Initial

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/go.opencensus.io/trace/spanbucket.go

@@ -0,0 +1,130 @@
+// 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]
+}