From 41d7ebc5c56317ebb40f5071838f29bad372cb51 Mon Sep 17 00:00:00 2001
From: Diptanu Choudhury <diptanuc@gmail.com>
Date: Sun, 11 Dec 2016 22:58:28 -0800
Subject: [PATCH] Refactored hoststats collector

---
 client/client.go     | 14 +++-----------
 client/gc.go         |  1 +
 client/stats/host.go | 24 ++++++++++++++++++------
 3 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/client/client.go b/client/client.go
index ffdfc9df9..ba616f2b8 100644
--- a/client/client.go
+++ b/client/client.go
@@ -141,8 +141,6 @@ type Client struct {
 
 	// HostStatsCollector collects host resource usage stats
 	hostStatsCollector *stats.HostStatsCollector
-	resourceUsage      *stats.HostStats
-	resourceUsageLock  sync.RWMutex
 
 	shutdown     bool
 	shutdownCh   chan struct{}
@@ -481,9 +479,7 @@ func (c *Client) GetAllocStats(allocID string) (AllocStatsReporter, error) {
 
 // HostStats returns all the stats related to a Nomad client
 func (c *Client) LatestHostStats() *stats.HostStats {
-	c.resourceUsageLock.RLock()
-	defer c.resourceUsageLock.RUnlock()
-	return c.resourceUsage
+	return c.hostStatsCollector.Stats()
 }
 
 // GetAllocFS returns the AllocFS interface for the alloc dir of an allocation
@@ -2104,20 +2100,16 @@ func (c *Client) collectHostStats() {
 	for {
 		select {
 		case <-next.C:
-			ru, err := c.hostStatsCollector.Collect()
+			err := c.hostStatsCollector.Collect()
 			next.Reset(c.config.StatsCollectionInterval)
 			if err != nil {
 				c.logger.Printf("[WARN] client: error fetching host resource usage stats: %v", err)
 				continue
 			}
 
-			c.resourceUsageLock.Lock()
-			c.resourceUsage = ru
-			c.resourceUsageLock.Unlock()
-
 			// Publish Node metrics if operator has opted in
 			if c.config.PublishNodeMetrics {
-				c.emitStats(ru)
+				c.emitStats(c.hostStatsCollector.Stats())
 			}
 		case <-c.shutdownCh:
 			return
diff --git a/client/gc.go b/client/gc.go
index 2c2120832..eb66ab170 100644
--- a/client/gc.go
+++ b/client/gc.go
@@ -163,6 +163,7 @@ func (a *AllocGarbageCollector) MakeRoomFor(allocations []*structs.Allocation) e
 
 		ar := gcAlloc.allocRunner
 		alloc := ar.Alloc()
+		a.logger.Printf("[INFO] client: garbage collecting allocation %v", alloc.ID)
 		ar.Destroy()
 		diskCleared += alloc.Resources.DiskMB
 		if diskCleared >= totalResource.DiskMB {
diff --git a/client/stats/host.go b/client/stats/host.go
index 49fb0fdcb..d1cd6ac8d 100644
--- a/client/stats/host.go
+++ b/client/stats/host.go
@@ -4,6 +4,7 @@ import (
 	"log"
 	"math"
 	"runtime"
+	"sync"
 	"time"
 
 	"github.com/shirou/gopsutil/cpu"
@@ -58,6 +59,8 @@ type HostStatsCollector struct {
 	numCores        int
 	statsCalculator map[string]*HostCpuStatsCalculator
 	logger          *log.Logger
+	hostStats       *HostStats
+	hostStatsLock   sync.RWMutex
 }
 
 // NewHostStatsCollector returns a HostStatsCollector
@@ -73,11 +76,11 @@ func NewHostStatsCollector(logger *log.Logger) *HostStatsCollector {
 }
 
 // Collect collects stats related to resource usage of a host
-func (h *HostStatsCollector) Collect() (*HostStats, error) {
+func (h *HostStatsCollector) Collect() error {
 	hs := &HostStats{Timestamp: time.Now().UTC().UnixNano()}
 	memStats, err := mem.VirtualMemory()
 	if err != nil {
-		return nil, err
+		return err
 	}
 	hs.Memory = &MemoryStats{
 		Total:     memStats.Total,
@@ -89,7 +92,7 @@ func (h *HostStatsCollector) Collect() (*HostStats, error) {
 	ticksConsumed := 0.0
 	cpuStats, err := cpu.Times(true)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	cs := make([]*CPUStats, len(cpuStats))
 	for idx, cpuStat := range cpuStats {
@@ -113,7 +116,7 @@ func (h *HostStatsCollector) Collect() (*HostStats, error) {
 
 	partitions, err := disk.Partitions(false)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	var diskStats []*DiskStats
 	for _, partition := range partitions {
@@ -143,11 +146,20 @@ func (h *HostStatsCollector) Collect() (*HostStats, error) {
 
 	uptime, err := host.Uptime()
 	if err != nil {
-		return nil, err
+		return err
 	}
 	hs.Uptime = uptime
 
-	return hs, nil
+	h.hostStatsLock.Lock()
+	defer h.hostStatsLock.Unlock()
+	h.hostStats = hs
+	return nil
+}
+
+func (h *HostStatsCollector) Stats() *HostStats {
+	h.hostStatsLock.RLock()
+	defer h.hostStatsLock.RUnlock()
+	return h.hostStats
 }
 
 // HostCpuStatsCalculator calculates cpu usage percentages