src/expvar/expvar.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 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 (
 	"bytes"
 	"encoding/json"
 	"fmt"
 	"log"
 	"net/http"
 	"os"
 	"runtime"
 	"sort"
 	"strconv"
 	"sync"
 	"sync/atomic"
 )

 // Var is an abstract type for all exported variables.
 type Var interface {
 	String() string
 }

 // Int is a 64-bit integer variable that satisfies the Var interface.
 type Int struct {
 	i int64
 }

 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 {
 	mu sync.RWMutex
 	f  float64
 }

 func (v *Float) String() string {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 	return strconv.FormatFloat(v.f, 'g', -1, 64)
 }

 // Add adds delta to v.
 func (v *Float) Add(delta float64) {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 	v.f += delta
 }

 // Set sets v to value.
 func (v *Float) Set(value float64) {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 	v.f = value
 }

 // Map is a string-to-Var map variable that satisfies the Var interface.
 type Map struct {
 	mu   sync.RWMutex
 	m    map[string]Var
 	keys []string // sorted
 }

 // KeyValue represents a single entry in a Map.
 type KeyValue struct {
 	Key   string
 	Value Var
 }

 func (v *Map) String() string {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 	var b bytes.Buffer
 	fmt.Fprintf(&b, "{")
 	first := true
 	v.doLocked(func(kv KeyValue) {
 		if !first {
 			fmt.Fprintf(&b, ", ")
 		}
 		fmt.Fprintf(&b, "%q: %v", kv.Key, kv.Value)
 		first = false
 	})
 	fmt.Fprintf(&b, "}")
 	return b.String()
 }

 func (v *Map) Init() *Map {
 	v.m = make(map[string]Var)
 	return v
 }

 // updateKeys updates the sorted list of keys in v.keys.
 // must be called with v.mu held.
 func (v *Map) updateKeys() {
 	if len(v.m) == len(v.keys) {
 		// No new key.
 		return
 	}
 	v.keys = v.keys[:0]
 	for k := range v.m {
 		v.keys = append(v.keys, k)
 	}
 	sort.Strings(v.keys)
 }

 func (v *Map) Get(key string) Var {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 	return v.m[key]
 }

 func (v *Map) Set(key string, av Var) {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 	v.m[key] = av
 	v.updateKeys()
 }

 func (v *Map) Add(key string, delta int64) {
 	v.mu.RLock()
 	av, ok := v.m[key]
 	v.mu.RUnlock()
 	if !ok {
 		// check again under the write lock
 		v.mu.Lock()
 		av, ok = v.m[key]
 		if !ok {
 			av = new(Int)
 			v.m[key] = av
 			v.updateKeys()
 		}
 		v.mu.Unlock()
 	}

 	// Add to Int; ignore otherwise.
 	if iv, ok := av.(*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) {
 	v.mu.RLock()
 	av, ok := v.m[key]
 	v.mu.RUnlock()
 	if !ok {
 		// check again under the write lock
 		v.mu.Lock()
 		av, ok = v.m[key]
 		if !ok {
 			av = new(Float)
 			v.m[key] = av
 			v.updateKeys()
 		}
 		v.mu.Unlock()
 	}

 	// Add to Float; ignore otherwise.
 	if iv, ok := av.(*Float); ok {
 		iv.Add(delta)
 	}
 }

 // 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.mu.RLock()
 	defer v.mu.RUnlock()
 	v.doLocked(f)
 }

 // doLocked calls f for each entry in the map.
 // v.mu must be held for reads.
 func (v *Map) doLocked(f func(KeyValue)) {
 	for _, k := range v.keys {
 		f(KeyValue{k, v.m[k]})
 	}
 }

 // String is a string variable, and satisfies the Var interface.
 type String struct {
 	mu sync.RWMutex
 	s  string
 }

 func (v *String) String() string {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 	return strconv.Quote(v.s)
 }

 func (v *String) Set(value string) {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 	v.s = value
 }

 // Func implements Var by calling the function
 // and formatting the returned value using JSON.
 type Func func() interface{}

 func (f Func) String() string {
 	v, _ := json.Marshal(f())
 	return string(v)
 }

 // All published variables.
 var (
 	mutex   sync.RWMutex
 	vars    = make(map[string]Var)
 	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) {
 	mutex.Lock()
 	defer mutex.Unlock()
 	if _, existing := vars[name]; existing {
 		log.Panicln("Reuse of exported var name:", name)
 	}
 	vars[name] = v
 	varKeys = append(varKeys, name)
 	sort.Strings(varKeys)
 }

 // Get retrieves a named exported variable.
 func Get(name string) Var {
 	mutex.RLock()
 	defer mutex.RUnlock()
 	return vars[name]
 }

 // 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)) {
 	mutex.RLock()
 	defer mutex.RUnlock()
 	for _, k := range varKeys {
 		f(KeyValue{k, vars[k]})
 	}
 }

 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")
 }

 func cmdline() interface{} {
 	return os.Args
 }

 func memstats() interface{} {
 	stats := new(runtime.MemStats)
 	runtime.ReadMemStats(stats)
 	return *stats
 }

 func init() {
 	http.HandleFunc("/debug/vars", expvarHandler)
 	Publish("cmdline", Func(cmdline))
 	Publish("memstats", Func(memstats))
 }
	// 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 (
	"bytes"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"runtime"
	"sort"
	"strconv"
	"sync"
	"sync/atomic"
	)

	// Var is an abstract type for all exported variables.
	type Var interface {
	String() string
	}

	// Int is a 64-bit integer variable that satisfies the Var interface.
	type Int struct {
	i int64
	}

	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 {
	mu sync.RWMutex
	f float64
	}

	func (v *Float) String() string {
	v.mu.RLock()
	defer v.mu.RUnlock()
	return strconv.FormatFloat(v.f, 'g', -1, 64)
	}

	// Add adds delta to v.
	func (v *Float) Add(delta float64) {
	v.mu.Lock()
	defer v.mu.Unlock()
	v.f += delta
	}

	// Set sets v to value.
	func (v *Float) Set(value float64) {
	v.mu.Lock()
	defer v.mu.Unlock()
	v.f = value
	}

	// Map is a string-to-Var map variable that satisfies the Var interface.
	type Map struct {
	mu sync.RWMutex
	m map[string]Var
	keys []string // sorted
	}

	// KeyValue represents a single entry in a Map.
	type KeyValue struct {
	Key string
	Value Var
	}

	func (v *Map) String() string {
	v.mu.RLock()
	defer v.mu.RUnlock()
	var b bytes.Buffer
	fmt.Fprintf(&b, "{")
	first := true
	v.doLocked(func(kv KeyValue) {
	if !first {
	fmt.Fprintf(&b, ", ")
	}
	fmt.Fprintf(&b, "%q: %v", kv.Key, kv.Value)
	first = false
	})
	fmt.Fprintf(&b, "}")
	return b.String()
	}

	func (v Map) Init() Map {
	v.m = make(map[string]Var)
	return v
	}

	// updateKeys updates the sorted list of keys in v.keys.
	// must be called with v.mu held.
	func (v *Map) updateKeys() {
	if len(v.m) == len(v.keys) {
	// No new key.
	return
	}
	v.keys = v.keys[:0]
	for k := range v.m {
	v.keys = append(v.keys, k)
	}
	sort.Strings(v.keys)
	}

	func (v *Map) Get(key string) Var {
	v.mu.RLock()
	defer v.mu.RUnlock()
	return v.m[key]
	}

	func (v *Map) Set(key string, av Var) {
	v.mu.Lock()
	defer v.mu.Unlock()
	v.m[key] = av
	v.updateKeys()
	}

	func (v *Map) Add(key string, delta int64) {
	v.mu.RLock()
	av, ok := v.m[key]
	v.mu.RUnlock()
	if !ok {
	// check again under the write lock
	v.mu.Lock()
	av, ok = v.m[key]
	if !ok {
	av = new(Int)
	v.m[key] = av
	v.updateKeys()
	}
	v.mu.Unlock()
	}

	// Add to Int; ignore otherwise.
	if iv, ok := av.(*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) {
	v.mu.RLock()
	av, ok := v.m[key]
	v.mu.RUnlock()
	if !ok {
	// check again under the write lock
	v.mu.Lock()
	av, ok = v.m[key]
	if !ok {
	av = new(Float)
	v.m[key] = av
	v.updateKeys()
	}
	v.mu.Unlock()
	}

	// Add to Float; ignore otherwise.
	if iv, ok := av.(*Float); ok {
	iv.Add(delta)
	}
	}

	// 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.mu.RLock()
	defer v.mu.RUnlock()
	v.doLocked(f)
	}

	// doLocked calls f for each entry in the map.
	// v.mu must be held for reads.
	func (v *Map) doLocked(f func(KeyValue)) {
	for _, k := range v.keys {
	f(KeyValue{k, v.m[k]})
	}
	}

	// String is a string variable, and satisfies the Var interface.
	type String struct {
	mu sync.RWMutex
	s string
	}

	func (v *String) String() string {
	v.mu.RLock()
	defer v.mu.RUnlock()
	return strconv.Quote(v.s)
	}

	func (v *String) Set(value string) {
	v.mu.Lock()
	defer v.mu.Unlock()
	v.s = value
	}

	// Func implements Var by calling the function
	// and formatting the returned value using JSON.
	type Func func() interface{}

	func (f Func) String() string {
	v, _ := json.Marshal(f())
	return string(v)
	}

	// All published variables.
	var (
	mutex sync.RWMutex
	vars = make(map[string]Var)
	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) {
	mutex.Lock()
	defer mutex.Unlock()
	if _, existing := vars[name]; existing {
	log.Panicln("Reuse of exported var name:", name)
	}
	vars[name] = v
	varKeys = append(varKeys, name)
	sort.Strings(varKeys)
	}

	// Get retrieves a named exported variable.
	func Get(name string) Var {
	mutex.RLock()
	defer mutex.RUnlock()
	return vars[name]
	}

	// 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)) {
	mutex.RLock()
	defer mutex.RUnlock()
	for _, k := range varKeys {
	f(KeyValue{k, vars[k]})
	}
	}

	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")
	}

	func cmdline() interface{} {
	return os.Args
	}

	func memstats() interface{} {
	stats := new(runtime.MemStats)
	runtime.ReadMemStats(stats)
	return *stats
	}

	func init() {
	http.HandleFunc("/debug/vars", expvarHandler)
	Publish("cmdline", Func(cmdline))
	Publish("memstats", Func(memstats))
	}