Make writeBroadcaster safe for concurrent use.

utils_test.go

@@ -124,3 +124,25 @@ func TestWriteBroadcaster(t *testing.T) {
 
 	writer.Close()
 }
+
+type devNullCloser int
+
+func (d devNullCloser) Close() error {
+	return nil
+}
+
+func (d devNullCloser) Write(buf []byte) (int, error) {
+	return len(buf), nil
+}
+
+// This test checks for races. It is only useful when run with the race detector.
+func TestRaceWriteBroadcaster(t *testing.T) {
+	writer := newWriteBroadcaster()
+	c := make(chan bool)
+	go func() {
+		writer.AddWriter(devNullCloser(0))
+		c <- true
+	}()
+	writer.Write([]byte("hello"))
+	<-c
+}