RFR: 8295839: G1: Single threaded phases (within parallel phases) report as using multiple threads in logs

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that changes log output to properly report single-threaded (sub-)phases  number of threads?

E.g.

 [87.104s][debug][gc,phases] GC(1412) Ext Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1, Workers: 6
[...]
[87.104s][trace][gc,phases] GC(1412) CLDG Roots (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0, Workers: 1
[87.104s][trace][gc,phases] GC(1412) CM RefProcessor Roots (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0, Workers: 1
[...] 

instead of

 [87.104s][debug][gc,phases] GC(1412) Ext Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1, Workers: 6
[...]
[87.104s][trace][gc,phases] GC(1412) CLDG Roots (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0, Workers: 6
[87.104s][trace][gc,phases] GC(1412) CM RefProcessor Roots (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0, Workers: 6
[...] 


Testing: local testing of some log files, gha

Thanks,
  Thomas

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

Commit messages:
 - properly report single threaded phases as such

Changes: https://git.openjdk.org/jdk/pull/10833/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10833&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295839
  Stats: 13 lines in 1 file changed: 0 ins; 4 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/10833.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10833/head:pull/10833

PR: https://git.openjdk.org/jdk/pull/10833