using System;

using System.Collections.Generic;

using System.Threading.Tasks;

using System.Threading;

​

public class FooBar {

​

    private readonly int n;

    private volatile bool foo = true;

    public FooBar(int n) {

        this.n = n;

    }

​

    public void Foo() {

        for (int i = 0; i < n; ++i) {

            lock (this) {

                if (!foo) {

                    Monitor.Wait(this);

                }

                foo = false;

                Console.Write("foo");

                Monitor.Pulse(this);

            }

        }

    }

​

    public void Bar() {

        for (int i = 0; i < n; ++i) {

            lock (this) {

                if (foo) {

                    Monitor.Wait(this);

                }

                foo = true;

                Console.Write("bar");

                Monitor.Pulse(this);

            }

        }

    }

}

​

public class Program {

    public static void Main() {

        var fooBar = new FooBar(5);

        var tasks = new List<Task>();

​

        tasks.Add(Task.Run(() => fooBar.Bar()));

        tasks.Add(Task.Run(() => fooBar.Foo()));

        Task.WaitAll(tasks.ToArray());

    }

}