src/time/sleep_test.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package time_test

 import (
 	"errors"
 	"fmt"
 	"math/rand"
 	"runtime"
 	"strings"
 	"sync"
 	"sync/atomic"
 	"testing"
 	. "time"
 )

 // Go runtime uses different Windows timers for time.Now and sleeping.
 // These can tick at different frequencies and can arrive out of sync.
 // The effect can be seen, for example, as time.Sleep(100ms) is actually
 // shorter then 100ms when measured as difference between time.Now before and
 // after time.Sleep call. This was observed on Windows XP SP3 (windows/386).
 // windowsInaccuracy is to ignore such errors.
 const windowsInaccuracy = 17 * Millisecond

 func TestSleep(t *testing.T) {
 	const delay = 100 * Millisecond
 	go func() {
 		Sleep(delay / 2)
 		Interrupt()
 	}()
 	start := Now()
 	Sleep(delay)
 	delayadj := delay
 	if runtime.GOOS == "windows" {
 		delayadj -= windowsInaccuracy
 	}
 	duration := Now().Sub(start)
 	if duration < delayadj {
 		t.Fatalf("Sleep(%s) slept for only %s", delay, duration)
 	}
 }

 // Test the basic function calling behavior. Correct queueing
 // behavior is tested elsewhere, since After and AfterFunc share
 // the same code.
 func TestAfterFunc(t *testing.T) {
 	i := 10
 	c := make(chan bool)
 	var f func()
 	f = func() {
 		i--
 		if i >= 0 {
 			AfterFunc(0, f)
 			Sleep(1 * Second)
 		} else {
 			c <- true
 		}
 	}

 	AfterFunc(0, f)
 	<-c
 }

 func TestAfterStress(t *testing.T) {
 	stop := uint32(0)
 	go func() {
 		for atomic.LoadUint32(&stop) == 0 {
 			runtime.GC()
 			// Yield so that the OS can wake up the timer thread,
 			// so that it can generate channel sends for the main goroutine,
 			// which will eventually set stop = 1 for us.
 			Sleep(Nanosecond)
 		}
 	}()
 	ticker := NewTicker(1)
 	for i := 0; i < 100; i++ {
 		<-ticker.C
 	}
 	ticker.Stop()
 	atomic.StoreUint32(&stop, 1)
 }

 func benchmark(b *testing.B, bench func(n int)) {

 	// Create equal number of garbage timers on each P before starting
 	// the benchmark.
 	var wg sync.WaitGroup
 	garbageAll := make([][]*Timer, runtime.GOMAXPROCS(0))
 	for i := range garbageAll {
 		wg.Add(1)
 		go func(i int) {
 			defer wg.Done()
 			garbage := make([]*Timer, 1<<15)
 			for j := range garbage {
 				garbage[j] = AfterFunc(Hour, nil)
 			}
 			garbageAll[i] = garbage
 		}(i)
 	}
 	wg.Wait()

 	b.ResetTimer()
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			bench(1000)
 		}
 	})
 	b.StopTimer()

 	for _, garbage := range garbageAll {
 		for _, t := range garbage {
 			t.Stop()
 		}
 	}
 }

 func BenchmarkAfterFunc(b *testing.B) {
 	benchmark(b, func(n int) {
 		c := make(chan bool)
 		var f func()
 		f = func() {
 			n--
 			if n >= 0 {
 				AfterFunc(0, f)
 			} else {
 				c <- true
 			}
 		}

 		AfterFunc(0, f)
 		<-c
 	})
 }

 func BenchmarkAfter(b *testing.B) {
 	benchmark(b, func(n int) {
 		for i := 0; i < n; i++ {
 			<-After(1)
 		}
 	})
 }

 func BenchmarkStop(b *testing.B) {
 	benchmark(b, func(n int) {
 		for i := 0; i < n; i++ {
 			NewTimer(1 * Second).Stop()
 		}
 	})
 }

 func BenchmarkSimultaneousAfterFunc(b *testing.B) {
 	benchmark(b, func(n int) {
 		var wg sync.WaitGroup
 		wg.Add(n)
 		for i := 0; i < n; i++ {
 			AfterFunc(0, wg.Done)
 		}
 		wg.Wait()
 	})
 }

 func BenchmarkStartStop(b *testing.B) {
 	benchmark(b, func(n int) {
 		timers := make([]*Timer, n)
 		for i := 0; i < n; i++ {
 			timers[i] = AfterFunc(Hour, nil)
 		}

 		for i := 0; i < n; i++ {
 			timers[i].Stop()
 		}
 	})
 }

 func BenchmarkReset(b *testing.B) {
 	benchmark(b, func(n int) {
 		t := NewTimer(Hour)
 		for i := 0; i < n; i++ {
 			t.Reset(Hour)
 		}
 		t.Stop()
 	})
 }

 func BenchmarkSleep(b *testing.B) {
 	benchmark(b, func(n int) {
 		var wg sync.WaitGroup
 		wg.Add(n)
 		for i := 0; i < n; i++ {
 			go func() {
 				Sleep(Nanosecond)
 				wg.Done()
 			}()
 		}
 		wg.Wait()
 	})
 }

 func TestAfter(t *testing.T) {
 	const delay = 100 * Millisecond
 	start := Now()
 	end := <-After(delay)
 	delayadj := delay
 	if runtime.GOOS == "windows" {
 		delayadj -= windowsInaccuracy
 	}
 	if duration := Now().Sub(start); duration < delayadj {
 		t.Fatalf("After(%s) slept for only %d ns", delay, duration)
 	}
 	if min := start.Add(delayadj); end.Before(min) {
 		t.Fatalf("After(%s) expect >= %s, got %s", delay, min, end)
 	}
 }

 func TestAfterTick(t *testing.T) {
 	const Count = 10
 	Delta := 100 * Millisecond
 	if testing.Short() {
 		Delta = 10 * Millisecond
 	}
 	t0 := Now()
 	for i := 0; i < Count; i++ {
 		<-After(Delta)
 	}
 	t1 := Now()
 	d := t1.Sub(t0)
 	target := Delta * Count
 	if d < target*9/10 {
 		t.Fatalf("%d ticks of %s too fast: took %s, expected %s", Count, Delta, d, target)
 	}
 	if !testing.Short() && d > target*30/10 {
 		t.Fatalf("%d ticks of %s too slow: took %s, expected %s", Count, Delta, d, target)
 	}
 }

 func TestAfterStop(t *testing.T) {
 	// We want to test that we stop a timer before it runs.
 	// We also want to test that it didn't run after a longer timer.
 	// Since we don't want the test to run for too long, we don't
 	// want to use lengthy times. That makes the test inherently flaky.
 	// So only report an error if it fails five times in a row.

 	var errs []string
 	logErrs := func() {
 		for _, e := range errs {
 			t.Log(e)
 		}
 	}

 	for i := 0; i < 5; i++ {
 		AfterFunc(100*Millisecond, func() {})
 		t0 := NewTimer(50 * Millisecond)
 		c1 := make(chan bool, 1)
 		t1 := AfterFunc(150*Millisecond, func() { c1 <- true })
 		c2 := After(200 * Millisecond)
 		if !t0.Stop() {
 			errs = append(errs, "failed to stop event 0")
 			continue
 		}
 		if !t1.Stop() {
 			errs = append(errs, "failed to stop event 1")
 			continue
 		}
 		<-c2
 		select {
 		case <-t0.C:
 			errs = append(errs, "event 0 was not stopped")
 			continue
 		case <-c1:
 			errs = append(errs, "event 1 was not stopped")
 			continue
 		default:
 		}
 		if t1.Stop() {
 			errs = append(errs, "Stop returned true twice")
 			continue
 		}

 		// Test passed, so all done.
 		if len(errs) > 0 {
 			t.Logf("saw %d errors, ignoring to avoid flakiness", len(errs))
 			logErrs()
 		}

 		return
 	}

 	t.Errorf("saw %d errors", len(errs))
 	logErrs()
 }

 func TestAfterQueuing(t *testing.T) {
 	// This test flakes out on some systems,
 	// so we'll try it a few times before declaring it a failure.
 	const attempts = 5
 	err := errors.New("!=nil")
 	for i := 0; i < attempts && err != nil; i++ {
 		delta := Duration(20+i*50) * Millisecond
 		if err = testAfterQueuing(delta); err != nil {
 			t.Logf("attempt %v failed: %v", i, err)
 		}
 	}
 	if err != nil {
 		t.Fatal(err)
 	}
 }

 var slots = []int{5, 3, 6, 6, 6, 1, 1, 2, 7, 9, 4, 8, 0}

 type afterResult struct {
 	slot int
 	t    Time
 }

 func await(slot int, result chan<- afterResult, ac <-chan Time) {
 	result <- afterResult{slot, <-ac}
 }

 func testAfterQueuing(delta Duration) error {
 	// make the result channel buffered because we don't want
 	// to depend on channel queueing semantics that might
 	// possibly change in the future.
 	result := make(chan afterResult, len(slots))

 	t0 := Now()
 	for _, slot := range slots {
 		go await(slot, result, After(Duration(slot)*delta))
 	}
 	var order []int
 	var times []Time
 	for range slots {
 		r := <-result
 		order = append(order, r.slot)
 		times = append(times, r.t)
 	}
 	for i := range order {
 		if i > 0 && order[i] < order[i-1] {
 			return fmt.Errorf("After calls returned out of order: %v", order)
 		}
 	}
 	for i, t := range times {
 		dt := t.Sub(t0)
 		target := Duration(order[i]) * delta
 		if dt < target-delta/2 || dt > target+delta*10 {
 			return fmt.Errorf("After(%s) arrived at %s, expected [%s,%s]", target, dt, target-delta/2, target+delta*10)
 		}
 	}
 	return nil
 }

 func TestTimerStopStress(t *testing.T) {
 	if testing.Short() {
 		return
 	}
 	for i := 0; i < 100; i++ {
 		go func(i int) {
 			timer := AfterFunc(2*Second, func() {
 				t.Errorf("timer %d was not stopped", i)
 			})
 			Sleep(1 * Second)
 			timer.Stop()
 		}(i)
 	}
 	Sleep(3 * Second)
 }

 func TestSleepZeroDeadlock(t *testing.T) {
 	// Sleep(0) used to hang, the sequence of events was as follows.
 	// Sleep(0) sets G's status to Gwaiting, but then immediately returns leaving the status.
 	// Then the goroutine calls e.g. new and falls down into the scheduler due to pending GC.
 	// After the GC nobody wakes up the goroutine from Gwaiting status.
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
 	c := make(chan bool)
 	go func() {
 		for i := 0; i < 100; i++ {
 			runtime.GC()
 		}
 		c <- true
 	}()
 	for i := 0; i < 100; i++ {
 		Sleep(0)
 		tmp := make(chan bool, 1)
 		tmp <- true
 		<-tmp
 	}
 	<-c
 }

 func testReset(d Duration) error {
 	t0 := NewTimer(2 * d)
 	Sleep(d)
 	if !t0.Reset(3 * d) {
 		return errors.New("resetting unfired timer returned false")
 	}
 	Sleep(2 * d)
 	select {
 	case <-t0.C:
 		return errors.New("timer fired early")
 	default:
 	}
 	Sleep(2 * d)
 	select {
 	case <-t0.C:
 	default:
 		return errors.New("reset timer did not fire")
 	}

 	if t0.Reset(50 * Millisecond) {
 		return errors.New("resetting expired timer returned true")
 	}
 	return nil
 }

 func TestReset(t *testing.T) {
 	// We try to run this test with increasingly larger multiples
 	// until one works so slow, loaded hardware isn't as flaky,
 	// but without slowing down fast machines unnecessarily.
 	const unit = 25 * Millisecond
 	tries := []Duration{
 		1 * unit,
 		3 * unit,
 		7 * unit,
 		15 * unit,
 	}
 	var err error
 	for _, d := range tries {
 		err = testReset(d)
 		if err == nil {
 			t.Logf("passed using duration %v", d)
 			return
 		}
 	}
 	t.Error(err)
 }

 // Test that sleeping (via Sleep or Timer) for an interval so large it
 // overflows does not result in a short sleep duration. Nor does it interfere
 // with execution of other timers. If it does, timers in this or subsequent
 // tests may not fire.
 func TestOverflowSleep(t *testing.T) {
 	const big = Duration(int64(1<<63 - 1))

 	go func() {
 		Sleep(big)
 		// On failure, this may return after the test has completed, so
 		// we need to panic instead.
 		panic("big sleep returned")
 	}()

 	select {
 	case <-After(big):
 		t.Fatalf("big timeout fired")
 	case <-After(25 * Millisecond):
 		// OK
 	}

 	const neg = Duration(-1 << 63)
 	Sleep(neg) // Returns immediately.
 	select {
 	case <-After(neg):
 		// OK
 	case <-After(1 * Second):
 		t.Fatalf("negative timeout didn't fire")
 	}
 }

 // Test that a panic while deleting a timer does not leave
 // the timers mutex held, deadlocking a ticker.Stop in a defer.
 func TestIssue5745(t *testing.T) {
 	ticker := NewTicker(Hour)
 	defer func() {
 		// would deadlock here before the fix due to
 		// lock taken before the segfault.
 		ticker.Stop()

 		if r := recover(); r == nil {
 			t.Error("Expected panic, but none happened.")
 		}
 	}()

 	// cause a panic due to a segfault
 	var timer *Timer
 	timer.Stop()
 	t.Error("Should be unreachable.")
 }

 func TestOverflowPeriodRuntimeTimer(t *testing.T) {
 	// This may hang forever if timers are broken. See comment near
 	// the end of CheckRuntimeTimerOverflow in internal_test.go.
 	CheckRuntimeTimerPeriodOverflow()
 }

 func checkZeroPanicString(t *testing.T) {
 	e := recover()
 	s, _ := e.(string)
 	if want := "called on uninitialized Timer"; !strings.Contains(s, want) {
 		t.Errorf("panic = %v; want substring %q", e, want)
 	}
 }

 func TestZeroTimerResetPanics(t *testing.T) {
 	defer checkZeroPanicString(t)
 	var tr Timer
 	tr.Reset(1)
 }

 func TestZeroTimerStopPanics(t *testing.T) {
 	defer checkZeroPanicString(t)
 	var tr Timer
 	tr.Stop()
 }

 // Test that zero duration timers aren't missed by the scheduler. Regression test for issue 44868.
 func TestZeroTimer(t *testing.T) {
 	if testing.Short() {
 		t.Skip("-short")
 	}

 	for i := 0; i < 1000000; i++ {
 		s := Now()
 		ti := NewTimer(0)
 		<-ti.C
 		if diff := Since(s); diff > 2*Second {
 			t.Errorf("Expected time to get value from Timer channel in less than 2 sec, took %v", diff)
 		}
 	}
 }

 // Test that rapidly moving a timer earlier doesn't cause it to get dropped.
 // Issue 47329.
 func TestTimerModifiedEarlier(t *testing.T) {
 	past := Until(Unix(0, 0))
 	count := 1000
 	fail := 0
 	for i := 0; i < count; i++ {
 		timer := NewTimer(Hour)
 		for j := 0; j < 10; j++ {
 			if !timer.Stop() {
 				<-timer.C
 			}
 			timer.Reset(past)
 		}

 		deadline := NewTimer(10 * Second)
 		defer deadline.Stop()
 		now := Now()
 		select {
 		case <-timer.C:
 			if since := Since(now); since > 8*Second {
 				t.Errorf("timer took too long (%v)", since)
 				fail++
 			}
 		case <-deadline.C:
 			t.Error("deadline expired")
 		}
 	}

 	if fail > 0 {
 		t.Errorf("%d failures", fail)
 	}
 }

 // Test that rapidly moving timers earlier and later doesn't cause
 // some of the sleep times to be lost.
 // Issue 47762
 func TestAdjustTimers(t *testing.T) {
 	var rnd = rand.New(rand.NewSource(Now().UnixNano()))

 	timers := make([]*Timer, 100)
 	states := make([]int, len(timers))
 	indices := rnd.Perm(len(timers))

 	for len(indices) != 0 {
 		var ii = rnd.Intn(len(indices))
 		var i = indices[ii]

 		var timer = timers[i]
 		var state = states[i]
 		states[i]++

 		switch state {
 		case 0:
 			timers[i] = NewTimer(0)
 		case 1:
 			<-timer.C // Timer is now idle.

 		// Reset to various long durations, which we'll cancel.
 		case 2:
 			if timer.Reset(1 * Minute) {
 				panic("shouldn't be active (1)")
 			}
 		case 4:
 			if timer.Reset(3 * Minute) {
 				panic("shouldn't be active (3)")
 			}
 		case 6:
 			if timer.Reset(2 * Minute) {
 				panic("shouldn't be active (2)")
 			}

 		// Stop and drain a long-duration timer.
 		case 3, 5, 7:
 			if !timer.Stop() {
 				t.Logf("timer %d state %d Stop returned false", i, state)
 				<-timer.C
 			}

 		// Start a short-duration timer we expect to select without blocking.
 		case 8:
 			if timer.Reset(0) {
 				t.Fatal("timer.Reset returned true")
 			}
 		case 9:
 			now := Now()
 			<-timer.C
 			dur := Since(now)
 			if dur > 750*Millisecond {
 				t.Errorf("timer %d took %v to complete", i, dur)
 			}

 		// Timer is done. Swap with tail and remove.
 		case 10:
 			indices[ii] = indices[len(indices)-1]
 			indices = indices[:len(indices)-1]
 		}
 	}
 }

 // Benchmark timer latency when the thread that creates the timer is busy with
 // other work and the timers must be serviced by other threads.
 // https://golang.org/issue/38860
 func BenchmarkParallelTimerLatency(b *testing.B) {
 	gmp := runtime.GOMAXPROCS(0)
 	if gmp < 2 || runtime.NumCPU() < gmp {
 		b.Skip("skipping with GOMAXPROCS < 2 or NumCPU < GOMAXPROCS")
 	}

 	// allocate memory now to avoid GC interference later.
 	timerCount := gmp - 1
 	stats := make([]struct {
 		sum   float64
 		max   Duration
 		count int64
 		_     [5]int64 // cache line padding
 	}, timerCount)

 	// Ensure the time to start new threads to service timers will not pollute
 	// the results.
 	warmupScheduler(gmp)

 	// Note that other than the AfterFunc calls this benchmark is measuring it
 	// avoids using any other timers. In particular, the main goroutine uses
 	// doWork to spin for some durations because up through Go 1.15 if all
 	// threads are idle sysmon could leave deep sleep when we wake.

 	// Ensure sysmon is in deep sleep.
 	doWork(30 * Millisecond)

 	b.ResetTimer()

 	const delay = Millisecond
 	var wg sync.WaitGroup
 	var count int32
 	for i := 0; i < b.N; i++ {
 		wg.Add(timerCount)
 		atomic.StoreInt32(&count, 0)
 		for j := 0; j < timerCount; j++ {
 			j := j
 			expectedWakeup := Now().Add(delay)
 			AfterFunc(delay, func() {
 				late := Since(expectedWakeup)
 				if late < 0 {
 					late = 0
 				}
 				stats[j].count++
 				stats[j].sum += float64(late.Nanoseconds())
 				if late > stats[j].max {
 					stats[j].max = late
 				}
 				atomic.AddInt32(&count, 1)
 				for atomic.LoadInt32(&count) < int32(timerCount) {
 					// spin until all timers fired
 				}
 				wg.Done()
 			})
 		}

 		for atomic.LoadInt32(&count) < int32(timerCount) {
 			// spin until all timers fired
 		}
 		wg.Wait()

 		// Spin for a bit to let the other scheduler threads go idle before the
 		// next round.
 		doWork(Millisecond)
 	}
 	var total float64
 	var samples float64
 	max := Duration(0)
 	for _, s := range stats {
 		if s.max > max {
 			max = s.max
 		}
 		total += s.sum
 		samples += float64(s.count)
 	}
 	b.ReportMetric(0, "ns/op")
 	b.ReportMetric(total/samples, "avg-late-ns")
 	b.ReportMetric(float64(max.Nanoseconds()), "max-late-ns")
 }

 // Benchmark timer latency with staggered wakeup times and varying CPU bound
 // workloads. https://golang.org/issue/38860
 func BenchmarkStaggeredTickerLatency(b *testing.B) {
 	gmp := runtime.GOMAXPROCS(0)
 	if gmp < 2 || runtime.NumCPU() < gmp {
 		b.Skip("skipping with GOMAXPROCS < 2 or NumCPU < GOMAXPROCS")
 	}

 	const delay = 3 * Millisecond

 	for _, dur := range []Duration{300 * Microsecond, 2 * Millisecond} {
 		b.Run(fmt.Sprintf("work-dur=%s", dur), func(b *testing.B) {
 			for tickersPerP := 1; tickersPerP < int(delay/dur)+1; tickersPerP++ {
 				tickerCount := gmp * tickersPerP
 				b.Run(fmt.Sprintf("tickers-per-P=%d", tickersPerP), func(b *testing.B) {
 					// allocate memory now to avoid GC interference later.
 					stats := make([]struct {
 						sum   float64
 						max   Duration
 						count int64
 						_     [5]int64 // cache line padding
 					}, tickerCount)

 					// Ensure the time to start new threads to service timers
 					// will not pollute the results.
 					warmupScheduler(gmp)

 					b.ResetTimer()

 					var wg sync.WaitGroup
 					wg.Add(tickerCount)
 					for j := 0; j < tickerCount; j++ {
 						j := j
 						doWork(delay / Duration(gmp))
 						expectedWakeup := Now().Add(delay)
 						ticker := NewTicker(delay)
 						go func(c int, ticker *Ticker, firstWake Time) {
 							defer ticker.Stop()

 							for ; c > 0; c-- {
 								<-ticker.C
 								late := Since(expectedWakeup)
 								if late < 0 {
 									late = 0
 								}
 								stats[j].count++
 								stats[j].sum += float64(late.Nanoseconds())
 								if late > stats[j].max {
 									stats[j].max = late
 								}
 								expectedWakeup = expectedWakeup.Add(delay)
 								doWork(dur)
 							}
 							wg.Done()
 						}(b.N, ticker, expectedWakeup)
 					}
 					wg.Wait()

 					var total float64
 					var samples float64
 					max := Duration(0)
 					for _, s := range stats {
 						if s.max > max {
 							max = s.max
 						}
 						total += s.sum
 						samples += float64(s.count)
 					}
 					b.ReportMetric(0, "ns/op")
 					b.ReportMetric(total/samples, "avg-late-ns")
 					b.ReportMetric(float64(max.Nanoseconds()), "max-late-ns")
 				})
 			}
 		})
 	}
 }

 // warmupScheduler ensures the scheduler has at least targetThreadCount threads
 // in its thread pool.
 func warmupScheduler(targetThreadCount int) {
 	var wg sync.WaitGroup
 	var count int32
 	for i := 0; i < targetThreadCount; i++ {
 		wg.Add(1)
 		go func() {
 			atomic.AddInt32(&count, 1)
 			for atomic.LoadInt32(&count) < int32(targetThreadCount) {
 				// spin until all threads started
 			}

 			// spin a bit more to ensure they are all running on separate CPUs.
 			doWork(Millisecond)
 			wg.Done()
 		}()
 	}
 	wg.Wait()
 }

 func doWork(dur Duration) {
 	start := Now()
 	for Since(start) < dur {
 	}
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package time_test

	import (
	"errors"
	"fmt"
	"math/rand"
	"runtime"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	. "time"
	)

	// Go runtime uses different Windows timers for time.Now and sleeping.
	// These can tick at different frequencies and can arrive out of sync.
	// The effect can be seen, for example, as time.Sleep(100ms) is actually
	// shorter then 100ms when measured as difference between time.Now before and
	// after time.Sleep call. This was observed on Windows XP SP3 (windows/386).
	// windowsInaccuracy is to ignore such errors.
	const windowsInaccuracy = 17 * Millisecond

	func TestSleep(t *testing.T) {
	const delay = 100 * Millisecond
	go func() {
	Sleep(delay / 2)
	Interrupt()
	}()
	start := Now()
	Sleep(delay)
	delayadj := delay
	if runtime.GOOS == "windows" {
	delayadj -= windowsInaccuracy
	}
	duration := Now().Sub(start)
	if duration < delayadj {
	t.Fatalf("Sleep(%s) slept for only %s", delay, duration)
	}
	}

	// Test the basic function calling behavior. Correct queueing
	// behavior is tested elsewhere, since After and AfterFunc share
	// the same code.
	func TestAfterFunc(t *testing.T) {
	i := 10
	c := make(chan bool)
	var f func()
	f = func() {
	i--
	if i >= 0 {
	AfterFunc(0, f)
	Sleep(1 * Second)
	} else {
	c <- true
	}
	}

	AfterFunc(0, f)
	<-c
	}

	func TestAfterStress(t *testing.T) {
	stop := uint32(0)
	go func() {
	for atomic.LoadUint32(&stop) == 0 {
	runtime.GC()
	// Yield so that the OS can wake up the timer thread,
	// so that it can generate channel sends for the main goroutine,
	// which will eventually set stop = 1 for us.
	Sleep(Nanosecond)
	}
	}()
	ticker := NewTicker(1)
	for i := 0; i < 100; i++ {
	<-ticker.C
	}
	ticker.Stop()
	atomic.StoreUint32(&stop, 1)
	}

	func benchmark(b *testing.B, bench func(n int)) {

	// Create equal number of garbage timers on each P before starting
	// the benchmark.
	var wg sync.WaitGroup
	garbageAll := make([][]*Timer, runtime.GOMAXPROCS(0))
	for i := range garbageAll {
	wg.Add(1)
	go func(i int) {
	defer wg.Done()
	garbage := make([]*Timer, 1<<15)
	for j := range garbage {
	garbage[j] = AfterFunc(Hour, nil)
	}
	garbageAll[i] = garbage
	}(i)
	}
	wg.Wait()

	b.ResetTimer()
	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	bench(1000)
	}
	})
	b.StopTimer()

	for _, garbage := range garbageAll {
	for _, t := range garbage {
	t.Stop()
	}
	}
	}

	func BenchmarkAfterFunc(b *testing.B) {
	benchmark(b, func(n int) {
	c := make(chan bool)
	var f func()
	f = func() {
	n--
	if n >= 0 {
	AfterFunc(0, f)
	} else {
	c <- true
	}
	}

	AfterFunc(0, f)
	<-c
	})
	}

	func BenchmarkAfter(b *testing.B) {
	benchmark(b, func(n int) {
	for i := 0; i < n; i++ {
	<-After(1)
	}
	})
	}

	func BenchmarkStop(b *testing.B) {
	benchmark(b, func(n int) {
	for i := 0; i < n; i++ {
	NewTimer(1 * Second).Stop()
	}
	})
	}

	func BenchmarkSimultaneousAfterFunc(b *testing.B) {
	benchmark(b, func(n int) {
	var wg sync.WaitGroup
	wg.Add(n)
	for i := 0; i < n; i++ {
	AfterFunc(0, wg.Done)
	}
	wg.Wait()
	})
	}

	func BenchmarkStartStop(b *testing.B) {
	benchmark(b, func(n int) {
	timers := make([]*Timer, n)
	for i := 0; i < n; i++ {
	timers[i] = AfterFunc(Hour, nil)
	}

	for i := 0; i < n; i++ {
	timers[i].Stop()
	}
	})
	}

	func BenchmarkReset(b *testing.B) {
	benchmark(b, func(n int) {
	t := NewTimer(Hour)
	for i := 0; i < n; i++ {
	t.Reset(Hour)
	}
	t.Stop()
	})
	}

	func BenchmarkSleep(b *testing.B) {
	benchmark(b, func(n int) {
	var wg sync.WaitGroup
	wg.Add(n)
	for i := 0; i < n; i++ {
	go func() {
	Sleep(Nanosecond)
	wg.Done()
	}()
	}
	wg.Wait()
	})
	}

	func TestAfter(t *testing.T) {
	const delay = 100 * Millisecond
	start := Now()
	end := <-After(delay)
	delayadj := delay
	if runtime.GOOS == "windows" {
	delayadj -= windowsInaccuracy
	}
	if duration := Now().Sub(start); duration < delayadj {
	t.Fatalf("After(%s) slept for only %d ns", delay, duration)
	}
	if min := start.Add(delayadj); end.Before(min) {
	t.Fatalf("After(%s) expect >= %s, got %s", delay, min, end)
	}
	}

	func TestAfterTick(t *testing.T) {
	const Count = 10
	Delta := 100 * Millisecond
	if testing.Short() {
	Delta = 10 * Millisecond
	}
	t0 := Now()
	for i := 0; i < Count; i++ {
	<-After(Delta)
	}
	t1 := Now()
	d := t1.Sub(t0)
	target := Delta * Count
	if d < target*9/10 {
	t.Fatalf("%d ticks of %s too fast: took %s, expected %s", Count, Delta, d, target)
	}
	if !testing.Short() && d > target*30/10 {
	t.Fatalf("%d ticks of %s too slow: took %s, expected %s", Count, Delta, d, target)
	}
	}

	func TestAfterStop(t *testing.T) {
	// We want to test that we stop a timer before it runs.
	// We also want to test that it didn't run after a longer timer.
	// Since we don't want the test to run for too long, we don't
	// want to use lengthy times. That makes the test inherently flaky.
	// So only report an error if it fails five times in a row.

	var errs []string
	logErrs := func() {
	for _, e := range errs {
	t.Log(e)
	}
	}

	for i := 0; i < 5; i++ {
	AfterFunc(100*Millisecond, func() {})
	t0 := NewTimer(50 * Millisecond)
	c1 := make(chan bool, 1)
	t1 := AfterFunc(150*Millisecond, func() { c1 <- true })
	c2 := After(200 * Millisecond)
	if !t0.Stop() {
	errs = append(errs, "failed to stop event 0")
	continue
	}
	if !t1.Stop() {
	errs = append(errs, "failed to stop event 1")
	continue
	}
	<-c2
	select {
	case <-t0.C:
	errs = append(errs, "event 0 was not stopped")
	continue
	case <-c1:
	errs = append(errs, "event 1 was not stopped")
	continue
	default:
	}
	if t1.Stop() {
	errs = append(errs, "Stop returned true twice")
	continue
	}

	// Test passed, so all done.
	if len(errs) > 0 {
	t.Logf("saw %d errors, ignoring to avoid flakiness", len(errs))
	logErrs()
	}

	return
	}

	t.Errorf("saw %d errors", len(errs))
	logErrs()
	}

	func TestAfterQueuing(t *testing.T) {
	// This test flakes out on some systems,
	// so we'll try it a few times before declaring it a failure.
	const attempts = 5
	err := errors.New("!=nil")
	for i := 0; i < attempts && err != nil; i++ {
	delta := Duration(20+i50) Millisecond
	if err = testAfterQueuing(delta); err != nil {
	t.Logf("attempt %v failed: %v", i, err)
	}
	}
	if err != nil {
	t.Fatal(err)
	}
	}

	var slots = []int{5, 3, 6, 6, 6, 1, 1, 2, 7, 9, 4, 8, 0}

	type afterResult struct {
	slot int
	t Time
	}

	func await(slot int, result chan<- afterResult, ac <-chan Time) {
	result <- afterResult{slot, <-ac}
	}

	func testAfterQueuing(delta Duration) error {
	// make the result channel buffered because we don't want
	// to depend on channel queueing semantics that might
	// possibly change in the future.
	result := make(chan afterResult, len(slots))

	t0 := Now()
	for _, slot := range slots {
	go await(slot, result, After(Duration(slot)*delta))
	}
	var order []int
	var times []Time
	for range slots {
	r := <-result
	order = append(order, r.slot)
	times = append(times, r.t)
	}
	for i := range order {
	if i > 0 && order[i] < order[i-1] {
	return fmt.Errorf("After calls returned out of order: %v", order)
	}
	}
	for i, t := range times {
	dt := t.Sub(t0)
	target := Duration(order[i]) * delta
	if dt < target-delta/2 \|\| dt > target+delta*10 {
	return fmt.Errorf("After(%s) arrived at %s, expected [%s,%s]", target, dt, target-delta/2, target+delta*10)
	}
	}
	return nil
	}

	func TestTimerStopStress(t *testing.T) {
	if testing.Short() {
	return
	}
	for i := 0; i < 100; i++ {
	go func(i int) {
	timer := AfterFunc(2*Second, func() {
	t.Errorf("timer %d was not stopped", i)
	})
	Sleep(1 * Second)
	timer.Stop()
	}(i)
	}
	Sleep(3 * Second)
	}

	func TestSleepZeroDeadlock(t *testing.T) {
	// Sleep(0) used to hang, the sequence of events was as follows.
	// Sleep(0) sets G's status to Gwaiting, but then immediately returns leaving the status.
	// Then the goroutine calls e.g. new and falls down into the scheduler due to pending GC.
	// After the GC nobody wakes up the goroutine from Gwaiting status.
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
	c := make(chan bool)
	go func() {
	for i := 0; i < 100; i++ {
	runtime.GC()
	}
	c <- true
	}()
	for i := 0; i < 100; i++ {
	Sleep(0)
	tmp := make(chan bool, 1)
	tmp <- true
	<-tmp
	}
	<-c
	}

	func testReset(d Duration) error {
	t0 := NewTimer(2 * d)
	Sleep(d)
	if !t0.Reset(3 * d) {
	return errors.New("resetting unfired timer returned false")
	}
	Sleep(2 * d)
	select {
	case <-t0.C:
	return errors.New("timer fired early")
	default:
	}
	Sleep(2 * d)
	select {
	case <-t0.C:
	default:
	return errors.New("reset timer did not fire")
	}

	if t0.Reset(50 * Millisecond) {
	return errors.New("resetting expired timer returned true")
	}
	return nil
	}

	func TestReset(t *testing.T) {
	// We try to run this test with increasingly larger multiples
	// until one works so slow, loaded hardware isn't as flaky,
	// but without slowing down fast machines unnecessarily.
	const unit = 25 * Millisecond
	tries := []Duration{
	1 * unit,
	3 * unit,
	7 * unit,
	15 * unit,
	}
	var err error
	for _, d := range tries {
	err = testReset(d)
	if err == nil {
	t.Logf("passed using duration %v", d)
	return
	}
	}
	t.Error(err)
	}

	// Test that sleeping (via Sleep or Timer) for an interval so large it
	// overflows does not result in a short sleep duration. Nor does it interfere
	// with execution of other timers. If it does, timers in this or subsequent
	// tests may not fire.
	func TestOverflowSleep(t *testing.T) {
	const big = Duration(int64(1<<63 - 1))

	go func() {
	Sleep(big)
	// On failure, this may return after the test has completed, so
	// we need to panic instead.
	panic("big sleep returned")
	}()

	select {
	case <-After(big):
	t.Fatalf("big timeout fired")
	case <-After(25 * Millisecond):
	// OK
	}

	const neg = Duration(-1 << 63)
	Sleep(neg) // Returns immediately.
	select {
	case <-After(neg):
	// OK
	case <-After(1 * Second):
	t.Fatalf("negative timeout didn't fire")
	}
	}

	// Test that a panic while deleting a timer does not leave
	// the timers mutex held, deadlocking a ticker.Stop in a defer.
	func TestIssue5745(t *testing.T) {
	ticker := NewTicker(Hour)
	defer func() {
	// would deadlock here before the fix due to
	// lock taken before the segfault.
	ticker.Stop()

	if r := recover(); r == nil {
	t.Error("Expected panic, but none happened.")
	}
	}()

	// cause a panic due to a segfault
	var timer *Timer
	timer.Stop()
	t.Error("Should be unreachable.")
	}

	func TestOverflowPeriodRuntimeTimer(t *testing.T) {
	// This may hang forever if timers are broken. See comment near
	// the end of CheckRuntimeTimerOverflow in internal_test.go.
	CheckRuntimeTimerPeriodOverflow()
	}

	func checkZeroPanicString(t *testing.T) {
	e := recover()
	s, _ := e.(string)
	if want := "called on uninitialized Timer"; !strings.Contains(s, want) {
	t.Errorf("panic = %v; want substring %q", e, want)
	}
	}

	func TestZeroTimerResetPanics(t *testing.T) {
	defer checkZeroPanicString(t)
	var tr Timer
	tr.Reset(1)
	}

	func TestZeroTimerStopPanics(t *testing.T) {
	defer checkZeroPanicString(t)
	var tr Timer
	tr.Stop()
	}

	// Test that zero duration timers aren't missed by the scheduler. Regression test for issue 44868.
	func TestZeroTimer(t *testing.T) {
	if testing.Short() {
	t.Skip("-short")
	}

	for i := 0; i < 1000000; i++ {
	s := Now()
	ti := NewTimer(0)
	<-ti.C
	if diff := Since(s); diff > 2*Second {
	t.Errorf("Expected time to get value from Timer channel in less than 2 sec, took %v", diff)
	}
	}
	}

	// Test that rapidly moving a timer earlier doesn't cause it to get dropped.
	// Issue 47329.
	func TestTimerModifiedEarlier(t *testing.T) {
	past := Until(Unix(0, 0))
	count := 1000
	fail := 0
	for i := 0; i < count; i++ {
	timer := NewTimer(Hour)
	for j := 0; j < 10; j++ {
	if !timer.Stop() {
	<-timer.C
	}
	timer.Reset(past)
	}

	deadline := NewTimer(10 * Second)
	defer deadline.Stop()
	now := Now()
	select {
	case <-timer.C:
	if since := Since(now); since > 8*Second {
	t.Errorf("timer took too long (%v)", since)
	fail++
	}
	case <-deadline.C:
	t.Error("deadline expired")
	}
	}

	if fail > 0 {
	t.Errorf("%d failures", fail)
	}
	}

	// Test that rapidly moving timers earlier and later doesn't cause
	// some of the sleep times to be lost.
	// Issue 47762
	func TestAdjustTimers(t *testing.T) {
	var rnd = rand.New(rand.NewSource(Now().UnixNano()))

	timers := make([]*Timer, 100)
	states := make([]int, len(timers))
	indices := rnd.Perm(len(timers))

	for len(indices) != 0 {
	var ii = rnd.Intn(len(indices))
	var i = indices[ii]

	var timer = timers[i]
	var state = states[i]
	states[i]++

	switch state {
	case 0:
	timers[i] = NewTimer(0)
	case 1:
	<-timer.C // Timer is now idle.

	// Reset to various long durations, which we'll cancel.
	case 2:
	if timer.Reset(1 * Minute) {
	panic("shouldn't be active (1)")
	}
	case 4:
	if timer.Reset(3 * Minute) {
	panic("shouldn't be active (3)")
	}
	case 6:
	if timer.Reset(2 * Minute) {
	panic("shouldn't be active (2)")
	}

	// Stop and drain a long-duration timer.
	case 3, 5, 7:
	if !timer.Stop() {
	t.Logf("timer %d state %d Stop returned false", i, state)
	<-timer.C
	}

	// Start a short-duration timer we expect to select without blocking.
	case 8:
	if timer.Reset(0) {
	t.Fatal("timer.Reset returned true")
	}
	case 9:
	now := Now()
	<-timer.C
	dur := Since(now)
	if dur > 750*Millisecond {
	t.Errorf("timer %d took %v to complete", i, dur)
	}

	// Timer is done. Swap with tail and remove.
	case 10:
	indices[ii] = indices[len(indices)-1]
	indices = indices[:len(indices)-1]
	}
	}
	}

	// Benchmark timer latency when the thread that creates the timer is busy with
	// other work and the timers must be serviced by other threads.
	// https://golang.org/issue/38860
	func BenchmarkParallelTimerLatency(b *testing.B) {
	gmp := runtime.GOMAXPROCS(0)
	if gmp < 2 \|\| runtime.NumCPU() < gmp {
	b.Skip("skipping with GOMAXPROCS < 2 or NumCPU < GOMAXPROCS")
	}

	// allocate memory now to avoid GC interference later.
	timerCount := gmp - 1
	stats := make([]struct {
	sum float64
	max Duration
	count int64
	_ [5]int64 // cache line padding
	}, timerCount)

	// Ensure the time to start new threads to service timers will not pollute
	// the results.
	warmupScheduler(gmp)

	// Note that other than the AfterFunc calls this benchmark is measuring it
	// avoids using any other timers. In particular, the main goroutine uses
	// doWork to spin for some durations because up through Go 1.15 if all
	// threads are idle sysmon could leave deep sleep when we wake.

	// Ensure sysmon is in deep sleep.
	doWork(30 * Millisecond)

	b.ResetTimer()

	const delay = Millisecond
	var wg sync.WaitGroup
	var count int32
	for i := 0; i < b.N; i++ {
	wg.Add(timerCount)
	atomic.StoreInt32(&count, 0)
	for j := 0; j < timerCount; j++ {
	j := j
	expectedWakeup := Now().Add(delay)
	AfterFunc(delay, func() {
	late := Since(expectedWakeup)
	if late < 0 {
	late = 0
	}
	stats[j].count++
	stats[j].sum += float64(late.Nanoseconds())
	if late > stats[j].max {
	stats[j].max = late
	}
	atomic.AddInt32(&count, 1)
	for atomic.LoadInt32(&count) < int32(timerCount) {
	// spin until all timers fired
	}
	wg.Done()
	})
	}

	for atomic.LoadInt32(&count) < int32(timerCount) {
	// spin until all timers fired
	}
	wg.Wait()

	// Spin for a bit to let the other scheduler threads go idle before the
	// next round.
	doWork(Millisecond)
	}
	var total float64
	var samples float64
	max := Duration(0)
	for _, s := range stats {
	if s.max > max {
	max = s.max
	}
	total += s.sum
	samples += float64(s.count)
	}
	b.ReportMetric(0, "ns/op")
	b.ReportMetric(total/samples, "avg-late-ns")
	b.ReportMetric(float64(max.Nanoseconds()), "max-late-ns")
	}

	// Benchmark timer latency with staggered wakeup times and varying CPU bound
	// workloads. https://golang.org/issue/38860
	func BenchmarkStaggeredTickerLatency(b *testing.B) {
	gmp := runtime.GOMAXPROCS(0)
	if gmp < 2 \|\| runtime.NumCPU() < gmp {
	b.Skip("skipping with GOMAXPROCS < 2 or NumCPU < GOMAXPROCS")
	}

	const delay = 3 * Millisecond

	for _, dur := range []Duration{300 * Microsecond, 2 * Millisecond} {
	b.Run(fmt.Sprintf("work-dur=%s", dur), func(b *testing.B) {
	for tickersPerP := 1; tickersPerP < int(delay/dur)+1; tickersPerP++ {
	tickerCount := gmp * tickersPerP
	b.Run(fmt.Sprintf("tickers-per-P=%d", tickersPerP), func(b *testing.B) {
	// allocate memory now to avoid GC interference later.
	stats := make([]struct {
	sum float64
	max Duration
	count int64
	_ [5]int64 // cache line padding
	}, tickerCount)

	// Ensure the time to start new threads to service timers
	// will not pollute the results.
	warmupScheduler(gmp)

	b.ResetTimer()

	var wg sync.WaitGroup
	wg.Add(tickerCount)
	for j := 0; j < tickerCount; j++ {
	j := j
	doWork(delay / Duration(gmp))
	expectedWakeup := Now().Add(delay)
	ticker := NewTicker(delay)
	go func(c int, ticker *Ticker, firstWake Time) {
	defer ticker.Stop()

	for ; c > 0; c-- {
	<-ticker.C
	late := Since(expectedWakeup)
	if late < 0 {
	late = 0
	}
	stats[j].count++
	stats[j].sum += float64(late.Nanoseconds())
	if late > stats[j].max {
	stats[j].max = late
	}
	expectedWakeup = expectedWakeup.Add(delay)
	doWork(dur)
	}
	wg.Done()
	}(b.N, ticker, expectedWakeup)
	}
	wg.Wait()

	var total float64
	var samples float64
	max := Duration(0)
	for _, s := range stats {
	if s.max > max {
	max = s.max
	}
	total += s.sum
	samples += float64(s.count)
	}
	b.ReportMetric(0, "ns/op")
	b.ReportMetric(total/samples, "avg-late-ns")
	b.ReportMetric(float64(max.Nanoseconds()), "max-late-ns")
	})
	}
	})
	}
	}

	// warmupScheduler ensures the scheduler has at least targetThreadCount threads
	// in its thread pool.
	func warmupScheduler(targetThreadCount int) {
	var wg sync.WaitGroup
	var count int32
	for i := 0; i < targetThreadCount; i++ {
	wg.Add(1)
	go func() {
	atomic.AddInt32(&count, 1)
	for atomic.LoadInt32(&count) < int32(targetThreadCount) {
	// spin until all threads started
	}

	// spin a bit more to ensure they are all running on separate CPUs.
	doWork(Millisecond)
	wg.Done()
	}()
	}
	wg.Wait()
	}

	func doWork(dur Duration) {
	start := Now()
	for Since(start) < dur {
	}
	}