simplier fix + test for race condition

staging/src/k8s.io/apimachinery/pkg/watch/streamwatcher.go

@@ -56,7 +56,6 @@ type StreamWatcher struct {
 	reporter Reporter
 	result   chan Event
 	done     chan struct{}
-	stopped  bool
 }
 
 // NewStreamWatcher creates a StreamWatcher from the given decoder.
@@ -88,20 +87,15 @@ func (sw *StreamWatcher) Stop() {
 	// Call Close() exactly once by locking and setting a flag.
 	sw.Lock()
 	defer sw.Unlock()
-	if !sw.stopped {
+	// closing a closed channel always panics, therefore check before closing
-		sw.stopped = true
+	select {
+	case <-sw.done:
+	default:
 		close(sw.done)
 		sw.source.Close()
 	}
 }
 
-// stopping returns true if Stop() was called previously.
-func (sw *StreamWatcher) stopping() bool {
-	sw.Lock()
-	defer sw.Unlock()
-	return sw.stopped
-}
-
 // receive reads result from the decoder in a loop and sends down the result channel.
 func (sw *StreamWatcher) receive() {
 	defer utilruntime.HandleCrash()
@@ -110,10 +104,6 @@ func (sw *StreamWatcher) receive() {
 	for {
 		action, obj, err := sw.source.Decode()
 		if err != nil {
-			// Ignore expected error.
-			if sw.stopping() {
-				return
-			}
 			switch err {
 			case io.EOF:
 				// watch closed normally
@@ -124,20 +114,7 @@ func (sw *StreamWatcher) receive() {
 					klog.V(5).Infof("Unable to decode an event from the watch stream: %v", err)
 				} else {
 					select {
-					// TODO: figure out how to test that sending the error after an externally stopped watcher
-					//       cannot block anymore because of the introduced done channel.
-					// The function receive checks under a lock whether the watch has been stopped,
-					// before an error from the watch stream is reported to the result channel.
-					// The problem here is, that in between the watcher might be stopped by
-					// calling the Stop method. In the actual code this is done by the
-					// cache.Reflector using the streamwatcher by a defer (method watchHandler)
-					// which is executed after the caller already stopped reading from the result channel.
-					// As a result the stopping flag might be set after the check
-					// and trying to send the error event blocks this send operation forever,
-					// because there will never be a receiver again.
-					// This results in dead go routines trying to send on the result channel, forever.
 					case <-sw.done:
-						return
 					case sw.result <- Event{
 						Type:   Error,
 						Object: sw.reporter.AsObject(fmt.Errorf("unable to decode an event from the watch stream: %v", err)),

staging/src/k8s.io/apimachinery/pkg/watch/streamwatcher_test.go

@@ -21,6 +21,7 @@ import (
 	"io"
 	"reflect"
 	"testing"
+	"time"
 
 	"k8s.io/apimachinery/pkg/runtime"
 	. "k8s.io/apimachinery/pkg/watch"
@@ -105,3 +106,16 @@ func TestStreamWatcherError(t *testing.T) {
 		t.Fatalf("unexpected open channel")
 	}
 }
+
+func TestStreamWatcherRace(t *testing.T) {
+	fd := fakeDecoder{err: fmt.Errorf("test error")}
+	fr := &fakeReporter{}
+	sw := NewStreamWatcher(fd, fr)
+	time.Sleep(10 * time.Millisecond)
+	sw.Stop()
+	time.Sleep(10 * time.Millisecond)
+	_, ok := <-sw.ResultChan()
+	if ok {
+		t.Fatalf("unexpected pending send")
+	}
+}