substack-concurrency-9.go

type Button struct { // contains a condition
    Clicked *sync.Cond
}

button := Button{Clicked: sync.NewCond(&sync.Mutex{})}

subscribe := func(c *sync.Cond, fn func()) { // allows us to register functions
    var goroutineRunning sync.WaitGroup      // to handle signals from conditions
    goroutineRunning.Add(1)
    
    go func() {
        goroutineRunning.Done()
        c.L.Lock()
        defer c.L.Unlock()
        c.Wait()
        fn()
    }()
    goroutineRunning.Wait()
}
var clickRegistered sync.WaitGroup
clickRegistered.Add(3)
subscribe(button.Clicked, func() {
    // do smth
    clickRegistered.Done()
})
subscribe(button.Clicked, func() {
    // do smth
    clickRegistered.Done()
})
subscribe(button.Clicked, func() {
    // do smth
    clickRegistered.Done()
})
    
button.Clicked.Broadcast()
clickRegistered.Wait()