This allows to lock a device by several independent processes and avoids indefinite locks of crashed processes (nonexistant pids are cleaned before attempting a mount).

• 这样做将允许 几个独立的进程锁定设备，避免对死掉的进程 进行无休止的锁定。（在尝试挂载前，不存在的进程号将被清除。）