What happens when you fill a channel, close it, then try to recv?

channel-fill-close-recv.go

// Q: What happens when you fill a channel, close it, then try to recv?
// A: You can keep reading the values until the buffer is empty, then
// the close operation takes effect

package main

import (
	"fmt"
	"time"
)

func main() {
	ch := make(chan struct{}, 3)
	fmt.Printf("len: %d cap: %d\n", len(ch), cap(ch))
  // fill
	for i := 0; i < cap(ch); i++ {
		ch <- struct{}{}
	}
  
  // close in 25ms
	go func() {
		time.Sleep(25 * time.Millisecond)
		close(ch)
		fmt.Println("Closed")
	}()
  
  // recv 1 every second; close should have happened before the 1st
	for i := 0; i < cap(ch)+1; i++ {
		time.Sleep(1000 * time.Millisecond)
		_, ok := <-ch
		fmt.Println(ok)
	}
}