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();
serviceCollection.AddScoped();
serviceCollection.AddTransient();
var servicepProvider = serviceCollection.BuildServiceProvider();
using (IServiceScope scope = servicepProvider.CreateScope(), scope2 = servicepProvider.CreateScope())
{
var scopeObj1 = scope.ServiceProvider.GetService();
var scopeObj2 = scope2.ServiceProvider.GetService();
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。
- 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。
- 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。
- HttpProtocol.ProcessRequests 方法内调用await FireOnCompleted();
- FireOnCompleted内部会循环执行
Stack
堆栈委托, object>>? _onCompleted; - 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!;
}
}
///
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(IHttpApplication 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, 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?
- 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);
- 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
- 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。)