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Timers in .NET

John Smith on January 27, 2020

A current C# project of mine required a timer where every couple of seconds a method would fire and a potentially fairly long-running process would...

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Katie Nelson • Jan 27 '20

How would you handle a cancellation token? I have a need for a timer that should stop firing on cancellation and also the DoWork method should immediately quit.

John Smith • Jan 28 '20

Hi Katie,

Take a look at this. hitting ctrl-c while its running or in the 5-second DoWork method will cancel gracefully and hopefully do what you want.

I plan to blog about it in more detail later but this should help.

	{
	"Logging": {
	"LogLevel": {
	"Default": "Information",
	"Microsoft": "Warning",
	"Microsoft.Hosting.Lifetime": "Information"
	}
	}
	}

view raw appsettings.Development.json hosted with ❤ by GitHub

	{
	"Logging": {
	"LogLevel": {
	"Default": "Information",
	"Microsoft": "Warning",
	"Microsoft.Hosting.Lifetime": "Information"
	}
	}
	}

view raw appsettings.json hosted with ❤ by GitHub

	using Microsoft.Extensions.DependencyInjection;
	using Microsoft.Extensions.Hosting;

	namespace tempy
	{
	public static class Program
	{
	public static void Main(string[] args)
	{
	CreateHostBuilder(args).Build().Run();
	}

	public static IHostBuilder CreateHostBuilder(string[] args) =>
	Host.CreateDefaultBuilder(args)
	.ConfigureServices((_, services) => services.AddHostedService<Worker>());
	}
	}

view raw Program.cs hosted with ❤ by GitHub

	<Project Sdk="Microsoft.NET.Sdk.Worker">

	<PropertyGroup>
	<TargetFramework>netcoreapp3.1</TargetFramework>
	<UserSecretsId>dotnet-tempy-2E552B51-4FEB-4B21-9AFC-4E4C7A69F645</UserSecretsId>
	</PropertyGroup>

	<ItemGroup>
	<PackageReference Include="Microsoft.Extensions.Hosting" Version="3.1.1" />
	</ItemGroup>
	</Project>

view raw tempy.csproj hosted with ❤ by GitHub

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

	namespace tempy
	{
	/// <summary>
	/// Thanks to this post https://stackoverflow.com/a/56666084/2041
	/// </summary>
	public class Worker : BackgroundService
	{
	private readonly ILogger<Worker> _logger;

	private Timer _timer;

	private Task _executingTask;

	private readonly CancellationTokenSource _stoppingCts = new CancellationTokenSource();

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

	public override Task StartAsync(CancellationToken stoppingToken)
	{
	_logger.LogInformation("Worker started at: {time}", DateTimeOffset.Now);

	_timer = new Timer(DoWork, null, TimeSpan.Zero, TimeSpan.FromSeconds(5));

	return Task.CompletedTask;
	}

	public override async Task StopAsync(CancellationToken stoppingToken)
	{
	_timer?.Change(Timeout.Infinite, 0);

	if (_executingTask == null)
	{
	await Task.CompletedTask.ConfigureAwait(false);
	}

	try
	{
	_logger.LogInformation("Worker stopping at: {time}", DateTimeOffset.Now);

	_stoppingCts.Cancel();
	}
	finally
	{
	await Task.WhenAny(_executingTask, Task.Delay(Timeout.Infinite, stoppingToken)).ConfigureAwait(false);
	}

	await Task.CompletedTask.ConfigureAwait(false);
	}

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

	await Task.CompletedTask.ConfigureAwait(false);
	}

	public override void Dispose()
	{
	_timer?.Dispose();

	base.Dispose();
	}

	private void DoWork(object state)
	{
	GC.KeepAlive(_timer);
	_timer?.Change(Timeout.Infinite, 0);
	_executingTask = DoWorkAsync(_stoppingCts.Token);
	}

	private async Task DoWorkAsync(CancellationToken stoppingToken)
	{
	if (!stoppingToken.IsCancellationRequested)
	{
	_logger.LogInformation("Worker starting DoWorkAsync at: {time}", DateTimeOffset.Now);

	Thread.Sleep(5000);

	_logger.LogInformation("Worker completed DoWorkAsync at: {time}", DateTimeOffset.Now);

	_timer.Change(TimeSpan.FromSeconds(5), TimeSpan.FromMilliseconds(-1));

	await Task.CompletedTask.ConfigureAwait(false);
	}
	}
	}
	}

view raw Worker.cs hosted with ❤ by GitHub

Gist here

gist.github.com/solrevdev/f28ab813...

Katie Nelson • Jan 28 '20

Thanks John. I see now the running timer callback is buried several levels down. Makes things a bit more complex, but I understand what you did.

John Smith • Jan 28 '20

Ahh yes, the timer's TimerCallback method signature needed to be void DoWork(object state) hence needing another method call that uses async Task accepting a CancellationToken.

But looking at it again I think that DoWorkAsync and RunJobAsync could just be the one method.

I'll take another look later and will try and explain more in another blog post.

Katie Nelson • Jan 28 '20

Great! Looking forward to it.