Understanding Service Lifetimes in C#

When building modern ASP.NET Core applications, managing service lifetimes is essential for memory management, performance, and thread safety.

Let's break down the three types of lifetimes: Scoped, Singleton, and Transient — with visual clarity, real-life examples, and proper code usage.

1.Scoped Services

• A single instance is created per HTTP request (or per scope in non-web apps).
• Suitable for services that work with a single request's data, like Entity Framework's DbContext.

Example
In the case of handling user authentication, a Scoped service like AuthService is created once per user request to manage login, logout, and token refresh, ensuring it operates within the scope of that particular HTTP request.

2.Singleton Services

• Created once and shared throughout the application's lifetime.
• Must be thread-safe, since it is shared across multiple requests and threads.

Example
In the case of password hashing during user registration or login, a Transient service like PasswordHasher is instantiated each time to securely hash passwords with a unique salt, providing a fresh instance for each hashing operation.

3.Transient Services

• A new instance is created each time the service is requested.
• Ideal for stateless operations or services that do not need to maintain any state.

Example
In the case of user authorization, a Singleton service like JwtTokenValidator is used to parse and validate JWT tokens efficiently across all requests without creating multiple instances.

Scoped vs Singleton vs Transient

Singleton: A single instance is created and shared throughout the application's lifetime. Ideal for shared, stateless services.

Scoped: A new instance is created per HTTP request. Useful when you want to maintain state within a single request, like with DbContext.

Transient: A new instance is provided every time the service is requested. Suitable for lightweight, short-lived operations.

Conclusion

Understanding service lifetimes helps in avoiding memory leaks, ensuring thread safety, and improving performance.

• Scoped for per-request logic like DbContext
• Singleton for app-wide shared logic
• Transient for short-lived, one-time tasks