You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: utils_unix.go
    path of file: ./repos/sealer/vendor/github.com/chzyer/readline
    
    the code of the file until where you have to start completion: // +build darwin dragonfly freebsd linux,!appengine netbsd openbsd solaris

package readline

import (
	"io"
	"os"
	"os/signal"
	"sync"
	"syscall"
)

type winsize struct {
	Row    uint16
	Col    uint16
	Xpixel uint16
	Ypixel 
    
func DefaultOnWidthChanged(f func()) {
	widthChangeCallback = f
	widthChange.Do(func() {
		ch := make(chan os.Signal, 1)
		signal.Notify(ch, syscall.SIGWINCH)

		go func() {
			for {
				_, ok := <-ch
				if !ok {
					break
				}
				widthChangeCallback()
			}
		}()
	})
}