[PR] Add spin-wait hint to BlockingMpscQueue producer-side busy loops [bookkeeper]

["merlimat (via GitHub)" <gi...@apache.org>]

merlimat opened a new pull request, #4831:
URL: https://github.com/apache/bookkeeper/pull/4831

   ### Motivation
   
   `BlockingMpscQueue.put()` and the timed `offer()` busy-spin on `relaxedOffer()` in a bare loop, with no pause hint. When the queue fills up under back-pressure (e.g. the journal queue with `enableBusyWait=true`), every blocked producer thread pins a core spinning at full speed — competing for CPU with the very consumer thread that needs to run to drain the queue.
   
   The consumer side (`take()` / `poll()`) already idles through `WAIT_STRATEGY.idle()`, which uses the `Thread.onSpinWait()` intrinsic (via `BusyWait.onSpinWait()`). The producer side was missing the same treatment.
   
   ### Changes
   
   Apply the same wait strategy in the `put()` and `offer(timeout)` spin loops. The producers still busy-spin (by design for this queue), but with the spin-wait hint that reduces power/pipeline contention and lets the sibling hyperthread — often the consumer — make progress.
   
   Verified with `BlockingMpscQueueTest` (4/4 pass) and module checkstyle.
   


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Re: [PR] Add spin-wait hint to BlockingMpscQueue producer-side busy loops [bookkeeper]

["merlimat (via GitHub)" <gi...@apache.org>]

merlimat merged PR #4831:
URL: https://github.com/apache/bookkeeper/pull/4831


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