unsafe_map_test.go

package main

import (
	"fmt"
	"log"
	"time"
)

type Record struct {
	a int
	b int
	c int
}

var (
	m     = make(map[string]Record)
	v1    = Record{1, 2, 3}
	v2    = Record{4, 5, 6}
	empty = Record{0, 0, 0}
)

func Check(m map[string]Record) {
	x := m["a"]
	if x != v1 && x != v2 && x != empty {
		log.Fatal("but got expected", x)
	}
}
func main() {
	fmt.Println("Hello world")
	m["a"] = v1
	go func() {
		for {
			m["a"] = v2
			Check(m)
		}
	}()
	go func() {
		for {
			m["a"] = v1
			Check(m)
		}
	}()
	go func() {
		for {
			delete(m, "a")
			m["a"] = v1
			Check(m)
		}
	}()
	for {
		time.Sleep(time.Second)
	}
}

when call delete function, other go routine may got nil of m