file lock example

file_lock.php

$file = fopen("counter.txt", "r+");

if (flock($file, LOCK_EX)) {
    $data = fread($file, 64);
    $data = trim($data);
    if (empty($data)) {
        $data = 0;
    }
    $data++;
    ftruncate($file, 0);
    fwrite($file, $data);
    fflush($file);
    flock($file, LOCK_UN);
} else {
    throw new \RuntimeException("File is locked");
}

fclose($file);%