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Author: nhachicha

driver-core/src/main/com/mongodb/internal/ExponentialBackoff.java

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+/*
+ * Copyright 2008-present MongoDB, Inc.
+ *
+ * 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 com.mongodb.internal.time;
+
+import com.mongodb.annotations.NotThreadSafe;
+import com.mongodb.internal.VisibleForTesting;
+
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.function.DoubleSupplier;
+
+import static com.mongodb.internal.VisibleForTesting.AccessModifier.PRIVATE;
+
+/**
+ * Implements exponential backoff with jitter for retry scenarios.
+ */
+@NotThreadSafe
+public enum ExponentialBackoff {
+    TRANSACTION(5.0, 500.0, 1.5);
+
+    private final double baseMs, maxMs, growth;
+
+    // TODO remove this global state once https://jira.mongodb.org/browse/JAVA-6060 is done
+    private static DoubleSupplier testJitterSupplier = null;
+
+    ExponentialBackoff(final double baseMs, final double maxMs, final  double growth) {
+        this.baseMs = baseMs;
+        this.maxMs = maxMs;
+        this.growth = growth;
+    }
+
+    /**
+     * Calculate the next delay in milliseconds based on the retry count.
+     *
+     * @param retryCount The number of retries that have occurred.
+     * @return The calculated delay in milliseconds.
+     */
+    public long calculateDelayBeforeNextRetryMs(final int retryCount) {
+        double jitter = testJitterSupplier != null
+                ? testJitterSupplier.getAsDouble()
+                : ThreadLocalRandom.current().nextDouble();
+        double backoff = Math.min(baseMs * Math.pow(growth, retryCount), maxMs);
+        return Math.round(jitter * backoff);
+    }
+
+    /**
+     * Calculate the next delay in milliseconds based on the retry count and a provided jitter.
+     *
+     * @param retryCount The number of retries that have occurred.
+     * @param jitter     A double in the range [0, 1) to apply as jitter.
+     * @return The calculated delay in milliseconds.
+     */
+    public long calculateDelayBeforeNextRetryMs(final int retryCount, final double jitter) {
+        double backoff = Math.min(baseMs * Math.pow(growth, retryCount), maxMs);
+        return Math.round(jitter * backoff);
+    }
+
+    /**
+     * Set a custom jitter supplier for testing purposes.
+     *
+     * @param supplier A DoubleSupplier that returns values in [0, 1) range.
+     */
+    @VisibleForTesting(otherwise = PRIVATE)
+    public static void setTestJitterSupplier(final DoubleSupplier supplier) {
+        testJitterSupplier = supplier;
+    }
+
+    /**
+     * Clear the test jitter supplier, reverting to default ThreadLocalRandom behavior.
+     */
+    @VisibleForTesting(otherwise = PRIVATE)
+    public static void clearTestJitterSupplier() {
+        testJitterSupplier = null;
+    }
+}