From MSDN:WaitHandle

The following code example shows how two threads can do background tasks while the Main thread waits for the tasks to complete using the static WaitAny and WaitAll methods of the WaitHandle class.

using System; using System.Threading; public sealed class App { // Define an array with two AutoResetEvent WaitHandles. static WaitHandle[] waitHandles = new WaitHandle[] { new AutoResetEvent(false), new AutoResetEvent(false) }; // Define a random number generator for testing. static Random r = new Random(); static void Main() { // Queue up two tasks on two different threads; // wait until all tasks are completed. DateTime dt = DateTime.Now; Console.WriteLine("Main thread is waiting for BOTH tasks to complete."); ThreadPool.QueueUserWorkItem(new WaitCallback(DoTask), waitHandles[0]); ThreadPool.QueueUserWorkItem(new WaitCallback(DoTask), waitHandles[1]); WaitHandle.WaitAll(waitHandles); // The time shown below should match the longest task. Console.WriteLine("Both tasks are completed (time waited={0})", (DateTime.Now - dt).TotalMilliseconds); // Queue up two tasks on two different threads; // wait until any tasks are completed. dt = DateTime.Now; Console.WriteLine(); Console.WriteLine("The main thread is waiting for either task to complete."); ThreadPool.QueueUserWorkItem(new WaitCallback(DoTask), waitHandles[0]); ThreadPool.QueueUserWorkItem(new WaitCallback(DoTask), waitHandles[1]); int index = WaitHandle.WaitAny(waitHandles); // The time shown below should match the shortest task. Console.WriteLine("Task {0} finished first (time waited={1}).", index + 1, (DateTime.Now - dt).TotalMilliseconds); } static void DoTask(Object state) { AutoResetEvent are = (AutoResetEvent) state; int time = 1000 * r.Next(2, 10); Console.WriteLine("Performing a task for {0} milliseconds.", time); Thread.Sleep(time); are.Set(); } } // This code produces output similar to the following: // // Main thread is waiting for BOTH tasks to complete. // Performing a task for 7000 milliseconds. // Performing a task for 4000 milliseconds. // Both tasks are completed (time waited=7064.8052) // // The main thread is waiting for either task to complete. // Performing a task for 2000 milliseconds. // Performing a task for 2000 milliseconds. // Task 1 finished first (time waited=2000.6528).