ASP.NET Hosting Tips — How to Cancel Tasks in .NET 4.0?

There are several requirements to permit the cancellation of a task. First, you need to generate a token that will help to co-ordinate cancellation. The token itself is an instance of the CancellationToken structure. The token is not instantiated using a constructor. Instead, you create an instance of the CancellationTokenSource class and read the token from its Token property.

.NET 4.0 introduces a lightweight struct called the CancellationToken that provides a mechanism to cancel synchronous and 카지노사이트추천 asynchronous operations. Here are some important members of this struct:

IsCancellationRequested — a Boolean property that can be polled by the code to find out if it has been cancelled or the cancellation has been requested

Register — to register a delegate for a callback when a cancellation request has been made.

When creating tasks that support cancellation, you pass the token to the Task’s constructor in addition to the delegate to execute. The token also needs to be accessible within the delegate so that you can access its properties and methods. These include the IsCancellationRequested property, which returns a Boolean value indicating whether cancellation has or has not been requested.

The final part of supporting cancellation is ensuring that your task can stop gracefully and leave the system in a valid state. Within long-running tasks you should periodically check if the task has been cancelled and, if it has, do any clean-up work before exiting. This may include closing files or database connections, completing or 카지노사이트추천 rolling back transactions and disposing of resources. It should be noted that requesting cancellation will never force a task to halt. If you ignore a cancellation request your task will continue executing until complete or until it throws an exception.

We can see this pattern in our first example below. In the Main method we create a CancellationTokenSource and use it to obtain a token. We then pass this token to our Task’s constructor. In this case the lambda expression that defines the Task’s actions calls a separate method. This is to make the structure of the task cancellation pattern easier to see. After the task has started, we wait for the user to press Enter before cancelling the task by calling the CancellationTokenSource’s Cancel method. This tells any tasks that used its tokens that they should stop executing.

The DoLongRunningTask method is called from within the parallel task. It simulates a long running process by looping one hundred times and pausing for 카지노사이트가입 one second between each iteration. Before the loop starts, the IsCancellationRequested property of the token is checked. As it is possible that the it could have been cancelled before it had actually started executing, this check allows it to be stopped without performing any work. The IsCancellationRequested flag is checked again during each iteration. If true, a message is displayed and the loop exits.

Try running the code and allowing a few iterations to complete before pressing Enter to cancel the task.

static void Main()

var tokenSource = new CancellationTokenSource();

var token = tokenSource.Token;

var task = new Task(() => DoLongRunningTask(token), token);

Console.WriteLine(«Press Enter to cancel»);

task.Start();

Console.ReadLine();

tokenSource.Cancel();

task.Wait();

task.Dispose();

Console.WriteLine(«Press Enter to exit»);

Console.ReadLine();

static void DoLongRunningTask(CancellationToken token)

if (token.IsCancellationRequested)

Console.WriteLine(«Cancelled before long running task started»);

return;

for (int i = 0; i <= 100; i++)

Console.WriteLine(«0%», i);

Thread.Sleep(1000);

if (token.IsCancellationRequested)

Console.WriteLine(«Cancelled»);

break;

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