golang讀寫鎖

golang讀寫鎖，其特征在於

1. 讀鎖：可以同時進行多個協程讀操作，不允許寫操作
2. 寫鎖：只允許同時有一個協程進行寫操作，不允許其他寫操作和讀操作

讀寫鎖共有四個方法

1. RLock：獲取讀鎖
2. RUnLock：釋放讀鎖
3. Lock：獲取寫鎖
4. UnLock：釋放寫鎖

使用例子如下

package main

import (
    "fmt"
    "sync"
    "time"
)

var gRWLock *sync.RWMutex

var gVar int

func init() {
    gRWLock = new(sync.RWMutex)
    gVar = 1
}

func main() {
    var wg sync.WaitGroup
    go Read(1, &wg)
    wg.Add(1)
    go Write(1, &wg)
    wg.Add(1)
    go Read(2, &wg)
    wg.Add(1)
    go Read(3, &wg)
    wg.Add(1)

    wg.Wait()
}

func Read(id int, wg *sync.WaitGroup) {
    fmt.Printf("Read Coroutine: %d start\n", id)
    defer fmt.Printf("Read Coroutine: %d end\n", id)
    gRWLock.RLock()
    fmt.Printf("gVar %d\n", gVar)
    time.Sleep(time.Second)
    gRWLock.RUnlock()

    wg.Done()

}

func Write(id int, wg *sync.WaitGroup) {
    fmt.Printf("Write Coroutine: %d start\n", id)
    defer fmt.Printf("Write Coroutine: %d end\n", id)
    gRWLock.Lock()
    gVar = gVar + 100
    fmt.Printf("gVar %d\n", gVar)
    time.Sleep(time.Second)
    gRWLock.Unlock()
    wg.Done()

}