fix: race condition in unsubscribe (#197)

waku/v2/broadcast.go

@@ -7,10 +7,17 @@ import (
 // Adapted from https://github.com/dustin/go-broadcast/commit/f664265f5a662fb4d1df7f3533b1e8d0e0277120
 // by Dustin Sallings (c) 2013, which was released under MIT license
 
+type doneCh chan struct{}
+
+type chOperation struct {
+	ch   chan<- *protocol.Envelope
+	done doneCh
+}
+
 type broadcaster struct {
 	input chan *protocol.Envelope
-	reg   chan chan<- *protocol.Envelope
-	unreg chan chan<- *protocol.Envelope
+	reg   chan chOperation
+	unreg chan chOperation
 
 	outputs map[chan<- *protocol.Envelope]bool
 }
@@ -20,8 +27,12 @@ type broadcaster struct {
 type Broadcaster interface {
 	// Register a new channel to receive broadcasts
 	Register(chan<- *protocol.Envelope)
+	// Register a new channel to receive broadcasts and return a channel to wait until this operation is complete
+	WaitRegister(newch chan<- *protocol.Envelope) doneCh
 	// Unregister a channel so that it no longer receives broadcasts.
 	Unregister(chan<- *protocol.Envelope)
+	// Unregister a subscriptor channel and return a channel to wait until this operation is done
+	WaitUnregister(newch chan<- *protocol.Envelope) doneCh
 	// Shut this broadcaster down.
 	Close()
 	// Submit a new object to all subscribers
@@ -39,14 +50,23 @@ func (b *broadcaster) run() {
 		select {
 		case m := <-b.input:
 			b.broadcast(m)
-		case ch, ok := <-b.reg:
+		case broadcastee, ok := <-b.reg:
 			if ok {
-				b.outputs[ch] = true
+				b.outputs[broadcastee.ch] = true
+				if broadcastee.done != nil {
+					broadcastee.done <- struct{}{}
+				}
 			} else {
+				if broadcastee.done != nil {
+					broadcastee.done <- struct{}{}
+				}
 				return
 			}
-		case ch := <-b.unreg:
-			delete(b.outputs, ch)
+		case broadcastee := <-b.unreg:
+			delete(b.outputs, broadcastee.ch)
+			if broadcastee.done != nil {
+				broadcastee.done <- struct{}{}
+			}
 		}
 	}
 }
@@ -57,8 +77,8 @@ func (b *broadcaster) run() {
 func NewBroadcaster(buflen int) Broadcaster {
 	b := &broadcaster{
 		input:   make(chan *protocol.Envelope, buflen),
-		reg:     make(chan chan<- *protocol.Envelope),
-		unreg:   make(chan chan<- *protocol.Envelope),
+		reg:     make(chan chOperation),
+		unreg:   make(chan chOperation),
 		outputs: make(map[chan<- *protocol.Envelope]bool),
 	}
 
@@ -67,14 +87,40 @@ func NewBroadcaster(buflen int) Broadcaster {
 	return b
 }
 
+// Register a subscriptor channel and return a channel to wait until this operation is done
+func (b *broadcaster) WaitRegister(newch chan<- *protocol.Envelope) doneCh {
+	d := make(doneCh)
+	b.reg <- chOperation{
+		ch:   newch,
+		done: d,
+	}
+	return d
+}
+
 // Register a subscriptor channel
 func (b *broadcaster) Register(newch chan<- *protocol.Envelope) {
-	b.reg <- newch
+	b.reg <- chOperation{
+		ch:   newch,
+		done: nil,
+	}
+}
+
+// Unregister a subscriptor channel and return a channel to wait until this operation is done
+func (b *broadcaster) WaitUnregister(newch chan<- *protocol.Envelope) doneCh {
+	d := make(doneCh)
+	b.unreg <- chOperation{
+		ch:   newch,
+		done: d,
+	}
+	return d
 }
 
 // Unregister a subscriptor channel
 func (b *broadcaster) Unregister(newch chan<- *protocol.Envelope) {
-	b.unreg <- newch
+	b.unreg <- chOperation{
+		ch:   newch,
+		done: nil,
+	}
 }
 
 // Closes the broadcaster. Used to stop receiving new subscribers

waku/v2/broadcast_test.go

@@ -37,6 +37,33 @@ func TestBroadcast(t *testing.T) {
 	wg.Wait()
 }
 
+func TestBroadcastWait(t *testing.T) {
+	wg := sync.WaitGroup{}
+
+	b := NewBroadcaster(100)
+	defer b.Close()
+
+	for i := 0; i < 5; i++ {
+		wg.Add(1)
+
+		cch := make(chan *protocol.Envelope)
+		<-b.WaitRegister(cch)
+
+		go func() {
+			defer wg.Done()
+
+			<-cch
+			<-b.WaitUnregister(cch)
+		}()
+
+	}
+
+	env := new(protocol.Envelope)
+	b.Submit(env)
+
+	wg.Wait()
+}
+
 func TestBroadcastCleanup(t *testing.T) {
 	b := NewBroadcaster(100)
 	b.Register(make(chan *protocol.Envelope))

waku/v2/protocol/relay/subscription.go

@@ -8,6 +8,8 @@ import (
 
 // Subscription handles the subscrition to a particular pubsub topic
 type Subscription struct {
+	sync.RWMutex
+
 	// C is channel used for receiving envelopes
 	C chan *protocol.Envelope
 
@@ -19,14 +21,14 @@ type Subscription struct {
 // Unsubscribe will close a subscription from a pubsub topic. Will close the message channel
 func (subs *Subscription) Unsubscribe() {
 	subs.once.Do(func() {
-		subs.closed = true
 		close(subs.quit)
-		close(subs.C)
-
 	})
+
 }
 
 // IsClosed determine whether a Subscription is still open for receiving messages
 func (subs *Subscription) IsClosed() bool {
+	subs.RLock()
+	defer subs.RUnlock()
 	return subs.closed
 }

waku/v2/protocol/relay/subscription_test.go

@@ -1,18 +0,0 @@
-package relay
-
-import (
-	"testing"
-
-	waku_proto "github.com/status-im/go-waku/waku/v2/protocol"
-	"github.com/stretchr/testify/require"
-)
-
-func TestSubscription(t *testing.T) {
-	e := Subscription{
-		closed: false,
-		C:      make(chan *waku_proto.Envelope, 10),
-		quit:   make(chan struct{}),
-	}
-	e.Unsubscribe()
-	require.True(t, e.closed)
-}

waku/v2/protocol/relay/waku_relay.go

@@ -300,9 +300,20 @@ func (w *WakuRelay) subscribeToTopic(t string, subscription *Subscription, sub *
 	for {
 		select {
 		case <-subscription.quit:
-			if w.bcaster != nil {
-				w.bcaster.Unregister(subscription.C) // Remove from broadcast list
+			func() {
+				subscription.Lock()
+				defer subscription.Unlock()
+
+				if subscription.closed {
+					return
 				}
+				subscription.closed = true
+				if w.bcaster != nil {
+					<-w.bcaster.WaitUnregister(subscription.C) // Remove from broadcast list
+				}
+
+				close(subscription.C)
+			}()
 			// TODO: if there are no more relay subscriptions, close the pubsub subscription
 		case msg := <-subChannel:
 			if msg == nil {