RFR: 8274112: (fc) Tune FileChannel.transferTo() [v6]

[Brian Burkhalter]

> Please consider this patch which would improve the performance of
> `FileChannel.transferTo()` on macOS and Windows.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8274112: Revert all changes except mapped transfer threshold

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5623/files
  - new: https://git.openjdk.java.net/jdk/pull/5623/files/65e3adca..778928ba

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5623&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5623&range=04-05

  Stats: 41 lines in 4 files changed: 1 ins; 22 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5623.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5623/head:pull/5623

PR: https://git.openjdk.java.net/jdk/pull/5623