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[2004-10-22 06:19 UTC] 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) PatchesPull RequestsHistoryAllCommentsChangesGit/SVN commits
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i just want to add a last comment to make clear that this bug is important. this is (i think) a much used type of program : <?php function do_something_in_mysql () { $link3 = mysql_connect('localhost','root','',false); // do some common queries here mysql_close($link3); echo "link3:"; var_dump($link3); } $link1 = mysql_connect('localhost','root','',false); echo "link1:"; var_dump($link1); do_something_in_mysql(); // here $link1 is UNUSABLE !! mysql_close($link1); echo "link1:"; var_dump($link1); ?> fails with : link1:resource(4) of type (mysql link) link3:resource(4) of type (mysql link) Warning: mysql_close(): 4 is not a valid MySQL-Link resource in ... on line 14 link1:resource(4) of type (Unknown) i think that closing a connection in the same environnement that it was open (like in the function here) is good programming so it shouldn't fail like that ! And the problem is *not* that the mysql_close closed all connections as shown by this example : <?php function do_something_in_mysql () { $link3 = mysql_connect('localhost','root','',false); echo "link3:"; var_dump($link3); // do some common queries here mysql_close($link3); } $link1 = mysql_connect('localhost','root','',false); $link2 = mysql_connect('localhost','root','',false); echo "link1:"; var_dump($link1); echo "link2:"; var_dump($link2); do_something_in_mysql(); // here $link1 is still USABLE mysql_close($link1); echo "link1:"; var_dump($link1); echo "link2:"; var_dump($link2); ?> here there is no failure : link1:resource(4) of type (mysql link) link2:resource(4) of type (mysql link) link3:resource(4) of type (mysql link) link1:resource(4) of type (Unknown) link2:resource(4) of type (Unknown) there would be one if we had closed $link2 after $link1 for example.