func (w *Writer) SetOutput(out io.Writer) {
	w.mutex.Lock()
	w.printer = newPrinter(out)
	w.mutex.Unlock()
}
func (w *Writer) SetOutput(out io.Writer) {
	w.mutex.Lock()
	w.printer = newPrinter(out)
	w.mutex.Unlock()
}
// SetOutput sets the output destination for log messages.