throw: all goroutines are asleep - deadlock

Given the following simple Go program

package main

import (
	"fmt"
)

func total(ch chan int) {
	res := 0
	for iter := range ch {
		res += iter
	}
	ch <- res
}

func main() {
	ch := make(chan int)
	go total(ch)
	ch <- 1
	ch <- 2
	ch <- 3
	fmt.Println("Total is ", <-ch)
}

I am wondering if someone can enlighten me as to why I get

throw: all goroutines are asleep - deadlock!

thank you

As you never close the ch channel, the range loop will never finish.

You can't send back the result on the same channel. A solution is to use a different one.

Your program could be adapted like this :

package main

import (
    "fmt"
)

func total(in chan int, out chan int) {
    res := 0
    for iter := range in {
        res += iter
    }
    out <- res // sends back the result
}

func main() {
    ch := make(chan int)
    rch  := make(chan int)
    go total(ch, rch)
    ch <- 1
    ch <- 2
    ch <- 3
    close (ch) // this will end the loop in the total function
    result := <- rch // waits for total to give the result
    fmt.Println("Total is ", result)
}

This is also right.

package main

import "fmt"

func main() {
	c := make(chan int)
	go do(c)
	c <- 1
	c <- 2
	// close(c)
	fmt.Println("Total is ", <-c)
}

func do(c chan int) {
	res := 0
	// for v := range c {
	// 	res = res + v
	// }
	for i := 0; i < 2; i++ {
		res += <-c
	}
	c <- res
	fmt.Println("something")
}