time: time.Before return an unexpected result #42056

ironzhang · 2020-10-19T03:21:53Z

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

$ go version
go version go1.14.3 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/zhanghui/Library/Caches/go-build"
GOENV="/Users/zhanghui/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/zhanghui/gopath/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/zhanghui/gopath"
GOPRIVATE=""
GOPROXY="http://goproxy.intra.xiaojukeji.com"
GOROOT="/usr/local/go"
GOSUMDB="off"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/03/x_5wmgc108z6rsmh0b4xc2800000gp/T/go-build618623655=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

This is my test case

import (
        "fmt"
        "syscall"
        "testing"
        "time"
)

func SetSysTime(t time.Time) error {
        tv := syscall.NsecToTimeval(t.UnixNano())
        return syscall.Settimeofday(&tv)
}

func TestTimeNow(t *testing.T) {
        n1 := time.Now()
        defer func() {
                SetSysTime(n1)
        }()

        t1 := n1.Add(2 * time.Hour)
        t2 := n1.Add(3 * time.Hour)
        if err := SetSysTime(t2); err != nil {
                t.Fatalf("set sys time: %v", err)
        }
        n2 := time.Now()

        fmt.Printf("n1=[%v], n2=[%v]\n", n1, n2)
        fmt.Printf("t1=[%v], t2=[%v]\n", t1, n2)

        if t2.Before(t1) {
                t.Errorf("t2 before t1, t2=[%v][%d], t1=[%v][%d]", t2, t2.UnixNano(), t1, t1.UnixNano())
        }
        if n2.Before(t1) {
                t.Errorf("n2 before t1, n2=[%v][%d], t1=[%v][%d]", n2, n2.UnixNano(), t1, t1.UnixNano())
        }
}

What did you expect to see?

I expected to see the test can pass.

What did you see instead?

when I run sudo go test，it failed, the output is

n1=[2020-10-19 11:19:20.762809 +0800 CST m=+0.000549490], n2=[2020-10-19 14:19:20.766093 +0800 CST m=+0.003840186]
t1=[2020-10-19 13:19:20.762809 +0800 CST m=+7200.000549490], t2=[2020-10-19 14:19:20.766093 +0800 CST m=+0.003840186]
--- FAIL: TestTimeNow (0.01s)
    time_test.go:35: n2 before t1, n2=[2020-10-19 14:19:20.766093 +0800 CST m=+0.003840186][1603088360766093000], t1=[2020-10-19 13:19:20.762809 +0800 CST m=+7200.000549490][1603084760762809000]
FAIL
exit status 1

The text was updated successfully, but these errors were encountered:

darren · 2020-10-19T05:31:13Z

https://golang.org/pkg/time/

Calling time.Now() before and after settimeofday always has hasMonotonic set
And time comparisons use the monotonic clock reading, so n2.Before(t1) uses the monotonic clock.

I think what you expect is just use wall clock n2.UnixNano() < t1.UnixNano() for comparison.

more info: https://go.googlesource.com/proposal/+/master/design/12914-monotonic.md

ironzhang changed the title ~~A bug of time package~~ time: time.Before return an unexpected result Oct 19, 2020

ironzhang closed this as completed Oct 19, 2020

golang locked and limited conversation to collaborators Oct 19, 2021

gopherbot added the FrozenDueToAge label Oct 19, 2021

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time: time.Before return an unexpected result #42056

time: time.Before return an unexpected result #42056

ironzhang commented Oct 19, 2020 •

edited

darren commented Oct 19, 2020 •

edited

time: time.Before return an unexpected result #42056

time: time.Before return an unexpected result #42056

Comments

ironzhang commented Oct 19, 2020 • edited

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

Does this issue reproduce with the latest release?

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

What did you do?

What did you expect to see?

What did you see instead?

darren commented Oct 19, 2020 • edited

ironzhang commented Oct 19, 2020 •

edited

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

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

darren commented Oct 19, 2020 •

edited