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Source file src/pkg/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		"net/http"
    30		"os"
    31		"runtime"
    32		"sort"
    33		"strconv"
    34		"sync"
    35	)
    36	
    37	// Var is an abstract type for all exported variables.
    38	type Var interface {
    39		String() string
    40	}
    41	
    42	// Int is a 64-bit integer variable that satisfies the Var interface.
    43	type Int struct {
    44		mu sync.RWMutex
    45		i  int64
    46	}
    47	
    48	func (v *Int) String() string {
    49		v.mu.RLock()
    50		defer v.mu.RUnlock()
    51		return strconv.FormatInt(v.i, 10)
    52	}
    53	
    54	func (v *Int) Add(delta int64) {
    55		v.mu.Lock()
    56		defer v.mu.Unlock()
    57		v.i += delta
    58	}
    59	
    60	func (v *Int) Set(value int64) {
    61		v.mu.Lock()
    62		defer v.mu.Unlock()
    63		v.i = value
    64	}
    65	
    66	// Float is a 64-bit float variable that satisfies the Var interface.
    67	type Float struct {
    68		mu sync.RWMutex
    69		f  float64
    70	}
    71	
    72	func (v *Float) String() string {
    73		v.mu.RLock()
    74		defer v.mu.RUnlock()
    75		return strconv.FormatFloat(v.f, 'g', -1, 64)
    76	}
    77	
    78	// Add adds delta to v.
    79	func (v *Float) Add(delta float64) {
    80		v.mu.Lock()
    81		defer v.mu.Unlock()
    82		v.f += delta
    83	}
    84	
    85	// Set sets v to value.
    86	func (v *Float) Set(value float64) {
    87		v.mu.Lock()
    88		defer v.mu.Unlock()
    89		v.f = value
    90	}
    91	
    92	// Map is a string-to-Var map variable that satisfies the Var interface.
    93	type Map struct {
    94		mu   sync.RWMutex
    95		m    map[string]Var
    96		keys []string // sorted
    97	}
    98	
    99	// KeyValue represents a single entry in a Map.
   100	type KeyValue struct {
   101		Key   string
   102		Value Var
   103	}
   104	
   105	func (v *Map) String() string {
   106		v.mu.RLock()
   107		defer v.mu.RUnlock()
   108		var b bytes.Buffer
   109		fmt.Fprintf(&b, "{")
   110		first := true
   111		v.doLocked(func(kv KeyValue) {
   112			if !first {
   113				fmt.Fprintf(&b, ", ")
   114			}
   115			fmt.Fprintf(&b, "%q: %v", kv.Key, kv.Value)
   116			first = false
   117		})
   118		fmt.Fprintf(&b, "}")
   119		return b.String()
   120	}
   121	
   122	func (v *Map) Init() *Map {
   123		v.m = make(map[string]Var)
   124		return v
   125	}
   126	
   127	// updateKeys updates the sorted list of keys in v.keys.
   128	// must be called with v.mu held.
   129	func (v *Map) updateKeys() {
   130		if len(v.m) == len(v.keys) {
   131			// No new key.
   132			return
   133		}
   134		v.keys = v.keys[:0]
   135		for k := range v.m {
   136			v.keys = append(v.keys, k)
   137		}
   138		sort.Strings(v.keys)
   139	}
   140	
   141	func (v *Map) Get(key string) Var {
   142		v.mu.RLock()
   143		defer v.mu.RUnlock()
   144		return v.m[key]
   145	}
   146	
   147	func (v *Map) Set(key string, av Var) {
   148		v.mu.Lock()
   149		defer v.mu.Unlock()
   150		v.m[key] = av
   151		v.updateKeys()
   152	}
   153	
   154	func (v *Map) Add(key string, delta int64) {
   155		v.mu.RLock()
   156		av, ok := v.m[key]
   157		v.mu.RUnlock()
   158		if !ok {
   159			// check again under the write lock
   160			v.mu.Lock()
   161			av, ok = v.m[key]
   162			if !ok {
   163				av = new(Int)
   164				v.m[key] = av
   165				v.updateKeys()
   166			}
   167			v.mu.Unlock()
   168		}
   169	
   170		// Add to Int; ignore otherwise.
   171		if iv, ok := av.(*Int); ok {
   172			iv.Add(delta)
   173		}
   174	}
   175	
   176	// AddFloat adds delta to the *Float value stored under the given map key.
   177	func (v *Map) AddFloat(key string, delta float64) {
   178		v.mu.RLock()
   179		av, ok := v.m[key]
   180		v.mu.RUnlock()
   181		if !ok {
   182			// check again under the write lock
   183			v.mu.Lock()
   184			av, ok = v.m[key]
   185			if !ok {
   186				av = new(Float)
   187				v.m[key] = av
   188				v.updateKeys()
   189			}
   190			v.mu.Unlock()
   191		}
   192	
   193		// Add to Float; ignore otherwise.
   194		if iv, ok := av.(*Float); ok {
   195			iv.Add(delta)
   196		}
   197	}
   198	
   199	// Do calls f for each entry in the map.
   200	// The map is locked during the iteration,
   201	// but existing entries may be concurrently updated.
   202	func (v *Map) Do(f func(KeyValue)) {
   203		v.mu.RLock()
   204		defer v.mu.RUnlock()
   205		v.doLocked(f)
   206	}
   207	
   208	// doLocked calls f for each entry in the map.
   209	// v.mu must be held for reads.
   210	func (v *Map) doLocked(f func(KeyValue)) {
   211		for _, k := range v.keys {
   212			f(KeyValue{k, v.m[k]})
   213		}
   214	}
   215	
   216	// String is a string variable, and satisfies the Var interface.
   217	type String struct {
   218		mu sync.RWMutex
   219		s  string
   220	}
   221	
   222	func (v *String) String() string {
   223		v.mu.RLock()
   224		defer v.mu.RUnlock()
   225		return strconv.Quote(v.s)
   226	}
   227	
   228	func (v *String) Set(value string) {
   229		v.mu.Lock()
   230		defer v.mu.Unlock()
   231		v.s = value
   232	}
   233	
   234	// Func implements Var by calling the function
   235	// and formatting the returned value using JSON.
   236	type Func func() interface{}
   237	
   238	func (f Func) String() string {
   239		v, _ := json.Marshal(f())
   240		return string(v)
   241	}
   242	
   243	// All published variables.
   244	var (
   245		mutex   sync.RWMutex
   246		vars    = make(map[string]Var)
   247		varKeys []string // sorted
   248	)
   249	
   250	// Publish declares a named exported variable. This should be called from a
   251	// package's init function when it creates its Vars. If the name is already
   252	// registered then this will log.Panic.
   253	func Publish(name string, v Var) {
   254		mutex.Lock()
   255		defer mutex.Unlock()
   256		if _, existing := vars[name]; existing {
   257			log.Panicln("Reuse of exported var name:", name)
   258		}
   259		vars[name] = v
   260		varKeys = append(varKeys, name)
   261		sort.Strings(varKeys)
   262	}
   263	
   264	// Get retrieves a named exported variable.
   265	func Get(name string) Var {
   266		mutex.RLock()
   267		defer mutex.RUnlock()
   268		return vars[name]
   269	}
   270	
   271	// Convenience functions for creating new exported variables.
   272	
   273	func NewInt(name string) *Int {
   274		v := new(Int)
   275		Publish(name, v)
   276		return v
   277	}
   278	
   279	func NewFloat(name string) *Float {
   280		v := new(Float)
   281		Publish(name, v)
   282		return v
   283	}
   284	
   285	func NewMap(name string) *Map {
   286		v := new(Map).Init()
   287		Publish(name, v)
   288		return v
   289	}
   290	
   291	func NewString(name string) *String {
   292		v := new(String)
   293		Publish(name, v)
   294		return v
   295	}
   296	
   297	// Do calls f for each exported variable.
   298	// The global variable map is locked during the iteration,
   299	// but existing entries may be concurrently updated.
   300	func Do(f func(KeyValue)) {
   301		mutex.RLock()
   302		defer mutex.RUnlock()
   303		for _, k := range varKeys {
   304			f(KeyValue{k, vars[k]})
   305		}
   306	}
   307	
   308	func expvarHandler(w http.ResponseWriter, r *http.Request) {
   309		w.Header().Set("Content-Type", "application/json; charset=utf-8")
   310		fmt.Fprintf(w, "{\n")
   311		first := true
   312		Do(func(kv KeyValue) {
   313			if !first {
   314				fmt.Fprintf(w, ",\n")
   315			}
   316			first = false
   317			fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
   318		})
   319		fmt.Fprintf(w, "\n}\n")
   320	}
   321	
   322	func cmdline() interface{} {
   323		return os.Args
   324	}
   325	
   326	func memstats() interface{} {
   327		stats := new(runtime.MemStats)
   328		runtime.ReadMemStats(stats)
   329		return *stats
   330	}
   331	
   332	func init() {
   333		http.HandleFunc("/debug/vars", expvarHandler)
   334		Publish("cmdline", Func(cmdline))
   335		Publish("memstats", Func(memstats))
   336	}
   337	

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