vendor/github.com/uber/jaeger-client-go/sampler.go - voltha-openolt-adapter - Gitiles

 // Copyright (c) 2017 Uber Technologies, Inc.
 //
 // 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 jaeger

 import (
 	"fmt"
 	"math"
 	"strings"
 	"sync"

 	"github.com/uber/jaeger-client-go/thrift-gen/sampling"
 	"github.com/uber/jaeger-client-go/utils"
 )

 const (
 	defaultMaxOperations = 2000
 )

 // Sampler decides whether a new trace should be sampled or not.
 type Sampler interface {
 	// IsSampled decides whether a trace with given `id` and `operation`
 	// should be sampled. This function will also return the tags that
 	// can be used to identify the type of sampling that was applied to
 	// the root span. Most simple samplers would return two tags,
 	// sampler.type and sampler.param, similar to those used in the Configuration
 	IsSampled(id TraceID, operation string) (sampled bool, tags []Tag)

 	// Close does a clean shutdown of the sampler, stopping any background
 	// go-routines it may have started.
 	Close()

 	// Equal checks if the `other` sampler is functionally equivalent
 	// to this sampler.
 	// TODO (breaking change) remove this function. See PerOperationSampler.Equals for explanation.
 	Equal(other Sampler) bool
 }

 // -----------------------

 // ConstSampler is a sampler that always makes the same decision.
 type ConstSampler struct {
 	legacySamplerV1Base
 	Decision bool
 	tags     []Tag
 }

 // NewConstSampler creates a ConstSampler.
 func NewConstSampler(sample bool) *ConstSampler {
 	tags := []Tag{
 		{key: SamplerTypeTagKey, value: SamplerTypeConst},
 		{key: SamplerParamTagKey, value: sample},
 	}
 	s := &ConstSampler{
 		Decision: sample,
 		tags:     tags,
 	}
 	s.delegate = s.IsSampled
 	return s
 }

 // IsSampled implements IsSampled() of Sampler.
 func (s *ConstSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
 	return s.Decision, s.tags
 }

 // Close implements Close() of Sampler.
 func (s *ConstSampler) Close() {
 	// nothing to do
 }

 // Equal implements Equal() of Sampler.
 func (s *ConstSampler) Equal(other Sampler) bool {
 	if o, ok := other.(*ConstSampler); ok {
 		return s.Decision == o.Decision
 	}
 	return false
 }

 // String is used to log sampler details.
 func (s *ConstSampler) String() string {
 	return fmt.Sprintf("ConstSampler(decision=%t)", s.Decision)
 }

 // -----------------------

 // ProbabilisticSampler is a sampler that randomly samples a certain percentage
 // of traces.
 type ProbabilisticSampler struct {
 	legacySamplerV1Base
 	samplingRate     float64
 	samplingBoundary uint64
 	tags             []Tag
 }

 const maxRandomNumber = ^(uint64(1) << 63) // i.e. 0x7fffffffffffffff

 // NewProbabilisticSampler creates a sampler that randomly samples a certain percentage of traces specified by the
 // samplingRate, in the range between 0.0 and 1.0.
 //
 // It relies on the fact that new trace IDs are 63bit random numbers themselves, thus making the sampling decision
 // without generating a new random number, but simply calculating if traceID < (samplingRate * 2^63).
 // TODO remove the error from this function for next major release
 func NewProbabilisticSampler(samplingRate float64) (*ProbabilisticSampler, error) {
 	if samplingRate < 0.0 || samplingRate > 1.0 {
 		return nil, fmt.Errorf("Sampling Rate must be between 0.0 and 1.0, received %f", samplingRate)
 	}
 	return newProbabilisticSampler(samplingRate), nil
 }

 func newProbabilisticSampler(samplingRate float64) *ProbabilisticSampler {
 	s := new(ProbabilisticSampler)
 	s.delegate = s.IsSampled
 	return s.init(samplingRate)
 }

 func (s *ProbabilisticSampler) init(samplingRate float64) *ProbabilisticSampler {
 	s.samplingRate = math.Max(0.0, math.Min(samplingRate, 1.0))
 	s.samplingBoundary = uint64(float64(maxRandomNumber) * s.samplingRate)
 	s.tags = []Tag{
 		{key: SamplerTypeTagKey, value: SamplerTypeProbabilistic},
 		{key: SamplerParamTagKey, value: s.samplingRate},
 	}
 	return s
 }

 // SamplingRate returns the sampling probability this sampled was constructed with.
 func (s *ProbabilisticSampler) SamplingRate() float64 {
 	return s.samplingRate
 }

 // IsSampled implements IsSampled() of Sampler.
 func (s *ProbabilisticSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
 	return s.samplingBoundary >= id.Low&maxRandomNumber, s.tags
 }

 // Close implements Close() of Sampler.
 func (s *ProbabilisticSampler) Close() {
 	// nothing to do
 }

 // Equal implements Equal() of Sampler.
 func (s *ProbabilisticSampler) Equal(other Sampler) bool {
 	if o, ok := other.(*ProbabilisticSampler); ok {
 		return s.samplingBoundary == o.samplingBoundary
 	}
 	return false
 }

 // Update modifies in-place the sampling rate. Locking must be done externally.
 func (s *ProbabilisticSampler) Update(samplingRate float64) error {
 	if samplingRate < 0.0 || samplingRate > 1.0 {
 		return fmt.Errorf("Sampling Rate must be between 0.0 and 1.0, received %f", samplingRate)
 	}
 	s.init(samplingRate)
 	return nil
 }

 // String is used to log sampler details.
 func (s *ProbabilisticSampler) String() string {
 	return fmt.Sprintf("ProbabilisticSampler(samplingRate=%v)", s.samplingRate)
 }

 // -----------------------

 // RateLimitingSampler samples at most maxTracesPerSecond. The distribution of sampled traces follows
 // burstiness of the service, i.e. a service with uniformly distributed requests will have those
 // requests sampled uniformly as well, but if requests are bursty, especially sub-second, then a
 // number of sequential requests can be sampled each second.
 type RateLimitingSampler struct {
 	legacySamplerV1Base
 	maxTracesPerSecond float64
 	rateLimiter        *utils.ReconfigurableRateLimiter
 	tags               []Tag
 }

 // NewRateLimitingSampler creates new RateLimitingSampler.
 func NewRateLimitingSampler(maxTracesPerSecond float64) *RateLimitingSampler {
 	s := new(RateLimitingSampler)
 	s.delegate = s.IsSampled
 	return s.init(maxTracesPerSecond)
 }

 func (s *RateLimitingSampler) init(maxTracesPerSecond float64) *RateLimitingSampler {
 	if s.rateLimiter == nil {
 		s.rateLimiter = utils.NewRateLimiter(maxTracesPerSecond, math.Max(maxTracesPerSecond, 1.0))
 	} else {
 		s.rateLimiter.Update(maxTracesPerSecond, math.Max(maxTracesPerSecond, 1.0))
 	}
 	s.maxTracesPerSecond = maxTracesPerSecond
 	s.tags = []Tag{
 		{key: SamplerTypeTagKey, value: SamplerTypeRateLimiting},
 		{key: SamplerParamTagKey, value: maxTracesPerSecond},
 	}
 	return s
 }

 // IsSampled implements IsSampled() of Sampler.
 func (s *RateLimitingSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
 	return s.rateLimiter.CheckCredit(1.0), s.tags
 }

 // Update reconfigures the rate limiter, while preserving its accumulated balance.
 // Locking must be done externally.
 func (s *RateLimitingSampler) Update(maxTracesPerSecond float64) {
 	if s.maxTracesPerSecond != maxTracesPerSecond {
 		s.init(maxTracesPerSecond)
 	}
 }

 // Close does nothing.
 func (s *RateLimitingSampler) Close() {
 	// nothing to do
 }

 // Equal compares with another sampler.
 func (s *RateLimitingSampler) Equal(other Sampler) bool {
 	if o, ok := other.(*RateLimitingSampler); ok {
 		return s.maxTracesPerSecond == o.maxTracesPerSecond
 	}
 	return false
 }

 // String is used to log sampler details.
 func (s *RateLimitingSampler) String() string {
 	return fmt.Sprintf("RateLimitingSampler(maxTracesPerSecond=%v)", s.maxTracesPerSecond)
 }

 // -----------------------

 // GuaranteedThroughputProbabilisticSampler is a sampler that leverages both ProbabilisticSampler and
 // RateLimitingSampler. The RateLimitingSampler is used as a guaranteed lower bound sampler such that
 // every operation is sampled at least once in a time interval defined by the lowerBound. ie a lowerBound
 // of 1.0 / (60 * 10) will sample an operation at least once every 10 minutes.
 //
 // The ProbabilisticSampler is given higher priority when tags are emitted, ie. if IsSampled() for both
 // samplers return true, the tags for ProbabilisticSampler will be used.
 type GuaranteedThroughputProbabilisticSampler struct {
 	probabilisticSampler *ProbabilisticSampler
 	lowerBoundSampler    *RateLimitingSampler
 	tags                 []Tag
 	samplingRate         float64
 	lowerBound           float64
 }

 // NewGuaranteedThroughputProbabilisticSampler returns a delegating sampler that applies both
 // ProbabilisticSampler and RateLimitingSampler.
 func NewGuaranteedThroughputProbabilisticSampler(
 	lowerBound, samplingRate float64,
 ) (*GuaranteedThroughputProbabilisticSampler, error) {
 	return newGuaranteedThroughputProbabilisticSampler(lowerBound, samplingRate), nil
 }

 func newGuaranteedThroughputProbabilisticSampler(lowerBound, samplingRate float64) *GuaranteedThroughputProbabilisticSampler {
 	s := &GuaranteedThroughputProbabilisticSampler{
 		lowerBoundSampler: NewRateLimitingSampler(lowerBound),
 		lowerBound:        lowerBound,
 	}
 	s.setProbabilisticSampler(samplingRate)
 	return s
 }

 func (s *GuaranteedThroughputProbabilisticSampler) setProbabilisticSampler(samplingRate float64) {
 	if s.probabilisticSampler == nil {
 		s.probabilisticSampler = newProbabilisticSampler(samplingRate)
 	} else if s.samplingRate != samplingRate {
 		s.probabilisticSampler.init(samplingRate)
 	}
 	// since we don't validate samplingRate, sampler may have clamped it to [0, 1] interval
 	samplingRate = s.probabilisticSampler.SamplingRate()
 	if s.samplingRate != samplingRate || s.tags == nil {
 		s.samplingRate = s.probabilisticSampler.SamplingRate()
 		s.tags = []Tag{
 			{key: SamplerTypeTagKey, value: SamplerTypeLowerBound},
 			{key: SamplerParamTagKey, value: s.samplingRate},
 		}
 	}
 }

 // IsSampled implements IsSampled() of Sampler.
 func (s *GuaranteedThroughputProbabilisticSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
 	if sampled, tags := s.probabilisticSampler.IsSampled(id, operation); sampled {
 		s.lowerBoundSampler.IsSampled(id, operation)
 		return true, tags
 	}
 	sampled, _ := s.lowerBoundSampler.IsSampled(id, operation)
 	return sampled, s.tags
 }

 // Close implements Close() of Sampler.
 func (s *GuaranteedThroughputProbabilisticSampler) Close() {
 	s.probabilisticSampler.Close()
 	s.lowerBoundSampler.Close()
 }

 // Equal implements Equal() of Sampler.
 func (s *GuaranteedThroughputProbabilisticSampler) Equal(other Sampler) bool {
 	// NB The Equal() function is expensive and will be removed. See PerOperationSampler.Equal() for
 	// more information.
 	return false
 }

 // this function should only be called while holding a Write lock
 func (s *GuaranteedThroughputProbabilisticSampler) update(lowerBound, samplingRate float64) {
 	s.setProbabilisticSampler(samplingRate)
 	if s.lowerBound != lowerBound {
 		s.lowerBoundSampler.Update(lowerBound)
 		s.lowerBound = lowerBound
 	}
 }

 func (s GuaranteedThroughputProbabilisticSampler) String() string {
 	return fmt.Sprintf("GuaranteedThroughputProbabilisticSampler(lowerBound=%f, samplingRate=%f)", s.lowerBound, s.samplingRate)
 }

 // -----------------------

 // PerOperationSampler is a delegating sampler that applies GuaranteedThroughputProbabilisticSampler
 // on a per-operation basis.
 type PerOperationSampler struct {
 	sync.RWMutex

 	samplers       map[string]*GuaranteedThroughputProbabilisticSampler
 	defaultSampler *ProbabilisticSampler
 	lowerBound     float64
 	maxOperations  int

 	// see description in PerOperationSamplerParams
 	operationNameLateBinding bool
 }

 // NewAdaptiveSampler returns a new PerOperationSampler.
 // Deprecated: please use NewPerOperationSampler.
 func NewAdaptiveSampler(strategies *sampling.PerOperationSamplingStrategies, maxOperations int) (*PerOperationSampler, error) {
 	return NewPerOperationSampler(PerOperationSamplerParams{
 		MaxOperations: maxOperations,
 		Strategies:    strategies,
 	}), nil
 }

 // PerOperationSamplerParams defines parameters when creating PerOperationSampler.
 type PerOperationSamplerParams struct {
 	// Max number of operations that will be tracked. Other operations will be given default strategy.
 	MaxOperations int

 	// Opt-in feature for applications that require late binding of span name via explicit call to SetOperationName.
 	// When this feature is enabled, the sampler will return retryable=true from OnCreateSpan(), thus leaving
 	// the sampling decision as non-final (and the span as writeable). This may lead to degraded performance
 	// in applications that always provide the correct span name on trace creation.
 	//
 	// For backwards compatibility this option is off by default.
 	OperationNameLateBinding bool

 	// Initial configuration of the sampling strategies (usually retrieved from the backend by Remote Sampler).
 	Strategies *sampling.PerOperationSamplingStrategies
 }

 // NewPerOperationSampler returns a new PerOperationSampler.
 func NewPerOperationSampler(params PerOperationSamplerParams) *PerOperationSampler {
 	if params.MaxOperations <= 0 {
 		params.MaxOperations = defaultMaxOperations
 	}
 	samplers := make(map[string]*GuaranteedThroughputProbabilisticSampler)
 	for _, strategy := range params.Strategies.PerOperationStrategies {
 		sampler := newGuaranteedThroughputProbabilisticSampler(
 			params.Strategies.DefaultLowerBoundTracesPerSecond,
 			strategy.ProbabilisticSampling.SamplingRate,
 		)
 		samplers[strategy.Operation] = sampler
 	}
 	return &PerOperationSampler{
 		samplers:                 samplers,
 		defaultSampler:           newProbabilisticSampler(params.Strategies.DefaultSamplingProbability),
 		lowerBound:               params.Strategies.DefaultLowerBoundTracesPerSecond,
 		maxOperations:            params.MaxOperations,
 		operationNameLateBinding: params.OperationNameLateBinding,
 	}
 }

 // IsSampled is not used and only exists to match Sampler V1 API.
 // TODO (breaking change) remove when upgrading everything to SamplerV2
 func (s *PerOperationSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
 	return false, nil
 }

 func (s *PerOperationSampler) trySampling(span *Span, operationName string) (bool, []Tag) {
 	samplerV1 := s.getSamplerForOperation(operationName)
 	var sampled bool
 	var tags []Tag
 	if span.context.samplingState.isLocalRootSpan(span.context.spanID) {
 		sampled, tags = samplerV1.IsSampled(span.context.TraceID(), operationName)
 	}
 	return sampled, tags
 }

 // OnCreateSpan implements OnCreateSpan of SamplerV2.
 func (s *PerOperationSampler) OnCreateSpan(span *Span) SamplingDecision {
 	sampled, tags := s.trySampling(span, span.OperationName())
 	return SamplingDecision{Sample: sampled, Retryable: s.operationNameLateBinding, Tags: tags}
 }

 // OnSetOperationName implements OnSetOperationName of SamplerV2.
 func (s *PerOperationSampler) OnSetOperationName(span *Span, operationName string) SamplingDecision {
 	sampled, tags := s.trySampling(span, operationName)
 	return SamplingDecision{Sample: sampled, Retryable: false, Tags: tags}
 }

 // OnSetTag implements OnSetTag of SamplerV2.
 func (s *PerOperationSampler) OnSetTag(span *Span, key string, value interface{}) SamplingDecision {
 	return SamplingDecision{Sample: false, Retryable: true}
 }

 // OnFinishSpan implements OnFinishSpan of SamplerV2.
 func (s *PerOperationSampler) OnFinishSpan(span *Span) SamplingDecision {
 	return SamplingDecision{Sample: false, Retryable: true}
 }

 func (s *PerOperationSampler) getSamplerForOperation(operation string) Sampler {
 	s.RLock()
 	sampler, ok := s.samplers[operation]
 	if ok {
 		defer s.RUnlock()
 		return sampler
 	}
 	s.RUnlock()
 	s.Lock()
 	defer s.Unlock()

 	// Check if sampler has already been created
 	sampler, ok = s.samplers[operation]
 	if ok {
 		return sampler
 	}
 	// Store only up to maxOperations of unique ops.
 	if len(s.samplers) >= s.maxOperations {
 		return s.defaultSampler
 	}
 	newSampler := newGuaranteedThroughputProbabilisticSampler(s.lowerBound, s.defaultSampler.SamplingRate())
 	s.samplers[operation] = newSampler
 	return newSampler
 }

 // Close invokes Close on all underlying samplers.
 func (s *PerOperationSampler) Close() {
 	s.Lock()
 	defer s.Unlock()
 	for _, sampler := range s.samplers {
 		sampler.Close()
 	}
 	s.defaultSampler.Close()
 }

 func (s *PerOperationSampler) String() string {
 	var sb strings.Builder

 	fmt.Fprintf(&sb, "PerOperationSampler(defaultSampler=%v, ", s.defaultSampler)
 	fmt.Fprintf(&sb, "lowerBound=%f, ", s.lowerBound)
 	fmt.Fprintf(&sb, "maxOperations=%d, ", s.maxOperations)
 	fmt.Fprintf(&sb, "operationNameLateBinding=%t, ", s.operationNameLateBinding)
 	fmt.Fprintf(&sb, "numOperations=%d,\n", len(s.samplers))
 	fmt.Fprintf(&sb, "samplers=[")
 	for operationName, sampler := range s.samplers {
 		fmt.Fprintf(&sb, "\n(operationName=%s, sampler=%v)", operationName, sampler)
 	}
 	fmt.Fprintf(&sb, "])")

 	return sb.String()
 }

 // Equal is not used.
 // TODO (breaking change) remove this in the future
 func (s *PerOperationSampler) Equal(other Sampler) bool {
 	// NB The Equal() function is overly expensive for PerOperationSampler since it's composed of multiple
 	// samplers which all need to be initialized before this function can be called for a comparison.
 	// Therefore, PerOperationSampler uses the update() function to only alter the samplers that need
 	// changing. Hence this function always returns false so that the update function can be called.
 	// Once the Equal() function is removed from the Sampler API, this will no longer be needed.
 	return false
 }

 func (s *PerOperationSampler) update(strategies *sampling.PerOperationSamplingStrategies) {
 	s.Lock()
 	defer s.Unlock()
 	newSamplers := map[string]*GuaranteedThroughputProbabilisticSampler{}
 	for _, strategy := range strategies.PerOperationStrategies {
 		operation := strategy.Operation
 		samplingRate := strategy.ProbabilisticSampling.SamplingRate
 		lowerBound := strategies.DefaultLowerBoundTracesPerSecond
 		if sampler, ok := s.samplers[operation]; ok {
 			sampler.update(lowerBound, samplingRate)
 			newSamplers[operation] = sampler
 		} else {
 			sampler := newGuaranteedThroughputProbabilisticSampler(
 				lowerBound,
 				samplingRate,
 			)
 			newSamplers[operation] = sampler
 		}
 	}
 	s.lowerBound = strategies.DefaultLowerBoundTracesPerSecond
 	if s.defaultSampler.SamplingRate() != strategies.DefaultSamplingProbability {
 		s.defaultSampler = newProbabilisticSampler(strategies.DefaultSamplingProbability)
 	}
 	s.samplers = newSamplers
 }
	// Copyright (c) 2017 Uber Technologies, Inc.
	//
	// 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 jaeger

	import (
	"fmt"
	"math"
	"strings"
	"sync"

	"github.com/uber/jaeger-client-go/thrift-gen/sampling"
	"github.com/uber/jaeger-client-go/utils"
	)

	const (
	defaultMaxOperations = 2000
	)

	// Sampler decides whether a new trace should be sampled or not.
	type Sampler interface {
	// IsSampled decides whether a trace with given `id` and `operation`
	// should be sampled. This function will also return the tags that
	// can be used to identify the type of sampling that was applied to
	// the root span. Most simple samplers would return two tags,
	// sampler.type and sampler.param, similar to those used in the Configuration
	IsSampled(id TraceID, operation string) (sampled bool, tags []Tag)

	// Close does a clean shutdown of the sampler, stopping any background
	// go-routines it may have started.
	Close()

	// Equal checks if the `other` sampler is functionally equivalent
	// to this sampler.
	// TODO (breaking change) remove this function. See PerOperationSampler.Equals for explanation.
	Equal(other Sampler) bool
	}

	// -----------------------

	// ConstSampler is a sampler that always makes the same decision.
	type ConstSampler struct {
	legacySamplerV1Base
	Decision bool
	tags []Tag
	}

	// NewConstSampler creates a ConstSampler.
	func NewConstSampler(sample bool) *ConstSampler {
	tags := []Tag{
	{key: SamplerTypeTagKey, value: SamplerTypeConst},
	{key: SamplerParamTagKey, value: sample},
	}
	s := &ConstSampler{
	Decision: sample,
	tags: tags,
	}
	s.delegate = s.IsSampled
	return s
	}

	// IsSampled implements IsSampled() of Sampler.
	func (s *ConstSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
	return s.Decision, s.tags
	}

	// Close implements Close() of Sampler.
	func (s *ConstSampler) Close() {
	// nothing to do
	}

	// Equal implements Equal() of Sampler.
	func (s *ConstSampler) Equal(other Sampler) bool {
	if o, ok := other.(*ConstSampler); ok {
	return s.Decision == o.Decision
	}
	return false
	}

	// String is used to log sampler details.
	func (s *ConstSampler) String() string {
	return fmt.Sprintf("ConstSampler(decision=%t)", s.Decision)
	}

	// -----------------------

	// ProbabilisticSampler is a sampler that randomly samples a certain percentage
	// of traces.
	type ProbabilisticSampler struct {
	legacySamplerV1Base
	samplingRate float64
	samplingBoundary uint64
	tags []Tag
	}

	const maxRandomNumber = ^(uint64(1) << 63) // i.e. 0x7fffffffffffffff

	// NewProbabilisticSampler creates a sampler that randomly samples a certain percentage of traces specified by the
	// samplingRate, in the range between 0.0 and 1.0.
	//
	// It relies on the fact that new trace IDs are 63bit random numbers themselves, thus making the sampling decision
	// without generating a new random number, but simply calculating if traceID < (samplingRate * 2^63).
	// TODO remove the error from this function for next major release
	func NewProbabilisticSampler(samplingRate float64) (*ProbabilisticSampler, error) {
	if samplingRate < 0.0 \|\| samplingRate > 1.0 {
	return nil, fmt.Errorf("Sampling Rate must be between 0.0 and 1.0, received %f", samplingRate)
	}
	return newProbabilisticSampler(samplingRate), nil
	}

	func newProbabilisticSampler(samplingRate float64) *ProbabilisticSampler {
	s := new(ProbabilisticSampler)
	s.delegate = s.IsSampled
	return s.init(samplingRate)
	}

	func (s ProbabilisticSampler) init(samplingRate float64) ProbabilisticSampler {
	s.samplingRate = math.Max(0.0, math.Min(samplingRate, 1.0))
	s.samplingBoundary = uint64(float64(maxRandomNumber) * s.samplingRate)
	s.tags = []Tag{
	{key: SamplerTypeTagKey, value: SamplerTypeProbabilistic},
	{key: SamplerParamTagKey, value: s.samplingRate},
	}
	return s
	}

	// SamplingRate returns the sampling probability this sampled was constructed with.
	func (s *ProbabilisticSampler) SamplingRate() float64 {
	return s.samplingRate
	}

	// IsSampled implements IsSampled() of Sampler.
	func (s *ProbabilisticSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
	return s.samplingBoundary >= id.Low&maxRandomNumber, s.tags
	}

	// Close implements Close() of Sampler.
	func (s *ProbabilisticSampler) Close() {
	// nothing to do
	}

	// Equal implements Equal() of Sampler.
	func (s *ProbabilisticSampler) Equal(other Sampler) bool {
	if o, ok := other.(*ProbabilisticSampler); ok {
	return s.samplingBoundary == o.samplingBoundary
	}
	return false
	}

	// Update modifies in-place the sampling rate. Locking must be done externally.
	func (s *ProbabilisticSampler) Update(samplingRate float64) error {
	if samplingRate < 0.0 \|\| samplingRate > 1.0 {
	return fmt.Errorf("Sampling Rate must be between 0.0 and 1.0, received %f", samplingRate)
	}
	s.init(samplingRate)
	return nil
	}

	// String is used to log sampler details.
	func (s *ProbabilisticSampler) String() string {
	return fmt.Sprintf("ProbabilisticSampler(samplingRate=%v)", s.samplingRate)
	}

	// -----------------------

	// RateLimitingSampler samples at most maxTracesPerSecond. The distribution of sampled traces follows
	// burstiness of the service, i.e. a service with uniformly distributed requests will have those
	// requests sampled uniformly as well, but if requests are bursty, especially sub-second, then a
	// number of sequential requests can be sampled each second.
	type RateLimitingSampler struct {
	legacySamplerV1Base
	maxTracesPerSecond float64
	rateLimiter *utils.ReconfigurableRateLimiter
	tags []Tag
	}

	// NewRateLimitingSampler creates new RateLimitingSampler.
	func NewRateLimitingSampler(maxTracesPerSecond float64) *RateLimitingSampler {
	s := new(RateLimitingSampler)
	s.delegate = s.IsSampled
	return s.init(maxTracesPerSecond)
	}

	func (s RateLimitingSampler) init(maxTracesPerSecond float64) RateLimitingSampler {
	if s.rateLimiter == nil {
	s.rateLimiter = utils.NewRateLimiter(maxTracesPerSecond, math.Max(maxTracesPerSecond, 1.0))
	} else {
	s.rateLimiter.Update(maxTracesPerSecond, math.Max(maxTracesPerSecond, 1.0))
	}
	s.maxTracesPerSecond = maxTracesPerSecond
	s.tags = []Tag{
	{key: SamplerTypeTagKey, value: SamplerTypeRateLimiting},
	{key: SamplerParamTagKey, value: maxTracesPerSecond},
	}
	return s
	}

	// IsSampled implements IsSampled() of Sampler.
	func (s *RateLimitingSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
	return s.rateLimiter.CheckCredit(1.0), s.tags
	}

	// Update reconfigures the rate limiter, while preserving its accumulated balance.
	// Locking must be done externally.
	func (s *RateLimitingSampler) Update(maxTracesPerSecond float64) {
	if s.maxTracesPerSecond != maxTracesPerSecond {
	s.init(maxTracesPerSecond)
	}
	}

	// Close does nothing.
	func (s *RateLimitingSampler) Close() {
	// nothing to do
	}

	// Equal compares with another sampler.
	func (s *RateLimitingSampler) Equal(other Sampler) bool {
	if o, ok := other.(*RateLimitingSampler); ok {
	return s.maxTracesPerSecond == o.maxTracesPerSecond
	}
	return false
	}

	// String is used to log sampler details.
	func (s *RateLimitingSampler) String() string {
	return fmt.Sprintf("RateLimitingSampler(maxTracesPerSecond=%v)", s.maxTracesPerSecond)
	}

	// -----------------------

	// GuaranteedThroughputProbabilisticSampler is a sampler that leverages both ProbabilisticSampler and
	// RateLimitingSampler. The RateLimitingSampler is used as a guaranteed lower bound sampler such that
	// every operation is sampled at least once in a time interval defined by the lowerBound. ie a lowerBound
	// of 1.0 / (60 * 10) will sample an operation at least once every 10 minutes.
	//
	// The ProbabilisticSampler is given higher priority when tags are emitted, ie. if IsSampled() for both
	// samplers return true, the tags for ProbabilisticSampler will be used.
	type GuaranteedThroughputProbabilisticSampler struct {
	probabilisticSampler *ProbabilisticSampler
	lowerBoundSampler *RateLimitingSampler
	tags []Tag
	samplingRate float64
	lowerBound float64
	}

	// NewGuaranteedThroughputProbabilisticSampler returns a delegating sampler that applies both
	// ProbabilisticSampler and RateLimitingSampler.
	func NewGuaranteedThroughputProbabilisticSampler(
	lowerBound, samplingRate float64,
	) (*GuaranteedThroughputProbabilisticSampler, error) {
	return newGuaranteedThroughputProbabilisticSampler(lowerBound, samplingRate), nil
	}

	func newGuaranteedThroughputProbabilisticSampler(lowerBound, samplingRate float64) *GuaranteedThroughputProbabilisticSampler {
	s := &GuaranteedThroughputProbabilisticSampler{
	lowerBoundSampler: NewRateLimitingSampler(lowerBound),
	lowerBound: lowerBound,
	}
	s.setProbabilisticSampler(samplingRate)
	return s
	}

	func (s *GuaranteedThroughputProbabilisticSampler) setProbabilisticSampler(samplingRate float64) {
	if s.probabilisticSampler == nil {
	s.probabilisticSampler = newProbabilisticSampler(samplingRate)
	} else if s.samplingRate != samplingRate {
	s.probabilisticSampler.init(samplingRate)
	}
	// since we don't validate samplingRate, sampler may have clamped it to [0, 1] interval
	samplingRate = s.probabilisticSampler.SamplingRate()
	if s.samplingRate != samplingRate \|\| s.tags == nil {
	s.samplingRate = s.probabilisticSampler.SamplingRate()
	s.tags = []Tag{
	{key: SamplerTypeTagKey, value: SamplerTypeLowerBound},
	{key: SamplerParamTagKey, value: s.samplingRate},
	}
	}
	}

	// IsSampled implements IsSampled() of Sampler.
	func (s *GuaranteedThroughputProbabilisticSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
	if sampled, tags := s.probabilisticSampler.IsSampled(id, operation); sampled {
	s.lowerBoundSampler.IsSampled(id, operation)
	return true, tags
	}
	sampled, _ := s.lowerBoundSampler.IsSampled(id, operation)
	return sampled, s.tags
	}

	// Close implements Close() of Sampler.
	func (s *GuaranteedThroughputProbabilisticSampler) Close() {
	s.probabilisticSampler.Close()
	s.lowerBoundSampler.Close()
	}

	// Equal implements Equal() of Sampler.
	func (s *GuaranteedThroughputProbabilisticSampler) Equal(other Sampler) bool {
	// NB The Equal() function is expensive and will be removed. See PerOperationSampler.Equal() for
	// more information.
	return false
	}

	// this function should only be called while holding a Write lock
	func (s *GuaranteedThroughputProbabilisticSampler) update(lowerBound, samplingRate float64) {
	s.setProbabilisticSampler(samplingRate)
	if s.lowerBound != lowerBound {
	s.lowerBoundSampler.Update(lowerBound)
	s.lowerBound = lowerBound
	}
	}

	func (s GuaranteedThroughputProbabilisticSampler) String() string {
	return fmt.Sprintf("GuaranteedThroughputProbabilisticSampler(lowerBound=%f, samplingRate=%f)", s.lowerBound, s.samplingRate)
	}

	// -----------------------

	// PerOperationSampler is a delegating sampler that applies GuaranteedThroughputProbabilisticSampler
	// on a per-operation basis.
	type PerOperationSampler struct {
	sync.RWMutex

	samplers map[string]*GuaranteedThroughputProbabilisticSampler
	defaultSampler *ProbabilisticSampler
	lowerBound float64
	maxOperations int

	// see description in PerOperationSamplerParams
	operationNameLateBinding bool
	}

	// NewAdaptiveSampler returns a new PerOperationSampler.
	// Deprecated: please use NewPerOperationSampler.
	func NewAdaptiveSampler(strategies sampling.PerOperationSamplingStrategies, maxOperations int) (PerOperationSampler, error) {
	return NewPerOperationSampler(PerOperationSamplerParams{
	MaxOperations: maxOperations,
	Strategies: strategies,
	}), nil
	}

	// PerOperationSamplerParams defines parameters when creating PerOperationSampler.
	type PerOperationSamplerParams struct {
	// Max number of operations that will be tracked. Other operations will be given default strategy.
	MaxOperations int

	// Opt-in feature for applications that require late binding of span name via explicit call to SetOperationName.
	// When this feature is enabled, the sampler will return retryable=true from OnCreateSpan(), thus leaving
	// the sampling decision as non-final (and the span as writeable). This may lead to degraded performance
	// in applications that always provide the correct span name on trace creation.
	//
	// For backwards compatibility this option is off by default.
	OperationNameLateBinding bool

	// Initial configuration of the sampling strategies (usually retrieved from the backend by Remote Sampler).
	Strategies *sampling.PerOperationSamplingStrategies
	}

	// NewPerOperationSampler returns a new PerOperationSampler.
	func NewPerOperationSampler(params PerOperationSamplerParams) *PerOperationSampler {
	if params.MaxOperations <= 0 {
	params.MaxOperations = defaultMaxOperations
	}
	samplers := make(map[string]*GuaranteedThroughputProbabilisticSampler)
	for _, strategy := range params.Strategies.PerOperationStrategies {
	sampler := newGuaranteedThroughputProbabilisticSampler(
	params.Strategies.DefaultLowerBoundTracesPerSecond,
	strategy.ProbabilisticSampling.SamplingRate,
	)
	samplers[strategy.Operation] = sampler
	}
	return &PerOperationSampler{
	samplers: samplers,
	defaultSampler: newProbabilisticSampler(params.Strategies.DefaultSamplingProbability),
	lowerBound: params.Strategies.DefaultLowerBoundTracesPerSecond,
	maxOperations: params.MaxOperations,
	operationNameLateBinding: params.OperationNameLateBinding,
	}
	}

	// IsSampled is not used and only exists to match Sampler V1 API.
	// TODO (breaking change) remove when upgrading everything to SamplerV2
	func (s *PerOperationSampler) IsSampled(id TraceID, operation string) (bool, []Tag) {
	return false, nil
	}

	func (s PerOperationSampler) trySampling(span Span, operationName string) (bool, []Tag) {
	samplerV1 := s.getSamplerForOperation(operationName)
	var sampled bool
	var tags []Tag
	if span.context.samplingState.isLocalRootSpan(span.context.spanID) {
	sampled, tags = samplerV1.IsSampled(span.context.TraceID(), operationName)
	}
	return sampled, tags
	}

	// OnCreateSpan implements OnCreateSpan of SamplerV2.
	func (s PerOperationSampler) OnCreateSpan(span Span) SamplingDecision {
	sampled, tags := s.trySampling(span, span.OperationName())
	return SamplingDecision{Sample: sampled, Retryable: s.operationNameLateBinding, Tags: tags}
	}

	// OnSetOperationName implements OnSetOperationName of SamplerV2.
	func (s PerOperationSampler) OnSetOperationName(span Span, operationName string) SamplingDecision {
	sampled, tags := s.trySampling(span, operationName)
	return SamplingDecision{Sample: sampled, Retryable: false, Tags: tags}
	}

	// OnSetTag implements OnSetTag of SamplerV2.
	func (s PerOperationSampler) OnSetTag(span Span, key string, value interface{}) SamplingDecision {
	return SamplingDecision{Sample: false, Retryable: true}
	}

	// OnFinishSpan implements OnFinishSpan of SamplerV2.
	func (s PerOperationSampler) OnFinishSpan(span Span) SamplingDecision {
	return SamplingDecision{Sample: false, Retryable: true}
	}

	func (s *PerOperationSampler) getSamplerForOperation(operation string) Sampler {
	s.RLock()
	sampler, ok := s.samplers[operation]
	if ok {
	defer s.RUnlock()
	return sampler
	}
	s.RUnlock()
	s.Lock()
	defer s.Unlock()

	// Check if sampler has already been created
	sampler, ok = s.samplers[operation]
	if ok {
	return sampler
	}
	// Store only up to maxOperations of unique ops.
	if len(s.samplers) >= s.maxOperations {
	return s.defaultSampler
	}
	newSampler := newGuaranteedThroughputProbabilisticSampler(s.lowerBound, s.defaultSampler.SamplingRate())
	s.samplers[operation] = newSampler
	return newSampler
	}

	// Close invokes Close on all underlying samplers.
	func (s *PerOperationSampler) Close() {
	s.Lock()
	defer s.Unlock()
	for _, sampler := range s.samplers {
	sampler.Close()
	}
	s.defaultSampler.Close()
	}

	func (s *PerOperationSampler) String() string {
	var sb strings.Builder

	fmt.Fprintf(&sb, "PerOperationSampler(defaultSampler=%v, ", s.defaultSampler)
	fmt.Fprintf(&sb, "lowerBound=%f, ", s.lowerBound)
	fmt.Fprintf(&sb, "maxOperations=%d, ", s.maxOperations)
	fmt.Fprintf(&sb, "operationNameLateBinding=%t, ", s.operationNameLateBinding)
	fmt.Fprintf(&sb, "numOperations=%d,\n", len(s.samplers))
	fmt.Fprintf(&sb, "samplers=[")
	for operationName, sampler := range s.samplers {
	fmt.Fprintf(&sb, "\n(operationName=%s, sampler=%v)", operationName, sampler)
	}
	fmt.Fprintf(&sb, "])")

	return sb.String()
	}

	// Equal is not used.
	// TODO (breaking change) remove this in the future
	func (s *PerOperationSampler) Equal(other Sampler) bool {
	// NB The Equal() function is overly expensive for PerOperationSampler since it's composed of multiple
	// samplers which all need to be initialized before this function can be called for a comparison.
	// Therefore, PerOperationSampler uses the update() function to only alter the samplers that need
	// changing. Hence this function always returns false so that the update function can be called.
	// Once the Equal() function is removed from the Sampler API, this will no longer be needed.
	return false
	}

	func (s PerOperationSampler) update(strategies sampling.PerOperationSamplingStrategies) {
	s.Lock()
	defer s.Unlock()
	newSamplers := map[string]*GuaranteedThroughputProbabilisticSampler{}
	for _, strategy := range strategies.PerOperationStrategies {
	operation := strategy.Operation
	samplingRate := strategy.ProbabilisticSampling.SamplingRate
	lowerBound := strategies.DefaultLowerBoundTracesPerSecond
	if sampler, ok := s.samplers[operation]; ok {
	sampler.update(lowerBound, samplingRate)
	newSamplers[operation] = sampler
	} else {
	sampler := newGuaranteedThroughputProbabilisticSampler(
	lowerBound,
	samplingRate,
	)
	newSamplers[operation] = sampler
	}
	}
	s.lowerBound = strategies.DefaultLowerBoundTracesPerSecond
	if s.defaultSampler.SamplingRate() != strategies.DefaultSamplingProbability {
	s.defaultSampler = newProbabilisticSampler(strategies.DefaultSamplingProbability)
	}
	s.samplers = newSamplers
	}