RFR: 8302122: Parallelize TLAB retirement in prologue in G1

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that parallelizes TLAB retirement and log buffer flushing (which [JDK-8297611](https://bugs.openjdk.org/browse/JDK-8297611) suggests?

* the parallelization has been split into java and non-java threads: parallelization of the latter does not make sense given how they are organized in a linked list. However non-java threads are typically very few anyway, and parallelization only starts making sense with low hundreds of threads anyway.
* `G1BarrierSet::write_region` added a new parameter that describes the JavaThread the write_region/invalidation (not sure why `write_region` isn't just an overload of `invalidate`) is  made for. The reason is previously when `BarrierSet::make_parsable()` (not sure why this is called this way either) is called to flush out deferred card marks, the card marks generated by that were added to the *calling thread's* refinement queue. This worked because the calling thread (the worker thread/vm thread) has always been processed after all java threads (which are the only ones that can have deferred card marks). So these deferred card marks' refinement entries were put into the worker thread's refinement queue. After parallelization this is not possible any more unless we deferred non java thread log flushing until after all java threads - I did not want to do that, so the change passes that explicit java thread through to `G1BarrierSet::write_region`. I think this is clearer anyway, and co
 rresponds to how `G1DirtyCardQueueSet::concatenate_log_and_stats` works.

Testing: tier1-5

Thanks,
  Thomas

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

Commit messages:
 - More warning workarounds
 - avoid inconsistent override error
 - cleanup
 - fixes
 - fixes
 - initial version, just making possibly_parallel_threads_do cover the same threads as threads_do

Changes: https://git.openjdk.org/jdk/pull/12497/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12497&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302122
  Stats: 398 lines in 17 files changed: 290 ins; 73 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/12497.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12497/head:pull/12497

PR: https://git.openjdk.org/jdk/pull/12497