Alternative solution to HostingEnvironment.QueueBackgroundWorkItem in .NET Core

Question

We are working with .NET Core Web Api, and looking for a lightweight solution to log requests with variable intensity into database, but don\'t want client\'s to wait for th

Answer 1

I know this is a little late, but we just ran into this issue too. So after reading lots of ideas, here's the solution we came up with.

    /// 

    /// Defines a simple interface for scheduling background tasks. Useful for UnitTesting ASP.net code
    /// 
    public interface ITaskScheduler
    {
        /// 

        /// Schedules a task which can run in the background, independent of any request.
        /// 
        /// A unit of execution.
        [SecurityPermission(SecurityAction.LinkDemand, Unrestricted = true)]
        void QueueBackgroundWorkItem(Action workItem);

        /// 

        /// Schedules a task which can run in the background, independent of any request.
        /// 
        /// A unit of execution.
        [SecurityPermission(SecurityAction.LinkDemand, Unrestricted = true)]
        void QueueBackgroundWorkItem(Func workItem);
    }


    public class BackgroundTaskScheduler : BackgroundService, ITaskScheduler
    {
        public BackgroundTaskScheduler(ILogger logger)
        {
            _logger = logger;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            _logger.LogTrace("BackgroundTaskScheduler Service started.");

            _stoppingToken = stoppingToken;

            _isRunning = true;
            try
            {
                await Task.Delay(-1, stoppingToken);
            }
            catch (TaskCanceledException)
            {
            }
            finally
            {
                _isRunning = false;
                _logger.LogTrace("BackgroundTaskScheduler Service stopped.");
            }
        }

        public void QueueBackgroundWorkItem(Action workItem)
        {
            if (workItem == null)
            {
                throw new ArgumentNullException(nameof(workItem));
            }

            if (!_isRunning)
                throw new Exception("BackgroundTaskScheduler is not running.");

            _ = Task.Run(() => workItem(_stoppingToken), _stoppingToken);
        }

        public void QueueBackgroundWorkItem(Func workItem)
        {
            if (workItem == null)
            {
                throw new ArgumentNullException(nameof(workItem));
            }

            if (!_isRunning)
                throw new Exception("BackgroundTaskScheduler is not running.");

            _ = Task.Run(async () =>
                {
                    try
                    {
                        await workItem(_stoppingToken);
                    }
                    catch (Exception e)
                    {
                        _logger.LogError(e, "When executing background task.");
                        throw;
                    }
                }, _stoppingToken);
        }

        private readonly ILogger _logger;
        private volatile bool _isRunning;
        private CancellationToken _stoppingToken;
    }

The ITaskScheduler (which we already defined in our old ASP.NET client code for UTest test purposes) allows a client to add a background task. The main purpose of the BackgroundTaskScheduler is to capture the stop cancellation token (which is own by the Host) and to pass it into all the background Tasks; which by definition, runs in the System.Threading.ThreadPool so there is no need to create our own.

To configure Hosted Services properly see this post.

Enjoy!