using System.Threading.Tasks;

using System.Threading;

using System.Linq;

using System;

​

public class Program

{

    public static void Main()

    {

        var sc = new SharedCounter(42);

        var tasks = Enumerable.Range(1, 100).Select(_ =>

        {

            return Task.Run(() =>

            {

                for (int i = 0; i < 10000; i++)

                {

                    sc.Increment();

                }

            });

        }).ToArray();

        Task.WaitAll(tasks);

        var val = sc.Value;

        Console.WriteLine(val);

    }

}

​

internal struct SharedCounter

{

    private readonly ThreadLocal<int> _counter;

    public SharedCounter(int initialValue)

    {

        _counter = new ThreadLocal<int>(true);

        _counter.Value = initialValue;

    }

​

    public void Increment() => _counter.Value++;

    public long Value

    {

        get => _counter.Values.Select(x => (long)x).Sum();

        private set

        {

        }

    }

}