diff --git a/starmap_test.go b/starmap_test.go
index ab32bc6..7566a24 100644
--- a/starmap_test.go
+++ b/starmap_test.go
@@ -2,7 +2,9 @@ package starmap
 
 import (
 	"fmt"
+	"math/rand"
 	"testing"
+	"time"
 )
 
 type Miaomiao struct {
@@ -39,3 +41,29 @@ func Test_Remote2(t *testing.T) {
 	fmt.Println(client.StoreMap(&Miaomiao{"suki", 1127, false}))
 	fmt.Println(client.GetMap("miaomiao"))
 }
+
+func Test_Math(t *testing.T) {
+	wg := NewWaitGroup(5000)
+	rand.Seed(time.Now().UnixNano())
+	waitfn := func(wg *WaitGroup, num int) {
+		defer wg.Done()
+		fmt.Println(num)
+		time.Sleep(time.Second * time.Duration(2+rand.Intn(3)))
+	}
+	for i := 0; i <= 3214670; i++ {
+		wg.Add(1)
+		if i == 34567 {
+			wg.SetMaxWaitNum(50000)
+		}
+		if i == 123456 {
+			wg.SetMaxWaitNum(210456)
+		}
+		if i == 323456 {
+			wg.SetMaxWaitNum(2104562)
+		}
+		go waitfn(&wg, i)
+	}
+	fmt.Println("Waiting~~~~~~~~~~")
+	wg.Wait()
+	fmt.Println(wg.allCount)
+}
diff --git a/sync.go b/sync.go
new file mode 100644
index 0000000..57405b5
--- /dev/null
+++ b/sync.go
@@ -0,0 +1,55 @@
+package starmap
+
+import (
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+type WaitGroup struct {
+	wg       *sync.WaitGroup
+	maxCount uint32
+	allCount uint32
+}
+
+func NewWaitGroup(maxCount int) WaitGroup {
+	return WaitGroup{wg: &sync.WaitGroup{}, maxCount: uint32(maxCount)}
+}
+
+func (swg *WaitGroup) Add(delta int) {
+	var Udelta uint32
+	if delta < 0 {
+		Udelta = uint32(-delta - 1)
+	} else {
+		Udelta = uint32(delta)
+	}
+	for {
+		allC := atomic.LoadUint32(&swg.allCount)
+		if atomic.LoadUint32(&swg.maxCount) >= allC+uint32(delta) {
+			if delta < 0 {
+				atomic.AddUint32(&swg.allCount, ^uint32(Udelta))
+			} else {
+				atomic.AddUint32(&swg.allCount, uint32(Udelta))
+			}
+			break
+		}
+		time.Sleep(time.Microsecond)
+	}
+	swg.wg.Add(delta)
+}
+
+func (swg *WaitGroup) Done() {
+	swg.Add(-1)
+}
+
+func (swg *WaitGroup) Wait() {
+	swg.wg.Wait()
+}
+
+func (swg *WaitGroup) GetMaxWaitNum() int {
+	return int(atomic.LoadUint32(&swg.maxCount))
+}
+
+func (swg *WaitGroup) SetMaxWaitNum(num int) {
+	atomic.AddUint32(&swg.maxCount, uint32(num))
+}