diff --git a/30-coordination/coordination/main.go b/30-coordination/coordination/main.go
index 12e0629..006813d 100644
--- a/30-coordination/coordination/main.go
+++ b/30-coordination/coordination/main.go
@@ -10,6 +10,7 @@ import (
 func main() {
 	main1()
 	main2()
+	main3()
 }
 
 func doSum(count int, val *int, waitGroup *sync.WaitGroup, mutex *sync.Mutex) {
@@ -39,13 +40,16 @@ func main1() {
 func calculateSquares(index, max, iterations int, r *rand.Rand, waitGroup *sync.WaitGroup, rwMutex *sync.RWMutex, squares map[int]int) {
 	for i := 0; i < iterations; i++ {
 		val := r.Intn(max)
+		// 读取锁
 		rwMutex.RLock()
 		square, ok := squares[val]
 		rwMutex.RUnlock()
 		if ok {
 			Printfln("%v %v RLock Cached value: %v = %v ", index, i, val, square)
 		} else {
+			// 写锁，当没有读到时，开启写锁
 			rwMutex.Lock()
+			// 重新读取值，防止缓存被其他goroutine修改
 			if square, ok := squares[val]; !ok {
 				squares[val] = int(math.Pow(float64(val), 2))
 				Printfln("%v %v Added value: %v = %v", index, i, val, squares[val])
@@ -72,5 +76,57 @@ func main2() {
 	}
 	waitGroup.Wait()
 	Printfln("Cached Value: %v", len(squares))
-
+}
+
+func generateSquares(max int, waitGroup *sync.WaitGroup, rwMutex *sync.RWMutex, readyCond *sync.Cond, squares map[int]int) {
+	// 开启写锁
+	rwMutex.Lock()
+	// 重新读取值，防止缓存被其他goroutine修改
+	Printfln("Generating data...")
+	for i := 0; i < max; i++ {
+		squares[i] = int(math.Pow(float64(i), 2))
+	}
+	// 关闭写锁
+	rwMutex.Unlock()
+
+	// 读锁开始广播
+	Printfln("Broadcasting condition")
+	readyCond.Broadcast()
+	waitGroup.Done()
+}
+
+func readSquares(id, max, iterations int, r *rand.Rand, waitGroup *sync.WaitGroup, readyCond *sync.Cond, squares map[int]int) {
+	readyCond.L.Lock()
+	for len(squares) == 0 {
+		readyCond.Wait()
+	}
+	for i := 0; i < iterations; i++ {
+		key := r.Intn(max)
+		Printfln("#%v,%v Read Index: %v = %v ", id, i, key, squares[key])
+		time.Sleep(time.Millisecond * 100)
+	}
+	readyCond.L.Unlock()
+	waitGroup.Done()
+}
+
+func main3() {
+	Printfln("\nmain3:")
+
+	var waitGroup = sync.WaitGroup{}
+	var rwMutex = sync.RWMutex{}
+	var readyCond = sync.NewCond(rwMutex.RLocker())
+	var squares = map[int]int{}
+
+	var r = rand.New(rand.NewSource(time.Now().UnixNano()))
+	numRoutines := 2
+	for i := 0; i < numRoutines; i++ {
+		waitGroup.Add(1)
+		go readSquares(i, 10, 5, r, &waitGroup, readyCond, squares)
+	}
+
+	waitGroup.Add(1)
+	go generateSquares(10, &waitGroup, &rwMutex, readyCond, squares)
+
+	waitGroup.Wait()
+	Printfln("Cached Value: %v", len(squares))
 }