TUN-2608: h2mux.Muxer.Shutdown always returns a non-nil channel

h2mux/activestreammap.go

@@ -13,24 +13,26 @@ type activeStreamMap struct {
 	sync.RWMutex
 	// streams tracks open streams.
 	streams map[uint32]*MuxedStream
-	// streamsEmpty is a chan that should be closed when no more streams are open.
-	streamsEmpty chan struct{}
 	// nextStreamID is the next ID to use on our side of the connection.
 	// This is odd for clients, even for servers.
 	nextStreamID uint32
 	// maxPeerStreamID is the ID of the most recent stream opened by the peer.
 	maxPeerStreamID uint32
+	// activeStreams is a gauge shared by all muxers of this process to expose the total number of active streams
+	activeStreams prometheus.Gauge
+
 	// ignoreNewStreams is true when the connection is being shut down. New streams
 	// cannot be registered.
 	ignoreNewStreams bool
-	// activeStreams is a gauge shared by all muxers of this process to expose the total number of active streams
-	activeStreams prometheus.Gauge
+	// streamsEmpty is a chan that will be closed when no more streams are open.
+	streamsEmptyChan chan struct{}
+	closeOnce        sync.Once
 }
 
 func newActiveStreamMap(useClientStreamNumbers bool, activeStreams prometheus.Gauge) *activeStreamMap {
 	m := &activeStreamMap{
 		streams:          make(map[uint32]*MuxedStream),
-		streamsEmpty:  make(chan struct{}),
+		streamsEmptyChan: make(chan struct{}),
 		nextStreamID:     1,
 		activeStreams:    activeStreams,
 	}
@@ -41,6 +43,12 @@ func newActiveStreamMap(useClientStreamNumbers bool, activeStreams prometheus.Ga
 	return m
 }
 
+func (m *activeStreamMap) notifyStreamsEmpty() {
+	m.closeOnce.Do(func() {
+		close(m.streamsEmptyChan)
+	})
+}
+
 // Len returns the number of active streams.
 func (m *activeStreamMap) Len() int {
 	m.RLock()
@@ -79,30 +87,27 @@ func (m *activeStreamMap) Delete(streamID uint32) {
 		delete(m.streams, streamID)
 		m.activeStreams.Dec()
 	}
-	if len(m.streams) == 0 && m.streamsEmpty != nil {
-		close(m.streamsEmpty)
-		m.streamsEmpty = nil
+	if len(m.streams) == 0 {
+		m.notifyStreamsEmpty()
 	}
 }
 
-// Shutdown blocks new streams from being created. It returns a channel that receives an event
-// once the last stream has closed, or nil if a shutdown is in progress.
-func (m *activeStreamMap) Shutdown() <-chan struct{} {
+// Shutdown blocks new streams from being created.
+// It returns `done`, a channel that is closed once the last stream has closed
+// and `progress`, whether a shutdown was already in progress
+func (m *activeStreamMap) Shutdown() (done <-chan struct{}, alreadyInProgress bool) {
 	m.Lock()
 	defer m.Unlock()
 	if m.ignoreNewStreams {
 		// already shutting down
-		return nil
+		return m.streamsEmptyChan, true
 	}
 	m.ignoreNewStreams = true
-	done := make(chan struct{})
 	if len(m.streams) == 0 {
 		// nothing to shut down
-		close(done)
-		return done
+		m.notifyStreamsEmpty()
 	}
-	m.streamsEmpty = done
-	return done
+	return m.streamsEmptyChan, false
 }
 
 // AcquireLocalID acquires a new stream ID for a stream you're opening.
@@ -170,4 +175,5 @@ func (m *activeStreamMap) Abort() {
 		stream.Close()
 	}
 	m.ignoreNewStreams = true
+	m.notifyStreamsEmpty()
 }

h2mux/activestreammap_test.go

@@ -0,0 +1,134 @@
+package h2mux
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestShutdown(t *testing.T) {
+	const numStreams = 1000
+	m := newActiveStreamMap(true, NewActiveStreamsMetrics("test", t.Name()))
+
+	// Add all the streams
+	{
+		var wg sync.WaitGroup
+		wg.Add(numStreams)
+		for i := 0; i < numStreams; i++ {
+			go func(streamID int) {
+				defer wg.Done()
+				stream := &MuxedStream{streamID: uint32(streamID)}
+				ok := m.Set(stream)
+				assert.True(t, ok)
+			}(i)
+		}
+		wg.Wait()
+	}
+	assert.Equal(t, numStreams, m.Len(), "All the streams should have been added")
+
+	shutdownChan, alreadyInProgress := m.Shutdown()
+	select {
+	case <-shutdownChan:
+		assert.Fail(t, "before Shutdown(), shutdownChan shouldn't be closed")
+	default:
+	}
+	assert.False(t, alreadyInProgress)
+
+	shutdownChan2, alreadyInProgress2 := m.Shutdown()
+	assert.Equal(t, shutdownChan, shutdownChan2, "repeated calls to Shutdown() should return the same channel")
+	assert.True(t, alreadyInProgress2, "repeated calls to Shutdown() should return true for 'in progress'")
+
+	// Delete all the streams
+	{
+		var wg sync.WaitGroup
+		wg.Add(numStreams)
+		for i := 0; i < numStreams; i++ {
+			go func(streamID int) {
+				defer wg.Done()
+				m.Delete(uint32(streamID))
+			}(i)
+		}
+		wg.Wait()
+	}
+	assert.Equal(t, 0, m.Len(), "All the streams should have been deleted")
+
+	select {
+	case <-shutdownChan:
+	default:
+		assert.Fail(t, "After all the streams are deleted, shutdownChan should have been closed")
+	}
+}
+
+type noopBuffer struct {
+	isClosed bool
+}
+
+func (t *noopBuffer) Read(p []byte) (n int, err error)  { return len(p), nil }
+func (t *noopBuffer) Write(p []byte) (n int, err error) { return len(p), nil }
+func (t *noopBuffer) Reset()                            {}
+func (t *noopBuffer) Len() int                          { return 0 }
+func (t *noopBuffer) Close() error                      { t.isClosed = true; return nil }
+func (t *noopBuffer) Closed() bool                      { return t.isClosed }
+
+type noopReadyList struct{}
+
+func (_ *noopReadyList) Signal(streamID uint32) {}
+
+func TestAbort(t *testing.T) {
+	const numStreams = 1000
+	m := newActiveStreamMap(true, NewActiveStreamsMetrics("test", t.Name()))
+
+	var openedStreams sync.Map
+
+	// Add all the streams
+	{
+		var wg sync.WaitGroup
+		wg.Add(numStreams)
+		for i := 0; i < numStreams; i++ {
+			go func(streamID int) {
+				defer wg.Done()
+				stream := &MuxedStream{
+					streamID:    uint32(streamID),
+					readBuffer:  &noopBuffer{},
+					writeBuffer: &noopBuffer{},
+					readyList:   &noopReadyList{},
+				}
+				ok := m.Set(stream)
+				assert.True(t, ok)
+
+				openedStreams.Store(stream.streamID, stream)
+			}(i)
+		}
+		wg.Wait()
+	}
+	assert.Equal(t, numStreams, m.Len(), "All the streams should have been added")
+
+	shutdownChan, alreadyInProgress := m.Shutdown()
+	select {
+	case <-shutdownChan:
+		assert.Fail(t, "before Abort(), shutdownChan shouldn't be closed")
+	default:
+	}
+	assert.False(t, alreadyInProgress)
+
+	m.Abort()
+	assert.Equal(t, numStreams, m.Len(), "Abort() shouldn't delete any streams")
+	openedStreams.Range(func(key interface{}, value interface{}) bool {
+		stream := value.(*MuxedStream)
+		readBuffer := stream.readBuffer.(*noopBuffer)
+		writeBuffer := stream.writeBuffer.(*noopBuffer)
+		return assert.True(t, readBuffer.isClosed && writeBuffer.isClosed, "Abort() should have closed all the streams")
+	})
+
+	select {
+	case <-shutdownChan:
+	default:
+		assert.Fail(t, "after Abort(), shutdownChan should have been closed")
+	}
+
+	// multiple aborts shouldn't cause any issues
+	m.Abort()
+	m.Abort()
+	m.Abort()
+}

h2mux/h2mux.go

@@ -353,9 +353,11 @@ func (m *Muxer) Serve(ctx context.Context) error {
 }
 
 // Shutdown is called to initiate the "happy path" of muxer termination.
-func (m *Muxer) Shutdown() {
+// It blocks new streams from being created.
+// It returns a channel that is closed when the last stream has been closed.
+func (m *Muxer) Shutdown() <-chan struct{} {
 	m.explicitShutdown.Fuse(true)
-	m.muxReader.Shutdown()
+	return m.muxReader.Shutdown()
 }
 
 // IsUnexpectedTunnelError identifies errors that are expected when shutting down the h2mux tunnel.

h2mux/h2mux_test.go

@@ -55,6 +55,8 @@ func NewDefaultMuxerPair(t assert.TestingT, testName string, f MuxedStreamFunc)
 			DefaultWindowSize:       (1 << 8) - 1,
 			MaxWindowSize:           (1 << 15) - 1,
 			StreamWriteBufferMaxLen: 1024,
+			HeartbeatInterval:       defaultTimeout,
+			MaxHeartbeats:           defaultRetries,
 		},
 		OriginConn: origin,
 		EdgeMuxConfig: MuxerConfig{
@@ -65,6 +67,8 @@ func NewDefaultMuxerPair(t assert.TestingT, testName string, f MuxedStreamFunc)
 			DefaultWindowSize:       (1 << 8) - 1,
 			MaxWindowSize:           (1 << 15) - 1,
 			StreamWriteBufferMaxLen: 1024,
+			HeartbeatInterval:       defaultTimeout,
+			MaxHeartbeats:           defaultRetries,
 		},
 		EdgeConn: edge,
 		doneC:    make(chan struct{}),
@@ -83,6 +87,8 @@ func NewCompressedMuxerPair(t assert.TestingT, testName string, quality Compress
 			Name:               "origin",
 			CompressionQuality: quality,
 			Logger:             log.NewEntry(log.New()),
+			HeartbeatInterval:  defaultTimeout,
+			MaxHeartbeats:      defaultRetries,
 		},
 		OriginConn: origin,
 		EdgeMuxConfig: MuxerConfig{
@@ -91,6 +97,8 @@ func NewCompressedMuxerPair(t assert.TestingT, testName string, quality Compress
 			Name:               "edge",
 			CompressionQuality: quality,
 			Logger:             log.NewEntry(log.New()),
+			HeartbeatInterval:  defaultTimeout,
+			MaxHeartbeats:      defaultRetries,
 		},
 		EdgeConn: edge,
 		doneC:    make(chan struct{}),

h2mux/muxedstream.go

@@ -17,6 +17,12 @@ type ReadWriteClosedCloser interface {
 	Closed() bool
 }
 
+// MuxedStreamDataSignaller is a write-only *ReadyList
+type MuxedStreamDataSignaller interface {
+	// Non-blocking: call this when data is ready to be sent for the given stream ID.
+	Signal(ID uint32)
+}
+
 // MuxedStream is logically an HTTP/2 stream, with an additional buffer for outgoing data.
 type MuxedStream struct {
 	streamID uint32
@@ -55,8 +61,8 @@ type MuxedStream struct {
 	// This is the amount of bytes that are in the peer's receive window
 	// (how much data we can send from this stream).
 	sendWindow uint32
-	// Reference to the muxer's readyList; signal this for stream data to be sent.
-	readyList *ReadyList
+	// The muxer's readyList
+	readyList MuxedStreamDataSignaller
 	// The headers that should be sent, and a flag so we only send them once.
 	headersSent  bool
 	writeHeaders []Header
@@ -88,7 +94,7 @@ func (th TunnelHostname) IsSet() bool {
 	return th != ""
 }
 
-func NewStream(config MuxerConfig, writeHeaders []Header, readyList *ReadyList, dictionaries h2Dictionaries) *MuxedStream {
+func NewStream(config MuxerConfig, writeHeaders []Header, readyList MuxedStreamDataSignaller, dictionaries h2Dictionaries) *MuxedStream {
 	return &MuxedStream{
 		responseHeadersReceived: make(chan struct{}),
 		readBuffer:              NewSharedBuffer(),

h2mux/muxreader.go

@@ -51,10 +51,12 @@ type MuxReader struct {
 	dictionaries h2Dictionaries
 }
 
-func (r *MuxReader) Shutdown() {
-	done := r.streams.Shutdown()
-	if done == nil {
-		return
+// Shutdown blocks new streams from being created.
+// It returns a channel that is closed once the last stream has closed.
+func (r *MuxReader) Shutdown() <-chan struct{} {
+	done, alreadyInProgress := r.streams.Shutdown()
+	if alreadyInProgress {
+		return done
 	}
 	r.sendGoAway(http2.ErrCodeNo)
 	go func() {
@@ -62,6 +64,7 @@ func (r *MuxReader) Shutdown() {
 		<-done
 		r.r.Close()
 	}()
+	return done
 }
 
 func (r *MuxReader) run(parentLogger *log.Entry) error {