using System;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Linq;

namespace ConsoleApplication1
{
  internal class Program
  {
    static void Main(string[] args)
    {
      int count = 10 * 1000 * 1000;
      int repeatCount = 50;

      int[] data = new int[count];
      Random rnd = new Random(0);
      for (int i = 0; i < count; i++)
      {
        data[i] = rnd.Next(10);
      }

      ReadOnlyCollection<int> roData = Array.AsReadOnly(data);

      Measure("array", () =>
      {
        for (int j = 0; j < repeatCount; j++)
        {
          long sum = 0;
          for (int i = 0; i < data.Length; i++)
          {
            sum += data[i];
          }
        }
      });

      Measure("R/O collection", () =>
      {
        for (int j = 0; j < repeatCount; j++)
        {
          long sum = 0;
          for (int i = 0; i < roData.Count; i++)
          {
            sum += roData[i];
          }
        }
      });

      Measure("Linq sum", () =>
      {
        for (int j = 0; j < repeatCount; j++)
        {
          int sum = data.Sum();
        }
      });

      Measure("R/O - linq sum", () =>
      {
        for (int j = 0; j < repeatCount; j++)
        {
          int sum = roData.Sum();
        }
      });

      Console.Write("Done. Press any key to exit...");
      Console.ReadKey();
    }

    public static void Measure(string message, Action callback)
    {
      long mem = GC.GetTotalMemory(true);
      long gcCount = GC.CollectionCount(0);

      DateTime now = DateTime.Now;
      Stopwatch stopwatch = Stopwatch.StartNew();
      callback();
      TimeSpan elapsed = stopwatch.Elapsed;
      TimeSpan elapsedReal = DateTime.Now - now;

      // DONTTOUCH:
      //  It is intended to call GetTotalMemory with forceFullCollection: false
      //  _before_ GC.CollectionCount call.
      double memDelta = (GC.GetTotalMemory(false) - mem) / (1024 * 1024.0);
      long gcCountDelta = GC.CollectionCount(0) - gcCount;

      Console.WriteLine(
@"-------
{0}:
  Elapsed:      {1}, MemDelta: {2:#,0.00MB}
  Elapsed real: {3}, GC count: {4}",
        message, elapsed, memDelta, elapsedReal, gcCountDelta);
    }
  }
}