How to tell if a session is active? [duplicate]

Question

Per request, there are a few different ways that you can tell whether or not a session has been started, such as:

$isSessionActive = (session_id() != ""); 

Or:

$isSessionActive = defined('SID'); 

However, these both fail if you start a session, then close it; session_id() will return the prior session's ID, while SID will be defined. Likewise, calling session_start() at this point will generate an E_NOTICE if you already have a session active. Is there a sane way to check if a session is currently active, without having to resort to output buffering, the shut-up operator (@session_start()), or something else equally as hacky?

EDIT: I wrote a patch to try to get this functionality included in PHP: http://bugs.php.net/bug.php?id=52982

EDIT 8/29/2011: New function added to PHP 5.4 to fix this: "Expose session status via new function, session_status"

// as of 8/29/2011 $isSessionActive = (session_status() == PHP_SESSION_ACTIVE); 

EDIT 12/5/11: session_status() on the PHP manual.

Answer 1

See edits to the original question; basically, PHP 5.4 and above now has a function called session_status() to solve this problem!

"Expose session status via new function, session_status" (SVN Revision 315745)

If you need this functionality in a pre-PHP 5.4 version, see hakre's answer.

Answer 2

I worked around this by adding a couple wrapper functions around the various session creation/closing/destroying functions. Basically:

function open_session() {      session_start();      $_SESSION['is_open'] = TRUE; }  function close_session() {    session_write_close();    $_SESSION['is_open'] = FALSE; }  function destroy_session() {    session_destroy();    $_SESSION['is_open'] = FALSE; }  function session_is_open() {    return($_SESSION['is_open']); } 

Hackish, but accomplished what I needed.