[Uid] Uuid v7 collisions

[vudaltsov]

Symfony version(s) affected

6.3.0

Description

From time to time I get UUID v7 collisions.

How to reproduce

<?php

// generate_uuids_v7.php

use Symfony\Component\Uid\Uuid;

require_once __DIR__.'/vendor/autoload.php';

for ($j = 0; $j < 100; ++$j) {
    $uuids = '';

    for ($i = 0; $i < 1_000_000; ++$i) {
        $uuids .= Uuid::v7()->toRfc4122()."\n";
    }

    file_put_contents('uuids_v7.txt', $uuids, $j === 0 ? 0 : FILE_APPEND);
}

php generate_uuids_v7.php && sort uuids_v7.txt | uniq -cd

Expected behavior

Empty

Actual output (native PHP v8.2.10, macOS Ventura v13.3.1)

   2 018b73a2-4779-7f97-b675-5ce7ed6e1812
   2 018b73a2-9c97-7484-8a67-420747e8164a
   2 018b73a3-0f1b-7ac9-89dc-2b7f1e3625aa
   2 018b73a3-4da3-7bf5-bf20-aeaa68c6b109
   2 018b73a3-d9de-7850-9463-f4ee48ebfb02
   2 018b73a4-d6f4-7c55-a660-22114e5bf692
   2 018b73a5-f11b-7c99-884b-d741e7686016

Possible Solution

No response

Additional Context

No response

[vudaltsov]

Originally posted in ramsey/uuid#518. Reproduced same issue in Symfony.

[OskarStark]

@fancyweb do you have an idea?

[vudaltsov]

For the record. Generating UUID v7 according to the standard (basically having smth like uuidFromTimeAndRandom(time_in_milliseconds(), random_int())) does not give any collisions. I checked that in ramsey/uuid v4.5.1.

So the problem is in the seed mechanism introduced by @nicolas-grekas here, which was also used by @ramsey in ramsey/uuid@0ba1ffb.

[vudaltsov]

Checked, it fixed the problem, thanks!