Concurrency Primer: Goroutines

Goroutines

This lesson explains the main concept clearly with beginner-friendly examples and background so you can learn why the code works.

A goroutine is a lightweight thread managed by the Go runtime.

func say(msg string) {
    for i := 0; i < 3; i++ {
        fmt.Println(msg)
    }
}

func main() {
    go say("world") // runs concurrently
    say("hello")    // runs in main goroutine
}

Scheduling

• The runtime multiplexes many goroutines onto a small set of OS threads.
• The default GOMAXPROCS is the number of logical CPUs.

Synchronizing with sync.WaitGroup

var wg sync.WaitGroup
for i := 0; i < 5; i++ {
    wg.Add(1)
    go func(id int) {
        defer wg.Done()
        fmt.Println("worker", id)
    }(i)
}
wg.Wait()