RFR: 8264707: HotSpot Style Guide should permit use of lambda [v2]

[Kim Barrett]

> Please review this proposal to permit the use of lambda expressions in
> HotSpot code, with some restrictions and suggestions for good usage within
> HotSpot code.  Lambda expressions were added in C++11, and provide a more
> expressive syntax for local functions, with a number of use-cases where they
> can improve readability by eliminating a lot of uninteresting boilerplate.
> 
> Some example uses are included, but are not part of the proposed change.
> They will be removed from the PR before it is pushed.  (In particular, the
> ScopeGuard utility uses move semantics, the use of which hasn't been
> approved or even discussed.)  They are given to show some of the benefits
> that might accrue from permitting the use of lambdas. In particular, they
> highlight some of the code reduction that is possible. Some of these code
> changes might be proposed in the future, using the normal PR process.
> 
> This is a modification of the Style Guide, so rough consensus among the
> HotSpot Group members is required to make this change.  Only Group members
> should vote for approval (via the github PR), though reasoned objections or
> comments from anyone will be considered.  A decision on this proposal will
> not be made before Wednesday 1-Sep-2021 at 12h00 UTC.
> 
> Since we're piggybacking on github PRs here, please use the PR review
> process to approve (click on Review Changes > Approve), rather than sending
> a "vote: yes" email reply that would be normal for a CFV.

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into permit_lambda
 - terminology fix
 - add scope guard and some example uses
 - G1 SATB filter lambda
 - new local functions section

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5144/files
  - new: https://git.openjdk.java.net/jdk/pull/5144/files/cc08f8b4..1fd7efbc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5144&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5144&range=00-01

  Stats: 40987 lines in 1478 files changed: 26921 ins; 8047 del; 6019 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5144.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5144/head:pull/5144

PR: https://git.openjdk.java.net/jdk/pull/5144