PHP solves session file blocking

How does PHP solve session file blocking? This article mainly introduces the blocking caused by PHP session file exclusive lock, and shares the solution to the blocking problem that is easily caused when PHP uses the default file session processor. I hope to be helpful.

PHP’s default session handler is session.save_handler = files (i.e. files). If the same client sends multiple requests concurrently (such as ajax sending multiple requests at the same time on the page) and the script execution time is long, the session file will be blocked and performance will be affected. Because for each request, PHP executes session_start(), it will obtain an exclusive lock on the file, and the exclusive lock will be released only after the request is processed. In this way, multiple requests at the same time will cause blocking. The solution is as follows:

(1) After modifying the session variable, immediately use session_write_close() to save the session data and release the file lock.

session_start();
 
$_SESSION['test'] = 'test';
session_write_close();
 
//do something

(2) Use the session_set_save_handler() function to implement custom session processing.

function open($savePath, $sessionName)
{
  echo 'open is called';
  return true;
}
 
function close()
{
  echo 'close is called';
  return true;
}
 
function read($sessionId)
{
  echo 'read is called';
  return '';
}
 
function write($sessionId, $data)
{
  echo 'write is called';
  return true;
}
 
function destroy($sessionId)
{
  echo 'destroy is called';
  return true;
}
 
function gc($lifetime)
{
  echo 'gc is called';
  return true;
}
 
session_set_save_handler("open", "close", "read", "write", "destroy", "gc");
register_shutdown_function ( 'session_write_close' );
 
session_start();
 
$_SESSION['foo'] = "bar";

Of course, after php 5.4.0, you can use it by implementing the SessionHandlerInterface interface or inheriting the SessionHandler class.

class MySessionHandler extends SessionHandler {
 
  public function __construct()
  {
  }
 
  public function open($save_path, $session_id)
  {
  }
 
  public function close()
  {
 
  }
 
  public function create_sid()
  {
  }
 
  public function read($id)
  {
  }
 
  public function write($id, $data)
  {
  }
 
  public function destroy($id)
  {
  }
}
 
$handler = new MySessionHandler();
 
//第2个参数将函数 session_write_close() 注册为 register_shutdown_function() 函数。
session_set_save_handler($handler, true);

You can implement and encapsulate the above code and use mysql or other in-memory database to manage session data. It can also solve the problem of session data sharing when using cluster
.

Related recommendations:

PHP uses redis to implement session instance sharing

php SessionIntroduction

php session validity period

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