11 - Getting into the routine

Covered in this module:

goroutines

goroutines

So far, all the function calls that have been shown are done synchronously. To call a function so that it runs concurrently to the invoker, use the go keyword:

package main

import (
    "fmt"
    "time"
)

func main() {
    go repeat("Pete", 3)

    repeat("Repeat", 5)

    time.Sleep(time.Millisecond * 10)
}

func repeat(str string, times int) {
    for i := 0; i < times; i++ {
        fmt.Println(str, i)
        time.Sleep(time.Microsecond * 5)
    }
}

prints

Repeat 0
Repeat 1
Pete 0
Pete 1
Repeat 2
Pete 2
Repeat 3
Repeat 4

Note

Your program will not wait for your goroutines to complete before closing. Once the goroutine that main is running on (usually refered to as the main routine) closes the app will close as well.

Only functions with no return values are eligible to be goroutines. There are no such restrictions on goroutine function parameters.

You will likely see a different pattern of printed strings each time you run the repeat example function above.

Go handles all the logic for spreading work and swapping routines on CPU threads for you, so you can spin up many goroutines without necessarily needing to think about how the work might be accomplished.

func main() {
    go ticker(100)
    go ticker(250)
    go ticker(333)
    go ticker(500)

    time.Sleep(time.Millisecond * 1050)
}

func ticker(waitMs int) {
    for i := 1; i <= 1000/waitMs; i++ {
        time.Sleep(time.Millisecond * time.Duration(waitMs))
        fmt.Printf("%v, ", waitMs * i)
    }
    fmt.Println()
}

prints

100, 200, 250, 300, 333, 400, 500, 500, 500, 600, 666, 700, 750, 800, 900, 1000, 
1000, 
999, 
1000,

Note

Go has a ticker implementation in the native package time (created by time.NewTicker()). The ticker above is just for teaching purposes.

You cannot return a value from goroutine directly, but go offers a construct called channel for communicating between goroutines that will be covered in the next module.

Hands on!

In the repo, open the file ./intermediate/11goroutines.go
Complete the TODOs
Run make 11 from project root (alternatively, type go run ./11goroutines.go)
Example implementation available on solutions branch