CORBA回调函数在C#项目环境中的应用

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哲学中有句话：存在就是真理。每种语言能在某个时期出现，并能在各个产品线广泛应用，说明它具有一定的生命力。

如果选择不同的语言能解决我们的不同方案，难道不是我们所期望的理由？本文选择C#语言主要是使用C#开发WEB服务器，完成HTTP+XML数据通信。因项目对实时性没有苛刻性，换句话讲，如果实时性高也不会选择HTTP+XML。

本文的描述可以说是《IIOP.NET与CORBA中间件应用技术》的一种扩展画面。以C#编写的Web服务器和CORBA中间件服务器结合体。

1、场景描述

计算机PC-2作为FEP服务器完成两项任务：

任务1：处理从ISCS（综合监控）主动上传的格式数据（HTTP+XML），并解析成对应的模拟量和数字量。其中ISCS为Web服务器的客户端，主动与PC-2实现连接，Web服务器的端口号：8080。连接方式为长连接。

任务2：把处理好的ISCS数据上传给PC-1，两者通讯方式以CORBA中间件实现。PC-2为中间件的服务端，PC-1为中间件的客户端。

任务1和任务2之间以共享队列的方式完成数据交换。任务2发现队列中有未取走的数据，会主动通知（接口onNotify）计算机PC-1。其通知机制也就是我们要讲的CORBA回调函数。

2、回调函数

软件模块之间总是存在着一定的接口，从调用方式上，可以把他们分为三类：同步调用、回调和异步调用。同步调用是一种阻塞式调用，调用方要等待对方执行完毕才返回，它是一种单向调用；回调是一种双向调用模式，也就是说，被调用方在接口被调用时也会调用对方的接口；异步调用是一种类似消息或事件的机制，不过它的调用方向刚好相反，接口的服务在收到某种讯息或发生某种事件时，会主动通知客户方（即调用客户方的接口）。回调和异步调用的关系非常紧密，通常我们使用回调来实现异步消息的注册，通过异步调用来实现消息的通知。同步调用是三者当中最简单的，而回调又常常是异步调用的基础。

对于分布式组件代理体系CORBA，异步处理有多种方式，如回调接口、事件服务、通知服务等。事件服务和通知服务是CORBA用来处理异步消息的标准服务，他们主要负责消息的处理、派发、维护等工作。

回调接口的原理很简单，CORBA客户和服务器都具有双重角色，即充当服务器也是客户客户。对一些简单的异步处理过程，我们可以通过回调机制来实现。

3、 CORBA接口文件定义

// **********************************************************************

// 2013.06.27

// liuxuezong, PSD, Shanghai, China

// **********************************************************************

#ifndef _RTSIPWEBSERVER_IDL_

#define _RTSIPWEBSERVER_IDL_

// version 1.0.0

module rtsip

{

struct point_stream

{

string pointcode;

octet type;

float value;

};

typedef sequence <point_stream> PointStreamList;

// This exception is raised every time a failure or error is

// detected in a treatment.

exception GeneralException

{

string error_msg;

};

interface EventHandler

{

void onNotify(in long changes);

};

interface FepManager

{

PointStreamList getPointsValue() raises(GeneralException);

void setEventHandler(in EventHandler handler) raises(GeneralException);

};

#endif

// EOF rtsipwebserver.idl

4、C#实现部分

1）、FepManagerServer.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Remoting.Channels;

using System.Runtime.Remoting;

using omg.org.CosNaming;

using Ch.Elca.Iiop;

using Ch.Elca.Iiop.Services;

using Ch.Elca.Iiop.Idl;

namespace FepWebService

{

class FepManagerServer

{

private static FepManagerImpl fepmanager = null;

public void run()

{

string nameServiceUrl ="corbaloc::localhost:10003/NameService";

// register the channel

int port = 10003;

IiopChannel chan =newIiopChannel(port);

ChannelServices.RegisterChannel(chan,false);

fepmanager = new FepManagerImpl();

string objectURI = "fepwebserver";

RemotingServices.Marshal(fepmanager, objectURI);

// publish the adder with an external name service

NamingContext nameService = (NamingContext)RemotingServices.Connect(

typeof(NamingContext), nameServiceUrl);

NameComponent[] name =newNameComponent[] {newNameComponent("fepwebserver") };

nameService.bind(name, fepmanager);

Console.WriteLine("Fep web server running");

Console.ReadLine();

// unpublish with external name service

nameService.unbind(name);

}

public bool isBindIiop()

{

return (fepmanager ==null ?false :true);

}

public void setQueue(PointQueue queue)

{

fepmanager.setQueue(queue);

}

public void onNotify(int changes)

{

fepmanager.onNotify(changes);

}

2）、FepManagerImpl.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using omg.org.CosNaming;

using Ch.Elca.Iiop;

using Ch.Elca.Iiop.Services;

using Ch.Elca.Iiop.Idl;

namespace FepWebService

{

///<summary>

/// the FepManagerImpl Implementation

///</summary>

public class FepManagerImpl : MarshalByRefObject, rtsip.FepManager, rtsip.EventHandler

{

private static rtsip.EventHandler handler_;

private static PointQueue queue_ = null;

public override object InitializeLifetimeService()

{

// live forever

return null;

}

public void setQueue(PointQueue queue)

{

queue_ = queue;

}

public rtsip.point_stream[] getPointsValue()

{

try

{

int nSize = queue_.GetCount();

nSize = (nSize > 1024 ? 1024 : nSize);

rtsip.point_stream[] points =new rtsip.point_stream[nSize];

for (int i = 0; i < nSize; i++)

{

rtsip.point_stream s =new rtsip.point_stream();

PointAttribute point = (PointAttribute)queue_.PopObj();

s.type = point.Type;

if (s.type ==PointAttribute.RTSIP_DATATYPE_DIGITAL)

{

s.value = Convert.ToByte(point.Value);

}

else

{

s.value = Convert.ToSingle(point.Value);

}

s.pointcode = point.PointCode;

points[i] = s;

}

return points;

}

catch (Exception e)

{

Console.WriteLine("exception: " + e);

}

return null;

}

public void setEventHandler(rtsip.EventHandler handler)

{

handler_ = handler;

}

public void onNotify(int changes)

{

try

{

if (handler_ != null && changes > 0)

{

handler_.onNotify(changes);

}

catch (Exception e)

{

Console.WriteLine("exception: " + e);

handler_ = null;

}

3）、PointQueue.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace FepWebService

{

public struct PointAttribute

{

public const byte RTSIP_DATATYPE_NULL = 0;

public const byte RTSIP_DATATYPE_ANALOG = 1;

public const byte RTSIP_DATATYPE_DIGITAL = 2;

public byte Type;

public string PointCode;

public string Value;

public PointAttribute(byte type,string pointcode,string value)

{

this.Type = type;

this.PointCode = pointcode;

this.Value = value;

}

public class PointQueue

{

#region Constants

public const string ObjectType = "FepWebService.PointAttribute";

#endregion Constants

private static RtsipQueue queue = new RtsipQueue();

public void PushObj(Object obj)

{

queue.enqueue(obj);

}

public Object PopObj()

{

return queue.dequeue();

}

public int GetCount()

{

return queue.getSize();

}

4）、RtsipQueue.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace FepWebService

{

public class RtsipQueue

{

private static int QUEUE_MAX_LEN = 4096;

private int m_nRead;

private static int m_nWrite;

private static Object[] data;

public RtsipQueue()

{

data = new Object[QUEUE_MAX_LEN];

m_nRead = 0;

m_nWrite = 0;

}

public int getSize()

{

int num = (m_nWrite - m_nRead + QUEUE_MAX_LEN) % QUEUE_MAX_LEN;

return num;

}

public Object dequeue()

{

if (m_nWrite == m_nRead)

{

return null;

}

Object obj = data[m_nRead];

m_nRead = (m_nRead + 1) % QUEUE_MAX_LEN;

return obj;

}

public void enqueue(Object obj)

{

int nWritep = m_nWrite;

Object pData = data[nWritep];

pData = null;

data[nWritep] = obj;

nWritep = (nWritep + 1) % QUEUE_MAX_LEN;

m_nWrite = nWritep;

}

5）、Program.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using rtsip;

using FepWebService;

using HybridDSP.Net.HTTP;

using System.Xml;

using System.IO;

using System.Threading;

namespace FepWebService

{

class RtsipHandler : IHTTPRequestHandler

{

public static PointQueue queue = new PointQueue();

public static FepManagerServer manager_ = null;

public RtsipHandler(FepManagerServer manager)

{

manager_ = manager;

}

public void ParseXML(string PointCode, string strXML)

{

XmlDocument XDoc =newXmlDocument();

XDoc.LoadXml(strXML);

XmlNodeList nodelist = XDoc.SelectNodes("/vjournal/description");

foreach (XmlNode nodein nodelist)

{

byte type = PointAttribute.RTSIP_DATATYPE_NULL;

string strValue = node.InnerText;

string strTemp = PointCode;

strTemp.ToLower();

if (strTemp.IndexOf("ai") > 0)

{

type = PointAttribute.RTSIP_DATATYPE_ANALOG;

}

else if (strTemp.IndexOf("di") > 0)

{

type = PointAttribute.RTSIP_DATATYPE_DIGITAL;

}

else

{

type = PointAttribute.RTSIP_DATATYPE_DIGITAL;

}

PointAttribute point =newPointAttribute(type, PointCode, strValue);

queue.PushObj(point);

}

public void HandleRequest(HTTPServerRequest request,HTTPServerResponse response)

{

Stream body = request.GetRequestStream();

long len = request.GetContentLength();

if (len > 0)

{

byte[] b = new byte[len];

body.Read(b, 0, Convert.ToInt32(len));

string strBody = Encoding.ASCII.GetString(b);

string strLocation = request.Get("content-location");

Console.WriteLine("content-location:{0}", strLocation);

int nIndex = strLocation.LastIndexOf("/") + 1;

int nSize = strLocation.Length - nIndex;

string PointCode = strLocation.Substring(nIndex, nSize);

Console.WriteLine("Body:{0}", strBody);

ParseXML(PointCode, strBody);

// "HTTP/1.1 200 OK\r\nContent-Length:0\r\n\r\n"

response.StatusAndReason = HTTPServerResponse.HTTPStatus.HTTP_OK;

response.ContentLength = 0;

response.Send();

}

public static void ProcessXmlData()

{

while (true)

{

if (manager_ != null && manager_.isBindIiop())

{

manager_.setQueue(queue);

}

int nCount = queue.GetCount();

if (manager_ != null && nCount > 0)

{

manager_.onNotify(nCount);

}

Thread.Sleep(50);

}

class RequestHandlerFactory : IHTTPRequestHandlerFactory

{

private static Thread _thread;

private static FepManagerServer manager_ = null;

public RequestHandlerFactory(FepManagerServer manager)

{

manager_ = manager;

_thread = new Thread(RtsipHandler.ProcessXmlData);

_thread.Start();

}

public IHTTPRequestHandler CreateRequestHandler(HTTPServerRequest request)

{

RtsipHandler rtsipHandle =newRtsipHandler(manager_);

return rtsipHandle;

}

class Program

{

static void Main(string[] args)

{

FepManagerServer manager =newFepManagerServer();

RequestHandlerFactory factory =newRequestHandlerFactory(manager);

HTTPServer server =newHTTPServer(factory, 8080);

server.Start();

manager.run();

server.Stop();

}

5、C++实现部分

省略

6、结束语

本文讲述了回调函数在CORBA中的使用情况，以C#工程典型的案例分析回调过程。远程函数调用结合回调函数功能，基本满足一般任务要求。