package main

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

var (
	x      int64
	wg     sync.WaitGroup
	rwlock sync.RWMutex
	lock   sync.Mutex
)

func main() {
	start := time.Now()
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go write()
	}
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go read()
	}
	wg.Wait()
	fmt.Println("cost:", time.Since(start))
}

func read() {
	//lock.Lock()
	rwlock.RLock()
	time.Sleep(time.Millisecond)
	//lock.Unlock()
	rwlock.RUnlock()
	wg.Done()
}

func write() {
	rwlock.Lock()
	//lock.Lock()
	x = x + 1
	time.Sleep(10 * time.Millisecond)
	//lock.Unlock()
	rwlock.Unlock()
	wg.Done()
}