Background Workers
Introduction
Background workers are simple independent threads in the application running in the background. Generally, they run periodically to perform some tasks. Examples;
- A background worker can run periodically to delete old logs.
- A background worker can run periodically to determine inactive users and send emails to get users to return to your application.
Create a Background Worker
A background worker should directly or indirectly implement the IBackgroundWorker
interface.
A background worker is inherently singleton. So, only a single instance of your worker class is instantiated and run.
BackgroundWorkerBase
BackgroundWorkerBase
is an easy way to create a background worker.
public class MyWorker : BackgroundWorkerBase
{
public override Task StartAsync(CancellationToken cancellationToken = default)
{
//...
}
public override Task StopAsync(CancellationToken cancellationToken = default)
{
//...
}
}
Start your worker in the StartAsync
(which is called when the application begins) and stop in the StopAsync
(which is called when the application shuts down).
You can directly implement the
IBackgroundWorker
, butBackgroundWorkerBase
provides some useful properties likeLogger
.
AsyncPeriodicBackgroundWorkerBase
Assume that we want to make a user passive, if the user has not logged in to the application in last 30 days. AsyncPeriodicBackgroundWorkerBase
class simplifies to create periodic workers, so we will use it for the example below:
public class PassiveUserCheckerWorker : AsyncPeriodicBackgroundWorkerBase
{
public PassiveUserCheckerWorker(
AbpTimer timer,
IServiceScopeFactory serviceScopeFactory
) : base(
timer,
serviceScopeFactory)
{
Timer.Period = 600000; //10 minutes
}
protected override async Task DoWorkAsync(
PeriodicBackgroundWorkerContext workerContext)
{
Logger.LogInformation("Starting: Setting status of inactive users...");
//Resolve dependencies
var userRepository = workerContext
.ServiceProvider
.GetRequiredService<IUserRepository>();
//Do the work
await userRepository.UpdateInactiveUserStatusesAsync();
Logger.LogInformation("Completed: Setting status of inactive users...");
}
}
AsyncPeriodicBackgroundWorkerBase
uses theAbpTimer
(a thread-safe timer) object to determine the period. We can set itsPeriod
property in the constructor.- It required to implement the
DoWorkAsync
method to execute the periodic work. - It is a good practice to resolve dependencies from the
PeriodicBackgroundWorkerContext
instead of constructor injection. BecauseAsyncPeriodicBackgroundWorkerBase
uses aIServiceScope
that is disposed when your work finishes. AsyncPeriodicBackgroundWorkerBase
catches and logs exceptions thrown by theDoWorkAsync
method.
Register Background Worker
After creating a background worker class, you should to add it to the IBackgroundWorkerManager
. The most common place is the OnApplicationInitialization
method of your module class:
[DependsOn(typeof(AbpBackgroundWorkersModule))]
public class MyModule : AbpModule
{
public override void OnApplicationInitialization(
ApplicationInitializationContext context)
{
context.AddBackgroundWorker<PassiveUserCheckerWorker>();
}
}
context.AddBackgroundWorker(...)
is a shortcut extension method for the expression below:
context.ServiceProvider
.GetRequiredService<IBackgroundWorkerManager>()
.Add(
context
.ServiceProvider
.GetRequiredService<PassiveUserCheckerWorker>()
);
So, it resolves the given background worker and adds to the IBackgroundWorkerManager
.
While we generally add workers in OnApplicationInitialization
, there are no restrictions on that. You can inject IBackgroundWorkerManager
anywhere and add workers at runtime. Background worker manager will stop and release all the registered workers when your application is being shut down.
Options
AbpBackgroundWorkerOptions
class is used to set options for the background workers. Currently, there is only one option:
IsEnabled
(default: true): Used to enable/disable the background worker system for your application.
See the Options document to learn how to set options.
Making Your Application Always Run
Background workers only work if your application is running. If you host the background job execution in your web application (this is the default behavior), you should ensure that your web application is configured to always be running. Otherwise, background jobs only work while your application is in use.
Running On a Cluster
Be careful if you run multiple instances of your application simultaneously in a clustered environment. In that case, every application runs the same worker which may create conflicts if your workers are running on the same resources (processing the same data, for example).
If that's a problem for your workers, you have two options;
- Disable the background worker system using the
AbpBackgroundWorkerOptions
described above, for all the application instances, except one of them. - Disable the background worker system for all the application instances and create another special application that runs on a single server and execute the workers.
Quartz Integration
ABP Framework's background worker system is good to implement periodic tasks. However, you may want to use an advanced task scheduler like Quartz. See the community contributed quartz integration for the background workers.