An example analysis of how to implement Ajax long polling in PHP

The traditional Ajax polling method, the customer service side at the user-defined time interval to the server to query the latest data. This method of pulling data takes a short time interval to ensure the accuracy of the data, but too short a time interval the customer sends multiple requests to the server in a short period of time.

Reverse Ajax, which is called long polling or comet. The server and customer service need to maintain a long-time request, which allows the server to return messages to the client when there is data.

This uses Ajax to request the data.php page to get the value of ' success ', requesting a time of 80 seconds. In these 80 seconds, if no return from the server ' success ' is kept in a connected state until there is a data return or ' success ' value of 0 to close the connection. The next request continues after the connection is closed.

Index.html

    <! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd "> 
Here is the infinite loop, the end condition of the loop is to get the return result to return the JSON data.

and accept the $_post[' time ' parameter to limit the cycle timeout and avoid excessive waste of resources. (browser close will not send a message to the server, use may have been looped down)

data.php

    <?php          if (Empty ($_post[' time ')) exit ();                Set_time_limit (0);//Infinite Request Timeout time                $i =0;                while (true) {                    //sleep (1);                    Usleep (500000);//0.5 seconds                    $i + +;                    If you get the data, return the data to the customer service immediately, and end the request                    $rand =rand (1,999);                    if ($rand <=15) {                        $arr =array (' success ' = "1", ' name ' = ' Xiaoyu ', ' text ' + $rand);                        echo Json_encode ($arr);                        Exit ();                    }                    Server ($_post[' time ']*0.5) seconds to tell the customer service end no data                    if ($i ==$_post[' time ') {                        $arr =array (' success ' = ' 0 ', ' name ' = ' Xiaoyu ', ' text ' = $rand);                        echo Json_encode ($arr);                        Exit ();                    }                }         ? >
Run effect: In the graph can see the request time of no data reached 40S, in the request of 40S to obtain the data request closes. After closing, proceed to the next request!