Example of using sync.Cond and broadcast feature

main.go

package main

import (
	"fmt"
	"sync"
	"time"
)

// Listen for broadcast.
// The wg waitgroup is to make sure the listen func is called before the broadcast happens.
func listen(name string, c *sync.Cond, wg *sync.WaitGroup) {
	fmt.Println(name + " started")
	wg.Done()
	c.L.Lock()
	c.Wait()
	fmt.Println(name + " was called")
	c.L.Unlock()
}

// Send broadcast
func broadcast(c *sync.Cond, wg *sync.WaitGroup) {
	fmt.Println("broadcast started")
	c.L.Lock()
	c.Broadcast()
	c.L.Unlock()

	time.Sleep(1 * time.Second)
	wg.Done()
}

func main() {
	cond := sync.NewCond(&sync.Mutex{})
	wg := &sync.WaitGroup{}

	wg.Add(2)
	go listen("Listener 1", cond, wg)
	go listen("Listener 2", cond, wg)
	wg.Wait()

	wg.Add(1)
	go broadcast(cond, wg)
	wg.Wait()
}