BUG: locks not working as expected

Description

The following code:

<?php
$arquivo_lock = fopen("test.txt","a");

if (flock($arquivo_lock,LOCK_EX|LOCK_NB)) { 
    echo "Yes";
} else {
    echo "No";
}

sleep(10);

fclose($arquivo_lock);
?>

Save the simple code above to the file test.php, for example. Now, in less than 10 seconds apart, open 2 (or more) tabs on your browser calling the file test.php and you will see every tab will show you Yes after some seconds. It should show Yes only on the first tab, all the other should return immediatly with No because I am using LOCK_NB flag.

This bug is pretty simple to reproduce and other people also confirmed it on Stackoverflow when I reported there.

PHP Version

8.x

Operating System

Confirmed at least on centos 9 stream and windows 11

Start by running the two-tab test.php reproduction with PHP 8.x on the reported CentOS 9 Stream and Windows 11 environments, focusing on flock with LOCK_EX|LOCK_NB. Trace the flock entry point and platform-specific locking behavior; done means the first request reports Yes while overlapping requests return No immediately, with coverage for the confirmed environments.