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 HTTP handler 以外，该包还会注册如下变量：
cmdlineos.Argsmemstatsruntime.Memstats有些时候导入该包的目的仅仅是为了“副作用”，即注册其提供的 HTTP handler 和上述变量； 可以按照如下方式导入该包：
import _ "expvar"
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
➜ ~ 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: %v\nbody: [%v]\n",err,body)
} else {
ctr.n = n
fmt.Fprint(w,"counter reset\n")
}
}
fmt.Fprintf(w,"counter = %d\n",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 = %s\n",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 #%d\n",<-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 的实现如下
// 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 的实现如下
// 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))
}
