lib/model, lib/protocol: Track closing connections (fixes #5828) (#5829)

lib/model/model.go

@@ -222,16 +222,8 @@ func (m *model) Stop() {
 	for id := range devs {
 		ids = append(ids, id)
 	}
-	m.pmut.RLock()
-	closed := make([]chan struct{}, 0, len(m.closed))
-	for _, c := range m.closed {
-		closed = append(closed, c)
-	}
-	m.pmut.RUnlock()
-	m.closeConns(ids, errStopped)
-	for _, c := range closed {
-		<-c
-	}
+	w := m.closeConns(ids, errStopped)
+	w.Wait()
 }
 
 // StartDeadlockDetector starts a deadlock detector on the models locks which
@@ -416,12 +408,16 @@ func (m *model) tearDownFolderLocked(cfg config.FolderConfiguration, err error)
 	// Close connections to affected devices
 	// Must happen before stopping the folder service to abort ongoing
 	// transmissions and thus allow timely service termination.
-	m.closeConns(cfg.DeviceIDs(), err)
+	w := m.closeConns(cfg.DeviceIDs(), err)
 
 	for _, id := range tokens {
 		m.RemoveAndWait(id, 0)
 	}
 
+	// Wait for connections to stop to ensure that no more calls to methods
+	// expecting this folder to exist happen (e.g. .IndexUpdate).
+	w.Wait()
+
 	m.fmut.Lock()
 
 	// Clean up our config maps
@@ -1440,23 +1436,39 @@ func (m *model) Closed(conn protocol.Connection, err error) {
 	close(closed)
 }
 
-// closeConns will close the underlying connection for given devices
-func (m *model) closeConns(devs []protocol.DeviceID, err error) {
+// closeConns will close the underlying connection for given devices and return
+// a waiter that will return once all the connections are finished closing.
+func (m *model) closeConns(devs []protocol.DeviceID, err error) config.Waiter {
 	conns := make([]connections.Connection, 0, len(devs))
+	closed := make([]chan struct{}, 0, len(devs))
 	m.pmut.Lock()
 	for _, dev := range devs {
 		if conn, ok := m.conn[dev]; ok {
 			conns = append(conns, conn)
+			closed = append(closed, m.closed[dev])
 		}
 	}
 	m.pmut.Unlock()
 	for _, conn := range conns {
 		conn.Close(err)
 	}
+	return &channelWaiter{chans: closed}
 }
 
-func (m *model) closeConn(dev protocol.DeviceID, err error) {
-	m.closeConns([]protocol.DeviceID{dev}, err)
+// closeConn closes the underlying connection for the given device and returns
+// a waiter that will return once the connection is finished closing.
+func (m *model) closeConn(dev protocol.DeviceID, err error) config.Waiter {
+	return m.closeConns([]protocol.DeviceID{dev}, err)
+}
+
+type channelWaiter struct {
+	chans []chan struct{}
+}
+
+func (w *channelWaiter) Wait() {
+	for _, c := range w.chans {
+		<-c
+	}
 }
 
 // Implements protocol.RequestResponse
@@ -2537,7 +2549,6 @@ func (m *model) CommitConfiguration(from, to config.Configuration) bool {
 
 		if toCfg.Paused {
 			l.Infoln("Pausing", deviceID)
-			m.closeConn(deviceID, errDevicePaused)
 			events.Default.Log(events.DevicePaused, map[string]string{"device": deviceID.String()})
 		} else {
 			events.Default.Log(events.DeviceResumed, map[string]string{"device": deviceID.String()})

lib/protocol/protocol.go

@@ -187,6 +187,7 @@ type rawConnection struct {
 	closeBox              chan asyncMessage
 	clusterConfigBox      chan *ClusterConfig
 	dispatcherLoopStopped chan struct{}
+	preventSends          chan struct{}
 	closed                chan struct{}
 	closeOnce             sync.Once
 	sendCloseOnce         sync.Once
@@ -240,6 +241,7 @@ func NewConnection(deviceID DeviceID, reader io.Reader, writer io.Writer, receiv
 		closeBox:              make(chan asyncMessage),
 		clusterConfigBox:      make(chan *ClusterConfig),
 		dispatcherLoopStopped: make(chan struct{}),
+		preventSends:          make(chan struct{}),
 		closed:                make(chan struct{}),
 		compression:           compress,
 	}
@@ -662,12 +664,13 @@ func (c *rawConnection) send(msg message, done chan struct{}) bool {
 	select {
 	case c.outbox <- asyncMessage{msg, done}:
 		return true
+	case <-c.preventSends:
 	case <-c.closed:
-		if done != nil {
-			close(done)
-		}
-		return false
 	}
+	if done != nil {
+		close(done)
+	}
+	return false
 }
 
 func (c *rawConnection) writerLoop() {