How can the stateless nature of HTTP pose challenges when trying to limit access to a PHP page to one user at a time?

The stateless nature of HTTP means that each request is independent, making it challenging to limit access to a PHP page to one user at a time. One way to solve this is by using session variables to track the number of users currently accessing the page. When a user accesses the page, increment a counter in the session variable. If the counter is already at 1, deny access to additional users. 

session_start();

if(!isset($_SESSION['user_count'])) {
    $_SESSION['user_count'] = 1;
} else {
    $_SESSION['user_count']++;
}

if($_SESSION['user_count'] > 1) {
    die("Access denied. Page is currently being accessed by another user.");
}

// Rest of your PHP code for the page goes here

// Decrement the user count when the user leaves the page
$_SESSION['user_count']--;

Keywords

HTTP stateless session management concurrency locking

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