About the for range traversal operation in channel in golang

note： channel If you want to use for range Traverse ,channel The closing operation must be carried out first .
Patients with a ：

func main(){
    
	wg.Add(2)
	write := make(chan int, 5)
	read := make(chan int, 5)
	go writechan(write)
	go readchan(write, read)
	//  Use for range The reason for traversal is that read channel  It's closed later 
	//  So you can use for range Traverse 
	for val := range read{
    
		fmt.Printf("main  by %d \n", val)
	}
	wg.Wait()
}

func writechan(ch chan int){
    
	for i:=0; i<100; i++{
    
		ch <- i
	}
	close(ch)
	wg.Done()
}

func readchan(write, read chan int){
    
	for val := range write{
    
		fmt.Printf(" The data read out is %d \n", val)
		read <- val
	}
	close(read)
	wg.Done()
}

Example 2 ：

package main

import "fmt"
//  Get data from existing channels 
//  Method 1 ： for  Dead cycle 
//  Method 2 ： for range
func main(){
    
	data := make(chan int, 1000)
	cal := make(chan int, 2000)
	wg.Add(1)
	go Putdata(data)
	for i:=0; i<4; i++{
    
		wg.Add(1)
		go Getdata(data, cal)
	}
	//  Wait for all the present process to end   close channel
	wg.Wait()
	close(cal)
	for val := range cal{
    
		fmt.Println(val)
	}
}

func Putdata(data chan int){
    
	defer wg.Done()
	for i:=1; i<=8000; i++{
    
		data <- i
	}
	close(data)
}

func Getdata(data, cal chan int){
    
	defer wg.Done()
	//  Note that although it is 4 Threads to get data ,  Per thread for range Dissimilarity 
	//  But you can still use for range Of 
	for num := range data{
    
		flag := true
		for i:=2; i<num; i++{
    
			if num % i == 0{
    
				flag = false
				break
			}
		}
		if flag{
    
			cal <- num
		}
	}
}