asp.net 中长尾链接实现推送 -- comet分类：DotNet 发布时间：2015/6/25 23:12:08
一般需求推送服务时，都会去第三方拿推送组件，如”极光“，”百度“，”小米"什么的，自己用.net实现推送服务端需要面对很多问题，比如C10K，但是企业内部使用往往用不了10K的链接，有个1K,2K就足够，这个时候完全可以自己实现一个推送服务，这样手机应用就不用走外网了。
使用.net实现推送服务有几个选择 1.是使用WCF 基于TCP的回调-针对.net To .net 端，经过7*24小时测试，2K左右的链接能稳定hold住，参考：http://www.cnblogs.com/wdfrog/p/3924718.html
3.使用Comet Request, 首先Comet Request 采用Asp.net + IIS,整整网页就好了，另外由于IIS应用程序池会定期回收，程序写的烂点也不影响，每天都给你一个新的开始，还有Comet 的实现网上代码很多，还有开源的SignalR可以用.
采用Comet方式的实现 1.服务端，使用IHttpAsyncHandler来Hold住请求，需要根据cookie或QueryString中带的UserId来区分不同的用户  
 using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace MangoPush.WebComet.Core
{
public class PushAsyncHandle : IHttpAsyncHandler
{
public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
{
var ar = new PushAsyncResult(context, cb, extraData);
CometRequestMgr.Instance.Add(ar);
return ar;
}
public void EndProcessRequest(IAsyncResult result)
{
}
public bool IsReusable
{
get { return true; }
}
public void ProcessRequest(HttpContext context)
{
throw new NotImplementedException();
}
}
}
  
 using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Threading;
namespace MangoPush.WebComet.Core
{
public class PushAsyncResult:IAsyncResult
{
private static int GId = 0;
private bool m_IsCompleted = false;
private AsyncCallback Callback = null;
public HttpContext Context;
private Object _AsyncState;
public DateTime AddTime{get;private set;}
public int Id { get; set; }
public PushAsyncResult(HttpContext context, AsyncCallback callback, object asyncState)
{
Context = context;
Callback = callback;
_AsyncState = asyncState;
AddTime = DateTime.Now;
Interlocked.Increment(ref GId);
int userId = int.TryParse(Context.Request["UserId"], out userId) ? userId : 0;
Id = userId;
if (userId == 0)
{
Release(JUtil.ToJson(new {Code=-1,Msg="未提供UserId" }));
}
}
public void Release(string msg)
{
try
{
try
{
Context.Response.Write(msg);
}
catch { }
if (Callback != null)
{
Callback(this);
}
}
catch { }
finally
{
m_IsCompleted = true;
}
}
public object AsyncState
{
get { return _AsyncState; }
}
public System.Threading.WaitHandle AsyncWaitHandle
{
get { return null; }
}
public bool CompletedSynchronously
{
get { return false; }
}
public bool IsCompleted
{
get { return m_IsCompleted; }
}
}
}
  
 using System;
using System.Collections.Generic;
using System.Collections.Concurrent;
using System.Linq;
using System.Web;
namespace MangoPush.WebComet.Core
{
public class CometRequestMgr
{
public static readonly CometRequestMgr Instance = new CometRequestMgr();
private ConcurrentDictionary<int, PushAsyncResult> Queue = new ConcurrentDictionary<int, PushAsyncResult>();
private CometRequestMgr()
{
var timer = new System.Timers.Timer();
timer.Interval = 1000 * 30;
timer.AutoReset = false;
timer.Elapsed += (s, e) =>
{
try
{
var list = Queue.Select(ent => ent.Value).ToList();
#region 清理完成链接
foreach (var it in list)
{
if (it.IsCompleted)
{
try
{
PushAsyncResult c = null;
Queue.TryRemove(it.Id,out c);
}
catch (Exception ex)
{
continue;
}
}
}
#endregion
}
catch (Exception ex)
{
}
finally
{
timer.Start();
}
};
timer.Start();
}
public void Add(PushAsyncResult ar)
{
Queue[ar.Id] = ar;
}
public void BroadCastMsg(string msg)
{
msg +="," + DateTime.Now.ToString();
foreach (var c in Queue)
{
try
{
c.Value.Release(JUtil.ToJson( new {Code=0,Msg= msg}));
}
catch { }
finally
{
PushAsyncResult outIt=null;
Queue.TryRemove(c.Key,out outIt);
}
}
}
}
}
 2.网页端，使用ajax方式发起访问，特别注意的是需要设置timeout,这样如果断线或者服务端挂了重启，可以自动修复  
 $(function () {
function long_polling() {
var _url = ''/pushService.act?userId='' + $("#userId").val();
console.log(_url);
var ajaxRequest = $.ajax({
url: _url, //请求的URL
timeout: 1000 * 60 * 3, //超时时间设置，单位毫秒
type: ''get'', //请求方式，get或post
data: {}, //请求所传参数，json格式
dataType: ''json'', //返回的数据格式
success: function (data) { //请求成功的回调函数
console.log(data);
if (data.Code == 0) {
$(''#msg'').append(data.Msg + "<br/>");
}
},
complete: function (XMLHttpRequest, status) { //请求完成后最终执行参数
if (status == ''timeout'') {//超时,status还有success,error等值的情况
ajaxRequest.abort();
console.log("超时");
}
if ($("#btn").val() == "停止") {
long_polling();
}
}
});
}
$("#btn").click(function () {
if ($("#btn").val() == "启动") {
long_polling();
$("#btn").val("停止");
} else {
$("#btn").val("启动");
}
});
$("#btnCls").click(function () {
$("#msg").text("");
});
});
 3.Winform端，采用WebClient发起请求，并且使用AutoResetEvent控制超时重连(相当于心跳包)  
 private void Do()
{
try
{
while (Enable)
{
Console.WriteLine("发起请求!");
var url = @"http://192.168.9.6:9866/pushService.act?userId=18";
using (var wc = new WebClient())
{
wc.Encoding = Encoding.UTF8;
#region 回调处理
wc.DownloadStringCompleted += (s, e) => {
if (e.Error != null)
{
Console.WriteLine(e.Error);
}
else if (e.Cancelled)
{
Console.WriteLine("Be Cancelled!");
}
else
{
Console.WriteLine(e.Result);
}
autoReset.Set();
};
#endregion
var uri = new Uri(url);
wc.DownloadStringAsync(uri);
var isOK= autoReset.WaitOne(1000 * 60 * 5);
if (!isOK)
{
wc.CancelAsync();
}
}
}
}
catch (Exception ex)
{
Console.WriteLine("错误" + ex.Message);
}
finally
{
if (Enable)
{
ThreadPool.QueueUserWorkItem(o => { Do(); }, null);
}
}
}
 4.Android端 1.类似WinForm端，目前采用AsyncHttpClient,写法跟Js差不多，需要设置timeout 2.由于android会回收进程，需要AlarmManager，定期检查推送服务是否还存活 3.android系统重启，开关网络，调整时间，需要订阅相应广播，调整AlermManager,触发平率。
总结: 整个能支持10K,100K,2000K链接的，挺不容易，但是一般中小企业使用1K,2K甚至0.1K足矣，3,4百行代码就完事，至少可以让员工不用连3G，4G了，NND，提速降价，也不知道降那去了。 最后整2个图片
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