golang并发编程中为什么会导致输出不同的数组长度？

我正在用 golang 编写一个简单的程序用于并发测试，但不明白 capitalized 每次数组大小的不同输出！

data := []rune{'a', 'b', 'c', 'd'}
var capitalized []rune

capit := func(r rune) {
    capitalized = append(capitalized, unicode.toupper(r))
    fmt.printf("%c done!n", r)
}

fmt.printf("before: %cn", capitalized)
for i := 0; i < len(data); i++ {
    go capit(data[i])
}
time.sleep(100 * time.millisecond)
fmt.printf("after: %cn", capitalized)

输出：

b done! a done! d done! c done! after: [d b c a]

a done! d done! c done! b done! after: [d b a]

d done! a done! c done! b done! after: [b]

d done! a done! c done! b done! after: [a b c]

d done! b done! a done! c done! After: [B C]

正确答案

go：数据竞争检测器

您存在数据竞争。

$ go run -race racer.go
before: []
==================
warning: data race
write at 0x00c000012018 by goroutine 8:
  main.main.func1()
      racer.go:14 +0xc4
  main.main.func2()
      racer.go:20 +0x3e

previous read at 0x00c000012018 by goroutine 7:
  main.main.func1()
      racer.go:14 +0x44
  main.main.func2()
      racer.go:20 +0x3e

goroutine 8 (running) created at:
  main.main()
      racer.go:20 +0x199

goroutine 7 (running) created at:
  main.main()
      racer.go:20 +0x199
==================
a done!
==================
warning: data race
write at 0x00c000012018 by goroutine 9:
  main.main.func1()
      racer.go:14 +0xc4
  main.main.func2()
      racer.go:20 +0x3e

previous write at 0x00c000012018 by goroutine 10:
  main.main.func1()
      racer.go:14 +0xc4
  main.main.func2()
      racer.go:20 +0x3e

goroutine 9 (running) created at:
  main.main()
      racer.go:20 +0x199

goroutine 10 (running) created at:
  main.main()
      racer.go:20 +0x199
==================
d done!
b done!
c done!
after: [b c]
found 2 data race(s)
exit status 66
$

racer.go：

package main

import (
    "fmt"
    "time"
    "unicode"
)

func main() {
    data := []rune{'a', 'b', 'c', 'd'}
    var capitalized []rune

    capIt := func(r rune) {
        capitalized = append(capitalized, unicode.ToUpper(r))
        fmt.Printf("%c done!n", r)
    }

    fmt.Printf("Before: %cn", capitalized)
    for i := 0; i < len(data); i++ {
        go capIt(data[i])
    }
    time.Sleep(100 * time.Millisecond)
    fmt.Printf("After: %cn", capitalized)
}