Introducing Go

Chapter 10. Concurrency

Large programs are often made up of many smaller subprograms. For example, a web server handles requests made from web browsers and serves up HTML web pages in response. Each request is handled like a small program.

It would be ideal for programs like these to be able to run their smaller components at the same time (in the case of the web server, to handle multiple requests). Making progress on more than one task simultaneously is known as concurrency. Go has rich support for concurrency using goroutines and channels.

Goroutines

A goroutine is a function that is capable of running concurrently with other functions. To create a goroutine, we use the keyword go followed by a function invocation:

package main

import "fmt"

func f(n int) {
    for i := 0; i < 10; i++ {
        fmt.Println(n, ":", i)
    }
}

func main() {
    go f(0)
    var input string
    fmt.Scanln(&input)
}

This program consists of two goroutines. The first goroutine is implicit and is the main function itself. The second goroutine is created when we call go f(0). Normally, when we invoke a function, our program will execute all the statements in a function and then return to the next line following the invocation. With a goroutine, we return immediately to the next line and don’t wait for the function to complete. This is why the call to the Scanln function has been included; without it, the program would exit before being given the opportunity to print all the numbers.

Goroutines are lightweight and we can easily ...