non-blocking.go

package main

import "fmt"

/*
Basic sends and receives on channels are blocking. However, we can use select with a default
clause to implement non-blocking sends, receives, and even non-blocking multi-way selects.
*/
func main() {

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

	// Here’s a non-blocking receive. If a value is available on messages then select will
	// take the <-messages case with that value. If not it will immediately take the default case.
	select {
	case msg := <-messages:
		fmt.Println("received message", msg)
	default:
		fmt.Println("no message received")
	}

	/*
		A non-blocking send works similarly. Here msg cannot be sent to the messages channel,
		because the channel has no buffer and there is no receiver. Therefore the default case
		is selected.
	*/
	msg := "hi"
	select {
	case messages <- msg:
		fmt.Println("sent message", msg)
	default:
		fmt.Println("no message sent")
	}

	// We can use multiple cases above the default clause to implement a multi-way
	// non-blocking select. Here we attempt non-blocking receives on both messages and signals.
	select {
	case msg := <-messages:
		fmt.Println("received message", msg)
	case sig := <-signals:
		fmt.Println("received signal", sig)
	default:
		fmt.Println("no activity")
	}
}