kvclient(ticdc): fix the workerpool data race (#10195)

close #10095

cdc/kv/region_worker.go

@@ -41,6 +41,7 @@ import (
 var (
 	regionWorkerPool workerpool.WorkerPool
 	workerPoolOnce   sync.Once
+	workerPoolLock   sync.Mutex
 	// The magic number here is keep the same with some magic numbers in some
 	// other components in TiCDC, including worker pool task chan size, mounter
 	// chan size etc.
@@ -402,6 +403,8 @@ func (w *regionWorker) processEvent(ctx context.Context, event *regionStatefulEv
 
 func (w *regionWorker) initPoolHandles() {
 	handles := make([]workerpool.EventHandle, 0, w.concurrency)
+	workerPoolLock.Lock()
+	defer workerPoolLock.Unlock()
 	for i := 0; i < w.concurrency; i++ {
 		poolHandle := regionWorkerPool.RegisterEvent(func(ctx context.Context, eventI interface{}) error {
 			event := eventI.(*regionStatefulEvent)
@@ -858,6 +861,8 @@ func getWorkerPoolSize() (size int) {
 func InitWorkerPool() {
 	workerPoolOnce.Do(func() {
 		size := getWorkerPoolSize()
+		workerPoolLock.Lock()
+		defer workerPoolLock.Unlock()
 		regionWorkerPool = workerpool.NewDefaultWorkerPool(size)
 	})
 }