From eaad4fa3c4ec54e0546e2862ed487c29463cf640 Mon Sep 17 00:00:00 2001
From: yanyiwu <i@yanyiwu.com>
Date: Mon, 20 Apr 2015 22:05:20 +0800
Subject: [PATCH] BUG FIXED: RoundRobinCounter.Add will cause a out of range
 crash when index >= len(rrc.Values)

---
 go/stats/duration_counter.go      | 11 ++++-------
 go/stats/duration_counter_test.go | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 7 deletions(-)
 create mode 100644 go/stats/duration_counter_test.go

diff --git a/go/stats/duration_counter.go b/go/stats/duration_counter.go
index 50a8bce43..69c8be61d 100644
--- a/go/stats/duration_counter.go
+++ b/go/stats/duration_counter.go
@@ -23,14 +23,11 @@ func NewRoundRobinCounter(slots int) *RoundRobinCounter {
 	return &RoundRobinCounter{LastIndex: -1, Values: make([]int64, slots), Counts: make([]int64, slots)}
 }
 func (rrc *RoundRobinCounter) Add(index int, val int64) {
+	if index >= len(rrc.Values) {
+		return
+	}
 	for rrc.LastIndex != index {
-		rrc.LastIndex++
-		if rrc.LastIndex >= len(rrc.Values) {
-			if index >= len(rrc.Values) {
-				break //just avoid endless loop
-			}
-			rrc.LastIndex = 0
-		}
+		rrc.LastIndex = (rrc.LastIndex + 1) % len(rrc.Values)
 		rrc.Values[rrc.LastIndex] = 0
 		rrc.Counts[rrc.LastIndex] = 0
 	}
diff --git a/go/stats/duration_counter_test.go b/go/stats/duration_counter_test.go
new file mode 100644
index 000000000..aa9d61c87
--- /dev/null
+++ b/go/stats/duration_counter_test.go
@@ -0,0 +1,19 @@
+package stats
+
+import "testing"
+
+func TestRobinCounter(t *testing.T) {
+	rrc := NewRoundRobinCounter(60)
+	rrc.Add(0, 1)
+	rrc.Add(50, 2)
+	if rrc.Count() != 2 {
+		t.Fatal()
+	}
+	if rrc.Sum() != 3 {
+		t.Fatal()
+	}
+	/*
+		index out of range
+	*/
+	rrc.Add(61, 1)
+}