GO 读写锁sync.RWMutex（1）

作者: 尼桑麻 | 来源:发表于2019-03-27 00:38 被阅读0次

GO 读写锁sync.RWMutex（1）
Golang学习笔记之互斥锁(Mutex)
锁
GO 读写锁sync.RWMutex（2）
go sync包的读写锁RWMutex的使用
golang并发编程读写锁sync.RWMutex
Go超时锁的设计和实现
Golang包——sync
Go 语言的锁
golang-读写锁 sync.RWMutex

继GO语言锁机制（1）后，我们继续来探讨GO语言的锁机制

sync.RWMutex (读写锁，R代表度,W代表写)

读写锁是读/写互斥锁的简称。在Go语言中，读写锁由sync.RWMutex类型的值代表。与sync.Mutex类型一样，这个类型也是开箱即用的。
顾名思义，读写锁是把对共享资源的“读操作”和“写操作”区别对待了。它可以对这两种操作施加不同程度的保护。换句话说，相比于互斥锁，读写锁可以实现更加细腻的访问控制。

例子

demo2

package sync_26_28

import (
    "github.com/wonderivan/logger"
    "sync"
    "time"
)

var book = []string{"床前明月光", "疑是地上霜", "举头忘明月", "低头思故乡"}
//var blackboard = &atomic.Value{}

var blackboard string
var page int

var rwmutext = sync.RWMutex{}

type Student struct {
    Name  string
    Rtext string
}

type Teacher struct {
    Name  string
    Wtext string
}

func (s *Student) read() {
    logger.Info(s.Name + " request read ...")
    rwmutext.RLock()
    defer rwmutext.RUnlock()
    logger.Info(s.Name + " start read ")
    //s.Rtext = blackboard.Load().(string)
    s.Rtext = blackboard
    time.Sleep(time.Second)
    logger.Info(s.Name + " end read " + s.Rtext)
}

func (t *Teacher) write(index int) {
    logger.Info(t.Name + " request write ...")
    rwmutext.Lock()

    if index == page {
        logger.Info(t.Name + " start write ...")
        t.Wtext = book[page]
        time.Sleep(time.Second * 3) // 写这句花了 3秒钟
        //blackboard.Store(t.Wtext)
        blackboard = t.Wtext
        page++
        //logger.Info(t.Name+" finish. blackboard: ", blackboard.Load())
        logger.Info(t.Name+" finish. blackboard: ", blackboard)
        rwmutext.Unlock()
        time.Sleep(time.Second * 3) // 写完休息一下给学生们读
    } else {
        logger.Info(t.Name + " end 放弃 ...")
        rwmutext.Unlock()
    }

}

func RwTest01() {
    sa := &Student{Name: "S-a"}
    sb := &Student{Name: "S-b"}
    sc := &Student{Name: "S-c"}
    ta := &Teacher{Name: "T-a"}
    tb := &Teacher{Name: "T-b"}

    go startWrite(ta)
    go startWrite(tb)
    time.Sleep(time.Second * 1) // 粗鲁的控制，让老师写开始写
    go startRead(sa)
    go startRead(sb)
    go startRead(sc)

}
func startRead(s *Student) {
    for i := 0; i < 1000; i++ {
        s.read()
    }
}

func startWrite(t *Teacher) {
    for i := 0; i < 4; i++ {
        t.write(i)
    }
}

RWMutex的四种操作方法

RLock（） //读锁定
RUnlock（） //读解锁
Lock（） //写锁定
Unlock（） //写解锁

RWMutex的使用主要事项

这个例子意思就是两个老师在看一本只有四页的书，把书里的内容写到黑板上，有三个学生一直在读黑板上的内容。
1.a老师在写的时候，b老师写不了
写锁的时候要等待写锁的结束
2.老师们在写新内容的时候，要确保学生们都看完了黑板上内容
写锁的时候要等待读锁的结束
3.老师们写的是时候整个身子挡住了黑板，学生们得到老师写完了，离开黑板才能看间写的内容
读锁要等待写锁的结束
4.黑板就在哪里学生们都可以看到
读锁无需等待读锁借宿
值得一提的是读锁虽然不需要等待读锁的结束，不过确是有最大读锁限制的。

2019-03-27 12:58:33 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-a request write ...
2019-03-27 12:58:33 [INFO] [untitled/sync_26_28/demo_rwmutex.go:43] T-a start write ...
2019-03-27 12:58:33 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-b request write ...
2019-03-27 12:58:34 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:34 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:34 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:36 [INFO] [untitled/sync_26_28/demo_rwmutex.go:50] T-a finish. blackboard:  床前明月光
2019-03-27 12:58:36 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:36 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:36 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 床前明月光
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 床前明月光
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 床前明月光
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:54] T-b end 放弃 ...
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-b request write ...
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:37 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 床前明月光
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 床前明月光
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 床前明月光
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:38 [INFO] [untitled/sync_26_28/demo_rwmutex.go:43] T-b start write ...
2019-03-27 12:58:39 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-a request write ...
2019-03-27 12:58:41 [INFO] [untitled/sync_26_28/demo_rwmutex.go:50] T-b finish. blackboard:  疑是地上霜
2019-03-27 12:58:41 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:41 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:41 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 疑是地上霜
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 疑是地上霜
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 疑是地上霜
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:54] T-a end 放弃 ...
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-a request write ...
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:42 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 疑是地上霜
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 疑是地上霜
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 疑是地上霜
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:43 [INFO] [untitled/sync_26_28/demo_rwmutex.go:43] T-a start write ...
2019-03-27 12:58:44 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-b request write ...
2019-03-27 12:58:46 [INFO] [untitled/sync_26_28/demo_rwmutex.go:50] T-a finish. blackboard:  举头忘明月
2019-03-27 12:58:46 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:46 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:46 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 举头忘明月
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 举头忘明月
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 举头忘明月
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:54] T-b end 放弃 ...
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-b request write ...
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:47 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 举头忘明月
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 举头忘明月
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 举头忘明月
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:48 [INFO] [untitled/sync_26_28/demo_rwmutex.go:43] T-b start write ...
2019-03-27 12:58:49 [INFO] [untitled/sync_26_28/demo_rwmutex.go:39] T-a request write ...
2019-03-27 12:58:51 [INFO] [untitled/sync_26_28/demo_rwmutex.go:50] T-b finish. blackboard:  低头思故乡
2019-03-27 12:58:51 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:51 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:51 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-c end read 低头思故乡
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-c request read ...
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 低头思故乡
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-a request read ...
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 低头思故乡
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:28] S-b request read ...
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:54] T-a end 放弃 ...
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-b start read 
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-c start read 
2019-03-27 12:58:52 [INFO] [untitled/sync_26_28/demo_rwmutex.go:31] S-a start read 
2019-03-27 12:58:53 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-b end read 低头思故乡
2019-03-27 12:58:53 [INFO] [untitled/sync_26_28/demo_rwmutex.go:35] S-a end read 低头思故乡

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