package main

import (
	"runtime"
	"runtime/metrics"
	"testing"
	"time"
)

func TestSleepAccounting(t *testing.T) {
	names := []string{
		"/cpu/classes/gc/mark/assist:cpu-seconds",
		"/cpu/classes/gc/mark/dedicated:cpu-seconds",
		"/cpu/classes/gc/mark/idle:cpu-seconds",
		"/cpu/classes/gc/pause:cpu-seconds",
		"/cpu/classes/gc/total:cpu-seconds",
		"/cpu/classes/idle:cpu-seconds",
		"/cpu/classes/scavenge/assist:cpu-seconds",
		"/cpu/classes/scavenge/background:cpu-seconds",
		"/cpu/classes/scavenge/total:cpu-seconds",
		"/cpu/classes/total:cpu-seconds",
		"/cpu/classes/user:cpu-seconds",
	}
	prep := func() []metrics.Sample {
		mm := make([]metrics.Sample, len(names))
		for i := range names {
			mm[i].Name = names[i]
		}
		return mm
	}
	m1, m2 := prep(), prep()

	dur := time.Second

	runtime.GC() // update /cpu/classes metrics
	metrics.Read(m1)
	time.Sleep(dur)
	runtime.GC() // update /cpu/classes metrics
	metrics.Read(m2)

	for i := range names {
		if m1[i].Value.Kind() == metrics.KindBad {
			continue
		}
		t.Logf("%s %0.3f\n", names[i], m2[i].Value.Float64()-m1[i].Value.Float64())
	}

	for i := range names {
		if names[i] == "/cpu/classes/user:cpu-seconds" {
			if dt := m2[i].Value.Float64() - m1[i].Value.Float64(); dt > (dur / 2).Seconds() {
				t.Errorf(`BUG: time.Sleep has contributed to "user" rather than "idle" CPU class`)
			}
		}
	}
}

/cpu/classes/user:cpu-seconds
	Estimated total CPU time spent running user Go code. This may
	also include some small amount of time spent in the Go runtime.
	This metric is an overestimate, and not directly comparable
	to system CPU time measurements. Compare only with other
	/cpu/classes metrics.

/cpu/classes/idle:cpu-seconds
	Estimated total available CPU time not spent executing
	any Go or Go runtime code. In other words, the part of
	/cpu/classes/total:cpu-seconds that was unused. This metric is
	an overestimate, and not directly comparable to system CPU time
	measurements. Compare only with other /cpu/classes metrics.

$ go1.20 test /tmp/sleep_test.go -cpu=1,8
--- FAIL: TestSleepAccounting (1.00s)
    sleep_test.go:45: /cpu/classes/gc/mark/assist:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/mark/dedicated:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/mark/idle:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/pause:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/total:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/idle:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/scavenge/assist:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/scavenge/background:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/scavenge/total:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/total:cpu-seconds 1.001
    sleep_test.go:45: /cpu/classes/user:cpu-seconds 1.001
    sleep_test.go:51: BUG: time.Sleep has contributed to "user" rather than "idle" CPU class
--- FAIL: TestSleepAccounting (1.00s)
    sleep_test.go:45: /cpu/classes/gc/mark/assist:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/mark/dedicated:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/mark/idle:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/gc/pause:cpu-seconds 0.001
    sleep_test.go:45: /cpu/classes/gc/total:cpu-seconds 0.002
    sleep_test.go:45: /cpu/classes/idle:cpu-seconds 7.010
    sleep_test.go:45: /cpu/classes/scavenge/assist:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/scavenge/background:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/scavenge/total:cpu-seconds 0.000
    sleep_test.go:45: /cpu/classes/total:cpu-seconds 8.013
    sleep_test.go:45: /cpu/classes/user:cpu-seconds 1.002
    sleep_test.go:51: BUG: time.Sleep has contributed to "user" rather than "idle" CPU class
FAIL
FAIL	command-line-arguments	2.121s
FAIL