Broadcaster: all goroutines are asleep - deadlock

The code below (http://play.golang.org/p/ikUtdoKOo5) is supposed to broadcast a message to a number of clients. But it does not work and I can't figure out why.

<!-- golang -->

package main

import "fmt"

type Broadcaster struct {
	Clients []Client
}

func (b *Broadcaster) Broadcast(msg string) {
	for _, c := range b.Clients {
		go func() {
			c.Inbox() <- msg
		}()
	}
}

type Client interface {
	Inbox() chan string
}

type TestClient struct {
	Messages chan string
}

func (tc TestClient) Inbox() chan string {
	return tc.Messages
}

func main() {
	client1 := TestClient{Messages: make(chan string)}
	client2 := TestClient{Messages: make(chan string)}
	broadcaster := Broadcaster{Clients: []Client{client1, client2}}

	broadcaster.Broadcast("sos")

	fmt.Printf("client1: '%s'\n", <-client1.Messages)
	fmt.Printf("client2: '%s'\n", <-client2.Messages)
}

<br>
Error:

go run main.go
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
        /Users/artem/projects/gocode/src/github.com/artemave/broadcaster/main.go:36 +0x1f3

goroutine 3 [chan send]:
main.func·001()
        /Users/artem/projects/gocode/src/github.com/artemave/broadcaster/main.go:12 +0x5f
created by main.(*Broadcaster).Broadcast
        /Users/artem/projects/gocode/src/github.com/artemave/broadcaster/main.go:13 +0xcd

goroutine 4 [chan send]:
main.func·001()
        /Users/artem/projects/gocode/src/github.com/artemave/broadcaster/main.go:12 +0x5f
created by main.(*Broadcaster).Broadcast
        /Users/artem/projects/gocode/src/github.com/artemave/broadcaster/main.go:13 +0xcd

<br>
UPDATE:

The go vet tool reveals the problem:

% go vet
main.go:12: range variable c enclosed by function

Your problem is the usage of the variable c in the closure.
Since c is a single variable, at the time when the go routines are executed, c will most likely be set to client2, and both messages will be broadcasted to that client, and none to client1.

One way to fix it using function parameter:

func (b *Broadcaster) Broadcast(msg string) {
	for _, c := range b.Clients {		
		go func(c Client) {
			c.Inbox() <- msg    			
		}(c)
	}
}

This is a subtle bug brought on by the reassignment of c in the for-range loop. It looks a little strange, but you see this pattern in the std library in a few places:

func (b *Broadcaster) Broadcast(msg string) {
	for _, c := range b.Clients {
		c := c  // redeclare c for the closure
		go func() {
			c.Inbox() <- msg
		}()
	}
}

http://golang.org/doc/faq#closures_and_goroutines