Close a php connection - php

Question

i have a cron Job running following script every 5 min. However it seems that the script doesn't closes the connection once its run . How can I close the connection in this script?
function __construct($config)
{
$this->server = $config['server'];
$this->certificate = $config['certificate'];
$this->passphrase = $config['passphrase'];
// Create a connection to the database.
$this->pdo = new PDO(
'mysql:host=' . $config['db']['host'] . ';dbname=' . $config['db']['dbname'],
$config['db']['username'],
$config['db']['password'],
array());
// If there is an error executing database queries, we want PDO to
// throw an exception.
$this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
// We want the database to handle all strings as UTF-8.
$this->pdo->query('SET NAMES utf8');
}
// This is the main loop for this script. It polls the database for new
// messages, sends them to APNS, sleeps for a few seconds, and repeats this
// forever (or until a fatal error occurs and the script exits).
function start()
{
writeToLog('Connecting to ' . $this->server);
if (!$this->connectToAPNS())
exit;
while (true)
{
// Do at most 20 messages at a time. Note: we send each message in
// a separate packet to APNS. It would be more efficient if we
// combined several messages into one packet, but this script isn't
// smart enough to do that. ;-)
$stmt = $this->pdo->prepare('SELECT * FROM messages WHERE time_sent IS NULL LIMIT 20');
$stmt->execute();
$messages = $stmt->fetchAll(PDO::FETCH_OBJ);
foreach ($messages as $message)
{
if ($this->sendNotification($message->id, $message->token, $message->payload))
{
$stmt = $this->pdo->prepare('UPDATE messages SET time_sent = NOW() WHERE id = ?');
$stmt->execute(array($message->id));
}
else // failed to deliver
{
$this->reconnectToAPNS();
}
}
unset($messages);
sleep(5);
}
}

Answer 1

I may have misread, but apparently you are launching every 5 minutes a script that doesn't exit (infinite loop). So you're stacking the instances, until Earth (or more modestly, your server) eventually explodes.
To answer your question, PHP automatically frees all resources, including DB connexions, when the script execution has ended.
When a script runs for a very long time (like infinite), or there are very specific memory considerations, one can manually frees resources using unset($foo) or $foo = null.[1]
DB connexions can be closed and freed this way too, just with unset($this->pdo).
[1] see also What's better at freeing memory with PHP: unset() or $var = null