【原创】golang 之 expvar 使用
发布时间：2020-12-16 18:20:44 所属栏目：大数据 来源：网络整理
导读：源码说明 在 expvar.go 中有如下说明： expvar 包提供了一种标准化接口用于 公共变量 ，例如针对 server 中的操作计数器； expvar 以 JSON 格式通过 HTTP 的 /debug/vars 来暴露这些变量； 针对这些公共变量的 set 或 modify 操作具有原子性； 除了会添加 HT
源码说明在
产生“副作用”的代码： // Do calls f for each exported variable.
// The global variable map is locked during the iteration,// but existing entries may be concurrently updated.
func Do(f func(KeyValue)) {
mutex.RLock()
defer mutex.RUnlock()
for _,k := range varKeys {
f(KeyValue{k,vars[k]})
}
}
// 针对 /debug/vars 的回调函数
func expvarHandler(w http.ResponseWriter,r *http.Request) {
w.Header().Set("Content-Type","application/json; charset=utf-8")
fmt.Fprintf(w,"{n")
first := true
Do(func(kv KeyValue) {
if !first {
fmt.Fprintf(w,",n")
}
first = false
fmt.Fprintf(w,"%q: %s",kv.Key,kv.Value)
})
fmt.Fprintf(w,"n}n")
}
// 获取命令参数
func cmdline() interface{} {
return os.Args
}
// 获取内存统计信息
func memstats() interface{} {
stats := new(runtime.MemStats)
runtime.ReadMemStats(stats)
return *stats
}
// 包 expvar 默认提供的东东
func init() {
http.HandleFunc("/debug/vars",expvarHandler)
Publish("cmdline",Func(cmdline))
Publish("memstats",Func(memstats))
}
一个简单的使用示例： package main
import "expvar"
import "net"
import "fmt"
import "net/http"
var (
counts = expvar.NewMap("counters")
)
func init() {
counts.Add("a",10)
counts.Add("b",10)
}
func main() {
sock,err := net.Listen("tcp","localhost:8123")
if err != nil {
panic("sock error")
}
go func() {
fmt.Println("HTTP now available at port 8123")
http.Serve(sock,nil)
}()
fmt.Println("hello")
select {}
}
启动示例 server ? Golang ./expvar_usage_1 hello HTTP now available at port 8123 获取由 expvar 提供的内容 ? ~ curl http://localhost:8123/debug/vars
{
"cmdline": ["./expvar_usage_1"],"counters": {"a": 10,"b": 10},"memstats": {"Alloc":321496,"TotalAlloc":321496,"Sys":3084288,"Lookups":5,"Mallocs":4743,"Frees":98,"HeapAlloc":321496,"HeapSys":1769472,"HeapIdle":1040384,"HeapInuse":729088,"HeapReleased":0,"HeapObjects":4645,"StackInuse":327680,"StackSys":327680,"MSpanInuse":14080,"MSpanSys":16384,"MCacheInuse":4800,"MCacheSys":16384,"BuckHashSys":2357,"GCSys":131072,"OtherSys":820939,"NextGC":4194304,"LastGC":0,"PauseTotalNs":0,"PauseNs":[0,0],"PauseEnd":[0,"NumGC":0,"GCCPUFraction":0,"EnableGC":true,"DebugGC":false,"BySize":[{"Size":0,"Mallocs":0,"Frees":0},{"Size":8,"Mallocs":15,{"Size":16,"Mallocs":333,{"Size":32,"Mallocs":3926,{"Size":48,"Mallocs":101,{"Size":64,"Mallocs":30,{"Size":80,"Mallocs":28,{"Size":96,"Mallocs":8,{"Size":112,"Mallocs":4,{"Size":128,"Mallocs":7,{"Size":144,"Mallocs":3,{"Size":160,"Mallocs":16,{"Size":176,{"Size":192,{"Size":208,"Mallocs":24,{"Size":224,{"Size":240,"Mallocs":2,{"Size":256,"Mallocs":9,{"Size":288,"Mallocs":18,{"Size":320,{"Size":352,{"Size":384,{"Size":416,"Mallocs":26,{"Size":448,{"Size":480,"Mallocs":1,{"Size":512,{"Size":576,{"Size":640,{"Size":704,"Mallocs":6,{"Size":768,{"Size":896,{"Size":1024,{"Size":1152,"Mallocs":5,{"Size":1280,{"Size":1408,{"Size":1536,{"Size":1664,{"Size":2048,{"Size":2304,{"Size":2560,{"Size":2816,{"Size":3072,{"Size":3328,{"Size":4096,{"Size":4608,{"Size":5376,{"Size":6144,{"Size":6400,{"Size":6656,{"Size":6912,{"Size":8192,{"Size":8448,{"Size":8704,{"Size":9472,{"Size":10496,{"Size":12288,{"Size":13568,{"Size":14080,{"Size":16384,{"Size":16640,{"Size":17664,"Frees":0}]}
}
? ~
一个golang http包自带的绝佳示例这个示例完整展现了 expvar 包中可以使用的各种数据类型，示例代码如下 package main
import (
"bytes"
"expvar"
"flag"
"fmt"
"io"
"log"
"net/http"
"os"
"os/exec"
"strconv"
"sync"
)
// hello world,the web server
var helloRequests = expvar.NewInt("hello-requests")
func HelloServer(w http.ResponseWriter,req *http.Request) {
helloRequests.Add(1)
io.WriteString(w,"hello,world!n")
}
// Simple counter server. POSTing to it will set the value.
type Counter struct {
mu sync.Mutex // protects n
n int
}
// This makes Counter satisfy the expvar.Var interface,so we can export
// it directly.
func (ctr *Counter) String() string {
ctr.mu.Lock()
defer ctr.mu.Unlock()
return fmt.Sprintf("%d",ctr.n)
}
func (ctr *Counter) ServeHTTP(w http.ResponseWriter,req *http.Request) {
ctr.mu.Lock()
defer ctr.mu.Unlock()
switch req.Method {
case "GET":
ctr.n++
case "POST":
buf := new(bytes.Buffer)
io.Copy(buf,req.Body)
body := buf.String()
if n,err := strconv.Atoi(body); err != nil {
fmt.Fprintf(w,"bad POST: %vnbody: [%v]n",err,body)
} else {
ctr.n = n
fmt.Fprint(w,"counter resetn")
}
}
fmt.Fprintf(w,"counter = %dn",ctr.n)
}
// simple flag server
var booleanflag = flag.Bool("boolean",true,"another flag for testing")
func FlagServer(w http.ResponseWriter,req *http.Request) {
w.Header().Set("Content-Type","text/plain; charset=utf-8")
fmt.Fprint(w,"Flags:n")
flag.VisitAll(func(f *flag.Flag) {
if f.Value.String() != f.DefValue {
fmt.Fprintf(w,"%s = %s [default = %s]n",f.Name,f.Value.String(),f.DefValue)
} else {
fmt.Fprintf(w,"%s = %sn",f.Value.String())
}
})
}
// simple argument server
func ArgServer(w http.ResponseWriter,req *http.Request) {
for _,s := range os.Args {
fmt.Fprint(w,s," ")
}
}
// a channel (just for the fun of it)
type Chan chan int
func ChanCreate() Chan {
c := make(Chan)
go func(c Chan) {
for x := 0; ; x++ {
c <- x
}
}(c)
return c
}
func (ch Chan) ServeHTTP(w http.ResponseWriter,req *http.Request) {
io.WriteString(w,fmt.Sprintf("channel send #%dn",<-ch))
}
// exec a program,redirecting output
func DateServer(rw http.ResponseWriter,req *http.Request) {
rw.Header().Set("Content-Type","text/plain; charset=utf-8")
date,err := exec.Command("/bin/date").Output()
if err != nil {
http.Error(rw,err.Error(),500)
return
}
rw.Write(date)
}
func Logger(w http.ResponseWriter,req *http.Request) {
log.Print(req.URL)
http.Error(w,"oops",404)
}
var webroot = flag.String("root",os.Getenv("HOME"),"web root directory")
func main() {
flag.Parse()
// The counter is published as a variable directly.
ctr := new(Counter)
expvar.Publish("counter",ctr)
http.Handle("/counter",ctr)
http.Handle("/",http.HandlerFunc(Logger))
http.Handle("/go/",http.StripPrefix("/go/",http.FileServer(http.Dir(*webroot))))
http.Handle("/chan",ChanCreate())
http.HandleFunc("/flags",FlagServer)
http.HandleFunc("/args",ArgServer)
http.HandleFunc("/go/hello",HelloServer)
http.HandleFunc("/date",DateServer)
err := http.ListenAndServe(":12345",nil)
if err != nil {
log.Panicln("ListenAndServe:",err)
}
}
测试 ? ~ curl http://localhost:12345/counter counter = 1 ? ~ curl http://localhost:12345/counter counter = 2 ? ~ curl http://localhost:12345/counter counter = 3 ? ~ ? ~ curl -XPOST http://localhost:12345/counter -d '100' counter reset counter = 100 ? ~ curl http://localhost:12345/counter counter = 101 ? ~ curl http://localhost:12345/counter counter = 102 ? ~ curl -XPOST http://localhost:12345/counter -d '100a' bad POST: strconv.ParseInt: parsing "100a": invalid syntax body: [100a] counter = 102 ? ~ ? ~ curl http://localhost:12345/counter counter = 103 ? ~ ? ~ curl http://localhost:12345/ oops ? ~ ? ~ curl http://localhost:12345/go <a href="/go/">Moved Permanently</a>. ? ~ ? ~ curl -L http://localhost:12345/go <pre> <a href=".bash_history">.bash_history</a> <a href=".bash_profile">.bash_profile</a> <a href=".bash_sessions/">.bash_sessions/</a> <a href="http_-L.pcap">http_-L.pcap</a> <a href="http_-d.pcap">http_-d.pcap</a> <a href="http_-e.pcap">http_-e.pcap</a> <a href="http_-r.pcap">http_-r.pcap</a> <a href="workspace/">workspace/</a> </pre> ? ~ ? ~ curl http://localhost:12345/chan channel send #0 ? ~ curl http://localhost:12345/chan channel send #1 ? ~ curl http://localhost:12345/chan channel send #2 ? ~ ? ~ curl http://localhost:12345/flags Flags: boolean = true root = /Users/sunfei ? ~ ? ~ curl http://localhost:12345/args ./expvar_usage_2 % ? ~ ? ~ curl http://localhost:12345/go/hello hello,world! ? ~ ? ~ curl http://localhost:12345/date 2017年 1月12日 星期四 17时16分46秒 CST ? ~ curl http://localhost:12345/date 2017年 1月12日 星期四 17时16分51秒 CST ? ~ curl http://localhost:12345/date 2017年 1月12日 星期四 17时16分56秒 CST ? ~ curl http://localhost:12345/date 2017年 1月12日 星期四 17时16分58秒 CST ? ~ ? ~ curl http://localhost:12345/xx oops ? ~ curl http://localhost:12345/yy oops ? ~ packetbeat 中的使用在运行 packetbeat 时，console 上会周期性输出如下日志 2017/01/16 02:40:21.957781 logp.go:230: INFO Non-zero metrics in the last 30s: redis.unmatched_responses=1 libbeat.publisher.published_events=7 对应代码如下 // logExpvars 函数会以 Info 日志级别记录 integer 类型的 expvars 值在
// 指定 interval 内的变化情况；对于每一个 expvar 来说，变化量 delta
// 是从 interval 的开始进行记录和计算的；
func logExpvars(metricsCfg *LoggingMetricsConfig) {
// 没有配置或配置为 false
if metricsCfg.Enabled != nil && *metricsCfg.Enabled == false {
Info("Metrics logging disabled")
return
}
// 默认 interval 设置为 30s
if metricsCfg.Period == nil {
metricsCfg.Period = &defaultMetricsPeriod
}
Info("Metrics logging every %s",metricsCfg.Period)
ticker := time.NewTicker(*metricsCfg.Period)
prevVals := map[string]int64{}
for {
<-ticker.C
vals := map[string]int64{}
// 将注册到 expvar 中的全部 Int 类型内容保存到 vals 中
snapshotExpvars(vals)
// 构建 interval 时间内的所有 Int 类型 expvar 变量的 delta 差值字符串
metrics := buildMetricsOutput(prevVals,vals)
prevVals = vals
if len(metrics) > 0 {
Info("Non-zero metrics in the last %s:%s",metricsCfg.Period,metrics)
} else {
// 指定 interval 内所有 Int 类型的 expvar 变量均无变化
Info("No non-zero metrics in the last %s",metricsCfg.Period)
}
}
}
函数 // snapshotExpvars 对定义的全部 expvars 进行递归处理；针对 integer 类型
// 的内容，会对其 name 和 value 执行 snapshot 操作，保存到一个单独的
// (flat) map 中
func snapshotExpvars(varsMap map[string]int64) {
// 遍历当前已全局注册过的 expvar 变量
expvar.Do(func(kv expvar.KeyValue) {
switch kv.Value.(type) {
// 如果是 Int 类型，直接保存到 map 中
case *expvar.Int:
varsMap[kv.Key],_ = strconv.ParseInt(kv.Value.String(),10,64)
// 如果是 Map 类型，则递归处理其中的内容（其实是处理其中的 Int 类型内容）
case *expvar.Map:
snapshotMap(varsMap,kv.Value.(*expvar.Map))
}
})
}
函数 // buildMetricsOutput 负责计算 vals 和 prevVals 的差值 delta ；并构建
// 一个便于打印输出 delta 内容的字符串；
// 注：至少存在一个 expvar 变量的 delta 不为 0 才有非空字符串返回
func buildMetricsOutput(prevVals map[string]int64,vals map[string]int64) string {
metrics := ""
for k,v := range vals {
delta := v - prevVals[k]
if delta != 0 {
metrics = fmt.Sprintf("%s %s=%d",metrics,k,delta)
}
}
return metrics
}
在结束 packetbeat 运行时，console 上会输出如下日志 2017/01/16 10:41:44.727504 logp.go:245: INFO Total non-zero values: libbeat.publisher.published_events=12915 redis.unmatched_responses=23 tcp.dropped_because_of_gaps=4 2017/01/16 10:41:44.727537 logp.go:246: INFO Uptime: 1.22785826s 对应的代码如下 func LogTotalExpvars(cfg *Logging) {
if cfg.Metrics.Enabled != nil && *cfg.Metrics.Enabled == false {
return
}
vals := map[string]int64{}
prevVals := map[string]int64{}
snapshotExpvars(vals)
metrics := buildMetricsOutput(prevVals,vals)
Info("Total non-zero values: %s",metrics)
Info("Uptime: %s",time.Now().Sub(startTime))
}
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