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In earlier versions of PHP, session_register_shutdown() was an important function to ensure that session data can be saved correctly at the end of the script. Its main function is to automatically call session_write_close() at the end of the script life cycle to write data from $_SESSION back to the server-side session storage.
However, is this low-level session operation necessary when using modern frameworks such as Symfony? This article will discuss this issue in conjunction with Symfony's architecture and the development of the PHP language and propose a more elegant alternative.
In traditional PHP applications, we often encounter the following usages:
session_start();
session_register_shutdown();
// set up session data
$_SESSION['user'] = 'Alice';
The purpose of this is to automatically save the session state at the end of the script execution, preventing data from being written in some cases (such as the script exits abnormally or forgets to call session_write_close() ). However, this approach also exposes some design problems, such as excessive coupling with application layer code and excessive dependence on global state.
Symfony adopts a more modern and abstract session management mechanism. By default, it uses SessionInterface to provide access to the session and automatically manages the session's lifecycle through event listeners and service containers.
The usage of session in a typical Symfony controller is as follows:
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Session\SessionInterface;
public function example(Request $request, SessionInterface $session)
{
$session->set('user', 'Alice');
return $this->render('example.html.twig');
}
Symfony will automatically call session_write_close() after the request is processed, without the need for manual intervention by the developer. This means that using session_register_shutdown() in Symfony is not only unnecessary, but also breaks the framework itself's management of the session lifecycle.
In Symfony, the framework can be fully trusted to automatically handle the initialization and closing of sessions. More recommended practices include:
Dependency Injection SessionInterface : Using session through dependency injection can ensure its correct initialization and cleaning in the life cycle.
Manage configuration and storage with Session service : By configuring Symfony's session handler, you can store sessions in a database, Redis, or custom storage to improve performance and security.
Extend with event listeners : If you really need to execute some logic before session writes, you can register an event listener to the kernel.terminate or kernel.response events.
For example, a custom session handler can be configured in framework.yaml by:
