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) }