原文: https://gobyexample.com/non-blocking-channel-operations

Basic sends and receives on channels are blocking. However, we can useselectwith adefaultclause to implementnon-blockingsends, receives, and even non-blocking multi-wayselects.

Here’s a non-blocking receive. If a value is available onmessages

A non-blocking send works similarly. Heremsgcannot be sent to themessageschannel, because the channel has no buffer and there is no receiver. Therefore thedefaultcase is selected.

We can use multiplecase

package main

import "fmt"

func main() {
    messages := make(chan string)
    signals := make(chan bool)

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

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

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