.NET Core开发日志——依赖注入

依赖注入(DI)不是一个新的话题，它的出现是伴随着系统解耦的需要而几乎必然产生的。

在SOLID设计原则中，DIP(Dependency inversion principle)——依赖倒置，规定了“需依赖抽象，而非实现”的准则，该原则主要目的是通过引入抽象(比如接口)的方式降低模块之间的耦合性。与此原则相拟而又有所不同的是IoC(inversion of control)——控制反转设计原则。这项原则定义了应该由通用框架而非外部代码决定控制流(control flow)的概念。对控制反转的实现有数种技术，DI(Dependency injection)——依赖注入便是其中之一，而依赖注入技术同时又支持依赖倒置的设计原则，所以它被广泛使用并不是件令人意外的事情。

依赖注入的基本特性是借由一个对象提供对另一对象的依赖。这样的一个对象通常又被称为容器。容器负责被依赖对象的注册(register)，解析(resolve)与释放(release)，并具有将被依赖对象注入到依赖对象内部的功能。

在之前的ASP.NET开发过程中，要想使用到依赖注入技术必需依赖第三方类库，而在ASP.NET Core中，这项技术已经被引入到其自身的框架中。

容器

ASP.NET Core中使用ServiceProvider作为依赖注入的容器，它是在WebHostBuilder类中被引入的。

public IWebHost Build()
{
    ...

    IServiceProvider GetProviderFromFactory(IServiceCollection collection)
    {
        var provider = collection.BuildServiceProvider();
        var factory = provider.GetService<IServiceProviderFactory<IServiceCollection>>();

        if (factory != null)
        {
            using (provider)
            {
                return factory.CreateServiceProvider(factory.CreateBuilder(collection));
            }
        }

        return provider;
    }
}

注册

所需依赖的对象通过ServiceCollectionServiceExtensions中的各种扩展方法被加入到ServiceCollection类中。ServiceCollection类内部维护着一个ServiceDescriptor集合。而ServiceCollection又会被传入ServiceProvider的构造方法。

public static IServiceCollection AddTransient(
    this IServiceCollection services,
    Type serviceType,
    Type implementationType)
{
    ...

    return Add(services, serviceType, implementationType, ServiceLifetime.Transient);
}

public static IServiceCollection AddScoped(
    this IServiceCollection services,
    Type serviceType,
    Type implementationType)
{
    ...

    return Add(services, serviceType, implementationType, ServiceLifetime.Scoped);
}

public static IServiceCollection AddSingleton(
    this IServiceCollection services,
    Type serviceType,
    Type implementationType)
{
    ...

    return Add(services, serviceType, implementationType, ServiceLifetime.Singleton);
}

private static IServiceCollection Add(
    IServiceCollection collection,
    Type serviceType,
    Type implementationType,
    ServiceLifetime lifetime)
{
    var descriptor = new ServiceDescriptor(serviceType, implementationType, lifetime);
    collection.Add(descriptor);
    return collection;
}

解析

要想获得已注册的对象，可以通过ServiceProviderServiceExtensions类的扩展方法GetService。

public static T GetService<T>(this IServiceProvider provider)
{
    if (provider == null)
    {
        throw new ArgumentNullException(nameof(provider));
    }

    return (T)provider.GetService(typeof(T));
}

ServiceProvider的GetService方法其实是调用了它内部各种引擎的父类ServiceProviderEngine的方法。这些引擎间区别在于实现方式以及性能上，功能方面都是一样的。默认引擎是DynamicServiceProviderEngine。

private readonly IServiceProviderEngine _engine;

internal ServiceProvider(IEnumerable<ServiceDescriptor> serviceDescriptors, ServiceProviderOptions options)
{
  IServiceProviderEngineCallback callback = null;
  if (options.ValidateScopes)
  {
      callback = this;
      _callSiteValidator = new CallSiteValidator();
  }
  switch (options.Mode)
  {
      case ServiceProviderMode.Dynamic:
          _engine = new DynamicServiceProviderEngine(serviceDescriptors, callback);
          break;
      case ServiceProviderMode.Runtime:
          _engine = new RuntimeServiceProviderEngine(serviceDescriptors, callback);
          break;
#if IL_EMIT
      case ServiceProviderMode.ILEmit:
          _engine = new ILEmitServiceProviderEngine(serviceDescriptors, callback);
          break;
#endif
      case ServiceProviderMode.Expressions:
          _engine = new ExpressionsServiceProviderEngine(serviceDescriptors, callback);
          break;
      default:
          throw new NotSupportedException(nameof(options.Mode));
  }
}

public object GetService(Type serviceType) => _engine.GetService(serviceType);

ServiceProviderEngine类的CreateServiceAccessor方法创建了CallSite。

internal object GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
{
    if (_disposed)
    {
        ThrowHelper.ThrowObjectDisposedException();
    }

    var realizedService = RealizedServices.GetOrAdd(serviceType, _createServiceAccessor);
    _callback?.OnResolve(serviceType, serviceProviderEngineScope);
    return realizedService.Invoke(serviceProviderEngineScope);
}

private Func<ServiceProviderEngineScope, object> CreateServiceAccessor(Type serviceType)
{
    var callSite = CallSiteFactory.CreateCallSite(serviceType, new CallSiteChain());
    if (callSite != null)
    {
        _callback?.OnCreate(callSite);
        return RealizeService(callSite);
    }

    return _ => null;
}

假设注册是用的public static IServiceCollection AddSingleton(this IServiceCollection services, Type serviceType, Type implementationType)方法，那么之后的处理会生成一个SingletonCallSite对象并且包含ConstructorCallSite参数值。

private IServiceCallSite TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain)
{
    if (serviceType == descriptor.ServiceType)
    {
        IServiceCallSite callSite;
        if (descriptor.ImplementationInstance != null)
        {
            callSite = new ConstantCallSite(descriptor.ServiceType, descriptor.ImplementationInstance);
        }
        else if (descriptor.ImplementationFactory != null)
        {
            callSite = new FactoryCallSite(descriptor.ServiceType, descriptor.ImplementationFactory);
        }
        else if (descriptor.ImplementationType != null)
        {
            callSite = CreateConstructorCallSite(descriptor.ServiceType, descriptor.ImplementationType, callSiteChain);
        }
        else
        {
            throw new InvalidOperationException("Invalid service descriptor");
        }

        return ApplyLifetime(callSite, descriptor, descriptor.Lifetime);
    }

    return null;
}

private IServiceCallSite CreateConstructorCallSite(Type serviceType, Type implementationType, CallSiteChain callSiteChain)
{
    callSiteChain.Add(serviceType, implementationType);

    var constructors = implementationType.GetTypeInfo()
        .DeclaredConstructors
        .Where(constructor => constructor.IsPublic)
        .ToArray();

    IServiceCallSite[] parameterCallSites = null;

    if (constructors.Length == 0)
    {
        throw new InvalidOperationException(Resources.FormatNoConstructorMatch(implementationType));
    }
    else if (constructors.Length == 1)
    {
        var constructor = constructors[0];
        var parameters = constructor.GetParameters();
        if (parameters.Length == 0)
        {
            return new CreateInstanceCallSite(serviceType, implementationType);
        }

        parameterCallSites = CreateArgumentCallSites(
            serviceType,
            implementationType,
            callSiteChain,
            parameters,
            throwIfCallSiteNotFound: true);

        return new ConstructorCallSite(serviceType, constructor, parameterCallSites);
    }

    ...
}

private IServiceCallSite ApplyLifetime(IServiceCallSite serviceCallSite, object cacheKey, ServiceLifetime descriptorLifetime)
{
    if (serviceCallSite is ConstantCallSite)
    {
        return serviceCallSite;
    }

    switch (descriptorLifetime)
    {
        case ServiceLifetime.Transient:
            return new TransientCallSite(serviceCallSite);
        case ServiceLifetime.Scoped:
            return new ScopedCallSite(serviceCallSite, cacheKey);
        case ServiceLifetime.Singleton:
            return new SingletonCallSite(serviceCallSite, cacheKey);
        default:
            throw new ArgumentOutOfRangeException(nameof(descriptorLifetime));
    }
}

ServiceProvider真正解析的是这个生成出来的CallSite对象。

protected override Func<ServiceProviderEngineScope, object> RealizeService(IServiceCallSite callSite)
{
    var callCount = 0;
    return scope =>
    {
        if (Interlocked.Increment(ref callCount) == 2)
        {
            Task.Run(() => base.RealizeService(callSite));
        }
        return RuntimeResolver.Resolve(callSite, scope);
    };
}

public object Resolve(IServiceCallSite callSite, ServiceProviderEngineScope scope)
{
    return VisitCallSite(callSite, scope);
}

protected virtual TResult VisitCallSite(IServiceCallSite callSite, TArgument argument)
{
    switch (callSite.Kind)
    {
        case CallSiteKind.Factory:
            return VisitFactory((FactoryCallSite)callSite, argument);
        case  CallSiteKind.IEnumerable:
            return VisitIEnumerable((IEnumerableCallSite)callSite, argument);
        case CallSiteKind.Constructor:
            return VisitConstructor((ConstructorCallSite)callSite, argument);
        case CallSiteKind.Transient:
            return VisitTransient((TransientCallSite)callSite, argument);
        case CallSiteKind.Singleton:
            return VisitSingleton((SingletonCallSite)callSite, argument);
        case CallSiteKind.Scope:
            return VisitScoped((ScopedCallSite)callSite, argument);
        case CallSiteKind.Constant:
            return VisitConstant((ConstantCallSite)callSite, argument);
        case CallSiteKind.CreateInstance:
            return VisitCreateInstance((CreateInstanceCallSite)callSite, argument);
        case CallSiteKind.ServiceProvider:
            return VisitServiceProvider((ServiceProviderCallSite)callSite, argument);
        case CallSiteKind.ServiceScopeFactory:
            return VisitServiceScopeFactory((ServiceScopeFactoryCallSite)callSite, argument);
        default:
            throw new NotSupportedException($"Call site type {callSite.GetType()} is not supported");
    }
}

因为上例中CallSite的类型是Constructor，所以最终通过VisitConstructor方法获得所依赖的对象。

protected override object VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProviderEngineScope scope)
{
    object[] parameterValues = new object[constructorCallSite.ParameterCallSites.Length];
    for (var index = 0; index < parameterValues.Length; index++)
    {
        parameterValues[index] = VisitCallSite(constructorCallSite.ParameterCallSites[index], scope);
    }

    try
    {
        return constructorCallSite.ConstructorInfo.Invoke(parameterValues);
    }
    catch (Exception ex) when (ex.InnerException != null)
    {
        ExceptionDispatchInfo.Capture(ex.InnerException).Throw();
        // The above line will always throw, but the compiler requires we throw explicitly.
        throw;
    }
}

至于创建对象的方法是用反射，表达式树(Expression Tree)还是IL Emit，则取决于所使用的内部引擎。

释放

创建ServiceProviderEngine的时候会为其Root属性绑定ServiceProviderEngineScope类型的值，Root = new ServiceProviderEngineScope(this);。

在ServiceProviderEngineScope类内部有着用于释放资源的Dispose方法。

public void Dispose()
{
    lock (ResolvedServices)
    {
        if (_disposed)
        {
            return;
        }

        _disposed = true;
        if (_disposables != null)
        {
            for (var i = _disposables.Count - 1; i >= 0; i--)
            {
                var disposable = _disposables[i];
                disposable.Dispose();
            }

            _disposables.Clear();
        }

        ResolvedServices.Clear();
    }
}

internal object CaptureDisposable(object service)
{
    _captureDisposableCallback?.Invoke(service);

    if (!ReferenceEquals(this, service))
    {
        if (service is IDisposable disposable)
        {
            lock (ResolvedServices)
            {
                if (_disposables == null)
                {
                    _disposables = new List<IDisposable>();
                }

                _disposables.Add(disposable);
            }
        }
    }
    return service;
}

并不是所有对象都会通过ServiceProvider容器释放资源，只有容器自己创建的才可以。如果是新建对象再传入容器，容器不会为其作处理。

public void ConfigureServices(IServiceCollection services)
{
    // 容器创建了实例所以会释放它。
    services.AddScoped<Service1>();
    services.AddSingleton<Service2>();
    services.AddSingleton<ISomeService>(sp => new SomeServiceImplementation());

    // 容器没有创建实例所以不会释放它。
    services.AddSingleton<Service3>(new Service3());
    services.AddSingleton(new Service3());
}

注入

ASP.NET Core中最常用的是Constructor Inject(构造器注入)方式。在其MVC框架中，通过DefaultControllerActivator生成Controller时，就可以跟踪到依赖注入是如何被其使用的。

public virtual object Create(ControllerContext controllerContext)
{
    ...

    var serviceProvider = controllerContext.HttpContext.RequestServices;
    return _typeActivatorCache.CreateInstance<object>(serviceProvider, controllerTypeInfo.AsType());
}

DefaultControllerActivator的Create方法使用了TypeActivatorCache类，其内部用到了ActivatorUtilities.CreateFactory方法。

public class TypeActivatorCache : ITypeActivatorCache
{
    private readonly Func<Type, ObjectFactory> _createFactory =
        (type) => ActivatorUtilities.CreateFactory(type, Type.EmptyTypes);
    private readonly ConcurrentDictionary<Type, ObjectFactory> _typeActivatorCache =
           new ConcurrentDictionary<Type, ObjectFactory>();

    public TInstance CreateInstance<TInstance>(
        IServiceProvider serviceProvider,
        Type implementationType)
    {
        ...

        var createFactory = _typeActivatorCache.GetOrAdd(implementationType, _createFactory);
        return (TInstance)createFactory(serviceProvider, arguments: null);
    }
}

ActivatorUtilities类位于ServiceProvider同样的程序集中。

public static ObjectFactory CreateFactory(Type instanceType, Type[] argumentTypes)
{
    FindApplicableConstructor(instanceType, argumentTypes, out ConstructorInfo constructor, out int?[] parameterMap);

    var provider = Expression.Parameter(typeof(IServiceProvider), "provider");
    var argumentArray = Expression.Parameter(typeof(object[]), "argumentArray");
    var factoryExpressionBody = BuildFactoryExpression(constructor, parameterMap, provider, argumentArray);

    var factoryLamda = Expression.Lambda<Func<IServiceProvider, object[], object>>(
        factoryExpressionBody, provider, argumentArray);

    var result = factoryLamda.Compile();
    return result.Invoke;
}

留意BuildFactoryExpression方法中GetServiceInfo变量。

private static Expression BuildFactoryExpression(
    ConstructorInfo constructor,
    int?[] parameterMap,
    Expression serviceProvider,
    Expression factoryArgumentArray)
{
    var constructorParameters = constructor.GetParameters();
    var constructorArguments = new Expression[constructorParameters.Length];

    for (var i = 0; i < constructorParameters.Length; i++)
    {
        var constructorParameter = constructorParameters[i];
        var parameterType = constructorParameter.ParameterType;
        var hasDefaultValue = ParameterDefaultValue.TryGetDefaultValue(constructorParameter, out var defaultValue);

        if (parameterMap[i] != null)
        {
            constructorArguments[i] = Expression.ArrayAccess(factoryArgumentArray, Expression.Constant(parameterMap[i]));
        }
        else
        {
            var parameterTypeExpression = new Expression[] { serviceProvider,
                Expression.Constant(parameterType, typeof(Type)),
                Expression.Constant(constructor.DeclaringType, typeof(Type)),
                Expression.Constant(hasDefaultValue) };
            constructorArguments[i] = Expression.Call(GetServiceInfo, parameterTypeExpression);
        }

        ...
    }

    return Expression.New(constructor, constructorArguments);
}

GetServiceInfo变量申明了对GetService方法的调用，而此GetService其实正是对ServiceProvider的调用。

private static readonly MethodInfo GetServiceInfo =
    GetMethodInfo<Func<IServiceProvider, Type, Type, bool, object>>((sp, t, r, c) => GetService(sp, t, r, c));

private static object GetService(IServiceProvider sp, Type type, Type requiredBy, bool isDefaultParameterRequired)
{
    var service = sp.GetService(type);
    ...
    
    return service;
}

通过以上的处理，在创建Controller时，其构造方法中所需参数的类型也会被容器解析，创建相应实例，从而实现依赖注入功能。

生命周期

ASP.NET Core容器可以创建三种生命周期的对象：

• Transient， 每次取得的都是新的对象。
• Scoped， 每次ASP.NET请求生成不同的对象。
• Singleton，同一对象只会生成一次。

检视这三者类型的构造方法，可以很容易理解Scoped与Singleton是通过缓存的方式实现对象的重用。

public TransientCallSite(IServiceCallSite serviceCallSite)
{
    ServiceCallSite = serviceCallSite;
}

public ScopedCallSite(IServiceCallSite serviceCallSite, object cacheKey)
{
    ServiceCallSite = serviceCallSite;
    CacheKey = cacheKey;
}

public SingletonCallSite(IServiceCallSite serviceCallSite, object cacheKey) : base(serviceCallSite, cacheKey)
{
}

性能

由于ServiceProvider容器使用了反射，表达式树以及IL Emit方式创建对象，可能会对其性能有所担忧，但实际检测的结果，除了Runtime引擎表现不尽如人意外，其它引擎的性能还是在可接受范围内的。

public class GetServiceBenchmark
{
    private const int OperationsPerInvoke = 50000;

    private IServiceProvider _transientSp;
    private ServiceProviderMode _mode;

    [Params("Expressions", "Dynamic", "Runtime", "ILEmit")]
    public string Mode {
        set {
            _mode = (ServiceProviderMode)Enum.Parse(typeof(ServiceProviderMode), value);
        }
    }

    [Benchmark(Baseline = true, OperationsPerInvoke = OperationsPerInvoke)]
    public void NoDI()
    {
        for (int i = 0; i < OperationsPerInvoke; i++)
        {
            var temp = new A(new B(new C()));
            temp.Foo();
        }
    }

    [GlobalSetup(Target = nameof(Transient))]
    public void SetupTransient()
    {
        var services = new ServiceCollection();
        services.AddTransient<A>();
        services.AddTransient<B>();
        services.AddTransient<C>();
        _transientSp = services.BuildServiceProvider(new ServiceProviderOptions()
        {
            Mode = _mode
        });
    }

    [Benchmark(OperationsPerInvoke = OperationsPerInvoke)]
    public void Transient()
    {
        for (int i = 0; i < OperationsPerInvoke; i++)
        {
            var temp = _transientSp.GetService<A>();
            temp.Foo();
        }
    }

    private class A
    {
        public A(B b)
        {

        }

        [MethodImpl(MethodImplOptions.NoInlining)]
        public void Foo()
        {

        }
    }

    private class B
    {
        public B(C c)
        {

        }
    }

    private class C
    {

    }
}

// ***** BenchmarkRunner: Finish  *****

// * Export *

// * Detailed results *
GetServiceBenchmark.NoDI: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=Dynamic]
Runtime = ; GC = 
Mean = 5.5175 ns, StdErr = 0.0116 ns (0.21%); N = 15, StdDev = 0.0449 ns
Min = 5.4490 ns, Q1 = 5.4860 ns, Median = 5.5207 ns, Q3 = 5.5641 ns, Max = 5.5972 ns
IQR = 0.0781 ns, LowerFence = 5.3688 ns, UpperFence = 5.6813 ns
ConfidenceInterval = [5.4695 ns; 5.5654 ns] (CI 99.9%), Margin = 0.0480 ns (0.87% of Mean)
Skewness = 0.15, Kurtosis = 1.67


GetServiceBenchmark.Transient: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=Dynamic]
Runtime = ; GC = 
Mean = 43.1601 ns, StdErr = 0.0677 ns (0.16%); N = 15, StdDev = 0.2620 ns
Min = 42.7731 ns, Q1 = 42.9117 ns, Median = 43.2403 ns, Q3 = 43.3580 ns, Max = 43.5392 ns
IQR = 0.4464 ns, LowerFence = 42.2421 ns, UpperFence = 44.0276 ns
ConfidenceInterval = [42.8800 ns; 43.4402 ns] (CI 99.9%), Margin = 0.2801 ns (0.65% of Mean)
Skewness = -0.2, Kurtosis = 1.59


GetServiceBenchmark.NoDI: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=Expressions]
Runtime = ; GC = 
Mean = 5.6964 ns, StdErr = 0.0388 ns (0.68%); N = 33, StdDev = 0.2226 ns
Min = 5.5148 ns, Q1 = 5.5603 ns, Median = 5.6042 ns, Q3 = 5.6769 ns, Max = 6.2460 ns
IQR = 0.1166 ns, LowerFence = 5.3854 ns, UpperFence = 5.8518 ns
ConfidenceInterval = [5.5561 ns; 5.8368 ns] (CI 99.9%), Margin = 0.1404 ns (2.46% of Mean)
Skewness = 1.48, Kurtosis = 3.69


GetServiceBenchmark.Transient: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=Expressions]
Runtime = ; GC = 
Mean = 43.6662 ns, StdErr = 0.0995 ns (0.23%); N = 13, StdDev = 0.3586 ns
Min = 43.1083 ns, Q1 = 43.5089 ns, Median = 43.6051 ns, Q3 = 43.7178 ns, Max = 44.6669 ns
IQR = 0.2089 ns, LowerFence = 43.1956 ns, UpperFence = 44.0311 ns
ConfidenceInterval = [43.2368 ns; 44.0957 ns] (CI 99.9%), Margin = 0.4295 ns (0.98% of Mean)
Skewness = 1.41, Kurtosis = 5.18


GetServiceBenchmark.NoDI: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=ILEmit]
Runtime = ; GC = 
Mean = 5.6016 ns, StdErr = 0.0071 ns (0.13%); N = 13, StdDev = 0.0255 ns
Min = 5.5547 ns, Q1 = 5.5896 ns, Median = 5.5996 ns, Q3 = 5.6226 ns, Max = 5.6400 ns
IQR = 0.0330 ns, LowerFence = 5.5401 ns, UpperFence = 5.6721 ns
ConfidenceInterval = [5.5712 ns; 5.6321 ns] (CI 99.9%), Margin = 0.0305 ns (0.54% of Mean)
Skewness = -0.47, Kurtosis = 2.12


GetServiceBenchmark.Transient: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=ILEmit]
Runtime = ; GC = 
Mean = 43.1397 ns, StdErr = 0.0726 ns (0.17%); N = 15, StdDev = 0.2812 ns
Min = 42.7061 ns, Q1 = 42.9064 ns, Median = 43.1052 ns, Q3 = 43.3093 ns, Max = 43.6443 ns
IQR = 0.4028 ns, LowerFence = 42.3022 ns, UpperFence = 43.9135 ns
ConfidenceInterval = [42.8392 ns; 43.4403 ns] (CI 99.9%), Margin = 0.3006 ns (0.70% of Mean)
Skewness = 0.28, Kurtosis = 1.9


GetServiceBenchmark.NoDI: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=Runtime]
Runtime = ; GC = 
Mean = 6.4814 ns, StdErr = 0.0762 ns (1.18%); N = 100, StdDev = 0.7617 ns
Min = 5.4979 ns, Q1 = 5.8327 ns, Median = 6.3039 ns, Q3 = 6.9775 ns, Max = 8.0420 ns
IQR = 1.1448 ns, LowerFence = 4.1155 ns, UpperFence = 8.6947 ns
ConfidenceInterval = [6.2231 ns; 6.7397 ns] (CI 99.9%), Margin = 0.2583 ns (3.99% of Mean)
Skewness = 0.52, Kurtosis = 1.94


GetServiceBenchmark.Transient: Job-NHLENA(Toolchain=InProcessToolchain, RunStrategy=Throughput) [Mode=Runtime]
Runtime = ; GC = 
Mean = 581.5066 ns, StdErr = 1.6962 ns (0.29%); N = 15, StdDev = 6.5695 ns
Min = 571.4934 ns, Q1 = 576.3829 ns, Median = 580.8121 ns, Q3 = 587.2645 ns, Max = 596.3317 ns
IQR = 10.8816 ns, LowerFence = 560.0605 ns, UpperFence = 603.5869 ns
ConfidenceInterval = [574.4834 ns; 588.5297 ns] (CI 99.9%), Margin = 7.0232 ns (1.21% of Mean)
Skewness = 0.58, Kurtosis = 2.48


Total time: 00:03:11 (191.85 sec)

第三方容器

如果想用第三方容器替换ASP.NET Core原有的容器也是可以办到的。以最常见的Autofac为例，有两种实现方式：

借助ConfigureContainer方法，要先在Program类中挂载AddAutofac方法。

public class Program
{
    public static void Main(string[] args)
    {
        CreateWebHostBuilder(args).Build().Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args).ConfigureServices(services => services.AddAutofac())
            .UseStartup<Startup>();
}

然后在Startup类中加入ConfigureContainer方法。

public void ConfigureContainer(ContainerBuilder builder)
{
    builder.RegisterModule(new DefaultModule());

}

例中的DefaultModule类按照Autofac的通用方式实现。

public class DefaultModule : Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterType<HelloWorld>().As<IHelloWorld>();
    }
}

如果不想使用ConfigureContainer方法，也可以直接利用ConfigureServices方法：

public IServiceProvider ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    var containerBuilder = new ContainerBuilder();
    containerBuilder.RegisterModule<DefaultModule>();
    containerBuilder.Populate(services);
    var container = containerBuilder.Build();
    return new AutofacServiceProvider(container);
}

需要注意的是，使用这种方式时，ConfigureServices方法的返回类型要从void改成IServiceProvider。