ListProcessingBenchmarks.cs

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Threading.Tasks;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkRunner.Run<PersonAgeSumPerformanceBenchmark>();

[MemoryDiagnoser]
public class PersonAgeSumPerformanceBenchmark
{
    private List<Person> _peopleList = default!;
    private const int RandomSeed = 12345;

    [Params(10, 1_000, 10_000, 100_000)]
    public int NumberOfPeople { get; set; }

    public class Person
    {
        public int Age { get; set; }

        public Person(int age)
        {
            Age = age;
        }
    }

    [GlobalSetup]
    public void SetupPeopleList()
    {
        var randomGenerator = new Random(RandomSeed);
        _peopleList = new List<Person>(NumberOfPeople);
        for (int index = 0; index < NumberOfPeople; index++)
        {
            _peopleList.Add(new Person(randomGenerator.Next(1, 100)));
        }
    }

    [Benchmark(Baseline = true)]
    public int SumAgesUsingForeachLoop()
    {
        int totalAgeSum = 0;
        foreach (Person person in _peopleList)
        {
            totalAgeSum += person.Age;
        }
        return totalAgeSum;
    }

    [Benchmark]
    public int SumAgesUsingListForEachMethod()
    {
        var totalAgeSum = 0;
        _peopleList.ForEach(person => IncrementAgeSum(ref totalAgeSum, person.Age));
        return totalAgeSum;

        static void IncrementAgeSum(ref int sum, int ageToAdd)
        {
            sum += ageToAdd;
        }
    }

    [Benchmark]
    public int SumAgesUsingForLoop()
    {
        var totalAgeSum = 0;
        for (int index = 0; index < _peopleList.Count; index++)
        {
            totalAgeSum += _peopleList[index].Age;
        }
        return totalAgeSum;
    }

    [Benchmark]
    public int SumAgesUsingWhileLoop()
    {
        int totalAgeSum = 0;
        int index = 0;
        while (index < _peopleList.Count)
        {
            totalAgeSum += _peopleList[index].Age;
            index++;
        }
        return totalAgeSum;
    }

    [Benchmark]
    public int SumAgesUsingDoWhileLoop()
    {
        if (_peopleList.Count == 0) return 0;
        var totalAgeSum = 0;
        var index = 0;
        do
        {
            totalAgeSum += _peopleList[index].Age;
            index++;
        } while (index < _peopleList.Count);

        return totalAgeSum;
    }

    [Benchmark]
    public int SumAgesUsingSpanForeachLoop()
    {
        var totalAgeSum = 0;
        foreach (var person in CollectionsMarshal.AsSpan(_peopleList))
        {
            totalAgeSum += person.Age;
        }
        return totalAgeSum;
    }

    [Benchmark]
    public int SumAgesUsingParallelFor()
    {
        var totalAgeSum = 0;
        Parallel.ForEach(_peopleList, 
            () => 0,   
            (person, loopState, localAgeSum) => localAgeSum + person.Age,
            localAgeSum => Interlocked.Add(ref totalAgeSum, localAgeSum));

        return totalAgeSum;
    }
}