RFR: 8261154: Memory leak in Java_java_lang_ClassLoader_defineClass0 with long class names [v2]

[Claes Redestad]

> This patch resolves a potential memory leak in Java_java_lang_ClassLoader_defineClass0
> 
> I've not figured a good way to write a regression test. A crude way to manually verify the leak and the fix is provided by the added microbenchmark that triggers the malloc in ClassLoader.c and the associated leak.
> 
> E.g., running this with `/usr/bin/time -v $BUILD_DIR/images/jdk/bin/java -Xmx256m -jar $BUILD_DIR/images/test/micro/benchmarks.jar LookupDef.*WeakClass.loadLong -f 0 -i  N | grep "Maximum resident set"` yields:
> 
> Baseline:
> N = 20     Maximum resident set size (kbytes): 544860
> N = 50     Maximum resident set size (kbytes): 818532
> N = 100    Maximum resident set size (kbytes): 1388560
> N = 200    Maximum resident set size (kbytes): 2124296
> Patch:
> N = 20     Maximum resident set size (kbytes): 480476
> N = 50     Maximum resident set size (kbytes): 764040
> N = 100    Maximum resident set size (kbytes): 782920
> N = 200    Maximum resident set size (kbytes): 921272

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  Dial back cleanups and focus patch on the bug at hand

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2407/files
  - new: https://git.openjdk.java.net/jdk/pull/2407/files/972696ec..f25b5f98

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2407&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2407&range=00-01

  Stats: 10 lines in 1 file changed: 0 ins; 5 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2407.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2407/head:pull/2407

PR: https://git.openjdk.java.net/jdk/pull/2407