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TMP Add ExponentialBackoff
I manually copied it from mongodb#1899.
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‎driver-core/src/main/com/mongodb/internal/time/ExponentialBackoff.java‎

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/*
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* Copyright 2008-present MongoDB, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.mongodb.internal.time;
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import com.mongodb.internal.VisibleForTesting;
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import java.util.concurrent.ThreadLocalRandom;
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import java.util.function.DoubleSupplier;
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import static com.mongodb.assertions.Assertions.assertTrue;
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import static com.mongodb.internal.VisibleForTesting.AccessModifier.PRIVATE;
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/**
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* Provides exponential backoff calculations with jitter for retry scenarios.
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*/
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public final class ExponentialBackoff {
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// Constants for transaction retry backoff
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@VisibleForTesting(otherwise = PRIVATE)
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static final double TRANSACTION_BASE_MS = 5.0;
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@VisibleForTesting(otherwise = PRIVATE)
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static final double TRANSACTION_MAX_MS = 500.0;
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@VisibleForTesting(otherwise = PRIVATE)
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static final double TRANSACTION_GROWTH = 1.5;
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// TODO-JAVA-6079
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private static DoubleSupplier testJitterSupplier = null;
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private ExponentialBackoff() {
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}
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/**
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* Calculate the backoff in milliseconds for transaction retries.
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*
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* @param attemptNumber 0-based attempt number
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* @return The calculated backoff in milliseconds.
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*/
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public static long calculateTransactionBackoffMs(final int attemptNumber) {
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return calculateBackoffMs(TRANSACTION_BASE_MS, TRANSACTION_MAX_MS, TRANSACTION_GROWTH, attemptNumber);
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}
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public static long calculateRetryBackoffMs(final int attemptNumber) {
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return calculateBackoffMs(100, 10000, 2, attemptNumber);
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}
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private static long calculateBackoffMs(final double baseMs, final double maxMs, final double growth, final int attemptNumber) {
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assertTrue(attemptNumber > 0, "Attempt number must be greater than 0 in the context of transaction backoff calculation");
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double jitter = testJitterSupplier != null
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? testJitterSupplier.getAsDouble()
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: ThreadLocalRandom.current().nextDouble();
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return Math.round(jitter * Math.min(
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baseMs * Math.pow(growth, attemptNumber - 1),
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maxMs));
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}
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/**
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* Set a custom jitter supplier for testing purposes.
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*
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* @param supplier A DoubleSupplier that returns values in [0, 1) range.
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*/
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@VisibleForTesting(otherwise = PRIVATE)
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public static void setTestJitterSupplier(final DoubleSupplier supplier) {
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testJitterSupplier = supplier;
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}
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/**
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* Clear the test jitter supplier, reverting to default ThreadLocalRandom behavior.
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*/
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@VisibleForTesting(otherwise = PRIVATE)
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public static void clearTestJitterSupplier() {
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testJitterSupplier = null;
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}
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}

‎driver-core/src/test/unit/com/mongodb/internal/time/ExponentialBackoffTest.java‎

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/*
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* Copyright 2008-present MongoDB, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.mongodb.internal.time;
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import org.junit.jupiter.api.Test;
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import java.util.function.DoubleSupplier;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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class ExponentialBackoffTest {
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/**
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* Expected {@linkplain ExponentialBackoff#calculateTransactionBackoffMs(int) backoffs} with 1.0 as
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* {@link ExponentialBackoff#setTestJitterSupplier(DoubleSupplier) jiter}.
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*/
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private static final double[] EXPECTED_BACKOFFS_MAX_VALUES = {5.0, 7.5, 11.25, 16.875, 25.3125, 37.96875, 56.953125, 85.4296875, 128.14453125,
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192.21679688, 288.32519531, 432.48779297, 500.0};
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@Test
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void testCalculateTransactionBackoffMs() {
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// Test that the backoff sequence follows the expected pattern with growth factor ExponentialBackoff.TRANSACTION_GROWTH
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// Expected sequence (without jitter): 5, 7.5, 11.25, ...
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// With jitter, actual values will be between 0 and these maxima
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for (int attemptNumber = 1; attemptNumber <= EXPECTED_BACKOFFS_MAX_VALUES.length; attemptNumber++) {
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long backoff = ExponentialBackoff.calculateTransactionBackoffMs(attemptNumber);
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long expectedBackoff = Math.round(EXPECTED_BACKOFFS_MAX_VALUES[attemptNumber - 1]);
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assertTrue(backoff >= 0 && backoff <= expectedBackoff,
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String.format("Attempt %d: backoff should be between 0 ms and %d ms, got: %d", attemptNumber,
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expectedBackoff, backoff));
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}
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}
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@Test
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void testCalculateTransactionBackoffMsRespectsMaximum() {
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// Even at high attempt numbers, backoff should never exceed ExponentialBackoff.TRANSACTION_MAX_MS
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for (int attemptNumber = 1; attemptNumber < EXPECTED_BACKOFFS_MAX_VALUES.length * 2; attemptNumber++) {
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long backoff = ExponentialBackoff.calculateTransactionBackoffMs(attemptNumber);
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assertTrue(backoff >= 0 && backoff <= ExponentialBackoff.TRANSACTION_MAX_MS,
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String.format("Attempt %d: backoff should be capped at %f ms, got: %d ms",
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attemptNumber, ExponentialBackoff.TRANSACTION_MAX_MS, backoff));
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}
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}
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@Test
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void testCustomJitter() {
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// Test with jitter = 1.0
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ExponentialBackoff.setTestJitterSupplier(() -> 1.0);
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try {
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for (int attemptNumber = 1; attemptNumber <= EXPECTED_BACKOFFS_MAX_VALUES.length; attemptNumber++) {
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long backoff = ExponentialBackoff.calculateTransactionBackoffMs(attemptNumber);
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long expected = Math.round(EXPECTED_BACKOFFS_MAX_VALUES[attemptNumber - 1]);
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assertEquals(expected, backoff,
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String.format("Attempt %d: with jitter=1.0, backoff should be %d ms", attemptNumber, expected));
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}
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} finally {
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ExponentialBackoff.clearTestJitterSupplier();
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}
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// Test with jitter = 0, all backoffs should be 0
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ExponentialBackoff.setTestJitterSupplier(() -> 0.0);
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try {
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for (int attemptNumber = 1; attemptNumber < EXPECTED_BACKOFFS_MAX_VALUES.length; attemptNumber++) {
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long backoff = ExponentialBackoff.calculateTransactionBackoffMs(attemptNumber);
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assertEquals(0, backoff, "With jitter=0, backoff should always be 0 ms");
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}
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} finally {
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ExponentialBackoff.clearTestJitterSupplier();
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}
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}
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}

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