11.3 互斥锁和读写锁

并发会产生的问题 -竞争

11.3.1 并发产生问题的代码

package main
import (
    "fmt"
    "sync"
)
var total int
var wg sync.WaitGroup
func add(){
    defer wg.Done()
    for i := 0; i < 100000; i ++ {
        total += 1
    }
}
func sub(){
    defer wg.Done()
    for i := 0; i < 100000; i ++ {
        total -= 1
    }
}
func main(){
    wg.Add(2)
    go add()
    go sub()
    wg.Wait()
    fmt.Println(fmt.Sprintf("total is: %d", total))
}

11.3.2 通过互斥锁解决并发问题

package main
import (
    "fmt"
    "sync"
)
var total int
var wg sync.WaitGroup
var lock sync.Mutex
func add(){
    defer wg.Done()
    for i := 0; i < 100000; i ++ {
        lock.Lock()
        total += 1
        lock.Unlock()
    }
}
func sub(){
    defer wg.Done()
    for i := 0; i < 100000; i ++ {
        lock.Lock()
        total -= 1
        lock.Unlock()
    }
}
func main(){
    wg.Add(2)
    go add()
    go sub()
    wg.Wait()
    fmt.Println(fmt.Sprintf("total is: %d", total))
}

11.3.3 读写锁

package main
import (
    "fmt"
    "sync"
    "time"
)
var rwLock sync.RWMutex
var wg sync.WaitGroup
func read(){
    defer wg.Done()
    rwLock.RLock()
    fmt.Println("读取数据")
    time.Sleep(time.Second)
    fmt.Println("读取成功")
    rwLock.RUnlock()
}
func write(){
    defer wg.Done()
    rwLock.Lock()
    fmt.Println("修改数据")
    time.Sleep(time.Second*10)
    fmt.Println("修改成功")
    rwLock.Unlock()
}
func main() {
    wg.Add(10)
    for i := 0;i<5;i++ {
        go read()
    }
    for i := 0;i<5;i++ {
        go write()
    }
    wg.Wait()
}