How to set expiration time of session in php

php session method for setting expiration time: first use memcache or Redis to save the session and set the expiration time; then create a session class, and when the session is written, the expiration time is also written; finally when reading , just judge whether it has expired based on the expiration time.

php session method to set expiration time:

1. PHP session validity period

The default session validity period of PHP is 1440 seconds (24 minutes). If the client does not refresh for more than 24 minutes, the current session will be recycled and invalid.

When the user closes the browser, the session ends and the session will also become invalid.

You can modify session.gc_maxlifetime in php.ini to set the session life cycle, but there is no guarantee that the session information will be deleted immediately after this time is exceeded. Because GC is started based on probability, it may not be started for a long time. Then a large number of sessions are still valid after exceeding session.gc_maxlifetime.

2. .session.gc_maxlifetime, session.gc_probability, session.gc_divisor description

session.gc_maxlifetime = 30 means that when the session file has not been accessed after 30 seconds, It is regarded as an expired session and is waiting for GC recycling.

The probability of GC process call is calculated through session.gc_probability/session.gc_divisor, and session.gc_divisor defaults to 1000.

If session.gc_probability = 1000, then the GC process is in It will be called every time session_start() is executed to perform recycling.

Increasing the probability of session.gc_probability/session.gc_divisor will help, but it will have a serious impact on performance.

3. Strictly control session expiration method

1. Use memcache/Redis to save the session and set the expiration time, because the recycling mechanism of memcache/redis is not based on probability. , which can ensure that the session becomes invalid after expiration.

2. Only use PHP to implement it, create a session class, and write the expiration time when the session is written. When reading, determine whether it has expired based on the expiration time.

<?php
/**
 * Session控制类
 */
class Session{
  /**
   * 设置session
   * @param String $name  session name
   * @param Mixed $data  session data
   * @param Int  $expire 超时时间(秒)
   */
  public static function set($name, $data, $expire=600){
    $session_data = array();
    $session_data[&#39;data&#39;] = $data;
    $session_data[&#39;expire&#39;] = time()+$expire;
    $_SESSION[$name] = $session_data;
  }
  /**
   * 读取session
   * @param String $name session name
   * @return Mixed
   */
  public static function get($name){
    if(isset($_SESSION[$name])){
      if($_SESSION[$name][&#39;expire&#39;]>time()){
        return $_SESSION[$name][&#39;data&#39;];
      }else{
        self::clear($name);
      }
    }
    return false;
  }
  /**
   * 清除session
   * @param String $name session name
   */
  private static function clear($name){
    unset($_SESSION[$name]);
  }
}
?>

demo:

<?php
session_start();
$data = &#39;123456&#39;;
session::set(&#39;test&#39;, $data, 10);
echo session::get(&#39;test&#39;); // 未过期，输出
sleep(10);
echo session::get(&#39;test&#39;); // 已过期
?>

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