COMET技术具体实现 结合PHP和JQUERY

具体看代码，费话不说

PHP服务端

$mem = new RTMEM();
if(!$mem->conn())
　　exit('no mem server');
if(!$mem->getstate())
　　exit('moonjksrv is not runing');
$alminfo = $mem->get('alm_info');
if(!$alminfo)
　　exit('no alarm');
$almobj = json_decode($alminfo);
if(!$almobj)
　　exit('no json data');
$lastmodif = isset($_GET['timestamp']) ? $_GET['timestamp'] : 0;
$currentmodif = $almobj->timestamp;
while ($currentmodif <= $lastmodif) // check if the data file has been modified
{
　　usleep(1000000); // sleep 1 second to unload the CPU
　　clearstatcache();
　　$alminfo = $mem->get('alm_info');
　　if(!$alminfo)
　　　　exit('no alarm');
　　$almobj = json_decode($alminfo);
　　if(!$almobj)
　　　　exit('no json data');
　　$currentmodif = $almobj->timestamp;
}

exit(json_encode($almobj));

以下是JS端

//comet ajax////
var Comet = function(options){
this.init(options);
};
Comet.prototype = {
constructor: Comet,
init:function(options){
this.options = {
url:"",
callback:function(){}
}
this.options = $.extend(this.options,options||{});
this.url = this.options.url;
this.callback = this.options.callback;
this.timestamp = 0;
this.noerror = true;
this.lock = true;
},
connect: function(){
this.lock = false;
this.ajaxLoop();
},
disconnect: function(){
this.lock = true;
},
ajaxLoop: function(){
if(this.url && !this.lock){
var _this = this;
$.ajax({
url:_this.url,
type:'get',
data:'timestamp=' + _this.timestamp,
dataType:'json',
cache:false,
success:function(json){
_this.timestamp = json['timestamp'];
_this.handleResponse(json);
_this.noerror = true;
},
complete:function(){
if (_this.noerror){
_this.ajaxLoop();
}else{
// if a connection problem occurs, try to reconnect each 1 seconds
setTimeout(function(){_this.ajaxLoop()}, 1000);
}
_this.noerror = false;
}
})
}
},
handleResponse: function(response){
this.callback(response);
},
doRequest: function(request){
if(this.url && !this.lock){
$.get(this.url, { 'msg': request } );
}
}
}
///////

var comet = new Comet({
url:'binsrv/rt_alm.php?type=getrtalm',
callback:function(json){ //接收到数据的处理
if(typeof(page)!="undefined" && typeof(page.processAlmData)=="function")
page.processAlmData(json);
}
});
comet.connect();

这样的话，服务器查询数据有更新才会返回AJAX请求，没有更新会直到超时（PHP默认30秒超时），这时COMET会重新连接

这样大大降低了频繁的AJAX请求，又没有降低实时性。