/
sampler.go
72 lines (59 loc) · 1.69 KB
/
sampler.go
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package tracer
import (
"math"
"sync"
"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
)
// Sampler is the generic interface of any sampler. It must be safe for concurrent use.
type Sampler interface {
// Sample returns true if the given span should be sampled.
Sample(span Span) bool
}
// RateSampler is a sampler implementation which randomly selects spans using a
// provided rate. For example, a rate of 0.75 will permit 75% of the spans.
// RateSampler implementations should be safe for concurrent use.
type RateSampler interface {
Sampler
// Rate returns the current sample rate.
Rate() float64
// SetRate sets a new sample rate.
SetRate(rate float64)
}
// rateSampler samples from a sample rate.
type rateSampler struct {
sync.RWMutex
rate float64
}
// NewAllSampler is a short-hand for NewRateSampler(1). It is all-permissive.
func NewAllSampler() RateSampler { return NewRateSampler(1) }
// NewRateSampler returns an initialized RateSampler with a given sample rate.
func NewRateSampler(rate float64) RateSampler {
return &rateSampler{rate: rate}
}
// Rate returns the current rate of the sampler.
func (r *rateSampler) Rate() float64 {
r.RLock()
defer r.RUnlock()
return r.rate
}
// SetRate sets a new sampling rate.
func (r *rateSampler) SetRate(rate float64) {
r.Lock()
r.rate = rate
r.Unlock()
}
// constants used for the Knuth hashing, same as agent.
const knuthFactor = uint64(1111111111111111111)
// Sample returns true if the given span should be sampled.
func (r *rateSampler) Sample(spn ddtrace.Span) bool {
s, ok := spn.(*span)
if !ok {
return false
}
r.RLock()
defer r.RUnlock()
if r.rate < 1 {
return s.TraceID*knuthFactor < uint64(r.rate*math.MaxUint64)
}
return true
}