- 首先看 ServiceCollection 的定义
//定义
public class ServiceCollection : IServiceCollection
{
private readonly List<ServiceDescriptor> _descriptors = new List<ServiceDescriptor>();
......
}
//接口定义
public interface IServiceCollection : IList<ServiceDescriptor>
{
}
由此可见,ServiceCollection 本身是一个 List<ServiceDescriptor> 的集合,下面我们来看一下 ServiceDescriptor 的定义
public class ServiceDescriptor
{
//重要的构造函数
public ServiceDescriptor(Type serviceType, Type implementationType, ServiceLifetime lifetime)
{
}
//重要的属性
/// <summary>
/// Service 的生命周期
/// </summary>
/// <value></value>
public ServiceLifetime Lifetime { get; }
/// <summary>
/// Service 的类型
/// </summary>
/// <value></value>
public Type ServiceType { get; }
/// <summary>
/// Service 的实现类型
/// </summary>
/// <value></value>
public Type ImplementationType { get; }
/// <summary>
/// Service 对象
/// </summary>
/// <value></value>
public object ImplementationInstance { get; }
/// <summary>
/// 创建 Service 对象的工厂
/// </summary>
/// <value></value>
public Func<IServiceProvider, object> ImplementationFactory { get; }
......
}
ServiceDescriptor 保存了 Service 类型和 Service 对象之间的关系以及 Service 的生命周期,下面来看一下 Service 的生命周期
public enum ServiceLifetime
{
/// <summary>
/// 单例
/// </summary>
Singleton,
/// <summary>
/// 范围内
/// </summary>
/// <remarks>
/// 在 ASP.NET Core 应用中,每一个请求会创建一个范围
/// </remarks>
Scoped,
/// <summary>
/// 瞬时
/// </summary>
Transient
}
再来看一下 IServiceCollection 提供的一些拓展方法
public static class ServiceCollectionServiceExtensions
{
//基本是3中形式,都是简单的封装
public static IServiceCollection AddSingleton(this IServiceCollection services, ...)
public static IServiceCollection AddScoped(this IServiceCollection services, ...)
public static IServiceCollection AddTransient(this IServiceCollection services, ...)
......
//最终都会调用同一个方法
private static IServiceCollection Add(
IServiceCollection collection,
Type serviceType,
Type implementationType,
ServiceLifetime lifetime)
{
var descriptor = new ServiceDescriptor(serviceType, implementationType, lifetime);
collection.Add(descriptor);
return collection;
}
}
这些方法的作用都是为了填充 ServiceCollection 中的 _descriptors 字段,IServiceCollection 有一个特别重要的方法,BuildServiceProvider,创建 ServiceProvider
public static class ServiceCollectionContainerBuilderExtensions
{
public static ServiceProvider BuildServiceProvider(this IServiceCollection services, ServiceProviderOptions options)
{
if (services == null)
{
throw new ArgumentNullException(nameof(services));
}
if (options == null)
{
throw new ArgumentNullException(nameof(options));
}
return new ServiceProvider(services, options);
}
}
- ServiceProvider,Service 的提供者,这是一个非常重要的类,也是容器的核心,主要用来创建 Service 对象的实例
public sealed class ServiceProvider : IServiceProvider, IDisposable{ //ServiceProvider 引擎
private readonly IServiceProviderEngine _engine;
//构造函数
internal ServiceProvider(IEnumerable<ServiceDescriptor> serviceDescriptors, ServiceProviderOptions options)
{
......
switch (options.Mode)
{
case ServiceProviderMode.Default: //.net core 默认是 true
if (RuntimeFeature.IsSupported("IsDynamicCodeCompiled"))
{
_engine = new DynamicServiceProviderEngine(serviceDescriptors, callback);
} else
{
// Don't try to compile Expressions/IL if they are going to get interpreted
_engine = new RuntimeServiceProviderEngine(serviceDescriptors, callback);
}
break;
case ServiceProviderMode.Dynamic:
_engine = new DynamicServiceProviderEngine(serviceDescriptors, callback);
break;
case ServiceProviderMode.Runtime:
_engine = new RuntimeServiceProviderEngine(serviceDescriptors, callback);
break;
case ServiceProviderMode.ILEmit:
_engine = new ILEmitServiceProviderEngine(serviceDescriptors, callback);
break;
case ServiceProviderMode.Expressions:
_engine = new ExpressionsServiceProviderEngine(serviceDescriptors, callback);
break;
default:
throw new NotSupportedException(nameof(options.Mode));
}
......
}
//从容器中获取对象
public object GetService(Type serviceType) => _engine.GetService(serviceType);
......
}
由此可见,ServiceProvider 创建对象的过程由 ServiceProviderEngine 接管,而 Engine 有4种,分别是 DynamicServiceProviderEngine,RuntimeServiceProviderEngine,ILEmitServiceProviderEngine,ExpressionsServiceProviderEngine,下面是他们之间的关系,
- 由上图可知,ServiceProvider 的最终的核心实现应该在 ServiceProviderEngine 这个抽象类中,下面我们来看一下这个类,我去掉了一些判断和记录日志的逻辑,让代码看起来更简洁
internal abstract class ServiceProviderEngine : IServiceProviderEngine, IServiceScopeFactory
{
private readonly Func<Type, Func<ServiceProviderEngineScope, object>> _createServiceAccessor;
protected ServiceProviderEngine(IEnumerable<ServiceDescriptor> serviceDescriptors, IServiceProviderEngineCallback callback)
{
_createServiceAccessor = CreateServiceAccessor;
Root = new ServiceProviderEngineScope(this);
RuntimeResolver = new CallSiteRuntimeResolver();
CallSiteFactory = new CallSiteFactory(serviceDescriptors);
CallSiteFactory.Add(typeof(IServiceProvider), new ServiceProviderCallSite());
CallSiteFactory.Add(typeof(IServiceScopeFactory), new ServiceScopeFactoryCallSite());
RealizedServices = new ConcurrentDictionary<Type, Func<ServiceProviderEngineScope, object>>();
}
//创建 Service 访问者
private Func<ServiceProviderEngineScope, object> CreateServiceAccessor(Type serviceType)
{
var callSite = CallSiteFactory.GetCallSite(serviceType, new CallSiteChain());
if (callSite != null)
{
//调用子类实现的 获得 Service 对象的委托来创建对象
return RealizeService(callSite);
}
return _ => null;
}
//调用目标工厂
internal CallSiteFactory CallSiteFactory { get; }
//默认运行时解析器
protected CallSiteRuntimeResolver RuntimeResolver { get; }
//根容器
public ServiceProviderEngineScope Root { get; }
//获得 Service 对象的委托,由子类实现
protected abstract Func<ServiceProviderEngineScope, object> RealizeService(ServiceCallSite callSite);
//获取 Service 对象
internal object GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
{
var realizedService = RealizedServices.GetOrAdd(serviceType, _createServiceAccessor);
return realizedService.Invoke(serviceProviderEngineScope);
}
//创建一个范围
public IServiceScope CreateScope()
{
return new ServiceProviderEngineScope(this);
}
}
这个类中有几个特别重要的对象,
- RuntimeResolver ,Service 对象的创建就是这个对象完成的,当然不同的子类,有不同的实现,
internal class DynamicServiceProviderEngine : CompiledServiceProviderEngine
{
//该类本身并没有定义 RutimeResolver 而是通过父类 CompiledServiceProviderEngine 的 ResolverBuilder 实现的
}
internal abstract class CompiledServiceProviderEngine : ServiceProviderEngine
{
//通过编译条件变量来确定是使用 ILEmit 还是使用 Expression
#if IL_EMIT
public ILEmitResolverBuilder ResolverBuilder { get; }
#else
public ExpressionResolverBuilder ResolverBuilder { get; }
#endif
public CompiledServiceProviderEngine(IEnumerable<ServiceDescriptor> serviceDescriptors, IServiceProviderEngineCallback callback) : base(serviceDescriptors, callback)
{
#if IL_EMIT
ResolverBuilder = new ILEmitResolverBuilder(RuntimeResolver, this, Root);
#else
ResolverBuilder = new ExpressionResolverBuilder(RuntimeResolver, this, Root);
#endif
}
......
}
internal class RuntimeServiceProviderEngine : ServiceProviderEngine
{
//该类本身没有对应的 RuntimeResolver,直接使用父类默认的 CallSiteRuntimeResolver
}
internal class ILEmitServiceProviderEngine : ServiceProviderEngine
{
private readonly ILEmitResolverBuilder _expressionResolverBuilder;
public ILEmitServiceProviderEngine(IEnumerable<ServiceDescriptor> serviceDescriptors, IServiceProviderEngineCallback callback) : base(serviceDescriptors, callback)
{
_expressionResolverBuilder = new ILEmitResolverBuilder(RuntimeResolver, this, Root);
}
......
}
internal class ExpressionsServiceProviderEngine : ServiceProviderEngine
{
private readonly ExpressionResolverBuilder _expressionResolverBuilder;
public ExpressionsServiceProviderEngine(IEnumerable<ServiceDescriptor> serviceDescriptors, IServiceProviderEngineCallback callback) : base(serviceDescriptors, callback)
{
_expressionResolverBuilder = new ExpressionResolverBuilder(RuntimeResolver, this, Root);
}
......
}
所以总结来看,有3个对应的 Resolver 分别是:CallSiteRuntimeResolver,ILEmitResolverBuilder,ExpressionResolverBuilder 这3个类都继承于 CallSiteVisitor<TArgument, TResult> 的泛型类,只是对应的泛型参数不太一样
- CallSiteFactory,调用目标工厂,主要用来根据 ServiceDescriptor 的定义创建对应的 ServiceCallSite 对象,然后根据该对象来创建 Service 的实例,这个对象比较复杂,下面来看一些简洁的源码
internal class CallSiteFactory
{
private const int DefaultSlot = 0;
private readonly List<ServiceDescriptor> _descriptors;
private readonly Dictionary<Type, ServiceDescriptorCacheItem> _descriptorLookup = new Dictionary<Type, ServiceDescriptorCacheItem>();
public CallSiteFactory(IEnumerable<ServiceDescriptor> descriptors)
{
_descriptors = descriptors.ToList();
Populate();
}
private void Populate()
{
/*
在实例化 CallSiteFactory 对象时,会将 ServiceDescriptor 对象转换成字典 Dictionary<Type, ServiceDescriptorCacheItem>,
ServiceDescriptorCacheItem 用来将同一个 ServiceType 的 ServiceDescriptor 聚合在一起,其中 ServiceDescriptorCacheItem
的 Last 属性,是取最后一个 ServiceDescriptor,这也就是为什么,我们 Add 同一个类型的多个实例时,获取当前类型的实例时,返回的是最后一个实例的原因
*/
foreach (var descriptor in _descriptors)
{
var cacheKey = descriptor.ServiceType;
_descriptorLookup.TryGetValue(cacheKey, out var cacheItem);
_descriptorLookup[cacheKey] = cacheItem.Add(descriptor);
}
}
}
private struct ServiceDescriptorCacheItem
{
private List<ServiceDescriptor> _items;
public ServiceDescriptor Last
{
get
{
return _items[_items.Count - 1];
}
}
public ServiceDescriptorCacheItem Add(ServiceDescriptor descriptor)
{
var newCacheItem = new ServiceDescriptorCacheItem();
newCacheItem._item = _item;
newCacheItem._items = _items ?? new List<ServiceDescriptor>();
newCacheItem._items.Add(descriptor);
return newCacheItem;
}
}
还有几个比较关键的方法,下面来看一下代码
/*
根据 ServiceType 创建 ServiceCallSite, 这个方法类似于一个职责链模式,
先尝试根据普通类型来创建,然后尝试创建泛型类型,最后尝试创建可枚举类型
*/
private ServiceCallSite CreateCallSite(Type serviceType, CallSiteChain callSiteChain)
{
var callSite = TryCreateExact(serviceType, callSiteChain) ??
TryCreateOpenGeneric(serviceType, callSiteChain) ??
TryCreateEnumerable(serviceType, callSiteChain);
return callSite;
}
//尝试获取简单类型对象
private ServiceCallSite TryCreateExact(Type serviceType, CallSiteChain callSiteChain)
{
if (_descriptorLookup.TryGetValue(serviceType, out var descriptor))
{
/*
descriptor.Last
这就是为什么在容器中添加同一个类型的实例多次后,返回的总是最后一个实例
*/
return TryCreateExact(descriptor.Last, serviceType, callSiteChain, DefaultSlot);
}
return null;
}
private ServiceCallSite TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, int slot)
{
if (serviceType == descriptor.ServiceType)
{
if (descriptor.ImplementationInstance != null)
{
//Add 时,直接指定实例对象时
callSite = new ConstantCallSite(descriptor.ServiceType, descriptor.ImplementationInstance);
}
else if (descriptor.ImplementationFactory != null)
{
//Add 时,指定实例工厂时
callSite = new FactoryCallSite(lifetime, descriptor.ServiceType, descriptor.ImplementationFactory);
}
else if (descriptor.ImplementationType != null)
{
//Add 时,指定类型时
callSite = CreateConstructorCallSite(lifetime, descriptor.ServiceType, descriptor.ImplementationType, callSiteChain);
}
return callSite;
}
return null;
}
//尝试获取泛型对象
private ServiceCallSite TryCreateOpenGeneric(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, int slot)
{
if (serviceType.IsConstructedGenericType && serviceType.GetGenericTypeDefinition() == descriptor.ServiceType)
{
var closedType = descriptor.ImplementationType.MakeGenericType(serviceType.GenericTypeArguments);
return CreateConstructorCallSite(lifetime, serviceType, closedType, callSiteChain);
}
return null;
}
//尝试获取枚举类型对象
private ServiceCallSite TryCreateEnumerable(Type serviceType, CallSiteChain callSiteChain)
{
if (serviceType.IsConstructedGenericType && serviceType.GetGenericTypeDefinition() == typeof(IEnumerable<>))
{
//获取泛型的第一个参数
var itemType = serviceType.GenericTypeArguments.Single();
var callSites = new List<ServiceCallSite>();
if (!itemType.IsConstructedGenericType && _descriptorLookup.TryGetValue(itemType, out var descriptors))
{
/*
循环该 ServiceType 所有的 ServiceDescriptor
这就是为什么在容器中添加同一个类型的实例多次后,通过 IEnumerable<T> 去获取时,返回的是多个实例
*/
for (int i = 0; i < descriptors.Count; i++)
{
var descriptor = descriptors[i];
var callSite = TryCreateExact(descriptor, itemType, callSiteChain, slot);
callSites.Add(callSite);
}
}
else
{
//这里的逻辑代表的是泛型中嵌套泛型的情况,是一个递归调用
}
return new IEnumerableCallSite(resultCache, itemType, callSites.ToArray());
}
return null;
}
private ServiceCallSite CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)
{
//获取公共的构造函数
var constructors = implementationType.GetTypeInfo()
.DeclaredConstructors
.Where(constructor => constructor.IsPublic)
.ToArray();
ServiceCallSite[] parameterCallSites = null;
if (constructors.Length == 0)
{
//如果没有获取到公共的构造函数会抛出异常
throw new InvalidOperationException(Resources.FormatNoConstructorMatch(implementationType));
}
else if (constructors.Length == 1)
{
//当只有一个构造函数时,优化处理逻辑
return new ConstructorCallSite(...);
}
//存在多个构造函数时,按照构造函数参数的个数倒序排列
Array.Sort(constructors, (a, b) => b.GetParameters().Length.CompareTo(a.GetParameters().Length));
//最优的构造函数
ConstructorInfo bestConstructor = null;
//最优构造函数的参数类型
HashSet<Type> bestConstructorParameterTypes = null;
for (var i = 0; i < constructors.Length; i++)
{
var parameters = constructors[i].GetParameters();
var currentParameterCallSites = CreateArgumentCallSites(...);
/*
默认参数最多的构造函数为最优的构造函数,但是要根据参数类型在容器中是否存在来判断,
如果参数多的构造函数,有个别参数在容器中不存在,那么该构造函数不是最优的
*/
if (currentParameterCallSites != null)
{
if (bestConstructor == null)
{
bestConstructor = constructors[i];
parameterCallSites = currentParameterCallSites;
}
else
{
if (bestConstructorParameterTypes == null)
{
bestConstructorParameterTypes = new HashSet<Type>(bestConstructor.GetParameters().Select(p => p.ParameterType));
}
//如果最优构造函数的参数类型,不是其他构造函数的参数类型的超级,抛出【有歧义】的异常
if (!bestConstructorParameterTypes.IsSupersetOf(parameters.Select(p => p.ParameterType)))
{
throw new InvalidOperationException(message);
}
}
}
}
return new ConstructorCallSite(lifetime, serviceType, bestConstructor, parameterCallSites);
}
-
由于 ServiceProvider 容器本身只支持构造函数注入,所以我们主要关注每个 Resolver 的 VisitConstructor 方法,
-
CallSiteRuntimeResolver (.net framework 4.6.2 + 默认使用的方式)
internal sealed class CallSiteRuntimeResolver : CallSiteVisitor<RuntimeResolverContext, object>
{
protected override object VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context)
{
object[] parameterValues;
if (constructorCallSite.ParameterCallSites.Length == 0)
{
parameterValues = Array.Empty<object>();
}
else
{
//循环获取每个参数类型的实例,如果参数类型还依赖于其它的类型,则会递归获取
parameterValues = new object[constructorCallSite.ParameterCallSites.Length];
for (var index = 0; index < parameterValues.Length; index++)
{
parameterValues[index] = VisitCallSite(constructorCallSite.ParameterCallSites[index], context);
}
}
return constructorCallSite.ConstructorInfo.Invoke(parameterValues);
}
}
- ILEmitResolverBuilder (.net core 默认使用方式)
/*
由于 IL 我懂的也不是很多,只是大概知道,需要把参数提前准备好放在堆栈上,然后调用 Newobj 就可以实例化对象,
源码很长,有兴趣想要研究的小伙伴,可以自行学习
*/
protected override object VisitConstructor(ConstructorCallSite constructorCallSite, ILEmitResolverBuilderContext argument)
{
foreach (var parameterCallSite in constructorCallSite.ParameterCallSites)
{
VisitCallSite(parameterCallSite, argument);
}
argument.Generator.Emit(OpCodes.Newobj, constructorCallSite.ConstructorInfo);
return null;
}
private GeneratedMethod BuildTypeNoCache(ServiceCallSite callSite)
{
//动态创建方法
var dynamicMethod = new DynamicMethod("ResolveService",
attributes : MethodAttributes.Public | MethodAttributes.Static,
callingConvention : CallingConventions.Standard,
returnType : typeof(object),
parameterTypes : new [] { typeof(ILEmitResolverBuilderRuntimeContext), typeof(ServiceProviderEngineScope) },
owner : GetType(),
skipVisibility : true);
var info = ILEmitCallSiteAnalyzer.Instance.CollectGenerationInfo(callSite);
var ilGenerator = dynamicMethod.GetILGenerator(info.Size);
//创建方法体
var runtimeContext = GenerateMethodBody(callSite, ilGenerator);
return new GeneratedMethod()
{
Lambda = (Func<ServiceProviderEngineScope, object>) dynamicMethod.CreateDelegate(typeof(Func<ServiceProviderEngineScope, object>), runtimeContext),
Context = runtimeContext,
DynamicMethod = dynamicMethod
};
}
- ExpressionResolverBuilder 可以理解为使用表达式树将 CallSiteRuntimeResolver 的代码翻译了一遍
internal class ExpressionResolverBuilder : CallSiteVisitor<object, Expression>
{
protected override Expression VisitConstructor(ConstructorCallSite callSite, object context)
{
var parameters = callSite.ConstructorInfo.GetParameters();
Expression[] parameterExpressions;
if (callSite.ParameterCallSites.Length == 0)
{
parameterExpressions = Array.Empty<Expression>();
}
else
{
//循环每一个参数,根据参数创建表达式
parameterExpressions = new Expression[callSite.ParameterCallSites.Length];
for (int i = 0; i < parameterExpressions.Length; i++)
{
parameterExpressions[i] = Convert(VisitCallSite(callSite.ParameterCallSites[i], context), parameters[i].ParameterType);
}
}
return Expression.New(callSite.ConstructorInfo, parameterExpressions);
}
}
- 总结一下
- ServiceCollection 只不过是用来定义 Service 的类型和定义以及生命周期
- Service 类型的创建是最终是通过不同的 RuntimeResolver 来实现的
- 源码中还包含大量对缓存的使用,如果没有缓存,这个容器的效率也就太低了,我在分析源码的时候直接略过了,原因是,我觉得缓存一定是在先实现后的基础上再加的,所以我们研究源码的过程中可以先忽略这些缓存的使用
- 关于 Service 的生命周期我没有细讲,单例和瞬时都非常好理解,其实最复杂的就是 Scope,有点绕的地方在于维护 IDisposable 类型的资源的释放,当然这个理解起来也不是很难,有兴趣的小伙伴可以自行研究
- 源码分析没有讲最基本的 IOC 概念和容器概念,想要理解这些,前提是要对容器的概念非常了解才行
|