Merge pull request #21434 from karalabe/ethstats-split-rwlock

ethstats: split read and write lock, otherwise they'll lock up

ethstats/ethstats.go

@@ -99,6 +99,7 @@ type Service struct {
 
 // connWrapper is a wrapper to prevent concurrent-write or concurrent-read on the
 // websocket.
+//
 // From Gorilla websocket docs:
 //   Connections support one concurrent reader and one concurrent writer.
 //   Applications are responsible for ensuring that no more than one goroutine calls the write methods
@@ -107,11 +108,11 @@ type Service struct {
 //     - NextReader, SetReadDeadline, ReadMessage, ReadJSON, SetPongHandler, SetPingHandler
 //   concurrently.
 //   The Close and WriteControl methods can be called concurrently with all other methods.
-//
-// The connWrapper uses a single mutex for both reading and writing.
 type connWrapper struct {
 	conn *websocket.Conn
-	mu   sync.Mutex
+
+	rlock sync.Mutex
+	wlock sync.Mutex
 }
 
 func newConnectionWrapper(conn *websocket.Conn) *connWrapper {
@@ -120,15 +121,17 @@ func newConnectionWrapper(conn *websocket.Conn) *connWrapper {
 
 // WriteJSON wraps corresponding method on the websocket but is safe for concurrent calling
 func (w *connWrapper) WriteJSON(v interface{}) error {
-	w.mu.Lock()
-	defer w.mu.Unlock()
+	w.wlock.Lock()
+	defer w.wlock.Unlock()
+
 	return w.conn.WriteJSON(v)
 }
 
 // ReadJSON wraps corresponding method on the websocket but is safe for concurrent calling
 func (w *connWrapper) ReadJSON(v interface{}) error {
-	w.mu.Lock()
-	defer w.mu.Unlock()
+	w.rlock.Lock()
+	defer w.rlock.Unlock()
+
 	return w.conn.ReadJSON(v)
 }
 
@@ -275,6 +278,7 @@ func (s *Service) loop() {
 				continue
 			}
 			go s.readLoop(conn)
+
 			// Send the initial stats so our node looks decent from the get go
 			if err = s.report(conn); err != nil {
 				log.Warn("Initial stats report failed", "err", err)