RFR: JDK-8319662 ForkJoinPool trims worker threads too slowly

[Viktor Klang]

On Mon, 20 Nov 2023 13:31:42 GMT, Doug Lea <dl at openjdk.org> wrote:

>> 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.)

I was thinking more about cases where system clock moves backwards in time. (currentTimeMillis() isn't spec:ed to be monotonic, right?)

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PR Review Comment: https://git.openjdk.org/jdk/pull/16725#discussion_r1399283296