throw: all goroutines are asleep - deadlock

Question

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

Answer 1

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)
}