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Wake the killed thread, not another waiter, on a monitor wait - #9847
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waitForObject waits with Object.wait, and a kill or raise woke it with notify, which wakes one arbitrary waiter on that monitor. When two threads waited on the same object, the other one could wake instead, see nothing pending, and wait again, leaving the killed thread blocked. concurrent-ruby waits this way, which made its CyclicBarrier spec time out joining killed threads now and then. Use notifyAll. Monitor waiters have to recheck their condition anyway.
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waitForObject waits with Object.wait, and a kill or raise woke it with notify, which wakes one arbitrary waiter on that monitor. When two threads waited on the same object, the other one could wake instead, see nothing pending, and wait again, leaving the killed thread blocked. concurrent-ruby waits this way, which made its CyclicBarrier spec time out joining killed threads now and then.
notify() could wake some other waiter instead of the killed thread. notifyAll() wakes them all; the rest just recheck and go back to waiting.
Should fix the occasional CI error
Concurrent::CyclicBarrier#number_waiting with waiting threads should be equal to the waiting threads countlike here: https://github.com/jruby/jruby/actions/runs/39355604931/job/118409545094?pr=9845.Related to ruby-concurrency/concurrent-ruby#862.