实现一个简单的服务端推方案-实例篇Polling(服务端阻塞读)

前面讲过一篇《实现一个简单的服务端推方案-实例篇Polling》，那篇文章服务端的实现是不停的轮循数据库，这篇将服务器端轮循数据库改为服阻塞的方式读取队列，减轻数据库服务器的压力。

客户端代码，JS库为prototype.js：

  

<script language="java script" type="text/java script" src="./prototype.js">


<script language="java script">
  var Class = {
    create: function() {
      return function() {
        this.initialize.apply(this, arguments);
      }
    }
  }
  var Comet = Class.create();
  Comet.prototype = {
      maxvid: 0,
      url: './backend.php',
      noerror: true,
      initialize: function(){
      },
      connect: function(){
          this.ajax = new Ajax.Request(this.url, {
              method: 'get',
              parameters: {
                  'maxvid': this.maxvid
              },
              onSuccess: function(transport){
                  var response = transport.responseText.eva lJSON();
                  this.comet.maxvid = response['vid'];
                  this.comet.handleResponse(response);
                  this.comet.noerror = true;
              },
              onComplete: function(transport){
                  if (!this.comet.noerror) setTimeout(function(){
                                           comet.connect()
                                           }, 5000);
                  else
                  this.comet.connect();
                  this.comet.noerror = false;
              }
          });
          this.ajax.comet = this;
      },
      handleResponse: function(response){
          $('content').innerHTML += '
  

   '
                                 + response['vid']    + ','
                                 + response['doorno'] + ','
                                 + response['rfsim']  + ','
                                 + response['optime'] + ','
                                 + response['ynopen']
                                 + '
  
';
      }
  }
  var comet = new Comet();
  comet.connect();


  

服务器端PHP代码，backend.php，队列使用gearman

  浏览器前端不要缓存结果，每次都要重新查询

$maxvid = $_GET["maxvid"];
error_log(date("[Y-m-d H:i:s]")." > "."maxvid: ".$maxvid."\n", 3 , "/usr/local/apache2219/logs/php_log");

$gmworker = new GearmanWorker();
$gmworker->setTimeout(60000);
$gmworker->addServer();
$gmworker->addFunction("getmsg", "getmsg");

if ( ($gmworker->work()) && ($gmworker->returnCode() == GEARMAN_SUCCESS) )
{
  echo $msg;
  ob_flush();  //必须有，不然是在PHP_BUFFER不会被发送到客户端
  flush();
  if ( connection_status() ) {
    error_log(date("[Y-m-d H:i:s]")." < ".$msg.",but connection aborted!\n", 3 , "/usr/local/apache2219/logs/php_log");
  } else {
    error_log(date("[Y-m-d H:i:s]")." < ".$msg."\n", 3 , "/usr/local/apache2219/logs/php_log");
  }
  //由于服务端阻塞读队列，无法感知客户端是否断开
  //所以当客户端中断后，后台PHP仍在阻塞读，这时如果队列有新的消息便会被读出但又无法送达前端，导致消息丢失
  //所以这里只能在发送后判断客户端连接状态，做特殊判断处理
}

function getmsg($job)
{
  global $msg;

  $msg = $job->workload();

  $result = "OK";

  return $result;
}

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