decorrelatedJitter and fullJitter delay calculation overflows

[kgrits]

Bug Report

Current Behavior

1. Delay.decorrelatedJitter() always returns the same value. If used with default setup - 0.

2. I couldn't find any limitation on attempts in ConnectionWatchdog, that's why I decided to test Delay.fullJitter() with a high number of attempts (100+). If I use any other value for base except the default one I get IllegalArgumentException: bound must be greater than origin.

Stack trace

Exception in thread "main" java.lang.IllegalArgumentException: bound must be greater than origin
	at java.base/jdk.internal.util.random.RandomSupport.checkRange(RandomSupport.java:246)
	at java.base/java.util.random.RandomGenerator.nextLong(RandomGenerator.java:739)
	at java.base/java.util.concurrent.ThreadLocalRandom.nextLong(ThreadLocalRandom.java:484)
	at io.lettuce.core.resource.Delay.randomBetween(Delay.java:331)
	at io.lettuce.core.resource.FullJitterDelay.createDelay(FullJitterDelay.java:57)

Input Code

decorrelatedJitter

Delay delay = Delay.decorrelatedJitter().get();
for (int i = 0; i < 10; i++) {
    System.out.println(delay.createDelay(i).toMillis());
}

fullJitter

var delay = Delay.fullJitter(Duration.ZERO, Duration.ofSeconds(30), 2, TimeUnit.MILLISECONDS);
for (int i = 0; i < 100; i++) {
    System.out.println(delay.createDelay(i).toMillis());
}

Expected behavior/code

Environment

• Lettuce version(s): 6.1.8.RELEASE
• Redis version: N/A

[mp911de]

The delay counter starts at 1, see:

https://github.com/lettuce-io/lettuce-core/blob/640be7c872c7266cd86259326acd02cb696994f3/src/main/java/io/lettuce/core/resource/Delay.java#L27

[kgrits]

Hey, thanks for your reply. My bad! Though I updated my code to start attempts at 1 and still got the same behavior for both Delay's.

Delay delay = Delay.decorrelatedJitter().get();
for (int i = 1; i < 10; i++) {
    System.out.println(delay.createDelay(i).toMillis());
}

Delay delay = Delay.fullJitter(Duration.ZERO, Duration.ofSeconds(30), 2, TimeUnit.MILLISECONDS);
for (int i = 1; i < 100; i++) {
    System.out.println(delay.createDelay(i).toMillis());
}

[mp911de]

Upon further investigation, DecorrelatedJitterDelay has a bug where the previous delay conversion was missing.

The full jitter implementation returns zero upon reaching 2^63 because the long value range exceeds. We should update the code to use the upper bound for jittering instead of falling back to zero.

[mp911de]

That's fixed now, thanks for reporting the issue.