src/runtime/runtime_test.go - go - Git at Google

 // Copyright 2012 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 runtime_test

 import (
 	"flag"
 	"fmt"
 	"io"
 	. "runtime"
 	"runtime/debug"
 	"sort"
 	"strings"
 	"sync"
 	"testing"
 	"time"
 	"unsafe"
 )

 // flagQuick is set by the -quick option to skip some relatively slow tests.
 // This is used by the cmd/dist test runtime:cpu124.
 // The cmd/dist test passes both -test.short and -quick;
 // there are tests that only check testing.Short, and those tests will
 // not be skipped if only -quick is used.
 var flagQuick = flag.Bool("quick", false, "skip slow tests, for cmd/dist test runtime:cpu124")

 func init() {
 	// We're testing the runtime, so make tracebacks show things
 	// in the runtime. This only raises the level, so it won't
 	// override GOTRACEBACK=crash from the user.
 	SetTracebackEnv("system")
 }

 var errf error

 func errfn() error {
 	return errf
 }

 func errfn1() error {
 	return io.EOF
 }

 func BenchmarkIfaceCmp100(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for j := 0; j < 100; j++ {
 			if errfn() == io.EOF {
 				b.Fatal("bad comparison")
 			}
 		}
 	}
 }

 func BenchmarkIfaceCmpNil100(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		for j := 0; j < 100; j++ {
 			if errfn1() == nil {
 				b.Fatal("bad comparison")
 			}
 		}
 	}
 }

 var efaceCmp1 any
 var efaceCmp2 any

 func BenchmarkEfaceCmpDiff(b *testing.B) {
 	x := 5
 	efaceCmp1 = &x
 	y := 6
 	efaceCmp2 = &y
 	for i := 0; i < b.N; i++ {
 		for j := 0; j < 100; j++ {
 			if efaceCmp1 == efaceCmp2 {
 				b.Fatal("bad comparison")
 			}
 		}
 	}
 }

 func BenchmarkEfaceCmpDiffIndirect(b *testing.B) {
 	efaceCmp1 = [2]int{1, 2}
 	efaceCmp2 = [2]int{1, 2}
 	for i := 0; i < b.N; i++ {
 		for j := 0; j < 100; j++ {
 			if efaceCmp1 != efaceCmp2 {
 				b.Fatal("bad comparison")
 			}
 		}
 	}
 }

 func BenchmarkDefer(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		defer1()
 	}
 }

 func defer1() {
 	defer func(x, y, z int) {
 		if recover() != nil || x != 1 || y != 2 || z != 3 {
 			panic("bad recover")
 		}
 	}(1, 2, 3)
 }

 func BenchmarkDefer10(b *testing.B) {
 	for i := 0; i < b.N/10; i++ {
 		defer2()
 	}
 }

 func defer2() {
 	for i := 0; i < 10; i++ {
 		defer func(x, y, z int) {
 			if recover() != nil || x != 1 || y != 2 || z != 3 {
 				panic("bad recover")
 			}
 		}(1, 2, 3)
 	}
 }

 func BenchmarkDeferMany(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		defer func(x, y, z int) {
 			if recover() != nil || x != 1 || y != 2 || z != 3 {
 				panic("bad recover")
 			}
 		}(1, 2, 3)
 	}
 }

 func BenchmarkPanicRecover(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		defer3()
 	}
 }

 func defer3() {
 	defer func(x, y, z int) {
 		if recover() == nil {
 			panic("failed recover")
 		}
 	}(1, 2, 3)
 	panic("hi")
 }

 // golang.org/issue/7063
 func TestStopCPUProfilingWithProfilerOff(t *testing.T) {
 	SetCPUProfileRate(0)
 }

 // Addresses to test for faulting behavior.
 // This is less a test of SetPanicOnFault and more a check that
 // the operating system and the runtime can process these faults
 // correctly. That is, we're indirectly testing that without SetPanicOnFault
 // these would manage to turn into ordinary crashes.
 // Note that these are truncated on 32-bit systems, so the bottom 32 bits
 // of the larger addresses must themselves be invalid addresses.
 // We might get unlucky and the OS might have mapped one of these
 // addresses, but probably not: they're all in the first page, very high
 // addresses that normally an OS would reserve for itself, or malformed
 // addresses. Even so, we might have to remove one or two on different
 // systems. We will see.

 var faultAddrs = []uint64{
 	// low addresses
 	0,
 	1,
 	0xfff,
 	// high (kernel) addresses
 	// or else malformed.
 	0xffffffffffffffff,
 	0xfffffffffffff001,
 	0xffffffffffff0001,
 	0xfffffffffff00001,
 	0xffffffffff000001,
 	0xfffffffff0000001,
 	0xffffffff00000001,
 	0xfffffff000000001,
 	0xffffff0000000001,
 	0xfffff00000000001,
 	0xffff000000000001,
 	0xfff0000000000001,
 	0xff00000000000001,
 	0xf000000000000001,
 	0x8000000000000001,
 }

 func TestSetPanicOnFault(t *testing.T) {
 	old := debug.SetPanicOnFault(true)
 	defer debug.SetPanicOnFault(old)

 	nfault := 0
 	for _, addr := range faultAddrs {
 		testSetPanicOnFault(t, uintptr(addr), &nfault)
 	}
 	if nfault == 0 {
 		t.Fatalf("none of the addresses faulted")
 	}
 }

 // testSetPanicOnFault tests one potentially faulting address.
 // It deliberately constructs and uses an invalid pointer,
 // so mark it as nocheckptr.
 //
 //go:nocheckptr
 func testSetPanicOnFault(t *testing.T, addr uintptr, nfault *int) {
 	if GOOS == "js" {
 		t.Skip("js does not support catching faults")
 	}

 	defer func() {
 		if err := recover(); err != nil {
 			*nfault++
 		}
 	}()

 	// The read should fault, except that sometimes we hit
 	// addresses that have had C or kernel pages mapped there
 	// readable by user code. So just log the content.
 	// If no addresses fault, we'll fail the test.
 	v := *(*byte)(unsafe.Pointer(addr))
 	t.Logf("addr %#x: %#x\n", addr, v)
 }

 func eqstring_generic(s1, s2 string) bool {
 	if len(s1) != len(s2) {
 		return false
 	}
 	// optimization in assembly versions:
 	// if s1.str == s2.str { return true }
 	for i := 0; i < len(s1); i++ {
 		if s1[i] != s2[i] {
 			return false
 		}
 	}
 	return true
 }

 func TestEqString(t *testing.T) {
 	// This isn't really an exhaustive test of == on strings, it's
 	// just a convenient way of documenting (via eqstring_generic)
 	// what == does.
 	s := []string{
 		"",
 		"a",
 		"c",
 		"aaa",
 		"ccc",
 		"cccc"[:3], // same contents, different string
 		"1234567890",
 	}
 	for _, s1 := range s {
 		for _, s2 := range s {
 			x := s1 == s2
 			y := eqstring_generic(s1, s2)
 			if x != y {
 				t.Errorf(`("%s" == "%s") = %t, want %t`, s1, s2, x, y)
 			}
 		}
 	}
 }

 func TestTrailingZero(t *testing.T) {
 	// make sure we add padding for structs with trailing zero-sized fields
 	type T1 struct {
 		n int32
 		z [0]byte
 	}
 	if unsafe.Sizeof(T1{}) != 8 {
 		t.Errorf("sizeof(%#v)==%d, want 8", T1{}, unsafe.Sizeof(T1{}))
 	}
 	type T2 struct {
 		n int64
 		z struct{}
 	}
 	if unsafe.Sizeof(T2{}) != 8+unsafe.Sizeof(uintptr(0)) {
 		t.Errorf("sizeof(%#v)==%d, want %d", T2{}, unsafe.Sizeof(T2{}), 8+unsafe.Sizeof(uintptr(0)))
 	}
 	type T3 struct {
 		n byte
 		z [4]struct{}
 	}
 	if unsafe.Sizeof(T3{}) != 2 {
 		t.Errorf("sizeof(%#v)==%d, want 2", T3{}, unsafe.Sizeof(T3{}))
 	}
 	// make sure padding can double for both zerosize and alignment
 	type T4 struct {
 		a int32
 		b int16
 		c int8
 		z struct{}
 	}
 	if unsafe.Sizeof(T4{}) != 8 {
 		t.Errorf("sizeof(%#v)==%d, want 8", T4{}, unsafe.Sizeof(T4{}))
 	}
 	// make sure we don't pad a zero-sized thing
 	type T5 struct {
 	}
 	if unsafe.Sizeof(T5{}) != 0 {
 		t.Errorf("sizeof(%#v)==%d, want 0", T5{}, unsafe.Sizeof(T5{}))
 	}
 }

 func TestAppendGrowth(t *testing.T) {
 	var x []int64
 	check := func(want int) {
 		if cap(x) != want {
 			t.Errorf("len=%d, cap=%d, want cap=%d", len(x), cap(x), want)
 		}
 	}

 	check(0)
 	want := 1
 	for i := 1; i <= 100; i++ {
 		x = append(x, 1)
 		check(want)
 		if i&(i-1) == 0 {
 			want = 2 * i
 		}
 	}
 }

 var One = []int64{1}

 func TestAppendSliceGrowth(t *testing.T) {
 	var x []int64
 	check := func(want int) {
 		if cap(x) != want {
 			t.Errorf("len=%d, cap=%d, want cap=%d", len(x), cap(x), want)
 		}
 	}

 	check(0)
 	want := 1
 	for i := 1; i <= 100; i++ {
 		x = append(x, One...)
 		check(want)
 		if i&(i-1) == 0 {
 			want = 2 * i
 		}
 	}
 }

 func TestGoroutineProfileTrivial(t *testing.T) {
 	// Calling GoroutineProfile twice in a row should find the same number of goroutines,
 	// but it's possible there are goroutines just about to exit, so we might end up
 	// with fewer in the second call. Try a few times; it should converge once those
 	// zombies are gone.
 	for i := 0; ; i++ {
 		n1, ok := GoroutineProfile(nil) // should fail, there's at least 1 goroutine
 		if n1 < 1 || ok {
 			t.Fatalf("GoroutineProfile(nil) = %d, %v, want >0, false", n1, ok)
 		}
 		n2, ok := GoroutineProfile(make([]StackRecord, n1))
 		if n2 == n1 && ok {
 			break
 		}
 		t.Logf("GoroutineProfile(%d) = %d, %v, want %d, true", n1, n2, ok, n1)
 		if i >= 10 {
 			t.Fatalf("GoroutineProfile not converging")
 		}
 	}
 }

 func BenchmarkGoroutineProfile(b *testing.B) {
 	run := func(fn func() bool) func(b *testing.B) {
 		runOne := func(b *testing.B) {
 			latencies := make([]time.Duration, 0, b.N)

 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
 				start := time.Now()
 				ok := fn()
 				if !ok {
 					b.Fatal("goroutine profile failed")
 				}
 				latencies = append(latencies, time.Since(start))
 			}
 			b.StopTimer()

 			// Sort latencies then report percentiles.
 			sort.Slice(latencies, func(i, j int) bool {
 				return latencies[i] < latencies[j]
 			})
 			b.ReportMetric(float64(latencies[len(latencies)*50/100]), "p50-ns")
 			b.ReportMetric(float64(latencies[len(latencies)*90/100]), "p90-ns")
 			b.ReportMetric(float64(latencies[len(latencies)*99/100]), "p99-ns")
 		}
 		return func(b *testing.B) {
 			b.Run("idle", runOne)

 			b.Run("loaded", func(b *testing.B) {
 				stop := applyGCLoad(b)
 				runOne(b)
 				// Make sure to stop the timer before we wait! The load created above
 				// is very heavy-weight and not easy to stop, so we could end up
 				// confusing the benchmarking framework for small b.N.
 				b.StopTimer()
 				stop()
 			})
 		}
 	}

 	// Measure the cost of counting goroutines
 	b.Run("small-nil", run(func() bool {
 		GoroutineProfile(nil)
 		return true
 	}))

 	// Measure the cost with a small set of goroutines
 	n := NumGoroutine()
 	p := make([]StackRecord, 2*n+2*GOMAXPROCS(0))
 	b.Run("small", run(func() bool {
 		_, ok := GoroutineProfile(p)
 		return ok
 	}))

 	// Measure the cost with a large set of goroutines
 	ch := make(chan int)
 	var ready, done sync.WaitGroup
 	for i := 0; i < 5000; i++ {
 		ready.Add(1)
 		done.Add(1)
 		go func() { ready.Done(); <-ch; done.Done() }()
 	}
 	ready.Wait()

 	// Count goroutines with a large allgs list
 	b.Run("large-nil", run(func() bool {
 		GoroutineProfile(nil)
 		return true
 	}))

 	n = NumGoroutine()
 	p = make([]StackRecord, 2*n+2*GOMAXPROCS(0))
 	b.Run("large", run(func() bool {
 		_, ok := GoroutineProfile(p)
 		return ok
 	}))

 	close(ch)
 	done.Wait()

 	// Count goroutines with a large (but unused) allgs list
 	b.Run("sparse-nil", run(func() bool {
 		GoroutineProfile(nil)
 		return true
 	}))

 	// Measure the cost of a large (but unused) allgs list
 	n = NumGoroutine()
 	p = make([]StackRecord, 2*n+2*GOMAXPROCS(0))
 	b.Run("sparse", run(func() bool {
 		_, ok := GoroutineProfile(p)
 		return ok
 	}))
 }

 func TestVersion(t *testing.T) {
 	// Test that version does not contain \r or \n.
 	vers := Version()
 	if strings.Contains(vers, "\r") || strings.Contains(vers, "\n") {
 		t.Fatalf("cr/nl in version: %q", vers)
 	}
 }

 func TestTimediv(t *testing.T) {
 	for _, tc := range []struct {
 		num int64
 		div int32
 		ret int32
 		rem int32
 	}{
 		{
 			num: 8,
 			div: 2,
 			ret: 4,
 			rem: 0,
 		},
 		{
 			num: 9,
 			div: 2,
 			ret: 4,
 			rem: 1,
 		},
 		{
 			// Used by runtime.check.
 			num: 12345*1000000000 + 54321,
 			div: 1000000000,
 			ret: 12345,
 			rem: 54321,
 		},
 		{
 			num: 1<<32 - 1,
 			div: 2,
 			ret: 1<<31 - 1, // no overflow.
 			rem: 1,
 		},
 		{
 			num: 1 << 32,
 			div: 2,
 			ret: 1<<31 - 1, // overflow.
 			rem: 0,
 		},
 		{
 			num: 1 << 40,
 			div: 2,
 			ret: 1<<31 - 1, // overflow.
 			rem: 0,
 		},
 		{
 			num: 1<<40 + 1,
 			div: 1 << 10,
 			ret: 1 << 30,
 			rem: 1,
 		},
 	} {
 		name := fmt.Sprintf("%d div %d", tc.num, tc.div)
 		t.Run(name, func(t *testing.T) {
 			// Double check that the inputs make sense using
 			// standard 64-bit division.
 			ret64 := tc.num / int64(tc.div)
 			rem64 := tc.num % int64(tc.div)
 			if ret64 != int64(int32(ret64)) {
 				// Simulate timediv overflow value.
 				ret64 = 1<<31 - 1
 				rem64 = 0
 			}
 			if ret64 != int64(tc.ret) {
 				t.Errorf("%d / %d got ret %d rem %d want ret %d rem %d", tc.num, tc.div, ret64, rem64, tc.ret, tc.rem)
 			}

 			var rem int32
 			ret := Timediv(tc.num, tc.div, &rem)
 			if ret != tc.ret || rem != tc.rem {
 				t.Errorf("timediv %d / %d got ret %d rem %d want ret %d rem %d", tc.num, tc.div, ret, rem, tc.ret, tc.rem)
 			}
 		})
 	}
 }
	// Copyright 2012 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 runtime_test

	import (
	"flag"
	"fmt"
	"io"
	. "runtime"
	"runtime/debug"
	"sort"
	"strings"
	"sync"
	"testing"
	"time"
	"unsafe"
	)

	// flagQuick is set by the -quick option to skip some relatively slow tests.
	// This is used by the cmd/dist test runtime:cpu124.
	// The cmd/dist test passes both -test.short and -quick;
	// there are tests that only check testing.Short, and those tests will
	// not be skipped if only -quick is used.
	var flagQuick = flag.Bool("quick", false, "skip slow tests, for cmd/dist test runtime:cpu124")

	func init() {
	// We're testing the runtime, so make tracebacks show things
	// in the runtime. This only raises the level, so it won't
	// override GOTRACEBACK=crash from the user.
	SetTracebackEnv("system")
	}

	var errf error

	func errfn() error {
	return errf
	}

	func errfn1() error {
	return io.EOF
	}

	func BenchmarkIfaceCmp100(b *testing.B) {
	for i := 0; i < b.N; i++ {
	for j := 0; j < 100; j++ {
	if errfn() == io.EOF {
	b.Fatal("bad comparison")
	}
	}
	}
	}

	func BenchmarkIfaceCmpNil100(b *testing.B) {
	for i := 0; i < b.N; i++ {
	for j := 0; j < 100; j++ {
	if errfn1() == nil {
	b.Fatal("bad comparison")
	}
	}
	}
	}

	var efaceCmp1 any
	var efaceCmp2 any

	func BenchmarkEfaceCmpDiff(b *testing.B) {
	x := 5
	efaceCmp1 = &x
	y := 6
	efaceCmp2 = &y
	for i := 0; i < b.N; i++ {
	for j := 0; j < 100; j++ {
	if efaceCmp1 == efaceCmp2 {
	b.Fatal("bad comparison")
	}
	}
	}
	}

	func BenchmarkEfaceCmpDiffIndirect(b *testing.B) {
	efaceCmp1 = [2]int{1, 2}
	efaceCmp2 = [2]int{1, 2}
	for i := 0; i < b.N; i++ {
	for j := 0; j < 100; j++ {
	if efaceCmp1 != efaceCmp2 {
	b.Fatal("bad comparison")
	}
	}
	}
	}

	func BenchmarkDefer(b *testing.B) {
	for i := 0; i < b.N; i++ {
	defer1()
	}
	}

	func defer1() {
	defer func(x, y, z int) {
	if recover() != nil \|\| x != 1 \|\| y != 2 \|\| z != 3 {
	panic("bad recover")
	}
	}(1, 2, 3)
	}

	func BenchmarkDefer10(b *testing.B) {
	for i := 0; i < b.N/10; i++ {
	defer2()
	}
	}

	func defer2() {
	for i := 0; i < 10; i++ {
	defer func(x, y, z int) {
	if recover() != nil \|\| x != 1 \|\| y != 2 \|\| z != 3 {
	panic("bad recover")
	}
	}(1, 2, 3)
	}
	}

	func BenchmarkDeferMany(b *testing.B) {
	for i := 0; i < b.N; i++ {
	defer func(x, y, z int) {
	if recover() != nil \|\| x != 1 \|\| y != 2 \|\| z != 3 {
	panic("bad recover")
	}
	}(1, 2, 3)
	}
	}

	func BenchmarkPanicRecover(b *testing.B) {
	for i := 0; i < b.N; i++ {
	defer3()
	}
	}

	func defer3() {
	defer func(x, y, z int) {
	if recover() == nil {
	panic("failed recover")
	}
	}(1, 2, 3)
	panic("hi")
	}

	// golang.org/issue/7063
	func TestStopCPUProfilingWithProfilerOff(t *testing.T) {
	SetCPUProfileRate(0)
	}

	// Addresses to test for faulting behavior.
	// This is less a test of SetPanicOnFault and more a check that
	// the operating system and the runtime can process these faults
	// correctly. That is, we're indirectly testing that without SetPanicOnFault
	// these would manage to turn into ordinary crashes.
	// Note that these are truncated on 32-bit systems, so the bottom 32 bits
	// of the larger addresses must themselves be invalid addresses.
	// We might get unlucky and the OS might have mapped one of these
	// addresses, but probably not: they're all in the first page, very high
	// addresses that normally an OS would reserve for itself, or malformed
	// addresses. Even so, we might have to remove one or two on different
	// systems. We will see.

	var faultAddrs = []uint64{
	// low addresses
	0,
	1,
	0xfff,
	// high (kernel) addresses
	// or else malformed.
	0xffffffffffffffff,
	0xfffffffffffff001,
	0xffffffffffff0001,
	0xfffffffffff00001,
	0xffffffffff000001,
	0xfffffffff0000001,
	0xffffffff00000001,
	0xfffffff000000001,
	0xffffff0000000001,
	0xfffff00000000001,
	0xffff000000000001,
	0xfff0000000000001,
	0xff00000000000001,
	0xf000000000000001,
	0x8000000000000001,
	}

	func TestSetPanicOnFault(t *testing.T) {
	old := debug.SetPanicOnFault(true)
	defer debug.SetPanicOnFault(old)

	nfault := 0
	for _, addr := range faultAddrs {
	testSetPanicOnFault(t, uintptr(addr), &nfault)
	}
	if nfault == 0 {
	t.Fatalf("none of the addresses faulted")
	}
	}

	// testSetPanicOnFault tests one potentially faulting address.
	// It deliberately constructs and uses an invalid pointer,
	// so mark it as nocheckptr.
	//
	//go:nocheckptr
	func testSetPanicOnFault(t testing.T, addr uintptr, nfault int) {
	if GOOS == "js" {
	t.Skip("js does not support catching faults")
	}

	defer func() {
	if err := recover(); err != nil {
	*nfault++
	}
	}()

	// The read should fault, except that sometimes we hit
	// addresses that have had C or kernel pages mapped there
	// readable by user code. So just log the content.
	// If no addresses fault, we'll fail the test.
	v := (byte)(unsafe.Pointer(addr))
	t.Logf("addr %#x: %#x\n", addr, v)
	}

	func eqstring_generic(s1, s2 string) bool {
	if len(s1) != len(s2) {
	return false
	}
	// optimization in assembly versions:
	// if s1.str == s2.str { return true }
	for i := 0; i < len(s1); i++ {
	if s1[i] != s2[i] {
	return false
	}
	}
	return true
	}

	func TestEqString(t *testing.T) {
	// This isn't really an exhaustive test of == on strings, it's
	// just a convenient way of documenting (via eqstring_generic)
	// what == does.
	s := []string{
	"",
	"a",
	"c",
	"aaa",
	"ccc",
	"cccc"[:3], // same contents, different string
	"1234567890",
	}
	for _, s1 := range s {
	for _, s2 := range s {
	x := s1 == s2
	y := eqstring_generic(s1, s2)
	if x != y {
	t.Errorf(`("%s" == "%s") = %t, want %t`, s1, s2, x, y)
	}
	}
	}
	}

	func TestTrailingZero(t *testing.T) {
	// make sure we add padding for structs with trailing zero-sized fields
	type T1 struct {
	n int32
	z [0]byte
	}
	if unsafe.Sizeof(T1{}) != 8 {
	t.Errorf("sizeof(%#v)==%d, want 8", T1{}, unsafe.Sizeof(T1{}))
	}
	type T2 struct {
	n int64
	z struct{}
	}
	if unsafe.Sizeof(T2{}) != 8+unsafe.Sizeof(uintptr(0)) {
	t.Errorf("sizeof(%#v)==%d, want %d", T2{}, unsafe.Sizeof(T2{}), 8+unsafe.Sizeof(uintptr(0)))
	}
	type T3 struct {
	n byte
	z [4]struct{}
	}
	if unsafe.Sizeof(T3{}) != 2 {
	t.Errorf("sizeof(%#v)==%d, want 2", T3{}, unsafe.Sizeof(T3{}))
	}
	// make sure padding can double for both zerosize and alignment
	type T4 struct {
	a int32
	b int16
	c int8
	z struct{}
	}
	if unsafe.Sizeof(T4{}) != 8 {
	t.Errorf("sizeof(%#v)==%d, want 8", T4{}, unsafe.Sizeof(T4{}))
	}
	// make sure we don't pad a zero-sized thing
	type T5 struct {
	}
	if unsafe.Sizeof(T5{}) != 0 {
	t.Errorf("sizeof(%#v)==%d, want 0", T5{}, unsafe.Sizeof(T5{}))
	}
	}

	func TestAppendGrowth(t *testing.T) {
	var x []int64
	check := func(want int) {
	if cap(x) != want {
	t.Errorf("len=%d, cap=%d, want cap=%d", len(x), cap(x), want)
	}
	}

	check(0)
	want := 1
	for i := 1; i <= 100; i++ {
	x = append(x, 1)
	check(want)
	if i&(i-1) == 0 {
	want = 2 * i
	}
	}
	}

	var One = []int64{1}

	func TestAppendSliceGrowth(t *testing.T) {
	var x []int64
	check := func(want int) {
	if cap(x) != want {
	t.Errorf("len=%d, cap=%d, want cap=%d", len(x), cap(x), want)
	}
	}

	check(0)
	want := 1
	for i := 1; i <= 100; i++ {
	x = append(x, One...)
	check(want)
	if i&(i-1) == 0 {
	want = 2 * i
	}
	}
	}

	func TestGoroutineProfileTrivial(t *testing.T) {
	// Calling GoroutineProfile twice in a row should find the same number of goroutines,
	// but it's possible there are goroutines just about to exit, so we might end up
	// with fewer in the second call. Try a few times; it should converge once those
	// zombies are gone.
	for i := 0; ; i++ {
	n1, ok := GoroutineProfile(nil) // should fail, there's at least 1 goroutine
	if n1 < 1 \|\| ok {
	t.Fatalf("GoroutineProfile(nil) = %d, %v, want >0, false", n1, ok)
	}
	n2, ok := GoroutineProfile(make([]StackRecord, n1))
	if n2 == n1 && ok {
	break
	}
	t.Logf("GoroutineProfile(%d) = %d, %v, want %d, true", n1, n2, ok, n1)
	if i >= 10 {
	t.Fatalf("GoroutineProfile not converging")
	}
	}
	}

	func BenchmarkGoroutineProfile(b *testing.B) {
	run := func(fn func() bool) func(b *testing.B) {
	runOne := func(b *testing.B) {
	latencies := make([]time.Duration, 0, b.N)

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	start := time.Now()
	ok := fn()
	if !ok {
	b.Fatal("goroutine profile failed")
	}
	latencies = append(latencies, time.Since(start))
	}
	b.StopTimer()

	// Sort latencies then report percentiles.
	sort.Slice(latencies, func(i, j int) bool {
	return latencies[i] < latencies[j]
	})
	b.ReportMetric(float64(latencies[len(latencies)*50/100]), "p50-ns")
	b.ReportMetric(float64(latencies[len(latencies)*90/100]), "p90-ns")
	b.ReportMetric(float64(latencies[len(latencies)*99/100]), "p99-ns")
	}
	return func(b *testing.B) {
	b.Run("idle", runOne)

	b.Run("loaded", func(b *testing.B) {
	stop := applyGCLoad(b)
	runOne(b)
	// Make sure to stop the timer before we wait! The load created above
	// is very heavy-weight and not easy to stop, so we could end up
	// confusing the benchmarking framework for small b.N.
	b.StopTimer()
	stop()
	})
	}
	}

	// Measure the cost of counting goroutines
	b.Run("small-nil", run(func() bool {
	GoroutineProfile(nil)
	return true
	}))

	// Measure the cost with a small set of goroutines
	n := NumGoroutine()
	p := make([]StackRecord, 2n+2GOMAXPROCS(0))
	b.Run("small", run(func() bool {
	_, ok := GoroutineProfile(p)
	return ok
	}))

	// Measure the cost with a large set of goroutines
	ch := make(chan int)
	var ready, done sync.WaitGroup
	for i := 0; i < 5000; i++ {
	ready.Add(1)
	done.Add(1)
	go func() { ready.Done(); <-ch; done.Done() }()
	}
	ready.Wait()

	// Count goroutines with a large allgs list
	b.Run("large-nil", run(func() bool {
	GoroutineProfile(nil)
	return true
	}))

	n = NumGoroutine()
	p = make([]StackRecord, 2n+2GOMAXPROCS(0))
	b.Run("large", run(func() bool {
	_, ok := GoroutineProfile(p)
	return ok
	}))

	close(ch)
	done.Wait()

	// Count goroutines with a large (but unused) allgs list
	b.Run("sparse-nil", run(func() bool {
	GoroutineProfile(nil)
	return true
	}))

	// Measure the cost of a large (but unused) allgs list
	n = NumGoroutine()
	p = make([]StackRecord, 2n+2GOMAXPROCS(0))
	b.Run("sparse", run(func() bool {
	_, ok := GoroutineProfile(p)
	return ok
	}))
	}

	func TestVersion(t *testing.T) {
	// Test that version does not contain \r or \n.
	vers := Version()
	if strings.Contains(vers, "\r") \|\| strings.Contains(vers, "\n") {
	t.Fatalf("cr/nl in version: %q", vers)
	}
	}

	func TestTimediv(t *testing.T) {
	for _, tc := range []struct {
	num int64
	div int32
	ret int32
	rem int32
	}{
	{
	num: 8,
	div: 2,
	ret: 4,
	rem: 0,
	},
	{
	num: 9,
	div: 2,
	ret: 4,
	rem: 1,
	},
	{
	// Used by runtime.check.
	num: 12345*1000000000 + 54321,
	div: 1000000000,
	ret: 12345,
	rem: 54321,
	},
	{
	num: 1<<32 - 1,
	div: 2,
	ret: 1<<31 - 1, // no overflow.
	rem: 1,
	},
	{
	num: 1 << 32,
	div: 2,
	ret: 1<<31 - 1, // overflow.
	rem: 0,
	},
	{
	num: 1 << 40,
	div: 2,
	ret: 1<<31 - 1, // overflow.
	rem: 0,
	},
	{
	num: 1<<40 + 1,
	div: 1 << 10,
	ret: 1 << 30,
	rem: 1,
	},
	} {
	name := fmt.Sprintf("%d div %d", tc.num, tc.div)
	t.Run(name, func(t *testing.T) {
	// Double check that the inputs make sense using
	// standard 64-bit division.
	ret64 := tc.num / int64(tc.div)
	rem64 := tc.num % int64(tc.div)
	if ret64 != int64(int32(ret64)) {
	// Simulate timediv overflow value.
	ret64 = 1<<31 - 1
	rem64 = 0
	}
	if ret64 != int64(tc.ret) {
	t.Errorf("%d / %d got ret %d rem %d want ret %d rem %d", tc.num, tc.div, ret64, rem64, tc.ret, tc.rem)
	}

	var rem int32
	ret := Timediv(tc.num, tc.div, &rem)
	if ret != tc.ret \|\| rem != tc.rem {
	t.Errorf("timediv %d / %d got ret %d rem %d want ret %d rem %d", tc.num, tc.div, ret, rem, tc.ret, tc.rem)
	}
	})
	}
	}