RFR: 8229517: Support for optional asynchronous/buffered logging [v16]

[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:

  Implement the new discard policy: drop the incoming message.
  
  This patch also fix a bug. meta messages append to the temp logs instead
  of directly calling output->write_blocking(). This guranatees logsites are non-blocking.

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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/e19e90a8..be83aafd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3135&range=15
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3135&range=14-15

  Stats: 47 lines in 3 files changed: 22 ins; 6 del; 19 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