PHP implements Ajax long polling
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, but 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 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 there is 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
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(); } } ?>
Operating effect: In the picture, you can see that the request time without data reaches 40S. If data is obtained during the 40S request, the request will be closed. After closing, continue with the next request!

Reasons for PHPSession failure include configuration errors, cookie issues, and session expiration. 1. Configuration error: Check and set the correct session.save_path. 2.Cookie problem: Make sure the cookie is set correctly. 3.Session expires: Adjust session.gc_maxlifetime value to extend session time.

Methods to debug session problems in PHP include: 1. Check whether the session is started correctly; 2. Verify the delivery of the session ID; 3. Check the storage and reading of session data; 4. Check the server configuration. By outputting session ID and data, viewing session file content, etc., you can effectively diagnose and solve session-related problems.

Multiple calls to session_start() will result in warning messages and possible data overwrites. 1) PHP will issue a warning, prompting that the session has been started. 2) It may cause unexpected overwriting of session data. 3) Use session_status() to check the session status to avoid repeated calls.

Configuring the session lifecycle in PHP can be achieved by setting session.gc_maxlifetime and session.cookie_lifetime. 1) session.gc_maxlifetime controls the survival time of server-side session data, 2) session.cookie_lifetime controls the life cycle of client cookies. When set to 0, the cookie expires when the browser is closed.

The main advantages of using database storage sessions include persistence, scalability, and security. 1. Persistence: Even if the server restarts, the session data can remain unchanged. 2. Scalability: Applicable to distributed systems, ensuring that session data is synchronized between multiple servers. 3. Security: The database provides encrypted storage to protect sensitive information.

Implementing custom session processing in PHP can be done by implementing the SessionHandlerInterface interface. The specific steps include: 1) Creating a class that implements SessionHandlerInterface, such as CustomSessionHandler; 2) Rewriting methods in the interface (such as open, close, read, write, destroy, gc) to define the life cycle and storage method of session data; 3) Register a custom session processor in a PHP script and start the session. This allows data to be stored in media such as MySQL and Redis to improve performance, security and scalability.

SessionID is a mechanism used in web applications to track user session status. 1. It is a randomly generated string used to maintain user's identity information during multiple interactions between the user and the server. 2. The server generates and sends it to the client through cookies or URL parameters to help identify and associate these requests in multiple requests of the user. 3. Generation usually uses random algorithms to ensure uniqueness and unpredictability. 4. In actual development, in-memory databases such as Redis can be used to store session data to improve performance and security.

Managing sessions in stateless environments such as APIs can be achieved by using JWT or cookies. 1. JWT is suitable for statelessness and scalability, but it is large in size when it comes to big data. 2.Cookies are more traditional and easy to implement, but they need to be configured with caution to ensure security.


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