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// Copyright 2018, OpenCensus Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package metric
import (
"math"
"sync"
"sync/atomic"
"time"
"go.opencensus.io/internal/tagencoding"
"go.opencensus.io/metric/metricdata"
)
// gauge represents a quantity that can go up an down, for example queue depth
// or number of outstanding requests.
//
// gauge maintains a value for each combination of of label values passed to
// the Set or Add methods.
//
// gauge should not be used directly, use Float64Gauge or Int64Gauge.
type gauge struct {
vals sync.Map
desc metricdata.Descriptor
start time.Time
keys []string
gType gaugeType
}
type gaugeEntry interface {
read(t time.Time) metricdata.Point
}
// Read returns the current values of the gauge as a metric for export.
func (g *gauge) read() *metricdata.Metric {
now := time.Now()
m := &metricdata.Metric{
Descriptor: g.desc,
}
g.vals.Range(func(k, v interface{}) bool {
entry := v.(gaugeEntry)
key := k.(string)
labelVals := g.labelValues(key)
m.TimeSeries = append(m.TimeSeries, &metricdata.TimeSeries{
StartTime: now, // Gauge value is instantaneous.
LabelValues: labelVals,
Points: []metricdata.Point{
entry.read(now),
},
})
return true
})
return m
}
func (g *gauge) mapKey(labelVals []metricdata.LabelValue) string {
vb := &tagencoding.Values{}
for _, v := range labelVals {
b := make([]byte, 1, len(v.Value)+1)
if v.Present {
b[0] = 1
b = append(b, []byte(v.Value)...)
}
vb.WriteValue(b)
}
return string(vb.Bytes())
}
func (g *gauge) labelValues(s string) []metricdata.LabelValue {
vals := make([]metricdata.LabelValue, 0, len(g.keys))
vb := &tagencoding.Values{Buffer: []byte(s)}
for range g.keys {
v := vb.ReadValue()
if v[0] == 0 {
vals = append(vals, metricdata.LabelValue{})
} else {
vals = append(vals, metricdata.NewLabelValue(string(v[1:])))
}
}
return vals
}
func (g *gauge) entryForValues(labelVals []metricdata.LabelValue, newEntry func() gaugeEntry) (interface{}, error) {
if len(labelVals) != len(g.keys) {
return nil, errKeyValueMismatch
}
mapKey := g.mapKey(labelVals)
if entry, ok := g.vals.Load(mapKey); ok {
return entry, nil
}
entry, _ := g.vals.LoadOrStore(mapKey, newEntry())
return entry, nil
}
func (g *gauge) upsertEntry(labelVals []metricdata.LabelValue, newEntry func() gaugeEntry) error {
if len(labelVals) != len(g.keys) {
return errKeyValueMismatch
}
mapKey := g.mapKey(labelVals)
g.vals.Delete(mapKey)
g.vals.Store(mapKey, newEntry())
return nil
}
// Float64Gauge represents a float64 value that can go up and down.
//
// Float64Gauge maintains a float64 value for each combination of of label values
// passed to the Set or Add methods.
type Float64Gauge struct {
g gauge
}
// Float64Entry represents a single value of the gauge corresponding to a set
// of label values.
type Float64Entry struct {
val uint64 // needs to be uint64 for atomic access, interpret with math.Float64frombits
}
func (e *Float64Entry) read(t time.Time) metricdata.Point {
v := math.Float64frombits(atomic.LoadUint64(&e.val))
if v < 0 {
v = 0
}
return metricdata.NewFloat64Point(t, v)
}
// GetEntry returns a gauge entry where each key for this gauge has the value
// given.
//
// The number of label values supplied must be exactly the same as the number
// of keys supplied when this gauge was created.
func (g *Float64Gauge) GetEntry(labelVals ...metricdata.LabelValue) (*Float64Entry, error) {
entry, err := g.g.entryForValues(labelVals, func() gaugeEntry {
return &Float64Entry{}
})
if err != nil {
return nil, err
}
return entry.(*Float64Entry), nil
}
// Set sets the gauge entry value to val.
func (e *Float64Entry) Set(val float64) {
atomic.StoreUint64(&e.val, math.Float64bits(val))
}
// Add increments the gauge entry value by val.
func (e *Float64Entry) Add(val float64) {
var swapped bool
for !swapped {
oldVal := atomic.LoadUint64(&e.val)
newVal := math.Float64bits(math.Float64frombits(oldVal) + val)
swapped = atomic.CompareAndSwapUint64(&e.val, oldVal, newVal)
}
}
// Int64Gauge represents a int64 gauge value that can go up and down.
//
// Int64Gauge maintains an int64 value for each combination of label values passed to the
// Set or Add methods.
type Int64Gauge struct {
g gauge
}
// Int64GaugeEntry represents a single value of the gauge corresponding to a set
// of label values.
type Int64GaugeEntry struct {
val int64
}
func (e *Int64GaugeEntry) read(t time.Time) metricdata.Point {
v := atomic.LoadInt64(&e.val)
if v < 0 {
v = 0.0
}
return metricdata.NewInt64Point(t, v)
}
// GetEntry returns a gauge entry where each key for this gauge has the value
// given.
//
// The number of label values supplied must be exactly the same as the number
// of keys supplied when this gauge was created.
func (g *Int64Gauge) GetEntry(labelVals ...metricdata.LabelValue) (*Int64GaugeEntry, error) {
entry, err := g.g.entryForValues(labelVals, func() gaugeEntry {
return &Int64GaugeEntry{}
})
if err != nil {
return nil, err
}
return entry.(*Int64GaugeEntry), nil
}
// Set sets the value of the gauge entry to the provided value.
func (e *Int64GaugeEntry) Set(val int64) {
atomic.StoreInt64(&e.val, val)
}
// Add increments the current gauge entry value by val, which may be negative.
func (e *Int64GaugeEntry) Add(val int64) {
atomic.AddInt64(&e.val, val)
}
// Int64DerivedGauge represents int64 gauge value that is derived from an object.
//
// Int64DerivedGauge maintains objects for each combination of label values.
// These objects implement Int64DerivedGaugeInterface to read instantaneous value
// representing the object.
type Int64DerivedGauge struct {
g gauge
}
type int64DerivedGaugeEntry struct {
fn func() int64
}
func (e *int64DerivedGaugeEntry) read(t time.Time) metricdata.Point {
return metricdata.NewInt64Point(t, e.fn())
}
// UpsertEntry inserts or updates a derived gauge entry for the given set of label values.
// The object for which this gauge entry is inserted or updated, must implement func() int64
//
// It returns an error if
// 1. The number of label values supplied are not the same as the number
// of keys supplied when this gauge was created.
// 2. fn func() int64 is nil.
func (g *Int64DerivedGauge) UpsertEntry(fn func() int64, labelVals ...metricdata.LabelValue) error {
if fn == nil {
return errInvalidParam
}
return g.g.upsertEntry(labelVals, func() gaugeEntry {
return &int64DerivedGaugeEntry{fn}
})
}
// Float64DerivedGauge represents float64 gauge value that is derived from an object.
//
// Float64DerivedGauge maintains objects for each combination of label values.
// These objects implement Float64DerivedGaugeInterface to read instantaneous value
// representing the object.
type Float64DerivedGauge struct {
g gauge
}
type float64DerivedGaugeEntry struct {
fn func() float64
}
func (e *float64DerivedGaugeEntry) read(t time.Time) metricdata.Point {
return metricdata.NewFloat64Point(t, e.fn())
}
// UpsertEntry inserts or updates a derived gauge entry for the given set of label values.
// The object for which this gauge entry is inserted or updated, must implement func() float64
//
// It returns an error if
// 1. The number of label values supplied are not the same as the number
// of keys supplied when this gauge was created.
// 2. fn func() float64 is nil.
func (g *Float64DerivedGauge) UpsertEntry(fn func() float64, labelVals ...metricdata.LabelValue) error {
if fn == nil {
return errInvalidParam
}
return g.g.upsertEntry(labelVals, func() gaugeEntry {
return &float64DerivedGaugeEntry{fn}
})
}