Description:
------------
This issue affects custom session handlers (as defined with session_set_save_handler()), in which the write function attempts to access a *global object*.

When upgrading a custom session handler (calling a perl daemon), from php5.1 to php5.2, the session was never written owing to a "Call to a member function xxx() on a non-object" error.

This seemingly occurs because global objects get destructed *before* session_write_close() is called, during php's shutdown sequence.

I worked around the issue using register_shutdown_function("session_write_close"); near the top of the script.
register_shutdown_function() does take effect when a script is terminated using exit(); I would have to call "session_write_close();" after having finished writing to the session.
This error also still springs up sometimes when the memory limit is reached.

This behaviour-change was painful but could be an intentional change by the php team (?) I am reporting it because it may be an unintentional change, and I have seen that it has also affected other users including Drupal users
(e.g. this Zend Forums thread:
http://www.zend.com/forums/index.php?t=msg&th=3464
and Drupal: http://drupal.org/node/92802)

Cheers
Amir

Reproduce code:
---------------
<?php
//apologies: this is more than 20 lines.
//I have amended the php manual example to use a rudimentary object, just for illustration purposes.
class sess {
        var $savePath;
        var $id;
        function getSavePath() {
                return $this->savePath;
        }
        function setSavePath($savePath) {
                $this->savePath= $savePath;
        }
        function getFilePath() {
                return $this->getSavePath().'/sess_'.$this->getId();
        }
        function getId() {
                return $this->id;
        }
        function setId($id) {
                $this->id= $id;
        }
}

function open($savePath, $session_name)
{
  global $sess;
  $sess= new sess;
  $sess->setSavePath('/tmp');
  return(true);
}

function close()
{
  return(true);
}

function read($id)
{
  global $sess;
  $sess->setId($id);
  if(file_exists($sess->getFilePath())) {
        return (string) file_get_contents($sess->getFilePath());
  }
}

function write($id, $sess_data)
{
  global $sess;
  if ($fp = fopen($sess->getFilePath(), "w")) {
    $return = fwrite($fp, $sess_data);
    fclose($fp);
    return $return;
  } else {
    return(false);
  }

}

function destroy($id){
  global $sess;
  return(unlink($sess->getFilePath()));
}

function gc($maxlifetime)
{
  global $sess;
  foreach (glob($sess->getSavePath()."/sess_*") as $filename) {
    if (filemtime($filename) + $maxlifetime < time()) {
      unlink($filename);
    }
  }
  return true;
}
session_set_save_handler("open", "close", "read", "write", "destroy", "gc");
session_start();
print "session id : " . session_id() . "<br>";
if(!$_SESSION['hi']) {
        $_SESSION['hi']='ho';
} else {
        $_SESSION['ts']=time();
}
print "session data: <pre>"; print_r($_SESSION);
print "\nclass data: \n "; print_r($sess);


Expected result:
----------------
session written ok

Actual result:
--------------
session id : 8b2596bea65174ce950bb47140edfe2a
session data:

Array
(
    [hi] => ho
)

class data: 
 sess Object
(
    [savePath] => /tmp
    [id] => 8b2596bea65174ce950bb47140edfe2a
)


Fatal error:  Call to a member function getFilePath() on a non-object in /var/www/sesstest.php on line 52