RFR: 8283276: java/io/ObjectStreamClass/ObjectStreamClassCaching.java fails with various GCs

[Peter Levart]

This is a continuation of effort from https://github.com/openjdk/jdk/pull/9533 to fix the ObjectStreamClassCaching test which is failing with various GCs != G1. The test class contains 2 test methods:
- test2CacheReleaseUnderMemoryPressure - this one was not logically changed at all - just one method was inlined
- test1CacheEffectiveness - this one now uses a different strategy which doesn't involve calling System.gc() in order to trigger reference processing in GC which is, as test failures reveal, sometimes to aggressive and triggers processing not only WeakReference(s) but also SoftReference(s). Instead, the test now gradually builds up memory pressure while checking what's happening to two WeakReference(s): ref1 - wrapping a cached ObjectStreamClass instance; and: ref2 - wrapping a new Object() instance. The "effectiveness" of caching is confirmed by verifying that weakly reachable new Object() referent of ref2 is GC-ed earlier than softly reachable ObjectStreamClass referent of ref1.
The test now contains several @run(s) with explicitly selected set of GC algorithms: G1, Parallel, ZGC, Shenandoah.

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

Commit messages:
 - ObjectStreamClassCaching test rework - run with various GCs

Changes: https://git.openjdk.org/jdk/pull/9684/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9684&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8283276
  Stats: 89 lines in 1 file changed: 62 ins; 11 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/9684.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9684/head:pull/9684

PR: https://git.openjdk.org/jdk/pull/9684