How to understand the php session operating mechanism

The php session operating mechanism is that the client passes the session id to the server, and the server then finds the corresponding file based on the session id and deserializes it to get the session value, and then serializes it when saving. Transform and then write

The knowledge point I will share today is the session running mechanism in PHP. It is not unfamiliar to developers who are familiar with PHP, but it is not very understandable for those who are just getting started. Next, in the article, I will introduce the session running mechanism in PHP in detail, which has a certain reference effect. I hope it will be helpful to everyone

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PHP session operating mechanism meaning:

PHP session operating mechanism is that the client will use the session id Passed to the server, the server finds the corresponding file according to the session id. When reading, it deserializes the file content to get the session value. When saving, it is first serialized and then written to

PHP session Mechanism classification

There are two mechanisms for session in PHP, namely the default mechanism and the user-defined session processing mechanism.

Default mechanism

php.ini configuration:

session.save_handler = files

uses disk files to implement PHP sessions. It has the following It consists of several parts:

session_start()

session_start() is the beginning of the session mechanism, which has a certain probability of starting garbage collection. This probability is determined based on the configuration of php.ini, because in some systems session.gc_probability = 0, that is, the probability is 0, then there is no garbage collection

Assign value to $_session

Adding a new value will only be maintained in memory. When the script execution ends, write the value of $_session to the folder specified by session_id, and then close the related resources. At this stage, it is possible to perform operations to change the session_id, such as destroying an old session_id and generating a new session_id. This is generally used in custom session operations

Example:

if (isset($_COOKIE[session_name()])) {
          　　setcookie(session_name(),'',time() -42000,'/');//旧session cookie过期
        　　}
        　　session_regenerate_id();//这一步会生成新的session_id
       　　//session_id()返回的是新的值

Write session operations

In script At the end, the session write operation will be performed, and the value in $_session will be written to the file named by session_id. It may already exist, and a new file may need to be created.

Destroy session

The cookies sent by the session are generally instant cookies, which are stored in memory and will expire when the browser is closed. , but if you just want to log out instead of closing the browser, then you need to destroy the session in the code. There are many methods.

Example:

1. setcookie(session_name(),session_id(),time() -8000000,..);//退出登录前执行
2. usset($_SESSION);//这会删除所有的$_SESSION数据，刷新后，有COOKIE传过来，但是没有数据。
3. session_destroy();//这个作用更彻底，删除$_SESSION 删除session文件，和session_id

##User-defined session processing mechanism

php.ini configuration

session.save_handler = user

The user-defined processing mechanism can be divided into the following parts

session_start()

Execute open( $save_path,$session_name) statement opens the session operation handle

Execute read($id) to read data from it

Note

:$save_path returns true directly in this case

End of script execution

Execute write($id,$sess_data) statement

Destroy session

It should be noted that if the user needs to destroy the session, he must first execute destroy and then execute step 2

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