In the traditional AJAX polling method, the client queries the server for the latest data at user-defined intervals. This method of pulling data requires a short time interval to ensure the accuracy of the data. However, if the time interval is too short, the customer service side will send multiple requests to the server in a short period of time.
Reverse AJAX, which is the so-called long polling or COMET. The server and client need to maintain a long-term request, which allows the server to return messages to the client when it has data.
Here we use AJAX to request the data.PHP page to obtain the value of 'success', and the request time reaches 80 seconds. If no 'success' is returned from the server during these 80 seconds, the connection status will remain until data is returned or the value of 'success' is 0 before the connection is closed. After closing the connection, continue the next request.
index.html
<!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" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<script type="text/javascript" src="http://s1.hqbcdn.com/??lib/jquery/jquery-1.7.2.min.js"></script>
</head>
<body>
<p id="msg"></p>
<input id="btn" type="button" value="测试" />
<script type="text/javascript" >
$(function(){
$("#btn").bind("click",{btn:$("#btn")},function(evdata){
$.ajax({
type:"POST",
dataType:"json",
url:"data.php",
timeout:80000, //ajax请求超时时间80秒
data:{time:"80"}, //40秒后无论结果服务器都返回数据
success:function(data,textStatus){
//从服务器得到数据，显示数据并继续查询
if(data.success=="1"){
$("#msg").append("<br>[有数据]"+data.text);
evdata.data.btn.click();
}
//未从服务器得到数据，继续查询
if(data.success=="0"){
$("#msg").append("<br>[无数据]");
evdata.data.btn.click();
}
},
//Ajax请求超时，继续查询
error:function(XMLHttpRequest,textStatus,errorThrown){
if(textStatus=="timeout"){
$("#msg").append("<br>[超时]");
evdata.data.btn.click();
}
}
});
});
});
</script>
</body>
</html>This is an infinite loop. The end condition of the loop is to obtain the return result and return Json data.
And accepts the $_POST[‘time’] parameter to limit the loop timeout to avoid excessive waste of resources. (The browser will not send a message to the server when it is closed, and the use may continue in a loop)
data.php
<?php
if(empty($_POST['time']))exit();
set_time_limit(0);//无限请求超时时间
$i=0;
while (true){
//sleep(1);
usleep(500000);//0.5秒
$i++;
//若得到数据则马上返回数据给客服端，并结束本次请求
$rand=rand(1,999);
if($rand<=15){
$arr=array('success'=>"1",'name'=>'xiaoyu','text'=>$rand);
echo json_encode($arr);
exit();
}
//服务器($_POST['time']*0.5)秒后告诉客服端无数据
if($i==$_POST['time']){
$arr=array('success'=>"0",'name'=>'xiaoyu','text'=>$rand);
echo json_encode($arr);
exit();
}
}
?>Operation effect: In the picture, you can see that the request time without data reaches 40S , if data is obtained in the 40S request, the request is closed. After closing, continue with the next request!
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