RFR: avoid extra park of vthread when using fixed thread pool [v2]

[Alan Bateman]

On Mon, 30 Aug 2021 12:03:23 GMT, Miao Zheng <duke at openjdk.java.net> wrote:

>> The CustomScheduler test was indeed failing with this change but it's due to a test issue where it runs the scheduler tasks on the current thread. I've remove that case from the test so I think we are good to go now.
>
> @AlanBateman Thanks for your review.

@miao-zheng The copyright header on the test is causing problems for a script that checks the copyright header on files. It doesn't seem to match the headers on files contributed by THL A29 Limited or Tencent. Can you check this?

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PR: https://git.openjdk.java.net/loom/pull/59