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ArraySumBenchmark.cs
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ArraySumBenchmark.cs
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using System;
using System.Diagnostics;
using System.Linq;
// Naive benchmark of summing over and array of structs, array of classes
// and and array of classes that aren't laid out contiguously in memory.
//
// Compiled: Visual Studio 2013
namespace ArraySumBenchmark
{
public static class Program
{
private const int SIZE = 10000000;
struct MyStruct
{
public int A;
public int B;
public MyStruct(int a, int b)
{
A = a;
B = b;
}
}
class MyClass
{
public readonly int A;
public readonly int B;
public MyClass(int a, int b)
{
this.A = a;
this.B = b;
}
}
public static void Main()
{
var sequentialOrder = Enumerable.Range(0, SIZE).ToArray();
var randomOrder = new int[SIZE];
sequentialOrder.CopyTo(randomOrder, 0);
Shuffle(randomOrder);
MyStruct[] structs = MakeArrayOfStructs();
Action<int[]> SumStructs = (int[] readOrder) =>
{
long sum = 0;
foreach(var index in readOrder)
sum += structs[index].A + structs[index].B;
};
Console.WriteLine("\n-- Access Array of Structs Sequentially --");
Measure(() => SumStructs(sequentialOrder));
Console.WriteLine("\n-- Access Array of Structs Randomly --");
Measure(() => SumStructs(randomOrder));
MyClass[] classes = MarkArrayOfClasses();
Action<int[]> SumClasses = (readOrder) =>
{
long sum = 0;
foreach(var index in readOrder)
sum += classes[index].A + classes[index].B;
};
Console.WriteLine("\n-- Access Array of Classes Sequentially --");
Measure(() => SumClasses(sequentialOrder));
Console.WriteLine("\n-- Access Array of Classes Randomly --");
Measure(() => SumClasses(randomOrder));
var nonContiguousClasses = MakeArrayOfNonContiguousClasses();
Action<int[]> SumNonContiguousClasses = (readOrder) =>
{
long sum = 0;
foreach(var index in readOrder)
sum += nonContiguousClasses[index].A + nonContiguousClasses[index].B;
};
Console.WriteLine("\n-- Access Array of Non-Contigous Classes Sequentially --");
Measure(() => SumNonContiguousClasses(sequentialOrder));
Console.WriteLine("\n-- Access Array of Non-Contigous Classes Randomly --");
Measure(() => SumNonContiguousClasses(randomOrder));
Console.WriteLine("Press Enter to exit.");
Console.ReadKey(true);
}
/// <summary>
/// Fisher-Yates Shuffle ~O(n)
/// </summary>
private static void Shuffle<T>(T[] arrayToShuffle)
{
var rnd = new Random();
var i = arrayToShuffle.Length;
while (i > 1)
{
var j = rnd.Next(--i);
var temp = arrayToShuffle[i];
arrayToShuffle[i] = arrayToShuffle[j];
arrayToShuffle[j] = temp;
}
}
private const int ITERATIONS = 5;
private static void Measure(Action action)
{
var watch = new Stopwatch();
long elapsed = 0;
GC.Collect();
foreach (var i in Enumerable.Range(0, ITERATIONS))
{
watch.Start();
action();
watch.Stop();
elapsed += watch.ElapsedMilliseconds;
watch.Reset();
}
Console.WriteLine("Elapsed time: {0}", elapsed / ITERATIONS);
}
private static MyStruct[] MakeArrayOfStructs()
{
MyStruct[] structs; // Reference
// Create array of structs on heap and point reference to it.
structs = Enumerable.Repeat(new MyStruct(1, 3), SIZE).ToArray();
return structs;
}
private static MyClass[] MarkArrayOfClasses()
{
MyClass[] classes; // Reference
// Create array of class references on heap and point each reference to instance of class on heap.
classes = Enumerable.Repeat(new MyClass(1, 3), SIZE).ToArray();
return classes;
}
/// <summary>
/// Attempt to create an array of references to non-contiguous classes by
/// allocating junk objects between the objects that are referenced in the final array
/// </summary>
private static MyClass[] MakeArrayOfNonContiguousClasses()
{
MyClass[] junk1 = new MyClass[SIZE]; // Reference
MyClass[] junk2 = new MyClass[SIZE];
MyClass[] classes = new MyClass[SIZE];
foreach (var i in Enumerable.Range(0, SIZE))
{
junk1[i] = new MyClass(0, 2);
junk2[i] = new MyClass(1, 1);
classes[i] = new MyClass(junk1[i / 2].A + junk2[i / 3].A, junk1[i / 4].B + junk2[i / 5].B);
}
return classes;
}
}
}