Explaining thread safety

gistfile1.cs

    class Foo
    {
        static string bar;
        internal static readonly Random RANDOM = new Random();
        internal const int SLEEP1 = 10;
        internal const int SLEEP2 = 25;

        public void Baz(string value)
        {
            bar = "#1: " + value;
            Thread.Sleep(RANDOM.Next(SLEEP1));
            bar = "#2: " + value;
            Thread.Sleep(RANDOM.Next(SLEEP2));
            Console.WriteLine("ThreadId: {0} bar: {1}", Thread.CurrentThread.ManagedThreadId, bar);
        }
    }

    class Foo2
    {
        [ThreadStatic]
        static string bar;

        static readonly Random RANDOM = Foo.RANDOM;

        public void Baz(string value)
        {
            bar = "#1: " + value;
            Thread.Sleep(RANDOM.Next(Foo.SLEEP1));
            bar = "#2: " + value;
            Thread.Sleep(RANDOM.Next(Foo.SLEEP2));
            Console.WriteLine("ThreadId: {0} bar: {1}", Thread.CurrentThread.ManagedThreadId, bar);
        }
    }

    class Foo3
    {
        string bar;

        static readonly Random RANDOM = Foo.RANDOM;

        public void Baz(string value)
        {
            bar = "#1: " + value;
            Thread.Sleep(RANDOM.Next(Foo.SLEEP1));
            bar = "#2: " + value;
            Thread.Sleep(RANDOM.Next(Foo.SLEEP2));
            Console.WriteLine("ThreadId: {0} bar: {1}", Thread.CurrentThread.ManagedThreadId, bar);
        }
    }

    class Program
    {
        const int MAXTHREADS = 32;

        static void Main(string[] args)
        {
            ThreadPool.SetMaxThreads(MAXTHREADS, MAXTHREADS);

            Console.WriteLine("Sequential");
            for (int i = 0; i < MAXTHREADS; i++)
            {
                Payload(i);
            }

            Console.WriteLine();
            Console.WriteLine("Threaded - Thread Unsafe");
            for (int i = 0; i < MAXTHREADS; i++)
            {
                int k = i;
                ThreadPool.QueueUserWorkItem(s => Payload(k));
            }

            Wait();

            Console.WriteLine();
            Console.WriteLine("Threaded - Thread Static");
            for (int i = 0; i < MAXTHREADS; i++)
            {
                int k = i;
                ThreadPool.QueueUserWorkItem(s => Payload2(k));
            }

            Wait();

            Console.WriteLine();
            Console.WriteLine("Threaded - Thread Instance");
            for (int i = 0; i < MAXTHREADS; i++)
            {
                int k = i;
                ThreadPool.QueueUserWorkItem(s => Payload3(k));
            }

            Wait();

            Console.WriteLine();
            Console.WriteLine("Press ENTER to exit");

            Console.ReadLine();
        }

        static void Wait()
        {
            int t, c;
            do
            {
                ThreadPool.GetAvailableThreads(out t, out c);
            }
            while (t < MAXTHREADS);
        }

        static void Payload(int i)
        {
            var f = new Foo();
            f.Baz(i.ToString());
        }

        static void Payload2(int i)
        {
            var f = new Foo2();
            f.Baz(i.ToString());
        }

        static void Payload3(int i)
        {
            var f = new Foo3();
            f.Baz(i.ToString());
        }
    }    class Foo
    {
        static string bar;
        static readonly Random RANDOM = new Random();

        public void Baz(string value)
        {
            bar = "#1: " + value;
            Thread.Sleep(RANDOM.Next(100));
            bar = "#2: " + value;
            Thread.Sleep(RANDOM.Next(100));
            Console.WriteLine("ThreadId: {0} bar: {1}", Thread.CurrentThread.ManagedThreadId, bar);
        }
    }

    class Foo2
    {
        [ThreadStatic]
        static string bar;

        static readonly Random RANDOM = new Random();

        public void Baz(string value)
        {
            bar = "#1: " + value;
            Thread.Sleep(RANDOM.Next(100));
            bar = "#2: " + value;
            Thread.Sleep(RANDOM.Next(100));
            Console.WriteLine("ThreadId: {0} bar: {1}", Thread.CurrentThread.ManagedThreadId, bar);
        }
    }

    class Foo3
    {
        string bar;
        static readonly Random RANDOM = new Random();

        public void Baz(string value)
        {
            bar = "#1: " + value;
            Thread.Sleep(RANDOM.Next(100));
            bar = "#2: " + value;
            Thread.Sleep(RANDOM.Next(100));
            Console.WriteLine("ThreadId: {0} bar: {1}", Thread.CurrentThread.ManagedThreadId, bar);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ThreadPool.SetMaxThreads(8, 8);

            Console.WriteLine("Sequential");
            for (int i = 0; i < 16; i++)
            {
                Payload(i);
            }

            Console.WriteLine();
            Console.WriteLine("Threaded - Thread Unsafe");
            for (int i = 0; i < 16; i++)
            {
                int k = i;
                ThreadPool.QueueUserWorkItem(s => Payload(k));
            }

            Wait();

            Console.WriteLine();
            Console.WriteLine("Threaded - Thread Static");
            for (int i = 0; i < 16; i++)
            {
                int k = i;
                ThreadPool.QueueUserWorkItem(s => Payload2(k));
            }

            Wait();

            Console.WriteLine();
            Console.WriteLine("Threaded - Thread Instance");
            for (int i = 0; i < 16; i++)
            {
                int k = i;
                ThreadPool.QueueUserWorkItem(s => Payload3(k));
            }

            Console.ReadLine();
        }

        static void Wait()
        {
            int t, c;
            do
            {
                ThreadPool.GetAvailableThreads(out t, out c);
            }
            while (t < 8);
        }

        static void Payload(int i)
        {
            var f = new Foo();
            f.Baz(i.ToString());
        }

        static void Payload2(int i)
        {
            var f = new Foo2();
            f.Baz(i.ToString());
        }

        static void Payload3(int i)
        {
            var f = new Foo3();
            f.Baz(i.ToString());
        }
    }