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continuous_meter.go
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continuous_meter.go
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// (c) 2019-2020, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package uptime
import (
"math"
"time"
)
var (
convertEToBase2 = math.Log(2)
_ Meter = &continuousMeter{}
_ Factory = &ContinuousFactory{}
)
// ContinuousFactory implements the Factory interface by returning a continuous
// time meter.
type ContinuousFactory struct{}
// New implements the Factory interface.
func (ContinuousFactory) New(halflife time.Duration) Meter {
return NewMeter(halflife)
}
type continuousMeter struct {
running bool
halflife float64
value float64
lastUpdated time.Time
}
// NewMeter returns a new Meter with the provided halflife
func NewMeter(halflife time.Duration) Meter {
return &continuousMeter{
halflife: float64(halflife) / convertEToBase2,
}
}
func (a *continuousMeter) Start(currentTime time.Time) {
a.update(currentTime, true)
}
func (a *continuousMeter) Stop(currentTime time.Time) {
a.update(currentTime, false)
}
func (a *continuousMeter) update(currentTime time.Time, running bool) {
if a.running == running {
return
}
a.Read(currentTime)
a.running = running
}
func (a *continuousMeter) Read(currentTime time.Time) float64 {
timeSincePreviousUpdate := a.lastUpdated.Sub(currentTime)
if timeSincePreviousUpdate >= 0 {
return a.value
}
a.lastUpdated = currentTime
factor := math.Exp(float64(timeSincePreviousUpdate) / a.halflife)
a.value *= factor
if a.running {
a.value += 1 - factor
}
return a.value
}