From 4bffea4f107e21cc48498f8974d5142bb3f0cac7 Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Tue, 24 Jul 2018 13:36:12 +0200
Subject: [PATCH] Fix: Limit historical performance data

in order not to consume an endless amount of memory

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 .gitignore |  1 +
 main.go    | 18 ++++++++++++------
 ring.go    | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 64 insertions(+), 6 deletions(-)
 create mode 100644 ring.go

diff --git a/.gitignore b/.gitignore
index fdeda75..f556e37 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 request-log
+webcheck
diff --git a/main.go b/main.go
index 68f9efb..ea62e1b 100644
--- a/main.go
+++ b/main.go
@@ -19,7 +19,10 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-const dateFormat = time.RFC1123
+const (
+	dateFormat             = time.RFC1123
+	numHistoricalDurations = 300
+)
 
 var (
 	cfg = struct {
@@ -54,7 +57,7 @@ const (
 
 type checkResult struct {
 	DumpFile  string
-	Durations []time.Duration
+	Durations *ringDuration
 	Message   string
 	Start     time.Time
 	Status    checkStatus
@@ -64,8 +67,11 @@ type checkResult struct {
 }
 
 func newCheckResult(status checkStatus, message string, duration time.Duration) *checkResult {
+	r := newRingDuration(numHistoricalDurations)
+	r.SetNext(duration)
+
 	return &checkResult{
-		Durations: []time.Duration{duration},
+		Durations: r,
 		Message:   message,
 		Start:     time.Now(),
 		Status:    status,
@@ -76,7 +82,7 @@ func (c *checkResult) AddDuration(d time.Duration) {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 
-	c.Durations = append(c.Durations, d)
+	c.Durations.SetNext(d)
 }
 
 func (c *checkResult) DurationStats() string {
@@ -84,7 +90,7 @@ func (c *checkResult) DurationStats() string {
 	defer c.lock.RUnlock()
 
 	var (
-		s             = stats.LoadRawData(c.Durations)
+		s             = stats.LoadRawData(c.Durations.GetAll())
 		min, avg, max float64
 		err           error
 	)
@@ -176,7 +182,7 @@ func main() {
 				lastResult.DumpFile = fn
 			}
 		} else {
-			lastResult.AddDuration(result.Durations[0])
+			lastResult.AddDuration(result.Durations.GetCurrent())
 		}
 
 		lastResult.Print()
diff --git a/ring.go b/ring.go
new file mode 100644
index 0000000..fa51a02
--- /dev/null
+++ b/ring.go
@@ -0,0 +1,51 @@
+package main
+
+import (
+	"sync"
+	"time"
+)
+
+type ringDuration struct {
+	store   []time.Duration
+	current int
+
+	lock sync.RWMutex
+}
+
+func newRingDuration(maxLen int) *ringDuration {
+	return &ringDuration{
+		store:   make([]time.Duration, 0, maxLen),
+		current: -1, // Initial value to start the ring with element 0
+	}
+}
+
+func (r *ringDuration) SetNext(i time.Duration) {
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
+	next := r.current + 1
+	if next == cap(r.store) {
+		next = 0
+	}
+
+	if next == len(r.store) {
+		r.store = append(r.store, 0)
+	}
+
+	r.store[next] = i
+	r.current = next
+}
+
+func (r *ringDuration) GetAll() []time.Duration {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	return r.store
+}
+
+func (r *ringDuration) GetCurrent() time.Duration {
+	r.lock.RLock()
+	defer r.lock.RUnlock()
+
+	return r.store[r.current]
+}