Service lifetimes in .NET (singleton, scoped, transient)

Last time I checked the lifetimes of different types of services and want to share with you my findings.

Application

Having such controller:

    [ApiController]
    [Route("[controller]")]
    public class FooController : ControllerBase
    {

        private ISingletonService _singleton1;
        private ISingletonService _singleton2;
        private IScopedService _scoped1;
        private IScopedService _scoped2;
        private ITransientService _transient1;
        private ITransientService _transient2;

        public FooController(
            ISingletonService singleton1,
            ISingletonService singleton2,
            IScopedService scoped1,
            IScopedService scoped2,
            ITransientService transient1,
            ITransientService transient2)
        {
            _singleton1 = singleton1;
            _singleton2 = singleton2;
            _scoped1 = scoped1;
            _scoped2 = scoped2;
            _transient1 = transient1;
            _transient2 = transient2;
        }

        [HttpGet]
        [Route("Singleton")]
        public List<string> Singleton()
        {
            return new List<string> { 
                _singleton1.GetGuid(), 
                _singleton2.GetGuid() };
        }

        [HttpGet]
        [Route("Scoped")]
        public List<string> Scoped()
        {
            return new List<string> { 
                _scoped1.GetGuid(), 
                _scoped2.GetGuid() };
        }

        [HttpGet]
        [Route("Transient")]
        public List<string> Transient()
        {
            return new List<string> { 
                _transient1.GetGuid(), 
                _transient2.GetGuid() };
        }
    }

and such startup (full repo address in the end of post)

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddTransient<ITransientService, TransientService>();
            services.AddScoped<IScopedService, ScopedService>();
            services.AddSingleton<ISingletonService, SingletonService>();

            services.AddControllers();
        }

I queried each endpoint (singleton, scoped, transient) two times. Here are the results:

Singleton

first request

second request

Conclusion

• doesn’t matter how many times you request endpoint. There is only one instance.

Singleton service is created

• first time they’re requested and is not destroyed
• by developer

When useful?

• caching
• configuration
• global rules

Scoped

first request

second request

Conclusion:

• each request generates new Guid
• same instance is shared in the boundary of single request

each time you access the page the service is createdwhen useful?

• persist state throughout application per request

Transient

first request

second request

Conclusion

• each request generates new Guids
• new Guid (new instance) of service is created on each access to instance

Transient service is created

• each time they’re requested from the service container

When useful?

• weightless stateless services

Link to the repo: https://github.com/simplyaboutcode/ServiceLifetime