介绍与应用
expvar 是 exposed variable的简写
expvar包是 Golang 官网为裸露Go利用外部指标数据所提供的规范对外接口，能够辅助获取和调试全局变量。
其通过init函数将内置的expvarHandler(一个规范http HandlerFunc)注册到http包ListenAndServe创立的默认Server上
如以下案例:
package mainimport ( "encoding/json" "expvar" "fmt" "github.com/gin-gonic/gin" "net/http" "runtime" "time")func main() { router := gin.Default() //初始化一个gin实例 router.GET("/debug/vars", GetCurrentRunningStats) //接口路由，如果url不是/debug/vars，则用metricBeat去获取会出问题 s := &http.Server{ Addr: ":" + "6666", Handler: router, ReadTimeout: 5 * time.Second, WriteTimeout: 5 * time.Second, MaxHeaderBytes: 1 << 20, } s.ListenAndServe() //开始监听}var CuMemoryPtr *map[string]stringvar BTCMemoryPtr *map[string]interface{}// 开始工夫var start = time.Now()// calculateUptime 计算运行工夫func calculateUptime() interface{} { return time.Since(start).String()}// currentGoVersion 以后 Golang 版本func currentGoVersion() interface{} { return runtime.Version()}// getNumCPUs 获取 CPU 外围数量func getNumCPUs() interface{} { return runtime.NumCPU()}// getGoOS 以后零碎类型func getGoOS() interface{} { return runtime.GOOS}// getNumGoroutins 以后 goroutine 数量func getNumGoroutins() interface{} { return runtime.NumGoroutine()}// getNumCgoCall CGo 调用次数func getNumCgoCall() interface{} { return runtime.NumCgoCall()}// 业务特定的内存数据func getCuMemoryMap() interface{} { if CuMemoryPtr == nil { return 0 } else { return len(*CuMemoryPtr) }}// 业务特定的内存数据func getBTCMemoryMap() interface{} { if BTCMemoryPtr == nil { return 0 } else { return len(*BTCMemoryPtr) }}var lastPause uint32// getLastGCPauseTime 获取上次 GC 的暂停工夫func getLastGCPauseTime() interface{} { var gcPause uint64 ms := new(runtime.MemStats) statString := expvar.Get("memstats").String() if statString != "" { json.Unmarshal([]byte(statString), ms) if lastPause == 0 || lastPause != ms.NumGC { gcPause = ms.PauseNs[(ms.NumGC+255)%256] lastPause = ms.NumGC } } return gcPause}// GetCurrentRunningStats 返回以后运行信息func GetCurrentRunningStats(c *gin.Context) { c.Writer.Header().Set("Content-Type", "application/json; charset=utf-8") first := true report := func(key string, value interface{}) { if !first { fmt.Fprintf(c.Writer, ",\n") } first = false if str, ok := value.(string); ok { fmt.Fprintf(c.Writer, "%q: %q", key, str) } else { fmt.Fprintf(c.Writer, "%q: %v", key, value) } } fmt.Fprintf(c.Writer, "{\n") expvar.Do(func(kv expvar.KeyValue) { report(kv.Key, kv.Value) }) fmt.Fprintf(c.Writer, "\n}\n") c.String(http.StatusOK, "")}func init() { //这些都是自定义变量，公布到expvar中，每次申请接口，expvar会主动去获取这些变量，并返回 expvar.Publish("运行工夫", expvar.Func(calculateUptime)) expvar.Publish("version", expvar.Func(currentGoVersion)) expvar.Publish("cores", expvar.Func(getNumCPUs)) expvar.Publish("os", expvar.Func(getGoOS)) expvar.Publish("cgo", expvar.Func(getNumCgoCall)) expvar.Publish("goroutine", expvar.Func(getNumGoroutins)) expvar.Publish("gcpause", expvar.Func(getLastGCPauseTime)) expvar.Publish("CuMemory", expvar.Func(getCuMemoryMap)) expvar.Publish("BTCMemory", expvar.Func(getBTCMemoryMap))}运行程序，并申请127.0.0.1:6666/debug/vars
<details>
<summary>后果如下：</summary>
{ "BTCMemory": 0, "CuMemory": 0, "cgo": 1, "cmdline": [ "/var/folders/9t/839s3jmj73bcgyp5x_xh3gw00000gn/T/go-build1753052226/b001/exe/1" ], "cores": 8, "gcpause": 0, "goroutine": 3, "memstats": { "Alloc": 1516104, "TotalAlloc": 1516104, "Sys": 71961616, "Lookups": 0, "Mallocs": 12075, "Frees": 1237, "HeapAlloc": 1516104, "HeapSys": 66650112, "HeapIdle": 63930368, "HeapInuse": 2719744, "HeapReleased": 63930368, "HeapObjects": 10838, "StackInuse": 458752, "StackSys": 458752, "MSpanInuse": 46376, "MSpanSys": 49152, "MCacheInuse": 9600, "MCacheSys": 16384, "BuckHashSys": 4156, "GCSys": 4227128, "OtherSys": 555932, "NextGC": 4473924, "LastGC": 0, "PauseTotalNs": 0, "PauseNs": [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ], "PauseEnd": [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ], "NumGC": 0, "NumForcedGC": 0, "GCCPUFraction": 0, "EnableGC": true, "DebugGC": false, "BySize": [ { "Size": 0, "Mallocs": 0, "Frees": 0 }, { "Size": 8, "Mallocs": 251, "Frees": 0 }, { "Size": 16, "Mallocs": 4258, "Frees": 0 }, { "Size": 24, "Mallocs": 490, "Frees": 0 }, { "Size": 32, "Mallocs": 1194, "Frees": 0 }, { "Size": 48, "Mallocs": 745, "Frees": 0 }, { "Size": 64, "Mallocs": 572, "Frees": 0 }, { "Size": 80, "Mallocs": 72, "Frees": 0 }, { "Size": 96, "Mallocs": 84, "Frees": 0 }, { "Size": 112, "Mallocs": 2268, "Frees": 0 }, { "Size": 128, "Mallocs": 79, "Frees": 0 }, { "Size": 144, "Mallocs": 19, "Frees": 0 }, { "Size": 160, "Mallocs": 164, "Frees": 0 }, { "Size": 176, "Mallocs": 11, "Frees": 0 }, { "Size": 192, "Mallocs": 16, "Frees": 0 }, { "Size": 208, "Mallocs": 73, "Frees": 0 }, { "Size": 224, "Mallocs": 5, "Frees": 0 }, { "Size": 240, "Mallocs": 4, "Frees": 0 }, { "Size": 256, "Mallocs": 30, "Frees": 0 }, { "Size": 288, "Mallocs": 28, "Frees": 0 }, { "Size": 320, "Mallocs": 50, "Frees": 0 }, { "Size": 352, "Mallocs": 11, "Frees": 0 }, { "Size": 384, "Mallocs": 30, "Frees": 0 }, { "Size": 416, "Mallocs": 25, "Frees": 0 }, { "Size": 448, "Mallocs": 3, "Frees": 0 }, { "Size": 480, "Mallocs": 0, "Frees": 0 }, { "Size": 512, "Mallocs": 9, "Frees": 0 }, { "Size": 576, "Mallocs": 18, "Frees": 0 }, { "Size": 640, "Mallocs": 57, "Frees": 0 }, { "Size": 704, "Mallocs": 8, "Frees": 0 }, { "Size": 768, "Mallocs": 1, "Frees": 0 }, { "Size": 896, "Mallocs": 19, "Frees": 0 }, { "Size": 1024, "Mallocs": 26, "Frees": 0 }, { "Size": 1152, "Mallocs": 23, "Frees": 0 }, { "Size": 1280, "Mallocs": 36, "Frees": 0 }, { "Size": 1408, "Mallocs": 1, "Frees": 0 }, { "Size": 1536, "Mallocs": 3, "Frees": 0 }, { "Size": 1792, "Mallocs": 22, "Frees": 0 }, { "Size": 2048, "Mallocs": 7, "Frees": 0 }, { "Size": 2304, "Mallocs": 3, "Frees": 0 }, { "Size": 2688, "Mallocs": 38, "Frees": 0 }, { "Size": 3072, "Mallocs": 6, "Frees": 0 }, { "Size": 3200, "Mallocs": 2, "Frees": 0 }, { "Size": 3456, "Mallocs": 3, "Frees": 0 }, { "Size": 4096, "Mallocs": 20, "Frees": 0 }, { "Size": 4864, "Mallocs": 2, "Frees": 0 }, { "Size": 5376, "Mallocs": 15, "Frees": 0 }, { "Size": 6144, "Mallocs": 6, "Frees": 0 }, { "Size": 6528, "Mallocs": 1, "Frees": 0 }, { "Size": 6784, "Mallocs": 2, "Frees": 0 }, { "Size": 6912, "Mallocs": 0, "Frees": 0 }, { "Size": 8192, "Mallocs": 3, "Frees": 0 }, { "Size": 9472, "Mallocs": 2, "Frees": 0 }, { "Size": 9728, "Mallocs": 3, "Frees": 0 }, { "Size": 10240, "Mallocs": 8, "Frees": 0 }, { "Size": 10880, "Mallocs": 8, "Frees": 0 }, { "Size": 12288, "Mallocs": 0, "Frees": 0 }, { "Size": 13568, "Mallocs": 0, "Frees": 0 }, { "Size": 14336, "Mallocs": 0, "Frees": 0 }, { "Size": 16384, "Mallocs": 0, "Frees": 0 }, { "Size": 18432, "Mallocs": 1, "Frees": 0 } ] }, "os": "darwin", "version": "go1.16.7", "运行工夫": "30.037286084s"}</details>
其中，expvar包会默认携带memstats，该字段内含 各种内存堆栈以及GC的一些信息，具体可见源码正文
<details>
<summary>src/runtime/mstats.go</summary>
src/runtime/mstats.go
// A MemStats records statistics about the memory allocator.type MemStats struct { // General statistics. // Alloc is bytes of allocated heap objects. // // This is the same as HeapAlloc (see below). Alloc uint64 // TotalAlloc is cumulative bytes allocated for heap objects. // // TotalAlloc increases as heap objects are allocated, but // unlike Alloc and HeapAlloc, it does not decrease when // objects are freed. TotalAlloc uint64 // Sys is the total bytes of memory obtained from the OS. // // Sys is the sum of the XSys fields below. Sys measures the // virtual address space reserved by the Go runtime for the // heap, stacks, and other internal data structures. It's // likely that not all of the virtual address space is backed // by physical memory at any given moment, though in general // it all was at some point. Sys uint64 // Lookups is the number of pointer lookups performed by the // runtime. // // This is primarily useful for debugging runtime internals. Lookups uint64 // Mallocs is the cumulative count of heap objects allocated. // The number of live objects is Mallocs - Frees. Mallocs uint64 // Frees is the cumulative count of heap objects freed. Frees uint64 // Heap memory statistics. // // Interpreting the heap statistics requires some knowledge of // how Go organizes memory. Go divides the virtual address // space of the heap into "spans", which are contiguous // regions of memory 8K or larger. A span may be in one of // three states: // // An "idle" span contains no objects or other data. The // physical memory backing an idle span can be released back // to the OS (but the virtual address space never is), or it // can be converted into an "in use" or "stack" span. // // An "in use" span contains at least one heap object and may // have free space available to allocate more heap objects. // // A "stack" span is used for goroutine stacks. Stack spans // are not considered part of the heap. A span can change // between heap and stack memory; it is never used for both // simultaneously. // HeapAlloc is bytes of allocated heap objects. // // "Allocated" heap objects include all reachable objects, as // well as unreachable objects that the garbage collector has // not yet freed. Specifically, HeapAlloc increases as heap // objects are allocated and decreases as the heap is swept // and unreachable objects are freed. Sweeping occurs // incrementally between GC cycles, so these two processes // occur simultaneously, and as a result HeapAlloc tends to // change smoothly (in contrast with the sawtooth that is // typical of stop-the-world garbage collectors). HeapAlloc uint64 // HeapSys is bytes of heap memory obtained from the OS. // // HeapSys measures the amount of virtual address space // reserved for the heap. This includes virtual address space // that has been reserved but not yet used, which consumes no // physical memory, but tends to be small, as well as virtual // address space for which the physical memory has been // returned to the OS after it became unused (see HeapReleased // for a measure of the latter). // // HeapSys estimates the largest size the heap has had. HeapSys uint64 // HeapIdle is bytes in idle (unused) spans. // // Idle spans have no objects in them. These spans could be // (and may already have been) returned to the OS, or they can // be reused for heap allocations, or they can be reused as // stack memory. // // HeapIdle minus HeapReleased estimates the amount of memory // that could be returned to the OS, but is being retained by // the runtime so it can grow the heap without requesting more // memory from the OS. If this difference is significantly // larger than the heap size, it indicates there was a recent // transient spike in live heap size. HeapIdle uint64 // HeapInuse is bytes in in-use spans. // // In-use spans have at least one object in them. These spans // can only be used for other objects of roughly the same // size. // // HeapInuse minus HeapAlloc estimates the amount of memory // that has been dedicated to particular size classes, but is // not currently being used. This is an upper bound on // fragmentation, but in general this memory can be reused // efficiently. HeapInuse uint64 // HeapReleased is bytes of physical memory returned to the OS. // // This counts heap memory from idle spans that was returned // to the OS and has not yet been reacquired for the heap. HeapReleased uint64 // HeapObjects is the number of allocated heap objects. // // Like HeapAlloc, this increases as objects are allocated and // decreases as the heap is swept and unreachable objects are // freed. HeapObjects uint64 // Stack memory statistics. // // Stacks are not considered part of the heap, but the runtime // can reuse a span of heap memory for stack memory, and // vice-versa. // StackInuse is bytes in stack spans. // // In-use stack spans have at least one stack in them. These // spans can only be used for other stacks of the same size. // // There is no StackIdle because unused stack spans are // returned to the heap (and hence counted toward HeapIdle). StackInuse uint64 // StackSys is bytes of stack memory obtained from the OS. // // StackSys is StackInuse, plus any memory obtained directly // from the OS for OS thread stacks (which should be minimal). StackSys uint64 // Off-heap memory statistics. // // The following statistics measure runtime-internal // structures that are not allocated from heap memory (usually // because they are part of implementing the heap). Unlike // heap or stack memory, any memory allocated to these // structures is dedicated to these structures. // // These are primarily useful for debugging runtime memory // overheads. // MSpanInuse is bytes of allocated mspan structures. MSpanInuse uint64 // MSpanSys is bytes of memory obtained from the OS for mspan // structures. MSpanSys uint64 // MCacheInuse is bytes of allocated mcache structures. MCacheInuse uint64 // MCacheSys is bytes of memory obtained from the OS for // mcache structures. MCacheSys uint64 // BuckHashSys is bytes of memory in profiling bucket hash tables. BuckHashSys uint64 // GCSys is bytes of memory in garbage collection metadata. GCSys uint64 // OtherSys is bytes of memory in miscellaneous off-heap // runtime allocations. OtherSys uint64 // Garbage collector statistics. // NextGC is the target heap size of the next GC cycle. // // The garbage collector's goal is to keep HeapAlloc ≤ NextGC. // At the end of each GC cycle, the target for the next cycle // is computed based on the amount of reachable data and the // value of GOGC. NextGC uint64 // LastGC is the time the last garbage collection finished, as // nanoseconds since 1970 (the UNIX epoch). LastGC uint64 // PauseTotalNs is the cumulative nanoseconds in GC // stop-the-world pauses since the program started. // // During a stop-the-world pause, all goroutines are paused // and only the garbage collector can run. PauseTotalNs uint64 // PauseNs is a circular buffer of recent GC stop-the-world // pause times in nanoseconds. // // The most recent pause is at PauseNs[(NumGC+255)%256]. In // general, PauseNs[N%256] records the time paused in the most // recent N%256th GC cycle. There may be multiple pauses per // GC cycle; this is the sum of all pauses during a cycle. PauseNs [256]uint64 // PauseEnd is a circular buffer of recent GC pause end times, // as nanoseconds since 1970 (the UNIX epoch). // // This buffer is filled the same way as PauseNs. There may be // multiple pauses per GC cycle; this records the end of the // last pause in a cycle. PauseEnd [256]uint64 // NumGC is the number of completed GC cycles. NumGC uint32 // NumForcedGC is the number of GC cycles that were forced by // the application calling the GC function. NumForcedGC uint32 // GCCPUFraction is the fraction of this program's available // CPU time used by the GC since the program started. // // GCCPUFraction is expressed as a number between 0 and 1, // where 0 means GC has consumed none of this program's CPU. A // program's available CPU time is defined as the integral of // GOMAXPROCS since the program started. That is, if // GOMAXPROCS is 2 and a program has been running for 10 // seconds, its "available CPU" is 20 seconds. GCCPUFraction // does not include CPU time used for write barrier activity. // // This is the same as the fraction of CPU reported by // GODEBUG=gctrace=1. GCCPUFraction float64 // EnableGC indicates that GC is enabled. It is always true, // even if GOGC=off. EnableGC bool // DebugGC is currently unused. DebugGC bool // BySize reports per-size class allocation statistics. // // BySize[N] gives statistics for allocations of size S where // BySize[N-1].Size < S ≤ BySize[N].Size. // // This does not report allocations larger than BySize[60].Size. BySize [61]struct { // Size is the maximum byte size of an object in this // size class. Size uint32 // Mallocs is the cumulative count of heap objects // allocated in this size class. The cumulative bytes // of allocation is Size*Mallocs. The number of live // objects in this size class is Mallocs - Frees. Mallocs uint64 // Frees is the cumulative count of heap objects freed // in this size class. Frees uint64 }}</details>
对于各个字段的意义 可参考：
1、Alloc uint64 //Go语言框架 堆空间调配的字节数2、TotalAlloc uint64 //从服务开始运行至今分配器为调配的堆空间总和，只减少，开释时不缩小3、Sys uint64 //服务当初应用的零碎内存4、Lookups uint64 //被runtime监督的指针数5、Mallocs uint64 //服务malloc的次数6、Frees uint64 //服务回收的heap objects的字节数7、HeapAlloc uint64 //服务调配的堆内存字节数8、HeapSys uint64 //零碎调配的作为运行栈的内存9、HeapIdle uint64 //申请但未调配的堆内存或者回收了的堆内存（闲暇）字节数10、HeapInuse uint64 //正在应用的堆内存字节数10、HeapReleased uint64 //返回给OS的堆内存，相似C/C++中的free11、HeapObjects uint64 //堆内存块申请的量12、StackInuse uint64 //正在应用的栈字节数13、StackSys uint64 //零碎调配的作为运行栈的内存14、MSpanInuse uint64 //用于测试用的构造体应用的字节数15、MSpanSys uint64 //零碎为测试用的构造体调配的字节数16、MCacheInuse uint64 //mcache构造体申请的字节数(不会被视为垃圾回收)17、MCacheSys uint64 //操作系统申请的堆空间用于mcache的字节数18、BuckHashSys uint64 //用于分析桶散列表的堆空间19、GCSys uint64 //垃圾回收标记元信息应用的内存20、OtherSys uint64 //golang零碎架构占用的额定空间21、NextGC uint64 //垃圾回收器检视的内存大小22、LastGC uint64 // 垃圾回收器最初一次执行工夫。23、PauseTotalNs uint64 // 垃圾回收或者其余信息收集导致服务暂停的次数。24、PauseNs [256]uint64 //一个循环队列，记录最近垃圾回收零碎中断的工夫25、PauseEnd [256]uint64 //一个循环队列，记录最近垃圾回收零碎中断的工夫开始点。26、NumForcedGC uint32 //服务调用runtime.GC()强制应用垃圾回收的次数。27、GCCPUFraction float64 //垃圾回收占用服务CPU工作的工夫总和。如果有100个goroutine，垃圾回收的工夫为1S,那么就占用了100S。28、BySize //内存分配器应用状况以上参考golang程序的监控神器----expvar
社区同行开发的expvarmon工具，能够在命令行终端以图形化的形式实时展现特定的指标数据的变动，（expvarmon 即expvar monitor）
go get github.com/divan/expvarmon
启动方才的程序，而后执行如下命令，可实时查看利用指标变动 （期间能够进行不同qps的申请）
expvarmon -ports="http://localhost:6666/debug/vars" -i 1s
参考 给expvarmon插上数据长久化的“翅膀”
官网库或出名我的项目中的应用
src/net/http/triv.go 中应用了这个包
另外
golang.org/x/tools@v0.1.6/cmd/godoc/main.go
golang.org/x/tools@v0.1.6/go/internal/gccgoimporter/gccgoinstallation_test.go
go/test/bench/garbage/parser.go
也有应用
以及后面提到的expvarmon
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