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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < strong aria-hidd
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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
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< hr >
< h2 id = "92-syncmutex互斥锁" > < a class = "header" href = "#92-syncmutex互斥锁" > 9.2. sync.Mutex互斥锁< / a > < / h2 >
< p > 在8.6节中， ， ， （ ） < / p >
< p > < u > < i > gopl.io/ch9/bank2< / i > < / u > < / p >
< pre > < code class = "language-go" > var (
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
}
func Balance() int {
sema < - struct{}{} // acquire token
b := balance
< -sema // release token
return b
}
< / code > < / pre >
< p > 这种互斥很实用， ， ： < / p >
< p > < u > < i > gopl.io/ch9/bank3< / i > < / u > < / p >
< pre > < code class = "language-go" > import " sync"
var (
mu sync.Mutex // guards balance
balance int
)
func Deposit(amount int) {
mu.Lock()
balance = balance + amount
mu.Unlock()
}
func Balance() int {
mu.Lock()
b := balance
mu.Unlock()
return b
}
< / code > < / pre >
< p > 每次一个goroutine访问bank变量时（ ） ， ， ， ， < / p >
< p > 在Lock和Unlock之间的代码段中的内容goroutine可以随便读取或者修改， ， ， ， < / p >
< p > 上面的bank程序例证了一种通用的并发模式。一系列的导出函数封装了一个或多个变量， （ ， ） ， （ ） < / p >
< p > 由于在存款和查询余额函数中的临界区代码这么短——只有一行， ， ， （ ） ： ， ， < / p >
< pre > < code class = "language-go" > func Balance() int {
mu.Lock()
defer mu.Unlock()
return balance
}
< / code > < / pre >
< p > 上面的例子里Unlock会在return语句读取完balance的值之后执行， ， < / p >
< p > 此外， ， （ ） ， ， < / p >
< p > 考虑一下下面的Withdraw函数。成功的时候， ， ， < / p >
< pre > < code class = "language-go" > // NOTE: not atomic!
func Withdraw(amount int) bool {
Deposit(-amount)
if Balance() < 0 {
Deposit(amount)
return false // insufficient funds
}
return true
}
< / code > < / pre >
< p > 函数终于给出了正确的结果， ， ， ： ， ， < / p >
< p > 理想情况下，取款应该只在整个操作中获得一次互斥锁。下面这样的尝试是错误的：< / p >
< pre > < code class = "language-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
}
< / code > < / pre >
< p > 上面这个例子中， ， ， （ ： ， ， ） ， ， < / p >
< p > 关于Go的mutex不能重入这一点我们有很充分的理由。mutex的目的是确保共享变量在程序执行时的关键点上能够保证不变性。不变性的一层含义是“没有goroutine访问共享变量”， ， ： ， （ ： ） ， ， ， ， ， ， （ ： < a href = "https://stackoverflow.com/questions/14670979/recursive-locking-in-go/14671462#14671462" > 更详细的解释< / a > ， ， ） < / p >
< p > 一个通用的解决方案是将一个函数分离为多个函数， ： ， ， ， ， ： < / p >
< pre > < code class = "language-go" > func Withdraw(amount int) bool {
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)
}
func Balance() int {
mu.Lock()
defer mu.Unlock()
return balance
}
// This function requires that the lock be held.
func deposit(amount int) { balance += amount }
< / code > < / pre >
< p > 当然， ， ， ， < / p >
< p > 封装（ ） ， ， ， ， （ ， ） ， < / p >
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