tailscale/util/clientmetric/clientmetric.go

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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package clientmetric provides client-side metrics whose values
// get occasionally logged.
package clientmetric
import (
"bytes"
"encoding/binary"
"encoding/hex"
"fmt"
"io"
"sort"
"strings"
"sync"
"sync/atomic"
"time"
)
var (
mu sync.Mutex // guards vars in this block
metrics = map[string]*Metric{}
numWireID int // how many wireIDs have been allocated
lastDelta time.Time // time of last call to EncodeLogTailMetricsDelta
sortedDirty bool // whether sorted needs to be rebuilt
sorted []*Metric // by name
lastLogVal []scanEntry // by Metric.regIdx
unsorted []*Metric // by Metric.regIdx
// valFreeList is a set of free contiguous int64s whose
// element addresses get assigned to Metric.v.
// Any memory address in len(valFreeList) is free for use.
// They're contiguous to reduce cache churn during diff scans.
// When out of length, a new backing array is made.
valFreeList []int64
)
// scanEntry contains the minimal data needed for quickly scanning
// memory for changed values. It's small to reduce memory pressure.
type scanEntry struct {
v *int64 // Metric.v
lastLogged int64 // last logged value
}
// Type is a metric type: counter or gauge.
type Type uint8
const (
TypeGauge Type = iota
TypeCounter
)
// Metric is an integer metric value that's tracked over time.
//
// It's safe for concurrent use.
type Metric struct {
v *int64 // atomic; the metric value
regIdx int // index into lastLogVal and unsorted
name string
typ Type
// The following fields are owned by the package-level 'mu':
// wireID is the lazily-allocated "wire ID". Until a metric is encoded
// in the logs (by EncodeLogTailMetricsDelta), it has no wireID. This
// ensures that unused metrics don't waste valuable low numbers, which
// encode with varints with fewer bytes.
wireID int
// lastNamed is the last time the name of this metric was
// written on the wire.
lastNamed time.Time
}
func (m *Metric) Name() string { return m.name }
func (m *Metric) Value() int64 { return atomic.LoadInt64(m.v) }
func (m *Metric) Type() Type { return m.typ }
// Add increments m's value by n.
//
// If m is of type counter, n should not be negative.
func (m *Metric) Add(n int64) {
atomic.AddInt64(m.v, n)
}
// Set sets m's value to v.
//
// If m is of type counter, Set should not be used.
func (m *Metric) Set(v int64) {
atomic.StoreInt64(m.v, v)
}
// Publish registers a metric in the global map.
// It panics if the name is a duplicate anywhere in the process.
func (m *Metric) Publish() {
mu.Lock()
defer mu.Unlock()
if m.name == "" {
panic("unnamed Metric")
}
if _, dup := metrics[m.name]; dup {
panic("duplicate metric " + m.name)
}
metrics[m.name] = m
sortedDirty = true
if len(valFreeList) == 0 {
valFreeList = make([]int64, 256)
}
m.v = &valFreeList[0]
valFreeList = valFreeList[1:]
m.regIdx = len(unsorted)
unsorted = append(unsorted, m)
lastLogVal = append(lastLogVal, scanEntry{v: m.v})
}
// Metrics returns the sorted list of metrics.
//
// The returned slice should not be mutated.
func Metrics() []*Metric {
mu.Lock()
defer mu.Unlock()
if sortedDirty {
sortedDirty = false
sorted = make([]*Metric, 0, len(metrics))
for _, m := range metrics {
sorted = append(sorted, m)
}
sort.Slice(sorted, func(i, j int) bool {
return sorted[i].name < sorted[j].name
})
}
return sorted
}
// NewUnpublished initializes a new Metric without calling Publish on
// it.
func NewUnpublished(name string, typ Type) *Metric {
if i := strings.IndexFunc(name, isIllegalMetricRune); name == "" || i != -1 {
panic(fmt.Sprintf("illegal metric name %q (index %v)", name, i))
}
return &Metric{
name: name,
typ: typ,
}
}
func isIllegalMetricRune(r rune) bool {
return !(r >= 'a' && r <= 'z' ||
r >= 'A' && r <= 'Z' ||
r >= '0' && r <= '9' ||
r == '_')
}
// NewCounter returns a new metric that can only increment.
func NewCounter(name string) *Metric {
m := NewUnpublished(name, TypeCounter)
m.Publish()
return m
}
// NewGauge returns a new metric that can both increment and decrement.
func NewGauge(name string) *Metric {
m := NewUnpublished(name, TypeGauge)
m.Publish()
return m
}
// WritePrometheusExpositionFormat writes all client metrics to w in
// the Prometheus text-based exposition format.
//
// See https://github.com/prometheus/docs/blob/main/content/docs/instrumenting/exposition_formats.md
func WritePrometheusExpositionFormat(w io.Writer) {
for _, m := range Metrics() {
switch m.Type() {
case TypeGauge:
fmt.Fprintf(w, "# TYPE %s gauge\n", m.Name())
case TypeCounter:
fmt.Fprintf(w, "# TYPE %s counter\n", m.Name())
}
fmt.Fprintf(w, "%s %v\n", m.Name(), m.Value())
}
}
const (
// metricLogNameFrequency is how often a metric's name=>id
// mapping is redundantly put in the logs. In other words,
// this is how how far in the logs you need to fetch from a
// given point in time to recompute the metrics at that point
// in time.
metricLogNameFrequency = 4 * time.Hour
// minMetricEncodeInterval is the minimum interval that the
// metrics will be scanned for changes before being encoded
// for logtail.
minMetricEncodeInterval = 15 * time.Second
)
// EncodeLogTailMetricsDelta return an encoded string representing the metrics
// differences since the previous call.
//
// It implements the requirements of a logtail.Config.MetricsDelta
// func. Notably, its output is safe to embed in a JSON string literal
// without further escaping.
//
// The current encoding is:
// * name immediately following metric:
// 'N' + hex(varint(len(name))) + name
// * set value of a metric:
// 'S' + hex(varint(wireid)) + hex(varint(value))
// * increment a metric: (decrements if negative)
// 'I' + hex(varint(wireid)) + hex(varint(value))
func EncodeLogTailMetricsDelta() string {
mu.Lock()
defer mu.Unlock()
now := time.Now()
if !lastDelta.IsZero() && now.Sub(lastDelta) < minMetricEncodeInterval {
return ""
}
lastDelta = now
var enc *deltaEncBuf // lazy
for i, ent := range lastLogVal {
val := atomic.LoadInt64(ent.v)
delta := val - ent.lastLogged
if delta == 0 {
continue
}
lastLogVal[i].lastLogged = val
m := unsorted[i]
if enc == nil {
enc = deltaPool.Get().(*deltaEncBuf)
enc.buf.Reset()
}
if m.wireID == 0 {
numWireID++
m.wireID = numWireID
}
if m.lastNamed.IsZero() || now.Sub(m.lastNamed) > metricLogNameFrequency {
enc.writeName(m.Name())
m.lastNamed = now
enc.writeValue(m.wireID, val)
} else {
enc.writeDelta(m.wireID, delta)
}
}
if enc == nil {
return ""
}
defer deltaPool.Put(enc)
return enc.buf.String()
}
var deltaPool = &sync.Pool{
New: func() interface{} {
return new(deltaEncBuf)
},
}
// deltaEncBuf encodes metrics per the format described
// on EncodeLogTailMetricsDelta above.
type deltaEncBuf struct {
buf bytes.Buffer
scratch [binary.MaxVarintLen64]byte
}
// writeName writes a "name" (N) record to the buffer, which notes
// that the immediately following record's wireID has the provided
// name.
func (b *deltaEncBuf) writeName(name string) {
b.buf.WriteByte('N')
b.writeHexVarint(int64(len(name)))
b.buf.WriteString(name)
}
// writeDelta writes a "set" (S) record to the buffer, noting that the
// metric with the given wireID now has value v.
func (b *deltaEncBuf) writeValue(wireID int, v int64) {
b.buf.WriteByte('S')
b.writeHexVarint(int64(wireID))
b.writeHexVarint(v)
}
// writeDelta writes an "increment" (I) delta value record to the
// buffer, noting that the metric with the given wireID now has a
// value that's v larger (or smaller if v is negative).
func (b *deltaEncBuf) writeDelta(wireID int, v int64) {
b.buf.WriteByte('I')
b.writeHexVarint(int64(wireID))
b.writeHexVarint(v)
}
// writeHexVarint writes v to the buffer as a hex-encoded varint.
func (b *deltaEncBuf) writeHexVarint(v int64) {
n := binary.PutVarint(b.scratch[:], v)
hexLen := n * 2
oldLen := b.buf.Len()
b.buf.Grow(hexLen)
hexBuf := b.buf.Bytes()[oldLen : oldLen+hexLen]
hex.Encode(hexBuf, b.scratch[:n])
b.buf.Write(hexBuf)
}