Worker.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace AspNetCore.WorkerSample
{
	public class Worker : BackgroundService
	{
		private readonly ILogger<Worker> _logger;
		private Task _executingTask;
		private CancellationTokenSource _cts;

		public Worker(ILogger<Worker> logger)
		{
			_logger = logger;
		}

		public override Task StartAsync(CancellationToken cancellationToken)
		{
			_logger.LogWarning("Worker service started.");

			_cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
			_executingTask = ExecuteAsync(_cts.Token);

			return _executingTask.IsCompleted ? _executingTask : Task.CompletedTask;
		}

		public override Task StopAsync(CancellationToken cancellationToken)
		{
			if (_executingTask == null)
			{
				return Task.CompletedTask;
			}

			_logger.LogWarning("Worker service stopping.");

			_cts.Cancel();

			Task.WhenAny(_executingTask, Task.Delay(-1, cancellationToken)).ConfigureAwait(true);

			cancellationToken.ThrowIfCancellationRequested();

			_logger.LogWarning("Worker service stopped.");

			return Task.CompletedTask;
		}

		protected override async Task ExecuteAsync(CancellationToken stoppingToken)
		{
			while (!stoppingToken.IsCancellationRequested)
			{
				_logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
				await Task.Delay(1000, stoppingToken);
			}
		}
	}
}