Refactor the api/metrics push controller; add CheckpointSet synchronization (#737)

* Checkpoint

* Finish tests

* Checkpoint

* Checkpoint (builds)

* Checkpoint + RWMutex interface

* Comments

* Remove commitLock

* Apply feedback

example/prometheus/main.go

@@ -33,11 +33,11 @@ var (
 )
 
 func initMeter() *push.Controller {
-	pusher, hf, err := prometheus.InstallNewPipeline(prometheus.Config{})
+	pusher, exporter, err := prometheus.InstallNewPipeline(prometheus.Config{})
 	if err != nil {
 		log.Panicf("failed to initialize prometheus exporter %v", err)
 	}
-	http.HandleFunc("/", hf)
+	http.HandleFunc("/", exporter.ServeHTTP)
 	go func() {
 		_ = http.ListenAndServe(":2222", nil)
 	}()

exporters/metric/prometheus/prometheus.go

@@ -18,7 +18,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
-	"time"
+	"sync"
 
 	"go.opentelemetry.io/otel/api/metric"
 
@@ -30,7 +30,6 @@ import (
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/export/metric/aggregator"
 	"go.opentelemetry.io/otel/sdk/metric/controller/push"
-	integrator "go.opentelemetry.io/otel/sdk/metric/integrator/simple"
 	"go.opentelemetry.io/otel/sdk/metric/selector/simple"
 )
 
@@ -42,6 +41,7 @@ type Exporter struct {
 	registerer prometheus.Registerer
 	gatherer   prometheus.Gatherer
 
+	lock     sync.RWMutex
 	snapshot export.CheckpointSet
 	onError  func(error)
 
@@ -134,41 +134,49 @@ func NewRawExporter(config Config) (*Exporter, error) {
 // 	http.HandleFunc("/metrics", hf)
 // 	defer pipeline.Stop()
 // 	... Done
-func InstallNewPipeline(config Config) (*push.Controller, http.HandlerFunc, error) {
-	controller, hf, err := NewExportPipeline(config, time.Minute)
+func InstallNewPipeline(config Config, options ...push.Option) (*push.Controller, *Exporter, error) {
+	controller, exp, err := NewExportPipeline(config, options...)
 	if err != nil {
-		return controller, hf, err
+		return controller, exp, err
 	}
 	global.SetMeterProvider(controller.Provider())
-	return controller, hf, err
+	return controller, exp, err
 }
 
 // NewExportPipeline sets up a complete export pipeline with the recommended setup,
 // chaining a NewRawExporter into the recommended selectors and integrators.
-func NewExportPipeline(config Config, period time.Duration) (*push.Controller, http.HandlerFunc, error) {
-	selector := simple.NewWithHistogramDistribution(config.DefaultHistogramBoundaries)
+//
+// The returned Controller contains an implementation of
+// `metric.Provider`.  The controller is returned unstarted and should
+// be started by the caller to begin collection.
+func NewExportPipeline(config Config, options ...push.Option) (*push.Controller, *Exporter, error) {
 	exporter, err := NewRawExporter(config)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	// Prometheus needs to use a stateful integrator since counters (and histogram since they are a collection of Counters)
-	// are cumulative (i.e., monotonically increasing values) and should not be resetted after each export.
+	// Prometheus uses a stateful push controller since instruments are
+	// cumulative and should not be reset after each collection interval.
 	//
 	// Prometheus uses this approach to be resilient to scrape failures.
 	// If a Prometheus server tries to scrape metrics from a host and fails for some reason,
 	// it could try again on the next scrape and no data would be lost, only resolution.
 	//
 	// Gauges (or LastValues) and Summaries are an exception to this and have different behaviors.
-	integrator := integrator.New(selector, true)
-	pusher := push.New(integrator, exporter, period)
-	pusher.Start()
+	pusher := push.New(
+		simple.NewWithHistogramDistribution(config.DefaultHistogramBoundaries),
+		exporter,
+		append(options, push.WithStateful(true))...,
+	)
 
-	return pusher, exporter.ServeHTTP, nil
+	return pusher, exporter, nil
 }
 
 // Export exports the provide metric record to prometheus.
 func (e *Exporter) Export(_ context.Context, checkpointSet export.CheckpointSet) error {
+	// TODO: Use the resource value in this exporter.
+	e.lock.Lock()
+	defer e.lock.Unlock()
 	e.snapshot = checkpointSet
 	return nil
 }
@@ -187,10 +195,16 @@ func newCollector(exporter *Exporter) *collector {
 }
 
 func (c *collector) Describe(ch chan<- *prometheus.Desc) {
+	c.exp.lock.RLock()
+	defer c.exp.lock.RUnlock()
+
 	if c.exp.snapshot == nil {
 		return
 	}
 
+	c.exp.snapshot.RLock()
+	defer c.exp.snapshot.RUnlock()
+
 	_ = c.exp.snapshot.ForEach(func(record export.Record) error {
 		ch <- c.toDesc(&record)
 		return nil
@@ -202,10 +216,16 @@ func (c *collector) Describe(ch chan<- *prometheus.Desc) {
 // Collect is invoked whenever prometheus.Gatherer is also invoked.
 // For example, when the HTTP endpoint is invoked by Prometheus.
 func (c *collector) Collect(ch chan<- prometheus.Metric) {
+	c.exp.lock.RLock()
+	defer c.exp.lock.RUnlock()
+
 	if c.exp.snapshot == nil {
 		return
 	}
 
+	c.exp.snapshot.RLock()
+	defer c.exp.snapshot.RUnlock()
+
 	err := c.exp.snapshot.ForEach(func(record export.Record) error {
 		agg := record.Aggregator()
 		numberKind := record.Descriptor().NumberKind()

exporters/metric/prometheus/prometheus_test.go

@@ -15,31 +15,35 @@
 package prometheus_test
 
 import (
+	"bytes"
 	"context"
-	"log"
+	"io/ioutil"
+	"net/http"
 	"net/http/httptest"
+	"runtime"
 	"sort"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/api/kv"
 	"go.opentelemetry.io/otel/api/metric"
 	"go.opentelemetry.io/otel/exporters/metric/prometheus"
-	"go.opentelemetry.io/otel/exporters/metric/test"
+	exportTest "go.opentelemetry.io/otel/exporters/metric/test"
+	"go.opentelemetry.io/otel/sdk/metric/controller/push"
+	controllerTest "go.opentelemetry.io/otel/sdk/metric/controller/test"
 )
 
 func TestPrometheusExporter(t *testing.T) {
 	exporter, err := prometheus.NewRawExporter(prometheus.Config{
 		DefaultSummaryQuantiles: []float64{0.5, 0.9, 0.99},
 	})
-	if err != nil {
-		log.Panicf("failed to initialize prometheus exporter %v", err)
-	}
+	require.NoError(t, err)
 
 	var expected []string
-	checkpointSet := test.NewCheckpointSet(nil)
+	checkpointSet := exportTest.NewCheckpointSet(nil)
 
 	counter := metric.NewDescriptor(
 		"counter", metric.CounterKind, metric.Float64NumberKind)
@@ -116,7 +120,7 @@ func TestPrometheusExporter(t *testing.T) {
 	compareExport(t, exporter, checkpointSet, expected)
 }
 
-func compareExport(t *testing.T, exporter *prometheus.Exporter, checkpointSet *test.CheckpointSet, expected []string) {
+func compareExport(t *testing.T, exporter *prometheus.Exporter, checkpointSet *exportTest.CheckpointSet, expected []string) {
 	err := exporter.Export(context.Background(), checkpointSet)
 	require.Nil(t, err)
 
@@ -138,3 +142,58 @@ func compareExport(t *testing.T, exporter *prometheus.Exporter, checkpointSet *t
 
 	require.Equal(t, strings.Join(expected, "\n"), strings.Join(metricsOnly, "\n"))
 }
+
+func TestPrometheusStatefulness(t *testing.T) {
+	// Create a meter
+	controller, exporter, err := prometheus.NewExportPipeline(prometheus.Config{}, push.WithPeriod(time.Minute))
+	require.NoError(t, err)
+
+	meter := controller.Provider().Meter("test")
+	mock := controllerTest.NewMockClock()
+	controller.SetClock(mock)
+	controller.Start()
+
+	// GET the HTTP endpoint
+	scrape := func() string {
+		var input bytes.Buffer
+		resp := httptest.NewRecorder()
+		req, err := http.NewRequest("GET", "/", &input)
+		require.NoError(t, err)
+
+		exporter.ServeHTTP(resp, req)
+		data, err := ioutil.ReadAll(resp.Result().Body)
+		require.NoError(t, err)
+
+		return string(data)
+	}
+
+	ctx := context.Background()
+
+	counter := metric.Must(meter).NewInt64Counter(
+		"a.counter",
+		metric.WithDescription("Counts things"),
+	)
+
+	counter.Add(ctx, 100, kv.String("key", "value"))
+
+	// Trigger a push
+	mock.Add(time.Minute)
+	runtime.Gosched()
+
+	require.Equal(t, `# HELP a_counter Counts things
+# TYPE a_counter counter
+a_counter{key="value"} 100
+`, scrape())
+
+	counter.Add(ctx, 100, kv.String("key", "value"))
+
+	// Again, now expect cumulative count
+	mock.Add(time.Minute)
+	runtime.Gosched()
+
+	require.Equal(t, `# HELP a_counter Counts things
+# TYPE a_counter counter
+a_counter{key="value"} 200
+`, scrape())
+
+}

exporters/metric/stdout/example_test.go

@@ -17,7 +17,6 @@ package stdout_test
 import (
 	"context"
 	"log"
-	"time"
 
 	"go.opentelemetry.io/otel/api/kv"
 	"go.opentelemetry.io/otel/api/metric"
@@ -29,7 +28,7 @@ func ExampleNewExportPipeline() {
 	pusher, err := stdout.NewExportPipeline(stdout.Config{
 		PrettyPrint:    true,
 		DoNotPrintTime: true,
-	}, time.Minute)
+	})
 	if err != nil {
 		log.Fatal("Could not initialize stdout exporter:", err)
 	}

exporters/metric/stdout/stdout.go

@@ -29,7 +29,6 @@ import (
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/export/metric/aggregator"
 	"go.opentelemetry.io/otel/sdk/metric/controller/push"
-	integrator "go.opentelemetry.io/otel/sdk/metric/integrator/simple"
 	"go.opentelemetry.io/otel/sdk/metric/selector/simple"
 )
 
@@ -120,8 +119,8 @@ func NewRawExporter(config Config) (*Exporter, error) {
 // 	}
 // 	defer pipeline.Stop()
 // 	... Done
-func InstallNewPipeline(config Config, opts ...push.Option) (*push.Controller, error) {
-	controller, err := NewExportPipeline(config, time.Minute, opts...)
+func InstallNewPipeline(config Config, options ...push.Option) (*push.Controller, error) {
+	controller, err := NewExportPipeline(config, options...)
 	if err != nil {
 		return controller, err
 	}
@@ -129,16 +128,22 @@ func InstallNewPipeline(config Config, opts ...push.Option) (*push.Controller, e
 	return controller, err
 }
 
-// NewExportPipeline sets up a complete export pipeline with the recommended setup,
-// chaining a NewRawExporter into the recommended selectors and integrators.
-func NewExportPipeline(config Config, period time.Duration, opts ...push.Option) (*push.Controller, error) {
-	selector := simple.NewWithExactDistribution()
+// NewExportPipeline sets up a complete export pipeline with the
+// recommended setup, chaining a NewRawExporter into the recommended
+// selectors and integrators.
+//
+// The pipeline is configured with a stateful integrator unless the
+// push.WithStateful(false) option is used.
+func NewExportPipeline(config Config, options ...push.Option) (*push.Controller, error) {
 	exporter, err := NewRawExporter(config)
 	if err != nil {
 		return nil, err
 	}
-	integrator := integrator.New(selector, true)
-	pusher := push.New(integrator, exporter, period, opts...)
+	pusher := push.New(
+		simple.NewWithExactDistribution(),
+		exporter,
+		append([]push.Option{push.WithStateful(true)}, options...)...,
+	)
 	pusher.Start()
 
 	return pusher, nil

exporters/metric/test/test.go

@@ -17,6 +17,7 @@ package test
 import (
 	"context"
 	"errors"
+	"sync"
 
 	"go.opentelemetry.io/otel/api/kv"
 	"go.opentelemetry.io/otel/api/label"
@@ -36,9 +37,10 @@ type mapkey struct {
 }
 
 type CheckpointSet struct {
+	sync.RWMutex
 	records  map[mapkey]export.Record
-	resource *resource.Resource
 	updates  []export.Record
+	resource *resource.Resource
 }
 
 // NewCheckpointSet returns a test CheckpointSet that new records could be added.

exporters/otlp/otlp_integration_test.go

@@ -111,7 +111,7 @@ func newExporterEndToEndTest(t *testing.T, additionalOpts []otlp.ExporterOption)
 
 	selector := simple.NewWithExactDistribution()
 	integrator := integrator.New(selector, true)
-	pusher := push.New(integrator, exp, 60*time.Second)
+	pusher := push.New(integrator, exp)
 	pusher.Start()
 
 	ctx := context.Background()

exporters/otlp/otlp_metric_test.go

@@ -16,6 +16,7 @@ package otlp
 
 import (
 	"context"
+	"sync"
 	"testing"
 
 	colmetricpb "github.com/open-telemetry/opentelemetry-proto/gen/go/collector/metrics/v1"
@@ -60,10 +61,11 @@ func (m *metricsServiceClientStub) Reset() {
 }
 
 type checkpointSet struct {
+	sync.RWMutex
 	records []metricsdk.Record
 }
 
-func (m checkpointSet) ForEach(fn func(metricsdk.Record) error) error {
+func (m *checkpointSet) ForEach(fn func(metricsdk.Record) error) error {
 	for _, r := range m.records {
 		if err := fn(r); err != nil && err != aggregator.ErrNoData {
 			return err
@@ -662,7 +664,7 @@ func runMetricExportTest(t *testing.T, exp *Exporter, rs []record, expected []me
 		recs[equiv] = append(recs[equiv], metricsdk.NewRecord(&desc, &labs, r.resource, agg))
 	}
 	for _, records := range recs {
-		assert.NoError(t, exp.Export(context.Background(), checkpointSet{records: records}))
+		assert.NoError(t, exp.Export(context.Background(), &checkpointSet{records: records}))
 	}
 
 	// assert.ElementsMatch does not equate nested slices of different order,
@@ -726,7 +728,7 @@ func TestEmptyMetricExport(t *testing.T) {
 		},
 	} {
 		msc.Reset()
-		require.NoError(t, exp.Export(context.Background(), checkpointSet{records: test.records}))
+		require.NoError(t, exp.Export(context.Background(), &checkpointSet{records: test.records}))
 		assert.Equal(t, test.want, msc.ResourceMetrics())
 	}
 }

sdk/export/metric/metric.go

@@ -16,6 +16,7 @@ package metric // import "go.opentelemetry.io/otel/sdk/export/metric"
 
 import (
 	"context"
+	"sync"
 
 	"go.opentelemetry.io/otel/api/label"
 	"go.opentelemetry.io/otel/api/metric"
@@ -39,10 +40,6 @@ import (
 // single-threaded context from the SDK, after the aggregator is
 // checkpointed, allowing the integrator to build the set of metrics
 // currently being exported.
-//
-// The `CheckpointSet` method is called during collection in a
-// single-threaded context from the Exporter, giving the exporter
-// access to a producer for iterating over the complete checkpoint.
 type Integrator interface {
 	// AggregationSelector is responsible for selecting the
 	// concrete type of Aggregator used for a metric in the SDK.
@@ -70,17 +67,6 @@ type Integrator interface {
 	// The Context argument originates from the controller that
 	// orchestrates collection.
 	Process(ctx context.Context, record Record) error
-
-	// CheckpointSet is the interface used by the controller to
-	// access the fully aggregated checkpoint after collection.
-	//
-	// The returned CheckpointSet is passed to the Exporter.
-	CheckpointSet() CheckpointSet
-
-	// FinishedCollection informs the Integrator that a complete
-	// collection round was completed.  Stateless integrators might
-	// reset state in this method, for example.
-	FinishedCollection()
 }
 
 // AggregationSelector supports selecting the kind of Aggregator to
@@ -173,6 +159,19 @@ type CheckpointSet interface {
 	// of error will immediately halt ForEach and return
 	// the error to the caller.
 	ForEach(func(Record) error) error
+
+	// Locker supports locking the checkpoint set.  Collection
+	// into the checkpoint set cannot take place (in case of a
+	// stateful integrator) while it is locked.
+	//
+	// The Integrator attached to the Accumulator MUST be called
+	// with the lock held.
+	sync.Locker
+
+	// RLock acquires a read lock corresponding to this Locker.
+	RLock()
+	// RUnlock releases a read lock corresponding to this Locker.
+	RUnlock()
 }
 
 // Record contains the exported data for a single metric instrument

sdk/metric/controller/push/config.go

@@ -15,6 +15,8 @@
 package push
 
 import (
+	"time"
+
 	sdk "go.opentelemetry.io/otel/sdk/metric"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
@@ -30,6 +32,14 @@ type Config struct {
 	// Resource is the OpenTelemetry resource associated with all Meters
 	// created by the Controller.
 	Resource *resource.Resource
+
+	// Stateful causes the controller to maintain state across
+	// collection events, so that records in the exported
+	// checkpoint set are cumulative.
+	Stateful bool
+
+	// Period is the interval between calls to Collect a checkpoint.
+	Period time.Duration
 }
 
 // Option is the interface that applies the value to a configuration option.
@@ -59,3 +69,25 @@ type resourceOption struct{ *resource.Resource }
 func (o resourceOption) Apply(config *Config) {
 	config.Resource = o.Resource
 }
+
+// WithStateful sets the Stateful configuration option of a Config.
+func WithStateful(stateful bool) Option {
+	return statefulOption(stateful)
+}
+
+type statefulOption bool
+
+func (o statefulOption) Apply(config *Config) {
+	config.Stateful = bool(o)
+}
+
+// WithPeriod sets the Period configuration option of a Config.
+func WithPeriod(period time.Duration) Option {
+	return periodOption(period)
+}
+
+type periodOption time.Duration
+
+func (o periodOption) Apply(config *Config) {
+	config.Period = time.Duration(o)
+}

sdk/metric/controller/push/push.go

@@ -23,77 +23,61 @@ import (
 	"go.opentelemetry.io/otel/api/metric/registry"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	sdk "go.opentelemetry.io/otel/sdk/metric"
-	"go.opentelemetry.io/otel/sdk/resource"
+	controllerTime "go.opentelemetry.io/otel/sdk/metric/controller/time"
+	"go.opentelemetry.io/otel/sdk/metric/integrator/simple"
 )
 
+// DefaultPushPeriod is the default time interval between pushes.
+const DefaultPushPeriod = 10 * time.Second
+
 // Controller organizes a periodic push of metric data.
 type Controller struct {
 	lock         sync.Mutex
-	collectLock  sync.Mutex
 	accumulator  *sdk.Accumulator
 	provider     *registry.Provider
 	errorHandler sdk.ErrorHandler
-	integrator   export.Integrator
+	integrator   *simple.Integrator
 	exporter     export.Exporter
 	wg           sync.WaitGroup
 	ch           chan struct{}
 	period       time.Duration
-	ticker       Ticker
-	clock        Clock
+	clock        controllerTime.Clock
+	ticker       controllerTime.Ticker
 }
 
-// Several types below are created to match "github.com/benbjohnson/clock"
-// so that it remains a test-only dependency.
-
-type Clock interface {
-	Now() time.Time
-	Ticker(time.Duration) Ticker
-}
-
-type Ticker interface {
-	Stop()
-	C() <-chan time.Time
-}
-
-type realClock struct {
-}
-
-type realTicker struct {
-	ticker *time.Ticker
-}
-
-var _ Clock = realClock{}
-var _ Ticker = realTicker{}
-
 // New constructs a Controller, an implementation of metric.Provider,
-// using the provided integrator, exporter, collection period, and SDK
-// configuration options to configure an SDK with periodic collection.
-// The integrator itself is configured with the aggregation selector policy.
-func New(integrator export.Integrator, exporter export.Exporter, period time.Duration, opts ...Option) *Controller {
+// using the provided exporter and options to configure an SDK with
+// periodic collection.
+func New(selector export.AggregationSelector, exporter export.Exporter, opts ...Option) *Controller {
 	c := &Config{
 		ErrorHandler: sdk.DefaultErrorHandler,
-		Resource:     resource.Empty(),
+		Period:       DefaultPushPeriod,
 	}
 	for _, opt := range opts {
 		opt.Apply(c)
 	}
 
-	impl := sdk.NewAccumulator(integrator, sdk.WithErrorHandler(c.ErrorHandler), sdk.WithResource(c.Resource))
+	integrator := simple.New(selector, c.Stateful)
+	impl := sdk.NewAccumulator(
+		integrator,
+		sdk.WithErrorHandler(c.ErrorHandler),
+		sdk.WithResource(c.Resource),
+	)
 	return &Controller{
-		accumulator:  impl,
 		provider:     registry.NewProvider(impl),
-		errorHandler: c.ErrorHandler,
+		accumulator:  impl,
 		integrator:   integrator,
 		exporter:     exporter,
+		errorHandler: c.ErrorHandler,
 		ch:           make(chan struct{}),
-		period:       period,
-		clock:        realClock{},
+		period:       c.Period,
+		clock:        controllerTime.RealClock{},
 	}
 }
 
 // SetClock supports setting a mock clock for testing.  This must be
 // called before Start().
-func (c *Controller) SetClock(clock Clock) {
+func (c *Controller) SetClock(clock controllerTime.Clock) {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 	c.clock = clock
@@ -162,53 +146,15 @@ func (c *Controller) tick() {
 	// TODO: either remove the context argument from Export() or
 	// configure a timeout here?
 	ctx := context.Background()
-	c.collect(ctx)
-	checkpointSet := syncCheckpointSet{
-		mtx:      &c.collectLock,
-		delegate: c.integrator.CheckpointSet(),
-	}
-	err := c.exporter.Export(ctx, checkpointSet)
+	c.integrator.Lock()
+	defer c.integrator.Unlock()
+
+	c.accumulator.Collect(ctx)
+
+	err := c.exporter.Export(ctx, c.integrator.CheckpointSet())
 	c.integrator.FinishedCollection()
 
 	if err != nil {
 		c.errorHandler(err)
 	}
 }
-
-func (c *Controller) collect(ctx context.Context) {
-	c.collectLock.Lock()
-	defer c.collectLock.Unlock()
-
-	c.accumulator.Collect(ctx)
-}
-
-// syncCheckpointSet is a wrapper for a CheckpointSet to synchronize
-// SDK's collection and reads of a CheckpointSet by an exporter.
-type syncCheckpointSet struct {
-	mtx      *sync.Mutex
-	delegate export.CheckpointSet
-}
-
-var _ export.CheckpointSet = (*syncCheckpointSet)(nil)
-
-func (c syncCheckpointSet) ForEach(fn func(export.Record) error) error {
-	c.mtx.Lock()
-	defer c.mtx.Unlock()
-	return c.delegate.ForEach(fn)
-}
-
-func (realClock) Now() time.Time {
-	return time.Now()
-}
-
-func (realClock) Ticker(period time.Duration) Ticker {
-	return realTicker{time.NewTicker(period)}
-}
-
-func (t realTicker) Stop() {
-	t.ticker.Stop()
-}
-
-func (t realTicker) C() <-chan time.Time {
-	return t.ticker.C
-}

sdk/metric/controller/push/push_test.go

@@ -22,7 +22,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/benbjohnson/clock"
 	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/api/kv"
@@ -33,17 +32,10 @@ import (
 	"go.opentelemetry.io/otel/sdk/export/metric/aggregator"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/sum"
 	"go.opentelemetry.io/otel/sdk/metric/controller/push"
+	controllerTest "go.opentelemetry.io/otel/sdk/metric/controller/test"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
-type testIntegrator struct {
-	t             *testing.T
-	lock          sync.Mutex
-	checkpointSet *test.CheckpointSet
-	checkpoints   int
-	finishes      int
-}
-
 var testResource = resource.New(kv.String("R", "V"))
 
 type testExporter struct {
@@ -56,69 +48,27 @@ type testExporter struct {
 
 type testFixture struct {
 	checkpointSet *test.CheckpointSet
-	integrator    *testIntegrator
 	exporter      *testExporter
 }
 
-type mockClock struct {
-	mock *clock.Mock
-}
-
-type mockTicker struct {
-	ticker *clock.Ticker
-}
-
-var _ push.Clock = mockClock{}
-var _ push.Ticker = mockTicker{}
+type testSelector struct{}
 
 func newFixture(t *testing.T) testFixture {
 	checkpointSet := test.NewCheckpointSet(testResource)
 
-	integrator := &testIntegrator{
-		t:             t,
-		checkpointSet: checkpointSet,
-	}
 	exporter := &testExporter{
 		t: t,
 	}
 	return testFixture{
 		checkpointSet: checkpointSet,
-		integrator:    integrator,
 		exporter:      exporter,
 	}
 }
 
-func (b *testIntegrator) AggregatorFor(*metric.Descriptor) export.Aggregator {
+func (testSelector) AggregatorFor(*metric.Descriptor) export.Aggregator {
 	return sum.New()
 }
 
-func (b *testIntegrator) CheckpointSet() export.CheckpointSet {
-	b.lock.Lock()
-	defer b.lock.Unlock()
-	b.checkpoints++
-	return b.checkpointSet
-}
-
-func (b *testIntegrator) FinishedCollection() {
-	b.lock.Lock()
-	defer b.lock.Unlock()
-	b.finishes++
-}
-
-func (b *testIntegrator) Process(_ context.Context, record export.Record) error {
-	b.lock.Lock()
-	defer b.lock.Unlock()
-	labels := record.Labels().ToSlice()
-	b.checkpointSet.Add(record.Descriptor(), record.Aggregator(), labels...)
-	return nil
-}
-
-func (b *testIntegrator) getCounts() (checkpoints, finishes int) {
-	b.lock.Lock()
-	defer b.lock.Unlock()
-	return b.checkpoints, b.finishes
-}
-
 func (e *testExporter) Export(_ context.Context, checkpointSet export.CheckpointSet) error {
 	e.lock.Lock()
 	defer e.lock.Unlock()
@@ -147,29 +97,9 @@ func (e *testExporter) resetRecords() ([]export.Record, int) {
 	return r, e.exports
 }
 
-func (c mockClock) Now() time.Time {
-	return c.mock.Now()
-}
-
-func (c mockClock) Ticker(period time.Duration) push.Ticker {
-	return mockTicker{c.mock.Ticker(period)}
-}
-
-func (c mockClock) Add(d time.Duration) {
-	c.mock.Add(d)
-}
-
-func (t mockTicker) Stop() {
-	t.ticker.Stop()
-}
-
-func (t mockTicker) C() <-chan time.Time {
-	return t.ticker.C
-}
-
 func TestPushDoubleStop(t *testing.T) {
 	fix := newFixture(t)
-	p := push.New(fix.integrator, fix.exporter, time.Second)
+	p := push.New(testSelector{}, fix.exporter)
 	p.Start()
 	p.Stop()
 	p.Stop()
@@ -177,7 +107,7 @@ func TestPushDoubleStop(t *testing.T) {
 
 func TestPushDoubleStart(t *testing.T) {
 	fix := newFixture(t)
-	p := push.New(fix.integrator, fix.exporter, time.Second)
+	p := push.New(testSelector{}, fix.exporter)
 	p.Start()
 	p.Start()
 	p.Stop()
@@ -186,10 +116,15 @@ func TestPushDoubleStart(t *testing.T) {
 func TestPushTicker(t *testing.T) {
 	fix := newFixture(t)
 
-	p := push.New(fix.integrator, fix.exporter, time.Second)
+	p := push.New(
+		testSelector{},
+		fix.exporter,
+		push.WithPeriod(time.Second),
+		push.WithResource(testResource),
+	)
 	meter := p.Provider().Meter("name")
 
-	mock := mockClock{clock.NewMock()}
+	mock := controllerTest.NewMockClock()
 	p.SetClock(mock)
 
 	ctx := context.Background()
@@ -201,9 +136,6 @@ func TestPushTicker(t *testing.T) {
 	counter.Add(ctx, 3)
 
 	records, exports := fix.exporter.resetRecords()
-	checkpoints, finishes := fix.integrator.getCounts()
-	require.Equal(t, 0, checkpoints)
-	require.Equal(t, 0, finishes)
 	require.Equal(t, 0, exports)
 	require.Equal(t, 0, len(records))
 
@@ -211,9 +143,6 @@ func TestPushTicker(t *testing.T) {
 	runtime.Gosched()
 
 	records, exports = fix.exporter.resetRecords()
-	checkpoints, finishes = fix.integrator.getCounts()
-	require.Equal(t, 1, checkpoints)
-	require.Equal(t, 1, finishes)
 	require.Equal(t, 1, exports)
 	require.Equal(t, 1, len(records))
 	require.Equal(t, "counter", records[0].Descriptor().Name())
@@ -231,9 +160,6 @@ func TestPushTicker(t *testing.T) {
 	runtime.Gosched()
 
 	records, exports = fix.exporter.resetRecords()
-	checkpoints, finishes = fix.integrator.getCounts()
-	require.Equal(t, 2, checkpoints)
-	require.Equal(t, 2, finishes)
 	require.Equal(t, 2, exports)
 	require.Equal(t, 1, len(records))
 	require.Equal(t, "counter", records[0].Descriptor().Name())
@@ -271,7 +197,12 @@ func TestPushExportError(t *testing.T) {
 			fix := newFixture(t)
 			fix.exporter.injectErr = injector("counter1", tt.injectedError)
 
-			p := push.New(fix.integrator, fix.exporter, time.Second)
+			p := push.New(
+				testSelector{},
+				fix.exporter,
+				push.WithPeriod(time.Second),
+				push.WithResource(testResource),
+			)
 
 			var err error
 			var lock sync.Mutex
@@ -281,7 +212,7 @@ func TestPushExportError(t *testing.T) {
 				err = sdkErr
 			})
 
-			mock := mockClock{clock.NewMock()}
+			mock := controllerTest.NewMockClock()
 			p.SetClock(mock)
 
 			ctx := context.Background()
@@ -303,10 +234,7 @@ func TestPushExportError(t *testing.T) {
 			runtime.Gosched()
 
 			records, exports := fix.exporter.resetRecords()
-			checkpoints, finishes := fix.integrator.getCounts()
 			require.Equal(t, 1, exports)
-			require.Equal(t, 1, checkpoints)
-			require.Equal(t, 1, finishes)
 			lock.Lock()
 			if tt.expectedError == nil {
 				require.NoError(t, err)

sdk/metric/controller/test/test.go

@@ -0,0 +1,58 @@
+// 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 test
+
+import (
+	"time"
+
+	"github.com/benbjohnson/clock"
+
+	controllerTime "go.opentelemetry.io/otel/sdk/metric/controller/time"
+)
+
+type MockClock struct {
+	mock *clock.Mock
+}
+
+type MockTicker struct {
+	ticker *clock.Ticker
+}
+
+var _ controllerTime.Clock = MockClock{}
+var _ controllerTime.Ticker = MockTicker{}
+
+func NewMockClock() MockClock {
+	return MockClock{clock.NewMock()}
+}
+
+func (c MockClock) Now() time.Time {
+	return c.mock.Now()
+}
+
+func (c MockClock) Ticker(period time.Duration) controllerTime.Ticker {
+	return MockTicker{c.mock.Ticker(period)}
+}
+
+func (c MockClock) Add(d time.Duration) {
+	c.mock.Add(d)
+}
+
+func (t MockTicker) Stop() {
+	t.ticker.Stop()
+}
+
+func (t MockTicker) C() <-chan time.Time {
+	return t.ticker.C
+}

sdk/metric/controller/time/time.go

@@ -0,0 +1,59 @@
+// 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 time // import "go.opentelemetry.io/otel/sdk/metric/controller/time"
+
+import (
+	"time"
+	lib "time"
+)
+
+// Several types below are created to match "github.com/benbjohnson/clock"
+// so that it remains a test-only dependency.
+
+type Clock interface {
+	Now() lib.Time
+	Ticker(lib.Duration) Ticker
+}
+
+type Ticker interface {
+	Stop()
+	C() <-chan lib.Time
+}
+
+type RealClock struct {
+}
+
+type RealTicker struct {
+	ticker *lib.Ticker
+}
+
+var _ Clock = RealClock{}
+var _ Ticker = RealTicker{}
+
+func (RealClock) Now() time.Time {
+	return time.Now()
+}
+
+func (RealClock) Ticker(period time.Duration) Ticker {
+	return RealTicker{time.NewTicker(period)}
+}
+
+func (t RealTicker) Stop() {
+	t.ticker.Stop()
+}
+
+func (t RealTicker) C() <-chan time.Time {
+	return t.ticker.C
+}

sdk/metric/example_test.go

@@ -17,7 +17,6 @@ package metric_test
 import (
 	"context"
 	"fmt"
-	"time"
 
 	"go.opentelemetry.io/otel/api/kv"
 
@@ -29,7 +28,7 @@ func ExampleNew() {
 	pusher, err := stdout.NewExportPipeline(stdout.Config{
 		PrettyPrint:    true,
 		DoNotPrintTime: true, // This makes the output deterministic
-	}, time.Minute)
+	})
 	if err != nil {
 		panic(fmt.Sprintln("Could not initialize stdout exporter:", err))
 	}

sdk/metric/integrator/simple/simple.go

@@ -17,6 +17,7 @@ package simple // import "go.opentelemetry.io/otel/sdk/metric/integrator/simple"
 import (
 	"context"
 	"errors"
+	"sync"
 
 	"go.opentelemetry.io/otel/api/label"
 	"go.opentelemetry.io/otel/api/metric"
@@ -27,9 +28,9 @@ import (
 
 type (
 	Integrator struct {
-		selector export.AggregationSelector
-		batchMap batchMap
+		export.AggregationSelector
 		stateful bool
+		batch
 	}
 
 	batchKey struct {
@@ -44,24 +45,26 @@ type (
 		resource   *resource.Resource
 	}
 
-	batchMap map[batchKey]batchValue
+	batch struct {
+		// RWMutex implements locking for the `CheckpoingSet` interface.
+		sync.RWMutex
+		values map[batchKey]batchValue
+	}
 )
 
 var _ export.Integrator = &Integrator{}
-var _ export.CheckpointSet = batchMap{}
+var _ export.CheckpointSet = &batch{}
 
 func New(selector export.AggregationSelector, stateful bool) *Integrator {
 	return &Integrator{
-		selector: selector,
-		batchMap: batchMap{},
-		stateful: stateful,
+		AggregationSelector: selector,
+		stateful:            stateful,
+		batch: batch{
+			values: map[batchKey]batchValue{},
+		},
 	}
 }
 
-func (b *Integrator) AggregatorFor(descriptor *metric.Descriptor) export.Aggregator {
-	return b.selector.AggregatorFor(descriptor)
-}
-
 func (b *Integrator) Process(_ context.Context, record export.Record) error {
 	desc := record.Descriptor()
 	key := batchKey{
@@ -70,7 +73,7 @@ func (b *Integrator) Process(_ context.Context, record export.Record) error {
 		resource:   record.Resource().Equivalent(),
 	}
 	agg := record.Aggregator()
-	value, ok := b.batchMap[key]
+	value, ok := b.batch.values[key]
 	if ok {
 		// Note: The call to Merge here combines only
 		// identical records.  It is required even for a
@@ -92,7 +95,7 @@ func (b *Integrator) Process(_ context.Context, record export.Record) error {
 			return err
 		}
 	}
-	b.batchMap[key] = batchValue{
+	b.batch.values[key] = batchValue{
 		aggregator: agg,
 		labels:     record.Labels(),
 		resource:   record.Resource(),
@@ -101,17 +104,17 @@ func (b *Integrator) Process(_ context.Context, record export.Record) error {
 }
 
 func (b *Integrator) CheckpointSet() export.CheckpointSet {
-	return b.batchMap
+	return &b.batch
 }
 
 func (b *Integrator) FinishedCollection() {
 	if !b.stateful {
-		b.batchMap = batchMap{}
+		b.batch.values = map[batchKey]batchValue{}
 	}
 }
 
-func (c batchMap) ForEach(f func(export.Record) error) error {
-	for key, value := range c {
+func (b *batch) ForEach(f func(export.Record) error) error {
+	for key, value := range b.values {
 		if err := f(export.NewRecord(
 			key.descriptor,
 			value.labels,

sdk/metric/integrator/simple/simple_test.go

@@ -29,7 +29,7 @@ import (
 
 // These tests use the ../test label encoding.
 
-func TestUngroupedStateless(t *testing.T) {
+func TestSimpleStateless(t *testing.T) {
 	ctx := context.Background()
 	b := simple.New(test.NewAggregationSelector(), false)
 
@@ -60,7 +60,6 @@ func TestUngroupedStateless(t *testing.T) {
 	_ = b.Process(ctx, test.NewCounterRecord(&test.CounterBDesc, test.Labels1, 50))
 
 	checkpointSet := b.CheckpointSet()
-	b.FinishedCollection()
 
 	records := test.NewOutput(test.SdkEncoder)
 	_ = checkpointSet.ForEach(records.AddTo)
@@ -81,17 +80,18 @@ func TestUngroupedStateless(t *testing.T) {
 		"lastvalue.b/C~D&E~F/R~V": 20, // labels2
 		"lastvalue.b//R~V":        30, // labels3
 	}, records.Map)
+	b.FinishedCollection()
 
 	// Verify that state was reset
 	checkpointSet = b.CheckpointSet()
-	b.FinishedCollection()
 	_ = checkpointSet.ForEach(func(rec export.Record) error {
 		t.Fatal("Unexpected call")
 		return nil
 	})
+	b.FinishedCollection()
 }
 
-func TestUngroupedStateful(t *testing.T) {
+func TestSimpleStateful(t *testing.T) {
 	ctx := context.Background()
 	b := simple.New(test.NewAggregationSelector(), true)
 
@@ -116,12 +116,12 @@ func TestUngroupedStateful(t *testing.T) {
 
 	// Test that state was NOT reset
 	checkpointSet = b.CheckpointSet()
-	b.FinishedCollection()
 
 	records2 := test.NewOutput(test.SdkEncoder)
 	_ = checkpointSet.ForEach(records2.AddTo)
 
 	require.EqualValues(t, records1.Map, records2.Map)
+	b.FinishedCollection()
 
 	// Update and re-checkpoint the original record.
 	_ = caggA.Update(ctx, metric.NewInt64Number(20), &test.CounterADesc)
@@ -132,19 +132,18 @@ func TestUngroupedStateful(t *testing.T) {
 	// As yet cagg has not been passed to Integrator.Process.  Should
 	// not see an update.
 	checkpointSet = b.CheckpointSet()
-	b.FinishedCollection()
 
 	records3 := test.NewOutput(test.SdkEncoder)
 	_ = checkpointSet.ForEach(records3.AddTo)
 
 	require.EqualValues(t, records1.Map, records3.Map)
+	b.FinishedCollection()
 
 	// Now process the second update
 	_ = b.Process(ctx, export.NewRecord(&test.CounterADesc, test.Labels1, test.Resource, caggA))
 	_ = b.Process(ctx, export.NewRecord(&test.CounterBDesc, test.Labels1, test.Resource, caggB))
 
 	checkpointSet = b.CheckpointSet()
-	b.FinishedCollection()
 
 	records4 := test.NewOutput(test.SdkEncoder)
 	_ = checkpointSet.ForEach(records4.AddTo)
@@ -153,4 +152,5 @@ func TestUngroupedStateful(t *testing.T) {
 		"sum.a/C~D&G~H/R~V": 30,
 		"sum.b/C~D&G~H/R~V": 30,
 	}, records4.Map)
+	b.FinishedCollection()
 }

sdk/metric/sdk.go

@@ -370,6 +370,7 @@ func (m *Accumulator) Collect(ctx context.Context) int {
 	checkpointed := m.collectSyncInstruments(ctx)
 	checkpointed += m.observeAsyncInstruments(ctx)
 	m.currentEpoch++
+
 	return checkpointed
 }