Backend DevelopmentPHP Tutorial一个iframe实现长轮询，通过PHP查询数据库并用JS更新页面内容的程序，问题是并不是每一条MYSQL的INSERT消息都能显示到页面，求帮忙分析下哪里有问题
首先，这是一个仿客服咨询的实时通讯系统，主要目的是将模拟前台用户发送的消息（通过手动INSERT进MYSQL数据库实现）由服务器实时推送到前台客服页面上，大致结构如下：
1、在前台kefu.html页面上有一个iframe，这个iframe请求后台query.php查询程序（iframe在页面上隐藏了）
2、query.php通过一个while(true)死循环并设置set_time_limit(0)，然后，在循环中不断的进行SQL查询，将用户发送的未读的消息查询出来，并通过输出<script></script>JS代码，操作父页面的区，将查询出来的消息结果输出到页面上
3、我通过手动INSERT一些数据，来模拟用户的消息提交， 默认消息是未读状态，当query.php读取后，会改变其为已读状态
现在的问题是：当我打开页面后（或者关闭页面再重新打开程序），一般最开始插入的数据都不能被显示到页面上，但是这些消息的状态却已经被query.php改为已读（也就是query.php已经查询到这条记录并发送JS代码到前端了），而当我继续插入很多条之后，前端才开始显示记录，并且之前INSERT的记录都是被标记为已读状态了，但是却没有显示到前台kefu.html页面上，要插入很多条之后，或者等一段时间后才能恢复正常
整个程序并没有问题，因为之后的程序就是正常的可以一条一条显示了，插入一条前台就显示一条（但是偶尔中途也会丢失一条）
我猜测问题的根源可能有两点：
1、PHP的脚本并没有被结束
2、JS可能有缓存导致虽然接收到了数据，但没有更新
不过以上两点我都不确定，我觉得可能问题没这么简单，应该是违反或者没有注意某个机理而造成的。
具体代码如下，还请各位帮忙看看问题出在了什么地方，也可以本地测试下，谢谢了。
测试方法：
手动在数据库中INSERT数据，然后观察前台kefu.html页面是否能及时收到并更新消息
数据库建表：
CREATE TABLE msg(
id int(11) NOT NULL auto_increment,
pos varchar(20) NOT NULL default '',
rec varchar(20) NOT NULL default '',
content varchar(200) NOT NULL default '',
isread` int(1) NOT NULL default '0',
PRIMARY KEY(id)
);
插入数据示例：
insert into msg(rec,pos,content,isread) values('admin','zhangsan','hello',0);
回复讨论(解决方案)
前台kefu.html代码：
<?php setcookie('username','admin');?><!doctype html><html> <head> <title>在线客服系统</title> <meta charset="utf-8" /> <script> //测试浏览器是Chrome 27.0.1453.93 var xhr = new XMLHttpRequest(); //由query.php程序调用的JS函数，用来输出内容到前台页面 function comet(msg,rand){ var content = ''; //获取用户发送给前台的消息，并拼接好 content = '<span onclick="reply(this);" style="cursor:pointer;">' + msg.pos + ' </span>' + '对你说：<br/> ' + msg.content + '<br/>'; var msgzone = document.getElementById('msgzone'); //把拼接的消息赋值给消息显示区域 msgzone.innerHTML += content; } //点击某个用户名，然后回复的span会显示该用户名 function reply(reobj){ document.getElementById('rec').innerHTML = reobj.innerHTML } //前台客服回复时，调用的函数 function huifu(){ var rep = ''; //接收前台发送的用户名字 var rec = document.getElementById('rec').innerHTML; //前台发送的消息内容 var content = document.getElementsByTagName('textarea')[0].value; if(rec == '' || content == ''){ alert('请选择回复人并填写回复内容');//简单判断回复对象和内容不能为空 return; } //sendmsg.php是专门配套前台发送消息用的，就是把消息INSERT进数据库 xhr.open('POST','sendmsg.php',true); xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded'); xhr.onreadystatechange = function(){ if(this.readyState == 4 && this.status == 200){ if(this.responseText == 'ok'){ //当确定前台发送的消息INSERT进数据库后，把这条消息显示到消息区域内 rep += '你对 ' + rec + '说：<br/> ' + content + '<br/>'; var msgzone = document.getElementById('msgzone'); msgzone.innerHTML += rep; document.getElementsByTagName('textarea')[0].value = ''; } } } xhr.send('rec='+rec+'&content='+content); } </script> <style> #msgzone{ border:1px solid #ececec; width:500px; height:500px; overflow:scroll; } </style> </head> <body> <h1 id="在线客服系统-客服端">在线客服系统--客服端</h1> <!-- 消息显示区域 --> <div id="msgzone"></div> <!-- 用户名区域 --> 回复：<span id="rec"></span><br/> <!-- 回复内容区域 --> <textarea> </textarea><input type="button" value="回复" onclick="huifu();" /> <!-- 隐藏的iframe，其中加载了query.php来不断查询数据库是否有要推送的消息 --> <iframe src="query.php" width="0" height="0" iframeBorder="0"></iframe> </body></html> 后端查询query.php代码：
<?phpset_time_limit(0);ob_start();echo str_repeat(' ',4000),'<br/>';ob_flush();flush();$i = 0;require 'conn.php';//连接数据库文件//不断循环查询消息while(true){ //查询接收者为admin，并且是未读的消息 $sql = 'select * from msg where rec = "admin" and isread = 0 limit 1'; $result = $conn -> query($sql); //提取查询结果 $rs = $result -> fetch_assoc(); if(!empty($rs)){ //将这条消息更新为已读状态 $sql = 'update msg set isread = 1 where id = "'.$rs['id'].'" limit 1'; $conn -> query($sql); //转换为JSON格式准备发送给JS $rs = json_encode($rs); //通过paren调用父窗体的comet()函数，并将转换的JSON数据传送过去，comet()函数可以在kefu.html代码中找到 echo '<script>'; echo 'parent.window.comet(',$rs,',',mt_rand(1,1000000),')'; echo '</script>'; } ob_flush(); flush(); //防止查询次数过多，设置的每1秒查询一次 sleep(1);} 数据库连接conn.php代码：
<?php $conn = new mysqli('localhost','root','jackson613','test'); $conn -> query('set names utf8'); 建议还是采用AJAX的轮询方式，这种的后台查询脚本里没有主动结束脚本执行，可能存在一定问题。
我测试的是只能显示一个 后面的都显示不出来
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