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observer.go
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/
observer.go
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package mq
/*
bs := NewObserver()
chBroadcast := bs.Run()
chA := bs.Listener()
chB := bs.Listener()
var wg sync.WaitGroup
wg.Add(2)
go func() {
for v := range chA {
fmt.Println("A", v)
}
wg.Done()
}()
go func() {
for v := range chB {
fmt.Println("B", v)
}
wg.Done()
}()
for i := 0; i < 3; i++ {
chBroadcast <- i
}
bs.RemoveListener(chA)
for i := 3; i < 6; i++ {
chBroadcast <- i
}
close(chBroadcast)
wg.Wait()
*/
type Observer struct {
// 这是消费者监听的通道
chBroadcast chan int
// 转发给这些channel
chListeners []chan int
// 添加消费者
chNewRequests chan (chan int)
// 移除消费者
chRemoveRequests chan (chan int)
}
// NewObserver 创建一个广播服务
func NewObserver() *Observer {
return &Observer{
chBroadcast: make(chan int),
chListeners: make([]chan int, 3),
chNewRequests: make(chan (chan int)),
chRemoveRequests: make(chan (chan int)),
}
}
// Listener 这会创建一个新消费者并返回一个监听通道
func (bs *Observer) Listener() chan int {
ch := make(chan int)
bs.chNewRequests <- ch
return ch
}
// RemoveListener 移除一个消费者
func (bs *Observer) RemoveListener(ch chan int) {
bs.chRemoveRequests <- ch
}
func (bs *Observer) addListener(ch chan int) {
for i, v := range bs.chListeners {
if v == nil {
bs.chListeners[i] = ch
return
}
}
bs.chListeners = append(bs.chListeners, ch)
}
func (bs *Observer) removeListener(ch chan int) {
for i, v := range bs.chListeners {
if v == ch {
bs.chListeners[i] = nil
// 一定要关闭! 否则监听它的groutine将会一直block
close(ch)
return
}
}
}
func (bs *Observer) Run() chan int {
go func() {
for {
// 处理新建消费者或者移除消费者
select {
case newCh := <-bs.chNewRequests:
bs.addListener(newCh)
case removeCh := <-bs.chRemoveRequests:
bs.removeListener(removeCh)
case v, ok := <-bs.chBroadcast:
// 如果广播通道关闭,则关闭掉所有的消费者通道
if !ok {
goto terminate
}
// 将值转发到所有的消费者channel
for _, dstCh := range bs.chListeners {
if dstCh == nil {
continue
}
dstCh <- v
}
}
}
terminate:
//关闭所有的消费通道
for _, dstCh := range bs.chListeners {
if dstCh == nil {
continue
}
close(dstCh)
}
}()
return bs.chBroadcast
}