RFR: 8309667: TLS handshake fails because of ConcurrentModificationException in PKCS12KeyStore.engineGetEntry [v2]

[Weijun Wang]

> A different fix after https://github.com/openjdk/jdk/pull/14506 was closed.
> 
> Still haven't made the attributes set immutable but at least it is populated before an entry is added to `entries` and it will never be modified later.
> 
> I tried the newly added `AttributesMultiThread.java` test hundreds of times and only observed failures before this fix (~%2 failure rate).

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  rewrite method comment

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15909/files
  - new: https://git.openjdk.org/jdk/pull/15909/files/24be313b..71a960b4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15909&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15909&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15909.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15909/head:pull/15909

PR: https://git.openjdk.org/jdk/pull/15909