RFR 8056248: Improve ForkJoin thread throttling

[Martin Buchholz]

Approved.  Thanks for doing this.


On Fri, Aug 29, 2014 at 3:43 AM, Paul Sandoz <paul.sandoz at oracle.com> wrote:

> Hi,
>
> Please review fixes by Doug to For/Join to improve thread throttling (e.g.
> for nested parallel streams). This fix resulted in a lot of internal
> refactoring and clean up.
>
> In addition a new system property was added
> "java.util.concurrent.ForkJoinPool.common.maximumSpares" (which i suspect
> will only very rarely be used), so a CCC will be required:
>
>  http://cs.oswego.edu/pipermail/concurrency-interest/2014-July/012838.html
>
>  * <li>{@code java.util.concurrent.ForkJoinPool.common.maximumSpares}
>  * - the maximum number of allowed extra threads to maintain target
>  * parallelism (default 256).
>
>   https://bugs.openjdk.java.net/browse/JDK-8056248
>
> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8056248-fj-thread-throttling/webrev/
>
>
> --
>
> Once this review is complete i think we should also backport to 8u40, and
> likewise for the CompletableFuture updates (which i forgot to mention in a
> previously related email).
>
> Both these updates have been soaking in the 166 repo for a month or two.
> No related test failures were reported for a JPRT run with both patches.
>
> Paul.
>