会话关闭功能，似乎没什么用

Question

I've spend several days, I've searched a lot, here and via Bing I've fully explored OFFICIAL PHP page at: http://php.net/manual/en/ref.session.php

-- All comments, all functions.

But NOTHING HELPED. ABSOLUTE.

There's only one thing I need:

Invoke some function after SESSION is closed (for example, user has closed his browser).

Here is the point: AGAIN --- Invoke some function after user closed agent --- i.e session ID doesn't valid anymore

So, I've tried, to use old-style approach i.e override default session handler:

via,

session_set_save_handler("sess_open", "sess_close", "sess_read", "sess_write", "sess_destroy", "sess_gc");

that something looks like this:

function sess_close() {
    print "Session closed.
";
    return true;
}

function sess_read($sess_id) {
    print "Session read.
";
    print "Sess_ID: $sess_id
";
    return '';
}

function sess_write($sess_id, $data) {
    print "Session value written.
";
    print "Sess_ID: $sess_id
";
    print "Data: $data

";
    return true;
}

function sess_destroy($sess_id) {
    print "Session destroy called.
";
    return true;
}

function sess_gc($sess_maxlifetime) {
    print "Session garbage collection called.
";
    print "Sess_maxlifetime: $sess_maxlifetime
";
    return true;
}

But this also doesn't work when a user closes browser. Why this doesnt work?