"); var obj = Activator.CreateInstance(type); var method = type.GetMethod("Execute"); int i = 0, t1 = Environment.TickCount, t2; //var input = new object[] { 2 }; //for (int j = 0; j &lt; 10000000; j++) //{ // input[0] = j; // var output = method.Invoke(obj, input); // i = (int)output; //} //t2 = Environment.TickCount; //MessageBox.Show((t2 - t1).ToString() + Environment.NewLine + i.ToString()); t1 = Environment.TickCount; for (int j = 0; j &lt; 100000000; j++) { i = Execute(j); } t2 = Environment.TickCount; MessageBox.Show("Native: " + (t2 - t1).ToString() + Environment.NewLine + i.ToString()); var func = (Func&lt;int, int&gt;) Delegate.CreateDelegate(typeof (Func&lt;int, int&gt;), method); t1 = Environment.TickCount; for (int j = 0; j &lt; 100000000; j++) { i = func(j); } t2 = Environment.TickCount; MessageBox.Show("Dynamic delegate: " + (t2 - t1).ToString() + Environment.NewLine + i.ToString()); Func&lt;int, int&gt; funcL = Execute; t1 = Environment.TickCount; for (int j = 0; j &lt; 100000000; j++) { i = funcL(j); } t2 = Environment.TickCount; MessageBox.Show("Delegate: " + (t2 - t1).ToString() + Environment.NewLine + i.ToString()); } </code></pre>
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    1. COA wild guess would be that in the Native case, the compiler can inline the function, while in the Delegate cases it cannot, and has to perform the method calls. Can you check the generated low-level code?
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    2. COThe problem is not that delegates are slow, it is that regular method calls are so very fast. When used in code like this, they should take *zero* cycles as the jitter optimizer entirely eliminates the call and inlines the code. You are mostly measuring the cost of the for() loop.
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    3. COThe diassembly shows a call. However, even though it's in Release mode, I don't know if that's 100% reliable because I was in VS for that test.
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