TaskFactory.StartNew Method (Action<Object>, Object, CancellationToken)


Creates and starts a Task.

Namespace:   System.Threading.Tasks
Assembly:  mscorlib (in mscorlib.dll)

public Task StartNew(
	Action<object> action,
	object state,
	CancellationToken cancellationToken


Type: System.Action<Object>

The action delegate to execute asynchronously.

Type: System.Object

An object containing data to be used by the action delegate.

Type: System.Threading.CancellationToken

The CancellationToken that will be assigned to the new Task

Return Value

Type: System.Threading.Tasks.Task

The started Task.

Exception Condition

The provided CancellationToken has already been disposed.


The exception that is thrown when the action argument is null.

Calling StartNew is functionally equivalent to creating a Task using one of its constructors and then calling Start to schedule it for execution.

Starting with the .NET Framework 4.5, you can use the Run method with an Action object as a quick way to call StartNew with default parameters. For more information and code examples, see Task.Run vs Task.Factory.StartNew in the Parallel Programming with .NET blog.

The following example defines an array of 6-letter words. Each word is then passed to an Action<T> delegate, which scrambles the word and displays the original word and its scrambled version.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

public class Example
   public static void Main()
      CancellationTokenSource cts = new CancellationTokenSource();
      CancellationToken token = cts.Token;
      var tasks = new List<Task>();
      Random rnd = new Random();
      Object lockObj = new Object();
      String[] words6 = { "reason", "editor", "rioter", "rental",
                          "senior", "regain", "ordain", "rained" };

      foreach (var word6 in words6)
         tasks.Add(Task.Factory.StartNew( (word) => { Char[] chars = word.ToString().ToCharArray();
                                                      double[] order = new double[chars.Length];
                                                      bool wasZero = false;
                                                      lock (lockObj) {
                                                         for (int ctr = 0; ctr < order.Length; ctr++) {
                                                             order[ctr] = rnd.NextDouble();
                                                             if (order[ctr] == 0) {
                                                                if (! wasZero) {
                                                                   wasZero = true;
                                                                else {
                                                      Array.Sort(order, chars);
                                                      Console.WriteLine("{0} --> {1}", word,
                                                                        new String(chars));
                                                    }, word6, token));

      try {
      catch (AggregateException e) {
         foreach (var ie in e.InnerExceptions) {
            if (ie is OperationCanceledException) {
               Console.WriteLine("The word scrambling operation has been cancelled.");
            else {
               Console.WriteLine(ie.GetType().Name + ": " + ie.Message);
      finally {
// The example displays output like the following:
//    regain --> irnaeg
//    ordain --> rioadn
//    reason --> soearn
//    rained --> rinade
//    rioter --> itrore
//    senior --> norise
//    rental --> atnerl
//    editor --> oteird

Note that the example initializes a single random number generator, which is protected by a lock. For the need of a lock, see "The System.Random class and thread safety" in the Random class topic. To handle the possibility of corruption of the random number generator, a cancellation token is passed to task. If two random numbers equal zero, the method assumes that the random number generator is corrupted and sets the cancellation token. Before sorting the chars array that contains the six characters in a word, the method calls the CancellationToken.ThrowIfCancellationRequested method to throw an OperationCanceledException if the token has been canceled.

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 5.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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