From ff77a29b0ae45d9ea8d5cf988e441a8a49db7b3a Mon Sep 17 00:00:00 2001
From: Justin Li <jli.justinli@gmail.com>
Date: Tue, 22 Jul 2014 12:42:56 -0400
Subject: [PATCH] Thread safe, but unsafe

---
 stats/percentile.go | 24 ++++++++++++++++--------
 stats/stats.go      | 11 ++++++++++-
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/stats/percentile.go b/stats/percentile.go
index 9ca3a4a..534a447 100644
--- a/stats/percentile.go
+++ b/stats/percentile.go
@@ -3,6 +3,8 @@ package stats
 import (
 	"math"
 	"sort"
+	"sync/atomic"
+	"unsafe"
 )
 
 type Percentile struct {
@@ -10,17 +12,23 @@ type Percentile struct {
 
 	samples int64
 	offset  int64
-	values  []float64
+
+	values []float64
+	value  *unsafe.Pointer
 }
 
 func NewPercentile(percentile float64, sampleWindow int) *Percentile {
+	initial := 0
+	ptr := unsafe.Pointer(&initial)
+
 	return &Percentile{
 		percentile: percentile,
-		values:     make([]float64, 0, sampleWindow),
+
+		values: make([]float64, 0, sampleWindow),
+		value:  &ptr,
 	}
 }
 
-// Not thread safe.
 func (p *Percentile) AddSample(sample float64) {
 	p.samples++
 
@@ -55,14 +63,14 @@ func (p *Percentile) AddSample(sample float64) {
 		copy(p.values[idx+1:], p.values[idx:])
 		p.values[idx] = sample
 	}
+
+	value := p.values[p.index()]
+	atomic.SwapPointer(p.value, unsafe.Pointer(&value))
 }
 
 func (p *Percentile) Value() float64 {
-	if len(p.values) == 0 {
-		return 0
-	}
-
-	return p.values[p.index()]
+	pointer := atomic.LoadPointer(p.value)
+	return *(*float64)(pointer)
 }
 
 func (p *Percentile) index() int64 {
diff --git a/stats/stats.go b/stats/stats.go
index 99d460a..8ea9777 100644
--- a/stats/stats.go
+++ b/stats/stats.go
@@ -106,6 +106,10 @@ func (s *Stats) RecordEvent(event int) {
 	s.events <- event
 }
 
+func (s *Stats) RecordTiming(event int, duration time.Duration) {
+	// s.timingEvents <- event
+}
+
 func (s *Stats) handleEvents() {
 	for event := range s.events {
 		switch event {
@@ -178,7 +182,12 @@ func (s *Stats) handleEvents() {
 	}
 }
 
-// RecordEvent broadcasts an event to the default stats tracking.
+// RecordEvent broadcasts an event to the default stats queue.
 func RecordEvent(event int) {
 	DefaultStats.RecordEvent(event)
 }
+
+// RecordTiming broadcasts a timing event to the default stats queue.
+func RecordTiming(event int, duration time.Duration) {
+	DefaultStats.RecordTiming(event, duration)
+}