Regression in LinkedTransferQueue since JDK17?

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Hello!

Our application contains a work queue based on LinkedTransferQueue. After
some initial load, I leave the server idle only to notice that one of the
subscriber threads is spinning after a period of time.

I've only noticed this problem while testing on 17.0.3 as well as the
version of JDK18 currently shipped with Ubuntu 22.04 LTS (build
18-ea+36-Ubuntu-1 - sorry, no idea what this version really means). I
suspect the problem is related to a recent refactoring in LTQ:
https://bugs.openjdk.org/browse/JDK-8246677

I've managed to implement a test case that reliably fails after a few
minutes (attached). When running under the debugger I can see a single
subscriber thread is spinning
in java.util.concurrent.LinkedTransferQueue#awaitMatch while performing a
timed poll():

       while ((item = s.item) == e) {
            if (needSweep)                               // FALSE
                sweep();
            else if ((timed && nanos <= 0L) || w.isInterrupted()) {
                if (s.casItem(e, (e == null) ? s : null)) {
                    unsplice(pred, s);   // cancelled
                    return e;
                }
            }
            else if (stat <= 0) {                       // TRUE (stat = 0)
                if (pred != null && pred.next == s) {   // FALSE (pred !=
null but pred.next != s)
                    if (stat < 0 &&
                        (pred.isData != isData || pred.isMatched())) {
                        stat = 0;
                        Thread.yield();
                    }
                    else {
                        stat = 1;
                        s.waiter = w;
                    }
                }
            }
            ...
        }

It's as if the subscribers race each other to poll the empty queue
eventually causing one of the subscribers to get stuck in an infinite loop.
Cheers,
Matt

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