From e06f1e0323255c57a34d86960c86c028bb34e7f9 Mon Sep 17 00:00:00 2001
From: Cameron Sparr <cameronsparr@gmail.com>
Date: Tue, 17 Jan 2017 15:01:12 -0800
Subject: [PATCH] Run scheduled flushes in background

doing this unblocks incoming metrics while waiting for a flush to take
place.

we have to create a semaphore so that we can
'skip' flushes that try to run while a flush is already running.

closes #2262
---
 CHANGELOG.md   |  1 +
 agent/agent.go | 15 +++++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c9c85953f..fd37abcb8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 ### Bugfixes
 
 - [#2077](https://github.com/influxdata/telegraf/issues/2077): SQL Server Input - Arithmetic overflow error converting numeric to data type int.
+- [#2262](https://github.com/influxdata/telegraf/issues/2262): Flush jitter can inhibit metric collection.
 
 ## v1.2 [2017-01-00]
 
diff --git a/agent/agent.go b/agent/agent.go
index ab64154e0..a9e42643a 100644
--- a/agent/agent.go
+++ b/agent/agent.go
@@ -286,6 +286,7 @@ func (a *Agent) flusher(shutdown chan struct{}, metricC chan telegraf.Metric) er
 	}()
 
 	ticker := time.NewTicker(a.Config.Agent.FlushInterval.Duration)
+	semaphore := make(chan struct{}, 1)
 	for {
 		select {
 		case <-shutdown:
@@ -295,8 +296,18 @@ func (a *Agent) flusher(shutdown chan struct{}, metricC chan telegraf.Metric) er
 			a.flush()
 			return nil
 		case <-ticker.C:
-			internal.RandomSleep(a.Config.Agent.FlushJitter.Duration, shutdown)
-			a.flush()
+			go func() {
+				select {
+				case semaphore <- struct{}{}:
+					internal.RandomSleep(a.Config.Agent.FlushJitter.Duration, shutdown)
+					a.flush()
+					<-semaphore
+				default:
+					// skipping this flush because one is already happening
+					log.Println("W! Skipping a scheduled flush because there is" +
+						" already a flush ongoing.")
+				}
+			}()
 		case metric := <-metricC:
 			// NOTE potential bottleneck here as we put each metric through the
 			// processors serially.