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<?php
/*
* This file is part of the Predis package.
*
* (c) 2009-2020 Daniele Alessandri
* (c) 2021-2025 Till Krüss
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
require __DIR__ . '/shared.php';
// This is an implementation of an atomic client-side ZPOP using the support for
// check-and-set (CAS) operations with MULTI/EXEC transactions, as described in
// "WATCH explained" from http://redis.io/topics/transactions
//
// First, populate your database with a tiny sample data set:
//
// ./redis-cli
// SELECT 15
// ZADD zset 1 a 2 b 3 c
//
// Then execute this script four times and see its output.
//
function zpop($client, $key)
{
$element = null;
$options = [
'cas' => true, // Initialize with support for CAS operations
'watch' => $key, // Key that needs to be WATCHed to detect changes
'retry' => 3, // Number of retries on aborted transactions, after
// which the client bails out with an exception.
];
$client->transaction($options, function ($tx) use ($key, &$element) {
@[$element] = $tx->zrange($key, 0, 0);
if (isset($element)) {
$tx->multi(); // With CAS, MULTI *must* be explicitly invoked.
$tx->zrem($key, $element);
}
});
return $element;
}
$client = new Predis\Client($single_server);
$zpopped = zpop($client, 'zset');
echo isset($zpopped) ? "ZPOPed $zpopped" : 'Nothing to ZPOP!', PHP_EOL;
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