RFR: JDK-8319662 ForkJoinPool trims worker threads too slowly

[Doug Lea]

On Mon, 20 Nov 2023 11:23:54 GMT, Viktor Klang <vklang at openjdk.org> wrote:

>> This update cascades timeouts to trim subsequent workers after the first  keepAlive inactive period.
>
> src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 2140:
> 
>> 2138:             Thread.interrupted();               // clear for next park
>> 2139:             if (deadline != 0L &&               // try to trim on timeout
>> 2140:                 deadline - System.currentTimeMillis() < TIMEOUT_SLOP) {
> 
> Since `currentTimeMillis()` is fetched from system time, I think it might be more appropriate to use nanoTime() to track delays.

It would be better, but absolute-time Unsafe.park only operates at millisecond accuracy (and even at that may misfire early, requiring TIMEOUT_SLOP.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/16725#discussion_r1399210760