This code snippet describes how to read a "select statement" based fan-in channel in Go, as a range, without deadlocks or strange race conditions. The key to get this right is to use "ok-variables" from the input channels to see if they are closed, and if so, set the channels to nil. Then, if in the for loop you continue until both inputs are ni…

read_fanin_as_range.go

package main

import "fmt"
import "time"
//import "runtime"

func numberGenerator() <-chan int {
    c := make(chan int)
    go func() {
        for i := 1; i <= 10; i++ {
            c <- i
            time.Sleep(1000)
        }
        close(c)
    }()
    return c
}

func fanIn(input1, input2 <-chan int) <-chan int {
    c := make(chan int)
    go func() {
        for input1 != nil || input2 != nil {
            select {
            case v, ok1 := <-input1:
                if !ok1 {
                    input1 = nil
                    fmt.Println("Set input1 to nil")
                    continue
                }
                c <- v
            case v, ok2 := <-input2:
                if !ok2 {
                    input2 = nil
                    fmt.Println("Set input2 to nil")
                    continue
                }
                c <- v
            }
        }
        close(c)
        fmt.Println("Closed fan in chan")
        return
    }()
    return c
}

func main() {
    //runtime.GOMAXPROCS(2)

    c1 := numberGenerator()
    c2 := numberGenerator()
    cfanin := fanIn(c1, c2)

    for v := range cfanin {
        fmt.Println(v)
    }
}