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// 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.
// The expvar package 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, simply link this package into your program:
// import _ "expvar"
//
package expvar
import (
"bytes"
"fmt"
"http"
"json"
"log"
"os"
"runtime"
"strconv"
"sync"
)
// Var is an abstract type for all exported variables.
type Var interface {
String() string
}
// Int is a 64-bit integer variable, and satisfies the Var interface.
type Int struct {
i int64
mu sync.Mutex
}
func (v *Int) String() string { return strconv.Itoa64(v.i) }
func (v *Int) Add(delta int64) {
v.mu.Lock()
defer v.mu.Unlock()
v.i += delta
}
func (v *Int) Set(value int64) {
v.mu.Lock()
defer v.mu.Unlock()
v.i = value
}
// Map is a string-to-Var map variable, and satisfies the Var interface.
type Map struct {
m map[string]Var
mu sync.Mutex
}
// KeyValue represents a single entry in a Map.
type KeyValue struct {
Key string
Value Var
}
func (v *Map) String() string {
v.mu.Lock()
defer v.mu.Unlock()
b := new(bytes.Buffer)
fmt.Fprintf(b, "{")
first := true
for key, val := range v.m {
if !first {
fmt.Fprintf(b, ", ")
}
fmt.Fprintf(b, "\"%s\": %v", key, val.String())
first = false
}
fmt.Fprintf(b, "}")
return b.String()
}
func (v *Map) Init() *Map {
v.m = make(map[string]Var)
return v
}
func (v *Map) Get(key string) Var {
v.mu.Lock()
defer v.mu.Unlock()
return v.m[key]
}
func (v *Map) Set(key string, av Var) {
v.mu.Lock()
defer v.mu.Unlock()
v.m[key] = av
}
func (v *Map) Add(key string, delta int64) {
v.mu.Lock()
defer v.mu.Unlock()
av, ok := v.m[key]
if !ok {
av = new(Int)
v.m[key] = av
}
// Add to Int; ignore otherwise.
if iv, ok := av.(*Int); ok {
iv.Add(delta)
}
}
// TODO(rsc): Make sure map access in separate thread is safe.
func (v *Map) iterate(c chan<- KeyValue) {
for k, v := range v.m {
c <- KeyValue{k, v}
}
close(c)
}
func (v *Map) Iter() <-chan KeyValue {
c := make(chan KeyValue)
go v.iterate(c)
return c
}
// String is a string variable, and satisfies the Var interface.
type String struct {
s string
}
func (v *String) String() string { return strconv.Quote(v.s) }
func (v *String) Set(value string) { v.s = value }
// IntFunc wraps a func() int64 to create a value that satisfies the Var interface.
// The function will be called each time the Var is evaluated.
type IntFunc func() int64
func (v IntFunc) String() string { return strconv.Itoa64(v()) }
// StringFunc wraps a func() string to create value that satisfies the Var interface.
// The function will be called each time the Var is evaluated.
type StringFunc func() string
func (f StringFunc) String() string { return strconv.Quote(f()) }
// All published variables.
var vars map[string]Var = make(map[string]Var)
var mutex sync.Mutex
// Publish declares an 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
}
// Get retrieves a named exported variable.
func Get(name string) Var {
return vars[name]
}
// RemoveAll removes all exported variables.
// This is for tests; don't call this on a real server.
func RemoveAll() {
mutex.Lock()
defer mutex.Unlock()
vars = make(map[string]Var)
}
// Convenience functions for creating new exported variables.
func NewInt(name string) *Int {
v := new(Int)
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
}
// TODO(rsc): Make sure map access in separate thread is safe.
func iterate(c chan<- KeyValue) {
for k, v := range vars {
c <- KeyValue{k, v}
}
close(c)
}
func Iter() <-chan KeyValue {
c := make(chan KeyValue)
go iterate(c)
return c
}
func expvarHandler(w http.ResponseWriter, r *http.Request) {
w.SetHeader("content-type", "application/json; charset=utf-8")
fmt.Fprintf(w, "{\n")
first := true
for name, value := range vars {
if !first {
fmt.Fprintf(w, ",\n")
}
first = false
fmt.Fprintf(w, "%q: %s", name, value)
}
fmt.Fprintf(w, "\n}\n")
}
func memstats() string {
b, _ := json.MarshalIndent(&runtime.MemStats, "", "\t")
return string(b)
}
func cmdline() string {
b, _ := json.Marshal(os.Args)
return string(b)
}
func init() {
http.Handle("/debug/vars", http.HandlerFunc(expvarHandler))
Publish("cmdline", StringFunc(cmdline))
Publish("memstats", StringFunc(memstats))
}
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