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// Copyright (c) 2021 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package com.uber.m3.tally;
import com.uber.m3.util.Duration;
import com.uber.m3.util.ImmutableMap;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* Default implementation of a {@link Histogram}.
*/
class HistogramImpl extends MetricBase implements Histogram, StopwatchRecorder {
private final Type type;
private final ImmutableMap tags;
private final ImmutableBuckets specification;
// NOTE: Bucket counters are lazily initialized. Since ref updates are atomic in JMM,
// no dedicated synchronization is used on the read path, only on the write path
private final CounterImpl[] bucketCounters;
private final ScopeImpl scope;
HistogramImpl(
ScopeImpl scope,
String fqn,
ImmutableMap tags,
Buckets buckets
) {
super(fqn);
this.scope = scope;
this.type = buckets instanceof DurationBuckets ? Type.DURATION : Type.VALUE;
this.tags = tags;
this.specification = buckets;
// Each bucket value, serves as a boundary de-marking upper bound
// for the bucket to the left, and lower bound for the bucket to the right
this.bucketCounters = new CounterImpl[buckets.asValues().length + 1];
}
@Override
public void recordValue(double value) {
int index = toBucketIndex(Collections.binarySearch(specification.getValueUpperBounds(), value));
getOrCreateCounter(index).inc(1);
}
@Override
public void recordDuration(Duration duration) {
int index = toBucketIndex(Collections.binarySearch(specification.getDurationUpperBounds(), duration));
getOrCreateCounter(index).inc(1);
}
private CounterImpl getOrCreateCounter(int index) {
if (bucketCounters[index] != null) {
return bucketCounters[index];
}
List bucketsBounds =
this.type == Type.VALUE
? specification.getValueUpperBounds()
: specification.getDurationUpperBounds();
// To maintain lock granularity we synchronize only on a
// particular bucket leveraging bucket's boundary as a sync target
synchronized (bucketsBounds.get(Math.min(index, bucketsBounds.size() - 1))) {
// Check whether bucket has been already set,
// while we were waiting for lock
if (bucketCounters[index] != null) {
return bucketCounters[index];
}
bucketCounters[index] = new HistogramBucketCounterImpl(scope, getQualifiedName(), index);
return bucketCounters[index];
}
}
static int toBucketIndex(int binarySearchResult) {
// Buckets are defined in the following way:
// - Each bucket is inclusive of its lower bound, and exclusive of the upper: [lower, upper)
// - All buckets are defined by upper bounds: [2, 4, 8, 16, 32, ...]: therefore i
// in this case [-inf, 2) will be the first bucket, [2, 4) -- the second and so on
//
// Given that our buckets are designated as [lower, upper), and
// that the binary search is performed over upper bounds, if binary
// search found the exact match we need to shift it by 1 to index appropriate bucket in the
// array of (bucket's) counters
if (binarySearchResult >= 0) {
return binarySearchResult + 1;
}
// Otherwise, binary search will return {@code (-(insertion point) - 1)} where
// "insertion point" designates first element that is _greater_ than the key, therefore
// we simply use this an index in the array of counters
//
// NOTE: {@code ~binarySearchResult} is equivalent to {@code -(binarySearchResult) - 1}
return ~binarySearchResult;
}
@Override
public Stopwatch start() {
return new Stopwatch(System.nanoTime(), this);
}
ImmutableMap getTags() {
return tags;
}
private Duration getUpperBoundDurationForBucket(int bucketIndex) {
return bucketIndex < specification.getDurationUpperBounds().size() ? specification.getDurationUpperBounds().get(bucketIndex) : Duration.MAX_VALUE;
}
private Duration getLowerBoundDurationForBucket(int bucketIndex) {
return bucketIndex == 0 ? Duration.MIN_VALUE : specification.getDurationUpperBounds().get(bucketIndex - 1);
}
private double getUpperBoundValueForBucket(int bucketIndex) {
return bucketIndex < specification.getValueUpperBounds().size() ? specification.getValueUpperBounds().get(bucketIndex) : Double.MAX_VALUE;
}
private double getLowerBoundValueForBucket(int bucketIndex) {
return bucketIndex == 0 ? Double.MIN_VALUE : specification.getValueUpperBounds().get(bucketIndex - 1);
}
private long snapshotCounterValue(int index) {
return bucketCounters[index] != null ? bucketCounters[index].snapshot() : 0;
}
// NOTE: Only used in testing
Map snapshotValues() {
if (type == Type.DURATION) {
return null;
}
Map values = new HashMap<>(bucketCounters.length, 1);
for (int i = 0; i < bucketCounters.length; ++i) {
values.put(getUpperBoundValueForBucket(i), snapshotCounterValue(i));
}
return values;
}
Map snapshotDurations() {
if (type == Type.VALUE) {
return null;
}
Map durations = new HashMap<>(bucketCounters.length, 1);
for (int i = 0; i < bucketCounters.length; ++i) {
durations.put(getUpperBoundDurationForBucket(i), snapshotCounterValue(i));
}
return durations;
}
@Override
public void recordStopwatch(long stopwatchStart) {
recordDuration(Duration.between(stopwatchStart, System.nanoTime()));
}
enum Type {
VALUE,
DURATION
}
/**
* Extension of the {@link CounterImpl} adjusting it's reporting procedure
* to adhere to histogram format
*/
class HistogramBucketCounterImpl extends CounterImpl {
private final int bucketIndex;
protected HistogramBucketCounterImpl(ScopeImpl scope, String fqn, int bucketIndex) {
super(scope, fqn);
this.bucketIndex = bucketIndex;
}
@Override
public void report(ImmutableMap tags, StatsReporter reporter) {
long inc = value();
if (inc == 0) {
// Nothing to report
return;
}
switch (type) {
case VALUE:
reporter.reportHistogramValueSamples(
getQualifiedName(),
tags,
(Buckets) specification,
getLowerBoundValueForBucket(bucketIndex),
getUpperBoundValueForBucket(bucketIndex),
inc
);
break;
case DURATION:
reporter.reportHistogramDurationSamples(
getQualifiedName(),
tags,
(Buckets) specification,
getLowerBoundDurationForBucket(bucketIndex),
getUpperBoundDurationForBucket(bucketIndex),
inc
);
break;
}
}
}
}
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