配置InstanceContextMode为Single时Autofac WCF集成服务异常

问题核心 #

WCF服务同时配置InstanceContextMode.Single、Autofac单例注册、Autofac拦截器时无法正常运行，但任意两个组合均正常。

解决方案 #

1. 调整Autofac服务注册逻辑 #

移除服务实现类的SingleInstance()注册，改用InstancePerLifetimeScope()，确保拦截器能正常生成代理：

builder.RegisterType<MyService>()
       .As<IMyService>()
       .InstancePerLifetimeScope()
       .EnableInterfaceInterceptors()
       .InterceptedBy(typeof(MyInterceptor));

2. 自定义Singleton实例提供器 #

实现IInstanceProvider，让WCF的单例实例从Autofac获取带拦截器的代理：

public class AutofacSingletonInstanceProvider : IInstanceProvider
{
    private readonly IComponentContext _context;
    private readonly Type _serviceType;
    private object _instance;

    public AutofacSingletonInstanceProvider(IComponentContext context, Type serviceType)
    {
        _context = context;
        _serviceType = serviceType;
    }

    public object GetInstance(InstanceContext instanceContext, Message message)
    {
        return _instance ??= _context.Resolve(_serviceType);
    }

    public object GetInstance(InstanceContext instanceContext)
    {
        return GetInstance(instanceContext, null);
    }

    public void ReleaseInstance(InstanceContext instanceContext, object instance)
    {
        // 单例模式下不释放实例
    }
}

3. 扩展AutofacServiceHostFactory #

重写工厂类，为Singleton服务绑定自定义实例提供器：

public class CustomAutofacServiceHostFactory : AutofacServiceHostFactory
{
    protected override AutofacServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses)
    {
        var host = base.CreateServiceHost(serviceType, baseAddresses);
        var serviceBehavior = host.Description.Behaviors.Find<ServiceBehaviorAttribute>();
        
        if (serviceBehavior?.InstanceContextMode == InstanceContextMode.Single)
        {
            foreach (var endpoint in host.Description.Endpoints)
            {
                endpoint.Behaviors.Add(new AutofacSingletonEndpointBehavior(Container, serviceType));
            }
        }
        
        return host;
    }
}

public class AutofacSingletonEndpointBehavior : IEndpointBehavior
{
    private readonly IComponentContext _context;
    private readonly Type _serviceType;

    public AutofacSingletonEndpointBehavior(IComponentContext context, Type serviceType)
    {
        _context = context;
        _serviceType = serviceType;
    }

    public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters) { }
    public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime) { }
    public void Validate(ServiceEndpoint endpoint) { }

    public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
    {
        endpointDispatcher.DispatchRuntime.InstanceProvider = new AutofacSingletonInstanceProvider(_context, _serviceType);
    }
}

4. 保留WCF服务的Singleton配置 #

服务类上维持InstanceContextMode.Single设置：

[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class MyService : IMyService
{
    // 服务实现代码
}

原因说明 #

当WCF启用InstanceContextMode.Single时，服务实例由WCF托管并复用；而默认Autofac WCF集成的单例注册逻辑会生成独立的代理实例，两者生命周期管理冲突，导致异常。通过自定义实例提供器，让WCF的单例实例直接来自Autofac的代理生成流程，既满足单例复用需求，又能正常触发拦截器逻辑。

内容的提问来源于stack exchange，提问作者user1542652