This is a simple example where two threads share the work. This example can be used where two workers are sharing / exchanging work Traffic signalling Typically in this pattern two threads share the work static AutoResetEvent FirstWorktodo = new AutoResetEvent(false); static AutoResetEvent SecondWorkTodo = new AutoResetEvent(false); int Main() { Console.WriteLine("starting two threads"); ThreadPool.QueueUserWorkItem(FirstWork); ThreadPool.QueueUserWorkItem(SecondWork); FirstWorktodo.Set(); // signal the firstOne to begin with } static void FirstWork(object o) { while (true) { FirstWorktodo.WaitOne(); Console.WriteLine("FirstWork starting."); Thread.Sleep(2000); Console.WriteLine("FirstWork ending."); SecondWorkTodo.Set(); } } static void SecondWork(object o) { while (true) { SecondWorkTodo.WaitOne(); Console.WriteLine("secondWork starting."); Thread.Sleep(2000); Console.WriteLine("SecondWork ending."); FirstWorktodo.Set(); } }

The output goes like ... starting two threads FirstWork starting. FirstWork ending. secondWork starting. SecondWork ending. FirstWork starting. FirstWork ending. secondWork starting. SecondWork ending..........

Similarly to exchange work with four threads --- Typically Traffic Signal work.... static AutoResetEvent SecondWorkTodo = new AutoResetEvent(false); static AutoResetEvent FirstWorktodo = new AutoResetEvent(false); static AutoResetEvent ThirdWorktodo = new AutoResetEvent(false); static AutoResetEvent FourthWorktodo = new AutoResetEvent(false); static void FirstWork(object o) { while (true) { FirstWorktodo.WaitOne(); Console.WriteLine("FirstWork starting."); Thread.Sleep(2000); Console.WriteLine("FirstWork ending."); SecondWorkTodo.Set(); } } static void SecondWork(object o) { while (true) { SecondWorkTodo.WaitOne(); Console.WriteLine(" SecondWork starting."); Thread.Sleep(2000); Console.WriteLine(" SecondWork ending."); ThirdWorktodo.Set(); } } static void ThirdWork(object o) { while (true) { ThirdWorktodo.WaitOne(); Console.WriteLine(" ThirdWork starting."); Thread.Sleep(2000); Console.WriteLine(" ThirdWork ending."); FourthWorktodo.Set(); } } static void FourthWork(object o) { while (true) { FourthWorktodo.WaitOne(); Console.WriteLine(" FourthWork starting."); Thread.Sleep(2000); Console.WriteLine(" FourthWork ending."); FirstWorktodo.Set(); } } int main() { Console.WriteLine("starting two threads"); ThreadPool.QueueUserWorkItem(FirstWork); ThreadPool.QueueUserWorkItem(SecondWork); ThreadPool.QueueUserWorkItem(ThirdWork); ThreadPool.QueueUserWorkItem(FourthWork); FirstWorktodo.Set(); }

....the output is like... starting two threads FirstWork starting. FirstWork ending. SecondWork starting. SecondWork ending. ThirdWork starting. ThirdWork ending. FourthWork starting. FourthWork ending. FirstWork starting. FirstWork ending. SecondWork starting. SecondWork ending. ThirdWork starting. ThirdWork ending. FourthWork starting. ...............