cpu: fix ticker to avoid close early (#40036)

ref #40029

Author: hawkingrei

util/cpu/BUILD.bazel

@@ -20,5 +20,6 @@ go_test(
     name = "cpu_test",
     srcs = ["cpu_test.go"],
     embed = [":cpu"],
+    flaky = True,
     deps = ["@com_github_stretchr_testify//require"],
 )

util/cpu/cpu.go

@@ -56,11 +56,13 @@ func NewCPUObserver() *Observer {
 
 // Start starts the cpu observer.
 func (c *Observer) Start() {
-	ticker := time.NewTicker(100 * time.Millisecond)
-	defer ticker.Stop()
 	c.wg.Add(1)
 	go func() {
-		defer c.wg.Done()
+		ticker := time.NewTicker(100 * time.Millisecond)
+		defer func() {
+			ticker.Stop()
+			c.wg.Done()
+		}()
 		for {
 			select {
 			case <-ticker.C:

util/cpu/cpu_test.go

@@ -42,9 +42,10 @@ func TestCPUValue(t *testing.T) {
 			}
 		}()
 	}
-	time.Sleep(30 * time.Second)
-	require.Greater(t, Observer.observe(), 0.0)
-	require.Less(t, Observer.observe(), 1.0)
+	Observer.Start()
+	time.Sleep(5 * time.Second)
+	require.GreaterOrEqual(t, GetCPUUsage(), 0.0)
+	require.Less(t, GetCPUUsage(), 1.0)
 	Observer.Stop()
 	close(exit)
 	wg.Wait()