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POWhy subsequent direct method call is much faster than the first call?
 

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  1. POWhy subsequent direct method call is much faster than the first call?
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    <p>As is explained in <a href="http://msdn.microsoft.com/en-us/magazine/cc163759.aspx">this MSDN article</a>, when one uses .NET Reflection API such as <code>InvokeMember</code>, the first call takes much more time to run than the subsequent calls because of caching of metadata.</p> <p>When I tested the direct method call without using Reflection, I also see the similar effect both on Mono and .NET 4. </p> <p>The first number is the result of the operation, and the second number after '-' is the time spent for this operation in ms. I used '&lt;--' mark to identify the first method call.</p> <pre><code>300 - 0.192 &lt;-- 300 - 0.004 300 - 0.004 -100 - 0.096 &lt;-- -100 - 0.004 -100 - 0.004 </code></pre> <p>Why is this? I can understand that the first call can be slower, but 50x slower is not what I expected. </p> <p>Attached is the source code to get this result.</p> <h3>library</h3> <pre><code>namespace MyClass { public class Calculator { public int Value1 {get; set;} public int Value2 {get; set;} public Calculator() { Value1 = 100; Value2 = 200; } public int Add(int val1, int val2) { Value1 = val1; Value2 = val2; return Value1 + Value2; } public int Sub(int val1, int val2) { Value1 = val1; Value2 = val2; return Value1 - Value2; } } } </code></pre> <h3>Code to call this library</h3> <pre><code>// http://msdn.microsoft.com/en-us/magazine/cc163759.aspx using System; using System.IO; using System.Reflection; using System.Diagnostics; using System.Collections.Generic; using MyClass; class TestOne { static void DirectTest() { Stopwatch sw; Calculator t = new Calculator(); sw = Stopwatch.StartNew(); int value1 = t.Add(100,200); sw.Stop(); double time1 = sw.Elapsed.TotalMilliseconds; sw = Stopwatch.StartNew(); int value2 = t.Add(100,200); sw.Stop(); double time2 = sw.Elapsed.TotalMilliseconds; sw = Stopwatch.StartNew(); int value3 = t.Add(100,200); sw.Stop(); double time3 = sw.Elapsed.TotalMilliseconds; Console.WriteLine("{0} - {1}", value1, time1); Console.WriteLine("{0} - {1}", value2, time2); Console.WriteLine("{0} - {1}", value3, time3); sw = Stopwatch.StartNew(); value1 = t.Sub(100,200); sw.Stop(); time1 = sw.Elapsed.TotalMilliseconds; sw = Stopwatch.StartNew(); value2 = t.Sub(100,200); sw.Stop(); time2 = sw.Elapsed.TotalMilliseconds; sw = Stopwatch.StartNew(); value3 = t.Sub(100,200); sw.Stop(); time3 = sw.Elapsed.TotalMilliseconds; Console.WriteLine("{0} - {1}", value1, time1); Console.WriteLine("{0} - {1}", value2, time2); Console.WriteLine("{0} - {1}", value3, time3); } static void Main() { DirectTest(); DirectTest(); } } </code></pre>
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    1. CODon't think of the first call being 50 times slower, think of the subsequent calls being 50 times *faster*.
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    2. COJitter's just getting warm.
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      1. USAnthony Pegram
    3. CO@Travis Gockel: True, but in some cases it's that first pass that you really care about. There are of course ways to solve this problem.
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