fix(coderd/database): improve pubsub closure and context cancellation (#7993)

mafredri · web-flow · commit 518300a26c8d · 2023-06-13T15:19:56.000+03:00
diff --git a/coderd/database/pubsub.go b/coderd/database/pubsub.go
@@ -163,6 +163,8 @@ func (q *msgQueue) dropped() {
 // Pubsub implementation using PostgreSQL.
 type pgPubsub struct {
 	ctx        context.Context
+	cancel     context.CancelFunc
+	listenDone chan struct{}
 	pgListener *pq.Listener
 	db         *sql.DB
 	mut        sync.Mutex
@@ -228,7 +230,7 @@ func (p *pgPubsub) Publish(event string, message []byte) error {
 	// This is safe because we are calling pq.QuoteLiteral. pg_notify doesn't
 	// support the first parameter being a prepared statement.
 	//nolint:gosec
-	_, err := p.db.ExecContext(context.Background(), `select pg_notify(`+pq.QuoteLiteral(event)+`, $1)`, message)
+	_, err := p.db.ExecContext(p.ctx, `select pg_notify(`+pq.QuoteLiteral(event)+`, $1)`, message)
 	if err != nil {
 		return xerrors.Errorf("exec pg_notify: %w", err)
 	}
@@ -237,19 +239,24 @@ func (p *pgPubsub) Publish(event string, message []byte) error {
 
 // Close closes the pubsub instance.
 func (p *pgPubsub) Close() error {
-	return p.pgListener.Close()
+	p.cancel()
+	err := p.pgListener.Close()
+	<-p.listenDone
+	return err
 }
 
 // listen begins receiving messages on the pq listener.
-func (p *pgPubsub) listen(ctx context.Context) {
+func (p *pgPubsub) listen() {
+	defer close(p.listenDone)
+	defer p.pgListener.Close()
+
 	var (
 		notif *pq.Notification
 		ok    bool
 	)
-	defer p.pgListener.Close()
 	for {
 		select {
-		case <-ctx.Done():
+		case <-p.ctx.Done():
 			return
 		case notif, ok = <-p.pgListener.Notify:
 			if !ok {
@@ -292,7 +299,7 @@ func (p *pgPubsub) recordReconnect() {
 func NewPubsub(ctx context.Context, database *sql.DB, connectURL string) (Pubsub, error) {
 	// Creates a new listener using pq.
 	errCh := make(chan error)
-	listener := pq.NewListener(connectURL, time.Second, time.Minute, func(event pq.ListenerEventType, err error) {
+	listener := pq.NewListener(connectURL, time.Second, time.Minute, func(_ pq.ListenerEventType, err error) {
 		// This callback gets events whenever the connection state changes.
 		// Don't send if the errChannel has already been closed.
 		select {
@@ -306,18 +313,25 @@ func NewPubsub(ctx context.Context, database *sql.DB, connectURL string) (Pubsub
 	select {
 	case err := <-errCh:
 		if err != nil {
+			_ = listener.Close()
 			return nil, xerrors.Errorf("create pq listener: %w", err)
 		}
 	case <-ctx.Done():
+		_ = listener.Close()
 		return nil, ctx.Err()
 	}
+
+	// Start a new context that will be canceled when the pubsub is closed.
+	ctx, cancel := context.WithCancel(context.Background())
 	pgPubsub := &pgPubsub{
 		ctx:        ctx,
+		cancel:     cancel,
+		listenDone: make(chan struct{}),
 		db:         database,
 		pgListener: listener,
 		queues:     make(map[string]map[uuid.UUID]*msgQueue),
 	}
-	go pgPubsub.listen(ctx)
+	go pgPubsub.listen()
 
 	return pgPubsub, nil
 }
diff --git a/coderd/database/pubsub_test.go b/coderd/database/pubsub_test.go
@@ -45,11 +45,11 @@ func TestPubsub(t *testing.T) {
 		event := "test"
 		data := "testing"
 		messageChannel := make(chan []byte)
-		cancelFunc, err = pubsub.Subscribe(event, func(ctx context.Context, message []byte) {
+		unsub, err := pubsub.Subscribe(event, func(ctx context.Context, message []byte) {
 			messageChannel <- message
 		})
 		require.NoError(t, err)
-		defer cancelFunc()
+		defer unsub()
 		go func() {
 			err = pubsub.Publish(event, []byte(data))
 			assert.NoError(t, err)
@@ -72,6 +72,91 @@ func TestPubsub(t *testing.T) {
 		defer pubsub.Close()
 		cancelFunc()
 	})
+
+	t.Run("NotClosedOnCancelContext", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		connectionURL, closePg, err := postgres.Open()
+		require.NoError(t, err)
+		defer closePg()
+		db, err := sql.Open("postgres", connectionURL)
+		require.NoError(t, err)
+		defer db.Close()
+		pubsub, err := database.NewPubsub(ctx, db, connectionURL)
+		require.NoError(t, err)
+		defer pubsub.Close()
+
+		// Provided context must only be active during NewPubsub, not after.
+		cancel()
+
+		event := "test"
+		data := "testing"
+		messageChannel := make(chan []byte)
+		unsub, err := pubsub.Subscribe(event, func(_ context.Context, message []byte) {
+			messageChannel <- message
+		})
+		require.NoError(t, err)
+		defer unsub()
+		go func() {
+			err = pubsub.Publish(event, []byte(data))
+			assert.NoError(t, err)
+		}()
+		message := <-messageChannel
+		assert.Equal(t, string(message), data)
+	})
+
+	t.Run("ClosePropagatesContextCancellationToSubscription", func(t *testing.T) {
+		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
+		defer cancel()
+		connectionURL, closePg, err := postgres.Open()
+		require.NoError(t, err)
+		defer closePg()
+		db, err := sql.Open("postgres", connectionURL)
+		require.NoError(t, err)
+		defer db.Close()
+		pubsub, err := database.NewPubsub(ctx, db, connectionURL)
+		require.NoError(t, err)
+		defer pubsub.Close()
+
+		event := "test"
+		done := make(chan struct{})
+		called := make(chan struct{})
+		unsub, err := pubsub.Subscribe(event, func(subCtx context.Context, _ []byte) {
+			defer close(done)
+			select {
+			case <-subCtx.Done():
+				assert.Fail(t, "context should not be canceled")
+			default:
+			}
+			close(called)
+			select {
+			case <-subCtx.Done():
+			case <-ctx.Done():
+				assert.Fail(t, "timeout waiting for sub context to be canceled")
+			}
+		})
+		require.NoError(t, err)
+		defer unsub()
+
+		go func() {
+			err := pubsub.Publish(event, nil)
+			assert.NoError(t, err)
+		}()
+
+		select {
+		case <-called:
+		case <-ctx.Done():
+			require.Fail(t, "timeout waiting for handler to be called")
+		}
+		err = pubsub.Close()
+		require.NoError(t, err)
+
+		select {
+		case <-done:
+		case <-ctx.Done():
+			require.Fail(t, "timeout waiting for handler to finish")
+		}
+	})
 }
 
 func TestPubsub_ordering(t *testing.T) {
