watcher

source := NewSource()
w1, err := source.Watch()
if err != nil {
	panic(err)
}
w2, err := source.Watch()
if err != nil {
	panic(err)
}

if source.watchers.Len() != 2 {
	panic("watchers's len should be 2")
}

wg := sync.WaitGroup{}
wg.Add(2)
go func() {
	v, err := w1.Next()
	if err != nil {
		panic(err)
	}

	fmt.Println(v)
	wg.Done()
}()
go func() {
	if err := w2.Stop(); err != nil && err != ErrWatcherStopped {
		panic(err)
	}
	_, err := w2.Next()
	if err == nil {
		panic(err)
	}

	wg.Done()
}()

time.Sleep(time.Second)
source.Update("hello")

wg.Wait()

if source.watchers.Len() != 1 {
	panic("watchers's len should be 1")
}

if err := w1.Stop(); err != nil {
	panic(err)
}
time.Sleep(time.Second)
if source.watchers.Len() != 0 {
	panic("watchers's len should be 0")
}

Output:

hello