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| title | author | description | monikerRange | ms.author | ms.custom | ms.date | uid |
|---|---|---|---|---|---|---|---|
| Background tasks with hosted services in ASP.NET Core | guardrex | Learn how to implement background tasks with hosted services in ASP.NET Core. | >= aspnetcore-2.1 | riande | mvc | 02/15/2018 | fundamentals/host/hosted-services |
Background tasks with hosted services in ASP.NET Core
By Luke Latham
In ASP.NET Core, background tasks can be implemented as hosted services. A hosted service is a class with background task logic that implements the IHostedService interface. This topic provides three hosted service examples:
- Background task that runs on a timer.
- Hosted service that activates a scoped service. The scoped service can use dependency injection.
- Queued background tasks that run sequentially.
View or download sample code (how to download)
The sample app is provided in two versions:
- Web Host – The Web Host is useful for hosting web apps. The example code shown in this topic is from the Web Host version of the sample. For more information, see the Web Host topic.
- Generic Host – The Generic Host is new in ASP.NET Core 2.1. For more information, see the Generic Host topic.
IHostedService interface
Hosted services implement the IHostedService interface. The interface defines two methods for objects that are managed by the host:
-
StartAsync(CancellationToken) -
StartAsynccontains the logic to start the background task. When using the Web Host,StartAsyncis called after the server has started and IApplicationLifetime.ApplicationStarted is triggered. When using the Generic Host,StartAsyncis called beforeApplicationStartedis triggered. -
StopAsync(CancellationToken) - Triggered when the host is performing a graceful shutdown.
StopAsynccontains the logic to end the background task and dispose of any unmanaged resources. If the app shuts down unexpectedly (for example, the app's process fails),StopAsyncmight not be called.
The hosted service is activated once at app startup and gracefully shutdown at app shutdown. When IDisposable is implemented, resources can be disposed when the service container is disposed. If an error is thrown during background task execution, Dispose should be called even if StopAsync isn't called.
Timed background tasks
A timed background task makes use of the System.Threading.Timer class. The timer triggers the task's DoWork method. The timer is disabled on StopAsync and disposed when the service container is disposed on Dispose:
The service is registered in Startup.ConfigureServices with the AddHostedService extension method:
Consuming a scoped service in a background task
To use scoped services within an IHostedService, create a scope. No scope is created for a hosted service by default.
The scoped background task service contains the background task's logic. In the following example, ILogger is injected into the service:
The hosted service creates a scope to resolve the scoped background task service to call its DoWork method:
The services are registered in Startup.ConfigureServices. The IHostedService implementation is registered with the AddHostedService extension method:
Queued background tasks
A background task queue is based on the .NET 4.x QueueBackgroundWorkItem (tentatively scheduled to be built-in for ASP.NET Core 3.0):
In QueueHostedService, background tasks in the queue are dequeued and executed as a BackgroundService, which is a base class for implementing a long running IHostedService:
The services are registered in Startup.ConfigureServices. The IHostedService implementation is registered with the AddHostedService extension method:
In the Index page model class, the IBackgroundTaskQueue is injected into the constructor and assigned to Queue:
When the Add Task button is selected on the Index page, the OnPostAddTask method is executed. QueueBackgroundWorkItem is called to enqueue the work item: