map_leak.go

package main

import (
	_ "net/http/pprof"
	"net/http"
	"log"
	"math/rand"
	"runtime"
	"fmt"
	"hash/fnv"
)

const (
	entries = 10000001
	repeats = 100000
)

var charsRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")

func main() {
	go func () {
		log.Println(http.ListenAndServe("localhost:6060", nil))
	}()

	hashmap := make(map[uint64]bool, entries)
	hashes := make([]uint64, entries)

	for repeat := 0; repeat < repeats; repeat++ {
		fmt.Printf("==== \nRepeat: %6d \n", repeat)
		fmt.Printf("Number of elements: %6d \n", len(hashmap))
		printAllocs()
		for index := 0; index < entries - 1; index++ {
			key := generateKey()
			hashes[index] = key
			hashmap[key] = true
			delete(hashmap, hashes[index + 1])
		}
		key := generateKey()
		hashes[entries - 1] = key
		hashmap[entries - 1] = true
		delete(hashmap, hashes[0])
	}
}

func generateKey() uint64 {
	return hash64(randomString(64))
}

func hash64(s string) uint64 {
	h := fnv.New64a()
	h.Write([]byte(s))
	return h.Sum64()
}

func randomString(n int) string {
	b := make([]rune, n)
	for i := range b {
		b[i] = charsRunes[rand.Intn(len(charsRunes))]
	}
	return string(b)
}

func printAllocs() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	fmt.Printf("Heap size: %6d MB \n", m.Alloc / 1e6)
}

go build map_leak.go
./map_leak.go

...
go tool pprof ./map_leak  http://localhost:6060/debug/pprof/heap