From 8a1c6440d5ecea16bca03c41b46d570e61936d22 Mon Sep 17 00:00:00 2001
From: Ashray Jain <ashrayj@palantir.com>
Date: Sat, 19 Jan 2019 13:59:00 +0000
Subject: [PATCH] Rescale samples on reads too

Previously, we were only rescaling on updates. This meant that
histograms would latch on to last updated values and stay at those
values until the next update for a reader who reads the histogram
periodically instead of decaying with time.
---
 sample.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sample.go b/sample.go
index fecee5e..1546486 100644
--- a/sample.go
+++ b/sample.go
@@ -146,6 +146,7 @@ func (s *ExpDecaySample) Update(v int64) {
 func (s *ExpDecaySample) Values() []int64 {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
+	s.rescaleIfNeeded(time.Now())
 	vals := s.values.Values()
 	values := make([]int64, len(vals))
 	for i, v := range vals {
@@ -164,6 +165,7 @@ func (s *ExpDecaySample) Variance() float64 {
 func (s *ExpDecaySample) update(t time.Time, v int64) {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
+	s.rescaleIfNeeded(t)
 	s.count++
 	if s.values.Size() == s.reservoirSize {
 		s.values.Pop()
@@ -172,6 +174,9 @@ func (s *ExpDecaySample) update(t time.Time, v int64) {
 		k: math.Exp(t.Sub(s.t0).Seconds()*s.alpha) / rand.Float64(),
 		v: v,
 	})
+}
+
+func (s *ExpDecaySample) rescaleIfNeeded(t time.Time) {
 	if t.After(s.t1) {
 		values := s.values.Values()
 		t0 := s.t0