當ServiceContract非常多的情況下，比如要self-host hundred of service的時候，or更多的時候，每次hosting都是建立一個tcp listen.這樣，host的init工作會占用非常多的時間和資源。對于一些對start有較快需求的case,這明顯會影響用戶體驗。本文意在尋求一種技術手段解決這個問題，讓service只有在運行時才host。我們姑且稱之為host just in time吧

當ServiceContract非常多的情況下，比如要self-host hundred of service的時候，or更多的時候，每次hosting都是建立一個tcp listen.這樣，host的init工作會占用非常多的時間和資源。對于一些對start有較快需求的case,這明顯會影響用戶體驗。本文意在尋求一種技術手段解決這個問題，讓service只有在運行時才host。我們姑且稱之為host just in time吧

先說一下思路。

client如果能發送消息給service,并且消息可達，先決條件就是消息到達service之前，service已經被host,注意，是說消息到達之前，而并不是在客戶端發送消息之后，這就給我們提供了一個可以做手腳的時期，即消息從客戶端發送出去到消息在被服務端接收之前這段時間，如果我們能Inspect它，并根據其self description，便能在消息發送到真正的服務之前，host那個service,而做這樣一個事情，rounter明顯是最在行的了。下面是實現host just in time的原理圖。

按照上面的思路，做了一個簡單的demo，過程如下

首先創建Contracts項目Jillzhang.Wcf.HostJIT.Contracts，包含兩個ServiceContract:ICalculator和IActivity，代碼分別為：

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只模擬對這兩個ServiceContract的host just in time

建立好契約項目之后，新建服務項目:Jillzhang.Wcf.HostJIT.Services,添加兩個類：Caculator和Activity，分別實現ICalculator和IActivity，其代碼如下：

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!");
}
}
}

接著，我們需要簡歷本實例中最重要的項目：Jillzhang.Wcf.HostJIT.Dispatcher，這個項目的release自身就是一個對wcf service的self-host的hosting app.為了實現路由，截獲以及調度的功能，實現了路由接口IRounter和類Dispatcher，下面是他們的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);
}
}
}
}
}

通過代碼可以看出，首先Dispatcher是一個有路由功能的服務，它會根據message中Header中的To判斷要調用的Service是哪一個，然后判斷是否已經承載了那個最終目的的Service，如果沒有，host frist and add it to hostTable ,host之后，就可以將消息調度給真正的服務了。

app.config的代碼如下：

<?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>

而在這個項目中，我們開始只需要host IRounter契約。host代碼為：

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();
}
}
}
}

建立客戶端程序Jillzhang.Wcf.HostJIT.Client，并且將app.config更改為：

<?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為：

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，在解決方案中設置多啟動項目，啟動Jillzhang.Wcf.HostJIT.Client和Jillzhang.Wcf.HostJIT.Dispatcher，f5,然后按照提示進行輸入

會得到下面的效果：

客戶端：

服務端：

最終驗證效果和原來想象中一致。OK!

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