When using session_write_close() in a shutdown function at the end of my script - PHP just dies. There is no error logged, response headers (firebug), or data (even whitespace!) returned. I have full PHP error reporting on with STRICT enabled and PHP 5.2.1.

My guess is that since session_write_close() is being called after shutdown - some fatal error is being encountered that crashes PHP before it has a chance to send the output or log anything.

This only happens on the logout page where I first:

...
    //If there is no session to delete (not started)
    if ( ! session_id())
    {
        return;
    }

    // Get the session name
    $name = session_name();

    // Delete the session cookie (if exists)
    if ( ! empty($_COOKIE[$name]))
    {
        //Get the current cookie config
        $params = session_get_cookie_params();

        // Delete the cookie from globals
        unset($_COOKIE[$name], $_SESSION);

        //Delete the cookie on the user_agent
        setcookie($name, '', time()-43200, $params['path'], $params['domain'], $params['secure']);
    }

    // Destroy the session
    session_destroy();
...

then 2) do some more stuff 3) issue a redirect and 4) finally, after the whole page is done the register_shutdown_function(); I placed earlier runs and calls session_write_close() which saves the session to the database. The end.

Since this blank response only occurs on logout I'm guessing that I'm not restarting the session properly which is causing session_write_close() to die fatally at the end of the script.