RFR: 8288899: java/util/concurrent/ExecutorService/CloseTest.java failed with "InterruptedException: sleep interrupted" [v4]

[Doug Lea]

On Wed, 16 Aug 2023 10:33:58 GMT, Doug Lea <dl at openjdk.org> wrote:

>> src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 442:
>> 
>>> 440:      * queues are at odd indices. Worker phase ids masked with SMASK
>>> 441:      * match their index. Shared (submission) queues are at even
>>> 442:      * indices. Grouping them together in this way simplifies and
>> 
>> @DougLea Interesting—so by having the worker queues at odd indices increases the likelihood of the then adjacent submission queues already having been prefetched?
>
> More-or-less. At top-level, both kinds of queues should be sampled with approx the same probability, which is simpler if they are all in the same array. But we also need to identify what kind they are without looking at them, leading to odd/even scheme. One disadvantage is that there are usually many fewer submission queues, so there can be a lot of wasted probes (null slots). But still cheaper than alternatives because of cache locality etc.

(I also added some similar wording to the internal docs.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/14301#discussion_r1297226372