發佈訂閱模型 Golang實現

本地博客實例代碼由《Go 高級編程》提供，在經過自己測試、註釋之後，發佈到博客，以後有時間繼續完善

---

type (
	subscriber chan interface{}
	topicFunc  func(v interface{}) bool
)

//發佈者對象
type Publisher struct {
	m           sync.RWMutex             //m 用來保護subscribers 增加刪除訂閱者時使用寫鎖  向訂閱者發消息時候使用讀鎖
	buffer      int                      //訂閱隊列的緩存大小
	timeout     time.Duration            //發佈超時時間
	subscribers map[subscriber]topicFunc //訂閱者信息
}

//構建一個發佈者對象， 可以設置發佈超時時間和緩存隊列的長度
func NewPublisher(publishTimeout time.Duration, buffer int) *Publisher {
	return &Publisher{
		buffer:      buffer,
		timeout:     publishTimeout,
		subscribers: make(map[subscriber]topicFunc),
	}
}
//添加一個新的訂閱者, 訂閱全部主題
func(p *Publisher) Subscribe() chan interface{} {
	return p.SubscribeTopic(nil)
}

//添加一個新的訂閱者，訂閱過濾器篩選後的主題
func (p *Publisher) SubscribeTopic(topic topicFunc) chan interface{} {
	ch := make(chan  interface{}, p.buffer)
	p.m.Lock()
	p.subscribers[ch] = topic
	p.m.Unlock()
	return ch
}
//退出訂閱
func (p *Publisher) Evict(sub chan interface{}) {
	p.m.Lock()
	defer p.m.Unlock()
	delete(p.subscribers, sub)
	close(sub)
}
//發佈一個主題
func (p * Publisher) Publish(v interface{}) {
	p.m.RLock()
	defer p.m.RUnlock()

	var wg sync.WaitGroup
	//同時向所有訂閱者寫消息 可以用topic過濾消息
	for sub, topic := range p.subscribers {
		wg.Add(1)
		go p.sendTopic(sub, topic, v, &wg)
	}
	wg.Wait()
}
//關閉發佈者對象 同時關閉所有訂閱者管道
func (p *Publisher) Close() {
	p.m.Lock()
	defer p.m.Unlock()
	for sub := range p.subscribers {
		delete(p.subscribers, sub)
		close(sub)
	}
}

//發送主題 可以容忍一定的超時
func (p *Publisher) sendTopic(sub subscriber, topic topicFunc, v interface{}, wg *sync.WaitGroup) {
	defer wg.Done()
	if topic != nil && !topic(v) {
		return
	}
	select {
	case sub <- v:
	case <-time.After(p.timeout):
	 }
}

func main() {
	p := NewPublisher(100 * time.Millisecond, 10)
	defer p.Close()

	all := p.Subscribe()
	golang := p.SubscribeTopic(func(v interface{}) bool {
		if s, ok := v.(string); ok {
			return strings.Contains(s, "golang")
		}
		return false
	})

	p.Publish("hello, world!")
	p.Publish("hello, golang!")
	p.Publish("hello test!!!")

	go func() {
		for msg := range all {
			fmt.Println("all:", msg)
		}
	}()
	go func() {
		for msg := range golang {
			fmt.Println("golang:", msg)
		}
	}()
	time.Sleep(time.Second * 3)
}

//運行結果

golang: hello, golang!
all: hello, world!
all: hello, golang!
all: hello test!!!