code4fun:host wcf service just in time

当ServiceContract非常多的情况下，比如要self-host hundred of service的时候，or更多的时候，每次hosting都是建立一个tcp listen.这样，host的init工作会占用非常多的时间和资源。对于一些对start有较快需求的case,这明显会影响用户体验。本文意在寻求一种技术手段解决这个问题，让service只有在运行时才host。我们姑且称之为host just in time吧

先说一下思路。

client如果能发送消息给service,并且消息可达，先决条件就是消息到达service之前，service已经被host,注意，是说消息到达之前，而并不是在客户端发送消息之后，这就给我们提供了一个可以做手脚的时期，即消息从客户端发送出去到消息在被服务端接收之前这段时间，如果我们能Inspect它，并根据其self description，便能在消息发送到真正的服务之前，host那个service,而做这样一个事情，rounter明显是最在行的了。下面是实现host just in time的原理图。

按照上面的思路，做了一个简单的demo，过程如下

首先创建Contracts项目Jillzhang.Wcf.HostJIT.Contracts，包含两个ServiceContract:ICalculator和IActivity，代码分别为：

ICalculator：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
namespace Jillzhang.Wcf.HostJIT.Contracts
{
[ServiceContract]
public interface  ICalculator
{
[OperationContract]
int Add(int a, int b);
}
}

IActivity：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
namespace Jillzhang.Wcf.HostJIT.Contracts
{
[ServiceContract]
public interface IActivity
{
[OperationContract]
void Excute();
}
}

demo只模拟对这两个ServiceContract的host just in time

建立好契约项目之后，新建服务项目:Jillzhang.Wcf.HostJIT.Services,添加两个类：Caculator和Activity，分别实现ICalculator和IActivity，其代码如下：

Caculator：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Jillzhang.Wcf.HostJIT.Contracts;
namespace Jillzhang.Wcf.HostJIT.Services
{
public class Calculator : ICalculator
{
public int Add(int a, int b)
{
return a + b;
}
}
}

Activity：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Jillzhang.Wcf.HostJIT.Contracts;
namespace Jillzhang.Wcf.HostJIT.Services
{
public class Activity:IActivity
{
public void Excute()
{
Console.WriteLine("activity is running!");
}
}
}

接着，我们需要简历本实例中最重要的项目：Jillzhang.Wcf.HostJIT.Dispatcher，这个项目的release自身就是一个对wcf service的self-host的hosting app.为了实现路由，截获以及调度的功能，实现了路由接口IRounter和类Dispatcher，下面是他们的code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.Collections;
using Jillzhang.Wcf.HostJIT.Services;
namespace Jillzhang.Wcf.HostJIT.Dispatcher
{
[ServiceContract]
public interface IRounter
{
[OperationContract(Action = "*", ReplyAction = "*")]
Message ProcessMessage(Message msg);
}
[ServiceBehavior(AddressFilterMode = AddressFilterMode.Any)]
public class Dispatcher : IRounter
{
public static readonly Hashtable hostTable = new Hashtable();
public Message ProcessMessage(Message msg)
{
string to = msg.Headers.To.ToString();
string serviceName = "";
//todo:if no host,host first
if (to.IndexOf("8031") > -1)
{
if (!hostTable.ContainsKey("Calculator"))
{
ServiceHost host = new ServiceHost(typeof(Calculator));
host.Opened += new EventHandler(delegate(object sender, EventArgs arg)
{
Console.WriteLine("Calculator service is opened!");
});
host.Open();
hostTable.Add("Calculator", host);
}
serviceName = "Calculator";
}
else
{
if (!hostTable.ContainsKey("Activity"))
{
ServiceHost host = new ServiceHost(typeof(Activity));
host.Opened += new EventHandler(delegate(object sender, EventArgs arg)
{
Console.WriteLine("activity service is opened!");
});
host.Open();
hostTable.Add("Activity", host);
}
serviceName = "Activity";
}
//todo:rounter the message
using (ChannelFactory<IRounter> channelFactory = new ChannelFactory<IRounter>(serviceName))
{
var chanenl = channelFactory.CreateChannel();
using (chanenl as IDisposable)
{
return chanenl.ProcessMessage(msg);
}
}
}
}
}

通过代码可以看出，首先Dispatcher是一个有路由功能的服务，它会根据message中Header中的To判断要调用的Service是哪一个，然后判断是否已经承载了那个最终目的的Service，如果没有，host frist and add it to hostTable ,host之后，就可以将消息调度给真正的服务了。

app.config的代码如下：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.serviceModel>
<services>
<service name="Jillzhang.Wcf.HostJIT.Services.Calculator">
<host>
<baseAddresses>
<add baseAddress="net.tcp://127.0.0.1:8031"/>
</baseAddresses>
</host>
<endpoint address="Calculator" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Contracts.ICalculator"></endpoint>
</service>
<service name="Jillzhang.Wcf.HostJIT.Services.Activity">
<host>
<baseAddresses>
<add baseAddress="net.tcp://127.0.0.1:8032"/>
</baseAddresses>
</host>
<endpoint address="Activity" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Contracts.IActivity"></endpoint>
</service>
<service name="Jillzhang.Wcf.HostJIT.Dispatcher.Dispatcher">
<host>
<baseAddresses>
<add baseAddress="net.tcp://127.0.0.1:8030"/>
</baseAddresses>
</host>
<endpoint address="" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Dispatcher.IRounter"></endpoint>
</service>
</services>
<client>
<endpoint  address="net.tcp://127.0.0.1:8031/Calculator" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Dispatcher.IRounter" name="Calculator"></endpoint>
<endpoint  address="net.tcp://127.0.0.1:8032/Activity" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Dispatcher.IRounter" name="Activity"></endpoint>
</client>
</system.serviceModel>
</configuration>

而在这个项目中，我们开始只需要host IRounter契约。host代码为：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
namespace Jillzhang.Wcf.HostJIT.Dispatcher
{
class Program
{
static void Main(string[] args)
{
using (ServiceHost host = new ServiceHost(typeof(Dispatcher)))
{
host.Opened += new EventHandler(delegate(object sender, EventArgs arg)
{
Console.WriteLine("dispatcher service is opened!");
});
host.Open();
Console.Read();
}
}
}
}

建立客户端程序Jillzhang.Wcf.HostJIT.Client，并且将app.config更改为：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.serviceModel>
<client>
<endpoint behaviorConfiguration="via" address="net.tcp://127.0.0.1:8031/Calculator" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Contracts.ICalculator" name="Calculator"></endpoint>
<endpoint behaviorConfiguration="via" address="net.tcp://127.0.0.1:8032/Activity" binding="netTcpBinding" contract="Jillzhang.Wcf.HostJIT.Contracts.IActivity" name="Activity"></endpoint>
</client>
<behaviors>
<endpointBehaviors>
<behavior name="via">
<clientVia viaUri="net.tcp://127.0.0.1:8030/"/>
</behavior>
</endpointBehaviors>
</behaviors>
</system.serviceModel>
</configuration>

Programe.cs为：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
using Jillzhang.Wcf.HostJIT.Contracts;
namespace Jillzhang.Wcf.HostJIT.Client
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("press any key when dispatcher service is ok!");
Console.Read();
CallCalculator();
CallActivity();
CallCalculator();
CallActivity();
Console.ReadKey(true);
}
static void CallCalculator()
{
using (ChannelFactory<ICalculator> channelFactory = new ChannelFactory<ICalculator>("Calculator"))
{
var channel = channelFactory.CreateChannel();
using (channel as IDisposable)
{
Console.WriteLine(channel.Add(1, 2).ToString());
}
}
}
static void CallActivity()
{
using (ChannelFactory<IActivity> channelFactory2 = new ChannelFactory<IActivity>("Activity"))
{
var channel = channelFactory2.CreateChannel();
using (channel as IDisposable)
{
channel.Excute();
}
}
}
}
}
好了，在解决方案中设置多启动项目，启动Jillzhang.Wcf.HostJIT.Client和Jillzhang.Wcf.HostJIT.Dispatcher，f5,然后按照提示进行输入

会得到下面的效果：

客户端：

服务端：

最终验证效果和原来想象中一致。OK!

demo项目：https://files.cnblogs.com/jillzhang/Jillzhang.Wcf.HostJIT.rar