Bug #75190 [Nab]: Impossible to close PDO connection when extending PdoStatement using $this

Edit report at https://bugs.php.net/bug.php?id=75190&edit=1 ID: 75190 Updated by: nikic@php.net Reported by: ian at oshaughnessy dot cc Summary: Impossible to close PDO connection when extending PdoStatement using $this Status: Not a bug Type: Bug Package: PDO related Operating System: Debian 9 PHP Version: 7.0.23 Block user comment: N Private report: N New Comment: I remember fixing this issue... and indeed, the pdo_dbh get_gc handler returns def_stmt_ctor_args: https://github.com/php/php-src/blob/master/ext/pdo/pdo_dbh.c#L1382 As such this should not be an actual leak (like it was on PHP 5), but the destruction is delayed until the next cycle GC. Explicitly calling gc_collect_cycles() may resolve the problem. Previous Comments: ------------------------------------------------------------------------ [2017-10-05 20:42:00] adambaratz@php.net You could pass an empty array for the ctor args. It's not strictly required that you pass a reference to the PDO object. I'm not sure this is a PDO issue, so much as a side effect of PHP's reference counting. For the sake of clarity, I'd recommend avoiding doing what you're doing here. Basically, because it's easy to create situations like this one. If you want the statement to have a reference to the connection, I'd recommend composition over inheritance. That is, creating your own PDO and PDOStatement classes that wrap the built-ins. There is the separate point that it's awkward that you can't close a connection without destructing the PDO object. If that's an issue you want to address, please file a feature request ticket. Or better still, put together an RFC to hash out the details with the internals community. ------------------------------------------------------------------------ [2017-09-11 15:58:13] ian at oshaughnessy dot cc Description: ------------ The only way to close a PDO connection is to set the resource variable to null (thereby destroying the PDO object); however, when extending the PdoStatement class, it's required that $this is passed as an option to the PDO object for Pdo::ATTR_STATEMENT_CLASS. In doing this, a reference to the PDO object is created, making it impossible to destroy the PDO object since a lingering reference continues to exist after $pdo is set to null. The only way to fix this issue is to use Pdo::setAttribute() after the PDO parent constructor has been run. Test script: --------------- <?php echo "Test 1 (PdoTestBroken)\n"; echo "new PdoTestBroken\n"; $pdo1 = new PdoTestBroken($dsn, $username, $password, []); echo "Destroy \$pdo\n"; $pdo1 = null; echo "----------------------------\n\n"; echo "Test 2 (PdoTestWorks)\n"; echo "new PdoTestWorks\n"; $pdo2 = new PdoTestWorks($dsn, $username, $password, []); echo "Destroy \$pdo\n"; $pdo2 = null; echo "----------------------------\n\n"; class PdoTestBroken extends Pdo { public function __construct($dsn, $username, $passwd, $options) { echo "PdoTest1::__construct()\n"; $options[self::ATTR_STATEMENT_CLASS] = [ 'PdoStatementTest', [ $this, ] ]; parent::__construct($dsn, $username, $passwd, $options); } public function __destruct() { echo "PdoTest1::__destruct()\n"; } } class PdoTestWorks extends Pdo { public function __construct($dsn, $username, $passwd, $options) { echo "PdoTest2::__construct()\n"; $self = parent::__construct($dsn, $username, $passwd, $options); $this->setAttribute(PDO::ATTR_STATEMENT_CLASS, [ 'PdoStatementTest', [ $self, ] ]); } public function __destruct() { echo "PdoTest2::__destruct()\n"; } } class PdoStatementTest extends PdoStatement { } Expected result: ---------------- The connection to close. Actual result: -------------- The connection does not close due to hidden reference variable. Script Results: Test 1 (PdoTestBroken) new PdoTestBroken PdoTest1::__construct() Destroy $pdo ---------------------------- Test 2 (PdoTestWorks) new PdoTestWorks PdoTest2::__construct() Destroy $pdo PdoTest2::__destruct() ---------------------------- PdoTest1::__destruct() ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=75190&edit=1