340 lines
6.8 KiB
Go
340 lines
6.8 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package expvar provides a standardized interface to public variables, such
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// as operation counters in servers. It exposes these variables via HTTP at
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// /debug/vars in JSON format.
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//
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// Operations to set or modify these public variables are atomic.
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//
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// In addition to adding the HTTP handler, this package registers the
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// following variables:
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//
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// cmdline os.Args
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// memstats runtime.Memstats
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//
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// The package is sometimes only imported for the side effect of
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// registering its HTTP handler and the above variables. To use it
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// this way, link this package into your program:
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// import _ "expvar"
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//
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package expvar
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import (
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"bytes"
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"encoding/json"
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"fmt"
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"log"
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"math"
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"net/http"
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"os"
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"runtime"
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"sort"
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"strconv"
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"sync"
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"sync/atomic"
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)
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// Var is an abstract type for all exported variables.
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type Var interface {
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// String returns a valid JSON value for the variable.
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// Types with String methods that do not return valid JSON
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// (such as time.Time) must not be used as a Var.
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String() string
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}
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// Int is a 64-bit integer variable that satisfies the Var interface.
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type Int struct {
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i int64
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}
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func (v *Int) String() string {
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return strconv.FormatInt(atomic.LoadInt64(&v.i), 10)
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}
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func (v *Int) Add(delta int64) {
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atomic.AddInt64(&v.i, delta)
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}
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func (v *Int) Set(value int64) {
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atomic.StoreInt64(&v.i, value)
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}
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// Float is a 64-bit float variable that satisfies the Var interface.
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type Float struct {
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f uint64
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}
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func (v *Float) String() string {
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return strconv.FormatFloat(
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math.Float64frombits(atomic.LoadUint64(&v.f)), 'g', -1, 64)
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}
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// Add adds delta to v.
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func (v *Float) Add(delta float64) {
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for {
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cur := atomic.LoadUint64(&v.f)
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curVal := math.Float64frombits(cur)
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nxtVal := curVal + delta
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nxt := math.Float64bits(nxtVal)
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if atomic.CompareAndSwapUint64(&v.f, cur, nxt) {
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return
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}
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}
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}
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// Set sets v to value.
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func (v *Float) Set(value float64) {
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atomic.StoreUint64(&v.f, math.Float64bits(value))
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}
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// Map is a string-to-Var map variable that satisfies the Var interface.
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type Map struct {
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mu sync.RWMutex
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m map[string]Var
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keys []string // sorted
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}
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// KeyValue represents a single entry in a Map.
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type KeyValue struct {
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Key string
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Value Var
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}
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func (v *Map) String() string {
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v.mu.RLock()
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defer v.mu.RUnlock()
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var b bytes.Buffer
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fmt.Fprintf(&b, "{")
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first := true
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v.doLocked(func(kv KeyValue) {
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if !first {
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fmt.Fprintf(&b, ", ")
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}
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fmt.Fprintf(&b, "%q: %v", kv.Key, kv.Value)
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first = false
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})
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fmt.Fprintf(&b, "}")
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return b.String()
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}
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func (v *Map) Init() *Map {
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v.m = make(map[string]Var)
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return v
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}
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// updateKeys updates the sorted list of keys in v.keys.
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// must be called with v.mu held.
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func (v *Map) updateKeys() {
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if len(v.m) == len(v.keys) {
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// No new key.
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return
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}
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v.keys = v.keys[:0]
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for k := range v.m {
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v.keys = append(v.keys, k)
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}
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sort.Strings(v.keys)
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}
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func (v *Map) Get(key string) Var {
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v.mu.RLock()
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defer v.mu.RUnlock()
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return v.m[key]
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}
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func (v *Map) Set(key string, av Var) {
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v.mu.Lock()
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defer v.mu.Unlock()
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v.m[key] = av
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v.updateKeys()
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}
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func (v *Map) Add(key string, delta int64) {
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v.mu.RLock()
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av, ok := v.m[key]
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v.mu.RUnlock()
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if !ok {
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// check again under the write lock
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v.mu.Lock()
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av, ok = v.m[key]
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if !ok {
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av = new(Int)
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v.m[key] = av
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v.updateKeys()
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}
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v.mu.Unlock()
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}
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// Add to Int; ignore otherwise.
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if iv, ok := av.(*Int); ok {
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iv.Add(delta)
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}
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}
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// AddFloat adds delta to the *Float value stored under the given map key.
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func (v *Map) AddFloat(key string, delta float64) {
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v.mu.RLock()
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av, ok := v.m[key]
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v.mu.RUnlock()
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if !ok {
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// check again under the write lock
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v.mu.Lock()
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av, ok = v.m[key]
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if !ok {
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av = new(Float)
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v.m[key] = av
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v.updateKeys()
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}
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v.mu.Unlock()
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}
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// Add to Float; ignore otherwise.
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if iv, ok := av.(*Float); ok {
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iv.Add(delta)
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}
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}
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// Do calls f for each entry in the map.
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// The map is locked during the iteration,
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// but existing entries may be concurrently updated.
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func (v *Map) Do(f func(KeyValue)) {
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v.mu.RLock()
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defer v.mu.RUnlock()
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v.doLocked(f)
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}
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// doLocked calls f for each entry in the map.
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// v.mu must be held for reads.
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func (v *Map) doLocked(f func(KeyValue)) {
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for _, k := range v.keys {
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f(KeyValue{k, v.m[k]})
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}
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}
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// String is a string variable, and satisfies the Var interface.
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type String struct {
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mu sync.RWMutex
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s string
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}
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func (v *String) String() string {
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v.mu.RLock()
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s := v.s
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v.mu.RUnlock()
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b, _ := json.Marshal(s)
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return string(b)
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}
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func (v *String) Set(value string) {
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v.mu.Lock()
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defer v.mu.Unlock()
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v.s = value
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}
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// Func implements Var by calling the function
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// and formatting the returned value using JSON.
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type Func func() interface{}
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func (f Func) String() string {
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v, _ := json.Marshal(f())
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return string(v)
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}
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// All published variables.
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var (
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mutex sync.RWMutex
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vars = make(map[string]Var)
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varKeys []string // sorted
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)
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// Publish declares a named exported variable. This should be called from a
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// package's init function when it creates its Vars. If the name is already
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// registered then this will log.Panic.
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func Publish(name string, v Var) {
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mutex.Lock()
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defer mutex.Unlock()
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if _, existing := vars[name]; existing {
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log.Panicln("Reuse of exported var name:", name)
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}
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vars[name] = v
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varKeys = append(varKeys, name)
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sort.Strings(varKeys)
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}
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// Get retrieves a named exported variable. It returns nil if the name has
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// not been registered.
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func Get(name string) Var {
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mutex.RLock()
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defer mutex.RUnlock()
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return vars[name]
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}
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// Convenience functions for creating new exported variables.
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func NewInt(name string) *Int {
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v := new(Int)
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Publish(name, v)
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return v
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}
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func NewFloat(name string) *Float {
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v := new(Float)
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Publish(name, v)
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return v
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}
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func NewMap(name string) *Map {
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v := new(Map).Init()
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Publish(name, v)
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return v
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}
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func NewString(name string) *String {
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v := new(String)
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Publish(name, v)
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return v
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}
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// Do calls f for each exported variable.
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// The global variable map is locked during the iteration,
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// but existing entries may be concurrently updated.
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func Do(f func(KeyValue)) {
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mutex.RLock()
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defer mutex.RUnlock()
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for _, k := range varKeys {
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f(KeyValue{k, vars[k]})
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}
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}
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func expvarHandler(w http.ResponseWriter, r *http.Request) {
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w.Header().Set("Content-Type", "application/json; charset=utf-8")
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fmt.Fprintf(w, "{\n")
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first := true
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Do(func(kv KeyValue) {
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if !first {
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fmt.Fprintf(w, ",\n")
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}
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first = false
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fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
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})
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fmt.Fprintf(w, "\n}\n")
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}
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func cmdline() interface{} {
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return os.Args
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}
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func memstats() interface{} {
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stats := new(runtime.MemStats)
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runtime.ReadMemStats(stats)
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return *stats
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}
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func init() {
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http.HandleFunc("/debug/vars", expvarHandler)
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Publish("cmdline", Func(cmdline))
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Publish("memstats", Func(memstats))
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}
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