Cronjob Überlappung verhindern – flock()

$fp = fopen(sys_get_temp_dir().DIRECTORY_SEPARATOR."lock.txt", "w+");

if (flock($fp, LOCK_EX | LOCK_NB)) { // do an exclusive lock
    // YOUR CODE GOES HERE

    flock($fp, LOCK_UN); // release the lock
} else {
    echo "Couldn't get the lock!";
}

fclose($fp);

Quelle: https://stackoverflow.com/questions/5428631/php-preventing-collision-in-cron-file-lock-safe