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POwhy in this simple test the speed of method relates to the order of triggering?
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copied!<p>I was doing other experiments until this strange behaviour caught my eye.</p> <p>code is compiled in x64 release.</p> <p>if key in 1, <strong>the 3rd run of List method cost 40% more time than the first 2</strong>. output is </p> <pre><code>List costs 9312 List costs 9289 Array costs 12730 List costs 11950 </code></pre> <p>if key in 2, <strong>the 3rd run of Array method cost 30% more time than the first 2</strong>. output is </p> <pre><code>Array costs 8082 Array costs 8086 List costs 11937 Array costs 12698 </code></pre> <p>You can see the pattern, the complete code is attached following (just compile and run): {the code presented is minimal to run the test. The actually code used to get reliable result is more complicated, I wrapped the method and tested it 100+ times after proper warmed up}</p> <pre><code>class ListArrayLoop { readonly int[] myArray; readonly List<int> myList; readonly int totalSessions; public ListArrayLoop(int loopRange, int totalSessions) { myArray = new int[loopRange]; for (int i = 0; i < myArray.Length; i++) { myArray[i] = i; } myList = myArray.ToList(); this.totalSessions = totalSessions; } public void ArraySum() { var pool = myArray; long sum = 0; for (int j = 0; j < totalSessions; j++) { sum += pool.Sum(); } } public void ListSum() { var pool = myList; long sum = 0; for (int j = 0; j < totalSessions; j++) { sum += pool.Sum(); } } } class Program { static void Main(string[] args) { Stopwatch sw = new Stopwatch(); ListArrayLoop test = new ListArrayLoop(10000, 100000); string input = Console.ReadLine(); if (input == "1") { sw.Start(); test.ListSum(); sw.Stop(); Console.WriteLine("List costs {0}",sw.ElapsedMilliseconds); sw.Reset(); sw.Start(); test.ListSum(); sw.Stop(); Console.WriteLine("List costs {0}", sw.ElapsedMilliseconds); sw.Reset(); sw.Start(); test.ArraySum(); sw.Stop(); Console.WriteLine("Array costs {0}", sw.ElapsedMilliseconds); sw.Reset(); sw.Start(); test.ListSum(); sw.Stop(); Console.WriteLine("List costs {0}", sw.ElapsedMilliseconds); } else { sw.Start(); test.ArraySum(); sw.Stop(); Console.WriteLine("Array costs {0}", sw.ElapsedMilliseconds); sw.Reset(); sw.Start(); test.ArraySum(); sw.Stop(); Console.WriteLine("Array costs {0}", sw.ElapsedMilliseconds); sw.Reset(); sw.Start(); test.ListSum(); sw.Stop(); Console.WriteLine("List costs {0}", sw.ElapsedMilliseconds); sw.Reset(); sw.Start(); test.ArraySum(); sw.Stop(); Console.WriteLine("Array costs {0}", sw.ElapsedMilliseconds); } Console.ReadKey(); } } </code></pre>

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