Go program start from main function and stop when main function exit

package main

import (
    "fmt"
)

func main() {
    fmt.Println("Hello, playground")
}

package main

import (
    "fmt"
)

func main() {
    go func() {
        fmt.Println("Hello, playground")
    }()
}

package main

import (
    "fmt"
)

func main() {
    done := make(chan struct{})
    go func() {
        fmt.Println("Hello, playground")
        close(done)
    }()
    <-done
}

package main

import (
    "fmt"
    "net/http"
)

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintln(w, "Hello, World")
    })

    http.ListenAndServe(":8000", nil)
}

for {
        rw, err := l.Accept()
        if err != nil {
            select {
            case <-srv.getDoneChan():
                return ErrServerClosed
            default:
            }
            if ne, ok := err.(net.Error); ok && ne.Temporary() {
                if tempDelay == 0 {
                    tempDelay = 5 * time.Millisecond
                } else {
                    tempDelay *= 2
                }
                if max := 1 * time.Second; tempDelay > max {
                    tempDelay = max
                }
                srv.logf("http: Accept error: %v; retrying in %v", err, tempDelay)
                time.Sleep(tempDelay)
                continue
            }
            return err
        }
        connCtx := ctx
        if cc := srv.ConnContext; cc != nil {
            connCtx = cc(connCtx, rw)
            if connCtx == nil {
                panic("ConnContext returned nil")
            }
        }
        tempDelay = 0
        c := srv.newConn(rw)
        c.setState(c.rwc, StateNew, runHooks) // before Serve can return
        go c.serve(connCtx)
    }