if ((spins = spinsFor(pred, s.isData)) > 0)
randomYields = ThreadLocalRandom.current();
}
else if (spins > 0) { // spin
--spins;
if (randomYields.nextInt(CHAINED_SPINS) == 0)
Thread.yield(); // occasionally yield
}
else if (s.waiter == null) {
s.waiter = w; // request unpark then recheck
}