<?php
namespace Aws\DynamoDb;
use Aws\DynamoDb\Exception\DynamoDbException;
/**
* The locking connection adds locking logic to the read operation.
*/
class LockingSessionConnection extends StandardSessionConnection
{
public function __construct(DynamoDbClient $client, array $config = [])
{
parent::__construct($client, $config + [
'max_lock_wait_time' => 10,
'min_lock_retry_microtime' => 10000,
'max_lock_retry_microtime' => 50000,
]);
}
/**
* {@inheritdoc}
* Retries the request until the lock can be acquired
*/
public function read($id)
{
// Create the params for the UpdateItem operation so that a lock can be
// set and item returned (via ReturnValues) in a one, atomic operation.
$params = [
'TableName' => $this->config['table_name'],
'Key' => $this->formatKey($id),
'Expected' => ['lock' => ['Exists' => false]],
'AttributeUpdates' => ['lock' => ['Value' => ['N' => '1']]],
'ReturnValues' => 'ALL_NEW',
];
// Acquire the lock and fetch the item data.
$timeout = time() + $this->config['max_lock_wait_time'];
while (true) {
try {
$item = [];
$result = $this->client->updateItem($params);
if (isset($result['Attributes'])) {
foreach ($result['Attributes'] as $key => $value) {
$item[$key] = current($value);
}
}
return $item;
} catch (DynamoDbException $e) {
if ($e->getAwsErrorCode() === 'ConditionalCheckFailedException'
&& time() < $timeout
) {
usleep(pow(10, -6) * rand(
$this->config['min_lock_retry_microtime'],
$this->config['max_lock_retry_microtime']
));
} else {
break;
}
}
}
}
}
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