perf: reduce timer in write_control

conn.go

@@ -454,13 +454,18 @@
 		}
 	}
 
-	timer := time.NewTimer(d)
 	select {
 	case <-c.mu:
-		timer.Stop()
-	case <-timer.C:
-		return errWriteTimeout
+	default:
+		timer := time.NewTimer(d)
+		select {
+		case <-c.mu:
+			timer.Stop()
+		case <-timer.C:
+			return errWriteTimeout
+		}
 	}
+
 	defer func() { c.mu <- struct{}{} }()
 
 	c.writeErrMu.Lock()

conn_test.go

@@ -148,6 +148,31 @@ func TestFraming(t *testing.T) {
 	}
 }
 
+func TestConcurrencyWriteControl(t *testing.T) {
+	const message = "this is a ping/pong messsage"
+	loop := 10
+	workers := 10
+	for i := 0; i < loop; i++ {
+		var connBuf bytes.Buffer
+
+		wg := sync.WaitGroup{}
+		wc := newTestConn(nil, &connBuf, true)
+
+		for i := 0; i < workers; i++ {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				if err := wc.WriteControl(PongMessage, []byte(message), time.Now().Add(time.Second)); err != nil {
+					t.Errorf("concurrently wc.WriteControl() returned %v", err)
+				}
+			}()
+		}
+
+		wg.Wait()
+		wc.Close()
+	}
+}
+
 func TestControl(t *testing.T) {
 	t.Parallel()
 	const message = "this is a ping/pong messsage"