实现一个简单的服务端推送方案-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：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
<script language="JavaScript" type="text/javascript" src="./prototype.js"></script>
</head>
<body>
<script language="JavaScript">
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.evalJSON();
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 += '<div>'
+ response['vid'] + ','
+ response['doorno'] + ','
+ response['rfsim'] + ','
+ response['optime'] + ','
+ response['ynopen']
+ '</div>';
}
}
var comet = new Comet();
comet.connect();
</script>
<div id="content"></div>
</body>
</html>
服务器端PHP代码，backend.php，队列使用gearman
<?php
ignore_user_abort(true);
header("Cache-Control: no-cache, must-revalidate");
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
ob_flush();
flush();
//控制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;
}
?>