using System;

using System.Linq;

using System.Threading.Tasks;

​

public class Program

{

    static int counter = 0;

​

    static void Main()

    {

        var ts = Enumerable.Range(0,100).Select(x => Foo()).ToArray();

        Task.WhenAll(ts).Wait();

        counter.Dump();

    }

​

    static Task Foo() => Task.Run(()=>

    {

        for(int i = 0; i < 100000; i++)

            Set();

    });

static object locker = new object();

static void Set()

{

    lock(locker)

        counter++;

    }

}