RFR: 8300917: Regression 2x and bimodal startup on Mac aarch64 in b27

[Per Minborg]

This PR proposed to reduce contention in synchronized methods mainly by doing I/O operations outside synch blocks.

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Commit messages:
 - Reduce contention

Changes: https://git.openjdk.org/jdk/pull/12193/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12193&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300917
  Stats: 42 lines in 1 file changed: 15 ins; 14 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/12193.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12193/head:pull/12193

PR: https://git.openjdk.org/jdk/pull/12193