cyclic_barrier.go

package main

import (
	"fmt"
	"sync"
)

func main() {
	var wg sync.WaitGroup
	cb := NewCB(5)

	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			name := fmt.Sprintf("task #%d", id+1)
			for b := 0; b < 2; b++ {
				fmt.Printf("%s is waiting at the barrier #%d.\n", name, b+1)
				cb.Await()
				fmt.Printf("%s has crossed the barrier #%d.\n", name, b+1)
			}
		}(i)
	}
	wg.Wait()
}

type cb struct {
	sync.Mutex
	p int
	n int
	b chan struct{}
}

func (cb *cb) reset() {
	cb.Lock()
	defer cb.Unlock()

	cb.n = cb.p
	close(cb.b)
	cb.b = make(chan struct{})

}

func (cb *cb) Await() {
	cb.Lock()
	cb.n--
	n := cb.n
	b := cb.b
	cb.Unlock()

	if n > 0 {
		<-b
	} else {
		fmt.Println("All parties have arrived to the barrier, lets play...")
		cb.reset()
	}
}

func NewCB(parties int) *cb {
	cb := &cb{
		p: parties,
		n: parties,
		b: make(chan struct{}),
	}
	return cb
}

Live code - https://play.golang.org/p/mvIHuFmLVV

Output:

task #5 is waiting at the barrier #1.
task #1 is waiting at the barrier #1.
task #2 is waiting at the barrier #1.
task #3 is waiting at the barrier #1.
task #4 is waiting at the barrier #1.
All parties have arrived to the barrier, lets play...
task #4 has crossed the barrier #1.
task #4 is waiting at the barrier #2.
task #3 has crossed the barrier #1.
task #3 is waiting at the barrier #2.
task #5 has crossed the barrier #1.
task #5 is waiting at the barrier #2.
task #1 has crossed the barrier #1.
task #1 is waiting at the barrier #2.
task #2 has crossed the barrier #1.
task #2 is waiting at the barrier #2.
All parties have arrived to the barrier, lets play...
task #2 has crossed the barrier #2.
task #1 has crossed the barrier #2.
task #4 has crossed the barrier #2.
task #3 has crossed the barrier #2.
task #5 has crossed the barrier #2.