src/expvar/expvar_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 expvar

 import (
 	"bytes"
 	"encoding/json"
 	"fmt"
 	"net"
 	"net/http/httptest"
 	"reflect"
 	"runtime"
 	"strconv"
 	"sync"
 	"sync/atomic"
 	"testing"
 )

 // RemoveAll removes all exported variables.
 // This is for tests only.
 func RemoveAll() {
 	varKeysMu.Lock()
 	defer varKeysMu.Unlock()
 	for _, k := range varKeys {
 		vars.Delete(k)
 	}
 	varKeys = nil
 }

 func TestNil(t *testing.T) {
 	RemoveAll()
 	val := Get("missing")
 	if val != nil {
 		t.Errorf("got %v, want nil", val)
 	}
 }

 func TestInt(t *testing.T) {
 	RemoveAll()
 	reqs := NewInt("requests")
 	if i := reqs.Value(); i != 0 {
 		t.Errorf("reqs.Value() = %v, want 0", i)
 	}
 	if reqs != Get("requests").(*Int) {
 		t.Errorf("Get() failed.")
 	}

 	reqs.Add(1)
 	reqs.Add(3)
 	if i := reqs.Value(); i != 4 {
 		t.Errorf("reqs.Value() = %v, want 4", i)
 	}

 	if s := reqs.String(); s != "4" {
 		t.Errorf("reqs.String() = %q, want \"4\"", s)
 	}

 	reqs.Set(-2)
 	if i := reqs.Value(); i != -2 {
 		t.Errorf("reqs.Value() = %v, want -2", i)
 	}
 }

 func BenchmarkIntAdd(b *testing.B) {
 	var v Int

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			v.Add(1)
 		}
 	})
 }

 func BenchmarkIntSet(b *testing.B) {
 	var v Int

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			v.Set(1)
 		}
 	})
 }

 func TestFloat(t *testing.T) {
 	RemoveAll()
 	reqs := NewFloat("requests-float")
 	if reqs.f != 0.0 {
 		t.Errorf("reqs.f = %v, want 0", reqs.f)
 	}
 	if reqs != Get("requests-float").(*Float) {
 		t.Errorf("Get() failed.")
 	}

 	reqs.Add(1.5)
 	reqs.Add(1.25)
 	if v := reqs.Value(); v != 2.75 {
 		t.Errorf("reqs.Value() = %v, want 2.75", v)
 	}

 	if s := reqs.String(); s != "2.75" {
 		t.Errorf("reqs.String() = %q, want \"4.64\"", s)
 	}

 	reqs.Add(-2)
 	if v := reqs.Value(); v != 0.75 {
 		t.Errorf("reqs.Value() = %v, want 0.75", v)
 	}
 }

 func BenchmarkFloatAdd(b *testing.B) {
 	var f Float

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			f.Add(1.0)
 		}
 	})
 }

 func BenchmarkFloatSet(b *testing.B) {
 	var f Float

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			f.Set(1.0)
 		}
 	})
 }

 func TestString(t *testing.T) {
 	RemoveAll()
 	name := NewString("my-name")
 	if s := name.Value(); s != "" {
 		t.Errorf(`NewString("my-name").Value() = %q, want ""`, s)
 	}

 	name.Set("Mike")
 	if s, want := name.String(), `"Mike"`; s != want {
 		t.Errorf(`after name.Set("Mike"), name.String() = %q, want %q`, s, want)
 	}
 	if s, want := name.Value(), "Mike"; s != want {
 		t.Errorf(`after name.Set("Mike"), name.Value() = %q, want %q`, s, want)
 	}

 	// Make sure we produce safe JSON output.
 	name.Set("<")
 	if s, want := name.String(), "\"\\u003c\""; s != want {
 		t.Errorf(`after name.Set("<"), name.String() = %q, want %q`, s, want)
 	}
 }

 func BenchmarkStringSet(b *testing.B) {
 	var s String

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			s.Set("red")
 		}
 	})
 }

 func TestMapInit(t *testing.T) {
 	RemoveAll()
 	colors := NewMap("bike-shed-colors")
 	colors.Add("red", 1)
 	colors.Add("blue", 1)
 	colors.Add("chartreuse", 1)

 	n := 0
 	colors.Do(func(KeyValue) { n++ })
 	if n != 3 {
 		t.Errorf("after three Add calls with distinct keys, Do should invoke f 3 times; got %v", n)
 	}

 	colors.Init()

 	n = 0
 	colors.Do(func(KeyValue) { n++ })
 	if n != 0 {
 		t.Errorf("after Init, Do should invoke f 0 times; got %v", n)
 	}
 }

 func TestMapCounter(t *testing.T) {
 	RemoveAll()
 	colors := NewMap("bike-shed-colors")

 	colors.Add("red", 1)
 	colors.Add("red", 2)
 	colors.Add("blue", 4)
 	colors.AddFloat(`green "midori"`, 4.125)
 	if x := colors.Get("red").(*Int).Value(); x != 3 {
 		t.Errorf("colors.m[\"red\"] = %v, want 3", x)
 	}
 	if x := colors.Get("blue").(*Int).Value(); x != 4 {
 		t.Errorf("colors.m[\"blue\"] = %v, want 4", x)
 	}
 	if x := colors.Get(`green "midori"`).(*Float).Value(); x != 4.125 {
 		t.Errorf("colors.m[`green \"midori\"] = %v, want 4.125", x)
 	}

 	// colors.String() should be '{"red":3, "blue":4}',
 	// though the order of red and blue could vary.
 	s := colors.String()
 	var j interface{}
 	err := json.Unmarshal([]byte(s), &j)
 	if err != nil {
 		t.Errorf("colors.String() isn't valid JSON: %v", err)
 	}
 	m, ok := j.(map[string]interface{})
 	if !ok {
 		t.Error("colors.String() didn't produce a map.")
 	}
 	red := m["red"]
 	x, ok := red.(float64)
 	if !ok {
 		t.Error("red.Kind() is not a number.")
 	}
 	if x != 3 {
 		t.Errorf("red = %v, want 3", x)
 	}
 }

 func BenchmarkMapSet(b *testing.B) {
 	m := new(Map).Init()

 	v := new(Int)

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			m.Set("red", v)
 		}
 	})
 }

 func BenchmarkMapSetDifferent(b *testing.B) {
 	procKeys := make([][]string, runtime.GOMAXPROCS(0))
 	for i := range procKeys {
 		keys := make([]string, 4)
 		for j := range keys {
 			keys[j] = fmt.Sprint(i, j)
 		}
 		procKeys[i] = keys
 	}

 	m := new(Map).Init()
 	v := new(Int)
 	b.ResetTimer()

 	var n int32
 	b.RunParallel(func(pb *testing.PB) {
 		i := int(atomic.AddInt32(&n, 1)-1) % len(procKeys)
 		keys := procKeys[i]

 		for pb.Next() {
 			for _, k := range keys {
 				m.Set(k, v)
 			}
 		}
 	})
 }

 func BenchmarkMapSetString(b *testing.B) {
 	m := new(Map).Init()

 	v := new(String)
 	v.Set("Hello, !")

 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			m.Set("red", v)
 		}
 	})
 }

 func BenchmarkMapAddSame(b *testing.B) {
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			m := new(Map).Init()
 			m.Add("red", 1)
 			m.Add("red", 1)
 			m.Add("red", 1)
 			m.Add("red", 1)
 		}
 	})
 }

 func BenchmarkMapAddDifferent(b *testing.B) {
 	procKeys := make([][]string, runtime.GOMAXPROCS(0))
 	for i := range procKeys {
 		keys := make([]string, 4)
 		for j := range keys {
 			keys[j] = fmt.Sprint(i, j)
 		}
 		procKeys[i] = keys
 	}

 	b.ResetTimer()

 	var n int32
 	b.RunParallel(func(pb *testing.PB) {
 		i := int(atomic.AddInt32(&n, 1)-1) % len(procKeys)
 		keys := procKeys[i]

 		for pb.Next() {
 			m := new(Map).Init()
 			for _, k := range keys {
 				m.Add(k, 1)
 			}
 		}
 	})
 }

 func BenchmarkMapAddSameSteadyState(b *testing.B) {
 	m := new(Map).Init()
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
 			m.Add("red", 1)
 		}
 	})
 }

 func BenchmarkMapAddDifferentSteadyState(b *testing.B) {
 	procKeys := make([][]string, runtime.GOMAXPROCS(0))
 	for i := range procKeys {
 		keys := make([]string, 4)
 		for j := range keys {
 			keys[j] = fmt.Sprint(i, j)
 		}
 		procKeys[i] = keys
 	}

 	m := new(Map).Init()
 	b.ResetTimer()

 	var n int32
 	b.RunParallel(func(pb *testing.PB) {
 		i := int(atomic.AddInt32(&n, 1)-1) % len(procKeys)
 		keys := procKeys[i]

 		for pb.Next() {
 			for _, k := range keys {
 				m.Add(k, 1)
 			}
 		}
 	})
 }

 func TestFunc(t *testing.T) {
 	RemoveAll()
 	var x interface{} = []string{"a", "b"}
 	f := Func(func() interface{} { return x })
 	if s, exp := f.String(), `["a","b"]`; s != exp {
 		t.Errorf(`f.String() = %q, want %q`, s, exp)
 	}
 	if v := f.Value(); !reflect.DeepEqual(v, x) {
 		t.Errorf(`f.Value() = %q, want %q`, v, x)
 	}

 	x = 17
 	if s, exp := f.String(), `17`; s != exp {
 		t.Errorf(`f.String() = %q, want %q`, s, exp)
 	}
 }

 func TestHandler(t *testing.T) {
 	RemoveAll()
 	m := NewMap("map1")
 	m.Add("a", 1)
 	m.Add("z", 2)
 	m2 := NewMap("map2")
 	for i := 0; i < 9; i++ {
 		m2.Add(strconv.Itoa(i), int64(i))
 	}
 	rr := httptest.NewRecorder()
 	rr.Body = new(bytes.Buffer)
 	expvarHandler(rr, nil)
 	want := `{
 "map1": {"a": 1, "z": 2},
 "map2": {"0": 0, "1": 1, "2": 2, "3": 3, "4": 4, "5": 5, "6": 6, "7": 7, "8": 8}
 }
 `
 	if got := rr.Body.String(); got != want {
 		t.Errorf("HTTP handler wrote:\n%s\nWant:\n%s", got, want)
 	}
 }

 func BenchmarkRealworldExpvarUsage(b *testing.B) {
 	var (
 		bytesSent Int
 		bytesRead Int
 	)

 	// The benchmark creates GOMAXPROCS client/server pairs.
 	// Each pair creates 4 goroutines: client reader/writer and server reader/writer.
 	// The benchmark stresses concurrent reading and writing to the same connection.
 	// Such pattern is used in net/http and net/rpc.

 	b.StopTimer()

 	P := runtime.GOMAXPROCS(0)
 	N := b.N / P
 	W := 1000

 	// Setup P client/server connections.
 	clients := make([]net.Conn, P)
 	servers := make([]net.Conn, P)
 	ln, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		b.Fatalf("Listen failed: %v", err)
 	}
 	defer ln.Close()
 	done := make(chan bool)
 	go func() {
 		for p := 0; p < P; p++ {
 			s, err := ln.Accept()
 			if err != nil {
 				b.Errorf("Accept failed: %v", err)
 				return
 			}
 			servers[p] = s
 		}
 		done <- true
 	}()
 	for p := 0; p < P; p++ {
 		c, err := net.Dial("tcp", ln.Addr().String())
 		if err != nil {
 			b.Fatalf("Dial failed: %v", err)
 		}
 		clients[p] = c
 	}
 	<-done

 	b.StartTimer()

 	var wg sync.WaitGroup
 	wg.Add(4 * P)
 	for p := 0; p < P; p++ {
 		// Client writer.
 		go func(c net.Conn) {
 			defer wg.Done()
 			var buf [1]byte
 			for i := 0; i < N; i++ {
 				v := byte(i)
 				for w := 0; w < W; w++ {
 					v *= v
 				}
 				buf[0] = v
 				n, err := c.Write(buf[:])
 				if err != nil {
 					b.Errorf("Write failed: %v", err)
 					return
 				}

 				bytesSent.Add(int64(n))
 			}
 		}(clients[p])

 		// Pipe between server reader and server writer.
 		pipe := make(chan byte, 128)

 		// Server reader.
 		go func(s net.Conn) {
 			defer wg.Done()
 			var buf [1]byte
 			for i := 0; i < N; i++ {
 				n, err := s.Read(buf[:])

 				if err != nil {
 					b.Errorf("Read failed: %v", err)
 					return
 				}

 				bytesRead.Add(int64(n))
 				pipe <- buf[0]
 			}
 		}(servers[p])

 		// Server writer.
 		go func(s net.Conn) {
 			defer wg.Done()
 			var buf [1]byte
 			for i := 0; i < N; i++ {
 				v := <-pipe
 				for w := 0; w < W; w++ {
 					v *= v
 				}
 				buf[0] = v
 				n, err := s.Write(buf[:])
 				if err != nil {
 					b.Errorf("Write failed: %v", err)
 					return
 				}

 				bytesSent.Add(int64(n))
 			}
 			s.Close()
 		}(servers[p])

 		// Client reader.
 		go func(c net.Conn) {
 			defer wg.Done()
 			var buf [1]byte
 			for i := 0; i < N; i++ {
 				n, err := c.Read(buf[:])

 				if err != nil {
 					b.Errorf("Read failed: %v", err)
 					return
 				}

 				bytesRead.Add(int64(n))
 			}
 			c.Close()
 		}(clients[p])
 	}
 	wg.Wait()
 }
	// 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 expvar

	import (
	"bytes"
	"encoding/json"
	"fmt"
	"net"
	"net/http/httptest"
	"reflect"
	"runtime"
	"strconv"
	"sync"
	"sync/atomic"
	"testing"
	)

	// RemoveAll removes all exported variables.
	// This is for tests only.
	func RemoveAll() {
	varKeysMu.Lock()
	defer varKeysMu.Unlock()
	for _, k := range varKeys {
	vars.Delete(k)
	}
	varKeys = nil
	}

	func TestNil(t *testing.T) {
	RemoveAll()
	val := Get("missing")
	if val != nil {
	t.Errorf("got %v, want nil", val)
	}
	}

	func TestInt(t *testing.T) {
	RemoveAll()
	reqs := NewInt("requests")
	if i := reqs.Value(); i != 0 {
	t.Errorf("reqs.Value() = %v, want 0", i)
	}
	if reqs != Get("requests").(*Int) {
	t.Errorf("Get() failed.")
	}

	reqs.Add(1)
	reqs.Add(3)
	if i := reqs.Value(); i != 4 {
	t.Errorf("reqs.Value() = %v, want 4", i)
	}

	if s := reqs.String(); s != "4" {
	t.Errorf("reqs.String() = %q, want \"4\"", s)
	}

	reqs.Set(-2)
	if i := reqs.Value(); i != -2 {
	t.Errorf("reqs.Value() = %v, want -2", i)
	}
	}

	func BenchmarkIntAdd(b *testing.B) {
	var v Int

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	v.Add(1)
	}
	})
	}

	func BenchmarkIntSet(b *testing.B) {
	var v Int

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	v.Set(1)
	}
	})
	}

	func TestFloat(t *testing.T) {
	RemoveAll()
	reqs := NewFloat("requests-float")
	if reqs.f != 0.0 {
	t.Errorf("reqs.f = %v, want 0", reqs.f)
	}
	if reqs != Get("requests-float").(*Float) {
	t.Errorf("Get() failed.")
	}

	reqs.Add(1.5)
	reqs.Add(1.25)
	if v := reqs.Value(); v != 2.75 {
	t.Errorf("reqs.Value() = %v, want 2.75", v)
	}

	if s := reqs.String(); s != "2.75" {
	t.Errorf("reqs.String() = %q, want \"4.64\"", s)
	}

	reqs.Add(-2)
	if v := reqs.Value(); v != 0.75 {
	t.Errorf("reqs.Value() = %v, want 0.75", v)
	}
	}

	func BenchmarkFloatAdd(b *testing.B) {
	var f Float

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	f.Add(1.0)
	}
	})
	}

	func BenchmarkFloatSet(b *testing.B) {
	var f Float

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	f.Set(1.0)
	}
	})
	}

	func TestString(t *testing.T) {
	RemoveAll()
	name := NewString("my-name")
	if s := name.Value(); s != "" {
	t.Errorf(`NewString("my-name").Value() = %q, want ""`, s)
	}

	name.Set("Mike")
	if s, want := name.String(), `"Mike"`; s != want {
	t.Errorf(`after name.Set("Mike"), name.String() = %q, want %q`, s, want)
	}
	if s, want := name.Value(), "Mike"; s != want {
	t.Errorf(`after name.Set("Mike"), name.Value() = %q, want %q`, s, want)
	}

	// Make sure we produce safe JSON output.
	name.Set("<")
	if s, want := name.String(), "\"\\u003c\""; s != want {
	t.Errorf(`after name.Set("<"), name.String() = %q, want %q`, s, want)
	}
	}

	func BenchmarkStringSet(b *testing.B) {
	var s String

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	s.Set("red")
	}
	})
	}

	func TestMapInit(t *testing.T) {
	RemoveAll()
	colors := NewMap("bike-shed-colors")
	colors.Add("red", 1)
	colors.Add("blue", 1)
	colors.Add("chartreuse", 1)

	n := 0
	colors.Do(func(KeyValue) { n++ })
	if n != 3 {
	t.Errorf("after three Add calls with distinct keys, Do should invoke f 3 times; got %v", n)
	}

	colors.Init()

	n = 0
	colors.Do(func(KeyValue) { n++ })
	if n != 0 {
	t.Errorf("after Init, Do should invoke f 0 times; got %v", n)
	}
	}

	func TestMapCounter(t *testing.T) {
	RemoveAll()
	colors := NewMap("bike-shed-colors")

	colors.Add("red", 1)
	colors.Add("red", 2)
	colors.Add("blue", 4)
	colors.AddFloat(`green "midori"`, 4.125)
	if x := colors.Get("red").(*Int).Value(); x != 3 {
	t.Errorf("colors.m[\"red\"] = %v, want 3", x)
	}
	if x := colors.Get("blue").(*Int).Value(); x != 4 {
	t.Errorf("colors.m[\"blue\"] = %v, want 4", x)
	}
	if x := colors.Get(`green "midori"`).(*Float).Value(); x != 4.125 {
	t.Errorf("colors.m[`green \"midori\"] = %v, want 4.125", x)
	}

	// colors.String() should be '{"red":3, "blue":4}',
	// though the order of red and blue could vary.
	s := colors.String()
	var j interface{}
	err := json.Unmarshal([]byte(s), &j)
	if err != nil {
	t.Errorf("colors.String() isn't valid JSON: %v", err)
	}
	m, ok := j.(map[string]interface{})
	if !ok {
	t.Error("colors.String() didn't produce a map.")
	}
	red := m["red"]
	x, ok := red.(float64)
	if !ok {
	t.Error("red.Kind() is not a number.")
	}
	if x != 3 {
	t.Errorf("red = %v, want 3", x)
	}
	}

	func BenchmarkMapSet(b *testing.B) {
	m := new(Map).Init()

	v := new(Int)

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	m.Set("red", v)
	}
	})
	}

	func BenchmarkMapSetDifferent(b *testing.B) {
	procKeys := make([][]string, runtime.GOMAXPROCS(0))
	for i := range procKeys {
	keys := make([]string, 4)
	for j := range keys {
	keys[j] = fmt.Sprint(i, j)
	}
	procKeys[i] = keys
	}

	m := new(Map).Init()
	v := new(Int)
	b.ResetTimer()

	var n int32
	b.RunParallel(func(pb *testing.PB) {
	i := int(atomic.AddInt32(&n, 1)-1) % len(procKeys)
	keys := procKeys[i]

	for pb.Next() {
	for _, k := range keys {
	m.Set(k, v)
	}
	}
	})
	}

	func BenchmarkMapSetString(b *testing.B) {
	m := new(Map).Init()

	v := new(String)
	v.Set("Hello, !")

	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	m.Set("red", v)
	}
	})
	}

	func BenchmarkMapAddSame(b *testing.B) {
	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	m := new(Map).Init()
	m.Add("red", 1)
	m.Add("red", 1)
	m.Add("red", 1)
	m.Add("red", 1)
	}
	})
	}

	func BenchmarkMapAddDifferent(b *testing.B) {
	procKeys := make([][]string, runtime.GOMAXPROCS(0))
	for i := range procKeys {
	keys := make([]string, 4)
	for j := range keys {
	keys[j] = fmt.Sprint(i, j)
	}
	procKeys[i] = keys
	}

	b.ResetTimer()

	var n int32
	b.RunParallel(func(pb *testing.PB) {
	i := int(atomic.AddInt32(&n, 1)-1) % len(procKeys)
	keys := procKeys[i]

	for pb.Next() {
	m := new(Map).Init()
	for _, k := range keys {
	m.Add(k, 1)
	}
	}
	})
	}

	func BenchmarkMapAddSameSteadyState(b *testing.B) {
	m := new(Map).Init()
	b.RunParallel(func(pb *testing.PB) {
	for pb.Next() {
	m.Add("red", 1)
	}
	})
	}

	func BenchmarkMapAddDifferentSteadyState(b *testing.B) {
	procKeys := make([][]string, runtime.GOMAXPROCS(0))
	for i := range procKeys {
	keys := make([]string, 4)
	for j := range keys {
	keys[j] = fmt.Sprint(i, j)
	}
	procKeys[i] = keys
	}

	m := new(Map).Init()
	b.ResetTimer()

	var n int32
	b.RunParallel(func(pb *testing.PB) {
	i := int(atomic.AddInt32(&n, 1)-1) % len(procKeys)
	keys := procKeys[i]

	for pb.Next() {
	for _, k := range keys {
	m.Add(k, 1)
	}
	}
	})
	}

	func TestFunc(t *testing.T) {
	RemoveAll()
	var x interface{} = []string{"a", "b"}
	f := Func(func() interface{} { return x })
	if s, exp := f.String(), `["a","b"]`; s != exp {
	t.Errorf(`f.String() = %q, want %q`, s, exp)
	}
	if v := f.Value(); !reflect.DeepEqual(v, x) {
	t.Errorf(`f.Value() = %q, want %q`, v, x)
	}

	x = 17
	if s, exp := f.String(), `17`; s != exp {
	t.Errorf(`f.String() = %q, want %q`, s, exp)
	}
	}

	func TestHandler(t *testing.T) {
	RemoveAll()
	m := NewMap("map1")
	m.Add("a", 1)
	m.Add("z", 2)
	m2 := NewMap("map2")
	for i := 0; i < 9; i++ {
	m2.Add(strconv.Itoa(i), int64(i))
	}
	rr := httptest.NewRecorder()
	rr.Body = new(bytes.Buffer)
	expvarHandler(rr, nil)
	want := `{
	"map1": {"a": 1, "z": 2},
	"map2": {"0": 0, "1": 1, "2": 2, "3": 3, "4": 4, "5": 5, "6": 6, "7": 7, "8": 8}
	}
	`
	if got := rr.Body.String(); got != want {
	t.Errorf("HTTP handler wrote:\n%s\nWant:\n%s", got, want)
	}
	}

	func BenchmarkRealworldExpvarUsage(b *testing.B) {
	var (
	bytesSent Int
	bytesRead Int
	)

	// The benchmark creates GOMAXPROCS client/server pairs.
	// Each pair creates 4 goroutines: client reader/writer and server reader/writer.
	// The benchmark stresses concurrent reading and writing to the same connection.
	// Such pattern is used in net/http and net/rpc.

	b.StopTimer()

	P := runtime.GOMAXPROCS(0)
	N := b.N / P
	W := 1000

	// Setup P client/server connections.
	clients := make([]net.Conn, P)
	servers := make([]net.Conn, P)
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
	b.Fatalf("Listen failed: %v", err)
	}
	defer ln.Close()
	done := make(chan bool)
	go func() {
	for p := 0; p < P; p++ {
	s, err := ln.Accept()
	if err != nil {
	b.Errorf("Accept failed: %v", err)
	return
	}
	servers[p] = s
	}
	done <- true
	}()
	for p := 0; p < P; p++ {
	c, err := net.Dial("tcp", ln.Addr().String())
	if err != nil {
	b.Fatalf("Dial failed: %v", err)
	}
	clients[p] = c
	}
	<-done

	b.StartTimer()

	var wg sync.WaitGroup
	wg.Add(4 * P)
	for p := 0; p < P; p++ {
	// Client writer.
	go func(c net.Conn) {
	defer wg.Done()
	var buf [1]byte
	for i := 0; i < N; i++ {
	v := byte(i)
	for w := 0; w < W; w++ {
	v *= v
	}
	buf[0] = v
	n, err := c.Write(buf[:])
	if err != nil {
	b.Errorf("Write failed: %v", err)
	return
	}

	bytesSent.Add(int64(n))
	}
	}(clients[p])

	// Pipe between server reader and server writer.
	pipe := make(chan byte, 128)

	// Server reader.
	go func(s net.Conn) {
	defer wg.Done()
	var buf [1]byte
	for i := 0; i < N; i++ {
	n, err := s.Read(buf[:])

	if err != nil {
	b.Errorf("Read failed: %v", err)
	return
	}

	bytesRead.Add(int64(n))
	pipe <- buf[0]
	}
	}(servers[p])

	// Server writer.
	go func(s net.Conn) {
	defer wg.Done()
	var buf [1]byte
	for i := 0; i < N; i++ {
	v := <-pipe
	for w := 0; w < W; w++ {
	v *= v
	}
	buf[0] = v
	n, err := s.Write(buf[:])
	if err != nil {
	b.Errorf("Write failed: %v", err)
	return
	}

	bytesSent.Add(int64(n))
	}
	s.Close()
	}(servers[p])

	// Client reader.
	go func(c net.Conn) {
	defer wg.Done()
	var buf [1]byte
	for i := 0; i < N; i++ {
	n, err := c.Read(buf[:])

	if err != nil {
	b.Errorf("Read failed: %v", err)
	return
	}

	bytesRead.Add(int64(n))
	}
	c.Close()
	}(clients[p])
	}
	wg.Wait()
	}