address comments

Signed-off-by: Ryan Leung <[email protected]>

pkg/ratelimit/runner.go

@@ -144,15 +144,13 @@ func (cr *ConcurrentRunner) Start() {
 
 func (cr *ConcurrentRunner) run(task *Task, token *TaskToken) {
 	start := time.Now()
-	defer func() {
-		RunnerTaskExecutionDuration.WithLabelValues(cr.name, task.name).Observe(time.Since(start).Seconds())
-		RunnerSucceededTasks.WithLabelValues(cr.name, task.name).Inc()
-	}()
 	task.f(task.ctx)
 	if token != nil {
 		token.Release()
 		cr.processPendingTasks()
 	}
+	RunnerTaskExecutionDuration.WithLabelValues(cr.name, task.name).Observe(time.Since(start).Seconds())
+	RunnerSucceededTasks.WithLabelValues(cr.name, task.name).Inc()
 }
 
 func (cr *ConcurrentRunner) processPendingTasks() {
@@ -198,11 +196,13 @@ func (cr *ConcurrentRunner) RunTask(ctx context.Context, name string, f func(con
 		opt(task)
 	}
 
-	cr.processPendingTasks()
 	cr.pendingMu.Lock()
-	defer cr.pendingMu.Unlock()
+	defer func() {
+		cr.pendingMu.Unlock()
+		cr.processPendingTasks()
+	}()
 	if task.priority >= constant.High {
-		// We use the max task number to prevent the OOM issue.
+		// We use the max task number to limit the memory usage.
 		// It occupies around 1.5GB memory when there is 20000000 pending task.
 		if len(cr.pendingHighPriorityTasks) > maxHighPriorityTaskNum {
 			RunnerFailedTasks.WithLabelValues(cr.name, task.name).Inc()