Github user kl0u commented on a diff in the pull request:
https://github.com/apache/flink/pull/4901#discussion_r147657820
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/rest/handler/legacy/metrics/DoubleAccumulator.java
---
@@ -0,0 +1,260 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.flink.runtime.rest.handler.legacy.metrics;
+
+/**
+ * An interface for accumulating double values.
+ */
+interface DoubleAccumulator {
+
+ /**
+ * Adds the given value to this accumulator.
+ *
+ * @param value value to add
+ */
+ void add(double value);
+
+ /**
+ * Returns the current value of this accumulator.
+ *
+ * @return current value of this accumulator
+ */
+ double getValue();
+
+ /**
+ * Returns the name of this accumulator type. This name is used as a
suffix for exposed metrics.
+ *
+ * @return name of this accumulator type
+ */
+ String getName();
+
+ /**
+ * A factory for {@link DoubleAccumulator}s. This allows us to
regenerate a new set of accumulators for each metrics
+ * without re-evaluating the "agg" query parameter or re-using existing
accumulators.
+ *
+ * @param <A> DoubleAccumulator subclass
+ */
+ interface DoubleAccumulatorFactory<A extends DoubleAccumulator> {
+ /**
+ * Creates a new accumulator with the given initial value.
+ *
+ * @param init initial value
+ * @return new accumulator with the given initial value
+ */
+ A get(double init);
+ }
+
+ /**
+ * Factory for {@link DoubleMaximum}.
+ */
+ final class DoubleMaximumFactory implements
DoubleAccumulatorFactory<DoubleMaximum> {
+ private static final DoubleMaximumFactory INSTANCE = new
DoubleMaximumFactory();
+
+ private DoubleMaximumFactory(){
+ }
+
+ @Override
+ public DoubleMaximum get(double init) {
+ return new DoubleMaximum(init);
+ }
+
+ public static DoubleMaximumFactory get() {
+ return INSTANCE;
+ }
+ }
+
+ /**
+ * Factory for {@link DoubleMinimum}.
+ */
+ final class DoubleMinimumFactory implements
DoubleAccumulatorFactory<DoubleMinimum> {
+ private static final DoubleMinimumFactory INSTANCE = new
DoubleMinimumFactory();
+
+ private DoubleMinimumFactory(){
+ }
+
+ @Override
+ public DoubleMinimum get(double init) {
+ return new DoubleMinimum(init);
+ }
+
+ public static DoubleMinimumFactory get() {
+ return INSTANCE;
+ }
+ }
+
+ /**
+ * Factory for {@link DoubleSum}.
+ */
+ final class DoubleSumFactory implements
DoubleAccumulatorFactory<DoubleSum> {
+ private static final DoubleSumFactory INSTANCE = new
DoubleSumFactory();
+
+ private DoubleSumFactory(){
+ }
+
+ @Override
+ public DoubleSum get(double init) {
+ return new DoubleSum(init);
+ }
+
+ public static DoubleSumFactory get() {
+ return INSTANCE;
+ }
+ }
+
+ /**
+ * Factory for {@link DoubleAverage}.
+ */
+ final class DoubleAverageFactory implements
DoubleAccumulatorFactory<DoubleAverage> {
+ private static final DoubleAverageFactory INSTANCE = new
DoubleAverageFactory();
+
+ private DoubleAverageFactory(){
+ }
+
+ @Override
+ public DoubleAverage get(double init) {
+ return new DoubleAverage(init);
+ }
+
+ public static DoubleAverageFactory get() {
+ return INSTANCE;
+ }
+ }
+
+ /**
+ * {@link DoubleAccumulator} that returns the maximum value.
+ */
+ final class DoubleMaximum implements DoubleAccumulator {
+
+ public static final String NAME = "max";
+
+ private double value;
+
+ private DoubleMaximum(double init) {
+ value = init;
+ }
+
+ @Override
+ public void add(double value) {
+ this.value = Math.max(this.value, value);
+ }
+
+ @Override
+ public double getValue() {
+ return value;
+ }
+
+ @Override
+ public String getName() {
+ return NAME;
+ }
+ }
+
+ /**
+ * {@link DoubleAccumulator} that returns the minimum value.
+ */
+ final class DoubleMinimum implements DoubleAccumulator {
+
+ public static final String NAME = "min";
+
+ private double value;
+
+ private DoubleMinimum(double init) {
+ value = init;
+ }
+
+ @Override
+ public void add(double value) {
+ this.value = Math.min(this.value, value);
+ }
+
+ @Override
+ public double getValue() {
+ return value;
+ }
+
+ @Override
+ public String getName() {
+ return NAME;
+ }
+ }
+
+ /**
+ * {@link DoubleAccumulator} that returns the sum of all values.
+ */
+ final class DoubleSum implements DoubleAccumulator {
+
+ public static final String NAME = "sum";
+
+ private double value;
+
+ private DoubleSum(double init) {
+ value = init;
+ }
+
+ @Override
+ public void add(double value) {
+ this.value += value;
+ }
+
+ @Override
+ public double getValue() {
+ return value;
+ }
+
+ @Override
+ public String getName() {
+ return NAME;
+ }
+ }
+
+ /**
+ * {@link DoubleAccumulator} that returns the average over all values.
+ */
+ final class DoubleAverage implements DoubleAccumulator {
+
+ public static final String NAME = "avg";
+
+ private double sum;
+ private int count;
+
+ private DoubleAverage(double init) {
+ sum = init;
+ count = 1;
+ }
+
+ @Override
+ public void add(double value) {
+ this.sum += value;
+ this.count++;
+ }
+
+ @Override
+ public double getValue() {
+ if (count == 0) {
--- End diff --
`count` cannot be `0` right? Because we set it to `1` in the constructor.
---
