RFR: 6383195: javax.crypto.spec.PBEKeySpec is not thread safe

[Bradford Wetmore]

Simple fix to a long-standing threading bug to help clear the backlog.

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Commit messages:
 - 6383195: javax.crypto.spec.PBEKeySpec is not thread safe

Changes: https://git.openjdk.org/jdk/pull/9668/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9668&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6383195
  Stats: 86 lines in 2 files changed: 84 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9668.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9668/head:pull/9668

PR: https://git.openjdk.org/jdk/pull/9668