116 lines
2.8 KiB
Go
116 lines
2.8 KiB
Go
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// Copyright 2017, OpenCensus Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package trace
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import (
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"encoding/binary"
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)
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const defaultSamplingProbability = 1e-4
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var defaultSampler Sampler
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func init() {
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defaultSampler = newDefaultSampler()
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}
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func newDefaultSampler() Sampler {
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return ProbabilitySampler(defaultSamplingProbability)
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}
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// SetDefaultSampler sets the default sampler used when creating new spans.
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func SetDefaultSampler(sampler Sampler) {
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if sampler == nil {
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sampler = newDefaultSampler()
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}
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mu.Lock()
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defaultSampler = sampler
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mu.Unlock()
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}
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// Sampler is an interface for values that have a method that the trace library
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// can call to determine whether to export a trace's spans.
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type Sampler interface {
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Sample(p SamplingParameters) SamplingDecision
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}
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// SamplingParameters contains the values passed to a Sampler.
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type SamplingParameters struct {
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ParentContext SpanContext
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TraceID TraceID
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SpanID SpanID
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Name string
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HasRemoteParent bool
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}
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// SamplingDecision is the value returned by a Sampler.
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type SamplingDecision struct {
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Sample bool
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}
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// ProbabilitySampler returns a Sampler that samples a given fraction of traces.
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//
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// It also samples spans whose parents are sampled.
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func ProbabilitySampler(fraction float64) Sampler {
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if !(fraction >= 0) {
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fraction = 0
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} else if fraction >= 1 {
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return AlwaysSample()
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}
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return probabilitySampler{
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traceIDUpperBound: uint64(fraction * (1 << 63)),
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}
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}
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type probabilitySampler struct {
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traceIDUpperBound uint64
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}
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var _ Sampler = (*probabilitySampler)(nil)
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func (s probabilitySampler) Sample(p SamplingParameters) (d SamplingDecision) {
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if p.ParentContext.IsSampled() {
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return SamplingDecision{Sample: true}
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}
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x := binary.BigEndian.Uint64(p.TraceID[0:8]) >> 1
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return SamplingDecision{Sample: x < s.traceIDUpperBound}
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}
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// AlwaysSample returns a Sampler that samples every trace.
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func AlwaysSample() Sampler {
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return always{}
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}
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type always struct{}
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var _ Sampler = always{}
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func (a always) Sample(p SamplingParameters) SamplingDecision {
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return SamplingDecision{Sample: true}
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}
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// NeverSample returns a Sampler that samples no traces.
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func NeverSample() Sampler {
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return never{}
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}
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type never struct{}
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var _ Sampler = never{}
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func (n never) Sample(p SamplingParameters) SamplingDecision {
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return SamplingDecision{Sample: false}
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}
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