From 401bc7ce94ab39081d1e73608873b556ef906153 Mon Sep 17 00:00:00 2001
From: jmacd <jmacd@lightstep.com>
Date: Sat, 26 Sep 2020 00:05:03 -0700
Subject: [PATCH] Start transient Accum

---
 api/global/internal/meter.go      |  3 ++
 api/metric/metrictest/meter.go    |  3 ++
 api/metric/noop.go                |  3 ++
 api/metric/sdkapi.go              |  3 ++
 sdk/metric/sdk.go                 |  4 +++
 sdk/metric/transient/transient.go | 60 +++++++++++++++++++++++++++++++
 6 files changed, 76 insertions(+)
 create mode 100644 sdk/metric/transient/transient.go

diff --git a/api/global/internal/meter.go b/api/global/internal/meter.go
index b45f4c94490..f57d80e3a55 100644
--- a/api/global/internal/meter.go
+++ b/api/global/internal/meter.go
@@ -123,6 +123,9 @@ func (inst *instrument) Descriptor() metric.Descriptor {
 	return inst.descriptor
 }
 
+func (inst *instrument) Unref() {
+}
+
 // MeterProvider interface and delegation
 
 func newMeterProvider() *meterProvider {
diff --git a/api/metric/metrictest/meter.go b/api/metric/metrictest/meter.go
index 40524cac33c..83dd2253a3a 100644
--- a/api/metric/metrictest/meter.go
+++ b/api/metric/metrictest/meter.go
@@ -80,6 +80,9 @@ func (i Instrument) Descriptor() apimetric.Descriptor {
 	return i.descriptor
 }
 
+func (i Instrument) Unref() {
+}
+
 func (a *Async) Implementation() interface{} {
 	return a
 }
diff --git a/api/metric/noop.go b/api/metric/noop.go
index 97867d9b7d6..5612cb1b74b 100644
--- a/api/metric/noop.go
+++ b/api/metric/noop.go
@@ -40,6 +40,9 @@ func (noopInstrument) Implementation() interface{} {
 	return nil
 }
 
+func (noopInstrument) Unref() {
+}
+
 func (noopInstrument) Descriptor() Descriptor {
 	return Descriptor{}
 }
diff --git a/api/metric/sdkapi.go b/api/metric/sdkapi.go
index 122c9ba6d2f..48b952fa30d 100644
--- a/api/metric/sdkapi.go
+++ b/api/metric/sdkapi.go
@@ -50,6 +50,9 @@ type InstrumentImpl interface {
 
 	// Descriptor returns a copy of the instrument's Descriptor.
 	Descriptor() Descriptor
+
+	// @@@
+	Unref()
 }
 
 // SyncImpl is the implementation-level interface to a generic
diff --git a/sdk/metric/sdk.go b/sdk/metric/sdk.go
index 4e16f279828..da9625c8dc4 100644
--- a/sdk/metric/sdk.go
+++ b/sdk/metric/sdk.go
@@ -154,6 +154,10 @@ func (inst *instrument) Descriptor() api.Descriptor {
 	return inst.descriptor
 }
 
+func (inst *instrument) Unref() {
+	// This is a no-op for the standard Accumulator.
+}
+
 func (a *asyncInstrument) Implementation() interface{} {
 	return a
 }
diff --git a/sdk/metric/transient/transient.go b/sdk/metric/transient/transient.go
new file mode 100644
index 00000000000..7d93f6a4bb1
--- /dev/null
+++ b/sdk/metric/transient/transient.go
@@ -0,0 +1,60 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package transient
+
+import (
+	"context"
+	"fmt"
+
+	"go.opentelemetry.io/otel/api/metric"
+	"go.opentelemetry.io/otel/label"
+	export "go.opentelemetry.io/otel/sdk/export/metric"
+	sdk "go.opentelemetry.io/otel/sdk/metric"
+)
+
+type Accumulator struct {
+	standard *sdk.Accumulator
+}
+
+var (
+	ErrAsyncNotSupported = fmt.Errorf("transient asynchronous instruments not supported")
+
+	_ metric.MeterImpl = &Accumulator{}
+)
+
+func NewAccumulator(processor export.Processor, opts ...sdk.Option) *Accumulator {
+	return &Accumulator{
+		standard: sdk.NewAccumulator(processor, opts...),
+	}
+}
+
+func (a *Accumulator) RecordBatch(ctx context.Context, labels []label.KeyValue, measurements ...metric.Measurement) {
+	a.standard.RecordBatch(ctx, labels, measurements...)
+}
+
+func (a *Accumulator) NewSyncInstrument(descriptor metric.Descriptor) (metric.SyncImpl, error) {
+	return a.standard.NewSyncInstrument(descriptor)
+}
+
+func (a *Accumulator) NewAsyncInstrument(
+	descriptor metric.Descriptor,
+	runner metric.AsyncRunner,
+) (metric.AsyncImpl, error) {
+	return metric.NoopAsync{}, ErrAsyncNotSupported
+}
+
+func (m *Accumulator) Collect(ctx context.Context) int {
+	return 0
+}