ManualResetEvent

 private static Mutex m = new Mutex();

        static bool p = true;
        public static void A()
        {
            while (true)
            {
                m.WaitOne();
                p = !p;
                Thread.Sleep(5000);
                Console.WriteLine(Thread.CurrentThread.Name);
                m.ReleaseMutex();
            }
        }

        public static void B()
        {
            while (true)
            {
                m.WaitOne();
                //Thread.Sleep(500);
                Console.WriteLine(Thread.CurrentThread.Name);
                Console.WriteLine(p);
                m.ReleaseMutex();
            }
        }