Added performant in-process message broker to data's routing subpackage

pkg/data/routing/broker.go

@@ -0,0 +1,56 @@
+package routing
+
+import "sync"
+
+const DefaultRingCapacity = 1 << 8 // Best if power of 2 (or so I am told)
+
+// Broker manages topics and issues publisher/subscriber handles.
+type Broker struct {
+	mu     sync.RWMutex
+	topics map[string]*TopicRing
+}
+
+func NewBroker() *Broker {
+	return &Broker{
+		topics: make(map[string]*TopicRing),
+	}
+}
+
+// getOrCreateRing handles the race condition where a subscriber might attach
+// to a topic before the publisher has created it, and vice versa.
+// This is because we allow either a publisher or a subscriber to 'create' the topic
+func (b *Broker) getOrCreateRing(topicKey string, requestedCap int) *TopicRing {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	ring, exists := b.topics[topicKey]
+	if !exists {
+		cap := requestedCap
+		if cap <= 0 {
+			cap = DefaultRingCapacity
+		}
+		ring = newTopicRing(cap)
+		b.topics[topicKey] = ring
+	}
+	return ring
+}
+
+// RegisterPublisher returns a fast-path Publisher.
+func (b *Broker) RegisterPublisher(topicKey string, capacity int) Publisher {
+	ring := b.getOrCreateRing(topicKey, capacity)
+	return &ringPublisher{
+		ring: ring,
+	}
+}
+
+// RegisterSubscriber attaches a consumer to a topic and returns a fast-path Subscriber.
+// We don't allow subscribrs to specify a buffer capacity size.
+// As a general rule, a publisher takes precedence over a subscriber
+func (b *Broker) RegisterSubscriber(topicKey string) Subscriber {
+	ring := b.getOrCreateRing(topicKey, 0)
+	consumer := ring.addConsumer()
+	return &ringSubscriber{
+		ring:     ring,
+		consumer: consumer,
+	}
+}