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package missinggo
import (
"sync"
"time"
)
// Monotonic time represents time since an arbitrary point in the past, where
// the concept of now is only ever moving in a positive direction.
type MonotonicTime struct {
skewedStdTime time.Time
}
func (me MonotonicTime) Sub(other MonotonicTime) time.Duration {
return me.skewedStdTime.Sub(other.skewedStdTime)
}
var (
stdNowFunc = time.Now
monotonicMu sync.Mutex
lastStdNow time.Time
monotonicSkew time.Duration
)
func skewedStdNow() time.Time {
monotonicMu.Lock()
defer monotonicMu.Unlock()
stdNow := stdNowFunc()
if !lastStdNow.IsZero() && stdNow.Before(lastStdNow) {
monotonicSkew += lastStdNow.Sub(stdNow)
}
lastStdNow = stdNow
return stdNow.Add(monotonicSkew)
}
// Consecutive calls always produce the same or greater time than previous
// calls.
func MonotonicNow() MonotonicTime {
return MonotonicTime{skewedStdNow()}
}
func MonotonicSince(since MonotonicTime) (ret time.Duration) {
return skewedStdNow().Sub(since.skewedStdTime)
}
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