kubernetes/staging/src/k8s.io/apimachinery/pkg/util/waitgroup/waitgroup.go

type SafeWaitGroup …

// Add adds delta, which may be negative, similar to sync.WaitGroup.
// If Add with a positive delta happens after Wait, it will return error,
// which prevent unsafe Add.
func (wg *SafeWaitGroup) Add(delta int) error { … }

// Done decrements the WaitGroup counter.
func (wg *SafeWaitGroup) Done() { … }

// Wait blocks until the WaitGroup counter is zero.
func (wg *SafeWaitGroup) Wait() { … }