loop iterator variable error

[woodliu]

What version of Go are you using (go version)?

1.17.2

$ go version

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\liuch\AppData\Local\go-build
set GOENV=C:\Users\liuch\AppData\Roaming\go\env
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.17.2
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=NUL
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\liuch\AppData\Local\Temp\go-build463971690=/tmp/go-build -gno-record-gcc-switches

go env Output

$ go env

What did you do?

From golang wiki, i test "Using goroutines on loop iterator variables", the code as below,

    var vs []int
    for i := 0; i < 100; i++ {
        go func(val int) {
            vs = append(vs,val)
        }(i)
    }
    time.Sleep(time.Second * 3)
    sort.Ints(vs)
    fmt.Println(len(vs),vs)

What did you expect to see?

It shoud print the length of vs is 100， and the number of vs is from 0 ~ 99.

What did you see instead?

The length changes everthing i run the code, like
95 [0 1 2 6 7 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99]

Why it lose some value, and what should i do if i want to match the expection? Thanks!

[woodliu]

Because lack of lock....