SequenceBarrier#waitFor(sequence) bug?

Julian F

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Sep 28, 2023, 4:32:27 AM9/28/23

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When using a BlockingWaitStrategy, I expect that SequenceBarrier#waitFor(sequence) should block until the value at sequence is ready for consumption. This was the case in 2.x.

But in 3.x, waitFor often returns nextSequence - 1. I believe that this is due to a delay between the sequence being claimed and the sequence being ready for consumption. Is this a bug?

Thank you,

Julian

Julian F

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Sep 28, 2023, 10:57:13 AM9/28/23

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I'm attaching a simple recreation of the behavior I'm seeing. You can run with `mvn test`.

wait-for-bug.tar.gz

Julian F

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Sep 29, 2023, 2:39:41 PM9/29/23

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Just adding links to the relevant source.

When debugging, I found that the blocking wait strategy returns the a sequence greater than or equal to sequence on line 56 of waitFor. But on line 63, sequencer.getHighestPublishedSequence returns sequence - 1.

https://github.com/LMAX-Exchange/disruptor/blob/3.4.4/src/main/java/com/lmax/disruptor/ProcessingSequenceBarrier.java#L51

In 2.10.4, waitFor simply defers to the wait strategy, so sequence - 1 can never be returned with a blocking wait strategy.

https://github.com/LMAX-Exchange/disruptor/blob/2.10.4/code/src/main/com/lmax/disruptor/ProcessingSequenceBarrier.java#L40

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