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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 (
"time"
)
// samplePeriod is the minimum time between accepting spans in a single bucket.
const samplePeriod = time.Second
// defaultLatencies contains the default latency bucket bounds.
// TODO: consider defaults, make configurable
var defaultLatencies = [...]time.Duration{
10 * time.Microsecond,
100 * time.Microsecond,
time.Millisecond,
10 * time.Millisecond,
100 * time.Millisecond,
time.Second,
10 * time.Second,
time.Minute,
}
// bucket is a container for a set of spans for a particular error code or latency range.
type bucket struct {
nextTime time.Time // next time we can accept a span
buffer []*SpanData // circular buffer of spans
nextIndex int // location next SpanData should be placed in buffer
overflow bool // whether the circular buffer has wrapped around
}
func makeBucket(bufferSize int) bucket {
return bucket{
buffer: make([]*SpanData, bufferSize),
}
}
// add adds a span to the bucket, if nextTime has been reached.
func (b *bucket) add(s *SpanData) {
if s.EndTime.Before(b.nextTime) {
return
}
if len(b.buffer) == 0 {
return
}
b.nextTime = s.EndTime.Add(samplePeriod)
b.buffer[b.nextIndex] = s
b.nextIndex++
if b.nextIndex == len(b.buffer) {
b.nextIndex = 0
b.overflow = true
}
}
// size returns the number of spans in the bucket.
func (b *bucket) size() int {
if b.overflow {
return len(b.buffer)
}
return b.nextIndex
}
// span returns the ith span in the bucket.
func (b *bucket) span(i int) *SpanData {
if !b.overflow {
return b.buffer[i]
}
if i < len(b.buffer)-b.nextIndex {
return b.buffer[b.nextIndex+i]
}
return b.buffer[b.nextIndex+i-len(b.buffer)]
}
// resize changes the size of the bucket to n, keeping up to n existing spans.
func (b *bucket) resize(n int) {
cur := b.size()
newBuffer := make([]*SpanData, n)
if cur < n {
for i := 0; i < cur; i++ {
newBuffer[i] = b.span(i)
}
b.buffer = newBuffer
b.nextIndex = cur
b.overflow = false
return
}
for i := 0; i < n; i++ {
newBuffer[i] = b.span(i + cur - n)
}
b.buffer = newBuffer
b.nextIndex = 0
b.overflow = true
}
// latencyBucket returns the appropriate bucket number for a given latency.
func latencyBucket(latency time.Duration) int {
i := 0
for i < len(defaultLatencies) && latency >= defaultLatencies[i] {
i++
}
return i
}
// latencyBucketBounds returns the lower and upper bounds for a latency bucket
// number.
//
// The lower bound is inclusive, the upper bound is exclusive (except for the
// last bucket.)
func latencyBucketBounds(index int) (lower time.Duration, upper time.Duration) {
if index == 0 {
return 0, defaultLatencies[index]
}
if index == len(defaultLatencies) {
return defaultLatencies[index-1], 1<<63 - 1
}
return defaultLatencies[index-1], defaultLatencies[index]
}
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