即

// Loading the First session.
session_name('first_session_name');
session_start();
// Now we have first session VARiables available in $_SESSION
$_FIRST_SESSION = $_SESSION;
// End current session.
session_wrITe_close();
// Just to make sure nothing remains in the session.
unset($_SESSION);
// Now set the second session name.
session_name('second_session_name');
// Check and see if the second session name has a session id.
if (isset($_COOKIE['second_session_name']))
    // There's already a session id for this name.
    session_id($_COOKIE['second_session_name']);
else
    // We need to generate a new session id as this is the first time.
    session_id(sha1(mt_rand()));
session_start();
$_SECOND_SESSION = $_SESSION;