I would like to present how to make background services in asp.net core with IHostedService.

What is IHostedService

You can use IHostedService to create background tasks in asp.net core projects. I used Quartz.NET to similar purposes in the past. I do not want to compare them because it is not purpose of this article :-). So, if you want to create background task you can do that by implementing IHostedService. It’s very simple 🙂

How can we use it

I would like to create very very simple background task which creates GUIDs every 10 seconds and save them in memory cache. Don’t worry I’ll display them on website 😉 We need to create some base class BackgroundService. I create something similar like BackgroundService from here

BackgroundService:

using Microsoft.Extensions.Hosting;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace Letys.HostedService.Example.Services
{
  public abstract class BackgroundService : IHostedService, IDisposable
  {
    private Task task;
    private readonly CancellationTokenSource cancellationTokens = new CancellationTokenSource();

    protected abstract Task ExecuteAsync(CancellationToken stoppingToken);
    
    public virtual Task StartAsync(CancellationToken cancellationToken)
    {
      this.task = this.ExecuteAsync(this.cancellationTokens.Token);
      return this.task.IsCompleted ? this.task : Task.CompletedTask;
    }

    public virtual async Task StopAsync(CancellationToken cancellationToken)
    {
      if (this.task != null)
      {
        try
        {
          this.cancellationTokens.Cancel();
        }
        finally
        {
          await Task.WhenAny(task, Task.Delay(Timeout.Infinite, cancellationToken));
        }
      }
    }

    public virtual void Dispose()
    {
      this.cancellationTokens.Cancel();
    }
  }
}

After that we can create our background task class – ExampleGuidService:

using Letys.HostedService.Example.Models;
using Microsoft.Extensions.Caching.Memory;
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace Letys.HostedService.Example.Services
{
  public class ExampleGuidService : BackgroundService
  {
    public const string ExampleGuidsKey = "ExampleGuids";
    private IMemoryCache memoryCache;

    public ExampleGuidService(IMemoryCache memoryCache)
    {
      this.memoryCache = memoryCache;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
      while (!stoppingToken.IsCancellationRequested)
      {
        GenerateNewExampleGuid();
        await Task.Delay(1000*10, stoppingToken);
      }
    }

    private void GenerateNewExampleGuid()
    {
      ExampleGuid example = new ExampleGuid
      {
        Timestamp = DateTime.Now,
        Guid = Guid.NewGuid()
      };

      var cacheEntryOptions = new MemoryCacheEntryOptions()
                                    .SetSlidingExpiration(TimeSpan.FromHours(24));

      if (!this.memoryCache.TryGetValue(ExampleGuidService.ExampleGuidsKey, out List<ExampleGuid> cacheEntry))
      {
        cacheEntry = new List<ExampleGuid>();                
      }

      cacheEntry.Add(example);
      this.memoryCache.Set(ExampleGuidService.ExampleGuidsKey, cacheEntry, cacheEntryOptions);
    }
  }
}

This is our ExampleGuid:

using System;

namespace Letys.HostedService.Example.Models
{
  public class ExampleGuid
  {
    public Guid Guid { get; set; }
    public DateTime Timestamp { get; set; }
  }
}

We can register ExampleGuidService in Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
  services.AddMemoryCache();
  services.AddMvc();
  services.AddSingleton<IHostedService, ExampleGuidService>();
}

Now we can add ExampleGuids action and view:

public IActionResult ExampleGuids()
{
  if (!this.memoryCache.TryGetValue(ExampleGuidService.ExampleGuidsKey, out List cacheEntry))
  {
    cacheEntry = new List();
  }
  return View(cacheEntry);
}

@model IEnumerable<Letys.HostedService.Example.Models.ExampleGuid>

@{
  ViewData["Title"] = "ExampleGuids";
  Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>ExampleGuids</h2>

<p>
  <a asp-action="Create">Create New</a>
</p>
<table class="table">
  <thead>
    <tr>
      <th>@Html.DisplayNameFor(model => model.Guid)</th>
      <th>@Html.DisplayNameFor(model => model.Timestamp)</th>
    </tr>
  </thead>
  <tbody>
  @foreach (var item in Model) {
    <tr>
      <td>@Html.DisplayFor(modelItem => item.Guid)</td>
      <td>@Html.DisplayFor(modelItem => item.Timestamp)</td>
    </tr>
  }
  </tbody>
</table>

As you can see every 10 seconds ExampleGuidService creates new guid.