Project Loom VirtualThreads hang

[Ron Pressler]

> On 5 Jan 2023, at 12:36, robert engels <rengels at ix.netcom.com> wrote:
> 
> which is interesting because the #1 consumer is still the ForkJoin pool parking while waiting for work - even though the system and idle percentages are so low.

Parks in the scheduler are usually a result of workers being starved for work due to a high relative rate of contention. A high relative contention rate is usually an application problem and shouldn’t be common in well-architected ones. Try adding more instances of a queue+producers+consumers, and you should see fewer parks. Alternatively, reduce the scheduler’s parallelism with `-Djdk.virtualThreadScheduler.parallelism=N` where N is smaller than the number of cores. In these situations (that typically arise only in artificial benchmarks) the result could even be improved overall performance.

— Ron