Cancellation Token Provider

A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. To handle the possible cancellation of the operation, ABP provides ICancellationTokenProvider to obtain the CancellationToken itself from the source.

When To Use Manual Cancellation Tokens

ABP automates cancellation token usage wherever possible. For example, in ASP.NET Core applications, ABP automatically obtains the CancellationToken from the HttpContext.RequestAborted and uses it in database queries and other cancellable places. So, most of the times, you don't need to deal with CancellationToken objects to pass them between methods.

You do not need to use the ICancellationTokenProvider unless you want to add cancellation support in your own logic or to pass a cancellation token to a method outside of the ABP framework.

ICancellationTokenProvider Service

ICancellationTokenProvider is an abstraction to provide CancellationToken for different scenarios.

Generally, you should pass the CancellationToken as a parameter for your method to use it. With the ICancellationTokenProvider you don't need to pass CancellationToken for every method. ICancellationTokenProvider can be injected with the dependency injection and provides the token from it's source.

Example:

using System.Threading.Tasks;
using Volo.Abp.DependencyInjection;
using Volo.Abp.Threading;

namespace MyProject
{
    public class MyService : ITransientDependency
    {
        private readonly ICancellationTokenProvider _cancellationTokenProvider;

        public MyService(ICancellationTokenProvider cancellationTokenProvider)
        {
            _cancellationTokenProvider = cancellationTokenProvider;
        }

        public async Task DoItAsync()
        {
            while (_cancellationTokenProvider.Token.IsCancellationRequested == false)
            {
                // ...
            }
        }
    }
}

Built-in Providers

• HttpContextCancellationTokenProvider: The default provider for ASP.NET Core applications. It simply provides a CancellationToken that is source of the web request from the HttpContext.RequestAborted.

• NullCancellationTokenProvider: A built in provider and it supply always CancellationToken.None. It is used if no other providers can be used.

Implementing a Custom Cancellation Token Provider

You can easily create your ICancellationTokenProvider implementation by creating a class that implements the ICancellationTokenProvider interface, as shown below:

using System.Threading;

namespace AbpDemo
{
    public class MyCancellationTokenProvider
        : ICancellationTokenProvider, 
          ITransientDependency // Can also be singleton or scoped
    {
        public CancellationToken Token { get; } // TODO: Return a cancellation token
    }
}