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Source file src/expvar/expvar.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// Package expvar provides a standardized interface to public variables, such
     6	// as operation counters in servers. It exposes these variables via HTTP at
     7	// /debug/vars in JSON format.
     8	//
     9	// Operations to set or modify these public variables are atomic.
    10	//
    11	// In addition to adding the HTTP handler, this package registers the
    12	// following variables:
    13	//
    14	//	cmdline   os.Args
    15	//	memstats  runtime.Memstats
    16	//
    17	// The package is sometimes only imported for the side effect of
    18	// registering its HTTP handler and the above variables.  To use it
    19	// this way, link this package into your program:
    20	//	import _ "expvar"
    21	//
    22	package expvar
    23	
    24	import (
    25		"bytes"
    26		"encoding/json"
    27		"fmt"
    28		"log"
    29		"math"
    30		"net/http"
    31		"os"
    32		"runtime"
    33		"sort"
    34		"strconv"
    35		"sync"
    36		"sync/atomic"
    37	)
    38	
    39	// Var is an abstract type for all exported variables.
    40	type Var interface {
    41		String() string
    42	}
    43	
    44	// Int is a 64-bit integer variable that satisfies the Var interface.
    45	type Int struct {
    46		i int64
    47	}
    48	
    49	func (v *Int) String() string {
    50		return strconv.FormatInt(atomic.LoadInt64(&v.i), 10)
    51	}
    52	
    53	func (v *Int) Add(delta int64) {
    54		atomic.AddInt64(&v.i, delta)
    55	}
    56	
    57	func (v *Int) Set(value int64) {
    58		atomic.StoreInt64(&v.i, value)
    59	}
    60	
    61	// Float is a 64-bit float variable that satisfies the Var interface.
    62	type Float struct {
    63		f uint64
    64	}
    65	
    66	func (v *Float) String() string {
    67		return strconv.FormatFloat(
    68			math.Float64frombits(atomic.LoadUint64(&v.f)), 'g', -1, 64)
    69	}
    70	
    71	// Add adds delta to v.
    72	func (v *Float) Add(delta float64) {
    73		for {
    74			cur := atomic.LoadUint64(&v.f)
    75			curVal := math.Float64frombits(cur)
    76			nxtVal := curVal + delta
    77			nxt := math.Float64bits(nxtVal)
    78			if atomic.CompareAndSwapUint64(&v.f, cur, nxt) {
    79				return
    80			}
    81		}
    82	}
    83	
    84	// Set sets v to value.
    85	func (v *Float) Set(value float64) {
    86		atomic.StoreUint64(&v.f, math.Float64bits(value))
    87	}
    88	
    89	// Map is a string-to-Var map variable that satisfies the Var interface.
    90	type Map struct {
    91		mu   sync.RWMutex
    92		m    map[string]Var
    93		keys []string // sorted
    94	}
    95	
    96	// KeyValue represents a single entry in a Map.
    97	type KeyValue struct {
    98		Key   string
    99		Value Var
   100	}
   101	
   102	func (v *Map) String() string {
   103		v.mu.RLock()
   104		defer v.mu.RUnlock()
   105		var b bytes.Buffer
   106		fmt.Fprintf(&b, "{")
   107		first := true
   108		v.doLocked(func(kv KeyValue) {
   109			if !first {
   110				fmt.Fprintf(&b, ", ")
   111			}
   112			fmt.Fprintf(&b, "%q: %v", kv.Key, kv.Value)
   113			first = false
   114		})
   115		fmt.Fprintf(&b, "}")
   116		return b.String()
   117	}
   118	
   119	func (v *Map) Init() *Map {
   120		v.m = make(map[string]Var)
   121		return v
   122	}
   123	
   124	// updateKeys updates the sorted list of keys in v.keys.
   125	// must be called with v.mu held.
   126	func (v *Map) updateKeys() {
   127		if len(v.m) == len(v.keys) {
   128			// No new key.
   129			return
   130		}
   131		v.keys = v.keys[:0]
   132		for k := range v.m {
   133			v.keys = append(v.keys, k)
   134		}
   135		sort.Strings(v.keys)
   136	}
   137	
   138	func (v *Map) Get(key string) Var {
   139		v.mu.RLock()
   140		defer v.mu.RUnlock()
   141		return v.m[key]
   142	}
   143	
   144	func (v *Map) Set(key string, av Var) {
   145		v.mu.Lock()
   146		defer v.mu.Unlock()
   147		v.m[key] = av
   148		v.updateKeys()
   149	}
   150	
   151	func (v *Map) Add(key string, delta int64) {
   152		v.mu.RLock()
   153		av, ok := v.m[key]
   154		v.mu.RUnlock()
   155		if !ok {
   156			// check again under the write lock
   157			v.mu.Lock()
   158			av, ok = v.m[key]
   159			if !ok {
   160				av = new(Int)
   161				v.m[key] = av
   162				v.updateKeys()
   163			}
   164			v.mu.Unlock()
   165		}
   166	
   167		// Add to Int; ignore otherwise.
   168		if iv, ok := av.(*Int); ok {
   169			iv.Add(delta)
   170		}
   171	}
   172	
   173	// AddFloat adds delta to the *Float value stored under the given map key.
   174	func (v *Map) AddFloat(key string, delta float64) {
   175		v.mu.RLock()
   176		av, ok := v.m[key]
   177		v.mu.RUnlock()
   178		if !ok {
   179			// check again under the write lock
   180			v.mu.Lock()
   181			av, ok = v.m[key]
   182			if !ok {
   183				av = new(Float)
   184				v.m[key] = av
   185				v.updateKeys()
   186			}
   187			v.mu.Unlock()
   188		}
   189	
   190		// Add to Float; ignore otherwise.
   191		if iv, ok := av.(*Float); ok {
   192			iv.Add(delta)
   193		}
   194	}
   195	
   196	// Do calls f for each entry in the map.
   197	// The map is locked during the iteration,
   198	// but existing entries may be concurrently updated.
   199	func (v *Map) Do(f func(KeyValue)) {
   200		v.mu.RLock()
   201		defer v.mu.RUnlock()
   202		v.doLocked(f)
   203	}
   204	
   205	// doLocked calls f for each entry in the map.
   206	// v.mu must be held for reads.
   207	func (v *Map) doLocked(f func(KeyValue)) {
   208		for _, k := range v.keys {
   209			f(KeyValue{k, v.m[k]})
   210		}
   211	}
   212	
   213	// String is a string variable, and satisfies the Var interface.
   214	type String struct {
   215		mu sync.RWMutex
   216		s  string
   217	}
   218	
   219	func (v *String) String() string {
   220		v.mu.RLock()
   221		defer v.mu.RUnlock()
   222		return strconv.Quote(v.s)
   223	}
   224	
   225	func (v *String) Set(value string) {
   226		v.mu.Lock()
   227		defer v.mu.Unlock()
   228		v.s = value
   229	}
   230	
   231	// Func implements Var by calling the function
   232	// and formatting the returned value using JSON.
   233	type Func func() interface{}
   234	
   235	func (f Func) String() string {
   236		v, _ := json.Marshal(f())
   237		return string(v)
   238	}
   239	
   240	// All published variables.
   241	var (
   242		mutex   sync.RWMutex
   243		vars    = make(map[string]Var)
   244		varKeys []string // sorted
   245	)
   246	
   247	// Publish declares a named exported variable. This should be called from a
   248	// package's init function when it creates its Vars. If the name is already
   249	// registered then this will log.Panic.
   250	func Publish(name string, v Var) {
   251		mutex.Lock()
   252		defer mutex.Unlock()
   253		if _, existing := vars[name]; existing {
   254			log.Panicln("Reuse of exported var name:", name)
   255		}
   256		vars[name] = v
   257		varKeys = append(varKeys, name)
   258		sort.Strings(varKeys)
   259	}
   260	
   261	// Get retrieves a named exported variable.
   262	func Get(name string) Var {
   263		mutex.RLock()
   264		defer mutex.RUnlock()
   265		return vars[name]
   266	}
   267	
   268	// Convenience functions for creating new exported variables.
   269	
   270	func NewInt(name string) *Int {
   271		v := new(Int)
   272		Publish(name, v)
   273		return v
   274	}
   275	
   276	func NewFloat(name string) *Float {
   277		v := new(Float)
   278		Publish(name, v)
   279		return v
   280	}
   281	
   282	func NewMap(name string) *Map {
   283		v := new(Map).Init()
   284		Publish(name, v)
   285		return v
   286	}
   287	
   288	func NewString(name string) *String {
   289		v := new(String)
   290		Publish(name, v)
   291		return v
   292	}
   293	
   294	// Do calls f for each exported variable.
   295	// The global variable map is locked during the iteration,
   296	// but existing entries may be concurrently updated.
   297	func Do(f func(KeyValue)) {
   298		mutex.RLock()
   299		defer mutex.RUnlock()
   300		for _, k := range varKeys {
   301			f(KeyValue{k, vars[k]})
   302		}
   303	}
   304	
   305	func expvarHandler(w http.ResponseWriter, r *http.Request) {
   306		w.Header().Set("Content-Type", "application/json; charset=utf-8")
   307		fmt.Fprintf(w, "{\n")
   308		first := true
   309		Do(func(kv KeyValue) {
   310			if !first {
   311				fmt.Fprintf(w, ",\n")
   312			}
   313			first = false
   314			fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
   315		})
   316		fmt.Fprintf(w, "\n}\n")
   317	}
   318	
   319	func cmdline() interface{} {
   320		return os.Args
   321	}
   322	
   323	func memstats() interface{} {
   324		stats := new(runtime.MemStats)
   325		runtime.ReadMemStats(stats)
   326		return *stats
   327	}
   328	
   329	func init() {
   330		http.HandleFunc("/debug/vars", expvarHandler)
   331		Publish("cmdline", Func(cmdline))
   332		Publish("memstats", Func(memstats))
   333	}
   334	

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