Goroutines

A goroutine is a lightweight concurrent function started with the go keyword. The Go runtime multiplexes goroutines onto OS threads—far cheaper than one thread per task in Java.

Starting goroutines

go func() {
    fmt.Println("async")
}()
time.Sleep(time.Millisecond) // wait in playground demos

Main exits immediately without waiting—use channels, sync.WaitGroup, or time.Sleep in lessons so output appears before exit.

Compared to other models

• Node.js — single-threaded event loop; Go runs true parallel goroutines on multiple cores
• Python — GIL limits CPU parallelism in threads; Go goroutines scale for CPU and I/O
• Rust — async/threads with ownership; Go GC simplifies shared heap (with sync discipline)

Important interview questions and answers

1. Q: Goroutine vs OS thread?
   A: Goroutines are smaller, scheduled by Go runtime on a thread pool—millions are practical.
2. Q: What happens if main returns while goroutines run?
   A: Program exits—unfinished goroutines are terminated.

Self-check

1. What keyword starts a goroutine?
2. Why use WaitGroup or channels instead of Sleep in production?

Tip: Main exits without waiting for goroutines—use channels, WaitGroup, or brief time.Sleep in playground demos so output appears.