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<?php

/*

* This file is part of the Predis package.

*

* (c) 2009-2020 Daniele Alessandri

* (c) 2021-2026 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, static 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;