CallContext 类 官方教程+个人体会

CallContext 是类似于方法调用的线程本地存储区的专用集合对象，并提供对每个逻辑执行线程都唯一的数据槽。数据槽不在其他逻辑线程上的调用上下文之间共享。当 CallContext 沿执行代码路径往返传播并且由该路径中的各个对象检查时，可将对象添加到其中。

当对另一个 AppDomain 中的对象进行远程方法调用时，CallContext 类将生成一个与该远程调用一起传播的 LogicalCallContext 实例。只有公开 ILogicalThreadAffinative 接口并存储在 CallContext 中的对象被在 LogicalCallContext 中传播到 AppDomain 外部。不支持此接口的对象不在 LogicalCallContext 实例中与远程方法调用一起传输。

注意
CallContext 中的所有方法都是静态的，并且在当前 Thread 中的调用上下文上操作。

注意
此类生成链接要求。如果直接调用方没有基础结构权限，则会引发 SecurityException。有关更多信息，请参见 链接要求。

官网介绍:

服务端 CS控制台程序:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Tcp;

namespace CallContextApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            ChannelServices.RegisterChannel(new TcpChannel(8082));

            RemotingConfiguration.RegisterActivatedServiceType(typeof(HelloServiceclass));

            Console.WriteLine("Press enter to stop this process.");
            Console.ReadLine();
        }
    }
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.Remoting.Messaging;
using System.Security.Principal;

namespace CallContextApplication
{
    [Serializable]
    public class LogicalCallContextData:ILogicalThreadAffinative
    {
        int _nAccesses;
        IPrincipal _principal;

        public string numOfAccesses {
            get {
                return string.Format("The identity of {0} has been accessed {1} times.", _principal.Identity.Name, _nAccesses);
            }
        }

        public IPrincipal Principal {
            get {
                _nAccesses++;
                return _principal;
            }
        }

        public LogicalCallContextData(IPrincipal p)
        {
            _nAccesses = 0;
            _principal = p;
        }
    }
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Permissions;
using System.Text;
using System.Runtime.Remoting.Messaging;
using System.Security.Principal;

namespace CallContextApplication
{
    public class HelloServiceclass:MarshalByRefObject
    {
        static int n_instance;

        public HelloServiceclass()
        {
            n_instance++;
            Console.WriteLine(this.GetType()+"has been created. Instance # ={0}",n_instance);
        }

        ~HelloServiceclass()
        {
            Console.WriteLine("Destroyed instance {0} of HelloServiceClass",n_instance);
        }

        [PermissionSet(SecurityAction.LinkDemand)]
        public String HelloMethod(String name) {
            Console.WriteLine();
            Console.WriteLine("Called HelloMethod on instance {0} with the '{1}' parameter.",n_instance,name);

            LogicalCallContextData data = (LogicalCallContextData)CallContext.GetData("test data");
            IPrincipal myprincipal = data.Principal;

            if (myprincipal.Identity.Name=="Bob")
            {
                Console.WriteLine("\nHello {0},you are identified!",myprincipal.Identity.Name);
                Console.WriteLine(data.numOfAccesses);
            }
            else
            {
                Console.WriteLine("Go away!You are not identified!");
                return String.Empty;
            }
            return "Hi there "+name+".";
        }
    }
}

客户端 CS控制台程序:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Tcp;
using System.Runtime.Remoting.Messaging;
using System.Security.Principal;
using System.Security.Permissions;
using CallContextApplication;

namespace CallContextClientApplication
{
    public class Program
    {
        [PermissionSet(SecurityAction.LinkDemand)]
        public static void Main(string[] args)
        {
            Console.WriteLine("按任意键开始.");
            Console.ReadLine();

            GenericIdentity ident = new GenericIdentity("Bob");
            GenericPrincipal prpal = new GenericPrincipal(ident,new string[]{"Level1"});

            LogicalCallContextData data = new LogicalCallContextData(prpal);

            CallContext.SetData("test data", data);

            Console.WriteLine(data.numOfAccesses);

            ChannelServices.RegisterChannel(new TcpChannel());

            RemotingConfiguration.RegisterActivatedClientType(typeof(HelloServiceclass), "tcp://localhost:8082");

            HelloServiceclass service = new HelloServiceclass();

            if (service==null)
            {
                Console.WriteLine("Could not locate server.");
                return;
            }

            Console.WriteLine();
            Console.WriteLine("Calling remote object");
            Console.WriteLine(service.HelloMethod("Caveman"));
            Console.WriteLine(service.HelloMethod("Spaceman"));
            Console.WriteLine(service.HelloMethod("Bob"));
            Console.WriteLine("Finished remote object call");
            Console.WriteLine();

            LogicalCallContextData returnedData = (LogicalCallContextData)CallContext.GetData("test data");

            Console.WriteLine(data.numOfAccesses);
            Console.WriteLine(returnedData.numOfAccesses);
        }
    }
}

个人体会:

可以了解一下这位大师项目中用到的体会:http://blog.sina.com.cn/s/blog_7325e5ea0100orc9.html

CallContext

在处理多组件共用Context时非常有用,比如常见的EF 可以将实例的DBEntity存储在其中,可以一次访问只实例化一次,便于管理且不用多次实例访问对象

public static class DbContextHelper
    {
        private static DbContext context = null;
        private const string SessionKey_DbContext = "Entities";
        public static DbContext GetDbContext()
        {
            if (CallContext.GetData(SessionKey_DbContext) == null)
            {
                CallContext.SetData(SessionKey_DbContext, new Entities());
            }
            return CallContext.GetData(SessionKey_DbContext) asEntities;
        }
    }