copying from src to dst big file

threaded.go

func (dd *opts) run() error {
	var thread int64
	var names []string
	done := make(chan bool)
	size := getsize(*dd.src)

	for i := int64(0); i < size; i += *dd.buffersize {
		dstname := partfile + strconv.FormatInt(i, 10)
		names = append(names, dstname)

		go parts(*dd.buffersize, *dd.src, dstname, done)
		thread++

		if thread > 16 {
			<-done
			thread--
		}

		fmt.Printf("\rSpawning %d threads", thread)
	}
	fmt.Println()

	for thread > 0 {
		<-done
		thread--
	}

	file, err := os.OpenFile(*dd.dst, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0777)
	defer file.Close()
	handle(err)

	for _, name := range names {
		data, err := ioutil.ReadFile(name)
		handle(err)

		_, err = file.Write(data)
		handle(err)

		//os.Remove(name)
		fmt.Printf("\rCompiling .... %s", name)
	}
	fmt.Println()

	return nil
}

func parts(buffersize int64, src, dst string, done chan bool) {
	destination, err := create(dst)
	handle(err)
	destination.Close()

	buff := make([]byte, buffersize)

	read, err := unix.Open(src, unix.O_RDONLY, 0777)
	defer unix.Close(read)
	handle(err)

	write, err := unix.Open(dst, unix.O_WRONLY, 0777)
	defer unix.Close(write)
	handle(err)

	_, err = unix.Read(read, buff)
	handle(err)

	_, err = unix.Write(write, buff)
	handle(err)

	done <- true
}