Net6 DI源码分析Part3 CallSiteRuntimeResolver,CallSiteVisitor

CallSiteRuntimeResolver

CallSiteRuntimeResolver是实现了CallSiteVisitor之一。

提供的方法主要分三个部分

1. 自有成员方法

   1. Resolve提供服务
   2. VisitCache
   3. 私有构造函数

2. 重写父类方法

   1. VisitDisposeCache(ServiceCallSite transientCallSite, RuntimeResolverContext context)
      
      调用父类VisitCallSiteMain ，并把创建出来的服务添加到context.Scope.CaptureDisposable

      return context.Scope.CaptureDisposable(VisitCallSiteMain(transientCallSite, context));
      

   2. object VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)

      1. 先找对应callSite.Value是否有值如果有直接返回
      2. 如果没有直接调用 VisitCallSiteMain创建服务并把对象rootServiceProviderEngine内。
      3. 创建的服务放入callSite.Value。

          if (callSite.Value is object value)
          {
              return value;
          }
      
      var lockType = RuntimeResolverLock.Root;
      ServiceProviderEngineScope serviceProviderEngine = context.Scope.RootProvider.Root;
      if (callSite.Value is object resolved)
      {
          return resolved;
      }
      resolved = VisitCallSiteMain(callSite, new RuntimeResolverContext
      {
          Scope = serviceProviderEngine,
          AcquiredLocks = context.AcquiredLocks | lockType
      });
      serviceProviderEngine.CaptureDisposable(resolved);
      callSite.Value = resolved;
      return resolved;
      

   3. VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)

      1. 先去serviceProviderEngine.resolvedServices拿,有的话直接返回如果没拿到执行步骤2去创建。serviceProviderEngine.resolvedServices.TryGetValue(callSite.Cache.Key, out object resolved)
      2. VisitCallSiteMain创建对象
      3. 把创建后的对象加入对应Scope的 disposable列表
      4. 把创建后的对象加入对应Scope的 resolvedServices列表

          if (resolvedServices.TryGetValue(callSite.Cache.Key, out object resolved))
          {
              return resolved;
          }
          resolved = VisitCallSiteMain(callSite, new RuntimeResolverContext
          {
              Scope = serviceProviderEngine,
              AcquiredLocks = context.AcquiredLocks | lockType
          });
          serviceProviderEngine.CaptureDisposable(resolved);
          resolvedServices.Add(callSite.Cache.Key, resolved);
          return resolved;
      

3. 实现父类抽象方法

   1. VisitConstructor
      1. 给构造方法提供参数（如果有参数递归调用VisitCallSite创建参数对象）
      2. 直接调用ServiceCallSite的ConstructorInfo反射创建对象。

         object[] parameterValues;
          if (constructorCallSite.ParameterCallSites.Length == 0)
          {
              parameterValues = Array.Empty<object>();
          }
          else
          {
              parameterValues = new object[constructorCallSite.ParameterCallSites.Length];
              for (int index = 0; index < parameterValues.Length; index++)
              {
                  parameterValues[index] = VisitCallSite(constructorCallSite.ParameterCallSites[index], context);
              }
          }
      
          return constructorCallSite.ConstructorInfo.Invoke(BindingFlags.DoNotWrapExceptions, binder: null, parameters: parameterValues, culture: null);
      

   2. override object VisitConstant(ConstantCallSite constantCallSite, RuntimeResolverContext context)
      
      直接返回CallSite对象的DefaultValue
      
      return constantCallSite.DefaultValue;
   3. VisitServiceProvider
      
      return context.Scope;
   4. override object VisitIEnumerable(IEnumerableCallSite enumerableCallSite, RuntimeResolverContext context)
      
      根据ServiceCallSites直接循环调用VisitCallSite创建实例，然后根据实例创建集合返回

        var array = Array.CreateInstance(
        enumerableCallSite.ItemType,
        enumerableCallSite.ServiceCallSites.Length);
        for (int index = 0; index < enumerableCallSite.ServiceCallSites.Length; index++)
        {
            object value = VisitCallSite(enumerableCallSite.ServiceCallSites[index], context);
            array.SetValue(value, index);
        }
        return array;
      

   5. VisitFactory
      
      return factoryCallSite.Factory(context.Scope);

体力活都给CallSiteFactory了

CallSiteVisitor

1. 方法

   1. VisitCallSite(ServiceCallSite callSite, TArgument argument)

      1. 保证Stack安全
      2. 根据callSite的Cache.Location去调用不同策略的Cache方法。

      switch (callSite.Cache.Location)
           {
               case CallSiteResultCacheLocation.Root:
                   return VisitRootCache(callSite, argument);
               case CallSiteResultCacheLocation.Scope:
                   return VisitScopeCache(callSite, argument);
               case CallSiteResultCacheLocation.Dispose:
                   return VisitDisposeCache(callSite, argument);
               case CallSiteResultCacheLocation.None:
                   return VisitNoCache(callSite, argument);
               default:
                   throw new ArgumentOutOfRangeException();
       }
      

   2. VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)

      1. 根据不同CallSiteKind去调用不同策略的创建服务方法。

          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.Constant:
                   return VisitConstant((ConstantCallSite)callSite, argument);
               case CallSiteKind.ServiceProvider:
                   return VisitServiceProvider((ServiceProviderCallSite)callSite, argument);
               default:
                   throw new NotSupportedException(SR.Format(SR.CallSiteTypeNotSupported, callSite.GetType()));
           }
         

2. 虚方法
   1. TResult VisitNoCache(ServiceCallSite callSite, TArgument argument) => VisitCallSiteMain(callSite, argument);
   2. TResult VisitDisposeCache(ServiceCallSite callSite, TArgument argument) -> isitCallSiteMain(callSite, argument);
   3. TResult VisitRootCache(ServiceCallSite callSite, TArgument argument) -> VisitCallSiteMain(callSite, argument);
   4. TResult VisitScopeCache(ServiceCallSite callSite, TArgument argument) => VisitCallSiteMain(callSite, argument);

   根据生命周期策略由子类实现对应存储机制。

3. 抽象方法
   1. TResult VisitConstructor(ConstructorCallSite constructorCallSite, TArgument argument);
   2. TResult VisitConstant(ConstantCallSite constantCallSite, TArgument argument);
   3. TResult VisitServiceProvider(ServiceProviderCallSite serviceProviderCallSite, TArgument argument);
   4. TResult VisitIEnumerable(IEnumerableCallSite enumerableCallSite, TArgument argument);
   5. TResult VisitFactory(FactoryCallSite factoryCallSite, TArgument argument);

   根据服务注册时的创建机制策略由子类实现对应的创建对象机制。

CallSiteVisitor负责这活怎么干！。CallSiteRuntimeResolver负责干活

1. 调用 VisitCallSite在内部区分出scope并调用具体实现方法缓存方法 (CallSiteResultCacheLocation),
   
   -> VisitCache方法
   
   -> 但是在缓存前得先得到被缓存的对象，这时通过调用（VisitCallSiteMain）创建对象
   
   -> VisitCallSiteMain根据提供的callsite类型去调用实现的抽象方法创建对应对象
   
   -> 根据cache对应的方法缓存步骤1.1的结果。
2. return cahce的结果。

整体的获取对象流程大约如下

CallSiteRuntimeResolver.Resolve -> CallSiteVisitor->VisitCallSite callSite.Cache.Location VisitRootCache/VisitScopeCache/ VisitDisposeCache/ VisitNoCache -> CallSiteRuntimeResolver.VisitCache/ VisitRootCache -> VisitRootCache -> CallSiteVisitor.VisitCallSiteMain 根据callSite.Kind CallSiteRuntimeResolver.VisitFactory（abstract TResult VisitFactory）递归调用 VisitCallSite