Memory/resource leaks in the wrapper connection

[morozov]

Q	A
BC Break	no
Version	2.12.1

If a wrapper connection is instantiated, establishes a driver-level connection and then is unreferenced, it doesn't get garbage-collected by PHP until GC kicks in (in the best case) and doesn't close the underlying connection.

Example 1
On each iteration, the previously instantiated connection should be destructed and close its driver connection but it isn't the case:

for ($i = 0; $i < 5; $i++) {
    $conn = DriverManager::getConnection([
        'driver' => 'pdo_pgsql',
        'host'   => 'localhost',
        'port'   => '5432',
        'user'   => 'postgres',
        'password' => 'Passw0rd',
        'dbname' => 'postgres',
    ]);

    echo $conn->fetchOne('SELECT SUM(numbackends) FROM pg_stat_database'), PHP_EOL;
}

// 1
// 2
// 3
// 4
// 5

Adding $conn->close() to the loop solves the problem however it doesn't do anything than removing the reference to the driver-level connection:

dbal/lib/Doctrine/DBAL/Connection.php

Lines 772 to 775 in de5464d

	public function close()
	{
	$this->_conn = null;
	}

This means that during iteration the object doesn't get destructed.

Example 2

There seems to be an internal circular reference between the wrapper and some of its components that doesn't let the connection to be destructed (see refcount=2):

$conn1 = DriverManager::getConnection([
    'driver' => 'pdo_pgsql',
]);
xdebug_debug_zval('conn1');
// conn1: (refcount=2, is_ref=0)=class Doctrine\DBAL\Connection { ... }

$conn2 = new stdClass();
xdebug_debug_zval('conn2');
// conn2: (refcount=1, is_ref=0)=class stdClass {  }

[morozov]

TADA!

dbal/lib/Doctrine/DBAL/Connection.php

Line 222 in de5464d

$this->_expr = new Query\Expression\ExpressionBuilder($this);

[morozov]

TADA!

dbal/lib/Doctrine/DBAL/Connection.php

Line 1877 in de5464d

$this->_schemaManager = $this->_driver->getSchemaManager($this);

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