RFR: 8274349: ForkJoinPool.commonPool() does not work with 1 CPU [v2]

[Martin Buchholz]

On Fri, 1 Oct 2021 05:10:17 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> A regression introduced in Java 17 will give the default FJ pool a parallelism of zero in a uniprocessor environment. The fix restores this to a value of 1. See bug report for details.
>> 
>> Testing:
>>  - new regression test
>>  - tiers 1-3
>> 
>> Thanks,
>> David
>
> David Holmes has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Updated TCK test component from @martin

Marked as reviewed by martin (Reviewer).

I always try to avoid Thread.sleep or polling in tests, so I would write the test like this:

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ForkJoinPool;

public class ForkJoinUniProcessor {
    public static void main(String[] args) throws InterruptedException {
        // If the default parallelism were zero then this task would not
        // complete and the test will timeout.
        CountDownLatch ran = new CountDownLatch(1);
        ForkJoinPool.commonPool().submit(() -> ran.countDown());
        ran.await();
    }
}

-------------

PR: https://git.openjdk.java.net/jdk/pull/5784