blocking key deadlock problem

[JasonHu520]

问题场景：

if kl == nil {
		l.lock.RUnlock()
		l.lock.Lock()
		kl = newBlocker(l.limit)
		l.keyMap[key] = kl
		kl.addRef()
		l.lock.Unlock()

1. In a concurrent scenario, when aquire a single key, the obtained key maybe nil and no secondary check is performed, which may result in the same key being overwritten.

if kl.loadRef() < 0 {
			l.lock.Unlock()
			panic("internal error: refs < 0")
		}
		if kl.loadRef() == 0 {
			delete(l.keyMap, key)
		}
		kls = append(kls, kl)
	}
	for _, kl := range kls {
		kl.release()
	}

2. When the key is released, there is a problem with the reference count judgment, resulting in the repeated release of the key's lock