#30525 [Fbk->NoF]: mysql_close() fails in some situations with shared links

ID: 30525 Updated by: php-bugs@lists.php.net Reported By: l dot cameron2 at ugrad dot unimelb dot edu dot au -Status: Feedback +Status: No Feedback Bug Type: MySQL related Operating System: Fedora Core 2 PHP Version: 5.0.2 New Comment: No feedback was provided for this bug for over a week, so it is being suspended automatically. If you are able to provide the information that was originally requested, please do so and change the status of the bug back to "Open". Previous Comments: ------------------------------------------------------------------------ [2005-03-07 22:31:13] sniper@php.net Please try using this CVS snapshot: http://snaps.php.net/php5-latest.tar.gz For Windows: http://snaps.php.net/win32/php5-win32-latest.zip ..and update the version field if this still happens, otherwise close this report. ------------------------------------------------------------------------ [2004-10-22 06:19:48] l dot cameron2 at ugrad dot unimelb dot edu dot au Description: ------------ Preface: I *do* understand that by default MySQL connections are shared in PHP. I also note that in older versions a single mysql_close() would close all of the links; see #9107: there now there appears to be reference counting before finally closing the TCP connection -- which is IMHO better than the older behaviour, but the implementation has its own bugs: PHP appears to keeps an internal count of the number of times a link has been duplicated. When the link count is <= 0, the underlying TCP connection is actually closed. * close() reduces the link count by 1 * setting the connection to null *also* reduces the link count by 1 -- even if that link has already been close()d Currently the only workarounds for this are to: [1] Set new_link to true every time you mysql_connect() -- potentially creating a lot of TCP connections and slowing the program down [2] close() the link, but never set it to null and hope that PHP won't clean it up until the end of the program: This *will* fail sometimes though; see the example at http://www.levi.id.au/mysql4.php.txt [3] Never mysql_close() links, only set them to null and hope that PHP will in fact clean up the TCP connection before MySQL runs out of available connections (admittedly only a problem when you have a lot of simultaneous connections to your database) -- this does work now, but we're not supposed to assume anything about when PHP does its object destruction. The third is really the only viable solution; but is dependent on the internal implementation of the MySQL extension. At best, the current situation is that if you ever have shared links, you should never call mysql_close if you ever expect to use that database again in your program. Reproduce code: --------------- Simple example: #!/usr/local/bin/php -q <? $conn1 = mysql_connect('localhost:3306', 'levi', 'DaCr0n!'); $conn2 = mysql_connect('localhost:3306', 'levi', 'DaCr0n!'); mysql_select_db('surveytest', $conn1); mysql_select_db('surveytest', $conn2); mysql_close($conn1); $conn1 = null; mysql_close($conn2); $conn2 = null; ?> See also the example at http://www.levi.id.au/mysql4.php.txt Expected result: ---------------- Blank output. Actual result: -------------- PHP Warning: mysql_close(): 1 is not a valid MySQL-Link resource in /home/levi/public_html/mysql2.php on line 10 <br /> <b>Warning</b>: mysql_close(): 1 is not a valid MySQL-Link resource in <b>/home/levi/public_html/mysql2.php</b> on line <b>10</b><br /> (If I remove the mysql_close($conn1); it works) (If I remove the $conn1 = null; it also works) ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=30525&edit=1