Go: Read/Write variable locking - demo showing the problem when accessing the variable directly and via a read lock when a slow write lock is running

rwmutex.go

package main

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

type C struct {
	sync.RWMutex
	i     int
	files []string
}

func (c *C) Init() {
	c.Lock()
	c.files = make([]string, 0)
	for i := c.i; i < c.i+5; i++ {
		c.files = append(c.files, fmt.Sprintf("file%d", i))
		time.Sleep(time.Millisecond * 500)
	}
	c.i += 5
	c.Unlock()
}

func (c *C) GetFiles() []string {
	c.RLock()
	defer c.RUnlock()
	return c.files
}

func main() {
	c := &C{}
	c.Init()

	go func() {
		ticker := time.NewTicker(time.Second * 5)
		for {
			select {
			case <-ticker.C:
				c.Init()
			}
		}
	}()

	wait := make(chan bool, 1)

	go func() {
		ticker := time.NewTicker(time.Second * 1)
		for {
			select {
			case <-ticker.C:
				fmt.Println("c.GetFiles>>", c.GetFiles())
			}
		}
	}()

	go func() {
		ticker := time.NewTicker(time.Second * 1)
		for {
			select {
			case <-ticker.C:
				fmt.Println("c.files>>", c.files)
			}
		}
	}()

	<-wait
}