(PHP 5 >= 5.4.0, PHP 7, PHP 8)
SessionHandlerInterface::open — Inicializar una sesión
Reinicializa una sesión existente, o crea una nueva. Llamado cuando una sesión se inicia o cuando se invoca a session_start().
pathLa ruta donde almacenar/recuperar la sesión.
nameEl nombre de la sesión.
El valor devuelto (normalmente true en caso de éxito, false en caso de error). Observe que este valor es devuelto internamente a PHP para su procesamiento.
The suggestion that you should free the lock as soon as possible is WRONG (and for some reason, I can't downvote it right now).
Releasing the lock before the write() call is as effective as not using locks at all. The whole point is that a concurrent read() HAS to be blocked until the session is closed, otherwise you'll have race conditions.
If you care about the performance aspect, you should take care to call session_write_close() as soon as possible instead.Note that once $sessionName has been used to provide a value for $sessionId from the cookie data it is totally redundant as all further reading and writing of the session data is controlled by $sessionId.
If, for any reason, it becomes necessary to identify the value for $sessionName which is associated with the current $sessionId then you should use the value that was passed on the open() method. Attempting to use a value from an alternative source could have unexpected side effects.