ch9: fix code format

ch9/ch9-02.md

@@ -2,49 +2,49 @@
 
 在8.6節中，我們使用了一個buffered channel作爲一個計數信號量，來保證最多隻有20個goroutine會同時執行HTTP請求。同理，我們可以用一個容量隻有1的channel來保證最多隻有一個goroutine在同一時刻訪問一個共享變量。一個隻能爲1和0的信號量叫做二元信號量(binary semaphore)。
 
+<u><i>gopl.io/ch9/bank2</i></u>
 ```go
-gopl.io/ch9/bank2
 var (
-    sema    = make(chan struct{}, 1) // a binary semaphore guarding balance
-    balance int
+	sema    = make(chan struct{}, 1) // a binary semaphore guarding balance
+	balance int
 )
 
 func Deposit(amount int) {
-    sema <- struct{}{} // acquire token
-    balance = balance + amount
-    <-sema // release token
+	sema <- struct{}{} // acquire token
+	balance = balance + amount
+	<-sema // release token
 }
 
 func Balance() int {
-    sema <- struct{}{} // acquire token
-    b := balance
-    <-sema // release token
-    return b
+	sema <- struct{}{} // acquire token
+	b := balance
+	<-sema // release token
+	return b
 }
 ```
 
 這種互斥很實用，而且被sync包里的Mutex類型直接支持。它的Lock方法能夠獲取到token(這里叫鎖)，併且Unlock方法會釋放這個token：
 
+<u><i>gopl.io/ch9/bank3</i></u>
 ```go
-gopl.io/ch9/bank3
 import "sync"
 
 var (
-    mu      sync.Mutex // guards balance
-    balance int
+	mu      sync.Mutex // guards balance
+	balance int
 )
 
 func Deposit(amount int) {
-    mu.Lock()
-    balance = balance + amount
-    mu.Unlock()
+	mu.Lock()
+	balance = balance + amount
+	mu.Unlock()
 }
 
 func Balance() int {
-    mu.Lock()
-    b := balance
-    mu.Unlock()
-    return b
+	mu.Lock()
+	b := balance
+	mu.Unlock()
+	return b
 }
 ```
 
@@ -58,9 +58,9 @@ func Balance() int {
 
 ```go
 func Balance() int {
-    mu.Lock()
-    defer mu.Unlock()
-    return balance
+	mu.Lock()
+	defer mu.Unlock()
+	return balance
 }
 ```
 
@@ -73,12 +73,12 @@ func Balance() int {
 ```go
 // NOTE: not atomic!
 func Withdraw(amount int) bool {
-    Deposit(-amount)
-    if Balance() < 0 {
-        Deposit(amount)
-        return false // insufficient funds
-    }
-    return true
+	Deposit(-amount)
+	if Balance() < 0 {
+		Deposit(amount)
+		return false // insufficient funds
+	}
+	return true
 }
 ```
 
@@ -89,14 +89,14 @@ func Withdraw(amount int) bool {
 ```go
 // NOTE: incorrect!
 func Withdraw(amount int) bool {
-    mu.Lock()
-    defer mu.Unlock()
-    Deposit(-amount)
-    if Balance() < 0 {
-        Deposit(amount)
-        return false // insufficient funds
-    }
-    return true
+	mu.Lock()
+	defer mu.Unlock()
+	Deposit(-amount)
+	if Balance() < 0 {
+		Deposit(amount)
+		return false // insufficient funds
+	}
+	return true
 }
 ```
 
@@ -108,26 +108,26 @@ func Withdraw(amount int) bool {
 
 ```go
 func Withdraw(amount int) bool {
-    mu.Lock()
-    defer mu.Unlock()
-    deposit(-amount)
-    if balance < 0 {
-        deposit(amount)
-        return false // insufficient funds
-    }
-    return true
+	mu.Lock()
+	defer mu.Unlock()
+	deposit(-amount)
+	if balance < 0 {
+		deposit(amount)
+		return false // insufficient funds
+	}
+	return true
 }
 
 func Deposit(amount int) {
-    mu.Lock()
-    defer mu.Unlock()
-    deposit(amount)
+	mu.Lock()
+	defer mu.Unlock()
+	deposit(amount)
 }
 
 func Balance() int {
-    mu.Lock()
-    defer mu.Unlock()
-    return balance
+	mu.Lock()
+	defer mu.Unlock()
+	return balance
 }
 
 // This function requires that the lock be held.