RFR: 8291065: Creating a VarHandle for a static field triggers class initialization [v10]

[Chen Liang]

> Also fixed the bug with NPE in `IndirectVarHandle::isAccessModeSupported`.
> 
> A few implementation-detail methods in VarHandle are now documented with the implied constraints to avoid subtle problems in the future. Changed `IndirectVarHandle` to call `asDirect` lazily to accomodate the lazy VarHandle changes. Also changed VarHandleBaseTest to report the whole incorrect type of exception caught than swallow it and leaving only a message.
> 
> Current problems:
> - [ ] The lazy var handle is quite slow on the first invocation.
>    - As seen in the benchmark, users can first call `Lookup::ensureInitialized` to create an eager handle.
>    - After that, the lazy handle has a performance on par with the regular var handle.
> - [ ] The class-loading-based test is not in a unit test
>    - The test frameworks don't seem to offer fine-grained control for class-loading detection or reliable unloading
> 
> 
> Benchmark                                            Mode  Cnt  Score   Error  Units
> VarHandleLazyStaticInvocation.initializedInvocation  avgt   30  0.817 ± 0.012  ns/op
> VarHandleLazyStaticInvocation.lazyInvocation         avgt   30  0.805 ± 0.007  ns/op
> 
> 
> Benchmark                                            Mode  Cnt     Score     Error  Units
> Benchmark                                            Mode  Cnt   Score    Error  Units
> LazyStaticColdStart.methodHandleCreateEager            ss   10  36.890 ±  2.891  us/op
> LazyStaticColdStart.methodHandleCreateLazy             ss   10  18.340 ±  1.537  us/op
> LazyStaticColdStart.methodHandleInitializeCallEager    ss   10  50.000 ±  5.590  us/op
> LazyStaticColdStart.methodHandleInitializeCallLazy     ss   10  90.550 ± 10.142  us/op
> LazyStaticColdStart.varHandleCreateEager               ss   10  36.610 ±  2.685  us/op
> LazyStaticColdStart.varHandleCreateLazy                ss   10  18.200 ±  1.811  us/op
> LazyStaticColdStart.varHandleInitializeCallEager       ss   10  71.680 ± 11.097  us/op
> LazyStaticColdStart.varHandleInitializeCallLazy        ss   10  72.090 ±  4.494  us/op

Chen Liang has updated the pull request incrementally with one additional commit since the last revision:

  Split ensureInitialized

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13821/files
  - new: https://git.openjdk.org/jdk/pull/13821/files/f414e8f8..acca36fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13821&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13821&range=08-09

  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13821.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13821/head:pull/13821

PR: https://git.openjdk.org/jdk/pull/13821