chore: export MsgQueue from pubsub package (#25707)

<!--

If you have used AI to produce some or all of this PR, please ensure you have read our [AI Contribution guidelines](https://coder.com/docs/about/contributing/AI_CONTRIBUTING) before submitting.

-->

Makes `MsgQueue` exported, so it can be used in pubsub implementations outside PGPubsub.

coderd/database/pubsub/pubsub.go

@@ -56,14 +56,14 @@ type msgOrErr struct {
 	err error
 }
 
-// msgQueue implements a fixed length queue with the ability to replace elements
+// MsgQueue implements a fixed length queue with the ability to replace elements
 // after they are queued (but before they are dequeued).
 //
 // The purpose of this data structure is to build something that works a bit
 // like a golang channel, but if the queue is full, then we can replace the
 // last element with an error so that the subscriber can get notified that some
 // messages were dropped, all without blocking.
-type msgQueue struct {
+type MsgQueue struct {
 	ctx    context.Context
 	cond   *sync.Cond
 	q      [BufferSize]msgOrErr
@@ -74,11 +74,11 @@ type msgQueue struct {
 	le     ListenerWithErr
 }
 
-func newMsgQueue(ctx context.Context, l Listener, le ListenerWithErr) *msgQueue {
+func NewMsgQueue(ctx context.Context, l Listener, le ListenerWithErr) *MsgQueue {
 	if l == nil && le == nil {
 		panic("l or le must be non-nil")
 	}
-	q := &msgQueue{
+	q := &MsgQueue{
 		ctx:  ctx,
 		cond: sync.NewCond(&sync.Mutex{}),
 		l:    l,
@@ -88,7 +88,7 @@ func newMsgQueue(ctx context.Context, l Listener, le ListenerWithErr) *msgQueue
 	return q
 }
 
-func (q *msgQueue) run() {
+func (q *MsgQueue) run() {
 	for {
 		// wait until there is something on the queue or we are closed
 		q.cond.L.Lock()
@@ -125,7 +125,7 @@ func (q *msgQueue) run() {
 	}
 }
 
-func (q *msgQueue) enqueue(msg []byte) {
+func (q *MsgQueue) Enqueue(msg []byte) {
 	q.cond.L.Lock()
 	defer q.cond.L.Unlock()
 
@@ -149,15 +149,15 @@ func (q *msgQueue) enqueue(msg []byte) {
 	q.cond.Broadcast()
 }
 
-func (q *msgQueue) close() {
+func (q *MsgQueue) Close() {
 	q.cond.L.Lock()
 	defer q.cond.L.Unlock()
 	defer q.cond.Broadcast()
 	q.closed = true
 }
 
-// dropped records an error in the queue that messages might have been dropped
-func (q *msgQueue) dropped() {
+// Dropped records an error in the queue that messages might have been Dropped
+func (q *MsgQueue) Dropped() {
 	q.cond.L.Lock()
 	defer q.cond.L.Unlock()
 
@@ -195,7 +195,7 @@ func (l pqListenerShim) NotifyChan() <-chan *pq.Notification {
 }
 
 type queueSet struct {
-	m map[*msgQueue]struct{}
+	m map[*MsgQueue]struct{}
 	// unlistenInProgress will be non-nil if another goroutine is unlistening for the event this
 	// queueSet corresponds to. If non-nil, that goroutine will close the channel when it is done.
 	unlistenInProgress chan struct{}
@@ -203,7 +203,7 @@ type queueSet struct {
 
 func newQueueSet() *queueSet {
 	return &queueSet{
-		m: make(map[*msgQueue]struct{}),
+		m: make(map[*MsgQueue]struct{}),
 	}
 }
 
@@ -243,19 +243,19 @@ const BufferSize = 2048
 
 // Subscribe calls the listener when an event matching the name is received.
 func (p *PGPubsub) Subscribe(event string, listener Listener) (cancel func(), err error) {
-	return p.subscribeQueue(event, newMsgQueue(context.Background(), listener, nil))
+	return p.subscribeQueue(event, NewMsgQueue(context.Background(), listener, nil))
 }
 
 func (p *PGPubsub) SubscribeWithErr(event string, listener ListenerWithErr) (cancel func(), err error) {
-	return p.subscribeQueue(event, newMsgQueue(context.Background(), nil, listener))
+	return p.subscribeQueue(event, NewMsgQueue(context.Background(), nil, listener))
 }
 
-func (p *PGPubsub) subscribeQueue(event string, newQ *msgQueue) (cancel func(), err error) {
+func (p *PGPubsub) subscribeQueue(event string, newQ *MsgQueue) (cancel func(), err error) {
 	defer func() {
 		if err != nil {
 			// if we hit an error, we need to close the queue so we don't
 			// leak its goroutine.
-			newQ.close()
+			newQ.Close()
 			p.subscribesTotal.WithLabelValues("false").Inc()
 		} else {
 			p.subscribesTotal.WithLabelValues("true").Inc()
@@ -325,7 +325,7 @@ func (p *PGPubsub) subscribeQueue(event string, newQ *msgQueue) (cancel func(),
 		func() {
 			p.qMu.Lock()
 			defer p.qMu.Unlock()
-			newQ.close()
+			newQ.Close()
 			qSet, ok := p.queues[event]
 			if !ok {
 				p.logger.Critical(context.Background(), "event was removed before cancel", slog.F("event", event))
@@ -436,7 +436,7 @@ func (p *PGPubsub) listenReceive(notif *pq.Notification) {
 	}
 	extra := []byte(notif.Extra)
 	for q := range qSet.m {
-		q.enqueue(extra)
+		q.Enqueue(extra)
 	}
 }
 
@@ -445,7 +445,7 @@ func (p *PGPubsub) recordReconnect() {
 	defer p.qMu.Unlock()
 	for _, qSet := range p.queues {
 		for q := range qSet.m {
-			q.dropped()
+			q.Dropped()
 		}
 	}
 }

coderd/database/pubsub/pubsub_internal_test.go

@@ -13,135 +13,6 @@ import (
 	"github.com/coder/coder/v2/testutil"
 )
 
-func Test_msgQueue_ListenerWithError(t *testing.T) {
-	t.Parallel()
-	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
-	defer cancel()
-	m := make(chan string)
-	e := make(chan error)
-	uut := newMsgQueue(ctx, nil, func(ctx context.Context, msg []byte, err error) {
-		m <- string(msg)
-		e <- err
-	})
-	defer uut.close()
-
-	// We're going to enqueue 4 messages and an error in a loop -- that is, a cycle of 5.
-	// PubsubBufferSize is 2048, which is a power of 2, so a pattern of 5 will not be aligned
-	// when we wrap around the end of the circular buffer.  This tests that we correctly handle
-	// the wrapping and aren't dequeueing misaligned data.
-	cycles := (BufferSize / 5) * 2 // almost twice around the ring
-	for j := 0; j < cycles; j++ {
-		for i := 0; i < 4; i++ {
-			uut.enqueue([]byte(fmt.Sprintf("%d%d", j, i)))
-		}
-		uut.dropped()
-		for i := 0; i < 4; i++ {
-			select {
-			case <-ctx.Done():
-				t.Fatal("timed out")
-			case msg := <-m:
-				require.Equal(t, fmt.Sprintf("%d%d", j, i), msg)
-			}
-			select {
-			case <-ctx.Done():
-				t.Fatal("timed out")
-			case err := <-e:
-				require.NoError(t, err)
-			}
-		}
-		select {
-		case <-ctx.Done():
-			t.Fatal("timed out")
-		case msg := <-m:
-			require.Equal(t, "", msg)
-		}
-		select {
-		case <-ctx.Done():
-			t.Fatal("timed out")
-		case err := <-e:
-			require.ErrorIs(t, err, ErrDroppedMessages)
-		}
-	}
-}
-
-func Test_msgQueue_Listener(t *testing.T) {
-	t.Parallel()
-	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
-	defer cancel()
-	m := make(chan string)
-	uut := newMsgQueue(ctx, func(ctx context.Context, msg []byte) {
-		m <- string(msg)
-	}, nil)
-	defer uut.close()
-
-	// We're going to enqueue 4 messages and an error in a loop -- that is, a cycle of 5.
-	// PubsubBufferSize is 2048, which is a power of 2, so a pattern of 5 will not be aligned
-	// when we wrap around the end of the circular buffer.  This tests that we correctly handle
-	// the wrapping and aren't dequeueing misaligned data.
-	cycles := (BufferSize / 5) * 2 // almost twice around the ring
-	for j := 0; j < cycles; j++ {
-		for i := 0; i < 4; i++ {
-			uut.enqueue([]byte(fmt.Sprintf("%d%d", j, i)))
-		}
-		uut.dropped()
-		for i := 0; i < 4; i++ {
-			select {
-			case <-ctx.Done():
-				t.Fatal("timed out")
-			case msg := <-m:
-				require.Equal(t, fmt.Sprintf("%d%d", j, i), msg)
-			}
-		}
-		// Listener skips over errors, so we only read out the 4 real messages.
-	}
-}
-
-func Test_msgQueue_Full(t *testing.T) {
-	t.Parallel()
-	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
-	defer cancel()
-
-	firstDequeue := make(chan struct{})
-	allowRead := make(chan struct{})
-	n := 0
-	errors := make(chan error)
-	uut := newMsgQueue(ctx, nil, func(ctx context.Context, msg []byte, err error) {
-		if n == 0 {
-			close(firstDequeue)
-		}
-		<-allowRead
-		if err == nil {
-			require.Equal(t, fmt.Sprintf("%d", n), string(msg))
-			n++
-			return
-		}
-		errors <- err
-	})
-	defer uut.close()
-
-	// we send 2 more than the capacity.  One extra because the call to the ListenerFunc blocks
-	// but only after we've dequeued a message, and then another extra because we want to exceed
-	// the capacity, not just reach it.
-	for i := 0; i < BufferSize+2; i++ {
-		uut.enqueue([]byte(fmt.Sprintf("%d", i)))
-		// ensure the first dequeue has happened before proceeding, so that this function isn't racing
-		// against the goroutine that dequeues items.
-		<-firstDequeue
-	}
-	close(allowRead)
-
-	select {
-	case <-ctx.Done():
-		t.Fatal("timed out")
-	case err := <-errors:
-		require.ErrorIs(t, err, ErrDroppedMessages)
-	}
-	// Ok, so we sent 2 more than capacity, but we only read the capacity, that's because the last
-	// message we send doesn't get queued, AND, it bumps a message out of the queue to make room
-	// for the error, so we read 2 less than we sent.
-	require.Equal(t, BufferSize, n)
-}
-
 func TestPubSub_DoesntBlockNotify(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Context(t, testutil.WaitShort)

coderd/database/pubsub/pubsub_test.go

@@ -3,6 +3,7 @@ package pubsub_test
 import (
 	"context"
 	"database/sql"
+	"fmt"
 	"testing"
 	"time"
 
@@ -201,3 +202,132 @@ func TestPGPubsubDriver(t *testing.T) {
 		}
 	}, testutil.IntervalMedium, "subscriber did not receive message after reconnect")
 }
+
+func Test_MsgQueue_ListenerWithError(t *testing.T) {
+	t.Parallel()
+	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
+	defer cancel()
+	m := make(chan string)
+	e := make(chan error)
+	uut := pubsub.NewMsgQueue(ctx, nil, func(ctx context.Context, msg []byte, err error) {
+		m <- string(msg)
+		e <- err
+	})
+	defer uut.Close()
+
+	// We're going to enqueue 4 messages and an error in a loop -- that is, a cycle of 5.
+	// PubsubBufferSize is 2048, which is a power of 2, so a pattern of 5 will not be aligned
+	// when we wrap around the end of the circular buffer.  This tests that we correctly handle
+	// the wrapping and aren't dequeueing misaligned data.
+	cycles := (pubsub.BufferSize / 5) * 2 // almost twice around the ring
+	for j := 0; j < cycles; j++ {
+		for i := 0; i < 4; i++ {
+			uut.Enqueue([]byte(fmt.Sprintf("%d%d", j, i)))
+		}
+		uut.Dropped()
+		for i := 0; i < 4; i++ {
+			select {
+			case <-ctx.Done():
+				t.Fatal("timed out")
+			case msg := <-m:
+				require.Equal(t, fmt.Sprintf("%d%d", j, i), msg)
+			}
+			select {
+			case <-ctx.Done():
+				t.Fatal("timed out")
+			case err := <-e:
+				require.NoError(t, err)
+			}
+		}
+		select {
+		case <-ctx.Done():
+			t.Fatal("timed out")
+		case msg := <-m:
+			require.Equal(t, "", msg)
+		}
+		select {
+		case <-ctx.Done():
+			t.Fatal("timed out")
+		case err := <-e:
+			require.ErrorIs(t, err, pubsub.ErrDroppedMessages)
+		}
+	}
+}
+
+func Test_MsgQueue_Listener(t *testing.T) {
+	t.Parallel()
+	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
+	defer cancel()
+	m := make(chan string)
+	uut := pubsub.NewMsgQueue(ctx, func(ctx context.Context, msg []byte) {
+		m <- string(msg)
+	}, nil)
+	defer uut.Close()
+
+	// We're going to enqueue 4 messages and an error in a loop -- that is, a cycle of 5.
+	// PubsubBufferSize is 2048, which is a power of 2, so a pattern of 5 will not be aligned
+	// when we wrap around the end of the circular buffer.  This tests that we correctly handle
+	// the wrapping and aren't dequeueing misaligned data.
+	cycles := (pubsub.BufferSize / 5) * 2 // almost twice around the ring
+	for j := 0; j < cycles; j++ {
+		for i := 0; i < 4; i++ {
+			uut.Enqueue([]byte(fmt.Sprintf("%d%d", j, i)))
+		}
+		uut.Dropped()
+		for i := 0; i < 4; i++ {
+			select {
+			case <-ctx.Done():
+				t.Fatal("timed out")
+			case msg := <-m:
+				require.Equal(t, fmt.Sprintf("%d%d", j, i), msg)
+			}
+		}
+		// Listener skips over errors, so we only read out the 4 real messages.
+	}
+}
+
+func Test_MsgQueue_Full(t *testing.T) {
+	t.Parallel()
+	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitShort)
+	defer cancel()
+
+	firstDequeue := make(chan struct{})
+	allowRead := make(chan struct{})
+	n := 0
+	errors := make(chan error)
+	uut := pubsub.NewMsgQueue(ctx, nil, func(ctx context.Context, msg []byte, err error) {
+		if n == 0 {
+			close(firstDequeue)
+		}
+		<-allowRead
+		if err == nil {
+			require.Equal(t, fmt.Sprintf("%d", n), string(msg))
+			n++
+			return
+		}
+		errors <- err
+	})
+	defer uut.Close()
+
+	// we send 2 more than the capacity.  One extra because the call to the ListenerFunc blocks
+	// but only after we've dequeued a message, and then another extra because we want to exceed
+	// the capacity, not just reach it.
+	for i := 0; i < pubsub.BufferSize+2; i++ {
+		uut.Enqueue([]byte(fmt.Sprintf("%d", i)))
+		// ensure the first dequeue has happened before proceeding, so that this function isn't racing
+		// against the goroutine that dequeues items.
+		<-firstDequeue
+	}
+	close(allowRead)
+
+	select {
+	case <-ctx.Done():
+		t.Fatal("timed out")
+	case err := <-errors:
+		require.ErrorIs(t, err, pubsub.ErrDroppedMessages)
+	}
+	// Ok, so we sent 2 more than capacity, but we only read the capacity, that's because the last
+	// message we send doesn't get queued, AND, it bumps a message out of the queue to make room
+	// for the error, so we read 2 less than we sent.
+	require.Equal(t, pubsub.BufferSize, n)
+}