RFR: 8348960: [leyden] compiler/c1/TestConcurrentPatching.java is stuck [v3]

[Vladimir Ivanov]

On Tue, 4 Feb 2025 13:43:27 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/share/compiler/compileBroker.cpp line 421:
>> 
>>> 419:   assert(_lock->owned_by_self(), "must own lock");
>>> 420: 
>>> 421:   CompileTask* task;
>> 
>> I assume these changes aren't strictly needed (`_queue` is always drained under the lock).
>
> While `_queue` is drained under the lock, it is being _added to_ without a lock, which means we are using `empty` under concurrent queue modification, which is, per NBQ docs, not guaranteed to work well. (ABA problems.)

Thanks for the clarification. I missed that `NonblockingQueue::empty()` is not thread-safe.

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PR Review Comment: https://git.openjdk.org/leyden/pull/30#discussion_r1941699216