Can multiple users accessing a PHP script create multiple instances of a Singleton class?

Multiple users accessing a PHP script can indeed create multiple instances of a Singleton class if the script is not properly implemented to handle concurrency. To ensure that only one instance of the Singleton class is created, you can use a locking mechanism such as a mutex or a file lock to prevent multiple instances from being created simultaneously. 

class Singleton {
    private static $instance;
    private static $lock;

    private function __construct() {}

    public static function getInstance() {
        if (!isset(self::$instance)) {
            self::$lock = fopen("singleton.lock", "w");
            flock(self::$lock, LOCK_EX);
            if (!isset(self::$instance)) {
                self::$instance = new Singleton();
            }
            flock(self::$lock, LOCK_UN);
            fclose(self::$lock);
        }
        return self::$instance;
    }
}

Keywords

PHP Singleton class multiple users instances concurrency

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