main.go

package main

import (
	"container/list"
	"fmt"
	"time"
)

func main() {

	cache := list.New()
	ch := make(chan string, 3)
	exitCh := make(chan interface{})

	go func() {
		for i := 0; i < 5; i++ {
			time.Sleep(100 * time.Millisecond)
			select {
			case msg := <-ch:
				fmt.Println("from channel:", msg)
			default:
				msg := cache.Front()
				if msg != nil {
					cache.Remove(msg)
					fmt.Println("from cache:", msg.Value)
				}
			}
		}
		close(exitCh)
	}()

	for i := 0; i < 5; i++ {
		msg := fmt.Sprintf("message %d", i)
		select {
		case ch <- msg:
			fmt.Println("sent to channel:", msg)
		default:
			cache.PushBack(msg)
			fmt.Println("sent to cache:", msg)
		}
	}
	<-exitCh
}

//	Output:
//
//	sent to channel: message 0
//	sent to channel: message 1
//	sent to channel: message 2
//	sent to cache: message 3
//	sent to cache: message 4
//	from channel: message 0
//	from channel: message 1
//	from channel: message 2
//	from cache: message 3
//	from cache: message 4