package main

import (
	"fmt"
	"runtime"
)

var retained [][]byte // 全局变量，用来保持对象可达

func printMemory(stage string) {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)

	fmt.Printf("%s: HeapAlloc=%d MiB, TotalAlloc=%d MiB\n",
		stage,
		m.HeapAlloc/1024/1024,
		m.TotalAlloc/1024/1024)
}

func main() {
	runtime.GC()
	printMemory("开始")

	for i := 0; i < 20; i++ {
		block := make([]byte, 1024*1024) // 每次创建约 1 MiB 的底层数组
		block[0] = byte(i)
		retained = append(retained, block)
	}
	printMemory("分配后")

	retained = nil // 程序不再持有这些数组
	runtime.GC()
	printMemory("GC 后")
}