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StartNew Method (Action(Object), Object, CancellationToken)

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

Creates and starts a Task.

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

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

Parameters

action
Type: System.Action<Object>

The action delegate to execute asynchronously.

state
Type: System.Object

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

cancellationToken
Type: System.Threading.CancellationToken

The CancellationToken that will be assigned to the new Task

Return Value

Type: System.Threading.Tasks.Task
The started Task.

ExceptionCondition
ObjectDisposedException

The provided CancellationToken has already been disposed.

ArgumentNullException

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.Tasks;

public class Example
{
   public static void Main()
   {
      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];
                                                      lock (lockObj) {
                                                         for (int ctr = 0; ctr < order.Length; ctr++)
                                                             order[ctr] = rnd.NextDouble();
                                                      }
                                                      Array.Sort(order, chars);
                                                      Console.WriteLine("{0} --> {1}", word,
                                                                        new String(chars));
                                                    }, word6));

      Task.WaitAll(tasks.ToArray());
   }
}
// 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.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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