```go
// Package pubsub implements a simple multi-topic pub-sub library.
package pubsub

import (
    "sync"
    "time"
)

type (
    subscriber chan interface{}         // 订阅者为一个管道
    topicFunc  func(v interface{}) bool // 主题为一个过滤器
)

// 发布者对象
type Publisher struct {
    m           sync.RWMutex             // 读写锁
    buffer      int                      // 订阅队列的缓存大小
    timeout     time.Duration            // 发布超时时间
    subscribers map[subscriber]topicFunc // 订阅者信息
}

// 构建一个发布者对象, 可以设置发布超时时间和缓存队列的长度
func NewPublisher(publishTimeout time.Duration, buffer int) *Publisher {
    return &Publisher{
        buffer:      buffer,
        timeout:     publishTimeout,
        subscribers: make(map[subscriber]topicFunc),
    }
}

// 添加一个新的订阅者，订阅全部主题
func (p *Publisher) Subscribe() chan interface{} {
    return p.SubscribeTopic(nil)
}

// 添加一个新的订阅者，订阅过滤器筛选后的主题
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
}

// 退出订阅
func (p *Publisher) Evict(sub chan interface{}) {
    p.m.Lock()
    defer p.m.Unlock()

    delete(p.subscribers, sub)
    close(sub)
}

// 发布一个主题
func (p *Publisher) Publish(v interface{}) {
    p.m.RLock()
    defer p.m.RUnlock()

    var wg sync.WaitGroup
    for sub, topic := range p.subscribers {
        wg.Add(1)
        go p.sendTopic(sub, topic, v, &wg)
    }
    wg.Wait()
}

// 关闭发布者对象，同时关闭所有的订阅者管道。
func (p *Publisher) Close() {
    p.m.Lock()
    defer p.m.Unlock()

    for sub := range p.subscribers {
        delete(p.subscribers, sub)
        close(sub)
    }
}

// 发送主题，可以容忍一定的超时
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):
    }
}
```

```go
import "path/to/pubsub"

func main() {
    p := pubsub.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!")

    go func() {
        for  msg := range all {
            fmt.Println("all:", msg)
        }
    } ()

    go func() {
        for  msg := range golang {
            fmt.Println("golang:", msg)
        }
    } ()

    // 运行一定时间后退出
    time.Sleep(3 * time.Second)
}
```


发布订阅模型