sdks/go/pkg/beam/core/metrics/metrics.go - beam - Git at Google

 // Licensed to the Apache Software Foundation (ASF) under one or more
 // contributor license agreements.  See the NOTICE file distributed with
 // this work for additional information regarding copyright ownership.
 // The ASF licenses this file to You 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 metrics implements the Beam metrics API, described at
 // http://s.apache.org/beam-metrics-api
 //
 // Metrics in the Beam model are uniquely identified by a namespace, a name,
 // and the PTransform context in which they are used. Further, they are
 // reported as a delta against the bundle being processed, so that overcounting
 // doesn't occur if a bundle needs to be retried. Each metric is scoped to
 // their bundle, and ptransform.
 //
 // Cells (or metric cells) are defined for each Beam model metric
 // type, and the serve as concurrency safe storage of a given metric's values.
 // Proxys are exported values representing the metric, for use in user
 // ptransform code. They don't retain their cells, since they don't have
 // the context to be able to store them for export back to the pipeline runner.
 //
 // Metric cells aren't initialized until their first mutation, which
 // follows from the Beam model design, where metrics are only sent for a bundle
 // if they have changed. This is particularly convenient for distributions which
 // means their min and max fields can be set to the first value on creation
 // rather than have some marker of uninitialized state, which would otherwise
 // need to be checked for on every update.
 //
 // Metric values are implemented as lightweight proxies of the user provided
 // namespace and name. This allows them to be declared globally, and used in
 // any ParDo. Further, as per the design, they can be declared dynamically
 // at runtime.
 //
 // To handle reporting deltas on the metrics by bundle, metrics
 // are keyed by bundleID,PTransformID,namespace, and name, so metrics that
 // are identical except for bundles are treated as distinct, effectively
 // providing per bundle deltas, since a new value cell is used per bundle.
 package metrics

 import (
 	"context"
 	"fmt"
 	"sort"
 	"sync"
 	"time"

 	"github.com/apache/beam/sdks/go/pkg/beam/log"
 	"github.com/apache/beam/sdks/go/pkg/beam/model/fnexecution_v1"
 	"github.com/golang/protobuf/ptypes"
 )

 // Metric cells are named and scoped by ptransform, and bundle,
 // the latter two of which are only known at runtime. We propagate
 // the PTransformID and BundleID via a context.Context. Consequently
 // using metrics requires the PTransform have a context.Context
 // argument.

 type ctxKey string

 const bundleKey ctxKey = "beam:bundle"
 const ptransformKey ctxKey = "beam:ptransform"

 // beamCtx is a caching context for IDs necessary to place metric updates.
 //  Allocating contexts and searching for PTransformIDs for every element
 // is expensive, so we avoid it if possible.
 type beamCtx struct {
 	context.Context
 	bundleID, ptransformID string
 }

 // Value lifts the beam contLift the keys value for faster lookups when not available.
 func (ctx *beamCtx) Value(key interface{}) interface{} {
 	switch key {
 	case bundleKey:
 		if ctx.bundleID == "" {
 			if id := ctx.Context.Value(key); id != nil {
 				ctx.bundleID = id.(string)
 			} else {
 				return nil
 			}
 		}
 		return ctx.bundleID
 	case ptransformKey:
 		if ctx.ptransformID == "" {
 			if id := ctx.Context.Value(key); id != nil {
 				ctx.ptransformID = id.(string)
 			} else {
 				return nil
 			}
 		}
 		return ctx.ptransformID
 	}
 	return ctx.Context.Value(key)
 }

 // SetBundleID sets the id of the current Bundle.
 func SetBundleID(ctx context.Context, id string) context.Context {
 	// Checking for *beamCtx is an optimization, so we don't dig deeply
 	// for ids if not necessary.
 	if bctx, ok := ctx.(*beamCtx); ok {
 		return &beamCtx{Context: bctx.Context, bundleID: id, ptransformID: bctx.ptransformID}
 	}
 	return &beamCtx{Context: ctx, bundleID: id}
 }

 // SetPTransformID sets the id of the current PTransform.
 func SetPTransformID(ctx context.Context, id string) context.Context {
 	// Checking for *beamCtx is an optimization, so we don't dig deeply
 	// for ids if not necessary.
 	if bctx, ok := ctx.(*beamCtx); ok {
 		return &beamCtx{Context: bctx.Context, bundleID: bctx.bundleID, ptransformID: id}
 	}
 	return &beamCtx{Context: ctx, ptransformID: id}
 }

 const (
 	bundleIDUnset     = "(bundle id unset)"
 	ptransformIDUnset = "(ptransform id unset)"
 )

 func getContextKey(ctx context.Context, n name) key {
 	key := key{name: n, bundle: bundleIDUnset, ptransform: ptransformIDUnset}
 	if id := ctx.Value(bundleKey); id != nil {
 		key.bundle = id.(string)
 	}
 	if id := ctx.Value(ptransformKey); id != nil {
 		key.ptransform = id.(string)
 	}
 	return key
 }

 // userMetric knows how to convert it's value to a Metrics_User proto.
 type userMetric interface {
 	toProto() *fnexecution_v1.Metrics_User
 }

 // name is a pair of strings identifying a specific metric.
 type name struct {
 	namespace, name string
 }

 func (n name) String() string {
 	return fmt.Sprintf("%s.%s", n.namespace, n.name)
 }

 func newName(ns, n string) name {
 	if len(n) == 0 || len(ns) == 0 {
 		panic(fmt.Sprintf("namespace and name are required to be non-empty, got %q and %q", ns, n))
 	}
 	return name{namespace: ns, name: n}
 }

 type key struct {
 	name               name
 	bundle, ptransform string
 }

 var (
 	// mu protects access to store
 	mu sync.RWMutex
 	// store is a map of BundleIDs to PtransformIDs to userMetrics.
 	// it permits us to extract metric protos for runners per data Bundle, and
 	// per PTransform.
 	store = make(map[string]map[string]map[name]userMetric)

 	// We store the user path access to the cells in metric type segregated
 	// sync.Maps. Using sync.Maps lets metrics with disjoint keys have concurrent
 	// access to the cells, and using separate sync.Map per metric type
 	// simplifies code understanding, since each only contains a single type of
 	// cell.

 	countersMu      sync.RWMutex
 	counters        = make(map[key]*counter)
 	distributionsMu sync.RWMutex
 	distributions   = make(map[key]*distribution)
 	gaugesMu        sync.RWMutex
 	gauges          = make(map[key]*gauge)
 )

 // TODO(lostluck): 2018/03/05 Use a common internal beam now() instead, once that exists.
 var now = time.Now

 // Counter is a simple counter for incrementing and decrementing a value.
 type Counter struct {
 	name name
 	// The following are a fast cache of the key and storage
 	mu sync.Mutex
 	k  key
 	c  *counter
 }

 func (m *Counter) String() string {
 	return fmt.Sprintf("Counter metric %s", m.name)
 }

 // NewCounter returns the Counter with the given namespace and name.
 func NewCounter(ns, n string) *Counter {
 	mn := newName(ns, n)
 	return &Counter{
 		name: mn,
 	}
 }

 // Inc increments the counter within the given PTransform context by v.
 func (m *Counter) Inc(ctx context.Context, v int64) {
 	key := getContextKey(ctx, m.name)
 	cs := &counter{
 		value: v,
 	}
 	m.mu.Lock()
 	if m.k == key {
 		m.c.inc(v)
 		m.mu.Unlock()
 		return
 	}
 	m.k = key
 	countersMu.Lock()
 	if c, loaded := counters[key]; loaded {
 		m.c = c
 		countersMu.Unlock()
 		m.mu.Unlock()
 		c.inc(v)
 		return
 	}
 	m.c = cs
 	counters[key] = cs
 	countersMu.Unlock()
 	m.mu.Unlock()
 	storeMetric(key, cs)
 }

 // Dec decrements the counter within the given PTransform context by v.
 func (m *Counter) Dec(ctx context.Context, v int64) {
 	m.Inc(ctx, -v)
 }

 // counter is a metric cell for counter values.
 type counter struct {
 	value int64
 	mu    sync.Mutex
 }

 func (m *counter) inc(v int64) {
 	m.mu.Lock()
 	m.value += v
 	m.mu.Unlock()
 }

 func (m *counter) String() string {
 	return fmt.Sprintf("value: %d", m.value)
 }

 // toProto returns a Metrics_User populated with the Data messages, but not the name. The
 // caller needs to populate with the metric's name.
 func (m *counter) toProto() *fnexecution_v1.Metrics_User {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	return &fnexecution_v1.Metrics_User{
 		Data: &fnexecution_v1.Metrics_User_CounterData_{
 			CounterData: &fnexecution_v1.Metrics_User_CounterData{
 				Value: m.value,
 			},
 		},
 	}
 }

 // Distribution is a simple distribution of values.
 type Distribution struct {
 	name name

 	// The following are a fast cache of the key and storage
 	mu sync.Mutex
 	k  key
 	d  *distribution
 }

 func (m *Distribution) String() string {
 	return fmt.Sprintf("Distribution metric %s", m.name)
 }

 // NewDistribution returns the Distribution with the given namespace and name.
 func NewDistribution(ns, n string) *Distribution {
 	mn := newName(ns, n)
 	return &Distribution{
 		name: mn,
 	}
 }

 // Update updates the distribution within the given PTransform context with v.
 func (m *Distribution) Update(ctx context.Context, v int64) {
 	key := getContextKey(ctx, m.name)
 	ds := &distribution{
 		count: 1,
 		sum:   v,
 		min:   v,
 		max:   v,
 	}
 	m.mu.Lock()
 	if m.k == key {
 		m.d.update(v)
 		m.mu.Unlock()
 		return
 	}
 	m.k = key
 	distributionsMu.Lock()
 	if d, loaded := distributions[key]; loaded {
 		m.d = d
 		distributionsMu.Unlock()
 		m.mu.Unlock()
 		d.update(v)
 		return
 	}
 	m.d = ds
 	distributions[key] = ds
 	distributionsMu.Unlock()
 	m.mu.Unlock()
 	storeMetric(key, ds)
 }

 // distribution is a metric cell for distribution values.
 type distribution struct {
 	count, sum, min, max int64
 	mu                   sync.Mutex
 }

 func (m *distribution) update(v int64) {
 	m.mu.Lock()
 	if v < m.min {
 		m.min = v
 	}
 	if v > m.max {
 		m.max = v
 	}
 	m.count++
 	m.sum += v
 	m.mu.Unlock()
 }

 func (m *distribution) String() string {
 	return fmt.Sprintf("count: %d sum: %d min: %d max: %d", m.count, m.sum, m.min, m.max)
 }

 // toProto returns a Metrics_User populated with the Data messages, but not the name. The
 // caller needs to populate with the metric's name.
 func (m *distribution) toProto() *fnexecution_v1.Metrics_User {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	return &fnexecution_v1.Metrics_User{
 		Data: &fnexecution_v1.Metrics_User_DistributionData_{
 			DistributionData: &fnexecution_v1.Metrics_User_DistributionData{
 				Count: m.count,
 				Sum:   m.sum,
 				Min:   m.min,
 				Max:   m.max,
 			},
 		},
 	}
 }

 // Gauge is a time, value pair metric.
 type Gauge struct {
 	name name

 	// The following are a fast cache of the key and storage
 	mu sync.Mutex
 	k  key
 	g  *gauge
 }

 func (m *Gauge) String() string {
 	return fmt.Sprintf("Guage metric %s", m.name)
 }

 // NewGauge returns the Gauge with the given namespace and name.
 func NewGauge(ns, n string) *Gauge {
 	mn := newName(ns, n)
 	return &Gauge{
 		name: mn,
 	}
 }

 // Set sets the gauge to the given value, and associates it with the current time on the clock.
 func (m *Gauge) Set(ctx context.Context, v int64) {
 	key := getContextKey(ctx, m.name)
 	gs := &gauge{
 		t: now(),
 		v: v,
 	}
 	m.mu.Lock()
 	if m.k == key {
 		m.g.set(v)
 		m.mu.Unlock()
 		return
 	}
 	m.k = key
 	gaugesMu.Lock()
 	if g, loaded := gauges[key]; loaded {
 		m.g = g
 		gaugesMu.Unlock()
 		m.mu.Unlock()
 		g.set(v)
 		return
 	}
 	m.g = gs
 	gauges[key] = gs
 	gaugesMu.Unlock()
 	m.mu.Unlock()
 	storeMetric(key, gs)
 }

 // storeMetric stores a metric away on its first use so it may be retrieved later on.
 // In the event of a name collision, storeMetric can panic, so it's prudent to release
 // locks if they are no longer required.
 func storeMetric(key key, m userMetric) {
 	mu.Lock()
 	defer mu.Unlock()
 	if _, ok := store[key.bundle]; !ok {
 		store[key.bundle] = make(map[string]map[name]userMetric)
 	}
 	if _, ok := store[key.bundle][key.ptransform]; !ok {
 		store[key.bundle][key.ptransform] = make(map[name]userMetric)
 	}
 	if _, ok := store[key.bundle][key.ptransform][key.name]; ok {
 		panic(fmt.Sprintf("metric name %s being reused for a second metric in a single PTransform", key.name))
 	}
 	store[key.bundle][key.ptransform][key.name] = m
 }

 // gauge is a metric cell for gauge values.
 type gauge struct {
 	mu sync.Mutex
 	t  time.Time
 	v  int64
 }

 func (m *gauge) set(v int64) {
 	m.mu.Lock()
 	m.t = now()
 	m.v = v
 	m.mu.Unlock()
 }

 func (m *gauge) toProto() *fnexecution_v1.Metrics_User {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	ts, err := ptypes.TimestampProto(m.t)
 	if err != nil {
 		panic(err)
 	}
 	return &fnexecution_v1.Metrics_User{
 		Data: &fnexecution_v1.Metrics_User_GaugeData_{
 			GaugeData: &fnexecution_v1.Metrics_User_GaugeData{
 				Value:     m.v,
 				Timestamp: ts,
 			},
 		},
 	}
 }

 func (m *gauge) String() string {
 	return fmt.Sprintf("time: %s value: %d", m.t, m.v)
 }

 // ToProto exports all collected metrics for the given BundleID and PTransform ID pair.
 func ToProto(b, pt string) []*fnexecution_v1.Metrics_User {
 	mu.RLock()
 	defer mu.RUnlock()
 	ps := store[b]
 	s := ps[pt]
 	var ret []*fnexecution_v1.Metrics_User
 	for n, m := range s {
 		p := m.toProto()
 		p.MetricName = &fnexecution_v1.Metrics_User_MetricName{
 			Name:      n.name,
 			Namespace: n.namespace,
 		}
 		ret = append(ret, p)
 	}
 	return ret
 }

 // DumpToLog is a debugging function that outputs all metrics available locally to beam.Log.
 func DumpToLog(ctx context.Context) {
 	dumpTo(func(format string, args ...interface{}) {
 		log.Errorf(ctx, format, args...)
 	})
 }

 // DumpToOut is a debugging function that outputs all metrics available locally to std out.
 func DumpToOut() {
 	dumpTo(func(format string, args ...interface{}) {
 		fmt.Printf(format+"\n", args...)
 	})
 }

 func dumpTo(p func(format string, args ...interface{})) {
 	mu.RLock()
 	defer mu.RUnlock()
 	countersMu.RLock()
 	defer countersMu.RUnlock()
 	distributionsMu.RLock()
 	defer distributionsMu.RUnlock()
 	gaugesMu.RLock()
 	defer gaugesMu.RUnlock()
 	var bs []string
 	for b := range store {
 		bs = append(bs, b)
 	}
 	sort.Strings(bs)
 	for _, b := range bs {
 		var pts []string
 		for pt := range store[b] {
 			pts = append(pts, pt)
 		}
 		sort.Strings(pts)
 		for _, pt := range pts {
 			var ns []name
 			for n := range store[b][pt] {
 				ns = append(ns, n)
 			}
 			sort.Slice(ns, func(i, j int) bool {
 				if ns[i].namespace < ns[j].namespace {
 					return true
 				}
 				if ns[i].namespace == ns[j].namespace && ns[i].name < ns[j].name {
 					return true
 				}
 				return false
 			})
 			p("Bundle: %q - PTransformID: %q", b, pt)
 			for _, n := range ns {
 				key := key{name: n, bundle: b, ptransform: pt}
 				if m, ok := counters[key]; ok {
 					p("\t%s - %s", key.name, m)
 				}
 				if m, ok := distributions[key]; ok {
 					p("\t%s - %s", key.name, m)
 				}
 				if m, ok := gauges[key]; ok {
 					p("\t%s - %s", key.name, m)
 				}
 			}
 		}
 	}
 }

 // Clear resets all storage associated with metrics for tests.
 // Calling this in pipeline code leads to inaccurate metrics.
 func Clear() {
 	mu.Lock()
 	store = make(map[string]map[string]map[name]userMetric)
 	counters = make(map[key]*counter)
 	distributions = make(map[key]*distribution)
 	gauges = make(map[key]*gauge)
 	mu.Unlock()
 }

 // ClearBundleData removes stored references associated with a given bundle,
 // so it can be garbage collected.
 func ClearBundleData(b string) {
 	// No concurrency races since mu guards all access to store,
 	// and the metric cell sync.Maps are goroutine safe.
 	mu.Lock()
 	pts := store[b]
 	countersMu.Lock()
 	distributionsMu.Lock()
 	gaugesMu.Lock()
 	for pt, m := range pts {
 		for n := range m {
 			key := key{name: n, bundle: b, ptransform: pt}
 			delete(counters, key)
 			delete(distributions, key)
 			delete(gauges, key)
 		}
 	}
 	countersMu.Unlock()
 	distributionsMu.Unlock()
 	gaugesMu.Unlock()
 	delete(store, b)
 	mu.Unlock()
 }
	// Licensed to the Apache Software Foundation (ASF) under one or more
	// contributor license agreements. See the NOTICE file distributed with
	// this work for additional information regarding copyright ownership.
	// The ASF licenses this file to You 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 metrics implements the Beam metrics API, described at
	// http://s.apache.org/beam-metrics-api
	//
	// Metrics in the Beam model are uniquely identified by a namespace, a name,
	// and the PTransform context in which they are used. Further, they are
	// reported as a delta against the bundle being processed, so that overcounting
	// doesn't occur if a bundle needs to be retried. Each metric is scoped to
	// their bundle, and ptransform.
	//
	// Cells (or metric cells) are defined for each Beam model metric
	// type, and the serve as concurrency safe storage of a given metric's values.
	// Proxys are exported values representing the metric, for use in user
	// ptransform code. They don't retain their cells, since they don't have
	// the context to be able to store them for export back to the pipeline runner.
	//
	// Metric cells aren't initialized until their first mutation, which
	// follows from the Beam model design, where metrics are only sent for a bundle
	// if they have changed. This is particularly convenient for distributions which
	// means their min and max fields can be set to the first value on creation
	// rather than have some marker of uninitialized state, which would otherwise
	// need to be checked for on every update.
	//
	// Metric values are implemented as lightweight proxies of the user provided
	// namespace and name. This allows them to be declared globally, and used in
	// any ParDo. Further, as per the design, they can be declared dynamically
	// at runtime.
	//
	// To handle reporting deltas on the metrics by bundle, metrics
	// are keyed by bundleID,PTransformID,namespace, and name, so metrics that
	// are identical except for bundles are treated as distinct, effectively
	// providing per bundle deltas, since a new value cell is used per bundle.
	package metrics

	import (
	"context"
	"fmt"
	"sort"
	"sync"
	"time"

	"github.com/apache/beam/sdks/go/pkg/beam/log"
	"github.com/apache/beam/sdks/go/pkg/beam/model/fnexecution_v1"
	"github.com/golang/protobuf/ptypes"
	)

	// Metric cells are named and scoped by ptransform, and bundle,
	// the latter two of which are only known at runtime. We propagate
	// the PTransformID and BundleID via a context.Context. Consequently
	// using metrics requires the PTransform have a context.Context
	// argument.

	type ctxKey string

	const bundleKey ctxKey = "beam:bundle"
	const ptransformKey ctxKey = "beam:ptransform"

	// beamCtx is a caching context for IDs necessary to place metric updates.
	// Allocating contexts and searching for PTransformIDs for every element
	// is expensive, so we avoid it if possible.
	type beamCtx struct {
	context.Context
	bundleID, ptransformID string
	}

	// Value lifts the beam contLift the keys value for faster lookups when not available.
	func (ctx *beamCtx) Value(key interface{}) interface{} {
	switch key {
	case bundleKey:
	if ctx.bundleID == "" {
	if id := ctx.Context.Value(key); id != nil {
	ctx.bundleID = id.(string)
	} else {
	return nil
	}
	}
	return ctx.bundleID
	case ptransformKey:
	if ctx.ptransformID == "" {
	if id := ctx.Context.Value(key); id != nil {
	ctx.ptransformID = id.(string)
	} else {
	return nil
	}
	}
	return ctx.ptransformID
	}
	return ctx.Context.Value(key)
	}

	// SetBundleID sets the id of the current Bundle.
	func SetBundleID(ctx context.Context, id string) context.Context {
	// Checking for *beamCtx is an optimization, so we don't dig deeply
	// for ids if not necessary.
	if bctx, ok := ctx.(*beamCtx); ok {
	return &beamCtx{Context: bctx.Context, bundleID: id, ptransformID: bctx.ptransformID}
	}
	return &beamCtx{Context: ctx, bundleID: id}
	}

	// SetPTransformID sets the id of the current PTransform.
	func SetPTransformID(ctx context.Context, id string) context.Context {
	// Checking for *beamCtx is an optimization, so we don't dig deeply
	// for ids if not necessary.
	if bctx, ok := ctx.(*beamCtx); ok {
	return &beamCtx{Context: bctx.Context, bundleID: bctx.bundleID, ptransformID: id}
	}
	return &beamCtx{Context: ctx, ptransformID: id}
	}

	const (
	bundleIDUnset = "(bundle id unset)"
	ptransformIDUnset = "(ptransform id unset)"
	)

	func getContextKey(ctx context.Context, n name) key {
	key := key{name: n, bundle: bundleIDUnset, ptransform: ptransformIDUnset}
	if id := ctx.Value(bundleKey); id != nil {
	key.bundle = id.(string)
	}
	if id := ctx.Value(ptransformKey); id != nil {
	key.ptransform = id.(string)
	}
	return key
	}

	// userMetric knows how to convert it's value to a Metrics_User proto.
	type userMetric interface {
	toProto() *fnexecution_v1.Metrics_User
	}

	// name is a pair of strings identifying a specific metric.
	type name struct {
	namespace, name string
	}

	func (n name) String() string {
	return fmt.Sprintf("%s.%s", n.namespace, n.name)
	}

	func newName(ns, n string) name {
	if len(n) == 0 \|\| len(ns) == 0 {
	panic(fmt.Sprintf("namespace and name are required to be non-empty, got %q and %q", ns, n))
	}
	return name{namespace: ns, name: n}
	}

	type key struct {
	name name
	bundle, ptransform string
	}

	var (
	// mu protects access to store
	mu sync.RWMutex
	// store is a map of BundleIDs to PtransformIDs to userMetrics.
	// it permits us to extract metric protos for runners per data Bundle, and
	// per PTransform.
	store = make(map[string]map[string]map[name]userMetric)

	// We store the user path access to the cells in metric type segregated
	// sync.Maps. Using sync.Maps lets metrics with disjoint keys have concurrent
	// access to the cells, and using separate sync.Map per metric type
	// simplifies code understanding, since each only contains a single type of
	// cell.

	countersMu sync.RWMutex
	counters = make(map[key]*counter)
	distributionsMu sync.RWMutex
	distributions = make(map[key]*distribution)
	gaugesMu sync.RWMutex
	gauges = make(map[key]*gauge)
	)

	// TODO(lostluck): 2018/03/05 Use a common internal beam now() instead, once that exists.
	var now = time.Now

	// Counter is a simple counter for incrementing and decrementing a value.
	type Counter struct {
	name name
	// The following are a fast cache of the key and storage
	mu sync.Mutex
	k key
	c *counter
	}

	func (m *Counter) String() string {
	return fmt.Sprintf("Counter metric %s", m.name)
	}

	// NewCounter returns the Counter with the given namespace and name.
	func NewCounter(ns, n string) *Counter {
	mn := newName(ns, n)
	return &Counter{
	name: mn,
	}
	}

	// Inc increments the counter within the given PTransform context by v.
	func (m *Counter) Inc(ctx context.Context, v int64) {
	key := getContextKey(ctx, m.name)
	cs := &counter{
	value: v,
	}
	m.mu.Lock()
	if m.k == key {
	m.c.inc(v)
	m.mu.Unlock()
	return
	}
	m.k = key
	countersMu.Lock()
	if c, loaded := counters[key]; loaded {
	m.c = c
	countersMu.Unlock()
	m.mu.Unlock()
	c.inc(v)
	return
	}
	m.c = cs
	counters[key] = cs
	countersMu.Unlock()
	m.mu.Unlock()
	storeMetric(key, cs)
	}

	// Dec decrements the counter within the given PTransform context by v.
	func (m *Counter) Dec(ctx context.Context, v int64) {
	m.Inc(ctx, -v)
	}

	// counter is a metric cell for counter values.
	type counter struct {
	value int64
	mu sync.Mutex
	}

	func (m *counter) inc(v int64) {
	m.mu.Lock()
	m.value += v
	m.mu.Unlock()
	}

	func (m *counter) String() string {
	return fmt.Sprintf("value: %d", m.value)
	}

	// toProto returns a Metrics_User populated with the Data messages, but not the name. The
	// caller needs to populate with the metric's name.
	func (m counter) toProto() fnexecution_v1.Metrics_User {
	m.mu.Lock()
	defer m.mu.Unlock()
	return &fnexecution_v1.Metrics_User{
	Data: &fnexecution_v1.Metrics_User_CounterData_{
	CounterData: &fnexecution_v1.Metrics_User_CounterData{
	Value: m.value,
	},
	},
	}
	}

	// Distribution is a simple distribution of values.
	type Distribution struct {
	name name

	// The following are a fast cache of the key and storage
	mu sync.Mutex
	k key
	d *distribution
	}

	func (m *Distribution) String() string {
	return fmt.Sprintf("Distribution metric %s", m.name)
	}

	// NewDistribution returns the Distribution with the given namespace and name.
	func NewDistribution(ns, n string) *Distribution {
	mn := newName(ns, n)
	return &Distribution{
	name: mn,
	}
	}

	// Update updates the distribution within the given PTransform context with v.
	func (m *Distribution) Update(ctx context.Context, v int64) {
	key := getContextKey(ctx, m.name)
	ds := &distribution{
	count: 1,
	sum: v,
	min: v,
	max: v,
	}
	m.mu.Lock()
	if m.k == key {
	m.d.update(v)
	m.mu.Unlock()
	return
	}
	m.k = key
	distributionsMu.Lock()
	if d, loaded := distributions[key]; loaded {
	m.d = d
	distributionsMu.Unlock()
	m.mu.Unlock()
	d.update(v)
	return
	}
	m.d = ds
	distributions[key] = ds
	distributionsMu.Unlock()
	m.mu.Unlock()
	storeMetric(key, ds)
	}

	// distribution is a metric cell for distribution values.
	type distribution struct {
	count, sum, min, max int64
	mu sync.Mutex
	}

	func (m *distribution) update(v int64) {
	m.mu.Lock()
	if v < m.min {
	m.min = v
	}
	if v > m.max {
	m.max = v
	}
	m.count++
	m.sum += v
	m.mu.Unlock()
	}

	func (m *distribution) String() string {
	return fmt.Sprintf("count: %d sum: %d min: %d max: %d", m.count, m.sum, m.min, m.max)
	}

	// toProto returns a Metrics_User populated with the Data messages, but not the name. The
	// caller needs to populate with the metric's name.
	func (m distribution) toProto() fnexecution_v1.Metrics_User {
	m.mu.Lock()
	defer m.mu.Unlock()
	return &fnexecution_v1.Metrics_User{
	Data: &fnexecution_v1.Metrics_User_DistributionData_{
	DistributionData: &fnexecution_v1.Metrics_User_DistributionData{
	Count: m.count,
	Sum: m.sum,
	Min: m.min,
	Max: m.max,
	},
	},
	}
	}

	// Gauge is a time, value pair metric.
	type Gauge struct {
	name name

	// The following are a fast cache of the key and storage
	mu sync.Mutex
	k key
	g *gauge
	}

	func (m *Gauge) String() string {
	return fmt.Sprintf("Guage metric %s", m.name)
	}

	// NewGauge returns the Gauge with the given namespace and name.
	func NewGauge(ns, n string) *Gauge {
	mn := newName(ns, n)
	return &Gauge{
	name: mn,
	}
	}

	// Set sets the gauge to the given value, and associates it with the current time on the clock.
	func (m *Gauge) Set(ctx context.Context, v int64) {
	key := getContextKey(ctx, m.name)
	gs := &gauge{
	t: now(),
	v: v,
	}
	m.mu.Lock()
	if m.k == key {
	m.g.set(v)
	m.mu.Unlock()
	return
	}
	m.k = key
	gaugesMu.Lock()
	if g, loaded := gauges[key]; loaded {
	m.g = g
	gaugesMu.Unlock()
	m.mu.Unlock()
	g.set(v)
	return
	}
	m.g = gs
	gauges[key] = gs
	gaugesMu.Unlock()
	m.mu.Unlock()
	storeMetric(key, gs)
	}

	// storeMetric stores a metric away on its first use so it may be retrieved later on.
	// In the event of a name collision, storeMetric can panic, so it's prudent to release
	// locks if they are no longer required.
	func storeMetric(key key, m userMetric) {
	mu.Lock()
	defer mu.Unlock()
	if _, ok := store[key.bundle]; !ok {
	store[key.bundle] = make(map[string]map[name]userMetric)
	}
	if _, ok := store[key.bundle][key.ptransform]; !ok {
	store[key.bundle][key.ptransform] = make(map[name]userMetric)
	}
	if _, ok := store[key.bundle][key.ptransform][key.name]; ok {
	panic(fmt.Sprintf("metric name %s being reused for a second metric in a single PTransform", key.name))
	}
	store[key.bundle][key.ptransform][key.name] = m
	}

	// gauge is a metric cell for gauge values.
	type gauge struct {
	mu sync.Mutex
	t time.Time
	v int64
	}

	func (m *gauge) set(v int64) {
	m.mu.Lock()
	m.t = now()
	m.v = v
	m.mu.Unlock()
	}

	func (m gauge) toProto() fnexecution_v1.Metrics_User {
	m.mu.Lock()
	defer m.mu.Unlock()
	ts, err := ptypes.TimestampProto(m.t)
	if err != nil {
	panic(err)
	}
	return &fnexecution_v1.Metrics_User{
	Data: &fnexecution_v1.Metrics_User_GaugeData_{
	GaugeData: &fnexecution_v1.Metrics_User_GaugeData{
	Value: m.v,
	Timestamp: ts,
	},
	},
	}
	}

	func (m *gauge) String() string {
	return fmt.Sprintf("time: %s value: %d", m.t, m.v)
	}

	// ToProto exports all collected metrics for the given BundleID and PTransform ID pair.
	func ToProto(b, pt string) []*fnexecution_v1.Metrics_User {
	mu.RLock()
	defer mu.RUnlock()
	ps := store[b]
	s := ps[pt]
	var ret []*fnexecution_v1.Metrics_User
	for n, m := range s {
	p := m.toProto()
	p.MetricName = &fnexecution_v1.Metrics_User_MetricName{
	Name: n.name,
	Namespace: n.namespace,
	}
	ret = append(ret, p)
	}
	return ret
	}

	// DumpToLog is a debugging function that outputs all metrics available locally to beam.Log.
	func DumpToLog(ctx context.Context) {
	dumpTo(func(format string, args ...interface{}) {
	log.Errorf(ctx, format, args...)
	})
	}

	// DumpToOut is a debugging function that outputs all metrics available locally to std out.
	func DumpToOut() {
	dumpTo(func(format string, args ...interface{}) {
	fmt.Printf(format+"\n", args...)
	})
	}

	func dumpTo(p func(format string, args ...interface{})) {
	mu.RLock()
	defer mu.RUnlock()
	countersMu.RLock()
	defer countersMu.RUnlock()
	distributionsMu.RLock()
	defer distributionsMu.RUnlock()
	gaugesMu.RLock()
	defer gaugesMu.RUnlock()
	var bs []string
	for b := range store {
	bs = append(bs, b)
	}
	sort.Strings(bs)
	for _, b := range bs {
	var pts []string
	for pt := range store[b] {
	pts = append(pts, pt)
	}
	sort.Strings(pts)
	for _, pt := range pts {
	var ns []name
	for n := range store[b][pt] {
	ns = append(ns, n)
	}
	sort.Slice(ns, func(i, j int) bool {
	if ns[i].namespace < ns[j].namespace {
	return true
	}
	if ns[i].namespace == ns[j].namespace && ns[i].name < ns[j].name {
	return true
	}
	return false
	})
	p("Bundle: %q - PTransformID: %q", b, pt)
	for _, n := range ns {
	key := key{name: n, bundle: b, ptransform: pt}
	if m, ok := counters[key]; ok {
	p("\t%s - %s", key.name, m)
	}
	if m, ok := distributions[key]; ok {
	p("\t%s - %s", key.name, m)
	}
	if m, ok := gauges[key]; ok {
	p("\t%s - %s", key.name, m)
	}
	}
	}
	}
	}

	// Clear resets all storage associated with metrics for tests.
	// Calling this in pipeline code leads to inaccurate metrics.
	func Clear() {
	mu.Lock()
	store = make(map[string]map[string]map[name]userMetric)
	counters = make(map[key]*counter)
	distributions = make(map[key]*distribution)
	gauges = make(map[key]*gauge)
	mu.Unlock()
	}

	// ClearBundleData removes stored references associated with a given bundle,
	// so it can be garbage collected.
	func ClearBundleData(b string) {
	// No concurrency races since mu guards all access to store,
	// and the metric cell sync.Maps are goroutine safe.
	mu.Lock()
	pts := store[b]
	countersMu.Lock()
	distributionsMu.Lock()
	gaugesMu.Lock()
	for pt, m := range pts {
	for n := range m {
	key := key{name: n, bundle: b, ptransform: pt}
	delete(counters, key)
	delete(distributions, key)
	delete(gauges, key)
	}
	}
	countersMu.Unlock()
	distributionsMu.Unlock()
	gaugesMu.Unlock()
	delete(store, b)
	mu.Unlock()
	}