framework/web/Session.php
public function destroy()
    {
        if ($this->getIsActive()) {
            $sessionId = session_id();
            $this->close();
            $this->setId($sessionId);
            $this->open();
            session_unset();
            session_destroy();
            $this->setId($sessionId);
        }
    }
public function destroy()
    {
        if ($this->getIsActive()) {
            $sessionId = session_id();
            $this->close();
            $this->setId($sessionId);
            $this->open();
            session_unset();
            session_destroy();
            $this->setId($sessionId);
        }
    }
Frees all session variables and destroys all data registered to a session.

This method has no effect when session is not [[getIsActive()|active]].
Make sure to call [[open()]] before calling it.
@see open()
@see isActive