[8u] RFR 8249846: Change of behavior after JDK-8237117: Better ForkJoinPool behavior

[David Alvarez]

Hi,

I would like to request a review for JDK-8249846

During the backport of JDK-8237117 a regression was added that affected
how the DefaultForkJoinWorkerThreadFactory works. The idea was to change
the context for threads in the commonPool, but it ended up affecting the
threads in all pools created with that factory. This patch decouples the
commonPool from the DefaultForkJoinWorkerThreadFactory

  Bug: https://bugs.openjdk.java.net/browse/JDK-8249846
  Webrev:
http://cr.openjdk.java.net/~alvdavi/webrevs/8249846/webrev.8u.jdk.00/

My original intention when writing the patch was to make the CommonPool
use the InnocuousForkJoinWorkerThreadFactory [1] in all cases,
regardless of whether a SecurityManager is installed or not, as we are
already creating threads with an innocuous AccessControlContext for
commonPool threads even when there is no SecurityManager installed.
However, the InnocuousForkJoinWorkerThreadFactory creates
InnocuousForkJoinWorkerThreads [2], which have some more nuances, like
the erase of ThreadLocal variables or avoid setting an
UncaughtExceptionHandler. I was afraid of introducing more regressions
with this change (in fact, one jtreg test [3] did fail because it was
setting an uncaught exception handler), that is why I decided to go for
a new factory (DefaultCommonPoolForkJoinWorkerThreadFactory) that mimics
current behavior, even if it means the behavior of the common pool if a
SecurityManager is installed during initialization is still not the same
as if the SecurityManager is installed after initialization.


David

--
[1]
http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/file/4d586f39fed3/src/share/classes/java/util/concurrent/ForkJoinPool.java#l3429
[2]
http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/file/4d586f39fed3/src/share/classes/java/util/concurrent/ForkJoinWorkerThread.java#l231
[3]
http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/file/4d586f39fed3/test/java/util/concurrent/forkjoin/ThrowingRunnable.java#l66