模块简单设计——用Jetty实现一个client adapter

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模块简单设计

首先看看下面的应用场景

传统的服务器端为若干个客户端提供服务，一般需要开启多个服务器端进程。为了进一步提升服务器端的处理能力，可以如图所示将服务解耦为两部分（adapter与workers），它们之间通过消息队列传输数据，其中workers处理具体业务，adapter负责接入请求以及反馈结果，具体包含下面两个工作。

1，将所有客户端的请求发送到消息队列（进而传给后台处理）

2，后台处理完毕后将结果返回响应队列，client adapter获取到结果后返回给相应客户端。

我们选择用Jetty（8），redis以及php简单实现这个场景，主要用到jetty的continuation机制和redis的list数据结构

A，先配置一个服务器如下，同时开启一个守护线程阻塞监听response queue（用到json lib库以及jedis库）

package test;

import java.util.HashMap;
import java.util.List;

import org.eclipse.jetty.continuation.Continuation;
import org.eclipse.jetty.server.*;
import org.eclipse.jetty.server.nio.SelectChannelConnector;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.eclipse.jetty.util.thread.QueuedThreadPool;

import org.json.simple.*;

import redis.clients.jedis.Jedis;

public class PJetty{
	
	public static HashMap<String,Continuation>globalMap = new HashMap<String,Continuation>();
	
	// 用一个守护线程阻塞等待结果队列返回数据
	public static class DaemonThread extends Thread{
		
		private JSONObject obj = new JSONObject();

		private Jedis jedis = new Jedis("127.0.0.1",6379);
		private List<String> res;
		
		public void run(){
			
			while(true){
				// 阻塞等待响应队列
				res = jedis.brpop(0, "response_queue");
				
				// 获取结果信息
				String response = res.get(1);

				obj=(JSONObject) JSONValue.parse(response);
				String request_sid = obj.get("request_sid").toString();
				String result = obj.get("results").toString();
				
				if(request_sid == null){
					continue;
				}
				
				// 通过消息中的连接的sessonid获取到响应的continuation实例，然后设置结果信息再唤醒实例
				Continuation con = globalMap.get(request_sid);
				if(con == null){continue;}
				globalMap.remove(request_sid);
				
				//客户端异常断开这里会抛错
				try{
					con.setAttribute("results", result);
					con.resume();
				} catch(Exception e){
					continue;
				}
			}
			
		}
	}
	
	public static void main(String[] args) throws Exception {
		
		//开启守护线程去阻塞等待响应结果队列，唤醒请求
		DaemonThread dt = new DaemonThread();
		dt.start();
		
		//设置connectors
		SelectChannelConnector connector1 = new SelectChannelConnector();
		connector1.setPort(1987);
		connector1.setThreadPool(new QueuedThreadPool(5));
		
		Server server = new Server();
		server.setConnectors(new Connector[]{connector1});

		//使用servlet处理请求
		ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
		context.setContextPath("/");
		context.addServlet(new ServletHolder(new NonBlockingServlet()), "/fetch");
		server.setHandler(context);
		
        server.start();
        server.join();
	}
}

B，实现自定义的servlets接受前端client连接，将请求信息传入队列request queue

package test;

import java.io.IOException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.eclipse.jetty.continuation.Continuation;
import org.eclipse.jetty.continuation.ContinuationSupport;
import org.json.simple.JSONObject;

import redis.clients.jedis.Jedis;

public class NonBlockingServlet extends HttpServlet {

	/**
	 * generated serialize number
	 */
	private static final long serialVersionUID = 3313258432391586994L;
	
	
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException
	{
		// 用sleeptime来模拟后台工作量
		 String sleepTime = request.getParameter("st");
		 if(sleepTime == null){
			 sleepTime = "0";
		 }
		 
	     // 查看结果队列是否返回此连接的请求结果
	     Object results = request.getAttribute("results");
	     if (results==null) // 如果异步处理尚未返回结果
	      {
	       Continuation continuation = ContinuationSupport.getContinuation(request);
	 
	       if(continuation.isInitial()){
	    	   // 设置连接超时时间
		    	continuation.setTimeout(10000);
	    	   	response.setContentType("text/plain");
			    response.getWriter().flush();
			    
			    HttpSession session=request.getSession();
			    String sid = session.getId();
			    
				Jedis jedis = new Jedis("127.0.0.1",6379);
			    //将请求连接sessionid以及请求内容encode后传到处理队列中
			    JSONObject obj=new JSONObject();
			    obj.put("request_sid",sid);
			    obj.put("params",sleepTime);
			    
			    jedis.lpush("request_queue", obj.toJSONString());
			    
			    //将连接和continuation实例做个映射关系存到全局hashmap中，不确定这里是否应该加锁
			    PJetty.globalMap.put(sid, continuation);
	       }
	       
	       // 判断是否超时
	       if (continuation.isExpired())
	       {
	         // 返回超时Response
	    	 response.getWriter().println("timeout");
	   	     response.getWriter().flush();  
	         return;
	       }
	 
	       // 挂起HTTP连接
	       continuation.suspend(); 
	 
	       return; // or continuation.undispatch();
	     }
	 
	     // 连接恢复后返回结果
		 response.getWriter().println("Got Result:\t" + results);
		 response.getWriter().flush();  
	}
}

C，实现后端worker.php（可以自定义worker进程数，进程数多能获取更好的并发）（用到predis库）

#!/root/bin/php
<?php

require_once("lib/Predis/Autoloader.php");

function worker_thread()
{
        Predis\Autoloader::register();
        $redis = new Predis\Client('tcp://127.0.0.1:6379');

                while(true){
                        try{
                                $request = $redis->brpop("request_queue", 0);
                        } catch(Exception $e){
                                continue;
                        }
                        /** demo
                         array(2) {
                         [0]=>
                         string(13) "request_queue"
                         [1]=>
                         string(55) "{"request_sid":"q0muxazo8k1h1k3uw85wuayh","params":"4"}"
                         }
                         */
                        $request = json_decode($request[1], true);
                        // sleep represents work loads
                        sleep(intval($request["params"]));
                        $results = array("request_sid"=>$request["request_sid"], "results"=>$request["params"]);
                        $response = json_encode($results);
                        $redis->lpush("response_queue",$response);
                }
}

//开启多个worker进程提供服务
for ($worker_nbr = 0; $worker_nbr < 5; $worker_nbr++) {
        $pid = pcntl_fork();
        if ($pid == 0) {
                worker_thread();

                return;
        }
}

?>

运行效果如下：

root # for((i=10;i>=1;i--)) ; do lynx -dump http://127.0.0.1:1987/fetch?st=$i & done
[1] 14112
[2] 14113
[3] 14114
[4] 14115
[5] 14116
[6] 14117
[7] 14118
[8] 14119
[9] 14120
[10] 14121
root # Got Result:     3
Got Result:     4
Got Result:     2
Got Result:     7
Got Result:     1
Got Result:     9
Got Result:     6
timeout
timeout
timeout

[1]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[2]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[3]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[4]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[5]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[6]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[7]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[8]   Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[9]-  Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i
[10]+  Done                    lynx -dump http://127.0.0.1:1987/fetch?st=$i

这只是一个简单的demo，为了防止redis，workers进程挂掉或者客户端异常断开，还需要做些异常处理，比如设置请求超时，捕获一些空指针等，超时需要将continuation从globalMap中剔除。

redis数据库中存储的内容如下，可以看出虽然经后台处理后顺序变化了，但是对应关系正确：

redis 127.0.0.1:6379> lrange request_queue 0 15
 1) "{\"request_sid\":\"igiwkwnb715aphw8uvtfa6rj\",\"params\":\"3\"}"
 2) "{\"request_sid\":\"wsrglxa3h6ef19ik5i0nbiiys\",\"params\":\"2\"}"
 3) "{\"request_sid\":\"tyiqoj6awj5t16ddpqusftwc8\",\"params\":\"6\"}"
 4) "{\"request_sid\":\"1052tgkiyy7c31bmxjtbom7ca\",\"params\":\"5\"}"
 5) "{\"request_sid\":\"17jo1xwnnkd3h1mhcqcfplrl5k\",\"params\":\"8\"}"
 6) "{\"request_sid\":\"1xk521sq6vmmf6enxauwzduj9\",\"params\":\"4\"}"
 7) "{\"request_sid\":\"1cxnir1slgjiq1o2n3xwznh0kk\",\"params\":\"9\"}"
 8) "{\"request_sid\":\"961vf8hao3stsv4vt1qif3ws\",\"params\":\"7\"}"
 9) "{\"request_sid\":\"35pfn5au6p8qdbri17p636si\",\"params\":\"10\"}"
10) "{\"request_sid\":\"1ca4wy8qsfr7av0hwk8xtlqhp\",\"params\":\"1\"}"

redis 127.0.0.1:6379> lrange response_queue 0 15
 1) "{\"request_sid\":\"tyiqoj6awj5t16ddpqusftwc8\",\"results\":\"6\"}"
 2) "{\"request_sid\":\"igiwkwnb715aphw8uvtfa6rj\",\"results\":\"3\"}"
 3) "{\"request_sid\":\"wsrglxa3h6ef19ik5i0nbiiys\",\"results\":\"2\"}"
 4) "{\"request_sid\":\"35pfn5au6p8qdbri17p636si\",\"results\":\"10\"}"
 5) "{\"request_sid\":\"1052tgkiyy7c31bmxjtbom7ca\",\"results\":\"5\"}"
 6) "{\"request_sid\":\"1cxnir1slgjiq1o2n3xwznh0kk\",\"results\":\"9\"}"
 7) "{\"request_sid\":\"17jo1xwnnkd3h1mhcqcfplrl5k\",\"results\":\"8\"}"
 8) "{\"request_sid\":\"961vf8hao3stsv4vt1qif3ws\",\"results\":\"7\"}"
 9) "{\"request_sid\":\"1xk521sq6vmmf6enxauwzduj9\",\"results\":\"4\"}"
10) "{\"request_sid\":\"1ca4wy8qsfr7av0hwk8xtlqhp\",\"results\":\"1\"}"