Merge pull request #6199 from icecrime/event_subscription_refactoring

Event subscription refactoring

utils/jsonmessagepublisher.go

@@ -0,0 +1,61 @@
+package utils
+
+import (
+	"sync"
+	"time"
+)
+
+func NewJSONMessagePublisher() *JSONMessagePublisher {
+	return &JSONMessagePublisher{}
+}
+
+type JSONMessageListener chan<- JSONMessage
+
+type JSONMessagePublisher struct {
+	m           sync.RWMutex
+	subscribers []JSONMessageListener
+}
+
+func (p *JSONMessagePublisher) Subscribe(l JSONMessageListener) {
+	p.m.Lock()
+	p.subscribers = append(p.subscribers, l)
+	p.m.Unlock()
+}
+
+func (p *JSONMessagePublisher) SubscribersCount() int {
+	p.m.RLock()
+	count := len(p.subscribers)
+	p.m.RUnlock()
+	return count
+}
+
+// Unsubscribe closes and removes the specified listener from the list of
+// previously registed ones.
+// It returns a boolean value indicating if the listener was successfully
+// found, closed and unregistered.
+func (p *JSONMessagePublisher) Unsubscribe(l JSONMessageListener) bool {
+	p.m.Lock()
+	defer p.m.Unlock()
+
+	for i, subscriber := range p.subscribers {
+		if subscriber == l {
+			close(l)
+			p.subscribers = append(p.subscribers[:i], p.subscribers[i+1:]...)
+			return true
+		}
+	}
+	return false
+}
+
+func (p *JSONMessagePublisher) Publish(m JSONMessage) {
+	p.m.RLock()
+	for _, subscriber := range p.subscribers {
+		// We give each subscriber a 100ms time window to receive the event,
+		// after which we move to the next.
+		select {
+		case subscriber <- m:
+		case <-time.After(100 * time.Millisecond):
+		}
+	}
+	p.m.RUnlock()
+}

utils/jsonmessagepublisher_test.go

@@ -0,0 +1,73 @@
+package utils
+
+import (
+	"testing"
+	"time"
+)
+
+func assertSubscribersCount(t *testing.T, q *JSONMessagePublisher, expected int) {
+	if q.SubscribersCount() != expected {
+		t.Fatalf("Expected %d registered subscribers, got %d", expected, q.SubscribersCount())
+	}
+}
+
+func TestJSONMessagePublisherSubscription(t *testing.T) {
+	q := NewJSONMessagePublisher()
+	l1 := make(chan JSONMessage)
+	l2 := make(chan JSONMessage)
+
+	assertSubscribersCount(t, q, 0)
+	q.Subscribe(l1)
+	assertSubscribersCount(t, q, 1)
+	q.Subscribe(l2)
+	assertSubscribersCount(t, q, 2)
+
+	q.Unsubscribe(l1)
+	q.Unsubscribe(l2)
+	assertSubscribersCount(t, q, 0)
+}
+
+func TestJSONMessagePublisherPublish(t *testing.T) {
+	q := NewJSONMessagePublisher()
+	l1 := make(chan JSONMessage)
+	l2 := make(chan JSONMessage)
+
+	go func() {
+		for {
+			select {
+			case <-l1:
+				close(l1)
+				l1 = nil
+			case <-l2:
+				close(l2)
+				l2 = nil
+			case <-time.After(1 * time.Second):
+				q.Unsubscribe(l1)
+				q.Unsubscribe(l2)
+				t.Fatal("Timeout waiting for broadcasted message")
+			}
+		}
+	}()
+
+	q.Subscribe(l1)
+	q.Subscribe(l2)
+	q.Publish(JSONMessage{})
+}
+
+func TestJSONMessagePublishTimeout(t *testing.T) {
+	q := NewJSONMessagePublisher()
+	l := make(chan JSONMessage)
+	q.Subscribe(l)
+
+	c := make(chan struct{})
+	go func() {
+		q.Publish(JSONMessage{})
+		close(c)
+	}()
+
+	select {
+	case <-c:
+	case <-time.After(time.Second):
+		t.Fatal("Timeout publishing message")
+	}
+}