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moby--moby/pkg/pubsub/publisher.go

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package pubsub
import (
"sync"
"time"
)
var wgPool = sync.Pool{New: func() interface{} { return new(sync.WaitGroup) }}
// NewPublisher creates a new pub/sub publisher to broadcast messages.
// The duration is used as the send timeout as to not block the publisher publishing
// messages to other clients if one client is slow or unresponsive.
// The buffer is used when creating new channels for subscribers.
func NewPublisher(publishTimeout time.Duration, buffer int) *Publisher {
return &Publisher{
buffer: buffer,
timeout: publishTimeout,
subscribers: make(map[subscriber]topicFunc),
}
}
type subscriber chan interface{}
type topicFunc func(v interface{}) bool
// Publisher is basic pub/sub structure. Allows to send events and subscribe
// to them. Can be safely used from multiple goroutines.
type Publisher struct {
m sync.RWMutex
buffer int
timeout time.Duration
subscribers map[subscriber]topicFunc
}
// Len returns the number of subscribers for the publisher
func (p *Publisher) Len() int {
p.m.RLock()
i := len(p.subscribers)
p.m.RUnlock()
return i
}
// Subscribe adds a new subscriber to the publisher returning the channel.
func (p *Publisher) Subscribe() chan interface{} {
return p.SubscribeTopic(nil)
}
// SubscribeTopic adds a new subscriber that filters messages sent by a topic.
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
}
// SubscribeTopicWithBuffer adds a new subscriber that filters messages sent by a topic.
// The returned channel has a buffer of the specified size.
func (p *Publisher) SubscribeTopicWithBuffer(topic topicFunc, buffer int) chan interface{} {
ch := make(chan interface{}, buffer)
p.m.Lock()
p.subscribers[ch] = topic
p.m.Unlock()
return ch
}
// Evict removes the specified subscriber from receiving any more messages.
func (p *Publisher) Evict(sub chan interface{}) {
p.m.Lock()
delete(p.subscribers, sub)
close(sub)
p.m.Unlock()
}
// Publish sends the data in v to all subscribers currently registered with the publisher.
func (p *Publisher) Publish(v interface{}) {
p.m.RLock()
if len(p.subscribers) == 0 {
p.m.RUnlock()
return
}
wg := wgPool.Get().(*sync.WaitGroup)
for sub, topic := range p.subscribers {
wg.Add(1)
go p.sendTopic(sub, topic, v, wg)
}
wg.Wait()
wgPool.Put(wg)
p.m.RUnlock()
}
// Close closes the channels to all subscribers registered with the publisher.
func (p *Publisher) Close() {
p.m.Lock()
for sub := range p.subscribers {
delete(p.subscribers, sub)
close(sub)
}
p.m.Unlock()
}
func (p *Publisher) sendTopic(sub subscriber, topic topicFunc, v interface{}, wg *sync.WaitGroup) {
defer wg.Done()
if topic != nil && !topic(v) {
return
}
// send under a select as to not block if the receiver is unavailable
if p.timeout > 0 {
select {
case sub <- v:
case <-time.After(p.timeout):
}
return
}
select {
case sub <- v:
default:
}
}