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

cmd/datad/main.go

@@ -3,171 +3,312 @@ package main
 import (
 	"context"
 	"fmt"
+	"math/rand"
+	"runtime"
+	"strconv"
+	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
-	"github.com/google/uuid"
 	"gitlab.michelsen.id/phillmichelsen/tessera/pkg/data"
 	"gitlab.michelsen.id/phillmichelsen/tessera/pkg/data/routing"
 )
 
-type SeqPayload struct {
+/*
-	Seq uint64
+Realistic-ish market-data style test.
+
+Model:
+- 1 publisher per topic (instrument / feed partition)
+- Each message carries a strictly increasing sequence number (per topic)
+- Subscribers validate in-order, gap-free delivery
+- Publishers send with bursty pacing to approximate L3-ish behavior:
+  send BurstSize messages back-to-back, then sleep to maintain AvgRate.
+
+Defaults are intentionally moderate. Increase topics/rates to stress.
+*/
+
+const (
+	NumTopics       = 8 // topics/instruments/partitions
+	SubsPerTopic    = 6 // fan-out per topic
+	RingCapacity    = 1 << 14
+	TestDuration    = 60 * time.Second
+	AvgRatePerTopic = 500_000 // msgs/sec per topic (average)
+	BurstSize       = 512     // burst messages then sleep to preserve avg
+
+	// If true, subscribers spin-poll (TryReceive). If false, blocking Receive.
+	UseTryReceive = false
+)
+
+type topicStats struct {
+	published atomic.Uint64
 }
 
-type streamStats struct {
+type subStats struct {
-	sent       uint64
+	received atomic.Uint64
-	observed   uint64
+	errors   atomic.Uint64
-	missed     uint64
-	lastSeen   uint64
-	lastReport time.Time
 }
 
 func main() {
-	ctx := context.Background()
+	fmt.Printf("Market-Data Routing Test\n")
+	fmt.Printf("Topics: %d | Subs/Topic: %d | Duration: %v\n", NumTopics, SubsPerTopic, TestDuration)
+	fmt.Printf("AvgRate/Topic: %d msg/s | BurstSize: %d | Mode: %s\n\n",
+		AvgRatePerTopic, BurstSize, modeName())
 
-	// ---- Knobs ----
+	broker := routing.NewBroker()
-	N := 10
-	duration := 5 * time.Second
-	totalTargetPerSec := 5_000 // total across all streams
-	// ----------------
 
-	rt := routing.NewInprocRouter()
+	topics := make([]string, NumTopics)
+	for i := 0; i < NumTopics; i++ {
+		topics[i] = fmt.Sprintf("FUT_L3_%02d", i)
+	}
 
-	senders := make([]data.Sender, N)
+	// Create publishers first to size the rings.
-	receivers := make([]data.Receiver, N)
+	pubs := make([]routing.Publisher, NumTopics)
+	for i := 0; i < NumTopics; i++ {
+		pubs[i] = broker.RegisterPublisher(topics[i], RingCapacity)
+	}
 
-	for i := range N {
+	// Per-topic published counters (ground truth).
-		st, err := rt.OpenStream(data.StreamID(uuid.New()))
+	tStats := make([]*topicStats, NumTopics)
-		if err != nil {
+	for i := range tStats {
-			panic(err)
+		tStats[i] = &topicStats{}
-		}
+	}
-		senders[i] = st.Sender()
+
-		receivers[i] = st.Receiver()
+	// Subscribers: attach evenly, validate ordering.
-	}
+	var subsWG sync.WaitGroup
-
+	sStats := make([][]*subStats, NumTopics) // [topic][sub]
-	perStreamTarget := totalTargetPerSec / N
+	for ti := 0; ti < NumTopics; ti++ {
-	if perStreamTarget == 0 {
+		sStats[ti] = make([]*subStats, SubsPerTopic)
-		perStreamTarget = 1
+		for si := 0; si < SubsPerTopic; si++ {
-	}
+			sStats[ti][si] = &subStats{}
-
+		}
-	fmt.Printf("N=%d duration=%s totalTarget=%d/s perStreamTarget=%d/s\n",
+	}
-		N, duration, totalTargetPerSec, perStreamTarget)
+
-
+	ctx, cancel := context.WithTimeout(context.Background(), TestDuration)
-	stopAt := time.Now().Add(duration)
+	defer cancel()
-
+
-	stats := make([]streamStats, N)
+	start := time.Now()
-
+
-	var wg sync.WaitGroup
+	for ti := 0; ti < NumTopics; ti++ {
-	wg.Add(N + 1)
+		topic := topics[ti]
-
+		for si := 0; si < SubsPerTopic; si++ {
-	// Publisher: per-stream sender sequence in envelope payload.
+			sub := broker.RegisterSubscriber(topic)
-	go func() {
+			stats := sStats[ti][si]
-		defer wg.Done()
+			subsWG.Add(1)
-
+
-		tick := time.NewTicker(1 * time.Millisecond)
+			go func(topicIndex int, subIndex int, subscriber routing.Subscriber, st *subStats) {
-		defer tick.Stop()
+				defer subsWG.Done()
-
+
-		perTick := perStreamTarget / 1000
+				var expected uint64 = 0
-		rem := perStreamTarget % 1000
+
-		remAcc := make([]int, N)
+				for {
-
+					if ctx.Err() != nil {
-		seq := make([]uint64, N)
+						return
-
+					}
-		for time.Now().Before(stopAt) {
+
-			<-tick.C
+					var (
-
+						env data.Envelope
-			for i := range N {
+						ok  bool
-				n := int(perTick)
+						err error
-				remAcc[i] += rem
+					)
-				if remAcc[i] >= 1000 {
+
-					n++
+					if UseTryReceive {
-					remAcc[i] -= 1000
+						env, ok, err = subscriber.TryReceive()
-				}
-
-				for j := 0; j < n; j++ {
-					seq[i]++
-
-					env := data.Envelope{
-						Payload: SeqPayload{Seq: seq[i]},
-					}
-					_ = senders[i].Send(ctx, env)
-					stats[i].sent++
-				}
-			}
-		}
-	}()
-
-	// Consumers: detect missed sender sequence numbers.
-	for i := range N {
-		idx := i
-		rx := receivers[i]
-
-		go func() {
-			defer wg.Done()
-
-			for time.Now().Before(stopAt) {
-				env, ok, err := rx.TryReceive()
 						if err != nil {
+							st.errors.Add(1)
+							cancel()
 							return
 						}
 						if !ok {
+							runtime.Gosched()
 							continue
 						}
+					} else {
+						env, err = subscriber.Receive(ctx)
+						if err != nil {
+							// Context cancellation is normal at end of test.
+							if ctx.Err() != nil {
+								return
+							}
+							st.errors.Add(1)
+							cancel()
+							return
+						}
+					}
 
-				p, ok := env.Payload.(SeqPayload)
+					seq, parseOK := parseSeq(env)
+					if !parseOK {
+						st.errors.Add(1)
+						cancel()
+						return
+					}
+
+					if seq != expected {
+						// Out-of-order or gap detected.
+						st.errors.Add(1)
+						cancel()
+						return
+					}
+
+					expected++
+					st.received.Add(1)
+				}
+			}(ti, si, sub, stats)
+		}
+	}
+
+	// Publishers: bursty pacing to approximate “average rate with bursts”.
+	var pubsWG sync.WaitGroup
+	for ti := 0; ti < NumTopics; ti++ {
+		pub := pubs[ti]
+		stats := tStats[ti]
+		pubsWG.Add(1)
+
+		go func(topicIndex int, p routing.Publisher, st *topicStats) {
+			defer pubsWG.Done()
+
+			// Maintain AvgRatePerTopic as an average by sleeping after bursts.
+			// burstDuration = BurstSize / AvgRatePerTopic seconds
+			burstNs := int64(0)
+			if AvgRatePerTopic > 0 {
+				burstNs = int64(time.Second) * int64(BurstSize) / int64(AvgRatePerTopic)
+			}
+			if burstNs <= 0 {
+				burstNs = 1
+			}
+
+			var seq uint64 = 0
+
+			// Optional small jitter to avoid perfect lockstep across topics.
+			jitter := time.Duration(rand.Intn(200)) * time.Microsecond
+
+			nextBurstAt := time.Now().Add(jitter)
+
+			for {
+				if ctx.Err() != nil {
+					return
+				}
+
+				now := time.Now()
+				if now.Before(nextBurstAt) {
+					time.Sleep(nextBurstAt.Sub(now))
+				}
+
+				// Send BurstSize messages back-to-back.
+				sendTime := time.Now()
+				for i := 0; i < BurstSize; i++ {
+					if ctx.Err() != nil {
+						return
+					}
+
+					env := data.Envelope{
+						SendTime:   sendTime,
+						Descriptor: data.Descriptor{Key: "SEQ"}, // keep your existing descriptor usage
+						Payload:    formatSeq(seq),
+						// Any other fields you use can be set here.
+					}
+
+					p.Publish(env)
+					seq++
+				}
+				st.published.Add(uint64(BurstSize))
+
+				// Schedule next burst to maintain average rate.
+				nextBurstAt = nextBurstAt.Add(time.Duration(burstNs))
+			}
+		}(ti, pub, stats)
+	}
+
+	// Wait for timeout, then stop and drain.
+	<-ctx.Done()
+
+	// Ensure publishers exit.
+	pubsWG.Wait()
+
+	// Subscribers may still be blocked; cancel again and wait.
+	cancel()
+	subsWG.Wait()
+
+	totalTime := time.Since(start)
+
+	// Report.
+	var totalPublished uint64
+	var totalReceived uint64
+	var totalErrors uint64
+
+	for ti := 0; ti < NumTopics; ti++ {
+		pub := tStats[ti].published.Load()
+		totalPublished += pub
+
+		var topicRecv uint64
+		var topicErr uint64
+		for si := 0; si < SubsPerTopic; si++ {
+			topicRecv += sStats[ti][si].received.Load()
+			topicErr += sStats[ti][si].errors.Load()
+		}
+		totalReceived += topicRecv
+		totalErrors += topicErr
+
+		// Each subscriber should have received ~published for that topic.
+		avgPerSub := uint64(0)
+		if SubsPerTopic > 0 {
+			avgPerSub = topicRecv / uint64(SubsPerTopic)
+		}
+
+		fmt.Printf("Topic %s: published=%d | avg_received_per_sub=%d | sub_errors=%d\n",
+			topics[ti], pub, avgPerSub, topicErr)
+	}
+
+	pubRate := float64(totalPublished) / totalTime.Seconds()
+	deliveriesRate := float64(totalReceived) / totalTime.Seconds()
+
+	fmt.Printf("\nTotal Time:        %v\n", totalTime)
+	fmt.Printf("Total Published:   %d msgs\n", totalPublished)
+	fmt.Printf("Total Deliveries:  %d (published * subs/topic, minus cancellations)\n", totalReceived)
+	fmt.Printf("Publish Rate:      %.2f msgs/sec (aggregate)\n", pubRate)
+	fmt.Printf("Delivery Rate:     %.2f deliveries/sec (aggregate)\n", deliveriesRate)
+	fmt.Printf("Validation Errors: %d\n", totalErrors)
+
+	if totalErrors == 0 {
+		fmt.Printf("Result: PASS (in-order, gap-free until cancellation)\n")
+	} else {
+		fmt.Printf("Result: FAIL (see errors above; test cancels on first detected issue)\n")
+	}
+}
+
+func modeName() string {
+	if UseTryReceive {
+		return "TryReceive (spin)"
+	}
+	return "Receive (blocking)"
+}
+
+// formatSeq encodes the per-topic sequence into a string payload.
+// This compiles whether Envelope.Payload is string or interface{} accepting string.
+func formatSeq(seq uint64) string {
+	// Keep it cheap to parse: decimal only.
+	return strconv.FormatUint(seq, 10)
+}
+
+func parseSeq(env data.Envelope) (uint64, bool) {
+	// If you later switch Payload to a structured type, change this accordingly.
+	s, ok := env.Payload.(string)
 	if !ok {
-					// If your Payload is pointer/interface-heavy, adjust accordingly.
+		// If Payload is defined as string (not interface{}), remove this type assert and just use env.Payload.
-					continue
+		// This branch is for interface{} payloads where non-string could appear.
+		return 0, false
 	}
 
-				stats[idx].observed++
+	// Fast path: no extra fields.
-
+	// If you later include pubID:seq, you can parse with strings.Cut.
-				if stats[idx].lastSeen == 0 {
+	if strings.IndexByte(s, ':') >= 0 {
-					stats[idx].lastSeen = p.Seq
+		_, right, ok := strings.Cut(s, ":")
-					continue
+		if !ok {
+			return 0, false
+		}
+		s = right
 	}
 
-				if p.Seq > stats[idx].lastSeen+1 {
+	v, err := strconv.ParseUint(s, 10, 64)
-					stats[idx].missed += (p.Seq - stats[idx].lastSeen - 1)
+	return v, err == nil
-				}
-				stats[idx].lastSeen = p.Seq
-			}
-		}()
-	}
-
-	wg.Wait()
-
-	var totalSent, totalObs, totalMiss uint64
-	minDrop, maxDrop := 100.0, 0.0
-
-	for i := range N {
-		totalSent += stats[i].sent
-		totalObs += stats[i].observed
-		totalMiss += stats[i].missed
-
-		den := stats[i].observed + stats[i].missed
-		dropPct := 0.0
-		if den > 0 {
-			dropPct = 100.0 * float64(stats[i].missed) / float64(den)
-		}
-		if dropPct < minDrop {
-			minDrop = dropPct
-		}
-		if dropPct > maxDrop {
-			maxDrop = dropPct
-		}
-
-		fmt.Printf("stream[%02d] sent=%6d observed=%6d missed=%6d lastSeen=%6d drop=%5.2f%%\n",
-			i, stats[i].sent, stats[i].observed, stats[i].missed, stats[i].lastSeen, dropPct)
-	}
-
-	totalDen := totalObs + totalMiss
-	totalDrop := 0.0
-	if totalDen > 0 {
-		totalDrop = 100.0 * float64(totalMiss) / float64(totalDen)
-	}
-
-	fmt.Printf("\nTOTAL sent=%d observed=%d missed=%d drop=%.2f%% (min=%.2f%% max=%.2f%%)\n",
-		totalSent, totalObs, totalMiss, totalDrop, minDrop, maxDrop)
 }

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,
+	}
+}

pkg/data/routing/inproc.go

@@ -1,130 +0,0 @@
-package routing
-
-import (
-	"context"
-	"errors"
-	"sync"
-	"time"
-
-	"gitlab.michelsen.id/phillmichelsen/tessera/pkg/data"
-)
-
-type InprocRouter struct {
-	mu      sync.RWMutex
-	streams map[data.StreamID]*inprocStream
-}
-
-func NewInprocRouter() *InprocRouter {
-	return &InprocRouter{
-		streams: make(map[data.StreamID]*inprocStream),
-	}
-}
-
-func (r *InprocRouter) OpenStream(id data.StreamID) (data.Stream, error) {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-
-	s := r.streams[id]
-	if s != nil {
-		return s, nil
-	}
-
-	s = newInprocStream(id)
-	r.streams[id] = s
-	return s, nil
-}
-
-type inprocStream struct {
-	id data.StreamID
-
-	seq    uint64
-	latest data.Envelope
-
-	streamClosed bool
-	mu           sync.RWMutex
-}
-
-func newInprocStream(id data.StreamID) *inprocStream {
-	return &inprocStream{
-		id: id,
-	}
-}
-
-func (s *inprocStream) ID() data.StreamID {
-	return s.id
-}
-
-func (s *inprocStream) Sender() data.Sender {
-	return &inprocSender{stream: s}
-}
-
-func (s *inprocStream) Receiver() data.Receiver {
-	s.mu.RLock()
-	cur := s.seq
-	s.mu.RUnlock()
-
-	return &inprocReceiver{
-		stream:      s,
-		lastSeenSeq: cur,
-	}
-
-}
-
-type inprocSender struct {
-	stream *inprocStream
-}
-
-func (tx *inprocSender) Send(ctx context.Context, env data.Envelope) error {
-	if err := ctx.Err(); err != nil {
-		return err
-	}
-
-	s := tx.stream
-	s.mu.Lock()
-	defer s.mu.Unlock()
-
-	if s.streamClosed {
-		return errors.New("stream closed")
-	}
-
-	env.SendTime = time.Now().UTC()
-
-	s.seq++
-	s.latest = env
-
-	return nil
-}
-
-func (tx *inprocSender) SendBatch(ctx context.Context, envs []data.Envelope) error {
-	panic("unimplemented")
-}
-
-type inprocReceiver struct {
-	stream      *inprocStream
-	lastSeenSeq uint64
-}
-
-func (rx *inprocReceiver) TryReceive() (data.Envelope, bool, error) {
-	s := rx.stream
-	s.mu.RLock()
-	defer s.mu.RUnlock()
-
-	if s.streamClosed {
-		return data.Envelope{}, false, errors.New("stream closed")
-	}
-
-	if s.seq == 0 || s.seq == rx.lastSeenSeq {
-		return data.Envelope{}, false, nil
-	}
-
-	rx.lastSeenSeq = s.seq
-	return s.latest, true, nil
-}
-
-func (rx *inprocReceiver) ReceiveNext(ctx context.Context) (data.Envelope, error) {
-	panic("unimplemented")
-}
-
-func (rx *inprocReceiver) Seq() uint64 {
-	return rx.lastSeenSeq
-}

pkg/data/routing/interfaces.go

@@ -0,0 +1,25 @@
+package routing
+
+import (
+	"context"
+
+	"gitlab.michelsen.id/phillmichelsen/tessera/pkg/data"
+)
+
+// Publisher is the write-side handle given to data sources.
+type Publisher interface {
+	Publish(env data.Envelope)
+}
+
+// Subscriber is the read-side handle given to consumers (data sinks).
+type Subscriber interface {
+	// Receive blocks until a message is available or the context cancels.
+	// Best for general low-latency consumers that shouldn't burn CPU.
+	// Typically more than enough for most situations
+	Receive(ctx context.Context) (data.Envelope, error)
+
+	// TryReceive attempts to read one message lock-free.
+	// Returns (envelope, true, nil) if successful, or false if nothing is available.
+	// Polling TryReceive without a wait will most likely spike the CPU
+	TryReceive() (data.Envelope, bool, error)
+}

pkg/data/routing/router.go

@@ -0,0 +1,201 @@
+// router.go
+package routing
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"sync/atomic"
+
+	"gitlab.michelsen.id/phillmichelsen/tessera/pkg/data"
+)
+
+var ErrDisconnected = errors.New("subscriber disconnected: failed to consume fast enough")
+
+// IMPLEMENTATIONS
+
+// Implements the Publisher interface
+type ringPublisher struct {
+	ring *TopicRing
+}
+
+func (p *ringPublisher) Publish(env data.Envelope) {
+	p.ring.publish(env)
+}
+
+// Implements the Subscriber interface
+type ringSubscriber struct {
+	ring     *TopicRing
+	consumer *ringConsumer
+}
+
+func (s *ringSubscriber) Receive(ctx context.Context) (data.Envelope, error) {
+	return s.ring.receive(ctx, s.consumer)
+}
+
+func (s *ringSubscriber) TryReceive() (data.Envelope, bool, error) {
+	return s.ring.tryReceive(s.consumer)
+}
+
+// ringConsumer represents a single subscriber's read state within a TopicRing
+// The 56-byte pads are added to prevent 'False Sharing' due to 64-byte cache sizes
+type ringConsumer struct {
+	ID uint64 // monotonically increasing identifier
+	_  [56]byte
+
+	Cursor atomic.Uint64 // next expected sequence number, advanced monotonically
+	_      [56]byte
+
+	Dead atomic.Bool // set true if the consumer has fallen behind ring capacity, consumer should be disconnected
+	_    [56]byte
+
+	notify chan struct{} // size-1 wakeup channel for subscribers to block whilst waiting for new data
+}
+
+// TopicRing is a broadcast ring buffer for a topic
+// It is designed to be minimize locks, same 56-byte pads used here as well
+// The publisher appends sequentially whilst each subscriber maintains its own cursor (ringConsumer)
+// We typically aim for a capacity that is power-of-two sized for reasons beyond my knowledge
+type TopicRing struct {
+	Capacity uint64
+	Mask     uint64
+	Ring     []data.Envelope
+
+	_         [56]byte
+	writeTail atomic.Uint64
+
+	_                 [56]byte
+	cachedMinConsumer uint64
+
+	consumers atomic.Pointer[[]*ringConsumer] // Copy-on-Write slice
+	mu        sync.Mutex
+	nextSubID uint64
+}
+
+// newTopicRing creates a TopicRing
+// The capacity should be specified as a power-of-two (as the N in 2^N)
+func newTopicRing(pow2 int) *TopicRing {
+	cap := uint64(1)
+	for cap < uint64(pow2) {
+		cap <<= 1
+	}
+	t := &TopicRing{
+		Capacity: cap,
+		Mask:     cap - 1,
+		Ring:     make([]data.Envelope, cap),
+	}
+
+	empty := make([]*ringConsumer, 0)
+	t.consumers.Store(&empty)
+	return t
+}
+
+// addConsumer registers a new subscriber on the ring
+// The consumer starts at the current write tail
+func (t *TopicRing) addConsumer() *ringConsumer {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	t.nextSubID++
+	c := &ringConsumer{
+		ID:     t.nextSubID,
+		notify: make(chan struct{}, 1),
+	}
+	// Start at the current write tail so we don't read historical data
+	c.Cursor.Store(t.writeTail.Load())
+
+	// Copy-on-write update
+	old := *t.consumers.Load()
+	newSubs := make([]*ringConsumer, len(old), len(old)+1)
+	copy(newSubs, old)
+	newSubs = append(newSubs, c)
+	t.consumers.Store(&newSubs)
+
+	return c
+}
+
+// publish appends one message to the ring and notifies subscribers (with the 'notify' channel)
+// Assumes a single publisher per topic
+func (t *TopicRing) publish(env data.Envelope) {
+	seq := t.writeTail.Load() // we expect only one publisher per topic
+	// in the case we do want more than one publisher, switch to using atomic.AddUint64
+
+	if seq-t.cachedMinConsumer >= t.Capacity {
+		t.enforceCapacity(seq)
+	}
+
+	t.Ring[seq&t.Mask] = env
+
+	t.writeTail.Store(seq + 1)
+
+	subs := *t.consumers.Load()
+	for _, c := range subs {
+		select {
+		case c.notify <- struct{}{}:
+		default:
+		}
+	}
+}
+
+// enforceCapacity 'evicts' consumers that have fallen beyond the ring capacity
+func (t *TopicRing) enforceCapacity(targetSeq uint64) {
+	subs := *t.consumers.Load()
+	newMin := targetSeq
+
+	for _, c := range subs {
+		if c.Dead.Load() {
+			continue
+		}
+		cCursor := c.Cursor.Load()
+		if targetSeq-cCursor >= t.Capacity {
+			c.Dead.Store(true) // Evict slow consumer
+		} else if cCursor < newMin {
+			newMin = cCursor
+		}
+	}
+	t.cachedMinConsumer = newMin
+}
+
+// receive blocks until a new message is available, the consumer is evicted, or the context is cancelled
+// Ordering is preserved per consumer (naturally)
+func (t *TopicRing) receive(ctx context.Context, c *ringConsumer) (data.Envelope, error) {
+	for {
+		if c.Dead.Load() {
+			return data.Envelope{}, ErrDisconnected
+		}
+
+		currentCursor := c.Cursor.Load()
+		availableTail := t.writeTail.Load()
+
+		if currentCursor < availableTail {
+			env := t.Ring[currentCursor&t.Mask]
+			c.Cursor.Store(currentCursor + 1)
+			return env, nil
+		}
+
+		select {
+		case <-ctx.Done():
+			return data.Envelope{}, ctx.Err()
+		case <-c.notify:
+		}
+	}
+}
+
+// tryReceive is a non-blocking variant of receive
+// Returns immediately if no new data is available
+func (t *TopicRing) tryReceive(c *ringConsumer) (data.Envelope, bool, error) {
+	if c.Dead.Load() {
+		return data.Envelope{}, false, ErrDisconnected
+	}
+
+	currentCursor := c.Cursor.Load()
+	availableTail := t.writeTail.Load()
+
+	if currentCursor >= availableTail {
+		return data.Envelope{}, false, nil
+	}
+
+	env := t.Ring[currentCursor&t.Mask]
+	c.Cursor.Store(currentCursor + 1)
+	return env, true, nil
+}