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

 // Copyright 2013 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"
 	"internal/race"
 	"internal/testenv"
 	"os"
 	"os/exec"
 	"reflect"
 	. "runtime"
 	"strings"
 	"testing"
 	"time"
 	"unsafe"
 )

 var testMemStatsCount int

 func TestMemStats(t *testing.T) {
 	testMemStatsCount++

 	// Make sure there's at least one forced GC.
 	GC()

 	// Test that MemStats has sane values.
 	st := new(MemStats)
 	ReadMemStats(st)

 	nz := func(x interface{}) error {
 		if x != reflect.Zero(reflect.TypeOf(x)).Interface() {
 			return nil
 		}
 		return fmt.Errorf("zero value")
 	}
 	le := func(thresh float64) func(interface{}) error {
 		return func(x interface{}) error {
 			// These sanity tests aren't necessarily valid
 			// with high -test.count values, so only run
 			// them once.
 			if testMemStatsCount > 1 {
 				return nil
 			}

 			if reflect.ValueOf(x).Convert(reflect.TypeOf(thresh)).Float() < thresh {
 				return nil
 			}
 			return fmt.Errorf("insanely high value (overflow?); want <= %v", thresh)
 		}
 	}
 	eq := func(x interface{}) func(interface{}) error {
 		return func(y interface{}) error {
 			if x == y {
 				return nil
 			}
 			return fmt.Errorf("want %v", x)
 		}
 	}
 	// Of the uint fields, HeapReleased, HeapIdle can be 0.
 	// PauseTotalNs can be 0 if timer resolution is poor.
 	fields := map[string][]func(interface{}) error{
 		"Alloc": {nz, le(1e10)}, "TotalAlloc": {nz, le(1e11)}, "Sys": {nz, le(1e10)},
 		"Lookups": {eq(uint64(0))}, "Mallocs": {nz, le(1e10)}, "Frees": {nz, le(1e10)},
 		"HeapAlloc": {nz, le(1e10)}, "HeapSys": {nz, le(1e10)}, "HeapIdle": {le(1e10)},
 		"HeapInuse": {nz, le(1e10)}, "HeapReleased": {le(1e10)}, "HeapObjects": {nz, le(1e10)},
 		"StackInuse": {nz, le(1e10)}, "StackSys": {nz, le(1e10)},
 		"MSpanInuse": {nz, le(1e10)}, "MSpanSys": {nz, le(1e10)},
 		"MCacheInuse": {nz, le(1e10)}, "MCacheSys": {nz, le(1e10)},
 		"BuckHashSys": {nz, le(1e10)}, "GCSys": {nz, le(1e10)}, "OtherSys": {nz, le(1e10)},
 		"NextGC": {nz, le(1e10)}, "LastGC": {nz},
 		"PauseTotalNs": {le(1e11)}, "PauseNs": nil, "PauseEnd": nil,
 		"NumGC": {nz, le(1e9)}, "NumForcedGC": {nz, le(1e9)},
 		"GCCPUFraction": {le(0.99)}, "EnableGC": {eq(true)}, "DebugGC": {eq(false)},
 		"BySize": nil,
 	}

 	rst := reflect.ValueOf(st).Elem()
 	for i := 0; i < rst.Type().NumField(); i++ {
 		name, val := rst.Type().Field(i).Name, rst.Field(i).Interface()
 		checks, ok := fields[name]
 		if !ok {
 			t.Errorf("unknown MemStats field %s", name)
 			continue
 		}
 		for _, check := range checks {
 			if err := check(val); err != nil {
 				t.Errorf("%s = %v: %s", name, val, err)
 			}
 		}
 	}

 	if st.Sys != st.HeapSys+st.StackSys+st.MSpanSys+st.MCacheSys+
 		st.BuckHashSys+st.GCSys+st.OtherSys {
 		t.Fatalf("Bad sys value: %+v", *st)
 	}

 	if st.HeapIdle+st.HeapInuse != st.HeapSys {
 		t.Fatalf("HeapIdle(%d) + HeapInuse(%d) should be equal to HeapSys(%d), but isn't.", st.HeapIdle, st.HeapInuse, st.HeapSys)
 	}

 	if lpe := st.PauseEnd[int(st.NumGC+255)%len(st.PauseEnd)]; st.LastGC != lpe {
 		t.Fatalf("LastGC(%d) != last PauseEnd(%d)", st.LastGC, lpe)
 	}

 	var pauseTotal uint64
 	for _, pause := range st.PauseNs {
 		pauseTotal += pause
 	}
 	if int(st.NumGC) < len(st.PauseNs) {
 		// We have all pauses, so this should be exact.
 		if st.PauseTotalNs != pauseTotal {
 			t.Fatalf("PauseTotalNs(%d) != sum PauseNs(%d)", st.PauseTotalNs, pauseTotal)
 		}
 		for i := int(st.NumGC); i < len(st.PauseNs); i++ {
 			if st.PauseNs[i] != 0 {
 				t.Fatalf("Non-zero PauseNs[%d]: %+v", i, st)
 			}
 			if st.PauseEnd[i] != 0 {
 				t.Fatalf("Non-zero PauseEnd[%d]: %+v", i, st)
 			}
 		}
 	} else {
 		if st.PauseTotalNs < pauseTotal {
 			t.Fatalf("PauseTotalNs(%d) < sum PauseNs(%d)", st.PauseTotalNs, pauseTotal)
 		}
 	}

 	if st.NumForcedGC > st.NumGC {
 		t.Fatalf("NumForcedGC(%d) > NumGC(%d)", st.NumForcedGC, st.NumGC)
 	}
 }

 func TestStringConcatenationAllocs(t *testing.T) {
 	n := testing.AllocsPerRun(1e3, func() {
 		b := make([]byte, 10)
 		for i := 0; i < 10; i++ {
 			b[i] = byte(i) + '0'
 		}
 		s := "foo" + string(b)
 		if want := "foo0123456789"; s != want {
 			t.Fatalf("want %v, got %v", want, s)
 		}
 	})
 	// Only string concatenation allocates.
 	if n != 1 {
 		t.Fatalf("want 1 allocation, got %v", n)
 	}
 }

 func TestTinyAlloc(t *testing.T) {
 	const N = 16
 	var v [N]unsafe.Pointer
 	for i := range v {
 		v[i] = unsafe.Pointer(new(byte))
 	}

 	chunks := make(map[uintptr]bool, N)
 	for _, p := range v {
 		chunks[uintptr(p)&^7] = true
 	}

 	if len(chunks) == N {
 		t.Fatal("no bytes allocated within the same 8-byte chunk")
 	}
 }

 func TestPhysicalMemoryUtilization(t *testing.T) {
 	got := runTestProg(t, "testprog", "GCPhys")
 	want := "OK\n"
 	if got != want {
 		t.Fatalf("expected %q, but got %q", want, got)
 	}
 }

 type acLink struct {
 	x [1 << 20]byte
 }

 var arenaCollisionSink []*acLink

 func TestArenaCollision(t *testing.T) {
 	if GOOS == "darwin" && race.Enabled {
 		// Skip this test on Darwin in race mode because Darwin 10.10 has
 		// issues following arena hints and runs out of them in race mode, so
 		// MAP_FIXED is used to ensure we keep the heap in the memory region the
 		// race detector expects.
 		// TODO(mknyszek): Delete this when Darwin 10.10 is no longer supported.
 		t.Skip("disabled on Darwin with race mode since MAP_FIXED is used")
 	}
 	testenv.MustHaveExec(t)

 	// Test that mheap.sysAlloc handles collisions with other
 	// memory mappings.
 	if os.Getenv("TEST_ARENA_COLLISION") != "1" {
 		cmd := testenv.CleanCmdEnv(exec.Command(os.Args[0], "-test.run=TestArenaCollision", "-test.v"))
 		cmd.Env = append(cmd.Env, "TEST_ARENA_COLLISION=1")
 		out, err := cmd.CombinedOutput()
 		if race.Enabled {
 			// This test runs the runtime out of hint
 			// addresses, so it will start mapping the
 			// heap wherever it can. The race detector
 			// doesn't support this, so look for the
 			// expected failure.
 			if want := "too many address space collisions"; !strings.Contains(string(out), want) {
 				t.Fatalf("want %q, got:\n%s", want, string(out))
 			}
 		} else if !strings.Contains(string(out), "PASS\n") || err != nil {
 			t.Fatalf("%s\n(exit status %v)", string(out), err)
 		}
 		return
 	}
 	disallowed := [][2]uintptr{}
 	// Drop all but the next 3 hints. 64-bit has a lot of hints,
 	// so it would take a lot of memory to go through all of them.
 	KeepNArenaHints(3)
 	// Consume these 3 hints and force the runtime to find some
 	// fallback hints.
 	for i := 0; i < 5; i++ {
 		// Reserve memory at the next hint so it can't be used
 		// for the heap.
 		start, end := MapNextArenaHint()
 		disallowed = append(disallowed, [2]uintptr{start, end})
 		// Allocate until the runtime tries to use the hint we
 		// just mapped over.
 		hint := GetNextArenaHint()
 		for GetNextArenaHint() == hint {
 			ac := new(acLink)
 			arenaCollisionSink = append(arenaCollisionSink, ac)
 			// The allocation must not have fallen into
 			// one of the reserved regions.
 			p := uintptr(unsafe.Pointer(ac))
 			for _, d := range disallowed {
 				if d[0] <= p && p < d[1] {
 					t.Fatalf("allocation %#x in reserved region [%#x, %#x)", p, d[0], d[1])
 				}
 			}
 		}
 	}
 }

 var mallocSink uintptr

 func BenchmarkMalloc8(b *testing.B) {
 	var x uintptr
 	for i := 0; i < b.N; i++ {
 		p := new(int64)
 		x ^= uintptr(unsafe.Pointer(p))
 	}
 	mallocSink = x
 }

 func BenchmarkMalloc16(b *testing.B) {
 	var x uintptr
 	for i := 0; i < b.N; i++ {
 		p := new([2]int64)
 		x ^= uintptr(unsafe.Pointer(p))
 	}
 	mallocSink = x
 }

 func BenchmarkMallocTypeInfo8(b *testing.B) {
 	var x uintptr
 	for i := 0; i < b.N; i++ {
 		p := new(struct {
 			p [8 / unsafe.Sizeof(uintptr(0))]*int
 		})
 		x ^= uintptr(unsafe.Pointer(p))
 	}
 	mallocSink = x
 }

 func BenchmarkMallocTypeInfo16(b *testing.B) {
 	var x uintptr
 	for i := 0; i < b.N; i++ {
 		p := new(struct {
 			p [16 / unsafe.Sizeof(uintptr(0))]*int
 		})
 		x ^= uintptr(unsafe.Pointer(p))
 	}
 	mallocSink = x
 }

 type LargeStruct struct {
 	x [16][]byte
 }

 func BenchmarkMallocLargeStruct(b *testing.B) {
 	var x uintptr
 	for i := 0; i < b.N; i++ {
 		p := make([]LargeStruct, 2)
 		x ^= uintptr(unsafe.Pointer(&p[0]))
 	}
 	mallocSink = x
 }

 var n = flag.Int("n", 1000, "number of goroutines")

 func BenchmarkGoroutineSelect(b *testing.B) {
 	quit := make(chan struct{})
 	read := func(ch chan struct{}) {
 		for {
 			select {
 			case _, ok := <-ch:
 				if !ok {
 					return
 				}
 			case <-quit:
 				return
 			}
 		}
 	}
 	benchHelper(b, *n, read)
 }

 func BenchmarkGoroutineBlocking(b *testing.B) {
 	read := func(ch chan struct{}) {
 		for {
 			if _, ok := <-ch; !ok {
 				return
 			}
 		}
 	}
 	benchHelper(b, *n, read)
 }

 func BenchmarkGoroutineForRange(b *testing.B) {
 	read := func(ch chan struct{}) {
 		for range ch {
 		}
 	}
 	benchHelper(b, *n, read)
 }

 func benchHelper(b *testing.B, n int, read func(chan struct{})) {
 	m := make([]chan struct{}, n)
 	for i := range m {
 		m[i] = make(chan struct{}, 1)
 		go read(m[i])
 	}
 	b.StopTimer()
 	b.ResetTimer()
 	GC()

 	for i := 0; i < b.N; i++ {
 		for _, ch := range m {
 			if ch != nil {
 				ch <- struct{}{}
 			}
 		}
 		time.Sleep(10 * time.Millisecond)
 		b.StartTimer()
 		GC()
 		b.StopTimer()
 	}

 	for _, ch := range m {
 		close(ch)
 	}
 	time.Sleep(10 * time.Millisecond)
 }

 func BenchmarkGoroutineIdle(b *testing.B) {
 	quit := make(chan struct{})
 	fn := func() {
 		<-quit
 	}
 	for i := 0; i < *n; i++ {
 		go fn()
 	}

 	GC()
 	b.ResetTimer()

 	for i := 0; i < b.N; i++ {
 		GC()
 	}

 	b.StopTimer()
 	close(quit)
 	time.Sleep(10 * time.Millisecond)
 }
	// Copyright 2013 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"
	"internal/race"
	"internal/testenv"
	"os"
	"os/exec"
	"reflect"
	. "runtime"
	"strings"
	"testing"
	"time"
	"unsafe"
	)

	var testMemStatsCount int

	func TestMemStats(t *testing.T) {
	testMemStatsCount++

	// Make sure there's at least one forced GC.
	GC()

	// Test that MemStats has sane values.
	st := new(MemStats)
	ReadMemStats(st)

	nz := func(x interface{}) error {
	if x != reflect.Zero(reflect.TypeOf(x)).Interface() {
	return nil
	}
	return fmt.Errorf("zero value")
	}
	le := func(thresh float64) func(interface{}) error {
	return func(x interface{}) error {
	// These sanity tests aren't necessarily valid
	// with high -test.count values, so only run
	// them once.
	if testMemStatsCount > 1 {
	return nil
	}

	if reflect.ValueOf(x).Convert(reflect.TypeOf(thresh)).Float() < thresh {
	return nil
	}
	return fmt.Errorf("insanely high value (overflow?); want <= %v", thresh)
	}
	}
	eq := func(x interface{}) func(interface{}) error {
	return func(y interface{}) error {
	if x == y {
	return nil
	}
	return fmt.Errorf("want %v", x)
	}
	}
	// Of the uint fields, HeapReleased, HeapIdle can be 0.
	// PauseTotalNs can be 0 if timer resolution is poor.
	fields := map[string][]func(interface{}) error{
	"Alloc": {nz, le(1e10)}, "TotalAlloc": {nz, le(1e11)}, "Sys": {nz, le(1e10)},
	"Lookups": {eq(uint64(0))}, "Mallocs": {nz, le(1e10)}, "Frees": {nz, le(1e10)},
	"HeapAlloc": {nz, le(1e10)}, "HeapSys": {nz, le(1e10)}, "HeapIdle": {le(1e10)},
	"HeapInuse": {nz, le(1e10)}, "HeapReleased": {le(1e10)}, "HeapObjects": {nz, le(1e10)},
	"StackInuse": {nz, le(1e10)}, "StackSys": {nz, le(1e10)},
	"MSpanInuse": {nz, le(1e10)}, "MSpanSys": {nz, le(1e10)},
	"MCacheInuse": {nz, le(1e10)}, "MCacheSys": {nz, le(1e10)},
	"BuckHashSys": {nz, le(1e10)}, "GCSys": {nz, le(1e10)}, "OtherSys": {nz, le(1e10)},
	"NextGC": {nz, le(1e10)}, "LastGC": {nz},
	"PauseTotalNs": {le(1e11)}, "PauseNs": nil, "PauseEnd": nil,
	"NumGC": {nz, le(1e9)}, "NumForcedGC": {nz, le(1e9)},
	"GCCPUFraction": {le(0.99)}, "EnableGC": {eq(true)}, "DebugGC": {eq(false)},
	"BySize": nil,
	}

	rst := reflect.ValueOf(st).Elem()
	for i := 0; i < rst.Type().NumField(); i++ {
	name, val := rst.Type().Field(i).Name, rst.Field(i).Interface()
	checks, ok := fields[name]
	if !ok {
	t.Errorf("unknown MemStats field %s", name)
	continue
	}
	for _, check := range checks {
	if err := check(val); err != nil {
	t.Errorf("%s = %v: %s", name, val, err)
	}
	}
	}

	if st.Sys != st.HeapSys+st.StackSys+st.MSpanSys+st.MCacheSys+
	st.BuckHashSys+st.GCSys+st.OtherSys {
	t.Fatalf("Bad sys value: %+v", *st)
	}

	if st.HeapIdle+st.HeapInuse != st.HeapSys {
	t.Fatalf("HeapIdle(%d) + HeapInuse(%d) should be equal to HeapSys(%d), but isn't.", st.HeapIdle, st.HeapInuse, st.HeapSys)
	}

	if lpe := st.PauseEnd[int(st.NumGC+255)%len(st.PauseEnd)]; st.LastGC != lpe {
	t.Fatalf("LastGC(%d) != last PauseEnd(%d)", st.LastGC, lpe)
	}

	var pauseTotal uint64
	for _, pause := range st.PauseNs {
	pauseTotal += pause
	}
	if int(st.NumGC) < len(st.PauseNs) {
	// We have all pauses, so this should be exact.
	if st.PauseTotalNs != pauseTotal {
	t.Fatalf("PauseTotalNs(%d) != sum PauseNs(%d)", st.PauseTotalNs, pauseTotal)
	}
	for i := int(st.NumGC); i < len(st.PauseNs); i++ {
	if st.PauseNs[i] != 0 {
	t.Fatalf("Non-zero PauseNs[%d]: %+v", i, st)
	}
	if st.PauseEnd[i] != 0 {
	t.Fatalf("Non-zero PauseEnd[%d]: %+v", i, st)
	}
	}
	} else {
	if st.PauseTotalNs < pauseTotal {
	t.Fatalf("PauseTotalNs(%d) < sum PauseNs(%d)", st.PauseTotalNs, pauseTotal)
	}
	}

	if st.NumForcedGC > st.NumGC {
	t.Fatalf("NumForcedGC(%d) > NumGC(%d)", st.NumForcedGC, st.NumGC)
	}
	}

	func TestStringConcatenationAllocs(t *testing.T) {
	n := testing.AllocsPerRun(1e3, func() {
	b := make([]byte, 10)
	for i := 0; i < 10; i++ {
	b[i] = byte(i) + '0'
	}
	s := "foo" + string(b)
	if want := "foo0123456789"; s != want {
	t.Fatalf("want %v, got %v", want, s)
	}
	})
	// Only string concatenation allocates.
	if n != 1 {
	t.Fatalf("want 1 allocation, got %v", n)
	}
	}

	func TestTinyAlloc(t *testing.T) {
	const N = 16
	var v [N]unsafe.Pointer
	for i := range v {
	v[i] = unsafe.Pointer(new(byte))
	}

	chunks := make(map[uintptr]bool, N)
	for _, p := range v {
	chunks[uintptr(p)&^7] = true
	}

	if len(chunks) == N {
	t.Fatal("no bytes allocated within the same 8-byte chunk")
	}
	}

	func TestPhysicalMemoryUtilization(t *testing.T) {
	got := runTestProg(t, "testprog", "GCPhys")
	want := "OK\n"
	if got != want {
	t.Fatalf("expected %q, but got %q", want, got)
	}
	}

	type acLink struct {
	x [1 << 20]byte
	}

	var arenaCollisionSink []*acLink

	func TestArenaCollision(t *testing.T) {
	if GOOS == "darwin" && race.Enabled {
	// Skip this test on Darwin in race mode because Darwin 10.10 has
	// issues following arena hints and runs out of them in race mode, so
	// MAP_FIXED is used to ensure we keep the heap in the memory region the
	// race detector expects.
	// TODO(mknyszek): Delete this when Darwin 10.10 is no longer supported.
	t.Skip("disabled on Darwin with race mode since MAP_FIXED is used")
	}
	testenv.MustHaveExec(t)

	// Test that mheap.sysAlloc handles collisions with other
	// memory mappings.
	if os.Getenv("TEST_ARENA_COLLISION") != "1" {
	cmd := testenv.CleanCmdEnv(exec.Command(os.Args[0], "-test.run=TestArenaCollision", "-test.v"))
	cmd.Env = append(cmd.Env, "TEST_ARENA_COLLISION=1")
	out, err := cmd.CombinedOutput()
	if race.Enabled {
	// This test runs the runtime out of hint
	// addresses, so it will start mapping the
	// heap wherever it can. The race detector
	// doesn't support this, so look for the
	// expected failure.
	if want := "too many address space collisions"; !strings.Contains(string(out), want) {
	t.Fatalf("want %q, got:\n%s", want, string(out))
	}
	} else if !strings.Contains(string(out), "PASS\n") \|\| err != nil {
	t.Fatalf("%s\n(exit status %v)", string(out), err)
	}
	return
	}
	disallowed := [][2]uintptr{}
	// Drop all but the next 3 hints. 64-bit has a lot of hints,
	// so it would take a lot of memory to go through all of them.
	KeepNArenaHints(3)
	// Consume these 3 hints and force the runtime to find some
	// fallback hints.
	for i := 0; i < 5; i++ {
	// Reserve memory at the next hint so it can't be used
	// for the heap.
	start, end := MapNextArenaHint()
	disallowed = append(disallowed, [2]uintptr{start, end})
	// Allocate until the runtime tries to use the hint we
	// just mapped over.
	hint := GetNextArenaHint()
	for GetNextArenaHint() == hint {
	ac := new(acLink)
	arenaCollisionSink = append(arenaCollisionSink, ac)
	// The allocation must not have fallen into
	// one of the reserved regions.
	p := uintptr(unsafe.Pointer(ac))
	for _, d := range disallowed {
	if d[0] <= p && p < d[1] {
	t.Fatalf("allocation %#x in reserved region [%#x, %#x)", p, d[0], d[1])
	}
	}
	}
	}
	}

	var mallocSink uintptr

	func BenchmarkMalloc8(b *testing.B) {
	var x uintptr
	for i := 0; i < b.N; i++ {
	p := new(int64)
	x ^= uintptr(unsafe.Pointer(p))
	}
	mallocSink = x
	}

	func BenchmarkMalloc16(b *testing.B) {
	var x uintptr
	for i := 0; i < b.N; i++ {
	p := new([2]int64)
	x ^= uintptr(unsafe.Pointer(p))
	}
	mallocSink = x
	}

	func BenchmarkMallocTypeInfo8(b *testing.B) {
	var x uintptr
	for i := 0; i < b.N; i++ {
	p := new(struct {
	p [8 / unsafe.Sizeof(uintptr(0))]*int
	})
	x ^= uintptr(unsafe.Pointer(p))
	}
	mallocSink = x
	}

	func BenchmarkMallocTypeInfo16(b *testing.B) {
	var x uintptr
	for i := 0; i < b.N; i++ {
	p := new(struct {
	p [16 / unsafe.Sizeof(uintptr(0))]*int
	})
	x ^= uintptr(unsafe.Pointer(p))
	}
	mallocSink = x
	}

	type LargeStruct struct {
	x [16][]byte
	}

	func BenchmarkMallocLargeStruct(b *testing.B) {
	var x uintptr
	for i := 0; i < b.N; i++ {
	p := make([]LargeStruct, 2)
	x ^= uintptr(unsafe.Pointer(&p[0]))
	}
	mallocSink = x
	}

	var n = flag.Int("n", 1000, "number of goroutines")

	func BenchmarkGoroutineSelect(b *testing.B) {
	quit := make(chan struct{})
	read := func(ch chan struct{}) {
	for {
	select {
	case _, ok := <-ch:
	if !ok {
	return
	}
	case <-quit:
	return
	}
	}
	}
	benchHelper(b, *n, read)
	}

	func BenchmarkGoroutineBlocking(b *testing.B) {
	read := func(ch chan struct{}) {
	for {
	if _, ok := <-ch; !ok {
	return
	}
	}
	}
	benchHelper(b, *n, read)
	}

	func BenchmarkGoroutineForRange(b *testing.B) {
	read := func(ch chan struct{}) {
	for range ch {
	}
	}
	benchHelper(b, *n, read)
	}

	func benchHelper(b *testing.B, n int, read func(chan struct{})) {
	m := make([]chan struct{}, n)
	for i := range m {
	m[i] = make(chan struct{}, 1)
	go read(m[i])
	}
	b.StopTimer()
	b.ResetTimer()
	GC()

	for i := 0; i < b.N; i++ {
	for _, ch := range m {
	if ch != nil {
	ch <- struct{}{}
	}
	}
	time.Sleep(10 * time.Millisecond)
	b.StartTimer()
	GC()
	b.StopTimer()
	}

	for _, ch := range m {
	close(ch)
	}
	time.Sleep(10 * time.Millisecond)
	}

	func BenchmarkGoroutineIdle(b *testing.B) {
	quit := make(chan struct{})
	fn := func() {
	<-quit
	}
	for i := 0; i < *n; i++ {
	go fn()
	}

	GC()
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
	GC()
	}

	b.StopTimer()
	close(quit)
	time.Sleep(10 * time.Millisecond)
	}