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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.vespa.zookeeper;
import java.time.Duration;
import java.util.Random;
/**
* Calculate a delay using an exponential backoff algorithm. Based on ExponentialBackOff in google-http-client.
*
* @author mpolden
*/
public class ExponentialBackoff {
private static final double RANDOMIZATION_FACTOR = 0.5;
private final Duration initialDelay;
private final Duration maxDelay;
private final Random random;
public ExponentialBackoff(Duration initialDelay, Duration maxDelay) {
this(initialDelay, maxDelay, new Random());
}
ExponentialBackoff(Duration initialDelay, Duration maxDelay, Random random) {
this.initialDelay = requireNonNegative(initialDelay);
this.maxDelay = requireNonNegative(maxDelay);
this.random = random;
}
/** Return the delay of given attempt */
public Duration delay(int attempt) {
if (attempt < 1) throw new IllegalArgumentException("Attempt must be positive");
double currentDelay = attempt * initialDelay.toMillis();
double delta = RANDOMIZATION_FACTOR * currentDelay;
double lowerDelay = currentDelay - delta;
double upperDelay = currentDelay + delta;
long millis = (long) Math.min(lowerDelay + (random.nextDouble() * (upperDelay - lowerDelay + 1)),
maxDelay.toMillis());
return Duration.ofMillis(millis);
}
private static Duration requireNonNegative(Duration d) {
if (d.isNegative()) throw new IllegalArgumentException("Invalid duration: " + d);
return d;
}
}
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