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eventstream.go
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eventstream.go
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package eventstream
import (
"sync"
)
// Predicate is a function used to filter messages before being forwarded to a subscriber
type Predicate func(evt interface{}) bool
var es = &EventStream{}
func Subscribe(fn func(evt interface{})) *Subscription {
return es.Subscribe(fn)
}
func Unsubscribe(sub *Subscription) {
es.Unsubscribe(sub)
}
func Publish(event interface{}) {
es.Publish(event)
}
type EventStream struct {
sync.RWMutex
subscriptions []*Subscription
}
func (es *EventStream) Subscribe(fn func(evt interface{})) *Subscription {
es.Lock()
sub := &Subscription{
es: es,
i: len(es.subscriptions),
fn: fn,
}
es.subscriptions = append(es.subscriptions, sub)
es.Unlock()
return sub
}
func (es *EventStream) Unsubscribe(sub *Subscription) {
if sub.i == -1 {
return
}
es.Lock()
i := sub.i
l := len(es.subscriptions) - 1
es.subscriptions[i] = es.subscriptions[l]
es.subscriptions[i].i = i
es.subscriptions[l] = nil
es.subscriptions = es.subscriptions[:l]
sub.i = -1
// TODO(SGC): implement resizing
if len(es.subscriptions) == 0 {
es.subscriptions = nil
}
es.Unlock()
}
func (es *EventStream) Publish(evt interface{}) {
es.RLock()
defer es.RUnlock()
for _, s := range es.subscriptions {
if s.p == nil || s.p(evt) {
s.fn(evt)
}
}
}
// Subscription is returned from the Subscribe function.
//
// This value and can be passed to Unsubscribe when the observer is no longer interested in receiving messages
type Subscription struct {
es *EventStream
i int
fn func(event interface{})
p Predicate
}
// WithPredicate sets a predicate to filter messages passed to the subscriber
func (s *Subscription) WithPredicate(p Predicate) *Subscription {
s.es.Lock()
s.p = p
s.es.Unlock()
return s
}