```go
package main

import (
"fmt"
"sync"
"time"
)

type User struct {
email string
orders []*Order
}

type Order struct {
no string
createdAt time.Time
}

func main() {

total := 0
for {
user := &User{email: "xxxx"}
wg := sync.WaitGroup{}
wg.Add(6)
for i := 0; i < 6; i++ {
go func() {
defer wg.Done()
user.orders = append(user.orders, &Order{})
}()
}
wg.Wait()
total += 1
fmt.Println(user, len(user.orders), "total=", total)
time.Sleep(time.Millisecond * 200)
}
}
```

这是代码，大家可以跑一段时间，然后看看会不会出现空指针