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Goroutines demystified

bluepaperbirds profile image bluepaperbirds ・1 min read

In programming languages, code is often split up into functions. Functions help to make code reusable, extensible etc.

In Go there's a special case: goroutines. So is a goroutine a function? Not exactly. A goroutine is a lightweight thread managed by the Go.

If you call a function f like this:

f(x)

it's a normal function. But if you call it like this:

go f(x)

it's a goroutine. This is then started concurrently.

If you are new to Go, you can use the Go playground

Goroutine examples

Try this simple program below:

package main

import (
    "fmt"
    "time"
)

func say(s string) {
    for i := 0; i < 3; i++ {
        time.Sleep(100 * time.Millisecond)
        fmt.Println(s)
    }
}

func main() {
    go say("thread")
    say("hello")
}

Execute it with:

go run example.go

So while say('hello') is synchronously executed, go say('hello') is asynchronous.

Consider this program:

package main

import (
    "fmt"
    "time"
)

func main() {
    go fmt.Println("Hi from goroutine")
    fmt.Println("function Hello")

    time.Sleep(time.Second) // goroutine needs time to finish
}

Then when I ran it:

function Hello
Hi from goroutine

Program exited.

As expected, the goroutine (thread) started later.

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