// Created on savesnippets.com · https://savesnippets.com/1AY7dvIiFf1j9Z
<?php
function atomicWrite(string $path, string $contents, int $mode = 0644): bool {
    $dir  = dirname($path);
    $tmp  = tempnam($dir, '.atomic-');
    if ($tmp === false) return false;
    try {
        if (file_put_contents($tmp, $contents, LOCK_EX) === false) return false;
        chmod($tmp, $mode);
        return rename($tmp, $path);  // atomic on the same filesystem
    } finally {
        if (file_exists($tmp)) @unlink($tmp);
    }
}

atomicWrite('/var/lib/myapp/state.json', json_encode(['ok' => true]));