Go Select Statement Demonstration

Introduction

This lab aims to test your knowledge of Go's select statement, which allows you to wait on multiple channel operations.

Select

In this lab, you are given two channels, c1 and c2, which will receive a value after some amount of time. Your task is to use select to await both of these values simultaneously, printing each one as it arrives.

• You should use the select statement to wait on both channels.
• You should print the value received from each channel as it arrives.

## We receive the values `"one"` and then `"two"` as
## expected.
$ time go run select.go
received one
received two

## Note that the total execution time is only ~2 seconds
## since both the 1 and 2 second `Sleeps` execute
## concurrently.
real 0m2.245s

There is the full code below:

// Go's _select_ lets you wait on multiple channel
// operations. Combining goroutines and channels with
// select is a powerful feature of Go.

package main

import (
    "fmt"
    "time"
)

func main() {

    // For our example we'll select across two channels.
    c1 := make(chan string)
    c2 := make(chan string)

    // Each channel will receive a value after some amount
    // of time, to simulate e.g. blocking RPC operations
    // executing in concurrent goroutines.
    go func() {
        time.Sleep(1 * time.Second)
        c1 <- "one"
    }()
    go func() {
        time.Sleep(2 * time.Second)
        c2 <- "two"
    }()

    // We'll use `select` to await both of these values
    // simultaneously, printing each one as it arrives.
    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.Println("received", msg1)
        case msg2 := <-c2:
            fmt.Println("received", msg2)
        }
    }
}

Summary

This lab tests your ability to use the select statement in Go to wait on multiple channel operations. By completing this lab, you will gain a better understanding of how to use select to coordinate concurrent goroutines.