e.lock.Lock()
	defer e.lock.Unlock()

	return e.tryUpdate(func() error {
		return e.alloc.Release(item)
	})

}

func (e *Etcd) ForEach(fn func(int)) {
	e.lock.Lock()
	defer e.lock.Unlock()
	e.alloc.ForEach(fn)
}

// tryUpdate performs a read-update to persist the latest snapshot state of allocation.
func (e *Etcd) tryUpdate(fn func() error) error {