Refactor Shutdown into a separate interface to revert breaking change.

inmem.go

@@ -230,10 +230,6 @@ func (i *InmemSink) AddSampleWithLabels(key []string, val float32, labels []Labe
 	agg.Ingest(float64(val), i.rateDenom)
 }
 
-func (i *InmemSink) Shutdown() {
-	// Do nothing. InmemSink does not have cleanup associated with shutdown.
-}
-
 // Data is used to retrieve all the aggregated metrics
 // Intervals may be in use, and a read lock should be acquired
 func (i *InmemSink) Data() []*IntervalMetrics {

metrics.go

@@ -5,7 +5,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/hashicorp/go-immutable-radix"
+	iradix "github.com/hashicorp/go-immutable-radix"
 )
 
 type Label struct {
@@ -173,7 +173,9 @@ func (m *Metrics) UpdateFilterAndLabels(allow, block, allowedLabels, blockedLabe
 }
 
 func (m *Metrics) Shutdown() {
-	m.sink.Shutdown()
+	if ss, ok := m.sink.(ShutdownSink); ok {
+		ss.Shutdown()
+	}
 }
 
 // labelIsAllowed return true if a should be included in metric

prometheus/prometheus.go

@@ -394,10 +394,6 @@ func (p *PrometheusSink) IncrCounterWithLabels(parts []string, val float32, labe
 	}
 }
 
-// Shutdown is not implemented. PrometheusSink is in memory storage.
-func (p *PrometheusSink) Shutdown() {
-}
-
 // PrometheusPushSink wraps a normal prometheus sink and provides an address and facilities to export it to an address
 // on an interval.
 type PrometheusPushSink struct {

sink.go

@@ -22,6 +22,10 @@ type MetricSink interface {
 	// Samples are for timing information, where quantiles are used
 	AddSample(key []string, val float32)
 	AddSampleWithLabels(key []string, val float32, labels []Label)
+}
+
+type ShutdownSink interface {
+	MetricSink
 
 	// Shutdown the metric sink, flush metrics to storage, and cleanup resources.
 	// Called immediately prior to application exit. Implementations must block
@@ -39,7 +43,6 @@ func (*BlackholeSink) IncrCounter(key []string, val float32)
 func (*BlackholeSink) IncrCounterWithLabels(key []string, val float32, labels []Label) {}
 func (*BlackholeSink) AddSample(key []string, val float32)                             {}
 func (*BlackholeSink) AddSampleWithLabels(key []string, val float32, labels []Label)   {}
-func (*BlackholeSink) Shutdown()                                                       {}
 
 // FanoutSink is used to sink to fanout values to multiple sinks
 type FanoutSink []MetricSink
@@ -82,7 +85,9 @@ func (fh FanoutSink) AddSampleWithLabels(key []string, val float32, labels []Lab
 
 func (fh FanoutSink) Shutdown() {
 	for _, s := range fh {
-		s.Shutdown()
+		if ss, ok := s.(ShutdownSink); ok {
+			ss.Shutdown()
+		}
 	}
 }