GoRoutines

A goroutine is a lightweight thread of execution.

package main

import (
    "fmt"
    "time"
)

func f(from string) {
    for i := 0; i < 3; i++ {
        fmt.Println(from, ":", i)
    }
}

func main() {

    // Suppose we have a function call f(s).
    // Here’s how we’d call that in the usual way, running it synchronously.
    f("direct")

    // To invoke this function in a goroutine
    // use go f(s). This new goroutine will
    // execute concurrently with the calling one.
    go f("goroutine")

    // You can also start a goroutine for an anonymous function call.
    go func(msg string) {
        fmt.Println(msg)
    }("going")

    // Our two function calls are running
    // asynchronously in separate goroutines now.
    // Wait for them to finish (for a more robust approach, use a WaitGroup).
    time.Sleep(time.Second)
    fmt.Println("done")
}

When we run this program, we see the output of the blocking call first, then the output of the two goroutines. The goroutines’ output may be interleaved, because goroutines are being run concurrently by the Go runtime.

$ go run goroutines.go
direct : 0
direct : 1
direct : 2
goroutine : 0
going
goroutine : 1
goroutine : 2
done

Next we’ll look at a complement to goroutines in concurrent Go programs: channels.