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"
 	"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 for an interval so large it overflows does not
 // result in a short sleep duration.
 func TestOverflowSleep(t *testing.T) {
 	const big = Duration(int64(1<<63 - 1))
 	select {
 	case <-After(big):
 		t.Fatalf("big timeout fired")
 	case <-After(25 * Millisecond):
 		// OK
 	}
 	const neg = Duration(-1 << 63)
 	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 TestOverflowRuntimeTimer(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping in short mode, see issue 6874")
 	}
 	// This may hang forever if timers are broken. See comment near
 	// the end of CheckRuntimeTimerOverflow in internal_test.go.
 	CheckRuntimeTimerOverflow()
 }

 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()
 }
	// 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"
	"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 for an interval so large it overflows does not
	// result in a short sleep duration.
	func TestOverflowSleep(t *testing.T) {
	const big = Duration(int64(1<<63 - 1))
	select {
	case <-After(big):
	t.Fatalf("big timeout fired")
	case <-After(25 * Millisecond):
	// OK
	}
	const neg = Duration(-1 << 63)
	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 TestOverflowRuntimeTimer(t *testing.T) {
	if testing.Short() {
	t.Skip("skipping in short mode, see issue 6874")
	}
	// This may hang forever if timers are broken. See comment near
	// the end of CheckRuntimeTimerOverflow in internal_test.go.
	CheckRuntimeTimerOverflow()
	}

	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()
	}