读写锁是针对读写的互斥锁
基本遵循两大原则：
1、可以随便读，多个goroutine同时读
2、写的时候，啥也不能干。不能读也不能写
RWMutex提供了四个方法：
func (*RWMutex) Lock // 写锁定
func (*RWMutex) Unlock // 写解锁
func (*RWMutex) RLock // 读锁定
func (*RWMutex) RUnlock // 读解锁
一、随便读
package main
import (
"sync"
"time"
)
var m *sync.RWMutex
func main() {
m = new(sync.RWMutex)
// 多个同时读
go read(1)
go read(2)
time.Sleep(2*time.Second)
}
func read(i int) {
println(i,"read start")
m.RLock()
println(i,"reading")
time.Sleep(1*time.Second)
m.RUnlock()
println(i,"read over")
}运行结果：
1 read start
1 reading
2 read start
2 reading
1 read over
2 read over
可以看出1 读还没有结束，2已经在读
二、写的时候啥也不能干
package main
import (
"sync"
"time"
)
var m *sync.RWMutex
func main() {
m = new(sync.RWMutex)
// 写的时候啥也不能干
go write(1)
go read(2)
go write(3)
time.Sleep(2*time.Second)
}
func read(i int) {
println(i,"read start")
m.RLock()
println(i,"reading")
time.Sleep(1*time.Second)
m.RUnlock()
println(i,"read over")
}
func write(i int) {
println(i,"write start")
m.Lock()
println(i,"writing")
time.Sleep(1*time.Second)
m.Unlock()
println(i,"write over")
}输出：
1 write start
1 writing
2 read start
3 write start
1 writing over
2 reading
2 read over
3 writing
3 write over
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