🐹 Go - Take Best Pattern
Updated at 2013-12-04 01:27
Fan-in. Use the channel which is ready to talk first by merging multiple channels.
package main
import (
"fmt"
"math/rand"
"time"
)
func boring(msg string) <-chan string {
c := make(chan string)
go func() {
for i := 0; ; i++ {
c <- fmt.Sprintf("%s %d", msg, i)
time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
}
}()
return c
}
func fanIn(input1, input2 <-chan string) <-chan string {
c := make(chan string)
go func() {
for {
select {
case s := <-input1:
c <- s
case s := <-input2:
c <- s
}
}
}()
return c
}
func main() {
c := fanIn(boring("Joe"), boring("Ann"))
for i := 0; i < 10; i++ {
fmt.Println(<-c)
}
fmt.Println("You're both boring; I'm leaving.")
}
Use only the first passed value from a channel.
package main
import (
"fmt"
"net/http"
"sync"
)
type response struct {
resp *http.Response
url string
}
func get(url string, r chan<- response, wg *sync.WaitGroup) {
defer wg.Done()
resp, err := http.Get(url)
if err == nil {
return
}
if resp == nil {
return
}
select {
case r <- response{resp, url}:
default:
}
}
// if the channels is not closed, following responses will
// be left to waiting for someone to read the channel
func closeAfterAllTries(r chan response, wg *sync.WaitGroup) {
wg.Wait()
close(r)
}
func main() {
takeFirst := make(chan response)
urls := []string{
"http://code.jquery.com/jquery-1.9.1.min.js",
"http://cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js",
"http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js",
"http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.9.1.min.js",
}
wg := sync.WaitGroup{}
for _, url := range urls {
wg.Add(1)
go get(url, takeFirst, &wg)
}
go closeAfterAllTries(takeFirst, &wg)
r := <-takeFirst
fmt.Println(r) // can be nil struct if all fail
}