RFR: 7124710: interleaved RedefineClasses() and RetransformClasses() calls may have a problem [v8]

[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 per Dan's request

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10032/files
  - new: https://git.openjdk.org/jdk/pull/10032/files/36c4ba60..63b5589f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10032&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10032&range=06-07

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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