RFR: 7124710: interleaved RedefineClasses() and RetransformClasses() calls may have a problem [v2]

[Alex Menkov]

> The problem is RedefineClasses does not update cached_class_bytes, so subsequent RetransformClasses gets obsolete class bytes (this are testcases 3-6 from the new test)
> 
> cached_class_bytes are set when an agent instruments the class from ClassFileLoadHook.
> After successful RedefineClasses it should be reset.
> The fix updates ClassFileLoadHook caller to not use old cached_class_bytes with RedefineClasses (if some agent instruments the class, new cached_class_bytes are allocated for scratch_class) and updates cached_class_bytes after successful RedefineClasses or RetransformClasses.

Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:

  updated comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10032/files
  - new: https://git.openjdk.org/jdk/pull/10032/files/a3558d0a..d86ae7fa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10032&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10032&range=00-01

  Stats: 5 lines in 1 file changed: 3 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10032.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10032/head:pull/10032

PR: https://git.openjdk.org/jdk/pull/10032