go并发编程之六(sync之读写锁RWMutex)

旧城等待， 2022-04-23 08:32 360阅读 0赞

> `RWMutex`读写锁相关的介绍使用

### 文章目录 ###

*   *   *  1. 读写锁的定义
         *  2. 读写锁的使用

### 1. 读写锁的定义 ###

涉及到俩个角色：读者和写者。  
读者只读数据，写者修改它。当写者访问操作数据时，其他任何线程（读者或写者）都无法共享此数据的访问权限。  
当写者释放数据时，多个读者同时读取该数据时可以正常访问。

读锁：只在写锁被锁定时，读锁才会起作用  
写锁：会锁定写锁和读锁锁定的所有区域

### 2. 读写锁的使用 ###

package main
    
    import (
    	"fmt"
    	"sync"
    	"time"
    )
    
    type Stock struct { 
    	good map[int]int
    	rw sync.RWMutex
    }
    
    var wg sync.WaitGroup
    
    // 获取当个商品对应的库存
    func (s *Stock)Get(k int) { 
    	s.rw.RLock()
    	defer func() { 
    		s.rw.RUnlock()
    		wg.Done()
    	}()
    	time.Sleep(time.Second * 5)
    	fmt.Println("locker is ", s.rw.RLocker() ,k," val reading ",s.good[k], " time: " ,time.Now().UnixNano())
    }
    
    func (s *Stock)Set(k,v int) { 
    	s.rw.Lock()
    	defer func() { 
    		wg.Done()
    	}()
    	s.good[k] = v
    	s.rw.Unlock()
    	fmt.Println(k," is writing ",v, " time: " ,time.Now().Unix())
    }
    
    func main() { 
    
    	stock := Stock { 
    		good : make(map[int]int,10),
    	}
    	wg.Add(30)
    	for i := 1 ; i<= 10 ; i++ { 
    		go stock.Set(i,100)
    	}
    	for i := 1 ; i<= 10 ; i++ { 
    		go stock.Get(i)
    		go stock.Get(i)
    	}
    	wg.Wait()
    }

不加锁的情况下打印：  
fatal error: concurrent map writes  
参考文章：[https://blog.csdn.net/simatongming/article/details/79075820][https_blog.csdn.net_simatongming_article_details_79075820]

> 我们使用命令

go run main.go --race

打印结果：

fatal error: 4 is writing 100 time: 1548748976692000300  
concurrent map writes2 is writing 100 time: 1548748976692000300  
6 is writing 100 time: 1548748976692000300

加锁打印结果：  
2 is writing 100 time: 1548751973  
3 is writing 100 time: 1548751973  
6 is writing 100 time: 1548751973  
4 is writing 100 time: 1548751973  
5 is writing 100 time: 1548751973  
8 is writing 100 time: 1548751973  
7 is writing 100 time: 1548751973  
9 is writing 100 time: 1548751973  
10 is writing 100 time: 1548751973  
1 is writing 100 time: 1548751973  
locker is &\{ \{0 0\} 0 0 20 0\} 10 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 1 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 6 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 1 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 5 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 8 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 5 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 2 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 3 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 2 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 10 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 8 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 7 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 4 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 9 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 7 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 4 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 9 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 3 val reading 100 time: 1548751978371000300  
locker is &\{ \{0 0\} 0 0 20 0\} 6 val reading 100 time: 1548751978371000300

> 可以看到，我们虽然对读锁加了阻塞，但是所有的good数据都还是同时过了5s读出来了，只有写操作，才会  
> 阻塞读，这样我们就能避免读到脏数据

更多更详细的解释可以参看这篇文章 ： [https://medium.com/golangspec/sync-rwmutex-ca6c6c3208a0][https_medium.com_golangspec_sync-rwmutex-ca6c6c3208a0]

[https_blog.csdn.net_simatongming_article_details_79075820]: https://blog.csdn.net/simatongming/article/details/79075820
[https_medium.com_golangspec_sync-rwmutex-ca6c6c3208a0]: https://medium.com/golangspec/sync-rwmutex-ca6c6c3208a0