map booboo

buggy-also.go

package main

import (
	"sync"
	"time"
)

// cache allows manipulating cached data.
type cache struct {
	// Concurrent access control to maps
	sync.RWMutex
	ip map[string]string
}

func (c cache) spam() {
	c.Lock()
	defer c.Unlock()
	c.ip["foo"] = "bar"
}

func main() {
	c := cache{	sync.RWMutex{}, make(map[string]string) }

	for i := 0; i < 10000; i++ {
		go c.spam()
	}
	time.Sleep(time.Second)
}

buggy.go

package main

import (
	"sync"
	"time"
)

// cache allows manipulating cached data.
type cache struct {
	// Concurrent access control to maps
	sync.RWMutex
	ip map[string]string
}

func (c cache) spam() {
	c.Lock()
	defer c.Unlock()
	c.ip["foo"] = "bar"
}

func main() {
	c := cache{	
    ip: make(map[string]string),
  }

	for i := 0; i < 10000; i++ {
		go c.spam()
	}
	time.Sleep(time.Second)
}

fixed.go

package main

import (
	"sync"
	"time"
)

// cache allows manipulating cached data.
type cache struct {
	// Concurrent access control to maps
	*sync.RWMutex
	ip map[string]string
}

func (c cache) spam() {
	c.Lock()
	defer c.Unlock()
	c.ip["foo"] = "bar"
}

func main() {
	c := cache{	&sync.RWMutex{}, make(map[string]string) }

	for i := 0; i < 10000; i++ {
		go c.spam()
	}
	time.Sleep(time.Second)
}