mirror of https://go.googlesource.com/go
418 lines
9.1 KiB
Go
418 lines
9.1 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. As of Go 1.22, the /debug/vars request must
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// use GET.
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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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//
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// import _ "expvar"
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package expvar
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import (
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"encoding/json"
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"internal/godebug"
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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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"slices"
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"strconv"
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"sync"
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"sync/atomic"
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"unicode/utf8"
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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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type jsonVar interface {
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// appendJSON appends the JSON representation of the receiver to b.
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appendJSON(b []byte) []byte
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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 atomic.Int64
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}
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func (v *Int) Value() int64 {
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return v.i.Load()
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}
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func (v *Int) String() string {
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return string(v.appendJSON(nil))
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}
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func (v *Int) appendJSON(b []byte) []byte {
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return strconv.AppendInt(b, v.i.Load(), 10)
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}
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func (v *Int) Add(delta int64) {
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v.i.Add(delta)
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}
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func (v *Int) Set(value int64) {
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v.i.Store(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 atomic.Uint64
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}
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func (v *Float) Value() float64 {
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return math.Float64frombits(v.f.Load())
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}
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func (v *Float) String() string {
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return string(v.appendJSON(nil))
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}
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func (v *Float) appendJSON(b []byte) []byte {
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return strconv.AppendFloat(b, math.Float64frombits(v.f.Load()), '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 := v.f.Load()
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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 v.f.CompareAndSwap(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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v.f.Store(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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m sync.Map // map[string]Var
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keysMu sync.RWMutex
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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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return string(v.appendJSON(nil))
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}
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func (v *Map) appendJSON(b []byte) []byte {
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return v.appendJSONMayExpand(b, false)
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}
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func (v *Map) appendJSONMayExpand(b []byte, expand bool) []byte {
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afterCommaDelim := byte(' ')
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mayAppendNewline := func(b []byte) []byte { return b }
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if expand {
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afterCommaDelim = '\n'
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mayAppendNewline = func(b []byte) []byte { return append(b, '\n') }
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}
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b = append(b, '{')
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b = mayAppendNewline(b)
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first := true
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v.Do(func(kv KeyValue) {
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if !first {
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b = append(b, ',', afterCommaDelim)
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}
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first = false
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b = appendJSONQuote(b, kv.Key)
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b = append(b, ':', ' ')
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switch v := kv.Value.(type) {
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case nil:
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b = append(b, "null"...)
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case jsonVar:
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b = v.appendJSON(b)
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default:
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b = append(b, v.String()...)
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}
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})
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b = mayAppendNewline(b)
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b = append(b, '}')
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b = mayAppendNewline(b)
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return b
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}
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// Init removes all keys from the map.
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func (v *Map) Init() *Map {
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v.keysMu.Lock()
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defer v.keysMu.Unlock()
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v.keys = v.keys[:0]
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v.m.Clear()
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return v
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}
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// addKey updates the sorted list of keys in v.keys.
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func (v *Map) addKey(key string) {
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v.keysMu.Lock()
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defer v.keysMu.Unlock()
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// Using insertion sort to place key into the already-sorted v.keys.
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i, found := slices.BinarySearch(v.keys, key)
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if found {
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return
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}
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v.keys = slices.Insert(v.keys, i, key)
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}
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func (v *Map) Get(key string) Var {
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i, _ := v.m.Load(key)
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av, _ := i.(Var)
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return av
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}
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func (v *Map) Set(key string, av Var) {
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// Before we store the value, check to see whether the key is new. Try a Load
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// before LoadOrStore: LoadOrStore causes the key interface to escape even on
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// the Load path.
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if _, ok := v.m.Load(key); !ok {
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if _, dup := v.m.LoadOrStore(key, av); !dup {
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v.addKey(key)
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return
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}
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}
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v.m.Store(key, av)
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}
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// Add adds delta to the *[Int] value stored under the given map key.
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func (v *Map) Add(key string, delta int64) {
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i, ok := v.m.Load(key)
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if !ok {
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var dup bool
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i, dup = v.m.LoadOrStore(key, new(Int))
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if !dup {
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v.addKey(key)
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}
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}
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// Add to Int; ignore otherwise.
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if iv, ok := i.(*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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i, ok := v.m.Load(key)
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if !ok {
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var dup bool
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i, dup = v.m.LoadOrStore(key, new(Float))
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if !dup {
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v.addKey(key)
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}
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}
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// Add to Float; ignore otherwise.
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if iv, ok := i.(*Float); ok {
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iv.Add(delta)
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}
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}
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// Delete deletes the given key from the map.
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func (v *Map) Delete(key string) {
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v.keysMu.Lock()
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defer v.keysMu.Unlock()
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i, found := slices.BinarySearch(v.keys, key)
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if found {
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v.keys = slices.Delete(v.keys, i, i+1)
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v.m.Delete(key)
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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.keysMu.RLock()
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defer v.keysMu.RUnlock()
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for _, k := range v.keys {
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i, _ := v.m.Load(k)
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val, _ := i.(Var)
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f(KeyValue{k, val})
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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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s atomic.Value // string
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}
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func (v *String) Value() string {
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p, _ := v.s.Load().(string)
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return p
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}
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// String implements the [Var] interface. To get the unquoted string
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// use [String.Value].
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func (v *String) String() string {
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return string(v.appendJSON(nil))
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}
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func (v *String) appendJSON(b []byte) []byte {
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return appendJSONQuote(b, v.Value())
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}
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func (v *String) Set(value string) {
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v.s.Store(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() any
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func (f Func) Value() any {
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return f()
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}
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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 vars Map
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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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if _, dup := vars.m.LoadOrStore(name, v); dup {
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log.Panicln("Reuse of exported var name:", name)
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}
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vars.keysMu.Lock()
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defer vars.keysMu.Unlock()
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vars.keys = append(vars.keys, name)
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slices.Sort(vars.keys)
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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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return vars.Get(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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vars.Do(f)
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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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w.Write(vars.appendJSONMayExpand(nil, true))
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}
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// Handler returns the expvar HTTP Handler.
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//
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// This is only needed to install the handler in a non-standard location.
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func Handler() http.Handler {
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return http.HandlerFunc(expvarHandler)
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}
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func cmdline() any {
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return os.Args
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}
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func memstats() any {
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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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if godebug.New("httpmuxgo121").Value() == "1" {
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http.HandleFunc("/debug/vars", expvarHandler)
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} else {
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http.HandleFunc("GET /debug/vars", expvarHandler)
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}
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Publish("cmdline", Func(cmdline))
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Publish("memstats", Func(memstats))
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}
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// TODO: Use json.appendString instead.
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func appendJSONQuote(b []byte, s string) []byte {
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const hex = "0123456789abcdef"
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b = append(b, '"')
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for _, r := range s {
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switch {
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case r < ' ' || r == '\\' || r == '"' || r == '<' || r == '>' || r == '&' || r == '\u2028' || r == '\u2029':
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switch r {
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case '\\', '"':
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b = append(b, '\\', byte(r))
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case '\n':
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b = append(b, '\\', 'n')
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case '\r':
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b = append(b, '\\', 'r')
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case '\t':
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b = append(b, '\\', 't')
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default:
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b = append(b, '\\', 'u', hex[(r>>12)&0xf], hex[(r>>8)&0xf], hex[(r>>4)&0xf], hex[(r>>0)&0xf])
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}
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case r < utf8.RuneSelf:
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b = append(b, byte(r))
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default:
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b = utf8.AppendRune(b, r)
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}
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}
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b = append(b, '"')
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return b
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}
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