Hosted Services & Background Tasks in ASP.NET Core
💡 Concept Name
Hosted Services & Background Tasks in ASP.NET Core
📘 Quick Intro
Hosted services are long-running background tasks in ASP.NET Core apps. You register them using `IHostedService` or `BackgroundService`. They're ideal for scheduled jobs, queues, and background processing.
🧠 Analogy / Short Story
Imagine your app is a restaurant. The front desk (controllers) serves customers, but cleaning staff (hosted services) work in the background. They start with the restaurant and work quietly behind the scenes, ensuring everything runs smoothly.
🔧 Technical Explanation
ASP.NET Core apps can host background services using the `IHostedService` interface or by extending the `BackgroundService` class.
These services are started automatically when the app starts and can be used to run continuous or periodic background work.
You register them using `services.AddHostedService
🎯 Purpose & Use Case
- ✅ Schedule recurring background jobs (cron-style)
- ✅ Process queues or messages asynchronously
- ✅ Monitor services or API health regularly
- ✅ Perform batch processing or report generation
- ✅ Long-running computation without blocking UI threads
💻 Real Code Example
// Sample Hosted Service
public class DailyJobService : BackgroundService
{
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
while (!stoppingToken.IsCancellationRequested)
{
Console.WriteLine("Running job at: " + DateTime.Now);
await Task.Delay(TimeSpan.FromHours(24), stoppingToken);
}
}
}
// Register in Program.cs
builder.Services.AddHostedService<DailyJobService>();
❓ Interview Q&A
Q1: What interface must a hosted service implement?
A: `IHostedService`
Q2: What's the preferred base class for background jobs?
A: `BackgroundService`
Q3: How are hosted services registered?
A: Using `AddHostedService
Q4: Are hosted services thread-blocking?
A: No, they're asynchronous and non-blocking.
Q5: How do you gracefully stop a service?
A: Use the `CancellationToken` passed to `ExecuteAsync()`.
Q6: Can multiple hosted services run in one app?
A: Yes, you can register multiple.
Q7: What lifecycle method starts a hosted service?
A: `StartAsync()`
Q8: What about stopping it?
A: `StopAsync()`
Q9: Can hosted services depend on DI services?
A: Yes, they support constructor injection.
Q10: Where can you see logs of background services?
A: Through `ILogger
📝 MCQs
Q1: What interface is required for a hosted service?
- A. IStartup
- B. IService
- C. IRunAsync
- D. IHostedService
Q2: Which method runs continuously in `BackgroundService`?
- A. ExecuteAsync()
- B. StartLoop()
- C. BeginAsync()
- D. RunProcess()
Q3: What method is used to stop a hosted service?
- A. StopAsync()
- B. EndService()
- C. Cancel()
- D. Dispose()
Q4: How do you inject a scoped service into a hosted service?
- A. Using constructor
- B. Register in Program.cs
- C. Using static service locator
- D. Create scope using IServiceScopeFactory
Q5: When does a hosted service start in ASP.NET Core lifecycle?
- A. Before middleware loads
- B. After routing setup
- C. After the application starts
- D. During DI configuration
Q6: Which of the following is NOT a valid use case for hosted services?
- A. Background email sender
- B. Real-time chat UI rendering
- C. Static file middleware
- D. Scheduled report generator
Q7: What happens if a hosted service throws an unhandled exception?
- A. It restarts automatically
- B. It may crash the app unless handled
- C. It retries automatically
- D. Nothing happens
Q8: Which namespace contains `BackgroundService`?
- A. System.Threading
- B. Microsoft.Extensions.Hosting
- C. Microsoft.AspNetCore.Hosting
- D. System.Hosting
Q9: What return type does `ExecuteAsync()` use?
- A. void
- B. bool
- C. Task
- D. Task<bool>
Q10: What attribute can you use to schedule tasks in production-ready hosted services?
- A. [Schedule]
- B. [Timer]
- C. [Execute]
- D. None - you must use `Task.Delay()` or 3rd-party libraries like Quartz.NET
💡 Bonus Insight
You can combine `Channel
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