runtime: shrink map as elements are deleted 缩容 垃圾回收 GC 内存

runtime: shrink map as elements are deleted

runtime: shrink map as elements are deleted · Issue #20135 · golang/go · GitHub https://github.com/golang/go/issues/20135

package main

import (
	"fmt"
	"runtime"
)

func main() {
	// runtime: shrink map as elements are deleted · Issue #20135 · golang/go · GitHub https://github.com/golang/go/issues/20135

	v := struct{}{}

	a := make(map[int]struct{})

	for i := 0; i < 10000; i++ {
		a[i] = v
	}

	runtime.GC()
	printMemStats("After Map Add 100000")

	for i := 0; i < 10000-1; i++ {
		delete(a, i)
	}

	runtime.GC()
	printMemStats("After Map Delete 9999")

	for i := 0; i < 10000-1; i++ {
		a[i] = v
	}

	runtime.GC()
	printMemStats("After Map Add 9999 again")

	a = nil
	runtime.GC()
	printMemStats("After Map Set nil")
}

func printMemStats(mag string) {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	fmt.Printf("%v：memory = %vKB, GC Times = %v\n", mag, m.Alloc/1024, m.NumGC)
}

　

After Map Add 100000：memory = 277KB, GC Times = 1
After Map Delete 9999：memory = 278KB, GC Times = 2
After Map Add 9999 again：memory = 102KB, GC Times = 3
After Map Set nil：memory = 102KB, GC Times = 4