Net6 DI源码分析Part5 在Kestrel内Di Scope生命周期是如何根据请求走的？

Net6 DI源码分析Part5 在Kestrel内Di Scope生命周期是如何根据请求走的？

在asp.net core中的DI生命周期有一个Scoped是根据请求走的，也就是说在处理一次请求时，Scope生命周期所提供的服务是同一个实例。它是用IServiceScope是实现的。但是我们要知道何时构建的IServiceScope以及IServiceScope何时被销毁掉
先说结论IServiceScope是根据当前的RequestServicesFeature内作为_scope成员存在的，只要知道RequestServicesFeature何时创建，何时销毁就了解整http request DI的生命周期

netcore中DI生命周期。

在net core 默认的DI中你直接build 出来的servicepProvider 用它去获取的实例对象Scoped & Singleton 是具有相同生命周期的。
如果需要有Scoped生命周期的实例，你需要通过serviceProvider创建一个IServiceScope实例，然后通过该实例获取到的服务实例会跟着IServiceScope一同销毁从而达到Scoped生命周期。

DI生命周期案例 1

ServiceCollection serviceCollection = new ServiceCollection(); serviceCollection.AddSingleton<MySingletonClass>(); serviceCollection.AddScoped<MyScopedClass>(); serviceCollection.AddTransient<MyTransientClass >(); var servicepProvider = serviceCollection.BuildServiceProvider(); using (IServiceScope scope = servicepProvider.CreateScope(), scope2 = servicepProvider.CreateScope()) {     var scopeObj1 = scope.ServiceProvider.GetService<MyScopedClass>();     var scopeObj2 = scope2.ServiceProvider.GetService<MyScopedClass>();     Console.WriteLine(object.ReferenceEquals(scopeObj1, scopeObj2)); //false } //Scoped Constructor //Scoped Constructor //False //Scoped Dispose //Scoped Dispose Console.ReadLine(); 

RequestServicesFeature

为什么说http request DI 的生命周期是根据RequestServicesFeature来的。通过DI生命周期案例了解到需要创建一个scope生命周期，要有一个IServiceScope实例。
那么在http feature中RequestServicesFeature做了对该接口的封装。也用于提供RequestSerivces服务。

1. IServiceScope的创建： HttpContext获取RequstServiceProivder是根据RequestServicesFeature.RequestServices。在RequestServices属性的get方法内创建_scope。并返回给该scope对应的ServiceProvide供后续使用。
2. IServiceScope的销毁：在RequestServicesFeature.Dispose 方法内又调用了_scope属性（IServiceScope）的同名方法从而进行销毁由此提供的所有service。那么只要销毁了当前请求的RequestServicesFeature 实例就销毁了。当前http requst 的scope生命周期的所有服务。

RequestServicesFeature 是何时被销毁的。

1. HttpProtocol.ProcessRequests 方法内调用await FireOnCompleted();
2. FireOnCompleted内部会循环执行 Stack<KeyValuePair<Func<object, Task>, object>>? _onCompleted;堆栈委托
3. requestServiceFeature.Dispose在此刻被调用，其内部Dispose了IServiceScope。自此ServiceScope生命周期结束。

RequestServicesFeature 简化代码

public class RequestServicesFeature : IServiceProvidersFeature, IDisposable, IAsyncDisposable {     private IServiceScope? _scope;     private readonly HttpContext _context;       public RequestServicesFeature(HttpContext context, IServiceScopeFactory? scopeFactory)     {         _context = context;         _scopeFactory = scopeFactory;     }       public IServiceProvider RequestServices     {         get         {             _context.Response.RegisterForDisposeAsync(this);             _scope = _scopeFactory.CreateScope();             _requestServices = _scope.ServiceProvider;             return _requestServices!;         }      }       /// <inheritdoc />     public ValueTask DisposeAsync()     {         switch (_scope)         {             case IAsyncDisposable asyncDisposable:                 var vt = asyncDisposable.DisposeAsync();                 if (!vt.IsCompletedSuccessfully)                 {                     return Awaited(this, vt);                 }                 vt.GetAwaiter().GetResult();                 break;             case IDisposable disposable:                 disposable.Dispose();                 break;         }     } } 

HttpProtocol

该类是处理http协议的 ProcessRequests作为重要方法之一，用来使用我们构建好的IHttpApplication 处理request
httpontext的创建，以及我们编排好的http中间件管道都是在这里被执行的。同时调用FireOnCompleted, RequestServicesFeature就是在这里被销毁的。

private async Task ProcessRequests<TContext>(IHttpApplication<TContext> application) where TContext : notnull {     while (_keepAlive)     {         var context = application.CreateContext(this);         // Run the application code for this request         await application.ProcessRequestAsync(context);         if (_onCompleted?.Count > 0)         {             await FireOnCompleted();         }         application.DisposeContext(context, _applicationException);     } }  protected Task FireOnCompleted()     {         var onCompleted = _onCompleted;         if (onCompleted?.Count > 0)         {             return ProcessEvents(this, onCompleted);         }           return Task.CompletedTask;           static async Task ProcessEvents(HttpProtocol protocol, Stack<KeyValuePair<Func<object, Task>, object>> events)         {             while (events.TryPop(out var entry))             {                 try                 {                     await entry.Key.Invoke(entry.Value);                 }                 catch (Exception ex)                 {                     protocol.Log.ApplicationError(protocol.ConnectionId, protocol.TraceIdentifier, ex);                 }             }         }     } 

RequestServicesFeature 是如何注册到HttpProtocol _onCompleted;堆栈委托中的

HttpProtocol委托堆栈中 RequestServicesFeature 是什么时候被注册进去的呢？

1. RequestServicesFeature.RequestServices属性的Get方法调用了方法内有一句这样的代码 _context.Response.RegisterForDisposeAsync(this);
2. HttpResponse的RegisterForDisposeAsync调用了抽象方法abstract void OnCompleted。实现该方法的是在完成的DefaultHttpResponse
3. DefaultHttpResponse的OnCompleted把委托注册到HttpProtocol.OnCompleted方法注册到_onCompleted中，实际代码体现为 HttpResponseFeature.OnCompleted(callback, state);这里HttpResponseFeature.就是就是HttpProtocol，（HttpProtoccol是个IFeatureCollection接口的实现。）