Adding upstream version 1.21.8.upstream/1.21.8

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 997 insertions, 0 deletions

diff --git a/src/expvar/expvar.go b/src/expvar/expvar.go
new file mode 100644
index 0000000..300d8c2
--- /dev/null
+++ b/src/expvar/expvar.go
@@ -0,0 +1,373 @@
+// 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 provides a standardized interface to public variables, such
+// as operation counters in servers. It exposes these variables via HTTP at
+// /debug/vars in JSON format.
+//
+// Operations to set or modify these public variables are atomic.
+//
+// In addition to adding the HTTP handler, this package registers the
+// following variables:
+//
+//	cmdline   os.Args
+//	memstats  runtime.Memstats
+//
+// The package is sometimes only imported for the side effect of
+// registering its HTTP handler and the above variables. To use it
+// this way, link this package into your program:
+//
+//	import _ "expvar"
+package expvar
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"math"
+	"net/http"
+	"os"
+	"runtime"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+)
+
+// Var is an abstract type for all exported variables.
+type Var interface {
+	// String returns a valid JSON value for the variable.
+	// Types with String methods that do not return valid JSON
+	// (such as time.Time) must not be used as a Var.
+	String() string
+}
+
+// Int is a 64-bit integer variable that satisfies the Var interface.
+type Int struct {
+	i int64
+}
+
+func (v *Int) Value() int64 {
+	return atomic.LoadInt64(&v.i)
+}
+
+func (v *Int) String() string {
+	return strconv.FormatInt(atomic.LoadInt64(&v.i), 10)
+}
+
+func (v *Int) Add(delta int64) {
+	atomic.AddInt64(&v.i, delta)
+}
+
+func (v *Int) Set(value int64) {
+	atomic.StoreInt64(&v.i, value)
+}
+
+// Float is a 64-bit float variable that satisfies the Var interface.
+type Float struct {
+	f atomic.Uint64
+}
+
+func (v *Float) Value() float64 {
+	return math.Float64frombits(v.f.Load())
+}
+
+func (v *Float) String() string {
+	return strconv.FormatFloat(
+		math.Float64frombits(v.f.Load()), 'g', -1, 64)
+}
+
+// Add adds delta to v.
+func (v *Float) Add(delta float64) {
+	for {
+		cur := v.f.Load()
+		curVal := math.Float64frombits(cur)
+		nxtVal := curVal + delta
+		nxt := math.Float64bits(nxtVal)
+		if v.f.CompareAndSwap(cur, nxt) {
+			return
+		}
+	}
+}
+
+// Set sets v to value.
+func (v *Float) Set(value float64) {
+	v.f.Store(math.Float64bits(value))
+}
+
+// Map is a string-to-Var map variable that satisfies the Var interface.
+type Map struct {
+	m      sync.Map // map[string]Var
+	keysMu sync.RWMutex
+	keys   []string // sorted
+}
+
+// KeyValue represents a single entry in a Map.
+type KeyValue struct {
+	Key   string
+	Value Var
+}
+
+func (v *Map) String() string {
+	var b strings.Builder
+	fmt.Fprintf(&b, "{")
+	first := true
+	v.Do(func(kv KeyValue) {
+		if !first {
+			fmt.Fprintf(&b, ", ")
+		}
+		fmt.Fprintf(&b, "%q: ", kv.Key)
+		if kv.Value != nil {
+			fmt.Fprintf(&b, "%v", kv.Value)
+		} else {
+			fmt.Fprint(&b, "null")
+		}
+		first = false
+	})
+	fmt.Fprintf(&b, "}")
+	return b.String()
+}
+
+// Init removes all keys from the map.
+func (v *Map) Init() *Map {
+	v.keysMu.Lock()
+	defer v.keysMu.Unlock()
+	v.keys = v.keys[:0]
+	v.m.Range(func(k, _ any) bool {
+		v.m.Delete(k)
+		return true
+	})
+	return v
+}
+
+// addKey updates the sorted list of keys in v.keys.
+func (v *Map) addKey(key string) {
+	v.keysMu.Lock()
+	defer v.keysMu.Unlock()
+	// Using insertion sort to place key into the already-sorted v.keys.
+	if i := sort.SearchStrings(v.keys, key); i >= len(v.keys) {
+		v.keys = append(v.keys, key)
+	} else if v.keys[i] != key {
+		v.keys = append(v.keys, "")
+		copy(v.keys[i+1:], v.keys[i:])
+		v.keys[i] = key
+	}
+}
+
+func (v *Map) Get(key string) Var {
+	i, _ := v.m.Load(key)
+	av, _ := i.(Var)
+	return av
+}
+
+func (v *Map) Set(key string, av Var) {
+	// Before we store the value, check to see whether the key is new. Try a Load
+	// before LoadOrStore: LoadOrStore causes the key interface to escape even on
+	// the Load path.
+	if _, ok := v.m.Load(key); !ok {
+		if _, dup := v.m.LoadOrStore(key, av); !dup {
+			v.addKey(key)
+			return
+		}
+	}
+
+	v.m.Store(key, av)
+}
+
+// Add adds delta to the *Int value stored under the given map key.
+func (v *Map) Add(key string, delta int64) {
+	i, ok := v.m.Load(key)
+	if !ok {
+		var dup bool
+		i, dup = v.m.LoadOrStore(key, new(Int))
+		if !dup {
+			v.addKey(key)
+		}
+	}
+
+	// Add to Int; ignore otherwise.
+	if iv, ok := i.(*Int); ok {
+		iv.Add(delta)
+	}
+}
+
+// AddFloat adds delta to the *Float value stored under the given map key.
+func (v *Map) AddFloat(key string, delta float64) {
+	i, ok := v.m.Load(key)
+	if !ok {
+		var dup bool
+		i, dup = v.m.LoadOrStore(key, new(Float))
+		if !dup {
+			v.addKey(key)
+		}
+	}
+
+	// Add to Float; ignore otherwise.
+	if iv, ok := i.(*Float); ok {
+		iv.Add(delta)
+	}
+}
+
+// Delete deletes the given key from the map.
+func (v *Map) Delete(key string) {
+	v.keysMu.Lock()
+	defer v.keysMu.Unlock()
+	i := sort.SearchStrings(v.keys, key)
+	if i < len(v.keys) && key == v.keys[i] {
+		v.keys = append(v.keys[:i], v.keys[i+1:]...)
+		v.m.Delete(key)
+	}
+}
+
+// Do calls f for each entry in the map.
+// The map is locked during the iteration,
+// but existing entries may be concurrently updated.
+func (v *Map) Do(f func(KeyValue)) {
+	v.keysMu.RLock()
+	defer v.keysMu.RUnlock()
+	for _, k := range v.keys {
+		i, _ := v.m.Load(k)
+		val, _ := i.(Var)
+		f(KeyValue{k, val})
+	}
+}
+
+// String is a string variable, and satisfies the Var interface.
+type String struct {
+	s atomic.Value // string
+}
+
+func (v *String) Value() string {
+	p, _ := v.s.Load().(string)
+	return p
+}
+
+// String implements the Var interface. To get the unquoted string
+// use Value.
+func (v *String) String() string {
+	s := v.Value()
+	b, _ := json.Marshal(s)
+	return string(b)
+}
+
+func (v *String) Set(value string) {
+	v.s.Store(value)
+}
+
+// Func implements Var by calling the function
+// and formatting the returned value using JSON.
+type Func func() any
+
+func (f Func) Value() any {
+	return f()
+}
+
+func (f Func) String() string {
+	v, _ := json.Marshal(f())
+	return string(v)
+}
+
+// All published variables.
+var (
+	vars      sync.Map // map[string]Var
+	varKeysMu sync.RWMutex
+	varKeys   []string // sorted
+)
+
+// Publish declares a named exported variable. This should be called from a
+// package's init function when it creates its Vars. If the name is already
+// registered then this will log.Panic.
+func Publish(name string, v Var) {
+	if _, dup := vars.LoadOrStore(name, v); dup {
+		log.Panicln("Reuse of exported var name:", name)
+	}
+	varKeysMu.Lock()
+	defer varKeysMu.Unlock()
+	varKeys = append(varKeys, name)
+	sort.Strings(varKeys)
+}
+
+// Get retrieves a named exported variable. It returns nil if the name has
+// not been registered.
+func Get(name string) Var {
+	i, _ := vars.Load(name)
+	v, _ := i.(Var)
+	return v
+}
+
+// Convenience functions for creating new exported variables.
+
+func NewInt(name string) *Int {
+	v := new(Int)
+	Publish(name, v)
+	return v
+}
+
+func NewFloat(name string) *Float {
+	v := new(Float)
+	Publish(name, v)
+	return v
+}
+
+func NewMap(name string) *Map {
+	v := new(Map).Init()
+	Publish(name, v)
+	return v
+}
+
+func NewString(name string) *String {
+	v := new(String)
+	Publish(name, v)
+	return v
+}
+
+// Do calls f for each exported variable.
+// The global variable map is locked during the iteration,
+// but existing entries may be concurrently updated.
+func Do(f func(KeyValue)) {
+	varKeysMu.RLock()
+	defer varKeysMu.RUnlock()
+	for _, k := range varKeys {
+		val, _ := vars.Load(k)
+		f(KeyValue{k, val.(Var)})
+	}
+}
+
+func expvarHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	fmt.Fprintf(w, "{\n")
+	first := true
+	Do(func(kv KeyValue) {
+		if !first {
+			fmt.Fprintf(w, ",\n")
+		}
+		first = false
+		fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
+	})
+	fmt.Fprintf(w, "\n}\n")
+}
+
+// Handler returns the expvar HTTP Handler.
+//
+// This is only needed to install the handler in a non-standard location.
+func Handler() http.Handler {
+	return http.HandlerFunc(expvarHandler)
+}
+
+func cmdline() any {
+	return os.Args
+}
+
+func memstats() any {
+	stats := new(runtime.MemStats)
+	runtime.ReadMemStats(stats)
+	return *stats
+}
+
+func init() {
+	http.HandleFunc("/debug/vars", expvarHandler)
+	Publish("cmdline", Func(cmdline))
+	Publish("memstats", Func(memstats))
+}
diff --git a/src/expvar/expvar_test.go b/src/expvar/expvar_test.go
new file mode 100644
index 0000000..ee98b5e
--- /dev/null
+++ b/src/expvar/expvar_test.go
@@ -0,0 +1,624 @@
+// 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"
+	"crypto/sha1"
+	"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.Load() != 0.0 {
+		t.Errorf("reqs.f = %v, want 0", reqs.f.Load())
+	}
+	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 TestMapDelete(t *testing.T) {
+	RemoveAll()
+	colors := NewMap("bike-shed-colors")
+
+	colors.Add("red", 1)
+	colors.Add("red", 2)
+	colors.Add("blue", 4)
+
+	n := 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 2 {
+		t.Errorf("after two Add calls with distinct keys, Do should invoke f 2 times; got %v", n)
+	}
+
+	colors.Delete("red")
+	n = 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 1 {
+		t.Errorf("removed red, Do should invoke f 1 times; got %v", n)
+	}
+
+	colors.Delete("notfound")
+	n = 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 1 {
+		t.Errorf("attempted to remove notfound, Do should invoke f 1 times; got %v", n)
+	}
+
+	colors.Delete("blue")
+	colors.Delete("blue")
+	n = 0
+	colors.Do(func(KeyValue) { n++ })
+	if n != 0 {
+		t.Errorf("all keys removed, 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 any
+	err := json.Unmarshal([]byte(s), &j)
+	if err != nil {
+		t.Errorf("colors.String() isn't valid JSON: %v", err)
+	}
+	m, ok := j.(map[string]any)
+	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 TestMapNil(t *testing.T) {
+	RemoveAll()
+	const key = "key"
+	m := NewMap("issue527719")
+	m.Set(key, nil)
+	s := m.String()
+	var j any
+	if err := json.Unmarshal([]byte(s), &j); err != nil {
+		t.Fatalf("m.String() == %q isn't valid JSON: %v", s, err)
+	}
+	m2, ok := j.(map[string]any)
+	if !ok {
+		t.Fatalf("m.String() produced %T, wanted a map", j)
+	}
+	v, ok := m2[key]
+	if !ok {
+		t.Fatalf("missing %q in %v", key, m2)
+	}
+	if v != nil {
+		t.Fatalf("m[%q] = %v, want nil", key, v)
+	}
+}
+
+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)
+			}
+		}
+	})
+}
+
+// BenchmarkMapSetDifferentRandom simulates such a case where the concerned
+// keys of Map.Set are generated dynamically and as a result insertion is
+// out of order and the number of the keys may be large.
+func BenchmarkMapSetDifferentRandom(b *testing.B) {
+	keys := make([]string, 100)
+	for i := range keys {
+		keys[i] = fmt.Sprintf("%x", sha1.Sum([]byte(fmt.Sprint(i))))
+	}
+
+	v := new(Int)
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		m := new(Map).Init()
+		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)
+			}
+		}
+	})
+}
+
+// BenchmarkMapAddDifferentRandom simulates such a case where that the concerned
+// keys of Map.Add are generated dynamically and as a result insertion is out of
+// order and the number of the keys may be large.
+func BenchmarkMapAddDifferentRandom(b *testing.B) {
+	keys := make([]string, 100)
+	for i := range keys {
+		keys[i] = fmt.Sprintf("%x", sha1.Sum([]byte(fmt.Sprint(i))))
+	}
+
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		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 any = []string{"a", "b"}
+	f := Func(func() any { 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, 1)
+	go func() {
+		for p := 0; p < P; p++ {
+			s, err := ln.Accept()
+			if err != nil {
+				b.Errorf("Accept failed: %v", err)
+				done <- false
+				return
+			}
+			servers[p] = s
+		}
+		done <- true
+	}()
+	for p := 0; p < P; p++ {
+		c, err := net.Dial("tcp", ln.Addr().String())
+		if err != nil {
+			<-done
+			b.Fatalf("Dial failed: %v", err)
+		}
+		clients[p] = c
+	}
+	if !<-done {
+		b.FailNow()
+	}
+
+	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()
+}