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// Copyright 2017, OpenCensus 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 trace
import (
"encoding/binary"
)
const defaultSamplingProbability = 1e-4
func newDefaultSampler() Sampler {
return ProbabilitySampler(defaultSamplingProbability)
}
// Sampler decides whether a trace should be sampled and exported.
type Sampler func(SamplingParameters) SamplingDecision
// SamplingParameters contains the values passed to a Sampler.
type SamplingParameters struct {
ParentContext SpanContext
TraceID TraceID
SpanID SpanID
Name string
HasRemoteParent bool
}
// SamplingDecision is the value returned by a Sampler.
type SamplingDecision struct {
Sample bool
}
// ProbabilitySampler returns a Sampler that samples a given fraction of traces.
//
// It also samples spans whose parents are sampled.
func ProbabilitySampler(fraction float64) Sampler {
if !(fraction >= 0) {
fraction = 0
} else if fraction >= 1 {
return AlwaysSample()
}
traceIDUpperBound := uint64(fraction * (1 << 63))
return Sampler(func(p SamplingParameters) SamplingDecision {
if p.ParentContext.IsSampled() {
return SamplingDecision{Sample: true}
}
x := binary.BigEndian.Uint64(p.TraceID[0:8]) >> 1
return SamplingDecision{Sample: x < traceIDUpperBound}
})
}
// AlwaysSample returns a Sampler that samples every trace.
func AlwaysSample() Sampler {
return func(p SamplingParameters) SamplingDecision {
return SamplingDecision{Sample: true}
}
}
// NeverSample returns a Sampler that samples no traces.
func NeverSample() Sampler {
return func(p SamplingParameters) SamplingDecision {
return SamplingDecision{Sample: false}
}
}
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