using System;

using System.Linq;

using System.Threading;

using System.Threading.Tasks;

​

static class Program

{

    static void Main()

    {

        int concurrency = 0;

        Action action = new Action(() =>

        {

            var current = Interlocked.Increment(ref concurrency);

            Console.WriteLine(@$"Started an action at {DateTime

                .Now:HH:mm:ss.fff} on thread #{Thread

                .CurrentThread.ManagedThreadId} with concurrency {current}");

            Thread.Sleep(1000);

            Interlocked.Decrement(ref concurrency);

        });

        Action[] actions = Enumerable.Repeat(action, 12).ToArray();

        var options = new ParallelOptions() { MaxDegreeOfParallelism = -1 };

        Parallel.Invoke(options, actions);

    }

}