non-blocking channel options _ golang

package main

import (
    "fmt"
)

func main() {

    message := make(chan string)
    signals := make(chan bool)

    select {
    case msg := <-message:
        fmt.Println("received message", msg)
    default:
        fmt.Println("no message received")
    }

    msg := "hi"

    select {
    case message <- msg:
        fmt.Println("sent message", msg)
    default:
        fmt.Println("no message sent")
    }

    select {
    case msg := <-message:
        fmt.Println("received message", msg)
    case sig := <-signals:
        fmt.Println("received signal", sig)
    default:
        fmt.Println("no activity")
    }

}

no message received
no message sent
no activity