How does browser behavior, such as multiple requests from Firefox, impact the execution of PHP scripts?

When multiple requests are made from a browser like Firefox, it can lead to PHP scripts being executed concurrently, causing potential issues with shared resources or data integrity. To prevent this, you can implement a locking mechanism using PHP's flock() function to ensure only one instance of the script runs at a time.

$lockFile = "script.lock";
$lockHandle = fopen($lockFile, "w");

if (flock($lockHandle, LOCK_EX)) {
    // PHP script code here

    flock($lockHandle, LOCK_UN);
} else {
    echo "Could not obtain lock, script is already running.";
}

fclose($lockHandle);