com.google.api.gax.core.Distribution Maven / Gradle / Ivy
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package com.google.api.gax.core;
import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLongArray;
/**
* Distribution records values from {@code 0} (inclusive) to {@code endValue} (exclusive) and
* computes their percentiles.
*
* Methods may be called concurrently.
*/
public class Distribution {
private final AtomicLongArray buckets;
private final AtomicInteger count = new AtomicInteger(0);
public Distribution(int endValue) {
Preconditions.checkArgument(endValue > 0);
buckets = new AtomicLongArray(endValue);
}
// TODO(pongad): remove this when google-cloud-java no longer calls it.
@Deprecated
public long getNthPercentile(double percentile) {
return getPercentile(percentile);
}
/**
* Get the percentile of recorded values. If called concurrently with {@link #record(int)}, the
* result is an approximate.
*/
public int getPercentile(double percentile) {
// NOTE: This implementation uses the nearest-rank method.
// https://en.wikipedia.org/wiki/Percentile#The_nearest-rank_method
//
// If called concurrently with record, this implementation biases low.
// Since we read count before iterating the array, more elements might have been recorded
// and we might not iterate far enough to be fair.
// Still, this probably won't matter greatly in practice.
Preconditions.checkArgument(percentile > 0.0);
Preconditions.checkArgument(percentile <= 100.0);
long targetRank = (long) Math.ceil(percentile * count.get() / 100);
long rank = 0;
for (int i = 0; i < buckets.length(); i++) {
rank += buckets.get(i);
if (rank >= targetRank) {
return i;
}
}
return buckets.length();
}
/**
* Records a new value.
*
*
The value must not be negative. To help with distributions with long tails, if the given
* value is greater than or equal to {@code endValue}, the value {@code endValue-1} is recorded
* instead.
*/
public void record(int value) {
Preconditions.checkArgument(value >= 0);
if (value >= buckets.length()) {
value = buckets.length() - 1;
}
buckets.incrementAndGet(value);
count.incrementAndGet();
}
@Override
public String toString() {
return MoreObjects.toStringHelper(this)
.add("endValue", buckets.length())
.add("count", count.get())
.toString();
}
}