api/internal/notifier/notifier.go

package notifier

import (
	"context"
	"sync"
)

// A Notifier is a synchronization primitive for waking upp all listeners at once.
type Notifier struct {
	mutex sync.Mutex
	ch    chan struct{}
}

// Broadcast wakes all listeners if there are any.
func (notifier *Notifier) Broadcast() {
	notifier.mutex.Lock()
	if notifier.ch != nil {
		close(notifier.ch)
		notifier.ch = nil
	}
	notifier.mutex.Unlock()
}

// C gets the channel that'll close on the next notification.
func (notifier *Notifier) C() <-chan struct{} {
	notifier.mutex.Lock()
	if notifier.ch == nil {
		notifier.ch = make(chan struct{})
	}
	ch := notifier.ch
	notifier.mutex.Unlock()

	return ch
}

// Wait waits for the next `Broadcast` call, or the context's termination.
func (notifier *Notifier) Wait(ctx context.Context) error {
	select {
	case <-notifier.C():
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}