Async metrics (#92)

* Set metric kind for SumObserver and UpDownSumObserver #89

* Cast to array aggregator instead of sum aggregator

* Add TODO to handle UpDdownCounters and UpDownObservers

* Update metrics exporter to otel v0.11.0 (#91)

* Update metrics exporter: kv -> label

* Update metrics exporter to otel v0.11.0

* Update metrics example to v0.11.0

* Update dependency on deprecated cloud monitoring package

* Update otel SDK dependency to v0.11.0

* Prepare for releasing v0.11.0 (#93)

* Modify default aggregation in the custom selector

Co-authored-by: Nail Islamov <nilebox@users.noreply.github.com>

exporter/metric/metric.go

@@ -421,12 +421,12 @@ func recordToMdpbKindType(r *export.Record) (googlemetricpb.MetricDescriptor_Met
 
 	var kind googlemetricpb.MetricDescriptor_MetricKind
 	switch mkind {
-	case apimetric.CounterKind, apimetric.UpDownCounterKind:
+	// TODO: Decide how UpDownCounterKind and UpDownSumObserverKind should be handled.
+	// CUMULATIVE might not be correct as it assumes the metric always goes up.
+	case apimetric.CounterKind, apimetric.UpDownCounterKind, apimetric.SumObserverKind, apimetric.UpDownSumObserverKind:
 		kind = googlemetricpb.MetricDescriptor_CUMULATIVE
 	case apimetric.ValueObserverKind, apimetric.ValueRecorderKind:
 		kind = googlemetricpb.MetricDescriptor_GAUGE
-	// TODO: Add support for SumObserverKind and UpDownSumObserverKind.
-	// https://pkg.go.dev/go.opentelemetry.io/otel@v0.6.0/api/metric?tab=doc#Kind
 	default:
 		kind = googlemetricpb.MetricDescriptor_METRIC_KIND_UNSPECIFIED
 	}

exporter/metric/selector.go

@@ -17,7 +17,6 @@ package metric
 import (
 	apimetric "go.opentelemetry.io/otel/api/metric"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
-	"go.opentelemetry.io/otel/sdk/metric/aggregator/array"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/sum"
 )
@@ -31,6 +30,8 @@ var _ export.AggregatorSelector = selectorCloudMonitoring{}
 //
 // NOTE: this selector is just to ensure that LastValue is used for
 // ValueObserverKind and ValueRecorderKind.
+// All other metric kinds have Sum default aggregation
+// c.f. https://github.com/open-telemetry/opentelemetry-go/blob/master/sdk/metric/selector/simple/simple.go
 //
 // TODO: Remove this once SDK implements such a
 // selector, otherwise Views API gives flexibility to set aggregation type on
@@ -47,13 +48,6 @@ func (selectorCloudMonitoring) AggregatorFor(descriptor *apimetric.Descriptor, a
 		for i := range aggPtrs {
 			*aggPtrs[i] = &aggs[i]
 		}
-	// NOTE: `array` gives the option to use Sum, Count, Max, Min, Quantile and Points (most flexible),
-	// so chosen for future implementations rather than `sum`.
-	case apimetric.CounterKind, apimetric.UpDownCounterKind, apimetric.SumObserverKind, apimetric.UpDownSumObserverKind:
-		aggs := array.New(len(aggPtrs))
-		for i := range aggPtrs {
-			*aggPtrs[i] = &aggs[i]
-		}
 	default:
 		aggs := sum.New(len(aggPtrs))
 		for i := range aggPtrs {