使用 go 遇到的一个奇怪问题，求教

下面这段代码在长时间运行后，有一定的机率会出错，RandString(32) 返回的全是 0.

从网上查的资料全局变量应该不会被回收才对。

package helper

import (
	"math/rand"
	"time"
)

const _charsetRand = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789@#$"

var _seededRand = rand.New(rand.NewSource(time.Now().UnixNano()))

// RandStringWithCharset rand string with charset
func RandStringWithCharset(length int, charset string) string {b := make([]byte, length)
	l := len(charset)
	for i := range b {b[i] = charset[_seededRand.Intn(l)]
	}
	return string(b)
}

// RandString rand string
func RandString(length int) string {return RandStringWithCharset(length, _charsetRand)
}

// RandInt rand int between [min, max)
func RandInt(min int, max int) int {
	if min <= 0 || max <= 0 {return 0}

	if min >= max {return max}

	return _seededRand.Intn(max-min) + min
}

// RandMax rand int between [0, max)
func RandMax(max int) int {
	if max <= 1 {return 0}

	return _seededRand.Intn(max)
}