DOTNET CORE源码分析之IServiceProvider、ServiceProvider、IServiceProviderEngine、ServiceProviderEngine和ServiceProviderEngineScope
首先谈一下IServiceProvider
IServiceProvider只提供给了一个根据类型获取对象的功能，试想一下IOC总得有一个找到对象，具体如下
public interface IServiceProvider
{
object GetService(Type serviceType);
}
再谈一下ServiceProvider
ServiceProvider实例化了IServiceProvider，也就是实现了GetService，用于获取容器中实际对象，但是它是借助于IServiceProviderEngine（这个接口稍后再介绍），具体如下：
public object GetService(Type serviceType)
{
return this._engine.GetService(serviceType);
}
另外ServiceCollection中有一个方法BuildServiceProvider（存在于类ServiceCollectionContainerBuilderExtensions中），返回值对象类型就是ServiceProvider
/// <summary>
/// Extension methods for building a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> from an <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />.
/// </summary>
public static class ServiceCollectionContainerBuilderExtensions
{
/// <summary>
/// Creates a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> containing services from the provided <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />.
/// </summary>
/// <param name="services">The <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" /> containing service descriptors.</param>
/// <returns>The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" />.</returns>
public static ServiceProvider BuildServiceProvider(
this IServiceCollection services)
{
return services.BuildServiceProvider(ServiceProviderOptions.Default);
}
/// <summary>
/// Creates a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> containing services from the provided <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />
/// optionaly enabling scope validation.
/// </summary>
/// <param name="services">The <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" /> containing service descriptors.</param>
/// <param name="validateScopes">
/// <c>true</c> to perform check verifying that scoped services never gets resolved from root provider; otherwise <c>false</c>.
/// </param>
/// <returns>The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" />.</returns>
public static ServiceProvider BuildServiceProvider(
this IServiceCollection services,
bool validateScopes)
{
return services.BuildServiceProvider(new ServiceProviderOptions()
{
ValidateScopes = validateScopes
});
}
/// <summary>
/// Creates a <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" /> containing services from the provided <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" />
/// optionaly enabling scope validation.
/// </summary>
/// <param name="services">The <see cref="T:Microsoft.Extensions.DependencyInjection.IServiceCollection" /> containing service descriptors.</param>
/// <param name="options">
/// Configures various service provider behaviors.
/// </param>
/// <returns>The <see cref="T:Microsoft.Extensions.DependencyInjection.ServiceProvider" />.</returns>
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((IEnumerable<ServiceDescriptor>) services, options);
}
}
必须要结合一下IServiceProviderEngine、ServiceProviderEngine和ServiceProviderEngineScope对象才能具体知道ServiceProvider是怎么获取IOC容器中的对象了
在使用BuildServiceProvider的时候，最终会调用new ServiceProvider((IEnumerable<ServiceDescriptor>)services,options),然后就是调用如下函数：
internal ServiceProvider(
IEnumerable<ServiceDescriptor> serviceDescriptors,
ServiceProviderOptions options)
{
IServiceProviderEngineCallback callback = (IServiceProviderEngineCallback) null;
if (options.ValidateScopes)
{
callback = (IServiceProviderEngineCallback) this;
this._callSiteValidator = new CallSiteValidator();
}
switch (options.Mode)
{
case ServiceProviderMode.Dynamic:
this._engine = (IServiceProviderEngine) new DynamicServiceProviderEngine(serviceDescriptors, callback);
break;
case ServiceProviderMode.Runtime:
this._engine = (IServiceProviderEngine) new RuntimeServiceProviderEngine(serviceDescriptors, callback);
break;
case ServiceProviderMode.Expressions:
this._engine = (IServiceProviderEngine) new ExpressionsServiceProviderEngine(serviceDescriptors, callback);
break;
case ServiceProviderMode.ILEmit:
this._engine = (IServiceProviderEngine) new ILEmitServiceProviderEngine(serviceDescriptors, callback);
break;
default:
throw new NotSupportedException("Mode");
}
}
就是说最终还是根据ServiceProviderMode来判断需要实例化哪种ServiceProviderEngine，现在简单举例DynamicServiceProviderEngine。DynamicServiceProviderEngine最终还是继承ServiceProviderEngine，
所以上面说的GetService其实就是调用了ServiceProviderEngine的GetService
public object GetService(Type serviceType)
{
return this.GetService(serviceType, this.Root);
}
其中this.Root就是实例化的ServiceProviderScope。上面的this.GetService(serviceType,this.Root)会调用如下函数：
internal object GetService(
Type serviceType,
ServiceProviderEngineScope serviceProviderEngineScope)
{
if (this._disposed)
ThrowHelper.ThrowObjectDisposedException();
Func<ServiceProviderEngineScope, object> orAdd = this.RealizedServices.GetOrAdd(serviceType, this._createServiceAccessor);
this._callback?.OnResolve(serviceType, (IServiceScope) serviceProviderEngineScope);
ServiceProviderEngineScope providerEngineScope = serviceProviderEngineScope;
return orAdd(providerEngineScope);
}
最终就是调用Func<ServiceProviderEngineScope, object> orAdd = this.RealizedServices.GetOrAdd(serviceType, this._createServiceAccessor);其中RealizedServices是ConcurrentDictionary<Type, Func<ServiceProviderEngineScope, object>> RealizedServices { get; }，this._createServiceAccessor是Func<ServiceProviderEngineScope, object>,通过这个委托根据ServiceProviderEngineScope获取最终的对象,也就是说，如果服务存在的话就从字典中获取，不存在就添加到队列上，并直接返回。另外在实例化ServiceProviderEngine的时候实例化了this._createServiceAccessor = new Func<Type, Func<ServiceProviderEngineScope, object>>(this.CreateServiceAccessor);其中CreateServiceAccessor是一个函数，定义如下：
private Func<ServiceProviderEngineScope, object> CreateServiceAccessor(
Type serviceType)
{
IServiceCallSite callSite = this.CallSiteFactory.CreateCallSite(serviceType, new CallSiteChain());
if (callSite == null)
return (Func<ServiceProviderEngineScope, object>) (_ => (object) null);
this._callback?.OnCreate(callSite);
return this.RealizeService(callSite);
}
就DynamicServiceProviderEngine而言，RealizeService的定义如下：
protected override Func<ServiceProviderEngineScope, object> RealizeService(
IServiceCallSite callSite)
{
int callCount = 0;
return (Func<ServiceProviderEngineScope, object>) (scope =>
{
if (Interlocked.Increment(ref callCount) == 2)
Task.Run<Func<ServiceProviderEngineScope, object>>((Func<Func<ServiceProviderEngineScope, object>>) (() => base.RealizeService(callSite)));
return this.RuntimeResolver.Resolve(callSite, scope);
});
}
RuntimeResolver是ServiceProviderEngine的一个属性。到此为止，IOC容器的数据就可以获取到了。下篇博客会继续说明this.RuntimeResover.Resolve下的事情。
