throttle.go
func (t *throttle) Capacity() (c uint64) {
	t.mu.Lock()
	c = t.bucket.Capacity()
	t.mu.Unlock()

	return
}
func (t *throttle) Capacity() (c uint64) {
	t.mu.Lock()
	c = t.bucket.Capacity()
	t.mu.Unlock()

	return
}
// LOCKS_EXCLUDED(t.mu)