0%
March 24, 2024

Read Write Lock for Go

go

We study the following locks:

package main

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

var wg sync.WaitGroup
var mutex sync.RWMutex

func write() {
	defer wg.Done()

	mutex.Lock()
	fmt.Println("Writing ...")
	time.Sleep(time.Second * 1)
	mutex.Unlock()
}

func read() {
	defer wg.Done()
	mutex.RLock()
	fmt.Println("Reading ...")
	time.Sleep(time.Second * 1)
	mutex.RUnlock()
}

func main() {
	for r := 0; r < 10; r++ {
		wg.Add(1)
		go write()
	}
	for r := 0; r < 10; r++ {
		wg.Add(1)
		go read()
	}
	wg.Wait()
}
  • In RWMutex, when we are writing we use Lock() to block any read and write access until we Unlock() it.
  • However, when we use RLock(), we are telling compiler we allow concurrent reads.
  • If we execute the code above, we have: 
    Writing ...
    and 1s later: 
    Reading ...
Reading ...
Reading ...
Reading ...
Reading ...
Reading ...
Reading ...
Reading ...
Reading ...
Reading ...
    and then the following 1s later one another: 
    Writing ... // 1s
Writing ... // 1s
Writing ... // 1s
Writing ...
Writing ...     .
Writing ...     .
Writing ...     .
Writing ...
Writing ... // 1s