Do not create a global statsd "previous instance"

this basically reverts influxdata#887

at some point we might want to do some special handling of reloading
plugins and keeping their state intact, but that will need to be done at
a higher level, and in a way that is thread-safe for multiple input
plugins of the same type.

Unfortunately this is a rather large feature that will not have a quick
fix available for it.

fixes influxdata#1975
fixes influxdata#2102

CHANGELOG.md

@@ -45,6 +45,15 @@ plugins, not just statsd.
 will change te default behavior for users who were not specifying these parameters
 in their config file.
 
+- The StatsD plugin will also no longer save it's state on a service reload.
+Essentially we have reverted PR [#887](https://github.com/influxdata/telegraf/pull/887).
+The reason for this is that saving the state in a global variable is not
+thread-safe (see [#1975](https://github.com/influxdata/telegraf/issues/1975) & [#2102](https://github.com/influxdata/telegraf/issues/2102)),
+and this creates issues if users want to define multiple instances
+of the statsd plugin. Saving state on reload may be considered in the future,
+but this would need to be implemented at a higher level and applied to all
+plugins, not just statsd.
+
 ### Features
 
 - [#2123](https://github.com/influxdata/telegraf/pull/2123): Fix improper calculation of CPU percentages
@@ -91,6 +100,7 @@ in their config file.
 - [#1449](https://github.com/influxdata/telegraf/issues/1449): MongoDB plugin always shows 0 replication lag.
 - [#1825](https://github.com/influxdata/telegraf/issues/1825): Consul plugin: add check_id as a tag in metrics to avoid overwrites.
 - [#1973](https://github.com/influxdata/telegraf/issues/1973): Partial fix: logparser CLF pattern with IPv6 addresses.
+- [#1975](https://github.com/influxdata/telegraf/issues/1975) & [#2102](https://github.com/influxdata/telegraf/issues/2102): Fix thread-safety when using multiple instances of the statsd input plugin.
 
 ## v1.1.2 [2016-12-12]
 

plugins/inputs/statsd/statsd.go

@@ -32,8 +32,6 @@ var dropwarn = "E! Error: statsd message queue full. " +
 	"We have dropped %d messages so far. " +
 	"You may want to increase allowed_pending_messages in the config\n"
 
-var prevInstance *Statsd
-
 type Statsd struct {
 	// Address & Port to serve from
 	ServiceAddress string
@@ -244,17 +242,10 @@ func (s *Statsd) Start(_ telegraf.Accumulator) error {
 	s.done = make(chan struct{})
 	s.in = make(chan []byte, s.AllowedPendingMessages)
 
-	if prevInstance == nil {
-		s.gauges = make(map[string]cachedgauge)
-		s.counters = make(map[string]cachedcounter)
-		s.sets = make(map[string]cachedset)
-		s.timings = make(map[string]cachedtimings)
-	} else {
-		s.gauges = prevInstance.gauges
-		s.counters = prevInstance.counters
-		s.sets = prevInstance.sets
-		s.timings = prevInstance.timings
-	}
+	s.gauges = make(map[string]cachedgauge)
+	s.counters = make(map[string]cachedcounter)
+	s.sets = make(map[string]cachedset)
+	s.timings = make(map[string]cachedtimings)
 
 	if s.ConvertNames {
 		log.Printf("I! WARNING statsd: convert_names config option is deprecated," +
@@ -271,7 +262,6 @@ func (s *Statsd) Start(_ telegraf.Accumulator) error {
 	// Start the line parser
 	go s.parser()
 	log.Printf("I! Started the statsd service on %s\n", s.ServiceAddress)
-	prevInstance = s
 	return nil
 }