https://talks.golang.org/2012/waza.slide#57

replicate-db_1.go

package main

import (
	"fmt"
	"math/rand"
	"time"
)

// Query a replicated database
// Teardown of late finishers is left as an exercise.

// Conn comment
type Conn int

// DoQuery comment
func (c Conn) DoQuery(q string) Result {
	r := Result(q)

	time.Sleep(time.Duration(rand.Int()) * time.Second)

	return r
}

// Result comment
type Result string

// Query comment
func Query(conns []Conn, query string) Result {
	ch := make(chan Result, 1) // buffered
	for _, conn := range conns {
		go func(c Conn) {
			select {
			case ch <- c.DoQuery(query):
			default:
			}
		}(conn)
	}
	return <-ch
}

func main() {
	conns := []Conn{1, 2, 3}
	r := Query(conns, "SELECT * FROM users")
	fmt.Println(r)

	time.Sleep(5 * time.Second)
}

replicate-db_2.go

package main

import (
	"fmt"
	"math/rand"
	"time"
)

// Query a replicated database
// Teardown of late finishers is left as an exercise.

// Conn comment
type Conn int

// DoQuery comment
func (c Conn) DoQuery(q string) Result {
	r := Result(q)

	time.Sleep(time.Duration(rand.Int()) * time.Second)

	return r
}

// Result comment
type Result string

// Query comment
func Query(conns []Conn, query string) Result {
	ch := make(chan Result)
	done := make(chan struct{})
	defer close(done)
	for _, conn := range conns {
		go func(c Conn) {
			select {
			case ch <- c.DoQuery(query):
			case <-done:
			}
		}(conn)
	}
	return <-ch
}

func main() {
	conns := []Conn{1, 2, 3}
	r := Query(conns, "SELECT * FROM users")
	fmt.Println(r)

	time.Sleep(5 * time.Second)
}

task.go

func Query(conns []Conn, query string) Result {
    ch := make(chan Result, len(conns))  // buffered
    for _, conn := range conns {
        go func(c Conn) {
            ch <- c.DoQuery(query)
        }(conn)
    }
    return <-ch
}