Go by Example: Non-Blocking Channel Operations

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.

 
package main

import "fmt"

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.

 
    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")
    }
}

$ go run non-blocking-channel-operations.go 
no message received
no message sent
no activity

Next example: Closing Channels.

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