What are the potential risks of running multiple instances of the same PHP script for different users accessing the same HTML/PHP file?

Running multiple instances of the same PHP script for different users accessing the same HTML/PHP file can lead to issues such as race conditions, data corruption, and performance degradation. To mitigate these risks, you can use locking mechanisms like file locking or database transactions to ensure that only one instance of the script can access and modify shared resources at a time.

// PHP code snippet implementing file locking to prevent concurrent access to shared resources
$lockFile = fopen("lock.txt", "w");

if (flock($lockFile, LOCK_EX)) {
    // Critical section: code that accesses and modifies shared resources
    flock($lockFile, LOCK_UN); // Release the lock
} else {
    echo "Could not acquire lock, please try again later.";
}

fclose($lockFile);