RFR: 8229517: Support for optional asynchronous/buffered logging [v12]

[Xin Liu]

> This patch provides a buffer to store asynchrounous messages and flush them to
> underlying files periodically.

Xin Liu has updated the pull request incrementally with one additional commit since the last revision:

  Change option AsyncLogBufferEntries to AsyncLogBufferSize.
  
  AsyncLogBufferSize is the memory budget in bytes for Asynchronous Logging.
  User can specify it in shorthand form. eg. -XX:AsyncLogBufferSize=10M.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3135/files
  - new: https://git.openjdk.java.net/jdk/pull/3135/files/1d5e5407..c67d74e8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3135&range=11
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3135&range=10-11

  Stats: 22 lines in 6 files changed: 9 ins; 3 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3135.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3135/head:pull/3135

PR: https://git.openjdk.java.net/jdk/pull/3135